Australian Coal Geology Volume 6 1986 - CGG by GSAustralia

CONTENTS

Aus tra lian Coal

Volume 6 ~

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D. S. Hamilton: Depositional Systems and Coal Seam Correlation in the Greta Coal Measures of the Muswellbrook region.

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D. J. Martin: Sedimentary depositional environments and some igneous intrusions in the SydneyGunnedah Basin.

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< A. C. Hutton: Duaringa - a bipartite oil shale deposit.

JOURNAL OF THE COAL GEOLOGY GROUP GEOLOGICAL SOCIETY OF AUSTRALIA

K. C. Morrison & C. A. Bacon: Comparison between the Fingal and Langloh Coalfields, Tasmania Basin.

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J. W. Hunt, A. T. Brake! & M. Smyth: Origin and distribution of the Bayswater Seam and its correlatives in the Permian Sydney and Gunnedah Basins, Australia.

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L. H. Hamilton & M. R. Salehi: Use of SEM for coal petrology.

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C.R. Ward:

Review of mineral matter in coal.

Book Reviews:

111

VOLUME 6

1986

ISSN 0725-4938

l COAL GEOLOGY GROUP OF THE GEOLOGICAL SOCIETY OF AUSTRALIA

Chairman: Dr. C.W. Mallett Vice-Chairman: Mr. J .C. Anderson Hon. Secretary: Mr. L.R. Grimstone Hon. Treasurer: Mr. P.E. Balfe Committee: Dr. L.H. Hamilton Mr. E.A. Pryor Hon. Editor: Mr. J .W. Beeston

Address for editorial matters: Hon. Editor Australian Coal Geology GPO Box 1820 Brisbane. 4001 Address for other matters: Hon. Secretary Coal Geology Group 16 Dome Street Eight Mile Plains. 4123.

Price to non-members, $10.00 per issue

CONTENTS Volume 6 D. S. Hamilton: Depositional Systems and Coal Seam Correlation in the Greta Coal Measures of the .Muswellbrook region.

D. J. Martin: Sedimentary depositional environments and some igneous intrusions in the SydneyGunnedah Basin.

A. C. Hutton: Duaringa - a bipartite oil shale deposit.

K. C. Morrison & C. A. Bacon: Comparison between the Fingal and Langloh Coalfields, Tasmania Basin.

J. W. Hunt, A. T. Brakel &.M. Smyth: Origin and distribution of the Bayswater Seam and its correlatives in the Permian Sydney and Gunnedah Basins, Australia.

L. H. Hamilton & M. R. Salehi: Use of SEM for coal petrology.

C.R. Ward: Review of mineral matter in coal.

Book Reviews:

111

EDITORIAL

A recent trend in papers relating to coal geology, both in this Journal and in other venues as well, is the introduction of sedimentology, particularly with regard to the consideration of coal measure depositional environments. This trend has introduced a new dimension to the coal geologist, and one in which some may not feel particularly comfortable. For years petroleum geologists have included such assessment into their appreciation of petroleum source and reservoir rocks, and the importance of both to a direct understanding of local conditions, as well as the interpretation and development of general models. This awareness is now spreading to coal geologists, and the techniques are proving just as useful. The remainder of the twentieth century will see major changes in the exploration for, extraction and development of coal in Australia, and one of them will be the increase in amount and percentage gross of coal won by underground mining techniques. The present need for structural and lithological control on mine rocks will magnify, and tha understanding of coal associated lithologies will need to keep pace. The papers in this journal relating to such matters will make a contribution to that understanding, and make a fitting accompaniment to those papers dealing with the more traditional forms of coal studies. Of these, also, it is pleasing to see a range of topics from revues of established knowledge, to most recent advances in research. The Coal Geology Group is a balance of scientists, engineers, miners and managers, and it is fitting that the Australian Coal Geologist continue to provide a balance of information for their use.

DEPOSITIONAL SYSTEMS AND COAL SEAM CORRELATION IN THE GRETA COAL MEASURES OF THE MUSWELLBROOK REGION By D. S. Hamilton ABSTRACT

Long standing coal seam correlation problems exist between the Muswellbrook and Savoy Trig. Station areas within the Greta Coal Measures. This study attempts to resolve the correlation problems using a new approach which involves the interpretation of depositional systems from the recognition of genetically-related sedimentary facies in drill core. Geophysical log responses were used in conjunction with the drill core interpretation. Alluvial and deltaic depositional systems are recognised in the Greta Coal Measures. Alluvial conditions prevailed during the initial stages of the coal measures and are represented by the pelletoidal elayrock facies. Coal seams within the facies are the Lewis/Loder Coal Members in the Muswellbrook area, and the Balmoral Coal Member in the Savoy Trig. Station area. These coal members are similar in many respects and are thought to correlate. Deltaic conditions were established after deposition of the pelletoidal clayrock facies in response to a base level change. A thick coal-bearing sequence termed the volcanolithic elastic facies was deposited during this time. Analysis of drill core from the volcano-lithic elastic facies highlights that significantly different sedimentary processes operated in the two areas and indicates that the sequence in the Savoy Trig. Station area was deposited in a lower delta plain setting whilst the sequence in the Muswellbrook area was deposited in a predominantly upper delta plain. Significant differences are also recognized in coal seam characteristics between the two areas, and these differences are attributed to the contrast in depositional setting. The results of this study do not support the existing coal seam correlations between the Muswellbrook and Savoy Trig. Station areas. However, it has not been possible to propose alternative correlations due to the dissimilar nature of the coal-bearing sequences. The interpretation of depositional

systems from the drill core has established a better understanding of the development of the coal measures and it is hoped that this,study will provide a sound basis for further'correlation work. INTRODUCTION

The Early Permian Greta Coal Measures are an economically important coal-bearing sequence in the Upper Hunter Valley. Three mines currently exploit the coal measures, the Muswellbrook and Bayswater Collieries, and the Drayton Coal Mine. A new mine is proposed in the Black Hills area by Mt Sugarloaf Collieries Pty Ltd (Figure 1). In 1982/1983 a total of 2.3 million tonnes of coal was produced from

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1i1uh• e Hb100 •

(!) s•,\-•••• HoJ

MUSWELLBROOK (

AREA ,. ,,1 e., .... ., .• , Co•h••• Co 41 1J '"'• \\

a, o-.

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P L

A176

Coll, f' • t P l

Co• • Co

A205

SCALE

4 2 -6 km ~ = 0- ~=

Figure 1: Location of mining and exploration in the Muswellbrook region.

the three mines. The coal is marketed as a high volatile, low ash steaming coal for export and domestic consumption. Despite a lengthy history of exploration and mining, coal seam correlations within the Greta Coal Measures in the Muswellbrook region remain tentative. A new approach, which involves interpretation of depositional systems and facies using drill core, was carried out in an attempt to resolve the correlation problems. The study was based on detailed examination of drill core from eleven fully cored company and departmental drill holes (Figure 2). InterAberdeen GN

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c,:•" oos ,e }

Mu swe llbr ook OOH 270

Working Party of the Standing Committee on Coalfield Geology of New South Wales; (c) to assess the value of environmental interpretation in the correlation of coal seams. The cross-sections and diagrams have been greatly simplified for publication and more detailed work is presented in Hamilton (1984). I. McDonald, J . Beckett and C.R. Weber made contributions to the drill core interpretations. The Greta Coal Measure Working Party is currently reviewing the stratigraphic subdivisions of the Greta Coal Measures as the present terminology is confused and inadequate. The stratigraphic subdivisions us ed in this paper are therefore provisional but take into account forthcoming changes proposed by the Working Party (J. Rogis, personal communication, 1984).

MUSWELL BAOOK

METHODS USED ....o,,..,.,r~

DM Ba l moral DD H 1

Black Hill s DOH 7 \ •

/ • B l ack Hills DDH ~10CD3

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D~1. Savoy c{DH 1

'"""'"' o~::.:::, c;:; \ "''•°''

D r ay t on Coa l Mine F 11 1 I

SCALE

= --...,.=======--111111km

Figure 2: Borehole locations.

pretation of geophysical log responses from fourteen rotary drill holes was used in conjunction with the drill core exam4lation. The principal objectives of this study were: (a) to gain an understanding of the history and depositional systems of the Greta Coal Measures from the identification of sedimentary facies; (b) to help resolve correlation problems within the coal measures, in cooperation with the Greta Coal Measure

The methods used in this study principally involve the interpretation of depositional systems from drill core, requiring the recognition and integration of a number of genetically related sedimentary facies. The sedimentary facies recognised in drill core have counterparts forming in modern day depositional systems. This type of approach was introduced by Fisher & McGowen, (1967) in their study of the Tertiary Wilcox Group of Texas. Hamilton & Beckett, (1984) applied a similar approach to drill core of Permian strata from the Gunnedah region. The criteria used for the interpretation of sedimentary facies in this study ai·e outlined in HamiltoJ;J. & Beckett, (1984) and Tadros & Beckett, (1983). All eleven drill holes were examined and a log of the depositional facies prepared. The logs are presented in Hamilton, (1984). All eleven drill holes were examined and a log of the depositional facies prepared. The logs are presented in (Hamilton, 1984). The interpretations obtained were then used in conjunction with geophysical log responses to evaluate the correlation potential of the coal seams. The geophysical logs used are the gamma-ray and coal bulk density logs.

GEOLOGIC SETTING The Greta Coal Measures outcrop on the crest of the Muswellbrook Anticline and cover an area of about 35km2 in the Muswellbrook region (Figure 3). Robinson (1963) considered that the coal measures conformably overlie the Gyarran Volcanics and are in turn conformably overlain by the

~ ...., ~ G,oup

□ G,eta Coal MeHurft

D o•wooe1

Group

SCALE

0 2 - - ==

4 6 = - - km

Figure 3: Generalized geology of the Muswellbrook region.

marine Maitland Group. Early workers divided the coal measures into two lithologically dissimilar units. Reggatt, (1938) named these two units the "Muswellbrook and Skeletar Stages" and Booker, (1953) later named them the Muswellbrook and Skeletar Formations. A review of the stratigraphy (refer to Robinson, 1963) by the Standing Committee saw the Muswell-

brook Formation replaced by Rowan Formation on the grounds of synonymy involving the Muswellbrook Seam. The Skeletar Formation as originally defined has a very restricted distribution, contains no coal, and is composed mainly of rhyolite, chert and white tuffaceous shales containing Glossopteris and Gangamopteris (Robinson, 1963). The overlying Rowan Formation contains economic coal seams intercalated with sandstone, siltstone, mudstone and minor conglomerate. The boundary between the formations was revised by the Standing Committee (1975) and arbitrarily placed at the base of the lowermost coal of the Rowan Formation. This revision resulted in a markedly different Skeletar Formation from the one originally defined, and the unit now contains a distinctive pelletoidal clayrock sequence and has a wide distribution. The boundary between the formations as it presently stands is not valid, at least in the area currently explored by Muswellbrook Coal Company, since distinctive pelletoidal claystones overlie the lowermost coals in the Rowan Formation by up to 10 metres (J. Rogis, personal communication, 1984). This anomaly has prompted Rogis to propose several changes to the stratigraphy. The changes include the dropping of the term Rowan Formation, reassignment of the Skeletar Formation (as originally defined) to the underlying Dalwooq Group, and the inclusion of the pelletoidal clayrock sequence as part of the Greta Coal Measures without separate formational identification. The changes proposed by Rogis provide a logical solution to the stratigraphic problems, at formation level, in the Greta Coal Measures and have been followed in this study (Figure 4). Although outcrop of the coal measures is is continuous along the length of the Muswellbrook Anticline, exploration and mining activity has been concentrated in two more restricted areas. One to the east and northeast of Muswellbrook township, termed the Muswellbrook area, and the other to the south and southeast to Muswellbrook township, termed the Savoy

STRATI ffiN'HI C CQ.lffl Fffi TI£ ffiE TA CQl>I,. r:£ASLRES (f Il£ MJS,ULffiOO< REGION <after Staldilll Cornn ttee 1915)

MEMllH GROUP

FORMATION Savoy TJt...ig . S tau.on a,ua

~b,toolz. tVte.a

Ma!tlarld Gro..p Flemng Coal 1"6rtler

HI 11 tc:p Coal f'ffitler

Hal Jett Coal l'BltJer Rcwm Fonratim Greta Coal l'easures

l'\Jswel lbrcd< Coal l"e1ber

Broojlan Coa l l"ertJer

St He! 1er s Coal l"ertJer

Gr ass trees Coo l l"erber

Lewi s Coal l"erber

Puxtrees Coal l"ertJer Ayrrnle Scrdstcre l"e1ber

Lolder Coal l"ertJer

Halnoral Coal l"e1ber

Skeletar hxmmm ~lraxl Grcw

REVISED STRATIGRAPHI C COLUMN FOR THE GRETA COAL MEASURES OF THE MUSWELLBROOK REGION (this study) MEMllfR GROUP

FORMATION I F ACl f S Mu~we.llb1t oolz a-t e.a

Sav olJ TJtiq. Station aJte.a

MaI tland Group unnamec1 Fleming Coa I Member Greta Coa l Measures

?H1l lt oo Co2! Member

Voicano-I1 thl c Clast1c facIes

?Brou\Jh21:: Coa I MenllJer Hal Jett Coal Member ?G r ass tree s Coi>l Member

MUSl·/e 11 brook Coal Merrtler

s HPI 1ers Coal Merner Pel letmdal Cic¥"Ork fac1es Da I wood Group

Lewi s/Locer Coe>! Merrtler

Skeietar Formation

Figure 4: Revision of the Greta Coal Measures stratigraphy (based on discussions with J. Rogis, 1984).

?Puxtrees Coal MerrtJer ?Ayrdale Sandstone MefltJer Balmoral Coal MerrtJer

Trig. Station area. The Muswellbrook area is mined by the Muswellbrook Coal Company; Drayton and Bayswater Collieries mine coal in the Savoy Trig. Station area. Knowledge of the coal measures in the two mining areas is very detailed but little correlation between the two areas has been undertaken. Not surprisingly, separate coal seam nomenclatures have evolved within the coal measures in the two mining areas· (Figure 4) and correlation of the seams between the two areas is tentative.

DEPOSITIONAL SYSTEMS OF THE GRETA COAL MEASURES The Greta Coal Measures can be divided into two principal facies; a basal facies, characterized by distinctive pelletoidal clayrocks and intercalated dull coal seams, and an overlying facies containing brighter coal seams interbedded with typical elastic sequences of volcano-lithic siltstone, sandstone and conglomerate. The basal pelletoidal clayrock facies makes up only a small portion of the Greta Coal Measures but contains the economically important Balmoral and Lewis/Loder Coal Members. These coal seams have a generally dull profile and occur in the top part of the facies. The overlying volcano-lithic elastic facies makes up the majority of the Greta Coal Measures and contains the many coal seams of economic interest (Figure 4).

PELLETOIDAL CLA YROCK F ACIES The pelletoidal clayrock sequence forms the basal facies of the Greta Coal Measures, and in places rests on the highly weathered surface of the Gyarran Volcanics. The origin of this sequence is disputed. Loughnan (1973, 1975) described the rocks in the Wingen area, as well as correlatives in the Gunnedah Basin to the north (Leard Formation), and suggested that they were derived from lateritized soil profiles developed on the deeply weathered Werrie Basalt in a humid and semi-tropical climate. He further suggested that the rocks accumulated a:s both colluvium around the lower slopes of the weathered

basalt, and as alluvial deposits which were spread outward over the alluvial plain. Tobin (1980) studied the pelletoidal sequence in the Balmoral area and considered that the rocks were derived from a local volcanogenic source and deposited on a river flood plain as a result of overbank flooding. (McPhie, 1984) has suggested that the correlative Leard Formation sequence is linked to the weathering of the silicic Boggabri Volcanics rather than the Werrie Basalt. Apart from the disputed origin of these rocks, there is general agreement that they were deposited in an alluvial plain environment. Facies Description. Colluvial and alluvial deposits were recognised from drill core in this study. The colluvial deposits lack evidence of sediment transport; they are unstratified and grade indistinguishably into the underlying volcanics. The pellets within these deposits are irregularly shaped and angular. The allQvial deposits in contrast, display many features consistent with sediment transport. They are stratified and the pellets are rounded and commonly flattened parallel to the bedding planes. Upwardfining, erosively based pelletoidal conglomerate and sandstone sequences present in the drill core are interpreted as fluvial channel-fill and overbank/splay facies; interbedded carbonaceous claystone with minor coal bands are attributed to floodplain deposition. The · Balmoral and Lewis/Loder Coal Members directly overlie, and in part interfinger with the pelletoidal clayrocks and are thus considered to have been deposited in the same alluvial plain environment. VOLCANO-LITHIC CLASTIC FACIES

Analysis of the drill core indicates that the volcano-lithic elastic facies was deposited in a deltaic environment. Based on the association of the interseam sedimentary facies, it has been possible to recognize both upper and lower delta plain deposits. The lower delta plain is generally considered to be that part of the delta which

lies within the zone of tidal influence, whereas the upper delta plain is essentially the continuation of the alluvial valley and is dominated by fluvial processes (Coleman & Prior, 1980; Saxena, 1979). The significant contrast in sedimentary processes between the upper and lower delta plains should imprint characteristics which are recognizable in the rock record. Deposits of the lower delta plain should display the effects of marine or tidal reworking whilst upper delta plain deposits will commonly resemble typical alluvial plain sequences. It may not be possible to distinguish upper delta plain and alluvial plain facies without knowledge of the framework sand-body geometries (Kaiser & others, 1978), however in this study the upper delta plain deposits were interpreted largely by their close spatial association with recognizable lower delta plain facies. Facies description. Marine reworking and tidal influence typical of a lower delta plain setting is recognized throughout the volcano-lithic elastic facies in the Savoy Trig. Station area. In the Muswellbrook area however, evidence of this marine reworking is absent in all but the top part of the sequence (ie. the interval above the Hallet Seam). The sequence m the Muswellbrook area is thus considered to be comprised predominantly of upper delta plain deposits. Only the interval above the Hallett seam shows features typical of a lower delta plain. (a) Muswellbrook Area. Principal component facies are indicated by their geometry and interrelations are overbank/floodplain, crevasse-splay, marsh or lacustrine and coalswamp deposits which closely resemble modern analogues (Fisher & others, 1969; Coleman & Prior, 1980). Interdistributarybay facies, which display evidence of tidal influence, are present in the interval _above the Hallett Seam. The overbank/floodplain facies are typically siltstone and fine sandstone with laminations, fine cross-stratification and root traces. These deposits have a finely jagged pattern on the gamma-ray log (Figure 5) which demonstrates the finely interbedded nature of the siltstone and sandstone. Crevasse-splay deposits are fine to coarse-sandstone units intercalated with

GAMMA

COAL MEMBER

RAY

200

SERRA TE D

FLEMING

.. HALLETT

5(),,,

MUSWEL LBROOK

... ST.HELIERS 70•

FI NELY

...

JAGGED

UPPER

200

...

LODER

.,. _ _

_ _ _ __

LITHOLOGY

FACIES

~ lnterdlstrlbutary bay

LEWIS

~ Siltstone interbedded with

~ wilh crevasse splay

E:J lentlcular bedded sandstone

□ Fine

~ Marsh

■ Coal Swamp

■ Coal

~ Overbank floodpla in

aandstOM

lnterbedded with

: ~t;~~:.:

siltstone

carbonaceous

Figure 5: Gamma-ray log of Muswellbrook Coal Company Rotary Drillhole 321 in the Muswellbrook area.

the floodplain facies. They range from a few centimetres to several metres in thickness. Erosi vely-based , coarse: sandstone units up to 3m thick are attributed to small-scale channel facies which perhaps supplied sediment to the crevassesplay facies. Major distributary-channel facies, which are generally characterized by thick, massively-bedded, medium to coarsesandstone units, are noticeably absent from the sequence in the Muswellbrook area. Marsh or lacustrine deposits are fine siltstone and claystone with abundant carbonaceous material. The coal seams represent deposits of the peat swamp facies and are very thickly developed in this area. The coal can be as much as 40% of the total sequence (Figure 6). COAL MEMBER

FLEMING

HALLETT

MU SW ELLBROOK

~ "'

ST. HEUER$

UPPER

LEWI S

LOOE R

FACIES

LITHOLOGY

inte rdl, tr ltwt., , ba r

fUlt•I -

•i>••r

tentk:uler b.ckted aand• t -

L l - 1111

c:,• ., ....

ln terbedded wltll

~ 0.erbank ltoodplaln

□ Fine 1and1tone

CJ - ..

E3c:1, , ,,_

■ ~ ···-

■ c~•

lnt e r~ w flh ailt s l Sliltstone , c:arbon■c: ■ou■

Figure 6: Gamma-ray log of Muswellbrook Coal Company Rotary Drillhole 322 in the Muswellbrook area.

The sequence shows features typical of deposition in an extensive upper delta plain swamp which probably flanked the main distributary network. Well developed levees largely protected the swamps from contamination by channel deposits and enabled thick accumulations of peat. Clastic detritus was probably only introduced during major flood episodes as overbanks and as crevasse splays which breached weak points in the levees. The interval above the Hallett Seam was deposited in a lower delta plain setting. This interval is characterised by interdistributa ry-bay and crevasse-splay facies which have a distinctive serrated pattern on the gamma-ray log (Figure 5). The appearance of tidal influence in this part of the sequence probably marks the onset of the marine transgression which deposited the overlying marine Branxton Formation. (b) Savoy Trig. Station area. The dominant sedimentary facies interpreted from the drillcore study are interdistribu tary-bay, crevasse-spla y, distributary-channel, marsh and peat swamp facies. These facies display features similar to modern deltaic sediments such as those described by Coleman & Prior, (1980); Fisher & others, (1969); and Coleman & Gagliano, (1965). Minor distributarymouth bar, saltmarsh and overbank deposits are also recognized in the drill core. lnterdistributa ry-bay facies are the most common interseam unit. They consist of rippled and lenticular bedded sandstone/siltstone laminite sequences with common bioturbation (Figure 7). The bedding characteristics are attributed to the regular alternation of traction currents and suspension settling during slack water; such processes are indicative of tidal influence (see Reineck & Singh, 1975). Fine to coarse-sandstone units interbedded with the interdistributa ry-bay facies represent crevasse splays. The splays are generally upward coarsening and display laminations and fine cross-stratification. Small-scale upward-coarsening crevasse-splay cycles evident on the gamma-ray log (Figure 8) are similar to the interdistributa ry bay-fill sequences described by Elliott, (1974).

Figure 7: Typical interdistributary-bay facies with crevasse-splay sandstone on right-hand side. Each core is approximately 4.5cm in diameter.

GAMMA

COAL MEMBER

RAY

UPWAiRD COARSENING

suggests that the crevasse-splay cycle may have been an important process for coal formation in the Savoy Trig. Station area. Infilling of the bays by crevasse-splay sands provided a platform for expanding marshland areas and enabled peat accumulation. Foundering of the site, following abandonment, re-established interdistributary-bay conditions which then became a favoured site for subsequent infilling by crevasse-splay sands. Figure 9 shows a typical sequence of crevasse-splay and interdistributary-bay facies in the drill core. The distributary-channel deposits consist of thickly bedded, medium to coarse sandstone from 3m to 6m thick and display a blocky pattern on the gamma-ray log (Figure 8). Lateral facies equivalents of the channel deposits are distributary mouthbar sands which have been subjected to varying degrees of marine reworking. Marsh deposits consist of siltstone and carbonaceous claystone with minor coal bands. The thick coal seams represent the peat swamp facies. The sequence in the Savoy Trig. Station area is typical of a lower delta plain environment. The presence of tidal influence in the sediments and the prominence of upward-coarsening bay-fill sequences are characteristic of the processes on the lower delta plain. MARKER HORIZONS

200

FACIES

OOm

LITitOLOGY

r-:-;:,

L J Ol•trlbutary mouth bar

~ Sandstone,

~ Dl•trlbute,y charNMI

E::::) Slltatone lnt■rbedded with

CrawaHe

apl■J

F3 tnt•rdlstrlbutery bay

f=::::j with creY■He •~•Y

rn ~

minor conglomerate

~ lentlcular bedded sandstone

Sutstone, carbonaceous clayatone

■ Coal awamp

lntardlatrlbutary ba1

■ Coel swamp Figure 8: Gamma-ray log of borehole Drayton Coal Mine Fllll in the Savoy Trig. Station area.

The prominence of interdistributary-bay and crevasse-splay facies in the sequence

Inter-seam marker horizons within the Greta Coal Measures are known only in the Savoy Trig. Station area. Several sandy facies, in particular the Ayrdale Sandstone and to a lesser extent the Brougham and Hilltop sandstones, persist throughout the Savoy Trig. Station area and have been used as marker horizons. The absence of these units in the Muswellbrook area has contributed to the correlation problems between the two areas. Ayrdale Sandstone. The Ayrdale Sandstone forms a very distinctive stratigraphic unit between the underlying Balmoral Seam and overlying Puxtrees Seam. It consists predominantly of sandstone with minor siltstone and conglomerate. The unit is up to 30m thick in the south and thins to the northeast. The sandstone is generally underlain and overlain by a siltstone/fine

Figure 9: Sequence shows typical interdistributary-bay deposits (A) which have been infilled by crevassesplay sandstones (B). Abandonment of the crevasse splay re-established interdistributary bay conditions which are represented by the deposits at (C). Lower left-hand corner is the base, upper right-hand corner is the top and each length of core is approximately lm

Figure 10: Upward-coarsening sequence showing distributary mouth-bar facies of the Ayrdale Sandstone. The Ayrdale Sandstone is also known locally as the Balmoral sandstone. Lower left-hand corner is the base, top right-hand corner is the top and each length of core is approximately lm.

sandstone laminite sequence. As a depositional unit, the Ayrdale Sandstone records the entry of river-borne sediment into an extensive interdistributarybay environment and consists of a number of different facies. In places it forms distributary mouth-bar facies (figure 10), elsewhere it forms distributary-channel and crevasse-splay facies. The type of facies presevered depends on the amount of sediment input and degree of marine reworking at the site of deposition. Figure 11 shows the distribution of facies. The main depocenter is located in the southwest where thick distributary mouth-bar and minor distributary-channel facies are preserved depends on the amount of seditfieast and are replaced by laterally equivalent interdistributary-bay laminites. Figure 12 modified from Tobin, (1980) shows isopachs and sand/shale ratios of the Ayrdale Sandstone in the authorisation 173 area (Drayton Coal Mine). The isopachs show the main depocenter in the southest and indicate that the sandstone was supplied by a southeasterly flowing system. The lobate geometry of the isopachs suggests marine reworking of the sediment and the sand/shale ratiQ map demonstrates the main direction of this marine reworking. The sand/shale ratio map also shows the sandy facies thinning to the northeast.

* Brougham sandstone. The Brougham sandstone forms a prominent unit between the underlying Grasstrees Seam and the overlying Brougham Seam. This unit is not as persistent as the Ayrdale Sandstone and has not been formally named. However, it has proven useful as a marker horizon and facilitated coal seam correlations. It consists predominantly of sandstone with minor silty and carbonaceous bands and is interpreted as being deposited from distributary channels. it Hilltop sandstone. - The Hilltop sandstone overlies the Brougham Seam. The Hilltop sandstone has not been formally named as it is not well developed over the entire area. Where present it consists of sandstone interbedded with subordinate sandstone/siltstone laminite. It was deposited mostly as crevasse splays but in places it forms distributary-channel facies.

Aberdeen

MUSWELLBROOK

App roxima te l1m1t of Ayrda le Sand s tone

~~ / • and equivalen1s

--'--._ AIN OIR

_: ~

-::

.!!!_a-r~ y~

SE IM

ies~_=- _

- •-

. •·••

~ - - :\

\/ :;._· -=-

a- - - _

--::..

ba r - - _ ~

- - -- - --- - ---=- =---:SCALE

=::,;o..,..IIIIIC2=

=>4~~6km

Figure 11: Distribution of fac ies in the Ayrdale andstone.

This sandstone has also proven useful as a marker horizon. In outcrop, such as at the Bayswater and Drayton mines, the Brougham and Hilltop sandstones display point-bar characteristics (Diessel, personal communication, 1984). This is not entirely inconsistent with the interpretation of distributary-channel facies however, Fisher & others (1969); Saxena (1979); and Bernard & others (1970) have all documented point-bar sequences in delta plain deposits, although it is true that they are generally'restricted to the upper delta plain (cf. Hamilton & Beckett, 1984). Distributary channels may meander on the lower delta plain, particularly if the channels cut into sandy substrates.

DEPOSITIONAL HISTORY The Greta Coal Measures were deposited in both alluvial and deltaic systems. Alluvial conditions prevailed during the initial development of the coal measures as evidenced by the basal pelletoidal clayrock facies which were derived from weathering

(* Readers should note that these are informal li thostratigraphic names and, as such, are not recognised by the Stratigraphic Nomenclature Committee of the Geological Society of Australia. They should not be misinterpreted as having any formal status. Ed.)

(b) Sand/Shal, Ratio

(a) lsopachs G N

~1 Main direction 5

1 ' 14

111

, fu

5 14 --------27 ------44 \

4 \

Direction of

l ,) ma~ine reworking

~ ""'

SCALE 05

0 5

25 km

Figure 12: Isopachs (a) and and/ hale Ratio (b) of the Ayrdale Sandstone in authorisation 173 (modified

from Tobin 1980). Contours are in metres.

and erosion of a perhaps local volcanogenic source. Deltaic conditions followed , and dominated the depositional history of the coal measures. The deltaic conditions were established in response to a base level change, either tectonic depression, isostatic subsidence or a glacio-eustatic rise of sea level. The Ayrdale Sandstone is considered to mark the onset of the base level change as it is the first unit in the sequence to display marine influence. Deltaic progradation following the base level change was accompanied by aggradation of the coastal plain and resulted in deposition of the thick coal-bearing volcano-lithic elastic facies. The Savoy Trig. Station area was the site of the lower delta plain sedimentation; the Muswellbrook area was less affected by marine influence as it occupied the topographically higher upper delta plain. Onlv the interval above the Hallett Seam in the Muswellbrook area displays marine influence. The coal-forming conditions were terminated by a basin-wide transgression which deposited marine strata of the

Maitland Group.

COAL SEAM CORRELATIONS Coal seam correlations are well established within the Muswellbrook area, and also within the Savoy Trig. Station area. Correlation between the two areas, however, is not well established. Tentative correlation of coal seams between the two areas (Figure 4) has been suggested by the Standing Committee (1975). The suggested correlations are the: (1) Loder Coal Member to the Balmoral Coal Member; (2) Lewis Coal Member to the Puxtrees Coal Member; (3) St Heliers Coal Member to the Grasstrees Coal Member; (4) Muswellbrook Coal Member to the Brougham Coal Member; and (5) Fleming Coal Member to the Hilltop Coal Member. The results of the present study do not support the existing correlations. It is here suggested that the Lewis/Loder Coal Member is equivalent to the Balmoral Coal Member, but it has not been.possible to confirm correlations of the remaining seams. Additionally, the Hilltop Coal Member is thought to correlate to an unnamed coal

seam which lies stratigraphically above the Fleming Coal Member (W. Morris, personal communication, 1985).

GAMMA IAY

IUU DfHSITY

GAMMA IA Y

1UU D(NSITY

MUSWELLBROOK AREA

Coal seams in the Muswellbrook area are very consistent and are easily recognized on the geophysical logs (Figure 13). The fairly uniform nature of the seams has enabled confident correlation. GAMMA IA Y

COAi.-

IUI.K DfNSITY

I REMN:; •••'" , repaatad by

poa,lbl4 , awar••

'•"" FU--. HAllfTT

MUSWRUaOOK A.., ST-IDS

l::,,=:;:----:-:=f:=:;;;;,;;;;-- - - • pllS:'::l:~;• of UPPH LEWIS LOWH LEWIS

=-±~ .-

--::-t---:------::---::;;;;;;,;;;i. . .l ~ LEWIS

Figure 13: Coal seam correlation in the Muswellbrook area.

The basal coal, the Loder Coal Member is only developed over the eastern half of Muswellbrook Coal Company's Colliery Holding. The overlying Lewis Coal Member, persists throughout the area and commonly contains two to three splits separated by prominent dirt bands (Figure 13). This coal member is characterised by dull coal for the basal splits, with the top ply (approximately 2m thick) generally brighter. The St Heliers Coal Member is 2m to 10m above the Lewis Coal Member. It is thickly developed over the area· and contains up to four splits. The St Heliers Coal Member is overlain by the Muswellbrook Coal Member which lies 2m to 6m above. These seams commonly coalesce to make up a very thick interval of coal (Figure 13). The Hallett Coal Member overlies the Muswellbrook Coal Member by 2m to 10m and contains one seam. The Fleming Coal

Member is the topmost economic coal in the Muswellbrook area and overlies the Hallett Coal Member by 2m to 12m. A number of thin seams (generally less than lm in thickness) occupy the 10-20m interval between the top of the Fleming Seam and the top of the coal measures. The coal seams are very thickly developed in this area and seam splitting, although present, is minor over the bulk of the area but increases towards the eastern boundary of Muswellbrook Coal Company's Colliery Holding. SAVOY TRIG. STATION AREA

Coal seams in the Savoy Trig. Station area are generally not as thickly developed and are more commonly split than coals in the Muswellbrook area. Intrusions are widespread throughout the sequence and,

GAMMA RAY

alJlI DDCSITY

GAMMA RAY

IUll[ DDCSITY

GAMMA RAY

auu: DlNSITT

COAL MOa11t

AYIDAl.f

SANDST<»«

Figure 14: Coal seam correlation in the Savoy Trig. Station area.

together with small scale faults, disrupt the coaly horizons. The coal seams are however still recognizable on the geophysical logs (Figure 14). In addition, correlations in this area are made substantially easier by the . occurrence of the marker horizons. The basal coal is the Balmoral Coal Member. It is a thick dull coal which commonly develops two to three splits separated by prominant dirt bands (Figure 14). The Balmoral Coal Member is overlain by the Ayrdale Sandstone. The sandstone is a marker horizon which facilitates correlation of the overlying Puxtrees Coal Member. The Puxtrees Coal Member contains two main splits separated by interdistributary bay laminites. The Grasstrees Coal Member is 81:Il to 30m above the Puxtrees Coal Member although this interval can be much greater where igneous intrusions are present. The Grasstrees Coal Member is variable over the area and contains up to five thin splits. The Brougham

Coal Member is 4m to 10m above the Grasstrees Coal Member and contains up to four splits. The topmost coal in the Savoy Trig. Station area is the Hilltop Coal Member. It is a thinly developed, pyritic coal which lies just below the marine Branxton Formation . CORRELATION BETWEEN MUSWELLBROOK AND SAVOY TRIG. STATION AREAS The Lewis/Loder Coal Member is considered to correlate with the Balmoral Coal Member. The geophysical traces are comparable (Figures 13 and 14), the seams are characterized by dull coal, and both directly overlie and, in part interfinger with, the distinctive pelletoidal clayrocks. Based on the close association with the pelletoidal clayrocks, the seams are thought to have accumulated in an alluvial plain setting.

The base level change followed accumulation of the Lewis/Loder-Balmoral coal and brought about a deltaic setting in the region. Lower delta plain conditions were established in the Savoy Trig. Station area while upper delta plain conditions prevailed in the Muswellbrook area. Consequently, the sequence above the Lewis/LoderBalmoral Coal Members in each of the two areas different processes of sedimentation. The coal members in the two areas are also quite different. The geophysical traces are not comparable and the coals display different characteristics such as thickness and seam splitting. Correlation of the seams has not been possible due to the significant differences in coal seam characteristics. The difference between the coal members may be related to the contrasting environments of deposition. For example, coal seam characteristics in the Muswellbrook area may be accounted for by the sedimentary processes on the upper delta plain. The upper delta plain is largely an area of sediment by-pass. Bed-load sediment carried by the distributary network is confined by strongly constructed levees and transported further basinward where it is deposited in the lower delta plain/delta front area. Also, the upper delta plain builds mainly by aggradation which is largely restricted to episodes of major floods. Thus lengthy periods of peat accumulation with infrequent interruption by contaminating sediments characterize the upper delta plain setting. Thick peats can form in this stable, slowly subsiding environment. In contrast, the lower delta plain environment, such as occurs in the Savoy Trig. Station area, is an area of active sedimentation and rapid subsidence. Delta lobes are constructed by distributary mouth-bar, distributary-ch annel and crevasse-splay facies and provide a base for peat accumulation. Foundering of the delta lobes upon abandonment terminates the peat accumulation. This process is then quickly followed by a new progradational cycle. Peat accumulation in this environment is short-lived when compared to the upper delta plain swamps. The resultant coal seams are thinner and more commonly split than their counterparts in the upper delta plain.

Tectonic control may also significantly influence coal seam characteristic s. Unstable rapidly subsiding areas may result in thin, commonly split coal seams whereas more stable areas will develop coals which are thick and less commonly split. The coal-forming conditions envisaged for the sequence overlying the Lewis/LoderBalmoral Coal Members are somewhat analogous to the situation described by Frazier & others, (1978) in modern coastal Louisiana. Frazier & others, (1978) studied the environments of peat accumulation in coastal Louisiana and found that the thickest peats were encountered in the stable inland swamps. Thinner peats were genetically related to subsiding marshes on overlapped delta lobes in the peripheral areas. With the aid of radiocarbon dates they also found that each thick inland peat may be time correlative with several coastal marsh peats. The correlation of individual thick inland peats with several coastal marsh peats is very significant and may be applicable to the Greta Coal Measures sequence. The marine influenced Ayrq.ale Sandstone is thickly developed in the Savoy Trig. Station area but thins to the northeast, and no correlative may be prevailed in the Muswellbrook area while distributary mouth bar facies of the Ayrdale Sandstone were being deposited further basinward. Thus it is probably that the St Heliers Coal Member in the Muswellbrook area is, at least in part, time equivalent to the Ayrdale Sandstone. It is also probable that at least part of the St Heliers Coal Member is equivalent to the Puxtrees Coal Member since the latter directly overlies the Ayrdale Sandstone. On this basis, it is strongly suggested that the existing coal seam correlations (Standing ·Committee, 1975) are not entirely valid. However, it has not been possible to establish which coal members in the Savoy Trig. Station area equate to which parts of the coal members in the Muswellbrook area. DISCUSSION

The approach of interpreting depositional systems from drill core was applied to the Greta Coal Measures in an attempt to solve long standing coal seam correlation problems between the Muswellbrook and

Savoy Trig. Station areas. The study demonstrated that contrasting depositional environments prevailed in the two areas for a major part of the coal measures history, and that the contrast in depositional environments, and their associated sedimentary processes, may account for the dissimilar coal-bearing sequences. The difficulties experienced in correlation in the past are due to the fact that many of the coal members may not actually correlate directly. Applying the technique of interpreting depositional systems and facies from drill core to solve coal seam correlation problems has been a worthwhile exercise in the Greta Coal Measures. Although it has not produced a new "correlation table" it has established a better understanding of the develop-

ment of the coal measures and may provide a sound basis for further correlation work. ACKNOWLEDGEMENTS I would like to extend special thanks to John Rogis and Claus Diessel for their many ideas and critical review of the manuscript. I am grateful to Muswellbrook Coal Company Limited, Drayton Coal Pty Ltd., Bayswater Colliery Company Ltd. and Mt Sugarloaf Collieries Pty Ltd. for making available company information and drillcore, and to the members of the Greta Coal Measure Working Party for their cooperation. I would also like to thank Sue Bigham who skilfully drafted the diagrams. This paper is published with permission of the Secretary of the New South Wales Department of Mineral Resources.

REFERENCES Bernard, H.A., Major, C.F. Jnr, Parrott, B.S., & Le Blanc, R.J. Sr., 1970: Recent sediments of southeast Texas: A field guide to the Brazos alluvial and deltaic plains and the Galveston barrier island complex. University of Texas (Austin), Bureau of Economic Geology Guidebook 11 . Booker, F.W., 1953: The geology and coal resources of the Singleton-Muswellbrook Coalfield. Ph.D. Thesis, University of Sydney (unpubl.). Coleman, J.M. & Prior, D.B., 1980: Deltaic Sand Bodies. American Association of Petroleum Geologists - Continuing Education Course Note Series 15. Elliott, T., 1974: lnterdistributary bay sequences and their genesis. Sedimentology 21, 611-622. Fisher, W.L., & McGowen, J .H., 1967: Depositional systems in the Wilcox Group (Eocene) of Texas and their relation to occurrence of oil and gas. American Association of Petroleum Geologists Bulletin 53, 30-54 . Fisher, W.L., Brown, L.F., Scott, A.J. , & McGowen, J .H., 1969: Delta Systems in the Exploration for Oil and Gas: A Research Colloquium. Bureau of Economic Geology, University of Texas, Austin. Frazier, D.E., Osanik, A., & Elsik, W.C., 1978: Environments of peat accumulation-Coastal Louisiana, in Gulf Coast Lignite Conference: Geology, Utilization, and Environmental Aspects - University of Texas (Austin), Bureau of Economic Geology - Report of Investigations No.90. Hamilton, D.S. , 1984: Depositional systems and coal seam correlation in the Greta Coal Measures of the Muswellbrook Region. Geological Survey of New South Wales - Coal Geology Branch Report CGB 1984-048. Hamilton, D.S., & Beckett, J ., 1984: Permian depositional systems in the Gunnedah region. Geological Survey of New South Wales Quarterly Notes 55, 1-18.

Kaiser, W.R. , Johnston, J .E., & Bach, W .N., 1978: Sand-body geometry and the occurrence of lignite in the Eocene of Texas. University of Texas (Austin), Bureau of Economic Geology - Geological Circular 78-4 . Loughnan, F.C., 1973: Kaolinite clayrocks of the Koogah Formation, New South Wales. Journal of the Geological Society of Australia 20, 329-349. Loughnan, F.C., 1975: Correlatives of the Greta Coal Measures in the Hunter Valley and Gunnedah Basin, N.S.W. Journal of the Geological Society of Australia 22 , (2), 243-253. McPhie, J ., 1984 : Permo-Carboniferous silicic volcanism and palaeogeography on the western edge of the New England Orogen, northeastern New South Wales. Australian Journal of Earth Science 31, 133-146. Raggatt, H.G., 1938: Evolution of the Permo-Triassic basin of east-central New South Wales. D.Sc. Thesis, University of Sydney (unpubl.) Reineck, H.E., & Singh, I.B. , 1975: Depositional Sedimentary Environments. 439pp. SpringerVerlag, Heidleburg. Robinson , J .B., 1963 : Revised stratigraphic nomenclature for the Greta Coal Measures in the Muswellbrook area. Report Joint Coal Board New South Wales., CR63/8 (unpubl.). Saxena, R.S., 1979: Facies Models and Subsurface Exploration Methods for Deltaic Sandstone Reservoirs . 60pp. PESA, Australia Distinguished Lecture Course, Adelaide. Standing Committee on Coalfield Geology of New South Wales, 1975: Report of Subcommittee for the Northern Coalfield - stratigraphic nomenclature. New South Wales Geological Survey Records 16(1). 9-105.

Tadros, V.Z., & Beckett, J., 1983: Interpretation and correlation of depositional environments: Gunnedah Basin Coal Exploration Programme. New South Wales Department of Mineral Resources - Coal Geology Branch Report CGB 1983-037 (unpubl.). (GS 1983/305). Tobin, C.D., 1980: The Geology of the Balmoral area, New South Wales. University of Newcastle B.Sc. (Hons) Thesis (unpubl.).

D. S. HAMILTON New South Wales Department of Mineral Resources Bent Street, Sydney, N.S.W. 2000. Present address: 214 Kiora Road, Miranda, N.S.W. 2228.

SEDIMENTARY DEPOSITIONAL ENVIRONMENTS AND SOME IGNEOUS INTRUSIONS IN THE SYDNEY-GUNNEDAH BASIN By D. J. Martin

ABSTRACT A suite of teschenitic sills and lopoliths is intruded into the Permian strata of the Sydney-Gunnedah Basin. They vary from 0.2m to more than 50m thick, but about 75% are less than 5m. Dilational emplacement was by crack propagation enhanced by the hot volatiles evolved from the magma, although existing fractures favourably orientated with respect to contemporary tectonic stresses were reactivated. Volatiles derived from coal contributed to intrusion of coal seams. The frequency of intrusion of sediments from different depositional environments was greatest in shallow marine and lower delta plain laminite and coal. Bright coal plies, with high vitrinite content, are more vulnerable than dull coal. Softening of vitrinite by hot gases ahead of the advancing magma, leading to the formation of weak, easily fractured coke, facilitates preferential intrusion.

has.been investigated (Figure 1). The intrusions are commonly in the form of sills, or of convex lopoliths. The teschenite consists predominantly of titansahlite, labradorite feldspar and titanomagnetite. Olivine, titanian biotite, the titanium-rich amphibole kaersutite and abundant analcime may he present.

+ +

r ·-· - · /

..,·,. I

+ ' •·.·

L. - +-•_.7

< + ":, +

~ -:,

. -'f\

· j .. _. 0 .

L:::,.:_:_; ~~ :<

+ ••. :·:Y~- -0

INTRODUCTION The site at which an igneous intrusion is emplaced is determined by the subtle interplay of a number of factors, not all of which can be evaluated. Its geographical location is influenced by the tectonic regime at the time of intrusion, in relation to the orientation of pre-existing fractures and faults. The stratigraphic level at which a sill is intruded is determined not only by inherent properties of th~ magma, but also by the lithology of the sedimentary rocks, the nature of the interlayer boundaries and so indirectly by the depositional environments of the sediments. The presence of coal seams increases the complexity of the situation, because of the varying abundance and behaviour of the coal macerals.

THE INTRUSIONS A suite of small to medium-sized basaltic (teschenitic) intrusions in the Permian sediments of the Sydney-Gunnedah Basin

(I] Pre - Permian bas ement

Fau lt acti ve post Carboniferous

- ·- · Study a rea

100 km

·Figure 1: The study areas in relation to the Lachlan Craton, the New England orogen, and the Permian sediments of the orogenic fore-deep. After Jones & others, 1984. Locations shown are G = Gunnedah; N Newcastle; P Prospect; R Rylstone; S Scone; W = Wollongong.

Geochemically the intrusions form an undersaturated sodic lineage, from analcime basanite through hawaiite to mugearite and benmorite. The volatile content, mkinly cbz, is fairly· high. An Mg number (atomic l00Mg/(Mg+Fe 2 +)) greater than 67, a high Ni content ( > 250ppm) and the presence of mantle

~ 84 Yo

0-5 m

0- 5 m ~

'73¾-I

3 3

UJ 20

1')

>u z

:::,

a::

u... 10

'#40 50 'flJ TOTAL DI STRIBUTION n=2 58

0 o-51-5 5 10

O 051-5 510

SO )50

GUNf\lEDAH BASI N n =1 8 3

0 ()lj1-5 510

30 40

RYLSTON E AR EA

SO >SO

n =7 5

THICKNESS OF IGNEOUS INTERSECTION (ml Fiirure 2: The ize-frequenc~· distributions of igneous intersections in Department of Mineral Resources diamond dri ll-core from the Gunnedah basin

(Authorisation o. 216) and the Rylstone area (Authorisation 230). About 75% are less than 5m thick.

xenoliths, attest the high pressure origin of the magma of the primary intrusions (Martin, 1985), while others appear to have fractionated olivine and clinopyroxene during their ascent (Martin, in prep.). They resemble in composition the associated Jurassic and Tertiary volcanics (Abbott, 1969; Bean, 1975; Jensen, 1907). A size-frequency study of igneous intrusions intersected in the N.S.W. Department of Mineral Resources drilling programmes in the Gunnedah Basin and in Rylstone Authorisation No. 230 shows that the majority (about 75%) of intersections are less than 5m thick (Figure 2). Some of the smaller ones which are in contact with coal have undergone alteration to "white trap", composed largely of clay and/or carbonate alteration products of the teschenite. However, many are relatively fresh, and most larger intrusions in this study have differentiated into geochemically evolved layers and broad zones.

ed into the pore spaces of country rocks such as sandstone and conglomerate, or was confined within intrusions emplaced in fine-grained rocks such as siltstone or claystone. Evidence from drill core and from underground workings in coal mines suggests that emplacement was commonly by dilational intrusion, rather than by stoping (H!llllilton, 1968; French, 1982). The intrusion expanded marginally by the growth of thin stringers of magma through a network of cracks, behind which the advancing magma coalesced into a wedge (French, 1982). The vplatile content of the magma increased the rate of crack propagation at the leading edge of the intrusion (Spera, 1984), and by lowering the viscosity of the magma also increased its rate of injection (Spence & Turcotte, 1985). High-angle joints in fairly flat-lying sills are interpreted as joints normal to the cooling surface of the intrusion. Water which could not be accommodated in hydrated minerals saturated the remaining melt (Burnham, 1979), and decreased solubility of water in the cooling magma would lead to continuing loss of steam via the marginal joints to the surrounding sedimentary rocks.

EMPLACEMENT The lower pressure and temperature of the magma, when emplaced at high crustal level, caused exsolution of C02 and some 1{0 as superheated steam. This was releas-

GUNNEDAH BASIN - DISTRIBUTION OF INTRUSIONS SHALLOW MARINE DIGBY FORMATION STONY

BI.AO<

COALS

l.FPER DB.TA PLAIN LOWER DELTA PLAIN

HOSK6SOtS

SHALLOW MARINE

SHAl..1.0W MARINE

SHELF

FOfMA'OON DELTA FRONT

~--~--~-7WATERMARK PRODELTA

OWER DB.TAl'V'-lV...'V'.IYV'.'Y'I PLAIN DELTA~

FOFMA'OON MARINE

MARINE SHELF PORCUPINE FORMATION

MAULE$ CREEK FORMATION l.EAR) FOFMA'00N

(b)

NO. OF INTRUSIONS

Figure 3: (a) Stratigraphic succession and environments of deposition in the Gunnedah Basin (from Beckett & others, 1983). (b) Frequency of intrusion into sediments and coal of th e \·a rious depositional environments. Vertica l scale dia gram-

RELATIONSHIP OF INTRUSIONS TO DEPOSITIONAL ENVIRONMENTS In the Gunnedah Basin, by far the greatest number of igneous intersections is found in the delta plain and shallow marine environments of deposition (Beckett & others., 1983) of the Black Jack and Napperby Formations (Figure 3). Intrusions are especially frequent in the coal-bearing upper delta plain facies, and the flood plain and braided stream deposits of the tuffaceous stony coal facies (Beckett & others, 1983; Hamilton & Beckett, 1984). In the Rylstone area (Figure 4), intrusions are most frequent in the lower delta plain environments of the Glen Davis and Long Swamp Formations (Moloney & Bradley, 1984). The frequency of intrusion at boundaries

ma tic. Diag-omt! crosshatching. intrusions on coal: sq ua res. intru~ion s in marine and deltaic sedimPnts: vertical lin es. in lower delt a plain sed imen ts: finp stipple. in upper plain sedim ents: hea \·~• ~t ippl P. in alluvial sedim ents.

between different strata or within a lithological unit can be analysed by means of a contingency matrix, similar to that used in construction of a facies model (Figure 5). An analysis of drill-logs from the Gunnedah Basin (Figure 5a) shows that coal plies, siltstone and claystone in the Black Jack Formation, and interbedded or interlaminated siltstone-sandstone sequences of the shallow marine Napperby and Purlewaugh Formations, are preferentially intruded. Frequency of intrusion in other lithologies is randomly distributed. Few intrusions occur in the Hoskissons Seam in most areas, but in the Gunnedah-Breeza area the Hoskissons Seam is intruded by major sills and dikes. To check the general distribution of boundaries . in the stratigraphic successsion, all boundaries in a single deep drill-hole (D.D.H. Goran 1) were scored in the same manner, and were found

RYLSTONE AREA

- DISTRIBUTION OF INTRUSIONS

FARMERS CREEK

UPPER DELTA PLAIN/

FORMATION

ALLUVIAL CHANEL

GN'SND3TONE

UPPER DELTA PLAIN CH~NNEL

STATE MINE CREEK FM.

LOWER DELTA PLAIN

:? ,cc:

~II

ANGUS PLACE SA BAAL BONE

DEEP INTERDISTRIBUTARY BAY FORMATION GLEN DAVIS

FM .

LOWER DEL TA PLU1

LONG

LOWER DELTA PLAIN/

SWAMP

SHALLOW INTEROISTRIBUTARY BAY/

FORMATION

DISTRIBUTARY CHANNELS

LIDSDALE COAL

FAN DELTA

BLACKMANS FLAT C G

BRAIDED STREAM

LITHGOW COAL

LOWER DELTA PLAIN

...

./'

,I'

'V'>< 0

.,.,

I(:

MARRANGAROO CG

BRAIDED STREAM

NILE Sl.BCR:ll.P

LOWER DELTA PLAIN/ MARINE

I<;

(a)

(b)

NO. OF INTRUSIONS

Figure 4: (a) Stratigraphic succession in the Rylstone area, and environments of deposition (Moloney & Bradley, 1984). (b) Frequency of intrusion in the various environments. Shading as in Figure 3. RYLSTONE AREA - INTRUSION BOUIOARIES

GUNNEDAH BASIN - INTRUSION BOUNDARIES

COAL csxs CS COAL +14

COAL csxs CS

CGP

COAL •4

-4

csxs

•2

CGP

-5

csxs

-4

,.3

CS +10

~=206

x·=44 n = 77

n:119

-6

-1

CGP

+16

LA +5

-4

•5

CGP

Figure 5: Matrices showing number of lithological transitions which are intruded. The numbers in the squares represent (0 - E), where O is the observed frequency of intrusion between two lithologies, and Eis the expected proportion of the total varience. Only values > 2 are shown. Number of degrees of freedom is 48. (a) For the Gunnedah Basin, the critical value of X' is exceeded at all levels of significance. (b) For the Rylstone area, X' is less than the critical value, but the sample size is small. Coal plies, and fissile lithologies are preferentially intruded. Abbreviations for non-coal rocks (Ward & others, 1984) are CSXS = carbonaceous claystone; CS = claystone; SI = siltstone; SA = sandstone; LA = laminate (thinly interbedded or interlaminated siltstone and sandstone); CGP = pebble conglomerate.

to have a random distribution, with 2 less than the critical value. A similar analysis was made of drill-logs from the Rylstone area (Figure 5b). Coal plies, claystone or mudstone, and siltstonesandstone sequences are preferentially intruded though the data as a whole are randomly distributed, probably because the sample size is rather small for the large number of degrees of freedom. The Lithgow Coal, a massive dull, inertinite-rich coal correlated with the Hoskissons and Bayswater Seams (Beckett & others, 1983) is not intruded. In summary (Figure 6) it can be seen that intrusions reach a maximum in the lower delta plain environment, decreasing through shallow marine and upper delta plain to a minimum in alluvial plainalluvial fan settings. Intrusion in coal follows the same trend in the non-marine environments.

stratigraphic level. This was attempted only in the Rylstone area, where the drillholes were more closely spaced. It was found that, at a stratigraphic level similar to the intrusion, a ply of 60-90% brightness commonly occurred. A 'brightness index' was derived from the median logged coal brightness of the ply, weighted for the ply thickness. This was plotted against intruded ply thickness (Figure 7). Most of the intruded plies are 0.5m or less in thickness, and greater than 100 on the brightness index, i.e. thin, bright plies are most commonly intruded. 1000

:I SO(

•0 •

e GLEN DAVIS COAL 0 LONG SWAMP FM. COAL

■

LIDSOAI.E CGAL

•o c, ~o •o

15 ~ ~

.,.,'.,., f

• !•

•~ ••

•

~ 100

"'i

;

• l!5

•

1u::o-----:~.,,...------c-,,,~ -----:-' ,.s

INTRUDED PLY THICKNESS lnl

Figure 7: Brightness index vs. thickness of in truded coal ply. See text for explanation. 0 N

DISCUSSION

Figure 6: Summary of frequency of intrusion in sedimentary rocks from various depositional environments, in the Gunnedah and Rylstone areas. Shading as in Figure 3.

INTRUSIONS ON COAL

The brightness of coal plies where intrusion occurred in coal seams, was inferred from correlation with the seam brightness . profile (Moloney & Bradley, 1984) in the nearest drill-hole not intruded at that

The frequency of intrusion of sediments formed in different depositional environments appears to be correlated with the abundance of fissile lithologies (Figure 5). Intrusions into conglomerates may be due to the high effective porosity of the coarse sandy matrix. The brightness of coal is due to high vitrinite content. A summary of wholeseam data for the northern coalfields of the Sydney Basin (Cook, 1975) shows that about half the seams have a vitrinite content of more than 70%. The maceral content of coals varies with their environment of formation. Continuously high water

tables prevented oxidation of raw humus before gelification could occur (Hunt, 1982), and favoured the development of high vitrinite coals in permanent wetlands (Figure 8). Dull coals rich in inertinite and low in vitrinite may have formed when oxidation of vegetable matter occurred before isolation from atmospheric influence (Hunt, 1982). The coal of the BayswaterLithgow-Hoskissons complex, which formed in the vast delta plain, covering much of the Sydney-Gunnedah basin during marine regression (Beckett & others, 1983) is commonly (though not invariably) dull. This was probably due to sub-aqueous oxidation and possibly some reworking of the peat in a back barrier or lagoon setting (Hunt & Telfer, 1983). Alluvial plain and alluvial fan conditions favoured both oxidation and inwash of mineral matter, producing stony coals rich in inertinite (Warbrooke, 1984). Some differences in maceral composition probably relate to floristic changes (Cook, 1975). Retallack (1980) suggested that the drier environment of the upper delta plains supported plants with more lignified tissue. It is suggested that the vulnerability of coal to intrusion depends on its vitrinite content, other factors being equal. The correlation of frequency of intrusion of coal with depositional environment and with vitrinite content (Figure 6 and 7) supports this hypothesis.

Vitrinite is fusible between about 400°C and 450°C, the exact temperature interval depending on the coal rank. Mineralogical evidence shows that the temperature of intrusion of basaltic magmas is in the range 1100°C-1250°C. Volatiles evolved from the magma and from the coal would increase the rate of crack propagation, and heat the coal ahead of the advancing edge of the intrusion. The marginal "fingers" of magma and the coalescing wedge behind them could raise a thin vitrinite-rich ply to fusion temperature. Further heating of the softened vitrinite would produce coke. Experimental work (Cook & Wilson, 1969) has shown that both stability and hardness of coke decrease when vitrinite content of the coal is above about 60% or below about 45%. Increase of rank has a similar but smaller effect on coke characteristics for the same vitrinite content. It seems likely that high vitrinite content is the critical factor, in that initial softening of vitrinite-rich plies adjacent to a feeder dike allows preferential penetration by magma, and that weaker coke structure favours continued advan.ce of the magma. However, pre-existing fractures in the country rocks would also be penetrated easily by magma. It may be that this contributes to the intrusion of the Hoskissons coal in the Gunnedah-Breeza area, perhaps along lowangle fractures- associated with the nearby Hunter-Mooki thrust system and the Eocene Liverpool Volcano. However, the bright coal of the Melville seam below the Hoskissons is not intruded (Tadros, 1985).

CONCLUSIONS ~ i~'!fnitt ... -~~-~~-~~-~~-~ •~,~1nert 1nit•

Macera! comp osi tiQn and

• fu s1n 1r,

D, pos i ti onal Environment

Figure 8: Macera! content of coals from different environments of deposition in the marginal coal basi ns of Eastern Australia. After Hun t, 1984. Shading as in Figure 3. Lower delta plain coals are rich in vitrinite. Upper delta plain coals are much more variable. while alluvial settings are characterised by coals with less vitrinite and semifusini te.

1. Intrusions in the Sydney-Gunnedah Permian sediments are preferentially emplaced in fissile rocks and in coal seams. 2. Intrusions decrease in frequency from a maximum · in lower delta plain facies, through shallow marine and upper delta plain, to a minimum in alluvial plain/alluvial fan facies.

3. The vulnerability of coal to intrusion is correlated with its vitrinite content, and with its environment of formation. Massive dull coals are intruded less often than bright seams. Preferential intrusion of vitrinite-rich plies probably involves heating by volatiles ahead of the intrusion, softening of vitrinite and subsequent formation of weak coke, easily fractured by dilational crack propagation powered by volatiles from the magma and the coal.

ACKNOWLEDGEMENTS I thank the N.S.W. Department of Minerals and Energy for permission to use drilling information, and personnel of the Coal Geology Division for their generous assistance. Dr. S. O'Reilly and Dr. N.Z. Tadros critically read the manuscript and made suggestions which substantially improved it, though any errors present are my own.

REFERENCES Abbott, M.J., 1969: Petrology of the Nandewar Volcano, N.S.W. Contrib. Mineral. Petrol. 20, 115-34. Bean, M.J., 1975: Petrology and petrochemistry of igenous rocks in the Mullaley area of New South Wales. J. Proc. R oy. Soc. N.S. W. 108, 131-46. Beckett, J. , Hamilton, D.S. & Webster, C.R. , 1983: Permian and Triassic stratigraphy and sedimentation of the Gunnedah-NarrabriCoonabarabran region. Geol. Surv. N.S. W. , Quart. Notes 51, 1-16. Burnham, C.W., 1979: Magmas and hydrothermal fluids. In H.L. Barnes (Ed.) Geochemistry of hydrothermal ore deposits. J . Wiley & Sons, New York. 71-136. Cook, A.C. & Wilson, R.G. , 1969: Rank and type varia tions in coals from the Southern and South Western Coalfields, New South -Wales, and their influence upon coking. Proc. Aust. Ins t. Min. Met. 232, 27-39. Cook, A.C. & Wilson, R.G. , 1969: Rank and type variations in coals from the Southern Western Coalfields, New South Wales, and their influence upon coking. Proc. Aust. Inst. Min. Met. 232, 27-39. French, D.H. , 1982: The mineralogy and petrology of an alkali basalt intrusive complex near Gunnedah, N.S.W. Univ. Newcastle, Ph.D. thesis (unpubl.). Hamilton, D.S., & Beckett, J ., 1984: Permian depositional systems in the Gunnedah region. Geol. Surv. N.S. W. , Quart. Notes 55, 1-18. Hamilton, L.H., 1968: Interaction of coal and magma. M.Sc Thesis, Univ. N.S.W. (unpubl.). Hunt, J. , 1982: Relationship between microlithotype and maceral composition of coals and geological setting of coal measures in the Permian basins of Eastern Australia. Aust. Coal Geol. 4. 484-502. Hunt, J ., 1984: Depositional environment, maceral composition and sulphur content, and composition of Permian coals of Eastern Australia. Proc. 18th Symposium, Adu. Study Sydney Basin, 31-34. Hunt, J . & Telfer, A., 1983: Commonwealth Scientific & Industrial Research Organisation, Division of Fossil Fuels, Unpubl. Report. J ensen, H.I., 1907: The geology of the Warrumbungle Mountains. Proc. Linn. Soc. N.S. W. 32, 557-626.

Jones, J .G. , Conaghan, P .J. , McDonnell, K.L. , Flood, R.H., & Shaw, S.E. , 1984: Papuan Basin analogue and a foreland basin model for the Bowen-Sydney Basin. In J.J. Veevers (Ed.) Phanerozoic earth history of Australia. Oxford, Clarendon Press, 243-63. Martin, D.J. , 1985: Microstructure, geochemistry and differentiation of a primary layered teschenite sill. Geol. Mag. 122, 335-50. Moloney, J. & Bradley, G. , 1984: Geology and coal resources of the Rylstone Authorisation No.230, Stage 1 and Stage 2 drilling programmes. N.S.W. Dept. Min. Res. Coal Geol. Rept. 1984-006 (un-publ. ). Retallack, G., 1980: Late Carboniferous to Middle Triassic megafossil floras from the Sydney Basin. In Herbert, C. & Helby, R. (Eds.), A Guide to the Sydney Basin, Geol. Suru. N.S. W. Bull. 26, 384-429. Spence, D.A. & Turcotte, D.L., 1985: Magma-driven propagation of cracks. J . Geophys. Res. 90, 575-80. Spera, F.J ., 1984: Carbon dioxide in petrogenesis III: role of volatile in the ascent of alkaline magma with special r eference to xenolithbearing mafic lavas. Contrib. Mineral. Petrol 88, 217-232. Tadros, N .Z., 1985: Geology, depositional en vironments and coal resources of the Breeza area. Geol. Suru. N.S. W. Quart, Notes 59, 1-18. Warbrooke, P., 1984: Coal-forming environments in the Greta, Tomago and Newcastle Coal Measures. Proc. 18th Symposium, Adu. Study Sydney Basin, 35-42. Ward, C.R., Comino, J. & Waltho, A., 1984: Classification and systematic description of coalbearing rocks in drill cores. In Geol. Soc. Aust. Abstracts, 7, 536-7.

D. J . MARTIN School of Earth Sciences Macquarie University North Ryde N.S.W. 2113.

DUARINGA- A BIPARTITE OIL SHALE DEPOSIT By A. C. Hutton

ABSTRACT Duaringa oil shale deposit, located 110 km west of Rockhampton, Queensland, is part of the Tertiary sequence of the Duaringa Basin and is defined topographically by four tableland areas. The deposit contains two oil shale intervals that are separated by a thick claystone section approximately 500m thick. Interbedded brown to dark greyish-brown oil shale, brown coal, carbonaceous shale and claystone are the dominant lithologies in the lower oil shale unit. The younger oil shale unit contains dominantly grey to olive-green oil shale and claystone; coaly intervals are rare in this unit. The oil shales have different physical and petrographic properties. The are termed lamosites because they contain abundant lamellar alginite derived from planktonic algae. Both lamosite units were deposited in fresh to slightly brackish water, lacustrine environments. The deposit is unusual in that it is the only Australian Tertiary oil shale deposit that contains two types of low-vitrinite lamosites with significantly different properties from each other.

INTRODUCTION The Duaringa oil shale deposit is part of the Tertiary sequence of the Duaringa Basin, an elongate north-northwest trending basin, centred 110 km west of Rockhampton (Figure 1). The geology of the basin, topographically defined by four tableland areas which attain a maximum height of 140m above the surrounding plains, has been given by Green & others, (1979). Kirkegaard & others, (1970) described the Duaringa Basin as an elongated trough located between a folded zone to the west and the Connors Arch and Gogango Overfolded Zone to the east. Mapping and drilling have indicated a normal fault along the western margin of the basin (Green & others, 1979) and seismic studies, together

with structure contours constructed from drilling data by Southern Pacific Petroleum NL and Central Pacific Minerals NL (SPP/CPM), have delineated three subbasins which correspond to topographic highs. A drilling programme during 1978-79 by SPP/CPM delineated two thin but laterally extensive oil shale seams in the upper 100m of the Tertiary sequence. On the basis of Fischer assays for 59 fully cored drill holes, the upper part of the sequence has been divided into seven units (Green & others, 1974). The Geological Survey of Queensland drilled a stratigraphic hole, GSQ Duaringa l-2R in the southern sub-basin and penetrated more than 100m of Tertiary sediment. A lower oil shale unit was intersected below 650m. In this paper the two oil shale units are referred to as the upper and lower oil shale units. The lower seam of the upper oil shale unit is 10 to 15m thick with shale oil yields of 63 to 92 LTOM. 20 to 25m of mudstone separates the lower oil shale seam from the thinner upper seam which averages Sm in thickness. Grades for the latter range from 46 to 66 LTOM. Combined in-ground resources of both seams (based on 40 LTOM cutoff) is estimated at 3.72Xl09 barrels (Southern Pacific Petroleum, NL, 1984; Central Pacific Minerals NL, 1984). Resources of the lower oil shale unit have not been determined. The age of the Duaringa deposit has yet to be determined beyond doubt. Hekel (1972), on the basis of pollen assemblages, suggested an Early Miocene to Late Oligocene age for the upper 150m of the upper oil shale unit, and Foster (cited in Green & others, 1979) has given a similar age for the interval from 725.09 to 729.03m in GSQ Duaringa-1/2A. Foster (1980) dated one sample from the upper unit as Unit III of the Tertiary (latest Oligocene to early Miocene) but subsequent work has shown that Malvacewumpollis estalae, on which the data was based, is an unreliable marker

, ~--' Prospective Area

.- ... , ' NoArtrheearn

:,-' ... _} '

, ... ✓

·~'

.. Sampled Drill Hole

"-1..,_~-,

2"'o

2 l3.-

.... ,.../·-----,

Central Area

1so•E

kilometres

22•s

Dingo

Southern Area

Duarlnga

24"S

C 0

___.100

kilometre•

•

! 1so•E

Figure 1: Location of the Duaringa oil shale deposit , Duaringa Basin, Queensland. Authorities to Prospect for the Duaringa deposit are the shaded areas in the inset.

unit and Unit III begins in Middle to Late Eocene. McMinn (1980) assigned a Middle to Late Eocene age to the upper oil shale unit of the deposit.

TERMINOLOGY Oil shales contain organic matter, derived from a variety of precursors, which can be designated by maceral terminology as defined by Stach & others, (1975; 1982) and the International Committee for Coal

Petrology, (1963; 1971; 1975) providing the maceral alginite is subdivided into two types - lamalginite and telalginite (Hutton, 1982). Liptinite is the most important constituent in most oil shales because it not only deters many of the chemical and physical attributes of the parent shale but is also the major oil-yielding component. Thus any classification of oil shales discriminatory criterion. Such a classification was proposed by Hutton (1982) (Figure 2).

NERTNTE

TERRESTRIAL OIL SHALE

............... , , ,

( Botryococcus )

I I

LAC US TRINE

MARINE

OIL SHALE

'I LAMOSITE

LAMALGNTE

(BlueGreen Algae)

LAMOSITE

LAMALGHTE

TEL ALG.. rTE

(Green Algae)

( T asmanilid s)

LAMALGNTE

( Dino flagellates. Acri ta rchs )

Fij!urP 2: C' lmss ificntion of oil ~hnlP~.

The Duaringa deposit contains six rock types - lamosite, carbonaceous lamosite, coal, carbonaceous shale, claystone and sandstone. These rocks are defined as follows: i. Lamosite is a brown to dark greyishbrown or green to olive grey laminated or massive oil shale composed of at least 5 per cent by volume (%vol.) lamalginite with accessory telalginite, vitrinite, inertinite, sporinite and rare bitumen. ii. Carbonaceous lamosite is a dark brown to black laminated or massive lamosite that contains not less than 5% vol. vitrinite, inertinite and/or liptinite derived from terrestrial plants; two types occur - that composed of interlayered lamosite and • coal and that which is predominantly lamosite but which contains abun-

dant disseminated vitrinite and/or inertinite. m. Coal is a dark greyish-brown to black rock that contains not less than 50 %vol. vitrinite and/or inertinite with accessory liptinite (such as resinite, cutinite, sporinite, liptodetrinite but not alginite) derived from terrestrial plants; coal with > 5 %vol. liptinite is termed a cannel coal and is regarded as an oil shale (Figure 2). 1v. Carbonaceous shale is a dark grey to black shale or claystone that contains < 50 %vol. vitrinite, inertinite and/or liptinite; alginite is normally not present. v. Claystone is a laminated or massive rock containing < 5 %vol. organic matter; where organic matter occurs vitrinite is the dominant organic matter; claystone in the lamosite-

bearing units contains minor lamalginite whereas that occurring in coaly units contains minor liptinite derived from terrestrial plants. VI . Sandstone is generally a massive rock c_ontaining < 5 %vol. organic matter; sandstone has the same organic assemblages as claystone but has sand-sized mineral matter. Duaringa lamosite is a Rundle-type lamosite because it contains abundant lamalginite derived from freshwater precursors such as Pediastrum (a thinwalled, stellate colonial algae) and Septodinium (a freshwater dinoflagellate). In Rundle-type lamosite the alginite occurs as discrete lamellar whereas lamalginite in Green River-type lamosite occurs as continuous layers up to several millimeters in length.

and gastropod fragments are minor constituents. Vitrodetrinite is a minor but ubiquitous constituent of all lamosite samples of the lower unit. Phytoclasts of texto-ulminite (up to 0.9mm in length) with abundant leaf resinite also occur. % 0

-c

Organic Matter

100

•

.,,iii J:.

100

• a. a.

Lamalglnlte

- - - Vltrlnlte ........ Terreetrlal

Llptlnlte

700

ORGANICPETROGRAPHY LOWER OIL SHALE UNIT This unit comprises interbedded brown to dark greyish-brown lamosite, grey, greyishgreen and white claystone, and minor sandstone. Within the lamosite beds carbonaceous lamosite, brown coal and thin layers of claystone occur. Lamalginite with orange to yellowishorange fluorescence is the dominant liptinite in the lamosite. It occurs with Botryococcus telalginite (yellow fluorescence), an intensely fluorescing form of lamalgini te (green to yellow fluorescence), vitrodetrinite and sparse sporinite. Samples commonly contain up to 30 %vol. alginite with 46 %vol., the largest recorded percentage, at a depth of 1011.4 7m (GSQ Duaringa 1-2A). In alginite-rich samples, lamellae coalesce and the discrete nature of the alginite is not observable in sections perpendicular to bedding. In sections parallel to bedding numerous coalescing subcircular forms, each representing an algal body, can be observed. Samples with < 10 %vol. lamalginite have discrete alginite ranging in length from 0.01mm to 0.1mm. Liptodetrinite is abundant in the lower grade samples. Ostracodes, including fragments and complete valves, pyrite (fine-grained anhedral, euhedral and rarely framboidal)

800

900

iii J:.

(/)

_______.,,.,,~---············

1000

1100

• ll

_,0 1200

1302.7m

Fig urf' :l: Ahuncl nnrP of org:rn ir mnttf'r in isf'IPr-tPd !SnmplPis from d rill holP GSQ Dunrin gn l-2 R

Lamosite from the lower oil shale unit generally has more abundant alginite than lamosite from the upper oil shale unit (Figure 3). Thus it is to be expected that shale oil yields would be higher for samples from the lower oil shale unit.

resinite, resinite bodies, sporinite and cutinite) and elarite-related carbominerite. Lamalginite was not found in any of the brown coal samples. The brown coals of the lower oil shale unit are therefore similar to those of the Rundle-Stuart deposit.

Claystone has liptodetrinite and sparse lamalginite. Total liptinite is generally less than 1 %vol. of the rock. Carbonaceous lamosite is typical of that in the Rundle-Stuart deposit and contains lamalginite-rich layers (up to 10mm thick) interlaminated with thin vitrite, elarite or clarite-related carbominerite. Vitrinite comprises up to 14 %vol. of some samples. Brown coal, sampled at depths of 727.3m, 914.43m, 915.32m, and 1067.3m in GSQ Duaringa l-2R, contains vitrite (comprising texto-ulminite, minor euulmmite, corpohuminite and very minor leaf resinite), elarite (comprising textoulminite, corpohuminite, attrinite, leaf

The upper oil shale unit comprises two lamosite seams (intervals B and D, Figure 4) interbedded with elastic intervals (intervals A-Az, C and E, Figure 4). The underlying elastic interval A-Az has two thin seams of lamosite that contain or~ge fluorescing Pediastrum-type lamalginite, with minor lamalginite derived from Cleistosphaeridium and telalginite derived from Botryococcus. These lamosites are similar to those of the lower oil shale unit although separated by a thick elastic interval.

DD-28

DD-20

UPPER OIL SHALE UNIT

ll SG 3

LTOM 0

200 20 TEL

ll ALGINITE LAM O

ALGINITE

152· 5

Az A

163-3

Figure 4: Abundance of organic matter in elected samples from drill holes 00-28 and 00-20: hoth holes are located in the northern part of the deposit. (TEL - telalgin ite: LAM - lamalginite: SG specific gravity of th e oil hale: LTOM - Fischer assay in litres per tonn e at 0% moisture. Dotted lines give %vol. vitrini te in coa ly sa mples: informal stratigraphic units are shown by letters: dep• ths are in metres. )

Interval C contains several low grade lamosite layers with the same organic assemblage as the lamosite of intervals B and D. Intervals B (divided into Ba, Bb and Be on the basis of shale oil yield) and D comprise interbedded lamosite and claystone. The lamosite is typically grey to olive grey and contains abundant green to greenishyellow fluorescing lamalginite. Lamalginite occurs with Botryococcus telalginite, in_tensely fluorescing lamalginite and lamalginite derived from the fresh-water dinoflagellate Septodinium. Sparse to very rare vitrodetrinite, sporinite, liptodetrinite and bitumen are minor constituents. Lamalginite differs from that in lamosite from the Rundle-Stuart, Condor and Byfield deposits in both form and fluorescence colour although much of the lamalginite in all deposits is derived from Pediastrum. Lamellae range in length from 0.005mm to 0.01mm. Very rich samples are generally composed of lamalginite, 0.02 to 0.08mm long, with simple processes that can be observed in sections parallel to bedding. Lamalginite abundance is variable over short intervals (Figures 5 and 6) as is the case in the Rundle-Stuart, Condor and Byfield deposits. Botryococcus telalginite fluoresces greenish-yellow to orange and is only rarely • replaced by pyrite. Colonies in claystone and low grade lamosite are extremely wellpreserved. Branches, and unicellular algae at the extremities of branches, are clearly recognizable. This form suggests an affinity with the Pila-type of Botryococcus. Structure is poorly preserved in colonies in richer lamosit~s and the form cannot be identified. Telalginite abundance is generally < 2 %vol. of the bulk rock however one sample contained 25 %vol. (Figure 7). In many hand-specimen samples Botryococcus occurs as white, ovoid spots up to 1mm in diameter. An above-average abundance of telalginite accounts for the high shale oil yields obtained for several intervals of the Duaringa deposit. Bone and fungal fragments occur in several samples. Non-fluorescing brown to black monolocular and tetralocular teleutospores are the most abundant form of fungal fragments but fragments of

0D47

LTOM SG 3_ _ _ _ _ o _..,.o_--'200 20

\I\

ALGINITE

TEL 0

LAM

130·0

Figure 5: Abundance of organic matter in DD-8, a drill hole located in the southern part of the deposit. (symbols as for Figure 4)

hyphae are also present. Pennate diatoms were found in samples from two drill holes from the central part of the deposit. One sample from a depth .of 55m in DD-55 constituted 9% of the bulk rock. Duaringa is the only Australian Tertiary oil shale deposit in which diatoms are known to occur although Tertiary deposits such as those in the Nevis Valley (New Zealand), Libros (Spain), Shandong (China) and Aleksinac (Yugoslavia) contain diatoms (Hutton, 1982). Only minor fluorescence emanates from the groundmass of Duaringa samples from the upper oil shale unit. REFLECTANCE DATA LOWER OIL SHALE UNIT

Reflectance data for vitrodetrinite, ulminite and corpohuminite were measured in samples from GSQ Duaringa 1-2R. Romax values ranged from 0.21 to 0.42 (vitrodetrinite, 4 samples), 0.24 to 0.47% (ulminite, 9 samples) and 0.40 to 0.45% (corpohuminite, 5 samples). Reflectance profiles for ulminite and corpohuminite increase at approximately 0.15% per 1000m.

00-8

L TOM 0

'.I',

LAM

ALGINITE

'I,

100 10 TEL

...-------.. ---

LAM

TEL

-60-0

Figure 6: Abundance of organic matter in DD-56, a drill hole located in the central part of the deposit. (symbols as for Figure 4)

268 -Jm

DD-56

LTOM

% ALGINITE

LAM

o TEL

- 4 9-0

- 5 3·0

Figure 7: Abundance of organic matter in DD-47 : a drill hole located in the southern part of the deposit: (symbols as for Figure 4)

Reflectance values for both corpohuminite and ulmitLite are marginally higher than corresponding values for Rundle and Stuart samples but this may be related to increased depth of burial. Extrapolation of the reflectance profile to shallower depths however, gives similar reflectance values (for both macerals) to those in samples at equivalent depths in the Rundle-Stuart deposit. (This assumes that neither the Rundle-Stuart deposit nor the Duaringa deposit has undergone greater erosion than the other.) UPPER OIL SHALE UNIT Humic matter is much less abundant in Duaringa lamosite than in lamosite Ofrom Rundle-Stuart or Condor deposits. R max values for vitrinite were recorded from twelve drill holes (Table 1) but in only seven holes were data taken from five or more

samples. Mean of the R max values for the macerals ulminite, corpohuminite and vitrodetrinite were 0.26%, 0.31 % and 0.22% respectively. No significant change in vitrinite reflectance with depth was noted. Inertodetrinite is a minor component in most samples and is most abundant in claystone samples. The reflectance of inertodetrinite was measured where it was observed during the normal traverse for measuring vitrodetrinite reflectance. Reflectance values range from 0.38 to 2.44%. Samples from five drill holes contain vitrodetrinite with a pink body colour as well as grey vitrodetrinite; both types of vitrodetrinite are generally free of internal reflections. Reflectance values for the pink vitrodetrinite (Table 2) are variable but are generally within the range for grey vitrodetrinite. The colour difference is

TABLE 1 Reflectance Data, Upper Oil Shale Unit, Duaringa Reflectance {% ) Average of ROmax values

Range of R0 max values

Number of Samples

vitrodetrini te vi trodetrini te ulminite vi trodetrini te vi trodetrini te vi trodetrini te vi trodetrini te vi trodetrini te corpohuminite ulminite corpoh umini te vitrodetrini te vi trodetrini te ulminite corpoh umini te ulminite corpoh umini te ulminite corpoh umini te

0.19 0.20 0.27 0.23 0.22 0.24 0.25 0.24 0.32 0.24 0.22 0.27 0.16 0.30 0.3 1 0.23 0.32 0.27 0.36

0.16-0.22 0.16-0 .23

11 17 1 22

vi trodetrini te ulminite corpohuminite

0.22% 0.26% 0.31%

Hole

Maceral

DD-1 DD-5 DD-8 DD-9 DD-10 DD-15 DD-19 DD-28 DD-31 DD-37 DD-52 DD-59 Mean values

0.13-0.32 0.21-0.25 0.17-0.31 o._20-0.30 0.16-0 .35

0.13-0.19

9 5

11 1 1 1 1 2

1 1 1 1 1 1

TABLE 2 Comparison of Reflectance Data for Pink and Grey Vitrinite, Upper Oil Shale Unit, Duaringa Deposit

DD-1

Drill Hole DD-5

DD-8

DD-10

DD-19

0.29

0.21

0.22

0.24

0.30

0.26-0.30 2

0.14-0.40 7

0.06-0.48 5

0.17-0.32 2

0.22-0.33 4

0.19

0.20

0.23

0.24

0.16-0.22 11

0.16-0.23 17

0.13-0.32 22

0.17-0.31 9

0.16-0.35 11

Reflectance (%)

Pink Vitrinite Mean of R0 max values Range of R0 max values Number of samples

Grey Vitrinite Mean of ROmax values Range of R0 max values Number of samples

unlikely to be due to contamination in block preparation or polishing because pink vitrodetrinite also occurs in samples from the Rundle deposit. It is possible that precursor type, localized variations in condtions during coalification or partial biochemical degradation may be the cause of the colour difference.

DISCUSSION COMPARISON OF THE UPPER AND LOWER OIL SHALE UNITS Lithologically the Duaringa deposit comprises three distinct units - a stratigraphically younger unit with grey to olive grey ("Duaringa-type") lamosite, a middle claystone unit with negligible organic matter and a stratigraphically older unit with greyish-brown dark to brown ("Rundle-type") lamosite. The two lamositedominated units can be distinguished by different: 1. hand-specimen colours of the lamosite; 11. fluorescence colours of lamalginite; 111. relative proportions of humic matter;

1v. reflectance of vitrinite macerals; v. abundance of lamalginite and therefore probable grades of the lamosite; and vi. precursor algae. Lamosite of the lower oil shale unit contains a microflora that is similar to that found in lamosite from the Rundle-Stuart deposit and reflectance data for the lower oil shale unit of the Duaringa deposit is more closely related to reflectance data for the Rundle-Stuart deposit than to the data for the upper oil shale unit. Features common to the lower oil shale unit and the Rundle-Stuart deposit include: i. dominance of orange fluorescing lamalginite; 11. similar vitrodetrinite abundance; 111. presence of Cleistosphaeridium-type lamalgini te; iv. abundance of intensely fluorescing lamalgini te; v. occurrence of carbonaceous lamosite; v1. are composed of several lamosite seams interbedded with claystones; vii. presence of abundant cannel coals with layers of vitrite, clarite and clarite-related carbominerite.

The lower oil shale unit therefore seems to be an equivalent of the Rundle-Stuart oil shale sequence with minor differences between lamosite from the two localities probably related to local variations in conditions at the time of deposition. Although palynological data is not available at present, reflectance data and organic components indicate a similar age for the Rundle-Stuart deposit and lower oil unit of the Duaringa deposit. The upper oil shale unit at Duaringa probably represents a local, stratigraphical ly younger sequence with a different microfloral assemblage. Reflectance data for vitrinite in Condor lamosite and coal are much higher than the values obtained for Duaringa and RundleStuart deposit. The higher reflectance values for the Condor deposit may be related either to a more rapid rate of maturation than in the Rundle-Stuart and Duaringa deposits or to a significance difference in age. If the latter is responsible for the higher reflectance values, the Condor deposit (and by inference the Byfield deposit as well since it has similar organic constituents and reflectance values for vitrinite as the Condor deposit) is older than the Rundle-Stuart deposit. Tertiary oil shale of Queensland could therefore be of three distinct ages, that is, • pre-Late Eocene/late Oligocene (Condor and Byfield), Late ~ocene/Late Oligocene (Rundle-Stuart and lower oil shale unit of the Duaringa sequence) and post-Late Eocene/late Oligocene (upper oil shale unit of Duaringa). VERTICAL VARIATION IN ORGANIC

MATTER Vertical variation in the type and/or abundance of organic matter occurs on megascale variation, three scales macroscale variation and microscale variation. Megascale variations are manifested as variations in type of organic matter as illustrated by the differences in the type of lamosite and abundance of coaly matter in the lower oil shale unit compared to the central claystone and upper oil shale units. Although several coal layers are interbedded with lamosite in the lower oil shale unit, a thick coal-dominant unit, as occurs in other Tertiary oil shale deposits, does not occur in the Duaringa deposit. Thus no ma-

jor change in the environment of deposition, from lacustrine to coal-swamp, as occured in the Rundle-Stuart, Condor and Byfield deposits, occurred during the accumulation of the Duaringa sequence. Macroscale variations in the type and abundance of organic matter are perceptible as changes from lamosite to claystone or high grade to low grade lamosite on a scale from several centimetres to greater than one metre. These changes are readily apparent in the lower oil shale unit but less so in the upper oil shale unit where lamosite is generally more massive. Boundaries between units B or D (the main oil shale units) and other units are gradational; for example, at the base of unit D in DD-8, claystone grades upwards into low grade lamosite which in turn grades into higher grade lamosite. Mean alginite abundance for closelyspaced spot samples (selected from 2m intervals for which modified Fischer assays were known) is not always a good indicator of the shale oil yield. In DD-8 a sample with 40 %vol. lamalginite was taken from an interval with > 30 LTOM whereas a sample with < 5 %vol. lamalgi.nite was taken from an interval which assayed at 90+ LTOM. The percentage of alginite is variable over small intervals (Figures 5 and 6). Microscale changes are manifested as changes in the abundance of components rather than changes in the type of components. For example, several lamosite samples have thin < 0.05mm) claystone laminae in lamosites (upper and lower oil shale units) and many lamosite samples from the lower unit have laminae ( < 1mm thick) of coal and/or carbonaceous lamosite. In most cases, the boundaries between lithotypes are gradational. An understanding of vertical changes in the type and abundance of organic matter is important in most stages of exploration and mining. A high proporation of cannel coal or carbonaceous lamosite in Rundle-type oil shale will give high carbon values, in both the raw and spent shale, as well as high Fischer assays. Vitrinite in lamosite will also increase the carbon content of the spent shale. Where spot samples are taken for analysis, macroscale variations in the type and abundance of organic matter could be a

factor leading to the collection of nonrepresentative samples. For example the sample from DD-47, with >20 %vol. telalginite, would give a much higher Fischer assay than a sample with the commonly-occurring {approximately 2 %vol.) amount of telalginite. Such differences in the type of organic matter are easily detected by petrographic analysis. Thus organic petrography should be an important facet of most stages in the exploitation of oil shale. The lower oil shale unit of the Duaringa deposit, which occurs 500 to 600m below the upper oil shale unit, was not discovered until the stratigraphic hole GSQ Duaringa l-2R was drilled by the Geological Survey of Queensland. Because it occurs at such depth, the lower oil shale unit is unlikely to have been discovered during routine exploration drilling for oil shale because most Tertiary oil shales are near-surface deposits and deep holes, such as the stratigraphic hole, are normally not part of exploration programmes. Its discovery shows that conditions that produce oil shale may re-occur, within a basin, after a relatively long period during which a thick elastic intervals was deposited. All Tertiary oil shale-bearing basins should have at least one deep stratigraphic hole to determine the nature of the complete section and especially to see if deeper oil shale intervals occur. Although the lower oil shale unit is unlikely to be an economic unit, it has significant resources; (samples assayed from GSQ Duaringa 1-2R by the Geological Survey of Queensland gave an average oil yield of 80 LTOM (40 LTOM cutoff) over intervals totalling 35m (minimum mining thickness of 2m) with another 17m giving oil yeilds > 30 LTOM). Alginite content is a reliable predictor of shale oil yield for Duaringa lamosite (Figure 8). The goodness of fit for the line of best fit for the first order linear regression equation where percentage alginite, in twenty four splits from samples sent for modified Fischer assay, plotted against Fischer assay (litres per tonne at 0 % moisture) is 0.892. The correlation coefficient is 0.945. All samples contained lamalgini te with minor Botryococcus telalginite and humodetrinite. Alginite content ranged from 2 %vol. (corresponding to an assay of 1 LTOM) to 28 %vol. (133 LTOM).

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ENVIRONMENT OF DEPOSITION

It has previously been inferred that Australian Tertiary lamosites were deposited as lacustrine sediments (Beasley, 1945; Hutton, 1978; Green & Bateman, 1981; Henstridge & Missen, 1981). Such inferences were made although the algal precursors had not been identified. Although any interpretation of the environment of deposition of an oil shale is dependent on a sound knowledge of the mineralogy, sedimentary structures and fossils (both macro- and micro-fossils) present in the oil shale, identification of the microfloral components permits some generalizations to be made. Six freshwater planktonic algae have been identified to genus lev~l (three to the genus Pediastrum and one each to the colonial green alga Botryococcus, to the dinoflagellate Septodinium and to the

acritarchs Cleistosphaeridium and Leiofusa) and the presence of several other algae have been demonstrated. Thus Australian lamosites are probably derived mostly from planktonic algae. In contast, the Green River lamosite from the United States of America is possibly derived from filamentous cyanobacteria much of which has undergone biodegradation by bacteria and fungi . Thus to transpose the environment of deposition for the Green River deposit to Australian Tertiary oil shales is misleading. Pediastrum is the dominant alga in Duaringa lamosite. At least three types have been recognised and all are well-preserved - generally better preserved than algae in the Rundle-Stuart deposit. Pediastrum is a blooming colonial green alga that, under laboratory conditions, swarms during the day. It has been identified in Tertiary sediments in India (Mathur, 1963; 1964 ; Kar, 1968; Salujha & others, 1969; Singh & others, 1973, and Singh & Khanna, 1978), Australia (Cookson, 1953), Indonesia (Wilson & Hoffmeister, 1958) and Japan (Matsuoka & Hare, 1977). Two of the Indian and the Australian occurrences were associated with Botryococcus; the sediments were believed to be of freshwater lacustrine origin. Pediastrum, together with Botryococcus, was found in Cainozoic sediments of Lake George, New South Wales (Singh & others, 1981). The occurrence of Pediastrum, which has a salinity tolerance of 1.7 g/1 , was believed to be an indicator of water depths of at least 7m for "reasonably long periods". Botryococcus was thought to indicate open water. A water depth of at least 7m is therefore not unreasonable for the ancestral Lake Duaringa. Duaringa lamosite contains at least three, and possibly more, species of Pediastrum. Thus water conditions were probably favourable, and possibly optimum, for divergent evolution of the Pediastrum genus. Previous to the present erosional cycle, the Duaringa deposit was much larger than the Condor or Rungle-Stuart deposit. Thus the Tertiary lake covered a much larger area and this may have been conducive . to the divergent evolution of the Pediastrum genus. However, although conditions were optimum for the growth of Pediastrum, larger inputs of elastic sedi-

ment produced relatively low grade lamosites. Five stages of sedimentation can be recognised in the Duaringa deposit. (a) Rundle-type conditions with cyclic sedimentation of lamosi te, carbonaceous lamosite and claystone existed when the lower lamosite unit of GSQ Duaringa l-2A was deposited. The lake was shallow (possibly less than 10m) and was subjected to periodic flooding. During flood times, abundant sediment was deposited by streams which drained the undulating hills that flanked the lake. The nutrient supply increased markedly and planktonic algae flourished. Sporadic dry periods resulted in marginal areas drying up; it is considered unlikely, however, that the entire lake dried up. Marginal zones would have been characterized by low lying areas with algal-inhabited shallow pools. Carbonaceous layers of the lower oil shale unit probably represent both allochthonous plant matter brought into the lake by floods (represented by thin .coaly layers interbedded with lamosite) with the thicker coaiy layers representing limited encroachment of marginal swamps along waterways. Periods of flooding were probably infrequent. Partial degradation of plant matter would increase the nutrient supply and promote algal growth. Interbedded coal-carbonaceous shale and lamosite probably indicate fluctuating conditions. Anoxic conditions below or just above the sediment-water interface, associated wfth the rapid accumulation of algal matter, probably promoted the accumulation and preservation of algal matter. (b) During the second stage, abundant clay-sized elastic detritus entered the lake. This stage is now represented by the thick sequence of claystone of interval A. Conditions were unsuitable for the vigorous growth of algae when this unit was deposited. (c) During the third stage the lower lamosite seam of the upper unit (Interval B) was deposited. Water depths and

salinity parameters were probably similar to those occurring when the lower oil shale unit was deposited. Algal bodies would have sunk to the bottom of the lake and mixed with incoming fine-grained mineral matter. Rapid burial inhibited bacterial degradation and much of the algal matter was preserved with only little alteration. Pyrite is much less abundant in the Duaringa deposit than elsewhere but reducing conditions probably still prevailed. Very little humic matter entered the basin at this time. Minor incursions of elastic sedimentation are indicated by elaystone layers. (d) Algae were unable to survive during the fourth stage and the elaystone of interval C were formed. The rapid input of elastic sediment and consequently muddy waters, possibly inhibited algal growth. (e) The fifth stage is now represented by the upper lamosite seam (interval D); prevailing conditions when the interval was formed would have been similar to those during the third stage.

SUMMARY Duaringa oil shale depo~it is part of the Tertiary Duaringa Basin succession and comprises two oil shale units, separated by a thick (500 to 600m) sequence of elaystone with only sparse to rare organic matter, which contain different lithologies and different organic assemblages within these lithologies. The lower oil shale unit contains interbedded lamosite (characterised by orange fluorescing lamalginite), brown coal, carbonaceous shale and elaystone. R 0 max values for ulminite range from 0.12 to 0.42% for vitrodetrinite, 0.24 to 0.47% for ulminite and 0.40 to 0.45% for corpohuminite. The petrographic properties of the lamosite and the range of vitrinite reflectance values are similar to corresponding properties of lamosite from the Rundle deposit. The upper oil shale unit contains yellow

to green fluorescing lamalginite. Coaly intervals are rare in the upper unit. Vitrinite reflectance values range from 0.16 to 0.27% for vitrodetrinite, 0.23 to 0.30% for ulminite and 0.22 to 0.36% for corpohuminite. For the upper oil shale unit the percentage of alginite in the parent rock is directly proportional to the Fischer assay (LTOM). Thus alginite content is a good predictor of shale oil yield for the upper oil shale unit. Lamalginite in both units is derived, dominantly, from the freshwater , colonial alga Pediastrum and other planktonic algae. The freshwater dinoflagellate Septodinium is a precursor for a small proportion of the lamalginite in the upper oil shale unit whereas Cleistosphaeridium is a precursor for a small proportion of the lamalginite in the lower oil shale unit. Petrographic data suggest that the lower oil shale unit has significant resources of shale oil but it is unlikely to be exploited because of the depth at which it occurs. The older oil shale unit was not discovered until the stratigraphic hole, GSQ Duaringa 1-2R was drilled. The discovery of the lower oil shale unit, at depth, is significant in that it illustrates that two alginite-bearing oil shales, with different petrographic properties, can form iri the one basin given suitable conditions. It draws to the attention of those carrying out exploration for Tertiary oil shale that at least one stratigraphic hole should be drilled through the complete Tertiary sequence in order to fully ascertain the nature of the succession.

ACKNOWLEDGEMENTS Southern Pacific Petroleum NL, Central Pacific Minerals NL and the Geological Survey of Queensland supplied samples and unpublished data. The author acknowledges their co-operation with gratitude. Petrographical analyses of the samples were carried out as part of a Commonwealth Postgraduate Research Scholarship at the University of Wollongong.

REFERENCES Central Pacific Minerals NL, 1984 Annual Report 1983. Cookson. I.C., 1953: Records of the occurrence of Botryococcus braunii, Pediastrum and the Hystrichasphaerideae in Cainozoic deposits of Australia. Memoirs of the Natural Museum, Melbourne 18, 107-123. Foster, C.B. , 1980: Report on Tertiary spores and pollen from core samples from the Hillsborough and Duaringa Basins. Geological urvey of Queensland Record , 1980/2 (unpub.). Green. P.W., Dixon, D.A., and Pope, G.J ., 1979: Duaringa Basin drilling programme 1978-1979. Southern Pacific Petroleum Report, Q66 (unpublished). Hekel, H., 1972: Pollen and spore assemblages from Queensland Tertiary sediments. Geological Survey of Queensland Publication 355, Palaeontological Paper (30). Hutton, A.C., 1982: Organic Petrology of Oil Shales. PhD Thesis (University of Wollongong). International Committee for Coal Petrology, 1963: International Handbook of Coal Petrology, 2nd Edition, Centre National de la Recherche Scientifique, Paris. International Committee for Coal Petrology, 1971: International Handbook of Coal Petrology, 2nd Edition, Centre National de la Recherche Scientifique, Paris. International Committee for Coal Petrology, 1975: International Handbook of Coal Petrology, 2nd Supplement 2nd Edition, Centre National de la Recherche Scientifique, Paris. Kar, R.K ., 1968: A fossil resembling Pediastrum from the Barren Measures sequence of Jharia Coalfield. Bihar, India. Palaeobotanist 16, 216-218. Kirkegaard. A.G., Shaw, R.D., and Murray, C.G., 1970: Geology of the Rockhampton and Port Clinton 1:250 000 Sheet areas. Geological 'uruey of Queensland Report 38. Mathur, K., 1963: Occurrence of Pediastrum in Subathu Formation (Eocene) of Himachal Pradesh, India. Science and Culture 29, 250. Mathur. K., 1963: On the occurrence of Botryococcus in Subathu Beds of Himachal Pradesh, India, Science and Culture 30, 607-608.

Matsuoka, K. , and Hase, K., 1977: Fossil Pediastrum from the Pleistocene Hamamatsu Formation around Lake Hamana, Central Japan. Transactions and Proceedings of the Palaeontological Society of Japan 104, 432 441. McMinn, A., 1980: Palynology of the Tertiary Duaringa oil shale, Queensland. New South Wales Geological Survey Report, GS 1980/4, (unpublished). Salujha, S.K., Srivastava, N.C., and Rawat, M.S., 1969: Microfloral assemblage from Subathu sediments of simla Hills. Journal Palaeontological Society India 12, 25-40. Singh, G., Opdyke, N.D., and Bowler, J .M., 1981: Late Cainozoic stratigraphy, palaeomagnetic chronology and vegetational history from Lake George, N.S. W. Journal of the Geological Society of Australia 28, 435-452. Singh, H.P ., and Khanna, A.K., 1978: Some fossil species of Pediastrum in the Subathu Formation of Himachal Pradesh. Palaeobotanist 25, 466-474. Singh, H.P., Khanna, A.K .. and Sah. S.C.D.. 1973: Probl ems and prospects of Tertiary palynology in Northern India. Bulletin India Geologists Association 6, 71-77 . Southern Pacific Petroleum NL. 1984: Azµiual Report 1983. Stach, E., Mackowsky, M.-'fh., Teichmuller, M.. Taylor, G.H., Chandra, G., and Teichmuller. R. , 1975: Stach's Textbook of Coal Petrology. Gebruder Borntraeger, Berlin. Stach, E., Mackowsky, M.-Th., Teichmuller, M .. Taylor, G.H., Chandra, G. , and Teichmuller. R. , 1982: Stach's Textbook of Coal Petrology. Gebruder, Berlin, 3rd Edition. Wilson, L.R., and Hoffmeister, W.S., 1953: Four new species of fossil Pediastrum. American Journal of Science 251, 753-760.

A. C. HUTION Department of Geology, University of Wollongong, P.O. Box 1144, Wollongong, NSW 2500, Australia

COMPARISON BETWEEN THE FINGAL AND LANG LOH COALFIELDS, TASMANIA BASIN By K. C. Morrison & C. A. Bacon

ABSTRACT

All of Tasmania's proven and probable reserves of black coal, and all current production is from seams of Triassic age. The coal occurs as a minor component in an interbedded sequence of lithic sandstone, mudstone, silt~tone, conglomerate, claystone and rare tuff. This sequence comprises the upper sequence of the Upper Parmeener Super-Group. The Parmeener Super-Group is the lithostratigraphic unit which constitutes the complete stratigraphy of the Tasmania Basin. Some aspects of the stratigraphy, sedimentology , coal petrology and palaeobotany of the coal measures in the Fingal and Langloh areas are analysed and compared. The results suggest that in both areas coal formation occurred as part of a Karnian age fluvial system which best fits the meandering stream/point bar model. Climatic conditions at the time are considered to have been generally humid, with pronounced seasonality, and free of significant ice, despite the high latitude. The two areas are suggested as typical and representative of the Upper Triassic coal measures across the basin. INTRODUCTION

A small black coal industry exists in Tasmania, producing some 300,000 tonnes per year of sub-bituminous steaming coal from two underground mines in the northeast of the State. All current production is used by domestic industry as boiler fuel and for cement making. In recent years, the replacement of oilfired industrial boilers with boilers using cheaper fuels, and the expectation that a coal-fired power station with be constructed within the next decade, have encouraged a marked increase in exploration activity within the State.

One outcome of this activity is that the combined efforts of the State Department of Mines and industry are generating sufficient data for the development of a basin analysis approach towards understanding the coal geology of the State. This will be of great use in predicting ultimate recoverable reserves. This paper compares the general geology of two areas of current exploration, on opposite sides of the Tasmania Basin, shown in Figure 1. The areas are: (1) Fingal Tier, in the northeast including the two operating collieries, Duncan and Blackwood, and the recently proven Mt Nicholas deposit. (2) Langloh, in the southwest where exploration has been in progress for the past three years and a small deposit has been defined.

COAL IN THE TASMANIA BASIN

The term Tasmania Basin refers to the structural basin containing the body of Late Carboniferous to Late Triassic sedimentary rocks known as the Parmeener SuperGroup (Banks, 1973; Forsyth & others, 1974). The Parmeener • Super-Group is typically about 1 km thick. The dominant rock type within the basin area is Jurassic dolerite which has impregnated the basin sediments with extensive networks of stocks, dykes, sheets and sills. Extensive faulting and graben structures are genetically related to the dolerite intrusions. Both the faulting and the thermal output of the dolerite have had a detrimental, although eratic, effect on coal quality within the basin. The Parmeener Super-Group is essentially composed of: (1) A lower sequence, Carboniferous and Permian in age, of marine lutites and

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(2) An upper sequence, mostly Triassic in age, of non-marine siliceous elastics. The upper part of this sequence is dominantly composed of lithic sandstone while the lower part is composed dominantly of quartz sandstone. This sequence is known as the Upper (Division of the) Parmeener Super-Group. The outcrop distribution of rock types in the Upper and Lower Divisions of the Parmeener Super-Group is shown in Figure 1. Coals and carbonaceous mudstones are associated with non-marine units throughout the Super-Group. Within the Lower Parmeener Super-Group one coalbearing sequence exists. This contains the Mersey Coal Measures and correlates of Early Permian (Late Sakmarian-Early Artinskian) age. Coals occur throughout the Upper Parmeener Super-Group, but the thickest seams and best quality coals occur in the lithic sandstone sequence, Late Triassic age, at the top of this Division, and to a lesser extent in the Cygnet Coal Measures (Late Permian age) at the base of the Upper Parmeener Supergroup. Widespread, small scale, coal mining has occurred since the early 1800's with over 50 mines having worked coal hosted in a variety of sandstones of both Permian and Triassic age. Many of the coals however were of poor quality with high ash and/or sulphur contents and many occurred in thin discontinuous seams. In Figure 1 the locations of all known coal seams of 1.5 metres or more in thickness, are plotted and they are all hosted in the lithic sandstone sequence which is clearly the minor rock type in terms of areal extent. Because of the degree to which faulting has produced repeated exposure of the Parmeener Super-Group section and the widespread sample points from over 100 years of mining and prospecting, the correlation of thickest coals with lithic sandstone host rocks reflects a real and exclusive association. The corollary of this observation is that it is likely that seams thick enough to sustain viable mining in the foreseeable future will

GEOLOGY OF THE FINGAL AREA The solid geology of the Final Tier area and the Mt Nicholas-Fingal coal fields is shown in Figure 2. The oldest rocks in the area are folded quartzwackes of the Silurian Mathinna Beds, which have been intruded by granites and adamellites of Devonian age. · These rocks form the basement upon which the near flat-lying Parmeener Super-Group sediments were unconformably deposited. On Fingal Tier the sandstone unit immediately overlying the Lower Parmeener Super-Group sediments is a fine to coarse grained quartzose sandstone, ranging in thickness from 0-50m. This sandstone is present over part of the Mt Nicholas area. The quartzose sandstone grades up into a dominantly lithic sandstone sequence with minor interbedded mudstone, siltstone, claystone, carbonaceous mudstone, coal, rare conglomerates and rare tuff. The coalbearing sequence reaches a maximum thickness of about 400m. There are eight major coal seams on Fingal Tier, shown diagrammatically in Figure 3. These have been labelled seams A-H by the Department of Mines. Some, notably the A and B seams, are better described as carbonaceous intervals, as they consist of plies of coal less than 0.5 metres thick, interbedded with carbonaceous mudstone and claystone over intervals of 5-l0m. All the coals are sub-bituminous and medium rank with a high inherent ash and low sulphur content. They have only a small ( < 10%) component of bright coal. The Duncan seam is Seam F in this sequence while the East Fingal seam is Seam G. No other seams are named on Fingal Tier. Jurassic dolerite has intruded the Parmeener Super-Group sediments and now caps most of the higher country in the area. The lithic sandstone itself, which comprises the bulk of the sedimentary pile, is well to moderately well sorted and compositionally immature, consisting predominantly of medium subangular grains of metamorphic quartz, plus minor feldspars,

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volcanic rock fragments, metamorphic rock fragments, opaques and disseminated organic debris. White matrix clays typically comprise 10-20% of the sandstone. In outcrop the lithic sandstone occurs as sets of trough cross-bedding with rare thin basal conglomerate lag deposits. Accumulations of fine coaly debris often define bedding surfaces and pieces of silicified wood, some several metres long, are found both as lone fragments and in conjunction with conglomerates. Fining-up cycles occur both within the sandstone units and between units of differing lithologies. Absolute ages concerning the coalfields are given by a basalt at the base of the section and a tuff, near the top of the section, shown in Figure 3. On the Nicholas Range, a Triassic basalt which overlies the Lower Parmeener Super-Group sediments north of St Marys has been dated as 233 ± 5 my (Calver and Castleden, 1981). An air fall tuff outcropping in the Denison Rivulet, southeast of St Marys, has been dated using the K-Ar content of biotite contained in the tuff, at 214±1 my (Bacon & Green, 1984}. Several other outcrops of tuff have been found in the Fingal Tier region. A microfloral assemblage found in siltstone stratigraphically below the tuff (Forsyth, 1980) belongs to the Craterisporites rotundus Zone de Jersey 1975 and is therefore probably of Karnian age. This concurs with the age derived from the tuff.

GEOLOGY OF THE LANGLOH AREA The Langloh prospect, shown in Figure 4, is a small wedge-shaped fault block of coal bearing Upper Triassic lithic sandstone located some 80km northwest of Hobart. The fault block is bounded on the western side by a Tertiary graben and on the eastern and southern sides by Jurassic dolerite. Drilling indicates that the dolerite forms a floor to the sandstone and this floor dips at about 4 ° to the west. To the north, the Triassic is overlain by a sheet of Tertiary basalt and the extent of the Triassic in the subsurface is unknown. A basalt neck on the western edge of the prospect is related to a system of faults, the largest of which

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SAND, CLAY, FERRICRETE FAULT

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Figure 4: Geology of the Langloh area.

defines the eastern edge of the Tertiary graben. In the southeast of the area Triassic quartz sandstone outcrops and drilling confirms that this unit underlies the lithic sandstone. A series of three coal seams has been •located by drilling, and a -small deposit of moderate ash, low sulphur, sub-bituminous steaming coal, suitable for open-cut mining,

has been proven. The graphic log through , the coal-bearing section (Figure 5) shows that the seams are each 1-1.5 metres thick and normally- have abrupt non-erosional roof and floor contacts. In some cases the roof contact on the top seam shows minor erosion with a mud pebble conglomerate filling shallow scours into the underlying coal. The coals are separated from each

other by grey silty mudstone units, the upper mudstone being typically 20 cm thick and the lower, 1-1.5 metres. Both the coal and the mudstone interburden thicken from the east to the west. The mudstone shows abundant ripple lamination and soft sediment deformation structures and is often interlaminated with siltstones. In places it is rich in coaly material. The lithic sandstone ranges from very fine to coarse grained but usually cross-bedding about 0.5 to 1.0 metres in thickness. Fragments of silicified wood are used as a mapping aid where their presence as surficial lag indicates lithic sandstone subcrop. Scour and full structures are common within the sandstone and in some cases the scoured depression is filled with mudstone plug or mud pebble conglomerate. The finer grained sandstones exhibit flaser and small scale cross bedding, and are commonly rich in coaly debris: Preliminary investigation shows that the microfloras from the mudstone interburden of the Langloh coalfield is similar to that of the Craterisporites rotundus Zone de Jersey 1975 (S.M. Forsyth, personal communication. The microflora indicates that the deposit may be correlated with part of the main (economic) coal bearing interval at Fingal, and, in the absence of any radiometrically dateable rocks, is taken to be Karnian or early Late Triassic in age. Megaspore studies support the correlation with Fingal _(Dettman, 1961). The range of lithologies, their bedding structures, grain size, fabric and composition, as observed in outcrop and drill core, is essentially identical to those in the Fingal region. To date no tuffs have been recognised at Langloh.

STRATIGRAPHY AND DEPOSITIONAL ENVIRONMENT The sedimentary sequences encountered in drill holes at both Fingal and Langloh have been analysed using the Markov chain method (Miall, 1973). There has been some criticism of significance tests on Markov chains produced from transition matrices which have non-independent major diagonals composed

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Figure 5: Stratigraphic column, Langloh.

PROCESSES

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CHANNEL , POINT BAR LAKE , POND

COAL

0-05

TIER

0 -33

SANDSTONE

CHANNEL , POINT BAR

( n = 2948 trans iti ons ) Figure 6: Markov chain analysis interpretation, Fingal Tier.

PROCESSES

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LANGLOH

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Figure 7· Markov chain analysis interpretation, Langloh.

BAR

0-17

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POINT

LAKE , POND.

COAL •

CHANNEL ,

PEAT SWAMP WITH INTERMITTENT FLUVIAL INFLUX

of zeros (Carr, 1982; Powers & Easterling, 1982). However, when compared with an alternative method using log linear models on the same data (Carr, 1982), the major upward transitions are revealed by either method. Providing the results are used in combination with other observations and the user accepts some random lithotransitions within the set, Markov chains should show the most significant stratigraphic couplets and thereby infer something about the sedimentary processes which produce the observed section. Figures 6 and 7 show tree diagrams composed of the positive values from the different matrices and schematic vertical sections with environmental interpretations of the various lithologies encountered. At Fingal the major upward transitions are : claystone to coal, sandstone to mudstone and siltstone to sandstone. Although major conglomerates were encountered at the base of, or within sand units, there were insufficient to qualify for scoring in the transitions matrix. The prominence of sandstone up to mudstone and siltstone back to sandstone transitions suggests that fully developed fining-up sequences are much less frequent than partly developed sequences which are covered by an intervening pulse of sand. In the case of frequent sandstone to mudstone transitions the intervening siltstone facies is missing, however there is usually a fining-up trend within the sandstone immediately underlying the mudstone. Coal is always associated with mudstone and thin underlying clay bands. A generalised description of the section is a sequence of medium to coarse sandstone containing several coal-mudstoneclay intervals. Within the host sandstone, there are some siltstone/mudstone intervals rich in carbonaceous debris and fining-up sections form the floor rocks to most of the coal seams. The dominance of sandstone in terms of total thickness is shown by the sandstone to lutites plus coal ratio of approximately 3.5:1. At Langloh the drilling has to a large degree repeatedly sampled the same section. Thin, laterally discontinuous conglomerates are common and always occur within a sandstone, which forms the matrix

Figure 8: Fining up int.erval of fine sand to silt, Fingal Tier. Soft sediment deformation features preserved in the siltstone. Laminae 1-l0mm wide.

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to these conglomerates, or immediately above the top coal seam. The association of mudstone with coal is very strong and the section shows a clearer fining-up trend comprising sandstone, siltstone, mudstone and coal, than was revealed by the Fingal data. The ratio of sandstone to lutites plus coal in the thickest section drilled is approximately 3.9:1. The same range of lithofacies is recognised in both areas and the stratigraphic relationships of the lithofacies is the same in both areas. Examples of the main rock type associations are shown in Figures 8 to 12. The lithic sandstone sequence has traditionally been assigned a fluviatile origib (Hale, 1962; Kind, 1979; Bacon, 1979); and the combination of stratigraphy, lithofacies and sedimentary structures recorded in the present work is consistent with this interpretation. Although no direct evidence for channel morphology has been obtained, the

rocks observed at both Fingal and Langloh are assigned to the meandering stream/point bar type of fluvial depositional environment on the available data. Observations which support this interpretation are: (1) There is consistent segregation of the sandstone and the silty mudstone plus coal intervals, suggesting thai. the sands were channel deposits, the lutites were overbank flood deposits and the peat . swamps existed in depressions on the flood plain. All of the non-tuff dirt bands observed in coal seams are grey silty mudstone identical to the thicker mudstone floor and interburden units, suggesting that the peat swamps were at times covered by sediment-laden flood water. Plane and ripple stratified siltstones occur in interbedded units with fine sandstones, or less commonly with silty mudstones. Overall siltstone is less abundant than mudstone and is

interpreted as a traditional (levee bank) facies deposited proximal to but outside the channels (Figure 8). (2) Frequent examples of channel sands which have clearly migrated laterally and eroded the top part of the main seam in the Duncan Mine have been observed by one of the authors (C.B.) and have been documented by Kind (1979). At the sand/coal contacts the coal locally dips steeply and is faulted and slickensided due to compaction of the peat at the time of sand deposition. (3) The medium to coarse grained sandstone which is by far the most frequent lithology, occurs as trough cross-bedded sets which are interpreted to have been deposited by migrating bars within the channel (Figure 9). Thin discontinuous sheets and linear stringers of pebbles are scattered through the sandstone units and these are interpreted as bed load channel deposits (Figure 10). The longitudinal bar sands and transverse, high angle, planar cross bedded sands typical of flood and waning flow deposits in braided streams are not present. (4) Analysis of the drill core stratigraphy shows a consistent fining-upward trend in a sand dominated section. The pattern is well demonstrated at Langloh where the coal-mudstone interval is underlain by either mudstone or siltstone, but always grades down to medium to coarse sandstone through approximately ten metres of floor rocks. The dominance of sandstone and the relative paucity of levee and flood plain deposits implies that for much of the life of this fluvial system the channels migrated through older sand deposits.

The sedimentation patterns implied by the Markov chain analyses can be explained in terms of the main elements and processes of a meandering fluvial system. Deposition at a fixed point begins with a channel deposit of sandstone (plus or minus conglomerates), which is part of a point bar or channel bar. As the meander moves away from this point a levee bank of interbedded fine sandstone, siltstone and mudstone is deposited. Levees are not well preserved in

Figure 10: Mud pebble conglomerate in coarse sandstone matrix, Langloh. Pebbles 1-5cm in diameter.

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Figure 12: Coal seam with mudstone bands and trough cross bedded roof sandstone, Douglas River, (near Fingal).

the areas studied, indicating that the streams were continuously changing their courses and reworking previously deposited sand. Miall (1977), points out that point bar cycles of _greater than 20 metres thickness are produced by stacking channel units without the intervention or overbank units. These thick sand units give no indication of the depth of the channels, as they represent several episodes of channel deposition. Therefore it is necessary to examine the section over drill hole scale rather than outcrop scale thickness to observe the true nature of the stratigraphic section. As a meander moves further away, the fixed point origin is then below a cut off meander or depression behind the levee. Muds accumulate in these depressions or oxbow lakes during periods of overbank flooding and peat swamps develop during the non-flood periods. Periodic influxes of muddy water cause lenses of mud and clay and dirt bands to be interstratified with the peat (Figure 11). As the meander returns, channel sands or conglomerates are deposited over the peat. To produce the sharp roof contacts observed (Figure 12) the environment of deposition must sink at a rate adequate to prevent erosion by the returning channel.

COAL PETROGRAPHY Macera! analyses of coals from both the Langloh and Fingal areas are shown in Figures 13 and 14. The coal from both areas is low in ex.inite and in inertinite, with semifusinite being the dominant inertinite maceral. This contrasts with the other Triassic inertinite-rich coals known in Australia which all have inertodetrinite as the dominant inertinite maceral (Smyth, 1981). A minor difference between the Langloh and Fingal coals occurs in the composition of the ex.i.a.ite macerals. The dominant ex.inite maceral is sporinite in Langloh coal, and cutinite in Fingal coal. The vitrinite content of both rarely exceeds 25% . Some parts of the Langloh coalfield have been affected by the intrusion of Jurassic dolerite and increase in rank over part of the coalfield has resulted. The reflectance

LANGLOH MACERAL

COMPOSITION VITRIN IT E

0 LANGLOH SEAM A D SEAM B 6 SEAM C 0 KEMPTON SEAM

INER TI NITC

EXINITE

Figure 13: Macera! analyses, Langloh.

of both ex.inite and vitrinite increases with rank, but the reflectance of ex.inite increases at a faster rate, and above a vitrinite reflectance of approximately 1.3% exinite macerals become indistinguishable from vitrinite. As the mean maximum vitrinite reflectance of the coal from part of

FINGAL MACERAL

COMPOSITION

V IT R I N ITE

M2 SEAM , MT NICHOLAS

SEAM , MT NICHOLAS

DUNCAN

BLUE

SEAM

E XI N I T E

I N E RTI N IT E

Figure 14: Macera! analyses, Fingal.

the Langloh coalfield reaches 3.6%, exinite macerals cannot be distinguished. Coals unaffected by dolerite in the Langloh coalfield have a mean maximum vitrinite reflectance of 0.57% which is similar to that of the Fingal Valley coals. The Duncan seam (Fingal) has a mean maximum vitrinite reflectance of 0.56%. As semifusinite is formed by partial decay or oxidation of woody plant material, and inertodetrinite can similarly be formed by the in situ oxidation of cellular tissues (Diessel 1982) the maceral composition of the coals indicates that the peat swamp dried out at times allowing the peat to oxidize. The fact that the peat was subaerially exposed for periods of time is further demonstrated by an exposure in the Duncan Colliery, where the impressions of tree roots can be seen immediately above the top of the coal seam, suggesting that trees grew on the peat surface. In both areas the coals have persistent inherent ash (non-dirt band) contents of around 15-25%, indicating a steady influx of elastics to the peat swamps. The gross maceral compositions of the seams examined so far show inadequate differences for this approach to be used as a method of seam correlation. Further work on a more detailed ply by ply basis may enable maceral composition to be used for seam correlation at some future stage. In a meandering stream regime, many coal swamps would exist contemporaneously over a wide lateral extent, but a separate ecological identities. Each seam would have a petrographic character reflecting local vegetation, groundwater and river flood conditions at the time of peat deposition. The observed seam characters at Fingal and Langloh are in accord with those expected in such environments.

PALAEOBOTANY l\facrofloral assemblages from the Late Triassic coal measures have been examined and documented by Townrow (1962). The flora of the coal measures is dominated by f ilicaleans (ferns), pteridosperms (seed ferns) and

ginkgoaleans (maiden hair trees). Cycad leaves and scouring rushes are also reasonably common. The filicalean family Osmundaceae is represented by the sterile leaves Cladophlebis, while the pteridosperm family Corystospermaceae, is represented by the leaves Dicroidium, Xylopteris and Hallophyllum. The and Ginkgoites ginkgoaleans Sphaenobaeria (Czekanowskia) are abundant in places but conifers are rare. The leaf Phoenicopsis elongata is probably ginkgoalean. Cycadophyte leaves such as Pterophyllum are reasonably common. The stems of scouring rushes (Equisetum spp.) are found throughout the Triassic. Petrified wood from the Fingal and Langloh areas has been collected and examined. The excellent state of preservation of several samples collected from the Langloh area enable a number of deductions to be made regarding the climate at the time of growth. The growth rings are widely spaced, up to 10 mm apart in one specimen (Figure 15). This indicates that there were excellent seasonal growth conditions prevailing during the life of the plant. A reconstruction of the vegetation of eastern Australia during Triassic times has been proposed by Retallack (1977). The floral associations in the Tasmanian Triassic coal measures would largely fit into the broadleaf forest (Dicroidietum odontopteroidum) community as defined by Retallack (1977). At one fossil locality in north-eastern Tasmania, the fossil flora contains various . species of Xylopteris and varieties of Dicroidium odontopteroides (Bacon, 1979). This association suggests a xerophytic woodland community. The xerophily of Xylopteris is suggested by the reduced leaf area, compared with leaves of the related genus Dicroidium. The wider, more irregular midrib of Xylopteris is probably due to the lignification of the leaves (Townrow, 1962 in Retallack, 1977). The flora of the coal measures is envisaged as consisting of xerophytic woodlands of Dicroidium odontopteroides and Xylopteris spp. growing on levee banks and flood plains while in wetter areas such as in • abandoned channels, and lower lying parts of the flood-plains a broadlead forest

Figure 15: Transverse section through silicified wood, from the Langloh area. Growth rings approximately 10mm wide.

association of ferns, seed ferns, maiden hair trees and cycads grew, with scouring rushes growing in the wetter areas. Partly coalified tree roots and silicified logs in roof rocks at the Duncan Colliery and in the Douglas River respectively suggest that trees were growing in and on top of the peat swamps. Preservation of the wood by coalification or silicification appears to have depended on reducing or oxidising conditions which would have prevailed in the peat swamps and the channel bars respectively. The plant fossils imply marked seasonality, with abundant free water, light and warmth, at least in the growing season, and an absence of climatic extremes likely to stunt growth or kill the plants.

PALAEOCLIMATE A relatively unifonp. global climate, free

of polar ice and with broad expanses of subtropical to warm temperate conditions for the Late Triassic is suggested by the wide range in latitude for some species of the pelecypod genus Monotis (Westermann, 1973) in Frakes (1979). Distribution of fossil flora in the Late Triassic supports this con• clusion. From a study of various species of • ferns, the Euramerican paleofloristic region between 55°N and 15°N is interpreted by Barnard (1973) in Frakes (1979) as representing a sub-tropical to warm temperate climate. Temperature conditions have been assessed by Knaut and Epstein (1976) in Frakes (1979), who used the oxygen and deuterium isotope compositions of cherts to estimate that air temperatures in the western and central regions of the USA ranged from 20°-34° during the Triassic and decreased after that. Triassic temperatures were at least 20°C warmer than at present in this region, at 15° latitude.

Tasmania was located within 20° of the South Pole throughout the Permo-Triassic (Embleton, 1973; Frakes, 1979). Although the Permian marine sediments of the Tasmania Basin were clearly deposited in • cold water conditions (Clarke & Farmer, 1976; Rao, 1981a, 1981b) there is evidence in the Triassic rocks of climatic change to warmer, more humid conditions. Banks & others (1978) describe vertebrate, invertebrate and plant fossils in fluviatile mud pebble conglomerates of Early Triassic age near Hobart. Bones from amphibians, fish and reptiles, together with abundant arthropods and rare plant fragments from rushes, mosses, conifers, maiden hair trees, ferns and seed ferns have been recovered from this site. Many of these fossils are contained in mudstone clasts. A reconstruction of the paleoenvironment describes a meandering str.eam system providing habitats for the plants and animals whose fossils are preserved at the site. During dry periods, ponds and clay pans formed and subsequent flooding of the area produced pebbles composed of rolled clay, some containing bone fragments from the surfaces of the clay pans. The presence of cold blooded animals and plants suited to humid conditions, plus evidence of a climatic regime involving periods of drought followed by periods of flooding, imply that glacial conditions had abated by the Early Triassic. Evidence from the Late Triassic rocks and fossils at Fingal and Langloh indicate that a humid climate without temperature extreme, prevailed. Clasts of reworked mudstone occur throughout the stratigraphic section in both areas, suggesting episodes of drying and flooding. The high inertinite composition of Tasmania Basin coals can be explained by frequent drying and partial oxidation of the peat deposits. There is no evidence of structures due to freeze/thaw processes in the Tasmania Basin coal measures. Collapse breccias, wedging and severe convolution and disruption of bedding compatible with periglacial conditions are common in some Permian coal measures in the Sydney Basin such as can be seen at the Aberdare North Colliery.

The evidence points towards the Late Triassic climate being more uniform and considerably warmer than the present climate.

CONCLUSION S All known black coal seams in the Tasmania Basin, 1.5 metres or greater in thickness, are hosted in the Late Triassic lithic sandstone sequence. All seams thick enough to sustain viable mining will probably be found in this sequence. The coal measures at Fingal and Langloh are part of a Karnian age meandering stream system. The sedimentary section is dominated by channel sandstones and interbedded coal/mudstone units represent overbank peat swamp deposits. Fingal and Langloh are probably representative of all Karnian age coal deposits in the basin. Climatic indicators from sedimentology, coal petrology and palaeobotany imply a generally humid climate with marked seasonality and alternating periods of drying and flooding. Growth patterns in fossil wood indicate an absence of climatic extremes and there is no evidence in the rocks or fossils, of freezing conditions despite Tasmania's high latitude in the Late Triassic.

ACKNOWLEDGEMENTS The authors would like to thank a number of people for their assistance in the compilation if this paper. Dr R. Hill, University of Tasmania, worked on the fossil wood and provided expertise, equipment and advice for sample preparation, photography and interpretation of results. Mr S. Forsyth, Tasmanian Mines Department, produced a palynological date from Langloh rocks and donated time and advice on various palaebotanical problems. Mrs J. Pongratz drafted the diagrams, Miss J. Mackey cut thin sections as required and Mrs V. M. Smith typed the manuscript. This paper was made possible by financial support from Capricorn Mining Limited, and is published with the permission of the Director of Mines and Capricorn Mining Limited.

REFERENCES Bacon, C.A., 1979: Regional Geology of the Apsley River Area, northeastern Tasmania (Part A) and sedimentology of the Late Triassic Coal Measures in northeastern Tasmania (Part B). Unpub. BSc. (Hons) Thesis, University of Tasmania. Bacon, C.A. & Everard, J .L. , 1981: Triassic Rhyolitic Ashfall Tuff near Bicheno, Tasmania. Search 12(6), 177-178. Bacon, C.A. & Green, D.C., 1984 : A radiometric age for a Triassic tuff from eastern Tasmania. Tas.Dept.Mines Unpub.Rep. 1984/29. Banks, M.R., 1973: General Geology In The Lake Country of Tasmania. Symp.Roy.Soc.Tas. 25-34 . Banks, M.R.; Cosgriff, J .W. & Kemp, N.R., 1978: A Triassic Stream Community. Aust.Nat.Hist. 19(5), 150-157. Barnard, P.D.W., 1973: Mesozoic floras In Hughes, N.F. (Ed). Organisms and Continents Through Time, Special Papers in Pa/,aeontology 12. Palaeontological Association , London, 175-188. Calver, C.R. & Castleden, R.H., 1981: Triassic basalts from Tasmania Search 12(1-2), 40-41. Carr, T.R., 1982: Log linear models, markov chains and cyclic sedimentation. J .Sed.Pet. 52(3), 905-912. Clarke, M.J. & Farmer, N. 1976: Biostratigraphic Nomenclature for Late Palaeozoic Rocks in Tasmania . Pap .Proc.Roy. Soc. Tasm. 110, , 91-109. Diessel, C.F.K. , 1982: An appraisal of coal facies based on maceral characteristics Aust. Coal Geology 4, 474-483 . Dettmann, M., 1961: Lower Mesozoic megaspores from Tasmania and South Australia . Micropaleont. 7(1), 71-86. Embleton, B.J . 1973: The Palaeolatitude of Australia through Phanerozoic Time. J .Geol.Soc.Aust. 19(4), 474-482. Forsyth, S.M. 1984 : Palynological report on a Triassic siltstone underlying pyroclastics, Denison Rivulet. In Bacon, C.A. and Green, D.C. A radiometric age for a Triassic tuff from eastern Tasmania . Tas.Dept . Mines Unpub.Rep. 1984/29. Forsyth, S.M. Farmer, N. Gulline, A.B. Banks, M.R. Williams, E. Clarke, M.J., 1974: Status and Subdivision of the Parmeener Super-Group. Pap.Proc. Roy.Soc. Tasm . 108, 107-110. Frakes, L.A., 1979: Climates Throughout Geologic Time. Elsevier Scientific Publishing Company Amsterdam. Hale, G.E.A., 1962: The Triassic System of Tasmania in Spry, A., and Banks, M.R. (Eds) The Geology of Tasmania. J .Geol.Soc.Aust. 9(2), 217-231. Kind, H.D., 1979: Sedimentation Pattern in the Triassic at Fingal Colliery, northeastern Tasmania. Abstract, Fourth Australian Geological Convention, Hobart. Knauth, L.P. & Epstein, S. 1976: Hydrogen and oxygen isotope ratios in nodular and bedded c herts . Geoc him Cosmochim Acta 40:1095-1108 in Frakes, L.A. 1979. Climates

Throughout Geologic Time, Elsevier Scientific Publishing Company, Amsterdam. Miall, A.O. 1973: The markov chain analysis applied to ancient alluvial plain succession. Sedimentology 20, 347-364. Miall, A.O., 1977: A review of the braided stream depositional environment. Earth Sci.Rev. 13, 1-62. Playford, G., 1965: Plant microfossils from Triassic sediments near Poatina , Tasmania. J .Geol.Soc.Aust. 12(2), 173-210. Playford, M., 1968: Palynological Report on some Triassic coal seams. Appendix 2 in Threader, V.M., 1968: Interim Report on the Geology and Coal Resources of the northeast coalfield of Tasmania. Unpub.Rep.Dept.Mines Tasm. Powers, D.W. & Eastering, R.G., 1982: Improved methodology for using markov chains to describe cyclic sediments J .Sed.Pet. 52(3), 913-923. Rao, C.P., 1981(a): Geochemical differences between tropical (Ordovician) and subpolar (Permian) carbonates, Tasmian, Australia. Geology 9, 205-209. Rao, C.P. , 1981(b): Criteria for recognition of coldwater carbonate sedimentation: Berriedale Limestone (Lower Permian), Tasmania, Australia. J .Sed.Pet. 51 , 491-506. Retallack, G.J., 1977: Reconstructing Triassic vegetation of eastern Australasia : A new approach to the biostratigraphy of Gondwanaland. Alcheringa 1, 247-278. Smyth, M., 1982: Coal encounters of the third kind: Triassic. Coal Geology 2(4), 161-178. Townrow, J .A. , 1962: Palaeontology of the Triassic. In SPRY, A. & Banks, M.R. (Eds). Geology of Tasmanian. J .Geol.Soc.Aust. 9(2), 224-226. Townrow, J .A., 1964: A speculation on the RhaetoTasmani a. of climate Liassi c Pap.Proc.R .Soc.Tasm. 98, 113-118. Westermann, G.E.G., 1973: The Late Triassic bivalve Monotis. In Hallam, A. (Ed.), Atlas of Palaeobiogeography, Elsevier Amsterdam 251-258.

K. C. MORRISON Petrecon Australia Pty Ltd 192 Macquarie Street Hobart 7000 Tasmania. C. A. BACON Department of Mines, Tasmania P.O. Box 56 Rosny Park, 7018 Tasmania.

ORIGIN AND DISTRIBUTION OF THE BAYSWATER SEAM AND CORRELATIVES IN THE PERMIAN SYDNEY AND GUNNEDAH BASINS, AUSTRALIA By

J . W. Hunt, A. T. Brakel, and M. Smyth ABSTRACT The Bayswater seam and its correlatives are petrographically unique in the marginal Permian Sydney and Gunnedah Basins of eastern Australia. They are characterised by low average vitrinite contents, in contrast to the underlying and overlying highvitrinite coals which constitute the main coal type found in the basins. Moreover, the inertinite in the Bayswater seam contains a high proportion of inertodetrinite, in comparison to other inertinite-rich coals which are confined to the regressive top of the Permian sequence. In this respect the Bayswater seam and correlatives closely resemble the inertinite-rich coals of the Australian Permian epicratonic basins, such as the Cooper and Oak.lands Basins. Palynological evidence, although sparse, indicates that the Bayswater seam and the high-vitrinite coals were formed from similar flora. The distribution of sulfur and mineral matter in the Bayswater seam and correlatives is similar to that in the underlying and overlying coals. The circumstantial evidence suggests that the coal type is the result of a unique process, acting on the same flora that gave rise to the other Permian coals. The Bayswater seam was formed following a widespread shallow marine transgression throughout the Sydney and Gunnedah Basins. The widespread and approximately synchronous appearance of inertinite-rich coals, suggests a regional influence on the accumulation of the peat. A tectonically related origin is supported by the wide distribution of coarse elastic deposits which overlie the marine strata and in places interfinger with the Bayswater seam and its correlatives. In this paper formation of the inertiniterich coals by relative withdrawal of the water table due to progressive elevation of the peat is conjectured. In this setting, substantial sub-aerial oxidation and degradation of the peat-forming material would have occurred before permanent

burial beneath the water table. Such a hypothesis is further supported by the observation that vitrinite-rich probable correlatives of the Bayswater seam are found where the underlying marine rocks are thickest. In these areas wetter conditions were preserved longer due to relative subsidence.

INTRODUCTION The Bayswater seam* and correlatives nea.r the base of the Late Permian coal measures (Figure 1) comprise coal that is petrographically unique in the Sydney and Gunnedah Basins (Figure 2). Throughout most of their geographic range these seams overlie a widespread shallow marine interval, which in its maximum development in the Sydney Basin is known as the Kulnura Marine Tongue (KMT). At the time when the Bayswater seam and correlatives were deposited, marine conditions prevailed in the Bowen Basin to the north (Brakel, 1985).

The Bayswater seam in the north of the Sydney Basin is correlated petrographically with the Woonona, Lithgow/Lidsdale and Ulan seams in the south and west, the Bowens Road seam in the Gloucester Basin (a Permian outlier to the northeast) and the Hoskissons seam in the Gunnedah Basin (Figure 2) (Hunt, 1981; Hunt & others, unpubl. data). The ·seams occupy similar stratigraphic positions in the basins and, CRATON WEST

OROGEN EAST

Figure I : Simplified s iratigrnphiC' s uccession in the Permi Hn hasins.

NEW ENGLAND FOLD BELT

LEGEND lsop1ch (ml of M1rr ■ ngaroo and corr1l1tiv11

Conglomer ■ U lsop ■ ch (m)

of Kulnur ■ Marine

Ton1u1 and corr1l11 ivu

32°

VITRINITE CONTENT OF

THE BAYSWATER SEAM & CORRELATIVES

•e

>&o¼ I0 - 40¾

<400/o

GLOUCESTER BASIN

Bowens Road seam

LACHLAN FOLD BELT

seams

N.T.

I ,

OLD.

~----L7 \

S . A.

SOO

L__J km

Fig-ure 2: Location of the Permian hasins. structural rl!'ments. isopachs of the Kulnura Marine Tongue ancl Mnrrang-nroo Conglomerate nncl correlnti\·es. (Aft!'r Herhert & others (in prep.) nncl Hamilton (in

100 km

150°

prep.)). Vitrinite con tent of the Rn~,swater seam ancl c-mTelat ives. ancl location of sample sites ancl petrographic cross sections are also sho\\"n .

within the limits of resolution of the 'Per mian palynological zones, are time equivalent. An exception may be the Ulan seam in the west which is argued to be a little younger than the others (McMinn, 1984), but this conclusion is based on the lowest occurrence of the spore Microreticulatisporites bitriangularis, which may not be as reliable an index fossil as previously thought (P. Price, personal communication). Throughout most of their geographic range the seams are recognised as dull coals of diverse thickness (0.5 to 20m), with varied mineral matter and sulfur contents. They are unusual in the Upper Permian successions because of their high average inertinite contents. However the coals are petrographically unique in the basins marginal to the Permian craton because of the high proportion of inertodetrinite in the inertinite (Figure 3). The widespread but temporally restricted distribution of this coal suggests that its formation was due to an unusual and shortlived control. The nature of the control is the focus of this paper. The prevailing conditions during accumulation of the peats can be reconstructed in terms of inferred tectonic and depositional setting, palaeoclimate and palaeoflora, and the petrography of the coals and their sulfur and mineral matter contents. Variation of maceral and microlithotype composition and sulfur content and composition in other seams in the basins has previously been discussed by Hunt (1982) and Hunt & Hobday (1984). *Because of the current state of flux in coal seam nomenclature, where the designations Coal, Coal Member, Seam or seam may be used, and the difficulty of definitively relating many of the samples discussed herein, we have chosen to refer to all coally intervals as "seams".

CHARAcrERISTICS AND VARIABIIJTY The Bayswater seam and equivalents have been correlated on the basis of their stratigraphic position and petrographic composition. In the east and south of the Sydney Basin the seams are absent from some areas (e.g. site Min Figure 2), and the

relationship of the seams in the northeast (site Lin Figure 2) to the Bayswater seam is uncertain. In the east the identification of seams as Bayswater correlatives is based solely on their stratigraphic position overlying the KMT. Physical continuity of the Bayswater seam and correlatives throughout the basins has not been investigated at a regional scale. However, local studies (Holmes, 1976; Hamilton, 1985) and mining suggest that they have a sheet-like geometry in the Gunnedah and northern and western Sydney Basins. In the Sydney Basin the coals may split towards the Permian depocentre in the northeast near Newcastle. PETROGRAPHIC COMPOSITION Variations in microlithotype compositions of the Bayswater seams were described by (Hunt, 1982). Spatial variation of the microlithotypes follows the pattern seen in the coal measures as a whole, with fineness of banding increasing from the orogenproximal to the craton-proximal parts of the basins. In the following section the petrographic composition of the seams is described using the parameters "vitrinite content" and "semifusinite ratio" (proportion of structured to unstructured inertini te = semifusinite + fusinite/total inertinite), both on a mineral-matter-free basis. Locations of sampling points are shown in Figure 2. The unique character of the Bayswater seam in comparison with other Late Permian coals is shown in sections from locations K, F and N in Figure 2 (Figures 4a, b and c). The succession covers three transgressive/regressive depositional cycles which are recognised throughout the basins. Low-vitrinite coals(< 40%) are confined principally to the top of the succession (Figure 4c) and the Bayswater seam (Figure 4b). Low semifusinite ratios are characteristic of the Bayswater seam and correlatives, and are rare in other coals (Figure 5). Spatial Variation. Coals of the Bayswater interval are unusual in the first instance because of their medium - to high - inertinite contents (Figur\:l 5), compared with other Late Permian coals. Spatial variation of the average vitrinite content for the Bayswater and correlatives is shown

• Figure '.3 (al l\lassed inertodetrinite (I}. t~·piral of the Ba,·swater seam. "·ith minor semifusinite (SF). _pi;rinite (, ). rntinite (C') and mineral matter ( 1). (b) Thin \'itrinite (\ ) band between len, es of semifusinite (SF) in the Bavswater seam. (cl Sem ifusinite (SF) and b;nd ma crinite ( 1a) in the Ba~•swater sea m.

(dl \ 'it rinite (V) groundma with inertodet rinite (I). sporinite (, ). micrinite (Mi) and quartz (Ql in the Ba~·swater seam. All photomicrographs have been t.aken in reflected plane polarised light under oil immersion. The longer side of the photomicrograph is approximately 0.2 mm.

in Figure 2. The main feature of the distribution is the dominance of low-vitrinite coals throughout the Gunnedah and the northern, western and southern Sydney Basin, with increasing vitrinite contents towards the central and northeastern Sydney Basin. Temporal Variation. Most of the seam sections analysed show a relatively highvitrinite, macroscopically-bright lower section and a low-vitrinite, macroscopicallydull upper section. Macroscopic data may be used to estimate vitrinite content (Diessel, 1965). However, caution is required where high contents of disseminated mineral matter are present because they also may give the coal a dull appearance. A composite profile of the Bayswater seam including data from Britten & Smyth (1973) shows a bright base, dull mid dle and bright top (Figure 6; location K in Figure 2), which is paralleled by a general decrease then increase in vitrinite content and the semifusinite ratio. The range of

vitrinite content in the middle section is probably a function of subsection thickness; as the sampled thickness decreases variation increases. The top of the Bayswater seam in DDHSl is 3m below the overlying vitrinite-rich Ravensworth seam. Macroscopic data from the Hoskissons seam in a section (Figure 7; location D-E in Figure 2) from the Gunnedah Basin suggest that the bright basal ply is characteristic of the thicker eastern part and is developed only locally elsewhere. In the east a bright top section is also present, similar to the Bayswater seam in DDHSl (Figure 6). Macroscopic profiles of the Lithgow and Woonona seams from the west and south of the Sydney Basin are shown in Figure 8 (locations A,B,C in Figure 2). The Lithgow seam in the west has a mainly dull profile. Vitrinite content is medium to low and the semifusinite ratio is consistently low. In the south and east the Woonona seam becomes brighter to the east. The average vitrinite content of the Woonona seam 1s

e % VITRINITE + EX INITE (mmf) @ Continued on F,gure 4b

1"E\'.-t~.::~o~gl~6t~~ ~~ · - '¾~o_V_IT~R_IN~I_T_E~+_E~X_IN_l~T-'E--'(~m_m~f') ~

ARCHERFIELO ~ SANDSTONE ~ BULGA FM

seam

U w

.., Walla,ah

:n N~;~a~,n

FOYBROOK EAST OOH 25 seam

u J:

Fass,re,n

W'----~~ z

Wallarah

Seve ral

Great Nonhe,n

uncorate d

~ ~~se~•'~,;~t ,

2top

:::Eo Upper ~O Arties c.,~ Lower

~ Australas,an 4

Z ►

Lower P1k)t

~ Hartley H,11

8~ Pikes Gully

1- 2

UJ :::E;

_,a;

Upper

100m

Liddell

Montrose Waveh,11

s &

Lower Fe,n Valley 7

Barrett

west 1 Borehole II - ta

Hebden+

M AITLAND GROUP-marine @ Calculated from microhthot ype analyses m00H 25 @ Calculated fOf other mine Of bore samples ,n the same area + From FOYBROOK BOWMANS CREEK OOH6 ~ Burrowing • Clean coal sample OTHE R

seam

Redbank Creek Wambo

f----!-:---'-:----'--f--c--L--+,,J--,---+-,-,J--,----1 ~ Burrowing

h 0 SEMIFUSINITE RATIO @

SEMIFUSINIT E + FUSINITE

highest, decreasing upwards a little, in Bootleg 2A where the semifusinite ratio is medium. The overlying coals in Bootleg 2A have high vitrinite contents and medium semifusinite ratios (Hunt, unpubl. data). However, in Bootleg 8 further west, the vitrinite content in the Woonona seam decreases upwards from high to low and the semifusinite ratio decreases from medium to low. In Camden 61 to the south (location B in Figure 2), vitrinite content and the semifusinite ratio are both low and decrease upwards in the W oonona seam. SULFUR AND MINERAL MA TIER

WQ.

::Em G len Munro

Ov,

H,11

~;;

Art hur

0 0

Moun t

<--'

:,:"<OV>

z> - a: >- a:

t::w

~ , P1ercef1eld

Vau,i

SEMIFUSINITf:. + FUSINITE

V>a:

w, "'"

o 1 60,d float sample OTHER • Raw coal sample I N ERTINITE

4(c}

0 SEMIFUSINI T E RAT IO

Figure 4: Temporal variation of vitrinite content a nd the sem ifusini te ratio in a) t hP lowpr rPgressivP LntP Permi an cycle. h) t he middle Late Pe rmian rPgressivP cycle a nd c) t he upper Late Per mian regressivP cycle - locations K. F a nd N in Fig ure 2.

_,:::,

20 0

C( en woodl ands

~5 Blakef1eld

" :E

Whybrow

80 60

,-.

• % VITRINITE +EXINITE (mmf) 10

INERTINIT E

SYDNEY BASIN BHP BROKE DDH 104

100m

Broome+ 0

Bayswater

Cont,n~•;::.::.::.~:,::

lluv,o-deltatc Conglomerate o 1·60rd float sample • Clean coal sample

+ =~o~e0A0R~~ MITCHEL LS. _ _ ~ ~ - ~.......~ OTHER INE RTI NITE

+-~--+-~--<

0 SEMIFUSINITE RATIO

4{b}

SE MIFUSINITE + FUSINIT E

Sulfur content, the forms of sulfur, and mineral matter content and composition in the Bayswater coals have similar distributions to those seen in the Late Permian coals in general (Hunt, 1985b,c), and will not be treated in great detail here. Mineral matter content and composition characterised in terms of ash content and composition (Hunt, 1985c) are variable in the

VITRINITE

EXINITE 100

..f

Upper part ol upper coal measures Lower part of upper coal measures

Bayswater seam and

cor relat1ve1 140 Number of composite sam ples

High

OTHER INERTINITE

Semifusinite Rat io

SEMIFUSINITE + FUSINITE

LEGEND Margina l basins - upper coal measures (Lale Perm ,an) GUNNEDAH

BOWEN

Oepositk>nal Environment

Fluvia l

Figure 5: Variations in time and space of maceral cornpo ition of Late Permian coals from the marginal basin .

Bayswater seam and correlatives at a regional scale and show the same range of variation as in the overlying and underlying vitrinite-rich coals. Sulfur content in the Permian coals is categorised as high ( > 1% dry ash free daf), medium (0.55 to 1% daf) or low ( < 0.55% daf) and the sulfur is mainly organically bound. The sulfur is usually evenly distributed in the coals, although several samples of the Bayswater and Woonona seams have high sulfur contents probably due to pyrite present in the top of the coal (Hunt, unpubl. data). Sulfur content in the Bayswater seam and correlatives is low to medium in proximity to the orogeri (New England Fold Belt in Figure 2) in the northeast, increasing towards the western shelf where the Lithgow and Lidsdale seams contain around 0.80%, a little higher than most other ·medium sulfur seams in the basin.

CONTROLS OF COAL TYPE Coal type is determined in the first of

biochemical stage of coalification during deposition and early diagenesis. It is a function of the peat-forming flora, depositional setting, climate and edaphic conditions in the mire. The factor that immediately determines the degree of decomposition of organic material in a mire is access to oxygen and even low levels of dissolved oxygen in water ( > 8%) are capable of maintaining oxidising conditions (Moore & Bellamy, 1974). The oxygen supply determines whether peat formation will occur at all, the potential for preservation increasing with decreasing oxygen supply. The optimum condition for the accumulation of organic matter is rapid descent into the reducing zone of the mire (Moore & Ballamy, 1974) where the processes of microbial oxidative decomposition are greatly reduced and with increasing depth of burial are totally arrested (Flaig, 1968). Thus, depending on the Eh and pH of the mire waters, the position of the water table relative to the peat surface during deposition and in early diagenesis is considered to e o/oVITRINITE +EXINITE ( mmt J SYDNEY BASIN WITTINGHAM COAL MEASURES

LIDDELL SHAFT

LEGEND

:tmb 08

•• 8

-~=-

OTHER INERTINITE

0 SEMIFUSINITE RATIOSEMIFUSINITE -+ FUSINITE

Figure 6: Temporal viariation of vitrinite content and the semifusinite ratio in the Bayswater Coal - location K in Figure 2.

BRIGALO 1 BORAH 1 BRIGALO 2 TUNMALALEE 1

BANDO 1

TRINKEY 1 c'ooLANBILLA 1/2

West

CAROONA4 DOONA1 GUNNEDAH16 GUNNEDAH16 I I

V+E

East

·o . •

·o .•

• . ·O.•

B_F· •. ·o. m.

LOP MACROSCOPIC COAL FACIES

IIIIII D. 0Mb

PETROGRAPIC COMPOSITION

Db. OB. Bd , B

UDP = UPPER DELTA PLAIN D = D•II . < !'lo briiht Dmb s D•II rwiur briih1, 1- 100/o LOP = LOWER DELTA PLAIN SHALLOW MARINE D•II nd hi1ht , 10 - 401/o SM Db MS = MARINE SHELF DB = lot1rb1ndod, 40-&0l/e 8d = Bri1ht nd dull, 60 - 901/o B = Bri9ht ,> 90% bri1ht

j3 16J

Y+E } 11 io Fi9. 4 SFR

Figure 7: Spatial and tempora l variation in elastic facies (after Hamilton in prep.) and petrographic composition of the Hoskissons seam in the Gunnedah

Basin (after CSIRO. 1977). Section DE and location H in Figu~e 2; labelling of petrographic composition diagram as for Figure 4.

be a criticial factor in the determination of coal type. The water table level in a mire fluctuates during its depositional history at' several scales. Factors responsible for water table fluctuations of varying magnitude and period are local ones such as depositional environment, regional factors such as climate and tectonism (subsidence), and global factors such as eustasy. Their possible influence on the formation of the Bayswater seam and correlatives will be considered later.

(Stach & others, 1982) in the formation of inertinite. The kind of vitrinite or inertinite preserved and its association in the microlithotypes are determined both by the type and succession of peat-forming floras, and by physical and chemical processes of disintegration and sedimentation in the mire. The origin of the inertinite macerals is of particular relevance to the origin qf the Bayswater coals.

ORIGIN OF THE MACERALS

Vitrinite (Figures 3b and d) forms by mild oxidation . of humic material, a process which is minimised by a high water table. Although inertinite is formed largely from the same original material as vitrinite, inertinite precursors are uncommon in modern mires. Most workers attribute the formation of inertinite (Figures 3a,b,c and d) to intense oxidative decomposition (mainly biological) in the peat-forming stage (Stach & others, 1982) and this is generally assumed to be sub-aerial oxidation due to drying out of the peat surface. Inundation by oxygenated water is also proposed as a mechanism of oxidative decomposition

Semifusinite and fusinite (Figures 3b and c), which are defined by the presence of botanical structure, are thought to originate in the structural parts of plants lingin and cellulose. Band macrinite (Figure 3c), which is optically similar to semifusinite but lacking cellular structure, is assumed to represent partly humified structured material (Diessel, 1982) subsequently oxygenated by lowering of the water table. Inertodetrinite (Figure 3a), the other main inertinite maceral in the Permian, could be derived through the comminution of either structured or unstructured inertinite: an example of the latter is found in reed swamps which produce little lignin (Stach & others, 1982). Reed swamps are usually associated with a. rising water table

"western sands" in the Gunnedah Basin (Figure 7) (Hamilton, 1985), and the Marrangaroo Conglomerate (Figure 8) in the Sydney Basin. This fluvial facies, which progressively truncates older Permian units to the west, extends eastwards as a broad, braided, alluvial sheet (Havord & others, 1984) which in the east is conformable with the shallow marine sediments of the KMT. The Lithgow and Lidsdale seams which overlie the Marrangaroo Conglomerate are split (Figure 8) and partly eroded by an upper wedge of craton-derived sediments, the Blackmans Flat Conglomerate. In the south, shallow marine and barrier-bar facies are recognised on margins of the Marrangaroo Conglomerate (Havord & others, 1984) and the Woonoona seam overlies both the Marrangaroo Conglomerate and shallow marine sands (Figure 8). The Lithgow and Lidsdale seams, and the Marrangaroo Conglomerate where the coal is absent, are elsewhere overlain by sediments deposited probably in a pro-delta or an interdistributary bay setting, on the basis of upward-coarsening sedimentary cycles, common bioturbation and a spinose acritach flora (Bembrick, 1983). The Woonona seam in the south is overlain by lower deltaic plain sediments (Havord & others, 1984).

and flooding, and wooded vegetation in modern mires is indicative of a lower longterm mean water table (Falini, 1965; Ivanov, 1981). However, the physical breakdown of structured material is the generally accepted mechanism for the formation of inertodetrinite (Stach & others, 1982) which in Permian deposits contains partly preserved botanical structure in many cases and has the same range of reflectivities as the semifusinite and fusinite with which it is associated. STRATIGRAPIDC CONTEXT

Along the northeast margin of the Sydney and Gunnedah Basins, the Bayswater seam and correlatives overlie a widespread shallow marine unit. Isopachs of the best development of this unit, the KMT of the Sydney Basin, are shown in Figure 2. The shallow marine unit coarsens upwards to nearshore sands, which over much of its geographic range form a characteristic bioturbated silty sandstone, the Arkarula Sandstone in the Gunnedah Basin (Figure 7), (Britten & Hanlon, 1975; Hamilton, 1984) and the Archerfield Sandstone in the Gunnedah and Sydney Basins (Britten, 1975). However, in the west the shallow marine unit is overlain by a thin sheet of cratonderived quartzose sediments known as the LITHGOW

West

A L/DSDALE /SEAM

WWCD6 V+E

BOOTLEG 8

V+E I

j SFR

[II SFR

LOP . 0 .

CAMDEN 61

. • .

. •. •• • C .

• M/1RRA_NGAR90. CONG~O.MERATE . •.

•

• . •. •

... . . BF.

.r ·

. .

WOONONA SEAM

•

,~l m

COAL FACIES - as in fig . 7 OE POSITIONAL ENVIRONMENTS - as in f ig. 7 PETROGRAPHIC COMPOSITION - as in Fig. 7

Figurf' H: Spntinl and tPmpornl variation of thf' cla~tir farif's and pPtrogrnph ir mm position of lhf' Lit hgm,· anrl Woononn spnms from thf' southf'rn S~•rln P,. Basin. Clas tic fa cies after Herbert & other s (in prep.), Lithgow senm after Smyth (19fi7): Woonona spnm in Bootleg 2A anrl in C'11mden fil (unp uhlished ('SIRO dnt11). Section AGRC' in Figure :t labelling of petrogntphic composition diagrams as for Figure fi .

SFR 0

25km

Against the orogen in the Gunnedah Basin, the Hoskissons seam overlies deltaic sediments of the first Late Permian regressive cycle (Figure 7). The top of the seam in west of the basin was partly eroded by a second pulse of craton-sourced elastics (Hamilton, 1985). The Hoskissons seam is overlain by lacustrine sediments (Tadros, 1986). A similar situation is envisaged in the north of the Sydney Basin. Where shallow marine sediments pinch out towards the orogen (Uren, 1983), the Bayswater seam interfingers with coarse braided alluvium and probable debris flow sediments towards the orogen (Uren, 1985) and is overlain by sandy piedmont deposits (Cameron & others, 1982). The Bayswater seam also coalesces with the overlying and underlying vitrinite-rich seam towards the orogen (Uren, 1983), but is recognisable in the middle part of the combined seam where it retains its distinctive dull profile (Uren, 1985). Basinwards it is overlain by lower deltaic plain sediments (Beckett & McDonald, 1984). The Bowens Road seam in the Gloucester Basin overlies an upward coarsening shallow marine succession, considered to be a correlative of the KMT (Lennox & Wilcock, 1985) in the Sydney Basin. It is overlain and split by coarse, probably braided alluvium derived from the New England Orogen.

ORIGIN OF THE BAYSWATER SEAM AND CORRELATIVES LOCAL INFLUENCES

Flora. The possibility that a significant change in the peat-forming flora through the seam was responsible for the unique petrographic composition of the Bayswater seams was postulated by Britten and Smyth (1973). Such a change could have been due to an autogenic floral succession in the mire (cf. Smith, 1962), and virtually all Permian coal seams show an upward decrease in vitrinite content (Smyth & Cook, 1976). Such a hypothesis may be tested by palynological/palaeobotanical evidence, although few such studies of the coals have been made. The Permian flora was shown to be dominated by a low diversity assemblage of pteridophytes and gymnosperms on the

basis of palynological (Foster, 1979) and palaeobotanical studies (Gould, 1975; Gould & Delevoryas, 1977). In a study of the Bayswater seam in DDHSl , S2 and S7, (Barton, 1978) found that there is no significant difference between palynomorphs in vitrinite- and inertinite-rich parts of the seam and that the pteridophytes (30% av.), glossopterids (30% av.) and other gymnosperms (20% av.) are dominant throughout. In a study of the Ulan seam in the south west of the Gunnedah Basin, McMinn, (1984) found that the microflora in the seam is dominated by the pteridophytes (>40%) and gymnosperms (>25%) but that the glossopterids are rare. Articulates, represented by Retusotriletes (Good & Taylor, 1975), average from 1 to 5% of the palynomorphs in the coal samples. There is no indication in the fairly coarse palynological zoning for the Permian that a significant climatic or floral event took place during the formation of the Bayswater seams. Moreover, petrographicallysimilar coals may have existed for a longer period in the west of the Sydney Basin (McMinn, 1984) and in the Gunnedah Basin (Hunt & Telfer, unpubl. data), while "normal" high-vitrinite coals were forming in the east. Coals petrographically similar to the Bayswater seam formed throughout the Permian in the epicratonic Cooper Basin (Hunt & Smyth, in prep.). The content and composition of exinite in the Bayswater coals is similar to that in the Permian coals as a whole. Exinite content ranges from 2 to 5% in most cases. This is in contrast to high exinite contents reported in northern hemisphere black durains, which are usually interpreted as sub-aquatic oozes (e.g. Reidnouer & others, 1967). The components of the exinite maceral group in the Bayswater seam are similar to those in the underlying and overlying coals (Figure 9). Thus there is no evidence for any major detectable change in the flora during deposition of the Bayswater seam and correlatives. Depositional Association. The position of the Bayswater seam and correlatives, overlying regressive shallow marine sands over much of their range, suggests that they are deposited in a lagoon setting behind a barred shoreline (Britten & Smyth, 1973; Hamilton, 1985). It is possi-

RESINITE 10 0

BAYSWATER SEAM

0 •

Upper part in OOHS I (Fog . 6) Lower part 1n OOHSI (F,g . 6 )

WITTINGHAM C.M.

::;i:nt,~~ J:;:'!~ter

100 .__....__,___;.____,,____,_-----'..____,,____,_--''---~ 100

SPORINITE

CUTINITE

Figure 9: Composition of exinite in the Bayswater seam and the seams of the Wittingham Coal Measures. Bayswater seam in DDHSl and S2 (location K in Figure 2). Wittingham Coal Measures after Hunt (1985a), excluding the Bayswater seam.

ble that the unique composition of the Bayswater seams is due to deposition in this environment. However; the association of the Bayswater seams with a lagoonal environment is an over simplification because the seams overlie a range of proximal and distal environments throughout the basins including shallow marine, fan delta, lower deltaic plain, upper deltaic plain and braided fluvial. Furthermore there are three regressive cycles in the upper Permian. and inertinite-rich seams are found in the base of only the middle one (Figure 4b). " Normal" high-vitrinite seams are developed in the base of the upper and lower cycles (Hebden and Borehole/ Moolarben seams respectively). The marine to terrestrial transition in the lower cycle differs from the other two in being a straightforward grading from delta front to lower delta plain sediments without any intervening beach or barrier sands. However, in the upper cycle, shallow marine rocks in the top of the Tamago Coal Measures pass upwards into shoreface, beach and barrier sands of the Waratah Sandstone (Warbrooke, 1981). The overlying Borehole seam (Figure 4c) was deposited in a complex fluvio-deltaic to lagoonal backbarrier swamp setting but is vitrinite-rich. Diagenetic Environment. The differentiation of type, as envisaged for the Permian coals, includes processes · which take place both prior to deposition and early in diagenesis. Oxidation due to fluctuations of

the water table affects peat below the depositional surface and can be regarded as an early diagenetic process. Water table fluctuations expose peat to an oxidising environment for varying periods depending on the duration and magnitude of the fluctuations and the local subsidence rate at the depositional site. Several pathways, based on drying or flooding or both; could theoretically have created the petrographic profile of the Bayswater seams. Four theoretical pathways intended to illustrate the possible development of the thicker Bayswater and Hoskissons seams are outlined in Figure 10. Two of the pathways involve either deep flooding (PATH 4) or deep desiccation (PATH 3) to achieve oxidation of the peat. Of these, deep flooding by oxygenated waters would lead to the cessation of peat accumulation and possibly a downwards decrease in oxidation. However, the presence in places of bright bases in thin dull coals and the presence of 30% and more vitrinite interbedded with inertinite in the dull upper part of a seam is unexpected. Termination in a lacustrine elastic unit might be expected but has not been reported for the Bayswater seam or correlatives. Conaghan (1982) envisaged continued accumulation of peat in flooded situations by shedding of material from floating peat mats, but modern floating peat mats are found in low latitudes, whereas the Bayswater seam and correlatives have accumulated in high latitudes. Deep drying of the peat profile (PATH 3) may produce the most intense oxidation near the top of the coal and band macrinite would be expected in the lower part of the profile. However, band macrinite is rare in the Bayswater coals. To account for basal vitrinite-rich plies found in thinner coals it would be necessary to postulate in this model that the drying affected the thinner coals less than the thicker coals. A detrital texture in the inertinite could be achieved by biological activity (Stach & others, 1982). However, deep drying (say > 1 m) of modern mires leads to decomposition of peat above the new water table with an upward increase in mineral matter by ablation (Ivanov, 1981). All other factors being equal, the rate of decomposition is regulated by climate and the mire may well

-1B

-W

SFR

W = Position of the water Ubl• -Top of the put --- Top of the WIIH table wilh lime + Water Ubl1 above the put - W1ttr table below thl peat

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I I

\ I I I

+ 3

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-w

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conditions in early di agenes is

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SFR = Sem ifusinite ratio in the coal

Figure 10: Models suggested for the temporal development of peat-formin g mires to produce a petrographic profile similar to that in the Bayswater seam from location K (figure 2). PATH 1 = shallow nooding, PATH 2 = shallow oxidation . PATH 3 = deep oxidation. PATH 4 = deep flooding. Left hand scale = position of water table ( ± or - ) with respect to the mire surface (variable scale). Right hand scale labelled as in Figure 5.

stabilise at the new water table position. Following deposition of the basal vitrinite-rich ply in a terrestrial mire, continued deposition during shallow flooding by oxygenated water (PATH 1) would ·allow for the bright base provided that the water did not deeply penetrate the pre-existing peat. In this case, the detrital texture of the inertinite in the upper dull part would be produced by subaqueous deposition. Shallow flooding (in the decimetre range or above) (Diessel, 1970) would normally lead to an increase in mineral matter content. Depending on depth, shallow flooding would result in a change from woody to other plant facies (often Sphagnum in modern mires, (Ivanov, 1981) and articulates in the Carboniferous, (Hacquebard and Barss, 1970)). However, mineral matter is not preferentially associated with either the vitrinite-rich or inertinite-rich plies in the Bayswater seam (Figure 11), and there is no evidence of any significant floral change. A second sub-aerial hypothesis is shallow drying with continued peat accumulation following initial deposition of vitrinite-rich peats in topographic lows across the basins. In this case (PATH 2) withdrawal of the water table wou1d only be in the decimetre range, which, in modern environments, may favour growth of a woody flora (Ivanov, 1981). A gradual lowering then raising of the water table would account for the upward decrease then increase in vitrinite content and the semifusinite ratio, MINERAL MATTER 100

BAYSWATER SEAM

~ As 1n Fig. 9

• ••

100 .__..,,___.___,~..,___.__ _,_

INERTINITE

..,,___.___,___,. 100

VITRINITE -t

EXINITE

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apparent in the thicker sections of the Bayswater seam and correlatives. Snyman (1961) envisaged a similar situation in the South African Gondwanan coals he investigated, but with seasonal re-working by flooding and re-deposition of the oxidised peat surface in stagnant water to form a hypautochthonous coal. This process was also proposed by Hacquebard & Donaldson, (1969) for the formation of coals in a slowly subsiding limnic basin. REGIONAL INFLUENCES Climate. Only a highly generalised firstorder time trend can be established for climate in the Permian. On palaeobotanical and palaeomagnetic evidence the Australian basins were at high latitudes throughout the Permian and the climate was sub-polar to cool temperature (Krausel, 1961; Retallack, 1977; Frakes, 1979; Quilty, 1984; Embleton, 1984). Glaciation was at a maxium in the Early Permian and amelioration of climatic conditions to cool temperate in the Late Permian has been suggested on the basis of isotopic, sedimentological, palaeobotanical and palaeontological evidence (Gould, 1972; Crowell & Frakes, 1985; Rao & Green, 1982; Quilty, 1984). A regionally reduced humidity would be consistent with the petrographic composition of the upper Bayswater seam, assuming that it was the product of a low and not high water table. However, there is no detectable change in the composition of the palaeoflora which might also be expected to accompany a change in climate. Tectonics. To date the tectonic regime of the Bayswater coals and the underlying marine incursion has not been studied in detail but several settings have been suggested. A widely held view is that the Sydney Basin developed as a foredeep to the New England Fold Belt (Diessel, 1970; Herbert, 1980). Orogenic uplift was accompanied by sinking of the adjacent basin, allowing entry of the sea. Clastics in the regressive coal measure wedge were rapidly shed from the freshly-elevated orogen as molasse-type deposits. An elaboration of this view is the foreland basin model proposed by Jones & others, (1984) in which the three cycles of transgression and regression in the Late Per-

mian of the Sydney Basin are correlated with events in the neighbouring orogen. Subsidence and flooding associated with the KMT mark the beginning of the second Late Permian cycle of expansion in the New England orogen. Progradation produced an overall upward-coarsening, volcanolithic, orogen-sourced piedmont, in which the wettest environments occurred at the start of its deposition. The coals overlying the marine flooded phase in the lower and upper Late Permian regressive cycles are vitrinite-rich, consis.tent with high (although probably not submergent) water tables predicted by the model of Jones & others, (1984). However, the Marrangaroo Conglomerate and correlatives, which immediately overlie the KMT and its correlatives,.are derived from the craton (Havord & others, 1984). The presence of this significant craton-derived unit is not accounted for at this stage in the tectonic cycles of Jones & others, (1984). A tectonic scenario in which the eastern side of the Sydney Basin subsided with respect of the Blue Mountains Shelf west of the Lapstone basement fault (Figure 2) has been developed by Brakel (1985). A,eustatic origin for the Kulnura Marine Tongue is excluded by the presence along the western basin margin of the overlying braidedfluvial deposit of the Marrangaroo Conglomerate which would not be expected in response to a lessening of relative topographic relief by a eustatic sea level rise. The Marrangaroo eventually overrode the marine unit as a prograding fandelta wedge; it truncates the basal Late Permian and older rocks towards the west (Havord & others, 1984) and is thus related to an increase in relative topographic relief of the craton, such as could have been caused by subsidence in the basin. The same subsidence would have admitted the Kulnura marine incursion of the sunkland area. The absence of the KMT west of the Lapstone Monocline strongly suggests that the Lapstone basement fault (Figure 12) (Harrington & Brakel, 1981) was active at the time, downthrowing the central and eastern parts of the basin. The subsidence allowed the sea to cover the basin up to the Lapstone line, while on the emergent Blue Mountains Shelf the drop in base level caused the alluvial fan apron of the Mar-

rangaroo Conglomerate to form in response, eventually to reach the sea as a fan delta. In the Gunnedah Basin, the area of subsidence was probably controlled by basement faults bordering an Early Permian rift zone located along Qureshi's (1984) Meandarra Gravity Ridge. After the sunklands were filled by shallow marine to proximal fluvial facies sediments, the Bayswater peats accumulated in mires on the resulting emergent, subdued-relief surface. The continuity of the coals in the Gunnedah Basin where they have been mapped in the subsurface (Holmes, 1976; Hamilton, 1984) suggests tbat they were formed as a nearly continuous blanket, approximately synchronous over most of the basin. Tectonic stability with little or no subsidence is implied. The peat itself may have drawn the water table up with it as accumulation continued, as in raised bogs. At first the peat was preserved in reducing conditions below the water table, but further subsidence in the depocentre, of probably only a matter of decimetres, gradually lowered the water table around the basin margin. This produced conditions of sub-aerial oxidation in the peat in all regions except the most low-lying areas of the central and eastern Sydney Basin. These low-lying areas produce the most vitrinite-rich coals and coincide with the thickest development of the KMT, that is, areas of greatest subsidence, in the northeast (Figure 2). The dull coal facies is best developed where the KMT is thin or absent. This relationship has been used to predict the distribution of vitrinite in the Bayswater seam and correlatives in Figure 12.

DISCUSSION The unique petrographic composition of the Bayswater and correlative seams poses two questions: (1) why the high inertinite content? and (2) why the particular type of inertinite? The available floral evidence leads to the conclusion that the composition of the peatforming flora was not significantly different from that of other coals. The high inertinite content was the result of fluctuations of the water table rather than flora. The spatial variations of bandwidth in

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LACHLAN FOLD BELT

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500

L__J km

F'igure 12: Vit.rinite content of the Bayswater sea m and correlatives based on the observed relationship between composition and the develop ment of the KMT. The 50 m isopach of the Kulnura Marine Tongue is after Herbert & other (in prep.): major fault within the Sydney Ba in are after Harrington (1982).

100 km

150°

the microlithotypes and sulfur and mineral matter in the seams is in general similar to that in the overlying and underlying seams, which supports the deposition of the peat under a high water table with subsequent early diagenetic oxidation. The shallow drying case is, however, the one most consistent with the petrography of the Bayswater seams as previously discussed. The wide distribution of the Bayswater seams suggests a regional control of peat accumulation and composition. The explanation may lie in the fact that deposition of the KMT was initiated by &. major downthrow caused by movement on the Lapstone basement fault. Subsequent filling in of the basin eventually led to the initiation of the Bayswater seams, first in hollows and then over the entire area. This basal peat was vitrinite-rich with high semifusinite ratios due to high water tables in the wet, emergent conditions. Peat accumulation persisted in the cool humid climate. The modern day analogues are the high latitude blanket mires (Moore & Bellamy, 1974). Thus the Bayswater seams covered, without major break, several hundreds of kilometres, as do peats in Siberia and northern Canada today. The high inertinite content is due to subsidence east of the hingeline, which pass~s through Lapstone in the west, Muswellbrook in the north and Wollongong in the south (Figure 12). This movement lowered the water table west of the hingeline with subsequent oxidation of the organic matter. Complete destruction was prevented by the cool moist climate and even seasonal freezing. The severity of the oxidation has broken down most of the organic matter into inertodetrinite.

CONCLUSIONS The Bayswater seam and correlatives were formed following tectonically initiated deposition of the Kulnura Marine Tongue throughout most of the Sydney and

Gunnedah Basins. Filling in of the basin with sediment led to the development of peat over a wide area of previously diverse depositional environments. No significant floral changes occurred during accumulation of the peat. The extremely inertiniterich nature of the coal is due to the subsidence cast of the tectonic hingeline which lowered the water table with respect to the peat surface west of the hinge line, permitting severe sub-aerial oxidation. The coals overlying maximum thicknesses of the KMT are the most vitrinite-rich due to relative subsidence and maintenance of the higher water table in the centre of the basin. The severity of oxidation has cornminuted much of the inertinite to inertodetrinite. The unique petrographic composition and lateral extensiveness of these coals is due to a unique tectonic control.

ACKNOWLEDGEMENTS This study was initiated during the Permian Coals of Eastern Australia Project (78/2617) supported under the National Energy Research, Development and Demonstration Program administered by the Department of Resources and Energy. Thanks are due to the many companies and institutions which supplied samples and/or data for this study, in particular to Blue Metal Industries Pty Ltd; Esso Australia Pty Ltd; the Australian Gas Light Co. Pty Ltd; and the NSW Department of Mineral Resources. The assistance of Delhi Petroleum Pty Ltd in the preparation of the figures is greatly appreciated. A.T. Brakel publishes with the permission of the Director, Bureau of Mineral Resources. The organisation and synthesis presented here reflects substantially a re-evaluation of parts of the above project by J.W. Hunt, while a candidate for a Ph.D degree at the School of Earth Sciences, Macquarie University, under the supervision of Drs. P.J. Conaghan and J.G. Jones.

REFERENCES Barto, C., 1978: A palynological and sedimentological study of the Bayswater seam at Ravensworth. Hons-Thesis, Univ. Sydney (unpubl.). Beckett, J . & McDonald, I., 1984: The depositional geology of the Jerry's Plains Subgroup. Abstracts 18th Symposium on Advances in the S tudy of the Sydney Basin, Newcastle Univ .. 44-46.

Bembrick, C.S., 1983: Stratigraphy and sedimentation of the Late Permian Illawarra Coal Measures in the W.estern Coalfield, Sydney Basin, New South Wales. J . Proc. R. Soc. NSW, 116, 105-117. Brakel, A.T. , 1985: Global sea level change as a method of correlating the Late Permian coal measures in the Sydney, Gunnedah and

Bowen Basins. BMR J . Aust. Geol. Geophys. (in press). Britten, R.A., 1975: Singleton-Muswellbrook District, in Traves, D.M. and King, D. (Eds), Economic geology of Australia and Papua New Guinea. 2. Coal, Australas. Inst. Min . Metall., Monograph 6, 191-2p5. Britten, R.A. & Hanlon, F.N., 1975: North-western Coal Field in Traves, D.M. and King, D. (Eds), Economic geology of Australia and Papua New Guinea. 2. Coal, Australas. Inst. Min. Metall., Monograph 6, 236-244. Britten, R.A. & Smyth, M., 1973: The Bayswater Coal member of the Singleton Coal Measures of New South Wales. Australas. Inst. Min. Metall. , Proc., 248, 37-47. Cameron, R.G., Conaghan, P.J. & Parbury C.F.R. , 1982: Piedmont depositional regimes within the Ravensworth alluvial embayment, Wittingham Coal Measures, northern Sydney Basin. Abstracts, 16th Symposium on Advances in the Study of the Sydney Basin, Newcastle Univ., 32-34. Conaghan, P.J., 1982: Lacustrine (Gilbert) deltas in the Permian coal measures of eastern Australia and India; implications for the widespread hydroponic origin and deep-water diagenesis of Gondwanan coals. Abstracts 16th Symposium on Advances in the Study of the Sydney Basin, Newcastle Univ., 6. Crowell, J .C. & Frakes, L.A., 1975: The Late Paleozoic glaciation. In Campbell, K.S.W. (Ed), Gondwana Geology, Aust. Nat. Univ. , Canberra, A.C.T., 313-331. CSIRO, 1977: Report on the Hoskisson Seam from Gollins Gunnedah DDH16, Gunnedah Area, New South Wales. CSIRO Minerals Research Laboratory, Division of Mineralogy, Location Report 392. Diessel, C.F.K., 1965: Correlation of macro- and micropetrography of some New South Wales coals. Proc. 8th Commonwealth Mining and Metallurgical Congress 6, 669-677. Diessel, C.F.K., 1970: Paralic coal seam formation. Proc. 8th Inst. Fuel Con{., Brisbane, 14.1-14.22. Diessel, C.F.K., 1982: An appraisal of coal facies based on maceral characteristics. Aust. Coal Geol., 4(2), 474-483. Continental 1984: B .J .J., Embleton, palaeomagnetism, in Veevers, J.J. (Ed), The Phanerozoic Earth history of Australia, Oxford Univ. Press, 11-16. Falini, F., 1965: On the formation of coal deposits of lacustrine origin. Geol. Soc. Am. Bull., 76, 1317-1346. Flaig, W., 1968: Biochemical factors in coal formation; in Murchison, D. and Westoll, T.S. (Eds.}, Coal and coal-bearing strata, Oliver and Boyd, 197-232. Foster, C.B. , 1979: Permian plant microfossils of the Blair Athol Coal Measures, Baralaba Coal Measures and basal Rewan Formation of Queensland. Geol. Surv. Queens/. Publ., 372, Palaeontological Paper 45. Frakes, L.A. , 1979: Climates throughout geological time, Elsevier Amsterdam. Good, C.W. & Taylor, T.N., 1975: The morphology and

systematic position of the Calamitean elaterbearing spores. Geoscience Man., XI, 133-139. Gould, R.E., 1972: Some palaeobotanical evidence on the Upper Permian climate of the Bowen Basin, Queensland. Abstract 44th Congr. Aust. N.Z. Assoc. Adu., Sydney, 3, 32. Gould, R., 1975: A preliminary report on petrified axes of Vertebraria from the Permian of eastern Australia, in Campbell, K.S.W. (Ed.), Gondwana geology, Aust. Nat. Univ., Canberra, 109-116. Gould, R. & Delevoryas, T., 1977: The biology of Glossopteris: evidence from petrified seedbearing and pollen-bearing organs. Alcheringa, 1, 387-399. Hacquebard, P.A. & Donaldson, J .R., 1969: Carboniferous coal deposition associated with flood-plain and limnic environments in Nova Scotia, in Depples, E.C. and Hopkins, M.E. (Eds.), Environments of coal deposition, Geol. Soc. Am. Spee. Pap. 114, 143-191. Hacquebard, P .A. & Barss, M.S., 1970: Palaeogeography and facies aspects of the Minto Coal Seam, New Brunswick, Canada. Compte Rendu 6th Congres International de Stratigraphie et de Geologie du Carbonifere. Sheffield, 1967, 861-872. Hamilton, D.S., 1984: Deltaic depositional systems, coal distribution and quality, and petroleum potential, of the lower Black Jack Formation, Gunnedah Basin, New South Wales . Abstracts, Seventh Aust. Geol. Conv., 12, 20?°-208. Hamilton, D.S., 1985: Deltaic depositional systems, coal distribution and quality, and petroleum potential, Permian Gunnedah Basin, N.S.W., Australia. Sediment. Geol., 46, 35-75. Harrington, H.J . & Brake!, A.T., 1981: The Lapstone basement fault and development of the western section of the Sydney Basin. Abstracts, Symposium on Geology and Colliery Development in the Western Coalfield NSW, Coal Geology Group, Geol. Soc. Aust., 10. Havord, P., Herbert, C., Conaghan, P.J., Hunt, J.W. & Royce, K., 1984: The Marrangaroo conglomerate - its distribution and origin in the Sydney Basin. Abstracts Seventh Aust. Geol. Conv., 12, 221-223. Herbert, C., 1980: Depositional development of the Sydney Basin, in Herbert, C. & Helby, R. (Eds.), A guide to the Sydney basin, NSW Geol. Surv. Bull., 26, 11-52. Holmes, G.G. , 1976: Goulburn Valley coal drilling. Geol. Surv. NSW Q. Notes 23, 2-14. Hunt, J .W., 1981: Petrographic correlation of Sydney Basin coals. Abstracts 15th Symposium on Advances in the Study of the Sydney Basin, Newcastle Univ., 13. Hunt, J .W. , 1982: Relationship between microlithotype and maceral composition of coals and geological setting of coal measures in the Permian Basins of eastern Australia. Aust. Coal Geol., 49(2), 484-502. Hunt, J.W., 1985a: Chapter 19, Coal type trends in the Permian basins, in Permian Coals of Eastern Australia. A report to the National Energy Research, Demonstration and Development

Council. Hunt, J .W., 1985b: Chapter 20. Sulfur in the Perrnian coals, in Permian Coals of &stern Australia. A report to the National Energy Research, Demonstration and Development Council. Hunt, J.W., 1985c: Chapter 22. Ash content and composition of the Permian coals, in Permian coals of &stern Australia. A report to the National Energy Research, Demonstration and Development Council. Hunt, J .W. & Hobday, D.K., 1984: Petrographic composition and content of coals associated with alluvial fans in the Sydney and Gunnedah Basins, Eastern Australia. Spee. Publ. Int. Assoc. Sediment., 7, 43-60. Ivanov, K.E., 1981: Water movements in mirelands. Thomson, A. and Ingram, H.A.P. , (Trans.), Academic Press, London, 276pp. Jones, J .G., Conaghan, P.J., McDonnell, K.L. , Flood, R.H. & Shaw, S.E. , 1984: Papuan Basin analogue and a foreland basin model for the Bowen-Sydney Basin, in Veevers, J .J., (Ed.), The Phanerozoic Earth history of Australia , Oxford Univ. Press, 243-261. Krause!, R. , 1961: Palaeobotanical evidence of climate, in Nairn, A .E .M. (Ed) , Descriptive palaeoclimatology, Interscience, New York, 227-254. Lennox, M. & Wilcock, S., 1985. The Stoud-Gloucester Trough and its relationship to the Sydney Basin. Proceedings 19th Symposium on Advances in the Study of the Sydney Basin, Newcastle Univ., 37-41. McMinn, A. , 1984: Palynology of the Ulan seam at Ulan Colliery. Unpubl. Palynological Report 1984/3, Uppubl. Geol. Surv. Rep. No. GS1984/051, Geol. Surv. NSW. Moore, P.D. & Bellamy, D.J ., 1974: Peatlands, Paul Esk (Scientific Books) London. Quilty, P .G., 1984: Phanerozoic climates, (vii) Permian, in Veevers, J .J . (Ed),Phanerozoic Earth history of Australia, Oxford Univ. Press, 49. Qureshi, I.R. , 1984: Wollondilly-Blue Mountains gravity gradient and its bearing on the origin of the Sydney Basin. Aust. J . Earth Sci., 31, 293-302. Rao, C.P. & Green, D.C., 1982: Oxygen and carbon

isotopes of Early Permian cold-water carbonates, Tasmania, Australia. J. Sediment. Petrol., 52, 1111-1125. Reidnouer, D. , Williams, E.G. & Dutcher, R.R., 1967: The relationship between paleotopography and sulfur distribution in some coals of western Pennsylvania. Econ. Geol., 62 , 632-647. Retallack, G.J. , 1977: Triassic palaeosols in the Upper Narrabeen Group of New South Wales. Part II: Classification and Reconstruction. J . Geol. Soc. Aust., 24(1), 19-36. Smith, A.H.V., 1962: The palaeoecology of Carboniferous peats based on the miospores and petrography of bituminous coals. Proc. Yorkshire Geol. Soc., 33(4,19), 423-474. Smyth, M., 1967: Coal Petrology applied to the correlation of some New South Wales Permian coals. Australas. Inst. Min. Metall. Proc., 233, 7-16. Smyth, M. & Cook, A.C. , 1976: Sequence in Australian coal seams. Math. Geol., 8(5), 529-547. Snyman, C.P. , 1961: A comparison between the petrography of South African and some other Palaeozoic coals. Nuwe reeks, 16, 37pp. Stach, E., Mackowsky, M. Th. , TeichmUller, M., Taylor, G.H. Chandra, D. & Teichmiiller R. , (Eds.) 1982: Textbook of coal petrology, Third Edition, Gebruder Borntraeger, Berlin, Stuttgart. Tadros, N.Z., 1986: Lacust.facies - upper Black Jack Formation - Gunnedah. Q. Notes, Geol. Surv. NSW, 62, p.31. Uren, R.E., 1983: Facies and sedimentary environments of the Wittingham Coal Measures, near Muswellbrook. Abstracts 17th Symposium on Advances in the Study of the Sydney Basin , Newcastle Univ. 30-33. Uren, R.E., 1985: The margin of a marine incursion in the Wittingham Coal Measures, Upper Hunter Valley. Proceedings 19th Symposium on Advances in the Study of the Sydney Basin , Newcastle Univ. , 45-48. Warbrooke, P .R. , 1981: Depositional environments of the upper Tomago and lower Newcastle Coal Measures, New South Wales. Ph.D. Thesis, Newcastle Univ. (unpubl.).

J.W. HUNT, CSIRO Division of Fossil Fuels, North Ryde, N.S.W. 2113. (Present address: Delhi Petroleum Pty. Ltd. 101 Grenfell Street, Adelaide S.A. 5000).

AT. BRAKEL, BMR Division of Continental Geology, Canberra. A.C.T. 2600.

M. SMYTH, CSIRO Division of Fossil Fuels, North Ryde, N.S.W. 2113.

USE OF SEM FOR COAL PETROLOGY By L. H. Hamilton & M. R. Salehi

ABSTRACT The common lack of success of previous scanning electron microscope (SEM) studies on coal is attributed largely to inexperience and over-reliance on the secondary electron mode of imaging. Good images of coal macerals can be gained by using a combination of techniques, with backscatter imaging playing an important role. Suggestions are given on how the average reader may obtain optimal results in using the SEM for coal petrography. The best results are obtained with low rank coals provided they are coated with carbon to prevent charging effects. Most macerals can be identified but there are problems yet to be resolved, for example, with micrinite, suberinite and some very thin cutinite. Structures such as pores are readily observed in anthracite but macerals are difficult to identify in coals of this rank.

INTRODUCTION The scanning electron microscope (SEM) has great potential for the study of coal, especially at high magnifications, but this potential has been seldom realized. Various workers have reported some success, but this relies mostly on special conditions such as botanical structures observable in broken fragments of brown coal (Augustyn & others, 1976), or the association of certain minerals with macerals (Stanton & Finkleman, 1979). Much of the lack of success by previous workers is attributed to a lack of experience with the SEM and too much reliance on the secondary electron (SE) mode of imaging. The SE mode essentially relates to surface topography and not to composition, hence it is useful with polished sections only when they have been "etched" by the polishing method or some other means. The backscatter electron (BS) mode of imaging has been found useful because it responds to average atomic number of density, and this is related to maceral composition. The aim c;,f

this paper is to pass on our experience with this so that the average reader can obtain usefl4 results with the SEM comparable with those obtained by the light microscope. This involves a discussion on operating techniques, a tabulated identification scheme, and minor problems as yet unresolved. In some respects this paper can be considered as an extension of a similar scheme by Stanton & Finkelman (1979).

EFFECT OF COAL RANK With brown coal, better images generally can be obtained with polished sections in the SEM than with the light microscope, even with an oil immersion objective. This applies particularly· with the BS mode which gives detail useful for studying palaeobotany as well as coal petrography (Figures 1, 2 and 3). Carbon coating of the specimen is necessary because of the tendency of charging due to the interaction of the electron beam with the coal surface. The SE mode is less useful than the BS mode because of charging effects and edge effec~ which complicate the image (Figures 2 and 3). Shrinkage cracks in brown coals can cause charging, hence freshly polished sections are recommended, and specimens should not be left under strong electron beams any longer than necessary as the electron beam can damage the coal surface. With bituminous coals the SEM complements the light microscope by showing greater textural detail in certain circumstances (Figures 4, 5 and 6). Most of the information obtainable in the light microscope is obtainable with the SEM provided that both the SE and BS modes of imaging are employed simultaneously. Edge effects and charging are less of a problem with bituminous coals than with brown coals. There are also limitations, compared with the light microscope,-· in identifying some exinite macerals - possibly because of the specimen coating needed to suppress surface charging.

With anthracite (Figures 7, 8 and 9), the structure of the coal is very clear (e.g. pores) but macerals are difficult to identify by both BS and SE modes in the SEM. Charging is not a problem with high rank coals and coating is unnecessary.

EXPERIMENTAL CONDITIONS SPECIMEN PREPARATION Success with SEM work depends largely on specimen preparation and operating conditions. Specimens have to be polished carefully with respect to surface relief. Too much relief is to be avoided because strong topography can affect the BS images at high magnification. Nevertheless slight relief is useful for maceral identification in the SE image. Preparation for the SEM should be the same as that for the light microscope.

Figure 1: Photomicrograph of a brown coal in light microscope, reflected light, plain polarized, air objective, X240.

Specimen size, up to 76 mm diameter x 20 mm height (in our instrument), is unimportant if the specimen is coated. Otherwise the smaller the specimen is, the better, for avoiding surface charging. Specimens are generally best left unmounted in the resin. A special mounting medium can be used for particulate coal specimens (Moza & others, 1978). Before coating, specimens should be cleaned in an ultrasonic bath. A coating of carbon, as thin as possible, is necessary for best results with solid state BS detectors (brown coal up to 500.A , low rank coal up to 200.A and medium rank coal up to 100.A ). Carbon is the best coating material for BS work because of its low atomic number. It is also suitable for SE work but is not as good as gold. For BS work a gold coating is useless oecause of its high atomic number - although it is ideal for highlighting surface relief.

~·

·'·

Figure 2: Similar to Figure 1, in SEM, SE mode.

• J~ ·' 'r!f!!:• ":> ~- , ~ . . .. ... ;},j. ~ ..

.... ~ .. ,... i f ~ ~ ~, ~

Figure 3: Similar to Figure 1, in SEM, BSE mode.

Storage of the specimen for long periods in a vacuum only marginally improves results. This allows for some degasification of the coal. Heating at 100°C does little to improve results and it is undesirable to sul>ject the specimen to higher temperatures that will damage the coal. INSTRUMENT OPERATION Results vary with instrument and with operator. Good results were obtained on a JOEL35 SEM with a solid state ring backscatter detector and secondary electron detector. Slightly different results were previously obtained with a Robinson scintillating backscatter detector operated at a less intense vacuum than normal (Robinson & Robinson, 1978). Work in CSIRO with such a detector has been successful with a Cambridge SEM with normal vacuum and without the need of coating the materials (J. Corcoran personal communication).

Figure 4: Photomicrograph of a bituminous coal in light microscope, reflected light, plain polarised, oil objective, x700.

The most important operating variable is the accelerating voltage. This affects the image contrast and resolution. With the BS mode, contrast increases with accelerating voltage but resolution of fine structure decreases due to the greater beam penetration and wide area of electron scattering. With the SE mode better images are obtained at lower accelerating voltages. Generally the optimal voltage is the highest ol>tainable with minimum surface charging. This is commonly in the mid-range (15-20 kV) for coal study. Although much lower voltages are commonly used for biological work, BS images on coal require a higher voltage. The electron beam needs to be aligned and adjusted carefully. The beam aperture should generally be mid-range. The best results are obtained after the instrument has "warmed up". It is best to have the specimen as close as practical to the detector. This provides a better resolution in the SE image and a

Figure 5: Similar to Figure 4, in SEM, SE mode.

Figure 6: Same as Figure 4, in SEM, BSE mode.

greater contrast in the BS image. Specimen tilt is not necessary for BS work and it is most practical (in this instrument) to have the specimen surface approximately horizontal. For SE imaging some tilt is necessary for highlighting relief but not so much that shadowing becomes a problem. Coal specimens are best rotated (around the vertical axis) so that the bedding is aligned in the direction of the SE detector to suppress shadows.

SEM MODES OF OBSERVATION Each IllJ)de of observation in the SEM gives different information and it is desirable to have BS and SE images displayed simultaneously. The most useful mode is BS which responds to density (more

Figure 7: Photomicrograph of an anthracite in light microscope, reflected light, cross polarised, air objective, x400.

accurately - atomic number) contrast. The SE mode is used for examining relief. With high voltage beams some BS response is combined with the SE response. Cathodoluminescence should be useful for material that fluoresces under the light microscope but the normal detectors available in the SEM are apparently not sensitive enough at present for maceral identification. Oil shales and coals with megaspores were examined in the cathodoluminescence mode with disappointing results. X-ray analysis is useful for mineral matter determination and minor elements in macerals. This is also assisted by staining with inorganic substances. Staining may be useful for maceral identification in conjunction with the BS mode and with XRA but results so far are not conclusive.

;j;.

'-I~·

Figure 8: Same as Figure 7, in SEM, SE mode.

Figure 9: Same as Figure 7, in SEM, BSE mode.

IDENTIFICATION OF MACERALS AND MINERALS

Morphology, as indicated by relief or by contrasting grey levels, is the best aid to interpretation with the SE mode. Morphology can be used with SEM images in the same way as it is used with light microscope images (Stach & others, 1982). A little more care, however, is needed to be sure the images relate to macerals and not to artifacts (e.g. surface charging). Macerals are readily distinguished from minerals in the BS mode, and further information on minerals is easily obtained by X-ray analysis. With BS images grey levels (brightness) are useful for determining maceral groups with the following general rule for magnifications of up to xlO00. Exinite is darker than vitrinite, inertinite is brighter

Macera! Group

Macera!

Morphology

BS Grey Level

vitrinite

desmocollinite telocollinite gelocollinite

groundmass distinct layers distinct ovoid boundaries, structureless cell structure

intermediate

inertinite

exinite

fusinite semi-fusinite macrinite inertodetrinite sclerotinite sporinite

cutinite resinite alginite exsudatinite mineral matter

than vitrinite. and mineral matter is brighter than inertinite (see Figure 6). Exceptions to this general rule are discussed later. A similar rule does not apply for SE images. Problematical macerals are micrinite, suberinite and fluorinite. In the SEM micrinite and suberinite have not been readily distinguished from their surroundings (usually vitrinite). Fluorinite has not been observed but is expected to be similar to resinite. The grey levels of some of the inertinite macerals in BS images are equal to that of vitrinite but the macerals can still be identified by their structure. Relief due to polishing is usually lowest for vitrinite although some semi-inertinite has low relief also. Exinite has a relief similar to or greater than inertinite but resinite is lower and may be .similar to vitrinite.

structureless, but with distinct boundaries fragmental fungal structure spore shaped (ovoid to lenticular with central cavity) elongated, laminar or serriate mainly ovoid, homogeneous ovoid and inhomogeneous secondary cavity filling varied

low-intermediate bright-intermediate " "

" "

bright-intermediate

Polishing Relief in SE mode low " "

very high high "

high

low

high

low

high

low

moderate to low moderate to low low

low low very bright

moderate to very high

PRESENT LIMITATIONS Present limitations might be solved with further work. At present the reflected light microscope produces better maceral differentiation with high rank coals than does the SEM. With moderate rank coals some macerals are still problematical. Transitional vitrinite/semi-inertinite is difficult to identify. Suberinite and very thin cutinite can be difficult to detect. High magnification has unexpected problems - the grey levels in the BS images are sometimes reversed possibly due to beam penetration, interface effects, and trace elements. This applies only to very fine grained exinite macerals. The effect is probably related to the shape of the maceral as well as its fine size and elemental composition. This is the subject of further study.

CONCLUSIONS The SEM is useful for coal petrography. It is also very useful for detecting structures not seen in the light microscope. With brown coals the clear definition achieved with the SEM should be useful for extending the links between coal petrography and palaeobotany. As technology improves, the usefulness of the SEM for coal petrography will be further extended (e.g. • with cathodoluminescence). ACKNOWLEDGEMENTS This work was supported by an ARGS grant. Acknowledgement must also be made for the assistance of the electron microscope staff at Queensland Institute of Technology.

REFERENCES Augustyn, D., Iley M. & March H. , 1976: Optical and SEM study of brown coals. Fuel 55, 25-38. Moza A., Strickier D.W. & Austin L.G., 1978: A moun ting medium for coal particles. Scanning Electron Microscopy 1978 1, 289-291. Robinson V.N.E. & Robinson B.W., 1978: Materials characterisation in a scanning electron microscope environment cell. Scanning Electron Microscopy 1978 1, 595-602. Stach E., Mackowsky M.-Th., Teichmilller M., Taylor G.H., Chandra D. & Teichmfiller R. , 1982: Stach's textbook of coal petrology. Gebruder Borntraeger, Berlin, 3rd Edition.

Stanton R.W. & Finkleman R.B. , 1979: Petrographic analysis of bituminous coal: optical and SEM identification of constituents. Scanning Electron Microscopy 1979 1, 465-471.

L.H. HAMILTON, M.R. SALEHI, Department of Applied Geology, Queensland Institute of Technology, G.P.O. Box 2434, Brisbane, 4001.

REVIEW OF MINERAL MATTER IN COAL By

C. R. Ward

ABSTRACT Material classed as "mineral matter" in Australia coals is divided, for convenience, into a crystalline "mineral" fraction and a range of non-crystalline "other inorganic" components. Many different techniques may be used to investigate this material, supplementing assessments based on traditional chemical and petrographic methods. The most effective technique, however, for crystalline particles at least, is to isolate the minerals from the coal by electronic lowtemperature (oxygen plasma) ashing, and determine the mineralogy of the residue by x-ray diffraction processes. The mineral fraction of Australian bituminous coals is mostly made up of well crystallized kaolinite, with variable amounts of quartz, siderite,' montmorillonite and various mixed-layer clay minerals. Pyrite, feldspar, apatite, calcite and a range of other minerals are also present in some samples in minor amounts. The mineral assemblage in the coal is generally quite different to that of the shaley rocks in the associated non-coal sequence, and much of the mineral fraction is thought, in various ways, to be of authigenic or diagenetic origin. The minerals and other inorganics may affect mining, by controlling factors such as the abrasiveness of the coal with respect to mining machinery or the toxicity of dusts released to the mine atmosphere. They may also affect coal preparation, through processes such as slaking or dispersion in water. The various components interact with each other, when the coal is used, affecting aspects such as ash behaviour in combustion, coke and slag performance in the blast furnace and the generation of gas or liquid products in coal conversion. An understanding of the nature and distribution of minerals in different coal deposits may help alleviate problems in some of these areas of the coal industry.

MINERALS AND MINERAL MATTER As defined by the Standards Association of Australia (1982), the term "mineral matter" refers to "the minerals and other inorganic material in, and associated with coal". This all-embracing definition encompasses three classes of material, namely: a) discrete, crystalline mineral particles in the coal or associated strata (e.g. intra-seam non-coal bands); b) inorganic elements or compounds, usually excluding nitrogen and sulphur, incorporated in the organic molecules of the coal; c) dissolved inorganic compounds in: the coal's pore water or surface water. In the geological sense, only the discrete, crystalline inorganic compounds can be classed as true "minerals". Such "minerals" can, however, also be formed by crystallization of any dissolved constituents as the coal dries out with exposure or storage. Kiss & King (1977) and Given & Spackman (1978) have pointed out that non-crystalline inorganic materials (i.e. the inorganic components of organic compounds and the dissolved salts in pore waters) are of great significance in low rank coals, such as the brown coals of Victoria. Kiss & King (1979) suggested that these consti'tuents should be differentiated from the crystalline components, and separate the "mineral matter", as defined above, into a "minerals" fraction and an "inorganics" fraction when discussing low rank coals. In high rank coals, on the other hand, such as the bituminous coals of eastern Australia, the great majority of the non-organic material appears to occur in crystalline or "mineral" form.

OCCURRENCE OF MINERALS IN COAL The minerals in coal are often visible in hand specimen, and can frequently be

observed in examii:ration of drill cores, outcrops or mine exposures. Such megascopic occurrences include thick bands or lenticles of clay-rich or pyritic material, rounded pellets or nodules of mineral matter and dispersed crystals or . nodular masses of mineral material within the coal, as well as minerals that form coatings on, or infillings in, cleats and other fractures. X-radiography of coal samples has been used in Australia since the middle 1950's to investigate further the distribution of minerals at a megascopic scale (Durie & Swaine, 1971). With the aid of special equipment, such as that described by Jones (1970), the technique is now employed routinely in many laboratories to record the general distribution of megascopic mineral contaminants in driU cores of coal seam.s (Doolan & others, 1979; Day & others, 1982). As well as this megascopic mineral matter, however, a very significant amount of microscopic mineral material also occurs in coal. The minerals found in coal have been described from a micro-petrographic point of view by ICCP (1963), Marshall & Tompkins (1964), Mackowsky (1968) and Stach & others (1975). A comprehensive review of the minerals in a range of Australian coals, as revealed by petrographic studies, is given by Kemezys & Taylor (1964). Microscopic data reveal that many of the minerals in coal occur in a very intimate association with the coal's organic constituents. Apart from the megascopic bands, lenticles and nodules described above, minerals may occur as isolated euhedral crystals, as broken, presumably detrital fragments, as microscopic nodules or, in some cases (e.g. with pyrite), as submicroscopic crystalline aggregates or framboids. Many minerals, however, such as silica, clay, sulphide and phosphate minerals, also occur as petrifactions, representing infillings of cell cavities in the individual coal macerals (e.g. Balme and Brooks, 1953; Cook, 1962; ~eeston, 1981). Australian coal seams often contain persistent layers, or bands, of non-coal material. These are usually no more than a few centimetres in thickness, and are mostly made up of clay or clay-rich material

(Britten, 1979). Together with mineralogical contaminants derived from any incorporated roof and/or floor strata, these non-coal, intra-seam bands generally produce the bulk of the mineral matter in run-of-mine coal products. Along with any particles of dense, stony coal, these large masses of mineral material can be separated, fairly readily, from the clean coal in a preparation plant. The actual marketed or "clean coal" product, however, still contains the more intimately associated mineral constituents, and these must be taken into account in several aspects of coal utilization (Brown & others, 1964; Stewart & Wall, 1979).

DETERMINA'TION OF MINERAL MATTER CONTENT The terms "mineral matter" and "ash" in coal are not synonymous. The ash represents the inorganic residue left after combustion of the coal, while the mineral water is the inorganic component in the coal before any combustion takes place. Since many of the minerals in coal react in some way during combustion, the ash can be considered as the non-combustible fraction of the mineral water. Determination From Chemical ~alysis It has long been the practice, in coal analysis, to calculate the proportion of "mineral matter" from the coal's ash yield and the proportion of other key inorganic constituents. The most widely used formulae for such calculations are the K.M.C. (King-Maries-Crossley) formula (King & others, 1936) and the Parr formula (Parr, 1928; Rees, 1966) details of which are given in Figure 1. The use of these formulae is critically reviewed by Stolz (1980). More recently, Pollack (1979) has put forward a method of calculation based on the actual inorganic elements found in the coal sample itself. The K.M.C. is the most comprehensive of the traditional formulae, taking into account a greater range of possible mineral contaminants than the Parr formula. Both are used in expressing analystical results to a dry, mineral-matter free (d.m.m.f.) basis,

King-Maries-Crossley (KMC) Fo~ula • MM = 1.13 A + 0.5 Spyr + 0.8 CO2 + 2.85 Sso4- 2.85 Sash + 0.5 Cl Parr Formula MM = 1.08 A + 0.55 S where MM

A C02 = Spyr = Sso4 Sash =

Percentage of mineral matter in coal Percentage ash of coal Percentage carbonate carbon dioxide in coal Percentage pyritic sulphur in coal Percentage sulphate sulphur in coal Percentage of sulphur in ash Percentage total sulphur in coal Percentage chlorine in coal.

* Several minor modifications to this formula have also been published. Figure 1: Formulae for calculation of percent mineral matter from other analytical data. -

and such data are used in many coal classifications (e.g. ASTM, 1984). The formulae are based, however, on certain assumptions regarding the minerals present in coals generally, and as such do not necessarily give a precise measure of the ac: tual proportion of mineral material. Com~ parative studies, such as those of Brown & others (1959), suggest that, for Australian coals at least, these formulae cannot be relied upon for precise estimates of mineral matter content. A more direct method of mineral matter determinatio n, used by Hicks & N,agelschmidt (1943), Nelson (1953), and Brown & others (1959), involves heating the coal, in air, at a temperature of 200°C, increasing to around 370°C until the organic matter is destroyed and a constant weight of inorganic residue is obtained. Although this temperature is not as high as that used in conventional ashing of coal (up to 815°C), it is still sufficiently high for

many minerals, such as pyrite, siderite, sulphates and some clay minerals to suffer irreversible reactions involving changes of mass and/or crystal structure. Brown & others (1979) indicate a number of corrections, based on the pyritic sulphur and carbonate CO2 contents of the coal, to allow for these changes in the air oxidation process. Another method of determination of the total mineral matter was applied to coals by Radmacher & Mohrhauer (1955). This involves dissolving the minerals in hydrochloric and hydrofluoric- acids, and regarding the percentage loss of mass as an estimate of the mineral matter content. Although a number of corrections are still required for precise results (Brown & others, 1979), the technique appears to be a fairly reliable indicator of total mineral content. However, the minerals themselves are destroyed in the acid. solution process, and thus are not available, as a residue, for

any further study. In addition, as discussed below, some minerals found in coals are insoluble, even in hydrofluoric acid, while the possibility exists that some of the organic components may also be affected by the acid treatment. Petrographic Assessment of Mineral Content The relative proportions of the different constituents of coal, recognizable under the miscroscope, can be determined to a reasonable degree of precision by modal analysis or point count techniques (l.C.C.P., 1963). Quantitative assessments can be made of the relative proportions of major minerals or mineral groups (e.g. quartz, carbonate, pyrite, clay) in crushed percentages of other constituents (macerals or microlithotypes) reported on a mineral-free basis. Although the percentages of the different components in maceral analysis are often given to the first decimal place, Davis (1984) and several other workers suggest that the probable error inherent in point counting is such that the data derived are only adequate if reported to the nearest al:r solute one per cent. The precision and reproducibility are too low, compared to the chemical methods, for quantitative assessment of the total mineral content. Moreover, of course, many occurrences of mineral material in coal may not be recognized under the microscope, due to their small size, low reflectance or intimate association with coal macerals. Aided by the use of fluourescence microscopy to distinguish some minerals from certain organic components (Teichmuller & Wolf, 1977), and possibly by greater use of thinsection, rather than polished-section techniques, petrographic studies can, however, provide valuable data on the mode of occurrence of the major mineralogical constituents. Hydrogen Peroxide Oxidation of Organic Constituents An alternative to oxidation at relatively high temperatures is to remove the organic matter from coal with an aqueous oxidizing

agent such as concentrated by hydrogen peroxide. This technique has long been uses! for the removal of organic matter from soils and sediments (Gross, 1971), and was applied to coals in independent studies by Nalwalk & Friedel (1972) and Ward (1974). The coal is reacted with 100 volume (35%) hydrogen peroxide at temperaturEis up to 100°C, and the organic matter is destroyed, with a slow, effervescent reaction, over a period of several days. High rank coals react more slowly than low rank coals, and Nalwalk & Friedel (1972) report that up to six weeks may be required for complete oxidation of American anthracite. Small samples of Australian bituminous coals, however, are usually oxidized essentially to completion after only a few days of treatment (Ward, 1974). The mineral residue left by this oxidation process can be recovered from the supernatant liquid by means of a laboratory centrifuge, and allowed to dry in the laboratory atmosphere. This prevents any dehydration and associated changes in composition or structure of the clay minerals, providing a distinct advantage, for subsequent studies, over higher-temperature oxidation techniques. However, minerals in the coal that are soluble in water, such as chlorides and many sulphate minerals, or minerals, such as carbonates, that react with the organic acids formed in the peroxide solution during oxidation, will not be recovered as mineral residues. New inorganic compounds, such as insoluble calcium oxalates, may also be formed in some cases by reaction between these .organic acids and the minerals in the coal. Pyrite in the coal appears to act as a catalyst, causing the peroxide to decompose spontaneously to oxygen and water. Such coals require special treatment (Nalwalk & Friedel, 1972), and some oxidation of the sulphide minerals may take place in the process. Although a low-cost method of isolating insoluble mineral matter from coal, comparative studies by Ward (1974) indicate that hydrogen peroxide oxidation is unreliable, by itself, for determining total mineral matter content. Most coals have lower mineral yields from peroxide oxida-

:~ ) J

Figure 2: Electronic low-temperature (oxygen plasma) asher, suitable for isolation of minerals from coal.

tion than from other methods, probably due to removal of soluble species in the course of the reaction, while others may be affected by the formation of new minerals as indicated above. Analysis of the soluble fraction may, however, be of value in improving the precision of the technique for quantitative assessments.

Electronic Low-Temperature (Oxygen Plasma) Ashing The most widely used method of isolating the minerals from coal is to remove the organic matter with an electronically excited oxygen plasma. This technique, originally described by Gleit (1963), was first applied to coal by Gluskoter (1965). It has now been used as both a technique for

precise estimation of mineral matter content (Frazer & Belcher, 1973; Miller & others, 1979) and a means of isolating the minerals from the coal for further study (Gluskoter, 1967; O'Gorman & Walker, 1971). Using apparatus illustrated in Figure 2, the coal is exposed, in an evacuated chamber, to a slow stream of oxygen that has passed through a high-energy electromagnetic field produced by a radiofrequency oscillator. The energy is converted to a mixture of atomic and ionic species and slowly destroys the organic matter, leaving a light-coloured, dry mineral residue. .. The oxygen plasma technique, described by some authors as "electronic lowtemperature ashing" (L.T.A.) and by others

as "radio-frequency oxidation" (R.F.O.) forms the basis for most recent studies of mineral matter in coal. Oxidation takes place at temperatures of around 150 to 200°C, so that some dehydration of minerals may occur, but the effects of this dehydration are less significant than for higher-temperature oxidation processes. In many cases, such as with the clay minerals, they can be reversed by rehydration if required. Particularly with low rank coals, the inorganic components of the coal's organic matter may form additional crystalline residues in the course of the oxidation process. These can be minimized, however, according to Miller & others (1979), by special operating techniques. Frazer & Belcher (1973) show that. for typical Australian bituminous coals, the radio frequency oxidation technique gives a yield of mineral water 0.2 to. 0.4% greater than that obtained by air oxidation at higher temperature, and that the combined water content of the mineral matter (H20+) is up to 0.3% higher. This, in turn, gives a higher value for the carbon content, and a lower value for hydrogen, when these parameters are recalculated to a d.m.m.f. basis. The operating procedures for the radio frequency oxidation technique, to given accurate, reproducible measurements of the total mineral matter content, fo r Australian bituminous coals, are discussed by Frazer & Belcher (1973). More recently, they have been set out by the Standards Association of Australia (1981), as an alternative to the air-oxidation process for mineral matter determination. Other factors, such as air-dried moisture and the residual organic carbon contents of the mineral matter are also taken into account, in conjunction with the proportion of oxidation residue, for precise results.

ANALYSIS OF MINERAL WATER Many of the analyses routinely applied to coal, such as the determination of carbonate carbon dioxide, pyritic sulphur and sulphate sulphur, provide valuable data on the abundance of particular mineral groups. These can be supplemented by

chemical data from analysis of the coal ash, or even, using techniques such as X-ray fluorescence (Kuhn & others, 1975) of the coal sample itself. Brown & Swaine (1964), Durie & Swaine (1971), Shibaoka (1971, 1972) and Swaine (1975, 1977) discuss the inorganic characteristics of Australian coals, including their trace elements, on the basis of such analyses, and suggest how the different constituents might occur in the various coal deposits. Such analyses do not, however, provide a direct identification of the actual mineral species present. Only a normative mineralogy, using techniques such as thQse outlined by Pollack (1979), can be obtained from data of this type. The actual identify of many of the minerals in coal is also difficult to determine under the microscope, especially with polished section techniques. The various sulphide minerals are, of course, the exception to this. Staining techniques (Warne, 1962) may allow identification of the different carbonates, but the clay minerals, which make up the bulk of the mineral matter in most Australian coals, cannot be adequately identified by their optical properties at all (Grim, 1968). X-ray diffraction of coals, without any prior oxidation of the organic matter, was used by Mitra (1954) and Rekus & Haberkorn (1966) to identify the minerals present in a number of Indian and American coals. The organic matter itself gives a fairly diffuse diffraction pattern, allowing the sharp diffraction effects of the crystalline mineral particles to be differentiated. However, if the minerals are present only at low concentrations, relative to the sample as a whole, their diffraction effects are difficult, if not impossible, to separate from the background pattern of the organic material. Warne (1964, 1975) studied the minerals in a series of Australian coal samples by differential thermal analysis of the coal in a nitrogen atmosphere. The nitrogen acted to suppress the thermal effects associated with heating of the coal's organic matter, allowing the minerals to be identified by their individual thermochemical reactions. The lower limits of detection for the various

minerals, however, as a percentage of the whole coal sample, ranged from 0.5 to 1% for pyrite and marcasite to over 30% for some of the clay minerals, and such analyses are therefore only useful, at least for the clay minerals, with relatively impure coals. X-ray diffraction, thermal analysis and other techniques, such as infra-red spectrometry and electron microscopy, are much more satisfactory tools for mineral identification if applied to the residues isolated by coal oxidation. X-ray diffraction has been used on residues from airoxidation by Hicks & Nagelschmidt (1943), Dixon & others (1964) and Brown & others (1964), on hydrogen peroxide residues by Ward (1974) and on residues from electronic low-temperature ashing by Gluskoter (1967), O'Gorman & Walker (1971), Soong & Gluskoter (1977), Painter & others (1978) and Finkelman & others (1981). The scanning electron microscope has been used, often as a supplement to other methods, by Schiehing & others (1978), Russell & Rimmer (1979), Andrejko & others (1983) and Allen & Vander Sande (1984). Frost & others (1977) discuss the use of X-ray photoelectron spectroscopy in a study of sulphides from coal, while Raymond & Gooley (1979) describe the use of electron probe microanalysis. Only limited use, however, has been made of thermal analysis in studies of oxidation residues (O'Gorman & Walker, 1973). Trace elements and their relation to coal minerals have been studied by Bohor & Gluskoter (1973), Gluskoter & others (1977) and Ward (1980a). More recently, stable isotope ratios in minerals isolated from coal have been studied by authors such as Gould & Smith (1979), Shieh & Suter (1979) and Botz & Hart (1983). X-ray diffraction (XRD) still represents the main technique of mineral identification for most studies. Details of its use on oxidation residues, including special techniques for clay mineral studies and methods for limited quantitative analysis, are given by Ward (1977) and Russell & Rimmer (1979). Fourier transform infra-red (FTIR) spectrometry also has considerable potential as a quantitative tool in coal mineral in-

vestigations and its use in this way is discussed by Painter & others (1978).

MINERALS IN AUSTRALIAN BITUMINOUS COALS Summaries of the minerals present in Australian bituminous coals are given by Marshall & Tompkins (1964) and Kemezys & Taylor (1964) on the basis of petrographic data, and by Ward (1974, 1978), Doolan & others (1979), and Westermann (1983) from X-ray diffraction studies of oxidation residues. These are supplemented by a considerable amount of geochemical data, including the works of Brown & others (1959), -Shibaoka (1972), Corcoran (1979), Hunt (1983) and Slansky (1984). Ward (1978) describes a mineralogical study of 28 seams of Permian and Mesozoic age in the main coal basins of N.S.W. and Queensland, based mainly on samples that had been previously analysed for other properties by CSIRO Division of Fossil Fuels. The minerals in the coal seam composites (excluding any non-coal intra-seam bands) were isolated using oxygen plasma ashing or, in some cases, hydrogen peroxide oxidation techniques, and subjected to X-ray diffraction study. A number of intra-seam, non-coal bands, as well as the lutites (shales and mudstones) from the roof and floor of selected seams were also examined by X-ray diffraction, and their mineralogy compared to that of the clean coal materials. X-ray diffractograms of the oxidation residues of typical coals from eastern Australia are illustrated in Figure 3. These diffractograms are based on randomly oriented powder samples of the mineral material, and as such indicate the bulk mineralogy of the oxidation residues. Further details of the clay minerals can be obtained by separating out the fraction with an effective diameter finer than 2 pm and allowing it to form an air-dried cloriented aggregate" film on a flat glass slide (Gibbs, 1970). X-ray diffractograms of typical clay fractions, based on such aggregates, including those obtained after saturation of the clay with ethylene glycol and after heating to various temperatures, are given in Figure 4.

e) F

Cu K~ Radiation

Figure 3: X-ray diffractograms of mineral matter fro some bituminous coals. a) Harrisburg-Springfield (No.5) seam, Illinois Basin, U.S.A. b) Balgownie seam, Sydney Basin, N.S.W. c) Bulli seam, Sydney Basin, N.S.W. d) Globe seam, Maryborough Basin, Qld. e) Nipan No.10 seam, Bowen Basin, Qld.

Degrees 2&

Minerals: Ap-apatite; Cq-coquimbite; et-calcite; D-dolomite; E-expandible-lattice clay minerals; F-feldspar;

Go-goyazite I-illite (or mica) K-kaolinite P-pyrite Q-quartz Sd-siderite Sz-szmolnockite.

A summary of the minerals found in Australian coals, based on a combination of both types of analysis, is given in Table 1. Terms used to describe the various processes of mineral formation are listed in Table 2.

7 . 15

QUARTZ Quartz is present in all but a few bituminous coals from eastern Australia. It may constitute up to half of the mineral matter in some coals (Ward, 1978), but mostly makes up only about 10% of the various oxidation residues. In many cases at least some of the quartz is very fine grained, being present, along with clay minerals, in the fraction separated for orientated ag- • gregate study. Kemezys & Taylor (1964) found that quartz in Australian coals typically occurs as angular grains in clay-rich layers, and is probably of detrital origin. However, microcrystalline quartz (chalcedony) may also be found as an infilling of cell lumens in the coal macerals, as discret.e lens-shaped bodies, and as veins cutting across the coal structure. This suggests that some of it was deposited by authigenic processes, 'e ither at the same time as, or shortly after the original plant debris. Recent studies, such as those of Renton & Cecil (1979), Davis & others (1984) and several authors in a compilation by Raymond & Andrejko (1983) has shown that a large proportion of the silica in modern-day peats is of biogenic origin. It may be present as skeletal fragments, representing diatom frustrules or sponge spicules, or as discrete particles (phytoliths) incorporated within plant cell structures. Such occur-

(I)

:w;,· 12 . 1

(II)

(IV)

11 .3

(IV)

7 . 15

e) 3 .58 3 .54

Figure 4: Oriented aggregate x-ray diffractograms of clay fractions from some Australian coals: a) Victoria Tunnel seam, Sydney Basin, N.S.W. b) 'C' seam (Moura), Bowen Basin, Qld. c) Main Lower seam (Blackwater), Bowen Basin, Qld. d) Lithgow seam , Sydney Basin, N.S.W. e) Moody seam (Baralaba), Bowen Basin, Qld. For each example: i-air-dried; iii-heated to 300°C ii-glycol saturated; iv-heated to 600°C "d" spacings indicated in Angstrom units. After Ward (1978)

10 Cu K.c Radiation

Degrees 2S

TABLE 1: Principal Minerals id Australian Bituminous Coals Silicates Quartz - SiO2 Feldspar - K.AlSiJOs Kaolinite - AbSi2Os(OH)4 Illite - KAb(AlSi3)O1o(OH)2 Montmorillonite - Na(A1Mg)S4O,o(OH)2 Chlorite - (MgFeAl)s(AlSi)4 O, o(OH)s Mixed-layer clay minerals Carbonates Siderite - FeCOJ Calcite - CaCOJ Dolomite - (CaMg)COJ Dawsonite - NaAICOJ(OH) Sulphides Pyrite - FeS2 Sphalerite - ZnS Galena - Pbs Millerite - NiS Sulphates Gypsum - CaSO4.2H20 Barite - BaSO4 Coquimbite - Fei{SO4)J.9H20 Szomolnokite - FeSO•. H2O Natrojarosite - NaFeJ(SO4h(OH)s Phosphates Apatite - CasF(PO.)J Goyazite - SrA6(PO4h(OH)sH2O Others Anatase - TiO2

rences, as well as silica precipitated in the pores of the peat shortly after burial, could account for much of the fine-grained quartz in the coal samples. FELDSPAR Feldspar is a common constituent of many non-coal strata, at least in the coal bearing sequences of New South Wales (Loughnan, 1966). With some exceptions, however, it is only present in small quan-

tities, if at all, in most Australian bituminous coals (Ward, 1978). Kemezys & Taylor (1964) indicate that, where it occurs, feldspar generally appears as small, relatively unaltered grains in clayrich layers, and thus is probably detrital, or even pyroclastic in origin. The mineral may be too coarse, as a detrital constituent, to penetrate very far into the coal swamp, or alternatively it may be readily subject to diagenetic alteration by the waters of the peat deposit.

TABLE 2: Modes of formation for minerals in coal. a) TIMES OF MINERAL FORMATION

SYNGENETIC - at the time the plant debris accumulated. EARLY DIAGENETIC - shortly after burial by more peat or other sediment. LATE DIAGENETIC - processes associated with deeper burial and rank advance. EPIGENETIC - after the coal reached its present rank. b) PROCESS OF MINERAL FORMATION

DETRITAL INPUT - solid particles washed or blown into peat swamp. AUTHIGENESIS (or NEOFORMATION )precipitated from solution or by biogenic processes. DIAGENETIC ALTERATION -formed by interaction of other minerals with peat or swamp waters or by rank advance.

CARBONATE MINERALS The carbonate minerals siderite, calcite and dolomite are common, in varying proportions, in the oxidation residues of Australian coals. Kemezys & Taylor (1964) identified ankerite, rather than dolomite, as being present on the basis of petrographic studies, but X-ray diffraction data obtained by Taylor (1969) and Ward (1978) indicate that the main carbonate mineral, other than calcite and siderite, has the characteristic crystal structure of dolomite. Siderite is found as spheroidal nodules, mostly up to 2mm in diameter, but ranging up to 5mm across (Kemezys & Taylor, 1964). In some seams these nodules may coalesce to form large ellipsoidal masses, or they may become concentrated into more extensive layers. Kemezys & Taylor (1964) and Beeston (1981) suggest, on the basis of

petrographic data, that the siderite was formed very early in the coal's history, before the rank of the seams had advanced to the brown coal sta£e. It mav be the result of interaction between iron in the peat's pore water and C02 produced by fermentation of the organic matter (Gould & Smith, 1979). Calcite and dolomite (or ankerite), on the other hand, occur mostly in veins or as cleat infillings. They also occur as infillings of cell lumens in fusinite or semifusinite, and as replacements of some of the coal macerals. Small nodules of these minerals do exist, but such occurrences are relatively rare. Unlike the siderite, most of the calcite and dolomite was apparently formed at a relatively late stage in the coal's history, after the majority of the compaction had taken place. They are possibly derived from calcium in the organic compounds, released as part of the rank advance process.

PYRITE AND THE SULPHATE MINERALS

According to the pet:rographic studies of Kemezys & Taylor (1964), at least some pyrite is present in almost all unweathered Australian bituminous coals. It occurs as euhedral crystals, as small, polycrystalline nodules or "framboids", as veins or cleat coatings and as infillings or replacements of plant structures. Considered as a proportion of the total mineral water, however, pyrite is relatively rare in oxidation residues isolated from these coals. Even in coals with, by Australian standards, a high proportion of pyritic sulphur, the mineral matter, when fresh, contains no more than about 10% by weight of pyrite. In many coals from the Illinois Basin, by contrast (Rao & Gluskoter, 1973), pyrite makes up over 30% of the isolated mineral material. Pyrite, especially in the framboidal form, reacts with atmospheric oxygen during prolonged storage or exposure of the coal to form a range of hydrous iron sulphate minerals. Some oxidation of the pyrite may also take place during the electronic low . temperature ashing process (Frazer & Belcher, 1973). Minerals such as coquimbi te (Fe2(SO4h .9H2O) , szomolnock ite FeSO4 .H2O) and jarosite (KFeJ(SO4MOH) 6 ) are common in such oxidized pyritic coals (Ward, 1978), but pyrite is found in the oxidation residues of fresher materials. Sulphuric acid, produced by pyrite oxidation, may also react with any calcite in the coal to form gypsum (Rao & Gluskoter, 1873), and the gypsum may in turn dehydrate, during plasma ashing, to form minerals such as bassanite (CaSO4. ½H 2O) or even anhydrite (CaSO4). The presence of bassanite in the coal mineral matter has been suggested by Pearson & Kwong (1979) as a useful indicator of oxidation that might reduce the performance of an otherwise effective coking coal. Pyrite has long been recognized to be most abundant in coals that are overlain by marine strata (e.g. Williams & Keith, 1963), and thus is less common in Australian coals than in some overseas deposits. It is, however, a significant constituent of the mineral matter isolated from seams such as

the Greta seam of New South Wales and the Garrick seam in Queensland. The pyrite appears to form by bacterial reduction of sulphate ions in marine water, apparently as it permeates through the peat bed shortly after burial. Where the pores of the peat are filled with fresh water, however, and the amount of available sulphate is low, the main iron mineral to form appears instead to be siderite. •Small amounts of other sulphate minerals, apart from pyrite, may be recognized in petrographic studies of coal polished sections. Kemezys & Taylor (1964) note the presence of marscasite (a polymorph of pyrite), sphalerite (ZnS), galena (Pbs) and chalcopyrite (CuFeS2), while Lawrence & others (1960) have described millerite (NiS) in cleat fractures of the Bulli seain in N.S.W. Hatch & others (1976) also describe large concentrations of sphalerite, mainly as cleat ·infillings, in a number of coals of the eastern United States. As well as being a product of reactions associated with pyrite oxidation, some sulphate minerals may occur in their own right as inherent mineral components of essentially unaltered coals. Kemezys & Taylor (1964) have described gympsum veins in coal at Leigh Creek, S.A., and suggested that the material formed, probably as a groundwate r deposit, due to the arid climate of the area. Similar veins have been noted, by the author, in outcropping bituminous coals in southern Utah, U.S.A. Barite has also been found at Leigh Creek (Kemezys & Taylor, 1964), occurring. as veins and more irregular masses, and as a vein infilling in the basal part of a coal seam in the Blackwater area. Minerals such as bassanite and anhydrite may also form directly from the organic components of the coal in the course of the plasma ashing process. Nankervis & Furlong (1980) describe the production of bassanite from the calcium and sulphur in the organic matter of low rank' coal, liberated as the hydrocarbon compounds are destroyed by oxidation. Like the bassanite formed from dehydration of gypsum, this material may break down to anhydrite if the temperature rises above about 200°C.

PHOSPHATE MINERALS Small amounts of apatite are found in a number of Australian coals. Cook (1962) described an apatite petrification in a coal from the Ipswich area of Queensland, while Ward (1978) and Corcoran (1979) have noted its occurrence in several other Australian coals. A more complex alumino-phosphate mineral of the goyazite group has been reported by Ward (1974, 1978) and Doolan & others (1979) in several coal seams of eastern Australia. Such minerals have been found in soils (Norrish, 1968) and also occur in other rocks, some, but not all of which are associated with coal seams (Loughnan & Ward, 1971). They are particularly noteworthy since, unlike apatite, they are insoluble in acids, even hydrofluoric acid, and thus would not be included in mineral matter determinations based on acid-solution processes.

CLAY MINERALS The clay minerals represent the most abundant constituents in Australian bituminous coals. The relative abundance and crystal structure of the different species, compared to those in the rocks associated with the coal seams, are discussed in some detail by Ward (1978) and Westermann (1983).

Kaolinite Well crystallized kaolinite, mixed, perhaps, with some poorly crystalline material, is the dominant clay mineral in most bituminous coals from eastern Australia. In many cases it is, in fact, the only clay mineral detected by X-ray diffraction methods. Petrographic studies show that at least some of this kaolinite occurs as cell cavity infillings in the coal Il}acerals (Balme & Brooks, 1953), or as bands, pellets and vermicular aggregates of crystalline material. It may also be found as a cleat infilling, and is probably present in thin layers of shaley material within the coal. Kaolinite is also present in many shales and mudstones in Australian coal-bearing sequell:ces (~o?ghnan, 1966), but with the

exception of the intra-seam non-coal bands and some of the lutites in the immediate roof and floor of the seam (Ward, 1978), it is usually poorly crystallized and present in minor proportions relative to other clay minerals. The intra-seam bands, and some of the other sediments intimately associated with the coal, are mostly dominated by well-crystallized kaolinite, and many, consisting almost entirely of this material, are described by authors such as Loughnan (1971, 1978) as "kaolinite clayrocks", "flint clays" or "kaolin-coal tonsteins". Loughnan (1978) suggests that much of the kaolinite in these kaolinite clayrocks is of detrital origin, introduced from lateritic or bauxitic weathering of exposed source areas nearby, while several other authors, such -as Price & Duff (1969) believe that these rocks may represent altered volcanic ash. On the other hand, authors such as Keller (1968) suggest that the kaolinite in these materials was produced by in situ alteration of other, mainly detrital clay minerals in a coal-forming or related environment, while Moore (1964) suggests that precipitation in a colloidal material associated with decomposing organic matter may also be involved. The fact that kaolinite is more abundant, relative to other clay minerals, in coal than in the shales and mudstones, other than flint clays, elsewhere in the sequence suggests that some process of kaolinite formation is inherently associated with the accumulation of coal seams. While this process may be any one, or a combination of those thought to form the kaolinite in flint clays, the occurrence of kaolinite as an infilling of cell cavities in coal macerals, and as nodular masses, apparently built up in the original peat accumulation, suggests that much of the kaolinite was formed, in the original peat, by an authigenic, or "neoformation" process before or shortly before burial. Other kaolinite, found as infillings of cleat and other fractures, apparently represents further precipitation, or at least, remobilization of the original kaolinite, at a later stage in the coal's burial history. Kaolinite is more abundant, relative to other clay minerals, in sediments intimately associated with present-day peat deposits

in the Snuggedy Swamp, South Carolina, U.S.A. Staub & Cohen (1978) suggest that, in this area, the kaolinite has been formed by leaching of the clays beneath the peat due to infiltration of organic acids from above. Renton & Cecil (1979), on the other hand, believe that the kaolinite forms in this and other similar areas by interaction of silica and alumina in the waters of the peat, with the silica and alumina being derived, in turn, from inorganic material released by breakdown of the various plant constituents during the peat accumulation process. Renton & Cecil (1979) also suggest that, if chemical conditions in the peat swamp become more alkaline (e.g. due to a marine incursion) other clay minerals, as well as kaolinite, inay be formed in this way.

lllite Although common in the associated noncoal strata, illite is completely absent, as a discrete mineral constituent, in the oxidation residues of most Australian bituminous coals (Figure 5). The mineral. mostly occurs, with one or more other components, in the form of mixed-layer or interstratified clay minerals (Figure 4b), and is discussed separately in that context below. The small amount of "free" illite that does occur in Australian coals is probably of detrital origin. Its low concentration may simply reflect a low proportion of detrital input to the peat swamps generally, or alternatively indicate that the mineral, in its pure form, is susceptible to alteration, by the swamp waters, to other mineral species. Other coals such as those in parts of South Africa (Gaigher, 1980) or in the Illinois Basin of the U.S.A. (Ward, 1977) are quite rich in illite, and this may be due, in these areas, to either a neo-formation process under more marine conditions (Renton & Cecil, 1979) or simply a different mineral assemblage in the detritus supplied generally to the coal basin.

Montmorillonite and Mixed-layer Clay Minerals Montmorillonite and mixed-layer clay minerals containing montmorillonite repre-

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sent the principal clay minerals, other than kaolinite, in Australian bituminous coals. Relatively pure montmorillonite, without any mixed-layer effects, is characterized, in oriented aggregate X-ray diffraction, by a basal J00l) crystallographic "d" spacing of 17,1 A on glycol saturation, collapsing to 10 A on heating. Such material is found in many of the coals from the Newcastle Coal Measures of the Sydney Basin (Figure 4a), and in several coals from other areas, such as some seams in the Theodore district of Central Queensland. More commonly, however, the nonkaolinite clay is a mixed-layer mineral, made up of regular or irregular interstratifications, in varying proportions, of illite, montmorillonite and chlorite. The regularly interstratified material is characterized by an integral series of "d" spacings, with diffraction peaks showing spacings usually between 22° and 24 A for air-dried samples and 26 to 28 A for glycolsaturated material. The regular structure is • retained in some samples after heating (Figure 4d), but in others the material collapses to give a broad diffraction peak between 10 and 11 A (Figure 4c). The irregular mixed-layer minerals, by contrast, generally give only a single, broad diffraction peak at around 12 A air-dried and 15 A under glycol saturation0 collapsing to a value between 10 and 11 A on heating. Mixed-layer clay minerals with these characteristics are also a common constituent of the lutites in the Permian coalbearing sequences of the Sydney Basin (Loughnan & Craig, 1961; Hamilton, 1968), where they occur as lath-like particles mostly less than 1 µm in size. Though possibly modified to some extent by interaction with the peat-forming environment, those in the coals are therefore also most likely to be of detrital origin. Montmorillonite is also common in the non-coal strata of the Newcastle Coal Measures- (Loughnan, 1966), where it is generally regarded as being of pyroclastic origin. Although such minerals may also be formed by authigenic processes in organicrich soils (William & others, 1966), the occurrence of montmorillonite in coals of the northern Sydney Basin, and probably those

ROOF

COAL

12 . 2

FLOOR

10 .0 17 .0

7 .1

7. 1

7.1

10 .0

20 C u K-" R a d i a t i o n

Degrees 29

Figure 5: Oriented aggregate x-ray diffractograms for clay fraction of roof, floor and coal seam, Victoria Tunnel seam, Sydney Basin, N.S.W. For each sample: a)-air dried b)-glycol saturated c)-heated to 400°C "d" spacings indicated in Angstrom units.

of other areas as well, is thought to reflect volcaniclastic contamination of the detritus supplied to the region generally.

Chlorite Ward (1978) describes the occurrence of iron-rich chlorite in the mineral matter of several coals of semi-anthracitic rank from the Baralaba area of Central Queensland (Figure 4e). The presence of chlorite in these coals is significant, since the mineral is generally destroyed in the acid conditions expected of the peat. Indeed, comparative studies show that, chlorite may be present in the roof and/or floor strata of some

seams, but completely absent from the mineral residue of the coal itself (Figure 5). Kisch (1968) has noted that chlorite is present in the sediments associated with the coal in the Baralaba area, but not in the strata associated with the lower rank seams elsewhere in the region. This suggests that the chlorite is possibly of metamorphic origin, derived from the kaolinite and/or the expandible-lattice clay minerals in a similar way to that described by authors such as . Weaver & Beck (1971) in other deeply buried sediments. However, Rao & Gluskoter (1973) and Ward (1977) have also reported chlorite in the relatively low rank coals of the Illinois Basin, and thus a detrital origin is also possible, at least in some areas of coal-bearing successions.

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SIGNIFICANCE OF MINERALS IN COAL The minerals and other inorganic constituents of coal act as dilutants, reducing the proportion of hydrocarbon compounds and hence the amount of heat energy or other useful products available from each saleable tonne. Most of the minerals, however, also have the potential to react in some way, or at least to undergo some change in composition or crystal structure when the coal is actually used. Such changes can take place during coal preparation or storage, as well as in the course of combustion, coking, gasification or liquefaction operations. COAL MINING, PREPARATION AND STORAGE Minerals can be associated with a number of problems in the mining, preparation and storage of coal and coal mine products. Accumulations of finely inteigrown quartz and dolomite or siderite, for example, commonly found as lenticles, bands or concretionary masses in coal seams, can give rise to undue abrasion of the cutting surfaces on mining machinery, particularly in underground mines, resulting in additional maintenance costs for the coal-winning operation. Such masses may also provide problems in the subsequent coal crushing operation. Oxidation of pyrite, particularly that present in framboidal form, represents the principal source of acid pollution in water from coal mines and stock piles. The formation of this acid can result in considerable costs due to corrosion of equipment in the mine and preparation plant, as well as problems with discharge of the acidified water into the environment at the project site. The dust generated in the course of coal mining and handling consists not only of organic particles, but also of mineral matter, either as discrete fragments or incorporated with the coal macerals. Both coal dust and quartz particles have long been known to cause pneumoconiosis of workers in the coal industry, with quartz having particularly severe physiological effects (George, 1953). Data on the effects of other minerals are not as readily available, but Martin & others (1977) report that kaolinite, illite and mica, at least, have a

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greater fibrogenic capacity than mineralfree coal dust. Since much of the dust in mining operations is produced from the seam itself, the nature of the minerals present must have some influence on the hazards that can result. Less directly, the minerals in coal may be related to the occurrence of gas outbursts in underground mines. Botz & Hart (1983) suggest that ascending waters may flush out kaolinite from the pores in the coal, particularly those of the inertinite macerals in tectonically disturbed zones, and re-deposit it in the pores and fractures of the overlying roof strata. This process increases the capacity of the seam to contain highpressure gas, and at the same time reduces the strength of the coal itself. Monitoring the occurrence of kaolinite in certain bands of the seam may therefore provide a basis for the prediction of faults and potential outburst zones. Clay minerals, particularly swelling clays such as montmorillonite, can also be significant in coal preparation processes. Many such clays slake on immersion in water, and, if present in the coal or its intra-seam bands, can generate an undue proportion of fines in different partc, of the coal cleaning circuit. Fracturing associated with drying out of these clays can produce further fines in coal stockpiles or refuse emplacements. In some cases, the clay minerals are highly dispersive, and readily form suspensions of fine solid particles in water. The suspended clay can affect the density of separating media .in some of the cleaning processes, or form a high-ash coating on the otherwise clean coal . particles. Such clays are also difficult to remove from suspension using settling equipment such as thickeners, and problems can also arise with recycling of water to the preparation plant or discharge of plant water to the surrounding environment. The presence of such materials can be identified by tests on crushed coal fractions (Berkovitch & others , 1959; Grano & Whitmore, 1982). Indeed, tests of this type are typically incorporated into assessments of seam washability characteristics (Standards Association of Australia, 1979).

The minerals in coal and associated strata also affect the composition of the refuse derived from preparation plants (Ward, 1980b) and the nature of the leachate from exposed emplacements of refuse materials. Swelling clays, for example, may be a cause of mechancial instability in stockpiles and refuse dumps, while pyrite is typically associated with acid water generation. Mineral rich refuse components, however, can also represent potential sources of valuable by-products. Cobb & others (1979) describe a significant zinc resource in refuse derived from a coal rich in sphalerite, while Anderson (1980) discusses the potential use of kaolinite in coal refuse as an alumina source. Other authors, such as Gilbert & others (1958), Tanfield (1971) and Waters (1977) describe the use of claybearing coal refuse for brick manufacture and various types of construction materials.

MINERAL BERAVIOUR IN COAL COMBUSTION Even before the coal is burned, in installations such as modern power stations, it is ground _or pulverized to particles around 75,im in size. Large masses of hard minerals, such as quartz (H = 7) or possibly pyrite (H = 6 to 6.5), can give rise to excessive abrasion or wear on the grinding surfaces (Coleman & others, 1977); Sligar, 1979), resulting in additional costs due to reduced life of mill components. Quartz, though not necessarily in coarse particles, is common in many Australian coal seams. Most of the minerals in coal undergo significant chemical changes at the temperatures associated with the combustion of coal samples. Kaolinite, for example, dehydrates at about 450°C, pyrite oxidizes to material such as haematite at 500°C while calcite breaks down to calcium oxide at around 800°C (Figure 6). The products liberated by these reactions add to the proportion of volatile matter recorded in proximate analysis (Scholz, 1980) leaving only the solid oxide remnants to form the coal's ash residue. A coal with 10% mineral matter, for example, will have an ash yield in proximate analysis also of 10% if the mineral matter consists entirely of quartz, but will only yield 5.6% ash if the mineral

matter is made up entirely of calcite. The changes that take place in coal mineral assemblages at different temperatures have been discussed by many authors, including O'Gorman & Walker (1973), Mitchell & Gluskoter (1976), Nankervis & Furlong (1980) and Mraw & others (1983). These changes, of course, also include interactions with the inorganic components of the coal's organic matter. New mineral phases formed under different conditions include mullite (AleS,2O13), cristobalite (SiO2), haematite, magnetite and anhydrite, as well as the calcium silicates gehlenite (Ca2AbSiO1 ), akermanite (Ca2MgSi2O1 ), bredigite (Ca 2SiO4 ) and anorthite (CaAl2Si2Oa). A range of sodium silicates may also be formed in some cases, while, if the temperature is high enough, at least some of the minerals may fuse to form a non-crystalline glass. The reactions that form these minerals are also often associated with the release of volatile inorganic materials. They interact to control processes such as slagging or fu. sion of the coal ash and deposition of solid condensates (fouling) on exposed boiler surfaces. A comprehensive review of these and other factors in the combustion of Australian coals is given in a series of papers compiled by Stewart & Wall (1979). Most Australian bituminous coals are dominated by kaolinite in their mineral assemblage, and, since kaolinite does not fuse until temperatures of around 1700°C are attained (Grim, 1968), the resultant ash is generally quite refractory under furnace operating conditions. Coals with a subor-

Kaolinite AliS½Os(Om • AJ..i03 + 2SiO2 + 2~0 Pyrite 4Fe8i + 1102 • 2Fe,zO3 + 8SO2 Calcite CaCO3 • CaO + CO2

Figure 6: Mineral reactions in coal combustion.

103

dinate amount of mixed-layer clay also appear to have a refractory ash, but those containing abundant montmorillonite, chlorite or degraded illite generally has ash fusion (deformation) temperatures, as determined in the laboratory, between 1000 and 1300°C (Ward, 1978) .. Significant proportions of carbonate minerals, pyrite, sulphates or iron oxides in the coal can also produce low ash fusion temperatures, even though the associated clay may be 9uite refractory in nature. The interplay of processes that control ash behaviour is very complex, and depends on factors such as the atmosphere, temperature and coal chemistry involved. With pulverized fuel, it also depends on the distribution of minerals and other inorganic constituents in the coal, and the opportunities that the different components have to react with each other in the combustion chamber. Laboratory investigations are typically carried out on mineral matter isolated by plasma oxidation, or ash produced at standard temperatures such as 815°C, with the ash or mineral particles re-heated all together in a bulk mass. Under pulverized fuel conditions, on the other hand, the ash is formed by rapid heating, once only, of coal and mineral particles which may or may not make contact with each other before combustion is complete. As indicated by Mraw & others (1983), an inadequate appreciation of these different processes can give rise to unpredictable behaviour of coal ash materials.

MINERALS IN COKING COALS Although traditionally regarded as inert dilutants in coke manufacture (Stach & others, 1975; Bateman & Coulter, 1977), the minerals in coal would be expected to undergo changes, at the temperatures reached in industrial carbonization processes, similar to some of the reactions that take place in combustion operations. Mineralogical reactions in the environment of coke formation, however, are very poorly documented. The total proportion of mineral matter is the main factory, other than coal rank and type, that determines the amount of usable coke, per tonne of coal, obtainable from a

104

given carbonization process. Callcott (1975) gives a simple formula to predict too specific yield of total carbon solids, for Australian coals, based on proximate analysis data, but notes that the prediction may be erroneous if unusual mineral assemblages are present. The mineral matter in a coking coal is also of great significance to the performance of the coke in the blast furnace. Minerals containing sulphur (e.g. pyrite) or phosphorus (e.g. apatite), for example, provide contaminants that are transferred through the coke to the iron and steel products, and the coal is not acceptable if such minerals are present in significant amounts. The composition of the mineral matter in the coke derived from the coal is also a factor in determining the proportions of other constituents, such as limestone, needed in the blast furnace charge to prod uce an appropriate slag. Kaolinite-rich coals, in particular, tend to produce a coke ash with a high alumina content, which, according to Callcott (1975), makes slagging operations more costly. Brown & others (1964) indicate that the addition of a small amount of montmorillonite or other fine mineral material to the high volatile coking coals from the Newcastle area, N.S.W ., leads to an increase in the strength or stability index of the coke produced. Callcott (1975) explains this phenomenon by suggesting that the montmorillonite increases the rate at which gases escape from the plastic layer, and hence reduces the tendency for fissures etc. to develop. An alternative explanation, of course, may lie in the strengthening of the coke's pore walls by fused and hardened montmorillonite derivatives. The same phenomenon is not observed, however, if montmorillonite is added to higher rank coals, while an excess of montmorillonite, even in high volatile feedstocks, causes a serious deterioration in coke strength properties. Interaction of minerals from the original coal can also take place within the coke as it is used in the various metallurgical processes. Coin & others (1982) describe some of these reactions, particularly the interaction between quartz and certain coke

macerals to form silicon carbide deposits. A full understanding of these reactions is of great significance in predicting and controlling processes such as coke degradation in blast furnace operation.

GASIFICATION AND LIQUEFACTION As well as being simple dilutants to the organic matter, minerals and other inorganic constituents can also react, in various ways, during coal gasification and liquefaction processes. These processes tend to take place at lower temperatures than coal combustion, with more reducing conditions and longer residence times (Mraw & others, 1983), and as a result the mineralogical products are often chemically different and better crystallized than the various combustion residues. Fusion, agglomeration and sintering of mineralogical residues can take place during gasification or liquefaction, to an extent depending on factors such as the chemistry of the mineral matter or the degree of particle contact. In some processes, such as the Lurgi gasifier (Cudmore, 1984), the final products should be refactory in nature, while in others they should fuse to form a molten slag. The various particles may also interact, at temperatures well below conventional ash fusion points, to form sintered agglomerates in fluidized-bed reactors (Mraw & others, 1983). An account of the minerals present in solid residues from solvent refining of coal is given by Wakeley & others (1979). Quartz, calcite, rutile, sphalerite and possibly siderite appear to survive the solvent extraction process in an essentially unaltered state. The clay minerals, however, undergo fragmentation and probably dehydration, while pyrite (FeS2) is reduced progressively to pyrrhotite (FeS). A range of calcium sulphate minerals is also present in the residues, some perhaps formed by interaction of calcium carbonate minerals (calcite, aragonite and the metastable polymorph vaterite) was precipitated in the reactor by a particular sub-bituminous coal. It is also possible that some of the minerals in coal act as natural catalysts for gasification or liquefaction processes. Hut-

tinger & Krauss (1981) indicate that iron, derived from pyrite and other components of the mineral matter, can accelerate methane formation in hydrogasification processes, while oxides and carbonates of alkalis and alkaline earths can act as sulphur scavengers to promote the iron formation. Mraw & others (1983) summarize the results of several workers who suggest that the yields of liquid products from coal by hydrogenation processes are significantly increased if pyrite is present. This is usually ascribed to some form of catalytic effect, either by the pyrite itself or by the Fe or the H2S produced by pyrite decomposition. Gray (1978), on the other hand, suggests that pyrite and other minerals in the coal act only as internal dilutants, reducing the tendency for the macerals to agglomerate and thus allowing the hydrogen to diffuse and react more completely with the organic matter. M~kherjee & Chowdhury (1976) show that the percentage conversion by hydrogenation, for Assam coals, increases with the mineral matter content. However, the degree of conversion also depends on the type of mineral matter present, with a high proportion of iron or pyritic sulphur, as well as a high proportion of kaolinite, being associated with particularly high conversion values. Rottendorf & Wilson (1980), on the other hand, found that hydrogenation of a Hunter Valley (Liddell) coal, with a low natural pyrite content, gave results that were apparently independent of the mineral matter.

CONCLUSIONS Despite the diverse and extensive studies that have been carried out on the organic components, only a limited amount of knowledge has been built up, over the years, on the nature, origin and significance of the mineral constituents present in Australian coal seam. Such investigations reg uire traditional chemical and petrographic techniques to be supplemented by X-ray diffraction and other methods of mineralogical study, combined with isolation of the minerals from the coal by processes such as oxygen-plasma ashing.

105

Australian bituminous coals contain mineral assemblages that are quite different to those in the associated non-coal rock strata. They are dominated, for the most part, by well-crystallized kaolinite, with quartz, siderite, calcite, dolomite and montmorillonite or mixed-layer clay minerals as the other principal constituents. Minerals such as pyrite, feldspar, apatite and goyazite are also present in some seams. Part of the mineral fraction is undoubtedly detrital, washed or blown into the peat swamp as part of the regional sedimentation pattern. Other minerals, however, such as the pyrite, siderite, apatite and probably the kaolinite, are products of chemical or biochemical processes active at the coal's deposition site. A few minerals, particularly the calcite and dolomite, as well, perhaps, as the clay mineral chlorite, owe their origin to effects associated with rank advance, while others, such as gypsum, may have been deposited by groundwater activity. The minerals and other inorganic constituents of coal play a significant part in

determining the behaviour of the coal during mining, and in the course of the various combustion, carbonization, gasification and liquefaction processes. Mineral interactions in coal utilization are often quite .different from those that occur in laboratory tests, due partly to variations in the opportunity for particle-to-particle interaction. The role of minerals in processes ranging from coal mining to coal liquefaction is not always clear, and further research, specifically on Australian coals, is most definitely warranted. Along with other tests and analyses, a systematic study of the nature and distribution of mineral contaminants in the coals of a particular areas, such as an individual colliery holding, may be of great benefit as part of the mine planning process. Such a study would perhaps provide a. more rational basis for understanding and predicting quality trends, and allow particular types of material to be better identified for blending or other specific purposes. Through use of its multi-disciplinary technical expertise, the geological profession has much to offer the coal industry in this regard.

REFERENCES Allen, R.M. & Vander Sande, J.B., 1984: Analysis of sub-micron mineral matter in coal via scanning transmission electron microscopy. Fuel, 63, 24-29. American Society for Testing and Materials, 1984: "Annual Book of ASTM Standards: Volume 05.05, Gaseous Fuels - Coal and Coke". Amer.Sac. Testing & Materuils, Philadelphia. Anderson, L., 1980: The Pechiney H+ process and New South Wales coal washery refuse as a source of alumina. Dept. Min. Res. , N.S.W., Chem. Lab., Unpublished Report. Andrejko, M.J., Raymond, R. & Cohen, A.D., 1983: Biogenic silica in peat: possible source for chertification in lignites; In Eds: Raymond R. & Andrejko M .J. Mineral Matter in Peat, Los Alamos National Laboratory, Report LA9907-OBES, 25-37. Balme, B.E. & Brooks, J.D. , 1953: Kaolinite petrifications in a New South Wales Permian coal seam. Aust. J . Sci., 16 (2), 65. Bateman, K.W. & Coulter, W.N., 1977: Commercial evaluation of coking coal from borehole data. Proc. Symp. on Coal Borehole Evaluation, Australas. Inst. Min . Metall., Brisbane, 134-145.

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Beeston, J .W., 1981: Wood structures preserved in high-rank bituminous and semi-anthracitic coal, central Queensland. Pa/,aeobotanist, 28-29, 155-160. Berkovitch, I. , Mankerman, M., & Potter, N.M., 1959: The shale breakdown problem in coal washing: Part 1 - Assessing the breakdown of shales in water. J. Inst. Fuel 32, 579-589. Bohor, B.F. & Gluskoter, H.J., 1973: Boron in illite as an indicator of palaeosalinity of Illinois coals. J . Sedim. Petrol., 43(4), 945-956. Botz, R.W. & Hart, G.H., 1983: Mineralogical, petrographical and geochemical investigations of outbursting in Australia coal mines. Proc. Austra/,as. Inst. Min. Metall. 286, 41-49. Britten, R.A. , 1979: Coal in the seam. In McC. Stewart I. & Wall T.F. Eds: Pulverized Coal Firing the effects of mineral matter Dept. Chem. Eng., Univ . of Newcastle, NSW, pp Ll.l-Ll.11. Brown, H.R. , Clark, M.C. & Durie, R.A. , 1959: Characteristics of the ashes from Australian coals. CSIRO Division of Coal R esearch Tech. Comm. 33.

Brown, H.R., Durie, R.A. & Schafer, H.N.S., 1959: The inorganic constituents of Australian coals. I the direct determination of the total mineralmatter•content. Fuel 38, 295-308. Brown, H.R. & Swaine, D.J ., 1864 : Inorganic constituents of Australian coals. J . Inst. Fuel 37, 422-440. Brown, N.A., Belcher, C.B. & Calicott, T.G., 1964: Composition, determination, and effects of mineral matter in N.S.W. coke-making coals. Proc. Symp. on Inorganic Constituents of Fuel, Inst. Fuel (Australian Membership), 201-214. Calicott, T.G., 1975: Coking for the Australian steel industry. In Cook, A.C. Ed. Australas. Inst. Min. Metall., Wollongong, 232-243 . Cobb, J .C., Masters, J.M., Treworgy, C.G. & Helfinstine, R.J. , 1979: Abundance and recovery of sphalerite and fine coal from mine waste in Illinois. Illinois State Geol. Suru. ., Illinois Minerals Note 71 . Cook, A.C., 1962: Fluorapatite petrifications in a Queensland coal. Aust. J . Sci. 25, 94 . Coin, C.D.A., Gill, W.W. & Hart, A.T., 1982: Blast furnace coke reactions. BHP Tech. Bull. 26(1), 31-33. Coleman, J .R. , Bosio, M. & Lindner, E., 1977: South Australian coals and their troublesome impurities. Proc. Symp. on Coal Borehold E valuation , Australias Inst. Min. Metal., Brisbane, 159-169. Corcoran, J ., 1979: Mineral matter in Australian steaming coals·- a survey. In McC. Stewart I. & Wall T.F. Eds: Pulverized Fuel Fir;ing - the effects of mineral matter Dept. Chem. Eng. , Univ. of Newcastle, NSW. Cudmore, J .F., 1984 : Coal utilization. In Ward C.R. Ed: Coal Geology and Coal Technology Blackwells, Melbourne, 113-150. Davis, A., 1984 : Coal petrology and petrographic analysis: In Ward C.R. Ed: Coal Geology and Coal Technology Blackwells, Melbourne, 74-112. David A., Russell, S.J., Rimmer, S.M. & Yeakel, J .D., 1984: Some genetic implications of silica and aluminosilicates in peat and coal. Int. J . Coal Geol. 3, 293-314. Day, J.C., Doolan, K.J. & Jones, R.H., 1982: Improvements in the evaluation and characterization of coal. BHP Tech. Bull. 26(1). 14-17. Dixon, K. , Skipsey, E. & Watts, K., 1964 : The distribution and composition of inorganic matter in British coals; Part 1, Initial study of seams from the East Midlands Division of the National Coal Board. Inst. Fuel, J . Nov., 485-493. Doolan, K.J., Mills, J .C. & Belcher, C.B., 1979: The analysis and characterization of mineral matter and ash. In Stewart I.McC. & Wall T.F. Eds: Pulverized Coal Firing - the effects of mineral matter Dept. Chem. Eng., Univ. of Newcastle, N.S.W., L3.1-L3.ll. Durie, R.A . & Swaine, D.J. , 1971: Inorganic constituents in coal. Coal Res. in CSIRO 45, 9-19.

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Hicks, D. and Nagelschmidt, G., 1943: The chemical and x-ray diffraction analysis of the roof and clod from some South Wales seams and of the mineral matter in the coal. Med. Res. Council Spee. Rep. 244, 153-185. Hunt, J .W., 1983: Ash content and composition of the Perrnian coals; in "Permian Coals of Eastern Australia", unpubl. End of Grant Report, National Energy Research Development and Demonstration Program, Canberra. Huttinger, K.J. & Krauss, W., 1981: Catalytic activity of coal minerals in hydrogasification of coal. Fuel 60, 93-102. International Committee for Coal Petrology, 1963: "International Handbook of Coal Petrography", 2nd Edition; Centre National de Recherche Scientifique, Paris. Jones, R.H., 1970: A bore core radiography unit; Journal of Physics, E: Scientific Instruments 3 363-366. Kemezys, M. & Taylor, G.H., 1964: Occurrence and distribution of minerals in some Australian coals. J. Inst. Fuel 37, 389-397. Keller, W.D., 1968: Flint clay and a flint clay facies. Cln.y and Cln.y Minerals 16, 113-128. King, J .G. , Maries, M.B. & Crossley, H.E., 1936: Formulas for the calculation of coal analyses to a basis of coal substance free from mineral matter. J . Soc. Chem. Ind. 55, 277-281. Kisch, H.J ., 1968: Coal rank and lowest-grade regional metamorphism in the southern Bowen Basin, Queensland, Australia. Geol. en Mijnbouw 47(1), 28-36. Kiss, L.T. & King, T.N., 1977; The expression of results of coal analysis: the case for brown coals. Fuel 56, 340-341. Kiss, L.T. & King, T.N., 1979: Reporting of low-rank coal analysis - the distinction between minerals and inorganics. Fuel 58, 547-549. Kuhn, J.K. , Harfst, W.F. , & Shimp, N.F., 1975: X-ray fluorescence analysis of whole coal. Advances in Chemistry Series No. 141, Amer. Chem. Soc., Washington D.C. Lawrence, L.J., Warne, S.St.J. , & Booker, M., 1960: Millerite in the Bulli coal seam. Aust. J. Sci. 23, 87-88. Loughnan, F.C., 1966: A competitive study of the Newcastle and Illawarra Coal Measure sediments of the Sydney Basin, N.S.W . J . Sedim. Petrol. 36(4), 1016-1025. Loughnan, F.C., 1971 : Refractory flint clays of the Sydney Basin. J . Aust. Ceram. Soc. 7(2), 34-43. Loughnan, F.C., 1978: Flint Clays, tonsteins and the kaolinite clayrock facies. Cln.y Minerals 13, 387-400. Loughnan, F.C. & Craig, D.C., 1961: A complex interstratified clay mineral in the pottery shale from Marrangaroo, N.S.W. Aust. J . Sci 23(1)), 379. Loughnan, F.C. & Ward, C.R. , 1971: Pyrophyllitebearing flint clay from Cambewarra Mountain, Sydney Basin, N.S.W. Cln.y Minerals Bulletin, 9, 83-94 . Mackowsky, M.-Th., 1968: Mineral matter in coal. In Murchison D.G. & Westoll T.S. Eds: Coal and Coal-bearing Strata, Oliver and Boyd, London, 309-321.

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Price, N.B. & Duff, P.McL.D., 1969: Mineralogy and chemistry of tonsteins from Carboniferous sequences of Great Britain. Sedimentology 13, 45-69. Radmacher, W. & Mohrhauer, P., 1955: The direct determination of the mineral matter content of coal. Brennst. Chemie 36. 236. Rao, C.P. & Gluskoter, H.J. , 1973: Occurrence and distribution of minerals in Illinois coals. Ill. State Geol. Suru. , Gire. 476. Raymond, R. & Andrejko, M.J. (Eds), 1983: Mineral Matter in Peat: its occurrence, form and distribution. Los Alamos National Laboratory, Publication No. LA-9907-OBES, Los Alamos, New Mexico. Raymond, R. & Gooley, R., 1979: Electron probe microanalyzer in coal research. In Karr G. Ed: Analytical Methods for Coal and Coal Products, Vol. ill, Academic Press, 337-356. Rees, O.W. , 1966: Chemistry, uses and limitations of coal analyses. Illinois State Geol. Surv. , Rept. Inv. 220. Rekus, A.F. & Haberkorn, A.R. , 1966: Identification of minerals in single particles of coal by the x-ray powder method. J . Inst. Fuel 39, 474-477. Renton, J .J . & Cecil, C.B. , 1979: The origin of mineral matter in coal. In Donaldson A.C. & others, Eds: Carboniferous Short Course and Guidebook, Eastern Sectional Meeting, Am. Ass. Petrol. Geol. Rottendorf, H. & Wilson, M.A., 1980: Effects of in-situ mineral matter and a nickel-molybdenum catalyst on hydrogenation of Liddell coal, Fuel 59, 175-180. Russell, S.J. & Rimmer, S.M., 1979: Analysis of mineral matter in coal, coal gasification ash, and coal liquefaction residues by scanning electron microscopy and x-ray diffraction. In Karr C. Ed: Analy tical Methods for Coal and Coal Products, Volume III, Academic Press, New York, 133-162. Scheihing, M.H. & Gluskoter, H.J., 1978: Interstitial networks of kaolinite within pyrite framboids in the Meigs Creek Coal of Ohio. J . Sedim. Petrol. 48(3) , 723-732 . Scholz, A., 1980: Correlation between the content of volatile matter and mineral matter in hard coals. Fuel 59, 197-200. Shibaoka, M., 1971: A geochemical study of the inorganic constituents of the Bowen Basin and other Queensland coals. Proc. Second Bowen Basin Symp. Geol. Surv. Qld. Report 62. Shibaoka, M. , 1972: Silica/alumina ratios of the ashes from some Australian coals. Fuel 51, 278-283. Shieh, Y.-N. & Suter, T.G., 1979: Formation conditions of authigenic kaolinite and calcite in coals by stable isotope determinations. Clays and Clay Minerals 27(2), 154-156. Slansky, J .M., 1984: Chemical composition of mineral matter in coals and their sedimentary environment. Abstr. 18th Symp. on Advances in the Sydney Basin Dept. Geol. , Univ. of Newcastle. N.S.W. , 85-90. Sligar, N.J ., 1979: Factors contributing to abrasive wea r from coal. In Stewart I.McC. & Wall T.F. Eds: Pulverized Coal Firing - the effects of

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Warne, S.St.J .. 1964: Identification and evaluation of minerals in coal by differential thermal analysis. --;J. Inst. Fuel 38, 207-217. Warne. S.St.J. , 1975: An improved differential thermal analysis method for the identification and evaluation of calcite, dolomite and ankeri te in coal. J . Inst. Fuel September, 142-145. Waters. P.L.. 1977: Pilot plant aims at waste red uction. Mining Review- June. 4-5. Weaver. C.E.. & Beck. K.C.. 1971: Clay-water diagenesis during burial: how mud becomes gneiss. Geol. Soc. Amer. Spee. Paper 134. Westermann. M., 1983: A study of the mineral matter contained in the coals and associated stra ta of the Illawa rra Coa l Meas ures, Western Coalfield. N.S.W. Unpubl. B.App.Sc. thesis, N.S.W. Institute of Technology.

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Williams. E.G. & Keith, .L., 1963: Relationship between sulphur in coals and the occurrence of marine roof beds. Econ. Geol. 58, 720-729. • Willman, H.B., Glass. H.D. & Frye. J .C., 1966: Mineralogy of glacial tills and their weathering profiles in Illinois. Illinois State Geol. Suru .. Circul.ar 400.

C.R. WARD, Department of Applied Geology, University of New South Wales, P.O. Box 1, Kensington, 2033.

BOOK REVIEWS

'Coal Geology and Coal Technology' edited by Colin R. Ward, Blackwell Scientific Publications (Australia) Pty Ltd. 107 Barry Street, Carlton, Victoria, Australia, 3053, recommended retail price A$39.95.

'Coal Geology and Coal Technology' sets out to be treatise on coal. It is edited by an Australian coal geologist, but includes an international panel of chapter contributors. The copy is an easy to handle, soft cover edition with quite readible text, although some might find the print size a little small. Illustrations are not over-abundant, but in general are sufficient to complement the text, and generally clear and easy to follow. All are in black and white. Many are referred to other publications. The editor has made a considerable contribution to the text, and as such, the volume has a high level of conformity. The contents are both an attempt to cover the established knowledge of coal geology and technology as well as to bring the reader up to date with the industry in the 1980's. With regards to the latter, the chapter with the extraordinarily understated title of 'Introduction' presents an overview of coal mining and production statistics for most of the coal mining countries of the world (sadly, but understandably excluding the USSR and China). Although destined to become dated, this chapter is a most useful and well presented source of data, and one which will undoubtedly reach a much wider audience than coal geologists and engineers. The treatment of the geological facets of coal includi.'lg petrology and sedimentology are reasonably well covered, yet the Australian · coal geologist may be disappointed not to see more examples from Australia, for which there still remains a need. However, the basics are still there, and the reader can use the bibliography for

further investigation of current literature on such recent topics as fluorescence in coal petrography, and coal measure deposition in Australia. Nonetheless the chapter on coal measure sedimentation is a must for anyone entering the field of coal exploration. The technical facts of coal are not only handled well and with great clarity, but probably form one of the better treatments of the subject available. All of the information on coal analysis, classification and utilization required by a practising coal geologist is available in a readily accessible form and are a must for coal geology students, as are the chapters in coal mining geology and coal and the environment. This, of course, is the major relevance of the book. Colin Ward is know chiefly for his background as a lecturer at the New South Wales Institute of Technology and presently at the University of New South Wales, and this book is definitely for students. As an up to date text book on coal for students its production is not before time. Australian students could have benefited from greater Australian input, but at least this text book has a considerable proportion. The aspects of technology are much more than one normally finds in a text book on coal, and this will also be greeted favourably by those lecturing in the subject. The impact of this book on future generations of students will remain to be seen, but it may be possible to monitor, if in future years geologists are found to be spelling 'autochthonous' and 'allochthonous' incorrectly, as unfortunately occurs in bold print on page 159. For students and those who wish to reeducate themselves, the book is recommended. If for no other reason, because it is dedicated to Ken Mosher. JAMES W. BEESTON

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'Coal In Queensland - The Late Nineteenth Century, 1875-1900', by R.L. Whitmore, University of Queensland Press, Box 42, St Lucia, 1985, 338pp. Price: $35.00.

In 1981 Professor Whitmore published "Coal In Queensland: The First Fifty Years", an historical account of coal mining developments and practice in Queensland to 1875. Following this widely acclaimed work, Whitmore's second study of coal mining history in this State has been keenly awaited by those with an interest in mining history. The wait has indeed been wor.. thwhile. First impressions of the book are excellent: handsomely presented with an attractive dust jacket, hard cover binding, and printed on good quality, low gloss stock, it would make an appealing addition to any library. The typeface is crisp and clear, and the wide outer margins of the page result in a format which is easy to read and looks pleasantly uncluttered. The work is amply illustrated with 81 black and white plates and 36 line diagrams and maps. The opening chapter describes briefly the economic, political and industrial life of Queensland during the last quarter of the nineteenth century, and effectively creates a social backdrop for the later discussions of mining history. The following chapter traces the geological exploration of the State's coal-bearing areas, not only for the period which is the principal subject of the book, but for the entire nineteenth century. The geolocial picture is developed by considering the contribution of each worker, the interplay of ideas, and the changing perceptions through which geological thought evolved. This is a fine chapter, containing vivid descriptions of many of the famous pioneers of Queensland geology, while at the same time developing a geological framework for each of the individual coalfields described in the ensuing chapters. Brief discussion is also given of the exploratory equipment in use at the time. The two chapters which follow deal with the legislation under which coal mining was practiced in the late nineteenth century,

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and the industrial relations climate which prevailed at the time. The relationship between the coal mining industry and the broader social development of the State is thus established. The main body of the book traces the development of coal mining in various areas. The Bundamba Field and the North Ipswich Field are considered, appropriately in view of their relative following chapters, which deal with the areas of the east and west of Ipswich, the Burrum Field, and Central and Northern Queensland are less expansive, but again the weight given to each is generally appropriate to its overall importance. For some source of historical detail appears to show through, while areas such as Blair Athol receive descriptions which are slightly lacking in depth. Such, however, is in the nature of history: often the preservation of information is imcomplete, and a certain patchiness of detail is thus almost inevitable. The final chapter deals with the nineteenth century miner and his technology, and gives brief but worthwhile descriptions of the miners and their backgrounds, their methods and tools of exploration, mine design, mining equipment, and the coal preparation techniques employed at the time. Sources of information are carefully documented throughout, with detailed endnotes provided after each chapter. A selected bibliography is a useful feature for the reader who is hungry for further information. A reasonably comprehensive index is also included. In summary, the book represents a most significant contribution to the literature on Australian mining hi3tory . It is authoritative, and combines a wealth of detail with an easy, lucid style which makes it a pleasure to read. The thoroughness of research and quality of presentation are even better than was the case for Whitmore's first book, and I can only look forward to his next with the keenest of anticipation. PAUL E. BALFE