Abstracts No.1: Coal, Tin Surficial Deposits and Geology of NE Tasmania, 1990, Launceston

Geological Society of Australia

ABSTRACTS Number 1

Coal, Tin Surficial Deposits and Geology of N.E. Tasmania Nov. 7-9 1980

SYMPOSIUM SURFICIAL

ON C O A L ,

DEPOSITS

OF N O R T H - E A S T

AND

TIN, GEOLOGY

TASMANIA

LAUNCESTON, TASMANIA,

1980

ABSTRACT VOLUME and EXCURSION

GUIDES

Edited by D.C. Green S P.R. Williams

CONTENTS

FOREWORD

N.J. TURNER A Summary of the Geology of North Eastern Tasmania

M.P. McClenaghan Petrology and Geochemistry of the Granitic Rocks of the North East of Tasmania

F.L. SUTHERLAND Tertiary Volcanic Rocks amongst the Surficial Deposits of N.E. Tasmania

B.C. BATCHELOR The Southeast Asian Tin Province (Malaysia and Indonesia)

C.R. WARD Why Tasmanian Coal?

10

F.C. LOUGHNAN Kaolin: An Exportable Product

10

R.J. HENDERSON

Case Studies Illustrating the Uses of SIROTEM

11

W.H. KOPPE Aspects of Coal Exploration in N.E. Tasmania

12

D.E. LEAmN Geophysical Exploration of the East Coast Coalfield, Tasmania

15

R.H. CASTLEDEN Coal Exploration, Fingal Exempt Area

14

THREADER

The Geology of the Duncan Colliery

C.R. CALVER Description and Marys, Geological Setting of Triassic Basalt North of St N.E, Tasmania

16

17

C.A. BACON Triassic Pyroclastics near Bicheno in North-Eastem Tasmania

17

D,J. JENNINGS Tin in Northeast Tasmania

18

W.W.-S. YIM

Sampling Problems in Alluvial Tin Exploration

19

K. MORRISON The East Geology of Placer Tin, Ringarooma Valley, North Tasmania

20

W.E. BAKER Biogeochemistry of Gold and its Application to Prospecting

21

T.G. SUMMONS The Occurrence of Chromite in the Andersons Creek Area, Beaconsfield, Tasmania

21

J.R. BISHOP The Piezoelectric Exploration Technique for Mineralised Quartz Veins

11

22

EXCURSION

1.

GUIDES

The Lutwyche Vein System at the Aberfoyle M i n e , North-east Tasmania Collins, I. Keyes)

23

Fingal Valley - St Marys Area (C.R. Calver, Castleden)

27

Tonganah - Pioneer - South Mt Cameron Areas (D.J. Jennings, J . C . van Moort)

29

4.

Barnes Hill Chromite Mine (T.G. Summons)

31

5.

Lisle Goldfield (W.E. Baker)

32

6.

Duncan and New Cornwall Adits (V.M. Threader)

33

2.

3.

DIRECTORY OF SUPPORTERS

34

111

FOREWORD

On behalf of the Tasmanian Division of the Geological Society of Australia Inc., and the Specialist Groups in Economic Geology and Coal Geology, we welcome participants to the 1980 Symposium held in Launceston. Like its predecessor, the 1978 Burnie meeting, the assured success of this function is largely due to generous support from exploration and mining companies, together with the Tasmanian Department of Mines. The papers to be presented at the Symposium are grouped in sessions and in order of presentation. Abstracts have been printed essentially as received with minor adjustments to permit a uniform format. We acknowledge the help and enthusiasm of those who have contributed papers and assisted in the organisation of excursions. Particular mention is made of the assistance given by Mrs Claire Humphries and Mr Michael Dix in preparation of the text and layout. Organising Committee:

Editors:

J.C. van Moort (Convener) C.R, Calver (Secretary) W.E. Baker (Treasurer) P.S. Manchester D.W. Russell C.H. Tassell

D.C. Green P^R^ Williams

STRATI6RAPHIC QUATERNARYCRETACEOUS

^

REFERENCE

Superfical

deposibs, fluviolacustrine

wibk i n i e r c a l a b e d Low

TRIASSICL. CARBONIFEROUS

angle

Parmeener

Tertiary

^^

basalb a n d

marine

Crebaceous

and

TASMANIA

fig.l

deposits (see

andesibe.

JURASSIC

Supergroup -fluviolacustrine

^

y

\)

f i g u r e 5J

Dolerifce

shallow (see figure 4 )

deposibs.

OF TAWVAR RIVER 353-375my |

DEVONIAN

and mmor

unconformlby

glaciomarine

WEST

FOR N O R T H E A S T E R N

J

EAST OF TAIAAR RIVER granitoids

364-398 my.

|

|

granitoids

cave deposits kigk angle unconformiky

kigk

E

angle

unconformity

. _ 0 . . 0

stable marine slaclf

dtposibs:

unstable marine • • o' ' •°

1. sandstone and mudsbone;

SILURIAN

2. mainly skallow waber

limestone;

3. skallow marine and terrestrial sandstone and conglomerabe.

basin deposibs:

1. micaceous quarbzwacke burbidite and mudstone 2. predominantly mudstone. (entire sequence known as Matkinna Beds).

ORDOVICIAN CAMBRIAN PRECAIABRIAN

m

( d o t ornament mafic rocUs.)

indicates ultra

Tasmania Department of Mines

PRE-CARBONIFEROUS GEOLOGY OF NORTH EASTERN TASMANIA (EXCLUDING FURNEAUX GROUP)

sASoooomN -

fig ?

Unconformity

Upright

Possible

Plunging

Normal

bkrusb faulb, beetk on upper plabe. faulb, block on downbkrown side.

I

ii

dexbral

anbicliwe fold

k i n g e , sinistral

and

vergence.

Approximate

position of pre - Carbon i ferous

Tamar Fracbure. Overburned

syncline.

Segmenbs of composibe - f i g u r e 2.

cross-section

A SUMMARY

OF THE

GEOLOGY By

OF

NORTH

EASTERN

TASMANIA

N . J . Turner

Geological Survey of Tasmania The rocks of pre-Carboniferous age that outcrop east of the Tamar River (fig. 2) are markedly different from those that outcrop to the west. It is therefore convenient, both geographically and geologically, to take the Tamar River as the western boundary of the area to be discussed in this summary. The southern boundary is the Fingal Valley and other boundaries are formed by the sea. The Furneaux Group and other islands off north eastern Tasmania have similar geology. As well as the pre-Carboniferous group of rocks there are two younger stratigraphic/structural units in north eastern Tasmania. All three are shown in the stratigraphic reference in Figure 1. Important aspects of each unit are illustrated in Figures 2, 3, 4 , 5. The following notes supplement the diagrams. Pre-Carboniferous

Rocks

(figs.

1, 2 and

3)

Except for the predominantly mudstone sequence east and south-east of Lefroy, the Mathinna Beds contain substantial proportions of both quartzwacke, derived from turbidity currents, and interbedded mudstone. Neither volcanic rocks nor carbonates are present. Sedimentary structures in probably Early Devonian parts of the Mathinna Beds near Scamander and St Marys give various directions of turbidity current flow from the SW-SE quadrant (30, 29-Turner). Provenance of the quartzwacke is unknown. Early to Middle Devonian orogenesis caused dynamic metamorphism of very low grade and generated folds and slaty cleavage on mainly north to north westerly trends (32). After the main, early deformation, emplacement of granodiorite, adamellite and alkali granite occurred in broadly that order (8, 12-Groves, 18-McClenaghan). The accompanying thermal metamorphism of the Mathinna Beds reached pyroxene hornfels facies at Piccaninny Point (20) and melting occurred at Bridport (24). However, in both cases the effects are restricted to the immediate vicinity of granodiorite contacts. Aureoles are generally of much lower grade. They vary in width from 5 km to less than one metre (18-Turner, 29-Turner) depending on form of intrusion, dip of contact, volume of granitoid, and other factors. Gravity data (15) indicates that the main granodiorite masses are sheets (see fig. 3). Structural features and gravity data indicate that the early, hypersthene-bearing porphyry near St Marys has a similar form but with an associated feeder (29-Turner, 14). These sheet-like forms imply forcible intrusion of magma causing widespread roof-lifting. In comparison, the main adamellite in Blue Tier Batholith is thought (11) to have been emplaced permissively along pre-existing, sub-rectangular fractures by lateral dilation combined with roof-lifting in a situation of regional tension. There is as yet little known about the three dimensional shape of this intrusion. The partly unroofed alkali granite masses at Blue Tier and Mt Paris (18-McClenaghan, 19) are domes and the former has a low density plug beneath it (15) . There appears to be sub-horizontal sheeting of component rocktypes at Blue Tier (for discussion of the form of intrusion at Blue Tier see 12-Groves, 18-McClenaghan). A sheeted dome may also be the form of the adamellite/alkali granite mass which extends from north-east of Scottsdale to possibly south of Rossarden (34). Roof-lifting and/or stoping would

have been important mechanisms during dome emplacement. Localised and mild regional deformations intervened between and post-dated granitoid emplacement. They produced mineral alignments in some granitoids (18-Turner, 18-Williams) and crenulation cleavage in the Mathinna Beds (18-Turner). These strains may be related to movement on the Tamar Fracture (32) which is the postulated major shear located at or near the Tamar River that brought the Mathinna Beds into juxtaposition with the contrasting Palaeozoic deposits west o£ the Tamar River (33). Mineralization Three main classes of primary metallic mineralisation occur in the Mathinna Beds and granitoids of north-eastern Tasmania (12-Groves). Gold, and gold and silver, with accessory sulphides occur in discordant quartz veins generally in Mathinna Beds remote from outcropping granitoids (e.g. Lefroy, Mathinna - Beaconsfield, is similar) but sometimes in or near granodiorite (e.g. Lisle). Copper and lead-zinc-silver occur in small deposits in quartz/sulphide veins in the Scamander district (e.g. Orieco). Tin and tin/tungsten deposits show a close spatial association with alkali granites being either in fractures in adjacent Mathinna Beds (e.g. Aberfoyle, Storeys Creek, Mt Paris) or in greisens within alkali granite (e.g. Mt Paris, Anchor Mine on Blue Tier). The Aberfoyle mine at Rossarden and the Storeys Creek mine are the only presently operating mines in preCarboniferous mineralisation in north-eastern Tasmania. The Tasmania gold mine at Beaconsfield is being reopened. Parmeener Supergroup (figs. 1 and 4) Marked stratigraphic attenuation of the north-eastern Tasmania Parmeener sequence relative to other parts of the island indicates that the north-east was palaeographically distinct during much of the period of deposition of the Parmeener Supergroup. The palaeotopography had northerly to north-westerly trends, no doubt reflecting Devonian structure. North-eastern Tasmania was a highland area during deposition of the lower marine sequence (7). It may also have been intermittently exposed during deposition of the upper marine sequence since that succession is relatively thin in the north-east but has a similar age range to elsewhere in Tasmania. Other differences in conditions during deposition of the upper marine sequence are indicated by the fact that the limestone in the north-east has a greater time range than those elsewhere. There has been no significant commercial exploitation of limestone in the north-east (13) but Parmeener limestone has been quarried near Hobart (unit 2 in fig. 4) and on Maria Island (unit 4 in fig. 4). The upper freshwater sequence (unit IC) is absent from north-eastern Tasmania and the lower part (unit IB) of the Triassic sequence is virtually absent. The latter is characterised by fluvial, quartz sandstone of west to north-west derivation. Absence of these two sequences from north-eastern Tasmania suggests that it was again highland (25-Banks). The upper part of the Triassic sequence (unit lA) is characterised by lithic sandstone of different provenance but similar environment to the underlying quartz sandstone. Interbedded with it are impure coal seams (29-Castleden) formed from transported and locally derived organic matter.

About 90% of the total of about eleven million tonnes of mainly steaming coal mined in Tasmania has come from the Triassic seams in the Fingal Valley and adjacent areas (21). Collieries are presently operating near Fingal and at Mt Nicholas. Late Mesozoic and Cainozoic Deposits (figs. 1 and 5) In the Jurassic Period a huge volume of tholeiitic dolerite was intruded, via large plug-like feeders (14), mainly into the upper part of the Parmeener Supergroup (25-Spry). It formed sills up to about 500 m thick, dykes and bodies that have irregular and unpredictable form. Faulting preceded and accompanied dolerite intrusion (25-Spry in Solomon) and probably persisted (25-Carey in Solomon, 31) as the predominantly north-west trending faults of Cretaceous and early Tertiary age. These faults were involved in the development of Bass Basin which was initiated in the area north of Boobyalla (fig. 5) in the Early Cretaceous and developed progressively to the north-west during the Tertiary (23). Fault controlled deposition peripheral to the main basin occurred in a Cretaceous graben at Boobyalla (10, W.R. Moore, pers. comm.) and in a system of Palaeocene grabens (25-Banks, 9, 16) that developed over and near the site of the old Tamar Fracture. Sediments in these grabens were derived mainly from dolerite and the Parmeener Supergroup. However, at Beaconsfield, near the western edge of the Tamar Graben, chromite from Cambrian ultramafic rocks formed placer deposits (26). These are currently being mined. The oldest sediments preserved on the horst which comprised most of north-eastern Tasmania are Oligocene-Miocene fluvial deposits of granitoid and Mathinna Beds provenance. The sediments occur in the ancestral channels of the main contemporary drainage systems either as dissected remnants or as deep leads. Basalt of Middle Miocene age commonly overlies them (18Brown and McClenaghan). Placer deposits of cassiterite occur in the sediments and are being worked in a number of places (e.g. Pioneer - see 3). Deep chemical weathering effected north-east Tasmania several times during the Cainozoic producing laterite and causing deep kaolinisation of granitoids. Kaolinised material at Tonganah is being worked as a clay resource. Late Cainozoic deposits include mainly talus and stream alluvium in inland areas with thin marine, marginal marine and aeolian deposits on erosive marine terraces along the northern coast (18-Baillie) and on Flinders Island (27). Selected References: 1.

BAILLIE, P.W.; TURNER, N.J.; COX, S.F. 1980. Geological atlas 1:50 000 series. Zone 7 Sheet 24 (8416S). Boobyalla. Department of Mines, Tasmania.

2.

BANKS, M.R. 1973. General geology, in BANKS, M.R. (ed.). The Lake Country of Tasmania. 25-34. Royal Society of Tasmania : Hobart.

3.

BROWN, A.V. 1978. Tertiary lead and basin - Winnaleah Map Sheet. Unpubl.Rep.Dep.Mines Tasm. 1978/7.

4.

BROWN, A.v.; McCLENAGHAN, M.P.; MOORE, W.R.; TURNER, N.J.; McCLENAGHAN, J.; WILLIAMS, P.R.; BAILLIE, P.W.; CORBETT, K.D.; CORBETT, E.B.; COX, S.F,; GROVES, D.I.; PIKE, G.P. 1977. Geological atlas 1:50 000 series. Zone 7 Sheet 32 (8415N). Ringarooma. Department of Mines,

5.

Tasmania.

CALVER, C.R.; CASTLEDEN, R.H.

In press.

Triassic basalts from Tasmania.

Search.

6.

CASTLEDEN, R.H.; CALVER, C.R.; TURNER, N.J.; BAILLIE, P.W. In prep. Geological atlas 1:50 000 series. Zone 7 Sheet 49 (8514N). St Marys.

Department

of Mines,

Tasmania.

7.

CLARKE, M.J.; FARMER, N.; GULLINE, A.B. 1976. Tasmania Basin - Parmeener Supergroup. Monogr.Ser.australas.Inst.Min.Metall. 7:438-443.

8.

COCKER, J.D. 1980. Regional geology of the southern Furneaux Group. Group. Pap.Proa.R.Soc.Tasm. 114:44-68.

9.

CROMER, W.C. 1980. A late Eocene basalt date from northern Tasmania. Search. 11:294-295.

10.

FORSYTH, S.M. 1980. Preliminary palynological investigation of Boobyalla DDH 2, 1977-79, north-east groundwater investigation. Unpubl.

11.

GEE, R.D.; GROVES, D.I. 1971. Structural features and mode of emplacement of part of the Blue Tier Batholith in north-east Tasmania. J.geol.Soc.Aust. 18:41-55.

12.

GROVES, D.I.; COCKER, J.D.; JENNINGS, D.J. lith. Bull.geol.Surv.Tasm. 55.

13.

JENNINGS, I.B.; NOLDART, A.J.; WILLIAMS, E. 1967. Geology and mineral resources of Tasmania. Bull.geol.Surv.Tasm. 50.

14.

LEAMAN, D.E.; RICHARDSON, R.G.

Rep.Dep.Mines

coalfields.

Tasm.

1980/37.

1980.

Unpubl.Rep.Dep.Mines

15.

LEAMAN, D.E.; SYMONDS, P.A. 1975. Tasmania. Pap.geol.Surv.Tasm.

16.

MATTHEWS, W.L. Department

1979.

1977.

The Blue Tier Batho-

Gravity survey of the east-coast Tasm.

Gravity survey of north-eastern 2.

Longford Basin geology (1:100 000 map sheet).

of Mines,

Tasmania.

17.

McCLENAGHAN, M.P.; BAILLIE, P.W. 1975. Geological atlas 1:250 000 series. Sheet SK-55/4. Launceston. Explan.Rep.Dep.Mines Tasma.

18.

McCLENAGHAN, M.P.; TURNER, N.J.; BROWN, A.V.; WILLIAMS, P.R.; BAILLIE, P.W.; MOORE, W.R. In press. Geological atlas 1:50 000 series. Zone 7 Sheets 32 and 49 (8416S and 8415N). Boobyalla and Ringarooma.

19.

Explan.Rep.Dep.Mines

Tasm.

McCLENAGHAN, M.P.; WILLIAMS, P.R. In prep. Geological atlas 1:50 000 series. Zone 7 Sheet 33 (8515N). Blue Tier. Department of Mines, Tasmania.

20.

McNEIL, R.D. 1965. area, Tasmania.

The geology of the Mt Elephant-Piccaninny Point Pap.Proc.R.Soc.Tasm. 99:27-50.

21.

NOLDART, A.J, 1975. Inst.Min.Metall.

22.

QUILTY, P,G. 1972. The biostratigraphy of the Tasmania marine Tertiary. Pap.Proc.R.Soc.Tasm. 106:25-44.

23.

ROBINSON, V.A. 1974. Geologic history of the Bass Basin. Petrol.Explor.Ass. 14:45-49.

J.Aust.

24.

SKRZECZYNSKI, .R.

contact

aureole.

Triassic coal in Tasmania. 6:300-301.

1971.

The Bridport

granodiorlte

Monogr.Ser.australas.

and its

B.Sc.Hons.thesis, University of Tasmania : Hobart.

25.

SPRY, A.H,; BANKS, M.R. (eds.). 1962. J.geol.Soc.Aust. 9(2):1-362.

The geology of Tasmania.

26.

SUMMONS, T..G.; GREEN, D.C.; EVERARD, J.L. In press. The occurrence of chromite in the Andersons Creek area, Beaconsfield, Tasmania.

27.

SUTHERLAND, F.L.; KERSHAW, R.C., 1971. The Cainozoic geology of Flinders Island, Bass Strait. Pap.Proc.R.Soc.Tasm. 105:131-177.

28.

TURNER, N„J.

econ,Geol.

1980.

Composite geological profile across Tasmania.

Unpubl.Rep.Dep.Mines

29.

Tasm.

1980/38.

TURNER, N.J.; CASTLEDEN, R.H.; CALVER, C.R.; BAILLIE, P.W. In prep. Geological atlas 1:50 000 series. Zone 7 Sheet 49 (8514N). St Marys.

Explan.Rep.Dep.Mines

Tasm.

30.

WILLIAMS, E. 1959. The sedimentary structures of the Upper Scamander sequence and their significance. Pap.Proc.R.Soc.Tasm. 93:29-32.

31.

WILLIAMS, E. 1969. The repeated development of identical joint patterns, north-east Tasmania. Geol.Mag. 106:362-369.

32.

WILLIAMS, E. 1979. Tasman fold belt system in Tasmania. Explanatory notes for the 1:500 000 structural map of pre-Carboniferous rocks of Tasmania.

33.

WILLIAMS, E.; THREADER, V.M.

in Tasmania, 34.

Department

of Mines, 1971.

Tasmania.

Tectonic

setting

of ore

deposits

[Section 3, 41st ANZAAS Congress, Brisbane].

BLISSETT, A.H. 1959. The geology of the Rossarden - Storeys Creek district. Bull.geol.Surv.Tasm. 46.

A COMPOSITE GEOLOGICAL CROSS-SECTION IN NORTH EASTERN TASfAKNIA

Rock types as in figure 1.

from TURNER

1980

Symbols in addibion t o figure 2 Transitional InlriAsive

boundary

boundary

Unspecified

boundary

Boundary derived from gravity d a t a . Bedding trace - configuration poorly c o n t r o l l e d .

Bedding trace - configiAration controlled by detailed s t r u c t u r a l map. Projected position and scaled lengtK of supplementary s t r u c t u r a l profile. Cleavage trace-dominant, late, first, etc. Trace of foliation in granitoid.

N.6. TKe inferred configurations of geological s u r f a c e s skov^n on t k e profile are c o n s i s t e n t witW s t r u c t u r a l d a t a on tiae source m a p s . Since t k e fold wave-lengths in some u n i t s are siriort relative to t k e density of d a t a along tke profile line tke configurations are r e g a r d e d a s poorly controlled.

fold vergence. Fig. 3

RIBBON SECTION OF PARMEENER SUPERGROUP FROM SOUTH EAST TO NORTH EAST TASMANIA

Tasmania Deparbmenb of Mirws. CompilakiOM based on Clarke, Farmer and Guilline, TS^Calver £Castl«fllen(inpress), C3lver,pers. com.J bacon^ pers.com.; ForsytW, pers. com.

IUPPER FRESHWrnil

A. AAainly liiViic feldspakUic sandslone wikW coal seanrMyminor basall and minor acid volcanics. B. Mamly well sorted quartz sandstone. C. A^inly (^uartx sandstone witli coal seams.

I UPPER MARINE I SEQUEHCE

Extremely varied sequence of mainly calcareous siltstor»e, siltstone, mudstone and limestone. Arkosic and qlouconitic rocks subordinate.

LOWER FRESHWATER SEQUENCE

AAainly coarse - grained, well - sorted , cross-bedded quartz sandstone witk coal seams in places. Entire unit rarely more tkan 30m tkick.

SEQUENCE (C) AMD TAUSSIG ( A AMD »

STRATlGRIkPHY 6. STRUCTURAL SETTING OF LATE MESOZOIC L CAINOZOiC DEPOSITS

Compiled by Turner N . J 6. Forsytk S.M. from Robinson,'74; Cromer/80; Matthews/74 ; Brown, 7 8 ; Moore (pers. com.) ; QuiUy,'72; Sutherland, 7 0 ; F o r s y t k ; 8 0 ; Banks,'62. Tasmania Department of Mirws.

Marine d e p o s i t s - i n N.E.Tas. ikese are sands, clays and minor peats. Basalt

I

LOWIA lAARIME SEQUENCE

I

Very varied association of siltstone, mudstone, sandstone, conglomerate underlain in places by tbick tillite and rkytkmites.

Andesiie (radiometric age of associated appinite given). Terrestrial deposits - i n N 6. N.E.Tas. tkese are carbonaceous clays, sands 6. gravels.

PETROLOGY

AND

GEOCHEMISTRY

THE

NORTH By

EAST

OF

THE

GRANITIC

OF

TASMANIA

ROCKS

OF

M . P . McClenaghan

Geological Survey o£ Tasmania The majority of granitic bodies that make up the Blue Tier and Scottsdale Batholiths may be divided, on petrographic evidence, into three types; granodiorites, adamellites and alkali granites. Marker variation diagrams for the major and trace elements of the Blue Tier Batholith show that these types correspond to three chemical suites. For each suite there is an approximately linear relationship between Si02 and the other elements forming trends characteristic of that suite. The difference between the suites is clearest for the CaO and MgO trends. Individual rocks can be assigned to the appropriate suite on the basis of their T i , Rb and Sr ratios. The trends for analyses from the Gardens, Scamander T i e r , George River and Pyengana Plutons show slight differences. The analyses from Scottsdale Batholith rocks are similar to those from the Blue Tier Batholith except that the adamellites are more sodic and slightly less potassic. The linear relationships between Si02 and other elements suggests that the restite model of granitoid genesis (White and Chappell, 1977) may be applicable. Using the criteria of this model it is concluded that the granodiorite suite probably had an igneous source rock while the adamellite and alkali granite suites were derived from sedimentary rocks. The slightly different trends of the granodiorite pluton rocks may indicate their genesis from a different source rock or by different degrees of melting from the same source rock. In the latter case the source rock composition is estimated, based on the values at which the trend lines from the plutons intersect. The trend lines for one of the alkali granite masses (Lottah) show an unusual pattern with a number of elements trending to zero at the high and low end of the Si02 range for the b o d y . Using the unmixing model of the restite theory this implies that these granites were derived from a source rock of almost the same composition as the granite itself. It seems probable that some other model will be required to explain the origin of this granite. Comparison of the trends for major elements for the Gardens, Pyengana, Poimena and Lottah bodies with trends for I- and S-type granitoids of similar age on the mainland in the Kosciuscko and Moruya Batholiths shows that there are marked dissimilarities. The proposed I-types of the Blue Tier Batholith, the Gardens and Pyengana Plutons, are more potassic and less aluminous than the Moruya and Jindabyne suites. The Lottah body shows a very different pattern to the mainland suites having flat trends for both CaO and MgO instead of strongly negative trends. The pattern of chemical variation shown on the Marker diagrams for the granitoids of the north-east of Tasmania makes any model of genesis based on a single source magma unlikely. Reference: A.J.R. WMITE and B.W. CHAPPELL, 1977. Ultrametamorphism and granitoid g e n e s i s . Tectonophysics^ 43, p p . 7 - 2 2 .

TERTIARY

VOLCANIC

ROCKS

DEPOSITS

OF N . E .

By

AMONGST

THE

SURFICIAL

TASMANIA

F.L. Sutherland

The Australian Museum, Sydney Basaltic lavas erupted into a number of drainage systems in northeast Tasmania (Tamar River, Pipers River, Pipers Brook, St Patricks River, Little Forester River, Ringarooma River). Some cap higher isolated regions (Sidling, Blue Tier). Other flows descend below Bass Strait, where plugs and flows have been identified from magnetic anomalies. The oldest basalts overlie Middle-Upper Eocene sediments (Lower Tamar) and may be equivalent to the Upper Eocene flows at Devonport (38 m.y.) The youngest dated flows overlie Miocene sediments and in the WinnaleahRingarooma area give Middle Miocene ages (15.6-16 m.y.). Flow successions reach up to 250 m in thickness and near Blue Tier are underlain by more than 200 m of pyroclastics. Individual flows in the Tamar Valley reach 120 m in thickness. Some flows have displaced the drainage (St Patricks River, Ringarooma River), but the Tamar River has cut down through the thickest basalt sections. About fifty volcanic centres have been found or inferred and pyroclastics are exposed at Blue Tier, Forest Lodge, Boobyalla and Pipers River. Some centres are aligned along fault systems (e.g. Tamar Trough). Some faults mapped displacing basalt successions at St Patricks River are discounted on detailed examination. The lavas include olivine nephelinite, basanite, alkali olivine basalt, hawaiite, transitional olivine basalt, olivine tholeiite and quartz tholeiite. The tholeiitic association is confined to coastal strips extending from Cape Portland to Anderson Bay and Noland Bay and inland through St Patricks River to Epping. The alkali basalt association is found in the main granite areas and along the Tamar Trough. The reason for this distribution is uncertain, but may be due to greater degrees of mantle melting under a region of thinner crust. Studies on oliA^ne nephelinites from Lugurata, Flinders Island and Scottsdale suggest derivation by 4-6% melting of garnet peridotite mantle, with tholeiites forming at around 20-25% melting. A number of lavas carry xenoliths of mantle peridotite, which may be accompanied by clinopyroxene and spinel magacrysts (Corra Lynn, Blessington), pyroxenites (Winnaleah) and pyroxenites, gabbros and sanidinites (Scottsdale). Wehrlite inclusions in basalt at East Arm suggest that olivine and clinopyroxene played a role in the fractionation process. Alluvial sapphire, spinel and zircon are probably derived as megacrysts from the basalts, by analogy with other Australian occurences. The cause of the volcanism is uncertain. It was not directly associated with the main uplift and faulting of Tasmania in late Cretaceous to Palaeocene times and in Bass Basin took place in a subsiding region. One possibility is the northward passage of the Tasmanian lithosphere over anomalies in the mantle that were associated with earlier volcanism.

THE

SOUTHEAST

ASIAN

TIN by

PROVINCE

(MALAYSIA

AND

INDONESIA)

Brian C . Batchelor

Department of Geology, University of M a l a y a , Kuala Lumpur, Malaysia The S.E« Asian Tin Province which extends from Belitung Island (Indonesia) over 2700 km through Malaya, Thailand and Burma, accounts for 70% of the tin mined this century and half of the w o r l d p r e s e n t reserves. These deposits occupy the pre-Tertiary Sundaland core, separated from Far East deposits by the Red River Suture. 95% of production derives from placers. The region's productivity is due to a fortunate combination of a particular tectonic history and mineralisation styles, and Late Cenozoic subaerial processes acting on a deeply weathered, partially peneplaned continent. Tin mineralisation is related to S-type (highly evolved, K2O- and Si02- rich ilmenite-series) granitoids with high initial Sr^'^/Sr^^ (>0.708), suggesting derivation by anatexis of continental crust. In Malaya and Indonesia the Province is subdivided into 2 granitoid belts of contrasting character:- (I) Main Range Belt contains the 3 largest fields (Kinta Valley, Bangka Island, Kuala Lumpur), Virtually all recorded tin production (6,500,000 t) derives from placers. Deposits are associated with late Carboniferous and late Triassic granitoids. Mineralisation is confined to the batholith roof zones, as impounded ore bodies at granitoid margins or in hydrothermal stockworks. Greisen-bordered vein-swarms in granite, and similar swarms that halo granite cusps are the commonest mineralisation type. Though individually of limited size (i.e. too small to pay for hard rock mining), their aggregate amount of tin is very large. Weathering of the host rock and preferential removal of lighter barren components allowed such deposits to be the major placer source. (II) Eastern Belt. Recorded production (900,000 t Sn) includes a significant deep mined component from extensive lodes in argillites and volcanics within contact aureoles of Permian to mid Triassic plutons. There is an important Fe-Sn association. The Eastern Belt represents a former volcano-plutonic arc of Circum-Pacific type. The Main Range Belt probably resulted from crustal anatexis of the leading edge of a western craton as it attempted to subduct beneath the Eastern Belt following late Triassic collision. Discontinuously rising Late Cenozoic eustatic sea levels and accompanying climatic changes have been the major controls on Sundaland sedimentation, facilitating subdivision into Sundaland Regolith (SR; Late Miocene to Early Pliocene), Old Alluvium (OA; Early Pliocene to Early Pleistocene), Transitional Unit (TU; Middle Pleistocene) and Young Alluvium (late Quaternary). The SR including eluvial/colluvial placers, first developed under a semi-arid climate. The OA represents a piedmont fan facies (with placers) adjacent to bedrock scarps, grading downslope into a finer alluvial plain facies. Near the end of the Early Pleistocene, increased precipitation resulted in stream entrenchment forming residualelutriational and braided stream channel placers. Following lateritisation, another braided stream entrenchment formed TU placers. Reworking to form beach placers followed during two major transgressions across the Sunda Shelf. A drop of sea-level following the Riss-Wurm transgression resulted in deep meander incision and placer destruction, and although subsequent fill was generally tin-barren, these young valleys have been deceptive offshore exploration targets. Of paramount economic importance are piedmont fan, braided stream and residual-elutriational placers formed on the emergent Sundaland continent within OA and T U , and localised on the flanks of

positive granite features and in adjacent bedrock troughs, particularly those eroded along limestone-granite contacts. Seismic interpretation of stratigraphic *pay* horizons should provide the main basis for offshore drill target definitation and delineation of placer boundaries.

WHY

TASMANIAN

By

COAL?

Colin R . Ward

N.S.W. Institute of Technology Recent events in Australia and throughout the world have focussed attention on coal as a source of energy and hydrocarbon materials. Although the reasons behind the resurgence in demand are complex, Australia is in a good position to supply the increasing local and overseas market for this commodity, and it is generally expected that our coal industry will grow dramatically until at least the end of the century. The coal resources of Australia embrace a wide range of materials from high rank semi-anthracites in parts of the Bowen Basin to the extensive low rank brown coals of Victoria. Each deposit is best suited to a particular type of application, or combination of uses, depending on the petrographic and chemical properties of the coal, as well as the location and disposition of the seams concerned. Australia has sufficient * demonstrated recoverable reserves* of black coal to satisfy demand growing at the present rate for only another 45 years. If large-scale liquefaction plants are introduced, or if large areas of coal are sterilized by conflicting land u s e s , this life will be considerably shortened. It is essential that exploration of new deposits, and the systematic evaluation of known coal-bearing areas be continued at as high a level as possible, to maintain continuity of supply and to ensure that other developments proceed,with a full knowledge of all the factors involved. The coal industry of Tasmania is small by world standards, but highly important to several local industries. Most of the coal is relatively high in inertinite macerals and mineral matter, so that its usefulness for purposes other than combustion is limited. Although reserves are often thought to be low, they are likely to be increased with further exploration in several areas. Because of the complex geologic setting, this exploration will be difficult, and expertise from a wide range of fields will be needed for its successful completion.

KAOLIN:

AN

EXPORTABLE

By

F.C. Loughnan

PRODUCT

University of New South Wales In the exploration for ore deposits in Australia, the non-metallic minerals are frequently overlooked despite the fact that most if not all such minerals are essential to industry in this country. Indeed, imports satisfy much of our requirements yet it is conceivable that this country could develop into a major exporting nation of non-metallics. The kaolins afford a good example in this respect. 10

The world

currently produces more than 8 million tons annually from deposits of hydrothermal^ weathered and transported origins with the major suppliers being Georgia, Cornwall and U.S.S.R. Of this production the paper industry consumes nearly 50%, for both filling and coating purposes, followed by refractories, rubbers, ceramics and a wide array of lesser users including paints, plastics and pesticides. For each of these products the kaolin must have specific physical and rheological properties and to achieve these generally beneficiation is necessary. For the higher priced kaolins, such as those used in paper coating, this beneficiation is quite extensive and considerably adds to the cost. Paper kaolins are currently being produced at three localities in Australia; at Pittong and Lai Lai near Ballarat in Victoria and at Gabbin in Western Australia. All of these deposits have formed by deep weathering. However, production is limited. Although a wide array of kaolinitic clays are used in the production of refractories, international trade is mainly restricted to flint clays, a contraction of 'flint-like fireclay', and their calcined product, chamotte. Flint clays are extraordinarily dense, indurated clayrocks composed essentially of well-ordered kaolinite and range in texture from very fine grained to oolitic, conglomeratic and coarsely brecciated. South Africa and the Appalachian States and Missouri in the U . S . A . are the main suppliers although chamotte is also being produced from kaolin clay at lone, California. Australia imports most of its requirements for chamotte despite the fact that probably the largest reserves of flint clay in the world are to be found in the Permian, Triassic and Jurassic non-marine strata of the Sydney Basin. Indeed, it is possible that other coal measure strata in eastern Australia contain extensive deposits of this material. In the Sydney Basin these deposits have also proven valuable as marker horizons. Kaolin is also extensively used as a filler and extender in both natural and synthetic rubbers; to improve tensile strength, abrasion resistance and rigidity. Such kaolins are classified as hard or soft depending on whether they impart hardness to the rubber. Australia still imports some of its requirements in this respect, although of late there has been a noticeable tendency to use more of local materials. Ceramic kaolins are of necessity low priced and are mostly obtained locally. Hopefully a greater awareness of the economic potential of nonmetallic minerals, particularly kaolins, will promote more intensive exploration in the future. CASE

STUDIES

ILLUSTRATING By

THE

USES

OF

SIROTEM

R . J . Henderson

Geoex Pty Ltd, Adelaide Sirotem, a digital, computerised TEM system was originally developed to detect sulphides in difficult circumstances such as beneath thick, conductive overburden. This objective has been achieved and the technique has since been found useful for high-resolution resistivity mapping of structure in coal, oil-shales and alluvial deposits. Casestudies from Elura, Leigh Creek, Queensland, South Africa and U.S.S.R. will be examined to illustrate all these various applications.

11

ASPECTS

OF

COAL

EXPLORATION By

IN N . E .

TASMANIA

W.H. Koppe

Shell Company of Australia The Shell Company of Australia is currently engaged in exploration for coal in two contiguous Exploration Licence areas covering 2250 km of north-east Tasmania. Since early 1978 18 787 m of mainly cored drilling has been completed in 45 holes. Although coal has been mined on a small scale in the region since late last century, systematic exploration has been implemented only in the last twenty years. The very high cost of the deep boreholes necessary for exploration ensures that a full assessment of the regions coal resources will be a protracted and expensive process. The prospective sequence for all coal exploration is the uppermost part of the Triassic upper Parmeener Supergroup. This 400 m thick fluviatile coal measure sequence is conformably underlain by barren Triassic sediments, and overlain with regional discordance by dolerite which was intruded into the Triassic sequence during the mid Jurassic. In general the coal measures are now concealed beneath a thick dolerite capping, the exceptions being scarp exposures along valleys eroded into dolerite plateaux. Major faulting has occurred along north westerly and north easterly trends, but there has been virtually no folding, and the regional dip of 1° to to the south-east is relatively uniform. Coal seams of economic significance are between 1 and 4 m thick with a tendency to seam splitting and variation of roof lithologies. The coal itself is hard, very dull, of High Volatile Bituminous rank with a high inherent ash and low sulphur content. A combination of relatively high specific energy and favourable ash fusion properties make it ideal for power generation although its ash content is generally above the tolerances of the export market. The occurrence of most of the regions coal resources beneath thick dolerite cover, poses distinct exploration problems. From holes which, by virtue of their high individual cost, are necessarily widely spaced, the exploration geologist is faced with assessing seam thickness and quality variations, roof and floor variations as well as the incidence of faults and other geological mining constraints. Geophysical techniques can make a valuable contribution to the understanding of the distribution of faults and intrusions, but the critical aspects of seam, roof and floor characteristics can only be obtained from drill holes. This limitation serves to emphasise the importance of obtaining the maximum amount of relevant coal quality and geotechnical information from each intersection of potentially mineable coal.

12

GEOPHYSICAL

EXPLORATION

OF T H E

EAST

COAST

COALFIELD,

TASMANIA By

D.E„ Leaman

Geological Survey, Tasmania A suite of geophysical methods has been used to make a structural evaluation of a large portion of Eastern Tasmania. The region examined includes the Nicholas, Fingal, Lewis Hill and Seymour coalfields. Detailed examination has been restricted to Fingal Tier. The evaluation is based on two gravity surveys; one regional with a nominal one kilometre station spacing, the other restricted to Fingal Tier with a nominal 300 m spacing. Analysis of the Bouguer anomalies using filter, residual and continuation procedures coupled with a three dimensional model interpretation suggests that: -

-

the Triassic coal-bearing section is generally in excess of 300 m thick; the capping dolerite sheets are very irregular in form and thickness; there are several large feeders and many lesser pipes; the section is extensively faulted.

The gravity surveys have defined areas in which the coal bearing section is thick, where dolerite may truncate the workable seams, where the cap is thin or where dolerite has removed the section entirely. This information has been used to guide the drilling programme and reduce costs. The gravity surveys have been supplemented by surface and airborne magnetic surveys. The magnetic surveys yield useful confirmatory data but lack the resolution of the gravity coverage. Surface magnetic surveys are recommended as an aid to geological mapping and resolution of boundary location and talus/outcrop problems. The resistivity method has been tested on the coastal plain at Seymour with disappointing results. Trials were directed at shallow seam tracing. Much better results were obtained by seismic reflection methods in the same environment. High resolution seismic reflection techniques were extended to dolerite-covered areas, as on Fingal Tier, following extended assessment of shot, geometry and frequency problems. Some twelve kilometres of traverse have now been shot and results of preliminary processing are encouraging. Some optimisation of field and processing conditions is still necessary but there is hope that seam tracing and fault location will be routinely possible. In the case of each of the three methods yielding some successful results in this challenging geological environment new procedures, field and processing, have been developed. Standard practices, not specially modified to match the objectives, would fail or lead to misleading results.

13

COAL

EXPLORATION, By

FINGAL

EXEMPT

AREA

R.H. Castleden

Geological Survey of Tasmania Exploration for coal in the Fingal area commenced in 1960 with limited diamond drilling by the Department of Mines for the Cornwall Coal Company N.L. This *ahead-of-mine' drilling was designed to prove the existence of the Duncan Mine seam in the vicinity of this mine operated by the company near Fingal. Threader (various Department of Mines unpublished reports) has provided summaries of coal exploration activity ranging from this initial phase until mid-1979. At this time exploration by the Department of Mines increased in an area exempted from the Mining Act of 1929. This area is located to the south and east of the Duncan Mine and comprises approximately 94 square kilometres. To date, 61 diamond/percussion drill holes have been completed. Time-tabling on the project involves an assessment of measured/indicated reserves over the entire Fingal Exempt Area during 1981/82. Coal seams of workable thickness occur in Triassic sediments belonging to the Upper Parmeener Supergroup apparently conformably overlying Lower Parmeener Supergroup glaciomarine siltstone and mudstone. Basement rocks consist of a micaceous quartzwacke turbidite sequence of Siluro-Devonian age (Mathinna Beds) which have locally been intruded by a suite of Devonian granitic rocks. The coal measure sedimentary rocks suffered intrusion by dolerite during Jurassic times, this has resulted in the presence of thick sills, minor dykes and major centres of intrusion ('feeders*) in the sedimentary pile under investigation. Faulting, contemporaneous (?) with dolerite intrusion and also of Tertiary age, has caused periodic offsetting of the coal seams. Erosion to the present day has resulted in the formation of a landscape of rugged disposition, with dolerite talus mantling the areas of higher relief and occasionally occupying valley floors. The lowest member of the Upper Parmeener Supergroup in the Fingal Exempt Area consists of a series of quartz arenites and associated siltstone and mudstone. These are overlain by a lithic arenite sequence containing up to eight recognizable coal-developing intervals. Minor quartz arenites reappear below the topmost member of interbedded lithic arenites and siliceous conglomerate. Coal members have a high inertinite content with abundant dispersed mineral matter. Exploration for coal in the area is complicated by the nature of the dolerite intrusions and faulting. Exploration guidelines which have proved useful are outlined. (i)

Areas of excessively thick dolerite need to be avoided. These areas are delineated by the following geophysical methods: (a)

(b) (c)

gravimetric - gravity survey generally with one kilometre station spacing, but this is reduced to nominally 250 m in the Exempt area. magnetometric - airborne and ground magnetometer. seismic - high-resolution reflection seismic surveys yield finer details concerning the shape of dolerite intrusion centres and will hopefully indicate any disruption in the major coal seams. 14

(ii)

Nominal two kilometre exploration drilling grid; exact location guided by the results of the detailed gravity survey.

(iii)

Closer spaced drilling to upgrade reserves to a measured category in favourable areas. For this exercise, drillsite separation is nominally one kilometre.

(iv)

Pre-collaring of drill-holes by a percussion rig has been moderately successful.

(v)

Due to the problems associated with drilling dolerite talus, these areas have been avoided where possible.

(vi)

Towards the lowermost part of the lithic arenite sequence attention has been focussed on two seams as a result of their quality and overall continuity. These are the Duncan seam and the East Fingal seam.

Problems to be overcome before a meaningful estimate may be placed on coal reserves in the Fingal Exempt Area are due to: (i)

Transgressive and unpredictable nature of dolerite intrusions.

(ii)

Difficulty in delineating faults with throws of less than 20 m.

(iii)

Lenticular nature of the majority of the coal horizons.

(iv)

Lack of stratigraphic markers in the Upper Parmeener Supergroup, hence the need to drill to the Lower Parmeener Supergroup.

(v)

Splitting of the East Fingal seam.

Because of these problems., it is difficult to place a figure on reserves. A conservative estimate would be 30 million tonnes measured in situ and 50 million tonnes indicated in situ. A full appraisal of reserves must await the completion of diamond drilling, an assessment of geophysical parameters, and a careful examination of the results of chemical analysis. A representative analysis for the Duncan seam as intersected in 50 mm diameter diamond drill core is: Thickness (m)

1.5-3.0

Moisture as received (% W/W)

3-5

Proximate analysis dry basis (% W/W) Fixed Ash Volatiles carbon 30

30

Ash fusion temperature (°C) 1500-1600

15

40 % Sulphur <0.5

Specific energy (dry basis) MJ/kg 18-22

Washability Cumulative floats. Mass Ash SI.40 SI.60

F1.40 F1.60 F1.80

sr. 80

THE

GEOLOGY

OF

By

Cumulative sinks, % Mass Ash

24 72 84 100

10

100

18 22

28

30

16

THE

DUNCAN

76

30 36 60 70

COLLIERY

V.M. Threader

Geological Survey of Tasmania The Duncan coal mine in the Fingal Valley has a variety of mining problems; unstable roof conditions, faulting, sedimentary bands, floor heave, intrusions, variable seam thickness and seam splitting. These are all contributory factors to the difficulties of mining. The marginal quality of the coal and the thick overburden are economic factors which, together with the mining difficulties already mentioned make it extremely difficult for the exploration geologist to convert in situ reserves into recoverable reserves. A brief history of the coal mine is given and current theories of the environment of deposition are discussed. A geological map of the coal mine is presented and discussed. The degree of success attained in the Duncan colliery in overcoming the mining problems is the key to assessing the likelihood of any real growth in the coal mining industry in the valley. The experience gained in the Duncan and other collieries previously worked in the district and the knowledge of their geological setting should allow new mines to be planned in such a way that many of these difficulties can be overcome.

16

DESCRIPTION

AND

GEOLOGICAL

SETTING

BASALT

NORTH

OF

ST M A R Y S ,

By

C.R., Calver

N.E.

OF

TRIASSIC

TASMANIA

Department of Mines, Tasmania A flat-lying Permian sequence of dominantly marine sedimentary rocks (the Lower Parmeener Supergroup) overlies deformed basement rocks and onlaps a basement high centred north of St Marys. An erosional disconformity marks the base of the Triassic coal measures (the Upper Parmeener Supergroup), dominantly composed of lithic sandstone. Two conformable units of alkali olivine basalt are found within the lowermost beds of the Triassic, cropping out along the northern and eastern slopes of the Nicholas Range and on St Patricks Head. The upper unit has a considerably wider extent than the lower, and overlaps it in all directions. Field relationships indicate that these units were emplaced as both flows and as shallow intrusions. Air-fall material is rarely found. The two units are petrographically similar except that the lower unit contains plagioclase megacrysts, rarer olivine and darker-coloured (more titaniferous) augite. Both units have a distinctively high content of combined alkalis and of titania. A whole-rock K-Ar minimum age of 233± 5 m . y . has been obtained from the lower u n i t . These are the first contemporaneous igneous rocks to be recorded from the Parmeener Supergroup. TRIASSIC

PYROCLASTICS

NORTH-EASTERN By

NEAR

BICHENO

IN

TASMANIA

C . A . Bacon

Department of Mines, Tasmania Extensively altered, rather poorly welded ash-fall tuffs of rhyolitic to rhyodacitic composition occur both in situ and as loose talus blocks at five localities near Bicheno, in north-eastern Tasmania. Three closely spaced tuff layers, up to 0.75 m thick, have been intersected in a drill core. These tuff layers and the four outcrops may represent the same stratigraphic horizon. The rocks contain phenocrysts of embayed quartz, kaolinized feldspar and altered vermiculite in a devitrified matrix -of quartz and kaolinite, in which may be discerned relict glass shard and bubble structures. In some localities the vermiculite has been thermally exfoliated suggesting heating to more than 3 0 0 d u r i n g the intrusion of nearby Jurassic dolerite. Rhyolite pebbles found within Quaternary river gravels are probably derived from a Triassic rhyolite flow, now either totally eroded or buried. The pyroclastics are found in a fluvial sequence of lithic arenites, mudstones, shales, siltstones and coal, belonging to the Upper Freshwater Sequence of the Parmeener Super Group. Macroflora and microfloral evidence indicates a Late Triassic, probably Karnian, age for the pyroclastics.

17

TIN

IN N O R T H E A S T By

TASMANIA

D.J. Jennings

Department of Mines, Tasmania Tin occurs in northeast Tasmania as lode cassiterite, associated with mineralized granites of the Blue Tier Batholith of Devonian age and as alluvial deposits. The form of occurrence of lode tin with granite is extensively documented (e.g. Reid and Henderson, 1928; Groves and McCarthy, 1978). Geological field evidence, the location of old mines and theoretical models suggest a concentration of primary cassiterite locally in flattish zones at high levels in the granite and in overlying remnants of metamorphosed sediments. With such large areas of granite presently exposed it is obvious that much of the roof zone has been removed by erosion, and with it much cassiterite. Although remnants of source lodes for some alluvial deposits can be located, often the source lode has been totally eroded. Fluctuations in relative sea level controlled the rate of erosion of the Blue Tier Batholith and its sedimentary cover, and dictated the site of subsequent sedimentation, and with it local deposits of alluvial cassiterite. Emergence of the land mass at a late stage resulted in the exhumation of Tertiary river channels, with their local enrichments of cassiterite. Exploitation of these deposits has been complicated by their geometry, and the protection afforded by overlying basalt flows. Major alluvial tin mines operated in several localities at the break in slope where tributary torrent creeks from the Blue Tier Massif join the flood plain of the ancient Ringarooma river. The natural concentration of alluvial cassiterite depends upon the winnowing effect of moving water and the greater density of this mineral than of other weathered rock components. These characteristics have always been exploited in mining and in exploration. Traditional exploration methods are to search out the mineral directly with shovel and pan. Pitting, and drilling in areas surrounding known tin deposits, is an extension of this philosophy. A more sophisticated approach is to attempt to interpret the pre-depositional Tertiary geomorphology and hence anticipate suitable buried topographical traps, and test them. Originally deeper ground was tested with hand drills and subsequently mechanical drills such as percussion rigs and the Conrad pit sampler. A more recent' innnovation, tried with varying success, is the reverse circulation drill, and a foundation drill with a cubic metre bucket. Attempts to adjust standard and innovative geophysical techniques to alluvial tin search have produced limited success. Attempts have been made to locate cassiterite and associated heavy minerals directly, relying on magnetic or electrical response, but more generally to define depositional traps in the subsurface bedrock topography. A combination of resistivity, gravity and seismic methods, with adequate drilling control, has achieved some success in interpreting the concents of Tertiary sedimentary basins. Major complications in the interpretation of geophysical data are the widespread but unpredictable occurrence of silcrete and ferricrete in the Tertiary succession; the physical similarity between weathered granite bedrock and overlying sediment of identical composition; fluctuations in water table, and the extremely small and dispersed amount of cassiterite required to make an economically viable deposit. 18

Alluvial tin mining has employed similar principles for decades with surges of development in line with advances in technology. Sluice boxes have been in part replaced by jigs and spirals. The original requirements of a gravity water supply and a gradient for tailings disposal have been largely eliminated by the advent of the diesel engine and pressure pump, and massive earth-moving equipment including scrapers. The major alluvial tin mines of the past were located on deep leads at the foot of the Blue Tier massif, peripheral to the South Mount Cameron basin. The major known reserves are still extensions of these deposits. References: Groves, D.I. and McCarthy, T.S. 1978 : Fractional crystallisation and origin of tin deposits. Mineral.Deposlta,, 13, pp.11-26. Reid, A.M. and Henderson, Q.J. Tasm.Bull.,

1928 : Blue Tier tin field.

Geol.Surv.

38.

SAMPLING

PROBLEMS

By

IN

ALLUVIAL

TIN

EXPLORATION

W.W. -S. Yim

Department of Geology, University of Tasmania, GPO Box 252C, Hobart, Tasmania Accurate assessment of the tin content of a placer deposit is difficult because of sampling problems. Nevertheless, as ore reserve estimations are based on these samples, an attempt should be made in sampling to obtain a sample that is representative of the deposit. The sampling problems encountered during soil and stream sediment geochemical surveys, drilling and laboratory analysis are briefly reviewed. The possibility of sampling errors is large at low tin concentrations since tin occurs as discrete particles of cassiterite. Although these errors may be minimised by adopting sample pre-concentration and homogenisation procedures, soil and stream sediment geochemical surveys could not be used to identify concealed placers. It is often difficult to correlate between adjacent drill-holes because of local variations in tin distribution, and to provide an accurate assessment of the ore grade from the recovered drill-hole samples. The ore grade is best determined after bulk sampling with plant-scale recovery. Quantitative mineralogical studies of pre-concentrated samples are less prone to sampling errors and may provide further information useful to exploration. Much may be learnt about the erratic distribution of tin in placers through a study of pit exposures.

19

THE

GEOLOGY

OF

PLACER

NORTH By

TIN,

EAST

RINGAROOMA

VALLEY,

TASMANIA

K. Morrison

Amdex Mining Limited Three main styles of placer tin deposits are recognised. (1)

Deposits of coarse black cassiterite in poorly-sorted, boulder-rich sediments at relatively elevated sites.

(2)

Deeply buried deposits of relatively fine-grained black and brown cassiterite, with abundant ilmenite and monazite, in a sedimentary sequence dominated by stratified gravels, trough cross-bedded granules, planar cross-bedded sands, and peat u n i t s . This type occurs at a major break in basement slope.

(3)

Shallow surficial deposits of red, yellow and black cassiterite, plus accessory spinel and gold, in a fining-upwards sequence of pebbles, sands and clays. This type is restricted to the present Ringarooma River and preserved remnants of elongated zones which run essentially parallel to the river.

A maximum age for sedimentation is inferred as Late Oligocene Early Miocene by pollen dating. A regional basalt age of 16 m . y . (Brown, 1977) temporally separates Type 2 and Type 3 deposits. Sedimentological and palaeobotanical evidence is consistent with a depositional model involving a pre-basalt series of braided fluvial fans flowing into, and being transgressed b y , a body of fresh water.

20

BIOGEOCHEMISTRY

OF

TO By

GOLD

AND

ITS

APPLICATION

PROSPECTING W . E . Baker

Geological Survey of Tasmania Theories o£ the transport of gold fall generally into two classes ionic/colloidal and organometallic. Studies at the Department of Mines, Tasmania, strongly support an organic mechanism of gold mobilization. The literature dealing with the gold content of plants is somewhat controversial and does not offer encouragement for use of biogeochemical methods in gold prospecting. Analytical techniques have been developed w h i c h , although very much on trial, allow determination of gold down to about 5 ppb (ng/g). Application of these techniques to various plant species in the Lisle Basin, N.E. Tasmania, suggests that biogeochemical studies of gold may be usefully applied to prospecting for gold.

THE

OCCURRENCE CREEK

OF

CHROMITE

IN T H E

ANDERSONS

AREA, BEACONSFIELD , TASMANIA By

T . G . Summons

Department of Mines, Tasmania Lateritic weathering of the Andersons Creek Ultramafic Complex during the late Mesozoic resulted in an initial in situ concentration of chromite. Later erosion of the laterite profile occurred, resulting in the deposition of sediments containing low grade concentrations of chromite, in a ?paralic environment during ?Palaeocene -?early Eocene time. Significant concentration of chromite was effected in the transitional environment represented by both fluviatile and ?marine processes during the ?early Eocene. Subsequently continental conditions of deposition were established in the mid Eocene, with minor concentrations of chromite formed by the re-working of pre-existing chromite deposits.

21

THE

PIEZOELECTRIC

EXPLORATION QUARTZ

TECHNIQUE

FOR

MINERALISED

VEINS

By J.R. Bishop Mitre Geophysics Pty Ltd, Elliott, Tasmania Quartz is piezoelectric, that is, electric charges will appear on certain surfaces of a quartz crystal when a stress is applied. The piezoelectric exploration technique utilises this property for the detection of quartz veins or pipes. A seismic source is used to stress a quartz body and resulting charges on the surface of the quartz body set up an electric field which is measured by recording voltages between electrodes placed on the ground. These charges will only occur if the crystals forming the quartz vein or pipe are suitably aligned. Assuming that the constituent crystals have these preferred orientations (and recent laboratory experiments have confirmed their existence in quartz mylonites), then the location of a quartz body is determined in the following manner. The elapsed time between onset of the seismic signal and the arrival of a signal at the electrodes is recorded. Since the time taken for the signal to travel from the body to the electrodes is effectively zero (the electromagnetic signal travels at the speed of light), the elapsed time is the time taken for the seismic signal to reach the quartz body. If the seismic velocity of the host rock is known, then the distance from the shotpoint to the body may be calculated. Recordings from several shotpoints in different positions will locate the quartz body. Research into the application of piezoelectricity for the detection of quartz veins or pipes (associated with mineralisation) has been carried out in the U.S.S.R., for over twenty years, but only recently has the method been investigated in the West. The Russian literature states that detection distances of several tens of metres have been achieved above ground and up to nearly one hundred metres underground. Despite the long history of development in the U.S.S.R., the method is not yet used there on a routine basis and research both here and in Canada confirms that signal levels are low and noise levels are high. However, it is expected that with more sophisticated recording and excitation equipment than has been tried hitherto, the method could be used to advantage in the detection of mineralised quartz veins such as occur in north-east Tasmania.

22

EXCURSION GUIDES

EXCURSION 1 (Leader - P . L . F , THE

LUTWYCHE

VEIN

Collins) SYSTEM

NORTH-EAST By

AT THE A B E R F O Y L E

MINE,

TASMANIA

P.L.F. Collins^, I. Keyes^.

^Geological Survey of Tasmania, Department of Mines, Tasmania ^formerly of Aberfoyle Tin Limited, Rossarden, Tasmania The Aberfoyle tin-tungsten deposit, located at Rossarden, is the largest mine within a small but significant tin and tungsten mineral field associated with the Ben Lomond Granite in north-eastern Tasmania. The only other producing mine in the field is the Storeys Creek tungsten mine at Storys Creek, three kilometres to the north. Total production from the Aberfoyle mine to the end of 1978 is approximately 2 102 000 t of ore milled for 15 375 t Sn and 5 272 t WO3. In 1979, about 25 000 t of ore was milled for 154 t of cassiterite concentrates (114 t Sn) and 155 t of wolframite concentrates (111 t WO3). The Aberfoyle mine has recently entered into a new phase of development with an underground extension into the Kookaburra-Lutwyche vein system, located approximately 800 m north-northeast of the main Aberfoyle shaft (Spiers Shaft, fig. 1). Geology

The geology of the area and geological setting of the deposit are described in detail by Blissett (1959) and Kingsbury (1965). Host rocks of the mineralisation are the Mathinna Beds of probable Silurian to Early Devonian age (Williams, 1979). The Mathinna Beds are composed of conformable sequences of graptolite-bearing deep water sediments, mainly mudstone and interbedded mudstone, siltstone and turbidite quartzwacke, and have been intruded by several altered, pre-ore, mafic sills and dykes up to 0.5 m wide. The sediments were intensely folded along NW-SE trending axes during a period of orogenesis correlated with the Tabberabberan Orogeny. Quartz was mobilized into irregular * country' quartz veins which may be confused with ore veining. The Mathinna Beds were intruded by the post-kinematic Ben Lomond Granite which crops out over an area of 130 km^ and has been dated by K-Ar methods at 365-342 Ma (McDougall and Leggo, 1965). The granite is a coarsegrained, porphyritic, leucocratic (pale cream or pink) biotite granite with a finer grained margin frequently containing tourmaline and muscovite, and is intruded by numerous irregular dykes and masses of grey porphyritic microgranite. Local bulges in the granite may be topped with cupolas of aplite such as beneath Aberfoyle, where the cupola is 320 m below surface and has an irregular east-west elongation (Robinson, 1956). The pale grey aplite consists of grains of irregular quartz, sericitized orthoclase, albite laths and muscovite exhibiting a hypidiomorphic granular texture with minor sphalerite and rare molybdenite. Little cassiterite and wolframite occur in the granite itself, e.g. in greisen at Rex Hill and Gipps Creek on the western edge of the granite (Blissett, 1959; Kingsbury, 1965). Contact metamorphism is reflected by weakly biotitized sediments and chiastolite slate within 60 m of the aplite. An aplite cupola has not been located beneath the 23

Kookaburra-Lutwyche veins but biotite occurs in sediments in a deep drill hole (Kingsbury, 1965). A period of prolonged erosion and peneplanation was followed by the deposition o f Late Carboniferous-Late Triassic marine and freshwater sequences which were later intruded by Jurassic dolerite (e.g. Ben Lomond Plateau). Erosion has since removed the bulk of the post-ore cover, almost restoring the pre-Permian surface. Small deposits of recent cassiteritebearing alluvials occur in creeks. Mineralisation The quartz-cassiterite-wolframite veins of the Aberfoyle deposit are genetically related to the aplite cupola which presumably is an apophysis of the main granite body that crops out 1.5 km to the south-east. The Aberfoyle vein system comprises up to eight main veins (up to 1.5 m) forming a steep west-dipping sheeted zone about 70 m thick and 500 m long. General strike is 010°-020'' with dips of 60°-65°W in the upper levels, flattening to 45''-50°W in the lower levels. The Aberfoyle deposit was found through a small outcrop of veining in Aberfoyle Fault, one of several north to north-east trending pre-ore faults, but the veins proper were hidden beneath the Permian sediments (fig. 1). Economic mineralisation extends from the cupola almost to the surface. Cassiterite and wolframite occur throughout the vein system, but mine production statistics indicate a vertical zonation with the ratio of wolframite to cassiterite increasing with depth. A quartz capping o f the cupola (the 'Contact Vein') is associated with some greisenization of the aplite, and although mainly barren quartz, may contain masses of cassiterite (Blissett, 1959). The Aberfoyle vein system has been described by Lyon (1957) and Blissett (1959), and the mineralogy of the veins has been described by Edwards and Lyon (1957). Although the Lutwyche vein system is almost transverse to the Aberfoyle system (fig. 1), both the form and mineralogy of the veins are similar. A variably developed muscovite selvedge precedes all other mineral deposition in the veins which occurred in the following paragenetic sequence of three overlapping stages (after Edwards and Lyon, 1957): Early

Cassiterite, wolframite, fluorite, muscovite, apatite, topaz and triplite with rare bismuth;

Intermediate

Quartz plus sulphides (arsenopyrite, pyrite, pyrrhotite, chalcopyrite, sphalerite, stannite, tetrahedrite and molybdenite(?);

Late

Carbonates (calcite, siderite, rhodocrosite), minor sulphides (chiefly galena, with tetrahedrite and matildite), scheelite (alteration of wolframite), marcasite, secondary pyrite, magnetite, hematite and bismuth.

The first two stages are of primary deposition, and the last stage includes both primary deposition and secondary remobilization. Lutwyche

Vein

System

Whereas the top of the Aberfoyle veins were eroded prior to the Late Carboniferous sedimentation, the Lutwyche vein system appears to have escaped erosion and hence presents a unique opportunity for examination of the surface expression of the top of a major vein system and of ore grade 24

Battery^vein LUTWYCHE VEIN SYSTEM

KOOKABURRA SYSTEM

SECTION

THROUGH

LUTWYCHE CROSS Fig 1

CUT

VEIN

veins in the same system at depth. At the surface, there are two sets of veins located within a zone of silicified quartzwacke which forms a ridge dissected by Aberfoyle Rivulet [fig. 1). The Lutwyche vein system comprises numerous cassiteriteand wolframite-bearing quartz stringer veins up to 10 cm thick, occurring within a'NW-SE trending zone approximately 30 m wide and at least 150 m long, and dipping 50°W (fig. 1). Individual veins generally dip 45°-65°SW and strike 140°-150°. Towards the northern edge of the Lutwyche vein system is a second transverse set of near-vertical quartz veins (Battery vein, fig. 1) striking 040°-050®. The Battery veins are less than 10 cm thick and contain relatively abundant cassiterite. At depth, on 13 Level, some 300 m below the surface, there are three sets of main veins, summarised as follows: (1)

Lutwyche Veins (Footwall Vein, Hanging Wall Vein, South Hanging Wall Vein). These strike ISO'^-IGO^, dip 40''-50''SW and are generally 30-50 cm thick but may be up to 80 cm thick;

(2)

Pay/Prospect Veins. These veins have a north-south strike, dip 65°-75°W and are generally 25-40 cm thick;

(3)

Battery Vein. This vein is vertical, strikes 045"" and is generally 50-70 cm in thickness but may be up to one metre thick.

Near the ventilation borehole on 13 Level the earlier Battery Vein is dissected by several splits of the Lutwyche Footwall Vein. Other vein relationships are unknown. Each of the main veins exhibit en echelon structures, particularly at the lateral extremity of a vein. The mineralogy is similar to the Aberfoyle veins with wolframite, cassiterite and sulphides, chiefly sphalerite and chalcopyrite, being locally abundant. There is evidence of two phases of veining in the Hanging Wall Vein as indicated by wolframite blades (transverse to the vein) occurring on the edge of the vein and two adjoining sets of wolframite blades in the middle of the vein.

Acknowledgements The assistance and co-operation of Aberfoyle Tin Limited, particularly P.J. McGushin, G. Beattie and A. Titley, are acknowledged.

References BLISSETT, A.H. 1959. Bull.geol.Surv.Tasm.

The geology of the Rossarden-Storeys Creek district; 46, 120pp.

EDWARDS, A.B.; LYON, R.J.P. 1957. Mineralization at Aberfoyle tin mine, Rossarden, Tasmania, australas,Inst.Min.Metall.Proc. 181:93-145. KINGSBURY, C.J.R. 1970. Cassiterite and wolframite veins of Aberfoyle and Story's Creek, in McAndrew, J. ed.. Geology of Australian ore deposits, 2nd ed. Publ. 8th commonw.miniinetall .Congr. LYON, R.J.P. 1957. The Aberfoyle vein system, Rossarden, Tasmania. australas.Inst.Min.Me tall.Proc. 181:75-91.

25

McDOUGALL, I.; LEGGO, P.J. 1965. Isotopic age determinations on granitic rocks from Tasmania. J.geol.Soc.Aust. 12:295-332. WILLIAMS, E, 1979. Tasman fold belt system in Tasmania. Explanatory notes for the 1:500 000 structural map of pre-Carboniferous rocks of Tasmania. Revd.ed. Department of Mines^ Tasmania, 29.

26

EXCURSION 2 (Leaders - C. C a l v e r , FINGAL

R. C a s t l e d e n )

VALLEY

-

ST MARYS

AREA

The Parraeener Supergroup in north-east Tasmania unconformably overlies folded and metamorphosed sediments of the Mathinna Beds, or lies directly on granite basement. The Supergroup, formally subdivided by Forsyth et.al. (1974) consists of a lower part, mostly Permian in age, which contains marine, glacio-marine and freshwater sequences. The upper part, mostly Triassic in age, is a freshwater sequence which contains significant coal measures and two concordant Triassic basalt flows. This excursion examines these sequences in the Fingal Valley - St Marys area. The itinerary may be altered to suit participant preferences. Detailed description of the basalt exposures at locality 6, and the drill hole log at locality 8 are given after the itinerary. Locality numbers are indicated on the accompanying map. (i)

Launceston (Midland Highway) Conara Junction - 9.00-9.30

(ii)

Conara Junction (Esk Highway) Fingal -

(iii)

Fingal to saddle between Mts Durham and Nicholas. Locality 1: Lithic sandstone of Upper Parmeener Supergroup (Triassic) 10.00-10.30 Locality 2 (optional): Jurassic dolerite dyke intruding Upper Parmeener Supergroup mudstone and lithic sandstone

(iv)

From (iii) to Locality 3 via the Avenue Road (Forestry Commission Plantation area) and Cato»s Road. Locality 3: Sandstone-siltstone-limestone interval in the Lower Parmeener Supergroup (Upper glacio-marine division) 10.30-11.00

(v)

From (iv) to Locality 4: Unconformity between the Siluro-Devonian Mathinna beds and Permian Lower Parmeener Supergroup sediments, minor Neptunian dykes (?)

(vi)

Glossopterisf^?)

and

Gangamopteris

(?) locality

11.15-11.30

From (vi) to Locality 6: Two conformable (?) basalt units within the lowermost beds of the upper freshwater division of the Parmeener Supergroup at Webber'Falls

Lunch: (viii)

11.00-11.15

From (v) to Locality 5: Lower freshwater sequence in the Lower Parmeener Supergroup.

(vii)

9.30-10.00

11.30-12.30 12.30-1.00

From (vii) to Locality 7: Coal seam (unidentified) occurrence above Triassic(?) basalt. Exposed on the Forestry Commission 'S' road. Hydro-plastic deformation at base of the basalt 1.00-2.00 27

(ix)

From (vii) via St Marys to the Valley Road/ 'MG' Road and Locality 8: Examination of unidentified coal seams exposed during construction of the Tasmanian Pulp and Forest Holdings 'MG' road

2.00-4.00

(x)

Return to Launceston

4.00-5.15

Locality 6 - Webber Falls area Two units of Triassic basalt are well-exposed in this two-tiered waterfall in Scales Creek, on the north side of the Nicholas Range. The uppermost beds of the Permian Lower Parmeener Supergroup are exposed at the bottom of the falls. These beds are a thin poorly sorted glauconitic pebbly sandstone unit overlain by a few metres of poorly-stratified grey mudstone containing scattered ice-rafted dropstones. Further down the creek, the glauconitic sandstone overlies richly fossiliferous calcareous mudstone and limestone. The base of the freshwater Upper Parmeener Supergroup is exposed just above the base of the lower falls. This is a sharply defined, apparently erosional surface overlain by a prominent quartzose pebble-conglomerate bed 0.5 m thick. This grades up into a carbonaceous mudstone which is conformably overlain by the lower basalt unit, about 15 m thick. The carbonaceous mudstone is oxidised immediately adjacent to the base of the flow and the basalt is highly altered and amygaloidal near the contact. The lower unit contains scattered labradorite megacrysts up to 3 cm in length. Its upper contact is exposed in the landslip to the west of Webber Falls. There, carbonaceous plant-bearing mudstone beds which contain irregular or lenticular fragments of altered basalt (probably of airfall origin) overlie the lower unit. About two metres of sandstone and carbonaceous mudstone are sandwiched between the two basalt units. The conformable lower contact of the upper unit (about 20 m thick) is exposed, just above the base of the upper falls. Flame-structures of altered sedimentary rock penetrate the base of the basalt, attesting to the unconsolidated nature of the sediment at the time of basalt emplacement. The upper contact, at a level just above the top of the falls, is not exposed but is overlain by lithic sandstones typical of the bulk of the coal measures, which may be seen in the road cutting near the crossing of Lohreys Road over Scales Creek. Reference FORSYTH, S.M. et.ai., 1974. Status and subdivision of the Parmeener Supergroup, Tasmania. Pap.Proc.R.Soc.Tasm. 108:107-109.

28

50m

Lithic Sandstone

Sandstone

Mucfstone

Hornfels 'A

- Basalt CL

O oc o cr UJ

Q3

LT)

30

—I -J

Hornfels Dykes

<

-

K

CL CL

3

°§3

Amygdular

zones

CO

cr

Quartz • Sandstone Member o o

LU LU

Z

O O o

Megocrysts 20

o Basalt,

I]

cr

o O o Q o O O o o ^

q:

Hydroplasftc at contact

-Basalt

LO

brecciated

effects

LU

a.

CL

3

< Ll

10 Columnar

cr

i L u

LU ^

O

-Qlz.Sst. Mb.

'Mudstooe

LOWER PARMEENER SUPERGROUP

Glauconitic Sandstone Calcareous Muds tone & Limestone

WEBBER

FALLS

LITHOLOGY

Jointing

DEPT OF MINES FINGAL DIAMOND DRILL HOLE I'

Numerals 600,500 etc

indicate heightjn metres, above sea level.

NO. 55

LEGEND QUATERNARY

Dolerite talus (day, sand, gravei

Lithic sandstone-fine

boulders)

to fine medium grainsize

Lithic sandstone-medium to coarse grainsize Siltstone Mudstone, claystone Shale Carbonaceous mudstone, etc. Coal traces, coal veins, coal bands, carbonaceous laminae

TRIASSIC (UPPER PARMEENER SUPER-GROUP)

- . . .

NS^

Thin beds shown in true stratigraphic position within another unit e.g. mudstone band within a sandstone. Interbedded units; beds generally > km in thickness e.g. interbedded sandstone and siltstone. Interlaminated units; beds generally < km in thickness e.g. siltstone and mudstone laminite. Breccia

•

•

o o o o o o o o o o o o o o o o o o

(Fault

Zone

Clay- or mud-pellet

conglomerate

Quartz pebble conglomerate Coal Quartzose sandstone-fine

to coarse grainsize

Mudstone, etc. with scattered grit

PERMIAN (LOWER PARMEENER SUPER-GROUP)

Limestone Conglomerate

SILURO-DEVONIAN

^^^

Mudstone, sandstone, slate, quartzite

IGNEOUS ROCKS JURASSIC I T T v T ^ Dolerite I . V . ^ ^

DEVONIAN

- y \

Granite

Unit showing contact thermal £.6. hornfelsed mudstone.

metamorphism

EXCURSION 3 ( L e a d e r s - D. J e n n i n g s , J . TONGANAH

-

PIONEER

-

van M o o r t )

SOUTH

MT C A M E R O N

AREAS

Devonian granitic rocks belonging to the Scottsdale and Blue Tier Batholiths intrude folded meta-sedimentary rocks of the Mathinna Beds in north-eastern Tasmania and Furneaux Group islands. The granitic rocks range in composition from granodiorite to alkali granite, and tin mineralisation is associated with the alkali granite intrusions. The unroofing of the Blue Tier Batholith, in particular, has released a significant volume of cassiterite, which has become concentrated in Tertiary alluvial fan and deep lead environments. Deep chemical weathering of granite of the Scottsdale Batholith during the Tertiary produced thick clay horizons, which are presently being exploited for industrial uses. The excursion examines the development of the clay deposits at Tonganah, the concentrations of cassiterite at Pioneer, South Mt Cameron and Gladstone and also visits sites showing the Tertiary basalt flows which cover extensive areas of north-east Tasmania. 1

Launceston to Sideling Lookout

- an easterly traverse from Tertiary clays of the Tamar Valley, across wooded hills of Jurassic dolerite (to Nunamara) and thence across folded Mathinna Beds to the Sideling Lookout. 2.

Sideling Lookout to Tonganah

- panoramic view from Sideling Lookout across Scottsdale Batholith and basalt plateau, to the screen of Mathinna Beds (Mount Horror) and Blue Tier Batholith (Mount Cameron); with Furneaux Islands on horizon. Journey to Tonganah traverses Scottsdale basalt plateau, lava flows locally resting on, or confined by, ridges of Devonian Granodiorite, and elsewhere capping considerable depths of Tertiary gravels. Agriculture declines beyond the edge of the basalt; road passes Mount Stronach (Mo. prospect). 5.

Tonganah Clay Pit to Branxholm

- mine in deeply weathered granite. by A.P.P.Me for paper manufacture.

Material refined and processed

Route to Branxholm traverses granite ridges with intervening alluvial flats, developed as lucrative hop fields. Emerge into Tullendena Valley, developed farm land with soils overlying granodiorite, - more fertile than granite soils. Over Legerwood Sideling on homfelsed Mathinna Beds and across Ringarooma basalt plateau. 4.

Branxholm to Derby

- road-cutting shows contact between basalt flow and underlying Tertiary sediments. Route to Derby follows present Ringarooma River running in niche eroded between granite massif of Blue Tier to south and basalt-capped, (possible lacustrine?) Tertiary sediments to north. 5.

Derby (Briseis) Mine Site - can be viewed from the town hill to the west, prior to entry.

29

6.

Derby to Pioneer

- lunch will be taken at Derby. The route to Pioneer traverses the Winnaleah basalt plateau - overlying the Tertiary sediments infilling the valley of the Tertiary ^Ringarooma* River. The highland of the Blue Tier is conspicuous to the south, and remnant Tertiary basalt plugs appear on the plateau to the north. 7.

Pioneer to Mount Cameron

- the Pioneer Mine occupies a site where the torrent stream of the Tertiary *Wyniford* River emerged from the hills. Currently worked by Amdex Mining, it was previously worked by Vern Wood and the Pioneer Tin Mining Company. The route north follows the eastern rim of the Mount Cameron basin with the present Ringarooma River further east. 8>

The New Clifton Mine (Mount Cameron) to Gladstone

- the mine occupies the site of a shallow alluvial fan where Clifton Creek emerges from a gully in the southern flank of Mt Cameron. The problems associated with scraper activity, and the Blue Lake of the old Endurance Mine are visible. The route to Gladstone skirts the eastern flank of Mt Cameron. 9.

The Fly-by-Night. Mine (Gladstone)

- the mine, originally an alluvial/elluvial working overlies intensely altered, stanniferous microgranite near a granite/Mathinna Beds contact. Itinerary for Fieldtrip to Sites in North-east Tasmania Departure

Arrival

Travel (mins.)

1. Launceston 8.00 a.m. 50 2. Sideling Lookout, 30 9.05 a.m. 3. Tonganah Clay Pit 10.25 a.m. 20 15 4. Branxholm 11.00 a.m. 5. Derby Mine site 11.55 a .m. 5 25 6. Derby Pool 12.40 p.m. 15 7. Pioneer Mine 2.15 p.m. 8. New Clifton Mine 3.00 P .m.l5 155 9. Fly-by-Night 3.55 p.m. Total

Stay (mins.)

Sideling Lookout 8.50 a.m. Tonganah Clay Pit 9.35 a.m.

15 50

Branxholm 10.45 a.m.

15

Derby Mine site 11.15 a.m. Derby Pool 12.00 noon Pioneer Mine 1.05 p.m. New Clifton Mine 2.30 p.m. Fly-by-Night 3.15 p.m. Launceston 6.30 p.m.

40 40 70 30 40

330 or 5 hrs 30 mins

30

-

300 or 5 hrs 00

EXCURSION 4 ( L e a d e r - T. Summons)

BARNES

HILL

CHROMITE

MINE

It is proposed to visit the B a m e s Hill Mine near Beaconsfield and examine (mining operations permitting) the following features: 1.

Disseminated chromite in the serpentinite beneath B a m e s Hill (see fig. I);

2.

Older Laterite - Zone III (weathered serpentinite) and

3.

The Lower Clay member (see fig. II);

4.

The Chromite member (see figs. II and III);

5.

The (see conglomerate figs. II overburden and III). (Older and Younger Conglomerates)

basal Zone II (intermediate smectite zone);

However, all these exposures should be regarded as being of transitory status only, since all occur in an operating mine, and may not be visible at the time of the excursion.

LEGEND River alluvium

and swamp

Sand derived

from Cainoioic

Boulder

- cobble gravel

deposits.

Boulder - cobble - pebble Ferrunginous

laterite.

Sand day

and granule

Laterite

PERMIAN { I

ORDOVICIAN

P

and

serpentinite).

siltstone.

and

derived

with disseminated

Slate and

greywacke

P * [ Badger Head Group

from either pyroxenite

rocks in Cambrian - sandstone,

of the Andersons

Creek

- Barnes

Hill

-

peridotite.

host.

slate

Geological Boundary approximate. Geological Boundary

area,

or

chromite.

andphyllite.

iary -

—

chert Tree

gabbro

Serpentinite Serpentinite

Septa of metamorphic PR0TER0Z0lc||*

Geology

strata

conglomerate.

Cabbage Tree Formation - quartz sandstone with — a n d quartz conglomerate. 'nrfnrf ^f^^nsition beds between serpentinite and Cabbage f . ^ yA Formation. Layered pyroxenite

Figure I.

(Cg) + Ts.

from Permian

gravel.

(over Cambrian

I Pebbly mudstone

conglomerate

derived

observed. -

position

- position

inferred.

Beaconsfield

mite/yellow

7 Paleosol/H Chromne l>75vol%) silica 'shall grit' + sand Tbp) ?Paleosol/H

Brown lignitic

A P

day

clay lens

Yellow day and pebble gravel

Reef quart/ cobble pebble with a quart/ sand matrix conglomerate. Cg-2)

Silica "shell grit' lignitic day and f< W vol%).

conglomertte (Younger \

\

brown chromite

Brown lignitic !

+ quart/

!<

50 vol %/.

I

clay.

o ? Paleosol/H

A P

A P

Figure II. Detailed section mine, facing south

7

of

Chromite

the highest

Coalesced strands.

Orange-green day smectite/ and disseminated chromite (<5 vol%j.

Silty. dark green ^ smectite day with kaolinitic clay pellets and streaks/layers of chromite f< 25 vol%)

Sihca 'shell grif Sedimentary unit brown lignitic Tc-1 day and chromite (5 W vol % i,gf,f grggn clay with chromite bands <3mm thick

level

Probable equivalent Range Upper Beach

Schistose cobble/pebble si/e fragments in a sericite/kaolinitic matrix. (Older conglomerate. Cg-1)

layer

of the Barnes

Hill

of Rifle system.

Bedding defined by silica platelets.

Probable equi1 valent of Rifle ' Range Lower beach system.

<

Cg 2 I

Boulder-cobble-pebble

Tbp

I

Beach placer

I *

Green/yellow/brown (equivalent to Tc-I

conglomerate.

or strand

rich in heavy minerals

(>90

mass %

chromite)

TERTIARY

CAMBRIAN

Tbp

I I -Es

I

days containing silica platelets at the Rifle Range Prospects.)

and

chromite.

Post mining surface.

Serpentinite. -es\

\

(SECTION BASED ON COSTEANS A N D STRIKES APPROX. 1 0 5 ° ) AH levels shown

Figure III.

Cross

section,

Barnes

Hill

mine,

facing

north

in

metres.

Tc-l

EXCURSION 5 ( L e a d e r - W.E.

Baker) LISLE

GOLDFIELD

The Lisle goldfield 20 km south-west of Scottsdale was discovered late in 1978 by C. and E. Bessell. This field became the richest alluvial find in Tasmania and in four years of peak production is believed to have yielded about 250 000 ozs. There has been intermittent activity over the years but more recently only part-time prospectors occupy the area. Lisle is situated in a wide upland valley about 200 m above sea level. The head of the valley is closed by a broad divide standing at 600 m whilst the sides to east and west are bounded by steep ridges which rise to 500 m. The wide valley floor, approximately four kilometres across, indicates a considerable age. The main drainage is effected by Lisle Creek on the east and Bessell Creek on the west. The floor of the valley is underlain by deeply weathered Devonian granodiorite which intrudes Silurian (Mathinna Beds) sandstone and shale. These latter rocks have been considerably indurated by the intrusive events. Geological study of the area is difficult due to the extensive scree on the ridge slopes and heavy vegetation. On the floor of the valley thick alluvial deposits, in places auriferous, cover the weathered granodiorite and much of the area is under mature radiata pine forest. The excursion to Lisle will examine some sites of early mining activity that are still accessible and the character of the alluvials. Prospecting dishes will be available. Gold production has recently commenced at one of the prospecting sites and it is hoped to time the arrival to see the later stages of clearing up a days run. If time permits, outcrops of the granodiorite and Mathinna Beds outside the Lisle Valley will be visited.

32

EXCURSION 6 ( L e a d e r - V . M . DUNCAN

Threader) AND

NEW

CORNWALL

ADITS

The total production of coal in Tasmania is approximately 12 million tonnes, 90% of this has come from the Fingal Valley and most of this production came from the old Cornwall Mine near St Marys. This mine ceased production in January 1964 and the Cornwall Coal Company stepped up production from its other mine: the Duncan, to maintain supply to its remaining customers. The Duncan is now the only producing coal mine in the state but the company is bringing a new mine, next to the old Cornwall Mine, into production. The mines work by the bord and pillar method and access is by adits on the slopes of the Break O'Day valley. It may not be possible to visit the innermost working areas of the mine due to transport difficulties but a new working face within walking distance of the adit portal should provide sufficient items of geological interest. It should also be possible to visit the new Cornwall adit which is situated in the Nicholas Range and lies 12 km north-east of the Duncan portal.

33

D I R E C T O R Y O F SUPPORTERS

A

A

ABERFOYLE LIMITED

233 Collins Street, Melbourne Victoria 3000 Telephone: 63 9412

A M D E X

MINING

LIMITED

1 19 YORK ST. SYDNEY A U S T R A L I A TELEPHONE

20Dn

29-3BD1

ALCOA AUSTRALIA A m o c o Minerals Australia C o m p a n y

A L C O A OF A U S T R A L I A (W.A.) LIMITED Exploration Division 4 BENNETT STREET, EAST PERTH. W.A. 6000 TELEPHONES 25 6677, 25 6970

2 0 1 - 2 0 9 Pacific H i g h w a y , North Sydney, NSW 2 0 6 0

APOLLO INTERNATIONAL MINERALS N.L. 33rd Floor BHP House 140 William Street Melbourne, Victoria 3000 Australia

The Broken Hill Proprietary Company Limited BHP House 140 William Street Melbourne Victoria 3000 Australia

Telephone: Bus.: (03) 67 7678 602 4033 Telex: 32985

34

DIRECTORY O F SUPPORTERS

CAPRICORN MINING LIMITED

CLEVELAND TIN LIMITED LUINA, TASMANIA. 7321 Telephone: 004/39 1180

153 Dorcas Street, South Melbourne. P.O. Box 326, South Melbourne, Victoria 3205. Telex: AA 33427 Telephone: 690 5900

Telex: Cletin 59051

A m e m b e r of t h e A b e r f o y i e g r o u p .

The Cornwall Coal Company No Liability 93 YORK S T R E E T , LAUNCESTON, T A S M A N I A

C.R.A. EXPLORATION PTY. LIMITED

7250

T E L E P H O N E : 31 9522

(A Subsidiary ol Conzinc Wollnto ol Australia Limited)

P.O. BOX 62 CABLE ADDRESS : " C O R N C O A L " ,

LAUNCESTON

ELECTROLYTIC ZINC COMPANY OF AUSTRALASIA LIMITED

ENDEAVOUR RESOURCES LIMITED

WEST COAST MINES P.O. B O X 2 1 R O S E B E R Y TASMANIA 7470

AUSTRALIA

T E L E P H O N E (004) - 73 1104 TELEX AA58588 T E L E G R A M S A N D CABLES •ZINCORE' ROSEBERY

35

DIRECTORY OF SUPPORTERS

Industrial ^ Mining Investigations Pty. Limited GOLD FIELDS EXPLORATION PTY LTD. Consolidated

M Subsidiary Gold Fields

of (Aust.)

Ltd,)

S U I T E

3 7 0

AUSTRALIA

SQUARE

9

TELEX

No.

AA22204

TELEPHONE! 2 7 8 1 4 5

SYDNEY, N . S . W . 2 0 0 0 A U S T R A L I A

Gold Fields House, Sydney Cove. 2000.

NEWMONT

HOLDINGS

( I N C O R P O R A T E D

I05 BATHURST.

A PENNZOIL SUBSIDIARY 8

WEST

OF

STREET,

TELEPHONE 92 0223

PENNZOIL OF

COIMmiMY

AUSTRALIA

LIMITED

INCORPORATED DELAWARE, U S A

DUVAL NORTH

INTERNATIONAL

SYDNEY, TELEX 22098

NEW

CORPORATION

SOUTH

WALES

CABLES:

2060

"PENNZAL"

36

KEPPEL

IN

PTY.

VICTORIA)

STREET.

NEW S O U T H

WALES.

2795

LTD.

DIRECTORY OF SUPPORTERS

ESSO AUSTRALIA LTD.

COMALCO

COMSTAFF PTY. LTD.

COMALCO LIMITED Incorporated

in

Victoria

95 Collins Street Melbourne Australia

WHITE INDUSTRIES LIMITED P.O. 50X1320. NQFtTH SYDNEY 20«0 T«!ftphont; 8223777

37