Geology of Australian Coal Basins by GSAustralia

Geology of Austrolion Coql Bosins Geological Society of Australia Incorporated Coal Geology Group

SPECIAL PUBLICATION No. 1

edited by CR Ward, HJ Harrington, CW Mallett & JW Beeston

1995

Editors Associate Professor CR Ward Department of Applied Geology The University of New South Wales, Sydney NSW 2052

Dr HJ Harrington Department of Geology The Australian National University, Canberra ACT 0200 and:

Department of Geology and Geophysics The University of Sydney, NSW 2006

Dr CW Mallett Division of Exploration and Mining Commonwealth Scientific and Industrial Research Organisation PO Box 883, Kenmore Qld 4069 Dr JW Beeston Ceological Survey Division Department of Minerals and Energy, Queensland, GPO Box 194, Brisbane Qld 4001

Published by the Geological Society of Australia, Coal Geology Group Suite 504 Wynyard House 301 George Street Sydney NSW 2000

Australia O Geological Society of Australia (Incorporated), 1995 ISSN 1323-9562

rsBN 0 909869 96 0

Issued May 1995

Examples on how to reference this volume: WARD, C.R., HARRINGTON, H.J., MALLETT, C.W. & BEESTON, J.W., 1995: Geology of Australian coal basins. Geological Society of Australia CoaI Geology Group Special Publication, L. WARD, C.R. & SWAINE, D.J., 1995: Minerals and inorganic constituents . In Ward, C.R., Harrington, H.J., Mallett, C.W. & Beeston, J.W. (Editors): Geology ofAustralian coal basins. Geological Society of Australia Coal Geology Group Special Publication, 1, 93-110. Cover photo: Palaeogeography of Australia during Permian time slice 1 (250-248My), see Brakel & others, page 8. Copywritten by and reproduced with permission of the Australian Geological Survey Organisation

(from "Australia: Evolution of a Continent").

PREFACE Just on ten years have elapsed since the initial proposal was put for the Coal Geology Group to collaborate with the Bureau of Mineral Resources (now the Australian Geological Survey Organisation) to produce a monograph on Australian coal deposits as one of a series to mark the bicentennial of European settlement in 1988. An Editorial Committee was appointed, and after due deliberation, including discussions with a broader-based Advisory Board, the contents ofthe volume were drawn up and the various authors invited to prepare their contributions. Although a number of the necessary manuscripts were received in good time, it became clear as the bicentennial year approached that compiling the necessary information, particularly for the major coal basins of Australia, was a bigger job than had initially been anticipated. It was obviously inappropriate to bring out an incomplete work to mark such a significant occasion, and when the deadline could not be met the project was temporarily deferred. Similar problems arose for the other projects on the BMR's original list, and all of the volumes for the proposed series seem to have progressively run out of steam. Spurred on by the subsequent pasding ofthe bicentennial year for the discovery of coal in Australia (made by escaping convicts near Newcastle in 1791), a second phase of work was agreed to by the Coal Geology Group in order to complete the task. Although a certain amount of re-writing was necessary in some instances, the extra time was beneficial in many cases. It allowed a number of more recent developments, such as a better understanding of structure in the Bowen Basin and the results of extensive sedimentological studies in the Gunnedah Basin, to be taken more fully into account. It also allowed advantage to be taken of modern desk-top publishing techniques, so that the volume could be made available at a reasonable level of cost. The monograph itself involves contributions of two different types. The first eight papers deal with Australian coal deposits in general, including their geologic setting and quality characteristics and the history ofAustralian coal discovery, exploration and

research. The remainder deal with the geology of the individual coal deposits, either at a basin, regional or coalfield scale. It was always the intention of the volume to focus on geological interpretation, providing information where possible on the origin of the coal and coal-bearing successions as well as a summary of the basic descriptive data. Such interpretations are clearly better developed in some areas than in others, partly due to the nature of the information available. Indeed, by bringing together the current state ofknowledge on the different aspects and geographic areas in the one volume, it is hoped that comparisons can be drawn and opportunities identified for future geological work. The editors would like to thank the individual authors for their contributions, for their patience with the long compilation time, and for accepting without undue complaint most of the amendments made to their manuscripts in the editorial process. We would also like to thank the many colleagues who acted as formal or informal referees, as well as those who assisted in identifying the most

appropriate authors for the different individual tasks. Thanks are due to a number of organisations for allowing release of information, and to the various publishers (listed separately) for permission to reproduce extracts from copyright material. The Australian Geological Survey Organisation, which initiated the project, assisted substantially by providing copies of the map of Australian coal resources to accompany the volume, and CSIRO Division of Exploration and Mining provided invaluable assistance with drafting of the text-figures. A considerable amount of word processing, photocopying, mailing and other assistance was also provided at different stages of the project by the Department of Applied Geology at the the University of New South Wales. Finally we would like to thank the Geological Society of Australia Coal Geology Group for agreeing to make this volume, probably the most significant compilation to date on Australian coal geology, the first in its new Special Publication series.

CR Ward HJ Harrington CW Mallett JW Beeston

Geology of Australian Coal Basins

AFFILIATIONS AND ADDRESSES OF CONTRIBUTORS D Agnew NSW Department of Mineral Resources PO Box 51, Singleton NSW 2330 M Armstrong NSW Department of Mineral Resources PO Box 536, St Leonards NSW 2065

PJ Ashton Western Collieries Ltd 44 Wittenoom St, Collie WA 6225

AF Carr Coal Consultant

formerly Geological Survey of Queensland GPO Box 194, Brisbane QId 4001

DG Chapman Western Collieries Ltd 44 Wittenoom St, Collie WA 6225

BA Coxhead Queensland Coal Board QMEC, 61 Mary St, Brisbane Qld 4000

CA Bacon Mineral Resources Tasman ia PO Box 56, Rosnv Park Tas 7018

CFK Diessel

P Balfe Department of Minerals and Energy GPO Box 194, Brisbane Qld 4001 BE Balme Department of Geology University of Western Australia Nedlands WA 6009 WJ Bamberry NSW Department of Mineral Resources PO Box 51, Singleton NSW 2330 CM Barton Generation Victoria 15 William Street, Melbourne Vic 3000

J Beckett N.S.W. Department of Mineral Resources PO Box 51, Singleton NSW 2330 JW Beeston Geological Survey Division Department of Minerals and Energy, Queensland GPO Box 194, Brisbane Qld 4001

PA Bennett Queensland Coal Board QMEC, 61 Mary St Brisbane Qld 4000

MT Betlinski

Department of Geology University of Newcastle, Callaghan NSW 2038

JN Dunster Comalco Aluminium Ltd 12 Creek St, Brisbane Qld 4000 RG Elms Consultant 10 Boston Way, Booragoon WA 6154 formerly Western Collieries Ltd

AJ Falkner

University of Queensland St Lucia Qld 4067

PG Flood Department of Geology and Geophysics University of New England, Armidale NSW 2350

AG Galligan NSW Department of Mineral Resources PO Box 536, St Leonards NSW 2065 GS Gloe Consultant, Beaumaris Vic 3193 formerly State Electricity Commission of Victoria PW Gosconbe

Mineral Resources Consuitant 120 Ninth Avenue, St Lucia Qld 4067

HJ llarrington

Western Coliieries Ltd 44 Wittenoom St Collie WA 6225 MS Biggs Callide Coalfields Limited PO Box 144, Biloela Qld 4715 M Bocking Pacific Power GPO Box 5257, Sydney NSW 2001

Department of Geology The Australian National University GPO Box 4, Canberra, ACT, 0200 and Department of Geology and Geophysics, The University ofSydney, NSW 2006 formerly Australian Geological Survey Organisation

RM Hocking

PF Bolger

Camp, Scott & Furfey Pty Ltd

Consultant Engineers 390 St Kilda Road, Melbourne 3000 formerly Rural Water Resources Commission M Bosio Coal Consultant, Beaumont, SA formerly Electricity Trust of South Australia

M Bradshaw Australian Geological Survey Organisation GPO Box 378, Canberra, ACT, 0200

AT Brakel Australian Geological Survey Organisation GPO Box 378, Canberra ACT 0200 SH Brennan Electricity Trust of South Australia PO Box 6, Eastwood SA 5063

Geological Survey of Western Australia 100 Plain St East Perth WA 6004

GR Holdgate Monash University Clayton Vic 3168

M Howes Pacific Power GPO Box 5257, Sydney 2001 WW Hughes

Coal Compensation Board PO Box 689, Strawberry HiIIs NSW 2012

formerly Ulan Coal Mines Ltd AC Hutton

Department of Geology University of Wollongong Northfields Avenue, Wollongong NSW 2500

M Ives

DJ Brockway

State Electricity Commission of Victoria 15 William St, Melbourne Vic 3000 CM Brown (deceased) Australian Geological Survey Organisation PO Box 378, Canberra ACT 0200

DJ Douglas and Partners Pty Ltd 1 National Avenue, Newcastle West NSW 2302

K Brown Earth Data Pty Ltd PO Box 430, Maitland NSW 2320

D Johnson NSW Department of Mineral Resources PO Box 51, Singleton NSW 2330

JH Bryan

DP Johnson

McElroy Bryan and Associates Pty Limited, PO Box 34, Willoughby NSW 2068 AW Burgess Placer Pacific Pty Ltd Kidston Gold Mine formerly Cailide Coalfields Limited

RK Johns

Geological Survey of South Australia PO Box 151 Eastwood SA 5063

Department of Earth Sciences, James Cook University Townsville Qld 4811 BG Jones Department of Geology University of Wollongong Northfields Avenue, Wollongong NSW 2500

Geology of Australian Coal Basins

G Rose

PR Kenley Geological Survey of Victoria 140 Bourke St, Melbourne Vic 3000

NSW Department of Mineral Resources PO Box SSO, St Leonards, NSW 2065 SG Scott

AP Kershaw

Department of Geography, Monash lJniversity Clayton Vic 3168 AG Kremor Consuitant formerly Electricity Trust of South Australia

Department of Minerals and Energy, Queensland

S Kristensen

MJ Sniffin

CRA Exploration Pty Ltd

GPO Box 194, Brisbane Qld 4001

M SmYth

CSIRO Division of Petroleum Resources PO Box 136, North RYde NSW 2113

21 Wynyard St, Belmont WA 6104

NSW Office of EnergY PO Box 536, St Leonards NSW 2065

ER Lindner

GM SPringbett

PO Box 6, Eastwood SA 5063

formerly Electricity Trust of South Australia HRE Staines

Electricity Trust of South Australia

G and S Resources, Adelaide

JII Lord

Geologicai Survey of Western Ar,stralia 100 Plain St, Perth WA 6000

formerlY Department of Minerals and Energy, Queensland

TP Maher CSIRO Division of Coal & Energy Technology PO Box 136, North RYde NSW 2113 CW Mallett CSIRO Division of Exploration and Mining PO Box 883, Kenmore QId 4069 SG Matheson

Department of Minerals and Energy, Queensland GPO Box 194, Brisbane Qld 4001 RG Matthews Western Collieries Ltd 44 Wittenoom St, Collie WA 6225

BA McConachie Comalco Aluminium Ltd

12 Creek St, Brisbane QId 4000

I McDonald formerly

NSW Department of Mineral Resources

CT McElroy McElroy Bryan and Associates Pty Limited PO Box 34, WilloughbY NSW 2068 T Mclennan

CSIRO Division of Exploration and Mining PO Box 883, Kenmore QId 4069

DC Mengel formerlv Department of Minerals and Energy, Queensland GM Meyer Western Mining CorPcration 168 Greenhill Road, Parkside 5063

VT Moran Coai Consultant, CoIIie WA

D Sullivan

formerly CSIRO Division of Exploration and Mining

'DJ Swaine

CSIRO Division of Coal and Energy Technology PO Box 136, North RYde NSW 2113

NZ Tadros

N.S.W. Department of Mineral Resources PO Box 53-6, St Leonards NSW 2065

GH TaYlor

Research School of Earth Sciences

Australian National UniversitY

GPO Box 4, Canberra ACT 0200

BR Thomson (deceased) Geological SurveY of Victoria 115 Victoria Parade, FitzroY 3065 MP Thornton Department of Minerals and Energy, Queensland GPb Box 194, Brisbane Qld 4001

J Thrift

Runge Mining GPO Box 2774,Brisbane Qld 4001

JM Totterdell

Australian Geological Survey Organisation GPO Box 378, Canberra ACT 0200

MP Walker

Queensland Coal Board QUEC, 61 MarY St, Brisbane Qld 4000

P Warbrooke BHP Minerals PtY Ltd PO Box 619, HawthorneYic 3122

A Norman Consultant Geologist formerly NSW Department of Mineral Resources

CR Ward Department of ApPlied Gg-olqgv UniversitY of New South Wales SydneY NSW 2052

RB Patrick

J Webb

C Pattison Geocontext PtY Ltd PO Box 519, Annerley, Brisbane Qld 4103 - - formerly CSIRO Diviiion of Exploration and Mining

CR Weber

Caliide Coalfields Limited PO Box 144, Biloela Qld 4715

C Peck

Pacific Power GPO Box 5257, SYdneY NSW 2001

RL Webster

North Broken Hill Ltd

Cornwall Coal ComPanY PO Box 402 Fingal, Tas 7214

PO Box 1903R, Melbourne Vic 3001

BJ Pesram

Tarong"Coal - Pacific Coal Pty Limited PO Box 36, Nanango Qld 4615

B Preston Coal & Allied OPerations PtY Ltd

AT Wells

Australian Geological Survey Organisation GPO Box 3?8, Canberra ACT 0200

GEWilford

PO Box 75?, Muswellbrook NSW 2333

J Preston

Australian Geological Survey Organisation GPO Box 378, Canberra ACT 0200

AN Yeates Australian Geological Survey Organisation

BHP Petroleum GPO Box 1911R, Melbourne Vic 3001

GPO Box 3?8, Canberra ACT 0200

formerly CRA ExPloration R Rigby

DePartment of GeologY La Trobe UniversitY Bundoora Vic 3083

EKYoo

The lteicastle Wallsend Coal Company Pty Ltd PO Box 156, Cessnock NSW 2325

NSW Department of Mineral Resources PO Box 6ee, St Leonards NSW 2065

Geology of Australian Coal Basins

PERMISSION TO REPRODUCE COPYRIGHT MATERIAL .

Australasian Institute of Mining and Metallurgy PO Box 660 Carlton South Vic 3053 (Minerals and inorganics - Figure 6; Nymboida Coalfield, New South Wales - Figure l).

Australian Academy of Science GPO Box 783

Canberra ACT 0200 (Gippsland Basin - Figures 6 and l0).

Australian Geological Survey Organisation GPO Box 378

Canberra ACT 0200

(Palaeogeographic settings of Australian coal measures - Figures I to l0).

Australian Mineral Foundation 63 Conyngham St Frewville SA 5063 (Palaeogeographic settings of Australian coal measures - Figure 4)

AustralianPetroleumExplorationAssociation 167 Macquarie St Sydney NSW 2000 (Palaeoclimate and depositional settings of Australian coal measures -Figure 12; Cretaceous Coals of the Gippsland and Otway Basins, Victoria -Figure 2).

BlackwellscientificPublications PO Box 378

Carlton Vic 3053

(Petrographic constituents of Australian coals - Figures l7 and l8).

Butterworth Heinemann Limited Linacre House Jordon HiIl Oxford, OX2 8DP United Kingdom (Coal resources, quality and utilization - Figure 12).

Dr DF Branagan Department of Geology and Geophysics University of Sydney NSW 2006 (History of Australian coal discovery, exploration and geological research -Figures l and2).

Professor KSW Campbell Department of Geology Australian National University PO Box 4 Canberra ACT 0020 (Palaeoclimate and depositional settings of Australian coal measures - Figure 9).

Elsevier Science Publishers PO Box 330 1000 AH Amsterdam The Netherlands (Palaeoclimate and depositional settings of Australian coal measures - Figure 7).

Geological Society of Australia Incorporated

504 Wynyard House, 301 George Street Sydney NSW 2000 (Palaeoclimate and depositional settings of Australian coal measures- Figure 2; Bowen Basin -Figure 3; Cretaceous coals of the Gippsland and Otway Basins, Victoria - Figure 2).

NSW Department of Mineral Resources PO Box 536 St Leonards NSW 2065 Palaeoclimate and depositional settings of Australian coal measures- Figures 5 and 9; Minerals and Inorganic Constituents - Figure 5; Sydney Basin-Southern -Figure 7).

University of Newcastle Department of Geology Callaghan NSW 2308 (Minerals and inorganic constituents -Figure 4; Sydney Basin-Newcastle - Figures 3 and 5).

Geology of Australian Coal Basins

CONTENTS PART 1 - GEOLOGICAL SETTING AND PROPERTIES OF AUSTRALIAN COAL BASINS

PalaeographicsettingsofAustralianCoalMeasures(Brakel & others) PalaeoclimateandDepositionalSettingsofAustralianCoalMeasures(Johnson) ... Floras of Australian Coal Measures, withNotesontheirAssociatedFaunas(Balme & others) Petrographic Constituents of Australian Coals (Diessel & Smyth) Rank and Vitrinite Reflectivity (Beeston) MineralsandlnorganicConstituents(Ward &Swaine) HistoryofAustralianCorilDiscoveryrExplorationandGeologicalResearch(Bryan &others) Coal Resources, Quality and Utilization (Maher & others)

.......1 .....17 .......4I . . . . . 63 . . . . . . . . 83

........93 ........ 111 . . . . . 133

PART 2 - PERMIAN COAL DEPOSITS: Sydney Basin Sydney-GunnedahBasinOueruiew (Tadros) Hunter Coalfield (Sniffin & Beckett) NewcastleCoalfield (Agnew&others) SouthernCoalfield (Armstrong&others) WesternCoalfield (Yoo & others)

GunnedahBasin(Tadros).....

...163 . . .177

.......197 .....2L3 ......23L .....247

Bowen Basin (Mallett & others)

.......34L

GalileeBasin(Scott& others)

CooperBasin(Beeston)

......353

Arckaringa Basin (McConachie & Dunster)

. . . . . . . 361

CollieandWilgaBasins(Ashton&others) PerthBasin(Kristensen) CarnarvonBasin(Hocking) CanningBasin(Yeates) AshfordArea,N.S.W. (Flood) OaklandsBasin,N.S.W(Yoo). GloucesterBasin,N.S.W.(Hughes) MountMulliganCoalfreld,Queensland(Matheson) CalenBasinrQueensland(Brakel)

.......369 .....387

........395 ......401 .......407

......4LI ........417 .....431

........435

PART 3 - MESOZOIC AND TERTIARY COAI DEPOSITS:

TasmaniaBasin(Bacon) IpswichCoalfreld(Staines & others) TarongBasin(Pegram) CallideBasin(Biggs &others) Clarence-Moreton, Surat, Eromanga, Nambour and Mulgildie Basins (Goscombe & Coxhead)

&others) Mar5rboroughBasin,Queensland(Thornton) Nymboida Coalfreld, New South Wales (Wells) LeighCreekCoalfreld(Springbett

Cretaceous Coals of the Gippsland and Otway Basins, Victoria (Ward) GippslandBasin(Barton& others) Murray Basin in Victoria and New South Wales (Brown & others) OtwayBasin,Victoria(Barton) CainozoicBasinsof SouthAustralia (Kremor & others) BremerBasin,WesternAustralia(Elms & others)

Geology of Australian Coal Basins

.....441,

.......455 ......465 ......471, . . . 489

......513 .....525 . . .529 . . . . 533

........541 . . . . 561

.....573 . ... ...577

......585

Pa;rt 1 r Geological Setting and Properties of Australian Coal Basins

Geology of Australian Coal Basins

ffialaeogeographic settings of Australian coal measures

The oldest Australian coals are Carboniferous in age and economically insignificant. All subsequent geologicql Periods up to the Tertiary, however, have provided at least some economic coal deposits. The most important are the Permian black coals and the

Tertiary brown coals.

The coals formed in a variety of palaeogeographic settings. The purpose ofthis paper is to provide a brief overview of the settings of each major coalbearing sequence and basin. A separate paper by Johnson (this volume) discusses the palaeoclimate and depositional environments in detail. The palaeogeographic maps presented here were compiled as part of the Australian Palaeogeographic Mapls Project, undertaken between 1984 and 1987 by the Bureau of Mineral Resources (BMR) (now AGSO) and the Petroleum Division of the Australian Mineral Industries Research Association (APIRA), with the support of a number of petroleum and

mineral exploration companies.

AT Brakel GE Wilford

JM Totterdell and M Bradshaw

Continent-wide palaeogeographic maps were compiled for the entire Phanerozoic of Australia, but only the nine featuring the major coal depositional episodes are included here. The methodology of Cook (1982, 1988) was used:

after a review ofthe available literature and unpublished sources, data sheets summarizing the significant lithostratigraphic and biostratigraphic information were compiled. The data were then compiled into summary stratigraphic charts, used not only for inter- and intra-basinal correlations, but also to establish the locations of major time breaks or major changes in sedimentation or tectonism. The charts were then used to identify sedimentologically significant time intervals, referred to as'time slices' (Figure 1). The 'time slice' approach depicts, in a more generallized way than a 'snapshot', the palaeogeogeography for a period of time. The

technique overcomes the problem that it is seldom

possible to delineate precise continent-wide time lines; however, it suffers from the diffrculty that the longer the period of time represented by the time slice, the less precise is the palaeogeographic map.

With the time slices established, it was possible to compile data maps for each slice at a scale of 1:5 000 000. These maps, together with a map outlining the the structural elements of the continent for each Period, were used to construct interpretive palaeogeographic maps showing generallized depositional environments, and, in some versions (1:5 000 000 and L:10 000 000), other features such as sediment types and stream flow trends.

Palaeogeographic studies bring together many

sub-disciplines of the geosciences, with the aim of presenting the geography of an area during a selected time in the past. The emphasis in this paper is on the successive changes in the broad depositional environments and eustacy. While the tectonic processes controlling basin development will be mentioned, the amplification of this aspect is left to other authors in this volume and elsewhere.

It is not possible here to acknowledge individually the very large number of people who contributed to a project of such wide scope as this one: detailed lists are given in AGSO's published cornmentary notes on the maps for each Period.

Palaeogeography

ERA

-1-l'ilocene

C RETAC EO U S

CzZ

Paleocene

Cz1

Maastrichtian

K11

Campanian

K10

C' nt^^ian

K8 K7 K6

llannmenien

Albian

JURASSIC

Callovian Bathonian Baiocian Aalenian Tna raeia n

200

TR IASS IC

Pliensbachian Sinemrrrian Hettanoian Rhaetian Norian Carnian Ladinian Anicien Scvthian

falarien Kannian PE RM IAN

K4 K3 K2 K1 .tl n

J7 J6 J4

----r J3 J2 J1

h6 T5

---15Jl

----t P7 t

Sakmarian

Asselian

Westphalian

Stephanian

CARBON I FERO US

un0uilan Artinckien

O l\ c)

Tithonian Kimmeridoian 0xfordian

l\ o a IIJ

Cz3

Aotian Barremian Havterivian Valanoinian Berriasian

300

Cz4

Eocene

FIGU RE

--.lLrZUf

0ligocene

TE RTIARY

100

Miocene

O l\ O

TIME SLICE

EPOCH

PERIOD

Namurian

c5 c4

Visean

c3 c2

Tournasian

Figure 1. Positions of time slices and selected time slice maps.

Geology of Australian Coal Basins

CARBONIFEROUS There are no economic occurrences of Carboniferous coal in Australia. Small occurrences are, however, known from along the northern margin of the Sydney Basin in New South Wales (Diessel, 1975), and from the Pascoe River in far north Queensland (Carr, 1975). The geological setting ofthe Pascoe River deposits is poorly known, but the New South Wales occurrences, which range from Early to Late Carboniferous in age, originated on a sedimentary apron between the flank of an Andean-type volcanic arc (McPhie, 1987) and the sea to the northeast. The older coals tended to be paralic, but increasing numbers of fresh-water coals later appeared, forming in a distal braidplain setting encroached on at times by alluvial fans.

appropriate tectonic conditions. Deltaic and meandering-fluvial systems were the most productive, but braided fluvial (including alluvial fan), fluvio-lacustrine (including raised bog), and back-barrier settings were also significant. Climate played a key role in peat preservation. Low palaeotemperatures greatly retarded organic decomposition, allowing vegetable matter to accumulate in situations and to thicknesses otherwise not possible, analogous to the peatlands of modern Canada (Martini & Glooschenko, 1985). The Early Permian initiation of the Sydney-Bowen Basin in an extensional or transtensional tectonic setting is directly related to activity along the palaeo-Pacific margin of Gondwana, which had a history of subduction, arc magmatism, strike-slip movements, arc migration, and crustal

The question has often been asked why there is so little coal in the Australian Carboniferous when this was the main coal-forming Period in the Northern Hemisphere. For much of the time Australia lay in proximity to the southern pole, and thus had a cold climate (McElhinny, 1973). This is, however, also true of much of the Permian, at which time it did not impede the most widespread coal measures deposition the continent has known.

extension-related magmatism (Totterdell, 1990). The development of intracratonic basins further west may also have been controlled by the stresses developed by plate interactions along the margin. The formation of basins along the Western Australian coast can be related to a phase of crustal extension preceding the rifting off of some Gondwanan fragments which are now lodged in Asia.

Pre-requisites for the formation of coal are:

The coal basins to which the sea had access in the Early Permian (Sydney, Tasmania, Arckaringa and northern Perth Basins) followed a common

(1) adequate conditions for the growth ofplants, so that 'available; a supply of vegetable matter is (2) sufficient oxygen-deficient water to protect the plant remains from oxidation; and (3) active subsidence to accommodate sediments that

will bury and preserve the peat.

It appears that conditions in the Carboniferous basins were often suitable for plant growth, judging by the abundant plant fossils commonly present. Although by Seaham Formation time the climate was cold and plant growth slow (with tundra communities according to Retallack, 1980), the low temperatures also greatly slowed down decomposition of the biomass that did form. The sediment thicknesses in the basinal areas, moreover, show that there was adequate subsidence and burial. The factor that may have been missing during the Australian Carboniferous was humidity at a critical time. If the precipitation (as either snow or rain) was low, few wetlands may have existed during dry summers. Except for a few small favoured locations,

relatively low annual organic productivity, combined with dry summers, could have prevented peat

sedimentary evolution during the time interval Permian 1-4, of initial marine conditions regressing to coal measures deposition. Basins dominated by rift volcanism (Gunnedah, Werrie, Gloucester, and Bowen Basins) have a thick volcanic pile substituting for all or most of the basal marine sequence, while basins beyond the reach of the sea (Pedirka, Cooper, and Galilee Basins, and the Strathmuir Synclinorium) have fluvial sequences instead. The Collie and southern Perth Basins followed a different path, with coal measures being either the initial deposits or taking over from a thin basal glacigene layer. This probably arose because these areas were at first occupied by the Yilgarn ice cap, with peatlands developing later on a poorly drained landscape patchily covered by ice-retreat sediments. The Denison Trough succession also appears to have begun directly with coal measures, at least on the

trough margins; the base of the unit in the deepest part ofthe trough has not been intersected by drilling, and may well lie on a fluvial or volcanic substrate.

accumulation.

Permian time slice 2

PERMIAN

A coal-forming fluvial setting, including alluvial fan and lacustrine facies, prevailed in the Reids Dome beds of the Denison Trough (Draper & Beeston, 1985). The eastern Galilee Basin was partly occupied by rivers and some lakes, but without peat development (Hawkins, 1978), and a shallow repository also began forming in the Lovelle Depression to the west (Hawkins & Harrison, 1978). In the Cooper Basin, a fluvial sequence ranged vertically and laterally from braided (Tirrawarra Sandstone) to meandering streams (Patchawarra Formation) (Thornton, 1979), with the latter facies containing the most coal.

By the time of the Permian-Carboniferous boundary, the southwestern half of the Australian continent was covered by ice sheets, and the rest was dotted with local valley glaciers (Brakel & Totterdell, 7992). No coal was deposited except for very minor occurrences in the Cooper and Arafura Basins.

Significant coal deposition only began following the early to middle Sakmarian deglaciation. It is striking that most of the coal was formed in two intervals of time, Permian 3-4 and Permian 6-7, the latter having the volumetrically greatest and areally most widespread coal development. All humid depositional environments on land were potentially capable of preserving coal-forming peat, given

The Sue Coal Measures (southern Perth Basin) and the Collie Coal Measures began their long period of deposition at this time.

Palaeogeography

Ftgrre 2Jata"ogeography of Australia during Permian time slice 3'

Permian time slice 3 The late Sakamarian continent (Figure 2) remained in the grip of the tectonic setting which had earlier

initiated the basins along the eastern and western margins and in the interior. A belt of rift-related volcanics dominated the Sydney-Bowen region.

A notable fall in sea level affected many Australian basins at this time, particularly those in the far southeast. In the Tasmania Basin, fluvial sediments, including the Mersey CoaI Measures and equivaleirts, extended southeastwards across most of the state (Clarke, 1989) as the sea retreated.

Fluvial coal measures were also deposited in the Denison Trough (Bowen Basin) and the Galil-ee, southern Cooper, Collie, and Perth Bas-ins' The Denison Trough (Reids Dome beds) and Cooper Basin (Patchawarra Formation) also contained lakes. The Nappamerri Trough of the Cooper Basin has a concentfation ofchannel belt sandstones, because it subsided slightly faster than adjacent areas and attracted the drainage, whereas slower subsidence is indicated for the Patchawarra Trough (Wells & O'Brien, 1989). The Aramac Coal Measures iormed in both depocentres of the Galilee Basin,

with clastic components being fed in from neighbouring highs (Hawkins, 1978). The Pedirka and Arckaringa Basins, in central and South Australia, developed coal measures in the Purni and Mt Toondina Formations in the later half of the time interval (Youngs, 1975; Townsend, 1976), as clastic input from the adjacent erosional highlands d6clined and peatlands-were able to form. Thle Sue Coal Measures continued accumulating in

the southern Perth Basin, but the northern half of the basin remained marine until the close of the interval, when the fluvial facies of the Irwin River Coal Measures extended across the region. The Sydney Basin, being mostly shallow marine,-

*ur not a coal-forming area at this time, except for

small, sporadic, unecdnomic lenses in the southern portion,'which represent marshes behind the iringing barrier bars of a fa! delta complex (Evans & oiheis, 1983). Evidence ofseasonal ice,rafting in the associated sequence shows that the climate was still moderately c6ld. Minor uneconomic coal also occurs in the meandering stream facies of the upper Carmila beds in the Stralhmuir Synclinorium of .enttat eastern Queensland (Jensen & others, 1966)'

Geology of Australian Coal Basins

ENVIRONMENTS

unctassified

l,rTi,"y,,,r,

ffi

0,,,,,,

COASTAL

MARINE

erosional

i,T,i:!::f,i:l

inteftidat/ N

shallow

supratidal N\\N p-200m water depth)

ffiIil dettaic rufiFoil,,f,i!!'o\l,rt

Figure 3. Palaeogeography ofAust"

The eastern Carnarvon Basin experienced a series of diverse events, the most notable-being the construction of the large delta complex of the Wooramel Group (Lavering, 1985).-With more than twice the area of the.Mississippi delta, this complex must have been fed by a comparably large drainage

lystem, probably extending to the central Australian highlands and possibly part of Antarctica as well (Brakel & Totterdell, 1992). Despite deltas commonly being a favourable environment for peat formation, no peat has been preserved as coal in the Wooramel delta. The reasons for the absence ofcoal are uncertain. The transgressive marine conditions in which the delta was built would have precluded the presence of coal according to the model of Van Wagoner and others (1990), because coal seams are held to form towards the end of r-egressive cycles. However, many examples of undoubtedly transgressive coais are known (Diessel, 1992; Holdgate,7992), and this model has therefore been disputed.

Permian time slice 4 A renewed cooling of the climate during this time slice brought a return of local glaciers [o western Victoria and the highlands along the western

Sydney Basin (Figure 3). Volcanism in the SydneyBowen region had ceased, and the only subaerialeruptive activity was in local centres in the New England Orogen. There was a reversion to marine tra!sgression in many basins, ending coal deposition in the Tasmania, northern Perth, and Bowen Basins. However, an apron of coalescing fan deltas, constructed south of a rising hinterland, formed a prograding coastline in the northern Sydney Basin early in the time interval, while a similar line of alluvial fans and distal alluvial plains extended northwesterly into the Gunnedah Basin. The Gunnedah Basin was divided into two major sub-basins by the Boggabri Ridge. Peat, aggrading in raised bogs on the fan surfaces, gave rise to the important seams of the Greta Coal Measures and their equivalents. Subaerial deposition was ended bya relative sea level rise, which also submerged the western margin of the Sydney Basin. Flooding was diachronoqs, and took some time to penetrate northwards deep into the Gunnedatr-Basin. The small Gloucester Basin north of Newcastle, which preserves a wave-dominated and coal-bearing fan delta system (the Dewrang Group), also felt ihe effects of this marine encroachment (Lennox & Wilcock, L985; Hughes, this volume).

Palaeogeography

On the western flank of the Bowen Basin, the large Aldebaran Sandstone delta, supplied by detritus eroded off the Anakie High and probably the Galilee Basin area, at first filled the Denison Trough and then spilled over the confining Comet P-latform (Brakel, 1989). The northern tip of thg basin was occupied by the alluvial fan of t-he Collinsville Coal Meaiures,-advancing mainly from the west before the marine transgreision had reached the area, andeventually meeting the sea as a fan delta. The small Blair Athol and Wolfang Basins north of Clermont were topographic depressions at the time, aqd a-!so the site-ofraised peat bogs (Smyth, 1980)' The Calen Basin in the Strathmuir Synclinorium, meanwhile, received coal measure sediments in a predominantly lower delta plain setting (Brakel, this volume).

Fluvial coal measures continued to collect in the southern Perth Basin and nearby smaller basins. Border faults, affecting sedimentation, were active in the Collie Basin, and may have restricted deposition to within the presently preserved basin (Pirk, 1982). Wilson (1989), however, believes that the Collie basin was part of a wider depositional atea. Sedimentation in the Arckaringa and Pedirka Basins came to an end, as subsidence ceased and the basins filled. The southern Cooper Basin twice saw-the development of laige lakes, approximately 250 by 150krnin size. In bbth cases these extended diachronously westwards. This suggests blocking of the drainage'at the northeastern end of the basin and backfilling of the lakes towards the southwest (Stuart, 1976), perhaps because of ponding as. a result of global-eustatic highstands, ortectonic movement along the Karmona trend. The first lake (in which the Murteree Shale accumulated) was infilled by deltas and the reclaimed territory converted to peatlands (the Epsilon Formation), which were in turn inundated when the second lake (site of the Roseneath Shale) formed and encroached westwards (Thornton, 1979).

Highlands still existed west of the Bowen Basin to beyond Cairns in north Queensland, as a remnant effect of earlier igneous and tectonic activity. They also persisted in the western New England - Yarrol region between the Sydney - Bowen trough and the sea. A small intermontane basin near "ritern was able to accrue coal measures (Flood, Ashford this volume), which were preserved by later down-faulting. The time slice ended in a major episode of uplift and folding, perhaps due to the docking of the Curtis terranl. This episode affected a large portion of

eastern Austraiia, and generated hiatuses from the Sydney to the Bowen and Galilee Basins.

Permian time slice 6 The Permian 5 interval had seen a major rise in sea level, which had inundated many basins. The general pattern for the rest of the Late Permian was [hat of a long period of regression, again culminating in coal measures deposition, but the^re were manyltariations on the general trend. Brief

marine inlursions at times interrupted non-marine sedimentation. The development of large progradational complexes on both sides ofthe conlinent (Figure 4) points to a eustatic dro,p-in sea level, starting in Permian 6, as the cause of the regression. However, the eastern basins were also

affected by local tectonism. The Sydney - Bowen Basin took on the nature of a foreland basin, with episodic thrusting and transpression along the eastern-bounding Hunter - Mooki - Goondawindi

fault system.

The Sydney, Gunnedah and Gloucester Basins filled with deltait'and fluvial coal measures (Tomago Coal Measures and equivalents), as clastics poured in from adjacent uplifted areas in New England and to a lessef extent from the western highlands of the Lachlan Fold Belt. The major anticlines in the northern Sydney Basin were also active. The main proeradation diiection was southerly along the basin ^axe's, but most detritus was introduced into the depositional system from the sides via alluvial fans. Earlv in the interval, subsidence of the eastern parti of the basins biiefly admitted the sea (the kulnura Marine Tongue and equivalents), and promoted the growthlf an extensive alluvial fan ipron along tlie western margins (Marangaroo

Cbnglomerite) (Hunt & others, 1986). Another Formation and marlne incursion (Dempsey -eustatic in nature (Brakel, equivalents), this time 1086), marked the end of the time slice.

Volcanoes were active in the southeastern Sydney Basin at the start of the interval (the Gerringong

latitic eruptions). Later, felsic volcanism began^^

further notth o.t the eastern side of the basin off Newcastle, contributing tuffs to the Tomago Coal Measures. One of these tuffs, the Thornton Claystone, originated in a lateral blast eruption whiih devastaied a forest and laid out the tree truncks in a NE-SW orientation (Diessel & others, 1985). Granitic intrusion accompanied uplift and consequent erosion in New England. A major eruptive region developed where magma broke through to Ihe surface-between Drake and Armidale, generiting terrestrial felsic volcanics (including the Annalee Pyroclastics). The Bowen Basin remained marine at first, with continuing transgression in the west and onto the Springsur-e Shelf-leading into the .southern Galilee Blsin] Dropstones werelafted in by seasonal ice (Draper, 1933). Late in the interval a coal--prone . deltaic facies prograded from the north (Moranbah Coal Measurei and German Creek Formation), to be interrupted by the same eustatic highstand responsible for the Dempsey Form-ation in the Svdnev Basin. The small Moorlands Basin, between tlie GJlilee and Bowen Basins north of Clermont, experienced three marine episodes interspersed with paialic and fluvial interludes, including peatland development (Sorby & Scott, 1988).

Extensive fluvial coal measures deposition resumed in the Galilee Basin, and later in the Cooper Basin, to enlarge these basins to their greatest-ever areal extent. butflow from both basins was into the Bowen Basin sea via the Springsure Shelf embayment. The Galilee Basin was bordergi^Uy . highlinds of moderate relief, with some uplift in the eait (Hawkins, 1978). In the Cooper Basin, at the time of basal Toolachee Formation deposition, subsidence was greatest at the southeaste-rn end, and especially in the troughs, -while the adjacent.. anticlinal ridges, such as the Gidgealpa-MerrimeliaInnamincka culminations, stood above the depositional plain. Some lakes were present within the peatlands.

Rifting in two places on the site of the later Laura Basin-on Cape-York Peninsula, attegd-ed by s.ome rhyolitic volianism, allowed entry of the sea in

Geology of Australian Coal Basins

IRONMENTS

tl ft

unctassiried

F--

erosionat

tv,!,v,,v" tv!v!vv!vJ t!,v,.""v,

rlf1l,oJ,irc C0ASTAL racustrine

depositionat, ied

unictassif

truviat

MARTNE

i|lriA'llfi, ffirrrr,,, ffiffi i3lriAil!{!,oruot

ffiintertidat/. N9la1^oyt supratidat N\\N (0-200m water depth) llii!.i.i.i.i.tiii!.i..,.i

ff[ff[fllo'u"' m?!ffi:J|i,1!{'ifl,,t

Figure 4. Palaeogeography of Australia during Perrnian time slice 6. places. It also led to the initiation ofparalic and fluvial facies, some with impure coal seams (de Keyser & Lucas, 1968). The small Mount Mulligan

and Olive River Basins preserved wholly terrestrial coal measures sequences, in the former because of

down-faulting (Wells, 1989a,b).

The Oaklands Basin in southern New South Wales, which was initiated during Permian 5, was collecting fluvial coal measures (Yoo, this volume). The Perth Basin, apart from the Sue Coal Measures in its south, also had minor coals deposited in the fluvial to shallow marine Wagina Sandstone of its northern half. Large deltaic complexes in the Bonaparte Basin (Hyland Bay Formation) and Fitzroy Trough of the Canning Basin (Condren Sandstone) suggest that there was considerable erosion in the central Australian hinterland. Despite their size, comparable to the Mississippi delta or larger, the deltas contain only some thin uneconomic coal seams (Milligan, 1975; Lord, L975).

Permian time slice 7 The last Permian time slice, though short, represents the culmination of the Late Permian

progradation, when very few marine domarns were left within the present day coastlines. It was characterized by the most widespread coal deposition the continent has ever known, with coal being deposited in every non-marine basin from Cape York to Tasmania and across to Perth.

After the eustatic interruption at the end of Permian 6, the subsiding Sydney-Bowen foredeep was again overwhelmed by detritus shed from actively rising highs in the orogen to the east, and to a lesser extent from westerly sources (Figure 5). The Sydney Basin was at first occupied by deltaic peatlands, but with continuing southerly progradation alluvial fans advanced into the depositional site from the north and northeast. In the northern proximal areas, raised peat bogs formed on the fan surfaces during quiescent periods, leading to coal seams becoming sandwiched between thick conglomerates. Large volumes of tuff were contributed to the Newcastle and Wollombi Coal Measures, mostly from volcanic centres along the Northumberland Ridge to the east. One eruption took the form of a Mt. St. Helens - type laterally directed blast, which devastated a forest and laid out the tree trunks in an ENE-WSW orientation, with a thick blanket of volcanic ash completely overwhelming the peat swamp in which

Palaeogeography

t'--$-,;,- ,{ ENVIRONMENTS LAND

unctassiried e

W ,l!!i,!i,,r, COASTAL

MARINE very shallow (0-20m water depth)

rosional

depositional, unclassified

fluvial

lflllfil 0,,,,,, m9lx[?i,;i,i!{'oTl,,t

Figure 5. Palaeogeography of Australia during Permian time slice 7. the trees were growing (Diessel, 1985). The climate was still cold temperate (Riek, 1972). The upper Black Jack Group of the Gunnedah Basin, upstream from the Sydney Basin, exhibits a simitrar

depositional history of upper delta plain facies being covered by fluvial plain and alluvial fan coal measures (Hamilton & Beckett, 1984; Tadros, this volume). Again a southerly drainage system prevailed. As with the Sydney Basin, volcanic ash was repeatedly showered over the region, in this case mainly originating from the eruptive complexes in New England.

The Bowen Basin history at this time (Fairhill Rangal interval) was also one of infilling, with marine and deltaic facies being succeeded by fluvial systems. A cool temperate climate prevailed over the region (Rigby, 7972), and peatlands were widespread

until Rewan Group times. Progradation initially followed a radial pattern from the basin sides, before

proceeding along the basin axis. Palaeocurrent measurements by Jensen (1975) show southerly- and northerly-directed currents in the north and south of the exposed portion of the basin respectively, converging on the central area, consistent with

tributaries supplying a trunk drainage flowing easterly out of the basin.

The higher sulphur levels (Hunt & Brakel, 1989) and high boron contents (Swaine, 1971) in the coals of the central eastern margin area confirm that the last remnant of the sea occupied this area before its final expulsion. A few spinose acritarchs reported from near the base of the Rewan Group in the southeastern Bowen Basin (Foster, 1979) hint that the sea was still not far away when coal deposition ended there. Much addition of tuff is again evident in the coal measures, and, although their locations are not established, the source vents probably lay along the eastern side of the basin (Connors Arch and Auburn High). The volcanic arc would have had at least one gap, similar to the gaps in the modern Cascades and Sunda Arcs, to allow out the drainage from the Bowen Basin. The Galilee and Cooper Basins continued as large expanses of coal-prone fluvial deposition, draining easterly into the Bowen Basin. Differential subsidence in the Cooper Basin troughs attracted

meandering streams to the lower areas (Wells & O'Brien, 1989); lake-dominated areas also existed, some bordered by erosional highs (Thornton, 1979). The state of the small basins at Oaklands and far north Queensland was little changed. Tasmania had a progradational, coal-forming setting similar to the

Geology of Australian Coal Basins

ENVIRONMENTS LAND

unctassiried erosional de positional, unclassified

W,l!!l,ii,,r, 00ASTAL

fluvial

Figure 6. Palaeogeogra

tacustrine

MARINE

ffir,,,,,,/ ffiffi i3!rilllli!,o,r,o) |jl$-----ffi,Eil i nt e

ft da t i

lii:i:iiiiiiiiiiiil supratidat

s ha t t ow

N\\N p-200m water depth)

ffi a,u,i, mi!#ril,i,i!i',ifl,n

of Australia

Triassic time slice 5.

main eastern Australian basins, as a former marine embayment was filled in by the Cygnet Coal Measures and equivalent fluvial formations. Much of the sediment appears to have been sourced in northern Victoria Land, and may have reached its final resting place after up to 2000km of transport via an arcuate river system (Barrett & Fitzgerald, 1985). Postulated uplift and erosive areas in NE, NW,and SW Tasmania (Banks & Clarke, 1987) imply some contribution of detritus from these regions as well.

In the southwestern corner ofthe continent, deposition of the uppermost Sue Coal Measures was succeeded by the Sabina Sandstone, which contains only minor coal. The Sabina Sandstone, although predominantly fluvial, seems to become increasingly paralic towards the north (Playford & others, 1976), a factor that hints at a marine incursion in the north ofthe basin. The central Fitzroy Trough was occupied a large fluvial lobe, supplied from the Kimberley uplands,

which incorporated minor coals (the Hicks Range Sandstone Member of the Hardman Formation). A marine intrusion then resulted in deposition of shallow marine and coastal sediments, but as progradation began to be re-asserted there was

eventually a return to minor coal emplacement (Cherrabun Member) (Towner & Gibson, 1983). The large delta in the Bonaparte Basin was drowned by a marine transgression, after which a smaller delta was re-established in a lagoonal tract behind a prograding barrier bar. The northern sector of the basin was maintained as a marine shelf throughout the Late Permian (Bhatia & others, 1984). This portion of the continent had a warmer climate than any other region at any time during the Permian, becoming warm temperate to tropical (Dickins, 1978), and this may have been one of the factors involved in the lack of economic coal in the deltaic facies of the Bonaparte Basin and the Fitzroy

Trough.

TRIASSIC Although coal measure deposition ceased in the latest Permian, fluvial and fluvio-lacustrine conditions continued in eastern Australia throughout the Early Triassic. The lack of Early Triassic coal has been attributed to a change to a relatively dry climate (Frakes & Rich, 1982), however, Jensen (1975) has demonstrated that the climate in at least the Bowen Basin region was

Palaeogeography

ENVIRONMENTS LAND

unctassified

ffi l!!!i,'i,,r, C0ASTAL

MARINE

erosionat

i3!riA'lJ!{!,*ri

',:,li:',:!f,i:l

tacustrine

ffi ,rrr,,, m

ffi pr,v, ffi'!Ji!,',1fr'/, N

?X!1!";hwaterdepth)

lfffi a,r,,i, m\!{f,l,,i,i!{,oill,,t

Figure 7. Palaeogeography of Austra ia during Jurassic time slice 7. temperate and humid. The appearance of labyrinthodonts and other Amphibia in the Early Triassic of the Bowen Basin (Thulborn, 1986) suggests a relatively warm climate and an environment of meandering streams and pools. The cessation of coal deposition was accompanied by a progressive decrease in the relief of source areas, and changes in local climate, vegetation and the rate of denudation (Jensen, 1975). A combination of a subtle change in climate and local tectonic influences has been cited as the reason for the lack of Early Triassic coal in the Sydney Basin (McElroy, 1969).

There are minor occurrences of Middle Triassic coal (e.g. the Nymboida Coal Measures in northern New South Wales). However, it was not until i;he Late

Triassic that the widespread deposition of coal recommenced. In Queensland, deposition occurred in several relatively small isolated intermontane basins - the Ipswich, Tarong and Callide Basins (Figure 6, Triassic time slice 5) - following a period of Middle Triassic deformation that halted deposition in the Bowen and Galilee Basins. Coal was deposited in dominantly fluvial environments within these basins. Coal measures of equivalent age in northern New South Wales (the Red Cliff and

Evans Head Coal Measures) were deposited in alluvial fan to fluvial flood plain environments (Wells, this volume). The large alluvial plain present in Tasmania during the Late Triassic (Carnian) was also the site of coal accumulation. Coals were deposited under cool temperate conditions in dry forest moor environments affected by fluctuating water tables. Peat-forming conditions were occasionally interrupted by the introduction ofthick channel deposits (Forsyth, 1989).

Late Triassic coal was deposited in small fluvial-lacustrine basins in South Australia (Leigh Creek coalfield and the Boolcunda and Springfield Basins). Coal is also present in minor quantities in the fluvio-deltaic Mungaroo Formation in the Carnarvon Basin (Hocking, this volume).

JURASSIC Terrestrial environments predominated in Australia during the Jurassic, except for the marine margin on the North West Shelf. Much of the continent was located in high mid-latitudes, and global climates were mild with a significant polar ice cap lacking.

Geology of Australian Coal Basins

ENVIRONMENTS LAND

Figure 8. Palaeogeography of Austra a during Cretaceous time The mild, humid climatic regime, and a setting of cratonic stability, were reflected in wides-p,read fluvio-lacustrine deposition characterized by coal swamps (Bradshaw & Yeung, 1992). The maximum extenf of this depositional regime occurred in the Middle to Late Jurassic in central and eastern Australia, as shown in Figure 7 for Jurassic time slice 7.

Although coal measures are common in the Jurassic of eastdrn Australia, the seams tend to be thinner, more lenticular, and lower in quality than those of the Permian coals. Locally, however, they are sufficiently well-developed to be economic. The Walloon Coal Measures of the Clarence-Moreton Basin are mined in Queensland (Goscombe & Coxhead, this volume), and significant -resources have also been identified in tlie Surat, Mulgildie and Laura Basins (Queensland Coal Board, 1989).

In the Perth Basin, the Cattamarra Coal Measures Member and equivalents were deposited as fluvial facies in Jurasiic time slice 4 (Kristensen, this volume). Later, in Jurassic time slices 7 and 9, minor lignitic seams were incorporated into the fluvio-delltaic portions of the Yarragadee Formation.

CRETACEOUS The mild, humid climatic regime of the,JJrrassic continued into the Cretaceous, and coal deposition persisted in eastern Australia. However, terrestrial ^environments were replaced by marine conditions during a major transgiession in the Ap-tian. By the middle Aptian, the sea was retreating from the heart of the continent and significant coal deposition occurred in the Styx and Maryborough Basins and in the Stanwell area, in coastal Queensland (Figure 8, Cretaceous time slice 6). Coal formation also occurred along the southern margin, in the Gippsland, Bass, Otway and Great Ausiraiian BightBasins' through much of the Cretaceous, as that region evolved from the Australia-Antactica rift valley system to a marine margin. Australia had begun a slow equatorward movEment, and by the Late Cretaceous,. rainforest cover and deep wbathering were extensive.

CAINOZOIC The continent continued its northerly drift throughout the Cainozoic, and raigfor-est conditions persis1ed into the Early Tertiary. In the Early

PalaeogeograPhY

Figure 9. Pa

phy of Australia during Cainozoic time slice 2.

Paleocene, conifer-dominated wet forests thrived in

the southeast (Latrobe Group, Eastern View Formation) while rainforests existed in the centre (Harris & Twidale, 1991). Although carbonaceous material was commonly incorporated in most fluvial Paleocene units, the thicker economic lignite accumulations were mostly restricted to the tectonically active Otway, Gippsland and Bass Basins of the southeast.

the production of lignite at many places across the continent, particularly along its southern coast. Along part ofthe palaeo-Queensland coast, graben formation associated with plate movements in the Coral Sea created a series of lakes that favoured oil shale rather than lignite formation. By the Early Oligocene climatic cooling became more pronounced, and ice became increasingly widespread in Antarctica. The rate of Australia's equatorward movement accelerated at about 44 Ma, enabling the

Global warming began in the Late Paleocene, and by the Early Eocene, year-round humidity allowed mangroves to flourish around the coasts of the southeast, while sub-tropical to tropical rainforests grew in inland areas (Macphail & others, 1994). By this time, the deep chemical weathering across the continent that had typified much of the Late Cretaceous had been replaced by conditions that increasingly favoured mechanical erosion, resulting in the alluviation of channels (Figure 9, Cainozoic time slice 2), and the creation of swamps suitable for rapid plant growth, peat accumulation, and burial.

Circum-Antarctic Current to isolate Antarctica from warmer waters to the north more efficiently. From Early Oligocene to mid-Miocene times (Figure 10, Cainozoic time slice 4), increasingly seasonal rainfall patterns became established across Australia, with year-round rainfall, necessary for peat formation, being mainly restricted to Tasmania and the Latrobe Valley of southeastern Victoria.

The climate cooled during Middle to Late Eocene time, a period characterized by the maximum development of non-seasonal sub-tropical to warm temperate rainforest (Macphail & others, 1994), and

From the mid-Miocene onwards, the continent has been situated between the high-rainfall belts of the Southern Ocean and the Equatorial Zone, effectively preventing major peat formation.

Geology of Australian Coal Basins

ENVIRONMENTS

ffi

unctassified

erosionat

t:,li:',W# 1"""",,,"J tvvvvvv,v!L

tv"""",,"vt

fluvial

wffi,l;,!i,,;,,,, coASrAL

racustrine

ffirrrrr,, inteftidal/

ffiPr'Y'

supratidal

mffi deltaic

MARINE very shallow (0-20m water depth)

N m

rhal/or.v (0-200m water depth)

bathyat to abyssat

7//7,4 b 2 0 0 m wa r d pt h ) Figure 10. Palaeogeography of Australia during Cainozoic tirne slice 4.

REFERENCES BANKS, M.R. & CLARKE, M.J., 1987: Changes in the geography of the Tasmania Basin in the late Paleozoic. In McKenzie, G.D. (Editor): Gondwana six: stratigraphy, sedimentology, and paleontology. American Geophysical Union, Geophysical Monograph, 4L, l-4.

BRAKEL, A.T., 1989: Permian coal measures in the exposed part of the Bowen Basin. In Harrington, H.J. & others: Permian coals of eastern Australia. Bureau of Mineral Resources, Australia, Bulletin, 231, 69-91.

BRAKEL, A.T.: This volume. Calen Basin, Queensland.

BARRETT, P.J. & FITZGERALD, P.G., 1985: Deposition of the lower Feather Conglomerate, a Permian braided river deposit in southern Victoria Land, Antarctica, with notes on the regional paleogeography. Sedimentary Geology, 45, 189-208.

BRAKEL, A.T. & TOTTERDELL, J.M., 1992:ThE Permian palaeogeography of Australia. Bureau of

BHATIA, M.R., THOMAS, M. & BOIRIE, J.M., 1984: Depositional framework and diagenesis of the Late Permian gas reserviors ofthe Bonaparte Basin. APEA Journal, 24, 299-313.

Coal. Australia and Papua New Guinea - 2: Metallurgy, Australasian Institute of Mining and Monograph,6, 56-57.

BRADSHAW, M.T. & YEUNG, M., 1992:

Palaeogeographic Atlas of Australia. Volume 8 Jurassic. Bureau of Mineral Resources, Canberra

BRAKEL, A.T., 1986: Global sea-level change as a method of correlating the Late Permian coal measures in the Sydney, Gunnedah, and Bowen

Basins, eastern Australia. BMR Journal of Australian Geology and Geophyslcs, 10, L7-22.

Mineral Resources, Australia, Record 1990 /60, Palaeogeography 19.

CARR, A.F., 1975: Pascoe River district, Q. In Traves, D.M.& King, D. (Editors): Economic Geology of

CLARKE, M.J., 1989: Lower Parmeener Supergroup. In Burrett, C.F. & Martin, E.L. (Editors): Geology and mineral resources of Tasmania. Geological Society of Australia, Special Publication, 15, 295-309. COOK, P.J., 1982: The Cambrian palaeogeography of Australia and opportunities for petroleum

exploration. APEA Journal, 22, 42-64.

Palaeogeography

t4 COOK, P.J., 1988. Palaeogeographic atlas of Australia. Volume 1 Carnbrioz. Bureau of Mineral Resources,- Canberra.

GOSCOMBE, P.J. & COXHEAD, 8.A., this volume. Clarence-Moreton, Surat and Eromanga Basins (including the Nambour and Mulgildie Basins).

DE KEYSER, F. & LUCAS, K.G., 1"968: Geology of the Hodgkinson and Laura Basins, north Queensland. Bureau of Mineral Resources, Australia, Bulletin, 84.

HAMILTON, D.S. & BECKETT, J., 1984: Permian depositional systems in the Gunnedah region. Geological Suruey of New South Wales, Quarterly Notes,55, 1-19.

DICKINS, J.M., 1978: Climate of the Permian in Australia: the invertebrate faunas.

HARRIS, W.K. & TWIDALE, C.T., 1991: Revised age for Ayers Rock and the Olgas. Transactions ofthe Royal Society of South Australia,115, 109.

P alae o ge o gr ap hy, P al ae ocli matol ogy, P alae oec ology, 23, 33-46.

DIESSEL, C.F.K., 1975: The Carboniferous coals of New South Wales. 1n Traves, D.M. & King, D. (Editors): Economic Geology of Australia and Papua New Guinea Coal. Australasian - 2:Metallurgy, Institute of Mining and Monograph,6, 58-63. DIESSEL, C.F.K., 1985: Tuffs and tonsteins in the coal measures of New South Wales, Australia. l}idme Congrd.s International de Stratigraphie et de Gd.ologie du Carboniftre, Madrid, 1983, Compte

Rendu, 4, 197-209.

DIESSEL, C.F.K., 1992: The problem of syn- versus post-depositional marine influence on coal composition. Proceedings of the 26th Symposium on Aduances in the Study of the Sydney Basin. Department of Geology, University of Newcastle, NSW, 154-163. DIESSEL, C.F.K., BROWN, K.J. & PRESTON,8., 1985: 19th Newcastle Symposium excursion notes for 16th May, 1985 - Thornton Brick Company quarry and R.W. Miller's old test pit at Ironbark. Department of Geology, University of Newcastle, N.S.W.

DRAPER, J.J., 1983: Origin of pebbles in mudstones in the Denison Trough. Proceedings of the Sym.posium on the Perrnian Geology of Queensland. Geological Society of Australia, Queensland Division, Brisbane, 305-316. DRAPER, J.J. & BEESTON, J.W., 1985: Depositional aspects of the Reids Dome beds, Denison Trough. Queensland Gouernrnent Mining Journal, 86, 200-210. EVANS, P.R., SEGGIE, R.J. & WALKER, M.J., 1983: Early Permian stratigraphy and palaeogeography, southern Sydney Basin. 17th Symposium on Aduances in the Study ofthe Sydney Basin, Abstracts (supplernent). Department of Geology, University of Newcastle. FLOOD, P.G., this volume. Ashford area, New South Wales.

FORSYTH, S.M., 1989: Upper Parmeener Supergroup. 1n Burrett, C.F. & Martin, E.L. (Editors): Geology and mineral resources of Tasmania. Geological Society of Australia, Special Publication, 15, 309-334. FOSTER, C.B., 1979: Permian plant microfossils of the Blair Athol Coal Measures, Baralaba Coal

Measures, and basal Rewan Formation of Queensland. Geological Suruey of Queensland, Publication, 372. FRAKES, L. & RICH, P., 1982: Paleoclimatic setting and paleogeographic links ofAustralia in the Phanerozoic. /n Rich, P.V & Thompson, E.M. (Editors): The fossil uertebrate record of Australasia. Monash University Offset Printing

Unit, Melbotrne, 28-52.

HAWKINS, P.J., 1978: Galilee Basin a review of petroleum prospects. Queensland- Gouernment Mining Journal, 79, 96-LL2. HAWKINS, P.J. & HARRISON, P.L,, 1978: Stratigraphic and seismic investigations in the Lovelle Depression, western Galilee Basin. Queensland Gouernrnent Mining Journal, 79, 623-650.

HOCKING, R.M., this volume. Carnarvon Basin, Western Australia. HOLDGATE, G.R., 1992: Variations of brown coal

composition in response to r:elative sea level changes - La Trobe Valley, Victoria. Proceedings of the 26th Symposium on Advances in the study of the Sydney Basin. Department of Geology, University of Newcastle, NSW, 150-153.

HUGHES, W.W., this volume. Gloucester Basin, New South Wales.

HUNT, J.W. & BRAKEL, A.T., l-989: Relationship between geological setting and coal type and quality in the Permian basins. In Harrington, H.J. & others: Permian coals of eastern Australia. Bureau of Mineral Resources, Australia, Bulletin,

23r,301-332. HUNT, J.W., BRAKEL, A.T. & SMYTH, M., 1986: Origin and distribution of the Bayswater seam and correlatives in the Permian Sydney and Gunnedah Basins, Australia. Australian Coal Geology,6, 59-75. JENSEN, A.R., 1975: Permo-Triassic stratigraphy and sedimentation in the Bowen Basin, Queensland. Bureau of Mineral Resources, Australia, Bulletin, r54. JENSEN, A.R., GREGORY, C,M. & FORBES, V.R., 1966: Geology of the Mackay 1:250 000 Sheet area, Queensland. Bureau of Mineral Resources,

Australia, Report, LO4. JOHNSON, D.P., this volume. Palaeoclimate and depositional settings of Australian coal measures. KRISTENSEN, S.E., this volume. Perth Basin, Western Australia. LAVERING, I.H., 1985: Permian environments and palaeogeography of the onshore Carnarvon Basin and implications for petroleum prospectivity. PESA Journal, T, 40-46. LENNOX, M. & WILCOCK, S., 1985: ThE Stroud-Gloucester Trough and its relation to the Sydney Basin. Proceedings of the 19th Sym.posium

on Aduances in the Study of the Sydney Basin.

Department of Geology, University of Newcastle, NSW, 37-41. LORD, J.H., 1975: Canning Basin, W.A..In Traves, D.M. & King, D. (Editors): Economic Geology of Coal. Australia and Papua New Guinea - 2: Metallurgy, Australasian Institute of Mining and Monograph, 6, 277-279.

Geology of Australian Coal Basins

l5 MACPHAIL, M.K., ALLEY, N., TRUSWELL, E.M. & SLUITER, I.R., 1994: Early Tertiary vegetation: evidence from spores and pollen. 1n Hill, R.S. (Editor): History of the Australian Vegetation:

Cretaceous to Recent. Cambridge University Press,

London, 189-261.

MARTINI, I.P. & GLOOSCHENKO, W.A., 1985: Cold climate peat formation in Canada, and its relevance to Lower Permian coal measures of Australia. Earth-Science Reuiews, 22, I07-L40. McELHINNY, M.W., 1973: Palaeomagnetisrn and plate tectonics. Cambridge University Press, London.

McELROY, C.T., 1969: Narrabeen Group sedimentation. In Packham, G.H. (Editor): The geology of New South Wales. Journal of the Geological Society of Australia, 16, 439-443.

McPHIE, J., 1987: Andean analogue for Late Carboniferous volcanic arc and arc flank environments of the western New England Orogen, New South Wales, Australia. Tectonophy slcs, 138, 269-288.

MILLIGAN, E.N., L975: Bonaparte Gulf Basin, N.T. In Traves, D.M. & King, D. (Editors): Economic 2: Geology of Australia and Papua New Guinea Coal. Australasian Institute of Mining and Metallurgy, Monograph, 6, 280. PARK, W.J., 1982: The geology of the Muja Sub-Basin a model for the Collie Basin, Western Australia. Australian Coal Geology, 4, 379-340. PLAYFORD, P.E., COCKBAIN, A.E. & LOW, G.H., 1976: Geology of the Perth Basin, Western Australia. Geological Suruey of Western Australia,

Bulletin,124.

QUEENSLAND COAL BOARD, 1989:37th Annual

Reuiew 1987-88. Queensland Coal Board, Brisbane

RETALLACK, G., 1980: Late Carboniferous to Middle Triassic megafossil floras from the Sydney Basin. In Herbert, C. & Helby, R. (Editors): A guide to the Sydney Basin. Geological Suruey of New South W ale s Bulletin, 26, 384-430.

RIEK, E.F., 1972: Ecological inference from the Australian Permian insects. 44th ANZAAS Congress, Sydney (1972), Abstracts, Section 3 Geology.

RIGBY, J.F., L972: The flora of the Kaloola Member of the Baralaba CoaI Measures, central Queensland. Geological Suruey of Queensland Publication, 352, 1-16. SMYTH, M., 1980: Thick coal members: products of an inflationary environment? Coal Geology, 2, 53-76. SORBY, L.A. & SCOTT, S.G., 1988: Geology and coal resources of the Moorlands Basin, central

Queensland. Geological Survey of Queensland, Record L987/54. STUART, W.J., 1976: The genesis of Permian and Lower Triassic reservoir sandstones during phases of southern Cooper Basin development. The APEA Journal, 16, 37-48.

SWAINE, D.J., 1971: Boron in coals of the Bowen Basin as an environmental indicator. .In Davis, A. (Editor): Proceedings of the Second Bowen Basin Symposium, Brisbane, 1970. Geological Suruey of Queensland Report, 62, 41-48. TADROS, N.2., this volume. Gunnedah Basin, New South Wales.

THORNTON, R.C.N., 1979: Regional stratigraphic analysis ofthe Gidgealpa Group, southern Cooper

Basin, Australia. Geological Survey of South Australia, Bulletin, 49. THULBORN, R.A., 1986: Early Triassic tetrapod faunas of southeastern Gondwana. Alcheringa, lO, 297-313. TOTTERDELL, J.M., 1990: Notes to accompany a 1:5 000 000 scale Permian structure map of Australia. Bureau of Mineral Resources, Australia, Record 1990 / 40 (Palaeogeography 17).

TOWNER, R.R. & GIBSON, D.L., 1983: Geology of the onshore Canning Basin, Western Australia.

Bureau of Mineral Resources, Australia, Bulletin, 2L5.

TOWNSEND , LJ., 1976:. Stratigraphic drilling in the Arckaringa Basin, 1969-1971. Geological Suruey of South Australia, Report of Inuestigations, 45.

VAN WAGONER, J.C., MITCHUM, R.M., CAMPION, K.M. & RAHMANIAN, V.D., 1990: Siliciclastic sequence stratigraphy in well logs, cores, and outcrops: concepts for high-resolution correlation of time and facies. AAPG Methods in Exploration Series, 7 .

WELLS, A.T., 1989a: Late Permian coal measures beneath the Olive River Basin, Queensland. 1z Harrington, H.J. & others: Permian coals of eastern Australia. Bureau of Mineral Resources, Australia, Bulletin, 231, 17 I-77 3. WELLS, A.T., 1989b: The Late Permian Mount

Mulligan coal measures, Queensland. In Harrington, H.J. & others: Permian coals of eastern Australia. Bureau of Mineral Resources, Australia, Bulletin, 231, 17 5-17 7 WELLS, A.T., this volume. The Nymboida, Red Cliff and Evans Head Coal Measures, northeastern .

New South Wales.

WELLS, A.T. & O'BRIEN, P.E., 1989: Late Permian Gidgealpa Group, Cooper Basin of South Australia and Queensland. 1n Harrington, H.J. & others: Permian coals of eastern Australia. Bureau of Mineral Resources, Australia, Bulletin, 231, 149-169.

WILSON, A.C., 1989: Palaeocurrent patterns in the implications for Collie Coal Measures - the models. Professional sedimentation and basin Papers, Geological Suruey of Western Australia,

Report,25,85. YOO, 8.K., this volume. Oaklands Basin, New South Wales.

YOUNGS, 8.C., 1975: The Early Permian Purni Formation of the Pedirka Basin. Geological Suruey of South Australia, Quarterly Geological Notes,54,

5-L2.

Palaeogeography

WSt;1foclimate depositional settings of Australian coal measures

The coal-bearing sequences in Australia range-from C".fo"if"rous t6 Teitiary (Traves & King, 1975), utrd ut" distributed widely across the Australian continent in both onshore and offshore basins (Figure 1). The most econo-mically significant of ihu-r" u..rr-ulations are of Permian and Tertiary age, with minor but important deposits in the Mesozoic as well.

This chapter summarises the wide range of palaeoclim.tes and depositional settings in which hustralian coals accumulated, concentrating on otrtttot" examples where coal exploration and minine have vielded comprehensive data' i"Tor.fratio" is also available, however, from deeper basin and offshore situations where similar ."o""".". have provided petroleum sources (Smith, igAZ; Xantsler & others, 1983; Cook. & others, iSSSi. A comprehensive documentation of coal d"potitio.tul iystems including.many Australian has-been published since the original draft "*impt"s p.p"r by Dieisel (1992)' This manusc-ript has "-fitii't from the comments of Peter Crosdale' be""ittf",i

PALAEOCLIMATE OF AUSTRALIAN COAL MEASURES

DP Johnson

Interpretation of the palaeoclimate of Australian c-al <ieposits is based-on three forms of evidence: palaeomagnetism, sedimentary facies and oxygen isotooe daia (Fieure 2). Palaeomagnetism has been estimate" palaeolatitudes for Australia at "r"a'to different times during its geologic history (Embleton, 1973; Veevers, 1984). Following-an io""totiut'tocation during the Late Precambrian and Elrlv Palaeozoic. Australia moved toward the polar .esidn between the Late Silurian and the Late F"-r-iu". Apart from a minor poleward reversal in th" Lutu Juiassic, however (Figure 3), Australia has be"n *oltl.tg back towards the equator since the Triassic. an*d following the final break up of Gondwanaland in the-Late Cretaceous-Early Tertiary, has continued to move steadily northwirds. Although ancient palaeoclimatic zones mav not necessarily have paralleled the present latitudinal climatii variations, these changes in indicate a long-term, secular oalaeolatitude ^oscillation in Australian palaeoclimate, being-warm in ttre Early Palaeozoic, declining to peak coolness in l-tt" F"tt"i"h and returning to walmness during the Mesozoic and Cainozoic.

As summarised by Frakes (1979), Frakes & Rich tiggZl and Quilty (1984), the palae-oclimate of Australia has also been interpreted from s"di*ettt.ry lithofacies and biofacies, with r"ppotti"g b*yg"tt isotope data- A v-e-ry warm Early Paiaeozoif paialoclimate is attested by the ;ia;;p;";d'Iimestones containing diverse corals and associated faunas that characterise Australian Cambrian to Devonian marine sequences' The corresponding terrestrial se-quences coltain d6siccation cracks and aeolian "u"poiit"t, r"ai-""tt, and have no significant organic deposits' The Early Carboniferous was also warm in Australia, with an isolated reefal limestone developed in the far north-west (Roberts & Veevers, igZg), ana scattered oolitic limeston-es in the eastern oart of the continent. However, the Late ^Carboniferous sediments show evidence of increasingly cold conditions--Dropstones are common in marine"sequences, and tillites, varvites and fluvioslacial ileposits characterise the Lower d^tUo-niferous of New South Wales. Thin coals were

Paleoclimate and depositional settings

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times.

The Permian was characterised by extreme lefrigeratio_n, which persisted unt-il the early Late Permian. Major ice sheets occupied the southeastern

half of the continent, with smaller ice-bodies present in the west. Preserved striated pavements an-d tillites, however, seem restricted to southern Australia. Cold Permian climates are supported by oxygen isotope_data, which indicate average temperatures for seawater in southern Auitralia of 4 to 15oC (Rao & Green, 1982) and for fresh *ut"rt in eastern Australia of 15 to 16oC (Botz & others, 1986). However, by the end of the Permian, preservation of marine invertebrates typical of Tarmgr wlte_rs suggests the passing of the glacial srtuatron. Palaeomagnetic data indicate that Australia remained in high p"t.";l;tii;des until the Triassic, and hence this deglaciation was a response to global warming rather tFan continental drifi. Coal accumulation occurred throughout the Permian, but the major deposits formed in the Late Permian, following the deglaciation phase.

Australian palynological and isotopic data. The main coal occurrences are in the Middle Jurassic of -eastern Australia, a fact which indicates peak humidities at this time. Drier conditions prevailed in t_hg Early and I-ate Jurassic of eastern-Australia, and throughout the Jurassic to the west. The Cretaceous was a time of global high sea levels,

with temperatures warming during the frrst half and cooling- during the second half of tlie period. Despite Australia's continued location in relatively high latitudes, however, the palaeofloras indicate temperate climates. Coals are concentrated in the early Cretaceous, particularly along eastern Australia. Th-e Tertia-ry was a time of continued global cooling,

following the trend started in the mid-Cretaceous and resulting in the Miocene development of the Antarctic ice-sheet. The availabilitlof a wealth of isotopic, palynological and microfaunal data means 300 Ma 200

Triassic sedimentation in Australia is predominantly non-marine, and the abrupt disaipearance of coal at the Permian-Triassic boundarv-indicates a marked change in palaeoclimate. Triissic coals are minor, and restricted to Middle and Late Triassic sequences. In general it appears the climate was temperate, perhaps cooler to the southeast and warmer and drier in the northwestern part of the continent. Non-marine sedimentation persisted during the Jurassic, apart from marine transgressionJin marginal areas of the continent inlhe Late Jurassic. The Jurassic-globe l_qcked polar ice-caps and strong climati-q gradients (Hallam, I975), and a widespreid generally temperate situation is supported by -

Figure 3. Change in Australia's palaeolatitude with time with reference to a central location point (24'S, 134'E) (from Veevers, 1984).

Paleoclimate and depositional settings

accumulation is related to local water-tables, and the nature of the inter-seam sediments is a result of stream channel behaviour. The paralic settings, however, are marginal marine environments where oeat accumulation is related to sea-level changes, 'and interseam sediments in such areas are controlled largely by shoreline movements and paralic sedimentation processes. Unconfined ileatlands develop as regional blankets over a ilre-existing subslrate, and are unrelated to the sediments 6ithet above them or below them.

that Tertiary palaeoclimates are known in greater detail than are previous periods. Isotope evidence indicates that substantially ice-free condilions probably existed throughout the Palaeocene and Eocene (Miller & others, 1987). Tertiary coal accumulation was mainly i? the Oligocene-Miocene, but minor amounts also accimulated in the Palaeocene-Eocene. Kemp (1978) has proposed widespread high humidity in southern Ausfralia during the Eocene, based on rainforest

microflora. Continued high humidity, but with lower temperatures is also indicated during the Oligbcene-Miocene (Kemp, 1978), due not only to elo6al cooling but also, in southern Australia, to the Elear rep"t.tlion of Australia from Antarctica and the development of cold, circum-polar ocean currents south of th-e Australian continent. During this time, central Australia contained Iakes and wooded areas (Stirton & others, 1967). Continued northward continental drift since the Miocene, however, has shifted Australia into hotter and drier climatic zones, as seen by increasing aridity in the central Australia region.

Studies of both modern peats (Sjors, 1963; Clymo, 1983) and ancient coals (Hacquebard & Donaldson, 1969; Marchioni, 1980) show that-peat can accumulate in a range of peatland types, with each type supported by a diffeient vegetation assemblage' Recent work, particularly in Canada (Wells & Pollett, 1985;Zoltai & Pollett, 1983), has recognised three peatland types - fen, swamp and bog - qitf q

fourth environm-ent (marsh) wheie organic soil but no peat is deposited. A major determinant of neatland ves'etation is the-nutrient status of the waters: min-erotrophic peatlands have high nutrient status with waters derived from overland or groundwater flow, while ombrotrophic-peatlands [ave low nutrient status with waters derived from atmospheric precipitation. The characteristics of these three environments are listed in Table 1.

In summary, the Australian climate during the^^ Phanerozoit was a result of three interacting effects: palaeolatitudinal drift culminating in-a polar iocation for the continent during the Permian, global warming during the Triassic and Jurassic, which imposed-widespread temperate climates, and chinging palaeo-oceanographic regimes which causJd regional cooling of souther-n Australia during the Oligocene-Miocene. Major-coal measures were formed-at five stages during these secular climatic variations: Late Pirmian, Late Triassic, Middle Jurassic, Early Cretaceous and mid-Tertiary (Oligocene-Miocene), and hence peat accumulation occu-rred in a variety of palaeoclimatic settings. No single palaeoclimate is most appropriate fo1 pgqt ucc-n*.rl"tion, except for the requirement of high humidity to promote plant growth.

Peatland type can be assessed from maceral and microlithoiype analyses of coal, but only if allowance is made foitwo problems. Firstly, liptinite becomes difficult to idenfify at ranks above a vitrinite reflectance of 1.0 io 1.57o, and its abundance tends to be underestimated in higher rank coals. Secondly, dull coals may represent the result of oxidation and ablation of their iarent organic accumulations, with only part ofthe original peatland flora preserved.

Devonian and Carboniferous coals Although plant materials are not uncommon as fossils in the Devonian sequences of Australia (Gould, Lg75), coal itselfiJ very rare. Thin layers of coaly materiai (vitrinite), however, are reported from Late Devonian piedmont deposits in the Amadeus Basin (Playford & others, 1976).

DEPOSITIONAL SETTINGS AND PEATLAND TYPES Coal accumulation can occur in five major types of

depositional settings: topographic basins, alluvial fans, fluvial plains, paralic environments and unconfined peatlands. Each of these settings creates

Carboniferous coals are also rare in Australia, in contrast to the widespread accumulations of such deposits in the North-ern Hemisphere. The best knbwn Carboniferous coals lie peripheral to the Svdnev Basin. where several thin, dirty coals occur *ittti" a tuff-bearing, glacio-fluvial sequence

a distinctive sedimentary architecture in terms of both the sedimentological nature of the sequences and the gross geometiy of the units de,velop-ed- The topograplic basins,.alluvial fans and fluvial plains are non-marrne environments where peat

Table L. Peatland Clasbificatibn and Characteristics PEATLANDS OMBROTROPHIC

MINEROTROPHIC :K moderate - high nutrient status

* low nutrient status le very acid waters, PH 3-4

* slightly acid waters, PH 5-6 * ground water / overland flow

* rain / snow moisture

FENS

SWAMPS

BOGS

sedges / rushes / grass + trees

trees / herbs

moss/herbs/*trees

Geology of Australian Coal Basins

2t (Rattigan, 1964; Diessel, 1975). Peat in this area accumulated in both non-marine and paralic environments, commonly overlying sandy seat-earths, and the plant materials from which they were derived included both trees and reed-like vegetation (Diessel, 197 5).

Gangamopteris and Lelstotheca characterised the cooler Early Permian and had only a restricted, perhaps higher altitude occurrence in the Late Permian. Presumably a range of poorly preserved herbs, mosses and other lower plants were associated with this macroflora as well.

Permian Coals

Permian peat accumulated in a range of depositional systems including topographic basins, alluvial fans, fluvial plains and paralic environments, as well as unconfined peatlands. Typical deposits ofeach type are indicated below, with more detailed and possibly alternative explanations also presented in other parts of this volume.

The Early Permian coal measures of Australia occur as regressive phases within mainly marine sequences in the major basins (e.g. the Sydney and Bowen Basins), and also as smaller accumulations in topographic basins such as the Blair Athol, Wolfang and CollieAVilga Basins. Late Permian coal measures are more widespread in the major basins, however, indicating a relative sea-level fall that affected the entire craton and allowed non-marine sediments to prograde across these previously

marine depressions.

The Permian macroflora preserved in the clastic units is well known (Gould, 1975; Retallack, 1980), and is assumed also to represent the peat-forming flora. Diessel (1982) proposed a vegetation scheme ranging from a dry forest with Walkomiella and Sphenophyllum to a wet forest with glossopterids and lycopods, a reed moor with Phyllotheca, and, finally a moor lake with botryoccocoid algae (Figure 4). Retallack (1980) emphasised the floral associations with depositional environment, but also considered that some plants such €is Glossopteris and Phyllotheca characterised the warmer Late Permian, while the corresponding species

Topographic basin peat q.c cumulations Several small topographic basins were formed by erosion into basement outside the major depositional basins of Australia, and some of these contain thin, non-marine coal-bearing sequences. The Blair Athol Basin in central Queensland, 6 to Skm across and about 250m deep, contains four seams, with the thickest being up to 33.5m thick (Osman & Wilson, 1975). The coal overlies basal conglomerates representing colluvial to alluvial deposits filling the eroded basement valley, and there are thin interseam sandstone and mudstone units. The coal itself is predominantly a dull coal (307o vitrinite), with very low ash (77o) and sulphur (0.37o). Deposition occurred in an isolated valley, with a marked decrease in sediment influx to allow the accumulation of the very thick peat bed.

DRY SWAMP

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HUMIC COLLO VITRAIN (bright coal), CtARAIN (banded bright coal), DURO-CLARAIN (banded coal)

ILARO-DURAIN (banded dull coal), SOME DURAIN (dullcoal)

Figure 4. Permian peatland vegetation envisaged by Diessel (1982).

Paleoclimate and depositional settings

COMPLETE

PUTREFACTION ORGANIC MUD

DURAIN (dullcoal), CANNEL AND BOGHEAD COAL, OIL SHALE

22 The low ash and the high inertinite content of the coal indicate peat accumulation in an ombrotrophic peatland prone to dryness, perhaps a raised bog environment (Smyth, 1980).

The Collie and Wilga Basins in Western Australia are elongate depressions up to 40km long and 25km across, possibly formed by Permian gla-cial erosion (Lord,-1^975), or more likely basement faulting (Park, 1982). They contain up to 1300m of Permian sediments, and are part of a more widespread system (Ashton & others, this volume).-The coal tneasures in these two basins consist of fluviatile sandstone, mudstone and numerous coals, oveqlying a basal tillite and glaciofluvial sequence. Seams range from 0.5 to 4.8m thick, apart from one seam whiih is 13.7m thick, and are tiaceable across the full extent of their host basins. The coal is generally a low ash material (2.8Vo). Peat accumulation in this area is thought to have been in valley-wide, probably ombrotrophic, peatlands, -perh4ps alternating with phases of fluvial deposition.

Alluaial fan peat deposits Alluvial fan sequences with coals were deposited along the tectonically active northeas-t-ern margin of the Sydney and Gunnedah Basins of New South Wales (Diessel, 1980; Brownlow, 1981; Hunt & Hobday, 1984; Thomson & others, 1993)- The sequences thin and fine balinwa-rds, and are chiracterised by wedges of pebble to cobble conglomerate and coarse sandstone successions

(Figure 5A).

The Maules Creek Formation in the Gunnedah Basin forms a wedge with an extrapolated maximum thickness of 1000m (Hunt & Hobday, 1984), and consists of lithic conglomerate, sandstone and minor coal seams. The formation thins westward, terminating in a thin paralic sequence. Coal seams are 0.5 to 6.0m thick, and Hunt & Hobday (1984)

report that they generally show upwqrd-dulling or al[ernating inter-banded/ bright profiles, with vitrinite +liptinite averaging 757o. T}r'e s-ulphur content of the coal is low (<0.57a da0, although sulphur levels are higher in basal and upper seams and in the thin western lithofacies.

The Newcastle Coal Measures (Branagan & Johnson, 1970; Diessel, 1980; Hunt & Hobday, 1984) in the Sydney Basin are up to 400m thick, although

the sequence was probably thicker still in the area (now offshore) to the east. The upper parts of the sequence are characterised by thick, fan-shaped, voltanolithic conglomerates and coarse sandstone units (Figure 5B)-, with tuff associated with the coal seams. Diposition of the conglomerates-occurred in braided fans, with lenticular to sheet-like pebbly sandstones deposited in more distal braided streams. Beddlng is generally subhorizontal, with large-scale cross bedding and _common scour surTaces. However, some conglomerates display giant forests (up to 30m high) inclined at 5 to 40' (Hunt & Hobday, 1984). These are arcuate in plan and contain intiasets of cross-bedded sandstone which have very variable azimuths. Deposition is thought to have occurred in freshwater gravelly fan-d-eltas, with redistribution of sediment by longshore processes and p-al4eocurrents varying sisnificantlv between fan lobes. This coarse rJq.r"tt." overlies and grades southwestward into thinner, upward-fining units of sandstone and shale, deposited in high-sinuosity streams.

The main seams within the Newcastle Coal Measures are commonly 3 to 6m thick and persist laterally for 10 to 20km. Seam splits are common' howevei, and there is a tendency for s.eams to coalesce'westward, away from the active basin margin (Figure 5C). Claystone bands are also aid well-preserved volcanic glass shards "o-ilrott, that at least some of these claystones indicate represent penecontempora4eous -volcanic ash falls Most of the coal itself ir

(Herbert & H"lby, 198b). inherently a high ash material (up-to 2-!%), an!,sea- ptofrles .ie generally upwaid-dulling, with some ilternating profiles. The coal displ-ays a seneral type trend through the Newcastle sequence, iritn Urigftler coals at the base (80% vitrinite) and duller cdals at the top (40Vo vittinite), although there is considerable-down dip variation within seams (Hunt & Hobday, 19841. Semifusinite is the dominant inertinite maceral, and sulphur contents are relatively low (<0.57o daf). The high vitrinite contents indicate peat accumilation in waterlogged swamps around the lower parts of the alluvial fans and on the surrounding fluvial plains. The peatlands in this instance pr6bably colonised inactive fans, pe-rhaps maintain-ed by groundwater discharge in mid to lower fan areas. Some seams are observed to thin up the associated fan surface, grading into organic soils (Hunt & Hobday, 1984).

Fluuial plain peat dePosits River-controlled systems occur in both hinterland and coastal situations (where they are commonly labelled upper deltaic plain). Fluvial plain coal measures are generally laterally eltensive sequences, corimonly with internal cy-c-licity. Fluvial plain coal measures-form most-of the Uppel Permian ieqo"nc"t in the major Australian basins, for example the Illawarra and Wittingham-Coal Measirres in the Sydney Basin and the Blackwater Group in the Bow6n Basin. Many other Permian sequ6nces with uneconomic coals, however' are also of fluvial origin, such as the Patchawarra Formation ofthe Coopei Basin (Stuart, 1976; Thornton, 1978; Smyth, 1984) and the Coorabin Coal Measures in the-Oaklands Basin (Yoo, 1982). The Illawarra Coal Measures of the southern Sydney Basin contain seven upward-fining cycles, eqch 10 to 30m thick (Bowman, 1980; Arditto, 1991). The base of each cycle is made up of coarse, lithic sandstones, sometimes massive but generally with festoon or other large-scale cross-bidding. The-remainder of each cvcle consists of siltstones, mudstones, interbLdded sandstones and coal, with tuff present in one cycle as well. Although Bowman (1980) believes deposition to be lower deltaic because of distributary patterns seen in sandstoneisop-ach. maps, depoiition of these sediments is clearly within a flLvial iystem. Coals are numero-us' but generally thin and dirty. Seam thickness and quality vary across the coilfield area (Wilson, 1975a), but the economic coals are laterally extensive and (except for the Bulli seam) have moderate ash (L5 to 26Vo db) and low sulphur (0.57o) levels. .

The Wittingham Coal Measures in the northern Svdnev BaJin are a fluvial sequence, dominated by

liihic iandstones but with a coal-rich central section (Robinson, 1969). Many of the majgr qeams {!1n-laV multidireitional, zig-zag splitting (Britten, 1-975; Britten & others, 1575): indicating rapid and common alternation of clastic deposition with peat accumulation as fluvial channel and crevasse splay

Geology of Australian Coal Basins

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Paleoclimate and depositional settings

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24 deposits invaded the peatlands. The thickness ofthe main coal seams ranges from 2 to 10m (Britten, I975), and the coal is of moderate vitrinite content

(approximately 607o). As an example, the Liddell seam has a relatively uniform profile, and is mainly made up of banded coal with few dirt bands (Marchioni, 1980). Dull coal is associated with the dirt bands, and is thought to have formed under high water conditions rather than in a dry peatland. The Liddell peatland was dominated by trees and herbs with oscillating water levels producing the banded coals.

The Blackwater Group is a coal-bearing fluvial sequence which was deposited across the entire Bowen Basin (Dickins & Malone, 1973; Jensen, 1975; Staines & Koppe, 1980). A tuff-bearing interval with very dirty coals in the middle of the sequence (the Fort Cooper CoaI Measures) sepalates the cleaner coal sequences of the Moranbah Coal

Measures below and the Rangal Coal Measures above.

The Moranbah Coal Measures consist of volcanolithic sandstones, siltstones, mudstones and coal, with conglomerate being significant only on the eastern side of the basin. To the west the formation contains three to eight major coal seams with an aggregate thickness of 15 to 30m, which split to the east and form up to 24 separate coal beds (Koppe, 1978). Individual seams can be traced up to 100km

along strike (Figure 6). Six interfingering fluvial litholacies, interpreted as fluvial channel, proximal splay/levee, distal splay, marsh, lake and peatland deposits (Table 2), have been described by Johnson (1984). This fluvial sequence passes southwards into paralic coal measures (German Creek Coal Measures) and marine units (Koppe, 1978). The Patchawarra Formation of the Cooper Basin is a

basin-wide non-marine unit deposited in fluvial, shoreline and lake environments (Stuart, 1.976;

Thornton, 1978; Smyth, 1979). Stuart (1976) recognised regional facies changes from conglomeratic fluvial clastics to sandstones and mudstones with coal, lacustrine shoreline sandstones and offshore muds. The coal in this sequence appears to have accumulated mainly in the distal fluvial deposits on flat plains around a large Iake Iocated in the centre of the basin, with lesser amounts in fluvial channel areas. Channel-belt coals tend to be the brightest coals (Smyth, 1984), indicating that the duller coals may be due to excessive waterlogging in much the same way as has been suggested for the Liddell seam ofthe Sydney Basin (above) or less woody vegetation.

Pcr.ralic peats Paralic coal measures are generally underlain or overlain by, and commonly interfinger with marine sequences. Examples are the basal Black Jack Coal Measures in the Gunnedah Basin, the Greta and Tomago Coal Measures in the Sydney Basin, 4nd the Colliniville Coal Measures and German Creek Formation in the Bowen Basin. Minor, poorly documented occurrences along basin margins were probably also deposited in paralic, perhaps lan-delta, environments, such as the Clyde and Yarrunga Coal Measures of the southern Sydney Basin (Gostin & Herbert, 1973; Herbert, 1980), and the coal measures at Rugby in Queensland (Staines & Koppe, 1980). The basal part of the Black Jack Coal Measures is a transgressive sequence approximately 100m thick,

consisting of a lower deltaic succession ove4lin by shallow marine deposits (Hamilton, 1985). The deltaic sequence contains distributary and splaysandstonei encased in finer grained lagoonal and interdistributary deposits (Figure 7)' Coals are generally thin (1m) and discontinuous, excep-t for the Melvillei Coal Member which can be traced for 150km along strike. The coal is cleaner, seams are more abundant and individual seams are thicker in areas of maximum deltaic sand deposition, indicating that peat accumulated on delta lobes but then became thinner as it passed laterally into marsh, lagoonal and interdistributary bay deposits. The Greta Coal Measures occur along the northeastern margin of the Sydney Basin, and are

laterally equivalent to the marine Farley and RutherfordFormations (Herbert, 1980; Hamilton, 1986). Coal measure deposition in this area was terminated by marine sedimentation of the Maitland Group. The dreta Coal Measures are approximately 60 to-100m thick, and in places contain a lower unit of pelletoidal claystone and conglomerate with minor coil layers, interpreted as colluvial and alluvial deposits developed on the Early Permian volcanics (Loughnan, 1975). This is then overlain by coal measures sequences of two types (Hamilton, 1986). The lower of these two coal measures sequences represents fluvial overbank deposits, consisting miinly of laminated siltstones and fine sandstones with minor coarse sandstone units (<3) and abundant thick coals. Coal may form up to 407o of these sequences, and major channels are rare in the areas of main coal accumulation. The upper coal measures sequence represents paralic deposits, consisting mainly of rippled and lenticular bedded sandstone and siltstone laminites with common bioturbation. Small channel units of medium to coarse sandstone, 3 to 6m thick, are also present and the coals are thin with multiple splits. Thus, the Greta Coal Measures, at least in the upper Hunter area, were deposited during a regional transgression with volcanics and colluvial to alluvial deposits overlain by fluvial and then paralic coal measures and finally by open marine strata. The Collinsville Coal Measures formed at the northern end of the Bowen Basin, and are

stratigraphically equivalent to the marine Gebbie Group (Rbid, 1929; Dickins & Malone, L973, Staines & Koppe, 1980; Martini & Johnson,- 1987). The coal measures are up to 210m thick, and consist of three parts, a lower and an upper sequence sepa_rated_by lhe marine Glendoo Sandstone Member (Webb & Crapp, 1960). The lower coal measures sequen-ce has a very similar depositional pattern to that of the Greta Coal Measures in the Sydney Basin, being dominated by fluvial facies in the lower part and paralic facies in the upper part. The Glendoo Sandstone Member represents a sandy shoreline, indicating a temporary marine inundation of the peatland areas before deposition of the paralic upper coal-bearing sequence. Th,e paralic interseam se<iiments are characterised by fine to coarse quartz sandstones, abundant micaceous partings and thin, laminated carbonaceous silty units. Undulose plane beds, ripples (including ladder and truncated forms), wavy bedding and bioturbation are common structures, and plant macrofossils are very rare. The basal coal seam was formed in swamps covering abandoned braided stream deposits, and is made up of massive, dull coal with high as}, (207o) and

relatively iow sulphur (L%o). Tlne overlying coals

Geology of Australian Coal Basins

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Paleoclimate and depositional settings

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Figure 7. Stratigraphic section showing context of paralic coal, Melvilles Coal Member, Gunnedah Basin, New South Wales (from Hamilton, 1985).

GE88IE CREEK

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o 1...-.r (non ccal-bearing) 3okm Approximate scaie f----I FLUVIAL.PARALIC l: -J (coal bearina) Figure 8. Lithofacies relationships of the paralic Collinsville Coal Measures, Queensland (frorn Martini & Johnson, 1987).

Geology of Australian Coal Basins

Table 2. Flutiat lithofacies of the Moranbah coal Measures. Name

Siltstone/

Sandstone

Siltstone

ClaYstone

Clay rhythmite Coal

to 25m

to 1.5m

to 1.0m

5-10m

sheet

sandstone

to 30m

Itreigtrt 25-50m GeometrY lwidth to 4km lshaPe sheet, lens-ribbon

sheet

>10km to 1.5km mound, wedge, sheet lens

sheet'

sheet-bedded sheet-bedded

to 1km wedge, lens,

General internal channel to accretion structure

to 4km

>12km

sheet-bedded sheet-bedded

bedded

Bedding

thin to medium thin to medium thin

medium to very thick

laminatedand homogeneous

homogeneous to wispy

cross-strata

laminated,

laminated

medium to

pale,mid-grey mid-greY

carbonaceous

coarse, and

siltstones, and siltstone

frne clayey

claystones

Sedimentary large- to small-scale structures

Lithology

cross-

to laminated

dark grey

litharenite

Other features tendencY for

uPward frning of sediment and structures

laminated,

lenticular bedding common

including ripple drift

litharenite

thin to medium thin

rare mud common penecontemp- cracks,rare oraneous amPhibians deformation, footPrints especially carbonaceous convolute Partings

grades to

mid-grey

high volatile

clayshale with bituminous pale grey siltY coal laminae and

ripples wave ripples

fossiliferous

kaolinitic tonsteins

claystone carbonaceous

partings

bedding and load casts

Plant remains coalifred logs and coarse debris

fine to coarse fine debris rare rootlets debris

rare stumps

many stumps whole Phyllotheca

fine debris no stumps

common

vitrinite rich lower part,

inertinite rich upper part

Vertebraria and rootlets peatland lake marsh Depositional river and , proximal splay distal splay sPlaY channels "nvito.trnettt ii)' Blanket peatlands covering abar]doned delta lobes' developed from peats that formed in fluvio-paralic producing extensive coals of medium thickness and

and paralic envilonments, and these seams are

n""eiallv brishter, with low to moderate as]r. (8-L7Vo) ind *oa"rat6to high total sulphur levels (1-6Vo)' Both the Gebbie Group and the Collinsville Coal M"urotut are overlain by the open marine Blenheim Formation, indicating a basinwide transgressron

(Figure 8).

While the eenerallv paralic nature of deposits such ur-Itrl Ci"[u and ioliinsville Coal Measures is well suoported bv the presence ofbioturbation in i"i"-rt"u." ottit., sulphurous coal and stratigraphic to marine sequences' the particular "o"-i""t""." d6positional situation of such deposits is -rarely in detail. Although many authors list "riu-UGtt"a lower deltaic plain or back-barrier for sqch ;;;;;;*;; thb peat accumulation could have been in any of at least fhree situations: flanking distributaries, capping. i) -' Small peatlands and on back-barrier flats, producing

.."uu..u splays

thin, discontinuous, commonly d-irty co-als, s-uch as itrorL i" the deltaic lower part of the Black Jack Fot*atio" (Hamilton, 1985) or above the Wall Sandstone in the Gebbie Group (Martini & Johnson, 1987).

ieasonable quality, such as the Melvilles Coal Member in the Gunnedah Basin (Hamilton, 1985).

iii) Continuous peatlands developed landward of prograding muddy/sandy coastlines, producing extJnsive ioals, c-ommonly thick and of hig\ quality, snctt as the main seams of the Collinsville Coal Measures (Martini & Johnson, 1987)'

(Jnconfined peatland d'eposits, Blanket tnires Unconfined peatlands may-extend over-hundreds of kilometres, in contrast to the tens of kilometres associated with the topographic basin, """"t"tiu paralic depositional systems' Such and Ff""i"t varietv of ;;;;;6;a ^peatlands'also cover i wide indepenterrains, and may develop ".L--"*iiti"e ientlv of. r"ather than integrally with, clastic a"p"Jitiohul systems. Posslble examples are the gu-ut;ui"t- H6skissons seam horizon of the Sydgey Svdnev ;;eb;;;"dah Basins, the Bulli seam of the Bowen the of seam Middle Goonyeila n.ri" utta tftu Basin. The Bayswater and Hoskissons seams may not be, coeval nor have accumulated continuously "t""it"i" ;;;;;; i"tre Mt Coricudgv Anticline, but thev are a

Paleoclimate and depositional settings

ENVIRONMENTAL

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,T, : FLOOR 9. Nature of an unconfined peatland coal, Bulli seam, New South Wales. Figure - A. Regional cross-section show:ing relationship to clastic sequences (Bunny,_1972). B. Seam section of Bulli seam showing continuity of plies (fiom Britten & others, 1975). correlative pair of very widespread coals (Beckett, Hamilton &Weber, 1983,in Hamilton, 1985). The Bayswater seam is 2 to 1lm thick (R^obinson, 1969), covers an area of more than 1500km', and sharply overlies a sandstone of unusually great extent (Britten & Smyth, 1973).

Hunt (personal communication, 1984 in Hamilton, 1985) has interpreted the clastics under the seam to be alluvial fan and braided fluvial sands to the west, and barrier and deltaic systems to the east. Similarly the Hoskissons seam is 2.4 to l8.0m thick and extends for over 15Okm along strike. It overlies fluvial sands to the west, but rests upon thin beach

l', 1

0-L0

and nearshore sands or interdistributary bay silts to the south and east (Hamilton, 1985). The coal in both seams is low in sulphur (0.5V" db) and of moderate ash content (commonly l5-20Vo). Both seams are well banded; the Bayswater seam is dull, apart from its brighter bottom and top plies, with much more inertinite than the seams immediately above and below (Britten & Smyth, 1973).

The Bulli seam extends over a distance of >130km (Figure 9A) along the western margin of the-Sydney BaJin, is up to 4m thick, and is generally of low sulphur (0.3-0.\Eo),low ash (9-727o) and of low to

Geology of Austnalian Coal Basins

29 moderate vitrinite content (30-60Vo) (Edwards, 1975). Liptinite is generally rare, and where present is mainly sporinite, resinite and leaf cutinite (Cook & Wilson, 1969). The seam is clean with a consistent, upward-dulling profile, but there is rapid deterioration of coal quality to the south where the unit thins into carbonaceous shale (Wilson, 1975a). Although there are regional variations in coal type, the seam has a

persistent ply structure (Figure 98) traceable over distances of>50km (Britten & others, 1975; Shibaoka & Bennett, 1975).

Thickness variations in the seam are due to erosion of the top, to irregularities associated with pre-depositional topography and to differential subsidence (Shibaoka & Bennett, 1975). Although sandstone channels occur in the roof strata (Diessel & others, 1967), clastic units have not been mapped within the seam and the only major dirt band occurs

sporadically in the upper part ofthe coal bed (Wilson, 1975).

The Goonyella Middle seam in the Bowen Basin extends over more than 150km along the western edge of the Bowen Basin (Staines & Koppe, 1980). The coal is up to 9m thick, with low sulphur (0.\Vo), low ash (approximately 87o), and low to moderate vitrinite (30 to 80%) (Queensland Coal Board, 1978) and an upward-dulling profile (Beeston, 1974). Both the ply structure and the claystorie bands (tonsteins) within the seam are regionally persistent (Staines & Koppe, 1980), indicating that peat accumulated simultaneously over a wide area. Although the enclosing Moranbah Coal Measures are fluvial, and some seams interfinger with clastic sediments, the Goonyella Middle seam is regionally extensive and, apart from crevasse splays which split the top ply (Johnson, 1984), uninterrupted by clastics. The Bayswater-Hoskissons, Bulli and Goonyella Middle seams are all seams of unusually large regional extent. Each seam also has an individually persistent profile which is uninterrupted by clastic units. Typically the coals of these seams are low in ash, low in sulphur and of low to moderate vitrinite content. These features indicate peat accumulation

in freshwater peatlands ofregional extent, in areas not experiencing active clastic deposition. The consistent seam profiles indicate essentially uniform conditions over a large area, responding only to regional changes in climate or base level which altered the nature of peat preservation. Lateral changes in coal type reflect the variations in the original peatland flora and hydrology which would be expected across such a regional landscape. Terrigenous sediments (which are probably tuffs) occur as widespread dirt bands within the seam, or towards the top of the coal as the peatland was encroached by clastic systems. Commonly the seam has a sharp base and may overlie a variety of substrates, indicating that the peatland developed where clastic sedimentation had ceased, perhaps due to climatic or sea-level changes. The HoskissonsBayswater and Bulli seams mark major litho-

Triassic Coals Most of the Triassic coals in Australia were not developed until the late Triassic (Woods, 1975), and although extensive coal measures have been encountered offshore (Cook & others, 1985), only minor coals formed even in the major onshore basins. Minor coals occur, for example, in the essentially coal-barren Wianamatta Group of the Sydney Basin (Herbert, 1980) and the Moolayember Member of the Bowen Basin (Dickins & Malone, 1973). Widespread, but often uneconomic coals are present at Fingal in the smaller, onshore Tasmania Basin (Morrison & Bacon, 1986), and economic coals are restricted to small topographic basins peripheral to larger depositional basins, such as in the Callide, Tarong and Ipswich areas in Queensland and the Leigh Creek area in South Australia (Table 3, Wilson, 1975b). All reported Triassic coals occur in freshwater, fluvial plain sequences.

At Fingal and Langloh, several coal seams occur within sandstone-dominated sequences that have been formed in meandering river and point bar environments (Morrison & Bacon, 1986). Medium to coarse channel sands with large-scale trough

cross-beds are the main lithofacies, and form stacked sequences tens of metres in thickness. These sands have an erosive contact with the tops of the seams, and are commonly fining-upward. The

overbank lithofacies consists of mudstone and silty mudstone with rippled sandstone beds. The peatland lithofacies is represented by dull coal with high inherent ash (15 to 257o) and very low sulphur levels, and with common silty mudstone interbeds.

Maceral analyses show that the coal is low in vitrinite and liptinite, and that the liptinite is

mainly sporinite and cutinite. The macroflora in the coal measures is dominated by filicaleans, pteridosperms, gingkoaleans and equisetaleans, and has common cycad leaves but only rare conifer remains (Townrow, 1962). This floral assemblage, the high ash yield, and the inertinite-rich nature of the coal indicate a relatively dry swamp or fen environment, which allowed considerable subaerial exposure of the peat during its deposition. The Blackstone Formation at the top of the Ipswich Coal Measures in the Ipswich Basin of Queensland (Falkner, 1986), contains channel lithofacies with large-scale cross-beds and lateral accretion bedding. The interseam and thick seam-splitting sections are composed of interbedded sandstones and mudstones, which interfinger with the coal seams. The coal ranges from a layered, vitrinite-rich, low ash material to a homogeneous, inertinite-rich, high-ash

material, reflecting peatland environments that ranged from high water-table areas removed from clastic influx to drier areas with significant clastic deposition. Clayey dirt-bands (tonsteins) are abundant and appear to represent diagenetically altered silicic tuffs.

stratigraphic boundaries, which confirms that

Coal measures in the Callide, Tarong and Leigh Creek areas appear to have formed in similar fluvial environments. The seams all contain numerous dirt bands, and the coal measures all grade laterally into

Unconfined peatland coals occur along the stable western margins of the Sydney-Gunnedah-Bowen Basins where slow, even subsidence allowed accumulation of thick, widespread peats, presumably on broad, flat coastal plains.

The peats in these smaller Triassic basins accumulated in fluvial plains with the peatlands

peatland development marked an interlude between depositional episodes.

clastic sequences towards the basin margins. The coals themselves are generally dull, except for those of the Ipswich Coal Measures, and have low sulphur levels but very high ash yields, even after washing (Table 3).

Paleoclimate and depositional settings

Table 3. Nature of Coal in small Triassic Basins Basin

Callide

Tarong

Leigh Creek

Ipswich

Area (km2)

ca. 180

ca.200

<25

ca.250

Sequence thickness (m)

> 300

> 250

to 1000

1250

Sequence nature

basal volcanics, conglomerate and sandstone

basal conglomerate and sandstone

carbonaceous shale,

minor grits

volcanics at base, shale & sandstone

Main seam

Callide

Meandu

Telford

(several)

thickness (m)

10-26

10-34

6-18

nature

dull, semifusinite rich

to 10 bright, high mineral matter

ash (Vo)

7-13

ca. 22 at Fl 1.80

t0-27

ca. 22 (washed)

sulphur (7o)

<0.3

<0.4

0.5-9.0

<0.4

Reflectance (Rv max.7o)

0.50

0.56

0.9-1.0

COAL

adjacent to meandering river systems and commonly invaded by crevasse-splays. The coals have low liptinite contents (<207o, mmf basis), with the liptinite being mainly cutinite, but cover a wide spectrum of vitrinite/inertinite ratios (Smyth, 1980). The Triassic flora was dominated by gymnosperms (corystosperms, peltasperms, cycads), ginkoaleans and ferns (Gould, L975), a flora quite different to that of the Permian. The original peatlands were

evidently small, interfluvial swamps ranging from relatively dry to wet situations and commonly subjected to clastic influx from overbank sedimentation. Volcanics are present at the base of the coal measures at Callide, Ipswich and Fingal, and dirt bands in several seams have been interpreted as altered tuff layers, so it is likely that peat accumulation occurred in conjunction with contemporaneous volcanic activity.

Jurassic Coals Extensive Jurassic coal measures are well developed in the Surat-Eromanga, Clarence- Moreton, Maryborough and Laura Basins in eastern Australia, where the coals crop out or lie at relatively shallow depths. Widespread coal measures also occur at greater depths in the offshore Perth and Carnarvon Basins. Apart from the Walloon Coal Measures of the Surat Basin, however, the coals of these sequences are generally thin and uneconomic. The Surat Basin contains five thick cycles of Jurassic sediments, with each cycle consisting of a lower sandstone unit deposited in a braided river system and an upper unit of finer sandstone, siltstone, mudstone and commonly coal, deposited in a meandering river or in some cases a paralic environment (Exon, 1976; 1980). Fluvial input was from the west, as shown by the westward increase in the percentage of sandstone within the sequence (Power & Devine, 1970), the presence of thicker sand bodies on that side ofthe basin (Exon, 1976), and palaeocurrent trends in the basal sandstone beds (Martin, 1980). Small alluvial fan deposits (5-10km radius) occur along the western margin of the basin (Moore & others, 1986). Sedimentation in the upper part of the fifth cycle continued into the Cretaceous to form a sixth cycle.

Although Exon (1980) proposed that these cycles could be correlated with world-wide sea-level oscillations, sedimentation in the basin was overwhelmingly non-marine during the Jurassic, but with substantial paralic and marine deposition in the Cretaceous.

Thin coals are developed in the second of these cycles in the lower part of the sequence. The upper part of this particular cycle is represented by the Walloon Coal Measures, a Jurassic unit some 300 to 550m thick. The thicker seams in this unit tend to occur where the sequence itself is thickest, and in the well-explored area of shallow coal near subcrop, the coal occurs as a series of small accumulations 1 to 5km across, each containing several seams. The individual deposits ofthis type are separated by areas where the seams are thinner. Although

coal-rich units can be traced laterally for some distance (Swarbrick, 1973), individual seams repeatedly split and anastomose, and cannot be correlated reliably over distances greater than a few kilometres (Figure 10). Thick seams pass laterally within 50 to 200m to thin seams split by clastic wedges, or grade rapidly into carbonaceous shales (e.g. Jones & Patrick, 1980). Common tuff marker beds have, however, have been used to help establish stratigraphic correlation. Detailed mapping within individual deposits confirms the fluvial nature of the sequence (Mclean-Hodgson & Kempton, 1980; Leblang & others, 1980). Three depositional facies have been recognised by Mclean-Hodgson and Kempton (1980), and other published descriptions indicate that a similar facies classification is probably applicable elsewhere in the Walloon Coal Measures. These facies are: i) Channel deposits: Elongate, lenticular bodies, generally 5 to 10m thick, which are composed of pale grey labile sandstones. The bases ofthese bodies are sharp or erosional, but the sandstones pass gradationally both upwards and laterally into finer overbank units. Large-scale cross-bedding occurs in the lower parts, with massive sandstone and cross-laminated units also common.

Geology of Australian Coal Basins

3l ii) Overbank deposits: Laterally extensive bodies, generally less than 5m thick, which are composed of pale grey fine sandstones, grey to dark brown siltstones, mudstones and carbonaceous shales. Concretions of siderite, limestone and iron oxide are common. Basal contacts may be interbedded or laterally gradational with channel deposits, and bedding structures are generally on a small scale, showing flat and cross-laminae, slump structures and load casts.

APPROX SCATE

IN METRES

330

iii) Peatland deposits: Laterally-extensive bodies,

generally 1 to 10m and even up to 20m thick, which are composed of coal and carbonaceous shale with mudstone and, rarely, fine sandstone partings. The upper and lower contacts may be gradational to overbank deposits, but are commonly sharp, meeting sandstone above and mudstone below. Individual seams are split by numerous clastic

r,0

partings, which can form tp to 50Vo of the coal bed. These partings commonly thicken laterally, passing from mudstone into fine or medium sandstone. The peat in these deposits accumulated in low-gradient river systems that are generally considered to be meandering, although detailed mapping may show an anastomosing model is more appropriate. The rapid lateral facies changes and the correlation of intra-seam stone-bands with clastic wedges indicates that peat accumulated in inter-fluvial overbank basins which were periodically invaded by channels and crevasse splays. Freshwater conditions are indicated by the very low sulphur levels (Table 4) and the complete absence of marine microfossils (Gould, 1980). The presence of interbedded tuffs implies penecontemporaneous volcanism, and the high ash levels of the seams may be due to incorporation of volcanic ash as

l0 Km 1l

azstc]51,

well as to a high rate of fluvial influx.

Although the whole-seam ash values are high, peat accumulation was autochthonous. This is shown by seam profiles in which mineral matter is concentrated in stone-bands and is not distributed throughout the coal (Jones & Patrick, 1980), by the common occurrence of rootlets in units immediately under the seams, and by the delicate nature of plant fossils in the surrounding strata. The nature ofthe original peatland flora can be determined from both the macrofossils in the sequence and from coal petrology. Plant macrofossils are abundant, and include representatives ofthe liverworts, lycopods, equisetaleans, ferns, seed-ferns, cycadeoids, possible pentoxyaleans, and conifers (Gould, 1980). A common, but not exclusive pattern, is for the fine-grained sediments beneath the seams to contain dominantly spore-bearing herbaceous plants and rootlets, while the sediments above the seams contain mainly conifers. The coal itself appears to consist mainly of conifer material,

with herbaceous and cycadeoid plants (Gould, 1980).

r.0

10. Stratigraphic sections showing limited Figure - lateral extent and seam splitting in the Jurassic Walloon Coal Measures (from Leblang & others, 1980).

Apart from the wide variation in ash levels, the nature of the coal is remarkably consistent (Table 4).

A detailed study at Austinvale (Leblang & others, 1980) shows that most coal seam sub-sections contain more than 807o vitrinite plus 'resinous vitrinite', with the resinous vitrinite including

low-reflectivity vitrinite, resin- impregnated vitrinite and suberinitic tissue. Liptinite content is 70Vo or less, and is mainly made up of resinite with minor sporinite and cutinite. The inertinite content

is up to 447o, varying inversely with vitrinite, and the inertinite is mainly semifusinite. The resinous nature ofthe coals supports the coniferous nature of the flora, since most conifers contain resins within specialised ducts or impregnated in the plant tissue. Assessment of the floral evidence and comparison with living analogues also suggest that the Walloon peatlands

Paleoclimate and depositional settings

Table 4. Nature of Coals in Walloon Coal Measures AREA

Wandoan

Acland

Rosewood

Millmerran

SEAM

typical upper CM

Acland lower CM

several

5.7

5.0

PROXIMATE

ANALYSIS (air dry) Moisture (7o)

10.5

4.0

Ash (7o)

36.4

20.0

L7.0

t6.2

Volatiles (7a)

22.0

39.5

38.6

42.0

Fixed carbon (7o)

31.1

.J C!. D

38.7

36.8

Total Sulphtr (Vo)

0.22

0.5

0.8

0.7

Vitrinite (7o) Liptinite (Vo) Inertinite (Vo) Mineral Matter (Vo)

75-95

3.5

1.2-L8

Data source

Jones & Patrick (1980), proximate

MACERAL ANALYSIS

Mclean-Hodgson & Kempton (1980), all analysis on raw coal, data on washed coal maceral content on

Queensland Coal Board (1978), analyses an as sold basis

washed coal, F 1.60

were coniferous swamps. No anatomical evidence of adaptation to waterlogging has been identified (Gould, 1980), and this, together with the high

proportion offusinite (Leblang & others, 1980) indicates that the peatland was relatively dry rather than waterlogged. The climate was probably moist and temperate.

Cretaceous Coals In contrast to the largely non-marine Jurassic sedimentation pattern, Australian Cretaceous sequences are mainly marine in origin (Exon &

Senior, 1976). However Cretaceous coal measures do occur in several small onshore basins, such as the Maryborough and Styx Basins in Queensland and the Wonthaggi area in Victoria, and are extensive in the subsurface Gippsland, Eromanga and Eucla Basins. Typically the coal measures are Aptian in age, and developed during regressive sedimentation that followed the Albian transgression. The coals are thin, dirty, generally discontinuous and commonly inertinite-rich. The inertinite typically consists of well-preserved, thick-walled fusinite or semifusinite (Cook, 1975), indicating that the typical peatlands were dry swamps. Deposition was apparently in fluvial plain settings, though there are no detailed facies analyses to confirm this interpretation.

deposits. The main coals are 10 to 30m thick, with many thinner (1 to 2m) seams also being present (Table 5), and the peatlands that formed them were probably small flood plain swamps. These sequences pass laterally into marine units (e.g. Elms & others, 1982), or are overlain by transgressive marine sequences (e.g. Meyer, L982; Smith, 1982). The coals are huminite-rich, have moderate ash yields (t2 to lSVo) and a moderate sulphur (2 to 37o) content. Palynological studies indicate that the flora was probably a subtropical rainforest in the Early to Middle Eocene (Smith, 1982; Wood, 1981 in Meyer 1982), becoming a cool-temperate mixed

sclerophyll-rainforest in the Iate Eocene (Smith, 1982).

In contrast to these older deposits, the main Oligocene-Miocene coals are thicker (30 to 130m), cleaner (< 57o ash, and 4Vo sulphur), and richer in huminite macerals (Table 5). The coal occurs within a major regressive sequence up to 1600m thick (Abele & others, 1976), with the thickest peat generally having accumulated in slowly subsiding basins that developed on structural highs. Clastic units within the seams are very rare in the Latrobe Valley, and those that do occur are restricted to seam tops or major seam splits. The associated

Tertiary Coals

fluvial channel deposits occur at laterally equivalent horizons to the coal seams (Smith, 1982).

Known Tertiary coal measures in Australia are

In the Gelliondale-Alberton area there was an

largely restricted to the southern margin of the continent, where they occur in the Gippsland Basin and in a number of isolated smaller basins. The coal measures are generally either Cretaceous- Eocene or Oligocene-Miocene (Johns, 1975b; Abele & others, 1976; Smith,1982; Elms & others, 1982; Holdgate, 1982; and Meyer, 1982). The Cretaceous-Eocene coal measures are part of

the non-marine sequence overlying the Cretaceous unconformity that was formed during rifting of the southern continental margin. The sequences are thin (<150m) and generally contain sandy fluvial

unconfined peatland which extended seawards to interfinger with coastal barrier sands (Holdgate, 1982). At its seaward edge the sulphur levels in this coal are markedly higher (2.7 to 3.6%) than in those

further inland, indicating the influence of more brackish conditions (Figure 11).

Five macroscopic lithotypes are recognised within the Latrobe Valley brown coal seams (Edwards, 1947; George, 1982). These lithotypes vary from 'pale', which is soft, friable and non-gelified to 'dark', which is a hard, strong, high density coal in which gelification, particularly of the woody fragments, is

Geology of Australian Coal Basins

Table 5. Tertiary Coals. Area

Esperance, W.A.

Kingston, S.A.

Latrobe Valley, Vic.

Gelliondale, Vic.

Age

M-U Eocene

M. Eocene

Oligo-Miocene

to 50m

Seam Extent

Thickness

Moisture Volatiles Ash (dry) Sulphur

7x35km

5x50km

to 10m

to 12m

ca. 25x50km 30-130m

l6Vo

47Vo

45-5\Vo

5O-70Vo

6x8km

12Vo

15Vo

1.-\Va

66Vo 5LVo 3-4Vo

2Vo

3Vo

< lVo

< l%o

ca. 80Vo

?ca. 80Vo 12-l9Vo

73-97Vo

92Vo

3-9IVo

I-3Vo

7-3Vo

Coal Composition

Huminite Liptinite Inertinite Minerals Data sources

to IjVo to 5Vo ta 5Va Elms & others (1982), proximate

7% < lVo lVo

Meyer (1982).

George (1982).

Greer & Smith (1982).

analyses on a 60Vo

moisture basis. common. Maceral analyses indicate that huminite is

the main constituent (73 to 96Vo),with humodetrinite dominant in paler lithotypes and humotelinite in darker lithotypes (George, 1982). Inertinite and mineral matter are low in all lithotypes, but liptinite is markedly more abundant in pale lithotypes which are composed mainly of liptodetrinite and sclerotinite. Ash yields are less than 5% (dry basis), and, although they do vary between particular coal fields and with depth in a particular coal seam (George, 1982; King & others, 1983), the composition of the ash is similar for all lithotypes.

Pollen studies indicate that a wide variety of vegetation associations existed in the Latrobe Valley peatlands (Luly, & others, 1980; Kershaw & Sluiter, 1982; Sluiter & Kershaw, 1982). Nothofagus is the dominant taxon in all coals, though it forms a greater component of the paler lithotypes. This tree produces large quantities ofwidely dispersed pollen

n F-l

t'l l: --l F.-

but tends not to be a swamp dweller, so its presence tells little about the peatland apart from a wet, cool, temperate climate. All lithotypes are dominated by rainforest taxa, particularly Myrtaceae and Casuarinaceae, with sclerophyll components (Pteridophyta, Epacrid aceae, Restionaceae/ Centrolepidaceae and some Proteaceae such as Banksia markedly more common in darker lithotypes (Sluiter & Kershaw, L982). The very low ash yields and the lack of seam splits have been thought to indicate ombrotrophic peatlands, perhaps raised bogs (Smith, L982; Kershaw & others, in press). The paler lithotypes have been argued by Luly & others (1980) and Sluiter & Kershaw (7582) to be open-water communities, and to be drier peatlands by Mackay & others (1985). The abundance of woody material and of the Restionaceae indicate minerotrophic conditions, such as a swamp or fen peatland, for the darker lithotypes. The paler lithotypes constitute

I-E6ENO Codl 3.om! A I And C

lnt..3.om Cloyt A.O Yi.or Sondg lnt..aon Sdds And Solek Fo.holro^ SuDcoor Md Ov.rburdln l^l.rb.od.d SondsAdcby3 grea^c Borna Co.Mlas_xhry Pornl Ftrfiotro

' si'+-

rc.13-6,09gond L.masro^. Lore5 e^trd^ca Forootro. Ht Lrn€5ton6And UI 3o3ol T..!'€.y vd<o.'cs-Sttual.ckr Greg 8osm.^l And

o' L

s .,Y' t.

"f'.

BorFol For vslrcol Ostr,bunod O1% iolol Su19hu.iO.y8o3rs)

r ra.! Scob:Ho.rzo.lol

609 W.rqht.d Avlrog. Mo.3tur. Conl.nl u. &a a^oly3.d {R Ml R.cdarad

braonlol

Scola

v6trcd s6la

Figure 11. Sedimentary context of the Tertiary brown coal, Alberton-Gelliondale area (from Holdgate, 1982).

Paleoclimate and depositional settings

34 only a minor part of the coal seams, and are characterised by much higher total pollen counts and by lower wood contents. Together these features indicate slow accumulation rates and possibly ombrotrophy, which probably limited thegrowth of large trees, during formation of the paler lithotypes. Statistical analyses of the cyclic development of the lithotypes shows cycles that tend to lighten upwards (Mackay & others, 1985). Such a cycle would

indicate evolution ofthe peatland from minerotrophic swamp/fen to more ombrotrophic treed bogs, which is in fact, a very common pattern for modern peatlands (Wells & Pollett, 1983).

AUSTRALIAN COAL-FORMING PEATLANDS Depositional Models for Australian Coal Measures The peatlands which formed Australian coal measures existed in a wide range of depositional settings, each of which could have occurred in

different tectonic situations. In many cases peat accumulated in volcanically active settings, as shown by the common tuffs within the coal measures and by tonsteins, many of which are also interpreted as altered volcanic ash (Diessel, 1965) within individual seams. Topographic basins contain variable sequences, depending on the scale ofthe depression and the local circumstances. For instance the Blair Athol Basin was isolated from clastic influx during peat accumulation, allowing accumulation of thick ombrotrophic peats, while in contrast, the Collie Basin was a larger depression containing fluvial

plain systems which alternated with peatland development.

Alluvial fan systems are characterised by fanshaped conglomeratic deposits which pass laterally into sandy fluvial plain deposits. Seam splitting is common, and seams tend to coalesce basinwards. Cyclic development is common, but the lateral continuity of the individual cycles is limited. Fluvial plain systems form most of Australia's coal measures. In general three depositional facies can be recognised within such systems: channel, overbank and peatland. Channel sandstones or conglomerates and overbank fine sandstone/ siltstone/shale units conform to well known sedimentary models, with the unit geometries and proportions of each depending on the river system involved. Plant fossils are common, and the sandstone petrography commonly reflects the source terrane. Peatlands were commonly swamps and fens, as would be expected where there was substantial overland water flow. In lower-rank measures, such as the Jurassic and Triassic coals, the peatland flora can be well established, but in the higher-rank Permian coals the macroflora is usually assumed to be that preserved in the various interseam units. Seams may be laterally continuous, or display multiple splitting if there were repeated incursions of fluvial deposits into the peatland. Coal type varies widely, commonly with low to moderate amounts of vitrinite, indicating that low and fluctuating groundwater levels were present to allow peat degradation.

Paralic systems characterise the Early to Middle Permian coal measures, but were rare at other times. Paralic systems include deltas, barrier shorelines and prograding sandy/muddy shorelines.

A wide range of peatland situations occurs, with the most extensive probably occurring on abandoned delta lobes, or on coastal plains landward of the barrier or prograding delta.systems. The interseam sediments are characterised by thinly bedded to medium bedded units with wavy or flaser bedding, abundant ripple marks and ripple bedding, abundant micaceous partings, bioturbation and common pyrite. Plant macrofossils are rare. The sandstones in these sequences are commonly quartzose, possibly reflecting destruction of feldspar and lithic fragments by marine reworking. The coals commonly have moderate to high vitrinite contents, reflecting high groundwater levels, near sea-level, on the flat coastal areas. IJnconfined peatlands provided the sites for accumulation of several extensive, low-ash,

low-sulphur coals with very consistent seam profiles. These seams are uninterrupted by clastic units, and overlie sediments formed in a wide range of previous environments. The Permian Bayswater-Hoskissons, Bulli and Goonyella Middle seams are examples of this type of deposit.

Cyclic Development of Coal Measures Coal measures inherently represent the result of deposition alternating between two contrasting types of sedimentary facies: transported clastics, probably deposited rapidly on the one hand, and in sifu plant materials free of clastics, probably deposited much more slowly on the other. These two contrasting, mutually exclusive situations recur repeatedly, so that any coal measure sequence is to some extent cyclic, even though the reasons for this cyclicity are not well established. In fact coal measures cyclicity exists on three scales: a) Formation scale: Formation-scale cycles, typically hundreds of metres in thickness, are controlled by

tectonic or eustatic events leading to basinwide transgressive-regressive cycles (Brakel, 1986). The Jurassic cycles in the Surat Basin which Exon (1980) has correlated with global sea-level changes, and the cyclic alternation oflacustrine shales with fluvial plain coal measures in the Cooper Basin (Stuart, 1976) are good examples of such successions (Figure 12). The control ofpeat accumulation by major regressive and transgressive cycles, probably due to relative sea-level changes has been described, for example, by Martini & Johnson (1987) and by Hamilton (1991). b) Depositional sequence scale: These are cycles metres to tens of metres thick that are more commonly controlled by processes inherent within the particular depositional system. The cyclic alternation of alluvial fan conglomerates with coal due to fan switching and peat accumulation on inactive fan lobes, such as those of the Newcastle Coal Measures, or the fining-upwards cycles developed by migrating river channels, such as in the Illawarra Coal Measures, are examples of this type ofsequence.

Duff (1967) confirmed statistically the fining-upward cycles in the Illawarra Coal Measures, and considered that they were due to sedimentary processes within the depositional systems. However he found that the Newcastle Coal Measures cycles did not match any known alluvial or deltaic cycles. Johnson & Cook (1973) found both frning-upward and oscillating cycles in the upper part ofthe Newcastle Coal Measures. They noted that the

Geology of Australian Coal Basins

.Gdbb..o-u.do sil

Svror 5ilrat

ooncoala. fbr Codid'ot'. Fn Hootot Stl watlbout.a fh Adori 5!r Bi.lhrdd ra Hollon Srl Fm €v..0r..^ Pr.c'o'cr Sal

Scr'.qbol Stl

ool

XUMOANILL A RIOG€

.c,oic. srt

EAST (CECIL PLAINS SYNCLIN€)

2000

t::.:. A

5OO Xilrd.t..t

MUFTEREE

Appror. t4 Miles

No.C-l

MURTEREE

I o o ..LAKE" CLASTICS (DELTA-FRONI

[]

SANOS ANO PRODELlA MUDS )

F-r]:l DISTFIBU]ARY CLASTICS I:.' 12. Formation scale cycles. Figure * A.Walloon Coal Measures (from Exon' 1980). B.Patchawarra Formation (from Stuart, 1976).

oELTA.PLAIN TO LAGOONAI

CLAsrtcs AND coaL

FLOOD-PLAIN CLASTICS

controls are difficult to define, for while the order of sediments deposited and their lateral variations can be explained by Iocal environmental controls, such as peitland dynamics or stream gradient changes, initiation of the cycles themselves often represents a response to internal basin tectonics.

Within coal seams, the small upward-dulling cycles commonly observed in black coals (Smyt}:,, 1972; Smyth &-Cook, 1976), and the upward-lightenin-g cycies in the Tertiary brown coals (Mackay & others, 1985), are the equivalent to these clastic depositional cycles in a peatland setting. The peatland cycles represent the peat-fo-rming environment responding to a particular situation, perhaps a slightly different climate or changed groundwaterlevel. The responses within each cycle iepresent changes inherent that peatland's

development, for instance the upward evolution of peatland flora that would be expected at constant water levels (Figure 4). c) Event scale: Individual cycles centimetres to metres

thick are probably controlled by individual sedimentition events, commonly though not

necessarily on a seasonal scale. Examples are lacustrine varves or bedding planes offossil leaves separated by sand or silt laminae, wit]J the latter possibly representing seasonal leaf ^falls (Retallack, igsol. Wltfri" coal seams, Hunt (1984) considered that microlithotype variations at the 50 micron scale, equivalent to 0.5mm of peat,-probably-r-eflect seasonai variations in the peatland water table'

Paleoclimate and depositional settings

Depositional control of peat thickness and coal type Coal type is dependent on many factors, but mainly the nature of the peatland flora and the style and rate ofpeatification. To a large extent these are both governed by the nutrient status and elevation of the

peatland groundwaters. Nutrient status governs the llora whiCh will grow, and also the level of microbial activity causing degradation of the organic

materials. Groundwater levels control the flora, since some plants can tolerate standing water where others cannot, and the higher the groundwater Ievels the less chance for direct oxidation and ablation of the peat. The balance between plant productivity and

microbial degradation limits peat thicknesses, provided there is subsidence to allow accumulation (Fielding, 1987). Modern studies (Sjors, 1963; Clymo, 1983; Wells & Pollett, 1983) show considerable variety of vegetation within a peatland, including variations in ombrotrophy and minerotrophy due to local elevation or distance from streams.

Shoalhaven Group and Illawarra Coal Measures. /n Herbert, C. & Helby, R. (Editors): A Guide to

the Sydney Basin. Geological Suruey of N.S.W.

Bulletin,26, IL6-I32.

BRAKEL, A.T., 1986: Global sea-level change as a method of correlating the Late Permian coal measures in the Sydney, Gunnedah, and Bowen Basins, eastern Australia. BMR Journal of Australian Geology and Geophysics, 10, 17-22. BRANAGAN, D.F. & JOHNSON, M.W., 1970: Permian sedimentation in the Newcastle Coalfield, N.S'W. Proceedings of the Australasian Institute of Mining and Metallurgy, 235, 1.-36.

BRITTEN, R.A., 1975. Singleton-Muswellbrook district. In Traves, D.M. and King, D. (Editors): Economic Geology of Australia and Papua New Guinea - 2: Coal. Australasian Institute of Mining and Metallurgy, Monograph, 6, 791-205. BRITTEN, R.A. & SMYTH, M., 1973: The Bayswater Coal Member of the Singleton Coal Measures of New South Wales. Proceedings of the Australasian

Institute of Mining and Metallurgy,248, 37-47

Australian coal seams show a correspondingly wide variation in coal type within individual depositional systems. Even relatively uniform seams, such as the Liddell seam (Marchioni, 1980), display' marked variations in banding that probably reflect changes in the original peatland. Hunt (1984, 1989) found that vitrinite-rich coals in the Late Permian typify paralic settings, while vitrinite-poor coals typify Iluvial and alluvial plain settings, apparently reflecting generally lower and fluctuating groundwater levels in the latter environments. However, he also found that, while depositional setting has a stronger effect, coals formed in tectonically active areas where there is continual subsidence tend to be higher in vitrinite or brighter than those which accumulated under more stable conditions.

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International Journal of CoaI Geology, L2, 589-634.

HUNT, J.W. & HOBDAY, D.K., 1984: Petrographic composition and sulphur content of coals associated with alluvial fans in the Permian Sydney and Gunnedah Basins, eastern Australia. 1n Rahmani, R.A. & Flores, R.M. (Editors): Sedimentology of Coal and Coal-bearing Sequences. Special Publications of the International Association of Sedimentologists, 7, 43-60.

JENSEN, A.R., 1975: Permo-Triassic stratigraphy and sedimentation in the Bowen Basin, Queensland. Bureau of Mineral Resources Geology and Geop hy sic s Bulletin, 154.

Paleoclimate and depositional settings

38 JOHNS, R.K., 1975a: Leigh Creek Coalfield, Boolcunda Basin and Springfreld Basin, South Australia. In Traves, D.M. & King D. (Editors): Economic Geology of Australia and Papua New Guinea - 2: Coal. Australasian Institute of Mining and Metallurgy Monograph, 6, 301-305.

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MARCHIONI, D.L., 1980: Petrography and depositional environment of the Liddell seam, upper Hunter Valley, New South Wales.

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International Journal of CoaI Geology, l, 35-61" MARTIN, K.R., 1980: Early Jurassic sedimentation in the Surat Basin. Coal Geology, 1, 71-81. MARTINI, P. & JOHNSON, D.P., 1987: Cold-climate, fluvial to paralic coal-forming environments in the Permian Collinsville Coal Measures, Bowen Basin, Australia. International Journal of Coal Geology, 7, 365-388.

JOHNSON, K.R. & COOK, A.C., 1973: Cyclic characteristics of sediments in the Moon Island Beach Subgroup, Newcastle Coal Measures, New South Wales . Mathematical Geology, S, 91-110.

McLEAN-HODGSON, J. & KEMPTON, N.H., 1980:The Oakey-Dalby region, Darling Downs Coalfield: stratigraphy and depositional environments. Coal Geology, L, 1'65-t77 .

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MEYER, G.IvI., 1982: Geology of the Kingston lignite

KANTSLER, A.J., PRUDENCE, T.J.C., COOK, A.C. & ZWIGULIS, M., 1983: Hydrocarbon habitat of the Cooper/Eromanga Basin, Australia. APEA

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KERSHAW, A.P. & SLUITER,I.R., 1982: ThC application of pollen analysis to the elucidation of Latrobe Valley brown coal depositional environments and stratigraphy. Australian Coal Geology,4, 169-183. KERSHAW & others, in press [DETAILS NOT GIVEN]

KING, T.N.W., GEORGE, A.M., HIBBERT, W.D. & KISS, L.T., 1983: Variation of Coal Properties Part 2: Latrobe Valley coals. with Lithotype

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MILLER, K.G., FAIRBANKS, R.G. & MOUNTAIN, G.S., 1987: Tertiary oxygen isotope synthesis, sea level history, and continental margin erosion. Paleoceanography, 2, L-L9. MOORE, P.S., HOBDAY, D.K., MAI, H. & SUN,2.C., 1986: Comparison of selected petroleum-bearing basins in Australia and China. The APEA Journal,26, 285-?. MORRISON, K.C. & BACON, C.A., 1986: Comparison between the Fingal and Langloh coalfields, Tasmania Basin. Australian Coal Geology,6, 4l-57. OSMAN, A.H. & WILSON, R.G., 1975: Blair Athol coalfield. 1n Traves, D.M. & King, D. (Editors): Economic Geology of Australia and Papua New Guinea - 2: Coal. Australasian Institute of Mining and Metallurgy, Monograph, 6, 376-380. PARK, W.J., 1982: The geology of the Muja Sub-basin, a model for Collie, W.A. Australian Coal Geology, 4(2),319-340. PLAYFORD, G., JONES, B.G. & KEMP, E.M., 1976: Palynological evidence for the age ofthe synorogenic Brewer Conglomerate, Amadeus Basin, Central Australia. Alcheringa, l, 235-243. POWER, P.E. & DEVINE, S.B., 1970: Surat Basin, subsurface stratigraphy, history and Australia petroleum.- Bulletin of the Atnerican Association of Petroleum Geology, 54, 2410-2437 COAL BOARD, L978: Queensland QUEENSLAND - Coals: typical physical and chemical properties and classification, 6th edition. Queensland Coal Board, Brisbane. P.G., 1984: Phanerozoic climates and QUILTY, - environments of Australia. In Veevers, J.J. (Editor): Phanerozoic Earth History of Australia. Clarendon Press, Oxford, 48-57 -

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Geology of Australian Coal Basins

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P aleoclim ate

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ZOLTAI, S.C. & POLLETT, F'C., 1983: Wetlands in Canada: their classification, distribution and.use. In Gore, A.J.P. (Editor); Mires: Swamp, Bog, Fen A: Regional Studies. Elsevier, and. Moor Amsterdam- , 245-268.

and depositional settings

Wloras of Australian coal measur€sr with notes on their associated Mesozoic faunas

BE Balme AP Kershaw and JA Webb

Structured plant communities, often containing trees, are a prerequisite for the formation of persistently thick, laterally extensive peat deposits, which are potential progenitors of commercial coal seams. The arborescent habit evolved, apparently independently, in several vascular plant groups during the Middle Devonian but the oldest workable coals occur in the Lower Carboniferous. Highly carbonaceous sediments have been reported in Australia from the Devonian on but the oldest known prospectively mineable seams are of Early Permian age. They occur in the Sydney and Bowen Basins and represent peats formed during the early successional phases of the Glossopteris -Flora, which became established following the regional waning of the Late Palaeozoic glaciation. Since the Early Permian, peat has accumulated wherever favourable biological and sedimentological circumstances existed and coal is present, virtually throughout the geological column, in one or other of the Australian sedimentary basins. Coal formation is governed by the interaction of sedimentological, climatic and floral factors, the last two being the most important. The main climatic control on peat swamp development is rainfall. Today peat swamps form only in humid climates; the rainfall is essential not only for plant growth, but also to provide the high water tables necessary to preserve peat. Temperature is less important, as present day peat swamps occur both in cooler regions, e.g. central and northern Europe, as well as \{/armer equatorial areas such as southeast Asia (Schopf, 1973). Nevertheless, temperature (rather

than lack of light) is a controlling influence on plant growth (and hence peat formation) at high latitudes. During the Late Palaeozoic and most of the Mesozoic, Australia consistently occupied high palaeolatitudes (Veevers, 1984) and the bulk of the coal deposits throughout this time accumulated between 50o and 70oS. At present these latitudes encompass Antarctica, which is too cold for peat-forming vegetation to survive, so temperatures for much of the Permian and Mesozoic must have been warmer than those of equivalent latitudes today. Whether the prolonged polar (light-free) winters implied by these high palaeolatitudes are consistent with the diversity and abundance of the Mesozoic floras is a topic of continuing debate (Douglas & Williams , L982; Axelrod, 1984).

Peat deposits are formed by specialised plants adapted to water-logged, usually acid substrates. Because of these physiologically stressful conditions, the vegetation of peat swamps is often poor in species, relative to the communities growing on

adjacent better drained areas. Thus it is not surprising that plant communities in Late Palaeozoic and Mesozoic coal seams have low diversities, whereas floras from the surrounding flood plains, levees and hills contain a much larger number of species. The dominant plants of the coal swamps varied according to the Period e.g. glossopterids in the Permian and Dicroidium in the

Triassic. In fact, the evolution ofspecialised plant communities capable of establishing themselves and growing in peat swamps may have been a necessary prerequisite for coal measures to form (Gould & Shibaoka, 1980). Reconstructing the vegetation of coal swamps and nearby environments is fraught with uncertainty. In general, such reconstructions are "guesswork based....on the empathy of field worker(s) with (their) material" (Holmes, 1982). Although most

Floras of Australian Coal Measures

Australian coals represent virtual in situ peat-forming material (Gould, 1981), ascertaining which plants actually contributed to the coal is never easy and becomes progressively more difficult with increasing geological age. Plant macrofossil remains within coal are normally degraded and indeterminate, although coalifred plant specimens sometimes protrude from the coal into the overlying sediment. Plant remains in shales immediately adjacent to coal seams may represent flood plain species rather than the actual peat swamp vegetation, although consistent associations of particular plants are a good guide to the coal swamp flora.

Similarly the spore-pollen assemblage extracted from a coal is likely to include species with a wide range of habitats and to be biased towards wind -pollinated plants with a high pollen output (e.g. the araucarian conifers in the Jurassic and Early Cretaceous and Nothofagus in the Tertiary). Nevertheless, consistent plant microfossil assemblages within coal seams also provide a guide to the composition of the original peat swamp flora. Any attempt to reconstruct the vegetation of ancient coal deposits must consider both palynological and macrofossil evidence and this is the approach adopted in the present review. Relating the two sources of data presents formidable obstacles in pre-Tertiary deposits, principally because most dispersed spore and pollen species can only be related to their parent plants in broad terms. This will probably be always true, but there has been a steady increase in recent years in the documentation of spores and pollen associated with fossil reproductive structures and as additional information accumulates a more sophisticated synthesis will emerge.

PERMIAN COAL FLORAS It is a little over one hundred years since Neumayr coined the term Glossopteris -Flora for the closely

similar plant fossil associations that are found in the Late Palaeozoic coal measures of India and the continents of the southern hemisphere. By accentuating the essential Palaeozoic unity ofthe now dispersed fragments of Gondwana the concept of a single, huge, homogeneous floral province

stimulated the early speculations on relative continental movement that initiated the modern global tectonic paradigm. As a basis for palaeophytogeographic interpretation tlris stress on -floral uniformity and stasis has proved less fruitful. Strata containing the leaf genus Glossopteris span a time interval of over 40 million years, almost the length of the Tertiary, and o^ccur-sporadically over a land area of roughly 50 x 10" km'. During this time the continental area of Australia rotated clockwise through about 30o and moved towards the equator. It is therefore inconceivable that the complexities of plant evolution and changing patterns of regional distribution evident in the Tertiary were not matched by comparable developments during the Permian. A more dynamic approach to Permian palaeobotany and phytogeography has been stimulated by the great volume of palynological information that has become available during the past 30 years and by the resurgence of interest in Late Palaeozoic seed plants thit has followed the discovery, during the

iame period, of a large number of reproductive structures attributable to glossopterids. Recent

Australian accounts that have been principally concerned with the macrofossil record, include reviews by Gould (1976) of Late Palaeozoic floral sequences, Retallack (1980) who adopted an ecological approach in his discussion of the Permian "Glossopteris deciduous swamp forests" of the SydneyBasin and, more recently, the splendidly illustrated, semi-popular treatment by White (1986). Kemp & others (1977), Foster (1982), Price (1983), Backhouse (1991) and Gilby & Foster (1988) have contributed syntheses of Australian Permian palynological data, in papers that emphasise the applications of plant microfossils to biostratigraphy, but incidentally provide important information on successional changes in regional floras ofthe Late Palaeozoic. The applicability of palynological results to palaeophytogeographic studies of Palaeozoic Gondwana was intimated by Truswell (1980) in a preliminary analysis which indicated the existence of floral sub-provinces within the region.

Structure and composition of glossopterid communities

Maerofossil eaidence Permian peats were deposited over a prolonged period in-a variety of tectonic settings, climates and sedimentary environments. Nevertheless, some generalisations are possible concerning the floras [hat produced them, without too gross indulgence in over-simplification. Fossil remains categorised as the Glossopferls-Flora, with the possible exception of some microfossils, are those of components of stratified communities that colonised alluvial and delta plains, in both coastal and upland regions. These communities consisted of hygrophilous plants and the dominant elements, at least in some places, were trees over 40m high with at least 120 annual growth rings (Retallack, 1980). Their silicifred trunks are common at some localities, especially in the Bowen and Sydney Basins. These woods with their seasonal growth rings are closely comparable anatomically. They are referred to the genus Araucarioxylon (or Dadoxylon), but probable cordaitanthalean wood has also been reported (Gould & Shibaoka, 1980). Araucarioxylon trunks are associated with septate, aerenchymatous axes known as Vertebraria and Gould ( 1975) has argued convincingly that these were underground structures analogous to the aerating tissues found in the roots of certain present day, semi-aquatic, angiosperms. Some Vertebraria may have functioned as pneumatophores and it is also likely that others weie partly aerial in the manner of the roots of the extant genus Rhizophora. By far the most profuse remains of the Glossopteris -Flora are detached spatulate to lanceolate leaves. They include the eponymous genus Glossopteris, Gangamopteris, Noeggerathiopsis (so,metimes refeired to Cordaites), various scale leaves and, less commonly, Palaeou ittaria and S urangep hy l-lum' Noeggerathiopsis is regarded as cordaita-nthalean by most authors and Rigby (1984) created the genus Pantophyllu;'n to accommodate leaves of the Noegferathiopsis -type with preserved cuticle.The othir"four genera aird scale l-eaves are believed to have belonged to glossopterids. Gg,ngamopteris occurs most frequently in Lower Permian coal measures and GTossopteris is more abundant and

morphologically diveise in the Upp-e-r Permian but the lwo genera are gradational and known to occur on the same stem (Rigby, 1967). It may be, as Retallack (1980) hinted, that their distinguishing

Geology of Australian Coal Basins

characters were principally climatic responses and that the more diffuse venation of Gangamopteris was physiologically advantageous in the colder post-glacial conditions of the Early Permian. Because oftheir abundance, and the rarity of specimens attached to axes, Glossopteris and Gangamopteris are thought to represent the foliage ofdeciduous trees and this is probably true ofthe parent plants of other simple 'broad leaf genera associated with them. Discovery of reproductive elements associated with, and attached to, other glossopterid organs has stimulated renewed interest in the group during the past three decades. Ovulate structures of glossopterids have now been described from all Gondwana continents: about 14 genera have been generally accepted and these have generated a diversity of structural interpretations. Speculations have been restrained to some extent bv the description of petrified female fructifications of the Dictyopteridium-type from Queensland by Gould & Delevoryas (L977) although homologies of the various elements of even these structures are still

debated (see Retallack & Dilcher, 1981). Mcloughlin (1990a,b) has reviewed the glossopterid

inflorescences that occur in the Upper Permian of eastern Australia and listed the female fructifications Plumsteadio (Figure t), Austroglossa, Rigbya, Partha, Ottokaria, Cornetia and, Senotheca. They are known only from compressions and their structures have been variously interpreted but,

whatever the narrower affinities of the glossopterids, it is clear that they were gymnospermous and that their ovules were borne on "megasporophylls", adnate to what appear to be normal foliar leaves. It is therefore reasonable to infer that the seed-bearing organs were deciduous and dispersed by wind, particularly as some genera produced winged seeds which, if isolated, would be classified as Sarnaropsis, Nuntmulospermum or Indocarpus

Intact glossopterid male reproductive structures so far described from Australia are Squdmella (White, 1978) and Eretmonia (Rigby & others, 1988) and it is probable that Nesowalesia, a small disc-like structure bearing numerous sporangia on one surface (Pant, 1977; Rigby & Chandra, 1990) also belongs to the group. These genera possess frnely ribbed anther-sacs of the Arberiella -type. In Squamella they occur on the adaxial surfaces of fertile bracts, which are arranged in a tight spiral helix at the terminations of short shoots. The genera Eretmonia and Glosso/heca are individual microsporangiate bracts, analogous to those of Squamella, and are widely distributed in the Gondwana Permian. They contain taeniate diprotosaccate pollen referable to Protohaploxypinus (Figure 2) which is abundant and ubiquitous as a dispersed form in the upper Lower and Upper Permian of Australia and the other Gondwanan countries. The apparent lack of variety of Australian Permian plant macrofossil remains has commonly led to the inference that their parent floras were similarly impoverished. It may be true that the overstorey normally consisted of a single dominant species but it is clear from palynological evidence that the lower levels offorest structure comprised a great diversity of seed and spore-producing plants. The remarkable morphological heterogeneity displayed by dispersed pollen grains (Figure 2), especially in the Upper

Floras of Australian

Permian, contrasts tantalisingly with the almost complete absence of gymnospermous macrofossils, apart from glossopterids and possibly cordaitanthaleans. Coniferopsids are probably represented by the rare Walkomiella, although even in this genus the reproductive structures appear atypical (White, 1961), and cycadophytes have been described by Rigby and by Mcloughlin in papers awaiting publication. Occasional specimens of strongly dissected leaves with a relatively long petiole, superficially resembling ginkgophytes, occur in the Irwin River Coal Measures and the Upper Permian of the Sydney Basin but they may also be attributable to a sphenophyte, such as Gondwanophyton.

Apart from glossopterid leaves, pith casts of sphenophytes are the most abundant macrofossils. These have been customarily identified as Phyllotheca, or even less reasonably Schizoneurd, but recent authors have referred them to the more non-committal form genus Paracalarnites. The recent discovery of silicified sphenophyte stems in the Permian of the Bowen Basin has enabled Beeston (1986) to demonstrate that at least some of these stem casts belonged to calamitaleans (Leptocalamiles Beeston). Most Australian Permian casts appear to represent stems less than 2 cm in diameter, presumably those of plants with a habit similar to the living Equisetum, but some were probably the size of small trees (Rigby, 1966) and others may have been climbers (Rigby, 1962). Some Permian equisetalean plants formed dense, fringing, reed-like stands, marginal to floodplain lakes (Johnson, 1984, Rayner, 1992). Their foliage has been assigned to several genera, distinguished primarily by the symmetry, arrangement and degree of fusion of the leaf whorls. These include the phyllothecaceous taxa Phyllotheca, Um,bellaphyllites, Raniganjia, Austroannularia and Lelsotheca (= Stellotheca) and., in the Upper Permian, the schizoneuraceous genus Schizoneura. Another order of sphenophytes, the Sphenophyllales, is represented by sporadically distributed specimens of Sphenophyllum and Tryzygia.

A small herbaceous Late Permian lycopod has been assigned to the extant genus Selaginellaby Townrow and Wood & Beeston (1986) have recently recorded the heterosporous strobilus Skilliostrobus from the basal Rewan Group in the Bowen Basin. However, in the main, lycopsids are represented only by stem compressions and a few isolated leaves. Most are poorly preserved and their nomenclature is in need of revision but, in Australia, Permian lycopsids do not appear to have been as varied, abundant and large as they were in South America and southern Africa (cf. Anderson & Anderson, 1985). The characteristic Gondwana species Cyclodendron leslii has been reported from several localities in eastern and Western Australia but Rigby (1983) believed that the only undoubted records are those from the Reids Dome beds in the Bowen Basin (see also Beeston, 1990). Unequivocal pteridophyte remains are virtually confined to the Bowen Basin from where petrified stems and petioles of the tree-fern Palaeosmunda and isolated leptosporangiate sporangia have been described (Gould, 1970; Gould & Delevoryas, 1977). Pinnate fronds are abundant at some localities, especially in eastern Australia, but no undoubtedly fertile specimens have been illustrated. Sterile foliage ofthis type has been classified variously as

Coal Measrrres

Geology of Australian Coal Basins

Sphenopteris, Alethopteris, Cladophlebis, Dichotomopteris and Neomariopteris and, although many, perhaps most, specimens are no doubt ferns, some may represent peltasperms or other gymnosperms.

The characteristically Late Carboniferous frond genus Botrychiopsls, for example, which ranges into the lowermost Permian coal sequences in the Sydney Basin is associated with seeds and gymnospermous wood and generally is regarded as a "pteridosperm", although this cannot be firmly demonstrated. Dunedoonia is an interesting frond with reticulately' veined pinnules from the Upper Permian and may be a fern, "pteridosperm", cycadophyte or a glossopterid with compound leaves (Holmes, L977). Bergiopteris (Rigby, 1989) and Blechnoxylon (Etheridge, 1899) are other rare gymnospermous elements and the peltasperm Dicroidium first occurs i! the uppermost Permian of the Sydney Basin above the highest coal seam (Retallack, 1980). P alyno lo gic al eu idenc e

Dispersed spores and pollen are recoverable from almost any fresh, unmetamorphosed, Permian sediment and for practical purposes provide the principal basis for regional correlation ofAustralian coal measures (see, for example, Kemp & others, 7977 ; Price, 1983). They also have considerable potential as guides to Late Palaeozoic phytogeography and although, as Chaloner & Lacey (1973) argued, there are difficulties in applying them, these may not be as fundamental as some have suggested. Detailed investigations, using scanning and transmission electron-micrography (e.g. Millay & Taylor, 1974), have demonstrated that, in principle, exine structure may serye as effectively as that of other organs as a key to phylogeny, so there is little question that wider application of more sophisticated techniques will result in revolutionary modifrcation of existing concepts of floral provincialism during the Permian. Some progress has been made in this direction by Foster & Price (1981) but present understanding of the morphology and relationships of Australian Permian spores and pollen is still based almost entirely on observations using optical microscopy.

Altho'gh plant microfossils have been extensive,ly applied to Austre]ian Permian biostratigraphy there are only a few published systematic accounts. The most comprehensive of these is Foster's palynological study of the Blair Athol and Baralaba Coal Measures in the.region 9f the Bowen Basin

resemble those known from other Australian Permian coal measures and form the main basis for generalisations offered in the present account. The feature of Permian assemblages that most palpably distinguishes them from those ofearlier periods is the presence of a heterogeneity of gymnosperm pollen grains, particularly saccate (mainly protosaccate) forms. Foster illustrated a

total of 143 species, 73 from the Baigendzhinian Blair Athol sequence and 134 from the Chhidruan

Baralaba Coal Measures, of which 66 were pollen. Because wind-dispersal was probably universal, Permian spore and pollen spectra are likely to be more representative of their parent floras and hence more varied than those of Tertiary and Holocene deposits. Allowing for this, and for the possibility that some of the species are artefacts of taxonomy, it is still evident that the microfossil assemblages represent strongly diversified plant communities, especially those of the Late Permian. To facilitate discussion, components of these assemblages are grouped here into a small number of morphological categories, the general features ofwhich are indicated by representative examples of each illustrated in Figure 2.

i) Spores: Seventy-seven of the species described were miospores, 66 trilete and 11 monolete. Most lacked pronounced exinal modification, apart from sculpture, although a number of zonocavate forms that may have derived from lycophytes were present. Presumably most of the structurally simple species were produced by sphenophytes or ferns, but very few reproductive structures from Gondwanan representatives of either of these groups have yielded spores. Sporangia of fertile pecopterid fronds from the Permian of India contain spores referable to T hy mo s p or a, O s m u ndac idite s and, H o t iditrilet e s (Pant & Misra, L976,1977; Lele & others, 1981) and Gould & Delevoryas (1977) illustrated forms resembling Horriditrileles from isolated silicifi ed leptosporangia from Queensland. These dispersed spore genera are all common in the Australian Late Permian. Dulhuntyispora is an especially distinctive genus which is characteristic of the Australian Upper P"rrrriun atttrough it r".rg". f*t" ttr" "fp"r-Lo*". Permian (Backhouse, 1901). The genus occurs throughout Australia, but appeari to be most common and diverse in the eanningBasin (Price, 1933). It is known from the Permiair of southern Africa (Anderson, 1977) and occurs as a recycled element in Tertiary and Holocene sedimenti in the Antarctica Peninsula (Kemp, 1972, Askin & Elliot,

(Foster, 1979). In their principal broad characteristics these Queensland assemblages Figure 1. Representative Permian coal province flora. A. Gangamopteris cyclopteroides I.eietmantel, X 0.8; glossopterid leaf; Upper Permian, Newcastle Coal Measures, New South Wales. B. Plumsteadia semnes Rigby, X 1; glossopterid female reproductive structure; Lower Permian, Blair Athol Coal Measures, Queensland. C. Noeggerathiopsis sp., X 0.8; cordiatanthalean leaves; locality unknown. D. Sphenopteris lobifolia Morris, X 0.8; fern-like foliage; Upper Perrnian, Newcastle Coal Measures, New South

Wales. E. Glossopteris sp., X 0.8; glossopterid leaves; Upper Permian, Illawerra Coal Measures, New South Wales. F. Vertebraria indica Royle, X 0.8; internal cast of glossopterid axis; Upper Permian, Newcastle Coal Measures, New South Wales. G. Walkomiella australis (Feistmantel) Florin, X l; conifer axis; Upper Permian, Newcastle Coal Measures, New

South l[ales.

H. Raniganjia bengaslensls (Feistmantel) Rigby, X 1; equisitalean axis and leavesl Upper Permian, Baralaba

Coal Measures, Queensland. I. Stellotheca robusta Surange snd Prakash, X 0.8; equisitalean axis and leaves; Upper Permian, Newcastle Coal Measures, New South l9ales. Note: Photographs for Figures 3.1B, D, H and I were supplied by John Rigby, Geological Survey of Queensland, whose help is gratefully acknowledged.

Floras of Australian Coal Measures

ffi,ffi,ffi,

SPORES

ffiW W.

W SULCATE & POLYPLICATE POLLEN

@,w.@

ffi.ffi

TAEN IATE DISACCATE POLLEN

ffi W,, 17

MONOSACCATE POLLEI\i NON.TAEN IATE DISACCATE POLLEN

ffi?A @'

W.ffi

Scale E 50 pm

Figure 2. Representative examples of Permian plant microfossils grouped into five broad morplological categories. 26. Falcisporites L7. Striatoabietes 8. Dulhuntyspori l."Horriditriietes 18, 21. Protohaploxypinus 27. Limitisporites 9. Microbaculispora 2. Apiculatisporis 3.

Eetusotriletes

1-O.

Didecitriletes

4. Phaselisporites

11-. Praecolpatites

5, Osmundacidites 6. Laeuigatosporites

12, 13. Vittatina 14. Cycadopites 15, 16. Marsupipollenites

7. Indotriradites

19, 20. Striatopodocarpites 28. Platysaccus 29. S cheuring ipollenite s 22. Potonieisporites 23. Plicatipollenites

24. Vitreisporites 25. Alisporites

Geology of Australian Coal Basins

47 1982) and in the Oligo-Miocene of the Himalayan front, north-eastern India (Venkatachala & Kar, 1990). No other Gondwanan records exist and its absence from the intensively studied Permian palynological assemblages of Peninsula India,-in fariicular, has important palaeophytogeographic implications.

ii) Monosaccate pollen: Large radially and

bilaterally symmetrical monosaccate pollen grains, bearing trilete, dilete or monolete tetrad scars are especially characteristic of the Australian Late Carbonifbrous and earliest Permian. They are abundant in periglacial sequences and are subsidiary components of assemblages f,rom Early Permian ioal measures but occur less often in younger sediments. Radial specimens of this type are aisigned to such genera as Plicatipollenites and Barakaiites, and pollen with grossly similar morphology is known to have been produced by me.nbersii the Cordaitanthales (Meyen, 1984) and certain Late Permian conifers (Clement-Westerhof, 1974; Archangelsky & Cuneo, 1987). Bilateral, monolete pollen grains, resembling the genus Potonieisporites, occur in Stephanian voltziacean strobili (Iiharadwaj, 1964) and it is reasonable to infer that dispersed specimens indicate a coniferalean component in their parent flora.

iii) Disaccate taeniate pollen: In this category the

exoexine of the proximal face is di.ssected by narrow

sub-parallel clefts, giving rise to apparent bands of traniverse thickening (taeniae). Plants that produced this type ofpollen were in e-xistence during ihe Late Carboniferous but reached their acme of abundance, diversity and dispersion during tbe - Permian, when they spread throughout the World and assemblages from some seams of the Baralaba Coal Measures contain over 7jVo disaccate taeniate pollen (Foster, 1979).They disappeared towards the end of the Triassic, although it is possible that the Gnetales and Welwitschiales are surviving derivatives of Late Permian members of the group.

At least some glossopterids possessed protosaccate taeniate pollen (Gould & Delevoryas, 1977) and closely similar grains to those from the Gondwanan genui Arberiella are present in Angaran Late Permian synangia, atlributed by Meyen (1984) to the Peltaspermales. This is usually regarded as an example of homeomorphy, but it seems an equally proper first assumption that the glossopterids were inoie closely allie&to coeval lineages beyond the Gondwana province than has been supposed. Taeniate pollen produced by Permiqn and Triassic conifers (townrow, 1967; Clement-Westerhof, 1974)' on the other hand, clearly represents parallelism. It has relatively broad clefts and taeniae and, usu-ally, a short monolete tetrad scar at the proximal pole (Figure 2). Dispersed pollen with these characters is ass'igned to Luiatispolites (or Taeniaesporites) and is abundant in the Australian Lower Triassic, although occasional specimens occur in the uppermost Permian coal measures. iv\ Disaccate non-taeniate pollen: The distinction between monosaccate and disaccate pollen is not absolute and in some species that are regarded here as essentially disaccate, the laterally,expanded sacci are joined by narrow strips of inflated.exoexine (protosaccus). Most Permian non-taeniate saccate pbllen fall into one of three morphological iategories, although differentiation between them is probably largely arbitrary. One- incorp-orates forms witn a froximai tetrad scar and includes such

genera as Limitisporites, Vestigisporites and Triadispora. Som-e of these superficially resemble oollen of the Euramerican Permian voltziacean cone that !"tr.tt IJllmannia, but Foster (1983) believes that [hey differ from it in important lespects.and none can be confidentlylegarded as coniferalean. One of the two groups that lack tetrad scars has sacci with baseJ that are separated distally by a relatively broad area of thin exine. In genera such as Alisp6rites and Pteruchipollenites (sensu Foster, 19?9) no germinal area is clearly delimited, but a

well-defined sulcus characteris es Falcisporites, a peltaspermalean pollen genus whic,\ occurs first in Australia in Upper Permian coals. Vitreisp.orites, found in Lowei hnd Upper Permian coals, is a small but distinctive form whlch appears identical with pollen of C ay tonia nt hu s although similar -grains have now been reported from Angaran peltasperms (Gomankov & Meyen, 1986). Specimens in the third category have an oval outline

in polar view, a thin corpus that is often scarcely oeiceotible. and sacci that are almost in contact itong th"it'distal bases. Such forms are more comiron in Lower Permian coals, especially in the Perth and Collie Basins, and have been assigned by most recent authors to Scheuringipollenites, although the older generic name Vesicgspor@-seems equalli appropriate-. Pollen with grossly similar mbrph-oloL* oicurs in disparate l,ate Palaeozoic plant sroopt suih as the callipterids, Callistophytales and Feltdspermales (sensu Meyen, 1984). v) Sulcate and' polyplicate forns: This class comprises a heterogeneity of asac-cate gymnosperm poll6n grains. It includes monosulcate pollen i efer ab-l e t o C y c ad o p ities an d M a r s,up ip o ll e nit e s, polyplicate genera such as Praecolpatites, Weyiandites and Ephedripites. Species of Vittatina

and Tiwarisporis are technically -polyplicate but may have arisenTrom the reduction ofdisaccate taeniate forms belonging to glossopterids. Another representative ls Pretricolpipollenites, a trisulcate foim that simulates tricolpale angiosperm pollen and, at least under optical micro-sco,p-y, is not

obviously distinguishable from the Mesozoic genusEucommiidites.Little can be inferred concerning the plants that produced these varied pollen. 'Marsupipol[enites has been isolated from sporangia associit6d with glossopterids (Pant & Nautiyal, 1960) and grains almost certainly belonging to Weylandites occur in the synangiryrt' Rugat!t'-e.c9' described by Pant & Basu (1977) from the Nidpur Beds, India, but the affinities of both of their.parent planis are obscure. Pretricolpipollenites may have belonged to a bennettitalean if-the comparison with Eucoilmiidites is valid and Ephedripites is conceivably gnetalean, but pollen of the Cycadopitestype is known from peltasperms, cycadaleans, b"ennettitaleans, pentoxylileans, gnetaleans and ginkgoaleans.

Summary In an idealised reconstruction, a typical fully

developed Permian coal swam-p plant community consisfed of open forest with few dominant.s-pecies' These w"re *'ainly broad-leafed glossopterids, s<ime at least of which were deciduous, but

cordaianthaleans and conifers probably occurred as associates. They grew on waterlogged peat and pos ses sed undeiglound axes with aerenchymatic iirsou which seried an aerating and perhaps also a strengthening function. By inferenc-e,-both the pollen and s6eds of fhese plants were wind-dispersed.

Floras of Australian Coal Measures

Ferns, lycopsids, sphenophytes and varied gymnosperms made up the subordinate tree stratum and understorey, and a variety ofchlorophytic algae (including Botryococcus and zygnematalean species) colonised the swamp waters. Most of these have left no record, other than their spores, pollen grains or resting cysts, but the seed-plants, in particular, were diverse at a high taxonomic level. The gymnosperm orders represented are conjectural but pollen grains comparable to those of glossopterids, peltasperms, cordaitanthaleans and conifers are present, associated with a variety of morphological types without clear analogues among the pollen of Iiving or fossil plants. Forests containing broad-leafed deciduous trees with annual growth rings indicate seasonal contrasts, moderate to heavy rainfall and a temperate climate with winter frosts but warm to hot summers. Modern climatic analogues of the Late Permian Australian vegetational formations are therefore those of the mid-latitude eastern United States and western to central Europe.

MESOZOIC COAL FLORAS Coal measures accumulated intermittently in Australia during the Mesozoic, and almost all of the resulting sequences seem to have formed in fluvial swamps, often with internal lakes, developed on the low-lying reaches of floodplains adjacent to either meandering or, less commonly, braided rivers. The Late Triassic Ipswich Basin and the Early Cretaceous Otway Basin (Falkner, 1986; Duddy, 1985) represent well-known examples. With the possible exception of the Early Jurassic Cattamarra Coal Measures in the Perth Basin, none of the major Mesozoic coal-bearing sequences shows any evidence of marine influence.

Similar fluvial environments existed in Australia throughout the entire Mesozoic, but accumulation of coal was restricted largely to the Late Triassic (Carnian), the Early Jurassic, the Middle Jurassic (Bathonian) and the Early Cretaceous (Aptian and Albian). A combination of the climatic and floral factors discussed above must have been responsible for this periodicity, but it seems likely that availability of sufficient rainfall was of over-riding importance, together with the development of a plant community able to tolerate the coal swamp environment. The interplay of these factors for each period is discussed further below.

Triassic The Triassic floras of Gondwana are remarkably uniform. They consist largely of endemic species (Figure 3), although there are some cosmopolitan forms such as pleuromeian lycopods (Retallack, 1975) and dipteridacean ferns (Webb, 1982). The floras are dominated by the distinctive and easily recognised corystosperm seed-fern Dicroidium, which first appeared in the latest Permian and became extinct in the latest Triassic (Retallack, t977a, 1980). The morphology of Dicroidium shows evidence ofa broad evolutionary trend during the Triassic, changing from mostly large, bipinnate fronds in the Early Triassic to mostly small,

unipinnate leaves in the Late Triassic. Dicroidium

was able to adapt successfully to a variety of habitats and topographic situations at latitudes from 30oS to 80oS, including swamp, heath and forest, and apparently ranged in form from ground cover to shrubs to small trees (Anderson & Anderson, 1983). The taxonomy of Dicroidiumhas undergone two recent revisions; Retallack (t977a) recognised 40 taxa,25 ofthem being present in Australia, whereas Anderson & Anderson (1983) defined 31 taxa (9 of them completely new), 21 of which are present in Australia. Further study of the Australian species may necessitate more changes; Anderson & Anderson (1983) noted that "nomenclatural consensus (is) a remote possibility". The Early Triassic flora of Australia is best known from the Sydney and Lorne Basins, sediments of which were deposited in coastal or near coastal environments (Holmes & Ash, 1979; Retallack, 1980; White, 1986). The flora comprises about 20 species and is more diverse than the Late Permian megaflora, perhaps as a result of ameliorating climatic conditions. The Triassic configuration of the Pangaean supercontinent caused relatively humid conditions to exist over the southeastern margin of Gondwana, i.e. present day eastern Australia (Robinson, 1973; Parish & others, 1982). Thus the eastern Australian coastal climate during the Early Triassic was apparently sub-humid, cool temperate,

with periodic drier conditions (Retallack, 1977b). However, red beds accumulated in inland areas, where an arid climate with large seasonal temperature variations and low rainfall was probably in evidence (Kutzbach & Gallimore, 1989).

Along the Early Triassic coast, conifers (Voltziopsis and a ?podocarp) clothed the hills, while on the floodplains the vegetation was dominated by Dicroidium (? as a heath), with gleicheniacean (Gleichenites), dicksoniacean (Coniopteris), In the review of Mesozoic coal floras that follows, marattiacean (Rienitsia) and ?osmundacean most attention is paid to the coal swamp plants. The (Cl ado p hlebis) ferns, equis etal eans (N e o cal amites) floras of adjacent environments and intervening and lycopods (Pleurorneia - Cylomeia, Skilliostrobus periods, however, are also covered for the sake of and Isoeies) growing close to standing water. In continuity. Figure 3. Representative Middle and Late Triassic flora and fauna: Ar. Lioestheria ipsuiciensis (Mitchell), X 5; conchostracanl Late Triassic, Ipswich Coal Measures, Queensland. B. Linguifoliun lilleanum Arber, X 1; ?cycadophyte; Late Triassic, Mt Nicholas Coal Measures, Tasmania. C. Rissikia media (Tennison-Woods) Townrow, X 2; conifer - Podocarpaceae; Middle Triassic, Esk Formation, Queensland. D. Taeniopteris carruthersii Tenison-Woods, X 2; ?cycadophyte; Late Triassic, Ipswich Coal Measures, Queensland. E. Pseudoctenis sp. nov., X 0.75; Cycadales; Middle Triassic, Esk Formation, Queensland. F. Pseudoctenis grossa Holmes, X 1; Cycadales; Middle Triassic, Esk Formation, Queeneland. G. Linguifolium tenison-woodsii (Etheridge) Retallack, X 1.5; ?cycadophyte; Middle Triassic, Bryden Formation, Queensland. H. Dicroid.ium crassinervis (Geinitz) Anderson and Anderson, X 1; pteridosperm; Late Triassic, Ipswich Coal Measures, Queensland. l. Dicroidium od.ontopteroides (Morris) Gotham, X 1: pteridosperm; Late Triassic, Ipswich Coal Meesures, Queensland.

Geology of Australian Coal Basins

Floras of Australian Coal Measures

50 places Pleuromeia apparently formed extensive, partly submerged, monospecific stands on the edges of lakes (Retallack, 1975). Other seed-ferns, such as the peltasperm Lepidopferls, possible cycadophytes (Taeniopteris), and probable ginkgophytes (Chiropteris, Rhipidopterls) were also present.

Middle Triassic floras were considerably more diverse (30-40 species, Rigby, 1977; Playford & others, 1982), but still dominated by Dicroidium, which underwent a radiation at this time. The more diverse flora may reflect a general improvement in climate, with warmer temperatures and increased rainfall. Although some Middle (and Late) Triassic species of Dicroidiur?? possess thick cuticles, this may be an adaptation for low nutrient levels (e.g. in sandy soils) and does not necessarily imply arid conditions; many other Dicroidium species of this age have very thin cuticles (Anderson & Anderson, 1983). A warmer, wetter climate is also indicated by the presence of dipteridacean (Dictyophyllum) and marattiacean ferns (Ogmos and. Marantoidea; Webb, 1983); extant species of both families occur predominantly in tropical rain-forests. Bennettital ean (Zamites, Anomozamites) and cycadalean (Pseudoctenis, Nilssonio) species made their appearance in Australia in the Middle Triassic (Figures 3E, 3F). The large size of many of these fronds (Hill & others, 1965) further suggests a warm climate at this time, as today large leaf size is a general indicator of warmer temperatures (Schopf, 1973). Voltziacean and podocarp conifeis (Rissikia and Heidiphyllum respectively; Figure 3C), as well as more genera of ginkgophytes (Ginkgoites, Sphenobaiera), ? cy cadophytes (Linguifolium, Yabiella; Figure 3G) and pteridosperms (Pachydermophyllum) also occur in Middle Triassic floras. A single genus ofpossible glossopterid affinity is present. Early Triassic coal measures are lacking in Australia, and Middle Triassic coals are not common, although they do occur in the Clarence-Moreton Basin at Nymboida. The coal forming plants appear to have been mainly Dicroidium, with contributions from many of the ferns present. Growing on the adjacent floodplain was a diverse flora ofcycadophytes, gingkophytes, ferns and pteridosperms, while the adjacent hills were apparently dominated by conifer forests with an understorey ofherbaceous and shrubby plants, including some species of Dicroidium (Holmes, 1982).

At the generic level, Late Triassic floras in Australia are little different to those of Middle Triassic age, although many new species, particularly of Dicroidium, are present. Some new genera appeared, including the seed-fern Dejerseya, which became quite common in some areas in Queensland (Webb, 1986).

Diversity and composition of the floras varied; the Tasmanian Late Triassic floras contained about 40 species, 10 of them liverworts and mosses (Townrow, 1964), whereas the Ipswich Coal Measures flora in Queensland had at least 50 species and apparently lacked bryophytes entirely (Hill & others, 1965; Webb, 1986). Furthermore the average leaf-size of the Tasmania floras was small, and Bennettitales and Cycadales were rare, whereas in the Ipswich flora fronds of the same species (e.g. Dicroidium odontopteroides) were more than twice as large, and Bennettitales and Cycadales were common. This difference may be due to climatic factors. Today leaf size tends to be smaller and bryophytes more

abundant (but less diverse) in cool climates, so the Tasmanian floras may have grown in a cool climate (Townrow, 1964). The Queensland floras, 1500km away, apparently lived in a somewhat warmer climate. The Late Triassic coal swamp vegetation consisted largely ofherbaceous and shrubby Dicroidium (Figures 3H, 3I) and Dejerseya. The coal seams formed principally from the accumulation of leaves, stems and pollen of Dicroid,iurn, with contributions from Dejerseya and probably also from ferns (Webb, 1986; Falkner, 1986). The adjacent flood-plains carried a much more diverse flora of ?cycadophyte (Figures 38, 3D), ginkgoalean and voltziacean conifer trees with an understorey offerns, equisetaleans, Dicroidium and. other pteridosperms.

Most of the productive Triassic coal measures in eastern Australia are Carnian in age, a fact which may reflect the time of greatest radiation of Dicroidium, the dominant coal-forming plant. In addition, the climate at this time may have been wetter than previously, because even though the most extensive development of fluvial sedimentation in Australia was during the Early and Middle Triassic (Yeates & others, 1986), coal swamps were most widespread in the Late Triassic, and formed at localities well inland (e.g. Leigh Creek in South Australia).

Fluvial environments were extensive in Western Australia during the Triassic, yet coal seams are thin and rare (Yeates & others, 1986). Western Australia occupied consistently lower palaeolatitudes than eastern Australia during this time, and so presumably experienced a warmer climate. In addition, Western Australia lay along the southern edge ofTethys, and experienced an extremely seasonal, monsoonal climate with a summer rainfall maximum (Parish & others, 1982). The lack of winter rain probably inhibited the high rates of plant growth necessary for coal formation. Eastern and Western Australia had fairly distinct microfloras during the Middle and Late Triassic (Ipswich and Onslow microfloras respectively Dolby & Balme, 1976), and this probably reflects climatic differences as well as the geographic separation.

Jurassic The Triassic-Jurassic boundary was marked by some notable floral changes in Australia (Gould, Ig76; Retallack, L977a), resulting in an overall decrease in diversity, so that the Early Jurassic floras had only 20-25 species. Dicroidiurn and several other genera (e.g. Yabiella, Linguifolium) became extinct and were replaced by the bennettitalean Otozamites, the caytonialean Sagenopteris, the matoniacean fern Phyllopteris, the Pentoxylales (leaves assigned to Taeniopteris daintreei) and several conifers,

including araucarians (White, 1981; Rozefelds, 1983). Except for the Pentoxylales and some of the conifers, these new genera were cosmopolitan and occurred in coeval Northern and Southern Hemisphere floras. As a whole, the Jurassic floras of Gondwana contained fewer endemics than those of the Triassic (Gould, 1981), and this presumably reflects relatively uniform climatic conditions worldwide at that time. The absence of Jurassic (and Cretaceous) red-beds in Australia indicates that the climate was humid or sub-humid, and temperatures are generally believed to have been warm (e.g. Veevers, 1984).

Geology of Australian Coal Basins

As well as the newly evolved genera mentioned above, the Early Jurassic floras contained equisetalea ns (E quisetum), dipteridacean, dicksoniacean and ?osmundacean ferns (D ic ty o p hy ll u rn, C o ni o pt e r i s and. Cl ad op hlebis respectively), lycopods (Selaginella, Isoetes), pteridosper ms (P ac hy p t e r i s, " T hinnfeldia" ), cycadaleans (Nilssonia), several podocarpacean conifers (Ris sikia, Elatocladus, Allocladus ) and

cheirolepidacean conifers (known only from Classopollis pollen). The conifers, bennettitaleans and Pentoxylales, which dominated the floras both in terms of individuals and species, were probably trees; silicified and coalified stems attributed to the Pentoxylales and Coniferales often exceed 30cm in

diameter. Thus a mature Early Jurassic forest probably contained several layers oftrees with an understorey of ferns and pteridosperms; equisetaleans and lycopods occurred in moister environments adjacent to streams or standing water. Early Jurassic coal measures are present in the northern Perth Basin, Western Australia (Playford & others, 1975). The presence of peat swamps on the east coast of Gondwana at this time probably indicates more humid climates for that area than in the Late Triassic. Middle Jurassic floras are similar to but more diverse than those ofthe Early Jurassic, and contain about 40 species (Gould, 1974, 1981; Rigby, 1978). Additional genera include bryophytes, lycopods, maratti acean fern s (M ar attia), osmundacean ferns (O s m undac a uli s), B ennettital es (P tilo p hy ll um), the podocarp Mataia and the araucarian Araucaria. Ginkgophytes are conspicuous by their absence throughout the Jurassic, despite their abundance in Northern Hemisphere floras of the same age. Although Equisetum, Cladophlebis, Taeniopteris and Otozamites are often locally abundant, the dominant elements of the Middle Jurassic floras are undoubtedly the conifers. Middle Jurassic coals (the Walloon Coal Measures) are widespread in central eastern Australia, and are believed to be composed largely of conifer material (Gould, 1981). Araucarian pollen (Callialasporites) often dominates the microfloras of the coal seams, conifer cuticles are common in the coal, and conifer stems and twigs sometimes protrude from the coal into the overlying sediment. Resinite, presumably derived from conifer resin, is abundant in some of the seams. However, ferns probably also contributed signifrcantly to the coal, as fern spores are abundant in the seams and ferns dominate the floras in shales underlying the coal (conifer remains often predominate in the sediments overlying the coals). The Middle Jurassic coal swamp flora was apparently dominated by araucarian trees with an understorey of ferns, cycadeoids and equisetaleans (Gould, 1981). Several present-day conifers (e.g. New Zealand swamp kauri and swamp cypress in the U.S.A.), grow in similar water-logged environments. However, the fact that the Walloon coals are thin suggests either that a stable environment was not present for a long enough period, or that production of plant material was not prolifrc, and it may be that Jurassic conifers were not particularly well-adapted to swamp environments.

During the Middle Jurassic the area of accumulation of the Walloon Coal Measures extended from about 55oS to 6505 latitude; both floral diversity and

oxygen isotope data indicate a humid cool to warm

temperate climate (Gould, 1981).

Late Jurassic floras are not associated with coal deposits. In fact few Australian megafossil localities of this epoch are known, so that most palaeobotanical information has been derived from palynology. It appears that podocarp and araucarian ionifers continued to dominate the floras, but diverse pentoxylalean, bennetitalean and filicean components were also present (Dettmann, 1981).

Cretaceous Like the Jurassic floras, the Cretaceous floras of Gondwana are quite cosmopolitan, and show a degree of world-wide uniformity at least until near the close of the Period (Gould, 1981). However, endemic Gondwanan forms are present, such as the Pentoxylales (Drinnan & Chambers, 1985) and some podocarps and araucarians. Australian Cretaceous floras show signifrcant alliances with other Gondwanan regions, but there are differences. Several ferns (Aculea, Amanda), for example, are restricted to Australia (Douglas, 1973). The Australian Late Jurassic flora underwent significant modification towards the end of the Period, although the Jurassic-Cretaceous boundary does not coincide with marked floral changes (Dettmann, 1981). The Early Cretaceous (Neocomian-Aptian) floras contained prolific and diverse g'ymnosperms, including podocarp (e.g. B ellarinea), araucarian (Arauc aria) and occasionally cheirolepidacean conifers (Cantrill, 1989; Dettmann, 1981), as well as Pentoxylales (Taeniopteris, Sahnia; Figure 4A) and Bennettital es (Ptilop hy llum). ln addition, pteridosper s1s (" ft,ienitsie", " Thinnfeldia"), f erns (Gl e ic h e nit e s, Adi antit e s, O ny c hi o p s i s, Cladophlebls; Figure 4B), hepatics (Figure 4C), bryophytes, lycopods (Lycopodium) and Equisetales (Phyllotheca, Equiseturn) were present. Many of these genera also occurred in the Late Jurassic, but several new genera appeared in the Cretaceous, e.g. the ferns Aculea and. Phyllopteroides (Figures 4A, 4D, 4F). Ginkgophytes (Ginkgo) also reappeared and became quite abundant.

The diversity of the Early Cretaceous flora is illustrated at Koonwarra, a single locality in the Aptian of Victoria, which probably contains over 60 species of plants (Drinnan & Chambers, 1986; Dettmann, 1986). At least 10 of these are bryophytes, several ofwhich have been assigned to extant genera, e.g. Riccardia, Dendroceras. A mosaic of plant communities appears to be represented; forests were dominated by evergreen podocarp and araucarian conifers, along with Pentoxylales and deciduous ginkgophytes; the understorey was composed of ferns, pteridosperms and bryophytes. The forest communities seem to have been mainly confined to the hills. River floodplains were dominated by ferns, some semi-submerged, principally osmundacean and dicksoniacean, together with equisetaleans, isoetaleans, bryophytes an-d lycopods (Douglas, 1983). Although the Victo;ian floras grew in polar latitudes (70o to 80oS, Veevers, 1984) their floral diversity, together with faunal and isotopic evidence, suggests a cool

temperate climate with moderately high rainfall (Douglas & Williams, 1982). The large number of bryophytes present supports this conclusion, a_s does th-e small siZe of bennettitalean fronds in the flora. Similar fronds in Indian strata of the same age are several times as large, and grew in a much warmer climate some 30" of latitude north of Victoria.

Floras of Australian Coal Measures

Geology of Australian Coal Basins

In the mid-Cretaceous, the floras underwent a progressive change as the Bennettitales declined and araucarians assumed increasing dominance; taxodiacean conifers (Gienitzia; Figure 4E) also appeared (Dettmann, 1981; Cantrill, 1989). However, ferns, particularly Dicksoniaceae and Osmundaceae, continued as important floral elements and new fern genera appeared in the Albian (e.g. Alamalus and Amanda - Douglas, 1973). Undoubted angiosperm pollen first appeared in the early Albian. Bennettitales and ginkgophytes either disappeared from, or became extremely rare in Victorian Albian floras, but were still common in Queensland floras of the same age. A general increase in leaf size from Aptian to Albian in Victoria floras may imply a progressive warming of the southern Australian continent over this period (Cantrill, 1989), reflecting the progressive northward drift of Australia during this time.

coal swamps. However, faunal remains and trace fossils arebccasionally found preserved in floodplain and channel sediments that accumulated adjacent to the swamps. Several small, restricted deposits in Australia, probably representing accumulations in floodplains or oxbow lakes, have yielded prolific and beautifully preserved insect, crustacean and./or fish faunas. These include Denmark Hill in south-east Queensland (Late Triassic), Talbragar, central New South Wales (Early Jurassic) and Koonwarra, central Victoria (Early Cretaceous). Much of the present knowledge of Australian non-marine invertebrates and fish has been derived from these localities. However, for a more complete picture of the terrestrial faunas, especially the reptiles and amphibia, it is necessary to consider fossils from sediments not associated with coal seams, and this approach has been followed in the present discussion.

The gymnospermous flora during the Early and Middle Cretaceous seems to have had a

A diverse insect fauna, both terrestrial and aquatic, inhabited the floodplains, rivers and freshwater lakes of Australia's basins during the Triassic. Beetles, cockroaches and crickets were abundant, and bugs, caddis flies, cicadas, book lice, scorpionflies, lacewings and dragonflies were also common (Riek, 1979; Rozefelds, 1986). Freshwater limuloids ("king crabs") probably lived in the rivers (Pickett, 1984). Aquatic crustaceans were represented by a shrimp-like syncarid (Brooks, Lg62), a freshwater isopod (Nicholls, 1943) and several genera ofconchostracans (Figure 3A); these last-mentioned crustaceans have a bivalved chitinous shell and lived in large numbers in temporary pools on flood plains (Tasch & Jones, 1969; Webb, 1979).

pan-Australian distribution, which contrasts with the regional differences evident in the cryptogam floras (Dettmann, 1981). For example, different species of the osmundacean fern Phyllopteroides are present in the Queensland and Victorian Albian floras (Cantrill & Webb, 1987), and this may reflect the latitudinal climatic differences between the two areas, which were at 55oS and 70oS respectively during the Albian (Veevers, 1984)., Coal measures occur in Aptian sediments in Victoria, and also in the Albian of Queensland. Petrographically the coals ofthese sequences are similar to those in the Middle Jurassic; they are vitrinite-rich with little inertinite, and petrographic variations are relatively small. Gould & Shibaoka (1980) deduced from this similarity that both Cretaceous and Jurassic coals were formed largely from conifer material. Ilowever, the Victorian Cretaceous megafossil floras associated with coal seams contained abundant ferns (Douglas, 1983) and fern spores, especially those of the Dicksoniaceae, which are often aggregated (Dettmann, 1981; D. Cantrill, personal communication, 1989). Nevertheless, podocarp pollen is also present, so both conifers and ferns probably dominated the coal swamp flora in the Early Cretaceous.

Late Cretaceous floras are virtually unknown from megafossil remains, and no Australia coal measures ofthat age exist. Palynological evidence indicates that podocarp conifers dominated the flora, with abundant ferns and bryophytes also present (Dettmann, 1981). Dicotyledonous families became progressively more common towards the end of the Cretaceous, with Nothofagus pollen appearing in the Senonian.

MESOZOIC COAL MEASURES FAUNAS Vertebrate and invertebrate fossils are almost completely absent from coal seams themselves, probably Lecause of the difficult environmentai ionditions and the low preservation potential of the

Triassic

At least three genera of unionid bivalves burrowed in the river and lake beds (McMichael, 1956). The streams, rivers and lakes were also home to a diverse fish fauna of more than 20 genera, dominated by palaeoniscids but with holosteans,

catopterids, lungfrsh and sharks also present (Long, 1982).

Carnivorous labyrinthodont amphibians swam in the rivers and walked across floodplains, as shown by footprints preserved in shaley sediments (Thulborn, 1986a). At least 12 genera oflabyrinthodonts, sorne several metres long, are known from Triassic continental sediments of Australia (Warren, 1982; Thulborn, 1986b). Reptiles were also present, although rare by comparison to the abundant labyrinthodonts. Tracks attributed to a lizard-like reptile (lepidosaur) and two species ofbipedal carnivorous dinosaurs (theropods) are known in floodplain shales overlying coal seams (Thulborn, 1986a). Six genera of reptiles, including a lepidosaur and two thecodonts, have also been desiribeil from bone material (Molnar, 1982;

Thulborn, 1986b).

Jurassic The o$ly-n-on-marine invertebrate fossil to have been described from Jurassic sediments in Australia is an

A. Phyllopteroides laeuis Cantrill and Webb (fern - Osmundaceae) and Taeniopteris daintreei McCoy (upper left; Pentoxylales), X 0.8; Strzelecki Group. B. Clad.ophlebis cf. oblongo Halle, X 0.7; fern; Strzelecki Group. C. Hepaticites sp., X 1; liverwort; Strzelecki Group. D. Phyllopteroides serrata Cantrill and TVebb, X 6; fern - Osmundaceae; Otway Group. E. Geinitzia tetragona Cantrill and Douglas, X 5; conifer - Taxodiaceae; Otway Group. F. Aculea bifida Dowglas, X 1.4; fern; Strzelecki Group.

Floras of Australian Coal Measures

Early Jurassic cicada (White, 1981). However, the Cretaceous sediments (see below) indicate that limuloids, crustaceans (syncarids and conchostracans), unionid bivalves and a variety of insects were all present. Apart from the insects, the Jurassic representatives of these groups were probably little different from their Triassic counterparts. The frsh fauna of Australian Jurassic rivers was

dominated by holosteans, with a single genus of palaeoniscids and a primitive teleost also present (Long, 1982). One genus of labyrinthodont amphibian and freshwater pliosaur also inhabited the rivers, probably preying on the fish (Molnar, 1982; Warren, 1982).

Several dinosaurs have been recorded, including the 12m long sauropod Rhoetosaurus. Footprints of at least two genera ofcarnivorous theropods and a quadripedal herbivorous dinosaur are known in roof shales of Jurassic coal seams (Molnar, 1982).

Cretaceous An abundant and diverse insect fauna inhabited the floodplains, lakes and streams associated with coal swamps in the Cretaceous, and over 70 species, representing 12 Orders, have been recorded (Jell & Duncan, 1986). In terms of diversity the fauna is dominated by bugs, beetles and flies, but dragonflies, scorpionflies, parasitic wasps, fleas, mayflies, midges, stoneflies, caddis flies, damsel flies and cockroaches were also present. The majority of the fauna can be referred to insect families with living representatives, and a number of the species may belong to, or be closely related to, living genera. Several crustacean groups (conchostracans, cladocerans, ostracodes and syncarids) lived in the temporary floodplain lakes (Talent, 1965; Jell & Duncan, 1986), and limuloids probably inhabited the nearby rivers and streams (Riek & Gill, 1971). Arachnids, represented by spiders and harvestmen, crawled amongst the floodplain vegetation (Jell & Duncan, 1986). Oligochaete worms and unionid bivalves burrowed in the bottom sediments of lakes and streams respectively, and freshwater bryozoans were also present (Jell & Duncan, 1986). Vertebrates were diverse and abundant during the Cretaceous. Swimming in the rivers were several genera of fish, including holsteans, palaeoniscids, teleosts and lungfish, as well as at least one genus of turtle (Long, 1982; Molnar, 1982). Preying on the fish were a labyrinthodont amphibian (Warren & others, 1991) and a freshwater plesiosaur (Rich &

Rich, 1989). From the evidence ofboth tracks and skeletal remains, the reptilian fauna was moderately diverse, consisting of several genera of ornithopods and theropods (including Allosaurus), as well as lepidosaurs, a large sauropod, an iguanodont and a pterosaur (Molnar, 1982; Rich & Rich, 1989). A number ofbird feathers have also been recovered from Lower Cretaceous lake sediments in Victoria, but the precise affinities of these cannot be determined (Talent & others, 1966).

TERTIARY COAL FLORAS Brown coal deposits ofvarious thicknesses are commonly encountered in the Tertiary sedimentary basins of Australia. Many of these have attracted

palynological study, as pollen is generally well-preserved within them and in the associated interseam sediments. However, the main emphasis has been on the documentation of taxa derived mainly from surrounding dry land vegetation, for construction of regional vegetation histories (e.g. Kershaw & Sluiter, t982a; Tulip & others, 1982) or biostratigraphies (e.g. Martin, 1973), with little attention paid to the flora which made up the coal itself. Similarly, despite the wealth of macroscopic plant remains in coal, palaeobotanists have tended to concentrate on interseam and other fine-grained sediments, because ofa higher degree of preservation ofdiagnostic plant parts such as whole leaves and reproductive organs (e.g. Christophel, 1981). Only in the Latrobe Valley of Victoria, has there been significant palynological and plant macrofossil study aimed at the documentation of Tertiary coal floras and their vegetational and environmental relationships. The present review is restricted to results from that area.

History of Studies in the Latrobe Valley Much of the early work on the strata of the Latrobe Valley was undertaken by Isahel Cookson and her associates at Melbourne lJniversity in the 1950s and 1960s, and concentrated on the establishment of botanical affinities from both preserved pollen and macrofossil remains. This work was summarised, and its palaeogeographic and environmental implications examined by Duigan (1966). Baragwanath & Kiss (1964) concurrently undertook pollen analysis ofthe coal as a basis for seam identification and correlation. This early research was limited on the one hand by a lack of information on the present-day ecology and aspects ofpollination ofrecorded taxa, and on the other by a paucity of data on geological variation within, and stratigraphical relationships between the individual coal seams.

More recent studies have been undertaken on macerated plant macro-remains by the University of Adelaide (Blackburn, 1981; 1985) and on pollen by workers at Monash University (Luly & others, 1980;

Kershaw & Sluiter, 1982b; Sluiter & Kershaw,1982; Whitelaw, 1983; Sluiter, 1984). The major focus of interest for both types of study has been the relationship between the flora and the variation within the coals as indicated by lithotype banding. Lithotypes in this area are defined on the basis of colour (see paper by Diessel in this volume), with five types (i.e. dark, medium dark, medium light, light and pale) being identified (George, 1975). These lithotypes also vary a great deal in other physical and chemical properties, which in turn influence their utilisation characteristics. Such factors are considered to have developed at the time of coal formation, in response to different depositional environments (Gloe, 1984). A time-frame for these studies has been provided by the stratigraphic palynological work of Partridge (1971) and Stover & Partridge (1973), which correlated the onshore coals with a well-dated offshore marine succession. The most intensively studied coals are the Morwell and Yallourn seams, which are respectively of Late Oligocene-Early Miocene and mid-Miocene age. These seams are clearly separated from the older Traralgon seams of mid- to Late Eocene age, which have only been examined palynologically.

Geology of Australian Coal Basins

Figure 5. Present-day distributions of selected taxa recorded in the Oligo-Miocene coals of the Latrobe Valley.

Floristic Composition A large proportion of those taxa from the Morwell and Yallourn seams, whose botanical affinities have been fairly well established, is shown on Table 1. It is heartening to see that many of these taxa have been recognised from both pollen and macrofossils. However, some bias is likely, in that identification from one form of analysis has had some influence on the search for affinities in the other. There are also still a number of taxa recognised that have not been matched with extant forms. Information on the community relationships of taxa can be provided by a comparison of macrofossil and pollen floras. Taxa recorded as macrofossils are likely to have existed close to the sampling site, since the relatively large size and fragility of diagnostic remains would inhibit survival during transport over long distances. Pollen, however, can be dispersed by wind or by water over long distances, although the pollen of many plants is seldom deposited far from its source. The taxa in Figure 5 have been grouped to allow some assessment of floral relationships. Taxa represented in groups 1, 2 and 4 (Table 1) are likely to have been growing in the local depositional basin close to the sampling position. Of these, group 2 is the largest, containing taxa identified from both

pollen and macrofossils. A comparison between groups 1 and 4 demonstrates that there are also many more local taxa identifred by their pollen than other features, probably due to a combination of greater chances of preservation of resistant pollen and easier identification to genus or family level. Of the small group of taxa identified by macrofossils alone, Zanniaceae, Azolla, and. Notelaea have pollen and spores that have proved difficult to determine in modern pollen samples containing parent plants. Taxa in group 3 are also likely to have occurred in the depositional basin due to their presence as macrofossils, but their wide pollen dispersal also means that it is possible that they, or some component species, grew further afield, in

surrounding dry land vegetation. Taxa ofgroup 5 could have been growing anywhere within the broad region, but their apparent absence as macrofossils, especially the highly represented Nothofagus types, suggests that they had their major presence outside the depositional basin. One potential complication of this model of macrofossil and pollen representation is the inwash of material through stream activity. However, evidence for autochthonous organic material that includes in situ root systems and vertical tree

stumps, as well as extremely low inorganic matter values, demonstrates that the coals accumulated in

Floras of Australian Coal Measures

Table 1. Taxa recorded from the Latrobe Yalley Oligocene-Miocene coals' grouped according to pollen and/or,macrofossil representation and disperCal ability of pollen. Group 1 - recorded only as microfossils

other Proteaceae types

E xocarpos type (Santalaceae)

Gle icheni a (Gleicheniaceae)

Rhamnaceae

Notelaea (Oleaceae) D arlingia type (Proteaceae) other Proteaceae types

GroupS-recordedas macrofossils and pollen with wide dispersal

AIyxia (Apocynaceae)

Myrtacea type Zamiaceae type AzoIIa (Azollaceae)

Group2-recordedas macrofossils and pollen with limited dispersal M ic r ocachry s (Podocarpaceae) D acry carpus (Podocarpaceae)

his (Araucariaceae)

Araucaria (Araucariaceae)

allitris (Cupressaceae)

P odocarp u s (Podocarpaceae) D ac ry diu m(Podocarpaceae)

Phyllocladus (Podocarpaceae) Lagarostrobus(Podocarpaceae) Casuarinaceae Cunoniaceae

Elaeocarpus (Elaeocarpaceae) Myrtaceae

Group 4 - recorded only as pollen with a limited dispersal

Myrtaceae types

Fagraea (Loganiaceae) T as rnani a (Winteraceae) Drosera (Droseracaea) Liliaceae/Arecacea Lycopodiaceae Polypodiaceae

Cyathaceae/Dicksoniaceae

Group 5 - recorded only as Pollen with wide dispersal /ler (Aquifoliaceae) S p he no ste rnon (Aquifoliaceae ) Q

uintinia (Escalloniaceae)

Au stobuxus types (Euphorbiaceae) M ac aranga I M allotu s (Euphorbiaceae)

B ank sia type (Proteaceae)

Cupanieae (Sapindaceae)

D iospyro s type (Ebenaceae)

Sapotaceae

P oly scias type (Araliaceae)

Vitaceae Leguminaceae

Nothofagus b ras sii type (Fagaceae) Nothofagus menziesii type (Fagaceae)

Polygalaceae

Randia (Rubiaceae)

Loranthaceae Itielicope type (Rutaceae)

Gyrostomaceae

Epacridaceae Cyperaceae Restoniaceae Typhaceae/Sparganaceae

Moraceae

Poaceae

low energy swamp environments. This situation contrasts with the interseam sediments, which resulted partly from high energy water flow and often coniain iemains of a high diversity of regional and streamside plants.

unseasonal environments, suggests that the conditions that allowed this mix of taxa do not exist at the present time.

e) Dry lo.nd enaironm.ents

A simplifred picture of the kinds of vegetation existing in tlie Latrobe Valley basin during the accumulation of the younger coal seams is shown in Figure 6. This picture is constructed from both pollen and macrofossil evidence. Vegetation variation is most clearly illustrated as stages in a hydroserial succession from open water through swamp to raised bog. The presence -of open water is suggested by a lack of evidence for local -v-egetation. Thl*sediment matrix is composed of small plant fragments likely to have been washed into the area, while pollen assemblages are dominated by taxa capable of long distance dispersal, particularly Nothofagus. S-hallow water areas were pr-obably coloni'se-d by a limited number of tree of shrub taxa, of which the conifers Agathis and Lagarostrobus were prominent in places, emergent above angiosperms includlng species of Myrtaceae and Eld,eocarpus. On drier s*amp surfaces, a glgPn+ layer dominated by Restionaieae rushes, with the fern Gteichenia scrambling amongst it, became increasingly important astid shrubs and trees such as E pacri*di ceae, B ank sio an d C a s u ar in a,- a ssoci ated today with sclerophyll vegetation rather than rainforest. A variety of angiosperms and g"ymnosperms made up the rainforest component'

Information on dry land vegetation types can be gained from the examination of those taxa with wide pollen dispersal preserved in coal sa-mples, and from ihe variety of types in interseam sediments. A statistical comparison of the representation of taxon pairs from Yallourn and Morwell seam samples (Sluiter & Kershaw ,1982) has revealed the existence of substantial variation within the oredominantlv rainforest-covered catchment. It is iik"ty thut .ool t"-p".ate rainforest characterised by Nothofagus, warm temperate rainforest containing significant levels of Cunoniaceae and Quintinii, and warm temperate to sub-tropical rainforest dominated by Myrtaceae, Elaeocarpus and Sapindaceae formed an altitudinal sequence suirounding the Latrobe Valley. Precipitation levels must have been higher than today, probably in excess of 1400mm, in order to support such a rainforest, but temperatures may have been little different from the present. Varying proportions of the major rainforest types in the sequence suggest that temperature leveli fluctuated during the period of interest. Few ofthe taxa recorded in the regional vegetation are present in the area today. It has been suggestel

thaf highland New Guinea, with its wet-unseasonal type ofllimate, provides the closest modern analogue of the Victorian Oligocene-Miocene vegetition and environments (Duigan, 1966). However, the present diverse rangq of distributions of component plants, as exemplified i! Figure 5, with component taxa restricted to both higher and lower latitudes as well as highly seasonal and

b) Coal suatnp aegetation

Although shown as a simple successional sequence in the illustration, the actual seral patterns are much more variabie in the coals themselves, with each seral stage able to replace any other in a sradual or abrupt manner. It is thought that Ehanging rates 6fbasin subsidence provided the primirytontrol over water levels, and, consequently, over the vegetation and local depositional environments.

Geology of Australian Coal Basins

6LE ICHEN IA

BANKSIA

CASUAR I NA

M IXED GYMNOSPERMS

MIXED

EPATR I DAT EAE

RESTIONACEAE

A6ATH IS

ANGIOSPERMS

LAGAROSTROBUS

rc F

o F J

succession in relation to lithotype varia

Figure 6. Generalised picture ofh Valley coals. YALLOURN SEAM

a rffiMffi

-Illlllllrrr

(Mld Mlocene)

hH EE

MORWELL I SEAM

(Lala Ollgocano Early Mloccno)

TRARALGON I

W F

[[L

SEAM

(L8te Eocena)

TRARALGON II SEAM

(Mld Eocene)

tFH

The high representation of sclerophyll taxa on the drier swamp surfaces, within a region dominated by rainforest, requires some explanation. As general environmental conditions were wet and mild, it is unlikely that climate exerted any significant influence. There is, however, evidence for the presence of two other factors associated with sclerophyll vegetation: fire and low nutrient levels. Fire is indicated by charcoal particles, which generally increase in abundance from open water to raised bog sediments in line with increased sclerophylly, while low nitrate levels, which generally accompany low nutrient status, are suggested by common root nodules and proteoid roots. Low nutrient levels might also be inferred from the low energy environment, which would have

restricted nutrient inwash from the surrounding catchment, while many available nutrients would have been locked up in the accumulating organic deposits. The situation would have been most critical for those communities perched furthest above the water table and which may have had to rely on atmospheric nutrient fall-out. e

LlthoryP.. o

h c

5 10 15 20 2

ffi

oo,r arr ueoium oarr

u"oirr risnt

l--l

* 3

:oo

gr:

=o O> lO oJ

3n o o

.,nn, oo," SCALE % Figure 7. Averaged values for eelected pollen taxa - from lithotype samples covering maior coal

seams in the Latrobe Valley.

within the Latrobe

) Ve getationllithotype relationship s

The hydroseral model illustrated in Figure 6 can also atcommodate lithotype variation to a large extent, as increasing darkness of colour correlates

well with the vegetation succession from open water to raised bog. The pale and light lithotypes probably formed under different water depths, while swamp vegetation is generally recorded froql the mediumlig-ht lithotype. the darkness of medium-dark and dirk lithotypes is probably due to some oxidation of accumulated sediment as the swamp surface grew above water level, exaggerated in places by high levels ofcharcoal.

Floras of Australian Coal Measures

An examination of vegetation/lithotype relationships in Figure 7 suggests that the observed degree of correspondence between lithotype and vegetation variation in the younger coal seams is not a universal feature ofthe coals. This diagram provides selected information for seams ranging from the oldest Traralgon coal to the Yallourn seam. Nothofagus indicates the degree ofrepresentation of regional vegetation while Epacridaceae, Restionaceae and. Gleichenia indicate the degree of representation of a distinctive, sclerophyllous, coal swamp vegetation. The general increase in proportions of the local taxa from the oldest to the youngest sequence suggests that there has been a gradual development of a coal flora in the coal-forming basin from mid-Eocene to the mid-Miocene. This scenario has also been proposed from macrofossil evidence covering just the Morwell and Yallourn seams (Blackburn, 1985). As lithotype variation has existed through the whole period, vegetation probably evolved in response to the existence of a variety of depositional environments and vegetation in itself has had little influence on lithotype definition. One broad implication of the development of brown coal vegetation and environments is the possible

significant role these extensive systems have had in the evolution of a component of typically Australian sclerophyll vegetation which now dominates this region and many other parts of the continent.

ACKNOWLEDGEMENTS Dr Stephen Mcloughlin read the original draft of the Permian section, which was written in 1987, and provided comments that greatly assisted its revision.

REFERENCES ANDERSON, J,M., 1977: The biostratigraphy of the Permian and Triassic - Part 3: A review of Gondwana Permian palynology with particular reference to the northern Karoo Basin, South Africa. Memoirs of the Botanical Suruey of South Africa,4l, 1-133. ANDERSON, J.M. & ANDERSON, H.M., 1983: Palaeoflora of southern Africa: Molteno Formation (Triassic). Volurne 1. Introduction, Dicroidium. A.A. Balkema, Rotterdam. ANDERSON, J.M. & ANDERSON, H.M., 1985: Palaeoflora of southern Africa. A.A. Balkema, Rotterdam.

ARCIIANGELSKY, S. & CUNEO, R., 1987: Ferugliocladaceae, a new conifer family from the Permian of Gondwana. Reuiew of Palaeobotany and Palynology, 51, 3-30. ASKIN, R.A. & ELLIOT, D.H., 1982: Geologic implications of recycled Permian and Triassic palynomorphs in Tertiary rocks of Seymour

Island, Antarctic Peninsula. Geology, lO, 547-55r. AXELROD, D.I., 1984: An interpretation of Cretaceous and Tertiary biota in polar regions. Palaeogeography, Palaeoclimatology, Palaeoecology,45, L04-147. BACKHOUSE, J., 1991: Permian palynostratigraphy of the Collie Basin, Western Australia. Reuiew of Palaeobotany and Palynology, 67, 237-3I4.

BARAGWANATH, G.E. & KISS, L., 1964: Report on palynological investigation of Victorian brown coals. State Electricity Commission of Victoria, Scientific Division. BEESTON, J.W., 1986: Leptocalamites, a new genus of calamitacean wood from Queensland. Publications of the Geological Society of Queensland, 387, 51-58. BEESTON, J.W., 1990: Cyclodendron leslii (Seward) Kriiusel and associated palynomorphs in the Early Permian Reids Dome Beds, Queensland, Australia. Alcheringa, 14, 325-330 .

BHARADWAJ, D.C., L974: Potentiosporites Bhard., ihre Morphologie, Systematik und Stratigraphie. Fortschrift Geologie Rheinland und Westphalen,

12,45-54. BLACKBURN, D.T., 1981: Floristic control on lithotype banding within the Yallourn seam, Yallourn Open Cut: evidence from megafossil assemblages. State Electricity Commission of

Victoria, Palaeobotany Project, Major Report No. 2.

BLACKBURN, D.T., 1985: Palaeobotany of the Yallourn and Morwell coal seams. State Electricity Commis sion of Victoria, Palaeob otany Project, Major Report No 3. BROOKS, H.K., 1962: The Palaeozoic Eumala- costraca of North America. Bulletin of American Palaeontology, 44, 163-338.

CANTRILL, D.J., 1989: An Albian coniferous flora from the Otway Basin, Victoria: taxonomy, palaeoecology and palaeoclimatology. PhD thesis, Department of Botany, University of Melbourne.

CANTRILL, D.J. & WEBB, J.A., 1987: A reappraisal of Phyllopteroides Medwell (Osmundaceae) and its stratigraphic significance in the Lower Cretaceous of eastern Australia. Alcheringa, ll, 59-85.

CHALONER, W.G. & LACEY, W.S., 1973: ThE distribution of Late Palaeozoic floras. Special Papers in Palaeontology, L2, 271-289. CHRISTOPHEL, D.C., 1981: Tertiary megafossil floras of Australia as indicators of floristic associations and palaeoclimate. In Keast, A. (Editor): Ecological Biogeography of Australia, W. Junk, The Hague, 380-390.

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Geology of Australian Coal Basins

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Geology of Australian Coal Basins

MEGASCOPIC AND MICROSCOPIC COAL CONSTITUENTS

ffietrographic constituents of Australian coals

CFK Diessel and M Smyth

Like those of other countries, most seams of humic coal in Australia appear to be stratified when viewed in outcrop or drill core. In brown coals the individual layers within the seams differ from each other in properties such as colour, textrrre and desiccatibn pattern, while in black coals they differ from each other mainly in the texture and lustre of the particular materials concerned. The features that allow this differentiation into megascopic components, called lithotypes, have been inhiriteil from the original peat bed, and reflect responses to fluctuations in the water table at the tim-e of peat accumulation. These fluctuations

resulted in both changes to the floral assemblage that formed the plant debris and changes in the biochemical conditions under which this plant debris was actually converted into peat. The sapropelic coals, on the other hand, such as the cannel and boghead coals (torbanites) found in some Australian sequences, display little differentiation ofthis type, since they were formed as organic oozes from spores and algae respectively, and accumulated on the bottoms of laEes and ponds beyond the influence of minor fluctuations in the water table (Dulhunty, 1944).

The visual appearance of the different lithotypes is in turn an expression of their microscopic constituents. These include the basic, relatively

homogeneous organo-petrographic entities known as maceials, and the natural associations of macerals, known as microlithotypes, that occur at an intimate scale within the coal bed. The three groups of

components, macerals, microlithotypes- and lithotypes, are generally described with reference to the International or Stopes-Heerlen Classification System for coal petrographic constituents (ICCP, 1963), but a number of minor modifications to this system have also been developed for Australian use.

COAL MACERA,LS As with the minerals that make up inorganic rocks, coals are composed of small and relatively macerals. They a-re th-e homogenous cbnstituents basic organo-petrographic-entities ofcoal, and each different type represents the product of partic-ular components and/or particular coal-forming plant -coalification. of

A large number conditions of macerals are formed from the cellulose- rich and lignin-rich cell walls of wood and herbaceous pl4nts, but leaf cuticles, spores, pollen, seeds, resins, oils and other vegetable matter also frequentlycontribute to the formation of peat and coal. The classification of coal macerals as used in Australia for both brown and black coals has been developed by the Standards Association of Australia. A summary of this classification is given in Table 1.

Maceral Analysis Maceral analyses of bituminous coals are carried.out by reflected light microscopy on polished particulate biocks which have been prepared from coal samples crushed to minus lmm. The point-count method is generally applied, advancing the _sample-by equal 6teps on-the microscope stage and r,ecording-the material under the inlersection of the cross lines in the ocular. Because the precision ofthe result is determined by the size of the sample population, a

Petrographic C onstituents

Ta61C f .,, hbfGldssifi.eCtion o-f cofil.,.meceralS'Cecordiil$ to AS:2856/1986a.

Maceral Group

Maceral Subgroup

VITRINITE

Telovitrinite

Macerals Tertinite, Texto-ulminite, and Eu-ulminite indicate increasing humifrcation in wood tissue at low coal rank. Telinite (not used in' AS 2856) and. Telo-collinite are black coal equivalents.

D"tr""ttrt"tt"

Att"*/.

humification. They combine to form Desmocollinile in higher rank coals.

iig"tintt, occurs as

G"l""

granular bands or fracture fillings of humic acid. Eugelinite is homogeneous and massive.

INERTINITE

Telo-inertinite

Fusinite shows highest reflectance and relief of oxidised cell tissue. Semifusinite is less distinct in relief, reflectance, and cell structure. Sclerotinite consists of fungal remains.

Detro-inertinite

Inertodetrinite and Micrinite are detrital inertinite (exc. sclerotinite) ranging in diameter between 30 and 2pm, and <2pm,

partly oxidised plant matter. The precursors of -Resinite, Cutinite, Sporinite, Alginite, and' no subgroups LIPTINITE Suberinite are plant resins, cuticles, spores and pollen, algae, and cork cells. Liptodetrinile is fragmented liptinite. Exsudatinite, Fluorinite, and Bituminite are secondary liptinites. made between pre-polymerisation and postminimum of 500 counts is usually carried out for polymerisation macerals. Following suggestions by most routine analyses. Smith & Cook (1980) and Smith (1982) the term Brown coals are treated in a similar manner, but in vitrinite therefore covers the relevant maceral group addition to the 500 points counted in white light it is in both brown (lower rank) and black (higher rank) Australian practice (George, 1982) to repeat the coal deposits. maceral count in fluorescent mode. The reason for this procedure is the diffrculty of distinguishing the Teloaitrinite Subgroup low-reflecting liptinites of brown coal from mineral inclusions in white light. In the first count a The products of biochemical coalification depend on distinction is made only between vitrinite and the kind ofplant tissue affected by this process and inertinite macerals, while liptinite and minerals on the process operating conditions. Humifrcation of remain undifferentiated. These components are then lignin-rich wood often tends to stop short of total identified in the second round by making use of the of cell texture, and the macerals of the breakdown liptinite macerals, fluorescence of the various strong telovitrinite therefore show vitrinite subgroup while vitrinite and inertinite are assigned to the various stages of cell wall preservation. In the remainder. The results obtained by the two modes brown coal maceral textinite (Figure 1) the cell are then combined to give a complete brown coal tissue appears relatively ungelified, whereas in maceral analysis based on a total of 1000 points. texto-ulminite (Figure 2) the cell walls appear swollen. A complete closure of the cell lumens occurs The Vitrinite Group in eu-ulminite (Figure 3). With changes due to The term'vitrinite' covers all macerals formed from compaction and further gelification, these three macerals are all represented by telocollinite wood, bark, root, and other cell tissues which have (Figures 4, 5, 10) in higher rank coals, material been subjected to humification of varying intensity. largely equivalent to that described informally as Humification is a process of biodegradation by which 'Vitrinite A'by Brown & others (1964). vegetable matter is eventually converted into colloidal humic acids, initially under conditions of partial oxidation with the aid of bacteria. In the D et rou itrinit e Sub group formation of vitrinite, humification is followed by gelifrcation when the peat becomes waterlogged and The soft tissues ofreeds and herbaceous plants the biochemical environment changes to reducing disintegrate more readily during humification than and anaerobic. The resulting product possesses the lignified cell walls of most wood tissues. The moderately high IVC and relatively low O/C ratios. result is a mixture of colloidal humic acid and fragmented plant debris, which coagulates to form Advanced humifrcation leads to a total attrinite in soft brown coal. On further compaction disintegration of plant tissues and peptisation (dispersal) of the developing humus colloids. In peat and gelification attrinite is converted to densinite, in which the partially or wholly humified attrital cell deposits the peptised humic acids constitute a dark fragments begin to loose their identity. When this coloured hydrosol which, on drying, coagulates and process is completed in bituminous coal the material gelifies to form the cementing agent in dried peat. is described as desmocollinite (Figures 5, 6, 8, 10, This material serves the same purpose as part of the LL, 12,13 and 15). All three macerals belong to the huminite group of macerals in brown coal and, after vitrinite subgroup detrovitrinite (equivalent to the polymerisation, as part of the vitrinite group in material described as 'Vitrinite B' by Brown & bituminous coal. In the Australian classification of others, 1"964) and constitute the vitrinitic coal macerals (AS 2856, Standards Association of groundmass and cement of the coal. Australia, L986a) no terminological distinction is

Geology of Australian Coal Basins

""3 fig.tru 1. Textinite in ' 'r; photomicrograph -subbituminous-coalof a ,'

from

Western Australia. The true lensth of the frame is 0.2 rnm.

Incident light, oit immersion.

2. Texto-ulminite in Figure - photomicrograph of a subbituminous coal from Western Australia. The true length of the frame is 0.2 mm. Incident light, oil immersion.

Figure 3. Photomicrograph showing the transition from texto-ulminite to eu-ulminite in a subbituminous coal from Western Australia. The true length of the frame is O.2mm. Incident light, oil immersion.

:.); t.

,r:i: I lit.'..'

:@';n,,, .r,.;- $ . rl

..1:'.. '€t;'..

fP ,t -

lt1.:.,f,,r.'

&'.*l

t'';.; r, . .":' 3 l" g't'

r..: it. I &"

i 't..'

{

j .i,6

Petro graphic Constituents

loaitrinite Sub group

Coalified humus gels without any inclusions form the subgroup gelovitrinite. Because of their mainly colloidal nature, they occur in cavities, cleats and fissures. Oval or spherical bodies ofgelovitrinite are called corpocollinite (Figure 5), irrespective of whether they originated as a secretion from the Iiving cell or by secondary infrllings. Compacted coalified gels are referred to as eugelinite (Figure 6) when filling fractures or occurring on bedding planes, while a granular and slightly porous variety exclusive to low rank coals is referred to as porigelinite.

The Inertinite Group The inertinite maceral group comprises coal

constituents which possess high reflectance in incident light microscopy. They are rich in carbon and have relatively high O/C ratios, arising from some oxidation of their precursors either during

periods of low water table or influx of aerated surface water by partial oxidation, microbiological action, or even burning of some of the accumulated plant material in the peat swamp prior to burial (Gould & Shibaoka, 1980). The name inertinite indicates that the macerals of

this group were thought to lack fusibility during coke making. However, in Australian coals this is true only for fusinite and other group members with an Rv,max in oil >1.87o (Diessel, 1983). The actual degree of fusibility of the other inertinite components is rank-dependent, and is highest in medium volatile bituminous coals.

Telo-inertinite Subgroup Like the vitrinite group, the inertinite group has

been divided into three subgroups based on the degree of cell tissue preservation. The telo-inertinite

subgroup comprises textured inertinites, among which the widespread but volumetrically unimportant fusinite (Cook, 1975) shows the highest degree of cell tissue preservation (except for some mechanical breakage, Figure 7), as well as the highest degree ofreflectance and polishing relief. Its most common mode of formation is by incomplete combustion of the parent plant tissue. The

lower-reflecting semifusinite (Figures 4, 6, 10 and 11), on the other hand, may also be a product of aerobic biodegradation with some humification. Wood-derived inertinite displays better preserved plant cells than, for example, leaf-derived semifusinite. Leaf-derived semifusinite seems to be more common in Australian coals than in the Carboniferous coals of the Northern Hemisphere, probably due to the deciduous nature ofthe cold climate Permian Gondwana flora (Diessel, L983; Taylor & others, 1989). The only plant-specific member of the inertinite group is sclerotinite, which consists of fungal remains, mainly in the form of spores and, to a lesser extent, mycelium and hyphae.

Detro-inertinit e Subgroup Fusinitised detrital plant fragments constitute the detro-inertinite subgroup, within which two different macerals are distinguished on the basis of size. Inertodetrinite (Figures 8, 9, 10 and 12) consists of fragmented inertinite ranging in the longest diameter between 30 and 2pm whereas micrinite (Figures 9, 10 and 12) consists of smaller inertinite grains. According to Teichmi.iller (1974), much of the micrinite forms at the rank level of

sub-bituminous coal from lipid-rich material by a disproportionation process, which results in the formation of liquid and gaseous hydrocarbons and leaves behind micrinite as a carbon-rich residue. Because of the difficulty in distinguishing very fine grained inertodetrinite from micrinite (sensu stricto), AS 2856 (Standards Association of Australia, 1986a) regards all inertinite with particles <2pm as micrinite (sensu lato). Gelo -inertinite Sub group

The gelo-inertinite subgroup contains macrinite as the only defined representative. This maceral has a complex origin, with humification and gelification of plant tissue followed by drying and oxidation. Two varieties of macrinite can be distinguished, one which consists ofdetrital angular to rounded bodies, many of them small enough to be grouped as

inertodetrinite (Taylor & others, 1989). This 'corpomacrinite' (Figure 6) is probably the result of desiccation of humic colloids (angular) followed by dispersal (rounded). The other variety (Figure 7), occurs as elongated bands or laminae ('lammacrinite') and probably represents dried humic groundmass which would have formed desmocollinite had the peat remained submerged under water.

The Liptinite Group The members of the liptinite group are characterised by high aliphatic and high volatile matter contents, as well as large tar yields when pyrolysed. The atomic IVC ratio is likewise higher than for all other macerals. Under the microscope liptinite macerals of low rank coals show a high degree oftranslucency in transmitted light and a low reflectance when viewed

in incident light. Another optical characteristic is the strong fluorescence after excitation with short wavelength radiation.

Although no subgroups have been defined, a distinction can be made between primary and secondary liptinites. Both categories show the characteristics mentioned above, the primary liptinites consisting of coalified plants or parts of plants and the others forming a group of secondary products of thermal condensation and dissociation reactions.

Primary Liptinites The decay-resistant protective skins (exines) of spores and pollen grains constitute the maceral sporinite (Figure 12), which is the most common

representative of the primary liptinites in Australian and other coals. Since the spore and pollen exines are usually compacted, they appear as small, flattened lenses in sections normal to bedding. The maceral cutinite (Figure 13) is formed from cuticles, the waxy cover developed on plant leaves and young shoots. Under the microscope these materials appear as straight or wavy lines of translucent (in transmitted light) or rather dark (in reflected light) material, usually with palisade ridges on one side.

Resinite (Figures 14 and 15) is a maceral derived from a number of different source materials, such as resins and waxes, and the appearance ofresinite in coal varies accordingly. It occurs in resin ducts preserved in some telovitrinites, in the form of isolated resin bodies, and in the form ofdiffuse impregnations in desmocollinite. Resinite displays a

Geology of Australian Coal Basins

Figure 5. Photomicrograph of a high volatile bituminous coal from New South Wales, showing telocollinite (light grey in upper part), alginite (elongated, dark lines), sporinite (short, flat, dark lenses), inertodetrinite (small, irregular, white bodies), rnicrinite (small, white specks), corpocollinite (two oval, light grey bodies near centre), and desmocollinite (medium grey groundmass in central and lower portion of frame. The true length of the illustrated area is 0.2 mm. Incident light, oil immersion.

Figure 6. Photomicrograph of a medium volatile bituminous coal from Queensland illustrating desmocollinite (top) and eugelinite (below) as grey infillings in cell lumens of semifusinite. The true length of the frame is 0.2 mm. Incident light, oil immersion. !*h*

..ira ':ial -.r:arr

Figure 7. Fusinite and semifusinite of various reflectance levels in photornicrograph of a subbituminous coal from Queensland. The true length of the frame is 0.22 mm. Incident light, oil immersion.

!L -r

-* f -.--!"

lr: :a!i" ?* r* ,:b,i;ti'

&+*

-{s" '"$_4$i 1Dl

Figure 8. Several clusters ofdensely packed inertodetrinite (grey to white fragments) occurring in a grey groundmass of desmocollinite with black specks of clay in a photomicrograph of a New South Wales high volatile bituminous coal. The true length of the frame is 0.2 mm. Incident light, oil immersion.

Petrographic Constituents

Figure 9. Photomicrograph of a

band of fine inertodetrinite

grading into micrinite (both very light grey) in a medium volatile

bituminous coal from Queensland. Enclosed in the band are numerous disseminated pyrite gtains (white) of similar size as micrinite. The true length of the frame is 0.2mm. Incident light, oil immersion.

Figure 10. Photornicrograph of a lens of "corpomacrinite' (grey, near top) together with inertodetrinite and semifusinite (light grey to white), plus some sporinite (short, flat, dark lenses) in a high volatile bituminous coal from New South Wales. The " vitrinite at the top and near the centre is telocollinite, the remaining groundmass is desmocollinite. The true length of the frame is O.2mm. Incident light, oil immersion. Figure 11. Photomicrograph of a high volatile bituminous Queensland coal with a band of macrinite (light grey) in centre and set in a medium to dark gley matrix of desmocollinite containing some inertodetrinite (white). Light grey semifusinite with swollen cell walls occurs near the top. The true length of frame is 0.2 mm. Incident light, oil irnrnersion. From Diessel (1992).

:l:lit:',,..:.:ari:iii.l' . ::lr,ir,'ri:.ilirltir' . ., i ..1 ... r..r,,.,.:..,*:irri..:..r.i ..trr

..'

rrr::ir.r

.._ri l:,',i&,

:fff:$!'

-1",ffi!*

iffilffibKs$

Figure 12. Photomicrograph of a New South Wales high volatile bituminous coal showing sporinite (flat, elongated, dark lenses) in a matrix of desmocollinite (grey), together with inertodetrinite and micrinite (both almost white), plus some black grains of clay. The true length of the frame is 0.2mm. Incident light, oil immersion.

Geology of Australian Coal Basins

Figure 13. Photomicrograph of high volatile bituminous coal from New South Wales showing several pairs of cutinite (thin, black lines) enclosing medium to dark grey resinous vitrinite ('phyllovitrinite'), and separated by desmocollinite. The true length of the frame is 0.2mm. fncident light, oil immersion.

Figure 14. Photomicrograph of resin bodies occupying resin ducts in telovitrinite from a New South Wales high volatile bituminous coal. The true length of the frame is 0.2mm. Incident light, oil immersion.

Figure 15. Photomicrograph of strands of dark grey resinite from a Queensland high volatile bituminous coal set in a gtoundmass of light grey desmocollinite containing some grains of inertodetrinite (white). The true length of the frame is 0.2mm. Incident light, oil lmmerslon.

Figure 16. Photomicrograph of a

ai"tg"Sv;qty;I};1Jubir-rinite .&*

together with black patches of .t'' grinular clay in a high volatile 'l-. 1.- ' &

Petrographic Constituents

wider range of optical properties than the other liptinite macerals. Remnants of Botryococcus-like algae constitute much of the alginite found in coal. This maceral consists of small, more or less spherical bodies referred to as telalginite, in contrast to lamalginite (Hutton & others, 1980) which occurs as thin, anastomosing lamellae formed by algal mats. Since many algae can exist only in the presence of water, they are concentrated in boghead and other subaqueous deposits. However, the large amount of lichen-based algal matter produced in Recent cold climate peatlands suggests that some alginite might have accumulated in supra-aqueous environments as well. The presence in coal of alginite is probably

underestimated, as not all liptinite of algal origin may be recognised as such (Liu & Taylor, 1987). This appears to be particularly true for the maceral liptodetrinite which consists of degraded liptinite fragments.

Suberin-impregnated cell walls of cork tissue in coal form the maceral suberinite (Figure 16). This material usually traces the outline of the cells of such tissues, but in biodegraded varieties it becomes aligned with bedding due to the disappearance of the corpocollinitic cell fillings. A particularly high proportion of suberinite occurs in the Jurassic Walloon Coal Measures of the Surat Basin.

b) Second.ary Liptinites In addition to the above-mentioned primary liptinite group macerals, most of which can be related to distinct plants or parts ofplants, there are several secondary liptinites representing products formed during the coalification process. Since they passed through a fluid stage in the course of their formation, these liptinites do not possess any morphological identity; the individual masses assume the shape of the openings in the coal into which they have migrated. Fluorinite is one of these constituents, commonly found as an infilling of cell cavities. It is usually black in white light under oil immersion, but displays very intense fluorescence when irradiated with blue or blue-violet light. Exsudatinite is similar, but the fluorescence intensity is lower and the maceral more frequently fills cleats and fissures instead. Bituminite, the third of the secondary liptinites, has a clay-like, granular appearance with diffuse outlines.

Macerals as Palaeo-environmental Indicators Facies studies of Australian bituminous coals have shown that macerals, when grouped according to

genetic principles, are useful indicators oftheir respective depositional conditions. Particular maceral combinations that correlate well with specific sedimentary environments have been identified by reference to the tissue preservation index (TPI) and the gelification index (GI) of Diessel (1986). These indices are defined as follows: T elou itr inite + T elo-iner tinit e TPI = Detro- + Gelouitrinite+ Detro- + Gelo-inertinite

Vitri nit e + Gel o-iner tinite GI= T elo-ine rtinite + D etr o-in er tinit e The choice of the macerals incorporated in the two indices is based on the consideration that, unless the conditions of preservation were extremely poor, much of the wood formed in a forested peatland would have been converted into either fusinite or

semifusinite in a relatively dry peat, or into any of the telovitrinite macerals under wetter conditions. By contrasting these structured macerals with the tissue-derived unstructured macerals, a measure is obtained of the proportion of wood which contributed to the peat and was preserved in it. The tissue preservation index thus becomes a'wood ratio', although in Permian coals a notable contribution to the amount of semifusinite is also made by the abundant leaflitter produced by the deciduous Gondwana flora. A low TPI suggests either an absence offorest moor conditions or large-scale destruction ofwood due to extreme conditions such as dryness. In the latter case, the remaining coal should contain a high proportion of relatively stable liptinite macerals, including sporinite and resinite, as well as degraded residues of fusinite and semifusinite in the form of inertodetrinite. Based on a large number of analyses, Diessel (1982, 1985a) suggests that the quantitative relationship between telo-inertinite and inertodetrinite is governed by the depositional environment of the peat as follows:

a) Coals formed under mildly oxidising,

autochthonous conditions are rich in telo-inertinite, with a telo-inertinite/inertodetrinite ratio of 4ll to 8/L.

b) Coals in which humified vegetable matter was

moved in aerated water by hypautochthonous or allochthonous dispersal show a low

telo-inertinite/inertodetrinite ratio, with values between 2/t and l/4.

c) Coals which have been formed under strongly

oxidising conditions represent materials in which inertodetrinite and liptinite are the last surviving remnants of the peat before it disappears, and this can also be expected to result in a low telo-inertinite ratio.

The gelification index, which is not the same in the present discussion as that used by George (1982), gives an indication ofthe relative dryness or wetness ofthe peatland. The presence or absence of remnant cell tissue is not considered, but emphasis is put on the degree of humification and gelifrcation. This is achieved by contrasting the abundance of gelified structured and unstructured vitrinite macerals plus macrinite (that the latter has been affected by some drying is of no consequence since it

lost its cell structure frrst) to the proportion of telo-inertinite and detro- inertinite macerals, all of which show little or no gelifrcation. Combinations of GI and TPI can be used to define four coal facies, the main characteristics of which are summarised in Table 2. Based on sedimentary settings in the Sydney Basin, some typical index values are listed in Table 3. A representative seam formed in the appropriate setting is also listed for each depositional environment, but in most cases the facies indices have been derived from the constitution of more than one coal seam. A different approach has been taken by Warbrooke (1987), who combined maceral analyses with coal ash-based geochemical information to obtain two ratios, defined in this case as:IV factor = Inertinite x

100

(Inertinite + Vitrinite)

SiOzx 100 SALfactor = giaz+AlzOs)

Geology of Australian Coal Basins

7t Table,2. Coal characteris*tion b51 ,faeies indices.(Affer DieCsel,,199, ): High TPI Coal Type: Bright to bright banded; wood-derived

telo-vitrinite.

Origin: In forested peatlands (telmatic

High GI

swamps). Mild humification and

strong gelification of plant tissues

Coal type: Dull banded;

wood-derived

Low GI

telo-inertinite (fusinite and semifusinite). Origin: In forested peatlands (terrestrial swamps). Mild humifrcation and gelifrcation.

b) a maceral may be associated with tp to 57o of

other macerals in a microlithotype without the other macerals being taken into account for the classification of the microlithotype.

Low TPI Coal Type: Bright banded; tissue derived

detrovitrinite plus corpocollinite, Origin: Either in forested peatlands

from anaerobically decomposed wood

or in tree-less marshes. Telmatic or limnotelmatic. Advanced

humification and strong gelification of plant tissues. Coal Type: Dull to dull banded; tissue-derived inertodetrinite.

Microlithotypes can be monomaceral (95Vo or more of the one maceral), bimaceral and trimaceral as shown in Table 5. They may also be contaminated with mineral matter, and associations of coal and minerals are called carbominerites (Stach & others, 1982). Carbominerites are further subdivided according to the dominant mineral present, with the coal component consisting of any microlithotype. Although the actual proportions of the contributing maceral groups can vary within individual microlithotypes, genetically related coals show good correlations between their maceral and microlithotype group contents. Some of the relationships between maceral and microlithotype percentages found in New South Wales coals (modified after Diessel & Callcott, 1965) are listed below:

Vitrite= Vitrite+ tr

Origin: Either in

(Vitrinite\2

"b:::=w

nertite= 0.55 I nertinite

T rim.ace r it e s= 0.6 (I n ertinite + Lip tin it e) + 0. 0 5

relatively dry peatlands from aerobically decomposed plants

Another well-established correlation between maceral and microlithotype percentages, after Smyth (1970) and Bennett & Taylor (1970), is:

as sub-aqueous

Vitrinite= Vitrite + Clarite + 0.5 (Trimacerite + Vitrinertite)

(autochthonous) or sediment (hypautochthonous).

Table 4 indicates the relationships established by applying these two parameters to Hunter Valley coals where the depositional environments were already reasonably well known.

COAL MICROLITIIOTYPES Microlithotypes describe how the macerals are associated with one another in the naturally occurring bands within the coal. In order to define clearly the different microlithotypes the International Committee for Coal Petrology has agreed that:-

a) the minimum band width for microlithotypes should be 50m or the minimum surface area should be 50 x 50m, and

The correlation between individual macerals and microlithotypes, however, is more complex and less well defined.

Microlithotyp e Analysis Microlithotype analysis can be carried out by two methods: the 2O-point ocular method or the selon-la-ligne method. In the frrst case a 20-point crossline graticule, which covers an area of50 by 5Opm, is inserted into the microscope eyepiece. The maceral under each of the 20 intersection points is identified, its percentage of the whole field taken into account, and the appropriate microlithotype name is determined from the result (Stach & others, 1982).

In the selon-la-Iigne method only one datum point is used and the natural band, 50pm or more wide, into

rabre s; cocr raaies inaS;;-l"irf*q$if#l.$f$ffi$i**:i[

ii'd n,todnev Besin or New

Abandoned Delta

Greta

0.40

Itandard Error 0.26t

Lower Delta Plain

Rathluba

0.85

0.059

10.76

2.139

Backbarrier (transgressive)

Wynn

0.90

0.103

2.60

o.497

B ackbarrier (regressive, proximal)

Bayswater

0.67

0.289

0.64

o.228

B ackbarrier (regressive,

distal) Upper Delta/ Alluvial Valley

Borehole

t.52

0.376

4.86

o.470

Dudley

1.50

0.053

3.68

0.264

Braidplain (sandy) Braidplain (gravelly)

Bulli

r.23

0.059

1.04

0.051

Wallarah

t.49

0.096

0.78

0.089

Depositional Environment

Type seam

Mean

TPI

Petrographic Constituents

Mean GI

Jtandard

3.58

0.262

Error

Table 4. Approximate IV and,SA! rangCs in relation to depositionsl::enviionmenlS f6p20 Hunter Valley coals based on 155 sampleb. (After Warbiooke, 1987). Depositional Environment Reed Marsh

Type Seam Greta

Fen

Borehole

Wet Forest Swamp

Victoria Tunnel

Wet / Dry Forest Swamp

Fassifern

Relatively Dry Forest Swamp

Wallarah

which this one point falls in considered. All macerals in the natural band are identified and their proportions estimated, allowing the appropriate microlithotype classification to be identified.

Combined Maceral and Microlithotype Analysis A combined analysis of macerals and microlithotypes gives information on macerals, microlithotypes, and the mean maceral composition of the microlithotypes. If the analysis is done using the 20-point ocular, one point ofthe graticule is assigned to do the maceral count. Points are not counted unless at least 10 intersections fall within one coal particle. In the selon-la-ligne method the one datum point only is used: the maceral under this and the natural band in which it occurs are counted.

The Influence of Depositional Environment on Microlithotype Composition Microlithotype analyses are useful in a number of ways. In applied coal petrography they help to explain differences in mechanical strength of coal, which is dependent on the association of macerals, or to explain why coals of the same rank and maceral composition may have different coking properties. However, it is in the reconstruction of depositional environments that microlithotypes have proved invaluable, in Australia, over the past few years. Coal type, expressed in terms of microlithotype composition, is as much determined by the depositional environment as is the case for macerals. The environment is responsible for the type of vegetation, the depth of water in which it grows, the rate of subsidence in the peat swamp, and the degree of biochemical alteration which the vegetable matter undergoes before burial and preservation. Depositional environments can be considered on a number of scales, from the

Table 5. The composition of the common micrblithotype groups. Mierolithotype

uroup

Maceral GrouP comPosition

Monomaceral:

Vitrite Liptite Inertite

Vitrinite Liptinite Inertinite

>95Vo >95Vo >95Vo

Bimaceral:

Clarite Durite Vitrinertite

Vitrinite + Liptinite >95Vo >95Vo Inertinite +

Liptinite

Vitrinite + Inertinite

>95Vo

IV Factor 15-35

5-35 5-35 35-65 45-85

SAL Factor

45-60 60-80 80-90 65-85 55-75

microscopic scale of individual microlithotype bands to the scale of sedimentary basins.

Smith (1962) made a palynological and petrological study of English Carboniferous coals. He found that variations in microlithotype compositions upward through a seam were accompanied by variations in the spore populations. Coal rich in vitrite plus clarite is associated with Lycospores - the plus Lycospore phase and coals rich in durite with the Densospore phase. inertite are associated Between these two phases a transition phase is always present, with yet another spore assemblage and a high proportion ofvitrinertite and the trimacerite group microlithotypes duroclarite (vitrinite inertinite + liptinite), clarodurite (inertinite with associated vitrinite + liptinite), and vitrinertoliptite (liptinite vitrinite + inertinite). These studies indicate that wet forests give rise to coals rich in vitrite plus clarite, while small plants in a relatively dry environment produce those rich in durites plus inertites. Smith (1962) also believed that plants follow a natural sequence: each plant community produces edaphic conditions which lead to its own demise and eventual replacement by a plant community better suited to the new environment. Studies by Smyth & Cook (1975) have shown that Australian Permian and Triassic coal seams follow a pattern of change in their microlithotype compositions similar to Smith's pattern. Vitrite-rich coal at the base of seams passes upwards to vitrite-poor coal at the top. F luuio- D e lt aic Enu iron men t s

Peat forms in many locations throughout the world

in fluvio-deltaic environments. In a study of the Sydney-Gunnedah Basin, Hunt & Hobday (1984) have subdivided the fluvio-deltaic sediments into the depositional facies listed below. Hunt (1982) has constructed a microlithotype classification scheme, based on the fineness of the microbanding in coal as expressed by the proportion of trimacerite, which has been correlated with the depositional environments as follows: braided fluvial (alluvial fans) meandering fluvial upper delta plain lower delta plain

medium banded very finely banded finely banded medium banded

Fluu io- Iacust rine Enaironment s

In the intracratonic Cooper Basin, coals from the Patchawarra Trough (Figure 17) all have low vitrite plus clarite contents (<507o), and their microlithotype compositions correspond to those of the coals represented in the meandering fluvial environmenl indicated above. Thornton (1979) has proposed that the depositional environments of these sediments were as follows:

Geology of Australian Coal Basins

IOO INTERMEDIATES

lnlermedioles l0 0eposrlronol environmenls

90 0urrle . lnerlrle

Areo domrnol€d by overbonk deposrls, lokes ond swomps

r00

---- ChonnPl bell

VITRITE

DURITE

CLAR ITE

Reslracled seo

Figure 17. Microlithotype composition of coals from sorne depositional environments of the Gidgealpa Group, Patchawarra Trough, Cooper Basin. (After Smyth, 1984).

100

INERTITE

Q- st'.lt

@ -Trough

lllll oeltric -undif f erentiated ['.]] Fan Detta - Fluvio 0ettaic

area dominated by overbank deposits, lakes and

Braided Fluviat Piedmont Heandering Fluvial - Flood Basin

swamps

ii) area dominated by coal swamps iii) area dominated by channel deposits

EARLY PERMIAN

iv) channel belt

lOO INTERMEDIATES

v) upper coastal plain vi) lower coastal plain vii) restricted sea or lake The microlithotype compositions of the coals from the above environments are plotted in Figure L8.

Although the microlithotype composition of coals from several of the depositional environments is similar, the lake or restricted sea coals are quite different petrographically from those ofthe overbank deposits. On the other hand the lake coals and channel belt coals are similar, probably due to the fact that both of these environments represent relatively high water levels in the original swamp.

Sed.imentary Basins The largest scale at which coal type is related to

depositional environment is that of the sedimentary basin. Petrographic composition is dependent on whether the peat has accumulated in a stable slowly subsiding intracratonic basin or an unstable rapidly subsiding marginal basin (foredeep, foreland basin). The composition of coals formed in different tectonic settings has been described by Shibaoka & Smyth (1975) for occurrences of Australian Permian and Triassic sediments. Coals which form in the troughs of rapidly subsiding marginal basins are most likely to be rich in vitrinite and vitrite-plus-clarite. Coals which form on the shelves of marginal basins or in slowly subsiding cratonic basins, however, are most likely to be poor in vitrinite and vitrite-plus-clarite (or rich in inertinite and durite plus inertite).

r00 INERTITE

r00 VITRITE

DURITE

CLARITE

@ - st'ett

@ - Trougtr

Upper Detta Plain - Fluviat

[ii] =

Lorer Detia Ptain

Ei.,'l Braided Ftuviat Piedmont E} Meandering Fluvial - Flood Basin LATE PERMIAN

Figure 18. Microlithotype composition of coals frorn several depositional environments in the Sydney and Gunnedah Basins, of Early and Late Permian age. (After Hunt & Hobday, 1984).

Petrographic C onstituents

and each of them is less than 5mm wide, the whole unit is regarded as a mixed lithotype, with the name allocated depending on whether bright or dull coal bands predominate. In recent years the visual identification of lithotypes has been supplemented by bore core radiography (Jones, 1970) which generally leads to seam subdivisions similar to those obtained from well executed lithotype analysis.

COAL LITHOTYPES The various associations of macerals and

microlithotypes have their macroscopic expression in the form of lithotypes. These are macro-petrographic units which are identified by a set of physical properties, such as colour, lustre, texture and fracture pattern. Although the method of identification of the various lithotypes is somewhat subjective, valuable information regarding coal composition, coal origin, seam correlation, and coal utilisation can be gained from lithotype analysis. When applied to bituminous coal the result of such an analysis is often referred to as a'brightness log'. The terminology used in such logs is summarised by the Standards Association of Australia (1982;

Since brown coal is less compacted than higher-rank coal, its lithotypes are much thicker and the bed moisture content is considerably higher. Bed moisture reaches up to 7UVo in the Latrobe Valley coals of Victoria, which means that the coal tends to shrink signifrcantly on exposure. The resulting desiccation patterns displayed by a drying coal face are lithotype-specific, because they are related to the texture, the degree of humification and gelification, and other physical properties, among which colour is the property actuaily used to describe the different lithotypes present.

1986b).

Macro-petrographic coal seam logging is frequently the first step in the assessment of a bore core or a newly exposed coal face. Even when a full lithotype analysis is not carried out, lithotype groupings are commonly used to divide the seam into subsections which are then sampled separately in detailed analysis programs.

Lithotype analysis is carried out by recording the width or thickness of each lithotype in bore core or outcrop, with the aid of a measuring tape, and noting the readings either in writing or in coded form. The visual identification of lithotype colour for brown coals can be supported by the determination of the colour index using a colorimeter on a ground sample of air-dried coal of each major seam component which gives a numerical value for the 'degree of brownness' (Attwood & others, 1984). Higgins & others (1980) and Mackay & others (1985) have found that the colour index determined in this way can be correlated quite well with more conventional lithotype logs.

The following discussion is concentrated upon the Iithotypes of humic coals, i.e., those which have been derived from essentially autochthonous peat deposits by the normal processes of coalification. Not included in the discussion are the sapropelic coal types, cannel coal and boghead coal, both ofwhich are the result of subaqueous deposition of dispersed spores (cannel) and algae (boghead). These Iithotypes are characterised by a conchoidal fracture, greasy lustre, and general lack of

stratification.

Brown Coal Lithotypes

Lithotype Analyses

Several classifications exist for brown coal lithotypes, depending on the relative importance

Because ofthe striking differences in appearance between brown and black coal, different procedures are followed for lithotype analysis in each case.

attributed to their various physical properties. In some cases textural features are emphasised, and terms such as earthy, fibrous, woody or xylitic are used. These terms are also applicable to Australian brown coals (Edwards, 1947) but the distinct colour banding ofthe extensive deposits in the Latrobe Valley of Victoria (Baragwanath, 1962) led George (1975; 1982) to develop a more descriptive lithotype classifi cation (Table 6).

The lithotypes of black coal differ mainly from each

other in lustre. They range from bright to dull with a complete range of interlaminated gradations between the extremes. Mixed lithotypes are identified on the basis of predominance of the one or the other end member, with a minimum band width of Smm (Diessel, 1965). In order to be recorded separately, a lithotype must be five or more millimetres wide, so that if a number of thin laminae of bright and dull coal occur in succession

There has been continuing discussion in the international literature (for example Jacob, 1968; Teichmtller, 1950; 1958; Teichmiiller & Thomson,

Table 6. Brown coCl lithotype classification for air-dried coal. (Modified after George, 1975; 1982). Gelificetion

Weathering Regular pattern of

Strength

Lithotype and Colour

Texture

DARK - black brown to dark brown

High wood content - small pieces

Extensive

MEDIUM DARK dark brown to medium brown MEDIUM LIGHT medium brown to light brown

High to medium wood content -

Common but not extensive

Regular pattern of wide cracks

Fairly strong,

IJncommon, confrned to wood

Irregular pattern of shallow cracks

Medium physical properties

Random pattern of

Soft, low density

M-d

M-l

Strong, hard, dense

deep, wide cracks

hard, dense

large pieces High to low wood content - well preserved

LIGHT - lisht

Medium to low

brown

wood content

Rare

fine cracks

Geology of Australian Coal Basins

'tD

Table,,?. The maeeral,composition,of:brown coal lithotypes in,,fhe Yallourn Seam, Yallourn open cut. Modified after George (1982). Maceral (Sub-)Group

Maceral Textinite Texto-ulminite Eu-ulminite

t.2

3.2

t6.4

2.L 12.9

0.7

14.6

7.8

1.5 5.3

16.2

4.0

1.8

0.5

32.0

23.6

16.8

10.3

7.3

Attrinite

32.2

51.1

64.5

70.5

63.5

Densinite

2r.3

8.6

1.2

53.5

59.7

65.7

70.9

63.5

5.2

r.4

1.6

0.2

0.8 5.7

1.2 5.3

0.7

4.3

1.0 9.5

9.5

11.9

8.1

6.7

Sporinite

0.6

0.4

Cutinite Resinite Suberinite Liptodetrinite

1.6

0.5

2.0 0.4

0.4

0 1.7

1.6 1.8

3.3 1.0 0.2 3.2

1.1

2.0

2.8

t2.t

2.6

3.7

7.8

10.5

23.7

0.4 0.7

0.2 0

0 0

1.3

0.7

0.6

1.0

2.4

TELO.INERTINITE

2.4

DETRO-INERTINITE Inertodetrinite

MINERALS

0.9 0.2 0

0.6 0.6 0.4

1.0 0.6 0

TELOVITRINITE

DETROVITRINITE Eugelinite

Porigelinite Corpogelinite GELOVITRINITE

LIPTINITE Semifusinite Fusinite Sclerotinite

1958; Hagemann & Hollerbach, 1979;von der Brelie & Wolf, 1981) concerning the origin of the widespread colour banding in brown coal and questioning its suitability as a facies indicator. However, as shown in Table 7, the colour-based lithotypes identified in Australian brown coals are also characterised by distinct maceral assemblages, and this supports the principle on which lithotype classification is based in general.

Black Coal Lithotypes Polymerisation of the humic acids at the sub-bituminous coal rank stage, together with the ongoing compaction and concomitant loss of bed moisture during further coalification, leads to marked changes in the physical characteristics of coal. In response to increasing molecular condensation in higher rank coals, the colour banding in lower rank materials is replaced by the degree of lustre as the main basis for lithotype classification. Historically, four lithotypes have been distinguished, first by Fayol (quoted by Freund, 1952), and later by Stopes (1919); these were referred to as vitrain, clarain, durain, and fusain. Because strict application of this four-fold lithotype divisions to the often thinly laminated Australian coals usually results in poor resolution, Diessel (1965) introduced the lithotype classification listed in Table 8. This terminology has also been incorporated into Australian Standards (Standards Association of Australia , 1982; 1986), providing a series of terms for megascopic description of Australian higher rank coal seams. Many coals have a characteristic lithotype make-up by which they can be identified for the purpose of seam correlation. The maceral composition of the

0 0

r.2 1.9 7.8

0.3

2.t

1.4

2.4 0.5 0.7

lithotypes also follows distinct trends, as demonstrated in Table 9, although the wider range of coalification encountered in black coals, compared with brown coals, results in a greater variability of lithotype composition between different coal seams (Diessel, 1965). The main reasons for this are the loss of identity of liptinite with metamorphic changes in high rank coals, and the fact that a matt or dull lustre is a function of surface roughness, which in coal is related to a heterogeneous maceral composition irrespective of the actual maceral blend which gives rise to the overall dull appearance.

Lithotype Facies and Depositional Conditions The origin of lithotypes in both brown and black coals has been the subject of much discussion both in Australia and overseas. Depending on the modern analogue chosen for comparison and the technique employed in the investigation, opposing conclusions about identical lithotypes have in fact been reached in some cases. The light brown and pale brown coals of the Latrobe Valley are an example; botanical studies have suggested a limnic or limnotelmatic environment, whereas geochemical and petrographic evidence favours a rather dry terrestrial setting. Part of the problem is that drifting and redistribution of organic matter can occur, even in an essentially autochthonous peat accumulation, while some vegetable matter is also stable under a variety of geological conditions. As shown in Table 7, the proportion of telovitrinite in Victorian brown coal decreases from 32Vo in the dark lithotypes to 7.SVo in the pale lithotypes, a trend which is carried mainly by the gelifred members of the telovitrinite subgroup. A similar

Petrographic C onstituents

Table 8. Black coal lithotypes, modified after,:Diessel (1965). Lithotype Bright coal (Vitrain)

Banded bright coal

Banded coal

Banded dull coal

Mainly dull coal containing thin (less than 5mm) bright bands ranging in proportion between 10 and 40Vo;uneven fracture.

Dull coal (Durain)

Matt lustre and uneven fracture; may contain 107o of bright coal bands less than 5mm thick.

Fibrous coal (Fusain)

Dull with satin sheen; friable, may contain up to 70Vo of other coal lithotypes less than 5mm thick.

Shaly coal

Coaly shale, mudstone, siltstone, sandstone etc.

Contains between 30 and 60Vo of clay and silt either in intimate mixture with coal or in separate bands each less than 5mm thick. Consists of alternating laminae (each less than 5mm thick) of non-coal and coal, the latter not exceeding 40Vo oftotal.

(Clarain)

(Duroclarain)

(Clarodurain)

Shale, mudstone, siltstone, sandstone etc.

Mainly bright coal containing thin (less than 5mm) dull coal bands ranging in proportion between 10 and 40Vo; even fracture. Contains bright and dull coal bands (all less than 5mm) ranging in

proportion between 40 and 60Vo each.

Carbonaceous shale, mudstone,

siltstone etc.

-r."-: contain up to I}Vo dull coal in bands less than 5mm thick.

Any sediment containing 60 to 90Vo finely disseminated carbonaceous matter. Any sediment containing less than l|Vo carbonaceous matter.

decrease is shown by gelovitrinite, and also by

densinite, the more gelified member of the detrovitrinite subgroup. These trends are balanced by an increase in less gelified or non-gelified macerals, such as attrinite, as well as an increase in Iiptinite, particularly liptodetrinite and sporinite, within the light coloured lithotypes.

Liptinite macerals survive well in subaqueous, reducing conditions, as shown by their widespread occurrence in oil shales and other sediments, but liptinite has also been found to possess a good preservation potential in oxidising environments (von der Brelie & Wolf, 1981), provided conditions are not too alkaline (Taylor & Warne, 1960). On the

other hand, the concentration of biochemically gelified plant tissues in the dark lithotypes suggests anaerobic conditions in a waterlogged peat, whereas the predominance of largely ungelified attrital tissue fragments in the light lithotypes appears to be more

indicative of intensive humification under some aerobic influence.

The above conclusion is at variance with Luly & others (1980) and Kershaw & Sluiter (1982) who, on the basis of palynological studies, concluded that the

dark lithotypes represent a relatively dry environment while the light lithotypes represent wet to open water conditions. However, Markov chain analyses of lithotype sequences in the Morwell seam of the Latrobe Valley (Mackay & others, 1985) have led to the recognition of many depositional cycles which begin above a sharp basal contact with dark lithotypes, inferred to represent wet conditions followed by a drier milieu as the lithotype colour Iightens upward. This notion is analogous to the suggestions of Smith (1962) and Smyth & Cook (1976) who suggest that the observed cyclicity from bright to dull lithotypes in Australian black coals is a response to repeated episodes offlooding and subsequent drying ofthe peat. Beeston (1982), however, takes the opposite view and regards the upward increase of dull coal in many seam profiles

as being caused by the allochthonous deposition of

inertinite in progressively deeper water.

The question of wet or dry formation in black coal lithotypes has mainly involved the dull varieties. Notwithstanding the obvious differences in age, geological setting, vegetable sources etc. for the two types of coal deposits, some of the compositional trends shown in Table 9 covering transitions from

bright to dull lithotypes in Australian high-rank coals follow a similar pattern to those listed in Table 7 for the dark to pale brown lithotypes of the lower rank coals. This is particularly so in the case of telovitrinite, which shows a marked decline with replacement by detrovitrinite in the brown coal and by detro-inertinite in the black coal. Telovitrinite is also replaced, though to a lesser extent, in both coals by sporinite.

It is significant that coherent plant tissue has been replaced in these cases by a residual attritus (attrinite in the brown coal and inertodetrinite in the black coal), none of which has been subjected to biochemical gelification but which has possibly been subjected to different intensities ofdrying. Attrinite cannot be regarded as a precursor ofinertodetrinite in bituminous coal, because studies of Latrobe Group coals which occur at great depth in the off-shore Gippsland Basin have shown that with increasing rank the attrinite converts into desmocollinite (Palmer, 1986) by a rank-related process which has been called vitrinitisation or geochemical gelification. This is in contrast to the biochemical gelification which occurs during the peat stage ofcoal development in response to the depositional environment (Stach & others, 1982).

In the above example it has been assumed that the dull (inertinite-rich) coal in Australian deposits was mainly formed in a relatively dry environment. The Australian coalfields contain many examples of socalled'dry durains', shown, for example, by the good correlation of the proportion of dull and banded dull coal with the amount of conglomerate in the

Geology of Australian Coal Basins

Table 9. The maceral composition of black coal lithotypes of a Cential Q'ueensland coking coal. (After Diessel, f992). Lithotypes Macerals and ^'^-:*^-^" -"B Bd BD Db D F uroups Telovitrinite 84.4 67.0 46.4 L2.2 0.2 0 Detrovitrinite 6.8 14.8 19.6 11.0 2.0 1..2 VITRINITE 9L.2 81.8 66.0 23.2 2.2 L.2

Sporinite 0.4 0.8 2.0 1.8 4.0 0.2 Cutinite000.60.200 Resinite 3.0 2.4 1.0 0.4 0 0 LIPTINITE 3.4 3.2 3.6 2.4 4.0 0.2 Telo-inertinite 2.6 7.2 20.0 45.0 26.6 94.L Detro-inertinite 1.2 4.4 7.2 17.8 50.2 3.6 Gelo-inertinite 0.4 0.4 2.4 6.4 9.8 0 INERTINITE 4.2 t2.0 29.6 69.2 86.6 97.7 MINERALS 1.2 3.0 0.8 5.2 7.2 1.0 Newcastle Coal Measures (Warbrooke, 1981), the basinward decrease in inertinite content and concomitant increase in vitrinite in the Bulli seam in the Southern Coalfield of the Sydney Basin (Cook & Wilson, 1969), or, in the case of the Dudley seam, the increase in vitrinite from the flank of the Lochinvar Anticline into the Lake Macquarie Syncline of the Newcastle Coalfield (Warbrooke & Roach, 1986). The high concentration of inertodetrinite-rich dull coals in the Maules Creek Formation on the flank of the Boggabri Ridge in the Gunnedah Basin, and the marked contrast to the high vitrinite coals in the adjacent Maules Creek Sub-basin (Diessel, 1985a) also suggest the influence of drying, as do the mudcracks which have been found to penetrate into the particularly dull top section ("the blacks") of the Bulli seam in Wongawilli Colliery near the margin of the Southern Coalfreld of New South Wales (Diessel & others, 1967). In such cases the disseminated mineral

matter content is usually higher than for bright lithotypes, possibly because of the relative concentration of organic matter due to the oxidative removal ofpeat (Johnson & Cook, 1973; Cook & Johnson, 1975).

However, the point must be made again that aerated water can cause oxidation and that the place of origin is not always the place of burial. In the same way that small amounts of inertinite occur as accessories in oil shales, large concentrations of inertinite have been found together with Botryococcus- type telalginite in some dull coals. As has been mentioned before, the inertinite often consists of inertodetrinite and, occasionally, such structures as graded bedding and micro cross-lamination (Bailey, 1981; Diessel, 1982; 1985), as well as the high proportion of adventitious mineral matter, give evidence of the dispersed nature of these occurrences. Marchioni (1.980) describes a characteristic association of clastic dirt bands in the Liddell Seam of the Hunter Valley with

overlying and underlying dull lithotypes rich in durite and clarodurite due to "the increased level and circulation of groundwater before and after a period of inundation during which clastic material was deposited". The result is a 'wet durain'which accumulated in free-standing water in a manner not unlike that assumed by Beeston (1982).

THE PETROGRAPHIC CHARACTERISTIC S OF AUSTRALIAN GONDWANA COALS There is convincing geological evidence ofa Late Palaeozoic landmass which appears to have included much of present day Australia, Antarctica, southern Africa, peninsular India, Madagascar and parts of South America. This large southern continent, called Gondwanaland, was characterised by a cool to cold climate and a biological development which differed from the evolutionary trends occurring elsewhere at the time. Since most of Australia's coals are of

Permian age, they, together with the less important Carboniferous and Triassic coals (Gould & Shibaoka, 1980), belong to the Gondwana lineage which ended with the breakup of the continent beginning in the Jurassic Period.

Many misconceptions persist, particularly in the European literature, about many aspects of Australian Gondwana coals. At the root of this is the unfounded belief that a once-coherent landmass would have uniform conditions over its whole area. The result has been that scant observations made by occasional visitors to various parts of the former Gondwanaland area have been interpreted to apply to all the fragments of the hypothetical continent. Many of the generalisations about the origin, geological setting, and composition of Gondwana coals have been extrapolated to include all Australian coals, usually in complete disregard of conflicting evidence. David's classical (1907) work on the Newcastle and adjacent Coalfields alone contains sufficient information on the geological setting of the coal, the seam characteristics, coal composition and interseam sediments to refute many of the general claims made about Gondwana coals. Examples of these include: a) Gondwana coals formed in shallow epicontinental basins.

This is not true for many eastern Australian coalfields, which formed in the foredeep (foreland basin) to the New England Fold Belt (Sydney, Gunnedah, and Bowen Basins). b) Gondwana coal seams are thicker than Carboniferous seams because of lower rates of subsidence.

This is true for coals with a cratonic setting, but not true for those with a foredeep setting, where subsidence rates were high and the thickness distribution is similar to that of equivalent Carboniferous coals in the Northern Hemisphere. c) The peat-producing Gondwana forests consisted

only of stunted trees.

This is true for the Early to Middle Permian coals, but not for those of the Late Permian. In the Newcastle Coal Measures, for example, numerous tree trunks have been found up to 1 m in width. d) Gondwana coal measures are mainly of

freshwater origin.

This is not true for Australian foredeep deposits, where well-documented marine transgressions and regressions have affected delta and barrier beach settings in the three main coal basins.

Petrographic Constituents

Table 10. Comparison beiween average maceral compositions gf Aus_tralian Perrnian and Eufbpeah and Ameiicen CarbonifCnoue 66als,(all weshed). (Modified after Taylor & others, fgST). Permian (n = 67)

Group

Carboniferous (n = 40)

MaceraUsubgroup ltleanrzo Range t'fif#u

v..eanzo Range t$fffu

Telovitrinite Detrovitrinite

31.8 32.8

VITRINITE Sporinite

Cutinite Resinite LIPTINITE

Micrinite Macrinite Semifusinite Fusinite Inertodetrinite INERTINITE MINERALS TPI (micrinite included) TPI (micrinite excluded) GI (micrinite included) GI (micrinite excluded)

33.6 33.4

1.r02

35.3

1.181

o./

13.1

0.504

0.7

2.6 8.8

0.1 19

3r.7

38.6 40.1

1.242 1.100

55.2

53.2

1.733 64.4

3.2 0.7 2.5

tr.2

tl.4

0.671 0.104 0.266

6.4

2t.0

0.562 9.9

16.2

2.t

5.6 17.6

5.1 3.4

t5.7

34.8

4.5 8.1

11.0

25.0

0.136 0.392 1.026 0.332 0.590

19.1

3.9

6.1 2.9 4.7

13.8 5.8 8.0

34.6 3.9

55.2 10.0

1.880 22.5 0.228 3.3

23.5

3.6

0.96 1.00 1.94

2.09

e) Gondwana coals are or may be allochthonous

because they do not contain seat earths and contain many dirt bands.

This is not true at all for Australian coal seams, many of which contain well-developed. Vertebraria roots at the base. Because of the cold Permian climate, the seat earths are less weathered than the Carboniferous underclays. The presence of tree stumps in growth position in the petrifred forests of the Newcastle Coal Measures provide further evidence of autochthony. Many dirt bands are probably altered tuff, and those of epiclastic origin appear to result from a combination of climate and geological setting.

fl Gondwana coals are dull because of high inertinite contents, and they lack the many bright lithotypes found in Carboniferous coals.

This is true for most coals in a cratonic setting. However, the foredeep coals (e.9. the coals of the Tomago and Newcastle Coal Measures in the Sydney Basin or the Maules Creek Formation in the Gunnedah Basin) display the same gradation from vitrinite-rich bright coals in the lower portion to inertinite-rich dull coals near the top of the sequence as shown, for example, by the European Ruhr coals. Likewise, there is a lateral shift from predominantly bright coals near the rapidly subsiding orgenic margin of the Sydney-Gunnedah-Bowen foredeep to its less actively subsiding cratonic margin. The above comments have been made in order to emphasise the diversity of Australian and possibly Gondwana coals, rather than to infer similarity to Carboniferous coals. This diversity is particularly noticeable from a petrographic comparison between the two sets of coals. As shown in Table 10, the range of abundance for most macerals is greater in the Australian coals than the range for the corresponding macerals in Carboniferous coals,

2.5

8.1

33.7 7.3

1.066

0.261 0.617 0.621 0.319 0.555

0.228 0.310

1.t92 0.279

0.89 1.00

3.66 4.95

which means that, in spite of the higher mean percentage of vitrinite and lower mean percentage of inertinite in the Carboniferous deposits, some Australian coals are evidently very rich in vitrinite, as has been illustrated by Smyth (1968), Edwards (1975), Bennett & Taylor (1970), and Taylor & Shibaoka (1976). According to Cook (1975), vitrinite contents of Australian coals range from 5Vo to more than 807o.

It is noticeable in Table 10 that, within the vitrinite

group, the proportions of detrovitrinite (i.e. desmocollinite) are very similar, and that the variations in vitrinite percentages are due to differences in the abundance oftelovitrinite. The magnitude of this difference is similar to the contrast between the high semifusinite content of the Australian coals compared to their Carboniferous counterparts. This means that the average proportion ofpreserved plant tissues is similar in both sets of coals, although their degree of

gelification is higher in the Carboniferous materials. This is shown by the tissue preservation and gelification indices listed in Table 10.

Micrinite is normally included under detro-inertinite in the calculation of the two indices, because the total amount of micrinite is small in Australian coals and much of it consists of finely fragmented inertinite debris. However, in the Carboniferous coals used for the comparison, there is a higher percentage of micrinite which has been formed by molecular dissociation of liptinite, thus warranting its exclusion from the index calculation. Another difference between the two coals is the higher proportion ofsporinite in the Carboniferous deposits. This is related to differences in the contributing vegetable matter. Spore-producing pteridophytes dominated the Carboniferous flora, while the Permian Glossopteris flora contained more g"ymnospermous plants resulting in a lower

Geology of Australian Coal Basins

availability of spores for inclusion in the peat deposits.

Apart from their wide ranges in distribution, Australian coal macerals are at variance with many Carboniferous coals in a number of properties, including the high degree of fusibility in inertinite during carbonisation. Coking experiments and mass balance calculations between coal and coke (Diessel, 1983; Diessel & Wolff-Fischer, 1986, 1987) have demonstrated that tp to 507o of the inertinite contained in Australian coking coals fuses either partially or completely during coking. This may be the reason that a lower vitrinite content is necessary for Australian coals to produce high quality metallurgical coke. The work of Cook (1971), Edwards & others (1971) and Edwards & Cook (1972) shows, for example, that the highest coke stabilities are obtained from coals with a vitrinite content of around 557a. This is a low figure compared with the average vitrinite

content of 65Vo commonly required for high-stability coking blends from Carboniferous coals of similar rank. It is also noteworthy that, when made under identical conditions, cokes produced from Australian coal show larger anisotropy domains than cokes from similar-rank Carboniferous coals (Ng & others, 1987).

Different grades of fusibility are indicated by concomitant fluorescence intensities (Diessel, 1985b), and it has been found that both inertinite and vitrinite are more strongly fluorescent in Permian than in Carboniferous coals (Diessel & Wolff-Fischer, 1986, 1987). The above-mentioned analysis results suggest that

the cokability of the Carboniferous coals is actually lower than that of rank- and type-equivalent Australian Permian coals, but this deficiency is usually more than balanced by the above-mentioned higher vitrinite contents of the Carboniferous coking coal blends. The reasons for such differences between the two sets of coals are not entirely clear. According to Cook (1981) it is the result of a complex interaction of geological, climatic, and biological factors, while Taylor & others (1989) favour climate and admixtures of algal liptodetrinite as the main reason for the different grades in inertinite reactivity.

Taylor & others (1989) suggest that the warm Carboniferous climate produced inertinite by hot-drying of exposed plants and peat whereas in the cold Gondwana swamps proto-inertinite was formed by freeze-drying, leading to similar but not identical products.

BARAGWANATH, G.E., 1962: Some aspects of the formation of brown coal, and of the behaviour of brown coal ash in water tube boilers, with special reference to Victorian deposits. Australasian Institute of Mining and Metallurgy Proceedings, 202, L3L-249. BEESTON, J.W., 1982: Coal sedimentation in the Reids Dome Beds, Bowen Basin: a depositional model. Australian Coal Geology, 4, 503-504.

BENNETT, A.J.R. & TAYLOR, G.H., 1970: A petrographic basis for classifying Australian coals. Australasian Institute of Mining and Metallurgy Proceedings,233, l_5. BRELIE, G. von der, & WOLF, M., 1981: Zur Petrographie und Palynologie heller und dunkler Schichten im rheinischen Hauptbraunkohlenfltjz. Fortschritte der Geologie uon Rheinland und Westfalen,29, 95-163. BROWN, H.R., COOK, A.C., & TAYLOR, G.H., 1964:

Variation in the properties ofvitrinite in isometamorphic coal. Fuel, 43, lll-124. COOK, A.C., 1971: Vitrinite content and coke strength. FueI,5O, 4l-52. COOK A.C., 1975: The spatial and temporal variation ofthe type and rank ofAustralian coals. ln Cook A.C. (Editor): Australian Black Coal - its occurrence, mining, preparation, and use. Australasian Institute of Mining and Metallurgy, Illaw arra Branch, 63-84. COOK, A.C., 1981: Temporal variation of type in Australian coal seams. Centres Recherche Exploration-Production Elf Aqitaine , 5, 443-459. COOK, A.C., & JOHNSON, R.D., 1975: Seam thickness, quality, and structure variations in the Bulli coal, Sydney Basin, N.S.W. Australasian Institute of Mining and Metallurgy, Annual Conference, South Australia, B, 537-550. COOK, A.C. & WILSON, R.G., 1969: Rank and type

variations in coals from the Southern and Southwestern Coalfields, New South Wales, and their influence upon coking. Australasian Institute of Mining and M etallurgy Proceeding s, 232, 27 -39. DAVID, T.W.E., 1907: The geology of the Hunter River coal measures, New South Wales. Geological Suruey of New South Wales Mernoir,4, I-372.

DIESSEL, C.F.K., 1965: Correlation of macro- and micropetrography of some New South Wales coals.

Eighth Comm.onwealth Mining and Metallurgical C o ngre s s, M elb ourne, Pr ocee ding s, 6, 669 -67 7 .

DIESSEL, C.F.K., 1982: An appraisal of coal facies based on maceral characteristics. Australian Coal Geology,4, 474-483. DIESSEL, C.F.K., 1983: Carbonization reactions of

inertinite macerals in Australian coals. Fuel,62, 883-892.

DIESSEL, C.F.K., 1,985a: Macerals as facies indicators. Dixiime Congris International se Stratigraphie et

REFERENCES ATTWOOD, D.H., BOLGER, P.F., GEORGE, A.M., & MURDOCH, C. McC., 1984: Measurement of the colour ofdry soft brown coal. State Electricity Commission of Victoria, Research and Deu elopment Departmenl, Report SOl84/7 3.

BAILEY, J., 1981: The geology of the Broke - Mt. Thorley area. B.Sc. Honours Thesis, The

University of Newcastle, New South Wales.

de G6ology du Carbonif?re, Madrid 1983, Compte Rendu,3,367-373. DIESSEL, C.F.K., 1985b: Fluorometric analysis of inertinite. Fuel, 64, 1542-1546.

DIESSEL, C.F.K., 1986: On the correlation between coal facies and depositional environments. 20th Symposium on Advances in the Study of the Sydney Basin, Uniuersity of Newcastle, Proceedings, 19-22.

Petrographic C onstituents

80 DIESSEL, C.F.K., 1992: Coal-bearing Depositional Systems. Springer Verlag, Berlin, Heidelberg, New York, London, Paris, Tokyo, Hong Kong, Barcelona, Budapest. DIESSEL, C.F.K. & CALLCOTT, T.G., 1965: Petrographic features of N.S.W. coals. B.1LP. Technical Bulletin, 9, 2-8. DIESSEL, C.F.K., DRIVER, R.C. & MOELLE, K.H.R., 1967: Some geological investigations into a fossil river system in the roof strata of the Bulli Seam.

Australasian Institute of Mining and Metallurgy, Proceedings, 221, 19-37 .

DIESSEL, C.F.K. & WOLFF-FISCHER, E., 1986: Vergleichsuntersuchungen an Kohlen und Koksen zur Frage der Inertinitreaktivitiit. Glilckauf- Forschung shefte, 47, 204-2II. DIESSEL, C.F.K. & WOLFF-FISCHER, E., 1987: Coal and coke petrographic investigations into the fusibility of Carboniferous and Permian coking coal. International Journal of CoaI Geology, g, 87-108.

DULHUNTY, J.A., L944: Origin of the New South Wales torbanites. Linnean Society of New South Wales, Proceedings, 69, 26-48. EDWARDS, A.B., 1947: Coal types in the Yallourn and Latrobe brown coal seams. Australasian Institute of Mining and. Metallurgy Proceedings, 146/47, 23-69. EDWARDS, G.E., 1975: Marketable resources of Australian coal. In Cook, A.C. (Editor): Australian Black Coal - its occurrence, mining, preparation, and use. Australasian Institute of Mining and

Metallurgy, Illawarra Branch, 85-108.

EDWARDS, G.E. & COOK, A.C., L972'. The design of blends for the production ofmetallurgical coke with particular reference to long term aspects of using New South Wales coals. Ausfralasian

Institute of Mining and, Metallurgy Proceedings, 244, t-I0.

EDWARDS, G.E., READ, H.W. & TEAGUE, J.H., 1971: A petrographic approach to the coking of coals from the Illawarra Coal Measures of the Southern Coalfield. Australasian Institute of Mining and Metallurgy Proceedings, 239, 4L-49. FREUND, H., 1952: Handbuch der Mikroskopie in der Technik, Band e, Teil 1. Umschau Verlag, Frankfurt am Main.

HIGGINS, R.S., KISS, L.T., ALLARDICE, D.J., GEORGE, A.M. & KING, T.N.W., 1980: Properties of brown coals from the Latrobe Valley - a basis for the evaluation of quality. State Electricity Commission of Victoria, Research and Deuelopment Departmenf, Report SC/80/17. HUNT, J.W., 1982: Relationship between microlithotype and maceral compositions of coals and geological setting of coal measures in the Permian basins of eastern Australia. Australian CoaI Geology, 4, 484-502. HUNT, J.W. & HOBDAY, D.K., 1984: Petrographic composition and sulphur content of coals associated with alluvial fans in the Permian

Sydney and Gunnedah Basins, eastern Australia.

I nte rnat ion al As s oc iati on of S e dime ntol o gists,

Special Publication, 7, 43-60.

HUTTON, A.C., KANTSLER, A.J., COOK, A.C, & MCKIRDY, D.M., 1980: Organic matter in oil shales. APEA Journal, 20, 44-68. INTERNATIONAL COMMITTEE FOR COAL

PETROLOGY, 1963: International Handbook of Coal Petrology (2nd Edition) with supplements 1971 and 1975. Centre National de Recherche Scientifique, Paris.

JACOB, H., 1968: Zur Genese der hellen Straten von Braunkohlenflijzen. Zeitschrift der deutschen geologischen Gesellschaft, 118, 102-110.

JOHNSON, K.R. & COOK, A.C., 1973: Cyclic characteristics of sediments in the Moon Island Beach Subgroup, Newcastle Coal Measures, New South Wales. Mathematical Geology, S, 91-110.

JONES, R.H., 1970: A bore core radiography unit. Journal of Physics, E: Scientific Instruments, S, 363-366. KERSHAW, A.P. & SLUITER,I.R., 1982:ThE application ofpollen analysis to the elucidation of Latrobe Valley brown coal depositional environments and stratigraphy. Australian Coal Geology,4, 169-186.

LIU, S.Y. & TAYLOR, G.J., 1987: Liptodetrinite of algal origin in inertinite-rich coals. 2Isl Symposium on Aduances in the study of the Sydney Basin, Uniuersity of Newcastle, Proceedings, 57-60.

GEORGE, A.M., 1975: Brown coal lithotypes in the

LULY, J., SLUITER, I.R. & KERSHAW, A.P., 1980: Pollen studies ofTertiary brown coals: preliminary analyses of lithotypes within the Latrobe Valley, Victoria. Monash Publications in Geography,23.

GEORGE, A.M., 1982: Latrobe Valley brown coal -

MACKAY, G.H., ATTWOOD, D.H., GAULTON, R.J. & GEORGE, A.M., 1985: The cyclic occurrence of brown coal lithotypes. State Electricity Commission of Victoria, Report No. S0/85/93.

Latrobe Valley deposits. State Electricity Commission, Fuel Department, Petrological Report No. 17.

lithotypes: macerals: coal properties. Australian CoaI Geology, 4, l-11-130.

GOULD, R. & SHIBAOKA, M., 1980: Some aspects of the formation and petrographic features ofcoal members in Australia, with special reference to the Tasman Orogenic Zone. Australian Coal

MARCHIONI, D.L., 1980: Petrography and depositional environment of the Liddell seam, upper Hunter Valley, New South Wales.

International Journal of Coal Geology, l, 35-61.

Geology, 2, 1,-29.

HAGEMANN, H.W.& HOLLERBACH, A., 1979: Relationship between the macropetrographic and organic geochemical compositions of lignites. Aduances in Organic Geochernistry, 12, 631-638.

NG, N., CROSDALE, P.J., ROBERTS, O.C. & SMITH, G.B., 1987: Coking coal characterisation by etching and fluorescence techniques. End ofGrant Report, National Energy Research, Development and Demonstration Program, Project No. 873.

Geology of Australian Coal Basins

PALMER, D.C., 1986: Investigations into the palaeoenvironment of, and porosity and permeability distribution in Fortescue A-3, an offshore development oil well, Gippsland Basin,

Victoria. B.Sc. Thesis, University of Newcastle, New South Wales.

STOPES, M.C., 1919: On the four visible ingredients of banded bituminous coal. Royal Society, Proceedings, B, 90, 470-487.

TAYLOR, G.H., LIU, S. & DIESSEL, C.F.K., 1989:The cold climate origin of inertinite-rich Gondwana coals. International Journal of Coal Geology, Ll,

SHIBAOKA, M. & SMYTH, M., 1975: Coal petrology and the formation of coal seams in some Australian sedimentary basins. Economic Geology, 70, r463-t473. SMITH, A.H.V., 1962: The palaeoecology of Carboniferous peats based on the miospores and petrography of bituminous coals. Yorkshire Geological S ociety, P roceeding s, 33, 423-47 4. SMITH, G.C., 1982: A review of the Tertiary Cretaceous tectonic history ofthe Gippsland Basin and its control on coal measure sedimentation. Australian CoaI Geology, 4, 1-38. SMITH, G.C. & COOK, A.C., 1980: Coalifrcation paths of exinite, vitrinite and inertinite. Fuel, 59,

64t-646. SMYTH, M., 1968: The petrography of some New South Wales Permian coals from the Tomago Coal

L-22.

TAYLOR, G.H. & SHIBAOKA, M., 1976: The rational

use ofAustralia's coal resources. Institute of Fuel, Biennial Conference 1976, Preprinfs, 8.1-8.15. TAYLOR, G,H. & WARNE, S. ST. J., 1960: SOMC Australian coal petrological studies and their geological implications . International Committee for Coal Petrology, Proceedings, 3, 75-83. TEICHMULLER, M., 1950: Zum petrographischen Aufbau und Werdegang der Weichbraunkohle (mit Beriicksichtingung genetischer Fragen der Steinkohlenpetrographie). Geologisches Jahrbuch, 64,429-488. TEICHMULLER, M., 1958: Rekonstruktion verschiedener Moortypen des Hauptfltizes der niederrneinischen Braunkohle . Fortschritte der Geologie u on Rheinland und Westfalen, 2, 599-6\2.

SMYTH, M., 1984: Coal microlithotypes related to sedimentary environments in the Cooper Basin, Australia. International Association of Sedirnentologists, Special Publication, 7, 333-347.

TEICHMULLER, M., 1974: Uber neue Macerale der Liptinitgruppe und die Entstehung des Mikrinits. Fortschritte der Geologie uon Rheinland und Westfalen, 24, 37 -64. TEICHMULLER, M. & THOMSON, P.W., 1958: Vergleichende mikroskopische und chemische Untersuchungen der wichtigsten Fazies-Typen im Hauptfltiz der niederrheinischen Braunkohle. Fortschritte der Geologie uon Rheinland und Westfalen, 2, 573-598.

SMYTH, M., & COOK, A.C., 1975: Sequence in Australian coal seams. Mathematical Geology, 8,

THORNTON, R.C.N., 1979: Regional stratigraphic analysis ofthe Gidgealpa Group, southern Cooper

Measures. Australasian Institute of Mining and

Metallurgy, Proceedings, 225, L-9. SMYTH, M., 1970: Type seam sequences for some Permian Australian coals. Australian Institute of M ining and Metallurgy, Proceeding s, 233, 7 -16.

529-547. STACH, E., MACKOWSKY, M,-TH., TEICHMULLER, M., TAYLOR, G.H., CHANDRA, D. & TEICHMULLER, R., 1982: Coal Petrology, 3rd Edition, Gebruder Borntraeger, Berlin-Stuttgart. STANDARDS ASSOCIATION OF AUSTRALIA, 1982: Guide to the evaluation ofhard coal deposits using borehole techniques. Australian Standard 251.9.

STANDARDS ASSOCIATION OF AUSTRALIA, 1986A: Coal - maceral analysis. Australian Standard 2856. STANDARDS ASSOCIATION OF AUSTRALIA, 1986b: Symbols for graphical representation ofcoal seams and associated strata. Australian Standard 2916.

Basin, Australia. Geological Suruey of South Australia, Bulletin 49. WARBROOKE, P.R., 1981: Depositional environments of the upper Tomago and lower Newcastle Coal Measures, New South Wales. Ph.D. Thesis, University of Newcastle, New South Wales. WARBROOKE, P.R., 1987: Depositional and chemical

environments in Permian coal forming swamps from the Newcastle area.27st Symposium on Aduances in the Study of the Sydney Basin, Uniuersity of Newcastle, Proceedings, 1-10.

WARBROOKE, P.R. & ROACH, M.J., 1986: ThE relationship between seam splitting, coal-forming environments and coal properties in the Newcastle Coal Measures.20th Sym'posium on Aduances in the Study ofthe Sydney Basin, Uniuersity of Newcastle Proceedings, 23-27 .

Petrographic Constituents

ffi woal rank and vitrinite reflectivity

JW Beeston

NEW SOUTH WALES

Figure 1. Isoreflectance maps for the top of the Permian coals in the Bowen, Sydney, Galilee and Cooper Basins.

Coal rank parameters are an integral part of characterising coals and coal deposits, and vitrinite reflectance is a common measurement of rank.

Information ranging from details of individual

reflectance measurements to complex isoreflectance maps (Figure 1) is commonly incorporated in exploration surveys and basin analysis studies. Coal is a complex suite of organic-rich rocks produced through low-temperature metamorphism of peat, with varying influence from pressure and time. The degree of physico-chemical change is known as 'rank', and is measured by chemical or physical analysis. Measurement of chemical constitution, through parameters such as carbon and oxygen content, requires bulk analysis. It is therefore affected by variations in maceral content and composition (which in turn are related to biofacies and depositional environment), and hence is not always sufficiently accurate as a basis for rank

discrimination. Physical microscopic techniques have the advantage of being applicable to individual macerals (or sub-macerals). Measurement of light reflectivity from the polished surface of a coal is one such technique that has been widely used to measure rank. Mean maximum reflectance (in polarised light), under oil immersion, of telocollinitic vitrinite,

Rank & Reflectivity

REACTIVES

(moss)

o - EMERALO x - AP 2O9 GREGOF/ a - AP 2OA/ 2I8 OAKY CREEK + - ai zoe t ag GERMAIT oREEX A - MORANBAH tr - GOONYELLA - MAXIMUM FLUIOITY (ddM)

-too 40 o.6

l.t

t.2

1.3

1.4

1.5

1.6

MAXIMUM REFLECTAI.ICE % IN OIL Figure 2. Variations in Gieseler Plastometer maximum fluidity (dial divisions per minute) with coal rank (as depicted by mean maximum reflectance of vitrinite) and coal type (as depicted by vitrinite + liptinite percentage), of various coals in the German Creek Formation and the Moranbah Coal Measures, central Queensland. has proven to be particularly accurate in rank

determination, and has the further advantage of being a quick, cheap, and reproducible technique.

RANK AND COKING COAL The physical and chemical properties ofcoal change quite dramatically with increasing rank. One of the main trends is the emission of volatile substances

(hydrogen, oxygen, nitrogen, sulphur) with a resultant relative increase in carbon content. [It is significant to note that these volatile substances are emitted in the form of methane (CHa), carbon dioxide (C0z), carbon monoxide (CO), free nitrogen (Nz) and hydrogen sulphide (HzS)1. When coals are artificially heated, they readily emit volatiles and leave a carbon-rich residue. They also show the potential to become fluid with rising temperature. Low rank coals emit their contained volatiles at low temperatures, prior to any melting, and produce a crumbly powdery residue. High rank coals emit their volatiles at high temperatures.

Medium rank coals, however, emit volatiles at the

same temperatures at which they become fluid. This coincidence causes the coal to froth. The weakly resistive liquid coal material frlls with bubbles to

form an expanded, carbon-rich material with a large surface area and a strong resilient framework, known as'coke', which is used predominantly in the smelting of iron ore.

In Australia, coking coals (those that will form coke) generally fall in the reflectance range 0.80 to 1.80%, with high fluidity coals (100 dial divisions per minute (ddm) maximum fluidity as measured by the Gieseler Plastometer test) occurring in the narrower range 1.00 to L.40Vo (Figure 2). The fluidity also

depends on the petrographic constitution. As it is chiefly the vitrinitic components that become fluid, those coals with high vitrinite contents become the

most fluid for a given rank level.

The type of vitrinite is also important. Coals with a high desmocollinite content (formed primarily from cellulose-rich plant tissues) show higher fluidities compared to coals with high telocollinite contents (formed from lignin-rich plant tissues) (Beeston, 1983; 1.985). Sediments containing coals that have reached the rank levels suitable for use as coking feedstock occur in the Permo-Triassic Bowen Basin, Cooper Basin and Jurassic Laura Basin in Queensland, and the Permo-Triassic Gunnedah and Sydney Basins in New South Wales. Those in the Cooper and Gunnedah Basins occur at depths that preclude their amenability to mining under present day technology (see papers by Beeston and Tadros in this volume). Those in the Bowen and Sydney Basins have been raised to shallow depths through uplift and erosion, and are amenable to shallow underground and opencut mining (Figure 1).

RANK AND STRUCTURE Vitrinite reflectance can be a useful tool in interpreting depositional structures and structural deformation. Reflectivity increases with increasing temperature and time (and therefore generally with depth of cover), and reaches a maximum with maximum depth of burial (Figure 3). After uplift and erosion, however, and a consequent decrease in depth (and temperature), the reflectivity remains at the same maximum value.

Geology of Australian Coal Basins

Collinsville Shelf

SHH1.

20km

4. Isoreflectance map of the German Creek

complex history of uplift and erosion has created a present basin margin unlike the previous subsidence margin, which would have run north-south somewhere west of Emerald (Figure 4).

2. Theodore to Baralaba. o ,EFLECTANCE

(moxtmum n ot/)

Figure 3. Average depth-reflectance profile for the Bowen Basin, Queensland. Whereas modern-day down-hole temperature measurements can be misleading with regards to coalification temperatures, the vitrinite reflectance gives a measure of maximum temperature (and therefore depth) attained, and consequently provides an indication of how much subsequent erosion has

taken place. Many of the coals presently near the surface in the Bowen and Sydney Basins are semi-anthracitic to anthracitic in rank (>3.00Vo Rv max) indicating that they were previously buried to a far greater depth (Beeston, 1985; Figure 3), and that up to several kilometres of strata have been eroded since maximum coalification took place. Reflectance maps such as shown in Figure 2 indicate the shapes of basins at the stage of maximum burial, and therefore delineate such structures as basement highs and margin uplift. The isoreflectance contours in general tend to be parallel to the margins of the basin, particularly if post-depositional deformation has not been severe. In the Bowen Basin, however, two areas in particular show a variation from this

trend.

l. Comet Ridge. Whereas the reflectance trends along the Collinsville Shelf roughly parallel the present basin margin and run essentially north-south, their continuation on the Comet Ridge also continues to run north-south, even though the present subcrop trends east-west. It is obvious in this area that a

The reflectance trends on the eastern margin of the exposed Taroom Trough, between Theodore and Baralaba, show a westward increase towards the centre ofthe trough, but do not lie parallel to the trough margin. Reflectance values are around 0.57o at subcrop near Theodore, but increase to 2.07o at subcrop at Baralaba to the north.

Ifthe isoreflectance contours can be assumed to

normally parallel the subcrop, based on the model of rank increase through depth ofburial seen elsewhere in the basin, then some significant event must have occurred to vary them to their present configuration. Based on the suggestion by Mallett & others (1990) ofTriassic thrust faulting in the area, and applying the rank gradients determined for the region generally (Beeston, 1981), an estimate can be made of the amount of loading required to create isoreflectance trends equivalent to the present configuration. This would correspond to a hypothetical thrust wedge (or equivalent) running NW-SE, parallel to the present thrust system east of Banana and Baralaba and forming an extension of the folded zone to the north. A wedge approximately 1.25km thick at the present thrust zone and diminishing to zero thickness near Theodore would be required (roughly equivalent to a reflectance difference of 0.6Vo). This is in agreement with the thrust slices suggested for the area by Miyazaki & Korsch (1993). Such an interpretation suggests that, at the time of maximum depth of burial and coalification, the region around Moura./Baralaba either received an increase in subduction through thrust compaction, was uplifted by several kilometres through thrust fault repetition, or suffered a combination of both. As the present eroded subcrop surface parallels the

Rank & Reflectivity

(/r,

-1.0 -

lsoreflectance

Figure 5. A model of low-angle overthrusting to explain the, reflectan-ce_anomaly in-tne Baralaba-Moura ared. A. Rank lines tb be expected due to basin burial increase towards the axis. B. Ilypothetical overthrust of material prior to maximum coalification. C. Resultant isoreflectance trends that are observed today. Taroom Trough, the'mountain-building' model

(Figure 5) is preferred.

Isoreflectance maps, including cross-sections, can also aid in the assessment of post-depositional

structural deformation. This is well demonstrated in HOM Shotover 1, drilled on the Shotover Anticline in the central Bowen Basin (Figure 6). The depth-reflectance gradient indicates at least one major thrust fault at around 1450m, with a resultant repetition of the coal measures at 1000m and 1800m.

Similar reflectances on slickensided coal at around 1450m suggest that the same coal is included within the fault brecciation. Other anomalous results in the well are interpreted as cavings from shallower depth. This structural interpretation is substantiated by repetition of in-seam geophysical log characteristics (Hbuston Oil & Minerals, 1977) and by seismic reflection data (Geosurveys of Australia Pty Ltd, 1970).

RANK AND INTRUSIONS Coal shows considerable change with increasing temperature over geologic time, as outlined earlier. When subjected to artificial rapid temperature increase it demonstrates remarkable reactions, such as described under'rank and coking coal'. It is not surprising, therefore, that igneous bodies have had a noticeable effect upon coals in intruded strata.

In Queensland it has been estimated that some

5000Mt of coal has been lost from the Bowen Basin through the action ofigneous intrusions, and even then this figure does not take into account the amount of heat-affected material eroded prior to the present day (Hamilton, 1985). This, of.course, ielates to ioal seams that have been directly intruded, such as the Havilah seam exposed in Rosella Creek, north Bowen Basin (Figures 7 and 8). The Havilah seam reaches thicknesses of up to 5m, and crops out for about 250m along the bank ofthe creek. Small to large lenticular masses of fine-grained, acid intrusive rock are dis-persed throrighout the seam. The remainder of the coal

Geology of Australian Coal Basins

DEPTH . REFLECTANCE PROFILE

HOM SHOTOVER

. - Cullings Somple * - Coving A - Foult Cool

OEPTH

Figure 7. Outcrop of the intruded Havilah Seam in Rosella Creek.

\ \I

*\. * *t\

+. \ AA A

Figure 8. Relict banding and lenticular intrusive pods observed in the Havilah Seam. shows the original bedding planes, with the duller bands intact and the brighter bands swollen into an METRES

open coke-mosaic structure.

At the margins of the intrusive pods the coke displays a radial contraction structure. In some cases, evidence of fluidal mobility of the coal can be seen, with stringers of resolidifred coke running into the intrusive body. Release of volatiles at the margins of the intrusive pods has altered the igneous rock to a'white-trap', (Kisch & Taylor, 1966), yielding carbonates, silica and kaolinite. These minerals became mobile at the time of formation, and veining is evident both in the intrusive and the coke.

o, a

+ +

++ +

f 1.8

2.O

Figure 6. Depth-reflectance profile for HOM Shotover I showing increase in reflectance with depth, disruption of profile by fault repetition, and the effect of sample cavings.

But what is the effect on unintruded coal seams? Analysis of seams encountered in a fully cored borehole in the northern Bowen Basin (Wodehouse NS1) indicates that carbonisation by intrusion was only local, with the effects dissipating within single seams in such a way that some parts of the seams were completely unaffected (Beeston, 1978; Figure 9). Optical properties (reflectance, bireflectance) of the macerals were affected by factors including the temperature of the intrusion, the confining pressure, and volatile matter retention, with irregularly distributed proportions of volatile matter being recorded. Although the base results indicate that the unaffected coals are of semi-anthracite rank (1.90 to

Rank & Reflectivity

88 2.9 \Vo refl ectance ), heat-affected vitrinite shows reflectances in excess of IO.O7o.

RANK AND MACERAL DEFINITION In order to characterise the reactivity of a coal, it is useful to distinguish the reflectance distribution of the various components. Certain vitrinites and inertinites in the one coal may have overlapping reflectance ranges, yet do not function in a like

manner either physically or chemically. Some of these inertinites, however, are considered to have some degree of reactivity during carbonisation, and it has been suggested (Diessel, 1982) that this can be determinedpartly by their reflectivity. A reflectogram can be produced for the coal, using a combined reflectance and maceral analysis technique. Random reflectance is measured (without polarised light), which does not require sample rotation. Several reflectograms have been calculated (Beeston, 1983) for coal samples with similar maceral proportions from the Rangal Coal Measures, central Queensland (Table 1; Figure 10). Three important features of these coals are demonstrated.

At any rank (designated by mean maximum reflectance of telocollinite), there is wide spread of vitrinite reflectance and a wider spread of inertinite reflectance.

. Figure 9. Depth-reflectance profile, Wodehouse NS=l, north Blowen Basin (after Beeston, 1978).

With increasing rank, the mean reflectance of vitrinite and inertinite both increase, with vitrinite showing the greatest gain.

o In the low and medium rank coals, the vitrinite reflectance range overlaps the inertinite reflectance range, pertaining to about20Vo inertinite by volume. This overlap increases dramatically in the high rank coals. [In meta-anthracites the mean reflectance of

vitrinite exceeds that of inertinite (Alpern & Lemos de Sousa, 1970)l .

RANK AND OIL GENERATION The generation ofpetroleum from buried orgalic matter is generally considered to be a result of chemical cracking through increase in temperature. An inventory of occurrences in petroleum-bealing sedimentary basins has generally led to belief in a threshold temperature above which oil begins to form, and further, a maximum temperature above which oil no longer remains stable; the two temperatures defining an oil window.

Vitrinite reflectances of 0.7Vo and 1.37o ate

commonly cited as the approximate values defining this winclow (Kantsler & others, 1978; Hood & :

Tah:le 1;,Petroglaphic an€lysbs $inerd'fte,b . basis):bf cba-ib selec_ted i-or reftecto-gbCfi.,,

analysi6.

Sample

Vitrin. Exin. Inert. Vo

RftrXT REFLECTAiICE

tr' OIL

reflectograms of wen Basin" Queensland.

Emerald Curragh L. Lindsay Strathconan Yarrabee

trace trace

bl) 54 50

Geology of Australian Coal Basins

44 46 45 46 50

max

Ri Rv andou andon

0.73 L.22 1.57 2.25 2.54

0.59 1.16

0.68

t.49

2.L0 2.50 2.69

1.96 2.41

t.72

others, 1975; Teichmiiller in Stach & others, 1975). Depth-reflectance profiles determined for vitrinite from borehole data are useful in relating geothermal limits to stratigraphy, and compilation studies can then relate regional geothermal trends to the distribution of potential source rocks.

RANK TRENDS AROUND AUSTRALIA

Ashford Basin The Permian Ashford Coal Measures crop out as a discontinuous linear belt from west of Bonshaw, on the Queensland/New South Wales border, to south of Ashford in New South Wales (see Flood, this volume). Britten (1975) records a reflectance from

the basin of L.067o.

Arckaringa Basin The Permian Arckaringa Basin comprises a thin, widespread, intracratonic sequence of Carboniferous to Permian rocks wholly contained within northern South Australia (see McConachie & Dunster, this volume). Reflectances recorded by Beeston & Wood (1986) from a borehole in the north include a value of 0.25Vo for desmocollinite and 0.3LVo for

gelocollinite.

Bowen Basin The Permo-Triassic Bowen Basin," central-east Queensland, is discussed elsewhere in this paper, and by Mallett & others (this volume). It contains coals with vitrinite reflectance ranging from 0.35Vo to 3.57o. Rank levels are generally accepted to be the result of coalification from temperature increases due to depth of burial during Permo-Triassic and/or Jura-Cretaceous depositional/structural events.

Calen Coal Measures The Calen Basin (Brakel, 1989), which now occurs

(see Hocking, this volume). The coals are classified by chemical analysis as sub-bituminous in rank.

Collie Basin Known preservation of the Sakmarian to Late Permian Collie Coal Measures occurs in three separate structural basins at Collie, Wilga and Boyup Brook (see Ashton & others, this volume). Vitrinite reflectance values reported from these coals range from 0.3 to 0.\Vo.

Cooper Basin The Permo-Triassic Cooper Basin occurs in south-west Queensland beneath the Eromanga Basin (Figure 1; see also Beeston, this volume). Reflectances of vitrinite measured in the basin range from <0.3Vo to 57o (Figure 11; Hawkins & others, 1989). Geothermal gradients show a marked variation, with high gradients attributed to the presence of a granitic basement.

Eromanga Basin The Eromanga Basin lies in the south-west of Queensland, and contains Jurassic to Cretaceous strata, some of which are coal-bearing (see Goscombe & Coxhead, this volume). Vitrinite reflectance measurements for some of these coal-bearing strata range from <O.57o to I.!Vo (Hawkins & others, 1989). The areas west of the Canaway Fault appear to be those that have experienced the highest geothermal gradients

(Figures 11 and 12).

Galilee Basin The Galilee Basin in central Queensland contains Carboniferous to Triassic sediments including several coal-rich formations (see Scott & others, this volume). Isoreflectance maps compiled for the major coals shows two main geothermal areas, one in the

as two outcrop areas north-west of Mackay (see

Brakel, this volume), is occupied by the mid-Permian Calen Coal Measures. A reflectance value of 3.777o recorded from the basin is considered to result from the metamorphic effect of extensive intrusions of probable Cretaceous age (Koppe,

NAPPAMERRI TROUGH ( DIO Baryulah 1 )

1975a).

Callide Basin The Callide Basin was formed as a downwarp of Palaeozoic sediments of the Yarrol Basin during the early Triassic, and is overlain by the Jurassic Precipice Sandstone (see Biggs & others, this volume). The vitrinite reflectance value of O.5L7o measured on coal from the basin suggests only moderate burial beneath the overlying Jurassic

strata.

Canning Basin The Canning Basin occurs in the northern part of Western Australia. It contains shallow marine, paralic and terrestrial deposits, ranging from Ordovician to Early Cretaceous (see Yeates, this volume). Vitrinite reflectance measurements in petroleum wells in the basin range fromO.37o to 3.007o at depths up to 3000m (Burne & Kantsler, 1977; Kantsler & others, 1978).

0.50 0.70 0.90 1.10 1.30

Carnarvon Basin

1.50

Rv. max%

The Carnarvon Basin is an elongate basin extending along the western and north-western coastline of Western Australia between Geraldton and Karratha

Figure 11. A depth-reflectance profile calculated foi a borehole through the Eromanga and Cooper Basins, in the Nappamerri Trough area (from Hawkins & others, 1989).

Rank & Reflectivity

n [,r (r.-J-

limit ot 'basal Jurassic' unil

Rv.max<O.5 %

Fv,max O.5 - O.7 %

l,'.1

Rv.max O.7 - 0.9 %

ffi

Rv,max O.9 - 1.3%

I iiiil::

i:iiiil

Rv,max >1.3 %

'basal Jurassic' unit

Figure 12. Vitrinite reflectance zones for the top of the 'basal Jurassic' (from Ilawkins & others, 1989). Koburra Trough in the east and one in the Lovelle Depression in the west (Hawkins & Green, L993; Scott & Beeston, 1993). Overall, values range from 0.4Vo to l.lVo (Scott & Beeston, 1993). The lower Aramac Coal Measures are confined to the western central part of the Koburra Trough, with reflectances ranging from 0.47% (Beeston, 1976) to 0.777o (Jackson & others, 1981) being recorded, and to the Lovelle Depression, where reflectances range ftom 0.427o to 0.69Va.

Gippsland Basin The Gippsland Basin is a post-Jurassic passive margin basin located in the south-eastern part of the

Australian continent (Figure 1). It occupies a total area of about 46 000km', with aroundTs%olying offshore beneath the waters of Bass Strait and the Tasman Sea. The basin is filled with Cretaceous and Tertiary terrestrial and marine sediments, which reach a thickness of more than 10 000m in the offshore depocentres and contain, in addition to coal, a substantial position of Australia's known petroleum resources. Reflectances range ftorn <0.47o to 7.0Vo over a depth range from 1 to 3.5km (Kantsler & others, 1978).

Gloucester Basin The Gloucester Basin is a north-south trending, asymmetrical synclinal structure located north of Newcastle (see Hughes, this volume). Vitrinite reflectance varies from 0.7IVo in the south to a

maximum of around !.207o in the east-central part of the basin (Hughes & others, 1984). The vertical gradient of vitrinite reflectance also varies with geographical location. In the north it is around 0.4% per 100m, in the central part of the basin around 0.06Vo per 100m and on the western side of the basin it is 0.047o per 100m.

Ipswich Basin The Ipswich Coal Measures form a coal-bearing late

Triassic unit unconformably overlying the Carboniferous Neranleigh - Fernvale beds and being unconformably overlain in places by Late Triassic Early Jurassic sediments of the Bundamba Group -of the Moreton Basin (Mengel, 1975; Staines & others, this volume). Vitrinite reflectances range from 0.92

to t.29Vo, presumably the result of considerable burial beneath now-removed Moreton Basin sediments.

Laura Basin The Laura Basin lies in north Queensland, to the east of the Coen Inlier and north of the Hodgkinson Province. It contains Jurassic-Cretaceous sediments which are partly correlative with similar sediments in the adjacent Carpentaria Basin to the west.

Vitrinite reflectance measurements from the Bathurst Range area range ftom <L.\Vo to l.8Va, with much of the variation showing an increase in a

south-easterly direction through the one sequence of coal measures. This rank range is the highest for Jurassic coals in Australia, producing coals with coking properties.

Leigh Creek The Leigh Creek coalfield is located in central South Australia approximately 55Okm north of Adelaide (Springbett & others, this volume). The field consists of four small isolated Triassic basins spread over a distance of 20km. Leigh Creek coals are low rank (Lignite A to Sub-bituminous C).

Maryborough Basin The Tiaro Coal Measures form a coal-bearing sequence of late Jurassic age in the Jura-Cretaceous Maryborough Basin, a fault block depression on the eastern margin of the New England Orogen (KoPpe, 1975b; Day & others, 1983). Reflectances range from 1.98 to 3.02Vo, the result of extensive intrusive

activity in the area.

The Cretaceous Burrum Coal Measures are exposed in the Burrum Syncline of the Maryborough Basin. The coal sediments are overlain unconformably by Tertiary sediments (Koppe, 1975b). Reflectances range from 0.94 to l.O07o, suggesting that a considerable amount of Cretaceous material must have been removed. The Tertiary Elliott Formation is 2m thick (Day & others, 1983).

Geology of Australian Coal Basins

Mount Mulligan

Sydney - Gunnedah Basin

The Mount Mulligan Coal Measures are preserved in a fault block preserved as a mesa. Stratigraphically they unconformably overlie a Devonian basement, and are overlain unconformably by Triassic sediments (Hawthorne , 197 5). A vitrinite reflectance of 0.817o is recorded from a coal sample taken from disused mine workings. The overlying Triassic Pepper Pot Sandstone is 300m thick (Day & others, 1983), and the rank ofthe coal would suggest that a considerable amount of overburden has been

The Sydney-Gunnedah Basin is up to 600km long and 200km wide, and extends offshore to the edge of the continental shelf. It is continuous with the Bowen Basin to the north (see chapters this volume). Reflectances measured in the Sydney Basin range up to >2.007o, with isoreflectance maps for the surface showing an increase from 0.6Vo in the north-west to >l.}Vo in the east, and the top of the Permian coals from <0.7Vo in the north-west to >L.47o in the east (Figure 1; Middleton, 1989). Detailed discussion on rank in the Sydney Basin can be found in Middleton (1989) and Diessel (1975).

removed.

Nambour Basin The Nambour Basin is a small Jurassic-Cretaceous basin on the coast of southern Queensland (McKellar, 1994). A reflectance measurement from the Landsborough Sandstone at Caloundra of l.28Vo suggests considerable burial and metamorphism prior to uplift.

Rank in the Gunnedah Basin it is generally quite low, ranging from <0.5 to 0.7Vo (Hamilton & others, 1988; 1994).

Tarong Basin The Tarong Basin is a north-south elongated

strike-slip pull-apart basin within the late

Oaklands Basin

Palaeozoic Yarraman Block (see Pegram this

The Oaklands Basin is a Permo-Triassic sedimentary basin in southern New South Wales, totally concealed by the Cainozoic sediments of the eastern Murray Basin (see Yoo, this volume).

1975).

volume). Vitrinite reflectance values range from 0.57 to 0.59Vo, suggesting that maximum depth of burial was not particularly great, beneath the heavily eroded overlying Oakvale Conglomerate (Wilson,

Otway Basin

Tasmania Basin

Brown coals of the Otway Basin occur within Early Tertiary sediments around the eastern margins of the Lower Cretaceous Otway Ranges and within mid-Tertiary sediments extending from Altona to the Bacchus Marsh area in the north-east part of the basin (see Barton, this volume). Vitrinite reflectances recorded from the basin range from <0.57o to 6.UVo, indicating a variable geothermal history for different parts ofthe basin (Cooper & others, 1993).

The Tasmania Basin is a structural basin extending over a large part of central and eastern Tasmania (see Bacon, this volume). The Early Permian coals in the basin have vitrinite reflectances ranging from 0.45 to 0.57o,w}aile the Late Permian coal measures have values commonly around 0.5 to 0.6Vo.

Perth Basin The Perth Basin is a half-graben extending from the Murchison River to the south coast of Western Australia, a distance of about 1000km. It is bounded to the east by the Darling Fault and to the north by the Northampton Block. Its western and southern offshore limits have not been clearly defined, but

they probably lie under the continental slope. Vitrinite reflectance ranges from 0.3 to >4.00Vo, over depths from the surface to almost Skm (Kantsler & Cook, 1979).

Styx Basin The early Cretaceous Styx Coal Measures unconformably overlie Permian sediments in the elongate north-south trending Strathmuir Synclinorium. They are overlain in part by thin Quaternary sediments. Reflectances of vitrinite range from 0.82 to 0.93%, suggesting that considerable overburden has been removed.

Surat Basin The Surat Basin forms part of the Great Australia Basin. It is separated from the Eromanga Basin by the Nebine Ridge to the west and from the Clarence-Moreton Basin by the Kumbarilla Ridge to the east (see Goscombe & Coxhead, this volume). Vitrinite reflectance values at the base of the sequence range up to 0.8Vo, with reflectances in the major coal measures (the Walloon Sub-Group) ranging from <0.5 to >0.657o (Scott & Beeston, 1993).

REFERENCES ALPERN, B. & LEMOS DE SOUSA, M.J., 1970: Sur le pouvoir reflecteur de la vitrinite et de la fusinite des hoilles. Cornpt Rendu Academic Science Paris,

271,956-959. BEESTON, J.W., 1976: The petrography of some shallow coal seams of the eastern flank of the Galilee Basin. Queensland Gouernment Mining Journal, 78 (908), 264-267. BEESTON, J.W., 1978: Coal reflectivity, rank and carbonisation in Departmental borehole Wodehouse NS 1. Queensland Gouernrnent Mining Jou.rnal,79, 159-164. BEESTON, J.W., 1981: Coal rank variation in the Bowen Basin. Geological Survey of Queensland Record l98L/48. BEESTON, J.W., 1983: The role of coal petrology in the Geological Survey of Queensland. Geological Survey of Queensland Record L983/2. BEESTON, J.W., 1985: Coal rank and type variation in the Bowen Basin, and the influence on coal quality. Bowen Basin Coal Symposium. Geological Society of Australia Abstracts, 17, 185-190. BEESTON, J.W. & WOOD, G.R., 1986: Quantitative autofluorescence variation in a low rank Permian palynomorph assemblage. Geological Suruey of Queensland Publication, 387 , 29-40 . BRITTEN, R.A., 1975: Ashford Coal-field, N.S.W. In Traves, D.M. & King, D. (Editors): Economic 2: Geology of Australia and Papua New Guinea Coal. Australasian Institute of Mining and

Metallurgy, M onograph, 6, 258-260.

Rank & Reflectivity

92 BURNE, R.V & KANTSLER, A.J., L977: Geothermal

constraints on the hydrocarbon potential ofthe Canning Basin, Western Australia. BMR Journal of Australian Geology & Geophy sics, 2, 27 1-288.

COOPER, G.T., HILL, K.C. & WLASENKO, M., 1993:

Thermal modelling in the eastern Otway Basin. The APEA Journal, 33(l), 205-214.

DIESSEL, C.F.K., 1975: Coalification trends in the Sydney Basin, New South Wales..In Campbell, K.S.W. (Editor): Gondwana Geology, Australia. National University Press, Canberra, 195-309. DIESSEL, C.F.K., 1982: On the reactivity of inertinite macerals in coal during carbonisation. The Uniuersity of Newcastle, Departm.ent of Geology Research Reports , L. GEOSURVEYS OF AUSTRALIA PTY LTD, 1970: Final report, Shotover seismic survey, A.P. 14lP, Queensland, for United Petroleum Reserves N.L. Retained by the Department of Minerals and Energy, Queensland, as C.R. 3266.

KANTSLER, A.J. & COOK, A.C., 1979: Maturation patterns in the Perth Basin. The APEA Journal, 19(1), 94-106.

KANTSLER, A.J., SMITH, G.C. & COOK, A.C., 1978: Lateral and vertical rank variation: Implications for hydrocarbon exploration. The APEA Journal, 18(1), 143-156.

KISCH, H.J. & TAYLOR, G.H., 1966: Metamorphism and alteration near an intrusive-coal contact. Economic Geology, 61, 343-361. KOPPE, W.H., 1975a: Calen Coal Measures, Q. /n Traves, D.M. & King, D., (Editors): Economic geology of Australia and Papua New Guinea Coal. Australasian Institute of Mining and

- 2.

Metallurgy, Monograph, 6, 250-25L. KOPPE, W.H., 1975b: Maryborough Basin, Q. 1z Traves, D.M. & King, D., (Editors): Economic geology of Australia and Papua New Guinea Coal. Australasian Institute of Mining and

- 2.

Metallurgy, Monograph, 6, 320-323.

HAMILTON, D.S., NEWTON, C.B., SMYTH,M., GILBERT, T.D., RUSSELL, N., McMINN, A. & ETHERIDGE, L.T., 1988: The petroleum potential ofthe Gunnedah Basin and overlying Surat Basin sequence, New South Wales.The APEA Journal, 28(r),218-24L.

MALLETT, C.W., RUSSELL, N. & McLENNAN, T., 1990: Thermal history of the Bowen Basin. In Beeston, J.W., (Compiler): Bowen Basin

HAMILTON, D.S., NEWTON, C.B., SMYTH, M., GILBERT, T.D., RUSSELL, N., McMINN, A. & ETHERIDGE, L.T., 1988: Petroleum potential of the Gunnedah and Surat Basins, New South Wales. Geological Suruey of New South Wales,

McKELLAR , J.L., 1994: Stratigraphic relationships in the Nambour Basin, southeastern Queensland, Queensland Geology, 6, L-17 .

Memoir, Geology 12, 367-388.

HAMILTON, L. H., 1985: Igneous intrusion in the Bowen Basin. 1n, Bowen Basin Coal Symposium, Geological Society of Australia Abstracts, L2, 107-108.

HAWKINS, P.J., ALMOND, C.S., CARMICHAEL, D.C., SMITH, R.J. & WILLIAMS, L.J., 1989: Kerogen characterisation, and organic and mineral diagenesis of potential source rocks in Jurassic units, southern Eromanga Basin, Queensland. In, O'Neil, B.J., (Editor): The Cooper and Eromanga Basins, Australia. Proceedings of the Petroleum Exploration Society of Australia, Society of Australian Engineers, Australian Society of Exploration Geophysics (SA Branch), Adelaide, 583-599.

HAWKINS, P.J. & GREEN, P.M., 1993: Exploration results, hydrocarbon potential and future strategies for the northern Galilee Basin. The APEA Journal, 33, 280-296. HOOD, A., GUTJAHR, C.C.M. & HEACOCK, R.L., 1975: Organic metamorphism and the generation of petroleum. American Association of Petroleum Geologists, Bulletin, 59(6), 986-996. HOUSTON OIL AND MINERALS,1977: Final Report, No. L Shotover, Shotover Anticline Prospect, Queensland, Australia. Held by the Department of Minerals and Energy, Queensland, as CR5457. JACKSON, K.S., HORVNIH,Z. & HAWKINS, P.J., 1981: An assessment ofthe petroleum prospects

for the Galilee Basin, Queensland. The APEA

J ournal, 2l(l), 17 2-186.

Symposiurn L990. Geological Society of Australia (Queensland Division), 15-20.

MENGEL, D.C., 1975: Ipswich Coalfield, Q. In Traves, D.M. & King, D., (Editors): Economic geology of

Australia and Papua New Guinea

2. Coal.

- Metallurgy, Australasian Institute of Mining and . Monograph, 6, 290-297 MIDDLETON, M.F., 1989: Chapter 25.ln, Harrington, H.J., Brakel, A.T., Hunt, J.W., Wells, A.T., Middleton, M.F., O'Brien, P.E., Hamilton, D.S., Beckett, J., Weber, C.R., Radke, S., Totterdell, J.M., Swaine, D.J. &Schmidt, P.W., 1989: Permian coals of eastern Australia. Bureau of Mineral Resouces, Bulletin, 231, 333-35 1.

MIYAZAKI, S. & KORSCH, R.J., 1993: Coalbed methane resources in the Permian of Eastern Australia and their tectonic setting. The APEA Journal,33, 161-175. SCOTT, S.G. & BEESTON, J.W., 1993: Coal seam methane potential of some Queensland coal basins. New deueloprnents in coal geology - a symposium. Coal Geology Group (GSA Inc.), Brisbane, 81-94. STACH, E., MACKOWSKY, M-Th, TEICHMULLER, M., TAYL.OR, G.H.,CHANDRA, D. & TEICHMULLER, R., L975: Stach's textbook of coal petrology. Gebruder Borntraeger Berlin

Stuttgart.

WILSON, R.G., 1975: Tarong Coal-field, Q. 1n Traves, D.M. & King, D., (Editors): Economic geology of

Australia and Papua New Guinea - 2. Coal.

Australasian Institute of Mining and Metallurgy, Monograph, 6, 288-290.

Geology of Australian Coal Basins

ffiinerals

and inorganic

constituents

As defined by the Standards Association of Australia (1982), the term "mineral matter" refers to "the minerals and other inorganic material in and associated with coal". This encompasses three classes of material, namely: a) discrete, crystalline mineral particles in the coal or associated strata (e.g. intra-seam non-coal bands); b) inorganic elements or compounds, with the exception ofnitrogen or sulphur, incorporated in the coal's organic molecules; c) dissolved inorganic ions or compounds in the

coal's pore or surface water.

CR Ward

and DJ Swaine

Kiss & King (1977, 1979) have pointed out that the non-crystalline inorganic materials are of great significance in low rank coals, such as the brown co-als of Victoria, while Ward (1978) and other workers have shown that the inorganic fraction of higher rank (e.g. bituminous) coals is dominirted by crystalline components in true "mineral" form.

Apart from nitrogen and sulphur, the principal inbrganic elements in most Australian coals are essentially the same as the elements found in relative abundance in other crustal rocks. A wide range of other elements, however, may be present in trac! amounts (Swaine,1979; Cahill & Mills, 1983), either incorporated in some way within-the crystalline mineral fraction or intimately associated with the coal's organic matter. Many of the minerals and other inorganics in Australian coals react or undergo changes at high temperature, and some of the compone!ts of the mineral matter may be lost from the solid phase during carbonisation or combustion processes. The ash of-the coal therefore typically represents only the non-volatile or non-combustible residue of the mineral matter. The relation between mineral matter and ash is complex, particularly in low-rank coals. Kiss (1982), for example, indicates that up to one-third of the ash produced by combustion of Victorian brown coals may be derived from fixation of organic sulphur by calcium, sodium or magnesium originally present in non-crystalline form.

EARLY II{\MSTIGATIONS IN BITUMINOUS COALS Although many of the pioneering investigations of Australian coal deposits made at least passing reference to the occurrence ofparticular mineral or inorganic constituents, very little_specifrc infoimation on aspects such as ash composition or mineral matter content of Australian bituminous coals is available from reports published prior to the 1950's. Notes on the percentage of mineral matter in a number of Queensland coals, however, based on ash determinitions for prepared, mineral-rich composites, are given by de Jersey (1949). A number of different techniques, then recently developed for mineral matter determination, were evaluated for Australian bituminous coals by Brown, Durie & Schafer (1959). These included acid digestion of the mineral components (Radmacher & M6hrhauer, 1955), heating for a protracted period at 370oC, and calculations based on ash percentage and other chemical data (King & others, 1936). Ash composition and several other inorganic chaiacteristics for Australian bituminous coals were also discussed by Brown, Clark & Durie (1959) and

Minerals and Inorganic Constituents

Clark & Swaine (1964), while Clark & Swaine (1962) produced a comprehensive account of the trace elements in coals from a range of New South Wales frelds. Early petrographic studies of Australian coals, such as the work of Marshall (1953), provided further information on the minerals and their mode of occurrence, while more detailed notes on particular components were given by Balme & Brooks (1959), Lawrence & others (1960) and Cook (1962). Kemezys & Taylor (1964) subsequently extended this work tb produce a very comprehensive discussion of the minerals in Australian bituminous coals from the petrographic point of view.

LATER IT{\'E STIGATIONS The traditional tools of microscopy and chemical a-na!y.sis_ supplemented during -were the 1960's and-progressively 1970's by a number of sophisticated instrument-al techniques. Warne (1964) investigated the minerals present using differential thermalanalysis on the whole coal sample, while Jones (1970) described the use ofx-radiography to indicate macroscopic mineral distribution in coal seam drill

22121

\ izLi2o GP

l'ilt i

/ \-"tSl ,ilrtrJ

?oo/

Cu Ku Rad iat ion

Oxidising the organic matter and isolating the minerals by ashing bituminous coal at low temperature (120-L50oC) in an electronically-excited oxygen plasma, applied in the USA by Gluskoter (1965), was evaluated for Australian materials by Frazer & Belcher (1973), who showed it to represent the most reliable of the available methods fof determining the percentage of total mineral matter. Ward (1974) also investigated the use of hot, concentrated hydrogen peroxide to remove the organic matter and isolate an unaltered mineral fraction, finding it a potentially useful substitute, but with more limited application than the plasma ashing process.

Mi!eralogical studies of peroxide or oxygen plasma residues, using x-ray diffraction and othir analytical methods, have provided valuable information about the mineral species actually represented in Australian coals, particularly regarding minerals, such as the clay minerals, that are difficult to ldentify precisely under the microscope (Figure 1). Summaries of the minerals present, as indicated by these techniques, are givenby Doolan & others (1979) and Ward (1978, 1986). Studies of ash chemistry, supported in some cases by isolation and study of the actual mineral matter, have also been carried out by authors such as Shibaoka (1971; L972), Ward (1980), Hunt (1989), Slansky (1984; 1985) and Tadros (1983) for a range of Australian bituminous and sub- bituminous coals. These have attempted to relate particular elements to components in the mineral matter, or establish the influence oftectonic and depositional processes on mineral distribution in individual coalieams. Further studies, including isotope geochemical evalga-tions of particular mineral components, were carried out by Gould & Smith (1979), Botz & Hart (1983) and Botz & others (1986), providing information, among other things,-on the piobable temperatures and relative time sequences of mineral formation.

MINERAL MATTER II\TYESTIGATIONS IN BROWN COALS

Ap Ap

cores. Durie & Swaine (1971) also discuss early work involving the application ofx-ray diffraction and infra-red absorption spectrometry to whole-coal materials.

Degrees 20

Figure 1. X-ray diffractograms of oxidation residues from a range of Australian bituminous coal seams - Ward, 1978. Ap apatite Ct . calcite Cq - cocquimbite D - dolomite E - expandable-lattice clay minerals F - feldspar Go - goyazite-group mineral Gp - gypsum I - illite J - jarosite K - kaolinite Q - quartz S - siderite

Ash, sulphur and other characteristics of the brown coals of Victoria are discussed to some extent by early workers such as Edwards (1953), and several noteworthy mineral occurrences in particular deposits are described, mainly on the basis of macroscopic observations, by Baker (1946), Edwards & Baker (1951) and Gloe (1960). These and other aspects of brown coal mineral matter, as well as its relevance to the combustion process, are further discussed in a comprehensive review by Baragwanath (1962). Based on a systematic chemical study, Durie (1961) showed that the bulk of the inorganic elements in these coals occurs as cations associated with

carboxylic acid groups in the actual organic matter. The possible sources of these components were further discussed by Baragwanath (1962). Other chemical studies at that time (Burns & others, 1962) also ruled out the presence or even the possibility of minerals in carbonate form.

Geology of Australian Coal Basins

Special methods were developed for mineral matter analysis of Victorian brown coals (e.g. Kiss, 1966), based mainly on direct determination of elemental abundances in the whole coal using x-ray fluorescence and analysis ofthe acid-soluble fraction by atomic absorption spectrophotometry (Kiss, 1982). This approach ultimately resulted in the recognition of crystalline mineral components and other inorganics (e.g. dissolved salts and carboxylic associates) as separate entities in reporting

analytical results (Kiss & King, tg77;1979). It also allowed the composition of the ash or other residue to be calculated from the original mineral matter data for combustion and many other technological processes.

MINERALS IN AUSTRALIAN BITUMINOUS COALS In contrast to coals from many parts of the Northern Hemisphere, where pyrite is often a major constituent (e.g. Rao & Gluskoter, L973; Ward,

I977), the mineral fraction of Australian bituminous coals is chiefly dominated by kaolinite and a limited range of other clay minerals (Ward, 1978; 1986). Quartz and a number of carbonate minerals are common accessories, and may themselves be abundant in some samples, but sulphides such as pyrite are only significant in seams that are

It may constitute up to half of the mineral matter in some samples (Ward, 1978), but mostly makes up only about L07o of the oxidation residue isolated from the seam.

Kemezys & Taylor (1964) found the quartz in Australian coals to be present either as angular, presumably detrital particles or as cell infillings, veins and lenticular bodies, originally of a chalcedonic nature, precipitated in some way within the original peat bed. Gould (1975) also described plant tissue in the coal measures near Blackwater in Queensland that had been well preserved by early-formed impregnations of siliceous material. Oxygen isotope studies by Botz & others (1986) indicate that the fine grained (chalcedonic) quartz of at least some Australian coals was formed at temperatures of about 52oC, consistent with precipitation at the brown coal stage ofrank advance.

Feldspar

Quartz

Although common in many of the non-coal strata in eastern Australia (Loughnan, 1966), feldspar is only present in small quantities, if at all, in most of the coals themselves. An exception, however, was noted by Ward (1978) in a coal from the Theodore district near Moura in the Bowen Basin. Kemezys & Taylor (1964) indicate that most of the feldspar recognised under the microscope occurs as small, relatively unaltered grains, and is probably detrital or even pyroclastic in origin.

Quartz is present in all but a few bituminous coals from eastern Australia.

Pyrite and Related Minerals

intimately associated with marine strata.A list of the minerals identified in Australibn bituminous coals is given in Table 1.

Table 1; Principal minerals in Australian bituminous coals . \trard, 1986. Silicates Quartz

Feldspar

Kaolinite

Illite

Montmorillonite Chlorite Mixed-layer clay minerals Carbonates Siderite Calcite Dolomite Dawsonite

Sulphides Pyrite Sphalerite Galena

Millerite Sulphates Gypsum

Barite Coquimbite Szomolnokite

Natrojarosite

Phosphates Apatite Goyazite Gorceixite

SiOz

KAlSigOs AlzSizOs(OH)a KAlz(AlSia)Oro(OH)z

Na(AlMg)SirOro(OH)z

(MgFeAl)e(AlSi)aOro(OH)a

FeCOs CaCOs (CaMe)COa

NaAlCOe(OH) FeSz

ZnS PbS

NiS CaSO+.2HzO BaSO+ Fez(SOa)s.9HzO

FeSOr.HzO NaFea(SOr)z(OH)e CarF(POa)g

SrAlg(POl)z(OH)sHzO BaAls(POa)z(OH)sHzO

Others Anatase

TiOz

Petrographic analyses of unweathered Australian bituminous coals almost invariably note the presence of at least some pyrite (Kemezys & Taylor, 1964), typically as cell infrllings, isolated euhedra or veins and similar bodies. Traces of other sulphides, such as galena, sphalerite and chalcopyrite, are also reported in some samples, while Lawrence & others (1960) describe the presence of millerite (NiS) in cleat fractures of one particular seam. The amount of sulphide present, however, usually represents only a small proportion of the total mineral matter, and pyrite is rarely present in sufficient concentrations to be detected in x-ray diffractograms of oxidation residues. The pyrite that does occur is most abundant in seams, such as the Greta seam of the Sydney Basin or the Garrick seam of the Bowen, that are overlain within a relatively short stratigraphic interval by marine beds. This occurrence is consistent with its formation from interaction of dissolved iron and HzS, the latter being produced by bacterial reduction of SOa in the sea water permeating through the peat bed. The virtual absence ofpyrite and other sulphides from most Australian seams

reflects the fact that the economic coals mainly occur in thick terrestrial successions, and were flushed by waters with a low sulphate content at the critical stage of their geological development. A range of iron sulphate minerals is also present in some samples (Ward, 1978), apparently derived from atmospheric oxidation of pyrite with exposure or storage. Together with other sulphates, such as gypsum, bassanite and anhydrite, however, some of these may also be produced by interaction of either pyrite or organic sulphur compounds in the course of the plasma-ashing process.

Minerals and Inorganic Constituents

Siderite Siderite is common as a minor constituent in many Australian bituminous coals (Ward, L978), and, in the absence of significant amounts of pyrite, usually represents the most abundant source of iron in the mineral matter. It mostly occurs as small nodules and similar bodies (Kemezys & Taylor, 1964), or as an infilling of cell lumens in particular maceral components (Beeston, 1981).

The mineral is thought to have been formed at an early stage in the coal's diagenetic history, probably by interaction of iron in the pore water with

dissolved COz released by fermentation of the organic matter (Gould & Smith, 1979).

Calcite and Dolomite Calcite and dolomite (or ankerite) are abundant components in the mineral matter of some Australian bituminous seams, but are almost completely absent from others. In contrast to siderite, these minerals occur mainly as veins and fracture fillings. They appear to have mostly formed at a relatively late stage of the diagenetic process, after most of the compaction and presumably most of the rank advance. Calcium is common in the inorganic matter of sub-bituminous and lower rank coals, where it occurs mainly as an associate of the carboxylic groups (Miller & Given, 1978). On the basis of its occurrence in the field, Ward (1986) suggested that the calcite in at least some Australian bituminous coals may have been formed when this material was released from organic combination in the course of

rank advance.

Phosphate Minerals Cook (1962) has described the occurrence ofapatite petrifactions in a coal from the Ipswich area, while

Ward (1978), Corcoran (1979) and Ward & others (1992) have noted the presence of apatite in a number of other Australian seams. Goyazite and related aluminophosphate minerals of the crandallite group have also been identified in a number of Australian coal samples (Ward, 1974; 1978; Doolan & others, 1979; Ward & others, L992). Both the apatite and the crandallite-group minerals are probably authigenic in origin, representing the inteiaction of calcium ions or aluminous complexes with phosphatic material derived from decomposition of the organic matter.

Montmorillonite itself is relatively abundant in the coals of some areas, such as the Newcastle Coalfield of New South Wales (Ward, 1989), and illite with essentially no interstratification is noted by Ward (1978) in a seam from the Moura district in Queensland. A separate chlorite phase is also present in a few seams, including several of semi-anthracite and higher rank in the northern and south-eastern Bowen Basin.

Most of the non-kaolinite clay fraction, and indeed much of the kaolinite as well, is found in the coal as thin bands and laminae associated with the maceral components. Bands of clay-rich material a few centlmetres thick, persisting over quite extensive areas, are also present in many seams, (a6li,rrite, on the other hand, also occurs as cell cavity infillings within the coal (Balme & Brooks, 1953), as rounded pellets and vermicular crystal aggregates (Kemez,ys & Taylor, 1964), or as an infilling of cleats and other fractures. Three different types ofprocesses were probably

involved in the formation of the clay minerals in Australian coal seams:

1) Detrital input: Although modified in some cases

by peat-swamp processes, the non-kaoli!ite clays in many Australian bituminous coals closely resemble clay minerals found in shales and other fi!e-grained sediments elsewhere in the associated coal-bearing sequence. The mixed-layer clays, in particular, fal! int-o this category, and probably represent material washed or blown in to accumulate with the original organic deposit. Loughnan (1975) also notes the presence ol lateritic palaeosols associated with some Australian coal-measure strata, and hence it is also possible that at least part of the relatively honomineralic kaolinite assemblages also originated in this way. 2) Pyroclastic input: Bands and other admixtures of montmorillonite are found in many seams of the northern Sydney Basin, as well as in other areas of eastern Austraiia. This material is distinctly different to the other non-kaolinite components, and is thought by many authors (e.g. Holmes, 1983) to represent altered volcanic debris that locally overwhelmed the peat swamp. A number of pelletal claystone bands are also regarded by many authors as tuffaceous deposits within individual coal seams' Spherical halloysite aggregates thought to represent altered pyroclastic dust particles are reported in some coals from the northern Sydney Basin by Ward & Roberts (1990). 3) Authigenic precipitation: T};,e almost ubiquitous

Clay Minerals With the relatively low proportions of pyrite, quartz and carbonate present in most cases, the mineral matter in the bulk of Australian bituminous coals is usually dominated by the clay minerals. A number of different clay species may be present within any individual coal sample, but well-crystallised kaolinite is typically the most abundant and distinctive component, not only of the clay fraction but also of the entire mineral matter.

well crystallised kaolinite in Australian bituminous coals, especially the material occurring as cell infillings and vermicular aggregates, appears to represent a clay fraction formed by in situ prbcipitation in some way, either alon_g with the original plant debris or in the pores of,thg peat deposit. Some of the processes by which tb_is might have been accomplished are discussed by Ward (1986).

MINERAL DISTRIBUTION IN INDIVIDUAL

The non-kaolinite clays are usually represented by

SEAMS

(Figure 2). A distinctive regularly interstratified illi[e-montmorillonite-chlorite mineral (Loughnan & Craig, 1961) is present, however, in the Lithgow seam of the western Sydney Basin.

Most studies of mineral matter or geochemical characteristics of Australian bituminous coals (e.g. Ward, 19?8; Slansky, 1985) are based on studies of full-seam composites or typical produ-cts from key mining areas.-A small number of studies, however,

an irregularly interstratified illite-montmorillonite or illite-montmorillonite-chlorite component

Geology of Australian Coal Basins

VICTORIA TUNNEL SEAM SYDNEY BASIN

C SEAM, MOURA

MAIN LOWER SEAM, BLACKWATER

BOWEN BASIN

q^,

\//

5.O

./ii'

715

.,|l\

1l ,\'

\J\-;, I

L'*

Cu Ku Radiatton

DAWSON SEAM, BARALABA BOWEN BASIN

lzrs I 1I

Cu K" Radiation

2. Oriented-aggregate x-ray diffractograms of clay fractioBs concentrated from oxidation residues of Figure - Australian bitum-inous coals,-showing d spacing of peaks in Angstrom units - Ward, 1978. a)air-dried b) glycol saturated c)heat-ed to 300"C d) heated to 600oC

Minerals and Inorganic Constituents

98 have attempted to address the details of the mineral

distribution within individual coal beds, either from consideration of seams at particular localities on a ply-by-ply basis or by comprehensive study of-late_ral lrends in particular seams over extensive coalfield areas.

Mineral Distribution in Coal Seam Profiles A study in the Sydney Basin by Ward (1989) has noted that the relative amounts of quartz and non-kaolinite clays decrease, and well-crystallised kaolinite increase, at least for some seams, progressively from base to top ofthe coal bed (tr'igure 3). This is thought to reflect a declining input of detrital sediment, relative to the aclumulation of organic matter, as the original peat swamp developed.

The associated increase in kaolinite in such cases is probably an increase by default as detrital input to the swamp from the same source as other basin sediments declined while other mineral-forming

processes continued to operate. The wellirystallised kaolinite may have been derived from a number of sources, including the development of lateritic weathering of the hinterland associated

with the more extensive peat-swamp conditions, better preservation of tuffaceous debris in the absencb of other mineral contaminants, in-situ

leaching or some other type of authigenic process

within the swamp or the resulting peat deposit. Such a transition, particularly if authigenic Drocesses of kaolinite formation are involved, is also tonsistent with the buildup of major coal seams in areas such as a raised bog environment (McCabe, 1987).

Smyth & Cook (1976) have noted that many-of the sea--s in eastern Australia exhibit a general upward increase in inertinite macerals, relative to vitrinite, and indicate that this may reflect exposure to the atmosphere with drying out of the pe-at bed' Ward (1989isuggests that chemical or biochemical leaching of clays and other material in the upper

KATOOMBA SEAM Clarence CollierY m

Sample

Roof

0.0

c2 0.4 0.8

1.2 1.6

2.0

2.8

c5 c6

3.2

3.6

c8 c9

Floor 4.0

c10

4.2 40

CoK< Radiation

Degrees 2g

F.iEure 3. Vertical variation in mineral matter constitution, as expressed by x'ray diffractograms for - oxidation residues, for a Sydney Basin coal seam - IVard, 1989' G - goyazite-group

mineral, K - kaolinite, Q'quartz

Geology of Australian Coal Basins

part of the peat bed, associated with this process, may have been involved in breaking down whatever detrital silicates were introduced, leaving an insoluble alumina-rich residue which ultimately crystallised to form the kaolinite. Several such profiles appear to be superimposed in at least one instance, suggesting that a number of cycles of this type may be repeated in the accumulation of individual coal seams.

Mineral Matter and Seam Split Developnent Warbrooke & Roach (1986) have described the variations in mineral matter composition associated wittr two different types of seam split development in the Newcastle Coalfield of the Sydney Basin. In one type, referred as "tectonic splitting" (Figure 4), the petrographic character, thickness pattern and ash distribution suggest that seam divergence was associated with the onset of wetter conditions due to increased subsidence, a process that ultimately resulted in a single, short-lived influx of fluvial sediment between the particular coal plies. Dryer conditions, however, with increased oxidation of the peat and formation of inertinite macerals, apparently prevailed away from this rapidly subsiding zone.

In the other type of split, referred to as "sedimentary splitting", seam divergence is thought to be associated with areas of more continuous fluvial activity. Petrographic and other data suggest that drier conditions prevailed in the actual split area, along with increased siliciclastic input from

repeated flooding episodes.

The drier conditions in this instance were probably related to the greater abundance ofless compactable overbank sediment in the coal towards the split zone, which resulted in lesser rates ofpeat accumulation for a given organic input and hence led to more frequent drying out between individual flood events. Increased siliciclastic input, in the coalesced zone of the tectonic splits and in the divergence zone for the sedimentary types, is associated in both cases with higher mineral matter and ash values (Figures 4a,b). The mineral matter in these areas is also richer in quartz, feldspar and montmorillonite (Figures 4c-0. Kaolinite and apatite, on the other hand, are more abundant in the wetter areas, derived perhaps from components released with plant decay in the drier zones and re-deposited in FIGURE I.

TECTONIC SPLITTING

SEDIMENTARY SPLITTING Borehole Seom

L------rJ Yord

Dudlay Seam offcctcd by Sedimcntory Splilling

in lhis orco.

tuh 9/o(db)

FEr.DSPrn

coot

Ftuviot Chonnelc.

VE= 30

cFt.60 A3h ?o(o)

aPAfItts

loztro--l

Figure 4. Mineralogical variations associated with different split types in seams of the Newcastle Coal Measures, Sydney Basin - Warbrooke & Roach, 1986.

Minerals and Inorganic Constituents

lo0 the different geochemical environment by authigenic processes.

Mineral Matter Trends Across Coalfield Areas A comprehensive study by Tadros (1988) has allowed detailed mapping of trends in ash composition, most notably the SiOz/AlzOs mole ratio in the inherent ash ofthe clean coal, for an extensive seam in the Gunnedah Basin (Figure 5). High values for this ratio (10:1) are developed in the south-west of the basin, in an area where the inherent ash of the clean coal is between 20 and 307o immediately adjacent to a major seam split zone. Except for two other areas with relatively high values, one south of Narrabri and one south-east of Gunnedah, however, the SiOz/AlzOs ratio for the seam in the remainder of the basin is significantly and uniformly lower.

Although some authigenic material may also be present, the area of coal with high-silica ash in the south-west is thought by Tadros (1988) to reflect the input of fine detrital sediment from a quartzose source associated with the adjacent Lachlan Fold Belt. The areas with lower values in the east, by contrast, are thought to represent a greater abundance of clays formed in turn by aluminosilicates derived from deeper weathering of the (then) more stable New England Block.

MINERAL MATTER IN LOWER.RANK COALS Although ash yield and composition depend to some extent on the actual conditions ofthe ashing process, ash analyses for lower-rank coals generally show lower percentages of SiOz and AlzOs, and higher percentages of SOs, CaO, MgO, FezOa and NazO than those of typical Australian bituminous materials. Experimental work by Durie (1961) and other early workers has shown that much of the sodium ofVictorian brown coals is present as a water-soluble component, including but not entirely made up of NaCl, while most of the calcium and magnesium, the rest of the sodium and at least some of the iron is present as exchangeable cations, presumably associated with carboxylic groups in the organic matter. Similar trends have been shown for a range of low-rank coals from South Australia by Ward (1992). Based on this type of information, Kiss & King (1977) divided the "mineral matter" (used in its broadest sense) into two components:

Clay and sandy material are the main mineral contaminants in the Victorian brown coals, although significant amounts of pyrite and marcasite are also present in particular parts of some seams. The exact nature of the clay minerals in Victorian brown coals, however, is not well documented. Kiss & King (1977) indicate that kaolinite is the dominant clay component, while Baragwanath (1962) notes the presence of bauxite minerals in some areas as well. Much of the material appears to be of detrital origin, being particularly abundant near the top and base of the individual coal beds. Clay and sand, however, are also found as irregular clastic dykes up to 0.3 m wide within some seams, apparently derived from remobilisation, before mining, of unconsolidated overburden or interseam sediments (Gloe, 1960). As well as fragmental material, veins and similar bodies of micro-crystalline silica are also present in some seams. Gloe (1960) describes veins and irregular bodies of this type up to 0.3m wide in seams of the Morwell area, while Baker (1946) describes silicified brown coal in seams near Parwan and Altona in the Otway Basin. The silica is thought

to represent material precipitated from circulating waters, probably of artesian origin for the Morwell occurrences (Baragwanath, 1962) and possibly derived from basaltic magmas in the Parwan-Altona deposits.

Marcasite and pyrite represent another common group of authigenic minerals in Victorian brown coals. They may occur as lumps or nodules, as replacements of plant tissues and as thin veins cutting across woody fragments or in fractured coal zones. Marcasite replacements of fossil wood are particularly common in the coal seams of the Bacchus Marsh area (Edwards & Baker, 1951).

After selective removal of other inorganic constituents, Ward (1992) notes that quartz is the dominant mineral in the Tertiary brown coals of South Australia, with minor amounts of kaolinite and, in some cases, small amounts of pyrite. Doubly-terminated euhedral crystals of quartz are prominent in the mineral fraction from one area (the Bowmans deposit), suggesting an authigenic origin, but in other materials the quartz occurs as irregularly-shaped angular grains and is probably a detrital contaminant to the organic matter.

b) an "inorganics" fraction, made up of the NaCl and other Na, the Mg, Ca and non-pyritic Fe.

Well-crystallised kaolinite is the dominant mineral component of the low-rank coal from the Triassic Leigh Creek deposit, occurring as infillings of cell cavities and as the matrix between individual inertinite particles. Much of this material may be of authigeniC origin, precipitated in situ within the pores of the original peat deposit. The kaolinite in the Tertiary coals of South Australia, however, is poorly crystallised, and may simply represent iletrital influx into the precursor peat accumulation.

These two components are reported separately in

Inorganics

a) a "minerals" fraction, represented by the SiOz, AlzOe, TiOz, KzO and FeSz identified in the coal by XRF and other analyses, and

routine analysis, and typical values for run-of-mine coal from Morwell in the Gippsland Basin are given in Table 2.

Minerals With the dominance of organically-associated inorganic constituents, the total percentage of crystalline mineral particles is quite low in mqny loiv-rank coal deposits. In Victorian brown coals, for example, the proportion of minerals as such is typically less than 0.\Vo on a dry coal basis.

As indicated by Durie (1961), Baragwanath (1962), Kiss & King (1977; 1979) and other workers, the non-mineral inorganics are by far the dominant components of the mineral matter, as-broqdly defined, in Australian lower-rank coals. The principal components of this fraction t1s sedirrm, ialciuin, magnesium and non-pyritic iron,-altho-ugh recent work-(e.g. Kiss, 1982; Ward, 1992) has shown that a certain amount of aluminium is also present in some seams in a non-crystalline, acid-soluble form'

Geology of Australian Coal Basins

101

;"e,Hff;';r:,i

"rx"".,i*'\

i,'l=ffi|;\.. i;,iR$\q. /

rNiJ \\l','i ,':);'I,::;{ iJ;ffi:r"\-*.t,,", ,,\,'t

,,"\{.,,,," ,, *,.

,,,,,,,,').,-"',,'.,,,,,

)

",,,'\'t "".,',"r"\

,.,,,,",".,.,,N*',,"

-EI

)

.,^s ,

r"rop

_,-,\et'

\Qq \'1,-'.\

"\ :.:":.:'lt,;"i'ts:"' ,-':{..:-ld,::".r ", : r/ .

.,,"",',,,'.,'t -x: !,,",,.*",,",'r I

"'}D{*'-"'\

\llli' ;:\]ijri'\i, l"l 4)l ;l' ii;'i ;iii

, \,,hS#,;i1i;r;:r,:':irirg "."' " . \,.l;11 i.11,.;;l"l1,l1l' \ \ .,:,. .. :rNi',].,,4.1',1;li

"\,"

.r,\'',,

-",:.\"'"-,.",',"/

',j"l;..";,7

. ; ./'l;ii1i:i;:/ I ,::I' \:"1\" " . I':'r"i I'l . ;;i;:xl;;i sik"ki,;4'; """,' --',,.," r1'.

NEW ENGLAND FOLD BELT

I '\

t:* ^

-',,

"')t,,a*.\,,irl,

*\NffiiltltltrlliN :'X' I N' )*d.;"Hl\l'l'

Gunnedah

l.l:

! .:. :.\:. l* l*i.d'i';'FFi,l, l

NrlrN$ . :\' :

:. ":"\*',';\.:.: x \': .'\,',,' ', '','\,"' \',,

r:N,,N.,i',il,,1 .\ , \."' .".'1. ,

,.'"" ,", - . \ - ,,\\..."""_"".l""'.".'.t.,""" "' \...."..'t.'.,",,"1'"'." ) " "\.\, " .l',".'.,,.i.".,."..t,"".. \ - 4 " t..".',,/"'".,'"/','"'"" ,

; l: "..[,i;/r i :/n :/( 'l

"' 1".' ./"" ./"':"..'/:":"'/,,:,"".',.

)/1//## '#Xfiffii{"":1 ffiffiii

,,\ .,\

v 1 ""*," -/..'." .y., .'./"" "...,,.""

\9. ko

{ ':.1.t.f,";.;.il"i+til.j,;"iL.:

i ,.\".'".N.',,,.,-,,',,'','-,"',".' s

\:"\.:.:N-1,;";.

.NN$( 98

40km

Figure 5. Lateral variation of SiOz/AlzOs mole ratio (1.60 float fraction) for the Hoskissons Coal Member in the Gunnedah Basin - Tadros, 1988.

Minerals and Inorganic Constituents

lo2 vertically throughout the thick individual coal beds. Sodium and magnesium, for example, along with chlorine, tend to be concentrated near the top ofthe seam (Figure 6), while, with some exceptions, iron and aluminium tend to be concentrated near the base. Calcium appears to reach its peak, ifany, at some point within the actual coal bed.

Much of the sodium and some of the calcium appear to be present, with chloride and in some cases sulphate, as dissolved ions in the coal's pore water. The bulk of the non-mineral inorganic elements, however, are readily extracted from the coal by ion exchange processes or with dilute hydrochloric acid (Ward, L992), and are thought to be present as salts of carboxylic acids. The non-mineral iron and aluminium, on the other hand, are generally removed only by acid treatment; they probably occur as organometallic complexes or possibly in hydroxyl form.

Rather than introduction and incorporation with particular components of the plant debris in the original peat swamp, the distribution pattern of the inorganics within the seams suggests that the different components owe their origin to post-depositional migration of ions on a large scale through the pores ofthe individual coal deposits. Supported by the experimental work of Brockway & Borsaru (1985), Kiss & others (1985) suggest that the inorganics were mainly introduced by upward flow of water from aquifers beneath the seams. The coal is thought to have acted as an ion exchange medium. Ions bonding most strongly to the organic matter are thought to have migrated slowly through the pore structure and hence become concentrated

Even though the same elements were probably the dominant inorganic constituents of the vegetation that formed the coal (Baragwanath, 1962), detailed studies by Hibbert & others (1981), King & others (1983) and Kiss & others (1985) have failed to reveal any direct correlation between the abundance ofany of these components and the individual lithotype units present within the coal seams. There are, however, at least in some seams, significant variations in the abundance of particular elements

Table 2, ,Minerel matter charactCiistics of Morwell b'fown CO'al - KisS,& KiUgn 1979; a) Minerals and Inorganics in Morwell Coal (as mined) Month

- Moisture As rec'd

Amount dug (t)

4 5 6 7 8

M&I

Dry basis

59.7 60.4 60.0 59.8 58.1 58.8 58.8 59.7

91 900 120 300 93 600 240 410 45 500 41 800 25 060 1 13 600

(wt Vo)

Ash

(wt Vo, db)

(wt Vo, db) calc.

1.9 3.9 4.4 3.8 3.0 2.5 5.7 5.0

3.0 5.4 5.8 5.1 5.5 4.0 .7 6.0

3.0

148.3

752.5 150.3

148.6 138.8 L42.5 142.7 148.3

5.3

5.7 5.0 5.3

4.3 7.9 6.4

NOTE: M & I = Minerals and Inorganics

b) Constituents of Minerals and Inorganics Fractions Month Coal minerals (wt Vo, dry basis)

SiOz AlzOe KzO TiOz FeSz 0.62 0.15 0.011 0.008 0.06 2.37 0.36 0.014 0.047 0.0 2.44 0.49 0.024 0.030 0.0 1.90 0.40 0.019 0.028 0.11 L.43 0.26 0.013 0.025 0.32 0.68 0.19 0.003 0.012 0.? 2.84 0.76 0.012 0.063 0.32 2.67 0.45 0.016 0.037 0.11

I 2 .l

4 5

6 7

Inorganics (wt Vo, dry basis)

Fenp

Fet

0.17 0.20 0.13 0.13 0.13 0.13 0.22 0.27 0.08 0.22 0.09 0.09 0.14 0.29 0.19 0.24

0.36 0.43 0.62 0.55 0.78 0.79 0.75 0.69

0.25 0.32 0.42 0.31 0.45 0.46 0.45 0.42

0.16 0.L7 0.15 0.L4 0.17 0.17 0.20 0.22

0.10 0.10 0.11 0.10 0.L2 0.11 0.13 0.17

0.33 0.39 0.28 0.37 0.4?

0.48 0.71 0.36

NOTE: M& I = Minerals and Inorganics Fet Fenp

= Total iron

= Non-pyritic iron

= Total sulphur

c) Ash analysis of Morwell coal (calculated) Ash analysis (wt Vo) (calculated)

Month

SiOz

AlzOe

KzO

TiOz

FezOs

CaO

MgO

N.zO

SOa

0.26 0.88 0.53 0.55 0.48 0.28 0.79 0.58

9.42 3.50 3.30 7.52 6.27 2.98 5.23 5.38

15.40 15.00 20.28 25.6L

t2.37

7.L2 4.32 3.59 3.68 4.37 5.32 3.40 4.66

27.t8

4r.87

0.36 0.26 0.43 0.37 0.25 0.19 0.15 0.25

13.67 10.00

4.94 6.77 8.69 7.79 4.95 4.40 9.58 7.06

16.61 11.33

20.43 44.59 43.28 37.02 27.25 15.75 35.81

2 3

4 5

t3.24 15.15

Geology of Australian Coal Basins

10.03

t4.24 17.68 9.42 10.93

18.35 12.42 18.03

2r.92 27.79 22.38 14.11

t.03

----\-

sir\

-r

irr

Minerals and Inorganic Constituents

104

near the base of the seams, while more loosely bonded ions migrated rapidly and built up

preferentially near the top ofthe coal bed.

TRACE ELEMENTS IN AUSTRALIAN COALS Trace elements in coal are generally regarded as those elements present at < 0.L%o (1000pg/g or 1000ppm). Almost every element of the periodic table is present in coals to some extent, although many of them are in extremely low concentrations. A list of the more common trace elements in

Australian coals is given in Table 3.

Methods of Analysis Apart from a few special cases, such as fluorine, the principal methods used for determining the trace elements in Australian coals are optical emission spectroscopy (OES), atomic absorption spectrometry (AAS), x-ray fluorescence spectrometry (XRF), spark source mass spectrometry (SSMS), proton induced x-ray emission analysis (PIXE) and instrumental neutron activation analysis (INAA). XRF, PIXE and INAA have the advantage of being able to work directly on the coal, while OES, SSMS and AAS are usually applied to the ash or a solution of the ash, though the values are mostly corrected and reported to a "whole-coal" basis. Some of the earliest studies of trace elements in

Australian coals were those of Pilkington (1957) and Durie & Schafer (1958), with a phenylfluorone spectrometric method for determining germanium. Clark & Swaine (1962) used OES to determine a wide range of trace elements in bituminous coals from NSW and Queensland, while AAS was first

applied by Durie & others (1963) and Belcher & Brooks (1963). Special techniques have also been developed in the use of these techniques for a number of elements, such as scandium (Swaine, 1964), boron (Dale, 1979), cadmium (Godbeer & Swaine, 1979) and mercury (Doolan, 1982). A radiochemical separation method (RNAA) was also developed for low concentrations of mercury and selenium by Porritt & Swaine (1976).

X-ray fluorescence was first used on brown coals by Sweatman (1963) and Kiss (1966), and became more widely applied following the work of Mills & others (1981). INAA has been used for trace elements in both low-rank and high rank materials (Bone & others, 1981; Cahill & Mills, 1983; Fardy & others, 1984), providing information on many elements at low concentrations not available by other techniques, while Dale & Fardy (1985) describe the use of PIXE, SSMS and inductively coupled plasma emission spectrometry (ICPAES) in trace element studies. Proton induced gamma ray emission (Clayton & Dale, 1985) and a pyrohydrolysis method (Godbeer & Swaine, 1987) have also been used for the special problem of fluorine determination in Australian coal deposits.

Mode of Occurrence of Trace Elements Although the total concentration of particular trace elemenls in coal can generally be determined to a high degree ofprecision by one or more ofthese methods, an indication of the way in which the elements actually occur within the coal is often based only on speculation. Some may represent

Table S. Trace elementb in New South Wales and Queenslsnd bituminous coals (ttglil - Swaine, f979. Element Ag As B

Ba Be Cd CI Co

Cr Cu F Ga Ge

Hg La Mn Mo

Ni P Pb Sc Se

Ti U

w Y Zn

Range of contents

Mean content

<0.2 1 <1-55 1.5 - 300 <40 - 1000 <0.4 8 0.05 0.20 <100 - 1000 <0.6 - 30 <1.5 - 30 2.5 - 40 15 - 500 1-20 <0.3 - 30 0.026 0.40 <4-50 2.5 - 900 <0.3 6 0.8 - 70 30 - 4000 1.5 - 60 <0.3 - 30 o.2t 2.5 <0.9 - 1,5 <20 -- 1000 8 <0.2 400 - 4000 0.4-5 4-90 <4-20 1-25 t2-73 6-400

<0.5 3

<100 1.5

0.10 150 4 6 15

80 4 6

0.10 10

150 1.5 15

310 10 3

0.79 <3 100

2.7 900 2

<10 7

25 100

Geology of Australian Coal Basins

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Following similar work in the USA (Gluskoter & others, L977), Ward (1980) investigated the relative distribution of selected trace elements among the different density fractions of a series of finely crushed, otherwise clean coals from a range of Australian bituminous seams. Some elements, such as copper, lead, zinc and molybdenum, showed a marked increase in relative concentration in the higher R.D. fractions (Figure 7), and were interpreted as having a mode of occurrence mainly associated with the mineral components. Chromium and strontium displayed a similar, but less well marked trend. The presence of such elements, in these coals at

least, probably reflects discrete bodies ofsulphide, carbonate, phosphate or other mineral species associated with the maceral components. Other elements, notably boron, nickel, vanadium, zirconium, cobalt and beryllium, were found to be concentrated mainly in the light fractions of the coal, a pattern thought to indicate an occurrence

mainly, though not necessarily entirely, in a form more closely associated with the organic compounds. Germanium, however, was unusual in that it showed a strong association with the mineral matter in some coals, and an equally strong association with the organic matter in others.

Trace Element Concentrations Comparison of the data in Table 3 to the results of overseas studies (e.g. Gluskoter & others, 1977)

indicate that most trace elements in Australian bituminous coals are no more abundant, and in many cases are significantly less abundant, than those of equivalent elements in coals from other mining areas. Australian coals typically have low sulphur contents, with pyritic sulphur representing only a minor part of this total, and hence the elements usually associated with sulphide minerals, such as As, Cd, Cu, Hg, Pb, Se andZn, are especially low in Australian deposits. Only Mn, P and Zr appear to be significantly higher in Australian coals, compared at least to American seams. Swaine (1980) suggests that the coals of New South Wales tend to contain more boron, manganese, molybdenum and nickel than those of Queensland, but that some Queensland coals contain significantly

higher proportions ofphosphorus than do typical N.S.W. materials. Ward (1978) also notes the presence of apatite, and in some cases crandallite-group minerals, more commonly in Queensland coals than in N.S.W. deposits.

Boron, which was first studied in Australian coals by Swaine (1962; L967; I97I), is one of the most interesting trace elements from a palaeogeographic point of view. A wide range of values is developed in the different coal measure successions (Figure 8), and these display a marked correlation with the interpreted influence of marine conditions on the original depositional system.

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Clark & Swaine (1962) have discussed some of the possibilities for a number of elements in Australian bituminous coals, drawing on information on the inorganic elements found in plants and the mineral constituents known at the time to be present.

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To. , 1,1 ",r-'oor,.o Figure 8. Boron content of coals in major New South Wales and Queensland sequences - Partly after Swaine, 1971. Present-day sea water contains about 5ppm B (Goldschmidt, 1954), compared to around 0.015ppm B in fresh water (Bowen, 1979). Although some boron in coals may occur as an associate of the

mineral fraction (e.g. Bohor & Gluskoter, 1973), most of the element in Australian coals appears to be contained within the organic components (Swaine, 1971; Ward, 1980). The seams with a high boron content are typically those intimately associated with marine strata, and it is probable that incursion of sea water during the early stages of coalification gave rise to boron transfer by adsorption on to the coal or by some chemical fixation process into the hydrocarbon compounds.

REFERENCES BAKER, G., 1946: Microscopic quartz crystals in brown coal, Victori a. Am.erican Mineralogist, 31, 22-30. BALME, B.E. & BROOKS, J.D., 1953: Kaolinite petrifactions in a New South Wales coal seam.

Australian Journal of Science, 16(2), 65. BARAGWANATH, G.E., 1962: Some aspects of the formation and nature of brown coal, and of the behaviour ofbrown coal ash in water tube boilers,

with special reference to Victorian deposits. Proceedings of the Australasian Institute of Mining and Metallurgy, 2O2, l3t-249.

BEESTON, J.W., 1981: Wood structures preserved in high-rank bituminous and semi-anthracitic coal,

central Queensland . Palaeobotanist, 28-29, 155-160.

BELCHER, C.B. & BROOKS, K.A., 1963: ThC determination of strontium in coal ash by atomic absorption spectrophotometry. Analytica Chimica Acta, 29, 202-205. BOHOR, B.F. & GLUSKOTER, H.J., 1973: Boron in illite as an indicator of palaeosalinity of Illinois coals. Journal of Sedimentary Petrology, 43(4),

945-956. BONE, K.M., SCHAAP, H.A. & HUGHES, T.C., 1981: Analysis ofbrown coal ash by neutron activation analysis. Report SO/81/36, State Electricity Commission of Victoria. BOTZ, R.W. & HART, G.H., 1983: Mineralogical, petrographical and geochemical investigations of outbursting in Australian coal mines. Proceedings of the Australasian Institute of Mining and Metallurgy, 286, 4l-49.

Geology of Australian Coal Basins

to7 BOTZ, R.W., HUNT, J.W, & SMITH, J.W., 1986: Isotope geochemistry of minerals in Australian bituminous coals. Journal of Sedimentary Petrology, 56( 1), 99-1 11. BOWEN, H.J.M., t979: Enuironmental Chemistry of the Elernents. Academic Press, London. BROCKWAY, D.J. & BORSARU, R.M., 1985: ION

concentration profrles in Victorian brown coals.

Proc. International Conference on Coal Science, Sydney, October, 1985, Pergamon Press, 593-596. BROWN, H.R., CLARK, M.C. & DURIE, R.A., 1959:

Characteristics ofthe ashes from Australian coals. Technical Communication 33, CSIRO Division of Coal Research. BROWN, H.R., DURIE, R.A. & SCHAFER, H.N,S., 1959: The inorganic constituents of Australian coals: I

determination ofthe total - the direct mineral-matter content. Fuel, 38, 295-308.

DOOLAN, K.J., MILLS, J.C. & BELCHER, C,B., 1979: The analysis and characterization ofmineral matter and ash. In, Stewart I.McC. & Wall, T.F.(Editors): Combustion of Puluerized Coal - the effect of mineral matter. Department of Chemical Engineering, University of Newcastle, N.S.W.,

L3.1- L3.11.

DURIE, R.A., 1961: The inorganic constituents in

Australian coals: III Morwell and Yallourn brown coals. FueI, 40,- 407 -422.

DURIE, R.A. & SCHAFER, H.N.S., 1958: Germanium in Australian coals. Technical Comm. 27, CSIRO Coal Research Section.

DURIE, R.A., SCHAFER, H.N.S. & SWAINE, D.J., 1963: Application of atomic absorption spectrophotometry to analysis of inorganic constituents in Victorian brown coals. Investigation Report 36, CSIRO Division of Coal Research.

BROWN, H.R. & SWAINE, D.J., 1964: Inorganic constituents ofAustralian coals. Journal of the

DURIE, R.A. & SWAINE, D.J., 1971: Inorganic constituents in coal. Coal Research in CSIRO,45, 9-19.

BURNS, M.S., DURIE, R.A. & SWAINE, D.J., 1962: Significance of chemical evidence for the presence of carbonate minerals in brown coals and lignites.

EDWARDS, A.B., 1"953: The composition of Victorian brown coals. In, Coal in Australia. Publications of

Institute of Fuel, 37 , 422-440 .

FueI, 41(4),373-383.

CAHILL, R.A. & MILLS, J.C., 1983: Trace element concentrations in Australian brown coals. Proceedings of the Australasian Institute of Mining and Metallurgy, 285,39-43. CLARK, M.C. & SWAINE, D.J., 1962: Trace elements in coal. Technical Communication 45, CSIRO Division of Coal Research. CLAYTON, E. & DALE, L.S., 1985: Determination of fluorine in NBS coal and coal fly ash by protoninduced gamma ray emission and spark-source mass spectrometry. Analytical Letters, 18(A12), 1533-1538. COOK, A.C., 1962: Fluorapatite petrifactions in a Queensland coal. Australian Journal of Science.,

25,94.

CORCORAN, J., L979: Mineral matter in Australian steaming coals - a survey. /n, Stewart, LMcC. & Wall, T.F.(Editors): Com.bustion of Puluerized Coal - the effects of mineral matter. Department of Chemical Engineering, University of Newcastle, N.S.W.

the Sth Empire Mining and Metallurgical Congress, Australasian Institute of Mining and

Metallurgy, 6, 7 27 -7 53. EDWARDS, A.B. & BAKER, G., 1951: Some occurrences of supergene iron sulphides in relation to their environments of deposition. Journal of Sedimentary Petrology, 21,34-46. FARDY, J.J., McORRIST, G.D. & FARRAR, Y.J., 1984: The analysis ofcoals and fly ash for trace elements and natural radioactivity. Proceedings of the Au s tr alian C oal S c ienc e C onfere nc e, 1 59-166. FRAZER, F.W. & BELCHER, C.B., 1973: Quantitative determination of the mineral matter content of coal by a radiofrequency oxidation technique.

FueI,52, 4l-46.

GLOE, C.S., 1960: The geology of the Latrobe Valley coalfield. Proceedings of the Australasian Institute of Mining and Metallurgy, 194, 57 -125. GLOE, C.S., 1979: The brown coal reserves of Victoria. Proceedings of a Symposium on Estimation and Staternent of Mineral Reserues, Sydney, Australasian Institute of Mining and Metallurgy, 49-61.

DALE, L.S., 1979: The emission spectrographic determination of boron in silicate materials. Applied Spectroscopy, 33, 404-406.

GLUSKOTER, H.J., 1965: Electronic low temperature ashing of bituminous coal. Fuel, 44, 285-29L.

DALE, L.S., FARDY, J.J. & CLAYTON, E., 1985: Trace element abundance data for coals using instrumental methods of analysis. Proceedings of

GLUSKOTER, H.J., RUCH, R.R., MILLER, W.G., CAHILL, R.A., DREHER, G.B. & KUHN, J.K., 1977: Trace elements in coal: occurrence and distribution. Illinois State Geological Suruey,

the International Conference on Coal Science, Sydney, October, 1985, Pergamon Press, 857-860.

Circular 499.

DE JERSEY, N.J., 1949: The chemical and physical properties and classifrcation of some Queensland coals. Uniuersity of Queensland Papers, Department of Geology, 3(7 ).

GODBEER, W.C. & SWAINE, D.J., 1979: Cadmium in coal and fly ash. /n, Hemphill, D.D. (Editor):

DOOLAN, K.J., 1982: The determination of traces of mercury in solid fuels by high-temperature combustion and cold-vapour atomic absorption spectrometry. Analytica Chimica Acta, L4O, 187-195.

GODBEER, W.C. & SWAINE, D.J., 1987: Fluorine in Australian coals. Fuel, 66, 7 94-7 98.

Trace Substances in Enuironmental Health

XIII. University of Missouri, Columbia, 254-261.

GOLDSCHMI DT, V. M., 195 4: Ge ochemi stry . Oxford Press.

Minerals and Inorganic Constituents

108 GOULD, R.E., 19?5: A preliminary report on petrifred axes of Vertebraria from the Permian of eastern

Australia. /rl, Campbell, K.S.W.(Editor): Gondwana Geology . Australian National University Press, Canberra, 109-115.

GOULD, K.W. & SMITH, J.W., 1979: The genesis and isotopic composition of carbonates associated with some Permian Australian coals. Chenical Geology, 24,137-150.

HIBBERT, W.D., SMITH, G,C. & KISS, L.T., 1981: Variation of coal properties with lithotype, Part 1: Morwell open cut. Report SO/81/32, State

Electricity Commission of Victoria.

HOLMES, G.G., 1983: Bentonite and fullers earth in New South Wales. Mineral Resources 45, Geological Survey of N.S.W.

HUNT, J.W., 1983: Ash content and composition of Permian coals. In: Permian Coals of Eastern

Australia. End of Grant Report, National Energy Research, Development and Demonstration Program, Canberra.

JONES, R.H., 1970: Abore core radiography unit. Journal of Physics, E: Scientific Instruments, 3: 363-366. KEMEZYS, M. & TAYLOR, G.H., 1964: Occurrence and

distribution of minerals in some Auptralian coals. Journal ofthe Institute ofFuel,37, 389-397.

KING, J.G., MARIES, M.B. & CROSSLEY, H.E., 1936: Formulas for the calculation of coal analyses to a basis of coal substance free from mineral matter. Journal of tlte Society of Chemical Industry,55, 277-28L.

KING, T.N.W., GEORGE, A.M., HIBBERT, W.D. & KISS, L.T., 1983: Variation of coal properties with lithotype, part 2: Latrobe Valley coals. Report SO/83/55, State Electricity Commission of Victoria. KISS, L.T., 1966: X-ray fluorescence determination of brown coal inorganics. Analytical Chemistry, 38,

173l-L735. KISS, L.T., 1982: Chemistry of Victorian brown coals. Australian CoaI Geology, 4( 1), 153-168. KISS, L.T., BROCKWAY, D.J., GEORGE, A.M. & STACY, W.O., 1985: The distribution of minerals, inorganics and sulphur in brown coals. Proceedings of the International Conference on Coal Science, Sydney, October, 1985, Pergamon Press, 589-592. KISS, L.T. & KING, T.N., 1977: The expression of

results ofcoal analysis: the case for brown coals. Fuel, 56,340-341.

KISS, L.T. & KING, T.N., 1979: Reporting of low-rank coal analysis - the distinction between minerals and inorganics. FueI,58, 547-549. LAWRENCE, L,J., WARNE, S. STJ. & BOOKER, M., 1960: Millerite in the Bulli coal seam. Australian Journal of Science,23, 87-88.

LOUGHNAN, F.C., 1966: A comparative study of the

Newcastle and Illawarra coal measure sediments of the Sydney Basin. Journal of Sedimentary Petrology, 36(4), 10 16-1025.

LOUGHNAN, F.C., 1975: Laterites and flint clays in the Early Permian of the Sydney Basin, Australia, and their palaeoclimate implications. Journal of Sedimentary Petrology, 45(3), 591-598.

LOUGHNAN, F.C. & CRAIG, D.C., 1961: A complex interstratiflred pottery shale from Marrangeroo, N.S.W. Australian Journal of Science,23,379. MARSHALL, C.E., 1953: The physical constitution of the Permian coal seams of New South Wales. 1n, Coal in Australia. Publication of the Sth Ernpire Mining and Metallurgical C ong re ss, Australasian

Institute of Mining and Metallurg!,6,54-92. McCABE, P.J., 1987: Facies studies of coal and coal-bearing strata. In, Scott, A.C. (Editor): Coal and Coal-bearing Strata: recent advances. Geological Society Special Publication, 32, 51-66. MILLER, P.N. & GIVEN, P.H., 1978: A geochemical study of the inorganic constituents of some low-rank coals. Report, Contract EX-76-C-01-2494,U.5. Dept of Energy, Coal Research Section, Pennsylvania State University. MILLS, J,C., TURNER, K.E., ROLLER, P.W. & BELCHER, C.B., 1981: Direct determination of trace elements in coal: wavelength-dispersive x-ray spectrometry with matrix correction using Compton scattered radiation. X'ray Spectrometry, 10, 131-137. PILKINGTON, E.S., 1957: A survey of some Australian sources of Germanium. Australian Journal of Applied Science, 8, 98-111. PORRITT, R.E. & SWAINE, D.J., 1976: Mercury and selenium in some Australian coals and fly ash. Institute of Fuel Conference,Sydney, Preprint Paper 18, 18.1-18.9. RADMACHER, W. & MOHRHAUER, P., 1955: ThC

direct determination of the mineral matter content of coal. Brennstoff-Chemie,36' 236.

RAO, C.P. & GLUSKOTER, H.J., 1973: Occurrence and distribution of minerals in Illinois coals. Illinois State Geological Survey Circular 476.

SHIBAOKA, M., 1971: A geochemical study of the inorganic constituents of the Bowen Basin and other Queensland coals. Proceedings ofthe Second Bowen Basin Symposium. Geological Suruey of Queensland., Report 62. SHIBAOKA, M., 1972: Silica/alumina ratios of the ashes from some Australian coals. Fuel,51, 278-283. SLANSKY, J.M., 1984: Chemical composition of mineral matter in coals and their sedimentary environment. Proceedings of the 18th Symposium on Aduances in the Study of the Sydney Basin, Department of Geology, University of Newcastle,

N.S.W.,85-90. SLANSKY, J.M., 1985: Geochemistry of hightemperature coal ashes and the sedimentary environment of the New South Wales coals, Australia. International Journal of Coal Geology, 5, 339-376.

SMYTH, M. & COOK, A.C., 1976: Sequence in Australian coal seams. Mathematical Geology,

8(5),529-547. STANDARDS ASSOCIATION OF AUSTRALIA, 1982: Glossary of terms relating to solid mineral fuels part 2'. terms relating to coal mining and geology. Australian Standard 2418, Part 2.

SWAINE, D.J., 1962: Boron in New South Wales Permian coals. Australian Journal of Science., 25, 265.

Geology of Australian Coal Basins

109

SWAINE, D.J., 1964: Scandium in Australian coals and related materials. Proceedings of the 148th National Meeting, Diuision of Fuel Chemistry, American Chemical Society, 8(3), 17 2-L7 7 . SWAINE, D.J., 1967: Inorganic constituents in Australian coals. Mitteilungen der Naturforschenden Gesellschaft in Bern, Neue Folge, 24,49-61.

SWAINE, D.J., 1971: Boron in coals of the Bowen Basin as an environmental indicator. Proceedings ofthe Second Bowen Basin Symposium, Geological Suruey of Queensland Report,62, 4l-47.

SWAINE, D.J., 1979: Trace elements in Australian coals and fly ashes. In, Stewart, I.McC. & Wall, T.F. (Editors): Combustion of Puluerized CoaI - the effect of mineral matter. Department of Chemical Engineering, University of Newcastle, N.S.W., w3.14-W3.18. SWAINE, D.J., 1980: Trace element aspects of coal mining, preparation and storage. /n, Hannan J.C. (Editor): Enuironmental Controls for CoaI Mining. Earth Resources Foundation, University of Sydney, 264-274. SWEATMAN, T.R., NORRISH, K. & DURIE, R.A., 1963: An assessment ofx-ray fluorescence spectrometry for the determination of inorganic constituents in brown coals. Miscellaneous Report 177, CSIRO Division of Coal Research. TADROS, N.2., 1988: Depositional controls on quality of the Hoskissons Coal Member, Black Jack Formation, Gunnedah Basin. Quarterly Notes, Geological Survey o/N.S. W.,70, l-L4. WARBROOKE, P.R. & ROACH, M.J., 1986: The relationship between seam splitting, coal-forming environments and coal properties in the Newcastle Coal Measures. Proceedings of the 20th Symposium on Aduances in the Study of the Sydney Basin, Department of Geology, University of Newcastle, N.S.W., 23-27 .

WARD, C.R., 1974: Isolation of mineral matter from Australian bituminous coal using hydrogen peroxide. FueI, 53, 220-22I. WARD, C.R., 1977: Mineral matter in the Harrisburg-Springfield (No. 5) coal Member of the Carbondale Formation, Illinois Basin. Illinois State Geological Survey, Circular 498. WARD, C.R., 1978: Mineral matter in Australian bituminous coals. Proceedings of the Australasian Institute of Mining and Metallurgy, 267,7-25. WARD, C.R., 1980: Mode of occurrence of trace elements in some Australian coals. Coal Geology,

2(2),77-98.

WARD, C.R., 1986: Review of mineral matter in coal. Australian CoaI Geology, 6, 87-110. WARD, C.R., 1989: Minerals in bituminous coals of the Sydney Basin (Australia) and the Illinois Basin (U.S.A.). International Journal CoaI Geology, L3,

455-479. WARD, C.R., 1992: Mineral matter in Triassic and Tertiary low-rank coals from South Australia. International Journal of Coal Geology, 20, 185-208. WARD, C.R., & ROBERTS, F.I., 1990: Occurrence of spherical halloysite in bituminous coals of the Sydney Basin, Australia. Clays and Clay Minerals, 38(5), 501-506. WARD, C.R., SAXBY, J.D. & CORCORAN, J.F,, 1992: Phosphorus minerals in Australian coals. Proceedings of Symposiurn on Fossil Fuel Research and C o - op er ati on, Sy dney Universities Consortium of Geology and Geophysics, University of Technology, Sydney, l3-2L. WARNE, S. St J., 1964: Identification and evaluation of minerals in coal by differential thermal analysis. Journal of the Institute of Fuel, 38,207-217 .

Minerals and Inorganic Constituents

111

EARLY DISCOVERIES AND INITIAL MINE DEVELOPMENTS

ffiistory of

Australian

coal discovery, explor ation and geological rese a'tch

JH Bryan, GH Taylor, CA Bacon, RK Johns, PR Kenl"y, JH Lord I CT McElroy, DC Mengel and G Rose

The early European settlers in Australia, many of them convicts, became aware of the natural resources of the country as they travelled away from the original settlements. Observations were made of coal outcrops in New South Wales and Tasmania prior to 1800, in Queensland and Victoria around 1825, in Western Australia in the mid-1840's and in South Australia in 1857. The timing of these discoveries was clearly related to the proximity of the coalfrelds to the various settlement sites. Although some coal was mined for domestic consumption and gas production, much of the early enthusiism in coal prospecting was also related to the discovery of iron ore at Mittagong in New South Wales in 1801 and at Port Dalrymple in Tasmania in 1804.

The first positive record of coal discovery in Australia-refers to an occurrence on the banks ofa creek, possibly the entrance to Glenrock Lagoon, some 6km south-east of Newcastle. In 1791 a party of escaping convicts, led by William and Mary Bryant, found several large pieces of coal which led th6m to further coal apparently in situ (Ellis, 1969). Six years later, in 1797, three shipwrecked sailors reported coal at Coal Cliff, south of Sydney, le-ading to an examination of the outcrop by explorer George Bass. In the same year Lieutenant Shortland R.N., while pursuing escaped convicts, also came across good cbal closiinside a sheltered harbour near the entrance of the Hunter River.

Scientific input to coal exploration was given by Sir

Joseph Banks, the botanist, who arranged for -- drilling equipment to be brought to SydneV !n-1799. The first dril-l hole was sunk on the banks of the Hawkesbury River in 1799 and the second was on the George's River near the mouth of Prospect Creek. Two thin coal horizons were struck at a depth about 30m in the second hole, located within the

Triassic Wianamatta Group.

New South \ilales In 1850, Samuel Stutchbury arrived in Sydney as the first Government Geologist of New South Wales, and almost immediately submitted a report on the coal sequence and fossils at Newcastle. Stutchbury gave the colony much sound advice on mining methods and the need to maintain proper mine plans, before returning to Elgland in 1855. No permanent Government Geologist was appointed

ifter Stutchbury until L874, when C.S. Wilkinson

took office and began the first large scale geological survey of coal areas in New South Wales. The Rev. W.B. Clarke was one of the first to understand the structure of the Sydney Basin and, on the basis of outcrops at Newcastle and Wollongong, predicted in 1847 that coal would be found under the settlement of Sydney itself (Clarke, t847). This prediction was not fully verified until 1890, when the first Cremorne Bore (Figure 1) struck cindered coal2.2m (7 feet 314 inches) thick at about 840m (2800 feet).

Clarke also led early stratigraphic research on Australian coal measures, proposing a four-fold general classification of the "Permo-Carboniferous" sequence around Newcastle and Maitland in 1861, wit=h the "Upper Coal Measures", the "IJpper Marine Series", the "Lower Coal Measures" and the "Lower Marine Series" (Clarke, 1861). Etheridge (1891)

History

tr2 included in his palaeonotological work a remarkably modern correlation chart using this nomenclature for the Sydney Basin and the Gunnedah region (Table 1). Although superseded by more modern nomenclature, these units still provide a conceptual framework for geological studies in the present day. Over the years, helped by a vague analogy with coal measures in Europe (Vallance, 1975; 1982), the term "Permo-Carboniferous" became entrenched to describe the age of the Newcastle Coal Measures and their equivalents (Murray, 1983). Andrews (1928) tentatively used "Permian" (in quotes) but it was not until the comprehensive palaeontological

and stratigraphic analysis ofRaggatt (1938) that the Permian age of the sequence found general acceptance in geological writings. The term "Kamilaroi" was proposed by David (1932) to cover the Permian System extending into the Carboniferous, but lapsed after limited usage.

Hunter Valley Area Based on the discoveries by Shortland and others

around Newcastle, significant coal mining activity

was established in the lower Hunter region during the early part of the 19th Century. Further up the valley, coal seams were discovered in the Rix's

Creek area near Singleton in 1873.

The early history of coal discovery and mining in Australia is virtually that of the Hunter River district, the history of which is well documented by Branagan (I972). J.D. Dana (author of the renowned System of Mineralogy) made many pertinent observations on the coal measures at Newcastle in 1840, including analytical data for three coal seams (Dana, 1849). Subsequent early recordings of coal outcrops are included in the writings of ministers of religion, particularly the Rev. W.B. Clarke (e.g.

Clarke, 1864, 1867).

Strzelecki's Physical Description of New South Wales and Van Diemen's Land (Strzelecki, 1845) included good detailed sections of the coal measures, although the published version of his geological map of eastern Australia was quite inadequate. J.B. Jukes' geological map of Australia (Jukes, 1847) included the Hawkesbury and Wianamatta rocks of the Sydney District, and his work is an excellent summary of the geology of the Sydney "coal basin". The early years of coal exploration and the early development of coal geology in Australia were tied closely to government funding, and to participation by geologists in the employ of the State or Colonial governments. Each Colony (now State) made a contribution in some way to the early development of Australian coal geology, usually in direct proportion to the extent of its natural coal resources and its need or ability to exploit them. The first detailed surface geological map of coal in the Hunter region, prepared by the Newcastle Coal and Copper Co., appeared in 1855. This map covered the general extent ofthe Victoria Tunnel seam at Burwood, where coke from the seam was used in the smelting of copper ores from New Zealand and South

Australia. Beautifully executed geological sections of the Victoria Tunnel workings prepared by the company (Figure 2) indicate an awareness of the value ofgeological data, even at this early date. The outstanding work of T.W. Edgeworth David and others, starting in 1886, brought a flood of data to swell the geological input into coal mining

development. David's observations in the Hunter River coalfields, including a detailed geological map "from Newcastle to Singleton and from Port Stephens to Lake Macquarie", were published in 1907, bringing together some 20 years of work in this complex area (David, 1907). The monumental work far exceeds David's typically modest claim of being "... little more than a detailed description of the geological maps and sections accompanying ...", containing as it does a wealth of historical, economic, interpretative and philosophical material to instruct and delight the reader. David published much in the interim, including an account in 1886 of the discovery and proving of the Greta coal seam at Deep Creek (David, 1887). In 1887 he also published a description ofthe sequence ofthe different coal measures in the Sydney Basin and their contained coal seams, including much definitive data on the Tomago Coal Measures (David, 1888). In 1888 he published a map of the actual line of outcrop of the "then quite unproved Greta Coal Measures" from Farley to Deep Creek in the central Hunter region (David, 1889), and in 1890 a correlation and geological summary of New South Wales coal deposits in general (David, 1890a, b), drawing on work in other areas as well as the Hunter region.

Western Coalfield Outcrops of coal were discovered in the Lithgow Valley in 1824, and Strzelecki recorded coal in the Vale of Clwydd in 1840. Coal was probably first mined in the Western Coalfield by Andrew Brown at Bowenfels. Some of the most signifrcant geological works of the

early 20th Century are the major memoirs by J.E. Carne (1903, 1908) on the regional geology, kerosene shale deposits and mineral resources of the Western Coalfield region. As well as detailing numerous seam sections, bore records and mining operations, Carne also traced the coal measures of the Sydney Basin north-westwards from the Hunter Valley to Talbragar, and made the first correlations between the Western Coalfield and the coals of the Gunnedah district.

Southern Coalfield After the initial discovery of coal in the Southern

Coalfield in May 1797, there appears to have been little real activity in the Wollongong area until about 1850. From 1888 to 1890, John McKenzie and T.W.E. David submitted reports on sections of various coal seams exposed in adits close to Mt Kembla. Further to the south, small pockets of the Clyde Coal Measures at the head of the Clyde River had also been prospected. A geological survey of the Southern Coalfield was commenced by Jaquet in 1901 and completed by L.F. Harper, with the results being published as a substantial Memoir (Harper, 19 15).

Tasmania The first recorded discovery of coal in Tasmania was

made by the French explorer La Billardiere and his party in 1793, during an attempt to climb Mt La Perouse on the south coast of Tasmania (La Billardiere, 1800). After settlement in 1803, numerous discoveries of coal were made in various parts of the island. A shipwrecked sailor found coal on Schouten Island south of the Freycinet Peninsula on the east coast in 1809, and in 1815 James Kelly found an "immense bed" of (brown) coal on the northern shores of Macquarie Harbour, whilst rowing around Tasmania in a whaleboat. Despite

Geology of Australian Coal Basins

ll3

Figure 1. Drilling of the first Cremorne bore, 1890 (Branagan & Williarns, 1990).

IIi story

tl4

TABLE l. Stratigraphy of the coal measures and associated strata in New South Wales as described by Etheridge (1891).

Tun Carbonifcrous and Pclmo-Carl-ronifcrous Itortnations of N. S. Wales. Ilurtcr llilcr

IIla$ trrrir

0orl-lieltl.

Nerccastlc

GrouP.

coal-Measures

Llol-licld.

Lioll.dcld.

Bu.lli, Groztlt.x

Lilhgou

llfittagong

Natnoi,

G roupt.x

Groupt.*

Group.*

tto

ditttr

ditto

(Uuplorcn.)

(L nprovcn.)

(Lrnproven.)

(L:nproren.)

(LInprorcn.)

(Ulprorcn.)

(Uuplorcn.)

(Unprorcn.)

cl i

/errr, lie,

Gunncdsh or Neuloi

trnd Li!hgow Cool-licld.

Prtxlull irc Ct'rrl-lUe rr-l surcs, rvitlt U/or"op-l

trtittagotrg

Itluc llountiliD

Corl.flcltl

Dentltsey

["** a

(

o F4

z o

Group.

f.l Miild.le Coal-Measures lzl

Prodrrctilc Oonl-lIea -l I

Tonrago, or East Maitlan,cll

sures, rvilh Glossop-

teris, &.c. l

Io Upper Marine Series t i E ct-t

ilIulbring bcds. I l. Irnclinitrl Shnlcs \f rrrrc Ror:k. I 2. Nowra Grit.

3. Bmnrtorr bcrls, | 3. Conjola bcds.

rvitir crratics-

l\-allernrang bcds.

)

Grou2t.lcrya, Grottlt. Greta uroup. u?'etct

I Productivc Coal-Ilcc-l

Lower Coal.[eas[res I

sures, rvith Glnssop-l

I'erleltraria, teris. I'ertelrariq,l teris,

Unconfornity ?

l. Rha.copteris bctls.

CABBONIFER,OIIS ...

(Hidden by orcrlap.) (Eiddcn by ovcr'lnp.

3. Rhacopteris

(Unprorcn.)

(Unprore n.)

tlitto

d.itto ?

(Urrprovcn.)

(Unproren')

Rhocopteris and Lepidodendron

Unconfornity ?

I\{t. Lanrbic Sand-l t stones and Qunrt-l !

zitc.

Lcpidorleudron beds of Goonoo

Goonoo.

bcds.

beds.

)

SILUN,IAN

luP')

2. Ilorinc bcds, uithl Producltts, Conuil laria, &c. Lepidodendron

DEVONIAN

(Ilidden by orer.

&c.

Iarley Group.

Lo,**

ditto

I }loruian Limestone. I

I This classilication is provisional : the Group may hovc to bc closseal rrith the Middle Coal-Mcasures.

Geology of Australian Coal Basins

ll5

vtrRTleAt OF STRATA IN

S trET]I@SV BU RWOOD GULLY

AT END or MAIN RUN

'*rbft e<a)(€

crorio

(Sof fr erv.

t"Ylyot^"o cd-' .o['I*Pe6"

bl ntt C4/ tah lat Slac &an*. a ,o

tt o

6,9 E-r4t.9raL----

3{t,So'asatc ,%az*ac fu'z y,r.t& Bua-- -*fur-..rJ, v Figure 2. Part of a column section at Victoria Colliery, dated 1860 (Branagan, tg72).

History

+ F

116

the very numerous discoveries ofcoal on the south coast, at Adventure Bay and in the headwaters of the Coal River, no successful mining occurred until 1834, when the colonial Government opened a coal mine at Saltwater River on the Tasman Peninsula. Prior to this, a small scale mining attempt at Coal Head, Macquarie Harbour, was made by the prison authorities, and is mentioned in the narrative of the convict Alexander Pearce.

The existence of coal in the Fingal Valley near St Mary's was known from as early as 1843, but due to access difficulties well-organised mining did not

commence in earnest until 1888. Early prospecting for coal in the Fingal Valley was generally undertaken without direct geological advice; prospectors found many seam outcrops in the creeks and gullies (Figure 3), and mining was commenced

from these points. Several significant north-south faults separated the individual mine areas, and

mineable blocks, bounded by geological hazards, were delineated as mining proceeded.

The first commercial coal mining venture was made

at Southport by a syndicate led by Charles Swanston, one of two Attorneys General of the day. Whilst the syndicate received some Government assistance to sink the shaft, and the company achieved a measure of short-lived paper prosperity, the venture ultimately failed.

Western Australia A German naturalist, Preiss, first reported finding coal (probably fossiliferous carbonaceous shale) on the Murray River, south of Perth. Eventually, a small mining company was formed to explore this find. The company engaged Dr Ferdinand von Sommer, who arrived on 15 February L847 to become the first geologist to be employed in Western Australia.

During the 1840's coal mining started on Schouten Island and near Jerusalem (Colebrook) in the headwaters of the Coal River, while in the 1850's work was begun on a grand scale near the Denison Rivulet. This venture also failed, like many of the early mining activities, due to a massive expenditure on infrastructure, leaving no funds for undergrnund development. The Mersey Valley coalfield was opened up in the 1850's and many small mines worked in this field intermittently, the last one closing in 1962. The New Town coalfield, near Hobart was also worked in the 1850s, with sporadic activity frnally ceasing around 1910.

While the Murray River report was being considered, A.C. Gregory, the Assistant Surveyor-General for the Colony, with his two brothers reported finding coal on the Irwin River on 9 September 1846 (Maitland, 1900). Nearby, at Eradu on the Greenough River, coal was found in 1906 in a calyx bore, but further drilling showed only lenticular seams of poor quality. A discovery (the only natural exposure in the coalfield) was made on the Collie River near Survey Station 17 in 1883, but was not reported for six years (Maitland, 1900). Prospecting continued upstream on the Collie River until a shaft near Survey Station T26, sunk to 15m, discovered a 3.4m seam. H.P. Woodward, a Government Geologist, was

An ambitious project began at Seymour in 1861 with the aim of mining coal and using the 'slack' or waste coal to retort kerosene. Although the retorting project failed, coal continued to be mined at Seymour intermittently until 1964, and at Dalmayne, north-east of Seymour from 1915 to 1954.

SECTION oFA HrLL BEllv€€tr S-T MARY'S PASS^noFIl'lCAL N EA R

Mi CROOMS I

c_ir i_ ,.

-9,i1

"..t''/ ,

A (h'rrn,r/trrrt B l7b>r (oul .l(ar,r,.,rt'-l'rtrtt/.rhrrrt ..C CLr,r1,V 7'1'71r7/nrrtrtrtr rocl D lt rtr(,r'trnr' :,7,/rfc trlA liryt t1 (orrrk ,fptr tlcra' rlud ot/rt'r' J'hr/1,r E ("r,tr',rt n/tr/r ,lrtrt ,'/q cnl.(/["trtr'r at( //t, /tr'/,/,/r.t /7 r,r1 t'o((ttdzd . F f Ir/.,'t. ryJt(ft, irl lr rztt/atllrd ,'/a,q .1./4lr.r h..rarrrfu17t ttai H t^/L (kut,'t4 rtt rur .

Figure 3. Cross-section of coal-bearing strata near Fingal, Tasmania (Selwyn, 1855).

Geology of Australian Coal Basins

tL7 sent to report on the find early in 1891, and that year Dr J.R.M. Robertson, a coal expert, visited Collie and recommended that a series of test holes should be drilled.

1901; Dunstan, 1901; Cameron, 1905; Morton, 1923; Reid, 1928).

The Government commenced a drilling programme in April 1892 and raised a bulk sample of the coal to test for railway purposes (Maitland, 1893; Woodward, 1894). During 1895, the Government drove an exploratory tunnel near Survey Station T26, and the Collie Coal Mining District was declared open for selection on 23 March 1896. Commercial production commenced with the arrival of the railway late in 1898, and the Government, having been responsible for the early exploration and development of the coaifield, withdrew from these activities. Private exploration, however, continued in the area for many years.

Queensland Knowledge of the southeast Queensland area was gathered rapidly by explorers and pioneers during the years that followed the first European exploration of the Brisbane River by John Oxley in 1.823-24. The first recorded observation of coal in Queensland was made by Major Edmund Lockyer who, on 13 September 7825, noted a bed of coal cropping out in the bank of the Brisbane River, close to the present location of the Kholo Bridge near Ipswich. Ludwig Leichhardt, the i11-fated explorer and naturalist, observed coal at various places during his epic journey of 1844-45 from Moreton Bay to Port Essington. He recorded coal occurrences in the Surat Basin south of Chinchilla, and in the Bowen Basin on the Comet and Mackenzie Rivers. The latter discovery was close to the Blackwater deposits which were to be of major significance more

than a century later.

Numerous observations of coal were made

throughout the State during the latter half of the nineteenth century. Many of these discoveries came about as a matter of chance; pastoralists opening up the country for agriculture noted coal in the banks of streams or as they dug wells, dams and bores, and prospectors scouring the creeks and sinking shafts in search for gold or other valuable minerals sometimes happened upon coal instead. Often discoveries went unrecorded, being passed on only by work of mouth, and it was left to the Government Geologists of the time to investigate these rurnours systematically and report on their findings. The first geological stydies.of Queensland coal measures were carrred out in the early 1850's by W.B. Clarke and Samuel Stutchbury, first Geological Surveyor of New South Wales. By 7872 sufficient information had been gathered for Richard Daintree to publish the first geological map of Queensland (Daintree, I872), and the main coal-bearing areas of the State are shown on the map with remarkable accuracy. In addition to Clarke, Stutchbury and

Daintree, the major contributors to this early phase of exploration included many of the great names of early Australian geology such as Augustus Charles Gregory, Julian Tenison-Woods, Robert Logan Jack, William Rands, Robert Etheridge Jnr. and Andrew Gibb Maitland (e.g. Jack, 1879, 1887; Maitland, 1889; Rands, 1891). During the first half of the twentieth century the work of evaluating the State's coal resources was continued by the Geological Survey, with the contributions of Benjamin Dunstan, W.E. Cameron, L.C. Ball, J.H. Reid, and C.C. Morton being espccially noteworthy (e.g. Ball,

Although steam-driven rotary drilling equipment was available in the latter half of the nineteenth century, it was used rarely in Queensland. Daintree recommended in 1873 that diamond drillholes be sunk in the Ipswich, Darling Downs, Mary River and Rockhampton districts to test for coal, but the idea was not taken up. Robert Logan Jack (1879) revived interest in the use of diamond drilling equipment, and in 1884 the Government acquired three rigs which were put to use at Pelican Creek (near Collinsville), Burrum, and on the Darling Downs.

Victoria Black Coal Black coal was first discovered in outcrop in Early Cretaceous strata at Cape Paterson in southwest Gippsland by the explorer William Hovell in 1826. In 1858, Selwyn identified black coal from a hand bore near Wonthaggi (Figure 4), and reconnaissance mapping by C.S. Wilkinson (1865) revealed the existence of thin black coal seams in Early Cretaceous sediments near Apollo Bay. Royal Commissions on Coal in 1889-1901 and 1905-1906 called for increased geological surveying for black coal in south-west Gippsland, which was considered to have the greatest promise at that time. In response to the first of these, J. Stirling (1892, 1899) produced a series ofreports, mine plans and geological maps giving details of these Early Cretaceous coal measures. A bore sunk for water at Wonthaggi intersected almost 2rn of black coal at a depth of about 5m in 1908, and the surrounding land was reserved by the Government as the site for a State Coal Mine

(Knight, 1969). Drilling by the Mines Department outlined an estimated 20Mt of coal, sufficient to justify the opening of the Wonthaggi State Coal Mine in 1910.

Brown Coal Brown coal was found atLal Lal (1857-58), and in deep leads at Creswick, Ballarat, Daylesford and McKirley's Creek (near Neerim) in the 1860's. The first reports of brown coal in the Gippsland Basin were in 1873 at a location 5km northeast of Moe, where the coal was exposed on the south side of the Latrobe River.

In 1879, Godridge recognised further outcrops of brown coal on the Latrobe River, north of Yallourn, and this later became the site of the Great Morwell Coal Mining Company's open cut at Yallourn North. Interest in brown coal continued at a low ebb, but small mines were developed at Altona (1888), Boolarra and Yallourn North (1889), Benwerrin (1899) and Deans Marsh (1901). A Mines Department bore at Gelliondale intersected 60m of brown coal at a depth of 14m in 1912. In 1913, on the advice of H. Herman, recently

appointed Director of the Geological Survey, the Mines Department commenced boring to locate a site for a brown coal mine to serve a power station and associated briquetting works. By 1918 suffrcient coal had been proved for this purpose at Yallourn in

the Latrobe Valley, laying the foundations for one of the world's maior brown coal mining regions.

Hi story

r18

South Australia The search for coal in South Australia began with the establishment of the Colony in 1836. The importance of coal as a fuel was clearly appreciated at the outset, since Colonel William Light, the first Surveyor General, and been instructed to site the capital (Adelaide) near a port, arable land, fresh water and a readily useable coal seam. A "Mine and Quarry Agent and Geologist" was appointed, but locating coal deposits had a low priority as there was a readily available supply of wood fuel. Coal exploration was conducted in a desultory fashion over the ensuing 75 years; discoveries were

fortuitous and generally associated with drilling for underground water supplies. On several occasions the Government offered financial rewards for the discovery of a commercially viable coalfield, and unsuccessful coal exploration expeditions were funded at various times by private enterprise and Government sources.

Broutn CoaI (Lignite) Lignite (brown coal) was intersected at a depth of 22min a borehole at North Adelaide in 1857. The first attempt to mine coal in the State was made at this site in 1858, but there was ultimately no production. Lignite was subsequently discovered near Pidinga in 1885, but the remote location of the deposit precluded more exploration. Further investigation of Tertiary lignites took place in the 1920s and 1930s as a consequence of developments in Victoria using lignite of the same general type and age. The Department of Mines expanded its drilling capacity and embarked on a comprehensive drilling programme to prove the extent and quality of the known Tertiary lignite deposits, but none of these deposits matched the Latrobe Valley with regard to seam thickness, extent, mineability or quality.

Black (Sub-bituminous) Coal In 1888 coal-bearing shale of Triassic age was discovered during excavation ofa railway dam near

Leigh Creek. The Government Geologist, H.Y.L. Brown, mapped the limits of these coal measures in 1889 (Brown, 1891), and on Brown's recommendations the Government undertook drilling to trace the extent of coal in the area generally. World War II provided a stimulus to interest in local coal development. Following appraisal of the geological structure of the Telford Basin by the Government Geologist, L.K. Ward (Ward, 1943), the Adelaide Electric Supply Company considered development of the Leigh Creek deposits by open-cut extraction with Government assistance. Mining was

initiated in 1943 to provide coal for electricity generation, and in 1948 management was taken over by the newly-created Electricity Trust of South Australia. A summary of geological work at Leigh Creek in the ten-year period from 1941 is given in a comprehensive report by Parkin (1953), which includes contributions on particular aspects by S.B. Dickinson, C.Kerr Grant, E. Anderson and G.H. Taylor.

DETAILED ASSESSMENT OF COALFIELD STRATIGRAPHY AND STRUCTURE Coal geology in Australia continued to develop during the first half of the twentieth century in

much the same way as it had during most of the century before. Geological mapping and drilling programs, supplemented by a number of palaeontological studies, yielded a steadily increasing amount of information on the stratigraphy and structure ofthe different coal-bearing regions. These studies also provided much of the framework needed to build up an

understanding ofthe geologic history ofthe country in general.

The development ofan orderly system oftopographic maps after the Second World War provided a base for the publication of geological maps at standard scales. These replaced the random collection ofvery useful but variable scale geological maps of the pre-1950 period, and by the 1970s geological maps at a scale of 1:250 000 were available for most of Australia. The Bureau of Mineral Resources (BMR) was responsible for much of the mapping in Queensland and Western Australia as well as the Northern Territory and the Australian Capital Territory, while the relevant State Geological Surveys carried out this task in other regions. The geologists from the State Geological Surveys and the BMR who compiled the 1:250 000 series of maps provided an invaluable basis for subsequent exploration of coal and other minerals by private companies; in central Queensland, for example, the joint GSQIBMR mapping program fortuitously preceded the rapid 1960's growth in the Japanese market for coking coal.

New South Wales Geological work in New South Wales expanded on the foundations laid by the early geological surveys of the principal coalfield areas. L.J. Jones re-mapped the southern portion of the MaitlandCessnock-Greta Coalfield between 1925 and L927, supplementing David's work in the light of new data from collieries, shafts and drill holes (Jones, 1928). This included publication ofstructure contours on the top of the Greta Coal Measures (Jones, 1939), and added an important marker bed, the "Fenestella Shales". By 1929, Jones had also produced large scale maps of the Newcastle Coalfield, but regrettably these have never been published. The unpublished D.Sc. thesis of Raggatt (1938) was a thoroughly scientific appraisal ofthe Sydney

Basin, with much emphasis on the palaeontology and stratigraphic correlation of the Hunter Valley sequences. The theme of this thesis was extended by Booker (1954; 1960) and Booker & others (1954). The Coal Geology Section of the Broken Hill Proprietary Co. Ltd was established in 1922, and had also developed by the 1950's into a powerful workforce engaged in drilling and mapping in the Newcastle area. A series of large-scale drilling programmes by the Bureau of Mineral Resources and the Joint Coal Board in the Upper Hunter Valley in the early 1950's includecl work by Foskett, Burton, Bursill, Konecki, Veevers and Reynolds. Booker (1953) reported on the coal resources ofthe Cranky Corner Basin, reinforcing the earlier work of David (1907) and Walkom (1913). Much detailed work on the Singleton Super-group, the equivalent in the Upper Hunter of the Newcastle and Tbmago Coal Measures, was published by Robinson (1969) and Britten (1972). In collaboration with McKenzie of BHP, Britten also published a revised subdivision and nomenclature of the

Geology of Australian Coal Basins

119

t2&te cf.9d

,tFaO cfEaadebne

btrlct of Shale |J'of.&vttbru I Jnptt Sum.t ofc.al

,I N

dDr' ir*ffr9.

ls"AaZ &.*ne")

l!d-itaIc

/OM, fshalo

#'6aLB./t..,bh) 7.,6*h.k (, ar{// Slal..

lo:63luta

4 Fe e

t i fl ad .,fa adsto n c mdi h),rystotto

&FecTZral

';-r-?a.l

:*i

'f-Tn:

| 9Foc'&anng

ront 95 Fttr

do-

IVo

lu tat

,/o A & lz'c

I a nlc l.fft e. [eI b uw z. -It t I t' ::' ( /8;8. c

/./t, t..lchTn. 0ot'ct-nncnt l)u'loyu t.

tlLrrtelr t'olht Itlio

Figure 4. Geological section of shaft in Cretaceous coal near Cape Woolamai, Victoria (Selwyn, 1858).

IIi story

120 Newcastle Coal Measures (Britten & McKenzie, 1969). Petroleum exploration programmes by Australian Oil and Gas Corporation Limited and other companies in the 1960s and 1970s also added much to the knowledge of stratigraphy and structure of the Sydney Basin, particularly in its central portion (Stuntz, 1972).

Little systematic geological rvork was done in the Southern Coalfield after Harper's (1915) Memoir until geological work was initiated by Australian Iron and Steel Pty. Ltd. This included consultative work by E.A. Rudd who mapped the dykes and faults in the area of productive mines in great detail. The A.LS. Coal Geology Section, established at Wollongong in the late 1940's, has indeed contributed much to knowledge of the detailed stratigraphy and mine geology of this region (Wilson & others, 1958; Wilson, 1975). The Geological Survey of New South Wales

recommenced detailed mapping in the Southern Coalfield in the early 1950s, (Hanlon, 1952; 1953), revising the stratigraphic nomenclature of the Triassic and Permian sequences (Hanlon & others, 1952; Joplin & others, L952). Hanlon also carried out detailed seam correlation studies to the south-west in the Moss Vale-Berrima-Bundanoon area.

The Geological Survey of N.S.W. (Rayner, 1954, 1955) produced very detailed maps of the Cullen Bullen-Lidsdale area in the Western Coalfield, but unfortunately these maps were never published. Mapping of a large area of the Western Coalfield, extending south and east into the Southern Coalfield, was compiled by McElroy and Relph in 1956, with the object of recording basic geology before the terrain was rendered less accessible by the rising waters of the Warragamba Dam (McElroy & Relph, 1961). Other mapping by the Geological Survey of N.S.W. included that of Whiting & Relph (1956) in the Burragorang Valley area, McElroy & Relph (1961) in the Burragorang-KanangraMittagong area, McElroy & Rose (1962) in the Clyde River-Ulladulla area and Bowman (197 4) in the Wollongong-Kiama-Robertson area.

In 1961, the Standing Committee on Coalfield

Geology of N.S.W. was established under the aegis of the Department of Mines (now Mineral Resources). Commencing from a small base of about 10 geologists representing the Geological Survey, the Joint Coal Board and major coal producing companies, this committee has expanded over the years to include more than fifty representatives of over 40 organisations. The Committee has acted as an indispensable forum for discussion and implementation, by the diverse bodies involved in the N.S.W. coal industry, of many matters relating to stratigraphic nomenclature, geological practices and resource appraisal techniques.

Drilling by private companies, the Electricity

Commission of N.S.W., and the Department of Minerals and Energy has continued to provide vast amounts of data on the coal resources in all coalfields of N.S.W. up to the present day. Records show a sharp increase in coal drilling from 68 L44m in 7971-72 to 267 313m in 1981-82 (Figure 5), before declining to a level of around 50 000m per year.

Queensland Powell Duffryn Technical Services carried out an appraisal of the Queensland coal industry in the late

1940s (Powell Duffryn Technical Services, 1949), finding that the techniques of coal exploration, and particularly drilling, were mostly outdated, poorly-planned and uncoordinated. As a result of their recommendations, the Drilling Branch of the Department of Mines was substantially expanded

and re-equipped, and a new Coal Section was formed in the Geological Survey of Queensland. These two organisations worked together through the 1950s with the object of proving sufficient

reserves in the vicinity of operating collieries in the West Moreton field to justify mine expansion and modernisation. As this need was met, investigations were undertaken in other areas of the State, firstly at Burrum, and subsequently at Collinsville, Nebo, Baralaba, Moura, Theodore and Blackwater. This programme of systematic Government exploration has been continued to the present day, extending throughout the Bowen Basin, as well as the Surat, Moretbn, Eromanga, Galilee, Callide and Wolfang Basins.

Another important step in the systematic exploration of the State's coal-bearing provinces was taken in 1950 with the initiation of a joint programme of geological mapping by the Bureau of Mineral Resources and the Geological Survey of Queensland. A series of geological maps at a scale of 4 miles to the inch (later 1:250 000) was produced from this programme, with accompanying Explanatory Notes and Bulletins. This work was an important basis for most subsequent coal exploration. Major involvement in coal exploration by private companies began in 1957 when Sir Leslie Thiess, who had been associated with opencut coal mining at Callide and Blair Athol for several years, commissioned Dr F.W. Whitehouse to seek bituminous steaming coal suitable for blending with sub-bituminous Callide coal for export. Whitehouse's work led to the discovery of soft coking coal at Kianga, but the product was not suitable to Japanese steel producers at the time. Hiroshito Okano, a geologist with the Mitsui organisation of Japan, recommended exploration near Moura with the aim of discovering hard coking coal between the soft coking Kianga deposit and the semi-anthracite at Baralaba, 60km to the north. This exploration was successful and led to the opening of the Moura open-cut in 1961.

In 1960 the San Francisco based Utah Construction

and Mining Company set up in Australia. The company believed that Queensland offered bright coking coal prospects -cleposits for the discovery of large suitable for open-cut mining, and appointed Australian geologist Don King as exploration manager. Initial work in the Moura-Theodore area found-only non-coking coal, but pursuing a similar line of reasoning to Okono concerning the systematic increase in rank away from the tectonically disturbed area to the east, King switched investigations to the area around Blackwater townsh-ip. Programmes of field mapping and noncored drilling revealed a large deposit of shqllow, high-grade coking and non-coking coal s-outh of the Central Railway near Blackwater. The deposit was in close proximity to, and in the same stratigraphic unit as old colliery workings in the area, but was of better quality and much more extensive.

Further reconnaissance along the western flank of the Bowen Basin subsequently revealed vast reserves ofhigh quality coking coal along a strike

Geology of Australian Coal Basins

t2l length of about 250km. A string of eight large open-cut mines was developed by Utah and other operators to extract coal from these reserves.

Western Australia Although most geological studies for coal in Western Australia have been confined to the Collie Basin, there has been, since the mid-1960s, a series of company exploration programmes in the Canning Basin. Some of these have been successful in locating carbonaceous sediments and minor coal seams. This work was based largely on the subsurface stratigraphic data derived from BMR mapping and oil exploration activities in the Canning Basin. Petroleum and coal exploration was also carried out in the Perth Basin, and details of this have been summarised by Lord (1975). The search for concealed coal basins analogous to the Collie Basin on the Yilgarn Block has continued since the Collie discovery in 1883. So far two other basins have been found, the first being the Wilga Basin, discovered in 1918, and the second near Boyup Brook, discovered in the 1980's by the Griffin Coal Company.

South Australia Utah Development Company Ltd acquired title over the southern part of the Arckaringa Basin in 1971, to investigate an occurrence ofcoal that had been noted in a bore at Lake Phillipson in 1902-1905.

300

Recognition that the coal measures were of Early Permian (Artinskian) age in 1957 fostered a hope that coking coals similar to those of the Bowen Basin of Queensland might exist in the area. The occurrence was also adjacent to the route ofa proposed new railway connecting Tarcoola and Alice Springs. Drilling has since disclosed extensive deposits of low-rank, high-volatile, non-coking, steaming coal. The private sector, encouraged by Utah's success, showed a growing interest in coal search, a response engendered by knowledge that additional coal would be required to fuel expanded power station requirements. Drilling to probe basal Tertiary (Eocene) sediments in embayments marginal to the Eucla, Murray, Otway, Northern St Vincent and other basins resulted in the discovery of several significant new lignite deposits.

Gravity, airborne magnetic and resistivity surveys were conducted over known coal deposits on the western margin of the Murray Basin in L977, and geophysical data were reinterpreted to indicate other possibly similar sub-basins in the region. Drilling between 1979 and 1981 by CSR Limited was also successful in disclosing a new lignite deposit at Sedan since proven to contain 230Mt of in situ coal resources.

Western Mining Corporation Ltd undertook reconnaissance drilling which led to the discovery,

METRES DRILLED (Thousands)

1965

1970

1975

1980

1985

1990

YEAR ENDED JUNE Joint Goal Board Data Figure 5. Aggregate length of exploration drilling per year for coal in New South Wales, prepared from Joint Coal Board data.

History

L22

in 1979, of the Kingston Tertiary lignite deposit in

an embayment of the adjacent Otway Basin. Sub-bituminous coal of Jurassic age was also intersected in drilling undertaken by the Department of Mines in the Polda Basin in L977 , and following successful application of the technique at Leigh Creek, high resolution reflection seismic surveys were undertaken by the Department of Mines to investigate coal seams at Lock.

Victoria By 1950 nearly 6Mt of brown coal per year was being produced in Victoria from the Yallourn open-cut, then Australia's largest coal mine. Between 1941 and 1955 systematic drilling to locate additional shallow brown coal was extended by the State Electricity Commission of Victoria to other parts of the Latrobe Valley. At first little attention was paid to geological structure, and the depth of bores was limited by engineering considerations. Nevertheless, some understanding of the stratigraphy and properties of the various seams gradually emerged through the pioneering work of A.B. Edwards, D.E. Thomas and W. Baragwanath (Edwards, 1945, 1950; Thomas & Baragwanath, 1949-51; Baragwanath, 1962). By 1980, Gloe and his colleagues in the State Electricity Commission of Victoria (SE-CV) had developed a comprehensive three-dimensional picture ofthe geological structure and stratigraphy ofthe Latrobe Valley Depression and adjacent areas to the south-east, and had produced reliable maps of the concealed subcrop of the major coal seams (Gloe, 1960, 1975, 1984). These were backed up by structure contour and isopach maps and crosssections enabling greatly improved estimates of the coal resources and definition of the main coalfields.

In 797 4 the Department of Mines resumed its interest in coal exploration, and drilling at Stradbroke demonstrated the presence of a substantial new brown coal field. Investigations moved to the Yarram-Alberton area in 1979. From 1977 to 1983 various exploration companies mounted brief but intensive drilling campaigns, notably in the Alberton Depression, the Port Phillip Basin, the Murray Basin, and, to a lesser extent, in the Gippsland and Otway Basins. From 1977-79 CRA carried out exploration in the Gelliondale coalfield under a joint venture with International Oil Proprietary (IOP), and this work was continued after 1979 by ARCO and IOP. Minor exploration was carried out in the Murray and Otway Basins by SECV in collaboration with the Department of Minerals and Energy (DME) during 1979. Drilling in the Alberton area by DME and SECV from 1979 to 1982 demonstrated the presence of substantial additional brown coal resources in the AlbertonSeaspray Depression. A change of Government policy in November 1980 spurred exploration by private companies outside those parts of the Gippsland coalfield which had been explored by Government drilling. This resulted in the recognition of substantial additional resources in the Murray and Port Phillip Basins by CRA, and minor extensions in the marginal areas of the Gippsland Basin. Much of this new coal, however, is deeply buried and/or overlain by basalt, and compares unfavourably with the large, shallow, low-ash brown coals of the Latrobe Valley area.

Tasmania Geological studies of Tasmanian coal, up until the 1970s, were based mainly on periodie visits by geologists from the Tasmanian 6gel6,gical Survey, including T.D. Hughes, F. Blake, J. Baird and V. Threader. The first geological appraisal ofa coal drilling programme on the Fingal Tie,r, south of the present entry to the Duncan Mine, was made by

Baird (1961).

In the period from 1973 to 1981, the Department of Mines geologists, particularly V. Threader and C. Bacon, supervised closely spaced drilling programs on the Fingal Tier south and east of the Duncan Mine. A total of 72 holes were put down, involving more than 30 000m of open hole and core drilling. Since 1982, Carol Bacon of the Department

of Mines has been compiling reports from both historical and recently acquired inforrnation on all of the Tasmanian coalfields (Bacon, 1990). These carefully researched works, now numbering more than 20, incorporate the results of the active coal exploration period from 1977 to 1982.

In the late 1970's the company operating the colliery in the Fingal Valley commenced exploration adjacent to old mine areas on Mt Nicholas, and subsequently extended geological mapping and

drilling to Tower Hill, St Pauls River and Royal

George. Between 1978 and 1985 the Cornwall Coal Co. N.L. drilled a total of 50 exploratory drill holes, some being related to the opening of a new mine (Blackwood Colliery) in 1980, adjacent to the old

Cornwall Mine Workings. Geologists involved with those mapping and drilling programmes included C. Parbury and J. Bryan.

Away from the Fingal Valley and the East Coast coalfields recent exploration has not been very successful in locating readily mineable coal deposits. The Woodbury deposit, a deposit in the York Plains Coalfield with open-cut potential, was drilled in the 1980's, and a small resource of open-cut coal was also delineated at Langloh in the Hamilton district.

COAL PETROLOGY AND RELATED STUDIES Although others had been working in the fi,eld before his arrival, the appointment of Professor C.E. Marshall to the Edgeworth David Chair of Geology in the University of Sydney represented a c:legree of commitment to coal petrology which had not previously been seen in Australia. Marshall arrived in Sydney in 1949, having previously been at the University of Nottingham. His name was already well known through the book The Nature and Origin of Coal Seams (Raistrick & Marshall, 1939), and through his subsequent publications. Most of Marshall's microscope examinations were made using thin sections, which were in common use until the 1960s, except in Germany. Thin sections of bituminous coal are diffrcult to make, since the vitrinite needs to be less than 7pm thick to be translucent. Nevertheless, Marshall had accumulated an outstanding collection of thin sections of Carboniferous coals from the Northern Hemisphere and brought these with him to Slrdnsy where they were much used by his colleagues and students. (Marshall had also worked for some time in the United States, so his collection included more than just British coals). With Dr Denis Tompkins and others, Marshall initiated a range of studres

Geology of Australian Coal Basins

123

making use of, but not limited to, the microscopy of coal. These studies included characterising Australian Permian coals in terms of properties such as carbonisation, and making comparisons with Carboniferous coals (Marshall, 1953; Marshall & Tompkins, 1961). Even before Marshall arrived, Dr J.A. Dulhunty had been carrying out petrological and palynological work at Sydney University on Australian fossil fuels: peat, various kinds ofcoal, and,oil shales, especillly torbanite, which was then being retorted commercially at Glen Davis to make motor spirit (Dulhunty, L944). Dulhunty used polarising microscopy to show the nature and structure of the algal bodles in torbanite. He became increasingly interested in the physical and chemical properties of fossil fuels, especially coal, and in the underlying reasons for this variability, and it was on these questions that he, with Penrose, Harrison and other cblleagues, concentrated during the 1950s (Dulhqnty & others, 1951). Dulhunty and Marshall thus both led groups, within the same Department, whose work was complementary. At about the time Marshall arrived, palynology was oeing carried out at several Australian centres (in

addilion to the University of Sydney); by Dr Isabel Cookson in the University of Melbourne (especially on Tertiary pollen), by Dr Noel de Jelsey in the Geological Survey of Queensland (on Permian and Mesozoic sporomorphs) and by Dr Rasil Balme in the University-of Western Australia, who carried out a pioneering study of spores in the Collie Coalfield in his B.Sc. Honours year. Balme had hoped to work towards a Ph.D. degree with Marshall in Nottingham, but this plan had to change when Marshall came to Australia. Instead Balml went, in 1949, to work with the National Coal Board in England for three years. His studies there were mainly on the palynology of British Carboniferous coals.

At the time of Balme's departure, CSIRO was setting up its Coal Research Section in Sydney' B-y early 1951, Mr John Hennelly had palynology w-ell undilr way there, drawing on foundations provided by the work of Dulhunty and de Jersey. In 1952 B-alme returned to Australia, joining the CSIRO Coal Research Section to take charge ofboth the palynology and petrology ofcoal. His subsequent ilalynolo[ical work laid the modern foundations of Permian spore/pollen systematics in Australia. The coal petrol-ogical work took the form of systematic, whol-e seam, quantitative studies using a large

number of pollshed blocks of coal and measu-ring the intercepts of the bands. In this way the whole thickness ofthe seam could be traversed using reflected light microscopy. There were also specific for example of the forms of inorganic studies

sulphur -in Australian coals.

During the late 1940s and early 1950s' Australia had sriffered from inadequate supplies of black coal from New South Wales. This prompted other states to look more closely at their own resources. Victoria had long been using its brown coal resources for electricity generation and briquette manufacture and, with expansion of this production, an increasing effort began to go into the geology and petrologylf brown coal. The State Electricity Commiision of Victoria not only carried out its own research but also supported work at the University of Melbourne and elsewhere. For example, microtome sections of brown coal were prepared in

the University of Melbourne's Botany Department and, togetherwith conventional sections, these were exa.mined by Dr Austin Edwards of CSIRO, based in the Geology Department of the same University (e.8. Edwards,-1945, L947). This tradition of carrying out and supporting research began with Dr Herman in the eariy days of the SECV. It was carried on very ably by Dr George Baragwanath, whose interests sp".tnird the che*mistry, geology and petrology of brown coal (Baragwanath, 1962), and opened the way to a substantial research establishment in Meibourne and a geological/petrological branch led for many years by Dr Claus Gloe.

In South Australia, the unreliability of coal

shipments from New South Wales led the State Goiernment to initiate large scale mining at Leigh Creek. In support ofthis effort, the Geological Survey of South Australia decided to make a petrolbgical study ofthe Leigh Creek coal and any -othe.s wtrictr had any prospect of use' Accordi'lglY, Geoff Taylor was sent in late 1950 to work with Marshali and Dulhunty in the University of Sydney. On returning to Adelaide in mid-1951 he made a comprehensive petrological study of LejSh Creek coal-(incorporat-ed in a compilation by Parkin, 1953), becoming interested enough in this area of work to travel to Germany in mid-1953 for further study. There he worked as a Ph.D. student under Professor Erich Stach, making a comparative petrogocial study of the coking behaviour of German and Australian coals. Taylor returned to join the CSIRO Coal Research Seition (later the Division of Coal Research and now the Division of Coal and Energy Technology) at the end of 1955 to join Balme and others already working in the field. In the following period Balme was able to concentrate on palynology, producing work which has been the foundation of much modern Permian and Mesozoic palyno-stratigraphy. Taylor concentrated on coal petrology, principally using reflected light microscopy and quantitative analysis with polished grain mounts, which by-1956 were well on the way to becoming the standard techniques that they have remained. The CSIRO group [as remained active ever since, although palynology did not survive long in the Division of Coil nesi-arch after Balme's departure. Dr Slade Warne, Professor Alan Cook, Dr Michelle Smyth, D-r Hanan Kisch, Dr Michio Shibaoka, Mr Nigel Russell, Dr John Hunt and others joined the group, each contributing original petrological work on Australian coals, oil shales and petroleum source rocks. Warne later joined the University of Newcastle concentrating his research princiPally on mineralogy, making extensfue and innovative use of

thermal inalysis techniques. Cook (see below) jgined the Joint Coal Board and later the University of Wollongong. Smyth, Shibaoka and Russell remain at CSIRO-(although Dr Shibaoka has since retired). Shibaoka had d=one much on coalfield geology in Japan before coming to Australia to pursue, not only further such studies but also to carry out very productive work on the petrology of.coal utilisation especially liquefaction and combustion. Smyttr has alio contributed much on coalfield petrology, her emphasis having moved progressively to the miiroscopy of pelroleum source rocks and-problems of oetrol6tim s-eneration. Hunt also moved into the peiroleum fieid. Since 1980 Taylor' now at ANU and working with Mrs Susie Liu, has returned to an the use of transmission electron earlier'interest

Ilistory

t24 microscopy to examine coal and carbonaceous rocks. Dr Miryam Glikson, who studied with Taylor, has also used TEM in the study (at ANU) of oil shales and subsequently in examining a range of carbonaceous rocks in the University of Queensland.

In 1961 Dr Claus Diessel came to Australia to join what was to become the University of Newcastle. He had studied in Essen under Professor Mackowsky who was famous for her petrological work related to the industrial uses of coal. At Newcastle Diessel has worked on a wide range of problems including the geology of coal measures and coal seam deposition, adding much understanding of facies and the geological basis of petrological properties. His use of reflectance has extended to carbonaceous fragments in rocks which have undergone low grade metamorphism, so linking studies of coal rank to the assessment of metamorphic grade. Diessel has worked extensively on industrial topics, including the microscopical studies of liquefaction products and residues, coke-making and combustion of coal. He is particularly well known for his work on inertinite which, he has shown, plays an important role in making strong coke from many Australian coals.

After his earlier work in the National Coal Board in England, in CSIRO and the Joint Coal Board, Cook (in 1964) joined the body which was to-become the University of Wollongong. Soon after that University formally came into being he was appointed Professor and Head of the Geology Department, retiring from this position in 1990. Coal work of many kinds (including collaboration with industry), oil shale studies and the geology ofpetroleum generation have all been important areas of research for Cook and his colleagues, especially Dr Adrian Hutton on oil shales. A wide range of carbonaceous rocks have been studied - not only from Australia, but from many south-east Asian localities as well. Cook has contributed especially to the study of dispersed organic matter in petroleum source rocks. Coal petrology has been studied in several ofthe state geological surveys, although in most, the work has been intermittent. The greatest degree of continuity has been in Queensland with Dr Alan Davis, Dr James Beeston, Dr Barbara Jakeman and others having made contributions to understanding the large and diverse range of Queensland coals. In Victoria, the brown coal studies in the State Electricity Commission (referred to above) have been continued by Miles George, Glenda Mackay, Dr Greg Smith (of the BHP Group) and others to make the Victorian brown coals amongst the best known and understood low-rank coals anywhere.

Within the coal industry itself, there has for many years been petrological work in the BHP group, both at Newcastle and at Port Kembla. Some of this work was concerned with characterisation of coal held by the company, but much related to innovative research on the preparation and carbonisation of coals. For example Dr Charles Coin, of BHP Central Research Laboratories and more recently with the Australian Coal Industries Research Laboratories, has done much in the field of coke microscopy. Nancy Ng and others at ACIRL have also carried out petrological work on behalf of the coal industry. There has also been much collaborative effort put into the Working Group on petrography of the Standards Association of Australia, under the long-standing chairmanship of Harold Read.

In addition to the work already mentioned, there have been petrological studies by enthusiastic individuals and small groups at other institutions. For example, Dr Colin Ward, initially at the NSW Institute ofTechnology and since 1984 at the University of New South Wales, has made a particular study of minerals in coal. Dr Lloyd Hamilton, initially the University of New South Wales and CSIRO and subsequently at the Queensland University of Technology, has worked especially on the effect ofigneous intrusions on coal as well as on applied studies. He has also adapted specialised techniques, including scanning electron microscopy, for use with coal. Thus the forty years since Professor Marshall arrived have seen very great activity and development of new understanding. From being perhaps amongst the less well-known coals in the world the Australian coals are now arguably amongst the best (perhaps the best) known. Certainly publications on Australian coals contain, overall, some of the best documented information on coal type and coal rank. This development of understanding embraces the physical nature of coal, the properties of the components and their

behaviour during preparation, carbonisation, combustion and liquefaction. The skills applied have included progressively more refined use of quantitative light microscopy, reflectance measurement, fluorescence techniques and electron mrcroscopy.

The Australian effort has not, of course, occurred in isolation, but has involved good communication, and commonly collaboration, with people in other parts of the world. It was fortunate that the International Committee for Coal Petrology (ICCP) was set up in the early 1950s. This body has provided an important means of keeping coal petrologists throughout the world in touch with one another. The ICCP's work has also been important in establishing agreed definitions and standardised procedures for coal petrology. The ICCP's first meeting in Australia was held at Wollongong early in 1990. Past achievements and the healthy state of the art in Australia give reason to expect further progress. In two universities (Wollongong and Newcastle) and in CSIRO, coal petrology and related studies are a particular strength. With a wide range of research in progress at many institutions, there is a firm base for future development.

RECENT DEVELOPMENTS IN EXPLORATION METHODS The growth of the coal mining industry in Australia from 1960 was accompanied by a very substantial increase in coal exploration activities, particularly in New South Wales and Queensland. Exploration expenditure by both the public and the private sector has increased greatly during this period, reaching a peak in 1982 when over $100M was spent on coal exploration by companies alone (Ward, 1982). The lift in coal production during the 1960s was in response to the growth ofthe Japanese steel industry, and really involved only coal with coking properties. Although the growth of this industry slowed down in the 1970s, Australian coal production continued to expand as a greater share of the total market was secured in Japan, together with other markets in Taiwan, South Korea, Europe and South America. Emphasis turned to steaming

Geology of Australian Coal Basins

125 coal exports in the latter part ofthe 1970s, and

sediments. An extremely efficient means of obtaining relatively accurate geological information over large areas of poor outcrop was established using these drilling methods.

exploration activity saw a resurgence, culminating in 1981-82 when some 260 000m of drilling was carried out in New South Wales alone by the coal mining industry and government.

Drilling Technology Several developments in drilling equipment have had a significant beneficial impact on coal exploration since the early 1960s. A triple tube core barrel with a split inner tube was developed in Australia by the Joint Coal Board (Mosher & others, 1957) and became available soon after for general use in all types of core drilling. The split inner tube in the core barrel and the use of diamond bits increased primary core recovery and enabled cores of friable, brittle coal to be recovered in an almost undisturbed state.

Further improvements accompanied the trend to cores of larger diameter which took place in the latter part ofthe 1970s. As analytical tests on coking coal became more numerous and more sophisticated, these larger cores came to be needed where coal seams were sampled in several plies. The standard core size of the early 1970s was either NQ3 (45.1mm) or NMLC (51.9mm), and even larger core sizes HQ3 (61.lmm) or HMLC (63.5mm) are now generally accepted as standard by modern coal geologists.

The other significant advance in drilling technology was the introduction of wireline drilling rigs capable of recovering the coring tube without pulling the entire string of rods at the end of each run. The advantages of this technology were more immediately apparent to coal explorers in New South Wales, where drill holes in the underground mining areas were often up to 300m deep.

Open-cut Coal Exploration The relatively shallow coal deposits of the Bowen

The use of large diameter (150 and 200mm) coring for obtaining bulk samples of the coal seams was also introduced during these early exploration programmes, using similar truck mounted rotary drilling rigs (Figure 6). The shallow depths of the coal seams made this bulk sampling technique a cheaper alternative to trial pit excavation. The limit of oxidisation (LOX-line) of each potentially mineable seam in a deposit was delineated by drilling to determine the position of the open-cut low-wall. The extent of the partly oxidised zone between the seam subcrop and its limit of oxidisation was located with an accuracy of about 30m in this way. Chip samples were collected at regular intervals (usually every 0.5m) through the seam and tested for those parameters which best indicated oxidation. These were usually crucible swelling number (CSN) for coking coals or moisture content and specific energy for non-coking coals.

Geophysical Techniques Geophysical techniques have been used for some time in the Australian coal industry as a means of measuring, directly or indirectly, rock properties related to geological, geotechnical or other mining-related parameters. Geophysical methods have not, however, always met with wide industry acceptance; they have often been regarded as expensive, with the results obtained speculative or, at best, only approximations to reality. Indeed it could be said that even today, although acceptance of these techniques has improved, it is still restricted to the few methods which have very high resolutions and accuracies. Seismic methods and downhole geophysical techniques, first developed for the petroleum industry, began to be applied to and adapted for use

Basin were amenable to exploration techniques different from those generally used in New South Wales. The methods that evolved in Queensland were more suited to the flat to slightly undulating, sparsely populated terrain which typifies much of the Bowen Basin, and indeed most other coal bearing areas in that State.

in the coal industry from the early 1960s (seismic methods) and the mid-1960s to early 1970s (wire-line logging methods). Their introduction arose from increased demand for coal at that time, accompanied by technological advances in the areas

The search for open-cut coal had a high priority, and drilling was therefore designed to test the strata within 100m or so of the surface. Rotary rigs of the Mayhew 1000 type were used extensively in the 1960's, and indeed are still in use today. Air compressors, either on-board the drill truck or on a separate water truck, were used to provide the circulation medium, and the general lack of water in the immediate subsurface enabled non-cored holes to be drilled rapidly and relatively cheaply. One rig with a competent operator and two offsiders could drill 2 or 3 holes to about 100m each day, and in the mid-1970s the overall cost per metre was in the order of $8.00 for open hole drilling. The technique of 'open holing' down to the top of the coal and then coring the seam, a method referred to as 'touch coring', was used extensively. The coring technique developed for the Mayhew rigs differed from the more widely adopted wireline techniques in that a double tube barrel was attached to the drill string with core retrieval effected by pulling the rods from the drill hole. Tungsten chip coring bits were found to be more than adequate for use with air or

water circulation in the softer, shallow coal measure

of computer technology and electronics miniaturis ation.

In 1968, the Geological Survey of Queensland

engaged a contractor to conduct seismic reflection surveys at Moura and Ipswich, but relatively poor records were obtained from the shallow coal seams.

Further experimental geophysical surveys were conducted at Moura in 1970 by the Bureau of Mineral Resources, in conjunction with the Geological Survey, to develop techniques and to delineate the limitations of various geophysical methods for coal .exploration. Methods tested in that program were seismic reflection and refraction, gravity, resistivity, induced polarisation, magnetics and electromagnetics. Because of a need to solve mining problems in some of their underground collieries in NSW and

Queensland considerable developments in geophysical applications were also instigated by the BttP Co Ltd. Among the problems addressed in this way were the advance detection of geological anomalies following the commissioning of an early

longwall mine at Appin in the 1960s (Taylor, 1965) and stress-related outburst problems at Leichhardt

History

126 Colliery in Queensland during the mid-1970s. The

company's persistence in this work probably stemmed to a large degree from the fact that the majority of BHP operations at that time were deep underground mines, where drilling costs were high. The increasing number of large open-cuts in

Queensland, however, meant that many of the problems of underground mining were not experienced in that State. Geological anomalies, where present, could be resolved to a large extent by very close-spaced drilling at relatively inexpensive rates.

Seismic Reflection Seismic reflection techniques have been used in Australian coalfields since 1963 to map coal seam continuity and structure, mostly in areas where boreholes are widely spaced (Taylor, 1965). An early survey of this type by Mines Administration Pty Ltd over parts of the Bowen Basin for petroleum exploration was useful in mapping the broad basinal structure and the depth to the topmost coal seam, while the shothole cuttings from this survey provided additional assistance to some of the early exploration programs. In general, however, success with seismic methods in the early stages was limited by poor resolution, and faults with displacements of less than 15m could generally not be detected. This was in part due to the recording of low frequency signals and the use oflarge explosive qharges, so that the surveys were unable to resolve effectively reflectors at less than 400m, let alone any smallscale anomalies at lesser depths.

In 1967 and 1971 the BHP Co Ltd conducted surveys south of Blackwater which were successful in locating major structures, but were still unable to resolve faults with displacements of less than 3m. The inability of the method at that time to resolve small-scale features of importance in underground coal mining meant that it was little used as a mapping tool. It was not until 1978 that BHP, building on initial developments made by the National Coal Board (NCB) in Britain, conducted high resolution seismic surveys over its underground colliery holdings near Blackwater

(Harman, 1981).

Results obtained in this case clearly demonstrated that, under favourable conditions, the technique was capable of resolving small scale structural and sedimentological anomalies. Considerable success has been achieved since that time, and the accuracy and resolution of seismic reflection has been significantly enhanced, through the application of modern digital recording and computer processing techniques.

In- seam Seismic Method.s The in-seam seismic (ISS) technique, developed in Europe in the early 1960's (Krey, 1963) was introduced to Australia by BHP in 1974 for a survey

at Leichhardt colliery. The technique relies on the capacity of coal seams to act as guides for seismic waves, thus enabling the detection of discontinuities by transmission or non-transmission (Asten & others, 1981). BHP and others have developed ISS technology and expertise with various configurations, including face-to-face, face-to-borehole, and borehole-to-borehole arrangements.

Geophysical Logging Tests of downhole geophysical techniques were conducted by the Geological Survey ofQueensland

and Mines Administration in two boreholes at Ipswich in 1958. The results, however, were not particularly encourag"ing. Schlumberger conducted more successful trials in a GSQ borehole at North Ipswich in 1965, and commercial wireline logging services were introduced to the Australian coal industry in the mid to late 1960's by Austral Geo Prospectors, who had considerable experience with downhole logging for the petroleum industry. Single point resistivity and natural gamma tools were used successfully, but the most effective device was found to be the gamma-gamma or density tool, which was particularly responsive to coal and provided accurate definition of seam boundaries. Initially, single probes were run in the hole and data were recorded in analogue form on chart paper. Sondes were not generally calibrated, with the result that the logs could only be used qualitatively as a guide to lithology and for seam definition.

Combination sondes were introduced during the 1970s, allowing multiple functions to be recorded from the same tool to save logging time and to simplify log comparisons. The widely used'Coal Combination Sonde' (CCS) records caliper, natural gamma and gamma-gamma (density) responses, a combination which has proven to be ideal for coal seam resolution. Equipment design utilised a remotely controlled single-arm caliper which decentralised the tool in the borehole, reducing backscatter from the radioactive source in the sonde. Calibration of the tools and the application of computer technology for digital recording and reprocessing has enabled quantitative and semiquantitative estimates of some coal quality parameters as well as more reliable lithological interpretations. The most obvious consequence of the introduction of wireline logging technology as a standard part of open-cut coal exploration programmes, has been an increase in the level ofconfidence concerning seam depths and thicknesses in non-cored holes, and a consequent decrease in the number of cored holes drilled. Several companies have done considerable work on the quantitative interpretation of geophysical logs (e.g. Renwick, 1981; Haigh & Edwards, 1982). Use of quantitative techniques for the banded coal seams in the Surat and Galilee Basins of Queensland, in particular, has proven to be of significant benefit to deposit evaluation.

Other Geophysic al Methods Other geophysical methods used in the coal industry, although relatively inexpensive, have moderate to low resolution and are therefore only capable of broadly delineating subsurface geological features. These include magnetic, gravity, and surface electrical techniques. Magnetometers have been used in coal areas mostly for mapping of near-surface geology and igneous intrusions (Henderson, 1967), using ground-based methods or low-altitude airborne surveys with helicopters. The effectiveness of the method for structural mapping is largely dependent on the magnetic susceptibility of the strata concerned, which may be enhanced by mineralisation or emplacement of intrusions preferentially along fault planes (e.g. Wootton, L97 4). The most useful application has been in the identification of dykes, which are normally missed by drilling programs. Both magnetometer and gravity surveys were conducted by BHP in the area south of Blackwater in the late 1960s but results were poor and

Geology of Australian Coal Basins

L27

Figure 6. Drilling and logging of large-diameter drill core through a coal seam (Australian Coal Association).

Ilistory

r28 interpretation difficult. During the mid-1970s Utah experimented with portable magnetometer surveys for structural delineation during exploration and evaluation ofits underground coal resources. Results were again very poor, and the trials were discontinued after a couple of years. More recently, the University of New England's Geophysical Research Institute has used high-resolution proton precession magnetometers with considerable success for finding thin dykes and sills at several locations in the Bowen Basin (Stanley, 1985).

Australian organisations, and has been employed on a variety of coal mining and exploration projects both in Australia and overseas.

The use of gravity surveys in the past has been restricted to locating concealed sedimentary basins and to delineating their areal extent. The Blair Athol deposit in Central Queensland is one such area, and was found to give a good gravity response

ASTEN, M.W., GREZEL, K.J. & LEUNG, L., 1981: In-seam seismic techniques for coal exploration.

in detailed surveys by BMR in the late 1950s. During the early 1970s BHP, in a search for gold mineralisation associated with similar isolated sedimentary basins in the Clermont area of central Queensland, targeted several areas for drilling following gravity surveys. The Wolfang Basin was subsequently discovered and was found to contain extraordinarily thick coal seams. In L982 and 1983 BP Australia used a detailed gravity survey over known fault zones in the Winchester South coal deposit to evaluate the ability ofthe technique to delineate structurally disturbed zones. Preliminary results indicated that the method can be effective in broadly delineating these zones when used in conjunction with drill hole control. The Geological Survey of Queensland conducted similar surveys in 1984 over parts of the adjoining Lake Vermont coal deposit. Surface resistivity and transient electromagnetic (TEM) methods have been used extensively since the early 1970s to delineate basin geometries, seam subcrops and zones ofcoked and oxidised coal (Dodds & Haigh, 1982). Attempts to use these methods to delineate small scale structures and faults have had limited success, partly due to variable electrical characteristics offault planes and random surface effects.

Data Processing Methods Coal exploration programs typically include the gathering of large amounts of geological, geophysical and coal quality data from drilling programs and

related mapping activities. Following developments in computer technology in the 1960s, computerbased data processing systems were increasingly applied in various ways to coal exploration and mine geology programs throughout the 1970's and 1980's, and are now almost universally used as the prime focal point for geological studies throughout the Australian coal industry. Some of the earliest work in computer applications

to Australian coalfield geology involved the application of trend-surface analysis to coal seam

structure and isopach studies in the Wollongong and Newcastle districts of the Sydney Basin by Cook & Shiels (1968), Cook (1969) and Johnson (1974). Dr K.R. (Bob) Johnson subsequently became one of the leaders in introducing and developing computer technology for geological data processing in the Australian coal industry. Other developments in computer technology and its application are discussed by authors such as Goscombe & others ,1977), Wootton (1981), Dubrovich (1982) and Grimstone & others (1982). A comprehensive and powerful range of coal exploration and mining software has since been developed by several

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Geology of Australian Coal Basins

131

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History

133

COAL RESOURCES IN AUSTRALIA

ffioal

resources, quali ty and utilisation TP Maher, M Bosio, ER Lindner, DJ Brockway, AG Galligan, VJ Moran, C Peck, MP Walker, PA Bennett and BA Coxhead

The majority of the identified black coal resources of Australia are Permian, occurring in the Bowen Basin in Queensland and the Sydney-Gunnedah Basin in New South Wales (Figure 1). Other smaller, but still significant Permian deposits are present in the Galilee Basin in Queensland, the Oaklands and Gloucester Basins in New South Wales, the Arckaringa Basin in South Australia and the Collie and Perth Basins in Western Australia. Thick coal seams have been intersected in the Cooper Basin during petroleum exploration, but the coal is very deep and beyond economic consideration at the present time.

Triassic coal basins in Australia (Figure 2) are somewhat more limited in extent, but black coals of Triassic age are mined in the Callide, Tarong and Ipswich Basins in Queensland, the Telford Basin in South Australia, and in the north-eastern part of the Tasmania Basin. In recent years, intensive exploration of the Jurassic coal measures in the Surat-Moreton Basin in Queensland (Figure 3) has also identified large resources ofblack coal at shallow depths, but no significant exploitation of these resources has taken place to date. Small coal deposits ofboth Jurassic and Cretaceous age have, however, previously been worked in Queensland and Victoria. The major brown coal deposits of Australia are of Tertiary age, and are found in the Latrobe Valley area of the Gippsland Basin in Victoria (Figure 4). Small deposits of Tertiary brown coal, however, occur in most states, and mining of some of those in South Australia is currently under consideration for domestic power station supply.

Reporting of Coal Resources The administration of titles relating to exploration and mining of coal in Australia is controlled by individual State Governments, and, until recently, each State had its own code or set of guidelines for reporting coal resources. In 1986, however, the Government Geologists' Conference ratified an

'Australian Code for the Reporting of Identified Coai Resources and Reserves'(Galligan & Mengel, 1986). The term'Resources'is used in this Code to refer to all of the coal in silu which may have potential for use, with the categories 'Measured', 'Indicated' and

'Inferred' to describe the level of confidence attached to the assessment. 'Reserves', on the other hand, are those Resources which are planned to be mined and for which such planning has been undertaken. Figure 5 shows the categories for Identified (Measured plus Indicated) Resources and Reserves as defined in the new Code. Since the Code was adopted at about the same time as resource estimates were being prepared for this paper, it has not been possible to categorise all of the coal in Australia in terms of the newly defined

subdivisions, particularly those subdivisions relating to Reserves. Resource/Reserve estimates for the present discussion have been supplied by each State, and the criteria used may therefore still vary between States. On an Australia-wide basis, however, the Measured and Indicated Resource categories can be reasonably correlated, and this paper concentrates mainly on these two classes. Quantitative estimates of Inferred Resources have been made by all States except Queensland, where orders of magnitude within specified ranges (e.g. 'very large', 1000Mt) are used instead.

Coal Resources, Quality and Utilisation

134 The mineability of the coal is best expressed by the various classes of Reserves (In Situ, Recoverable and Marketable). For many deposits, however, insufficient exploration data are available to enable planning of extraction, while mining of others has not as yet been planned, and hence Reserve estimates cannot be stated for all of the nation's coal Resources.

The identifred black coal resources ofAustralia are

given in Table 1. In summary, these resources are:-

In situ Resources Measured + Indicated Resources: ..........69 669Mt 57 249lN'[t

+ Very Large (Queensland)

To provide some indication of the likely future mining method, black coal resources can also be subdivided into those with potential for open cut

mining and those potentially extractable only by underground mining methods. This process suggests the following categorisation for the Measured + Indicated Resources: Potential for Opencut Mining:

Also, with judicious blending, some steelmakers now use significant proportions of 'non-coking'coal in coke manufacture. Many modern coal preparation

Black Coal Resources

Inferred Resources:

Traditionally, black coal resources have been classified as involving either coking or non-coking coal. However, the distinction has become less pronounced in recent years, particularly with regard to the soft coking coals of New South Wales which are increasingly being sold as thermal coals.

26 745Mt

Potential for Underground Mining: .......+Z g24Mt

Within the categories of Measured and Indicated Resources, some 387o therefore have potential for open cut extraction. Further details of the distribution of Measured plus Indicated Resources by State and potential method of mining are also given in Figure 6.

plants are designed to produce multiple products (both coking and thermal coal) from seams which previously gave rise only to a single product stream. The major coking coal resources of Australia occur in the Bowen Basin in Queensland and the Sydney-Gunnedah Basin in New South Wales. The Department of Minerals and Energy, Queensland estimates that the Measured plus Indicated Resources of coking coal in the Bowen Basin amount to some L4297Mt, of which 2787Mt are potentially mineable by open cut methods.

In New South Wales, however, the tonnage of coking coal has not been clearly identifred, for the reasons outlined above. The majority of coal in the southern part of the Basin is nevertheless of coking quality, and many of the seams from the Newcastle-Hunter Valley region can also be benefrciated to produce coking coatr. Lesser quantities ofcoking coal occur in the Gunnedah Basin as well.

Brown Coal Resources A summary of the brown coal resources in Australia, on a State by State basis, is given in Table 2. In estimating the brown coal resources for Victoria, included in that table, the Geological Survey of Victoria has adopted a classification system which

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Figure l. Location

Geology of Australian Coal Basins

135

Figure 2. Location of Australian Triassic coal basins.

1 Callide 2 loswich 3 Tarong 4 Tasmania 5 Telford Figure 3. Location ofAustralian Jurassic and Cretaceous coal basins.

I I

t I

I I

1000km I

Surat-Moreton

Mulgildie

4 5

Styx Maryborough Poldo

Coal Resources, Quality and Utilisation

136

Figure 4. Location of Australian Tertiary coal basins.

1000km

BASIN

1 Gippsland 2 Otway 3 Murray 4 St Vincent 5 Bremer

broadly correlates with that used for black coal resources. In addition, however, the Survey has quantified two other categories: 'Identified Inferred Sub-economic Resources' and'Inferior Coal'. Identified Inferred Sub-economic Resources are determined by geological interpolation in extensions of known coalfields down to depths of 500m, while Inferior Coal refers to that part of the resource coal with an ash yield (dry basis) of between l0 and.30Vo. Considerable tonnages oflnferior Coal have been sufficiently explored to be classed as Measured or Indicated Resources, but in the present discussion all Inferior Coal is included in the last column of Table 2 together with the Identified Inferred Sub-economic resources. All of the resources listed in Table 2 are considered to be potentially mineable by open cut methods.

The tonnage ofblack coal produced in 1990-91 shows almost a four-fold increase over the l97O-7L production, which itself was some 53Mt (Figure 8). Saleable production (tonnage remaining after preparation) shows a similar trend, increasing from 45Mt in 1970 to L66.6Mt in 1990-91.

Although the total quantified resources of Victoria amount to some 211 000Mt, the Geological Survey of Victoria estimates that only around one half of this coal, 99 000Mt, is economically mineable. Economically mineable in this context is that coal lying at depths of <300m, with a minimum seam thickness of 3m, an ash content of<L}Vo and an overburden to coal ratio of<2:1.

longwall mining equipment with resultant increases in productivity.

COAL PRODUCTION AND CONSUMPTION

Saleable coal production and the method of mining for each basin is given in Table 4. The black coal mining industry in Australia is highly mechanised, and overall productivity as measured by the raw coal output is over four tonnes per employee per hour. More than two thirds of the coal is produced by open cut mining methods. Most underground mining is concentrated in New South Wales where some 61Mt were produced by this method in 1990-91. In recent years, many ofthe underground mines have been upgraded by the installation of

Brown coal is currently mined in Victoria at three localities (see section entitled BROWN COAL IN VICTORIA), and is principally used as a fuel source for electricity generation. Small quantities, however, are used for industrial purposes and briquette manufacture. Total production in 1991-92 was approximately 47Mt, all of which was produced by open cut methods. In the larger mines, the coal is recovered by bucket wheel excavators.

Coal Mining

Coal Consumption in Australia

Black coal is mined in all Australian States except Victoria (Figure 7), and, in 1990-91, production of raw black coal in Australia amounted to 204.7Mt. Queensland and New South Wales dominate the production figures, (Table 3), and these two States are also responsible for all Australian coal exports.

In 1990-9L, approximately one-third of Australia's

saleable black (serni-anthracite to sub-bituminous) coal production was also consumed in Australia (Figure 9). As indicated in Table 5, three-quarters of this material was used as fuel for electricity generation, with the other user of particular

Geology of Australian Coal Basins

tg7 RESOURCES

significance being the domestic iron and steel industry.

l--;rr*- I m*rTc';; r-l

----j----

A breakdown ofthe use ofcoal for different purposes in the various states over an eleven-year period is given in Table 6. This shows stabilisation in total consumption for New South Wales, despite some increase in use for electricity generation, due to significant down-turns in iron and steel production at Newcastle and Port Kembla. Total consumption, however, has risen in Queensland, due mainly to increases in power station usage.

RESERVES

INDICATED

Coal consumption in South Australia has stabilised over the period in question, due mainly to substitution by natural gas, but this trend is expected to be reversed in the future as new coal-fired power generating capacity is built. Western Australia has shown a slow growth in coal usage, with demand for both power production and general industry, although this may also be affected in the future by increased natural gas consumption.

Figure 5. Terminology used in assessment and reporting of Coal Resources and Reserves in Australia (Galligan & Mengel, 1986).

There has been steady growth followed by decline in the use of coal in Tasmania, with consumption by paper mills, cement plants and general industry.

Table 1. Identified black coal resources by hasin, state and:,potential mini'ng method (based on, Sniffin ' & others, 1986 and other sourc€s)'.

Age

State

Basin

Potential

Indicated (tonnes x '

Open-cut ,Inderground Measured + Measured +

QUEENSLANT (1)

E frl

NEW SOUTH WALES (2)

SOUTH

AUSTRALIA WESTERN

AUSTRALIA

a a &

Galilee Sub Total SydneyGunnedah Oaklands Gloucester Ashford Sub Total

(tonnes r

(tonn^es x

106)

100)

55 19

2t 76r

27 28t 2585 29 866 31 905

19 468

1388 104

Verv Larse (3 1 380

4t 920

43 300

3260

r43

1388

1410

45 2t0

46 620

Arckaringa

2786

t40

2926

I 475

490

9965

Collie

436 480 916

305 230 535

741

345_

354-

Perth Sub Total

145 1

TOTAL

23 150

44 528

67 679

Callide

22t

553 57r_

774 579 438

rtz4

1791

505

530

438

TASMANIA

Sub Total Tasmania

667 25

SOUTH

Telford

150

AUSTRALIA

Very Large

33 436

TOTAL

t2 437

Total Inferred

19 507

D r'1

55 19

2585 24 346

Tarons

SOUTH

Inferred

13 929

Surat-Moreton >D Mulgildie QUEENSLANI (4) a9) Stvx trE<

Inferred

I 0b)

Ipswich

U]O

Indicated

(ton4es x

QUEENSLANT

AUSTRALIA

Potential Jnderground

Potential

106)

Bowen

Open-cut

Total

Measured +

842

1629 7

2471 5028

110 4

5t42

110 5 131

PoIda

310

TOTAL

5441

TOTAL

150

5021

Sub Total

GRAND

710

29 433

46 168

56 939 + Very

Larse Large Large

Large 300

300

300 + Laree

Very Large Small Verv Large

310

5452

75 602

tL 204

46 055

(1) Queensland Opencut Resources generally based on maximum 60m overburden. (2) NSW Opencut limit 300m depth and 10:1 linear overburden ratio. (3) Inferred Resource for Queensland are not quantified and are not divided into potential open-cuVunderground. (4) Minor coal production occurs in Maryborough Basin but resources estimates are not available.

Coal Resources, Quality and Utilisation

10 10

57 249 +

Verv Large

138

MEASI,RED AND INDICATED RESOURCES 30000

Most electricity in Tasmania, however, is generated by hydro-power, and coal-fired plants are not likely to be installed until all economically viable sites for hydro-electricity generation are fully developed. Black coal consumption in Victoria is very small. As discussed in more detail below, however, all of Australia's brown coal is currently produced in this State, with most being consumed at power stations adjacent to large open-cut mines. Usage of raw brown coal for power generation in 1991-92 amounted to 45Mt, with a further l,.94Mt being used to make O.72Mt of briquettes.

25 000

20 000 million

tornes

Arrstrelian Coal Exports

15000

Exports ofblack coal from Australia have been growing steadily since the early 1960s (Figure 1-0), and in 1984 Australia overtook the U.S.A. to become the world's leading coal exporting nation. Total exports in 1990-91 were'approximately 113Mt (Table 7), with an increase of nearly 137a between 1990 and 1991. AboutSOTo ofthe exported coal went to Japan, !9Vo to Europe,9To to South Korea and.6Vo to Taiwan. Over 50Vo of the exports were of metallurgical (coking) coal, with the remainder being thermal coal. The thermal (steaming) coal market, in particular, has grown in recent years, mainly for electricity generation but also for cement manufacture and other combustion purposes.

10000

5000

QLD NSW SA

TAS

state Figure 6. Measured and indicated coal Resources in Australia by State and probable mining method.

Figure 7. Location of principal Australian coal mining centres.

f- - --ji, ; .)--, 1rl0

MINItt|G CENTRE

BASIN

AGE Permian Permian Permian Permian

Bowen

2 3

Bowsn

4 5

Mackay Clermont Blackwater Moura

Bowen

Pemian

Callide

Talong

Tarong

loswich

Triasic Triasic Triasic

Gunnedah Hunter Newcastle Western Southern Latrobe Valley Anglesea Bacchus Marsh Fingal Leigh Creek

6unnedah Sydney Sydney Sydney Svdnev Gippsfand

Collie

I 10 11

12 13 14 15 16 17 18 19

Bowen Bowen

0tway 0tway Tasmania Telford

Pottsforcnlexport

Permian Psrmian Permian Permian

Pemian Tediary Tediary Tertiary Triassic

Triasic Permian

Geology of Australian Coal Basins

139

!F,e.$

ilfr"€rtiifif*..bro $.ieo,atrcgourde$..$nr'i'bfiCinle$d..St$$e '..g:":.Ificfitifid ,(fi*ifil#'$$ebilr jrofi,,,StefiXUyi...$$8fi ).:,, BASIN

STATE

INFERRED

INDICATED

(m)

DEPTH

Gippsland

Victoria

MEASURED +

CATEGORY

(tonnes r 106)

(tonnes x 106)

0-300

80 163

4651

300 - 500

4235 500

2739

0-300 0-300 0-300

Otway

Murray

300 - 500

Sub Total South Australia

0-500

St. Vincent

39 240 2739

54 516 30 280

2524

970

54 516 30 280 84 776

41 989

Sub Total

3462

Bremer

614

760

TOTAL

8874

43 879

160 1

130

84 776

Typical properties of Yarrabee semi-anthracite are given in Table 8. The coal has a fairly low ash, low sulphur, relatively high phosphorus and a high specific energ'y. The Hardgrove grindability index is high, which indicates a rather soft coal.

CHAR.A,C TERISTIC S OF AUSTRALIAN

SEMI.ANTHRACITES

The only semi-anthracite currently mined in Australia is won from a deposit at Yarrabee in the Bowen Basin of Queensland. In past years, however, material classed as semi-anthracite, produced by localised effects of intrusive igneous bodies, was also mined from two collieries near Mittagong in the Sydney Basin of New South Wales.

Yarrabee coal is sold on the local market as a high-energy, non-polluting fuel for domestic and general industrial purposes and for the manufacture of home-heating briquettes.

The New South Wales material was used locally as fuel and also exported to New Caledonia for use in nickel smelting, until quality control and economic problems eventually caused the mining operations to

250

80 663 4235 84 898 938

cease.

(tonnes x 106)

15 000 19 599

Murrav

Western Australia

INFERIOR + INFERRED SI'B-ECONOMIC

It is also exported for steam-raising, cement production and manufacture of home-heating briquettes, as well as for smelting, carbide, lime and ferro-alloy production and as a non-coking blend component in the iron and steel industry.

Million tonnes

200 150 100

1.97a-71

1975-76

1980-81 Year

m Baw coal

1985-8 6

Saleable coal

Figure 8. Black coal production in Australia, L97O-71 to 1990-91.

Coal Resources, Quality and Utilisation

1990- 91

140

Table 3. Australian black coal production by state, Lgg0-gl (Joint Coal Board and Queensland Coal Board, 1991). Saleable Coal Raw Coal Production^ Production^ (Tonnes x 103) (Tonnes x 103) 80 116 96 697 New South Wales 78 363 99 895 Queensland 5206 5206 Western Australia 2527 2527 Australia South 350 585 Tasmania 166 562 204 910 TOTAL CHARACTERISTIC S OF AUSTRALIAN BITUMINOUS COALS

State

Bituminous coals are mined on a large scale in New South Wales and Queensland, where they range from low- to high-volatile in rank. High-volatile bituminous coals are also mined to a limited extent in Tasmania.

10")

PERMIAN

65 306 59 033

Bowen SydneYGunnedah Collie

6273

80 116 34376 45740

5206 4165 1041 628 97 574 53 054 1337 1014 323 3989 3989 5141 5L4I 2527 2527 298 52 350

150

TRIASSIC Ipswich Callide Tarong Telford Tasmania

344 t2723

62r

2039 L972 JURASSIC Surat-CRETACEOUS Moreton MarYborough 13

2052 1972

Typical properties ofcoals from a range of Queensland deposits are given in Table 8. Low -u olatile bitumin ous c oals Low volatile bituminous coals in Queensland are won mainly from the Dysart seam in the Norwich Park, Saraji and Peak Downs mines of the central Bowen Basin. Others are produced from different seams in the same basin at Curragh, German Creek, Riverside and Collinsville. The coals have a mean

maximum vitrinite reflectance of 1.2 to 1.67o. Some contain over'I}Vo vitrinite, which gives them high

Most of these low-volatile bituminous coals are high quality "hard coking'coals", and form an excellent lbw-volatile component of coke-making blends. Almost all production is exported for use in metallurgiCal processes, although low-volatile coal from one mine (Curragh) is also used for steam-raising applications.

Million M illion tonnes

150 I

100

197 0-71

Figure 9. Usage

766024 LL2269 53755 TOTAL swelling and coking properties, even tJrough the fluidity is only moderate. Sulphur and other impurities are usually only present in relatively small proportions.

Queensland Bituminous Coals

200

Table 4. SCleable blaak cobl production by tr*asin, 1990-91 (Joint CbaI BoCrd,and Queensland Coal Boaid' I991)r. Saleable OPen Under' Basin Age ground Production Cut (Tgnnes r

1975-76

m Dornest ic to ofAustralian black coal' 1970-71

1985-86

1980- 81 Year r. .-:-r-l

IL.,nnrl l-l^ p!, I t

1990'91.

Geology of Australian Coal Basins

1990-91

t4t

Million Tonnes 130 120 110 100 90 80 70 60 50 40 30 20 10 0

1980 '81 ',82 '83 '84 '85

'Bb

'97 '88 '89 '90

'91

Figure 10. Black coal exports from Australia, 1980 to 1991.

Med.ium-aolat ile Bituminous C oals Medium volatile bituminous coals in Queensland are mostly found in the Bowen Basin. Seams of significance for this type of material include:

Blackwater area (Aries, Castor, Pollux and Orion seams)

Tieri area (Aquila, Tieri, Corvus and German Creek seams)

o .

Dysart area (Harrow Creek and Dysart seams) Moranbah area (Goonyella Middle and Lower seams)

. .

Glenden area (Upper Newlands seam)

Collinsville area (Bowen, Blake, Scott, Denison and Garrick seams)

Tahle S. eonsumption of btatk coal in Australia by majlr consumer groups' I990;9,1:,,(Joint Goal.:Boatd, and,Queen5land. l

,,CoCl.Board,,1091). tonnes r 10"

percentage

Electricity Generation

38 412

75.4

Steel Industry

7395 863 396 2523 1335 50 924

14.5

Cement Industry

Metallurgical Coke (other) Metal Processing Other Consumers Total

L7 0.8 5.0 2.6 100.0

. .

Moura area (Moura and Nipan series of seams)

Blair Athol (No.3 seam)

Typical properties of some of these coals (e.g. Curragh and Oaky Creek) are shown in Table 8. Depending on their ash and petrographic cornposition, the medium volatile coals are used either as coking coals or thermal coals. Volatile matter ranges from 21 to SlVo (air-dry) and mean maximum vitrinite reflectance from 0.9 to l.2Vo. Crucible swelling number is usually high in the coking coals, and both Gray-King coke type and Gieseler plasticity moderate to high. The petrographic composition of these coals is variable, as is the phosphorus content, but ash is generally low and sulphur low to rnedium. They can be blended with a wide range of other coals for

metallurgical coke production.

Medium volatile thermal coals from Queensland have a wide range of ash values and a medium to high specifrc energy. Sulphur is low to medium, and Hardgrove Grindability Index medium to high, but the ash fusion characteristics and phosphorus content are rather variable. They provide a good source of combustion fuel when matched to the design ofthe plant concerned. The coal from Blair Athol in the western Bowen Basin is unusual in a number of respects. The seam, approximately 30m in thickness, is the thickest bituminous coal seam worked in Australia. A naturally low ash makes washing unnecessary, sulphur is low, phosphorus is very low and the ash fusion (deformation) temperatures high. However, the hydrogen content is low and the oxygen content high, due to a high percentage of inertinite, and this

Coal Resources, Quality and Utilisation

L42 Table:..6;. eonsumpf ion of bl$ck e'oCl in fiusttClib bVconbumefs Cnd states' 1980 - 1991 .

(Joint CoCl Board and QueenCland Coal Board, 1991) (tonnes x 10").

ew South Wales ,

Powerstations ........... Steel industry Coke works Cement industry

Other .

ueensland Powerstations ........... Coke works Cement industry Metalprocessing ......... Other . uthAustralia........... Powerstations ........... Steel industry Other . estern Australia Powerstations ........... Cement industry Metalprocessing ......... Other . asmanla .. . Cement industry Paper mills

Other

1980

1986

1987

1988(a)

1989

1990

1991

23 44O 14934

25 022

25 495

27 846

27 485

18 456

18 560

19 815

27 444 20 t65

7071

5247

56 17

6047

287

308

402 630

395

615

606

6349 310 415 596

6430

285 429

19 890 6601 330

28 t47 20 438

6933 5142

tl 359

12 131

8968

9801 73

t2 773 t0 282 74

72I

4rs

3L7

320

394 568

Jtc 537

13 200 10 708

13 771 11 513

t4 289

11 816 79

256

27r

205

26r

299

22t

228

1202

15 95

1594

1691

1646

1508 454

r657 509

274

455

458

465

472

2861 1694

3570 2398

3693

3969 2683

4145 2952

3818

3864

2660

27 49

11 16

1l-85 60

t229

1 140

1 107

1064 51

3012

3599

2309

2865

4325 3521

5364 4238

IlI2

3001 2778

3067 2362

2448

150

48;

540 L42

2t6

496 238

537 267

5187 4182 164 576 265

397

436

438

447

402

2t8

78 196

L37

128

r.86 66 90 30

ctoria .

214

t02

236

228

2t9 108

t26

165 635

326

(a t 53 week year.

makes the specific energy somewhat low and the coal very reactive. Precautions are necessary to

avoid spontaneous heating in storage.

High-Volatile Bituminous C oals High volatile bituminous coals are mined in several different basins of Queensland, including parts of the Bowen Basin. Seams falling into this category include: Bowen Basin:

Gordonstone (German Creek seam) Gregory (Lilyvale seam)

Moreton Basin:

Ebenezer ) Jeebropilly ) Oakleigh )

Walloon Coal Measures

Tarong Basin: Meandu (King seam)

from 8 to 28Vo (air-dried) and specific energy values from about 22 to 28MJ/kg. Sulphur and phosphorus are usually low, Hardgrove grindability moderate and ash fusion temperatures variable but normally fairly high. Poorer quality products are used locally (e.g. in power generation), while the higher quality coals are exported. A blend component for coke production can also be made in some cases by appropriate preparation processes.

Utilisation of Queensland Bituminous Coq'Is within Austro.lia The Australian market for Queensland-produced coals is confined almost exclusively to within the producing state. Local consumption in 1990-91 was 13.gMt, but is increasing by an average of approximately \Vo per year. Market demand is mainly for thermal coals. Due to the absence of a Queensland-based steel industry, requirements for

coals suitable for metallurgical coke production are

<70 000t/y.

Maryborough Basin: Burgowan (Ellengowan seam)

The only high volatile bituminous coal mined in Queensland essentially as a coking coal is produced from the Lilyvale seam at Gregory in the Bowen Basin. This coal is at the lower end of the high volatile range, with around.32Vo (air-dried) volatile matter and a mean maximum vitrinite reflectance of 0.98 to 1.06Vo.It has low to medium sulphur and a medium phosphorus content, with high values for crucible swelling number, Gray-King coke type and Gieseler fluidity. The proportion of reactive macerals is over TUVo,whie}i' helps to make the coal a good component for metallurgical coke production.

The Queensland Electricity Commission is the major domestic coal consumer of Queensland coals. This organisation produces almost all of Queensland's electricity, in coal-fired power stations strategically located throughout the State. Coal usage in 1990-91 was L1.5Mt, a figure also predicted to increase at an annual rate ofabout \Vo. All power stations planned for the future are designed to burn coal, a policy that takes advantage ofthe availability oflarge coal deposits which can be mined cheaply and can guarantee long term supply. Coal quality is a secondary consideration, since quality factors can be taken into account in power station design which aims at maximising resource utilisation and minimising generating costs. Consistent with this approach, mine site location of power stations and buining of run-of-mine coal, to avoid transport and

The other high volatile bituminous coals mined in Queensland are used as thermal coals. They have a wide range of properties, with ash levels varying

High-ash metallurgical coke is producq4 in Queensland at the Bowen State Coke Works. Coking

Typical properties of some of these coals are given in Table 8.

preparation costs, is followed as far as possible.

Geology of Australian Coal Basins

143

Table 7. Australian ctral €xports by destination' 1990;91 (Joint Coal Board and Queensland Coal Board; 1991). 1991

1990

Country Japan Other SE Asia .. China .

Quantity

Ave value ($A/tonne)

('000 tonnes)

3 116 415

66.25

60 378

I 110 797

63.31

24 t90

Quantity

Value ($,foo0)

55 400

20 837

('OOO tonnes)

Value ($A'000) 3 4tt 214 I 280 468

t7 284

7025

37r 747

52.92

9271 5732

583 490

62.93 64.00 63.61

63.t7

335

21 '.185

3577

163 947 12 399 657 442 35 864

Taiwan

455 6543

43.61 42.77 56.14 53.41 45.38 54,18

OtherAsia .....

HongKong.... Indonesia......

3 145

Malaysia .. .. ..

697

Korea, Rep. of . .

Philippines....

319 9061

8095

498 529

6r.58

India . .

5 105

Israel .

270 532 691

62.3L 60.15 48.86 59.63 64.81

56.50 52.93 65.01 45.83 38.55 55.71 53.03 38.10

38 974 137 151 13 632 508 676 37 235 20 650 354 479

6t7

Ave value

(gA./tonne)

321 11 802

676 454

366 857 30 479 25 601 49 358

I497

318 048 16 234 26 001 4t 228 97 018

TotalA.sia......

44332

4 725 74L

56.04

93 839

6 275 t72

56.21

Europe

l9 568

r 072 036

22 375

I 189 331

53.r6

1 108

69 303

54.79 62.52

76 968

59.53 58.43

Iran ..

Pakistan ...... Turkey

Belgium/Lux . .. Bulgaria Denmark .. . .. .

1659 2957 270

69 678 163 433

981-

59 t25

5516

268 596

r03 229

Sweden

1534 869 530

United Kingdom

4002 142

33 403 235 924 8342

Other Countries

2692

158 063

Algeria

Argentina.....

403 336

France

Germany ... ... Greece Italy . .

Netherlands . . .

t4 t49

42.01

55.27 52.48 60.29 48.70

Portugal

Romania . ... .. Spain .

Yugoslavia.....

46 854

1 189

Chile. . Egvpt .........

304 279

25 690 2t 736 68 669 L6 672 16 185

New Caledonia

19 140

7355

Brazil

Fiji ...

SouthAfrica...

1045

67.27 53.89 63.07 58.95 58.90 68.70 63.79 64.65 57.73 54.86 58.03 54.30 52.40

479 530 810 1720

t293 40 1936 4115 541 111 1396

5664 59 763

tL29 608 4720_

3969 450 304

1181

6247 4108

32.49

Grand Total .. ..

106 592

6 955 830

55.88

120 183

Utiliso.tion of Queensland Erport Coals A total of 62Mt of coal was exported from Queensland during 1990-9L. Coking coal exports continued to increase gradually to 4lMt, but thermal coal exports remained static at 21Mt. Japan remained the major consumer with total sales of

233 636 28 742

701

cement industry in 1990-91. A further 560 000t of thermal coal was also consumed in the same year by a wide range of other-indus_tries, including food processing, paper, pulp and board manufacturing, brick and pottery manufacturing, hospitals, ships' bunkers and a variety of small consumers.

2705 49 250 64 945 36 145 275 5t2

L20

Cement is manufactured at three locations in Queensland, namely Darra (burning Ipswich coals), Rockhampton (burning Blair Athol coal), and Townsville (burning Collinsville coal). A total of 247 000t of coal were consumed by the Queensland

206 223 27 441 3841 82 509 286 519

681 460

1841

United States . .

Mount Isa Mines for lead smelting, and the remainder by small industries engaged in forge and foundry work. The metal industry is also a direct user of thermal coal, such as in using coal, consuming L.6Mt in 1990-91.

2314 74 959

19 269 106 018 36 604 29 949

64 28

coal requirements are about 70 000t/y, and this coal is supplied unwashed from the Bowen seam at Collinsville. Most of the coke produced is used by

111 195

48.32

60.92 64.64

38.72

50.r2 50.73

34.7t 59.12

50.59 45.51 64.51

57.5t 59.48 58.36

58.87 63.84 63.38 57.59 53.77

65.10 55.47 52.22

15 18

64.67 53.80

6 698 139

55.73

30Mt, 487o of all Queensland exports. Queensland coal was exported to 33 countries during 1990-91.

Metallurgical coking coals from the Bowen Basin represent the bulk ofthe Queensland export coal trade. Such coals cover the whole range of bituminous rank, but are predominantly made up of medium-volatile bituminous materials. The leading buyers of Queensland coking coal in 1990-91 were Japan (17.3Mt), India (4.8Mt), South Korea (3.1Mt) and the United Kingdom (2.sMt). Thermal coals were exported from Queensland to 18 countries in 1990-91. The leading markets were Japan (12.8Mt), Netherlands (2.6Mt), Hong Kong (1.?Mt) and Denmark (1.lMt). The thermal coal market offers potential for industry expansion in the short-term and traditional coking coal producers are tending to produce better quality products to increase market share in a static export market. The principal use of Queensland export thermal coals is foi the generation of electricity. Unlike the feedstock for local power stations, quality is of prime

importance, with the export market generally demanding low to medium ash, high asb fusion temperatures, high specific energy and low sulphur,

Coal Resources, Quality and Utilisation

L44

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{S frzA 5 fr 3,i E 5 6 E F{ AiEig3 Geology of Australian Coal Basins i

r45 as well as giving attention to other key properties.

The current principal suppliers to the power utilities are the Blair Athol, Newlands, Moura, Curragh, Oaky Creek and South Blackwater mines. Queensland thermal coals ranging from high-volatile bituminous to semi-anthracite have also found markets in the overseas cement manufacturing industry. The principal markets for this coal are in Japan and the Pacific Rim countries, with some use in Europe as well. Other industries in overseas countries which import Queensland coals include the chemical industry, pulp and paper manufacture, textiles and general small industry where steam raising is required.

New South Wales Bituminous Coals Typical properties for New South Wales bituminous coals are given in Table 9. The coals cover the whole range of bituminous rank but, in contrast to Queensland where medium-volatile coals predominate, the greater proportion consists of high-volatile coals. Low -u olatile Bituminous C oals Commercial coals of low-volatile bituminous rank are restricted to the South Coast (Illawarra) area of the Sydney Basin, with the Bulli seam being by far the most important. Low-volatile coals in the Balgownie and Tongarra seams, however, are also mined to a limited extent. The range of volatile matter is approximately 18 to 24Vo on a dry basis (d). The ash level can be relatively high in the raw coal, but can usually be reduced to satisfactory levels, e.g. l07o (d) by appropriate preparation methods. The air-dried (ad) inherent moisture is only about l7o, and there is normally no difficulty in meeting a total moisture specification of 77o. The sulphur content is very low, approximately 0.4Vo (d), and this is a great advantage in any market area. The crucible swelling number is usually 5 to 7, the Gray-King coke type F to G3, the Gieseler plasticity 50 to 1.000 dial divisions per minute with a plistic range of about 90oC, and Audibert-Arnu dilatation is in the range -30 to +30Vo. The phosphorus content is variable, e.g. 0.01 to 0.08% (d). The mean maximum reflectance of the vitrinite normally falls within the range l.L to 1.37o and, even though the vitrinite content is only moderate (e.g. 457o) and the inertinite content rather high, (e.g.\OVo), the coal is an excellent low-volatile component of coking blends. It is a high quality 'hard coking coal', and provides a good example of how low predictions of coke strength based on

Medium-volatile Bituminous C oals Medium-volatile bituminous coals in New South Wales are restricted to the Bulli seam in the southwestern part of the Sydney Basin (Burragorang Valley and Tahmoor)r-the Wongawilli seam in the South Coast area, the Katoomba seam in the Western Coalfield and a small deposit at Ashford in the far north of the state. The Bulli seam in the areas indicated above has 26 to 307o volatile matter (dry basis), with inherent

moisture typically 1.57o (air-dried), total moisture 'lVo, asjn g.5n Gd), total sulphur O.4Vo and crucible swelling number 6. Gieseler fluidity is variable, but can be as high as 2000 dial divisions per minute. The mean maximum reflectance of the vitrinite is usually around 1.07o, and the vitrinite content of the order of 40 to 50Vo. Gray-King coke type varies from F to G4 and Audibert-Arnu dilatation ranges from -30 to +35Vo. Phosphorus is variable from about 0'01 to 0.097o (dry basis). This coal is an excellent'semi-hard coking coal'for use as the medium-volatile component of coking blends. A thermal (steaming) coal is also produced by appropriate coal preparation methods and, in s6me instances, by blending with coal from the Western Coalfield of the Sydney Basin. Typical specifications for this material are: inherent moisture 2Vo (ad), total moisture 8Vo, ash 167o (ad), Hardgrove grindability in-dex 50 and ash fusion temperature (flow) >1550'C. The Wongawilli seam of the Sydney Basin, after

suitable coal preparation, yields a high-fluidity, medium-volatile coking coal with inherent moisture typically 1.37o (air-dried), total moisture 7%, ash I0 to-L4Vo (ad), volatile matter 26Vo (ad), total sulphur 0.557o (ad), and a typical crucible swelling number of 8. The vitrinite content is around 70%o, andmean maximum vitrinite refl ectance approximat ely L.LVo. The coal has a Gray-King coke type G1 to G9, and a Gieseler fluidity from 200 to >5000 dial divisions per minute with a plastic range of 90 to 120oC. Audibert-Arnu dilation ranges from +160 to +300Vo and phosphorus content is usually <0.017o. Coal fromthe Wongawilli seam is a most useful component of a coking blend when ext_ra_fluidity and sweiling are required, and has the added bonuses of low sulphur and very low phosphorus. Unwashed Wongawilli coal and middlings obtained from its preplration are also used locally as steaming coals.

Northern Hemisphere Carboniferous coal properties can underestimate coke quality when applied without modification to the Southern Hemisphere Permian coking coals.

The Katoomba seam from the western Sydney Basin is mostly a high-inertinite coal. It is an excellent source of steaming coal, with typical total moisture of 8Vo, inherent moisture 3Vo (ad), ash L47o (ad), volatile matter 287o (ad) and crucible swelling number 1. The gross specific energy of this coal is around 28MJ/kg (ad), the ash fusion temperature (flow) >140OoC and the Hardgrove Grindability

Research has shown that some of the semifusinite, which comprises the largest part of the inertinite

The Ashford coal from northern New South Wales has a generally high and variable ash. It is not

fraction, has appreciable reactivity in the coking process. In addition, fine grained micrinite, another component of the inertinite, can add considerable strength to the final coke structure. A low-volatile steaming coal is also produced from the Bulli seam of the Sydney Basin. This coal finds use in some metallurgical processes and in boiler and cement plants specifically designed for such a fuel.

Index around 48. mined at present, but in the past it h?,s-been used as a high-ash run-of-mine fuel for a small local power station.

High-a olatile Bituminaus Coals Apart from those discussed abovg, all commercially pioduced coals of New South Wales are of high-volatile bituminous rank when classified on a dr-y, ash-free basis. Those of the Western Coalfreld

Coal Resources, Quality and Utilisation

L46

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Geology of Australian Coal Basins

r47

Table lO. Coal consumption in New South lYales by,consumer groups (.toint Coal Bbard, 1991)(tonnes x 10"'). Consuners Railways

Electricitygeneration ............................... Coke - metallurgical (other) Lime, plaster, asphalt, shale, etc Cement and cement goods .

Bricks, tiles, pottery, etc . . . Chemical, drugs, medicines ... Soap, oils, inks, matches, paints, etc . . . Iron and steel (as received basis) . Other engineering and metal trades Textile and clothing Skin and leather Food - brewing and malting Food - milk and meat procesing Food - sugar refining Food - other, tobacco, etc . ..

Woodworking, furniture Paper and printing Rubber

Hotels, institutions,miscellaneous industries Laundries and dry cleaners Hospitals Miner's coaVColliery consumption SmaII industrial and domestic consumers (estimated) . . .

1986.87

1987.88

1988-89

1989-90

18 555

18 959

20 269

20 282

301 22

324

321

316

19 880 315

401

42r

4rl

390 25 98

24 94

23 84

25 85

395 26 92 6318

1990-91

5288

6022

6722

6279

27 28

30 24

31 25

20 77 55 37

23 79 59 36

81 49 38 L4 50

82 95 39

15 13 4

13 4

25 84 57 36 18 57

11 L2 6

11 11 5

13 12 4

48 1

27 aBA 27 482 2a 327 Total . 25 153 26 322 (Lithgow and Ulan seams) are essentially steaming O.05Vo phosphorus (dry basis), 0.01 to 0.067o chlorine coals, although some low-ash products are also sold and a Hardgrove Grindability Index of 40 to 55. as non-coking materials for metallurgical purposes. Typical properties include total moisture I to 97o, Steaming coals used for local power generation, inherent moisture 2.5 to 3.\Vo (ad), ash 11 to l97o however, are generally of poorer quality, with ash in (ad), volatile matter 29 to 32Vo (ad) and total the range 18 to 307o (d) and average gross specific sulphur 0.6 to 0.8Vo (ad). The gross specific energ'y of energy on a 7Vo moisture basis of approximately the coal is typically 26.5 to 29.3 MJ&g (ad), the ash 23.SMJ/kg. However, the Electricity Commission of fusion temperature (flow) 1400 to >1560oC, and the New South Wales has begun to source a higher proportion ofits coal supplies from private Hardgrove grindability index 45 to 52. producers, in order to lower costs and provide a consistent coal feed at 18 to 22Vo as}a for its power The large number of seams mined in the Hunter, stations. This is expected to clecrease operational Newcastle and Gunnedah Coalfields of the Sydney problems as well as lower the dust burden to the and Gunnedah Basins yield many different coking electrostatic precipitators or fabric filters. and steaming products. The coking coals are so called 'soft coking'products and are an importent Coals from the Greta Coal Measures are generally cheaper component of coke oven blends. Total moisture is normally 7 to 8Vo, inherent moisture 2 to lower in inherent mineral matter than those of the 3.\Vo (ad), ash 6 to l27o (ad), volatile matter 33 to overlying Upper Permian sequences. The Greta 42Vo (ad) and total sulphur 0.4 to l.2Vo (ad). The coal seam from the South Maitland area has been used, partly for this reason, in domestic heating and typically has a crucible swelling number of 3 to 7, a railway locomotives, and for gas making by Gray-King coke type from G to G4, and Gieseler fluidity 10 to 5 000 dial divisions per minute with a carbonisation processes. In recent years, however, it plastic range of 60 to 105oC. Audibert-Arnu dilation has been used mainly for ash control in (coking) coal ranges from -35 to +LjOVo, mean maximum blends and for specialised chemical purposes. reflectance of vitrinite from 0.62 to 0.85Vo, Typical properties are: total moisture TVo,inherent phosphorus content 0.001 to O.06Va (d) and moisture 27o (ad), as}r 6.57o (ad), volatile matter 4l7o (ad), total sulphur O.9Vo (ad), crucible swelling Hardgrove Grindability Index 35 to 60 (commonly 45 to 55). number 6, Gray-King coke type G4, and Gieseler fluidity 1400 dial division per minute with a plastic range of 100oC. Audibert-Arnu dilation is +207o, Coals with some properties at the poorer end of this content 667o and mean maximum vitrinite range are sometimes sold as 'semi-soft coking coals', reflectance of the vitrinite 0.7Vo. The phosphorus or as pulverised coal injection (PCI) or'briquetting content is 0.037o (d) and the Hardgrove Grindability coals'for coking blends. Coals with very low Index is around 32. phosphorus contents may be sold for special metallurgical purposes such as nickel smelting. Coals of the Greta Coal Measures are also mined for low ash unwashed steaming coals in the Muswellbrook area, and, more recently, in the Export steaming coals from these areas also cover a very wide range of properties. Total moisture is Boggabri area. The latter coai, if washed, could normally between 8 and 107o, inherent moisture 2.5 become the lowest-ash coal produced in New South to 3.57o (ad), ash 11.5 to 20Vo (ad), volatile matter 29 Wales. There is, in addition, a small production from the Tangorin seam in the East Maitland area, a €oal to 37Vo (ad) and total sulphur 0.35 to L.jVo (ad). which has the distinction of being the only very high Gross specific energy of the coal is usually 25.5 to 29 MJ/kg (ad). The crucible swelling number is sulphur coal mined in Australia. Total sulphur for this material is about 5.57o (d). Fortunately, the ash typically 1 to 3 and the ash fusion temperature (flow) 1300oC to >1600oC. The coals have 0.01 to is low and other properties are satisfactory, allowing

Coal Resources, Quality and Utilisation

r48 the coal to be blended with low-sulphur coals to meet required specifi cations.

Utilisation of New South Wales Biturninous Coals within Australia Coal consumption in New South Wales by consumer groups is shown in Table 10. Total consumption in 1990-91 amounted to approximately 27.5Mt. Of this,

72Vo was used for electricity generation, providing over 90Vo of the electric power used within the State.

Table,ll: lfypical properties of Tssrnanian bituminous coals (,Ioint CbaI,Boatd and Cornwall Coal Company data). Seam:

Type:

Duncan

Blue Thermal

6.0

6.7 16.8

Thermal

Total Moisture (Vo as) Inherent Moisture (7o ad) Ash (7a d)

Volatile Matter (7o d)

20.2 25.3

31.1

54.5

52.1

24.84 33.12 83.3 4.79

25.7t 33.t2

Approximately 237o was used for iron and steel production, mainly for coke manufacture at Port Kembla and Newcastle steelworks. An additional 7.L7o was used to produce coke for other metallurgical processes, such as foundries. Cement manufacture accounted for l.4Vo, while the remaining 2.\Vo was widely spread over general industry.

Fixed Carbon (7o d) Gross Specific Energy (MJ/kg, ad) Gross Specific Energy (MJ/ke, daO Carbon (Vo d,af) Hydrogen (Vo dag

Chlorine (7o d)

Approximately 1.OMt of New South Wales coal was used in other States of Australia in 1990-91. Of this, about 0.8Mt was clean coal supplied from the coal preparation plant at Port Kembla steelworks to the Whyalla steelworks in South Australia.

0.67

0.63

Vitrinite (7o)

Semifusinite (7o) Other Inertinite (7o) Minerals (7o)

35 10 28 2L

Crucible Swelling Number

Utilisation of Neus South Wales Export Coals

Gray-King Coke Type Gieseler Maximum Fluidity (ddm) Maximum Dilatation (7o) Hardgrove Grindability Index Ash Deformation Temperature ('C)

Total exports of coal from New South Wales in 1990-91 were over 51Mt, of which 32Mt was thermal coal and 19Mt was coking coal. Japan was the largest market, with nearly 28Mt or 54Vo of the total. The principal other export markets were Europe (which took 7.6Mt, mainly thermal coal), South Korea (6.7Mt, around 63Vo of which was thermal coal) and Taiwan (4.2]['[t,727o therrnal coal). In addition, the United Kingdom was an important market for coking coal and The Netherlands, Hong Kong and France were important markets for thermal coal. While the bulk of Queensland's exports are medium and low-volatile bituminous coal, those from New South Wales are mainly of high-volatile bituminous rank. Such coals include materials classed as 'soft coking coals', which do not command as high a price as lower volatile 'hard coking coals'but are still sought after as a major component of coking blends. Despite the large number of mines and even larger number of seams represented, particularly in the Hunter Valley area, the properties of these coals are similar enough for a number of brands to be grouped together as equivalent (e.g. 'Newcastle A', 'Newcastle B'etc.). Coals of somewhat lower quality are generally sold as 'semi-soft coking coals' or'briquetting coals'for coke making. Others are used for pulverised coal

injection (PCI) into blast furnaces to replace part of the coke requirement. Some very high volatile coals, such as those from the Greta or Liddell seams, are used for chemical purposes or for gas production by carbonisation, while coals with very low levels of impurities, such as phosphorus and sulphur, may find use in metal smelting operations. The market for low-volatile'hard coking coals'is

currently rather stagnant, due to recession in the world steel industry and oversupply from various countries. The main source of such coal in New South Wales is the Bulli seam of the southern Sydney Basin, a seam with a high proportion of inertinite macerals (mainly semifusinite). Experience in Australian and overseas steel plants has proven that coke ofthe highest quallty can be mad-e from suitable blends involving Bulli seam coal.

Nitrogen (Vo dafl Sulphur (Vo d.af) Oxygen diff. (Vo daf) Phosphorus (7o d) Reflectance (Rv, max)

Exinite (7o)

Ash Sphere Temperature ('C) Ash Hemisphere Temperature ('C) Ash Flow Temperature ('C)

Pyritic Sulphur (7o d) Sulphate Sulphur (7o d) Orsanic Sulohur (7o d)

81.6 4.93

1.5

L.4S

0.45 10.0 0.033

0.55

52-56 1260 1530 1540 1550 0.10 0.00 0.26

ll.4

0.006

6 0

I 52-56 1250

L420

t440 1470

* Data not available.

The vast majority of export thermal coals from New South Wales are used for power generation. Their advantages over other coals for this purpose include high speiific energ"y, low sulphur, very low chlorine, generally high ash fusion temperatrrres, a low [endency towards slagging and fouling, satisfactory grindability and good flame stability. Another property which is now receiving more appreciatio!

than in the past is the generally low proportion of potentially toxic trace elements.

After power generation, the cement industry is the largest user of New South Wales steaming c_oal.s._ High ash unwashed coals are generally used within the State for this purpose, since they have sufficient specific energy to provide heat for the process and ash of a type that can be incorporated into the clinker produced. Export coals for cement manufaiture, however, are not usually so high in ash. Some countries, such as Spain, prefer low-volatile coals for cement production, but most use medium- or high-volatile coals for this particular application.

Tasmanian Bituminous Coals About 857o of the market for locally-produced coal in Tasmania is washed coal supplied by the major producer from two underground mines'-Both are iocated in the Fingal Valley in the north-east of the State. One mine works the Duncan seam near Fingal and the other the blue seam at Mount NicLolas. Typical properties ofthese coals are given in Table 11. two olher small open-cuts supply the balance of the market with unwashed coal having similar as-mined properties but of generally lower quality.

Geology of Australian Coal Basins

149

Table 12:. Typibal properties of Collie coal (V..I. Mora\ 1992: pbrbonal commuhication). Proximate Analysis

As Mined

Moisture,% Ash, Vo Volatile Matter, Vo Fixed Carbon, 7o Sulphur, 7o

26.0 6.5

27.0

40'5 0.5

Gross Specific Energy, MJ/kg

20.5

Ultimate Analysis

Dry, ash-free Basis

Carbon,Vo Hyd,rogen, Vo Nitrogen, 7ot Sulphur, 7o

75.6

Oxygen by difference, 7o

18.7

Gross Specific Energy, MJ/kg Carbonate Carbon, Vo Relative Density Hardsrove Grindability Index

29.7

4.1 1.3

0.3

0.1 dry basis 1.32

Ash Fusion Temperatures

Deformation 1340'C Hemisphere 1390'C Flow 1430'C Aeh Analysis (7a) SiOz 5I.7

AlzOs FezOs CaO MgO NazO KzO TiOz PzOs SOe

27.0 11.1 1.8 1:6

0.6 0.3 1.5

0.9 2.7

Although the coals are of Triassic age, their properties are similar in many respects to sorne of the Permian coals from New South Wales and Queensland. They are medium- to high-volatile bituminous coals, generally high in inertinite and Iow in hydrogen (subhydrous): They tend to have a high proportion of inherent mineral matter which makes washing difficult, but the sulphur content is very low. The coal is washed at Fingal to give a high-ash steaming coal. Typical properties of this material

include a total moisture of LO.57o, inherent moisture 6.0Vo (ad), ash 20.5Vo (d), volatile matter 26Vo (d) and fixed carbon 527o (d). The gross specific energy (as frred) is 23.6MJ/kg, total sulphur 0.35Vo (d), Hardgrove Grindability Index 55, and ash fusion temperatures from deformation at 1200 to 1300oC to flow at >1400oC.

All Tasmanian coal is used within Tasmania, either for firing industrial boilers or in kilns. Most of the boilers are fired using chain grate or spreader stokers, but approximately 257o of the current coal output is used in pulverised form for firing a cement kiln. Although high in inherent mineral matter, Fingal Valley coal presents few difficulties for the user provided the plant is designed for the fuel. Difficulties from slagging or corrosion are rare, no doubt due to the low sulphur content and the high ash fusion characteristics. Some consideration is necessary to deal with the large volume of ash residue, but vegetation grows readily on ash dumps and no significant pollution problems are known from water run-off.

Possible Future Use of Australian Bituminous Coals for Conversion Processes Following the oil price rises of the 1,970s, much research and development attention was paid to the possible conversion of coals into liquid fuels, particularly for transport use. Such interest has now Iargely abated, due to the relatively low cost and ready availability of natural crude oil. However it may well be rekindled in the future as oil reserves become more depleted and oil prices rise again. Coal liquefaction has been shown to be technically feasible in large demonstration plants, e.g. the H-Coal and Exxon Donor Solvent processes, and indeed on a commercial scale in the Sasol plants in South Africa. Australian coals have been surveyed for such use (Joint Coal Board and Queensland Coal Board, 1981) and much research has been done on a

small scale. This will facilitate the use of Australian black coals for conversion processes when economic conditions become favourable.

SUB.BITUMINOUS COALS Sub-bituminous coals in Australia are produced commercially at Collie in Western Australia, Leigh Creek in South Australia and Callide in Queensland.

Western Australia Sub-bituminous coal has been mined for many years

in the Collie coalfield, approximately 200km south of Perth. Production has increased steadily over the years reaching 5.SMt in 1991-92 (see also Tables 3 and 4). Approximately 807o of this is obtained from open-cut mines and 207o from underground operations.

Typical properties of Collie coal are shown in Table 12. When freshly mined it is hard and tough, even by bituminous coal standards, but when allowed to dry in air for several days it begins to fret on exposed surfaces and its particle size breaks down. At its normal 26% rnoisttrre level it is dry or only damp to the touch, indicating that the moisture is mostly located on internal surfaces. It is ground readily in this state to pulverised fuel with conventional equipment, and is thus adaptable for use in most of the normal applications of black coal except coke-making. Even in that area, however, it can also be a useful blend component. Collie coal has been used for ships'bunkers, gas-making and locomotive purposes in the past, and it is currently used on a large scale for

electricity generation, cement-making and metallurgical reduction (Table 13). In smaller installations, it has proved particularly adaptable to firing by underfeed stokers. It has been regarded as less than ideal in some areas of application, however, because ofits propensity to spontaneous combustion. This problem can be largely overcome

Table 13. Conbumption of Collie coel,by industry, 190f-92 (V;J. Moran, 1992, personal communication). lndustry

Percentage

Steam raising for electricity generation Process heat for alumina production Cement and lime production Ilmenite reduction

Nickel matte smelting Miscellaneous (includine brick colourin

1 1

Coal Resources, Quality and Utilisation

11 4 7

150

with better understanding of the factors involved, and quantities in excess of 0.5Mt are now regularly stored for long periods. The stockpiles are formed from'as-crushed' material with the natural distribution ofparticle sizes, and they are consolidated by rolling as progressive layers are built up. For smaller tonnages, where selected size ranges may be required, the expedient ofrendering stacks impermeable to air cannot readily be practised, but in such cases keeping the coal at the as-mined moisture level during transport and storage by means of water sprays is sufficient and effective in preventing spontaneous combustion

Underground mining at Collie has traditionally been by boril and pillar techniques, but between 1984 and 1987 research and mining experiments were carried out to establish the feasibility of caving methods in the weak, water-saturated strata typical of present workings. These experiments, involving drainage of selecteil aquifers to relieve pressure combined with Wongawilli extraction, were successful, and as a consequence that system now accounts for 40Vo of underground production. With its improved recovery and its potential to give economic access to thinner and deeper seams, it will be a significant factor influenclng future prospects for the Collie field.

problems.

In boiler applications for electricity generation, the coal has characteristics which give efficient stable burning without the need for specialised equipment. Normal hot-air-swept mills are used with coal moisture reduced to about I47o at the point of ignition. Fouling on furnace and convection surfaces is light, being readily removed by conventional sootblowers, but superheaters suffer a build up of hard deposit over long periods and require mechanical cleaning at annual overhauls. In grinding for pulverised firing the coal itself behaves well, being neither excessively hard nor too plastic, but the mineral matter component, particularly that from dilution during opencut mining, is abrasive beyond normal expectation and design limits. This characteristic has been traced to'hard silica grains of particle size 0.1 to 1.0mm which occur in much of the overburden, with a lesser contribution from pyrite occurring in the coal itself. Proper supervision of mining practice currently keeps such problems under control without a need for washing. Coal from the underground mines shows less of this problem because sandstone dilution is negligible, the few in-seam bands being made up of shaley material. A certain amount of Collie coal is also used in the upgrading of ilmenite to synthetic rutile by a direct reduction process. The coal has proven to be particularly suitable for this process, by virtue of its low ash yield, its complete lack of swelling properties and its particular combination of reactivity and ash fusion temperature. It is noteworthy that low sulphur content adds a property which makes this coal suitable for sponge iron production by the same rotary kiln process. Future utilisation of coal in Western Australia is inhibited by a large excess of natural gas available by pipeline from off-shore sources in the north-west, and also by the fact that there are no new, apparently economic uses for the coals that are now known. A possible exception to this might be sponge iron production in rotary kilns, as discussed above, where large, high grade iron ore resources could be exploited. Although there are other known resources of coal in the state, these are either of lower quality than Collie or are in only very early stages of evaluation. Electricity generation from the better of these prospects can be foreseen in the future. Combustion trials in an atmospheric fluidised-bed pilot plant have been conducted by Mullins & others (1985) on Collie and Esperance coals from Western Australia and Leigh Creek and Bowmans coals from South Australia. Results indicated that viable operation could be achieved with Collie and Leigh Cleek coals, but that this merely matched present performance with pulverised-fuel firing.

South Australia South Australia has vast resources of coal, mostly of low rank (Table 14). High rank coal occurs in sediments of the Cooper and Pedirka Basins in inferred quantities of hundreds of billions of tonnes at depths from 1300 to 4000m, but these deposits are nbt mineable at the present time. The low rank coals are commonly classed as 'lignites', under the ASTM classification system' They are intermediate in rank between the sub-bituminous coals of Western Australia and Queensland and the brown coals of Victoria. Only the Leigh Creek coalfield is in production at Present, with an output of 2 to 3Mt per year. The coalfield is operated bythe Electricity Trust of South Australia (ETSA) to produce fuel for its Northern and Playford Power Stations, which have a current capacity of 740MW.

Like all low rank coals, the South Australian lignites have more moisture and volatile matter and leis fixed carbon than higher rank deposits. The relatively high oxygen content of low-rank coals tends to be present as carboxyl and hydroxyl groups, which are much less abundant or completely absent in bituminous coals. The carboxyl group can be present in the salt form; hydrogen has been leplaced by metal cations, more often calcium and sodium, which are typically referred to as'organically-bound mineral matter'. Hydroxyl groups are thought to account for the high reactivity of low-rank coals. High-moisture lignites, associated during their formation or in more recent geological times with strongiy saline aquifers, may also have a substantial content ofchlorine, generally present as sodium chloride in the pore water. The South Australian lignites, also referred to as brown coals when they have a total moisture content of 507o or more, are characterised by low specific energ'y and variously by high percentages of moisiure, ash, alkalis (especially sodium), chlorine and sulphur. These properties can affect their utilisation in several ways, but the technologies that could be employed to remove the unwanted components do not appear economical at present. Because oftheir characteristics the distance ofthe deposits from industrial and population centres.' South Australian lignites do not appear promising for small or rnedium scale utilisation. However some of the state's lignite deposits appear to be economical for power generation, as already

practised with Leigh ereek coal. This is de-spitetheir high utilisation cost, due to the fact that they have tobe burnt in large boilers designed with appropriate features.

Geology of Australian Coal Basins

151

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Coal Resources, Quality and Utilisation

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152 The negative effects caused by certain components of

Corrosion

the lignites when burned in pulverised fuel (PF) power utility boilers are as follows:

Low Efficiency

The cost ofutilisation is also negatively affected by the high moisture content of these coals. The boiler efficiency for brown coals of about 55Vo moisture would be around 72 to 747o, against 88Vo for a good bituminous coal of <107o moisture, due almosl entirely to the difference in moisture level. As the efficiency decreases, more coal has to be burnt for the same electric output. Also with increasing moisture there is a consequent reduction in the flame temperature and a decrease in heat transfer to the furnace wall, which means that a larger furnace is required to absorb the same amount of heat.

When fouling is present, high temperature corrosion can ocCur in the superheater and reheater as the steel tubing is attacked by complex inorganic salts formed by the-reaction of the iouling deposit with the flue gas. Coals with significanl concentrations of sodium and sulphur, particularly if accompanied by chlorine, are ilotentiallycorrosive. In recent years hightemperature corrosion has been p-revented, to a

Abrasion The main components affected by abrasion in a boiler are the convection section (superheater, reheater and economiser) and the pulverisers. With lignites the mass of ash passing through the boiler is higher than for higher rank coals with the same percentage of ash, because when the specific energy is low more coal has to be fired for the same steam output. Abrasion in the convection section depends on the mass of ash passing through the boiler and the velocity of the gases. As the mass of ash increases the velocities of the gases in the convection and air heater sections must be reduced for abrasion control. This reduction requires a larger boiler and consequently a more expensive one. Abrasion in

larg^e extent, by designing the boilers so that the

me[al temperature does not exceed 590-oC, together with the use, in some cases' of corrosion resistant alloys.

Atmospheric Emission For units burning coal with up to a certain concentration of sulphur, acceptable ground level concentrations ofSOz can be achieved by dispersing the flue gases from a tall stack. The Noithernlower Station at Port Augusta has a 200m stack, which is adequate for Leigh Creek coal, but for most of the other South Australian lignites this solution would not be sufficient' It would be possible to reduce sulphur dioxide emission by adding calcium-based materials to the coal prior io burning, in order to- absorb-sulphur dioxide in the furnace. This method works best at the low combustion temperatures which are characteristic ofbrown coals because oftheir high moisture content. The main method of reducing sulphur dioxide emission extensively used ove-rseas is by scrubbing the flue gases, but these facilities are expensive to install and operate.

the pulverisers depends primarily on the percentage of quartz in the coal, and pulveriser overhauls are a significant maintenance cost.

Slagging Slagging is the accumulation of fused ash deposits on surfaces predominantly exposed to radiant heat. Slag in the boiler furnace impedes heat transfer, and large slag accumulations dislodged and falling from above may also damage the tubes in the furnace hopper. The propensity for slagging depends on ash composition and furnace and buiner design, with crude indication of the likely severity of slag formation given by the ash fusion temperature - the lower it is the higher the probability that slagging will occur. South Australian lignites tend to have low ash fusion temperatures because of their often high alkali content.

Particulate emission from South Australian lignites would be comparatively easy to control with electrostatic precipitators. As is the case with Leigh Creek coal, the precipitability of these fly ashes would be good because of t!eir sulphur and sodium content. The emission of nitrogen oxides (NO") in burning most of the state's lignites are not expected to be high, as the combustion temperatures of these high moisture coals are lower fhan for higher rank materials.

Fouling Fouling is the formation of ash deposits on tubes in the ionvection section of the boiler. These deposits grow in the shape of fins in the opposite diiection to the gas flow, are often very adherent to the tubes and harden with time. If they are allowed to accumulate they may force a boiler shut-down by restricting or, in extreme cases, blocking the gas passages by bridging across the tubes. The tendency for a coal to cause fouling is dependant on its inorganic constituents, but, as fouling is a complex phenomenon, it is diffrcult to predic"t fouling s^enetity from coal'analysis alone. It is well established, however, that sodium is a major contributor to fouling an{ !ha-t the ratio of sodium to ash is a crude guide. The larger this ratio the greater the potential to cause severe fouling.

Since the middle 1950s, Leigh Creek coal has been a convenient fuel for the generation of electricity in South Australia at the Playford Power Station. The experience gained by ETSA in using this low quality coil, in spite of the disadvantages listed above,-w?,sput to good use when it was decided in 1976 to build the ne* Northern Power Station at Port Augusta" The boiler plant was specified in great detail to ensure that tendered designs would suit Leigh Creek coal. The two 250MW (electric) boilers bought by ETSA and successfully commissioned in 1985 have the following characteristics:

Low.gas velocities, to minimise convection section abrasion;

Comparatively low heat release rates in the furnace for control of slagging;

n An upper limit to the furnace exit gas temperature for control of fouling;

Gas recirculation from the precipitator outlet to the secondary air in order to lower combustion zone and furnace exit gas temperature for control of slagging, fouling and NO* emission;

Once-through water/steam system, providing substantial superheater wall surface in the

Geology of Australian Coal Basins

153

furnace to lower the furnace exit gas temperature;

Larger spacing of elements in the convection section and a adequate number of automatic sootblowers to offset fouling to some degree.

Table 15. Typical properties of Callide eoal (Queensland CoaI Board, 1992). 15.5 9.6 16.4 24.6 49.4

Equilibrium Moisture (Vo at 30"C,97% humidity) Inherent Moisture (7o ad) Ash (7o ad)

Volatile Matter (Vo ad)

Queensland Sub-bituminous coal is mined in Queensland at two open cut mines in the Callide Basin, about 80km south-west of Gladstone. The coal is of Triassic age with typical properties as indicated in Table 1.5. Callide coal is sub-bituminous in rank, with a mean maximum vitrinite reflectance of <0.57o and a carbon content of approximately 77 to 78Vo (dafl. It is sub-hydrous with a hydrogen content of only 3.8 to 3.97o (daf) and also has very low nitrogen (<L.27o daO. The oxygen content is approximately lTVo (daf), and the coal completely lacks any swelling, caking or coking properties. The coal has high inherent moisture and medium ash. The percentage of volatile matter is only medium as a consequence of a high inertinite content and the coal's low hydrogen content. Gross specific energy is about 29MJkg on a dry, ash-free basis but only just over 2OMJ/kg on a natural bed moisture basis. The coal is soft, having a Hardgrove Grindability Index of nearly 90. Ash fusion (deformation) temperatures can be as low as 1300oC, but flow temperatures are generally about 1500'C.

Fixed Carbon (7o ad) Gross Specific Energy (MJ/kg, ad) Gross Specific Energy (MJ/kg, daO Carbon (Vo daf) Hydrogen (Vo da0 Nitrogen (Vo daf) Sulphur (Vo daf) Oxygen diff. (Vo daf) Phosphorus (7o ad)

2L.74 29.38 76.8 3.81 1.18

0.36 17.9 0.06 0.02

Chlorine (7o ad) Crucible Swelling Number

0.53 89 1300

Reflectance (Ru, max) Hardgrove Grindability Index Ash Deformation Temperature ('C) Ash Sphere Temperature ("C) Ash Hemisphere Temperature ("C) Ash Flow Temperature ('C)

15 17

1543

r570 0.19

Pyritic Sulphur (7o ad)

Sulphate Sulphur (% ad) Organic Sulphur (7a ad)

0.03

0.08

Analysis of Ash (7o) 38.1 33.8 15.6

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0.30 2.83 2.02 0.25 0.10 0.92 2.52

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NaeO KzO PzOs SOs

Callide coals finds its greatest use for generation of electricity in the power station at Gladstone, where some problems are experienced with boiler deposit formation. It is also used in alumina and cement clinker processing plants and for general industry in the Gladstone area, and has found some use for fuelling modern coal-fired bulk ships using the port of Gladstone.

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BROWN COAL IN VICTORIA

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Brown coal is mined commercially in Victoria, where brown coals of Tertiary age constitute the major coal deposits. Brown coals occur in the Murray, Otway and Gippsland Basins, with the Gippsland Basin including the Latrobe Valley which contains about 857o of the State's total coal resource. Brown coals in both the Gippsland and Otway Basins are strongly banded as a result of their different environments and,/or the coalification reactions that subsequently occurred (George, 1975; 1982). The properties that vary with stratigraphic banding are those which relate to the organic coal substance, e.g. carbon, hydrogen, oxygen, volatile matter and gross specific energy (dry, mineral matter free). Moisture is also layer-dependent. For classification purposes the bands have been divided into five lithotypes based upon colour, texture, degree of gelifrcation, weathering pattern and physical properties. The lithotypes are described as dark (Dk), medium dark (M-d), medium light (M-l), light (Lt) and pale (Pa). There are minor but significant differences in the chemical and physico-chemical properties of the lithotypes. Figure 11 shows the relationship between lithotype, colour index, carbon and volatile matter in a representative section from a bore core in the Loy Yang area.

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Coal Resources, Qua lity and Utilisation

154

Table 16. Average:analyses of brown coals from the Gippsland Basin (State Eleetridity Commisbion:bf Victoria) (Reproduced"ffom,Durie, l99l); :'

Yallourn

Location

Yallourn

Gelliondale

Loy Yang

Morwell

Gormandale

Seam

Yallourn

Gelliondale

Morwell 1 & 2

Latrobe

665

55.1

1.7

5.7

62.8 1.3

Morwell 1 613

Traralgon 1*

64.8

3.0

1.6

50.3 48.0

49.4 44.9

49.8 48.9

48.3

51.5 46.9

52.3 5.0 47.4

1.3 67.5

3.3

r.4 68.5

26.r

67.4 4.8 0.48 0.69 26.6 0.72 25.0

0.59 0.35 25.8 0.38 26.2

4.9 0.60 0.30 25.0 0.33 26.4

6.9

7.0

7.9

8.4

Moisture (7o) Ash (% db) Volatiles (7o db) Fixed Carbon (7o db) Minerals and Inorganics (7o db) Carbon (Vo dmif)

Hydrogen (Vo dmif) Nitrogen (Vo dmif) Organic Sulphur (Vo dmif) Oxygen (Vo dmif)

Total Sulphur (7o db) GDSE (MJ/kg) NWSE (MJ/ke)

4.8 0.57 0.24 26.9 0.28

48.7 2.0 69.2

4.8

North

Extension

47.6

1.3

3.8

68.1 4.9 0.53 0.80 25.7 0.81 26.4 10.1

69.5 4.9 0.63 0.23 24.7 0.36 26.0 10.7

db = dry basis, dmif = dry mineral and inorganic free.

Average analyses for Victorian brown coals are given in Tables 16 to 18, which also serve to illustrate the variations that exist between seams and between coalfield areas. However averaging masks the property changes that occur in any one area as a result of lithotype variations. This is illustrated in Table 18, which gives statistical data on samples selectod on a lithotype basis in the Loy Yang area. The weighted mean is that from all results taking account of the total thickness of each lithotype as a proportion of the thickness of a coal seam. It is obvious that there is a significant variation in coal

properties in the various lithotypes. For instance, moisture varies from 56 to 687o, carbon from 68 to 72Vo and oxygen 2lto27Vo.

A comprehensive statistical analysis of a large number of coal samples, selected on a lithotype basis for all major coalfields, has been published by Brockway & Borsaru (1987).

In addition to lithotype dependence, a small effect due to rank variation has been observed in the organic matter of some thick Latrobe Valley seams.

For example, in the Morwell Open Cut there is a small deciease in moisture and volatile matter and a small increase in carbon and specific energy with depth (Perry & others, 1982). This effect is gene,rally mihimal, however, and does not significantly affect the data in Table 18. Other properties of Victorian brown coals, such as the propoitions of minerals and inorganic ions,-a-re not lithotype-dependent nor strongly influenced by in depositional environment, but they can changes -both vertically and laterally within a seam and vary between seams as well. A major volume on the science of Victorian brown coals has been compiled by Durie (1991). _

Gippsland Basin Average analyses of known coals in various areas of the Gippsland Basin are given in Table 16. The major seams are the Yallourn, Gelliondale, Morwell I and 2, Traralgon 1 and 2, and the Latrobe. Examples of each are given in the table, and,,with_ the exception of the Gelliondale, they are all found

in the Latrobe Valley.

Table 17. Average analyses of brown coals from the Otway Basin.(State Electricity Cimmission of Victbria, reproducdd:from DuriC; f991). Location

Altona

Bacchus Marsh

Port Phillip Basin

Depression

Anglesea

Wensleydale

Torquay Basin

Port Campbell Embayment

Seam

Altona

Maddingly

A1 + B Group*

Moisture (7o) Ash (7o db)

58.7

60.5 7.4 49.8 42.8

46.4

Volatiles (% db) Fixed Carbon (7o db) Minerals and Inorganics (% db) Carbon (Vo dmif)

12.6

47.2 40.2

3.5

68.6x

67.6 4.9 0.59

3.8 47.0

45.7

49.2

51.0

70.r

66.3*

,.)

5.0 4.9* Hydrogen (% dmif) 0.71 Nitrogen (Vo dmif) 2.75 1.6 Organic Sulphur (Vo dmif) 2L.5 25.2 Oxygen (7o dmif) 2.85 t.74 2.6x Total Sulphur (7o db) 27.4 25.6 22.5 GDSE (MJ/kg) 72.t 8.3 7.4 NWSE ( dmif = dry mineral and inorganic free GDSE = gross dry specific energy NWSE = net wet specific energy * = db - dry basis + A1 = is the main upper seam of Anglesea; B group consists of up to four seams. Analyses of the coals are similar and hence averages are given in the table.

Geology of Australian Coal Basins

50.8 3.3

4.6x

2.6* 25.8 11.1

155

Table 18. Statistical Cnaly3€s of,lithotype samples from the Loy Yang area (State Electricity Commission of Victoria).

ifi E; E: 6> iE Eb ,si ilJ E

FaA Moisture (7o) Ash* (7o db)

62.2 2.7 55.6 66.7 1.0 0.5 0.5 2.3 50.9 2.4 46.0 56.3 Volatiles (% db) 48.4 2.5 42.9 55.9 Fixed Carbon (7o db) 0.8 0.5 0.3 2.1 Minerals and Inorganics* (Vo db) 69.4 1.1 67.6 72.2 Carbon (Vo dmif) 4.9 0.3 4.5 5.8 Hydrogen (% dmif) 0.51 0.04 0.43 0.6 Nitrogen* (Vo dmif) 0.31 0.08 0.23 0.5 Organic Sulphurx (Vo dmif) 24.8 1.3 212 26.8 Oxygen (Va dmif) 0.31 0.08 0.23 0.5 Total Sulphur* (Vo db) 26.8 0.6 25.7 28.6 GDSE (MJ/kg) 8.3 0.9 6.6 10.8 NWSE (MJ/ke) db = dry basis dmif = dry mineral and inorganic free GDSE = gross dry specific energy NWSE = net wet specific energ'y x Properties not necessarily related to lithotype.

Prorimq.te Analysis The single most important property of Gippsland Basin brown coals is arguably their average moisture content, which generally ranges from 52 to 677o.However, owing to the layered nature of the coal, bands with moisture contents well below and well above average are commonly encountered. For instance some layers of coal in the Yallourn open-cut exceed 70% moisture, and coals with high wood content can in fact reach 807o. Ash is generally low in Gippsland Basin coals. In most areas it is below 6Vo (dry basis), while in the three main open cut mines it is normally below 3Vo. Indeed in large areas of the Loy Yang open cut the ash is below 17o. Despite this, severe fouling can occur when the coal is burnt in a power station or industrial boiler. This is due to tlie mode of occurrence of the ash-forming constituents in the coal, which is mainly as inorganic ions bound to carboxylic functional Eroups. The cations are predominantly Na*, \fr.g2*,'Caz*, Fe2* and Fe3*.

Aluminium in a form believed to be a cationic hydroxo complex is also found in some Victorian brown coal, particularly near the base of seams and adjacent to the interseam sediments. Sodium chloride is also observed. The occurrence ofdiscrete mineral particles comprising predominantly quartz, kaolinite, muscovite and pyrite/marcasite is sporadic, and usually only in small amounts. Ash from the combustion of brown coal results from a series of reactions that occur between the inorganic elements present in the coal, organic sulphur and oxygen.

Volatile matter is generally found to be in the range 45 to 557o on a dry basis, but values as high as 60Vo have been observed from some very pale coals. Some of this volatile matter is made up of carbon dioxide released from the decomposition of carboxylic groups, and does not contribute to the specific energ"y of the volatile components.

Ultima.te Analysis Average carbon, hydrogen and oxygen contents on a dry mineral and inorganics free (dmi0 basis generally fall within the ranges 65 to 7lVo, 4.5 to 5.5Vo and.24 to SOVo respectively. The high oxygen

content is characteristic of Victorian brown coals. About halfofthe oxygen is present in carboxylic and phenolic functional groups and the rest is believed to be present in carbonyl, ester and ether groups. The carbon, hydrogen and oxygen contents generally reflect both the age ofthe seam in question and the lithotypes present. Mean carbon contents increase from the younger seams (Yallourn 67.57o,

Gelliondale 67.47o) to the older seams (Morwell 68.\Vo, Traralgon 68.LVo) while oxygen decreases (Yallourn 26.9Vo compared with Traralgon 25.7Vo). However the differences are small and there is not generally a large rank variation in Gippsland Basin coals. Within any seam the effect of coal lithotype can be discerned in the lower oxygen and higher carbon and hydrogen contents for the lighter coloured lithotypes.

Nitrogen and sulphur, on the other hand, do not appear to be rank or lithotype dependent. These constituents are uniformly low in the Latrobe Valley seams that are currently utilised, averaging about 0.6% (dmmfl for nitrogen and <0.47o (d) for sulphur. However sulphur can vary significantly both within seams and between the different coalfield areas.

In some areas sulphur has been found to increase markedly at the interface between coal and basement clay (King & others, 1983), and high sulphur is also associated with thin interseam sediments at Loy Yang (Kiss & others, 1985). Sulphur has also been observed to increase markedly in the eastern coal fields and towards the coast, as can be seen from Figure 12. In the Yallourn-Morwell and Loy Yang-Flynn areas, sulphur contents are generally 0.3 to 0.47o (d) with values increasing towards the east (e.g. from 0.5 to 2.0Vo in the Rosedale and Gormandale areas up to 3 to \Vo in the Coolungoolum and Stradbroke areas). Sulphur contents of 5 to 77o are observed in the small Glenco deposit, which is the most easterly field and adjacent to overlying marine sediments in the basin fill (Kiss & others, 1985). The higher sulphur contents are believed to be a result of marine influence.

Specific Energy The average gross dry specifrc energy (GDSE) of Gippsland Basin brown coals is generally in the range 25 to 28MJ/kg. However, individual values are dependent on coal lithotype and the presence of ash-forming constituents, and range from about 24 to 37MJ/kg. The highest values are found in pale lithotype coals with low ash values. The predominant influence of moisture on specific energy is seen in the net wet specific energ'y (NWSE) shown in Table 15. For the Yallourn seam, which has the highest moisture content (66.\Vo), the average NWSE is only 6.9MJ/rg (compared with a GDSE of 26.1MJ/kB). For Latrobe seam coal which has a similar GDSE of 26.OMJ/kg but a significantly lower moisture content (52.37o), the average NWSE

is 10.IMJlkg.

P hy sic o- chemia al P ropertie s

The major use for the brown coals of the Gippsland Basin is in power generation, and since the

Coal Resources, Quality and Utilisation

156

physico-chemical properties of the coal undoubtedly affect its ignition and combustion characteristics, these properties have been studied in some detail. The properties ofinterest are true and apparent density (measured using helium and mercury displacement techniques respectively), porosity (defined as the volume of dry coal particles occupied by voids and calculated from the true and apparent densities) and surface area (measured by gaseous absorption of carbon dioxide on dry granular coal at 0oC and calculated using the Dubinnin equation).

True and apparent densities of Gippsland Basin coals have been found to fpll within the ranges 1.25 to 1.50 and 0.6 to L.2g/crn" respectively. Porosity values generally range from 30 to 507o, although there are only small differences between the average porosities for samples from the major coalfields (35 to 437o) with the possible exception of the Latrobe seam from Yallourn North Extension, for which an average porosity of about 2IVo }ras been reported from a limited number of samples (Higgins & others, 1980). For dry coal the surfacg area generally falls within the range 200 to 300m'/g. Although it is difficult to isolate the influences of individual physico-chemical properties of brown coal from one another and from chemical properties, porosity at least has been shown to have a significant effect on the ignition characteristics of brown coal (Allardice & Ledger, 1975).

Otway Basin A number of separated depressions containing brown coal deposits have been discovered in the Otway Basin. These include the Torquay and Port Phillip Basins, the Ballen Graben and the Port Campbell Embayment (Gloe, 1984). Average analyses for brown coals of the Otway Basin are given in Table 16, and it can be seen that in general the ash is higher (3 to 13Vo (d)) and the moisture lower (607o or less) than for coals of the Gippsland Basin in the Latrobe Valley. Another marked difference is that the Otway Basin coals generally have higher sulphur contents (1.5 to SVo dry basis).

Murray Basin Although brown coal is known to exist in the Murray Basin, the seams appear to be thin and too deep for economic development. Only limited analyses have been performed, but the coal appears to be similar to that in some of the older Latrobe Valley seams. Average moisture and ash have reported to be 56 and. IlVo respectively. The gross dry specific energy is about 2lMJkg while the net wet specific energy is approximately 9MJ/kg.

Current Utilisation of Victorian Brown Coals Most current brown coal production in Victoria is from the Gippsland Basin, with a small amount coming from the Otway Basin as well.

Gippsland Basin All coal production from the Gippsland Basin is

currently won from three open cut mines in the Latrobe Valley. The current annual rate exceeds 47Mt, and is expected to increase to more than 60Mt over the next decade, largely as a result of increased production from the Loy Yang Open Cut. Electricity Generation The vast majority of Gippsland Basin coal is used for

electricity generation, with about 45Mt used for this purpose in 1991-92 out of 47Mt mined. Brown-coalfired boilers with a capacity of over 5200MW(e) are currently installed, and this will be increased to over 6200MW(e) in the next few years with the commissioning of Loy Yang B Power Station.

The combustion of brown coal with such a high moisture content and severe ash fouling has, however, led to difficulties in its utilisation. The coal

is used without significant external pre-drying, and the boilers are designed to operate on bed-moist coal with a nanow range of moisture contents. All the coal moisture enters the boiler and an increase in average moisture by 3 or 47o ma! lead to flame instability. To accommodate the large volume of water vapour released from the coal during drying

Figure 12. Regional distribution of sulphur in Latrobe Valley coals (Durie, 1991).

Geology of Australian Coal Basins

157

and combustion in the boiler, and to give time for heat to be exchanged between the combustion between the combustion gases and the boiler tubes, the combustion chambers have about three times the volume of black coal boilers with the same steam output.

briquettes, in the absence of oxygen, ^u_ndeJ a controlled temperature profile to 800oC. The by-product tar is used as a fuel for heating the retort, and is also sold commercially as a boiler fuel.

Until 1991, Australian Portland Cement Pty Ltd (APCL) also produced char in a partial

Although the ash is low, severe boiler fouling may result from the mode of occurrence of the ashforming materials in the coal itself. Much of the ash is formed from reactions during combustion of the inorganic ions in the water phase of the coal and bound to carboxylate groups. The nature ofthe ash deposits depends on the temperature regime they experience. At temperatures above 1000oC, sodium, calcium, magnesium and iron present in the coal react with the clay and quartz particles and may form low melting point silicates and aluminosilicates. At temperatures below 1000oC, simple and

Dry Coal Production

sulphur in coal, oxygen and sodium, calcium and magnesium. The ash deposits accumulate on heat transfer surfaces, even in the presence of on-load cleaning (steam or water sootblowing), requiring the boiler to be shut down for cleaning when the limits of operational flexibility are reached.

Venture involving a Lurgi subsidiary, Dry Coal Pty Limited (80Vo) and Valley Char, an Australian Char subsidiary (2OVo), and will produce up to 150 000t of dry coal per annum. The product has a number of applications as a fuel and char feedstock. In the first instance the dry coal will be used to provide auxiliary fuel for Loy Yang B Power Station.

The aluminium hydroxy complexes present in the coal in some areas, notably around interseam sediments at Loy Yang and adjacent to the base of the seam at Yallourn, can also cause particulate emissions. In areas where the concentrations of the

Otway Basin

complex mixed sulphates form from reactions of

usual ash-forming materials are significant, the aluminium in this form, which is intimately dispersed through the coal, gives an ash which consists essentially of AlzOs. The^bulk density of this ash can be as low as 40kg/mo, and it can escape from electrostatic precipitators under some conditions, particularly during on-line rapping. Briquette Production Briquettes are produced in the Latrobe Valley from Yallourn coal. The raw coal is crushed and dried to abott 157o moisture and then pressed through extrusion dies without the addition of any binding agent. About 2.7t of coal are used to produce 1t of briquettes, and a further lt of coal is used to produce the steam for drying the process coal. Because of their low moisture content, the briquettes have a net specifrc energy about 2lMJ/kg. With their low ash content (<27o) they make an ideal fuel for industrial and domestic purposes. Total production ofbriquettes in 1991-92 was 0.72Mt, of which 0.46Mt was used by Australian industry for either process heat or char production. A further 0.09Mt was used by the State Electricity Commission of Victoria for auxiliary fuel in Latrobe Valley power stations, and 0.01Mt was used domestically. A total of about 0.08Mt of briquettes was exported to a number of countries by the Coal Corporation ofVictoria, and around a further 0.08Mt of briquettes was held in storage. Char Production Char has been produced from Yallourn briquettes by two different processes:

Australian Char Pty Ltd currently use about 130 000t ofbriquettes annually to produce 65 000t of lump char, which is in turn used as a high purity carbon feedstock for industry and as a metallurgical and electrochemical reductant. The char is produced by heating

combustion retort. Most of the material was used as an integral fuel for pelletised clinker in cement production, but this production has now ceased.

A demonstration plant using Steam Fluid Bed Drying technology originally tested and patented at Monash University and further developed and commercialised by Lurgi has been constructed in the Latrobe Valley. The plant is owned by a Joint

Two small open cut mines currently extract coal from the Otway Basin. The largest of these is located at Anglesea, and the coal is used for power generation on-site by Alcoa of Australia to sgpply

electricity to a nearby aluminium refining plant. About 1.1Mt of coal is mined annually for this purpose out ofa total economically recoverable reserve of 120Mt.

The other mine is situated at Bacchus Marsh, where about 50 000t ofbrown coal is extracted annually. About 40 000t ofthis is used for steam raising by a particle board manufacturer in the Bacchus Marsh area. Most of the remaining L0 000t is used in various horticultural products.

Future Uses of Victorian Brown Coals Elec tric ity Generation

Electricity generation is expected to remain the predominant use for Victorian brown coals into the foreseeable future. New plant is currently under construction such that coal production for electricity generation is expected to exceed 60Mt annually by about 1996.

New Technologies for Power Generation from Victorian Broutn Coal The State Electricity Commission of Victoria (SECV) is currently undertaking a research program on new technologies for producing electricity from brown coal. This program, which commenced in 1989, has the aim of demonstrating technology that will convert brown coal to electricity at lower cost and higher efficiency than is achieved with conventional pulverised-coal fired steam power stations (SECV Research and Development Department, 1992). The program is organised into three phases:

. . .

laboratory and pilot-scale; proving-scale; and demonstration-scale.

Coal Resources, Quality and Utitisation

158

Two alternatives being investigated in parallel during phase 1 of the program are hydro-thermal drying of coal for direct combustion into a coal-fired turbine, and integrated gasification combined-cycle using steam fluidised- bed drying of the coal. Each of these offers increased effrciency, partly through improved drying of the coal and partly through the use of gas turbine combined cycles.

By 1992 substantial progress had been made on both projects. The hydro-thermal drying pilot plant and coal-fired turbine combustor simulator were operated continuously to provide performance data on the drying process and to evaluate combustion and ash deposition characteristics ofthe dried coal. a range of treatment processes for the waste-water produced from hydro-thermal drying was also investigated, including pilot-scale tests on component manufacturers' equipment. Laboratoryscale investigations of steam fluidised-bed drying were completed, following agreement between the SECV and Lurgi to construct a 150 000t per year drying plant (see above) in the Latrobe Valley. A coal gasifrcation development unit was constructed at the SECV's Herman Research Laboratory and commissioned during 1992. This unit is being used to evaluate the High-Temperature Winkler gasification process for brown coal and to investigate hot gas clean-up for removal of dust and

alkali species from the product gas.

A new concept for the coal gasifrcation process, which integrates coal drying with gas cooling, was developed during 1991. This concept shows promise of significantly reducing the cost of an integrated gasification combined-cycle plant. Cost evaluations for commercial development based on each of the systems show potential to reduce the cost of energy sent out by up to 30Vo and reductions in greenhouse emissions by 257o.

Briquette and, Char Prod.uction Briquette and char production are also expected to continue for the foreseeable future. The possible use of low ash (4Vo) coal from Loy Yang for briquette production is under investigation, and results appear promising. Char produced from Loy Yang briquettes could have <2Vo ash, and hence an increased value over the material produced from Yallourn coal briquettes. Methods of further reducing the ash-forming constituents of brown coal char are also under investigation and, if economic, have the potential to produce a very high purity carbon feedstock for industry.

Dry Brown Coal

gas which is the current preferred source ofprocess heat for many industries. However, it is expected that, as the cost of natural gas increases in the future, some industries will shift to the use of dry powdered brown coal as an energy source.

The Solar Dried (brown) Coal Slurry Process (SDCS) has been developed for the production ofan economic lump product largely free of frnes. In this process brown coal is mixed with water to produce approximately 36% solids by weight, and finely ground to a mass median diameter of about 10m. Chemical additives may be introduced before or during grinding. Some macropores are destroyed

during grinding, while others are filled with colloidal particles. The SDCS is slowly dried in air to produce a hard, densified product. The product also has potential for use as a fuel in industry, for the production of hard lump char by carbonisation, and other processes where briquettes are used, but its utilisation has not proceeded at present for economic reasons.

Liquefaction of Victorian Brown Coal Despite their high oxygen content, the high reactivity of Victorian brown coals has led to considerable research into their liquefaction characteristics, and a number of investigations have been carried out to produce oil from the coal (Allardice & others, 1991). Liquefaction studies included both batch autoclave and continuous reactor studies. A number ofprocesses have been examined, including hydrogenation, flash pyrolysis and CO-steam/alkali digestion. A range of catalysts have also been examined. The most significant liquefaction project involved hydrogenation of Victorian brown coal in the Brown Coal Liquefaction (Victoria) Pty Ltd (BCLV) pilot plant, which processed about 5Ot/day of dry coal in two hydrogenation stages. The pilot plant operation achieved its major objectives of high oil yield (>50Vo dry basis), stable operation, effective ash removal and long catalyst life. Both Morwell and Yallourn coals were processed in the pilot plant. Operation of

the plant ceased in 1990.

Other Possible Uses The high reactivity, low ash and low cost ofthe material suggest other potential uses for Victorian brown coal. Amongst these are:

Gasifrcation (including in situ gasifrcation) for production oftowns gas, synthesis gas and industrial fuel gas (see above);

power generation from brown-coal-burning gas

turbines;

The technical problems associated with handling,

storage and transport ofdry brown coal powder have largely been solved; brown coal powder is now extensively used in Germany and will be used in future in Victoria. As discussed above, the

production ofsteam fluidised-bed dried coal at the Lurgi/Australian Char plant will potentially lead to an industrial source of dried coal for industries other than power generation. Also in Victoria, Australian Portland Cement Pty Ltd have successfully demonstrated the drying, milling and firing of brown coal in a pilot plant using a small industrial burner.

The main impediments to the extensive use of dry powdered brown coal are economic factors, as the product has to compete with relatively cheap natural

. .

production of activated carbon; and production of electrode carbons.

REFERENCES ALLARDICE, D.J. & LEDGER, R.C., 1985: Ignition of Latrobe Valley coals: factors affecting the ignition behaviour. State Electricity Commission of Victoria, Research and Deuelopment Department Report, 312. ALLARDICE, D.J., CAMIER, R.J. & PERRY, G.J., 1991: Overview ofliquefaction studies on Victorian brown coal. First Japan /Australia

Joint Technical Meeting on Coal, Melbourne.

Geology of Australian Coal Basins

159 BROCKWAY, D.J. & BORSARU, R.M., 1987: Statistical analysis of data from the Brown Coal Evaluation Program. State Electricity Commission of Victoria, Research and Deuelopment Department Report, SC/87/119.

DURIE, R.A. (Editor), 1991: The Science of Victorian Brown CoaI: Structure, Properties and Consequences for Utilisation. Butterworth

Heinemann Ltd, Oxford.

GALLIGAN, A. & MENGEL, D.C., 1987: Australian Code for the Reporting of Identified Coal Resources and Reserves. Australian Mineral Industry Quarterly, 39(2), 49-5L.

GEORGE, A.M., 1975: Brown coal lithotypes in the

Latrobe Valley. State Electricity Cornmission of Victoria, Planning and Inuestigation Department, Petrological Report, L7.

GEORGE, A.M., 1982: Latrobe Valley brown coal

lithotypes, macerals, coal properties. Australian Coal Geology, 4(1), 111-130.

GLOE, C.S., 1984: The geology, discovery and assessment of the brown coal deposits of

Victoria. 1n Woodcock, L.T. (Editor): Victoria's

Broutn Coal - a huge fortune in chancery. Australasian Institute of Mining and Metallurgy, Melbourne.

HIGGINS, R.S., KISS, L.T., GEORGE, A.M. & KING, T.N.W., 1980: Properties of brown coals from the Latrobe Valley - a basis for the evaluation of quality. Stdte Electricity Commission of Victoria, Research and Deuelopment Department, Report,

sc/80/17.

Report, SO/83/85.

KISS, L.T., BROCKWAY, D.J., GEORGE, A.M. & STACY, W.O., 1985: The distribution of minerals, inorganics and sulphur in brown coal.

In: Proceedings of the International Conference on Coal Science, International Energy Agency, Sydney, 589-592.

MULLINS, P.J,, NANCARROW, P.C. & LA NAUZE, R.D., 1985: Fouling and corrosion during fluidized-bed combustion of South and Western Australian coals. 1n, Wibberley, L.J. (Editor): Specialists workshop on the effects ofcoal ash in combustion systems, Proceedings of the Symposium on CoaI Ash in Combustion Sysferns,Department of Chemical Engineering, University of Newcastle, Newcastle, 129-139. PERRY, G.J., ALLARDICE, D,J. & KISS, L.T., 1982:

Variation of Victorian brown coal characteristics and hydrogenation potential. FueI, 6I, 1060. QUEENSLAND COAL BOARD, 1991:40th Annual Report, 1990-91. Queensland Coal Board, Brisbane.

QUEENSLAND COAL BOARD, 1992: Queensland Coals: typical physical and chemical properties and classification (8th edition). Queensland Coal Board, Brisbane.

JOINT COAL BOARD, 1991: Neu South Wales Coal Yearbook, 1990-91. Joint Coal Board, Sydney.

JOINT COAL BOARD & AUSTRALIAN COAL INDUSTRY RESEARCH LABORATORIES LIMITED, 1978: Blending Australian Coals with Japanese Coals to meet the Metallurgical Coke Requirements of Japanese Steel Mills. Joint Coal Board, Sydney (Reprinted 1983).

JOINT COAL BOARD & QUEENSLAND COAL BOARD, 1981: Survey of Australian Black Coals ofConversion Potential. Joint Coal Board, Sydney.

QUEENSLAND DEPARTMENT OF MINES, 1986: Queensland resources ofblack coal, June, 1986. Queensland Gouernment Mining Journal, 87, 257-260.

SNIFFIN, M., SAYERS, P. & BECKETT, J., 1986: Nelu South Wales CoaI Resources and Reserues, 1986. New South Wales Department of Mineral Resources, Sydney.

STANLEY, D.R., 1986: Brown coal resources of Victoria an overview. Victorian Department of

-Industry, Technology and Resources, Unpublished Report, 1986/25.

JOINT COAL BOARD & QUEENSLAND COAL BOARD, L987:. Australian Black Coals. Joint Coal Board, Sydney.

JOINT COAL BOARD & QUEENSLAND COAL BOARD, l99L: Australian Black Coal Statistics, 1991. Joint Coal Board, Sydney. KING, T,N., GEORGE, A.M., HIBBERT, W.D. & KISS, L.T., 1983: Variation of coal properties with lithotype, Pafi 2. State Electricity Cornmission of Victoria, Research and Deuelopment Department,

STATE ELECTRICITY COMMISSION OF VICTORIA, 1992: Research and Development Annual Report, 1991-92.

Coal Resources, Quality and Utilisation

l6l

Parrt? r Permian Coal Deposits

Geology of Australian Coal Basins

r63

BASIN DEFINITION

ffiydney-Gunnedah Basin overview

NZ Tadros

The Sydney-Gunnedah Basin (Figure 1) constitutes the southern part ofthe larger Sydney-Bowen Basin, which is a composite structural basin extending for 1700km from sbuthern New South Wales to central Queensland. The Sydney-Gunnedah Bas-in is-u-p to ObOkm long and 200km wide, and extends offshore to the edge ofthe continental shelf. It is bounded by a regionil unconformable boundary with the Lac[lan Fold Belt to the west and the New England Fold Belt to the east, and is continuous with the Bowen Basin to the north.

Bembrick & others (1973, 1980) defined a boundary between the Sydney-Gunnedah and Bowen Basins along a transverse structural high 40km north of Nariabri. They also defined a boundary between the Sydney and Gunnedah Basins along the Mt Coricudgy Anticline, running south-west from a point near Muswellbrook (Figure 1). Subsequentworkers, however, have modified these structural subdivisions (Bradley & Moloney, 1983; Hamilton, 1985; Bradley & others, 1985; Hill, 1986; West & Bradley, 1986; Etheridge, 1987), based mainly- on aspecti of stratigraphy and sedimentation within the Sydney and Gunnedah Basins.

In particular, Bradley & Moloney (1983) s-uggested thal the Mt. Coricudgy Anticline, although characterised by a zone ofthinning and appears to have been active throughout deposition ofthe coal measures, did not control deposition of all component formations. They also pointed out that the itratigraphic sequence ofthe western Sydney Basin canbe recognised as far north as Coolah. West & Bradley (1986) subsequently argued that a more appropriate (but still arbitrary) boundary -

between the Sydney and Gunnedah Basins may be taken along a line from Coolah to Dunedoo and thence easfwards over the Liverpool Range (Figure 1). This line corresponds with a major Landsat lineament (Scheibner, in Bradley & others, 1985). Hill (1986) also suggested that the structural high north ofNarrabri does not exist, and that the Gunnedah Basin sediments extend as far north as Bellata and may extend further north towards the Queensland border. The Sydney-Gunnedah Basin forms one continuous

depositional basin (Figure 1), with prominent structural subdivisions which are evident from total gravity, magnetic, Landsat and ERTS-1 satellite imagery, and seismic cross sections (Tad_ros, 1988). The subdivision into two structural sub-basins, as originally proposed by Bembrick & others (1973,1980), has-been adopted with some modification by Tadros (1988, 1993c), and is used in the present discussion.

TECTONIC SETTING AND EVOLUTION Apart from local variations, the Sydney and Gunnedah Basins shared similar histories and their formation was controlled by the same tectonic processes. Together with the Bowen Basin, theyevolved as one large complex over a long period from the Late Carboniferous to the Middle Triassic. The basins display many features consistent with those ofa foreland basin. Their present configuration is that of a composite structural trough, extending _ along the western and southern margins of the New Ensl-and Fold Belt (marginal orogenic belt) and seplrating this orogeniCbelt from the older Lachlan tr'otd Sett (the Carboniferous continental craton) to the west. The sediment pile is asymmetrical, with

Sydney-Gunnedah Basin Overview

164

REFERENCE

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SYDNEY

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Figure 1. Location and structural setting of the Sydney-Gunnedah Basin (modified from Tadros, 1993c). the thickest accumulation near the eastern margin along the east-dipping Hunter-Mooki Fault System (Figures 1 and 2). The sequence thins to the west where it onlaps the cratonic Lachlan Fold Belt, which represented a cratonic region at that time. It should be noted that this present configuration of the Sydney-Gunnedah Basin only began to appear

after a mid-Permian period of deformation (diastrophism of Leitch , 197 4) in the New England Fold Belt, when the Hunter-Mooki Thrust System developed (Herbert, 1980a). The early history ofthe basin has been difficult to unravel from surface investigations of what amounts to a remnant (structural) basin. Nevertheless, several tectonic

Geology of Australian Coal Basins

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Sydney-Gunnedah Basin 0verview

166 models have been proposed for the origin of the

Sydney-Gunnedah Basin prior to the mid-Permian deformation in the New England Fold Belt region.

Many of these were summarised by Harrington (1982) and discussed in detail by Scheibner (1989, 1993) and Murray (1990). They include a basin initiated by Late Carboniferous and Early Permian volcanic rifting between the Lachlan and the New England regions but a foredeep in the Late Permian and Triassic (Scheibner lg74;1976), and a pull-apart basin formed by a major strike slip movement along the Burunga - Goondiwindi - Mooki Fault System in the latest Carboniferous and earliest Permian (Harrington & Korsch, 1979, 1985; Harrington, 1982, 1987). Scheibner (1993) has indicated that the strike-slip (pull-apart) model of Harrington & Korsch (1979, 1985) and Harrington (1982, 1987) does not work well, particuiarly since Murray & others (1989) have found that the Meandarra Gravity Ridge (see Tadros, this volume) extends for more than L200km and has a length-to-width ratio of 27 (Figure 3), much larger than for strike-slip regimes which typically have a length-to-width ratio between five and ten. Furthermore, it is now accepted that the time of formation of the Hunter-Mooki Fault System was no earlier than that of the sediments truncated by the fault itself, such as the Maules Creek Formation in the Gunnedah Basin which is of Early Permian Upper Stage 4 age (Thomson, 1984, 1986; Thomson & Flood, 1984), and not in the Late Carboniferous and Early Permian as suggested by Runnegar (1970, I974), Harrington & Korsch (1979), Brownlow (1981) and Harrington (1984a, b). Hammond (1987) applied the crustal extension (rifting) model of Gibbs (1984) and Lister & others (1986) to the Bowen Basin, and made observations on northeast-trending zones which bound domains of different surface structural and geological features. Mallett & others (1988) subsequently extended these observations south to the Sydney-Gunnedah Basin. More recently, Murray (1990) suggested a model for the Bowen Basin based on a volcanic rift in a back-arc position relative to the Early Permian 'Camboon Volcanic Arc'(Figure 3). The nature of a possible magmatic arc immediately east of the Gunnedah and Sydney Basins is uncertain (Scheibner, 1993), but a similar model is envisaged for the two basins. Proponents ofa volcanic rift origin for the Sydney-Gunnedah Basin argue that the bimodal Dalwood-Werrie-Gunn-edah-Boggabri volcanics, which formed during the latest Carbonferous or Early Permian, represented the start of extensional stresses in the area. Their composition and trace element signatures, in particular their Ti/V ratios, identify them as intra-plate basalts, which are characteristic of incipient and small-scale rifting (Martin & Tadros, 1990). Scheibner (1976) argues that, under the influence of tensional stress caused by convergence at the eastern leading margin ofthe Australian Plate, a volcanic rift developed which produced large quantities of ignimbrites and other calc-alkaline volcanics, associated with terrestrial and paralic sedimentation, which heralded the initiation of the basin.

Murray (1990) elaborated on the nature and composition of the volcanic rocks in the Sydney-Gunnedah-Bowen Basin, and emphasised the view that the association of continental rifts exclusively with bimodal volcanism is incorrect. It

appears that the volcanic rocks in such continental rifts are the result of mantle upwelling. Stretching ofthe lithosphere by pure shear can generate large volumes of mafic volcanism, which can produce silicic volcanism by crustal melting. Murray's (1990) model for the Early Permian inception of the Bowen Basin (Figure 3), showing a rift beneath the Taroom Trough forming by back-arc extension, is based on the premise that extension preceded and caused the passive upwelling of mantle by decrease in pressure as a result of a change in plate motions such as cessation of subduction. The vast amount ofsubsurface data from deep drilling programs in 1981-1982 by the New South Wales Department of Mineral Resources allowed detailed study of the strato-tectonic development of the Gunnedah Basin. Tadros (1988, 1993a) provided evidence that the basin also displays features consistent with a volcanic rift origin, and thus supported the original proposal ofScheibner (I974, 1976).

Basin fill in the Early Permian was localised in small, rapidly subsiding troughs. The troughs were separated by highlands and ridges consisting of silicic and mafic volcanics. Fine-grained lacustrine sediments accumulated in the most rapidly subsiding areas in the troughs (the Maules Creek Sub-basin, Bohena and Bando Troughs in the Gunnedah Basin; Tadros, 1993c), whereas prograding volcanic - lithic alluvial fan and piedmont deposits accumulated on the flanks of the highs and ridges and on the trough margins and ultimately filled the lakes and covered the trough areas with thick sequences offluvial sandstones and conglomerates (Tadros, 1993b). Small amounts of quartz-rich sediment derived from the Lachlan Fold Belt were also deposited in the trough areas. In the Sydney Basin, deposition began with alluvial (Clyde Coal Measures) and marine (Wasp Head Formation) conditions within grabens or half grabens, possibly related to extension comparable to the conditions that formed the Reids Dome Beds in the Bowen Basin (Tye & Fielding, 1994). The style of sedimentation of that period is typical of tectonically controlled volcanic rift sub-basins (Tadros, 1993b). Deposition in these sub-basins reflects subsidence of the underlying half-grabens, whereas the highs and ridges represent more stable basement structures and define the rift compartments.

Murray (1990) also suggested that the Early Permian rift stage in the Bowen Basin was followed by a mid-Permian thermal relaxation or sag stage and a final Late Permian to Middle Triassic foreland basin stage. The same stages apply to the whole Sydney-Gunnedah-Bowen Basin system (Scheibner, 1993).

There is no agreement on the timing and duration of the thermal relaxation - sag stage. The most acceptable and favoured interpretation, however, is that it occurred during the latest Early Permian to earliest Late Permian, and was soon succeeded by foreland tectonics which controlled basin development to the Middle Triassic (Tadros, 1993b).

This is clearly indicated by changes in style of sedimentation from localised fluvial and lacustrine deposition within several small trough areas controlled by tectonic subsidence of half-grabens (rift compartments) to basin-wide marine deposition caused by regional subsidence and widespread marine incursion. This regional subsidence is

Geology of Australian Coal Basins

t67

Figure 3. Structural setting of the Sydney-Bowen Basin, showing the Meandarra Gra_vity^ Ridge, the Camboon - Volcanics and the Ne1[ England andLachlan Fold ilelts (mddified from Tadros, f993b after Murray, 1990). interpreted to have been caused by thermal relaxation or sag ofthe lithosphere. The tectonic setting of thermal relaxation-.sag stage was soon superimposed by foreland tectonics. Strong deformation and uplift of the Devonian, Carboniferous and Early Permian rocks in the New

England region resulted in tectonic stacking ofthe thrust sheets and consequent loading of the cratonic margin (the foreland area), which caused subsidence and rapid sedimentation in the foreland basin in the Late Permian. Tectonic loading of the eastern edge of the craton also resulted in a 'forebulge' along the western basin margin. The basin fiil was derived

Sydney-Gunnedah Basin Overview

168

principally from the rising eastern orogenic region (now the New England Fold Belt), and also in part from the forebulge area in the craton ofthe Lachlan Fold Belt to the west. During episodes when sediment influx from the craton was significant, orogen-derived sediments (dominantly volcano-lithic) were intermixed along the basin axis with quartz-rich sands derived from the craton (Tadros, 1993b).

Consistent with typical foreland basins, marine sedimentation changed to fluvio-deltaic deposition in the Late Permian, with progradation westwards and south-westwards across the Sydney-Gunnedah Basin. This change may reflect westward movement of the main basin axis with time, due to continued westward displacement of the foreland thrust belt (Murray, 1985). The westward movement could also have been due to stacking and build-up of sediments in the east, forcing fluvial deposition westward (Tadros, 1993b).

Late Permian plutonism and associated felsic volcanism in the New England Fold Belt region was concomitant with rapid subsidence of the foreland basin, which accommodated up to a kilometre of coal measure sediments in the Gunnedah Basin, some 2km in the Sydney Basin and several kilometres in the Bowen Basin. Volcanism in the New England Fold Belt region contributed large quantities of volcanogenic material to the sequence, including tuff and tuffaceous sediments, particularly'in the Gunnedah Basin. The volcanogenic sediments in the Newcastle Coal Measures and in the overlying Triassic sediments of the coastal section of the Sydney Basin were derived from the volcanics present in the Northumberland Ridge, a meridional ridge, offshore between Sydney and Newcastle, discovered by Sydney Oil Co. and named by Brakel (1984) (Harrington, 1984b, 1989). The volcanic activity in the Late Permian marked the onset of an important event in the basin's history. Renewed thrusting in the New England Fold

Belt region resulted in east-west compressional movements, intermittent at the start but gaining momentum at the end of the Permian (Tadros, 1993b). Compressional movements were accommodated mostly by the Hunter-Mooki Fault System, and also by structural readjustments in the basin. Movements on the thrust fault are indicated by episodic influxes of coarse-grained volcano-lithic sediments, sourced from the New England Fold Belt region in the east, into the basin in the Late Permian. Cannibalisation of sediments and intraformational unconformities within the Late Permian upper part of the Black Jack Group in the Gunnedah Basin attest to the episodic uplift in the northern part ofthe basin (Tadros 1993b; see also Gunnedah Basin discussion by Tadros, this volume).

Compressive deformation intensified towards the end of the Permian and caused major uplift and basin tilting, particularly in the north and north-east ofthe Gunnedah Basin (Tadros, 1986b; Tadros & others, 1987). As a result, coal measure sedimentation was terminated and a thick section of the Permian sequence was eroded.

Uplift and basin tilting in the north and north-east of the Gunnedah Basin are indicated by a regional

angular unconformity between the Permian and Triassic sediments (Tadros, this volume). Subsidence and deposition in the south ofthe Gunnedah Basin appear to have been interrupted for only a short period, during which an unknown

(probably small) portion of the Permian section was eroded (Tadros, 1986b). Consequently, the unconformity in the south is less distinct than in the north.

In the Sydney Basin, Herbert (1993) has shown that a significant hiatus separated the Late Permian coal

measures from the overlying Narrabeen Group. The hiatus is represented by a disconformity over most of the basin, except where a significant part of the Permian sequence has been eroded in the folded and uplifted Hunter Valley and Newcastle areas.

Much of the Sydney-Gunnedah Basin probably achieved depositional base level in the earliest Triassic. Renewed tectonism in the elevated, highly deformed New England Fold Belt region, together with resumed subsidence in the foreland, allowed deposition of easterly-sourced coarse lithic conglomerates. Deposition gradually changed to westerly sourced quartz-rich sands from the forebulge areas in the Lachlan Fold Belt region (Ward, 1972; Tadros, 1986b). Tuff and tuffaceous sediments, which characterise the Late Permian coal measures, are not present in the Early and Middle Triassic sediments, indicating an abrupt reduction in eruptive volcanic activity in the orogen and that tectonism was mainly confined to folding and thrusting. The stratotectonic development of the SydneyGunnedah-Bowen Basin was terminated towards the end of the Middle Triassic by major compressive deformation and uplift. Jones & others (1984) associated this deformation and uplift of the basin with a contemporaneous phase of very low igneous activity in the New England Fold Belt region, describing it (page 260) as "an apparent minimum in igneorrs activity in the orogen not matched at any other time in the interval 260 to 220Ma ago" (i.e.

mid Late Permian to earliest Late Triassic).

Jones & others (1984) linked the waning of magmatic activity to rise and erosion of the foreland. Harrington (1984b) and Harrington & Korsch (1985) suggested that the uplift was caused by the frnal accretion or'docking'of the Gympie Terrane, a possible exotic terrane, at the eastern edge of the New England Fold Belt. However, Murray (1985) suggested that this terrane was accreted in the Early Triassic.

STRATIGRAPITY AND DEPOSITIONAL HISTORY

Early Permian The earliest Permian sediments in the Sydney Basin consist of isolated occurrrences of fluvial, coastal plain and marine sediments deposited on an older Palaeozoic basement. These are represented in the south by the Talaterang Group, consisting of the Clyde Coal Measures, Pigeon House Creek Siltstone and the Wasp Head Formation (Fielding & Tye, 1994; Tye & Fielding, 1994) deposited on older Palaeozoic basement, and in the Newcastle and Hunter regions by the fluvio-lacustrine sediments of

the Seaham Formation (Table 1).

A major tectonic movement in the Early Permiad caused the initial basin subsidence and initiated widespread marine transgression throughout the Sydney Basin, forming the Shoalhaven Group (including the Yadbro and Tallong Conglomerates and the Pebbly Beach Formation at the base) in the

Geology of Australian Coal Basins

169

south and west and the Dalwood Group in the Newcastle region. The Yarrunga Coal Measures were deposited at this time in the southern Sydney Basin, in a paralic zone (Herbert, 1980a) or coastal plain environment (Tye & Fielding, 1994) that moved westwards as the transgression took place (Herbert, 1980a). Thick basaltic and rhyolitic sequences were also formed, such as the Lochinvar Foimation and Gyarran Volcanics in the Sydney

Basin and the Boggabri Volcanics and Werrie Basalt in the Gunnedah Basin. A thick lacustrine sequence (Goonbri Formation), equivalent in age to the uppermost part of the Dalwood Group (Table 1), was alsb deposited in the Maules Creek Sub-basin of the eastern Gunnedah Basin and in the Bohena and Bellata Troughs of the Mullaley Sub-basin (Tadros, 1993d).

A temporary regression, which started late in the EarlyPermian, interrupted the deposition of the Dalwood Group and allowed the accumulation of a thick fluvio-deltaic sediment wedge (the Greta Coal Measures). This wedge prograded southwards from tectonically active areas in the New England region. It reached the Hunter Valley and Newcastle areas but did not prograde to the southern part ofthe Sydney Basin. Marine conditions continued uninterrupted in the south, forming the sequence from the Wasp Head Formation to the Snapper Point Formation and the Wandrwandian Siltstone (Table 1). Deposition also commenced in the western part of the basin at this time, with a thick transgressive shoreline and near-shore deposit (Snapper Point Formation) which was mainly derived from the Late Devonian quartzite of the Lachlan Fold Belt (Herbert, 1980a). The equivalents of the Greta Coal Measures in the Gunnedah Basin, the Leard and Maules Creek Formations, were deposited over a sequence of weathered basal volcanics, the Boggabri Volcanics and the Werrie Basalt.

Mid-Permian Rapid subsidence followed this phase of deposition in the mid-Permian and led to a transgressive marine inundation of the Greta Coal Measures and its equivalents. The transgression was developed first in the Sydney Basin, with deposition of the Branxton Formation of the Maitland Group in the Hunter Valley region. It subsequently spread northwards and resulted in deposition of the Porcupine Formation in the Gunnedah Basin. The presence ofice-rafted dropped pebbles and boulders in these formations is thought to indicate a cold climate, which persisted until at least the end of Maitland Group time (Brakel, 1984).

A regressive-transgressive episode interrupted the open marine shelf deposition and formed near-shore sand sheets (the Muree Sandstone in the north and the Nowra Sandstone in the south). These beds were overlain by the finer-grained offshore sediments of the Mulbring Siltstone in the north, the Berry Siltstone in the south and west and the Watermark Formation in the Gunnedah Basin (Table 1). Marine transgression in the Gunnedah Basin changed the pattern of alluvial sedimentation (Maules Creek Formation) to one of coastal fan development (fan delta of Beckett & others, 1983) or ice-dominated deltas in a marine-shelf environment (Hamilton, 1993), and formed the lower part of the Porcupine Formation. The upper part of the Porcupine Formation and the lower part of the

conformably overlying Watermark Formation represent deepening of the marine-shelf

environment (Hamilton, 1993).

Late Permian The main period of coal deposition (i.e' peat accumulation) in the Sydney-Gunnedah Basin

commenced very early in the Late Permian-, after the mid-Permian p6riod of diastrophism. Rapid subsidence associated with conlinuing uplift and

volcanism in the New England region resulted in increased erosion and transport ofsediment westwards and south-westwards into the basins' Sedimentation was by prograding fluvio-deltaic svstems which formed the Tomago Coal Measures, the Wittingham Coal Measures and the Black Jack Group (Ta6le 1). The Sydney-Gunne{a! Basin also received sediment from the Lachlan Fold Belt by progradation of alluvial systems, northwards and easfwards in the Sydney Basin and south-eastwards in the Gunnedah Basin. These sediments formed the lower part of the Illawarra Coal Measures and the Brigalbw Formation and Clare Sandstone within the Black Jack Group (Table 1). Two marine incursions interrupted terrestrial sedirnentation for short periods during this main coal-forming interval. The first incursion, c,aused by tectonic subtidence (Brakel, 1986), resulted in deposition of the Kulnura Marine Tongue and its lateral equivalents in the Sydney Basin, the Bulga and Archerfield Formations in the north and the Erins Vale Formation in the south. In the Mullaley Sub-basin of the Gunnedah Basin, north of the Liverpool Range, the marine incursion is represented by the Arkarula Formation. The marine iniursion did not reach the west, where sedimentation was dominated by the westerly sourced braided fluvial wedge of the Marrangaroo Conglomerate in the Sydney Basin and its

equivalent, the Brigalow Formation of the Black Jack Group, in the Gunnedah Basin (Table L).

The return to terrestrial sedimentation marked a very important event, the establishment of basin-wide swamps in which peat accumulated as a nearly continuous blanket over the emergent, subdued-relief surface resulting from the infilling of the preceding marine embayment (Brakel, 1984). That peat formed the Bayswater seam and the Woonbna Coal Member in the Sydney Basin and the Hoskissons Coal and lJlan seam in the Gunnedah Basin. Widespread peat formation was followed by continued southward progradation ofthe and Wittingham Coal Measures in the northern Sydney Basin ind the south-eastward progradation of the upper quartz-rich unit (Clare Sandstone) ofthe upper part ofthe Black Jack Group in the Gunnedah Basin (Table 1). The deposits of the second marine incursion-, whigh was probably eustatically controlled (Brakel 1986), are very extensive in the Sydney Basin and c-omprise the Waits Sandstone/Denman Formation and the Waratah Sandstone/Dempsey Formation sequences in the north, the Baal Bone Formation in the west and the Darkes Forest Sandstone/Bargo Claystone sequence in the south (Table 1). The Dempsey/ Denman incursion did not reach the Gunnedah Basin, but its lateral equivalents are represented by freshwater lacustrine sediments (the organic-rich mudstone-dominated Benelabri Formation) in the upper part ofthe Black Jack GrouP in the eastern nilf of tne Mullaley Sub-basin (Tadros 1986a, b; 1993e).

Sydney-Gunnedah Basin Overview

170

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Geology of Australian Coal Basins

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17l Coal measure sedimentation resumed after those

incursions, with the southward progradation of maior fluvial/deltaic systems from the north of the Svdnev Basin. This regression resulted in deposition of th" Wollombi and Newcastle Coal Measures in the north, the upper part of the Illawarra Coal Measures int-he south and west, and the uppermost part of the Black Jack Group (the Nea Sub-group) in ihe Gunnedah Basin (Table 1). Sedimentation during this interval, particularly in the northern Sydney Basin and in the Gunnedah Basin, was. influenced by the encroachment of conglomeratic braided fluvial systems and an abundance of tuff and pyroclastic <ietritus. The tuff and conglomerate were inainly derived from the tectonically active New England Fold Belt region, e-xcqpt for those of the Newcastle Coal Measures, which were apparently derived from the Northumberland-!idge t6 ifre easl of the present coastline (Brakel, 1984).

In the Late Permian a major depositional break and a period of structural readjustment,-uplift and erbsion are evident in the northern Gunnedah Basin and the Hunter Valley in the Sydney Basin. An angular unconformity is present in the-northern Gu-nnedah Basin between the Triassic Digby Formation and the Permian sediments of the Millie and Black Jack Groups (Tadros, 1986b; Tadros & others, 1987). In the Hunter Valley Dome Belt a significant depositional break occurred between the Lite Permian coal measures and the overlying basal Narrabeen Group. An unconformity is also present over the Lochinv-ar Anticline, where the Newcastle Tomago Coal Measures sequence hqs_been

complitely eroded and the Triassic Munmorah Conllomerate of the Narraleen Gr-oqp rests-dir-ectly on t[e underlying marine Maitland Group (Herbert, 1980a).

Triassic Deposition resumed in the Early-Triassic, when *ujor alluvial systems progra4ed southwards and sorith-westwardl over the eroded surfaces of the coal measures or the underlying Permian sediments. Thick conglomerate sequences, formed by large alluvial fans and outwash sediments, were introduced from the New England FoId Belt region across the Hunter-Mooki Fault System to the Hunter Valley (the Munmorah and Widden Brook Conglomerates) and the south-eastern Gunnedah Basln (Bomera Conglomerate Member in the lower part of the Digby Formation). These conglomerates bass laterallvlnto pebbly sandstones representing butwash maferial cieposiled ahead of the fans, and gradually become more sandy (Burra-Moko Head Sandstone) along the western margins of the basin (Herbert, 1980a). In the south, the sediments were finer grained and more sandy, forming the Scarb-orough Sandstone and the lower'Pebbly facies' of the Bulgo Sandstone (Ward, 1972). They are interbeddJd with green and grey claystone and siltstone units (the Stanwell Park Claystone and Wombarra Shale in the south, the Dooralong Shale in the east and the Caley Formation in the west), which represent fine-griined outwash and overbank sedimenfs intercalated with the alluvial fan braided stream deposits (Herbert, 1980a). Deposition continued in the Sydney Basin, but with sighificant changes in stream grad]ent and flow diiection. In the northern Sydney Basin, low-gradient streams flowed to the south-east para-llel to the basin axis-and dep-osited largequantities offine-grained red and green overbank sediments (the Tuggerah Formation and Patonga

Claystone). The western-margin received more on"-rt"ose sediments at that time from the west, with deposition of the Banks Wall Sandstone in the Svdnev Basin (Bembrick, 1980) and the upper part ni th" binbln Formation in the Gunnedah Basin (the Ut"au S"andstone Member north of the Liverpool nu"gu and the Wollar Sandstone in the south-west)' TheYvolcanic facies'of the Bulgo Sandstone (Ward, 1972) was deposited in the sogth-ern Sydney Basin bv westerlv and south-westerly flowing streams fiom an exposed area, probably consisting of the Permian G-erringong Vblcanics, further to the east' Widespread palaeosol horizons formed on topof the Gunnedah Basin deposits at the end of that phase (Jian, 1991). These have been attributed to eouilibrium conditions between loading by the oierthrust New England Fold Belt and a forebulge development in thelraton (Jian & Ward, 1993)' Renewed basin subsidence resulted in deposition of

the Napperby Formation in the Gunnedah Basin' Well-d6veloped upward-coarsening sequences of laminated siltstone/claystone, interbedded sandstone/siltstone laminites and sandstone form derived from the the lower part of the sequence, -and represent progradation New Englind Fold Belt of lacust"rine deltas. The uppef part consists of fl uvially-deposited, irregularly interbedded sandstdne a.rd siltitotte sequences. Jian & Ward (1993) believe that contemporaneous volcanic activitv in the New England Fold Belt, or possibly

the apiearance of the incipient Nand-ewar Igneous C omplex ( Nan dewar Volcanoe-s ), produced-the very distiirctive green sandstone of the Deriah Formation at the top oTthe Gunnedah Basin Triassic sequence' Subsidence in the Sydney Basin caused limited

transgression and an upward transition to fluvioldeltaic deposits of ttre upper Nqrrabeen Group (Newport and Terrigal Formations). Sediments derived from the New England Fold Belt did not reach the southern and western basin areas where, instead, thick red-brown claystone and siltstones were deposited (the Bald Hill Claystone- and the Wentworth Falls Claystone Member). These are thought to have been formed as terrestrial piedmont depoiits (Ward, 1972; Herbert, 1980a)'

Uplift of the Lachlan Fold Belt to the south-east of thL Svdnev Basin caused tilting and erosion of the

Late Fermian and Earlv to Middle Triassic sediments in the southern Sydney Basin (Herbert, 1980a) and the subsequent deposition ofcoarse quartzose sand (Hawliesbury Sandstone). The sand was probably derived from Late Devonian quartzites in thi Lachlln Fold Belt. Tilting of the basin to the north-east resulted in easterly and north-easterly current directions (Standard, 1964; Herbert, 1980a)' Equivalent lithologies to the Hawkesbury Sandstone arL not present in-the Gunnedah Basin, as the New Englanti Fold Belt remained the dominant source of sed"iments for that part of the basin complex (Jian & Ward, 1993). The last phase of tectonic develop-ment of the Sydney Basin is attributed to 'shutting-o of quartzose sand r"ppty from the Lachlan Fold Belt concomitant with raoid-subsidence of the Hawkesbury alluvial plain u.rh thu deposition of the Wianamatta Group. Herbert (1080a,b) related deposition of the Wianamatta Group to a single regressi-ve cycle,. sradins upwards from subaqueous shallow-marine 6r estu"arine laminated silt of the Ashfield Shale through a sandy barrier island.complex (represented by the"Minchinbury Sandstone) and adjacent

Sydney-Gunnedah Basin Overview

QLD. N.S.W.

Figur_e 4._Location of coalfields within the Sydney-Gunnedah Basin (Standing Committee on Coalfield

Geology of New South Wales, 1985).

Geology of Australian Coal Basins

L73 lagoonal and peat marsh deposits (the basal Brlngelly Shale), to alluvial conditions with extensive adjacent flood basins, levees and back swamps which formed the Razorback Sandstone Member and the remainder of the Bringelly Shale). The Napperby Formation in the Gunnedah Basin records a gross regressive cycle from lacustrine lake-basin to lacustrine delta systems and ultimately to fluvial sedimentation, with the main sediment-source being from the New England Fold

Belt. A major mid-Late Triassic episode of deformation caused reverse faults and uplifted small blocks from which the upper part of the Napperby Formation was removell-(ttamitton & others, 1988). This episode of deformation also terminated deposition in the Sydney Basin.

SUBDIVISION INTO COALFIELDS The Sydney-Gunnedah Basin has been formally divided into five separate coalfield areas (Standing Committee on Coalfield Geology of New South Wales, 1985), the boundaries of which are defined on the basis of prominent physiographic features and major geographic groupings of coal mining activities (Figure 4). For example, the boundary between the Hu-nter and Western-Coalfields in the south and the Gunnedah Coalfield in the north is taken at the divide of the Liverpool Range. The coalfields also represent, for the most part, distinct d-epositional and tectonic elements of the basin, and each coalfield has a characteristic coal measure stratigraphy. Because these same physiograpbi", depositionai and tectonic elements also control coal mine devclopments in the region, each coalfield is also recognised as a distinct activity centre within the New South Wales coal industrY.

Table 2; CoaI Resources of the Sydney-Gunnedeh Basin Coalfields (New South Wales Department of Mineral Resburces, 1994) COALFIELD

IN SITU

RECOVERABLI RESERVES RESOURCES (Mt) (Mt)

Hunter

61 100

4890

Newcastle Southern Western Gunnedah

10 700 L7 045

1050 1160

29 965 38 000

1420

Total

156 810

10 135

1615

COAL RESOURCES The five main coalfrelds of the Sydney-Gunnedah Basin contain the majority of the coal resources in New South Wales. In conjunction with the Queensland coalfields, they are the major producers oiblack coal in Australia for domestic use and export. Resources of approximately 157 000Mt of in situ coal, with ash of <357o (Table 2), are present at

depths <600m throughout all the Sydqgy- Gunnedah Baiin coalfields. The exception is the Southern Coalfreld of the Sydney Basin, where mining is expected to exceed thii depth limitation during the

next decade (Coal Resources Development Comrnittee, 1994). Those coalfields which have been actively explored

(e.s. the Hunter and Newcastle Coalfields) have a hiiher level of confidence in their reported The Gunnedah Coalfield (i.e. the ""forrt""r. Gunnedah Basin north of the Liverpool Range), on the other hand, is an example of an area which has been subjected to only limited exploration, and therefore a high proportion of its coal resources ha're a lower confidence level. A brief account of the in situ resources and recoverable reserves for each coalfield is provided in other discussions in this volume, but a summary is given in Table 2.

REFERENCES BECKETT, J., HAMILTON, D.S. & WEBER, C.R., 1983: Permian and Triassic stratigraphy and sedimentation in the Gunnedah - Narrabri Coonabarabran region. Geological Suruey of New South Wales, Quarterly Notes,51, 1-16. BEMBRICK, C.S., 1980: Geology of the Blue Mountains, western Sydney Basin. 1n Herbert, C. & Helby, R. (Editors): A Guide to the Sydney Basin. Geological Suruey of New South Wales, Bulletin, 26, l-35-161' BEMBRICK, C.S., HERBERT, C., SCHEIBNER, E. & STUNTZ, J., 1973: Structural subdivision of the New South Wales portion of the Sydney - Bowen Basin. Geological Suruey of New South Wales, Quarterly Notes, 11, 1-13. BEMBRICK, C.S., HERBERT, C., SCHEIBNER, E. & STUNTZ, J. 1980: Structural subdivision of the Sydney Basin. /n Herbert C. & Helby R. (Editors): AGuide to the Sydney Basin, Geological Suruey of New South Wales, Bulletin,26,3-9. BRADLEY, G.M. & MOLONEY, J., 1983: Structural control on sedimentation of the coal measures in the Rylstone drilling area. Abstracts, 17th Symposium on Aduances in the Study of the Sydiey Basin. Department of Geology, University of Newcastle, 44-47 .

BRADLEY, G.M., YOO, E.K., MOLONEY, J., BECKETT, J. & RICHARDSON, S., 1985: Svdnev Basin, New South Wales Petroleum Data Package. Geological Survey of New South Wales, Report GS1985/004.

BRAKEL, A.T., 1984: Correlation of the Permian coal measures sequences of eastern Australia. In Permian Coals of Eastern Australia, Volume 1,

Chapter 17, National Energy Research, Development and Demonstration Council, Report on Project 78/2617.

BRAKEL, A.T., 1986: Global sea-level change as a method of correlating the Late Permian coal measures in the Sydney, Gunnedah and Bowen of Basins, eastern Australia. BMR Journal 'J'7-22. Australian Geology and Geophysics, 10, BROWNLOW, J.W., 1981: A thermal model for the origin ofthe Sydney and Gunnedah Basins. Abitracts, 15th Symposium on Aduances in the Study of the Sydney Basin. Department of Geology, University of Newcastle, 10-12' COAL RESOURCES DEVELOPMENT COMMITTEE,

1994: Effects of land Ltses on coal resources. NSW

Department of Mineral Resources.

Sydney-Gunnedah Basin Overview

174 ETHERIDGE, L.T., 1987: New stratigraphic and structural data from the Surat and Gunnedah Basins and implications for petroleum exploration. Geological Suruey of New South Wales, Quarterly Notes,66, 1-21. FIELDING, C.R. & TYE, S.C., 1994: Stratigraphy of the Talaterang and Shoalhaven Groups in the

HERBERT, C., 1980a: Depositional development of the Sydney Basin. 1n Herbert, C. & Helby, R. (Editors): A Guide to the Sydney Basin, Geological Suruey of New South Wales, Bulletin,26, Il-52.

southernmost Sydney Basin. Proceedings, 28th

HERBERT, C., 1980b: Wianamatta Group and Mittagong Formation. 1n Herbert, C. & Helby, R. (Editors): A Guide to the Sydney Basin, Geological Suruey of New South Wales, Bulletin,26,255-272.

GIBBS, A.D., 1884: Structural evolution of extensional basin margins. Journal of the Geological Society of London, l4l, 609-620.

HERBERT, C., 1993: Tectonics of the New England Orogen reflected in the sequence stratigraphy of the Narrabeen Groupl'coal measures of the Sydney Basin. 1n Flood, P.G. & Aitchison, J.C. (Editors): New England Orogen, eastern Australia. University of New England, Armidale, 127-135.

HAMILTON, D.S., 1985: Deltaic depositional systems, coal distribution and quality, and petroleum potential, Permian Gunnedah Basin, New South Wales, Australia. Sedimentary Geology, 45, 35-7b.

HILL, M.B.L., 1986: Geology of the Deriah Forest area implications for the structure and stratigraphy -of the Gunnedah Basin. Geological Suruey of New South Wales, Quarterly Notes,62, 1-16.

HAMILTON, D.S., 1993: Genetic stratigraphic framework. In Tadros, N.Z. (Editor): The Gunnedah Basin, New South Wales. Geological Suruey of New South Wales, Memoir Geology,12,

JIAN, F.X., 1991: Genetic stratigraphy, depositional systems, sandstone petrography and diagenesis of the Triassic in the Gunnedah Basin, New South Wales, Australia. PhD thesis, University of New

Sym.posium on Aduances in the Study of the Sydney Basin. Department of Geology, University of Newcastle , 2L2-219.

I45-t64.

South Wales.

HAMILTON, D.S., NEWTON, C.B., SMYTH, M., GILBERT, T.D., RUSSELL, N., MCMINN, A. & ETHERIDGE, L.T., 1988: The petroleum potential ofthe Gunnedah Basin and overlying Surat Basin sequence, New South Wales. APEA Journal,28, 2t8-241. HAMMOND, R., 1987: The Bowen Basin, Queensland, Australia: an upper crustal extension model for its early history. In 87 BMR Research Symposium, Applied Extension Tectonics, Bureau of Mineral Resources (Australia), Record 1987 /51, 131-139.

JIAN, F.X. & WARD, C.R., 1993: Triassic depositional episode. 1n Tadros, N.Z. (Editor): The Gunnedah Basin, New South Wales, Geological Survey of New South Wales, Memoir Geology, 12, 297-326. JONES, J.G., CONAGHAN, P.J., MCDONNEL, K.L., FLOOD, R.H. & SHAW, S.E., 1984: Papuan Basin analogue and a foreland basin model for the Bowen - Sydney Basin. In Veevers J.J. (Editor): Phanerozoic Earth History of Australio. Clarendon Press, Oxford, 243-26L

HARRINGTON, H.J., 1982: Tectonics and the Sydney Basin. Abstracts, L6th Symposium on Aduances in the Study of the Sydney Basin. Department of Geology, University of Newcastle, 15-19.

LEITCH, 8.C., 197 4: The geological development of the southern part of the New England Fold Belt. Journal of the Geological Society of Australia,2l,

HARRINGTON, H.J., 1984a: Tectonic models for eastern Australian basins. 1n 13th BMR Symposium, Bureau of Mineral Resources (Australia), Record 1984/27,7 .

LISTER, G.S., ETHERIDGE, M.A. & SYMONDS, P.A., 1986: Detachment faulting and the evolution of passive continental margins. Geology, 14, 246-250.

HARRINGTON, H.J., 1984b: Tectonic history. 1z Permian Coals of Eastern Australia, Volume 1,

Chapter 28, National Energy Research, Development and Demonstration Council, Report on Project 78/2617.

HARRINGTON, H.J., 1987: Tectonic setting of Permian coal basins ofeastern Australia. Proceed,ings, 1987 Pacific Rim Congress, 793-796. HARRINGTON, H.J., 1989: Tectonic History. In Permian Coals of Eastern Australia, Bureau of

Mineral Resources, Bulletin, 231, 377 -394.

133-156.

MALLETT, C.W., HAMMOND, R.S. & SULLIVAN, T.D., 1988: Implications for the Sydney Basin of upper crustal extension in the Bowen Basin. Proceedings 22nd Symposium on Aduances in the Study of the Sydney Basin. Department of Geology, University of Newcastle, 1-8.

MARTIN, D.J. & TADROS, N.2., 1990: Basement morphology, Permian and Jurassic teschenites of the Gunnedah Basin. Abstracts, 1}th Australian Geological Cqnuention. Geological Society of

Australia, 233-234"

MURRAY, C.G., 1985: Tectonic setting of the Bowen Basin. Abstracts, Bowen Basin CoaI Symposiurn. Geological Society of Australia Coal Geology Group, Brisbane, 5-16.

HARRINGTON, H.J. & KORSCH, R.J., 1979: Structural history and tectonics ofthe New England - Yarrol Orogen. 1n Crust and Upper Mantle of Southeast Australia: Summaries of Papers presented at a Symposium held in Canberra, February 1979. Bureau ofMineral Resources (Australia), Record 197212, 49_51.

MURRAY, C.G., 1990: Tectonic evolution and metallogeny of the Bowen Basin. Proceedings, Bowen Basin Syrnposium. Geological Society of Australia, Queensland Division, 20I-212.

HARRINGTON, H.J. & KORSCH, R,J., 1985. Deformation associated with the accretion of the Gympie Terrane in eastern Australia. In Leitch E.C. (Editor): 3rd Circum-Pacifrc Terrane Conference, Extended Abstracts, Geological Society of Australia, Abstracts,14, 104-108.

Geology of Australian Coal Basins

175 NEW SOUTH WALES DEPARTMENT OF MINERAL RESOURCES, 1994: 1994 New South Wales Coal Industry Profile. Coal and Petroleum Geology Branch, NSW Department of Mineral Resources.

TADROS, N.2., 1993b: Tectonic evolution. /n Tadros, N.Z. (Editor): The Gunnedah Basin, New South Wales. Geological Suruey of New South Wales, Memoir Geology, L2, 47-54.

RUNNEGAR, B.N., 1970: The Permian faunas of northern New South Wales and the connection between the Sydney and Bowen Basins. Journal of the Geological Society of Australia, 16, 697-710.

TADROS, N.2., 1993c: Structural elements. 1n Tadros, N.Z. (Editor): The Gunnedah Basin, New South Wales. Geological Survey of New South Wales, Memoir Geology, 12, 55-86.

RUNNEGAR, B.N., 1974: The geological framework of New England. 1n Murray, C.G. & Runnegar, B. (Editors): 1974 Field Conference, New England area. Geological Society of Australia, Queensland

TADROS, N.2., 1993d: Influence of structural elements on the basin frll. In Tadros, N.Z. (Editor): The Gunnedah Basin, New South Wales. Geological Suruey of New South Wales, Memoir Geology,12,

Division, Brisbane, 9-19.

87-92.

SCHEIBNER, E., 1974: A plate tectonic model of the Palaeozoic tectonic history of New South Wales.

Journal of the Geological Society of Australia,2O, 405-426.

SCHIIIBNER, 8., 1976: Explanatory Notes on the Tectonic Map of New South Wales. Geological Survey of New South Wales, Sydney.

SCHEIBNER, E., 1989: The tectonics of New South Wales in the second decade of application of the plate tectonics paradigm. 45th Clarke Memorial Lecture. Journal and Proceedings, Royal Society of New South Wales,l22,33-74. SCHEIBNER, E., 1993: Tectonic setting. 1n Tadros, N.Z. (Editor): The Gunnedah Basin, New South Wales, Geological Suruey of New South Wales, Memoir Geology, 12, 33-46. STANDARD , J.C., 1964: Stratigraphy, structure and petrology ofthe Hawkesbury Sandstone. PhD

thesis, University of Sydney.

STANDING COMMITTEE ON COALFIELD GEOLOGY OF NEW SOUTH WALES, 1985: New definitions of coalfields, Sydney and Gunnedah Basins. Minfo (New South Wales Mining and Exploration Quarterly), 9, 52-53. TADROS, N.2., 1986a: Lacustrine facies - upper Black Jack Formation, Gunnedah Basin. Geological Suruey of New South Wales, Quarterly Notes,62, 31.

TADROS, N.2., 1986b: Sedimentary and tectonic evolution, upper: Black Jack Formation, Gunnedah Basin. Geological Suruey of New South Wales, Quarterly Notes, 65, 20-34. TADROS, N.2., 1988: Structural subdivision of the Gunnedah Basin. Geological Suruey of New South Wales, Quarterly Notes,73, I-20.

TADROS, N.2., 1993a: History. 1n Tadros, N.Z. (Editor): The Gunnedah Basin, New South Wales. Geological Suruey of New South Wales, Memoir Geology, l2, 19-30.

TADROS, N.2., 1993e: Upper Black Jack depositional episode. In Tadros, N.Z. (Editor): The Gunnedah Basin, New South Wales, Geological Suruey of New South Wales, Memoir Geology, L2,245-296. TADROS, N.2., WHITE}IOUSE, J. & MOFFITT, R.S., 1987: Geology and coal resources ofthe Narrabri area. Geological Suruey of New South Wales, Quarterly Notes, 68, 1-18. THOMSON, S., 1984: The sedimentary and tectonic setting of the Maules Creek Formation, east of the Boggabri Ridge, Gunnedah Basin, New South Wales. MSc (preliminary) thesis, University of New England, Armidale. THOMSON, S., 1986: An analysis of Early Permian deposition in the Gunnedah Basin, New South Wales. MSc thesis, University of New England,

Armidale. THOMSON, S. & FLOOD, P.G., 1984: Reassessment of the tectonic setting and depositional environment of the Early Permian Maules Creek Coal Measures, Gunnedah Basin, New South Wales. Abstracts, 18th Syrnposium on Aduances in the Study of the Sydney Basin. Department of Geology, University of Newcastle, 77 -80.

TYE, S.C. & FIELDING, C.R., 1994: Sedimentology of the Talaterang and Shoalhaven Groups in the southernmost Sydney Basin. Proceedings, 28th Symposium on Advances in the Study of the Sydney Basin, Department of Geology, University of Newcastle, 220-227 .

WARD, C.R., 1972: Sedimentation in the Narrabeen Group, southern Sydney Basin, New South Wales. Journal of the Geological Society of Australia, 19, 393-409. WEST, P.H. & BRADLEY, G.M., 1986: The Gunnedah and Sydney Basins a re-appraisal. Abstracts, 20th Symposium on -Aduances in the Study of the Sydney Basin. Department of Geology, University of Newcastle, 1.

Sydney-Gunnedah Basin Overview

L77

$ydney Basin r

Hunter Coalfield

The Hunter Coalfield of the Sydney Basin is situated some 150km north of Sydney and covers an area of approxirnately 2100km". It is 50km across, and extends northwestwards from Cessnock to Muswellbrook and then north to Murrurundi, a distance of approximately 120km. Figure 1 shows some of the important geological features of the coalfield. The Hunter Coalfield is the largest coal producing area in New South Wales. Most of the resource is thermal quality coal, with low to medium ash coal for export and high ash coal for domestic power generation. Soft coking coal is also produced from

the Hunter Coalfield, mainly for the export market.

STRATIGRAPHY

MJ Sniffin and J Beckett

Three coal measure sequences occur in the Hunter

Coalfield: the Early to Mid Permian Greta Coal

Measures, the Late Permian Wittingham Coal Measures and the overlying Late Permian Wollombi Coal Measures. The Wittingham and Wollombi Coal Measures are also collectively referred to as the Singleton Supergroup. Comprehensive works detailing the stratigraphy of the Hunter Coalfield have been published by several authors (e.g. David, 1907; Raggatt, 1938; Booker, 1960; Basden, 1969; McKellar, 1969; Rattigan & McKenzie, 1969; Robinson, 1,969; Britten, L972, 1976; Herbert, L976,1980a; McClung, 1980; Brakel, 1984; Hamilton, 1986). Table 1 summarizes the currently accepted stratigraphy within the coalfield and describes the lithologies and depositional

environments for each major rock unit.

The Permian stratigraphy of the Hunter Coalfield is complicated by marked lateral variations in lithology and thickness of the numerous units. This variation is a result ofseveral factors, including alternating marine transgressions and regressions, tectonism outside the basin and the growth of intra-basin structures such as the Muswellbrook and

Lochinvar Anticlines.

Greta Coal Measures The Greta Coal Measures crop out in two localities in the Hunter Valley: around the crest of the Muswellbrook Anticline and along the Lochinvar Anticline (see Figure 1). In both of these areas (Table 1) they conformably overlie Carboniferous to Early Permian sediments and volcanics (Basden, 1969; Hamilton, 1986). The Lochinvar structure, however, lies mainly in the Newcastle Coalfield and is discussed separately by Agnew & others (this volume).

In the Muswellbrook area the Greta Coal Measures average >200m in thickness. They are divided into two formations, the Skeletar Formation and the Rowan Formation. The Skeletar Formation, at the base of the sequence, conformably overlies the Gyarran Volcanics (Standing Committee on Coalfreld Geology, 1975). It is a non-coal bearing sequence, consisting ofrhyolite, chert, and white tuffaceous shales containing Glossopteris and Gangamopteris (Robinson, 1.963). It averages 120m in thickness. The overlying Rowan Formation consists of sandstone, siltstone, mudstone, coal and minor conglomerate. It averages 110m in thickness and contains up to six economic coal seams. The boundary between the two formations was revised

Sydney Basin

178

Figure 1. Locality diagram for the Ilunter Coalfield. by the Standing Committee on Coalfield Geology of New South Wales (1975), and is now defined as the base of the lowermost coal of the Rowan Formation. To the south, in the vicinity of the Lochinvar Anticline, the Greta Coal Measures are considerably thinner; they average 63m in thickness in the type

area near Greta (Raggatt, 1938). The coal measures rest conformably above the Farley Formation of the Dalwood Group. The primary lithologies are conglomerate, sandstone with subordinate siltstone, and mudstone. There are several coal seams, the most important being the Greta seam which is up to 11m in thickness near Cessnock (Basden, 1969).

Geology of Australian Coal Basins

t79 Table l. Stratigraphy of the Hunter Coalfield. DEPOSITIONAL ENVlRONlvlt:NT S INATIGI]API-IY

f--]t

LI IFIOLOGY

lqls; loli:

9lll,

TJASINWARD

9ond, Or6vol.

lqF t4t l.(l l(Jl

-->

Polnl b6r lov6o ovorbank:-lnclu(16! aom6 r€llcl Forllary .lluvlal l6rr6cr

dgIoallg

r; 1:

8!r.ll

l Lr!.:

i) \1

Hl;:r

(Bod Losd)

Torrl0.l Ftrmdll6 Palonoa Cl6yolo. Cll,lon luqOornh Fmlallon Sulpq-p Wlddoi Ito6FTdi?

Sandrlon6,lnlorboddod .andston.

Mlx.d Load)

-oiorioillctr!r @p

Coal S6dmr, ciayrtoo(lull6coou!), Slll!lon6, S6ndclmc,

Wollo'nbl

S lngloton

Co6l Mo6uoo

-Dwlc;-IA€E--iaDglarlt.'1:\,:h'grlitl \oDlr Troc Flat Wsll!

Sondllm

Suoer

!Vltllnghnm

91ryop

Cooglomo.ol

-llc dl

o-l

Maitlsnd

l,lulb.lnq

ohalo

SMdslm6, glllsl@€

Forma I lon

mlE bo6ly bondc

Sondolono

Eranxlon

Formtrllon

Mlryollbr@k oroo

Coal

Form6tlon

Msasuros o U

Oyqrron

Group

Volcdnlco

Corl gomr,

Cl.oIo

Co6l Moouroq f arloy Form6tlon

nuthorlord Fm Allondolo F Lochlnvo. Fm

Coal Ssams

p6llct clayslm,

Sands tone

!lllslw,

6tor!on Volconlco

o €

Lll. JohnBlone

Siltsl0(16, chort

Ftryolllo, Acld lo b6rlc volc6rlcs f pyrrclasl lcr

Soohom Formallor

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LDP

0ELIA --<(ntver domrrrtod ) PLAIN F LO\'/fN NELIA PLAIN -+ DFI TA

FRONT

---'--

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longlom.r!1., Scndltm,

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'LocNrwor aroa'

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-,-+

PRooELTA

Sllt!lm Gro ta

owER ---r--*Yl-!!)l-'-'"96rrrroal-or'g1! ( TroiTCuiisor oodjiruJ LowER oELTA PLAI'I =---r-

9lltelm, clayelono, v.ry mlE llm Crclmd !udal(n

Group

Pl \,1'r

lllhlc !8ndolm,

Sallwelor Crook

Irluroo

----1/ nrLl A

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PLArr

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ol Nl<-= olrll# <liir

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CHAIINEL DEPOSITS

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\_ Conglomoralo !nd !6nd!lono

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rnd !lll!lono. Clay!ton.

Corl S6mr, cldyltm, lult, Slll.lm, S.ndllm,

Jody! Plalns o o

o^d Silla

f,l^.!lvs 6Dddod. Cro.! boddod rnd horlronl6lly boddod eu.rIt a!nd!lono snd mlE Ellt6lqE

llav kesbrrry Sandslons

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Flowr

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ffi uPPEn

---=LowEri

E[tERGENT

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b6o8ll !lllslm. Bsndolm

voLcANrc TESFIAI N

voN6d lhol.

Acld, lntefrpdlalo E baslc volcanlcs snd Py.@l6ollc!

Formotion

Although the Greta Coal Measures are known to be continuous, they are only known in detail around the Muswellbrook and Lochinvar Anticlines. Correlation problems exist in the sequence even between the northern and southern ends ofthe Muswellbrook Anticline (Hamilton, 1986).

Table 2 illustrates the stratigraphy ratified by the Standing Committee on Coalfield Geology of New South Wales (1975), and also Hamilton's (1986) suggested coal seam correlations in the area. No detailed correlation of the Greta Coal Measures has yet been attempted between the Lochinvar and Muswellbrook outcrop areas.

Maitland Group The mid-Permian Maitland Group conformably overlies the Greta Coal Measures. This sequence is

divided into three formations, namely the Branxton Formation, the Muree Sandstone (McClung, 1980) and the Mulbring Siltstone. The sediments are marine shelf deposits, with a total thickness ranging from 300m in the north near Muswellbrook to more than 1200m in the south near Lochinvar. The Maitland Group is exposed on the flanks of the Lochinvar and Muswellbrook Anticlines (McKellar, 1969). The Branxton Formation in this area typically consists of sandstone, siltstone, and conglomerate with some tillitic material. Herbert

Sydney Basin

180

Table 2. Coal seam nomenclature of the Greta Coal Measures (Muswellbrook Region). Standing Committee on Coalfreld Geology of New South Wales (1975) Muswellbrook Area

Savoy Trig. Station

Hamilton (1986) Muswellbrook Area

?Hilltop

Unnamed Greta

Fleming

Coal Measures

Hallett Lewis

Loder

Fleming

Hilltop

Muswellbrook St. Heliers

Brougham

Hallett Muswellbrook St, Heliers

Brougham Grasstrees Puxtrees

were ice-rafted.

Overlying the Branxton Formation is the Muree Sandstone, a cliff-forming sandstone exposed around the Lochinvar Anticline. This unit is typically <30m thick in the Singleton area, but thickens to over 80m southwest of Mulbring (McKellar, 1969). It is continuous in the subsurface to the northwest of Lochinvar, but it is not in evidence north of Singleton. The Mulbring Siltstone crops out around all of the

major anticlines in the Hunter Coalfield, except along the southern nose of the Lochinvar Anticline where the Triassic Narrabeen Group rests directly on the Muree Sandstone (Rattigan & McKenzie, 1969). Raggatt (1938) and Booker (1960) suggest that this *as due to non-deposition of the Late Permian strata on a rising anticlinal structure. However, David (1907), Rattigan & McKenzie (1969), and McClung (1980) concur that the absence of the Mulbring Siltstone was due to uplift and erosion prior to deposition of the Narrabeen Group sediments. Apart from the predominance of siltstone, minor_ li[hologies present in the Mulbring Siltstone include claystone and thin sandstone lenses. The unit is typically 330m in thickness (McKellar, 1969), and some horizons contain large calcareous concretions and glendonites (Summerhayes, 1982).

Singleton Supergroup The boundary between the Maitland Group and the overlying Late Permian coal measures is transitional (Britten, 1972; Stuntz, 1972a). The

coal-bearing Singleton Supergroup is typically 1500m thick (Menzies, 1981); it is subdivided into the lower Wittingham Coal Measures (1200m thick) and the overlying Wollombi Coal Measures (300m thick). The sequence thins to the southwest and wedges out completely east of Broke along the southern extension of the Lochinvar Anticline (Britten, 1975). The two major coal measure units are separated by the Watts Sandstone, a unit which, with the underlying Denman Formation, forms a

characteristic marker horizon throughout the coalfield (see also Yoo & others, this volume)' On the basis of this marker horizon, the Wollombi and Wittingham Coal Measures have been correlated with the Newcastle and Tomago Coal Measures of the Newcastle Coalfield (Britten, 1972; Stuntz,

Grasstrees Puxtrees

Ayrdale Ss

Ayrdale Ss Balmoral

(1980b) has suggested that some of the sediments

Savoy Trig. Station

Area

Balmoral

Lewis/Loder

Witting h ann C o al M e as ure s The Wittingham Coal Measures are subdivided into

two important coal-bearing subgroups, the lower Vane Subgroup and the overlying Jerrys Plains Subgroup (Table 1). The boundaries ofeach subgroup are recognized by distinctive coal-barren marker units: the Saltwater Creek Formation, the Archerfield Sandstone, and the Denman Formation. The Saltwater Creek Formation is the basal unit of the Wittingham Coal Measures. It is transitional in character, passing upwards from dark marine siltstone and shale to a sandstone-dominated unit at the base of the coal-bearing sequence (Britten, 1972). The lithology of this interval is characteristically a quartz-lithic sandstone with minor siltstone and claystone bands. The unit varies from 10 to 100m in thickness and thins on to the Muswellbrook Anticline. It is best developed to the east of the Camberwell Anticline. Vane Subgroup The Vane Subgroup, overlying the Saltwater Creek Formation, is subdivided into two formations, the Foybrook Formation and the overlying Bulga Forrnation. The Foybrook Formation is a coal-bearing sequence containing up to six economically important coal seams. Table 3 lists the important seams and illustrates a tentative corlelation between the beds in the different areas of the Hunter Coalfield (R. Hall, personal communication). Interseam sediments include

Table 3. Coal seam nomenclature in the Vane Sub gtoup (Foybrook Formation). MUSWELLBROOK AREA Wynn

HOWICK AREA

FOYBROOK

AREA

Rotten

Lemington

Rose

Seams

Roach

Edderton

Clanricard Bengalla Edinglassie Ramrod Creek

1972a).

Geology of Australian Coal Basins

Roberts Pikes Gully

Pikes Gully

Arties

Liddell Barrett

Hebden

181

Table 4. Stratigraphic revisions to the Jerrys Plains Subgroup. Standing Committee on Coalfield Geology 1975

FORMATION

Standing Committee on Coalfield Geology 1985 FORMATION MEMBER

MEMBER

COAL SEAM

Watts Sandstone Denman Formation

Mt Leonard Formation Whylrow Coal Member Althorpe Claystone Member

Althorpe Formation Malabar Formation

Redbank Creek Coal Member Wambo Coal Member Whynot Coal Member

Blakefield Coal Member

Formation

Redbank Creek seam Wambo seam

Whynot seam Blakefreld seam

SUBGROUP

Burnamwood

Whybrow seam

Saxonvale Member

Glen Munroe Coal Member Woddlands Hill Coal Member

Mt Ogilvie Formation

Fairford Claystone Tongue Mt Arthur Coal Member Piercelield Coal Member

Milbrodale Formation

Mt Thorley Formation

Fairford Claystone Tongue Mt Arthur Coal Member Piercefield Coal Member Vaux Coal Member

Fairford Formation Burnamwood Formation

Glen Munro seam Woocllands Hill seam

Arrowfield seam Bowfield seam Warkworth seam Mt Arthur seam Piercefield seam Vaux seam

Broonie Coal Member

Broonie seam Bayswater seam

Archerfreld Sandstone

siltstone, lithic sandstone and conglomerate, and display characteristic high energy channel deposits. These coal seams have a tendency to split, reflecting the effects of these channel clastics overtopping the coal swamps.

The overlying Bulga Formation consists of widespread laminated siltstones with abundant burrows and pyritic phases (Britten, 1975). It is usually <20m thick, and is best developed along the southwestern edge of the coalfield. The Bulga Formation is overlain by the Archerfield Sandstone which is a widespread massive sandstone and a regionally signifrcant marker horizon. The Archerfield Sandstone forms the floor of one of the most important coal seams in the Hunter Valley, the Bayswater seam ofthe Jerrys Plains Subgroup.

Jerrys Plains Subgroup The Jerrys Plains Subgroup includes a complete cycle of terrestrial coal measure sedimentation up to 800m thick. The Standing Committee on Coalfreld Geology of New South Wales (L986) has redefined the formations of the subgroup, elevating the various claystone marker bands identified as members by Britten (L972) to formation status. Table 4 shows the comparison between the former stratigraphy and the revised stratigraphy ofthe Jerrys Plains Subgroup.

Fifteen economically important coal seams occur within the subgroup (Figure 2), all of which are currently mined at some locality in the Hunter Coalfield. A description of each seam, its quality, and average thickness is given in the Standing

Committee's (1986) report on the stratigraphy of the Jerrys Plains Sugbroup. The Jerrys Plains Subgroup is made of generally coarser clastic sediments than the Vane Subgroup. Interseam lithologies are typically lithic sandstone, shale and conglomerate, with siltstone, carbonaceous claystone and tuff also occurring throughout the sequence. The units form a conformable succession and in many cases the boundaries between formations are transitional. The lowermost unit in the Jerrys Plains Subgroup is the Burnamwood Formation, a sequence of sandstone and siltstone along with numerous coal seams. Its base is defined by the base of the distinctive, thick, dull coal of the Bayswater seam. The Burnamwood Formation was subdivided by the Standing Committee on Coalfield Geology of New South Wales (1986) to create a new formation, the Mount Thorley Formation. The top of the redefined Burnamwood Formation is now marked by the Fairford Formation, a massive siltstone (tuffaceous) unit previously named the Fairford Claystone Tongue. Coal seams within the Burnamwood Formation are the Bayswater, Broonie, Vaux, Piercefield, and Mount Arthur seams. The Fairford Formation overlies a consistently upward-dulling section of the Mount Arthur seam. It is typically 1 to 2m thick, and forms one of the most distinctive white claystone marker horizons in the Hunter Coalfield. The overlying Mount Thorley Formation represents a continuation of the same coal-forming environment

Sydney Basin

182

DEPTH

DOYLES CHEEK DOll 1 1

COAL SEAMS

ou 5 ,(

FORMATION

o vu

WATTS SANDS]'ONE 1

J_i

OENMAN FORMATION WHYBFOW

MT LEONARO FORMATION

WHYBROW

ALTHOHPE FORMATION

V1 il

a-:!-z

FEOBANK CFEEK

. .__-:)

:) WAMBO WFffI.PT A

MALABAR

WHYNOT

FORMATION

IJJ

Y/HYNOT

tt)

'+;': BLAK EF IE LD

SAXONVALE MEMBEB

:_-_?

V) MT OGILVIE

OLEN MUNFO

FORMATION

WOODLANDS HILL

;-5-

I:\

WOODL.ANDS HILL

;--,<

--r-;.i?.\ =

ABROWFIELD

MT THORLEY FORMATION

BowFTELD

wARKwoRTH

z F

MT ARTHUB PIEBCEFIELD

VAUX EROONIE

BROONIE

Figure 2. Stratigraphic nomenclature of the Jerrys Plains Subgroup (after BAYSWATER Standing Committee on ABCIIE Coalfield Geology of New VANE 'JL.J FORMATION BULGA '_.L l Sca South lYales, 1986). 'rD lo97.6Om --: The base of the Mount Ogilvie Formation coincides as the Burnamwood Formation. It averages 106m in with the base of the Woodlands Hill seam. However, thickness and contains the Warkworth, Bowfreld, the defined top of the formation has been change4 to and Arrowfield coal seams. Other lithologies present coincide with the top of the Saxonvale Member. The are sandstone, conglomerate and shale, as well as Mount Ogilvie Formation typically consists of claystone bands. sandstone, shale, carbonaceous mudstone and clavstone bands. It includes the Glen Munro and The Milbrodale Formation was identified to Hill coal seams. Woodlands overcome confusion associated with the previously (Table 4) which named Fairford Claystone Tongue has been misidentified in several areas of the The Saxonvale Member is a pale cherty claystone to Hunter Coalfield (Beckett & McDonald, 1984). The siltstone marker unit, and typically averages 1.5m Milbrodale Formation consist of waxy white in thickness. It can be easily correlated due to a in 0.6m and-averages siltstone claystone to cherty distinctive high gamma response on downhole thiikness. It occuis throughout the coalfield and has geophysical logs tstanding Committee on Coalfreld been correlated with the base of the Woodlands Hill Geoloiy of New South Wales, 1986). coal seam.

-r

Geology of Australian Coal Basins

183

Conformably overlying the Saxonvale Member is the Malabar Formation. The base of this formation is marked by the Blakefield coal seam, while the the top has been redefined to coincide with the base of the very distinctive Althorpe Claystone, now elevated to formation status. The Malabar Formation typically consists of sandstone, siltstone, shale and conglomerate, with minor claystone, and averages 1,60m in thickness. It contains the Redbank Creek, Wambo, Whynot, and Blakefield coal seams. The Althorpe Formation is a light coloured (almost white) claystone that averages 2rn in thickness and

thick. Up to ten coal seams occur within the sequence.

Britten (L972) has described the strata of the Wollombi Coal Measures in detail. In a later paper (Britten, 1975) he noted four important differences between the Wollombi Coal Measures and the underlying Wittingham Coal Measures. These are the greater number of tuffaceous claystones in the upper sequence, the more banded nature ofthe coal seams, the lack of economic coal in the Wollombi Coal Measures, and the increasingly dull character of the coal seams towards the top of the Wollombi sequence. The individual subgroups are defined by the Standing Committee of Coalfield Geology of New South Wales (1975) and are briefly described below.

forms a persistent unit within the Jerrys Plains Subgroup. The underlying Redbank Creek coal seam is usually associated with the formation, and assists in stratigraphic correlation. Its lithology varies from a soapy claystone to a cherty hard siltstone.

Apple Tree Flat Subgroup

The Mount Leonard Formation is a coal bearing coarse clastic unit that defines the top ofthe Jerrys Plains Subgroup. Lithologies in this unit range from massive sandstone to conglomerate with intercalated thin coal seams. The Whybrow seam is contained within this formation, and the total unit averages 40m in thickness.

The Apple Tree Flat Subgroup consists of two distinct formations. The Abbey Green Coal at the base contains the lowermost coal of the Wollombi measures. The coal in this sequence is usually overlain by the Monkey Place Creek Tuff Member. The Charlton Formation at the top of the subgroup contains an inferior coal seam, known as the

The Denman Formation is no longer regarded as part ofthe Jerrys Plains Subgroup, even though it is still considered part of the Wittingham Coal Measures. There is a distinct lithological change from the underlying sandstone arid conglomerate of the Mount Leonard Formation to the interbedded shale, siltstone, and minor sandstone of the Denman Formation. The sequence, often described as a laminite, can be correlated with the Dempsey

Formation of the Newcastle Coalfield, the Baal Bone Formation of the Western Coalfield, and the Bargo Claystone of the Southern Coalfield, (Brakel, 1984). The unit is typically burrowed, and averages 20m in thickness.

Wollombi Coal Measures The lowermost unit of the Wollombi Coal Measures

Stafford seam.

Horseshoe Creek Subgroup

The Horseshoe Creek Subgroup contains two coal bearing and two non-coal bearing formations. The lowermost unit, the Clifford Formation, consists of sandstone, minor tuffaceous claystone, and vestigial coal beds. The overlying Alcheringa Coal contains coal with a number of distinctive interbedded claystone units. The Strathmore Formation above this is predominantly a shaly sequence which gives way, at the top of the sequence, to the Lucernia Coal, a coal-bearing sequence with three named seams: the Carramere, Rombo, and Eyriebower seams.

Doyles Creek Subgroup

is a coal-barren formation named the Watts Sandstone (see Table 1). This unit forms a continuous marker horizon which separates the underlying Wittingham Coal Measures from the rest of the overlying Wollombi succession. It crops out and forms a distinctive cliff line in the western part ofthe coalfield area.

Two formations are named within the Doyles Creek subgroup: the Pinegrove Formation and the

The Watts Sandstone averages 30 to 60m in thickness. It consists generally of massive, medium grained, even-textured sandstone (Britten, 1975), and is postulated to correlate with the Waratah Sandstone of the Newcastle Coal Measures, the Darkes Forest Sandstone of the Southern Coalfield (Britten, L972), and the Angus Place Sandstone of

The Glen Gallic Subgroup is the uppermost unit of the Wollombi Coal Measures. It consists of three coal seams with a high percentage of tuffaceous claystone beds. The Dights Creek Coal at the base of the subgroup contains the heavily-banded Hobden Gully seam at the base and the Hillsdale seam at the top, the latter being separated from the underlying Hobden Gully seam by the distinctive tuffaceous claystone marker horizon of the Nalleen Tuff (Member). The overlying Redmanvale Creek Formation is barren of coal and consists primarily of coarse conglomerate, while above this the Greigs Creek Coal contains the only seam, the Greigs Creek seam, that has ever been mined from the Wollombi Coal Measures. This seam generally contains few stone bands. Where it is present, it defines the top of the Wollombi Coal Measures.

the Western Coalfield (Bembrick, 1983).

The Wollombi Coal Measures have been subdivided into four subgroups. In ascending order these are: the Apple Tree Flat, Horseshoe Creek, Doyles Creek, and Glen Gallic Subgroups (Table 1). These subgroups contain numerous thin, banded coal seams which split and merge and locally attain thicknesses of up to two metres. Tuffaceous claystones are characteristic throughout the succession, thus adding to the banded nature ofthe

overlying Waterfall Gully Formation. An inferior coal seam, the Wylies Flat seam, with numerous stone bands and tuffaceous claystones, occurs within the Pinegrove sequence. Glen Gallic Subgroup

coal.

Narrabeen Group

The type section for the Wollombi Coal Measures is located in the southwestern part of the coalfield (DM Doyles Creek DDH 11), where the unit is 274m

The Wollombi Coal Measures are conformably overlain by the coarse sandstones, conglomerates, and minor claystones of the Narrabeen Group

Sydney Basin

184 (Table 3). The Narrabeen Group sediments are easily recognizable in the Hunter Coalfield, as they comprise the rugged cliffs which form the western margin of the Hunter Valley. In many places the conglomerates directly overlie the Greigs Creek seam (Britten, 1975) with little evidence of any washout or erosion.

TECTONICS AND STRUCTURE The major synsedimentary structures which formed during the Permian in the Hunter Coalfield are the Lochinvar, Muswellbrook, Camberwell, and Sedgefield Anticlines, the Belford and Loder Domes and the Bayswater and Rix's Creek Synclines (Figure 1). Two major fault systems outline the commercial boundaries of the coalfreld: the Hunter-Mooki Thrust Fault to the east and the Mount Ogilvie Fault to the west (Stuntz, L972b; Brakel, 1984). All these structures were formed during the Permian and continued to be active to

varying degrees until the Triassic.

The asymmetric development of the Sydney Basin has been compared to that ofa retroarc basin (Dickinson, 1974; Herbert, L976; Jones, 1983). Rapid subsidence between the (then) New England Volcanic Arc and the cratonic Lachlan Fold Belt resulted in the deposition and preservation of up to 5000m of sediment during the Permian.

A combination of factors (Roberts and Engel, 1986) appears to have contributed to the formation of the n-oitheastern part of the Sydney Basin including the Hunter Coalfield. These are: . sea level changes resulting in transgressions and regressions; . volcanism asssociated with a subduction zone; . rifting during subsidence of the Sydney Basin; . faulting along the basin margin uplift of the basin; r deformation of the New England Orogen; . significant changes in climate. Rifting parallel to the present day Hunter Thrust in the vicinity of Newcastle initiated the formation of a trough in the present Hunter Coalfield, referred to as the Ayr Volcanic Rift (Scheibner, 1973). This event marked the beginning of the formation of the Sydney Basin during the Currabubula Tectonic Stage (Herbert, 1976; Scheibner, 1976; Herbert, 1980a).

England Orogen formed the New England Fold Belt durlng the Hunter Tectonic Stage (Scheibner, 1973). The New England Orogen thereafter provided the major source of sediment supply throughout the Permian and Triassic to the Hunter Valley area. Large scale folding and thrust faulting occurred during the Mid to Late Permian. The major stresses were taken up by the (then) Hunter-Mooki Thrust System, resulting in tilting and folding of Early Permian sediments in the Hunter Coalfreld. Syndepositional folding and faulting continued during the Late Permian, and is evidenced in structirres such as the Mirswellbrook and Lochinvar Anticlines over which thinning of the sequence occurs. Coalification studies (Diessel, 1975) have shown that the Lochinvar Anticline was active during the formation of the Greta Coal Measures, and other evidence suggests that there was also relative movement between the Muswellbrook and Lochinvar Anticlines and the Bayswater Syncline

(Harrington & Brakel, 1984).

The Mount Ogilvie Fault was active during coal measure deposition, and effectively tilted the Upper Hunter region to the south (Stuntz, L972b; Harrington & Brakel, 1984). The principal evidence for this is the very thick sediment wedge (up to 2000m) developed in the southwestern part of the coalfield area. DE PO SITIONAL ET{VIRONMENT

Permian sedimentation in the the Hunter Coalfield is characterized by four major episodes of deltaic to fluvial deposition (including coal formation), which are separated by three easily recognizable marine transglessive events (without coal) of varying extent and duration (Table 3).

Greta Coal Measures The Greta Coal Measures represent the first episode of constructive delta deposition in the Hunter Coalfield. They consist of a sequence formed by fluvial and deltaic sediment which prograded into the basin from uplifted source areas in the New England Fold Belt.

In the northern part of the coalfield, near

Sea level changes during the Permian were both

eustatic and tectonic in origin (Brakel, 1986). Marine transgressions were furthered b,y subsidence concomitant with uplift in the New England Orogen, and by vigorous sediment loading in the basin (Herb-ert,-1976). It was during the regressive phases of sea level, however, that the major coal forming environments existed. A number of mechanisms promoted such falls in sea level, including folding in lhe New England Fold Belt, uplift associated with the intrusion of granitic plutons within the Fold Belt, and the development of syndepositional folding within the basin (Roberts & Engel, 1986). Active periods of volcanism throughout the Permian led to dtposition of widespread tuffs in the Hunter Valley. fhese tuffs are quite distinctive, and are used as marker horizons for stratigraphic correlation. Deformation and cratonization (the Hunter-Bowen Orogeny of Carey & Browne, 1938) within the New

Muswellbrook, the coal-bearing Rowan Formation was deposited on a subaerially weathered and colluvially distributed Carboniferous to Early Permian volcanic terrain (Loughnan, 1975). Upper delta plain conditions prevailed in the Muswellbrook area and were characterized by overbank/flood plain, crevasse-splay, marsh or lacustrine,-lnd _coal swamp deposits (Loder through to Muswellbrook seamJ), while interdistributary bay sediments which display some tidal influences (lower delta plain) chalacterize the interval above the Hallett seam (Hamilton, 1986).

In the southern part ofthe coalfield, along the western limb of the Lochinvar Anticline, the Greta Coal Measures prograded over marine sediments (H"ihetford an,i Fitl"y Formations), described bi Herbert (1980a) as prodelta and delta-front deposits. The Greta Coal Measures are continuous around the nose of the Lochinvar Anticline into the Newcastle Coalfield, and are more fully Cescribed by Agnew & others (this volume).

Geology of Australian Coal Basins

185

Maitland Group

SAND SIIT CLAY

Rapid subsidence ofthe basin led to a transgressive marine inundation of the Greta Coal Measures and

resulted in the deposition ofthe Branxton Formation. Close to the present position of the Hunter Thrust the basal part ofthe Branxton Formation is represented by conglomeratic fan delta deposits, but away from this area the base ofthe sequence often contains a thick, marine shoreline sandstone deposit (Cessnock Sandstone). Further basinward, and upward in the sequence as the transgression proceeded, the Branxton Formation grades into marine shelf deposits of silty, pebbly sandstone.

After deposition of the Branxton Formation, a significant marine regression is represented in the sequence by the Muree Sandstone. Like the basal section of the Branxton Formation, this unit exhibits a lateral facies change from proximal conglomeratic fan-delta deposits in the Belford Dome and Lake Liddell areas to interbedded sandstone and siltstone (laminite) deposits in more distal areas south of Cessnock. McClung (1980) describes the trend of these facies change as roughly parallel to the present line of the Hunter Thrust. A return to deeper marine shelf conditions followed the deposition of the Muree Sandstone, and coincided with the introduction of large amounts of prodelta silt and clay into the Hunter Coalfield. The Mulbring Siltstone was deposited., during a period of maximum transgression, in the quiet waters of a shallow sea. The occurrence ofglauberite pseudomorphs (glendonites) in this sequence is interpreted by Summerhayes (1982) to indicate high salinity during deposition, which may have arisen from rapid progradation and isolation ofseawater bodies.

Wittingham Coal Measures The Mulbring Siltstone gradually coarsens upwards into sandstone-dominated deposits of the Saltwater Creek Formation. This unit represents a transition from a marine delta front to a river-dominated lower delta plain environment, and marks the first major

Late Permian deltaic progradation in the Hunter Coalfield.

Thin, discontinuous coal deposits are known to occur in the upper part of the Saltwater Creek Formation close to the Hunter Thrust. These coals generally formed on the top of transitory sub-aerial distributary mouth bar sand deposits (Figure 3).

Foybrooh Forrnation The Foybrook Formation is thought to have formed as a river-dominated delta system which prograded to the south and southeast from the New England Fold Belt. Regional isopach data for the Vane Subgroup as a whole (Figure 4) show two major sediment supply sources, one from north of Muswellbrook and the other centred on the Camberwell area north of Singleton. Deposition from the southern (Camberwell) source area appears to have been divided into two lobes, which split to the southwest and southeast over the thickest known parts of the Saltwater Creek Formation. The geometry of the Foybrook Formation in the southern area may have been partially influenced by an incipient'high' that subsided more slowly, and ultimately resulted in the formation of the anticlinal Loder Dome structure.

80 70

60 50 40

30 20

Figure 3. Typical facies associations of the Saltwater Creek Formation. The Foybrook Formation thins and onlaps the Lochinvar Anticline (Stuntz, 1972a) to a much greater extent than the Loder Dome, located some 20km to the east. The Loder Dome in turn shows a more marked effect on the deposition of the Foybrook Formation than does the Muswellbrook Anticline, thus indicating a substantial east to west time difference in the development of these

anticlinal structures.

Interpretation of the formation isopachs along the western limb of the Muswellbrook Anticline is complicated by erosion of the top of the formation prior to deposition of the overlying Bulga Formation and Archerfield Sandstone, which are represented in this area (C. Weber, personal communication) by shoreline deposits, distributary mouth bar deposits and channel sandstones. Cross sections of the Foybrook Formation, particularly across the southern delta lobes, show a regional en-echelon development of the coal seams in the lower part of the sequence (Hebden to Pikes Gully seams). The major coal forming environment migrated away from the source area as the lobe developed, and can be correlated with a lateral facies change from lower to upper delta plain

conditions. Between the Pikes Gully seam and the coal seams at the top of the sequence (Lemington or Wynn seams), the Foybrook Formation generally exhibits upper delta plain to fluvial-alluvial facies associations (Figure 5). The coals in this section of the unit formed prior to an extensive marine incursion. They exhibit characteristics that reflect deposition in a

marginal environment, tending towards lower delta plain conditions. Figure 5 shows the facies association in the Foybrook Formation in the Camberwell area of the southern lobe, and Figure 6 shows the facies association on the northern lobe of the Muswellbrook area.

Bulga Forma.tion o.nd. Archerfield Sandstone The marine incursion which resulted in deposition of

the Bulga Formation -Archerfield Sandstone sequence was almost certainly related to tectonic

Sydney Basin

186

activity and subsidence of the Hunter (and Gunnedah) Coalfreld. The transgression completely inundated the southern lobes ofthe Foybrook Formation, but terminated at about the position of the 150m isopach on the northern lobe (Figure 4), in a line trending approximately northwest frorn Muswellbrook. The incursion co-incided with the change from the (lobate) river dominated deltaic deposition of the Foybrook Formation to wave/current dominated deltaic deposition for the Bulga Formation- Archerfield Sandstone-Bayswater seam interval (Beckett & McDonald, 1984). Regional interpretations show the Archerfield Sandstone consistently to represent a shoreline environment, generally comprising

Figure 4. Isopachs of the Vane Subgroup, showing outcrop of the Vane Subgroup and other major rock units. beach/barrier beach - lagoon deposits. Occasionally, however, distributary mouth bar deposits overlain by non meandering distributary channel sandstones occur in the section. Uren (1985) has suggested that, near the margins of the marine incursion in the Muswellbrook area, the Bulga Formation - Archerfield Sandstone sequence formed as a single regressive unit, with complete reworking or non-deposition during the transgressive phase. A similar situation occurs in the southern delta lobe of the Foybrook Formation near Camberwell. The Bulga Formation is absent on the proximal parts of this lobe, and the Archerfreld Sandstone thins markedly to the northeast where it is erosively overlain by thick, coarse grained

Geology of Australian Coal Basins

187

SILT SAND CLAY m

ARCHERFIELD SANDSTONE

-0 -10

-20 -30 -40 -50 LEMINGTON

-60

SEAMS

-70 -80 -90 - 100

-'l 10

F - 120

o L

- 130

o o t

- 140

o L

- 150

- 160 PIKES GULLY SEAM

-170

ARTIES SEAM

- 180 UPPER LIDDELL SEAM

- 190 MIDDLE LIDDELL

- 200 SEAM LOWER LIDDELL

-210 SEAM -220 - 230 - 240

UPPER BARRETT SEAM

LOWER BARRETT SEAM

- 250

Figure 5. Stratigraphy of the Foybrook Formation in the Camberwell area.

- 260 HEBDEN SEAM

channel sandstones. The overlying Bayswater seam of the Jerrys Plains Subgroup is often eroded as well.

Jerrys Plains Subgroup

The Bulga Formation - Archerfield Sandstone interval thickens to the southwest of the Hunter Coalfield, and both the transgressive and regressive depositional phases are preserved in a section at least 150m thick. This unit is named the "Kulnura Marine Tongue" in the Newcastle Coalfield, and forms a lateral equivalent to the sequence

The vertical and lateral associations ofsedimentary facies within the Jerrys Plains Subgroup indicate that the sequence developed primarily as one or

comprising the Bulga Formation, Archerfield Sandstone, and the lower part of the Jerrys Plains Subgroup.

more prograding, river-dominated delta sequences beginning and ending with a marine incursion. The major delta building episodes originated from source areas outside the Hunter Coalfield, and the relative position of the individual deltas directly controlled the development of the different coal seams in the sequence.

Sydney Basin

188

SILT SAND CLAY

-0

BAYSWATER SEAM

WYNN SEAM

-10

,20 -30

-40 -50 EDDERTON SEAM

-60 CLANRICARD SEAM

-80 BENGALLA'A' SEAM

-90

z. BENGALLA'B' SEAM

o F

-100 BENGALLA'C' SEAM

- 110 - 120

BENGALLA'C' SEAM (Lower split)

E = o r :z o o d.

o L

- 130 - 140 -150 EDINGLASSIE

SEAM

- 160 - 170 -180

RAMROD CREEK'A'SEAM

- 190 - 200 - 210

RAMROD CREEK'8'SEAM

- 220

The progradation ofthe Archerfield Sandstone shoreline deposit was accompanied by progradation of a back-barrier coal swamp which formed the Bayswater seam. This basal unit of the Jerrys_ Plains Subgroup represents the culmination of a wave/current dominated deltaic depositional sequence (Figure 7).

Alluvial fan and high energy-fluvial deposits characterize the basal sequence ofthe Jerrys Plains Subgroup adjacent to the Hunter Thrust. Alluvial fan ind braiiled river conglomerates interfinger with or rest erosively on the Bayswater seam, replacing the typical Jerrys Plains Subgroup sequence. The conglomerate apron is rarely >2km wide, but appears to have supplied major distributary channel syStems. The depositional axes of these systems parallel the Thrust for up to several tens of kilometres, and evidently were influenced by the synsedimentary tectonic structures present in the coalfield area. There is a marked decrease in the number and thickness of coal seams adjacent to the

Figure 6. Stratigraphy of the Foybrook Formation in the Muswellbrook area.

Hunter Thrust, probably due to channel clastics overtopping the coal swamps and disrupting seam continuity. Deposition of the Bayswater seam was followed bydefta progradation, and the environment developed

into a river-dominated lower delta plain. The sediments form an alternating sequence of interdistributary bay laminities and upwardcoarsening crevasse-splay sandstones, with intermittent, even-grained tabular cross-bedded distributary channel sandstones. The river-dominated lower delta plain coals are thin, and are commonly split by crevasse-splay and channel deposits.

The best-developed lower delta plain coals in the Hunter Coalfield generally form on the stable base of abandoned distributary channel sandstones or above thick crevasse-splay sandstone deposits (e.g. the Broonie and Vaux seams). Coals associated with interdistributary bay laminities and thin

Geology of Australian Coal Basins

189

BAYSWATER SEAM

coalswamp

emergent 30

ARCHERFI ELD

beach

SANDSTONE

lower and

upper beach 10

Figure 7. Typical wave-dominated lower delta plain sequence (modified from Beckett & McDonald, 1984).

BULGA

Marine

shelf deposits

FORMATION

or posr rr o r'rnr rnc

crevasse-splay sandstones are comparatively thinner and more banded than those associated with distributary channel sandstones (Figure 8).

Upper delta plain conditions, with meandering distributary channels and overbank environments, were established following deposition of the Vaux seam. Channel sandstones or conglomerates in this part ofthe sequence grade upwards through point bar sediments to levee deposits and then to floodplain and coal swamp deposits (Figure 9). Each upward-fining sequence of this type tends to be erosively overlain by a channel deposit or abbreviated by a repetition of the floodplain and coal swamp facies. Coal seams formed in the upper delta plain environment tend to be thicker and laterally more continuous than those in the lower delta plain successions. The upper delta plain is typically an area of sediment by-pass where the distributary network is well established, and strong levee banks control the transport of sediment further basinward towards the lower delta plain area (Hamilton, 1986). Thus, both the channels and adjacent coal swamps in the sequence were allowed to develop uninterrupted for longer periods, compared with those of the lower delta plain environment. The Piercefield and Mount Arthur seams are examples of these upper delta plain coal deposits, and average between 3 to 5m in thickness.

Lower delta plain conditions were gradually re-established in response to an advancing sea level, with the first indications of a change in environment in evidence after deposition of the Glen Munro seam (Figure 2). The marine transgression extended as far north as Scone, and culminated in deposition of a tidaVcurrent influenced laminite (Denman Formation), the base of which forms the top of the Jerrys Plains Subgroup. A major delta lobe is thought to have developed in the Jerrys Plains Subgroup from a source area north ofScone, and prograded towards the south and southwest in a similar depositional pattern to that of the underlying Foybrook Formation. The depositional axis of this lobe was parallel to the

rs----l

Hunter Thrust for some distance, and then veered to the west of the Muswellbrook Anticline (Figure 10). Another major delta lobe can also be recognized in the Jerrys Plains Subgroup (Figure 10), with a depositional axis parallel to the western limb of the Loder Anticline and with a source area probably to the northwest of Camberwell. The interpretation of the geometry of this is complicated by the subsequent erosion of much of the Jerrys Plains Subgroup to the west of the Loder Anticline, but its maximum thickness (750m) appears to occurs beneath a thick cover ofoverlying strata southwest of Bulga. More rapid subsidence on the northern or

"Muswellbrook" lobe resulted in a marine incursion

between the deposition of the Whynot and Wambo seams, before the transgression that formed the more widespread Denman Formation. After this, the environment in that area returned to lower delta plain conditions.

Denman Formation and \Matts Sandstone The siltstone-sandstone laminites of the Denman Formation show bedding and sedimentary structures consistent with deposition in a tidally influenced shallow marine environment. Together with the coarser arenites of the overlying Watts Sandstone, they provide the record of a transgressive-regressive depositional event between deposition ofthe Wittingham Coal Measures and the overlying Wollombi Coal Measures. The marine incursion covered most of the Jerrys Plains Subgroup, but because ofsubsequent erosion its limit in the southern part of the Hunter Coalfield cannot be established. Its geographical limit on the northern lobe, however, appears to have been a

slightly greater than that of the incursion which deposited the Bulga Formation and Archerfield Sandstone sequence, with borehole data to the west of Scone (Menzies, 1981) showing that the Denman Formation is present even on the proximal parts of this lobe.

Sydney Basin

190

coal swamD

VAUX SEAM

interdistributary bay with crevasse splays crevasse splays and swamp interbedded

overbank to swamD coal swamD to swamp

BROONIE SEAM

levee to overbank

distributarv channel

BROONIE SEAM

interdistributary bay

with crevasse splays BROONIE SEAM

interdistributary bay coal swamp

BAYSWATER SEAM

SCALE(m)I STRATIGRAPHY

'120

DEPOSITIONAL FACIES

GLEN MUNRO SEAM

Figure 8. Typical river-dominated lower delta plain sequence (modified from Beckett & McDonald, 1984).

coal swamp channel to point bar crevasse splay'

WOODLANDS I-IILL SE.AM

ffi

coal swamp and tuff

-owrhtnmswam,I'

channel to point bar and levee stacked channel

to point bar -60

-40

MOUNT --'\-

L0WER ARTHUR SEAM

lveiEenl to surarnp coal swamn

overbank' channel to point bar and levee overbank to swamp

coal swamp

overbank crevasse splay overbank

-20 PIERCEFIELD SEAM

coal swamp and tufl

interdistributary bay -0 E (m) | STRATIGRAPHY

and crevasse splay DEPOSITIONAL FACIES

Geology of Australian Coal Basins

Figure 9. Typical upper delta plain sequence (modified from Beckett & McDonald, f984).

191

l-0. Isopachs of the Jerrys Plains Subgroup, showing outcrop of other units and major axes of Figure - sediment distribution network.

Sydney Basin

192 The boundary between the Denman Formation and the overlying Watts Sandstone is transitional at the

distal margins of the Hunter Coalfield delta lobes. It

is marked by a gradual increase in sand content in an upward-coarsening sequence ofdelta front and distributary mouth bar deposits. These sediments are generally overlain by coarse grained, high-energy fluvial channel deposits. Further on to

the underlying delta lobes ofthe Jerrys Plains Subgroup, these coarse grained channel deposits predominate and form the typical Watts Sandstone lithologies which are commonly unconformable with the underlying marine laminites of the Denman Formation.

Wollombi Coal Measures Progradation of the Watts Sandstone and continued deposition of high-energy channel and associated floodplain deposits resulted in a rapid transition from the marine conditions of the Denman Formation to the upper delta plain and fluvial depositional environments of the Wollombi Coal Measures sequence. Lower delta plain facies associations are recognized only in the lower parts of the Wollombi Coal Measures in the area southeast of Denman. This area corresponds to the interlobe region between the two main delta lobes in the Jerrys Plains Subgroup shown in Figure 10. The fluvial deposits of the Wollombi Coal Measures are characterised by a high proportion'of coarse channel deposits, with rapid channel migration resulting in the abbreviation or erosion oflaterally equivalent coal swamps. Seam splitting and erosion is common and makes regional coal seam correlation diffrcult. North of the Denman area, deposition of the Triassic Widden Brook Conglomerate (Herbert, 1980a) was also either partly comtemporaneous with the coal measures or was preceded by erosion of the topmost part of the Wollombi sequence. The lack of coal seam continuity, along with a high proportion of tuffaceous claystone horizons, has made the Wollombi Coal Measures an unattractive target for coal exploration in all but a few isolated areas. Resource potential exists in the far south of the Hunter Coalfield near Broke (Moffitt, 1983) and in the area north of Denman (Menzies, 1981), where because of a reduced thickness of Denman Formation the coal seams are spatially closer to the economic upper seams of the Jerrys Plains Subgroup.

ECONOMIC COAL SEAMS The Greta Coal Measures and the Wittingham Coal Measures (Foybrook Formation and Jerrys Plains Subgroup) are the major sources of commercial coal in the Hunter Coalfield. The Greta Coal Measures occur at depths of more than 600m over most of the area, and it is only where the coal measures are associated with major structural features, such as the Muswellbrook Anticline, that the sequence occurs at reasonable mining depths. Seam thicknesses tend to be greater in the Muswellbrook area than those in the Savoy Trig. Station area to the south and the seams show less splitting (Hamilton, 1986). The coal seams are commonly split and separated by persistent non-coal intervals, and many of the seams are affected by igneous

intrusions. Seam continuity is also often disrupted by small scale faulting. The coal seams of the Foybrook Formation are characterized by erratic splitting, which has

resulted in the adoption of the various nomen-

clatures shown in Table 3. The coal seams are best developed in the vicinity of the Muswellbrook Anticline, with the thickest seam being the Liddell seam which reaches a maximum of 14m (including splits of the overlying Arties seam) in the Foybrook

area (Britten, 1.975). Towards the south, multiple splits develop in most of the seams and the seams tend to thin and deteriorate. Igneous intrusions are less common than in the Greta Coal Measures. The coal seams of the Jerrys Plains Subgroup have

the highest economic potential in the Hunter Coalfield. This is partly due to their superior thickness and quality, but more importantly it is because the coal subcrops extensively and is at shallow depths over a large area.

The Bayswater seam (Table 4) is the lowest seam in the Jerrys Plains sequence, and is an important

source of thermal coal. It varies in thickness from 1 to 14 m, generally thickening towards the south, and is distinctive because of its general dull character and high inertinite content.

The Broonie through to Warkworth seams are brighter coals, but are subject to extensive splitting and coalescence. These features have hindered regional seam correlation in the coalfield. The total thickness of the interval ranges from 100 to 300m, with cumulative coal thicknesses ranging from 12m to in >50m. The thickness of the section generally increases away from the major anticlinal structures, and this thickening usually coincides with an increase in the total coal content of the sequence. The Bowfield through to Blakefield seams are also extensively split, but several of the upper seams in this interval contain distinctive stone bands which assists in correlation. The individual seams vary in thickness from 0.3m to >4m over most of the area. The upper sequence of seams (Whynot through to Whybrow seams) range in aggregate coal thickness from 4 to 17m to the south of the Muswellbrook Anticline. These seams are usually split, and are characterized by association with several distinctive tuffaceous claystone marker beds.

COAL QUALITY The quality of the coal in the Hunter Coalfield varies considerably from seam to seam, within seams, and between the different formations and coal measure sequences across the coalfreld. The pattern of variation is further complicated because of correlation difficulties on a regional scale due to: r the large number of seams; r the complex lateral variation and splitting of seams;

r historical nomenclature resulting from

geographical isolation of the original colliery holdings. The economic coal deposits in the coalfield can be grouped into three areas: the northern area where the Greta Coal Measures are mined, the central area of Foybrook Formation coal and the southern group ofdeposits belonging to the Jerrys Plains Subgroup. Up to 30 seams and seam splits are mined and a range ofdifferent coal products is produced. Some

indicative quality.parameters of coals from the three major areas are given in Table 5.

Up to six seams and their splits are mined from the Greta Coal Measures along the core of the Muswellbrook Anticline in the north of the coalfield.

Geology of Australian Coal Basins

193

Table 5. Indicative coal quality for the Hunter Coalfield. THERMAL (Range) RAW COAL (Range) SPECIFICATIONS WITTINGHAM COAL MEASTIR ES - Jerrys Plains Subgrr )up 8-10 Moisture Total (a.r.\ Vo (a'd-b.) Vo

As}: Vo

Volatiles 7a Sulphur 7a

Phosporus 7o Specific Energy (kcaVkg)

c.S.N. H.G.I.

I I

Def. Temp. Flow Temp. oC

8-11 2-3

8-30 25-36 0.3-1.0 0.02-0.4 5070-7410

50-60 1250+

I I

48-55 1300-L550 1500-L600+

45-58 1270-1500+ 1340-1600+

7.0-9.5 2.5-3.0 5.0-L6.0 31.0-35:0 0.7-1.2 0.01-0.1 6450-6750

9.0 2.0 10.0-11.0 34.0-35.0 0.4 0.04 4780-6950

1-8

L-4

Def. Temp. Flow Temp. oC

8-10 2.0-3.0 7.0-8.5 31-36 0.4-0.6 0.01 7740-74L0 4-5 50-60 1200-1300 1400-1600

7.0-9.0 1.8-3.1 6.4-L3.7 36.0-39.4 0.4-0.8 0.006-0.07 6920-8120 2.5-7.0 41-53 1180-1580+ 1360-1580

7.0-42.0 33.0-37.0

Phosphorus 7o Specifrc Energy (kcalikg)

c.s.N. H.G.I.

2.5-3.5 8.5-14.0 29-35 0.4-1.0 0.01-0.03 6600-7050

7.0-10.0 1.8-3.5 4.9-26.L 30.4-41.3 0.4-0.8 0.006-0.05 57L0-7265

(a.d.b") 7o

As}:^ Vo

Vane Subgroup - Foybrook Fo :mation Moisture Total (a.r.) Vo Volatiles 7, Sulphur 7o

COKING (Range)

GRETA COAL MEASURES - RT wan Formation Moisture Total @.r.) Vo

7.0-9.0

(a.d.b.) Vo

2.0,3.0

Ash Vo

11.0-18.0 30.0-36.5

Yolatlles Vo Sulphur 7o Phosphorus 7o Specifrc Energy (kcaVkg)

0.7 -L.7

0.01-0.1 6200-7000

C.S.N.

L-3

t.-3

L-5

H.G.I.

35-50

40-50 1300-1375 1430-1500

35-50

Def. Temp. oC Flow Temp. oC

1300 1400

Most of this coal is marketed as either low to medium ash, medium volatile, thermal quality coal for export or as medium to high ash, medium volatile thermal coal for the domestic market. An export quality semi-soft coking coal is also produced by'wash-ing ahd blending of several seams from the coal measures. The organic sulphur content of the Greta coals tends to be high which impairs the marketability of these coals.

1160 1370

volatile soft coking coal. Several collieries, however, mine only the lower seams of the subgroup (Bayswaier, and Ravensworth seams) to supply thermal coal for domestic power consumption.

COAL MINING GEOLOGY

Liddell, Arties and Pikes Gully) and their splitscurrently being mined. Foybrook Formation coals are primarily sold as thermal quality coals, both to the export market and for local consumption b-y the Liddel and Bayswater power stations. Several commercial blends of low ash, medium volatile, high fluidity coking coals are produced to supply the export markets.

Although several underground mines are in operation, it is the predominance of large scale (>2Mtly) open-cut mines which makes the Hunter Coalfield unique in New South Wales. Approximately 11 400Mt of in situ coal resources hive been delineated in the coalfield with open cut mining potential. Stripping ratios are low because of the thickness of the coal, the high number of seams in close proximity to one another and the shallow depth of the coal. The seams also tend to crop out along the flanks of major structures, increasing theiilateral extent and further enhancing the viability of surface mining operations.

The southern group of deposits embraces the seams of the Jerrys Plaini Subgroup. Fifteen named seams occur in this sequence, and every seam ofthe subgroup is curiently mined at some location in the Hunter Coalfield. Most of the coal is marketed as low to medium ash, medium volatile, low sulphur thermal coal for export and as low ash, medium

Two types of surface mining are practiced in the coalfreld: strip mining and open-pit mining (Kukla & others, 1986). Both draglines and truck and shovel methods are used, depending upon many factors including the number of seams to be mined, the thickness of the interburden and the economic working depth of the pit.

The coal seams of the Foybrook Formation crop out along the flanks of the Muswellbrook Anticline in the central area of the coalfield. Up to 10 seams occur in the sequence, with the middle four (Barrett,

Sydney Basin

194 Apart from some instability following periods of wet weather, the removal and stacking of large amounts of overburden material does not cause significant geotechnical problems. Several mines use an intermediate haulage system to remove overburden material from the mine site, resulting in handling diffrculties and delays to the onset ofrehabilitation efforts.

A significant amount of coal in the Hunter Coalfield is affected by other land uses. These land uses include national parks, urban development, infrastructure, water storage, prime agricultural land, Commonwealth land and natural features. It is estimated that 19 240Mt of coal is affected by other land uses (Coal Resource Development Committee,

Pit-wall stability is generally good in the coalfield, except for open cuts which mine close to major structural zones and have steep dips in the high-walls or low-walls. Isolated pioblems occur in walls adjacent and parallel to major joint planes, dykes, faults and major thrust zones.

REFERENCES

Seam dips tend to be less than 10o, but a few open pits extract coal by truck and shovel methods from strata dipping at higher angles. These mines are located on the flanks of major anticlinal structures, and do have some low-wall instability problems.

Intrusions are not a major problem in the Hunter Coalfield, since dykes and sills tend to affect only small areas in individual coal seams. In some areas, however, particularly in the Greta Coal Measures, significant areas of coal have been devolatilized to form an anthracitic material. The underground mines in the Hunter Coalfield are often extensions of open cut operations.-Longwall

units are currently in operation, but the majority of the underground mines use the bord and pillar method for coal extraction. Because of lateral facies changes, roof conditions may vary over short distances (Robinson, 1979), and in thicker seams coal may be left in the roof both to provide better roof control and to improve product quality. Roof stability problems are also encountered in underground mines which are located close to synclinal features. Jointing and faulting associated with these features can sometimes cause problems, particularly in coals with a well defined cleat.

All underground mines currently avoid production from areas with a gradient steeper than a 1:4 grade due to poor productivity. Steeper grades usually occur in areas where individual seams split, but such areas represent only a small percentage of the total coal reserves.

COAL RESOURCES AND RESER\rES

1994).

BASDEN, H., 1969: Greta Coal Measures. 1n Packham, G.H. (Editor): The Geology of New South Wales. Journal of the Geological Society of Australia, 16(1), 323-329. BECKETT, J. & MCDONALD, I., 1984: The

depositional geology ofthe Jerrys Plains

Subgroup. Abstracts 18th Symposiurn on Aduances

in the Study of the Sydney Basin. Department of Geology, University of Newcastle, 44-46. BEMBRICK, C.S., 1983: Stratigraphy and sedimentation of the Late Permian Illawarra Coal Measures in the Western Coalfield, Sydney Basin, New South Wales. Journal of the Proceedings of the Royal Society of New South Wales,lt6, 105-1r.7.

BOOKER, F.W., 1960: Studies in Permian sedimentation in the Sydney Basin. New South Wales Department of Mines, Technical Report, 5 (for 1957), 10-62.

BRAKEL, A.T., 1984: Chapter 3: Sydney Basin Permian Coal Measures, Stratigraphy and Sedimentation. 1n H.J. Harrington & J.W. Hunt (Editors): Permian Coals of Eastern Australia, National Energy Research Development and Demostration Council, Report on Project r978/2t67 ,3.1-3.49. BRAKEL, A.T., 1986: Global sea-level change as a method of correlating the Late Permian coal measures in the Sydney, Gunnedah, and Bowen Basins, eastern Australia. BMR Journal of Australian Geology and Geophysics, 10, 17-22. BRITTEN, R.A., 1972: A review of the stratigraphy of the Singleton Coal Measures and its significance to coal geology and mining in the Hunter Valley

region of New south Wales . Proceedings of Annual Conference, Australasian Institute of Mining and Metallurgy, Newcastle, Ll-22.

The Hunter Coalfield is the largest coalfield in New South Wales, expressed both in terms of coal resources and in terms ofcurrent coal production. The coal resources and are based on the following

BRITTEN, R.A., 1975: Singleton-Muswellbrook district. In Traves, D.M. & King, D. (Editors): Economic

. o

CAREY, S.W. & BROWNE, W.R., 1938: Review of the Carbonierous stratigraphy, tectonics and palaeogeography of New South Wales and Queensland. Journal of the Proceedings of the Royal Society of New South Wales,7l,59I-6L4.

criteria:

coal with an in situ ash of <357o; seams with a minimum mineable thickness of 0.3m for open cut or 1.5m for underground

mrnrng; coal at depths of 600m or less where exploration has allowed continuity to be eslablished between observation ioints. More than 61 000Mt of in situ coal has been identifred in the Hunter Coalfield. Most of the resource evaluation, however, has been designed to test shallow open cut resources, and consequently these estimates do not necessarily reflect the full extent of the deeper-lying seams. Recoverable coal reserves in colliery holdings and exploration licences total 4890Mt (NSW Department of Mineral

Resources, 1994).

Geology of Australia and Papua New Guinea 2: Coal. Australasian Institute of Mining and -

Metallurgy, Monograph, 6, 191-205.

COAL RESOURCE DEVELOPMENT COMMITTEE, 1994: Effects of Land Use on Coal Resources. NSW Department of Mineral Resources, Sydney.

DAVID, T.W.E., 1907: Geology of the Hunter River coal measures, New South Wales. Geological Suruey of New South Wales, Memoir,4.

DICKINSON, W.R., L974: Plate tectonics and sedimentati on. Society of Economic Palaeontologists and Mineralogists, Special Publication,22, L-27.

Geology of Australian Coal Basins

195

DIESSEL, C.F.K., 1975: Coalification trends in the Sydney Basin, New South Wales. In Campbell,

K.S.W. (Editor): Gondwana Geology. Australian National University Press, Canberra, 295-309. HAMILTON, D.S., 1986: Depositional systems and coal seam correlation in the Greta Coal Measures of the Muswellbrook region. Australian Coal Geology,6,1-18. HARRINGTON, H.J. & BRAKEL, A.T., 1.984: Chapter 18: Synopsis ofgeological evolution ofthe Permian coal basins. .ln Harrington, H.J. & Hunt, J.W. (Editors): Permian Coals of Eastern Australia. National Energy Research Deueloprnent and Demonstration Council, Report on Project 1978 / 2167, 18.1-18.10. HERBERT, C., 1976: The depositional development of the basin. In Branagan, D.F., Herbert, C. & Langford-Smith, T. (Editors): An Outline of the Geology and Geomorphology of the Sydney Basin, Science Press, Sydney, 5-38. HERBERT, C., 1,980a: Depositional development of the Sydney Basin. InHerbert, C. & Helby' R. (Editors): A Guide to the Sydney Basin. Geological Survey of New South Wales, Bulletin,26, lI-57. HERBERT, C., 1980b: Evidence for glaciation in the Sydney Basin and Tamworth Synclinorial Zone. In Herbert, C. & Helby, R. (Editors): A Guide to the Sydney Basin. Geological Suruey of New South Wales Bulletin, 26, 27 4-293. JONES, B.G., 1983: Illawarra Coal Measures, Sydney Basin, N.S.W..In Williams, B.P.J. & Moore, P.S. (Editors): Fluvial Sedimentology Workshop, Australian Sedimentologists Group, Adelaide, South Australia, 366-375. KUKLA, G.T., BUFFIER, M.J., BALKS, R.J. & FARNELL, G.K., 1986. Open pit mining.ln Martin, C.H. (Editor): Australasian Coal Mining Practice. Australasian Institute of Mining and Metallurgy, Monograph, 12, 203-215. LOUGHNAN, F.C., 1975: Laterites and flint clays in the Early Permian of the Sydney Basin and their palaeoclimatic implications. Journal of Sedimentary Petrology, 45, 591-598.

McCLUNG, G., 1980: Permian marine sedimentation in the northern Sydney Basin. In Herbert, C. & Helby, R. (Editors): A Guide to the Sydney Basin. Geological Suruey of New South Wales, Bulletin,

26,55-72. McKELLAR, M.G., 1969. Maitland Group. 1n Packham, G.H. (Editor): The Geology of New South Wales. Journal of the Geological Society of Australia, 16(1), 329-334. Coal MENZIES, I.A., 1981: Permian - Scone Survey of Exploration Programme. Geological

New South Wales, Report GS1981/067.

MOFFITT, R.S., L983: Summary report on the coal resources of the Wollombi area: the Wollombi coal drilling programme, 1981. Geological Survey of New South Wales, Report GS1983/049. NSW DEPARTMENT OF MINERAL RESOURCES, 1994: 1994 New South Wales CoaI Industry Profile. Coal and Petroleum Geology Branch, NSW Department of Mineral Resources, Sydney.

RAGGATT, H.G., 1938: Evolution of the PermoTriassic basin of east-central New South Wales. Joint Coal Board (New South Wales), Report CR 38/1.

RATTIGAN, J.H. & MCKENZIE, P.J., 1969: Permian of the Hunter Valley. In Packham, G.H. (Editor): The Geology of New South Wales. Journal of the Geological Society of Australia, 16(1), 313-319.

ROBERTS, J. & ENGEL, B.A., 1986: Depositional and tectonic history ofthe southern New England Orogen. Australian Journal of Earth Sciences,

34(1), 1-20. ROBINSON, J.B., 1963: Revised stratigraphic nomenclature for Greta Coal Measures in the Muswellbrook area. Joint Coal Board (New South Wales), Report CR63/8. ROBINSON, J.8., L969: Singleton Coal Measures. In Packham, G.H. (Editor): The Geology of New South Wales. Journal of the Geological Society of Australia, 16( 1), 350-354. ROBINSON, J.8., J"979: The Singleton- Muswellbrook Coalfield. Mine and Quarry Mechanisation, 167-L7L.

SCHEIBNER, E., 1973: A plate tectonic model of the

Palaeozoic tectonic history of New South Wales. Journal of the Geological Society of Australia,20

(4), 405-426.

SCHEIBNER, E., 1976: Explanatory Notes on the Tectonic Map of New South Wales, Scale 1:L 000 000. Geological Survey of New South Wales.

STANDING COMMITTEE ON COALFIELD GEOLOGY OF NEW SOUTH WALES, 1975: Report of the Northern Coalfield Subcommittee. Geological Survey of New South Wales Records, 16(1), 9-105.

STANDING COMMITTEE ON COALFIELD GEOLOGY OF NEW SOUTH WALES, 1986: Stratigraphy of the Jerrys Plains Subgroup of the Wittingham Coal Measures in the Singleton- Muswellbrook Coal District of the Hunter Valley. Geological Suruey of New South Wales Records,22(L),

L29-r43. STUNTZ, J., 1972a: The subsurface distribution of the 'Upper Coal Measures', Sydney Basin, New South Wales. Annual Conference, Australasian Institute of Mining and Metallurgy, Newcastle, 1.-9.

STUNTZ, J., L972b: Hunter Valley coal drilling operations: basic results, history and briefgeology of scout bores drilled by the New South Wales

Department of Mines during 1968-1971. Geological Survey of New South Wales, Report GSr972/445.

SUMMERHAYES, G.J., 1982: Notes on the geology of the Muswellbrook 1:25 000 sheet. Geological Survey of New South Wales, Report GS 1982/064. UREN, R.E., 1985: The margin of a marine incursion in the Wittingham Coal Measures, Upper Hunter Valley. Proceedings, 19th Symposium on Aduances in the Study of the Sydney Basin, Department of Geology, University of Newcastle, 45-48.

Sydney Basin

197

ffiydney Basin r

The Newcastle Coalfield occupies a belt 30 to 60km wide along the coast of New South Wales, to the- . north of Svdnev (Figure 1). Coal has been mined in the Newcdstle area-for more than 180 years, and the coalfreld is still an area of considerable economic importance.

Coalfield

The Newcastle Coalfield incorporates the outcrop areas of the Newcastle and Tomago Coal Measures east of the Lochinvar Anticline, as well as the outcrop areas of Greta Coal Measures on the

Newcastle

anticliire itself. It also incorporates the Cranky Corner Basin, and the mining and exploration areas of the Tuggerah-Lake Macquarie region (Figure 1).

STRATIGRAPHY The stratigraphic sequence in the Newcastle

D Agnew, M Bocking'

K Brown, M Ives, D Johnson, M I{owes, BPreston, R RigbY' PWarbrooke and CR Weber

Coalfield (Tu6t" 1) co-mprises alternating marine and non-marine Permian sediments and volcanics, overlain by non-marine Triassic rocks. The basement in this area consists mostly of deformed Carboniferous strata similar to those exposed in the New England Fold Belt, which generally comprise acid lavis, pyroclastics and volcanic-derived sediments.

Dalwood GrouP The Dalwood Group overlies the Carboniferous Seaham Formation and consists mostly of marine sediments, volcanic and pyroclastic r,ocks (Table 1). The basal section comprises shale, siltstone and lithic sandstone alternating with basalt, volcanic breccia and tuff, while the remaining part of the sequence comprises conglomerate,- lithi-c and felspathic sandstone, siltstone and shale with minor limestone, marl and coal. Many rock types are tuffaceous and erratic pebbles thought to have been emplaced by ice rafting are found throughout.

Greta Coal Measures The Greta Coal Measures form a thin wedge of oredominantlv terrestrial coal-bearing strata lying ionformably between the marine Dalwood and Maitland Groups. They crop out along the flanks of the Lochinvar Anticline and in the Cranky Corner Basin, but detailed correlation between these occurrences is yet to be achieved. Little is known of the southerly or easterly extent of these coal measures beneath the overlying Permian and Triassic sediments. The sequence is commonly only-60 to ?5m thick, and comprises mostly sandstone and congl-omerate with some minor siltstone and shale as well as the coal seams. Along the eastern limb of the Lochinvar Anticline the sequence has been divided

stratisraphicallv into four formations (Britten, f gZS)ithbse beiirg the Neath Sandstone, 4urri Kurri Conglomerate, Kilchener Formation and Paxton Foriation (Figure 2). Further stratigraphic subdivision is-based on the splitting behaviour of ttre two major coal units.

Maitland Group The Maitland Group consists of about 1200m of oredominantlv marine sediments conformably lying between the Greta Coal Measures and the Tomago Coal Measures. The basal units, the Branxton Formation and the Muree Sandstone, consist of sandstone and sandy siltstone, with the Muree Sandstone being an excellent marker horizon. The Mulbring Siltstone forms the upper section of this

Sydney Basin

198

--***\:::::Fat:;:;r;:;:;:::; >F - <:i:iii!!i!!iilii!!t.lrji. l-\iHl.:ti:

/)-*Z7f)t)iii[::t:::::::l

f __!izsf./.1:i:i:1:1:1 j||':':':'#E' L-*_*t:ffiA:: ^* * Sll::l:il:i:lI

$-*----J rl J

i-S7,.,t,'

i*-fa-:*=

F -ili:i:i:,r,1

'/L

7l^*-**vi'/**J 4&*"*4

:-t:+t4 Z *n_*,4:i.r:lL\:l:i!!.1\<l,t,a^

-^i**\J

MAITLAND. '::':':':':':'r:'r:':'1:':/^ .-,ft

ztr\!

--*

:l: /4*2

I 4 -*:::-: s_{====1. dr:r:r:r::/

:-_---'---*

:_-*-_-_-*-*-*-****'z i-_-3 -.:*:-:*:-:*:/ /-:/ ,-----/ v_-/

KURRI KURRI

CESSNOCK

* :

- MOND*1#:*:*:*:* fidKY t:-TER

o N o q

NEWCASTLE

:,].

Section Fig.5

:::::I r:iri:l

UKE

'1":

MACOUARIE

,!l

Section Fig.8

,l'

:l ,1,

OUATERNARY

ffi

o,,Kti HNlilFlA,

TRIASSIC

WYON

LE GEND

H t**l

t-'l tt

N K\\\\

NORAH HEAD

OUATERMRY SEDIMEMTS

MRMBEEN GROUP & HAWKESBURY SANDSTONE NEWCASTLE COAL MEASURES

ffi

{

TOMAGO COAL MEASURES

PERMIAN

m ffi

MAITUND GBOUP GRETA COAL MEASURES DALWOOD GROUP

gqsJoRE CARBONIFEROUS

NEWENGUND

FON BELT NEWCASTTE COALFIELD

BAUNDARY

20km

BROKEN BAY

Figure l. Location and surface geology in the Newcastle Coalfield (modified from Sydney Basin 1:500 000 sheet, compiled by Geological Survey of New South lVales, 1969).

Geology of Australian Coal Basins

r99 being by Brown & Preston (L985), who divided the coal measures into three subgroups: the Wallis Creek, the Four Mile Creek and the Hexham Subgroups (Figure 3).

MAITLAND GROUP (marine)

tEtttocKsA t*

PELTON

-' ;;

SEAM

There is a marked unconformity along the eastern

a ut

T. ]a

PAXTON FORMATION

KURRI, KURRI

flank of the Lochinvar Anticline within the Wallis Creek Subgroup (Blayden, 1971), the discovery of which led to the proposal that the sequence below the unconformity be called the Mount Vincent Formation thereby subdividing the sequence into four major rock units. However, this unconformity appears to be a localised feature, and the stratigraphic classification proposed by Brown & Preston (1985) appears to be more representative.

\IEATH JANDSTONE

A major marine incursion, known as the Kulnura Marine Tongue, occurs within the Tomago Coal Measures to the south-west of Newcastle. This unit appears to be located stratigraphically towards the top of the Wallis Creek Subgroup, and consists rnostly of grey siltstone.

KEARSLEY KITCHENER

GRETA

FORMATION

SEAM

8 Hourvtlr

nnNnt [rFaaTt

F IU (r CI

Newcastle Coal Measures

DALW00D GR0UP (marine)

The Newcastle Coal Measures are the equivalent of the Wollombi Coal Measures of the Hunter Coalfield (Sniffen & Beckett, this volume), and are restricted to the north-eastern corner ofthe Sydney Basin.

Figure 2. Stratigraphy of the Greta Coal Measures (after Britten, 1975) group and consists of dark siltstone with minor claystone and sandstone.

Tomago Coal Measures The Tomago Coal Measures are the equivalent of the Wittingham Coal Measures in the upper Hunter Valley. The sequence thickens to the east, ranging from approximately 600m at outcrop near Maitland to >1200m in the Williamtown area, and contains mostly sandstone, siltstone and tuffaceous claystone together with numerous coal seams. A number of stratigraphic correlations have been proposed for the Tomago sequence, the most recent

The dominantly fluvial sequence has a maximum known thickness of 450m, and consists of conglomerate, sandstone, siltstone, tuff and numerous coal seams. The Newcastle Coal Measures have been divided into five stratigraphic units (Figure 4). The basal unit of the sequence is the Waratah Sandstone, a sheet like, medium grained lithic sandstone which forms a very good marker horizon. This is overlain by the Lambton and Adamstown Subgroup, containing numerous seams of relatively bright coal

Table.l. Stratigraphy of the Northern Sydney Basin (after Brakel, 1986). MACDONALD TROUG}I (UPPER HT'NTER) NARRABEEN GROUP WOLLOMBI COAL

L. MACQUARIE TROUGH (LOWER HI]NTER)

PERIOD

NARRABEEN GROUP

Triassic

NEWCASTLE COAL MEASURES

MEASURES

SINGLETON SUPERGROUP

I Dempsey Fm

Denman Fm TOMAGO

WITTINGHAM I Bulga Fm

I Kulnura M.T. COAL MEASURES

COAL MEASURES

MAITLAND GROUP GRETA COAL MEASURES

Mulbring Siltstone Muree Sandstone Branxton Formation Rowan Formation Skeletar For:mation

GYARRAN VOI,CANICS

Mulbring Siltstone MAITLAND GROUP

Muree Sandstone

Branxton Formation

Permian

GRETA COAL MEASURES

DALWOOD

Farley Formation Rutherford Formation

GROUP

Allandale Formation Lochinvar Formation

Seaham Formation

Sydney Basin

Carboniferous

200

r'1ii4BtRS Aht D

FORI'IATItJIJ

LI IHOLOGY

I]AI.1ED SEAI"lS koroloh Scrdslo0e Shole ond lofi,rnoled sa^a5lofe aorbonoaeous mudslonp

Shorflond [o.tr,cr,on Llpi i" Sondqote seom

Lefeohdns Ilol ILoystone Mem&r

Lor.. :cndjlle reofi

r nor b'olUrbolron

Ih,n 5io^y (rcI s$m5 srprmlsl d!51,nr lrve lulloc!c!s (1!y!l!np Dorf. g.ey ond block lrm ncle-i shole. m,nor sondslont to":rCs top r,fumerors th n l!i{caeous (Loysione beCs onC lon,,nF,n Zonei AbunCanl Ir,otrLot on lhro!!hoUl, phose! of iJrfi,

0emfser Forfl,ol,on

\.,'byt

burrow,ng

Flot (loy5lone Mer,b6

--lrtjr-tu Lov$ B!llo, seom

Sond!lone, minor shole. muCsione. c{oyslone ond cool

v,bod5 6ully [lolstone l'lember

lronborh [nrnlol ron

Brn il eld srcm

a d l

0or c'Cso^5 seomls)

Thoanlon (lol:lone

!'-,'cn seot

D lliicl

ve 1!1 foa€!rs a :i11.:a

3q( i,cncn - I'joillond stom

Alnrrck fo.fl,olroo

Asrilrl,elds s€om

Sond!bne fi,inor shole mudslo^e ond (ool

ac ilrin geom

c) t

O F

Lon;noleC sond:lore oiC 1\: t

Slor,et P,nch Formol,on

AbliCcnl b clu.bol of. m r.r

vorm burror,n3 lh,n :cr. ai shell lrcgmenls

z t c U

Scol h 0erry !eom(sl

5col( h

Lom,noled sonCsi$e numemus

Sondstme, mino. sho{e ,

Surveyor! beek Fgrulim

biolurbol'm.

UpP T

R.lhlubo Formol;on sc R

Roworlh (lotslone

Sondsione, shole, (oabonoceous mudslonP, (ool seom!

So.dsloE ond shole Hrno. brolurbol

l''lelfocd Formolion l'lorpelh tormotroo

o'd siale

thin (ooI se3is

llor!flh smm

Shole ond cml reom!

Freqwnl iqneo6 rnlrusrm Drshn(live .loYslone, tul tu(eNs

Tenombit SondsloE

Mulbring Siliston? o <l :d t

1985).

which tend to coalesce towards the west (Figure 5). The coal seams within the overlying Boolaroo Subgroup, however, are very banded and tend to split and deteriorate over short distances. As a result, the latter sequence contains no coal of economic significance. The complex geology of the Boolaroo Subgroup, together with the limited geological information available, has led to some miscorrelations within the sequence. The Moon Island Beach Subgroup, at the top ofthe succession,

is characterised by relatively dull coal and large volumes of coarse grained interseam sediment.

Differential subsidence and the presence oflarge lobate bodies of conglomerate and coarse grained sandstone have led to a complex three dimensional pattern of coal seam splitting and coalescing within the Newcastle Coal Measures. Sedimentary grain size generally increases upwards, as does the

Geology of Australian Coal Basins

201

SUB.GROUP

MEMBER

FORMATION

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Vales Point Coal Member

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Munmorah Conglomerate

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CowperTuff Member

Wallarah Coal

Moon lsland Beach Sub-Group

Karignan Conglomerate Member

Catherine Hill Bay Formation

Mannering Park Tuff Member Toukley Coal Member Buff Point Coal Member Teralba Conglomerate Member Booragul Tuff Member Awaba Tuff Member Chain Valley Coal Member 'Bolton Point Conglomerate Member

Great Northern Coal

Eleebana Formation Fassifern Coal Croudace Bay Formation

Belmont Conglomerate Member

Upper Pilot Coal Boolaroo Sub-Group

Reids Mistake Formation

Seahampton Sandstone Member

Lower Pilot Coal , Warners Bay Formation Hartley Hill Coal

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Australasian Coal

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Glebe Formation

Fern Valley Coal

Lambton Sub-Group

Tingara Conglomerate Member Edgeworth Tuff Member Upper Split Redhead Conglomerate Member Lower Split

Kotara Formation

Merewether Conglomerate Member

Victorian Tunnel Coal Shepherds Hill Formation Nobbys Coal Bar Beach Formation Dudley Coal Bogey Hole Formation

Nobbys Tuff Member Spring Hill Conglomerate Member Cockle Creek Conglomerate Member

Yard Coal

Coal

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Tighes Hill Formation Borehole Coal Waratah Sandstone

TOMAGO COAL MEASURES

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Ferndale Conglomerate Member

metres

Figure 4. Stratigraphic subdivision of the Newcastle Coal Measures (revised after Crapp & Nolan, 1975).

Sydney Basin

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Geology of Australian Coal Basins

203

MOON ISLAND

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TOMAGO COAL MEASURES

GRETA COAL MEASURES

Lithology

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Propodion ot pyroclastic material in coal seam horizons

Figure 6. Vertical variation in lithology in the Newcastle and Tomago Coal Measures (Warbrooke, 1981).

Figure 7. Vertical variation in the tuff content of Newcastle and Tomago coal seams (Warbrooke,

relative abundance of the conglomerate sheets (Figure 6).

DEP O SITIONAL EI{\TIRONMENT

Cranky Corner Basin

Greta Coal Measures

The Cranky Corner Basin is a saucer shaped outlier

north of the Hunter Thrust, containing Permian coal measures thought to be the equivalent of ^the Greta Coal Measur"s]It is approximately 25km2 in ar"a. The strata have a regional dip of5 to 10o to the north-west and are surrounded by Carboniferous volcanics. The sedimentary sequence in the basin comprises mostly coarse sandstone and polymictic conglomerate, together with three coal seams.

Contemporaneous Volcanic Activity With the exception of the basal portion of the Permian sequence, there is a marked increase within the Newcastle Coalfield in the relative abundance of pyroclastic sediments up the stratigraphic sequence. Tuffaceous sediments are fairly rare within the Greta Coal Measures, whereas the T<lmago Coal Measures contains abundant thin but persistent tuffaceous claystone horizons. The Newcastle Coal Measures, however, contains the greatest volume of pyroclastic sediment, with tuffaceous claystones of variable thickness and lateral extent occurring throughout the sequence. The thickness and abundance oftuffbands also increases up the Newcastle Coal Measures succession (Figure 7). Offshore from the present coast line is a meridional ridge, named the Northumberland Ridge by Brakel (1986). This was probably the site of the contemporaneous volcanism that supplied the tuffs of the Newcastle Coal Measures, and was also a possible source for some of the other alluvial sediments within the sequence.

1981).

The Greta Coal Measures were formed during a short-lived marine regression, which developed to the south of the rising New England Fold Belt. The initial influx of sediment was rapid, with coarse grained sediments being deposited almost directly

into the shallow sea in which the underlying Dalwood Group was deposited.

The Neath Sandstone, the lowest unit in the coal measures, probably represents a barrier bar system. This sheet-like sandstone unit is 10 to 20m thick, massive and even-grained. It is often bioturbated

toward the base.

Swamps developed behind these advancing barrier islands, with the accumulation of peat that subsequently formed the Lower and Upper Homeville seams. Braided river systems flowing through the swamps from the north and north-west deposited predominantly coarse clastics, splitting the Homeville seam (Abernethy Lens) and

separating the Homeville seam from the overlying Greta Seam (Stanford Lens). The Upper and Lower Homeville Seams coalesce in an elongated area south of Kurri Kurri, but further to the south and south-west the seam thins and becomes unrecognisable.

An upward-fining clastic sequence at the top of the Kurri Kurri Conglomerate was followed by the deposition of siltstone and shale which formed the floor of the Greta seam. Thick accumulations of peat developed, with no or very few non-coal bands and a low ash yield. Torbanite lenses in the lower section ofthe seam indicate deposition ofalginite-rich coal within the swamps under anaerobic conditions. Diessel (1986) considered that the Greta seam was deposited in front of a marine transgression and under conditions of almost complete sedimentary

Sydney Basin

204 by-passing. A marine influence on coal formation is shown by the high levels of pyritic sulphur in the upper section of the seam. The eastward-thickening Kearsley Lens, which forms the major split horizon in the Greta seam, probably represents the edge of contemporaneous clastic sedimentation, while widespread thin tuffaceous claystone bands within the seams also indicate the continuation of volcanic

activity.

The marine transgressive phase was interrupted by renewed coarse clastic sedimentation which encroached across the coastal swamps. Traces of the river systems are preserved as fossil channels in the roof of the Greta seam, and have been studied at several operating collieries (Rawlings, 1982). The channels are filled with conglomerates and coarse pebbly sandstones, typically fining upward, that commonly penetrate less than 0.5m into the coal seam.

The channel sands in the Paxton Formation fine upward into floodplain sediments beneath the Pelton seam. This seam in some places is almost directly overlain by fossiliferous and bioturbated marine sediments of the Branxton Formation, but elsewhere at least 12m of braided stream sediment was deposited before the transition into the marine sediments occurred.

A significant feature of the Greta Coal Measures is the common occurrence of sedimentary dykes and sills within the Greta seam. The composition of these dykes and sills ranges from fine clayey sandstone to pebble conglomerate. They are up to at least 2m thick. There are notable differences in the style of intrusion between the exposures at different locations; at Ellalong and Pelton Collieries for example, two dominant directions of intrusion have been noted, with one set appearing to originate from the floor and the second to penetrate down from the roof. Martini & Gloosechenko (1985) suggest that at least some of these dykes may have formed as the infill of polygonal ice wedges which developed in the upper part of the seam. Large sedimentary dyke and sill complexes at Aberdare North Colliery occur around erosion channels cut into the upper part of the Greta seam,

with the sills extending laterally into the seam for up to 100m. The intrusions appear to have been formed in response to loading by differential compaction around the channel. The trigger mechanism is thought to have been seismic shock, with emplacement occurring while the peat was relatively uncompacted. Differential compaction ratios between the contorted dykes and the surrounding coal are typically between 5:1 and 8:1.

Sedimentary dykes and sills do not seem to be common in the Greta Coal Measures of the upper Hunter Valley (Sniffen and Beckett, this volume), nor are they common in the Upper Permian coals of the Newcastle field.

Tomago Coal Measures The Tomago Coal Measures represent a transitional zone in sedimentation between the underlying

marine Maitland Group and the overlying Newcastle Coal Measures. Their transitional setting has been recognised in the stratigraphic subdivisjon Proposed by Blown & Preston (1985), who identified the presence of numerous brackish marine episodes intercalated with terrestrial coal measure deposition. Thin but persistent tuffaceous claystone

beds provide excellent marker horizons, which have

aided the stratigraphic interpretation.

The Tomago Coal Measures are divided into three subgroups. The basal Wallis Creek Subgroup, approximately 300m in thickness, is represented by an almost cyclical sequence of terrestrial coal-bearing formations and brackish marine phases of bioturbated siltstone, fine sandstone, mudstone and laminated shale. Coal beds include the Morpeth and Rathluba seams, that have a long history of mining in the Morpeth and East Maitland areas. The overlying Four Mile Creek Subgroup, approximately 160m in thickness, contains the major economic horizons of the Upper and Lower Donaldson seams and the Big Ben seam. The Lower Donaldson seam is separated from the underlying Big Ben seam by the Thornton Claystone, a unit that has been recognised as being oftuffaceous origin and that provides a definitive marker horizon throughout the coalfield area. The Four Mile Creek Subgroup is distinguished from the underlying Wallis Creek Subgroup and the overlying Hexham Subgroup by its increased sand content and higher mass ratio of coal to interseam sediments. Marine influence is absent in the Four Mile Creek Subgroup. The Hexham Subgroup is approximately 140m thick and is dominated by the bioturbated brackish to marine mudstone and laminite of the Dempsey Formation. The marine influence is reflected in the high sulphur values (up to 47o) for the immediately underlying Buttai seams, and the fact that sulphur values in the other seams of the Four Mile Creek Subgroup show a steady decrease down the sequence to the Ashtonfields seam. Sulphur values are also found to increase to the east away from the Four Mile Creek Anticline, a factor again coincidental with the development of the overlying Dempsey Formation. The Dempsey Formation is further characterised by distinctive tuffaceous claystone horizons, the Weakleys Flat Claystone Member and the Leneghans Flat Claystone Member. The appearance ofthe Sandgate seam towards the top of the Hexham Subgroup marks the transition to the terrestrial deposition of the overlying Newcastle Coal Measures.

The basal Wallis Creek Subgroup marks the transition from the marine conditions of the Maitland Group to the deltaic environment that prevailed throughout the Tomago Coal Measures. Further to the south, the Kulnura Marine Tongue is recognised as forming from an extensive marine incuision coeval with deposition within the Tomago Coal Measures (Herbert, 1976). The frequency of burrows and other bioturbation, and thelelatively high sulphur contents ofcoal and interseam sediments within the Wallis Creek Subgroup, suggest deposition in a lower delta plain environment, while the absence of marine influence within the overlying Four Mile Creek Subgroup suggests deposition in an upper delta plain setting. The uppermost Hexham Subgroup marks a return to the brackish/marine influence of a lower delta plain setting and ultimately a return to terrestrial conditions in the Newcastle Coal Measures. Some lingering brackish influence, however, has been recognised by Warbrooke (1978) to persist upwards into the basal Newcastle Coal Measures units.

Geology of Australian Coal Basins

205

Lower Newcastle CoaI Measures Sedimentation patterns in the Newcastle Coal Measures were controlled by continuing movements and associated volcanism in the adjacent New England Fold Belt and by differential subsidence associated with the Lochinvar Anticline. The

increasing sediment supply that resulted from this tectonic activity gradually frlled the basin in the Newcastle region. Coarsening of sediments and an increase in the proportion of pyroclastic material up the section (Figures 6 and 7) are a direct result of this tectonic setting. Differential subsidence within the area also played a significant role in the distribution of sediments, particularly the coal seams, which exhibit multiple splitting to the east away from the Lochinvar Anticline. In addition to tectonically-controlled splitting, however, splitting by sedimentary processes occurs within the seams due to active fluvial systems in the swamp during peat accretion (Warbrooke, 1981; Warbrooke & Roach, 1986). The quiet water conditions which prevailed during deposition of the uppermost Tomago Coal Measures allowed undisturbed, continuous deposition of highly bioturbated shale, siltstone and sandstone

laminites, which gradually become sandier and grade into the very fine grained sandstones ofa lower shoreface environment. These sandy sediments, which mark the base of the Waratah Sandstone, coarsen up to medium grained sandstones in response to increased wave energy through the surf and swash zones, and in some areas are capped by aeolian dune deposits. The sands are well sorted and contain large scale, very low angle, seaward-directed cross beds representing the old shore face and small-scale, high angle, landward-directed cross beds that resr.rlted from the migration of bars up the shore face.

Thin, irregularly distributed shale and siltstone deposits overlying the sandstone represent restricted back barrier lakes and lagoons. These were eventually covered by the swamps in which the Borehole seam developed, although channel sequences in the Waratah Sandstone and within the seam are remnants of drainage systems that still flowed through the swamp. Development of a widespread lake on the eastern side ofthe area abruptly terminated the Borehole seam swamp. These lacustrine deposits formed the Tighes Hill Formation, grading from organic rich mud through fine, evenly laminated shale into thin but laterally extensive siltstone and sandstone. Their coarsening-upward profiles represent small deltas building into the lake from river channels further to the west. The interval between the overlying Yard and Victoria Tunnel seams was dominated by swamps and river deposits. Meandering river deposits demonstrating typical frning up profiles predominate towards the base, but these sediments gradually change in character to become braided channel deposits at the top ofthe sequence. The meandering channel bedload and point bar conglomerates and sandstones usually have an erosional basal contact and contain both large and small scale crossbedding. They grade into the interbedded fine grained sandstone, siltstone and shale of the levee and floodplain deposits, which often contain ripple marks, cross bedding and crevasse splays. Multiple

stacking ofthese sequences is indicative ofchannel

meandering.

As the rivers increased in size and the sediments coarsened, the channels became internally braided, with numerous smaller channels now confined between the levee deposits. This produced a channel fill exhibiting a typical oscillatory profile. The sediment of these fills consists of conglomerate and coarse grained sandstone, which grades into the normal levee and floodplain sediments. Restricted lacustrine deposits are often associated with the channel sequences.

Clastic deposition between the Victoria Tunnel and Australasian seams reflects a change from the braided channel to the higher energy piedmontalluvial fan environment. The first evidence of this change is found in the Kotara Formation to the north-east, in the form ofa thick, laterally extensive, lobate conglomerate unit, the Merewether Conglomerate Member. To the south this unit degenerates firstly into a braided channel deposit, then a meandering river deposit with a noticeable decrease in grainsize from pebble conglomerate to medium-grained sandstone. Similar lobate conglomerate units higher in the sequence, each advancing further south, represent periods ofrapid, high energy, coarse sediment deposition with long periods of swamp development between each pulse. This trend culminated with the deposition of the Charlestown Conglomerate Member between the Montrose and Australasian seams. The Charlestown Conglomerate covers about half the coalfield, and reaches a thickness ofmore than 100m before lensing out to the west and thinning to the south. Typical profiles are similar to the coarse sections of the braided channel profile but are thicker, with less extensive floodplain deposits. The sediment deposited on this braidplain oscillated from large pebble conglomerate to coarse grained sandstone because of the superposition of narrow, shallow channels. Sedimentary structures include small to very large scale cross beds (up to 30m), mega ripples and scour structures. The interval between the Australasian and Fassifern seams is characterised by large volumes of tuffaceous material, mostly in the form of claystones which exist as both intraseam and interseam sediments. It appears that pyroclastic activity reached a peak in the Newcastle Coalfield during this period of coal measure deposition (Figure 7). The coal seams within this interval tend to split and coalesce over relatively short distances, often enclosing lenticular bodies ofcoarse grained clastic sediment, such as the Belmont Conglomerate which is developed in the Lake Macquarie area.

A notable feature ofthe sequence is that towards the west, where the coal measures lap on to the adjacent Lochinvar Anticline, and the seams within the Lambton, Adamstown and Moon Island Beach Subgroups coalesce due to the progressive thinning of the intervening non-coal strata, the only interval in which detrital sediments prevail to any extent is within the Boolaroo Subgroup. Penecontemporaneous vulcanicity has also

introduced a significant amount of other material into the Newcastle Coalfield area. Thin claystone and tonstein bands found in the coal seams are interpreted as ash fall tuffs by Diessel (1965; 1985) and Warbrooke (1981). These materials occur as thin, continuous bands, and are often used for correlation because of their great lateral extent; a claystone band in the Dudley seam, for exampJe, is 0.lm thick and covers a known area of 700km". They

Sydney Basin

206 sometimes contain remnants of glass shards, now altered to clays, with quartz, feldspar and biotite being common constituents.

Interseam tuffs in the sequence are also laterally persistent but are thicker, ranging from a few centimetres to tens of metres in thickness. They may be coarser grained, but are generally similar in composition to their intraseam counterparts. Emplacement was apparently sudden, because they effectively terminate the environment of the sediments beneath. Based on the presence of sedimentary structures such as parallel bedding, cross beds, ripple marks,

climbing ripples and scour structures, Warbrooke (1981) indicated that the tuffs were ash-fall deposits which, in some areas, had later been reworked by fluvial processes. Diessel (1985) has shown that all these structures, plus previously unexplained contorted bedding in some tuff units, could be formed by pyroclastic flow and surge deposits. He also found that fossilised tree stumps, originally growing in the top of seams at Swansea Heads and protruding into the overlying tuff, had been apparently snapped off, with many tilted in a south-westerly direction. Charring and damage to the bark and wood on the north-east side of several trees provide further support for a rapid emplacement of the hot material and destruction of the contemporaneous forests. The source ofthe volcanic debris was apparently located to the north-east of the present coast line. This interpretation is now favoured for the accumulation of thick tuffs, although some water reworking cannot be completely ruled out. Another feature of these thick tuff units is that they often underlie large conglomerate bodies (e.g. the Stockrington Tuff Member underlies the Charlestown Conglomerate Member and the Booragal Tuff Member underlies the Teralba Conglomerate Member). This suggests that the volcanic activity responsible for the tuff was also related to the later influx of coarse sediment into the area.

Upper Newcastle Coal Measures The upper Newcastle Coal Measures are characterised by coal seams and tuffaceous sediment interspersed with lobate conglomerate and sandstone bodies up to 80m in thickness, and appear to have been deposited in an alluvial floodplain

environment. The clastic sediments were apparently deposited in well-defined channels by high-energ'y, braided rivers, with some of the channels up to 4km wide and at least 50km long. As well as migrating laterally, the courses of these channels often switched locations across the floodplain.

Overbank and crevasse splay deposits, consisting of up to 3m of fine grained sandstone and mudstone, usually accumulated on top of the abandoned channels, which were typically bordered by peat swamps. The peat swamps and river channels co-existed, and there appears to have been no significant erosion of the peat swamp deposits by the rivers. Very few of the conglomerate bodies appear to have been deposited directly as alluvial fan deposits. The Fassifern seam and its splits constitute the thickest and most widespread coals in the upper Newcastle Coal Measures. The seam is represented

by only one coal bed in the north-west between Fassifern and Cooranbong, over a large area in the south-western Lake Macquarie region, and in a small area on the western shore of Budgewoi Lake (Figure 8). Elsewhere, however, it is split into two, and in places three separate seams by conglomerate and sandstone bodies, which collectively form the Bolton Point Conglomerate. Although these sandstones and conglomerates appear to have developed contemporaneously, channel migration and switching has resulted in them being separated in places by coal and tuff deposits, thus leading to recognition of a phased development concept. The lower Fassifern seam is up to 8m thick, and is present throughout the region. The basal section, which contains several mudstone and tuffaceous claystone bands, merges in places with the underlying Upper Pilot seam. The composition of the coal itself is consistent with formation in a dry forest swamp (Diessel, 1986). The lower phases of the Bolton Point Conglomerate were deposited in tributary channels, which were part of the same river system flowing to the south-west. The two major channels present in the northern halfofthe region broaden out to the south to form a sandy alluvial braidplain with local meander belts. The channel deposits contain 30 to 80m of gravel and sand in the north where the channels are narrow, and up to 15m ofsand on the braidplain. These channels appear to have coexisted with the seam at the time of deposition, and consequently more coal plies are present beneath the channel margins than beneath the central parts ofthe channels. The upper Fassifern seam, although not as widespread as the lower Fassifern seam, is present over most of the region. It is best developed in the south-west of the coalfield, to the west of Wyong, where it attains a thickness of more than 3m. The upper Fassifern seam is generally separated from the lower Fassifern seam by the lower phase of the Bolton Point Conglomerate, and was apparently formed on the river channel tops after the channels themselves had been abandoned. The Bolton Point Conglomerate also separates the upper Fassifern seam from the overlying Awaba Tuff in some areas. The upper phase of the Bolton Point Conglomerate appears to have been deposited in a similar fluvial system to that of the lower phase. The palaeochannel containing this phase is developed along the eastern coastal areas, where it contains up to 50m of conglomerate and sandstone. The Awaba Tuff, which is situated between the Fassifern and Great Northern seams is the most widespread unit in the upper Newcastle Coal

Measures. This tuff ranges from 1 to 27m in thickness, and is the result ofa period ofpronounced volcanic activity in the region. The tuff generally consists ofthree phases: a basal pyroclastic claystone which appears to have been deposited as an air fall vitric tuff and reworked locally, a relatively thick micaceous lithic sandstone which consists of reworked rhyodacitic volcanic material and an upper claystone and sandstone unit which also consists of reworked volcanic material. The Great Northern seam is present, at least in part, throughout most ofthe region. Several phases of a major alluvial channel system were deposited contemporaneously with the seam, however, and in some areas these appear to have resulted in the

Geology of Australian Coal Basins

207

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Sydney Basin

208 non-development of the entire coal bed. The channel deposits, which consist of conglomerate and sandstone, form part of the Teralba Conglomerate, the development of which, like that of the Bolton Point Conglomerate, can be divided into a number of phases.

The frrst depositional event to follow the blanket-like deposition of the Awaba Tuff was the establishment of a major, linear river channel. The base of the channel fill rests directly upon the middle facies of the tuff, suggesting that the channel coexisted with and/or eroded the upper phase ofthe tuffdeposits. The basal sections ofthe Great Northern seam are developed throughout the region on either side of this river channel, and the development of the remainder of the seam was contemporaneous with this same migrating braided river system, which ultimately deposited up to 80m of gravel and sand. Where the Great Northern seam underlies this lower phase of the Teralba Conglomerate it is generally from 3 to 5m in

thickness.

In the east of the coalfield the Great Northern seam is overlain by op to 3m ofgreenish tuffand tuffaceous sediments (the Booragul Tuffl, which is overlain in turn by a further system ofbraided channel deposits. These deposits constitute the upper portion of the Teralba Conglomerate. The Wallarah seam is present over all-but the north-west portion of the region. In some areas it is split, with the upper portion being known as the Vales Point seam. As with the Great Northern and Fassifern seams, alluvial channel deposits and

tuffaceous sediments were deposited contemporaneously with the various splits of these coal beds. The channel deposits include further phases of the Teralba Conglomerate and also the Karignan Conglomerate, while the tuffaceous sediments are mostly contained within the

Mannering Park Tuff.

Where it is a separate unit, the Wallarah seam is up to 5m thick and is developed on top ofeither the Mannering Park Tuff or the Teralba Conglomerate. The coal is typically dull and lacks stone bands, and like the Fassifern seam has a composition consistent with development in a dry forest swamp environment (Diessel, 1986). Two separate sets of alluvial deposits have formed above the Wallarah seam, one in the north and the other in the south. Both are known as the Karignan Conglomerate.

Coal-Forming Swamp Conditions Based on interpretation of lithotype, microlithotype and maceral analyses of the Greta, Tomago and Newcastle Coal Measures, Warbrooke (1981; 1984) has identified changes in the swamp environments of the Newcastle Coalfield with the regional depositional patterns. The seams of the Greta Coal Measures developed in wet, marine-influenced reed swamps, which were buffers separating the sea from contemporaneous terrestrial deposits. The seams in

the deltaic Tomago Coal Measures formed from wet reed swamps and wet forested swamps, and wet forested swamps became established throughout the region as the meandering fluvial deposits of the lower Newcastle Coal Measures accumulated. Drier forested swamps, however, are associated with the piedmont deposits in the upper Newcastle Coal Measures. These results have been confirmed by

Diessel (1986) using interpretations based on maceral analysis.

TECTONIC HISTORY AND STRUCTURAL GEOLOGY

Hunter Thrust The Hunter Thrust forms the north-western boundary ofthe coalfield and separates the Sydney Basin sequence from that of the New England Fold Belt. Displacement along the thrust is thought to be ofthe order of1 to 2km in places, and the angle of the thrust plane is between 5 and 10o. Many

near-vertical north trending faults disrupt the Carboniferous sediments along the north-eastern boundary of the coalfield.

Lochinvar Anticline The Lochinvar Anticline is the largest anticlinal

structure affecting the Permian sequence in the Hunter Valley. During the Late Permian this structural high separated the Newcastle depositional area from the remainder of the Hunter region, so that the western flank ofthe structure is taken as the boundary between the Newcastle and Hunter Coalfields. The anticline has a box fold symmetry, with dips on the crest seldom greater than 10o. The western flank is defrned by a zone of more steeply dipping rocks associated with the Mathews Gap Fault. The Greta Coal Measures crop out sporadically along this fold limb, with the outcrop pattern controlled by a

number of faults.

The eastern flank of the anticline has been identified by Blayden (1,971) as the Buchanan Monocline, and easterly dipping strata forming the steep limb of this monocline crop out in a 5km wide belt to the north and south of Maitland. The actual monocline is inclined at 10o to the east and has a gentle southerly plunge. Dips vary from 15o to 65o between Kurri Kurri and Maitland but decrease to approximately 5o further south.

Macquarie Syncline The Macquarie Syncline is the dominant structural feature of the Newcastle Coalfield. This very broad fold has a gentle plunge to the south, and although many localised variations do occur, dips on the limbs are df the order of 2 to 4o. A number of major structural cross folds are superimposed, however,

particularly in the north.

The syncline is bounded to the west by the Buchanan Monocline and to the north by the Mindaribba Syncline and the Morpeth Monocline. To the north-east it becomes the Medowie Syncline,

while in the vicinity of the Hunter River mouth it is modified by the Stockton Basin (Blayden, 1971). Relatively little is known of the Macquarie Syncline off-shore, although the gently dipping eastern limb continues for some distance beyond the present coast line and is probably terminated by the Northumberland Ridge. To the south, the syncline can be traced to the northern shores ofTuggerah Lake, but beyond this point it opens out into a much broader basin-like structure.

The axis of the Macquarie Syncline has an initial plunge to the south and south-east, but in the vicinity of Lake Macquarie it swings around to the south-west. The structure has an asymmetrical cross

Geology of Australian Coal Basins f

209 section, with the western limb being steeper and the coal measures on that side becoming thinner before eventually wedging out against the adjacent Lochinvar Anticline. Dips are less steep on the eastern limb, however, and the coal measures retain their thickness beyond the existing coast line. Thickness variations across the syncline have been shown to be the result of differential subsidence, with many localised steep dips attributed to differentiil compaction around thick palieochannels of conglomerate. As a result it appears that most of the teitonic activity responsible for formation of the syncline was post-depositional. The geometry of both the Lochinvar Anticline and the Macquarie Syncline are thought to be controlled by faulting between rigid blocks of basement.

Faults, Dykes and .Ioints A number of north-trending faults disrupt both the Carboniferous and Permian sediments along the north-eastern boundary of the Newcastle Coalfield. Eight such faults with displacements greater than 60h have been documented by Blayden (1971). Many lesser faults are also encountered throughout the coalfield, the most common being near vertical, normal faults with a north-west south-east trend and displacements from <1m to approximglgly 5p' Other normal, reverse, strike-slip and bedding plane faults have also been recorded. Igneous dykes are relatively commo4 throughout the aiea. The majority of these are parallel to and often associated with the north-west trending faults, although some east-west trending dykes are also encounlered. Most dykes are near vertical and less than 10m wide, although they often thicken out within coal seams. Some dyke swarms have been documented, as well as a few sills replacing individual coal seams.

The most common joint direction is NW-SE (125o mean), which is parallel to many of the faults and dykes.'A second iet strikes east-west (095o mean), but although well developed in the coal this set is often not n-oticeable in the interseam strata. The least intense joints trend NE-SW, but localised strike variati-ons are common. Almost all joints are near vertical, and the cleat in the coal has the same orientation pattern as the regional jointing.

ECONOMIC COAL SEAMS The Homeville seam in the Greta Coal Measures exists as an elongated tongue ofcoal up to 6m thick, extending to the iouth from its subcrop near Kurri Kurri. Towards the east and west the seam is split by the Abernethy Lens, with the upper_split generally being thicker east ofCessnock. The overlying Greta seam has its maximum developm-entln the vicinity of Cessnock, where it attaini thicknesses of up to 1lm, but thins rapidly to the south. It is split by the Kearsley Lens, with the upper portion of the seam being of lower quality and tiighei in sulphur than the lower part.

The seams within the Tomago Coal Measures are typically split, and also vary greatly in both thickneis and lateral extent. This is a function of their depositional environment. The Rathluba seam varies b-etween 1.5 and 3.0m in thickness and contains a number ofstone bands. The upper portion deteriorates in places, and the seam splits to the east of East Maitland. The Big Ben seam varies from

1.5 to 4.5m in thickness; it contains some variable mudstone beds which thicken towards the west and split the seam. The Donaldson seam varies in thickness from L.0 to 3.0m, and often consists of a number of splits which in places diverge and enclose up to 30m of sediment. The seam also contains a number of mudstone bands which vary greatly in thickness over short distances.

The Borehole seam is developed throughout the Newcastle Coal Measures, but is at its thickest in the Delta Syncline underlying the city of Newcastle. To the south of Newcastle, however, in a zone coinciding roughly with Lake Macquarie, the seam is split by contemporaneous fluvial activity. To the east of this zone the seam varies between 1.5 and 2.5m, whereas to the west it thickens in a north-westerly direction to approximately 2.5m. The Borehole seam combines with the overlying Yard, Dudley and Nobbys seams along the western margin of the coalfield to form the West Borehole seam. The Yard and Dudley seams on their own have limited resources, but in combination with the adjacent seams they form an important source of coling coal. The Nobbys seam, although thin, forms a useful marker horizon for correlating seams and seam combinations in the Lambton Subgroup. The topmost seam in the Lambton Subgroup, the Viitoria Tunnel seam, is best developed along the coast east of Lake Macquarie. A notable feaJure of this seam is the presence of a number of 'wants', in which carbonaceous mudstone has developed in place ofthe coal. The Australasian seam varies from 4 to 16m in thickness, but only the basal section, generally about 2.5rn thick, is of economic interest. The working section is best developed to the north and east of Lake Macquarie, and to the west the seam

converges with the underlying Montrose and Wave Hill seams. The Fassifern seam is generally 2.5 to 3m thick, but attains thicknesses of up to 8m in places. In some areas it exists as two or three splits,

wittr ttre working section usually confined to the middle split or combinations involving the middle split.

The Great Northern seam is developed in three areas: the Teralba-Awaba area where it is up to 6m thick, the Belmont-Wangi area where it is up to 7m thick and the Catherine Hill Bay - Vales Point area where it is approximately 3m thick. The seam usually contains thin mudstone bands throughout, and in areas to the south ofToukley, and to the south of Cooranbong, it combines with the Wallarah-Vales Point seam to form a section of coal up to 7m thick. The Wallarah seam at the top of the Newcastle sequence is mainly dull with thin bright bands and is 2-3m thick, but it can attain thicknesses of up to 5m. This seam may consist of up to three main splits including the Vales Point seam.

COAL QUALITY The Greta seam and the seams worked in the Tomago Coal Measures are mined to produce soft coking coal used for blending. These coals tend to have i relatively high sulphur content. The seams of the lower Newcastle Coal Measures are mined to produce both domestic and export quality coking and

thermal coal, whilst the coal extracted from the upper Newcastle Coal Measures is utilised mostly as tliermal coal for domestic power generation.

Sydney Basin

2to Table 2. Indicative coal quality for the Newcastle Coalfield. MEASURES

GRETA

TOMAGO

NEWCASTLE

SEAMS

Greta

Homeville

Donaldson

Big Ben

Rathluba

Borehole

Young Wallsend

Yard

Inherent Moisture (ad)

2.1

r.7

2.1

2.2

2.5

2.3

2.5

2.2

Ash (db)

6.4

5.9

L2.4

10.6

L2.8

10.0

14.2

8.0

Volatile Matter (db)

42.0

42.6

37.0

34.9

35.4

34.4

32.4

34.4

Sulphur (db)

L.24

0.84

0.8

1.14

1.05

0.51

0.45

0.48

Phosphorus (db)

0.03

0.02

0.01

o.o2

0.04

0.06

0.10

0.13

Carbon (dmmf) Hydrogen (dmm0

83.8

83.6

84,1

84,2

b.5

Nitrogen (dmmO Sulphur (dmmf)

83.6 5.9 2.0 0.81

2,0 0.75

2.0 0.93

84.5 5.5 2,L

0.90

5.7 2.0 0.73

0.52

84.7 5.3 2.0 0.47

84.7 5.3 2.0 0.48

Specific Energy (daO

35.6

35.3

35.r-

34.9

35.2

35.0

34.8

34.9

CSNo.

4-5

6.5

Gray-King Coke Type

G.G6

F.G4

HGI

Ash Fusion Flow Temp.

>1560

1430

1450

>1560

1500

>1560

Vitrinite (mmf)

Inertinite (mml)

Liptinite (mmO

Great

Wallarah

6.1 2,7

MEASURES SEAMS

NEWCASTLE Dudley

Nobbys

Victoria

Wave Hill

tustralasian

Fassifern

Tunnel

Northern

Inherent Moisture (ad)

2.6

2.4

2.7

2.9

3.1

3.0

Ash (db)

't2.t

15.5

I5.2

20.0

19.1

16.0

15.9

15.1

Volatile Matter (db)

33.4

31.7

30.3

29.8

29.7

29.0

27.8

Sulphur (db)

0.44

0.40

0.35

0.32

0.38

0,44

0.38

0.32

Phosphorus (db)

0.09

0.05

0.01

0.02

<0.01

0.02

0.01

Carbon (dmmf) Hydrogen (dmmO Nitrogen (dmmf)

84.3 5.4

83.8 5.4

83.7 6.4

84,1 5.0

84.7 5.1

84.8 4.9

Sulphur (dmm0

84.6 5.4 2.L o.46

Specific Eaergy (daO

34.9

CSNo.

2.0

1.9

1.7

t.7

1.6

0.37

0.35

0.43

0.48

0.39

0.35

34.7

34.9

34.8

34.5

34.2

34.3

34.1

6.5

4.5

2.6

2.5

Gray-King Coke Type

HGI

Ash Fusion Flow Temp.

1550

1500

>1560

Vitrinite (mmO

Inertinite (mmfl

Liptinite (mmfl

Geology of Australian Coal Basins

2tt Indicative analytical data for the various seams are

given in Table 2.

COAL MINING GEOLOGY The Greta Coal Measures crop out around the flanks of the Lochinvar Anticline, and the shallow underground resources have already been extensively mined in this area. The remaining mineable coal in this sequence is mainly confined to areas where the seams are deeper than 400m. There are currently two operating collieries in which the Greta Coal Measures are mined, one of which is in the Cranky Corner Basin. The Tomago Coal Measures have minor open cut and

shallow -underground mining potential, mlinly in the northern portion of the Newcastle Coalfieid. The central and southern areas ofthe field contain progressively deeper deposits of Tomago and Newcastle Coal Measures, with some minor deposits of open-cut potential in the Newcastle Coal Measures. Seams of the Tomago Coal Measures are now only mined from one operating colliery, and the bulk of the mining activity is concentrated within the Newcastle Coal Measures. The most extensively mined seams in the Newcastle Coal Measures are the Wallarah, Great Northern, Fassifern, Young Wallsend, Dudley and Borehole seams. Underground mining conditions are relatively good, with gentle dips in most areas, competent coarse grained interseam strata associated with many seams, and most faults and dykes being relatively minor. Ifowever, the complex three dimensional pattern of seam splitting and coalescing has a marked effect on mining activities.

Although most seams have relatively competent roof and floor rocks, problems are encountered where seams are located directly above or below tuffaceous 2laystones. In some areas these rock types deteriorate on exposure, resulting in vely poor roof conditions or floor heave, particularly where the Awaba Tuff Member constitutes the roof or floor of the Fassifern and Great Northern seams. A zone of claystone roof above the Great Northern seam also results in mining problems in some areas, affecting a number of the southern collieries in the Newcastle field. Most dykes and faults are relatively minor. The dykes are often associated with faults, and both sets of features have a preferred orientation throughout most of the coalfield. Mining in many collieries has been orientated to take account ofthese natural boundaries, but in some areas where igneous activity and faulting are concentrated br are more randomly orientated very difficult mining conditions exist. There have also been a number of instances of spontaneous combustion in the Greta seam in the Cessnock area.

legislation regarding the required minimum cover between workings and the sea floor. Because of problems of ventilation and transport, undersea mining conducted from shore-based pit-tops would be restricted to within 6 or 7km of the coast. Any mining beyond this would require the constructibn of elaborate off shore facilities. Exploration on the continental shelf would also be extremely costly.

COAL RESOURCES AND RESER\rES The Newcastle Coalfield contains an in situ coal resource of L0 700Mt, of which 4200Mt are affected by other land uses. These land uses include national parks, urban development, infrastructure and natural features such as lake foreshores and flood-prone land (Coal Resources Development Committee, 1994). The criteria used to defrne these resources are a minimum seam thickness of 1.5m, a maximum raw coal ash of 35Vo, and a maximum depth of 600m. Recoverable coal reserves in colliery holdings and exploration licences total 1050Mt (Coal Resburces Development Committee, 1994).

REFERENCES BLAYDEN, I.D., 1971: On the structural evolution of the Macquarie Syncline. PhD thesis, University of Newcastle.

BRITTEN, R.A., 1975: Singleton-Muswellbrook district. /n Traves, D.M. & King, D. (Editors): Economic Geology of Australia and Papua New Guinea 2: Coal. Australasian Institute of Mining and -

Metallurgy, M onograph, 6, 191-205.

BROWN, K.J. & PRESTON, B., 1985: A revision of the Stratigraphy of the Tomago Coal Measures. Proceedings of the 1.9th Symposiurn on Aduances in the Study of the Sydney Basin. Department of Geology, University of Newcastle, 50-5b. COAL RESOURCE DEVELOPMENT COMMITTEE, 1994: Effects of Land Use on CoaI Resources. NSW Department of Mineral Resources, Sydney. CRAPP, C.E. & NOLAN, R., 1975: Newcastle district. /n Traves, D.M. & King, D. (Editors): Economic Geology of Australia and Papua New Guinea 2: Coal. Australasian Institute of Mining and Metallurgy, M onograph, 6, 163-175.

DIESSEL, C.F.K., 1965: On the petrography of some Australian tonsteins. Max Richter Festschrift, C I au sthal -

Zellarfeld, 149-166.

DIESSEL, C.F.K., 1985: Tuffs and tonsteins in the coal

measures of New South Wales, Australia. Dixii.rne Congris International de Stratigraphie et de G6ologie du Carbonif?re, Madrid, 1,983.

DIESSEL, C.F.K., 1986: On the correlation between coal facies and depositional environments. Proceedings of the 20th Symposiurn on Ad,uances in the Study of the Sydney Basin. Department of Geology, University of Newcastle, lg-22.

With the introduction of longwall methods it has become extremely important to identify potential geological problems before commencement of mining. This has led to the introduction of horizontal drilling and in-seam seismic techniques to test the lateral continuity ofthe coal bed. Future mining in the Newcastle Coalfield is also under some threat from conflicts with expanding surface

HERBERT, C., 1976: The depositional history of the basin..In Branagan, D,, Herbert, C. & Langford-Smith, T. (Editors): The Sydney Basin. Science Press, Sydney, 5-37.

Limited undersea mining has also been undertaken from existing collieries without any major problems. The extent ofsuch operations is governed by current

MARTINI,I.P. & GLOOSECHENKO, W.A., 1985: Cold climate peat formation in Canada, and its relevance to Lower Permian coal measures of Australia. Earth Science Reuiews, 22, L07-140.

development.

Sydney Basin

213

d&S NS

.cw

ffiydney Basin -

Southern Coalfield

The Southern Coalfield embraces an area formerly divided into the Southern, South-western and Clyde River Coalfields. The location of the coalfield is

illustrated in Figure 1.

Coal was discovered in the area a few years after the first settlement in Sydney in 1788 and the first colliery was in operation by 1857 (Harper, 1915).

The Southern Coalfield now accounts for L7.6Vc of raw coal production in New South Wales (NSW

Department of Mineral Resources , 7994).

STRATIGRAPHY

M Armstrong WJ Bamberry AC Hutton and BG Jones

The economic coal seams of the Southern Coalfield occur in the terrestrial and paralic sediments of the Late Permian Illawarra Coal Measures. These coal measures overlie marine sediments of the Shoalhaven Group and are in turn overlain by the fluvial sediments of the Narrabeen Group and the Hawkesbury Sandstone (Tabie 1). The basal unit of the Shoalhaven Group is the Conjola Subgroup, which contains the Clyde River and Yarrunga Coal Measures. Although the stratigraphic relationship between these two coal measure sequences has not been adequately defined, they are regarded by Bembrick & Holmes (1976) as being stratigraphically equivalent but lithologically unconnected. Bembrick & Holmes (1976) believe the Yarrunga Coal Measures rest unconformably on Palaeozoic basement, while Shiels (1975) regards the Clyde River Coal Measures as occurring between the Pebbly Beach Formation and the basal Wasp Head Formation. The maximum known thickness of the Clyde River Coal Measures is 41m in the Clyde Valley; that of the Yarrunga Coal Measures is 65 m in drillhole intersections north of Jervis Bay. The sequence consists of siltstone, shale, minor sandstone and coal. The Illawarra Coal Measures rest conformably upon the Shoalhaven Group, with the boundary usually being gradational. In the Dapto area, however, the boundary between the two groups is well defined by the presence of latite members of the Gerringong volcanic facies. The coal measure sequence is disconformably overlain by the Narrabeen Group over most of the field, but in the extreme southern and south-western areas the Narrabeen Group is overlapped by the Hawkesbury Sandstone so that the Hawkesbury Sandstone rests unconformably on a reduced Illawarra Coal Measures section. The Illawarra Coal Measures generally average 200m in thickness, but attain a thickness of well over 400m in the north-eastern part of the field. Along the extreme southern and south-western margins, however, the coal measures are commonly <50m thick. The Standing Committee on Coalfield Geology of New South Wales (1971) subdivided the Illawarra Coal Measures into two subgroups. The lower unit, the Cumberland Subgroup, contains only minor thin seams, while the upper unit, the Sydney Subgroup, contains all of the economic coal seams. The Standing Committee has prepared a revised stratigraphy for the Illawarra Coal Measures (Standing Committee on Coalfield Geology of New South Wales, in press), and the results of this study constitute the basis of the following descriptions.

Sydney Basin

Figure 1. A. Location of the Southern Coalfield. B. Location of mines in the Southern Coalfield.

Geology of Australian Coal Basins

215

Table 1. Stratigraphy of the Southern Coalfield. AGE

SLIB.GROUP

GROUP WIANAMATTA GROUP

FORMATION BRINGELLY SHALE MINCHINBURY SANDSTONE ASHFIELD SHALE MITTAGONG FORMATION

HAWKESBURY SANDSTONE NEWPORT FORMATION

TRIASSIC

NARRABEEN GROUP

CLIFTON SUB-GROUP

GARIE FORMATION BALD HILL CLAYSTONE BULGO SANDSTONE STANWELL PARK CLAYSTONE SCARBOROUGH SANDSTONE WOMBARRA SHALE COALCLIFF SANDSTONE

BULLI COAL

SYDNEY SUB-GROUP

LODDON SANDSTONE BALGOWNIE COAL LAWRENCE SANDSTONE ECKERSLEY FORMATION

WONGAWILLI COAL KEMBLA SANDSTONE ALLANS CREEK FORMATION DARKES FOREST SANDSTONE BARGO FORMATION

ILLAWARRA COAL MEASURES PERMIAN

TONGARRA COAL

CUMBERLAND SUB-GROUP

WILTON FORMATION ERINS VALE FORMATION PHEASANTS NEST FORMATION BUDGONG SANDSTONE BERRY SILTSTONE NOWRA SANDSTONE WANDRAWANDIAN SILTSTONE

SHOALHAVEN GROUP CONJOLA SUB-GROUP

SNAPPER POINT FORMATION

PEBBLY BEACH FORMATION WASP HEAD FORMATION

Cumberland Subgroup The Curnberland Subgroup is quite variable in thickness, ranging from 60m in the south to 200m in the north-east. The sequence comprises two formations (Figure 2), which thin rapidly towards the western margin of the basin. They also lens out to the south and south-west, where they are overlapped by the Sydney Subgroup (Figures 3 to 5). Stratigraphic and sedimentological data for the Cumberland Subgroup are sparse over most of the Southern Coalfield, since relatively few exploration

drillholes penetrate this part ofthe succession.

The lower unit of the Cumberland Subgroup, the Pheasants Nest Formation, is characterised by flat-bedded lithic sandstone and latite, interbedded in places with carbonaceous claystone and coal. The latite members, which are restricted in outcrop to coastal exposures, are the Five Islands Latite Member, the Calderwood Latite Member, the Minnamurra Latite Member and the Berkerly Latite Member. Two lenticular coaly units in the Mount Kembla area are named the Unanderra and Figtree Coal Members. Application of this nomenclature, however, is restricted, due to a scarcity of outcrop and lack of penetrating bores. Plant remnants,

including rootlets, are common throughout this

formation and fossil logs (both in situ and locally transported) are present in outcrop. The overlying Erins Vale Formation consists of thin bedded to massive lithic sandstone with minor siltstone and conglomerate horizons. The sandstone is characterised by an abundance ofburrows, and was deposited on a shallow marine shelf. In the north-eastern part of the coalfield, the Erins Vale

Formation interfingers with the Kulnura Marine Tongue (Agnew & others, this volume), a silty unit containing numerous shelly fragments. A thin sequence of swaley cross-bedded and burrowed sandstone is also preserved at the top of the formation in some areas, reflecting upper shoreface conditions.

Sydney Subgroup The Sydney Subgroup is about 120m thick over a large part of the coalfield. It thins to <50m along the southern and south-western margins, but is up to 300m thick in the north-east. The unit is divided into 14 formations, as well as a number of members

which vary in their lateral extent.

The basal unit, the Wilton Formation, rests conformably upon the Erins Vale Formation. It

Sydney Basin

216 consists of Iaminite and fine grained sandstone above the Woonona Coal Member and coarse-grained

to conglomeratic, sublithic sandstone below this interval. The unit has a maximum thickness of 100m (Wass & others, 1969). In places, however, trough and planar cross-bedded quartz-lithic sandstone and pebble conglomerate mark the base of the formation and rest upon the underlying sediments with a locally disconformable contact. This basal unit is correlated with the Marrangaroo Conglomerate (McElroy & Relph, 1961), which is well-developed along the western margin of the basin and consists of coarse grained sublitharenite with minor conglomerate and carbonaceous siltstone interbeds. The lateral equivalent along the eastern margin of the coalfield is the Thirroul Sandstone (Standing Committee, 1994), but Bamberry (1991) suggests that this unit was sourced from the east. The Woonona Coal Member at the base of the Wilton Formation forms a broadly lenticular unit comprising dull coal and numerous bands of clayitone. This unit occupies a similar stratigraphic position to the Lithgow Coal in the Western Coalfield (Yoo & others, this volume), and has been correlated with this unit on the basis of its petrographic composition (Hunt & others, 1984). The Woonona Coal Member merges with the Tongarra Coal in the south of the Coalfield. The remainder of the Wilton Formation consists of flat-bedded to laminated, bioturbated claystone and siltstone with several upward coarsening sandstone units developed in the upper part ofthe section. Overlying the Woonona Coal Member in the western section of the coalfield is the Wanganderry Sandstone Member. This unit consists of coarse grained sandstone, and is similar in composition to fhe Marrangaroo Conglomerate (Yoo & others, this volume). The Tongarra Coal, overlying the Wilton Formation, consists ofdull and bright coal separated by bands of light-coloured claystone and carbonaceous shale. This seam is recognised over a large part ofthe

coalfield, and is subject to splitting in the Avon and Burragorang areas. It is thickest in the Dapto Macquarie Pass area, and becomes thinner and more interbanded away from this depocentre. The Tongarra Coal is overlain by the marine Bargo Formation, comprising a sequence of flat-laminated and bioturbated claystone, which passes upwards

into siltstone and fine-grained, quartz-lithic sandstone of the Darkes Forest Sandstone. Several metres above the base of the Bargo Formation is a tuffaceous claystone bed up to 0.7m thick. This unit is referred to as the Huntley Claystone Member. The Bargo Formation and the Darkes Forest Sandstone represent a single coarsening upwards unit reiognisable on a basin-wide scale (Stunt'2, 1972), with-correlatives in the Baal Bone Formation and Angus Place Sandstone in the Western Coalfield (Bembrict<, 1983) and the Denman Formation and Watts Sandstone in the Hunter Valley area (Sniffen & Beckett, this volume). The Allans Creek Formation, overlying the Darkes

Forest Sandstone, consists of up to four coaly or carbonaceous horizons separated by an interbedded sequence of claystone and siltstone with minor sandstone. The upper unit in the Mount Kembla area is the American Creek Coal Member, consisting of 4.4m of coal and dirt bands.

The Kembla Sandstone overlies the Allans Creek Formation with marked disconformity. The unit fines upward from trough and planar cross-bedded lithic s-andstone to thin-bedded and ripple cross-laminated sandstone and mudstone. Silicifred logs, pebble lenses and laterally discontinuous claysfone interbeds are common features in outcrop. The Wongawilli Coal is represented by a sequence, 9m to 1lm thick, ofcoal and carbonaceous claystone with laterally persistent pale claystone bands. The claystone baircls are composed of kaolinite and are unusually indurated, and hence are comparable to the kaolin tonsteins of the Westphalian Coal Measures of Europe (Loughnan, 1971). A particularly thick-(1m) claystone bed, known as the Farmborough Claystone Member, can be traced from coastal exposures through the subsurlace to the Burragorang Valley. The Wongawilli Coal

deteriorates in quality in both the northern and southern parts of the field, with an associated thick development of mudstone and claystone at the base of the formation.

The Eckersley Formation, immediately overlying the Wongawilli Coal, contains a number of recoglised member units (Figure 2). The basal section of the formation is commonly represented by interbedded and interlaminated siltstone and claystone with numerous bioturbated horizons, but the remaining section of the formation is characterised by planar cross-bedded sandstone and siltstone which, in turn, is often capped by carbonaceous shale and/or coal (Woronora, Hargrave and Cape Horn Coal Members). Many of these sequences exhibit fining-upwards sequences. The Eckersley Formation exhibits considerable lateral variation. For example, the Novice Sandstone Member, the Woronora Coal Member and the Hargrave Coal Member are limited to the north-eastern part of the coalfield whereas the stratigraphically higher Cape Horn Coal Member can be recognised as far west as the Burragorang Valley. The Woronora Coal Member may represent a possible split of the Wongawilli Coal (Wilson, 1976).

A pale-coloured, finely bedded, siliceous claystone and siltstone (Burragorang Claystone) occurs beneath the Balgownie Coal in the Burragorang Valley, and can be recognised in drill core as far south as Yerrinbool. This unit is not present in the central part ofthe coalfield, but re-appears further to the east and north-east. It is believed that the unit was eroded prior to the deposition of the Lawrence Sandstone within the central area. Towards the southern and south-western margins of the coalfield the Balgownie Coal and the Loddon Sandstone are not developed, because ofthe low rates of subsidence which occurred in these areas, and the Bulli Coal is separated from the Burragorang Claystone by a thin interval of carbonlceous claystone. Also in these areas, the claystone and coal of the lower Eckersley Formation merge with the upper Wongawilli Coal, and the Buriagorang Claystone rests directly on the

Wongawilli Coal.

The Balgownie Coal overlies the Burragorang Claystoie Member in the west and the Lawrence Sandstone in the east. It is a widespread and laterally continuous coal seam. The Loddon Sandstone occupies the interval between the Bulli Coal and the Balgownie Coal, and

Geology of Australian Coal Basins

217

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Sydney Basin

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Geology of Australian Coal Basins

219

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1 - DM Camden DDH 75 2 - DM Camden DDH 73 3 - DM Camden DDH 71 4 - DM Camden DDH 64 5 - DM Camden DDH 57 6 - DM Camden DDH 53 7 - DM Wollongong DDH 44 8 - DM Wollongong DDH 37 9 - DM Wollongong DDH 21 10 - DM Wollongong DDH 79 11 - AiS Dendrobium DDH 1 12 - DM Wollongong DDH 81 13 - AIS Nepean DDh 2A 14 - ARMCO Illawarra DDH 12 15 - ARMCO Illawarra DDH 8 16 - ARMCO Illawarra DDH 17 17 - Fitzroy Falls'F

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Figure 5. Location of cross-sections shown in Figures 3 and 4.

Geology of Australian Coal Basins

Coalfield Boundary

221 consists of lithic sandstone with minor siltstone, claystone and rare conglomerate. It commonly comprises two or more fining-upward seque-nces, and becomes more shaly towards the margins of the unit. The Loddon Sandstone occurs over most ofthe coalfield, except where the Bulli Coal and the Balgownie Coal merge, for example south of Bargo. the Loddon Sandstone is divided into two units near the northern boundary ofthe coalfield by the Balmain Coal Member. Where this seam is present, the unit between the Bulli Coal and the Balmain Coal Member is known as the Dural Sandstone Member. The unit between the Balmain Coal Member and the Balgownie Coal is the Penrith Sandstone Member. The Bulli Coal, of well-banded coal and minor claystone, forms the top of the hlg\ept fining-upwards sequence in the Loddon Sandstone. The 6ase of this seam is often marked by carbonaceous claystone containing abundant root traces. The Bulli Coal, formally defined as the uppermost unit of the Illawarra Coal Measures, is disionformably overlain by the Coal Cliff Sandstone of the Narrabeen Group. In some areas, however, a sequence of interlaminated carbonaceous and fine claitic sediment, referred to as the Wombarra Shale, conformably overlies the Bulli Coal instead. This carbonaceous sequence appears to have closer lithological affinities with the coal measures than with the coal-barren Narrabeen Group. The stratigraphic sequence ofthe Southern Coalfield can be traced-to the north to merge with the stratigraphies of the Newcastle and Hunter Coalfields (Hill & others, 1994).

Igneous Activity Igneous rocks occur throughout the Sogthern Coalfreld as dykes, sills and volcanic plugs or necks. Dykes may occur separately or as members of a swarm. They often display the same orientation as faults and joints and consist of olivine dolelite, monchiquiie or camptonite (Wilson, 1976). In the Burragorang district they are often composed of clay minerals, which are indicative of low temperature emplacement and late stage hydrothermal alteration (Mcl,ean & Wright, 1975).

Thick syenite intrusions are present in the vicinity of Mittagong, in the south-west. The Wongawilli seam in this area has been intruded by a syenite sill which has locally increased the coal rank to anthracite (Read, 1975). DE P O SITIONAL EI{VIRONMENTS

The Illawarra Coal Measures accumulated on the stable shelf margin of the Sydney Basin, and tle low subsidence rate issociated with this area is reflected by the sedimentary sequence. This is observable down to the scale of the coal seams, where widespread similarity in petrographic co-mposition indicaie stable depositional conditions (Shibaoka & Smyth, 1975). The inertinite content of the coal is high and increases towards the top of the seams. This upward increase reflects emerge-nce-of the peat above the water table during regional subsidence.

In the northern part ofthe coalfield, however, the coal measures thicken markedly over a north-westerly trending'hinge line' along the . Woronora Aniicline (Figure 6). The 'hinge line' effectively represents a boundary between the shelf and trough aieas ofthe basin, and the basin

suffered more rapid subsidence to the north-east of

this feature (Bembrick & others, 1973).

The Permian and Triassic sequence in the southern part of the Sydney Basin generally shows a broad iegressive tr-end from the nearshore marine and pa"ralic environments of the Shoalhaven Group to lh" ,rpp"r delta and alluvial plain settings of the Narri6een Group. The Cumberland Subgroup at the base of the Illawarra Coal Measures was largely

derived from a volcanic source to the east (Gerringong volcanic facies) and quartzose basement rocks ofthJLachlan Fold Belt to the south-west and west. Sedimentary structures and sequences in the Pheasants Nest Formation are indicative of fluviatile sedimentation, with periodic development of floodplain and swamp conditions. Such features are characteristic of delta plain environments, as was suggested by Bowman (L974;1980). This sequen66 probabiy graded laterally northwards into the paralic and shallow marine sequence of the upper Shoalhaven GrouP. Following the northward progradation of the Pheasant's Nest Formation, a transgressive episode resulted in the deposition of marine sediments over large areas of the Sydney Basin. Nearshore silty run-"dr (Erins Vale Fbrmition) and deeper water silts (Kulnura Marine Tongue) represent this marine incursion in the Southern Coalfield. The Erins Vale Formation represents sand accumulation on the southern shoieline of the broad estuarine Kulnura embayment. The formation is 37m thick in the Illawirra coastal section and becomes thicker and finer grained westwards and northwards where it grades into the Kulnura Marine Tongue. The Erins Vale Formation is characterised by intense bioturbation which produced the typically massive beds of poorly sorted fine-to-medium grained sandstone, 0.1m to 1m thick, with a few mudstone interbeds and scattered dropstones up to 0.2m in diameter. Some coalified woody material is present, especially on the tops-of tlre beds. At the t^op bf tn" Erin3 Vale Formation a local development of cross-bedded, well sorted sandstone accumulated as an emergent beach deposit (Jones & Hut.ton, 1984) during the subsequent regressive phase (Branagan

& others, 1976).

The Sydney Subgroup, containing the economic coal seami of tlie Soulhern Coalfield, was deposited during a major phase of delta progradation from the Newcistle region. The sequence coarsens--u-pwards from lower delta plain sediments in the Wilton Formation to morle fluvial-dominated upper delta plain deposits in the Eckersley Formation. The coals within the Sydney Subgroup reflect the stable depositional conditions of the shelf are-a, at the more-distal end of the southward-prograding deltaic wedge. This is indicated by the following features: . Splitting is virtually absent in the Illawarra Cbal Me"asures. Thd splits that do occur (i.e. in the Woonona and Tongarra seams) are in proximity to non-meandering channels. . The coals (with the exception of the Wongawilli Coal) are poor in vitrite plus clarite. This is .sc.ibud tb a greater deglee of-degradation of the peat due tlo slow bur-ial and preservation (Bri-tten & others, 1975). r The coals are characterised by their low sulphur content; all have lessthan 27o and

Sydney Basin

222 most have less than 0.57o sulohur. This indicates that the waters of the delta receiving basin had a low sulphate content, and probably represented a bracliish to fresh water embayment or lake rather than open marine conditions. This would also account for the relative scarcity of shoreface deposits in the Sydney Subgroup. The Sydney Subgroup is locally disconformable with the underlying units in places, especially along the south-western margin of the basin where the sandstone and conglomerate of the Marrangaroo Conglomerate equate with the alluvial facies of Havord & others (1984). In this area the Woonona Coal Member developed in interlobe areas of fluvial braided channel deposits derived from the Lachlan Fold Belt. Coastal outcrops of the Thirroul Sandstone, however, represent discrete distributary channel sequences with associated coal-bearing backswamp deposits. The Woonona Coal Member is characterised by a low vitrinite and high inertinite content, which enables the unit to be correlated with the Lithgow seam and other basin-wide equivalents

(Hunt & others, 1984). This unique petrographic character is ascribed to subaerial oxidation ofthe peat rising above the water table, with the intensity of degradation increasing towards more elevated

margrns.

The bulk of the Wilton Formation comprises

laminated and bioturbated interdistributary bay shale and delta margin sequences. Crevasse splay and overbank sands near the top of the formation are often capped by thin but laterally persistent beds of carbonaceous shale, palaeosol horizons and coal. The lack of lateral accretion products such as point bar deposits in the Wilton Formation is probably due to low sinuosity channel patterns in the lower delta plain distributary system. The Tongarra Coal formed as a blanket peat on the abandoned detrital lenses of interdistributary bay-fill sequences in the Wilton Formation. The

alternating bright (vitrinite-rich) and dull (inertinite-rich) bands in the coal reflect changing oxidation conditions and water table levels within the swamp. At the top of each coal ply the seam becomes very dull, indicating a period of emergence prior to the deposition of thin bands of overbank sediment.

The Tongarra Coal is locally overlain by very weathered sandstone representing lenticular distributary channel facies. The immediate overlying units comprise a single coarsening upwards unit consisting of shallow bay-fill and interdistributary bay facies (Bargo Formation) overlain by a sequence of distributary mouth-bar, distributary channel and crevasse splay sandstones (Darkes Forest Sandstone). Palynological evidence suggests synchronous basin-wide deposition of these formations and their correlatives (McMinn, 1985). The AIIans Creek Formation gradationally overlies this succession and comprises a fining upward sequence of crevasse splay, lacustrine and peat swamp deposits formed in interdistributary areas behind the river-dominated, southerly-prograding delta that produced the Darkes Forest Sandstone

unit.

The Kembla Sandstone marks the onset of

predominantly fluvial deposition in the upper Sydney Subgroup. The well-defined sequence in the Kembla Sandstone combined with the lobate isopachs and the southerly trending palaeocurrent data (Bowman, 1980) indicate a distributive

drainage pattern typical of lower delta plain settings. This southerly drainage pattern and the abundance of volcanogenic detritus in the Kembla Sandstone indicate derivation from the New England Fold Belt (Jones & Hutton, 1984). Silica, released during the early diagenetic breakdown of the volcanogenic detritus, was incorporated into the pores of logs deposited within the sandstone. The thicker sand-dominated multiple distributary or meandering channel facies are separated by thinner silty interdistributary or floodplain facies. Cross-bed set size decreases upwards through the sequence, and the top of the sandy section comprises ripple-bedded levee deposits cut and interspersed with crevasse splay sandstone. These overbank deposits are capped by floodplain siltstone, dark backswamp siltstone with common vitrinite-rich coalified woody fragments, and carbonaceous

lacustrine siltstone (Jones & Hutton, 1984).

The thick and banded nature ofthe overlying Wongawilli Coal, combined with the relatively high proportion of vitrite and clarite in the seam, also reflects a regional increase in subsidence rate (Britten & others, 1975). The great areal persistence of the Wongawilli Coal implies existence of extensive tracts of thick peat swamp and lacustrine deposits. More widespread interdistributary lacustrine facies occur in the basal Eckersley Formation, immediately overlying the Wongawilli Coal. Numerous burrows, mud cracks and thick carbonaceous shale beds characterise this particular horizon. The section of the upper part of the Sydney Subgroup from the Lawrence Sandstone to the Bulli Coal was deposited in a river-dominated environment, representing a transition from lower delta plain to upper delta plain environments. The sandstones in this part of the formation characteristically fine upwards, and are often capped by coal members. This cyclicity has been recognised by several workers (Booker, 1960; Duff, 1967; Bowman, 1974). Using an embedded Markov chain model, Jakeman (1980) recognised a fining upwards cycle comprising coal - coarse sandstone fine sandstone - interbedded fine clastics - mudstone - coal. This she attributed to point bar development in a predominantly upper delta plain or fluvial environment. The number of fining-upwards cycles increases with an increase in total formation thickness, a factor related to the total net subsidence ofthe area and reflected in the impersistency of thin coal members within the Upper Sydney Subgroup where the thickness of this sequence is reduced. Cyclicity is also preserved in the coals in the upper parts ofthe Sydney Subgroup. Smyth & Cook (1976) delineated cycles exhibiting an upward increase in the ratio of inertinite to vitrinite, and interpreted these as 'drying upwards' cycles due to varying degrees of oxidation with peat

accumulation above the water table .

The Bulli Coal marks the top of the uppermost

fining upwards sequence in the Illawarra Coal

Measures. The seam rests on a thick, competent sandstone containing impressions and silicifred remains of logs and tree stumps, which provided a stable foundation for prolonged and extensive peat accumulation. The sandstone is overlain by very carbonaceous overbank siltstone, and passes up into a palaeosol unit and the thick, well-banded Bulli coal seam. Banding within the seam probably

reflects differences in oxidation within the peat swamp. Both the coal seam and many bands within

Geology of Australian Coal Basins

223 the seam can be traced throughout the Southern Coalfield, indicating that the formation must have been deposited in a very broad shallow swamp or Iacustrine environment. The Bulli Coal varies from high volatile to medium volatile bituminous rank. These variations probably reflect variations in cover thickness since the rank increases northwards towards the centre of the basin (Facer & others, 1980). In places the Bulli Coal is capped by a thin overbank to shallow lacustrine unit of interlaminated sandstone and siltstone containing rare freshwater Unio fossils. The swampy conditions of the upper Illawarra Coal Measures gave way to fluviatile deposits of the Narrabeen Group (Ward, 1972). The absence of coal in the Narrabeen Group may be due to a lack of suitable peat-forming flora (Gould & Shibaoka, 1980) or may reflect a drier climate and the predominantly oxidising conditions on a better drained fluvial fl oodplain.

Further north, between Sydney and the Hawkesbury River, the coal measure sequence is thought to grade from a lower delta plain sequence in the lower half to an upper delta plain sequence towards the top. The majority of the upper part of the sequence was deposited in a fluvial point bar and braided stream environment (Herbert, 1983).

STRUCTURAL GEOLOGY The dominant structure in the Southern Coalfield is the northerly plunging Camden Syncline (Figure 6). This structure represents the axis of the Sydney Basin, and was active during sedimentation (Bowman & Mullard, 1986).

A series of folds with ESE trending axes are developed on the eastern limb of this syncline (Figure 7), plunging towards the north-west. Bowman (1974) has reported that these structures were active during Late Permian sedimentation. A number of similar trending faults, with throws up to 90 m, are also associated with the folding. Wilson (1969) states that these increase in throw with depth, suggesting that faulting was contemporaneous with sediment deposition. The predominant structures on the western limb of the Camden Syncline are a series of north-south trending monoclines and faults. Two of these features, which have displacements of up to 100m, are the Lapstone Monocline/I.{epean Fault and the Oakdale Monocline. These features are sub-parallel to the structure contours on the top of the Illawarra Coal Measures, and the direction of downwarping is always towards the basin centre. Displacement is greater on the western limb monoclines than in those on the eastern limb and the southern nose of the syncline. These structures represent hinge lines that separated the central areas of the basin, with a relatively high degree of subsidence, from the more stable shelf areas adjacent to the western margin. Two domes, the Mount Lindsay and the Mount Burke Domes, are located in the southern central part of the coalfield. These domes are approximately 3km in diameter, and are located close to the basin axis. Igneous activity is regarded as being the major

contributing factor in the formation of these structures (Wilson & others, 1958).

The majority of faults in the Southern Coalfield are normal faults, although strike-slip and high angle

reverse faults are known to exist as well (Bowman & Mullard, 1986). Displacement on these faults ranges up to 100m, and the faults themselves vary from single fractures to zones more than 100m wide. The displacement is known to vary both along strike and with depth. Horst and graben structures also exist in areas where a series ofparallel to subparallel

faults occur.

Interpretations of tectonic history suggest that the Southern Coalfield has been subjected to an east-west compressive stress, probably related to a subduction process to the east ofthe Australian continent (Scheibner, 1976). The Camden Syncline is the principal feature associated with this stress field. Bowman & Mullard (1986) state that the region was also subjected to NE-SW compression during the same period, a stress field associated with the formation of the faults and folds on the eastern limb of the Camden Syncline. Since the Cainozoic the Southern Coalfield has been subjected to a north-south compressional stress (Gray, 1982).

ECONOMIC COAL SEAMS The basal seam of the Illawarra Coal Measures, the Woonona Coal Member, occurs near the base of the Wilton Formation and crops out along the Illawarra escarpment. It consists of a thin, discontinuous coal seam which grades laterally into carbonaceous sediments (Bowman, 1970). The maximum recorded thickness is 5.7m at Mount Kembla. The Tongarra Coal is generally between 2 and 3m in thickness, and characteristically consists of interbanded dull and bright coal with interbanded tuffaceous claystone. The area ofits highest economic potential occurs to the south and west of Dapto. The American Creek seam consists mainly of carbonaceous shale and coal, with minor discontinuous sapropelic coal units. It has a maximum thickness of 7.5m, but local washouts and areas of non-deposition have contributed to its

discontinuous nature (Wilson, 1976).

The Wongawilli Coal consists of 3 to 9m of interbedded coal, carbonaceous claystone, claystone, tuff and sandstone (Bowman, 1970). The basal L.8m to 3.7m of the seam contains coal of commercial quality (Wilson, 7976), with best development between Wollongong and Berrima. The Woronora Coal Member consists of a coaly sequence with interbedded carbonaceous mudstone, siltstone and sandstone. This seam is best developed in the area underlying Woronora Reservoir. It reaches a maximum thickness of 12m, but does not contain any coal of economic significance. Due to the nature of the coal and the lack of characteristic banding, Bunny (1969) suggested that the seam was allochthonous in origin. The Balgownie Coal generally consists of interbanded dull and bright coal with minor interbedded mudstone in coastal exposures, but deteriorates to interbanded dull and bright coal, with the upper half consisting of carbonaceous mudstone, in the Burragorang Valley. The seam usually ranges from 1 to 1.5m in thickness, but reaches a maximum thickness of 4m in the north. It consists of dull and bright coal with carbonaceous mudstone at the base.

Sydney Basin

224

NEW SOUTH WALES

I /l \/-ebo \

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Llverpool a

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FAULTS A FOLOS

06'1o162026 coB 1

Figure 6. Structure contours on the top of the Illawarra Coal Measures in the Southern Coalfield. The Bulli Coal consists of 2 to 3m of interbanded bright and dull coal with minor carbonaceous mudstone interbeds and sideritic penny bands.

A similar replacement by non-coal sediments occurs in the central sector, while the seam is absent further south due to either contemporaneous erosion or non-deposition.

The area of greatest economic potential is restricted to the northern sector of the coalfield, but towards the northern boundary of the field the coal is replaced by carbonaceous mudstone and splitting of

-km Wilson (1976) has noted that the seam is relatively thick in the troughs of synclines and downthrown fault blocks and relatively thin on the crests of anticlines and upthrown fault blocks. As these

the seam occurs.

Geology of Australian Coal Basins

225

SUTHERLAND _+

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Figure 7. Named structural features in the Southern Coalfield (after Bowman & Mullard, 1986). features are not observed in the underlying seams, it is suggested that deposition was contemporaneous with faulting and differential subsidence.

COAL QUA,LITY AND UTILISATION The Illawarra Coal Measures contain up to eleven named seams, of which two, the Bulli and Wongawilli, are currently mined. The Balgownie and Tongarra seams were also mined until relatively recently. The Balgownie and Tongarra seams display greater variability in properties, and their economii development is more limited in geographic extent. Indicative coal analyses from these seams are detailed in Table 2. The Bulli seam is by far the most important seam in the region, providing the highest quality coking coal available in New South Wales. Although traditionally a source of low and medium volatile coking coal for domestic and export markets, the Bulli and Wongawilli seams are now also providing substantial tonnages offuel coal, either in the raw state or as a middlings product. The Bulli seam generally ranges from 2 to 3m in thickness. In the central and coastal areas of the coalfield it yields a low volatile, high rank coking coal. Volatile matter ranges from approximately 18 to 23Vo (air dried). The ash level may be relatively high in the raw coal, but can usually be beneficiated

to around 8 to ljVo (air dried). The sulphur content, like that of most other Australian coals, is very low (0.47o). The crucible swelling number is usually 5 to 7. Although the vitrinite content is only moderate (e.g. 45Vo) and the inertinite content rather high (e.g. 50Vo), the Bulli seam is an excellent low volatile component of coking blends.

In the Burragorang Valley and in the BargoTahmoor area the Bulli seam yields medium volatile, medium rank coking coal. Volatile matter ranges between 26 and 307o (air dried), ash is around 8.57o (air dried), total sulphur 0.4Vo (air dried) and crucible swelling number about 6. The

vitrinite content ranges from 40 to 50Vo and the fluidity ranges from medium in the Burrago{ang Valleyto high in the Bargo-Tahmoor area. This coal is an excellent semi-hard coking coal for use as a medium volatile component of coking blends.

The Wongawilli seam is present over the greater part of the coalfield, but it is, in general, a high-ash seam with both abundant dirt bands and a high percentage of inherent ash. The seam is mined as a ioking, steaming or cement works coal, but can also be washed to produce various coking and steaming fractions from the one area. The Wongawilli seam is mined at a number of collieries to yield a high fluidity, medium volatile coking coal. Typical properties ofthis coal are as

Sydney Basin

226

Table 2. Indicative eoal quality foi the Illawarra CoaI Measures. Wollongong

Bulli

Balgownie Wongawilli

Mittagong Burragorang Valley Bulli Tongarra Wongawilli

Proximate Analysis (Vo a.d,.) Inherent Moisture

0.9-2.4

1.1-1.4

Ash

8.2-12.9

10.9- 11.1

Volatile Matter

18.8-30.2 60.6-70.2

Fixed Carbon

Calorific Value (MJ/kg) (d.a.f.) Crucible Swelling Number Gray King Coke Type Hardgrove Grindability Index Ash Fusion Properties - Flow temperature (oC)

2.0

r.7

16.8 6.8 77.2

8.4

22.2-23.0 66.1-66.7

23.6 60.8

35.6

35.8

37.0

34.5

2-7

6-7

5-8

F-G4

G3.G8

G4-G9

G1 65

+1600 29-69 0.91- 1.31

1300 80

Carbon (d.a.f.) Hydrogen (d.a.f.) Nitrogen (d.a.f.) Oxygen (d.a.f.) Carbonates (d.a.f.) Phosphorus (d"b.)

85.4-88.9

87.5-89.0 4.8-5.0

0.01-0.09

3.9-5.2 0.3-0.5 0.01

Chlorine (d.b.) Total Sulphur (d.b.)

0.01-0:03 0.3-0.5

0.4

Roga Index Rv maxVo

t.4 15.6

1.L-2.0 10.5-17.9 24.2-30.8 52.3-63.2

r,32

1550

65-85 1.36-1.43

1.4-I.9 4.2-8.r 0.1-0.7

1.6- 1.7

Maceral Analysis (7o) Vitrinite 30-59 61 Liptinite tt-4 tr Micrinite 8-22 5 Semifusinite 2L-43 27 .f Fusinite 1-3 Mineral Matter 4-6 4 x dmmf follows: ash L4Vo (air dried), volatile matter 24 to 28Vo (air dried), crucible swelling number 7 to 8 and vitrinite content 60 to 80Vo. Wongawilli seam coal is ideally suited to blending in large proportions with high rank coking coal, especially where an increase in the ratio ofreactives to inerts is sought. The high vitrinite content can be used to make up for the deficiency of vitrinite in the Bulli seam, with the added bonus oflow sulphur and low phosphorous from the Wongawilli coal. The Balgownie seam is usually less than 1.2m thick, with its area of major economic development confined to the eastern side of the coalfield north of Wollongong. It thickens to 4m and improves in quality to the north-west near Campbelltown, but occu.rs at depths currently too great for economic mrnrng.

In its area of best economic development, the Balgownie seam has qualities similar to Bulli seam coal, and has some potential for extraction in conjunction with that overlying seam. The Tongarra seam has widespread occurrence, but deteriorates away from the area where it has been mined south of Dapto. In the area of economic development it is a high ash coal, similar to the Wongawilli seam but with a low proportion of

reactive macerals.

35.4 5

1500

+ 1600

0.8-1.0

5.1 1.9 5.5

*91.7 *3.2 *2.0 *2.4

*86.0 *5.1

0.8 0.10

0.005

0.05

0,6

-o.z

-o.n

1450 59 1.42

Ultimate Analysis (7o) 4.6-5.2

35.0 0-1

26.8 64.8

86.5-87.3 5.2-5.4 1.7-1.9 4.6-9.0 0.1-0.6 0.01 0.01-0.02 0,5-0.7

87.1

66-79

* 1.8

*7.0

tr-7

2-8

9-23

l-4

4-L3

COAL MINING GEOLOGY The predominant mining method practised in the Southern Coalfield is the longwall system. This system accounts for 88Vo ofthe output from South Coast mines and all of the output from the Burragorang Valley area. Although the method is potentially the most productive and safest available for the foreseeable future, some mines in the Southern Coalfield are not in a position to use the longwall system, due to inherent geological complexities and/or market limitations (Australian Coal Consultative Council, 1985). Roof conditions in the Southern Coalfreld are an important consideration in mining, as they can

contribute significantly to colliery operating costs.

The roof of the Bulli seam consists of mudstone, laminite or sandstone, with sandstone generally forming the most competent roof and mudstone the most incompetent. The coal and mudstone roof of the Wongawilli seam is subject to bed separation and

eventual failure associated with the formation of tension fractures (Wilson, 1975).

The inherent instability of any roof lithology may be exacerbated by the thickness of the beds, the presence of channel sandstones and associated cross bedding, the intensity ofjointing and joint-set intersections and the magnitude of lateral compressive stresses.

Geology of Australian Coal Basins

227

,a.ar€, Pxt fUct Coi.. and Urbd D.J.lop.nt,

LEGS

. ross YALE

tli[ or Co.r 1...!,.. t.dr. aOO. Cor.. lld lrr..t lcdc

oi c&t.. !!l oi a.ttt a.-

Figure 8. Extent of coal resources in the Bulli seam (after Australian Coal Consultative Council, 1985). Depending on the magnitude of the throw, faults may act as a barrier to coal mining. With the increasing usage of longwall techniques, however, even faults with a throw greater than one metre may be expected to present major obstacles to the economic extraction of parts of the Bulli and

Wongawilli seams.

and high capacity ventilation systems are required to keep these gas levels below prescribed safety limits. The gases, in combination with mylonised fracture systems, often give rise to outburst zones. Difficulties in mining have also been experienced where gas reservoirs in sandstones of the overlying Narrabeen Group have been tapped during the

formation of longwall goaves.

Hummock-shaped bodies of mudstone, referred to as stone-rolls, extend into seams in some areas from the floor. These features average approximately 1m in height and 4m in width. They are usually found in the Bulli seam, south of the Coledale Fault (Baker & others, 1986). The principal effect ofthese structures is to reduce in productivity and increase dilution of the run of mine coal product. The Southern Coalfield has experienced extensive destruction of its coal seams by igneous intrusions, with ingestion of the coal by igneous material and development of adjacent cindering. Unaltered

igneous material often constitutes a barrier to mining and altered (kaolinised) material can cause processing problems in coal preparation plants.

High levels of methane and carbon dioxide are a common feature of coal mining activities in the Southern Coalfield. The average gas concentration in the norfhern part of the coalfield is approximately 12 to 15mo per tonne of coal (Baker & others, 1986),

High remnant tectonic stresses exist throughout the majority of the Southern Coalfield, with a lateral component up to five times the vertical stress. Depending on roadway orientation, these stresses can exacerbate poor roof conditions and promote convergence of the roof and floor strata.

COAL RESOURCES AND RESERVES Saleable production from collieries within the Southern Coalfield is currently about 16Mt per year. The remaining life of reserves within colliery holdings is approximately 100 years, but factors such as coal quality, unforeseen geological hazards and sterilisation for socioeconomic reasons are likely to reduce this figure (Australian Coal Consultative Council, 1985). The geographic extent of Bulli and Wongawilli seam resources are illustrated in Figures 8 and 9.

Sydney Basin

228

"r'{ LfGEiO

ll6t

ot Co.t 1...!...

tOOi

Cor.r

Ert.rt

ol coxt.rt..

Ecorodc

LtiI

Crna...a

1o...

Lln.

ot lone.rllt

6aai

fhara Ara tanf SNt! tnt.urto'a .nd Ctnda. At.aa 16 tha South aDd F'aaa.

Figure 9. Extent of W'ongawilli seam resources (after Australian C""l';:;:;ltative The total in situ coal resource in the Southern Coalfield is estimated to be 17 045Mt of which 4085Mt are affected by other land uses. These land uses include national parks, infrastructure, stored waters, Commonwealth land and natural features. Coal in the Southern Coalfield has been considered as a resource if there is a minimum seam working section thickness of 1.5m and a maximum of 357o ash for the raw coal. No limits have been placed on the depth of the coal, because mining is likely to occur over the next decade at depths greater than 550m (Coal Resource Development Committee, 1994).

Total recoverable reserves for the Southern Coalfield are 1160Mt in colliery holdings and exploration licences (Department of Mineral Resources, 1994).

REFERENCES AUSTRALIAN COAL CONSULTATIVE COUNCIL, 1985: Study on the future of the New South Wales Southern and South-Western Coalfields. Report by Working Party No. 5. BAKER, C.J., MULLARD, B.W. & WALSH, L., 1986: Coal. In Sherwin L. & Holmes G.G.: Geology of the Wollongong and Port Haching 1:100,000 sheets, Geological Survey of New South Wales.

Council, 1985).

BAMBERRY, W.J., 1991: Stratigraphy and sedimentology of the Late Permian Illawarra Coal Measures, Southern Sydney Basin, New South Wales. PhD thesis, University of Wollongong.

BEMBRICK, C.S., 1983: Stratigraphy and sedimentation of the Late Permian Illawarra Coal Measures in the Western Coalfreld, Sydney Basin, New South Wales. Journal and Proceedings of the Royal Society of New South Wales, 116' 105-117. BEMBRICK, C.S., HERBERT, E. & STUNTZ, J., I.973: Structural subdivision of the New South Wales portion of the Sydney-Bowen Basin. Geological Suruey of New SouthWales, Quarterly Notes,ll, 1-13.

BEMBRICK, C.S. & HOLMES, G.G., 1976:AN interpretation of the subsurface geology of the Nowia-Jervis Bay area. Records of the Geological Suruey of New South Wales, 18(1)' 5-68. BOOKER, F.W., 1960: Studies in Permian sedimentation in the Sydney Basin. New South Wales Department of Mines, Technical Report 5 (for 1957), 10-62.

BOWMAN, H.N., 1970: Palaeoenvironment and revised nomenclature of the upper Shoalhaven Group and Illawarra Coal Measures in the Wollongong-Kiama area, New South Wales. Records of the Geological Suruey of New South

Wales, 12, I63-L82.

Geology of Australian Coal Basins

225 BOWMAN, H.N., L974: Geology of the Wollongong, Kiama and Robertson 1:50,000 sheets. Geological Survey of Nerry South Wales, Sydney. BOWMAN, H.N., L980: Southern Coalfield: upper Shoalhaven Group and Illawarra Coal Measures. InHetbert, C. & Helby, R. (Editors): A Guide to the Sydney Basin. Geological Suruey of New South Wales, Bulletin, 26, Il7 -I32.

BOWMAN, H.N. & MULLARD, B.W., 1986: Structural geology. 1n Sherwin L. & Holmes G.G. (Editors): Geology of the Wollongong and Port Hacking 1:100,000 sheets, Geological Survey ofNew South Wales. BRANAGAN, D.F., HERBERT, C. & LANGFORD-

SMITH, T., L976: An Outline of the Geology and Geomorphology of the Sydney Basin. Science Press, Sydney.

BRITTEN, R.A., SMYTH, M., BENNETT, A.J.R. & SHIBAOKA, M., 1975: Environmental

interpretations of Gondwana coal measure sequences in the Sydney Basin ofNew South Wales. In Campbell, K.S.W. (Editor): Gondwana Geology, Australian National University Press, Canberra, 233-247 . BUNNY, M.R., 1969: Geology and coal resources of the Southern Catchment Coal Reserve, southern Sydney Basin, New South Wales. Geological Suruey of New South Wales, Bulletin,22. COAL RESOURCE DEVELOPMENT COMMITTEE, 1994: Effects of Land Use on CoaI Resources. NSW Department of Mineral Resources, Sydney.

DUFF, P. McL. D., 1967: Cyclic sedimentation in the Permian coal measures of New South Wales.

Journal of the Geological Society of Australia, t4(2),293-307.

FACER, R.A., COOK, A.C. & BECK, A.E., 1980: Thermal properties and coal rank in rocks and coal seams of the southern Sydney Basin, New South Wales: a palaeogeothermal explanation of coalification. International Journal of CoaI Geology, l, 1-17. GOULD, R. & SHIBAOKA, M., 1980: Some aspects of the formation and petrographic features ofcoal members in Australia, with special reference to the Tasman Orogenic Zone. Coal Geology,2, l-29. GREY, N.M., 1982: Directions of stress, southern

Sydney Basin. Journal of the Geological Society of Australia, 29, 277 -284.

HARPER, L.F., 1915: Geology and Mineral Resources of the Southern Coalfield. Geological Survey of New

South Wales, Memoir Geology, 7 .

HUNT, J.W., ANDERSON, A., BRAKEL, A,T., McMINN, A. & SMYTH, M., 1984: The Bayswater seam and its equivalents: origin, distribution and utilisation in the Sydney and Gunnedah Basins. Ab stracts, 7 th Australian Geological C onu ention, Sydney, Geological Society of Australia, 264-266.

JAKEMAN, B.L., 1980: Quantitative analysis of sedimentation and structure relating to the Permian-Triassic succession of the Southern Sydney Basin. Ph.D. thesis, University of Wollongong. JONES, B.G. & HUTTON, A.C., 1984: Fluvio-deltaic and coal sequences in the northern Illawarra district, N.S.W., Geological Society of Australia, Sydney.

LOUGHNAN, F.C., 1971: Kaolinite claystones associated with the Wongawilli seam in the southern part ofthe Sydney Basin. Journal ofthe Geological Society of Australia, 18(3), 293-302. McELROY, C.T. & RELPH, R.E., 1961: Explanatory notes to accompany geological maps of the inner catchment, Warragamba storage. New South Wales Department of Mines, Technical Report 6 (for 1958), 65-80.

McLEAN, A.J. & WRIGHT, E.A., 1975: Burragorang region. 1n Traves, D.M. & King, D. (Editors):

Economic Geology of Australia and Papua New Coal. Australasian Institute of Guinea: 2 Mining and- Metallurgy, Monograph, 6, 219-224'

McMINN, A., 1985: Palynostratigraphy of the Middle Permian coal sequences ofthe Sydney Basin.

Australian Journal of Earth Sciences, S2(3), 301-309.

NEW SOUTH WALES DEPARTMENT OF MINERAL RESOURCES, 1994: 1994 New South Wales CoaI Industry Profile. Coal and Petroleum Geology Branch, NSW Department of Mineral Resources. READ, H.W., 1975: Berrima district. In Traves, D.M. & King, D. (Editors): Economic Geology of Australia and Papua New Guineal.2 - Coal. Australasian Monograph,6, Institute of Mining and Metallurgy, 224-226.

SCHEIBNER, E., 1976: Explanatory notes on the Tectonic Map of New South Wales, scale 1:1,000,000. Geological Survey of New South Wales, Sydney.

SHIBAOKA, M. & SMYTH, M., 1975: Coal petrology and the formation of coal seams in some Australian sedimentary basins. Econornic Geology, 70,1463-1473.

HAVORD, P., HERBERT, C., CONAGHAN, P.J., HUNT, J.W. & ROYCE, K., 1984: ThC Marrangaroo Conglomerate: its distribution and origin in the Sydney Basin. Abstracts, 7th Australian Geological Conuention, Sydney, Geological Society of Australia, 12,22I-223.

SHIELS, O.J., 1975: Clyde River Coalfield. /z Traves, D.M. & King, D. (Editors): Economic Geology of Coal. Australia and Papua New Guinea: 2 Australasian Institute of Mining and -Metallurgy, Monograph, 6, 227-230.

HERBERT, C. (Editor), L983: Geology of the Sydney 1:100,000 sheet. Geological Survey of New South Wales, Sydney.

SMYTH, M. & COOK,A.C., 1976: Sequence in Australian coal seams. Mathematical Geology, 8, 529-547.

HILL, M.B.L., ARMSTRONG, M., COZENS, S. & BYRNES, J., L994: Tracing the Bulli and Balgownie seams across the Sydney Basin. Proceedings, 28th Symposium on Aduances in the Study of the Sydney Basin, Department of Geology, University of Newcastle, 142-L50.

STANDING COMMITTEE ON COALFIELD GEOLOGY OF NEW SOUTH WALES, 1971: RePort of combined subcommittees for the Southern and Southwestern Coalfields. Records of the Geological Survey of New South Wales, 13(2), 115-130.

Sydney Basin

230 STANDING COMMITTEE ON COALFIELD GEOLOGY OF NEW SOUTH WALES, in press: A revised stratigraphy of the Illawarra Coal Measures, Southern Coalfreld of New South Wales. Records of the Geological Survey of New South Wales (in press).

STUNTZ, J., 1972: The subsurface distribution of the "Upper Coal Measures", Sydney Basin, New South Wales. Annual C onference, Australasian I nstitute of Mining and Metallurgy, Newcastle, 1-9.

WARD, C.R., 1972: Sedimentation in the Narrabeen Group, southern Sydney Basin, New South Wales. Journal of the Geological Society of Australia, 19(3), 393-409.

WILSON, R.G., 1969: Illawarra Coal Measures Southern Coalfield. 1z Packham, G.H. (Editor): of the Wales. Journal The Geology of New South Geological Society of Australia, 16(1), 370-379.

WILSON, R.G., 1975: Southern Coalfreld. 1n Traves, D.M. & King, D. (Editors): Economic Geology of Coa7. Australia and Papua New Guinea:2 Australasian Institute of Mining and -Metallurgy, Monograph, 6, 206-218. WILSON, R.G., WRIGHT, E.A., TAYLOR, B.L. & PROBERT, D.H. 1958: Review of the geology of the Southern Coalfreld, N.S.W. Australasian Institute of Mining and Metallurgy Proceedings, 187, 1.81-104.

WASS, R.E., WOOD, K.G., BUNNY, M.R. & GOLDBERY, R., 1969: Areview of some recent

studies in the Sydney Basin. Geological Society of Australia, Special Publication, 2, 7 -72.

Geology of Australian Coal Basins

23r

N-*Nydney Basin 'ffi

Western Coalfield

EK Yoo A Norman and I McDonald

The Western Coalfield is located at the western margin of the Sydney Basin. It is bounded in the west by the outcrop of the Illawarra Coal Measures and in the east by a straight line from Mount Lorimer through Merriwa to Wisemans Ferry. It extends north to Coolah and south to Warragamba Dam (Figure 1). The Illawarra Coal Measures in the Western Coalfield crop out along the road between Lithgow and Ben Bullen, swing north-easterly to Glen Davis and then extend north-westerly to Leadville parallel to the Lithgow-Mudgee road (Figure 2). There are also a number of coal measures outliers, including the areas around Airly Mountain, Cherry Tree Hill, Cumber-Melon Mountain, Barneys Reef and Pantoneys Crown. The term Illawarra Coal Measures (Clarke, 1866) was introduced to the Western Coalfield by Bryan &

others (1966) after the results ofdrilling and geological mapping had confirmed the continuity of coal-bearing sequences between the south coast and the western margin of the Sydney Basin. Previously the coai measures had been referred to as the Wallerawang Coal Measures, the Lithgow Coal Measures and the Western Coal Measures (Bembrick, 1983).

The Illawarra Coal Measures conformably overlie the Berry Siltstone of the Shoalhaven Group. They are overlain by the Caley Formation of the Narrabeen Group in the Lithgow area and by a conglomerate of the Digby Formation in the northern part of the coalfreld. The Narrabeen Group is overlain in turn by the Hawkesbury Sandstone and the Wianamatta Group in the south-eastern part of the coalfield, and by the Napperby Formation (subsurface only), the Purlawaugh Formation and the Pilliga Sandstone in the northern part of the coalfield (Table 1). Cretaceous sediments equivalent to the Bungil Formation of the Great Australian Basin occur under basalt flows in the western part of the Liverpool Range. Tertiary basalt occurs as a series of flows in the Liverpool Range and as flow remnants on topographic high elsewhere. Basalt also occurs as dykes, plugs within diatremes, most commonly in the Mount Coricudgy area. The coal measures dip gently to the east in the southern part of the coalfield and to the north-east in the northern part. They thicken eastward from 100m in the western margin area near Lithgow to approximately 900m at Wisemans Ferry, and from 50m north-west of Ulan to approximately 500m east of Kerrabee (Figure 2).

STRATIGRAPHY The stratigraphy of the Illawarra Coal Measures in the Lithgow area is well documented by Bembrick (1983). Some modifications have been made, however, by Yoo (1993) and these are incorporated along with Bembrick's nomenclature in Figure 3. This subdivision of the coal measures is generally applicable over the area extending from Lithgow northwards to Coolah at the western margin of the coalfreld, although the middle section of the coal measures (Newnes, Glen Davis and Denman Formations and Watts Sandstone) thins out towards

the northern boundary of the coalfield (Figure 4). Signifrcant changes also occur east of the Mt Tomah Monocline, which runs north-south through Kerrabee, Kelgoola and Glen Davis. East of the monocline the coal measures thickens rapidly and

Sydney Basin

232

49'30',

50'00'

50"30'

{r?*, ,,,,,,

I ,_!yyvj

--?U

Coala

Mt Lorimer

Cassilis

32"00'h\ r Leadville Dunedoe

Wollongong

Ulan underlain by f---f | | Area coal measures I Town \- Foad >- River L Mountain

Gulgong

32'30'

Mudgee

o----t Boreholes and cross section line

k""

Collieries

o Canyon @ Blue Mountains o larence

r Mt Coricudgy

@ Sp ringvale @ Angus Place @ Western Main

Qumbo Melon

IOJ Mt

o lvanhoe

@ lnvincible 33'00' @ Baal Bone @ C harbon @ Kandos No.3 @ Ulan

Cherry Tree Airly Mt

r Gospers Mt

Pantoneys

Capertee

Crown

Ben Bullen

Bores

I _@

Outten B

2 3

Wiseman

DM Ganguddy DDH 2 Wancol Glen Davis DDH 5 Elecom Birds Rock DDH 16 DM Narragamba DDH 4 10 DM Bungaba DDH 1

r0'6

ewnes Ju:nction

Lithgow Hartley Mt Victoria

Kurrajong

IJCML C295

12 UCML C42O

13 UCML C4O1 14 UCML C234 15 ERC Ulan DDH2 16 ERC Ulan DDH'15 17 ERC Ulan DDH 24 18 EL Wollar DDH4 19 EL Wollar DDH22 20 AB Bylong DDH 22 21 AB Bylong DDH 6 22 AB Bylong DDH 8

Katoomba * q--4qs .(u'-

nrith

a ()a

?"rd///y>r>

.--il----3ok'

Figure 1. Location of the Western Coalfield.

Geology of Australian Coal Basins

233

49"30'

150"30'-

50"00'

Tv I Basalt

Pilliga Sandstone r\r

,\ / I

Purlawaugh Formation Narrabeen Group

lllawarra Coal Measures Shoalhaven Group Devonian meta-sediments

lsopach of lllawarra Coal Measu res

Structure Contour on the base of Narrabeen Group Geological boundary Reverse Fault Normal Fault 4\

-1r Monocline

Syncline, plunged

+> Anticline,

plunged

32'30'

33'00'

O Bungaba Fault

@ CurryallFault @ Mt Caricudgy Lineament @ Mt Tomah Monocline @ Kurraiong Fault @ Lapstone Structural Complex

33'30'@ rurrrong svn.rint @ Wenbs Creek Anticline

E Wollar Shelf

tr Blue Mountains Shelf tr Macdonald Shelf tr Hornsby Plateau

0lrl Figure 2. Geology of the Western Coalfield.

Sydney Basin

'10

20km

234

Table 1. Stratigraphy of the Western Coalfield. PERIOD

NORTHERN PART

SOUTHERN PART GROUP

SUB-GROUP

FORMATION

MEMBER

GROUP

BASALT

TERTIARY

FORMATION BASALT

Bungil Formation

CRETACEOUS

Pillisa Sandstone

JURASSIC

Purlawaugh

Formation Wianamatta

Napperby

Ashfield Shale

Group

Formation

Mittagong Formation Hawkesbury Sandstone

Burralow Formation TRIASSIC

Banks Wall Sandstone Grose

Sub-Group

Wentworth Falls Clavstone Member

Mt York Claystone Burra-Moko Head Sandstone

Hartly Vale

Narrabeen Group

Claystone Member

Narrabeen Group

undifferentiated

Govetts Leap Sandstone Member Caley

Victoria Pass

Formation

Claystone Mernber Clwydd Sandstone

PERMIAN

Member Beauchamp

Falls Shale Member

ILLAWARRA COAL MEASURES Shoalhaven Group

Berry Siltstone Conjola Sub-Group

Snapper Point

Illawarra Coal Measures Shoalhaven Group

rndifferentiated

Formation

Bembrick's subdivision is not clearly applicable. The lithofacies of the upper and lower sections of the Illawarra Coal Measures in the western margin continue northwards into the Gunnedah Basin.

Nile Subgroup The Nile Subgroup is divided into three formations at Glen Davis, Grose Canyon and Kedumba Pass, as

well as in the Megalong and Jamison Valleys south of Katoomba (Goldbery, I972; Bembrick & Holmes,

7972). The lowermost formation, the Mount Marsden Claystone, consists mainly of claystone and siltstone with abundant plant remains and common sandstone interbeds. This interval grades upwards into the Coorongooba Creek Sandstone, a quartz-lithic sandstone with common conglomerate bands and siltstone interbeds and finally to the Gundangaroo Formation at the top of the sequence, which consists of interbedded quartz-lithic sandstone and carbonaceous siltstone with some coal beds. Although the Coorongooba Creek Sandstone is

Geology of Australian Coal Basins

235 LIIHOLOGICAL KE'T

K ATO 0I,'I BA

l...."...-

t'..t l. I coNGLoMERAIE l.'.1 .

I tt ti

FARMERS CREEK FORt\''lATlON

1.n,,n.,o,,.

F= tr=

MIDDLE RIVER

rLIE GAP SANDSIONE STAT

E MINE

CREEK FORMATION

INTERBEDDED AIIO

SAAL BONE

LAMINATED UNIT

FORMATION

l /\

DENMAN

TUBILL COAL Mbr'

\---r, MOoLARBEN \,/ coal vur. t| o

)F ,F

B GLEN DAVIS FORMATION NEWN€S FONMATION

coAL

__x_ tvA N lloE Mbr' -\,t SANDSTONE -.--.-ttUitpyOltG

SILICEOUS CLAYSTONE

SANGSTONE Mb.. LONG

ROOT ZONES SIYA MP

LIMESTONE NODULES

FORMATIO N

EROSIVE CONTACT

FINING UPWARDS UNIT

BLACKMANS FLAT

CULLEN

CONGLOMERATE

BURRAGORANG

COAL Mbr. MUDS TOilE

WATTS SANDS

m r.l II

* CLAYSTONE Mbr

CL^YSTONE

coat uu,.

]

COARSENING

U\I T

BULLEN

MAR RAN O AFOO

FORAMINIFERA. MANINE

CONOLOMERATE

ACNIIARCHS. BRACKISH TO MARINE MICROFOS

GUNOANgAROO FORMATION

VERTICAL. SCALE OIAGRAMMATIC

COORONGOOBA CREEK SANDSTONE

TOTAL SECTION

c0MM0NLY lo0 - reo M

MT, MARSOEN CLAYS

Figure 3. Generalised stratigraphic column for the Illawarra Coal Measures of the Western Coalfield (modified after Bembrick, 1983 and Yoo, 1993). not clearly recognised north of Glen Davis, the subgroup can be traced to the Gunnedah Basin. The Nile Subgroup is 50m thick at Glen Davis (type section), Rylstone and Coolah. It thickens north of Coolah (Figure 4).

the Blackmans Flat Conglomerate rapidly wedges out towards the east away from the basin margin in the Lithgow area (Bembrick 1983). The relationship between these four units are illustrated in detail by Bembrick (1983) and Havord & others (1984).

Cullen Bullen Subgroup

M arrang aroo C on g lomerq.t e

The Cullen Bullen Subgroup represents an interval of fluvial deposits towards the basal part of the Illawarra Coal Measures, and consists of coarse-grained, quartz-lithic to quartzose sandstone and conglomerate, fine to medium-grained sandstone and siltstone, and major coal seams. The basal unit is the Marrangaroo Conglomerate, which is overlain by an extensively developed coal seam, the Lithgow Coal. The Lithgow Coal is overlain by the Blackmans Flat Conglomerate, and the Lidsdale Coal is developed on the top of the Blackmans Flat Conglomerate. The Lithgow and Lidsdale Coals merge, however, and become a single thick coal as

The Marrangaroo Conglomerate crops out persistently throughout the Western Coalfield, ianging in thickness from 2 to 24m. The unit fines upward from a quartz-lithic pebbly sandstone or conglomerate to a medium to fine sandstone, and occasionally contains a series of upwards-fining sandstones north of Ulan. The conglomerate is up to 10 m thick between Lithgow and Ben Bullen, but its thickness is reduced to 2m at Cherry Tree Hill and between 3m and 8m north of Ulan. At Bylong the unit consists of fine to medium quartz-lithic and lithic sandstone, and siltstone, with minor coal beds up to 0.3m thick. A sandstone band, 0.5 to 3m thick

Sydney Basin

236

NS DM

Napierl Booyamurnal

Curryalll

JDp DM

JDPUlan15

wancor r'!lffi[*

Ulan10 Gangaddy2 GlenDavis5

Coal Swamp / Levee / Splays

WaftSi {Ansus:iFFiEe)ri $andstone

?",\

40m

\v/<

Vertical Scale

K$*""" oo"-

Bay /Minor Coal

Swamp

'l/ n\

-o"

\ea. \er

30km

Lagoon / Shallow I nte rd istri b utary

K-

Horizontal Scale

Figure 4. North-south cross section of the Illawarra Coal Measures in the Western Coalfield (for location see Figure 1). towardsthe top of the unit, is extensively bioturbated (McElroy Bryan & Associates, 1983). The Marrangaroo Conglomerate commonly overlies the Gundangaroo Formation of the Nile Subgroup with a sharp basal contact, and is overlain conformably by the Lithgow Coal. West of Lithgow,

however, it directly overlies the marine sediments of the Shoalhaven Group.

Lithgow Coal The Lithgow Coal overlies the upward-fining

Marrangaroo Conglomerate, and consists of uniformly dull coal and interbedded carbonaceous claystone. It ranges in thickness from <1m to 5m, and is the major economic coal seam in the Lithgow, Rylstone and Bylong areas. As it occurs above the well-exposed, bench-forming outcrops of the Marrangaroo Conglomerate, the seam is easily traceable in the field. Studies by Agnew & Bayly (1989) indicate that the Lithgow seam is correlated with the Coggan Coal, a unit in the Bylong area informally named by McElroy Bryan and Associates (1983; 1985). The coal is up to 5m thick east of Bylong, but thins abruptly west of Bylong. It is represented by a thin carbonaceous claystone band in the Wollar area, and ranges from 0.2 to 0.8m thick approximately 5m below the'IJlan seam'in the ljlan area (Figure 5).

Blackmans Flat Conglomerat e The Blackmans Flat Conglomerate is a

coarse-grained, often pebble-bearing quartzose

sandstone, developed over almost the entire Western Coalfield. It is one of the key units within the Illawarra Coal Measures. The conglomerate ranges in thickness from 2 to 5 m in most of the coalfield, but thickens to 10 m between Lithgow and Ben Bullen and reaches 14 m to the south-west of Mt Coricudgy.

Lidsdale Coal The Lidsdale Coal consists of dull coai with minor bright bands and carbonaceous claystone and siltstone. The unit ranges in thickness from 0.5 to 8m in most of the coalfield (Figure 4). It thins generally in the western margin area, but thickens to between 13 and 15m east ofBylong and Rylstone. The Lidsdale Coal contains the best-quality coal plies in the Ulan-Wilpinjong area.

The'Ulan seam', informally named in the lJlan area, has been variously correlated with: . the Lithgow and Bayswater Coals (Holmes,

r .

\975); the Irondale seam and the Newnes Formation in the Ulan-Wollar area (McMinn, 1985); and the upper Lidsdale seam (Agnew & Bayly, 1989).

Shiels & Kirby (1977) also suggested that a thin coal seam beneath the 'IJlan seam' could be correlated with the Lithgow Coal. This disparity of opinion has arisen mainly as a result of the paucity of subsurface geological and geophysical information that was available in earlier years to permit

Geology of Australian Coal Basins

237

^in O)

tr b0

fri o

o ! q b0

tr tr

o q)

o 0)

o o

a o O €g

tr tr (!

o lt

€

o o o h o o

H VJ €)

Sydney Basin

238 correlation of the stratigraphy in the Ulan area with that of the surrounding paits of the coalfield.

The'Ulan seam' can be divided into two sections (upper and lower), separated by a 0.3m thick tuffaceous claystone (Ply C-marker) occurring in the mi{dle of the seam. It also has been further subilivided into seven plies for coal quality purpose (Plies A to C in the upper section and plies C-lower to G in the lower section)(Johnstone & Bekker, 1g83; Barto & Delaney, 1989). The'Ulan seam' splits east of Wollar (Shiels & 1977; Lqrto & Delaney, 1989; Agnew & F.!v, Bayly, 1989). The east-west coal seam iorrelations based on the lithofacies and downhole geophysical log profiles indicate that only the lower seition of the 'Ulan seam' can be correlated with the Lidsdale Coal (Yoo, 1993).

Charbon Subgroup Goldbery (7972) used the term Charbon Subgroup to refer to all of the units in the Western Coalfreld from the top of the Nile Subgroup to the top of the Illawarra Coal Measures. The subgroup was later redefined by Bembrick (1983) to encompass only the lower delta plain sediments between tb-e top ofihe Cullen Bullen Subgroup and the base of the Wallerawang Subgroup (Figure 3).

Long Swamp Formation The Long Swamp Formation, which represents

approximately the lower half of the Charbon Subgroup, consists of medium to coarse lithic sandstone, siltstone, claystone, carbonaceous claystone, coal and minor tuff. The averaop thilkness'of the formation in the westernoiart of the coalfield is 30m, but this increases in an easterly direction to approximately 100m south-west of Mt Coricudgy. The unit is commonly root-penetrated towards the middle section, while a laminated sandstone/siltstone sequence towards the top section is frequently bioturbated. Some isolated round pebbles occurring in mudstone towards the base of the formation may also have been dropped from ice rafts (Bembrick, 1983). West of Wollar, the formation is represented by a thin tuffaceous claystone band ('UIan seam' C-marker) and an overlying coal seam (the upper part of the'Ulan seam') (Figure 5). The C-marker ply maintains a consistent thickness of 0.3 m from Ulan to Wilpinjong, then thickens eastwards at Wollar to split the upper section of the 'IJlan seam' further from the Lidsdale Coal (Figure 5). The interval equivalent to the C-marker is approximately 25 m thick at Bylong. The upper section of the 'Ulan seam', reaching up to 7m thick between Ulan and Wilpinjong, splits eastwards into thin multiple, discontinuous coal bands. At Bylong this interval is 20m thick (Yoo, 1993).

Irond.ale CoaI The Irondale Coal is a relatively thin, but persistent unit throughout the Western Coalfield (Bembrick, 1983). It overlies the Long Swamp Formation and underlies the Newnes Formation. The Irondale Coal consists of dull and bright coal with stone bands, and is generally m thickness. In the Wolgan area, it

increases to 2.3m.

The uppermost ply of the upper section of the 'Ulan seam'can be correlated between Ulan and Bylong (Yoo, 1993). Re-examination of borehole graphics

and downhole geophysical logs for the area from T,ithgow through Rylstone to Bylong indicates that the Irondale Coal is correlated with the uppermost

ply of the'IJIan seam' in the Ulan-Bylong area (Agnew & Bayly, 1989). This confirms the palynological evidence of McMinn (198b) that the top of the 'Ulan seam' outside the Ulan-Wollar area can be correlated with the top of the Irondale Coal. Newnes Formq.tion The Newnes Formation consists generally of fine to medium grained lithic sandstone and interbedded siltstone and claystone. The formation conformably overlies the Irondale Coal, and its upper limit is marked by the base of a thin coal/caibonaceous claystone band which is expressed by low density log values. The formation ranges from 8 to 13m in thickness between Lithgow and Ulan, then thins to 4m near Bylong. The sandstone within the formation typically has low gamma-log values in the Ulan area. This characteristic profile disappears as the lithology of the Newnes Formation and the lower part of the overlying Glen Davis Formation both

become similarly fine to medium-grained sandstones.

GIen Dauis Formation The Glen Davis Formation consists of carbonaceous claystone, claystone, siltstone, minor coal and sandstone. Oil shale (torbanite) is developed in the Glen Davis Formation at Newnes and Glen Davis. The formation is overlain by the Denman Formation in most of the Western Coalfield. It ranges in thickness from 17 to 26m throughout the coalfield. The Cockabutta Creek Sandstone Member (Yoo, 1993) which consists of light grey, quartzose to lithic-quartzose, very coarse-grained sandstone, occurs at the top of the formation in an oval shaped lobe bounded by Merotherie, Wollar and Ulan (Yoo, 1993). It is well exposed in the Ulan Mine opencut and in the Goulburn River diversion channel at the Ulan Mine. The sandstone fines upward and ranges in thickness from 2.5 to 9.8m. The Bungaba Coal Member (Yoo, 1993) is the topmost unit in the Glen Davis Formation. It consists of coal and carbonaceous/tufface<-rus claystone. Although this member is thin and variably banded, density-log profiles show it to be

continuously developed throughout the northern part of the Western Coalfield. At the type section, it is 3.47m thick, and overlies the Cockabutta Creek Sandstone Member. In the Ulan Mine opencut, this member is coalesced with the Moolarben Coal Member of the State Mine Creek Formation. Denman Formation The unit named the Baal Bone Formation by Bembrick (1983) has since been referred to as the Denman Formation by Yoo (1993). Recent studies within the Western Coalfield indicate that the genetically-related interval comprising the Denman Formation and the overlying Watts Sandstone in the Hunter Coalfield (Sniffin & Beckett, this volume) also has a distinctive and readily recognisable lithofacies in the Illawarra Coal Measures of the Western Coalfield. The interval grades vertically from uniform dark grey claystone through laminated claystone and fine sandstone with common bioturbation into fine-grained lithic sandstone of possible delta-front environment. Acritarchs and arenaceous foraminifers have been recovered from these sediments (Bembrick, 1983). The formation is 24m thick in the Lithgow area, and maintains this

Geology of Australian Coal Basins

239 thickness as far north as Rylstone and Bylong. It then thins to around 10m near Ulan and 1m near Coolah (Yoo, 1993).

Watts Sq.ndstone For similar reasons the unit referred to by Bembrick (1983) as the Angus Place Sandstone is referred to by Yoo (l-993) as the Watts Sandstone. The Watts Sandstone is a coarsening-upwards lithic sandstone overlying the Denman Formation. At Rylstone and north of Ulan the base of the unit is often marked by a coarse, cross-bedded lithic sandstone or, in some cases, a basal conglomerate, above which the sequence fines upwards. The Watts Sandstone is different from the sandstone ofthe overlying State Mine Creek Formation in being white in colour, coarser grained, cross-bedded and containing a calcareous matrix. Throughout the Western Coalfield the unit ranges from 5 to 15m thick, but it thins to 2m at Coolah (Yoo & others, 1983).

State Mine Creeh Formation The State Mine Creek Formation conformably overlies the Watts Sandstone and is overlain by the Gap Sandstone. It consists predominantly of sandstone, mudstone and carbonaceous claystone with minor coal and tuff interbeds. The thickness of the unit along the western basin margin is approximately 10m, but this increases gradually eastwards to 45m near Mount Corlcudgy. Burrowing in finely laminated claystone/siltstone and fine to medium lithic sandstone occurs towards the middle ofthe sequence. Three coal seams are generally present: the Moolarben Coal Member at the base, the'Turill Coal Member'in the middle, and the 'Lennox seam'or'Goulburn seam'as the topmost seam.

The Moolarben Coal Member (Bembrick, 1983) is a coal seam developed at the base of the State Mine Creek Formation. The 'Goulburn seam', named by McElroy Bryan and Associates (1983) in the Bylong area, is correlated with the Moolarben Coal Member. The Moolarben Coal Member overlies the Watts Sandstone east of Ulan, and coalesces with the Bungaba Coal Member where the Watts Sandstone and the Denman Formation have wedged out in the Ulan area itself (Yoo, 1993). The 'Turill Coal Member'is a coal seam developed in

the middle of the formation in the northern part of the Western Coalfield. The member generally thickens in an easterly direction, and reaches 4m east of Turill and Uarbry (Yoo & others 1983).

The'Lennox seam' or'Goulburn seam' is the topmost seam of the State Mine Creek Formation, and is developed locally in the Ulan area. It consists of carbonaceous claystone and a thin coal seam. The maximum thickness is 2.2rn in the Ulan area, but the unit thins out east of Ulan.

Wallerawang Subgroup The Wallerawang Subgroup represents a sequence of

fluvial to upper deltaic deposits in the upper part of the Illawarra Coal Measures. It consists of a fining-upwards lithic sandstone at the base of the subgroup, overlain by tuffaceous and carbonaceous claystone and coal. The subgroup is extensively developed throughout the Western Coalfield.

Gap Sandstone The Gap Sandstone is a persistent off-white to light grey upward-fining, coarse to very coarse-grained

lithic sandstone, commonly with pebbles at the base,

that is identifiable over most of the Western Coalfield. It is considered to be a sheet-sand, deposited in a fluvial environment. Its thickness is generally 3 to 5m over most of the area, increasing to 10m in some places. The sandstone thins out westwards in the area north of Ulan. F arrners Creeh F ormation

The Farmers Creek Formation, the uppermost unit of the Illawarra Coal Measures in the Western Coalfield, consists of coal, oil shale, carbonaceous and tuffaceous claystone, siltstone, claystone and lithic sandstone. The formation contains the Middle River Coal Member at the base, the Woodford Coal Member in the middle and the Katoomba Coal Member at the top, although none of these seams is continuous across the entire coalfield. It ranges from 6 to 20m in thickness along the basin margin, but thickens eastwards to 30m east of Bylong and 60m south-west of Mt Coricudgy. It is represented by 3m of coal and tuffaceous claystone in the Ulan area. In the Hartley Vale area there is a Lm band of grey claystone/siltstone laminite near the top of the

formation which is heavily bioturbated, and acritarchs are recorded from a similar stratigraphic level at Newnes Plateau (McMinn, 1980).

DE PO S ITIONAL EI{VIRONMENTS

Deposition of the Illawarra Coal Measures in the Western Coalfield commenced with accumulation of the prodelta to lower delta plain siltstones and sandstones of the Nile Subgroup during a general marine regression in the Sydney Basin. The deltas prograded from the north and north-east towards the Lachlan Fold Belt, and passed into a shoreline sandstone. This was overlain by a lower deltaic sequence, often containing a thin coal, at the top of the subgroup. A major change to an alluvial floodplain environment is represented by the Marrangaroo Conglomerate - Blackmans Flat Conglomerate sequence of the Cullen Bullen Subgroup. The quartzose sediments of the Marrangaroo Conglomerate were derived from the uplifted Lachlan Fold Belt to the west, and were incorporated into a fluvial environment which prograded into fan deltas towards the east. These lithofacies usually extend no further than 40km east from the Lachlan Fold Belt. Extensive swamps were established in the interlobe areas of these deltas and in the overbank areas ofthe alluvial plain, and these provided a suitable environment for deposition of the Lithgow Coal.

Further uplift of the Lachlan Fold Belt formed a second alluvial plain, and resulted in deposition of the Blackmans Flat Conglomerate. This braid plain was more extensive towards the east than the one that formed the Marrangaroo Conglomerate. However, it was less extensive in the Lithgow area, where it eventually pinched out into the swamps in which the Lithgow Coal was formed. These swamps built progressively back over the braid plain facies to form the overlying Lidsdale Coal. In the Lithgow area swamp deposition was continuous, forming a combined Lithgowllidsdale Coal as demonstrated by Bembrick (1983). On the western margin of the coalfield the reverse applied, and both braid plains apparently combined to form a series of fining-upwards sandstones.

Sydney Basin

240

Following subsidence of the region after this episode, delta systems prograding from the north-east initiated deposition of the Long Swamp Formation of the Charbon Subgroup. Coarseningupwards sequences typical of lower delta plain and interdistributary bay environments dominate this sequence in the south, while fining-upwards sequences of upper delta plain origin dominate the sequence north and east of Ulan. The Irondale Coal formed in an overbank swamp environment behind crevasse splay sands towards the top of the Long Swamp Formation, while the Newnes and Glen Davis Formations were deposited as overbank and swamp deposits with a significant tuff component in the lower delta plain. Both the Newnes and Glen Davis Formations pinch out near lJarbry, a feature which probably implies a gradual change of the depositional environment from lower delta to upper delta towards the north. An extensive marine incursion occurred in the coalfield at this time, leading to deposition of the Denman Formation. This formation thins significantly towards the north, indicating a more short-lived and shallow marine transgression in the northern part of the basin. Bembrick (1983) has interpreted an open marine bay environment for the Denman Formation, based on the presence of arenaceous foraminifers and a greater abundance of acritarchs than in the Long Swamp Formation. An abundance ofrounded pebbles to boulders, together with the presence of arenaceous foraminifers, also suggests a cold climate; the clasts were probably ice rafted from the source areas down the rivers and deposited in the interdistributary bays and marine shelf areas. The coarsening-upwards facies trend continues into

the Watts Sandstone, a distributary mouth bar-crevasse splay sand facies of the lower delta plain. This unit indicates the commencement of a rapid regression, with the overlying State Mine

Creek Formation representing a lower delta plain facies with a probable back-barrier swamp to form the Moolarben Coal Member. Other swamps occurred, but the resulting coals are much less extensive.

Deposition of the Wallerawang Subgroup commenced with build-up of a fining-upwards fluvial channel sandstone, the Gap Sandstone. This channel facies apparently prograded from the north-east, suggesting formation by a trunk stream which flowed south, parallel to the Lachlan Fold Belt, and discharged into a delta front area south of Lithgow. It also indicates uplift in the New England area at this time. The Farmers Creek Formation consists of alluvial point-bar/levee/floodplain sequences with extensive

floodplain swamps, which resulted in the deposition of the Middle River, Woodford and Katoomba Coal Members. Contemporaneous vulcanism in the New England area resulted in thick tuff bands within the Middle River seam. Vulcanism appears to have ceased, however, by the time the Katoomba seam was formed. In the southern part of the coalfreld the Farmers Creek Formation is predominantly a lower delta plain deposit, due to its proximity to the delta front at the southern end of the prograding clastic complex.

Deposition of the Illawarra Coal Measures was succeeded by the extensive development ofbraid plains that formed the basal Narrabeen Group,

brought about by further uplift of the New England Fold Belt (Ward, 1972).

STRUCTURAL GEOLOGY The major structural features of the Western Coalfield are the Lapstone Structural Complex (Pedram, 1983) and the Mount Tomah Monocline

(Figure 2).

The Lapstone Structural Complex consists of a north-south trending monocline, with a series of parallel faults lying to the west. The structure is most pronounced south of Kurrajong, where dips are up to 70o. To the north, however, around Grassy Hill, the dip of beds associated with the monocline decreases to 10o. In the McDonald River area, to the east of the monocline, there are a series of folds (Galloway, 1968) which appear to have been superimposed on flat-lying strata as a result of movements associated with the formation of the Lapstone Structural Complex. The Mt Tomah Monocline is located to the west of the Lapstone Structural Complex, and extends north to the Liverpool Range and south to the OrangevilleOakdale area in the Southern Coalfield (Scheibner, 1993). The coal measures thicken rapidly east of the monocline, and the structure probably developed contemporaneously with sedimentation. The monocline probably originated as a'hinge line'

during sedimentation (Bembrick & others, 1973) and

was subsequently reactivated. Browne (1969) and other workers have indicated that the Blue Mountains Plateau was uplifted during the Late Pliocene or Early Pleistocene (the Kosciusko Epoch), but more recent studies have suggested that uplift was initiated towards the end of Cretaceous or Late Palaeocene time (Young, I978 Wellman, 1979;

Branagan, 1985).

The structure is relatively simple throughout the remainder of the coalfield. Structure contours on the base of the Lithgow Coal indicate that the coal measures dip gently at between 1 and 2o to the east and north-east. There are however, a number of minor undulations and flexures where the dip increases to 10o, and these probably reflect buried basement topography or the effects of basement

structures.

Lineaments Studies of aerial photographs and satellite imagery, in conjunction with interpretation of aeromagnetic

data, have indicated a series of major NNE-SSW and north-south trending linear features that appear to correlate with magnetic anomalies in the basement rocks of the Western Coalfield (Mauger & others, 1984). The NNE trending Blackheath Lineament extends from the ground surface into the basement, and is parallel to the fold axes in the Early Palaeozoic basement. The north-south trending Lapstone Structural Complex - Kurrajong Fault system is also interpreted as being controlled by a major basement fault (Qureshi, 1984; Harrington &

Korsch, 1985).

The Gospers Mountain Lineament is coincident with an ENE trending structural zone in the Devonian basement (Mauger & others, 1984), while WNW

trending lineaments parallel the Lachlan River Lineament in the fold belt to the west (Scheibner, 1976). Some of the basin lineaments show evidence of multiple shear deformation (Mauger & others, 1984), which suggests that the basement structures

Geology of Australian Coal Basins

24t may have been reactivated after deposition commenced in the Sydney Basin. Geological fracture mapping by Shepherd & others (1981) and Shepherd & Huntington (1981) indicates a correlation between bad mining conditions in the Lithgow and Katoomba seams and joint zones and lineaments at the surface in the sandstones of the overlying Narrabeen Group.

Faults There are few major faults in the area of the coalfield to the west of the Lapstone Structural Complex or in the north-western part of the coalfield. The largest fault is the Kurrajong Fault, immediately west of this structure, which has displaced the western block down by 130m (David, 1902). This was originally believed to be a west-dipping normal fault system. However, Herbert (1989) reported that the fault is an east-dipping high-angle reverse fault system. At Clarence Colliery, near Newnes Junction, a number of

subvertical faults trending NNW with a displacement of up to 20m are also recorded, while a fault with a 5m displacement occurs in Hartley Main and Ivanhoe Collieries. Normal faults with displacements around lm are common in the mine workings of the Western Coalfreld.

Joints The most common and widespread joints in the Western Coalfield are planar, vertical NNW trending joints which form an orthogonal set with somewhat less prominent ENE trending joints. While the NNW joints correspond to the dominant cleat direction in the coal seams, the NNE and WNW fractures have a generally greater extent and can form linear zones associated with bad roof conditions.

Lithgow Coal The economic Lithgow Coal is recognised between Lithgow and Rylstone, and separately in the Bylong area. It has been extensively mined in the area between Lithgow and Ben Bullen since last century. In the Lithgow area the Lithgow Coal ranges from 1.5m to 4.6m in thickness, and consists generally of dull coal with minor bright bands and various tuffaceous/carbonaceous claystone bands. The seam has a raw coal ash ofbetween 14 and 35Vo (air dried). Washability testing (cumulative floats at 1.6RD) indicates yields of 85 to 92Vo wtt}r. 13 to 18Vo ash (air dried). The coal is a medium to high ash, medium to high volatile, low sulphur steaming coal. Areas of economic potential are shown in Figure 6.

East of Glen Davis the Lithgow Coal, referred to by Morris (1975) as the 'Capertee seam', is a thin coal seam interbedded with carbonaceous claystone. Based on the limited boreholes available, the seam does not appear to have an economic significance in this particular part of the field. The Lithgow Coal has also been extensively tested in the Airly Mountain, Cherry Tree Hill, Cumber Melon and Rylstone areas as well as around lJlan, Wollar and Bylong. Economic Lithgow Coal occurs across the entire Airly Mountain outlier and in parts of the Cherry Tree Hill outlier. The coal contains a number of claystone bands, which are more common in the middle to upper part of the seam. The best interval is considered to be the lower half, ranging from 2m to 3m in thickness. The raw ash ofthis section ranges from 20 to 27Vo (air dried), and the

theoretical yield (cumulative floats at 1.6 RD) ranges from 80 to 90Vo, with ash (air dried) at 13 to 777o.

Igneous Activity The major igneous activities affecting the area are a series of Triassic-Jurassic phonolite (tinguaite)latite-trachyte-syenite and teschenite intrusives, Jurassic to Tertiary diatremes and Tertiary basalt flows. The Triassic-Jurassic igneous intrusions occur randomly in a triangular area bounded by Rylstone, Botobolar, Wollar and Kerrabee. These rocks are a quenched alkaline suite ranging from a strictly K-feldspar facies, through mixed K-feldspar feldspathoid facies to a strictly feldspathoid facies

(Barron, 1989). K-Ar age dating indicates that these

igneous rocks formed between 66.9Ma and 220.9Ma before present. Teschenite sills 6km east ofBylong and on Tong Bong Mountain, 8km north-west of Rylstone, are lithologically identical to Tertiary dolerite in the area, but are dated as late Triassic (181Ma to 189Ma). A particularly extensive series ofbreccia vents and basalt flows, plugs, sills and dykes in the area east of Rylstone (Bradley & others, 1984) was probably related to a WNW trending basement structure

parallel to the Lachlan River Lineament. IVAI dating of basalts (Wellman & McDougall,1974; Embleton & others, 1985) indicates that the vulcanism at Rylstone is of Eocene age whereas that in the Blue Mountains area is Miocene, suggesting a progressive change in the location ofthe volcanic centre from north to south. However, a basalt cap Skm east of Bylong is dated at 12.2Ma to 12.9Ma, which suggests that volcanic activity in the Liverpool Range survived until the end of Miocene Epoch.

ECONOMIC COAL SEAMS

At Bylong, the Lithgow Coal consists of dull coal

generally free of stone bands. The seam thins rapidly west of Bylong, but thickens eastwards, reaching over 5m at the boundary of the Wollemi National Park. The raw coal ash of the seam is less than 20Vo over approximately two thirds of this area, and the seam is delineated as containing a potentially mineable resource. Washability testing suggests that yields (cumulative floats at 1.6 RD) are generally greater than 80Vo, with ash (air dried) ofbetween IA and t\Vo.

LIDSDALE COAL The Lidsdale Coal is persistent throughout the entire Western Coalfield. It has been locaily mined together with the Lithgow Coal by open cut methods north of Lidsdale and at the site of Mount Piper Power Station. The thickness is up to 2m and the raw ash ranges from 30 to 32Vo. In the Rylstone area the coal has a working section that varies from 1.5m to 3.0m thick, and a raw ash of 20 to 25Vo (Moloney

& others, 1983;Agnew & Bayly, 1989). In the Glen DavisA.{ewnes area a coal seam at a similar stratigraphic position to the Lidsdale seam is known to have coking properties. This seam ranges from 1.5 to 2.0m in thickness, with a raw ash of 13 to 20Vo (Morris, t975).

In the lJlan area, the Lidsdale Coal (the lower

section of the 'IJlan seam') is mined by longwall methods and the lower and upper sections of the 'IJlan seam'are mined by an opencut operation. The lower section of the'IJlan seam'is approximately 7m

Sydney Basin

242

Figure 6. Areas of coal seams in the Western Coalfield with economic potential.

Geology of Australian Coal Basins

243

thick and has a low ash percentage (7 to 13%), while the upper section of the seam (approximately 7m thick) is heavily banded. The raw ash of the upper section ranges from 11 to 45Vo (Shiels & Kirby, 1977). In the Coolah-Turill area, to the north-west, the Lidsdale Coal is 1.5 to 3.8m thick and is overlain by carbonaceous claystone. The seam increases in thickness and depth towards the Liverpool Range. The raw ash ofthe seam ranges from about 20 to 347o in this area. Washability testing of the seam at RD 1.6 yields 7l to 97 7o of product with 12 to 147o (air dried) ash. Torbanite is developed towards the top of the Lidsdale Coal in the Clandulla and Kandos areas.

IRONDALE COAL The Irondale Coal has been mined on a small scale by open-cut methods at Ivanhoe Colliery, and by underground methods in the Glen Davis and Newnes areas, for use in coke ovens at Lithgow. The seam is known to have a potential economic significance in the Wolgan and Cherry Tree Hill areas. In the Wolgan Valley, where the coal is referred to as the 'Wolgan seam', it is up to 2.4rn thick. In this area it consists of a high volatile, high fluidity, vitrain-rich, coking coal, with a swelling index of 4 to 7, which can be beneficiated to a product with I to llVo ash (Morris, 1975; Cox & others, 1980). These resources are presently enclosed within the Wollemi National Park.

The Katoomba seam is also recognised east of Rylstone, where it ranges from 1 m to 10 m in thickness. However, it contains a high proportion of claystone bands in this area. Washability testing at RD 1.6 indicates yields of 10 to 50Vo with 20 to 37Vo

(air dried) ash.

OIL SHALE Carne (1903; 1908) and Lishmund (1974) have identified 21 oil shale deposits at several horizons within the Illawarra Coal Measures in the Western Coalfield. At Glen Davis and Newnes the oil shale occurs in the Glen Davis Formation, at Blackmans Crown it is in the Farmers Creek Formation, and at Clandulla and Olinda it is within the Lidsdale Coal. The largest deposit occurs at approximately the Irondale Coal horizon between Baerami Creek and Widden Brook, although the oil shale is of comparatively low grade. The maximum yields of oil are obtained from the Glen Davis and Newnes deposits, where 478L/thave been recorded (Lishmund, 1974). In the Newnes area the oil shale ranges in thickness from 0.46 to 0.64m and is interbedded with coal and claystone, whereas at Glen Davis the oil shale ranges from 0.3 to 1.37m thick (Record Tracing No. 84 and 84A, NSW Department of Mineral Resources). The mining of oil shale at GIen Davis was abandoned in 1952, but based on the record tracing the thickness ranged from 0.95 m to 1.06 m. The extent of the Glen Davis and Newnes deposits is still to be fully investigated.

.TURILL COAL MEMBER'

COAL MINING GEOLOGY

The 'Turill Coal Member'in the State Mine Creek

Coal in the Western Coalfield is extracted predominantly by underground methods, and of the twelve operating collieries only the Ulan Mine has significant open-cut operations. A number of open-cut mines, however, have operated in the Lidsdale, Ivanhoe, Cullen Bullen and Ben Bullen areas since the 1950s.

Formation is potentially mineable in the TurillCassilis area in the northern part of the Western Coalfield. It varies from 1.5m in thickness near Turill to 4m at Cassilis. The depth to the seam also increases easterly, reaching 600m at Cassilis. The seam consists mostly of dull coal with common bright bands, and contains a few stone bands ofup to 0.25m in thickness. The raw ash of the seam is 23 to 45 % (air dried). Washability testing at RD 1.6 gives product yields of 50 to 907o wit}:' 77 to 25Vo (air dried) ash. A crucible swelling number ranging from 1 to 6 indicates some potential as a coking coal (Yoo & others, 1983).

MIDDLE RIVER COAL MEMBER The Middle River Coal Member commonly contains a high proportion ofinterbedded tuff, claystone and carbonaceous claystone, and for the most part has little economic significance. Recent compilation of borehole data, however, indicates that a.potentially economrc seam occurs in this formation in the Newnes Plateau area, where a 2m working section within the top of the Middle River Coal Member has a raw coal ash ofless than 35 7o.

KATOOMBA COAL MEMBER The Katoomba Coal Member is an economically significant seam in the Bell and Birds Rock Newnes Junction areas (Figure 6). It ranges in thickness from 1.5 to 3.0m and has a raw coal ash of t\ to 237o (air dried). The seam consists of mediumvolatile, low-sulphur steaming coal with a fairly high inertinite content. Washability testing at RD 1.6 indicates yields of 80 to 907o witt, ash at 8 to t17o (air dried).

Longwall mining is the most common underground extraction technique used in the Western Coalfield. Because of the simple structure of the area this technique has been very efficient, but has resulted in some problems with surface subsidence and cliff collapse.

In general, there have been few major constraints on coal mining in the Western Coalfield. The Lithgow and Katoomba seams, for the most part, are structurally undisturbed and have good roofrocks. Some problems, however, are associated with fault displacements, roof collapse related to local structural elements and seam convergence, igneous intrusions and groundwater inflow.

Seam discontinuities due to faulting are common at

Clarence, near Newnes Junction, and depending on

fault magnitude and frequency pose a significant risk to coal production. 'Slacky rolls', or areas of combined joints and minor faults, have also caused roof problems at Clarence. These zones of instability have been related to joints and lineaments trending NNW and NNE, identified using Landsat and aerial photo imagery (Shepherd & others, 1981). Another type of roof problem occurs in the southern half of the ioalfield, where the Lithgow and Lidsdale seams converge. The shale wedge between these two seams often causes roof collapse during bord and pillar mining of the Lithgow seam, and as a result

Sydney Basin

244 the upper part of the seam is generally left in place to ensure stable roofconditions. This problem is less serious, however, with longwall mining. A concentration of igneous intrusives occurs in the area bounded by Rylstone, IJlan, Widden Brook and Putty. The extent of cindering associated with these intrusions is uncertain, since the area is as yet unmined, but is probably far greater than the area affected by igneous activity in the south. Igneous intrusions are rare in the Lithgow Bullen - Cullen q1ea, thq largest being a 4m wide dyke at Hartley

Main Colliery near Bell, which only caused minor cindering of the coal seam. The sandstones of the Narrabeen Group form vertical cliffs above steep talus slopes along the

western margin of the coalfield. This has limited the exlent of open-cut mining to contour stripping along individual seam outcrops. With underground mining increasingly being conducted by longwall techniques, limitations have also been imposed on the proximity of mining to the cliff lines, to prevent cliff collapse during or after coal removal.

COAL RESOURCES AND RESER\rES The total in situ coal resource in the Western Coalfield is estimated to be 29 960Mt, of which 22 640Mt are affected by other land uses such as national parks. Coal in the Western Coalfield has been considered as a resource if there is a minimum seam thickness of 1.5m, a maximum raw coal ash of 35% and a depth of<600m (Coal Resources Development Committee, 1994). Areas of potentially economic coal for the Lithgow and Katoomba seams

BEMBRICK, C.S. & HOLMES, G.G.,1972: Further

occurrences ofthe Nile Subgroup. Geological Suruey of New South Wales, Quarterly Notes,6,

5-10. BRADLEY, G., YOO, E.K. & WEST, P., 1984: Geological mapping of Mesozoic to Tertiary diatremes and Illawarra Coal Measures east of Rylstone. Geological Suruey of New South Wales, Report GS84 /203. BRANAGAN, D.F., 1985: An overview of the geology of the Sydney Region. 1n Pells, P. (Editor): Engineering Geology of the Sydney Region, A.A. Balkema, Rotterdam. BROWNE, W.R., 1969: Geomorphology: general notes. In Packham, G.H. (Editor): The Geology of New South Wales . Journal of the Geological Society of Australia, 16( 1), 559-569. BRYAN, J.H., McELROY, C.T. & ROSE, G., 1966: Explanatory notes on the Sydney 1:250,000 Geological Sheet, 3rd Edition. Geological Survey of New South Wales, Sydney. CARNE, J.E., 1903: The kerosene shale deposits of New South Wales. Geological Suruey of New South Wales, Memoir Geology, 3.

CARNE, J.E., 1908: Geology and mineral resources of the Western Coalfields. Geological Suruey of New South Wales, Mernoir, 6. CLARKE, W.B. 1866: On the occurrence and geological position ofoil bearing deposits in New South Wales. Quarterly Journal of the Geological Society of London,22(I), 441.

are shown in Figure 6.

COAL RESOURCE DEVELOPMENT COMMITTEE, 1.994: Effects of Land Use on Coal Resources. NSW Department of Mineral Resources, Sydney.

Total recoverable coal reserves within colliery leases and exploration licences in the Western Coalfield are estimated to be 1420Mt (NSW Department of Mineral Resources, 1994).

COX, R., O'DEA, T.R. & GRAYLIN, R.K., 1980: Economic geology of the Wolgan coking coal deposit, Western Coalfield, New South Wales, Australia. Australasian Institute of Mining and

REFERENCES

DAVID, T.W.E., 1902: An important geological fault at Kurrajong Heights, New South Wales. Journal and Proceedings of the Royal Society of New South Wales,36, 359-370.

AGNEW, D. & BAYLY, K., 1989: A geophysical correlation of the lower Illawarra Coal Measures between Ulan and other areas in the Western Coalfield of N.S.W. Proceedings, 23rd Symposium on Aduances in the Study of the Sydney Basin, Department of Geology, University of Newcastle, 149-155. BARRON, L.M., 1989: Some rhyolite tuffs and Tertiary basalts, Mesozoic phonolites and trachytes from the Rylstone-Lue-Bulgaldie area. Geological Survey of New South Wales, Petrological Report 1989/19.

Metallurgy, Proceedings, 27 3, l-12.

EMBLETON, B.J.J., SCHMIDT, P.W., HAMILTON, L.H. & RILEY, G.H., 1985: Dating vulcanism in the Sydney Basin: evidence from K-Ar ages and palaeomagnetism. In Sutherland, F.L. (Editor): Vulcanism in Eastern Australia. Geological Society of Australia, New South Wales Diuision, Publication,l, 59-72. GALLOWAY, M.C., 1968: The stratigraphy of the Putty-Colo area, Sydney Basin. Journal and Proceedings of the Royal Society of New South

Wales,l0l(1), 23-36.

BARTO, C. & DELANEY, S.D., 1989: Wollar Authorisation No. 322, geology and coal resources. Electricity Commission of New South Wales.

GOLDBERY, R., 1972: Geology of the Western Blue Mountains. Geological Suruey of New South

BEMBRICK, C.S., 1983: Stratigraphy and sedimentation of the Late Permian Illawarra Coal Measures in the Western Coalfield, Sydney Basin,

HARRINGTON, H.J. & KORSCH, R.J., 1985: Tectonic model for the Devonian to Middle Permian of the New England Orogen. Australian Journal of

New South Wales. Journal and Proceedings of the Royal Society of New South Wales,116, 105-117.

BEMBRICK, C.S., HERBERT, C,, SCHEIBNER, E., & STUNTZ, J., 1973: Structural subdivision of the New South Wales portion of the Sydney-Bowen Basin. Geological Suruey of New South Wales, Quarterly Notes, 11, 1-13.

Wales, Bulletin,2O.

E arth Sciences, 32(2), 163-179.

HAVORD, P., HERBERT, C., CONAGHAN, P.J., HUNT, J.W. & ROYCE, K., 1984: Marrangaroo its distribution and origin in the Conglomerate Sydney Basin. -Abstracts Seventh Australian Geological Convention, Sydney, Geological Society of Australia, Abstracts , 12, 221-223.

Geology of Australian Coal Basins

245 HOLMES, G.G., 1975: Goulburn Valley coal drilling operations by the New South Wales Department ofMines during 1973 and 1974. Geological Survey of New South Wales, Report GS 1975/001.

QURESHI, I.R., 1984: Wollondilly - Blue Mountains gravity gradient and its bearing on the origin of the Sydney Basin. Australian Journal of Earth

JOHNSTONE, M.A. & BEKKER, C. 1983: Final geological report on Ulan Coal Mines Ltd Authorisation 58 and 202.

SCHEIBNER, E., 1976: Explanatory Notes on the Tectonic Map of New South Wales, scale

LISHMUND, S.R., 1974: Oil shale. The Mineral Industry of New South Wales, No. 30, Geological Survey of New South Wales, Sydney. MAUGER, A.J., CREASEY, J.W. & HUNTINGTON, J.F., 1984: The use of pre-development data for mine design: Sydney Basin fracture pattern analysis, 1:100 000 maps, extracts and notes. National Energy Research, Deueloprnent and Demonstration Council, Report on Project No. 81 / 1357.

McELROY BRYAN AND ASSOCIATES PTY LIMITED, 1983: Bylong Project Stage 1 Exploration Report. Prepared for Austen and Butta Ltd, Report l/30/3. McELROY BRYAN AND ASSOCIATES PTY LIMITED, 1985: Authorisation 342 South Bylong, Stage 1 Exploration Report. Prepared for Austen and

Butta Ltd, Report L/30/4. McMINN, A., 1980: Permian palynology of Elecom Lithgow Newnes DDH 31, north of Lithgow. Geological Survey of New South Wales, Palynology Report 1980/3. McMINN, A., 1985: Palynostratigraphy of the Middle Permian coal sequences ofthe Sydney Basin. Australian Journal of Earth Sciences, S2(3), 301*309. MOLONEY, J., BRADLEY, G. & WEST, P., 1983: ThC geology and coal resources ofthe Rylstone area, Authorisation 230: an interim report. New South Wales Department of Mineral Resources, Coal Geology Report 1983/006.

MORRIS, F.R., 1975: Western Coalfield. 1z Traves, D.M. & King, D. (Editors): Economic Geology of Australia and Papua New Guinea:.2 - Coal. Australasian Institute of Mining and Metallurgy, Monograph, 6, 230-235. NEW SOUTH WALES DEPARTMENT OF MINERAL RESOURCES, 1994: 1994 New South Wales CoaI Industry Profile. CoaI and Petroleum Geology Branch, NSW Department of Mineral Resources, Sydney.

PEDRAM, H., 1983: Structure and engineering Geology of the lower Blue Mountains, Sydney Basin, New South Wales. MSc thesis, University of Sydney.

Sciences, 31(3), 293-302.

1:1 000 000. Geological Survey ofNew South Wales, Sydney.

SCHEIBNER, E., 1993: Structural framework of New South Wales. Geological Suruey of New South Wales, Quarterly Notes,93, 1-36. SHEPHERD, J. & HUNTINGTON, J.F., 1981: Geological fracture mapping in coalfrelds and the stress fields ofthe Sydney Basin. Journal ofthe Geological Society of Australia, 28(3), 299-309. SHEPHERD, J., HUNTINGTON, J.F. & CREASEY, J.W., 1981: Surface and underground geological prediction of bad roof conditions in collieries of the Western Coalfreld, New South Wales, Australia. Institution of Mining and Metallurgy, Transactions, Section B, 90, B1-814.

SHIELS, O.J. & KIRBY, 8.C., 1977: Geological report on the Joint Drilling Program, Ulan Area. Joint Coal Board Report LR 77/1. WARD, C.R., 1972: Sedimentation in the Narrabeen Group, southern Sydney Basin, New South Wales. Journal of the Geological Society of Australia, l9(3), 393-409.

WELLMAN, P., 1979: On the Cainozoic uplift of the southeastern Australian Highland. Journal of the Geological Society of Australia,26, 7.-9.

WELLMAN, P. & MCDOUGALL, I.,1974: Potassium-argon ages on the Cainozoic volcanic rocks of New South Wales. Journal of the Ge o Io g ic aI S o c iety of Au s t rali a, 2l (3), 247 -27 2.

YOO, E.K., 1993: Stratigraphic and coal seam correlations of the Illawarra Coal Measures in the Ulan and Bylong areas, Western Coalfreld, Sydney Basin, New South Wales. Journal and Proceedings of the Royal Society of New South Wales,126, 73-86. YOO, E.K., WEST, P. & BRADLEY, G., 1983: Geology and coal resources ofthe Coolah-Binnaway -Mendooran area (Goulburn River - Binnaway 286). New Drilling Programme Authorisation - of Mineral Resources, South Wales Department Coal Geology Report 1983/022.

YOUNG, R.W., 1978: The study of landform evolution in the Sydney region. Australian Geographer,14, 7 1-93.

Sydney Basin

247

ffiunnedah

Basin

NZ Tadros

Figure 1. The Sydney, Gunnedah and Bowen Basins in New South Wales (modified from Tadros, 1993b).

BASIN STRUCTURE The Gunnedah Basin is a long structural trough, linking the Sydney Basin in the south with the Bowen Basin in the north to form a larger structural basin which extends along the eastern margin of Australia (Figure 1). Bembrick & others (1973) defined the Gunnedah Basin as a structural sub-basin bounded in the east along the HunterMooki Fault System by the New England Fold Belt, in the west by an unconformable contact with the Lachlan Fold Belt, in the north by a transverse structural high north of Narrabri and in the south by the Mount Coricudgy Anticline. Much of the sediment in the northern Gunnedah Basin is continuous with that of the Bowen Basin (Runnegar, 1970; Hill, 1986; Etheridge, 1987), but is present under thick Jurassic cover of the Great Australian Basin. Considering structural criteria, however, Tadros (1988c, 1993d) defrned a northern boundary for the Gunnedah Basin at a transverse structural high near Moree.

Major Structural Elements Structure contours on the top ofthe ?Late Carboniferous to Early Permian basal volcanics (Figure 2) broadly outline three NNW oriented troughs in the Gunnedah Basin, each of which lies between basement highs. The Boggabri Ridge (Russell, 1981) in the east separates the eastern Maules Creek Sub-basin (Thomson, 1986) from the central Mullaley Sub-basin of Tadros (1993d). The Rocky Glen Ridge (Yoo, 1988) in the west separates the Mullaley Sub-basin from the western Gilgandra Sub-basin ("Gilgandra Trough" of Yoo, 1988).

Gunnedah Basin

248

f,,io're 2. Structure contours on the top of the basal volcanics of the Gunnedah Basin, showing longitudinal ..tE-U""inJ and prominent highs and rfdges (modified from Tadros' 1993d).

Geology of Australian Coal Basins

249

\ t

ia'N

II 'c

NEW ENGLAND FOLD BELT

MULLALEY

l0 l0

SUB . BASIN

,,] .\

Bree73'

ruERE'V,CE

U*n*n volcnts otEroP

ll-l

w.* o*olt o.t-oP

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,t l4lefrd een: ol tte Bqggobd R49c

Figure 4. Isopachs (m) of Early Permian seiiiments (Leard, Goonbri and Maules Creek Formations), Mullaley Sub-basin (modified from Tadros, 1988c).

Figure 3. Outcrop of the Boggabri Ridge (Offenberg, 1971i Chesnut & others, 1973; Wallis, 1971; Hill, 1986) (modified from'ladros, 1993d). A number of WSW to SW trending transverse basement highs or ridges divide these longitudinal sub-basins into a series of smaller troughs, with orientation parallel to the basin axis (Tadros, 1988c; 1993d).

Longitudinal and q.ssociated structures i) Ridges Boggabri Ridge

Late Carboniferous to Early Permian silicic and mafic volcanics crop out in three separate and distinctive areas: west and south of Gunnedah, north of Boggabri (Hanlon, 1949a,c; 1950a), and in the Deriah Forest area to the east of Narrabri (Hill, 1986) (Figure 3). Borehole data indicate that the silicic and mafic volcanics are continuous in the subsurface between these outcrops. Those volcanics form a prominent basement ridge extending from a point 18km south-east ofBellata south through the Deriah Forest area to Baan Baa (Hill, 1986), through Boggabri to south-east ofGunnedah where the Hunter-Mooki Fault System truncates the ridge. Hanlon (1950a) suggested that the area in which the Boggabri Volcanics crop out probably represents an old structural high. Russell (1981) concluded that the outcrops form part of a prominent south to south-westerly trending basement high, and referred to it as the Boggabri Ridge. He suggested that the ridge was an original basement topographic high

which had subsequently undergone structural modifrcation.

Early Permian sediments lap on to the eastern and western sides of the Boggabri Ridge (Hanlon, L949a, 1950a; Tadros, 1981, 1982; Russell, 1981; Thomson, 1986; Hill, 1986). Thus during the Early Permian the ridge would appear to have separated the eastern half of the Gunnedah Basin into the Maules Creek and Mullaley Sub-Basins (Figure 2). Thomson & Flood (1984) and Thomson (1986) suggested that the Boggabri Ridge was not a continuous high, and that gaps existed which enabled sediments derived from the Lachlan Fold Belt to enter the eastern drainage system. Detailed structure contours on the basal volcanics (Figure 2) and isopachs of the Early Permian sediments in the Mullaley Sub-basin (Figure 4) confirm their views and suggest at least one possible location to the north ofGunnedah. Tadros (1988c) has pointed out that it is more than just a coincidence that at present there is low topographic reljef between the three major outcrop clusters of the Boggabri Ridge. Rocky GIen Ridge

The Rocky Glen Ridge (Figures 2 and 5) is present in the Coonabarabran area as a sub-crop ofOrdovician - Carboniferous metasediments, Carboniferous granites, and volcanics. Silicic volcanics, which are correlatives of the Boggabri Volcanics (Leitch & others, 1988) and consist of ignimbrite and ash-fall tuff, form the eastern flank ofthe ridge. Russell (1981) related a negative feature on the total gravity map to the presence of the acidic (silicic) volcanics in the area. Diilling by the New South Wales

Department of Mineral Resources during 1981-1982

Gunnedah Basin

250

Figure 5. Structural subdivision of the Gunnedah Basin. Majo,1 residual Bouguer gravity lineaments of Scheibner (1993) are also shown (modified from Tadros' 1993d).

Geology of Australian Coal Basins

251 confirmed Russell's suggestion that the "Rocky Glen High" was a prominent topographic feature onlapped partially by Permian sediments. The ridge is evident on aeromagnetic maps and corresponds to gravity highs extending from Dunedoo to Wee Waa. Yoo (1988) therefore suggested that the "Rocky Glen High "may extend south to the "Dunedoo High" and north to Wee Waa. It bounds the western margin of the Permian sediments in the Mullaley Sub-basin. ii ) Shelf Areas

The structure contours on the basal volcanics suggest that the western side of the Boggabri Ridge develops into a narrow shelf area, and that this shelf becomes wider in the north to the west of Boggabri (Baan Baa Shelf, Tadros, 1993d) and in the south to the west ofBreeza (Breeza Sheli Tadros, 1993d) (Figures 2 and 5). The contours also suggest that the shelf areas develop into the transverse structures of the Walla Walla Ridge and Bundella High respectively. As with the Boggabri Ridge, structure contours on the floor of the Gunnedah Basin (Figure 2) also suggest that the eastern margin of the Rocky Glen Ridge develops into broad, gently sloping shelfareas before it becomes steeper towards the main troughs of the Mullaley Sub-basin (Figure 5). These shelf areas also develop into or join the major transverse highs and ridges that bound the trough areas.

Throughout much of the history of the basin, the shelf areas were stable structures that subsided at signifrcantly slower rates than the neighbouring troughs. The largest of these structures is the Wollar Shelf (Tadros, 1993d) in the south, located between the Rocky Glen Ridge in the west and the Murrurundi Trough in the east. The Weetaliba Shelf (Tadros, 1993d), located between the Bando Trough and the Wee Waa Shelf (Tadros, 1"993d), lies west of the Bohena and Bellata Troughs ofTadros (1988c) (Figure 5).

iii) Sub-basins Maules Creek Sub-basin

The Maules Creek Sub-basin (Figure 5) is a remnant

structural basin, representing part of what was probably a large depositional basin covering an extensive area of the New England region in the east. The Mooki Fault System forms the eastern boundary ofthe sub-basin on the surface, and the eastern flank of the Boggabri Ridge forms the western margin. Results from a deep seismic reflection survey by the Australian Geological Survey Organisation (formerly Bureau of Mineral Resources) indicate a shallow fault bounding the Gunnedah Basin on the east (? the Mooki Fault), and that the Tamworth Belt appears to have been thrust over the eastern margin of the Gunnedah Basin (Maules Creek Sub-basin) for at least 15km (Korsch & others, 1993). The slope on the surface of the basal volcanics generally becomes steeper towards the Mooki Fault System. Thomson (1986) believes that the Boggabri Volcanics form the effective basement in the Maules Creek Sub-basin. Mullaley Sub-basin

The Mullaley Sub-basin (Figures 2 and 5) extends over the entire length of the Gunnedah Basin, from Moree in the north to the Mount Coricudgy Anticline in the south. A number of WSW to SW trending transverse structural highs or ridges divide the basin into a series of NNW oriented troughs

(Figure 5). Tadros (1988c) found a striking coriespondence between the high gravity anomalies on the Meandarra Gravity Ridge (Lonsdale, 1965) (Figure 6) and the trough areas. The troughs also contain the thickest sedimentary pile in the basin, particularly in the Early Permian sequence. The Meandarra Gravity Ridge is a distinct meridional linear gravity high on the BMR (now AGSO) total Bouguer gravity map of Australia (1976). This feature extends for 500km along the major structural trends of the Bowen and Gunnedah Basins from Meandarra in Queensland south to the Liverpool Range. A number of transverse trends, spaced 35 to 90km apart, disrupt the Meandarra Gravity Ridge over much of its length. Based on

computer-processed residual gravity images, Murray & others (1989) established that the ridge extends over alrnost the entire length of the Sydney-Bowen Basin. The highs in the Gunnedah Basin, which correspond to the discontinuities between the high gravity anomalies, have influenced sedimentation throughout the basin's history. During the Early Permian many of these transverse structures (and also the longitudinal ridges) acted as topographic features that supplied sediments to the trough areas. S.ome had a very pronounced effect on the overlying sediments, such as thinning of strata and deterioration of coal quality (Tadros, 1988c). Gilgandra Sub-basin

Although the area west of the Rocky Glen Ridge is largely unexplored, Yoo (1988) suggested an extension of the Permo-Triassic sediments westward into the Mount Foster Structural Zone (Scheibner, in Hamilton, 1985b) and northward to the northeasterly trending Cobar-Inglewood Kink Zone (Scheibner, ln Hamilton, 1985b) (Figures 2 and 5). This interpretation was based on sparse drilling, the presence of a number of elongate Permian outliers west of Mudgee, and the presence of Permian outcrops associated with "features of gravity lows with centres in the south and south-west of the Warrumbungle Range" (Yoo, 1988, page 22). A basement high near Baradine (uplifted basement of Yoo, 1988) divides the Gilgandra Sub-basin (Gilgandra Trough of Yoo, 1988) into a northern and a southern trough. Yoo (1988, page 24) postulated from total gravity anomalies and from a 40m intersection of Permian coal measure sediments in DM Worigal DDH L some 6km east of Baradine, that a thicker sequence would have developed in the area north of Baradine (Figures 2 and 5).

Transaerse structures and. troughs in the Mullaley Sub-basin Tadros (1988c) used the correspondence between the discontinuities in the Meandarra Gravity Ridge (Figure 6) and the structural highs to predict basement structure in areas of little or no borehole control, and to provide the basis for subdivision of the Mullaley Sub-basin into structural sub-units. He

interpreted discontinuities in the positive gravity anomalies over the transverse structural highs to have been influenced by thick basal volcanics of relatively lower density than the large, high-density mafic source underlying the basin. Tadros (1988c, 1993d) subsequently subdivided the basin into a series of north-westerly highs or ridges bounding large troughs.

Gunnedah Basin

252

Figure 6. Structure contours (m asl) on the basal volcanic units supe,rimpose4 on the total-field Bouguer grlvity anomaly map of the eastern part of the Gunnedah Basin, with partial correction for offset and iotati6n discusied ii the text (modif-ied from Tadros, 1988c, figure 2, and Tadros 1993d figure6.16).

Geology of Australian Coal Basins

253 i) Moree and Narrabri Highs and Bellata Trough The Moree High (Tadros, 1988c, 1993d) is the northernmost basement structure interpreted from the total-field Bouguer gravity anomaly map of the Gunnedah Basin (Figures 5 and 6). It appears that the high occupies a broad zone centred at Moree. Tadros (1988c, 1993d) has taken the Moree High as the most appropriate structural boundary between the Gunnedah and Bowen Basins. The Narrabri High (Exon, 1974, amended by Tadros, 1988c, 1993d) is a basement high present in the Narrabri - Wee Waa area. Structure contours on top of the basal volcanics (Figure 2) and the northward onlap of the Early Permian strata of the Bohena Trough to the south strongly support the existence of the Narrabri High (Tadros, 1988c, 1993d). ii) Walla Walla Ridge and Baradine High; Bohena, Bando, Pilliga and Tooraweenah Troughs. The Walla Walla Ridge (Tadros, 1988c) (Figure 5) is a significant transverse basement high which separates the Bohena Trough in the north from the Bando Trough in the south along a WSW trending line passing north of Boggabri. The Walla Walla Ridge stands more than 500m higher than the adjacent trough areas. Isopach maps of the Early Permian Leard, Goonbri and Maules Creek Formations (Figure 4), the Late Permian Porcupine and Watermark Formations, and

the Triassic Dieby Formation indicate that, although the Permian and Triassic sediments are continuous (draped) over the Walla Walla Ridge, they are considerably thinner than in the trough areas.

The south-westward continuation of the Walla Walla Ridge, named the Baradine High (Tadros, 1993d), separates the Gilgandra Sub-basin into the northern Pilliga Trough and southern Tooraweenah Troughs (Tadros, 1993d) (Figure 5). iii) Breeza Shelf; Bundella and Yarraman Highs Structure contours west of Breeza indicate a broad and high shelf area on the basal volcanic rocks. This was named the Breeza Shelf by Tadros (1993d) (Figures 2 and 5). The contours also suggest that the shelf area develops into a transverse high (Bundella High of Tadros, 1993d), which trends south-west to Bundella and appears to extend towards the Dunedoo High (Figure 5). This structure forms the southern boundary ofthe Bando Trough. The trend of this structure coincides with a significant change in the direction of the HunterMooki Fault System north of Breeza. Closer to the Breeza area, however, compressive lateral deformation associated with the Hunter-Mooki Fault System complicated the structure and caused en-echelon, high-amplitude anticlines and associated synclines. These structures now form the Breeza Fold Zone (Tadros, 1988c). There is also a basal structure, the Yarraman High (Tadros, 1988c) near "Yarraman", with a relief of some 300m on the surface of the basal volcanics rocks. As with other transverse basement structures in the

Mullaley Sub-basin, the Permian and Triassic sediments are continuous but thin over the Bundella and Yarraman Highs (Tadros, 1988c; 1993d). iv) Liverpool Structure and Murrurundi Trough A significant discontinuity in the anomalies of the Meandarra Gravity Ridge marks the northern

boundary of a 60km long meridional positive gravity anomaly to the west of Quirindi, Murrurundi and Scone (Figure 6). Tadros (1993d) named the discontinuity the Liverpool Structure, and suggested that it most probably represents a significant crustal fracture (a transfer fault) along which a large amount of displacement between the northern and southern basin compartments has taken place. The anomaly itself corresponds to the northtrending Murrurundi Trough of Tadros (1988c), who interpreted the trough from structure contours and isopachs of the Permian and Triassic sediments in the area south-west of Quirindi. Sparse borehole data indicate a rapid increase in thickness ofthe Permian and Triassic sequences, in addition to a deepening trough. v) Mount Coricudgy Anticline Stuntz (1972) was the first to identify the Mount Coricudgy Anticline from depth-to-basement contours interpreted from aeromagnetic maps. Bembrick & others (1973) subsequently defined the

trace of this anticline, from Muswellbrook to a point south of Rylstone, as the boundary between the structural Sydney and Gunnedah Basins. Seismic, magnetic and sparse borehole information provided the basis for the structure contours on basement are shown in Figure 2. The contours show rapid deepening ofthe basin and thickening ofthe Permian and Triassic sequences south-east towards the Macdonald Trough in the Sydney Basin (Tadros, 1988c; 1993d).

Faults Hunter-Moohi Fault System The Hunter-Mooki Fault System trends north-northwesterly and forms the present eastern boundary of the Gunnedah Basin (Figure 1). It dips at approximately 25o to the east, and truncates the Early Permian sequences of the Maules Creek Sub-basin (Hanlon, 1950b; Thomson & Flood, 1984; Thomson, 1986). Because of its low angle, the Mooki Fault System probably conceals a large area ofthe sub-basin.

In 199L the Australian Geological Survey

Organisation carried out a deep seismic profiling survey across the northern part ofthe basin. The results of this survey suggest that the sediments of the Maules Creek Sub-basin and the underlying basal volcanic units extend for at least 15km to the east beneath the Tamworth Zone (Korsch & others, 1993). Movement on the thrust possibly started after the mid-Permian period of deformation in the New England region and continued intermittently through successive compressional phases until the Middle to Late Triassic.

Boggabri Fault There is a significant disparity of several hundred metres in the vertical elevation of the Maules Cr:eek Formation across the Boggabri Ridge. This disparity can only be explained by upthrusting ofthe eastern sub-basin during the latest Permian to Triassic compressional movements. Although the Boggabri Fault (Tadros, 1993d; Tadros, 1988c amended) has partially accommodated this thrusting, the uplift iesulted in almost a complete removal of the Late Permian sediments from a large area of the Maules Creek Sub-basin. Only remnants of the Late Permian marine Porcupine Formation were preserved in the Deriah Forest area in the northern part ofthe sub-basin.

Gunnedah Basin

254

/r, '//.. ..i'ff*i;' \

*e* ENGLAND

\"?

FOLD BELT

\ \ I

r Bosgabri

I (ROCKY GI FN R DGE)

lGunnedali\

')1

Minor faulting appears to be associated in many instances with uplifting due to post-Permian intrusions (Russell, 1981). The Wilga Park anticlinal structure is also associated with normal faulting caused by intrusion of a ?Tertiary volcanic plug (Hamilton & others, 1988). Close-spaced drilling by coal exploration companies in the Maules Creek Sub-basin, east of the Boggabri Ridge (Thomson, 1986), has identified a number of north-westerly normal faults with vertical displacements ranging from 80 to 120m.

\ .\;

and West Bellata Faults near Bellata in the north. High-angle reverse faults bound at depth the Wilga Park and Nyora Anticlines in the north-west. The crests of these anticlines are affected by extensional normal faults (Hamilton & others, 1988).

MroyX

Figure 7. Structures within the Permian and Triassic strata, Mullaley Sub-basin (compiled from Russell 1981; Hamilton 1985a; Hamilton & others, 1988; modified from Tadros, 1993d). Russell (1981) inferred up-faulting from ERTS-1 imagery (Scheibner, 1973). The present

configuration, morphology and fracture pattern on the remnant outcrops of the ridge suggest the presence of a thrust fault (the "Boggabri Thrust" of Tadros, 1988c), trending NNW probably along a line now occupied by the Namoi River (cf. Tadros, 1988c; 1993d ).

Structure of the Permian and Triassic strata Hanlon (1948-1950), Kenny (1964), Russell (1981), Tadros (1985, 1988c, 1993d) and Tadros lz Tadros & others (1987) have described the structure ofthe Permian and Triassic strata in the Gunnedah Basin. The strata within the Gunnedah Basin generally reflect the structure on the top of the basal volcanic units (Russell, 1981); lvest of the Boggabri Ridge they dip gently towards the basin axis. East of the Boggabri Ridge, however, the strata dip gently to the east, with steeper dips near the Hunter-Mooki Fault System. Steep dips also occur near the intrusives in the Mullaley Sub-basin. A number of folds are locally superimposed upon the regional dip (Russeli, 1981; Tadros, 1985; Tadros lz Tadros & others, 1987), particularly in the Breeza Fold Zone (of Tadros, 1988c) and the NarrabriBohena-Wee Waa area (Figure 7). Some of these folds are diapiric domes related to the emplacement of post-Permian (Jurassic/Tertiary) igneous intrusions (i.e. the Mirrabooka and Wilga Park

Anticlines).

Faulting has been detected in drill core in many places in the Gunnedah Basin (Tadros, 1988c), particularly in the south-east near the Mooki Fault System (Figure 7). Etheridge (1987) also interpreted several faults from seismic surveys, such as the East

STRATIGRAPITY Hanlon (1948-1950), Manser (1965a,b), and Britten & Hanlon (1975), amongst many others, established stratigraphic schemes for various areas within the Gunnedah Basin. Russell (1981,) integrated the previous schemes and into a simplified stratigraphic framework for the basin. In subsequent work duiing the 1980s, Beckett & others (1983), Hamilton & Beckett (1984), Tadros & Beckett (1983) and Tadros (1986a,b) emphasised the importance of sedimentation and depositional environments in stratigraphic analysis. Tadros (L993a,0 has reviewed and described in detail the stratigraphy of the basin. He has also proposed a new stratigraphy, which has since been

modified to accommodate five formalised coal units in the Black Jack Group. The modifred stratigraphy is presented in Table 1.

Floor Rocks The exposed parts ofthe Boggabri Ridge provide the only known outcrops of the effective basement rocks in the Gunnedah Basin east of the Rocky Glen Ridge. Where intersected in drilling programmes (except in the westernmost holes west of the Rocky Glen Ridge), this basement consists mostly of undeformed lavas, tuffs and intercalated sediments. The boreholes intersected silicic volcanics in the west, and both intermediate to mafic volcanics and silicic volcanics in the east.

Hanlon (1949a), Russell (1981), and Beckett & others (1983) have correlated the silicic volcaniis with the Boggabri Volcanics (Hanlon, 1949c) and the intermediate to mafic volcanics with the Werrie Basalt, both of Early Permian age. On the basis of outcrop at Gunnedah, Hanlon (1949a) considered the Boggabri Volcanics and the Werrie Basalt to be coeval. The top part ofthe basal volcanics is deeply weathered, and this is taken to indicate an unconformity on the top of the basal volcanics sequence.

Metavolcanics, metasediments and minor ignimbritic volcanics of the Lachlan Fold Belt form much of the basement underneath the western part of the Gunnedah Basin, the Rocky Glen Ridge and the Gilgandra Sub-basin.

Bellata Group The Bellata Group (Table 1) (Tadros, 1993a,0 comprises all the Early Permian lithostratigraphic units in the Gunnedah Basin, viz. the Leard, Goonbri and Maules Creek Formations. This group

Geology of Australian Coal Basins

255

TABLE 1

Gunnedah Basin

256 unconformably overlies the basal volcanics, and the contact with the overlying Late Permian marine Millie Group varies from conformable to unconformable.

Within the Bellata Group, which comprises mainly fluvial, lacustrine and coal measure deposits, the Leard and Maules Creek Formations are broadly correlated with the Greta Coal Measures in the Sydney Basin, whereas the Goonbri Formation is time-equivalent of the uppermost part of the Dalwood Group (McMinn, 198L; Thomson, 1986).

Leard Formation

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The Leard Formation (Brownlow, 1981; re-defined by Tadros, 1993a,0 consists ofbuffcoloured kaolinitised pelletoidal claystone, originally described as "flint clay" by Loughnan (1973; 1975a,b) in the Wingen, Muswellbrook, Willow Tree and Gunnedah areas. Tadros (1982) described a 1,7.4m section in DM Boggabri DDH2, and extended the correlation to the western side ofthe Boggabri Ridge. The term has since been used to encompass all pelletoidal claystones which rest on the weathered volcanics in the Gunnedah Basin, north

ofthe Liverpool Range.

F.LD BLr

Leard Formation is a colluvial deposit mainly derived from weathering of the volcanics themselves. Clastic units interbedded with the pelletgidal claystone in the Maules Creek Sub-basin, as well as coal seams of the overlying Maules Creek Formation in places, also lie within the unit due to its diachronous nature (Thomson, 1986). Both colluvial and alluvial pelletoidal claystones are present in the Mullaley Sub-basin (Tadros, 1982; Beckett & others, 1983). Thomson (1986) considered the alluvial pelletoidal claystones to be finer grained and generally thicker than the colluvial deposits. The sequence may be associated with poor quality coal seams.

Thomson (1986) suggested that the deep weathering profile on the basal volcanics which produced the

Leard Formation developed from the Late Carboniferous through the Early Permian, until the remnant volcanic highs along the Boggabri Ridge were finally covered during deposition of the Porcupine Formation.

Goonbri Formation Thomson (1986) described a lacustrine unit of fine

grained lithic sandstone and siltstone in the Maules Creek Sub-basin that is different in character from the Leard Formation and the overlying Maules Creek Formation. Named the Goonbri Formation (Thomson, 1986; re-defined by Tadros, L993a,0, this unit is more than 125m thick in the Maules Creek Sub-basin (the lower boundary has not been intersected) and 105.6m in the Mullaley Sub-basin (Bellata Trough).

In the type section in DM Bellata DDH 1 (Tadros, 1993a,0, the formation consists mainly of dark, organic-rich siltstone, thin layers of coal and graded siltstone-claystone laminite, upward coarsening through burrowed, graded siltstone-claystone and laminated fine-grained sandstone and siltstone to

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The clasts are kaolinite clay pellets, generally <25mm in diameter and commonly containing relict volcanic textures (Loughnan, 1975a). The rock breaks with a conchoidal fracture. The boundary between this unit and the underlying basal volcanics is not readily distinguishable, as the

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\ Figure 8. Isopachs (m) of the Maules Creek Formation in the Mullaley and Maules Creek Sub-basins (modified from Tadros, 1993e). fine and medium-grained, moderately well sorted sandstone.

The Goonbri Formation overlies the basal volcanics and, where present, the Leard Formation. The Goonbri Formation is conformably overlain by the Maules Creek Formation, and has been assigned a Permian Stage 3 age (McMinn, 1981). Tadros (1993a,f) has indicated that the Goonbri Formation is present in the deepest parts of the Bellata and Bohena Troughs in the Mullaley Sub-basin. He has also re-defined the formation and assigned a new type section from DM Bellata DDH 1.

Maules Creeh Formqiion The Maules Creek Formation (Brownlow, 1981; re-defined by Tadros, 1993a,0 onlaps the east and west sides of the Boggabri Ridge. It is best developed east ofthe ridge, where it attains a thickness of >800m adjacent to the Mooki Fault System. West of the Boggabri Ridge, however (Figure 8), the formation is generally <100m thick.

In the Maules Creek Sub-basin the formation consists lithic conglomerate and coarse-grained sandstone, together with fine to medium lithic

sandstone, siltstone and claystone. Coal beds, up to 8m thick, are also present. In the Mullaley Sub-basin, Thomson (1986) recognised three lithologically distinct zones (Figure 9): a northern zone containing quartz-rich sandstone, a central zone consisting of volcanogenic sediments, and a south-eastern zone characterised by fine-grained sediments rich in coal. The Maules Creek Formation overlies and onlaps the Leard and Goonbri Formations and underlies the Porcupine Formation. The lower boundary is taken

Geology of Australian Coal Basins

257

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(Manser, 1965a,b; Evans, 1967; Runnegar, 1970; Bourke & Hawke, 1977; cf . Skilbeck & McDonald, 1993). The two formations interfinger in the central and southern parts of the Mullaley Sub-basin (Beckett & others, 1983), and along the eastern side of that sub-basin the Maules Creek Formation is overlapped by the Porcupine Formation. Brownlow (1981) assigned the Maules Creek Formation in the Mullaley Sub-basin to the Early Permian Lower Stage 4 (Morgan, 1976a,b), but McMinn (1993) assigned the majority of the formation in the Mullaley Sub-basin to Upper Stage 4, with only the base occasionally extending into the Lower Stage 4 interval.

Millie Group The Millie Group (Table 1) (Tadros, 1993a,f) comprises the marine sediments of the Porcupine and Watermark Formations. It has limited surface exposure, but extends in the subsurface over almost

Figure 10. Isopachs (m), Porcupine Formation (modified from McDonald & Skilbeck, 1991). the entire area of the Mullaley Sub-basin. The boundary with the underlying Bellata Group is conformable in the central part of the sub-basin, intercalating in the south and unconformable over the basal volcanics along the sub-basin margins. The base is diachronous, ranging from Late Permian Upper Stage 4 in the south-east to Lower Stage 5b in the north and west (McMinn, 1993). The formations of this group have been correlated with the Maitland Group in the Sydney Basin.

Porcupine Formation Outcrop of the Porcupine Formation (Hanlon, 1949a; re-defined by McDonald, Skilbeck & Tadros in Tadros, 1993a, fl is present mainly in the area east of Gunnedah and south-east towards Watermark, particularly at Porcupine Lookout and Mills Ridge to the east of Curlewis and in the Deriah Forest area east of Narrabri (Hill, 1986). In addition, two isolated outcrops of the formation occur north of Mount Kaputar (Russell, 1981). The formation is found in the subsurface throughout the Mullaley Sub-basin, but is only present immediately adjacent to the Mooki Fault System in the Maules Creek Sub-basin area (McPhie, 1984; Thomson, 1984). McDonald, Skilbeck & Tadros (ln

Tadros, 1993a, c), McDonald & Skilbeck (1991) and Skilbeck & McDonald (1993) have described in detail the lithology, stratigraphy and depositional setting of the Porcupine Formation. The thickness of the Porcupine Formation ranges from 0 to 10m along the western margin of the

Gunnedah Basin

258 Mullaley Sub-basin, 20 to 60m in the north and from 30m to >172m in the south-east. The thickest areas are in the south-east of the sub-basin (Figure 10). The Porcupine Formation consists of a sequence that characteristically fines upward from pebble

conglomerate through sandstone to shale and siltstone near the top. It is bioturbated almost throughout. The conglomerate has a high proportion of matrix, and its clasts are composed dominantly of silicic volcanics. Thomson (1986) suggested that this material is a result of subaqueous deposition of Boggabri Ridge detritus.

In most places in the Mullaley Sub-basin, north of the Liverpool Range, the Porcupine Formation overlies the Maules Creek Formation with a sharp but conformable boundary. Beckett & others (1983), however, have reported interfingering offacies of the Porcupine and Maules Creek Formations in the central part of the sub-basin. Along the sub-basin margins the Porcupine Formation is unconformable over the basal volcanics. The upper boundary of the Porcupine Formation is gradational with the lower boundary of the Watermark Formation. The Porcupine Formation represents a marine

incursion in the Gunnedah Basin. Skilbeck & McDonald (1993) advocate an environment in which a transgressive fan delta complex developed adjacent to a lowland fault escarpment. The coarse-grained sediment was delivered-to the marine environment and prograded irregularly by large-scale Gilbert-type foreset accretion processes. The base of the Porcupine Formation is diachronous,

ranging from Permian Upper Stage 4 in the southern and eastern Mullaley Sub-basin north of the Liverpool Range to Lower Stage 5b in the north and west (McMinn, 1993).

Wq.termark Fonnation Outcrop of the Watermark Formation (Hanlon, 1,949a; re-defined by Tadros, McDonald & Skilbeck ln Tadros, 1993a,fl is limited to a small area to the west of Gunnedah and Mount Watermark. The formation is present in the subsurface over much of the Mullaley Sub-basin, from Narrabri in the north to at least south of Quirindi, beyond the limit of borehole coverage underneath the Liverpool Range. The formation has a maximum recorded thickness of 230m in the Breeza-Quirindi area. Tadros, McDonald & Skilbeck (ln Tadros, 1993a,0 have described the lithostratigraphy of the Watermark

Formation in detail.

The Watermark Formation has an upward-fining

transitional boundary with the underlying Porcupine Formation. The lower part of the Watermark Formation forms an upward-fining sequence of sandy siltstone, dark grey siltstone and claystone. Fossil zones containing brachiopod shells and bryozoans are common. Bioturbation and burrowing is intense, and has destroyed most of the primary sedimentary structures. Where preserved, parallel lamination predominates the sedimentary structures, indicating that deposition was principally from suspension settling. The upper part of the Watermark Formation

consists of two lithologically distinctive units forming a major upward-coarsening succession. The lower unit, which is absent north of Boggabri, consists of a finely laminated siltstone and claystone

with little or no bioturbation. The upper unit consists of well-developed upward-coarsening

Figure 11. Isopachs (m) of the Black Jack Group in the Mullaley Sub-basin (modified from Tadros, 1993f).

sequences of grey laminated siltstone, silty

sandstone and siltstone/sandstone laminite at the top, with strongly bioturbated horizons. The percentage of sandstone increases towards the top of the sequence. Sporadic ice-rafted'dropped pebbles', secondary calcite'cone-in-cone' replacement zones and glendonite crystals distinguish the unit. The upper boundary is commonly gradational, but can be recognised by a change from clean, well-sorted, fine to coarse-grained sandstone to an organic-rich, coal-bearing sequence of lithic sandstone, siltstone, claystone and conglomerate. The top of the lower part of the Watermark Formation represents the maximum extent of the

marine transgression, which started with the deposition of the underlying Porcupine Formation. The upper part of the Watermark Formation represents marine regression and deposition of prodelta and delta-front facies, which formed the subaqueous part of the Black Jack delta system. The Watermark Formation spans much of the Late Permian Lower Stage 5b to Lower Stage 5c

palynological zones (McMinn 1993).

Black Jack Group The Black Jack Group (Tadros, 1993 a,{) crops out in a narrow north-north-west trending zone of discontinuous hills extending from Breeza to just north ofBoggabri. Less conspicuous outcrops are

present in the Caroona area in the south-east. Sediments of the Black Jack Group are present in the subsurface over much of the Mullaley Sub-basin. To the east and north ofthe outcrop zone, the Black Jack Group is mostly eroded or covered by

Quaternary alluvium.

Geology of Australian Coal Basins

259 The Black Jack Group averages approximately 200m in thickness over much of the area of the Mullaley Sub-basin north of the Liverpool Range. It thickens, however, from <50m in the west to >470m in the south-east (Figure 11).

Palynological assemblages indicate a Late Permian age for the Black Jack Group, extending from Lower Stage 5c to Upper Stage 5c. Microreticulatisporites bitriangularls first appears in the upper part of the sequence, above the Hoskissons Coal (McMinn, 1993).

Hanlon (1949a) originally named the sequence Black Jack Formation, describing it as a sequence of sandstone, shale, conglomerate and chert with thin bands of limestone and coal. Britten & Hanlon (1975) described its stratigraphy in the Gunnedah-Curlewis area in some detail. Beckett & others (1983) subsequently reviewed the original definition, and divided the sequence into a number of widespread sedimentary facies. Hamilton (1985a,b) and Tadros (1986a,b) further described the principal genetic sedimentary facies within the sequence, based on detailed sedimentological studies. Tadros (1993a,0 assigned group status to the unit, and described its lithostratigraphy in detail. His new stratigraphic subdivision of the Black Jack Group (Table 1) is based on lithological and genetic criteria.

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Tadros (1993a,O has divided the Black Jack Group into three subgroups: the Brothers Subgroup at the base, the Coogal Subgroup in the middle and the Nea Subgroup at the top (Table 1).

Figure 12. Isopachs (m), Melvilles Coal Member (mbdified from Hamilton, 1987; 1985a).

Brothers Subgroup The Brothers Subgroup (Table 1) (Tadros, 1993a,0 consists dominantly of lithic sandstone and siltstone and coal seams in the lower part (Pamboola Formation), with burrowed silty sandstone in the upper part (Arkarula Formation) in the eastern part of the Mullaley Sub-basin and quartz-rich sandstone (Brigalow Formation) in the west and north west of that sub-basin. i) Pamboola Formation The Pamboola Formation (Tadros 1993a,f) ranges in thickness from 89m in the north to >206m in the south-east; it is absent in the far west along the western margin of the Mullaley Sub-basin. The formation consists of lithic sandstone, siltstone, claystone, conglomerate and intercalated coals in generally coarsening-up and sporadic fining-up sequences. It contains interbeds, 3 to 15m thick, of fine to coarse-grained sandstone with finely macerated organic matter and coaly fragments and erosive pebbly bases. It also contains lenticular bedded, fine-grained sandstone and siltstone intercalated with parallel laminated sandstone and claystone containing abundant burrows, together

with intercalated minor units of ripple, parallel and wavy-laminated sandstone and siltstone fining-up to carbonaceous claystone and capped by coal seams. The most significant of the coal seams is the Melvilles Coal Member. The boundary between the Pamboola Formation and

the underlying Watermark Formation is conformable, marked by a change from well-sorted clean sandstone to either thick, erosive-based interbeds of fine to coarse-grained lithic sandstone, pebbly at the base, or to carbonaceous siltstone and Claystone with abundant plant debris. The boundary with the overlying sequence is marked in the south by a change from coal-bearing sequence to a

distinctive unit of fine to medium-grained sandstone with sporadic zones ofvery coarse detritus and abundance of sub-vertical mud-lined worm burrows. In the north the boundary is characterised by a change to a unit containing well-sorted mediumgrained sandstone, poorly-sorted, strongly bioturbated silty sandstone, and a distinctive bioturbated silty sandstone with silicic volcanic pebbles.

The Pamboola Formation is of Late Permian age, spanning the palynological range of Lower Stage 5c

(McMinn, 1993).

Meluilles Coal Member

An important unit of the Pamboola Formation, the Melvilles Coal Member (Hanlon, 1949a); re-defrned by Tadros, 1993a,O crops out near Gunnedah and is widely distributed over the eastern half of the Mullaley Sub-basin (Figure 12). The coal member is generally 2.5 to 3.5m thick in the eastern part of the Mullaley Sub-basin, but thickens south-west of Boggabri and thins towards the west. It consists of moderate to high-vitrinite coal with subordinate layers of fine-grained sandstone, carbonaceous siltstone and claystone, and tuff. Generally the Melvilles Coal Member has a consistent lithotype profile, which can be divided into two sections ieparated by a persistent shaly layer (Figure 13). The lower section consists of a basal ply of moderately bright coal disrupted by thin clastic layers and an overlying ply of variable, coal ralging fr6m dull to bright, but with an overall upward dulling profile. The upper section consists of a

moderately bright coal ply at the base with no

Gunnedah Basin

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Geology of Australian Coal Basins

261 apparent vertical change in coal character, and a top ply ofdull and bright coal and shaly and carbonaceous layers. Pyrite lenses, nodules and framboids are present throughout the coal member, locally concentrated towards the top.

Situated roughly in the middle of the Pamboola Formation, the Melvilles Coal Member is of Late Permian Lower Stage 5c age (McMinn 1993). ii) Arkarula Formation Britten & Hanlon (1975) introduced the name Arkarula Sandstone Member. Tadros (1993a,0 subsequently assigned a formation status to the unit, redefining it to encompass the overlying Allara Shale Member (Britten & Hanlon, 1975). The unit extends over much of the Mullaley Sub-basin south of Narrabri, except in the west and north-west of the sub-basin. The Arkarula Formation is around 25m thick in the

Gunnedah Colliery area, and 51m thick in the north of the Mullaley Sub-basin (cf. Figure 32). It consists ofan overall upward-fining sequence offine to medium-grained sandstone at the base with

distinctive sub-vertical, mud-lined worm burrows and sporadic zones ofvery coarse detritus, overlain by alternating sequences of a poorly sorted silty sandstone and siltstone. At the top, the formation contains finely interbedded sandstone and siltstone fining upward to laminated organic-rich siltstone and fine-grained sandstone with lenticular bedding, oscillation ripples, load casts, mud cracks and mud drapes.

From about 25km south-west of Boggabri northward to Narrabri, the lithology changes to well-sorted, medium-grained sandstone with a thin pebbly base. The sandstone may coarsen upwards and locally become conglomeratic, or it may change into poorly sorted, heavily bioturbated silty sandstone and mud-dominated sequences. A distinctive unit of poorly sorted pebbly sandstone, with an erosive base and crude upward-fining, may occur in the mud-dominated sequence. This unit contains silicic volcanic clasts up to pebble size in a bioturbated medium-grained silty sandstone matrix. In the northernmost part of the sub-basin, it may contain mud-dominated sequences with abundant disarticulated brachiopod shells (Hamilton, 1987).

In the north-west of the Mullaley Sub-basin the Brigalow Formation overlies, and grades laterally to the south-east with, the Arkarula Formation. Locally in the west, where the Arkarula Formation is absent, the Brigalow Formation overlies the Pamboola Formation. The Brigalow Formation has an overall upward-fining character, and is overlain by the Hoskissons Coal (Tadros, 1993a,0. The Brigalow Formation contains the first app e aran ce of D ul hunty i sp or a p aru it ho I a, which marks the boundary between Late Permian Lower and Upper Stage 5 palynological zones (McMinn, 1993).

Coogal Subgroup The Coogal Subgroup (Table 1) (Tadros, 1993a,0 has limited outcrop in the Gunnedah-Curlewis area. However, it extends in the subsurface over much of the Mullaley Sub-basin, from a few kilometres north of Narrabri to Quirindi in the south, and westward to the western margin of the sub-basin. The subgroup consists ofa thick coal seam (the Hoskissons Coal) at the base, overlain by an organic-rich mudstone-dominated unit (Benelabri Formation) in the east and middle parts of the Mullaley Sub-basin north of the Liverpool Range, and by a quartz-rich sandstone unit (Clare Sandstone) in the west. i) Hoskissons Coal The Hoskissons Coal (Tadros, 1993a,f) was identified informally by Hanlon (1949a) and more formally as a coal member by Britten & Hanlon (1975). With the exception of the area north of Narrabri, it extends over much of the Mullaley Sub-basin.

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iii) Brigalow Formation

Coonabarabran

The Brigalow Formation (Tadros, 1993a,O is present in the northern and western areas of the Mullaley Sub-basin (cf. Figure 32). It is up to 28m thick. The unit consists dominantly of medium and coarse-grained to pebbly quartzose sandstone, medium-bedded with a sharp base, and commonly erosively overlies the Arkarula Formation. Mediumscale tabular and trough cross-stratification is dominant. Subordinate fine-grained sandstone, thinly-interbedded with siltstone and carbonaceous siltstone, also occurs in the unit (Flamilton, 1987).

REFEFENCE

Figure 14. Isopachs (m), Hoskissons Coal (mbdified from Tadros, 19939).

Gunnedah Basin

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Geology of Australian Coal Basins

263

Figure 16. rsopachs, caroona coal Member (modified from Tadros, lgggb). The thickness of the Hoskissons Coal ranges from less than lm in the west to more than 12m in the north and to 18m in the south-east (Figure 14). The formation consists predominantly of vitrinitepoor, inertinite-rich (dull) coal, with subordinate Iayers of fine-grained sandstone, carbonaceous siltstone, claystone and tuff. It maintains a consistent lithotype profile over vast areas ofthe Mullaley Sub-basin (Figure 15). The coal is generally characterised by an upward-dulling profile, with two sections separated by a persistent tuffaceous marker. The lower section of the seam generally has a low mineral matter content and consists-of two major plies: a bottom ply consisting of inter-layered dull and bright coal with a tendenly for incre.ased brightness towards the base and a top ply consisting mostly of dull coal with a few thin bright layers and thin carbonaceous claystone and tufflayers. The upper section is generally high in mineral matter, and consists of three major plies: a bottom ply consisting of dull coal, a middie piy co!sisti!g of interlayered carbonaceous claystone, tuff, and dull and bright coal, and a variably

developed top ply consisting ofinterlayered-dull and bright coal with carbonaceous claystone and tuff layers grouped towards the top (Tadros, 1988b; 1993h).

The Hoskissons Coal overlies the Arkarula Formation in the centre and south of the sub-basin and the Brigalow Formation in the west and north. It is overlain by the Benelabri Formation in the east and the Clare Sandstone in the west. Along the

western margin of the sub-basin, the Hoskissons Coal is in fact split by the Clare Sandstone unit. ii) Benelabri Formation (Variation of published name: N.Z. Tadros) Tadros (1986a, b) first described a characteristic mudstone-dominated unit above the Hoskissons Coal in the eastern part of the Mullaley Sub-basin north ofthe Liverpool Range. Tadros (1993a,fl described this unit in detail and named it the Benelabri Mudstone Member. He also described two coal seams contained within it, but did not assign formal status to them awaiting results from the New South Waies Department of Mineral Resources drilling programmes in the south-eastern part of the yglleluy Sub-basin, north of the Liverpool Range. Drilling has since confirmed the correlations of the two coal seams (and others further up in the sequence) and the seam terminology is now widely accepted. The Benelabri Mudstone Member is herein elevated to formation status to accommodate the new Caroona and Howes Hill Coal Members. The Benalbri Formation is present over much of the eastern half of the Mullaley Sub-basin from Turrawan (25km south of Narrabri) to west of Caroona in the south-east, but is absent in the western parts of the sub-basin and in a south-easterly trending zone, 10 to 15km wide, between Breeza and Quirindi. The Benelabri Formation averages 20 to 30m in thickness. It reaches 35m in the north and is up to 68.35m thick in the south-east in the east Caroona area.

Gunnedah Basin

264

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Geology of Australian Coal Basins

265

Figure 18. Isopachs, Howes Hill Coal Member (modified from Tadros, 1998b). The formation has a characteristic overall upward-coarsening sequence of interbedded organic-rich mudstone, siltstone, coal seams and subordinate medium to fine-grained quartzose sandstone. The sequence is distinctly cyclical. Each cycle is represented by an upward-coarsening sequence, 3 to 5m thick, consisting oforganic-rich mudstone at the base, grading to mudstone/siltstone and graded siltstone/sandstone laminite with common burrows and passing into mainly sandstone at the top. Coal may develop in some cycles (the formation contains the Caroona Coal Member in the south-east). Sandstone layers increase towards the gpper cycles. Lenticular and flaser bedding, ripple lamination and desiccation cracks are common (Tadros, 1986a,b; 1993a,fl . The Benelabri Formation overlies the Hoskissons Coal, often with gradational boundary, and underlies the quartz-rich sandstone of the Clare Sandstone. It often contains the Howes Hill Coal Member at the top. Along the eastern and western

margins, the Benelabri Formation also interfingers with sediments of the Clare Sandstone. Locally, where the overlying Clare Sandstone is absent or removed by erosion, the Benelabri Formation may also be partly eroded and directly overlain by the

Wallala Formation.

McMinn (1993) assigned aLate Permian Upper Stage 5 age, associated with the appearance of Microreticulatisporites bitriangularls, to the interval containing the Benelabri Formation.

Caroona Coal Member (New name, N.Z. Tadros)

The Caroona Coal Member is the lowermost of the upper Black Jack coals, and is confined to the south-east corner of the Mullaley Sub-basin north of the Liverpool range (Figure 16). Stratigraphically, the coal member is located close to the base of the Benelabri Formation. A thin sediment wedge consisting of fine-grained sediment separates the Caroona Coal Member from the underlying Hoskissons Coal. Thickness of this wedge vary from a few centimetres in the west to 15m in the east and south-east. The coal member ranges in thickness from 2.3 to 3.4m in its central part, but has a tendency to split, attaining a greater aggregate thickness, towards the south-east (Figure l-6). The overlying sediments (and those of the underlying wedge) are mostly fine-grained and characteristic of the Benelabri

Formation.

The type section for the Caroona Coal Member is an interval 3.1m thick in DM Caroona DDH 3 (250025.6m E and 1531555.1m N), between 88.92m and 91.82m in depth (Figure 17). The Caroona Coal Member has a very consistent lithotype profile, consisting of a bright layered basal section (up to lm thick), a dull and minor bright layered middle section (up to 1.3m thick) and a bright layered upper section (averaging 0.5m in thickness). Thin carbonaceous claystone layers separate the three seam sections; these thicken in a south-easterly direction and split the coal into three discrete seams. Although generally brighter, the

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Geology of Australian Coal Basins

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the Clare Sandstone and overlies the fine-grained sediments of the Benelabri Formation.

McMinn (1993) assigned a Late Permian Upper Stage 5 age, associated with Microreticulatisporites bitriangularls, to the interval containing the Caroona Coal Member.

McMinn (1993) assigned a Late Permian Upper Stage 5 age, associated with Microreticulatisporites bitriangularls, to the interval containing the Howes Hill Coal Member. iii) Clare Sandstone The Clare Sandstone (Tadros, 1993a,{), referred to as the 'Clare Sandstone Member'by Waters (1971), has distinct Iithological characteristics and mappable boundaries (Tadros, 1993a,fl. It is present over an area extending from Narrabri to Quirindi and westward almost to Coonabarabran. The formation ranges in thickness from a few metres in the west and north of the Mullaley Sub-basin to more than 86m in the south-east.

Howes Hill Coal Member (New name, N.Z. Tadros)

More extensive than the Caroona Coal Member, the Howes Hill Coal Member ranges from 1m to 4.95m in thickness (Figure 18) and covers the southeastern quarter of the Mullaley Sub-basin north of the Liverpool Range. The unit is absent along a SE trending zone 5 to 10km wide in the east. The type section for the Howes Hill Coal Member is assigned to an interval 2.77rn thick in DM Howes Hill DDH 1 (21697lm E and 1537034m N), between depths of 425.45m and 428.22m (Figure 19). The Howes Hill Coal Member has a characteristic

upward-dulling lithotype profile, consisting of interlayered dull and bright coal plies at the base, dull coal with frequent bright layers in the middle, and mainly dull coal at the top (Figure 19). The plies are separated by very persistent thin carbonaceous claystone and tuff layers. As with the Caroona Coal Member, the coal plies of the Howes Hill Coal Member tend to be brighter in the south-east (Figure 19). The Howes Hill Coal Member is stratigraphically situated at the top of the Benelabri Formation. The coal member underlies the quartz-rich sandstone of

The unit consists of medium and coarse-grained quartz-rich sandstone, with locally developed quartz conglomerate. The sandstone generally forms medium-bedded units with Iow-angle, medium-scale tabular and trough cross stratification, and

sporadically changes to upward-fining thinner interbeds of sandstone/siltstone rich in plant debris and organic matter and topped with coal (cf. Figure 39). Sedimentary structures include small-scale trough cross-beds, fine climbing ripples, ripple-cross lamination, wavy and parallel lamination, clay drapes and laminated mud layers. The top of the formation generally consists of upward-fining sequence of interlaminated thin siltstone and claystone sequence topped with coal of the Breeza Coal Member (Tadros, 1993a,c). Sporadic coarsening-up sequences may also be present, with

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Geology of Australian Coal Basins

269

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internal erosional surfaces and palaeosols towards the top (Tadros, 1986b, 1993a,0. The lower boundary of the Clare Sandstone is defined by the top of the Hoskissons Coal or the top of the lowermost split of the Hoskissons Coal, and the upper boundary by the top of the Breeza Coal Member. In the eastern half of Mullaley Sub-basin, the Clare Sandstone inter-fingers with, and overlies, the Benelabri Formation. Along the extreme western margin it splits the Hoskissons Coal.

McMinn (1993) assigned a Late Permian Upper Stage 5 age, associated with Microreticulatisporites bitriangularls, to the Clare Sandstone. Breeza Coal Member (New name, N.Z. Tadros)

The Breeza Coal Member extends over much of the southern area of the Mullaley Sub-basin north of the Liverpool Range and generally attains a thickness between 5 and 7m (Figure 20).

An interval5.6m thick in DM Breeza DDH 1 (231887.95m E and 1541383.54m N), at depths of between 70.35m and 75.95 m, has been assigned as the type section for the Breeza Coal Member (Figure 21). The typical lithotype profile can be divided into five coal sections, separated by tuffor claystone layers from 0.05m to 0.35m thick (Figure 2I). The two lowermost coal sections consist of dull coal with minor bright layers, but there is a tendency for increased brightness towards the top. The middle section consists of a bright basal coal ply and a dull top ply. The basal of the two uppermost coal sections consists of dull coal with minor bright layers, and the top section consists ofdull-bright coal. The coal

l..a corg,or"r"," r"",r, flE;lJlEJ" Figure 23. Distribution of the Trinkey Formation of the Black Jack Group in the Mullaley Sub-basin (modified from Tadros, 1993f). member splits in the west, centre and south-east (Figures 21), but can still be recognised because the coal sections maintain their character. The Breeza Coal Member is present at the top of the CIare Sandstone. Lithic sandstone and conglomerate of the Wallala Formation are present directly over the coal member except along a zone a few kilometres wide in the east and south-east, where the overlying sediments are of intermixed quartz-rich and lithic composition.

McMinn (1993) assigned a Late Permian Upper Stage 5 age, associated with Microreticulatisporites bitriangularis, to the interval containing the Breeza Coai Member.

Nea Swbgroup The Nea Subgroup (Table 1) (Tadros, 1993a,0 generally has poor outcrop, but extends in the subsurface over almost the entire Mallaley Sub-basin. The subgroup generally consists of lithic conglomerate, sandstone, siltstone, claystone and coal in the lower part (Wallala Formation), and a fine-grained, tuffaceous coaly sequence (Trinkey Formation) in the upper part.

i) Wallala Formation The Wallala Formation (Tadros, 1993a,f) is present in the eastern and central parts of the Mullaley Sub-basin, between Boggabri and the CaroonaQuirindi area (Figure 22).It reaches a maximum of 55.5m in thickness. The formation consists of a sequence of lithic conglomerate, sandstone, siltstone, claystone and coal, with minor amounts of tuff and tuffaceous sediments (cf. Figure 41). Variably stratified granule

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Figure 24. Isopachs, Clift Coal Member (modified from Tadros, lg93b). to pebble conglomerate, consisting of varying proportions of silicic and mafic volcanics, cherts and jaspers in a lithic sand or clay matrix, dominates the sequence, particularly in the east and south-east. The conglomerate forms planar, medium to thickbedded units up to 5m in thickness, interbedded towards the top with low angle cross-bedded, coarse to fine-grained sandstone, siltstone and claystone (cf. Figure 41). Laterally, the conglomerate shows a gradual and progressive decrease in clast size in a westerly and south-westerly direction. Locally in the south-east, the basal part of the unit is quartz-lithic in composition, but the quartz content decreases rapidly upwards. At the top, the Wallala Formation commonly fines-up to thinly bedded, fine-grained sandstone, siltstone and claystone, with the Clift Coal Member at the top in the south (cf. Figure 41). The Wallala Formation overlies the Clare Sandstone and underlies the Trinkey Formation. The lower boundary is marked by the top of the Breeza Coal Member and its equivalents (Tadros, 1993a, fl. The upper boundary is marked by the base of the Clift Coal Member, which is present mainly in the south, but where this seam is absent the boundary is

marked by rapid increase in tuff and tuffaceous sediments (Tadros, 1993a,0. Fine grained sediments within the Wallala Formation are included with the Late Permian Upper Stage 5 sequence (McMinn, 1993).

ii) Trinkey Formation The Trinkey Formation (Tadros, 1993a,fl is present,

mainly in the subsurface, from Narrabri to Quirindi and to east of Coonabarabran (Figure 23). It reaches

up to 258m in thickness in the south-east towards Quirindi. The unit is dominated by finely-bedded claystone, siltstone and fine-grained sandstone, intercalated with thinly bedded to massive tuff and tuffaceous sediment, and an abundance of coaly matter and tuffaceous stony coal seams (cf.

Figure 46).

The Trinkey Formation contains minor fining-up sequences of cross-bedded lithic sandstone with scoured bases, together with siltstone and claystone showing fine cross-lamination, climbing ripples and root traces. The formation also contains up to 40m of medium to thickly-bedded, lithic, granule to pebble conglomerate, with chert and silicic volcanic clasts in a dominantly tuffaceous sandstone matrix (cf. Figure 46). The conglomerate beds are confined mainly to the south-east, between Gunnedah, Mullaley and Quirindi. Bed thickness and clast size increase towards the south-east, where the conglomerate forms a significant part of the sequence (Tadros, 1993a,fl. The Trinkey Formation also contains several coal seams, of which only two are correlated in the south: the Springfield Coal Member in the lower part of the formation and the Doona seam in the upper part. Coal seam correlation in the upper part is very difficult. The Doona seam can be mapped in the east and central area, where it is characterised by interlayered dull and bright coal at the base, dull coal or dull with minor bright plies in the middle, and interlayered dull and bright coal at the top. However, it loses character in the west, due to excessive splitting and quality deterioration.

Geology of Australian Coal Basins

271 The Trinkey Formation overlies the Wallala Formation and underlies the Triassic Digby Formation. The lower boundary of the unit is marked by the base of the Ciift Coal Member in the south, and where the seam is absent by a rapid increase of tuff and tuffaceous sediments, either as discrete beds or as a matrix in the conglomerate. The upper boundary is identified by the lithological contrast between the generally f,rne-grained tuffaceous coaly sequence of the Trinkey Formation and the basal conglomerate beds of the Digby Formation. The Digby sequence is free of coal, carbonaceous and coaly matter and tuff and tuffaceous sediments; even in the few occurrences where these conglomerates are in contact with conglomerate of the Trinkey Formation, the conglomerates differ in composition and allow easy recognition of the boundary. The conglomerates of the Digby Formation are mainly clast-supported, with the matrix and cement forming less than 30Vo of the total volume of the rock. The clasts are often larger in size than those of

the Trinkey Formation, ranging up to cobble grade, and are more diverse in colour because of the abundance ofred and greenjasper fragments and to a lesser extent different-coloured volcanic rock fragments. The matrix is generally sandstone, similar to the clasts in composition, and the cement is clayey but can be ferruginous close to the surface or in outcrop. The conglomerates of the Trinkey Formation are generally matrix-supported, and are rich in green volcanic clasts, tuff and tuffaceous matter. The clasts are generally small, ranging from granule to pebble size. The matrix is also rich in tuffaceous material, and forms up to 707o of the rock. The boundary between the Trinkey and the Digby Formations is erosive, and represents a PermoTriassic unconformity surface (Tadros, 1993d). McMinn (1993) assigned aLate Permian Upper Stage 5c age to the Trinkey Formation.

Clift Coal Member (New name, N.Z. Tadros)

McMinn (1993) assigned a Late Permian Upper Stage 5c age to the sediments of the Trinkgf Formation which contains the Clift Coal Member. Springfield CoaI Member (New narne, N.Z. Tadros) The Springfield Coal Member is present over much of the-south-eastern part of the Mullaley Sub-basin, north of the Liverpool Range, and is up to 4.8m thick in the central area (Figure 26). The type section for the Springfreld Coal Member is assigned to seam 9 in DM Trinkey DDH 1 (228904m E and L524844m N), which is 4.77m thick between 649.23m and 654.00m in depth. The thickness is up to 4.7m in the central area, but the coal member has a tendency to split and thin (with an accompanying loss of seam character) away from the central area. In the west, where splitting is excessive, correlation is speculative (Figure 27). The lithotype profile is characterised by several 'dulling-upwafd' cycles, ranging in thickness from 0.15m7o 2.Zm (Figure 27)."lhe basal section of the lowermost cycle consists of plies with up to 7007o bright coal, but brightness decreases rapidly in the upper plies. This bright-dull arrangement is repeated in overlying cycles, but with a general tendency for a decreased overall brightness towards the top of the seam (Figurc 27). Discrete sediment layers separate the coal cycles. These sediment layers vary in thickness from 0.1m to greater than 0.3m, and in composition from tuff to tuffaceous sediments in the central and eastern areas to claystone and carbonaceous claystone elsewhere.

McMinn (1993) assigned a Late Permian Upper Stage 5c age to the interval containing the sediments containing the Springfield Coal Member.

Igneous Intrusions and Extrusions

The distribution of the Clift Coal Member is

illustrated in Figure 24.

The type section for the Clift Coal Member is assigned to seams 5 and 6 in DM Clift DDH 2 (231312m E and 1538149m N). The total thickness of coal in these two seams is 5.34m, occurring between 157.97m and 167.38m in depth (Figure 25). The coal member ranges in thickness from 1.2m in the north-east and 3 to 4m in the south-east to more than 5m in the central-west. Where split in centraleast and in the west, thickness can exceed 10m. Generally, the Clift Coal Member has a

Splitting of the coal member by the volcanic-lithic sandstone of the Trinkey Formation also occurs Iocally in the north. The splitting strata are interpreted as channel-fills, ranging in thickness from 2.5 to 8m.

characteristic upward-dulling profrle consisting of five sections separated by persistent claystone or tuff layers from 0.05m to 0.3m thick (Figure 25). The lower two sections consist of interlayered dull and bright coal with increased frequency ofbright layers towards the base. In the upper sections, the bright layers are less common and even so they decrease progressively towards the top. In the s,outh-east the seam displays a similar trend, but with generally brighter ioal plies. The upper part of the Clift Coal Member loses character in the south-west, due to excessive splitting and deterioration of coal quality, making corlelation of all but the basal two sections speculative in that area (Figure 25).

Numerous sills, dykes and plugs of alkali-olivine basalt and teschenite have intruded the Permian and Triassic strata of the Gunnedah Basin, particularly in the central and southern regions. Some of these intrusions are exposed in the area between Breeza and Boggabri. Many authors have considered the intrusions to be Tertiary in age (Jensen, 1907a,b; Wilshire, 1958; Wilkinson, 1956; 1957a,b;1958; 1959; Wilshire and Standard, 1963; Manser, 1965a,b). However, Martin (1993) suggested that some are ofJurassic age, equivalent to the Garrawilla Volcanics which cover large areas in the Coonabarabran - Tambar Springs - Mullaley region and also occur in the north-east on the western side of the Nandewar Range (Dulhunty, 1986).

Martin (1993) found some stratigraphic control, with intrusions being preferentially emplaced in fissile rocks and in coal seams. She also suggested that bright (vitrinite-rich) coal allowed p-referential penetration by magma, and that soft_ening of vitrinite by hot gases ahead of the advancing magma led to the formation of weak, easily fractured coke which facilitated preferential intrusion.

This mechanism may explain the occurrence of numerous igneous intrusions in the Hoskissons Coal, which has a well-developed vitrinite-rich lower

Gunnedah Basin

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Geology of Australian Coal Basins

273 LACHLAN

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Figure 26. Isopachs, Springfield Coal Mernber (modified from Tadros, 1993b). section up to 3.5m thick in the Breeza-Gunnedah area. The Sylvandale Sill (Wilkinson, 1958; Britten

& Hanlon, L975), which is at least 100m thick, closely underlies the coal at Black Jack Mountain near Gunnedah and has carbonised the coal to a variable degree. An intrusion, probably in the form of a laccolith up to 90m thick, has cindered the Hoskissons Coal and'domed-up' the overlying strata in an area to the south of Long Mountain (Tadros, 1985). Further to the south-west a similar igneous intrusion, 110m thick, is situated 40m above the coal but has had no effect on it. Tadros (1985) noticed that only limited cindering has taken place where the igneous intrusion is situated above the coal seam or even in its upper part. Only a few thin igneous intrusions have been intersected in the Melvilles Coal Mernber. In the Breeza-Gunnedah area the Melvilles Coal Member is the least affected of all seams in the Black Jack Formation (Tadros, 1985).

DEPOSITIONAL SYSTEMS Figure 28 shows a comparison between depositional systems and lithostratigraphy of the Gunnedah Basin and the overlying Surat Basin. The terminology of the depositional systems is taken after Hamilton (1991), in which the depositional systems were named according to the most closely corresponding stratigraphic unit or units involved.

Depositional Systems of the Bellata Group Leard - Maules Creek AlluuiallLq.custrine Systemr

The onset of sedimentation in the Gunnedah Basin was marked by widespread accumulation of colluvial and alluvial material Leard Formation) in palaeovalleys on the weathered surface ofthe basal volcanics. This was followed by a very localised deposition of iacustrine facies in the most rapidly subsiding areas (Goonbri Formation). Sedimentation then continued concomitant with basin subsidence in alluvial and lacustrine environments. The first major genetic stratigraphic unit, the Leard - Maules Creek alluvial/lacustrine system, was deposited during this episode. The system derives its name from the lowermost Leard and uppermost Maules Creek Formations but includes the Goonbri lacustrine facies (Figure 28). The Goonbri lacustrine facies, which consists of dark massive siltstone, interbedded sandstone and siltstone, and overlying fine-grained sandstone, is restricted to the most rapidly subsiding central areas of the major sub-basins and troughs. It has been intersected in only six exploration drill holes,

three in the Maules Creek Sub-basin, one in the Bellata Trough (Etheridge, 1987) and two in the Bohena Trough (Tadros, 1993c,e).

The lithologically distinctive pelletoidal clayrocks

(broadly equivalent to the Leard Formation) consist

Contribution from Hamilton ( 1993a,b)

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Geology of Australian Coal Basins

275 L I

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Figure 28. Comparison between depositional systems and lithostratigraphy of the Mullaley Sub-basin and the overlying Surat Basin. The type log is a composite of four boreholes from the southern (DM Brown DDH 1), central (DM Denison DDH 1), western (DM Wilson DDH 1) and northern (DM Gorman DDH 1) parts of the sub-basin The conventional lithostratigraphic nomenclature for the Gunnedah Basin is illustrated on the right (modified from Hamilton,

Figure 29. Isopachs (m), Leard - Maules Creek alluvial/lacustrine system (modified from Hamilton, f 991).

1991, 1993a).

principally of grey and grey-brown clay-fragment sandstones and conglomerates derived from weathering of the basal volcanics (McPhie, 1984). An influx of volcano-lithic detritus from the Boggabri Ridge, and perhaps other local highlands, gradually overwhelmed the supply of this pelletoidal sediment and infilled the lake, giving interfingered boundaries. The volcano-lithic clastics, volumetrically make up the bulk of the Leard - Maules Creek alluvial/lacustrine system. Fine-grained and coaly floodplain and channel margin sediments are intercalated with thickly bedded cobble and granule conglomerates and upward-fining sandstone channel deposits.

The sequence thickens markedly to the east in the Maules Creek Sub-basin (Figure 29), probably in response to a more rapid subsidence rate. This is indicated by the geometry of the sandstone/ conglomerate bodies, by a decrease in clast size in an easterly direction, and by various lithofacies distribution patterns (Thomson, 1986; 1993). The

lithofacies distribution patterns clearly illustrate the narrow neck and widening downslope morphology of the braided alluvial channels emanating from the Boggabri Ridge (cf. Thomson, 1986, 1993).

Up to approximately 175m of sediment accumulated in two main depocentres of the Mullaley Sub-basin (Figure 29). Thomson (1986) subdivided the Maules Creek Formation in the Mullaley Sub-basin into

Figure 30. Isopachs (m), Porcupine - lower Watermark marine-shelf system (rnodified from Hamilton, 1991).

Gunnedah Basin

276 of the ice-dominated Yukon delta (Bering Sea) described by Dupre ( 1982 ).

Thomson (1986) interpreted the fining-up nature of the lower part of the sequence (Porcupine Formation) as a direct response to rising sea level and the relative decrease in reliefon the Boggabri Ridge. The upward increase in abundance of acid volcanic clasts at the expense of quartz is a response !o the shutting off of sediment supply from the Lachlan Fold Belt with rising sea-level. Finally, as the Boggabri Ridge was submerged, the propoition ofacid volcanic clasts decreased, and fine-giained se<iiments were deposited in deeper marine conditions. The New England Fold Belt does not appear to have contributed any sediment to the basin until the Upper Watermark - Lower Black Jack delta systems developed (Hamilton, 1987). The upper part of the sequence forms an upward-fining succession of sandy siltstone, dark-grey siltstone and finally claystone representing the maximum extent of transgression.

Upper Watermprh - Louter Black Jach Delta Systemsr Elorigate

2sk.

Figure S1. Net sandstone thickness (m), lower delta plain facies, Upper lfatermark - lower Black Jack delta systems (modified from Hamilton, 1985a).

three distinct zones (Figure 9). The most northerly zone contains quartz-arenite detritus derived from the Lachlan Fold Belt. Thomson (1986) suggested that rivers flowing in an easterly direction traversed this area in the Early Permian, and that much of the sediment was deposiied in the drainage basin east of the Boggabri Ridge. The central zone contains south-westerly flowing humid alluvial fan deposits derived from the Boggabri Ridge, with the alluvial fan system hindering peat accumulation to a considerable extent. The south-eastern zone was characterised by slow subsidence rates with less sediment influx, which resulted in the thick accumulation of peat. The Maules Creek Formation is fine grained and thin in this area (Figure 9).

Depositional Systems of the Millie and Lower Black Jack Groups Porcupine - Lower Watermarh Marine Shelf Systemt

Inundation of the basin by marine transgression transformed the earlier Permian alluvial conditions to a marine-shelf setting. Sedimentation was initially dominated by shallow-marine conditions, but with continued inundation the marine shelf setting deepened. Isopachs of the marine-shelf system (Figure 30) highlight depocentres in the northern and south-eastern parts of the Mullaley Sub-basin. Deposits of this episode comprise the Porcupine - lower Watermark marine-shelf system (Figure 28) (Hamilton 1993a,b), represented by a marine shelf sequence of bioturbated, silty lithic sandstones. Conglomeratic detritus within a silty sandstone matrix is abundant in the lower part of the system. This facies is similar to offshore deposits

South-westerly progradation of two major delta

systems ended the existence of marine-shelf conditions in the basin. These systems are named after the upper part of the Watermark Formation and lower part of the Black Jack Group (Figure 28),

the distribution of which approximately corresponds to the extent of deltaic deposition. Progradation commenced first in the northern part of the basin in a wave-modified delta system, and then shifted southward with time by the process of lateral delta switching. Diversion to the south would have been favoured by the regional configuration ofthe southward-broadening and deepening basin (Hamilton, 1985a). Regression continued in the south in a fluvial-dominated delta system, whilst in the north, minor reworking of the abandoned delta platform occurred. Prodelta sediments of finely laminated siltstone and claystone are thickly developed in the southern fluvial-dominated delta system. The prodelta sediments change vertically to well-developed upward-coarsening siltstone/sandstone cycles and multiple thin to medium, erratically upwardcoarsening sand units of delta-front and lower delta-plain origin. Prodelta clays are absent in the north.

In the south-east, coastal aggradation was contemporaneous with deltaic progradation and the sediments consist principally of sandstone, conglomerate and intercalated coals. i) Lower Delta-Plain Facies The net sandstone map of the lower delta plain facies (Figure 31) has a lobate to highly elongate geometry, indicating that it was deposited in a combination of fluvial-dominated and wave-modifred delta systems (Hamilton, 1985a). The principal sedimentary facies, as recognised in drill core, are distributary-channel, crevasse-splay and splaysubdelta, interdistributary-bay and marsh deposits. The sand bodies ofthe distributary and larger crevasse-splay channel fills are 3 to 15m thick, and merge laterally to form the framework of the delta platform. The interdistributary bay sediments were deposited in laterally extensive areas, and comprise burrowed and tidally sorted siltstone and fine sandstone. The crevasse splay sub-facies sediments

Geology of Australian Coal Basins

277

DEPOSITIONAL ENVIRONMENT

A G

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Figure 33. Depositional systems, Ifpper Black Jack depositional episode (modified from Tadros, Figure 32. Isopachs (m), Arkarula shallow-marine and Western bed-load fluvial systems system (modified from Hamilton, 1991). form upward-coarsening sequences of siltstone and fine sandstone, and the marsh deposits consist principally of claystone and siltstone with varying amounts of carbonaceous material as well as coals. Depositional Controls on Lower Delta-plain Coal Seams

Several coal seams are developed in the lower delta-plain facies, although only the Melvilles Coal Member has economic significance at the present time. Hamilton (1985a) investigated the relationship between these coals and their depositional setting by comparing coal occurrence and total coal thickness maps of the lower delta-plain facies to the geometry of the framework sandstones. The subsurface distribution and thickness of the coals was found to correlate well with areas of high net-sandstone thickness, a relationship that is consistent with a

deltaic setting.

The coal seams in the lower delta-plain facies range from 0.3 to 3.4m in thickness, but the majority are <1.0m. Only the Melvilles Coal Member is

consistently thicker than lm, although other seams attain 2m in some areas. The Melvilles Coal Member and the other thick seams are laterally extensive and have been confidently correlated, but correlation of the thinner seams has proven very difficult due to the spacing of exploration boreholes and the discontinuous nature of the coal beds. Hamilton (1985a) suggested that the contrast in thickness and lateral extent of the coal seams in the lower delta-plain facies was due to two distinct mechanisms of peat formation. The thicker, laterally extensive coals, particularly the Melvilles Coal Member, probably formed as blanket peats that covered large areas following delta abandonment. The thin, discontinuous coals, on the other hand,

1993g).

formed during active deltaic progradation, and occupied marshes that flanked distributary channels and capped infilled interdistributary bays. The Melvilles Coal Member overlies a variety of deltaic facies (Hamilton, 1985a). It displays a lobate geometry (Figure 12), which significantly overlaps with the net-sandstone distribution pattern of the lower delta-plain facies (Figure 31). Hamilton (1985a) suggested that seam thickness was strongly controlled by this underlying deltaic platform, with the areas of high net sandstone representing the ancient delta lobes which provided the most stable base for peat accumulation. These delta lobes were probably topographically higher, and were less affected by destructive marine influences than the interdistributary tracts, which were readily

inundated in the slowly subsiding coastal environment. Significantly, the thickest and best quality coal occurs in the topographically uppermost part of the lower delta plain.

In the south-eastern-most part of the basin, the Melvilles Coal Member splits into several seams, which are most commonly separated by distributarychannel and crevasse-splay deposits. This area was probably the site of active sedimentation and rapid subsidence during the time of the seam's

accumulation (Hamilton, 1985a).

Arkarulq Shallow -ma.rine Sy stem- and Western Bed-load. Fluuial System' Deposition of the delta systems was followed by a peiiod when marine conditions affected the Sydney, Gunnedah, and Bowen Basins. The Arkarula shallow-marine system (Figure 28) was deposited during this episode, deriving its name from the Arkarula Formation. Hamilton (1985a, 1987) subdivided the shallow-marine system into a northern tidal shelf system and a southern wavedominated delta system, based on contrasts in

Gunnedah Basin

278

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REFERENCE Borehole

oto2045 +4r

Figure 34. Sulphur percentage, Iloskissons seam (modified from Tadros, 1993b).

Figure 35. Raw coal isoash, Hoskissons Coal (modified from Tadros, 1993b).

depositional style between the northern and southern parts ofthe basin.

system flowed east to interfinger with and ultimately overlie the shallow-marine deposits.

The northern subfacies is characterised by tidal sand ridges up to 30m thick, together with tidal channel-fills. These sediments consist of fine to coarse sandstone with abundant pebble horizons commonly containing bioturbation and shell fragments.

Isopachs of the Arkarula shallow-marine system show depocentres in the north-central and south-central parts of the basin (Figure 32). To the south the marine strata are replaced laterally by active deltaic deposition. Two minor depocentres are recognised in the west (Figure 32), and these correspond to thickening of the Western bed-load

The wave-dominated delta subfacies is dominated by barrier beach and nearshore sand facies. The

sediments consist of strongly bioturbated silty

sandstone with prominent subvertical mud-lined burrows. The Arkarula Formation, which forms a valuable marker horizon in the Gunnedah area, is an example of this type of lithology. Lagoonal deposits of lenticular-bedded sandstone and siltstone also make up a significant component of the wave-dominated delta subfacies.

Although widespread, the marine transgression was only short-lived. Subsequent lowering of sea level was accompanied by deposition along the western basin margin of fluvial deposits, which Hamilton (1985a, 1987) referred to as deposits of the Western bed-load fluvial system. Towards the basin centre, the fluvial channels debouched into bay environments of the shallow-marine system to form small wave-dominated deltas with evidence of reworking by tidal processes and wave action. (Hamilton, 1985a, 1987). They are therefore intergradational laterally with the shallow marine deposits. The Western bed-load fluvial system is characterised by discrete blocky channel-fills dominated by bed-load deposits of medium to coarse-grained quartz-rich sandstones, generally upward-fining and erosively based. The fluvial

fluvial system.

Depositional Systems of the Upper Black Jack Group Detailed analysis of drill core and geophysical borehole data has allowed delineation of four depositional systems within the upper part of the Black Jack Group (Figures 10,28 and 33) (Tadros, 1993g): the Hoskissons peat swamp system at the base, overlain by the Lacustrine system in the east, a westerly derived fluvial system in the west, and an easterly derived fluvial system at the top.

Hoskissons Peq.t Swamp System Rapid lowering of sea level terminated marine conditions and provided an extensive platform of marine-reworked deltaic sediments. This platform was rapidly colonised by vegetation, and vast peat swamps were established (Beckett & others, 1983), forming the Hoskissons Coal. The Hoskissons peat-swamp system overlies nearshore, barrier beach and lagoonal deposits in the south and centre of the basin (Figure 33). Based on the associated underlying facies, Hamilton (1985a) suggested that the Hoskissons Coal formed mostly as a back-barrier lagoonal peat deposit.

Geology of Australian Coal Basins

279 However, the Hoskissons Coal extends over large areas in the north and west of the sub-basin, where it overlies and interfingers with the westerly derived fluvial sediments. This suggests that the peat swamps must have extended far inland, northwards and westwards, and that they were subject to the influence of the Western fluvial system (Figure 33). The peat swamps were surrounded by highlands in the east and west, and initially by a regressive marine environment in the south. Based on the presence of shoreline sands beneath the Hoskissons Coal in the south, Hamilton (1985a) suggested that the sea level fall may have been irregular, with

intervening short-lived stillstands rather than a gradual regression.

With each additional drop in sea level, a new extensive platform was exposed which probably led also to the development of new shoreline sands further to the south. The peat swamps rapidly encroached over the freshly exposed platform and the old shoreline sand deposits. At each stage, the shoreline sands probably acted as barriers which protected the outer edge of the peat swamps from inundation by the sea and sealed off the oxidising effects of sea water until the next sea level fall. The barriers also may have been effective in damming ground water flowing down from the highlands, so that the water table was nearly always high enough for the formation and preservation of the peat (Tadros, 1986b). This mechanism, if sustained for long periods and if accompanied by an appropriate rate of subsidence, can promote the growth of thick and extensive peats, low in mineral matter and sulphur (Teichmriller & Teichmiiller, 1968). A high water table would also have favoured the formation of the vitrinite-rich plies at the base of the Hoskissons Coal. Although the Hoskissons Coal is generally high in mineral matter (Figure 35), its lower section characteristically yields low ash and Iow sulphur (Figures 15 and 34). The low mineral matter and sulphur contents of the lower section of the Hoskissons Coal in the south and centre of the sub-basin may be attributed to a highly efficient barrier system. The higher ash yield of the upper section of the Hoskissons Coal can be attributed to a large supply of erosional detritus, contributed mainly by the western fluvial system which was active during peat formation (Tadros, 1988a, 1993g). The strong fluvial influence on the Hoskissons peats is evident on the isopach and isoash maps (Figures 14 and 35). Therefor-e, it seems most probable that the back-barrier lagoonal interpretation of Hamilton (1985a) for the Hoskissons Coal holds only for the lower section, particularly in the centre and south of the sub-basin (Tadros, 1988a, 1993g). Conditions of high water table in the swamp, which favoured the formation of vitrinite-rich coal at the base of the Hoskissons Coal, did not persist for very long. A falling water table exposed the peat to the oxidative effects of the atmosphere and promoted

the formation of inertinite-rich lithotypes, which characterise the top ply of the lower section. A subsequent gradual raising of the water table as a result of continued subsidence, particularly in the east, accounts for the upward increase of vitrinite in the upper section (Tadros, 1993g). Considerable subsidence must have taken place during and after the withdrawal of the sea, to accommodate the large thickness of peat now represented by up to 17m of coal in the Hoskissons

DESCRIPTION

SEDIMENTARY FACIES

r sANor il

r cwl

LAKE BASIN FACIES Sparse bunows/biolLrbalon

4m Desr..al on cracks cross bedded sandslone

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wavy lenlrcu ar and i aser beddina

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Graded nrudslone/sitslo.€ amin le

LAKE BASIN FACIES OrqanLc-rchmddslone

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r ch mudston€

PEAT SWAMP

Figure 36. Idealised vertical section showing sedimentary facies of the lake sequence, upper part of the Black Jack Group (modified from Tadros, 1993g). Coal (Figure 14). The presence of organic-rich mudstone and 'canneloid' coal at various levels

within the seam indicates varying rates of subsidence within the peat swamp.

Tadros (1988b, 1993g,h) indicated that liptinite increases in proportion towards the top of the Hoskissons Coal. This increase, and the absence of carbonates in the overlying freshwater sediments, suggest that the peat which produced the upper plies formed under non-oxidising (anaerobic) acidic conditions. Inertodetrinite macerals form a large proportion ofthe inertinite-rich upper plies and, in association with alginite, suggest transportation of degraded plant tissues into the lacustrine environment in which the sporinite and inertodetrinite accumulated. The top plies of the Hoskissons Coal are also rich in attrital/detrital inertodetrinite and desmocollinite macerals and in discrete and disseminated detrital mineral matter, suggesting that the swamp was rapidly subsiding and subject to flooding during peat

formation (Tadros, 1988b). Re-working of plant remains by flooding within the peat swamp formed 'hypautochthonous' coals rich in discrete and disseminated mineral matter (Teichmi.iller & Teichmiiller, 1982).

The increased rate of subsidence with a steadily rising water table in the eastern half of the sub-basin transformed the peat swamps into a large lake system. Biological and physical degradation products of the 'drowned' peat, together with wind or waterborne spores, provided the organic matter which intermixed with water-laid muds and autochthonous algae and formed the characteristic

Gunnedah Basin

280

gradational top of the Hoskissons Coal (Tadros, 1988b).

Lacustrine System

Over much of the eastern half of the Mullaley Sub-basin the top of the Hoskissons Coal is characterised by an upward gradation from humic coal through sapropelic coal to organic-rich mudstone, indicating the change from the peat swamp to a lacustrine system (Figure 33) (Tadros,

"l I

NEW ENGLAND

-l i\

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1986a,b).

i) Lake Margin Facies The lake margin facies is present mainly around the western, south-eastern and southern margins of the lake system. Figure 36 shows typical lake margin deposits overlain and underlain by lake basin facies sediments. Lithologically the lake margin facies consists of cross-bedded sandstone, interbedded sandstone and siltstone with common burrows, and abundant plant debris. Thin units of upward coarsening, moderately well-sorted sandstone also occur. Minor sedimentary structures include wavy, Ienticular and flaser bedding, ripple lamination with mud drapes, dewatering and scour-and-fill structures, desiccation cracks and reworked mud clasts (Figure 36) (Tadros, 1986a,b). The bedding and sedimentary structures of the lake

margin facies reflect the interaction between fluvial and lake processes. Lake shoreline wave processes resemblelhose along marine coasts, brit ire reduced in intensity and scale. They produce a variety of features, the most important being wind-tidal flats and delta facies (Galloway & Hobday, 1983a).

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REFERENCE Borehole

o.-J9--3i. Figure 37. Percentage sandstone, Lacustrine system, upper part of the Black Jack Group (modified from Tadros, 19939).

Wind-tidal flats form an important feature of the lake margin facies. In lake systems, lunar tides are negligible and have insignificant effect on lacustrine sedimentation. Wind-tidal flats in lakes, however, develop as a result of wind stress which causes impoundment of the upper layers of lake water against the shore while the bottom layers flow in the opposite direction in order to maintain equilibrium. Impounded water is released in response to changes in wind velocity or direction. The effect of this process on sedimentation resembles tidal influence, producing similar but smaller scale sedimentary structures such as wavy, lenticular and flaser bedding, ripple lamination and desiccation cracks (Figure 36). This environment is also favourable for burrowing organisms, as sedimentation rates are slow and periodic flooding provides a constant supply of nutrients (Tadros, 1986a,b).

branches transported during floods, is common in

Tadros (1986a,b; 1993g) has indicated that lacustrine deltas and associated deltaic facies in the Mullaley Sub-basin are fluvially dominated. Sediments were supplied by eastward and southeastward flowing streams of the western fluvial system (Figure 37). The streams debouched into the lake system and developed small, fluvially dominated lacustrine deltas and associated deltaic facies, including channel, mouth bar, crevasse splay and inter-channel marsh.

The lake margin facies pass laterally eastwards into (and interfinger with) the lake basin facies (Figure 36). The lake basin facies can be recognised in drill core on the basis of several criteria,

The channel deposits consist of medium-bedded, medium to coarse-grained sandstone units up to 3m thick. The sandstone generally has an erosive base and may contain reworked mudstone clasts at the base.

In drill core, mouth bar deposits are typically upward-coarsening, moderately well sorted, clean sandstones which range from fine to coarse-grained. Plant debris, including wood fragments and small

the mouth bar deposits.

Crevasse splays form upward-coarsening sandstone units with sharp bases and fine cross-stratification.

Interchannel marsh deposits consist of laminated fine sandstone, siltstone and carbonaceous claystone with thin coal layers. The palynological assemblages of the burrowed units

within the sequence are characterised by an absence

of spinose acritarchs (McMinn, 1993), suggesting that there was no marine influence on these units. The sequence is also characterised by the absence of chemical deposits, which suggests that the sediments were laid down in a freshwater

environment.

ii) Lake Basin Facies

including lithology, sedimentary structures and association with other facies.

Lithologically the lake basin facies is sedimentstarved, and consists of organic-rich mudstone grading to finely laminated carbonaceous claystone and siltstone towards the top (Figure 36). In general, the lake basin facies has a homogeneous appearance in core. The organic-rich mudstone is very dark grey to black in colour, oflow density (1.6 to 1".9 g.cm-3), breaks with a conchoidal fracture and resembles sapropelic coal. X-radiographs of the organic-rich mudstone show very fine (1 to 2mm thick), parallel, varved or graded laminations and an absence ofburrows. The lower part ofeach lamina consists of very fine silt grading upward to black sapropelic material (degraded organic muds).

Geology of Australian Coal Basins

281

Identified macerals are mainly inertodetrinite and a relatively high percentage ofliptinite group macerals, particularly sporinite and some aiginite. The lake basin facies is distinguished by a lack of cross-bedding and the presence of desiccation cracks and biogenic structures, including burrows, which suggest that deposition took place below wave base in deep, stagnant anaerobic waters. The alternation of finely laminated black sapropelic to organic-rich mudstone with fine siltstone and claystone is

attributed to seasonal fluctuation in sedimentation

rates. The siltstone laminae indicate influx of fluvial sediments during the wet season. The black sapropelic laminae suggest seasonal plant growth (blooming) and settling of degraded organic matter from surface waters on to the lake bed during seasons with low runoff and negligible sediment influx (Tadros, 1986a,b; 1993g). Recognition ofthe lake basin facies also depends on its association with overlying (and underlying) lake

margin deposits. iii) Depositional Style and Evolution Cyclic fluctuation of lake level and variations in sediment influx caused marginal sediments to interfinger with lake basin sediments in the Mullaley Sub-basin (Tadros, 1986a,b; 1993g). A cyclic pattern between the two facies can thus be recognised in core and from geophysical log patterns. The cycles are relatively'thin, ranging in thickness frorn 3 to 5m, and an average of six or seven cycles are present. Each cycle typically consists of organic-rich mudstone at the base, grading to mudstone/siltstone and graded siltstone/sandstone laminite, which in turn passes into sediment consisting mainly of sandstone at the top. Contact with the overlying cycle is either

Figure 38. Percentage sandstone, western fluvial system and lacustrine system (modified from Tadros, 1993g).

gradational or erosional. The erosion surface may be overlain by a thin upward-fining sequence of graded fine sandstone, siltstone and mudstone interbeds with sparse burrows, before passing upwards and basinwards into the organic-rich mudstone (Figure 36). Younger cycles are more sanddominated, marking the encroachment of the Western fluvial system over the Lacustrine system (Figure 36). Infilling of the lake with upwardcoarsening sediment sequences was finally accomplished by the continued lakeward progradation of crevasse splays and lacustrine deltas (Tadros, 1986a,b;1993g) (Figures 36 and 37). The cyclic pattern of the lake sequence is represented by mudstone of the lake basin facies

alternating upward-coarsening sequence from mudstone/siltstone to siltstone/sandstone laminite and finally to sandstone at the top.

Western Fluaial System Sediments of the Western fluvial system (Figure 33)

of the upper Black Jack sequence signify a major change in depositional and tectonic setting in the basin. This change is represented first by a period

characterised by almost total lack of deposition of terrigenous clastics during the accumulation of the Hoskissons peats, except along the western sub-basin margin, followed by an increase in the supply of the quartz-rich sands from the Lachlan Fold Belt region and progressive expansion of the western fluvial system until it eventually covered the entire sub-basin. The change probably developed in response to tectonic ioading of the eastern edge of the craton, which resulted in a 'foreswell' along the western basin margin. In the east, the quartz-rich sandstone is separated from the Hoskissons Coal by the lacustrine sediments (Tadros, 1993g). The percentage sandstone map for the interval between the Hoskissons Coal and the Breeza Coal Member (and their equivalents in the north), which represents the lithofacies pattern of the combined Western fluvial/Lacustrine systems (Figure 38),

displays a prominent fluvial style with strongly dip-oriented and confluent contour patterns. The major depositional elements recognised within this system are the south-easterly flowing contributory streams, expressed on the maps by high sandstone percentages representing elongate sand bodies emanating from the Lachlan Fold Belt in the west, and a trunk channel complex flowing south and south-easterly along the sub-basin axis. The streams were dra,wn to the east and south-east by the rapid subsidence, which initially caused the transformation of the Hoskissons peat swamps into the Lacustrine system and finally caused the infilling of the lake itself. i) Channel Fill Facies The channel fill deposits of the Western fluvial system consist mainly of medium and coarse-grained quartz-rich sandstone, with quartz conglomerate locally developed. In drill core the sandstone generally forms medium-bedded units with low-angle medium-scale tabular and trough cross stratification (Figure 39). However, large-scale trough cross-stratification cannot be positively identified in drill core, particularly in coarse-grained granule and pebble conglomerates. The sequence illustrated in Figure 39 shows a typical western (bed-load) fluvial sequence preserved along the western basin margin. The primary sedimentary structures and the character of the sandstone packages in core and outcrop (Tadros, in preparation) suggest that the system was dominated

Gunnedah Basin

282 Ss

C Cs Sl

Csl

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C Cs Sl

CSr

| | lYiT:'i9"P

by broad, shallow, low-sinuousity streams that carried bed-load material almost exclusively. Deposition was mainly in medium-scale dunes and small to medium-scale sand bars (Tadros, 19939). ii) Channel Margin Facies The channel margin facies in general overlies the channel fill facies and consists of finely interbedded sandstone, siltstone and carbonaceous siltstone. The deposits represent peripheral sedimentation in laterally restricted, ponded areas. Such sediments are rare in the west, but form a minor component of the fluvial system in the eastern part ofthe sub-basin. Some units grade upwards into thin coal seams.

Levees and crevasse splays form the two principal channel margin facies, and are readily reiognis-ed in drill core. The levee sequence displays rapid

interbedding of sandstone and siltstone, reflecting fluctuating but generally shallow flow depths. Primary sedimentary structures in the levee sequence include small-scale troughs, frne ripples, ripple cross lamination, climbing ripples, wavy and plane parallel lamination and abundant clay drapes. Levees support plant growth, and thus their sediments are rich in plant debris and organic matter. Crevasse splay deposits form elongate lobes or fan wedges originating at a crevasse channel cut in the levee. The sediment load of crevasse splays is dominated by silt and fine sand but can also be coarser in dominantly sandy bed-load streams, as is frequently the case with the western fluvial system (Tadros, 1993g). Internal structures such as climbing ripple cross lamination reflect rapid sedimentation. Other common structures include ripple and medium-scale trough cross lamination,

-- :<-'-'-'/

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mud drapes, graded bedding and scour-and-fill structures. IJpwald-coarsening sequences were sometimes developed as the crevasse splay continued to progr:ade with successive floods over the floodbasin. Colonisation by plants has resulted

/. ..' ....: --i/:-':'-:*J?i

REFEREN('L

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iii) Floodbasin Facies The Western fluvial system is dominated by a

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a(l = (..Ebn(tute

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in disturbance of underlying depositional structures and the formation of oxidised and leached zones (palaeosols). Abandonment of individual crevasse splays is indicated by upward-fining of grainsize and by a decrease in the scale of sedimentary structures, with macerated products of organic material commonly preserved on bedding surfaces, laminations and cross-bed planes.

\.t

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= S.ant rtr.r[, r

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bed-load axial channei complex and principal tributaries, indicating that a large percentage ofthe load transported was coarse sediment and that there was a significant lack of fines. Sediments were carried by a south-easterly contributory channel system via an axial drainage complex into a large inter-channel lacustrine system that developed as a result of a rapid subsidence in the eastern part of the Mullaley Sub-basin. Consequently, development of typical floodbasin deposits was limited to areas above the lake level and in the western region (Tadros, 1993g). Elsewhere, floodbasin deposits were modified by the lacustrine processes at the lake margins and deeper into the lake basin (as is discussed in detail with the lacustrine system).

The sand content of the floodbasin facies varies considerably, depending on the proximity to active channels and crevasse splay centres. Floodbasin deposits in the western part of the Mullaley Sub-basin, and iocally in some northern and southern areas, consist mostly of uniform, finely

Geology of Australian Coal Basins

283 incision was by south-westerly flowing channels, which were responsible for deposition of the sediments of the eastern fluvial system.

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l-. t

\,"

ilz

"l4\ (ROCRY GLEN *'OO''

Deposition of the Western fluvial system gradually diminished as the supply of the quartz-rich sands declined due to changes in the base level and the decreased rate of erosion in the Lachlan Fold Belt region.

roro asrr r/ . \.

rGunnedali\

ai .,I

.nl l/

'f '\

Coonabarabran "1

^/.

^\'/

-9 BEFERENCE

Figure 40 also shows a rapid change in thickness of the upper western fluvial sediments in the southern part ofthe basin, from an average of50m to as low as 5m, along a transverse south-westerly trend. Incision along this trend, although deep, did not reach the underlying lacustrine sequence because of the high subsidence rates, which allowed build-up of such a great thickness (up to 63m) of the upper western fluvial sediments, particularly along the main axial channel (Tadros, 1993g).

Borehole

o'J9-3ot' Figure 40. Isopachs (m), upper part of the western fluvial system (interval between the Howes Hill and Breeza Coal Members and their equivalents) showing incision due to erosion by the south-westerly flowing channels of the Eastern fluvial system. Erosion is most pronounced in the north where subsidence rates were low, with possible occasional uplift or stillstand. In the south-east where subsidence was rapid, a thicker sequence accumulated and was little affected by erosion (modified from Tadros, 1993g). laminated mudstone with sporadic sandstone or siltstone intercalations representing the distal 'feather edge' of large crevasse splays. Peat was also part of the floodbasin facies and accumulated in broad areas of sediment by-pass. Primary structures were sporadically destroyed by burrowing, plant growth and pedogenic processes. Desiccation cracks in mudstone horizons are rare, reflecting occasional exposure to wet and dry conditions (Tadros, 1993g). iv) Erosion and Termination The Western fluvial sequence was subjected to considerable intraformational and post-depositional erosion prior to deposition of the eastern fluvial sediments. Borehole evidence indicates that in most cases where sections of the western fluvial sequence (and occasionally the upper parts ofthe lacustrine sequence) are absent the sediments are always erosively overlain by the eastern (bed-load) channel facies (Tadros, 1993g). Exceptions are where mixing of the easterly and westerly derived sediments occurs in the south-east.

In the northern part of the Mullaley Sub-basin, isopachs ofthe upper western fluvial sequence (above the Lacustrine system) show contour patterns and rapid thickness changes (Figure 40),

which suggest significant fluvial incision into the upper strata of the underlying lacustrine sediments. The contours strongly suggest that the fluvial

The Breeza Coal Member and its equivalents in the north represent a significant period of minor terrigenous clastic deposition in the sub-basin (Tadros, 1993S). The widespread distribution ofthe seam suggests that the basinwide peat accumulation was controlled by a major tectonic event. The Breeza Coal Member coincides with a significant change in provenance from dominantly westerly-sourced quartz-rich sediments to easterly-sourced volcano-lithic detritus, suggesting a corresponding change in tectonic regime. However, some areas along the axial drainage system show evidence of intermixing of the two lithologies for a brief period after cessation of peat formation of the Breeza Coal Member. Intermixing is most evident in the south-east, where the boundary between the two systems is gradational. The sequence illustrated in Figure 41 from DM Wallala DDH 3, located close to the axial channel complex in the south-east, shows a typical

gradational change in lithologies.

At the base is a coarse-grained quartz-rich sandstone typical of the Western fluvial system. Towards the top, the quartz-rich sandstone is intermixed with an increasing proportion of lithic sandstone, which frnally dominates. The Breeza Coal Member, which is generally below the transitional zone, is split by fluvial channel deposits. It is poorly developed in DM Wallala DDH 3 and in other boreholes along the main axial channel. Generally, the eastern conglomerate units become poorer in quartz progressively upwards. Intermixing probably occurred during the transition from craton-controlled to orogen-controlled tectonics. It also may have resulted from erosion (and reworking) of the previously deposited western fluvial sediments by streams of the Eastern fluvial system in the north (Tadros, 19939). v) Depositional Controls on Coal Seams within the Lacustrine and Western Fluvial Systems The percentage sandstone map of the Lacustrine system (Figure 37) shows that in the south-eastern part of the Mullaley Sub-basin the system is mainly confined to the western side of the main axial channel of the Western fluvial system. The Caroona Coal Member is stratigraphically located in the basal part of the Lacustrine and Western fluvial systems, immediately above the Hoskissons Coal. The position of the axial channel immediately before deposition of the Caroona peats is shown on the percentage sandstone map of the Hoskissons to Caroona interseam interval (Figure 42) as a narrow

Gunnedah Basin

284

DM WALLALA DDH 3

DM WALLALA ODH 3

I 11

I 3

t P

tE s

Figure 41. Vertical profile of axial and tributary channel facies and overlying alluvial from de-posits of the New England derived Eastern fluvial system. The profile records part of the sequence above the Breeza seam in-DM Wallala DDH 3 showing a. zone of intefmixed lithologies at the base of the Eastern fluvial system (modified from Tadros, 19939). For reference see Figure 39.

il.. .ra

A2\

o*l

BELr (RocKY cr rN RrDcE,

LACHLAN F'LD

"Y ?+/ g

I Coonabarabran

./ ."&7

o€z

.y REFERENCE

Borehoie

o----l!-jo *, Figure 42. Percentage sandstone, Hoskissons - Caroona interseam interval (modified from Tadros' 1993g).

Geology of Australian Coal Basins

285

Figure 43. Percentage sandstone, Caroona (and/or Hoskissons) - Howes Hill interseam interval (modified from Tadros, 19939).

Figure 44. Percentage sandstone, Howes Hill (and/or Hoskissons) - Breeza interseam interval (modified from Tadros, 1993g).

Gunnedah Basin

286

r=-\

I .t--

\% \ \

p 2

2 3

' \,.

rGunnedali\

Coonabarabran

Figure 45. Percentage sandstone, Eastern fluvial system, upper part of the Black Jack Group (modified from Tadros, 1993g). south-westerly to southerly trending high-sand zone consisting of quartz channel-fill (Tadros, 1993g). The Caroona Coal Member is split and coal quality is at its lowest in boreholes in and around this zone, but the seam slightly improves away from it. The coal member thins abruptly and loses character in the west, where it changes to organic-rich mudstone of the lake basin sequence above the Hoskissons Coal. The overlying Howes HiIl Coal Member covers the

south-eastern quarter of the sub-basin, but is absent along a narrow zone occupied by the main axial channel that separates the coal member into an eastern and a western area (Figure 18). The coal, particularly in the western area, is underlain by channel margin, floodplain and lacustrine deposits (Figure 43). Disruption and seam splitting occurs mainly along the margins of the axial channel complex, as shown on the brightness profiles (Figure 19). Coal quality improves away from the immediate margin of the channel, but deteriorates in the area underlain by the lake basin sediments to the west and north-west.

The architecture of the sediments splitting the Breeza Coal lVlember indicates contemporaneous deposition from lacustrine and bed-load fluvial systems. The percentage sandstone map of the Howes Hill to Breeza interseam interval (Figure 44) defines a south-east trending axial channel complex of the Western fluvial system and small south-east trending tributary streams along the western basin margin. Elsewhere, clastic deposition is insignificant except for crevasse-splay development off the axial channel complex west of Breeza (Figure 44) (Tadros, 1993g). This arrangement continued during

accumulation of the Breeza Coal Member peats, and greatly influenced seam distribution and coal quality. Splitting of the seam is most pronounced in

Figure 46. Vertical profile of floodplain, channel margin facies of the New England derived mixed-load and alluvial fan systems in DM Gunnadilly DDH 1 (modified from Tadros, 19939). For reference see Figure 39. the south-east, where quartzose channel-fills of the axial complex were deposited. Minor splits, also by quartzose channel-fills, occur in the west from small south-easterly flowing tributary streams, and splitting in the central area is by fine-grained laminated lacustrine and marginal sandy crevasse-splay deposits (Tadros, 1993g).

Eastern Fluaial System Renewed tectonic activity in the New England region heralded a major change in the depositional setting of the Gunnedah Basin. The New England region became the major source of sediment to the

basin, and provided the detritus for the Eastern fluvial system (Figure 33) (Tadros, 1986b, 1"993S). This change is indicated by the lithofacies maps, particularly the percentage sandstone map (Figure 45) and the net sandstone and conglomerate maps (cf. Tadros, 1993g). The New England-derived sediments were carried by bed-load and mixed-load fluvial and alluvial fan systems, and consisted of axial and tributary channel fill, channel margin and floodplain facies. Sediment composition is volcano-lithic, and ranges from fine-grained sandstone to pebble conglomerate with interbedded claystone, siltstone and coal (Figure 41). Tuff and tuffaceous sediment, carbonaceous claystone and coal are also abundant,

particularly in the top part ofthe sequence.

Geology of Australian Coal Basins

287 RE FERENCE KLY-1

NRI.1B

Geological boundary 7

Borehole and number

MCM

Melvilles Coal Member Hoskissons Goal Digby Formation

ffi

[H lgneous intrusion

r.1:i:-1

lr: i;:'j"'rl

Upper Black Jack

Lower Black Jack

E: ll=.-:l t-.-,1 Leard ffi Basal

Porcupine and Waiermark Formations and Maules Creek Formations

MCM

volcanlc unlls

Q uaternary

alluvium

MCM

PKS-2

800

600

MCM

400

200

Pilliga Sandstone/ Purlawaugh Formation

Om VERTICAI. SCALE V:H lO: I

stony coal seams HC

SCALE

O246km Figure 47. Structural relationship between the top of the Hoskissons Coal and the base of the Digby Formation (modified from Tadros in Tadros & others, 1987). For location of section lines and boreholes see Figure 48.

Gunnedah Basin

288 160m. The conglomerate shows a gradual and progressive decrease in clast size towards the west. OM OENISON DDH 1 OM WALLA WALLA ODH 1 DM WALLA WALLA DOH 2 OM PARKES DOH 2 OM PARKES OOH 3 OM BOGGABRI OOH 1 DM BOGGABRI DOH 5 OM TULLAMULLEN ODH 1 DM ALAKE DDH 1 DM TURRAWAN DDH 1 OM TURRAWAN ODH 2A DM GORMAN DOH 1 DM NARRABRI DDH 1B OM KILLAFNEY DDH 1 OM DENISON WEST DOH 1 DME NARRAARI DDH 17

\\ \\\ z I

8tE-l

I.OCALITY MAP

orrobri

Boon Boo Boggobri

!\T \\

'l't

tt i*

SCALE

'j A\ \ \_ ?alor\ o

lolm

8Gt-l

'I,\'Nr'.

"',

\_\\

Two types of channel fill deposits have been recognised in drill core: axial and tributary. The axial channel fills are thick-bedded to massive pebble conglomerates and medium to coarse-grained sandstones with tabulat cross stratifrcation,

sometimes marked by pebble imbrication (Figure 41). Interbedded siltstone is rare but, where present, is laminated and from 0.1 to 2m thick.

Locally (in the central, southern and south-eastern parts of the Mullaley Sub-basin), a zone of intermixed lithology is present at the base of the axial channel sequence. The lower part ofthis zone consists of quartz-enriched lithic sandstone, which grades upwards into distinctly lithic sandstone and conglomerate (Figure 41). Enrichment in quartz sands at the base of the channel fill sediments is interpreted to have been caused partly by initial intermixing of the eastern and western fluvial sediments until the supply of the Lachlan Fold Belt material was completely shut off, and partly by reworking of the underlying quartz-rich western fluvial sediments (Tadros, 1993g). The tributary channel fills are transitional into the more proximal alluvial fan deposits preserved along the south-easternmost part of the Mullaley Sub-basin close to the present trace of the Hunter-Mooki Fault System. The conglomerate of the tributary channel fills is more dominant, coarser grained and more thickly bedded (beds 4 to 5m thick) than that of the axial channel fills (Figure 41). The conglomerates are predominantly clast-supported, but some matrix-supported conglomerates 1 to 2m thick are also present. ii) Channel Margin Facies The channel margin facies is represented by levee and crevasse splay deposits. It generally consists of laminated claystone/siltstone units 2 to 3m thick, interbedded with fine to medium-grained sandstone, siltstone and carbonaceous siltstone beds up to 1m

thick (Figure 41).

Figure 48. Isopachs of sediment wedge between the top of the Hoskissons Coal and the base of the Digby Formation (rnodified from Tadros iz Tadros & others, 1987). Over much of the Mullaley Sub-basin the sediments ofthe Eastern fluvial system are separated from the underlying quartz-rich sandstone of the Western fluvial system by the Breeza Coal Member and its equivalents, or locally by fine-grained laminated floodplain sandy siltstone and claystone (Figure 41) (Tadros, 1993g). i) Channel Fill Facies Conglomerate is the dominant lithology of the channel fill facies (Figure 33). The fragments in the sediments consist of varying proportions of silicic and mafic volcanics, chert and jasper, set in a lithic sand and clay matrix. The sediments generally form massive units 1 to 5m thick, with minor upward-fining tops. The aggregate thickness of these conglomeratic sequences ranges from 20 to 30m, except in the south-east where they exceed

Poorly sorted, irregularly bedded sandstone and siltstone with climbing ripples, wavy and planar laminations, root traces, soft-sediment deformation structures (Figure 46) and plant debris represent levees. Crevasse splays are represented by fine to coarse-grained sandstone arranged in either upward-coarsening or upward-fining sequences. Common sedimentary structures are climbing ripple and medium-scale trough cross-lamination, fine cross-stratification, mud drapes, graded bedding, scour-and-fill structures and macerated plant debris.

iii) Floodplain Facies Carbonaceous claystone and thick coal beds are an integral part ofthe floodplain facies, representing peaL swamps established in the broad interchannel areas (Figure 46). Subordinate, massive pebble conglomerates and cross-stratifred sandstone units up to 2.5m thick, with scoured pebbly bases, are interspersed with the floodplain facies and represent brief incursions of the river channel into the floodplain area (Figure 46). Alsg interspersed with the floodplain facies are upward-fining seque-nces of cross-bedded sandstone with scoured pebbly bases, overlain by siltstone and claystone. The siltstone and claystone at the top show fine crosslaminations, climbing ripples and root traces. These deposits are interpreted as lateral accretion units suih as point bars. Tuffs and tuffaceous sediments were alsb preferentially preserved on the floodplain.

Geology of Australian Coal Basins

2a9

Figure 49. Percentage sandstone, Breeza - Clift interseam interval (modified from Tadros' 1993g).

Hamilton & Beckett (1984) recognised volcanogenic sheet-flood deposits up to 5m thick, which they considered may have been deposited during single catastrophic events. Such volcanogenic detritus contributed up to l9Vo of the upper Black Jack sequence by contemporaneous volcanism as airfall and reworked overbank tuffaceous sediments. Tuffaceous stony coal is commonly preserved within the floodplain facies of the Eastern fluvial system (Tadros, 1986b; 1993g).

iv) Termination of the Eastern Fluvial System Extensive Late Permian plutonism and associated felsic volcanism in the New England Fold Belt (Scheibner, 1976) contributed large quantities of volcanogenic material to the basin during the Late Permian. Subsidence in the northern part of the basin was interrupted towards the end of the Late Permian by a period of structural readjustment and basin tilting, particularly in the north and north-east. As a result, the north-eastern side of the basin was uplifted and a thick section of the Permian sediments was eroded (Figures 47 and 48). Subsequently the northern Gunnedah Basin received sediments from both easterly and westerly

sources. These sediments prograded over most of the

Gunnedah Basin in a southerly direction and formed the unconformably overlying Digby Formation during the Early Triassic (Tadros, 1986b).

In the southern Gunnedah Basin, the rapid subsidence during the Late Permian was interrupted only for a short period, during which an unknown (probably small) portion of the upper Black Jack Group was eroded. Subsidence resumed in the Early Triassic and the basin in the south also received the easterly and westerly sourced sediments of the Digby Formation (Tadros, 1986b; Jian, 1991).

The unconformity between the Permian and Triassic sediments in the Gunnedah Basin is evident from the erosive nature and the angular relationship of the contact between the Black Jack Group and the overlying Digby Formation. Sections across the area show that the Digby Formation truncates the Black Jack Group progressively from west to east, leaving a wedge of Black Jack sediment thinning to the east (Figure 47 and 48). Palynological evidence (McMinn, 1985), also indicates a hiatus between the Black Jack Group and Digby Formation, with the gap equivalent mostly to Upper Stage 5.

Table 2. Coal Seam Narnes, Maules Creek and Vickery Project areas (After Thomson, 1986). Maules Creek nomenclature

Vickery nomenelature

Herndale Onavale Teston Thornfield Braymont Jeralong Merriown Velyama Nagero

Tralee

Gundawarra

Welkeree

Kurrumbedex Shannon Harbour Upper Shannon Harbour Lower Stratford Blue Valexx Cranleigh

Upper Northam Lower Northam

Therribri Flixton

Tarrawonga Templemore Stratigraphically equivalent to the Wilga seam described in early KCC reports. ++ Consists of Blue Vale Upper, Middle and Lower.

Gunnedah Basin

290

TN\

tr\

"""x

brl

BELT (RocKY GLEN RTDGE)

LACHLAN FOLD

.y I

*a,/

coonabarabran

'^c/'

*gy'

.JZ REFERENCE

. Borehole 1o o

2p.

-----1----J

Figure 50. Percentage sandstone, Clift - Springfield interseam interval (modified from Tadros, 1993g). v) Depositional Controls on Coal Seams within the Eastern Fluvial System The percentage sandstone map for the Breeza to Clift interseam interval (Figure 49) reflects the palaeogeography prior to accumulation of the Clift Coal Member peats and demonstrates the maior change in sedimentation following renewed tectonic activity in the New England Fold Belt. Large tributary streams emanated from the New England region and flowed south-westerly, pushing the axial channel complex basinward (compare Figures 44 and 49). This was accompanied by a dramatic change in sediment composition as the New England

tributaries input volcano-lithic detritus to the axial channel complex. A transition from quartzose to mixed quartz/volcano-lithic, and finally volcano-lithic sandstones and conglomerates is documented in borehole intersections of the Breeza to Clift interseam interval (Figure 41).

South-westward expansion of the tributary streams, including some lateral migration, continued throughout accumulation of the Clift Coal Member peats, accounting for seam splitting by volcano-lithic channel-fills and deterioration of coal quality in the north and south-east. Seam splitting in the south-west is also attributed to the south-westerly expansion ofthe tributary facies. The percentage sandstone map for the sequence overlying the Clift Coal Member shows this area to be the focus of coarse clastic deposition (Figure 50). The peat swamp of the Springfield Coal Member grew within an alluvial setting, as indicated by the

and south-wes nf,rlDuf,lon Irom

separating discrete interchannel areas. Coal quality is higher in the discrete interchannel areas in the south-east than in the sand-rich areas in the north and west. Peat accumulation in the uppermost part of the Eastern fluvial system was severely disrupted by large quantities of pyroclastic detritus, derived from contemporaneous volcanic activity in the New England Fold Belt. Air-fall tuff frequently mantled the peat swamps and choked the river systems, which gave rise to further inundation of the peat swamps by reworked tuffaceous sediments. These deposits intermittently arrested peat growth and inhibited the development of seam character and continuity. Tadros (1986b) noted that the sulphur content of the tuffaceous coals in the uppermost part ofthe eastern fluvial system is relatively high, averaging 0.85Vo, compared to that in the lower seams which averages 0.55Vo.

One horizon within the uppermost part of the Eastern fluvial system, represented by the Doona seam, displays moderate continuity and modest coal quality. This seam can be mapped in the eastern and central areas, but loses character in the west due to excessive splitting and deterioration ofcoal quality. Again, coal quality is better in discrete interchannel areas in the east and south-east than in the sand-rich areas in the north and west.

COAL SEAM GEOLOGY Maules Creek Sub-basin2 Up to 25 correlated seams, generally ranging in thickness from 1.5 to 3.5m, occur within the Early Permian Maules Creek Formation. The coal seams are generally thickest close to the Boggabri Ridge, and thin and split to the east (Figure 5L).

Geology of Australian Coal Basins

291

+h l=-l

MAC 18 MAC 14

R.L.345

F.1.337.475m

350

ilAC 19 1.316.177m

, REFERENCE

300

25A

E EI

240

150

100

Braymont seam

co t -unan",unrtur"a

c*r

"*,

i:,1t T?si).Mhw.h

J--l

.*,

brishr (> so%b.ishr )

bisht wirh dlrr ayers ( > 60% < eo% )

- intedayered dutl and baght ( > 40% < 60% bighl ) rrequenr brishr ravers

d-r' dlh rno o shr dvar, r.. * ro.,o..shr.

l-_l

U U

o U

o l

.1 00

o U (r

150

2AA

"*,

- dut (< r% brishr )

I fll

sn",

f]]

c"mn,""o,",ur"lur

"ou,

"o,', "nuu

f_-l n**a

250

Figure 52. Typical lithotype profile, Braymont searn (modified from T[hitehouse, 1993).

300

350

400

450

500

0 +

500 1000m T.D,802.18m

I"4AC 18 = KCC MAULES CERRK DDH 1B T.D. = Total depth below lhe surface

Figure 51. SW-NE cross section in the Maules Creek area showing typical coal seam splitting and coalescence, Maules Creek Sub-basin (modified from \Mhitehouse, 1993).

Very little borehole information is available for the region between Boggabri and Maules Creek in the north and Vickery in the south. The scarcity of data, combined with extensive splitting and coalescence of seams and the absence of other lithologically distinct rock units, has caused great difficulty in correlating the seams within and between the respective areas.

Within each of the three main areas up to L6 coal seams, the majority of which are less than 3.5m in thickness, have been named by exploration companies. The thickest seam encountered is the Braymo4t seam in the Maules Creek and Boggabri areas. This seam is exceptionally thick near Boggabri, attaining 9.0m, and generally averages greater than 5.0m. Thomson (1984, 1986, 1993) researched the geological setting of the Maules Creek Formation in considerable detail, relating coal seam splitting and coalescence to the pattern of fluvial channel migration which is in turn controlled by the effects of differential compaction, subsidence and the influence of irregularities in basement topography.

The seam names applicable to the Maules Creek and Vickery areas are listed in Table 2. Where appropriate, a similar operational nomenclature has been used by BHP Minerals Ltd

and AMAX Pacific Inc. (formerly AMAX Iron Ore Corp.) and Kembla Coal and Coke (KCC) in the Boggabri and Maules Creek areas respectively. BHP/AMAX have correlated coal seams in the Boggabri area for the stratigraphic section from the Templemore seam to the Braymont seam. The coal seams can generally be divided into two main sections: a lower section up to 1.5m in thickness, and in the case of the Braymont seam up to 3m (Figure 52), consisting ofbright-layered and bright-interlayered coal, and an upper section up to 2.5m in thickness, or greater in the case ofthe Braymont seam, consisting mainly of dull and dull-layered coal. Clastic layers, where present, usually consist ofcarbonaceous claystone, and can be developed in both sections. The lower section generally has a relatively uniform brightness profile and the upper section a succession ofthin upwards-decreasing brightness profiles.

Maceral analyses indicate that coal seams of the Maules Creek Formation have high vitrinite contents, ranging from 50 to 60Vo for the upper seams and 65Vo to greater than 80Vo for the lower qgams. The liptinite content also tends to be high. The liptinite-rich nature of the seams, in combination with the high vitrinite contents, results in very high fluidities, particularly for the lower seams.

Vitrinite reflectance ranges ftom 0.57o to 0.9Vo

(average 0.77o) and is highest in the basal seams.

The coal seams of the Maules Creek Formation fall into a number of broad groups based on coal quality variations, of which coking potential appears the most important. This trend is well established at Boggabri and Maules Creek, but is less clear at

Vickery.

The seams of the Maules Creek Formation are typically very low-ash, high-volatile, high specific energy, low-sulphur thermal and coking coals. The

Gunnedah Basin

292 top and middle seams contain thermal coal of low to moderate coking potential, while the lower seams contain coal of moderate to high coking potential. Overall, the lower seams of the Maules Creek Formation have a higher proportion of bright coal than the upper and middle seams, which, together with the increase in rank, partly accounts for the improved coking coal properties of the lower seams.

st t

3rf o\

' "'l

ie \''

FOLD BELr / .

.rrr\

seams. (ROCKY GLEN

rcrnn"outf 'st^a

RIDGE) .\

1l Coonabarabran I

pe/ ,4</ -<e/

Y 10

Figure 53. Isopachs, potential working section of tha Melvilles seam (modified from Tadros and Hamilton, 1993).

Mullaley Sub-basin

it;

Maules Creek Formation

Coal seams of the Maules Creek Formation in the

Mullaley Sub-basin are best developed south-west of Curlewis, and split eastward towards the Mooki Fault System. Seam splitting is accompanied by a deterioration in coal quality. The best potential is present in the Brown seam at depths between 150 and 500m in DM Brown DDH 1, some 9km south of Curlewis. The coal quality of the Brown seam is generally good. Raw coal ash varies from t7.8Vo to 27.37o. Yields from laboratory washability tests of the full seam range from 60Vo (CF 1.45 RD) to 977o (CF 1.60 RD), with an average of l17o ash in the float fraction. On a dry, ash-free (daO basis, the volatile matter ranges from 35 to 38Vo for the CF 1.60 RD fraction. Specific energy averages 34.5 MJ/kg. The CSN is low, ranging from 1 to 3 (Tadros,

\q \ \

2.\

'2\

NEW ENGLAND

FOLD BELT

LACHLAN \

I FoLD BELr / .

.a\

?'..

(RocKY GLFN RIDGE)

:L FI

'El

1985, 1993fl.

A working section up to 4m thick can be selected in the Brown seam, with raw coal ash ranging between 8 and ll7o. This coal may be washed to produce coal which is very low in ash at high product yields (Tadros, 1985, 1993f).

FOLD BELT

LACHLAN \

MJ/kg and crucible swelling number (CSN) from 1 to 7. Geiseler maximum fluidities are low to extremely high, ranging from less than 200ddpm for the top and middle seams to over 10 000ddpm for the lower

NEW ENGLAND

\%"

'z\ .a\

127o as}r with yields generally greater than 80%. Moisture for this coal ranges from 2 to 57o, volatile matter from 30 to 45Vo, specific energ'y from 29 to 34

Sulphur, chlorine and phosphorus are low by Australian standards. With the exception of the uppermost coals, the Herndale and Onavale seams, where up to 3.OTa sulphur (mostly pyritic) has been encountered, sulphur content is generally less than 0.4 to 0.SVo and mostly (807o to 90Vo of the total) as organic sulphur. Chlorine usually ranges from 0.02 to 0.067o and phosphorus is generally less than 0.02Vo. Trace eiements are also low in coal seams of the Maules Creek Formation.

:-' =./

Washing of raw coal from seams of the Maules Creek Formation to CF 1.60 RD produces coal of 3 to

For the washed coal, the Hardgrove grindability index (HGI) ranges from 35 to 59, with an average of 45. The bottom seams appear to have a marginally lower average HGI than top and middle seams. Ash fusion (flow) temperatures vary significantly, but are usually greater than 1500oC for the top and middle seams and 1300 to 1500oC for the lower seams. The lower ash fusion temperatures in the lower seams may result from increasing concentrations of FezOe, CaO and MgO.

J /

Coonabarabran

^o'/

. \<

t',

Black Jaek Group The Black Jack Group contains several correlated coal seams, of which only eight have economic potential. Of these, the Hoskissons and Melvilles seams are the most important. Distribution and coal lithotype characteristics of the other six seams have

Fisure 54. Raw coal isoash, Melvilles seim(modified from Tadros & Hamilton' 1993).

Geology of Australian C oal Basins

ooo

?JO

Table 3. Typical washed coal quality at CF 1.60 RD, Melvilles seam (after Tadros, r9s3b). Avera

Yield (%) Moisture (7o)

59.3 - 100.0

Ash (Vo)

Volatile matter (Vo)

75.0 2.9

1.3 - 4.3 10.6 - 30.6 10.5 - 40.9

15.6 32.8 48.7

Fixed carbon (7o) 3b.b - 69.8 Specific energ:y (MJ/kg) 22.5 - 29.4

csN

27.t

0_5.5

Table 4. Typical Washed Coal Quality at CF 1.60 RD, Iloskissons Seam (after Tadros, 1993b). Moisture (7o)

Range

2.5 - 5.7 Ash (%) 9.0 - 21.0 Volatile matter (7o) 23.0 - 31.0 Fixed carbon (7a) 47.0 - 610 Specific energy (MJ/kg) 29.0 - 80.0

CSN

Avera

o-2

4 13

26 57 26 0.5

CSN Crucible Swelling Number

Total sulphur (7o) 0.80 - 0.6 CSN Crucible Swelling Number

been discussed briefly above and more fully by Tadros (1993a,b).

Typical washed coal characteristics for the Melvilles seam (air dried basis) are shown in Tabie 3.

i) Melvilles Seam The Melvilles seam is generally around 2.5 to 3.5m thick in the eastern part of the Mullaley Sub-basin, but thickens south-west of Boggabri and thins towards the west (Figure 53). Thickening near Boggabri in the north and Breeza in the south-east is caused by splitting of the coal into two to three seams ranging in thickness from 1 to 2m. The coal has either been heat affected or intruded in a number of boreholes, Iocated principally along the eastern margin of the sub-basin.

ii) Hoskissons Seam

1.5

The Melvilles seam contains coal of good quality, and is consistently developed over-large aieas of the of the Mullaley Sub-basin. The seam has raw coal ash ranging from 9.5 to 33Vo (Figure 54), volatile

matter ofaround 337a and total sulphur ranging from 0.6 to L.2Vo.It has low to moderatelv high coking properties, with crucible swelling nuribers ranging from 1 to 5 and averaging 2.

The Hoskissons seam, which approximates the Hoskissons Coal (the mappable formation) varies in thickness from less than lm in the west to more than 12m in the north and 17m in the south-east (Figure 14). Where fully developed the formation typically consists oftwo sections separated by a persistent tuff or tuffaceous claystone layer that averages 0.1m in thickness. The Hoskissons seam has been affected by several igneous intrusions, particularly in the GunnedahBreeza region. The Sylvandale Sill (Wilkinson, 1958;

Britten & Hanlon, I975), which is at least 100m thick, closely underlies the seam at Black Jack

Mountain near Gunnedah, and has carbonised the coal to a variable degree. An intrusion, probably in the form of a lopolith up to 90m thick, has also cindered the Hoskissons seam and "domed-up" the overlying strata in an area to the south ofLong Mountain. Further to the south-west, however, a

BEFERENCE No work ng seclion

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FoLD BELr

I LACHT AN

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,s---r alfecled

= l-; I n

LACHLAN

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.'l

!r Coonabarabran

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Coonabarabran

25km

Figure 55. Raw coal isoash, Hoskissons seam (modified from Tadros, 1993b).

0.40

Figure 56. Isoash at CF 1.60 RD, potential working section of the Hoskissons seam (modified from Tadros, 1993b).

Gunnedah Basin

294

Table 5; Summary of thb in situ Aoal Be$ources of ,seans to,5OOm d€pth, Gunnedah Basin north of the Liverpool Range (Ta*ros, Iggsi).

Seam

Area

Inferred

Resources(Mt)

Doona Springfreld clift Breeza Howes Hill Caroona Sub-total Hoskissons Narrabri West Gunnedah Breeza

500 1900

2000 4000

Resource estimates are therefore confined to those resources which are present at depths <500m. The total coal resources to 600m depth of cover, including areas affected by National Parks and other land uses, are estimated at 38 000Mt. (see

Tadros, Sydney-Gunnedah Basin Oueruiew, this volume).

1000

800 10

4300 5400 2300 1700

Caroona

Sub-total Melvilles Sub-total Breeza Brown Several seams Maules Creek Boggabri Vickery Unallocated

located 250 to 400km from the port of Newcastle, compared with the Hunter Valley Coalfield which is much closer to the port at 70 to 110km. This extra distance adds to the cost ofthe rail freight and requires, among other factors, a lower mining cost.

13 700 2100 2100 500

600* 1200** 300x 200

Sub-total 28 900 Total (rounded) * Mineable in sifu Reserves ** Measured and Indicated Resources, of which 650Mt. are Mineable in situ Reserves similar igneous intrusion, 110m thick and situated 40m above the Hoskissons seam, has had no effect on the coal. Tadros (1985) notes that only limited cindering has taken place where the igneous intrusion is situated above or even in the upper part of the seam.

Although drilling has indicated the presence of coal seams, the coal resources of the Gilgandra Sub-basin are largely unknown. Considerable resources are present in the area between the Liverpool Range and the southern basin boundal'y, an area which includes the Murrurundi Trough within the northern part of the Hunter Coalfield and the Wollar Shelf underlying the northern part of the Western Coalfield. Coal resources within these areas have been discussed in detail elsewhere (See Tadros, Sydney-Gunnedah Basin Oueruiew, this volume; Sniffin & Beckett, this volume; Yoo & others, this volume).

Mullaley Sub-basin The coal resources of the Mullaley Sub-basin, north of the Liverpool Range, are almost totally contained in the Black Jack Group, which extends over some 807o of ttle area of the sub-basin. However the coal resource is too deep over large areas ofthe sub-basin

for current economic underground mining. It is also adversely affected by geological characteristics such as structure and igneous intrusions, and by

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medium-ash, high-volatile, low-swelling to non-swelling coal. It is also characterised by low sulphur, with values generally less than 0.57o (Figure 34). A coking fraction, however, with moderate ash and swell characteristics, can be obtained from the basal part of the working section.

Typical washed coal characteristics for the Hoskissons seam (air dried basis) are shown in Table 4.

16- Nu,abn I

s"l

The Hoskissons seam generally consists of a

Raw coal ash ranges from L2Vo to over SOVo for the full seam section (Figure 55). The ash of the 1.60 RD float fraction ranges from less than LOTo to just over 257o for yields ranging fuom 50Vo to 99Vo (Figure 56).

6r ^3/

rornsrrr

,.."^,"+\

^",^' e^ !

LACHLAN

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WEST GUNNEDAH

rnnedah{34

APEA

Coonabarabran

UI FI ul

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COAL RESOURCES

The Gunnedah Basin has considerable economic potential north of the Liverpool !.ange, with the Mullaley Sub-basin and the Maules Creek Sub-basin containing some 28 000Mt of potentially usable in situ coal (table 5) or 38% of the total in situ coal resources of New South Wales (Tadros 1993i). It should be noted that the coal resources of the Gunnedah Basin, north of the Liverpool Range, are

",/ ?

1.0 'z,o

Figure 57. Mullaley and Maules Creek Sub-basins sh6wing coal mines, coal project areas-and the Breeza.-Caroona. IYest Gunnedah and Narrabri coal resource areas (modified from Tadros' 1993i).

Geology of Australian Coal Basins

295

Table ?. Coal Resources, Maules Creek Formation, Maules Creek Sub-basin*. From Tadros (f993i).

Table 6. Coal Resources, Blaek Jack Group. From Tadros (f993i).

Inferred Resources(Mt.)

Mineable in situ Reserves(Mt.) Surface Under- Total

0-300m 300-500m 0-500m

1800 1500 3300 4200 5400 9600 Narrabri area 1300 3100 4400 West Gunnedah area 3000 5600 8600 10 300 15 600 25 900 Total Breeza area Caroona area

physiographic features such as deep alluvial cover and flood plains. Two major areas of underground mining potential are affected by the presence of national parks or

nature reserves. To the north the Mount Kaputar National Park partly overlies coal seams of the Maules Creek Formation and to the west the Pilliga Nature Reserve overlies coal seams of the Black Jack Group. Sterilisation of coal resources is also possible in the south-east, where coal seams of the Black Jack Group are present beneath a thick cover of fertile alluvium associated with the Namoi River. There are two colliery holdings in the Mullaley Sub-basin, Gunnedah Colliery and Preston Extended No.2 Colliery (Figure 57). These two collieries have been mining the Hoskissons seam for almost a century. Gunnedah Colliery started mining the Melvilles seam by open cut methods in the mid 1980s.

A maximum depth of 500m has been taken as the

economic limit for long-term mining in the Mullaley Sub-basin. In most cases, seams are affected by

splitting and by coal quality deterioration in a westerly direction. As a result, exploration in the sub-basin has concentrated on the potentially economic areas of shallow, better quality coal in the east. Borehoie spacing in this area is between 4km and 8km (sometimes less), whereas in the western and southern parts ofthe sub-basin it can be up to 24km. In the north-western areas, however, there is almost a total lack of borehole data. Examination of geological structure, coal quality, depth to coal seams and the geography of the present surface has enabled delineation offour areas (Caroona, Breeza, West Gunnedah and Narrabri) with potentially economic coal resources (Figure 57), along an eastern zone bounded by subcrop beneath thick alluvium of the Namoi Valley to the east and the 500m depth of cover limit on the main seams to the west.

In this zone, the Hoskissons seam typically is 5 to 6m thick, although it attains thicknesses in the order of 17m in the south-east. In contrast, the underlying Melvilles seam is mostly in the order of 2 to 3m in thickness. Those two seams can be washed to produce a low to medium-ash, medium-volatile, medium specific energy thermal coal of low to moderateioking potential. Coal seams above the Hoskissons seam generally range in thickness from 1.5 to 3.5m and contain medium to high-ash, medium-volatile thermal coal of low to moderate coking potential (Tadros & Hamilton, 1993). Coal resources for the Black Jack Group in the four areas have been calculated to either Inferred Class 1 or Class 2 status (Galligan & Mengel, 1987), based

Vickery project area Maules Creek

Total

155 345 330 830

155 310 320 785

310 655 650 1615

Unallocated 200Mt. Inferred Class 1 are not shown.

on borehole spacing, quality of information and geological conditions. Two resource depth categories have been used: 0 to 300m (surface and shallow underground mining potential) and 300 to 500m (deep underground mining potential).

In most cases, areas with shallow coal have been explored by boreholes up to 4km apart, allowing coal reiources to be calculated to Inferred Class 1 status. Areas with deeper coal generally have more widely spaced boreholes, around 8 to 12km, allowing these resources to be calculated to Inferred Class 2 status only. The remainder of the basin area either has insufficient informatiorr or contains coal of too high in ash to enable coal resources to be calculated even to the Inferred level. Coal resources for the Black Jack Group are summarised in Table 6. Further details of the four coal resource areas are given by Tadros & others ( 1ee3).

Maules Creek Sub'basin A number of important mining projects have been proposed for coal seams of the Maules Creek Formation in the Maules Creek Sub-basin. Three small surface mines are being developed at Vickery (Figure 57), of which one is currently producing thermal coal for export. The Maules Creek and Boggabri projects are planned for development in the mid to late 1990s. Coals of the Maules Creek Sub-basin were investigated by exploration companies in the 1970s, and areas with the best potential were selected for detailed assessment in the 1980s (Figure 57). Detailed accounts ofthe exploration history and analytical work are given by Tadros (19939), and of the coal resources of the sub-basin by Whitehouse ( 1993).

The company areas appear to contain the vast majorityof the coal resources available within the Maules Creek Sub-basin. Mineable In situ Reserves for the Boggabri, Maules Creek and Vickery Prqjgct areas are 16fSUt. Of these reserves, 830Mt or 51Vo are amenable to surface mining and 785Mt or 497o are amenable to underground mining. Due to a general lack ofexploration boreholes outside the company areas, it has only been possible to determine coal resources for a small part of the region between the Boggabri Project area to the no-rth and the Vickery Project area to the south. Inferred Resources (Class 1) of 200Mt, amenable to underground mining, have been defined in this area.

Gunnedah Basin

296

Information on coal resources for seams of the Maules Creek Formation in the Maules Creek Sub-basin is summarised in Table 7.

HAMILTON, D.S., 1987: Depositional systems of upper Permian sediments and their application to fuel mineral exploration, Gunnedah Basin. PhD thesis, University of Sydney.

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tsRITTFlN, R.A. & HANLON, F.N., 1975: North Western Coalfield. 1n Traves, D.M. & King, D. (Editors): Economic Geology of Australia and Papua New Guinea - 2: Coal. Australasian Institute of Mining and Metallurgy, Monograph,

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DULHUNTY, J.A., 1986: Mesozoic Garawilla Lavas beneath Tertiary volcanics of the Nandewar Range. Journal and Proceedings of the Royal Sot:iety of New South Wales,ll9,29 32.

DUPRE W.R., 1982: Depositional environments of the Yukon Delta, northeastern Bering Sea. Geologie en Mijnbouw, 61, 63 70.

ETHERIDGE, L.T., 1987: New stratigraphic and structural data from the Surat and Gunnedah Basins and implications for petroleum exploration. Geological Suruey of New South Wales, Quarterly Notes, 66, I-2I. EVANS, P.R., 1967: Review of the Permian palynoiogy of the Sydney Basin. Bureau of Mineral Resources (Australia), Record 7967 /703. EXON N.F., 1974: The geological evolution of the southern Taroom Trough and the overlying Surat Basin. The APEA Journal, 14, 50 58. GALLIGAN, A. & MENGEL, D.C., 1987:Australian Code for the Reporting of Identified Coal Resources and Reserves. Australian Mineral

Industry Quarterly, 39(2), 49-51. GALLOWAY, W.E. & HOBDAY, D.K., 1983: Terrigenous Clastic Depositional Systems: Applications to Petroleum, Coal, and Uranium Exploration. Springer, New York. HAMILTON, D.S., 1985a: Deltaic depositional systems, coal distribution and quality, and petroleum potential, Permian Gunnedah Basin, New South Wales, Australia. Sedimentary Geology, 45,

HAMILTON D.S., 1991: Genetic stratigraphy of the Gunnedah Basin, New South Wales. Australian

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HAMILTON, D.S., 1993b: Genetic stratigraphic framework. In Tadros, N.Z. (Editor): The Gunnedah Basin, New South Wales, Geological Suruey of New South Wales, Memoir Geology,12,

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HANLON, F.N., 1950a: Geology of the North-Western Coalfield: Part 7 . Geology of the Boggabri

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HANLON, F.N., 1950b: Geology of the North-Western Coalfield: Part 8. Geology of the Narrabri

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HILL, M.B.L., 1986: Geology of the Deriah Forest area r) implications for the structure and stratigraphy of the Gunnedah Basin. Geological Suruey of New South Wales, Quarterly Notes,62,7-76. JENSEN, H.I., 1907a: The geology of the Warrumbungle Mountains. Proceedings of the Linnean Society of Neu South Wales,32, 557-626.

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HAMILTON D.S., 1985b: Petroleum data package, Gunnedah Basin. Geological Survey of New South Wales, Report GS 1985/005.

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KENNY, E.J., 1964: Geological Survey of the

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Mineral Resources, 4O. KORSCH, R.J., WAKE-DYSTER, K.D. & JOHNSTONE, D.W., 1992: Preliminary geological results from deep seismic reflection profiling in the Gunnedah Basin and New England Orogen. Geological Society of Australia, Abstracts, 32, 27 KORSCH, R.J., WAKE-DYSTER, K.D. & JOHNSTONE, D.W., 1993: Deep seismic reflection profrling in the Gunnedah Basin: regional tectonics and basin responses. Petroleum Exploration Society of Australia, New South Wales Branch, Proceedings, New South Wales Symposium, 2nd June 1993,90-119. LEITCH, E.C., MORRIS, P.A. & HAMILTON, D.S., 1988: The nature and tectonic significance of Early Permian volcanic rocks from the Gunnedah Basin and the southern part of the New England Fold Belt. Proceedings, 22nd Symposium on Aduances in the Study of the Sydney Basin, Department of Geology, University of Newcastle, .

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LONSDALE, G.F., 1965: Southern Queensland contract reconnaissance gravity using helicopters, 1964. Bureau of Mineral Resources (Australia), Record L965/251.

LOUGHNAN, F.C., 1973: Kaolinite clayrocks of the Koogah Formation, New South Wales. Journal of the Geol ogical S ociety of Au stralia, 20, 329-3 41.

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evolution, upper Black Jack Formation, Gunnedah Basin. Geological Suruey of New South Wales, Quarterly Notes, 65, 20-34. TADROS, N.2., 1988a: Depositional controls on coal quality of the Hoskissons Coal Member, Black Jack Formation, Gunnedah Basin. Geological Suruey of New SouthWales, Quarterly Notes,7O, 1-14. TADROS, N.2., 1988b: Maceral composition: variations and significance to the formation of the

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TADROS, N.Z. & HAMILTON, D.S., 1993: Distribution, quality and utilisation potential of the main coal seams of the Mullaley Sub-basin. 1n Tadros, N.Z. (Editor): The Gunnedah Basin, New South Wales, Geological Suruey of New South Wales, Memoir Geology, L2, 445-484. TADROS, N.2., HAMILTON, D.S. & WHITEHOUSE, J., 1993: Coal resources of the Mullaley Sub-basin. In Tadros, N.Z. (Editor): The Gunnedah Basin, New South Wales, Geological Suruey of New South Wales Memoir Geology,12, 485-522. TADROS, N.2., WHITEHOUSE, J. & MOFFITT, R.S., 1987: Geology and coal resources ofthe Narrabri area. Geological Suruey of New South Wales, Quarterly Notes, 68, 1-18. THOMSON, S., 1984: The sedimentary and tectonic setting of the Maules Creek Formation, east of the Boggabri Ridge, Gunnedah Basin, New South Wales. MSc (preliminary) thesis, University of New England, Armidale. THOMSON, S., 1986a: An analysis of Early Permian deposition in the Gunnedah Basin, New South Wales. MSc thesis, University of New England,

Armidale.

THOMSON, S., 1986b: Early Permian sedimentation and provenance studies in the Gunnedah Basin, New South Wales. Abstracts, 20th Symposium on Aduances in the Study of the Sydney Basin, Department of Geology, Uniuersity of Newcastle, 15-18. THOMSON, S. & FLOOD, P.G., 1984: Reassessment of the tectonic setting and depositional environment of the Early Permian Maules Creek Coal Measures, Gunnedah Basin, New South Wales. Abstracts, 18th Syrnposium on Aduances in the Study of the Sydney Basin, Department of Geology, Uniuersity of Newcastle, 77-80. WALLIS, G.R., 1971: Narrabri 1:250 000 Geological Sheet SH/55-12. Geological Survey ofNew South Wales, Sydney. WATERS, D.D., 1971: The geology of the Black Jack King Jack district of New South Wales. BSc (Hons) thesis, University of Newcastle. WHITEHOUSE, J., 1993: CoaI resources of the Maules Creek Sub-basin. 1n Tadros, N.Z. (Editor): The Gunnedah Basin, New South Wales, Geological Suruey of New South Wales, Mernoir Geology, 12,

523-533. WILKINSON, J.F.G., 1958: The petrology of a differentiated teschenite sill near Gunnedah, New South Wales. Arnerican Journal of Science, 256, l-39.

WILKINSON, J.F.G., 1959: The geochemistry of a differentiated teschenite sill near Gunnedah, New South Wales. Geochimica Cosmochimica

Acta, 16, 123-150. YOO, E.K., 1988: The Rocky Glen Ridge and Gilgandra Trough, beneath the Surat Basin. Geological Suruey of New South Wales, Quarterly Notes,72,

t7-27.

Geology of Australian Coal Basins

299

ffiowen Basin

CW Mallett C Pattison

T Mclennan P Balfe and

D Sullivan

The Bowen Basin is one of the major coal basins of the world. No accurate figure can be given on the total amount of in situ cial, but estimates of coal occurring at depths of <300m in existing mine leases

amount [o apprbximately 20 000Mt.'Ihe Bowen Basin is pari^of a conneited glouP of Per-mial goal basins in Eastern Australia which includes the Sydney and Gunnedah Basins. The eastern part of . t6e fasin was severely deformed in the Triassic, and mineable coals are prbserved on protected tectonic platforms or syncline margins. The rank of the coal is closely relafed to the poiition ofTriassic thrust fronts and Early Cretaceous intrusions. These factors have corirbined to give relatively undeformed, shallow coal deposits with coking characteristics over large areai in the centre and on the northwestern-margin of the basin. Production for steam raising has bien carried out since the 19th Century, but itls only in the last thirty-years that th-e large reserves of ihallow coal been discovered and developed, largely for the export market. The Bowen Basin was an area of shallow-water or terrestrial sedimentation for most of the Permian. Coals accumulated throughout almost all this initiallv around the margins and in isolated oeriod. ^sites. but exteidins to cover virtually the whole basin in the latest Permian. The most favourable areas both for deposition and subsequent preservation of coals were on shelves and. platforms, *h"t" very extensive areas of peat co-uld be maintainei in stable conditions over long time intervals. Humid conditions allowed these peats to extend hundreds of kilometres inland from the

marine margin.

Tectonic Framework The Bowen Basin sequence crops out in an area from iai"so'n to 150oE between latitudes 27o to 26o5, and extends further to the south beneath Mesozoic cover' It is composed of a series of NNW-SSE trendingtroughs and highs, most of which were covered by sediirents at sdme time during the basin's history. On the western side of the basin these are known to overlie deformed early Palaeozoic or older meta-

morphic rocks.

The first-order basin orientation is NNW-SSE, roushlv parallel to the late Palaeozoic continental *aigiti. The whole basin suffered extensional and comiressive events, oriented-roughly-NE-SW. The first basin orientation is cut by NE-SW structures, which have been interpreted as transfer faults associated with early Permian extension (Hammond, 1937). There is a diiect link between the geometry of these crustal blocks, the sites of thick coal measure accumulation and their subsequent preservation

from structural deformation.

were involved in the Two tectonic phases -of Bowen Basin. Crustal extension the development ^early Permian produced linear zones of in the half-grabeirs, which subsequently became the centr-es for more regional crustal sag. There was a transition in the Kizanian, however, to a foreland basin geometry, with sedimentation focussed in the Tarooir Trough., as the magmatic arc rose along the eastern boundarY.

Extension processes controlled deposition in the Sakmarian-, with thick deposits restricted to narrow srabens and half-erabens. The best known ofthe Eraben areas is the Denison Trough in the Iouthwest, but similar linear belts of grabens also occurred aiong the eastern margin. The eastern

Bowen Basin

300 BOWEN BASIN MORPHO_TECTONIC

UNITS

with associated local unconformities (Ziolkowski & Taylor, 1985). Differential crustal movements in the Denison Trough largely ceased in the Tartarian,

creating a platform which continued to subside slowly in the latest Permian and Triassic. Similar reversal of graben bounding faults probably also occurred in other parts of the basin at the same time. The Triassic was marked by another strong compressive event, which is reflected very differently in various parts of the basin. This event formed the structural divisions now seen along the basin's length. The locus of thick deposition shifted to the south, where the Taroom Trough subsided

rapidly in the Early Triassic. Major overthrusting from the east resulted in the formation of the Nebo Synclinorium in the north, the Folded Zone in the centre, and the Taroom Trough in the south, with the westward propagation of thrust sheets varying in these areas.

Basin Morphotectonic Units The Bowen Basin is made up of first-order NNW-SSE trending platforms or shelves, separated by sedimentary troughs (Figure 1). In parts of the eastern margin the pattern is disrupted by the Gogango Overfolded Zone, which obscures earlier basin configurations. The units from west to east are Springsure Shelf, Denison Trough, Collinsville Shelf/Comet Platform, Taroom Trough, Connors and Auburn Arches (interrupted by the Gogango Overfolded Zone) and the Marlborough Trough.

h COt\4ET

PLATFORM

Figure 1. Morpho-tectonic units of the Bowen Basin. basins are dominated by calc-alkaline volcanics, with locally-sourced volcanogenic sediments which include sporadic coal measures. Extensive andesitic flows are restricted to the Sakmarian. Later deformations and covering strata obscure the original graben geometries along the eastern margin of the basin.

Crustal sag, which followed the initial graben formation, was greatest where graben formation had thinned the crust, with the result that these areas remained the centre of deposition. Sedimentation spilled over on to intervening basement highs by late Artinskian times. The magmatic arc was thrust up to the east in the Ufimian to Tartarian, and crustal loading formed a new trough along the foreland margin of the magmatic arc. Plutons were intruded in the east. In the Denison Trough, compression associated with this uplift reactivated normal faults of the earlier extension phase, but reversed their sense of movement. This initially caused some local facies variations around the grabens, but later led to positive inversion ofthe grabens and half-grabens,

Variations in deposition patterns and deformation styles occur along strike in these troughs and highs, and suggest that the crustal structure changes in a significant way across the second-order NE trends. These were called corridors by Hammond (1987), who believed they represented traces of deep-seated crustal transfer faults associated with early Permian crustal extension. Four major transfers are identified in Figure 1, the Collinsville Transfer which terminates Permian sediments in the north, the Bundarra and Blackwater Transfers, and the Moura Transfer where the Mesozoic cover approximately commences in the south. Between these major transfers, which terminate large structural features, are other transfers ofvarying significance. Morphotectonic units within the NNW-SSE troughs and highs are bounded by the major transfers. Western Margin

The Springsure Shelf is covered by a thin veneer of Permian sediments. The projection of the Blackwater Transfer marks the present erosional margin of the Permian, and represents a line of basement step up. Denison Trough Seismic sections have shown that, south of the Blackwater Transfer, initial sedimentation in the Denison Trough took place within two or three parallel zones ofnorth-south trending grabens and half-grabens. These are offset by smaller transfers at a spacing of about 15 to 20km. The half-grabens are deepest in the west, where 2300m of graben fill has been proven and 4000+m indicated on seismic traverses. The more easterly line of grabens usually has less than 1500m of sediment infill. The grabens have been subsequently inverted to form narrow anticlines over the areas of maximum subsidence.

Geology of Australian Coal Basins

301

North of the Blackwater Transfer, the northern extension ofthe Denison Trough changes in trend from N-S to NNW-SSE. The half-grabens in this area are much shallower, ranging from 800-1200m in depth, and sometimes deepen to the east rather thanlo the west. NNW-SSE striking reverse thrusts of Triassic age are also common. Small isolated basins in the Clermont area do not appear to be fault-controlled in the same way. Although there is a progressive exhumation of earlyPermian rift iediments from south to north, the thinner sequences north of the Blackwater Transfer are not a r-esult solely of erosion; they reflect a marked decrease in graben and half-graben formation. C

ollinsville Sh elf/Comet Platform

This tectonically positive shelflridge feature dips regionally to thb south. Outcropping cover rocks beiome successively older to the north, with most Permian sediments eroded north of the Bundarra Transfer. Permian sediments largely crop out on the shelf/ridge between the Bundarra and Blackwater Transferi, and Triassic sediments between the Blackwater and Moura Transfers. The eastern margin of the Collinsville Shelf dips gently eastw-ard into-a thrust-front boundary, which is interpreted as a reactivated buried rift-basin margin (Hammond, 1987). Further south, the margins of the Comet Ridge are not distinct. The transition in a NNW direition takes place at depth, and little information is available to d-efine the relationship. The transition from shelf to ridge is subjective, depending on the definition of the northern extension of the Denison Trough. Taroom Trough The Taroom Trough developed during the Foreland Basin Phase of the basin's tectonic history (Table 1). The distinctive morphotectonic units along its length were formed during the mid to late Triassic.when the eastern margin overthrust the Taroom Trough sediments. Between the Bundarra and Collinsville Transfers the sediments have been folded and faulted into the Nebo Synclinorium. NNW-SSE folding is broken up in this area up by north-south striking reverse faults, thoughl t6 be similar to the reactivated riftbounding faults of the Denison T19ugh. These faults and folds are truncated by NE-SW oriented transfers of minor to intermediate significance. Permian and Triassic sediments crop out in the synclinorium. From Bundarra to Blackwater the Taroom Trough is mainly made up of the Dawson Folded Zone, with outcrop of tighfly folded Permian Foreland Basin Phase sedimenti. The rocks are indurated but extremely weakly cleaved. Deformation decreases towards lhe thrust front, which is located along the margin of the Collinsville Shelf, and the area here is char-acterised by the more open folding of the Yarrabee Zone. Low-angle thrusts propagate on to the shelflridge to the west, and are often

oreferentiallv localised in coal seams. Triassic iediments ar-e confined to a narrow strip along the margin of the Collinsville Shelf. The northern and soutlreastern parts of the Dawson Folded Zone are covered with tertiary and Quaternary deposits, and it is difficult to determine the relationship of this feature to the surrounding units. The broad Mimosa Syncline extends south from the Blackwater Transfer. The syncline contains a great thickness of Triassic sedim6nts which have not been drilled through, and the oldest reliable seismic reflectors are the Late Permian coals. There is therefore little evidence from which to interpret the Permian depositional history of the area. The syncline abuts the Dawson Folded Zone across

the Biackwater Transfer. It is strongly asvmmetrical, with dips of 20o on the eastern limb an"d 5o on the western-limb. High-angle reverse faults parallel to the axis ofthe syncline occur along the noithern margin of the syncline. Esstern Margin The eastern margin of the Bowen Basin is thrust to the west over the Taroom Trough. It consists ofa core of older igneous basement interruqted by the Gogango Oveifolded Zone. This overfolded zone was def-irnied in the Triassic, and does not show the regional trends of the other parts of the basin. It ap"pears to be unrelated to the extensional fabric of

t66 early Permian tectonic framework.

A major graben sequence containing up to 4000m of Earlv Peimian sraben-fill sediments and volcanics exteids north fiom Marlborough, and underlies the Cretaceous Styx Basin. The sediments overlie Devonian and-Carboniferous volcanics of the Connors Arch, and a narrow strip of outcropping Connors Arch rocks separates the sediments from the Taroom Trough. The graben sequence is overthrust by the Gogangb Overfolded Zone, which itself may inlorporate some of the sequence in the south. To the south is the Auburn Arch, which terminates on the Moura Transfer. To the north is the Connors Arch, which is composed of a core of Palaeozoic to Cretaceous granites with some Late Devonian to Early Cretaceous volcanics. The subdivisions into the Northern, Central and Southern Bowen Basin used in this discussion are based on the positions of the northeast-trending Bundarra Transfer and Blackwater Transfer

features (Figure 1).

DEPOSITIONAL HISTORY

Stratigraphic SummarY Sedimentation in the Bowen Basin commenced during the Early Permian in separate NNW-SSE

,+Cble,,,X;... eotoniC..p"ffieub...of..the,.Bowen.rBaiin;

Main Basin Foreland Basin Phase Extension Phase

Eastern Margin

Age/Stage

Compression and sag

Overthrusts from east

Triassic

Compression and sag

Uplift,.intrusion and

Ufrmian to Tartarian

Extension and sag

Magmatic arc

volcanism

Bowen Basin

Sakmarian to Kungarian

302 tre,nding extensional troughs. Up to 2800m of sediment locally accumulated irthe Denison Trough in the southwestern part ofthe basin, and over 3000m of volcanics and interbedded sediments were deposited in the north east. Two to three thousand metres of sediments and volcanics accumulated in the central area of the basin near Marlborough, and -

withdrawal of the sea, first in the north, which gave rise to extensive marginal marine and deltaic peat deposits. These deposits are thickest in the noith, where over 1200m ofcontinuous coal measures are found, and decrease to 180m in the southwest. The basin has large areas ofTertiary and Quaternary cover, and lack ofcontinuity ofoutcrop has led to the establishment of differeni stratigraphic units of otherwise similar ages in various parts of the basin. The correlation of major

at least 1200m of predominantly terrestrial volcanics in the southeast. Thick coal measures were formed in the Denison Trough, and thin coals interbedded with volcanics in the eastern areas. Rare marine fossils are found in the eastern

formations is provided in Figure 2, which also relates the lithofacies to tectonic events.

sequences.

A marine incursion during the Artinskian led to the widespread accumulation of marine and mar-ginal-marine deposits. As with the older,

Stratigraphic C ontrols

predominantly non-marine sequence, the thickest d-eposits are found inthe Denison Trough and along the eastern margin of the basin. Although these marine beds extended over the volcanics in the southeast during the Artinskian, only thin and stratigraphically restricted sequences are known. Localised coals were deposited along the marine margins, for example at Collinsville, and in adjacent continental areas such as Blair Athol.

Shelly Macrofaunas

A comprehensive faunal zonation of the Bowen Basin was developed by Dickins (1964a, 1964b). Four faunas were designated I to IV, with Fauna III subsequently being split into Faunas IIIA-C. These faunas were equated with widespread rock units: Fauna I to the upper Lizzie Creek Volcanics, Fauna II to the Tiverton Subgroup, Fauna III to the Gebbie Subgroup and Fauna IV to the Blenheim Subgroup. Distribution lists of shelly species by faunal zone were published by Dickens & Malone (1973). With a few exceptions, each collection is referred to a Fauna without illustrations or detailed descriptions. Despite these difficulties, the zonation was applied in other basins of eastern Australia, and this provided the first marine faunal subdivision and

The depositional centres changed dramatically in the Late Permian, with maximum subsidence-in a NNW-SSE trough lying just to the west of the early Permian volcanics. Marine conditions w-ere widespread following initiation of this new configuration in the Ufimian, and no terrestrial deposits of this age are known. There was then a TECTONICS

SOUTHEAST

SOUTHWEST

3ENTP.AI,

COAI

NORTHERN

FACIES

,:ElAIlD

compression

Reran FM

Rewan FM

with local

Rewan FM

sag Rhhdr'l

UJ (n

(]M

Gyranda Flrt

FIat Top FM

a o

Bandanna FM

Black Alley

- RangaL t

Burngrove FM

Fairhill

Terrestial flood plain & flood basin

Rewan FM

Pearaddy FM

McMillan FM

Catherine EM /Crocker S/S

German CK- FM

Ingelara trM

Maria FM

Freitag

sest

Rangal CM

I\'

Port Cooper i

I IIa

Moranbah CM

III

loal trleasureJ

coal measures gradually extend

from the north to

eventually cover al,l the basin

ct z. J Barfield r!

sag

cc o l!

east Back ck Group

Uppe!

ts (t

Aldebaran FM

o BTae FM Pindari

Shallow & marginal

Blair

Athol

Lower

collinsvil-le

a !

Extension rifts

o Cahboon 6 z. VoJ.canics UJ

F6mrl

Cattle Ck. FM

Reids Dome

measures i

uarine-triisg";" with some coals "Io"

Lizzie "*'r" volcanics

I g"a"

Beds

UPP€T

Reids I

IJ.J

Doma

:ong. I

local coal

Tiv€rton FM

---'-----t Upper Reids t

Dome Beds

rrarine with

F sag

transgression

with no non marine

Blenheim FM

known

)xt,rack FM

10n

widespread

Ck.

-corrs T" wEstvolcanics (nainly terrestial) in east

Figure 2. Bowen Basin stratigraphic summary (modified after Draper & others, 1990). V coat measures present.

Geology of Australian Coal Basins

303

EVANS

R '1a

R 1a

'62-'66 '67-'69 -P3d P3c

PATEN PRICE PRICE 1 969 1 983 1 985 R 1a

R 1a

Upper

Upper 5c

Stage 5

P3b

Lower

L. pellucidus T. playtordii PP 5.2

Upper 5b

Lower 5c

PP 5.1 PP 4.3

Lower 5b

PP 4.2

. dulhuntyi D. inornata

Lower 5a

PP 4-1

ericianus

Upper 5a

Stage 5

PP6

D. stellata D. parvitholus

Stage 5 P3a Upper 4b

Upper Stage 4

Stage 4 Lower

Stage 4 P1c

P1b P1a

Stage 3

c2 c1

Stage

Stage 2

Stage

D. granulata

versus Lopadiospora

Upper 4a

PP 3,2

A. villosa

Lower 4

PP 3,1

P, sinuosus

PP 2.2

P. cicatricosus

PP 2.1

PPl

Stage 3 Stage 2

PP J.J-z

3.3 J.J, I

G. trisinus

P. pseudoreticulata

PC4

Striate Bisaccate Pollen Monosaccate Pollen

Figure 3. Microfloral zonations for the Bowen Basin (after Price, 1985).

correlation. Runnegar (1969) reviewed and qualified the application of Dickins' faunas. Based mainly on collections in the north of the

Basin, Dear (1972) largely supported Dickins' conclusions. He identified the Lizzie Creek and Homevale Faunas at the base of the section, and described four faunas within Fauna IV from localities at Exmoor, Scottville, Pelican Creek, and

Havilah.

Runnegar & McClung (1975) proposed a zonation for the Permian of eastern Australia based on Tomiopsis species, but limitations on its general application are imposed by the rare occurrence of some index species ( Waterhouse & Jell, 1983)"

Dickins (1983) incorporated later work into a threefold subdivision of his Fauna IV by recognising the Pelican Creek and Havilah assemblages of Dear (1972), and described their distribution in the basin. Waterhouse (with others) in a series of papers through the 1980s, proposed numerous brachiopod assemblage zones in the northeast and southeast of the basin, and specifically rejected Dickins' Faunas I-IV as a consistent basis of correlation. These new proposals have not found significant acceptance by other workers. Localised faunal descriptions and zonal divisions have also been proposed by Parfrey (1988). Briggs (1987) has correlated units in the Bowen Basin with those of other Permian basins in eastern Australia on the basis of productid brachiopod species. The inconsistencies between different workers

suggest that insufficient is known of the shelly macrofauna to allow the construction of a robust biostratigraphy for the Bowen Basin. Some general trends, however, can be observed in the faunas.

Diverse shelly faunas are found in the Sakmarian to early Artinskian and in the late Kungarian to

Kazanian. Late Artinskian to early Kungarian faunas are rarer, less diverse and endemic. Very few index species with limited time range and

widespread distribution are known, and correlations are based on partial ranges and assemblage zones. There are critical unresolved faunal relationships, such as the correlation of the Blenheim Formation in the north-east with the Denison Trough sequences.

Foraminifera A biostratigraphic zonation of benthonic foraminifera has been developed and applied in the Denison Trough and other areas of the Bowen Basin (Palmieri, 1983; 1990; 1994). This identified early (A1 to A5) and late Permian (8, C1 to C3) faunas in the same sequences containing shelly macrofaunas. The zonation shows much promise, with four faunas recognised in the section between the Freitag Formation and the Peawaddy Formation in the Denison Trough. Microflora

Microfloral zonations have provided useful correlations within different parts of the basin, but are subject to destruction in many areas. In addition to providing distinctive first appearances oftaxa, they reflect the major floral evolutionary changes and environmental conditions in the basin. A correlation of microfloral zonation schemes published by Price (1983) is given in Figure 3. This is a'best fit' correlation and it should be remembered that the criteria used are not always the same as the index species for the various schemes.

The Permian microflora in the Bowen Basin was initially characterised by monosaccate pollen. Striate bisaccate pollen then appeared, and

gradually became the dominant form. With increasing marine influence, acritarchs became a prominent component, and these persist to just before the end of the Permian. A distinctive acme of acritarchs (P3c) is used for local correlation in the southwestern part ofthe basin. The disappearance of the acritarchs was accompanied by a decline in

Bowen Basin

304 the proportion of striate bisaccate pollen in the assemblage.

Various workers have established assemblage, acme, and interval zones within these general floral trends. A sequence ofinterval zones has been described by Price (1983, 1985) which incorporates index species used by Evans (1967) and Paten (1969) up to zone PP3.1, and establishes new zonal boundaries in higher levels. Price described two lineages of species to support the general applicability of his zonation for widespread time

correlation. Detailed palynological studies are confined, however, to the southern part of the basin. Integration of Faunas

An integration offaunal and floral controls has been described by Draper & others (1990). This paper represents a considerable advance, but the zonal schemes used have yet to be described fully and are only available as summary tables. They have been based on a small number of sections, with few common. Little evidence is available on the distribution ofindex species throughout the basin and the influence of sedimentary facies on the palaeontological assemblages. Seismic Straligraphy

Seismic investigations in the southern part of the

basin have allowed the construction of a stratigraphy based on the onlap and truncation of beds revealed in long seismic sections. This stratigraphy is based on the recognition of surfaces representing synchronous non-deposition events, and is often difficult to reconcile with conventional lithostratigraphic units. It identifres phases of deposition within which the rocks may vary in facies, but in which the rocks together represent a single tectono-depositional episode. The bounding surfaces of these phases are diachronous, but the youngest and oldest rocks are usually present in the thickest sections. Each episodic event is related to a eustatic or local tectonic adjustment, and the effects of worldwide, basinwide, or local events cannot be differentiated without extensive regional data and good time control. This type of analysis has only been applied in the Denison Trough area by Ziolkowski & Taylor (1985), but has important implications for the whole of the Bowen Basin.

Deposition The southwestern, southeastern and northern parts of the Bowen Basin have distinct stratigraphic sections, and correlation between units is difficult. During the tectonic evolution of the basin, complementary depositional processes where taking place in different areas. The correlation of stratigraphic sections in Figure 2 has been related to sedimentation in the different phases of this tectonic evolution by Fielding & others (1990). Extension Phase and Post-extension Sag The earliest Permian sediments and volcanics are restricted to narrow grabens and half-grabens in the southwest (Denison Trough) and along the eastern margin of the basin (Figure 4). The only detailed information on the configuration of the extensional basins has been obtained from the Denison Trough (Ziolkowski & Taylor, 1985). The Reids Dome beds in the Denison Trough are entirely non-marine, with coal measures forming a large part of the section in association with lacustrine, fluvial and alluvial fan deposits.

The eastern sequences are dominated by volcanics and associated volcanic-derived sediments. In the Taroom Trough, t}-:,e Lizzie Creek Volcanics occur in the north and the Camboon Volcanics are found in the south-east. In the central area, however, the Gogango Overfolded Zone disguises the early basin configuration. A thick sequence of Carmila Beds lies to the east of the Connors Arch; the extension of this

Tuff Markers The Late Permian was characterised by extensive volcanism, with tuffs and volcanic sediments providing most of the detrital material for the coal measure sequences. The are innumerable tuff bands, now preserved as thin clay bands in the coal seams. Two specific horizons have been used for long range correlations. The first is the "P" tuff, which has been traced over a distance of over 300km from the north of the basin to the northern Denison Trough (Koppe, 1978; Draper & Balfe, 1985). This bed has a distinctive gamma-ray anomaly in geophysical logs, and is considered to be a reliable time-line marker. The second unit is the Yarrabee Tuff, which occurs at the base of the Rangal Coal Measures throughout the basin (Kempton, 1971; Matheson, 1989.) Other thinner tuffs have local value in correlation (Koppe & Mengel, 1973), but continuity of recognition is generally dependent on them remaining within a coal seam.

LA BINqO 2,16 OO

Figure 4. Distribution of Early Permian extensional rift basin sediments.

Geology of Australian Coal Basins

305 sequence northwards, between the Connors Arch and the coast, is poorly known and lacks age control.

Foreland Basin Phuse The locus of sedimentation shifted in the Foreland Basin Phase from earlier extensional basins to the Taroom Trough. Marginal coal measures were developed during the transition along the western and northern margins of the basin, with non-deposition and erosion in the southwest. These coal measures include the Collinsville Coal Measures and the Blair Athol Coal Measures. Marine influence increased, however, as the foreland basin became established, and in the late Ufimian and early Kazanian marine beds were deposited over virtually all of the Bowen Basin. The Blackwater Group, which is composed almost exclusively of coal measure sequences, was deposited during the Kazanian and the Tartarian. It was deposited first in the north, and gradually extended south, eventually reaching the southern

part of the basin in the latest Tartarian. At this time coal measures extended over all of the exposed Bowen Basin. Coal measure deposition was then followed in the Triassic by deposition of sandy fluvial deposits.

COAL DEPOSITS Coal seams occur at numerous levels throughout the Bowen Basin, but deposits of economic significance are restricted to four distinct groups described by Hawthorne (L97 4) and referred to as Groups I to IV by Staines & Koppe (1980). In addition to the four economica]ly important coal groups, a fifth sequence of extensive but uneconomic coal facies is also recognised. This group, which is characterised by abundant tuffaceous volcanic material intermixed with the coal, lies between Groups III and IV, and is herein referred to group IIIA. In the following

Group I Coal Measures The coal measures of Group I are the oldest coal-bearing sequences in the Bowen Basin. They are confined to extensional basins. Most are found in the southwest in the Denison Trough, but minor occurrences are also known in the eastern volcanic sequences. Reids Dome Beds

The Reids Dome beds are a non-marine, graben filling sequence of the Denison Trough, extending north along the western margin of the central Bowen Basin. Coal seams are widespread in the Reids Dome sequence, but have been subject to relatively little exploration. In the Denison Trough the Reids Dome beds are usually covered by significant thicknesses of marine sediment, and are generally too deep for mining.

A transitional zone exists between Springsure and Capella where rift basin formation was not strongly developed, resulting in the development of thinner sedimentary sequences. Subsequent sag was also less, leaving the Reids Dome beds close to the surface with only thin veneers of overlying marine deposits. The most extensively explored coal occurrence in the unit is located 30km southwest of Capella (Edenborough, 1985). Reconnaissance drilling by the Queensland Department of Mines has also delineated some coal measures in the Cullin-la-Ringo area south of Emerald. Isolated intersections in stratigraphic holes and petroleum exploration wells demonstrate the presence of widespread coal in the unit (Johnston, 1977). Capella

A sequence of sandy coal-bearing sediments overlying pre-Permian metamorphic and igneous rocks in the Capella area has been equated to the Reids Dome beds. Dating of the sequence, however, is based on palynomorph assemblages which are generally sparse, poorly preserved and lacking in diversity. The majority of samples indicate an age "no later than Stage 3" (Edenboroueh, 1985).

sections the distribution, depositional settings, facies relationships, and seam characteristics of these groups are discussed.

Upper

Coal unit

2OO o

o o E

Barren ilnit 300

Lower Coal unit 400

Barren unit Basement

I ++++

coat

l constomerate

Figure 5. NW-SW cross-section across the Capella deposit (after Edenborough, 1985). Lithology legend: solid = coal, dots = sandstones; circles = conglomerates; line hatching = silts and sands.

Bowen Basin

306 The coal measures are now fault-bounded on most sides, but to the east are overlapped unconformably by the Aldebaran Sandstone. This unit covers most of the postulated graben fault, which formed the depositional limit in the east. Its presence is supported by thick conglomerates occurring along the-eastern edge, which interdigitate with sandstone and coal measures to the northwest. The extent of original deposition is not clear, but is of similar area to fieeper giabens defined by seismic surveys in the Denison Trough. These are 4-5km wide, with a strike length of 15-20km between offsets along minor transfer faults. The thickening of the sedimentary sequence to the east, conglomerates along the eastern edge, and a regional easterly dip on tlie Reids Dome beds suggest that the half-graben may have the reverse symmetry to those further souih in the Denison Trough. Maximum subsidence was along the eastern margin. The faults exposed at the surface are easterly-

dipping reverse structures oriented NW-SE, and are

repiesentative of the late Triassic deformation on thb western margin of the central Bowen Basin. The pattern is a combination of early Permian extensional structures with NNW oriented graben-bounding normal faults, term_inated and 6ffset along NE oriented faults. Northwest-oriented reverse faults cut Permian and early Triassic sediments, and splay off from the earlier normal faults. Folds are associated with the reverse faults. This pattern is illustrated towards the'top of Figufe 2, which shows the southern portion of the structural zone containing the Capella deposit. The sequence has been divided into a lower and an upper c-oal-bearing unit, separated by a unit barren of ioal. Within these small basins, which experienced rapid subsidence, sedimentary facies inferdigitate frequently, with contemporaneous fluvial, lacustrine and marginal fans being deposited. No marine influence has been eniountered, and all the sequences can be related to intermontane valley-floor processes. The coal seams are generally thin, but locally they coalesce, as illus-trated in Figure 5, which shows a NW-SE section through the upper coal measure unit. The majority of coal seams occur in the u-pper coal unit. Tlie seams split and coalesce over short distances, making correlation difficult. Numerous seams have been identified and named (Edenborough, 1985). The coals are high in liptinite (6-l7Vo), with complementary low inertinite (25-49Vo). Vitrinite content decreases up section from 68 to 45Vo, and there is a corresponding decrease in crucible swelling number. The three lowest seams have strong caking properties, with a CSN around 7. Volatile matter is 37-4OVo (da0, and rank indicated by a mean maximum vitrinite reflectance (Rv-"*) of about 0.777o.

Cullin-la-Ringo This fault bounded deposit is divided into three lithological units: a lower upwards-fining sectionoverlain by a sequence of siltstone, mudstone and some fine sandsfone, which passes conformably upwards into coal measures composed of sandstone, .iltstone, conglomerate and coal seams. The coal has low ash ind sulphur. Vitrinite contents range from 34 to 54Vo, and il is classified (ASTM) a,s high volatile bituminous. It has a higher hydrogen content than other Bowen Basin coals, and its low ash, high specific ene;rg:y, and high ash fusion temper-atufes make it a potential steaming coal.

The seams vary greatly in thickness, with most lying in the range 1.0 to 5.0m. Some coal intersections, however, ire considerably thicker; a maximum clean seam thickness of 11.0m and extremely banded sections up to 36m thick have been encountered. The coal measures are generally conformably overlain by marine mudstones of the Cattle Creek Formation. Lizzie Creek Volcanics Coal measures informally referred to as the Crush Creek beds (Allen, 1976) or the Mount Devlin Coal Measures (Sternfell, 1975), are found interbedded with volcanics north of Collinsville (Figure 6). The volcanics in this area are confrned between two NNW striking faults, and the coal measures swi-ng in strike from E-W just north of Collinsville to N-S where they cross Pelican Creek at their southwestern liinit. The outcrop follows a similar pattern to that of the Collinsville Coal Measures (see below), but is displaced 1-2km to the north and west' The dip of the beds is generally ". Thg coal-bearinCse-quence is from 90 to 250m thick, and is thickest in thd east. Coals are found in two intervals, but only the lower section has signifrcant seam thicknesses' Interseam sediments include quartz-rich volcanic sandstone with pebble conglomerate, and subordinate siltitone. The coal measures contain inferior dull banded coal, in seams up to 4.2m thick. Volatile matter averages 28Vo (daf), with a moisture content of 1.7Vo and an ash of 24.6Vo. This suggests that the rank is comparable to that of the overlying Collinsville Coal Measures. No economic deposits have yet been found.

Group II Coal Measures The Group II coal depositional phase was characterised by shallow to marginal marine conditions. Subiidence and deposition were centred on the earlier rift basins, but thinner sequences are, spread widely throughout thebasi!. Coals are found ii scattered marginal areas of the basin, in the far north and southwest, and within basement depressions in the Clermont district-(Figure 7)' Eliewhere marine conditions existed throughout the

basin at this time.

Collinsville Coal M easure s The Collinsville Coal Measures occur in the north of the basin, where they rest unconformably on the Lizzie Creek Volcanics (Figure 6). The coal measures are divided into upper and lower sections by ttre marine Glendoo Sandstone Member (Webb & Crapp, 1960), which thickens as both coal-bearing units pass laterally into the Gebbie Formation to the

southeast (Figure 8).

There are nine persistent seams in the mine area (Figure 9). Depositional facies vary from initial

nori-marine fl uvial sandstone s to fossiliferous marine sandstones, and the thickness, uniformity, ^ petrographic characteristics and sulphur content of ioal seams reflect these changes' The coal measures accumulated in marginal

environments while the sea level oscillated during an overall transgressive phase. Depositional settings in the coal measures vary sequentially up sectio-n:. fluvial, fluvio-paralic, tidal flat, barrier stl?ndplain, tidal flat, paralic (Martini & Johnson, 1-987)' The sequence ii overlain by open marine beds of the Bldnheim Formation, which has an extensive basal conglomerate suggesiing a possible unconformable conlact. The uppei seams have higher v-itrinite contents, but t-tie brightest seam is the Denison'

Geology of Australian Coal Basins

307

,li i > 3!fi,

v v v v v u u u u u u ui v v v v v v v v v v v v r| uuuuuuuuuuuuuuuuuuuuuuuuu\

vvvvvvvvvvvvvl

,:("? \YPi r:

I t.)

\ i-S- _-__-__I___ tT.l.l

ALLUVTuM

--\F-./^

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COLLINSVILLL COALMLASURTS

r-l |I ' .1GLENooosANDsToNEMbER :r -t-"

rt77tF .REEK ceFFK v^r .aNrac LrzzrE volcANrcs

,,!\,y{%.:-_-_ luuul

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,_'-%_:i:*,h-i - LocALlrY MAP I

COLLINSVILLE

GOONYELLA

Figure 6. Geological sketch map of the Collinsville area.

Bowen Basin

R.AD RArLwAy FAULT

308 SECTPN A-B-C-D MI.IE

A sEcTnN

BORE

B c473

GEEBIE

C CREEK

D EXMO6R

8. Stratigraphic relationships of the Figure - Collinsville Coal Measures.

t-l tt l,l Iru lG

l= lo l< Iul

I> I

BLENHEIM SUBGROUP

Murray Seam

Little Garrick

UPPER COAL

Seam

o - 1m Garrick Seam 0.6 - 2.4m Peace Seam

MEASURES

U- 1m

GLENDOO SANDSTONE MEMBER

l< to lo

L IJ IJ l> ta lz

lllo

*z ud (r2 cc< <r tDF a

t_, I

9 J c L

Scott Seam

1 - 2.5m

Denison Seam

'1.3m

Potts Seam

LOWER

- 1m

Little Bowen

<f ](r J<

Lo_

< 1m

Seam

COAL

Bowen Seam 3.O

-.:

::.::'.'

uzztE cK VOLCANICS

.'i,;rll .lir');:

Blake Seam 0

cl 6l o6cl

,ol 6l

.l I

- 7.6m

MEASURES

6t ct

l J

lo lc lc 16 l<

I I

I I I

L_l

r.:'i',r ;

9. Coal seams and associated facies of the Fisure " Collinsville Coal Measures.

Figure 7. Distribution of Group II coals in the Bowen Basin.

near the top of the lower coal measures. Each seam shows a two to frve-fold increase in total sulphur from bottom to top. The basal Blake seam is up to 20m thick, but averages 7.5m in current pits. Ttre coa-l is dull,

massi;e, and has a high inherent ash but low sulphur (Table 2). It developed on an irregular snifa." of gravelly, braided-stream deposit-s, and is overlain bf a mor-e sandy sequence of pebb-ly-sandsand conglomerates with evidence of lateral channel migratiin and accretion in braided and meandering

channels. The Bowen searn is 4 to 8m thick, with higher vitrinite and sulphur levels.

Interbedded sandstones and siltstones between the Bowen and Scott seams are interpreted as deposits of a river-dominated lower delta-plain, where fluvial sDlavs. channels and lake deposits were intermixed #itf, tiaat and brackish water sediments. The seams vary considerably in brightness, with some much higirer sulphur contents. The Denison and Scott sei-s coaiesce over much of the area of the current mine workings. The Scott seam is overlain by tidal flat deoosits.-which qrade into fossiliferous barrier and stiandline sandJtones ofihe Glendoo Sandstone Member.

With the exception of the Garrick seam,-the seams in the upper cbal measures at Collinsville are all

Geology of Australian Coal Basins

309

Table 2. Coal seam characteristics in Collinsville Coal Measures (after Dempsey, f g8G).

SEAM Garrick Peace* Scott Denison Potts^ Lt.Bowen^ Bowen Elek"

AJn %

Y.M.T'

12-13 14-16 L5-20 20-25 13-15 72-14 t9-2t

25 24.5 24 20.5 26 2I-23 20

* !,"* seam data by Martini & Johnson, 1987 ^ Relates to Bowen East Open Cut only + Johnson, Robertson & Martini, 1985 less than 1m thick. Interseam sections are mainly sandy tidal flat and associated paralic deposits, but the lack of strong bioturbation suggests that conditions may have been brackish. Sulphur values are raised by the marine influence, and plies in the top ofthe Garrick seam can exceed 207o7otal sulphur.

All coal seams in the Collinsville Coal Measures are intruded in part, mainly by sills which range up to 40m in thickness. The intrusions can be regulai within specific seams or plies, or they can 5e highly irregular. Coked aureoles adjacent to the intrusions range from 20 to 50cm in width. In addition to these local effects, more regional effects can be seen in significant volurnes of devolatilised coal. A typical relationship of coal to an intrusion is illustrifed in

Figure 10.

The immediate contact between coal and sill is surrounded by ultra-low volatile coal, with volatile matter content (air dried basis) <97o. This is a natural in situ coke, and frequently shows columnar jointing. Material described as lowvolatile coal (Figure 10), contains approximately 9-L7Vo volatile matter. Such coals often extend further from the

intrusion,along the top ofthe seam than the base, because fluids associated with the intrusion migrate along the roof of the seam. Pronounced rank gradients ( R" changing from L.2 to 2.2Vo) may be found from the base to the top of the seam.

The carbon dioxide content of Collinsville coal is

have limited mining at !igh, and gas outbursts deplh Kerrick (L974) demonstrated from isotopic studies that the carbon in the gas has a magmltic

csN g-4 6-8 g-b 4-S t-2 8 2.8-4 0-2

Yit vo

sulphur

Rvma*vo

40 bl BB 62 2E f,Z 96 19

8.0

1.0b-1.1

Total+ 1.6

8.0 2.0

1.08-1.11 1.08-1.11

2.8

11.0*

1.0

1.1b-1.98

0.6

scattered throughout the mine workings. The thrusts steepen up to high-angle reverie structures in the centre of the syncline and on the western limb. lips in the eastern section range between 7 and 15o, and those in the less-deformed western area average 8o.

Clermont District

Blair Athol Coal Measures The Blair Athol Coal Measures are found in a NE-SW oriented basin approxirnately Skm long and 6km wide, covered in the northeast by basalts(Osman & Wilson 1975). The coal measures rest unconformably on metamorphics of the Anakie Group. Coal seams gre found in a roughly triangular area covering 1Okm" towards the southwest of the basin, but maximum seam development, along with maximum seam depths, occurs with low, irr^egular dips (1-2o) in a cenlral area covering 4.5km2.ihe seams are generally truncated by oxidation or erosion, and original coal deposition was more extensive than the present deposit (Figure 12 a-c). The central area ofthick, flat-lying coal is bounded by areas with steeper dips (up to 70), along the northwest and southwest outcrop margins and along a NE trending basement high which is the extension of the offset in the basin outline in the south. These steeper dips are not found in the east, where the seams rise towards the surface at 2-3o. The basal conglomeratic sequence also thins over the basement high in the southeast. Gloua6 surlq

origin.

The Collinsville Coal Measures lie in an

asymmetrical synclinal structure trending NNW and pitching gently to the south. The major deformation is related to a late Triassic compression, with overthrusting from the NE. This is expressed in reverse faults and associated folding (Figure 11). The intensity of deformation is grealest in the east, up against the Collinsville Fault, which forms the eastern boundary ofthe coal measures. This high-angle reverse fault has an estimated throw of 200m (Blaik, 1986).

Within the eastern limb of the syncline there are many small, low-angle thrusts with dips shallowing to the west. Many of these faults are zones rather than single structures. Bedding-plane faults are also

coklng coal

NOT TO SCALE

UVL coal

Figure 10. Sketch of intruded coal in the Collinsville area, showing spatial relationships between intrusion and affected coal. (after ' Johnson & others, f985). LV = low volatile coal; ULV = ultra-low volatile coal.

Bowen Basin

310 The coincidence of the thickest section with the deepest part of the deposit implies that contempbraneous basement subsidence controlled sediment accumulation and the thickness variations of the seams. The basin configuration is controlled by NE and NW striking feature,s, which represent the crustal framework utilised by earlier extension tectonics. Inversion of extension structures had commenced in the Early Permian rift basins at the time of deposition, and the basement was experiencing compression. This produced localised upiift and subsidence in areas ofregional sag and sediment accumulation, such as the northern extension of the line of the Denison Trough. However, the Early Permian grabens did not extend as far north as Blair Athol; regional sag was only of the order of a few hundred metres, and the area remained entirely terrestrial. The Blair Athol Coal Measures has a maximum

thickness of approximately 250m. The unit includes a lower conglomeratic section that can range up to 150m thick, comprising indurated conglomerate and sandstone, carbonaceous shale and minor dirty coal seams. The basal conglomerate of this unit thins rapidly towards the exposed-margins of the basin and is-discontinuous, filling hollows in the basement. This lower section also thins over a basernent high in the south-east of the coal-bearing area.

There is a transitional boundary from the lower unit to the upper part of the Blair Athol Coal Measures-, which ij irp to 100m thick. The uppe,r part is mainly composed of sandstone, siltstone- and coal, with seams up to 43m thick. The sandstones are quartzose, with associated metamorphic fragments. 'f'here are four major coal seams in the upper coal measures, referred to as seams numbered 1 to 4 from the surface down. The characteristics of the seams have been described by Preston (1985, 1988).

The oldest seam, No.4, has the widest distribution, but is split into two parts over most of the area. It forms a single seam up to 5m thick over the basement high in the southeast. The split thickness

oattern indicates that sediment influxes from the northwest and northeast interrupted peat formation over most of the basin, but did not overtop the peat in the aTea of the basement high. The seam has the highest inherent ash of all the sgams, with an .rrir.ge working section value of 16.6Vo (Table 3).

o o E

O o o

o cg o A d

o o

c O q)

The most important seam is the No'3 seam, which

has an average thickness of29m and an in situ resource of 240Mt. The coal is classed under the ASTM system as high volatile C bituminous coal. The seam is remarklable for its thickness and uniformity, and is best developed in the southwest and centrai areas ofthe coal basin. It thins to the north by loss within the basal section and in the east by"thinning throughout the whole section, and is lesithan half its maximum thickness over the basement high in the southeast. The coal is dull and massive, wit-h low mineral matter content,-but has relativeiy brighter sections at the base and top.- Fusain b-andJup to 15cm thick are commo,n' and lve stone bands 8 ta llm from the base provide useful

to tr

F H E C)

o o o

O 'r

marker beds.

The No. 2 seam is not found in the southeast, but

ranges in thickness from 0.3m in the southwest to 2.3ir in the centre and northeast of the freld. The overlying No. 1 seam is only pres-erved in two isolaiedlocations, and has a thickness of up to 8.9m'

Geology of Australian Coal Basins

31r

''...... No. l SEAM ---\.\

No.2 SEAM

:.-

No.4SEAM

\'_

No. 3 SEAM

REVERSE FAULT

/a ,

,,/.>

o/-

( '3\.-;...

/a\ /-t

/:1

\///

'>./\

.,,/

-v--+- No. 4 SEAM SPLIT LINE

Blair Athol Coal Measures

/t>

1000 metres

(a)

280

;4'"F^*, ,,[5"

260 260 210

210

220

(c)

No. rl

4(-& lko o

SCALE

rooom

t7'

Figure 12. Geological sketch map and cross-sections of the Blair Athol Basin (modified after Preston-'-1-985)' G;"1";idi;i.icft witU oiit.tops of major aeams; b) cross-section N-S 1A-A'); c) cross-section NIV-SE (B_B').

The upper part ofthe coal measures has been weatlrered to an off-white colour, and has been

cuts across the southwest corner of the coalfield, displacing seams No. 3 and No. 4.

However, Beeston (1978) showed that the white zone was part of the normal coal measures succession.

Wolfang Basin

considered to represent a younger formation.

The coal measures accumulated during a period of differential basement subsidence at scattered sites. Initial deposition laid down high-energy sediments in these aleas, interspersed with fluvial sands and peats. Palynology indicates that at least part of the section is equivalent to the Aldebaran Sandstone, which forms part of Stage 4.A, of Price (1973), with the basal conglomerate probably older (Osman &

Wilson, 1975).

The thick peat which formed the coal was compos-ed mainly of herbaceous plants, ferns and algae, and Smyth (1930) has postulated a raised bog setting. This is consistent with ttre widespread fusain bands which originate from the more frequent fires typical of this environment. Interseam sediments are fluvial flood-basin deposits, with minor migrating channel sandstone and overbank siltstone. The coal measures are rarely faulted, but some north-east trending normal and reverse faults have been encountered in old underground workings. A NE-trending reverse fault, dipping to the southwest,

The Wolfang Basin, described by Carr (1980), liesapproximately tZt<m southeast of Blair Athol, andboih basins contain very similar coal sequences' The

Wolfang Basin is clearly fault-controlled to the west. In contiast to Blair Athol, the main coal measure sequence at Wolfang is underlain by 9p to 50m of old-er coal measures composed of sandstone, mudstone and thin coals. These are assigned to palynological Stage 3, and correlated with the upper pari of tf,e Reids Dome beds. Price (1980) has iorrelated the main coal section at Wolfang with the top of the Cattle Creek Formation or the basal Aldebaran Sandstone (uppermost Stage 4). Above the interval correlated with the Reids Dome beds, the section contains a basal conglomerate up to 100m thick, overlain by coal measures up to 165m thick. Thirty-five to forty percent of the section thickness can be represented by coal. The coal seams compare closely with those at Blair Athol, with two seams up to 2.5m thick near the base, equivalent to No. 4 (Bbttom seam), a thick seam equivalent to No. 3 (Big seam) and a thin, laterally restricted upper searnequivalent to No. 2 (Top seam).

Bowen Basin

3t2 Table 3. Seam analyses for the Blair Athol Coal Measures (air dried basis).

Seam

Ash

No.l

3.6

32.3

8.2

No.2

6.7

33.8

8.2

No.3

8.2

27.6

7.5

No.4

16.6

(Upper) (Top)

(Big)

(Bottom)

Vol.

Moisture Sulphur

Matter

0.37o

The Wolfang seamiq found over an area of

approximately 4km'; it reaches a maximum thickness of 40m, and averages 30m. The seam thins to the north, east and south, but is faulted to the west. Apart from a few mudstone bands in the lower part of the seam, it is very clean. The coal is mainly dull, and fusain beds up to 1.6m thick are fairly common. The coal is classed as medium volatile to high volatile bituminous B under the ASTM classification, with an average ash of 9.77o. Sulphur averages 0.32Vo, phosphorus 0.0l7Vo and ash fusion temperatures are mainly above 160OoC. Specific energy is 28.3MJ/kg. The working section of the Top seam averages 2.75m thick, and is similar in most characteristics to the Wolfang Big seani. Its vitrinite content, however, is higher, being up to 707o. The Top seam is restricted to the southern two-thirds of the basin. The coals are relatively low rank with a mean maximum vitrinite reflectance (Rv-u* of 0.72Eo).

The similarities between the Blair Athol and Wolfang deposits suggest time equivalence and similar depositional conditions. The Wolfang deposit is covered by an average of 140m ofoverburden, which includes up to 50m of water- bearing basalt. Rugby Deposit

Twenty five kilometres southwest of Moranbah is an area, coverlng approximately 15km2 where thick Permian coal measures overlie conglomerates of uncertain age (Matheson, 1985). The coal measures are considered to belong to Group II by analogy with the similar coal measures at Clermont, and are overlain by sediments equivalent to the Blenheim Formation. Exploration in the Sullivan Creek and Eaglefield areas, to the north of Rugby, has intersected coal measures considered equivalent to those at Rugby and to the Collinsville Coal Measures (Matheson, 1989). The coal seam is found as an asymmetrically

lenticular body, thickest near to the basin margin but splitting into three seams to the northeast. The seam is made up of dull, non-coking coal with a high sulphur content. Vitrinite reflectance (Rv-"*) is 0.93Vo and volatile matter is 29.77o (da0 for the F1.6 fraction. Raw ash averages LTVo,but is highest in the lower part of the seam. Coal seams of the Aldebaran Sandstone / Freitag

Formation Scattered occurrences of coal measures are recorded in the upper Aldebaran Sandstone in the Emerald district (Edenborough, 1985; D'Arcy, 1988), and in

the overlying Freitag Formation near Tieri (Utah

Development Company, 1985). These coal measures formed in localised settings marginal to marine beds. Marine influence is often shown by high sulphur contents and associated burowed sediments.

At Taroborah two successions of coal measures occur among marine beds unconformably overlying the Retreat Granite and Devonian - Carboniferous sediments. Of five seams in the upper succession, the two top coal seams average 1.2m (A seam) and ^ 3.0m (B seam) over an area of approximately 30km'. The A seam, however, has up to I07o pyrite. The B seam has an average raw ash of 8.87o, and an average sulphur content of 2Vo. Sulphur contents are variable, with highest values (5.6Vo) in the north and the east. Sulphur content is also higher in the top of seams compared to the bottom. Coal rank is low, with volatile matter averaging 35.\Vo and moisture 9.27o.Tt,e A and B seam are probably equivalent to the Cetus and Cygnus seams in the Freitag Formation near Tieri. The lower coal-measures succession is thin but apparently widespread, and tentative correlation from Taroborah to Springsure is possible. In the Capella area, the Aldebaran Sandstone unconformably overlies the Reids Dome beds. Two seams (Edenborough, 1985) occur within the Aldebaran Sandstone. These are of low rank, with average moisture S.LTo,volatile matter 38Vo and vitrinite reflectance (Rv-"*) 0.66 to 0.74Vo. Typical vitrinite, liptinite and inertinite percentages are 49, 11 and 40 respectively.' The Freitag Formation includes thin and often split paralic coals, which subcrop in the Tieri area. Subsurface logs from drilling in the Denison Trough indicate that coal seams are often locally developed in this unit, but consistent widespread seams are not present.

Group III Coal Measures The lack of control or evidence for correlation initially limited the development of a stratigraphy for the late Permian coal measures, and current divisions are mainly based on five criteria summarised by Koppe (1978). These are indicated in Table 4. Such features have provided a workable basis for subdivision ofthe sequence, although Koppe (1978) has pointed out the potentially transgressive nature of some of the criteria used. They are all based on major regional events, such as sea level changes leading to the formation of the first coal, volcanic events of regional significance, and the overall climatic change that apparently took place at the end of the Permian coal-forming period.

A major transgression occurred in the Bowen Basin during the Kazanian, apparently as a result of a general rise in sea level. During the late Permian regression, peats were first established in the north ofthe basin, and later extended south, so that by the end of the Permian, coal measures are found over the whole of the basin. Group III coal measures are made up of the freshwater Moranbah Coal Measures in the north, which are transitional to the marine-influenced German Creek Formation in the central Bowen Basin (Figures 13 and 14). Group III coal measures sit conformably on marine beds, and are overlain by Group IIIA coal measures, which are distinguished by the presence of numerous tuff beds. Group III coals are best developed on the Collinsville Shelf and the Comet Platform, along the

Geology of Australian Coal Basins

313

western margin of the basin. Marine deposition took place during Group III time in the eastern part of the central Bowen Basin and all of the southern Bowen Basin. The sequence in the northern Bowen Basin thickens to the east, but elsewhere thicknesses are difficult to determine. The major area ofsubsidence shifted to the Taroom Trough, along the eastern margin of the basin (Flood, 1985), as the Taroom Basin was established in a foreland basin phase. CoaI Deposition Phases

A number of coal formation phases took place along the western margin of the basin, during which thick peats were accumulated with little ingress of terrigenous sediment. The coal seams formed are continuous for over 200km along strike, but the seams and splits are given different names in many of the mines. The seams can be correlated, however, even though the surrounding sediments change in lithofacies from terrestrial (fluvial) to intertidal and marine along the strike length. The nature of the coal seams themselves also changes with these variations in depositional environment.

Figure 13. Distribution of Group III coals.

There are five seam formation periods within the Group III coals, here identified by seam names that form part of each "superseam". These are illustrated in the correlation chart of Group III coals in Figure 15. In the Goonyella area to the north, the seams are less numerous and thicker than elsewhere. Here the seams accumulated in paludal conditions, entirely freshwater, and were separated by fluvial interseam sediments. In the central Bowen Basin, however, there were continued fluctuations of the sea level with respect to the peatlands, resulting in a complex interdigitation of deltaic and marine deposits with the coals. The depositional environments are related to the behaviour of the underlying crustal blocks, as established during the early Permian extension; the position of transfer faults coincides with the facies changes in the interseam sediments, and also with

the locations ofseam splitting.

Group lll coals

Group lll a coals

EMERALO ..7^,

souTH

''--"=-< ' I Moranbah Coal / Measuri:s . BASE OF MAJOR COALS

Bl€nh€im Fm

NORTHERN BOWEN BASIN

Maria Fm

CENTRAL BOWEN BASIN

Figure 14. North-south cross-section along the western edge of the Bowen Basin, indicating stratigraphic - relationships and thickness variations of coal measure units.

Bowen Basin

314 Dysart Coal Phase

P CoaI Phase

The first major coals above the marine sequence

This coal phase is distinguished by its association with the "P" tuff bed, which generally lies a few

were formed in this phase, and although they could possibly be time transgressive, they form a good, continuous marker over a crop length of 200km. The

relatively thin transition from marine beds to coal and the widespread distribution of coals over the area suggest that the sea withdrew rapidly from the shelf regions, particularly in the north. The coal seams which are correlated with this phase are the Goonyella Lower, Dysart, German Creek and Lilyvale seams. They are the most commercially important Group III seams, and provided approximately SOVa of the total Bowen Basin production in 1988. Seams range in thickness from 7m at Riverside to between 2 and 3m at Oaky Creek. The seam horizon is commonly split; one or two seams are found in the north and south, but numerous distinct splits have been recognised in the Peak Downs - Saraji area. Despite this variation, the splits form a coherent, linked and continuous 'superseam', with ply characteristics being maintained through the numerous splits along the 55km of strike length in the Peak Downs and Saraji mines (Milligan, 1975).

Harrow Creek Coal Phase Coals of this phase are also widely exploited. They include the Goonyella Middle seam in the north, the Harrow Creek seam from Peak Downs to Norwich Park, and the Corvus, Tieri and Aquila seams in the south. North of Peak Downs there is mainly only one

thick seam, from 7 to 1lm in thickness, with only thin, local splits. Two or three linked seams are found in the Peak Downs, Harrow Creek and Saraji mines, where the combined splits form the thickest seam (13m) of the Group III coals. At Norwich Park and south, three relatively thin seams continue all the way to Gregory. Although they are often split into two or even three splits, and are sometimes associated with tuffs, these thin seams retain remarkable continuity over this distance. The interseam sediments are deltaic and marine beds, and the widespread termination and re-establishment of thin peats over such a wide area was controlled by sea level fluctuations.

Table 4. Location of stratt**pnt"

metres below the coal. However the coal can also enclose the tufi or even lie as much as 17m above it. The coal is occasionally split north of Peak Downs, but to the south it is consistently split into two, and sometimes into three parts. In the north it is referred to as the "P seam", and is correlated with the "M seam" at Norwich Park, and the Pleiades seam further south. The thickness ofthe seam varies up to 6m north of Peak Downs, but to the south the seam thins to between 1 and 2m. The widespread coincidence of the coal with the tuff bed supports the suggestion that the coal phases are

essentially time equivalent. Q and S Coal Phases

During this time coal bearing facies were deposited only in the northern part of the basin; a marine transgression in the south led to the deposition of the Macmillan Formation overlying the German

Creek Coal Measures. No mines have been developed in these sequences, and exploration drilling has not been as intense as in other coal phases. The correlation of coal seams is therefore much less certain. Devey (1983) proposed correlation of the Goonyella Upper seam in the north with the "Q seam" of the Peak Downs and Saraji areas. In both areas the seam is known to split. The higher seams of the latest two coal phases are not well known but one, the "S seam" overlies the

Macmillan Formation at Norwich Park, and was formed as the coal measures prograded south over the marine tongue. The ash falls characteristic of the Group IIIA coal measures commenced when the regressing shoreline was located in the German Creek area, and the first coal seams overlying the Macmillan Formation to the south of German Creek contain numerous tuffs. The Group III seams are the prime source of coking coal in the Bowen Basin, and average coal characteristics for the various mines are given in Table 5. Although the southern deltaic coals have higher vitrinite contents than the fluvial coals in the

t*31X"*l"ri%il"

Group,II[ and fV coel measures

Base of Rewan Formation (equates approximately to top of last significant coal seam) GROUP IV COAL MEASURES ..............Top of abundant tuffs (base of first 'clean' coal seam)

GROUP IIIA COAL MEASURES

Base of abundant tuffs (base of first tuff banded coal) GROUP III COAL MEASURES

"P" tuff bed Base of first major coal above Kazanian marine beds

Geology of Australian Coal Basins

3r5 GM Goonyella Middle C Corvus HCK Harrow Creek GCK German Creek

Kirometres Suttor Creek Wards Weli

Goonyella Moranbah

German oaky

Dysart Norwich,Park Creek Creek

Peak Downs Saraji

1b. Correlation chart of Group III coal seams along the western margin of the Bowen Basin. Figure - (modified after Devey, 1982).

Measures by the appearance ofabundant tuffbeds in the lattei sequenie, thin tuffs were-also dep-osited during the accu^mulation of the Moranbah Coal Measires. The thin ash fali deposits, however, although common, were incorporated within other sedime--ntary units, and are only preserved in rare locations where reworking of the material did not take place. They can be seen, for-examp-le, in the interieam inteival between the Goonyella Lower and Middle seams in the Red Hill area. Hundreds of ash fall deposits, from 1 to 100mm thick, are also preserved in dark siltstone, which ac-cumulated on an isolated uncompressed peat island within the Goonyella Lower seam. The island was-apparently nevei overtopped by the fluvial channels that provided the-sediment for most of the interseam deposits. In most situations, however,-the tuffs were redistributed by surface processes and not preserved, but some of the thicker ones are preserved'in coal seams. The Goonyella Middle -tonstein (Koppe & Mengel, 1973), for example, is only 20 to 50mm thick but has been identified over more than 100km of strike length.

north, the variation in characteristics is controlled mainly by rank differences. These in turn are related to the tectonic setting of the mine sites and to the local intrusive history. Northern Bowen Basin The Moranbah Coal Measures found in the northern Bowen Basin (Koppe, 1978) are transitional to the laterally equivalent German Creek Formation in the central Bowen Basin. The formation is relatively uniform north of Peak Downs, but a transitional sequence is found between the Peak Downs and Noiwich Park mines. The coal measures are from 200 to 400m thick on the Collinsville Sheli but thicken to 760m at Kemmis Creek in the east. The Moranbah Coal Mgasures consist mainly of volcanic lithic sandstone, with lesser siltstone and coal. Quartz clasts form up to 20Vo, but more commonly less than I07o of the sandstone. Conglomerate is virtually absent from the western outciops, but is common in the thicker sections in the east. The sediments were mainly derived from a volcanic source, and one major tuff is recognised through the northern and central Bowen Basin. This tuff, referred to as the "P" tuff, is from 1 to 1.3m thick, and commonly occurs close to or within a coal seam. It is characterised by abundant euhedral bronze mica, and gives a distinctive gamma-ray anomaly on geophysical borehole logs.

Approximately 20m of coal is present over the noithern Bow-en Basin. The coal is concentrated into four or five seams in the west, but split into more than twenty thin seams in the east. The majol economic seams are the Goonyella Lower, which has several splits in places, the Goonyella Middle and the Goonyella Upper. In the area of current mining the Goonyetla Middle seam ranges from 7 to 10m and Goonyella Lower seam from 7 to 9m in

Although the Moranbah Coal Measures are distinguished from the overlying Fort Cooper Coal

Table 5. Quality characteristics of Group III coals. ]OONYELL, RIVERSIDE

PEAK

SARAJI

NORWICH PARK

GERMAN

OAKY CREEK

GREGORY

CREEK

DOWNS

25.5

23.9

2t.o

19.5

L7.2

21.0

28.9

32.0

ASH (as sold) 7a

8.0

9.8

9.5

9.3

8.5

8.0

8.5

RANK

1.t2

1.23

t.4

1.5

1.6

L.45

1.07

0.98

CRUCIBLE

7.5

8-9

8.5

8-9

EXINITE 7,

TRACE

INERTINITI

VOLATILE MATTER %

(Rv-.*) SWELLING No.

VITRINITE Vo

SOURCE: Queensland Coal Board, @TypicalPhysicalandChemicalPropertiesand

Classification.

Bowen Basin

316

Ramp 11

I A'

Metres

B-

h\ Bedding Traces

jil

Goonyella Middle Seam

Rider Metres

Siltstone l--_l Siltstone & Sandstone lE?l Sandstone

ffi

l'.::.i:r':il

000

2000

Figure 16. Hig!,wall sections of Goonyella Mine showing reversal of compactional dips around rneanders in the laterally migrating channel. The units A, A', A", A"t, B, Bt and C, C' are repeats of linear sinuous sediment bodies which migrate in and out of the highwall section. thickness. Between the Goonyella Middle and Goonyella Upper seams is a thinner seam, which is often associated with the "P" tuff. Goonyella and Riuerside Mines Sections from the Goonyella Lower seam to about the "P" seam are exposed in Riverside and Goonyella Mines. The interseam sediments in this area were laid down by fluvial systems, with channel, levee, overbank splay and lacustrine deposits represented (Godfrey, 1985; Johnson, 1982). Figure 16 illustrates the deposition of channel, splay and lacustrine sediments over the peat of the Goonyella Middle seam.

Most of the interseam sediments are characterised by high dips, ranging from 10o to 30o with respect to the coal seams. These arose from peat compaction during lateral migration of channel systems. The same thick, migrating channel sequence meanders in and out of the highwall sections between ramps 4 and 12 at Goonyella Mine. As the compactional dip is always towards the direction of lateral migration, the dip of the beds reverses on either side of the meanders. These lenses of obliquely dipping sandstone beds are up to 60m thick.

Strata described as "black clay bands" within the siltstone sequences have been associated with massive highwall failures where steep compactional dip is directed towards the open pit excavation. These beds have been shown to be essentially the same as surrounding lighter coloured beds (Seedsman & Emerson, 1985), except for higher water contents developed as a result of localised bedding plane shears. The time required for accumulation of the interseam

Centrsl Bowen Busin Group III coals in the Central Bowen Basin are found mainly in the German Creek Formation, the upper two-thirds of which represent coal measure facies. This sandy unit interdigitates with the volcanic lithic sandstones of the Moranbah Coal Measures, and its most northerly extent at any time-slice horizon depends on the sea level and shoreline position. The sandstone is distinguished from that of the Moranbah sequence by its quartz content, which usually ranges between 20 and 50Vo but can be as high as 80Vo. This sediment was sourced from west of the Bowen Basin, with the distinctive high quartz content being further increased by marine reworking of the sands prior to deposition. Koppe (1978) has indicated Saraji as the northern limit of paralic quartzose beds around the time of formation of the "P" seam.

In the area south of Norwich Park, the thin

continuous coals of the German Creek Formation are separated by extensive planar-bedded and typically burrowed sand sheets of deltaic or shallow marine origin. This continuity of even very thin coals is unique in the Bowen Basin. Seams of less than lm in thickness can be traced for over 100km, and, with occasional local exceptions, all of the seams (German Creek, Corvus 1 and 2, Tieri, Aquila and Pleiades) can be continuously traced from Norwich Park to Gregory Mine. The peat established itself over the flat depositional surface during times of low sea stand. Sea level rises did not necessarily cause inundation ofthese coals, but led to rapid rises in base level, drowning the peats in the lower parts of deltas. Brackish to fresh conditions were probably maintained behind barriers located further to the east than the present outcrops, which allowed the coals to maintain a relatively low sulphur content. Marine shell beds are occasionally found between the seams, but they are not in direct contact with coal.

sediments was much less than for the thick peat

Peak Downs and Saraji Mines

interseam depositional systems implies diachroneity of the coal seams throughout the area, the interseam sediments still represent distinct, limited-duration

This area spans the transition from the Moranbah Coal Measures to the German Creek Formation. The Dysart seam and its lower splits are associated with deltaic deposits, including, distributary mouth bars, interdistributary bays and low-sinuosity sand channels. The upper splits of the Dysart seam are separated by channel sands, some broad sand

beds. Even though the lateral migration of the

phases ofterrigenous incursion into the peat areas. This is significant for the Goonyella Middle and Lower seams, which are correlated with thick coal seams to the south.

Geology of Australian Coal Basins

317

SCALE

ffi Fluvial Channels N Deltaic distributaries

5Km

SEAM

,K,

o c)

.N*

/r*

DYSART UPPER 2 (S) DYSART LOWER 2 (S)

PARTING 4

PARTING 1

Figure 17. Facies of sediments between the splits of the Dysart Seam, Peak Downs Mine (after Archibold, 1982).

ISOPACH MAP

German Cre6k Soam to Corvua 2 Seam with positbn of Odtaic Charlncb.

rrf--5g%

LEGEND

Contows (metres)

+22-

Dehaic Ghamel ur

rJIm outlin€

lb.ine Eourdary (approx.) F.TT.I

>2l'

L.r-l

1O-21t

l=':_:]

17-1*r

l--l

h- frlr:triJy b.yt

\kt*\

o12SIfr

L===#

SURFACE

"U;

Prrs

Figure 18. Depositional environments of strata overlying the German Creek seam at German Creek Mine. sheets, and thick lenses of laterally migrating sand

German Creek Mine

This reflects the progradation ofthe delta during accumulation of the Dysart seam, and the establishment of paludal environments with localised fluvial channels.

Terrigenous sedimentation during and after formition of the German Creek seam was dominated by a deltaic channel system coming from the nbrthwest. This fed a seam split between the German Creek and German Creek Lower seams, and deposited a series ofthick sandy channel deposits over the German Creek seam in the present mine area (Figure 18). With drowning of the peat,-deltaic sediment tongues began prograding across the submerged plain. These iediment lenses quickly filled thi small basin, and were then overlain by sheet-bedded sandstone which accumulated during further slow subsidence. The prograding unit and the overlying sheet-bedded unit can be seen overlying the German Creek seam throughout the German-Creek Mine area. Marine influence, with common burrows, increases to the NE and SE of the mine lease. The deltaic system intruded into this

channels, similar to the Goonyella Mine (Figure 17).

Norwich Park Mine The Dysart seam is overlain in the north by inter-distributary bay sediments, which coarsen upwards from dark laminated siltstone to interbedded sandstone and siltstone and sheet sandstone beds. The initial sediments in the south of the mine are laminated muds, sheet-bedded sands and sandstone-siltstone interbeds. These are overlain by distributary mouth bar sands and massive distributary sand deposits (Godfrey, 1985).

Bowen Basin

318

with the overlying coal being relatively clean and

free of tuffaceous material. 80

coal, mst, carb mst 100

tuff coal

carb mst

tuff

110

coal carb mst

, inf coal

coal & mst 120

coal carb mst & mst

coal carb mst - inf coal croollltacurmst 130

Figure 19. Section of the lowest seam of the Fort Cooper Coal Measures in Cairns County 71 bore, Norwich Park area. area, and constructed a delta mouth bar in the south of the mine lease.

Group IIIA coals extend throughout the northern and central Bowen basin, but south of the line of the Blackwater transfer fault the tuffaceous interval contains only marine or burrowed marginal marine deposits (Thornton, 1985). In the north the unit is called the Fort Cooper Coal Measures, and has a thickness of up to 500m. Two stratigraphic units are recognised in the south of the central Bowen Basin, the sandy Fairhill Formation and the overlying Burngrove Formation. Both units total about 200m in thickness in the Blackwater area. A marine transgression within the sequence deposited a tongue of marine mudstone across the Comet Platform to form the lower part of the Burngrove Formation. This interval is equated with the Black Alley Shale of the southern Bowen Basin. In the southeast of the basin, around Moura, the Kaloola Formation (Quinn, 1985), with tuffaceous coals, is equated with the upper part of the Fairhill Formation (Anderson, 1985). The coals seams of Group IIIA are thick, but it is rare to find clean sections greater than 1m in thickness (Figure 19). Anderson (1985) reported tests from the uppermost seam at two localities, which after washing produced coal with ash ranging from 20 to 277o with a recovery of 55 to 70Vo. Muc}:' better results can be obtained from selecting clean coal sections, which are up to 2m thick in the Burngrove Formation in parts of the Blackwater and Lake Lindsay areas. Some of the cleaner coal plies display high vitrinite contents and very strong coking properties, but the high inherent ash limits the potential for economic exploitation of Group IIIA coal seams.

Group IV Coal Measures

The sequence in these mines is very similar to that

This interval of coal-bearing strata includes the Rangal Coal Measures in the northern and central areas of the Bowen Basin (Figure 20). In the southeast, the equivalent section has also been referred to as the Baralaba Coal Measures (see Figure 2). Quinn (1985), however, has suggested that this could be revised as the Baralaba Sub-group, taking in a lower section known as the Kaloola Formation (also regarded as the Kaloola Member of the Baralaba Coal Measures) and an upper section known elsewhere in the basin as the Rangal Coal Measures.

Group IIIA Coal Measures The coals of Group IIIA are distinguished by

Equivalent coals are also found in the Bandanna Formation in the Denison Trough to the southwest. A sequence oflow-ash coals occurs in the upper part of the Bandanna Formation, but this has not been differentiated from the underlying paralic tuffaceous beds which are equivalent to the Group IIIA coals. Group IV coals are mined in the Blackwater district, in the southeast at Moura, and in the far north of the basin at Newlands.

The deltaic channel systems do not persist stratigraphically higher than the Corvus seams, but

are replaced by widespread sheet sands. Burrowing and quartz concentrations indicate a maximum marine influence betwecn the Tieri and Aquila seams, which are correlated with the Goonyella

Middle seam further to the north. Oaky Creek and Gregory Mines

at the German Creek Mine, with local variations of deltaic facies. At Gregory the Lilyvale seam is overlain by micaceous coarse sandstone, well sorted strandline sandstone, lagoon and bay siltstone, laminated intertidal siltstone, and burrowed siltstone beds.

abundant associated tuffaceous beds and high inherent ash values. Seam thicknesses ofup to 30m are not uncommon, and coal can make up to 207o of the total section. The tuff bands may form more than 50Vo of the seam, with the remainder comprising interbanded coal, inferior coal and carbonaceous shale. The top ofthe unit is indicated by the appearance ofnon-tuffaceous coals, but in most areas this coincides with a prominent tuff, referred to as the Yarrabee Tuff Bed (Anderson, 1985; Matheson, 1990), which has been traced throughout the northern and central Bowen Basin. The Yarrabee tuff frequently occurs within a seam,

The base of the Group IV coal measures interval is indicated by the Yarrabee Tuff Bed over most of the basin, and by the transition from high-ash coals of Group IIIA to clean (low-ash) coals of Group IV where the Yarrabee Tuff Bed is not recognised. The thickness of the Group IV coal measures varies from 50m on the Collinsville Shelf in the northern Bowen Basin to more than 300m at Moura. The sequence thickens into the Taroom Trough. It is only known from faulted sequences to the east of the Collinsville Shelf and areas on and around the

Geology of Australian Coal Basins

319 There is a widespread appearance ofclean coals over the whole of the Bowen Basin at the base of the Rangal Coal Measures, and this is tlre distlnguishing characteristic of the formation. The tuffaceous interval appears to have stopped as suddenly as it started at the boundary between the Group III and IIIA coals, culminating in a final major eruption which deposited the distinctive Yairabee Tuff Bed (Matheson, 1990) over the whole basin. The Yarrabee TuffBed appears as a

consistently high gamma-ray marker in geophysical

logs, above which the coals are clean with low

inherent ash.

As this tuff generally occurs within a seam, formation boundaries, and the boundary between Group IIIA and IV coals, are also usually placed within a coal seam. The transition takes place within the Vermont seam and its equivalents in the north, and in the Pisces seam at Blackwater. A similar tuff is found in the base of the lowest clean seam at Moura (E seam), but it has not been used as a stratigraphic marker in this southeastern part of the basin.

A distinct change from grey to green takes place in the sandstones and siltstones at the top of the Rangal Coal Measures. This change occurs at or close to the uppermost coal seam or carbonaceous band, and is a result ofdistinct depositional and diagenetic changes. The overlying Rewan Formation is a terrestrial flood plain deposit, with meandering stream channel deposits and associated flood-basin siltstones and sandstones. The source ofthe sediments was similar to that of the coal measures, but the disappearance of the peat swamps and the reduced organic content have led to a chlorite-zeolite diagenetic suite of minerals, which give the rocks a characteristic green colour. The high carbon dioxide content in the coal-bearing sequence beneath has resulted in a clay-carbonate diagenetic mineral suite in the coal measures, giving the rocks a grey colour when fresh and a buff colour on weathering.

TH]ry

LOW RANK COALS

o o @

o ()

Figure 20. Distribution of the Rangal Coal Measures. Comet Platform in the central Bowen Basin, where it is from 100 to 200m thick. In the southern Bowen

Basin, equivalents to the Rangal Coal Measures in the Denison Trough are <100m thick. They disappear beneath the Mimosa Syncline to the east, and are approximately 300m thick where they crop out between Baralaba and Theodore. The persistence of strong seismic reflectors below the Triassic sequence across the Mimosa Syncline indicates the continuity of the Group IV coal measures.

The Rangal Coal Measures rest conformably on the Fort Cooper Coal Measures in the northern and central Bowen Basin, and the Burngrove Formation in the southern part of the central Bowen Basin. In the southeastern Bowen Basin the tuffaceous,

prominently burrowed Kaloola Formation (Quinn, 1985) passes conformably upwards into coal measules containing relatively clean coal seams.

Since Kempton (1971) first drew attention to the gamma marker and discussed the Yarrabee tuff bed, it has been widely used in exploration programs throughout the Bowen Basin. The name'Yarrabee Tuff Member" was reserved by Koppe and Anderson, and the unit was formally described by Matheson (1990). Matheson (1989) reviewed occurrences of this tuffhorizon in the central and northern parts of the basin. It averages 0.88m in thickness in the area to the east of Saraji and Peak Downs, but only averages 0.36m from Winchester South to Newlands in the northern Bowen Basin. No primary volcanic features are preserved, and no petrographic descriptions of shards or other diagnostic structures have been published. While bedded fossils within the unit are rale, roots andVertebraria are found in situ where it is overlain by coal seams. The tuffaceous

origin is interpreted from its distribution.

Two main coal seams occur within the Rangal Coal Measures in the northern part of the basin. The lower of these is the Vermont seam and its equivalents, which are usually associated with the Yarrabee TuffBed at the base ofthe sequence. The

upper seam is the Leichhardt seam. Both seams spfit locally. On the Comet Platform, the Rangal Cloal Measures overlie the Burngrove Formation and contain a greater number of seams. There are commonly-five seams, the lower one being associated with the Yarrabee Tuff Bed. There is, however, a suggestion that the two seam pattern from the north

Bowen Basin

320

Figure 21. Seam correlation in the Annandale area (Matheson, 1990 after Koppe,L9TA).

Geology of Australian Coal Basins

32t of the basin continues to the south, in that, while the lower three and the upper two seams often split and rejoin, it is rare for seams from these two sections to join (although there is a notable exception in Blackwater Mine). Up to nine searns are present in the southeast at Nipan, and up to four seams are developed at Rolleston in the southwest. The quality characteristics of Group IV coals are indicated in Table 6.

Leichardt Vermont

Leichardt Seam

The change between the coal measures to the Rewan Formation were probably the result of a general climate change ( Quinn, 1985).

Rangal C.M.

Northern Bowen Basin Yarrabee

The distribution of coal measures in the northern part of the basin is controlled by faulting and folding within the Nebo Synclinorium. The coal measures dip gently to the east or west into the synclines, and repeated sections are upthrown along a number of major northerly and north-northwesterly striking faults. Along the edge of the Collinsville Shelf the Rangal Coal Measures range between 25m and 112m in thickness.

Tuff Bed

Fort Cooper C.M.

A natural division in a north-south direction occurs in the Rangal Coal Measures between the Mackenzie River and Middlemount. This follows the pattern of the underlying tuffaceous formations where the most northerly extension of the Burngrove Formation is found in the same area. Two major seams are present in the north, referred to as the Vermont and Leichhardt seams over most of the area (Figure 21). One or two thin seams are found at the top of the Rangal Coal Measures, but they are not consistently developed. The regional geology of the Rangal Coal Measures has been reviewed by Matheson (1989) whose conclusions are followed here.

Figure 22. Typical graphic logs of the Vermont and Leichhardt seams at Poitrel. After Quinn (r.e85).

The seams commonly split and rejoin, particularly in the southeastern part of the Nebo Synclinorium. The Rangal sequence is also thicker in that area, rvith up

Table 6. Characteristics of Group IV Coals.

Vitrinite Exinite

Volatile Matter 7o

Ash(as

adb

(Ro vit max)7o

Newlands Hail Creek

25.8

14.0

0.90

0-1

19.9

10.5

1.3

6.5

Winchester South

21.0

14.0

1.15

Lake Vermont

2r.5

7.0-9.0

L.25

5-6.5

19-53

18.6-22.0

7.0-16.0

L.22-I.36

1.5-9.0

55-70

8.0

10.0

2.59

23.4-27.0

7.8-13.5

1.05

0.5-6.5

25.8-28.4 7.2-11.5

1.05

2-6.5

Curragh Yarrabee Blackwater South Blackwater Ensham Rolleston Baralaba Moura Theodore

sold)Vo

Rank

Crucible Swelling

Inertinite Vo

No.

40-56 34356

955 045 260 t 0-2 056 237 3

42-73 30-48

38-52

26.7

L2.7

0.8

0-1

28.7

10.6

0.58

t2.4

7.5

2.08

419 034

2-3

62-70

2-3

23-26

27.9-30.6 8.2-12.9 0.79-0.90 30.9-32.0 9.5-13.9 0.66

All data from Queensland Coal Board L986, except Lake Verrnont from Department of Minerals and Energy, eensland (personal communicaion).

Bowen Basin

322

16 NS 17

&rcKWATEft CNE€K

ALACKVATER CPE€K

irs.g

NS.142, 143,

Ns.r2

NS.ro, il

[ts30

N.S. t66

t72

N.Sz9 NS.35

N.S

ALACKWAT€R CREEK I

NS.26

N,S.24

N.s68 NS32 r,1565 NS.33

N.S. t56

t60

t7tR.

Figure 23. Some seam correlations in the Rangal Coal Measures in central Bowen Basin (from Staines' 1972). to 140m at Annandale and Walker Creek. Exploration in the far north and northeast has shown that the seams are generally intruded and coked, and often faulted, so that there is little prospect of significant economic coal being preserved.

With the exception of an area of approximately 500km'covering north Burton Downs, Lenton Downs, Lake Elphinstone, and the north of Kemmis Creek, the Yarrabee Tuff Bed is a readily identified marker within the stratigraphic section. From the Winchester South deposit northwards it is a-lways found within the lowest seam of the Rangal Coal Measures (upper part of the Vermont, Poitrel Middle, Hynds, Newlands Lower). Where this seam has coalesced with the highest of the Group IIIA coal seams (Girrah, Fort Cooper, Poitrel Lower, Byerwen, Blackeye) it occurs within the top few metres of the combined seam. In the Lake Vermont area the Yarrabee Tuff Bed lies between the Vermont and the Girrah seams. The Vermont seam and its equivalents have distinct characteristics below and above the Yarrabee Tuff Bed. The unbanded coal above the Yarrabee Tuff Bed ranges from 0.5 to 4m in thickness, and its profile in comparison to the lower part of the seam is

illustrated in Figure 22.

The Leichhardt seam contains the major coal resource of the Rangal Coal Measures in the northern Bowen Basin. Equivalent seams are the

Poitrel lJpper, Newlands Upper and Elphinstone seams. Seam thickness ranges up to a maximum of 7.2m at Newlands and 9m at Bee Creek. Thicknesses >5m are also found within the Picardy, Winchester South, Poitrel, Daunia, Burton Downs, Hail Creek and Annandale prospects. The Leichhardt seam is regarded as a steaming coal over most of the northern Bowen Basin. In vertical profile it is consistent in quality and bright-ness, -and

thin tonstein bands are piesent, particularly in the north. At Winchester and Poitrel a weakly coking coal product can be produced from the seam, and at Daunia and Hail Creek the seam is considered as a

coking coal. At Burton Downs and Lake Vermont it would-be possible to produce equal proportions of weakly coking and steaming products. Coking coals from the Rangal Coal Measures typically have low fluidity. The only mine currently operaling in the Rangal Coal Measures in the northern Bowen Basin

is afNewlands, producing a high volatile bituminous non-coking coal from the Newlands Upper (Leichhardt) seam. Central Bowen Basin The Rangal Coal Measures occur in the narrow Yarrabee Structural Zone, between the Dawson Folded Zone and the Collinsville Shelf, and further south, over the Comet Platform. The coal measures within the Yarrabe e Zone have fold axes striking NNW, with closures at 1-15km spacing. The folds are frequently truncated by NNE striking faults,breaking the coal seams into relatively small and structurally complex basins. The section is also repeated by a number of high-angle reverse faults.

A zone of low-angle thrust faults occurs along the edge of the Comet Platform, but betweer_r the thrusts the sequence is only mildly disrupted. The coal measuies overlie and gently dip off the western, southern and eastern edge of the Comet Platform.

It is not possible to demonstrate continuity of seams in the Yarrabee Structural Zone, but correlation of seams has been achieved along the edges of the Comet Platform (Staines, 1972; Johnson & others, L975). Figure 23 shows an example of seam correlatio=ns in the Rangal Coal Measures of the central Bowen Basin. Two main seams are usually present north of

Curragh Mine, similar to the situation in the northern Bowen Basin. The lower of these seams includes the Yarrabee Tuff Bed, and is the equivalent of the Vermont seam. The upper seam is thick and comparable to the Leichhardt seam in the north. In the Middlemount area, splits extend from the lower to the upper seam in a complex arrangement, furfher confused by faulting. Thin

Geology of Australian Coal Basins

323

< P|TD >.

P|TC ><P|TB >.

P|TA >

ARIES-CASTOR

Blackwater area (Figure 24). Where seams such as the Taurus occur, the contribution from the Orion, Pollux and Castor can still be differentiated. While seam configurations are relatively consistent in a N-S direction, closely spaced splits and combinations occur along E-W traverses. Depositional systems providing the interseam sediments were preferentially oriented along the basin axis, and controlled by movements on the underlying crustal blocks. Low-angle thrusts are common along the margin of the Comet Platform. The fault planes can lie within coal seams over long distances, forming thrust layers of coal up to ten times the true thickness of the seam at some localities and completely removing the coal at others. The characteristic profiles can be used to identify the seams in such structurally disrupted areas (D'Arcy, 1985).

POLLUX

54 ORION

321

El#

EFT]

Current and abandoned workings located further east near Bluff have the typical configuration of deposits within the Yarrabee Structural Zone. Seams in these faulted blocks can be correlated with platform sequences at Blackwater, and tied in using the Yarrabee Tuff Bed.

02m approx. Yerl. scale

Figure 24. Continuity of lithotype profiles in Rangal coal measures over a distande of 15km at Curragh Mine, Blackwater (after Svenson & Peterson, 1983). seams are found discontinuously near the top of the Rangal Coal Measures. Many splits and combinations of plies occur in the Blackwater area, and at the northern end ofthat area, near the Mackenzie River, the various seams combine to form the basal Mackenzie seam (Pisces, Orion and Pollux seams), Mammoth seam (Aries and Castor seams) and thin Cancer seam, a situation which parallels the seam arrangement further north. It is possible to recognise individual seams in their various combinations throughout the

Aries 1

&iu" 2 - Castor castor z)

r rrrrE==lIlrr FAR NORTH

Pollux

NORTH

,l a

rt rllr

The rank and structural setting of the coals vary widely throughout the Blackwater district, although rank increases to the east as the Folded Zone is approached. A wide range ofcoal products is produced, including steaming coal, coking coal and semi-anthracite. The coal seams have only been mined on the eastern side of the Comet Platform, but reserves have been delineated on the south and western margins. In the Ensham area the lower coals are thin, but the Aries and Castor seams are thick and well developed (Figure 25).

Extensive highwall exposures have allowed detailed study of the depositional environment of the coals and interseam sediments in the Blackwater area. The numerous splits and joins of the coal plies enclose discrete pods of interseam sediment, which individually represent the intrusion ofa terrigenous

Aries 1

6'n=:i Aries 22-2::Y

tries 22 ',Jtt-

caqgi

Pollux - Orion

lrrrrrrllllltrrrrr=:: CENTRAL

SOUTH

Figure 25. Cross-section of seams in the proposed Ensham open cut area, western Comet Platform.

Bowen Basin

324 found over a broad area in the southwest, on the Comet Platform and in the Denison Trough. Baralaba to Theodore

In the southeast the Group IV coals are only accessible for about 100km in a narrow strip

following the course of the Dawson River, where they dip to the west at from 6 to 20o. The Rangal Coal Measures rest conformably on the Kaloola Formation, which is characterised by abundant tuffs, and contains thin tuffaceous coals interbedded with deltaic and prodeltaic sandstones and siltstones. A prominent tuff occurs within or under the lowest seam of the Rangal Coal Measures (E seam) in the Moura mine sequence, at a comparable position in the section to the Yarrabee Tuff Bed. Closely spaced drilling has established the correlation of major seams in the area (Svenson & others, 1975). Six seams are recognised in the Moura mine area, but common splitting increases the number of seams to both the north and the south. Up to nine tuff-free coals occur in the Nipan-Theodore area to the south of Moura, and there are 12 seams in an upthrown block 10km west of the outcrop and just north of Moura township. The rank of the coal changes along strike, with vitrinite reflectance ranging from 0.67o in th south to 2.17o in the north. Mining at Moura is in seams with a range of reflectance between 0.8 and 0.957o, giving a variety of coking and steaming coal products.

Figure 26. Deltaic sediments above the Orion seam at Curragh. depositional episode into the peat swamp. All the lithological units can be related to a deltaic fluvial model, with associations of major channels, crevasse splays (channels and aprons) and interdistributary Iakes. The configurations of these systems indicate a northerly or northwesterly source. Typical deltaic tongues are present as illustrated in Figure 26. All interseam sections greater than 30m in thickness show a marked difference in bedding dip between the coal and the interseam beds. Southern Bowen Basin The Rangal Coal Measures (Quinn, 1985) crop out

along the eastern margin of the Mimosa Syncline from Baralaba to Theodore. Equivalents are also Moura Mine

Baialaba

The coal measures vary in thickness from 200m at Moura mine to 350m in the Nipan-Theodore area. When the individual interseam units are plotted sequentially, as in Figure 27, it can be seen that the sedimentary units converged on the Moura mine area from input sources in both the north and the south. An additional source from the east also comes into the Moura mine area in the top half of the section. This figure is a N-S section from Baralaba to Theodore, constructed from the seam correlation diagram of Svenson & others (1975) and BHP-Utah (1987). The section is exploded to separate clearly the various sedimentary episodes. The unshaded zones between sediment pods schematically represent the thick peats, which are now present as highly compressed coal seams. The thicker section near Theodore contains conglomerates, and

identifies the location of one of the major easterly-located sediment sources. Theodore

Kianga Nipan

r.rwcry

Figure 27. Schematic north-south cross section of the Rangal Coal Measures from Baralaba to Theodore. Interseam sediment pods which separate and split seams are exploded and plotted in stratigraphic sequence. See text for further explanation.

Geology of Australian Coal Basins

325

LITHOFACIES N

K IANGA

MOURA

data

4 5

6 7 8

100m

F=l D9

SKm

Mudstone Seam letter or number

Coal seam

Figure 28. Lithology distribution in the Rangal Coal Measures between Moura and Nipan (after !.edger & others, 1980). Heavy arrows indicate compactional dip and lateral rnigration directions of channel forms depositing the sediment. The interseam sequence in the coal measures is dominated by sandstones as shown in Figure 28. Deposition was mainly as channel s-ands, with associated silty splays and interdistributary muds. Some of these deposits were above water level, as shown by the presence ofmudcracks and vegetated levees. This is particularly the case in the south, between Kianga and Nipan, where the silty beds surrounding the seams contain a rich fossil plant assemblage, with tree stumps and small rooting

structures in situ.

Southwestern Area

The coal-bearing upper section ofthe Bandanna

Formation in the southwest is equivalent to the Rangal Coal Measures in other parts of the basin. The lower section of the Bandanna Formation is correlated with the upper Burngrove Formation, which contains no coal seams south of Springsure (Thornton, 1985). The Bandanna Formation crops out along the western margin of the Comet Platform and in folded sequences in the Denison Trough. Coals are developed locally, with up to four seams in the

section along the outcrop area 15km west of Rolleston. Seams are up to 5.8m thick, with low ash (7-107o),low rank (Rv-u* 0.56-0.6lVo), and volatile matter ranging ftom 27 to 32Vo.

Coal Measure Depositional Processes Although a range of environments have been involved in the formation of Bowen Basin coals, the great majority of the best deposits were formed in a similar depositional setting. This was on a broad, stable platform or shelf, with widespread fresh-water paludal peats. Alternation of distinct peat forming and terrigenous phases can be seen where subsidence is less, but this is masked where more rapid subsidence allowed the accretion of thicker sedimentary sections. The coal measures that accumulated in this type of setting include those of the Moranbah and Fort Cooper Coal Measures, the Fairhill and Burngrove Formations, the Rangal Coal Measures and the Bandanna Formation.

The synchronous accretion ofthe coal phases is established in two cases, the "P" and Pleiades seam in the Group III coals, and the Vermont/Pisces seam at the base of the Rangal Coal Measures, by the coincidence of the seams throughout the basin with

thin but distinctive tuff beds.

The alternation of coal-forming and terrigenous phases can also be seen in the lower-deltaic German Creek Coal Measures. The controlling factors in this alternation of deposition must have been at a large scale, and operating at least on a basinwide extent. They affected sea level, the base level ofterrestrial drainage, the supply of sediment and possibly plant growth and climate. The interseam sediments are only of two types. The first is volcanic tuffs, which are only preserved within coal seams unless they are abnormally thick. The second is a complex of upper-deltaic depositional units, which include sandy channels, levees, splays, interdistributary lakes and vegetated flood basins. The systems are analogous to modern deltaic systems in general configuration and

relationships of the various sedimentary bodies.

A distinguishing feature ofthe sequence is the very important role played in the sediment dynamics by peat compaction from terrigenous sediment loading. Terrestrial fluvial systems are little affected by substrate movements, and the controlling factors are external ones imposed on the area, such as the dimensions of sediment and water supply, and tectonic subsidence. Within paludal peat swamps, however, the area is largely inundated, sediment transport is inhibited, and drainage channels are less important. An additional critical factor is that, when terrigenous sediments enter this environment, a thick peat is unable to support their weight, and will compact dramatically under the loading pressure. The effect of peat compaction is seen in two important areas: the thickness of interseam sections and the geometric arrangement of beds within the

interseam units.

Bowen Basin

326

CHANNEL DISTRIBUTARIES

50-200m

Figure 30. Sketch illustrating the development of - compactional dip with o channel deposit, a=nd a typii:al interseam section which is produced. representative sample of the bedding cor,'frgurations developed is illustrated in Figure 29 and a model of the process in Figure 30.

t Figure 29. Interseam bedding features in a selection of highwalls in the Rangal Coal Measures. a. Moura Pit 3C; b. Moura Pit 1A; c and d Moura Pit 11A; e. Moura Pit 3D; f. South Blackwater Togara Pit. After Mallett 1983. An analysis of 33 sections from mines or prospects within the Bowen Basin (Mallett, 1985) has shown that the thickness ofinterseam sections overlying coal seams 1 to 3m thick ranges up to 65m, with half the interseam intervals being 10m thick or less. Although peat compaction plays a role in such cases, the thickness ofthe interseam sequences is also affected by external factors such as sediment supply. With seams greater than 3m thick, however, the overlying interseam intervals are either less than 5m or more than 20m thick, with most greater than 30m. Once the sedimentary loading exceeds the buoyant weight of a few metres of sediment, thick peats apparently cannot support it. They compact by a much greater distance than the thickness of the terrigenous sediment, and produce a depression in the peat which becomes filled with more terrigenous material. The subsidence produced by this loading correlates with the primary compaction stored up in the thick unloaded peats. A second important effect of large peat compaction is the compactional dip produced in the sediment bodies. A sediment body spread on the horizontal surface of a peat will deform with the peat. A widespread thin layer of sediment will gently downwarp the peat, but a thick strip loading such as an 8 to 15m thick strip of channel sand, will cause dramatic local compaction. As channel positions shift, one channel edge will be located on uncompacted peat and the other on sediments and partially compacted peat. When the peat is fully compacted, the leading edge of the migrating channel will be displaced down further than the following edge, so that the cross-section of the channel will become tilted and lie at an angle to the coal bed. This gives rise to the compactional dips which can be seen above all thick seams in the Rangal and Moranbah Coal Measures. A

The thicker and narrower the load, the steeper the compactional dip generated. There is a relationship between the type of depositional unit and compactional dip. Interdistributary lake deposits which deposit thin widespread units lie parallel to the coal (Figure 29d). Splay aprons which wedge from the source but are widespread, dip only gently to coal (Figure 29c), whereas linear channelised sediments-(Figure 29a,b) form the steepest dips. The sediments in these linear bodies are often sands as in a normal fluvial channel, but within paludal swamps the sediments carried may be interbedded silts and sands similar to splay deposits. These will also produce high dips, as it is the shape ofthe loading body which determines the dip rather than the lithology. Such steeply dipping channelised siltstones are common, and some of the steepest compactional dips seen, up to 35o in the Red Hill Pit at Gloonyella Mine, are in siltstones. Small r,adiating splays can become superimposed (Figure 290, and tend to remain parallel to the coal. The directions of compactional dip, and hence of channel migration o_r progradation inlhe Moura Mine area, is illustrated where known in Figure 31. The small sediment body indicated with an x in Figure 28 is a lens derived from the east. A section is well exposed on the highwall in Pit 3C, and the geometry-of the unit down dip from outc-{op has b-een derived irom bores. This is graphically illustrated in Figure 31. The sandstone lenses which dip steeply in the highwall are a section of linear strips which extend- to the west. The thickened sandstones areas down-dip are linked to the more sandy intervals in the highwall section. The strike and dip symbols relatelo the compactional dips and the heavy arrows to the sand transport direction based on crossbeds corrected for dip. It appears that the strips of sediment emerged at a point in the east, andmigrated from south to north, fanning {ro1n a

southwesterly to northerly direction through time.

A partial depositional/compactio4al dlp,\vnothesis was put forward by Flood & Brady (1985) to expla^in the sleep dips in highwalls in the southern part of

Geology of Australian Coal Basins

327

Figure 31. A small sediment wedge above the C seam at Moura, shown in section in Pit 3C. Moura mine. While topography on depositional surfaces will undoubtedly be present, it cannot explain the tilted channels with cross-bed dips exieeding 40o without a major component of compactional deformation. The compactional theory has been favoured by Britten (1972), Burgis (1974), Mallett (1983), Archibald (1983) and Godfrey (1985).

activity occurred between 235 and 240Ma, but was preceded by gabbroic and dioritic plutonism within the Gogango OverfoldedZone and around Marlborough at 250Ma (Murray, 1983).

IGNEOUS GEOLOGY

are all hornblende-bearing I-type granitoids (Murray, 1983) and are correlated with (Dickins & Malone, 1973), or slightly older than (Webb & McDougall, 1968), the deformation event which affected the Gogango Overfolded,Zone. This phase of deformation is also thought to have been accompanied by the intrusion of an extensive serpentinite laccolith, or sill, into Early Permian sediments in the Rockhampton-Marlborough district.

Palaeozoic Intrusions Granites of Ordovician, Middle Devonian and Late Carboniferous age have intruded the basement to the west of the Bowen Basin. Palaeozoic plutonism is represented along the eastern margin of the basin by Permo-Carboniferous rocks of the Urannah Complex in the north and the Auburn Complex in the sbuth (Webb & McDougall, 1968). The Urannah Complex comprises three distinct lithological and textural types of igneous rock. The most widespread is partially foliated and sheared diorite, or tonalite, extensively cut by dyke swarms. The second is massive adamellite, with few dykes, and the third group is made up of isolated granodiorite plutons in the south. The Auburn Complex comprises massive granodiorite, incorporating minor dioritic phases, and is

extensively intruded by diorite, aplite, dacite and andesite dykes. Isotopic age dating (K-Ar and Rb-Sr) of the complex indicates that emplacement of the western portion occurred during the MidCarboniferous and that the eastern portion was emplaced during the Late Permian to Early Triassic.

Permo-Triassic Intrusions The emplacement of the western portion of the AuburrrComplex was part of a widespread igneous event associated with the Hunter-Bowen Orogeny. These essentially contemporaneous granites extend from Marlborough in the north to the New England, area of northern New South Wales in the south, and were isolated to a linear belt that corresponded to a zone of Late Permian uplift (Webb & McDougall, 1968). Isotopic evidence indicates the major phase of

The intrusions consist predominantly of adamellite and granodiorite, with minor diorite and isolated gabbio and granite (Dickins & Malone, 1973)' They

Early Cretaceous Intrusions The next phase of igneous activity to affect the region occurred in the Early Cretaceous and comprised two spatially and chronologically distinct ignebus events (Figure 32). The earlier event involved the emplacement of the batholithic Hecate Granite (Paine & others, 1974) and minor plutonic bodies, sills and dykes into the Connors Arch and the Nebo Synclinorium. This is dated at 140 to 128Ma (Webb & McDougall, 1968; S.J. Marshallsea, pers comm); it is distinct from a later intrusive bvent at 118Ma and 112.5Ma, which was restricted to the northeastern coastal strip and the offshore islands ofthe Proserpine area. The intrusions associated with this initial phase of activity are exclusively epizonal in origin and in most cases concordant with the strata they intrude' Metamorphism of the country rock ranges from minor induration associated with the smaller sheet intrusions to hornfelsed rims and wide induration halos surrounding the larger bodies. Emplace-ment is thought to have been contemporaneous with folding

in the Nebo Synclinorium, with the larger intrusions exhibiting features indicative of forceful emplacement. It is also likely that contempor- - aneous uplift of the Connors Arch accompanied this phase of intrusion (Dickins & Malone, 1973)'

Bowen Basin

328 Moranbah and Fort Cooper Coal Measures being the most severely affected. A second major zone of sills extends from the Saraji area in the north to German Creek in the south. The sills have preferentially invaded coal seams of the German Creek Formation and the Moranbah Coal Measures over a continuous strike length of approximately 7Okm. Coal seams of the Rangal Coal Measures, however, are most extensively intruded in the Middlemount area. The sills within the German Creek Formation and the Moranbah Coal Measures range from a few centimetres to a maximum of 30m in thickness, while some within the Rangal Coal Measures (e.g. Middlemount) attain thicknesses in excess of 100m. The majority of sills along the eastern margin of the Nebo Synclinorium consist either of granodiorite or

feldspar porphyry, with subordinate dolerite, trachyte antl rhyolite examples also occurring in places. Sills occurring along the western margin of lhe Nebo Synclinorium and the northern Collinsville Shelf generally consist of trachyte, latite, quartz diorite (or andesite), feldspar porphyry, and subordinate dolerite. They range in texture from fine to coarse grained, are commonly porphyritic, and are compositionally related to similar examples found along the eastern margin of the Nebo Synclinorium. However, the sills along the western margin are generally thinner than counte-rparts in the east, this being especially noticeable for the diorite and feldspar porphyry examples. Sills intruding the Collinsville Shelf in the Norwich Park - German Creek area exhibit a similar compositional variation. They are typically fine grained, hlghly altered (especially when associated with coal seams), and contain a high percentage of calcite.

German

Creek

I il

exposeo cretaceous intrusions Extensive coal seam intrusion 1480 OO,E

1490 00'

Figure 32. Cretaceous intrusions in the Bowen Basin coal measures. Intrusions in the Bowen Basin fall into three broad categories: plutonic bodies, laccoliths and sills, and dykes. In many cases the distinction between plutonic bodies and laccoliths, however, is an arbitrary one. Plutonic Intrusions

Plutonic bodies occur exclusively in the northern Bowen Basin, and, apart from the Bundarra Granodiorite and isolated intrusions in the immediate vicinity, are located along the eastern margin of the Nebo Synclinorium. The plutons in the Bowen Basin are characteristically medium to coarse grained. With the exception of the Redcliffe Gabbro, they fall within the narrow compositional range of leuco-quartzdiorite to hornblende-biotitegranodiorite.

Igneous sills fall between two end points: those that are replacive in nature, and those that displace the overlying strata. At the extreme end of the former group are sills of only a few centimetres thick that occupy only a portion of the intruded coal seam, whilst sills in the latter group may occupy substantial domal structures. Transitional varieties exhibiting both characteristics over their subaerial extent rarely exceed a thickness of 30m. Meso-scale thickness irregularities occur within individual sills, and the cross-sectional form of these

sills varies from irregularly disjointed but essentially continuous igneous layers to "pinch and swell" or boudinage-style geometries. In extreme cases the sills consist of nothing more than a series ofisolated circular conduits surrounded by heat-affected coal. Dykes

Dykes occur mainly in the Nebo Synclinorium in the northern Bowen Basin, and around the German Creek Mine in the central Bowen Basin. They are found in swarms at disjunct localities, and in each

Igneous Sills

swarm they parallel the regional fracture trend.

Igneous sills represent the most common style of intrusion within the Bowen Basin. They show a preference for occurrence within or adjacent to hajor coal seams. The sills occur within two distinct zones in the northern Bowen Basin.

In the central Bowen Basin, ENE teschenite dykes are concentrated at German Creek, with minor occurrences at Oaky Creek. E-W dolerite dykes cut the Peak Downs mine. The grain size of the intrusion varies, with the margins generally

The major zone of sill activity in the northern Bowen Basin extends from Collinsville in the north to the Bee Creek area in the east and Suttor Creek in the west (Figure 32). Selective intrusion of all stratigraphic units up to the Rgwa-n Group-is evident within the zone, with the Collinsville,

Dykes are extremely rare on the Collinsville Shelf at the western margin of the northern Bowen Ba,sin, and are most common at scattered localities along the eastern margin and in the northwest near

finer-grained and more altered and commonly containing carbonaceous material.

Geology of Australian Coal Basins

329

CENTRAL BOWEN BASIN GOGANGO OVERFOLDED ZONE

FOLDED ZONE

Possible extereion faults reactivated in crust

Figure 33. Deep crustal structure as postulated in three NE-SW sections through the Bowen Basin: a) Baralaba; b) Blackwater; c) Goonyella (after Hammond, 1987). Eastern Creek. The most common orientation is NE, but strikes to the NW, north and east also occur. The composition of the dykes includes lamprophyre, basalt, dolerite, hornblende porphyry and rhyolite, and their thickness can be up to 15m. The hornblende porphyries and lamprophyres are invariably associated with plutonic intrusions. The more acid varieties (granodiorite and rhyolite) only occur along the eastern margin of the Nebo Synclinorium. Basaltic and doleritic dykes, however, are more widespread, with the majority of recorded examples having orientations from northeast to east. The dykes intruding the coal measure sequences share common morphological characteristics. Most have en-echelon plan geometries, where segment tips generally overlap slightly and curve gently toward one another. Dyke wall "jogs" (i.e. lateral displacements in the dyke wall) are a common feature of most dykes. In some instances lateral offsets and unconnected crack segments are clearly developed. Symmetrical and asymmetrical forking, branching and curvilinear traces are common. The dykes have been emplaced by forceful injection, with crack propagation and orientation controlled by regional in situ stress (Hammond & Pattison, 1988). However dykes in the Bundarra area have asymmetrical terminal forking, branching and curvilinear traces, which indicate emplacement during shear fracturing. Structural Re latio ns hip s

Structural controls on the location of intrusions in the Bowen Basin are major easterly-dipping reverse or thrust faults and the NE crustal transfer faults.

Intrusions associated with reverse faults, which include plutonic bodies and igneous sills, are most clearly evident in the Collinsville area, where the Jacks Creek Diorite, the Mt Poole and Mt Vista intrusive suites, and the Mt Leslie Diorite are localised along or adjacent to major high-angle, easterly-dipping reverse faults. Drill hole data and sill distribution patterns in the Collinsville mine area further indicate that the magma to form these intrusions rose through the upper levels ofthe crust along east-dipping, low-angled faults and propagated into the coal measure sequence predominantly in a westerly direction (Webb & Crapp, 1960). A similar scenario is found in the German Creek-Norwich Park area, where prevailing sill distribution patterns and morphological features indicate that the sills emanated from the east and propagated along coal horizons in a westerly to southwesterly direction. The apparent restriction of intrusions to the footwall of the Foxleigh Fault suggests that this structure acted as a primary magma conduit. Post-emplacement shortening, in the form of reverse faulting, bedding-parallel displacements and fault reactivations, is also evident in many of the Early Cretaceous intrusions. Although the timing of this compressional event is not known, it appears likely to have occurred at some time in the Cretaceous Period. The sites of many of the basement transverse faults coincide with the localisation of dyke swarms and the boundaries of significant sill intrusion. This relationship can be seen at German Creek and along

Bowen Basin

330

a) co

$ CENTRAL BOWEN

probably related to sills of a similar composition in the immediate vicinity. Sills of basaltic and trachytic composition also occur within the Moura mining lease area, where seams of the Rangal Coal Measures are selectively intruded (Chiu Chong, 1969). Although the trachyte sills are chemically related to the Mount Ramsay example, suggesting a common origin, their relationship to the basaltic varieties is uncertain (Houston, 1969). Plugs of a similar lithology and age to that of Mount Ramsay also occur, along with isolated basalt flows, in the Rockhampton district (Wellman, 1978).

Cenozoic Volcanism

SOUTHERN

BOWEN BASIN

Cenozoic volcanic activity in the Bowen Basin is represented by remnant plugs, fissures and basaltic flows of the Nebo, Clermont and Springsure Volcanic Provinces (Sutherland, 1978). These geographically isolated provinces are ofthe central volcanic type, and constitute the northern members of a chain of similar activity that occurs to the south along the entire eastern Australian continental margin. The major phase of activity in the Bowen Basin occurred between 31 and 27Ma.

fgneous Effects on Coal Deposits The most detrimental economic effect attributable to Early Cretaceous intrusive activity has been the widespread destruction or sterilisation of potential coal reserves. As magma has preferentially intruded coal seams, large potential reserves have been lost to the intrusion process. In many instances the intruded coal seams have been completely replaced by igneous material, but more commonly the intrusions have anastomosed through the seam, coking the surrounding, partially admixed coal. Additional coal losses, estimated by Hamilton (1985) as being in the order of 5000Mt, can also be attributed to uplift, erosion and large-scale metamorphism associated with the larger plutonic bodies.

t t

Graben bounding normal fault with mid Permian and Triassic reversal

J Y

Graben bounding normal lault

Triassic high angle reverse faults

with Triassic reversal

::,.::li:::: Troughs

containing significant Reids Dome Beds

Figure 34. Permo-Triassic structures of the Denison Trough (modified after Ziolkowski & Taylor, 1985).

the eastern side of the Nebo Synclinorium (Hammond & Pattison, 1988). North of Peak Downs, the transfer dividing the northern and central Bowen Basin coincides with a linear trace of Early Cretaceous plutons that includes the Bundarra

Granodiorite and other smaller plutonic intrusions.

Late Cretaceous Intrusions The initial intrusive epoch affecting the northern

Bowen Basin was followed in the latest Cretaceous

by minor igneous activity in the Baralaba area (Olgers & others, 1966). A single alkaline trachyte plug (or sill) crops out to form Mount Ramsay, and is

Where magmatic temperatures were high enough (ca. 1000oC), COz was liberated at the expense of methane. This accounts for present-day high seam-gas levels and related outbursting problems in the Collinsville area, where maximum desorbable gas levels have been found to be amongst the

highest in Australia (Williams, 1985).

Early Cretaceous magmatism may also have had an effect on the rank ofthe coal. Although depth of burial is generally regarded to be the major controlling factor in this regard (Beeston, 1986), subtle along-strike coal rank increases have been noted (Anderson, 1974) correspond. to the igneous intrusions. Local increasing occurrence of^that effects are illustrated in Figure 10.

Structural Geology The main structural features of the Bowen Basin are fold and thrust belts, which were established by a compressive event in the late Triassic. This resulted in the thrusting of the Connors and Auburn Arches and the Gogango Overfolded Zone westward over the basin sediments. The northern, central and southern parts of the basin, bounded by the major transfer faults established during the extension phase, reacted very differently to this compression, and distinctive structural domains now occur along the NNW trending crustal features of the basin (Figure 1). The Taroom Trough is represented structurally by the Nebo Syrrclinorium in the north, the Dawson Folded Zone in the centre, and the

Geology of Australian Coal Basins

331

uob

FAIR HILL FORMATION

t?#'!' I

a,-r,N

6 o

RANGAL i:::i (\coAL

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Figure 35. Structure ofthe Blackwater arear Mimosa Syncline in the south, and all show dramatically different structural styles. The extent to which thrusts have propagated to the west also differs between the northern, central and southern parts ofthe basin. Movements continued throughout the Mesozoic and Tertiary, and both minor and major transfers have continued to move over long periods. This is shown in the complex structures developed over inferred transfers, and the common displacement of Mesozoic and Tertiary dykes on bedding planes. Coal mines have selectively exposed the less deformed sequences in the basin and avoided the major faulted zones. The dominant structures observed are low-angle and bedding-plane thrusts and zones where shortening has been taken up. These reflect tectonic transport from the northeast.

The thrusts usually propagate up-section to the

southwest, but at South Blackwater thrusts high in the coal measures are observed to propagate down-section. There is often a distinct change of structural style with stratigraphic level at the mine scale, and this can persist over a large area of the mine. Many of the steeply dipping faults in the German Creek seam at German Creek Mine, for example, do not continue up to the overlying seams. At South Blackwater a major thrust lies in or adjacent to the Castor seam over most of the mine, but the structures shown in the underlying Pollux seam are mostly steep normal or reverse features. At other mines, such as Curragh, thrusts and associated structural features gradually step up section to the southwest. The faults which can be detected during exploration are those associated with signifrcant vertical

Bowen Basin

332 seams by analysis of seam and interseam thickness

anomalies, anil Haughton (1986) demonstrated the influence of sedimentary facies, such as sandstone bodies, on fault localisation.

Southern Bowen Basin A section from west to east across the southern Bowen Basin crosses the Springsure Shelf, Denison Trough, Comet Ridge, Mimosa Syncline_and the soutliern end of the Gogango Overfolded Zone, as illustrated in Figure 33a. The Permo-Triassic structures in the Denison Trough (Figure 34) have been described by Ziolkowski & Taylor (1985). Most structures south of the Blackwater Transfer are oriented close to north-south. The initial structures were faults bounding grabens and half-grabens during extension in the eally Permian. Faults in the more easterly grabens were reversed in the mid Permian, and all graben-bounding faults were reversed in the Triassic. Very few new faults wele generated during

the Triassic, reflecting a deep crustal transfer of compressive forces along existing structures. This contrasts with the central Bowen Basin, where numerous new northwesterly oriented reverse faults were formed, splaying off earlier north-south faults, in the Triassic.

Little is known of structures on the Comet Platform

and in the Mimosa Syncline, except in the area southeast of Blackwater (Figure 35). The structures in that part of the basin, however, may be influenCed by proximity to the central area, and not representative of the southern Comet Platform. Widespread thrusting is found in the Castor seam, near the top of the coal measures, in the vicinity of Cook and Sbuth Blackwater Collieries. Haughton (1936) demonstrated that anomalies in the Castor seam overlie faults in lower seams, and that they were influenced by sandstone bodies beneath the Castor seam (Figure 36).

Figure 36. Structure in Pollux seam in South Blackwater Mine, showing faults and sand bodies lying between the Pollux seam and the overlying Castor seam which contains the thrust (after Haughton, 1986). displacement of coal seams. The very common bedding plane or low-angle structures are usually overlooked, even in areas of extreme deformation such as at Curragh. Two techniques have been applied to help locate potential faulting: Mallett & others (1982) detected bedding plane thrusts in coal

Hammond & Mallett (1988) proposed a sticking thrust model for the area, with the thrust lying mainly in the Castor seam and propagating down-section when the overriding thrust sheet locked over thick sandstone interseam sections (Figure 37). Irregularities on lateral ramps assbciated with these thrusts could produce the

unusual seam distributions illustrated in Figure 38. The eastern margin of the Mimosa Syncline is affected by the Gogango Overfolded Zone. Deformation decreases westwards into the syncline, with thrust sheets overlying successively less

OVERTHRUST SEQUENCE

\ Figure 37. Sticking thrust model for South Blackwater Mine (after Hammond & Mallett f 988).

Geology of Australian Coal Basins

333

minor on the shelf, or associated with reactivated NE-SW transfers. The folded zone incorporates the Late Permian Blackwater Group and the underlying marine Back Creek Group, bufno coal has been reported from the zone. Beds ire asymmetrically folded, with dips from 40 to 70o, and represent approximately 507o shortening across a 50km wide zone (Hammond in Mallett &-others, 1988). Extremely weak bedding cleavage is found through the zone, which is characTerised by tight folds cut by numerous steeply dipping reverse faults. (Figure 33b). The Yarrab ee Zone, which includes Yarrabee Mine, lies between the Foxleigh and Jellinbah Faults and their northern extensions (Figure 35). Broad folds are truncated by faults, and restrict the possibilities for mineable coal resources. 38. Effects of lateral ramps associated with Figure - overthrusting at South Blackwater. a) before thrusting; b) after thrusting (after Hammond & Mallett, 1988).

deformed rocks. The thrusts which cut the coal measures at Moura have low fault plane dips, but move up section to the west in the dipping strata (Figures 39 and 40). Dip slip throws are up to 50m.

Central Bowen Basin A large percentage of Bowen Basin coal is mined from the eastern margin of the Collinsville Shelf in the central portion of the basin (Figure 35). The Taroom Trough is overthrust in this area by the Connors Arch, and (where the geology is known) is occupied by the Dawson Folded Zone. A margi!al thruit fold belt (Yarrabee Zone) occurs along the boundary between the Taroom Trough and the Collinsville Shelf. The boundaries of structural domains within the Taroom Trough are marked by steep, easterly-dipping reverse faults such as the Foxleigh and Jellinbah Faults. The Jellinbah Fault and its extensions to the north is taken as the westerly extent of the thrust front. Low-angle thrusts extend on to the shelf in some areas, particularly in the south. Deformation is usually

West of the Yarrabe e Zone, on the Collinsville Shelf, the coal measures dip gently to the east. They are folded about broad open structures and locally cut by low-angle thrust faults such as at the-Curragh mine. Hob-bs (1985) postulated these shallow thrusts as the westernmost expression of a decollement gradually rising to the west and daylighting in this Zone. Hammona (1988) suggested an origin based on

the inversion of buried half-grabens which lie below the Jellinbah Fault.

The Curragh mine, located on the eastern margin of the shelf, Iias exposed a number of shallowly-dipping thrusts, which form in-seam and interseam dup-lexes as they misrate up section towards a bearing of 230". 'ihicliened in-seam duplexes and associated zones of thinned coal are over 0.5km wide. The duplexes are truncated or displaced by faults which

paiallel the direction of,thrustjnS, oT follow suitably iligned sedimentary bodies. Above the thrust surface, shortening is accommodated by backthrusts and complex triangle zones (Figure 41). The coal measures on the Collinsville Shelf are

generally gently dipping with little str_uctural disturbance. Structures present are related to movement on transfers, as basement displacements

MINE AREA

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CLEAVAGE FRONT

MOURA

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Coal seams

200

FAULT

DETACHMENT

metres

Figure 40. Representative detailed cross-section through Moura Mine (after Hammond & Sullivan, 1988).

Bowen Basin

334

CASTOR SEAM

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Sheared rock

Figure 41. Highwall section at Curragh illustrating in-seam duplexes, back-thrusting, kink bands and triangle zones.

f igur. 42. Structures at Peak Downs and Saraji mines, located on the Collinsville Shelf (after Devey, 1983).

are accommodated in the cover sediments. The area of Peak Downs and Saraji mines illustrates the structural domains that occur on the shelf

(Figure 42). Normal NE trending faults occur in the northern domain of this figure. Details on the faults indicate a varied history of movement, with both extension and compression at different times. The southern domain is dominated by east-west normal faults and en echelon grabens, with some north-south striking normal faults dipping to the east and west. Throws of up to 30m occur in this domain. The next domain has NNE oriented normal faults

and monoclines, dipping to the west, with throws of ? to 14m. The southernmost domain has north-south striking normal faults and monoclines with downthrows to the east of up to 40m' These faults and monoclines require extension, which is consistent with the northern domains in Figure 42.

Northern Bowen Basin The structural character ofthe northern region of the basin is divided into two morpho-tectonic elements (Figure 43): the Nebo Synclinorium, which is essentially a fold and thrust belt and the Collinsville Shelf, which is a weakly deformed terrane with localised thrust faults along its eastern boundary with the Nebo Synclinorium' The Nebo Synclinorium is a structurally asymmetrical region, characterised by a series of broad, open, doubly plunging fold and dome structur-es and thrust and high-angle reverse and normal faults. The eastern side adjacent to the Connors Arch is characterised by a moderate to

steep, westward-dipping sedimentary sequence which is locally overturned. The eastern margin is locally highly iaulted, and systems of la-rge-s.cale hinteilan-d-dipping thrusts (e.g. the Collinsville Fault), back thrusts and steeply-dipping strike-sli-F faults have been recognised. The western side of the

Geology of Australian Coal Basins

335

Figure 43. Generalised solid geology and structure of the northern Bowen Basin (after Mclennan, 1990).

Bowen Basin

336

synclinorium is characterised by shallow to moderate eastward dips. Thrust structures dominate the-fabric ofthis region, cropping out on regional and meso-scales within the coal measure sequence and the overlying Triassic rocks. The major thrust system (Burton Range-Eastern Creek-Rosella Creek Thrust System) is continuous with that which crops out along most of the western side of the Taroom Trough, adjacent to the hinge zone with the Collinsville Shelf. The thrust systems are commonly dissected by northeast-trending, high-angle strike-slip faults.

The strike of the fold axes and the thrust and

high-angle reverse faults is most commonly north to northwesterly. Some fold structures, e.g. the Elphinstone Syncline, strike northeast, but their formation is probabiy due to updoming of the surrounding country rock by the emplacement of large intrusive bodies (Mt Gothhardt and Hillalong areas.). Normal faults strike to the northwest,

northeast and east-west. East-west oriented lineaments occur in localised areas of the northern Bowen Basin. These structures are well developed around the F_owen !ive1, north of the Redcliffe Tableland,

Newlands Mine and Suttor Creek. Movement on the east-west structures along the Bowen River may have res'1lted in uplift of the Bowen Basin sequence north of that area (Clare, 1985). A major NW-trending lineament can be seen in the western central region of the area. This lineament is partially defined by a line of Tertiary basalt plugs, and is traceable from Mt Sambo in the northwest through the Redcliffe Tableland to the southeast. The Nebo Synclinorium is locally extensively

ARCHIBALD, D.C., 1983: Sedimentary environments of the Peak Downs coal mine, Central

Queensland. In, Proceedings of a syrnposium on the Permian Geology of Queensland, Geological Society of Australia (Qld Division), Brisbane, 275-279.

BEESTON, J.W., 1978: New evidence for a Permian age for the Blair Athol white section. Queensland Gouernrnent Mining Journal, 7 9, I57 -158.

BEESTON, J.W., 1986: Coal rank variation in the Bowen Basin, Queensland. International Journal of Coal Geology,6, 163-179.

BHP-UTAH COAL LIMITED, 1987: Outline of operations, Moura Mine. Unpublished Report, BHP-Utah Coal Ltd.

BLAIK, M., 1986: Overview of Collinsville geology. Notes for Bowen Basin Geologist Group Meeting, 5th June, 1986. BRIGGS, D.J.C., 1987: Systematics and

biostratigraphy of the Permian Productidina and Strophalosia (Brachiopoda: Productida) of the Sydney-Gunnedah Basin and the New England Fold Belt. PhD thesis, Department of Geology and Mineralogy, University of Queensland.

BRITTEN, R.A., 1972: A review of the stratigraphy of the Singleton Coal Measures and its significance to coal geology and mining in the Hunter Valley region of New South Wales . Australasian Institute of Mining Metallurgy, Annual Conference Proceedings, Newcastle, lI-22. BURGIS, W.A., 1974: Environmental signifrcance of folds in Rangal Coal Measures of Blackwater, Queensland. Bureau of Mineral Resources,

intruded. The positions of intrusive swarms-in the east, particularly the large laccolith bodies, were influenced by regional-scale basement structures. Many of the dyke systems are orientated in a northeasterly direction, occupying tensional structures associated with major thrusts (Clare,

CARR, A.F., 1980: Coal resources of the Wolfang Basin. Geological Survey of Queensland, Record,

The Collinsville Shelf is a weakly deformed terrane.

CHIU CHONG, E.S., 1969: Coal resources:

1985).

Bedding dips shallowly to the east off the western margin, and steepens (2 to 15o) towards the eastern contact with the Nebo Synclinorium. The coal measure sediments along this contact are locally ' folded about open flexures, and are commonly associated with thrust faulting. Small-scale thrusts parallel to bedding are common in areas with Iocalised flexures and folds. Small-scale northeasterly and locally east-west trending high-angle faults are also a feature of the style of faulting in the contact region.

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Baralaba-Moura-Kianga-Theodore coalfi eld. Geological Survey ofQueensland, Report, 35, 1-3 1.

CLARE, R., 1985: Structure of the northern Bowen Basin. 1n, Proceedings of Bowen Basin Coal Symposium, Rockhampton. Geological Society of

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D'ARCY, R.K., 1985: An evaluation of underground coal resources in the northeast Blackwater area, south central Bowen Basin. Geological Survey of Queensland, Record 1985/13. D'ARCY, R.K., 1988: Departmental coal reconnaissance drilling in the Taroborah Area, southwest Bowen Basin. Geological Survey of Queensland, Record L987/50.

DEAR, J.F., I972: Preliminary biostratigraphic subdivision of the Permian faunas in the northern Bowen Basin, and their distribution throughout the basin. Geological Suruey of Queensland Report,49.

DEMPSEY, C.R., 1986: A summary of the mine geology and coal quality at Collinsville. Notes for Bowen Basin Geologist Group Meeting, 5th June, 1986.

Geology of Australian Coal Basins

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HAMMOND, R.L., 1987: The Bowen Basin, Queensland, Australia: an upper crustal extension model for its early history.

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HAMMOND, R.L. & PATTISON, C.I., 1988: Geological structure of coal mining areas in the Bowen Basin (197 IV: German Creek. Geomechanics of Coal Mining Report, 70. CSIRO Australia, Division of Geomechanics. HAMMOND, R.L. & SULLIVAN, T.D., 1988: Geological structure of coal mining areas in the Bowen I: Moura. Geomechanics of Coal Mining Basin Report,- 67. CSIRO Australia, Division of Geomechanics.

HAUGHTON, D.L., 1986: The development and distribution of sedimentary rocks in the Rangal Coal Measures, South Blackwater, Central Queensland. MSc Thesis, Queensland Institute of Technology.

HAWTHORNE, W.L., 1974: A review of the coal geology of the Tasman Geosyncline of Queensland. 1n, Denmead, A.K., Tweedale, G.W. & Wilson, A.F. (Editors): The Tasman d syrlposium. Geological Society Geosyncline of Australia -(Qld Division), Brisbane, 365-382. HOUSTON, B.R., 1969: Petrographic notes on some

alkaline trachytes from the Baralaba-Moura districts, central Queensland. Geological Suruey of Queensland Report, 35.

HOBBS, B.E., 1985: Interpretation and analysis of structure in the Bowen Basin. Proceedings of Bowen Basin Coal Symposium. Geological Society of Australia Abstracts, L7, l5l-152-

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Bowen Basin

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Geology of Australian Coal Basins

339 RUNNEGAR, B.N. & McCLUNG, G., 1975: A Permian time scale for Gondwanaland. 1n Campbell, K.S.W. (Editor): Gondwana Geology, Australian National University Press, Canberra, 425-44L. SEEDSMAN, R.W. & EMERSON, W.W., 1985: The role ofclay-rich rocks in spoil pile failures at Goonyella Mine, Queensland. International Journal of Rock Mechanics and Mining Sciences

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SMYTH, M. 1980: Thick coal members: products of an inflationary environment? Coal Geology, 2,

53-76. STAINES, H.R.E., 1972: Blackwater Coalfield, correlation of seams in the Rangal Coal Measures, Mackenzie River to Sirius Creek. Geological Suruey of Queensland Report, 7O. STAINES, H.R.E & KOPPE, W.H., 1.980: The geology of the northern Bowen Basin. 1n Henderson, R.A. & Stephenson, P.J. (Editors): The Geology and Geophysics of Northeastern Australlo. Geological Society of Australia, Queensland Division, Brisbane, 279-298. (also in Queensland Gouernment Mining Journal, 80, 172-195).

STERNFELL, E.K., 1975: Preliminary report on the Mt Devlin Coal Measures, Collinsville, Queensland. Davis Mining. SUTHERLAND, F.L., 1978: Mesozoic-Cenozoic

volcanism of Australia. /n. Scheibner, E. (Editor): The Phanerozoic structure ofAustralia and variations in tectonic style. Tectonop hy sic s, 48, 413-427.

SVENSON, D., CHUI CHONG, E.S. & TAYLOR, D.A., 1975: Theodore-Baralaba district. In Traves, D.M. & King, D.: Economic Geology of Australia and Papua New Guinea - 2: Coal. Australasian Monograph, Institute of Mining and Metallurgy, 6, 108-118. SVENSON, D. & PETERSON, M.S., 1983: Evaluation of coal properties for optimum economic development and utilisation of the coals in the

Rangal Coal Measures at Curragh, north of Blackwater, Central Queensland. 12, Proceedings of a symposium on the Permian Geology of Queensland, Geological Society of Australia (Qld Division), Brisbane, 57-72.

THORNTON, M.P., 1985: Regional characterisation of the upper Burngrove Formation. Proceedings of Bowen Basin Coal Symposium, Rockhampton. Geological Society of Australia, Ab stracts, 17, 275-276. UTAH DEVELOPMENT COMPANY LIMITED STAFF, 1985: Gregory Mine. Proceedings of Bowen Basin Coal Symposium. Geological Society of Australia, Abstracts, 17 , 29L-293. UTAH DEVELOPMENT COMPANY LIMITED STAFF, 1985a: Goonyella Mine. Proceedings of Bowen Basin Coal Symposium. Geological Society of Australia, Abstracts, 17, 283-285. WATERHOUSE, J.B. & JELL, J.S., 1983: The sequence of Permian rocks and faunas near Exmoor Homestead, north Bowen Basin. In, Proceedings of a symposium on the Permian Geology of Queensland, Geological Society of Australia (Qld

Division), Brisbane, 23L-267 .

WEBB, A.W. & MCDOUGALL,I.,1968: ThE geochronology of the igneous rocks of eastern

Australia. Journal of the Geological Society of Australia, 15, 313-346.

WEBB, E.A. & CRAPP, C.E., 1960: The geology of the

Collinsville Coal Measures. Proceedings of the Australasian Institute of Mining and Metallurgy, 193, 23-88.

WELLMAN, P., 1978; Potassium-argon ages of Cenozoic volcanic rocks from the Bundaberg, Rockhampton and Clermont areas of eastern

Queensland . Proceedings of the Royal Society of

Queensland, 89, 59-64.

WILLIAMS, R.J., 1985: Geological hazards to an underground mining in the Bowen Basin assessment. Proceedings of Bowen Basin -Coal Symposium, Rockhampton. Geological Society of Australia, Abstracts, 17, L69-17 3. ZIOLKOWSKI, W. & TAYLOR, R., 1985: Regional

structure ofthe north Denison Trough. Proceedings of Bowen Basin Coal Symposium. Geological Society of Australia, Abstracts, L7, 129-135.

Bowen Basin

341

ffi qLffialilee Basin M

SG Scott

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BowEN BASIN

ttr") ;

Figure 1. Location, Galilee Basin. The Galilee^Basin covers an area of approximately 247 000 km2 in central Queensland (Figure t). Itis a totally intracratonic basin and is filled with Late Carboniferous to Middle Triassic sedimentary rocks. These rocks are dominantly of fluvial origin, with

minor glacial material occurring towards the base of the succession (Gray & Swarbrick, 1975). The basin is almost entirely unconformably overlain by the Jurassic-Cretaceous Eromanga Basin. Only along the eastern margin are Permo-Triassic rocks exposed in a long, narrow gently curved belt. The maximum known stratigraphic thickness of the basin is 2818m, penetrated in the Koburra Trough by ENL Lake Galilee 1 (Allen, 1974). The principal tectonic elements of the basin are shoWn in Figure 2. The basin is divided into northern and southern parts by the east-west trending Barcaldine Ridge, located at approximately latitude 24o south. The northern part ofthe basin is subdivided by the Maneroo Platform and its easterly component, the Beryl Ridge, into the eastern Koburra Trough and the western Lovelle Depression. The southern part of the basin is divided into the western Powell (Main) Depression and the Springsure Shelfby the Pleasant Creek

Arch. Exploration within the basin is at a relatively immature stage, with only 50 petroleum wells and stratigraphic bores in the northern part and 53 petroleum wells and stratigraphic bores in the southern part (Figure 3). Coal exploration drilling has been confined to the exposed eastern margin of the basin, with 69 Departmental exploration bores having been drilled and over 1200 shallow coal exploration bores drilled by companies exploring in the Wendouree, Degulla and Pentland areas.

Galilee Basin

342

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STRATIGRAPIIY

Late Carboniferous and Early Permian

The stratigraphic succession of the Galilee Basin is

The Late Carboniferous and Early Permian Joe Joe Group was defined by Gray & Swarbrick (1975) as "that-succession of formations which is

partly related to stratigraphic successions in the Coop-er and Bowen Basins, with each basin having experienced a hiatus during some part of the middle

Permian (Figure 4). Major coal deposition occurred in the Galilee Basin during the Early Permian in the Aramac Coal Measures, as well as during the Late Permian in the Colinlea Sandstone and Bandanna Formation and their correlatives and the Betts Creek beds. Coal development within the basin is concentrated in the northern part. South ofthe Barcaldine Ridge coal seams are thin and sporadic. Detailed stratigraphic descriptions of the individual units are

givenln Gray & Swarbrick (1975) and Hawkins & others (1993).

unconformably overlain by the Colinlea Sandstone and its laterai correlative, and unconformably overlies strata of the Adavale and Drummond Basins or other pre-Late Carboniferous rocks". The Joe Joe Group iJ divided into four formations, in ascending order: the Lake Galilee Sandstone, theJericho F:ormation, the Jochmus Formation and the Aramac Coal Measures.

Lake Ga'Iilee Sand'stone The basal unit of the Galilee Basin is the Lake Galilee Sandstone, defined by Gray & Swarbrick (1975). This unit has been completely intersected in only three petroleum exploration wells, located

Geology of Australian Coal Basins

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Jericho Formation The Jericho Formation overlies the Lake Galilee Sandstone in the Koburra Trough (Gray & Swarbrick, 1975), but in the southern part of the basin it is the basal unit of the sequence (Figure 6). The Jericho Formation has not been recognised in the Lovelle Depression.

The Jericho Formation consists dominantly of mudstone and siltstone with subordinate sandstone. Near the Barcaldine Ridge, the unit contains localised thick and thin conglomerate beds (Hawkins

& others, 1993). Within the middle of the unit a sequence of mainly interbedded siltstone, mudstone and shale containing red zeolites is recognised and defined as the Oakleigh Siltstone Member (Gray & Swarbrick, 1975). The siltstone, mudstone and shale are dark grey and green, very hard, siliceous, strongly banded and varved.

Jochmus Formation The Jochmus Formation overlies the Jericho Formation in the eastern and southern parts of the basin and is the basal unit in the western part of the

Galilee Basin

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Geology of Australian Coal Basins

345

Figure 5. Areal extent of the Lake Galilee

Figure 6. Areal extent of the Jericho Formation.

Figure 7. Areal extent of the Jochmus Forrnation.

Figure 8. Areal extent of the Boonderoo beds.

basin (Figure 7). As defined by Gray & Swarbrick (1975) it can be divided into 3 units; a basal unit consisting mainly of sandstone, a middle unit made up dominantly of tuff and mudstone and an upper sandstone unit. The middle unit has been defined as the Edie Tuff Member.

similar in part to the Jochmus Formation (Figure 8) (Gray, 7977).

Sandstone.

Sandstones in the Jochmus Formation are generally light grey to green, and more rarely brown and reddish, fine to medium grained, labile and locally conglomeratic. Siltstones are light to medium grey and grey-green, hard, brittle and carbonaceous. Mudstones are grey-green, silty, tuffaceous in part and carbonaceous (Gray & Swarbrick, 1975).

In the north-eastern part of the basin, outcrops and intersections of the Boonderoo beds are lithologically

Aratnac Coa.l Measures The Aramac Coal Measures is the lateral equivalent of the upper Jochmus Formation, the uppermost

unit of the Late Carboniferous-Early Permian Joe Joe Group. The unit is developed on the western side ofthe Koburra Trough and across the Beryl Ridge into the southern Lovelle Depression of the northern part ofthe basin (Figure 9).

It comprises a lower, dominantly sandstone unit with minor coal and mudstone and an upper sandstone and subordinate coal unit (Hawkins & others, 1993).

Galilee Basin

346

Figure 9. Areal extent - Aramac Coal Measures.

Figure 10. Areal extent - Colinlea Sandstone.

Figure 11. Areal extent - Peawaddy Formation.

Figure 12. Areal extent - Black Alley Shale.

Late Permian

siltstone, mudstone and coal. It is only developed on the Springsure Shelf (Figure 11).

olinleq. S andstone and, equiu a,lent s

The Colinlea Sandstone in the Galilee Basin is continuous, across the Nebine Ridge, with the Colinlea Sandstone of the Bowen Basin. The unit is present over the eastern and south central Galilee Basin (Figure 10). It comprises mainly sandstone, siltstone, mudstone and coal. The sandstone is fine to coarse grained, conglomeratic in part, and sublabile to quartzose (Hawkins & others, 1993). In the southern part of the basin coal is either present

in very small proportions or is non-existent.

Peawadd.y Formation Within the Galilee Basin, the Peawaddy Formation comprises mainly sandstone with lesser amounts of

Away from the Springsure Shelf, across the Barcaldine Ridge and towards the Pleasant Creek Arch the unit thins rapidly and onlaps the underlying Colinlea Sandstone.

Black Alley Shale The Black Alley Shale of the central and south-central Galilee Basin consists of dark grey to black shale and siltstone with interbedded light green-grey tuffand fine to very fine, labile iandstone (Gray, 1976). The unit thins over the Barcaldine Ridge into the Koburra Trough,

eventually onlapping the underlying Colinlea Sandstone. It occurs, however, over most of the southern part of the basin (Figure 12).

Geology of Australian Coal Basins

347

Figure 13. Areal extent of the Bandanna Formation.

Figure 14. Areal extent ofthe Betts Creek beds.

Figure 15. Areal extent of the Rewan Formation.

Figure 16. Areal extent ofthe Dunda beds.

Band.anna Formation and equiaalent

north-eastern margin of the basin, Departmental coal drilling has indicated that the lithology of the sandstones of the upper part of the Upper Permian coal measures changes from predominantly labile to predominantly quartzose. This change is indicative of a change in sedimentary source, and it has been used to define the provenance ofthe Betts Creek beds (Scott & Hawkins, 1992).

The Bandanna Formation of the Galilee Basin consists of an interbedded sequence of sandstone, siltstone, mudstone and coal (Hawkins & others, 1993). Within the southern Galilee Basin, the

volume of coal in the unit is substantially lower than that in the northern part of the basin. The unit occurs within the north-eastern and southern areas of the basin (Figure 13).

Triassic

Betts Creek beds

Reuta,n Formation

The Betts Creek beds are the lateral equivalent of both the Colinlea Sandstone and Bandanna Formation. They occur in the northern and western areas of the basin (Figure 14), and comprise sandstone, interbedded siltstone, shale and coal (Hawkins & others, 1993). The sandstone is very fine to coarse and quartzose to sublabile. Along the

The Rewan Formation occurs within the eastern and central areas of the Galilee Basin (Figure 15). Although the sequence has been raised to group status in the Bowen Basin (Jensen, L975), formation status has been retained in the Galilee Basin by Day & others (1983). The unit consists mainly of interbedded light grey; fine to coarse grained,

Galilee Basin

348

Figure 17. Areal extent of the Clematis Sandstone.

Figure 18. Areal extent of the Moolayember Formation.

Clematis Sand,stone The Clematis Sandstone, originally named by Jensen (1926) in the Bowen Basin, has been mapped along the north-eastern margin of the Galilee Basin by Vine & others (1965) and Senior (1973); it has recognised and mapped in the subsurface by Casey (1970) and Vine (1973, 1976).

Within the basin the unit is confined to the eastern and southern central regions (Figure 17). As with the Rewan Formation, formation status has been retained for the Clematis Sandstone in the Galilee Basin even though it has been raised to group status in the Bowen Basin (Jensen, t975). The unit consists mainly of light grey, friable, fine to very coarse-grained, angular to subrounded quartzose sandstone with lesser amounts of grey or brown siltstone and mudstone (Hawkins & others, 1993).

Maolayember Formation

others, 1993).

The Moolayember Formation was originally described in the Bowen Basin (Reeves, 1947; Hill & Denmead, 1960) and was mapped in outcrop along the eastern margin of the Galilee Basin by Exon (1970), Vine & Doutch (1972) and Senior (1973). The sequence is found within the eastern and western areas of the basin (Figure 18). The Moolayember Formation, in the subsurface, comprises green, grey, brown, purple and red mudstone with minor siltstone and some medium to coarse-grained, pebbly sandstone (Hawkins & others, 1993).

Dunda beds

Warang Sandstone

Figure 19. Areal extent ofthe Warang Sandstone. sublabile to labile, in part quartzose sandstone, grey and green siltstone and mudstone (Hawkins &

The Dunda beds were identifred by Vine & others (1965), Olgers (1970) and Vine & Doutch (1972) from

outcrop along the central margin of the basin. In the subsurface, the unit is restricted to southern and central Koburra Trough area (Figure 16). The sequence comprises light grey, olive-grey, and yellow-grey, fine to coarse grained, poorly sorted, quartzose to labile sandstone and varicoloured mudstone and siltstone (Hawkins & others, 1993). The lower half is dominated by sandstone while the upper half is dominated by mudstone.

The Warang Sandstone occurs within the northern and western parts of the northern Galilee Basin (Figure 19). It was originally mapped at outcrop by Vine & others (1964) where it forms the rugged topography of the White Mountains and the Great Dividing Range along the north-eastern margin of the Galilee Basin. The unit consists of white to light grey and light green-grey, medium to very coarse grained, poorly sorted, quartzose to sublabile sandstone, interbedded siltstone, mudstone/shale and conglomerate (Gray, L977). Palynology suggests that the Warang Sandstone is a correlative of the upper Rewan Formation, Clematis Sandstone and

Geology of Australian Coal Basins

349 Coal quality and potential

lower and middle Moolayember Formation

(McKellar, 1977).

As there have been only two cores cut in the Aramac Coal Measures, there has been little analytical work done on the coals. Analyses of vitrains from GSQ Longreach 1-1B (Green & others, 1991) reported the

Major Coal-bearing Sequences Aramac Coal Meq,sures

following properties (air dried basis):

Structure The Aramac Coal Measures, as mentioned above, is developed only within western and central parts of the northern Galilee Basin. The deepest intersection has been in the Lovelle Depression in HPP Lovelle Downs 1 (1600m), whilst the shallowest has been in

the southern Koburra Trough in LMN Bellara 1 (757m). Development of the Aramac Coal Measures appears to have been dependent on fault movements (Hawkins & others, 1993); in both the Lovelle Depression and the Koburra Trough, the coal measures developed within assymetrical troughs formed by faulting. The Aramac Coal Measures is thickest on the south-western margin of the Koburra Trough in GSQ Longreach 1-18 (265.2m) and thinnest in the southern Koburra Trough at LMN Bellara 1 (31.0m) (Figure 8). Generally the unit is consistently thickest in the Lovelle Depression and thin over the Beryl Ridge to thicken again in the south-western Koburra Trough.

Depositional environment The Aramac Coal Measures are considered to have formed in a braided stream environment (Hawkins & others, 1993). The lower, coal-poor sequence represents a deposit from braided streams flowing at the distal margins of fans while the upper, coal-rich sequence represents the peat swamp phase. During this period tectonism declined, vegetation flourished and there was an expansion in the depositional sites. The Aramac Coal Measures repiesent a change in the climate of the Galilee Basin from essentially cold, dry, alkaline conditions with glacial influence depicted by the Joe Joe Group rocks to warm, humid, acid conditions. Coal facies As mentioned above the Aramac Coal Measures can be divided into two intervals: a lower interval

dominantly consisting of sandstone with minor mudstone and coal and an upper interval of sandstone and subordinate coal (Hawkins & others, 1993). The greatest development of coal in the unit is on the western side of the Cork Fault in the Lovelle Depression where, in HPP Lovelle Downs 1, the formation reaches a thickness of 272.0m and the aggregate coal thickness is 60.0m.

In the Koburra Trough, the greatest coal development is on the south-western margin, along the Maneroo Platform. In GSQ Longreach 1-18, the unit is 265.2m thick with an aggregate coal thickness of 29.0m. Coal from the Aramac Coal Measures is grey to black, brittle and predominantly dull (Gray & Swarbrick, 1975). Smith (in Green & others, 1991) attributed the anomalously low vitrinite reflectance values in the Aramac Coal Measures in GSQ Longreach 1-18 to bacterial reduction ofthe peat, producing lipids which were incorporated into the humic degradation products.

3.4Vo Moisture 39.O7o Volatile Matter 56.87o Fixed Carbon 0.87o Ash Specific energy 34.88 MJ/kg

Because of the depth to the coals in the Aramac Coal Measures, there appears to be little potential for mining. However the Aramac Coal Measures is considered a major source for both coal seam methane (Durie & others, 1992) and petroleum (Hawkins, 1978)

Bandannq. Format ion, Colinlea Sandstone and Betts Creek beds Structure The Bandanna Formation, Colinlea Sandstone and Betts Creek beds crop out along the eastern margin of the basin (Figures 10, 13 & 14). Both the Bandanna Formation and Colinlea Sandstone thin over the Barcaldine Ridge into the southern Galilee Basin, with coal development within these two formations decreasing to a minor component south of the Barcaldine Ridge. The Betts Creek beds are best developed within the main depo-centres of the

northern part ofthe basin, the Koburra Trough and the Lovelle Depression, and thin across the Beryl Ridge. Coal development is related to formation thickness, and coal is thickest where the unit is thickest. Depositional environments The strata of the Late Permian coal measures were deposited in fluviatile-dominated environments. Only freshwater microflora, spores, pollens and rare macroflora have been recovered from the Late Permian units (Hawkins, 1976). Sedimentary structures found in core, such as small scale cross-stratification (Hawkins, 1976), and in outcrop, such as trough cross-stratification (Vine & others, 1965) as well as the presence of significant coal

seams, indicate that the Late Permian sequence was

deposited in environment controlled by a major river syitem with associated peat swamps. Exactly where in this system, however, is a moot point. Wells (1989) listed the interpretations of a number of authors; these ranged from alluvial plain to delta plain. A piedmont facies was also suggested by Vine & others (1964).

Hawkins & others (1993) have suggested a three phase division of the Upper Permian sequence. The earliest phase, the lower Aramac Coal Measures and Colinlea Sandstone, was deposited in an alluvial plain environment dominated by southerly and easterly flowing rivers. Associated with these rivers were peat swamps. The river borne sediments would have been sourced from the rocks ofthe volcanic and metamorphic provinces to the north of the basin margins (Scott & Hawkins,1992). The second phase was associated with a reduction in stream gradlents and a rise in relative sea level. This led to a marine incursion into the southern and central regions of the basin, and hence to deposition

Galilee Basin

350

DEqJLLA VENDI]IJREE

MIRTNA

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Figure 20. Seam conelation - eastern margin Galilee Basin. of the Peawaddy Formation and the Black Alley Shale.

the south to thick, dull seams in the north (Beeston, t977).

The final phase of sedimentation in the Late Permian saw a return to fluvial conditions. The only

Coal quality and potential

difference was that in the central and southern areas the rivers carried sediment from a

volcano-lithic province, producing the labile sandstone based Bandanna Formation, while to the north and west the originai sediment source areas continued to provide volcanic and metamorphic based material. Coal facies Coal is present in three units of the Late Permian sequence; the Bandanna Formation, the Colinlea Sandstone and the Betts Creek beds. Along the

eastern margin and into the Koburra Trough, at least, the seams are continuous (Figure 20) (Scott &

Hawkins, 1992). Within the southern part of the

basin the coal facies, however, is very poorly developed.

There are three areas of maximum coal development, the Lovelle Depression, the western margin of the Koburra Trough along the Beryl Ridge, and within the Koburra Trough (Figure 11, Scott & Hawkins, 1992). The seams range in thickness from 0.15m to over 20m, with a maximum aggregate coal thickness of 45m. Petrographic analysis of coals from the eastern margin of the Koburra Trough has shown the coals to be low rank and subhydrous, ranging from thin, bright seams in

Only along the eastern margin of the northern Galilee Basin is coal from the Late Permian coal measures shallow enough to be mined. The coal seams are designated A through to G with most being relatively clean. The C seam includes numerous grey and fawn mudstone and siltstone bands. The coal itself is mainly dull, particularly in the lower seams in the north, but some bright bands are also present. The seams have a low dip to the west and south-west, generally at <5o, and the sequence is relatively undisturbed. The coal along the eastern margin of the Koburra Trough has been classified as high volatile bituminous C under the ASTM classification, and is subhydrous with a low sulphur content. A typical proximate analysis (air-dried basis) of a relatively clean seam would be:

Moisture Volatile Matter Fixed Carbon Ash

9.17o 29.4Vo 46.2Vo 15.SVo

The average specific energy is about 22 to 23 MJ&g and the crucible swelling number is either 0 or U2. There are currently only two Exploration Permits for coal within the Galilee Basin. Total Measured and Indicated Resources for these two areas, and

Geology of Australian Coal Basins

351

another which has been relinquished by the company, are 1675 and 910 million tonnes respectively (Queensland Coal Board, 1990).

Although coal was found in the Galilee Basin more than 80 years ago, none has yet been mined commercially. One of the many drawbacks to mining development is the basin's geographical isolation. Even ifany export product was viable and a rnarket available, the nearest port to a proven deposit is Abbot Point, some 430km by rail from Pentland in the northern part of the basin. The nearest railhead at present from any economic deposit between the Northern and Central Railways is Blair Athol which is some 180 to 200km away by an unsealed access road. Mining infrastructure is therefore completely lacking. Over and above these problems is the excessive thickness of Tertiary and Quaternary deposits, which would add considerably to the cost and difficulties of open cut mining.

DURIE, R.A., HAWKINS, P.J. & KUKLA, G.T., 1992: The Galilee Basin coal measures: A potential case for a well planned, methane resource ? - Aand R & D programme. integrated exploration Proceedings of the Symposium on coalbed methane research and deuelopment in Australia, 1, 81-97.

EXON, N.F., L970: Tambo, Queensland. 1:250 000 Geological Series - Explanatory Notes. Bureau of Mineral Resources, Canberra. GRAY, A.R.G., 1976: Stratigraphic relationship of Late Palaeozoic sediments between Springsure and Jericho. Queensland Gouernment Mining

Journal,77, 146-163.

GRAY, A.R.G., 1977: Stratigraphic drilling in the Hughenden 1:250 000 Sheet area, 1974-75. Queensland Gouernment Mining Journal, 78,

382-392.

The coal in the Galilee Basin has no coking potential, and is suitable only for use as an energy source. Its subhydrous nature and relatively low vitrinite content render it unsuitable for conversion processes. The coal from some of the better quality seams could be burned without beneficiation, but

GRAY, A.R.G. & SWARBRICK, C.F.J., 1975:

Coals of the Upper Permian formations may have the potential to act as a source and a reservoir for methane, which could be produced as coal seam gas. A number of companies have begun exploration into the potential of coal bed methane within the Galilee Basin.

HAWKINS, P.J., 1976: Facies analysis and economic significance of Late Permian strata in the northern Galilee Basin. Queensland Gouernment

water supply for preparation plants would pose a problem if some of the dirtier seams were eventually to be worked.

Another potential use for some of the coal from the Upper Permian formations is as oil shale. Such material, found as cannel coal and torbanite, is located in the Colinlea Sandstone to the south-east of Alpha, on the Springsure Shelf. The area is presently held under an Exploration Permit Minerals (EPM) with the principal aim of producing products approximately 3000 barrels of oil on site per day for consumption in the central Queensland region (Madre, 1987). Total Measured plus Indicated Resources of 90 million barrels of shale oil are estimated to be available. Oil yields from the torbanite are high and range from 200 to 650L/t, while the enclosing cannel coals yield from 20 to 250L/t.

REFERENCES

Nomenclature of Late Permian strata in the northeastern Galilee Basin. Queensland Gouernment Mining Journal, 7 6, 344-352.

GREEN, P.M., McKELLAR, J.L., CARMICHAEL, D.C.

& SMITH, R.J., 1991: Stratigraphic drilling report - GSQ Longreach I-lB. Queensland Resource Industries Record l99ll20.

Mining Journal, TT, L5-32.

HAWKINS, P.J., 1978: Galilee Basin - review of petroleum prospects.Queensland Gouernrnent Mining Journal, 79, 96-112.

HILL, D. & DENMEAD, A.K., (Editors), 1960: The geology of Queensland. Journal of the Geologieal Society of Australia, 7 .

JENSEN, A.R., 1975: Permo-Triassic stratigraphy and sedimentation in the Bowen Basin, Queensland. Bureau of Mineral Resources Geology and Geophy sics, Australia, Bulletin 154.

JENSEN, H.I., 1926: Geological reconnaissance between Roma, Springsure, Tambo and Taroom. Geological Suruey of Queensland Publication, 277.

MADRE, D.A., 1987: The Alpha Oil Shale deposit, the resource and its potential. Proceedings of the 4th

Australian Workshop on Oil Shale. Brisbane, December, 1987.

ALLEN, R.J., 1974: Hydrocarbon significance of Upper Palaeozoic sediments associated with the Koburra Trough, Galilee Basin. APEA Journal,

L4,59-65.

McKELLAR, J.L., L977: Palynostratigraphy of core samples from the Hughenden 1:250 000 Sheet area, northern Galilee and Eromanga Basins. Queensland Gouernment Mining Journal, 7 8, 393-399.

BEESTON, J.W., 1977: The petrography and rank of some shallow coal seams on the eastern flank of the Galilee Basin" Queensland Gouernrnent Mining Journal, 78, 264-267 .

OLGERS, F., 1970: Buchanan, Queensland, 1:250 000 Geological series. Bureau of Mineral Resources

CASEY, D.J., 1970: Northern Eromanga Basin. Geological Suruey of Queensland, Report,4l.

QUEENSLAND COAL BOARD, 1990: Queensland

DAY, R.W., WHITAKER, W.G., MURRAY, C.G.,

WILSON,I.H. & GRIMES, K.G., 1983:

Queensland Geology. Geological Suruey of Queen sland. Publication 383.

Geology and Geop hy sics, Au stralia, Explanatory

Noles Sheet SF/55-6. Coals. Sth Edition.

REEVES, F., 1947: Geology of the Roma district, Queensland, Australia. Anerican Association of Petroleum Geologists Bulletin, 31 (8), 1341-1371.

Galilee Basin

352 SCOTT, S.G. & HAWKINS, P.J., lgg2: Coal geology of

the northern Galilee Basin and its implications for coal seam methane investigations.

Proceedings ofthe Symposium on coalbed rnethane research and deuelopment in Australia, 5, 85-102.

SENIOR D.A., 1973: Jericho, Queensland. 1:250 000 Geological series - Explanatory Notes. Bureau of Mineral Resources Geology and Geophysics, Australia, Canberra.

VINE, R.R., 1973: The Galilee Basin. Bureau of Mineral Resources Geology and Geophysics, Australia, Record 197 3/53. VINE, R.R., 1976: Galilee Basin; In Leslie, R.8., Evans, H.J. & Knight, C.L., (Editors): Economic Geology of Australia and Papua New Guinea - 3. Petroleum. The Australian Institute of Mining and Metallurgy, Monograph , 7,316-321.

VINE, R.R., CASEY, D.J. & JOHNSON, N.E.A., 1964: Progress report, 1963, on the geology of the north-eastern Eromanga Basin. Bureau of Mineral Resources Geology and Geophysics, Australia, Record 1964/ 39. VINE, R.R., JAUNCEY, W., CASEY, D.J. & GALLOWAY, M.C., 1965: Geology of the Longreach-Jericho-Lake Buchanan area, Queensland. Bureau of Mineral Resources

Geology and Geophysics, Australia, Record

t965/245.

VINE, R.R. & DOUTCH, H.F., 1972: Galilee, Queensland, 1,:25Q 000 Geological series. Bureau of Mineral Resources Geology and Geophysics,

Australia, Explanatory No/es Sheet SF/55-10.

WELLS, A.T., 1989: Stratigraphy and Permian coal measures of the Galilee Basin, Queensland. 1z Permian coals of eastern Australia. Bureau of Mineral Resources, Bulletin, 231, 113-148.

Geology of Australian Coal Basins

353

ffiooper Basin

JW Beeston

Figure 1. Location map of the Cooper Basin. The Cooper Basin covers an area of 130 000 km-2, stretching from south-central Queensland into South

Australia (Figure 1). It is a totally intracratonic basin filled with Late Carboniferous to Middle Triassic fluvial sediments. Minor glacial material occurs at the base ofthe sequence (Day & others, 1983).

The Basin is covered by Jurassic and Cretaceous strata of the Eromanga Basin. Sediment thickness in the Cooper Basin is about 600m in the north and

about 1800m in the south (Petroleum Resource,

Assessment and Development Program, 1990), as indicated in the Nappamerri Trough by DSV

Burley 1 (Kantsler & others, 1984).

The principal tectonic elements are shown in

Figure 2.

STRATIGRAPHY The stratigraphic succession in the Cooper Basin is

similar to that in the Galilee Basin in that each

basin has experienced a hiatus during some part of the Middle P-ermian (Figure 3). Major coal deposition occurred during the_ea-rlV Permian in the Ar-amac Coal Measures in the Galilee Basin and in the Patchawarra Formation and its equivalents of the Cooper Basin. These strata were de-posited at about the same time as the coal in the Reids Dome beds of the Bowen Basin and the Mount Toondine

Formation of the Arckaringa Basin. Further significant coal deposition occurred during tbe Late P&mian in the Colinlea Sandstone and Bandanna Formation equivalents of the Galilee Basin, a4d in the Toolachee Formation and its equivalents in the Coooer Basin. Minor coals are also known in the Midhle Permian Epsilon Formation and Daralingie

Cooper Basin

354

sJSa \o

)

nO/t^

,<":'Xfu p\ "%

/^?ts-'

,/ a.s

4*'

\ Moolay er ber

o 6 a

\ Formi ttir n \

tr F

vYaran0

Nappameri Formation

Clomaiic Formation

Ee =@ 5-o EDr

lwar

Fo rmi rtion

\ \

Toolachee Toolachee Formation Formation

z Figure 2. Tectonic and structural elements of the Cooper Basin.

equivalent

Bandanna Fm correlative

-fiTrrrT{ Colinlea

. Sandstone \ I t correlative

larallnolo bods <

It\

loseneath Shale

tr /rp.ironrrR

TIJ

Murteree Shale

beds of the Cooper Basin. Detailed stratigraphic

descriptions ofthese and other units are given by Gatehouse (1972), Gray & Swarbrick (1975), Thornton (1979) and Evans (1980). Patehawarre

Late Carboniferous and Early Permian M errime li a F ortn q.t ion The basal unit in the Cooper Basin is the Merrimelia Formation, a sequence of glacio-fluvial conglomeratic sandstone with minor shale and

siltstone. The Merrimelia Formation is restricted in distribution, occurring only in the axial areas of the basin's western troughs (Thornton, 1979). It contains minor amounts of carbonaceous matter and rare plant fragments, trails and worm burrows. The formation has been described as a sequence of tillites, glacio-fluvial, glacio-lacustrine, interglacial and periglacial sediments (Battersby, 1975).

Tirrawarra Sandstone The Tirrawarra Sandstone, of Early Permian age,

overlies, apparently unconformably, the Merrimelia Formation, and consists of fluvial and braided stream quartzose sandstones with very minor carbonaceous siltstones, shales, and some very thin coal seams. The unit is restricted to the western troughs of the Cooper Basin (Thornton, 1979). It ranges in thickness from 15 to 75m. Three sedimentological subdivisions have been recognised in the basal sand sequence in some areas. The lower consists of channel conglomerates, sandstones and siltstones with an erosional lower contact. The middle is a more uniform well bedded braided stream sandstone, while the upper subdivision

Aramac GoalMeasures

Formation

.4,:gyl[,:gy

c] G

Merrimelia Formation

y' Jochmus , Formation

Jericho t

\ Formation / , Lake Galilee

\ a^-r^r---

Figure 3. Stratigraphy ofthe Cooper Basin (left) ond Galilee Basin (right), adapted from Gray & Swarbrick (1975), Thornton (1979), and Day & others (1983). consists ofchannel deposits ofsandstone and conglomerate with floodplain siltstones and some coals (Battersby, 1975).

P atc haw arro Fortnation

The Patchawarra Formation is a thick, extensive unit, consisting offlood-plain, deltaic and offshore sandstones, siltstones, shales, and coals. It extends across the entire Cooper Basin, but is thickest in the west (Thornton, 1979). The Formation commonly shows rapid thinning on to the observed crestal structures in the basin, suggesting some degree of uplift and erosion at the end of the Permian. There is also some evidence for faulting contemporaneous with deposition.

Geology of Australian Coal Basins

355 The sandstones in the Patchawarra Formation commonly show a frning upwards and the typical quadripartite zonation characteristic of point bar cleposits. Three subdivisions can be observed, the lower being mostly carbonaceous shales with,co-als, the middle thickly interbedded sandstones, shales and coals, and the upper dominantly shales

(Battersby, 1975).

Murteree Shale The Murteree Shale is a lacustrine sequence consisting of micaceous, partly carbonaceous shales. It is wideipread across the Cooper Basin, although there is some suggestion of a hiatus in the north (Thornton, 1979). The environment of deposition is dominantly lacustrine, chiefly a uniform shale/siltstone sediment combination. The abundant

carbonaceous matter present indicates it to be possible source rock for petroleum (Battersby, 1975).

Epsilon Forrnation The Epsilon Formation is a flood-plain to shoreline sequence of dominantly shale and siltstone that conformably overlies and interfingers with the Murteree Shale (Thornton, L979). Overall it averages about 60m in thickness, with the sandstones ranging up to 12m. Coals are also present, with seams ranging up to 4.5m. Although dominantly deposited in a flood plain environment, there is a dominance in some areas of lacustrine deposition.

Roseneath Shale

Figure 4. Isopach map, Patchawarra Formation.

The Roseneath Shale has similar rock types to the Epsilon Formation, conformably overlying and

Nappamemi Formation

inlerfingering with it (Thornton, 1979). It is also similar to the Murteree Shale, however its distribution is less widespread than both the underlying formations (Battersby, 1975). Some of this is due to non-deposition, but much is also due to extensive erosion at the end of the early Permian and at the end ofTriassic deposition. The Roseneath Shale is considered to be a possible petroleum source rock and also a seal for some hydrocarbon reservoirs.

The Nappamerri Formation is a fluvial seq-uence consisting mainly of interbedded shales, siltstones and sanditones. It is also widespread across the

Cooper Basin, but like the Toolachee Formation has been eroded to some extent in the west (Thornton, 1979). The formation represents the final phase of deposition in the Cooper Basin.

MAJOR COAL.BEARING SEQUENCES

Daralingie beds The Daralingie beds are a lower deltaic to flood plain sequence composed ofthin sandstones, shales and coals. They are widespread through the Cooper Basin, but absent in the north (Thornton, 1979)' They represent flood-plain deposition similar to that which formed the Epsilon Formation (Battersby, 1975). Some of the Jandstones have been identifred on electric log traces as appearing like typical lake-shoreline deposits.

Late Permian and Triassic Toolachee Formation and. equia a'lents The Toolachee Formation and its equivalents are a sequence of terrestrial sandstones, siltstones, sh-ales and coals. The Formation is widespread across the Cooper Basin, although it has been eroded in some areas in the west (Thornton, 1979). It can be subdivided in many areas into two lithological units, an upper unit of mostly carbonaceous shale with interb-edded sandstones and coals, and a lower unit of dominantly sandstone.

Patchawarra Formation Structure The Patchawarra Formation is the most significant unit for the present discussion, since it contains coal at depth. The shallowest point of the Patchawarra Form-ation in the basin, as interpreted from seismic data, is above an elevation ofabout -500m south of the iennappera Trough (Figure 2), an-d the deepest point is in-the Nappamerri Trough below an elevation of -3600m. The Patchawarra Formation obtains its greatest thickness in the north-east part of the Nappamerri Trough (Figure 4), where it is 600m thick' D ep ositional enuironment

(Thornton, 1979) has interpreted the Patchawarra Formation in the South Australian portion of the Cooper Basin as being dominated by !uvial channel deposits, whereas malginal areas to the south-east, west and north are dominated by overbank deposits, lakes and swamps (Figure 5).

Cooper Basin

Figure 5. Palaeogeography of the Patchawarra Formation, after Thornton

Coal facies The Patchawarra Formation has its greatest coal i".""1."-""t in the north-western sector of the 250 to .""itLi" Cooper Basin, where, in a formation Sbo- tiri.t, t^he aggregate thickness of the seams is

r"""iallv about 56ir. One coal seam' up to 25q but

over an area of at least 1500km"' [hi.k, "it"trds <5m in thickness (Johns, 1975)' are -otl't""*.

(1979)'

formations are, however, considered !o b9 majol- & others, 1984; ;;;;;t;At loipetroleum (Kantsler considerable h-ave may and 1978), ffu*ti"t, potential-for coal seam methane'

Toolachee Formation

Petrography ofthe coals from lhg-Fly Lake area 1979) ;i;hffi the Fatchawarra Trough (Smvth,varying from ;h;t ;;;ge of ma"e.al assJmblages

in inertinite' ;ir;r;ti.h in"vitrinite to those richproportion of high a contain coals ivfr"u oftt " microlithotypes, iuggesting th-at . .. inieimediate and inertodetrinite ;;;;;;i; ;"ch as des moiouiniteof the ase in the ;;;-;;;;;;, as in some coals Basinsame (Beeston, Bowen the of no-"'beds n"la" 1992).

CoaI QualitY and Potentia'l Because of the depth to the seams in the indicated Fuitfiu*utta Formation, little potential is The resource' coal extractive an ;;;;;";ti;t

Structure The Toolachee Formation contain coal at *pt|

(F\;";a). Th" elevation of the top of the Toolachee in the i."tL.li"ii ranges from below -3000-m and Trough NaPPamerri i-rough, F;;;h;;;;;a -C""o"t south of the S""cline to"above--i200m

Tenneppera Trough (Figure 7)'

D epos it ional ena ironment

The depositional environment of the Toolachee to have been-dominated bv ;A;;;; iJ "o*la"t"afloodplains, lakes,,and peat *Ju"a"ti"g streams, g r eam d irections t i th-s w t ig ;;";il; aTE o in t o n, to ),east (!'igure u)' dominantly from west

Geology of Australian Coal Basins

357

U o

-nette6-

F N =

Figure 6. Structural contours - Toolachee Formation.

Figure 7. Isopach map - Toolachee Formation.

Figure 8. Palaeogeography of the Toolachee Formation, after

Cooper Basin

358 Vrlflte. ClofltP

. Areo domrnsled by

Vdilte. Clorate Formolrons -

a Tooloch€e t! Roseneolh shole o Ipsrlon l Hurl€ree shole lolchmorro -

+ ilpper sloge 1'

overbonk deposds, lokes ond smmps

[honnel bell

9 Umer cooslol ploin

{cool'rich}

a Areo dominol€d bl

cro9o{ Plorn

co0l sromps

poof)

o Areo dominoted by

O Loke

chonnel deposils

x [ow5 stoqe 1 . Sloge 3'

+++ *uo x

ftv9 \

* .t.* "o8" .

lnlermediotes

.E ..t . 't',1 .\'t,',1-.a t -.

ir*+

90 0urile.lnerlile

lntermedroles

o ot o-Io at a, ov$ p I t'o x? 1, vr a

oo 8v

-a

.A a

i t, ox

ooor,

.?orl

a a-b a -a -r

Figure 9. Microlithotype compositions of coal seams from the Gidgealpa Group in Tindilpie 1, Tirrawarra 2, Mudrangie 1 and Cuttapirrie 1. (After Smyth, 1984).

Figure 10. Microlithotype compositions of coal seams in the Patchawarra Trough. (After

CoaI Facies

REFERENCES

Coal in the Toolachee Formation occurs in numerous seams up to 5m thick, with an aggregate coal thickness of 13m. The coal is described as black and

bituminous, varying from dull to bright and with common siderite lenses (Johns, 1975). Microlithotype analysis has shown that it contains a high proportion of intermediate and dull microlithotypes (Hunt, 1982).

COAL TYPE AND SEDIMENTARY ENIVIRONMENTS The coals in the Cooper Basin are mainly

inertinite-rich, a characteristic of Australian intra-cratonic Permian basins. They have low sulphur and mineral matter contents, indicating autochthonous deposition in a well drained environment (Hunt & Smyth, 1989). The inertinite is mainly botanically unstructured

90 Durrle.lner|le

Smyth, 1984).

BATTERSBY, D.G., 1975: Cooper Basin gas and oil fields. /n, Leslie, R.B., Evans, H.J. & Knight, C.L. (Editors): Economic geology of Australia and Papua New Guinea, Volume 3 - Petroleum. Australasian Institute of Mining and Metallurgy, Melbourne, Monograph, T, 32L-368. BEESTON, J.W., 1992: Coal facies depositional models, Denison Trough area, Bowen Basin. Queensland Geology,2, t-33.

DAY, R.W., WHITAKER, W.G., MURRAY, C.G., WILSON, I.H. & GRIMES, K.G., 1983:

Queensland Geology. Geological Suruey of Queensland Publication, 383. EVANS, P.R., 1980: Geology of the Galilee Basin. In Henderson, R.A. & Stephenson, P.J. (Editors): The geology and geophysics of northeast Australia. Geological Society of Australia, Queensland Division, 299-305.

fragmentary inertodetrinite. The microlithotypes are characteristically fi ne-banded.

GATEHOUSE, C.G., 1972: Formations of the Gidgealpa Group in the Cooper Basin. Australian Oil and Gas Reuiew, September 1972, 10-15.

Microiithotype compositions have been shown to depend on the formations in which they occur (Smyth, 1984) (Figures 9 and 10). Variability of depositional environments between the formations has led to coals deposited in environments such as lakes, channel belts, lower coastal plain and upper coastal plain exhibiting recognisable differences in microlithotype composition, particularly with regard to the inertinite-rich microlithotypes.

GRAY, A.R.G. & SWARBRICK, C.F.J., 1975: Nomenclature of Late Palaeozoic strata in the northeastern Galilee Basin. Queensland Gou ernment Mining Journal, 7 6, 344-352.

High vitrinite coals are associated with the fluvial and brackish water swamps, while lacustrine and deltaic coals show higher inertinite contents. Coals deposited in lacustrine conditions tend to show greater differentiation between the inertinitic and vitrinitic accumulations, while those formed on the upper deltaic plain show the greatest admixture of particles (Smyth, 1984).

HAWKINS, P.J., 1978: Galilee Basin - review of petroleum prospects. Queensland Gouernment Mining Journal, 79, 96-112. HUNT, J.W., 1982: Relationship between microlithotype and maceral composition of, coals and geological setting ofcoal measures in the Permian basins of eastern Australia. Australian Coal Geology, 4(2), 484-502. HUNT, J.W. & SMYTH, M., 1989: Origin of inertinite-rich coals of Australian cratonic

basins. International Journal of Coal Geology,

tt,23-46.

Geology of Australian Coal Basins

359 JOHNS, R.K., 1975: Permian coal in South Australia. In Traves, D.M. & King, D. (Editors): Economic geology of Australia and Papua New Guinea 2:

SMYTH, M., 1979: Hydrocarbon generation in the Fly area ofthe Cooper Basin. APEA Lake - Brolga 19, 108-114. Journal,

Coal. Australasian Institute of Mining and

SMYTH, M., 1984: Coal microlithotypes related to sedimentary environments in the Cooper Basin,

Metallurgy, Monograph, 6, 266-268. KANTSLER, A.J., PRUDENCE, T.J.C., COOK, A.C. & ZWIGULIS, M., 1984: Hydrocarbon habitat of the Cooper/Eromanga Basin, Australia. /z Demaison, G. & Murris, R.J. (Editors): Petroleum geochemistry and basin evaluation. Arnerican Association of Petroleum Geologists,

Memoir,35, 373-390.

Australia. International Association of Sedimentologists, Special Publication, 7, 333-347. THORNTON, R.C.N., 1979: Regional stratigraphic analysis ofthe Gidgealpa Group, southern Cooper Basin, Australia. Geological Suruey of S outh Australia, Bulletin, 49.

PETROLEUM RESOURCE ASSESSMENT AND DEVELOPMENT SUBPROGRAM, 1990: Petroleum Resources of Queensland (Review to June 30, 1989). Queensland Resource Industries Reuiew Series. Department of Resource Industries, Queensland.

Cooper Basin

361 l34of

_____L

140ot

&*ckaringa

I I

Basin

30.

SOUTH AUSTRALIA

BA McConachie and

JN Dunster r-^tt

kilometres

Figure 1. Location of the Arckaringa Basin in South Australia ( After Beeston & \ilood, 1986). The Arckaringa Basin comprises a thin, widespread, intracratonic sequence of Carboniferous-Permian rocks wholly contained within northern South Australia (Figure 1). The basin covers an area of over 80 000km2, and is mostly restricted to the subsurface. The basin is located in the remote dry northern region of South Australia, bordering the arid

interior ofthe Australian continent. It is crossed from north to south by the Stuart Highway and the standard gauge Alice Springs-Tarcoola rail link. The only major settlement in the region is Coober Pedy, which has a population in excess of 1000 people. Seven aboriginal tribes once occupied parts ofthe region (Tindale, 1940) but today the area is mainly pastoral leasehold and aboriginal land.

The Arckaringa Basin is bounded by outcrop of older rocks (Figure 2). It is disconformably overlain by up to 300m of late Jurassic to early Cretaceous strata forming part of the Eromanga Basin, and then by a veneer ofTertiary (Eocene) and Quaternary deposits. Two major depocentres are recognised within the basin, the Boorthanna and Phillipson Troughs. The Carboniferous to Permian sequence of the Arckaringa Basin can be divided into three lithostratigraphic units. The lowermost of these is a widespread glacigene sequence that was deposited over the underlying Precambrian and early to middle Palaeozoic basement rocks. This sequence is overlain by a fine-grained marine clastic unit and then by the Mount Toondina Formation, a marine to fluvio-lacustrine succession that contains sporadic well-developed coal measures.

Previous Work A variety ofdrilling has been undertaken in the

Arckaringa Basin, mostly for stratigraphic, water, mineral, coal and petroleum exploration work. The bulk of the drilling, however, has focused on the coal

Arckaringa Basin

362

32'

133 "

340

35'

36'

BITCHERA RIDGE Marla

uH-202

O-z\

COALFTELD Deposit

ilr-m#t 07@ Mount

,J*#-':K'Pi::::) ,t € -/ +ol

2Bo

FIS'

- -- -

|,,-,u,.J ',iill3il*\

uH-252 uH-3 1 0 UH-284

r Oodnadatta

East

ARCKARINGA Wintinna

Wintinna DePosit

;"-;il^ \ BA',N **.%u,

Meramangye-1

Deposit -

Coober

Pedv. .J t

29"

MOUNT

wooDs

Lake Phillipson

*l'

IiILIER

Deposit o

..-^i2

GAWLER CFATON

3Oo

STUART SHELF Zero Permian lsopach Coal Deposit

lOO km

Okm

Drillhole Town

Tarcoola - Alice Springs Railway

SCALE

Figure 2. Geological setting and extent ofthe Arckaringa Basin. potential ofthe basin. Stratigraphic correlations and cross-sections through various drillholes in the region are presented by Townsend & Ludbrook (1975), Moore (1982) and Hibburt (1993). Johns (1975) has briefly reviewed the coal deposits of the Arckaringa Basin and Clarke (1982) has reported on the coal exploration potential, sedimentary geology and tectonic history of the basin. The most recent major study of the basin was undertaken by Hibburt (1984).

STRUCTURE AND TECTONIC SETTING The Arckaringa Basin is sandwiched between basement rocks of the Officer Basin, Adelaide Geosyncline, Denison Block and Gawler Craton and the overlying Eromanga Basin.

Mostly restricted to the subsurface, the basin comprises generally thin, gently undulating, poorly lithified sedimentary rocks with several peripheral troughs up to 1300m deep (Hibburt, 1984).

Geology of Australian Coal Basins

363 Much of the upper pu-r', of the basin sequence has been removed by pre-Jurassic erosion, exposing

several bald basement highs in the central area and creating Permian outliers to the south. The northwest edge of the basin remains problematic but has been delineated by reinterpreting seismic data and tying with geological interpretations from hundreds of seismic upholes. The principal mapped faults bounding or displacing the Arckaringa Basin sequence are shown in Figure 2. The peripheral troughs are also believed to be at least partly fault bounded. This normal faulting is thought to have been synchronous with deposition. The distribution of the Arckaringa Basin rocks is constrained by thrusts west of Marla, and both offset and limited by wrench faults in the northern Wintinna Fault Zone. Elsewhere, seismic data show evidence of local intra-Permian uplift and erosion (Hibburt, 1993). The eastern and southern flanks of the basin contain numerous subsurface structures interpreted as salt diapirs. One exposed example is Mount Toondina itself, where Permian rocks form a piercement structure.

Vitrinite reflectance data suggest variable amounts of pre-Jurassic uplift and erosion ranging up to 1km. Minor late structuring occurred during the late Miocene (Hibburt, 1993) and during the Eocene resulting in channel formations which are still well preserved.

STRATIGRAPHY The Arckaringa Basin is commonly divided into

three lithostratigraphic units, the Boorthanna, Stuart Range and Mount Toondina Formations; the Mount Toondina Formation contains coal. All units have been recognised over much ofthe preserved area of the basin. The Stuart Range Formation, and the lower and upper Mount Toondina Formations are interpreted herein as lithofacies variations within a fluvio-deltaic-marine system.

Boorthanna Formation

Formation rarely exceeds 250m throughout the rest of the Arckaringa Basin. The unit is Early Permian (Stage 2/3) (Townsend, 1976). It is thought to have formed in a

predominantly quiet water, restricted marine environment, and may represent distal marine deposition associated with near-shore and fluvio-deltaic progradation of the overlying Mount Toondina Formation.

Mount Toondina Formation The Mount Toondina Formation probably

interdigitates with the Stuart Range Formation at a regional scale, but is probably unconformable with that unit locally. The Mount Toondina Formation is divided into two units (Figure 3). The lower unit is predominantly sandstone and siltstone with interbedded limestone, claystone and shale. The upper unit consists'of sandstone and siltstone commonly interbedded with carbonaceous claystone and coal seams. The Mount Toondina Formation attains a maximum thickness of 600m in the Boorthanna Trough. Figure 3 illustrates the distinctive geophysical log signatures of the upper and lower units. The density and gamma logs respond to the low densities and low radioactivity of the coals within the upper Mount Toondina Formation. The neutron and resistivity data indicate the presence ofthe thin calcareous bands within the lower unit, and the SP log suggests a change in water chemistry between the upper and lower units. The Mount Toondina Formation is Early Permian (Stage 3) (Gilby & Foster, 1988). The environment of deposition of the lower Mount Toondina Formation is interpreted to be the proximal offshore portion of a marine delta. The upper Mount Toondina Formation probably accumulated in fluvio-lacustrine upper to lower delta plain setting with widespread peat swamps commonly developed.

History of Nomenclature Development

The Boorthanna Formation is composed of two units, a lower pebbly to cobbly claystone and an upper sandy conglomerate with frning upward cycles. The rocks recognised in the formation include tillite, diamictite, rhythmically bedded sandstone and laminated mudstone. The formation exhibits variable thickness up to a maximum of 366m in Boorthanna-1 within the Boorthanna Trough. The sequence is of Late Carboniferous and/or Early Permian (Stage 2) age (Townsend, 1976). Its depositional environments are predominantly interpreted as glacigene, with a marine facies near the top of the unit.

Stuart Range Formation The Stuart Range Formation comprises homogeneous grey claystone or shale with minor siltstone and sandstone interbeds. Sandstone

content of the formation is highest in the north of the basin. The unit is widely distributed, with a reported thickness >500m in the Lake Phillipson area (Hibburt, 1993). This high value, however, is probably due to the inclusion of lower Mount Toondina Formation within the Stuart Range Formation in this particular area. The Stuart Range

Townsend & Ludbrook (1975) defined the

lithostratigraphic formations of the Arckaringa Basin. They introduced the term Boorthanna Formation and clearly indicated that the overlying Stuart Range Formation comprised the widespread overlying shale-dominated unit. Townsend and Ludbrook also expanded Freytag's (1965) definition of the Mount Toondina Beds, originally based on limited exposures of coal-bearing outcrop around the Mount Toondina piercement structure. Townsend & Ludbrook (1975) included both the coal-bearing section and the underlying sandstone dominated sequence within the Mount Toondina Formation. Cook (1981) reported that the shales in the lower 30m of the Mount Toondina Formation in drillhole Boorthanna-1, contained marine tasmanitids. Gilby (1983) also interpreted a restricted marine setting for the sandstone dominated section of the Mount Toondina Formation in the northern Arckaringa Basin. There is possibly still some confusion in the Lake Phillipson area where the Stuart Range Formation is shown as including typical marine sandstones of the lower Mount Toondina Formation (Hibburt, 1984, figure 1.2).

Arckaringa Basin

364

DRILLHOLE 695-O3

"9- . STRATIGFIAPHY

Elevation 147.74 m ^o*

Datum - Surface Total Depth 311.20 m Exploration Licence 695

-**t:rs*'".-" ."-"

LITHOLOGY LEGEND Core Loss

Soil

Limestone

Coal

-.f-

Claystone q,Q

Mudstone

Siltstone

Sandstone

o = o

C onglom erate

E =

qQ MT. wrLLouci1

o G

lough by

Lower

1:250 OOO SHEET

Drillhole 695-03 Arc kd n ngo

28. S

M ount

T oo nd ina Formati on

Figure 3. Lithostratigraphy and geophysical logs of drillhole 695'03.

Geology of Australian Coal Basins

365

A cored drillhole section through most of the Mount Toondina Formation in the northern part of the Wintinna coal deposit (see below), together with the overlying Eromanga Basin sequence, is illustrated in Figure 3.

COAL GEOLOGY OF THE UPPER MOUNT TOONDINA FORMATION Age and Distribution Outcrop of the coal-bearing upper Mount Toondina Formation is restricted to the area around the Mount Toondina piercement structure itself. Oxidised coal and highly weathered cross-bedded sandstones and siltstones are locally exposed (Figure 4).

Mostly the upper Mount Toondina Formation is known from drillhole information concentrated in and around the various coal deposits. Figure 5 shows a typical coal intersection from the a cored borehole in the Wintinna deposit, located in the north-central part ofthe basin (Figure 2). The extent ofthe coalfields is controlled by both depositional and erosional processes. The formation of coal appears iargely restricted to lower delta plain environments. The upper Mount Toondina Formation is mostly unconformably overlain by the Late Jurassic-Early Cretaceous Algebuckina Sandstone/Cadna-owie Formation and gentle but significant erosion appears to have occurred prior to the Mesozoic deposition. Key drillhole intersections of suspected coal-bearing Mount Toondina Formation in the north-west of the basin are prefixed by UH (seismic upholes) on Figure 2. These holes intersected thin coal seams which are outside the various known deposits and in areas where drilling for coal exploration has not yet been undertaken. Few ofthese samples have been

Figure 4. Photograph of coal outcrop at the Mount Toondina piercement structure (the white material is salt).

dated.

The coals of the upper Mount Toondina Formation are mostly Early Permian (Stage 3), with the upper section in some areas extending into Stage 4. A coal sample from uphole UIJ-284 at a depth of 63m has also been confirmed to be Permian. Samples from the cored drillhole Meramangye-1 between 70 and 72m, originally thought to be from the Mount Toondina Formation, have, however, been found to be Eocene (Neville Alley, SADME Palynological

Laboratory, personal communication, 1993).

Coal Quality Based on the American Society for Testing Materials coal classification, the coals of the upper Mount

Toondina Formation are regarded as

Lignite fuSub-bituminous C in rank. The rank varies little throughout the basin, indicating relatively uniform burial depths (assuming constant heat flows), and suggesting that uplift and erosion have been similar in the various areas.

Arckaringa Basin. Most parameters vary little, but the levels of key inorganic contaminants do differ significantly. The relatively high sulphur levels are probably related to the original lower delta plain (marginal marine) coal-forming environment. Chlorine and sodium in ash, on the other hand, are probably signiflrcantly affected by migration of the saline marine connate waters in the Algebuckina Sandstone/ Cadna-owie Formation of the overlying Eromanga Basin. Beeston & Wood (1986) described the Permian palynomorph assemblage in a typical seam sample from the Wintinna Coalfield. The coal contains a wide range of, palynomorphs, identified as megaspores, granulates, double-layered spores, laevigates, pollen, sporogenite, nodates, algae, and

mobilised exinite (exsudatinite).

COALFIELDS AND COAL DEPOSITS

The Lake Phillipson deposit is less deeply buried today. Its coal i:'as 25% volatile matter, compared to 22 to 23Vo for the deposits ofthe Arckaringa Coalfield and the Weedina deposit, both of which are located in the northern part of the basin. Relatively shallower burial is therefore interpreted for the Lake Phillipson area.

Table 1 also illustrates the coal resources ofthe Arckaringa Basin as presented by the South Australian Department of Mines and Energy (SADME, 1991). The tonnages refer to in situ coal, and do not relate directly to economically extractable material. No coal mining has been undertaken in the Arckaringa Basin to date.

Table 1 indicates the average coal quality parameters for the various known deposits in the

The coal measures discovered to date in the basin occur in six named deposits. These are Wintinna,

Arckaringa Basin

Figure 5. Photograph of typical dull, friable, coal seam core (dry, HQ size)

from drillhole 695-07 in the Wintinna deposit near Arckaringa Homestead. The photograph was taken during an

exploration

progTam described by Bourke &

others (1983).

East Wintinna, Murloocoppie and Westfield deposits in the Arckaringa Coalfield, plus the Weedina and Lake Phillipson deposits further to the south and east. Total measured, indicated and inferred resources are in excess of 20 x 109t in seams up to 9m thick. The coal is all low-grade, sub-bituminous rank, with a specific energ'y ranging between 16 and 18MJ/kg. Overburden thicknesses to the top of the uppermost seam are as shallow as 30m at Lake Phillipson, but are in excess of 130m for each ofthe other deposits.

Arckaringa Coalfield The widespread occurrence of coal in the northern Arckaringa Basin was discovered by Meekatharra Minerals Limited in 1980. Four deposits were delineated (Figure 2) with estimated total resources of around 10 x 109 t of coal. The deposits are referred to as the Wintinna, East Wintinna, Murloocoppie and Westfield deposits (Figure 2). The coals in each ofthe deposits are relatively uniform in composition and specific energy, but the sulphur contents of the individual deposits are variable.

Overburden at each of the coal deposits comprises poorly consolidated sandstones of the Algebuckina Sandstone/Cadna-owie Formation and grey siltstones and claystones of the Bulldog Shale. The Algebuckina Sandstone is a major saltwater, sub-artesian aquifer.

Wintinna d.eposit The Wintinna coal deposit is the largest in the Arckaringa Coalfreld. It occupies an elongate northwest trending trough 60km long and some 20km wide. The coal seams generally thin from north to south. In the north there are eight persistent seams with a cumulative coal thickness of up to 25m within a stratigraphic interval of 75m. In the south there are 10 persistent seams within a stratigraphic interval of up to 150m. These are the only seams named. In descending order they are the Gyalinna, Raspberry Creek, Isolation, Perentie,

Goorikiana, Mirakina, Arckaringa, Mt Barry, Nilkinna and Waddikee seams. Cumulative coal thickness in the south is about 15m. The depth to the top of the uppermost thick and potentially mineable coal seam varies between 140 and 240m. Coal of Permian age is common in the areas outside the coalfield itself. As part of the work for the present paper a sample of coal from Comalco drillhole 695-02 was submitted for palynological examination and found to be of Permian Stage 38 age (Neville Alley, SADME Palynological Laboratory, personal communication, 1993)

Typical quality of Wintinna coal on a dry basis, compared to an analysis on in situ coal, is shown in Table 2.

East Wintinna deposit The East Wintinna coal deposit contains 6 to 7 seams distributed over most of the area. Cumulative coal thickness is up to 20m within a stratigraphic interval averaging 60m. This coal deposit is the deepest in the Arckaringa Coalfield, with the uppermost potentially mineable coal seams occurring at depths between 220 and 300m.

Murlooeoppie d.eposit Eight persistent seams are contained within a 70m stratigraphic interval throughout the Murloocoppie coal deposit. Cumulative coal thickness in the area averages 20m, with the top of the uppermost thick coal seam being at depths of between 140 and 230m.

Westfield d.eposit The Westfield coal deposit comprises two persistent seams 30m apart. The upper of these seams varies from 6 to gmln thickness while the lower averages 1 to 2m. The depth to the top of the upper coal seam is between 145 and 215m.

Geology of Australian Coal Basins

367

rcbr; 1; eoar::tbposffb; tonrraE ttfi;5"$*fiti6ifff;ilrton; within the atc*ari -gc Besit "

Measured-

Ash

tonnes)

1 870

2 270

975

1 200

940

(million

Deposit

East Wintinna Deposit vlurloocoppie Deposit

Westfield Deposit Weedina Deposit Lake Phillipson Deposit

(million

/olatile Fixed Matter )arbon

MJ/kg

Na Vo

ash

t7.5

1.1

0.04

17.6

0.5

0.01

2 690

16.1

1".8

313

470

16.7

2.7

0.06

1 200

6 000

16.5

0.5

0.04

5 000

.iD

t6.2

0.7

r.24

Weedina Deposit The Weedina deposit was discovered by Getty Oil Development Company Limited in 1984. It occurs

within the Boorthanna Trough in the northeast

Arckaringa Basin. The coal deposit is over 40km long and 10 to 20km wide. Six majbr seams and several minor coal seams are present over the 150m thick coal-bearing stratigraphic interval. Individual seams are up to 8m thick with a cumulative thickness of 35 m. The coal measures are flat lying with 130 to 150m of overburden comprising the Bulldog Shale and the Algebuckina Sandstone/ Cadna-owie Formation of the Eromanga Basin. Typical quality of Weedina coal on a dry basis, compared to an in sifu analysis, is given in Table 3.

Lake Phillipson Deposit The Lake Phillipson deposit was the first major coal accumulation recognised in the Arckaringa Basin. The coal was discovered in the Lake Phillipson Bore, drilled by the South Australian Government between 1902 and 1905. It was delineated by Utah Development Company in 1972. The coal deposit is situated in two shallow

northwest trending synclinal limbs, referred to as the Main and West basins, within the Phillipson Trough in the southern Arckaringa Basin. The Main basin is over 60km and the West basin is about 50km in length. Six major and several thin coal seams have been delineated. The major seams are named in descending order, the Lake, Mabel Creek, Opal, Phillipson, Rankin and Utah seams. Individual seam thicknesses range up to 7m with a cumulative coal thickness of up to 25m.

' f [bl6 i;,rypiCCl..:{rlalitt,,,ot:Itriiltin- nC,,b oCi In situ

Moisture (7o)

Ash (7o)

6.10

Dry basis

Overburden is 30 to 70m thick to the top ofthe topmost seam. The cover rocks are poorly consolidated sandstone, siltstone and gravel ofthe Eromanga Basin succession. Coal quality is comparable to the other deposits of the Aickaringa Basln. The high sodium and chlorine levels (about 2%) may result in severe fouling and high temperature corrosion if the coal is used in conventional pulverised fuel boilers.

MINING FACTORS Caplygin and Kwitko (1992) reviewed th_e po_tential development of various coal deposits in South Australia, including those of the Arckaringa Basin. No coal mining in the Arckaringa Basin has been undertaken to date. The twin problems appear to be available markets and high potential mining costs. The poorly consolidated, saltwater saturated overburden is a significant impediment to the establishment of a viable industry. The coal resources, however, are vast, and could certainly provide a basis for several very large scale operations.

Infrastructure in the region is poorly developed. Many of the coal deposits are situated far from established towns ahd transport routes. The Lake Phillipson deposit is probably the most accessible, lying adjacent to the Alice Springs-Tarcoola railway line. Coal from the Arckaringa Coalfield and the Weedina deposit would be immediately suitable for

Table 3. Typical quality of Weedina coal (SADME, 1989). Analysis

Analysis

Specific Energy

tonnes)

Wintinna

Inferred

Moisture

Indicated Arckaringa Coalfield

Proximate Analysis

Coal Resources

Coalfield.lDeposit

In situ

Moisture (7o)

Ash (%)

t.o

Dry basis t2.2L

9.80

Specific Energy (MJ/kg)

16.5

26.7

0.46

0.75

Specifrc Energy (MJ/kg)

17.50

28.L4

Sulphur (7o)

Sulphur (7o) Chlorine (7o)

1.10

t.77

Chlorine (7a)

0.05

0.07

Sodium (7o)

0.09

0.15

0.04

Arckaringa Basin

368 conventional pulverised fuel power stations. Coal from the Lake Phillipson deposit, however, would require specialised treatment before use.

COOK, A.C., 1981: The organic petrology of samples from a selected group ofwells in or near the Arckaringa Block; a report prepared for Delhi

Petroleum Pty Ltd. Delhi Petroleum Pty Ltd.

CONCLUSIONS The outline of the northwest Arckaringa Basin has been remapped and extended, based on the results of recent petroleum expioration by Comalco in the

adjoining Officer Basin. Potential exists for shallow coal in the northwest of the basin, and the prospectivity must be considered good in view of the large deposits already discovered in other parts of the region. Further work is required, however, to distinguish between Eocene and Permian coals in this area.

Two widespread units have been recognised within the Mount Toondina Formation as a result of this study. The upper unit was deposited in a non-marine environment and contains the coal measures strata. The interpretation of the upper and lower Mount Toondina and the Stuart Range Formations as part of a prograding deltaic system should enable a

better understanding of the relationships and distributions of these rock units within the Arckaringa Basin sequence.

The coal measures of the Arckaringa Basin hold great future mining potential if their economic viability can be clearly demonstrated or if more accessible deposits can be discovered.

ACKNOWLEDGMENTS The authors thank Bos Stainton of Comalco Aluminium Limited for assistance with the preparation of this paper. George Kwitko and Serge Caplygin of the South Australian Department of Mines and Energy provided much appreciated background information. Neville Alley of the SADME Palynological Laboratory provided confirmation of the Permian age of the coal samples in drillholes 695-02 and UH-284.

FREYTAG, LB., 1965: Mount Toondina Beds - Permian sediments in a probable piercement structure. Transactions of the Royal Society of South Australia,89, 61-76.

GILBY, A.R., 1983: Permian palynology of the Stuart Range and Mount Toondina Formations, Arckaringa Basin, South Australia. BSc (Hons) Thesis. University of Adelaide.

GILBY, A.R. & FOSTER, C.B., 1988: Early palynology of the Arckaringa Basin, South Australia. Palaeontographica, B 209, (4-6),167-191. HIBBURT, J.E., 1984: A review of exploration in the Arckaringa Basin 1887-1983. South Australian Department of Mines and Energy, Report Book 8U1.

HIBBURT, J.E. (Editor), 1993: Petroleum exploration

and deueloprnent in South Australia. South Australian Department of Mines and Energy. 9th Edition.

JOHNS, R.K., 1975: Permian coal in South Australia. .In Traves, D.M. & King D., (Editors): Economic Geology of Australia and Papua New Guinea, Part 2: Coal. Australasian Institute of Mining and Metallurgy, Melbourne, Monograph 6, 266-268. MOORE, P.S., 1982: Hydrocarbon potential of the Arckaringa region, central South Australia. Australian Petroleum Exploration Association

Journal,22, 237-253.

SADME, 1989: Coal review - Weedina deposit. South Australian Department of Mines and Energy, Mineral Industry Quarterly, 55, 20-22. SADME, 1990: Coal - review of the Arckaringa Coalfield. South Australian Department of Mines and, Energy, Mineral Industry Quarterly,58,

24-25.

REFERENCES BEESTON, J.W. & WOOD, G.R., 1986: Quantitative autofluorescence variation in a low rank Permian palynomorph assemblage. Geological Suruey of Queensland Publication, 387, 29-40. BOURKE, D.J., DUNSTER, J.N., McCONACHIE, B.A.

& SENAPATI, N.S., 1983: Technical report on

1982 drilling programme, E.L. 695. Comalco Aluminium Limited Technical Report, EXQ 83/2.

CAPLYGIN, S. & KWITKO, G., 1992: The discovery and development of coal in South Australia. Australasian Institute of Mining and Metallurgy Annual Conference, Broken Hill, 107-113. CLARKE, J.D.A., 1982: Coal in the Arckaringa Basin, South Australia. Comalco Aluminium Report, EXQ 82/9.

SADME, 1991: Coal deposits in South Australia. South Australian Department of Mines and Energy, Inforntation Sheet,9. TINDALE, N.B., 1940: Results of the Harvard-Adelaide Universities anthropological expedition, 1938-1939. Distribution of Australian Aboriginal tribes: a field survey. Transactions ofthe Royal Society of South Australia,84, L40-231. TOWNSEND, I.J., 1976: A synthesis of stratigraphic

drilling in the Arckaringa Basin, 1969 - 1971.

South Australian Department of Mines and Energy Report of Inuestigation, 45.

TOWNSEND,I.J. & LUDBROOK, N.H., 1975: Revision of Permian and Devonian nomenclature of four formations in and below the Arckaringa Basin. Quarterly Geological Notes, Geological Suruey of South Australia, 54, 2-5.

Geology of Australian Coal Basins

369

ffi $er ollie and Wilga Basins

PJ Ashton, MT Betlinski and DG Chapman

Known preservation of the Sakmarian to Late Permian Collie Coal Measures occurs in three separate structural basins a-t Collie, Wilga and Boynp Brook (Figure 1), in the southwestern partof West6rn Australia. The Collie Basin, located nearly 160km south southeast ofPerth, is the largest of these features, being up to 27km long, 13km wide and covering an area of about 224krn. The Collie Basin is elongated, in a northwest -southeast direction, sub-parallel to major faults within the basin and regional trends in the surrounding basement rocks. It is divided into two asymmetrical lobes, separated in the south by exbosed basement rocks in a structure known as the St6ckton Ridge. In the north this ridge is covered by a veneer of faulted Permian sediment' The westerly lobe is called the Cardiff Sub-basin. The easterly lobe was originally subdivided by Lord (1952) into two sub-basins, the Shotts and Muja Sub-basins. However, stratigraphic and structural studies since 1981 have shown that continuity, of coal seams, folds and faults, exists within this lobe and so it was renamed the Premier Sub-basin by Wilson (1990). The basin lies within the Archaean rocks of the Yilgarn Block, which, in the Collie area, consist mainly of granite and granite-g!eiss intruded by mafic dykel and quartz veins. Migmatite and deform6d monzonite outcrop to the west, generally separating the granites from a belt made uq---.- doininantly of gneisses and metasediments (Wilde & Walker, 1E82).-The regional trend within the basement is mainly northwest-southeast, as show! by metamorphic foliations, migmatite layering and elongation of granitic plutons, but swings to a nortL-south trlnd along the Darling Fault, 35km west of Collie, and to an easterly trend along the southern margin of the Yilgarn Block (Williams, 1975).

The Darling Fault, 35km west of Collie, forms the present-day western edge of the Yilgarn Block and ilso markithe eastern Iimit of the Perth Basin. It is a west-dipping, high-angle, normal fault striking

north-south, with a maximum displacement of roughly 15km (Playford & others, 1976).

COLLIE BASIN STRATIGRAPHY The Permian sequence in the Collie Basin is blanketed mainly by sediments of Tertiary to Cretaceous age, and is only observable in accessible parts of underground and open-cut mines or in borehole samples. The oldest rocks within the basin are of the Sakmarian Stockton Formation, which rests unconformably on Archaean basement. These rocks are conformably overlaid by the Permi4n Collie Coal Measures, which are subdivided into three coal-bearing members separated by coal-barren intervals (Table 1; Figure 2). The coal measures are in turn covered uncoliformably by a veneer of sediment, the Nakina Formation, rang-i119 Cretaceous to Holocene (Backhouse & Wilson, 1988). The following is the long-accepted stratigraphy of the Collie Bisin but the reader is advised that this

is currently under review in the light ofrecent palynologiial studies by Backhouse (1990)'

Stockton Formation The Stockton Formation is the lowermost unit in the Collie Basin, resting on what is believed to be a

Collie and Wilga Basins

370

o o o >.

0 o

go o o o o ro q!

o o

F a (, 0

!q) Q

e 6i

o tr 6 o o C) o)

E o >i

0 o o

a0 q)

ti b! Er

Geology of Australian Coal Basins

37t

TABLE 1. Stratigraphic Correlation and Subdivision of the Collie Basin.

CARDIFF SUB-BASIN

PREMIER SUB.BASIN Northern and central areas

TERTIARY TO

Southern area

NAKINA FORMATION 5-30m

CRETACEOUS

CARDIFF MEMBER Bacchus Seam* Medusa Seam* Pygmalion Seam* Cardiff A Seam Cardiff No.1 Seam Cardiff No.2 Seam Cardiff Seam Neath Seam Abe Seamx Ben Seam* 60 - 90m COLLIEBURN MEMBER Collieburn No.1 Seam Orion Seamx Upsilon Seam* Alpha Seam Wyvern Seam Collieburn No.2 Seam Phoenix Seam

MUJA MEMBER Ate Seam Bellona Seam Ceres Seam

Diana Seam

ABSENT

Eos Seam Flora Seam Galatea Seam Hebe Seam Iona Seam*

PremierNo.1Seam.... PremierNo.2Seam.... PremierNo.3Seam....

90 - 120m CHICKEN CREEK MEMBER . Apis Seam . Uraeus Seam . Unicorn Seam

PremierNo.4Seam "..,

. Pegasus Seam

20m

PREMIER MEMBER

PremierNo.5Seam.... PremierNo.6Seam....

. Hydra Seam

Juno Seam (Upper)x . . Juno Seam (Lower)* . . Pan Seamx Leda Seam*

. Gryps Seam

. Chiron Seam

PremierNo.TSeam....

Icarus Seam

Griffin Seam Tantalus Seamx

160 - 200m

EWINGTON MEMBER Ewington No.1 Seam Iris Seam* Ewington No.2 Seam* Priam Seam* Moira Seam . Stockton Seam . Homer Seamx Wallsend Seam .

. Briareus Seam

Centaur Seam

Tethys Seam* Premier No.8 Seam Zephyrus Seam* Serapis Seamx Eros Seam* 120 - 150m EWINGTON MEMBER Ewington No.1 Seam

160 - 200m

EWINGTON MEMBER Ewington No.l Seam

Iris Seamx Ewington No.2 Seam Priam Seam* Moira Seam SfnnLfnn

Achilles Seam Ajax Seam

Homer Seamx Wallsend Seam

Ares Seam

Ewinston No.S Seam 90 - 100m

UP TO 330m ARCHAEAN

20 - 30m STOCKTON FORMATION UP TO 40m

50m

UP TO 20m

UNDIFFERENTIATED BASEMENT

*Provisional names for Companv internal usase.

Collie and Wilga Basins

372

PREMIER SUB.BASIN

CARDIFF SUB.BASIN E

<T z.< :ZL

EACCHUS

ECHO

MEDUSA NIOBE PYGMALION

cc LU @ LU = = lJ5 o CE

Southern area E

<T =< \ZL

CARDIFF A

CARDIFF No. CARDIFF No. MINOS

t ,:- I

ATE

CARDIFF

CE LIJ

NEATH

ABE

ul = = -= =

BEN

C0LLIEBURN No. 0R10il

BELLONA

tt -

EOS

l-l

FIORA

Northern and central

trrr" I tor,lA

UPSILON ALPHA

area E

<l-

=< YL

APIS

WWERN URAEUS

RHEA

ut oo

UNICORN

PEGASUS

trt

COLLIEEURN JANUS

ul = = Y u.t

t(J

z=.

PHOENIX

u.t

LLI

J J

o (J

,-,::,-:", CE

lrJ oo

HYDRA BRIAREIJS

PREMTER

.,uNo !

CHI RON

PAN FJ LEDA tJ PREMIERNo.T

ul =

ICARUS

::::::::.: No.G l-l

tlt = = CE tLt

GRYPS

CENTAUR

I I I

TETHYS tl PREMIER

No.8 H

ZEPHYRU. H

lFBt''' E

TANTALIS

7e. -

tEt

Ewrr,rGTolr{0.1

Eur I

EWINGTON No.1

o.r,rrr, ]J

#i$iirilr

== | ;#.,,,',,,E -

EI = ol FL v)

Zn&, r

ffi W

H l::ut,;

L|.l

=ol

ui <rL o F

at)

inrl

.l [H'Al'**', =

II srocrror F= => = l3= lJ.l HoMER

waLLsEitD

L_j E

z,_ ot+ J- FiYAtrGToilt{o.1 LU

h ffi

= o F !z c)

ct)

Figure 2. Stratigraphic succession of coal seams.

Geology of Australian Coal Basins

E -

ffi

373 glacially striated basement surface (Low, 1958). Pebble conglomerates and sandstones occur at the base of the unit, overlaid mainly by massive- to

There are also coal seams present in the Premier Sub-basin above the accepted upper boundary ofthe Muja Member that could be included in this interval.

proportions of irregularly shaped granite, dolerite and metasediment clasts. This material is thought to be of glacial to fluvioglacial origin. It is overlaid by a probably lacustrine sequence of mudstone, siltstone and fine-grained sandstone.

Nakina Formation

poorly-bedded, grey mudstone containing variable

The Stockton Formation is present throughout the Collie Basin, although its thickness varies dramatically. The unit has a maximum thickness of 330m in the Cardiff Sub-basin, but reaches only 40m in the northern half of the Premier Sub-basin and 20m in the southern half.

Collie Coal Measures In contrast to the Stockton Formation, the Collie Coal Measures contain an arenaceous sequence with thick felspathic sandstones, interbedded sandstone/shale units and minor siltstones, shales and mudstones, along with the various coal seams. The Ewington Member is the oldest component of the Collie Coal Measures and is the only member that can be correlated across the entire Collie Basin. Its thickness varies from 48 to 64m, including an aggregate thickness of up to 14m of coal in the southern portion of the Premier Sub-basin and an aggregate ofabout 16m ofcoal in the Cardiff Sub-basin.

The Collieburn Member is the middle coal-bearing member in the Cardiff Sub-basin. Although the individual coal seams cannot be readily correlated, the Collieburn Member has been equated to the Premier and Chicken Creek Members of the Premier Sub-basin. The Member has a thickness at its type section of roughly 340m and contains numerous coal seams with an aggregate coal thickness of about 20m.

The Premier Member is restricted to the northern

and central portions of the Premier Sub-basin, although it is correlated with the Chicken Creek Member to the south. Thickness of the Member is approximately 236m and the total thickness of coal is about 30m, including many thin seams. The Chicken Creek Member is confined to the southern portion of the Premier Sub-basin. This unit has a thickness of about 216m and a similar aggregate thickness of coal to the Premier Member. The Cardiff Member is only present in the Cardiff Sub-basin, although it has been correlated with the Muja Member in the Premier Sub-basin. The type section is 140m thick but this does not include a small group of seams preserved adjacent to the western margin of the Cardiff Sub-basin above the seams normally recognised within the unit. These latter seams may represent a fourth coal-bearing member, or they may be an upper component of the Cardiff Member. Assuming they can be placed within the Cardiff sequence, the Member thickness is at least 250m and the aggregate coal thickness around 23m. The Muja Member, with a type-section thickness of 145m and an aggregate coal thickness exceeding 26m, is the topmost member of the Collie Coal Measures in the Premier Sub-basin. It includes the

thickest seam in the Collie Basin, the Hebe Seam, which has an average thickness of nearly 12m.

The Nakina Formation consists of terrestrial sandstone, claystone and conglomerate, deposited on an irregular, eroded surface. It is present throughout the basin, ranging up to 40m in thickness.

STRUCTURE OF TIIE COLLIE BASIN The northeastern and southwestern boundaries of the Collie Basin are marked by a series of northwest-trending faults (Figure 3). The basin is made up of two major grabens, separated in part by a faulted basement high (Figure 4). Southwestdipping step faults predominate, especially in the eastern sub-basin, and, with northeast-dipping normal faults, produce further horst and graben structures within the basin. The larger boundary faults, on the southwestern sides of the two grabens, and possibly a regional tilt, have given rise to a general southwesterly dip, particularly in the Cardiff Sub-basin. Strata of the Cardiff Sub-basin form a broad southwest-plunging syncline. The Ewington Member subcrops in the north, the east and in the extreme southwest of this Sub-basin, and the deepest section, with 1 300m of strata, is developed towards the middle of the southwestern edge. A small, fault-bounded remnant of the Ewington Member also lies along the northeastern boundary, associated with the formation of the Stockton Ridge. The northern and central portions of the Premier Sub-basin form a partly closed structure confined by faults, with the basal beds reaching a depth of approximately 600m. Maximum fault displacement, next to the centres of the Shotts and Premier Synclines, is between 400 and 500m.

Apart from a doubly plunging syncline along its western boundary, the southern portion ofthe Premier Sub-basin is characterised by a westerly plunging synclinal structure. This structure owes its shape to drag folding along the northwest-southeast trending boundary fault, where dips reach up to 40o. Maximum preservation of Permian sediments in this portion of the Sub-basin is 880m. The Stockton Ridge is a horst-like structure bounded by the Muja and Jackson Faults, both of which appear to die out northwards. Permian sediments in the area where the two basin lobes join are strongly faulted and folded, but lack of published information makes an evaluation of their structure difficult. Remnant fault blocks containing only the Ewington Member are also preserved at various places along the basin margins due to step faulting or a decrease

in fault throw.

Folding in the Collie Basin generally takes the form of broad rolls and warps, with dips mainly varying between 1o and 12o. Localised complex folding occurs between some faulted blocks, with the sediments contorted into a series of anticlines and synclines having major axes perpendicular to the basin margins. Drag folding is also common next to faults in the Basin, often forming a wide zone of steeply dipping strata.

Faulting within the basin is generally normal, moderate to high angle (60-90o) and trending

Collie and Wilga Basins

374

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Geology of Australian Coal Basins

375

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sEcrroil I Figure 4a. Idealised sections through the Collie Basin: Sections I and 2. northwest-southeast. However, some low-angle normal faults have also been encountered. Several reverse faults have been intersected in underground and open-cut workings, but these typically have small throws and lack continuity. Faults at the basin margins have the largest throws,

with a maximum of at least 1300m on the Jack Fault at the western margin of the Cardiff

Sub-basin. The displacements generally decrease away from the centre of the sub-basins they define, and movement may not extend beyond the Collie Basin boundaries.

Basin-boundary faults have been exposed by mining in two locations, namely the southern portion of the Muja Fault (Muja Open-cut) in the Premier Su6-basin and the Rldge Fault in the Cardiff Sub-basin (WO-5H Open-cut). The Muja Fault is a normal fault that dipi at about 80o to the northeast and lies adjacent to a heavily sheared basementfault zone (Park, 1982). Fault-related drag on the ^ adjacent sediments has developed dips of up to 40u

The Ridge Fault is also a normal fault that dips at 65o to the southeast. Elsewhere, the existence of boundary faults has been inferred from drill holes that show basement in contact with, or close to, sediments stratigraphically well above the Ewington Member.

Faulting within the basin is generally sub-parallel to the boundary faults. Individual intra-basin faults have throws olless than 200m and appear to die out before crossing the edge of the basin' The larger of these faults piobably iepresent majgr b-lock faulting of the basem-ent, but they may also be due to tensional effects created by downwarping as the boundary faults were activated' Post-depositional compaction and slumping may also be involved in the faulting process.

ORIGIN OF THE COLLIE BASIN A number of proposals have been pu! forward to account for tlie olccurrence of isolated thick piles of

Collie and Wilga Basins

378

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Figure 4b. Idealised sections through the Collie Basin: Sections B and 4.

Perrnian sediments, such as the Collie Basin, within the Yilgarn Block. These proposals differ mainly in the role played by faulting, particularly marginal

faulting, in basin evolution.

As early as 1898, Maitland and others suggested that the Collie Basin was originally a shallow, erosional depression of limited extent, into which Permian sediments were deposited. Jack (1905) recognised that the basin was at least partly fault bounded, and Woolnough (1916) suggested that Permian deposition was much more widespread, and had been preserved only in localised areas, such as Collie, due to post-depositional faulting processes.

Lord (1952) supported Maitland's original view, adding that the depression was either a PreCambrian downwarp or formed by glacial scouring. In Lord's view, sedimentation in the Permian was followed by erosion with minor faulting and folding due to differential compaction and slumping near

the boundaries. No boundary faulting was envisaged, mainly due to the lack of indicative surface features. The glaciation theory was supported by Fairbridge (L952), who described the existence of tillites resting on a smooth, polished, fresh,. grarritic basement. Lowry (1976) supported Woolnough's idea that more widespread sedimentation occurred over the southwest in the early Permian, but added that this was followed by graben development which modified local sedimentation in the late Permian. The major faulting and tilting were thought to have occurred in the Neocomian, in conjunction with separation of the Australian and Indian Plates. Based on the predominant northerly palaeocurrent

direction, Wilde & Walker (1978) suggested that the Collie Basin was not a confined palaeo-topographic depression, and, further, that post-depositional tilting accounted for the overall southerly dip ofthe

Geology of Australian Coal Basins

377

strata. They supported both glacial action and tectonics as playing an important part in the formation of the basin, with tectonics in particular influencing deposition of the Collie Coal Measures.

Stockton Ridge die out northwards, it may be possible to colrelate seams between holes at the northern end of the basin when adequate drilling data are available.

The presence of the basal tillite at Collie does little to support or negate the theory of an original palaeo-topographic depression. The apparent variable thickness of tillite in the Collie Basin, as indicated by drilling, could suggest gross irregularities in the basement surface, but even the true thickness of the Stockton Formation is questionable in some holes as they may have been terminated on striking large granite boulders in the tillite rather than the true basement level.

The sedimentary sequence in the Wilga Basin is similar to the Ewington and Collieburn/Premier Members at Collie. This, together with the presence of the Sue Coal Measures in the South Perth Basin, suggests there was widespread and similar Permian seillmentation over the southwest of Western Australia from early Permian to Kazanian times. Further, it shows that tectonism, such as the faulting that produced the Stockton Ridge, had localised affects and did not interrupt the regional

The basal section of the Collie Coal Measures, the Ewington Member, can be traced across the Stockton Ridge, and appears to correlate with the basal sequence at Wilga and Boyup Brook, as well as the Sue Coal Measures, in the Bunbury Trough, in the southern part of the Perth Basin (Kristensen & Wilson, 1985). It is therefore unlikely that discrete depressions occurred at this stage. The glacial tillite probably provided a relatively level surface over which the coal measures were deposited.

Palaeocurrent directions for the Lower Permian have been taken only from the northern part ofthe Collie Basin, where the direction of stream flow appears to have been northerly. Such a drainage direction implies that the basin was not an enclosed, internally draining depression in the early Permian. Wilson (1989) measured a total of 1766mediumscale planar and trough cross-strata in existing and disused open-cuts within the Collie Basin. This data set identified a palaeocurrent mean for the Collie Coal Measures trending to the northwest, which represents the palaeoslope dip direction. Wilson found no evidence that the Collie Basin acted as a depocentre surrounded by inwardly dipping palaeoslopes. The conflict between the palaeocurrent direction and the overall southwesterly dip of the strata confirms that post-depositional tilting has taken place.

sedimentation pattern.

The tectonism associated with the breakup of the Australian and Indian Plates has been related to the formation of the Perth and Collie Basins by Lowry (1976) and Cockbain (1984). The Perth Basin is part of a complex rift-valley system associated with this breakup, which took place 125My ago. Development began with broad downwarps along the western and noithwestern margins in the Late Carboniferous and Early Permian (Table 2). Rift valleys began to form in the Late Permian and Early Triassic time (Johnstone & others, 1973). Rift arms may have extended east to include the Collie and Wilga Basins while the bordering shield areas were uplifted. The change from the infra-rift stage to a rift-valley complex, with subsidence along fault-bounded zones, is of uncertain age and may even have been postPermian (Veevers & others, 1984, Veevers & Cotterill, 1978).

SEDIMENTOLOGY OF THE COLLIE COAL MEASURES

Lithological Features The Collie Coal Measures are mainly arenaceous in character, with three major types of non-coal

material:

There is evidence that the sequence thickens towards the southwest in both the Premier and Cardiff Sub-basins. In the former, both the Premier Member and the Muja Member exhibit a pattern of

grain size varies from veryfine to,very coarse, wltn tne larger grain sizes being dominant.

thickening towards the southwestern boundary fault (Park, 1982). No such pattern is apparent, however, for the Premier Member in the northern and central areas of the Premier Sub-basin. The Collieburn Member in the Cardiff Sub-basin also appears to thicken towards the southwest, although the lack of full stratigraphic information makes this speculative, whilst the Cardiff Member shows an irregular thickening and thinning with no apparent systematic trend.

Commonly the very coarse-grained sandstones grade into granule conglomerates.

The grains ofthe sandstones are angular to sub-angular and usually display poor to - - moderate sorting. Quartz clasts, from pebble to boulder (500mm) in size, are scattered

throughout, with rounded quartz pebbles common as lag deposits at the base of cross-s ets.

The cyclicity of sedimentation in each sub-basin is similar and this has led to a broad correlation of the three coal-bearing successions. However, basinwide

The sandstones typically have a clay-rich

matrix, apparently derived from the decomposifion of feldspar grains. They often display planar, and, to a lesser exte-nt, trough-Jhaped cross-stratification. Scour and fill structuies are also present. The cross-bed sets are of medium scale, with thickness normally between 100 and 500mm and strong grain-size sorting in adjacent foreset laminae.

correlation of the individual seams is difficult above the lower Premier/Collieburn Members, but this should not automatically invoke contemporaneous faulting. The Hebe Seam has a unique thickness (12m) which shows that some major sedimentological difference existed between the sub-basins during this period of deposition.

Formation of the Stockton Ridge occurred after the deposition of the Lower Premier/Collieburn sediments. As most of the faults associated with the

Sandstones. The sandstone units are laterally continuous and can develop large thicknesses. They are commonly weakly lithified and are felspathic to arkosic in composition. Their

Interbedded Sandstones and Siltstones (Laminites). These units are up to several metres in thickness. They are composed of

Collie and Wilga Basins

378

Table 2. Possible tectonic history of southwestern Australia. C arb

onifero u s o r S ak marian :

Broad downwarps over western margin of Yilgarn Block. Glacial activity and tillite deposition, followed by extensive sedimentation including coal-measure deposition. Some regional downwarping or faulting resulting in cessation of coal-forming conditions.

Early Permian to Kazanian: Tensional stresses associated with early stages of rift- valley formation led to minor movement on the Darling Fault and initial development of the marginal faults (e.g. along Stockton Ridge and Jack Fault) of the Collie and (probably) Wilga Basins. Faults developed along existing basement Iineations. Deposition of the Collieburn and Premier Members in partly separated basins at Collie, and similar sediments elsewhere in the southwest of the Yilgarn Block.

Tq.rtariq.n: Widespread deposition of coal-bearing fluvial sediments. Further margin-fault movement at

thin beds of very fine- to fine-grained sandstone, with occasional coars.er fractions, interbedded with thin carbonaceous or micaceous siltstones, or both. The relative

proportion of argillaceous to arenaceous intercalations in these units is variable, with both dominating in different units. Sedimentary structures observed include upward fining, small-scale cross-bedding and convolute lamination.

Siltstones, Shales and Mudstones. Argillaceous units in the Collie Coal Measures are commonly <1m thick but may be several metres thick in some parts of the sequence. They range from horizontally bedded to massive, and can be dark grey to black when their carbon content is elevated. Minor coal bands are associated with these units. Argillaceous materials also occur as intraformational clasts within some of the sandstone bodies.

Depositional Environment The clastic sediments of the Collie Coal Measures display features of bed-load fluvial systems as defined by Galloway & Hobday (1983). They are characterised by a dominance of sand in broad, continuous belts. Sand isoliths of the interval between the Premier No.4 and Premier No.6 Seams, for example, highlight a linear, sand-rich zone trending roughly north-south down the basin (Figure 5). Average sandstone percentages for most of the seam interburdens in the Premier Member fall within the range of 50 to 90Vo, a range quoted by Galloway & Hobday (1983) as indicative of bed-load systems. Consequently, the large fluvial sheet sands of the Collie Coal Measures would appear to have resulted from the rapid lateral migration of bed-load channels.

Straight bed-load channels are typified by uniform, minor depths of basal scour, which explains the observed low relief at the base of sand units within the Collie Coal Measures, and the consequent

Collie, accompanied by deposition of the Cardiff and Muja Members. Presumably other sediments deposited later to achieve present degree of coalification.

Triassic to Early Cretaceous: Major rift development in the Perth Basin, increasing into the Cretaceous Period, with some uplift of shield areas east of the Darling Fault. Major faulting in the Yilgarn Block along pre-existing faults preserved isolated areas of Permian strata.

Early Cretaceous: Breakup of the Australian and Indian Plates.

Latter to P o st - C ret a.c e ous : Major erosion east of the Darling Fault, including partial removal of Permian and younger sediments at Collie and elsewhere on the Yilgarn Block. IJnconformable deposition of the Nakina Formation. preservation, as remnant flood-plain deposits, of laterally continuous sheet-like or tabular mudstone and siltstone units. Wilde & Walker (1978) also observed the bottom surfaces ofthe sandstone units to be mostly planar, displaying both erosional and non-erosional features. Lowry (1976) and Park (1982) postulated similar origins for the sandstone sequences. They suggested that the sand accumulated by lateral .accretion, with longitudinal and transverse bed forms coalescing as the stream courses migrated over the width of the drainage system.

The laminite components of the Coal Measures were deposited during overbank flow. They may also include some bed-load material built up in overbank deposits when severe flood events occurred. The carbonaceous argillaceous units (e.g. silty shales and mudstones) were deposited in floodplain areas in conjunction with shallow lacustrine conditions, an environment conducive to backswamp development and vegetation growth. Minor coal seams are therefore commonly found associated with such units.

In contrast to the sandstones, the laminite and argillaceous units were formed mainly by vertical

accretion. The coal seams were derived from accumulations of peat in swamp environments that formed following the cessation of high-energy fluvial

sedimentation.

The assemblage of lithofacies features in the Collie Coal Measures can be used, in conjunction with the

classification schemes for braided-stream deposits proposed by Miall (L977) and Rust (1978), to

determine an appropriate depositional model for the sequence. The main lithofacies are planar crossbedded sandstone units and subordinate trough cross-bedded sandstones. Minor lithofacies include lag-conglomerate deposits, intraclast-bearing sandstones, finely laminated sandstones and shales, massive to seat-earth siltstones and mudstones, and, of course, the coal seams.

Geology of Australian Coal Basins

379

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ColIie and Wilga Basins

, ' -4r -i-

380 The vertical lithofacies sequence in the Collie Coal Measures (Figure 6) closely resembles that of the Platte model for braided-stream deposits as defined

by Miall (1978). This model is thought to represent broad, very shallow rivers lacking well-defined topographic differentiation between active and inactive areas. Few fining-upward cycles are developed. The modern, braided Lower Platte River has, as an illustration, a bankfull width of around 0.5km and an average bankfull depth of between 0.2 and 0.5m. It is possible that parts of the sequence in the Collie Coal Measures, where trough cross-beds or fining-upward cycles become common, are closer to the South Saskatchewan model (Miall, 1978), of

which the Platte type is a variant.

The South Saskatchewan type represents broad, deep, low-sinuosity rivers with greater

differentiation than the Platte type between channel, bar and bar-top facies. The fining-upwards cycles, which can develop in this type of sandy, braided river, are similar to the point-bar cycles of meandering rivers. The modern South Saskatchewan River is roughly 0.6km wide and has an average channel depth of 3 to 5m. Miall (1985) emphasised that, although fluvial sediments can be categorised into a number of models, every possible gradation between any two of the models can be expected.

It is believed that the depositional environment in

the Collie region was influenced by tectonic activity. Coal-seam interburden thicknesses within the Cardiff and Premier Sub-basins show similar trends. In the Cardiff Sub-basin the interburden between the Griffin Seam and the Icarus Seam, from the Iimited data available, shows a tendency to increase towards the main southwestern margin of the basin, whilst the interburden between the Wyvern Seam and Collieburn No. 2 Seam, in the southwest of the Cardiff Sub-basin, also thickens towards the faulted basin margin.

In the north, however, where the data are concentrated away from the basin margin, the interburden thicknesses show no trend. It is believed that a major basement-margin fault exists on the southwest side of the Cardiff Sub-basin, and that syndepositional movement occurred on this fault. Further evidence from the Muja Member can be used to support the existence of growth faults. Park (1982), for example, observed wedge-shaped sandstone units adjacent to the Muja Fault in the Muja Open-cut, which could indicate small-scale localised movement. Large-scale drag has also produced a reversal of regional dip next to this fault.

It seems clear that the depositional history and

cyclic nature of sedimentation in the Collie Coal Measures has been influenced by recurrent activity on the basin-margin faults. Miall (1981) has described basin-fill models that can be applied to such alluvial depositional systems. His graben model, with transverse flow from the margins feeding longitudinal flow along the basin axis, could be used for the Collie Basin (Figure 7), and the palaeocurrent directions obtained by Wilde & Walker (1978), and also Wilson (1989), provide

support for this concept.

No record of sedimentation is present after the Permian until a thin cover of continental sandstone, claystone and conglomerate which was laid down on a gently undulating erosional surface in Cretaceous

to Tertiary times. This unit, the Nakina Formation, is commonly masked at the surface by Tertiary laterite and Recent sand.

COAL QUALITY Collie coal has the outward appearance of black coal but chemical and physical properties that cover a range normally represented by lignites, sub-bituminous coals and high volatile bituminous coals. It is classified using Seyler's Coal Chart as an ortho-lignite, and mean maximum vitrinite reflectance values of 0.3 to 0.57o support this classification. According to Lowry (1976), the rank of Collie coal suggests that a minimum of 460m of cover material must have been eroded from the sequence now exposed.

Chemical and other Characteristics The in silu moisture content of Collie coal ranges from 23 to 277o (Table 3), with mined values fluctuating according to seasonal variations. The moisture content quickly drops to 177o on exposure, leading to rapid decrepitation and almost to disaggregation within two to three months.

Inherent ash is low by Australian standards and most quality problems are associated with roof and floor diluents and occasional thin interlaminated dirt bands. The operating mines extract coals of in situ ash generally between 3 and IlVo. No washing facilities are required and most quality problems are solved by scheduling and blending during mining. Volatile matter in Collie coal varies between 25 and 30Vo, at a25Vo moisture basis. The volatile fraction produces about 5 to 78Vo liquor, 3 to 77o tar,5 to 18Vo free water, and 7 to l07o gases. Of the gases, some

Table 3. Summarised analytical data for Collie Basin coal. PROXIMATE ANALYSIS %

ULTIMATE

ASH FUSION

ASH ANALYSIS %

(Reducing oC)

ANALYSIS (dafl Vo

Moisture Ash Volatile Matter

27.0

Fixed Carbon

42.0

Specific Energy

20.5

25.0 6.0

c H N o s

0.5

SiOz 45.0 Alz0r 25.0 FezOe I2.0 CaO 3.0 MgO 1.5

0.05

TiOz

75.0 4.5 T.4

18.6

NazO KzO PzOs MnsOr SOe

3.0

Deformation Sphere Hemisphere

1330

0.1

Flow

1400

0.3

2.0

MJ/Kg

1.2

Geology of Australian Coal Basins

1200 1280

:181

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MUJA OPEN CUT

St Gm

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Fsc

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Collie and Wilga Basins

382

Individual seams display consistent hardness. However, values do not reflect the relative ease of grinding found during commercial coal preparation. Limited abrasion index data shows consistently low values between 30 and 8OmgFe/kg coal.

Lo0grtudlnol

Sandy braided river system - major sand deposition

Collie coal is highly reactive, ranging between 0.05 and 0.2mglmin (average 0.1mg/min) and is thus very suitable for direct-reduction processes.

Coal Petrology The lithotypes in Collie coal vary from dominantly dull banded durainous material to bright banded, vitrainous material. Banding is generally <1.5mm in thickness, with rare vitrain bands up to 50mm. Thick, dull bands are much more frequent, with dull sapropelic coal common, especially in plies near seam roofs. These sapropelic coals may be 1 to 2m thick. They have values of L2-30Vo Ash, and have often been logged in the past as "black shales" by

non-professionals.

The coal's petrographic characteristics can be used to distinguish between the various units within the sequence and to identify some of the individual seams. The lack of a good spread of data for the whole Basin precludes a definitive statement on

lateral seam variation, but the indication is that seams are uniform in maceral distribution.

Extensive sunkland swamp --coal seam deposition Figure 7. Schematic basin-fill model for the Collie Basin (modified after Miall, 1981). 30Vo is Cjz,24Vo CHa, LTVo Hz,lSVo CO,57a CzHa,4% Nz and 2Eo corrrplex hydrocarbons.

Ash fusion temperatures, for initial deformation in a reducing atmosphere, vary between 1040oC and 1600oC. The temperature is inversely proportional to the presence of fluxes, chiefly iron oxide but also calcium, magnesium and minor alkali oxides. Commonly, the bulk of the ash consists of the refractory components silica and alumina. Total silica ranges from 30 to 7\Vo, and is generally greater than 457o, while total alumina ranges between 20 and 40Vo. T}:'e total proportion of flux material ranges from zero to 507o, but is generally <307o.

Collie coals generally have low trace element concentrations (Davy & Wilson, 1984, 1989). However, individual seams may have elevated values as may random samples (e.g. higher lead levels in the upper seams of the Cardiff Member).

Fly ash produced by combustion of Collie coal is of low resistivity (3 x 106Q-m at 140oC and \Vo moisture), resulting in good electrostatic precipitation performance. The specific energy of Collie coal, at 25Vo moisture, varies between 18.0 and 22.5MJA<g, but is commonly around 20.5MJ/kg. On a dry, ash-free basis, the specific energy ranges between 28.5 and 31.6MJ/kg. The dry, ash-free value increases with depth, and coals of the Ewington Member typically have the highest values ranging between 29.6 and 31.6MJ/kg. The Hardgrove grindability index is variable (30110) with values between 40 and 70 most common.

Ewington Member. Of the three subdivisions of the Collie Coal Measures represented in the basin, the coals of the Ewington Member have the lowest vitrinite content, ranging from 13 to 28Vo. The Priam Seam is highly anomalous in this sequence, with 58Vo vitrinite. The liptinite content of the Ewington seams is high by Australian standards, and is consistently high in contrast to the variability in other members of the sequence. Total liptinite in coals of the Ewington Member varies between I and l8Vo. The liptinite macerals are mainly sporinite with rarer resinite, cutinite and alginite components.

Inertinite is abundant in these seams, varying between 50 and 68Vo.The inertinite is composed mainly of semifusinite and inertodetrinite, with lesser fusinite, sclerotinite, and rare macrinite and micrinite. Collieburn and Premier Members. Although the Collieburn and Premier Members appear stratigraphically equivalent, it is difficult to see this from their maceral assemblages because of a lack of data for the lower Collieburn. Data for the Collieburn Member is dominated by the seams in its upper portion (Phoenix No. 2 Seam and upwards), and, as expected, this part of the sequence best fits the top of the Premier Member. Petrographic data available for the Collieburn Member are very consistent. The vitrinite content of these seams is higher than for those of any other member, ranging from 60 to 757o. Liptinite is variable (1.7-8.2%), with sporinite and liptodetrinite as major constituents and rare amounts of resinite, cutinite, alginite and suberinite. Inertinite ranges between 18 and 357o, and is usually made up of semifusinite, fusinite, sclerotinite and inertodetrinite with minor macrinite and micrinite.

Geology of Australian Coal Basins

383

Although data are limited for seams below the Premier No. 4 Seam in the Premier Member, the trend is for lower vitrinite than the Collieburn Member (24-687o), with consistently and significantly higher liptinite contents (4-25Vo). The liptinite is mainly sporinite, with minor resinite and cutinite. The proportion of inertinite is highly variable (13-6L7o), with the lower values generally from the Premier No. 6 Seam and above. The inertinite is mainly semifusinite, with lesser amounts of inertodetrinite, fusinite and sclerotinite, and minor macrinite and micrinite.

Cardiff Member. Except where the Cardiff Seam is split, the Cardiff Member has a constant vitrinite content ofbetween 50 and 60Vo.T}r,e liptinite content is low by Collie standards at2-67o, but is again dominantly sporinite with lesser resinite and cutinite. Inertinite ranges from 35 to 45Vo (except for the Cardiff Seam splits) and is mainly semifusinite, fusinite, sclerotinite and inertodetrinite with minor micrinite and macrinite. Muja Member. The seams of the Muja Member are similar to those of the Cardiff Member (Sappal, 1982), but have a higher liptinite content (2-67o). The liptinite is usually sporinite and cutinite, with rare resinite and alginite. The vitrinite content of Muja Member seams varies between 34 and.707o, whilst inertinite ranges from 13 to 53Vo. Inertinite is generally >257o, being dominated by fusinite, semifusinite and inertodetrinite with minor micrinite.

Interpretation The lateral continuity of seams in the Collie Basin suggests that deposition mainly occurred on a wide, shallow, level, swampy plain. An initially slow syndepositional-subsidence rate is postulated, as suggested by the high inertinite content ofthe

seams in the Ewington Member. This high inertinite

content, indicative of comparatively 'dry' conditions, characterises Collie coals and is typical of Gondwana coals. These drier conditions changed to comparatively'moist' conditions during the deposition of the more vitrinite-rich Collieburn and Premier Member, suggesting that higher syndepositional-subsidence rates were initiated in post-Ewington times. Such an interpretation is consistent with the gross depositional model of initially widespread sedimentation followed by fault-influenced deposition and associated differences in development between the Cardiff Sub-basin and the Premier Sub-basin.

RESOURCES Most drilling in the Collie Basin has been limited to depths of <300m, and, as a result, the total coal resource has not been completely defined. In situ resources are currently estimated at approximately 1000Mt Measured, 700Mt Indicated and 60OMt

Inferred. Extractable open-cut coal in the basin is usually taken only to include seams greater than 1m thick, in areas with incremental stripping ratios generally less than 10:1, whilst extractable underground coal only includes seams greater than 2m thick. An evaluation by the Geological Survey of Western

Australia (Wilson & others, 1983) estimated extractable resources, with current mining technology, at 398Mt amenable to open-cut mining and 190Mt suitable for underground operations. However, the authors of this Chapter consider that the extractable resources are higher, with totals exceeding 500Mt available for open-cut mining and 320Mt for underground methods.

MINING FACTORS Six mines currently operate in the Collie Basin. In the southern area of the Premier Sub-basin, the Griffin Coal Mining Company Ltd. produces coal from two open-cut mines (Muja and Chicken Creek), whilst in the Cardiff Sub-basin, Western Collieries Ltd. operates a series of pits collectively termed W0-5. This company also operates three underground mines in the Cardiff Sub-basin (WD-2, WD-6 and WD-7).

In open-cut mining the main operating problems are related to the saturated and weakly lithified interburdens that are composed mostly of medium to very coarse-grained kaolinitic sandstones. This material, unless dewatered, requires a seamfollowing mining approach that limits extraction to gradients of one in five, and sometimes less in winter months. Under these conditions highwall stability is achieved by low batter angles of35-40o. Dewatering is a major part of the mining strategy in the Muja Open-cut, with each saturated interburden horizon, as well as two aquifers below the Hebe Seam, requiring dewatering. Depressurisation of ten aquifers, up to 200m below the Hebe Seam, is also carried out to assist in prevention offloor heave (Vogwill & Brunner, 1985), with partial water extraction down to 120rn below the Iona Seam. Underground mining is also considerably influenced by groundwater. The Wyvern Seam accounts for the bulk of production, and sits within a pressurised, saturated sequence of generally soft, porous sandstones that yield some 29Ml of water per day into the workings. In all, 6 to 8t of water are removed per tonne ofunderground coal produced. To achieve stability in bord and pillar underground workings, an average 2.4m working section is maintained leaving a 1 to 1.5m coal beam. Wongawilli-type total-extraction mining is also used to achieve higher recovery and productivity where possible. Dewatering for production areas is achieved by advanced development to effect predrainage. The installation of standpipes with gate valves in the roof and floor helps depressurise the immediate strata, whilst advance dewatering using surface bores is also necessary for development in deeper areas.

UTILISATION OF COLLIE COAL Collie coal has been used mainly for steam raising. Early demand for the coal was dominated by locomotives and steamships, but, since the coal is easy to grind, it is now commonly utilised in pulverised form, mainly for power generation. Other favourable characteristics for this purpose include its high volatile content (enabling stable flame and buiner conditions) and low ash yield. Of the coal mined at Collie, 76Vo is used by the State Energy Commission of W.A. in power stations at Muja, Kwinana and Bunbury. A further 13% is used

Collie and Wilga Basins

384 by the Alumina industry for on-site power generation. Several smaller industrial uses, including air preheating, concentrate drying and reduction in smelting processes (7%), and cement manufacture (4Vo) account for the remaining coal production.

In addition to combustion applications, Collie coal was used in the early 1950's for production of town gas from a carburetted water gas plant. The economics of manufacturing higher-grade products, such as char, briquettes or form coke from Collie coals, have also been assessed on numerous occasions. Although metallurgical applications for briquettes exist (and have proven very successful) no additional markets have yet opened in this area. The high moisture content of raw Collie coal, its tendency to spontaneous combustion and poor

SEAM NAME TO

EUDOXIS SEAM FLAMSTEEO SEAM GASSENOI SEAM

fos

140

GSS

040 040

HIPPABCHUS UPPER SPLII HIPPARCHUS LOWEN SPLII

LA GRANGE SEAM

140

rGs

0.50

070

MENELAUS SEAM

070

100

NANSEN SEAM PICABO SEAM

2 13

260

040

051

034

052

010 010 01a

020 02r

090

1 0t

long-term mechanical properties have all inhibited long-distance transport, such as would be required for the export market. It is possible that general utilization and export opportunities could be enhanced by char and briquette manufacture.

flEINEF SEAM SCHITLEA SEAM

WILGA BASIN

ZACH SEAM

a Es

s cs

IYCHO SEAM ULUGH SEAM VEANE S€AM WERNER S€AM

uts vfs wfs

030

AO-7Om ol s.ndslonc, sill and sh.le

Regional Setting The Wilga Basin is genetically similar to the Collie Basin (Ashton, 1984), with sediments occupying a narrow (0.5-3.5km) and deep (0.6km) lenticular graben-like structure approximately 14km long. The Geological Survey of Western Australia (1975) has tentatively subdivided this structure into the

East and West Wilga Sub-basins, but the basis of this is unclear and it appears unlikely that two completely separate structures exist.

Stratigraphy

ATTAS SEAM BULIIALOUS SEAM CURIE SEAM

DOAAOO SEAM EULEB SEAM FIFMICUS SEAM GEIMALOI SEAM HEVEL SEAM IilDUS UPPEB SPIIT INOUS LOWER SPLIT

cus

oos

EUS

076

152

000 1 1a

cfs

HES

0 9l 151

076 041

3 20 1a0 221 2 74 20E 198 152

JOLTIOT UPPEF SPLIT JOLLIOI TOWEB SPIIl KEPIER SEAM

JOU JOL

030 076 030

2 13

!AMBERT SEAM MARIUS SEAM

aas

0 10 0 15

064 046

(fs

MAS

Sedimentation commenced with a grey, conglomeratic diamictite up to 15m thick. Hard, granitic boulders within this unit may have prevented drill penetration through to undoubted basement material.

60-lom

252 130

ol sandstone

STOCKTON FM MUOSTONE

Above this interval is a blue-grey mudstone unit,

approximately 20m thick, which contains sporadic

greenstone and granite clasts. This distinctive unit closely resembles the Stockton Formation of the Collie Basin. It is overlaid in turn by a sequence of

fine to coarse-grained sandstones, 60m thick, which underlies the basal coal measures. The basal coal measures are very similar to the Ewington Member in the Collie Basin and are considered provisionally to be stratigraphically equivalent. This is supported by a very similar maceral assemblage in the coal seams. The sequence contains a number of seams or seam splits, with 14

defined to date over an 85m stratigraphic interval

(Figure 8).

Final correlation of seams above the Ewington Member equivalent is not possible until a more regional spread of drill holes is achieved. The available data suggest that a Collieburn Member equivalent is also present, with widely spaced seams over a large stratigraphic interval. Drilling in the northwest of the basin has also intersected what may be a Cardiff Member equivalent, but this has yet to be proven.

Figure 8. Stratigraphic succession of coal seams, \ililga Basin.

Structure Insufficient drilling has been carried out to fully define the structure of the Wilga Basin, and information is largely confined to the West Wilga Sub-basin where the sequence strikes roughly north-south and has a westerly dip of about 8o. Major faulting is also evident at and near the basin margins. Faults identified within the basin to date are normal in nature, with throws of between 6 and 120m.

Coal Quality Although available analytical data are almost restricted to the Ewington Member equivalent, the coal quality in the Wilga Basin appears to be similar to that of typical Collie coal. Ash values, on a 257o moisture basis, range between 4.5 and l2Vo in the

Geology of Australian Coal Basins

385

main seams. Moisture holding capacity tests, however, suggest that in sifu moisture for Wilga coal is probably closer to 227o. Total carbon and oxygen contents are comparable with the Ewington Member coals of the Collie Basin, and so it is surprising to find-that the. specific energ"y appears significantly lower, with a dry, ash-free average of 28.5 MJ/kg. Sulphur values are characteristically low (0.26-0.6IVo). Ash Fusion temperatures (initial deformation in a reducing environment) vary between 1100 and 1200oC, probably reflecting a noticeably higher siderite content compared to the coal at Collie.

Resources Due to limited structural knowledge, resource

estimates for the Wilga Basin are probably conservative. Geophysically logged holes have been used to provide Indicated resources outside areas defined by diamond drilling.

Total in sif u resources for the Ewington Member equivalent are 3OMt Measured and 5SMt Indicated. These estimates are based on only six cored holes in the West Wilga Sub-basin, supported by other non-cored, geophysically logged holes outside the cored borehole area. Significant resources may also occur in the Collieburn Member equivalent, mainly for potentiai underground mining, but such resources await further defrnition at the present time.

GALLOWAY, W.E.& HOBDAY, D.K., 1983:

Terrigenous Clastic Depositional Systems: applications to petroleum, coal and uranium exploration. Springer-VerJog, New York.

GEOLOGICAL SURVEY OF WESTERN AUSTRALIA, 1975: The Geology of Western Australia. Geological Suruey of Western Australia,

Memoir,2. JACK, R.L., 1905: Report on the Royal Cornmission on the Collie Coalfield. JOHNSTONE, M.H., LOWRY, D.C. & QUILTY, P.G., 1973: The geology ofsouthwestern Australia - a review. Journal of the Royal Society of Western Australia,56, 5-15. KRISTENSEN, S.E. & WILSON, A.C., 1986: A review of the coal andlignite resources of Western Australia. In Geology and Explorafion. Edited by D.A. Berkman, Council of Mining and Metallurgical Institutions Congress. 13th. 1986,

2,87-97. LORD, J.H., 1952: Collie Mineral Field. Geological Suruey of Western Australia Bulletin, 105 (1).

LOW, G.H., 1958: Collie Mineral Field. Geological Suruey of Western Australia Bulletin, f 05 (2). LOWRY, D.C., 1976: Tectonic history of the Collie Basin, Western Australia. Journal of the Geological Society of Australia, 23, 95-104.

MAITLAND, A.G., 1898: The Collie Coalfield.

Geological Survey of Western Australia. Annual Progress Report 1898, Part l, 13-21.

REFERENCES ASHTON, P.J., 1984: Wilga Exploration Summary Report. Western Collieries Ltd. Report No. 64. BACKHOUSE, J. & WILSON, A.C., 1988: New records of Permian and Cretaceous sediments from

southwestern Australia. Western Australia

Geological Suruey Professional Papers, Report,

25,7-5.

BACKHOUSE, J., 1990: Permian Palynostratigraphy of the CollieBasin, W.A. Reuiew of Palaeobotany and Palynology, 67, 237 -314.

CHAMBERLAIN, N.G., 1948: Preliminary report on the geophysical survey ofthe Collie coal basin. Bureau of Mineral Resources Geophysical Report, 1. (reproduced, in Geological Suruey of Western Australia Bulletin, 105, 157-163, 1952). COCKBAIN, A.E., 1984: Basins and barrels: the geological background into the search for fossil fuels in Western Australia. Journal of Royal Society of Western Australia,6T (1), 18-20. DAVY, R. & WILSON, A.C., 1984: An orientation study of the trace and other element composition of some Collie coals. Record 1984/3, Geological Survey of Western Australia. DAVY, R. & WILSON, A.C., 1989: Geochemical study of inorganic components of the Collie Coal Measures: Chemical analyses of samples from the Collie Coal Measures. Western Australia Geological Suruey, Professional Paper, No. 26, 1-30.

FAIRBRIDGE, R.W., 1952: The Permian of south western Australia. Cong. Int. Geol., 19th Sess. Alger., Symposium Series de Gondwana, L36146.

MIALL, A.D., 1977: A review of the braided river depositional environment. Earth Science Reviews,lS, 1-62. MIALL, A.D., 1978: Lithofacies types and vertical profile models in braided river deposits: a summary. In Miall, A.D. (Editor): Fluvial Sedimentolo gy. Canadian Society of Petroleurn Geologists Memoir, 5. MIALL, A,D., 1981: Analysis of fluvial depositional systems. American Association of Petroleum Geologists, Education Course Note Series, 20, 75. MIALL, A.D., 1985: Architectural element analysis: a new method of facies analysis applied to fluvial deposits. In Recognition of Fluvial Depositional Systems and their Resource Potential. Society of Economic Palynologists and Mineralogists, Short Course -19, 33-81.

PARK, W.J., 1982: The geology of the Muja Sub-basin A model for the Collie Basin, Western Australia. Australian Coal Geology, 4, 319-340. PLAYFORD, P.8., COCKBAIN, A.E. & LOW, G.H., 1976: Geology of the Perth Basin, Western Australia. Geological Suruey of Western

Australia Bulletin, LZA.

RUST, B.R., 1978: Depositional models for braided

alluvium. In Miall, A.D. (Editor): Fluvial Sedimentolo gy. Canadian Society of Petroleurn Geologists Memoir, 5, 605-625.

SAPPAL, K.K., 1982: Petrography of Collie coal from the Muja Sub-basin, Western Australia. Australasian Institute of Mining and Metallurgy, Annual Conference Proceeding s, 433-439. VEEVERS, J.J. (Editor), 1984: Phanerozoic Earth History of Australia . Clarendon Press, Oxford.

Collie and Wilga Basins

386 VEEVERS, J.J. & COTTERILL, D., 1978: Western margin of Australia: evolution of a rifted arch system. Geological Society of Arnerica Bulletin, 89, 337-355.

WILLIAMS, I.R., 1975: Chapter 1: Precambrian. In Geology of Western Australia. Geological Suruey of Western Australia Memoir, 2, 65-70.

VOGWILL, R.I.J. & BRUNNER, I.G., 1985: Dewatering anddepressurisation of the Muja Open Cut, Collie Basin, Western Australia. In Hydrogeology in the Service of Man. Mem.oirs of

WILSON, A.C., 1989: Palaeocurrent patterns in the Collie CoalMeasures - the implications for sedimentation and basin models. Western

the 18th Congress of the International Association of Hydrogeologists, Cambridge, Part

Australia Geological SurueyProfessional Papers, Report 25,85-gL.

4,207-223.

WILDE, S.A. & WALKER, I.W., 1978: Palaeocurrent directions in the Permian Collie Coal Measures,

WILSON, A.C., 1990: Collie Basin, in Geology and

WILDE, S.A. & WALKER, LW., 1982: Explanatory notes on the Collie 1:250 000 geological sheet, Western Australia. Geological Suruey of Western Australia.

WOOLNOUGH, W.G., 1916: Geology. In Report of the Royal Commission on the Collie Coal Industry. Western Australia Parliamentary Paper No 1916/ 14.

Collie, Western Australia. Geological Survey of Western Australia, Annual Report 1977, 4l-43.

Mineral Resources of Western Australia. Western Australia Geological Suruey Memoir, 3, 525-531.

Geology of Australian Coal Basins

387

GEOLOGICAL SETTING

Werth Basin

The Perth Basin is a half-graben extending from the Murchison River to the south coast of Western Australia; a distance of about 1000km. It is bounded to the east by the Darling Fault and to the north by the Northampton Block. fts western and southern offshore limits have not been clearly defined, but

they probably lie under the continental slope (Figure 1).

SE Kristensen

The basin covers an area ofabout 45 000km2 onshore and a similar area offshore. It contains up to 15 000m of Phanerozoic sediments ranging from Silurian to Tertiary, resting on a basement of Archaean and Proterozoic igneous and metamorphic rocks. Except in the Irwin River, Geraldton and Hill River areas, however, outcrop exposures ofthese rocks are generally poor. The dominant structural element of the Perth Basin is the Darling Fault, a growth fault which defines its eastern margin. The maximum throw of this fault is thought to exceed 15 000m. It probably developed during the Silurian, with the greatest movements taking place between the Middle Triassic and the early Cretaceous (Ashton & others, this volume). Several major structural subdivisions are recognised in the basin, separated by basement inliers and

shallow basement ridges. These include the Dandaragan and Bunbury Troughs, the Vasse Shelf, and the Coolcalalalya and Irwin Sub-basins. There is no evidence of compressional tectonism in the Perth Basin, and its tectonic style is characterised by normal faulting. It is generally held that this faulting is the result of draping and differential compaction over basement ridges, thought to have been positive features thrbughout the Phanerozoic (Playford & others, 1976), but

studies of coal rank/deformation relationships, particularly on the Vasse Shelf, suggest that some of these features may have been tectonically emergent in post-Permian and even post-Jurassic time.

Distribution of Coal-bearing Strata The Perth Basin has been known to contain significant quantities of coal since 1840, when outcrops of Permian coal were discovered at Irwin River. These lignitous coals are of relatively poor quality and were never commercially exploited. A number of trial underground workings have been dug, however, the most recent being in 1948.

More recent discoveries of economic significance are those of shallow Jurassic coal at Hill River and deeper-lying Permian coal on the Vasse Shelf. These deposits, as well as extensions of the historically known coals at Irwin River, are currently being evaluated. Permian and Mesozoic sediments are widespread throughout the Perth Basin, and account for most of the infilling sequence. Pre-Permian sediments are confined to the northern part, where more than 3000m ofSilurian red-beds are preserved. Sakmarian to Late Permian coal measures occur throughout the dominantly fluvial Permian sequence in the southern Perth Basin. In the north, however, coal-bearing strata are confined to a part ofan Early Permian sequence occurring in a succession where most of the rocks are of marine origin.

Perth Basin

Figure 1. Structural subdivisions of the Perth Basin.

Geology of Australian Coal Basins

Coal seams also occur in the Lower Jurassic, in a fluvial-deltaic sequence with evidence of marine incursions. Seismic surveys and stratigraphic wells show that these coals are distributed widely over the northern Perth Basin. Other coal has been noted in Early Cretaceous strata in the southern Perth Basin, notably at Alexandra Bridge, but the occurrences have no economic significance.

PERMIAN COALS The Perth Basin contains coals ranging in age from Sakmarian to Late Permian, but the thickest and most extensive seams are found in the early Permian Artinskian strata. The Artinskian coals are widespread in the subsurface of the entire basin, but only occur at mineable depths in two structural subdivisions, the Vasse Shelf in the south and the Irwin Sub-basin in the north.

Vasse Shelf The Vasse Shelf is a fault block in which Precambrian basement forms a terrace at depths

intermediate between the outcropping Leeuwin Block to the west and the more deeply buried Bundbury Trough to t^he east (Figure 2). It covers an areas ofabout 400km" onshore, but its northern extent under Geographe Bay is not well defined. It is bounded to the east by the Busselton Fault which has a throw of up to 5000m, and to the west by the Dunsborough Fault which has a thlow of at least 1000m. The faults converge to the south. The shelf area contains a Permian sequence up to 1800m thick, equivalent to the Sue Coal Measures in the Bunbury Trough (see below). The coal measures range in age from Sakmarian to Late Permian, and on the Vasse Shelf they are unconformably overlain by 80 to 250m of Early Cretaceous sediments. Coal

rank varies from bituminous in the Early Permian to lignitous in the Late Permian. Where basement is shallowest, the overlying Cretaceous sediments lie directly on Early Permian coal measures, and it is the Permian strata in these areas which have the best economic potential. The most extensively explored area ofthese beds is the southern portion of the shelf, where the Early Permian coal seams are truncated by the unconformity.

It is highly unlikely that the present day structures

Figure 2. Distribution of Early Permian coal measurea on the Vasse Shelf, with typical coal-measures section in the Vasse Shelf area. sandstones with abundant accessory garnet, which indicates that they are derived from the gneissic rocks of the adjacent Yilgarn Block. These sediments were deposited in a fairly high energy terrestrial environment such as a river valley. Coals and overbank sediments generally constitute only a

minor proportion of the sequence, but the interval near the base of the Permian has the best economic potential. These basal Permian coals are of Artinskian age,

define the depositional limits of the coal measures, or that they had any influence on Permian deposition. The similarity of the Permian sequence at Collie and Wilga to that of the Bundbury Trough

and are possibly equivalent to the Ewington Member in the Collie Basin. The measures consist of eight coal horizons in a cyclic sequence ofpoint bar deposits, occurring over a stratigraphic interval of 120m (Figure 2).

time when the Darling Fault and subsidiary structures were quiescent or less prominent features (Ashton & others, this volume). Subsequent movement during the Mesozoic resulted in coal measures west of the Darling Fault being buried in places to depths exceeding 5000m, probably until Neocomian time when tectonic activity resulted in the uplift of the Leeuwin Block and the adjoining Vasse Shelf. This activity was probably associated with the extrusion of the Bunbury Basalt and the intrusion of dolerite sills and dykes which have been intersected within Permian coal measures in the Bunbury Trough.

The lowermost seam lies about 250m above the Precambrian basement, which is itself directly overlain by a claystone unit similar to the Stockton Formation of the Collie Basin. As in the Collie sequence, this claystone unit is underlain by a basal tillite, and drop-stones, presumably of glacial origin, occur throughout the succession.

and Vasse Shelf supports the view that the coal measures were deposited over a wide area during a

Stratigraphy and Coal Deaelopments With the exception of possible glacigene sediments at the base, the Permian sequence on the Vasse Shelf consists predominantly of immature arkosic

Four of the seams in this interval are considered to have economic potential. They have been intersected by drill holes, over a strike length of 17km, at depths ranging between 180 and 450m. The thickest intersection is 4m in the informally named Osmington seam, and all the seams attain thicknesses in excess of 2m in places. Other seams present in the sequence attain workable thicknesses, but are less extensive and tend to be sterilised by their proximity to the major seams.

Perth Basin

Subcrop ol Goal measurc! Area ol Best Scam Development

3 t|l -l t

lll

200

1()

Figure 3. Distribution of coal measures in the lrwin River area, including a typical section of Irwin River Coal Measures.

Raw coal ash ranges from 77o to I57o (full seam) and gross specific eneigy varies from 28 to 3lMJ/kg on-a dry basis. The bed moisture of the coal is estimated to be about 10%. Sulphur contents are <I7o and chlorine is about 0.0L7o. Ash softening temperatures are fairly low at 1200oC, but the base tq acid- ratio, fouling ind slagging indices are well below the problem thresholds. Table 1 shows some typical

Structure High-resolution seismic data show that there is minimal structural disturbance in the coal-bearing strata that have been delineated in the Vasse Shelf to date. Dips are low, being less than 10o in the area studied.

analyses.

Coal Quality

Resources

In situ resources of the four principal seams delineated by drilling on 2km centres, for seams

The coals of the Vasse Shelf are rich in inertinite. They tend to have low proportions of volatile matter, and are anomalous in most classification systems. They are described as parabituminous, subhydrous coals under Seyler's classification and high volatile

thicker than-1.3m, are estimated at more than 200Mt in the Measured and Indicated category' These resources are accessible only by underground mining, but it appears likely that they lie in blocks sufficiintly larg-e-and undisturbed to allow use of highly productive extraction techniques.

bituminous A coals under the ASTM classification. They are non-coking and suitable only for combustion purposes.

Table 1. Typical analtsis of principal coal 6eams in the Vasse Shelf area. Seam

,ocation

T'ness (m)

Hz0Vo

AshVo

(ad)

Volatile Fixed Matter Carbon

Gross S.E.

Total Carbon H'rogen Vo iulphur 7o(ad)

Vo (ad)

(ad)

(MJ/I(G

(ad)

Rv,

itrinite

maxVo

CSN

M5 RBCHS

5.9 10.0

7.5

8.4

28.8 23.2

57.8 58.4

29.08 26.72

0.40 0.31

83.3 82.5

4.70 3.35

0.63 0.62

2.r9

0 0

t.75

8.0

6.7

24.8

60.5

28.43

0.51

85.8

4.4r

0.72

t.52

8.9

1.73

6.4

1.57

I .,t

59.0 59.4 58.3

28.06 28.49 28.20

0.73 0.55 0.67

0.73 0.67 0.63

29 22 21

tl2

RBCH3

25.4 25.2 27.0

85.3 84.8

WirrinE

6.7 8.6 7.4

t4.57

Mowen

M1 RBCHS

Upper Treeton Lower Treeton

Osmington upper split Osmington lower Split

1.90

82.31

Geology of Australian Coal Basins

4.44 4.88

39r

Eneabba

Deposit BEAG LE

RIDGE

DANDARAGAN

TROUGH

ktes!€J4

JullY .z

Galrdner 5

Range ? Deposit r

Jurien

F J

= f,

* ffi

OJ t& ld, lo ld

lndicated Resource

tcc

Typical Section of SEAM G, Catterman Coal Measure Member

ld,

Wongonderrah Deoosit

Cervant6s \ $ ".......'...,;' :,,',','r,,:,ll0,km ',,,:::rr,,,

Fault

Mutr*

PRINCIPAL AREAS OF COAL DEVELOPMENT IN THE HILL RIVER REGION

Figure 4. Principal areas of coal development of seam G, Cattamarra Coal Measures Member.

Irwin River Early Permian coal measures crop out in the Irwin River Sub-basin, about 100km southeast of Geraldton in the northern part of the Perth Basin. This sub-basin is bounded to the east by the Darling Fault and to the west by the Mullingara Ridge. It has essentially a synclinal structure, with the syncline axis close to the Darling Fault line. In contrast to the continental sequence in the southern Perth Basin, the Permian in the northern Perth Basin, the Irwin River Coal Measures, is a succession of mixed marine and terrestrial strata. The Early Permian fluvio-glacial sequence below these coal measures is up to 1500m thick, resting in turn upon Silurian and Proterozoic sediments. The Irwin River Coal Measures represent the result of an upper deltaic progradation into a dominantly marine and paralic sequence.

Coal Deuelopment The Irwin River Coal Measures in the Irwin Sub-basin are known to extend over a distance of about 40km between the Irwin River north branch and Woolaga Creek (Figure 4). The unit ranges in thickness from 60m in the north ofthis belt to 120m in the south. It dips easterly and crops out or subcrops below the Victoria Plateau Sandstone along the western boundary ofthe coal-bearing

deposits. Seam splitting and coalescing is a marked feature of the Irwin River Coal Measures.

Most of the earlier investigations in the area were concentrated near the original discovery at the north end of the Irwin Sub-basin (Johnson & others,1954), but exploratory drilling in the 1980s revealed that the best area of seam development lies in the central portions, between the Irwin River south branch and the Lockier River (Figure 3). Here the coal measures contain up to 10m of cumulative coal in 9 seams, between 0.5 and 3m thick in the best section, over a stratigraphic interval of 50m.

Table 2. Indicative coal quality of the lr*in River:Coal Medsures, A t05.2

110.4

112.0

127.4

1.78

0.54

33.2 13.0

3r.7

32.8

32.7 52.7 16.9

Total HzOVo

0.34 25.3

B 92.4 0.44 25.3

Ash% (db)

16.5

17.8

Volatile Matter% (db)

38.9

37.6

Fixed CarbonTo (db) Gross S.E. (MJ/kg)

44.6

25.0 34.1 27.2 38.7

17.8

17.4 0.52 0.10 71.9 4.6

0.58 0.14 72.3 4.7

Seam

Depth (m) Thickness (m)

SulphurTo (db) ChlorineTo (db) CarbonTo (d.a|)

HvdrosenTo (dafl

Perth Basin

3.2

0.16 72.1 4.7

13.7

54.2 16.8

0.65 0.21 74.L 4.3

t4.6

0.58 0.18 7 4.4 4.5

392

Coal Quality and Resourees The Irwin River coals are lignitous, with an in situ moisture content estimated at about 357o or more (Table 2). Coal in a typical borehole section with 9 seams and an aggregate 10m ofcoal has an average of 2I7o ash, 0.6Vo sulphur and a specific energy of 1SMJ/kg on an air dried basis. The coal should have an in-situ specific energy of about 13MJ/kg. The thicker seams are very banded, however, with ash values exceeding 30Vo and. correspondingly lower specific energies. The coals are notable for high chlorine and sodium contents, which could cause fouling and corrosion problems in many applications.

Structural information in the area is very sparse, since the Irwin River deposits have been drilled, mostly along strike, with boreholes at least 4km apart. There are, however, indications that the detailed structure of the deposit is more complex than the simple synclinal configuration inferred from outcrop. A resource of about 80Mt of coal is inferred in the area of thicker seam development, but only about 25Mt is thought to be recoverable by open-cut methods. The coal has recently been investigated as a possible source offuel for a vanadium ore treatment plant in the region, but the outcome of the study is not known.

Eradu Permian coal occurs in a deposit at Eradu, about 40km west of Geraldton, separated from the Irwin River Sub-basin by the Mullingarra Ridge. An assessment of available data, mostly bores and shafts sunk prior to 1943, shows that the coal

measures contain two seams, the lower of which is 2 to 2.5m thick and the upper 5.5 to 7m thick. The seams strike north easterly and dip to the southeast.

The coal measures at Eradu have in the past been considered to be Late Permian and are thought to grade laterally into Late Permian Wagina Sandstone. The Wagina Sandstone, with its age substantiated by palynology, has been intersected in recent drillholes to the northwest of the coal deposits, and minor carbonaceous stringers were encountered at this locality. It is known, however, that this formation unconformably overlies all of the older Permian units in the surrounding region. There is therefore no direct evidence that the Eradu coal is Late Permian, and the possibility also exists

that the unit is equivalent to the Irwin River Coal Measures described above.

Coal Quality and Resources Coal quality data for the Eradu sequence shows that the coals are of very low rank, with moisture content up to 407o. They could therefore be described as true lignites. The ash value is moderate, averaging about ISVo,but no sulphur determinations have been carried out. It is estimated that the specific energy as mined would be less than 14MJ/kg.

Available resources for the Eradu area are inferred to be about 40Mt.

JURASSIC COALS Although coal seams of economic significance are restricted to a relatively narrow stratigraphic interval in the lower Jurassic, the measures are widely distributed, onshore and offshore, in the subsurface of the northern Perth Basin.

Jurassic coal-bearing strata were first discovered in the Eneabba No. 1 Well in 1961 (Pudovskis, 1962), when an aggregate thickness of 12m ofcoal was intersected between 1943m and 1963m in the upper part of the Cockleshell Gully Formation known as the Cattamarra Coal Measures Member. This same horizon was subsequently discovered near the ground surface, in water bores and seismic shot holes, in the Hill River area.

Hill River The Jurassic coals at Hill River are the most extensively explored coal measures in Western Australia outside of the Collie region. Shallow coal measures have been found to occur within a 5 to

1Okm wide north-trending strip known as the Hill River Shelf, and to extend for at least 80km from Eneabba to Wongonderrah Spring. Three major deposits have been delineated, known as Eneabba, Gairdner Range and Wongonderra (Figure 4). The present configuration ofthese deposits is structurally controlled, resulting from post depositional faulting, folding and erosion processes.

Structure The Hill River Shelf is bounded to the east and west

by the Warradarge and Lesueur-Peron Fault systems respectively (Figure 4). This structural domain is located between the Beagle Ridge basement high, where the coal measures are eroded, and the Dandaragan Trough where they are overlain by 3000m or more of Late Jurassic and Early Cretaceous sediments. The Hill River coal deposits are structurally quite complex. They are divided into fault blocks which

each contain around 15 to 20Mt of undisturbed coal at relatively shallow depths. Seam dips within these

blocks are generally between 5o to 10o, with a maximum of 15o in places. Detailed drilling shows that there is a minimal zone of disturbance associated with even the major faults such as the Warradarge and Lesueur Fault systems.

Stratigraphy Coal seams of economic potential in the Hill River region occupy an interval 70 to 100m thick within the upper part of the Early Jurassic Cockleshell Gully Formation. This upper part of the sequence is known as the Cattamarra Coal Measures Member. In its type section in Eneabba No. 1 Well the Cattamarra Member is 512m thick, while the underlying Eneabba Member is 676m thick. The Cockleshell Gully Formation has generally been considered to be entirely terrestrial in origin. However, exploratory drilling for coal in the region has revealed that several marine incursions occur throughout the Cattamarra Coal Measures Member. D ep as itional Env ironrnent

The Eneabba Member underlying the Cattamarra sequence consists mainly of tabular cross-bedded pebbly sandstone, probably deposited in a high energy, braided stream flood plain setting. These rocks are succeeded by clays and silts ofthe Cattamarra Coal Measures Member, deposited in a quiescent environment such as an interdis-tributa_ry bay. The lower part of this unit shows evidence of deeper, open water sedimentation, the clays being thiCk, massive and lacking the structures associated with shallow water deposits. Siderite bands, shell beds and zones of marine and brackish water microfossils have been noted in this part of the

Geology of Australian Coal Basins

393 sequence, and thin beds of dirty, fusainous and probably allochthonous coal are common. The combination of these features is thought to indicate a near-shore environment.

The near-shore sediments grade upwards into strongly bioturbated flaser and ripple bedded laminites which form the seat earths of the lowermost coal seam. These strata are typical of estuarine or tidal flat environments, and also form partings within the coal seams. The partings, as well as the interseam sediments, probably represent periods ofincreased subsidence, resulting in drowning of the peat swamp, incursions of seawater, and increased clastic sedimentation from distributaries to the north and south. The high organic sulphur content ofthe coals is further

lo' 2l,-

The proportion of fluvial sandstone increases up the sequence, showing a general progradation ofthe delta system. The fluvial sandston"es contain abundant silicified wood, ranging from small fragments to tree trunks 3m long and 0.5m thick. Much of the silica has been recrystallised and the fine cell structure of the plants destroyed, but some specimens have been found with near-perfect tissue preservation.

OBlZotl

30'

evidence of marine influence.

The major coal horizons of the Cattamarra Member were deposited in a lower deltaic setting during regressive phases of a sequence formed by alternations between terrestrial and marine conditions. Accumulation of each coal horizon was terminated catastrophically by an influx of fluvial sand, as shown by the presence of erosional contacts in core holes between coal seams and their overlying sandstone roofbeds.

ao-

o Il

to'

Il I

to-

,o' 80-

Coal Seam Deuelopment

o HoRtzoil

The economic section of the Cattamarra Coal Measures unit contains four coal horizons over an interval varying between 70 and 100m thick. Figure 5 shows a typical section. The bulk of the coal resources at Hill River are contained in the lowermost seam (seam G), which is also the most laterally consistent. This seam is composed of six splits which are correlative throughout the Gairdner Range and Eneabba deposits (Figure 6). The area ofbest seam development, where the partings are thinnest, is centred in the northern portion of the Gairdner Range and embraces the southern portion of the Eneabba deposit. In this area the seam contains between 5 and 1lm ofclean coal. The splits in the seam diverge to the north and south, and individual coal beds thin out and interfinger with fluvial overbank sediments. The fluvial sediments in turn coarsen with proximity to

the main river distributaries.

The Wongonderrah deposit, south of Hill River, is

correlated with the northern deposits in a general way, but appears to be part of a separate depositional basin beyond the distributary system that marks the southern limit of the Gairdner Range deposit. The coal plies at Wongonderrah have thicker partings, but the cumulative coal thickness is comparable with that of seam G in the northern deposits, being up to 6m over a stratigraphic interval of 40m. However, infill drilling has shown that the seams are laterally discontinuous and eroded by fluvial palaeochannels.

00Ct

100 -

llOFigure 5. Typical section of coal measures in the Gairdner Range. Seams C and D, at the top of the coal-bearing interval, are of economic significance only in part of the Gairdner Range deposit, where they contain an aggregate ofup to 6m ofcoal excluding partings. Elsewhere they are thin, locally absent and often

deeply weathered.

Coal Quality Coal rank in the Hill River area varies from lignitous to high volatile bituminous. The highest rank seams are found in the Gairdner Range and the lowest at Eneabba. The principal seam (G) does not vary greatly in ash throughout the region, averaging about 157o. Sulphur content is wo to 1.5%, of which more than halfls organic in form. The lowest rank coals have in situ specific energies of about 15MJ/kg, and the highest about 22MJkg. In situ moisture correspondingly ranges from about 20Vo to over lOVo.

Perth Basin

394 COAL OUALITY (AS RECEIVED BASIS)

TOTAL

SPECTFTC

ASH

VOL. MATTER

JULPHUF

ENERGY (MJ/kg)

S/SE (q/MJ)

15.6

25.8

1.06

18.01

0.59

SEAM

SUB.

THICK.

,{OISTUR

SFCTION

r.16

Table 3. Indicative coal quality in the Gairdner Range. 13-21 Total Moisture 7o |

Ashvo

Volatile Matter Vo

Fixed Carbon 7o Gross S.E. (MJ/ke.)

Sulphur 7o

4.85

28.5

1.03

8.3

9.48

0.53

chlorine

Ash Fusion Temperature D.T.'C

S.T.oC H.T..C F.T.oC

Hardsrove Grindability Index

1.S

26.6

o.24

21.7

64.3

. 26.9

13.2

27.1

1.19

9.5

0.18

18.75

14.2"

1.79

0.63

0.98

3.67

0.79

25.0

21.3

t4 18

2.13

1.50

rIrc Ir_ r-

coAL (uNDlFF.) OIRTYCOAL SHALEYCOAL CAFBONACEOUS SHALE NON-COAL(UNDIFF.)

| I |

32-34 40-45 20-24

o'oz

I | I I

1'5 1150 1240 1280 1350 60

Gairdner Range Total in sifu resources at Gairdner Range are in aOOMt, most of which are in the Measured "f """"rr categories. The shallowest resources and Indicated in th"e Hill River region, with fresh *"ttl"ed "r" coal subcropping at depths of <10m.in places' Natorat e*i6soiet of seam G occur in Cockleshell Cotty, wheie the coal bed is 7 to 8m thick' A detailed feasibility study has proven QPpn-cut. ^ reserves of 95Mt. These reserves formed the basrs ot a oroposal to build a coal mine and adjacent power rtlti,i" at Gairdner Range' An electricity supply l"trd"t was submitted to the State Electricity Commission in 1990.

HILL RIVEF COAL PFOJECT

TYPICAL SECTION OF SEAM G FFOM CPCH 23

Figure 6. Typical section of sesm G from the IIiII River area.

Wongonderrah Because of the discontinuous nature of the seams'*i""uUtu open-cut coal resources at Wongonderrah are estimafed at less than 10Mt.

CRETACEOUS COALS

Although the coals appear banded dqU macroJcopically, they contain about 7O-Vo vitrinite' frl".n of this is in th-e form of desmocollinite, which oiobablv accounts for the dull appearance. The ti;h;; iank coal in the Gairdnei Range is weakly coking.

Coal of very low rank is known to occur in the Early Ci"[.."o"t"Leederville Formation of the southern p"ittt Basin. The coal is high in ash, rich in fusain u"a .o.ttui"s abundant syngene-tic pyrite' The seams localised in extent, and 3re-rarely over a uiu ""ty ttrict<. They appear to be allochthonous, metre denosited in a br-acliish or shallow marine The coals, however, have no economic ;;;it"il;t. significance.

Resources

REFERENCES

Eneabba

JOHNSON, W., de la HUNTY, L.E' & GLEESON, J'S', 1954; Th; geology ofthe Irwin River and Eradu

Figure 6 shows a typical borehole section of seam G, wi?fr anatytical daia on seam subsections (Table 3)' -

Extensive drilling by Renison Goldfields Cotttotiaut"d Ltd: his proven in-situ res-ources of itBMt ;t Eneabba, a lirge proportion of which is in the Measured category. No details of possibly

ru."u"tuUi" coal ar"e available, but from results of drilline bv Amax and Taylor Woodrow it is ""."i""t lstimatea tfrat itrii might amount to around 60Mt' The coal subcrops are overlain by Qu-atern-ary sediments up to 30m thick, downgrading the. ptotp""tt foi coal with a low stripping ratio in the atea.

dittti.tt aid toiionttding country' Geological

Suruey of Western Australia, Bulletin, LO$' PLAYFORD, P.E., COCKBAIN, A.E. & L.OW, G.H., 1976:'Geology of the Perth Basin-,- Western Australia. Giological Suruey of Western

Australia, Bulletin, 124' PUDOVSKIS, V', 1962: Eneabba No' l Well Completion Report. West Australian Petroleum Pty' T'1d'' Petroleum Search SubsidY RePort'

Geology of Australian Coal Basins

395

ffi

KJarnarvon

Basin

RM Hocking

1: Location and onshore structural Fisure - subdivisions of the Carnarvon Basin.

GEOLOGICAL SETTING The Carnarvon Basin is an elongate basin extending along the western and northwestern coastline of West"ern Australia between Geraldton and Karratha, a distance ofabout 1000km (Figure 1). The basin and its constituent sub-basins have been defined using their structural elements (Playford & others, 1975] Trendall & Cockbain, 1990), rather than the characteristics of their sedimentary sequences. The orientation of major structural elements south of latitude 23oS is dbminantly northwards. Between 22oS and 23oS, however, the orientation swings around and north of 22oS the basin trends northeast. The Carnarvon Basin is transitional into the offshore Canning Basin to the northeast, and into the Perth Basin to the south. Precambrian rocks flank the Basin -to the east.

Carnarvon Basin

396

r. egE

Sequence

l,looranel Eroup STBNT I 6RAPHY

BEDDtlt6

LtTH

KunguPian Kennedg Eroup

Art I nskian

Bgro 6roup J,looranel Eroup

Sakn- Cal lgtharra Fit

arian f,sse I

ian

Lgons Eroup

Steph-

anlan

Figur_e 2. Suqmary of sedimentary sequences known in the Carnarvon Basin, with emphasis on the Upper

Carboniferous-Perrnian sequence and the coal-bearing Tlooramel Group. Left hand column shows-all sequences known from Carnarvon Basin, with vertical lines indicating non.deposition. Time scale at left s.l_rows periods and epochs, and follows Harland & others (1982). Bedding and lithology shown on right in Wooramel Group is diagrammatic only. The basin has an onshore area ofabout 115 000km2 Southern Carnarvon Basin and an offshore area ofabout 535 000km2. Th" onshore portion ofthe basin ranges in width from The Byro, Bidgemia and Merlinleigh Sub-basins about 50 to 300km, but is generally 150 to 200km. (Figure 1) are primarily half-grabens, containing The offshore portion extends at least as far as the mainly Late Carboniferous and Permian sediments. Exmouth Plateau, more than 400km from the Lower Carboniferous and Devonian sediments, with basin's eastern margin. a Cretaceous veneer, are present in the northeastern part of the Merlinleigh Sub-basin, and Silurian The geology ofthe onshore Carnarvon Basin is sediments occur in the western part. Fault-bounded detailed in a comprehensive bulletin by Hocking & basement ridges, which are largely post-depositional others (1987) and a later review by Hocking (1990). features, separate the three sub-basins. Basement rocks are exposed along these ridges in the Carrandibby and Weedarra Inliers. Virtually all coal STRUCTURAL ELEMENTS exploration in the Carnarvon Basin has concentrated in the Early Permian strata of the The Carnarvon Basin can be readily divided into two western Merlinleigh and the central Byro groups of sub-basins. The first of these groups Sub-basins. contains predominantly Palaeozoic sediments, trends northwards, and constitutes most of the onshore part of the Carnarvon Basin. They were The Ajana and Wandagee-Yanrey Ridges separate comprehensively described first by Condon (1965, the Coolcalalalya and Merlinleigh Sub-basins from 1967, 1968) and later by Hocking & others (1987). the Gascoyne Sub-basin (Figure 1), and in most The second group contains large thicknesses of areas are included in the Gascoyne Sub-basin as its Mesozoic and Cainozoic sediments, is mainly easternmost part. The eastern boundary ofthese offshore and northeast-trending, and forms the ridges is marked by a series of major, northern Carnarvon Basin. For convenience, the down-to-the-east fault systems. The Gascoyne groups are referred to as the Palaeozoic and Sub-basin is a north-south elongated, uplifted platform which is tilted gently westwards. It Mesozoic sub-basins, respectively (Thomas & Smith, 1976), or the Southern and Northern Carnarvon contains primarily Silurian and Devonian Basin (Bradshaw & others, 1988; Cockbain, 1989). sediments, with minor Carboniferous and Permian

Geology of Australian Coal Basins

397

remnants, and in the Exmouth Gulf area contains Triassic and minor Jurassic sediments. A westwardthickening Cretaceous veneer mantles the older strata.

Northern Carnarvon Basin

v_-

In contrast to the north-south orientation and mainly Palaeozoic infrll of the Southern Carnarvon Basin, the Exmouth, Barrow and Dampier Sub-basins contain thick sequences of Mesozoic and Cainozoic sediments. The thickness of the underlying Palaeozoic sequence is unknown. The Exmouth Sub-basin is separated from the Exmouth Plateau Arch (Investigator Sub-basin), to the northwest, by the Kangaroo Syncline (sometimes referred to as the Kangaroo Trough). The Barrow and Dampier Sub-basins are faulted against the Rankin Platform to the north and northwest. All these units are grouped under'Northern Carnarvon Basin'in Figure 1. Their development, structure, infill and economic geology have been detailed by papers in Purcell & Purcell (1988).

-_a

:-F_-l

-.2:-=r-\_---._r_-

"'r.ro.

--jE-f --1_-J

-:-F:+

The Peedamullah and Lambert Shelves are areas of shallow basement, with onlapping Mesozoic and Cainozoic deposits which thicken offshore. Palaeozoic and Triassic sediments are present in the more westerly and northerly (deeper) parts of the Peedamullah Shelf. The shelves have faulted boundaries with the Barrow and Dampier Sub-basins, respectively

at-^i-r^i Glaciated '"

=-*-::# -7----+:

t-=+ :--t :l----t ---t

k_-_-_-t =-:-:+

+_= -t--_I-J

--{-no--)-: r--L-j

Coal has been intersected in the Mesozoic sequence

ofthe Carnarvon Basin by petroleum exploration wells, primarily in the Triassic Mungaroo Formation and the Jurassic Legendre Formation. In all cases it is offshore and at too great a depth to be econornic. SEDIMENTARY SEQUENCE The Carnarvon Basin contains sediments ranging in age from Silurian to Holocene (Figure 2). The Pioterozoic lJaroo and Badgeradda Groups, which occur at the basin margin, are not included in the Carnarvon Basin (Hocking & others, 1987). Only a

portion of the Permian sequence is a viable target for coal exploration. Palaeozoic deposition took place in terrigenous-

dominated continental and marine-shelf environments. The continental deposits are siliciclastic; they were formed in braided fluvial and, in areas near the basin margin, alluvial fan settings. The marine deposits contain both siliciclastic and carbonate deposits, and formed in shoreline, near-shore and marine-shelf settings. Red beds and evaporitic sediments, deposited in two major cycles totalling >4000m in thickness, dominate the Silurian sequence. The Devonian and Early Carboniferous sequences consist of approximately 2000m ofbraided fluvial, alluvial fan and near-shore siliciclastic sediments, interbedded with shallowmarine carbonates.

Folding, faulting and erosion took place in the mid-Carboniferous, before the deposition of a glacigene sequence (the Lyons Group),and an i-mmediately post-glacial u nit (the C allytharra Formation) in the Late Carboniferous and Early Permian (Sakmarian) (Figure 3). Together these are up to 2500m thick. After erosion in eastern areas in the early Artinskian, the glacigene sequence was followed by a major fluviodeltaic progradational phase (Fidure 4), forming the Wooramel Group. This lr'aded inio siliciclastic, marine-shelf deposition,

Figure 8. Asselian and Sakmarian palaeogeography of tne Carnarvon Basin (Ilocking' 1990). ND - non-deposition; Cfc - fluvioslacial; Sii - paralic to marine ehelf with floating ice sbelf Mmg-- mixed shelf, at times glacially influenced. forming the Byro and Kennedy Groups. The Wooramel, Byro and Kennedy Groups have a cumulative thickness of approximately 2900m. The Wooramel Group has been virtually the sole target for coal exploration programs in the Carnarvon Basin. A major re-orientation of the various depositional basini took place in the Late Permian. Deqositional loci shifted tb the northern Carnarvon Basin, where terrestrial and marine siliclastics, with minor carbonates, were deposited in the Late Permian and the Mesozoic. Carbonate deposition became dominant in the Late Cretaceous, and a thick prograding marine shelf developed in the Cainozoic.

Carnarvon Basin

398 .|

16'_

:-::

_-_-=7

'--=t=

_-_-_-t::: ---k

---€i

--:-Ml,M;--ffi t:- ^t:

:- {==- - +siJE:

=-j-;=4:=W -::---------&

'__-_-_-_:_-_-#:#l

--------------FE:*h

l=:-=ts_-:-#NA +__f:__a____wl

L=e =_=€ k=:t--\ :--J-----

::_&:

TECTONIC HISTORY The sub-basins of the Carnarvon Basin can be related to a plate-tectonic model and the progressive breakup of Gondwanaland (Veevers, 1984; Cockbain & Hocklng, 1990). The north-trending sub-basins are thought to have developed as a north-opening aulacogen ('failed arm') basin (Veevers & others, 1982; Veevers, 1984) in the late Ordovician to Silurian. Major tectonism occurred in the Silurian and mid-Carboniferous. The sub-basins subsequently developed into'infra-rift' (Falvey & Mutter, 1981), or pre-breakup basins during the Late Carboniferous and Permian. In the Silurian, they were fault-bounded; subsequently they had

onlapping margins. Tectonic arching of the north-trending sub-basins occurred in the Triassic, and pronounced infrarift basins developed in the northern Carnarvon Basin. They evolved from unconformity-bounded downwarps in the Triassic to fault-bounded rift basins in the Jurassic (Kopsen & McGann, 1985). These basins were closely related to the impending Jurassic breakup (at 160Ma) along the northwest Australian margin, and in the Jurassic they developed into the northeast-trending

rift valley

sub-basins.

-=-F=a

Major fault movements, associated with the breakup, occurred both onshore and offshore in the Jurassic, and fully delineated the present sub-basins. These movements had largely ceased by the Cretaceous, and the sub-basins developed frrst into rim basins (Veevers & others, 1982) and then into post-breakup, trailing-edge basins.

.-_-_-_-F:

COAL BEARING SEQUENCES

--t F=

+-# L--

Figure 4. Artinskian palaeogeography of the Carnarvon Basin (IIocking, 1990) ND - non-deposition/erosion; Cf - continental, fluvial; Si - paralic; Mi/Ms - fine to coarse clastic shelf; Dm - deep marine. Folding and faulting of the Palaeozoic sediments took place in the Late Triassic and the Jurassic, forming the presently expressed structural framework onshore. Lateritisation and silcretisation occurred in the Oligocene and Miocene. The Late Tertiary to Early Quaternary saw the onset of arid conditions in the Carnarvon Basin. The formation of duricrust calcrete was followed by alluvial and aeolian deposition and reworking in onshore areas, while calcareous deposition continued offshore. A compressive tectonic regime began in the Miocene, after collision of the Australian Plate with Timor. This led to reverse movement on many faults and the development of fault-controlled anticlines (inversion structures, Lowell, 1985) near the coast north of Carnarvon.

The only portion of the sequence in the Carnarvon Basin which appears prospective for coal is the Permian Wooramel Gioup (Hocking & others, 1987). This part of the succession contains sizeable 4u11a-plain and coastal-swamp deposits. Coastal swamp deposits also occur in the Cretaceous Nanutarra Formation and Yarraloola Conglomerate, on the Peedamullah Shelf (Figure 1). These units outcrop, and have never been buried more deeply (Hocking & others, 1987; Thompson & others, 1990), and henie the potential for coal preservation and maturation is low. Coal has been recorded from Mesozoic sediments in offshore areas, but for obvious reasons is uneconomic. The Wooramel Group was deposited in settings that graded from fluvial to wave-dominated deltaic. It contains the Cordalia Sandstone, the Moogooloo Sandstone, the Billidee Formation and Keogh Formation (Figure 2). Immediately prior to deposition of this sequence, in the early,Artinskian, the onshore Carnarvon Basin was largely emergent and subject to erosion. The unconformity can be identified in the eastern sub-basins, but not in the Gascoyne.Sub-basin where little of the Permian sequence is preserved. Deposition of the.g-roup . commenced in the mid-Artinskian, coincident with a major transgression, on a palaeoslope dropping to

the northwest.

In the Byro, Bidgemia and eastern Merlinleigh

Sub-basins, the Moogooloo Sandstone formed a westwards-directed prograding wedge, resting directly on the Callylharra Formation' Conditions were continental to very shallow marine, with deposition in low-sinuosity braided-fluvial,

Geology of Australian Coal Basins

399

delta-plain channel and (to a lesser extent) interchannel environments. In deeper parts of the basin to the west and northwest (where water depth was suffrcient), the Cordalia Sandstone was deposited on the Callytharra Formation. Deposition ofthe Cordalia Sandstone took place in offshore to shoreface environments, forming a prodelta sequence. The Moogooloo Sandstone continued to prograde, over the eordalia Sandstone, and formed a diachronous sand sheet. This sheet was deposited in delta-front and distributary-channel environments in a largely wave-dominated setting, and rested on a westwards-thickening prodelta sequence. Progradation then largely ceased and a regional flooiling surface developed as a result of continuing transgression, subsidence and compaction and a lessening of terrigenous input. The Billidee Formation formed in several progradational depositional episodes, each more distal, in low-energy marine-shelf to prodelta environments. Some areas of the shelf were shallower and subject to more wave action. Shoaling episodes took place, forming the Jimba Jimba Calcarenite Member and facies equivalents in the Kennedy Range area, in the central Merlinleigh Sub-basin (Figure 5). These shoaling episodes were followed by

lobate-delta building. In the central and southern Byro Sub-basin (and possibly west of the Clrrandibby Inlier, Figure 5), higher energy levels prevailed than further north, and-a lateral equivalent of the Billidee Formation, the Keogh Forination, was deposited in sub-tidal, tidal flat and delta-front environments. environments of the Wooramel The depositional -are difficult to assess in the subsurface to the Group west and north of the outcrop areas. The limited amount of data from petroleum wells and coal exploration boreholes suggest that deposition was primarily in marine shelf to offshore environm-ents, with a high-energy peak during deposition of the Moogooloo Sandstone at the time of maximum progradation. Thin coal seams in the Billidee Formation and Moogooloo Sandstone in Quail No.1 Well (Figure 5), indicate delta-plain conditions this far west, at least for a short time. The coal seams are in the middle of the Billidee Formation, as are the small deltas in the Kennedy range area, and they mark the most extensive progradational episode in the Billidee Formation.

Deposition of the Wooramel Group ceased in the late Arfinskian because of diminished sediment supply and continued transgression. The uppermost Billidee and Keogh Formations are separated from the Coyrie Formation, the lowermost unit of the Byro Group, by another major flooding surface. The Coyrie Formation formed largely in offshore marine conditions with restricted water circulation.

Thin seams of coal are known in the Wooramel Group in the Wandagee and the southern Byro Plains areas (Figure 5). Coal was first intersected at Wandagee in the Quail No. 1Well, at deptlrs of atleast 200m, in the Billidee Formation and Moogooloo Sandstone. Follow-up drilling indicated that the coal seams, which are of coking quality but less than 1 m thick, do not thicken markedly in any direction; they are shallowest near Quail 1 (Broken Hill Proprietary Company Ltd., 1976; Devlin, 1983). Untested areas remain to the southeast beneath the Cretaceous, to the east beneath the Coyrie Formation near Gooch Range, and to the north (near the Lyndon River on Mia Mia Station).

(A c0

z o c zt o

E tffil

H l:::::::::::::::

Post - Permian aover

Wooramel Group, shallow subcroP

beneath post - Permian

Permian, post - Wooramel GrcuP

ffi ffi

I . .......':...........':.:.:..l

Wooramel Group, outcroP Pre -Wooramel GrouP

Precambrian

Fisure 5: Distribution of Wooramel Group in - Merlinleigh, Byro and Bidgemia Sub'basins. Surface dlstriliution based on petroleum, mineral, and coal exploration drilling,data. Simplifi'ed from Hocling & others (1987).

Carnarvon Basin

400 Coal was recovered from BMR No. 8 (Mount Madeline) in the Byro Sub-basin, and also from some seismic survey shotholes in that area. Subsequent exploration has centred on the Keogh Formation, with the Moogooloo Sandstone as a secondary target, in the area between the Murchison River and the Carrandibby Inlier. There has been extensive drilling by severai companies but no economically viable deposits have been found. Delta-plain and delta-front deposits occur in the Wooramel Group in adjacent outcrop areas, but no detailed, integrated, environmental analysis has been made of the group as a whole in the Byro Sub-basin.

LeBIanc Smith (1990) classified the Permian coals in

the Carnarvon Basin as sub-bituminous, listing quality values of 3-llVo moisture, l2-28%o ash, 22-29Vo volatile matter, and a specific energy of 77 -28 MJ/kg. The coals have l.I to l.7Vo sulphur, and their ash fusion temperatures are considered to be in the 'coking'range.

A major problem with coal exploration in the Carnarvon Basin is the probable depth at which coal might be present. In areas where the Wooramel Group outcrops (Fig-ure 5), dips are normally between 10u and 20u, meaning that mining would become quite expensive over a relatively short Iateral distance. Away from outcrop, both the facies present and the depth of burial are commonly uncertain. In the southern Carnarvon Basin, and the Coolacalalaya Sub-basin of the Perth Basin, the extent of the group is uncertain because of extensive sand cover.

REFERENCES

DEVLIN, S.P., 1983: Final report on Exploration Licenses 09/12 Weer Dam, 09/13 Billamaberry, 09/25 Billamberry South, 09/26 Billamberry, and exploration licence applications 09/17 Manberry, 09/23 Barrabiddy 1, Merlinleigh Basin, W.A. Winning Pool SF50-13, Kennedy Range SF50-1: CRA Exploration Pty Ltd report. FALVEY, D.A. & MUTTER, J.C., 1981: Regional plate tectonics and the evolution ofAustralia's passive continental margins: Bureau of Mineral Resources, Geology and Geophysics, Journal ,6, L-29.

HARLAND, W.B., COX, A.V., LLEWELLYN, P.G., PICKTON, C.A.G., SMITH, A.G., & WALTERS,

R., 1982: A Geological Time Scale. Cambridge University Press, Cambridge. HOCKING, R.M., 1990: Carnarvon Basin. 1n Geology and Mineral Resources of Western Australia, Geological Suruey of Western Australia, Memoir, 3,457-495. HOCKING, R.M., MOORS, H.T. & van de GRAAFF, W.J.E., 1987: The geology of the Carnarvon Basin, Western Australia. Geological Suruey of Western Australia, Bulletin, L33. KOPSEN, E. & McGANN, G.J., 1985: A review of the hydrocarbon habitat ofthe eastern and central Barrow-Dampier Sub-basin, Western Australia. APEA J ournal, 25(L), L54-L7 6. LeBLANC SMITH, G., 1990: Coal. In Geology and Mineral Resources of Western Australia, Geological Suruey of Western Australia Memoir, 3,625-631. LOWELL, J.D., 1985: Structural Styles in Petroleum Exploration. OGCI Publications, Tulsa, Oklahoma.

BRADSHAW, M.T., YEATES, A.N., BEYNON, R.M.,

BRAKEL, A.T., LANGFORD, R.P., TOTTERDELL, J.M. & YEUNG, M., 1988: Palaeogeographic evolution of the North West Shelf Region. 1n Purcell, P.G. & Purcell, R.R. (Editors): The North West Shelf, Australia -

Proceedings of North West Shelf Symposium, Petroleum Exploration Society of Australia,

Perth, W.A., 29-54.

BROKEN HILL PROPRIETARY COMPANY LTD., 1976: Temporary reserve 5951H, Merlinleigh Basin, Western Australia. COCKBAIN, A.E., 1989: The North West Shelf. APEA

Journal, 29(l), 529-545.

COCKBAIN, A.E. & HOCKING, R.M., ].990: Phanerozoic. In: Geology and Mineral Resources of Western Australia, Geological Suruey of Western Australia, Mernoir, 3, 7 50-7 55.

CONDON, M.A., 1965: The geology of the Carnarvon Basin, Western Australia, Part 1: pre-Permian

stratigraphy. Bureau of Mineral Resources

Bulletin,77.

CONDON, M.A., 1967: The geology of the Carnarvon Basin, Western Australia, Part 2: Permian

stratigraphy. Bureau of Mineral Resources

Bulletin,77. CONDON, M.A., 1968: The geology of the Carnarvon Basin, Western Australia, Part 3: post-Permian stratigraphy, structure, economic geology. Bureau of Mineral Resources Bulletin, TT .

PLAYFORD, P.E., COPE, R.N., COCKBAIN, A.E., LOW, G.H. & LOWRY, D.C., 1975. Phanerozoic in geology of Western Australia. Geological S uru ey of We s tern Australia Memoir, 2, 223-445.

PURCELL, P.G. & PURCELL, R.R. (Editors), 1988: The

North West Shelf, Australia. Proceedings of North West Shelf Symposium, Petroleum Exploration Society of Australia, Perth, W.A. THOMAS, B.M. & SMITH, D.N., 1976: Carnarvori Basin, In Leslie, R.B., Evans, H.J. & Knight, C.L. (Editors): Economic geology of Australia and Papua New Guinea - 7. Petroleum. Australasian Institute of Mining and Metallurgy, Monograph, 6,126-155. THOMPSON, N.B., HOCKING, R.M., COLLINS, L.B., VOON, J.W.K. & MIDDLETON, M.F., 1990: Lower Cretaceous deposition on the southern North West Shelf, W.A. report for - final Meriwa Project 84. Minerals and Energy Research Institute of Western Australia, Report 55.

TRENDALL, A.F. & COCKBAIN, A.E., 1990: Introduction to Chapter 4: Basins. ,In Geology and Mineral Resources of Western Australia, Geological Suruey of Western Australia Memoir,

3,291-293. VEEVERS, J.J. (Editor), 1984: Phanerozoic Earth History of Australia. Claredon Press, Oxford. VEEVERS, J.J., JONES, J.G. & POWELL, C.MCA., 1982: Tectonic framework of Australia's sedimentary basins. APEA Journal, 22(l), 283-300.

Geology of Australian Coal Basins

401.

tr.annrng qLr

Basin

AN Yeates

The onshore segment ^of the Canning Basin occupies an area of 430 000km'in the northern part of Western Australia. It contains up to 18 000m of shallow marine, paralic and terrestrial deposits, ranging from Ordovician to Early Cretaceous.

Four principal depocentres were initiated at differ-ent times during the basin's evolution. Two of these are located on each side of the Broome Arch (Figure 1), a NW trending mid-basin feature initiated in the mid-Devonian that remained a relatively positive element throughout most of the basin's depositional history. The Kidson and Willara Sub-basins, south of the Broome Arch, had a relatively quiet tectonic development, but the Fitzroy and Gregory Sub-basins, north of the arch, were more active, being located within the major Fitzroy Graben structure. The terraces and shelfareas flanking the Fitzroy Graben were sites of thick clastic and carbonate deposition, especially in the Middle Devonian to Eally Carboniferous (Jackson & others, 1992). Permian sediments are widespread in the basin, and include very minor known coal occurrences within the graben. Subsidence in the graben ceased during a compressional event that gave rise to uplift and reverse faulting between the Middle Triassic and Early Jurassic.

STRUCTURAL FEATURES The northeastern and southwestern margins of the basin are shelfedges. Except where they are block-faulted in the north or where some of the older units are deformed on the Billiluna Shelf in the east, the sediments dip basinwards at a shallow angle and lap gently on to the Precambrian basement rocks. The southeastern edge of the basin, however, is faulted-bounded, with several major vertical fractures present. Two parallel depressions are located between the marglnal shelf areas, separated by the belt of more elevated basement rocks along the NW-trending Broome Arch. Each of these contains over 1Okm of little-deformed Palaeozoic and Mesozoic sediment. The southern depression comprises the Kidson and Willara Sub-basins, which are contiguous across a slight basement rise, the Munro Arch. They merge gently with their adjacent shelves in the southwest, and all but the northwestern part of the Broome

Arch, where a fault boundary is developed.

The other principal depression is the Fitzroy Graben, north of the Broome Arch. In contrast to the depocentres to the south, this area is partly flanked by structural terraces that have fault contacts with the northern shelves and with the Broome Arch

itself (Figure 2).

The Kidson Sub-basin was initiated by gentle subsidence, apparently with minimal faulting. It suffered little ileformation apart from axial sag and possible salt diapirism. However, deposition in the Fitzroy Graben was facilitated by periodic down-to-basin faulting, particularly from

mid-Devonian to Early Carboniferous times (e.g. Towner & Gibson, 1,983). The graben was a much more active tectonic element compared to the Kidson and Willara Sub-basins (Forman & Wales, 1981). This is revealed by angular unconformities mappable on the surface and in seismic sections, by shifting depocentres, and by the obvious fold and fault patterns.

Canning Basin

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Figure l. Structural features ofthe Canning Basin (Yeatee & others, 1984). The bounding faults ofthe graben and its adjacent terraces, though near-vertical normal faults at the s,urface, are interpreted to flatten at depth in detachment zones (Drummond & others, 1988; 1991). Down-to-basin movements on these faults allowed the great thickness of sediment to accumulate in the basin's two depocentres, the Gregory and Fitzroy Sub-basins. These depocentres are largely continuous over a gentle rise in the basement, inferred from gravity data, that runs continuously from basement outcrops at Bulka Hills in the north across the graben to about the Fenton Fault. This saddle, the Jones Rise of Yeates & others (1975a) is located in an area where stratigraphic and structural changes occur in the Permo-Tiiassic sequences of the two sub-basins.

Sub-basin, and tensional north-south trending faults (Rattigan, 1967; Smith, 1968; Crowe & others, 1978; Rixon, 1978), which often tilt the immediately adjacent rocks appreciably. The structure of the pre-Permian units is mainly concealed by younger rocks. Limited exposure of Farly Ordovician and Late Devonian units along the basin's northeast edge indicate that they are much more deformed than neighbouring Permo-Triassic units. Greater deformation is also evident on more basinward seismic sections, especially in the Fitzroy Graben. In contrast, however, Devonian outcrops on the Lennard Shelf are little deformed.

STRATIGRAPITY The Gregory Sub-basin is the lesser deformed depocentre in the Fitzroy Graben. It lacks the same abundance ofanticlines, and where present they are only incipient features. Lamproite intrusions aie currently unknown in the Gregory Sub-basin, but are common in the Fitzroy area (Jaques & others, 1984).

Up until mid-Triassic times a tensional tectonic regime was dominant in the Fitzroy Graben. However, between the Late Triassic and Early Jurassic the graben was affected by right-lateral regional coupling along its bounding faults during a period of regional compression between the Broome Arch and the Kimberley Block. This resulted in local reverse movements along its previously normal bounding faults, an en echelon arrangement of

east-trending anticlines across the Fitzroy

Ordovician to Early Carboniferous The oldest strata in the basin are the Carranya

Beds, paralic sandstones and conglomerates of Early Ordovician age that rest on the eroded Precambrian basement rocks. These strata grade laterally, as well as up the sequence, into shallow marine fine clastics

and carbonate deposits.

A Late Ordovician to Early Devonian red-bed and evaporite sequence (Foster & Williams, 1991) is present in the subsurface of the Kidson Sub-basin, overlain by the thin carbonate sequence ofthe Middle Devonian Mellinjerie Limestone. Further deposition did not occur in the Kidson Sub-basin, however, until Late Carboniferous times.

Geology of Australian Coal Basins

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Figure 2. Correlation of Late Carboniferous to Late Permian units in the Canning Basin (Yeates & others, 1984). The Fitzroy and Gregory Sub-basins were major depocentres during the early Palaeozoic, with carbonate sedimentation being dominant on the shallow terraces and shelves and a vast influx of clastic sediments being received in the deeper portions. Relatively undisturbed Devonian reef iomplexes occur on the Lennard Shelf, overlain by shallow marine sediments and interfingering in places with Late Devonian terrigenous

conglomerates.

Another carbonate province, of Middle Devonian to Early Carboniferous age, occurs in the Barbwire and Jurgurra Terraces, on the southern side ofthe graben, while coarse clastics of Late Devonian age, including the well-exposed Knobby Sandstone, occur on the Billiluna Shelf at the eastern end. Devonian sediments in the axial portion of the Fitzroy Graben

are succeeded by the Lower Carboniferous Anderson Formation.

Late Carboniferous to Early Permian Glaciation in the surrounding cratonic highlands during Stephanian and Sakmarian times was assocfuted with a gentle downwarping of the Kidson and Willara Sub-basins, and with subsidence facilitated by limited growth faulting in the Fitzroy Graben area. The Grant Group, a fluvial and shallow marine sequence containing diamictites and laminated clastics with dropstones, including material interpreted as tillite, was deposited throughout the basin, especially_in the laterally equivilent terrestrial Paterson Formation in the m-arginal areas to the south (Crowe & Towner, 1976d).

Canning Basin

404 The lowermost formation of the Grant Group, the Betty Formation, consists of fine to coarse, sparsely fossiliferous clastics, deposited first in the Fitzroy Graben during the Stephanian and then spreading

throughout the rest of the basin as the Sakmarian transgression proceeded. The overlying Winifred Formation contains fossiliferous limestone and minor coal (Singleton, 1965), while the Carolyn Formation, at the top of the sequence, consists of non-marine deltaic and shallow marine sediments deposited during the subsequent Sakmarian regressive phase. Sporadic tectonism followed deposition ofthe

Carolyn Formation in the Fitzroy Sub-basin (Guppy & others, 1958; Crowe & others, 1978), after which the Poole Sandstone was deposited unconformably on the Grant Group. Elsewhere in the basin, however, the boundary between these two units is conformable or only slightly disconformable. The Nura Nura Member in the lower part of the Poole Sandstone is restricted to the Fitzroy Sub-basin. This unit consists of braided to

meandering stream deposits, grading up through deltaic and lagoonal sediments to fossiliferous shallow marine carbonate and clastic deposits (Crowe & Towner, 1976b). It is overlain by the Tuckfieid Member, a more extensive unit of fine to very fine grained quartzose sandstone, spread throughout the basin generally, that tends to contain minor silty phases in the basin'perimeter areas. These silty deposits are carbonaceous in the north and northeast of the basin, and often contain plant fragments. The lithological features and sedimentary structures of the plant-bearing units suggest that they represent material formed in a delta-plain to lagoonal environment (Yeates & others, 1975a; Crowe & Towner, 1976a).

Like the Nura Nura Member, the uppermost unit of the Poole Sandstone, the Christmas Creek Member, is restricted in distribution to the Fitzroy Sub-basin. This unit is a coarse-grained fluvial sequence, laterally equivalent to the upper Tuckfield Member in the Fitzroy Sub-basin area (Crowe & Towner, 1976c). The uppermost units of the Poole Sandstone are in turn overlain by the shale and siltstonedominated, variably calcareous marine units of the Artinskian Noonkanbah Formation.

Late Permian A marine regression began in the Canning Basin late in the Artinskian, and in the Kidson Sub-basin a thin-bedded micaceous unit, the Triwhite Sandstone, was deposited in shallow marine conditions. The Broome Arch became emergent at this stage of the basin's development, and older Permian units on it were partly eroded (Figure 2). Subsidence continued in the north, however, involving limited down-to-basin faulting, and deposition in the Late Permian became confined to the area north of the Fenton Fault system in the Fitzroy Graben structure. The Liveringa Group is a sequence of fluvial to

deltaic and shallow marine deposits overlying the Noonkanbah Formation in the northern part of the Canning Basin. The lowermost unit of this sequence is the Lightjack Formation (Yeates & others, 1975b), a succession of thin to medium bedded micaceous siltstones and planar to lenticular-bedded sandstones coarser than the underlying Noonkanbah sequence. This is overlain, in the Gregory Sub-basin at least, by the Condren Sandstone, a sequence of

sandstones and siltstones of fluvial origin with an abundant Glossopteris-bearing flora (Yeates & others, 1975a). The formation lenses out farther to the northwest (Crowe & Towner, 1976d), and is not present at all in most of the Fitzroy Sub-basin

(Figure 2).

The Hardman Formation, the uppermost unit of the Liveringa Group in the Fitzroy Sub-basin, contains a fossiliferous shallow marine to intertidal unit at the base, a regressive interval in the middle with a Glossopteris-bearing fluvial sequence in the upper half, and a shallow marine to paralic regressive sequence at the top of the succession. The formation is laterally equivalent to the Godfrey Beds, a thin-bedded quartzose sandstone sequence, probably

paralic, with abundant Rhizocorallium burrows and rare plant debris in the Gregory Sub-basin.

In the western part of the basin, south of the Broome Arch, a sequence of fine clastics, the Chirup Formation, was deposited under coastal marsh conditions in the Wallal and Samphire Embayments (Gorter, in Foreman and Wales, 1981; Towner & Gibson, 1980). These beds may be a result of a Late Permian rifting associated with the early break-up of Gondwanaland (Carey, 1976; Yeates & others, 1987). Such deformation may also be responsible for a low-angle unconformity between the Late Permian and Early Triassic sediments in the Fitzroy Sub-basin.

Triassic A coarse fluvial deposit ofearliest Triassic age, the Millyit Sandstone, occurs above the Permian strata in the Gregory and south-eastern Fitzroy Sub-basins. This is overlain by the Blina Shale, a fine grained, bioturbated unit deposited in an environment of intermittently emergent shallow mudflats with fringing swamps as the sea once again transgressed into the basin from the north-west. The Blina Shale is capped in turn by the Erskine Sandstone, a sequence of fine sandy to silty sediments deposited in low energy rivers prograding across these mudflats as the Blina sea retreated. The top of the Triassic sequence is marked by the Culvida Sandstone, a plant-bearing sandy to silty unit of Middle Triassic age. The Culvida Sandstone is restricted in distribution to a small segment of the Gregory Sub-basin, reflecting the effects of right-lateral movements along the boundary faults of the Fitzroy Graben in Late Triassic or Early Jurassic times. Deposition of this unit was followed by a period of extensive erosion, after which a thin succession ofJurassic and Cretaceous strata was laid down on a vast planated surface south ofthe graben.

Jurassic and Cretaceous Up to 700m of marine and fluvial sediments, from Early Jurassic to Early Cretaceous in age, are preserved in the onshore Canning Basin. This sequence thickens, however, to around 4000m near the edge of the present-day continental shelf (Forman & Wales, 1981). The rock units involved, together with an indication of their lithology, origin and distribution, are summarised in Figure 3. The Jurassic-Cretaceous sequence in the onshore part ofthe basin appears to have been deposited in two unrelated cycles of essentially coal-barren clastic deposition. The first of these ranging from Oxfordian to Albian in age, was brought about by a transgression into the western part ofthe basin

Geology of Australian Coal Basins

405

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fluvral fluvra

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Figure 3. Correlation ofJurassic to Early Cretaceous units in the Canning Basin (Yeates & others, 1984). from the north-west, apparently associated with rifting between Australia and an adjoining land mass during the breakup of Gondwanaland. The second, from the south in Aptian to Albian times, was the result of a world-wide sea level rise. Minor, mainly surficial deposits of Tertiary and Quaternary material above the Cretaceous beds complete the stratigraphic succession.

including part of the Winifred Formation in the south (Singleton, 1965) and the Liveringa Group of the Fitzroy Sub-basin (Pickering, 1967, 1968; Galloway & Howell, 1975). Yeates & others (1975a) described minor occurrences from a drillhole intersection in the Condren Sandstone on the edge of Talbot Syncline south of the Pinnacle Fault, in the northwest of the Mt. Bannerman 1:250 000 sheet area.

COAL DEPOSITS Widely distributed coal seams (Towner & Gibson, 1983) are known from the results of a few drill holes in several Permian units, but none is commercial. These occurrences are largely found in paralic deposits with associated carbonaceous shales,

Yeates & others (1984) suggested that the axial portion of this syncline may be worth investigating on the chance that it may have been inherited from a depocentre in which swampy conditions more conducive to thicker coal deposits may have been present. Carbonaceous units present in the Poole

Canning Basin

406 Sandstone and upper Grant Group near Mount Bannerman could also be prospective targets for coal exploration.

REFERENCES CAREY, S.W., 1976: The Expanding Earth.

Deuelopments in Geotectonics, lO, Elsevier Science Publishers.

CROWE, R.W.A. & TOWNER, R.R., 1976a: Permian depositional history of the Noonkanbah 1:250,000 sheet area, Western Australia. Bureau of Mineral Resources, Record L976/24. CROWE, R.W.A. & TOWNER, R.R., 1976b: Environmental interpretation of the Permian Nura Nura Member of the Poole Sandstone,

Noonkanbah sheet area, Canning Basin: a gradation between fluvial and shallow water marine facies. Geological Suruey of Western Australia, Annual Report for 1975, 59-62.

CROWE, R.W.A. & TOWNER, R.R., 1976c: Permian

stratigraphic nomenclature, Noonkanbah sheet area, Western Australia. Geological Suruey of Western Australia, Annual Report for 1975, 56-58.

CROWE, R.W.A. & TOWNER, R.R.. 1976d: Definitions of some new and revised rock units in the

Canning Basin. Geological Survey-of Western Australia, Record 1976/24.

CROWE, R.W.A., TOWNER, R.R. & GIBSON, D.L,, 1978: Permian and Mesozoic geology of the Derby and Mount Anderson 1:250,000 sheet areas, Western Australia. Bureau of Mineral Resources, Record 1978/8.

DRUMMOND, B.J., ETHERIDGE, M.A., DAVIES, P.J. & MIDDLETON, M.F., 1988: Half-graben model

for the structural evolution ofthe Fitzroy Trough, Canning Basin, and implications for resource exploration. APEA Journal, 28(L), 76-86.

DRUMMOND,8.J., SEXTON, M.J,, BARTON, T.J, & SHAW, R.D., 1991: The nature of faulting along the margins of the Fitzroy Trough, and implications for tectonic development of the trough. Exploration Geophy sics, 22, Ill-116. FORMAN, D.J. & WALES, D.W. (Compilers), 1981: Geological evolution of the Canning Basin, Western Australia. Bureau of Mineral Resources,

Bulletin,2tO.

FOSTER, C.B. & WILLIAMS, G.E., 1991: Late

Ordovician -Early Silurian age for the Mallowa Salt of the Carribuddy Group, Canning Basin,

Western Australia, based on occurrences of Tetrahedraletes mendinerusis Strother &

Traverse, 1979. Australian Journal of Earth

Sciences , 38(2), 223-228 .

GALLOWAY, M.C. & HOWELL, D.J., 1975: Relinquishment report on TR 5851H to 5856H, 5878H to 5880H, Fitzroy Trough, Western Australia. Company Report, Esso Exploration and Production-Australia Inc. and Dampier Mining Company. GUPPY, D.J., LINDNER, A.W., RATTIGAN, J.H. & CASEY, J.N., 1958: The geology of the Fitzroy Basin. Bureau of Mineral Resources, Bulletin, 36.

JACKSON, M.J., DIEKMAN, L.J., KENNARD, J.M., SOUTHGATE, P.N., O'BRIEN, P.E. & SEXTON,

M.J., 1992: Sequence stratigraphy of the Devonian-Carboniferous Canning Basin and its use in the identification ofbasin floor fans and other petroleum plays. APEA Journal,32, 214-230. JAQUES, A.L., LEWIS, J.D.,SMITH, C.8., GREGORY, G.P., FERGUSON. J., CHAPPEL, B.W. & McCULLOCH, M.T., 1984: The diamond-bearing ultrapotassic (lamproitic) rocks of the West Kimberley region, Western Australia. 1n Kornprobst, J. (Editor): Kirnberlites - 1: Kim.berlites and Related Rocks. Elsevier, 225-254. PICKERING, R., 1967: Report on coal exploration in Temporary Reserves 3517H, 3518H, 3570H, 3571H, West Kimberley District, Western Australia. Thiess Bros Pty Limited. PICKERING, R., 1968: Report on coal exploration in Temporary Reserves 3518, 3571 and 3896, West Kimberley region, Western Australia. Thiess Bros Pty Limited. RATTIGAN, J.H., 1967: Fold and fracture patterns resulting from basement wrenching in the Fitzroy Depression, Western Australia. Proceedings of the Australasian Institute of

Mining and Metallurgy,223, 17-22. RIXON, L.K., 1978: Clay modelling of the Fitzroy Graben. BMR Journal of Geology and Geophysics, 31, 7l-76.

SINGLETON, A.E., 1965: Sahara No.l well completion report (West Australian Petroleum Pty Limited). Bureau of Mineral Resources, File 64/4L29. SMITH, J.G., 1968: Tectonics of the Fitzroy wrench trough, Western Australia. American Journal of Science,266,766-776. TOWNER, R.R. & GIBSON, D.L., 1980: Geology of the Late Carboniferous and younger rocks ofthe onshore Canning Basin, Western Australia. Bureau ofMineral Resources, Record 1980/30. TOWNER, R.R. & GIBSON, D.L., 1983: Geology of the onshore Canning Basin, Western Australia. Bureau of Mineral Resources, Bulletin,2l5. YEATES, A.N., BRADSHAW, M.T., DICKINS, J.M., BRAKEL, A,T. EXON, N.F., LANGFORD, R.P., MULHOLLAND, S.M., TOTTERDELL, J.M. & YEUNG, M., 1987: The Westralian Superbasin: an Australian link with Tethys. In McKenzie, K.C. (Editor): Shallow Tethys 2. Proceedings of the International Synposium on Shallow Tethys 2,Wagga Wagga, N.S.W., A.A. Balkema, Rotterdam, 199-213. YEATES, A.N., CROWE, R.W.A., TOWNER, R.R., WYBORN, L.A.I. & PASSMORE,V.L., I975A: Notes on the geology of the Gregory Sub-basin and adjacent areas ofthe Canning Basin, Western Australia. Bureau of Mineral Resources, Record L975/77. YEATES, A.N., CROWE, R.W.A., PASSMORE, V.L., TOWNER, R.R. & WYBORN, L.A.L, 1975b: New and revised stratigraphic nomenclature, northeast Canning Basin, Western Australia. Geological Survey of Western Australia, Annual Report for 1974,49-51. YEATES, A.N., WILSON, R.R. & CROWE, R.W.A., 1984: Regional Geology of the Canning Basin, W.A. In Purcell, P.G. (Editor): Proceedings of the Canning Basin Syrnposium, Geological Society of Australia Inc. and Petroleum Exploration Society of Australia Limited.

Geology of Australian Coal Basins

407

STRUCTURAL AND TECTONIC SETTING

&.hford ar ae.s NSW

PG Flood

The Permian Ashford Coal Measures crop out as a discontinuous linear belt some 30km in length from west of Bonshaw, on the QueenslandA.lew South Wales border, to south of Ashford in New South Wales (Figure 1). A small outlier of coal measures also occurs a further 30km to the south.

Along the eastern margin of this belt, the coal measures rest with a marked angular unconformity (Hanlon, 1947) upon a sequence of highly deformed late Carboniferous marine sediments (Texas beds) which Fergusson & Flood (1984) interpret as having formed within a west-dipping subduction complex. The coal measures may have been deposited in a west-dipping half-graben between two thrust slices of this subduction complex. The western margin of the coal measures belt is marked by a prominent high-angle thrust, the Severn Thrust, which dips at

5km

+++ +++ +++ + + ix ++

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Figure 1. Distribution of the Ashford Coal Measures (Pa); Carboniferous Texas beds (Ct); Late Carboniferous Ashford Granite (Cg).

Ashford Area

408

Table 1. Indicative quality of Ashford coal. Moisture (total) Moisture (air dried) Volatile matter (db)

8.07o 2.07o 24.6Vo

Sulphur Specific Energy

0.45%

/000cal\g

Hardgrove grindability index Ash Fusion Temperatures:

Deformation 1350oC Flow 1560oC Crucible swelling number 6 Gray-King coke type G-Go Gieseler fluidity 1000ddpm Vitrinite 57Vo Liptinite trace Micrinite ISVo Semifusinite 227o Fusinite 3% Mean maximurn vitrinite reflectance l.02Vo

BONSHAW SEAM (1.5m)

300 to 70o to the west and which has a throw of

approximately 300m (Owen & Burton, 1954).

The coal measures dip northwesterly at between 20o and 40o. They have been strongly deformed in places, and numerous slickensides have been produced within the coal seams by movement on the Severn Thrust (Ward, 1965). In some places the late Carboniferous Ashford Granite (Bundarra Plutonic Suite) has been thrust over the coal measures, while elsewhere the Texas beds occur above the coal measures sequence.

HISTORY OF GEOLOGICAL INI\TESTIGATIONS

ASHFORD SEAM (11m)

Coal was first discovered in 1884 by John MacDonald in the bed of Coal Gully, approximately 12km north of Ashford, and was first exploited at the turn of the century when a small colliery was opened by means of an inclined tunnel driven on the base of the seam. Mining was abandoned in 1925 after producing no rnore than 2000t (Britten, 1975). Between 1948 and 1950 drilling by the Bureau of Mineral Resources (Owen & Burton, 1954) intersected coal over a strike length of approximately 3km, centred on the old colliery workings. Subsequent drilling in 1956 by the Joint Coal Board outlined adequate reserves for the North-West County Council to build a small power station and mining to supply this installation commenced in 1958 (Robinson, 1956; Britten, 1963; Morris, 1965). In 1976 the Council transferred the Mining Leases to White Industries Limited, who have since carried out further drilling and open-cut development in addition to prospecting a much larger Authorisation area.

STRATIGRAPHY The Ashford Coal Measures comprise up to 300m of

mudstone, sandstone, and conglomerate, with two intercalated seams of carbonaceous shale and coal (Figure 2). The upper of these seams is referred to as the Bonshaw seam and the lower as the Ashford seam (Owen & Burton, 1954). The Ashford seam, which is worked by open-cut methods, is extremely variable, ranging frorn <2m to >15m in thickness.

- unconformity TEXAS BEDS

Figure 2. Stratigraphic section in DDH Nol (Owen & Burton, 1954). Random dots - conglomeratel regular dots - sandstone; lines - mudstonel solid black - coal. Upward-fining cycles - A. The prevalence of Gangamopteris associated with Glossopteris in the coal measures has led to correlation of the sequence with the early Permian Greta Coal Measures of the Hunter Valley (David, 1950). Detailed palynological studies (mentioned by Britten, 1963) have not been able to refine their age further than Permian. The composition of clasts within the conglomerate units indicate that their source was from erosion of

the Texas beds.

Geology of Australian Coal Basins

409

REFERENCEg

COAL QUALITY The coal ofthe Ashford seam is characterised by a high rank and high vitrinite content, a low sulphur content and a moderately low ash yield. It could be used as a medium volatile coking coal, but is used, without washing, as the feed to Ashford Power Station. Specifications of the run-of-mine coal are

indicated in Table 1.

DEPOSITIONAL MODEL Detailed sedimentological studies by Kimber (1977) and Flood (unpublished) suggest that clastic sediments within the Ashford Coal Measures were deposited by a series ofgravelly to sandy streams. The occurrence of large-scale inclined cross bedding similar to those recorded elsewhere in the Bowen and Sydney Basins (Flood & Brady, 1975) indicate that the inclined cross beds, which dip at an angle of 16o on to the top of the Ashford seam and which are up to more than 10m in height, were deposited as a crevasse-splay within a gradually subsiding peat swamp bordering the main fluvial channel. Several upward-frning cycles of sedimentation are evident from drill hole data in the area (see Figure 2). Combined with the absence of planar cross-beds, which are indicative ofbraided stream sedimentation, these suggest that the fluvial system could have been a meandering stream with large levees and extensive overbank sedimentation associated with crevasse-splay deposition on top ofa slowly subsiding peat swamp. Unfortunately, no palaeocurrent data are available to indicate the

direction of stream flow.

COAL RESOURCES The Coal Geology Branch of the New South Wales Department of Minerals and Energy (1984) have stated that the in situ coal reSources at Ashford total 2.5Mt. A total of 785 000t was mined in the period 1959 to 1974 (Britten, 1975), and production has continued since that time at about 100 000t per year. Open-cut resources within the colliery area have now been almost worked out. The sporadic and variable thickness ofthe coal, difficult underground mining conditions, limited resources, remoteness from export facilities and lack of rail transport all combine to render the area of little economic significance, except to maintain operation of the

existing Ashford Power Station.

BRITTEN, R.A., 1963: A geological appraisal of the coal resources ofthe Ashford Coalfield. Joint Coal Board, Unpublished Report No CR 63/1. BRITTEN, R.A., 1975: Ashford Coalfield, N.S.W.In Traves, D.M. & King, D., (Editors): Economic Geology of Australia and Papua New Guinea,2: Coal. Australasian Institute of Mining and Metallurgy, M onograph, 6, 258-260. DAVID, T.W.E. (Editor Browne, W.R.), 1950: The Geology of the Commonwealth of Australia. Arnold and Co., London. FERGUSSON, C.L. & FLOOD, P.G., 1984: A Late Palaeozoic subduction complex in the Border Rivers area of southern Queensland. Proceedings of the Royal Society of Queensland,95, 47-55.

FLOOD, P.G. & BRADY, S.A., 1985: Origin of large-scale cross beds in the late Permian coal measures of the Sydney and Bowen Basins,

eastern Australia. International Journal of CoaI Geology, 5, 231-245.

HANLON, F.N., 1947: The Geology of the Ashford Coalfield. Journal and Proceedings ofthe Royal Society of New South Wales, 8l, 24-33. KIMBER, P.8., 1977: The Ashford Coal Measures: their petrography and regional setting. B.Sc. (Honours) Thesis, University of New England, Armidale. MORRIS, F.R., 1965: Geological investigation at Ashford, January to June, 1965. Joint Coal Board, Unpublished Report No CR 65/1.

NEW SOUTH WALES DEPARTMENT OF MINERALS AND ENERGY, 1984: Coal in New South Wales: industry profile. N.S.W. Department of Minerals and Energy, Sydney. OWEN, H.B. & BURTON, G.M., 1954: Geological and geophysical surveys, Ashford Coalfield, New South Wales. Bureau of Mineral Resources, Geology and Geophysics Report,8, 1-66. ROBINSON, J.8., 1956: Ashford Coalfreld open-cut project. Joint Coal Board, Unpublished Report No. CR 56/8. WARD, C.R., 1"965: Tectonic deformation of coal at Ashford, N.S.W. Journal of the Mining and Geological Society, Uniuersity of N.5.W.,3, 89-104.

Ashford Area

4tt

aklands Basin, NSW EK Yoo

The Oaklands Basin is a Permo-Triassic sedimentary basin in southern New South Wales, totally concealed by the Cainozoic sediments of the eastein Murray Basin (Figure 1). The basin is dominated by the Ovens Valley Graben, a NW-SE trending structure that can be traced from

Wangaratta in Victoria to the Murrumbidgee River near Bringagee, west of Darlington Point. The basin is bounded to the east by Ordovician metasediments and Siluro-Devonian granite in the Daysdale-Urana-Coleambally area, and by granite to the southwest near Berrigan (Figure 2). Available data suggests that the noithern limit occurs south of the Muirumbidgee River. To the west, the Early, Permian and overlying Triassic sediments extend at least to Steam Plains (Yoo, 1982).

STRATIGRA.PHY The sediments of the Oaklands Basin are divided

into three units: the Early Permian llrana Formation, the Late Permian Coorabin Coal Measures and the Triassic Jerilderie Formation (Table 1). LJrana Formation

The Urana Formation consists of grey-green marine sediments including mudstone, siltstone, sandstone, diamictite and conglomerate of early Permian age,

unconformably overlying Silura-Devonian granite and Ordovician slates, phyllites and schists. These sediments have also been identified in a number of petroleum bores drilled in other Permian infrabasins below the western part of the Murray Basin. The

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1: Location of the Oaklands Basin and Figure - isopachs of the Lanes Shaft Coal Member.

Oaklands Basin

412

TCblb,,,1;:..Strstiglaphyii o'f..[h'b,.O,CElauds.'Barcin

and overlying section of the Murray Basin (Modified from Standing Committee on ,0oai,fielA;.G lugfi .1;of'1New;;iS--1$tfi:,.ltffUlEst1fi $.f$};

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KiI,i coal bearing strata correlated with the Loughmore Formation (McMinn, 1981).

sedimentary facies and depositional environment of the Urana Formation have been well documented by O'Brien (1981, 1986).

Coorabin Coal Measures The Coorabin Coal Measures disconformablv overlie the Urana Formation over an area of B000kin2 within and outside the Ovens Valley Graben (Figure 1). The thickest part of the unit is known to occur in an area between Jerilderie and lJrana under the thickest cover, comprising Triassic and Tertiary sediments (363m). The thickness of the coal measures ranges from 30m to 70m within the graben and 20 to 30m outside the graben in the east. The shallowing trend of the coal measures towards the northern graben margin suggests that there would be no coal measure development approximately 25km north of DM Waloona CDH 1 (Figure 1). The Coorabin Coal Measures are subdivided into three formations in the south: the Narrow Plain Formation, the Loughmore Formation and the Nowranie Creek Formation (Table 1; Standing Committee on Coalfield Geology of New Soutli Wales, 1978). Each formation contains point bar sequences which begin with a conglomerate or coarse sandstone and fine upwards through cross-bedded sandstone to siltstone or mudstone. The sequences usually end with coal (Morgan, tg77; Yoo, 1982). In the north, the coal measures consist of a fining upwards sequence which is correlated with the Narrow Plain Formation. The upper two formations are missing except in a bore near Bundure (DM Bundure CDH l-), which intersected

Narrow Plain Formation The Narrow Plain Formation is the basal point bar sequence of the Coorabin Coal Measures, and occurs both within the graben and outside it, east of Oaklands. The formation consists entirely of off-wbite quartzose micaceous sandstone, poorly consolidated, with conglomerate bands and sparse carbonaceous fragments cemented with clayey silt. The formation is assigned to the lower Stage 5 palynological zone ofEvans (1967) and Paten (1969). It unconformably overlies a weathered zone at the top of the Urana Formation (Stage 3 of Evans, 1967). Within the graben, the weathered zone is g!oq! 0.5m thick, and to the west of the graben in

DM Wood CDH 1, where the Urana Formation underlies the Jerilderie Formation, it is 4.3m thick.

The thickness of the Narrow Plain Formation varies, but generally decreases toward the graben margin. The maximum thickness of 34m is recorded in the type section at DM Oaklands RDH 3 in the south. The formation is about 30m thick in the northern part of the graben. Lanes Shaft Coal Member: The Lanes Shaft Coal Member occurs at the top of the Narrow Plain Formation, and is the main coal seam in the Oaklands Basin. Its thickness is 18m in the Oaklands-Coorabin area, 12m between Yanko Creek and Mclennons Bore Road, and more than 4m over most of the remainder of the basin (Figure 1). The overburden above the Lanes Shaft Coal Member is about 60m thick near Oaklands; it increases in thickness towards the north-west, reaching 340 to

Geology of Australian Coal Basins

413

\ \

.n IDM \

':iiiii\\

IEDI

f \ rdf

3 \-

'\.\ Figure 3. Inferred distribution of the Loughmore and Nowranie Creek Formations.

Figure 4. Inferred distribution of the Jerilderie Formation.

360m between AOG Jerilderie 1 and DM Yanko South CDH 1 (Figure 2). To the north of DM Yanko

Nowranie Creeh Formation

South CDH 1, however, the overburden gradually thins. The Lanes Shaft Coal Member is expected to extend 25km north of DM Waloona CDH 1.

Loughmore Formation The Loughmore Formation is the middle point-bar sequence of the Coorabin Coal Measures, and has been assigned to the upper Stage 5 palynological zone ofPaten (1969). It occurs in an area between Oaklands and Bundure (Figure 3), unconformably overlying the Lanes Shaft CoaI Member throughout most-of t-his area but overlying the Urana Formation at Bundure. The unit is unconformably overlain by the Nowranie Creek Formation, and where this is absent, by the Jerilderie Formation. It ranges in thickness from 7 to 18m in the south and is 13m

thick at Bundure.

The Loughmore Formation consists of poorly consolidated pebbly sandstone, siltstone, claystoneand carbonac-eous ilaystone with coal at the top. The sandstone is generally light grey in colour, isquartzose and micaceous in composition.and has a wtrite silty matrix with common coaly wisps. Tlre pebbles aie generally rounded to subangular white quartz up to 20mm in diameter. Coreen Creek Coal Member: The Coreen Creek Coal Member lies at the top of the Loughmore Formation and is generally poorly developed. It is ofvariable thickniss and ii <f .Stir thick i-n most of the area. A borehole at Bundure intersected a section ofthe Coreen Creek Coal Member 4.8m thick.

The Nowranie Creek Formation occurs in a small area south of AOG Jerilderie 1 in the graben (Figure 3), unconformably overlying the Loughmore Formation and unconformably overlain by the Jerilderie Formation. The unit consists of light grey claystone and carbonaceous claystone with abundant coaly partings in the upper half. The claystone is gen6rally weathered and ironstained at the t_o-p_ (Standing Committee on Coalfield Geology of New South Wales, 1978) and its thickness ranges from a few centimetres to >7m.

Jerilderie Formation The Jerilderie Formation overlies the Coorabin Coal Measures within and to the east of the graben, and overlies the Urana Formation outside the graben to the west (Figures 4 and 5). Its thickness ranges from 220m at thelype section (AOG Jerilderie 1, Wright & Stuntz, 1962) to 95m in the northern part and to the west ofthe graben at Steam Plains. The

Jerilderie Formation is unconformably overlain by the Tertiary Olney Formation.

The formation is divided into three lithological sequences, with a pebbly sandstone sequence at the baie, gravel bed in the middle and siltstone at the top. The sandstone consists of off-white, medium to very coarse grained quartzose and micaceous sediment in a matrix of white kaolinitic clay. Low to high angle cross bedding is common. The thickness oflhis sandstone is about 58m in the northern part. The sravel bed consists ofwell sorted subrounded to roun"cled pebbles of quartz (65Vo), chert (157o) and

Oaklands Basin

414

DM Waloona WRC

DM Morton

200m

CDH 1

cDH

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200m

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100

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Triassic

rE] @

Shepparton Formation

Late Permian

Calivil Sand

Early Permian

Olney Formation

Palaeozoic Jerilderie Formation

Geological boundary G eol o g i cal b ou n dary ( nf e rred

)

E @ E @ Fault Fault zone

Unconformity

Figure 5. Geological cross-sections through the Oaklands Basin.

Geology of Australian Coal Basins

Coorabin Coal Measures Urana Formation

granite metasediments

415 sandstone (6Vo),witt, minor quartzose sand (107a), and silt (4Vo).The thickness of this bed in the

northern part is 57m.

The claystone at the top of the formation consists of

off-white to light grey clay and silt with a variable proportion ofsand. The thickness ofthis claystone is 38m in the northern part. A thin micaceous/ carbonaceous band in the middle of the Jerilderie Formation contains a microflora of mid-Triassic age (McMinn, 1981).

STRUCTURE

Faulting The Ovens Valley Graben is a northwest trending structure which is 25km wide at Oaklands and 15km wide in the northern part of the basin. Seismic traverses across the basin (Palmer, 1977) and stratigraphic correlation between boreholes indicate the faulted nature of the graben margin. The Coorabin Coal Measures are steeply dipping along the graben margins. The maximum subsidence of the graben occurred near the location of AOG Jerilderie 1. Figure 5 shows that the displacement on the eastern margin fault, between AOG Jerilderie 1 and APE lJrana 1, is 170m. The Felton Woods Fault at Oaklands (Bunny & Milligan, 1979) is a southern extension of the eastern graben fault, which became a hinge fault. On the southern margin the coal measures within the graben are uplifted 40m (Figure 2). A small sub-parallel normal fault is also recognised to the east of the hinge fault in the Oaklands area (Kembla Coal and Coke Pty Ltd, 1986).

Folding Seismic survey data indicate that folds are developed within the graben, with axes trending parallel to the bounding faults. The major structure is a broad anticline which has parasitic folds on both limbs. The Norwanga Syncline (Blayden & Bunny, 1977) and the Wangamang Anticline (Milligan & Bunny, 1982) are flexures on the eastern limb identifred in the Oaklands area.

DEPOSITIONAL ETWIRONMENTS

The Permian coal measures may have been deposited over a wider area than that presently suggested by seismic and borehole information, with an unknown amount having been removed by subsequent erosion (Yoo, 1982; O'Brien, 1984).

Triassic The Oaklands Basin continued to subside during the Triassic, with fluvial sediments deposited over the coal measures. The region subsided more rapidly

during the mid-Triassic, which resulted in a large influfof gravel and coarse sand into the basin. The source area of these sediments is not certain, but thev mav have been derived from the Palaeozoic meiasediments to the east. Another possibility is that the well rounded quartz pebbles represent reworked clasts of Devonian conglomerate from the north. This period ofvigorous gravel deposition was followed by ilevelopment of a short-lived, minor overbank swamp environment, the sediments of which contain a-mid- Triassic microflora.

COAL QUALITY AND PETROGRAPIIIC CHARACTERISTICS The coal of the Lanes Shaft Coal Member is a

high-moisture, low-volatile sub-bituminous coal. Lustrous bands are commonly found in the upper part of the seam, and fine fusain laminae are contained throughout. Petrographic examination (Kembla Coal and Coke Pty Ltd,1986) indicates that the coal has a low vifrinite content (L6-187o), with high inertinite (62-72Vo), and high liptinite (5-97o). Proximate analysis data for the un-oxidised co-al, expressed on an air dried basis, are given in Table 2. TCbl 6 2,;,,,Tvnicat nt6ltjil of O akl ailds: :S$sia

Moisture Ash Volatile Matter Fixed Carbon Sulphur Specific Energy

L2 - 167o 13 - t97o

25 - 29Vo 40 - 45Vo 0.25Vo

19 - 20MJ/kg

Permian

COAL RESOURCES

A marine incursion from the west appears to have started in the early Permian, forming an embayment with its eastern margin in the Daysdale-UranaColeambally region (Yoo, 1982). Thick sequences of early Permian marine rocks were deposited in this embayment. More rapid subsidence appears to have occuried within the Ovens Valley Graben, resulting in deposition of a thick diamictite, siltstone and sanditone facies in the centre (O'Brien, 198L; 1986).

The rneasured in situ coal resources of the Oaklands Basin are estimated at 1200Mt in the CRAMitsubishi Joint Venture area near Oaklands. Another 3000Mt of inferred in situ resources have been estimated to occur in the northern part of the graben, with a minimum seam thickness of 4m and a maximum raw ash of 30Vo. With further investigation in the unexplored areas at least anothei 10 000Mt of in situ inferred resources may also be present. The coal identified to date is suitable for power generation and, if required, for

Following the regression of this early Permian sea' a thin sequence of Late Permian fluvial coal measures was intermittently deposited. Each formation within the Late Permian coal measures fines upwards, with channel sand at the base overlain by a point bar sequence deposited by meandering streams (Mor-gan, 1977; Yoo, 1982). Peat swamps were formed on the alluvial flood plains. Tbr. !hig-k-"st se_quence of coal measures occurs rn AOG Jerilderie 1, indicating that more subsidence occurred in the centre ofthe graben at this time.

gasification.

Overburden Thickness The overburden thickness above the seams of the Lanes Shaft Coal Member ranges from 60m in the south to 360m in the centre and north centre ofthe basin (Figure 2). A considerable proportion ofthe in situ coal in the Oaklands area, 880Mt, is known to huu" .r overburden ratio ofless than 5m3 per tonne

Oaklands Basin

416 and of this, 240Mt have <3m3 of overburden per tonne. There appears to be little potential, however, for open cut mining of the deeper coal. Underground mining would be subject to several problems associated with the poorly consolidated roof rocks,

as well as the presence of major aquifers above and below the coal seam.

Oxidation The Lanes Shaft Coal Member is overlain by Tertiary sediments along the southeastern and southern margin of the basin. Around this margin the coal has been exposed or buried under shallow cover for a long period, causing oxidation to variable depths. The oxidation zone in the coal thins towards the west and northwest, in conjunction with increasing seam depth. The economic value of the oxidised or partially oxidised coal is doubtful, as ash of over 20Vo is indicated, accompanied by a low specific energy.

Groundwater Since the discovery of coal in 1915 in a water bore, small scale underground mining has intermittently taken place in the Oaklands area. On every occasion, however, mining has encountered serious water probiems. The occurrence of groundwater in the Oaklands area has been investigated as part of a feasibility study for development of the coal (Kembla Coal and Coke Pty. Ltd., 1986). Three major aquifers have been identified immediately above and below the main coal seams (Loughmore Formation and

Narrow Plain Formation) and in the Tertiary Calivil Sand. Pumping tests indicate a wide variation in transmissivity, with values ranging from 59 to 1400mr/day tCoffey and Partners Pty Ltd, 1983). The groundwater is saline (a total dissolved solids content between 1000 and 10 000mg/l) and unsuitable for irrigation or domestic use. It also has the potential to contaminate surface water around the possible mine site at Oaklands, which is used downstream for irrigation purposes.

Trace Elements The coal in the top section of the seam in the Oaklands area is reported to be considerably higher in uranium and thorium than other Australian coals (Rice, 1984). However, drilling has shown that the uranium, thorium and potassium content of the seam at Oaklands increases only where the coal is weathered, and that the proportions of these elements decrease with depth towards the west and northwest (J. Lea, personal communication, 1985).

REFERENCES BLAYDEN, I.D. & BUNNY, M.R., 1977: Oaklands Project: Exploration Permit No. 3, Phase I exploration. Earth Resources Australia Pty Ltd. BUNNY, M.R. & MILLIGAN, I.M., 1979: Oaklands Project. Earth Resources Australia Pty Ltd, Report A49.

COFFEY AND PARTNERS PTY LTD, 1983: Oaklands groundwater and geotechnical investigation, Volume II. Coffey and Partners Pty Ltd, Report No. H46l3-AV.

EVANS, P.R., 1967: Upper Carboniferous and Permian palynological stages and their distribution in eastern Australia. Bureau of Mineral Resources, Record 1967/99.

KEMBLA COAL AND COKE PTY LTD, 1986: Oaklands Joint Venture: second six-monthly report,

Authorisation Nos 207, 250 and 345. Kembla Coal and Coke Pty Ltd.

McMINN, A., 1981: Palynological results from the Murray Infrabasin drilling project. Geological Survey of New South Wales, Report Palynology 1981/6.

MILLIGAN,I.M. & BUNNY, M.R., 1982: Geological report on 1981 drilling programme, E.P. 3 . Oaklands, N.S.W. Earth Resources Australia Pty Ltd, Report A117. MORGAN, R., 1977: Stratigraphy and palynology of the Oaklands Basin, New South Wales. Geological Suruey of New South Wales, Quarterly Notes, 29, 1-6.

O'BRIEN, P.E., 1981: Permian sediments beneath the Murray Basin. Bureau of Mineral Resources, Record, 1981/60.

O'BRIEN, P.E., 1989: Permian coals of the Ovens Graben, Oaklands area, New South Wales. 1z Harrington, H.J. (Editor): Permian Coals of Eastern Australia. Bureau of Mineral Resources B ulletin, 231, 184-188. PALMER, D., 1977: Interpretation of two seismic reflection traverses in the Oaklands Basin, north of Jerilderie. Geological Survey of New South Wales, Report GSI977 /142. PATEN, R.J., 1969: Palynologic contributions to petroleum exploration in the Permian formations of the Cooper Basin, Australia. APEA Journal,

9(2),79-87.

RICE, T.D., 1984: Trace elements in the Oaklands coal seam: a progress report. New South Wales Department of Mineral Resources, Chemical Laboratory Report 84/34.

STANDING COMMITTEE ON COALFIELD GEOLOGY OF NEW SOUTH WALES, 1978: Stratigraphy of the Coorabin Coal Measures. Records of the Geological Survey of New South Wales, L8(2),

t4t-146.

WRIGHT, A.J. & STUNTZ, J.,1962: AOG Jerilderie No 1, Murray Basin, New South Wales, well completion report. Unpublished Report, Australian Oil and Gas Corporation Ltd (Petroleum

- WRC 58).

YOO, E.K., 1982: Geology and coal resources of the

northern part of the Oaklands Basin. Geological

Suruey of New South Wales, Quarterly Notes, 49,

t5-27.

Geology of Australian Coal Basins

417

The Gloucester Basin is a north-south trending,

ffiloucester

Basin

asymmetrical synclinal structure, 40\m long and tOtm wide at iis widest point, located approximately 100km north of Newcastle (Figure 1). The basin occurs as a valley development between the Barrington Tops'range on the western side and the Mografri Rang-e on th-e eastern side, and has top6graphy virying from generally flat in the north to-undu-lating south of the Craven township.

Tectonic Setting

WW Hughes

The basin is a remnant inter-arch basin, developed in the early Permian behind the New EnglandArch, which itself existed during the collision of the East Australian and Pacific Plates (Figure 2). This collision resulted in development of a subduction zone with associated magmatic arch and sedimentary basins. The primary basin structures which have-impacted on the coal-bearing portion of the sequence were developed following the cessation of the volcanic activity asiociated with the magmatic arch formation. The Gloucester Basin was separated from the Sydney Basin to the west by a ridge comprising P-ermian volcanics and Carboniferous sediments' The strata in the south of the basin, however, were possibly contiguous with those of the.Sydney lasin, with ttre join ilong a narrow depression extending from theiouthern closure ofthe current Gloucester

Basin area.

Exploration History Coal was first discovered in the Gloucester Basin in the 1850s when Odenheimer (1855) located a seam now known as the Weismantel coal seam. Following this discovery there were a number of attempts to determine the extent and mineability of the coals within the basin. The first formal stratigraphic subdivision of the Gloucester Basin, however, was developed by Loughnan (1954). Surface mapping and a drilling program in the basin were carrieil-ouf in L970-77 by Avon Syndicate and

Noranda Australia Limited. A revised stratigraphic subdivision of the area was produced (George, 1971, 1975), although no potential mining areas were identified. BMI Mining Limited formed a joint venture with the Avon Syndicate and Noranda in 1977, and subsequently conducted an exploration program which defined two poteqtial -op-en-cut miriing areas, the Stratford and Wards River areas, in the-eastern portion of the basin (BMI Mining Ltd, L984a,1984b).

A program using high-resolution mini-SOSIE seismic techniques to guide drilling activity was initiated by Esio Australia Limited in conjunction with BMI Mining in 1981. A number of other activities, includlng surface mapping, aeroma.gnetic surveying and conslruction of a three-dimensional seismic model, were also incorporated in this program to supplement the drilling and seismic data (g,tltr"r & otliels, 1934). Although the work was u.rabl" to delineate a geologic structure containing a large amount (50Mt) o1 potentially economic- coal, it led"to the identificationbf several areas in the basin with at least some potential for economic coal development.

Gloucester Basin

4ta

A31 1

NEW SOUTH WALES

GLOUCESTE

BASIN I

\.cANBERqn

SIMPLIFIED GEOLOGY CROWTHERS ROAD CONGLOMERATE T-------:---1 tt

CRAVEN COAL MEASURES

WARDS RIVER CONGLOMERATE w

W ffi ffi

AVON COAL MEASURES

DEWRANG FORMATION

STRATIGRAPHY AND DEPOSITIONAL EI{VIRONMENTS The lowermost stratigraphic unit of the basin is the

Stroud Volcanics, which is coal-barren 4nd not discussed further in the present work. The overlying sequence has been divided into two groups, the Dewrang Group and the Gloucester Coal Measures, each of which has been further subdivided to give a total of eleven formations in the post-Stroud Volcanics succession (Table 1). The Dewrang Group is laterally persistent over most of the basin, but marked lateral facies changes do occur in the Gloucester Coal Measures, particularly along the western basin margin where almost the entire sequence is made up of conglomerate.

Stratford

Clear Hiil

A31 5

Generally the Dewrang Group was deposited in a marginal marine to shoreline environment which was quite stable and subject to few lateral variations. The Gloucester Coal Measures, by contrast, were deposited in a terrestrial fan-delta and accumulated during a period of tectonic instability. Table 1 also shows the positions of the gamma-ray markers (tuffs), coal seams and other units in relation to the formally-named rock units in the Gloucester Basin succession.

Dewrang Group The Dewrang Group has been subdivided into three formations, namely the Durallie Road Formation,

the Weismantel Formation and the Mammy Johnsons Formation. A description of each of these is as follows.

Durallie Road. Formation The Durallie Road Formation, between the Stroud Volcanics and the Weismantel Formation, consists generally of sandstone. In the north it is composed of fluviatile sandstone and conglomerate, whereas in the south it is a well-sorted marine sandstone. No coals have been located in this part ofthe

Wards River

stratigraphic sequence.

Weismantel Formation The Weismantel coal seam occurs at the base of this

formation, and is recognisable over a large part of the basin. Overlying the coal is a thick,

Figure 1. Location and simplified geology of the Stroud-Gloucester Trough.

Geology of Australian Coal Basins

419

Ncw England Alch

Esrly Permlan

Figure 2. Diagrammatic sketch showing possible tectonic development of the Gloucester and Sydney Basins. (After Branagan & others, 1976). coarsening-upwards shale horizon which is in turn overlain by a thick, bioturbated fine to medium grained sandstone. These units are also laterally

persistent.

The depositional environment of the Weismantel Formation shows a marked marine influence. The Weismantel coal seam was probably deposited in the landward parts of a back-barrier lagoon.

Accumulation of peat was terminated by a marine transgression, as shown by an increase in sulphur values in the top metre of the seam (BMI Mining Ltd, 1984a). The overlying shale represents deposition in the back-barrier lagoon itself, while the sandstone may represent a subaqueous barrier system.

Mammy Johnsons Formation The Mammy Johnsons Formation consists of coarse grained lithic sandstone, and is quite similar to the underlying Weismantel Formation. Bioturbation is not as common, however, and there are some coarse sandstone to conglomerate horizons suggesting a more near-shore, higher energ"y depositional environment. Coal seams also occur at the base of the coarsening-upward sequence, although they are

generally only thin or contain a large proportion of stone bands. None is as well developed as the Weismantel coal seam.

The top of the Mammy Johnsons Formation (and of the Dewrang Group) is a thick shale below the overlying Waukivory Creek Formation of the Gloucester Coal Measures.

Gloucester Coal Measures Table I ; Stiatigraphic suo-division of the GloU,sester BaCih (after HugheC & othdis, 1984)f :

Craven Sub-group Gloucester

Crowthers Road Conglomerate Woods Road Formation Bucketts Way Formationn Wards River Conglomerate

Coal

Measures

Wenhams Formation Speldon Formation Dog Trap Creek

Avon Sub-group

Dewrang Group Stroud Volcanics

Formation

Waukivory Creek Formation Mammy Johnsons Formation Weismantel Formation Durallie Road Formation

Marine-influenced deposition of the Dewrang Group was terminated by the progradation of fluviatile sediment over the back-barrier lagoonal deposits of the Mammy Johnsons Formation. Tectonism led to the uplift of a mountain range to the west of the present Gloucester Basin, subsequent erosion of whictr shed large quantities of clastic debris towards the east. The establishment of this westerly source influenced the deposition of the entire Gloucester Coal Measures sequence. The Gloucester Coal Measures have been subdivided into two sub-groups, the Avon Sub-group and the Craven Sub-group. These two sub-groups are separated bya marine transgressive sequence, the Speldon Formation. Each of the two sub-groups has been further divided as follows.

Auon Sub-group The Avon Sub-group comprises the lower 400m of the Gloucester Coal Measures. It has been subdivided into two formations, the Waukivory Creek Formation and the Dog Trap Creek Formation.

Waukivory Creek Formation The lithology of the Waukivory Creek Formation reflects the westerly sediment source, with a marked increase in grain size and an accompqnying change

in depositional environment in that direction. Coal

Gloucester Basrn

420 is well-developed on the eastern side of the basin, with the main seams in ascending order being:

Parkers Road coal seam Valley View coal seam Glen Road coal seam Rombo coal seam Tripie coal seam Avon Lower coal seam Avon coal seam

loads directly into a shallow marine environment where they were reworked to form offshore bars. In the north east ofthe basin, on the property "Speldon", these sands crop out and exhibit a marine fauna. The top split of the Glenview coal seam shows very high sulphur values (up to 7.SVo) supporting a marine or marginal marine environment.

Craaen Sub-group

The Waukivory Creek Formation is an essentially regressive.sequence, with deposition probably

occurring in an upper delta-plain environment. Thick (4-10m) medium grained sandstones occur throughout the bulk of this interval, representing point bar deposits of meandering fluvial channels. Dog Trap Creek Formation

The Dog Trap Creek Formation occupies the interval from the top ofthe Avon coal seam to the top ofthe Glenview coal seam. Deposition on the eastern side of the basin occurred in a lower delta-plain

environment, implying a partial transgression after the accumulation of the Avon seam.

In the vicinity of Stratford, the Avon seam is overlain by a finely laminated mudstone which probably accumulated in a freshwater lake. The thickness of this mudstone is highly variable, and can be related to movement along syndepositional faults which dropped large areas of the plain and allowed bodies of open water to develop. In some places the lacustrine mudstones are replaced by a thick (20m) stacked sand unit; this may represent a series of proximal crevasse splays or possibly channel bar deposits ofa sandy braided stream which was moving across the depression created by the syndepositional faulting. The middle section of the Dog Trap Creek Formation shows a more typical terrestrial sequence, ranging

from floodplain deposits of siltstone, mudstone and coal (Marker 2) to point bar sandstone beds. Bioturbated mudstone and poorly sorted sandstone were deposited during a marine transgression towards the top of the formation. The transgression was only a short-lived event, however, as movement on syndepositional faults led to a rising of the water table. A depositional hiatus followed, during which the Glenview coal seam was formed. As with all other formations the stratigraphic interval occupied by the Dog Trap Creek Formation

is represented almost exclusively by conglomerate on the western side of the basin. Speldon Formation

The Speldon Formation encompasses the interval from the top of the Glenview coal seam to the base of the Bowens Road Lower coal seam. It was deposited

during a marine transgression. In the central eastern part of the basin the unit contains a mixture of bioturbated mudstone, sandstone and poorly sorted conglomerate which represent deposition in an interdistributary bay. The mudstone represents delta-front deposits whereas the sands or conglomerate represent subaqueous splays. To the north and south the formation is composed almost entirely of bioturbated sandstone, similar in many respects to the thick sandstones of Mammy Johnsons Formation. It is suggested that these sands developed from the discharge of sandy river

The Craven Sub-group, approximately 1000m thick, has been subdivided into five formations. These are made up individually as follows: Wenhams Formation The Wenhams Formation, extending from the base of the Bowens Road Lower coal seam to top of the Bowens Road coal seam, represents deposition through a regression following the underlying transgressive succession. The Bowens Road Lower coal seam, like the Glenview seam, occurs between bioturbated sediments.

The Bowens Road seam contains up to 15m of dull coal, which formed in a peat swamp with a relatively low water table. The quality of the coal deteriorates rapidly toward the top of the seam, reflecting increasingly oxidising conditions. The Bowens Road seam formed at the start of a major regressive depositional cycle, and its overall dull character

reflects accumulation in a high-level alluvial plain setting. Wards River Conglomerate

This formation consists dominantly of conglomerate and sandstone and represents alluvial fan and braided stream deposits. It thickens rapidly towards the western side of the basin, reflecting the westerly provenance of sediment of the Gloucester Coal Measures. Except for the Clear Hill area, the Wards River Conglomerate in fact occupies the entire Gloucester Coal Measure sequence along the western margin of the basin. The Wards River Conglomerate is very much reduced in thickness on the eastern side of the basin. This suggests that only a few active braided stream systems spread right across the Permian

depositional plain.

Bucketts Way Formation The Bucketts Way Formation is a terrestrial suite of fine grained sandstones, shales and mudstones, which vary in grain size depending on proximity or otherwise of fluvial channels. Coal seams are numerous, but with the exception of the Roseville and Cloverdale seams they are generally thin, highly variable and of little economic significance. Frequent flood events are reflected by the preservation ofthin coal seams or by heavy banding

in the thicker seams.

The sediments of the Bucketts Way Formation were probably deposited in an upper delta plain

depositional environment. Woods Road Formation On the eastern side of the basin the Woods Road Formation, like the Bucketts Way Formation, consists of sediments deposited in an upper delta plain environment. Coal seams are numerous and thin. Sporadic conglomerate horizons spread both laterally and vertically through the formation; these

Geology of Australian Coal Basins

421

\aN

\:\\<-

,/y

-)s' \ j

/r-

) at.\'

---

:\' -t

2' r/,

r\-

:_ t

/a,

) ;\.\

'/t,

,,/,

\vl

\{ \r.--r l\

t\ /\

..-- 17r,-

)

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Figure 3. Palaeogeography at the time of deposition of the Woods Road Formation.

represent deposits of braided streams emanating from the contemporaneous fans that formed the Crowthers Road and Wards River Conglomerates to the west and north-west. Deposition at this time in the central part of the basin took place on an alluvial plain. Coal is much less widespread and the sequence is more sandy, reflecting the presence of low-sinuosity, sandy braided channels and associated floodplain areas

(Figure 3).

The Woods Road Formation is represented by conglomerate along most of the western side of the basin, except at the western end of Woods Road,

Craven, where an inter-fan depression existed during deposition. In this depression (referred to as the Clear Hill area), coal and freshwater lacustrine mudstone are interspersed with floodplain mudstone, siltstone and sandstone. The upper 200 to 300m of the Woods Road Formation is composed of fine to medium grained sandstone with interbedded siltstone. Coal development in this section is minimal. Such

sediments were probably deposited on an alluvial plain as outwash deposits of alluvial fans to the west. There are six tuffs throughout the Woods Road

Formation, which form laterally persistent marker horizons that can be correlated over large areas of

the basin (e.g. between the Jacks area in the north and the Clear Hill area in the west). The tuffs range in thickness up to a maximum of 14m, and represent air-fall deposids of vitric crystal lithic ash which may have been reworked by water. Crowthers Road Conglomerate The Crowthers Road Conglomerate, like the Wards River Conglomerate, is largely confined to the western side of the basin. Apart from the depression in the Clear Hill area, deposition of conglomeratic material was continuous long the western margin for the entire period of Gloucester Coal Measures accumulation.

Like the Wards River Conglomerate, the Crowthers Road Conglomerate represents an alluvial fan deposit. On the eastern side ofthe basin there are also rare conglomeratic horizons in the Woods Road Formation which represent distal braided channels emanating from these fans.

BASIN STRUCTURE

Structural Overview The Gloucester Basin is an asymmetricai synclinal structure with a north-south trending axis. With the exception of the Stratford Syncline, in which the

Gloucester Basln

422

Stratford potential mining area is located, there appears to be little folding present within the basin. Most of the deformation has been of a brittle nature, resulting in the development of an intense and complex fault pattern.

development. The Stratford area includes such an anomaly, and is discussed more fully elsewhere in this paper.

The basin has undergone numerous episodes of faulting, which are represented today as both

asymmetrical, north-plunging syncline. This part of the basin is also less structurally disturbed than the remainder of the eastern margin, with almost no major reverse faulting being present. The majority of both the north-south and east-west faults in the basin are contained within the eastern margin area.

high-angle and low-angle reverse faults and high-angle normal faults. The majority of the reverse faults have a north-south orientation while the normal faults tend to have an east-west orientation. There also appears to have been significant right-lateral wrenching on a number of major east-west normal faults, resulting in an east-west offset in the central part of the basin. The major normal faulting was contemporaneous with deposition of the Avon Sub-group and the lower part ofthe Craven Sub-group, and has significantly

impacted on coal seam development. Sections drawn with the Glenview coal seam as datum, for example, show significant faulting prior to the deposition of that particular bed. Movement on the normal faults, however, appears to have ceased during the deposition ofthe upper part ofthe Craven Subgroup, and the traces of these major syndepositional east-west faults appear to die out in a westerly direction underneath the Woods Road Formation. Some post-depositional normal faults are also present in the basin, and these often appear to have an associated right-lateral wrench component. The major reverse faulting is generally orientated

north-south, and occurred during the main contractional phase of basin development. The displacement of these faults ranges from about 1m to in excess of 500m. The high-angle reverse faults probably resulted from reactivation of the major basin-forming normal faults. The lesser scale, but still often substantial reverse faulting occurred during the early stage of contraction, with an original inclination of about 15o greater than that of bedding. Because ofthe steep bedding dips now present in the basin, however, these faults can have absolute dips ofup to 70o. Major tilting of the beds in the basin appears to have been associated with the late-phase compressional movement, which also resulted in

some reactivation of the east-west normal faults and

post-dated the majority of the reverse faulting. This movement probably took place in the late Permian. The basin itself can be divided into three broad

structural units: a complex, steeply-dipping eastern margin, a less complex, steeply-dipping western margin and a relatively flat-lying central section. These are discussed separately.

Eastern Margin Area This area comprises the eastern one-third of the basin. It varies in width from approximately 1km in both the north and south to a maximum of 4.5km in the central part ofthe basin. The sequence present in this area largely belongs to that part of the stratigraphic succession below the Jo-Doth Tuff, and is characterised as a complex, steeply-dipping section containing numerous reverse faults and a few normal faults with dips ranging up to 85o. While this zone has an overall steeply dipping character, it contains a number of structural anomalies which have locally produced shallower dips and improved the prospect of economic coal

The eastern and western margins join in the southern part of the basin to form a simple

Western Margin Area The western margin of the basin is less complex than the eastern margin, with dips being more uniform and ranging only up to about 40o. This zone has a maximum width of approximately 2km, but decreases in width in association with the southern and northern closures ofthe basin's overall synclinal

structure.

Unlike the eastern margin, there are no internal structural anomalies present within the western margin of the basin. There is, however, an anomalous area of coal development, in the Clear Hill area, located in the central portion of the western margin sector. The part of the sequence contained within the western margin varies with geographical location. In the southern closure area the western margin consists entirely of the Dewrang Group. The Avon and Craven Sub-groups become progressively included further to the north, with the Woods Road Formation being the uppermost unit included in the western margin area. Coincident with the inclusion of the upper formations within the western margin belt is the loss of the lower formations, causing the contact between the basement (taken as the Permian volcanics or the Carboniferous sequence) and the basin section to become younger. This feature has probably developed as a result ofthe on-lap ofthe basinal sequence over a pre-existing high, which was present in the central part of the western margin during deposition of the lower part of the sequence. The youngest sediments in contact with the basement along the western margin are part of the Bucketts Way Formation. The main faults associated with the western margin are the major basin margin fault and a series of normal faults trending roughly perpendicular to the basin margin. There appears to be little of the reverse faulting which is common in the eastern

margrn area.

The lesser degree of structural deformation along the western margin, relative to the eastern margin, is probably related to the difference in sediment type and thickness. The sediments along the western margin are mainly conglomerates and massive sandstones, which are as little as 700m thick around the Clear Hill area in the central part

ofthis tract. By contrast there is a fine-grained, laminated sequence up to 2300m thick in the eastern margin area,

The anomalous flat lying section 2km long on the western margin probably developed due to the protection by a remnant igneous body to the north-west of the Clear Hill area, which resisted the compressional movement that deformed the remainder of the western margin. An alternative explanation is that this area has indeed been

Geology of Australian Coal Basins

423

Spoldon Dog Tr€p

tr.._.....--...-.-......-\

Formallon

Creok

wauktvo.y c.ook Formoilo Mammy Johnsons

Formailon

Fo.msilon /

Figure 4. Diagrammatic section during deposition of the Wenhams Formation (not to scale). faulted, but that the steeply dipping section has

lesser amount of faulting and appears to be more

since been eroded.

uniform.

Central Area

Tectonic History The first Permian activity in the Gloucester Basin was the deposition of the Stroud Volcanics, with the

Between the eastern and western margins of the basin there is a central area in which the east-west dip component is less than 50. In the southern part of the basin this central area forms the synclinal nose, with a north-south dip component up to 10o

reflecting the basin plunge. In the northern part of the basin the central flat-lying area appears to be terminated by faulting.

The central flat-lying area is dissected by only a few north-south trending reverse faults and some east-west trending normal faults. These normal faults are extensions of the normal faults present in the eastern and western margins. The main east-west trending syndepositional faults do not appear to have reached the surface in this part of the basin. The subcrop within the central area consists mainly of the Woods Road Formation. Maximum sediment thickness in the basin, estimated at around 2300m, probably occurs at the intersection of this area and the eastern margin block. The change from the steeply dipping eastern margin to the area ofrelatively flat lying strata in the central part of the basin is also coincident with the basin's depositional centre. In this area the eastern portion of the basin formed a half graben into which a greater amount of sediment was deposited. With the onset of compressional stress, the sediments were compacted and faulted but the basement remained rigid, causing a series of fractures to radiate from the basement ridge. A reduction in sediment thickness of approximately lkm occurs across this feature; approximately 2.3km of sequence is present on the eastern side while only 1.3km of sequence is developed on the western side.

In the northern and southern portions of the basin the change from steeply dipping to relatively flat strata is much more gradual, with little faulting being apparent. In comparison with the complex structural junction between the eastern margin and the central flat area, the junction between the western margin and the central flat area displays a

Dewrang Group deposited during the restricted marine conditions which followed this volcanism. Depositional conditions for the Dewrang Group sediments ranged from brackish in the south to terrestrial in the north ofthe basin.

Tectonic activity increased following Dewrang Group deposition, with the formation of an asymmetrical graben (Figure 4) into which the Avon Sub-group was deposited. The majority of the syndepositional normal faulting in the basin occurred during the deposition of the Avon Sub-group and the overlying Speldon and Wenhams Formations. Faulting along the western margin associated with this syndepositional normal faulting was probably responsible for the opening of the depression in which the coals of the Clear Hill area were deposited. Wrenching, which caused the major offset of the central portion of the basin, also occurred

during this time.

Conditions during the remainder of the deposition period were fairly stable, with the north-eastern and central eastern portions ofthe basin receiving a greater accumulation of sediment than the western and southern portions. This condition manifests

itself in the present-day coal rank variation within the basin, which is described in more detail below.

A number ofvolcanic ash outbursts occurred during deposition ofthe Craven Sub-group and are present today as major tuff marker beds. One of these outbursts must have been of major proportions; the resultant ash deposit formed the Jo-Doth Tuff, which is a consistent unit 12m ihick occurring throughout the basin. Following the deposition of the Gloucester Coal Measures the basin underwent a period of major contraction, resulting in the reactivation and reversal of the north-south normal faulting and the development of most of the low-angle reverse faulting. This contractional phase, which probably occurred during the late Permian, also resulted in tilting of the basin similar to its present-day shape.

Gloucester Basin

424 The basin was then uplifted and exposed, resulting

in erosion to its present topographiial form. COAL SEAMS

Over 50 individual coal seams occur in the Gloucester Basin sequence. Only twenty of these, however, have been named, and only five are traceable for any substantial distance. Each ofthese f,ive main coal seams appears to have been associated with some form of depositional hiatus.

Significant coal seams are present throughout the whole eastern margin of the basin, with [he best coals being developed in the interval from the base of the Waukivory Creek Formation to the top of the Bucketts Way Formation. These coal seams are also present in the northern and, to a lesser extent, the southern margin areas. With the exception of the Clear Hill area, however, there are few coal seams in the western margin of the basin or in the central portion. The main coal seams present within the basin in ascending stratigraphic order are:

Weismantel coal seam

Avon coal seam Glenview coal seam Bowens Road coal seam Cloverdale coal seam

Glenview Coal Seam The Glenview seam is developed as one uniform single coal bed, located at the top of the Dog Trap Creek Formation. Like the Weismantel seam it appears to have been developed in a back-barrier swamp, resulting also in high sulphur levels. Sulphur is, however, more variable than for the Weismantel seam, with recorded raw sulphur values ranging from 0.7 to 7 .57o. This is due to protection of

the coal from the overlying transgressive sequence by a thin terrestrial succession.

The Glenview coal seam is present throughout a large part of the eastern margin of the basin, although its main development is to the north of the Stratford area. Its thickness increases to the north, and reaches a maximum of over 3m.

Bowens Road Coal Seam The Bowens Road coal seam is developed in the Wenhams Formation, and is recognisable throughout a substantial portion of the basin. It is a very dull coal, different from the other coals in the basin. The characteristics ofthe seam vary considerably throughout the basin, ranging from a major coal bed more than 12m in thickness north of the Stratford area to a very minor seam <1m thick

in other areas.

Weismantel Coal Seam The Weismantel coal seam is the thickest uniform coal seam present within the basin, and is up to 15m thick in the Wards River area. The seam was developed in a back barrier environment and is

overlain by marine sediments, however, with the result that it has a moderately high sulphur content (7.80Vo).

This seam represents significant change in the character of sedimentation and coal development within the Gloucester Basin. The coals below the Bowens Road seam generally have high proportions of inherent mineral matter which is retained on washing, resulting in a fairly high-ash washed coal product. Above the Bowens Road seam, however, the coal beds are generally more discretely banded, with the individual coal plies having lower levels of inherent mineral matter and the capacity to produce lower-ash coals after washing.

Cloverdale Coal Seam

The Weismantel seam thins and deteriorates in quality to the north on both the eastern and western sides of the basin. It can be traced along the majority of the eastern margin. The seam has also been traced for approximately 10km along the

The Cloverdale coal seam is the uppermost coal to show significant development over large areas. Some coal beds above the Cloverdale also show significant development, but these are more restricted in extent.

Avon Coal Seam

The Cloverdale seam is a banded seam with an overall thickness of between 5 and 10m. It is traceable over almost all of the eastern margin of the basin, although there is considerable variation in the relative amounts of coal and stone bands present. This seam appears to have little potential for economic development outside the Stratford area.

western margin of the basin, after which it appears t-o lap on t-o the bqsement. Because of its very steep dip, its reduced thickness and poorer quality, the seam is not considered an economic target outside the southern closure area, where it forms the main seam of the Wards River coal deposit.

The Avon coal seam is developed on the top ofthe Waukivory Creek Formation, and is the coal on which the main Stratford deposit is based. Unlike the Weismantel seam, the Avon coal seam is a banded seam, with generally one predominantly clean coal ply at the top and with the remainder made up of interbanded coal and non-coal material. Seam thickness ranges from more than 20m in the Stratford area to around 5m in the southern parts of the basin. The Avon coal seam is the most consistent recognisable seam in the basin, and has the greatest potential for economic development. It can be traced through the whole of the eastern margin and in the northern and southern closure areas. The seam is

often thickened by reverse faulting, giving it a maximum recorded thickness in boreholes of approximately 60m.

COAL QUALITY Each seam in the Gloucester Basin generally has a specific area of majr:r development. Quality and thickness generally deteriorate away from this area, with the rate of deterioration depending on the seam. The Avon and the Glenview seams have the most consistent quality characteristics and the Bowens Road and Cloverdale seams the greatest degree of variation among the five main coal beds.

Analytical Data The coals of the Gloucester Basin are classified as medium to high volatile bituminous coals. They generally have high raw ash values, high specific energy, medium to high volatile matter contents and are high-swelling coals. The Bowens Road coal seam is the exception in that it contains a low-swelling

Geology of Australian Coal Basins

425

coal. Unless they are associated with a marine transgressive event, the majority of seams have

ROSEVILLE

sulphur values of <O.7Vo. On washing at a relative density of 1.80, the Weismantel, Avon, Glenview and Bowens Road seams produce a coal with about 177o ash. Coals above the Bowens Road seam, however, tend to give a product with 10-137o ash under the same conditions. Analyses oftypical coals that could be produced from the main deposits in the basin are given in Table 2.

lOO ilatras

BOWENS ROAD

Table 2. Typical product coal quality from main Glouce'ster Basin deposits (air-dried

BOWENS ROAD LOWER

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Deposit Wards

River

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Coal Petrology

i----

With the exception of the Bowens Road coal seam, the vitrinite content of Gloucester-Basin coal is generally 65 to 7\Vo on a washed-product basis. The vitrinite content of the dull Bowens Road seam is normally around 45 to 50Vo.

varies from approximately O.7LVo for the Weismantel seam in the southern closure area to a maximum of around t.207o for the Parkers Road coal seam near DDH 23 (see Figure 1 for location), in the east-central part ofthe basin (Hughes & others, 1984). The vertical gradient in vitrinite reflectance also varies with geographical location. In the north it is around 0.47o per 100m, in the central part of the basin around 0.O67o per 100m and on the western side of the basin it is O.O4Vo per 100m. The pattern of rank variation shows that the initial deformation of the basin must have taken place while the coal was still immature. This is indicated by the fact that the rank of the coals in any specific area is related to depth below present ground level and not to stratigraphic position. This is shown by comparing rank profiles of DDH 20 and 23 (Figure 5) in the east-central part of the basin, where the rank of the coal is shown to be independent ofits stratigraphic location but very much dependent upon its depth below the ground surface level. The implication from this is that the depth of cover over the current surface ofthe basin represents almost as a mirror image of the basin shape during deposition. Figure 6 is developed on the basis of projecting the vertical rank trend of the topmost coal in any given geographic location back to a rank of 0.7lVo Rv-.* using an average reflectance gradient of 0.06Vo per 100m of cover. The area in the current central portion ofthe basin has had a significantly sreater amount of sediment removal than either the iorthern or southern ends ofthe basin. It can be deduced from this that there was less sediment deposited over the southern portion ofthe basin or

Avox

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The rank ofthe coal in the basin varies both laterally and vertically. Vitrinite reflectance (Rv-"*)

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5. Vitrinite reflectance profiles for selected Figure - boreholes (DDH 2O and DDH 23) in relation to coal eeam stratigraphy. See Figure I for borehole locatiohs (Ifughes & others, 1984).

that any additional sediment was preferentially removed at an early stage ofdiagenesis. Given the present rank difference of 0.25Vo Rv-u' between the Weismantel seam in the Wards River area and the Avon coal seam around Stratford, differential erosion of over 400m appears to have taken place from the Stratford area. In addition to this, when the actual difference in stratigraphic interval of700m is considered, there must have been a total ofover 1100m less sediment deposited above

Gloucester Basrn

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Figure 6. Differential erosion pattern along a north-south line, interpreted from coal rank variation (Hughes & others, 1984). the stratigraphically lower seam at Wards River than over the seams in the Stratford coal deposit.

Correlation with the Sydney Basin (upper Hunter Valley) Sequence

The rank variation is less significant in an east-west direction. The total stratigraphic sequence developed was not the sarne, however, since the part of the sequence below the Bowens Road seam is absent from the western margin of the basin due to the onlapping nature ofthe sequence. Once sedimentation was developed across the whole

The Permian sequence preserved in the Gloucester Basin can be correlated with the Permian of the Upper Hunter Valley section of the Sydney Basin (Figure 7). On the basis of the composition and sulphur content ofcoal, the Gloucester Coal Measures have been correlated with the Wittingham Coal Measures (Hunt & others, 1983). The coals of the Dog Trap Creek and Waukivory Creek Formations exhibit high vitrinite contents and medium semifusinite ratios, similar to those in the Foybrook Formation. Total sulphur content in the respective formations is highest in the upper and lower seams, because of the influence of marginal marine sedimentation in the overlying and

basin, the rate of sedimentation and the total sediment thickness above any given bed appears to have been very uniform.

In addition to the above trends, rapid rank variations, possible rank inversions and potential depositional hiatuses have been interpreted from the results of coal quality studies based on downhole geophysical logs. One such rank inversion is indicated in the middle of the Bowens Road coal seam, especially in the North Stratford area, where the upper coal ply consistently has a higher rank than the lower coal ply. The variation in vitrinite reflectance is generally about 0.047o. Similar rank inversions, although not as consistent, are also apparent in other coal seams. The most likely explanation of such rank inversions in beds other than the Bowens Road coal seam is that the section which is now uppermost was overthrust on the lower section during a later development phase. This explanation, however, is not applicable to the Bowens Road coal seam, as the apparent rank inversion is very consistent and no evidence of faulting is present within the seam. The origin of the inversion in the Bowens Road coal seam is currently unknown. Evidence of depositional hiatuses is provided by the reverse of the above, with major rank increases occurring over very small vertical intervals. Such a rapid rank increase is often associated with a significant reduction in volatile matter content without any significant change in the coal type. The only conclusion which can be drawn from these variations in rank is that the coal has undergone some very high stresses during deformation, which have resulted in the localised rank anomalies.

underlying stratigraphic units.

The marginal marine sediments of the Speldon Formation are correlatable with those of the Archerfield Sandstone and possibly the underlying Bulga Formation. This suggests a very wide ranging marine transgression. The top of the Bowens Road coal seam shows the distinctive low vitrinite content and low semifusinite

ratio which is characteristic of the Bayswater seam at the base of the Burnamwood Formation. The top of the Gloucester Coal Measure sequence probably corresponds with the mid-top section of the Jerrys Plains Sub-group.

Tuffs are a characteristic of both the Hunter Valley sequence and the Gloucester Coal Measures, especially in the Woods Road Formation. As a result of petrographic studies the Jo-Doth Tuff has been correlated with the Fairford Formation (Hughes & others, 1984). The Dewrang Group shows marked marine influence and is thought to represent a near-shore equivalent of the Maitland Group, with the Weismantel seam being a back-barrier coal possibly time-equivalent to the beach-barrier Muree Sandstone (M.J. Lennox personal communication). There does not appear to be a time equivalent to the Greta Coal Measures in the Gloucester Basin, although the top of the Stroud Volcanics may be equivalent to the Greta unit. The Stroud Volcanics are correlated with the Gyarran Volcanics in the Hunter Valley.

Geology of Australian Coal Basins

427

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Gloucester Basin

428

PROPOSED MINE AREA ESSO AUSTEAIIA LTD.

WARDS RIVER AREA , il.S.W.

Itl I

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COAL RESOURCES Economically mineable coals in the Gloucester Basin are restricted to areas where the geological structure gives rise to relatively flat-lying strata in an area ofwell-developed good quality coal at shallow depth. Because of the stluctural complexity in the basin, the occurrence of such areas is limited. Coal seams in the basin generally thin and

deteriorate in a westerly direction, with the result that the Bucketts Way and Woods Road Formations contain little or no coal. As these formations are developed over the large central flat lying area of the basin, this area is considered generaly non-prospective for economic coal development. The Crowthers Road and the Wards River Conglomerates also contain little or no coal. Except for the Clear Hill area near Craven, the presence of these formations over a large part of the western margin has also resulted in no known coal development in that particular sector of the basin. Two areas within the Gloucester Basin, the Wards River and Stratford areas (Figure 1), have potential for coal development, and these have been subjected

to extensive mine planning studies (BMI Mining Ltd, 1984a,b). Several smaller areas with potentially mineable coal resources have also been outlined by Hughes & others (1984).

Wards River Deposit The Wards River deposit is located in the southern extremity of the Gloucester Basin, approximately 40km from the town of Gloucester, and is bisectdd by the Main Northern Railway Line. The deposit is situated on the southern closure of the W-eismantel seam in the Dewrang Group; the seam in this area occurs as a single coal bed approximately 10m thick without major non-coal partings. The strata dip into a northerly-plunging syncline at angles of between 5 and 30o (Figure 8), and depths to seam subcrop are

approximately 10m.

The seam at Wards River continues in all directions away from the southern closure, and hence total coal resources could be regarded as open-ended. Increases in dip angle to 30o on both sides ofthe basin, however, limit the extent of readily mineable material. Mine planning studies have identified an in-situ resource of around 30Mt of high-r'olatile bituminous coal at the very southern end of the

Geology of Australian Coal Basins

429

PROPOSED MINE ARE A

\ \

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Figure 9. Simplified geological plan and section of the Stratford coal deposit. basin, with a typical product quality as shown in Table 2.

extensions to the resources are unlikely outside these areas.

Stratford Deposit The Stratford coal deposit is located approximately 12km south of Gloucester near the small hamlet of Stratford. The Main Northern Railway Line is approximately 2km from the deposit. The area is geologically complex (Figure 9), with a localised syncline containing the Avon seam of the Avon Sub-group and a northern extension of this feature containing a number of seams in the overlying Craven Sub-group. Subcrop depths are around 10m, and dips range from zero to around 30o. Accumulated coal thicknesses are highly variable, and range to more than 30m in places. The seams are highly banded, containing medium to high-volatile bituminous coal with typical quality parameters as indicated in Table 2.

Total in sifu mineable resources for the Stratford area are estimated at 72Mt. These can be subdivided into a number of separate potential mining blocks, each of which is associated with particular seams and structural features. The distribution of mineable coal is structurally controlled, and further

HYDROCARBON OCCURRENCES Oil has been identified in Gloucester Basin drill cores during the coal exploration program (Thornton, 1982), and a number of occurrences have since been noted in different stratigraphic intervals in various parts of the basin. Gaseous hydrocarbons, predominantly methane with minor traces of carbon -ttioxide and nitrogen, are also present within the basin (Hughes & others, 1984). The oil occurrences are located in the Durallie Road Formation in the Wards River area, the Speldon Formation around Stratford and the Bucketts Way Formation. The Durallie Road and Speldon Formations are both marine influenced, and have both been reported to contain numerous oil occurrences. To date no marine influence has been recognised in the Bucketts Way Formation, and oil has only been found in this formation in the core of one exploration borehole.

Gloucester Basin

430

REFERENCES

HUGHES, W.W., WILCOX, R.D. & WILCOCK, S.W., 1984: Regional exploration ofthe Gloucester

BMI MINING PTY LIMITED, 1984a: Gloucester Coal Project: geology and coal resources ofthe Stratford area. Unpublished report, BMI Mining Pty Limited. BMI MINING PTY LIMITED, 1984b: Gloucester Coal Project: geology and coal resources ofthe Wards River Area. Unpublished report, BMI Mining Pty Limited. GALLIGAN, A. & MENGEL, D.C., 1987:Australian Code for the Reporting of Identified Coal Resources and Reserves. Australian Mineral

Industry Quarterly, 39(2), 49-51.

GEORGE, A.M., 1971: Geology of the Gloucester Basin,

N.S.W. Noranda Australia Ltd, Report No. 155.

GEORGE, A.M., 1975: Gloucester Basin. 1n Traves, D.M. & King, D. (Editors): Economic Geology of

Australia and Papua New Guinea Coal. - 2: Australasian Institute of Mining and Metallurgy, Monograph, 6,255-258.

Basin. Esso Australia Limited.

HUNT, J.W., PHILIP, R.P. & TELFER, A., 1983: Petrography and geochemistry of coal from the Late Permian Avon and Stratford Coal Measures in the Gloucester Basin, N.S.W. CSIRO Report 1413R (Restricted).

LOUGHNAN, F.C., 1954: The Permian coal measures ofthe Stroud-Gloucester Trough. Journal and Proceedings, Royal Society of N.5.W.,88, 106-113. ODENHEIMER, F., 1855: Being a report on the geology and mineralogy of the Australian Agricultural Company's Port Stephens property. Joint Coal Board Report NR 1855/1. THORNTON, R.C.N., 1982: Oil occurrences in Esso Stratigraphic Corehole DDH20, Gloucester Basin. Unpublished report, Esso Australia Limited. WILCOX, R.D., 1984: Prediction of analytical properties of Gloucester coals. Unpublished report, Esso Australia Limited.

Geology of Australian Coal Basins

431

INTRODUCTION

ffiKount Mulligan Coalfield,

Queensland

SG Matheson

Mount Mulligan is located approximately 100km west of Cairns in northern Queensland. The mountain is a steep-sided rift block approximately 3.5km wide, L7km1ong and up to 300m high. It is composed of Mesozoic sandstone and conglomerate with the Mt Mulligan Coal Measures at the base.

PREVIOUS IT{VE STIGATIONS Coal was first discovered in the area by Bill Harris in 1907, during a search for gemstones, and

subsequent exploration between 1907 and 1910 result6d in a number of adits being driven under the mountain. Ball (1912) reviewed the geology and early development of the coalfield. The prospect o-f a railway linhto Dimbulah and markets beyond led to the commencement of mining in 1914, with production from a section ofgood quality coal ianging up to 0.9m in thickness. By L920, annual production had reached 23 000t, but in 1921 the worst mining disaster in Queensland's history occurred when an underground explosion killed 75 men.

The mine reopened after the disaster early in L922, and was acquired by the Queensland Government in 1923. It continued to operate for 36 years (Bell, 1978), but the introduction of diesel railway locomotives, the development of the coalfrelds of the Bowen Basin, the completion of the Tully Falls hydroelectric scheme and overheating of the mine caused the closure in 1957 ofboth the State Coal Mine and the King Cole Colliery, which had opened in 1941. The King Cole Mine was located at the site ofthe original prospecting adits, but had never produced more than 10,000t per year. Although in an area of geological instability, however, it had operated more efficiently than the State Mine. Total pioduction from the Mount Mulligan field over the years of its operation was 981 000t (Hawthorne, 1975); yearly figures are summarised by Whitby ( 1e75).

Authority to Prospect 168C was granted over the area to CRA Exploration Pty Ltd in 1974 and relinquished in 1977, while Authority to Prospect 272C was granted to International Mining Corporation NL in 1979 and relinquished in 1982. Two holes were drilled during this period. STRATIGRAPHY The basement rocks which crop out at the foot of Mt Mulligan are part of the Devonian Hodgkinson Formation, and consist of shale, slate, greywacke and siltstone. Tuffs, ignimbrites, breccias and porphyries of the Late Carboniferous to Early F".*iL" Featherbed Volcanics unconformabiy overlie this sequence, however, on the western

margins of the mountain.

Coal measures deposition commenced during the Late Permian (lower Stage 5c or upper Stage 5, International Mining Corporation, 1982) in a slowly subsiding terrestrial basin of limited extent. The Mount Mulligan Coal Measures so formed comprise conglomerate, sandstone, shale, mudstone a_nd coal, and-lie with an angular unconformity over the Hodgkinson Formation and the Featherbed Volcanics in part.

Whitby (1975) divided the coal measures into three units.lnitial deposition was restricted to the

Mount Mulligan Coalfield

432

north-west, forming a basal unit (Pum 1) with up to 60m of shale, siltstone and minor sandstone. A sharp increase in the rate of subsidence then gave rise to an enlargement of the basin area, followed by deposition of a massive cobble and pebble conglomerate succession (Pum 2), with minor interbedded sandstone. This latter sequence may be up to 270m thick in the north, but is only around 5m thick at the State Mine (Wells, 1984). A period of quiescence followed, and the productive coal measures, made up of siltstone and lithic sandstone with up to four coal seams, were deposited as the uppermost unit (Pum 3). The coal-bearing sequence may be up to 149m in thickness, although it shows considerable lateral variation. The Mt Mulligan Coal Measures are overlain by about 300m ofconglomerate and sandstone, a sequence referred to as the Pepper Pot Sandstone. A band of red tuff lies at the base of this Triassic sequence, which shows a slight angular

unconformity with the underlying Mt Mulligan Coal Measures, while white conglomeratic sandstone is found towards the top of the unit. McElroy & Bryan (1981) described an upper section ofthe Pepper Pot Sandstone above the white sandstone as thinly interbedded siltstone and claystone, and mapped it on the southern half of the mesa as a separate unit (Figure 1). De Keyser & Lucas (1968) postulated that the coal measures were deposited from the west and south-west, whereas uplift of the Hodgkinson Formation in the south and east provided a new source area in the early Triassic.

STRUCTURE A fault zone occurs on the eastern side of Mt Mulligan, and downwarping of the western side of this has affected the strata. The Featherbed Volcanics are also controlled to the west of Mt Mulligan by a major fault (Figure 1). Upthrow in both faults is towards the east, and the mountain has formed as a prominent mesa by erosion of the Hodgkinson Formation and resistance of the Pepper Pot Sandstone. Post-Triassic warping and minor faulting along Palaeozoic lines of weakness have deformed the Permo-Triassic strata on parts of the area as well. Faulting is known to occur in the Mt Mulligan Coal Measures from working sections in the mines (Morton, 1945), and is interpreted between drill holes (Connah, L952). A post-Triassic uplift is reflected in the Grindstone Hill Syncline (Whitby, 1975). Strata on the western limb of this syncline dip steeply (up to 70 or 80o) to the east, while dips of only 10 to 20o to the west are encountered on the eastern limb. Dips increase locally, however, near the faulted edges of Mt Mulligan itself. A monoclinal flexure also is observed in the Triassic strata at Emu Pocket in the north-west. The coal measures have been preserved, not necessarily by faulting (as has been suggested by previous workers) but by being protected from erosion by the overlying, more resistant sandstones (Whitby, 1975). The initial size of the coal basin is uncertain, but it probably extended to the north and north-east.

COAL SEAMS The coal seams at the State Mine range in thickness from 0.4m to about 1.7m. The No. 1 seam and the No. 2 seam are both banded, with up to 25Vo of each

seam consisting of non-coal material. The No. 2 seam was the thickest seam mined. The No. 3 seam averaged only 0.6m, but comprised clean coal and was the most extensively worked. The No. 4 seam consisted of thin, dirty coal, and was not worked at all (Hawthorne, 1975).

Only two seams are present at King Cole colliery, 1.7km south of the State Mine. The top seam, however, was the only one worked. It ranges in thickness from 0.8 to 2.1m, with an average of L.2m, being thickest in the north and deteriorating towards the south and west. The bottom seam is a poor quality banded seam 0.4m to 1.4m thick, although it is considered by Morton (1945) to be the equivalent of the No. 3 seam in the State Mine area. Seam sections in five boreholes drilled to the north of the State Mine in 1951 showed little similarity to

the sections in the colliery itself. Except in one instance, coal intersections of potential economic significance did not exceed 1m, and most of these appeared to be ofinferior quality in any event (Connah, 1952).

Two holes were drilled in 1980 by International Mining Corporation from the top of the mesa to depths of 554 and 653m. Both intersected two coal intervals, containing one or two coal seams which may be mineable in different parts of the field. The thickest seam intersected, in DDH 1, was 2.06m

thick. The upper productive unit of the coal measures has been found from mapping by Whitby (1975) and McElroy & Bryan (1981) to extend over much of the area, including the northwestern side of Mount Mulligan, suggesting that coal development could be widespread under much of the mesa. The coal measures clearly thin from north to south, and wedge out 700m south of King Cole Colliery where Triassic conglomerate overlies the Devonian basement. The seams in both mines also thin and wedge out rapidly to the west.

COAL QUALITY AND RESOURCES The coals of the Mount Mulligan field are classified as high-volatile A bituminous coals under the ASTM classification. They are low in rank, with an average mean maximum vitrinite reflectance of 0.75Vo. The coal was used mainly for steam-raising, with a raw ash yield of 15 to 237o and a specific energ"y of 24.0 to 27.6MJkg. These analyses, however, were made on face samples from underground, which may have been hand picked to give a favourable result. Analyses from the two holes drilled in ATP 272C show raw ash of 45Vo, a value reduced to 15-187o in the floats at RD 1.60 but with a yield of only 43 to 477o. Coking tests were carried out during early mine development (Ball, 1917), and coke works were completed in L922 and used intermittently until 1924 (Bell, 1978).

Coal resources in the Mount Mulligan area are only likely to be small. Powell Duffryn (1949) estimated that 460 000 and 715 000t were present in the No.1 and No.2 seams respectively above the worked areas of No.3 seam coal in the State Mine. International Mining Corporation (1982) indicated that, for a seam with an average thickness of 1.7m, in situ resources could be between 45 and 90Mt in the coalfield east of the syncline, depending on the area actually involved. The low thickness, high ash and low clean-coal yield of the seams, the necessity for

Geology of Australian Coal Basins

433

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ALT

Figure l. Geological map of the Mount Mulligan area (after McElroy & Bryan, 1981).

Mount Mulligan Coalfield

434 underground mining, and the infrastructure requirements for such an isolated area, however, make the Mount Mulligan field an economically unattractive prospect for mining operations.

INTERNATIONAL MINING CORPORATION N.L., 1982: Report for period 6/ll/79 to 6/1U82 - Final report for Authority to Prospect 272C. Unpublished report held by Queensland Department of Minerals and Energy as CR 11519.

REFERENCES

McELROY, C.J. & BRYAN, J.H., 1981: Results of drilling programme at Mt Mulligan, Authority to Prospect 272C. Unpublished report by McElroy Bryan and Associates Pty Ltd for International Mining Corporation N.L., held by Queensland Department of Minerals and Energy as CR 8372.

BALL, L.C., 1912: Mount Mulligan coalfield. Geological Suruey of Queensland Publication, 237.

BALL, L.C., 1917: Mount Mulligan coalfield.

Queensland Gouernment Mining Journal, 18, 444-453.

BELL, P., 1978: The Mount Mulligan disaster. Studies in North Queensland History,2, James Cook

University of North Queensland.

CONNAH, T.H., 1952: Scout drilling, Mount Mulligan coalfi eld. Queensland Gouernment Mining

Journal,54, 105-107.

DE KEYSER, F. & LUCAS, K.G., 1968: Geology of the

Hodgkinson and Laura Basins, north Queensland. Bureau of Mineral Resources, Bulletin, 84.

HAWTHORNE, W.L., 1975: The Mount Mulligan coalfield. In Traves, D.M. & King, D. (Editors): Economic Geology of Australia and Papua New Guinea, 2: Coal. Australasian Institute of Mining and Metallurgy, M onograph, 6, 252-254.

MORTON, C.C., 1945: King Cole colliery, Mount Mulligan. Queensland Gouernment Mining

Journal, 46,235-238.

POWELL DUFFRYN TECHNICAL SERVICES LTD, 1949: First report on the coal industry of Queensland. Report to the Queensland Gouernment, 3 volumes.

WELLS, A.T., 1984: The Late Permian Mount Mulligan Coal Measures, Queensland. .In Permian Coals of Eastern Australia. BMR and CSIRO Report on NERDDC Project 7 8/26L7 .

WHITBY, KJ., 1975: Geology and coal resources, Authority to Prospect 168C, Mitchell River area,

Queensland, Volumes I and II. Report prepared by Clifford McElroy and Associates for CRA Exploration Pty Ltd, held by Department of Minerals and Energy, Queensland as CR 5444.

Geology of Australian Coal Basins

435

ffialen Basin,

Queensland AT Brakel

The Calen Basin (Brakel, 1989), which now occurs as two outcrop areas north-west of Mackay (Figure 1), is bccupied by the mid-Permian Calen Coil Measures. The total area of outcrop is about 240km2 (Koppe, 1974). The measures generallf {ory subdued topography oflow strike ridges in relatively flat terrain, but west of Calen an upper quattz arenite bed forms steep ridges and near Mount Toby there are high, steep sided hills. On its northwestern side the basin is faulted partly against the Urannah Igneous Complex_of the Cbnnors Arch, which separates the coal measures from the Bowen Basin. It is also partly faulted asainst the older, freshwater Carmilla beds of the Strathmuir Synclinorium. Elsewhere, the basin boundaries are largely erosional, so that the underlying and surrounding Early Permian rocks of t]neLiizie-Creek Volcanics and the Carmilla beds are exposed. Further east, along the coast, is the Devonian to Carboniferous Campwyn Block. The sequence is intruded by sills, dykes, plugs and stocks of Permian to Cretaceous dolerite, rhyolite and granite.

STRATIGRAPHY Although the Calen Coal Measures have been known since the 19th Century, they were first named by Laing & Hill (1960). The formation is 350 to 400m thick, and there are no formally-named members' The top of the Calen Coal Measures is the present-day erosional ground surface. The base is variously th.e Lizzie Creek Volcanics or the contemporaneous Carmilla beds. A conspicuous quartz arenite marker unit ranges from 60 to 300m slratigraphically above the base, suggesting an overlap oT older-units. Divergences of strike with the Carmi-lla beds also suggest an unconformity, and an unconformity with the Lizzie Creek Volcanics is known near Butharra (Jensen & others, 1966;

Clarke & others, 1971).

The unit consists of coarse quartz sandstone with cross-stratification, thin pebble conglomerate, thinly interbedded sandstone and siltstone, claystone, carbonaceous shale and coal. It lacks the prominent tuffaceous and other volcanic detritus ofthe underlying Carmilla beds. The best surface exposures-of sandstone, siltstone and intruding sills and dykes are in cuttings on the Bruce Higlryay !n the southern area (Jensen & others, 1966). Two drill holes sunk by the Geological Survey ofQrreensland, Hillalong NS5 and 6, located on the southern area at 2loo4', 251' 5, 148056'47 "8 and 2 1000'27" S, 148052',8

respectively, intersected similar lithologies, as well as ioarse lithic labile arenite, and burrowed shale and arenite with flaser bedding; many arenites contain intraclasts of shale (Koppe, 1974).

EIWIRONMENT OF DEPOSITION The general depositional environment for the sequ6nce was one of dominantly lower delta-plain conditions punctuated at intervals by uppe-r delta-plain-to fluvial braided stream.episodes. Beds with both burrowing and flaser bedding record tidal

activity intermittently throughout th-e s-uccession' Thick quartzose units, at least one of which has a sheet glometry, suggest braided stream deposition, whereas thinner lithic arenites appear to occur within frning-upwards cycles of point-bar depos-its. The composition of the iithic sandstone may-refle^c-t the addition of substantial amounts of air-fall tuff to

Calen Basin

436

the system. High and low energy fluvial channel, floodplain and channelled swamp sub-environments have been recognised (Koppe, 1974). The depositional setting reflects a balance in sedimentation that usually kept the region just above sea level. Times when subsidence outpaced sedimentary buildup (due to tectonism, or to compaction following delta-lobe abandonment), and probable eustatic changes in sea level, resulted in advances of the sea and tidal influence. There may also have been periodic uplifts in the hinterland, causing braided sheet wash to invade normally

deltaic areas.

STRUCTURE The Calen Basin and underlying Permian section occupy a NW-trending trough, possibly a graben, between blocks of older rocks. At least some of the relative uplift of the Connors Arch is post-Permian.

Folding and Faulting The coal measures have been folded into a broad NW-trending syncline, in which dips are generally 20o or less. Locally, however, dips range to

near-vertical as a result of minor folding, faulting and shouldering aside of the rocks by intrusions. Structural disturbance is greatest in the northern area, where the Calen Coal Measures have been downthrown and tilted to vertical along the faulted western margin of the basin. The southern area is structurally simpler with lower dips, although some block faulting has taken place.

Igneous Intrusions Three types ofigneous intrusions have been emplaced in the Calen Coal Measures. In the northern area ofthe basin there are two large plugs of rhyolite, one of which has been intruded in turn by a granite stock. There is also a sill of microgranite and a large body of porphyritic dolerite (Clarke & others, 1971). These intrusions have disturbed the surrounding bedding and coked coal seams with which they have come into contact. In the southern area dykes and sills are numerous. They can be seen in road cutting exposures, and form almost one-third of the section intersected by GSQ Hillalong NS 5. They have extensively intruded

parts of the sedimentary sequence, with coal locally metamorphosed to anthracite rank, coked or even obliterated (Koppe, L97 4).

The exact age of the intrusives is not known, and can range from Late Permian to Cretaceous. Isotopic dates from post-Early Permian felsic intrusives elsewhere in the region show that there was some

activity in the Late Permian, but most were emplaced in Early Cretaceous times (Jensen & others, 1971). COAL DEPOSITS

Coal in the Calen Basin has been reported on by Jack (1887), Maitland (1889), Ball (1910), Saint-Smith (1920) and Reid (1924,1929). Analyses indicate t6.2 to 'J.7.SVo volatile matter, 60.0 to 62.3Vo fixed carbon and 16.2 to L7.3% ash (Ball, 1910).

Mining has been restricted to the area about 6km west of Calen, which was worked by the short-lived Calen Colliery $927-28) and Fleetwood Colliery (1932-39). These mines exploited a seam 2.6m thick that dips at 50o in the basal 150m of the Calen Coal

l++n

l***l f-,----1 l :r :r1 l': :-r:i

FIn 1,"'l Lizzie Creek Volcanics

N-l oo,",r" Wfr ,u,"n coat Measures cu,-,,u t"a" F'..1.1

Pre-Permia n Fa ult

Geological boundary

Mine

Figure 1. Geological rnap of the Calen Basin and surrounding area. Measures, lying 30 to 60m below the quartz arenite marker. Small tonnages of low-volatile thermal coal were produced (Clarke & others, 1971; Koppe, 1975). Even though the coal was of good quality, production ceased because of the prohibitively steep dip. Other surface appraisals and shallow-shafts have been

discouraging because of extensive folding, faulting, coking by intrusives and the general low thickness of the seams.

Drilling by the Geological Survey of Queensland in the less-disturbed southern part of the basin failed to find seams comparable in quality or thickness to the seams mined at Calen. The intensity of igneous intrusion is so great, and the structural dislocation in many areas so extensive, that there is little chance of preservation of economic coal resources.

Some small and uneconomic coal occurrences also exist in the underlying Carmilla beds. These all occur well to the south of the Calen Basin. Coal seams, none greater than 1m in thickness, are exposed in Black Waterhole Creek, 22km SW of

Geology of Australian Coal Basins

437

Mackay. There are also reports of coal in the Koota district, 23km SSE of Sarina, and at Oakey Creek, 22km north ofSt Lawrence (Jensen & others, 1966).

KOPPE, W.H., 1974: Departmental drilling in the Calen Coal Measures. Geological Survey of Queensland, Record, I97 4/36.

REFERENCES

KOPPE, W.H., 1975: Calen Coal Measures, Queensland..In Traves, D.M. & King, D. (Editors): Economic Geology of Australia and Papua New Guinea - 2: Coal. Australasian Institute of Mining and Metallurgy, Monograph, 6, 250-25I.

BALL, L.C., 1910: Coal at Black Rock Creek, near

Mackay. Queensland Gouernment Mining Journal,

LL,283-284.

BRAKEL, A.T., 1989: Calen Basin. In Harrington, H.J., Brakel, A.T., Hunt, J.W., Wells, A.T., Middleton, M.F., O'Brien, P.E., Hamilton, D.S., Beckett, J.,

LAING, A.C.M. & HILL, D., 1960: The Yarrol Basin (northern part).In Hill, D. (Editor): The Geology

Australia. Bureau of Mineral Resources, Australia, Bulletin, 231, 107-110.

MAITLAND, A.G., 1889: Geological features and mineral resources of the Mackay district. Geolog ic aI S uru ey of Queensland, Public ation, 53.

Weber, C.R., Radke, S., Totterdell, J.M., Swaine, D.J. & Schmidt, P.W.: Permian Coals of Eastern

CLARKE, D.E., PAINE, A.G.L. & JENSEN, A.R., 1971: Geology of the Proserpine 1:250,000 Sheet area, Queensland. Bureau of Mineral Resources, Australia, Report, 144. JACK, R.L., 1887: Geological features of the Mackay

district. Geological Survey of Queensland

REID, J.H., L924: Coal at Saint Helens, Mackay district. Queensland Gouernment Mining Journal,

25,84-85.

REID, J.H., 1929: Coal prospects. Mackay district.

Queensland Gouernment Mining Journal, 3O, 156-158.

Publication, S9.

JENSEN, A.R., GREGORY, C.M. & FORBES, V.R., 1966: Geology of the Mackay 1:250,000 Sheet

area, Queensland. Bureau of Mineral Resources,

Australia, Report, lO4.

of Queensland. Journal of the Geological Society of

Australia , 7 , 22L-222.

SAINT-SMITH, E.C., 1920: White and Moon's coal mine, near Hampden, Mackay district.

Queensland Gou ernrnent M ining J ournal, 21, 502.

Calen Basin

439

Part3rMesozoicand Tertiary Coal Deposits

Geology of Australian Coal Basins

441

K-asmania Basin CA Bacon

Figure 1. Black coal localities, Tasmania. The Tasmania Basin is a structural basin extending over a large part of central and eastern Tasmania (Figure 1). The basin is defined as the area containing the remnants of the Parmeener Super-Group (Banks, 1973), a flat-lying stratigraphic sequence that ranges from Late Carboniferous to Late Triassic. Coal occurs in three separate stratigraphic intervals within the Tasmania Basin, but all of the economically important resources are hosted in the Late Triassic pait of the sedimentary succession (Bacon, 1986; 1991). Less significant intervals of coal-bearing strata are found within the Early

Permian and the Late Permian beds of the Tasmania Basin sequence. Small deposits of brown coal ofTertiary age and localised development of Late Carboniferous oil shale are also known in Tasmania.

BLACK COAL IN THE PARMEENER SUPER.GROUP The Parmeener Super-group is up to 2000m thick, resting on a varied suite of Precambrian to Devonlan strata. It has been subdivided into two parts, a lower division, the Lower Parmeener Super-Group, that is dominantly of marine origin, and an upper division, the Upper Parmeener Super-Gioup, that is wholly of terrestrial

(offreshwater) origin (Figure 2).

The Lower Parmeener Super-Group is Late Carboniferous to Permian in age, and contains mostly marine and glacio-marine lutites, marls and minoi limestones, riitn a thick basal tillite. It also contains terrestrial, coal-bearing strata, represented by the Early Permian Preolenna and Mersey Coal Measures and their equivalents. The Upper Parmeener Super-GrouP is of fluvial origin. It is composed of Late Permian to Late Triissic clastics and overlies the marine rocks of the Lower Parmeener Super-group. A conformable relationship generally exists between the upper-and lower divisions of the Parmeener Super-Group, but

in northeastern Tasmania the boundary is slightly

Tasmania Basin

442

palynological grounds with the basal Brady Formation.

UPPER PARMEENER

SUPER.GNOUP

The Parmeener Super-Group was deposited in a largely stable environment. Banks (1962) suggests that the sheetlike form of the Lower Parmeener Super-Group indicates deposition in a shelf setting, with the rate of deposition being 0.003mm/year. Poor sorting of the Lower Parmeener Super-Group, as unusual feature for shelf sediments, may be partly due to deposition by drifting icebergs. Some tectonic instability is recorded in the Middle or Upper Artinskian of the Lower Parmeener Super-Group, coinciding in age with part of the Hunter-Bowen movement in New South Wales. This instability resulted in uplift and downwarping, and movement of the zone of maximum thickness.

UPPTR

MARIIIT

st0utNct

t0wtR FBTSHWATTR

st0u$rct

L()WER PARMEENER

Mcrsay

{Praolanna. Coal Measurls)

SUPER - GnOUP

t0wtR MASINE

st0uENcE

Figure 2. Subdivision of the Parmeener Super-Group (After Forsyth & others, LS74). disconformable. The disconformity coincides with a Late Permian to Middle Triassic hiatus, and thus the base of the Upper Parmeener Super-Group, in

northeastern Tasmania, is Middle Triassic.

The Permian-Triassic boundary lies within the

siliceous clastics that form the lower portion of the Upper Parmeener Super-Group in central and southern Tasmania. The lowest unit in these areas is the Late Permian Cygnet Coal Measures or its equivalents. The Cygnet Coal Measures.and equivalents are overlain by a sequence ofnon-coal bearing siliciclastics succeeded by a sequence of lithic and/or quartzose sandstones with minor coal occurrences. The upper part ofthe upper division is a lithic sandstone sequence hosting all the economically important coal occurrences known in Tasmania. This sequence is partly included in the lithic sandstone (upper) facies of the Brady Formation (McKellar, 1957) at Poatina and elsewhere, and is known under a variety of largely informal names e.g. Newtown Coal Measures, Langloh Coal Measures, Mt Nicholas Coal Measures and Kaoota Coal Measures. The stratigraphic position ofthe coal-bearing lithic

sandstone sequence is indicated in Figure 3. Although this sequence occurs several hundred metres above the Cygnet Coal Measures over much of the basin, capping the intervening interval of predominantly quartzose sandstone, the Cygnet Coal Measures are absent in the economically important Fingal Valley area in the north-east. Only a thin lenticular (0.6m) Middle Triassic quartz sandstone sequence separates the lithic sandstone succession in this area from underlying glaciomarine strata of the Lower Parmeener Super-Group. This quartz sandstone sequence is similar in lithology and approximately similar in age to the youngest qtattz sandstone horizons found elsewhere in the basin, and in particular can be correlated on

The Parmeener Super-Group was extensively intruded by tholeiitic magma during the mid-Jurassic. Part of this intrusion, the Red Hill Granophyre, has been dated at 170 My (Schmidt & McDougall, L977). More than 8000km3 of magma formed a nearly continuous body through the Permian and Triassic sediments over almost the whole island. The dolerite occurs most commonly as discordant sills up to around 500m thick, although dykes are also seen. Being resistant to erosion, the dolerite tends to dominate the landscape in the eastern part ofthe State, capping all ofthe high mountains and underlying the great Central Plateau

(Spry, 1962).

The east coast coalfields of Tasmania are covered by an eroded dolerite sheet 100 to 300m thick. A regional gravity survey (Leaman, 1981) has helped define target zones for coal exploration by delineating areas where the coal-bearing section is thickest, as well as faults, dolerite feeders and areas where dolerite intrusion has foreshortened or terminated the stratigraphic section.

From the cessation of Triassic sedimentation until Recent times, Tasmania has been subject to normal faulting of a north-northwesterly trend (Solomon, 1962). Horst and graben structures of major dimensions developed during the Late Cretaceous and early Tertiary, causing the individual coalfields to become fragmented and dislocated.

In southern Tasmania there were two phases of faulting, a Mesozoic compressional event which was active before and after dolerite intrusions and a later phase during the Early to Middle Tertiary (Berry & Banks, 1985).

DEPOSITIONAL EI{VIRONMENT OF COAL-BEARTNG SEQUENCES

Early Permian (Mersey Coal Measures, Preolenna Coal Measures and Equivalents) The Mersey Coal Measures and their equivalents were deposited as a thin sheet of fluvial sand which covered both the earlier Permian highland areas and

the earlier Permian sea floor. This sediment sheet ranges from 6 to 50m in thickness, with marked local thinning out against residual basement highs (Banks & Clarke, 1987). Some syndepositional faulting has been recognised in the Latrobe area (Banks, 1979). The dominant rock type is a well sorted siliceous, micaceous cross-bedded or ripple marked sandstone with either no marine invertebrate fossils or worm castings and some coaly

Geology of Australian Coal Basins

443

l.--:\-rrl ..

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Upper Marina Seqrencr

M,6ey Coal M!asures and aquivalenB

low:r Mrrine Sequrne

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sit3t.h

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SECTIOI{ THBOUGH PARMEEI{ER SUPER .GROUP

5r76 A

Figure 3. Section through Parmeener Super-Group (After Bacon, 1987).

debris. The distribution of this sequence is shown in

Figure 4.

Interbedding with grey siltstone is common, and thin coals were deposited around the margins of the depositional basin (Banks, 1962). The environment of deposition of the sand sheet is considered to be a wide sandy coastal plain.

Further into the basin, for example near Gould Sugarloaf, Bothwell, Ross and places to the south., interbeds of strongly bioturbated siltstone occur in the sand sheet. This material is presumably of glaciomarine origin, with dropstones and, rarely, a shelly fauna. At some localities poorly sorted beds occur which are thought to be rapidly built-up littoral deposits in these marine-influenced areas. In southeastern Tasmania the non-marine sequence contains a thin marine intercalation which has produced two cyclothems. The flora ofthis sequence is represented by the plants Glo s so p teri s, G ang am o pte r is and' C or daite s .

Where sampled the Mersey Coal Measures yield a Substage 36 microflora, which means that these coal

measur;s are signifrcantly older than the Greta Coal Measures in New South Wales and the Collinsville Coal Measures in Queensland. The algae Reinschia also occurs in coals and carbonaceous shales and at Mt Pelion is common enough to form torbanite (Banks, 1962).

Late Permian (Cygnet Coal Measures, Adventure Bay Coal Measures and Equivalents) The Cygnet Coal Measures and equivalent strata are considered by Banks & Clarke (1987) to have been deposited in fluvial or upper delta plain conditions. These rocks are overlain by sandstones containing the Early Triassic Kraeuselisporites saeptatus assemblage (Forsyth, 1984). The Cygnet Coal Measures and equivalents are absent from the north to the eastern part ofthe basin, and may be discontinuous elsewhere, possibly due to pre-Triassic erosion (Figure 5). The dominant rock type in the Cygnet Coal Measures is a well sorted siliceous to arkosic cross-bedded and ripple-marked sandstone, pebbly in places. Carbonaceous and siliceous, often miiaceous siltstones are commonly interbedded with this sandstone (Banks, 1962). During the Late Permian a sandy plan extended across part ofthe Tasmania Basin, which was flanked on the east and west by low hills and also broken up by hills. Whilst initialiy sandy, the overall frning upwards suggests and gradual lowering ofthe source area. The flora in this sequence includes the scouring rush Phyllotheca, and the plants Schizoneura, Ging amopteris, Glo siopteris and' Vertebraria. The vegelation preserved is domi-nantly ptJridospermateous, but evidence exists of rushes

Tasmania Basin

444 and larger woody gymnosperms. The only animal remains are worm tubes and castings.

Late Triassic Coal Measures

50Lm

Although usually obscured by a thick cover of dolerite, the Late Triassic coal-bearing lithic sandstone sequence is found discontinuously over most of eastern and southern Tasmania (Figure 6). Alluvial fining upwards cycles were noted in drill core by Threader (1968), suggesting that the lithic sandstone is offluvial origin. Bacon (1979) suggested, from Markov chain analysis of the cycles, that a meandering stream fluvial system of moderate to high sinuosity existed during the deposition of the lithic sandstone sequence. The arenites are thought to represent channel deposits, and the lutites and coals overbank deposits on extensive floodplains, while intraformational breccias and pebbly horizons represent channel lag deposits.

Figure 4. Distribution of the Mersey Coal Measures and equivalents: coal occurrences indicated by a solid circle.

The sequence has a higher ratio of arenite to lutite than is usually found in classical high-sinuosity meandering streams. This may be attributed to repeated erosion ofupper (overbank) parts ofcycles formed during channel migration, producing common, relatively thick (20m) sections, composed only of channel sandstones in which incomplete fining up cyclicity may still be discerned. Lateral and vertical changes in the relative abundance of arenite and lutite suggest temporal and spatial variation in the fluvial regime, with lutites more significant in the lowermost and uppermost parts of

the sequence.

Age of the Late Triassic Coals 0

50lm

Figure 5. Distribution of the Cygnet Coal Measures and equivalents : coal occurrences indicated by a solid circle (After Banks, 1962).

There is a gradual reappearance ofcoal in the Upper Parmeener Super-Group, following the dearth of coal seams in the Early Triassic quartz sandstone that occurs immediately above the Cygnet Coal Measures. Coalified logs but no coal seams are found in the Tiers Formation and its equivalents, and a gradual, but intermittent appearance of coal seams occurs in the Brady Formation and equivalents, often in association with quartzose sandstone. This culminates with generally thicker and economically more important coal seams in the lithic (upper) facies of the Brady Formation and equivalents, and in younger unnamed strata. Palynology indicates that at least the upper part of the Tiers Formation and equivalents are referable to the Ar atri s p orite s par u is pino s us As s emblage Zone

(Helby, 1973) and the Asseretospora gyrata microflora (de Jersey, 1975; Playford & others, 1982). The basal Brady Formation and equivalents are probably younger than the A. paruispinos.ts, Assemblage Zone, but contain a similar microflora similar to the A. gyrata type microflora of the upper Moolayember Formation in Queensland. In addition, equivalent units near Fingal contain basalt radiometrically dated at 233+ 5Ma (Calver & Castleden, 1981). 0 t,

50 Lrn

Figure 6. Distribution map of the Late Triassic lithic sandstone sequence. Coal seams 1.5m thick indicated by a solid circle.

Annulispora follicularis appears below the oldest widespread coal seam near Fingal (seam H in Figure 7), and in some areas below the top of the diachronous quartz sandstone facies, but it is only in the slightly higher horizons (seams A-G, possibly H) that microfloras occur that have been correlated with the Craterisporites rotundus Zone (Playford in Threader, 1968). Similar microfloras have been obtained from various other economically significant coal measures scattered throughout the Tasmanian

Geology of Australian Coal Basins

445

Biotite extracted from a Triassic tuff exposed in the Denison Rivulet has been radiometrically dated at 214+1Ma (Bacon & Green, 1984), approximating the 219+1Ma Karnian/Norian boundary age proposed by Webb (1981). This tuff crops out in the upper part of the lithic arenite sequence. On Fingal Tier, similar acid tuffs are restricted to that part of the sequence above the B seam. A spore assemblage from about 50m stratigraphically below the dated tuffbelongs again to the Craterisporites rotundus zone (Forsyth,

DALMAYNE CONGLOMERATE

1984b).

Macroflora

Tull

2'14 Ma'

Coalified plant remains of fair preservation are quite common in the coal-bearing sequence. The flora is dominated by filicales (ferns), pteridosperms (seed ferns) and ginkgoales (maiden hair trees). Cycad leaves and scouring rushes are also common. Taxa found include Cladophlebis, Dicroidium, Xylopteris, Ginkgoites, Sphenobaeria (Townrow, 1962) and Hoidephyllum.The plant association is comparable to the broadleafforest association of Retallack (t977).

Craterisporiles

The depositional environment of the Late Triassic coal measures was a terrestrial flood plain, with many streams of moderate to low sinuosity frequently changing direction and eroding existing overbank deposits. Areas in which peat accumulated were subject to frequent flooding and drying out. The remains of a variety of reptiles, fish and amphibians recovered from rocks of Early Triassic age near Hobart have been described by Banks & Clarke (1987). Growth rings indicating seasonal growth in fossilised wood from the coal measures at Langloh and Fingal (Morrison & Bacon, 1986) suggest that conditions during the Triassic were not

rolundus zone

a UJ E F

DUNCAN

trl

= o r, C.l

EAST

FINGAL

freezing.

Although Tasmania was within 20o of the south pole during the Triassic (Embleton, 1973) the climate at high latitudes was apparently warmer than at present. Studies of the distribution of fossil flora (Barnard, 1973), the range of some species of the pelecypod Monotis (Westermann, 1973), and examination ofoxygen and deuterium isotope compositions in cherts in the central USA (Knauth & Epstein, 1976) all conclude that global Triassic temperatures were warmer than at the present time.

PRINCIPAL COALFIELD AREAS

Basalt

233 Ma

History of Development The first recorded discovery of coal in Tasmania was made by the French explorer Labillardiere and his

Figure 7. Diagrammatic stratigraphic section, Fingal Tier. Basin, but in detail the nominated species C. rotundus has only been found near the top ofthe sequence in association with Annulispora densatus. In the Bowen Basin the C. rotundus Zone is considered to be Karnian (de Jersey, t975), and thus the main coal-bearing lithic sandstone sequence in Tasmania is considered to be Karnian (early Late Triassic). Although so far known from only one locality, the coal measure sequence passes up into strata with microflora attributed to the lower P oly c ing ul ati s p o r it e s c r e n u I at u s Zone (de Jers ey, 1975) ofprobable Norian age.

party in 1793, during an attempt to climb Mt La Perouse on the south coast of Tasmania. After European settlement in 1803, numerous discoveries of coal were made over the island. A shipwrecked sailor found coal on Schouten Island south of Freycinet Peninsula on the east coast of Tasmania in 1809, and in 1815 James Kelly found an "immense bed" of (brown) coal on the northern shores of Macquarie Harbour, while rowing around Tasmania in a whale boat.

Despite the very numerous discoveries of coal on the south coast, at Adventure Bay, in the headwaters of the Coal River and so on, no successful mining occurred until 1834 when the colonial Government opened a coal mine at Saltwater River on the Tasman Peninsula. Prior to this a small scale mining attempt at Coal Head, Macquarie Harbour

Tasmania Basin

446

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Figure 8. Entrance to adit at Mt Nicholas coal mine showing horse-drawn tramway, circa 1900. was made by the prison authorities, and is

mentioned in the narrative of the convict/cannibal Alexander Pearce. The first commercial coal mining venture was made by a syndicate led by Charles Swanston (one of two

Attorneys General of the day) at Southport. Whilst the syndicate received some Government assistance to sink the shaft, and the company achieved a measure of short-lived paper prosperity, the venture failed. During the 1840s coal mining started on Schouten Island and near Jerusalem in the headwaters of the Coal River, while in the 1850s work was begun near the Denison Rivulet by the Douglas River Coal Company, urged on by the eminent Dr. Joseph Milligan. Like many of the early mining activities, this venture also failed, due to a massive expenditure on infrastructure, which left no funds for underground development. The Mersey Valley coalfield was open up in the 1850s and many small mines worked in this field intermittently. The last one, Illamatha No. 2, closed in 1962. The New Town coalfield, near Hobart was also worked in the 1850's with the sporadic activity finally ceasing around 1910.

activities of any size. However, in 1886 a railway line was laid from St Marys to Conara, connecting with the Hobart-Launceston railway, and a means of transport for coal thus became available. Mining began on Mt Nicholas in earnest in 1888 (Figure 8). Several collieries have existed in this area, although today Blackwood Colliery (opened in 1980) is the only colliery to work on Mt Nicholas. Mining began intermittently at Fingal, south-west of Mt Nicholas, in the 1920s. Duncan Colliery opened in 1945 and is currently still in operation, supplying coal, with Blackwood, to a number of local secondary industries for steam raising purposes.

Coalfields in Early Permian Strata Preolenna Coalfield The Preolenna coalfield is located 20km south-west of Wynyard. The Preolenna Coal Measures are equivalent to the Mersey Coal Measures further east, and overlie a marine siltstone (the Inglis Siltstone and equivalents) in which is found a Tasmanite oil shale horizon. The Preolenna Coal Measures, which reach a maximum thickness of 50m, are overlain by a marine sandstone sequence, the Flowerdale Sandstone.

An ambitious project began at Seymour in 1861 with the aim of mining coal and using the "slack" or waste coal to retort kerosene. Although the retorting project failed, coal was mined at Seymour intermittently until 1964, and at Dalmayne, north-east ofSeymour, from 1915-1954. The Dalmayne colliery boasted a modern self-acting tramway which ran to Piccaninny Point, 15km north

The coal measures have been extensively faulted. Four seams of coal, 0.2 to 0.6m thick, are known in the Preolenna area, dipping at 14 to 25o . Historic mining actively was unsuccessful due to the nature of the seams, which frequently thin out and are disrupted by faulting.

of Seymour.

Mersey-Don Coalfield

The largest deposits of coal in Tasmania are in the north-eastern part of the State. Coal was known in the Fingal-Mt Nicholas area from around 1840, but the lack of any suitable access prohibited mining

Coal has been won intermittently from the Mersey Coal Measures in an area between the Mersey and Don Rivers. A total of 21 small collieries worked in this field between 1850 and 1962.

Geology of Australian Coal Basins

447 The coal measures in this area are 19 to 29m thick. They are underlain by siltstones and mudstones of the Spreyton Beds and overlain by the Kelcey,Tier Beds. Ttre seams are thin ( <1m thick), faulted, and are not laterally extensive. Mining was done by hand using both bord and pillar and longwall methods of extraction. _

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,"t Millsll I

Coalfields in Late Permian Strata Cygnet Coalfield

IOI tS I

J i

The Cygnet Coal Measures is the lowest unit of the Upper Parmeener Super-Group, underlain by glacio-marine mudstones of the Lower Parmeener Super-Group and overlain by quartzose sandstones. At Cygnet this coal measure sequence is about 30m thick, cropping out along the slopes of Mt Cygnet and Mt Heeney. Two seams, each <lm thick, have been mined from a number of adits driven in on outcrops. Jurassic dolerite caps Mt Cygnet and is faulted against the sedimentary sequence to the east of Heeneys Bluff, and the area in general is badly disrupted by faulting. These coal measures also crop out on Bruny Island at Adventure Bay, where they are known as the Adventure Bay Coal Measures. This sequence was mined briefly in the 1880s.

Coalfields in Triassic Strata -

(

I lt?

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Figure 9. Coal facies diagram showing environments - of formation of some coal seams (graph construction after Diessel, f 986).

The bulk of Tasmania's coal resources are in the

and forms a known horizon from which correlation of coal seams may be more confidently undertaken.

Coalfield.s

Fingal, Mt Nicholas and Dalymayne coalfields in the norfh-eastern part ofthe State. The basement rocks in this area are folded and cleaved Siluro-Devonian turbidite quartzwackes and Devonian granites, which are unconformably overlain by the largely marine Lower Parmeener Super-Group. The Lower Parmeener Super-Group is about 120m thick around Fingal and Dalmayne, but its thickness varies due to erosion prior to deposition of the overlying Upper Parmeener Super-Group.

At the base of the Upper Parmeener Super-Group is a thin unit ofquartzose sandstone, only 2 to 3m thick over most of the area. The rest of the Triassic sequence, about 350m thick, consists dominantly of medium-grained lithic sandstone, interbedded with mudstone, carbonaceous mudstone and coal. The lithic sandstone is typically thick-bedded and often shows trough cross-bedding. Intraformational breccia, with rip-up clasts of mudstone and coal, is common at the base of individual sandstone beds.

There are eight major coal seams on Fingal Tier, in the west, designated informally as seams A to H (Figure 7). Some, notably the A and B seams, are better described as carbonaceous intervals, as they consist of plies of coal less than 0.5m thick. All the seams are characterised by a high proportion of inherent ash, and have only a small (lo7o) component of bright coal. The coal is of medium ranli, with high ash and a low sulphur content, and

is suitable for steam-raising purposes.

No satisfactory marker horizons have been recognised in the fluvial sequence on Fingal ti"t, andin order to obtain a reliable correlation ofcoal seams it has been necessary in exploration to drill to the glacio-marine sequences of the Lower Parmeener Super-Group. This sequence dips gently to the east,

A conglomerate horizon (1 to 3m thick) on parts of Fingal Tier has proved to be a reasonably goodmarker where if is present. The conglomerate band (informally called the Dalmayne Conglomerate) is composedbf well-rounded pebbles and cobbles of green and white quartzite, acid pyroclastic rocks and slate, elongate to spherical in shape and set in a matrix of coarse-grained lithic sandstone. The conglomerate band is, however, too patchy in areal distribution to be of wider significance as a marker bed.

A number oftuffhorizons have been recorded in the eastern part of the Fingal Tier. The tuff is an acid, air-fall tuff, with the individual units around one metre thick. However, the patchy areal distribution of these tuffs also makes them of little use as marker horizons. A thick sill of dolerite intrudes the sequence above the coal-bearing sediments in the Dalmayne and Fingal Tier coalfields. This dolerite is commonly 100 to 200m thick and forms an extensive plateau, part ofthe central eastern highlands. The two seams which are of greatest economic interest on Fingal Tier are the Duncan seam (or F seam) and the East Fingal seam (G seam). The Duncan seam is current-ly mined at Duncan Colliery, and is the only seam to have been extensively worked. It tyfically consists of 2 to 3m of dull coal with minor clay and mudstone partings.-The raw ash of the coal-is approximat ely 30Vo and the specific energy 22 to 24MJlkg. The East Fingal seam is about 30m stratig-raphically below the Duncan seam. It is commonly split. The upper and lower splits (Gu and Gl seams) of the

Tasmania Basin

448 East Fingal (G) seam are commonly 1 to 2m in thickness, with the intra-seam sediments 0 to 10m in thickness. The coal quality is similar to that of the Duncan seam.

vtTn tNtTt

The Mt Nicholas coalfield, in the Nicholas Ranges north-east ofFingal Tier, is also capped by dolerite. The sedimentary sequence in this area is equivalent

to that at Fingal Tier and Dalmayne, although the coal seams are found in three intervals within the lithic sandstone sequence. The uppermost interval contains seams of poor quality coal, interbedded with claystone and mudstone, while the middle and lower intervals contain the seams which have been mined previously. The lower group of seams on Mt Nicholas is equivalent to the East Fingal interval further south.

Other Triq.ssie C oalfield,s Triassic coal has been also mined at a number of other places in eastern Tasmania. At Saltwater River, on the Tasman Peninsula, coal occurs in a small downfaulted wedge-shaped block of lithic sandstone, surrounded by coal-barren quartzose sandstones. Mining was conducted by the colonial government at this locality using convict labour in the early part of the 19th Century.

MrcntilrI[ -r- MAcRtNlTt + tNtnT00tTntiltTE

South of Dalmayne, near the Douglas River, Triassic coal was mined in the 1850s from shafts sunk into the coastal plain. Further north, at Seymour, coal was mined from a shaft in the 1880s ahd from a dip

adit during the 1920s and 1950s. At Newtown, neal Hobart, shafts were sunk directly into lithic sandstone in the 1880s.

At Kaoota, south of Hobart, and at Langloh in the Upper Derwent Valley coal has been mined from adits driven from outcrop. The area of these two coalf elds is quite s^mall, with Kaoota covering 1km2 and Langloh 10km2. The coal-bearing sectioni, around 100m thick at both locations, both rest on a dolerite floor. The intrusive dolerite has rafted up the lithic sandstone sequence, and these coalfield-s occur in remnants of the former cover above the dolerite unit.

fUSINI IE

STMITUSINITE

CUTINI IE

Significant occurrences ofTriassic coal are also found near Ben Lomond (the Stanhope Mt Christie coalfield) in the Midlands area-and in the south of Tasmania around Catamaran.

Current Mining Operations Four collieries currently produce coal in Tasmania, the two main operations being Duncan Colliery at Fingal and Blackwood Colliery on Mt Nicholas near St Marys. These two mines are owned and operated by the Cornwall Coal Company N.L., and coal at each is mined using the bord and pillar system. Two other small, privately-owned open-cuts are also in operation.

At Duncan Colliery, which has operated since 1945, coal is produced from the Duncan seam, which ranges from 2 to 5m in thickness. Geological conditions in the mine vary, since over most of the area the original seam roof of laminite and claystone has been eroded. Compaction and faulting are not uncommon and several dolerite intrusions have disrupted parts of the seam. Mining occurs from outcrop to a depth of 420m. The Blue seam is worked at Blackwood Colliery on Mt Nicholas. This seam is approximately 5m thick,

but only 3.6m is actually extracted. Coal is mined

Figure 10. Maceral componente of Permian coal aeama.

a) Total maceral percentages in Early and Late Permian coals. b) Inertinite maceralg of Early and Late Permian coals. c) Liptinite macerals in Early Permian seams.

Geology of Australian C oal Basins

449

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Figure 11. Graphic representation of the Merrywood, Blue and Duncan seams.

from outcrop to a total depth of around 300m under part of the Nicholas Range. Vertical loading stress, expressed as floor heave, is common in areas of greatest overburden thickness. Coal from both these collieries is treated in a washery near Fingal. The washed coal is used in a variety of domestic secondary industries as boiler fuel, and in the marking of cement. The open-cut coal is used, without washing, as a boiler fuel.

COAL PETROLOGY The black coals of Tasmania fall into two separate petrographic classes. The Early Permian coals tend to be richer in vitrinite, higher in sulphur and lower in ash than the younger Late Permian and Triassic coals, which are high in ash, low in sulphur and composed dominantly of inertinite macerals derived from oxidized woody tissue. Using the principles outlined by Diessel (1986), the Early Permian materials are thought to have formed in a

back-barrier environment with paralic influence, while the Late Permian and Triassic coals, frequently interbanded with mudstone and claystone, are believed to have formed under dry forest conditions.

Figure 9 is a plot of the gelifrcation index (Gl) against the tissue preservation index (TPI) for the piincipal Tasmania coal seams. The -gelification indexf defined by Diessel (1986), is the ratio of gelified residual tissue (telinite and telocollinite) to oxidized woody material (fusinite and semifusinite) in the coal, and is believed to reflect the moisture

level (or relative height of the water table) in the original peat swamp. The tissue preservation inde1, on the other hand, also defined by Diessel (1986), is the ratio of macerals derived from woody tissue (telinite, telocollinite, fusinite and semifusinite) to those, such as sporinite, alginite, inertodetrinite and desmocollinite, that have a non-woody origin, and is taken as a indicator ofthe general type ofvegetation from which the peat itself was formed.

Early Permian Coals The coals from the Mersey and Preolenna Coal Measures are characterised by a high vitrinite

content (40 to 607o) and a high liptinite (exinite) content (usually around \5 to 2OVo). Most of the vitrinite is in the form of varieties of collinite, rather than as preserved woody tissue. The dominant liptinite maceral is spori!ite, although alginite has b6en noted in some samples, indicating that the swamp was flooded for at least part, if not all of the perioci of peat formation, Graphic representations of the maceials in the various seams are given in Figure 10. The Early Permian coals are typically low in ash (8 to l27o), but relatively high in sulphur (3 to \Vo). Pyrite is commonly found as a cleat coating. Th-e coals generally have a specific energy (air-dried) of 26 to 50MJ/kg, and a vitrinite reflectance in the range of 0.45 to 0.5Vo. The coals have a low tissue preJervation index (0.25-0.75), suggesting that they

iormed in a habitat which did not produce significant quantities of woody tissue, while the ge-lification index of around 1 suggests a relatively

Tasmania Basin I

450

wet environment. They probably formed in an open moor habitat, a conclusion supported by the presence of alginite, indicating a subaqueous environment of deposition. The abundance of sporinite, which tended to collect in lakes and ponds, further supports this interpretation, as does the high proportion of collinite. The collinite was apparently derived from the decomposition of soft-tissued leaves, as well possibly as grasses and reed-like plants.

vtIR['ltIt

Late Permian Coals Few petrographic analyses are available for the Late Permian coal measures. The coal appears, however,

to be petrographically similar to the Late Triassic

coals (see below) with a high proportion of the coal being derived from wood which h-as become

txlNl rt

INTNTINIIT

fusinitised.

Late Triassic Coals The Late Triassic coals are very dull, with high raw ash percentages (25 to SOVo), low sulphur conlents (0.\Vo) and a raw (air-dried) specific energy of 20 to

MrcRlNlIt-tMAcnrNrIt l lNtnI00tIntNtTt

24MJ/kg.

Vitrinite reflectance for these coals is most commonly around 0.5 to 0.6Vo, although in some

instances where the coal has been affected by dolerite values of up to 3.|Vo are known. Column sections illustrating the megascopic character of selected seams are given in Figuie 1.1. The main component of these coals is inertinite, which makes wp 6O-707o of most seams by volume

(Figure 12). Vifrinite, usually in the form of collinite, makes up no more than l\Vo of the coal. l,iptinite is similarly low (5 to LOTo), with the dominant liptinite maceral being cutinite. Finely-d-ispersed mineral matter, mostly clays and quartz, fills cell lumens and is well dispersed throughout the plant material. This finely disseminated mineral matter cannot be r-emoved, and hence the coal cannot be washed to give less' than 18 to 20Vo ash.

FUStNT

STMITUSINITE

CUTIIIITE

o Ouncan Seam

Most of the seams contain mudstone or claystone bands, attesting to periodic inundation of the peat

Blur Scam

* Mrrrywood Saam

swamps with sediment-bearing floodwaters. Some of

the bands are apparently also derived from ash-fall material.

Duncan Searn The Duncan seam is mined at Duncan Colliery near Fingal. The dominant maceral group of this seam is inertinite, and overall the seam composition does

not vary greatly from ply to ply. The vitrinite content is low throughout the whole seam, with most of the vitrinite being made up of various forms of collinite. The vitrinite content is slightly higher (30Vo) at the base of the seam, possibly indicating the existence of wetter conditions at the time the peat swamp became established. The dominant inertinite maceral is semifusinite in all plies of the qea-m, but the amount of inertodetrinite is also quite high. Liptinite is distributed evenly throughout the seam, with cutinite being the dominant liptinite component.

All coal plies of the Duncan seam have a gelification index (GI) of 0.25, which indicates that the environment of coal formation was dry. The tissue preservation index has a value of 3 to 4 for most plies, which indicates that a substantial proportion of wood-derived macerals are present. The two

R tstN

tTt

SPONINITT

Figure 12. Maceral components of Late Triassic coal seam plies. a) Total maceral percentages. b) Inertinite macerals. c) Liptinite macerals. indices together indicate that the peat formed from accumulated woody material in a relatively dry environment, subject to frequent drying and oxidation which resulted in the abundance of inertinite. Periodical flooding of the peat swamp is also indicated by the presence of a number of claystone bands.

Geology of Australian Coal Basins

451

0f,.,P,,A'TBv,R

Figure 13. Location of brown coal deposits in Tasmania.

Blue Seam The Blue seam, mined at Blackwood Colliery on Mt Nicholas, is similar to the Duncan Seam, but has a higher vitrinite content. The vitrinite content is highest at the base ofthe seam ( OVo), and generally decreases towards the top (l0Vo). The dominant liptinite maceral is cutinite. The seam is extremely banded, containing about nine claystone and mudstone bands. The gelification index for the plies of the Blue Seam indicates that the environment was relatively dry,

but not as dry as that in which the Duncan seam was deposited. The TPI shows that about 50Vo of the macerals in the seam are derived from woody tissue.

Merrywood Seam The Merrywood Seam is mined intermittently in a small open-cut southwest of Fingal. The most

distinctive feature ofthis seam is the presence of three plies of paper coal, composed of tightly compacted Johnstonia leaves towards the top of the seam. The dominant maceral group in all plies except the paper coals is inertinite, mainly semifusinite, while the dominant liptinite maceral is cutinite.

The paper coals are composed of liptinite (mainly cutinite), vitrinite and large quantities ofclay particles. The Johnstonia leaves, which have a very lhin cuticle, are clumped together and matted with mineral matter. They may have been derived from a type of water-weed that carpeted a shallow pond during the times when the peat swamp was inundited. When the swamp dried out, the matted water-weed was apparently deposited on top of the peat. An influx of muddy water may also have iaused the water-weed mat to break up and be re-deposited with the mud, as one of the paper coal plies contains 90Vo of clay material.

Trias sic Peat Formation A considerable proportion ofthe coal in all three of these seams has evidently been derived from woody tissue, as shown by the tissue preservation indices for the various plies of each seam. The woody component is also fusinitised. The three seams are considered to have formed from peat which collected in a dry forest-moor environment. No evidence, such as graded bedding in inertodetrinite concentrations, has been found for subaqueous deposition in any of the coals. Pyrite is

I I I

Tasmania Basin I

i I

452

rare in the coals, indicating that the peat did not form in stagnant reducing waters. The variable but high concentrations of semifusinite

BANKS, M.R., 1979: A Permian fault in north-western Tasmania. Papers and Proceedings of the Royal Society of Tasrnania, 113, 185-191.

and inertodetrinite point to periodic oxidation ofthe peat, while the presence of a great many dirt bands (predominantly in the Blue seam) are the result of periodic flooding of the peat swamp. The paper coals at the top of the Merrywood Seam are possibly analogous with an open moor setting, and represent periods offlooding and algal bloom conditions over the swamp surface.

BANKS, M.R. & CLARKE, M.J. 1987: Changes in the geography of the Tasmania Basin in the Late

OTHER COAL AND OIL SIHLE DEPOSITS

BARNARD, P.D.W., 1973: Mesozoic floras. In Hughes, N.F. (Editor): Organisms and Continents through Time. Special Papers in Palaeontology,12, 175-188.

Brown Coal Lignite of Tertiary age has been found in small deposits in many places within Tasmania. The largest deposit is at Rosevale, near Westbury in northern Tasmania, where an indicated in situ resource of 118Mt of brown coal has recently been defined. Smaller deposits of lignite are also known on the northern shore of Macquarie Harbour, in the Tamar and Derwent Valleys, on King Island and at a number of localities along the North West Coast. The distribution of brown coal in Tasmania is shown in Figure 13.

Oil Shale One horizon of oil shale is known in Tasmania. This is ofLate Carboniferous age, stratigraphically below the Mersey Coal Measures and its equivalents. The shale horizon, which is about 2m in maximum thickness, does not pass either laterally or vertically into coal. It is composed of large numbers of bodies of Tasmanites punctatus (probably a green alga) in a matrix of very fine-grained sand and silt. The oil shale was deposited close to shore in a shallow

marine environment.

The oil shale was mined for a brief period during the 1920s and 1930s. Attempts were made to extract a fuel from the shale, but these efforts were non-commercial. More recently the shale has been examined as a potential source of road-making bitumen.

REFERENCES

Palaeozoic. In McKenzie, E.D. (Editor): Gondwana Six: stratigraphy, sedimentology and palaeontology. Geophysics Monograph, 41, l-14.

BANKS, M.R., COSGRIFF, J.W. & KEMP, N.R., 1978: A Triassic stream community. Australian Natural

History, 19, 150-157.

BERRY, R.F. & BANKS, M.R., 1985: Striations on minor faults and the structure of the Parmeener Super-Group near Hobart, Tasmania. Papers and Proceedings of the Royal Society of Tasmania, Ll9,

23-29. CALVER, C.R. & CASTLEDEN, R.H., 1981: Triassic basalts from Tasmania. Search,12, 40-4I. DE JERSEY, N.J., 1975: Miospore zones in the Lower Mesozoic of south eastern Queensland. In Campbell, K.S.W. (Editor): Gondwana Geology. Australian National University Press, Canberra, 159-172.

DIESSEL, C.F.K., 1986: On the relationships between coal facies and depositional environments. Proceedings of the 20th Symposium on Aduances in the Study of the Sydney Basin. Department of Geology, University of Newcastle.

EMBLETON, B.J., 1973l, The palaeolatitude of Australia through Phanerozoic time. Journal of

the Geological Society of Australia, 19, 47 4-482.

FORSYTH, S.M., 1984a: . Sheet 68 (8312S). Oatlands. Geological atlas 1:50 000 series, Explanatory Report Department of Mines, Tasmania. FORSYTH, S.M., 1984b: Palynological report on a Triassic siltstone underlying pyroclastics, Denison Rivulet. In Bacon, C.A. & Green D.C.: A radiometric age for the Triassic tufffrom eastern Tasmania. Department of Mines Tasmania, Unpublished Report 1984 I 29.

BACON, C.A., 1979: Regional geology of the Apsley River area northeastern Tasmania (Part A) and sedimentology of the Late Triassic Coal Measures in northeastern Tasmania (Part B). B.Sc. (Hons) Thesis, University of Tasmania.

FORSYTH, S.M., FARMER, N., GULLINE, A.B., BANKS, M.R., WILLIAMS, E. & CLARKE, M.J., 1974: Status and subdivision ofthe Parmeener Super-Group. Papers and Proceedings of the Royal Society of Tasmania, 108, 107-109.

BACON, C.A., 1986: Coal in Tasmania. Tasmania

HELBY, R.J., 1973: Review of Late Permian and Triassic palynology of New South Wales.

Department of Mines, Report 1986/43. BACON, C.A., 1991: The coal resources of Tasmania. Geological Suruey of Tasrnania, Bulletin,64.

Geological Society of Australia, Special

Publication, 4, L4l-155.

BACON, C.A., & GREEN, D.C., 1984: A radiometric age for a Triassic tuff from eastern Tasmania. Department of Mines Tasmania, Report 1984/29.

KNAUTH, L.P. & EPSTEIN, S., 1976: Hydrogen and oxygen isotope ratios in nodular and bedded cherts. Geochimica cosmochimica Acta, 4O,

BANKS, M.R. 1962: Permian..In Spry, A.H. & Banks, M.R. (Editors): The Geology of Tasmania. Journal of the Geological Society of Australia,9(2),

LEAMAN, D.E., 1981: Gravity survey of the east coast

189-2 15.

BANKS, M.R., 1973: General geology..In Banks, M.R. (Editor): The Lake Country of Tasmania. Royal Society of Tasmania, Hobart, 25-34.

1095-1108. coalfields. Bulletin of the Geological Suruey of

Tasmania,6O. McKELLAR, J.B.A., 1957: The geology of a portion of the Western Tiers. Records of the Queen Victoria Museum,7.

Geology of Australian Coal Basins

453 MORRISON, K.C. & BACON, C.A., 1986: Comparison between the Fingal and Langloh coalfields Tasmania Basin. Australian Coal Geology,6, 41-58. PLAYFORD, G., RIGBY, J.F. & ARCHIBALD D.C., 1982: A Middle Triassic flora from the Moolayember Formation, Bowen Basin Queensland . Geological Suruey of Queensland, Publication, 380, 1-52.

RETALLACK, G.J., 1977: Reconstructing Triassic vegetation ofeastern Australasia: a new approach to the biostratigraphy of Gondwanaland. Alcheringa, L, 247 -27 8. SCHMIDT, P.W. & McDOUGALL, J., L977: Palaeomagnetic and potassium-argon dating studies of the Tasmanian dolerites. Journal of the Geological Society of Australia, 24, 32L-328.

SOLOMON, M., 1962: The tectonic history of Tasmania. Journal of the Geological Society of Australia, 9(2), 3 1 1-339.

SPRY, A.H., 1962: Igneous activity..In Spry, A.H & Banks, M.R. (Editors): The Geology of Tasmania,

Journal of the Geological Society of Australia, s(2),255-284. SPRY, A.H & BANKS, M.R. (Editors), 1962: The Geology of Tasmania, Journal of the Geological Society of Australia, 9(2). THREADER, V.M., 1968: An interim report on the geology and coal resources ofthe north-east Tasmanian coalfields. Unpublished Report Department of Mines Tasmania. TOWNROW, J.A., 1962: Palaeontology of the Triassic. .In Spry, A.H & Banks, M.R. (Editors): The Geology of Tasmania, Journal of the Geological Society of Australia, g(2), 224-226. WEBB, J.A., 1981: A radiometric time scale for the Triassic. Journal ofthe Geological Society of Australia, 28, L07-l2L WESTERMANN, G.E.G., 1973: The Late Triassic bivalve Monotis. 1n Hallam, A. (Editor): Atlas of Palaeobiogeography. Elsevier, Amsterdam, 251-258.

Tasmania Basin

455

Knswich Coalfield

The city of Ipswich lies 40km west of Brisbane, and the Ips;vich coalfield occupies an area ofabout 250krrr" to the north, east, and southeast of the city (Figure 1). The coal-bearing area is traversed by tlie Bremer and Brisbane Rivers, the Warrego and Cunningham Highways, and the main railway westwards from Brisbane. It lies mostly within the local authority areas of Ipswich City and Moreton Shire, with a small extension into Brisbane City. The coalfield is in two parts: the North Ipswich area, lying generally north of the Bremer River, where mining has ceased; and the Bundamba area, which lies on the Bundamba Anticline and extends southwards from the railway for about 12km, from which all production now comes. Coal mined at

HRE Staines AJ Falkner and MP Thornton

North Ipswich came from seams of the Tivoli Formation; in the Bundamba area it is won mostly from seams of the Blackstone Formation (Table 1).

Mining has been carried on continuously in the Ipswich coalfield since about 1843, and the field was the principal producing coalfield of Queensland until the 1960s, when large-scale development of the coal deposits of the Bowen Basin in central Queensland commenced. The railway system was the principal user of Ipswich coal until the introduction of diesel locomotives in the 1950s. Subsequently the electricity-generating industry became, and remains, the greatest coal consumer.

IIISTORY Geological Investigations Despite the long-standing belief that coal was first discovered in the Ipswich area by Logan in 1827 (Denmead, 1955; Mengel, 1975), Whitmore (1981) has produced evidence that outcropping coal was seen by Oxley in 1824 and sampled by Lockyer in 1825. He could find no confirmation of Logan's

reported responsibility for early coal discoveries.

The first recorded geological examination was by Gregory in 1876, and there followed reports on the stratigraphy and flora of the coal measures by Carruthefs (L872), Tenison-Woods (1882, 1883), and Shirley (1898). Mining had commenced in the 1840s, but the first major geological survey of the producing coalfield was not made until late in the century by Cameron (1899). His first report was followed by a second, with special reference to the Bundamba District (Cameron, 1907). Further work during the period 1911-1913 was reported in the form of a set of geological maps (Cameron, 1923). The next major investigation was undertaken in the 1940s by Denmead (1955). He expanded on Cameron's geological mapping and made detailed inspections of every accessible mine opening. Following recommendations by Powell Duffryn Technical Services Limited (PDTS) in their report on the coal industry of Queensland (PDTS, 1949), an extensive diamond drilling programme was undertaken by the Department of Mines and the Queensland Coal Board. This exploration was accompanied by detailed geological mapping of the producing and prospective areas ofthe field by staff of the Geological Survey of Queensland. A series of detailed reports on the various sections of this investigation culminated in a summary report by Mengel & Carr (1976).

Ipswich Coalfield

456

OF IPSWICH COAL_ FIELD \

-\:1,.

+--e 1

)

.'PAci

REFERENCE \ r-

" ; I Undiff olluvium, Tertiory 5 I l: .lbosoll A sediments t.tll.9 J -"--r--Tertiory trochytes .

3 I I =;.ol

I' -\

t I-=l Bundombo Grurp

n ll

o 6 N

j o-

{

_:__

l-e-l

Blockslone Fm. lEdl> I qLl .o L6at Tollt_

I ll= =_l Tivoli ftn. ul

;'..9.

'?.

'\,

jI6; i6

Kholo Subgroup I a

? \

flr.l

Neronlci$r - Fernlole Beds

--------- Fold

-) // ',

rz): i/ ----)

_.1

Drillhole Foull

'i52

lrl

tr?

SCALE

345

8 KILOMETRES

SECTION A - B

d_o

o c

Figure 1. Geological map of the Ipswich coalfield.

Geology of Australian Coal Basins

457

Table l. Stratigraphic succession in the Ipswich Coalfield. Age

Group

Formation

Subgroup

Jurassic

Late Triassic to Jurassic

Thickness

Marburg Formation

Ripley Road Sandstone

365 m

Raceview Formation

120 m

Bundamba Group Woogaroo Subgroup

1n4-,^,n

30 m

unconformitv Blackstone Formation

240 m

Tivoli Formation

up to 500 m

Cribb Conglomerate

18m

Hector Tuff

upto3?m

Colleges Conglomerate

avge 160 m

Mount Crosby Formation

21-34 m

Weir Basalt

11 m

Brassall Subgroup

Late Triassic

Ipswich Coal Measures

500 m

Kholo Subgroup

?00 m

300 m

:t_-z\Z-',2-'t . uneonform ity ?Carboniferous

Neranleigh-Fernvale

Mining Developments The first commercial mine, the Pioneer Mine, was commenced by entrepreneur John Williams on the south bank ofthe Brisbane River at Redbank about

1843 to provide steamship fuel (Whitmore, 1981), and operated until 1848 (Fryar, 1900). Between 1846 and 1858 Williams operated the Moggill mine some 10.5km downstream on the opposite bank of the river. The seam at Redbank was worked again during three periods before 1900 (Whitmore, 1985).

There was short-lived coal-mining activity at

Woodend in 1848 and 1854 (Radstock Pit), and at Tivoli Creek in 1851. However, the frrst stable supply of coal came from Walter Gray's mine on the Garden seam which operated successfully from L854 to 1862 near the confluence ofTivoli Creek and the Bremer River (Whitmore, 1981).

The Tivoli seam was first mined about 1866 in the Tivoli mine, and other seams in the North Ipswich sequence were subsequently exploited. Coal from the North Ipswich district proved to be suitable for coke-making as well as steam-raising. Coke ovens were established at most of the pits from the 1870s, and some of them operated until the 1950s.

South of the Bremer River the Aberdare seam was discovered at Blackstone in 1866 and was first

worked in the Bundamba (later Aberdare) mine. Because of its superior quality this seam was the most sought after for many years to follow. It was mined extensively from the outcrop, and later from deep shafts. Also in 1866 the underlying Bluff seam was frrst worked in the brief operation of the Redhill Mine at Dinmore, but it was not worked continuously until the adjoining Aberdare (later Old Aberdare) Mine exploited it in 1870-77. The lower seams of the Blackstone Formation, particularly the better

quality Four Feet (or New Chum) seam, were opened up in the Bundamba and Dinmore areas in the early 1880s.

Development of the field continued into the 20th century with the establishment of major mines at North Ipswich and in the areas south of Bundamba and Dinmore which supplied coal for shipping, railways, and local industry, including electricity generation. However, overall development was haphazard and unplanned, and the lack ofa coordinated approach to exploitation of the field led to problems of supply, which were addressed by the 1949 PDTS report. The comprehensive Departmental drilling campaign which resulted from recommendations by PDTS operated from 1950 to L970 and provided a stimulus to planned developments of the field by establishing the quantity and extent of coal resources. Coal was produced entirely from underground mines

until 1966, when the first open-cut mine commenced in the Dinmore district. Open cut production steadily increased until it first exceeded underground production in 1985. In 1985-86

saleable production from underground mines was 1 349 000t, and from open-cut mines 1 745 000t. Most of the coal presently produced is won from the Bluf{ Four Feet and Bergin seams, mainly from collieries in the south of the freld. There are now no producing mines in the North Ipswich district. The principal use of Ipswich coal is electricity generation. An export market was established in 1980, and is steadily increasing.

STRUCTURE The structural setting of the intermontane Ipswich Basin is dominated by the D'Aguilar Block to the north and the Beenleigh Block to the southeast. An easterly unconformable relationship exists between the basin sediments and the Palaeozoic basement,

Ipswich Coalfield

458 and part of the northern boundary with the D'Aguilar Block north of Ipswich is faulted. Drillhole data indicate an absence of Ipswich Coal Measures west of the West Ipswich Fault. To the east of the West Ipswich Fault, the Early-Middle Triassic Toogoolawah Group of the Esk Trough does not underlie the Late Triassic Ipswich Coal Measures. South of Ipswich no drillholes have reached basement and most have stopped in volcanics, possibly of Triassic age, which are presumed to rest on basement (Cranfield & others, 1976).

The internal structure of the basin is characterised by a series ofnorthwesterly to northerly trending folds and faults and a subsidiary northeasterly fault trend. The regional dip is about 10o ranging between south and southeast, but is modified locally by

folding (Figure 1).

The Ipswich Anticline, an asymmetrical structure lying west of the city of Ipswich, trends northnorthwesterly and plunges to the south. This anticline, combined with the major West Ipswich Fault, exposes Kholo Subgroup sediments adjacent to the fault. Dips locally exceed 50o, but are usually less than 30o. Downwarping of the broad Booval Syncline to the east of Ipswich has preserved Tertiary sediments and basalts in a large area to the south of Booval (Mengel & Carr, 1976). The Bundamba Anticline has its apex at Ebbw Vale,

from where it plunges to the north and south. This fold is slightly asymmetric, with a steeper western limb, and is modified into two domes by a shallow east-west trending syncline about-halfway along its length. Dips are oTthe order of 10o to 15o with local steepening to 25o. Some subsidiary folds have been revealed by mine workings on the limbs of the main

anticline. The southern end of the Bundamba Anticline is intersected by another asymmetric anticline trending west-northwest. Dips on the western limb near the intersection of the two fold axes are very steep (50 to 60o), while further northwest the fold

tightens and the western limb is overturned.

The Spring Mountain Anticline is a low amplitude structure trending nortrrL-northwest which is exposed in Bundamba Group sediments to the southeast of the Ipswich coalfreld. It probably originated during or after deposition in the Ipswich Basin, and continued to develop during deposition ofthe overlying Moreton Basin. Numerous northwesterly trending faults are known in the Ipswich area, especially the North Ipswich district, and some northeasterly trending faults also occur in the Bundamba district. Most faults are normal, but reverse faults also occur, a notable example being the zone of overthrusting and dip reverial south of Dinmore railway station. Many faults exhibit large lateral variation in displacement indicative of the complexity of faulting in the Ipswich area.

STRATIGRAPHY

Ipswich Coal Measures The Late Triassic Ipswich Coal Measures comprise up to 1200m of coal-bearing sediments_that

aicumulated within the intermontane Ipswich Basin. The stratigraphic succession in the Ipqwich Basin (Table 1) consists of a lower unit, the Kholo

Subgroup, that is largely barren ofcoal, and an upper, coal-bearing unit, the Brassall Subgroup. The lpswicfr Coal Measures in the northern part of the 6asin unconformably overlie the Palaeozoic Neranleigh-Fernvale beds. To the south boreholes have intersected a sequence ofvolcanics ofpossible Late Triassic age below the Kholo Subgroup (Hawkins, 1956; Meyers, 1970; Almond, 1982). Sediments of the Bundamba Group unconformably overlie the Ipswich Coal Measures.

An abundant palaeoflora dominated by the genus Dicroidium is present in the Ipswich Coal Measures (Jones & de Jelsey, L947) and palynological investigations indicate a Carnian age for the unit (de Jersey, 1970; 1971). Fossil insects, freshwater bivalves, conchostracans, and dinosaur and amphibian footprints have also been found in the Ipswich Coal Measures.

Kholo Subgroup Allen (1961) defined six formations with a total of about 300m in thickness which constitute the Kholo Subgroup (Table 1). The Blackwall Breccia and Weir Basalt unconformably overlie the NeranleighFernvale beds. The Mount Crosby Formation and Colleges Conglomerate overlie older units of the Sub gioup disionformably or conformably, ol, th e Nerinleigh-Fernvale beds unconformably. The Hector Tuff and Cribb Conglomerate show conformable contacts. The Blackwall Breccia consists of 9m of sedimentary breccia derived from the underlying NeranleighFernvale beds. The Weir Basalt consists of 11m of altered vesicular basalt and is in places interbedded with the Blackwall Breccia. The dominant lithology of the Mount Crosby Formation (21-34m) is poorly sorted, polymictic pebble and cobble conglomerate interbedided with minor sandstone and tuff beds and several mudstone units up to 6m thick. The Colleges Conglomerate averages 160m thick and consists of clasf-supported polymictic pebble and cobble conglomerate interbedded with minor matrixsupported conglomerate, sandstones and mudstones. The Hector Tuff is a sequence up to 37m thick of carbonaceous mudstones interbedded with light-coloured tuffs and occasional coal bands. The Ciibb Conglomerate is the uppermost unit and consists of about 18m of polymictic pebble conglomerate, sandstone and carbonaceous mudstone.

Brassall Subgroup The Tivoli Formation and overlying Blackstone Formation conformably overlie the Kholo Subgroup and make up the Brassall Subgroup. The Tivoli Formation is best developed in the North Ipswich area where it is 480m thick. It can be divided lithologically into two sections. The lower section, up to L60m thiak, is dominated by mudstones; it has the Waterworks seam, a 16-30m sequence of coal interbedded with clastic sediment, at the base, and a few thin, unnamed coal seams above. The upper section of the Tivoli Formation is 320m thick and contains sandstones, mudstones and seven named coal seams (Figure 2). In the Bundamba area the Cooneana Sandstone Member constitutes the upper part of the Tivoli Formation, with 40m of iandstones, mudstones, and several lenticular coal seams.

The sandstones of the Tivoli Formation are generally coarse-grained and pebbly, and comprise

Geology of Australian Coal Basins

459 N.S. 566

- - -/o5

over half the compacted volume of the section. The mudstones are commonly micaceous and interbedded with rare, impure limestones. Washouts are a common feature of Tivoli Formation coal seams, which also split and rejoin and contain high proportions of interbedded clastic sediment.

l==l

'--'ltrc

rERnaPY

?GAROEN S

TANTIVY S.

E U

J g

The Blackstone Formation is up to 300m thick and contains seven coal seams (Figure 2). The floor of

the Rob Roy seam is defined as the base of the

Blackstone Formation. Sandstones are volumetrically less important in the Blackstone Formation, comprising about one-third of the total compacted volume. A few are pebbly. The coal seams are thicker, laterally more persistent and relatively

VERTICAL SCALE OF METRES

rnore abundant.

30t5030 =

;

All the coal seams of the Brassall Subgroup contain abundant, thin, laterally persistent, fawn-coloured

ll=--l-f

claystone bands (tonsteins) which are commonly

o E

used for seam correlation.

SEDIMENTOLOGY

Ipswich Coal Measures

iCLIPSE

300

The stratigraphic setting of the Ipswich Coal Measures and the palaeogeographic position of the Ipswich Basin suggest accumulation in an intermontane basin. The Ipswich Coal Measures show an overall frning-upward trend from the conglomerate-dominated Kholo Subgroup, through

o =

the Tivoli Formation which contains abundant pebbly sandstones, to the predominantly fine-grained Blackstone Formation.

TOPS S

THOMAS

ETMS S

The accurnulation of the Kholo Subgroup started with the eruption of basalt lavas and the deposition of locally derived gravels. This was followed by a thick gravel sequence that accumulated in an alluvial fan environment (Allen, 1961). Mudstones, in places interbedded with air-fall tuffs, were deposited in the more tranquil interfan areas. The Brassall Subgroup consists ofsandstones, mudstones, and coals that accumulated in river channel, floodplain and peat-mire environments in an alluvial plain setting. The Tivoli Formation is relatively poorly exposed in comparison with the Kholo Subgroup and Blackstone Formation, and has not been subjected to detailed interpretation. The abundance of coarse-grained pebbly sandstones and washouts in the coal seams suggests that river channel environments predominated during the accumulation of the Tivoli Formation.

THOMAS

ABEROARE

4A' BENLEY S. ELUF F.

z o

Y J

FOUR FEET

STRIPED

Blackstone Formation

EACON 6

RO8 ROY S

The Blackstone Formation is exposed in numerous open-cut mine highwalls, and has been the subject of a study by Falkner (1986). Carbonaceous mudstones form roughly two-thirds of the compacted volume of the Blackstone Formation, suggesting an areal dominance of floodplain environments.

Thick (5 to 10m) sandstone bodies in the Blackstone Formation are typically laterally extensive, have basal planar erosion surfaces, and display epsilon cross- stratification. These sandstone bodies record the migration of point bars in large meandering river systems. Common fining-upward sequences comprising thick

sandstone bodies, interbedded sandstones and mudstones, mudstones, and coals represent the transition from river channel, to levee, floodplain

J o>[

LEGEND

Fnm la.o . ol CONGLOMERATE

ll-

ffi I....o.I t..o.ol ffi

[-::':': I l.-

t.-.r

PEBBLY SANDSTONE SANDSTONE SILTSTONE

l---l MUDSTONE

COALY MUDSTONE

-l

COAL & MDST BEDS

lvvY

COAL COKED COAL I

t-a-.'l l{/'l

IGNEOUS INTRUSION IRON CARBONATE

Figure 2. Stratigraphic column of the Blackstone and Tivoli Formations.

Ipswich Coalfield

460 and peat-mire environments respectively. Laterally persistent sandstone beds 0.3m to 2m thick in the mudstone sequences are probably crevasse splay deposits. Coal seams lm to 10m thick represent lengthy

periods of peat accumulation in mire environments. Five coal facies, from end members of bright, parallel-laminated coals with low mineral content to dull, homogeneous and high mineral content coals are identified. These indicate a transition from restricted ponds distal to the river channel, to marsh, wet swamp, dry swamp and floodplain/mire

margin environments respectively. The limited lateral extent and high syngenetic mineral content of coal facies in the Blackstone Formation suggest rapid environmental change

within restricted, floodplain-hosted peat-mires.

The coal seams of the Ipswich Coal Measures contain abundant intraseam clastic bands 1cm to 10cm thick. These are of two types:

dark, carbonaceous mudstones with a lenticular geometry, and light-coloured kaolinite claystones (tonsteins), with a lateral persistence of many kilometres. Carbonaceous mudstones accumulated from floodwaters which occasionally covered the peat-mire, with deposition occurring preferentially at the mire margins. The tonsteins are often pelletal, show sharp upper and lower contacts with coal, and comprise essentially kaolinite with a volcanic mineralogy. The tonsteins are interpreted as distal fallout tephras that were preferentially

preserved and diagenetically altered in the

peat-mire environment (Falkner,1986).

lllll --",*,,*, ffi *nn*"

E *rnn*" f-l ^"***n

I p.!.cwmntYlclotm a x.s.una*

Facies maps of the Blackstone Formation compiled from over 350 boreholes show the extent ofchannel belts during interseam and seam split intervals (Figures 3a and 3b).

Figure 3. a. Facies map of the Bergin to Four Feet interseam interval. b. Faciee map of the Four Feet seam split interval.

During the Bergin to Four Feet seam interval (Figure 3a) a river channel system, represented by a sinuous belt dominated by sandstone facies, crossed the Bundamba area. Adjacent to the channels were floodplain areas characterised by mudstone deposits. In the central part ofthe area the Bergin and Four Feet seams coalesce indicating the presence of a peat-mire during this interval. The deposition of the Four Feet seam was interrupted by a north to south flowing river system that formed a split in the seam.

COAL DEPOSITS

A cross-section of the Blackstone Formation (Figure 4) shows vertically stacked channel sequences that suggest sediment deposition was influenced by structural controls. The preferential occurrence ofchannel sandstones above thick coal seams suggests compaction-controlled subsidence also occurred (Figures 3a, 3b and 4).During the accumulation of the Blackstone Formation high-sinuosity river channels flowed axially within the Ipswich Basin. Adjacent to the southerly flowing rivers were areally restricted, floodplain-hosted mires in which peat, volcanic ashfalls and riverborne sediment accumulated.

Seam Characteristics More than twenty coal seams have been worked in the Ipswich Coal Measures, with most production having come from seams in the Blackstone Formation. There are a number of minor seams which are either too thin or too banded to be of economic interest.

The coal seams characteristically contain many clastic beds, some of which are carbonaceous and lenticular. Many of them consist of fawn-coloured claystone of tuffaceous origin, and are sufficiently persistent to be used either singly or in groups as

marker beds to identify individual seams.

The seams split and rejoin in various combinations, and this tendency causes difficulties in correlation. Dykes and sills have intruded many of the seams. Dykes are more common than sills, and cause only very local metamorphism of the coal.

Geology of Australian Coal Basins

461

WEST NS 344

ffi l:::::::::::::::;:;:,1

E I

THoMAs{ ABERDARE

channel sandstone mudstone coal

EAST NS 587 Datum RLUFF FOUR

BERGIN

SIRIPED BACON ROB ROY

Ftgure 4. Dtagrammatic cross-section of the Blackstone Formation. of the Bundamba Anticline, and the bottom section in that area lies immediately above the Bergin seam.

Blackstone Formation The Thomas seam is the uppermost seam in the Blackstone Formation, occurring only on the western flank of the Bundamba Anticline. Eastward and southward it either disappears at the base of the Aberdare Conglomerate or has been removed by pre-Tertiary erosion. The seam ranges up to 10m in ihickness and splits westward into two sections. The Aberdare seam was formerly the most important producing seam on the field- It consists of twb sections ofcoal each up to 2m thick separated by a 0.3m section of thin coal and mudstone bands, and contains "remarkably constant" marker bands (Denmead,1955). In places it splits into units referred to as the'Aberdare Tops' and'Aberdare Bottoms', or combines with the Thomas seam. The Bluffseam is a thick banded seam ofup to 10m in thickness. It includes sections referred to as

'Tops','Middles', and'Bottoms', with-a distinctive maiker bed of dense light-coloured claystone, 0.25m to 1m thick, occurring between the Tops and the Middles. The seam splits into either two or three sections in various parts ofthe field. The Four Feet seam comprises a top section 3.6m thick, consisting of coal *ith thin mudstone beds and a sroup of two or three persistent light-coloured clavsto-ne marker beds at the base, and a bottom .".iiotr up to 2.5m thick with a persistent pair of marker b-eds about 1m from the base. These two sections diverge by up to 30m on the east and south

The Bergin seam ranges up to 6min thjckness and containJclastic beds wtrich are only of local use in

correlation.

The Striped Bacon and Rob Roy sealqs are the lowest two seams in the Blackstone Formation; the floor of the Rob Roy in fact marks the base of the formation. In the northern and northeastern parts of the Bundamba Anticline the seams are separate units with workable sections between 2m and 3m thick. In the west, southwest, and southeast, however, the seams coalesce to form a single very banded seam up to 15m in thickness.

Tiaoli Formation Coal seams in the Tivoli Formation show rapid lateral variation in thickness and composition. Many have been affected by washouts, which partially or whollv replace the seam with coarse-grained sandslon6s typical of the formation. The lateral variability of the seams and the interseam sandstones precludes confident projection of the North Ipswich seam nomenclature into the Bundamba district. The Cochrane seam is the uppermost seam in the Tivoli Formation in the Bundamba area. A section of about 2m with numerous brownish claystone beds is worked. and the seam is known to extend both eastwaids and southwards. The Ritchie seam is a

Ipswich Coalfield

462

rabre 2' rvpical *n6ii:rlrf,lfH?i#"*,r'i,;ttiill'##r"3"3:rl:.t.s sord) 'tsesed on Equilibrium moisture (7o)

Proximate analysis (7o air-dried) Inherent moisture Volatile matter Fixed carbon

2.7 30.6 50.5

Ash

16.2

100.0

At 30oC and 97o humidity (natural bed moisture) Volatile matter

Ultimate analysis (7o dry ash-free) 27.78

Relative density (air-dried) (ash content as above)

t.45

Hardgrove grindability

Carbon Hydrogen

83.60 5.46

Oxygen

0.34 8.98

Nitrogen Sulphur

L.49

Ash fusion temperature (oC)

Minor constituents (7o)

(semi.reducing atmosphere)

Deformation Hemisphere Spherical Flow

1380

>1600 >1600 >1600

Phosphorus

0.024

Chlorine

0.032

Sulphur (7o air-dried) Pyritic

Coking Properties 0.02 0.01 0.22

Sulphate Organic

37.81 35.77

Vo dry, ash-free Vo dry, mineral-free

Specific energy (air(dried) Gross MJ/kg

1-2Vz (Bundamba) 6 (North Ipswich) D (Bundamba) G6 (North Ipswich)

Crucible swelling no. Gray-King coke type

0.25

Ash analysis (Vo) SiOz

AlzOs FezOs

TiOz MnrO+ CaO

Mgo NazO KzO

Pzos SOs

loss on ignition

3.5

Petrographic analysis (7o volume) 59.42 29.72 2.28 2.28 0.38 L.54 0.78 0.33 0.48 0.28

Vitrinite Liptinite Inertinite

Mineral

100

Mean max. reflectance of vitrinite (R"max.)

t.02 t.49 100.0

0.91

Classification ASTM

Australian Standard (AS

high-volatile A bituminous

09273711602

2096-1987) less banded 3m seam which closely underlies the Cochrane in the mined area. The Taylor and Livermore seams are two closely associated coal beds, I to 2m thick and up to 2.5m

thick respectively, which underlie the CochraneRitchie combination in part of the mined area.

In the North Ipswich part of the field the uppermost worked seam is the Garden seam, which has a maximum thickness of 2.6m in the west and thins rapidly to the east. The Tantivy seam is a very banded seam up to 3.5m thick, but east ofthe Boxwood Fault it is joined by the Garden seam to produce a workable section of 6m. The Fiery seam is a banded seam which is commonly

split into two sections and ranges up to 7m in

thickness. West of the Boxwood Fault it is traversed by a washout, and east of this fault it is intruded by a sill. The Waterstown seam is a thin seam up to 2m thick with the cleaner coal in the upper part. The Tivoli seam is best developed to the east ofthe Boxwood Fault where it coalesces with underlying coal beds and where a section up to 3m was mined. Sections of 1.2m to 1.5m were mined in the past for use as coking coal. The Eclipse seam is economically the most

important seam in the Tivoli Formation. It ranges up to 4.6m in thickness, but usually only the bottom 3m was worked. There are two prominent

Geology of Australian Coal Basins

463 fawn-coloured claystone marker beds in the very banded upper part of the seam.

REFER,ENCES

The Benley seam is a banded seam up to 9m thick with a 0.15m fawn-coloured marker band at the middle. The lower part of the seam was worked over a small area in the north. The Waterworks seam is a thinly bedded interval of carbonaceous mudstone and coal from 16m to 30m thick which crops out along the northern margin of the coalfreld. It contains insufficient coal to be

workable.

Coal Properties The seams in the Ipswich coalfield are composed of mainly bright coal with numerous mudstone and claystone 6eds. Some interbedded dull and bright coal is present, but there is relatively little unbanded dull coal. Thick sections ofinterbedded coal and mudstone or claystone occur in some seams. All seams have a high ash yield, but beneficiation by washing produces a marketable product with ash <237o. The coal has a high vitrinite content, and a high mineral content which cannot be removed_by washing. It is high in high volatile matter and low in sulphur and chlorine. North Ipswich coal is slightly higher in rank than Bundamba coal, and hai better coking properties. Properties of the coal (as sold) are summarised in Table 2. _

The coal is classified as high-volatile bituminous under the ASTM system, and is used in steam raising for electricity generation. A low-ash coking fraction can be produced from North Ipswich coal, but washing yields are too low for economic production.

Resources Coal resources of the Ipswich field were reviewed in

detail by Mengel & Carr (1976). Subsequent exploration and development undertaken by mining companies, however, demonstrated the need for a reassessment, and this was conducted by the Department in 1984. In situ Measured and Indicated Reiources of the field amount to 575Mt, of which 474I[.[t would probably be mined by underground methods. Recovery of underground resources may be affected to varying degrees by undetected faulting, difficulty of access in already worked areas, mining conditions at depth, and restrictions required beneath surface development. Open-cut resources are less likely to be so affected. Resources were originally estimated in accordance

with the parameters stated by the Department of Mines (1968) and revised by Mengel (1977). The recent adoption of the new code proposed by Galligan & Mengel (1986) has not required any modification of the 1984 estimate other than to rename'reserves' as'resources'.

Production And Consumption During 1991-92 raw coal production from the IpswiCh freld totalled 2.15Mt, the bulk of which was extracted by open-cut methods. Total saleable coal production was 0.93Mt, the majority of which was exported to south-east Asian markets.

ALLEN, R.J., 1961: The Kholo Sub-Group of the Ipswich Coal Measures. Geological Suruey of Queensland Publication, 3OO. ALMOND, C.S., 1982: Stratigraphic Drilling report GSQ Ipswich 26. Queensland Gouernment Mining Journal,83, 514-523. CAMERON, W.8., 1899: Geology of the West Moreton or Ipswich coalfreld. Geological Suruey of Queensland Publication, 147 . CAMERON, W.E., 1907: The West Moreton (Ipswich) coalfield, second report (with special reference to the Bundamba district). Geological Suruey of Q uee n sland Publi c at ion, 2O 4. CAMERON, W.8., 1923: Geological map of the Ipswich and Bundamba coalfields. Geological Suruey of Queensland Publication, 27 l. CARRUTHERS, W., 1872: Notes on fossil plants from Queensland. In Daintree, R.: Notes on the Geology of Queensland. Quarterly Journal of the Geological Society of London,28(1), 350-356. CRANFIELD, L.C., SCHWARZBOCK, H., & DAY, R.W., 1976: Geology of the Ipswich and Brisbane 1:250 000 sheet areas. Geological Suruey of Queensland Report,95. de JERSEY, N.J., 1970: Triassic miospores from the Blackstone Formation, Aberdare Conglomerate and Raceview Formation. Geological Suruey of Q ueensland P ub li c at io n, 3 48. de JERSEY, N.J., 1971: Triassic miospores from the Tivoli Formation and Kholo Sub-Group. Geological Suruey of Queensland Publication, 353.

DENMEAD, A.K., 1955: The West Moreton (Ipswich) coalfield. Geological Suruey of Queensland Publication, 279 . DEPARTMENT OF MINES, 1968: Parameters for the calculating and reporting of coal reserves, Queensland . Queensland Gouernment Mining

Journal,69, 400-402. FALKNER, A.J., 1986: Sedimentology of the

Blackstone Formation, Ipswich Coal Measures, southeast Queensland. Ph.D. Thesis, University of Queensland. FRYAR, W., 1900: The coal mining industry and the coal resources ofQueensland. Annual Report of the Department of Mines Queensland for 1899, 156-164.

GALLIGAN, A.G. & MENGEL, D.C., 1986: Code for reporting ofidentified coal resources and

reserves. Queensland Gouernment Mining Journal, 87 , 201-203. HAWKINS, 8.W., 1956: Ipswich borehole N.S. 93' Cooneana Estate. Queensland Gouernment Mining Journal, 57, 2L4-2L8. JONES, O.A. & de JERSEY, N.J', 1947: The flora of the Ipswich Coal Measures - Morphology and floral succession. Department of Geology and Mineralogy, (J niuer sity of Queensland, P aper s, 3. MENGEL, D.C., 1975: Ipswich coalfield, Queensland. In Traves, D.M. & King, D., (Editors): Economic Geology of Australia and Papua New Guinea, 2 Coal. Australasian Institute of Mining and Metallurgy, MonograPh, 6, 290-297 .

Ipswich Coalfield

464 MENG_EL, D.C., 1977: The role of the Geological

Survey of Queensland in exploratory -oal drilling. Symposium on coal borehole evaluation, Australasian Institute of Mining and Metallurgy, Southern Queensland Branch, Brisbane, 2I4E:

SHIRLEY, J., 1898: Additions to the fossil flora of Queensland, mainly from the Ipswich Formation, Trias-Jura. Geological Suruey of Queensland

MENGPL, D.C. & CARR, A.F., 1976: Ipswich coalfield.

TENISON-WOODS, J.E., 1882: On various deposits o.f fossil plants in Queensland,. Proceedingi of the Linnaean Society of New South Wales, Z, 9b-+ 98.

Geological Suruey of Queensland Report, g4.

Publication, L28.

MEYERS, N.A., 1970: Correlation and lithofacies of Jurassic sediments met in exploration wells between Cecil Plains and Ipswich. Geological Survey of Queensland Report,40.

TENISON-WOODS, J.E., 1883: On the fossil flora of the coal deposits ofAustralia . Proceedings of the Linnaean Society of New South Wales,8, b4.

POWELL DUFFRYN TECHNICAL SERVICES LTD,

WHITMORE, R.L., l98I: Coal in Queensland, the first

1949: First report on the coal industry of

Queensland. Government Printer, Brisbane.

QUEENSLAND COAL BOARD, ISSB: Queensland, coals. Typical physical and chernical properties and clas sification. 7 th edition.

fifty years. University of Queensland Press, St Lucia, Queensland.

WHITMORE, R.L., lg85: Coal in Queensland, the late nineteenth century, 1875 - 1900. University of Queensland Press, St Lucia, Queensland.

Geology of Australian Coal Basins

465

STRUCTURAL AND TECTONIC SETTING

nffi

K arong Basin

BJ Pegrem

The Tarong Basin is a narrow, elongate structure,

trending approximately NNW-SS4. It is approximalely tOkm wide and 75km long, and.is unconformably developed on the late Palaeozoic Yarraman Block in southeast Queensland. The basin is regarded as closed beneath Tertiary cover to the NNW, and open beneath mainly Jurassic sediments of the'Moreton Basin to the south. The structural settings of the Mesozoic basins in southeast Queensland are described more fully by Day & others (t974) and Day & others (1983). The basin in the vicinity of the coal-bearing areas is characterised, somewhat paradoxically, by high energy massive alluvial fans which developed - . main-lv from the western side and low energy, thick (30m)-coal accumulations, suggesting subsidence relative to the basin margins and probable fault controls (Figure 1). A spectacular cutting on the Power Statiin-Yarramin road, near the eastern edee ofthe basin, has been identified by Flood & Galces (1986) as a talus slope debris flow deposit. Two other areas ofrestricted extent, 1lkm and 17km south from the first cutting, contain similar talus breccia material. These areas of talus breccia, localised by their gravitational mode of formation,are found 6nly at fhe eastern edge ofthe basin and suggest an eastern faulted margin. The possible mode of formation for the Taro-ng Basin

is a dextral strike-slip, pull-apart feature (Garces 1985, Flood & Garces 1986). Riglrt-lateral, strike-slip faults are evident in the coal-bearing areas as iecondary faults in the basin-fiIl, withlateral displacem6nts ranging between 20m and 450m.

HISTORY OF GEOLOGICAL INYESTIGATIONS Coaly intersections in water bores in the Tarong area were reported by a local resident to CRA Exploration geologists in 1967, during a mineral programme ln nearby areas. A subsequent search ievealed further reports of coal occurrences in records of the Geological Survey of Queensland. CRA was granted an Authority to Prospect for coal in 1968 and has maintained work in the basin under subsidiary companies since that time. Other companies which have worked in the area include Min-es Administration Pty. Ltd. (1974), BP Australia (1980), New Hope Collieries Pty. Ltd. (1980 to present) and Mobil Energy Minerals Australia Inc. (1984).

The early work by CRA consisted of open hole and core driliing whiCh indicated three main areas of thick shallow coal with high ash and low sulphur content, and with little potential other than as fuel for an on-site power station. The nature of the basin margins was unknown, but fault control was susn-ected. Within the basin a number of faults were posiulated. A unit termed the Oakvale Conglomerate (Jurassic), represented by cong*lomeratic sequences in the area, was considered to overlie the Tarong Beds (Wilson, 1975). Subsequent work, including mapping, qPen hole drilling with down-hole geophysics, and deep -.

stratigiaphic core drilling, identified seam splitting as a dbminant influence in the two main areas: Meandu in the south and Kunioon (south of

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Geology of Australian Coal Basins

467

Kingaroy) in the north (Figure 1). Potential coal mining ireas were delineated more accurately as exploratory work continued; five to six mining areas in each of the Meandu and Kunioon areas were defined with acceptable limits of overburden to coal ratio, coal thickness, coal quality and depth. Exploration work normally consiste4 of open-hole driiling, but the coal seams were subse,quently cored at selected sites. Coring was usually of 63.5mm diameter, but a numbei of large cores were also obtained with sizes between 100 and 250mm. Outcrops are minim.al in the area and no coal seam exposures were available for examination.

Bulk coal samples were obtained by a variety of methods before mining commenced, including groups of large cored holes, drilled shafts of I.22m diamdter, and test pits. Suitable analytical work was carried out on all cores and bulk samples commensurate with the requirements for power station steaming coal. Since 1978 at least one borehole at each drill site has been geophysically logged. Logs include natural

gamma, d-ens1ty, caliper, and where required iesistivity, self-potential, sonic and neutron etc. Geophysics has been used in areas of complex seam splifting to subdivide the thick seams into discrete recognisable sub-entities to clarify their geometry for mining purposes. Geotechnical data acquisition and interpretation also began during the latter part of exploration and continued into the feasibility stage.

The conglomeratic sequences were recognised as (or associated with) alluvial fan deposits. A central fan between the Meandu and Kunioon deposits and a southern fan in the Cooyar-Kooralgin area have since been identified, and recognition ofthe Jurassic Oakvale Conglomerate has been discontinued (Pegrem, 19S2). Another alluvial fan (mainly coniealed) to the north of the Kunioon deposit has also been identified from borehole data by Garces & Flood (1984).

Construction of the Tarong Power Station and the Meandu Mine resulted in a massive increase in the number ofsurface exposures available for study. These indicate a western source for the central fan, and have generally extended the knowledge ofthe depositional setting of the basin.

STRATIGRAPHY Details of the lithologies, distributions, relationships and ages ofthe regional stratigraphic units are given by Murphy & others (1976). In broad terms [he stratigraphic succession may be divided into three units: the Palaeozoic basement, the Triassic Tarong beds and the Tertiary and Quaternary cover. On the eastern side of the main coal-bearing areas of

the Tarong Basin the basement consists of metamorphic materials of the Palaeozoic Maronghi Creek beils. The basement on the western side, however, is made up of granites and granodiorites of the Permo-TriassicBoondooma Igneous Complex. The Tarong beds unconformably overlie these basement units, and are identified from palynological studies as being of Caryrian age. In the -souihwest, they are overlain by the Triassic-Jurassic Bundamba Group of the adjoining Moreton Basin. The Tarong beds, with a preserved thickness in the coal-bearing areas of the order of 450m, include

andstone s, conglomerate s, s iltstones, muds-ton-es,

claystones and substantial quantities of coal. The coarse clastic beds in the sequence consist of labile, arkosic to sub-arkosic, fine tb very coarse grained, poorly sorted sandstones and generally matrixsupported, polymictic conglomerates.

Lithological variations are ofte,n- quite--complex on a small sdale, both vertically and laterally. There is a general lateral decrease in grain- s-ize o.n a 6asin-wide scale in the main coal-bearing areas away from the central fan, with sediments passing from a mainly conglomeratic assemblage near the basin margin (proiimal deposits) via a sandy interval tda frner-grained assemblage (distal deposits) towards the basin centre. The Meandu area (south of the central fan) tends to contain more coarse material compared to the Kunioon area (north of the central fan)' Away from the central fan the strata in both coal-bearing areas show an overall fining-upwards vertical sequence for the whole of the basin fill. The rapiditv of lithological variation precludes identification of discrete stratigraphic units. The Tarong beds, first named by Hilf & Tw-eedale (1955)' have blen laterally and vertically subdivided only on the basis ofcoal seam correlations and an overall understanding of the sedimentological processes inherent in the basin's formation (Pegrem, 1986a). Seam names, positions and relative thicknesses are shown on Figure 2. The T4rong beds are overlain unconformably by the Tertiary Main Range Volcanics and by Quaternary sediments. The Main Range Volcanics comprise basalt flows and minor pyioclastics interbedded with siltstones, shales, sandstones and altered clays. ^ They occur on the topographically-higher parts of the irea and form two spurs, the Cooyar and Stuart Ranges, which trend northeasterly from the Bun-ya Mou-ntains. Extensive lateritisation is associated

with the Tertiary deposits, resulting in the development of ferti[e, red, friable, soils. The Quateinary sediments are unconsolidated and g-enerally occur as alluvium associated with the main stream courses.

COAL QUALITY The coal in the Meandu and Kunioon areas can be classified as high ash, high volatile, bituminous,.low sulphur steaming coal with weak c-oking properties. Stoire bands occrir in all seams and these are widely variable both in thickness and composition. Seam quality generally deteriorates down the sequente. S6ams low in the sequence are-generally

duil with few bright bands; they are not laterally continuous and contain numerous stone bands. Seams higher in the sequence are ge-nerally brighter (average 10Eo to 40Vo bright bands), laterally more continious and contain fewer stone bands. Lateral facies changes from coal to carbonaceous mudstones occur.

The King seam contains significant resources ofcoal in two of the Meandu mining areas suitable for direct feed to the adjacent power station. The oualitv specification for this coal is shown in tablei. Att seams below the King seam require washing to achieve this specifrcetion, mainly becausJof the number ofitone bands rather than the inherent ash of the coal itself.

Tarong Basin

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Geology of Australian Coal Basins

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469

Table 1. Specification of coel for'direct feed to Tarong Powor Station. I Moisture 14.07a maximum Volatile Matter (at I4Vo moisture) 22.0Vo minimum 28.0Vo maximum Ash (at 147o moisture) 0.55Vo maximum Sulphur Gross Speciflrc Energy (at L4Vo 19.38GJ/tonne moisture) Ash Fusion Temperature Hardgrove Grindability Index - 75mm Sizing - 3.35mm

1450o C (minimum)

50 minimum l00Vo 257o maximum

The mean maximum reflectance (wavelength 546nm) in oil (R.I. = 1.516) of vitrinite in the King seam coal

is 0.68Vo.

DEPOSITIONAL MODELS AND INTERPRETATIONS The presence ofalluvial fans, particularly the central fan between the Meandu and Kunioon deposits in the coal bearing area, is the key to understanding the depositional environment and to a degree the coal quality in the Tarong basin. The central fan, derived from the west, was a highenergy environment supplying sediments over a fan shaped area. The geometry of the f-an allowed lowenerg"y areas to develop on either side of the fan neck on the western margin of the basin, where conditions were conducive to thick coal seam accumulations. All of the thick seams (coalescence areas) tend to occur on the western side ofthe basin, with thinner split coals, in moderately complex fluvial, swamp and lacustrine environments, occurring towards the east and/or away from the fan area.

The accumulation of the sediment fill in the Tarong Basin was tectonically controlled. It was achieved by

lateral and vertical changes in a variety of depositional environments, including alluvial fans with proximal, medial and distal deposits, fluvial systems of braided and meandering streams, and alluvial plains with ephemeral lacustrine and persistent swamp developments.

The central fan contains typical fan deposits, including sheet-floods, debris-flows and channel fills, with a general decrease in sediment grain size down slope. The fluvial systems in the south (Meandu) appear to be braided, whereas in the north (Kunioon) only meandering streams appear to have been developed.

Sediment from the alluvial fans, carried via distributary streams, periodically flooded into the swamp areas, causing cessations of vegetation growth. Fluctuations in the delicate balance between clastic deposition and peat accumulation resulted in the coal/stone alternations. The entire basin fill in the coal-bearing areas shows an overall fining-upwards sequence. As the gradient off the fan decreased with progressive basin fill, the energ'y of deposition and the sediment grainsize

decreased; the coals in the upper part ofthe sequence also received fewer clastic incursions. Coal seam ash values decrease up the sequence and indeed tend to decrease up the section of each individual seam.

The large number of soft-sediment deformation structuies evident in both the mine and surrounding areas, as well as the thick coal accumulations, certainly suggest a wet palaeo-environment.

COAL MINING DEVELOPMENTS

In 1978 the Queensland State Government decided to proceed with the establishment of a L400MW Power Station at Tarong, fuelled by coal from the Meandu deposit. The Meandu Mining Lease of 4267ha wai granted in 1981. Overburden removal for the Meandu Mine began in August 1983, and coal mining commenced at the end of November in the same year.

About 4Mt had been mined as direct feed coal from the King seam by the end of March 1986. Initial output was lMt/y, but this is expected to increase to >SMt/y (or >6Mt of run of mine coal) at peak capacity. A comparison between the predicted geology and coal quantity/quality against the actual [eolo[y, from highwall mapping, and actual coal quantity/quality, as received by the power station proved to be quite satisfactory for the first two strips mined in the direct feed King seam (Pegrem, 1986b).

COAL RESOURCES AND MINING FACTORS Measured and Indicated open cut coal reserves of 183Mt of in situ, raw coal were delineated within Tarong's Meandu Mining Lease for the Tarong Power Station. This was equivalent to 140Mt of product coal at the power station's specifications. The requirement for the assumed 30 year life of the power station was regarded as 110Mt of product coal.

Total Measured and Indicated in situ resources within the Meandu Mining Lease and the Tarong Authority to ProsBect 235C, using an overburden to coal ratio of <Smo/t, were estimated at 370Mt. Additional coal resources, including inferred coal and potential underground resources, also occur

within the mining tenements, but it has not been necessary for these to be quantified accurately to date.

Thick seams and favourable stripping ratios are a characteristic in the Tarong Coalfield. At the Meandu Mine the overburden to coal ratio (prime overburden and interburden in cubic metres per tonne ofraw coal) is effectively 1:1 for the frrst 16 years of mine life. For the total probable 30 year life of the Power Station the same overburden to coal ratio is of the order of 2:1. The tectonic control of the whole basin and the proxirnity ofcoal areas to the high energy of deposition of the alluvial fan mean that a number of geological factors affect the mining operations. Seam thicknesses >30m, for example, require mining on more than one bench. The high ash yield of the seams, primarily as a result of clastic incursions, means the run of mine coal mostly requires washing and a certain amount of rejects need to be handled' Generally where stone bands exceed 0.7m in thickness they are removed separately during mining, a factor which requires pre-mining geological predictions from down-hole geophysics. In iome cases, geological input is required for recognition ofdark carbonaceous stone bands. Ash values increase with depth, both down the sequence and generally down each seam. Only parts

Tarong Basin

470 of the upper seams contain direct-feed coal and with increased depth changes are needed in the

preparation plant. The run of mine coal quality actually relales to bench selection. Qualiiy coritrol begins in the pit with knowledge of the depth of the bench being worked effectively indicating the expected run of mine quality.

Seam splitting and coalescence is a feature of Meandu, and geological input is necessary to define searn geometry for mining. Stream systems have be.en observed adjacent to and within the coal mining areas as occasionally extensive, stone band 'feeders'through coal, with a concomitant increase in ash laterally towards the stream system. Quality control and mining bench selection is best performed

in the light ofan understanding ofthe depositional environment of the coal-bearing sequence. Secondary faults, usually right-lateral, strike-slip

types, occur in the basin frll within and around the mining areas. These require predictive geological work to facilitate mining operations. The effects of differential compaction between coal and stone also results in faults and floor grade variations, particularly in areas ofseam splitting. There are no coal outcrops at Tarong, as compaction and weathering effects are quite marked in areas of oxidised coal near subcrops. Geological input is therefore required for identifying mine low-wall

limits.

(pull-apart) basin containing alluvial fan and

coal-rich fluviatile sediments. In Willmont, W.F., (Editor): 1986 Field Conference, The South Burnett District. Geological Society of Australia, Queensland Division, Brisbane, 77-81. GARCES, B. Jun., 1985: The sedimentology, depositional environments and development of the late Triassic Tarong Basin in southeast Queensland. M.Sc. Thesis, Department of Geology, University of New England. GARCES, B. Jun. & FLOOD, P.G., 1984: Alluvial fan and braided stream sedimentation within the late Triassic Tarong Basin, S.E. Queensland. Proceedings of the Eighteenth Symposiurn on Aduances in the study of the Sydney Basin, Department of Geology, Uniuersity of Newcastle, 81-84.

HILL, D. & TWEEDALE, G.W., 1955: Geological Map of the Moreton District with parts of the Darling Downs, Burnett and Wide Bay Districts, Queensland. Department of Mines, Brisbane.

MURPHY, P.R., SCHWARZBOCK, H., CRANFIELD, L.C. & MURRAY, C.G., 1976: Geology of the Gympie 1:250 000 Sheet area. Geological Survey of Queensland Report, 96. PEGREM, B.J., 1982: Geological Report, Tarong Coalfield. Unpublished Company Report, Pacific Coal Pty. Limited.

REFERENCES DAY, R.W,, CRANFIELD, L.C. & SCHWARZBOCK, H., 1974: Stratigraphy and structural setting of Mesozoic basins in southeastern Queensland and northeastern New South Wales. In Denmead, A.K., Tweedale, G.W. & Wilson, A.F., (Editors): The Tasman Geosyncline - a Syrnposium. Geological Society of Australia, Queensland Division, Brisbane, 319-362. DAY, R.W., WHITAKER, W.G., MURRAY, C.G.,

WILSON,I.H. & GRIMES, K.G., 1983:

Queensland Geology: a companion guide to the 1:2 500 000 scale geological map (1975). Geological Suruey of Queensland Publication, 383.

FLOOD, P.G. & GARCES, B. Jun., 1986: The Tarong Basin, Queensland: a Late Triassic strike-slip

PEGREM, B.J., 1986a: Geology of the Tarong area and Meandu coal mine. In Willmott, W.F., (Editor): 1986 Field Conference, The South Burnett District. Geological Society of Australia, Queensland Division, Brisbane, 82-gl. PEGREM, B.J., 1986b: The coal deposit: predicted versus actual. Proceedings of Symposium, Looking at Tarong. Darling Downs Institute of Advanced Education, Toowoomba, Queensland.

WILSON, R.G., 1975: Tarong coalfield, Queensland. In Traves, T.M. & King, D., (Editors): Economic Geology of Australia and Papua New Guinea, 2: Coal. Australasian Institute of Mining and

Metallurgy, Monograph, 6, 288-290.

Geology of Australian Coal Basins

471

LOCATION AND PHYSICAL GEOGRAPHY

ffi qfu#

The Callide coalfields are located some 120km south-west of Gladstone, and some 45Okm north-north-west of Brisbane in central Queensland (Figure 1). These coalfields cover an area ofabout 18 000ha, and are located within a north west-south east trending synclinal basin 22.Skm long by 8km wide. Present open-cut mining operations are located in the Dunn Creek, Trap Gully and The Hut areas, in the south as part of the Callide Mine and at Boundary Hill in the north-west of the basin

allide Basin

(Figure 1).

The Biloela region experiences warm, dry winters and hot summers, a typical seasonal climate for east-central Queensland. The temperature range varies from average daily July minimum temperatures of 5.1oC to average daily January

MS Biggs AW Burgess

maximum temperatures of 33.3oC. Annual mean rainfall in the region is approximately 700mm, with the majority of the rainfall occurring in the summer months.

and RB Patrick

The general description of the vegetation which

occurs throughout the basin is dry schlerophyll forest. Original vegetation patterns have, in places, been modified by clearing for pastures and timber extraction.

The area is dominatedby Eucalypfus species in the tallest stratum (10-25m) and three floristic associations can be defined by the presence or absence of particular Eucalyptus species. These floristic associations are seen to coincide largely

with lithological differentiation (Behets, 1987).

The basement rocks of the Rainbow Creek Beds and Muncon Volcanics support a dense cover characterised by the presence of Gympie Messmate (E. cloeziana). Other tall stratum flora include Narrow Leaved Red Iron Bark (.E. crebra), Lemon Scented Gum (8. citriodorou), Variable Barked and Pink Bloodwoods (8. dichromophloia and ,O. intermedia) and Black Cypress Pine (Callitris endlicheri). Sparse ground cover and heavy leaf mulch may occur due to the dense canopy cover. Coarse sandy soils derived from sandstones of the Callide Coal Measures and Precipice Sandstone support moderately dense vegetation characterised by the presence of Lemon Scented Gum in some areas and the Grey Box (,O. ntoluccana) in other areas. The tallest stratum is dominated by Pink Bloodwood, Black Cypress Pine and ironbarks.

The bloodwoods (.8. dichrornorphloia arrd E. intermedia) become more dominant in areas of basalt cover. The vegetation here is more open forest which permits growth to an abundant understorey.

In all the floristic associations the mid-stratum (2 to L0m) is dominated by Golden Wattle (Acacia crassa), Qu eensland Silverwattl e (Ac ac ia p odaly r iifolia), Sarsparilla (Sarsparilla sp.), Quinin e (Petalostigma pubescens) and Dogwood (Jacksonla sp.) with the lower stratum (0 to 2m) typically Red Natal (Rhynchelytrum repens), Kangaroo Grass (Themeda australis) and Spear Grass (Heteropogon contorus).

A study of the various topographic elements and vegetative covers by Biggs (1983a) highlighted marked contrasts between areas of Tertiary sediments in the west of the basin and the Mesozoic and Palaeozoic rocks in the east (Figure 2). Areas underlain by granitic intrusions or covered by

allide Basin

472

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Geology of Australian Coal Basins

473 Queensland Mines Department between 1947 and 1951 (Reid, 1945; L947a; t947b; Geological Survey of Queensland, t949; Shepherd, 1951a; 1951b) and consisted mainly of diamond coring. Cameron (1972) reported on a second drilling programme (1964 to 1968) used to delineate reseryes for most of the basin and in particular for the Trap Gully area. The Geological Survey of Queensland in total has drilled 83 holes for a total of 7653m (5621m cored).

With the commissioning of the Calcap Power Station (124MW) adjacent to the Callide Mine in 1965, coal production increased and a Bucyrus-Erie 480W dragline was introduced. A long term contract with Queensland Alumina Limited commenced in 1974 and resulted in the commissioning of a Bucyrus-Erie 1350W dragline and expansion ofthe annual production capacity to 2Mt.

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Tertiary sediments have subdued and undulating topography. The sub-tropical climate, with high summer temperatures coupled with moderate rainfall, has prompted decomposition and subsequent deposition of superficial material cover over much of the basin. The major stream systems drain south-westerly and often scour flat-topped, low ridges ofTertiary laterite occurring in the north-west of the basin. Topography becomes progressively higher towards the east and is dominated by scarps and incised plateaux up to 520m (eg. Mt Murchison, mid-way between the Dunn Creek and Trap Gully areas). Mesozoic sandstones and siltstones support sparse dendritic drainage and form prominent escarpments that delineate the basin from Palaeozoic strata to the east. Beyond the eastern margin of the basin the topography within the Palaeozoic sequence varies to 700m, with strike ridges common. Well defined, rugged and dissected terrain is associated with some radial drainage patterns upon intrusives of the Mt Gerard Complex, in the extreme north-west. Occasional remnants of Tertiary sheet basalts form elongate mesas of moderate relief within the basin.

EXPLORATION AND MINING HISTORY Coal was first discovered near Callide Creek by three alluvial gold prospectors in 1890 (Rands, 1891). Sporadic investigation followed (Ball, 1906), but coal production did not commence until 1945, when 402 tons were won from a small open pit. Details of this early production are given in a report by the Geological Survey of Queensland (1949). Mining operations of the two original syndicates were taken over by Thiess Callide Coal Pty Ltd, who became sole owners of all existing leases in 1950.

In early 1951, coal from Callide was exported to Victoria, with annual production peaking at 345 887t in 1952. Formal geological investigations had been carried out prior to this contract by the

Regional mapping of the Monto 1:250 000 sheet area was completed by the Geological Survey of Queensland (Dear & others, 1971) and a detailed palynological study was conducted by de Jersey (L974). Following the conditional surrender of the old tenement (AP 108C) and the granting of an enlarged Authority to Prospect (AP 188C, now Exploration Permit for Coal EPC 188) in 1976 covering the entire basin, extensive exploration commenced. This effort was rewarded in 1977 with the delineation of thick coal reserves in the Boundary Hill area at the north-western end of the basin. Grimstone (1977) and Grimstone & Roach (1978) produced comprehensive studies of the geology, structure and coal resources ofthe basin, particularly of the Dunn Creek, Trap Gully and Hut Deposits, enlarging on earlier work reported by Svenson & Hayes (1975).

In 1980 and 1981, respectively, further long-term supply contracts were signed with Queensland

Alumina Limited and the Queensland Electricity Generating Board (now Queensland Electricity Commission) resulting in the development of the Boundary Hill Mine which commenced coal sales in 1983. The following month coal mining began from the Trap Gully deposit, after construction of a haul road to existing coal handling facilities at the Callide Mine. Total annual coal production from the Callide Coalfields is currently 4Mt. Measured and Indicated reserves are currently calculated at 866Mt. Since L982, exploration activities have been directed towards ground geophysical surveys (galvanic resistivity, mini-sosie, SIROTEM, TSIM and magnetics), drilling (rotary chip and core), and downhole logging (caliper, gamma, density, neutron, sonic and SIROLOG; Biggs, 1990, 1991) throughout the basin. Such techniques aided in outlining deep coal reserves in the Kilburnie area (Figure 1). Callide Coalfields Pty Limited has now completed over 2300 drillholes for 167 000m (of which 24 000m are cored). This work has been supplemented by academic research into detailed facies analyses (Flood, 1982; 1985; Glikson & Fielding; 1991a) and various stratigraphic, sedimentological, structural, petrological and palynological topics covered by Honours theses (O'Sullivan, 1977; Stevens, 1978; Coates, 1982; Lumley, 1985; Behets, 1987; Waterfield, 1988; Sorbie, 1990).

REGIONAL TECTONIC SETTING The Mesozoic Callide coal basin lies at the western margin of the Dumgree Arch (Yarrol Shelf West; Murray, 1980). The Dumgree Arch is probably

Callide Basin

474 separated from regionally metamorphosed rocks of the Gogango Overfolded Zone by a major fault, concealed under the sediments of the Callide Basin (Dear & others, 1971; Figure 3). The Callide Basin is an intramontane, fault-bounded synclinal basin elongated along a north-west

trending axis and asymmetric with gentle (approximately 10o) dips. It was probably formed by downwarping and subsidence of Palaeozoic sediments during a time of regional extension and normal faulting in the Late Triassic (Dear & others, L971; Svenson & Hayes, Lg75; Murray, 1980). Figure 4 illustrates the stratigraphic relationships between the major units of the region.

REGIONAL STRATIGRAPITY Following the Middle-Late Devonian Tabberabberan Orogeny, a shallow unstable marine shelf (the western Yarrol Shelfl developed on the site of older Calliope Island Arc deposits, which consisted of andesitic volcanics and minor tuffaceous sediments with rare limestone lenses (Calliope beds, Kroombit beds; Murray, 1980). A marine transgression on the Yarrol Shelf during the Early Carboniferous was associated with alternating episodes of acidic to intermediate volcanism and related sedimentation. The Three Moon Conglomerate occurs along the eastern margins of the Callide Basin. This unit consists of a thick sequence of interbedded scoriaceous andesite and andesitic agglomerate overlain by andesitic to dacitic crystal vitric to crystal lithic tuffs, purple tuffaceous mudstones, minor andesitic flows, and agglomerates. Minor spilitic alteration probably has occurred (Biggs, 1983b). Murray (1980) thought that the source of the volcanics was a terrestrial andesitic to dacitic chain to the west of the shelf (the Connors - Auburn Arch).

The Early Permian Youlambie Conglomerate disconformably overlies the Three Moon Conglomerate and consists of boulder to pebble

conglomerate, conglomeratic mudstone, quartz-lithic sandstones, laminated siltstones, acid to intermediate pyroclastics and volcaniclastic sandstone. Inliers of the Youlambie Conglomerate overlying the Three Moon Conglomerate are reported south-east of the Callide Basin (Biggs, 1984). The unit crops out along the south-eastern, north-eastern and northern margins of the Callide Basin. O'Sullivan (1977) reported that this unit was exposed in stream beds beneath Triassic volcanics in the Oaky Creek (Hut) area (Figure 1). Considerable folding, faulting and erosion of the rocks in the Western Yarrol Shelf occurred before deposition of the Lower Permian Rainbow Creek Beds which are a terrestrial sequence of volcaniclastic pebble conglomerates, rhyodacitic tuffs, quartzose to feldspathic sandstones, and finely laminated carbonaceous mudstones unconformably laid down upon Devonian and Carboniferous strata, along the southern margins of the basin. Within this unit dips vary between 10 to 25o, except near the Rainbow Creek Fault Zone.

During the Late Permian to Middle Triassic, moder?tely sized (5 to 10km2), post-orogenic plutons were emplaced such as the Galloway Plains Tonalite (hornblende-biotite tonalite, leucogranodiorite) and the Mt Gerard Complex (hornblende diorite, granodiorite, gabbro). Minor dyke intrusions

(syenite, aplite) were associated with these plutons. Biggs (1983) considered that the Bouguer Anomaly Map (Bureau of Mineral Resources, 1967) indicated that the Galloway Plains Tonalite may be far more extensive than shown by its surface expression, and

that the Palaeozoic sequence may not be as thick as shown on regional cross-sections by Dear & others (1971). Granites exposed in embankments of the Boundary Hill railway spur line are probably part of the Galloway Plains Tonalite, and in this area form the margins to the Callide Basin. Although mantled by Tertiary sediments to the south of this area, drillhole intersections suggest that this granite also forms part of the basement to the Kilburnie Deposit. In contrast, however, an airborne rrragnetic survey reported by Parrington (1971) suggests that the Mt Gerard Complex is of smaller areal extent than shown on the Monto 1:250 000 map. A phase of Late Triassic normal faulting, e.g. Rainbow Creek Fault Zone occurred after these plutonic emplacements (Dear & others, 1971), and by the end ofthe Triassic tectonic conditions had stabilised. During this period acidic to basic volcanics and related sediments of the Muncon Volcanics were unconformably deposited upon folded Palaeozoic strata in several elongate basins. Later in the Triassic the Callide Coal Measures sequence was deposited with angular unconformity, and in some cases disconformity (Cameron L972, Coates, 1982) on these volcanics in a downwarping area. Thick, laterally extensive quartzose fluviatile 'sheet' sandstones ofthe Precipice Sandstone were then deposited by a braided river system in the Early Jurassic. These deposits covered most of the Callide Basin and represent a different style of sedimentation compared to the Callide Coal Measures. Uplift in the Late Jurassic and the subsequent erosion ofthe land surface then proceeded until the Tertiary. A period of laterisation prior to the development of an extensive sheet of Miocene olivine-bearing basalt is suggested by Dear & others (1971) and Grimstone (1977). These basaits are particularly extensive in the south-west areas of the basin, and at Dunn Creek basalt flows infill erosional gullies into both Tertiary and Mesozoic sediments. Extensive hornblende, olivine thin basaltic stocks and dykes of Miocene age (Waterfield, 1988) intrude sediments of the Callide Coal Measures at the Boundary Hill Mine. Extensive deposits of Quaternary cobble gravel have developed along the major river channels, especially Callide and Rainbow Creeks.

STRATIGRAPIIY OF THE MESOZOIC SEDIMENTS Muncon Volcanics The Muncon Volcanics were first described at Cania by Dear (1968) and first recognised unconformably underlying the Callide Coal Measures in railway cuttings south of the Dunn Creek Mine by Dear & others (1971). At Monto and Cania the unit is probably 500m thick. Within the Callide Basin, however, this unit crops out poorly and has an irregular thickness varying between 100 and 150m. Stratigraphic relationships suggest that in the north-east (O'Sullivan , L977) and at Trap Gully (Cameron, 1972; Coates, 1982) the unit is disconformably overlying coal measures sediments. Drillhole intersections to date at the Boundary Hill Mine and Kilburnie Deposit suggest that this

Geology of Australian Coal Basins

475

MESOZOIC & TERTIARY BASIN

DUMGREE ARCH. YARROL BASIN WEST

EASTERN LIMB MIMOSA SYNCLINE

YARROL BASIN EAST

MAJOR FAULT

INFERRED FAULT +

BOYNE VALLEY RIFT IN

DAWSON FOLDED ZONE

---_+-

PROSPECT CREEK FOLDED ZONE

CALLIOPE STRUCTURAL BLOCK

GOGANGO OVERFOLDED ZONE

COASTAL BLOCK

AUBURN ARCH

IGNEOUS INTRUSIVE

ANT|CLINAL AX|S

CALLIOPE STRUCTURAL BLOCK

SYN6L;NAL AXIS I

--+-

REGIONAL STRIKE & DIP UNCONFORMITY

Figure 3. Major regional tectonic units. SOUTH - EAST

NORTH - WEST

Angular unconlormity

Alluwlum (Auatemary) o_2om

unconsolldatsd sedlm€nts (16tlary) o-som Ollvln€ Baealt Cr€dlary)

Angular Unconformiiy

P.eclplce sandstone (Low6r Jurasslc) o_1 oom Basic Dyk€s, Stocks

callid€ coal M€asur€s (Upp6r Tnasslc) (1o-1som) Angular Uncontormily

.AAa!/VV-WVV\' 5 - 250h

an9ular unconrormrry

Mt. G€rard Complex

I I

angular unconlormity

Galloway Plalns Tonalite Thre€ Moon Conglom€rate (Lower Carbonlrerous)

(Low€r - Upp€r P€rmlan)

Angular UncooformitY

Upp€r Dowonlan (>15oom)

lntrusions, Dykos / Crriasslc) ?

STRATIGRAPHIC RELATIONSHIPS BETWEEN

THE MAJOR REGIONAL UNITS, CALLIDE BASIN NO SCALE - DI,AORA$,/{NC ONLY

riguenmajorunitsoftheCallideBasinsequence.

allide Basin

476

formation is in the order of 20 to 40m at these locations.

individual conglomerate lenses up to 15m thick) north of the Dunn Creek Mine.

The lower parts of the sequence are dominated by volcaniclastic conglomerates and sandstones. At Trap Gully, Coates (1982) described a poorly sorted polymictic conglomerate with 70mm clasts of trachyte and rhyolite set in a sandy andesitic rnatrix. Pebbly, lithic sandstones are often interbedded with the conglomerates, containing subangular intermediate volcanic rock fragments set in a clay cement. Pebbles of quartz, indurated siltstone and andesitic volcanics are common.

In the Dunn Creek Mine area Dear & others (1971) described a conglomerate with pebbles of white

Higher in the sequence the dominant lithologies are carbonaceous siltstones, tuffaceous sandstones and lapilli tuff, with rare andesitic and basaltic flows. The tuffaceous sandstones (O'Sullivan, 1977) are generally greenish-grey, with subangular grains of quartz, biotite, plagioclase, and andesitic rock fragments set in a quartz, calcite cement. Many of the thin andesitic and basaltic flows have phenocrysts of augite, hornblende and orthoclase. Some vesicular basalts have white and pink zeolitic infilling. Palynological evidence (de Jersey, 1974) and macrofossil remains (Dear & others, 1971) suggest an Early to Middle Triassic age for the unit.

Callide Coal Measures Dunstan (1915) introduced the name "Callide Series" for the sequence and correlated it with the Jurassic "Walloon Series" (now the Walloon Coal Measures). Subsequently Jensen (1923) used the name Callide Coal Measures and correlated the sequence with the Triassic Ipswich Coal Measures. The unit consists ofup to 180m ofgranule to pebble conglomerate, white and grey quartz-lithic

sandstones, carbonaceous grey siltstones, carbonaceous shales and seams of predominantly durainous, sub-bituminous steaming coal. A composite stratigraphic column is shown in Figure 5.

The coal measures have not been formally sub-divided, although informal sub-divisions have been used based on lithological grounds. Coal seam sub-divisions were first recognised by Reid (1945; 1947a;1947b), who described a basal conglomerate portion overlain successively by four seams called the Bottom, Sawmill, Callide and Marker seams (see Figure 5). This naming convention was continued by Dear & others (1971), Cameron (L972), Svenson & Hayes (1975), Grimstone & Roach (1978) and Flood (1985). At present separate naming conventions have been developed for each deposit, and, although ply relationships in each of these are well known, the lack of geophysically-logged drillholes between areas, together with seam splitting and

deterioration, does not currently allow definite lithostratigraphic comparison between deposits.

Palynological studies of cores from widely-spaced drillholes within the basin, however, (de Jersey, 1974; Sulllivan, I977; Stevens, 1978) suggest that the several thicker seams are chronostrati-

graphically equivalent across the basin. These workers also recognised a disconformity within the coal measures (see Figure 5).

Basal conglornerate member The basal conglomerate member was ascribed a Late Carnian age (early-middle Late Triassic) by de

Jersey (L974) and Stevens (1978). It is absent in the Kilburnie area, but is up to 40m thick (with

siltstone, quartzose sandstone, chert, and trachyte set in a sandy matrix. At the Hut deposit pebbles of purplish andesitic volcanics are more prevalent (O'Sullivan, 1977).In the Trap Gully area basal conglomerates disconformably overly tuffs and tuffaceous sandstones of the Muncon Volcanics. The conglomerate contains coarse subangular quartz and intermediate rock fragments in a matrix of interstitial post-depositional kaolinite (Coates, 1982). Sandstones of similar composition form thin interbeds. Towards the north-east Lumley (1985) described this unit in detail and recognised two types of conglomerate within his study area. The basal unit consists of a pebble-boulder polymictic orthoconglomerate with subrounded, poorly sorted pebbles (2mm to 10cm) of varied volcanics and indurated sediments and contain occasional small characteristic intraformational mudstone clasts set in a poorly cemented matrix displaying minor silica and iron oxides. The basal unit grades into a finer conglomerate with up to 307o matrix composed of sand-sized, subangular, well sorted quartz and minor rock fragments bonded by clays. The upper portion of the sequence is dominated by an intraformational diamictic conglomerate with common light brown to pink mudstone clasts set in a clay matrix. This conglomerate is fully clast-supported, with a finer grained matrix (up to SOVo) than the conglom erate stratigraphically

beneath it. The matrix consists of clays, quartz, and minor subangular orthoclase.

Bottom sean. horizon The bottom seam horizons often grade into or are interbedded with the Basal Conglomerate Member, and are also Late Carnian (de Jersey, 1974, Stevens, 1978). They consist of a variable number of coal seams 0.3 to 4.5m thick, irregularly developed throughout the basin, and are characterised by zig-zag seam coalescence alternating with grey to brown quartz-rich medium-coarse grained sandstones having an abundant kaolinite matrix. The only detailed proximate seam analyses reported are those of Cameron (1972) and CSIRO (1951), which indicate air-dried ash of 25.8 to 59.\Vo far individual ply samples from drillholes NS 32, 33 and 34. Further investigations are required to determine the continuity and detailed quality of individual coal seams within this member.

SawmiII ae@rn horizons This unit consists of the Sawmill seam, the Lower Sawmill-Wright seam (Figure 5) and interbedded sandstones and siltstones of early Rhaetian age (de Jersey, t974). This horizon is widely recognised throughout the southern and south-western portions of the basin, however seam splitting and deterioration is a prevalent characteristic. The Sawmill seam varies between 0.3 and 5.0m in thickness, although it averages 2.2m where it is mined in the "S" area of the Dunn Creek Mine. Here the range in ash is 16 to 39Vo (air-dried) and the seam contains a number of thin (approximately 5cm) brown, tonstein-like claystone bands. Exposures in the current highwall suggest a slight angular unconformity with the overlying Callide seam. The

Geology of Australian Coal Basins

477

COMPOSITE STRATIGRAPHIC COLUMN OF THE MESOZOIC SEDIMENTS, CALLIDE BASIN !2 (t)

= -UJ o o

-t

PRECIPICE

= u z, 6

SANDSTONE 150

U RIASSIC - JURASSIC DISCONFORMITY

HIGH ASH TOPS

tr White Clavstone .T

FandCALLIDE

SEAM MEMBER

F U

-E CE

Y I

.ALLTDE

SEAM

CALLIDE

o = J

COAL MEASURES

100

iF E

o N o

tr MARKER BED

t! I

FINISHING CYCLE

O MAJoR PARTING O BRAIDED STREAM DEPOSIT

SAWMILL SEAM LOWER SAWMILL WRIGHT SEAM

s2 U)

snwurr-r- sEAM HoRrzoNS

]

(t)

t F !

kJ BOTTOM SEAM HORIZONS

u J o o = *

z. z.

c) BASAL CONGLOMERATE MEMBER

U (L

UNCONFORMITY

U J

!c: =u) >u)

MODIFIED AFTER COATES, 1982,

MUNCON

FLOOD, 1945.

VOLCANICS

ot< ud

PALAEONTOGICAL DIVISIONS

o J=F

AFTER DE JERSEY 1974, STEVENS,197A.

Figure 5. Composite stratigraphic column of Mesozoic sediments in the Callide Basin.

allide Basin

478

NATURAL GAMIIA & SEAU THCKNESS

CAII-DE SEAT

LOGS

CALLIDE SEAM MEMBER

Dlsconformlty

U'i. Cl.trlo

sou 3099--

Angular Unconlormity LONG-SPACED DENSITY GEOPHYSICAL RESPONSE FROM BOUNDARY HILL MINE. THE MINE WORKING

SECTION COVERS VARIOUS PLIES OF THE "A' SEAM. MOD|FtED AFTER FLOOD (1982).

Figure 6. Typical geophysical log responses from the Callide Basin. LEFT. Downhole geophysical responses for the Callide seam, "B' Area, Dunn Creek Mine (modified after Flood, 1985).

RIGHT. Long-spaced density geophysical response from Boundary Hill Mine. The mine working section covers various plies ofthe'A' seam

Lower Sawmill-Wright seam currently appears to be extensively developed in the "A" and "S" areas of the Dunn Creek Mine, where it is separated from the Sawmill seam by partings 0.5 to 3.0m in thickness. It averages 1.1m thick where it is mined, with a variable ash of 25 to 427o (air-dried).

between these lithologies was the subject of a detailed facies analysis by Flood (1985), Behets (1987) and Waterfield (1988). The compilation of

Interbedded sandstones and siltstones are typical of those found throughout the basin. O'Sullivan (f977) described one of these sandstones as a quartz

sub-litharenite containing up to 90Vo quartz grains, 5Vo rock fragments and 57o plagioclase, mica, with accessory zircon, rutile, and tourmaline, rarely cemented, and with a clay matrix. The siltstones are commonly carbonaceous and contain angular qlJartz and mica fragments set in a clay matrix.

Callide Coal Seam. Member The Callide Coal Seam Member is the principal

economic coal seam horizon found throughout the

basin. It occurs as thick pods (up to 23m) of coal separated laterally by areas usually characterised by abundant simple seam splitting and deterioration in which the seam thicknesses are often around 4m.

In all mining areas, the Callide seam is divided into two to three major splits and the coal seams are separated by sandstone, siltstone, mudstone and carbonaceous shale. The spatial relationships

(rnodified after Flood, 1982).

drillhole information, in-pit quality drilling, and highwall mapping has enabled computer based modelling of structures and qualities at each deposit. Comparative geophysical log profiles of the Callide seam member at Dunn Creek and Boundary Hill Mines are shown in Figure 6. The predominantly dull coal has as an accessory only minor blebs of pyrite, and calcite occurrences on cleat surfaces are uncommon. However, a number

of distinctive nodular to oolitic, moderately hard and dense siderite bands, mostly grey to brown, can be

recognised. Similarly, thin, white, blocky indurated claystone to tonstein bands, with a characteristic subconchoidal fracture, are commonly observed. X-ray diffraction (XRD) analyses by Lumley (1985) and Behets (1987) indicated typical compositions of kaolinite, smectite, quattz ( approxima tely 70Vo), illite and minor iron oxides. Fine wavy laminations and the presence of flattened, intraformational claystone clasts to 1mm in length are features of these bands.

Interbedded sandstones commonly display trough cross-stratification and are quartz-rich (85 to 957o quartz) sublitharenites. The sandstones contain 5 to

Geology of Australian Coal Basins

479 lSVo plagioclase and siltstone rock fragments (commonly subangular to angular), wit}n 27o muscovite, rutile, magnetite and tourmaline, set in an uncemented, clay matrix (Stevens, 1978). The siltstones commonly contain up to 50Vo sub-angular quartz and rock fragments less than 2mm in size, set in an often recrystallised, iron-stained clay matrix containing minor sericite. The mudstones and shales contain abundant carbonaceous fragments, mainly surrounded by recrystallised clays, minor fine quartz, rock fragments and muscovite (around 107o). Siderite and iron oxide staining is ubiquitous (Lumley, 1985). The slight frssility in the shales is probably due to the presence of the muscovite (Stevens, 1978).

Mo.rker aeq.m. horizons The Marker seam horizons are characterised by zig-zag seam splitting and coalescing. The horizon consists of up to six currently recognised thin, irregularly developed coal seams interbedded with sandstones and siltstones. In many areas a number of seams are oxidised and the member is currently not economically viable. A detailed study in "D" area of the Dunn Creek Mine has highlighted a variation in thickness of 0.7 to 1.8m and in air-dried ash of 20 to 30Vo. Cameron (1972) reported similar variations in ash percentage (22 to 367o) at Trap Gully. The sandstones are usually light coloured, friable and porous with abundant subangular quartz grains (65 io 907o). They are moderately well sorted, with subordinate rock fragments (claystone, mudstone t07o), and minor (approximately and volcani cs biotite, orthoclase, rutile, SVo) chert, plagioclase, tourmaline and zircon. The matrix comprises 5 to 127o of the rock, and is mostly kaolinite (Lumley,

Early to Middle Jurassic age is assigned to the unit by Dear & others (1971).

STRUCTURE Major structures in the Callide Basin include the Rainbow Creek Fault Zone (Dear & others, 1971) and the Eastern Creek Fault Zone (Lumley, 1985; Behets, 1987; Sorbie, 1990). Both ofthese features trend to the north-west. Deformation structures within the basin are characterised by gentle open folds and minor high and low angle faulting (fault throws ar,e generally less than 15m). The maior structural elements within the Callide Basin and associated marginal areas are shown in Figure 7. The structural data shown in this figure are based on mapping by Grimstone (I977) with additional material from Honours students and mine personnel. Photolineament locations wele taken from a Landsat structural analysis by Walker (1985). A number of previous workers have attempted to describe the itructural history of the basin' Dear & others (1971) recognised two periods of movement along the Rainbow Creek Fault Zone: a pre-Permian movement phase, which separated the Youlambie Conglomerite and Kroombit Leds, and a second phaJe which downfaulted the Rainbow Creek beds to the south-west and possibly localised the deposition of the Callide Coal Measures. Svenson & Hayes (1975) suggested that the Callide Coal Measures formed in a downwarp and recognised a megascopic NW-SE trending gentle asyrimetric syncline (see Figure 7) in the south-west po-r"tion of the basin. Grimstone (1977) confirmed the

presence of this structure. Cameron (t972)

1985).

Precipice Sandstone The Precipice Sandstone is a scarp-forming unit (Figure 2), which overlies the Callide Coal Measures with both disconformable and angularly unconformable relationships towards the basin margins (Grimstone, 1977). Towards the north-east Lumley (1985) suggests that the top of the coal measures is usually represented by the first ferruginous band above the uppermost grey siltstone/shale in the sequence. Elsewhere the boundary can only be determined by palynology (Stevens, 1978). The type section was described by Whitehouse (1955) further to the south, and subsequently in more detail by Dear (1968) and

Martin (1976).

The unit is up to 100m thick and dominated in this region by a well sorted, cross-stratified orfhoquartzite with minor amounts of interbedded pebbly quartzose sandstone, siltstone, and tuff. The orthoquartzite exhibits high porosity, being composed of 95Vo quartz and chert, with around 17o rock fragments, plagioclase, muscovite, g-arnet, zircon, rutile, tourmaline and haematite bound by a microcrystalline kaolinitic cement. Features such as load casts and scour infilling are common. The siltstones are often "flaggy" and fissile, containing mainly quartz with minbf subangular to subrounded plagioclise set in a cement of muscovite, kaolin and quartz. Coates (1982) has described thin (up to O.tm) tuff marker beds in this unit. These are very fine grained, laminated and kaolinised and have a charicteristic pearly lustre. X-ray diffraction (XRD) studies have highlighted large amounts of quartz, illite and kaolinite. Based on plant remains, an _

interpreted the structure within the Trap Gully -area to consist of NW-SE trending fold structures with strike-slip faulting in the axial region of the majol anticline. Grimstone (7977) suggested that normal faulting at the margins of the Callide Tertiary Basin caused regional tilting of the Callide Basin towards the west which exposed its eastern margin' The Callide Basin has a complex structural history. The mode of formation of the basin is poorly understood because ofthe lack ofevidence for deformational structure of discernible Late Triassic age. However, the localised and conglomeratic nature of the Rainbow Creek beds, the Muncon Volcanics, and the basal portion of the Callide Coal Measures hint at a fault-controlled origin for the basin. The majority of deformation structures observed in outcrop and mine workings are of demonstrable post-Jurassic, pre-Tertiary age.

Intrusive dykes and sills ofprobable Tertiary age occur, but no faults of demonstrable Tertiary qgehave been observed. Regional tilting of the Callide Basin to the west, exposing the eastern flank, probably occurred as a result of fault movements ilong tie margins of the Callide Tertiary Basil. The defoimation siructures in the Callide Basin affect mine and drainage planning, but do not seriously affect coal recoveries.

Local Deposit Structure Broad open folds with axes trending in an

north-west/south-east direction are exposed at the Dunn Creek Deposit. Minor low angle faults svmmetrical about these structures are occasionally observed. Well developed north-west to south-east

Callide Basin

480

- _- T __ _ -_ _ --_ T-- ------

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Geology of Australian Coal Basins

481

Figure 8. Breccia dyke intruding the Callide Coal Measures, 18 Pit Highwall, Trap Gully deposits.

'''''

'i i'.: '' r ' "

:;;#:r

orientated joints occur throughout the mine workings, coinciding with prominent photolineaments of the same trend. Minor slump structures and low-angle reverse faults with throws greater than 2m are occasionally observed, and these features were probably developed during compaction and lithification of the coal measure sediments. The Trap Gully area has been divided into A and B Pits, with significant structural disturbances separating the areas (Figure 1). The A and B Pits are separated by a series of closely spaced NNW trending normal faults with cumulative throws up to 15m. Seam dips in the mining area are typically 5 to 10o, steepening to >50o in subcrop areas along the south-west basin margin. The A Pits are punctuated by a series of widely spaced low-angle reverse faults, with throws varying fiom2 to 15m, Complementary high angle normal faults, with throws <3m are also observed in

highwall exposures.

In the B Pits the strata dip 2-20o, increasing from south-east to north-west within the mining area. Dips increase to >50o along the north-west margins ofthe deposit, with associated closely spaced east-west trending faulting. Two east-west trending normal faults, with throws of 2 to 3m, are encountered towards the northern end of the B Pits. Current mine designs in the "B" area have been truncated adjacent to a major (probably normal) fault trending north-west/south-east that has downthrown the strata in the order of 10 to 20m to the north. Mini-Sosie surveys across the fault have failed to conclusively delineate the fault, but trials of other techniques, such as TSIM, optimum offset

and VSP seismic surveys have proved more promising. Further work with the aim of accurately iocating t-he position of this fault is continuing.

In the southern end of "B" pit an east-west trending brecciated zone occurs which cuts both the Callide Coal Measures and the Precipice Sandstone (Figure 8). The brecciated zone (which is up to 5m wide within the Callide seam) consists of a mixture

allide Basin

482 of cobble and boulder sized coal fragments, with sandstone, carbonaceous siltstone and claystone fragments from horizons from both above and below the Callide seam. Dip-slip movement across this structure is around lm, and outcrop evidence

indicates that its formation predates the weathering ofthe Precipice Sandstone. A thin igneous dyke appears to split away from the western breccia zone margin and cross-cut the Callide seam to the north. Rare fragments of igneous material are observed within the brecciated zone, and igneous dykes of probable Tertiary age are known within the Trap Gully area (Coates, 1982). The brecciated zone ii considered to have formed as the result of venting steam from the intersection ofan igneous intrusion with an aquifer beneath the Callide seam. The south-west margin of the Kilburnie deposit is truncated by a NNW-SSE trending fault (Figure 7). To the north the margins of the Kilburnie coal deposit have been delineated by a mini-SOSIE seismic survey, but the precise structure of these margins cannot be determined. The Callide Coal Seam Member in The Hut area is characterised by rapid lateral splitting and coalescence of seam plies and a slightly lower quality than same seam at Dunn Creek and Trap Gully. On the basis of recognised seam splits and downhole geophysical logs, the Callide seam has been subdivided into several distinct plies.

Structurally, dips are less than 5o and exploration drilling to date indicates that, while only minor faulting exists within the coal blocks, faults with throws in the order of 40m exist between the Northern Valley and Eastern Hillside areas. A number of north-west to south-east and north-south photolineaments has been observed (Walker, 1985). A NW to SE trending fault, with an upthrow of 10 to 15m to the east, occurs along the southern margin of the Eastern Hut area. The onlap of Mesozoic sediments across the Rainbow Creek Fault Zone indicates that minimal movement has occurred along this fault zone since the deposition of these sediments; outcrop evidence does not support the suggestion by Dear & others (1971) that this fault zone controlled the deposition of tlre Callide Coal Measures.

Complex deformation structures occur along the

western margin of the deposit near Boundary Hill (Figure 1). A number of different styles and trends of faulting were recognised by Burgess (1984; 1986a). Both high-angle and low-angle faults of three orientations are observed in the highwalls of the pit. Steeply dipping beds on the western pit margin and the variability of dips across the pit are indicative ofthe effects ofdrag folding against faulting, and probably reflect the basement

structure.

NNW-SSE trending high angle fault with associated steep dips (up to 40o). To the north the seam outcrop i.s controlled by north-south trending high-angle faulting and associated NNW-SSE en echelon low-angle faulting. The Galloway Plains Tonalite crops out to the west of the north-south trending faulted margin of the Mesozoic Callide Basin sediments, and is partially mantled by Tertiary sediments. Drillhole intersections of basement to the Coal Measures infer fault throws in the order of 70m. Associated drag folding has created seam dips along the western margin of the deposit of up to 80o.

COAL QUALITY Callide Basin coal is a sub-bituminous, non-coking coal. It is unusual in the context of other Australian coal seams in being very sub-hydrous (i.e. the coal matter has low hydrogen content). It is very dull (has a low vitrinite content) and poorly caking (zero crucible swelling number), and is one of the lowest specific energy coals (on a dry, mineral matter free basis) of any commercially mined in Australia. The coal is classified as sub-bituminous class A, ASTM and SAA K184 500 (Svenson & Hayes, 1975). Other distinctive features of Callide Basin coal are:-

. . . . r .

been recognised further to the south, but with

smaller throws of the order of 0.5 to 1.5m. The displacement of these faults is seen to decrease in the overlying Precipice Sandstone, and in some instances is restricted to the coal seam.

In the southern portion of the Boundary Hill Mine the Callide Seam outcrop is controlled by a

an anomalously high Hardgrove grindability index for the rank (Spero, 1991),

high moisture holding capacity, high oxygen content in the coal matter, low organic sulphur content, coal ash characterised by low silica and

extremely variable iron levels.

Even within the basin, there are considerable quality variations. Compared to Dunn Creek and Trap Gully coals, Boundary Hill coal has:-

higher inherent moisture and moisture holding capacity values,

o . .

lower ash and carbonates, higher volatile matter, higher total sulphur,-almost entirely due to an increase in pyritic sulphur content,

. .

threefold higher phosphorus levels,

n r

higher HGI values,

unusually high liptinite content and carbon char reactivity,

brighter appearance.

The three major fault trends within the mine are

NE-SW, E-W and NNW-SSE. The Six Metre Fault, a major high-angle normal fault, has a NE-SW orientation and is downthrown 6m to the southeast. A similar orientation and character of faulting has

medium to high phosphorus levels,

on a dry, mineral matter free basis, significantly lower carbon, hydrogen, and specific energy and higher oxygen values,

lower SiOz, lower SiO/AlzOs ratio and higher (twofold) CaO + MgO in the ash,

Typical physical and chemical properties of the coals are summarised in Table 1.

Inherent and total moisture levels increase from south to north along the basin. Total moisture varies irregularly between L2Vo and 20%. The Hardgrove grindability index varies between 70 and 89,

Geology of Australian Coal Basins

483

Table,,l, Woining,siCtioo conpbsit'b quatitt.parametbrsifor selbcted.depbsits,,in,..tLie..Callidb BCsin. ANALYSIS TYPE

DUNN CREEK TRAP GULLY

THE IIUT

KILBURNIE BOI.'NDARY HILL

Proximate Analyses (Vo ad) Inherent Moisture Volatile Matter Ash

Fixed Carbon Total

10.9 23.7 78.2 47.2 100.0

9.7 24.7

24.7

10.6 24.3

74.2

14.2

14.7

5r.4

9.7

l\.7

25.1 L2.8 50.4

100.0

50.4 100.0

100.0

15.0 13.6

t7.4

15.5

18.0

13.6

t2.7

15.1

19.0 16.0

20.80 19.84 23.34 29.34

22.76 20.82 25.20 29.97

2t.44

22.06 20.23 24.68 29.53

22.21 20.37 25.15 29.42

33.43 28.09

32.46 31.55

32.69

32.53 32.16

33.25 32.33

1.56 1.50

1.49

1.56 1.50

7.52

1.48 1.42

5t.4

Moisture (7o) Total Moisture Moisture Holding Capacity

Specific Energy (MJ/kg) Air Dried As Received

Drv Basis Dry, Ash Free Basis

20.06 23.74 29.70

Volatile ll'Iatter (Vo) Dry, Ash Free Basis Drv, Mineral Matter Free

Physical Testing Relative Density (air dried)

Relative Density (as received) Grindability (Hardgrove)

Dust Index Friability Index Abrasion Index (mglkg) Ash Fusion Temperature ("C reducing atmosphere) Deformation

1.43 89

7.0

1345

1334 1517

t470

Hemispherical

1543

Flow Slagging Index

t570 1376

1511 1561 1378

Sulphate Organic TOTAL

r.46 83

n/d n/d n/d

n/d n/d

28.6

1490 1550 1585

1300 7420 1440 1500 1328

13.8 25.5

13.5 27.5 16.0

Spherical

Sulphur (Vo ad) Pyritic

28.t7

>1600 1509

14.0

n/d

3.0

1270 1390 1.440

1500

1304

0.17 0.01 0.08 0.26

0.17 0.02 0.07 0.26

0.15 0.01 0.07 0.23

0.24 0.34

0.20 0.04 0.09 0.33

0.018 0.038 2.6

0.027 0.019

0.010

0.050 0.017 2.3

0.059 0.025 2.6

0.02 0.08

Minor Constituents (7o ad) Phosphorus

Chlorine Arsenic (ppm)

Fluorine(ppm) Barium ppm)

Carbonate (COzVo\

0.014 1.8

1.8 42

n/d

444

n/d

400

t.t7

1.00

1.03

depending on deposit area, while ash fuston

temperatures (initial deformation in reducing^ atmbsphere) vary between 1150oC and >1600oC for full-seam mining sections.

Vitrinite A (telocollinite) reflectances increase from 0.487o to 0.53Vo north to south, indicating minor rank variations within the basin. The total sulphur content of Callide coal is very low, generally less than0.37o, with the majority of the sulphur occurring in the form ofpyrite. Coal relative densities are high, 1.42 to 1.55 (air dried basis), possibly a reflection ofa high inertinite content.

The specific energy ofcoal from individual plies within eactr deposit area can vary between 13 and 26MJ4<g, (air dried basis). Spontaneous combustion commences afte-r a p_9r-l-o4 of 2 to 4 weeks in unconsolidated heaps, but Callide

n/d

2440

3500

1.04

0.80

coal can be stored for many years in properly

constructed stockpiles. Stevens (1978) believed that the texture and nature of the inertinite prevented the loss of moisture from

the coal.

COAL PETROLOGY Detailed observation of the Callide coal in hand specimen shows that much of the main Callide seam is of intermediate lustre, between what is conventionally regarded as vitrain and durain. A macroscopic log of the Callide seam at Dunn Creek Mine (Figure 9) shows considerable variety in facies, both in terms of lustre and degree of banding (bedding). A recent study by Giikson & Fielding (1991a) showed no consistent vertical trends, but rather that the coal seams displayed a random

allide Basin

484

uttl r€ltts

IOP OF

JE I

from distant channels. Correlation ofcoal plies by the use ofvertical petrographic profiles, geophysical logs, and clastic partings shows that component coal bodies range up to several square kilometres in extent, and have irregular patchwork geometry.

At several localities within the mine lease, the rootlata / coaly trrcaa

_t{ tl

'r31

Iroitlona

- nodular

9ra

and lansaa

- lultlcaoua

a Ero a

- 9trlt.

- ?1.!ll tlrno

Callide seam is known to be displaced by low-angle

thrust faults. The thrusts ramp at relatively high angles through inter-seam strata, but show a lower-angle disposition within coal seams. Fault planes can be recognised in the coal as low-angle, inclined or flat surfaces and layers occupied by a soft, friable, sooty coal. In microscopic observation this coal is seen to be brecciated. Elsewhere in the mine, sooty horizons have been identified as fusain layers and used as markers for correlation.

Previous workers (CSIRO, 1951; Svenson & Hayes, 1975; O'Sullivan, 1977; Stevens, 1978) have found that semifusinite and inertodetrinite were the most dominant macerals within the Callide Coal Seam Member. All workers have noted variations in the predominance of some macerals within individual seams, probably indicating successions of environmental changes.

More recently, the application of transmission electron microscopy (TEM) to the study of Callide coal (Glikson & Fielding, 1991a, 1991b; Faraj & others, 1991) has enabled a better understanding of the nature and origin of some of the less understood macerals such as micrinite and vitrinite B

o @r

(detrovitrinite).

o' @

laull plfna

@' @

fi' 6 6l)

Two forms of vitrinite appear to be present in Callide coal. Current conjecture about the dominance of vitrinite in Callide coal is currently being reviewed (Esterle, in press). Vitrinite A displays an average reflectance of 0.56% , implying a higher rank than the 0.497o reflectance for total vitrinite recorded in previous publications. Vitrinite B and A together show the most variation in macerals occurring in Callide coal samples. Under the TEM, the lower-reflecting vitrinite B, which forms bands often several hundred micrometres in

thickness, shows sub-micron electron-transparent laminae of lipid-rich material alternating with a more conventional vitrinite material. The vitrinite B is interpreted to represent accumulations ofleaves.

tOa h1

E u.i tLool r;L-rrTlfra-.?l or.E^r

,ill;l_l\

l5.Doo.n.rilr/I -

xad.di our/'Jll!;.Ahit

fltht b.nd.{

(Av.r.ea Lrat?.,

Figure 9. Dunn Creek Mine Lithofacies Profile, 87 Pit (after Behets, 1987).

arrangement of characteristics. Punctuating the

seam at intervals are clastic partings, mainly of

fawn tuffaceous claystone. In places these partings are laterally extensive over a few kilometres, and they have been used to correlate individual seam plies (Flood, 1985). The fawn claystones are interpreted to represent mainly reworked volcanic ash falls into peat mires, while other partings are seen as incursions of flood-borne sediments derived

Microspore studies by Stevens (1978) indicate plant types dominated by pteridosperms (seed ferns), cycads (rushes), lycopods (small low growing plants) with occasional Ginkgoales (Maidenhair Trees). Silicified tree stumps in growth position up to 800mm in diameter have been observed in partings between splits of the Callide seam in the'S'and'D' areas at Dunn Creek. Plant megafossil remains are only occasionally observed (mostly Dicroidium flora). The Callide coal has entered the oil window, and oil has been generated from some liptinite, cutinite and resinite, as evident from changes in fluorescence and the presence of exsudatinite in cell cavities and cleats. Vitrinite B is seen under the microscope to also be generating oil. Micrinite, the origin of which

has been much debated, occurs in selected horizons only, as lenticular bodies suggesting cell filling or filling of spaces between laminations in vitrinite B. TEM study shows the micrinite to consist predominantly of sub-micron pyrite and possibly other mineral particles absorbed on humic acids.

Inertinites are only common in some horizons, and are both autochthonous and allochthonous. Liptinite

Geology of Australian Coal Basins

485 macerals are usually concentrated within vitrinites or in inertodetrinites. Cutinite and resinite are associated as a rule with vitrinite B. Liptites appear

mostly in inertodetrinite, but exsudatinite can be seen in any ofthe vitrinites or inertinites.

Recent work on mineral matter by Ward (1990) has

indicated that the low-temperature (oxygen-plasma) ash residues of Callide coals consist mostly of kaolinite, quartz and siderite. Minor amounts (<20Vo) of mica, illite, expandable lattice clays, bassanite, pyrite and/or iron oxides, however, have also been recognised by X-ray diffraction ofthe plasma-ash material.

COAL SEAM DEPOSITIONAL EI{\rIRONMENTS The variable coal petrology and complex geometry of the Callide seam may be reasonably explained in terms of natural evolution of the subsiding alluvial

plain environment.

The Callide Coal Measures were deposited with angular unconformity, and in some cases disconformity, across various'basement' rocks (Youlambie Conglomerate, Rainbow Creek Beds and Muncon Volcanics) in a down-warping area. The unit forms a grossly frning upward succession, with thick conglomerates at the base, passing upward somewhat abruptly into coal-bearing, fine-grained clastic rocks. No marine indicators are present, and hence the sequence is interpreted as being of continental (alluvial) origin (Stevens, 1978; Flood, 1981; Behets, 1987; Glikson & Fielding, 1991a).

Post-intrusive uplift and faulting associated with the Galloway Plains Tonalite to the north-west and north provided a clastic source for the basal coal measure conglomerates in the north of the basin, the lithologies of which are suggestive of high energy environments of deposition, perhaps associated with

alluvial fans (Waterfield, 1988; Glikson & Fielding, 1991a).

The supply of coarse detritus then ceased, allowing finer-grained fluvial systems to become established, and under appropriate circumstances peat mires. An alluvial plain or alluvial valley environment then developed, with an associated fluvial system resulting in the deposition of extensive beds of sandstone, siltstone, claystone and coal. The coal seams were the product of long-lived peat swamps situated in the distal regions of a restricted flood plain environment. Eight facies have been described in detail by Behets (1987) and Waterfield (1988). Subsidence rates in the basin are believed related to the reactivation of faults in the basement and influenced the development of the coal seams. A decrease in depositional energy is apparent through time with respect to the coal measure sediments.

Palaeocurrent data from various parts ofthe preserved basin indicate consistently southward-flowing fluvial systems within the coal-bearing association. Facies mapping by Flood (1985) and Behets (1987) within the Callide seam interval has determined that palaeochannel belts ranged from 400m to at least 1700m in width, and were variable in orientation. Major channel deposits, however, account for only a modest proportion ofthe total sequence thickness. Furthermore, the channel bodies show tapering and 'feather'edges, implying that they were not significantly incised into the surrounding facies but were dominantly vertically-accreted fills of broad and shallow (up to 2m deep) channels. The taxonomically restricted flora forming the coal swamp (Stevens, 1978) suggest cool climatic

conditions during the formation of the Callide Coal Measures. Stevens (1978) suggested that, because of the low rank and high inertinite content, compaction ratios within the Callide Coal Measures could be in

Sloge 4. Stoge 2. AREAS SUBJECTED TO EFFECTS OF FLOWING WATER, ONLY DURING EXCESSIVE INFLOW.

Figure 10. Theoretical peat succession of Moore & Bellamy (1574).

Callide Basin

486

S KILBURNIE

N CAMPBELLS CREEK

BOUNDARY HILL

NORTH-SOUTH CROSS SECTION THROUGH BOUNDARY HILL, CAMPBELLS CREEK AND KILBURNIE DEPOSITS.

Vertical Exaggeration 1 O:1 approx. Figure 11. Coal seam cross-section through the Boundary Hill and Kilburnie deposits. the order of 2:7, in marked contrast to the compaction ratios of 10:1 or more interpreted in other coal basins. Stevens (1978) thus inferred that the thickness of consolidated peat may have originally been no more than 40m. Grimstone (1977) suggested the nature of sediment deposition within the Callide Coal Measures was controlled by regional base level changes. The sequence below the Callide seam reflects a regressive phase while the sequence above this unit represents a transgression. Stevens (1978) emphasised fluvial controls on the preservation of

the peat swamp, and suggested that the river systems at the time of deposition were fast-flowing and slowly meandering, and transported sedimenis rapidly through the basin. Moore & Bellamy (1974) recognise a number of stages of peat swamp development, representing various degrees to which the peat is subjected to continuous water in flow from streams beyond the immediate catchment (Figure 10). Smyth (1980) suggested that the Callide seam accumulated in a very stable basin, and formed under peat swamp conditions which varied between stages three and four of Moore and Bellamy's (1974) theoretical peat succession. With the accrual of peat, fluvial stream activity was confined to the margins of the peat swamp with the swamp's water supply derived from rain (Stage 3). With continuing peat growth, the peat was then inundated only when the water level of the basin rose during rainfall (Stage 4). The present authors contend that Smyth's (1980) model of peat accumulation, if extended and modified, may explain a number of features relating to the spatial relationships ofthe coal plies in each deposit and their relationships to interburden sediments.

Figure 11 is a cross-section through the Boundary Hill and Kilburnie deposits, showing the distribution of coal plies associated within the Callide seam. Coal plies coalesce in both deposits to

form a central core with an aggregate coal thickness of between 20 and 30m. Away from the core area, or the peat depositional centre, the coal plies may be split by fluvial sediments. A similar distribution of coal plies within the Callide seam is also known to occur at the Trap Gully Mine, the Dunn Creek Mine (Grimstone, L977; Flood, 1985), and The Hut deposit. The distribution of parting sediments is confined to deposit margin areas, as might be expected from peat swamps in stage 3 and 4 of Moore & Bellamy's theoretical peat succession. The parting intervals are considered to represent periods of increased fluvial activity within the peat swamp. The correlation ofthe high ash coal bands and thin bands of non-coal sediment with areas of thicker partings suggests that water was able to flow throughout the swamp during this fluvial period, but that only finely suspended sediment was able to reach the peat accumulation centres. Within the coal plies, ash as low as 4 to 67o (air dried) is occasionally observed, suggesting that the coal swamp at times reached a raised bog stage of development.

Grimstone (1977) recognised that the thickest coal accumulations in the southern portion of the Callide Basin were associated with the thickest development of the Callide Coal Measures. The association of the thickest aggregate accumulations of coal within the Callide seam with the thickest development of the Callide Coal Measures sequence as a whole may reflect differential subsidence rates within the basin (Grimstone , I977; Stevens, 1978). The Bottom, Sawmill and Marker seams differ from the Callide seam in thickness (normally around 5m), quality (around 207o ash, air dried), and seam splitting (more zig-zag splits). Seams within this part of the sequence often contain numerous thin claystones and grade laterally and vertically into carbonaceous siltstones. Fluvial processes are considered to have been more dominant in the formation of these beds than during the

Geology of Australian Coal Basins

487

development of the peat swamps within the Callide seam.

Cessation of coal measure deposition was caused by a phase of normal faulting involving the Rainbow Creek Fault to the north and east ofthe basin

associated with regional uplift. A period oferosion with little or no structural activity ensued through to the Jurassic.

The thick, laterally extensive quartzose fluviatile 'sheet' sandstones of the Precipice Sandstone were then deposited by a braided river system in the Early Jurassic. These deposits covered most of the Callide Basin and represent a different style of sedimentation compared to the Callide Coal Measures. Uplift in the Late Jurassic and the subsequent erosion ofthe land surface then proceeded until the Tertiary.

The Callide Basin sequence was tilted to the south-west during the Tertiary, exposing and eroding the eastern margins. The western margins were subsequently buried under sediments of the Tertiary Callide Basin. Faulting and the steepening of dips observed along the basin margin at Boundary Hill and Trap Gully, as well as volcanic activity exhibited by basalt flows that blanketed much of the eastern area, accompanied the tilting. Basalt dykes and stocks also intruded the Callide Coal Measures

in the north at Boundary Hill.

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Australasian Institute of Mining and Metallurgy, Brisbane, Qld, 187-198. BUREAU OF MINERAL RESOURCES, 1967: Bouguer anomalies, 1:250 000 Monto Sheet, G56 /82'2 (R). CAMERON, J.8., 1972: Callide Coalfield. Geological Suruey of Queensland Report,68. COATES, S.P., 1982: The stratigraphy and structure of the Trap Gully area, Callide Basin, east central Queensland. Unpublished Thesis, Department of Geology and Mineralogy, University of Queensland. CSIRO, 1951: Report on sample of Callide seam, Callide Coalfield, Queensland, taken from the open cut mine of Callide Open-cut Collieries Pty Ltd during February and April, 1951. Commonwealth Scientific and Industrial Research Organisation Location Report, 57. CSIRO, 1968: Report on seams from Callide Boreholes NS 80 and NS 81R, Callide District, Central Queensland. Commonwealth Scientific and Industrial Research Organisation Location

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de JERSEY, N.J., L974: Palynology and age of the Callide Coal Measures. Queensland Gouernrnent

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BIGGS, M.S., 1983a: An integrated Landsat study of the Collards Creek area, north-east of Biloela, central Queensland. Unpublished Report, CSR Coal Division. BIGGS, M.S., 1983b: AP3210M Collards Creek: Final Report, including progress exploration report for the six months ended, 4 February 1983. CSR Coal Division Report to Queensland Department of Mines, C.R. 12093. BIGGS, M.S., 1984: The role of Landsat digital analysis in geological exploration ofthe Collards Creek area, central Queensland. Landsat 84, Proceedings of the Third Australian Remote Sensing Conference. Brisbane (1984), 355-365. BIGGS, M.S., 1990: The use of new techniques in computerised data recording and downhole geophysical logging using SIROLOG during drilling programs at Callide Coalfields. 1n Beeston, J.W., (Compilet)'. Proceedings of Bowen Basin Symposium 1990, Geological Society of Australia (Qld Division), Mackay, September 1990, 163-180.

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FARAJ,8., MACKINNON, I.D.R. & GLIKSON, M., 1991: Characterisation of micrinite in the Late Triassic Callide Coal Measures. In Griffith, P. (Editor): Proceedings of Queensland Coal Symposium, Australasian Institute of Mining and Metallurgy, Brisbane, 3-8. FLOOD, P.G., 1981: Facies study of the Callide seam, central Queensland: implications for mine planning and design. Department of Geology and Geophysics, University of New England. FLOOD, P.G., 1982: Facies study of the Callide seam, Boundary Hill area, central Queensland. Unpublished Thesis, Department of Geology and Geophysics, University of New England. FLOOD, P.G., 1985: Facies study of the Callide seam, central Queensland: implications for mine planning and design. Australian Coal Geology, 5, L3-24.

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allide Basin

488 GLIKSON, M. & FIELDING, C.R., 1991a: The Late Triassic Callide Coal Measures, Queensland, Australia: coal petrology and depositional environment. International Journal of Coal Geology, 17, 313-332.

GLIKSON, M. & FIELDING, C.R., 1991b: Re-assessment of rank and maceral composition of Queensland coals: implications for hydrocarbon generation and other unexplained phenomena. 1n Griffiths, P. (Editor)'. Proceedings of Queensland Coal Syrnposium, Australasian Institute of Mining and Metallurgy, Brisbane, 23-30. GRIMSTONE, L.R., 1977: The geology of AP 188C and the evaluation of the Callide coalfield. Report, Thiess Brothers Pty. Limited. GRIMSTONE, L.R. & ROACH, C., 1978: Evaluation of the Callide Coalfield. Australasian Institute of Mining and Metallurgy, North Queensland Conference, September, 197 8. JENSEN, H.I., 1923: Some notes on the PermoCarboniferous and overlying systems in central Queensland. Proceedings of the Linnean Society of N.S.W., 48, 154-158.

LUMLEY, D., 1985: Palaeonenvironmental analysis of the Callide Coal Measures in the north eastern corner of the Callide Basin. Thesis, Department of Geology and Mineralogy, University of Queensland

MARTiN, K.R., 1976: Sedimentology of the Precipice Sandstone, Surat Basin, Queensland. Ph.D. thesis, University of Queensland.

MOORE, P.D. & BELLAMY, D.J.,lg74: Peatlands. Elek Science, London. MURRAY, G.C., 1980: General geology of Rockhampton area. In Hofmann, G.W. (Editor): 1980 Field Conference, Mount Morgan

Rundle Range

Yeppoon Area, Geological Society of Australia, Queensland Division, Brisbane, 4-20.

O'SULLIVAN,T.,l977: Geology of part of the

north-eastern Callide Basin, east-central Queensland. B.Sc. (Hons) thesis, Department of Geology and Mineralogy, University of

Queensland. PARRINGTON, P.J., 1971: Final Report AP 583M, Monto, Queensland. The Broken Hill Proprietary Company Ltd, Unpublished report to Queensland Department of Mines, CR3499A. RANDS, W.H., 1891: New discovery of coal near the Callide -Creek, Port Curtis District. Geological Suruey of Queensland Publication, 8O, I-4. REID, J.H., 1945: Callide coal. Queensland Gouernment

Mining Journal, 46, 47 -49.

REID, J.H., L947 a: Report on the Callide coalfield. Queensland Gouernment Mining Journal, 48,

t2-t7.

REID, J.H., 1947b: Callide coalfield. Queensland Gouernment Mining Journal, 48, 260-26L.

RENWICK, R., 1983: A detailed petrophysical study of the Kilburnie Coal prospect. The Shell Company of Australia Limited, Report CEPR 26/83. SHEPHERD, S.R.L., 195la: The Callide coalfield, upper Dunn's Creek section. Queensland Gou ernment Mining Journal, 52, 133-141. SHEPHERD, S.R.L., 195lb: The Callide coalfield, Petersen Gully section. Queensland Gouernment

Mining Journal, 52, 442-452.

SMYTH, M., 1980: Thick coal members: products of an inflationary environment? Coal Geology, 2(2), 53-76. SORBIE, A.J., 1990: Geology and morphostructure integrated with coalfreld computer databases, south eastern margin of the Callide Basin, central Queensland. B.Sc. (Honours) thesis, Department of Geology and Mineralogy, University of Queensland. SPERO, C., 1991: Developments in laboratory testing and evaluation of coal grindabllity. In Griffiths P. (Editor): Proceedings of Queensland Coal Symposium, Australasian Institute of Mining and Metallurgy, Brisbane, 7 3-82. STEVENS, J., 1978: A palynological and sedimentological study of the Callide Basin, east-central Queensland. Unpublished thesis, Department of Geology and Mineralogy, University of Queensland. SVENSON, D. & HAYES, S.W., 1975: Callide Coal Measures, Queensland. In Traves, D.M. & King, D. (Editors): Economic Geology of Australia and Papua New Guinea, Volume 2: Coal. Australasian Institute of Mining and Metallurgy,

Monograph, 6, 283-287 . WALKER, R.D., 1985: Callide Basin, Queensland: Landsat structural analysis. Unpublished report, Minerals Exploration and Development Group, CSR Limited.

WARD, C.R., 1990: Mineral matter analysis of coal samples from Callide coalfields, Queensland. Unisearch Limited Report R6851 for Callide

Coalfields Pty Limited.

WATERFIELD, D.W., 1988: Geology of the northwestern Callide Basin, east central Queensland. B.Sc. (Honours) thesis, Department of Geology and Mineralogy, University of Queensland.

WHITEHOUSE, F.W., 1955: Geology of the Queensland portion of the Great Australian Artesian Basin. 1n Artesian Water Supplies of Queensland, Departmental Co-ordinator of General Public Works, Queensland Parliamentary Papers, A 56.

Geology of Australian Coal Basins

489

ffi ffis

K#larenceMoreton, Sutat, Eromanga, Nambollr, and Mutgildie Basins

PW Goscombe

and BA Coxhead

The Clarence-Moreton, Surat, Eromanga, Nambour and Mulgildie Basins cover an area of approximately 1.325 million km2 (Figure 1). The common boundaries of the larger basins coincide with older subsurface structural features, namely the Kumbarilla Ridge between the Clarence-Moreton and Surat Basins and the Nebine Ridge between the Surat and Eromanga Basins. The Eromanga Basin is similarly separated from the Carpentaria Basin by the Euroka Arch. The Nambour and Mulgildie Basins are fault controlled structures adjoining the Clarence-Moreton and Surat Basins respectively. The Surat and Eromanga Basins collectively form the northern half of the Great Artesian Basin, which is one of the largest artesian systems in the world (Moore, 1986). The basins contain similar Jurassic and Cretaceous strata. The Jurassic sequence is almost exclusively non-marine in origin, having been formed by extensive river systems that drained much of the Eromanga and Surat Basins, with outlets to the sea by way of the northern Clarence-Moreton Basin (Exon & Burger, 1981; Wells & O'Brien, 1994) and

the Mulgildie Basin (Day & others, 1983). The Cretaceous sequence is largely of marine origin, following inundation of the Eromanga and Surat Basins by the sea from the north via the Carpentaria Basin (Smart & Senior, 1980).

The geological evolution of the basins followed a Late Triassic (Norian) orogeny (Day & others, 1983), also described by Korsch & others (1989) as due to

thermal relaxation following transtensional faulting of the pre-Jurassic rocks. Subsequent tectonism in this part of the Australian continent has been epeirogenic rather than orogenic, confined mainly to differential movement along pre-existing basement structures with mainly drape and compactional features generated in the Jurassic and younger sediments. Coal occurs in all five basins, but commercially significant deposits are restricted to the Middle Jurassic Walloon Coal Measures and its equivalents in the Clarence-Moreton, northern Surat and Mulgildie Basins.

Prior to 1987 only small scale underground mining

was carried out in the Rosewood, Walloon, Acland, Tannymorel, Mulgildie and Injune areas. In the late 1980s two large open cut mines were developed in the Amberley area, 1Okm south west of Ipswich, with each producing slightly less than lMt of saleable coal per annum.

Exploration over the past 25 years has outlined large near-surface deposits of coal in the Walloon Coal Measures of the Clarence-Moreton and Surat Basins. The unique high volatile, perhydrous properties of the coal have also focussed attention on theie deposits for possible production of a range of synthetic fuels, as well as for thermal coal developments. Figures compiled from the Department of Minerals and Energy, Queensland, estimates and company sources show near-surface resources of Walloon coals in the Clarence-Moreton, northern Surat and Mulgildie Basins amount to 4934Mt in situ. Further very large tonnages are inferred on geological grounds at depths >60m.

Jurassic Basins

490

4 CARPENTARTA BASIN

MULGILDIE BASIN

-_8 CLARENCE_MORETON BASIN

SURAT BASIN :/:\

CLARENCE.

Figure 1. Location of the Clarence-Moreton, Surat, Eromanga, Nambour and Mulgildie Basins.

Geology of Australian Coal Basins

49t STRATIGRAPHY OF THE BASINS The major stratigraphic units in the ClarenceMoreton, Surat, Eromanga, Nambour and Mulgildie Basins are shown in Table 1.

Clarence-Moreton Basin The Clarence-Moreton Basin is preserved as a northerly and northwesterly trending arcuate basin approximately 400km in length and up to 120km in width, covering an area of 43 000km2 in southeastern Queensland and northern New South Wales

(Figure 2).

The basin is bounded by pre-Permian basement metamorphics and granites of the New England Fold

Belt, represented by the Texas Block to the south and west; and the Yarraman, D'Aguilar and Beenleigh Blocks to the north and east. Much of the sediment deposited in the basin was derived from erosion of these older basement rocks, which are still exposed as elevated highlands today.

Deposition was initially restricted to intermontane basins located east of a north-south trending feature known as the West Ipswich Structure (Allen & others, 1960), comprising the West Ipswich Fault and the South Moreton Anticline. The West Ipswich Structure separated a tectonically active area to the east, previously the site of deposition for the Late Triassic Ipswich and Nymboida Basins, from the stabilised cratonic basement to the west. Conglomerates and coarse lithic sandstones of the Aberdare Conglomerate and Laytons Range Conglomerate were deposited on the eroded surfaces of the Ipswich and Nymboida Basins in a high energ"y fluviatile environment, heralding the formation of the Clarence-Moreton Basin. Less energetic fluvio-lacustrine conditions followed, with deposition of sub-labile to quartzose sandstone,

siltstone and mudstone of the Raceview Formation. Minor thin coal seams developed in this section, but are of little economic interest. The Ripley Road Sandstone, a massive, crossbedded, fine to coarse grained, sub-labile to quartzose sandstone up to 1200m thick, indicative of a more energetic fluviatile environment, was deposited over a progressively widening area, which extended eventually to the limits of the basin. The Aberdare Conglomerate, Raceview Formation and Ripley Road Sandstone were collectively described as the Woogaroo Subgroup in the Ipswich

area by Cranfield & Schwarzbbck (1972). More recent work by Wells & others (L990) has extended the name basin-wide. The subgroup also includes formations previously mapped as the Moorooka Formation (Houston, 1965a, 1965b), Helidon Sandstone (McTaggart, 1963; Gray, 1975a), and Wivenhoe Sandstone (Swindon, 1956, 1960). The thickness ofthe subgroup ranges widely from 150 to 1120m.

Overlying these sediments is the Marburg Subgroup (Wells & others, 1990), which is divided into a 500m thick lower unit, the Gatton Sandstone and a 250m thick upper unit, the Koukandowie Formation. The Gatton Sandstone consists mainly of medium to

very coarse grained, quartz- feldspathic-lithic sandstone, including beds of pebbly sandstone with

calcareous cement. Minor beds of conglomerate and siltstone/ shale are also present, together with fossil wood. Thin coal seams occur which correlate with a wider area of coal accumulation extending eastwards to the Nambour Basin and westwards to the Surat Basin. They have no economic significance but represent a relatively quiet period ofdeposition throughout the basin. The Koukandowie Formation is also a predominantly arenaceous unit, consisting offine to coarse grained quartzose to quartz-lithic sandstone with a variable sandstone/siltstone/shale sequence

at the base. Chamositic oolite beds containing acritarch-bearing horizons occur in claystones associated with the basal unit, and are thought to have been produced by gentle wave action in extensive shallow lakes which formed during low energy depositional phases, of an otherwise fluviatile environment (Day & Price, 1986).

The Marburg Subgroup, together with the underlying Woogaroo Subgroup and its equivalents, are known basin wide as the Bundamba Group

(Etheridge & others, 1985; Wells & others, 1990). As defined by Cranfreld & Schwarzb6ck (1972), the sequence includes sediments deposited from the Late Triassic (Rhaetian) to the Middle Jurassic (Bathonian). The Walloon Coal Measures, which overlie the Bundamba Group, consist of lithic and feldspathic labile sandstone interbedded with siltstone, mudstone, carbonaceous shale and coal. The siltstone and mudstone beds are commonly montmorillonitic, indicating that volcanism was active in proximity to the basin, possibly in the Gympie area to the northeast and in the Texas area to the southwest. Several tuffaceous marker beds have been identified over a strike length of 60km immediately east of the Kumbarilla Ridge (Mclean-Hodgson & Kempton, 1981). The coal bearing horizons are thick and commercially important in the northern part of the basin. The Walloon Coal Measures attain a maximum thickness of600m in the axial region ofthe Logan River Syncline in northern New South Wales. Up to 500m is preserved across the Kumbarilla Ridge west of Dalby and into the Surat Basin. The formation has, however, been either partly or wholly eroded over much of the Moreton Basin, especially along the crests of anticlinal structures such as the South Moreton Anticline, and on the upthrown side of faults such as the West Ipswich and Richmond Faults. In the Rosewood area, where the type section for the formation is defined (Cameron, 1970), the upper part of the coal measures has been removed by erosion.

High energy fluviatile conditions returned following deposition of the Walloon Coal Measures, as shown by the medium to coarse grained, cross-bedded quartz sandstones ofthe Kangaroo Creek Sandstone in the southern half of the Clarence-Moreton Basin. Erosion has reduced the present distribution ofthis formation to an outlier 180km by 60km along the axis of the Logan River Syncline, where it forms characteristic escarpments up to 90m high. The Kangaroo Creek Sandstone is overlain by lithic quartz sandstones containing beds of

Jurassic Basins

492

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-o q ! c d J

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Geology of Australian Coal Basins

493

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MAJOR JURASSIC COAL DEPOSITS 1. Rosewood 2. Oakey

]II

3. Millmerran

West lpswich Oo

r ooo

2000 3000 4000

Nambour

^ Basin U 500

aull

500

+++ ++

+++ l++ ++ + +tdse. + ++ +++ +++ ++ +++ ++++

Kumbarilli

;11:1i;:-t

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2000 3000 4000

Griman Ck Fm Surat Slst Cretaceous

Coreena Mbr Doncaster Mbr Kumbarilla beds /

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Triassic Palaeozoic

Grafton Fm Kangaroo Creek SS Walloon Coal Measures Bundamba Gp / Landsborough SS lpswich / Nymboida Coal Measures Undifferentiated Lower to Middle Triassic Undifferentiated Basement Rocks

Figure 2. Geology of the Clarence-Moreton and Nambour Basins.

Jurassic Basins

C la re n c e-M oret on

Basin Succession Nambour Basin Succession

1 J

494

montmorillonitic mudstone of the Grafton Formation. This unit contains plant fragments and reed impressions, with traces of coal exposed in clay pits south of Grafton (McElroy, 1969). It is the youngest sedimentary sequence in the southern part ofthe basin. In the northern Clarence-Moreton Basin fine to medium grained lithic to quartzose sandstones with siltstone, mudstone and minor thin pebble conglomerates of the Kumbarilla beds were {eposited along the western margin of the basin. These sediments indicate deposition under low energy fluviatile, deltaic and paludal conditions. Pre-Tertiary erosion has removed most of the formation prior to extrusion of extensive Tertiary basalts on the eroded surface, leaving a maximum preserved thickness east of the Kumbarilla Ridge of only 100m. To the southwest, the Kumbarillabeds interfinger with the Pilliga Sandstone across the Kumbarilla Ridge into the southern Surat Basin. The sedimentary succession preserved in the Clarence-Moreton Basin confirms that deposition continued there at least to the Late Jurassic (Oxfordian) in the north, and possibly to the Early Cretaceous (Neocomian) in the south. The

succession is entirely terrestrial, dominantly

fluviatile in origin, ind noteworthy for the commercially important coal seams of-the Walloon Coal Measures.

Nambour Basin The Nambour Basin is located northeast of the

Clarence-Moreton Basin. It is approximately 130km in length and u^p to 65km in width, covering a total area of 4l00km2 (Figure 2). As in the Clarence-Moreton Basin, the formative stages of the Nambour Basin were structurally controlled (Cranfreld & Schwarzbijck, 1926), with the western margin faulted against Palaeozoic basement rocks of the D'Aguilar and Beenleigh Blocks. The Brisbane Strait, which connected the

Nambour Basin to the Clarence-Moreton Basin, separates the two basement highs.

The depositional history ofthe basin parallels that of the eastern half of the Clarence-Moreton Basin. A comparable suite of high energy fluviatile quartzose sandstones and polymictic conglomerate was de_posited on the eroded surface of the Ipswich Coal Measures during the Late Triassic (Rhaetian), followed by up to 120m of quartzose and sub-labile sandstone interbedded with siltstone, mudstone and minor coal in the lower 60m deposited under less energetic fluviatile conditions. The coal is probably equivalent in age to that in the Raceview Formation of the Clarence-Moreton Basin.

During the Early Jurassic up to 400m of fine to medium grained sub-labile to labile sandstones containing sporadic coarse pebbly sandstone bands and acritarch-bearing ferruginous oolite (Day & Price, 1986) were deposited under fluviatile and lacustrine conditions. Minor thin coal seams up to 0.5m thick have been recorded in this interval-and equate with the thin coals in the Marburg Subgroup.

Geological mapping has yet to establish a precise correlation with formations of the Bundamba

Group in the Clarence-Moreton Basin, and consequently the name Landsborough Sandstone (Cranfield & Schwarzbtick, 1976) has been used to describe the stratigraphic sequence. The name Brighton beds has also been used to describe the upper 200m of the Landsborough Sandstone in part of the basin.

Surat Basin The Surat Basin is located to the west of the Clarence-Moreton Basin and extends from southern Queensland into northern New South Wales. It is approximately 800km in length from north to south and up to 450km in width, covering an area of

approximately 270 000km2 (Figure 3).

The Surat Basin contains up to 1800m of undeformed, predominantly quartz-rich continental Jurassic sediments, overlain by as much as 900m of mainly paralic fine grained sediments of Early Cretaceous age (Exon, 1980). The sediments were deposited on the eroded surfaces ofLate Carboniferous to Triassic rocks of the Bowen and Gunnedah Basins, as well as on older Palaeozoic basement rocks of the Tasman Fold Belt. Subsidence of the Late Carboniferous to Triassic sediments relative to the rest of the basin resulted

in the thickest deposition occurring about the Mimosa Syncline. To the west, the rock units interfinger with those of the Eromanga Basin across the Nebine Ridge; and to the east they interfinger with strata of the Clarence-Moreton Basin across the Kumbarilla Ridge.

Six major cycles of sedimentation have been identified in the northern Surat Basin (Exon, 1976, 1980; Exon & Burger, 1981). These sedimentary cyclothems consist of typically coarse quartzose sandstone grading to labile sandstone, siltstone,

mudstone and coal. Each was formed by initial deposition in braided streams, followed by deposition in meandering rivers and finally in swamps, lakes and deltas.

Exon (1976) linked the cyclothems to variations in the base level of erosion, which he suggested were caused by major eustatic changes in sea level during the Jurassic, probably in response to periodic changes in climate. Epeirogenic movements of the continental land mass may also have contributed to the cyclic sedimentation. Moore & others(1986) favour the latter view, and have proposed that the cycles were generated in response to convergent plate tectonism along the east coast ofAustralia. Irrespective oftheir origin the cycles are very relevant to the formation of coal in the Surat Basin.

Hawke & Bourke (1984) have divided the succession in the southern portion ofthe Surat Basin into four sedimentary units (Table 1). Progressive onlap ofthe Early Jurassic strata in a southerly direction, combined with general thinning and erosion of some Middle and Late Jurassic units, has resulted in preservation of a maximum thickness of L800m of Jurassic and Cretaceous sediments, compared with 2700m in the northern part ofthe basin.

Geology of Australian Coal Basins

495

I+ +1 Y A RRA[I ANi ,-t?

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LEGEND

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MAJOR JURASSIC COAL DEPOSITS 6

1. Brigalow

4. Taroom

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5. Mulgildie

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2000 3000

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Griman Ck Fm Surat Slst Coreena Mbr Doncaster Mbr Bungil Fm

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Precipice SS Bowen Basin

Permo-Triassic

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Figure 3. Geology of the Surat and Mulgildie Basins.

.furassic Basins

Surat Basin

Kumbarilla beds

Succession

)

Nlutsitoi" eurin Succession

496

Precipiee Sandstone and Eoergreen Formation The first of Exon's six cyclothems is represented by

Formation and Walloon Subgroup of the Injune Creek Group. The Hutton Sandstone consists of well sorted, cross-bedded, quartzose to sub-labile fluvial sandstone, with minor thin conglomerate bands and thin beds of siltstone and mudstone. The sandstone is typically very porous and permeable, forming an important aquifer in the subsurface. A maximum thickness of 250m is preserved in the Mimosa Syncline.

The sandstone has a maximum thickness of 150m in the northern part ofthe basin, and averages 40 to 50m elsewhere. It extends to the east through the Toowoomba Strait to merge with the Ripley Road Sandstone of the Clarence-Moreton Basin.

The Injune Creek Group was named by Swarbrick (1973) to cover a sequence offluviatile, paludal and lacustrine sediments up to 850m thick lying conformably on the Hutton Sandstone. The Group has been subdivided into a number of formations in the northeastern Surat Basin, of which the coal-bearing Walloon Subgroup and its lateral equivalents along the east flank of the Mimosa Syncline are of significant economic interest (Table 2).

the Precipice Sandstone and the Evergreen Formation. The Precipice consists mainly of quartzose sandstone deposited in a fluviatile transgressive environment, becoming finer grained in the upper part with minor siltstone bands.

The Evergreen Formation conformably overlies and

onlaps the Precipice Sandstone, and continues to the west across the Nebine Ridge into the eastern half of the Eromanga Basin. The formation comprises up to 260m of siltstone, mudstone and labile to sub-labile sandstone, deposited in a low energy fluviatile. deltaic and lacustrine environment. The mudstone is highly carbonaceous in places,

and contains well preserved fossil plant impressions. An acritarch-bearing oolitic ironstone horizon, similar to that found in the Marburg Subgroup of the Clarence-Moreton Basin, occurs towards the top of the formation. A predominantly fluvial facies up to 90m thick, the Boxvale Sandstone Member, was deposited in the upper portion of the Evergreen Formation along the northwestern edge of the Surat Basin. This unit contains a thin sequence ofsandstone, siltstone and coal, roughly equivalent to the coal horizon in the Iower Marburg Formation of, the Clarence-Moreton Basin and the upper Landsborough Sandstone of the Nambour Basin.

At the time the Precipice Sandstone and Evergreen Formation were being laid down in the north, an irregular sequence of basaltic flows and pyroclastic rocks with tuffaceous sandstone and claystone beds was accumulating on older Mesozoic and Palaeozoic basement rocks in the south. This sequence, known as the Garrawilla Volcanics, has been dated by K-Ar methods at 171 to 20l"Ma, indicating an Early Jurassic age (Hawke & Bourke, 1984). Estimated maximum thickness for the forrnation is 180m (Kenny, 1964).

Hutton Sandstone, Eurornbah Formation o.nd, Walloon Coal Measures The second of Exon's cyclothems is represented by

the Hutton Sandstone, together with the Eurombah

Table 2. Stratig"T$;1the Injune Creek Northern Surat Basin

Eastern Surat Basin

Westbourne Fm

Springbok SS

Springbok SS Walloon CM

Walloon Sub-group

Juandah CM Tangalooma SS Taroom CM

The Eurombah Formation, consisting of up to l00m of interbedded lithic sandstone and minor polymictic conglomerate, siltstone and mudstone, was deposited under fluviatile conditions in the northern part of the basin. The formation thins markedly away from its depocentre near Injune, particularly to the south where it cannot be distinguished in the sub-surface from the underlying Hutton Sandstone. The Walloon Coal Measures of the ClarenceMoreton Basin extend west across the Kumbarilla Ridge and into the eastern Surat Basin. In the northeastern part ofthe basin, the unit has been upgraded to subgroup status and subdivided into three formations, the Taroom Coal Measures, the Tangalooma Sandstone and Juandah Coal Measures (Jones & Patrick, 1981).

This terminology has only been applied to date in the outcrop zone around the Mimosa Syncline, although a similar three-fold subdivision into a lower coal-bearing unit, a middle sandstone/ siltstone unit and an upper coal-bearing unit has been identified throughout most of the Surat Basin (Swarbrick, 1973), and also in the ClarenceMoreton Basin. The oldest unit, the Taroom Coal Measures, consists of50 to 200m oflithic and feldspathic labile sandstone interbedded with siltstone, mudstone, carbonaceous shale and coal. Impure limestone and ironstone lenses may be interbedded in the siltstone and mudstones. The Tangalooma Sandstone consists of up to 200m of lithic and feldspathic labile sandstone with a carbonate cement. Upward fining sequences are commonly developed and thin coal lenses also occur

locally. The Juandah Coal Measures are represented by 50 to 200m oflithic and feldspathic sandstone, siltstone, mudstone and coal. The lithologies are similar in almost all respects to those of the Taroom Coal Measures, though with thicker coal seams more common towards the top of the formation. The uppermost coal member defines the top ofthe measures, and corresponds to the end of Exon's second sedimentary cycle.

A fluvial and paludal environment also prevailed in the southern part of the basin at this time, as

Geology of Australian Coal Basins

497 shown by the thickly bedded labile sandstone,

siltstone, dark mudstone and minor thin coal seams of the Purlawaugh Formation. The Purlawaugh Formation is 9 to 84m thick, and grades southward into the upper part of the Ukebung and Digilah Formations. Continuity with the Hutton/Walloon sequence has not been established (Hawke &

Bourke,1984).

Springbok Sandstone and Westbourne Formation The third of Exon's cycles is represented by the Springbok Sandstone and the Westbourne Formation. The Springbok Sandstone consists primarily of cross-bedded labile sandstone, with carbonaceous siltstone and mudstone, and rare thin coal and bentonite lenses. The depositional environment ranged from low energy fluvial to deltaic and paludal. The Springbok Sandstone is generally <50m thick although up to 150m has been recorded in petroleum wells in the central portion of the basin. The formation has equivalents in the Adori Sandstone on the Nebine Ridge, the Pilliga Sandstone in the south, and the basal Kumbarilla beds to the east. The Westbourne Formation is the uppermost unit of

the Gubberamunda Sandstone is generally <100m, although the unit thickens to >200m in the central Mimosa Syncline. The Orallo Formation consists of 150 to 200m of cross-bedded labile to sub-labile sandstone with minor conglomerate, carbonaceous siltstone, mudstone, bentonite and thin banded seams of coal. Fossil wood is ubiquitous, giving rise to the original name for the formation, the "Fossil Wood Stage" (Reeves, 1947). The unit is considered to have been deposited in a low energ'y fluvial to paludal

environment.

In 1912-1913, a tunnel was driven on a coal outcrop

located about 30km from Roma, but the seam proved to be too thin and too high in ash to be workable. Jensen (1926) later referred to the sequence as the "Orallo Coal Measures". The top of the Orallo Formation was selected by Exon (1976, 1980) to close his fourth cyclothem. His fifth cycle is represented by the Mooga Sandstone, the Bungil Formation and the Doncaster Member of the lower

Wallumbilla Formation.

Mooga Sandstone, Bungil Forrnation and.

Louer W allumbilla Formation

the Injune Creek Group, extending throughout the northern halfofthe Surat Basin and the eastern half of the Eromanga Basin. The formation consists of cross-bedded, quartzose to sub-labile sandstone, siltstone and mudstone with lenticular bentonite beds and thin coal seams.

The Mooga Sandstone consists of 50 to 150m of quartzose, sub-labile, upward-fining fluvial sandstone, with interbeds of siltstone and mudstone at the top. The basal section is permeable and acts as a major aquifer. The formation grades laterally into the upper part of the Hooray Sandstone along the eastern flank of the Nebine Ridge.

The cross stratification in the sandstone is commonly low-angle and, with evidence of some soft sediment deformation caused by slumping, deposition is thought to have been in a deltaic to paludal environment. The thickness of the formation generally ranges from 80 to 100m, although it thickens to approximately 200m in the axial region of the Mimosa Syncline. The Westbourne Formation interfingers to the south with the Pilliga Sandstone

Although continuity has not been confirmed, possible equivalents ofthis unit in the southern part of the Surat Basin include the Keelindi beds, which consist ofwell sorted and cross-stratified quartzose labile sandstone and interbedded shale and mudstone. The unit is up to 150m thick, but thins towards the margins of the basin. Its depositional environment was predominantly fluviatile.

and to the east with the lower Kumbarilla beds.

The Pilliga Sandstone consists of 100 to 300m of quartzose sandstone with minor interbeds of siltstone and mudstone. Thin pebble conglomerate bands also occur throughout the section. The depositional environment was high energy fluvial, which was in marked contrast to the low energy environment of the SpringbokAVestbourne sequence

in the north.

Gubberamund.a Sandstone and. Orallo

Formation

The fourth of Exon's sedimentary cycles is represented by the Gubberamunda Sandstone and the Orallo Formation. The Gubberamunda Sandstone consists of quartzose sub-labile sandstone with minor siltstone and mudstone beds, indicative of deposition in a moderating fluvial environment that ranged from high energy braided streams to low energy meandering rivers. The sandstones are permeable and form a major fresh-water aquifer in

the subsurface. To the west, the sandstones become finer grained

and grade laterally into the lower part of the llooray Sandstone across the Nebine Ridge. They also

interfinger with the upper part of the Pilliga Sandstone to the south, and have equivalents in the Kumbarilla beds to the east. Average thickness of

The Bungil Formation is a paralic sequence of labile sandstone, siltstone and mudstone with subordinate sub-labile quartzose sandstone and coal in environments ranging from deltaic and paludal to neritic (Day, 1964; Exon, 1976). The formation ranges in thickness from l00m in the north and west to 300m in the axial region of the Mimosa Syncline.

Equivalents of the Bungil Formation in the south are represented by the Drildool beds (Hawke & Bourke, 1984). This sequence consists of approximately l00m of lithic sandstone and interbedded siltstone and mudstone, with minor thin coal seams associated with carbonaceous siltstone and mudstone. The sediments contain numerous worm burrows and bioturbations as well as carbonised plant roots, indicating a paralic to paludal environment. The Drildool beds contain the youngest rocks of Cretaceous age preserved in the southern part ofthe Surat Basin. The Doncaster Member consists of 100 to 200m of marine carbonaceous mudstone with minor siltstone and fine-grained labile glauconitic sandstone. This unit was deposited during the peak of the Cretaceous marine transgression from the east, and was linked across the Nebine Ridge to marine sedimentation in the Eromanga Basin.

Jurassic Basins

498 The more calcareous strata contain a rich fauna which is predominantly molluscan (Day, 1964). Fossil logs are also commonly found in the Mitchell area (Exon, 1980). The top of the Doncaster Member defines the close of Exon's fifth sedimentary cycle.

Upper Wallumbilla Formation, Surat Siltstone and, Griman Creeh Formation Exon's sixth and last cyclothem is represented by the Coreena Member of the upper Wallumbilla Formation, the Surat Siltstone and the Griman Creek Formation. The Coreena Member contains 50 to 200m of paralic sediments, comprising interbedded mudstone, siltstone and frne-grained, thickly bedded lithic sandstone which is commonly glauconitic and calcareous. Belemnite coquinites have been recorded in the sequence, together with sporadic marine molluscs. The Coreena Member was deposited during regression of the Cretaceous sea to the northwest across the Nebine Ridge. The thickest development ofthe Coreena and the underlying Doncaster Member is in the central and southern portion of the Mimosa Syncline. The overlying Surat Siltstone consists ofl00 to 130m of interbedded siltstone and mudstone with lenses of fine grained glauconitic sands-tone (Gray, 7972). The siltstone is commonly micaceous and the mudstone is generally carbonaceous and pyritic. Small pelecypods are common. The

depositional environment was mainly neritic to paralic.

The Griman Creek Formation consists of up to 48m of labile glauconitic and commonly calcareous sandstone, with siltstone and minor mudstone. Intraformational conglomerate and thin coal lenses occur in the upper part of the formation, and molluscan coquinites are present in the lower part (Exon, 1980). The depositional environment ranged from predominantly neritic at the base of the formation to estuarine and fluvial at the top (Gray, L972), reflecting the final regression of the Cretaceous sea from the basin. The formation is the youngest Cretaceous unit preserved in the Surat Basin.

Mulgildie Basin The Mulgildie Basin is a narrow elongated trough of Jurassic sediments extending off the

northeastern portion ofthe Surat Basin (Figure 1). The confined distribution of the sediments is the result ofrifting along a system ofnorth-south faults which separate older basement rocks of the Yarraman Block to the east, from the Auburn Arch to the west (Figure 2). The basin is some l90km long and 20 to 50km wide, and covers an area of 5200km2.

The stratigraphic succession in the basin corresponds to the first and second cyclothems of Exon (1980) in the Surat Basin.

At the base of the first cycle is 60 to 150m of quartzose sandstone, the Precipice Sandstone, lying unconformably on coal-bearing strata thought to be equivalent to the Triassic Callide Coal Measures and Tarong beds (Svenson & Rayment, 1975). This is succeeded by 75 to 260m oflargely

argillaceous sediments, comprising sandstone, siltstone, shale and minor coal, that belong to the Evergreen Formation. The second cycle is represented by the Hutton Sandstone and the Mulgildie Coal Measures

(Svenson & Rayment, L975), comprising respectively 150 to 275m of sandstone and 150m of sandstone, siltstone, shale and coal. The Mulgildie Coal Measures are equivalent to the Walloon Subgroup ofthe Surat Basin.

Eromanga Basin The Eromanga Basin covers an area of approximately 1 000 000km2 in central Australia, and includes a large part of western Queensland, the Northern Territory, New South Wales and South Australia. It contains a maximum thickness of 2500m of Jurassic and Cretaceous sedimentary rocks which have facies equivalents or direct correlatives in the Surat Basin to the east, and the

Carpentaria Basin to the north.

As a consequence ofits size, the stratigraphy ofthe Eromanga Basin has developed on a regional rather than a basin-wide scale, with a strong state-by-state bias. The following generalised

description of the stratigraphy is given in terms of three partly integrated geologic columns, which are representative ofthe Queensland or eastern section, covering approximately 630 000km2; the Northern Territory and adjoining Queensland border regions, or northwestern section, covering approximately 120 000km2; and the South Australian or southwestern section, covering approximately 250 000km2. The term "basal Jurassic" is broadly used to describe equivalents ofthe Evergreen sequence in the Surat Basin that have been intersected in the Eromanga Basin by petroleum wells and deep stratigraphic holes (Anon, 1985). In the Queensland sector ofthe basin, up to 40m of siltstone and mudstone with minor fine grained labile sandstone were deposited on Early and Middle Palaeozoic rocks and the Late Carboniferous to Triassic sediments of the Galilee and Cooper Basins, under low energy fluvial and lacustrine conditions, There is a greater proportion of medium and coarse grained sandstone associated with the siltstone and mudstone in the South Australian sector, indicating a more energetic fluviatile environment. Minor lenticular coal seams have been recorded from the basal Jurassic in this area, which was deposited unconformably on Early Palaeozoic rocks, and on Late Carboniferous to Triassic sediments of the Cooper and Arckaringa Basins

(Figure 1).

The equivalent section in the northwestern sector of the basin is known as the Poolowanna Formation. This sequence also accumulated in a dominantly fluvial environment. 200m of interbedded fine grained sub-labile sandstone, siltstone and mudstone, with minor coal seams generally <0.5m thick, occur in the type section (Moore, 1986). The sequence becomes sandier to the west, and passes laterally into the basal beds of the otherwise overlying Algebuckina Sandstone. To the east it either pinches out or passes laterally into the "basal Jurassic" and the basal Hutton Sandstone (Moore, 1986).

Geology of Australian Coal Basins

499 The "basal Jurassic" and the Poolowanna Formation are conformably succeeded by the Hutton Sandstone over an extensive area of the central and southern Eromanga Basin. The Hutton Sandstone typically consists of a series of upward-fining sequences of quartzose and sub-labile sandstone with pebble conglomerate bands, grading to labile sandstone and minor beds of siltstone and mudstone.

A reversion to a more energetic depositional environment following the Westbourne Formation resulted in the accumulation of 100 to 200m of interbedded quartzose to sub-labile sandstone and siltstone in the Queensland sector of the basin, to which the name Hooray Sandstone is ascribed. The siltstone in this unit contains fine carbonaceous fragments, possibly at an equivalent horizon to the Orallo Formation of the Surat Basin.

The siltstone commonly contains plant and coal fragments, and thin lenticular coal seams occur sporadically in the upper part of the unit. The sediments were deposited in a high energy fluvial environment with some limited flood plain and lacustrine development. It has equivalents in the basal Algebuckina Sandstone in the northwest, which conformably overlies the Poolowanna Formation, where present, and onlaps Precambrian and Palaeozoic rocks elsewhere. The formation is up to 250m thick (Senior & others, 1978).

John (1985) has reported coal at the top ofthe formation in GSQ Wyandra No. 1. The Hooray Sandstone has equivalents in the upper Namur Sandstone Member and the Murta Member in the southwest (Armstrong & Barr, 1982) and the Algebuckina Sandstone in the northwest. The Namur and Algebuckina are as described above; the Murta Member consists of thickly-bedded siltstone with thinly interbedded fine-grained sub-labile sandstone (Ambrose & others, 1982).

As noted previously, Exon (1980) regards the Hutton Sandstone as the basal unit ofhis second upward fining sedimentary cycle in the Surat Basin where it

is overlain by the Walloon Subgroup. In the Eromanga Basin, equivalent fine-grained sediments, comprising sub-labile to labile partly calcareous sandstone and siltstone with minor carbonaceous mudstone and coal, are referred to as the Birkhead Formation (Senior & others, 1978). Up to 120m of these sediments were deposited conformably on the Hutton Sandstone in the central and southern parts of the basin, in a low energ'y fluvial and paludal environment (Paton, 1986). To the east, the formation grades across the Nebine Ridge into Walloon Subgroup equivalents in the basal section of the Injune Creek Group. In the Eromanga Basin though, the coal seams are thin, and as a consequence, the coal has little potential for commercial use.

Although Exon's sedimentary cycles pertain to the Surat Basin (Exon, 1980), it is evident that similar repetitive cycles occur in the central and eastern parts of the Eromanga Basin as well. The Springbok Sandstone, which marks the base of Exon's third cycle in the Surat Basin, has an equivalent in the Adori Sandstone in this area. This unit is composed mainly of sub-labile to labile sandstone with minor pebble bands and coarse sandstone lenses deposited in a high energy fluviatile environment (Senior & others, 1978). The Adori Sandstone has equivalents in the lower Namur Sandstone Member in the southwestern sector of the basin and the middle Algebuckina Sandstone in the northwest. Conformably succeeding the Adori Sandstone is the Westbourne Formation, a predominantly lacustrine sequence of siltstone, mudstone and minor thinly bedded sub-labile to quartzose sandstone containing fragmentary carbonaceous and coaly material (Senior & others, 1978). The Westbourne Formation is the uppermost unit of

the Injune Creek Group in the east, where, like its equivalent in the Surat Basin, it may contain thin coal seams. The lithology of the unit changes to the west however, to merge with the Namur Sandstone Member and the Algebuckina Sandstone.

Conformably overlying the Hooray Sandstone, the Murta Member and the Algebuckina Sandstone is the Cadna-owie Formation (Moore & Pitt, 1985). The lower part of this unit has up to 50m of siltstone and silty mudstone with interbeds of fine-grained labile sandstone and minor glauconite grading upwards to fine to medium-grained quartzose sandstone. The upper part is the Wyandra Sandstone Member, comprising up to 60m of fine to coarse-grained quartzose to sub-labile sandstone, pebbly in part, with minor siltstone interbeds towards the top in the more thickly developed sections. The sandstone is generally well sorted, porous and permeable, forming the youngest pressurised aquifer in the basin (Senior & others, 1978).

Marine bivalves, gastropods, dinoflagellates and arenaceous foraminifera have been recorded from the Cadna-owie Formation, indicating a dominantly paralic to shallow water marine environment. The formation coarsens upwards in the northwest, and at the margin of the basin shows evidence of cross-stratification, reflecting fluviatile rather than paralic conditions. This part of the sequence has been locally identified as the Mount Anna Sandstone Member. The marine transgression that began in the Neocomian with deposition of the Cadna-owie Formation spread basin-wide during the Aptian and Albian, resulting in deposition of a largely argillaceous sequence in which molluscan fossils and, to a lesser extent, gastropods, scaphopods and belemnites are common.

Widely known as the Wallumbilla Formation, this sequence is generally divided into two members, the Doncaster and Coreena Members, although this is not possib.le in the northwest where the whole sequence is more uniform.

In the eastern part ofthe basin, the Doncaster

Member consists of 150 to 200m of mudstone, siltstone and fine grained glauconitic sandstone in which soft sediment depositional structures, worm burrows and pyrite are common. The equivalent unit in the southwest is the lower part of the 200 to 320m thick Bulldog Shale, which is noteworthy for the presence ofa basal organic mudstone, 25m thick, with a distinctive gamma-ray response (Moore &

Pitt, 1985).

Jurassic Basins

500 The Coreena Member consists predominantly of fine grained labile glauconitic sandstone and siltstone with mudstone interbeds. Fossil wood and worm burrows are common in the upper part of the sequence.

The equivalents in the southwest are the upper part of the Bulldog Shale, the Coorikiana Formation (Moore & others, 1986), which is a relatively thin upward coarsening sequence of very fine-grained glauconitic sandstone and siltstone with argillaceous and calcareous cement, and the lower part of the Oodnadatta Formation. Shallow marine conditions prevailed to the end of the Albian and into the Cenomanian, with the deposition of somewhat more calcareous sediments known widely in the north and east of the basin as the Toolebuc Formation, Allaru Mudstone and Mackunda Formation (Anon, t985); and in the southwest as the Oodnadatta and Mackunda Formations (Moore & Pitt, 1985). The sediments of the Toolebuc, Allaru and lower

Oodnadatta Formations were deposited under relatively calm shallow marine conditions. By the Cenomanian, however, the sea had begun to recede and the Mackunda and upper Oodnadatta Formations were deposited in a regressive shallow marine to paralic environment. The Toolebuc Formation comprises 3 to 75m of carbonaceous and calcareous mudstone and Iimestone with minor thin interbeds of fine-grained calcareous labile sandstone and siltstone (Senior & others, 1978). It contains abundant bivalves such as Inocerdnxns sp. and Aucellina hughendenensis,

fish skeletons and teeth, radiolarians, globigerinids and dinoflagellates (Vine & Day, 1965). It is also characterised by a high gamma response, caused by uranium isotopes which have been concentrated in fish remains and organic carbon present in the formation. An oil-shale horizon up to 10m thick occurs in association with an organic rich facies in the northern part ofthe basin. The Alluru Mudstone consists of 150 to 400m of calcareous mudstone with interbeds of calcareous

siltstone and fine grained, partly calcareous labile sandstone. The sequence contains a rich marine fauna of bivalves, ammonites, gastropods and belemnites (Vine & Day, 1965). The Mackunda Formation is a marginal marine

sequence 60m thick of labile sandstone, siltstone

and mudstone, calcareous in part, containing bivalves, ammonites, belemnites, polyzoans and sharks'teeth (Day, 1966, 1967).

In the southwest, the Oodnadatta Formation consists of up to 300m of calcareous mudstone and siltstone with minor thin interbeds of fine-grained calcareous sandstone. The sequence contains a rich marine fauna of bivalves, ammonites and gastropods similar to those found in the laterally equivalent Toolebuc, Allaru and Mackunda Formations. The basal sediments of the overlying Winton Formation commonly show a well defined transition zone indicating an oscillating paralic and non-marine environment as the sea receded.

Apart from this, the Winton Formation consists of a non-marine sequence of fine to medium-grained

labile sandstone, siltstone, mudstone and lenticular coal seams, laid down under fluvial and lacustrine conditions. Coal seams up to 7m thick have been recorded in deep exploration wells in the central part of the basin, at depths ofaround 600m (Gray, 1975b). Plant fossil impressions of Sphenopteris erecta, P hyllopteris lanceolata and Cenomanian angiosperm leaves (White, 1974) are commonly found in association with abundant plant fragments and rootlets in the fine-grained sediments. The Winton Formation is the youngest Cretaceous unit preserved in the Eromanga Basin. It has been subject to extensive erosion, with thicknesses ranging typically from 400 to 700m, although up to 1200m has been recorded in structural lows protected from uplift and erosion during the Tertiary (Senior & others, 1978).

GEOLOGICAL HISTORY OF THE BASINS The geological evolution of the Clarence-Moreton, Surat, Eromanga, Nambour and Mulgildie Basins followed the Late Triassic (Norian) orogeny (Day & others, 1983; Korsch & others, 1989). Uplift at the end of the orogeny exposed the newly stabilised craton to erosion, with sediments being deposited in relatively small intermontane basins and

structural depressions.

Deposition in these developing basins began in the Late Triassic (Rhaetian) and became progressively more widespread towards the end of the Triassic as a result of eustatic changes and regional sagging. By the beginning of the Early Jurassic, sedimentation was well established over large areas ofeach basin. Deposition commenced in the Clarence-Moreton Basin, in small intermontane basins on the eroded and partly deformed Late Triassic strata of the Ipswich and Nymboida Basins (Figure 2). The Nambour Basin evolved at the same time as the Clarence-Moreton Basin and was connected to it throughout its depositional history by the Brisbane Strait (Day & others, 1974). The Clarence-Moreton and Nambour Basins received mainly fluviatile sediments during the

Rhaetian. Thin coal seams in the Raceview Formation near Ipswich, deposited during this period, are the oldest coal seams identified in the Clarence-Moreton, Surat and Eromanga Basins. A section of one of these seams 0.6m thick was mined briefly in the 1890s in the West Moreton Colliery, west of Ipswich. By the Jurassic, deposition offluvial sands and silts in the Clarence-Moreton Basin had spread across the Kumbarilla Ridge to the Surat Basin via the Toowoomba Strait (Figure 2). This fluviatile environment expanded further during the Early Jurassic, extending eventually to the Eromanga Basin across the Nebine Ridge and, for the first time, connecting the Clarence-Moreton, Surat, Eromanga, Nambour and Mulgildie Basins via one large fluvial system. Typical fluvial depositional conditions prevailed in all basins throughout most of the Early Jurassic. Notable exceptions were deposition of distinctive

Geology of Australian Coal Basins

50r oolitic ironstone horizons containing acritarch-

bearing zones over a wide area ofthe Surat, Clarence-Moreton and Nambour Basins at the end of the Early Jurassic (Toarcian).

Whilst the oolites and the acritarchs suggest deposition under paralic conditions, Day & Price (1986) consider that they were more likely to have developed under shallow lacustrine conditions, since no marine fossils have been positively identified in the horizons. Thin coal seams of no apparent commercial value developed at this time in the Boxvale Member of the Evergreen Formation in the Surat Basin, the lower Marburg Subgroup of the Clarence-Moreton Basin and in the Brighton beds of the Nambour Basin.

Cyclic fluvial and lacustrine conditions prevailed in the three major basins throughout the Middle Jurassic, probably in response to eustatic changes in sea level or epeirogenic movements varying the gradient of the major river systems draining the basins. The commercially significant Walloon Coal Measures and its equivalents were deposited in the Clarence-Moreton, northern Surat and Mulgildie Basins during this period, while inferior equivalents were deposited in the Birkhead Formation of the Eromanga Basin and the Purlawaugh Formation of the southern Surat Basin (Table 1).

Non-marine sedimentation continued throughout the Late Jurassic, with the formation of thin lenticular coal seams in the Westbourne Formation of the Surat and Eromanga Basins. However, by the Early Cretaceous (Neocomian) there is evidence of brackish water conditions having developed in the northern Eromanga and Surat Basins, presaging the change from a freshwater to a marine environment.

Thin coal seams in the Hooray Sandstone of the Eromanga Basin and the Orallo Formation of the northern Surat Basin were deposited early in this period. Later, in the Neocomian, a second interval of thin coal seams developed under paralic conditions in the Bungil Formation and Drildool beds of the Surat Basin. Eustatic changes in sea level in the early Aptian resulted in a major marine transgression that extended across the Eromanga Basin and over the Nebine Ridge into the Surat Basin. Epicontinental seas prevailed in both basins until the early Albian. Sedimentation in the Surat Basin became progressively more terrestrial, contracted northwards, and eventually ceased during the middle Albian. Thin coals were deposited in the Griman Creek Formation during the final period of sedimentation in the basin (Swarbrick, 1973). Marine conditions continued in the Eromanga Basin until the late Albian, before regressing northwards, enabling paralic and fluvio-lacustrine conditions to return during the Late Cretaceous (Cenomanian). Thin and lenticular coal seams were deposited in the Winton Formation during the final episode of Cretaceous sedimentation in the Eromanga Basin.

It is evident that conditions favouring coal formation

occurred periodically from the Late Triassic, when coal seams developed in relatively confined, structurally controlled precursors to the ClarenceMoreton and Nambour Basins, to the Late Cretaceous when seams formed on a broad scale as deposition in the Eromanga Basin came to an end.

For the most part, the largely stable tectonic setting and generally passive uniform subsidence was not conducive to the formation of thick coal seams. The coal horizons that did develop were generally widespread but contained only thin and discontinuous seams. The one notable exception is the extensive Middle Jurassic coal measure sequence deposited in the Surat, Clarence-Moreton and Mulgildie Basins, known respectively as the Walloon Subgroup, the Walloon Coal Measures and Mulgildie Coal Measures.

COAL OCCURRENCE AND FORMATION IN THE WALLOON COAL MEASURES The stratigraphic record of the Jurassic-Cretaceous basins reveals at least eight occasions when conditions were suitable for the deposition and preservation of coal measure sediments (Table 1). In every case, the coal measure strata occur at the top of an upward-fining non-marine sequence representing a progressive change from a fluvial to a paludal and in places a paralic environment. In the northern Surat Basin, where Exon (1976, 1980) recognised six such cyclothems, the coal measure facies are represented by the Evergreen Formation, Walloon Coal Measures (including the Walloon Subgroup where applicable), Westbourne Formation, Orallo Formation, Bungil Formation and Griman Creek Formation.

At least two of these horizons have coal-bearing equivalents in the Eromanga Basin, namely the Poolawanna Formation and other parts of the "basal Jurassic", and the Birkhead Formation. Coal also occurs in the Winton Formation in this basin as well. In the Clarence- Moreton Basin, coal is found in the Raceview Formation, the lower Marburg Subgroup and the Walloon Coal Measures. Apart from the coal seams in the Walloon Coal Measures of the northern Surat and ClarenceMoreton Basins and its equivalent in the Mulgildie Basin, the seams in the other basins rarely exceed 0.5m in thickness. The relatively thick coal seams of the Walloon facies are therefore the only coal deposits of economic interest in the basins. Seam Lithology The coal seams of the Walloon Coal Measures are typically interbanded with grey and brown mudstone and siltstone, and occasionally with thin beds of finely laminated shale containing a well preserved fossil flora. The bands are usually lenticular, variable in thickness and limited in areal extent, making accurate correlation between

exploration drillholes diffrcult.

Light coloured montmorillonitic claystone beds derived from decomposition of fine grained tuffs also occur, particularly in the northern part ofthe Clarence- Moreton Basin where they are thicker and more numerous than elsewhere. These beds tend to be persistent and can be used effectively as marker horizons on a local scale (Cameron, 1970), and also occasionally on a regional scale (Mclean-Hodgson & Kempton, 1981). The thicker beds also produce a somewhat higher gamma-ray response on downhole geophysical logs. Individual coal plies within the seams are generally <lm in thickness. They usually have a characteristic

Jurassic Basins

502

mid-lustrous canneloid texture, an absence of significant bright and dull banding, a sub-conchoidal fracture and poor cleat development. Aragonite commonly occurs on cleat surfaces, together with minor pyrite and iron carbonate nodules. The coal typically contains 70 to 90%o vitrinite and 10 to 20Vo liptinite, 5 to 15% of which is suberinite. There are normally only trace amounts of inertinite. Cook (1986) has reported a similar maceral composition for the Walloon facies coals of the Eromanga Basin.

Palaeobotany A study of isotopic temperatures and faunal realms of the southwest Pacific region during the Jurassic and Cretaceous by Stevens (1971) indicates that the palaeoclimate was warm-temperate during the Early and Middle Jurassic, but became progressively cooler during the Late Jurassic and cool-temperate in the Cretaceous.

At the time of deposition of the Walloon Coal Measures in the late Middle Jurassic (Callovian), the climate is thought to have been warm and relatively humid. These climatic conditions differed significantly from the sub-glacial to cool temperate conditions under which t}re Glossopferls-bearing coals of the underlying Permian Boweir Basin and the mainly Dicroidium-bearing coals of the Triassic Ipswich and Nymboida Basins were deposited. Some 25 species of trees, ferns and other macroflora have been identified from the Middle Jurassic period when the Walloon Coal Measures were deposited, but the fossil assemblage shows that coniferous gymnosperms are the most abundantly preserved (David, 1950). In addition, de Jersey (1959, 1960) has described some 40 species of microflora from the type area of the Walloon Coal Measures at Rosewood. Twenty eight of these were recorded as new species.

Gould (I975,1980) summarised the main macroflora as consisting of conifers (Mataia, Elatocladus, Araucaria, Allocladu s and Pagiophyllunc); ovuliferous scales and pollen-bearing cones, together with equisetaleans (Equisetum); ferns (Marattia, Hausmannia, C oniopteris, C ladop hlebis and O srnundacaulis); s e ed ferns (P ac hy p t eris ) ; cycadeoi ds (O to z amit e s and Ptilophyllum) as well as possible pentoxylale ans (Taeniopteris), liverworts (Thallites) and lycopods (Lycopodites).

Macrofloral species which characterise the Walloon Coal Measures, however, according to Gould (1975) ar e E qui s et um I at er al e, C I ado p hleb i s au s tr alis, Taeniopteris spatulata and Otozamifes sp. Gould (1975) also notes the conspicuous absence from the Walloon fossil assemblage of ginkgophyte leaves which are prominent in other Jurassic floras.

Depositional Model The Walloon Coal Measures are a freshwater succession of medium grained channel sands, finer grained levee and crevasse-splay sands and silts, and backswamp facies sedirnents. There is no evidence of any marine or marginal marine

deposition.

In view of this it is postulated that the measures

were deposited under low energy fluvial conditions on wide flood plains associated with mature, high sinuosity river systems. Extensive shallow water backswamps developed on the low lying portions of the floodplains, and incorporated areas ofdeeper water in abandoned stream channels and oxbow lakes. There was very little migration of the active river channels. Coniferous gymnosperms grew prolifrcally under the warm humid conditions in the shallow water areas of the backswamps, and a wide variety of other flora on the slightly more elevated drier areas of the associated flood plains. The coniferous gymnosperms, in particular the tall araucarians, generated acidic, reducing conditions in the deeper water lakes of the backswamps into which there was a continuous supply of air-borne and water-borne twigs, leaves, fronds, pollens and spores from the dense flora fringing the lakes. This provided ideal conditions for preservation of the lignin and exinitic components in the plant material, and for their subsequent conversion to peat. Floods periodically overtopped the levees bordering the active river channels, depositing coarse clastic material on or near the levees with progressively lesser amounts of finer grained argillaceous material farther out on the floodplains and in the backswamps. Subsequent minor reworking of the fine layers of silt and mud localised their distribution to shallow depressions on the floodplains and in the backswamps, giving rise to the lenticular mudstone partings which are typical of the Walloon coal seams. Less frequent major floods generated crevassesplay deposits across the floodplains and backswamps by breaching and reworking the levee bank sediments, as well as by carrying a heavier bed load of coarser grained sediments in the higher velocity flood waters. These floods were severe enough to carry the arenaceous sediments across

the backswamps and into the lakes to break the continuity of the accumulating peat deposits.

Maintenance of the backswamp environment close to the water table, through the effects of differential compaction combined with either slow regional epeirogenic downwarp or eustatic sea-level changes, maximised coal measure development. Under this depositional model, the thicker coal intervals in the major deposits are postulated to have developed at sites that were originally lakes. Much of the plant material deposited in them was transported there directly from the fringing forest vegetation by wind rather than water, thus preserving most of the lignin as well as the more resistant suberinitic and exinitic material (pollen, spores, resins and tannins) shed by the flora, particularly the coniferous gymnosperms. Fungal and bacterial degradation of the material was minimal, due to rapid submersion into an acidic and reducing environment at the bottom of the lakes. These conditions produced the perhydrous, vitrinite rich, high liptinite and low inertinite coal which is characteristic of the Walloon coals.

Geology of Australian Coal Basins

503

ELEVATION

Iil METRES 260

Goal

f:lril

Sandslono Slltston€

HORIZONTAL SCALE

2m 04 !.

20o (m 600 l0O

METRE9

VERTICAL EXAOOEFATION

Figure 4. Cross-sections through a typical Walloon coal deposit (based on the Austinvale deposit near Wandoan). The structural setting of the Walloon deposits reflects the absence of severe tectonic activity in this portion of the Australian land mass since the Jurassic. Seam dips are typically in the order of 1 to 20, and faults are generally limited to minor compactional displacements. The occurrence of large tonnages of near surface coal in compact, flat lying, structurally undisturbed deposits has focused attention on the Walloon Coal Measures as a potential future low cost open-cut coal source.

Major Coal Deposits The main coal deposits in the Walloon Coal Measures have a typically ovoid to crescent shaped form and extend up to l0km2 in area. The coal seams in these deposits thin progressively towards the margins of the deposits where they split and either lens out or grade laterally into carbonaceous shale and non-coal strata (Figure 4). The more persistent coal horizons are traceable from one coal deposit to the next, which may be tens of kilometres away, by means of thin coaly or carbonaceous bands of no commercial value. Geophysical downhole logs are an invaluable aid in establishing

As a result, exploration has progressively outlined approximately 5000Mt of measured and indicated resources in the Clarence-Moreton, Surat and Mulgildie Basins (Table 3).

correlative units within the measures.

Table 3. CoaI resources of the Walloon CoaI Mbasures and equivalents. LOCALITY CLARENCE.MORETON BASIN Amberley/Rosewood Oakey

Millmerran Other SURAT BASIN Macalister Brigalow Chinchilla Wandoan Taroom

MEASURED

(Mt)

INDICATED (Mt)

TOTAL (Mt)

t23

L44

120

390

510

562

846

1408

tL2

l].2

265

r20

385

115

100 130

175 575

tt1

Other MULGILDIE BASIN 55 Mulgildie 2L05 TOTAL Source: Queensland Department of Resource Industries, 1992'

Jurassic Basins

445 195 415

215 305 1020 31',0

415

110

2829

4934

504

Table 4. Physical and chemical properties of the major Walloon coal deposits (washed product at RD f .60). SURAT BASIN

CLARENCE-MORETON BASIN ROSEWOOI

WASHING YIELD (Vo) PROXIMATE ANALYSIS (ad) inherent Moisture (%) Ash (7,)

Volatile Matter (Vo) Fixed Carbon (7o)

nla 5.7 17.0 38.6 38.7

OAKEY

MILLMERRAN MACALISTER nJa

nla

BRIGALOW

nJa

9.3 12.5 40.5 37.7

77.9

4.5

5.0

t7.3

t6.2

40.4

42.0 36.8

8.0 14.0 39.0 39.0

79.0 6.6

77.5 6.0 1.1 0.5

5.9 1.0 0.5

37.8

CHINCHILLA WANDOAN

TAROOM 77

6.4

10.7

7.0

tt.7

8.8 43.8

10.0

42.4 39.5

36.7

44.8 38.2

ULTIMATE ANALYSIS (dAI) 7 9.1

77.8 6.1

L.2 14.2

1.1 0.3 14.7

0.91

0.96

0.94

0.97

51.79

54.47

26.5

53.97 26.4

78.5 6.4

Nitrogen (7o) Sulphur (7o)

t.7

6.6 1.1

0.8 12.6

0.5

7.2 0.7

t2.7

t2.5

14.9

t4.7

0.98

1.00

0.93

Oxygen (Vo) H/C ATOMIC RATIO

78.0

77.9 6.2

Carbon (%) Hydrogen (7,)

0.5

6.3 1.1 0.4

t4.2

VOLATILE MATTER (7odaf) SPECIFIC ENERGY (ad)

49.94

51.66

26.3

26.5

53.30 26.7

50.0 25.7

25.8

57.77 27.6

(MJhs) ]PECIFIC ENERGY (daf)

34.02

33.89

33.88

32.18

32.99

33.70

32.92

31.81

SULPHUR (% ad)

0.56

0.3?

0.53

0.4

0.28

0.33

0.01

0.004

0.006

0.004

0.36 0.006

o.44

PHOSPHORUS (7,)

0.006

0.005

0.018

CHLORINE (7o) RELATIVE DENSITY (ad)

0.01

0.09

0.01

0.02

0.03

0.01

1.35

nla nla

HARDGROVE

1500

1490

nla

1590 1600

1600 1600

1600

1350 1560 1570 1600

1400

nla

1300 1560 1560

t3 10 1360 1370

500 510

> 1560

L440

520

'MJ/ks)

1.39

nla

1.35

nla

1.33

1.38

GRINDABILITY INDEX ASH FUSION TEMPERATURE (reducins) Deformation('C) Spherical ("C) Hemisphere ('C) Flow ('C)

1600

1600 1600

nla 1600 1600

450

ASH ANALYSIS(%) SiOz

AlzOs FezOe

TiOz MngOa CaO

Mgo NazO KzO Pzos Sos

58.1 3 0.6 3.1 2.4

57.0 29.5 2.5

0.04

0.03 4.0

60.3 29.9 2.4

69.1 24.2

1.6

0.1 2.0

0.8 0.01 0.4

1.1

1.0

0.8

0.6 0.6

0.2 0.4 0.06

0.5 0.5

t.4

2.1

56.6 28.0 4.2 1.8

1.7

0.0 3.1 2.4 1.1

1.6 1.4 0.7

56.9 34.3

52.1 29.0

47.4

1.2

3.2 1.3

3.1 1.6

2.0 0.01

0.08

0.03

1.6

0.9 0.6 0.5 0.04

1.9

7.2 0.9 1.1

0.7 0.6

0.3

0.09 0.8 0.97

0.95

2.1 0.6 0.1 3.6 0.82

26.81

41.99

23.82

23.96

25.24

18.48

19.62

1o.22

5.5

8.8

4.61

3.9

3.6

2.4

1.9

1.14

Vitrinite

4 1 0 19

66 19

Exinite Semi-inertinite

tr tr

nJa

0.54

0.48

0.49

0.40

Ignition loss/undetermined FREE QUARTZ (in ash) FREE OUARTZ coal)

0.1

0.4

0.07 1.5

0.1 1.6 0.7

1.0

0.4 0.6 3.4 7.O7

PETROGRAPHIC ANALYSIS(7o)

Inertinite Mineral

tr,

(r+

nla

MEAN MAX. REFLECTANCE

Vitrinite (Rv max.)

nla

0.41

0.47

DATA SOURCE: Principallv Queensland Coals, 7th Edition-1986, The Queensland Coal Board' Co"t.tb,ttio"" "lto f.o- C

Very little exploratory drilling has been conducted at depths below 80 to 100m, and as a consequence virtually all of the defined resources are considered to be amenable to open cut development.

C larence- Mo

reton B a sin

The major coal deposits in the Clarence-Moreton Basin occur in the Rosewood, Oakey and

Millmerran areas (Figure 2).

Rosewood Area

The Rosewood coal deposits are located in the northern portion of the Clarence-Moreton Basin, 15 to 20km west-southwest of Ipswich' Coal was discovered in the area in the mid-1860s, but the first commercial mining operation did not commence until 1881 with the opening of the Walloon Mine (Whitmore, 1985).

More collieries were opened over the years, but production was always limited to small tonnages ior local industrial users in the Brisbane-Ipswich

Geology of Australian Coal Basins

505

Teble 5. Fischer asseys of coals from selected Walloon depoSits. CLARENCE-MORETON BASIN OAI{EY MILLMERRAN

SURAT BASIN TAROOM WANDOAN

COI{E (Vo) TAR (7o) WATER (7o)

77.8

69.5

68.5

10.8 7.9

L6.2

\7.6

5.2

GAS 9o

3.5

9.1

6.7 7.2

69.2 15.0 6.4 9.4

SOURCE: Queensland Coals, 7th Edition-1986, The Queensland Coal Board. Survey of Australian Black Coals of Conversion Potential, 1st Edition (Revised)-1978, Joint Coal Board & The Queensland Coal Board. region. Annual production eventually rose above 400 000t in the decade 1954-1963, with output being won from some l0 to 15 collieries. By 1980 though, production had dropped to 150 000t. The building of modern shiploading facilities at Fisherman Islands in 1983 has provided access to overseas markets and led to a revival of the field. New open pit mines have been developed at Jeebropilly and Ebenezer, south west of Ipswich, each producing almost lMtpa of saleable coal. Small tonnages also continue to be produced from the Oakleigh open cut and underground mines just

north of Rosewood.

Cameron (1970) identified 18 nambd coal seams, or combinations of seams in the area, seventeen of which have been mined at one time or another during the 100 year history of the field. The Department of Resource Industries (1992) report measured and indicated resources of 144Mt for the Rosewood area. Oakey Area

The Walloon Coal Measures in the Oakey area subcrop in a 15 to 20km wide northwest trending

zone north of the town of Oakey. Coal was first mined in the area in 1885, when George King, a major property owner in the Toowoomba-Oakey area, opened the Gowrie Colliery close to the main western railway line some 7km southeast of Oakey (Whitmore, 1985). Other small mines were opened in the ensuing years not far from Gowrie Colliery and near Acland, some 10 to 20km north of Oakey (Mengel, 1963a, 1963b). Production was never large, and the field was in decline for many years prior to the closure of the last mine in 1984.

Exploration since 1973 has traced the Walloon Coal Measures over a 60km strike length extending from Oakey to north of Dalby (Mclean-Hodgson & Kempton, 1981). Three major coal deposits have been outlined near Acland, namely Glen Roslyn, Sabine and Manning Vale; these are known collectively as the Acland deposits. The deposits contain an aggregate 510Mt of measured and indicated resources, with average overburden to coal ratios of<5:1 (Queensland Coal Board, 1985). A potential working section of 10-12m of coal has been reported.

A fourth deposit, Ownaview, is located 10km north of Dalby. Some 112Mt of indicated resources of coal have been outlined to date, much of it at shallow depth.

Millmerran Area The presence of coal in the Millmerran area has been known from water bores since the late 1800's. It was not until the early 1970's though, when the Commodore, Bringalily and Lochbar deposits south of Millmerran were discovered, and later the Felton East and Felton West deposits east of Millmerran, that the importance of the area was appreciated Nutter & others, 1981). The aggregate measured and indicated coal resources outlined in these deposits amounts to 1408Mt (Department of Resource Industries, 1992). The bulk ofthe coal is present at depths of <60m in typically banded seams ranging from 2 to 15m in thickness. The coal resources in the Commodore deposit, located 5km south of Millmerran, occur mainly in the Commodore seam, which averages 5.6m in thickness. Two minor seams, the Top and Bottom Rider seams, are also present. The in silu ash of the coal is 367o,but much of the intercalated non-coal material can be removed by washing to provide lower ash products (Table 4).

A trial mine has been established on the deposit and a number of bulk samples of the coal removed for testing. The coal consists almost entirely of vitrinite and liptinite, and has given high yields of liquid hydrocarbons in tests ofits conversion characteristics (Table 5).

Surat Basin Major coal deposits of economic interest in the Surat Basin occur in the outcrop zone of the Walloon Sub-group along the northern and northeastern margins of the basin (Jones & Patrick, 1981). They are identified herein as the Macalister, Brigalow, Chinchilla, Wandoan and Taroom areas (Figure 3). Macalister Area The Walloon Coal Measures in the Macalister area are located approximately 45km north west of Dalby, and to the south of where a small underground mine was operated between 1914 and 1919 at Warra. Warra is situated on the Kumbarilla Ridge, on the boundary between the ClarenceMoreton and Surat Basins. Three deposits, Kogan, Braemar and Tarcoola, which are referred to collectively as the Macalister deposits, occur near the top of the coal measure sequence in the Juandah Coal Measures. The coal is contained in six seams with an average aggregate thickness of 8m. Measured and indicated resources for the deposits total 385Mt (Department of Resource fndustries, 1992). A trial mining pit has provided bulk samples of the coal for testing and

marketing.

Jurassic Basins

506

Brigalow Area The Brigalow deposit, discovered in 1969-70, is located on the western flank of the Kumbarilla Ridge, approximately 20km northwest of the Macalister deposits and 25km southeast of the town of Chinchilla. The coal occurs in the Juandah Coal Measures, and is stratigraphically equivalent to the Macalister deposits. There are two seams of economic interest, the uppermost of which attains a maximum thickness of 16m and averages iOm

over the deposit.

The coal has 28% ash ln situ, but can be beneficiated by washing to provide a l2.5Vo ash product. A trial pit has been excavated on this seam and bulk samples extracted for pilot plant washability testing and marketing purposes.

Chinchilla Area Two significant coal deposits, Sefton Park and Rywung, along with several minor deposits, are Iocated in the Juandah Coal Measures near Chinchilla. The Sefton Park deposit is located 5km south west of Chinchilla, and contains 3OMt of measured and indicated coal resources in two banded seams ranging from 1.5 to 5.8m in thickness. Much of the resource has an overburden ratio of 2 bank cubic metres per tonne. The Rywung deposit is adjacent to the main western railway approximately 15km west of Chinchilla. It contains 75Mt of measured and indicated coal resources to a depth of 60m in three banded seams with an average aggregate coal thickness of 5.5m. A further two coal deposits, namely Glen Wilga and Haystack Road, are also present in the Chinchilla area. The Glen Wilga deposit is located in the Juandah Coal Measures, 12km southeast of Chinchilla between the Sefton Park and Brigalow areas. It consists of 13 seams containing 120Mt of

A trial mining pit has been excavated on the Austinvale deposit and bulk samples extracted for research in Australia and overseas on the suitability of the coal for conversion to synthetic liquid fuels. Exploration has also outlined several coal deposits along a 20km strike length ofthe Taroom Coal Measures centred some l5km to the northeast of Wandoan. Measured and indicated coal resources totalling 115Mt have been outlined at shallow depth in the main deposit, which is known as the Collingwood deposit. Taroom Area

The Taroom deposit, discovered in 1967, was the first of the large near surface deposits of Walloon coal found west of Toowoomba. The apparent suitability of the coal for low cost open-cut mining led to an upsurge in exploration activity in the 1970s and the subsequent discovery ofother large, but as yet undeveloped, coal deposits in the western Clarence-Moreton and Surat Basins. The Taroom deposit is located in the Taroom Coal Measures, 7km south of the town of Taroom. The deposit contains two coal seams of economic interest, an upper seam with an average thickness of 5m and a lower, somewhat inferior seam containing an aggregate 2 to 3m of coal (Coxhead & Brandt, 1981). Coal resources amount to 230Mt, some 170Mt of which occur within 60m of the surface.

Evaluation of the smaller deposits in the Taroom area has outlined a further 385Mt of measured and indicated coal resource!s within 80m of the surface in the Orazabah, Boxvale, Cattle Creek, Verbeena Park, Cowangah and Elimatta Deposits.

Mulgildie Basin

measured resources with an overburden ratio of 6 bank cubic metres per tonne. The Haystack Road deposit occurs in the Taroom Coal Meaiures, 25km southeast of Chinchilla, and consists of one thick seam containing 80Mt of indicated resources at an overburden to coal ratio of<10:1.

The principal occurrence of coal in the Mulgildie Coal Measures is located south of the township of Monto. Systematic exploration of the basin began in 1969 in an area where a small mine was operated from 1949 to 1966.

Another deposit of signifrcance in the Chinchilla area is the Horse Creek deposit, which is located 25km north ofthe town. Indicated coal resources totalling 295Mt have been outlined to date in the

The distribution of the coal measures is limited by faulting and erosion to a north-south trending outlier 20km long by 5km wide. Noteworthy seam combinations have been found in four horizons in the upper part ofthe coal measure sequence

deposit.

(Wakely & McAndrew, 1983). Individual seam

Wandoan Area

Numerous coal deposits occur within a 20km radius of Wandoan. Most occur in the Juandah Coal Measures (Jones & Patrick, 1981), in a northwest to westerly trending arc from Wandoan to the axis of the Mimosa Syncline.

Exploration since the mid-1970s has located three major coal deposits in the Juandah Coal Measures , namely Austinvale (Leblang & others, 1981), Woleebee and Summer Hill, containing in total some 57OMt of measured and indicated coal resources within 80m of the surface. A further 165Mt occur at shallow depth in the neighbouring Frank Creek, Wubagul and Glen Laurel deposits. Three coal seam horizons are typically present in the deposits, with individual seams ranging from I to 6m in thickness.

thicknesses range up to 2.5m in the lowermost A horizon and 3.3m in the overlying C horizon. All seams are irregular in thickness and degree of banding, in keeping with the lenticular form typical of all Walloon coals. Measured and indicated resources are 110Mt (Allen, 1984), which are potentially amenable to open-cut mining.

Coal Quality All Walloon coals exhibit a generally uniform appearance, with little obvious bright and dull banding due to the relatively homogeneous distribution of its macerals. Apart from the ash

percentage, which increases progressively from Taroom and Wandoan in the northwest to Millmerran and Rosewood in the southeast, the physical and chemical properties ofthe coal vary little from one deposit to the next (Table 4).

Geology of Australian Coal Basins

507

Table 6. ITydroliquefaction performance of coals from selected Walloon deposits. SURAT BASIN

CLARENCE-MORETON

BASIN

OAKEY MILLMERRAN WANDOAN TAROOM COAL CONVERSION 7, BY HYDROGENATION Overall - air dried - d.y, ash free - air dried Extract

89.1 46.3

ash free

70.7 6.1 9.3

Gas

58.4

:- lila?i"l*"" dry,

Insoluble Matter -

air dried x

4I.6

ash free

10.9

DISTILLATION OF EXTRACT 4OO'C Oil7o - air dried - dry, ash free Residue 7o - air dried - dty, ash free ITYDROGEN CONSUMPTION g/100g COAL Air dried Dry, ash free COAL EXTRACT CHARACTERISTICS Ash 7o - air dried Gross Specific Energy (MJ/kg) - dry, ash free Carbon Vo Hydrogen 7o - dry, ash free - dry, ash free Nitrogen % - dry, ash free Sulphur 7o Oxygen 7o - dry, ash free Hydrogen: Carbon Ratio Relative Density (25'C) CHARACTERISTICS OF OIL DISTILLING

71.0 92.0 64.0 83.0 7.0 9.0 29.0 8.0

90.0

69.0

73.0 93.0 66.0 84.0

7.0

13.0

9.0 27.0

10.0

7.0

30.0 38.0 36.0 46.0

22.5 34.4 35.8

35.0

46.O

33.0

29.O

54.7

37.0

36.0

0.52 0.80

0.82

1.36

1.06

* 2.00

0.50 36.67 85.76 0.96 0.27 5.22

0.20 39.45 87.50 7.96 0.80 0.20 3.60

0.40 40.o2 85.10 8.52 0.51 0.06 5.81

0.20 39.98 87.13 7.94 0.28

1.09 1.15

1.09 1.08

1.20 1.09

Gross Specifrc Energy (MJ/kg) Carbon 7o - dry, ash free

dry, ash free Nitrogen 7o dry, ash free Sulphur 7o dry, ash free Oxygen Vo dry, ash free Hydrogen: Carbon Ratio Relative Density (25" C) Kinematic Viscosity at 50"C (mm]/sec.) Kinematic Viscosity at 90'C (mm2/sec.) CHARACTERISTICS OF RESIDUE FROM DISTILLATION AT 4OO'C Water - air dried Lsh Vo - air dried Gross Specific Energy (MJ/kg) - dry, ash free Carbon 7o - dry, ash free Hydrogen 7o - dry, ash free Nitrogen 7o - dry, ash free Sulphur 7o Oxygen Vo - dry, ash free Hydrogen: Carbon Ratio Relative Density (25" C)

40.30 87.00 8.65 0.50 0.20 3.70

41.50 87.80 9.89 0.31 0.40

7.79

t.73

0.t2 4.53 1.09

0.97

AT <400'C Hydrogen 7o

* 1.39 1.00

* *<

1.19

1.00 5.32 2.20

0.30 0.60 37.04 87.60 6.59

1.96 1.35 1.01 t<

L.52

r.40

0.4I

0.30 4.10 0.90

0.70 35.04 91.50 7.L9 0.80 0.20 0.30 0.94

1. 13

1..20

1.90 ,<

87.66 6.43 3.98 0.88

t.t7

SOURCE:Queensland Coals, 7th Edition-1986, The Queensland Coal Board. x Includes moisture

* Data not available

Jurassic Basins

40.83 83.98 9.42 0.60 0.10 5.90 1.35

0.99 13.10

4.10

* 0.80 38.95 87.50 6.79 1.20

0.10 4.40 0.93 L.20

508

It is expected that selective mining of the coal in the Walloon seams will produce a raw coal product

Walloon coals contain characteristically high proportions (70-L007o) of vitrinite and liptinite, which give rise to their distinctive high volatile matter (> 50Vo da0 and perhydrous composition (> 6Vohydrogen, dafl. The unique hardness (HGI < 40) and the conchoidal fracture of the coals are a reflection of the high liptinite content (up to 20Vo), especially the high proportion of suberinite which originally formed the tough and fibrous

with ash in the range 28 to 367o for the ClarenceMoreton Basin deposits and 21 to 28Vo for the Surat Basin deposits. The latter values are similar to the ash percentages ofother coals now being burned for power generation in Queensland.

Several trends are evident in the coal analyses shown in Table 4 which suggest that the depositional environment became progressively more favourable in a westerly direction for peat accumulation, resulting in the development of comparatively thicker and cleaner coal seams in the Taroom-Wandoan area. For example, the reduction in the incidence of non-coal material in the seams from east to west across the Clarence-Moreton and Surat Basins is reflected in the inherent ash ofthe coals; petrographic analyses show mineral matter contents ranging from L97o at Rosewood to 7Vo at Taroom. Proximate analysis of the washed products at 1.60RD also show a reduction in ash percentage to the west.

The low sulphur and nitrogen contents of Walloon coal suggest that SO* and NO* emissions are likely to be within tolerances set by environmental

parts of the source plant material.

A similar trend is evident in the proportion of free quartz in the coal ash, which reduces from 26.8Vo at Rosewood to 19.6Vo at Wandoan. An antithetic increase from east to west in the calcium and magnesium oxide contents of the ash from3.!7o at Rosewood to 8.17o at Taroom suggests that the occurrence of each may be due to the relative distance ofthe deposits from the source of the detrital rock material. The sulphur content of Walloon coals is typically low (0.3 to 0.8Vo daf) in keeping with a freshwatLr paludal environment of deposition.

Coal Utilisation The increase in the production of Walloon coal in recent years has been largely, though not entirely due to overseas buyer interest following the installation of modern shiploading facilities at the rnouth of the Brisbane River. The coal is frnding favour with the operators of small industrial scale stoker-fired boilers, because of its good ignition and

Studies of the washing characteristics of the coal suggest that satisfactory yields of lower ash coal suitable for export can be readily achieved, with the best results expected from the Surat Basin deposits. The incidence of montmorillonitic clay bands in the seams of the Clarence-Moreton Basin could, however, have an impact on wash plant performance for coals from these deposits.

protection agencies where flue gas desulphurisation and nitrogen oxide control are not mandatory. Precipitation tests by Paulson & Kahane (1978) indicate that fly ash can be controlled by conventional electrostatic precipitators. The low rank (Rvma*= 0.\Vo), high moisture and high reactivity of Walloon coal suggests that it may be susceptible to spontaneous combustion, although this has not been found to be the case in practice. Indeed, laboratory tests aimed at forecasting spontaneous combustion give readings which are better than other coals that are already being stockpiled and transported successfully. As well as its very good combustion characteristics, extensive tests in Australia, West Germany, the USA and Japan have confirmed that Walloon coals have excellent potential as feedstock for conversion to solvent-refined coal and synthetic liquid fuels. This is also due to the highiy reactive nature of the coal, its maceral composition and volatile matter content. Table 5 gives evidence of the high yields of tar that can be produced by pyrolysis of Walloon coals.

burnout characteristics. The comparatively low generation of fines due to the hardness of the coal is also a positive factor with these boilers.

Walloon coal also performs particularly well in direct liquefaction processes, which typically require coal of a more rigorous specification for success. In this respect, the perhydrous composition (H >57o daf), high vitrinite and liptinite contents, the high volatile matter content, and the rank of the coal are important factors.

Ironically, the hardness of the coal (HGI < 40) and its adverse affect on milling costs is a factor preventing sales to the large power utilities, the major users of coal, which operate pulverised fuel

The very large tonnages ofnear surface coal which are amenable to low cost open cut mining, and which can be readily beneficiated to acceptable ash levels are also important considerations in

boilers.

Notwithstanding this, Walloon coals have been burnt successfully in pulverised fuel boilers at the Swanbank (near Ipswich) and Koolkhan (near Grafton) power stations, and the coals are regarded favourably by Queensland Electricity Commission as a future source of low cost coal for regional power generation. It is possible that the very good combustion characteristics imparted by the maceral composition and high volatile matter content of Walloon coals may allow a coarser grind to be used in pulverised fuel boilers, thereby avoiding the added costs ofincreased power consumption and reduced mill capacity.

contemplating the coal-to-oil potential of the Clarence-Moreton and Surat Basin deposits. Table 6 gives details ofthe hydroliquefaction performance of some of these Walloon coals.

REFERENCES ALLEN, G.E., 1984: Audit of Monto coal resources. Brigalow Mines Pty Limited, Brisbane. ALLEN, R.J., STAINES, H.R.E. & WILSON, E.G., 1,960: The Ipswich Basin. /n Hill, D. & Denmead, A.K. (Editors): The Geology of Queensland . Journal of the Geological Society of Australia, 7, 252-262.

Geology of Australian Coal Basins

509 AMBROSE, G., SUTTILL, R. & LAVERING,I., 1982: A review of the Early Cretaceous Murta Member in the southern Eromanga Basin. In Moore, P.S. & Mount, T.J. (Compilers): Eromanga Basin Symposium - sunxmary pdpers. Geological Society of Australia and Petroleum Exploration Society of Australia, Adelaide, 92-109.

DAY, R.W., WHITAKER,W.G., MURRAY, C.G.,

WILSON, I.H., & GRIMES, K.G., 1983:

Queensland geology: a companion volume to the 1:2 500 000 scale geological map (1975). Geological Suruey of Queensland. Publication, 383, 123-132.

DE JERSEY, N.J., 1959: Jurassic spores and pollen

ANON, 1985: Eromanga Basin lithostratigraphic nomenclature. Queensland Gouernment Mining

Journal,86, 446.

grains from the Rosewood Coalfield. Queensland Gouernment Mining Journal, 60, 346-366.

DE JERSEY, N.J., 1960. Spore Distribution and

ARMSTRONG, J.D. & BARR, T.M., 1982: ThC Eromanga Basin. In Moore, P.S. & Mount, T.J. (Compilers): Eromanga Basin Symposium summary papers. Geological Society of Australia and Petroleum Exploration Society of Australia,

Adelaide, 20-42. CAMERON, J.8., 1970: The Rosewood-Walloon Coalfield. Geological Suruey of Queensland Publication, 344. COOK, A.C., 1986: The nature and significance of the

organic facies in the Eromanga Basin. In Gravestock, D.I., Moore, P.S. & Pitt, G.M. (Editors): Contributions to the geology and hydrocarbon potential of the Eromanga Basin, Geological Society of Australia Special Publication, 12, 203-219.

COXHEAD, B.A. & BRANDT, 8.A., L981: Notes on the Taroom coal deposit and the possible utilisation ofits coal. CoaI Geology, 1(4), 179-183.

CRANFIELD, L.C. & SCHWARZBOCK, H., 1972: Nomenclature of some Mesozoic rocks in the Brisbane and Ipswich areas, Queensland. Queensland Gouernment Mining Journal, 73,

4t4-4L6.

CRANFIELD, L.C. & SCHWARZBOCK, H., 1976: Nambour Basin. 1n Leslie, R.B., Evans, H.J. & Knight, C.L. (Editors): Economic Geology of Australia and Papua New Guinea: 3

Petroleum. Australasian Institute of Mining and

Metallurgy, Monograph, 7, 450-452. DAVID, T.W.E. (Browne, W.R. Editor), 1950: Geology of the Commonwealth of Australia. E. Arnold, London.

Correlation in the Rosewood Coalfield. Geological Suruey of Queensland Publication, 295.

DEPARTMENT OF RESOURCE INDUSTRIES, 1992: Queensland Resources of Black Coal. Queensland Gouernrnent Mining Journal, 93, 13-19. ETHERIDGE, L.T., HAMILTON, D.S., MCDONALD, I., MCMINN, A. & SMYTH, M., 1985: Clarence-Moreton Basin stratigraphic drill hole. Geological Suruey of New South Wales, Quarterly Notes,60, 5-22. EXON, N.F., 1976: Geology of the Surat Basin in Queensland. Bureau of Mineral Resources, Australia Bulletin, 166. EXON, N.F., 1980: The stratigraphy of the Surat Basin, with special reference to coal deposits. Coal Geology, 1(3), 57-69. EXON, N.F. & BURGER, D., 1981: Sedimentary cycles in the Surat Basin and global changes of sea level. BMR Journal of Australian Geology and Geophy sics, 6, 153-159. GOULD, R.E., 1975: The succession of Australian pre-Tertiary megafossil floras. The Botanical Reuiew, 41(4), 466-468. GOULD, R.E., 1980: The coal-forming flora of the Walloon Coal Measures. Coal Geology, !(3), 83-105. GRAY, A.R.G., 1972: Departmental stratigraphic core drilling its scientifrc significance & value in - exploration. Queensland Department petroleum of Mines Record 7972/20. GRAY, A.R.G., 1975a: Bundamba Group: stratigraphic relationship and petroleum prospects. Queensland Gouernment Mining Journal, 76, 310*324.

DAY, R.W., 1964: Stratigraphy of the RomaWallumbilla area. Geological Suruey of Queensland Publication, 3L8. DAY, R.W., 1966: Lower Cretaceous macrofossils from the Tambo and Augathella 1:250,000 Sheet areas. Bureau of Mineral Resources, Australia, Record 1966/89, Appendix 1. DAY, R.W., 1967: A mixed Roma-Tambo fauna from the Tambo area. Queensland Gouernrnent Mining

Journal,68,10-12.

DAY, R.W., CRANFIELD, L.C. & SCHWARZBOCK, H., 1974: Stratigraphy and structural setting of Mesozoic basins in southeastern Queensland and northeastern New South Wales. .In Denmead, A.K., Tweedale, G.W. & Wilson, A.F. (Editors): The Tasman Geosyncline: a Symposium. Geological Society of Australia, Queensland Division, 319-363. DAY, R.W. & PRICE, P.L., 1986: Sunshine coast field excursion notes. Petroleum Exploration Society of Australia, Queensland Division.

GRAY, A.R.G., 1975b: Eromanga Basin. In Traves, D.M. & King, D. (Editors): Economic Geology of Coal. Australia and Papua New Guinea:2 Australasian Institute of Mining and -Metallurgy Monograph,6, 310-312.

HAWKE, J.M. & BOURKE, D.J., 1,984: Stratigraphy.ln Hawke, J.M. & Cramsie, J.N. (Editors): Contributions to the geology ofthe Great Australian Basin in New South Wales, Geological Suruey of New South Wales Bulletin, 31.

HOUSTON, B.R., 1965a: New and revised stratigraphic names in Queensland stratigraphy: the city of Brisbane. Queensland Gouernment Mining

Journal, 66, 22I-227

HOUSTON, B.R., 1965b: A geological map of the city of Brisbane. Geological Suruey of Queensland Publication, 323.

Jurassic Basins

510 JOINT COAL BOARD AND QUEENSLAND COAL BOARD, I978: Suruey of Australian Black Coals of Conuersion Potential. Joint Coal Board and Queensland Coal Board. JENSEN, H.I., 1926: Geological reconnaissance between Roma, Springsure, Tambo and Taroom. Geological Suruey of Queensland Publication, 277, 215. JOHN, 8.H., 1985: Stratigraphic drilling report, GSQ Wyandra 1 and GSQ Quilpie l. Queensland Gouernment Mining Journal,86, 37.

JONES, G.D. & PATRICK, R.B., 1981: Stratigraphy and coal exploration geology ofthe northeastern Surat Basin. Coal Geology, t(4), 153-163.

KENNY, E.J., 1964: Geological survey of the

Coonabarabran-Gunnedah district with special reference to the occurrence of subsurface water. Geological Suruey of New South Wales, Mineral

Resources,4O.

KORSCH, R.J., O'BRIEN, P.E., SEXTON, M.J., WAKE-DYSTER, K.D. & WELLS, A.T., 1989: Development of Mesozoic transtensional basins in easternmost Australia. Australian Journal of Earth Sciences, 36, 13-28.

LEBLANG, G.M., RAYMENT, P.A. & SMYTH, M., 1981: The Austinvale coal deposit, Wandoan: a palaeoenvironmental analysis. Coal Geology, 1(4), 185-195. McELROY, C.T., 1969: The Clarence-Moreton Basin. In Packham, G.H. (Editor): The Geology of New South Wales, Journal of the Geological Society of Australia, 16( 1), 457 -47 5. McLEAN-HODGSON, J. & KEMPTON, N.H., 1981: The Oakey-Dalby region, Darling Downs Coalfield: stratigraphy and depositional environments. CoaI Geology, L(4), 165-L77 . McTAGGART, N.R., 1963: The Mesozoic sequence of the Lockyer-Marburg area, southeast Queensland. Proceedings of the Royal Society of Queensland, 73, 93-104.

MENGEL, D.C., 1963a: Coal resources, Darling Downs (Oakey) Coalfield: Part 1- Balgowan Mine area; Part 2 Acland Mine area. Geological Suruey -of Queensland Publication, 314.

MENGEL, D.C., 1963b: Coal resources, Darling Downs (Oakey) Coalfield: Part 3 - Sugarloaf mine area; Part 4 - Willeroo Mine area. Geological Suruey of Queensland Publication, 315.

MOORE, P.S., 1986: An Exploration Overview of the Eromanga Basin. 1n Gravestock, D.I., Moore P.S. & Pitt, G.M. (Editors): Contributions to the Geology and Hydrocarbon Potential ofthe Eromanga Basin. Geological Society of Australia Special Publication, 12, 39-51. MOORE, P.S., HOBDAY, D.K., MAI, H, & SUN,2.C., 1986: Comparison of selected non-marine petroleum-bearing basins in Australia and China. The APEA Journal,26(1), 285-309.

MOORE, P.S. & PITT, G.M., 1985: Cretaceous subsurface stratigraphy of the southwestern Eromanga Basin. In Lindsay, J.M. (Editor): Stratigraphy, Palaeontology, Malacology: papers in honour ofDr Nell Ludbrook. Soufh Australian Department of Mines and Energy, Special Publication, 5, 269-286.

NUTTER, A,H,, THRIFT, J.A. & DAY, G.R., 1981: Geology and coal resources of the MillmerranToowoomba-Warwick region of southeast Queensland . Coal Geology, l(4), 143-152.

PATON, I.M., 1986: The Birkhead Formation: a Jurassic petroleum reservoir. In Gravestock, D.I., Moore, P.S. & Pitt, G.M. (Editors): Contributions to the geology and hydrocarbon potential of the Eromanga Basin, Geological Society of Australia Special Publication,12, 195-201. PAULSON, C.A.J. & KAHANE, R.B,, 1978: Technical-scale tests ofthe efficiency of

electrostatic precipitation ofthe fly ash from a sample of Wandoan seam coal under pulverised coal-fired combustion conditions. CSIRO Minerals Research Laboratories, Restricted Investigation Report 938R.

PRICE, P.L., FILATOFF, J., WILLIAMS, A.J., PICKERING, S.A. & WOOD, G.R., 1985: Late Palaeozoic and Mesozoic palynostratigraphical units. CSR Oil and Gas Division, Palynology Facility, Report 27 4/25.

QUEENSLAND COAL BOARD, L986: Annual Report, 1985-86. Queensland Coal Board, Brisbane, 56. REEVES, F., 1947: Geology of the Roma district, Queensland . Bulletin Arnerican Association Petroleum Geologists, 31 (8), 1341-1371. SENIOR, B.R., MOND, A. & HARRISON, P.L., 1978: Geology of the Eromanga Basin. Bureau of

Mineral Resources, Australia Bulletin, 767, 54-55.

SMART, J. & SENIOR, B.R., 1980: JurassicCretaceous basins of northeastern Australia. In Henderson, R.A. & Stephenson, P.J. (Editors): The Geology and Geophysics of Northeastern Australia. Geological Society of Australia, Queensland Division, Brisbane, 315-328. STEVENS, G.R., 1971: Relationship of isotopic temperatures and faunal realms to JurassicCretaceous palaeogeography, particularly of the south-west Pacifrc. Journal of the Royal Society of New Zealand, l, 145-158. SVENSON, D. & RAYMENT, P.A., 1975: Mulgildie Basin, Queensland..In Traves, D.M. & King, D. (Editors): Economic Geology of Australia and Papua New Guinea: 2 - Coal, Australasian Institute of Mining and Metallurgy, Monograph, 6, 318-320. SWARBRICK, C.F.J., 1973: Stratigraphy and economic potential ofthe Injune Creek Group in the Surat Basin. Geological Suruey of Queensland Report, 79.

SWINDON, V.F., 1956: The geology of the Rosewood-Wivenhoe area, with particular reference to the sandstones. B.Sc. (Hons) thesis,

Department of Geology, University of Queensland.

Geology of Australian Coal Basins

511 SWINDON, V.G., 1960: Marburg Sandstone of the type area. Journal of the Geological Society of Australia, 7 , 288-29L.

VINE, R.R. & DAY, R.W., 1965: Nomenclature of the Rolling Downs Group, northern Eromanga Basin. Queensland Gouernment Mining J ournal, 66, 4L6-421.

WAKELY,I. & McANDREW, M.R., 1983: AP303C exploration progress report for the six months ended J.1th June, 1983. Brigalow Mines Pty Limited, Brisbane. WELLS, A.T. & O'BRIEN, P.E., 1994: The Geology and Petroleum Potential of the Clarence- Moreton Basin, New South Wales and Queensland. AGSO

Bulletin,24l.

WELLS, A.T., O'BRIEN, P.E,, WILLIS, I.L. & CRANFIELD, L.C., 1990: A new lithostratigraphic framework for the Early Jurassic units in the Bundamba Group, Clarence-Moreton Basin, Queensland and New South Wales. BMR Journal of Australian Geology & Geophysics, tL,397-414.

WHITE, M.E., 1974: Plant fossils from the Gilbert River and Winton Formations and the Pascoe River area, Queensland. Bureau of Mineral Resources, Australia, Record L97 41I59. WHITMORE, R.L., L985: Coal in Queensland: the late Nineteenth Century. University of Queensland Press, 228-245.

Jurassic Basins

513

fueigh Creek Coalfield

GM Springbett AG Kremor and SH Brennan

The Leigh Creek coalfield is located in central South Australia approximately 55Okm north of Adelaide (Figure f ). The field consists of four small isolated Triissic basins spread over a distance of 20km, referred to as the Copley Basin (Lobe A), the Telford Basin (Lobe B) and the North Field (Lobes C and D) from south to north respectively. Coal was discovered in the area during the construction of a railway dam at Copley in 1888. Open cut mining commenced in the Telford Basin in 1943 and, although subsequently undertaken in Lobes C and D as well, is now restricted to this basin (Lobe B) alone, where over 2Mt of coal are produced annually. The coal is classified as lignite A to sub-bituminous C under the ASTM system; it provides fuel for power generation in two majqr ioal-fired stations at Port Augusta 25Okm to the south.

GEOLOGICAL SETTING The structural framework of South Australia is dominated by northeast to northwest trending faults and lineaments, which controlled basin development in the central and northern parts of the State. The major tectonic elements of central eastern South

Australia (Figure 1) include the crystalline Proterozoie to early Palaeozoic Adelaide Fold Belt. To the north, however, is a depositional area which received sedimentation from the late Palaeozoic onwards. Major depositional basins represented in this area are the Permian to Triassic Poolowanna Trough and Cooper Basin, the Jurassic to Cretaceous Eromanga Basin and the Tertiary to Quaternary Lake Eyre Basin.

The coal-bearing sediments of the Leigh Creek area unconformably overlie rocks of the Adelaide Fold Belt (Figures 1 and 2) and are of Late Triassic and Early Jurassic age. The full sequence, however, ispresent only in the Telford Basin. The Leigh Creek occurrences are isolated from sediments of equivalent age elsewhere in South Australia, including those of the Springfreld and Boolcunda Basins to the south and several other basins to the north (Figures l. and 3). The tectonic regimes which affected the region are indicated in Figure 3. Tectonic control of South Australia in the Late Triassic was related to a compressive stress field (Austin & Williams, 1978) or to isostatic rebound following compression

(Wopfner, 1985).

The Late Triassic of the region is characterised by fluvio-lacustrine sedimentation, and coal formation took place in all of the Triassic basins to a greater or lessei extent. A rift system signalled its impending development in the Late Triassic to Early Jurassic as a pie-rift swell along the southern margin of the

continent. This resulted in isostatic sag in the area of the Eromanga Basin, and the development of a rift shoulder in the northern part of the Adelaide Fold Belt where the Leigh Creek basins occur (Wopfner, 1985). This movement terminated Triassic sedimentation in the Leigh Creek area, and confined sedimentation in the Eromanga Basin to the area northeast of the Lake Eyre Lineament (Forbes, 1986). Sedimentation recommenced in the Leigh Creek basins and the Eromanga Basin in the Early Jurassic (Figure 3), a depositional event that was relatively short in the Leigh Creek area but continued until the end of the Early Cretaceous in the Eromanga Basin.

Leigh Creek Coalfield

5t4

Figure 1. Locality plan and regional geological setting, eastern South Australia.

Geology of Australian Coal Basins

515

QUATERNARY Alluvium

r:___1

--l

conglomc,otcr. gro"ctr, <toyr JURASSTC

sondrton' *ilh ploot rGmo,n!-

Cool -corurcr, <ool r.omr-

cAlrlBRlAN

WII,PTNA GROUP

- - -ffi

9oD<l

- -- -Ei

AroonoCrccltim"rronclrty Lrcrr ro.hotron pu.Dr.gr..n ihorcr _ Aior limutonc

-l

- - - -lW|

TRtASSIC

AOELAIDEAN

UMBER^TAN^ GROUP '. iji:::.:::::;

ff-Tl -l -

I YUON^MUIANA SUS.GTOUP

ffi l-rt+l

a>a { >a

IUNRA GIOUP

Di+. !,.ccio-------ffi fqult--

--./

Figure 2. Bedrock geology of the Leigh Creek area.

Leigh Creek Coalfield

:.o. O.c

516 PALYNO -

STA6T

A6E

TITHONIAN F

L06 IIAL TIME ZON6 Dnira olnl 'A( PK1

PJ6

l(.1

J o o =

c d

TAL LOV I AN BATHON IAN

Porker '8?

rt/ l4oore '86) E (

SPRINGFIELD AND BOOLCUNDA BASIT'IS

NORIAN

Em{4}'16A

EROI{AISA

EAStl,r

BASIN

5.2

PT5

tttt

5.1

=*i

[rS-. 4.7

tl 1

CARNIAN

csi

-l'

8AS

HIA US

-o t

pTt

ANISIAN

PI 2 J &

TONIC STATE

Wopfner '85 )

PJ2

LADIN IA N

OVERALL TEC-

SINEI-4URIAN

(

Itz t'1

PJ4

RHAET I AN

.OOPER BASIN AREA Moore ond [ostro'8/.

PJ3

HETTAN6 IAN

U F

TROU6H AREA

PJ5

BAJOCIAN

PLIENSBAC HIAN

POOLOWANNA

(Lobes A.B,C,0)

KIMHERID6E OXFORDIAN

L EI6H CREEK AREA

2.2

SCYTHIAN

PT1

Figure 3. Regional Triassic and Jurassic correlation for eastern South Australia.

The Late Jurassic to Early Cretaceous saw

downwarping of the Eromanga Basin, with contemporaneous faulting and uplift of the rift shoulder resulting in a marine incursion west and southwest of the Lake Eyre Lineament (Wopfner, 1985). Late Jurassic sediments occur unconformably above the Triassic in the Copley Basin (Figure 2), and Late Jurassic to Cretaceous marine and terrestrial sediments are also preserved in the sub-surface, west of the Norwest Fault, as far south as Leigh Creek (Kremor, 1987). A compressional stress regime was initiated in the Mid-Cretaceous, reaching a climax in the Late Oligocene to Early Miocene. At this time the rocks of the Adelaide Fold Belt were uplifted to form the Flinders Ranges (Ludbrook, 1980). The Late Triassic sediments of the Leigh Creek Coalfield are preserved within this uplifted Adelaidean block.

STRATIGRAPHY AND STRUCTURE OF THE LEIGH CREEK BASINS The four basins which comprise the Leigh Creek coalfield (Figures 2 and 4) vary considerably in size

and sediment thickness, but have a number of

characteristic features which relate to basin form and structure, sediment type and subcrop pattern. The sediments occur in small, elliptically shaped basins directly overlying the Adelaidean rocks, with dips in each directed towards the basin centre. Consequently, the full sequence subcrops form a pattern closely paralleling the basin shape. Grey carbonaceous mudstones are dominant or abundant in each basin, and are commonly interbedded with hard sideritic bands up to 0.5m thick. Coal, sandstone, pebbly sandstone and siltstone are also present. Plant remains are common throughout the sequence, while megafossils of the freshwater unionid lamellibranchs Unio eyrensis and Protouirgus jaenshi and remnants of the fish Leighiscus hillsi have also been recognised (Playford & Dettmann, 1965).

Iompressr on

+€

The sediments span the Carnian to Sinemurian Stages, with the major coal-bearing units being in the Carnian and Norian (Figure 3). Using the nomenclature of Price & others (1982), three biostratigraphic units are recognised (PT4.L, PT4.2 and PJ1), all of which are present in the Telford Basin (Figure 4). The Copley Basin includes PT4.2 while the PT4.1 unit has been recognised in the

North Field (Parker, 1987).

The coal measure sequence is generally blanketed by up to 10m ofQuaternary clay, sand, gravel and conglomerate. Flat lying sandstone, probable of Late Jurassic age, also partially overlies the sequence in the Copley Basin.

Copley Basin (Lobe A) The Copley Basin is a simple asymmetric northsouth trending basin measuring approximately 2.3km by 1.6km. It contains up to 300m of sediment, with bedding directed radially inward at between 10o and 40o. Coal occurs in two zones, and in the east the principal coal seam is thought to be dislocated by normal faulting (Johns & Townsend, 1975).

The lower portion of the sequence consists of 150m of mudstone with minor amounts of sandstone and coal. The informally-named "Lower Caal Zone"

occurs at the top of this sequence. It is then overlain

by up to 75m or strata consisting predominantly of sandstone with some siltstone and coal. The sandstone of this sequence is thickest in the centre of the basin, with siftstone and coal more common towards the margins. The interval referred to as the "IJpper Coal Zone" occurs within these sediments. They are then overlain by a further 75m of mudstone with minor sandstone and sporadic thin coal beds.

The Copley Basin shows the poorest coal seam development of the four Leigh Creek basins. The "Lower Coal Zone" contains the principal seam,

Geology of Australian Coal Basins

5{UTH

F:-l

H # i(-4) H 4;ail

erE= dodo 9Z

TF JET :I ;I E3 E EI FJ - Ss.

IFA

L E6EN D F

o STRATI6RAPHII IOLUMNS

IROSS SECTION

6 q

El td s"o* 9 a

ff El

Mudtton"

J F- s'tt'ron' IlL1L= e : I f;lHorn se,;es Ff, F:ll sonostom EI @ I Hl--'*.r ser,es ffi orover -// \\-_'/// 5_ Eiostrotigrophic

e 3 !: q

Nl Aosin Sediments includirg mudstone, cml, sordstone

ond siltstone

G F

6 6--1 Bosemnl uith sordstone,

B Fl1 sittstone,shole ond limeston€ I!

F ffi Diopirtc l,,torerrot

zone ts I Figure 4. Cross-section, schematic stratigraphic columns and correlation Leigh Creek Coalfields.

which ranges from 1.5 to 6m in thickness. One or two thin partings <0.5m thick are also generally present within this seam. The "IJpper Coal Zone", a further 15 to 20m up the sequence, contains up to 6 thin seams over an interval of 10 to 20m, but individual seams in this part of the section rarely exceed 1m in thickness.

Telford Basin (Lobe B) The Telford Basin is the largest of the four basins at Leigh Creek. It contains approximately 1000m of predominantly fine grained sediments (Figure 5), and covers a northwest to southeast trending elliptical shaped area some 7.5 by 4.5km in size. Coal occurs in three zones within the basin-fill sequence, informally referred to as the "Lower",

"Main" and "Upper Series" in ascending stratigraphic order (Figure 5).

Sedimentary Sequence The sequence in the Telford Basin is dominated by mudstones, particularly in the lower two-thirds of the basin frll (Figure 5). The oldest Triassic sediments unconformably overlie the Adelaidean basement, and consist of up to 50m of mudstone with minor interbeds of siltstone and sandstone and a thin basal pebbly sandstone. The sediments of the "Lower Series" occur above this interval, and include approximately 65m of mudstone interbedded with coal and occasional fine grained sandstone. The "Lower Series" and the "Main Series" are separated by between 50 and 115m of mudstone, above which the "Main Series" is represented by a zotte, consisting of coal, up to 20m in thickness. The interval between the "Main Series" and the "lJpper Series" varies from 650m thick in the northeast to <200m thick in the southwest. The coal zone ofthe "Upper Series" contains interbedded mudstone, siltstone and coal, with rninor fine

grained sandstone, and attains a maximum thickness of approximately 100m. Similar trends are developed to those in the "Main Series", with the coal and clastic sediments of the "IJpper Series" thickening to the northeast. A sequence up to 150m thick, made up predominantly of sandstone with some siltstone and mudstone and minor thin coal, overlies the "IJpper Series" coal zone. The Triassic to Jurassic unconformity occurs in this interval (Parker, 1987), with the overlying Jurassic represented by some 200m of interbedded mudstone, siltstone, fine grained sandstone containing thin hard sideritic bands.

Structure The Telford Basin is an asymmetrical elliptical basin, with beds dipping towards the structural centre. The northern, northeastern and eastern boundaries have an erosional contact with the underlying basement, and the Triassic beds display relatively low dip angles of 15 to 25o (Figure 4). Steeper dips, with angles up to 50o, are encountered in the basal sediments near the southern and western boundaries, but the upper parts ofthe sequence in this area ("IJpper Series" sediments) still retain more gentle dips of approximately 20o. The coal sequences and associated sediments of the Main and Lower Series are dislocated by numerous faults. Three dominant fault systems have been identified by Bogacz (1986) (Figure 6). These include:

i) complementary conjugate faults; ii) peripheral faults (longitudinal normal-slip faults);

iii) northeast to southwest trending tensional faults (conjugate normal-slip structures).

Leigh Creek Coalfield

5r8

THTTKNES'

A6E/

l'o I

TRENos lsrnlrl

STA6E

NE luxtts

sL/ -

0UATERNARY -r--

oo^0r,,

0EstRtPTt0x ANt) ENVIRONIIENTS OF OEPOSITION

Lo6

Ave. 5 m

Alluvlal ptrln grrvct,srnd,sllt&ctay.lnciudlng

[onlrlns scvcrrt lcnsrs of brovn flnt to vcry flnr gralncd srndstont vlth rbundant sllty hnlnatlons.

'-q -t!J d6!

<< o urC li Irn

Tetford 6ravcL

UPPER SERI€S 0VERBUR0Eil llght to dark grey,sltty mudstone-

0:posltrd ln hrurtrlnr/lloodpbln rnvlronnrnt vllh (r!v.ssr sphy :rndrtonr trffstona.

< 200m

Four najor upvards flnlng sequen(.s. Whtn tntlrely preserved lhay cornprlsa (froor top to bottom): 1.i thln,frlable coal scaets vlth abundant ctay Iamlna]ions. 2.) [anrlnaied,sllty,rarbonattous nudstonc. 3.1 flnc Aralncd lamlnattd silty sandstont-

4.) flnc io ntdlum gralned.quariz sandstont,often displaying

ooss bcddlng.

Iontacts rrc ArrdrtlonaL

100m - 150m

Deposltcd ln braldcd & neandcrlng fluvlat cnvlronncnts-

td G.

60m- 100m

UPPER SERIES C0AL ZONE : (Scrns 0,F,6.H,|,J,XIJoal scams tn-leiEii?i7T jTfr -iigfr Tgay,--sltty.nrudstoncs&orangctobronn,

slliy quartz sandslonts ln sonr ptrtcs. 0eposltrd h ftoodptrln pcri svraps & lalcs-

= J O

tlt U V)

6 :o

E, 'e F UU

=--rttlr:r :-=A-

@ o J

rudsfonas llAlN SERIES OVERBURDEN:0ark orrr to slltlt'hard bands"tnTlr6Eldadl-vtiF r!rF5loffi' to griy itdertttc 0eposltcd ln a trcustrlnc tnvlronncnt.

200m-650m

,t) cO

-<EUt

-Z_-_=4

O E O

LL J UJ F

t'lAlil SERIES t0AL Z0NE: (Scaa O) [oal & somc mudsione

5m -20m

p-a;Ttngs.

: Gray sltty nudstone,lnterbedded 0 s r a ysill y,s d c il t c " hi r d b a r s "-

L0WER SERIES 0VERBUROEX v l-ifi

50m - 115m

lA:5r

o v n

-T

Rarc lcnscs of oranga io brovn,very flnr gralned,quartz sandstone.

l}cposlted ln ftoodptaln & lacustrlnr envlronment. L0WER SERIIS COAL ZONI: (Stams V,W) loat vlth dark gray.

sliTfTfilToric l-JiFtn-liltrv ertlas a mu ds t on! sequ en ce v it h somt

25m- 120m

slttstone,sandstone

& gravelly sandstone-

0cposlied ln [aeustrlna/floodptaln envlronrnent vlth trevassc splay sandstonc & slltstonc. oo NU o= d,o UO FE o &, o-

BASEI1ENT: Anberoonr Fn,Batcanoona Fn,Taplcy Hll[ Fm.

St-iTrto-;il [mcstonc.

Figure 5. Stratigraphic column of the Telford Basin.

Geology of Australian Coal Basins

519

DOMINANT FAULT RELATIONSHIPS LOBE-B

o6ooT

B nP x f{ +[ of 'F

Bedding Peripheral faults Faults parallelto bedding Faults inclined to bedding Tensional laults

LOWER HEMISPHERE STEREO NET PROJECTION

COM PLEM ENTARY CONJ UGATE FAU LTS

Bedding

Homothetic fault

A Antithetic fault

6 Stress axes BRITTLE

DEFORMATION PLASTIC DEFORMATION DOMINANT JOINT AND BEDDING DEFECT RELATIONSHIPS LOBE.B N

7 TT

*$ DT

A A

Bedding defects Cathetal joints

L Normal slip joints and shear

cleavage of normal slip character

LOWER HEMISPHERE STEREO NET PROJECTION

FigUre 6. Structural features of the Telford Basin. (Note: Fault and joint orientations have a constant rel"ationship to the attitude of the beds, gradually changin-g orientation and adjusting to tle-basin . shape. The iensional faults are an exception and-are on-ly fbund in the north-west esctor of the basin.)

Leigh Creek Coalfield

520 Complementary conjugate faults are the most

common. They strike parallel to the basin margins and form sets which dip with, or are inclined

towards bedding surfaces. Faults which are parallel to the dip of the beds are inclined towards the centre of the basin at between 50o and 75o, while faults inclined to bedding dip towards the basin margins at between 600 and 85o. Fault throws are generally in the order of 0.5m to 10m, but may be as large a-s 35m. Complementary conjugate faults have developed gradually, as shown by the presence of pairs offaults which have been rotated as bedding gradually became more steeply dipping (Figure 6). These faults display both plastic and blittle deformation features.

Peripheral faults are longitudinal normal-slip faults which appear mainly in the marginal zone of the basin. These faults are characterised by steep dips (80o to 90o), and a very wavy and undulating form. Fault throws are generally in the order of 5m to 15m. The strike of these faults adjusts to the elliptical shape of the basin, and their presence contributes to the more intensive deformation at the basin margins. Tensional faults, which trend northeast to southwest, are present in the northwest sector of the basin. These are conjugate normal-slip structures which dip at between 50o and 80o and displace the peripheral and complementary conjugale fault systems. They display characteristics which indicate brittle deformation. The development of these faults is considered to be associated with the strike-slip movement of a major basement fault which trends parallel to the northeastern boundary of the "IJpper Series" strata. Many defects other than faults are present in the Telford Basin. These include cathetal joints, normal slip joints, shear cleavage of normal slip character and bedding defects (Bogacz, 1986), all of which

have been developed under a gravitational normal

stress field.

Bedding defects ofvarying character have been identified throughout the basin. They are considered to be secondary shear (or tendency to shear) strgctures on pre-existing weaknesses parallel to bedding, which resulted from compensation of space due to normal-slip fault displacements. Some bedding defects which display soft sediment deformation have also been created by gravitational sliding during sedimentation and/or diagenesis.

All of these geological structures are more prevalent at the exposed basin margins and decrease up the stratigraphic sequence. With the exception of the tensional faults, the development of these structures has been predominantly controlled by a gravitational-normal stress field and the vertical activity of basement faults.

CoaI Occurrence The coals of the "Lower Series" are the least developed in the Telford Basin, with a number of thin seams occurring in two discrete stratigraphic intervals (Figures 5). The lowermost of these intervals (W zone) contains up to six thin seams, often high in ash, with a maximum aggregate coal

thickness of 6m over an interval of approximately 10m. Individual seams rarely exceed 1m in

thickness. Coal occurs only in the east and is entirely absent in the west.

The second interval in the "Lower Series" (V zone) occurs 10 to 20m above the W zone and contains three to five seams spread over a 12m sequence. Individual seams in this unit are up to 5m thick, and aggregate coal thickness is generally 3m and 10m. The aggregate coal thickness is less consistent

than in the W zone, although both zones display thickening in the northwest and southeast and have no coal in the west and southwest. Coal in the "Main Series" is represented by one coal-bearing interval (Q seam). This interval is best developed on the northern, eastern and southeastern sides of the basin, where it varies between 14 and 20m in thickness. Partings are generally absent from the seam, or limited to mudstone bands less than lm thick, and tend to decrease in thickness and frequency away from the present basin margin. The total thickness of coal decreases significantly towards the southwest of the basin, with the aggregate thickness reduced to less than 5m in a

multi-seam sequence.

The coal-bearing zone of the "IJpper Series" contains seven identified seams (K, J, I, H, G, F and D) over a vertical interval of approximately 100m (Figure 5), but thin coal horizons are also often locally developed. Individual seam thicknesses are commonly between 0.5m and 5m, but reach a maximum of 10m where the F and G seams coalesce. Mudstone partings up to 1m do occur, but are not common. The cumulative thickness in the "IJpper Series" is up to 25m. Intraseam sediments are generally 5m to 10m t\ick, with a maximum of 20m. The subcrop of the Upper Series coal zone follows

the overall shape ofthe basin, but the distribution of the sequence is confined to the central and southern portions (Figure 4). As in the underlying units, maximum coal development occurs in the northeast, with the coal-bearing interval thinning towards the southwest.

Lobe C Lobe C is located within the North Field area, 3km north of the Telford Basin (Lobe B). It is an asymmetric basin trending northwest to southeast, with approximate dimensions of 2.5 x 1.4km. The stratigraphic sequence in Lobe C is up to 180m thick, and is dominated by mudstone. Coal occurs in

one zone approximately 15m from the base of the sequence (Figure 3), varying from a single seam up to 16m thick in the south to a multi-seam sequence of only around 2m in the north. Partings within the seams consist of sandstone and mudstone.

Except where Lobe C is joined by a narrow trough to Lobe D, the strata dip towards the structural centre of the basin. Dips range from between 50 and 30o along the western and southern margin to 70o along the northeastern margin, where the basin is in contact with diapiric material. The coal-bearing sequence is essentially unfaulted, although local basement faults displace the coal seam and are reflected as monoclinal folds in the overlying strata.

Lobe D Lobe D, also within the North Field area, is a

roughly elongate north-south basin measuring 1.8 by 2.5km (Figure 4). Coal occurs about 50m above basement, represented by two seams with LOm of intervening mudstone and minor sandstone that are overlain in turn by up to 50m of mudstone. Both seams show a high degree oflateral consistency.

Geology of Australian Coal Basins

521

Table l:.,Leigh Creek coal quality" Proximate Analysis

Coal Zone

Upper

Main Lower Lobe Cx Lobe Dx

Sulphur (db)

Fixed Carbon

Ash (db)

36.8

Volatile Matter (db) 32.0

Energy MJ/kg (in situ)

48.5

19.5

t5.2

4.5

32.9 28.9 27.4 29.9 36.0

38.4 32.5 30.8 30.4 35.0

47.7 46.5 44.8 39.6 49.5

13.9 21.0

L5.2 15.5

0.9

24.4 30.0

15. 1

L5.4

15.0

Moisture (in situ) Lobe A* Lobe Bx*

Specific

x Data from Johns (1975).

(db)

t2.3

4.2 0.7

*x Data from Kivior (1986). Average thicknesses are 7m and 9m for the lower

and upper seams respectively (Johns, L975), with a

mudstone parting 0.5m to lm thick commonly occurring in the lower seam.

The beds dip at least 10o on the basin margins, and are directed towards the basin centre. Several local undulations occur in the strata but in general dips are very regular. Faults have not been observed in the Lobe D basin.

COAL QUALITY Leigh Creek coals are low rank (Lignite A to Sub-bituminous C), with a typical quality as indicated in Table t. In situ moisture ranges from 27Vo to 37Vo, in slfa specifrc energy is in the order of 15MJ/kg, and ash is between t57o and 307o (dry basis). Sulphur varies from less than LVo in Lobes B and D to over 47o (db) in Lobes A and C. Total in situ resources for the four basins exceed 530Mt.

In the Telford Basin (Lobe B) ash decreases up the sequence fuom 24Vo in seams of the Lower Series to 27Vo and L4Vo (db) in the seams of the Main and Upper Series respectively (Table 1). A reciprocal change occurs in the percentage of in situ moisture. These variations correspond to a change in petrographic composition up the sequence (Figure 7). The Lower Series coals are rich in liptinite (commonly up to 20Vo) and inertinite (40Vo to 70Vo; Taylor, 1954;AMDEL, 1979). The Main Series coals have slightly less liptinite and inertinite (10 to lSVo and 40 to 60Vo respectively) and the Upper Series coals contain approximately equal amounts of vitrinite and inertinite with around 107a liptinite. The changes probably reflect evolving depositional conditions from an essentially lacustrine to a fluvio-lacustrine depositional system.

Late Triassic coal-bearing sediments are widespread in northern South Australia, with deposits to the north of Leigh Creek in the Simpson Desert Basin, and in the upper part of the Cooper Basin (Wiltshire, 1982; Moore, 1982). To the south, Late Triassic sediments occur near Springfield and Boolcunda in basins of similar size to the Telford and Copley Basins respectively.

Climatic conditions were favourable for plant growth over much of the State at times during the Late Triassic, and peat swamps developed where conditions allowed. In the basins north of Leigh Creek, widely distributed Late Triassic sediments overlie Middle Triassic and Permian sediments.

In contrast to sediments found in the larger northern basins, the Late Triassic Springfreld and Boolcunda Basins rest unconformably on Cambrian and Precambrian rocks. Deposition was controlled by local structures, which caused sediments to be supplied to proximal alluvial fan and fluvial floodplain environments. The structural setting of the Leigh Creek basins is similar to that of the Springfield and Boolcunda Basins, but whereas the two southern basins contain up to 200m of basal conglomerates the Leigh Creek basins contain no such coarse alluvial fan deposits. It is possible that laterally equivalent conglomerates and other sediments have since been eroded from the Leigh Creek area, however, vitrinite reflectance

PPfR StRrtS ilAtN StRtts l owa stRtts

GEOLOGICAL HISTORY

Regional Extent Many authors (Parkin, 1969; Johns , L97 5; Townsend, 1979) have postulated that the Leigh Creek coal occurrences are erosional remnants of intramontane basins formed by local subsidence and sedimentation. Work by Bogacz (1986) and Lemon (1986) has confirmed that the preservation and structure of these basins was controlled by local structural elements. However, the relationship between the Leigh Creek occurrences and other coeval sedimentation in the region is unclear.

tMRTtNtTE

UPItNtTt

Figure 7. Macerals in Telford Basin coals.

Leigh Creek Coalfield

522 measurements from Lobe B suggest that the basin represents a localised sediment accumulation or thickening. Isoreflectance lines are essentially parallel to the present ground surface rather than to the various stratigraphic horizons. Near-surface coals from the Main, Lower and Upper Series, separated by a stratigraphic thickness ofup to 800m, show an essentially identical Rv,max of 0.4 to 0.45%. However, measurements from more deeply buried coals, irrespective of their stratigraphic position, show increased Rv max with depth. Bostick's (1973) relationships between temperature, burial time and reflectance suggest that the low rank coals in Lobe B could have formed at quite shallow depths, and that only a small portion of the

stress freld and the vertical movements of basement faults (Bogacz, 1986). This is apparent from the types of structures preserved and the high frequency of structures adjacent to the basin margins. The development of the Lobe C basin is considered to be similar to that of the Telford Basin. The asymmetric shape, variations in dip and

gravitational normal structures within the coal-bearing formations of Lobe C indicate gentle synsedimentary subsidence, primarily controlled by a basement fault to the north. The formation and preservation of the Lobe D basin has been less influenced by basement structures. This is shown by more gentle and consistent dips, a more symmetrical overall shape, a thinner stratigraphic section, lower intensity of basin structures and an absence of faults. However, the structures observed are consistent with a gravitational-normal stress field, and the same mechanisms for development are postulated. The limited formation from the Copley Basin also suggests similar development mechanisms.

original stratigraphic sequence may actually be missrng.

It is apparent that local structural movements were

the main mechanism of basin subsidenee, and hence for sediment preservation. It is also likely that thinner sedimentary sequences were deposited away from these structures, especially in the Norian, with the lower preservation potential of the more distal sediments leading to their subsequent erosion.

A diapiric mechanism for the development of faults controlling basin subsidence has been postulated by Lemon (1986). Reactivation of diapirs during the Late Triassic would have caused movement resulting in the formation of a localised peripheral sink as surrounding basement rocks filled the volume excavated by the diapir. This could have provided a driving force for slow, steady subsidence and the accumulation and preservation of sediment in small basins. A diapiric body occurs between Lobes C and D, and these basins provide the only direct evidence for this mode of formation. Alternatively, reactivation of major faults could also provide the driving force for basin formation in the afea,

Basin Formation The development of the Leigh Creek coal basins apparently occurred in response to local syndepositional subsidence. This subsidence was primarily controlled in many places by basement faults. SIow and steady accumulation of sediment is characteristic of the Leigh Creek basins, which contain predominantly fine-grained lithologies, particularly mudstones. Synsedimentary activity of major basement faults within Lobe B is reflected in the asymmetry of the basin and the greater stratigraphic thickness found on the northern and eastern flanks. The northern and eastern boundaries ofLobe B display an erosional contact with basement, and the coal-bearing formations dip at approximately 15 to 20o. The southern and western boundaries, with dips of up to 50o, are considered to be influenced by faulting. Structures within Lobe B have been predominantly controlled by a gravitational-normal

i"k':& ,'rJb I

Three depositional phases are recognised in the Leigh Creek basins (Figure 8). Slow subsidence along local structural features beginning in the Early Carnian stage initiated the first phase of sediment accumulation and preservation (PT4.1). During this phase the Lower and Main Series of

l,:

Lobe

L.cusrrne

S-\ 7\LobeBf rrr..

\__>/

Lobe

Lorustrirc r Dettoic *

// /: rj

-\'

Depositional History

__-rr\ i

Lobe B 1 1.

,4 r'robe b'

-tt/1\ ----'; I

Lobe A i

Lobe A 1

...

PT4.1

PI L2

\\o

PJ1

Loie Trossic

Lote Trossic

Eoc[y Jurossic

(Corni an )

( Norion l

(Sinemlrion )

Figure 8. Generalised depositional history of the Leigh Creek basins. L EGEND

Depositionot low - depocentre

lnterpreted oreo of depositim

DePositiant high

Extent of preserved sediments

lnferred potoeocurrent

0Ir,'!l

Geology of Australian Coal Basins

Skms

523 Lobe B and the sequences in Lobes C and D were formed by a lacustrine depositional system. The high inertinite content of the coal and the common occurrence of palaeosols in the surrounding

sediments indicate shallow water deposition, with intermittent exposure of both sediment and peat.

The asymmetry of the sequences in Lobes B and C and the occurrence of sand in the sequence suggest that the major sediment source was from the northeast. However, as the basin slowly subsided, sediment input from other directions could also have

BOSTICK, N.H., 1973: Time as a factor in thermal metamorphism of phytoclasts (coaly particles). Compte Rendu Septiime Congrds International de Stratigraphie et de Gdologie du Carboniftre, Krefeld (1971), 2, 183-193. FORBES, B.G., 1986: Margin of the Eromanga Basin, South Australia: a review. In Gravestock, D.I., Moore, P.S. & Pitt, G.M. (editors), Contributions to the Geology and Hydrocarbon Potential ofthe Eromanga Basin, Geological Society of Australia, Special Publication, 12, 85-95.

contributed to the basin fill. By contrast, Lobe D is a symmetric accumulation of sediment without any obvious source direction. This reflects either radial sedimentation or the basin being more distal from the source area.

JOHNS, R.K., 1975: Leigh Creek Coalfreld, Boolcunda Basin and Springfield Basin, South Australia. In Traves, D.M. & King, D. (Editors): Economic Geology of Australia and Papua New Guinea: 2

The latter part of the Norian Stage was marked by a gradual change in depositional system and Iithofacies from a lacustrine mudstone to floodplain mudstone, siltstone and coal and finally to stacked sequences ofmeandering and braided fluvial

JOHNS, R.K. & TOWNSEND, I.J., 1975: Geology of the Leigh Creek Coalfield. Australasian Institute of Mining and Metallurgy, Annual Conference, June, 1975, Part B Whyalla, Leigh Creek and

sandstones representing the second depositional phase (PT4.2). The fluvial system, which probably flowed north from uplifted areas of the Adelaide

Fold Belt, supplied sediment to the structurally formed depocentres of Lobes B and A. Thick sequences of sediment formed at these centres, but elsewhere little or no deposition occurred as the fluvial system flowed through the-area. The final phase of deposition (PJ1) commenced after

a hiatus spanning the interval from the Late Norian

to the Sinemurian. This phase saw a return to lacustrine conditions, resulting in a sequence of mudstone with minor floodplain sandstone, siltstone and coal.

Sedimentation ceased in the Early Jurassic and did not recommence until the Late Jurassic, when alluvial fan sand blanketed most of the area. Cainozoic uplift has since led to erosion of these sediments, with rare remnant masses occurring on Adelaidean rocks and partially overlying the Copley Basin.

ACKNOWLEDGEMENTS The authors wish to thank the Electricity Trust of South Australia for their assistance in preparing this paper. We are also indebted to Alistair Muir, Irena Kivior, Tim Hopwood, David Gravestock and Keiran Slee for their helpful contributions and Mick

O'Brien for his critical appraisal of the manuscript.

Institute of Mining and

Coal. Australasian -Metallurgy, Melbourne, Monograph, 6, 301-305.

Adelaide. Lobe B, coal KIVIOR, I., 1986: Leigh Creek coalfreld quality summary. Electricity Trust- of South Australia, Report.

KREMOR, A.G., 1987: Late Torrens exploration area geological report. Electricity Trust ofSouth Australia, Report.

LEMON, N.L., 1986: Tectonic controls on sedimentation. Leigh Creek area, South Australia. Report to Electricity Trust of South

Australia.

LUDBROOK, N.H., 1980: A Guide to the Geology and

Mineral Resources South Australia. Government Printer, Adelaide.

MOORE, P.S., 1982: Mesozoic Geology of the Simpson Desert region, northern South Australia. ln Moore, P.S. & Mount, T.J. (Compilers): Eromanga Basin Symposiurn, sunln1ary papers. Geological Society of Australia Inc. and Petroleum Exploration Society of Australia, Adelaide. MOORE, P.S., 1986: Jurassic and Triassic stratigraphy and hydrocarbon potential ofthe Poolowanna Trough (Simpson Desert region), northern South Australia. In Gravestock, D.I., Moore P.S. & Pitt, G.M. (Editors): Contributions to the Geology and Hydrocarbon Potential of the Eromanga Basin. Geological Society of Australia, Special

Publication, \2, 39-5I.

MOORE, P.S. & CASTRO, C., 1984: Petroleum

REFERENCES AMDEL, 1979: Coal Petrology - Leigh Creek Coalfreld. Report to South Australian Department of Mines and Energy.

AUSTIN, P.M. & WILLIAMS, G.E., 1978: Tectonic development of Late Precambrian-Mesozoic Australia through plate motions possibly influenced by the earth's rotation. Journal of the Geological Society Australia,25 (L), l-22-

BOGLCZ, W., 1986: Telford Basin structural studies, Leigh Creek coalfield, South Australia. Ele-tricity Trust of South Australia, Report 86/5.

exploration in fluvio-lacustrine sequences, with examples from the Cooper and Eromanga Basins, Central Australia. 1n Jones, B.G. & Hutton, A.C. ( Editors ) : F luu io - deltaic sy s tenr s : faci e s analy s i s in exploration, Symposium Papers, Australian Sedimentologists Group, Geological Society of

Australia, 307-337. PARKER, F.M., 1987: Leigh Creek coal measures study: palynology of selected core and outcrop samples. Report to Electricity Trust of South

Australia. PARKIN, L.W., (Editor), 1969: Handbook of South

Australian Geology. Geological Survey of South Australia, Government Printer, Adelaide.

Leigh Creek Coalfield

524 PLAYFORD, G. & DETTMANN, M.E., 1965: Rhaeto-Liassic plant microfossils from the Leigh Creek Coal Measures, South Australia. Senckenbergiana Lethaea, 46, 127 -181.

TOWNSEND,I.J., 7979:. The correlation and depositional history ofthe Leigh Creek Coal Measures. Geological Suruey of South Australia, Quarterly Geological Notes, 70, 5-10.

PRICE, P.L., FILATOFF, J., WILLIAMS, A.J., PICKERING, S.A. & WOOD, G.R., 1982: Late Palaeozoic and Mesozoic palynostratigraphical units. CSR Oil and Gas Division, Palynology Facility, Report No. 27 4/25.

WILTSHIRE,M.J., 1982: Revision of the limits of the Eromanga Basin. In Moore, P.S. & Mount, T.J. (Compilers) : Eromanga Basin Symposium, Summary Papers. Geological Society of Australia Inc. and Petroleum Exploration Society of Australia, Adelaide, 59-68.

TAYLOR, G.H., 1954: The petrology of the Leigh Creek

coalfield in relation to its utilisation. Progress Report No. 3. Mining Reuiew Adelaide,97, 1

10-1 16.

WOPFNER, H., 1985: Post orogenic development of . north eastern South Australia and adjoining regions. /n Lindsay, J.M. (Editor): Stratigraphy, Palaeontology, Malacolo gy. South Australian Department of Mines and Energy Special Publication 5, 365-376.

Geology of Australian Coal Basins

525

Waryborough Basin, Queensland

MP Thornton

1. Onshore extent ofthe Burrum and Tiaro Figure - Coal Measures (Cainozoic removed).

The Maryborough Basin, located on the Queens-land coast near Fraser Island (Figure 1), was formed during the Late Triassic and filled with a Late Triassic to Cretaceous sequence ofterrestrial and marine clastic sediments and andesitic volcanics. Two coal-bearing units are present: the unproductive Tiaro Coal Measures of Jurassic age, anil the Early Cretaceous Burrum Coal Measures, which have been mined for more than L00 years. Previous geological investigations have mainly focussed on the Burrum deposits, but the Tiaro Coal Measures have also been the subject of more recent

investigations.

EXPLORATION AND MINING HISTORY Early workers in the Maryborough Basin included Stutchbury, Daintree, Gregory, Tenison-Woods, Rands and Jack. Oil exploration began in 1923, when three holes were drilled near Bundaberg. Other holes were drilled for petroleum north of Maryborough in 1955 and 1967, and regional seismic coverage of the basin is fairly extensive. The earlv 1950s to middle 1960s saw an increase in drilling for coal exploration by the Queensland Depariment of Mines (Hawthorne, !96O; Pearce,. tgeg; Chiu Chong, 1965), while geological mapping at a l:250 000 scale was conducted by the Geological Survey of Queensland and published during the late 1960s-and early 1970s (Ellis, 1968; Ellis &

Whitaker, 1976; Murphy & others, 1976). Details of

Maryborough Basin

526 the Burrum and Tiaro coal-bearing sequences were summarised by Koppe (1975) and Park (1975) respectively.

Exploration of the basin was continued in both the Burrum and Tiaro sequences by a number of companies in the L970s and 1980s, but this activity has so far failed to locate further coal resources. Re-mapping of the Gundiah Embayment area, aided by stratigraphic drilling, has also been discussed by Cranfield (1982). Detailed mapping of the region since then was used to compile the Maryborough geology map (1992). The first reported production of coal from the

Maryborough Basin took place in the Burrum Syncline in 1866, and from the turn ofthe century until the Second World War production averaged about 100 000t/y. Production increased during and after the war, aided by the opening of the Howard Power Station, and peaked in 1965 with an annual output of 160 795t. It has, however, declined since that time, with Howard Power Station closing in 1980, and only one mine, Burgowan Colliery, remains operational at the present time.

STRATIGRAPHY The stratigraphic succession in the Maryborough Basin is summarised in Table 1. The Myrtle Creek Sandstone at the base of the sequence was deposited by fluvial activity in the newly-formed basin during the Late Triassic or Early Jurassic. It is mainly distributed south of Childers along the western and southern margins of the basin, but is also recognised in the extreme north near Port of

Baffle Creek.

Fluvial and fluvio-deltaic conditions continued with deposition of the Tiaro Coal Measures in the Early to Middle Jurassic. This sequence is divided into two parts by a ferruginous oolite marker several centimetres thick (Cranfield, 1982), comparable to those recognised in the Surat, Moreton, Mulgildie and Nambour Basins. The coal measures are distributed along the basin margin south of

east-southeast of Tiaro, where they are heavily weathered and poorly preserved. The part of the unit beneath the oolite marker is essentially a series of sandstone-dominated

fining-upwards sequences, with siltstone more dominant near the base of the coal measures and again near the transition to the overlying oolite bed. Some discontinuous coal bands occur in the finer sediments, but these are not considered significant. The oolite marker itself is contained within a shaly facies, above which the coal measures contain predominantly siltstone. Coal seams are more abundant and better developed in this part ofthe section, with seams up to 3m thick known from drill holes and outcrop. In the Gundiah Embayment, however, the Tiaro Coal Measures are intruded by numerous porphyritic hornblende microdiorite bodies, which have caused Iocal disruption of bedding and coking of the coal seams. The Tiaro Coal Measures are overlain in the southern part of the basin, with an erosional contact in some areas, by the Jurassic to Cretaceous Grahams Creek Formation. This unit consists of andesitic volcanics and volcaniclastic sediments of terrestrial origin, and extends at least 80km east ofthe present coastline (Slater, 1982). It is not present, however, in the Gundiah Embayment.

A marine transgression gradually inundated the basin, commencing in the Late Neocomian and continuing into the Albian to form a thick succession of marine shales, sandstones and cherts known as the Maryborough Formation. This unit was deposited over most of the basin, resting with local unconformity on the Grahams Creek Formation or, in the Gundiah Embayment, on the Tiaro Coal Measures. According to McKellar (1980), the Maryborough Formation is Aptian. The marine transgression was followed by a return to terrestrial conditions, with deposition in the Early Cretaceous (possibly Albian) of the Burrum Coal Measures. This sequence occupies the eastern or coastal portion of the basin, and is

Childers, in the Gundiah Embayment, and Table 1. Stratigraphy of the Manyhorough Basin,,(af-ter Cranfield, 1982). FORMATION

AGE

Quaternary Tertiary

Elliott Formation ---- unconformity Burrum Coal Measures

Cretaceous

sandstone,siltstone, shale, coal

F''p-

LITHOLOGY Basalt Basalt Sandstone, claystone

Jurassic to Cretaceous

4A <41

>d Jurassic Triassic to Jurassic Triassic

Maryborough Formation Mudstone, shale, sandstone - - - - local unconformity - - Andesitic/trachytic fl ows Grahams Creek Formation - - local hiatus

Tiaro Coal Measures Myrtle Creek Sandstone ---- unconformity Brooweena Formation

Sandstone, shale, coal, oolite Sandstone, minor siltstone

Sedimentary breccia, volcanics

Geology of Australian Coal Basins

527

table::2, eoal analyses for the Marybotttugh Basin. Burrum Coal Measures Sample type

Moisture % Ash Vo (dry basis) Volatile matter (dry basis)* Volatile matter Vo (dmmf) Sulphur 7o (dry basis) Phosphoros 7o S.E. (MJ/ks) Crucible swell number Gray-King coke type Hardgrove grindability Classification

Burrum ncline raw

Goodwood

Anticli washed at S.G.1.6

2.2x

2.4*

12.5

8.4

30.0 33.4 0.67 0.17 35.75 8.5

28.3

Pig Creek Svncline raw 2.3*

30.3 0.52 0.041

Measures

raw >6.0 18.0 29.3

31.6 0.50 26.51

8.5

si-<z>

G7 82

644 (3)

4.4 31.3 32.4 0.79 0.006

Tiaro Coal

5_(4)

* values measured at 105oC unconformably overlain by Tertiary deposits. It

consists predominantly of terrestrial sandstones, siltstones, mudstones and coals in frning-upwards cycles, building to a total of about 1700m in thickness. Less common glauconitic sandstones, however, suggest some paralic interludes. Coal seams within the Burrum Coal Measures are mostly found in a 500m thick interval towards the middle of the unit. Closely-spaced drilling in the Burrum Coalfield has identified at least 13 separate seams, and widespread mine development has taken place in six ofthese. One other seam has been located in the Pig Creek Syncline and three others on the Goodwood Anticline, but these are banded, lenticular, and subject to splitting.

A long period of uplift and denudation followed the Iaying down of the Burrum Coal Measures, prior to deposition ofthe fluvial sandstones and claystones of the Tertiary Elliott Formation. Major Tertiary and Quaternary basalt flows are also located at Childers and Bundaberg, but other basalt areas are relatively small. The present-day coastal sector of the basin is covered by extensive beach and barrier sand deposits.

To the south, the structurally complex Gundiah

Embayment contains folds and reverse faults that continue still further south towards the Gympie area. The Tiaro Coal Measures cover the Gundiah Embayment, and extend northward in a narrow strip to Childers and eastward around the southern end of the Burrum Coal Measures. Dips are moderate to steep in this area, with local disruption, particularly in the Embayment, caused by igneous intrusions. These structures have been interpreted by Slater (1982) as representing a response to moderate to

strong compressional deformation during the Late Cretaceous Maryburian Orogeny.

COAL RESOURCES Coal resources in the Burrum Syncline were determined from the results of drilling and other investigations carried out by the Queensland Department of Mines in the late 1950s and early 1960s. With due allowance for coal already extracted or sterilised by previous mining, measured in situ underground resources were estimated at 6Mt.

STRUCTURE Only the western part of the Maryborough Basin is exposed at the present time (Figure 1), with the remainder lying offshore to the east. The western margin is mainly fault-bounded, although the basal uniti at the northern and southern ends overlie the Gympie Province basement rocks unconformably. The structure of the western margin is largely controlled by northwest-trending normal faults,

By June, 1965, some 7.gMt had been extracted,-and bj, June, L985, 9.3Mt had been extracted from the area by underground mining. The original in situ resour-ce was estimated at 15Mt. No estimate for reserves is given, however, due to mining out of the Burrum field and failure to locate further resources in either the Burrum or Tiaro Coal Measures.

downthrown to the east.

COAL QUALITY

Within the basin, the structures predominantly trend NNW, with subsidiary NE and SE trends in some areas to the north and south. In the central part of the basin, the Burrum Coal Measures lie in a ieries of broad, NNW-trending folds, with low to moderate dips on the limbs. Dips are somewhat steeper, however, in the north.

Typical coal properties for the Maryborough Basin ai6 shown inTable 2. The coal has a high specific energy, but a low ash fusion temperature and a tendency to clinker. Vitrirrite content is very high at

The northern part of the basin and the area to the east of Maryborough are structurally more co-mp-le-x. The Tertiary Ellioft Formation obscures rnuch of the sequence north of Howard, but seismic data gives some evidence of the complexity and indicates that it increases towards the north.

79Vo.

Burrum coals have been used mainly for steam raising and, to a lesser extent, for gas making. Tiaro coals ire generally low-rank (Rv-"* = 0.8Vo), non-coking, medium volatile materials, but are locally altered by intrusions (Diatomite Develbpment Pty Ltd, 1976) to anthracite and graphife bands (Rv-^* = 4.7Vo).

Maryborough Basin

528 KOPPE, W.H., 1975: Maryborough Basin. .In Traves, D.M. & King, D. (Editors): Economic Geology of Coal. Australia and Papua New Guinea: 2

REFERENCES CHIU CHONG, E.S., 1965: Coal resources - Burrum Coalfield. Geological Suruey of Queensland Report, 9.

CRANFIELD, L.C., 1982: Stratigraphic drilling in the southern Maryborough Basin, 1978-1980. Queensland Gouernment Mining Journal, 83, ].5-29.

DIATOMITE DEVELOPMENT PTY LTD, 1976: A-P 147C, Tiaro: Report for period ending March 2, 1975. Held by the Department of Minerals and Energy, Queensland as CR5182.

ELLIS, P.L., 1968: Geology of the Maryborough

1:250 000 sheet area. Geological Suruey of Queensland Report,26.

ELLIS, P.L. & WHITAKER, W.G., 1976: Geology of the Bundaberg l:250 000 sheet area. Geological Suruey of Queensland Report, 9O. HAWTHORNE, W.L., 1960: The Burrum Coalfreld. Geological Suruey of Queensland Publication, 296.

Australasian Institute of Mining andMetallurgy, M onograph, 6, 320-323.

McKELLAR, J.L., 1980: Palynostratigraphy of the Tiaro Coal Measures and Maryborough Formation in GSQ Maryborough 2. Queensland Government Mining Journal, 81, 599-604.

MURPHY, P.R., SCHWARZBOCK, H., CRANFIELD, L.C,, WITHNALL,I.W. & MURRAY, C.G., 1976: Geology of the Gympie 1:250 000 sheet atea. Geological Survey of Queensland Report,

96.

PARK, W.J., 1975: Tiaro district. 1n Traves, D.M. & King, D. (Editors): Economic Geology of Coal. Australia and Papua New Guinea: 2

Australasian Institute of Mining andMetallurgy, Monograph, 6, 317-318. PEARCE, L.G.G., 1963: Coal resources - Burrum coalfield. Geological Suruey of Queensland Report, L. SLATER, R.M., 1982: Six-monthly report for the

period ended 12th September, 1982, A-P 390C Tiaro. Held by the Department of Minerals and Energy, Queensland as CR11089.

Geology of Australian Coal Basins

529

ruymboida, Red Cliff and Evans Head Coal Measures, New South Wales

The Nymboida Coal Measures, Evans Head Coal Measures and Red Cliff Coal Measures occur in three separate inliers of possibly Middle and Late Triassic-coal-bearing strata that crop out at the margin of the southern Clarence-Moreton Basin in northeastern New South Wales (Figure 1). Coal has been extracted from underground workings in the Nymboida Coal Measures, but minor surface excavations in the Evans Head Coal Measures have yielded mainly carbonaceous shales with only thin beds of coal. Outcropping seams in the Red Cliff Coal Measures are also thin and discontinuous, with abundant non-coal bands. Subsurface intersections of these Triassic coal measures have also been encountered in petroleum exploration wells in the southern (New South Wales) pait of the Clarence-Moreton Basin, including MEO Kyogle No.1, MEO Sextonville No.1, ACS Tuilfmorgan'No.1, ER Rappville No.'1*, and BOC Clifden No. 3.

STRATIGRAPHY

Nymboida Coal Measures

AT Wells

The Nymboida Coal Measures (Lloyd, 1950) are composed of sandstone, shale, conglomerate, tuff, coal and minor basalt. The succession, which crops out from Nymboida to Kangaroo Creek, is described in some detail by McElroy (1963). The unit attains a maximum thickness of about 1070m, and contains a fossil flora that, according to Retallack & others (1976), indicates a mid-Triassic age. However, isotopic dating of an included basalt flow, the Dalmally Basalt, suggests that the Nymboida Coal Measures may be Late Triassic in age. The unit is very similar to the Ipswich Coal Measures succession (L.C. Cranfield, personal communication; see also Staines, this volume, and later discussion herein). The dominant lithology in the succession is quartzlithic sandstone. Abundant polymictic conglomerate, medium to light grey shale and siltstone, some coal and carbonaceous shale, one bed ofrhyolitic tuffand a basalt flow, however, are also present. The individual units within the sequence, from bottom to top, are as follows:

Cloughers Creek Formation (20m): a lenticular, coal-bearing shaly unit;

Bardool Conglomerate (180m): massive cobble conglomerate. This unit includes the Dalmally Basalt (15m thick), located 60m above the base of the Bardool Conglomerate, and the Goolang Siltstone Member (6m thick);

Copes Creek Tuff (24m): consisting of rhyolitic

tuff;

Basin Creek Formation (750m): sandstone, shale, conglomerate and coal seams. This unit includes the Georges Knob Conglomerate Member (15m) and the Farquhars Creek coal seam (up to 2m thick).

The beds of the Nymboida Coal Measures dip at low angles to the north-east, plunging beneath the Clarence-Moreton Basin sediments. Local major folding and faulting occurs in two well-defined zones.

MEO - Mid-Eastern Oil N.L.; ACS - Australia Cities Service Inc.; ER - Endeavour Resources Ltd.; BOC - Burmah Oil Co.

Nymboida, Red Cliff and Evans Head Coal Measures

530

ru El

Mr0ou

F=-A-=_=_lvrruum

cllAt MtAsunts

uPml JUfl As$c t::=-::=-f

t$t l-,llu** mMTnil I 0 nru.r rumsscl I tfl8

TRIAs$Ctlffi:l m [.::ni:Liri]wuocnnoo

uPPrR

sJB GsouP

Lowtfl JURASSICI:':iir'::':j

rfi Il "I

REFERENIf,

rPSWlol mAt MEAslSts UPPTR TRIASSIC

r-0uJtR

Mt0Drt TRrAssrc

PAt Atoz0tc

I{YMB(lItlA MAI MTASUES

& E0ulvAtEllls

o A[tAl{Il @ IIAIGY @ MITTMIRRAI{ @ TAIII{YMORN 6 R0stw!00 @ VtAtt00ll A IYATGUM @ lilt!18t1{ o B0tiAt80 @ c0At0Art O RAM()BI{IE @ 6LE},IREAGI{ @ M00I{EM

tPswlcll,/ Hyuaolon MEASUHES

E 14 I{YMBI,IDA E}

15 BEI) CLIFF

EI 16 EVAIIS HEAD

O 17 CHILLII{GHAM

75 !n

Figure 1. Geology of the Clarence-Moreton Basin, showing the Nymboida, Red Cliff and Evans Head Coal Measures at its southern and southeastern edges, and the Ipswich Basin and Esk Trough at its northern edge (after Cranfield & others, 1975).

Geology of Australian Coal Basins

53r Red Cliff Coal Measures The Red Cliff Coal Measures (McElroy, 1963) are composed of shale, sandstone, breccia and coal, with a total thickness estimated at about 600m. The contained fossil macroflora indicates a Late Triassic age (Flint & Gould, 1975; Flint & others, 1976). The stlata crop out around Red Cliff, 50km NE of Grafton, and dip at about 2O to 25o to the west.

A sedimentological study of the unit by O'Brien & others (1988) concluded that the sequence was deposited at the intersection of an alluvial fan with fluvial floodplain sediments. The fans are made up of debris flows, with diamictites produced by slumping, and the floodplain or distal alluvial fan deposits of siltstone, fine sandstone and coal. The coal is thought to have accumulated as raised bogs on the fan surface. The upper part ofthe seCtion, overlying the fan, is made up of braided stream channel-frll conglomerate beds.

Evans llead Coal Measures The Evans Head Coal Measures (McElroy, 1963) are a coal-bearing sandstone, carbonaceous shale and conglomerate succession. The coal seams, however, are thin and uneconomic. The unit occurs in outcrop around Evans Head, Goanna Headland, and near the airport approximately 4km WNW of Evans Head. Small quarries have been excavated in an outcrop of the Evans Head Coal Measures about 4km SW of Evans Head township.

At Goanna Headland, about 3km south ofEvans Head, carbonaceous shale, micaceous siltstone and cross-bedded quartzose sandstone, with approximately 1m of poor-quality coal at the top o-f the section, is exposed on a wave-cut platform and adjacent sea cliffs. The sediments mostly dip at iniermediate angles to the west, and in places show recumbent folding. They are unconformably overlain by the Ripley Road Sandstone of the Woogaroo Subgroup (see Goscombe & Coxhead, this volume), whiCh is well exposed on the crest of the sea cliffs and at Evans Headland a little further to the south. The sedimentary succession at Goanna Headland is interpreted as having been formed in a floodplain

envirbnment, with the thicker lenticular beds of cross-bedded sandstone being deposited as channel sands. The numerous thin interbeds of finer-grained sandstone in the carbonaceous shale are interpreted as crevasse splays, overbank deposits and thin floodplain sands. The known thicknesses of the Evans Head Coal Measures are 10m near the airport, 37m in a complete section at Evans Head and a minimum of 40m at Goanna Headland, and an estimated total thickness of about 300m.

COAL SEAMS Coal up to 2m in thickness, including bands, occurs in the Farquhars Creek seam of the Nymboida Coal Measures, about 250m above the base of the Basin Creek Formation. Lenticular coal seams up to 2m

thick also occur in the Cloughers Creek Formation, with two poor-quality seams in outcrop, 1.2m and 2.4m thick including non-coal bands.

The Nymboida.Coal Measures contain the only^ proven economic resource of coal, and a total of lbout 927,000t have been recovered from the succession. The coal has mainly been used as fuel in the Koolkhan Power Station at Grafton. McElroy

(1963, in Nicholson, 197 4) estimated 'proved' resources of254 000t and'probable and possible' resources of406 000t, along with 405 000t ofpillar coal and 254 000t ofthin coal. The coal in the Cloughers Creek Formation is low volatile bituminous coal, tending towards semianthracite. The Farquhars Creek seam is a

relatively high-ash, medium volatile bituminous coal with an 6xceptionally high specific energ'y of up to 36.3MJ/kg (dmmf basis)- Proximate analysis re-su!t9 (air-dried) indicate O.4Vo moisture, 18.27o ash,24.0Vo volatile matter and.57.47o fixed carbon. Ultimate analysis (dmmf basis) indicates 87 .TVo catbon, 5'6Vo hydrbgen, 4.9Vo oxlgen L.5% nitrogen and 0.7Vo sutptrur. The crucible swelling number is usual-ly between 7 and 8 and the Gray-King coke type G3.

AGE OF THE COAL MEASURES The Evans Head and Red Cliff Coal Measures have been assigned a Late Triassic age and correlated with the Ipswich Coal Measures of south-east Queensland (McElroy, 1963, 1969; Flint & Gould, t-OZS; trlint & others, 1976; de Jersey, 1958).

However, Retallack & others (1976) state that the fossil megaflora in the Nymboida Coal Measures is Middle Triassic, and more akin to the Esk Formation of the Toogoolawah Group. Isotopic dating of the Dalmally Basalt was used to support this conclusion, despite the fact that the dates indicate an age very close to those obtained for the Sugars and Weir Basalts in the Ipswich Coal Measures (Webb & McNaughton, 1978). The dating of the Dalmally Basalt and the age of the Nymboida Coal Measures are under further investigation by Wells & others (in preparation).

REFERENCES CRANFIELD, L.C., McELROY, C.T & SWARBRICK, C.F., 1975: Clarence-Moreton Basin, New South Wales and Queensland. In Traves, D.M. & King, D. (Editors): Economic Geology of Australia and Papua New Guinea - 2: Coal. Australasian Institute of Mining and Metallurgy, Monograph, 6, 328-333. De JERSEY, N.J., 1958: Macro- and micro-floras of

north-eastern New South Wales. Journal and

Proceedings of the Royal Society of New South

Wales,92,83.

FLINT, J.C.E. & GOULD, R.E., 1975: A note on fossil megafloras of the Nymboida and the Red Cliff Coal Measures, southern Clarence-Moreton Basin, N.S.W. Journal and Proceedings of the Royal Society of New South Wales,1O8,70-74. FLINT, J.C.E., LANCASTER, C.G., GOULD, R.E. & HENSEN, H.D., 1976: Some new stratigraphic data from the southern Clarence-Moreton Basin. Queensland Gouernrnent Mining Journal, 7 7, 397-401.

LLOYD, A.C., 1950: Clarence coal basin, Nymboida Coal Measures, progress report. Annual Report, New South Wales Department of Mines (for 1939-45),96. McELROY, C.T., 1963: The geology of the Clarence-Moreton Basin. Geological Suruey of New South Wales Memoir, 9.

Nymboida, Red Cliff and Evans Ilead Coal Measures

532 McELROY, C.T., 1969: The Clarence-Moreton Basin in New South Wales. .In Packham, G.H. (Editor): The Geology of New South Wales. Journal of the Geological Society of Australia, 16(7), 457-479. McELROY, C.T., 1975: Nymboida Coal-freld, New South Wales. In Traves, D.M. & King, D. (Editors): Economic Geology of Australia and Papua New Guinea Coal. Australasian - 2:Metallurgy, Institute of Mining and Monograph, .'0a ooo 4 V' 'JO_'JJ.

NICHOLSON, D.A., 1924: Clarence-Moreton Basin. In Markham, N.L. A Basden, H. (Editors): ?he Mineral fieposits of New South Wales. 'So*"y'of Geological N.S.W., bepariment of Mines] sydney, isg_s+s.

RETALLACK, G., GOULD, R.E. & RUNNEGAR, B., 1976: Isotopic dating of a Middle Triassic megafossil hora from near Nymboida, northeastern New South Waies. Proceedings of the Linnean Society of New South Wales, 101(2)' 77-773' WEBB, J.A. & MCNAUGHTON, N.J., 1978: Isotopic age of the Sugars Basalt. Queensland Gouernment Mining Journal,79, 59I-595.

WELLS, A.T., CRANFIELD, L.c., WEBB, J.A., FOSTER, D.A. & O'BRIEN, P.E., iN preparation: Precision in correlation of Triassic sedimentary se_quences in eastern Australia: evidence from dating the Dalmally Rasalt in t_he Nymboida Coal Measures, New South wales-

O'BRIEN, P.E., WELLS, A.T,, SMYTH, M. & RUSSELL, N.J., 1988: Alluvial fan and flood-basin sedimentation in the Triassic Red Cliff Coal Measures, New South Wales.

Australian Journal of Earth Sciences, 35(4), 491-503.

Geology of Australian Coal Basins

533

ffi qfuJretaceous coals of the Gippsland and Otway Basins,

Victoria

Apart from the well-known Tertiary brown coal deposits, discussed elsewhere in this volume, black coal of bituminous rank occurs at a number of localities in the Gippsland and Otway Basins in the southern part of Victoria. Minor occurrences are also known in the Murray Basin in the north-west of the State.

In many early reports the beds containing these coals are described as being ofJurassic age. This dating appears to have been based largely on palaeobotanical correlations with Jurassic deposits in Yorkshire and India by Seward (1904). Following the work of Kenley (1954), Cookson & Dettman (1958) and others (discussed by Dettmann & Douglas, 1988), however, the coals and their associated strata are now long recognised as Early Cretaceous deposits.

GIPPSLAND BASIN

CR Ward

The Gippsland Basin is a major east-west trending collapsed graben of late Mesozoic to Tertiary age, bounded in the north by the Palaeozoic rocks ofthe southern Lachlan Fold Belt and in the south by a belt ofPalaeozoic strata passing through Cape Litrap and Wilsons Promontory (Figure 1). Its tectonic setting and geological history, particularly with respect to its Tertiary sediments, are discussed in greater detail by numerous authors, including James & Evans (1971), Hocking (L972), Smith (1982) and Barton & others (this volume). The basin flill includes up to 4000m ofEarly Cretaceous strata, deposited in a series of east-west rifts formed as the basin was first developing. These strata, known as the Strzelecki Group (Douglas & Ferguson, 1988) were subjected to faulting, uplift and erosion prior to deposition of the better-known Late Cretaceous and Tertiary succession, and in the offshore portion form the economic basement for petroleum exploration in the basin area.

Nature and Distribution of Cretaceous Strata The Strzelecki Group crops out in two NE-SW trending blocks ofelevated country on the western margin of the basin, between Western Port Bay and Wilsons Promontory (Figure 2). The first of these, covering the area between Kilcunda, Korumburra and Moe is referred to by Thomas & Baragwanath (1950) as the Narracan Lobe; the second, extending from Foster towards Traralgon, is referred to as the Balook Lobe. Other outcrops occur between these blocks in the Tarwin Valley near Leongatha. The Strzelecki Group, also referred to as the Cape Patterson Beds (Selwyn, 1856) and the Korumburra Group (Stirling, 1899) rests unconformably on, or is faulted against the basin's Palaeozoic basement rocks. The sequence consists mainly of arkosic sandstones and mudstones, with minor lithic sandstones and conglomerates, and is thought to be mainly of fluvial origin (Douglas & Ferguson, 1988). Coaly tracings and thin coal seams are not uncommon in outcrop, and seams up to 3m in thickness are reported by Knight (1988). The beds ofthe Strzelecki Group have been deformed by a combination of tectonic processes and differential compaction (Edwards & others, L944), and dip in various directions at up to 20o. They are also cut by a number of NE-striking faults. The Tarwin Valley area represents a graben feature, bounded by horsts ofthe Narracan and Balook Blocks.

Cretaceous - Gippsland and Otway Basins

534

|,,, "

ffiit.,,,n

/xqlLDURA

Outcrop of Early Cretaceous beds

Approximate limits of subsudace Lato Cretaceous beds

,, t !- MURRAY r BASIN

Approximate limits of subsurtace Early Cretaceous beds Southern boundary ol subsurtace Early Cretaceous in Murray Basin

C,)r

100km

-l

360

ah,

!t rl

>t I

I \"ri.rr*ro'',

'-.t. Y,rB$

qANDENoNG

poRiLAND_1-brwAv=-if,rnc. \rr -RAqlN /- .

;

----'

t, 142"

148'

CAPE OTWAY

(PAUEqZ0|C H\GH)

Figure 1. Outcrops and subsurface distribution of Early Cretaceous strata in the Gippsland and Otway Basins (Douglas & others, 1988). Coal in the sequence was first discovered at Cape Paterson in 1825. It appears to occur throughout the Strzelecki Group, but is probably most common in the lower part of the sequence (Douglas & others, 1988). The coal has been worked, chiefly in the Narracan Block, since 1840, when mining began in the Kilcunda-Woolamai area (Kitson, 1905). The best-known deposits, however, are those of the Wonthaggi district, approximately 1Okm north-west of the first discovery at Cape Paterson.

Wonthaggi Coalfield The Wonthaggi coalfield is located to each side of a

fault-bounded ridge of Silurian basement rock, on which the town of Wonthaggi itself is built (Figure 3). Strzelecki Group strata occur in the area in two sub-basins, the Dudley basin to the north-west of the ridge and the Kirrak basin to the south-east. Coal was initially discovered in the area by Government drilling in 1858. A State Coal Mine

was established to supply fuel for railway locomotives in 1909, and several smaller private operations developed nearby. A cumulative production of 17.1Mt was extracted from the field prior to cessation of mining in 1968, with peak production levels of 600 000t/y in the early 1930s. Details of the geology of the field, together with an indication of its mining history, are given by Hunter & Ower (1914), Edwards & others (1944) and Knight (1969).

A total of eight separate seams were identified in the Dudley basin, occurring over a stratigraphic interval of some 300m. Only three of these seams, however, appear to have been worked to any significant extent, two of which are regarded as splits of the lowermost coal seam (Knight, 1969). The uppermost of the worked seams, referred to as the 'Top seam', has a maximum thickness of around 3m in the central part of the basin. The'Bottom seam', 75 to 105m below the upper, is the split seam, with each of the two plies being up to about 7.25m thick. Two persistent seams occur in the Kirrak basin, separated by some 150m of arkose and mudstone. The lower of these seams is probably equivalent to the Bottom seam in the Dudley basin, and reaches a maximum thickness of around 2.2m; the upper seam, however, is only up to 0.9m thick. The strata in the Dudley basin dip to the south at around 20o, while those in the Kirrak basin dip to either the east or the west at much lower angles. Faults, striking mainly E-W and dipping north at about 650, cut through both areas, producing a general rise in seam levels towards the central basement ridge (Figure 3). Throws on the faults commonly exceed 30m, and reach a maximum of over 200m in the Dudley basin area. Contemporaneous sedimentary processes have given riie to several 'floor rolls', 'wants' and .washout' structures in the Kirrak basin (Edwards & others, 1944; Knight, 1969), some of which are over 15m wide and up to 100m long. A number of

Geology of Australian Coal Basins

535

TAS,IIAN SEA

a,ls.9 STIIAIT

02040 I I O Hogan ls and

REFERENCE WELLS WfLJHPOOL

wooos/DE I ROsEDAL € I

W€LL/NGION PARK OUCK gAY I

80016 P00LE r

8 COLDEN AEACH IA ' 9 PERCH I l0 6ffP6ROR I ,i c^llN6l I

12 FLATHEAD I

ll wAH00 I

tTl

NORTH 5€A5PRAY

I KILOMETRES

Slrz elec ki G ro u p oulctop

S!tz e I ec k t Gt ou p su bsu ilac e

Palaeozoic outctop

t!7o 00

t480 00

Figure 2. Distribution of Strzelecki Group strata in the Gippsland Basin (Douglas & others, 1988).

dolerite dykes 1 to 2m wide are also present in the area, with associated cinder zones typically extending approximately 0.5m to each side of the intrusions in the various coal seams. The coal at Wonthaggi is a high-volatile bituminous coal, with 5 to 10Vo moisture (air-dried), 30 to 35Vo volatile matter and 6 to L27o ast, (Table 1). The gross specific energy is 26 to 28MJ/kg. According to Knight (1975) the remaining in situ

resources in the Wonthaggi field amount to some 6.8Mt. This is based on more than 400 boreholes, and includes seams from 0.4 to 1.7m in thickness.

The State Coal Mine was worked by underground methods, and most of the remaining coal would probably also need to be worked in this way. A small amount of coal may, however, be able to be extracted in the vicinity of the old pit-top installations by open-cut techniques (J.L. Knight, personal communication).

Kilcunda-Woolamai C oalfield Coal crops out on the coast between San Remo and Kilcunda, east of Phillip Island, and near the town of Woolamai some 6km to the north. Seams in the area are up to 0.9m thick (Kitson, 1905) and dip generally to the north.

The Kilcunda area was the site of the first coal

mining activity in Victoria in the 1840s, with early workings being based on adits driven into the coastal cliffs and some shafts further inland. Two

mines, the Victorian and the Kilcunda, were developed around 1910, working a northerly-dipping seam up to 0.7m thick, although drilling reported by Brown (1948) indicates that the seam thins out further down-dip. The Kilcunda Mine closed in 1946 and the Victorian in 1953, after extracting a combined total of some 500 000t. Mining was also

carried out at Woolamai during the late 1890s, and again between 1952 and 1966, with a cumulative production of a little over 50 000t.

Jumbunna-Outtrim Coalfield The Jumbunna-Outtrim coalfield is located in hilly country west of the Powlett River, approximately 1Skm north-east of Wonthaggi. Silurian basement

rocks crop out near Kongwak, Skm to the south-west, and Cainozoic deposits occur on the Powlett Plains to the east, but the remainder of the area is made up of Strzelecki Group strata of the Narracan Block. The Strzelecki Group in this area consists of blue-grey sandstones, grey and brown shales and carbonaceous, feldspathic and argillaceous sandstones (Kitson, 7917), dipping generalfy north-west at 25 to 350. Coal seams up to 1.8m in thickness occur in the section between Outtrim and Jumbunna, and thin coaly beds appear to be present elsewhere in the surrounding district. Coal was worked at Jumbunna between 1894 and 1929, and at Outtrim between 1894 and 1936 (Knight, 1972). The principal workings were

Cretaceous - Gippsland and Otway Basins

536

tc gRrDE tljillit!

500a

I tlM rturr

/::

".' 0l//t

-Sl|tf wrr ust

Figure 3. Geological map and simplified cross-sections cross-secti of the Wonthaggi Coalfield (Knight, L975). developed in a north-westerly dipping seam 0.9 to 1.6m thick, which was followed to a depth of 300m before the operation became uneconomic (Brown, 1948). Mining continued sporadically until 1,962, by which time a total of almost 3Mt had been

surrounding hillsides. A total of around 2Mt was produced from the field over this period, mainly from the 'Top' and'Main' seams but with some

extracted from the area (Knight,7975).

contribution from the'Middle' and'Deep' seams. Remaining resources are estimated at 1.63Mt (Knight, 1975).

Korumburra Coalfield

Other Gippsland Basin Fields

The Korumburra field is located 6km north of Jumbunna, and probably lies on a continuation of the same stratigraphic horizon within the Strzelecki Group. A total of five seams are present

Cretaceous coal has been worked at several other localities in the southern Gippsland Basin, although none ofthese provided significant production or has significant resources relative to the areas discussed above. Areas wi.th at least some coal resources or production history are discussed below. An indication of coal quality for these deposits, as well as for the better-known areas described above, is given in Table 1.

over an interval ofaround 180m (Table 2), dipping, as at Jumbunna, to the north-west. Coal was worked at Korumburra between 1893 and 1962 from shafts and adits sunk on the

Geology of Australian Coal Basins

537

Table 1. Indicative quality of Strzel":F G.r"yJ c.o3l.s !1 !_t.act< coal mir.*ing areas of the Gippsland Basin (Knight, 1975). Locality Moisture Dudley Basin Dudley area, Top seam Dudley area, Bottom seam 20 shaft, Top seam

McBride Tunnel, No. 3 Bench, Top seam McBride Tunnel, No. 4 Bench, Bottom seam 9 and 10 shaft Western area, Top seam Weastern area, Bottom seam

Gross

Ash

9.1

30.6

32.r2

47.9 52.80 50.0 47.7 52.15 50.95 55.08

12.4

8.06 10.7 6.3

20 shaft, Bottom seam

Proximate Analysis F.C V.M.

8.38 5.93 7.84 9.8 7.2

32.7

35.0 30.13 31.83 30.32 34.4 35.4

calorific value MJ/kg

7.02

26.0 28.2

6.4

27.49

11.0

27.5

9.34 11.30 6.76 6.4 9.3

27.4 27.7

8.3

27.5

49.7

8.4 7.4

27.6 26.4

49.4 48.7

28.5

27.6 27.7

Kirrak Basin Eastern area 18 shaft Kirrak area

9.4

Dnq

9.5 11.0

34.9 31.9

5.0 5.8 4.5 4.6 3.8 4.70 6.95 4.56

27.2 30.3

62.9 53.3

4.9

30.3

10.5

32.8

54.7

8.0

28.5 29.4

33.8 33.50 33.95 29.55

47.4 51.05 51.55 55.55 52.25

14.2

27.6

11.65 9.80 7.95 6.97

28.6

50.0 47.2

Other Victorian Coals

Jumbunna Korumburra Outtrim Kilcunda Woolamai Cape Paterson Mirboo North Boolarra

35.2r

n.d. 29.4

n.d.

L958). All of these have similar characteristics to the Mirboo North deposits.

Coo.luille Coalfield The Coalville field is located 45km NE of Korumburra, at the northern edge of the Narracan Block and only 10km west of Yallourn in the Latrobe Valley. Coal was extracted from hillside shafts in the area between 1884 and 1897, with average working thicknesses of around 0.7m (Kenny, 1948a). Total.production amounted to only 62 J_00.t,_an{ _ __. remaining resources are estimated by Knight (1975) at around 100 000t.

Mirboo North and adjacent Areas Coal was discovered in 1882 at Berrys Creek, Skm west of Mirboo North and 35km SW of Morwell, and mining in the area commenced in 1885. Kenny

(1948b), reports the seam in the mine workings to be up to about 1.5m thick and to dip ESE at27 to 36o. Additional coal seams are noted at Boolarra, 10km NE of Mirboo North (Murray, 1886a) and between

Yinnar South and Jeeralang Junction approximately 20km NE of Mirboo North (Kenny, 1948b; Knight, Table 2. Stratigraphic section in the

Cape Paterson Coal has also been worked at Cape Paterson, 7km SE of Wonthaggi and the site of the first discovery in Victoria. Seam thicknesses, however, are only 0.4

to 0.8m (Knight, 1975), the remaining resources of 40 000t too limited for significant exploitation.

Other Occurrences Thomas (1951) describes several coal occurrences in Strzelecki Group sediment near Foster, at the southern end of the Balook Block, but as with many other areas average seam thicknesses appear to be less than 0.5m. Coal-bearing Strzelecki Group strata also occur in the Welshpool area, 20km east of Foster (Kitson, 1902), but again do not appear to be of current commercial significance.

OTWAY BASIN

Korumburra Coalfield (after Knight, lg75r.

The Otway Basin extends along the south-western coast ofVictoria (Figure 1). It is bounded by Palaeozoic strata on the Dundas-Padthaway Ridge

Approximate Thickness 1.0 m 25 m 1.4 m 82 m Impersistent 55m 1.8 m 15 m 0.6 m

Coal seam or

in the west, the Lachlan Fold Belt in the north and the Mornington Peninsula - King Island Ridge in the east (Douglas & others, 1988).

Non-coal strata No.2 or Main seam Non-coal strata No.3 or Middle seam Non-coal strata No.4 or Deep seam Non-coal strata No.5 or Bottom seam

The Early Cretaceous strata of the Otway Basin are known as the Otway Group (Douglas & others, 1988). They crop out in the Otway Ranges, on the eastern side of the basin, and on the Merino High in the Casterton area to the west, but are overlain by a thick succession of younger strata in the central part. Coal occurs in both outcrop areas and has been encountered in associated boreholes, but no significant working has been carried out to date.

Lithology No.l or Top seam

Cretaceous - Gippsland and Otway Basins

538

Table 3. Analytical data for some coal samples from the Merino area (Douglas & others, 1988). Bore

Depth of

Moisture

Volatile Matter

Fixed carbon

Ash

sam

Merino 3 Merino 3 Muntham 2

124rr,

LT85E"

32.60Vo

29.650/o

lYg0E"

194m 11m

21.L57o 16.60Vo

27.807o

35.7570 29.357o

15.30Vo 28.65Vo

25.40%

Merino High

DETTMAN, M.E. & DOUGLAS, J,G., 1988:

Otway Group sediments crop out over an area of

J.A. (Editors): Geology of Victoria. Geological Society of Australia, Victorian Diuision, 234-240. DOUGLAS, J.G. & FERGUSON, J.A. (Editors), 1988:

some 1100km2 in the Merino-Casterton-Coleraine area near the western end of the Otway Basin. Also referred to as the'Wannon Beds'and the'Merino Group', the sediments consist mainly of light grey

to greenish grey mudstone (Douglas & others, 1988), with a certain amount of friable feldspathic sandstone, minor pebbly beds and several

lenticular coal seams.

Coal seams 0.15 to 0.3m thick occur in outcrops near Merino (Douglas & others 1988), and seams up to 0.6m thick have been noted at depths of 180 to 300m in boreholes in the Coleriane-Merino area (Baragwanath, l-950). The material is described as being of sub-bituminous rank with a relatively high ash yield (Table 3). The beds are flat-lying to gently dipping, although steeper dips are noted near faults and monoclinal structures. Rochow (in Wopfner & Douglas, 1971) describes up to 24 coal seams in the lower part of the Otway Group south of the Merino High, encountered at depths of 1000m or more by petroleum drilling. Seam thicknesses appear to range from 0.3 to 1.5m, with an average of 0.8m. Esplan (also in Wopfner & Douglas, 1971) has further identified Otway Group

sediments, including coal, in petroleum-well intersections of the Otway Group at depths of 300 to 2000m in the area east of the Merino High, but no information on thickness or quality is available from these beds.

Otway Ranges The Otway Ranges are a prominent physiographic and structural high near the eastern end of the Otway Basin. The structure of this area is complex (Medwell, in Wopfner and Douglas, 1971) and the stratigraphy is poorly known, although the lower part of the section does contain some thin coal seams (Douglas & others, 1988). Outcrops of coal occur in the Apollo Bay area (Munay, 1886b), and again at Devils Elbow, 10km to the north. The exposures at Apollo Bay possibly represent a single folded seam less than 0.35m thick, and a limited amount of mining has been carried out here. No coal was encountered, however, in boreholes sunk in the nearby Bellarine - Cape Otway region (Brown, 1948), even at depths of up to 850m.

REFERENCES BARAGWANATH, G.E., 1950: The possibilities of coal

in the Coleraine-Merino district. Department of Mines, Victoria, Report 1950/3. BROWN, G., 1948: Coal resources of Victoria. Mining and Geological Journal of Victoria, 3(4), 4-L5. COOKSON,I.C. & DETTMAN, M.E., 1958: Some trilete spores from Upper Mesozoic deposits in the eastern Australian region. Proceedings of the Royal Society of Victoria, 7O, 95-128-

Palaeontology. In Douglas, J.G. & Ferguson,

Geology ofVictoria. Geological Society of Australia, Victorian D iu ision. DOUGLAS, J.G., ABELE, C., BENDECK, S., DETTMAN, M.E., KENLEY, P.R., LAWRENCE, C.R., RICH, T.H.V. & RICH, P.V., 1988: Mesozoic. 1n Douglas, J.G. & Ferguson, J.A. (Editors): Geology of Victoria. Geological Society of Australia, Victorian Diuision, 237-250. EDWARDS, A.8., BAKER, G. & KNIGHT, J.L.,1944: The geology of the Wonthaggi Coalfield. Proceedings of the Australasian Institute of Mining and Metallurgy, L34, I-54.

HOCKING, J.8., 7972: Geological evolution and hydrocarbon habitat, Gippsland Basin. APEA Journal, tz(l), \32-737 .

HUNTER, S.B. & OWER, L.,7914: Geology of the State Coal Mine, Wonthaggi, Victoria. Proceedings of the Australian Institute of Mining Engineers, 14, 185-227 .

JAMES. E.A. AND EVANS, P.R., 1971: The stratigraphy ofthe offshore Gippsland Basin. APEA Journal, ll,

l-7 4.

KENLEY, P.R., 1954: The occurrence of Cretaceous sediments in southwestern Victoria. Proceedings of the Royal Society of Victoria, 66, 1-16.

KENNY, J.P.L., 1948a: Coalville Coalfield. Department of Mines Victoria, Report 1948/3. KENNY, J.P.L., 1948b: Scarlett's coal seam, Mirboo North. Department of Mines Victoria, Report L948/28.

KITSON, A.E., 1902: Report on the probable occurrence of coal in the Welshpool district. Record of the Geological Suruey of Victoria,

r(1),61-66. KITSON, A.E., 1905: Coal in the Kilcunda - San Remo district. Department of Mines Victoria, Report 1905/2483.

KITSON, A.E., 1917: The Jumbunna and Powlett Plains district, south Gippsland. Geological Suruey of Victoria Bulletin,40. KNIGHT, J.L., 1958: Scarlett's coal seam, Mirboo North. Department of Mines Victoria, Report t958/92. KNIGHT, J.L., 1969: The closing of the State Coal Mines, Wonthaggi. Mining and Geological Journal of Victoria, 6(6), 53-70. KNIGHT, J.L., L972: Notes on the Jumbunna and Outtrim Coalfrelds. Department of Mines Victoria, Report I972/43.

Geology of Australian Coal Basins

539 KNIGHT, J.L., L975: Wonthaggi and other Cretaceous coalfields, Victoria. In Traves, D.M. & King, D. (Editors): Economic Geology of Australia and Papua New Guinea Coal. Australasian - 2:Metallurgy, Monograph, Institute of Mining and 6, 356-359.

KNIGHT, J.L., 1988: Black coal..In Douglas, J.G. & Ferguson, J.A. (Editors): Geology of Victoria. Geological Society of Australia, Victorian Diuision, 496-498.

SEWARD, A.C., 1904: On a collection of Jurassic plants from Victoria. Record of the Geological Suruey of Victoria, L, 155-271.

SMITH, G.C., 1982: A review of the Tertiary-

Cretaceous tectonic history ofthe Gippsland Basin and its control on coal-measure sedimentati on. Au s t r ali an C o aI Ge olo gy, 4(l), 1-38.

STIRLING, J., 1899: Report on the brown coals and lignites of Victoria. Geological Suruey of Victoria Reports of Progress, lO, 73-83.

MURRAY, R.A.F., 1886a: Coal seams - Boolara. 1886/257L. Department of Mines Victoria, Report

THOMAS, D.E., 1951: Coal near Foster. Department of Mines Victoria, Unpublished Report 1951/8.

Bay. MURRAY, R.A.F., 1886b: Coal seams - Apollo 1886/9116. Department of Mines Victoria, Report

THOMAS, D.E. & BARAGWANATH, W., 1949-51: Geology of the brown coals of Victofia. Mining and Geological Journal of Victoria, 3(6), 28-55; 4(L), 36-52 4(2), 4I-63; 4(3), 36-50. WOPFNER, H. & DOUGLAS, J.G. (Editors), 1971:The Otway Basin of southeastern Australia. Special

SELWYN, A.R.C., 1856: On the geological structure of the Colony of Victoria, the basin of the River Yarra and part ofthe northern, northeastern and eastern drainage of Western Port. Notes and Proceedings of the Legislatiue Council,2.

Bulletin, Geological Suruey of South Australia and Geological Suruey of Victoria.

Cretaceous - Gippsland and Otway Basins

541

ffi qfuffiippsland

Basin

i HrwsourHwALEs irll[lt* l'--\ ^

CM Barton PF Bolger GR Holdgate BR Thompson

and RL Webster

ffi or,orar, @ attati, W'...:A cbpsmdasn A Bobe-PenolsTrough E KnglslandHigh F 0twaYBanges B Vlctorlanianga G TwqaYSub-basln C Basstnitsa D KinststendMoninfronBasenoilnidso -wri,ifficiiii' 1. Location of the Gippsland Basin and Figure - others in the Bass Strait region.

The Gippsland Basin is a post-Jurassic passive margin 6asin located in the south-eastern part of the

Austlralian continent (Figure 1). It occupies a total area of about 46 000km2, with around'75Vo lying offshore beneath the waters of Bass Strait and the Tasman Sea.

The Basin is filled with Cretaceous and Tertiary terrestrial and marine sediments, which reach a thickness of more than 10 000m in the offshore depocentres and contain, in addition to coal, a suLstantial position of Australia's known petroleum resources.

The stratigraphy, structure and economic resources of the Tertliary dtrata are now well known,through extensive driling for coal and petroleum. In contrast, the older Cretaceous seq-ue-nces' with le-sser economic importance, are relatively less explored. The sedimentary history of the Gippsland Basin has followed an essentially similar path to that of many other basins in Southern Australia formed since the Cretaceous break-up of Gondwanaland' However, the scale ofaccumulation ofcoal and hydrocarbon source rocks is unprecedented, and distinguishes the basin, for reasons still poorly understood, from

others of related tectonic setting'

Large scale open cut mining for brown coal has been carr-ied out in the western extremities of the Gippsland Basin since the late 1920s' Seam thicknesses and economically mineable reserves are

huge, and are larger than those known in most other browir coal basins of the world at the present time. Minins of this coal currently meets the need for electricity generation throughout Victoria, but other future developments, such as conversion ofthe coal to oil, are also being investigated.

)

: )

Gippsland Basin

542

AUSTMLIAI{ STAGES. FOMMII{IFEMI. At{0 sPoRE-POtLEil ZoilES

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SEASPFIAY GROUP

lrj

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Figure 2. Simplified stratigraphic column for the offshore Gippsland Basin (from James & Evans, 1971).

TECTONIC AND DEPOSITIONAL HISTORY

the Rosedale and the Foster Fault Systems (Figure 3).

Initial Basin Development and Deposition of

The new depocentre, referred to as the'Central Deep', was the site of the rapid accumulation of predominantly non-marine coarse quartzose sands, clays and coals. This sequence, called the Latrobe Group (Figure 4) was suggested by James & Evans (1971) to range from Late Cretaceous to Late Eocene rn age.

the Strzelecki Group

The formation of the Gippsland Basin began with

the development of an en echelon system of east-west rifts in the Late Jurassie to Early Cretaceous. This rift system, referred to by Carey (1970) as the Bassian Rift System, is thought to have developed due to collapse of a thermally elevated zone associated with separation of the Australian and Antarctic Plates. One of these rifts, the Strzelecki Graben (Hocking, 7972), underlies the Gippsland Basin. It is filled with up to 5000m of Late Jurassic to Middle Cretaceous arkosic sandstones, trrudstones and minor coal seams, including those formerly mined in the Wonthaggi area. This sequence, referred to as

the Strzelecki Group in the Gippsland Basin and the Otway or Merino Group in the Otway Basin (Richards & Hopkins, 1969; Abele & others, 1976; Blake, 1.985), was, howev^er, partly removed by eroslon ln some areas before renewed downwarping began later in the Cretaceous Period.

The palaeo-shoreline was close to the present continental shelf margin during the Late Cretaceous, but began to prograde westward in a series of steps during the Tertiary, probably as the result of the interplay of eustacy and sediment loading (Partridge, I971-; 7976). Increased marine

influence during the early Tertiary resulted in the depositional of coastal barrier sands, associated with thick back-carrier coals, near the continental shelf margin. The sand bodies constitute the matrix for some of the more important hydrocarbon reservoirs (Blake, 1985), while the development of back-barrier lignites during later periods of higher sea level was a major factor in the formation of the vast onshore Tertiary coal deposits.

Latrobe Group

Cobia Group (including Traralgon Formation)

At the beginning of the r,ate Cretaceous, when the major plates finally separated, the southern margin ofthe Australian continental plate began to collapse and a new series of depressions developed over the infilled Bassian rift grabens. The depression that was to become the Gippsland Basin developed above the infrlled and partly eroded Strzelecki Graben between two major east-west trending normal faults,

A sea-level lowstand during the Middle Eocene resulted in erosion and channel formation across some of the Gippsland Basin structural elements that were elevated tectonically at that time. During the Middle to Late Eocene, a subsequent marine transgression spread across much ofthe basin resulting in deposition of sediment in the channels and the more widespread deposition of the overlying

Geology of Australian Coal Basins

s43

Figure 3. Main structural elements of the Gippsland Basin; also showing estimated limits of marine ingression. Gurnard Formation (Figure 4). The unconformity between the Gurnard Formation and the coarse clastics of the Latrobe Group can be recognised as a major seismic horizon over much of the offshore part of the basin. The Gurnard Formation and associated Eocene channel deposits have been included in the Latrobe Group by J-ames & Evans (1971), but because of the impoitance of the erosional event in both the Gippsland and Otway Basins (Thompson, 1985), they have been allocated herein to a new unit, the Cobia Group. The onshore non-marine facies equivalent of the

Gurnard Formation includes the coal-rich Traralgon Formation. This sequence, which contains the oldest of the economically significant coal seams onshore, includes two thick and widespread coals known as the T1 and T2 seams. These dleposits accumulated on the coastal plain behind barrier sands in response to the Eocene transgression. The barrier sequence associated with the Eocene transgression ii located at deptlr tg t]re east of the present coastline, beneath the thick Late Oligocene [o Middle Miocene limestones and marls of the Seaspray Group. The seismic record indicates that the s-equence is located 30km from the present coastline in the area of the Perch and Dolphin petroleum fields (Blake, 1985), and is probably also iepresented by the gas sands of the Golden Beach stiucture. ReCent work by Hodgate (personal communication) suggests that the older T2 coal

crosses this structure beneath the T1 sands' indicating the presence ofan additional barrier

further east towards the Barracouta structure'

The "Latrobe" and "Cobia" unconformities are usuallv easv to discern in the seismic record and by drillin! offshore, but are difficult to recognise-- --

onshorl, particularly in the coal-rich Latrobe Valley

Depression where lignites of different ages overlie each other. In this area, where terrestrial sedimentary processes have dominated, it is doubtful whether the concept of conformable deposition is applicable. The time-equivalent sequence to the 400m thick section within the weitern area of the Latrobe Valley is represented by over 2000m of sediments in the basin centre offshore.

The Traralgon Formation attains a thickness of 500m in the Seaspray Depression onshore, and the individual coal se-ams can attain a thickness in excess of 100m. Coals of the Traralgon Formation are found outcropping on the Baragwanath Anticline and structures to the south, and probably once covered parts of the Strzelecki Ran-ges, which were at a low-elevation in the Eocene (Thompson, 1980; 1985). A number of depocentres have been recognised onshore, and there are numerous publications describing the distribution and characteristics of this formltion (Thomas & Baragwanath, 1949-51; Gloe, 1975; Thompson, 1980; Thompson & Walker, 1982; Holdgate, 1984, 1985b).

Gippsland Basin

544 o OI

oa u,

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-l

RELATIVE CHANGE IN SEA LEVEL

GIPPSLAND BASIN

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Figure 4. Stratigraphic units in the Gippsland Basin and their relationships to sea level changes.

Latrobe Valley Coal Measures and Seaspray Group A sea-level lowstand, accompanied by erosion of some of the structures elevated by wrench movements, occurred in the Gippsland Basin during the Early Oligocene. This was followed by a widespread transgression during the Late Oligocene, which resulted in the deposition of over 1500m of marls and limestones of the Seaspray Group in the eastern part of the basin (Figure 4). The disconformity between the Lakes Entrance Formation at the base of the Seaspray Group and the underlying Latrobe Group forms a major seismic reflector, attributed to another erosional event, and has resulted in the development of the'Latrobe Surface' (Brown, 1975). The transgression spread into the Seaspray and Lake Wellington Depressions, and a NE-SW trending barrier system, the Balook Formation (Thompson, 1980), was deposited approximately parallel to the Eocene barriers but some 50km to the west. This barrier complex has been buried by later deposits; it is now found in the sub-surface to the

east of Rosedale, in the Lake Wellington Depression, and to the east of Yarram, in the Seaspray depression (Figures 3 and 4). The coastal plain behind the new barrier system was again the site of coal swamp development, with the main depocentres located 30 to 40km to the west of the Tertiary coastline. The resulting sequence, with lignite seams over 100m thick in places, embraces the Morwell Formation and the overlying Yallourn Formation, which are the two main coal-bearing units of the Latrobe Valley Coal Measures, the principal coal-bearing sequence in the Latrobe Valley Depression and related areas in the western part of the basin.

Although it is common practice in the Gippsland Basin to regard all coal-bearing Tertiary sediments as part of the Latrobe Group or the more recently named Latrobe Valley Group (Hocking, 1976), the Morwell and Yallourn Formations are grouped for the present discussion as a separate unit, the Latrobe Valley Coal Measures (Figure 4). This terminology, introduced by Thomas & Baragwanath (1949), is more appropriate to a genetic discussion of

Geology of Australian Coal Basins

545 basin development, since the Latrobe Valley Group also embraces the Traralgon Formation, deposition ofwhich is attributed to different eustatic and tectonic events. The alternative terminology, however, is also commonly used in detailed geological descriptions (see below) ofthe strata in the Latrobe Valley Depression generally. The Balook Formation can be traced for a distance of over 60km in the subsurface of the Lake Wellington

and Seaspray Depressions, but only has a width of between 5 and 10km. Its occurrence represents the position of the Oligocene-Middle Miocene sea, which was stabilised in this location for a period ofabout 10 million years. The sequence consists of two main units, eactr of which is made up of a series of stacked barrier sands that, combined, reach the surprising vertical thickness of 400m. The occurrence of this great accumulation ofquartzose sands ofthe Balook Formation and the equally impressive development of equivalent-aged coals in the Latrobe Valley Depiession 30km to the west, have been attributed to the maintenance of isostacy during two high sea level stands in the Late Oligocene and Early Miocene. The relatively stable position of the palaeo-shoreline over this period is ascribed to the presence ofa growth fault beneath the barrier sands in a graben sensitive to loading (Thompson, 1980).

Thinner lignite seams of equivalent age are also of the found within the Alberton Coal Measures -southern extension Seaspray Depression, west of the of the Balook Formation barrier (Thompson & Walker, 1982). In both depressions, the younger lignites apparently conformably overlie the Eocene coals, wheie these are located on tectonically elevated blocks. In some areas, however, the disconformable nature of the relationship has been established by other considerations (Holdgate, 1982). Renewed tectonic activity towards the close of the

Middle Miocene resulted in the gradual elevation of the Strzelecki Highlands and other associated structures and resulted in the retreat of the Miocene seas. A final short-lived marine transgression then spread across the onshore area in the Pliocene, accompanied by the deposition of thin marine and lake deposits and minor lignites. Finally, uplift of the highlands resulted in the development of outwash fans across the plains and the establishment of the present-day coastal barrier system in a position located between that of the Middle Miocene and Late Eocene barriers.

Coal Formation The depositional history of the Gippsland Basin involves the gradual but intermittent marine invasion of a collapsing graben that was relatively

starved of sediments. The transgression was marked by sea-level still-stands during relatively high sea levels that allowed the development of coastal barrier systems, the location of which may have been structurally controlled. Periods of regression were marked by channel cutting and the development of erosional surfaces, but many of the earlief barrier systems were preserved by gradual subsidence.

The oldest systems preserved are the Late Cretaceous barriers located near the continental shelf break. The Middle Miocene barriers are located some 150km to the west, buried within the Lake Wellington and Seaspray Depressions, while the present coastal barrier system lies to east of this

Tertiary complex.

Thick coastal plain lignite accumulations are found landward of many of these barriers. In Gippsland, the onshore coals of economic importance can be related to two major marine transgressions, one in the Middle to Late Eocene and another in the Late Oligocene to Middle Miocene. The widespread and periistent occurrence of two major seams in each iequence may indicate that the transgressions occurred in stages. The major eustatic events, evidenced in the sedimentary pile, can be correlated Basin to the sedimentary cycles in the Otway (Thompson, 1985), and can be broadly related to the published worldwide sea level trends of Vail & others (1977). The stacking of delta facies reflects a balance between subsidence rates and rising sea levels in a fluvially dominated regime. Unlike the classical

prograding Mississippi delta, where lignite iormation-occurs duiing periods of low sea level as the delta progrades basinward, evidence from the Gippsland Basin indicates that the reverse is apiriicable. Sea-level highstands a-pparently-resulted in tne formation of relatively stable coastal barrier because ofaccompanying subsidence, and' as a consequence, the hydrological regime behind the coastal barrier was modified in a way which enhanced the formation and continued existence of peat swamps. Sediment loading near the barrier system resulted in the activation of growth faults-, siabilising the position of the coast for millions of years andallowing the gradual accumulation of massive coal seams to develop behind the vertically accreting barrier system. C

OALFIELD STRATIGRAPHY

In contrast to the situation in the offshore portion, completely continuous sedimentation was relitively rare in the onshore Gippsland Basin. Most of the

main economic coal-bearing sequences were formed between the Late Eocene and the Middle Miocene (Figure 5), and were affected by the period of tectonic uplift, compression and folding in the Late Miocene which terminated coal formation and produced a major erosional unconformity between the coal-bearing strata and the younger Pliocene to Holocene sediments. As a consequence, the extremely large and laterally continuous coal-bearing sequences of the onshore Gippsland Basin are now found in discrete coalfield areas, separated from each other by areas where the seams are either deeply buried or entirely removed by erosion (Figures 6 and 7). In consequence, a different stratigraphic nomenclature is usually applied in each area where the coal bearing sequences are not directly connected, or where infill drilling was not available at the time the particular coalfield was discovered. Commencing with the work of Hocking (1969) and Partridge (1971) most current workers (e.g. Gloe, I975,1976,1984; Holdgate, 1982, 1984; Smith, 1982, and Thompson, 1980) now recognise an essentially two-fold subdivision of the coal measure sequences. The subdivisions comprise tll upper non-marine Yarragon, Yallourn, Morwell and Alberton Formations, which are facies-equivalents to the similar-aged marine Seaspray Group, and the lower non-marine Traralgon and Yarram Formations that underlie all the above formations and are consequently more widespread.

Contention over the grouping ofthese upper and lower units still exists. Because of this duality,

Gippsland Basin

546 Thompson (1980) assigned the Yallourn (Yarragon), Morwell and Alberton Formations to the Latrobe Valley Coal Measures and the Traralgon-Yarram

around the edges of the Balook Block, where smaller outcrops of the underlying Yarram Formation gravels also occur. The Carrajung Volcanics are widespread in the subsurface ofthe Seaspray and Alberton Depressions. Lavas of presumed similar, or even older age, also occur in parts ofthe Latrobe Valley Depression, usually overlying Mesozoic basement or, more rarely, thin representatives of

Formations to the separate Latrobe Group contiguous with the similar units offshore (see above). In contrast Hocking (1976) places all the coal measures within the one unit, the Latrobe Valley Group. No angular unconformity has been recognised between the Traralgon and Morwell Formations in the Latrobe Valley Depression, although one or more disconformities could be present. However, an angular unconformity between the Alberton Formation and the Traralgon Formation has been suggested in the Alberton area (Holdgate, 1982; Thompson & Walker, 1982). As a result, where unconformities are difficult to recognise between formations, such as in the Latrobe Valley Depression, the collective term "Latrobe Valley Group" has been applied. Two Group names are, however, considered appropriate at Alberton and Gelliondale (Figure 5).

the Yarram Formation.

Traralgon Formation The Traralgon Formation is the oldest Tertiary unit which includes economic accumulations of brown coal. It is dated by fossils of the Nothofagidites asperus and lower Proteacidites tuberculatus zones as being Middle Eocene to Middle Oligocene. The unit is widespread throughout the onshore Gippsland Basin, with the exception of the Lakes Entrance Platform, and is known to extend offshore as well. The Traralgon Formation comprises interbedded gravels, sands, clays and major coal seams. Coarse grained sands and gravels predominate towards the base, coals and clays in the middle and sands, clays and minor coals near the top of the sequence.

Basaltic lavas and tuffs are interbedded with the coal-bearing sequences, and these provide some basis for chronostratigraphic control. However, most of the radiometrically dateable lavas come from outcrops in the hills surrounding the main coalfield areas, and can only be applied to the coal measures themselves by extrapolation. Better timestratigraphic control is obtained within the coal measures by palynological zonation, as most of the volcanics interbedded with the coals are too altered by weathering to provide suitable dating material. Considerable work remains to refine the present palynological zonation scheme, and also, where possible, to obtain further radiometric datings.

Economically mineable coal seams can be found in the Traralgon Formation where it subcrops or outcrops along the basin margins, or where it is not overlain by the Morwell and Yallourn Formations. Such areas include all the major coalfields along the Baragwanath Anticline (Gormandale, Willung, Holey Plains, Coolungoolun, Longford Dome, Stradbroke, Boodyarn and Won Wron) and also on the Loy Yang and Gelliondale Domes (Figure 6).

Yarram Formation and Carrajung Volcanics

Smaller areas of sub-basaltic sands, clays and lesser coal seams occurring west of the Yallourn Monocline, in the Moe Swamp Basin and at Thorpdale, are considered to be of equivalent age to the upper beds of the Traralgon Formation. These beds, however, are described herein as part ofthe Childers Formation. In most cases, they have no direct stratigraphic connection with the Traralgon Formation strata located elsewhere in the basin.

The Yarram Formation is the oldest Tertiary rock

unit in the onshore Gippsland Basin, and is dated from the Lygistepollenites balmei zone as Middle to Late Palaeocene. It is composed predominantly of coarse grained to pebbly sands, which infill former valleys in the pre-Tertiary basement, and contains no known coal seams of economic signifrcance. The

formation is found sporadically in the south-eastern

halfofthe onshore part ofthe basin and can be up to

The Traralgon Formation appears to onlap in a westerly direction. Along the Baragwanath Anticline most of this onlap occurs in the lower coarser grained beds. Thick gravel sequences (up to 200m) known as the Honeysuckle Hill Gravels (Gloe, 1975) underlie the coal seams at Holey Plains, and

47m thick.

The Yarram Formation is overlain by basaltic lavas and tuffs of the Carrajung Volcanics. These lavas have been dated radiometrically at Carrajung as 55Ma (Wellman, 1974). They crop out extensively EIOSTRATI6RAPHIC

HR0N0t06ttA IUATI PLI

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Geology of Australian Coal Basins

547

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-(t

BROWN COAL MINOR DEPOSITS OR DEEPLY BURIED

/, r'

/-{ x :-

BROWN COAL MlNOR DEPOSITS OR DEEPLY BURIEO {POORLY DEF]NEDI MARINE SEDIMENT MARGIN TOWN

COAL

FIi-LD

Figure 6. Coal distribution in the Gippsland Basin (after Barton, 1986). Coolungoolun and on the Longford Dome. Across the

n;;;g*-;;;tt A"ti"tirr" ifr" -?i" coal seams recog;ised are the Traralgon 1 and Traralgon2 ;;;;r,["a only the Vou"g-er Traralgon 1 s6am occurs'west of itre n"r"a.i"-n4ono"lfi.", where it extends as far as th"Traialgon Svncline. The fiut"tgo" 1 seam at Gormaidale and in the Flynns Creek Syncline can be over 100m thick. Further east, at Holey Plains, and Coolungoolun and on the Longford Dome, thinning, splitting and interseam erosion has reduced each of the Traralg";';;;;:1" abour 40m in

thickness.

where the Gelliondale B seam' legarde.d as.being of

the same age as the Traralgon Formatigt:,hut high moisture content ot-around b'("/o lrtocKrng," :.9-7e ;-Holdgate, 198?t; Greer & Smith, 1^9q?.). This is probibly due to a lack of burial on the Gelliondale bome; the same seam at Alberton (the Alberton C sea_m) has a moisture content ranging between 55 and 607o.

A large proportion of the total Traralgon Formation

a"""r;:l",lt$T$?:;ts1rri"",#SitAii;llfJl{nrn,.

Here-a number of seams combine to form an aggqgglte. t\ickness of,over 150m of coal in-places, Because of their greater age, the Traralgon fut nitte is known of the coal quality. The few the Formation seams have, wiitr-ro-" "*""piions, (u" ?or Gif psland samples analysed from the deeper- pe^tloleum.bores Sinl lowest moisture "iiii can be fouirh guri" .outJ. pn".r"o.rt"ijt indiiate simiiar quality to the coal of the shallower ro*"i -olrt"?"r deposits, but qith a lower moisture content of A ;h;;; a""p"il".iat or-fotai"g has occurred. around 30vo.The resource here is estimated to be in reverse situation o"""ir uiG"1ii""aaq ti"wever,

Gippsland Basin

548 excess of the combined resources of brown coal without limestone cover elsewhere in the basin, but the overburden cover would clearly prevent any future development.

Morwell Formation and Alberton Formation This complex unit of thick coal seams and lesser clay-sand sequences conformably overlies the Traralgon Formation in the Latrobe Valley Depression. At Alberton, however, the relationship is thought to be one of unconformity (Holdgate, 1982). Both the Morwell and Alberton Formations are confined to the onshore Gippsland Basin, west of the sand barriers that mark the maximum point of marine transgression for the Seaspray Group. The Morwell Forrnation extends across the Latrobe Valley Depression and grades into the Thorpdale Volcanics in the Moe Swamp Basin and on the Narracan Block. The western margins of the Alberton Formation occur at an uplifted subcrop edge east of Alberton and Yarram. Both the Alberton and Morwell Formations are dated as Late Oligocene and Early Miocene by the occurrence of the middle and upper Proteacidites tuberculatus zone and the lavas ofthe Thorpdale Volcanics. The Alberton seam at Gelliondale is also thought to be of similar age (Greer & Smith, 1982). Four of the five Latrobe Valley open-cut mines work seams of the Morwell Formation. The fi-rst mine was developed in the late 1890's at Yallourn North,

where the oldest seam, the Latrobe or Morwell 2 coal seam, cropped out. Mining of this seam was later to continue along strike at the Yallourn North Extension open-cut. Subsequent developments occurred at Morwell, where the Morwell 1 seam is mined, and at Loy Yang, where the Morwell 1A, 1B and Morwell 2 seams are mined. These developments have stimulated the accumulation of a substantial volume of geological knowledge on the Morwell Formation, and in more recent years, drilling in the deeper synclinal areas and at Alberton in South Gippsland has helped complete the overall geological picture. The Morwell 2 seam attains a maximum thickness of 140m in the area between Yallourn and Glengarry. It is usually overlain by the younger seams of the

Morwell Formation and by the Yallourn Formation, except where it has been uplifted along the Yallourn Monocline. The open cut developments of Yallourn North and Yallourn North Extension occur along this narrow subcrop zone. The seam in the subcrop area is also known as the Latrobe seam because it includes a limited component of the Morwell 1B seam. Elsewhere in the basin, however, there is a significant separation between the Morwell 2 and Morwell 18 seams, so that the term "Latrobe seam" has local significance only. The Morwell seam thins to the south and west,

where it is replaced by sediments and volcanics. At Morwell it has a reduced thickness of 40m. A second area ofthickening ofthe total coal seam interval occurs on the Loy Yang Dome, and three subseams described as the Morwell 24,28 and 2C combine to produce an aggregate thickness ofover 80m ofcoal. Open-cut development at Loy Yang commenced at the subcrop of the Morwell 24' and Morwell 28 seams in 1982.

The Morwell 2 seams extend as far as Gormandale and Rosedale. East ofthese areas they grade into barrier sands ofthe Seaspray Group.

The Morwell 18 seam conformably overlies the Morwell 2 seam, usually with an interseam sequence of clay and minor sand varying between 2m and 30m in thickness. The Morwell 18 seam has a wider extent and greater overall thickness than any other seam in the Latrobe Valley Depression, and covers some 650km2, mostly to the south of the Latrobe River. In the Loy Yang Dome area, between Traralgon Creek and the Rosedale Monocline, the seam reaches a maximum thickness of between 100 and L20m. Other major depocentres occur between Yinnar and Morwell and at Flynn Railway. East of Rosedale, the seam grades into barrier sands ofthe Seaspray Group, and north of the Latrobe River it grades into clays and minor sands. To the west of the Yallourn Monocline it grades into interbedded sediments, lavas and tuffs of the Thorpdale Volcanics.

In the Morwell-Driffield area, the Morwell 18 and overlying Morwell 1A seams combine to form the Morwell 1 coal seam, which is up to 165m thick. On the western flank of the Loy Yang Dome, the Morwell 1,A', 18 and Morwell 2 seams combine producing up to 230m of continuous low-ash coal.

The topmost coal seam in the Morwell Formation is the Morwell 1.A' seam. Where it is mined at Morwell (as part of the Morwell 1 seam) and at Loy Yang, this seam is up to 80m in thickness. Its extent and thickness, however, are reduced elsewhere in the basin, compared to the underlying Morwell 18, with most of the reduction being taken up by 80m thick sequences ofinterbedded clays, ligneous clays and minor thin coals (e.g. in the Traralgon Syncline and Yallourn to Glengarry area). East of Rosedale, the Morwell 1.A, seam grades laterally into Seaspray Group barrier sands. The break between the Morwell 1A and 18 seams at Morwell-Driffreld and Loy Yang is represented by lm of ligneous clay. Where the seams combine, however, it is represented by a dark coal lithotype band.

The Alberton Coal Measures (Thompson & Walker, t982) at Alberton and Gelliondale are not directly connected with the Morwell Formation, due to intervening uplift of the Baragwanath Anticline. They are, however, of the same age with fossils of the Proteacidites tuberculatus zone present. They also grade eastwards into an equivalent barrier sand sequence, which strikes northwards across the

centre ofthe seaspray and Alberton Depressions. Possible remnants to this barrier sequence are preserved on the Baragwanath Anticline, and within the downfaulted Gormandale Syncline extension (Holdgate, 1980) and Merrimans Creek Syncline (Thompson, 1979). This relationship suggests a continuous barrier sequence across the mouth of the Latrobe Valley extended for 15Okm between Port Albert in the south and Bairnsdale in the north.

At Alberton, the coal seams comprise an upper A seam, 55m thick, which is separated, from a lower B seam, 15m thick by a 12m clay split (Holdgate, 1982). The A seam extends at least as far as the Gelliondale Dome to the southwest, where it has been described as the Alberton seam (Greer & Smith, 1982). The B seam appears to join with an older seam of the Traralgon Formation, the C seam, combining across the Gelliondale Dome, to form the Gelliondale seam. To the west and north of Yarram, the Alberton Coal Measures remain to be fully defined. When not eroded, however, they grade

Geology of Australian Coal Basins

549

laterally into sands and clays of the Bodman Creek Formation (Thompson & Walker, 1982). Typically the Morwell and Alberton coal seams have a moisture content of between 58Vo and 63Vo, b:ot, where they are deeply buried or tightly folded, such as at Yallourn North, the moisture content may be reduced to 507o. In general, the ash constituents in low ash seams are uniform throughout the formation, but there are areas, such as at Flynn, where relatively high salt content and higher sulphur values occur, such as at Rosedale and parts of Alberton. Over half of the 35.8Mt of economically mineable brown coal reserves defined by Gloe (1980) in the Latrobe Valley occur in the Morwell Formation. The total possible geological resource of the Morwell Formation is 96.SMt (Holdgate, 1984).

Yallourn Formation The Yallourn Formation is the youngest coal-bearing

formation in the Latrobe Valley, and is dated by the zone fossil Triporopollenites bellus as being of Middle Miocene age. In a similar manner to the Morwell Formation, which it conformably overlies, the Yallourn Formation grades laterally eastwards into barrier sands ofthe Seaspray Group.

The Yallourn Formation is composgd mainly of the thick Yallourn coal seam, but in the deeper synclines may also include up to 200m of clay above that seam as well. Where the underlying Morwell 1A seam is fully developed, the two seams are separated by an interseam sequence, known as the Yallourn clay, which can be up to a further 5m in

thickness.

An unconnected coal-bearing sequence of equivalent age in the Moe Swamp Basin is known as the Yarragon Formation (Holdgate, 1985a). Coal seams of similar age have not been recorded at Alberton or Gelliondale, but ligneous clays overlying the Alberton Coal Measures contain the key zone fossil Triporopollenites bellus. The extent of the Yallourn seam in the Latrobe Valley Depression was modified to a greater extent by Late Miocene erosion than that of the underlying coal seams. However, isopachs suggest that most development occurred in the Maryvale and Yallourn areas, where a continuous seam up to 100m in thickness occurs. Elsewhere in the basin, seams >40m in thickness are restricted to the area south of the Latrobe River and up to the edge of the Loy Yang Dome, and down the Traralgon Syncline as far south as Churchill and Yinnar. Areas where the seam grades laterally into clays occur north-east of Tyers and southeast of Yinnar, while in most other areas the seam edges are determined by the subcrop

pattern.

The upper beds ofthe 200m thick Yarragon Formation in the Moe Swamp Basin contain coal seams. These include an upper 15m thick A seam and a lower 36m thick B seam on the Moe Monocline. Similar seams occur westwards at Yarragon, overlying the Thorpdale Volcanics. Both areas contain Triporopollenites bulles, and are therefore thought to be of the same age as the

Yallourn seam (Fraser, 1983).

Because of its lesser age and shallower depth of burial, relative to the Morwell seams, the Yallourn seam averages 65Vo-677o moisture where it is mined

in the Yallourn open cut. In the Traralgon and Latrobe Synclines, however, the seam can be buried by up to 200m of younger Yallourn and Haunted Hill Formation clays and, as a consequence, its moisture may be reduced to 60Vo. About 550km2 of the Latrobe Valley Depression are und,erlain by the Yallourn seam, from which 11.1x10e t were defined by Gloe (1980) as economically mineable.

Haunted llill Formation The Latrobe Valley Group in the western part of the

onshore Gippsland Basin is overlain by an extensive sheet of gravel, sand, silt and clay comprising the Haunted Hill Formation. This unit consists of a widespread sequence, up to 80m thick, of mottled coarse sand and fine gravel, clayey sand and gravel and sandy clays with lenticular beds ofpebble gravel and clay. In the highland areas north ofthe Latrobe Valley, the unit is often very pebbly, while between Morwell and Loy Yang, in the Traralgon Syncline, a distinctive clay facies is recognised. At Morwell Open Cut and Yallourn North Extension Open Cut, where extensive burning of the underlying coal has occurred, the Haunted Hill Formation consists of porcellanite and indurated claystone with accompanying breccias, fine gravel and sand. Laminated black and grey clays, which are localised in'fireholes'burnt in the underlying coal, are locally interbedded with, or more comrnonly overlie, typical Haunted Hill Formation sediments in the Morwell and Loy Yang Open Cuts.

Major tectonic movements in the Late Miocene resulting from NNW-SSE compression (Barton, 1981) folded the Latrobe Valley Group into essentially NE-SW trending structures (Figure 7). These major structures coincide with the configuration of the basement topography. More than 100m of Latrobe Group coals and clastic sediments were eroded from the anticlinal structures prior to deposition of the Haunted Hill Formation, thereby producing an angular unconformity between the Latrobe Valley Group coals, which sub-crop below the unconformity, and

the Haunted Hill Formation (Figure 8). The unconformity surface in these areas is characterised by erosional channels and weathering profiles in the coal at the interface, and is further modifred by deep fireholes from which the coal has been burnt, in some cases, after deposition of the Haunted Hill Formation. In structural lows, such as the Traralgon and Latrobe Synclines, a more complete Latrobe Valley Group sequence is preserved above the uppermost coal seam (the Yallourn seam) and no angular unconformity is recognised. Reducing conditions, which prevailed during Latrobe Valley Group sedimentation, allowed accumulation of coal and preservation of carbonaceous matter in clastic sediments together with the formation of authigenic siderite and pyrite. During the Late Miocene conditions were probably more oxidising, leading to the development of ferruginous palaeosols and locally abundant haematite cements in the Haunted Hill Formation.

COAL SWAMP DEPOSITIONAL EI{VIRONMENTS The great multiple seam thicknesses attained by Victorian (particularly Gippsland) brown coals are a characteristic which distinguishes them from most other brown coals in the world. Coupled with their overall low ash yield, this presents many difficulties

Gippsland Basin

550

r '

H Gts AN6LE JOINT TRENOS MCiW€LL OPEN CUT

STEREoORAPHTC

oecrE! I or €Qu^. rOLt, ^i.i' ^

pROJECTTON

HI6H AN6L E IOINTS

l*r.'.

-:__

E .olo rRENcs Loy yANG

MORWELL OPEN CUI

o99ror.d.r

LE6'ND 5 !cat:arri,; \' _a NIEa,r-

4[,1

.'fi .d.- t /

rrar or5J!.rror

A. SCHEMATC ViEW OF IYPICAL SIRUCIIJRES OEVELOPE: IN SEOIVENTS ABOVE A gASEMENI SHEAR

C. srEFEoGRApHrc pRolEcT oN PEcSiSiErr rN'ERME0IATE ANOLE JOrhrS

!'e!;s

MORWELL OPEN CUT

c:..w;rtt:/a

5 = l"E^n

Figure 7. Interpretive stress origins of some Latrobe Valley structures (after Barton, 1981). -

Figure 8. 'Concealed' outcrop of coal-bearing sequences in the Latrobe Valley.

Geology of Australian Coal Basins

551

may equally apply to the thicker Otway Basin coals such as at Bacchus Marsh and Anglesea (see Barton, Otway Basin, Victoria, this volume), but these coals have not been examined in as much detail as those of the Gippsland Basin.

in interpreting by analogy their depositional environments. Comparisons to present-day peat forming environments such as the Florida Everglades (Cohen, 1984), the Mississippi Delta (Kosters & Bailey, 1985) and the Canadian Tundra (Martini & Glooschenko, 1985) are unsatisfactory because most of these have little chance of accruing peat more than a few tens of metres in thickness before interruption by incursions of other sediment.

Distribution of Seams in Time and Space

By contrast, up to five major seams each containing over 100m of continuous low-ash coal have formed in Gippsland from original peat deposits many times this thickness. This situation also occurred simultaneously in several different parts of the basin, in some cases apparently continuously throughout a considerable part ofthe Tertiary Period during which many changes in climate and sea level occurred (Frakes, 1979; Vail & others, 1977).

Although late Tertiary folding has subsequently modified their original disposition (Holdgate, 1985b), the major coal seams in the Latrobe Valley occur as oval-shaped bodies ofcoal elongated along the centre ofthe depression. Each seam covers an area varying between 550 and 700km2, and each seam area includes one or more depocentres where continuous coal exceeds 100m in thickness (Figure 9). Up to almost 300m of almost continuous coal is locally developed where individual seams merge.

Maximum coal deposition is mostly on basement structural high areas. The coal depocentres of successive seams, however, are not spatially coincident (Holdgate, 1985b). They show evidence of migration from the western end of the depression for the Morwell 2 seam to a central valley position for the Morwell 18 and 1A seams, and then a return to

Because none of the current geological models for coal formation are satisfactory, when applied to Gippsland coals, the following features are thought to be important in understanding their exceptional

depositional setting. In many cases, these features

::\:::.:-,-

X""q.fu 61""."00,.&/ tt,,i._--l

iltit(

(

^-.-'-\y"N^"

Sirqtford

Q sor" Yotlourn

.Norih

)

'/Gotden 8€3ch

Yottourn

Morwett 1A

0utcrop edge KW of bqsin.

Limit of

0tigocene Miocene.

Morvett 2

Atberton A & B

,'r.h,/ -',^ \..)

Morwet[ 1B

Troro [gon

Figure 9. Major pre.erosional coal depocentres (80m coal) for the onshore Gippsland Basin.

Gippsland Basin

552 the westerly location for the Yallourn seam (Figure 9). This shifting of depocentres appears to be a consequence of differential compaction of the coal relative to its lateral sediment equivalents. The geometry of the Alberton Coal Measures in the Seaspray Depression is broadly similar, comprising

elongated oval-shaped bodies of coal (Holdgate, 1982). However, the direction of elongation in this area is meridional and parallel to the barrier sands of the marine Seaspray Group, whereas in the Latrobe Valley the dominant direction of elongation is normal to the barrier sequence. Further south, near Gelliondale and under Sunday Island, the seams broaden and appear to adopt a confrguration similar to that of the Latrobe Valley coal beds.

The effective surrounding of the main coal swamps by lakes was probably the major factor in the stabilisation of the coal swamp environments over long periods of time, thus allowing thick seams of low-ash coal to accumulate. Major influxes of sediment from the more destructive fluvial sources off the surrounding highlands (Barton, 1971) were

From the sparse data available, isopachs of the Traralgon Formation coal seams appear to indicate a similar elongated oval shape for the main coal depocentres, trending ENE from Stradbroke to Golden Beach parallel to the Baragwanath Anticline.

It is concluded from the above discussion that

extensive, thick peat swamps tended to form in elongated, oval-shaped areas, either immediately behind the barrier systems or within structural depressions located further inland, such as the Alberton, Latrobe Valley and Moe Depressions. Local structuring and differential compaction within these depressions appear to have controlled where the maximum coal seam thicknesses were developed

Facies Equivalents and Thick Seam Deposition In all directions, other than towards the marine barrier systems, the non-coal facies equivalents of the thick Morwell, Yallourn and Alberton seams are

.^tFdt

The maintenance of stable barrier sand sequences across the onshore Gippsland Basin was probably structurally controlled. The barriers prevented

Swamp Floras A number ofpalaeobotanical studies have been made on the floral constituents of the Gippsland coals, the variations of which contribute to the distinct lithotype banding (see following section on 'Coal Resources'), and assist with the interpretation of the coal's depositional environment. Microfossil studies (Baragwanath & Kiss, 1964; Harris, 1971; Partridge, L97L, L982; Kershaw & Sluiter, 1982) have detailed the abundant spore pollen assemblages deposited within the coal swamps, providing a basis for age classification and

predominantly clay sequences, which were deposited between the peat swamps and the higher ground surrounding the structural depressions (Holdgate, 1985). The clays are predominantly kaolinitic, and are considered to have been deposited in mainly lacustrine environments which, on the swamp margins, intertongued in a complex manner with the peat swamps. Other than on local structural highs, {

generally dissipated at the lake edges, with the suspended clay matter flocculating and settling under the acidic waters of the swamp margins. The lakes would also have provided (by lateral diffusion) a ready source ofnutrient-rich water for vegetation growth within the swamp itself.

significant marine transgressions into the coal swamps, but eustatic sea level changes did produce minor sand incursions into the swamps at their marine edges. This can be readily seen at Alberton, where the coals become sandier as the barriers are approached (Holdgate, 1982). Similar barrier sequences to the Traralgon Formation coal swamps are also recognised in the offshore Gippsland Basin (Partridge, 1982; Thorrlpson, 1985).

(Figure 10).

-I

such as the Loy Yang Dome and the Morwell Anticline, the lake systems periodically expanded to flood over the peat swamps, and these expansions are represented by the thin interseam sediments. Differential compaction also allowed migration of the lacustrine sequences over former coal swamp areas, causing a relocation of coal depocentres.

v.Lrar

':__

".::::,-"":

LrreGE rvtr P€.r -o?o*{ co^r r-_^c.uxur^r'ox

I :

o..t r"."",u1

toe.c'!6

los F@rktts d r{ oreo'6 Mf,G

Figure 10. Block model of brown coal accumulation in the Latrobe Valley; nominal size of base of block about 50km (after Barton, 1986).

Geology of Australian Coal Basins

553

Table l.In situ weighted coal-property averages for the rnain Eeams in-the Latrobe Valley. All weight percentages on a dry coal basisl samples are from boreholes. @

SEAM

t'xEE Ash E-." 'E+* ?&iHSEfl vo

BFEi €$;E

Volatile Net Wet (MJ/kg)

s5!g sEEE YALLOURN

11 065

MORWELL

18 862

TRARALGON

5 828

35 754 TOTAL * based on Gloe, 1980

6s.4 60.0 56.2 60.4

NazO

AlzOs

Matter Specific Vo Energy

3.2 2.7 2.6 2.8

52.7 50.6 50.9 51.1

correlation of the pollen type and abundance with lithotype. Macrofossil studies (Cookson & Duigan, 1950, 1951; Patton, 1958; Duigan, 1966; Blackburn, 1980, 1985) have also identifred t}re in si/u plant tissue and structures within the coal swamps, and their vertical variabilities within particular seams. From the above studies, the swamp forests were found to contain ancient representatives ofthe modern kauri pine (Aqathis sp), Norfolk Island Pine (Araucaria sp), Banksi a (Banksia sp), and Huon Pine (Dacrydium sp). The southern beech or myrtle (Nothofagus sp) grew on the surrounding hills and is only represented in the coal formations by

wind-blown pollen. Eucalyptus is not identified in the coal sequence, and it appears that this genus was either not adapted to swampy conditions or was not present at the time of deposition of the brown coal.

In vertically cyclical sequences (Mackay & others, 1985) light lithotypes comprising dominantly leaf coatings (cuticles) spores and pollens grade downwards through medium light and medium dark lithotypes into dark gelified plant debris and woody coals forming dark lithotypes. The origin of these lithotypes and their cycles remains controversial (see Diessel & Smyth, this volume), but is generally thought to at least partly originate from fluctuations ofwater levels (George, 1975; Blackburn, 1981; Mackay & others, 1986). In a comparison of the plant macrofossils in the Yallourrrand Morwell open cuts, Blackburn (1985) concluded that both seams contain assemblages now widely distributed in both mesic and xeric environments. However, assemblages in the Yallourn seam suggest lowland wet sclerophyll floras, controlled by water levels and by frequency and intensity of fires. By contrast, Morwell seam assemblages are relatively more mesic, with affrnitieslo modern secondary rain forests, tropical wet sclerophyll and tropical to subtropical swamp floras. Depositional environments also appeared to have been more homogeneous than for the Yallourn seam, although the latter conclusion may be influenced by the sample locations. Yallourn open cut is located near the western edge of the Yallourn seam, whereas Morwell open cut occurs within one of the Morwell seam depocentres. In a similar manner, frequency of lithotype banding and abundance olthe light and dark lithotype end members are more prevalent towards seam margins, such as in the western batters of Yallourn Open Cut (Mackay & others, 1986). By contrast, medium light

7.r 8.3 9.7 8.1

0.22 0.46 0.73 0.43

0.25 0.27 0.66 0.33

0.82 0.52 0.38 0.58

0.24 0.18 0.05 0.17

0.31 0.34 1.51 0.53

0.16 0'13 0.04

0.r2

and medium dark lithotypes are more prevalent in the coal depocentres such as in the Morwell seams at Morwell and Loy Yang oPen cuts.

COAL CHARACTERISTICS The Latrobe Valley coals can be classified as soft brown coal under the classifrcation of German coals (Stach, 1975). Their high moisture content (ranging frorn 487o to 7 07o) and resulting low specific energ:y (net wet specific energy of 5.8 to 11.5MJ/kg) makes the coal a low grade fuel. The ash levels in brown coals throughout the valley are extremely low

(Table 1), but there is a wide variation in other physical and chemical properties both laterally and vertically across the Latrobe Valley.

Prior to late 1950, the State Electricity Commission of Victoria carried out only proximate analysis on Victorian brown coals. However, following problems encountered in burning of coal from Morwell Open Cut, further ash analyses (minerals alrd inorganics) were commenced in the late 1950s and continue to date. Most of the analysed samples were taken from boreholes.

Average values for selected parameters- are listed in Table 1. These were calculated from values presented by Gloe (1980) and are based-on Gloe's defined category of 'economically winnable coal reserves'. Coat with ash above I07o was not included

in the determinations.

Moisture and Specific EnergY There is a general tendency for the moisture content

of the coal to decrease with depth, producing a downward increase in coal rank. This is due to the increase in the degree ofconsolidation with depth of

burial. There is, hbwever, also a general reduction in moisture from west to east as the general age of the seams increases, while local variations in moisture content are also evident. The bed moisture content is significantly higher than the coal's equilibrium rnoisture holding capacity. This means that the equilibrium moisture coirtent is a better quality parameter for brown coal

than the bed moisture content used for black coal (Kiss, 1982). As a consequence, the net wet value has been given for the specific energy ofthe coal in Table 1, ai it provides a good guide to the available energy of the'as mined'Pqoduct._A general increase in spicific energ'y occurs due to the loss of moisture with depth, and the lighter coloured coal lithotypes also tend to have higher specific energy values.

Gippsland Basin

554

Overall, of course, the low net wet specific energy values reflect the high moisture levels of the coal in general.

Ash Constituents The brown coals of the Latrobe Valley are arbitrarily classified as 'coal' only if the ash yield on combustion is <lOVo (dry coal basis). Material with between 10 and 30Vo ash is classified as 'inferior coal', while material with >30Vo ash is regarded as

'ligneous clay'. The average ash percentage of Latrobe Valley coals (dry basis) is between 1 and 4Vo.lt may be slightly higher elsewhere, but is generalTy <67o.

Within individual seams, the ash percentage tends to decrease from a level corresponding to inferior coal at the upper and lower contacts with the interseam strata to less th.ar, 0.5% in the central part of some coal beds. Inferior coal, mainly occurring in this way, accounts for between 4 and 7Vo of tir'e region's total economically mineable coal resources.

It has been assumed, in the past, that the ash is

derived solely from crystalline minerals occurring within the coal, but this assumption is not necessarily true for all brown coals since up to one third of the ash weight can also be derived from organic sulphur present (Kiss, 1982). A method of

direct chemical analysis is used to sub=divide the inorganic component of the coal into 'mineral' and 'inorganic'categories (Kiss & King, 1977). The 'minerals' occur as adventitious small discrete particles of clay, quartz and pyrite or marcasite. The greater part ofthe ash, however, appears to be derived from the'inorganic' constituents, the majority of which occur as cations bound to the coal substance via carboxylic acid groups (Murray, 1968). The major inorganic constituents in the coals are iron, titanium, potassium, chlorine, silicon, aluminium, magnesium and sodium. These apparently originated from the following processes:

. . .

constituents present in the original vegetation; dissolved or suspended material introduced into the swamp by water or wind at the time of deposition, and dissolved or suspended material introduced into the coal after its formation.

The 'mineral' components, introduced into the coal as adventitious particles, are generally unevenly distributed through the coal, whilst the'inorganic' constituents as defined above tend to be more uniformly dispersed. Sodium chloride, for example, can be present as a significant proportion (>L%o) of the ash in samples taken from the top of some seams at some localities. Relocation of sodium and other inorganics by ion-exchange processes operating through the water-saturated coal mass is considered to be the most signifrcant mechanism for this sodium concentration (see Ward & Swaine, this volume). Trace elements detected within the coal (Dimitriakis & others, 1976) are barium, strontium, zinc, arsenic, copper, cobalt, chromium, gallium, germanium, lanthanum, manganese, molybdenum, nickel, lead scandium, vanadium and zircon.

Sulphur occurs as pyrite or marcasite, as well as organic sulphur, with pyritic sulphur varying from a small to a large percentage of the total sulphur

present. There is a trend for organic sulphur to increase eastwards towards the western limit of the Tertiary marine sediments in the basin, with the values ranging from <0.!Vo at Yallourn in the west, for example , to >\Va south of Sale township. This eastward increase in sulphur is also reflected in the higher sulphur values for the Traralgon seam

(Table 1), as this seam mainly occurs to the east, near to and beneath the marine margins, in an area where the Yallourn and Morwell seams are generally absent.

Minerals such as qtartz, kaolinite and iron sulphides can comprise up to half the ash-forming constituents, and may also provide a useful indicator of sediment conditions at the time of deposition (Gloe, 1984). The influence which the surrounding palaeoenvironment had on the coal swamps can be seen if the weighted average ash constituents in each field area (Gloe, 1980) are compared to the coal seam isopachs for the Morwell 18 seam (Figure 11). It is apparent that proportion of 'minerals' tends to increase towards the seam boundaries, while other 'inorganics', such as sodium, magnesium and chlorine, tend to be proportionally higher in the main coal depocentres.

At the seam boundaries themselves, such as at Yinnar and Churchill, where the coal grades laterally into lacustrine clays, the iron content of the coal appears to increase proportionally. As the clays are high in iron and contain bands ofiron carbonate (siderite), it appears likely that iron precipitation occurred in the lake waters, with some of this iron entering by lateral diffusion into the adjacent swamp environment. A similar situation occurs in the Yallourn seam at Tyers, where another lake-swamp interface oqcurs.

Increases in organic sulphur in coal seams is generally considered indicative of proximity to marine conditions (e.g. Suggate, 1959; Horne & others, 1978). Organic sulphur tends to increase towards the marine barrier system in all Gippsland coals, as documented at Stradbroke (Thompson, 1980), Holey Plains-Coolungoolun (Holdgate, 1980), Alberton (Holdgate, 1982) and in the Latrobe Valley (Holdgate, 1985; Kiss & others, 1985). Where marine sediments stratigraphically overlie coals of the Traralgon Formation, the sulphur content tends to be higher in the uppermost seam, confirming that stratigraphic proximity to marine deposits controls the sulphur content (Holdgate, 1980). The weighted average sulphur content can also be used to indicate the position of maximum marine transgression on the Baragwanath Anticline (Thompson, L980; Holdgate, 1980). The distribution of sulphur is more complex in the Latrobe Valley, and sulphur appears to be higher in

the Morwell seams near the marine boundary than in the Yallourn seams. This relationship is indicative of a receding marine influence during deposition of the latter seam. Kiss & others (1985) consider that sulphates, derived from marine waters, formed the source for the in situ production of reduced sulphur species (HzS and S) and their incorporation in the reactive coal matrix.

Coal Type Variation Well-developed lithotype banding occurs within the thick onshore coal seams of the Latrobe Valley Group (Mackay & others, 1986), and a frve-fold classification of dark, medium-dark, medium-light, light and pale lithotypes, based on variations in

Geology of Australian Coal Basins

bbb

Figure 11. Isopachs of the total Morwell B18 seam, and relative percentages of minerals to inorganics for Latrobe Valley field areas. colour land texture of the coal, was established for these coals by George (1975). The darker lithotypes have greater gelification, with usually larger quantities of coarse grained tissue particles and lower liptinite than the light and pale lithotypes at the opposite end of the spectrum. Inertinite is rare in alf lithotypes, although small amounts of fusinite occur almost exclusively in the dark lithotypes (Bolger, 1984, 1985; Smith, 1980).

The lithotypes range in thickness from <1"0cm up to several metres, although within a particular lithotype band there may be considerable change in macroscopic and microscopic character. Medium-l1ght and medium-dark lithotypes are the most abundant in all seams, and appear to represent the most typical peat type from which the thick seams formed. The thickness and lateral extent of the lithotypes and the relationships between them vary bottr laterally and vertically within each seam.

Lithotype variation is best displayed by the Yallourn seam, which contains a high proportion of dark, (up to 24Vo by volume), and medium-dark (up to 687o by volume) lithotypes. In addition, where it is exposed in Yallourn Open Cut, several lithotype assemblages are recognisable. These include a basal unit comprising thinly bedded lithotypes ranging from dark to pale, and a massive marker horizon, comprising an extensive 10m to 15m thick dark-medium-dark zone and a prominent medium-light lithotype, containing abundant large stumps and logs. These assemblages can be correlated over several kilometres across the open cut, but undergo lateral changes to the east. The basal unit oftf,inly bedded lithotypes, ranging from dark to pale, is widespread in the Yallourn seam across the Latrobe Valley generally, and appears to

be an important facies relating to the-stability of the peats at the initiation of coal accumulation.

In contrast to the Yallourn seam, the Morwell seam does not have well-defined thick marker horizons' It contains few dark lithotype bands, but has up to 387o by volume of light lithotypes- Thin individual lithotype bands can be recognised over several hundied metres, but their thinness, combined with common lateral lithotype changes, preclude recognition of more laterally extensive marker horizons.

A common association in the Morwell seam is the presence of lightening upwards cycles (Smith, 1980; Mackay & others, 1985) comprising thin medium-dark and dark lithotypes grading up to light or pale lithotypes. The contact with the basal dirk or medium-dark lithotype of the overlying cycle may be either sharp or gradational through a medium-Iight lithotype. Although the Morwell seams show overall similarities across the Latrobe Valley, there are microscopic variations between coals at the major depocenties at Morwell and Loy Yang' Most notably, tha lighter lithotypes in the Morwell 1 Seam at Morwell are more gelified and contain lesser amounts of liptinite than their equivalents at Loy Yang. The Traralgon 1 seam is dominated by medium,-light

lithotypes (SO-AAEI) with subordinate medium-dark (up to 36Eo),lig}r.t(5-L7V") and minor dark (<57o) and pale lithotypes (O-IV,). No laterally extensive iithotype asiemblages can be identified, but the microp-etrographic properties of the lithotypes are consistent *ith those of the Morwell and Yallourn seam coals.

Gippsland Basin

556 The Traralgon 2 seam differs from the other Latrobe Valley Group coals in the onshore Gippsland Basin. The lithotypes are very poorly bedded with gradational boundaries, have poor colour differentiation and are distinguished largely on textural features. Microscopically, the lighter lithotypes contain small amounts of coarse tissue material, have a low abundance of gelified macerals and, in contrast to the overlying seams, do not contain large amounts of liptinite. Further variations in the Traralgon 2 seam occur on the eastern edge of the Baragwanath Anticline, where the seam has attained a higher rank than elsewhere. The coals in this area are brittle with a dull lustre, and Latrobe Valley type lithotypes cannot be readily identified. Coals occurring offshore in the Gippsland Basin (included within the Latrobe Group) are of higher rank than the onshore Latrobe Valley Group coals, reaching up to medium volatile bituminous rank (Smith, 1982). The variations in the offshore Latrobe Group coals are summarised by Smith (1982), who distinguished a suite of Middle to Late Eocene coals and an older Late Cretaceous to Early Eocene suite.

The Middle to Late Eocene coal seams are laterally extensive and thickest in the western parts of the central deep in the offshore Gippsland Basin. Maximum seam thicknesses are up to 30m, although the seams are more typically 2 to 5m thick. They consist of moderately well banded clarain and vitrain, with minor durain and contain high vitrinite and low inertinite (Smith, 1982). These coals are time equivalents to, and probably continuous with the Traralgon 2 seam, which is best developed in the coastal regions of the onshore part of the basin. Although the Traralgon 2 seam has not attained the same rank as the offshore coals, the

significant difference between it and the younger Latrobe Vn,lley coals suggests that the Traralgon 2 seam has closer affinities with the offshore coals. More detailed petrographic and stratigraphic analysis is required to establish the relationships between these coals and their lithotype assemblages. The Late Cretaceous to Early Eocene coals occurring offshore are typically lenticular, with major seam splits and partings of mineral matter. These coals are commonly 1 to 2m thick, but may reach 20m. They contain thin bands of clarain, vitrain and durain with minor fusain, and are distinguished from the overlying coals in that they contain significant amounts of inertinite (Smith, 1982).

Properties for Coal Utilisation The major use of raw brown coal in the Gippsland Basin is as feedstock to generate some 857o of Victoria's electricity needs. Up to 1Mt of briquettes are also produced for industrial and domestic use

per year. The high volatile contents and high hydrogen to carbon ratios ofthe brown coal favour gasification and conversion to hydrocarbon liquids (Perry, 1982), whilst the low ash, coupled with a commonly favourable coal structure, means that brown coals can be used as excellent feedstocks for the production ofhigh quality chars and carbons.

Ongoing research is being carried out into upgrading the brown coal into forms which are more convenient for transportation and combustion. An example is the production ofsolar dried high density coal from slurries of high moisture brown coal (Anderson & Woskobeonko, 1985).

COAL RESOURCES The total brown coal resource in the on-shore Gippsland Basin is estimated by Holdgate (1984) as 394 000Mt. Approximately one-third of this coal is classified as a Demonstrated Resource and the remainder as an fnferred Resource. Gloe (1979) has established Demonstrated Resources of 111 947Mt and Inferred Resources of 4300Mt. This gives a total of 116 247Mt for the onshore Gippsland Basin up to the present western limits of the Gippsland Limestone. Gloe's resource figures do not include the relatively minor quantities of brown coal in either the northeast of the Latrobe Valley, or in any discrete deposits of less than 10Mt. Seams of <3m thickness, which comprise comparatively minor amounts of coal and are diffrcult to defrne, are also excluded.

More recently, the Victorian Brown Coal Council (1983) has established reserves using the following

criteria:

. . . .

coal to waste ratio of >0.3;

maximum depth of 500m;

minimum seam thickness of 3.0m; inclusion of intra-seam sediments <0.5m thick as coal;

40Vo ash dry basis.

These reserves, termed Geological Resources in the VBCC report (VBCC, 1982) are given as 88 445Mt Demonstrated and 80 000Mt Inferred, giving a total of 168 445Mt.

Stanley (1986) presented a tabulation based on the work of Barton (1985) equating the Victorian Brown Coal Council resources with those of Gloe (1979), and provides an updated total'resource' of L72 874Mt to a general maximum depth of 500m. The Economic Reserves of the Gippsland Basin, under the criteria defined by Gloe (1979), were estimated at 44 l54Mt. The Victorian Brown Coal Council (VBCC, L982), has tabulated the extraction costs for an estimated useable total brown coal reserve of 48 982Mt.

A comprehensive review of the brown coal resources in the Gippsland Basin was presented in 1986 by the Interdepartmental Committee on Brown Coal Resource Boundaries (Latrobe Region Framework for the Future, Part 3), which identified a total of 98 000Mt based on the following criteria:

coal to waste ratio of >0.5;

" . r

minimum seam thickness of 3m; maximum depth of 300m; other criteria as for the VBCC estimate above.

Exclusions associated with towns, industrial sites and other areas amounted in this assessment to 3000Mt, leaving a total planning reserve of 68 000Mt.

Production from open cuts operated by the State Electricity Commission of Victoria between 1923 and June 1990 is tabulated in Table 2. The remainder of the production, which occurred between the mid-1880s and L924, was small, and comprised a

Geology of Australian Coal Basins

557

Table 2. Production reconds,for.SECV operations in thC Latrohe Valley, OPEN CUT

Morwell Yallourn Yallourn North Yallourn North Extension Loy Yang Total

CUMULATIVE COAL PRODUCTION (1923-1990) tonnes 356 713 586 610 490 369 16 620 1 40 I 394 768 72 432 811 1 065 651 664

total of <100 000t. This coal was won from open cuts at Yallourn North, Gelliondale and Won Wron, and from underground operations at Boolarra, Mirboo, Trafalgar and Hazelwood. Some 45Mt of coal were dug from the Latrobe Valley by the SEC during the 1989-90 statistical year. Most of this coal was used to produce electricity, but some 1.8Mt of coal were alsb used to produce briquettes and char.

REFERENCES ABELE, C., KENLEY, P.R., HOLDGATE, G. & RIPPER, D., 1976: Otway Basin. In Douglas, J.E. & Ferguson, J.A. (Editors): Geology of Victoria. Geological Society of Australia Special

Publication, 5, L98-229. ANDERSON, B. & WOSKOBEONKO, F., 1985: Solar

dried slurried low-rank coal. Proceedings of

Conference on Lignite Industry in Thailand,

September, L985, 18, 12.

BARAGWANATH, G.E. & KISS, L.E., 1964:

Palynological investigation of Victorian brown coals. State Electricity Commission of Victoria, Project Report 2.

BARTON, C.M., 1971: The Morwell interseam sands. Journal of the Geological Society of Australia,lT, L9L-204. BARTON, C.M., 1981: Regional stress and structure in relation to brown coal open cuts ofthe Latrobe Valley, Victoria. Journal of the Geological Society of Australia, 28, 333-339. BARTON, C.M., 1985: Upgraded resource quantities. State Electricity Commission of Victoria, Exploration and Geological Division Technical

Note, 122. BARTON, C.M., 1986: Latrobe Valley excursion guide. 1n Excursion Guide to Victorian Geology, Australian Academy of Science, Chapter 13-3.

BLACKBURN, D.T., 1980: Summary of the findings of a survey ofthe relationships between coal lithotypes and megafossil assemblages in the Yallourn Open Cut. Report to State Electricity Commission of Victoria Palaeobotany Project 1. BLACKBURN, D.T., 1981: Floristic control on lithotype banding within the Yallourn seam, Yallourn Open Cut: evidence from megafossil assemblages. Report to State Electricity Commission of Victoria Palaeobotany Prcject 2. BLACKBURN, D.T., 1985: Palaeobotany of the Yallourn and Morwell brown coal seams. Report to State Electricity Commission of Victoria Palaeobotany Project 3.

BLAKE, R., 1985: Seismic-stratigraphic interpretation of coastal barrier systems of Late Eocene age, offshore Gippsland Basin. 1n. Glennie, R.C. (Editor): Proceedings of Second South-east Australian OiI E xploration Sy rnp o siurn. Petroleum Exploration Society of Australia, Melbourne, 159-169. BOLGER, P.F., 1984: Lithofacies assemblages and boundary relationships of the Tertiary Latrobe Valley Group and overlying strata in the Latrobe Valley, Victoria. M.Sc. Thesis, Department of Earth Science, Monash UniversitY. BOLGER, P.F., 1985: Soft or weathered coal in the opening up area ofLoy Yang Open Cut' State Electricity Commission of Victoria, Exploration and Geological Division Technical Note, 106. BROWN, 8.R., 1975: Offshore Bass Basin, Bass Strait. 1n Traves, D.M. & King, D. (Editors): Economic Geology of Australia and Papua New Guinea: 2 Coal. Australasian Institute of Mining and 6, 364-365. Monograph, Metallurgy, CAREY, S.W., 1970: Australia, New Guinea and Melanesia in the current revolution in concepts of the evolution ofthe Earth. Search, l, 178-189. COHEN, A.D., 1984: The Okefenokee Swamp: a low-sulphur end-member of a shoreline-related depositional model for coastal plain coals. ln Rahmani, R.A. & Flores, R.M. (Editors): Sedimentology of CoaI and Coal-bearing Strata. Special Publication, International Association of Sedimentologists, 23 1-240. COOKSON, I.C. & DUIGAN, S.L., 1950: Fossil Banksia from Yallourn, Victoria, with notes on the morphology and anatomy of living species. Australian Journal of Science and Research,lS, 133-165.

COOKSON,I.C. & DUIGAN, S.L., 1951:Tertiary Araucariaceae from south-eastern Australia, with notes on living species. Australian Journal of Science and Research, L4, 4L5-449.

DIMITRIAKIS, P., RANKIN, D. & SCHAPP, H., 1976: The determination of minor and trace elements in brown coal ash by X-ray emission methods. Slate Electricity Commission of Victoria, P and I Department, Scientific Diuision Report, 321. DUIGAN, S.L., 1966: The nature and relationships of the Tertiary brown coal flora ofthe Yallourn area' Victoria. P alaeobotanist, 14, 199-20 1. FRAKES, L.A., 1979: Climates throughout Geological T ime. Elsevier, Amsterdam. FRASER, N., 1983: Exploration Licence 1800, Trafalgar: final report to Department of Minerals and Energy, Victoria. Unpublished Report, Coal and Synthetic Fuels Department, Esso Australia Limited. GEORGE, A.M., 1"975: Brown coal lithotypes in the Latrobe Valley deposits. State Electricity Commission of Victoria, Exploration and Geological Division, Petrological Report 17. GLOE, C.S., 1960: The geology of the Latrobe Valley Coalfield. Proceedings of the Australasian Institute of Mining and Metallurgy, 194,57-725. GLOE, C.S., 1975: Latrobe Valley coal frelds. /n Traves, D.M. & King, D. (Editors): Economic Geology of Coal. Australia and Papua New Guinea:2 Australasian Institute of Mining and -Metallurgy, Monograph,6, 345-359.

Gippsland Basin

558 GLOE, C.S., 1976: Brown coal. In Douglas, J.G. & Ferguson, J.A. (Editors): Geology of Victoria. Geological Society of Australia, Special Publication, 5, 378-389. GLOE, C.S., 1979: The brown coal reserves of Victoria. Proceedings of the Symposium on Estimation and Statement of Mineral Reserues. Australasian Institute of Mining and Metallurgy, Sydney, 49-61. GLOE, C.S., 1980: The economically winnable brown coal reserves in the Latrobe Valley. State Electricity Commission of Victoria, Exploration and Geological Division Report 26. GLOE, C.S., 1984: The geology, discovery and assessment of the brown coal deposits of Victoria. In Woodcock, J.T. (Editor): Victoria's Brown Coal in chancery. Australasian - a hugeoffortune Institute Mining and Metallurgy, Monograph,

11,79-109.

application ofpollen analysis to the elucidation of Latrobe Valley brown coal depositional environments and stratigraphy. Australian CoaI Geology,4, 169-183. KISS, L.T., 1982: Chemistry of Victorian brown coals. Australian Coal Geology, 4, 153-168. KISS, L.T. & KING, T ., 1977 : The expression of results ofcoal analyses: the case for brown coals. FueI,

56,340-34r.

KISS, L.T., BROCKWAY, D.J., GEORGE, A.M. & STACY, W.A., 1985: The distribution of minerals, inorganics and sulphur in brown coal. Proceedings of International Conference on CoaI Science, Sydney, 589-596. KOSTERS, E.C. & BAILEY, A., 1985: Characteristics of peat deposits in the Mississippi delta plain. American Association of Petroleum Geologists,

Round Table Abstracts, 1466-1467.

GREER, LR. & SMITH, G.C., 1982: Geology of the Gelliondale coalfield. Australian Coal Geology, 4,

71-89.

MACKAY, G.H., ATTWOOD, D.H., GAULTON, R.J, & GEORGE, A.M., 1985: The cyclic occurrence of

brown coal lithotypes. State Electricity

HARRIS, W.K., 1971: Tertiary stratigraphic palynology, Otway Basin. 1n Wopfner, H. & Douglas, J.G. (Editors): The Otway Basin of Southeastern Australia. Geological Surueys of South Australia and, Victoria Speciril Bulletin,

67-87. HOCKING, J.B., 1969: A summary of the stratigraphy and petrology of the Lower Tertiary sediments of the Lake Wellington Depression, east Gippsland. Geological Survey of Victoria, Report 1969/59. HOCKING, J.8., 1976: Geological evolution and hydrocarbon habitat, Gippsland Basin. The APEA Journal, L2, 132-137. HOLDGATE, G.R., 1980: Geology of the Holey Plains-Coolungoolun coalfrelds and the Willung-Merrimans Creek area. State Electricity Commission of Victoria, Exploration and Geological Division Report, L980/2. HOLDGATE, G.R., 1982: Brown coals and facies equivalents ofthe Alberton area, Gippsland, Victoria. Australian Coal Geology, 4, 57-70. HOLDGATE, G.R., 1984: Latrobe Valley brown coals: their subsurface distribution and the brown coal geological resources ofthe Gippsland Basin. Exploration and Geological Report 29. HOLDGATE, G.R., 1985a: Stratigraphy, structure and brown coals of the Moe area. Australian CoaI Geology, 5, l-I2.

HOLDGATE, G.R., 1985b: Latrobe Valley brown coals: their geometry and facies equivalents as a guide to depositional environment. Australian Coal Geology, S,53-68.

HORNE, J.D., FERM, J.C., CARRUCIO, F.T, & BAGANCZ, B.P., 1978: Depositional models in coal exploration and mine planning in the Appalachian region. American Association of P etroleum Ge olo g ist s B ull et in, 62, 237 9-2 4ll. JAMES, E.A. & EVANS, P.R., 1971: The stratigraphy of the offshore Gippsland Basin. The APEA

Journal, LL,7\-74.

KERSHAW, A.P. & SLUITER, I.R., 1982: ThE

Commission of Victoria, Research and Development Department Report, 50/85/93.

MACKAY, G.H., GAULTON, R,J., HOLDGATE, G.R. & GEORGE, A.M., 1986: The origin of Latrobe Valley brown coal lithotypes: a review. Abstracts, 72th International Sedimentological Congress, Canberra.

MARTINI, I.P. & GLOOSCHENKO, W.A., 1985: Cold climate peat formation in Canada and its relevance to Lower Permian coal measures of Australia. Earth Science Reuiews, 22, L07-140. MURRAY, J., 1968: The state of combination of the

inorganic ash-forming constituents of Yallourn brown coal. State Electricity Commission of Victoria, P and I Department, Scientific Diuision Report, MR-145. PARTRIDGE, A.D., 1971: Stratigraphic palynology of the onshore Tertiary sediments of the Gippsland Basin, Victoria. M.Sc. Thesis, School of Applied Geology, University of New South Wales. PARTRIDGE, A.D., L976: The geological expression of eustacy in the Early Tertiary of the Gippsland Basin. The APEA Journal, 16, 7 3-7 L PARTRIDGE, A.D., 1982: Palynological evidence for age and environment ofdeposition ofTertiary coals in the Gippsland Basin. Australian Coal Geology,4, 90-91. PATTON, R.T., 1958: Fossil wood from Victorian brown coal. Proceedings of the Royal Society ofVictoria, 70, t29-143. PERRY, G.M., 1982: Liquefaction of brown coal. Australian CoaI Geology, 4, 217 -227 . RICHARDS, K.A. & HOPKINS,8.M., 1969: Exploration in Gippsland and Otway Basins. ECAFE Natural Resources Symposium, Canberra.

SMITH, G.S., 1980: Macropetrology.In Higgins, R.S., Kiss, L.T., Allardice, D.J., George, A.M. & King, T.N.W.: Properties of brown coal from the Latrobe Valley, State Electricity Commission of Victoria, Research and Development Department, Report sc/80/17.

Geology of Australian Coal Basins

559 SMITH, G.C., 1982: A review of the Tertiary-Cretaceous tectonic history of the Gippsland Basin and its control on coal measure sedimentation. Australian Coal Geology, 4, 1-38. STACH, E. MACKOWSKY, M-TH., TEICHMULLER, M., TAYL.OR, G.H., CHANDRA, D. & TEICHMULLER, R., L985: Stach's Textbook of Coal Petrology (Srd Edition). Gebruder

Borntrdger, Stuttgart. SUGGATE, R.P., 1959: New Zealand coals: their geological setting and its influence on their properties. New Zealand Department of Scientific and Industrial Research Bulletin, 134. THOMAS, D.E. & BARAGWANATH, W., 1949-51: Geology of the brown coals of Victoia. Mining and Geological Journal of Victoria, g(6), 28-55; 4(1), 36-52; 4(2), 4L-53;4(3), 36-50. THOMPSON, B.R., 1980: The Gippsland sedimentary basin: a study ofthe onshore area. PhD Thesis, University of Melbourne.

THOMPSON, 8.R., 1985: The Gippsland Basin development and stratigraphy. 1n Glenie, R.C. (Editor): Proceedings of Second Southeast Australian Oil Exploration Symposiurn. Petroleum Exploration Society of Australia, Melbourne,

57-64. THOMPSON, B.R. & WALKER, G.M., 1982: ThC geology ofthe Seaspray Depression, Gippsland Basin. Australian Coal Geology, 4, 39-56.

VICTORIAN BROWN COAL COUNCIL, 1982: Victorian Brown Coal Resource Development Study: the brown coal resource. Victorian Brown Coal Council, Melbourne, 3.

VAIL, P.R., MITCHUM, R.M. & THOMPSON, S., 1977: Seismic stratigraphy and global changes ofsea level, global cycles ofrelative changes ofsea level. In Payton, C.E. (Editor): Seismic Stratigraphy: applications to hydrocarbon exploration. American Association of Petroleum Geologists, Mernoir 26, 4, 83-97.

WELLMAN,P., I974: Potassium-argon ages on the Cainozoic volcanic rocks of western Victoria, Australia. Journal of the Geological Society of Australia, 21, 359-368.

Gippsland Basin

561

WKrrray Basin in Victoria

and New South Wales

MELEOURNE

CM Brown

J Preston and CS Gloe 200 lm

Figure 1. Locality Map of the Murray Basin.

GEOLOGICAL SETTING The Murray Basin is a saucer-shaped, intracratonic basin of thin, flat-lying Cainozo^ic sediments which occupies an area of 300 000 km' and encompasses parts of northwest Victoria, southeast South Australia and western New South Wales (Figure L).

Groundwater investigations over the past 100 years have indicated the presence of extensive deposits of Tertiary lignite within the Eocene to mid-Miocene sediments of the basin. Although no economic deposits have been identified, the discoveries ofthe sub-economic Bower Coalfield in 1902, the Moorlands Coalfield in 1910, and the Anna Coalfield in L927 at the western margin of the basin (Figure 2) have encouraged exploration for coal in South Australia (Johns, 1975; Kress & others, 1978). In 1979 Western Mining Corporation discovered the Kingston deposit, which consists of 985Mt of lignite in contiguous Middle Miocene sediments of the Gambier Embayment in the Otway Basin (Figure 2).

In Victoria, groundwater bores have encountered widespread, thin but discontinuous coal seams within Eocene to mid-Miocene fluvio-lacustrine and paralic sediments beneath the Riverine Plain. In addition, CRA Exploration have discovered major deposits in the Kerang, Torrumbarry and Eucha regions of northern Victoria. No equivalent deposits have been identified within the New South Wales portion ofthe basin, although thick carbonaceous sediments occur beneath the Riverine Plain. The limited analyses carried out on the carbonaceous sediments indicate that they have undergone varying degrees of coalification. They

Murray Basin in Victoria and New South Wales

562

144"

Lgtr

o .

-^rq-i

2-11rl1l

agrDp

-f.

,- f'"l

t tttf ?

1|"+ .tf TRIVERINE

g,?J, PLAIN. o . ^ .

P*-,1,"lH m,,,i. ;.

'rft',lln'A Z :\i#ffi1 Cunutative thicknessot cnt nd tisnitic sedinents

Figure 2. Loca-tion_of boreholes that have encountered Tertiary coal in the New South Wales and Victorian parts of the Murray Basin. consist ofpeat and soft lignite, and generally have a low specific energy and high moisture, sulphur, salt and ash levels. Coal-bearing sediments occur at shallow depths around the basin margins, but are concealed by 80 to 130m of overburden on the Riverine Plain to the east; in the central areas, they occur at depths of up to 300m.

Potential for mining, in many areas, is constrained by unfavourable depths ofburial beneath watersaturated Tertiary sediments. Despite these limitations, only a small proportion of boreholes have intersected the coal-bearing succession, and large areas of the basin consequently remain unexplored. It.seems likely that further resources will eventually be identified. Other coal resources beneath the Murray Basin include sub-bituminous Permian coal in the Coorabin Coal Measures of the Oaklands infrabasin in New South Wales (Bembrick, 1974; Morgan,1977; O'Brien, 1981, 1986; Palese, I974;Yoo,1982). Permian coal has also been intersected in boreholes to the southeast of Deniliquin. In addition, Lower Cretaceous coal was intersected in DM Umalee CDH 1 which was drilled by the NSW Department of

Mineral Resources during 1981 near Ivanhoe in the northern part of the basin (Yoo, 1981).

CAINOZOIC SEDIMENTATION

Regional Setting Although the tectonic setting of the Murray Basin provided the primary control on its development, Cainozoic sedimentation patterns and the distribution of coal within the basin were strongly influenced by the interactions between superimposed secondary eustatic, paleoclimatic and tectonic controls. The Cainozoic history ofthe basin was characterised by slow subsidence rates, minimal compaction rates and low rates of sediment supply and/or preservation. The shallow marine and fluvial sediments that comprise the Tertiary succession form a relatively thin cover, with a maximum thickness of 600m in the western to central part of the basin. Beneath the northern, eastern and southern areas the succession is generally less than 200 to 300m thick (Brown, 1985; Brown & Stephenson, 1985). At least three major depositional sequences have been identified

Geology of Australian Coal Basins

563

MURBAY BASIN STRATIGRAPHV

NON. OE POSIr rON TROSION Of PRI TtRiIAR\

.to,s,un",",, ..

son, ',-

s/r :, - ;(ta" .- .,0"',, fli r,-".,o." 7. 1,r",, fioo,o-,,"

Figure 3. Eustatic interpretation of Tertiary stratigraphy gf lhe M_urray Eglt. Relative changes of sea level are based on global relative coastal on-lap curves ofVail & others (L977),

within the succession, each consisting of a package of genetically associated formations that are

separated by disconformities (Figure 3). These sequences show a close correlation with the second-order global cycles of relative coastal onlap and offlap (i.e. relative fall and rise in sea-level) as published by Vail & others (L977) and Vail & Mitchum (1979). Within each depositional sequence, palaeoclimatic factors have influenced fluvial discharge, sedimentation rates and sediment type. The configuration of underlying basement features, in combination with local tectonic movement, has also influenced variations in sediment thickness and facies distribution as well as surface and groundwater palaeodrainage patterns. However, despite evidence of major differential subsidence over underlying infrabasins, each ofthe three depositional sequences forms an extensive but thin and remarkably continuous blanket of sediment. The basin succession was therefore deposited over a topographically flat, low-lying and tectonically quiescent area of epicontinental seas.

Paleocene-Eocene-Early Oligocene Depositional Sequence At the base of the Murray succession (Figure 4a) weakly consolidated, medium to coarse-grained quartz sands ofPaleocene-Eocene age are confined to the deeper and more central parts of the basin (Warina Sand of the Renmark Group and synonymous lower Renmark beds in South Australia - Harris, 1,966; Thornton, L97 4, 1976; Lawrence, 1975)). Borehole logs indicate that the unit forms a series of massive multistorey sand bodies that are considered to have been deposited in a braided fluvial environment. Minor thin lenticular intercalations of fine-grained sand, silt and clay were deposited in lacustrine and floodplain environments. These are thin (a few centimetres thick), highly carbonaceous and contain abundant pyritised wood.

The Warina Sand is overlain by a more widely distributed blanket of unconsolidated, thinly bedded, carbonaceous sand, silt and clay with common interbeds of lignitic coal and peat (Olney Formation of the Renmark Group, and upper Renmark beds of South Australia - Harris, 1966; Lawrence, 1975;

Woolley, L978; Woolley & Williams, 1978). The formation extends beneath almost the entire Murray Basin, and is characterised by abundant carbonised and pyritic plant remains, including fossil logs, woody peat, and leaf litter debris. A cumulative thickness of several metres of carbonaceous sediments has been recorded in many bores drilled beneath the Riverine Plain, as well as in fault-bounded sub-basins near the basin margins.

The coal interbeds range from lignitic brown coal to peat consisting of woody plant debris. Many peats are still fibrous and are currently undergoing decay, so that, when cored, the odour of marsh gas has been reported (Yoo, 1981). The peaty coals are considered to be the deposits of extensive paludal environments; they grade laterally and vertically into carbonaceous clays and sands, deposited in floodplain and meandering environments. Other carbonaceous intervals have been logged as wood, presumably derived from fringing forest environments. Fossil logs and lignitic debris are also common within fluvial channel sands. In South Australia, where coal interbeds have been found to be sufficiently thick, they have been differentiated as the Morlands Lignite Member (Ludbrook, 1961;

Harris, 1966).

Sea levels remained high throughout the EoceneEarly Oligocene and, in the west, the upper part of the fluviatile sequence includes paralic and minor marine components. In the southwest these components are intercalated with Late Eocene to Early Oligocene shallow-marine glauconitic calcareous clay, thin limestones, some bryozoan and

Murray Basin in Victoria and New South Wales

564

minor carbonaceous sand (Buccleuch beds Ludbrook, 1961).

In the southwest, deposition of the Olney Formation was restricted to the Eocene-Early Oligocene, but it

continued until the Middle Miocene in the north and east. Deposition was probably intermittent during this extended period of sediment accumulation, and punctuated by a number ofstratal breaks. A maximum thickness of only 300m of sediment was preserved. The most prominent hiatus is considered to have occurred during the late Early Oligocene, accompanying a fall in sea level (Figure 4; Brown, 1983, 1985), but the extent and duration ofthe break may vary across the basin. Oligocene-Miocene components of the Olney Formation are Iithologically indistinguishable from Eocene-Lower Oligocene components, and hence the variously dated components are regarded as parts of a single lithostratigraphic unit (Brown, 1985; Brown & Stephenson, 1986).

Oligocene-Middle Miocene Depositional Sequence A major rise in sea level in the mid-Oligocene resulted in a dramatic change in sedimentation patterns in the western Murray Basin. This can be correlated with deposition of the marine and marginal-marine formations of the Oligocene to Middle Miocene Murray Group sequence (Figure 4b). Deposition of non-marine sediments continued to the east and north (younger components of the Olney Formation), but in the western areas the swamp and marsh environments of the Olney Formation were drowned by the marine transgression and consequently, accumulation of carbonaceous sediments ceased. In the west, the rates of terrigenous sediment input did not initially balance the combined rates of sea level rise and crustal subsidence, and hence the Murray Basin was partly flooded by a sediment-starved shallow epicontinental sea, resulting in development of a carbonate platform sequence.

During the initial marine transgression in the Oligocene, a thin layer of glauconitic calcareous clay (marl) of the Ettrick Formation (Ludbrook, 1961) accumulated over the plaiform. As sea level continued to rise, the calcareous clay was replaced up-sequence by Late Oligocene to mid-Miocene shallow-marine calcarenite, consisting of coarse-grained temperate-zone skeletal debris with a high quartz sand content (Gambier, Morgan, Pata and Dubbo Limestones, Mannum Formation Ludbrook, 1961, 1963; Lindsay & Bonnett, 1973; Lawrence, 1975). To the north and east the platform calcarenites grade into a narrow zone of glauconitic calcareous clay and thin limestone of the Winnambool Formation (Lawrence, 1975) deposited in restricted-platform and lagoonal environments (Figure 4b). The Winnambool Formation is a younger diachronous equivalent ofthe Ettrick Formation. These calcareous clay units in turn grade laterally into the Geera Clay, which consists of black, locally carbonaceous clay with minor dolomite and sand (Lawrence, 1975; Lawrence & Abele, 1976). The Geera Clay was deposited in a shallow to marginal-marine zone, including interdistributary and tidal flat environments. The Geera Clay in turn interfingers with deltaic and fluviolacustrine sand, silt, clay and peaty coal of the upper Olney

Formation.

Peat accumulation during the Late Oligocene-Middle Miocene was thus confined to the deltaic and fluvio-lacustrine environments of the eastern and northern parts ofthe basin (Figure 4b). As noted above, these Late Oligocene-Middle Miocene fluvial sediments are lithologically indistinguishable from the underlying Eocene-Early Oligocene fluvial sediments, and hence are included in the Olney Formation of the Renmark Group. As sea level began to fall in the mid-Miocene, the Winnambool Formation and Geera Clay appear to have partly prograded back over the top ofthe platform calcarenites so that the Geera Clay partly envelopes the marls which in turn envelop the calcarenites. A further major fall in sea level in the Late Miocene can be correlated with development of the Mologa Surface. a land surface associated with weathering and erosion in the basin and active entrenchment of adjacent highland valleys

(Macumber, 1978).

Late Miocene-Pliocene Depositional Sequence

Initiation of the late major Tertiary depositional sequence of the basin can be correlated with a short-lived marine transgression in the Late Miocene-Pliocene. The initial transgression resulted in the deposition of marine clay and marl of the

Bookpurnong beds, flanked by marginal-marine sand of the basal Loxton Sands in South Australia and stratigraphically equivalent Parilla Sand in Victoria and New South Wales (Figure 4c). It should be noted that the name Parilla Sandstone in South Australia is restricted to younger cross-cutting fluvial deposits (Carter, 1985; Brown & Stephenson, 1986). Further inland, coarse-grained quartzose sand and gravel of the fluvial Calivil Formation (Lawrence & Abele, 1976; Macumber, 1978) were deposited in a braided stream-channel environment; these form an extensive sand sheet underlying much of the eastern and northern Murray Basin. As a consequence ofrising base levels (rising sea level) and diminished potential for erosion, the locus of deposition also appears to have extended up the entrenchments within the previously incised palaeovalleys, which were then backfilled to form the youngest ofseveral entrenched Tertiary deep lead systems of northern Victoria (Hunter, 1,909;

Macumber, 1978). Characteristic intercalations of white kaolinitic clay within the Calivil Formation are locally differentiated as the Torrumbarry Clay. Only scattered carbonaceous debris occurs within the coarse-grained fluvial components of the formation, but the formation's clay content increases markedly beneath the western Riverine Plain where thin carbonaceous intervals have been encountered in boreholes such as Balranald No. 1 (Ludbrook, 7962). These are thought to have been deposited in fluvio-deltaic environments transitional to the marine and marinal-marine environments to the west.

The subsequent marine regression resulted in the formation of a prograding series of Pliocene beach ridges as well as younger inter-ridge and cross-cutting fluvial and estuarine quartz sand deposits (upper Loxton Sands and Parilla Sand-Ludbrook, 1961; Firman, 1973; Lawrence, 1975; Macumber, 1978), which together were deposited in a composite strand plain environment (Brown, 1983; 1985) and now form an extensive sand sheet. At the western edge of the basin, estuarine oyster beds of the Norwest Bend Formation were

Geology of Australian Coal Basins

565

PLIOCINE

PALAT Ot AC I E S

(c)

--Jr ":;.{Ti.:-= .\\,--'

souTntasi

<:.F

Figure 4. Diagrammatic representation of Tertiary palaeofacies in the Murray Basin (from Brown & Stephenson, 1985).

\{' \) I

MIOCENE PALAE OFAC I ES

(B)

souTxtAsT Bt6HUNOS

RAtGtS

EOC€NE

PALAEOFACIES SOUTHEAST NIGNLANDS

)

)SHEI'

deposited during a minor subsequent hishstand of sea level, and delineate the location of fpliocene ancestor of the River Murray (Twidale & others, 1978). In the east, the Pliocene regression can be correlated with deposition of fine-frained clastics and polymictic sand and gravel oflhe Shepparton Formation by aggradation in a flood plain environment.

Quaternary In the west of the Murray Basin, widespread aggradational fluvial-lacustrine sedimentation continued into the Quaternary (upper Shepparton Formation - Lawrence , I97 5) , resulting in development of the modern Riverine Plain (Butler & others, 1973). Further west, the Tertiary is partly

overlain by a thin veneer ofPleistocene lacustrine clay (B_lanchetown Clay - Firman, 1973), and then byan arid and semi-arid landscape of late Pleistocene to Holocene aeolian dunefrelds (Bowler & Magee, 1978).

Eustatic, Palaeoclimatic and Tectonic Influences on Cainozoic Sedimentation Jones & Veevers (t982) proposed a model ofregional tectonic cycles to account for the Tertiarv depositional sequences of the Murray Basin. They suggested that subsidence and sedimentation occurred in the basin as a consequence of periods of uplift and Cainozoic vulcanism ln the adjacent southeast highlands of Australia, and that nondepositional hiatuses can be correlated with

Murray Basin in Victoria and New South Wales

566

uplift and erosion of the basin accompanied by tectonic settling and volcanic quiescence in the highlands. Framework tectonics have clearly provided the primary control on development of the Murray Basin, but it also seems likely that fluctuations in the supply and preservation of sediment in the Murray Basin have been sensitive to global eustatic or tectono-eustatic influences and to consequent fluctuations in the erosive and depositional potential of the fluvial systems that traversed the basin (Brown, 1983; 1985). Depositional sequences in the Murray Basin appear to correlate with the global second order cycles of Vail & others (7977), Vail & Mitchum (1979) and Vail & Hardenbol (1979), although detailed third-order cycles have been identified only locally and incompletely (e.g. Lindsay, 1983). Deposition of laterally extensive packages of intercalated fluvio-deltaic, paralic and

ihallow-marine sediments appears to correlate with major periods of high global sea level, whereas nonpreservation because of erosion/ nondeposition appears to correlate with periods of lowered sea level.

It seems likely that the accumulation and

preservation of peat was enhanced during periods when groundwater tables and sedimentation rates rose as a consequence of rising sea levels and depositional baselevels. Peat accumulation was probably enhanced at sites where rates of groundwater rise, tectonic subsidence and sediment compaction were favourably balanced against rates of sediment input (Brown, 1980; Harris, 1980). When the rise in relative sea level occurred too rapidly and sediment input was too low, as during the Late Oligocene-Early Miocene marine transgression, swamp environments were drowned. During periods when relative sea level and groundwater tables fell too rapidly, on the other hand, carbonaceous materials were less likely to be preserved. Widespread peat accumulation during the Eocene-Middle Miocene appears to have coincided with relatively high sea levels and a prolonged period of high rainfall. Harris (1985) identified at least four episodes of deposition within the Early to Late Eocene sediments of southern Australia, and suggested that many of the Eocene brown coals were deposited near shorelines during periods of maximum marine transgression. Peat accumulation is also likely to have been enhanced during periods of warm temperatures, high rainfall, and high fluvial discharge. Oceanic temperatures (Shackelton & Kennett, 1975) and regional palynological studies suggest that Eocene palaeoclimates in southeastern Australia were iharacterised by warm temperatures and high rainfall (Kemp, 1978; Truswell & Harris, 1982).

Foraminiferal evidence from the Otway Basin also suggests that marine conditions may have been warn (McGowran, 1978a) or at least temperate with brief warmer intervals (Shafrk, 1983). In the Oligocene-Early Miocene the dominance of foraminiferal skeletal debris in the calcarenites of the Murray Group, suggests that palaeoclimates were mainly temperate, although minor extratropical incursions of warmer-water foraminifera have also been recorded in southern Australia (McGowran, 1978b).

In Oakvale 1 bore, in the northwest, sediments of the Geera Clay suggest that in the Oligocene the regional vegetation was dominated by evergreen

rainforest, with abundant Nothofagus brassi, dependent upon high annual precipitation (Truswell & others, 1985). In the mid-Miocene, nearby open freshwater and swamp conditions are indicated by abundant grass and sedge pollen, in combination with freshwater algae and dinoflagellates, as well as aquatic swamp vegetation characterised by Sparganium or Typha. At the Oakvale 1 site, rainfiil, although stlll high, became more seasonal during the Late Oligocene-Middle Miocene, as indicated by the increasing dominance of lVlyrtaceae and abundance of Araucariaceae (Truswell & others, 1985).

In contrast, palynological investigations of boreholes

beneath the Riverine Plain indicate that humid conditions prevailed in the east until at least the mid-Miocene (Martin, 1977 ; 1984). Palaeoclimatic conditions in the Eocene-mid Miocene were therefore conducive to the generation and preservation of extensive coal deposits. Palaeoclimates during the late Cainozoic, however, are thought to have been characterised by increasing seasonal aridity (Bowler, 1982), and only minor coal was deposited.

Minor tectonic reactivation of local basement structural features has also strongly influenced both Cainozoic sedimentation patterns and palaeodrainage patterns. Differential subsidenge-, for example, hasresulted in th-e preservation of thicker sequences in some areas relative to others. In addition, several modern groundwater discharge zones can be related to high pressures at permeability barriers created where the basal Renmark Aquifer pinches out against flanking basement highs, as for example beneath the western Riverine Plain. Such fault-bounded areas would have been favourable sites for the local maintenance of paludal swamp and marsh conditions. Several of the thicker coal deposits of the basin occur in small fault-bounded depiessions, where the accumulation of peat was enhanced by a combination of tectonic subsidence, high rainfall, high groundwater tables, and paludal swamp and marsh conditions'

MURRAY BASIN COAL DEPOSITS IN VICTORIA Brown coals have been recorded at many localities in the Murray Basin in Victoria (Gloe, 1976, 1"984; Gloe & Holdgate 1991), but in most areas seams are too thin and too deep for economic development. Shallow brown coalJ have been recorded in the Tertiary Renmark Group near Horsham, but resources are limited and of poor quality. The major developments appear to have been in fluvio-lacustrine swamps located in mature river valleys, particularly those associated with the ancient Loddon and Murray River systems (Figure 1). Extensive seams of this type reach significant thicknesses at depths of over 100m. Towards Mildura and the centre of the basin, the seams become thinner and occur at greater depths.

Background to Recent Discoveries Between 1980 and 1982, CRA Exploration Pty Ltd undertook a regional exploration program for brown coal and other commodities in the Murray Basin of Victoria (Brunker & others, 1986). Exploration drilling for brown coal totalled over 43 000m, consisting initially of several cored stratigraphic wells followed by a phase of reconnaissance rotary-mud drilling on 1Okm centres' As the progiam progressed and ideas relating to the iontrols of coal distribution were revised, follow-up

Geology of Australian Coal Basins

567

m€tr€ s o

SHEPPARTON FORMATION

Upper Pliocene - OuaternarY

PARILLA SANO

WUNGHNU GROUP

CALIVIL SAXD

Upper Pliocen€ - Lower Pliocene

from the incision of a pre-Palaeocene drainage system into Palaeozoic basement (an antecedent of the present-day Murray River system, with its northflowing tributaries). The Renmark Group sediments reflect this palaeotopographic control in sharp local variations in thickness, being thicker in basement lows and thinner (or absent) over prominent highs. Some basement highs, such as the Terrick-Terriik Range near Kerang, survived progressive burial of the pre-Tertiary landscape beneath the Renmark Group and younger sediments, and presently protrude to surface as inliers. The distribution and development of brown coals were therefore directly influenced by the configuration of the pre-Tertiary landscape in that palaeotopographic highs Iaterally constrained coal development at the time of coal formation. The limit of coal-development approximates regionally to the 100m depth-to-basement contour, as shown by

Figure 6.

RENHARK GROUP Palaeocene - Miocene

PRE-TERTIARY BASEIEI{T Devonian Granite

Figure 5. Stratigraphy of the Kerang area.

drilling provided further detail of deposits already

identified and demonstrated extensions to them. Geophysical logs provided most of the information required for lithologic and stratigraphic interpretation, and provided reliable identification of the coals themselves. The coals were conspicuous by their very low natural garnma, low gammagamma density and low neutron-neutron porosity values.

Several large brown coal accumulations were identified from this work between Kerang and Echuca, close to the southeastern margin of the basin.

Geological Setting As indicated above, the Murray Basin brown coals are contained within the Renmark Group, which is

the lowermost stratigraphic unit of the Tertiary sequence. The Renmark Group forms an almost continuous unit across the Murray Basin, and is divisible into the Warina Sand and the overlying Olney Formation. The Group ranges from Palaeocene to Oligocene in age in western areas, but ranges through to earliest Miocene (Figure 5) in the east, where nonmarine conditions persisted. Its Oligocene equivalents in the west are the shallow marine, nearshore Geera Clay and Ettrick Marl. The marine influence in the area was a major regional control in producing conditions favourable to coal accumulation in the eastern part of the basin. Lithologies in the Renmark Group include fine to coarse-grained quartz sands (occasionally weakly cemented), silts and siltstones (carbonaceous, dolomitic or calcareous), clays (usually carbonaceous) and brown coal. The Renmark Group sediments were deposited on an undulating palaeotopographic surface which resulted chiefly

Prior to the work by CRA Exploration, it had been thought that the half-grabens adjacent to northsout[ basement faults formed sites for coal accumulation. This no longer seems to be true, and none of the coal deposits identified in the southeastern Murray Basin can be interpreted to occupy such features. The thickest coal intersections in ttie Kerang area are not located adjacent to the Leaghur Fault but occur further to the east. The Loddon River system currently occupies the area immediately east of the Leaghur Fault, and it is likely that the ancestral Loddon occupied a similar position. The thicker coals further to the east appear lo represent accumulations away from this broad fluviatile environment, forming in quieter backswamps within pre-Tertiary palaeotopographic depressions.

Recognition of these relationships led to a shift in exploration emphasis from a search for tectonicallyinduced sites for coal accumulation (such as half-grabens) to a search for palaeotopographic lows in areas peripheral to major river systems, and resulted in the identification of more widespread coal deposits. Some coals, identified as discrete deposits early in the exploration program, were later proven to be laterally contiguous.

During the Pliocene, the sediments of the Renmark Group in southwestern areas were incised by river systems which deposited the Calivil Sands. This erosion locally resulted in partial or complete removal of the coal seams, with reworking of the eroded organic debris giving rise to some thin, impersistent allochthonous coal beds. The erosion was a secondary control on coal distribution, in terms both of areal extent and thickness variation' Coal distribution can therefore be regarded as having been determined by two erosion surfaces associated with Tertiary sedimentation in the southeast of the Murray Basin (Figure 7).

The Kerang Deposits In 1981, fifty bores totalling 8900m were drilled in

an area centred on Kerang and Cohuna. The brown coal resource identified by this work is contained in two seams, and is divided between two sub-basins, those ofKerang and Cohuna, separated by a prominent basement ridge (a subsurface northerly bxtension of the Terrick-Terrick Range granite).

Drillholes in the Kerang subbasin suggest that the two seams which occur within it are co-genetic,

Murray Basin in Victoria and New South Wales

568

Extent of coal- deposition prior to pre-Calivil erosion. Thinning of coals (to less than 5m. )

(direction

indicated

by arrow)

Basement

Depth to basement (m.)

10o

I BENDIGO Figure 6_. Distribu-ti-on of coal^developm_ent in the Renmark Group relative to basin palaeotopography. 1. Ke_rang Sub-basin; 2. Cohuna Sub-basin; 3. Torumbarry Sub-basin; 4. Tandaria Sub-bisii; b'. Echuca Sub-basin.

n€mely that the lower seam is a split of the upper (Figure 7). The two seams apparently coalesce northeastwards over a saddle feature in the NE-SW trending pglaeovalley which constitutes the Kerang subbasin. This saddle appears to represent a watershed between the westward palaeo-drainage into the ancestral Loddon River and the eastward palaeodrainage into the Murray River. The upper seam was apparently continuous in its development from one subbasin to the other. However, the lower of the two seams in the Cohuna sub-basin is not demonstrably co-genetic with it and, on present evidence, has to be regarded as a discrete seam development. The lower seam in the Kerang sub-basin attains a maximum intersected thickness of 15m, and lies at depths of 155 to 175m below the surface. The upper seam reaches a maximum intersected thickness of 40m in the north-east of the sub-basin, where its

thickness has been enhanced by coalescence with its lower split and where it has escaped the effects of pre-Calivil erosion. Elsewhere in the sub-basin, the upper seam lies at depths of 100 to 130m below the surface, and is often reduced in thickness due to pre-Calivil erosion ofthe upper part.

In the Cohuna subbasin, the lower seam ranges

between 6m and 15m thickness where intersected, and occurs at depths of 175 to 200m. It thickens Iocally near the southern margin of the subbasin, where over 20m of coal is present at 160m depth. The upper seam attains a thickness of 11m near Cohuna, but pre-Calivil erosion has affected the seam over a wide area, and in central areas has removed it completely. The seam lies at depths of between 95 and 120m. Like the lower seam, it thickens locally on the southern margin of the sub-basin.

Geology of Australian C oal Basins

569

KERANG

COHUN A

Sub-basln

Sub-basIn

FORTIATION

PARILLA

SAND

Pre,Calivil erosion surface

Figure 7. Stratigraphic setting of brown coal deposits in the Murray Basin. The total brown coal resource of the Kerang area is estimated at over 12Bt based on a cutoff thickness of 10m and over 15Bt at a 5m cutoff.- The latter estimate improves greatly when it is considered that the sub-basin west of the Loddon River contains 6m seams, and a total figure of over 20Bt is not unreasonable. The Kerang resource is unevenly distributed between the two sub-basins. Two thirds of it is contained within the Kerang sub-basin, where the maximum intersected thicknesses occur. 85-90Vo of this is contained within the upper seam. The resource ofthe Cohuna subbasin is evenly divided between the two coal seams. About three quarters of the total resource for the entire area is contained within the upper seam, which has a minimum overburden-to-coal ratio of 4:1. Most of the 108 core samples taken from five Kerang drillholes were from the upper seam. The average value for moisture content is 56Vo, ash 10.87o (dry basis) sulphur l.\Vo, specific energy (net wet) 8.9MJnrg. Oil yield, from six Fischer assays, is about 95L/t.

Torrumbarry-Tandarra Brown Coal The Torrumbarry-Tandarra deposit is contained within one single coal seam. Other seams do occur, but their thin and impersistent nature does not merit their inclusion in resource estimates. The resource is restricted to a basement palaeo-valley system, trending to the north, in which the coal-bearing Renmark Group sediments were deposited. The palaeo-valley shows a north-south trend in the area west of Dingee; it is sharply incised into the pre-Tertiary landscape, and shows a marked dendritic configuration. As a result, the coal seams are restricted in their distribution by pre-Tertiary basement palaeotopography. Coals were developed throughout the TandarraTorrumbarry palaeo-valley, apparently thickening along the valley axes and thinning laterally a_gainst its slopes. In addition, the main seam is-closely relateil to the basement palaeosurface, deepening

gradually northwards as the palaeo-valley slowly descends from the Tandarra area to the Gunbower-Torrumbarry area. Some shallowing of the coals laterally against the slopes of the palaeovalley is also evident. Maximum seam thickness is 12m. Depths to coal range from 87 to 105m in the south, and 108 to 178m in the north. The resource is estimated at 4 to SBt, with a 10m thickness cutoff, but increases to 6 to 7Bt, at a 5m cutoff. No cores have been taken, so that the coal quality is unknown.

Echuca Brown Coal Deposits Deposits of brown coal have also been identifred in the Echuca Sub-Basin, which extends up to 30km east of Echuca. The coals were formed in backswamps associated with the ancient MurrayGoulburn River system, the fluviatile environment of which appears to have limited coal development to

the northeast.

Two persistent seams occur in the area. The upper of these has a maximum thickness of Llm, and lies at depths of 1,20 to 153m. It appears to lens out to the nbrth and east into more fluviatile sediments, and is apparently limited to the south by the pre-Calivil unconformity. As a result of the latter,

lhe upper seam is limited in its areal distribution to the noitheastern part of the Echuca Sub-basin. The lower seam is unaffected by pre-Calivil erosion, and has a much greater lateral extent. It shows two areas of local thickening, one 25km east of Echuca and the second to the immediate southeast of that city. The seam in these areas reaches thicknesses of 10 and 14m respectively. The latter area of thickening is by far the broader of the two, and constitutes most of the resource in the sub-basin' It is, however, traversed by the Cadell Fault, the late age of which is indicated by displacement of the entire Tertiary sequence, including the coals. This reinforces the view that north-south fauits have made little direct tectonic contribution to the

localisation of brown coals.

Murray Basin in Victoria and New South Wales

570 The lower seam, reaching a maximum thickness of 14m, Iies at depths of L54 to 172m. Like the upper seam, it is limited in its northeasterly development by fryi9s change. To the south, being-unaffecfed by

pre-Qalivil erosion, it is limited simply by the rising pre-Tertiary basement which in fact outcrops further to the south again. Only one cored hole has intersected these coals, close to the northeasterly limit of their development. The analytical data from the cores are therefore considered to be unrepresentative ofthe coals contained within the Echuca Sub-basin as a whole. The resource is estimated to be 1Bt at a thickness cut-off of 10m, and up to 2Bt at a 5m cut-off thickness.

MURRAY BASIN COAL IN NEW SOUTH WALES In New South Wales, the availability of alternative sources of low-cost coals, as well as the isolation of the IVlurray Basin from potential markets, has resulted in a low level of interest in Murray Basin exploration. As described above, coal is known to occur within Eocene-mid Miocene sediments of the Olney Formation beneath almost the entire Riverine Plain, but the known occurrences are thought to be too discontinuous, too thin and too deep to be of economic significance. Water bores which have encountered a cumulative thickness of coal greater than 10m (generally over a 90m to 120m interval) are shown in Figure 2. In the Griffith region, irregular overlapping Ienses ofbrown coal occur at depths ofbetween 42 and 88m (Pels 1960; Wynn 1962; Frenda 1965). Resources of around 200Mt have been estimated in the region (Whitehouse, 1981). Thick sequences of coal ilso ?ppear to be particularly well developed in the Deniliquin-Wanganella-Wakool region, where a number of boreholes have encountered cumulative thicknesses of several tens of metres of coal. It seems likely tlat coals in this region may prove to be similar in character to those in adjaceni areas of northern Victoria. Further west, the Olney Formation occurs at

increasing depths ofburial and has consequently been intersected by fewer bores. In the Meninde-e region in the northwest a number of uranium exploration bores have intersected minor carbonaceous sediments at depth (Wecker, 19?1; Morgan, 1973) and Blackgate No. 1 (Comserv, 1980) encountered 14.7m of lignite at a depth of 163m (Baker, 1982). No significant deposifs have been identified, but it seems possible that areas near the basin margin may be prospective for small deposits, similar to those occurring in fault-bounded depressions in South Australia.

BOWLER, J.M., 1982: Aridity in the late Tertiary and Quaternary of Australia . In Barker, W.R. & Greensdale, P.J.M. (Editors): Euolution of the Flora and Fauna of Arid Australia. Peacock Publications, Frewville, South Australia, 35-4b. BOWLER, J.M. & MAGEE, J.W., 1978: Geomorphology of the Mallee region in semi-arid northern Victoria and western New South Wales. Proceedings of the Royal Society of Victoria, gO,

5-25. BROWN, C.M., 1980: Tertiary coal in the Murray Basin. 1ru Truswell, E.M. & Abel, R.S. (Editors): The Cainozoic evolution of continental southeast Australia: abstracts of a symposium held in Canberra, November, 1980. Bureau of Mineral Resources, Australia, Record 1980/67, 12-13. BROWN, C.M., 1983: Discussion: a Cainozoic history of Australia's southeast highlands. Journal of the Geological Society of Australia, 30, 483-486. BROWN, C.M., 1985: Murray Basin, southeastern Australia: stratigraphy and resource potential a synopsis. Bureau of Mineral Resources, Australia, Report, 264. BROWN, C.M. & STEPHENSON, A.E., 1985 Mutay Basin 1:1,000,000 scale geological map, preliminary edition. Bureau of Mineral Resources, Australia.

BROWN, C.M. & STEPHENSON, A.E., 1986: Murray Basin, southeastern Australia: subsurface stratigraphic database. Bureau of Mineral Resources, Australia, Report, 262.

BRUNKER, R.L., PRESTON, J.C. & RICHARDS, D.S., 1986: Multi-commodity exploration in the Murray Basin, Victoria. Proceedings, 1Sth Congress of CMMI, Singapore, 1116 May 1986. BUTLER, B.E., BLACKBURN, G., BOWLER, J.M., LAWRENCE, C.R., NEWELL, J.W. & PELS, S.,

1973: A geomorphic map of the Riuerine Plain of southeastern Australia. Australian National

University Press, Canberra.

CARTER, A.N., 1985: A model for depositional sequences in the Late Tertiary of southeastern

Australia. 1n Lindsay, J.M.(Editor): Stratigraphy, Palaeontology, Malacology: papers in honour of Dr Nell Ludbrook. South Australian Department of Mines and Energy, Special Publication, 5, 1,3-27 .

COMSERV PTY LIMITED, 1980: Well completion report, Blackgate No 1, Comserv (No 779)Pty Ltd. Geological Survey of New South Wales, Petroleum Well Completion File, 70.

FIRMAN, J.B., 1973: Regional stratigraphy of surficial deposits in the Murray Basin and Gambier Embayment. Geological Suruey of South

Australia, Rep ort of Inu estigation, 39.

REFERENCES BAKER, C.J., 1982: Coal exploration area at Menindee New South Wales. New South Wales Department of Mineral Resources, Coal Geology Report CGB 1982-034.

BEMBRICK, C.S., 1974: Murray Basin. 1n Markham N.L. & Basden H. (Editors): The Mineral Deposits of New South WaIes. Geological Survey of New South Wales, Sydney, 555568.

FRENDA, G.A., 1965: Stratigraphic studies near

Griffith, New South Wales, with special reference to the petrology of Cainozoic sediments. M.Sc. thesis, University of New South

Wales.

GLOE, C.S., 1976: Brown coal. In Douglas, J.G. & Ferguson, J.A. (Editors): Geology of Victoria. Geological Society of Australia Special Publication, 5, 378-389.

Geology of Australian Coal Basins

577 GLOE, C.S., 1984: The geology, discovery and assessment ofthe brown coal deposits of

Victoria. In Woodcock, J.T. (Editor): Victoria's Brown Coal a huge fortune in chancery. Australasian- Institute of Mining and Metallurgy, Monograph,11, 79-109.

GLOE, C.S. & HOLDGATE, G.R. 1991: Geology and resources. /n Durie, R.A. (Editor): The Science of Victorian Broutn C oal. Butterworth Heinemann, Sydney.

HARRIS, W.K., 1966: New and redefined names in South Australian lower Tertiary stratigraphy. Geological Suruey of South Australia, Quarterly Notes, 20, L-3. HARRIS, W.K., 1980: Eocene eustacy and the deposition oflignites in South Australia. ln Truswell, E.M. & Abel, R.S. (Editors): The Cainozoic evolution of continental southeast Australia: abstracts of a symposium held in Canberra, November, 1980. Bureau of Mineral Resources, Australia, Record 1980/67, 33. HARRIS, W. K., 1985: Middle to Late Eocene depositional cycles and dinoflagellate zones in southern Australia. 1n Lindsay, J.M. (Editor): Stratigraphy, Palaeontology, Malacology: papers in honour of Dr Nell Ludbrook. South Australian Department of Mines and Energy, Special

Publication, 5, I33-I44.

HUNTER, S.B., 1909: The deep leads of Victoria. Geological Suruey of Victoria Memoir, 7. JOHNS, R.K., 1975: Tertiary coal in South Australia. In Traves, D.M. & King, D. (Editors): Economic Geology of Australia and Papua New Guinea: 2 Coal. Australasian Institute of Mining and

Metallurgy, Monograph, 6, 366-371.

JONES, J.G. & VEEVERS, J.J., L982: A Cainozoic history of Australia's Southeast Highlands. Journal of the Geological Society of Australia,29,

L-12. KEMP E.M., 1978: Tertiary climatic evolution and vegetation history in the southeast Indian Ocean region. Palaeogeography Palaeoclimatology Palaeoecology, 24, 169-208. KRESS, A.G., LINDSAY, J.M. & HARRIS, W.K., 1978:

Appraisal drilling results, Anna coalfield, Murray Basin, South Australia. Geological

Survey ofSouth Australia, Report Book 78/89.

LAWRENCE, C.R., 1975: Geology, hydrodynamics and hydrochemistry of the southern Murray Basin. Geological Suruey of Victoria Memoir,30.

LUDBROOK, N.H., 1962: Woodside (Lakes Entrance) Oil Company N.L., Balranald No 1well, New South Wales: palaeontological report. South Australian Department of Mines, Report Book 55/66.

LUDBROOK, N.H., 1963: Correlation of the Tertiary rocks of South Australia. Transactions of the Royal Society of South Australia,87, 5-I5.

MACUMBER, P.G., 1978: Evolution of the Murray River during the Tertiary Period: evidence from northern Victoria. Proceedings of the Royal Society of Victoria, gO, 43-52. MARTIN, H.A., 1977: The Tertiary stratigraphic palynology of the Murray Basin in New South Wales: 1 - the Hay-Balranald-Wakool districts. Royal Society of New South Wales, Journal and Proceedings, ll0, 4l-47 .

MARTIN, H.A., 1984: The use of quantitative relationships and palaeoecology in stratigraphic palynology of the Murray Basin in New South Wales. Alcheringa, 8, 253-27 2. McGOWRAN, 8., 1978a: Early Tertiary foraminiferal

biostratigraphy in southern Australia: a progress report. In The Crespin Volume: essays in honour of Irene Crespin. Bureau of Mineral Resources, Australia Bulletin ,192, 83-95.

McGOWRAN, B., L978b: Stratigraphic record of early Tertiary oceanic and continental events in the Indian Ocean region. Marine Geology,26, 1-39. MORGAN, P.J., 1973: Report on exploration program, Menindee area, New South Wales, Exploration Licences 559, 560, 561,562. Geological Survey of New South Wales, Report GS 1973/262. MORGAN, R., 1977: Stratigraphy and palynology of the Oaklands Basin, New South Wales. Geological Suruey of New SouthWales, Quarterly Notes,29, 1-6.

O'BRIEN, P.8., 1981: Permian sediments beneath the Murray Basin. Bureau of Mineral Resources,

Australia, Record 1981/60.

O'BRIEN, P.E., 1986: Stratigraphy and sedimentology of Late Palaeozoic glaciomarine sediments beneath the Murray Basin, and their palaeogeographic and palaeoclimatic significance . BMR Journal of Australian Geology and Geophysics, 10, 53-63. PALESE, G., 1974 Oaklands Basin coal drilling program: basic results of 22 bores drilled by the New South Wales Department of Mines from

August 1973 to February 1974. Geological Survey of New South Wales, Report GS 1974/090

LAWRENCE, C.R. & ABELE, C., 1976: Tertiary, Murray Basin. 1n Douglas, J.G. & Ferguson, J.A. (Editors): Geology of Victoria. Geological Society of Australia, Special Publication, 5, 191-198.

PELS, S., 1960: The occurrence ofbrown coal near Griffith, New South Wales. Australian Journal

LINDSAY, J.M., 1983: Oligo-Miocene transgressive events in Geera Clay, Oakvale 1, northern Murray Basin. Geological Suruey of South Australia, Quarterly Notes, 85, 5-I2.

SHACKLETON, N.J. & KENNETT, J.P., 1975: Palaeotemperature history of the Cainozoic and the initiation ofAntarctic glaciation: oxygen and carbon isotope analyses in DSDP sites 277,279, 28L. In Houtz, J.P. & others (Editors): Initial

LINDSAY, J.M. & BONNETT, J.E., 1973: Tertiary stratigraphy of three deep bores in the Waikerie area of the Murray Basin. Geological Suruey of South Australia, Report of Inuestigation, SS. LUDBROOK, N.H., 1961: Stratigraphy of the Murray Basin in South Australia. Geological Suruey of South Australia Bulletin, 36.

of Science, 22, 426-427 .

Reports of the Deep Sea Drilling Project,29, 7 43-7 55.

SHAFIK, S., 1983: Calcareous nannofossil biostratigraphy: an assessment of foraminiferal events in the Eocene of the Otway Basin, southeastern Australia. BMR Journal of Australian Geology and Geophysics, 8, 1-17.

Murray Basin in Victoria and New South Wales

572 THORNTON, R.C.N., 1974: Hydrocarbon potential of the western Murray Basin and infrabasins. Geological Suruey of South Australia, Report of

Inuestigation, 4L.

THORNTON, R.C.N., 1976: Murray Basin and associated infrabasins. In Leslie, R.D., Evans, H.J. & Knight, C.L. (Editors): Economic Geology of Australia and Papua New Guinea:3 Petroleum. Australasian Institute of Mining and

Metallurgy, Monograph, 7, 97-94.

TRUSWELL, E.M. & HARRIS, W.K., 1982: ThE Cainozoic palaeobotanical record in arid Australia: fossil evidence for the origins of arid-adapted flora. In Barker, W.R. & Greensdale, P.J.M. (Editors): Euolution of the Flora and Fauna of Arid Australia. Peacock Publications, Frewville, South Australia, 67 -7 6. TRUSWELL, E.M., SLUITER, I.R. & HARRIS, W.K., 1985: Palynology of the Oligocene-Miocene sequence in the Oakvale-1 corehole, western Murray Basin, South Australia. BMR Journal of

Australian Geology and Geophyslcs, 9, 267-295.

TWIDALE, C.R., LINDSAY, J.M. & BOURNE, J,A., 1978: Murray Valley Gorge in South Australia: age and origin. Proceedings of the Royal Society of Victoria,90, 27-42.

VAIL, P.R. & HARDENBOL, J., 1979: Sea level change during the Tertiary. Oceanus, 22, 7l*79. VAIL, P.R. & MITCHUM, R.M., 1979: Global cycles of relative change in sea level from seismic stratigraphy. In Geological and geophysical investigations of continental margins, American Association of Petroleum Geologists, Memoir, 29, 468-472.

VAIL, P.R., MITCHUM, R.M., & THOMPSON, S.III, 1977: Global cycles ofrelative change of sea-level. In Seismic stratigraphy applications to hydrocarbon exploration, American Association of Petroleum Geologists Memoir, 26, 83-97. WECKER, R., 1971: Final report, Exploration Licence 314 (Menindee, New South Wales). Geological Survey of New South Wales, Report GS 1971/499.

WHITEHOUSE, J., 1981: Tertiary coal potential of the Murray Basin. New South Wales Department of

Mineral Resources, Coal Geology Report CGB 198 1-0 17.

WOOLLEY, D.R., 1978: Cainozoic sedimentation in the

Murray drainage basin. Proceedings of the Royal

Society of Victoria,90, 61-65.

WOOLLEY, D.R. & WILLIAMS, R.M., 1978: Tertiary

stratigraphy and hydrogeology ofthe eastern part of the Murray Basin, New South Wales. 1n Storrier, R.R. & Kelly, I.D. (Editors): The hydrogeology of the Riverine Plain of south east Australia, Proceedings of a Symposium held at Griffith New South Wales, July 28-29, 1977. Australian Society of Soil Science Inc., Riverina Branch, 45-65. WYNN, D.W., 1962: Narrandera, New South Wales, 4-Mile Geological Series, SI/55-10. Geological Suruey of New South Wales, Explanatory Notes. YOO, E.K., 1981: Murray infrabasin drilling program: DM Umalee CDH 1, near Ivanhoe. New South Wales Department of Mineral Resources, Coal Geology Report CGB 1981-028.

YOO, E.K., 1982: Geology and coal resources of the

northern part of the Oaklands Basin. Geological

Suruey of New South Wales, Quarterly Notes, 49, 15-27.

Geology of Australian Coal Basins

573

GEOLOGICAL SETTING

ffitway Basin,

Victoria CM Barton

Brown coals of the Otway Basin occur within Early Tertiary sediments around the eastern margins of the Lower Cretaceous Otway Ranges and within mid-Tertiary sediments extending from Altona to the Bacchus Marsh area in the northeast part of the basin (Knight, 1975). A small patch of Early Tertiary brown coal occurs at Lal Lal, 30km west of Bacchus Marsh outside the main basin. The general stratigraphic relationships of the coal-bearing strata are shown in Figure 1. The westerly brown coals of the Otway Ranges are included within the Torquay and Port Campbell Sub-basins, whilst the easterly brown coals of Altona-Bacchus Marsh occur within the Port Phillip Sub-basin. In both cases the terrestrial deposits, which include brown coals, grade seawards into marine sediments.

Local palaeodepositional centres are recognised for the brown coals around the Otway Ranges and for the isolated Lal Lal locality. In contrast, the main brown coals of the Port Phillip Sub-basin accumulated within an elongate palaeodepression which extended from Altona to Bacchus Marsh (see Barton & others, Gippsland Basin, this volume).

CENTRAL COASTAL BASIN DEPOSITS Bacchus Marsh Brown coal was discovered near Bacchus Marsh in 1884, and has since been worked at six localities north and south of the Werribee River (Ripper, 1975). The sole remaining mine is at Maddingley, 3km east of Bacchus Marsh, where the Maddingley No L Cut commenced in 1944 and was replaced by the Maddingley No 2 Cut in 1948. Annual production around 1985 was 87 500t, with a cumulative total of nearly 12Mt extracted from the area. The brown coals occur in the sands, clays and gravels ofthe upper part ofthe Palaeocene to Early Miocene Werribee Formation (Abele & others, 1976). This formation contains many thin seams, and attains a thickness of nearly 300m in the centre of the Ballen Graben to the west of Bacchus Marsh. The main Maddingley seam in this sequence averages some 28m in thickness, with a maximum known thickness of 48m. The seam, which is considered by Partridge (1971) to be Early Miocene, is covered by 6 to 60m ofoverburden sands, clays and gravels. It dips gently to the south-east, where it passes beneath an extensive basalt cover south of the Parwan River. Resources are given by the Coal Corporation of Victoria (Victorian Brown Coal Council, 1983) as 60Mt at Bacchus Marsh and 4500Mt at Maddingley. Roberts (1984) quotes unpublished estimates by O'Shea (1978) of 'workable coal reserves', based on seams down to 15m thick and 200m in depth with coal:overburden ratios of <0.5:1, as a total of approximately 400Mt.

Moisture in the coal varies from some 50 to 60Vo, and dry basis ash is generally <L07o. Equivalent values for the producing Maddingley No 2 Cut (Table 1) are around 60Vo and 67o respectively (Edwards, 1948).

Otway Basin, Victoria

574

THRONOLOGICA

BIO STRATI6RAPHIC UNITS OALYNOLO6

CAL ZONES

ALTONA & BATIHUS MARSH

AII6LESEA

BARWON DOWNS 6RABEN

BENWERRIN

MURRAY EASIN

LL"I sJ"I:

;

HrooLE

Figure 1. Stratigraphic nomenclature and age of units in the Otway and adjacent parts of the Murray Basin.

Lal Lal AI2m thick seam ofprobable Palaeocene (Abele & others, 1976) brown coal was discovered in 1857 within a small, structurally complex b.asin at Lal Lal, 30km west of Bacchus Marsh. Several seams occur in this deposit within clays, sands and gravels in the lower part of the Werribee Formation. Production started in 1864, representing the first recorded production of brown coal in Victoria generally (Thomas & Baragwanath, 1949-1953). Roberts (1984) quotes unpublished work by Ripper in which three periods of coal deposition were recognised and resources estimated at 10 to 20Mt. Reserves (Thomas & Baragwanath, 1949-1951), however, are estimated at 2.SMt. The average thickness of the top seam is 12m, and the coal:overburden ratio 1:2.7 (Roberts, 1984). Limited analyses (Table 1) show that the coal has close to 607o moisture and a variable ash percentage down to 37o (dry basis).

Altona to Bacchus Marsh Brown coal extends within the Werribee Formation, beneath a cover ofyounger volcanic rocks, for nearly 30km between Bacchus Marsh and Altona on Port Phillip Bay. Drilling indicates that the main seam is continuous between the two areas and occupies the central parts of a NW to SE trending palaeovalley, thus confirming the interpretation of Thomas &

Baragwanath ( 1949-195 1).

Altona A total of 200t of brown coal was extracted in 1888 from a 101m deep shaft in the Melbourne bayside suburb of Altona. Total production from the site is estimated at 31 780t. The Altona brown coal is overlain by the

predominant clays and marls of the Miocene Fyansford Formation (Torquay Group), and by the Late Miocene-Pliocene sands of the Brighton Group. A surface cover of newer volcanic basalt occurs over much of the area. Early bores (Thomas & Baragwanath, 1949-1951) revealed a main seam up to a maximum of 20m thick, thinning to the southwest and splitting into four seams to the north.

The moisture content of this coal is near 60Va and dry basis ash around 737o (Table 1).

DEPOSITS OF THE OTWAY RANGES (Including the Port Campbell Embayment and the Torquay Basin) Anglesea The main coalfield in this area is located along the south-western flanks of the Otway Ranges around Anglesea (George, 1975). Significant brown coal seams were encountered here in 1958, within a south-east plunging open syncline located some 3km northeast of Anglesea township. Production started from a small open cut in 1960 and continues up to the present time. The coal seams at Anglesea occur within the terrestrial sands, clays and gravels of the Eastern View Formation. The sequence is known to reach a local thickness of 300m, and is recognised as Paleocene to Eocene (Abele & others, 1976). The bulk of the coal occupies the Eocene part of the Formation. It comprises an upper 4,L seam, 25 to 40m thick, and an underlying B group with three to six seams having an aggregate coal thickness of 30m. The A1 seam is overlain by some 12 to 30m of younger sediments in the area of the mine. The coal-bearing sequence rests on Lower Cretaceous rocks. It is progressively overlain to the northeast and south by the Eocene Demons Bluff Formation and the succeeding Oligocene to Miocene marine Torquay Group sediments. Resources of 390Mt, excluding coal seams <3m

thick, are recognised in the Anglesea area (Victorian Brown Coal Council, 1983). Reserves are estimated at 70Mt in the A1 seam and 90Mt in the B group seams.

Drilling by Western Mining Corporation between

1979 and 1981 (Meyer,1982,1983) has revealed that the brown coal seams extend northeast from Anglesea around the northern flanks of the Otway Ranges. As at Anglesea itself, the coal-bearing strata rest upon and dip outwards from the uplifted rocks of the Lower Cretaceous Otway Group. Seams

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yi,tlr q" aggregate coal thickness of up to 21m were drilled in this area within a preserveii sequence, 20-140m thick, of the Eocene Eastern View Formation. Coals encountered at depths of <4bm, however, were unfortunately <5m in thickness. The moisture content of the coal, at near 47Vo, is similar to that at Anglesea, but ash, at around tgVo, is considerably higher (Table 1).

Other Localities Apart from the coal at Anglesea, three separate brown coal deposits occur, also within the Eastern View Formation, at Wensleydale, Deans Marsh and Benwerrin. Production started from Benwerrin in ]899, and by 1948, when production ceased, some 2 985 000t of coal had been extracted from the three deposits. Over 99Vo of this coal came from

Wensleydale.

The-three deposits in this area occur within separate small synclinal or downfaulted areas around tlie north-western flank of the Lower Cretaceous rocks of the Otway Ranges. Maximum known seam thicknesses at Wensleydale, Deans Marsh and B-enwerrin are 40m, 9m and 2.5m respectively (Gloe, 1984). Reserves are estimated by Knight (1,975) at a total of <sMt, including 3.75Mt at Wensleydale. The moisture content of the coal varies from an indicated

unusually dry 33Vo at Benwerrin to around 50Vo at the other two localities. Limited analyses show ash at <107o at Deans Marsh and at <4Vo (&ry basis) at Benwerrin and Wensleydale (Table 1).

In areas of the Port Campbell Embayment southwest of the Deans Marsh area, where the Eastern View Formation is laterally replaced by the paludaVmarine Dilwyn Formation,-economic brbwn c_oal seams are apparently absent (Holdgate & Gallimberti, 1980).

DEPOSIT SIZE AND PRODUCTION The Victorian Brown Coal Council (1983) has provided coal resource estimates of 9550Mt for the Otway Basin, using the same criteria as listed in the! Gippsland chapter, this volume, but with a 200m depth limit. This figure compares with an earlier estimate of 8060Mt by Gloe (1979) and an estimate by Stanley (1986) of 15 500Mt.

REFERENCES ABELE, C., KENLEY, P.R., HOLDGATE, G. & RIPPER, D., 1976: Otway Basin. 1n Douglas, J.G. & l'erguson, J.A. (Editors): Geology of Victoria. Geological Society of Australia Special

Publication, 5, 198-229.

EDWARDS, A.8., 1948: Coal types in the Maddingley brown coal seam, Bacchus Marsh. Proceediigi of

the Australasicin Institute of Mining and, Metallurgy, 150-151, 10 1-1 12. GEORGE, A.M., 1975: Tertiary coal measures - & Anglesea coalfield, Victoria. In Traves, D.M. King, D. (Editors): Economic Geology of Australia and Papua New Guinea: 2 Coal. Australasian Institute of Mining and -Metallurgy, Monograph,6, 359-360. GLOE, C.S., 1979: The brown coal reserves of Victoria. Proceedings, Syrnposium on Estimation and, Statement of Mineral Reserues. Australasian Institute of Mining and Metallurgy, 49-61.

GLOE, C.S., 1984: The geology, discovery and assessment ofthe brown coal deposits of

Victoria. .In Woodcock, J.T. (Editor): Victoria's Brown Coal a huge fortune in chancery. Australasian- Institute of Mining and Metallurgy, Monograph,11, 79-109. HOLDGATE, G.R. & GALIMBERTI, A.G., 1980: Brown coal exploration, Western Districts, Victoria. Exploration and Geological Division, State

Electricity Commission of Victoria, Geological Report, 1980/1. KNIGIIT, J.L., 1975: Tertiary Coal Measures Altona, Bacchus Marsh, Lal Lal, Wensleydale, Benwerrin and Deans Marsh Districts, Victoria. .Irr Traves, D.M. & King, D. (Editors): Economic Geology of Australia and Papua New Guinea: 2 Institute of Mining and - Coal. Australasian Metallurgy, Monograph, 6, 355-359. MEYER, G.M., 1982: Geology of the Kingston lignite deposit. Australian Coal Geology, 4,92-100. MEYEET G.M., 1983: Coal Exploration Progress Report, WMC Hootzpah Project. Victorian Department of Minerals and Energy, EL Report 659. O'SHEA, P.J., 1978: Geological report on sandstone quarries at Bald Hill, Bacchus Marsh. Geological Survey of Victoria, Unpublished Report 1978/15. PARTRIDGE,-A.D., 1971: Stratigraphic palynology of the onshore Tertiary sediments ofthe Gippsland Basin. M.Sc. thesis, University of New South Wales.

According to Gloe (1979) economic brown coal reserve estimates, to his specifred criteria, are 100Mt at Anglesea and 30Mt at Bacchus Marsh. The Victorian Brown Coal Council (1983) provide estimates, with recovery costs, for 934Mt of brown coal around Altona.

Total production of 11 796 010t has been recorded to 1986 from the Bacchus Marsh mines and 2t 122 22At fuom the rest of the Otway Basin, giving a total cumulative production of 32 942 070t foi theentire Otway Basin. A mining reserve estimate of 2605Mt, out of a total resource estimate of 19 600Mt, was estimated by the Victorian Brown Coal Council (1983) for deposits in the adjoining Murray Basin near Kerang. Current production from the Anglesea Open-cut, which produces electricity for aluminium smelting, stands at near 1Mt per annum.

RIPPER, D., t975: A review of the known brown coal deposits in the Lal Lal, Bacchus Marsh and Altona areas, with recommendations for additional exploration. Geological Survey of Victoria, Report 197 5/7L. ROBERTS, P.S., 1984: Explanatory notes on Bacchus Marsh and Ballan 1:50 000 Geological Maps. Victorian Department of Minerals and Energy, Geological Suruey Report, 76. STANLEY, D.R., 1986: Brown coal resources of Victoria, an overview. Geological Survey of Victoria, Report. THOMAS, D.E. & BARAGWANATH, W., 1949-1951:

Geology of the brown coals of Victoria. Mining and Geological Journal of Victoria, 3(6), 28-55; 4(I), 36-52; 4(2), 4l-63; 4(3), 36-50. VICTORIAN BROWN COAL COUNCIL, 1983: Victorian Brown Coal Resource Deuelopment Study: the brown coal resource ofAnglesea and other Otway Basin areas, 3, 1-5.

Geology of Australian Coal Basins

577

ain ozoic

Basins of South Australia

Brown coal resources in the southern part of South Australia, occur along the northern margins of the Otway Basin at Kingston-Lochaber and along the western margins of the Murray Basin at SedanAnna. The deposits may be grouped broadly within either the Otway or Murray Basins, but in view of their isolation and basin-margin location they are treated here under separate headings. The remainder of the known South Australian deposits occur further north, within the distinct Saint Vincents Basin and are considered separately.

OTWAY BASIN MARGINS . KINGSTON AND LOCHABER DEPOSITS

AG Kremor GM Meyer GM Springbett

J Thrift

and CM Barton

Coal deposits in the southeast region of South Australia have been known since 1979, when Western Mining Corporation discovered the Kingston and Lochaber lignite deposits. Both deposits are Middle Eocene in age, and are situated along the northern margin uf the Otway Basin (Figure 1). The Kingston deposit has a total resource of 985Mt, and has been considered large enough to warrant evaluation for supply to a local power station. The high water table in the area, with signifrcant quantities of water overlying the lignite, may make the deposit suitable for mining with floating dredges. Such a system has significant cost advantages, and steps are being taken to prove its viability. The deposit represents a significant source of energy for South Australia and could supply most of the State's energy requirements in the near

future.

Stratigraphy and Deposit Descriptions The Tertiary sequence containing the majority of the lignite deposits in this area was deposited on a local basement depression formed in soft, weathered Cambrian phyllites and calcsilicates and bounded, to the west, by a large body of intrusive Ordovician granite. Aeromagnetic intensity data suggest that the eastern limb of the trough was also formed on a large body of Ordovician granite, but, in this case, covered by a veneer of Cambrian and Permian rocks. The depression occurs within a regional basement high that separates the Otway, Troubridge and Murray Basins (Figure 1). The brown coals lie within a transgressive sequence ofTertiary clastics, and^are overlain by.a thick regressive sequence of Quaternary marine and non-marine sediments. The Tertiary sediments were deposited in three distinct phases:

a Middle Eocene phase involving the nonmarine, sands, gravels, lignites and carbonaceous muds of the Dilwyn Formation and the overlying marginal marine muds and sands of the Nirranda Sub-group.

a Late Eocene phase involving marginal marine, carbonate-rich clays and sands of the Nirranda Sub-group and non-marine muds of the Dilwyn Formation.

an Oligocene phase involving the open marine, polyzoan limestones of the Gambier Limestone and minor, un-named but time-equivalent, carbonate-rich clays and sands.

The only lignite bearing unit is the older phase of the Dilwyn Formation, which comprises a thick

Cainozoic Basins of South Australia

578

i.)

Kilometres

Murray \ Basin ),: xetrn

Troubridge Basin

. Lignite Occurrence " Barren Hole @ Palaeozoic Outcrop

'ATertiary Trough -.,7Om depth to Dilwyn Fm. '

KINGSTON DEPOSIT.

LOCHABER

j 'l ' DEPOSTT

KINGSTON

.t\. (

t{oNARACOORTE

Otwa y Biasin Figure 1. Location oflignite (brown coal) occurrences in southeastern South Australia. sequence of relatively clean, coarse grained, feldspathic sands and gravels overlain by the main lignite-bearing interval and cverlain again by interbedded carbonaceous muds, sands and lesser lignite seams.

The sediments of Quaternary age at Kingston grade from units deposited under shallow marine conditions at the base, through beach deposits to sub-aerial or back-barrier lagoonal sediments at the top.

The Kingston lignite deposit is lenticular in profile and extends for over 50km. The main section, however, occurs in two lobes up to 5km wide and 20km long. Maximum lignite thickness is 12m, and

overburden varies from 28m to over 70m depending on the topographic elevation of the ground surface. The floor of the main seam forms an elongate trough with a maximum relief of only 15m. The lignite is type B according to the ASTM ciassification. The ln sltu ash yield of the main seam is reasonably uniform over the deposit and averages 6.7%o (dry basis). Moisture content averages 55.}Vo, volatile matter 2I.7Vo, fixed carbon L7.2Vo, sulphur 1.3Vo and sodium 0.38Vo. The average net wet specific energy of the main seam lignite is 10.2MJlkg.

MURRAY BASIN MARGINS SEDAN AND ANNA DEPOSITS The Sedan and Anna lignite deposits are situated on the western margin of the Murray Basin (Thrift & Lonergan, 1984), approximately 80km northeast of Adelaide (Figure 2). The Sedan deposit has been

investigated as a possible source offuel for a domestic power station.

Stratigraphy and Deposit Descriptions The Sedan and Anna deposits contain a sequence of fluvial and marine Tertiary/Quaternary sediments deposited on a Cambro-Ordovician basement. The basement consists primarily of Kanmantoo Group metasediments and granites; it has an irregular topography which has had a considerable influence on subsequent sediment deposition. The main stratigraphic units of the coal-bearing sequence are summarised in Figure 3. The Eocene Renmark Beds at the base of the sequence comprise an upward fining fluvial sequence of sands, silts, clay and lignite, with maximum thickness developed in basement lows. The main lignites occur at the top of this sequence. Two lignite seams are developed in the Sedan deposit, with individual seam thicknesses of up to 6m. One lignite seam of approximately 4m in thickness is present in the Anna deposit. The overlying Oligocene Ettrick Formation was deposited during a marine transgression which covered the Sedan-Anna area from the south. The formation consists primarily of interbedded glauconitic sands, silts and clays, deposited in a

restricted marine environment. Bioturbation is common in the base of the formation, and shell banks are occasionally developed. The boundary with the overlying Miocene Mannum Formation (Figure 3) is gradational.

Geology of Australian Coal Basins

579

__l

SOUTH

rl rl ll lr

AUSTRALIA

rzri t'za'

sc^Lt r 15000000

roo o

200

400

o"'o"

tikANDLEroN I

-trr"*" ,'

llrfr

vrf

CIMBRAI ,z --:+

t'.

BLACK HtLil

MANNUM

Figure 2. Location ofthe Anna and Sedan coal deposits, South Australia.

Cainozoic Basins of South Australia I

580 SEDAN DEPOSIT

ANNA DEPOSIT

hrckness

Descnpfion

(n)

t c6n6ts

hplh

't--l

6-20

i;i--

| , - . I rO o

_-----1OOs t#

ffi ffi

ffi ffi tr:d

15{

MANNUM LtMESIONE

cteom sondy lossilferous ltmeslone 20'15 sondy ltmestone and cotcorentle tntbrbpdded with colcoreoE sift ono cloys.

the late Proterozoic to Early Palaeozoic Adelaide Geosyncline in the east. The basin overlies a faulted transition zone (the Torrens Hinge Zone) between these major regional structural elements. Basin formation commenced in the Tertiary (Ludbrook, 1980), and was controlled by movements along pre-existing basement faults (Figure 4).

fticrners

{;) _ l:::

BLANCHFoWN CLAY-strff Nttted red btown. grey. green silty ctoy

buft yeilow ro

ffi F:+l F14 ffi H+ F44 FH

Sedimentation began in the Middle Eocene, with

much of the depositional history of the basin being characterised by a prominent marine gulf and adjacent lowlands (Cooper, 1985). Coal occurs

UO O

throughout the basin, mainly within the Late

Eocene Clinton Coal Measures. Major shallow-lying occurrences are restricted to the northern end of the

ffi

tr U

){ o

r,so

48.0

Ed --.""H-! '" " FARMAT |TTR|CK tON gteen grpy ro 2 O-7 O Fjj-] - - ,, dotk grey etty.to, C,toucontltc. l-.. fosst!'terous pynttc,some and , I jt

basin, where the sediments were deposited in mainly marginal marine and deltaiCenvironments.

----.

ho'tzons 1ondr

Five coal deposits have been delineated in the northern part ofthe basin, and these characteristically occur within fault-controlled basement dep_ressions. The coal is typically high in moisture, with moderate ash and relatively high sodium, chlorine and sulphur contents. It can be classified as lignite B under the ASTM system or Soft Brown Class 15 under the IS0 system. Total resources in the northern part of the St Vincent Basin are in excess of 300OMt.

l---l 2s0 I

l.,l l:l

15-ss !

? lixl !" i7,'" :,:" : ; 1:: ::'', " "

r,,

ol I

I zo.o

t--l

L-.1

_esow

The Bowmans and the Lochiel Deposits are the largest in the St Vincent Basin in-terms of coal reserves, and have been investigated in some detail

Figure 3. Representative stratigraphy of the Mannum, Sedan and Anna deposits.

as potential fuel sources.

The Mannum Formation was deposited in a

Lochiel Deposit

higher-energy marine environment than the Ettrick Formation (Gray, 1983), and fossil shells found within it are generally broken and disarticulated. The formation consists primarily of interbedded sands, calcarenites and silty clays, with hard bands of limestone intercalated throughout. The succeeding Pleistocene Blanchetown Clay consists of mottled sandy clay deposited under lacustrine conditions. Surficial Holocene deposits of calcrete also cover most of the Sedan-Anna area. The total coal resources outlined in the area to date are 289.3Mt, with average coal quality parameters as

The Lochiel deposit is located 130km north of Adelaide, and is contained within a north-south elongate area 9km bl 61._t" in-size. The s_edimentary sequ-ence occurs in a half:graben controlled by north-south and east-west trending faults in the Precambrian quartzite basement. The floor of the half graben as well as the sediments dip at about 1o to the northwest. Although most of the fault movement occurred after deposition, sedimentation patterns indicate synsedimentary movement.

ST VINCENT BASIN _ LOCHIEL AND

The sequence is contiguous with the Northern St Vincent Basin at the northern end, but is truncated by the Ardrossan Fault to the west. It laps on to the basement in the east and south.

indicated in Table 1.

BOWMANS DEPOSITS

Stratigraphy and Deposit De seription

Geological Setting

The sediments of the Lochiel deposit, which thicken to a maximum of 170m in the north, were deposited on a Precambrian to Cambrian sequence during

The St Vincent Basin lies between the Archaean to Middle Proterozoic,Gawler Craton in the west and

Table 1','Average"in sita abal qualit;y ana,,iesources for the Anna and Sedan deposits. a) In situ coal resources Sedan-Anna area

Deposit

Measured

Indicated (mt)

Sedan

L23.7 58.4

107.1

Anna

(mt)

Total (mt) 230.9 58.4

289.3 b) Average in situ coal quality Sedan-Anna area

Total Moisture

Ash

(dry basis 7o)

(Vo)

Sedan

Anna

59.4 54

18.9

23.8

Sulphur Total (dry basis 7r) 5.59 3.83

Na Cl (dry basis 7o) (dry basis 7o)

Gross Dry

Specific Energy

(MJ/ke) 0.63 0.57

Geology of Australian Coal Basins

0.23

22.57

2L.6

58r Sedimentation commenced from the north in a Late Eocene fluvio-lacustrine environment. These sediments are represented by a fluvial channel sand facies of the Bumbunga Sand in the north, which is laterally equivalent over the remainder of the depositio a Bumbunga Sand distributar-y floodplain faiies and coarseninf upward cycles of the lacustrine Condowie Silt' The Kooliata Coal Zone conformably overlies the Condowie Silt, and consists of peat-swamp coal and lacustrine sand and silt cycles. Laterally equivalent to and surrounding these depositional environments was a heavily vegelated area which acted as a sediment trap to protect the peat-swamps from clastic sediment input.

An Oligocene marine transgression fr9-ry the south, superiirposed lagoonal sand and silt (Warrindi Silt) anh carbonaceous, estuarine silt (Tarella Silt) over the Kooliata Coal Zone. A period of gentle uplift and weathering-followed. the deposition of these sediments, before sedimentation reiommended in the Quaternary in a lacustrine environment (Hindmarsh Clay equivalent; Figure 5). The coal zone has an average thickness of 20m. It contains three correlatable coal-bearing intervals (locally identified as the F, G and H se-ams), separated by two well defined interbeds, up- to-4m thick, consiiting predominantly of sand and silt. The G seam is continuous throughout the deposit and averages 6.5m in thickness; lhg -F and H seams are present only in the northern half, and-average 1.8m and 2.6min thickness respectively. Maximum cumulative coal thickness is 20m, with the margins of all three seams representing facies changes from coal to sand. Partings within the seams are generally confined to near the margins'

Sedimentary cover over the coal varies between 19m and 70m, arid the total resource amounts to 365Mt in the Measured and Indicated categories.

n I

LE6 E ND

ST. VINt ENT BASIN SEDIMENTS

CI]AL DEPOSIT FAULTED BASIN MARGIN

APPROXIMATE BASIN MAR6I N

Figure 4. Coalfield location map for the Saint Vincent Basin. three major depositional episodes (Kremor, 1986). These are indicated in Figure 5, and include:

a late Upper Eocene fluvio-lacustrine system;

an Oligocene marginal marine-estuarine system; and

a Quaternary lacustrine sYstem.

Eight stratigraphic units, have been defined, but all ar6 informally named at the present time.

Compared to the coal in the Bowmans deposit and othei deposits in the basin the coal is high inmoisture, low in nelwet specific energy and low in sodium, chlorine and sulphur (Table 2)'

Bowmans Deposit The Bowmans coal deposit lies 100km north of Adelaide and some 30km south of Lochiel (Figure 4). Coal occurrence in the area is widespread, with a continuous coal zone between Bowmans and a number of smaller deposits nearby. However, an, elongate north-south trending body approTimately 9km by 4km contains most of the potentially

exploitable resources.

To the north, south and west the seams split and reduce in thickness within an essentially consistent thickness of Tertiary sediments. Rapid coal thinning and splitting also occurs towards shallow basement

in the east.

Stratigraphy and. Deposit D escriptions The Lochiel and Bowmans Deposits are separated by an uplifted Precambrian basement block. Although precise correlation between tbe two is- yet to be 6stablished, sediments were deposited in three

broadly equivalent phases ranging from Middle Eocene to Pleistocene in age.

Cainozoic Basins of South Australia

582

lrtt I

7 a

L/-

iE a

! e o 2

6 o 6

iil:1 tt

-o

d E

.:i: !!gi si ;;i F --

d :iEl

Al I I

:3 ir

!:i;

Er I s

ID C!

ad tr

I o bD

a c

o I

o o o o o

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€

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Geology of Australian Coal Basins

rl! ut[!I

ri!

583

Lochiel Bowmans

Principal economic interest centres on the three middle seams (81, 83 and C); these attain a maximum cumulative coal thickness of approximately 25m, separated by op to 4m of interseam sediments.

61.6 7.6

55.5 8.5

These middle seams are generally between 7 and 10m thick. However, they vary markedly in extent, with each phase of coal accumulation (ie, C to 83 to

15.1 2.9 0.48

14.0

TCble:2. AVeragein :sita edal quality for the tochiel, end.,Bowmans, ddpoCits.

Moisture (in situ Vo) Lower Heating Value (in situ MJ/kg) Ash (dry basis 7o) Sulphur (dry basis 7o) Chlorine (dry basis 7o) Sodium (drv basis 7r)

0.95

5.0 1.50 1.55

Deposition in the Bowmans deposit occurred in the

following phases:

. .

a Middle to Late Eocene fluvio-deltaic system; a late Eocene to Middle Oligocene marine to

marginal marine system; and

a Quaternary lacustrine system.

These relate respectively to the Late Eocene

fluvio-lacustrine sediments, the Oligocene marginal marine sediments and the Quaternary lacustrine sediments occurring at Lochiel (Figure 5). Total sediment thickness is relatively consistent at Bowmans, and commonly ranges from 110 to 130m. Three major stratigraphic units have been defined and two are informally named. The basal Tertiary

B1) becoming more restricted and localised in the north of the deposit. The upper and lower coal zones (A and D), are separated from the main coal interval by between 10 and 25m of sediments, and individual seams rarely exceed 1m in thickness. Sediments are essentially flat-lying, although gentle dips up to 20 do occur. Dips are most pronounced near shallow basement albng the eastern margin of the deposit. The main coal zone is overlain by between 60 and 80m of sediments. The resource totals approximately 1600Mt, and of this some 1250Mt is in the Measured and Indicated categories. The Bowmans Deposit contains coal of slightly higher rank than the Lochiel Deposit, and this is reflected by a lower moisture content and higher net wet specific energy. In addition, Bowmans coal contains higher proportions ofinorganics such as sodium and chlorine, as well as sulphur relative to Lochiel coal. Coal quality is summarised in Table 2.

REFERENCES

formation, the Late to Middle Eocene Clifton Coal Measures, overlies a Precambrian to Cambrian sequence and consists of approximately 70m of carbonaceous silt, sand and coal. It accumulated in a delta plain environment (Meakin, 1985).

COOPER, B.J., 1985: The Cainozoic St Vincent Basin: tectonics, structure, stratigraphy. South Australian Department of Mines and Energy, S pecial Publication, 5, 35-49.

The second phase of Tertiary sedimentation is represented by about 50m of predominantly frne silty sand. This is thought to belong to the Late Eocene to Middle Oligocene Rogue Formation, which is marine in origin and formed during a transgression from the south. In the south, moreover, this sequence becomes finer and contains glauconitic and fossiliferous intervals. The frnal phase of sedimentation is represented by a sequence

KREMOR, A.G., 1986: Depositional environments of the Lochiel coal deposit. Electricity Trust of South Australia, Reporb 86/11.

of the Quaternary Hindmarsh Clay, 10 to 15m thick, unconformably overlying the Tertiary sequence. This interval consists predominantly of clay and sandy clay, and formed in a lacustrine environment.

Five coal zones have been recognised within the Clinton Coal Measures over a vertical interval of approximately 60m. These have been informally named the A, 81, 83, C and D seams (Figure 5).

GRAY, J., 1983: Biofacies analysis of marine overburden, Sedan coalfield. B.Sc. (Hons) thesis, University of Adelaide.

LUDBROOK, N.H., 1980:A Guide to the Geology and Mineral Resources of South Australia. Government Printer, Adelaide.

MEAKIN, S., 1985: Palynological analysis of the Clinton Coal Measures, northern St Vincent Basin, South Australia. B.Sc. (Hons) thesis, University of Adelaide. THRIFT, J.A. & LONERGAN, T., 1984: Mannum Project: Sedan coal deposit, geology and reserves. CSR Internal Report 4.

Cainozoic Basins of South Australia

585

ffiremer Basin,

Western

Australia RG Elms RG Matthews

and DG Chapman

The Bremer Basin is the area underlain by Tertiary (and in some cases older) sediments extending discontinuously along the south coast of western Australia and irart ofthe adjacent continental shelf (Fisure f l. tfre basin is divided into two by out"cropping basement rock in the RavensthorpeHopet6rin irea. The eastern part of.the. Bremer Baiin is not well known until the vicinity of the Erp"tutt."-Norseman road, but-immediately east of thii road the basin extends without interruption from Esperance to the Eyre Highway and for an uncertain distance beyond. The Bremer Basin sediments extend along the coast from Walpole to Cape Arid. They exteld inland for some 100i<m to the north of Albany, where Western Collieries drill hole R168 intersected 50m of sediments 10km NNE of Cranbrook, and without break, for more than 200km north ofEsperance to Lake Cowan. Occurrences are known as far north as Coolgardie (Rollos Bore) and Lake Lefroy. The area over which the sediments occur is uncertain because of sparse outcrop and the discontinuous nature of their deposition. However, recent coal exploration has shown a greatelspread and depth of s-ediments within the Bremer Basin than pieviously recognised (Figure 1). The total thickness of the sediments onshore exceeds 200m' Outcropping Precambrian basement in the Ravenslhoipe area divides the Bremer Basin into an eastern and a western sub-basin, each of which is further discussed below. Little is known about a small occurrence recorded from the Walpole area, 100km west of Albany (Wilde & Walker, 1984). The Tertiary succession exposed near-N-orseman is referred to is the Eundynie Group, whilst that exposed between Cape Arid and Walpole belongs to th6 Plantagenet Group. (Playford & others, 1975). The Plantagenet Group consists (in ascending order) of the Weriilup Formation and the Pallinup

Siltstone.

STRATIGRAPHY

IYerillup Formation The Werillup Formation (Cockbain, 1968a) has been dated as Lafe Eocene. It is a paralic unit of grey and black clay, siltstone, sandstone, lig-nite, and carbonacLous siltstone, which overlies Precambrian rocks and is overlain conformably by the Pallinup Siltstone. The maximum known thickness is 49m in the Albany Aerodrome bore. The unit is known from discontinuous exposures near the coast, including those at Nornallp Inlet, Denmark, Esperance and the Fit-zge-rald River (Playford'& oihers, 1975)' It ir' also known in bores neai Esperance, and east of Norseman to the vicinity^of Balladonia. Lignites in-tlre fo-rmation are up to 5m thick around Nornalup-Inlet, 1.5m near

Aibany, up to 10m in the Tambellup-Cranbrook a.ea, ip t-o 1Zm in the Scadd?n a!93, up to 34m in the Heirtbreak area (50km NE of Norseman) and up to 10m in the Pine Hill area (85km north of Cape Arid).

Pallinup Siltstone The Pallinup Siltstone (Cockbain, 1968a) is a marine unit of whitir, brown, or red siltstone and spongolite. It rests on Precambrian basement rocks or conformably overlies the Werillup-Formation, and is overlain byQuaternary deposits. The formation

Bremer Basin

586 , COOLGARDIE

\-l

NORESMAN

)GnrrnDoNrA

-/-l

'-,-Kn ;' H'v-l!fl)r' ro rinr'i

RAVENSTHORPE

Pine Hirr

6/t

. Mt Merivale

I I

TAMBELLUP

-1 --> : oorT(,

w tO

-cS 0

Known occurrence of sediments Posslble occurrence ol sedlments 200km

Figure L. Location of sediments in the Bremer Basin' crops out discontinuously from North-cliffe to east of Esferance, and is exposed on each side of the Stiiling Range (Playford & others, 19?q). Plavford & othersI1975) reporled a thickness of 61m in the

Albany Aerodrome bore, and drilling by Western Collieiies Limited has shown a thickness of up to 80m east ofEsperance. A Late Eocene age is indicated by the Pallinup Siltstone fauna (Cockbain, 1968b)'

Eundynie Group The Eundynie Group is exposed around the margin

of Lake Cowan, neai Norseman. It contains the Norseman Limestone, the Cowan Dolomite and the Princess Royal Spongolite, although the stratigraphic relitionships between these units are uncerfain because ofthe poor outcrop. Cockbain (1968a), however, believes that the Princess Royal Sponeoiite is in part laterally equivalent to the other"two units ind in part overlaps them (Playford & others, 1975). It is suggested that all units correlate in part with ttre Pallinup Formation'

The maximum thickness of the Eundynie Group in

the Norseman area is probably about 20m. Its age is considered to be Late Eocene. A bore drilled in the floor of Lake Cowan (approximate surface RL 260m) reached basement at ii5m after passing through a sequence ofpyritic clav. 'soft biluminous mud' and clay with pebbles' fhis unit probably correlates with the Werillup

Formation and the Rollos Bore Beds (near Coolgardie; Playford & others,1975).

Drilling on Lake Lefroy encountered.basement at depths"of up to 90m (i.-e. at RL 200m). Dark brown running sattds are common at the base of the Tertiar:y sequence in holes dqep-e-r tha^n 60m. These ge""iatiy .outt" sands contain-black fossilised wood, ind are iquivalent to dark Iignitic clays-and black spongilitii clays found elsewhere around Lake All th6se units are thought to correlate with l-"t "-y. Formation. the Werillup The above rocks are overlain by pale coloured sands, sandy clays and clays. These are gla-Yconitic and .po.rgilitli in placei, and are generally similar to the fiattinup Siltstone (Green, 1982).

STRUCTURE The marine and paralic Tertiary sediments of the onshore Bremer ilasin are flat lying. No faulting or folding is known. The sediments were deposited over an ext"remely irregular surface of Precambrian rocks, which formed a number of islands and oromontories in Eocene times comparable to those of [he modern Recherche Archipelago (Playford &

others, L975).

The lisnites of the Bremer Basin were develoPed durinf late Middle to Late Eocene times over largeareas"of generally stable shield, with no rec-ognised structuril controls over sedimentation and lignite loimation. Deposition appears to have occurred in a

Geology of Australian Coal Basins

587

TCble 1. Analytical data and resource estimates for Western Australihn lignites" (brown coals). H

z o

ri pr a

frl

c{d

^?Fl

& H

11.6 17.3 11.8

14.4

-ica

Fl F1

o trl m

6il

z fEl

frl

9.4

20.8

16.0

6.5

8.5

Proximate Analvsis (607o moisure basis) Ash

11.9 15.9

Yolatile Vo Fixed C. 7o S. Vo

Net wet specific gravity MJ/kg

12.2 1.9

7.6 approx

10.0

16.3 13.4 7.7

1.8

6.5

9.1

8.3

8.5 approx

Ultimate analysis (Dry ash free basis) 57.7

45.8

5.3

Nitrogen 7o

3.5 0.3

Miscellaneous Data (60% moisture basis) 6.3 NaCl %

5.7

Carbon Vo Hydrogen Va

In situ Resources (106 tonnes)

Average seam thickness Average Overburden Ratio

1300(A)

500(A)

400(Infl

650(A)

100+(1)

bOO(Infl 1000(Infl

614(M) 10

3:1

1:1

10:1

7:1

1.6:1

85 1.5:1

l2:7

Notes: 1. Data from Western Collieries Ltd gources. 2. Data from CRA Exploration Pty Lrrnited sources. a"ta f as6a on 3 cored drill holes only, _while sqecific energy is based on one cored hole only 5: d;;t;;;k (reverse cycle ""rivti.'J drif samples available, but considered less reliable and hence-not quoted). M = *"u.L""d; 1 = indicated; A = assumed; Inf = inferred; N = net wet specific energy; I = data not available. series of separate or tenuously connected coal subbasins within a sinuous larger channel structure, possibly controlled by as yet unrecognised tectonic

features. The lignites were developed autochthonously along meandering fluvial systems and in associated swamps, lakes and lagoons. Both sedimentation and coal formation would have been mainly controlled by

eustatic changes in sea level. With sea level fluctuations and with epeirogenic uplift of the Yilgarn Block possibly an influence along the Jarrahwood Axis (Cope, L975), it is reasonable that there should be a series of locations where peat accumulation occurred and ultimately formed lignite. Such lignite occurrences would show differences in height above sea level and would also have been formed at somewhat different times in the Eocene. In support of this concept, there is evidence ofseveral lignite ages in the Scaddan deposit.

Lignite is known to occur at a range of elevations with respect to present sea level. East of Esperance, at two locations 30km apart, the base of the lignite is at respective RLs of -6m and +52m. Further north, in the Scaddan lignite deposit, the base of lignite ranges from RL 138m to RL 164m over a north-south strike length of 18km. Near Norseman the base of lignite is at RL 232m, while further north at Lake Cowan it is approximately at RL 140m.

The base of lignite in the western Bremer Basin is known to occur over a range of RLs from -1m to +13m. In the Green Range-South Stirling area, northeast of Albany, the base of lignite varies from RL 74m to RL 80m, while north of the Stirling Range it ranges from RL 208m to RL 217m.

Thus, in both the eastern and western parts of the Bremer Basin, lignites now occur over a vertical range in elevation of approximately 2,-20m, indiiating that the combined effect of sea level fluctuation and uplift of the Yilgarn Block since Eocene times is at least that figure. The presence of Tertiary marine sediments at RL 260m in Lake Cowan, moreover, indicates that the frgure is at

least 260m.

DEPOSITS IN THE WESTERN BREMER BASIN (the part of the basin west of Ravensthorpe)

Albany Area The stratigraphy of the Werillup and Pallinup Formations in this area is discussed in the section above. Drilling in the Marbellup area, just west of Albany aerodrome, has shown only thin (1.5m) poor-quality lignite to be present, separated from weathered basement by a thin (0.5m) transitional conglomerate.

South Stirling - Green Range Drillins southeast of the Stirling Range, near South Stirlin[, has recently shown the Cainozoic sediments to be niore than 90m thick. The Pallinup Formation in this area consists of 42m of grey to brown clay siltstone and sandstone. The Werillup Formation consists of up to 46m carbonaceous siltstones and lignitic clays with at least 10m of underlying.coarse sand and glauconitic clay. No significant lignite occurrence is known from this area.

Further southeast, at Green Range, a large resource of lignite has been inferred (Table 1). The typical

Bremer Basin .l

588 section of the Werillup Formation is 46m thick, with 5m of lignite at the base lying unconformably on

kaolinised granite basement. The lignite is overlain by 5m of dark brown, organic-rich claystone, which is overlain in turn by 36m of yellow, grey, greyish brown and greyish green well sorted sandstones to complete the Werillup sequence. The Pallinup Siltstone in this area is represented by 25m of cream to brown siltstone. It is capped by 9m of Quaternary clays (Kristensen, 1986).

Analytical details of the lignite are given in Table 1.

Cranbrook To the north of the Stirling Range, Tertiary

sediments up to 50m thick occur in a shallow, east-west oriented meandering channel which is approximately 5km wide and over 50km long. The lowermost unit of the Werillup Formation in this area is a coarse, unsorted and unlithified sand of fluvial origin. Overlying this sand is a unit of lignite and lignitic clay, which ranges up to a maximum thickness of 14m. This is followed by the Pallinup Formation, which is silty sandy clay from 2 to 20m thick, and overlain in turn by a thin (1 to 3m) veneer of Quaternary sand.

The lignite occurs in localised patches within the

main channel, in what where presumably restricted shallow swamps. The maximum lignite -thickness observed is 10m, but the main deposit has an average lignite thickness of 7.2m and a depth of cover which ranges from 6 to 16m. Analytical details of this lignite are given in Table 1.

marl-limestone, and minor conglomerate. This rests either unconformably on basement or on a thin Werillup Formation sequence, typically consisting of 4 to 5m oflignite, carbonaceous siltstone and sandstone, and pyritic fossiliferous sandstone.

Scaddan Some 5Okm north of Esperance, the irregular Precambrian basement surface is overlain by the Werrillup Formation, the basal unit of which varies in thickness from zero to more than 20m. This unit is an unlithified, poorly sorted, medium to coarse fluvial sand, within which are thin clay horizons, abundant wood fragments, and pyrite nodules.

Lignite and carbonaceous clay, which have been dated by palynology as late Middle to Late Eocene in age (Milne, 1983), form the next unit in the succession. These may be replaced, however, at some localities by a dark green glauconitic, spiculitic clay. The clay appears to be stratigraphically equivalent to the lignite although in places it overlies the lignitic unit. Several lignite occurrences have been identified in this region, the largest of which occurs in a buried pre-Upper Eocene drainage channel which has an approximate north-south trend. This deposit has a known length of 35km, a variable width of up to 7km, an average thickness of 10m and a sediment cover of 30m. The upper surface of the lignite exhibits gentle dips, while the base conforms in general terms to the basement topography (Figure 2).

EASTERN BREMER BASIN (that part of the basin east of Ravensthorpe)

Drilling of this deposit has delineated shallow in situ resource >600Mt accessible by opencut mining, and a total resource in excess of 1300Mt. The lignite is a low-energy fuel (Table 1), with high ash and salt

Esperance Area

Mount Hey

East of Esperance, between Mt Merivale and Condinup Peak, the Cainozoic sequence is relatively thick, and in places exceeds 90m. The typical sequence consists of a laterite capping up to 1.5m thick overlying the Pallinup Formation, which is up to 80m thick and consists largely of siltstones, with (fossiliferous, glauconitic, micaceous) sandstone,

This deposit is located some 40-50km ENE of Mt Ridley. The Cainozoic sequence in the area is thin, and the Tertiary sediments are overlain by a thin (1-3m) layer of calcrete, sand or silty clay. The Pallinup Formation in the area is typically between zero and 10m thick, although it contains a thickness of 20m of sand, silt and glauconitic clay in Western

pALLtNLip srLTsroNE

levels (Elms & others, 1981).

l---l ct"y and sandy silt caruonaceous sand, silt and clay

;l---.l WERILLUP FoRMATIoN I l---l r-isnite

SCADDAN DEPOSIT EAST_WEST CROSS-SECTION

L[-__l e"""r sand and minor clay (carbonaceous)

t_l

NOTE - 25:1 VERTICAL SCALE EXAGGERATION Figure 2. East.west cross-section through the Scaddan deposit.

Geology of Australian Coal Basins

589 Collieries borehole R620 where it directly overlies the weathered basement. The underlying Werillup Formation reaches a maximum observed thickness of 12m, and consists of lignite (4.5m) carbonaceous sand and clay with a coarse basal sand accumulation.

East of Norseman

Werillup Formation succession up to 14m thick, consisting ofbasal sands, lignitic and carbonaceous clays, and thin, poor-quality lignites.

DEPOSIT SIZE AND CHARACTER Resources amounting to over 5000Mt have been

Two apparently separate sedimentary sub-basins

are located approximately 50km southeast of Norseman, the northern one with an orientation of 3200 and the southern one with an orientation of 0200. These occurrences lie at the boundary ofthe Yilgarn Block with the Albany-Fraser Province.

estimated for these deposits (Table 1).

The coal at Scaddan is a fairly well-gelifred lignite consisting mainly of woody material, with high ash and salt percentages. It consists of approximately

The Tertiary sequence in this area is 53m thick. It consists of a Werillup Formation sequence 29.5m thick, overlain by a Pallinup Formation sequence up to 23.5m thick. The Werillup Formation consists of 20.5m of clay, 5m of lignitic clay and 4rn of grey to

80% vitrinite, I07o liptinite, \Vo inertinite and 57o mineral matter. Other Bremer Basin coals are generally similar, but have a higher proportion of liptinite (up to 30Vo) tn the maceral analysis. This is reflected in the anomalously high oil yields when the coal is subjected to Fischer analysis: for example, 140L/t in the case of Heartbreak coals.

Below the Werillup unit, and capped by a thin (1m) layer ofrounded quartz pebbles and cobbles, is a grey/black finely bedded hard micaceous laminated claystone. This claystone becomes pyritic, harder and more fissile with depth. Its age is interpreted as

The coals have potentially low mining costs, but suffer the disadvantages of high salt content and low specific energy. Test work on combustion of Scaddan lignite has shown it to possess high fouling and slagging characteristics. The utilisation potential of the lignites therefore depends on developments in coal to oil conversion, cleaning ofhigh-salt coal and coal combustion research.

black clay, and the Pallinup Formation is made up of 17m of clay with minor sand, 4m of pale brown limestone and 2.5m of glauconitic sand.

latest Carboniferous to Early Permian (Ingram, 1982), making it the only known sediment of this age within the Bremer Basin.

These Permian sedimertts, of unknown thickness, occur over an area some 30km in N-S extent and 4km in width. They may be preserved within as yet

undefined narrow, graben-like structures, possibly aligned in directions of0200 and 320o. The suggested 020o alignment is also possibly the main control for the localisation ofthe Scaddan lignite occurrences, with some modification by structures oriented at 3200.

Up to 26m of banded, clay-rich lignite occurs elsewhere in the area. Thirty-five metres of Iignite under 26m of cover has also been recorded some 2Okm east-north-east of Heartbreak Ridge (Table 1). The resource at this locality is estimated at 500Mt, with an average lignite thickness of 19m

(Kristensen, 1986).

Harms Lake In the Harms Lake area, some 35km southeast of Fraser Range, a sequence ofprobable Pallinup Formation stretches for a distance of 50km south of the Eyre Highway. The Pallinup Formation here consists of a partly sequence of grey, white and red clays, silt and sandstone, and white limestone, and is typically overlain by 1 to 6m ofoxidised

REFERENCES COCKBAIN, A.E., 1968a: The stratigraphy of the Plantagenet Group, Western Australia. Geological Suruey of Western Australia, Annual report (for 1967), 61-63. COCKBAIN, A.E., 1968b: The nautiloid Cimona inthe Plantagenet Group. Geological Suruey of Western Australia, Annual Report (for 1967),57-58. COPE, R.N., 1975: Tertiary epeirogeny in the southern part of Western Australia. Geological Suruey of Western Australia, Annual Report (for L974), 4A-46.

ELMS, R.G., MATTHEWS, R.D. & CHAPMAN, D.G., 1982: Notes on the geology ofthe lignite resources, Esperance, Western Australia.

Australian Coal Geology, 4, 101-110.

GREEN, C.D., 1982: Completion report on exploration to January, 1982, Exploration Permit 158, Lefroy Prospect, Western Australia. Western Collieries

Lirnited. INGRAM, 8.S., 1982: Palynology of a sample from the Norseman area. Report by Western Palynoservices for Western Collieries Limited.

ferruginous sand and clay. The maximum depth of sediment known is 43m.

KRISTENSEN, S.E., 1986: Summary of CRAE investigation into Bremer Basin lignites.

Pine Hill Drilling at the eastern end of the Bremer Basin, between Balladonia and Cape Arid some 20km south of Mt Coobaninya, has shown the existence of Cainozoic sediments to depths of at least 88m. The Tertiary sediments in this region are overlain by calcrete or a thin layer of oxidised ferruginous clay up to 4m thick. The Pallinup Formation (or equivalent) underlying this cover varies from 50 to 80m in thickness, and consists of glauconitic

MILNE, L.A., 1983: Palynology of Western Collieries boreholes DDH 90, 91 and 102 from near

fossiliferous clays and siltstones and white-yellow bioclastic limestone with some interbedded clay. This sequence is in turn underlain in places by a

Esperance.

PLAYFORD, P.E., COPE, R.N., COCKBAIN, A.E., LOW, G.H. & LOWRY, D.C., 1975: Chapter 2: Phanerozoic. 1n Geology of Western Australia: Geological Suruey of Western Australia, Memoir,

2,429-437. WILDE, S.A. & WALKER, I.W., 1984: Pemberton-Irwin Inlet. Western Australia 1:250 000 Geological Series Explanatory Notes. Western Australia Geological Survey, Perth.

Bremer Basin