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ABSTRACTS OF THE

SECOND AUSTRALIAN GEOLOGICAL CONVENTION HELD AT MONASH UNIVERSITY, CLAYTON 2-4

FEBRUARY 1 9 7 7

compiled by L . J . W y l d e , Research S c i e n t i s t , Australian Road Research Board

These Abstracts have been printed for the Organising Committee of the Second Geological Convention b y the Australian Road Research B o a r d , Vermont S o u t h , V i c t o r i a , with the kind permission of the Executive D i r e c t o r , Dr M . G . L a y . Opinions expressed by the Authors do not necessarily represent those of the Organising Committee or ARRB* R e f e r e n c e to or reproduction of any Abstract m u s t include a precise reference to the report and the A u t h o r ( s ) .

NATIONAL LIBRARY OF AUSTRALIA CARD NUMBER AND ISBN - 0 86910 072 6

TABLE OF CONTEMTS PAGE SEDIENTOLOGY

1A -

Belperio

Sediment Transport, inner shelf^Queensland

R.G.

Brown

Diagenetic features in mangrove tidal flats 5 Western Australia

A.M.

Depers

Diagenesis and trace elements, Lake

Illawarra

I.A.

Duddy

Diagenesis of the Otway Group

P.G.

Flood

Blackened grains in carbonate sediments

G.S.

Gibbons

Hydraulic equivalence and placers

B.G.

Jones

Diagenesis Gulf Basins in the Amadeus and Bonanarte

K.R.

Martin

Diagenesis in Precipice Sandstone

G.R. B.G.

Orme Thorn

Diagenesis in the Great Barrier Reef

S.A.

Reeckman

Diagenesis of Victorian Carbonates

Schwebel

Cementation in the Bridgewater Formation

Q.P.

Singleton

A review of carbonate diagenesis

PALAEONTOLOGY - 2A - 2B - 2C

Archer

Origin of the Kangaroos

D. D.

Christophel Blackburn

An Eocene flora from Maslin Beach South Australia (Or: Palaeobotanists bare all at Maslin's)

Dettmann

Australian Cretaceous phytogeography : a palynological perspective

Angiosperms - an assessment of the Australian pre-Tertiary record

New Evidence for a Silurian age of the earliest Baragwanathia flora

Pleistocene Man and Megafauna in Tasmania: Dated evidences from two Late Pleistocene Cave Bone-Bressias

J. M.

Douglas Garratt

Goede Harmon

PALAEONTOLOGY J.

CONTINUED

Hope

Pleistocene Extinctions and Man in Australia

Hos

Early Tertiary palm pollen in Australia

Kershaw

Changes in the flora and vegetation of north-eastern Australia during the Quaternary Period

Mallett

Ages of Victorian Vertebrate Fossil localities in Neog^ne Marine Strata

Martin

KEYNOTE ADDRESS: The Tertiary palynological record and the evolution of the Australian flora

Plane

Review of Australian Marsupial evolution

Rich

The problem of the Morwell Kangaroos

Rigby

Sanson

Review of pre-Cretaceous evidence of angiosperm progenitors- Gloss oyter is and others The evolution of the Grazing Macropodids and the significance of the Morwell Kangaroos

Thorne

A.H. Voisey R. K.

Wells Moriarty

D. R.

Williams Wells

Review of Fossil Man in A u s ^ l i a The tectono-sedimentary framework of organic evolution The late Pleistocene Fauna of Victoria Cave, Naracoote, South Australia A Late Pleistocene Marsupial Fauna at Dempsey f s Lake, Port August, South Australia

WEATHERING M

EXPLORATION

Antimony at Costerfield - a geochemical picture

Hill

EOQFFLSTRY

R.R. Keays 6.A. Travis

Palladium and iridium in nickel sulphide gossans

G. Kelly R.6. Taylor

Supergene sulphides, oxides and leached outcrops, Siberia Sn-Cu mine

R.E. Smith G. Willett

Multi-element geochemistry in the Bangamall Group

ISLAND ARCS A.J. Crawford R.R. Keays

The Cambrian greenstone belts of Victoria

P.R. Dengeling L.E. Pogson

The Halls Peak Pb-Zn-Cu deposits, Armidale, New South Wales

J.A.S.Dow

The discovery and preliminary evaluation of porphyry copper deposits in northern Sulawesi, Indonesia

The petrology of some young volcanic rocks from G. Rindjani, Sunda Arc

Foden

E.D. Gill

The plate tectonic theory in relation to the Australian caost and continental shelf

M. P. Gorton

Geochemistry and origin of Quaternary volcanism in the New Hebrides island arc

Fountain

A comparison of hydrothermal alteration effects in the Panguma and Waisoi copper deposits

Hamilton

Collision of the Banda Ace with Australia

G.G. Lowder

Nature and relationships of mineralisation and alteration in Sulawesi porphyry copper deposits

M.J. Primrose

The geology of the Pukekaikiore and Tama Lakes region of the Tongariro volcanic massif, North Island, New Zealand

Mineralogy and geochemistry of a felsic undersaturated shoshonitic intrusion from the Mount Dromedary Complex, N.S.W.

Purvis

W.D- Roots

Post-cretaceous subduction beneath the S.E. Australian margin? Support from volcanic age trends and new marine magnetic profiles

ACID IWIATISM

AND ORE

C.D.

Evolution of the Middle Proterozoic Chandabooka Caldera, and related basic to acid volcanics of the Chitanilga Volcanic Complex, northwestern Gawler Range volcanoplutonic province, South Australia

Branch

ACID MAGMATISM AND ORE (CONTINUED) L.T. Bryndzia T.A.P.Kwak

The geology and Geochemistry of the Bulla adamellite and its inclusions - a case for marginal contamination

P.J.

Evolution of hydrothermal brines associated with the Mole granite Glen Innes, New South Wales

Eadingtori

PAGE 37

B.L. Gulson

Comparison of mineralized and unmineralized acid volcanics

M.P. Hochstein

Mineralization of geothermal fluids discharged by the SURETAMATI geothermal system (New Hebrides )

Geochemistry of sphalerites from the May Day prospect, New South Wales

Geochemical, mineralogical and petrographic features of rocks around massive sulphide deposits in felsic volcanic sequen ces, Lachlan Fold Belt

I.A. Nicholls V.J. Wall

Recent studies in the Snowy River Volcanics, Eastern Australia

J.A. 01 atunji C. Cuff R.G; Taylor

Aspects of granitoids from the West Herberton region of the Herberton Mt. Garnet tinffeld

R.C. Price S.R. Taylor

Rare earth element geochemistry of granitoids from the North-East Victorian metamorphic belt and partial melting

Compositions of sphalerites from the Flin Flon - Snow lake mineralized belt of Canada

Jago S.R. Sangameshwar I.B. Lambert

S.R. Sangameshwar

SHIELD GEOLOGY AND MINERALIZATION R.

Keays

S.B. Lee

Palladium, Iridium and Gold in the ores and host rocks of Western Australia, with particular reference to Kambalda

Z4/4

Metasomatic alteration associated with the Broken Hill orebody, New South Wales L\5

SHIELD GEOLOGY AND MINERALIZATION (CONTINUED) W.R. Morgan

Ultramamafic body in Archean granulites near Corrigin, Western Australia

Purvis

Primary and secondary variation patterns in the geochemistry of Archaean met metavolcanic rocks

Tucker

The application of aeromagnetic interpretation with ground follow up to mapping in the Adelaide Geosyncline

LEAD-ZINC CARBONATE ROCKS G.D. De Ross D.J. Perkin

Epivolcanogenic ores in fold belt carbonate rocks - an epigeneticvolcanogenic ore type

Stratiform Copper, Deformations and diagenesis in Kapunda, South Australia

Drummond

ffTAFIORPHISFI C.D.A.Coin

The relation between Ca,Mn content of garnet

W.F. D'Arcy

Structures and metamorphism of the Northern Tip of the Willyama Block, Broken Hill, New South Wales

T.A.P.Kwak

Conditions of formation of the King Island Scheelite deposits, King Island Tasmania

E.M. Lohe

Aspects of the metamorphic mineral assemblages in the Neranleigh-Fernvale beds of the Brisbane metamorphics

Phillips

Low-intermediate pressure metamorphism at Broken Hill

Purvis

Metamorphism in two areas in the Yilgarn Block, Western Australia

Rogerson

Progress in mapping zonal low-pressure regional metamorphic mineral assemblages in the Wagga-Omeo metamorphic belt

i T O O T H I S N (CONTINUED) R.E.

Smith

The Hammers ley Basin Regional Hydrothermal Plumbing system

MINERALOGY W.

Mineralogy of the Cosgrove Leucitite

R.S. Bottrill J.B. Jones

Crystal chemistry of the AdamiteOlivenite series

A.K. Ferguson

The mineral chemistry of clinopyroxenes from alkaline rocks

A.K. Ferguson

Mineralogical aspects of the Camel's Hump and related trachytes in Victoria

G.S. Gibbons

Introduction to the Polarizing Microscope : Simple laboratory demonstrations

I.E. Grey B.M. Gatehouse I. Campbell P. Kelly

Structural studies on Davidite and related minerals

J.B. Jones E.R. Segnit

Chemical composition of opaline silicas

R.W. Le Maitre

The propagation of errors in mineral recalculations

E.R. Segnit J. Watts

Secondary phosphates from Moculta, South Australia

EXPERIMB1TAL AND THEORETICAL GEOCHEMISTRY A.H.

Ewald

Variability

of solubility products

T.H.

Green

Garnet-silicic liquid relations : a potential geothermometer-geobarometer

E XPERIFENTAL AND THEORETICAL GEOCHEMISTRY

(CONTINUED)

P.L. Hellman

The rare earth elements as geochemical indicators in altered basaltic rocks

B.J. Hensen

Stability relations of Osumilite in granulite facies metapelites

R.W. Le Maitre

On the partitioning of iron in igneous rocks

D.J. Patterson

The hydrothermal transport and deposition of Tin

F.L. Sutherland D. Stubbs D.C. Green

K-Ar dating of tertiary basalts, Northern Bowen Basin region, Queensland implications for petrologic models

The CSIRO-NPL system for the storeage and use of thermodynamic and physical property data for chemical process design

Turnbull

V.J. Wall

Non sulphide zinc bearing phases and the behaviour of zinc during metamorphism

PHYSICAL AND ( M I C A L PROCESSES IN DEFORMATION T.H. Bell

Progressive deformation and reorientation of fold axes in a ductile mylonite zone: The Woodroffe Thrust

I.A.Ben

Growth defects in metamorphic biotite

R.F. Berry A.E. Grady

Deformation styles and metamorphic conditions of the Aileu formation, North Coast, East Timor

J.N. Boland

The development of microstructures in experimentally deformed Carrara Marble

R.E. Chapman

Mechanics of Submarine sliding

Cohen

Deformed lineations in the Barron River Metamorphics

Corbett

Patterns of inhomogenous shear deformation in medium grade Willyama rocks, Broken Hill

C.J.L.Wilson

PHYSICAL AND CHEMICAL PROCESSES IN DEFORMATION (CONTINUED) D.W. Durney R.H. Vernon

Mineral concentrations around porphyroblasts

J.D. Fitzgerald T.H. Bell M.J. Rubenach

Deformation and metamo^phism in the Robertson River metamorphics, Georgetown Province, North Queensland

D.R. Gray

Some parameters which affect the morphology of crenulation cleavages

The mathematical description of inhomogeneous deformation

Hirsinger

R.J. Hoi combe E.H. Lowe

Structure and tectonic history of the Brisbane metamorphics in the Brisbane area

R.E. Hoi combe K.L. Williams

Deformation and recovery features in a naturally folded ilmenite crystal

R.R. Keays M.J. Glasson

Mobilization of Gold, Sulphur and Si 1icia during cleavage development in sediments

K.R. Kekulawala

Experimental studies on the hydrolytic weakening of quartz crystals

Analysis of pressure-solution deformation in oolitic limestones

Khaiami

D.H. Mainprice E.H. Rutter B.K. Atkinson B.

Marshall

The application of stress relaxation testing to the study of deformation in geological materials Concerning Kink Bands

B.W. Nisbet

Significance of transposition in the Chester Dome area, East Central Vermont

C.McA.Powell R.H. Vernon

Growth and deformational history of garnet porphyroblasts with inclusion spirals in a Karakoram schist

G.P. Price

The analysis of mineral fabrics by the photometric method

M.J. Rubenach T.B. Bell J. Fitzgerald

The significance of textures from the Robertson River metamorphics

D.B. Seymour

Sedimentary fabrics and strain analysis methods

PHYSICAL AND CHEMICAL PROCESSES IN DEFORMATION (CONTINUED) J.

Shore

The experimental extrusion of Yule Marble

J.E. Tibballs A.M. McLaren

Structures and textures in Microcline

I Van der Molen

Deformation of a partially molten rock

R.H. Vernon B.E. Hobfcs

Natural recovery and recrystalli;:ation of calcite in some deformed marbles

J.C. Wilkie

Deformation mechanisms in a suite of quartzites from Central Australia

R.W.T. Wilkins J. Barkas

Fluid inclusions, deformation and recrystallization in quartz-bearing tectonites

C.J.L.Wilson

Microstructure, composition and diffusive processes during deformation of Mica

BJVIRONEffTAL GEOLOGY AND HYDROLOGY C.D. Branch

State Subcommittee Reports; Federal Committee Reports

W.M.B.Carr

Land systems and extractive industries in Victoria

D.T.

Currey

Barmah-Millewa forest and the River Murray land forms and the environment

M. J.

DaLitz Peterson

Yarraville Sinking Village

D.C.

Green

Stable Isotopes (D/H and 0 1 8 / 0 1 6 in Hydrology

E.B.Joyce

G e o l o g i c a l conservation in A u s t r a l i a

E.B. Joyce

Victoria - State subcommittee report

E.M. McBriar

South Australia-State subcommittee report

McDonald

Sulphide swamplands and the implications of imposed drainage

P.G. Macumber

Hydro!ogical equilibria and the environment in the southern Murray Basin of South East Australia

N.C. Stevens

Queensland Statesubcommittee report

EDUCATION IN GEOLOGY D.

Branagan

The tertiary situation in Australia

Fardon

Tertiary education for mineral exploration

Learmonth

Secondary Earth Science - The Situation To-day

Marshall

Social Science in Geoscience Training

B. C.

Marshall Ward

Industry-based courses in Geology

Nicholson

Bridging the Gap

N.P. Schleiger D.

A Numerical coding method

Spencer-Jones Is geology meeting the challenge

ENGINEERING GEOLOGY

L.G. Alexander D. Denham G. Worotnicki

The near surface stress field near the site of the 1968 Meckering Earthquake

C.M. Barton

An engineering interpetation of Geological Data from the C.S.A. Mine, Cobar, New South Wales

C.M. Barton

Application of an image analysis computer in the determination of Block sorting and fabric

W . F . Cole

Clay mineralogy of some bore cores for the Melbourne undergournd rail loop

A.I. Cooney

Engineering Geology - Berwick Corridor

Geologic and man-induced factors influencing the rock slope stability of the Illawarra Escarpment, New South Wales

Evans

ENGINEERING GEOLOGY G. Harris A.D. Bell B. Marshall J. Page

Engineering geological investigations pertaining to the raising of Glen Innes water supply dam.

A.H. Spry

The compressive strength and texture of some Australian quartzites

P.M. Warburton

Finite-element analyses in the engineering and geological studies at the C.S.A. Mine, Cobar, New South Wales

COAL SYMPOSIA J.W. Beeston A.G. Galligan N.J. Zillman

The Relationship between Subsidence, Depth of Burial and Coal Quality in the German Creek Formation, Central Queensland

R.A. Britten

An Economic Classification of Coal Measure Sedimentation and Environmental Facies within the Singleton Super Group of N.S.W.

B.C. Gloe A.M. George

The Occurrence and Petrology of Latrobe Valley Brown Coals

Hamilton

Economic Aspects of Intrusions in Coal

Johnson

Could Geological Research Benefit the Underground Coal Mining Industry?

McDonald

A Tidal-Deltaic Environmental Interpretation of Jurassic Coal and Associated Sediments in the Surat Basin

Milligan

The Geology of some Australian Permian Coal Basins

Shepherd

Fault Swarms and Roof Failure in a N.S.W. Colliery

M. M.

Shibaoka Smyth

Petrographic Composition of Australian Coal Seams in relation to Geological and Botanical Factors.

V.M. Threader

Triassic Coal in Tasmania

C.R. Ward

Diagenesis in a Coal Swamp - Mineral matter Distribution in the Coals of the Illinois Basin, U.S.A.

SESSION 1A - SEDIMENTOLOGY GENERAL CONVENOR WEDNESDAY LECTURE

D r . G . R . ORME 2nd

FEBRUARY

THEATRE

R 7

9A V,

A. BELFERIC Geology Department, James Cock University, Townsvilie. SEDIMENT TRANSPORT PROCESSES ON THE INNER SHELF TOWNSVILLE, N. QUEENSLAND. The Burdekin River supplies a large suspended load of silt and clay to the continental shelf south of Townsville. The distribution of this recent sediment on the shelf is controlled by the frequency of occurrence of various sediment moving processes. These processes acting are:(1)

Littoral and sub-littoral drift.

(2)

Tidal scour and transport.

(3)

Advective transport by wind and wave generated currents.

(4)

Diffusive transport onto the middle shelf.

The character of the sediment supplied results in nett sediment movement being entirely in suspension with bottom sediment movement being of only localized significance. Mass sediment movement in suspension under various meteorological conditions has been measured and an empirical relationship forsuspended sediment movement based on wind speed end water depth is established. The dominance of processes (2) and (3) results in rapid lateral accretion onto the coast of the order of 1 km. per 1000 years compared with vertical accumulation rates of about 10 cm. per 1000 years and necligible movement ontc the middle shelf A.M. DEFERS Department of Geology, University of Wollongong, Wollongong, N.S.W. DIAGENESIS AND TRACE METAL ASSOCIATIONS IN LAKE ILLAWARRA, N.S.W. Lake Illawarra is a coastal estuarine lake located about 75 km south of Sydney. The lake is surrounded by a narrow coastal plain, which reaches a maximum width of about 10 km on the southern side of the lake. In the lake Fe, Mn, Cd, Co, Cr, Cu, Ni, Pb and Zn concentrations are seen to be directly related to the sediment distribution patterns and sediment constituents. There are distinct correlations between trace metals and: (a)

the percentage of silt and clay

(b)

the percentage

(c)

the percentage cf organic carbon

(d)

the percentage of carbonate

(e)

Fe and Mn

of sulphur

Iron and Mn hydroxides seem to be the chief scavengers for trace metals in the sediments.

I.R. DUDDY University of Melbourne

DIAGENESIS OF THE LOWER CRETACEOUS OTWAY GROUP

The fl uviatile Otway Group consists of at least 3 km of lenticular channel sandstones, often with basal mudstone conglomerates, interbedded with a spectrum of finer grained flood plain sediments. Locally the latter include lacustrine sediments, minor coal seams, carbonaceous shales and soil horizons. The sandstones are characterised by a high proportion of labile constituents of both terrigenous and volcanogenic origin. Terrigenous components include quartz, a variety of feldspars, micas and garnets while additional to grains of volcanic rocks the volcanogenic components include quartz, K feldspar, calcic plagioclase, biotite, amphiboles, pyroxene and altered glass now 'allophane'. The prevalence of rounded grains of altered glass points to synchronous vulcanicity rather than derivation by erosion of pre-existing volcanic rocks. Carbonate cemented 'cannonball'concretions developed before compaction was complete and provide the best indication of the original sandstone mineralogy. Pyrite concretions in sandstones and mudstones and siderite as concretions and bands associated with organic rich layers and in some soils, are also early diagenetic. Later diagenetic alteration in the sandstones has involved partial solution of grains leading to superpacking, and the development of interstitial chlorite. The zeolites heulandite and laumontite have also been recorded locally. Subaerial diagenesis has produced soils with distinctive textural chemical features, including podsols, gleys and immature alluvial soils. Intraformational weathering under conditions of water saturation has led to either complete kaolinisation in an open system or conversion to bentonite in a partially closed system.

BRIAN G. JONES Department cf Geology, University of Wollongong, Wollongong, N.S.W. DIAGENESIS OF SOME UPPER DEVONIAN TERRESTRIAL SEDIMENTS IN THE AMADEUS AND BONAPARTE GULF BASINS The Unandita Member of the Brewer Conglomerate, />madeus Basin, and the Ragged Range Conglomerate Member of the Cockatoo Formation, Bonaparte Gulf Basin, were both laid down as syntectonic terrestrial deposits in tri< Upper Devonian. For both units partial weathering and oxidation in the ^ source areas prior to short and rapid transportation arid burial providec fresh and weathered detrital grains. The ciagenetic sequences recorded in these two units are extremely similar and consist of: (a) syndepositional hematite grain coatings; (b) patchy development of carbonate cement, in the form cf lustre-mottling and calcrete; (c) compaction; (d) pressure solution and development of overgrowths of quartz (and feldspar in the Bonaparte Gulf Basin); (e) conditions in permeable zones in the rock become reducing with the consequent deposition of pyrite and chloritic clays; and (f) deposition of further carbonate and minor hematite cement. Effects of the present weathering cycle are superimposed on surface exposures of the unri'ts. These sequences of diagenetic effects can be accounted for by slight changes during lithification in the chemistry 6f the interstitial waters.

DR. G.S. GIBBCNS 8 Marsh Place, Lane Cove, N.S.W.

HYDRAULIC EQUIVALENCE AND PLACEP DEPOSITS. Natural processes involved in placer formation include avalanching, jigging, elutriation, and cyclic settling/erosion. Placers rarely if ever form by simple grain-settling or by simple winnowing; further the grainsize distribution of heavy minerals at their source is quite independent of the size distribution of accompanying lighter minerals. It is therefore net possible to make valid interpretations using simple hydraulic equivalence ratios based on Stokesian settling. Grain-size studies can be usee to identify the different types of deposit, but hydraulic ratios are different in different depositional situations

K.R. MARTIN , .. Department of Applied Geology, Queensland Institute of Technology, Box 246, North Quay. DIAGENETIC PROCESSES IN THE PRECIPICE SANDSTONE SURAT BASIN, QUEENSLAND The Precipice Sandstone is an extensive, fluviatile quartz a r e m t e of early Jurassic age which is an important aquifer in the Surat Basin. The formation shows little compositional variation along its 350km of outcrop at the northern eace of the basin and over most of its subsurface extent. The only exception'ir, this consistency occurs in the subsurface on the western side of the basin in the vicinity of the Rcira Ridge. Here the Precipice Sandstone is thinner and more varied in its grain size, composition and permeability than elsewhere. The main diagenetic processes which have affected the sandstone include silica solution and precipitation, carbonate cementation and the formation of diagenetic kaclinite. The sandstones tend to exhibit either silica precipitation features (mostly syntaxial quartz overgrowths) or silica solution features (e.g. microst.ylolites) but rarely both. A close association exists between the development of silica solution features and the content of biotite ir; the rock, and evidence suggests that the cecompcsition of biotite promotes silica solution. Two separate trends of diagenetic evolution have been recognised in the Precipice Sandstone depenaent mainly on whether the sandstone was initially biotite rich or biotite poor. The end result of the diagenetic processes is essentially the same ir each case, i.e. a minerelogically mature sandstone consisting almost entirely of cuartz and kaolinite.

SESSION IB - SEDireiTOLOGY DIAGENESIS CONVENOR WEDNESDAY LECTURE

Dr. G.R. 2nd

ORME

FEBRUARY

THEATRE

R 7

2 P M

R.G. BROWN Department of Geology, The University of Western Australia. STRATIGRAPHIC DISTRIBUTION OF DIAGENETIC FEATURES IN MANGROVE TIDAL FLATS OF EXMOUTH GULF, W.A. Diagenesis reflects tidal-flat zcnaticn in Exmcuth Gulf. A mangrove association imparts post-depositional fabrics and structures to siliciclastic and skeletal sediments, and generates lithe facies that become pyritic and carbonaceous in the subsurface- Upslcpe, gypsum and less stable sulphates develop as desiccation and oxidation influence subsurface sediments. Sediments units, which show prcgradational relationships, are influenced by sequential effects reflecting seaward migration of diagenetic processes. Initially imprints of bioturbation, crystallization, dissolution and other processes accentuates., ther. progressively overprint and ultimately destroy earlier-formed lithclogic features. At the landward margin, interaction of terrigenous and tidalflat influence generates gypsiferous and dolomitic sequences with red-bed attributes. P.G. FLOOD . _ n J Department of Geology and Mineralogy, University of Queensland, Brisbane, Queensland

OBSERVATIONS RELEVANT TO THE FORMATION OF BLACKENED GRAINS IN MODERN CARBONATE SEDIMENTS FROM THE GREAT BARRIER REEF Researchers (Sugden. 1966: Geol. Mag. 103, 250-256; Maiklem, 1967: J. Sedim. Petrol 37 (4), 1023-1030, Maxwell, 1968: Atlas of the Great Barrier Reef, 183; Palmieri , 1976: Qld. Govt. Min. u. 77 (899), 406-436) have reported the occurrence of blackened carbonate grains in some continental shelf sediments collected within the region of the Great Barrier Reef. Such grains generally occur on the Inner Shelf in the region of intermixing of the mainland terrigenous muds and the reef derived carbonate sediments. A variety of skeletal types: the large foraminifera Marginopora and Alveolinella, the green calcareous algae Halimeda, echinoderm spines, the calcareous skeletons cf several species of corals exhibit blackenirg. The author has observed similar blackened skeletal carbonate grains on the intertidal flats of a variety of platform reef types, notably the "low wooded island" (Steers, 1929, Geogr. J . 124, 232-257, 341-367), in the northern region of the Great Barrier Reef. The grains are predominant only on those reefs which are situated on the Inner Shelf and within the zone of influence of waters carrying terrigenous mud. Comparison of trace element ceochemical analyses of blackened and unstained carbonate particles from the continental shelf and the intertidal reef flat indicate significant enrichment of Fe, M n , Cu and Zn in the blackered particles. It is inferred that the blackened shelf sediments and the blackered intertidal sediments are produced in the same manner. Blackening is dependent, upon the availability of terrigenous m u d , source cf the iron. This is preferentially localised under reducing conditions which exist during burial on and withir the more porous skeletal particles. Mo time connotation should be placed upon the occurrence of such blackened carbonate particles.

8 G.R. ORME Department of Geology arid Mineralogy, University of Queensland

and

B.G. THOM Department of Geography, University of Sydney

DIAGENESIS IN A SEQUENCE CF HOLOCENE-PLEISTOCENE CARBONATE DEPOSITS OF THE NCRTHERNREGION OF THE GREAT BARRIER REEF A sequence of carbonate deposits drilled to a depth of 28 m at Bewick Island (Howick Group), during the Royal Society (London) and Universities of Queensland Expedition (1973) revealed a succession of reefal and lagoonal deposits consisting of biolithite, biosparite, unconsolidated biogenic sands and gravels, biomicrites, fossi1iferous micrite, breccias and conglomerates. There are considerable down the profile variations in chemistry, mineralogy and diagenetic fabrics, the most marked change occurring at -7m (below L.W.S. datum), which is considered to mark the base of the Holocene deposits. Above this level aragonite is a very important constituent, whereas below it low magnesium calcite is the dominant mineral. Variations in strontium relate to the aragonite content. Above -7m the sparites are cemented by acicular aragonite, but below this level calcite cements occur, the aragonite of molluscs and corals has inverted to calcite, and diagenetic fabrics resulting from aggrading neomorphism are common. Impurities become conspicuous below -12.2 m. Iron shows much variation, some layers being relatively enriched. At lower levels in the core patchy iron distribution gives rise to pseudobreccia. Quartz, which may be in part authigenic, is also a conspicuous constituent below -12.2 m. Although the contrast between the Holocene arid Pleistocene deposits in terms of mineralogy and Giagenetic fabrics is the most marked, other chanaes in composition and diagenetic fabrics may coincide with probable Pleistocene disconform!ties.

5. A. REECKMAN University of Melbourne DIAGENESIS OF SOME VICTORIAN TERTIARY CARBONATE SEDIMENTS Mid-Tertiary bioclastic calcarenites consisted originally of low and high Mg calcite and infrequent aragonite idens. Molluscari aragonite is now represented by moulds and there has been pronounced etching cf detrital quartz grains. Pressure solution has changed point contacts into face contacts with rare microstylolite junctions. Original high Mg calcite skeletal fragments have been converted into low Mg calcite without structural change. Internal sediment, has been trapped above larger skeletal fragments, Cement consists of fine grained mosaics of low Mg calcite and syntaxial overgrowths on echinoid fragments. The degrees of cementation varies greatly, in part related to microlithological variation but in large measure to the present day water regime be it vadose groundwater or in coastal sites, the sea. Contemporaneous "hard ground" is characterised by a cryptocrysta11ine calcite cement. Cryptocrystalline calcite also develops in proximity to weathered intercalated basalts and progressively replaces original carbonate ideas. In the transition from limestone to marl the additional components of terrigenous detritus, glauconite, pyrite etc. strongly affect carbonate diagenesis imparting greater variability to the products. Aragonite is unalterec in impervious beds but dissolved or replaced in coarser grained pervious layers. In addition to replacement of high by low Mg calcite ferrous iron is frequently introduced selective 1 v into skeletal fragments Cements are still fine grained mosaics but of varied carbonate species low Mg calcite, ferroan calcite and dolomite or ferroan dolomite - either singly or in sequential association. Dolomite and probably ferroan dolomite are seemingly random in distribution in both marls and limestone

D. SCHWEBEL School of Earth Sciences, The Flinders University of South Australia CEMENTATION OF THE BRIDGEWATER FORMATION : TEMPERATE LATITUDE CARBONATE DIAGENESIS The Pleistocene Bridgewater Formation was deposited under both marine and subaerial conditions. No cementation occurred while these skeletal grainstones were in the marine environment, but subsequent retreat of the sea and uplift have placed them under the influence of percolating groundwater where both vadose and phreatic zone cementation occurs. The styles of cementation vary between the vadose and phreatic zones. While the mineralogy of the cement is low Mg-calcite, its crystal habit varies considerably. In the vadose zone, pores are lined with sparry calcite cement, exhibiting meniscus characteristics. In the phreatic zone the pores are generally filied with sparry calcite and there is no evidence of precipitation from two pore fluid phases. The most striking textures occur in the near surface part of the vadose zone where the sediments have come under the influence of soil forming processes. CalCrete, which veneers all of the sediments, causes total breakdown of the primary textures of both the rock and the skeletal grains. Whisker cement is common in this zone. f S ^ n 0 ^ ! ! 1 ? 1 ' - 6 ° C C L T t h r o u 9*°ut the sediments and appear to have termed in situ during early stages of diagenesis.

O.P. SINGLETON University of Melbourne

IDS AND ODDS OR THE DIAGENESIS OF CARBONATE ROCKS

Of all common constituents in sedimentary rocks carbonate minerals are by far the most sensitive to changes in the physical and chemical environments. Logan and Semeniuk's iden concept facilitates the elucidation of the effects of such changes in terms of the mutual relationships between entities in space and time, that is of the sequential relationships of fabric and composition. In any dynamic situation individual idens may remain unchanged or be diminished, enlarged, replaced or substituted for. The effect of any one change is easy to decipher. Compounding or alternation of several such changes can be best unravelled on a synoptic basis using the iden concept. Such changes during diagenesis will be discussed, illustrated by examples from Victorian carbonate rocks.

SESSION 2A - PALAEONTOLOGY THE EVOLUTION OF THE AUSTRALIAN FLORA CRETACEOUS TO RECENT ( with emphasis on the ANGIOSPERM record) CONVENOR WEDNESDAY LECTURE

Dr. R. GOULD 2nd

FEBRUARY

THEATRE

9 A M, 2 P M

R 5

D.C. CHRISTOPHEL and D.T. BLACKBURN Department of Botany s University cf Adelaide

AN EOCENE FLORA FROM MASLIN BEACH, SOUTH AUSTRALIA A lens of Middle Eocene carbonaceous clay in the Willunga Basin at Maslir. Beach, South Australia has; been known since 1966 to contain a rich and diverse angiosperm flora. Since that date, various studies of the locality have been carried out on the remains of acarine mites, fungal spores and hyphae, dispersed cuticle and arigiosperm leaves. Following those preliminary studies, further collections have revealed approximately 200 distinct angiosperm leaf forms and also numerous flowers, fruits, and gymnosperm and vascular cryptogam remains. The fossils are preserved as finely detailed compressions in the clay, and the majority possess recoverable cuticle. Analysis of leaf size and margin type, as well as sedimentation, species diversity, and fungal remains suggests a sub-tropical deposition environment. Lack of detailed information on extant tropical leaf morphology has hindered the drawing of taxonomic conclusions., but the presence of the families Araliaceae, Podocarpaceae, Proteaceae, Apocynaceae, Lauraceae and Malvaceae is strongly suggested from the work to date. The long range aim of the project is to compare this flora with the extant sub-tropicaT Australasian flora as wel^ as with knov/n, but presently inadequately described, Tertiary floras from eastern Australia and Antarctica.

MARY E. DETTMANN Department of Geology & Mineralogy, University of Queensland

AUSTRALIAN CRETACEOUS PHYTOGEOGRAPHY: A PALYNOLOGICAL PERSPECTIVE

The wide dissemination and abundance of spores and pollen grains in sequences spanning the Cretaceous System in Australia offer considerable scope for the elucidation of Australian Late Mesozoic floral history. Dispersal routes* and relationships of the flora with contemporaneous floras of the partially fragmented Gondwanaland region, can be deduced from the palynological record and from postulated continental assemblies. Australian Early Cretaceous palynofloras are characterised by an abundance of gytr.nospermous derivatives, particularly of podocarpacean trisaccate grains. Angiosperms were introduced into the region during the middle Albian, later than in western Gondwanaland, During the Cenomanian and Turonian, angiosperms diversified concurrently with initial regional differentiation of the flora. Northerly palynofloras are distinguished by dominant Classopollis and inaperturate gymnospermous Gerivatives, together with diverse schizeaeceous and gleicheriiaceous forms. In southerly regions, bisaccate grains allied to Dacrvdium become established. Near the close of the Cretaceous (when floral interchange between New Zealand, Southtoierica,Antarctica, and Australia i L f ° 2 S l d e r e d t o . h a v e ,been feasible) possible protealean elements and Nothofagu? were introduced into southern Australian floras

J,6, DOUGLAS Department of Mines, Victoria

ANGIOSPERMS - AN ASSESSMENT OF THE AUSTRALIAN PRE-TERTIARY RECORD

Critical examination of plant fossil identifications strongly indicates that the oldest angiosperms known from Australia are of Early Cretaceous age. They are present in the Styx River Coal Measures, Queensland, and the Otway Group, Victoria. The Styx River assemblage, found in bore core is part of the PhvfLopteroides flora of Gould (1576) and contains dictotyledonous leaves regarded by Hill, et al. (1968), as early-middle Albian. The Victorian fossils, impressions and compressions, occur both ir outcrop samples and bore core from the Moonlight Head Eeds regarded by Dettmarm (1969) as early Albian. The Styx River assemblage contains typical mid-mesozoic plants, but the Otway Group fossils are in the youngest of a succession of assemblages and lack several groups characteristic of the earlier assemblages. A tentative allocation to the angiosperms of even older (Aptian) plant fossils (Douglas 1969) from the koonwarra Fish Beds, in the Gippsland Basin, Victoria, is more cifficult to substantiate. Earlier Australian Mesozcic floras are examined for any sugoestion of angiosperm progenitors, and the initiations of radiation discussed ine Late Cretaceous Winton, Waarre and Paaratte Floras, all with considerablP angiosperm content, are compared with succeeding Tertiary floras.

M.J. GARRATT Department of Mines, Victoria

NEW EVIDENCE FOR A SILURIAN (LUDLOVIAN) AGE OF THE EARLIEST BARAGWANATHIA FLORA

Recent stratigraphic mapping of the Siluro-Devonian marine clastic strata in the Yea--F1owerdale district of central Victoria has confirmed that there are two distinct plant graptolite assemblages containing elements of the Baraawanathia flora. Each horizon is located beneath 70 m of lithic, quartz, mica sandstones and congloirerates. They are separated by 1700 m of apparently unfossiliferous dark grey green siltstones. The upper horizon contains Nonoqraptus thomasi Jaeger, indicating a Siegenian age. The lower assemblage contains a varied flora, and graptclites collected by Schleiger and identified by Richards (U.K.) (pers. comm.) as Saetograptus sp., a genus which is restricted to the Lower Ludlovian. The associated sandstones and conglomerates of the Lov/er Plant Graptolite Horizon are separated by folding and faulting to Strath Creek, where they are overlain by thiri blue siltstones containing another Ludlovian assemblage of Bohemoqraptus bohemicus (Barrande). Pristiograptus dubius (Suess.) and Liriograptus sp. The different plant forms will be briefly commented upon.

D.P.C. HOS Department of Mines, South Australia EARLY TERTIARY PALM POLLEN IN AUSTRALIA Fossil pollen form genera attributable to palms are common in Paleoger.e sediments and show a wider distribution than at present, consistent with known higher temperatures during that period. Arecipites and Spinizonocolpites are generally rare in the Pal eocene and Eocene of Australia but abundant in some facies. They are not recorded in sediments younger than Eocene in southern Australia but continue to Early Miocene in Queensland where living palms produce the same pollen types. Palm pollen is generally unique but the same evolutionary trends are present as seen in many other families. From basic finely sculptured tectate monosulcate grains there developed many sculptural and apertural variations and few form species are confidently assigned to living genera. Most living palms are limited by water requirements and temperature to the tropics, but many live in the subtropics and the extreme range is to 4000 m i n altitude and 44° north and south latitudes, it is concluded that an assemblage of fossil palm pollen is indicative ot a tropical to subtropical palaeoclimate. A.P. KERSHAW Department of Geography, Monash University CHANGES IN THE FLORA AND VEGETATION OF NORTH-EASTERN AUSTRALIA DURING THE QUATERNARY PERIOD

Evidence for changes in the flora and vegetation is derived from pollen analysis of organic sediments on the Atherton Tableland. Several samples analysed from a thin coal seam, preserved beneath the Atherton basalt, provide some indication of early Quaternary vegetation while cores taker from crater lake sediments provide a continuous record of changes through the last 100 000 years or so. Most pollen types recorded from the older samples can be re ated to pollen of extant rain forest taxa within ?he region but several types notably Ncthofagus (brassii type), P a c r o c a r L and Dacrydium, are now not present on the Ai^traH ^ m a i n l a n d . There have been dramatic changes in the extent and rnirnncii-i™ „ . forests in North Queensland during the Ust 1 0 0 0 0 0 e ^rrL ™ m Phylloc'ladus and possibly Nothofaqus have L c o m e e x t i net "Call itris have been g r e a t l T ^ f d 1 n imporuTce w e Euc yp^s'ha^ increased in abundance. It is proposed that v e w rnnJHV • the end of the last -glacial' pen'od, comb? ed w U h a n ^ c ? e l s e ?n f E T ® e frequency associated with the activities of A b n H n i ^ i t . great changes in the vegetation cover of this are 9 " J g e ^ ^ h e T h * been a recent increase in sclerophyll vegetation at t I Z ^ l of Srier rain forest types and a possibly evolutionary replacement within rair forest of ancient taxa by those of more recent or gir

HELENE A. MARTIN School of Botany., University of New South Wales

THE TERTIARY PALYNOLOGICAL RECORD AMD EVOLUTION OF THE AUSTRALIAN FLORA

The first appearance of a number of modern taxa can be traced from the Late Cretaceous through the Tertiary, and there are some remarkable changes in abundance of some of the taxa. A reconstruction of the vegetation allows interpretation of the probable climate. About the mid Eocene» there was a great increase in the abundance of Nothofagus« A number of taxa, especially the proteaceous types become extinct from the mid-late Eocene. NGthofagus and many other associated taxa disappear about the mid-late Miocene after which the assemblages are dominated by Myrtaceae. There is a brief return of a restricted number of the old Nothofagus flora in the late Pliocene. The vegetation was rainforest throughout this time and grasslands did not develop until the Pleistocene. The dramatic floristic change in the mid-late Miocene indicates a decrease in humidity. A well-marked dry season did not develop until the Pleistocene. The above outline applies to south eastern Australia where the palynological record is the best. Evidence from Central Australia and Queensland indicate geographic variation. The fossil record contradicts several old theories about the evolution of the Australian flora and vegetation. J.F. RIGBY Geological Survey of Queensland

REVIEW OF PRE-CHEMICAL EVIDENCE OF ANGIOSPERM PROGENITORS - GLOSSOPTERIS AND OTHERS

Fossil plant organs similar to or sometimes identical with identifiable fossil angiosperm orcians occur in rocks in Late Palaeophytic and Mesophytic time. Leaves, fructifications and v/ood from the Permian Glossopteris flora show a degree of parallelism with corresponding organs of some modern angiosperms, but they also show a degree of parallelism with organs of other tracheophyte groups. It is concluded that Glossopteris is most probably allied with r.ori-coniferous gymnosperms. Any origin or source for angiosperms that depends on plant growth over long periods of time where they are incapable of fossilization is suspect. We need to know what a primitive angiosperm was like before we can say which isolated organs are angiosperms. In all probability the various characteristics considered to be typically angiospermous in modern plants first appeared randomly in one place, then another, over a very long period of time in angiosperm progenitors, and also by homop^asy in non-progenitor plants.

SESSION 2B - PALAEONTOLOGY AUSTRALIAN MARSUPIAL EVOLUTION CONVENOR

A. BARTHOLOMAI

THURSDAY

3rd

FEBRUARY

LECTURE

THEATRE

2PM

R 5

MICHAEL ARCHER Queensland Museum THE ORIGINS OF KANGAROOS On the basis of the meagre fossil record, kangaroos appear to have leaped into existence sometime prior to the middle Miocene. None of the fossil forms indicate which phalangeroid group was ancestral to the kangaroos, or even which of the three known kangaroo subfamilies is structurally the most primitive. Evidence is presented here, based on structure of unworn molar crowns, that the kangaroo molar exhibits an only slightly modified form of the selenodont molar, such as occurs in some phascolarctids, petaurids and phalangerids, and on this evidence, potoroines are structurally the most primitive subfamily. The great majority of characters of all the kangaroo subfamilies corroborate the evidence of the teeth and indicate that macropodines could not have been ancestral to potoroines. Consideration is also given to overall affinity within kangaroo subfamilies. A cladogram is constructed to summarize the data presented.

C.W. MALLETT Department of Geology, University of Melbourne THE AGES OF VICTORIAN VERTEBRATE FOSSIL LOCALITIES IN LATE NEOGENE MARINE STRATA Planktomc foraminiferal faunas indicate that Miocene marine in the Otway Basin and the Port Philip sedimentation Embayment continues at least into the N.17 zone of Blow. The youngest Miocene assemblages is identified by the presence of Globorotalia conomiozea Kennett jointed rarely in the latter part of its range by Globorotalia pleisotumida Blow & Banner. This assemblage is characteristic of the, Bairnsdalian Stage (type section not of Carter) and the Mitchellian Stage in Victoria and is correlated with the Kapitean Stage in New Zealand and most of the Messinian Staqe (of d Onofrio et al.) in Sicily. Globorotalia punctuculata (Deshayes) appears at the base of the Kalimnan Stage in Gippsland. This species is used to identify the base of the Pliocene in New Zealand, and appears slightly below or at the Miocene/ Pliocene boundary stratotype at Cape Rossello, Sicily. It has not been found in the Brighton Group (type Cheltenhamian in part) in the Port Philip Embayment, and the beds are considered to predate its appearance, and thus lie within the uppermost Miocene. A gradual withdrawal of the sea in Southern Australia in the late Miocene culminated in condensed sequences, low sediment accumulation rates mixed assemblages of well preserved and worn ferruginised fossils, including marine and terrestrial vertebrate remains. In the Port Philip Embayment the period of remani^ vertebrate accumulation occurred after the first appearance of Globorotalia conomiozea, and prior to the appearance of Globorotalia puncticulataand thus spans the interval approximately 5-7 million B.P. In Western Victoria at Hamilton and Minemite, the concentration of vertebrate remains may have been slightly earlier than in the Port Philip Embayment.

M.PLANE AUSTRALIAN TERTIARY MAMMALS Currently much manpower and time is being put into the search for fossil marsupials. A look at the record for the past twenty-five years shows us that proqress has been steady but sure. Some years ago we might have been tempted to believe that the middle to late Tertiary story was reasonably complete However, recent new finds urge us to show constraint. The early record tantalizes us but to date we have no pre-Miocene fauna. Speculation on the origins and early diversification of marsupials on this continent remain tentative but the number and dedication of the workers gives hope that in the next quarter-century some of the answers will be forthcoming.

T.H.V RICH National Museum of Victoria, Melbourne

THE PROBLEM OF THE MORWELL KANGAROOS In may 1975, fossil remains of the kangaroos Macropus titan and Protemnodon anak were found at the State Electricity Commission opencut mine at Morwell, Victoria. The specimens occurred in sediments deposited in a depression formed by combustion of the coal at the top of the Morwell Seam 1A. Above these kangaroo-bearing sediments is the PIio-Pleistocene Haunted Hill gravels. A preliminary palynological analysis of the sediments surrounding the fossils by Mr. Alan Partridge indicates a late Miocene age for the site. However, M. titan has never been recorded from sediments older than late Pliocene and P.anak, never older than Pleistocene. A possible explanation for thisunexpected range extension is the paucity of late Miocene and Pliocene sites in southern Australia.

G.D. SANSON Zoology Department, Monash University THE EVOLUTION OF THE GRAZING MACROPODS AND THE RELEVANCE OF THE MORWELL KANGAROOS Within the macropodines two adaptive grades of organization can be recognized, a browsing (Type-B) and a grazing (Type-G) grade. It is considered that Type-G forms evolved in response to the appearance of a more abrasive diet which probably mainly consists of grasses. No Type-G forms are known from sediments older than late Pliocene while the limited floristic record indicates the rise of grasses in late Mioceneearly Pliocene times. A lag between the appearance of grasses and grazing adaptations in the associated fauna is apparent in North America and such a lag may have occurred in Australia. Serological and karotypic evidence indicates that Macropus species represent a recent and explosive radiation. Within this context referral of Macropus titan from Morwell to the late Miocene represents a very significant range extension.

R. WELLS. K. MORIATY Flinders University

THE LATE PLEISTOCENE FAUNA OF VICTORIA CAVE, NARACOORTE, SOUTH AUSTRALIA

Major cave development in the Naracoorte area predates the last marine transgression in the late Pliocene. Following retreat of the sea around 700,000 yrs B.P. erosion of the overlying sediments exposed entrances to the caves allowing accumulation of fossils. A diverse fauna includes frogs, reptiles, birds and mammals. Stratigraphic analyses suggest 2 and possibly 1Lf 3 periods of accumulation of fossils. C and racemisation dating indicates an age in excess of 40,000 yrs B.P. The assemblage includes the extinct marsupial genera Thylacoleo, Palorchestes, Zygomaturus, Sthenurus, Procoptodon, Progemnodon, as well as the monotreme Zaglossus, the boid Wonambi naracoortensis and the megapode Progura naracoortensis. A multiple source hypothesis is advanced for the accumulation of the fossils.

D.WILLIAMS, R. Wells Flinders University

A LATE PLEIST0NCENE MARSUPIAL FAUNA AT DEMPSEY'S LAKE, PORT AUGUSTA SOUTH AUSTRALIA Erosion of sand dunes near Dempsey's Lake has exposed fossil marsupial remains. The assemblage includes Diprotodcn, Phascolonus, Protemnodon, Sarcophilus» and other genera no longer living in the region. The palaeoenvironment inferred from the sedimentary sequence of lunettes and desert dunes is one of increasing aridity until about 16,000 B.P., which agrees with the palaeo-climatic sequence of G.E. Williams (1973) for the area immediately to the north. Abundant evidence of human occupation is found as a superficial deposit, and suggests that Man arrived in the area sometime between 12,000 and 5,000 B.P. Cooper's (1959) suggestion that Man and the extinct marsupials coexisted at Dempsey's Lake is not borne cut because of their clear stratigraphic separation.

SESSION 2C - PALAEONTOLOGY FOSSIL

MAN

AUSTRALIA

CONVENOR

FRIDAY

4th

Dr. K. S . W . CAMPBELL

LECTURE

THEATRE

A . G0EDE . Department of Geography, University of Tasmania

and

FEBRUARY

9AM

R 5

R. HARMAN Department of Geology, Michigan State University

PLEISTOCENE MAN AND ME6AFAUNA IN TASMANIA: DATED EVIDENCE FROM TWO LATE PLEISTOCENE CAVE BONE BRECCIA SITES Cave deposits near Montagu in NW Tasmania have yeilded dated evidence of late survival of elements of the Pleistocene megafauna. Three stratigraphic units can be distinguished. The youngest (Bed 3) contains a fauna including the extinct species Macropus titan3 Protemnodon anak3 Sthenurus occidentalism Zaglossus sp. 9Thylacole'o oamifex and an unidentified diprotodontid. It originated as a solifluction deposit. C14 bone collagen dates indicate a minimum age of 10,000 years B.P. for the deposit while U/Th dating of a detrital stalactite in Bed 2 suggests that deposition of Bed 3 is unlikely to predate 20,000 years B.P. Contemporaneity of megafauna elements with aboriginal occupation in Tasmania appears likely as Bowdler has recently shown that such occupation dates back to at least 22,600 years B.P. Beginners Luck Cave in the Florentine Valley (South Central Tasmania) has yielded four stone implements and a probable bone implement from a bone breccia deposit containing some charred bone. Associated charcoal has been C14 dated at 12,600 ± 200 years B.P. The sediment is a solifluction deposit which entered a cave through a former entrance. It contains numerous angular limestone fragments indicative of frost weathering. Limited excavation has yielded bones representing eight species of mammals and two species of birds none of which are ext'inct. A U/Th date obtained from the base of a stalagmite formed on top of the breccia is in accord with the C14 date. Another site in the same cave has yielded remains of Sthenurus ocddentalis from which a C14 collagen date of approximately 14,500 years B.P. was obtained. The Florentine Valley cave site demonstrates at least sporadic aboriginal occupation of a truly inland site during the late Pleistocene.

J. HOPE AUSTRALIAN NATIONAL UNIVERSITY PLEISTOCENE

EXTINCTIONS AND MAN IN AUSTRALIA

Many species and genera of large marsupials" became extinct in Australia and New Guinea in the late Quaternary. As elsewhere in the world, these extinctions have been attributed both to climatic change and to the activities of man. The latter hypothesis has gained ground over the last few years with the accumulation of evidence indicating that man has lived in Australia for more than 30,000 years. The actual chronology of the extinctions and the related distributional changes in modern species is still poorly understood, mainly because of problems associated with dating material whose age is close to the limit of radiocarbon, and particularly with dating bone. A review of all dated fauna! sites in Australia and New Guinea suggests that the crucial date for the disappearance of extinct genera may be about 15,000 BP, although only smaller forms * and/or those occurring in coastal regions may have survived to that time. This date falls within the period of extreme aridity postulated for 17-13,000 BP, in southeastern Australia, but aridity per se cannot be invoked as a cause of the extinctions generally, and especially not in New Guinea. The date also implies that at least some of the extinct marsupials coexisted with man for a considerable time. There are, however, very few instances of unequivocal association of man and the extinct species, and it can be argued that they were not important in the economy of the early Aborigines. A. TH0RNE Australian National University

THE FIRST AUSTRALIANS - IMPLICATIONS FOR THE DEVELOPMENT OF MODERN MAN Until recently, human palaeontology in Australia was based on a handful of isolated and widely scattered skeletal remains. Their morphological variation has been provocative but inadequate for any detailed assessment of the long-term physical history of the first continental migrants or their antecedents. The last decade has seen a rapid expansion of skeletal data, from welldated sites in a relatively small area in the southeast of the continent. The new material confirms that the morphology indicated by some of the earlier fossils was wide spread and that a number of cranial forms were present that are not represented in contemporary populations. Taken overall the prehistoric remains demonstrate that significant and rapid morphological changes occurred in at least some parts of Australia during late Pleistocene and early Holocene times. These changes took at least two forms. continued....

22 A.Thorne, continued.

Development of the skeletal morphology that was observed ethnographically* from the range indicated by Pleistocene data, indicates the general nature of those non-Australian populations from which aboriginal Australians were derived. Together with new fossil material from Indonesia and other areas of south and southeast Asia, the hominid remains from Australia indicate the lone term patterns of physical characteristics in Asia and other parts of the Old World.

A.H. VOISEY Macquarie University THE TECTONO - SEDIMENTARY FRAMEWORK OF ORGANIC EVOLUTION Changes in the environment brought about by tectonic movements and volcanic activity ahve influenced the distribution, migration and even the existence of plants and animals- Of more fundamental importance is the fact that they have brought gases liquids and rock materials to the earth's surface. These have been distributed according to their chemical behavior in the waters and sediments lying on the crust. Minerals unstable under the new conditions break down to form new compunds which arc. There is abundant literature on research which has demonstrated the dependence of plants and animals on minor qualities of the trace elements. Each organism has its own particular requirements. Shortages of the essential element or elements seriously affects the well being of the organism depending upon it and this leads to its failure to compete and ultimate extinction. Because of the long intervals of time between major orogenies and progress towards the formation of stable end-products the available supply of elements must progressively decrease. Organisms will then suffer or prosper according to the satisfaction of their needs. Ore lineage which loses its trace element supply will deteriorate while another with a different requirement will not be affected. The cessation of tectonism will herald the end of all living things on earth. This state of stability to which the surface constantly aspires is interrupted by successive movements which renew the supplies and start another incomplete cycle. Mass extinctions may be related as much to shortages of trace elements as of nutrients and not necessarily as much due directly to tectonism as has generally been believed. Even in our times it has been observed that more plants and animals die during droughts than in floods which follow - but the remains of both groups may later be found in alluvial deposits.

SESSION 3

- WEATHERING AND EXPLORATION GEOCHEMISTRY

CONVENOR

Dr R.E. SMITH

THURSDAY

3rd

FEBRUARY

LECTURE

THEATRE

9AM 6

M. HILL Geological Survey of Victoria ANTIMONY

COSTERFIELD - A GEOCHEMICAL PICTURE

Stibnite occurrences in Victoria are epigenetic and of hydrothermal origin. The deposits at Costerfield, mined from 1860 to 1883 and from 1903 to 1925 represents the largest of these, as well as the largest Australian production to date. This area is the site of an ongoing large scale geochemical and drilling investigation for new reserves. Conventional geological investigations are hampered by poor outcrop, and a lack of knowledge of mineral distribution over this major anticline. Applied geochemistry has yielded a broad picture of hydrothermal antimony distribution which is believed to represent, in its simplest form, an accurate portrayal of structures that form the host domain for hydrothermal events. A tentative interpretation is offered of the present appreciation.

REID R. KEAYS Department of Geology, University of Melbourne

and

G.A. TRAVIS Western Mining Corporation

PALLADIUM AND IRIDIUM IN THE EVALUATION OF NICKEL GOSSANS IN WESTERN AUSTRALIA

Palladium and iridium show a strong positive correlation with Nickel in Western Australian nickel sulfide deposits, and their inertness during weathering, combined with depletion of the more mobile components, usually results in retention or enhancement of the primary values in gossans and other oxidised derivatives. Precious metal enrichment from background levels occurs in some lateritised barren ultramafic rocks, but the low values in most lateritic products and gossans derived from non-nickeliferous sulfide assemblages permit distinction from true nickel gossans. Material with 15-30 ppb Pd and 5-10 ppb Ir indicates a possible minor original nickel sulfide component (approx. < 0.6% Ni), and at higher levels the former presence and approximate grade of nickel sulfides can be confidently predicted from the precious metal values. Pd-Ir analysis has particular application to the recognition of a nickel sulfide component in highly leached gossans with low Ni-Cu values, to the evaluation of ferruginous, siliceous and clay-rich lateritised ultramafic products enriched in Ni and Cu, and to estimation of the nickel content in the parent sulfide assemblage.

25 G. KELLY and R.G. TAYLOR Geology Department, James Cook University of North Queensland, Townsville THE DEVELOPMENT OF SUPERGENE SULPHIDES, OXIDE ZONES AND LEACHED OUTCROPS FROM A COMPLEX SULPHIDE ORE AT THE SIBERIA Sn-Cu MINE EMUFORD HERBERTON The development of the profile is described with special reference to the interpretation of leached outcrops and gossans. Correct interpretation of the leached outcrop structure is necessary to fully interpret geochemical data. The diagrams below represent a summary picture. PRIMARY SULPHIDES RSENOPYRITE

SUPERGENE SULPHIDE ALTERATION J EARLY STAGE

ranulat or f r a g m e n t H - ^ - ; d cataclasis tex- j ure -

LEACHED OUTCROP DEVELOPMENT

| MIDDLE STAGE I LATE STAGE

Partial fract^ ! DIGENITE ure replaceCOVELLITE ment by | DELAFOSSITE Lacy, scorodite cell

Scoroditei ribbed cellular! boxvork Limonit e replacement 4>f scorodite ribs Scorodite eel lular

sponge | • w g ^ r r r z r ' — — t Linjionite replacement of sponge eached sponge

HALCOPYRITE

^ZZH

ranular matrix texture

DIGENITE

leavage and fracture

-j COVELLITE

©placement by

DELAFOSSITE j Limonitic bctxwork texture

PHALERITE Granular matrix texture lleavage and fracture re•lacement by

DIGENITE COVELLITE DELAFOSSITE

ITANNITE Iranular matrix texture

GALENA Massive granular texture

^ — Cleavage and grain boundary replacement by

DIGENITE COVELLITE Limonitic b^xwork texture DIGENITE COVELLITE Coarse grained hnglesite cells 7ine grained ccjlloform angleiiite Mai sicot litharge alteration Limonitic alteration 3oxwork anglesi te cells Massicot-litharge alteration Limonitic alteration

PYRRHOTITE Replacement) £ ssive texture by pyrite j rdseye texture plus cwork cellular text. marcasite d )d texture Cleavage and fractu replacement of marcasite-pyrite by

CHALCOCITE DIGENITE COVELLITE DELAFOSSITE Limonitic ce^ lular boxwork r Earth| spongy cells

PYRITE 'Iassive granular texture

j Grain bound- j DIGENITE : |ary replace- j - COVELLITE j ment by I Celjlular limonitic el|Lu:

replacement L

26 RAYMOND E. SMITH CSIRO, Division of Mineralogy, Wembley, W.A.

and

G . WILLETT Department of Geology, University of Sydney, N.S.W.

MULTIPLE-ELEMENT INVESTIGATIONS IN EXPLORATION GEOCHEMISTRY IN THE PROTEROZOIC BANGEMALL GROUP OF WESTERN AUSTRALIA Multi-element geochemical investigations have been directed at various types of surface sample materials to test the use of pathfinder element geochemistry in this type of weathering environment - (the depth of weathering can exceed 100 metres). Multi-element profiles have been obtained over Cu/Zn anomalies in parts of the Prospect shale, a unit known to carry anomalous Cu values throughout much of the region. Thin limonitic bands are common in several shale units and it is proposed that certain of these are weathered sulphide bands of "microgossans". An attempt is made to distinguish pyritic microgossans from microgossans derived from base metal sulphides.

SESSION 4 - GEOLOGY AND MINERALIZATION OF ISLAND ARCS Convenor: Dr I.A.Nicholls THURSDAY

3rd February

FRIDAY

4th

9 am

February 9 am

LECTURE THEATRE R7 ANTHONY J . CRAWFORD AND REID R. KEAYS Department of Geology, University of Melbourne THE CAMBRIAN GREENSTONE BELTS OF VICTORIA The results of detailed studies of the Heathcote Greenstone Belt and Mt. Wellington Greenstone belt are described, together with some observations by the authors on the Stavely Greenstone Belt. The Mt. Wellington Greenstone Belt is undoubtedly a dismembered ophiolite. Alpine-type or ophiolitic peridotites have been recorded at Howqua and Dolodrook, meta-gabbros at Cape Liptrap and metabasalts and metadolerites at Dookie, Tatong, Howqua, Jamieson and Liptrap. The metabasalts at Tatong, Howqua and Liptrap are characterized by the absence of olivine and the existence of clinopyroxene as the main phenocryst phase, occasionally accompanied by plagioclase, together rarely constituting more than 10% of these basalts. Metamorphic grade ranges from lower greenschist facies to prehnite-pumpellyite facies. Microprobe studies of Dookie, Tatong and Howqua clinopyroxenes indicate a pronounced Fe-enrichment trend characteristic of tholeiitic rock suites. This compliments the major and trace element chemistry study of these metabasalts and metadolerites, which indicates that they are an evolved low-K tholeiitic suite, having generally higher FeO* and Fe0*/Mg0 Ti, Sr, Y and P contents and lower Ni, Cr and MgO than typical MORB, as is predicted by the mineralogy. The northern and southern ends of the Heathcote Greenstone Belt are also composed predominantly of metadolerites beneath clinopyroxene-phyric metabasalts. However, the central section of the Heathcote Belt, around Lady's Pass, consists of basaltic andesites and andesites. The Stavely Belt is poorly exposed, but seems to be composed mainly of basaltic andesites, andesites and dacites. Serpentinites are also represented in this area.

PAUL R. DEN6ELING N.S.W. Geological Survey

and

LEONIE E. POGSON N.S.W. Institute of Technology

THE HALLS PEAK Pb-Zn-Cu DEPOSITS, ARMIDALE, N.S.W. Small, stratiform Pb-Zn-Cu sulphide deposits occur in tuffaceous, carbonaceaous shale horizons over a restricted stratigraphic interval within the Permian Halls Peak volcanic complex. These volcanics are situated near the western edge of the Nambucca Block in the southern part of the New England Fold Belt, some 50 km southeast of Armidale, New South Wales. They crop out over an area of about 150 sq km and overlie a thick proximal turbidite sequence. The strata consist of submarine tuff, flow and breccia units of andesitic, rhyodacitic and rhyolitic composition, interbedded with tuffaceous marine sediments such as pyritic carbonaceous mudstone, pebbly mudstone and pebbly arenite, together with completely unsorted and disorganized paraconglomerate. Flows form only a minor part of the volcanic sequence, and occur as lenticular bodies of restricted lateral extent. The sulphide deposits are thought to have formed on the flanks of a volcanic centre. Variations in metal ratios between the different deposits may reflect their place of formation relative to this eruptive centre. At Gibson's Open Cut Mine, intricate folding of the sulphide lenses and their intimate association with coarse clastic sediments (fluxoturbidites) indicate that the sulphides and their host rocks have slumped into their present position. The authors conclude that the Halls Peak volcanics were probably derived from either a single eruptive centre or an areally restricted group of small centres, and that the rocks presently exposed represent flank, rather than cone facies of the volcanic complex.

J.A.S. DOW Kennecott Explorations (Australia) Ltd., Sydney, N.S.W. 2001

THE DISCOVERY AND PRELIMINARY EVALUATION OF PORPHYRY COPPER DEPOSITS IN NORTHERN SULAWESI, INDONESIA

Two new porphyry copper districts have been recognised as a result of a recent exploration in northern Sulawesi, Indonesia. Within these districts porphyry copper mineralisation forms two essentially different, but related types of deposit, each with characteristic surface expression. Host rocks for copper mineralisation are quartz diorite porphyry phases of the Bone Diorite (middle to upper Miocene) which intrude the calcalkaline Bilungala Volcanics (Miocene). The geological setting is similar to many other island-arc porphyry copper deposits in the south west Pacific.

continued.

29 J • A. S. Dow

continued

The Sulawesi porphyry copper deposits were discovered by conventional reconnaissance stream silt geochemistry. Subsequent exploration involved detailed rock geochemical sampling and geologic mapping in conjunction with extensive pitting and trenching. More than twenty prospects were identified and six have been tested by diamond core drilling. The better copper mineralisation is largely confined to a specific intrusive phase. In addition, surface gold geochemistry, quartz vein abundance and alteration mapping have proved most useful in defining porphyry copper targets, particularly where these are covered by strongly leached cappings. Ore grade hypogene copper mineralisation is associated with at least four alteration mineral assemblages and supergene enrichment has been a significant process.

JOHN FODEN Department of Geology, University of Tasmania

THE PETROLOGY OF SOME YOUNG VOLCANIC ROCKS FROM G.RINDJANI, SUNDA ARC

G. Rindjani is an active compound strato-volcano on Lombok, in the Lesser Sunda Islands. Andesites probably form the bulk of the volcano, but the lavas range widely in composition, and include slightly nenormative olivine basalts, high-alumina basalts, dacites and rhyolites. Basalts and andasites are more porphyritic and less glassy than dacites and rhyolites. Plagioclase is present as phenocrysts in all rocks and is particularly abundant in the high alumina basalts and andesites. Ferromagnesious mineral assemblages vary from olivine with minor, sometimes markedly alluminous, clinopyroxene, in the olivine basalts, to augite and minor olivine in the high alumina basalts, augite and hypersthene with relicts of reacted olivine in the andesites, and amphibole and more biotite in the dacites and rhyolite. Ma/ y/ M g + Fe declines sharply from olivine to high alumina basalts, and this, together with rapid depletion of nickel and chromium abundances, is explicably by olivine and clinopyroxene fractionation. Chromium and particularly nickel are present in very low concentrations in the andesites and dacites. Alumina and strontium abundances are high in the high alumina basalts and andesites but are low in the dacites, which are also much richer in rubidium, variations consistent with substantial plagioclase dominated crystal fractionation. However, potassium-rubidium ratios are high (500-600) in the basalts and much lower in the andesites (350) and dacites (320), inconsistent with derivation of the andesites from the basalts by crystal fractionation of the observed phenocryst assemblages. Fractionation of hypothetical amphibole might have yielded andesites from high-alumina basalt magma, but derivation of andesites from olivine basalts appears impossible.

RUSSELL FOUNTAIN

A COMPARISON OF HYDROTHERMAL ALTERATION EFFECTS IN THE PANGUNA AND WAISOI COPPER DEPOSITS

The Panguna (Bougainville Is.) and Waisoi (Fiji) porphyry copper deposits are of similar age, and both are associated with multiple intrusions into host rocks of andesitic composition. They are both composite deposits with significant mineralization occurring in both intrusive and wall rock phases. The two deposits show very similar patterns of sulphide mineral zoning, quartz veinlet development and pyritic and propylitic halos. The effects of supergene alteration are relatively minor in each case. Hydrothermal alteration patterns in the two deposits differ significantly. At Panguna, a poorly mineralized core of sericite-clay alteration is surrounded by a well developed zone of biotite-K-feldspar alteration, which passes outwards into propylitic alteration. At Waisoi, a low grade core of sericite-clay alteration also exists, but only minor biotite alteration, and virtually no secondary K-feldspar occurs. The bulk of the rock in the Waisoi mineralized area have a uniform assemblage of chlorite, part albitized plagioclase with minor clay and calcite. This assemblage persists essentially regardless of copper grade and rock type. The degree of alteration of the intrusive rocks at Waisoi is greater than that of comparable rocks at Panguna. It is concluded that the extent and nature of hydrothermal effects at Waisoi and Panguna were essentially similar at the time of formation of the deposits, with the probably exception of lack of alteration K-feldspar at Waisoi. The atypical chloritic alteration assemblage now observed at Waisoi is though to be due to a post-mineralization hydrothermal event.

31 EDMUND D. GILL CSIRO Division of Applied Geomechanics, Mt. Waverley,Victoria 3149 THE PLATE TECTONIC THEORY IN RELATION TO THE AUSTRALIAN COAST AND CONTINENTAL SHELF 1.

The Gravity Map of Australia shows that the shelf is not simply an erosion bevel on the continental margin with local sinking to provide sedimentary basins, but is a fundamental crustal structure characterized by zones of +20 - 60 milligals. Where the shelf is narrow, as in S.E. Australia, these zones follow the shelf precisely.

These zones of denser crust occur in the Gulf of Carpentaria and in Torres Strait, but not in Bass Strait. This raises the question as to whether the Tasmanian area should be classified as a subplate.

The coast/shelf has changed status with time. At the time of rifting there was no shelf, and the coast was a plate edge. Since then Australia has pushed away from the mid-ocean ridge so that this coast which was a plate edge is now a trailing edge.

On Plate Tectonic Theory, coasts are ephemeral (especially in the Quaternary with its rapid glacio-eustatic shifts of sea level) and the shelves young - a view contrasting with that of the earlier Theory of the Permanence of Ocean Basins. However, there are lag effects from the old idea.

Isostasy, once a rather marginal concept in tectonics, is now a dominant one, because of seafloor spreading and drift (sometimes over an irregular geoid), and the general mobility of the crust envisaged in the Plate Tectonic Theory. During the Quaternary there were added ice-isostasy and water-isostasy effects. 10% of the present land surface was covered with ice, but 30% was covered in the glacial periods. There were massive shifts of weight from place to place with consequent isostatic effects, some of which only have as yet been worked out.

32 M.P. GORTON

GEOCHEMISTRY AND ORIGIN OF QUATERNARY VOLCANISM IN THE NEW HEBRIDES ISLAND ARC

Analyses of young volcanic rocks from the New Hebrides reveal the existence of two geochemical groups which may be identified on the basis of their contents of K2O and related trace elements. Low K2O rocks are believed to be comparable with conventional island arc volcanism, whereas the high K2O rocks are believed to be related to volcanism associated with tensional rifting. By comparison with high pressure experimental data it is concluded that these rocks can be derived by partial melting of hydrous mantle above the Benioff zone. However this mantle must have different concentrations of incompatible elements from that which is the source for ocean ridge tholeiites, and residual minerals must have rare earth element partition coefficients which differ from those of phenocrysts in volcanic rocks.

WARREN HAMILTON U.S. Geological Survey Denver, Colorado, 80225, U.S.A.

COLLISION OF THE BANDA ARC WITH AUSTRALIA Integration of marine geophysics (particularly seismic-reflection profiling, including deep-penetration multichannel records) with island geology defines tectonic processes now underway. The Banda Arc is ramping onto the Australia-New Guinea continent, pushing ahead a thin arcuate wedge of imbricated continental-shelf strata and melange. The non-volcanic, outer-arc Timor-Seram ridge is the top of the wedge, which lies t e c h n i cally above continental crust; oceanic and continental crystalline plates are in contact beneath the wedge at the inner side of the ridge. The tectonized wedge thins to a toe along the shallow trench (Timor-Seram Trough). The continental plate is bowed down by the advancing wedge and slides beneath it with gentle dip; shelf strata, and locally basement, are imbricated disharmonically upward into the moving wedge. Vogelkop is rotating away from the advancing arc. The inner volcanic arc stands about 125 km above subducted oceanic lithosphere. The deep basin between volcanic and outer ridges is downflexed behind the raised front of the onramping plate. New southward-subducting trenches are forming along the north base of the volcanic ridge in the Flores and Alor sectors: convergence of the major plates is continuing, but with reversing polarity.

33 G.6. LOWDER Kennecott Explorations (Australia) Ltd.,

Sydney N.S.W. 2001

NATURE AND RELATIONSHIPS OF MINERALISATION AND ALTERATION IN SULAWESI PORPHYRY COPPER DEPOSITS, INDONESIA

Sulawesi porphyry copper deposits differ from others in the south west Pacific in a number of important aspects. Among these (although not all shown by every deposit) are relatively high primary grades, supergene enrichment, restriction of ore to porphyry and immediate wall rock contact, widespread development of strong advanced argil lie alteration and presence of albite or montmorillonite (rather than potash feldspar) in the ore zone. Distinctive secondary mineral assemblages accompany the one supergene and three primary sulphide assemblages in the ore. Advanced argil lie alteration shows some similarity with solfataric alteration, but can be distinguished by higher-temperature mineral assemblages characterised by pyrophyllite, diaspore, andalusite, alunite, corundum, specularite, pyrite, bornite and chalcopyrite. The presence of secondary albite or montmorillonite instead of potash feldspar and the strong development of advanced argil lie alteration are thought to be related features. Reference to the alkali-alumina-silicawater systems shows that advanced argil!ic-minerals are stable over much wider pH/T ranges in the sodic or calcic cases compared with the potassic system. Possible equilibrium temperatures for various assemblages are also indicated. This information helps construct an ore deposit model which relates hydrothermal activity, mineralisation, alteration and lithology. MR. M.J. PRIMROSE Department of Geology & Geophysics, University of Sydney, Sydney.

THE GEOLOGY OF THE PUKEKAIKIORE AND TAMA LAKES REGION OF THE T0NGARIR0 VOLCANIC MASSIF, NORTH ISLAND,NEW ZEALAND

The Tama Lakes and Pukekaikiore are the oldest sections of Tongariro and lie on the saddle between it and Ruapehu. They are pre-last glaciation (16,000 yrs. b.p.). Pukekaikiore is the glaciated and faulted remnant of a vent, and has been affected by post-glacial volcanism of a more basic character. The Tama Lakes are 5 post-glacial explosion craters. They occur on the crest of the Tongariro-Ruapehu saddle and cut through continuous lava sheets. Their unusual topographic position was the result of a lake on the western side of the watershed, caused by damming, attributed to a Ruapehuan lava flow.

A . PURVIS Dept. of Geology and Mineralogy, University of Adelaide MINERALOGY AND GEOCHEMISTRY OF A FELSIC UNDERSATURATED SHOSHONITIC INTRUSION FROM THE MOUNT DROMEDARY COMPLEX, N.S.W. Dykes of garnet-bearing analcime phono!ite of shoshonitic affinities occur in the Tilba Tilba lake-Poole's Point area near Mount Dromedary, New South Wales. They have phenocrysts of zoned plagioclase, rimmed by alkali feldspar, melanite-andradite garnet and Ca-rich clinopyroxene in a groundmass of andradite, alkali feldspar, analcime, sodalite and cancrinite pseudomorphs after haiiyne or nosean. The crystallisation sequence appears to be as follows:plagioclase clinopyroxene garnet

13 -a o

alkali feldspar ii hauyne/nosean analcime sodalite cancrinite The analcime is close in composition to Na^A^Si^O^g. 3 H 2 0 , i.e. is approximately the composition of analcime which has been produced in the system NaAlSi 3 0 8 - NaAlSi0 4 - H 2 0 , coexisting with the low temperature melt. This suggests that the presence of high contents of H ^ Cl, C 0 2 and S 0 3 in the magma has lowered the minimum melting point in the system Na 2 0-K 2 0-Ca0Al 2 0 3 -Si0 2 -H 2 0-Cl-C0 2 -S0 3 fluid to produce a minimum melting assemblage composed of andradite, alkali feldspar, analcime, sodalite and hauyne or nosean. In addition to a high volatile content, the magma appears to have crystallised under high f0 2 conditions, as indicated by the presence of magnesian clinopyroxene ana andradite-rich garnet. The geochemistry shows high Na, K, Rb, Sr and Ba contents, but low contents of Ti, P, Zr, Nb, Sc and Y. This suggests a partial fractional crystallisation melting' model involving garnet, clinopyroxene and a phase or phases retaining Ti, Zr and Nb, but not involving the precipitation of plagioclase or of alkali feldspar. A major problem is seen in producing understurated, wollastonite normative liquids, which are minor but widespread components of shoshonitic intrusive complexes throughout the world, and are in places of more major importance (Assynt; Alaska).

35 W.D. ROOTS School of Earth Sciences, Macquarie University, North Ryde 2113 POST CRETACEOUS SUBDUCTION BENEATH THE S.E. AUSTRALIAN MARGIN? SUPPORT FROM VOLCANIC AGE TRENDS AND NEW MARINE MAGNETIC PROFILES

Subduction of the Tasman Sea floor beneath the S.E. Australian Margin is suggested as a possible cause of an observed E.W. age trend in the ages of Cainozoic basaltic volcanic rocks along this margin. In addition, truncation of Tasman Sea magnetic anomalies, absence of a magnetic smooth zone and marginal morphology all lend support to the proposal of subduction. New marine magnetic profiles run in the S.W. Tasman Sea suggest the need to reconsider the age of Tasman Sea opening, and thus total spreading history. A preliminary pre-Tasman Sea reconstruction is presented based upon the recognition and the changed time constraints proposed.

SESSION• 5 CONVENOR

- ACID MAGMATISM AND ASSOCIATED ORE DEPOSITS -

I.A.

NICHOLLS

WEDNESDAY

2nd

FEBRUARY

THURSDAY

3rd

FEBRUARY

LECTURE

THEATRE

2PM 2PM 2

C.D. BRANCH Department of Mines, Adelaide, South Australia EVOLUTION OF THE MIDDLE PROTEROZOIC CHANDABOOKA CALDERA AND THE ASSOCIATED CHITANILGA VOLCANIC COMPLEX,NORTHWESTERN GAWLER RANGE ACID VOLCANO-PLUTONIC PROVINCE,SOUTH AUSTRALIA The Carpentarian Gawler Range acid volcano-plutonic province extends over at least 85 OOO km 2 of the Archaean Gawler craton. In the Kokatha area during the first phase of volcanism 1558 ± 15 m.y. ago, alkali basalt, basaltic andesite, and dacite to rhyolite flows and thin ignimbrites with a preserved thickness of about 600 m were erupted from a stratovolcano centred outside the area. Next, in the premonitory caldera phase, a pile of acid domes and flows were constructed during effusive and explosive volcanic activity along the future caldera-margin fault zone. The Chandabooka caldera formed 1544 ± 36 m.y. ago during the eruption of the Chandabooka Dacite ignimbrite. The caldera facies of the ignimbrite form a compound cooling unit with a present thickness of 500 m around an offcentred resurgent dome. The outflow facies of the ignimbrite comprise two compound cooling units, separated by a thin airfall tuff which may indicate the time caldera subsidence began. In the post-caldera phase, rhyolite domes were erupted in the caldera moat around the northern margin of the resurgent dome. Outside the caldera a sequence 100 m thick of thin rhyolite ignimbrites in simple cooling units overlies the outflow facies of the Chandabooka Dacite with slight angular unconformity. Breccia pipes and thin acid dykes intrude the volcanics. All the volcanics below and above the Chandabooka Dacite are grouped in the Chitanilga Volcanic Complex: the total volcanic pile is about 1 km thick. Flat-topped stocks of the comagmatic leucocratic Hiltaba Granite and associated greisen dykes intruded the volcanics outside the caldera 1510 ± 38 m.y. ago. A swarm of large rhyodacite dykes dated at 1483 ± 41 m.y. intrudes the caldera facies of the Chandabooka Dacite. No economic mineral deposits have yet been found in the area, but the granite and greisens are enriched in U , Pb, Zn and the caldera-margin fault zone has a potential for mineralization similar to the San Juan Volcanic Field, U.S.A.

37 L. T . BRYNDZIA, T. A . P. KWAK Department of Geology, Latrobe University THE GEOLOGY AND GEOCHEMISTRY OF THE BULLA ADAMELLITE AND ITS INCLUSIONS A CASE FOR MARGINAL CONTAMINATION The Bulla adamellite complex consists of a central biotite zone, an intermediate cordierite-biotite zone and outer garnet-cordierite -biotite zone. Seven types of large inclusions (>2 cm min. diameter) are identified, namely types (i) amphibole-plagioclase (meta-basalt?) (ii) biotite-plagioclase-quartz with biotite clots (iii) biotite-plagioclasequartz without biotite clots (iv) cordierite-biotite (v) cordierite-garnet (vi) garnet and (vii) layered meta-sedimentary. The volume of these inclusions is near 3% throughout the complex. Types (ii) to (vi) above are derived from type (i) bydiffusional processes. The central zone of the complex contains only types (i) and (ii) while types (i) to (vii) occur in the other two zones with types (v) to (vii) being particularly common in the outer zone. All gradations of type (vii) inclusions occur ranging from hornfels to migmatites, the gradation depending on the residency time of the original hornfels in the adamellite magma and its subsequent partial melting. The volume of small inclusions (<2 cm max. diameter), which are biotite rich, increase dramatically from near zero to 6.2 volume percent at the margins. Extensive microprobe studies have indicated that almandine garnet, Fe-rich cordierite and biotite in the adamellite, inclusions, and contact rocks are very similar in composition. The garnet occurs both as large crystals with biotite rims and as small euhedral grains in plagioclase. Garnet did not crystallize in the magma but was formed by the fragmentation of type (vii) inclusions. Cordierite was formed similarly to garnet and also crystallized from the melt. Biotite in the adamellite shows a progressively increasing A l o c t a h e c * r d ' and Fe/Fe + Mg ratio towards the contact indicating the progressively changing conditions across the pluton. The complex is interpreted to have formed from an initial melt which was derived from the partial melting of igneous source material ("I-type"). On intrusion near or at the present site, approximately 16% hornfelsic material was added at the margins which yielded a largely mechanical mixture of small disrupted fragments, some new melt and the original adamellite magma. The zonation described is due to progessively increasing amounts of hornfelsic material introduced at the contact where the adamellite is indistinguishable from ones described as having been derived from a meta-sedimentary source ("S-type").

P.J. EADINGTON CSIRO Division of Mineralogy EVOLUTION OF HYDROTHERMAL BRINES ASSOCIATED WITH THE MOLE GRANITE, GLEN INNES, N.S.W. The Mole Granite is mineralized with magmatic-pegmatitic deposits of tungsten and bismuth and hydrothermal deposits of cassiterite and basemetal sulphides. The hydrothermal brines which effected mineralization evolved from a chloride type with a high salt content (50-60 wt %), through chloride brines with moderate salt content, to a carbonate type with low salt content (3 wt %). The high-salinity chloride brine is found in fluid inclusions in magmatic and pegmatitic minerals. It has a high density (1.1-1.2 g/cm^) and the observation that the salinity remained constant through a wide range of temperatures suggests that the brine remained separate from low-salinity groundwaters. The low-salinity brines are found in inclusions in hydrothermal deposits. These brines (density 0.7-0.8 g/cm^), not having the density contrast to resist mixing, could be expected to be entrained in a system of convecting groundwater. The carbonate brines are associated with the minerals quartz and adularia, and temperatures (250-300°C) are similar to those in modern geothermal systems such as Wairakei, N.Z. It is envisaged that such a geothermal system was the last stage of hydrothermal activity. B.L. GULS0N CSIRO Division of Mineralogy North Ryde, N.S.W. 2113

and

P. RANKIN DSIR Division of Soils, Wellington, New Zealand

COMPARISON OF MINERALIZED AND UNMINERALIZED ACID VOLCANICS The geochemistry of acid volcanics (dacites,rhyodacites) associated with mineralization around the Woodlawn Cu-Pb-Zn deposit is compared with that of similar unmineralized rocks from the Mt. Painter volcanics, A.C.T. The two suites of volcanics (allowing for perturbations due to mineralizing solutions in the Woodlawn rocks) have, in the main, similar major and trace element chemistries, initial Sr isotopic ratios of approximately 0.710 and rare earth element patterns. The zircons and their U-Pb arrays in the Woodlawn volcanics show varying effects of older zircons. Whole rock lead isotopic measurements cannot be used to distinguish the rock types. At this stage of the investigation the only significant difference between the volcanics lies in their cesium values. The Woodlawn volcanics have low Cs (<0.3 ppm) and Mt. Painter volcanics high Cs (> 5 ppm) values consistent with their derivation from pre-existing volcanic and sedimentary material, respectively.

39 M.P. HOCHSTEIN Geology Department, University of Auckland, New Zealand

MINERALIZATION OF GEOTHERMAL FLUIDS DISCHARGED BY THE SURETAMATI GEOTHERMAL SYSTEM (NEW HEBRIDES)

A study of hot springs and fumaroles on the island of Vanua Lava (New Hebrides) has shown that all the heat transferred to the surface (> 150 x 10 6 W) is derived from hot volcanic gases. The gases are condensed by meteoric surface waters; the condensates form a coherent rather acid ? (ph < 1.5) condensate layer which has an areal extent of more than 5 km . Volcanic rocks (basaltic andesites) within the condensate layer are continuously dissolved as indicated by plots of molar concentrations of major elements in surface rocks versus molar concentrations of the same elements in hot springs. The model explains the unusually high concentrations of Fe ( > 400 ppm) and AT( > 800 ppm) in the spring waters. Most of the mineralized spring waters are discharged by a hot river into Port Patterson Bay where most of the elements drop out of solution when mixed with seawater. The deposition rate in this bay is quite substantial and amounts per year to about 5 x 10 3 to of Fe, 12 x 10 3 to of A1 45 x 10 3 to of SO4 and 9 x 10 3 to of Si02. It is likely that a new ore deposit is being formed in this bay.

P.A. JAG0 AND Clifford McEleroy & Associates Pty. Limited

S.R. SANGAMESHWAR N.S.W. Institute of Technology

GEOCHEMISTRY OF SPHALERITES FROM THE MAY DAY PROSPECT, N.S.W. The May Day Prospect is located within the Silurian Mr. Hope Volcanics in western New South Wales. Lithological units occurring in the immediate vicinity include a sequence of sandstone, siltstone, carbonate rock, and acid tuffs and flows. The grade of metamorphism is lower greenschist facies. Lenticular bodies of Zn - Pb - Cu mineralization have been intersected along the contact between siltstones and the underlying massive pyroclastics. The mineralization is believed to be of the strataform volcanogenic type. The sulphide minerals present in order of abundance are: pyrite, sphalerite, galena, chalcopyrite, pyrrhotite and tetrahedrite, with nominal amounts of other minerals. CODtinued

P .A.Jago and S.R.Sangameshwar

continued.

Electron microprobe analysis of compositions of sphalerite (mol % FeS) were carried out and the results are discussed in the light of experimental studies of Scott and Barnes (1967,1971) and Scott (1973). The FeS content of sphalerite, coexisting with pyrite and/or pyrrhotite, ranges from 4.6 mol % FeS to 15.4 mol % FeS. The homogenous distribution of Fe in the sphalerite grains suggests that equilibrium has been attained between coexisting phases. Three levels of concentration of mol % FeS in the sphalerites are defined and these correlate with lithological variations. A distinct trend of increasing mol % FeS from the footwall to the hanging wall suggests a change in depositional environment. Assuming a temperature of 350°C for lower greenschist facies, pressures of 8.8 kb, 8.0 kb and 6.0 kb from the footwall to the hanging wall are indicated. Such a wide variation appears to be inconsistent with the relatively narrow zone of mineralization.

I.B. LAMBERT Baas Becking Lab., Canberra City, A.C.T. 2001 GEOCHEMICAL, MINERALOGICAL AND PETROGRAPHIC FEATURES OF ROCKS AROUND MASSIVE SULPHIDE DEPOSITS IN FELSIC VOLCANIC SEQUENCES, LACHLAN FOLD BELT

Drill core samples of rocks around known massive sulphide deposits are being assessed to establish geochemical, mineralogical and petrographic features which can be used in the search for other deposits of the same general type. The Woodlawn area has been studied in most detail and a more cursory investigation has been made of rocks adjacent to several small deposits in the Orange area. Samples and necessary background information were kindly supplied by Jododex and Aquitaine, respectively. The following features are common to both areas and should,therefore, constitute useful exploration guides: (i)

Country rocks are dacitic to rhyolitic tuff breccia, quartz prophyroid and shale

(ii) Distinct hydrothermal alteration aureoles occur around the massive sulphide lenses. Whilst they are most extensively developed in the foot wall, they can extend for more than a hundred metres into the hanging wall; along strike they can persist for at least several hundred metres. The altered rocks are variably chloritized, sericitized and silicified, and they contain scattered veinlets and dissemninations of sulphide mineralization. They have virtually no felspars or primary ferromagnesian minerals. (iii)The main chemical changes within the hydrothermally altered rocks are major enrichment of Fe, Mg, S and Si, more sporadic enrichment of A g , A1, Ba, Bi, Cd, Cu, K, M n , Pb and Zn, and major depletion of Ca and Na.

I.A. NICHOLLS and V.J. WALL Department of Earth Sciences, Monash University RECENT STUDIES IN THE SNOWY RIVER VOLCANICS, EASTERN VICTORIA Studies of the Lower Devonian Snowy River Volcanics by Monash University students have demonstrated the limited areal extent of many units, and underlined the problems of correlation between widely separated successions. Mapping of the Deddick Park area, at the north-eastern margin of the volcanic belt, has delineated up to 12 sub-units, mostly ignimbritic, within the Deddick Rhyodacite the lowermost regional unit of Ringwood (1955). Bulk rock compositions range from andesitic to rhyolitic, with a tendency to become more silicic upward in the sequence. The second regional unit, the Black Mountain Rhyodacite in this area is a uniform ignimbritic rhyodacite. Studies in the Gillingall and W-Tree areas north of Buchan have provided details on the contact between the volcanic successions and the overlying middleDevonian carbonate successions. In the Gillingall area, the contact between tuffs and tuffaceous sediments and basal dolomitic limestones is essentially conformable. At W-Tree, normal faults, with throws of up to 500 m separate the volcanic and carbonate sequences. The Mt. Elizabeth area, near Bruthen, includes an outlier of Snowy River Volcanics, consisting mainly of volcanic breccias, coarse agglomerates and major glassy ignimbritic units of rhyolitic composition. Beneath the volcanic succession is an east-west trendinq complex of rhyolitic and andesitic dykes,The volcanic succession is also intruded by hornblende diorite b o d i e s . It is believed that the M t . Elizabeth area represents an eruptive centre for the Snowy River Volcanics.

J.A. OLATUNJI, C. CUFF & R.G. TAYLOR, Geology Department, James Cook University of North Queensland, Townsville

ASPECTS OF GRANITOIDS FROM THE WEST HERBERTON REGION OF THE HERBERTON-MT.GARNET TINFIELD

The Mineralization of west Herberton is spatially related to the Elizabeth Creek Granite (ECG). Recent mapping has revealed two main phases: 1)

A pale grey-salmon pink coarse grained leniogranite (ECGI).

A grey, fine to medium grained biotite granite (ECGII).

The contact between the two phases is a narrow transition zone containing predominatly porphyritic microgranite and coarse grained granite porphyry. The former grades into ECGII and visa versa. continued.

J .A.Olatunji and. R.G.Taylor continued.

Field mapping and age dating establish a long period of intermittant and magmatism represented by six units; ECGI, (321 ± 11 m.y.), ECGII. (306 m.y.), Kalunga Granodjorite (305 m.y.), Watsonville Granite ( 295 ± 16 m.y.), Slaughter Yard Creek Volcanics ( 281 ± 3 m.y.). Whole Rock tin values are uniformly low , with ECGI averaging 1-3 ppm, and ECGII 2-3 ppm. Tin content in biotite in similarly low, i.e. Kalungu Granodiorite 20 ppm, Watsonville Granite, 10-30 ppm, ECGI 20-50 ppm,ECGII 30 ppm. Lithium contents are very low in the Elizabeth Creek granites, av. 20 ppm. However both ECGI and ECGII do show geochemical specialization in that they are enriched in Si02, K2O, Rb and F. In this sense they resemble many other granitoids associated with tin deposits.

R.C. PRICE

and

S.R. TAYLOR

RARE EARTH ELEMENT GEOCHEMISTRY OF GRANITOIDS FROM THE NORTH-EAST VICTORIAN METAM0RPHIC BELT AND PARTIAL MELTING Muscovite-biotite granitoids from the North-east Victorian Metamorphic Belt have rare earth element patterns characterized by (a) enrichment in the light rare earth elements (b) minor Eu depletion and (c) varying degrees of heavy rare earth element depletion. Three of the four muscovite biotite granites examined have rare earth element and major element chemistry consistent with a partial melting model involving an originally pelitic metamorphic parent. The compositions can be approximated very closely by a model involving 20% partial melting of an ultrametamorphosed pelitic sediment and contamination of this minimum melt, by the residue left after melting, in the ratio 60% melt: 40% residue. The fourth muscovite granite examined is different petrologically and geochemically from the other three, and although it would appear to derived by a similar mechanism its composition cannot be modelled using a pelitic source. A garnet-cordierite gneiss from the North-east Victorian Metamorphic Belt has a trace and major element composition which i;s also consistent with a partial melting model. A model involving 5% partial melting of a pelitic composition and contamination of the melt by the residue in the ratio 30% melt : 70% residue is consistent with the composition of the gneiss. Leucogranites which outcrop in the Upper Murray Valley east of the Metamorphic Belt are high level intrusions of highly fractionated granitic melt. They have Sr isotopic characteristics consistent with a source more primitive than that from which the muscovite-biotite granites derived and may be classified as 'I-types' rather than 'S-types', using the nomenclature of Chappell & White (1974).

S.R. SANGAMESHWAR

COMPOSITIONS OF SPHALERITE FROM THE FLIN FLON-SNOW LAKE MINERALIZED BELT OF CANADA

The massive sulphide deposits of the FT in Flon-Snow Lake mineralized belt occur in the Precambrian rocks belonging to the Churchill structural province. The ore deposits occur within the volcanic rocks and derived schists of the Amisk Group and the Kisseynew gneisses. Mineralogically these deposits are composed of varying amounts of pyrite, pyrrhotite, sphalerite and chalcopyrite with minor amounts of arsenopyrite, galena and sulphosalts. Regional metamorphism has affected the ore and the enclosing country rocks similarly. Mineralogical and structural evidence suggests that the ore deposits of the Snow Lake area have been affected by a higher grade of metamorphism than those in the Flin Flon area. Over 2,000 electron microprobe analyses of sphalerite compositions (mol % FeS) coexisting with pyrite, pyrrhotite and other phases, from about 240 samples representing the entire mineralized belt, were carried out to estimate the P-T conditions of metamorphism. Analyses of the results suggest that the coexisting phases, particularly pyrite, pyrrhotite or both, have apparently no influence on the iron contents of sphalerite, suggesting a lack of preservation of equilibrium compositions between coexisting phases. The coexistance of hexagonal Fei_ x S + monoclinic Fe^_ x S + pyrite, the trace element and sulphur isotopic compositions of pyrite pyrrhotite and sphalerite also lead to similar conclusions.

SESSION 6 - SHIELD GEOLOGY AND MINERALIZATION CONVENOR FRIDAY 4th FEBRUARY

2PM

LECTURE THEATRE R 7

REID R. KEAYS Department of Geology, University of Melbourne

PALLADIUM, IRIDIUM AND GOLD IN THE ORES AND HOST ROCKS OF WESTERN AUSTRALIA WITH PARTICULAR REFERENCE TO KAMBALDA Neutron activation analysis has been used to document the distribution of the precious metals Pd, Ir and Au in the ores and ultramafic host rocks of 14 nickel sulphide deposits in Western Australia. The strong correlation between these metals and the nickel sulphide contents of the rocks is interpreted in terms of a magmatic origin for the sulphides. The precious metals are ideal for studying the effects of subsequent modifications of the ores and host rocks. For example, (1) they have been used to show that talc-carbonate alteration of ultramafic rocks releases significant quantities of Au and S, but has a minimal effect on Ni; (2) they can be used to estimate the relative proportions of picritic melt to olivine cumulates in unmineralized meta-peridotites; and (3) their strong and systematic variation across ore zone? (for example, the Pd/Ir ratios of the matrix sulphides at Kambalda are a factor of ten greater than those of the massive sulphides)can be used to assess the effects of metamorphism on the nickel sulphide ores. A detailed documentation of the variation of the precious metals Cu, Ni and S in the thick basal ultramafic unit at Kambalda has permitted calculation of the partitioning coefficients of Pd (vL10) and Ir (^170) between the nickel sulphide and picritic silicate melts at the time of extrusion of the melts. It is suggested that the Pd and Ir contents of the spinifixtextured meta-picrites may be used to determine if they had come to equilibrium with a sulphide melt. This has widespread application in exploration for nickel sulphides.

S.D. LEE Department of Earth Sciences, Monash University

GENESIS OF AND PRE-METAMORPHIC ALTERATION AROUND THE BROKEN HILL OREBODY, N.S.W. The Broken Hill orebody is grossly conformable with the earliest recognizeable macrostructures in the area and shows a broad stratigraphic control with the enclosing rock units. This and other geometric features of the wall-rocks suggest that the ore has not been greatly remobilized, and hence any premetamorphic alteration should still be spatially associated with it. Graded bedding indicates that the major structures are downward facing and the resultant stratigraphic sequence contains most of the originally volcanic rocks (now amphiboles and acid gneisses)~below the orebody. Several asymmetrically-distributed chemical trends in the bulk-rock chemistry of the wall-rocks have been interrupted as the effects of pre-metamorphic alteration and other characteristics typically associated with stratiform "volcanogenic" massive sulfides. These are distinguished from other relatively symmetrical patterns which are ascribed to metasomatic and/or retrograde metamorphic processes. Thus, enrichment in Fe, Mg, and metals (Cu, Pb, Zn) and depletion in alkalies and Sr on the footwall are consistent with the presence of an alteration "pipe" beneath the orebody, while SiOz-Zr data and better-developed banding in the quartz-rich rocks above the orebody indicate the existence of well-layered, quartz-rich chemical sediments above the sulfides prior to metamorphism. The possible overall setting of the orebody in the light of plate-tectonic theory is discussed briefly.

W.R. MORGAN Dept. of Geology, W.A. Insitute of Technology

ULTRAMAFIC BODY IN ARCHEAN GRANULITES NEAR CORRIGIN, W.A. The ultramafic body occurs within granulites facies metamorphics of the Yilgarn block, between Corrigin and Kondinin, 210 km. ESE of Perth,Western Australia. The body is known only from aeromagnetic anomalies and diamond drilling; its outcrop is almost entirely obscured by a salt lake. The aeromagnetic anomalies suggest that the outcrop plan of the ultramafic has a half-moon shape 1.5 km. long by 1 km. wide. Its anomaly pattern contrasts strongly with the rectilinear pattern of anomalies representing dolerite dykes in the immediately surrounding country. continuea

W.R.Morgan continued.

The Electrolytic Zinc Co. of Australasia put down four^diamond drill holes to about 250 m . depth between 1969 and 1972. Cores from three of the holes have been examined in detail. The portion of the ultramafic "exposed" by the drilling can be divided into two units, an upper harzburgite and a lower amphibole Iherzolite. The harzburgite was composed of olivine and orthopyroxene, with minor chromite and brown spinel; it is now moderately to completely serpentinized. In the south of the body large prismatic phenocrysts of orthopyroxene are enclosed in a matrix of polygonal olivine. Further north the phenocrysts are strongly strained, and in the northernmost hole form lenticles of polygonized grains. These features are thought to have resulted from igneous emplacement rather than the metamorphism. In chemistry the harzburgite is similar to olivine-orthopyroxene cumulates found in maficultramafic intrusives. The amphibole Iherzolite is composed or varying amounts of olivine orthopyroxene, and tremolite, with minor clinopyroxene and magnetite. Modal analysis shows cyclic variations of olivine-rich rock grading upwards to pyroxene and tremolite-rich rock. One cycle grades to hornblendeplagioclase and clinopyroxene-plagioclase assemblages. Texturally, the rocks are metamorphic, but the cycles suggest an igneous origin. In chemistry the Iherzolites and the "gabbros" appear to be cumulates. There is evidence to suggest that the Iherzolite was emplaced later than the harzburgite, and that both rock units; are synorogenic. A . PURVIS Dept. of Geology & Mineralogy, University of Adelaide PRIMARY AND SECONDARY VARIATION PATTERNS IN THE GEOCHEMISTRY OF ARCHAEAN METAVOLCANIC ROCKS

Geochemical variation in Archaean metavolcanic rocks from Forrestonia W.A. is related to: 1)

variable amounts of partial melting of Archaean mantle;

fractional crystallisation of primary mantle derived melts;

alteration prior to, or during, metamorphism.

Partial melting models are consistent with an Archaean mantle having 1.5 2 times chondritic values for T , Zr, Nb, Y , Sc, Ca and A1, but nonchondritic values for Zn, Ga and P. Fractional crystallisation, involving olivine, pyroxenes and plagioclase, give rise to consistent major and trace element variation, at least for most of the elements listed above, and also for Cr, Ni, Co and Mg. Alteration causes non-primary variation in Ca, K, Na, Rb, Sr, Ba and in some cases Si contents. Rarely enrichment in Y and R.E.E. is observed.

DAVID H . TUCKER Bureau of Mineral Resources, Canberra City, A.C.T. 2601

THE APPLICATION OF AEROMAGNETIC INTERPRETATION WITH GROUND FOLLOW UP TO MAPPING IN THE ADELAIDE GEOSYNCLINE There is useful information to be derived from line by line interpretation of the available airborne magnetic data for the Adelaide Geosyncline. Such a study, of 0RR0R00 and other smaller areas has identified three main classes of bodies which are magnetic at or near the surface. These are: 1)

Steeply dipping 'magnetic sedimentary beds' in the Adelaide System

Igneous rocks including dolerites, carbonatites and kimberlites, and

Recent sediments which contain maghemite, and in some areas mask Class 1) and possibly Class 2) bodies.

A fourth class, basement inliers, is not discussed here. The first two classes are of particular interest because the sediments and basics are sometimes associated with base-metal mineralisation especially in diapiric structures. The ultrabasics might be of interest for rare earths and possibly diamonds. Ground follow up of selected anomalies has given additional detail.Magnetic beds can be multilayered within a total thickness of several hundred metres; individual layers are magnetically weathered to different depths, usually in the range 10-200 m , and give rise to complex anomalies. The main magnetic mjneral is metamorphically produced magnetite. Igneous rocks traversed in diapirs were mainly found to be magnetic at the surface; these range in size from 1 m to several hundred metres across, and have apparent susceptibilities usually up to 1000 x 10"® cgs units. Recent sediments are in some areas 100 m or more thick and can have a susceptibility in excess of 1000 x 10"® cgs units; they probably give rise to fault-step anomalies in the airborne data near the edges of plains of this material. The background susceptibility of Adelaide System sediments averages 55 x 10"® cgs units and can cause topography derived anomalies of 1-5 nT in the airborne data. Future airborne surveys in selected areas to map Class 1) bodies beneath 3) and to detect Class 2) bodies should use a magnetometer cycling at 0.1 seconds, with resolution of 1 nT or better, flown at a continuously recorded 80 m ground clearance, on lines 400 m apart or less.

SESSION 7

- LEAD - ZINC CARBONATE ROCKS

CONVENOR

FRIDAY

4th

LECTURE

V.J.

WALL

FEBRUARY THEATRE

2 R

PM 3

G.J. DE ROSS and Preussag (Aust) P.L.

D.J. PERKIN

EPIVOLCANOGENIC ORES IN FOLD BELT CARBONATE ROCKS AN EPIGENETIC VOLCANOGENIC ORE TYPE Banded and massive sulphides in pelitic sediments often occur immediately above acid to intermediate source rock volcanics and volcaniclastics and constitute a significant proportion of the bedded base metal sulphide deposits throughout the world. However,massive sulphide deposits in carbonate rocks with a volcanic association are apparently less common and certainly less widely recognized. This paper proposes an epigenetic mechanism for the emplacement of volcanogenic sulphide mineralization within carbonate rocks of fold belts. Distinctions are drawn between Epivolcanogenic ores in carbonates and the following related classical ore types: (i)

"Mississippi Valley Type" ores which develop in stable "Platform Cover" Sedimentary Basins are characterised by the absence of severe folding and deformation, not resting on or proximal to volcanics; and notable for the relatively low Ag values and low base metal values other than Pb and Zn. The origin of the metallifirous brines is probably basinal, and deposition of the sulphides occurs epigenetically during brine migration upwards and outward towards the basin margins.

(ii)

"Kuroko Type" ores are volcanogenic sulphides which are deposited contemporaneously with tuffaceous pelites at the water/sediment interface. Carbonates may form part of this sequence but synsedimentary banded ore will only form within the pelitic intervals.

(iii) "Hydrothermal Replacement Ore Type" - In classical hydrothermal terms, Cu-Pb-Zn sulphides in carbonate rocks may be related to nearby, but often hidden, intrusive granitic plutons which were thought to be the source of high temperature ore bearing solutions injected into the host rocks. Except for contact metasomatic ore types where the intrusive granite is exposed, many of-the so called "Hydrothermal Replacement" ore types in carbonate rocks may in fact be Epivolcanogenic type deposits. Features which characterise the Epivolcanogenic ore types are: (i)

Massive to semi-massive (Cu) PbZnAg (Hg) (Sn) ore within limestone or dolomite with generally some evidence of zonation of elements relative to the source vent.

(ii)

Ore may be closely associated with tuff bands in the carbonate rocks with overlie the differentiated volcanic sequence of basic to acid lavas and fragmentals.

(iii)

Ore is stratabound rather than stratiform, massive but cross-cutting, It is not banded or bedded as in sedimentary sulphides and lacks syndedimentary structures. Ore emplacement is post-carbonate deposition and occurs below the water-sediment interface during or

50 G.J. DE ROSS

and

D.J. PERKIN

cont. -

after diagenesis. (iv)

;

Sulphur is derived from entrapped or circulating connate fluids and the sulphide from where alkaline, low Eh, sulphur-bearing connate waters mix with base metal bearing brines emanating from porous zones or vents. Carbonate hosted ores in volcanic domains are often closely associated spatially with magniferous dolomite and barite.

(vi)

Epivolcanogenic ore types are invariably associated with major basement faults which parallel the tectonic grain and possibly controlled basin subsidence (active during sedimentation) while ore deposition often extends out from cross faults into the carbonate host rocks.

(vii)

Epivolcanogenic deposits had their peak development in EmsianGivetian times (Lower-Middle Devonian) which is notable world-wide as a period of extensive carbonate sedimentation, often following a period of significant volcanicity.

Proposed mechanisms for epivolcanogenic ore formation include: (i)

juvenile and/or leached volcanogenic fluids as a source of metals.

(ii)

porous conduits, such as faults, cross-faults, coarse grained fragmentals, breccias, tuff, coarse grained carbonate rocks and carbonate breccias to .distribute the metal ions.

(iii)

deposition in sulphur-bearing carbonate rocks during diagenesis the sulphide being derived from reduction of sulphate in the presence of carbon radicals.

Suggested examples of Epivolcanogenic sulphide deposits in carbonate rocks within Australia are: Renison Bell and Cleveland tin-copper deposits, Tas. Girofla-Lady Jane tincopper-zinc-lead deposits, Qld. and numerous other examples throughout the Tasman Geosyncline including Grieves Quarry near Warwick S.E. Qld. where preliminary diamond drilling has revealed up to 11m of 0.9%Cu, 3.0%Pb, 8.9%ZN, 3.4oz.Ag. Ovearseas examples of Epivolcanogenic massive sulphide deposits in carbonate rocks include: Tara Pb-Zn, Silvermines Pb-Zn-Ag, Tynagh Pb-Zn-Cu-Ag-Ba, Gortdrum Cu-Ag-Hg and other Irish Base Metal deposits in carbonates in Ireland. (Cu)-Pb-Zn of the Altai and Atasu Type in Central Kazakstan, U.S.S.R. Less obvious and less massive epivolcanogenic ore types associated with more basic-intermediate volcanism may possibly include the gold deposits of the Kalgoorlie region and the copper-bismuth-gold deposits of the Tenant Creek Province.

G.J. DE ROSS

and D.J. PERKIN cont..

- 3 The Epivolcanogenic model is considered to be an empirical as well as a conceptual blending of processes normally regarded as volcanogenic and therefore synsedimentary with mechanism of hydrothermal and patently epigenetic affinities.

A. DRUMMOND Utah Development Co., South Australia STRATIFORM COPPER, DEFORMATIONS AND DIAGENESIS AT KAPUNDA, SOUTH AUSTRALIA Kapunda is situated 80 km north east of Adelaide. It was Australia's first copper mine, but has been unproductive this century. During 1974-1976 Utah Development Company has undertaken an extensive exploration programme in an as yet unsuccessful attempt to outline an economic ore deposit. For the purposes of this paper the diagenetic time interval for a given bed is taken as that time between the deposition of the bed to when it was effectively sealed to further low-temperature physico-chemical changes. At Kapunda, the sediments were plastic throughout most of this time. The copper sulphides are hosted by relatively coarse dolomitic siltstone units within a finer clastic sequence of the Adelaidean Tapley Hill Formation. The age of the host is somewhat less than 750 m.y. The cupriferous rocks have two styles of mineralization, namely beddeddisseminated and vein. Textural features indicate that both types achieved their present form during diagenesis; the types are neither clastic nor brittle fracture infill. There is considerable evidence of pre-1ithification mobility of sulphides and host. A preferred orientation of sulphide grains and cupriferous vein growth is parallel to the regional schistocity and local structural elements. This preferred orientation occurred before 1ithification. The host sediments were cylindrically folded and evidence suggests that the folding is also pre-1ithification. No significant folding has occurred since 1ithification which is given an early Cambrian age. On this basis the diagenetic processes operated on the Kapunda host rocks for almost a quarter of a billion years.

SESSION 8 CONVENOR

- ET/WRPHISM -

V.J.

WALL

THURSDAY 3 r d FEBRUARY FRIDAY 4 t h FEBRUARY LECTURE THEATRE R 3

9am 4pm

53 CHARLES D.A. COIN Department of Geology and Mineralogy, University of Adelaide

THE RELATION BETWEEN Ca, Mn CONTENT OF GARNET AND THE BIOTITEGARNET Mg-Fe DISTRIBUTION COEFFICIENT AS AN INDICATOR OF METAMORPHIC GRADE

The usefulness of the Biotite - Garnet Mg-Fe distribution coefficient (K n ) as an indicator of metamorphic grade has, in the past, been negated by the interference of Ca and Mn in the garnet molecule. Various authors have constructed a variety of "correction factors11 which are all deemed unsatisfactory as they seem to be not widely applicable. Using a theoretical model of preferential replacement of Mn for Mg and Ca for Fe in the garnet molecule, a postulated relationship of Ca/Mn = a.b (K d ) is deduced. Applying data from a number of studies, it is found that the relationship is valid. The value 'b' is constant and the value 'a' is a direct and sensitive indicator of metamorphic grade.

W.F. D'ARCY Department of Geology and Geophysics, University of Sydney

STRUCTURES AND METAMORPHISM OF THE NORTHERN TIP OF THE WILLYAMA BLOCK, BROKEN HILL, N.S.W. The northern tip of the Willyama Block consists of slate, phyllite and quartzite. Two groups of folds are recognised. Slaty cleavage is the axial surface of one group, and a crenulation cleavage is axial plane to the other. Some phyllite horizons contain chlorite - white mica - quartz knots probably after cordierite. A few of these horizons contain sericitized chiastolite porphroblasts. Unconformably overlying the Willyama rocks are Adelaidean age rocks which show two groups of flexural-slip folds. The associated deformation was accommodated in the underlying rocks by siio on the slaty cleavage, and by decollement in dolomite just above the base of the Adelaidean rocks. Rare kink bands are near some of these zones of movement. Amygdaloidal metabasalt containing epidote, chlorite, prehnite and albite overlies the dolomite. A temperature of 350°C to 400°C is indicated. The metabasalt was overlain by probably 10 km of sedimentary rocks,indicating a pressure near 2.5 kbar. This metamorphism produced chlorite in the Willyama rocks without otherwise upsetting the rock fabric.

TEUNIS A.P. KWAK Department of Geology, Latrobe University CONDITIONS OF FORMATION OF THE KING ISLAND SCHEELITE DEPOSITS, KING ISLAND, TASMANIA The aim of this study is to determine the conditions of formation of the King Island Scheelite deposit (King Island, Tasmania, Australia) from its initial to its final crystallization. This was done by use of field studies, electron microprobe analyses and fluid inclusion studies. At the deposit, reactions between the chemically dissimilar calcic hornfels and marble have resulted in a zonation at their contact which ideally results in the development of green hornblende in the hornfels foilwed by a zone of green diopside-hedenbergite pyroxene, grossularite garnet, Fe-vesuvianite, wollastonite and finally marble. Superimposed on a largely subsequent to this is the tungsten-bearing skarn in the unaltered marble. The process^ involved a complex interaction between hornfels, marble and a saline fluid to produce a nearly pure diopside-hedenbergite pyroxene rock of the hornfels with anomalous Mo and W values and the skarn. Intermediate between the marble and skarn either a (1) wollastonite - vesuvianite - scheelite rock or a (2) amphibole-rich skarn zone occurs while between the hornfels and the pyroxene rock a hornflende-rich hornfels occurs. Case (1) occurs where the volumetric hornfels/skarn ratio in the immediate area is large while case (2) occurs where it is relatively small. The tungsten-bearing skarn consists of hedenbergitic pyroxenes with Mg relatively rich at the core which decreases to Mg-poor at the edge of the grains in both case (1) and (2). The quantity of Mg present in the pyroxene very much depends on the volumetric hornfels/skarn ratio, the Mg being derived largely from the hornfels. Skarn garnets are zoned grossularite to andradite in case (1) while the reverse is true in case (2). This is due to A1 being retained as grossularite garnet at the skarns periphery and released near the end of crystallization in case (2) but not case (1). In the case (2) skarns, fluid inclusion studies indicated homogenization temperatures, corrected for salinity and pressure (600 bars) of 350° ± 20°C at the core of garnet, 370 ± 20°C at two-thirds of the radius out and 505 - 510° ± 20°C at the edge. Salinities at the core are low (-5 weight percent equivalent NaCl) while at the 370° ± 20°C temperature they rise dramatically to near 30 weight percent NaCl or more which persists to the edge of the garnet. Tensional fractures, partly healed and filled with two-phase fluid occur everywhere up to approximately the 370° ± 20°C temperature where they terminate near a garnet growth layer containing minute wollastonite fibers. The phenomenon is interpretted to be due to faulting produced pressure-release causing the fluid to reach a two-phase area (boiling). Pyrrhotite in the skarn is always rimmed by pyrite indicating at their contact a temperature of 310°C and a fs 2 of 1 0 " 1 0 . Scheelite often has a central powellite-rich core (^ 30 mote percent) which falls abruptly (to < 1 mole percent) at a distance of half the radius of the crystals. Using pertiment thermodynamical data and writting reactions involving (a) andradite-hedenbergite, (b) wol1 astonite-quartz-calcite, (c) powel 1 ite-scheelite-molybdenite-tungstenite and finally (d) pyrite-pyrrhotite it is suggested the skarn began to form at 42 0 5 10 from a T = 350 ± 20°C, fo 2 < 1 0 " , fco 2 < K T ' , and fs 2 < 10" relatively dilute solution. At the interpretted faulting period 5 9 5 T = 370 ± 20°C, fg 2 - 10~° • and f$ 2 - 1 0 " - while the solution is fairly saline. Near the termination of the episode T = 505 - 510 ± 20°C, f0 2 " 10~ 2 * , f C Q 9 = 1 0 + 1 - 2 , and f s * 1 0 " 5 - 5 . Pressure varied between 400 2

continued

55 T .A.P.Kwak continued, to 600 bars being initially high, low at the period of faulting (hydrostatic) and high again at the termination of the skarn producing episode. In skarns f a n d f r o s e where the hornfels/marble ratio is low, the values of f s 2 > H 2 0 C02 with falling fo 2 and temperature to produce a mixture of epidote, calcite, ferrohastingsite, quartz and pyrite from the previously formed garnet skarn. This occurred near the skarn-marble interface. E.M. LOHE University of Queensland ASPECTS OF METAMORPHIC MINERAL ASSEMBLAGES IN THE NERANLEIGHFERNVALE BEDS OF THE BRISBANE METAMORPHICS Neranleigh-Fernvale sediments and volcanics are metamorphosed to lower greenschist facies of the Barrovian-type series. Metabasalt mineral assemblages are: 1)

Actinolite - epidote ± albite ± sphene ± chlorite ± calcite ± quartz

Chlorite - calcite ± albite ± quartz. This assemblage is relatively uncommon. Rare chlorite-montmorillonite occurs in the D'Aguilar Block. The metabasalts contain relict textures such as glass-cracking, variolites, and spherulites. The following conclusions can be drawn:

The metabasalts were originally wholly or partially hyaline

ii)

Metamorphism was virtually isochemical. Alteration involved only the addition of H 9 0 and for C 0 9 , and some variable modification of alkali L L levels.

iii) Chlorite + calcite-bearing rocks are chemically indistinguishable from actinolite + epidote-bearing rocks. pC0 ? represents an important metamorphic mineral control. The greywackes are partially recrystallized. blages are:

Metamorphic mineral assem-

Actinolite - epidote - albite - phengite - sphene - chlorite ± ferrostilpnomelane ± calcite.

Albite - phengite - ferrostilpnomelane - chlorite epidote ± actinolite.

± calcite ±

The following conclusions concerning the development of ferrostilpnomelane are drawn: 1)

It occurs as a replacement mineral of detrital K-feldspar and plagioclase.

Its alkali content usually reflects the host feldspar composition.

Associated altered ilmenite supplied Fe and Mn for the stilpnomelaneforming reactions.

The ferrostilpnomelane is relatively aluminous compared to its oxidized ferrostilpnomelane equivalent.

56 NEIL PHILLIPS Department of Earth Sciences, Monash University LOW-INTERMEDIATE PRESSURE METAMORPHISM AT BROKEN HILL Four prograde metamorphic zones of low-intermediate pressure type have been mapped in the Willyama Complex at Broken Hill. The three isograds have been folded and faulted during several later deformational events (Fig.l).

WILLYAMA

Fig, 1

COMPLEX

Distribution of metamorphic zones around Broken Hill.

The Sillimanite Isograd approximated univariance; the Sillimanite - K. feldspar Isograd is mostly obscured by products of partial melting and { retrogression and may well be divariant; the Two Pyroxene Isograd is strongly controlled by fluid and whole rock chemistry, as well as P and T. A metamorphic grid based on prograde assemblages imposes P - T limits during peak metamorphism, namely: Andalusite Zone Two Pyroxene Zone

3.5 kb.

400°C. 800°C

kb.

57 NEIL PHILLIPS

cont.. -

Further:

Two pyroxene geothermometry indicates an increase in temperature towards the S.E., though difficulties with this method have been ignored in the past.

GT - Bi pairs often record lower readjustment temperatures related to later events.

6T - Cd pairs, though rare, provide the most useful guide to pressure.

The breakdown of hornblende-plagioclase mafic rocks in two pyroxene granulites occurs at lower grade in Fe rich lithologies. Many mafic rocks, especially near mineralization, have high contents (< 22% FeO) and contain Granulite Facies assemblages whilst neighbouring, more magnesian lithologies contain hb - plag. Using different amphibole solution models a variable A 1^0 is found within mafic rocks of the Two Pyroxene Zone. A progressive grade increase to the S.E., as first suggested by Binns (1964),is indicated.

Reference

Binns, R.A., 1964, J . Geol. Soc. Aust., 11: 283-330.

A. PURVIS Department of Geology & Mineralogy, University of Adelaide

METAMORPHISM IN TWO AREAS IN THE YILGARN BLOCK WESTERN AUSTRALIA Metamorphism of ultrabasic and metasedimentary rocks at Mount Martin ( 25 km SE of Kalgoorlie) and at Diggers' Rocks (150 km S of Southern Cross) indicates conditions within the lower to middle amphibolite facies. Critical assemblages in iron-rich pelites are: 1)

almandine-chloritoid-chlorite-biotite-quartz;

almandine-staurolite-biotite-quartz;

almandine-andalusite-biotite-quartz;

almandi ne-si11imani te-bi oti te-quartz.

These indicate temperatures of 500-650°C and pressures of 3-5 kilobars. Metamorphic parageneses to be discussed in greater detail include:1)

breakdown products of Fe-rich chlorite;

breakdown products of Fe-rich calcic amphibole;

parageneses of gedrite;

composition and parageneses of garnets;

olivine-talc-anthophyllite-orthopyroxene relationships.

R. ROGERSON Department of Geology and Geophysics, University of Sydney

PROGRESS IN MAPPING ZONAL LOW-PRESSURE REGIONAL MFTAMORPHIC MINERAL ASSEMBLAGES IN THE WAGGA-OMEO METAMORPHIC BELT Over the past thirty years, many students of the University of Sydney have been engaged in mapping zonal low-pressure facies series mineral assemblages in the Wagga-Omeo Metamorphic Belt in N.S.W. and Victoria. This work is now almost complete and therefore this talk will be used to •i splay the zonal map and to review the problems encountered as well as the progress and results achieved. Four zones in pelitic rocks have been mapped in most areas: viz. chlorite, biotite, andalusite/cordierite and K-felspar zones. The problems encountered during the mapping include: 1.

the similarity between contact metamorphic assemblages surrounding granites and those of the low-pressure facies series regional metamorphism;

the obscuration of Ordovician metasediments by younger cover and intrusive bodies;

widespread retrogression, and

the lack of basic igneous compositions particularly in the low-grade rocks.

A variety of techniques have been used to overcome these problems, but certainly the most powerful has been the application of micro-textural and structural studies to metasediments to elucidate the metamorphic history. Guess-work is required to overcome the second problem. Zonal metamorphic maps, representing the intersection of isothermal planes with the presentday erosional surface are valuable in the three dimensional interpretation of metamorphic terrains when considered in the light of the geothermal gradient implied by the petrogenetic grid for pelitic rocks. Several distinct zonal patterms have been defined, but to what extent these patterns are the products of syn- and post-metamorphic deformation on a developing thermal regime is incompletely known at present. RAYMOND E. SMITH CSIRO Division of Mineralogy, Wembley, W.A., 6014

THE HAMERSLEY BASIN REGIONAL HYDROTHERMAL PLUMBING SYSTEM

Investigations have revealed the probably existence of a large hydrothermal alteration system that appears to have formed during hydrous metamorphism of the Proterozoic Hamersley Basin. Once-permeable flow tops of lavas are intensively altered to hydrothermal mineral associations. Mapping shows the permeable horizons were continuous in concert for at least 2.00km and perhaps as much as 350km along the north side of the basin. Geochemical work on the altered lithologies shows that intensive metasomatism accompanied alteration. It is proposed that the altered flow tops are the sites of an ancient plumbing system for hydrothermal solutions. Field work shows that the area over which this metasomatic alteration can 2 be recognised is very large - at least 15,000km and perhaps as much as 2 50,000km .

SESSION 9 - niNERALDGY CONVENOR

FRIDAY

4th

LECTURE

Dr. R.

SEGNIT

FEBRUARY THEATRE

9AM, R

2PM

BILL BIRCH

MINERALOGY OF THE COSGROVE (VICTORIA) LEUCITITE Olivine leucitite forms a small flow, of Pliocene age, at Cosgrove, Victoria. The lava is similar to those in the leucitite belt of Central an N.S.W. It contains olivine (Fe-j5^3-1) d diopsidic pyroxene phenocrysts, in a groundmass of diopsidic pyroxene, nepheline, leucite, Fe-Ti oxides and a biotite rich in Ba and Ti. A late-stage, coarse-grained differentiate of the lava contains clinopyroxene (zoned frram Ti-rich diopsidesalite to aegirine), nepheline, alkali feldspar, analcime, titaniferous magnetite, amphibole, aenigmatite and sodalite. Vesicles within the lava contain a free-growing mineral assemblage similar to that within the host lava, with the addition of apatite. High volatile pressures probably facilitated crystallization of this assemblage and the composition of the apatite may reflect the original composition of the volatile phase. The mineralogical variation within the Cosgrove occurrence is discussed in the light of likely fractionation effects. The paper will devote much of its duration to description of the phases present by means of slides. Chemical data on all main phases, especially pyroxenes will be presented. The emphasis will be towards the mineral assemblage in the vesicles and coarse grained phase, as the bulk lava is similar mineralogically to those already described from N.S.W. (Cundari, 1973).

A.K. FERGUSON Department of Geology, University of Melbourne

MINERALOGICAL ASPECTS OF THE CAMEL'S HUMP AND RELATED TRACHYTES IN VICTORIA The mineral chemistry of the mafic minerals from the trachytes of the Camel s Hump mamelon" have been studied to highlight the relative effects of crystal fractionation and the role of volatiles on the mineral assemblages. The assemblage ferrosahlite - fayalitic - olivine magnetite in the majority of trachytes ("anorthoclase trachytes") is replaced by an assemblage of arfvedsonite - aenigmatite - sodic hedenb urqite in trachytes that contain a fragmentary texture ("solvesburgites") The peralkaline tendency of some of the trachytes is only indicated by the latter mineral assemblage and is not apparent from the bulk rock data Based largely on field evidence and textures of the mafic minerals, it is postulated that the latter assemblage has crystallized largely from volatile-rich vapours and/or fluids percolating through the chilled trachyte near the base of the "mamelon". In addition the presence of pegmatoidal clots and cavities containing the assemblage alkali feldspar quartz - ferrorichterite - arfvedsonite - ferrosahlite is discussed A.K. FERGUSON Department of Geology, University of Melbourne

THE MINERAL CHEMISTRY OF CLINOPYROXENES FROM ALKALINE ROCKS

The compositional variation of clinopyroxenes from a variety of alkaline volcanic and related rocks, together with the coexisting minerals, has been investigated in detail. Special emphasis has been placed on the composition of pyroxenes occurring in peralkaline rocks and data is presented to demonstrate that a titanian-aegirine is in fact the last pyroxene composition observed after aegirine in many cases. The stability of the Na-rich clinopyroxene is shown to be essentially independent of silica content of the host liquid, but that the Mg/Fe ratio of the clinopyroxene is strongly dependant on the Mg/Fe ratio of the host liquid. In samples containing an alkali amphibole, a compositional gap is observed between the Na-rich and Ca-rich Clinopyroxenes. This is similar to Aoki's (1964) immiscibility gap which was later considered by Yagi (1966) to be due to lack of available data of intermediate compositions. In some lavas where amphibole is absent, however, almost continual zoning from a Ca-rich to a Na-rich clinopyroxene is observed, even within single crystals. The observed crystallization sequence of the mafic minerals, including the compositional gap in the clinopyroxenes if an amphibole is present, can be explained by the role of late-stage volatiles.

62 G.S. GIBBONS 8 Marsh Place, Lane Cove, N.S.W.

INTRODUCTION TO THE POLARISING MICROSCOPE: SIMPLE LABORATORY DEMONSTRATIONS

An overhead projector can be used with readily-available mineral samples to demonstrate basic principles of crystal optics relevant to mineral identification under the polarising microscope.

A normal slide projector can be used to demonstrate both orthoscopic and conoscopic relationships, using a large sheet of muscovite to show crystal-orientation clearly.

IAN E. GREY C.S.I.R.O. Division of Mineral Chemistry.

BRYAN M. GATEHOUSE Monash University Chemistry Department

IAN CAMPBELL & PATRICK KELLY Melbourne University, Earth Sciences Department.

STRUCTURAL STUDIES ON DAVIDITE AND RELATED MINERALS

The structures of the minerals senaite, crichtonite, loveringite, landavite and davidite have been determined from single crystal X-ray diffraction studies. The minerals are isotypic; i.e. they all have the same basic structure but have different elemental substitutions and somewhat variable occupation of some of the lattice sites. The structures are based on a nine-layer (hhc...) close-packed array of anions with large cations (A) partially occupying anion sites and with small cations (M) occupying both octahedral and tetrahedral interstices. The unit cell compositions for the various minerals are encompassed by the formula 0^ 0Mnn 18-<l4 36-38 The minerals are classified according to the dominant A cation which is lead in senaite, strontium in crichtonite, calcium in loveringite and uranium plus rare earths in davidite. The main types of M cations encountered are titanium, iron and chromium.

Details of both the compositional and structural variations in these minerals will be presented.

63 J.B. JONES and R.S. BOTTRILL

CRYSTAL CHEMISTRY OF THE ADAMITE-OLIVENITE SERIES Phosphates, arsenates and vanadates of stoichiometry AB (As0 4 ) OH are usually subdivided into two types! the libethenite group where A and B are identical and the adelite group where they are different. The commonest minerals in the libethenite group are libethenite itself (Cu 2 (P0 4 ) (OH)), olivenite ( C u 2 ( A s 0 4 ) (OH)) and adamite (Zn 2 (As0 4 )0H). Studies on the latter pair of minerals have confirmed that the space groups of olivenite and adamite are different although the difference in structure appears to be minor; that under the conditions we used for producing synthetic materials, there is incomplete chemical substitution between the two and that the cell dimensions vary in a systematic manner from olivenite to adamite. The evidence suggests that there are significant structural differences between the adelite and libethenite groups and that chemical substitutions between the two groups are unlikely to be continuous.

J.B. JONES Geology Department, the University of Adelaide

a n d

- - SEGNIT Decision of Mineral Chemistry

C S I R 0

CHEMICAL COMPOSITION OF OPALINE SILICA The composition of opaline silica is commonly referred to as Si0 2 .nH 2 0. Its chemical composition, however, is widely variable. Water content is commonly within the range 4 - 10%, but occasionally falls outside of these limits. Elements such as alkalies, calcium, magnesium, iron and aluminium are usually present in variable amounts. The content of these elements may be less than 0.05%, but in the case of iron-rich opals, may be higher than 25%. These impurities are usually present as physical admixtures of other minerals, although minor amounts may be adsorbed. Opals may be divided into a number of broad groups according to the type of "impurity" present. Trace element contents are also highly variable, and appear to depend on the environment of formation of the opal. They are probably mostly adsorbed onto the surface of the silica. The capacity of opaline silica to adsorb a wide variety of trace elements may be a useful geochemical tool in recognizing local concentrations of less common elements.

64 R . W . LeMAITRE Department of Geology, University of Melbourne

THE PROPAGATION OF ERRORS IN MINERAL

RECALCULATIONS

When using mineral analyses it is common practice to transform the original oxide data into cations, cation sums and r a t i o s , or end components. However, although the errors in the original oxides should je known - as most mineral analyses are now performed by electron microprobe - no theory has existed to predict the errors involved in the transformations. This theory is now presented in generalised form suitable for computer application. One important application is t h a t , by knowing the standard deviation of the total sum of cations on the basis of a certain number of oxygens, it is possible to test whether this value differs significantly from the formula v a l u e , thus providing an additional check on the "goodness" of the analysis.

The errors involved in the partitioning of iron between FeO and by assuming mineral stoichiometry is also investigated. E . R . SEGNIT and J . WATTS CSIRO Division of Mineral

Chemistry

SECONDARY PHOSPHATES FROM M O C U L T A , SOUTH AUSTRALIA T Phosphate rock from M o c u l t a , near Anaastnn Sm,th a m c + veins and cavities filled or a r t i , i f f ? i' South Australia, contains

s s a ^ r - f f l ' X f i n - i s ssssgftsw The first of the secondary minerals to form was anatitP wh.vh O C C u r s as white v e i n s , 1-2 mm w i d e , which o f t e n L n ' 5 1 C atl ngS in cavities. Apatite also forms a t e T a s reqaL f?^'" ° ' • , m 0 r e l n S i z e ) of s h o r t , colourless, transparent h e x a g o n a T i s m s UD L n T r m o r e m diamater. Other secondary minerals aroea? in L e t J™ ° the apatite. Wavellite occurs as c o a t i n g ^ I I C a S 6 S t o P° s t~date 9 radiating aggregates in Sv'Eles" a n f m r a V I T ^ T r ^ V J ^ georcixite group form radial clusters UD tn M nI crandal iteP individual needle-like forms are mad p 0? e y t h T s l n ^ n p 1 a t e S stacked along their C axis. Preliminary X - r a y e v i d e n c e ! „ h f f n ? the presence of one or more basic iron phosphates indicates

HPLIS

Sheaf-like aggregates of g o e t h i t e , possibly formed hv th* « -a * • y s i d e r i t e , often coat the apatite Alsn . t h e o x l d a t i o n of the secondary phosphates T e c a i c U e bar crvsJalsT^^0^^ With psilome^ane

crystallized m a n g a n i s e ^ S i l d l 0? t h T ™

l 0 n g )

SESSION 10

EXPEKirOTALTTHEORETICAL GEOQEMISW AND PETROLOGY

CONVENORS

WEDNESDAY

2nd

FEBRUARY

9AM

THURSDAY

3rd fEBRDARY

2PM

LECTURE

V.J. WALL

THEATRE

arid

Dr. W.

NESBIT

A.H. EWALD CSIRO M.R.L. Sydney

VARIABILITY OF SOLUBILITY PRODUCTS It is commonly assumed that every mineral has a solubility product which is a function of temperature and pressure only. It can be shown that this is so only for ideal crystals of fixed stoichiometry, for others the solubility product and the stoichiometry at final equilibrium will depend on the activity of the ions in the solution with which the crystal is in contact. Published data can be used to show that the sol utility product of CaF 9 varies by almost a factor of two as the Ca concentration changes from 10 to 10 molar. AgCl with chloride concentration.

A similar variation can be shown for

The change in stoichiometry probably does not extend throughout the crystal but is confined to a surface layer and may be established in relatively short time. This will lead to measured solubilities which will depend on the prehistory of the sample and may be responsible for the wide scatter of some published solubility measurements. The simple assumption of first order kinetics for the dissolution process and a plausible assumption regarding the rate of change of the solubility product, leads to equations which, under certain conditions, have a solution which corresponds to an oscillatory dependence of solubility on time Some observations on ZnS show such behaviour.

T.H. GREEN Macquarie University GARNET-SILICIC LIQUID RELATIONS: A POTENTIAL GEOTHERMOMETER - GEOBAROMETER? Melting experiments on a model pelitic composition yield garnet as an important residual phase at pressures above 7 kb. In this, and other compositions, the grossular content increases with increasing pressure, while the K n values for distribution of iron and magnesium between coexisting garnet and liquid are mainly sensitive to temperature, but also have a small pressure dependence, Thus for T £ 1 ,000 G, F^. is > 1, while at T > 1,000°C, K Q g a F f i q is < 1, with the implication that, for very restricted conditions, silicic magmas may fractionate garnet and produce derivative liquids which with a higher m £ number. Preliminary experiments with added MnO content demonstrate that higher spessartine garnets may be stable in silicic liquids to pressures as low as 2 kb, although the spessartine content of most natural garnets in Eastern Australian granitic rocks suggests that these have not formed at pressures below 4-5 kb. P.L. HELLMAN School of Earth Sciences, Macquarie University, North Ryde, N.S.W.

THE RARE EARTH ELEMENTS AS GEOCHEMICAL INDICATORS IN ALTERED BASALTIC ROCKS

A variety of outcrops around the world have been chosen to test the hypothesis that the rare earth elements (REE) remain fresh in absolute and relative abundance during low grade burial metamorphism and spilltization of basaltic rocks. The Bhoiwada section, India, provides a unique example of black tholeiite which has progressively altered by hydrothermal metamorphism to a green albite - chlorite spilite REE spectacularly increase in abundance and shift from tholeiitic REE patterns to an alkali - basalt pattern. It is suggested that adsorption processes in layer silicate phases were responsible for such REE enrichment and relative light REE increases. REE studies of calcite and Laumontite from India and calcite from the Othris Ophiolite,Greece indicate these phases to be absolutely depleted in REE and thus they act as simple REE diiutents. Studies from other areas confirm the results from India viz. KhE are not immobile during basaltic alteration. As REE are being used as immobile petrogenetic indicators in metabasalts from ophiolites, geosynclInes and low grade to greenschist facies regions, These results have important implications and indicate it is unwise to discriminate a i<aline basalt from tholeiite on the basis of REE. The Othris Ophiolite 111 ustrates such a case where supposed alkali basalts were precursors to mid ocean ridge basalts (MORB). A REE study of these basalts contradicts a previously published interpretation. REE studies from two east Australian ophiolites indicate a MORB origin is unlikely for metabasalts trom lumut and an island-arc or spreading ridge environment is possible for Heazlewood, Tasmania.

B.J. HENSEN School of Applied Geology, University of New South Wales STABILITY RELATIONS OF OSUMILITE IN GRANULITE FACIES METAPELITES

Osumlite, approximate composition K(Mg,Fe) 2 A l g S i ^ O ^ , has been reported recently from two granulite localities. The mineral has been synthesised in a model pelitic composition at 1000 and 1100 C and 3.6 - 6.3 kb conditions of low water and oxygen fugacity. Osumilite coexists, apparently stably, with hypersthene, cordierite and quartz(?) thus duplicating the mineral assemblage of one of the natural occurrences. Osumilite is in a divariant reaction relationship with cordierite and hypersthene i.e. osumilite £ cordierite + hypersthene + orthoclase + quartz. This reaction runs to the right with increasing pressure. Experimental data and field observations suggest that the joins osumilitegarnet and osumilite-sillimanite are not stable. It is suggested osumilite is involved in an invariant point in the system K 2 0-MgO-FeOAlgOg-SiOg with the phases cordierite, hypersthene, sapphirine, spinel, orthoclase and quartz. and 7 ± 2 kb.

The invariant point should occur at 1000 ± 100°C

R.W. LeMAITRE Department of Geology, University of Melbourne

ON THE PARTITIONING OF IRON IN IGNEOUS ROCKS

The partitioning of iron in igneous rocks is discussed both empirically and theoretically. Using the Clair data base of over 26,000 analyses it is shown that the partitioning of FeO and F e 2 0 3 in igneous rocks is correlated with bulk chemistry and the mode of occurrence i.e. plutonic or volcanic. In particular the Si0 2 ~ total alkali plot provides a useful means of predicting the Fe0/Fe 2 0 3 ratios. Theoretically the Fe0/Fe 2 0 3 can be predicted from a bulk rock analysis, given the mode and assuming mineral stoichiometry, but the errors involved in such a calculation are too high to be of much practical use. However, the method does provide a good check on the accuracy of the mode.

D. J . PATTERSON University of Tasmania

THE HYDROTHERMAL TRANSPORT AND DEPOSITION OF TIN

Experiments and speculation on the mode of transport of tin in hydrothermal iV solutions have in the past concentrated on various S n complexes. These are,however, unlikely to be significant in nature, as the SnIV/Sn boundary is 10-20 log fO? units above theU SO4-/H2S boundary over the pH range 2-10 at temperatures up to ca. 3 7 0 C , and probably up to magmatic temperatures. 11

Extrapolation of thermodynamic properties of simple S n complexes with -CI, -F and -OH ligands indicates that ca. 10-100 ppm of tin can be transported in the form of chloride complexes under geologically reasonable conditions at temperatures up to 350°C. Contributions due to complexing with -F and -OH are 2-5 orders of magnitude lower under the same conditions. Deposition of tin as cassiterite may take place from acid chloride solutions low in sulphur by increase in pH and/or oxygen fugacity. The predicted regions of high tin solubility and suggested modes of deposition are in excellent agreement with the depositional environment of relatively lowtemperature tin deposits such as Renison Bell, and provide a feasible mechanism for tin transport and deposition at higher temperatures. F.L. SUTHERLAND Department of Mineralogy & Petrology, Australian Museum

D . STUBBS & D.C. GREEN Isotope Geology Laboratory Geology Department, University of Queensland

K-AR DATING OF TERTIARY BASALTS, NORTHERN B0WEN BASIN REGION, QUEENSLAND - IMPLICATIONS FOR PETR0L0GIC MODELS Thirty K-Ar dates on the Nebo and east Claremont basaltic provinces suggest several episodes of Tertiary volcanism in the area. Early Eocene, early and late Oligocene, early Miocene and Pliocene eruptions (54m.y. - 3 m.y.) have been recognised. The dates fix times of lateritization and provide average erosion rates since the early Eocene. Repeated volcanism at the north end of the Bowen Basin suggests a major underlying structural weakness in the basement. The dating supports Well man and McDougall's scheme of migration of central volcanoes over a mantle magma source, but also identifies broad areas of contemporaneous peripheral activity. These extended overlapping provinces show crude penological zoning, with extrusions generally passing from outer peripheral undersaturated lavas to the inner peripheral basalts, with saturated lavas, lying around a focus of felsic rocks. These zones delineate the size and thermal profile of the magma source, which can be extrapolated back in space and time to spreading in the Coral Sea and south-east Papua.

69 ALAN TURNBULL Division of Mineralogy CSIRO, Port Melbourne THE CSIRO-NPL SYSTEM FOR THE STORAGE AND USE OF THERMODYNAMIC AND PHYSICAL PROPERTY DATA FOR CHEMICAL PROCESS DESIGN Computer programs for the storage, retrieval and use of basic thermodynamic and physical property data for chemical substances are described. Methods are presented for the collection, critical assessment and preprocessing of source data for files containing enthalpy, entropy and heat capacity data for 3000 compounds, enthalpy and excess entropy for 200 dilute solutions and critical properties and vapour pressure for 600 compounds.

Retrieval programs discussed allow the tabulation or plotting of many bas ic and derived thermodynamic properties for chemical substances or balanced reactions. Examples are given of the use of such data to infer the stability or corrosion resistance of materials and the feasibility, yield and heat release of reactions. A general purpose calculation program discussed allows the equilibrium composition to be found for complex systems with many species of phases, using the method of Gibbs energy minimization. Methods of correction for non-ideal behaviour in these systems are discussed, as well as methods for fixing, maximizing or minimizing any desired property of the system. Examples are given of the simulation of various laboratory experiments and industrial processes by this method. Further programs are described which allow the retrieval of critical properties of substances, the calculation of saturated vapour pressures and the estimation of physical and transport properties of fluids.

V.J.WALL Department of Earth Sciences, Monash University.

NON SULPHIDE ZINC BEARING PHASES AND THE BEHAVIOUR OF ZINC DURING METAMORPHISM

Gahnite, zincian ilmenite and silicates relatively enriched in zinc are common in metamorphosed mineralised terranes.

Around Broken

Hill (N.S.W.), -for example, much of the zinc in mineralised rocks away from the Main Lode is present in gahnite and zincian elmenite.

Assemblages involving these phases are stable only at rather low fs2t gahnite/zincian magnetite also having relatively wide fo2 fields. These phase relations suggest that the above zinc oxides can develop through metamorphic/metasomatic desulfidation of zinc-, iron sulphide precursors.

In fact in pelitic or other relatively aluminous hosts,

sphalerite should be uncommon at higher metamorphic grades.

The occurences of gahnite in veins, in/around pigmatites, retrograde schist zones and other metasomatic environments suggest its deposition from "metamorphic-hydrothermal" solutions.

Calculations of

gahnite solubility in aqueous fluids (200 - 600°C) buffered by mica feldspar - aluminium silicate equilibria indicate that of the order uf ppm Zn (aq.) can precipitate gahnite.

These relations suggest strong

limitations on the mobility of Zn during metamorphism and in oxidised hydrothermal fluids.

& Increases in pH, "Al precipitation of gahnite.

3+ and decreases in T°, EC1 effect the

These relations highlight the importance of

mining of locally equilibrated fluids in development of zincian oxide bearing deposits through metamorphic or other hydrothermal processes.

SESSION n

PHYSICAL AND STRUCTURAL PROCESSES

CONVENOR

Dr.

IN DER3RIWION

C.J.L.

WILSON

WEDNESDAY

2nd

fEERDART

9AM,

2PM

THURSDAY

3rd

FEBRUARY

9AM,

2PM

FRIDAY

4th

FEBRUARY

9AM

LECTURE

IAN A. BELL Department of Physics Monash University

THEATRE

and C.J.L. WILSON School of Earth Sciences. University of Melbourne

GROWTH EFFECTS IN METAMORPHIC BIOTITE

Metamorphic biotites from Cava di Mica (Italian Alps) examined by transmission electron microscopy contain planar defects on the (001) plane, superlattices, twins and a ndcrostructure causing; streaking, of k ^ 3n rows. The fault vectors associated with the planar defects are either R. = + 1/ 3 (010) R = i 1 / 6 ( 3 1 0 ) O P R 3 = " 1 / 6 (3 ^ 0) w i t h resPect t o tne 1M polytype. A stacking fault R^, R 2 or R^ is most likely to exist in the octahedral layer rather than in the potassium cation layer. The result of such a faylt on a unit layer of mica is effectively to rotate it through + 120 about c (this rotation is structurally equivalent to the common mica twin law). Short period mica polytypes (2M1 and 3T) can be described as 1M unit cells stacked with successive + 120° rotations between each cell, therefore the stacking faults R^, R2 and R may be responsible for mica polytypism. Furthermore many of the observed irdcrostructures can be generated by these stacking faults.

T B. BELL and M.J. RUBENACH James Cook University, Townsville

and

J.D. FITZGERALD Department of Earth Sciences Monash University

THE SIGNIFICANCE OF TEXTURES FROM THE ROBERTSON RIVER METAMORFHICS, NORTH QUEENSLAND The Robertson River Metamorphics consist of Proterozoic schist, phyllite quartzite and amphibolite which have suffered five deformation events. Prograde metamorphism accompanied the relatively intense Di and D2 events, and the well-defined chlorite, staurolite, staurolite-andalusrte and sillimanite zones are folded by the less intense D3, Di+ and D 5 events. The mineralogy and zonal sequence in the pelitic rocks is very similar to the Stonehavian sequence from the Scottish Highlands. Textural studies have shown that while many minerals nucleated and grew during both the D-, and D 2 events (e.g. muscovite, biotite, garnet, probably sillimanite), andalusite and staurolite are restricted to syn Do • Staurolite and andalusite porphyroblasts in some rocks have preserved the S 2 crenulation cleavage at an earlier stage in its development than is shown by the surrounding quartz-mica matrix. Samples collected close to isograde indicate quite complex "catalytic reactions" involving all mineral phases present; for example, at the sillimanite isograde staurolite has been replaced by quartz and muscovite, and sillimanite has nucleated in biotite reaction rims surrounding garnet. The overall prograde "reactions"can be deduced from the changes in mineral proportions across the isograde. T.H-. BELL The James Cook University of North Queensland PROGRESSIVE DEFORMATION AND REORIENTATION OF FOLD AXES IN A DUCTILE MYLONITE ZONE: THE W00DR0FFE THRUST

The structural geometry of a mylonite zone (the Woodroffe Thrust) and the country rock in its immediate vicinity is described. Mylonitic_schistosity formed axial plane to folds in country rock foliation and contain a mineral elongation lineation which is constant in orientation. However the fold axes (and associated intersection lineation) spread in orientation throughout the mylonitic schistosity but with a strong maximum parallel to the mineral elongation lineation. It is demonstrated that the fold axes formed initially at approximately 90° to mineral elongation but rotated with increase in strain towards and into it. Where this phenomenon was homogeneous on a macroscopic scale, rotation of large blocks of country rock relative to one another across zones of mylonitization accompanied reorientation of fold axes within the mylonite. The controversy of progressive simple versus progressive pure shear for mylonite zones is discussed in the light of recent fabric and other evidence. It is concluded that the inhomogeneous forms of both progressive pure shear and progressive simple shear played a part and that the former dominated initially but progressively gave way to the latter until brittle rupture with large simple shea* displacements on a zone lubricated by the formation of pseudotachy!ite , brought granulite over anphibolite f a d e s rocks.

R.F. BERRY and A.E. GRADY School of Earth Sciences, The Flinders University of South Australia

DEFORMATION STYLES AND METAMORPHIC CONDITIONS OF THE AILEU FORMATION, NORTH COAST, EAST TIMOR The Aileu Formation has four phases of deformation. The first recognisable phase (D^) is a schistosity (S^) which has only been found parallel to the compositional layering and quartz veining. This schistosity is defined by white mica and chlorite in the lowest grade area but is also associated with biotie, garnet and rare sillimanite in the high grade areas. The mineralogy indicates greenschist to amphibolite facies metamorphism in a medium pressure regime. The second recognisable phase (D2) produced tight to isoclinal folds in "the psammites and psammopelites and a transposition layering in the low grade pelitic rocks. It has an associated biotite schistosity in the higher grade areas. The third recognisable phase (D3) is characterised by mesoscopic chevron folds which are ubiquitous in the pelitic rocks and very common in psammites. These folds are polyclinal on the microscopic and mesoscopic scale. They commonly are associated with a crenulation differention layering and often a pressure solution clearage which, in the greenschist facies phyllites, has a concentration of semiopaque material along the fracture zone. The fourth phase (D4) has not been widely recognised on the microscopic scale. The most common style is angular crenulations. However, structural evidence suggests it has been an important macroscopic event causing open folds with a 5 kilometre wavelength. The earliest recognised phase was most effective in destroying sedimentary structures and imposed a totally new fabric. This was probably due to the higher temperatures and dewatering during prograde metamorphism. The second phase was less effective but despite the lower temperatures (and pressures?) it was still capable of intense transposition of greenschist facies pelites, and tight folds in high grade and quartz rich rocks. With conditions falling below those of the biotite isograd, chevron folds dominate the pelites indicating that interlayer slip has become the pre-^ dominant mechanism for deformation. The association with pressure solution cleavage indicates that stress initiated diffusion is also an active process on the scale of crenulations. The last phase has a completely different mode. Few mesoscopic folds have been produced while large scale open folds cut the area. This phase was associated with fine quartz calcite chlorite veins, perhaps as a response to lower confining pressure. There is no indication of a metamorphic pulse.

74 J.N.BOLAND THE DEVELOPMENT OF MICROSTRUCTURES IN EXPERIMENTALLY

DEFORMED

CARRARA MARBLE

Samples of Cararra Marble were deformed by S.M. Schmid in the Paterson gas apparatus at 3 kbars confining pressure. The experiments were conducted over the temperature range 600 C to 1050 C with strain rates —3 —1 ™~6 —1 varying from s x 10 sec to 5 x 10 sec . At low temperatures profuse twinning dominated the microstructure; with increasing temperature polygonal substructures were observed with a significant reduction in twin formation. At the higher temperatures, recrystallization was observed. The optical microstructures were correlated with the dislocation substructures. The variations in the dislocation density as a function of the deformation conditions will be presented, along with a discussion of the process of dynamic recrystallization. R.E.CHAPMAN University of Queensland

MECHANICS

SUBMARINE

SLIDING

There are great theoretical difficulties in accounting for extensive sliding of large rock masses by gravity without lubrication, even in the subaerial environment, which is mechanically more favourable than the submarine. Ye.7 sliding of large rock masses on very gentle angles of slope has been inferred from marine seismic records from the continental margin. A general expression for the critical angle of slope 0 at which unlubricatec gravitational sliding can take place is tan 0

( o/ e ) +

5 "tan <f>

where T0 is the initial shear strength of the material, a e the effective normal stress when ambient fluid (air or water) at normal hydrostatic pressure occupies the pore spaces, and tan <f> is the coefficient of friction (all at the potential sliding surface). 6, the factor by which the coefficient of friction is multiplied to take pore pressure into account, can be expressed 6

(1 - X) / (1 - X ) e

a /a

where X is the ratio of pore pressure to total overburden pressure, a is the effective stress (the differenceT between total overburden pressure f and the pore pressure), and the suffix e indicates the value of these parameters when the pores are filled with ambient fluid at normal hydrostatic pressure. Application of the first equation to the_ rand Banks and the Ranger slides (by the substitution of measured and estimated quantities for 0, a and <|>) supports previous hypotheses that these slides were triggered by earthquakes (very small values of T and 6): but it also suggests that the sliding surfaces were of silt or sand, rather than a mud that might have acted as a lubricant, because the slides did not apparently travel very far.

PETER COHEN University of Adelaide

DEFORMED LINEATIONS IN THE BARRON RIVER METAMORFHICS The analysis of a number of deformed bedding/slaty cleavage intersections occurring in the Barron River Metamorphics west of Gordonvale (North Queensland) revealed that three mechanisms of folding had been operating: (1) buckling by flexural slip (mainly in micaceous and pelitic layers), (2) buckling by tangential longitudinal strain (in competent pelites, chert horizons, and pre-deformation quartz veins), and (3) flattening of the buckle folds by pure shear. A fourth mechanism, simple shearing, occurred but was more of a secondary effect (failures in the micaceous layers)rather than a primary mechanism for deformation. Ingomogenieties in the folding processes were observed throughout the area, and it appeared that flattening was obviously more heterogeneous than the heterogeniety in the amount of buckling.

GREG CORBETT W.S. £ L.B. Robinson College, Broken Hill

PATTERNS OF INHOMOGENOUS SHEAR DEFORMATION IN MEDIUM GRADE WILLYAMA ROCKS, BROKEN HILL Irihomogenous shear folding is developed in andalusite grade interbedded pelites and psammites adjacent to Yanco Glen Hotel. These rocks are located on the dextral linib of a postulated recumbant macroscopic F1 fold and the sinistral linib of a moderately plunging F2 fold with a wavelength of several kilometers. With the first foliation preserved in the psammitic layers and the overprinting S2 crenulation more obviously developed in the less competent pelites a herring-bone structure may result. Due to the earlier F1 geometry a section of the structure is oriented with bedding at a low angle to the axial plane of the F2 fold thus folding does not develop but in response to a sinistral shear couple the strain is taken up as internal deformation within the layers. The first foliation (SI) acts as a marker indicating the style of the later deformation. When S2 is at a low angle to bedding the dextral SI in the psammite suffers increasing transposition into the S2 orientation moving up through^a graded unit. This results in the SI enveloping surface in each pelite reaching a sinistral vergence with bedding. These rocks may grade^into retrograde shear zones where bedding is rotated, thinned and cometimes obliterated by the S2 schistosity. Elsewhere the bedding plane may act as a kink boundary resulting in a reorientation of SI in the pelitic layers to give a dextral vergence. The S2 crenulation is not well developed here.

76 D.W. DURNEY and R.H. VERNON Macquarie University, N.S.W. 2113

MINERAL CONCENTRATIONS AROUND PORPHYROBLASTS Syn- and pre-deformational porphyroblasts commonly occupy a bowed portion of a schistose matrix. A local variation in bulk composition of the matrix is commonly associated with this bowing of the schistosity. In this study we describe some examples of these compositional variations and discuss the theory of their origin. Model experiments on finite strain and existing theoretical predictions of stress patterns in a deforming medium around a circular rigid object, while consistent with observed schistosity trajectories and the sense of diffusive flux around a porphyroblast, are not capable of describing the losses or gains of mobile components within the matrix. This is because of the condition, used in classical theory of elasticity, that V^cf) = 0 (where ^ is a stress function). A possible analytical solution to this problem has been found, which satisfies the conditions of stress equilibrium and may point the way to further and more realistic solutions. The result is based on the relationship: V 2a -

T = - I3 p ^

cos

20.—~ r2

(p -principal deviatoric stress at infinity, (r,0) = polar coordinates, all stresses taken compressive positive), and implies highest loss in T folialT areas and highest gain in !augenf areas. This provides a useful means of gauging the relative diffusive mobilities of minerals in metamorphic rocks. Described examples showing the behaviour of a known relatively immobile component such as graphite are in broad agreement with this result, although further complicating factors are probably also involved.

J.D. FITZGERALD and Department of Earth Sciences Monash University

T.H. BELL and M.J. RUBENACH The James Cook University

DEFORMATION AND METAMORFHISM IN THE ROBERTSON RIVER METAMORFHICS, GEORGETOWN PROVINCE,NORTH QUEENSLAND

The Robertson River Metamorphics are dominantly pelitic schists in which the metamorphism can be characterized by index minerals lying between well defined isograd and ranging from chlorite through biotite, garnet, staurolite, andalusite to sillimanite.' Since the lithologies vary from quartzites to micaceous and carbonaceous schists to meta-basalt and ipetagabbro, sane interesting contrasts in structural and metamorphic development are preserved. continued f

J.D.Fitzgerald, T.H.Bell and M.J.Rubenach

continued.

The dominant schistosity (S2) is a crenulation cleavage due to the second deformation and it was during this deformation event that most of the metamorphic index minerals grew. Prior to this event there was another now isoclinal deformation which was also a prograde metamorphism. Three post S2 deformations folded the isograd_ and produced crenulations but only rare retrogressive crenulation cleavage. However their geometric effects^are significant and the final event appears to have generated a theoretically possible but rarely, if ever seen, series of small circle lineation distributions.

M.J. GLASSON and RE ID R. KEAYS Department .of Geology, University of Melbourne MOBILIZATION OF GOID DURING DEVELOPMENT OF CLEAVAGE IN LOWER PALAEOZOIC SEDIMENTS FROM THE AURIFEROUS SLATE BELT OF CENTRAL VICTORIA The ^ development of cleavage during the deformation of geosynclinal sediments in the auriferous slate belt of Central Victoria resulted in an average loss of 9 and 10.5 per cent of their silica and sulphur, respectively. The quantities of gold, silver, arsenic, antimony Call determined by neutron activation analysis), copper and zinc released from the sedijnents was controlled by their pyrite contents, the main host foremost of these metals. For example, the average gold content of pyrite concentrates separated from the rocks is 480 ppb Au while the regression coefficient between sulphur and gold in 79 shales, slates, siltstones and greywackes is 0.81. Insufficient quantities of gold were released from the typical Lower Ordovician sediments to account for the gold production of the slate belt. For example, a column of sediments 40 km deep would have been required to have suppliedmthe 42,466 kg of gold produced at Clunes. The required quantities of gold could have been provided by black pyritic slates which have been shown to be strongly enriched in gold had these constituted a much larger proportion of the stratigraphic column than that observed in the field and if they had been subjected to intense deformation. The sediments which host the gold deposits could not have been the source of their gold and, the gold content of the former has nothing to do with the localization of the gold deposits. Exploration for large low-grade disseminated deposits- of the Carlin-type should be concentrated in areas of bedrock which overlie the deformed Lower Palaeozoic sediments.

D.R. GRAY School of Applied Geology, The University of New South Wales, Kensington SOME PARAMETERS WHICH AFFECT THE MORPHOLOGY OF CRENULATION CLEAVAGES The morphology and microstructure of individual crenulation cleavages are dependent on a complex interplay of the physical conditions,the pre-existing fabric and the operative deformation mechanisms. Many of these features and (or) factors are either not readily observable or obtainable from the final cleavage microfabric. However, observable features such as the metamorphic grad$ the microfolding, the pre-existing fabric and the cleavage microstructure provide some information on the parameters which affect differentiation in crenulated rocks. The pre-existing fabric is probably the singlemost important factor affecting the morphology and microstructure of crenulation cleavages. This fabric essentially predetermines the geometry of the associated crenukation folds, the mineralogy of the cleavage and the type of fabric modification associated with the development of the cleavage; certain cleavage types are more common in some rock fabrics than others. The metamorphic grade broadly specifies the pressure-temperature boundary condition (i.e. the field in stress-temperature space) for crenulation deformations. Since crenulation cleavages are most common under greenschist facies conditions or lower this implies temperatures below 450 C and pressures ranging from 2 kb to 10 kb (cf. Turner, 1968, p. 366). The microfolding appears to have little effect on the cleavage morphology, although it does determine the location and spacing of cleavages in crenulated rock fabrics. The cleavage microstructure indirectly provides information on the strain mechanisms responsible for development of the cleavages as finite structures. Observations indicate that solution processes play an important part in crenulation cleavage development. It is apparent therefore that the pre-existing fabric and the operative deformation mechanisms determine the morphology and ndcrostructure of crenulation cleavages. The physical conditions however dictate the nature and rates of the deformation mechanisms.

V. HIRSINGER Western Mining Corporation, Belmont, W.A. THE MATHEMATICAL DESCRIPTION OF OF INHOMOGENEOUS DEFORMATION The features by which the deformation in rocks is appreciated Present information in a variety of forms and to variable deg^es of certainty. To make the best use of structural geological observations a mathematical technique should be used that will respond to input of as many of these forms as is possible. continued.

79 V.Hirsinger

continued

Coordinate transformations are descriptions of a continuum that can be applied to describe deformation. Rock strain features such as deformed layering, lines or planes of no apparent deformation, deformed lineations and local homogeneously1 deformed objects can all be described in terms of the derivatives of a suitable transformation. By choosing a general form of transformation such relationships can be incorporated in numerical solutions of the finite heterogeneous deformation states concerned. For the analysis of plane strain, a multiple Fourier series based transformation provides a reasonably general basis for solution. In this paper the main elements of such a transformation are defined. The solutions of elements of the transformation for two similar fold models is described, as is the solution of more general deformations using deformed lineations. The possibility of solutions incorporating strain assumptions are also discussed. R.J. HOLCOMBE and E.H. LOHE University of Queensland STRUCTURE AND TECTONIC HISTORY OF THE BRISBANE METAMORPHICS IN THE BRISBANE AREA Palaeozoic basement rocks in the Brisbane area consist of two major units. The strongly deformed Bunya phyllite ("Brisbane Schists") have been considered to form the core of a major anticlinal structure (Denmead,1928) and to be separated from the surrounding fTundeformedn Neranleigh-Fernvale Group by high angle normal faults. Results of recent work indicate: 1. The prominent layering in the Neranleigh-Fernvale everywhere is a first generation, transposed bedding foliation. 2. The dominant layering in the Bunya phyllite is a second generation transposed layering accentuated by metamorphic differentiation. Slaty cleavage rather than a crenulation cleavage commonly parallels this layering. 3. The major anticlinal structure does not exist as postulated. The apparent antiform is formed, in part, by the different orientations of the two dominant layerings in the area outlining the west "limb" and "crest". A major third generation flexure forms the east "limb". 4. The first three generations of folds have sub-parallel fold axes and have formed during a single progressive deformation. 5. Large, gentle kinks overprint the earlier structures. 6. The eastern boundary of the Bunya phyllites is a major, low angle (20-40°) normal fault with a possible threw of 2-3 kms. 7

The Bunya phyllite is considered to be a unit of unknown thickness at an unknown stratigraphic position within the normal NeranleighFernvale sequence.

R.J. HOLCOMBE University of Queensland

and

K.L. WILLIAMS University of Sydney

DEFORMATION AND RECOVERY FEATURES IN A NATURALLY FOLDED ILMENITE CRYSTAL

A single tightly folded crystal of ilmenite has been found in drill core from Ducktown, Tennessee. The crystal has been bent to form a full fold with a wavelength of 0.5 cms and an amplitude of 0.6 cms. The grain contains many deformation features but, except for a few small areas of recrystallization, it is in optical continuity throughout. Prominent deformation features are: the fold itself; a parting parallel to {0001} (?); microboudinage; and intense {10T1} twinning on the limb areas. A total shortening of at least 30% is indicated across the grain. Optically observed recovery features are: subgrain boundaries normal to {0001} in the hinge areas and parallel to {0001} in the limbs; and small areas of recrystallization on the inner arcs of the hinges and at several other points of high local strain. The geometrical relationship between the observed deformation and recovery, features indicates that these processes were occurring simultaneously. Electron microprobe analyses indicate no statistically significant composition variations around the structure. Microhardness indentation tests around the fold give values covering the entire range of published Vickers hardness units for ilmenite. The limb areas are significantly harder than the hinge areas and this is interpreted to be related to work hardening associated with deformation twinning. K.R.S.S. KEKULAWALA Research School of Earth Sciences, A.N.U. Canberra, A.C.T. 2600 EXPERIMENTAL STUDIES ON THE HYDROLYTIC WEAKENING OF QUARTZ CRYSTALS

The emphasis in the experimental study of hydrolytic weakening in quartz has been brought back to natural crystals. However under conditions up to 3 kbar pressure and 1000°C in a gas apparatus, attempts to bring about hydrolytic weakening by introducing water into clear Brazilian type quartz or by taking up precipitated water in cloudy quartz have so far failed. On the other hand, two new observations are pertinent. First, Twet1 synthetic quartz which is weak when tested at 3 kbar and 800°C is stronger under the same conditions after heating for a few hours at 900°C at atmospheric pressure; the hardening is thought to be due to the precipitation of water otherwise available as OH for facilitating dislocation glide. Second, amethyst is similar to wet synthetic quartz in its stress strain behaviour as well as in its OH infrared absorption spectrum. The hydrolitic weakening mechanism is not yet clear; however the effective part of the OH may be associated with growth defects and so be dependent on the original conditions of growth.

R. KHAIAKE School of Earth Sciences, Macquarie University

ANALYSIS OF PRESSURE-SOLUTION DEFORMATION IN COLITIC LIMESTONES Ooliths have for long been recognized as excellent strain markers and often are used for analysis of ductile deformation in lijiiestones; however, not much work has been done on analysis of pressure-solution (P-S). In this work the problems involved in measuring pressure-solution strain, especially in weakly deformed rocks, and a comparison of some of the results with those of ductile deformation are described. The analysis of P-S strain is based on measurements of the shortening of the line that joins the centres of two ooliths and passes through their P-S contact. The orientation of this line is not generally the true direction of pressure-solution but it depends on the relative positions of the two centres. The value of P-S strain at each P-S contact is plotted linearly against itsrespectiveorientation. Such a plot usually shows a direction of statistical maximum P-S, and at 90° to this either a minimum (i.e. no apparent strain), or an elongation (growth, e.g. pressureshadows), or a second phase of P-S. Initally it was assumed that ooliths were originally in contact. The validity of this assumption depends on the packing of the grains, and it is very rare to see a section of an undeformed specimen in which all the grains are in contact. The strain absorbed by the ooliths in travelling towards each other should be taken into account, and this has been done by means of a numerical constant based on the standard deviation which is incoporated in a newly designed statistical procedure that calculated the absolute principle P-S strains and their orientation. The pressure-solution strain ellipsoid obtained by this analysis, compared to that of the ductile mechanical deformation for the same sample, can cometimes be used to indicate whether or not the two deformations are genetically related. The P-S strain ellipsoids range from completely flattened to higher up in the flattening field and strain ellipsoids of ductile deformation range from completely flattened to completely constrictional.

D.H. MAINPRICE Research School of Earth Sciences, Australian National University

E.H. BUTTER and B.K. ATKINSON Imperial College, London, .U.K.

THE APPLICATION OF STRESS RELAXATION TESTING TO THE STUDY OF DEFORMATION IN GEOLOGICAL MATERIALS A discussion of the machine dependent aspects of the stress relaxation test are given. A model of machine-specimen behaviour during relaxation is presented. The application of stress relaxation to the determination of parameters vdiich describe operative deformation mechanisms is presented in two sections (A) dislocation dynamics and (B) constitutive flow laws. In a dislocation dynamics analysis an assumed form of the velocity-stress relationship (e,g, Johnston-Gilman Equation) allows the thermal and athermal components of stress to be separated. In a flow study the form of the experimental law (exponential, power or linear) relating strain rate and stress, and activation parameters (Activation enthalpy and volume) can be determined. Examples of dislocation dynamics, flew law determination and brittle behaviour studies using stress relaxation to determine the parameters of the deformation processes are presented from experiments on calcite, galena and quartz, single and polycrystals.

DR. B. MARSHALL Department of Applied Geology, N.S.W.I.T.

CONCERNING

KINK

BANDS

Based on data pertinent to kirik bands caused in recent tuffs by the impact of volcanic bombs, the mechanism (s) by which kink bands form is (are) discussed in relation to recent literature. The inevitable formation of kink bands in foliated rocks is examined as a function of stress reorientation and decay. One mode of formation of kirik bands is discussed relative to the frequent development of intrafolial folds on sites of mechanical in homogeneity.

DR. B.W. NISBET Amoco Minerals, Bredbo 2694, New Soith Wales

SIGNIFICANCE OF TRANSPOSITION IN THE CHESTER DOME AREA EAST-CENTRAL VERMONT In a sequence of garnet-grade gneisses, schists and amphobolites from Keyes Mountain, Vermont, folds can be classified broadly into two groups : (1) Tight to isoclinal early folds with axial surfaces ( S t ^ ) d^PP^g shallowly to the north. These folds usually possess a strong axialsurface schistosity. (2) Open, late folds with axial surfaces dipping steeply to the east or west but with no axial-surface foliation. A zone some 150m thick has been recognized in these rocks in which most early folds are isoclinal, schistosity is relatively strongly developed and all layering has been transposed into parallelism with S]__2- I"ts boundaries are not discrete but are apparently also parallel to S]_2- This zone is interpreted as a region of high strain across which large relative motions may have occurred. Similar bodies has been found in other parts of the region and in all cases their boundaries are parallel to or coincident with what has previously been mapped as stratigraphic contacts. It is conjectured that more such T tectonic1 discontinuities are present in the Eastern Vermont Sequence and that extensive revision of the presently accepted stratigraphic relationships is necessary.

C.McA. POWELL and R.H. VERNON School of Earth Sciences, Macquarie University, North Ryde N.S.W. 2113

GROWTH AND DEFORMATIONAL HISTORY OF GARNET PORPHYROBLASTS WITH INCLUSION SPIRALS IN A KARAKORAM SCHIST Porphyroblasts of garnet in a graphitic mica schist show quartz spirals and intersecting graphitic Si spirals, the geometrical relationships of which are similar to observations of Schoneveld (1977) made on simulated porphyroblasts incorporating inclusions of aligned matrix grains (to form Si) and inclusions from quartz "pressure-shadows1^ while rotating relative to the matrix. Superimposed on rotational trails are crystallographically controlled growth zones. An interpretation in terms of relative rates of growth and rotation of the porphyroblasts is attempted, and metamorphic aspects of "pressure-shadow" mineral assemblages are discussed.

GRAHAM P. PRICE Research Scientist, Division of Applied Geomechanics,CSIRO, Mt. Waverley

THE ANALYSIS OF MINERAL FABRICS BY THE PHOTOMETRIC METHOD A method is described whereby limited observations of the optical properties of an aggregate of mineral grains in a single thin section are transformed into a pole figure representing the three-dimensional crystallographic orientation fabric pattern for the aggregate. The method is based on the variations in interference colours exhibited by thin slices of anisotropic mineral grains when rotated beneath a second fixed anisotropic plate (gypsum plate) and between fixed crossed polars. Interference colour variations are recorded as percentage transmission curves using monochromatic filters and a photometer. Theoretical percentage transmission curves are calculated for a single crystal in any three-dimensional orientation and these are used to convert the observed percentage transmission curves from five non-orthogonal planes into a pole figure. Presented are comparisons between fabric patterns measured on a universal stage and those calculated by this photometric method. The method is suitable for the complete analysis of c-axis fabrics for uniaxial minerals such as quartz, calcite and ice for basal plane fabrics of biaxial minerals such as biotite and kaolinite. Results for most biaxial minerals can, be less exact. The advantages of the method for analysing fabric variations are outlined.

D.B. SEYMOUR Geology Department, University of Tasmania, Hobart Tasmania 7001

SEDIMENTARY FABRICS AND STRAIN ANALYSIS METHODS The strain analysis methods of Matthews, Bond and van den Berg (1974) and Dunnet and Siddans (1971) are critically examined to determine the magnitudes of errors in the strain determinations which may arise if assumptions concerning the unstrained state of the analysed fabric do not hold. Data taken from sections of several actual unstrained sedimentary lithologies with fabrics ranging from slightly to strongly asymmetric (imbricate) with respect to bedding, were mathematically 'strained' by known amounts and the resulting data used as test input for the strain analysis methods. This technique has shewn that very large errors in the strain determination may occur if strained material which had a strongly imbricate fabric in the unstrained state is used with the assumption that its original fabric was bedding-symmetric. Lapilli tuffs are indicated as the best lithologies to use with these methods, although even slight asymmetry in their original fabrics may cause considerable errors in the strain determination at certain cleavage-bedding angles.

85 J. SHORE Research School of Earth Sciences, Australian National University, Canberra

THE EXPERIMENTAL EXTRUSION OF YULE MARBLE A griggs hot creep apparatus has been modified in order to hydrostatically extrude a cylindrical rock specimen. The specimen attains a maximum extensional strain of 2.6 as it passes through a tapered ceramic die. The preferred orientation generated in the deformed material can be related to strain rate and magnitude which are known at any position within the die. Barrelling, buckling and necking instabilities which conmonly occur in conventional compression and extension experiments are avoided in extrusion because of the rigid boundary conditions of the deformation. The apparatus employs coaxial pistons to generate the required experimental pressures. The inner piston compresses the NaCl pressure medium within an inner chamber to develop the hydrostatic extrusion pressure. The annular ram applies pressure in a surrounding area to resist the extrusion. Approximately 13 kb of extrusion pressure can be produced to oppose a maximum of 8 kb resistive pressure, g Strain rates of constant stress experiments vary from 10 to 10 /sec depending on thg differential stress and temperature. Temperatures in excess of 1000 C can be maintained by a graphic furnace placed around the die. A calibration experiment has related the output of the thermocouple in the die assembly to the radial and Longitudinal-temperature gradients about the specimens. Transducers and electronic servos record and control the temperature, pressures and inner piston displacement and allow constant stress or displacement experiments to be performed. Several textural regions .are observed in the extruded marble specimens. All extruded specimens have an upper undeformed region gradationalQinto an extensional area in the die taper. In experiments above 700 C, small syntectonically recrystallized grains • occupy thin zones along the die-specimen boundary. The center of the die hole contains strongly deformed original grains which have an elongation parallel to the specimen axis. Recrystallized grains present along the grain . t boundaries and twin lamellae of the elongated grains might have formed by an annealing process. These grains are less abundant at extrusions performed over 800°C and are very evident in 500 C experiments. Q Optically unresolvable material present at the die taper surface in one 500 C experiment may indicate mylonitization of the marble in this region. . X-ray fabric work reveals an extension fabric in the center of the die taper region and techniques are being employed to determine the preferred orientation at the die boundaries.

J.E. TIBRALLS

and

A.C. McLAKEN

Monash University

STRUCTURE AND TEXTURES IN MICROCLINE

In electron microscope studies of low-temperature, potassium-rich feldspars we have observed textures \*hich suggest that exsolution of albite stabilizes microscopic twinning in the microcline phase. Observations of exsolution and twinning textures in amazonites from Norway (Or75_g5) # and microclines from various localities will be reported and the mechanism by which albite - and pericline-twinned domains are stabilized will be discussed. IDE VAN OFR MOLEN Research School of Earth Sciences, A.N.U. Canberra

DEFORMATION OF A PARTIALLY MOLTEN ROCK The rheological properties of a system undergoing anatexis are changed considerably in comparison with the unmolten state by the development of a meltphase. Undrained triaxial experiments on partially molten Delegate Aplite are described. After the first hour the amount of melt formed at 800°C and 3 kb confining pressure does not change considerably for several hours; this amount depends mainly on the quantity of water that can be accommodated within the porespace in the rock. Thus by varying the quantity of water added to the specimen, the meltvolume can be controlled for the duration of a rheological experiment. Dry runs yield no detectable melt, runs with H2O yield about 5vol.% melt whereas runs with ^w.% H2O give about 10vol.% melt provided the porevolume is made large enough by straining the sample. After 100 min. heat treatment at 3 kb and 800°C, constant strainrate experiments (e =10" 3 to 10"7) were performed on runs with 0,^ and ^w.% H20 added. It is argued that at the strainrates and_^eltpercentages considered, partially molten granitic systems behave very much like granular aggregates such as studied in soil mechanics. When stress is applied melt is squirted out of grain boundaries normal to the highest compressive stress into grain boundaries and extension fractures parallel to the highest compressive stress until macroscopic failure occurs. An unjacketed dry run failed at 0.6 kb differential stress and 1.2% axial shortening. Jacketed dry run-.fail at 2.5 - 2.7 kb and 2.5 - 3.5% strain. The stress at which macroscopic failure occurs drops considerably when melt is present. At %w.% water failure occurs at 1.0 - 1.7 kb and 2.5-4% strain. At ^w.% water as much as 8% cataclastic flow occurs before failure at 0.5 - 1.0 kb. Thus far no consistent relationship between strainrate and failurestress or failure strain can be demonstrated.

R.H. VERNON M a c q u a m e University

and

B.E. HOBBS Monash University

"NATURAL RECOVERY AND RECRYSTALLIZATION OF CALCITE IN SOME DEFORMED MARBLES" Deformed marbles, principally from the Mr. Lofty Ranges, South Australia, have ^microstructures characterized by deformed relics of calcite in a matrix rich in relatively fine-grained, recrystallized calcite, with minor quartz and diopside. The deformed calcite relics contain numerous subgrains, and show abundant evidence of strain-induced migration of twin and grain boundaries. New grains have nucleated and grown preferentially along twins (and especially at twin intersections), at grain boundaries, and apparently randomly inside deformed relics. Probable mechanisms for recrystallization include bulge nucleation and subgrain nucleation. The paper will be concerned with the bearing of optical and transmission electron microscopy on the mechanisms involved in the syntectonic recovery and recrystallization of the calcite.

J.C. WILKTE Monash University Department of Earth Sciences,

DEFORMATION MECHANISMS IN A SUITE OF QUARTZITES FROM CENTRAL AUSTRALIA

Three deformed quartzites have been examined in an electron microscope. The • rocks come from isoclinal folds adjacent to a thrust zone and show increasing strain in the flattening field. There is a progressive change in the shape and intensity of the c -axis fabric with the increasing deformation. The dislocation substructures have been examined in a number of grains from each of the samples. In all cases the density of dislocations is low and there are numerous networks and subgrain boundaries. The lack of work hardening in these rocks indicates that there has been syntectonic recovery. The motion of the dislocations within the grains will be discussed in terms of how it can bring about: the preferred orientation of the c-axes.

R.W.T. WILKINS and CSIRO Division of Mineralogy, North Ryde

J. BARKAS Dept. of Geology £ Geophysics, University of Sydney

FLUID INCLUSIONS, DEFORMATION AND RECRYSTALLIZATION IN QUARTZ-BEARING TECTONITES In moderately deformed quartz-bearing tectonites, small (<10 ym) fluid inclusions are commonly associated with boundaries of deformation bands and lamellae. During syntectonic recrystallization such inclusions are almost entirely eliminated. The sweeping of solid, liquid and gaseous inclusions by migrating grain boundaries is well documented in the metallurgical literature and no doubt the process also occurs during the recrystallization of oxides and silicates. However, as syntectonic recrystallization of quartz appears to proceed by growth of suitably oriented subgrains, it is also necessary to explain hew fluid inclusions are eliminated from the cores of developing grains. It is commonly observed that, immediately in advance of a recrystallization front, stringers of inclusions develop along subgrain boundaries. We propose that voids develop along subgrain boundaries by a process similar to grain boundary sliding, and fluid diffuses from the fluid inclusions in the interior of the subgrains to the subgrain boundary region through the arrays of dislocations which accompany grain interior slip. The new fluid inclusions which accumulate in the subgrain boundary region eventually coa-' lesce into stringers. The intimate association of fluid inclusions with deformation and recrystallization features in quartz-bearing tectonites raises the question of whether the inclusions play an active or passive role in these processes.

89 C.J. L. WILSON Earth Sciences, University of Melbourne MICROSTRUCTURE, COMPOSITION AND DIFFUSIVE PROCESSES DURING DEFORMATION OF MICA Within an Alpine shear zone progressive foliation development from a massive pegmatite results in a feldspar-quartz-mica layering at Cava di Mica, Italian Alps. As a result of deformation numerous microstructural changes are recognised in the large old pegmatite muscovite and in loliths of coarse biotite. Old micas are passively rotated during strain to develop a strong preferred orientation. This is accompanied by bending, kinking, dissolution and grain boundary sliding; the physical behaviour of the muscovite differs from that of the biotites. Accompanying foliation development is the nucleation and growth of small new metamorphic muscovites and biotites that process strong preferred orientations. The old muscovite micas are phengitic with the new metamorphic muscovites differing little in composition although some are still more phengitic. Chemical composition of the biotites fall into 4 different fields with no significant variation between old deformed grains and new metamorphic biotites. Uranium distributions have been used to identify sites for water assisted diffusive processes of combined diffusion and infiltration. These are predominantly in intergranular regions particularly grain boundaries, kink zones and fractures. Some intragranular diffusion has been recorded in the more deformed micas and can be attributed to diffusion in the potassium inter layer region in the mica structure. The relative misorientation of mica grains with respect to one another also appears to have influenced the diffusivity.

SESSION 12 - ENVIRONMENTAL GEOLOGY CONVENOR

FRIDAY

4th

LECTURE

Dr. E.B. JOYCE FEBRUARY THEATRE

2PM R 5

POSTER SESSION CONVENOR WEDNESDAY LECTURE

Dr. J. PETERSON 2nd

FEBRUARY

9AM

CONCOURSE

A. BARTHOLOMAI Queensland Museum, Fortitude Valley, Queensland

GEOLOGICAL CONSERVATION IN QUEENSLAND

Conservation of geological features is a relatively new concept in Queensland and is only now beginning to be accepted. Although in earlier years certain features such as the intrusive plugs of the Glasshouse Mountains were set aside as National Parks, this was done mainly on scenic criteria, and various proposals for the protection of important teaching sites around Brisbane met with little response from the relevant authorities. More recently the Queensland Division of the Geological Society of Australia has attempted to publicize the concept by compiling a list of features throughout the State considered worthy of preservation, both large areas mainly of scenic and tourist value (Category A feature) and smaller scientific features of interest to the profession and students (Category B). In early 1976 a Commonwealth Government grant enabled the Society to employ a geologist to document most Category A features and to make proposals for their reservation as National or Environmental Parks. Protection of Category B features is considered to need new government legislation, and documentation of these features is postponed for the present. However a draft of possible legislation has been forwarded to the Queensland Government for consideration. An awakening of interest in preservation of geological features is sensed in the relevant State Government Departments and Local Authorities and it is hoped the first features will be gazetted as Parks or reserves in the next few years.

C.D. BRANCH Department of Mines, South Australia

GEOLOGICAL CONSERVATION IN AUSTRALIA - THE FEDERAL LEVEL

In 1974 the Geological Society of Australia Inc. established the Federal Committee for the Preservation of Geological Monuments in order to co-ordinate the activities of the Divisional Geological Monuments Sub-committees, and to liase with the Federal Government on matters such as the National Estate. Various criteria exist to identify geological monuments but the overriding objective is to preserve the minimum number of sites to represent adequately the geology and physiography of each State or Territory. Federal Government grants from the National Estate were awarded late in 1975 to the Queensland and South Australian Divisions which has allowed the selection, investigation, and documentation of geological monuments to begin in these States. No Federal Grants were made in 1976. However, in this year the Australian Heritage Committee was established by the Federal Government and a call made for nominations for places to be included in the Register of the National Estate. An implication in current literature is that future grants will be given only for the investigation of places on the Register. It is to be hoped that in practice grants will be divided between the investigation of places which may be proposed for the Register, and those already on it.

W.M.B. CARR Monash University

LAND SYSTEMS AND EXTRACTIVE INDUSTRIES IN VICTORIA

As a basis for regional land use planning, the Victorian Soil Conservation Authority has divided the state into land systems defined by climate, geology, altitude and landforms. These are subdivided into land components which can be mapped at a scale of 1:20,000. A system has been developed to assess the ability of the land components to support the production of concrete aggregate, road materials and topsoil. It is adapted from the limitations approach used by the United States Soil Conservation Authority for assessing the engineering uses of soils. The system also includes an estimation of the required erosion control measures which is based on the Universal Soil Loss Equation.

D.T. CURREY 61 Sylvander Street, North Balwyn BARMAH-MILLEWA FOREST AND THE RIVER MURRAY LAND FORMS AND THE ENVIRONMENT Forestry interests have been concerned that regulation of River Murray flows, leading to a reduction in natural flooding of the Barmah-Millewa forest in the Spring months and an increase in Summer flows inhibiting natural drainage, may detrimentally affect the forest. Water Supply authorities have been concerned also to overcome the problem posed by the "choke" in river capacity as it passed through the Barmah-Millewa forest area, and have undertaken investigations of possible supplementary by-pass routes around the choke. A geomorphic study included in the investigation has revealed that an old lake system traversed by the river between Picnic Point and Echuca has been a dominant influence in development of the present river profile and has provided the seasonally flood-prone environment in which the forest community has evolved. Topography, broadly identified by geomorphological studies, indicates that the opportunities for by-passing are better to the north side, around the forest area, than in the south within the forest area. E.R. DaLITZ, J.A. Peterson Honorary Secretary, Natural Disaster Action Committee Department of Geography, Monash University "YARRAVILLE SINKING VILLAGE:" A CASE FOR UPGRADING THE REQUIREMENTS FOR ENVIRONMENTAL AND GEQTECHNICAL SURVEY BEFORE RESIDENTIAL DEVELOPMENT ON FILLED LAND. A test drill to a depth of 457mm in nature! ground on the edge of a filled quarry site bounded by Williams town Road, Anderson Street and High Street, Yarraville, City of Footscray, was apparently sufficient geotechnical survey for issue of building permits to a developer for construction of 40 villa units (September 1970 - December 1971) on this site. The site was once a quarry and has been private land for 35 years at least During 1938 - 1946 the quarry was filled with carbonate lime (sugar sludge) and, before being sold to the developer, was used as a transport~depot. Heavy rains in February 1972 and February 1973 initiated serious subsidence which, aided by water and sewerage from broken plumbing, has continued, and all units have had to be condemned. The 'Yarraville Sinking Village," as it is now called, has attracted wide publicity and representation to Local and State Government Authorities by residents and citizen action groups (e.g. the Natural Disaster Action Committee) has now resulted in compensation being paid from insurance and public funds to the owners of the villa units. The liability for the laroe sum involved (about $28,000 for each unit) is at present subject to litigation. continued

E,R,DaLtTZ and J.A.PETERSON

continued.

Since October 1974 owners of new homes in Victoria have been protected by the House-builders Liability Act. Because of this builders are r.ow more likely to seek geotechnical surveys before building, and Local Government Councils (depending cn the outcome of the above mentioned litigation) may be more inclined to insist on closer supervision of these surveys. Such measures must add to building costs, and so far do not seem to have made provision for the accumulation of geotechnical information for future reference. Two further safe-guards are suggested. While the value of urban land increases> greater and greater geotechnical demands will be made on the<e areas. An amendment to the Local Government Act could be made to reouire all geotechnical information gathered to appear on M.M.B.W. Encumbrance Certificates. Ultimately this information could appear or. Certificates of Secondly, the subsidence at Yarraville might: easily have been avoided if archival maps and air photographs of the area had been consulted. Whether these archives should be keDt bv Local or State Government A"+^r->'+ios *hr>u"id be debated Before such archival material is destroyed

D.C. GREEN . . ^n . . e. . . Department of Geology and Mineralogy, University of Queensland, St. Lucia

STABLE ISOTOPES (D/H AND 0 1 8 / o 1 6 ) IN HYDROLOGY

A review is given of the application of stable isotope studies in various parts of the water cycle in the hydrosphere and lithosphere. Examples of geothermal and hydrothermal systems, the effects of evaporation and isotopic labelling are provided.

E.B. JOYCE Department of Geology, University of Melbourne GEOLOGICAL CONSERVATION IN VICTORIA About one-tenth of the area of the state of Victoria has now been recorded for geological conservation purposes. This work has been carried over about four years by a group which at present consists of six members. The areas so far covered are probably those with the greatest conservation problems as they surround the main population centres. However, they are probably also the best-known and most accessible areas in Victoria. To complete the survey of the state by this present method might take about another fifteen or twenty years. continued

94 E.B.Joyce, continued. Related work is to some extent being carried out in Victoria by other groups and organizations. Geologists of the Geological Survey of Victoria, including one of the Sub-committee members, are now working on geological aspects of Land Conservation Council reports. The Town and Country Planning Board also prepares regional accounts of areas in Victoria, and the Sub-committee has contributed to these reports, the most recent project being the listing and classification of geological features in the Campaspe-Loddon Region. It is obvious however that a complete survey of geological conservation sites in Victoria will need the full-time work of a geologist for a period of at least several months. Support will be needed from an organization such as the Heritage Commission, and the funds given to Queensland and South Australia in 1976 are an indication of what is now needed in Victoria.

E.B. JOYCE Department of Geology, University of Melbourne

GEOLOGICAL CONSERVATION

AUSTRALIA

The publication of the "Report of the National Estate" in 1974 helped to bring geological conservation to public attention, as the report featured a number of extracts from submissions made by the Federal Committee and the State Divisional Sub-committees on conservation of the Geological Society of Australia Incorporated. More recently grants by the Heritage Commission to the Divisions of South Australia and Queensland have enabled these states to appoint graduate geologists to work full-time for a period on the identification and documentation of geological features. In this symposium reports will be presented on the work in these two states, and the Federal convener will report on the general state of geological conservation in Australia. Short reports by the other states will lead into a general seminar on the future of geological conservation, including discussion of identification and documentation work still needed in the various states, techniques of classification, the definition of a "geological monument", legislation needed, protection of classified sites, and future cooperation with the Heritage Commission.

95 E. MAUD McBRIAR Geology Department, University of Adelaide GEOLOGICAL CONSERVATION IN SOUTH AUSTRALIA S

to r n n w « p n I n ! i a only four reserves have been created specifically o r o W t Z Z ? , 0 ? 1 J a V t e m s b u t m a n y ^ h e r reservations effectively 09lcal f ® a S u r e s a n d a review is being made to determine lllt.l 2«!l n d6d np« a L m !- : Geologists have a long record of watchfulZ l L t J P a l p a t i o n m this matter. Lake Callabonna Fossil Reserve protecting vertebrate remains of late Pleistocene age was proclaimed as early as 1901. Ediacara Fossil Reserve covering the type area of the famous Precambrian fauna was established in 1958. These are both located in remote parts of the State and the main problem for both has always been the policing of regulations applying to them. Perhaps the reserve which has received most publicity is that recently dedicated at Hallett Cove, the site of renowned Permian glacial features. Attempts to obtain there, in an area zoned for housing, a reserve of adequate size has taken twenty years and taught geologists many lessons about the law, planning, tactics, allies P.G.MACUMBER

HYDR0L0GICAL EQUILIBRIA AND THE ENVIRONMENT IN THE SOUTHERN MURRAY BASIN OF S.E. AUSTRALIA Recent work in the southern Riverine Plains indicates that a delicate hydro!ogical balance exists between the surface and groundwater flow regimes developed in the Loddon, Campaspe and Goulburn valleys. For instance the advent of large scale irrigation in the lower Loddon Valley in the late 1880 1 s caused a rapid rise in the regional water table leading to widespread salinization of the irrigation district. Recent work shows that the Lower Loddon Valley is a groundwater discharge zone existing at the down stream end of a regional groundwater flow system. In such an area water which enters the ground cannot overcome the upward potential gradient and will be subject to evapotranspiration in the vicinity of its entry point. The problems inherent in large scale flood irrigation in discharge zones include water logging and soil salinization leading to the destruction of deep rooted vegetation previously helping suppress the water table. The aerial extent of the discharge zone on the plains has been shown to respond rapidly to pressure changes in the deeply buried aquifers. Water logging problems and high salinities are not restricted to the Loddon Plains. The wet years 1973-75 saw a major loss of fruit trees in the Goulburn-Campaspe irrigation districts. Information from deepi piezometer system suggests that a gradual pressure rise of from t 0 ^ metre per year is occurring in the deep aquifers. If this rate continues these systems will become flowing artesian aquifers within 30 to 40 years. This would convert the eastern irrigation areas into regional groundwater discharge areas as is now the case for the Loddon Plains. A major loss in productivity and crop flexibility would inevitably result.

DOUGLAS c . MCDONALD

3 Myall Ave., Wahroonga, N.S.W. SULPHIDE SWAMPLANDS AND THE IMPLICATIONS OF IMPOSED DRAINAGE

Deposition of sulphides in estuarine swamps requires a good supply of sulphate and anaerobic conditions. Iron and other heavy metal ions are required to precipitate the sulphide which accumulates to appreciable quantities. Sulphide concentrations equivalent to 8% pyrite have been measured in swamp soils in N.S.W. Types of drainage imposed on these areas are: (1) Tide gates limiting entry of brackish water (2) Upstream dams limiting flow of fresh water (3) Indirect drainage associated with gravity flow pipelines (4) Natural drainage caused by burrowing. All of these drainage forms can be accompanied by a change in the water table level, providing aerobic conditions suitable for oxidation of sulphide mineralisation; the typical half equation for the oxidation of pyrite in these conditions being -2FeS2 + 19H20

aerated environment

34H+ 4HS0~ + Fe 2 0 3 + 30e

The increased acidity in the sediment will tend to leach calcium and magnesium from clay plates causing change in double layer potentials sufficient to disperse flocculated clays. The action of tide gates limiting salt water entry and thus reducing cation concentrations of clay double layers in the sediments also aids dispersal of clay floes. Clay floe dispersal and breakdown of any carbonate cements in the sediment together with oxidation of organic matter, makes the area more susceptible to erosion and subsidence. Drained areas of sulphide rich sediment have been found devoid of vegetation as a result of high acidity. Corrosion in iron and steel pipelines, while initiated by sulphide minerals in this type of environment, is supported by the high acidity of these drained sediments. Visual pollution in rivers and lakes fed by such sulphide rich areas is caused by oxidation of iron rich solutions. The brown precipitate of iron hydroxides, in one particular example cements sand and clay plates forming a film and foam that drifts afloat in tidal waters.

SESSION 13 - EDUCATION IN GEOLOGY CONVENOR

Dr. R. PLAYER

THURSDAY

3rd

FEBRUARY

LECTURE THURSDAY LECTURE

THEATRE 3rd

R 5

FEBRUARY

THEATRE

9 A M

2 P M

R 7

D.F. BRANAGAN Department of Geology & Geophysics, University of Sydney THE TERTIARY SITUATION IN AUSTRALIA The last few years have provided a breathing space for many geology teachers in tertiary institutions. Class numbers (particularly first year) have diminished considerably, in some places nearly to vanishing point. We seem to be at the beginning of an upswing in class sizes and perhaps some restriction is called for in the numbers being trained as professional geologists (as is effective in Brazil). While entrance to the professional geology ranks should be tight, there is an urgent need for more and better 'cultural' courses in geology for artsoriented students (?our future decision-makers) who are woefully ignorant of the methods of science and of the practical value of geology to the community. The absence of such 'popular' courses in geology contrasts with the welter of post-graduate diploma courses on every topic from mining investment to underground water which are offered by almost every university and C.A.E. Such courses certainly serve a useful purpose, particularly as refreshers for those who have been away from study for a few years, or who are changing the direction of their work. It will be a pity if such courses become an excuse for students to stay on at College for an additional year. Do the numbers taking these courses justify the energy which is expended on them by academics ? I suspect not. However tertiary administrators value such courses more highly than they do undergraduate courses, and departments are able to justify their own existence with a few such courses on paper and one or two students enrolled. There is at present little movement of students to different institutions for post-graduate work. Likewise there is little interchange of staff between academic institutions on a temporary basis, or between colleges and industry. These matters seem worth pursuing. We probably also need to accept that certain high level courses and research should only be handled by one or two institutions. The present restrictive financial climate might actually prove beneficial by causing such restrictive measures as a matter of course. The geological profession in Australia has so far shown little interest in developing clear educational aims (and even methods). Such aims need to be incorporated in a considered national geological sciences policy.

98 R.S.M. FARDON B.H.P. TERTIARY EDUCATION FOR MINERAL EXPLORATION

B.H.P. wants good field geologists well-trained in petrology, structural geology and stratigraphy, preferably through field courses. They need one course in the geophysical properties of rocks and minerals, and one in geophysics. Geophysicists should do at least two years of geology - they should be excellent geologists through geophysical means. We want self confident people, keen observers of data, but also keen to assess, judge, make decisions, write clear reports and argue well. But they must also second-guess their own conclusions. They judge by what they see, rather than by what they have learnt, are open, tolerant and good co-operators. Knowledge of computers, statistics, X-rays, mineral economics are useful optional extras to the above.

MARK LEARMONTH Koonung High School, Victoria SECONDARY EARTH SCIENCE - THE SITUATION TODAY In the examination of the secondary situation in Earth Science today it is important to decide exactly those areas to be included within this subject. Commonly four areas are included, viz: (a)

traditional geology

(b)

environmental geology

(c)

landform development

(d)

meteorology, oceanography and astronomy.

In Australia, the availability of materials and individual state education requirements seem to govern the quantity and nature of Earth Science taught in secondary schools. The secondary school is usually subdivided into junior (grades 7-10) and senior (grades 11-12) sections and this is a useful subdivision from which to view the present status of this subject. In the junior school, in Victoria at least, there has been a reasonable supply of traditional materials and ideas for students' activities to be treated within a general science course (usually a compulsory subject). This supply must be continued and enlarged, both in variety and quantity. The senior school, on the other hand, has been scarcely supplied in Victoria both in terms of teaching materials and teachers, and hence very few students have been studying the subject. There are now encouraging signs that this "vicious circle" is broken. In other states, the situation varies from being similar to Victoria to a firmly established subject in Tasmania. continued....

99 M,Learmonth,

continued.

Looking at the present situation there are several avenues of action possible, three of which are:(a)

development of "Australian" senior Earth Science teaching materials (both for theoretical and practical work).

(b)

more active support for the subject and participation in its development.

(c)

integration within other subject areas, especially Environmental Science, where no balanced understanding can be gained without Earth Science.

Earth Science seems,therefore, to be at a very important stage of its development and has a promising future.

BRIAN MARSHALL The New South Wales Institute of Technology SOCIAL SCIENCE IN GEOSCIENCE TRAINING The main arguments for including Social Science within Geoscience and comparable technological courses are presented. Based on such arguments, four divisions of social science are erected, depending upon whether they enhance cultural awareness, professional competence, social awareness, or non-technical career advancement. It is argued from attitudes displayed by certain staff and student-groups at The New South Wales Institute of Technology, that 3 and 4 year Geoscience courses can only afford time for Social Science having clearly demonstrable professional pertinence. Reflecting practices at N.S.W.I.T., Social Science is categorised according to whether taught by the faculty awarding the Geoscience degree, by another faculty or on an inter-faculty cooperative basis. These categories are discussed relative to the: (i)

concept of "demonstrable professional pertinence";

(ii)

proportion of the course to be devoted to them;

(iii)

distribution of the proportion through the course; and

(iv)

content of the proportion.

100

B. MARSHALL

and

C.R. WARD

Department of Applied Geology, The N.S.W. Institute of Technology INDUSTRY-BASED COURSES IN GEOLOGY The paper describes relationships that have developed with industry in response to the requirements of the Institute for both undergraduate and post-graduate courses. "Sandwich" training of undergraduate students (alternate semesters of full-time study and full-time employment) allows the student to fulfil a mandatory 12 months minimum of industrial experience prior to graduation, and enables him or her to appreciate the working conditions of a practising field geologist. The contact gained through this experience also enables The Institute to make the content of its courses more relevant to the needs of industry, and provides a number of flow-on benefits to the community generally. Post-graduate research for M.App.Sci., awards is also directed to the needs of industry, and most of the Department's post-graduate students are carrying out their studies on an external basis. For these students, especially those in remote locations, additional supervision is provided by a suitably qualified member of the employing organization, to supplement that from The Institute. Such arrangements have been extended, where appropriate into more substantial programmes of co-operative research, involving staff of The Institute and senior personnel from industry as well as the post-graduate students themselves. The results of both undergraduate and post-graduate programmes to date have been encouraging, and The Institute is currently considering the introduction of a doctoral programme with provision for external study. JILL NICHOLSON Geology Department, N . S . W . Institute of Technology. "BRIDGING THE GAP" - GEOLOGICAL EDUCATION AT FIRST YEAR TERTIARY LEVEL

The problems which exist in the teaching of 1st year geology at a tertiary institute are inherited from the high schools. Students enter the course with an intensive 2u geology strand, which may be biased towards the teacher's own interest, no geology at all, and all stages between these extremes. At the New South Wales Institute of Technology the first year lecture program which has been devised departs from the traditional fact after fact, descriptive type lecture. To cover the basic factual requirement supplementary printed notes are given to the students prior to the relevant lecture. Answer sheets are appended to the notes and each student is required to complete these and hand them in for assessment. As a follow up to the lectures, an integrated laboratory course has been developed. A laboratory manual which was written specifically for the 1st year course encompasses all the background information required to complete each practical exercise. A new type of guide to rock identification in the field, has been devised to assist students on their first major field mapping exercise.

N.P. SCHLEIGER Department of Mathematics, State College of Victoria at Coburg

A NUMERICAL CODING METHOD FOR CRINOID COLUMNAL CLASSIFICATION IN SILURO-DEVONIAN SEDIMENTS - A FIELD PROJECT FOR EARTH SCIENCE STUDENTS An interesting and useful field project involving the collecting, labelling ordering and observing and classifying much of the fossil fragments in oilurian and Devonian sediments from Central Victoria can involve the study of crinoid columnals and stem joints, Crinoid columnals and stem joint segments are possibly the most widespread shelly fossil debris in the coarse flysch sediments in central Victoria. It is rare to find crinoids complete as heads. Crinoids to this stage have proved to have little obvious stratigraphic value. However crinoid debris can be useful as palaeogeographic and paleoecological indicators. Elliptically shaped columnals are often elongated along current. Elliptic columnals can indicate current action operating during growth of a crinoid which may influence its feeding habits. Elliptic columnals can be due to deformation during transportation after death of the crinoid. Circular columnal plates can be stressed to elliptical ones during the deformation of the sediments containing them. The degree of brecciation of stem joints may indicated whether the crinoid was transported in a saltating slide or as a traction current. Such evidence may assist in determining the source and provenance of the elastic material found with the crinoid debris. It is possible to formulate a numerical coding system to describe the shape diameter and pattern of a crinoid columnal, the nature, shape and diameter of the central lumen, together with the smoothness of costation of the annalus. By establishing associations of columnal taxa at various outcrops, it is suggested that certain columnal patterns persist and thus come from the same common crinoid species. These crinoid species in turn can be associated with certain tabulate coral and brachiopod assemblages. The mathematical techniques employed can assist students in seeing relationships, in sizing samples and in testing them for significant differences.

102

DR. D . SPENCER-JONES, Director, Geological Survey of Victoria IS GEOLOGY MEETING THE CHALLENGE ? At the present time geology as a profession is passing through one of the slumps which have characterised its history. As long as the profession is tied to the vicissitudes of mineral exploration and mining activity it will be difficult to convince students that it is a worthwhile career. Nevertheless it will be the responsibility of governments and exploration companies to ensure that increasing attention is given to mineral resource assessment, management and conservation over the next 3 decades. It must be borne in mind that the next half century will see the consumption of a quantity of minerals and fuels exceeding that used throughout man's past history on this planet. In addition to the need for intensified exploration activity, it is obvious to those working in applied geology that there are broad areas of land use investigation and environmental study which ignore the contributions geologists and geomorphologists can make. Although hopefully attitudes are changing, it has been obvious that environment impact studies have been dominated by contributions from biologists, engineers and computer analysts. One example is where planning for the investigation of the quality of water in shallow lake systems or bays can ignore the fundamental contributions of outflow from the shallow aquifer systems in the catchment area. Another area in which geology is often ignored is in relation to land use and site investigations where the engineering geology aspects are ignored or dismissed in favour of the consideration of aesthetic values and the physical characteristics of a few inches of soil. An intelligent awarenees of the natural or artificial geological hazards are just as important when considering the safety and well being of any community. I would suggest that the tertiary training institutions in geology should constantly be researching fields in which their graduates can make a sound contribution to solving community problems and the realization of multidiscipline participation.

103

SESSION l/J - ENGINEERING GEOLOGY CONVENOR

PROFESSOR B. HOBBS

WEDNESDAY

2nd

FEBRUARY

9AM

THURSDAY

3rd

FEBRUARY

9AM

LECTURE L.G. ALEXANDER Division of Applied Geomechanics, CSIRO, Syndal , Victoria.

THEATRE

D DENHAM

and G. WOROTNICKI

Bureau of Mineral Resources, Canberra.

Division of Applied Geomechanics, CSIRO, Syndal, Victoria.

THE NEAR SURFACE STRESS FIELD NEAR THE SITE OF THE 1968 MECKERING EARTHQUAKE

Determinations of principal stress axes, from measurements in mines and tunnels and from focal mechanism solutions of recent earthquakes, indicate the presence of regional compressive stresses acting close to horizontal throughout the Australian continental crust. The axes of the maximum principal stresses are predominantly east-west and the values are higher than would be expected if all the stress was caused by gravity loading. Until recently all the over-coring measurements in Australia had been taken at sites remote from the epicentres of large earthquakes. However in February 1976 shallow (<10 m) overcoring measurements, using USBM borehole deformeters and, in one instance, CSIRO hollow inclusion stress gauges, were carried out at seven sites along a 200 km north-south traverse near the 1968 Meckering (Western Australia) earthquake. The measurements were made in competent granite sited in areas of low topographic relief. The results indicate high regional major compressive stress acting about 77°±5° E of N. This is in good agreement with the 91° direction for the pressure axis obtained from the earthquake focal mechanism, and the field observations of surface faulting, which were made shortly after the earthquake took place. The highest stress values (15 to 25 MPa) were observed at the sites furthest away from the epicentre; the lowest stresses were in the epicentral area near Northam, W.A. where the maximum principal stress near surface was about 6.5 MPa; the magnitude of the stress increases with distance away from the epicentral area at about 0.2 KPa/m. We conclude that shallow overcoring measurements in massive competent rock can give consistent results on a regional scale and could well be used to investigate stresses in areas of high earthquake risk in regions (such as Australia) where shallow earthquakes occur. High stresses can exist in such regions even at very shallow depths below surface.

104 C,M, BARTON Division of Applied Geomechanics,CSIRO, Mt. Waverley, Victoria AN ENGINEERING INTERPRETATION OF GEOLOGICAL DATA FROM THE C.S.A. MINE, COBAR, NEW SOUTH WALES Geological data, from a structural analysis of the C.S.A. mine, provides the basis for determination of the character of the rock mass and the stability of the underground openings. Laboratory rock-sample strengths and in situ fracture intensities, within the different structural domains, are related in a rock mass classification to provide indications of Q a medium to strong rock mass with friction, angles within the range 35 to 45 • Evidence is presented from considerations of joint roughness and joint wall strength that, under the present stress regime, shear is unlikely to occur along the'dominant joints within the body of the rock. Application of empirical rating systems known as rock structure rating (RSR) rock mass rating (RMR) and support index (Q) provide variable recommendations which generally conform to the current level of mine support. Discrepancies in the support recommendations are discussed. Results from the geological investigations provide the basis for the selection of input parameters and the establishment of an idealised type cross-section for an associated finite element analysis. The finite element studies closely inter-relate with the geological work and are described in a complementary convention paper.

C.M. BARTON, Division of Applied Geomechanics, SCIRO, Mt. Waverley, Victoria APPLICATION OF AN IMAGE ANALYSIS COMPUTER IN THE DETERMINATION OF BLOCK SORTING AND FABRIC

An image analysis computer is used to determine axial-dimension distributions and preferred orientations of clasts (>-5$) exposed in spoil piles at Goonyella Mine in Queensland. The techniques are applicable to other very coarse sediments which are difficult to analyse by traditional methods. Determination of the total maximum intercept length of all clasts, on an approximately planar exposure, provides a reliable indication of preferred orientation. Size - number frequencies of clast length are adjusted to weight frequencies (correlation coefficient at N = 16 = 0.989) and used in the calculation of statistical sorting parameters. Results from different sample localities are consistent with known mechanisms of sorting.

105

W.F. COLE and C.J. LUCUCKI Division of Building Research, CSIRO, Melbourne

CLAY MINERALOGY OF SOME BORE CORES FOR THE MELBOURNE UNDERGROUND RAIL LOOP The Melbourne Underground Rail Loop Authority is constructing an underground rail loop to connect with the existing surface railway system. This loop will be tunnelled in very different rock types in each half of the city, Silurian sediments in the east and Tertiary basalts in the west, and new underground stations will also be located in these rock types. The paper reports on the clay mineralogy of samples taken from bore holes for the Flagstaff Station located in the Tertiary basalts, and for the Museum Station located in the Silurian sediments. At Flagstaff all basalt flows are highly weathered and considerable amounts of Montmorillonite have been developed throughout the basalt profile. Where the basalt is non-vesicular the montmorillonite occurs in horizontal and vertical partings. In vesicular basalts the montmorillonite fills vesicles and fracture zones. At the interface of vesicular basalt and the underlying Werribee formation there is a layer several inches thick of pure montmorillonite. At Museum the Silurian sediments are extensively weathered down to a depth of about 20 metres. They show joints and fracture zones filled with secondary clay brought down from the surface., Montmorillonite is not an important component in these profiles. Quartz, kaolinite and mica are the dominant minerals. A.M. COONEY

ENGINEERING GEOLOGY - BERWICK CORRIDOR Bedrock comprises Silurian (?) sediments and Devonian granodiorite. Two thin volcanic sequences, tentatively correlated with the Flinders Basalt and Thorpdale Volcanics, are exposed at Berwick. A veneer of Baxter sandstone crops out south of Narre Warren. Quaternary alluvium and colluvium are widespread. Deep residual halloysite and kaolinite soils developed during the Tertiary under humid tropic to sub-tropic climates. Shallow residual soils developed under cooler climates current since the late Tertiary. Montmorillonite occurs in some residual soils. Rocks are generally moderately to highly weathered in outcrop and have medium to high strength. continued....

106

A.M.Cooney, cont.,

Soils are residual or sedimentary and are further subdivided on morphology and sedimentology. They generally range from clays to clay silts, and from CL to CH on the unified soil classification. Consistencies vary from firm to hard. Soil types have distinctive grain size distribution, plasticites and clay mineralogy. Shallow brackish sodium chloride ground water forms two distimct potentiometric surfaces: one, in the Koo-wee-rup Plain, slopes towards Western Port; the other, in the depression at Narre Warren, slopes towards Port Phillip. In places the potentiometric surface near Narre Warren is- at or slightly above ground surface. A 1:25,000 engineering geology map has been prepared.

RICHARD EVANS School of Applied Geology, University of New South Wales, Kensington,N.S.W.

GEOLOGIC AND MAN-INDUCED FACTORS INFLUENCING THE ROCK SLOPE STABILITY OF THE ILLAWARRA ESCARPMENT, N.S.W. Rock failures of a toppling or general degradational nature are common on the Illawarra Escarpment, near the Greater Wollongong area. Although isolated falls occur along the entire length of the escarpment, failures are concentrated near Coal cliff. The geologic and geomorphic factors influencing rock failures are slope inclination; rock type, due mainly to expandable clay minerals; seismicity (both high earthquake intensity and high horizontal stresses); jointing and faulting which strongly determine the drainage courses; water; physical weathering with resultant fabric changes leading to a decrease in the strength, and aiding fretting and undercutting; and creep of the weathered sandstones and claystones. The possible man-induced factors are difficult to prove but could include land clearing; dams, which load the escarpment and alter the groundwater regime; mining subsidence; vibrations from railways, roads and mining; water from housing; and mine dumps which may load the escarpment. A consideration of possible failure mechanisms, namely bearing capacity failure sliding along a plane, and the influence of cleft water pressures shows that the values of the horizontal stress may preclude these possibilities. However weathering and creep of the basal claystones and subsequent stress relaxation in the more weathered material is likely to cause differential settlement and this combined with the influence of cleft water pressures will produce toppling failures.

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G . HARRIS Munroe, Johnson & Associates Pty., Ltd., Consulting Engineers

A.D.M. BELL School of Applied Geology, University of N.S.W.

BRIAN MARSHALL Department of Applied Geology, N.S.W.Institute of Technology

J . PAGE Municipal Engineer, Glen Innes Council

ENGINEERING GEOLOGICAL INVESTIGATIONS PERTAINING TO THE RAISING OF GLEN INNES WATER SUPPLY DAM The need for an increased municipal water supply storage at Glen Innes is presented. The storage can be increased by lifting the height of the existing dam on Beardy Waters, by building a new dam downstream of the existing one, or by placing a supplementary dam on the Mann River. Details of hydrologic problems related to increasing storage on Beardy Waters and the Mann River are presented, and these are followed by an outline of the site investigation implemented at the existing dam site in relation to raising the concrete-arch wall. Aspects arising from the investigation such as: strength and homogeneity of the existing wall, depth of weathering of the granodiorite and leakage around the concrete wall, discontinuity patterns in the granodiorite and their influence on stressing the raised wall, are discussed and conclusions are presented as to economic feasibility of the raising. A.H. SPRY AMDEL, South Australia THE COMPRESSIVE STRENGTH AND TEXTURE OF SOME AUSTRALIAN QUARTZITES

Precambrian to Palaeozoic quartzites (45 samples) from various localities in Australia have unconfined compressive strengths ranging from 172 to 441 MPa (25 000 to 64 000 psi). The strength of non metamorphic quartzites derived from pure quartz sandstones depends on texture and structure. The dominant textural variation can be described in terms of the proportion of mutual-impingement (welded, pressure-solution, pressolved) as against cemented grain boundaries. No correlation was found between this aspect of the texture and the compressive strength and it is suggested that variations in compressive strength of the quartzites tested are due to subtle lithological variations and may largely depend on the proportion of micro-defects present.

108 P.M. WARBURTON Division of Applied Geomechanics, CSIRO, Mt. Waver!ey, Victoria FINITE-ELEMENT ANALYSIS IN THE ENGINEERING AND GEOLOGICAL STUDIES AT THE C.S.A. MINE, C0BAR, NEW SOUTH WALES Finite-element analyses have been undertaken undertaken as part of an engineering and geological study at the C.S.A. Mine, Cobar, New South Wales. The input to the model required appropriate simplification and interpretation of structure, fabric and material properties. Geological considerations are described in an associated convention paper. At present the model assumes plane-strain conditions. Goodman discontinuity elements are used to represent the shear or fault zones, and nonlinear material properties are assigned to both the continuum and discontinuity elements. The initial finine-element study complemented the geological investigation by back-analysing the development of the mine at that time. Currently, however, the model is being used to analyse the next phase of mining, which involves open-stope developments through most of an existing crown pillar. Results obtained at each stage show stresses and displacements and predict the behaviour along the discontinuities and the effects of interactions between multiple stopes. The theoretical studies are being designed to interact closely with a continuing program of field measurements. It is hoped that the liaison will provide a check on the mathematical model and suggest possible ways of improving it.

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COAL s w o s i m

CONVENOR: GEOFF TAYLOR THURSDAY

3rd F E B R U A R Y

9 am

L E C T U R E T H E A T R E Rl

J.W. BEESTON, A.G. GALLIGAN and N.J. ZILLMAN Geological Survey of Queensland.

THE RELATIONSHIP BETWEEN SUBSIDENCE, DEPTH OF BURIAL AND COAL QUALITY IN THE GERMAN CREEK FORMATION, CENTRAL QUEENSLAND. Detailed petrographic and lithologic studies carried out on Queensland Department of Mines bore cores from the upper part of the Permian German Creek Formation, Central Queensland have been used to interpret relative subsidence and maximum depth of burial of the unit. Vitrinite reflectance analyses of the Pleiades and German Creek seams show an increase in coal rank towards the north-east, indicating a greater maximum depth of burial in that direction. The thickness of sediments between the two seams also increases northeasterly suggesting a greater rate of depositional subsidence in that area, and a possible relationship between maximum depth of burial and relative subsidence during deposition. Petrographically the German Creek seam is relatively homogeneous over the whole of the area, and the main change in coal quality is related to the increase in rank. The coal ranges from sub-bituminous in the northwest to semi-anthracitic intthe northeast, with the reflectance values ranqinq from 0.45 to 2.06 per cei.t. Reserves of 1350 million tonnes of raw coal in situ are indicated within the coking coal range, at depths less than 300 m.

110

R.A. BRITTEN Joint Coal Board, Cessnock, N.S.W. AN ECONOMIC CLASSIFICATION OF COAL MEASURE SEDIMENTATION AND ENVIRONMENTAL FACIES WITHIN THE SINGLETON SUPER GROUP OF NEW SOUTH WALES A classification of coal measure sediments and sedimentary environments is presented in a manner that emphasises those features which are applicable within the Singleton Super Group (Singleton Coal Measures) within the Hunter Valley of New South Wales. The relationships between the various lithologies and associated sedimentary environments can be displayed in a way that shows how similar lithologies may be derived from different environmental facies within a typical coal measure sequence. This raises the question of the relative merits of classifying coal measure sediments, either according to their environment of deposition or their lithology. The relative merits of each are discussed in relation to the practical aspects of mining and also the needs of interpretative geology. A scheme is presented which may be applied to both. This scheme envisages the assimilation of both kinds of data into a computer, which may then be retrieved in terms of lithologies or environmental facies according to choice. The lithological classification is universally used; the environmental classification of coal measure sediments, although generally accepted, is not yet widely used. Therefore, although it can be shown than an environmental classification of coal measure sediments can be usefully superimposed on the lithological classification, the former must necessarily be subordinate to the latter. It is concluded that a simple lithological classification is appropriate for most practical mining purposes, especially for open-cut operation; but an environmental classification can be advantageously used to assist geological interpretation for the planning and development of underground mines. B.C.S. GLOE and A.M. GEORGE THE OCCURRENCE AND PETROLOGY OF LATROBE VALLEY BROWN COALS One of the major brown coal deposits of the world is located in the Latrobe Valley of Victoria. The coal occurs as thick seams beneath a thin cover of sands and clays in the Tertiary Gippsland Basin. Two large and two small 9pen ailts have been developed by the State Electricity Commission of Victoria in this area and provide the fuel for large thermal power stations and the manufacture of a transportable fuel in the form of briquettes. The techniques and standards employed in brown coal petrology differ significantly from those used for hard coal. Brown coal macerals were first defined by the International Commission of Coal Petrology in 1971 and over 20 macerals have now been established. Using fluorescent light in addition to normal reflected light quantitative micropetrographic analysis has been carried cut on a number of Latrobe Valley coal samples and the maceral content has been found to provide an effective basis for describing variations in the nature of the coal. A lithotype classification has been developed for Latrobe Valley coals based on microscopic characteristics. In thepartially dried coal faces of open cuts a colour banding dueto lithotype can be seen and the classification is based on the colour, texture, degree of gelification, weathering pattern and physical properties of air dried coal.

Ill

LLOYD H. HAMILTON

ECONOMIC ASPECTS OF INTRUSIONS IN COAL

Intrusions can increase or decrease the usefulness of coal. Generally large or subjacent intrusions increase the rank of coal, e.g. from lignite to anthracite (or pseudoanthracite), and this increases the calorific value of the coal but reduces its value as a source of hydrocarbons. Dykes in bituminous coals generally have deleterious effects such as increasing the ashcontent and decreasing the uniformity of a seam. Basic intrusions are common in Australian black coals and their presence and effects are seldom easy to forecast. Prediction of occurrences and effects is assisted by knowledge on structural relations of intrusions in coal seams, aureole development, means of correlation of exposures of igneous rocks, and with knowledge on the interaction of coal and magma. MAL

JOHNSON

COULD GEOLOGICAL RESEARCH BENEFIT THE UNDERGROUND COAL MINING INDUSTRY

At times, the function of coal geology is considered complete following surface investigations of coal deposits and an assessment of broad ranges of coal qualities and quantities in a proposed mining block. This, however, is but the beginning of the geological task in coal mining. The need for increased geological research in underground coal mining is discussed using as a model, the geological conditions in the Rangal coal measures south of Blackwater Queensland as encountered in the developing Leichhardt and Cook Collieries. LEON MCDONALD Thiess Bros. Pty., Limited, Mining Division, Rocklea, Queensland.

A TIDAL-DELTAIC ENVIRONMENTAL INTERPRETATION OF JURASSIC COAL AND ASSOCIATED SEDIMENTS IN THE SURAT BASIN. A paleoenvironmental interpretation is attempted for the Jurassic coal bearing sequence in the Surat Basin, the Walloon Coal Measures and surrounding formations are regarded as being deposited during the progradation of a large tidally influenced delta, analogous to the modernNiger Delta, followed by the transgressive retreat of tidally influenced environments. continued

112

L.McDonald continued,

Two coal rich intervals are identified in the sequence. One interval low in the Walloon Coal Measures formed during the prcgrading phase while the other, containing the most prospective seams, was deposited during the transgressive phase at the top of the Walloon. The coals are interpreted as being deposited in localised fresh water swamps adjacent to regularly meandering tidal channels, with the configuration of deposits related to the meanders. In sequence the upper Evergreen Formation is interpreted as representing shallow marine and prodelta mud environments; the Hutton Sandstone as a Barrier bar complex; the Eurombah Formation and basal Walloon as tidal creek environments; the overlying Walloon as tidal and fluvial channels with adjacent back swamps; the Springbok Sandstone as tidal channel fill deposits and the Westbourne Formation as supratidal and tidal flat facies The sequence has similarities with Cretaceous non marine sections of the western interior in the U.S.A.

TED

MILLIGAN

THE GEOLOGY OF SOME AUSTRALIAN PERMIAN COAL BASINS

The stratigraphy and structure of an intracratonic coal basin in South Australia is compared and contrasted with that of a fore-deep coal deposit in the North-west Bowen Basin of Queensland. Reference is made to some other Permian coal basins in Australia. J,

SHEPHERD FAULT SWARMS AND ROOF FAILURE IN A NEW SOUTH WALES COLLIERY

Hundreds of minor, normal faults and rare thrusts occur in swarms in the Greta Coal seam at Aberdare East Colliery, Cessnock. This colliery is one of a small number of mines still working in the South Maitland Coalfield which has a long history of recurring mining difficulties, particularly due to roof control. Fault swarms have not previously been recognised in Australia. Cross cutting relationships of the faults and their interactions of multiple slickenlines on fault surfaces indicate that four phases of fault movements have occurred since Permian times. The most common, WNW-ESE trending faults are sub-parallel to at least 10 named faults which cross the Lochinvar Anticline. Two fault swarms are coincident with roof failure. The effect of faults on mining has been quantified using a new concept called the zone of influence, a rectangular area of specified width around a fault in which a fault has potentially deleterious effects on roof conditions. Statistical studies suggest that normal, oblique slip faults are much more damaging to mining than dipslip faults. Even faults with throws as small as 3 mm appear to influence mining conditions over several metres. The zone of influence has important ?eomechanical implications.

113

M. SHIBAOKA and MICHELLE SMYTH

PETROGRAPHIC COMPOSITION OF AUSTRALIAN COAL SEAMS IN RELATION TO GEOLOGICAL AND BOTANICAL FACTORS

The petrographic properties of coal seams, such as their maceral and microlithotype composition and type of exinite are determined by a number of factors, of which the most important are conditions of sedimentation, and vegetation in and around sedimentary basins. The former is fundamentally controlled by the tectonic framework of a basin and the latter by evolutionary changes. For Permian and Triassic coal seams, which account for most of the black coal reserves in Australia, the variation in petrographic composition can be explained mainly by differences in the environment of sedimentation. However, in the case of petrographic variations between coal seams of different geological ages, particularly those of post-Tnassic age, the vegetation is a significant factor. Both factors to some extent affect the cherrical properties of the individual microscopic constituents of coal seam.

V.M. THREADER 43 Kingston Heights, Kingston Beach, Tasmania. TRIASSIC COAL IN TASMANIA The Triassic System is virtually confined to the central and eastern portions of the State with the highest known development of coal occurring in the Fingal - St. Marys district. Eight seams of coal of varying thickness, quality and lateral extent are present in a.200 m stratigraphic thickness and each seam is the end product of a fining upwards sedimentary cycle. Exploration drilling on a 1 km grid is in progress. Much of the area is capped by 200-400 m of dolerite and a gravity survey is being conducted to assist the choice of drilling sites. Seam correlation is difficult but a combined study of macerals, tonsteins and plant spores and detailed logging is expected to solve most of the problems

114

COLIN R. WARD . . _ Department of Geology, New South Wales Institute of Technology. DIAGENESIS IN A COAL SWAMP - MINERAL MATTER DISTRIBUTION IN THE COALS OF THE ILLINOIS BASIN, U.S.A. A study of the lateral variation in the mineral matter of the principal coal seams cf the Illinois Basin has been carried out, covering an area of 100,000 Km 2 throughout Illinois, Indiana and Western Kentucky. The study is based on X-ray diffraction analysis of low tempe-ature ash (radio-frequency oxidation) residues prepared from the coals, with qaantitative assessment of non-clay materials checked against independent chemical analysis. Following special dispersion techniques, oriented-aggregate diffraction analysis was carried out on the clayminerals, and a semi-quantitative evaluation of the less than 2-micrometer fraction was performed. The mineral assemblage in the coal is dominated by cuartz, calcite and pyrite with a clay fraction consisting of illite, kaolinite and randomly interstratified clay minerals. The relative proportions of these constituents vary both vertically through the seam section and laterally across the basin, and are particularly well expressed by the inverse relationship between kaolinite ana the expandable clay minerals. These variations have been interpreted in th« light of the other geological features of the basin, and are thought to reflect the balance between sediment supply and basin subsidence throughout the area. Kaolinite is less abundant and expandable clays more so in shelf and distributary channel areas where the supply of sediment is greatest, but it becomes dominant at the expense of mixed-layer clays in the more basinward, sediment-starved regions. Pyrite and calcite also appear to reflect this trend. The kaolinite is thought to have formed by interaction of dissolved silica and alumina in the peat swamp, aided by the catalytic action of organic acids. These organic acids may also have dissolved a certain amount of the expandable clay, and together with some regrading of illite by potassium fixation in areas of marine influence, produced a slightly greater ratio of illite to mixed-layer clays than that observed in the associated non-coal strata. Pyrite was precipitated by bacteriaT action from the sulphate-rich more reducing portions of the basin, and is also thought to reflect some marine influence, while organic sulphur compounds are relatively more abundant in the channel and shelf regions and part of the iron is present in the form of siderite. Although similar coal-bearing sequences are not present in Australia, the study provides a basis for comparison when sufficient data becomes available.