Issuu

REGISTERED FOR POSTING AS A PUBLICATION - CATEGOR Y ( 8 )

COAL GEOLOGY JOURNAL OF THE COAL GEOLOGY GROUP OF THE GEOLOGICAL SOCIETY OF

AUSTRALIA

INCORPORATED

D t s Pt.A"( c. OP'-/ $ lo- O'O

VOLUME PART 4 (139-218)

SURAT-MORETON BASIN SYMPOSIUM SPECIAL EDITION NO. 2

BRISBANE

JUNE

1981

COAL GEOLOGY GROUP OFTHE GEOLOGICAL SOCIETY OF AUSTRALIA INCORPORAT ED

Office Bearers 1978-1979 Surat-Moreton Basin Symposium Sub-committee 1980 Chairman: J. W. Beeston Vice-Chairman : P.A. Rayment Hon. Secretary: W. B. Gould Hon. Treasurer: G . M . Leblang

Hon. Editor: W. L. Hawthorne Geological Survey of Queensland Mineral House, 41 George Street, Brisbane, 4000 Price $ I 0.00 per issue

ISSN O156-4684

REGISTERED FOR POSTING AS A PUBLICATION - CATEGORY ( B)

COAL GEOLOGY JOURNAL OF THE COAL GEOLOGY GROUP OF THE GEOLOGICAL SOCIETY OF AUSTRALIA

INCORPORATED

VOLUME

PART 4 (139-218)

SURAT-MORETON BASIN SYMPOSIUM SPECIAL EDITION NO. 2

CONTENTS OF VOLUME I, PART 4 Page . 139 Acknowledgme nts . . . . . . . 142 Editorial. . . . . . . . . . . 142 . Report Sub-committee Symposium Publications A. H. NUTTER, J. A . THRIFT & G. R. DAY Geology and coal resources of the Millmerran-Too woomba-Warw ick region of Southeast . 143 Queensland . . . . . . . . . . . . . . . . . . . . . G . D. JO ES & R. B. PATRICK Stratigraphy and coal exploration geology of the northeastern Surat Basin. . . . . . 153 J. McLEA -HODGSO & N. H . KEMPTON The Oakey-Dalby region , Darling Downs Coalfield: Stratigraphy and depositional . 165 environments . . . . . . . . . . . . . . . . . . . . BRANDT . A B. A . COXHEAD & B. . 179 otes on the geology of the Taroom coal deposit and possible utilisation of its coal . G. M. LEBLANG, P.A . RAYME T & M . SMYTH . 185 The Austinvale coal deposit---Wand oan . A palaeoenvironm ental analysis DIESSEL K. . F C. & R. E. GUYOT . 197 Petrographic studies on insoluble residues of hydrogenated coals . M. SHIBAOKA, A . J. R. BENNETT & H. ECHIGO . 209 Some characteristics of Wandoan coal in relation to hydrogenation

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EDITORIAL

The seven papers presented in this volume complete the published record of the SuratMoreton Ba in Symposium. In contrast to the seven papers published previously, these papers are all geological in content, and constitute a valuable addition to the published literature on the Jurassic coal resources of southeast Queensland . Exploration for coal in the northern Surat Basin has enabled subdivision of the Walloon Coal Measures in that region , which is recorded here, and it is pleasing to note that this subdivision has provoked discussion, which may result in this subdivision being extended into the Moreton Basin. Another pleasing aspect of the symposium is that many of the companies exploring in the two basins have demonstrated their willingness to publish details of their discoveries. SYMPOSIUM SUB-COMMITTEE REPORT

This edition of Coal Geology marks the conclusion of a two part special eries of selected papers from the Surat-Moreton Basin Symposium held in Toowoomba, 29 to 31 August 1979. The special format adopted for these two editions has been designed to present the various papers to their be t advantage. onetheless, this has incurred increased costs. Their production would not have been possible but for a significant number of donations from Mining and Exploration companies, acknowledgements for which appear in both editions. The underlying philosophy of the Coal Geology Group since its conception has been closer liaison between the three levels of Government, Industry and Academia. It was with this in mind that the Surat-Moreton Basin Symposium was initiated. A quick review of the papers published in these two volumes readily assures us that our hopes were realised , with overwhelming enthusiasm. We have been grateful for the opportunity to produce both the Symposium, and the published proceedings, and sincerely thank all those who were involved.

142

GEOLOGY AND COAL RESOURCES OF THE MILLMERRAN-TOOWOOM BAWARWICK REGION OF SOUTHEAST QUEENSLAND By A. H. Nutter, J. A. Thrift & G . R. Day ABSTRACT

The coal resources of the MillmerranToowoomba-Warwick region are contained in the Walloon Coal Measures, deposited in the Moreton Basin during Middle to Late Jurassic times. The Walloon Coal Measures comprise a sequence of sandstones, siltstones shales carbonaceous mudstones and coal se;ms. Th~ coal seams are banded and commonly contain less than _50% coal. Within the region, the lower section of the coal measures appears to contain all the seams of reasonable thickness while the upper section is characterised by numerous thin seams with no significant coal thicknesses detected to date. Several potentially economic coal deposits, amenable to surface mining, have been located, occurring in structurally sim ple situations. with no major faulting, and dips averaging one to two degrees. The deposits in the western part of the region , near M illmerran, are characterised by one major coal seam ranging between two and nine m in thickness. In contrast, the deposits in the central part of the region , near Pittsworth, contain up to six seams with individual thicknesses from two to fifteen m, and generally exhibit a higher raw ash content than the Millmerran deposits. The banded nature of the coal seams results in a high raw ash content, however, much of the inert material can readily be removed by beneficiation to provide a uniform product. T_he characteristics of the coal- perhydrous, high volatile matter content, high ash fusion temperature , high reactivity and low sulphur- make it highly suitable for power generation and conversion to other energy forms. INTRODUCTION

The presence of coal in the region (Fig. I) was recorded over I00 years ago and small collieries have operated for varying periods in the past in the Tannymorel, Killarney, Warwick, Allora, Clifton, Toowoomba and <Jakey districts. Coal has also been recognised m many of the numerous water bores drilled

within the area, and records of these bores have provided valuable information used in the planning of our exploration work. During the early l 970's Millmerran Coal Pty Ltd undertook exploration within a number of Authorities to Prospect (A to P) on the Darling Downs and located several potential coal deposits. During 1976 a Joint Venture was formed between Millmerran Coal Pty Ltd , Mitsui Iron Ore Development Pty Ltd and Amax Iron Ore Corporation with the aim of further exploring the coal deposits of the area, leading up to development of the resources. At the same time, the Authorities to Prospect were amalgamated to form one Au_thority- A to P 203C. Systematic explo:at1on has been carried out over approximately two-thirds of the area, and a number of potentially economic coal deposits amenable to surface mining have been delineated . Over 75 000 m of drilling have been completed, and exploration is continuing in the so utheast portion of the region. The contents of the paper are based on the results of exploration work carried out by the Jomt Venture Consortium up to June 1979, an? the authors wish to express their apprec1at1on to Millmerran Coal, Mitsui and AMAX for permission to present the paper. A brief description of the regional geology of the area is presented in order to provide a framework within which details 0f the coal resources located in the western and central portions of the A to P may be more readily described. REGIONAL GEOLOGY

Authority to Prospect 203C (Fig. 2) is situated on the western margin of the Moreton Basin, which is separated from the Surat Basin to the west, by the Kumbarilla Ridge. This ridge lies immediately east of Goondiwindi, and runs in a north-northeasterly direction towards Warra, between the Texas Block in the south and the Yarraman Block to the north. Triassic sediments within the Surat and Moreton Basins thin towards this ridge and in some cases pinch out against it, however, 143

, , ,' -- :....'✓

: 151 ~ :.

'~\

I ,

GECIL PL.

L., ~

:A.to P. 203C · ··· ···r · • ........

• • • • • • : :MILLMERRAN

20 °: :

··•··

•· •••• ••••

CJ' TERTIARY Undifferentiated Volcanics D . CRETACEOUS Kumbarilla Beds D ~ASSIC Walloon Coal Measures ~ 0

Marburg Format ion

JURASSIC

c;::J

PRE-JURASSIC Undifferentiated Sediments and Volcanics 5

Fig. I. Loca lity Plan Authority to Prospect 203C.

post-Early Jurassic sediments are laterally continuous across the ridge . Stratigraphic units recognised in the SW portion of the Moreton Basin are hown on Figure 3. In the western part of the Moreton Basin the Texas Beds, of probable Carboniferous age, form the basement rocks on which later sediments were unco nformably deposited. The Texas Beds comprise a meta morphosed and intru ded sequence of in terbedded sediments and volca nics, a nd o utcrop prominentl y about 40 km southeast of Millmerran. Sedimentation within the Mo reto n Basin began in Late T riassic times but it was not until Ea rl y Jurassic times tha t it reached the western area of the basin with the deposition of the Marburg Formatio n. T he Marburg Formatio n crops o ut a nd is present in subcrop margin al to the Texas Beds; it co nsists la rgely of high energy fl uviati le sediments deposited by streams draining the Texas Block. Medium to coarse-grained quartzose to sublabile sand stones form the predominant lithology with 144

subordinate pebble conglomerates, iltstones, mudstones, ironstone, and very minor coal seams. The formation is transitional with the overlying Walloon Coal Measures, the upper boundary being taken as the top of the uppermost pebbly horizon. (Cameron J. B. G.S .Q. Pub 344, 1970) The lateral equivalents of the Marburg Formation in the Surat Basin are the Hutton Sandstone and the Evergreen Formation. T he Wa lloon Coal Measures contain all the coal resources of economic importance in the a rea, and subcrop over much of the region , however, they are poorl y exposed, a nd are known ma inly from boreho le in tersections. T he measures comprise a sequence of (lithic labile) sandstones, siltstones, shale, carbonaceous mudstones, coa l seams and minor limesto nes, deposited in a low energy fluviati le environment. The coal measures are broadly divisible into five units illustrated in Figure 4.

SURAT

f/2

~ ~---..!i:l ILOCK

·~ns\?)?V

V New South Wales

SIMPLIFIED STRUCTURAL SETTING SURAT - MORETON BASIN o- ==so- .... 100==- -200 - km

D WALLOON COAL MEASURES Fig. 2. Simplified Structural Setting, Surat-Mo reton Basin.

I. Lower Transition Unit

The basal unit of the Walloon Coal Measures comprises a non coal bearing sequence 30 to 50 m in thickness. Sediments grade upwards from the coarser sandstones of the Marburg Formation to the finer grained sediments of the coal bearing sequence; the proportion of argillaceous sediments within the sequence also increa es. 2. Lower Coal Bearing Unit This is between 70 and 100 m in thickness and is characterised by mudstones, carbonaceous mudstones, coal seams and sandstones deposited in a low energy paludal and flood plain environment. The Juras ic peat-forming swamps must have experienced repeated flooding during their lifetime, and a high proportion of argillaceous material was introduced. The resultant coal seams are generally thin and very banded, with much splitting and lensing of plies. This unit contains all the coal developments of economic interest located to date

within the area of the A to P. In the western portion of the A to P, three coal deposits have been delineated - Commodore I, Commodore 2 and Lochbar (Fig. I). The principal seam of economic interest in all three deposits is the Commodore Seam which is considered to have been laterally continuous between the deposits. The seam has been removed by erosion north and east of Commodore I and also between Commodore I and Lochbar, and is thin and deteriorated between Commodore I and Commodore 2. Thin lenticular seams named the Top Rider and Bottom Rider occur above and below the seam respecti vely, and are of only localised economic interest. The Felton area is separated from the deposits in the Millmerran region by the present day Condamine River which has substantially eroded the Walloon Coal Measures and made coal seam correlations between Felton and Commodore somewhat tenuous. In the Felton deposits, named Felton East and Felton West (Fig. 1), up to six coal seams have been intersected with a major seam occurring in a similar stratigraphic position to that of the Commodore Seam in the Millmerran area. Three seams above this major seam are of localised economic importance in the Felton area. 3. " Barren" Unit Above the Lower Coal Bearing Unit , there is a more arenaceous zone between I 0 and 70 m in thickness containing only very minor bands of coal. 4. The Upper Coal Bearing Unit This unit is up to 150 m in thickness and represents a further phase of coal formation in the middle to upper Walloon Coal Measures. The coal seams in this zone appear to be thinner and more discontinuous than in the lower zone. Correlation of coal facies is possible over considerable distances, however, individual coal plies appear to be lensoidal in character. Over much of the region this sequence has been eroded and has only been recorded to date in two areas; to the west of Millmerran and to the north of Pittsworth (Fig. I). The upper coal zone appears to be 145

QUATERNARY TERTIARY

JURASSIC TO LOWER CRETACEOUS

uuuuu uuuu uu uuu V Y Y V V V V V V

soil and alluvium

TRANSITION UNIT

(0-100m)

(0-60m)

volcanlcs

( 0-100m)

KUMBARILLA BEDS

(0-600m)

UPPER COAL BEARING UNIT (0-150m)

Middle

to MIDDLE TO UPPER JURASSIC

WALLOON COAL MEASURES (110-430m)

''BARREN • UNIT

(10- 70m)

Upper

Jurassic

LOWER COAL BEARING UNIT (70-100m)

LOWER JURASSIC

MARBURG FORM (0-400m)

TRANSITION UNIT (30-50m)

PALAEOZOIC

TEXAS BEDS Fig. 4. T ypica l Section Walloon Coal Measures.

Fig. 3. Stra tigraphic nit in the Western Part of the Moreton Basin (around Texas Block only).

more consistent to the west of Millmerran, and three banded but correlateable coal seams have been intersected at depth . To the north of Pittsworth, only thin lenticular seams are developed. 5. The Upper Transition Unit This is up to 60 m in thickness and represents a gradational zone from the Walloon Coal Measures to the overlying Kumba rilla Beds. The Walloon Coal Measures are conformably overlain by the Kumbarilla Beds, which are of Late Juras ic to Early Cretaceous age. The Kumbarilla Beds crop on the western margin of the area forming prominent northouth trending strike ridges. The equence is largely of fluviatile origin and consists of fine to medium-grained lithic to quartzose sandstones, with lesse r proportions of well bedded iltstone, mudstone and some conglomerate. The Kumbarilla Bed are the lateral equivalents of the tratigraphic interval Springbok Sa nd stone to Bungil Formation in the Surat Basin. La ter sedimentation in the western Moreton Basin is not preserved and the eroded surface of the Walloon Coal Measures is 146

partially covered by remnants of widespread Tertiary volcanic . The volcanics are thickest in the Main Range a rea near Toowoo mba a nd thin to the west. Remnant basalt caps such as Commodore Peak, Captains Mountain and Mt. Domville occur near Millmerran . Quaternary alluvium and soil blanket much of the area, the thickest developments occurring near the Condamine River, where up to I 00 m of interbedded sands, silts, clays and gravels have been deposited . The sediments are commonly weathered a nd ferruginised to varying degrees and in a few places an ironstone horizon marks the lower boundary. The Me ozoic sediments in the western Moreton Ba in have been warped into a series of gentle folds . On the western margin of the area , sediments dip gently (2 °-3 °) into the Surat Basin while, to the east, the sediments dip gently into the Moreton Ba in. In the centre of the A to P, sediments appear to dip radially away from the Texas Block . No major faulting has been delineated by exploration activities. COAL DEPOSITS O F TH E LOWER COAL BEARING UNIT

Five coal deposits amenable to surface mining have been delineated to date (Fig. I)

_./ . ..._ -~-

'1y· \ t

I ,.-•

- --===

<IOO-

STRUCTURE CONTOUR (5 metre interval)

• -

SUICROP, USE OF COMMODORE SEAM

~ ANTICLINE

I000=----==

=2000=----==

::::::, lOOOrnetres

-+ ---+ ._

SYNCLINE LINE OF CROSS-SECTION

Fig. 5. Commodore I- Structure Contours, Base of Commodore Seam .

containing a total of approximately 1500 million tonnes of measured and indicated (Class I and 2) reserves. In the western area, three deposits have been located in clo e proximity to the township of Millmerran- Commodore I with reserves of 210 million tonnes; Commodore 2 with reserves of 230 million tonnes; and Loch bar with reserves of 40 million tonnes. North

In the central area, two deposits have been defined, situa ted approxim ately 30 km southwest ofToowoomba and 10 km due sout h of Pittsworth. The Felton East deposit contains reserves of 390 million tonnes, and the Felton West deposit 610 million tonnes. The majority of these reserves are available at low stripping ratios and with less than 60 m of overburden . Approximately one third of South

SOX CUT

450m

400m

350m

West

East

SOX CUT

450m

400m ?

SOTTOAI

350m 0

HORIZONTAL

SCALE

1000

2000

3000metres

- -==- -= = - -== VERTICAL EXAGGERATION • 10 , 1

D D -

UNCONSOLIDATED MATERIAL WALLOON COAL MEASURES COAL

Fig. 6. Commodore I- Cross Sections.

147

the area of the A to P remains to be investigated, however, reconnaissance drilling has indicated several other prospective areas worthy of more detailed evaluation . Descriptions of the Commodore I and Felton East deposits are presented to illustrate the main differences and characteristics of the deposits in the Millmerran and Pittsworth a reas. COMMODOR E 1 COAL DEPOSIT

The Commodore I coal deposit is situated approximately 5 km south of the township of M illmerran in undulating farm land (Fig. 1). Over this region , the lower part of the Walloon Coal Measures is present, conformably overlying the Marburg Formation. The regional structural trend is approximately north-south , but, south of Millmerran, transverse folding has produced a shallow eastward extending trough in which the coal seams of the Commodore deposit have been preserved . The deposit is structurally uncomplicated and the dominant feature is a northnortheasterly plunging anticline at the western margin of the trough (Fig. 5). To the west of this anticline, the strata dip westward at 3 to 5 c . To the east, is the broad east-west trending trough which has been gently folded into a number of subordinate, sub-parallel

LEGEND ,....,.,. bou,d.,.y __,. A~O- ltructu,. _ , 1• - -1

........--- anticlne ~ ayncline

line of

- - crosa-section

Scale

4km

Fig. 7. Felton East- Structure Contours. Base of MW Seam.

148

synclines and anticlines (Figs. 5 and 6). Dips in the deposit are generally less than 3 °. Three coal seams are recognised in the deposit. In ascending stratigraphic order, they are the Bottom Rider, Commodore Seam and Top Rider (Fig. 6) . The Commodore Seam is economically the most important, however, in some areas the Top Rider attains a thickness of greater than I m and in those zones it could possibly be recovered during surface mining operations. The Bottom Rider occurs about 50 m above the base of the Walloon Coal Measures. It is thin but persistent, and has an average thickness of0.5 m with local developments up to 0.9 m. The seam is separated from the overlying Commodore Seam by an average of 3 m of strata, ranging up to 6 m in the southwest. The Commodore Seam is the principal seam of economic interest, and is well developed over the whole deposit, averaging about 5.6 m in thickness. Post-Jurassic erosion has removed part or all of the seam in two places along the crest of the western anticline (Fig. 5). The seam is typically banded and consists of dull coal with a few bright bands and numerous stone interbands. The bright bands generally comprise less than 20% of the coal and tend to be more common towards the base of the seam. The intraseam bands are usually carbonaceous shale and grey to brown mudstone with a few siltstone and fine sandstone bands and rare ironstone bands. Generally, the lower part of the seam contains fewer partings than the upper sections. Major intersealll' splits (greater than 0.9 m thick) are laterally extensive and can often be recognised over several kilometres. However, the majority of stone bands are usually thin and tend to lense out rapidly . An exception is a 0.1 m thick oolitic band, which occurs in the middle of the seam. This band has been recognised in numerous cores, however, it is not considered to be a useful marker horizon as it is difficult to identify and is not laterally continuous over the whole area. The Commodore Seam is best developed in the central portion of the deposit, to the east of, and adjacent to , the western an ticline. In this area, the seam consists of a single section of banded coal ranging between 6 and 9 m in thickness. To the east, the seam thins to less than 5 m and splits into two sections sep-

arated by up to 3.5 m of sediments. The seam is also split to the west of the anticline, and the upper and lower ections are up to 4.5 m apart and are approximately 2 m and 4.5 m thick respectively. The Top Rider occurs over much of the deposit , but has been removed by erosion from the crests of the western and central anticlines (Figs. 5 and 6). The seam varies in character from a few thin coal plies up to several metres of banded coal. It is be t developed in the broad trough where the

northern and southwestern synclines meet (Fig. 5) and attains a thickness in excess of 3 m. The Top Rider typically includes a high proportion of carbonaceous shale and mudstone partings, commonly with seam splits up to several metres in thickness. The seam is separated from the underlying Commodore Seam by between 5 and 25 m of strata. COAL QUALITY The coal is fairly typical of Walloon coals and is characterised by a high hydrogen

Table I-Average Coal Analyses Commodore Seam and Felton East Main Seam

COMMODORE I

a.d. Basis Moisture % Ash %

Volatile Matter % Fixed Carbon % Total Sulphur % Specific Energy MJ /kg Chlorine % Phosphorus % d.a f Basis Carbon % Hydrogen % Nitrogen % Sulphur % Oxygen % Carbonates % Macera/ Analysis Vitrinite % Exinite % lnertinite % Minerals % R o max. (vitrinite) Ash Fusibility Temps. (reducing atmosphere) Deformation °C Spherical °C Hemisphere °C Flow °C Ash Analysis ( d.bJ SiO 2 Al 2 O 2

Fe 2O 2 Cao MgO TiO 2 a2O K 2O

P 2O 2 Mn 2O 4 SO 2 Silica Ratio H.G.I. R.D .

FELTON EAST

Fl.60

Ra w

Fl .80

Raw

5.0 16.2 42.0 36.8 0.53 26.70

5.8 36.7 32.6 24.8 0.47 18.20 0.03

5.5 27.0 37.0 30.5 0.44 22.47

6.5 43.4 29.2 21.2 0.41 15.87

0.006 79.04 6.59 1.16 0.67 12.54 0.22

0.011 73.74 6.85 1.08 0.86 17.47 1.38

66 19 tr. 15 0.49

78.54 6.73 1.21 0.65 12.87 0.36 69 17 tr. 14 0.49

1590 1600 1600 1600

1515 1600 1600 1600

58.1 30.6 3.05 2.05 0.8 1 2.36 0.46 0.48 0.09 0.04 0.78 91 35 1.35

55.9 30.3 5.67 2.75 0.95 1.77 0.43 0.44 0.07 0.14 0.86 86 45 1.57

1600 1600 1600 69.5 22.6 1.84 1.01 0.51 1.67 0.29 0.30 0.09 0.04 0.20 95 32 1.64

149

content, high volati le matter, high content of reactive macerals, high a h fusion temperatures, low sulphur and low Hardgrove Grindability Index. Average coal quality parameters for the Commodore Seam are given in Table I. On an ash-free basis the coa l consists almost entirel y of the reactive macerals vitrinite and exinite, with only a trace of inert constituents. The exinite content is high , averaging 19% a nd occurs both as a separate readily identifiable maceral fraction, and as a finely divided "mulch" within the vitrinite. Thi latter feature results in the vitrinite ha ing a slightly lower reflectance in oil tha n expected for a coal of this type. The mean maximum reflecta nce mea ured ranges from 0.47% to 0.53% and average 0.49%. The banded nature of the coal results in a high raw ash content, however, much of the relatively inert material can readily be removed by beneficiation to provide a uni form product. The characteristics of the coal make it suita ble for power generatio n a nd conve rsion to other energy forms. Samples of coal from the Commodore Sea m ranging from I O kilograms to I 000 tonnes are currently being tested at various coal conversion research centres in Australia, Japan, Britain and America . Orga nisations undertaking this work include the Mitsui Solvent Refined Coal Con ortium, Commonwealth Scientific and lndu trial Research Organi ation, Australian Coal Industry Re-

search Laboratories and the National Coal Board. FELTON EAST COAL DEPOSIT The Felton East coal deposit is situ ated approximately 15 km southeast of Pittsworth and 30 km so uthwest of Toowoomba. The deposit is bounded by partial erosion a nd thick a llu vium to the south and south west, and basalt cover to the north and east (Fig. I). The Felton West deposit is adjacent to the Felton East deposit , but effectively separated from it by a tongue of basalt cover. The coal occurs in several seams which display a high degree of splitting a nd band ing. The strata have been gently folded (Fig. 7) into a series of northeast trending sub-parallel synclines and a nticlines with dips ra nging up to 3 but averaging only I c . The structure of the area is dominated by a northeast to northnortheast trending anticline. Up to five coal sea ms are recognised in the depo it. In ascending stratigraphic order they are the 88, 8 , M, T a nd H Seams (Fig. 8), with the M a nd T Seams being the main seams of economic importance. The BB Seam is a thin, (less than 2 m) well ba nded coal sea m, a nd can o nl y be recogn ised over the northern part of the deposit. The seam deteriorates, and is no t recognised , in the sout h and west. The B Seam is separated from the 88 Seam by an average of 30 m of strata and is recognisable only in the southern part of the EAST

WEST

,som •oom 350m

JOO m

SOUTH

NORTH

450m

,oom 350m

JOOm

HORIZONTAL

VERTICAL EXAGGHATM>N • lO d

Fig. 8. Felton East - Cross Sections.

150

[\';J UNCONSOllDATED MATERIAL

SCALE

'ooo,__-== I OOO---== = 0 - - - =====

lOOOm,trH

D WALLOON COAL MEASURES -COAL

area. To the north it occurs progressively closer to the base of the M Seam, and coalesces with the M Seam in the eastern part of the deposit (Fig. 8). The seam varies from a thin coal ply to several plies each up to 2 m in thickness. The M Seam or Main Seam is the principal seam of economic interest, and occurs over a wide area of both the Felton East and Felton West deposits. The workable seam ranges from 3 m to 13 m and averages 7 m in thickness. The seam is typically very banded, and consists primarily of dull coal with a few bright bands and numerous stone inter bands. Generally the seam is thickest in the troughs of synclines and thinnest on the crests of anticlines. The T Seam averages 3 m in thickness, and is separated from the underlying M Seam by a sequence of mudstones, siltstones and shales ranging from 2 to 16 m in thickness. The structure contours for the seam show much the same undulating fold structures as the M Seam. The T Seam has been eroded from the northern part of the area. The H Seam has only been recogni sed in a few bores in . the Felton East area, and has apparently been removed by erosion over much of the deposit. The seam averages 4 m in thickness and occurs between I O and 20 m above the T Seam. The H Seam is better preserved and developed in the Felton West deposit, where it is of economic significance. In Felton West, a further seam (the G Seam) is preserved, occurring approximately IO m above the H Seam. The G Seam also averages 4 m in thickness. COAL QUALITY The greater amount of banding in the Felton East coal seams results in a higher raw ash content than the Commodore Seam, and this is reflected in the proximate analyses and specific energy (Table I). However, the coal is

essentially very similar to the Commodore I coal, and is again characterised by a high hydrogen and high reactive maceral content, high volatile matter, high ash fusion temperatures , low sulphur and low Hardgrove Grindability Index. Washability testwork on large diameter coal seam cores has shown that much of the relatively inert material can be readily removed by beneficiation to provide products suitable for power generation and conversion. ENVIRONMEN TAL CONSIDERAT IONS

An environmental reconnaissance of the region has been carried out. The purpose of the study was to describe the area based on existing information, and to assess and classify regions of importance with regard to the effect that surface coal mining may haxe on the environment. Detailed studies have also been undertaken for the Commodore I deposit and Millmerran area, and are currently being carried out for the Felton deposits and Pittsworth region . The Joint Venture, in conjunction with agronomists from the Darling Downs Institute of Advanced Education, commenced a series of revegetation trials on the exposed spoil from the Commodore I trial box cut in December 1977. In January 1979, an area of approximately I ha was graded on the side of the spoil pile and more trials established on two depths of top soil (approximately .25 m and .5 m) . These trials are being regularly monitored for plant emergence and density, a.nd will investigate the response of a number of applications and the effect of top soil and top soi l depth on revegetation of the spoil. Data from these trials will be used to design COll)prehensive rehabilitation plans aimed at maximising the future land use potential of surface mined lands in the area.

REFERENCES CAMERON, J. B., 1970: The Rosewood-Walloon Coalfield. Pubis. Ceo/. Sun. Qd, 344 . CRANFIELD, l. C. , MCELROY, C. T. & SWARRRICK , C. F. J. , 1975: The Clarence-Moreton Basin, New South Wales and Queensland, i11 Traves, D . M. & King, D .(Eds), Economic Geology of Australia and Papua Nell' Guinea, Vol. 2., 328-333. Australas. Inst. Min . Metal!. , Melbourne. CRANFIELD, l. C., SCHWARZROCK, H . & DAY , R. W. , 1976: Geology of the Ipswich and Brisbane I :250 000 Sheet Areas. Rep. Ceo/. Surv. Qd, 95.

DAY, G . R. , 1978: Felton East report. Coal Di visio n, AMAX Iron Ore Corporation Company Report (unpubl.). DEPARTMENT OF MINES, 1968: Parameters for the calculation and reporting of coal reserves, Queen sland. Qd Govt Min. J ., 69, 400-402. ExoN, N. F. , 1976: Geology of the Surat Basin in Queensland. Bull. Bur. Miner . Resow·. Ceo/. Geophys. Aust. , 166. MENGEL, D. C. , I 977: The role of the Geological Survey of Queensland in exploratory coal drilling. in

151

preprint of papers presented in Coal Borehole Evaluation Sym posium, 2 1-35. Australas. Inst. Min . Metall. , Melbourne. MOND, A., 1973: Dalby, Qd- 1:250 000 Geological Series. Exp/an . Notes. Bur. Miner. Resour. Geol. Geophys. Aust. OLGERS, F. , 1974: Warwick , Qd- 1:250 000 Geological Series. Exp/an. No tes. Bur. Miner. Resour. Geol. Geophys. Aust. O" EILL. D. C. & DAY, G. R .. 1979: Felton West report. Coal Division, AMAX Iron Ore Corporation Compa ny Report (unpubl.). TTER. A. H .. 1977: Geological report P ARK . W . J. & Commodore I. Coal Divi ion. AM AX Iron Ore Corporation Company Report (unpubl.). ROACH. W .. 1952: H is1ory of coal mining in Queensland. QdGovt Min. J. 53, 775-782. SE:--:IOR. D .. 1973: Goondiwindi , Qd- 1:250 000 Geological Series. Exp/an . otes. Bur. Miner. Resour. Geol. Geophys. Aust. SwARllRICK , C. F. J., 1973: Stratigraphic and economic potential oft he Injune Creek Group in the Surat Basin. Rep. Geol. Surv. Qd, 79. THRI FT, J. A.. 1978: Loch bar report. Coal Di vision, AMAX Iron Ore Corporation Company Report (unpubl.) THRI FT, J . A., 1978 : Commodore 2 report. Coal D ivision, AMAX Iron Ore Corporation Company Report (unpubl.)

152

A. H . UTTER J. A . THRIFT G . R . DAY , Amax Iron Ore Corporation, AMP Place, I O Eagle Street, Brisbane, Ql d. 4000. PRESE T ADDRESSES A . H . UTTER , Jacia Mine M anagement and Co nsulting Service , 44 K ing's Park Road , West Perth, W .A . 6005. J. A. THRIFT, Thie Bros Pty Ltd , Kerry Road, Archerfield , Qld . 4108 . G. R. DAY , Amax Exploration (Australia) Incorpora ted , 55 Macquarie Street, Sydney, N .S.W. 2000.

STRATIGRAPHY A D COAL EXPLORATIO GEOLOGY OF THE ORTHEASTER SURAT BAS! By G. D . Jones & R. B. Patrick ABSTRACT Recent exploration by Brigalow Mines Pty Limited in Authorities to Prospect for coal covering an area between Chinchilla and lnjune has enabled refining of the stratigraphy of major coal horizons occurring within the Jurassic strata of the northeastern Surat Basin. Detailed photogeology, field mapping and exploratory drilling have confirmed the presence of continuous andstone units above the two major coal horizons in the Walloon Coal Measures, as suggested by Swarbrick ( 1973). These two coal horizons occur at the top of the Taroom Coal Measures (lower) and the Juandah Coal Measures (upper) and are separated by a thick sandstone equence called the Tangalooma Sandstone. These three new formations are discussed with reference to the recent exploration. The Walloon Coal Measures have been raised to Subgroup status in the Surat Basin. Twenty-eight coal deposits have been defined by exploratory drilling and broad scale field mapping, with photogeology, resistivity and more detailed field mapping being used more recently to site exploratory drilling. These deposits are shallow open-cut coal prospects within the Taroom and Juandah Coal Measures where individual coal seams have thickened and coalesced . Reserves totalling over 1700 million tonnes of raw in situ coal have been identified. Coal quality parameters are fairly consistent throughout the various coal deposits, although coals from the Taroom Coal Measures exhibit slightly higher rank and significantly lower inherent ash. The low rank , high volatile sub-bituminous coal is eminently suitable for conversion to synthetic fuels and for electricity generation. The Queensland Government has recently nominated the Wandoan-Taroom area as the priority site for the lmhausen coal-to-oil feasibility study. INTRODUCTION Brigalow Mines Pty Limited is a company jointly owned by Thiess Holdings Limited and

M.I.M. Holdings Limited. The company currently holds five Authorities to Prospect in its own right, and has an 80% share in eight other Authorities in the Surat Basin. These Authorities cover ground containing shallow Walloon Coal Measures mostly within the Mimosa Syncline. They are located from near Chinchilla in the south east to lnjune in the west (Fig. I). STRATIGRAPHY A D GEOLOGY

GE ERAL The regional geology of the Surat Basin has been described in detail by Exon ( 1976, 1979) and Zillman ( 1979). The major structural element affecting Triassic and Jurassic sedimentation in the southern Bowen and northeastern Surat Basins is the Ta room Trough, bounded in the east by the Burunga-Leichhardt fault zone and in the west by the ebine Ridge. The thickest Mesozoic sediments are found in the north south trending Mimosa Syncline, and were deposited in the subsiding Taroom Trough. Dips in the Mimosa Syncline seldom exceed one or two degrees, and no major faulting is known to affect the Jurassic sediments. STRATIGRAPHY

Based ·on a considerable amount of noncored and cored drilling, together with photogeological and field mapping carried out by Brigalow Mines since 1974, some changes to the existing stratigraphic subdivision and nomenclature are proposed . Figure 2 shows the current nomenclature, the proposed nomenclature and the informal subdivision of the lnjune Creek Group made by Swarbrick ( 1973), based on stratigraphic drilling carried out in 1967-70 and 1970-72 by the Geological Survey of Queensland (G.S.Q.). The most significant difference is the subdivision of the Walloon Coal Measures (applicable at least to the northern Surat Basin) into (i) Taroom Coal Measures (lower coal horizon) 153

INJUNE

LOCALITY MAP

ROM Bymount Glen Alden

0Jngarf1eld Sp1on Kop Cowangoh Waterloo

21 22 23 2L

Ktnnoul

25 26

Verbena Pork

9 Cottle Creek 10 Box vole

28 29

Orozobah

Kerong

13 1L

Pony Plains Orogoncrest

Turkey Hill Summer Hill

16 17 18 19 20

Fronk

Creek

Wubagul

SCALE

Burungo Gulugubo Wo1tong1 - Stanley Pork Columboolo Rywung Bokmg Boord Lollolind1 Sefton Pork

Mud Creek Anchor Bar Aust1nvole Woleebee

F ig. I. Briga low Mines Authorities to Prospec t Location Map.

K,tometres

Previous Nomenclature

Li thostratigr aphi c Intervals After Swarbrick ( 1973)

GUBBERAMUNDA SANDSTONE

Lithology

GJBBERAMUNOt\ SANDSTONE

Metres

WESTBOURNE FORMATION

New Nomenclat ure

-=:= -.-

---

WEST BOURNE FORMATION

100

---

SPRINGBOK SANDSTONE

9 200

0..

:::>

::;:

a::

300

<.!)

7&8

JUANDAH COAL MEASURES

<I') ~

w w a::

( Swarbrick , Gray & Exon, 1973)

0..

:::>

a:: <.!)

- -....,.....,..., -

400

WALLOON

Cl)

COAL

:::> -,

MEASURES

:::>

l/)

- - -500

·------

TAN GALO OMA SANDSTONE z 0

g _J

::;:

TAROOM

<I') ~

COAL

. ·--

MEASURES

3&4 ---

700

EUROMBAH FORMATION

er w

O(l) ~ ---

<I')~

~o Z 800

HUTTON SANDSTONE

- --

- -

~~-:"'2 :.,________ "" .. , ... c·

EUROMBAH FORMAT ION

=> ::;:

HUTTON SANDSTONE after Swarbrick ( 1973)

Fig. 2. Stratigraphy of the Northeastern Surat Basin.

155

(ii) Tangalooma Sandstone (iii) Juandah Coal Measures (higher coal horizon) It is proposed that the Walloon Coal Measures become the Walloon Subgroup. This new subdivision can be related to Swarbrick's ( 1973) intervals. The Ta room Coal Measures include intervals 3, 4 and much of interval 5. The Tangalooma Sandstone is equivalent to the upper part of interval 5 plus interval 6, whilst the Juandah Coal Measures correspond substantially with intervals 7 and 8. Formal definitions of these units and a redefinition of the Walloon Subgroup are included in the appendix. LITHOLOGIE S OF THE WALLOO SUBGROUP

Taroom Coal Measures Lithologies developed in the Taroom Coal Measures include sand.s tone, siltstone, mudstone, carbonaceous shale and coal, with thin beds of ironstone (siderite weathering to haematite) and limestone. The sandstones are light grey to grey, fine to medium grained, lithic and feldspathic labile rocks, often with high matrix/cement contents (generally clay). Clastic fragments are predominantly volcanic, with fine sediments also commonly represented, and are subrounded to subangular. The freshness and angularity of many feldspar clasts indicate a not too distant volcanic source. Calcite is a commonly occurring cement and may constitute 60% of the rock, having replaced lithic clasts and other cements. Siltstones and mudstones are grey to grey-brown and may be carbonaceous in parts. Freshwater limestones in the sequence often exhibit cone-in-cone structure. Tangalooma Sandstone The Tangalooma Sandstone is characteri sed by light grey to grey, fine to mediumcoarse grained lithic or feldspathic , labile sandstones, similar in provenance to those in the Taroom Coal Measures. They commonly have an argillaceous matrix, with carbonate cement common . Upward fining sequences are often present, occasionally culminating in siltstone and mudstone deposition. Thin coal seams may also be present. Juandah Coal Measures Lithologies developed in the Juandah Coal Measures include sandstone, siltstone, mud156

stone, carbonaceous shale, ironstone, limestone and coal. In most respects the lithologies are similar in composition and appearance to the Taroom Coal Measures. CYCLICAL SEDIMENTAT ION AND PALAEOENVI RONMENT

Sedimentation in the Surat Basin has been divided by Exon ( 1976) into five major cycles, the second of which is the Hutton Sandstone/ Eurom bah Formation/ Walloon Coal Measures sequence. The cycles represent alternations from depositional episodes of higher energy to low energy, with a general trend in each cycle from mature sandstones to more labile sandstones, siltstones and mudstones with occasional coal seam development, especially in Walloon times. The palaeogeograph ic setting during deposition of the Walloon Subgroup was probably a subsiding flu vial plain in which stream channels beca me more stable, allowing accumulation of peat in swamps, with occasional overbank deposition (stone bands). Within the Walloon Subgroup the cyclical model can be further developed. Two subcycles, each commencing with a channel sand/point bar sequence and culminating with peat swamp type deposition, can be rethe is first The cognised. Hutton/ Eurombah/Taro om Coal Measures the is second the and sequence, Tangalooma/Ju andah Coal Measures sequence. Each subcycle represents a period of stability and decreasing fluvial activity, with the thickest peat accumulation occurring near the top of each coal measure sequence. Local variations in rate of subsidence, brought about by differential compaction in underlying sediments, affected seam morphology. This contributed to seam splitting and deterioration in coal quality due to increase in ash content. The conditions favouring peat accumulation during the Taroom Coal Measures times were interrupted by a change in base level, which was reflected by the deposition of point bar/channel facies sediments (the Tangalooma Sandstone). Another period of stabilisation followed , with peat forming conditions becoming more common . Maximum swamp development occurred at the top of the Juandah Coal Measures as migrating stream channels stabilised.

ANCHOR BAR

WOLEEBEE

NORTH - WEST RJ02

R849

- ,---

Jl..lb.NDAH

COAL MEASURES

R124

R4SJ

R 351 SPRINGBO K SANDSTONE

SOUTH-EAST

L---

R612

R623

R500 R61'.

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

r---_

VERBENA PARK

CATTLE CREEK

SOUTH - EAST

NORTH- WEST

R728

206 TANGAI..OO MA SANDSTONE

R701

R02S Cffi

R024

R1200

Rn2

R1202

R729

TAROOM

COAL MEASURES

--:::::-- .....--

-...... ~~ .... p~

HORIZ~ TAL VERTICAL

-.J

Fi g. 3. La tera l sca m develo pment.

SC ALE

,oo

SCALE

These conditions were disturbed again by increased fluvial activity, with the point bar/channel facies sediments of the Sprin gbok Sandstone being deposited. Thi s represented the end of the major Jurass ic coal forming period in the Surat Bas in . LATE RAL DEVELOPM ENT OF COAL SEAMS M ajo r coal seam deve lopment in both the T aroom a nd Jua nd a h Coal Measures is co ncentrated in horizon which are laterally persistent. Throughout the Mimo a Syncline these horizons generally contain some coaly material. which may range from a twelve metres thick coal seam to thin coal bands with associated carbonaceou s shale. The lateral tran sition from a thick seam to thin coal bands can occur over tens of metres and may be accomplishe d by rapid plitting of coal plies and or by their deterioration to carbonaceou mudstones. Splitting is often complex. a nd wi thin deposit the combi natio n of plies formi ng the working section can be quite co mplex. Figure 3 illu stra tes la tera l sea m development in the Ju andah a nd T aroom Coal Measures. Similari ties betwee n the two coal measure sequences occur in overall lithological characteristics. in coal quality and to ome extent seam distribution . EXPLORAT IO

TECH IQ ·Es

HISTORY OF COAL EXPLORAT IO The previously mentioned stratigraphic a nd geological features associated with coal measure de elopment in the Surat Basin have led to an interesting history of coa l exploration by governmen t bodies and exploration co mpanies. Early information on the occurrence of coal was based on ge nerall y unrelia ble da ta from sca ttered water bores. Howeve r. stratigraphic drilling by the G .S.Q. and Burea u of Mineral Resources (B. M .R.) which was completed in the early 70's, tied in with wells drilled during petroleum exploration programmes . sti ll provides a good framework for the stratigraphy o f the Surat Basin (Swarbrick ef al .. 1973). Briga low Mines Pty Limited first selected Authorities to Prospec t for coal based on the frequency of water bore coa l in tersec tio ns. Alt ho ugh Swa rbrick ·s report indicated that two majo r coal bearing horizo ns occurred 158

within the Walloon Coal Measure , severa l features affected the early exploration programmes, including: (i) lenticular develo pment of coal deposits with rapid seam thinning, sea m splittin g a nd sea m deterioration away from "coal depocentres " (areas of maximum peat accumulatio n); (i i) the thick a nd vertically transitional na ture o f the Wa lloon Coal Meas ures; (iii) possibility of economic coal seams other than those occurring in the two major horizon s; (iv) full a se sment ofan area necessi tated by the relinquishme nt requirements of the Authorities. Early exploratio n therefore concentrated o n sco ut drilling a t a bout 5 km spacin g to a maximum depth of I 00 m, over the entire area of the Authorities. It was after this phase of explora tion that it became apparent that potential for substa ntial coal reserves ex isted o nl y in two main coal ho rizo ns, i.e. Taroom and Jua nd ah Coal Measures, a nd areas were relinquished after the outcrops of these coal measures were delineated. Durin g the seco nd and subsequent phases of exploration, a number of now well known coal deposits were located in both the Juandah and Taroom Coal Measures. Correlation of seams and rock units within the deposits, as well as correlation throughout the two coa l measures, pro ed difficult owin g to the lenticularity of the earn formation. The Juras ic coal of the area have relatively uniform vitrinite contents and hence undiagnostic brightne slogs in contrast wit h most sea ms in the Permian coal basins. Correlation of seams from depo it to deposit was neither a ttempted nor po sible during the early phases of exploration, however, the ea rly ideas o n the development of coal accumulatio n about "coal depocentres" necessitated a more deta iled stud y of the stratigraphy . Thi s study, invol vi ng photogeolog y a nd field ma ppin g, together with resistivity surveys and fo llow-up drilling programmes, comprised a new approach by Brigalow Mines to coal exploration within the Sura t Basin . PHOTOGEO LOGY A D FIELD MAPPING The Injune Creek Group is characterised by sparse outcrop and subdued topogra phic

expression; about 90% of the outcrop that exists consists of calcareous cemented sandstones. However, the top and base of the group, which is over 800 metres thick, are fairly readily discernible from the topographic expressions of the Gubberamunda Sandstone and the Hutton Sandstone. Consultants were approached during 1978 to determine, in as much detail as possible, the stratigraphy and tructure of the Walloon Subgroup and relate the e to the known coal deposits in order to define areas of greatest coal exploration potential. The combination of very low dips (generally less than I ), the poor topographic expression of lithological differences and the transitional nature of most unit boundaries made reliable photogeological interpretation extremely difficult. The four formations comprising the Injune Creek Group, as outlined in Swarbrick ( 1973), were each photogeologically recognised. However, it was difficult to correlate the photogeology with Swarbrick's ( 1973) subdivision of the Injune Creek Group into eleven intervals. The six intervals of the Walloon Coal Measures were combined to form the three formations as outlined above. This photogeological interpretation was only accomplished by recognising very subtle geomorphic, topographic and /or tonal changes, using highpower stereoscopy. The lithological differences and resultant topographic expressions for the four more important formations can be summarised as follows: (i) Springbok Sandstone: resistant, paletoned hills and ridges. (ii) Juandah Coal Measures: soft, pale-toned unit with characteristic "break-away" topography and rare outcrop. (iii) Tangalooma Sandstone: similar to Springbok Sandstone in that it forms resistant hills; dark toned. (iv) Taroom Coal Measures: soft, mottledtoned unit often showing "break-away" topography. RESISTIVITY SURVEYS Following the photogeological study of the area, which incorporated the delineation of the outcrops of the major coal horizons, a new approach was adopted to locate areas of coal accumulation within the outcrop zones. Consultants were commissioned to conduct Schlumberger array vertical electric soundings to test for the presence of coal to a depth

of 50 m. These res1st1v1ty soundings were completed on an approximate 2 km grid over and down-dip from the outcrop of the Juandah and Taroom Coal Mea ures. The geophysical method works on the principle that the most resistive rock unit occurring in the Jurassic strata of the region is coal, and resistivity anomalies can reflect areas of thicker and shallower coal deposits. The magnitude of the resistivity (.. gee-resistance") is proportional to the thickness of coal seams and inversely proportional to the depths at which the seams occur. Therefore, the thicker and shallower coal is indicated by a higher resistivity anomaly . As may be expected with some geophysical methods, the resistivity survey had problems with its early use and interpretations. The major problem associated with the initial surveys was the recognition of the effects on the "gee-resistance" of superficial deposits, whether they be deep weathering profiles or surface gravel deposits. A conductive superficial anomaly, such as that caused by a deep weathering profile may suppress the effects of a Jurassic resistor (i.e. coal) occurring at depth. Conversely, a shallow resistive anomaly may reflect superficial layers such as river gravels, rather than coal within the Juras ic strata. However, it has been found that the effects from these superficial anomalies can be largely overcome once the electrical nature of the surface material is known. In the northeastern Surat Basin, these problem areas are confined mainly to. thick floodplain deposits of gravel, especially in the Dawson River valley and major tributaries. EXPLORATORY DRILLI

After the resistivity surveys indicated.areas of thicker coal accumulation within the two coal measures, exploratory chip drilling was employed to confirm the presence of the coal anomalies and to aid the geological and stratigraphic interpretation of the area. The generally soft nature of the non-coal strata and the hard brittle nature o_fthe coal. coupled with the use of high-volume compressors, has enabled relatively easy and precise chip logging of shallow drillhole , i.e. less than 90 metres. This method of drilling has proved to be a cost and time effective follow up to photogeology and resistivity surveys. Downhole geophysical logging has recently been employed as an aid to refine coal/stone 159

boundaries a nd to correlate sea ms a nd rock units. This method of logging is especially useful in deeper holes where water circulation is necessary for efficient drilling, and the time lag for return of cuttings increases, making accurate logging difficult and sometimes impossible. Once a potential coal prospect has been located , the area is chip drilled on a 400 m grid, with coal seam coring at selected sites to enable more precise correlation and to supply sa mples for analysis. This drilling and associated coal a nalysis has enabled the delineation of substa ntial coa l reserves suitable for open-cut extraction. DAT A PROCESS! G One of the feature associated with some coal exploration programmes is the time-lag between collecting the data, whether it be drillhole information or a nalytical information , and the proces ing and utilisation of the ast quantity of information. With many explora tion programmes , and especia ll y those in the Su rat Basi n where rapid facies changes are a co nstant challenge to the geologist, an up-to-date written and gra phical account of

the explorat ion drill logs must be kept to ensure a n efficien t drilling programme is conducted . It ha s been found that the best method to ach ieve thi is to log directly onto coding forms using suitable codes for rock types, structures etc. , and to encode a ll informa tion , including analytical data, onto a computer ma naged database. The data are then processed and the information is presented in any form required , including written logs, graphic logs, cross-sections, coal isoquality maps, structure contours, and mine planning drawings, reserve calculations, etc. COAL RESO RCES million tonnes of raw in situ coal 1700 O ver have been outlined by exploration in the Authorities from Chinchilla to Injune, of which 385 million tonnes are mea ured reserves and 265 million indica ted (Class I) reserves, with the majority of the reserves situated aro und the town of Wa ndoan (over 1200 million tonnes of raw in situ coal within 28 km of Wandoan). The coal from both the Jua nd a h and Taroom Coal Measures is typically perhydrous, high volati le sub-bitumin ous wit h a

Table 1-Juandah Coal Measures-Typical Coal Analysis Data Raw Coal

Washed Coal Fl.60 77.8

Yield % PROXIMATE A ALYSIS (A IR DRIED) % Inherent Moisture Vol atile Matter Ash Fixed Carbon

10.5 36.4 22.0 31.1

10.8 42.1 8.6 38.5

SPEC IFIC E ERGY MJ/ Kg

21.46

26.36

TOTAL SULPHUR %

0.22

0. 18

75.83 6.80 0.92 0.44 16.57 0.75

77.18 6. 10 0.94 0.34 15.46 0.20

AL YSIS (D RY ASH FREE) % Carbon Hydrogen Nitrogen Sulphur Oxygen Carbon Diox ide PETROGRAPH IC ANALYSIS % Vitrinite Exinite lnert inite Mineral Matter Vitrinite plus exinite (Minera l matter free)

73 8 II 8 88

REFLECT A CE (RO max %)

0.41

160

low rank (Ro max. %about 0.4). The Ta room Coal Measures coal however exhibit a slightly higher rank , as might be expected, owing to their deeper burial, as well as a lower inherent ash content. Coal deposits from the Juandah Coal Measures, on which the majority of analyses by Brigalow Mines Pty Ltd have been done, exhibit little geographical variation in their coal quality parameters. The only major variations occur in the raw coal ash % which is proportional to the total thickness of stone bands within the seams. Inherent ash %, as reflected by wa hed coal analyses, is similar for all deposits tested. Macera I analysis of the seams also reflect the high volatile nature of the coal, with vitrinite, resinous vitrinite and exinite constituting between 80 and 90% of the mineral matter free material of most seam sub-sections analysed. Table I shows typical coal quality data from the Juand a h Coal Measures. Vertical variations of coal quality parameters are practically insignificant. A slight decrea e in vitrinite content immediately below a stone band is the only significant variation observed. (Leblang et al. , 1979). The coals from both coal measures in the northeast Surat Basin have been shown to be eminently suitable for:

(i) conver ion to liquid fuels via direct hydrogenation or pyrolysis methods (ii) solvent refined coal (SRC) (iii) power generation usi ng a run-of-mine product and /or coal extracts from the above conversion processes. In December, 1978 the Queensland Government nominated the WandoanTaroom area as the priority site for the Imhausen study as the area not only had large reserves of open-cut coals of suitable quality but also potentially adequate water resources to meet the demands of a conversion plant. The Imhausen study involves a joint feasibility study on the conversion of Australian coals into liquid fuels funded by the Government of the Federal Republic of Germany and the Australian Commonwealth Government , and the Governments of the States of ew South Wales, Queensland and Victoria.

ACK OWLEDGEME 1TS The authors thank Brigalow Mines Pty Ltd for permission to publish this paper, and also thank the members of the Thiess Bros Pty Limited - Mining Division staff who helped with the typing and drafting of the manuscript.

REFERE CES ExoN,

F .. 1976: Geology of the Surat Basin in Queensland. Bull. Bur. Miner . Resow·. Ceo/. Geophys. Aust., 166. EXON, . F., 1980: The stra tigraphy of the Surat Basin with special reference to coal deposits. Coal Geology, I (3). LERLA:--:G. G. M .. RAYMENT. P.A . & SMYlH. M .. 198 1: The Austinvale coal deposit - Wa nd oa n. A palaeoenvironmental analysis. Coal Geology. I (4) . SwARRRICK . C. F. J ., 1973: St ratigraphy and economic potential of the lnjune Creek Group in the Surat Basin. Rep. Ceo/. Sun·. Qd, 79. SWARRRICK , F. J ., GRAY , A. R. G . & EXON. . F .. 1973: Injune Creek Group- amendments and

an add iti on to the strat igraphic nomenclature in the Surat Basi n. Qd Go,•t Mi11. J.. 74, 57-63. ZILLMAN. N. J.. 1979: General geology a nd coal resources. in Beeslon, J . W. (Ed.) 1979 field conference. Taroom-Wandoan-M illmerran . Gcol. Soc. Aust.. Qd Div .. field trip guidebook.

G. D . JO ES R. B. PATRICK Thiess Bros Pty Ltd - Mining Di visio n, AMP Place, I 0 Eagle Street, Brisbane, Qld. 4000.

APPE DIX Definiti ons of

ew or Revised Stratigraphic Units of the lnjune Creek Group. WALLOO

ortheastern Surat Basin.

SUB-GROUP

Previously termed the Walloo n Coal Mea sures. the unit has been upgraded to sub-group sta tu s to include the three new formations described below, namely the Taroom Coal Measures. the Ta nga looma Sandstone. and the Jua ndah Coal Meas ures.

161

Taroom Coal Measures Derivation of Name:

Ta room township (grid reference 78l000E 7161000N, Taroom Sheet 8846)

Previous Usage:

New name. Previousl y interva ls 3. 4 and 5 of the lnjune Creek Group (Swarbrick 1973).

Distribution:

Crops out along strike from south-east of Wandoan 10 lnjune. Intersected m subsurface in numerou s coa l exploration holes and deep petroleum wells.

Type Section:

G .S.Q. Roma I (grid reference 798700E, 71 2 1000N Taroom Sheet 8846) Occur-i; between the depths of 100.9 metres and 252.1 metres (approx.)

Lithology:

Fine to medium grained lithic and fe ld spathic sandstone predominates, especially towards the base or the formation. lnterbedded siltstone, mudstone, carbonaceous shale and coal. The si ltstone is grey and hard and genera ll y con tains interbeds of mudstone and ironstone. Impure limestones occasiona ll y occur interbedded with siltstone and ironstone. There is an increase in the thickness of coal members towards the top of the unit. Three coal members can be correlated within the formation but at present are not defined. The top most coal member (as found in the Taroom coal deposit) marks the top of the unit.

Thickness:

range: average: type section:

Relation ships and Boundary Criteria:

Within the northeastern Surat Basin the Taroom Coal Measures conformab ly overly the Eurombah Formation although the boundary is gradational. The top of .the formation is generally the last major coal member underlying the Tangalooma Sandstone.

50 10 200 metres 180 metres. The formation thins towards Injune. 151 .2 metres (approx.)

Tangalooma Sa11dsro11e Deri vation o f Name:

" Tangalooma .. homestead (grid reference 744070E. 711781 ON M uggleton sheet 8745).

Previous Usage:

New name. Previousl y interval 6 of the Injune Creek Group (Swa rbrick , 1973).

Distribution:

Can be traced along strike from south-east ofWandoan 10 lnjune. Intersected in the subsurface in numerous coal exploration holes and deep petroleum wells.

Type section:

G.S.Q. Roma 5 (grid reference 740070E, 7117800N Muggleton sheet 8745). Occurs between the depths of 97.2 metres and 180.4 metres (approx.)

Lithology:

Predominantly medium gra ined lithic or feld spathic labile sandstone commonly with carbonate cement. Upward finin g sequences are commonly developed , beginning with lag conglomeratic bands of fossil wood debris, ironstone and mudstone clasts a nd culminating in siltstone and mudstone. Thin coal members may also be present but do not persist laterally for any great distance. Carbonate-rich siltstones are also common a nd ca n be traced along the surface strike for several kilometres.

Thickness:

range: a verage: type section :

Rel a tionships and Bound ary Criteria :

The Tangalooma Sandstone conformably overlies the Taroom Coal Measures. In outcrop, the base or the unit is marked by the last resistant sandstone uni t, whilst in subsurface it corresponds to the top of the last major coal member in the Taroom Coal Measures. The top of the Tangalooma Sandstone is grada tional but is marked by a general increase in lower energy environment sediments.

50-200 metres 150 metres 83.2 metres (approx .)

J11a11dah Coal Measures Derivation of Name:

Parish of Juandah, Fortescue Count y, Qld. (Wandoan Sheet 8845)

Previous Usage:

New name. Previously intervals 7 and 8 of the Injune Creek Group (Swarbrick 1973).

Distribution:

Crops out along strike from south of Wandoan to Injune. Intersected in the subsurface in numerous coal explora tion holes and deep petroleum wells.

162

Type Section:

G.S.Q. Roma 4 (grid reference 783300E. 7093800N Wandoan Sheet 8845). Occurs between the depths of 254.2 metres and 413.6 metres.

Lithology:

pward fining sequences of fine to medium grained· lithic and feldspathic sandstone. siltstone, mudstone and coal. Coal members become more common towards the top of the unit. The bulk of the coal reserves outlined to date within the northeastern Surat Basin occur within these measures. Individual coal members can be up to 15 metres thick but are commonly much thinner and exhibit rapid lateral thickness variations. The formation is typified by sparse outcrop.

Thickness:

range: average: type section:

Relation hip and Boundary Criteria:

The Juandah Coal Measures conformably overlies the Tangalooma Sandstone. The top of the unit is marked by the last major coal member below the Springbok Sandstone. This boundary can be observed in outcrop as well as in subsurface borehole intersections.

50 to 200 metres 160 metres. The formation thins towards lnjune. 159.4 metres (approx.)

163

THE OAKEY-DALBY REGIO , DARLING DOWNS COALFIELD: STRATIGRAPHY AND DEPOSITIO ALE VIRO MENTS By J. McLean-Hodgson & ABSTRACT The Oakey-Dalby region of the Darling Downs coalfield covers a sixty kilometre strike length of the lower part of the Jurassic Walloon Coal Measures. The stratigraphic section investigated by drilling is up to 250 m thick and, with the aid of downhole petrophysical logs, has been divided into seven rock units including three widely persistent coal seam intervals. Three principal lithological sequences have been identified in the section and show evidence of cyclic deposition in a fluvial environment. The most prospective coal horizon is the Acland-Sabine coal interval which has been traced throughout the area . Drilling has delineated shallow open-cut reserves in a number of deposits aggregating over 1000 million tonnes in situ . The coal is characteristically high-ash and occurs in a banded seam up to 18 m thick. It is classified as per-hydrous, high volatile bituminous. Detailed subdivision and correlation of the Acland-Sabine coal interval has been facilitated in drillholes by the presence of laterally extensive time-stratigraphic markers, conspicuous on gamma ray logs. Recognition of the three lithological cycles on petrophysical logs has enabled detailed sedimentological facies analysis to be carried out. It is concluded that deposition was within a meandering stream and flood plain environment in which channel, overbank and backswamp facies can be recognised.

I TRODUCTION The area covers some 600 square kilometres and is comprised of Authorities to Prospect (A to P) l 29C (Shell) and 205C (Shell/Oilmin .L. , Petromin .L. , Transoil .L.) situated 160 km west of Brisbane in the Darling Downs region of south east Queensland (Fig. I). The two A 's to P cover a 60 km strike length of the lower portion of the Walloon Coal Measures outcropping along the northeastern edge of the Cecil Plains Syncline in the Moreton Basin . The Moreton Basin is continuous with the Surat Basin across the

. H. Kempton

Kumbarilla Ridge (Exon , 1976) which is situated west of Dalby. Coal mining has been carried out in the area since 1913 and as many as four collieries were operating in 1954. The privately owned Acland o. 3 Colliery, where the basal section of the thick Acland coal seam is worked , is now the only remaining coal mine on the Darling Downs. Recognising the potential for large scale open cut mining in the area, Shell's exploration efforts have been concentrated on shallow occurrences of this principal coal horizon. Within the two A's to P more than 460 chipholes and 50 coreholes have been completed since exploration commenced in 1973. Petrophysical wireline logs have been run in all holes on a routine basis by BPB Instruments (Australia) Pty. Ltd. at a scale of I :200. Logs obtained normally included Gamma Ray, Caliper, Long Spaced Density (L.S.D ., 48 cm spacing), High Resolution Density (H .R.D. , 23 cm spacing) and Bed Resolution Density (B.R.D ., 15 cm spacing). Detail logs at a scale of I :20 were obtained over coal seam intersections greater than I m thick and all seam and parting thicknesses used in geological and reserve evaluation have been measured from the H.R.D. or B.R.D. logs at this scale. In addition, petrophysical logs were used for detailed stratigraphic and coal seam ply correlations, as an aid to lithology identification, and for semiquantitative comparisons of the ash content and specific energy of the coal where cores were not _taken . This work is a natural extension of the coal exploration drilling and feasibility studies carried out by Shell and the Shell/Oilmin Joint Venture since 1973. Contributions from all members of the Shell coal geology group have been made from time to time during exploration of the area and their work , some of which is cited in the references, is gratefully acknowledged. STRATIGRAPHY

The Middle Jurassic Walloon Coal Measures occur between the Late Jurassic-Early 165

Geological boundary

Coal deposits

0 km

Fig. I. Geology and location of coal deposits

Cretaceous Kumbarilla Beds and the Early Jurassic Marburg Formation. The full Walloon Coal Measures section attains a thickne of 450 to 500 m in the south, but erosion ha removed the upper half in the tudy area. Regional dips are very low southward, with local variations being mostly due to differential compaction. Lithofacies analysis has indicated a southerly source for the elastic material in the Dalby area based on an increase in sandstone percentages of the formation in this direction (Meyers, 1970). Late Oligocene to Early Miocene basalt and Qu aternary deposits, over I 00 m thick in places, now conceal much of the Walloon Coal Measures . The more resistant basalt ex trusions locally form hill s around which Mesozoic sed iments a re preserved .

The Jurassic section in the area is comprised of 300 m of elastic and coal sequences which can be divided into seven informal rock units, six of which are in the lower part of the Walloon Coal Measures and the seventh in the underlying Marburg Formation (Fig. 2). Detailed stratigraphic correlation was greatly facilitated by the presence ofa number of widespread high gamma ray marker horizons readily recognisable on the wireline logs. Most of these horizons are less than 30 cm thick a nd are continuous over more than 60 kilometres. Their mineralogy 1 together with their large areal extent and relatively high gamma radi at ion suggests that these elaystones a re altered igneous rocks now bentonitic tuffs. As such they have been recognised as time strati-

' The high ga mma ra y emittin g pa rt ings a re represented in ha nd specimen by pa le green clays to nes with ra re carbonaceo us detritus. A sa mple of o ne of the clays to ne ba nds was subjected to X-ra y diffraction a nalysis whic h identified the d ominant clay mineral as mo ntmo rillo nite. traces of kaolinite and quartz also being recorded . Hea vy liquid separation yielded small amo unt s of fairly clear. brown pleoch ro ic bi o tite. No spherulitic o r o ther te xtures co uld be o bserved in this sectio n but the sub-circular pleochroic pa tc hes which occur arc interp reted as seconda ry product s after biotite phenoc rysts (Steveson. 1979).

166

[ZJ Th ickly bedded sandstone 'Mlipanna 2 Coal Interva l

f::<<I lnterbedded sandstone and rrodstone llIIII) Mudstone

1111 Coal and carbonaceous shale [iJ Tuff marker

CD Rock uni t

"::A __.,.....---.7

4 I 5

Marburg Formation

Fig. 2. G eneralised composite stra tigraphic section

0NAVIEW

MYALL

Basalt -

Walloon Coal Measures

EJ] Alluvium

100]

Fig. 3. Cross-section showing basalt-coal measures- alluvium re lationship

graphic markers and have been used extensively in correlatio n, structural studies, and facies analysis.

DESCRIPTIO OF ROCK UNITS The seven rock units into which the stratigraphic column has been subdivided (Fig. 2) are described as follows (from the top down): Rock unit 1 (40 m thick) Mainly massive, medium grained, labile sandstone with argillaceous matrix, inter-

metres

2000

rupted by thin inter beds of fine sandstone and mudstone.

Rock unit 2 (75 m thick) , Waipanna coal interval Predominantly thinly bedded , fine grained labile sandstone, siltstone and mudstone. A few fining upward sandstone bodies up to 2 m thick are present. Four banded coal intervals (A, B, C, D) are recognised ranging from 5 to 10 m in thickness (McLean-Hodgson , 1978). Coal percentage ranges from 10-60% with 167

ONAVIEW

MYALL

MT. PLEASANT IRVINGOALE

MANNING-

SUM,£RS

HLL

TARKO

VALE

GLEN ROSLYN

SABINE

IR25

itief ~

BW48

DA 23

:~:t~~~:n luff marker

BW30

AC 211

BW87

--==----a ~

~ J075 l 6 BW h

a ~ ACl40

Torko luff marker

--------------60km---------------

Fig. 4. Correla tion di agra m. ga mma ray- L.S.D. logs

coal grading to carbonaceous shale. Coal intervals are persistent but coal seams exhibit rapid lateral changes.

Rock unit 3 (28-35 m thick) Light grey medium grained sandstone up to I 0 m in thickness with abrupt base, fining upwards to interbanded very fine grey labile sandstone and mudstone. This cycle is repeated throughout the unit. Thin limestone layers are present. A few thin coaly and carbonaceous shale beds are present in the interbedded sandstone and mudstone sections. Rock unit 4 (15-60 m thick), Acland-Sabine coal interval This unit has been traced throughout the two A's to P and contains the principal seams of economic interest in the region . The coal mined in the underground colliery at Acland is the bottom 2-3 m of a section of interbanded coal and shale which can occur up to 18 m thick. This basal section has been referred to as the Aeland working seam (Mengel, 1963) and the name Aeland seam has been extended here to cover the gross seam interval. Stratigraphically below the working seam Mengel named two other seams- the Sabine Top seam and Sabine Bottom seam. The use of the name Sabine has been retained here for a number ofcorrelatable seam splits. The unit ranges in thickness from 20 to 60 m depending on development of the elastic component. Two widespread bentonitic elaystone partings, referred to here as the Glen Roslyn tuff marker and the Tarko tuff marker, have been used as stratigraphic markers. 168

Acland coal seam

This is a banded coal and elastic interval up to 33 m in thickness. There are four coal seams, numbered A l-A4, in this interval (op. cit., Taylor and Brunton, 1977). The A I coal seam ranges from 3 to 15 m in thickness and is split by numerous thin argillaceous and rare arenaceous bands, inferior coal and carbonaceous shale. These partings can comprise up to 50% of the seam. In localised areas the seam can deteriorate to carbonaceous shale. The A I seam is separated from the lower A2 coal seam by a elastic parting, designated as the "A l-A2 elastic parting", which ranges in thickness from 0.1 m to 20 m. Where it is less than I m thick it is usually a light brown mudstone. As the parting thickens it becomes more arenaceous a nd up to 20 m of light grey, labile, medium grained sandstone grading upwards to grey mudstone have been intersected, together with thin bands of siderite. The A2 coal seam averages I to 1.5 m in thickness and has similar banded coal characteristics to the A I coal seam. It can be locally absent. The A2 seam is separated from the lower A3 coal seam by the Glen Roslyn luff marker, a soft puggy elaystone, light brown to green in colour. It is present over the entire area except for one drillhole locality and has been used as a datum horizon for structure contour mapping. The A3 and A4 coal seams together average 2 to 3 m in thickness. Both seams can be up to 2 m thick and are split by a carbonaceous mudstone or carbonaceous shale. The A4 unit can be absent. These seams contain fewer elastic partings, inferior coal and carbonaceous shale laminae than the A I and A2

seams. Together they make up the working section currently being mined in the Acland Colliery. Sabine coal seams

Up to 11 coals seams (SI to SI I) have been grouped in this interval, only four of which are persistent (S3, S4, S8 and S9). The seams are generally less than I m in thickness and contain few elastic partings. The principal seams, the S3 and S4, usually occur together forming a 2 to 3 m interval of wide lateral extent. The thinner S8 and S9 coal seams are separated by the Tarko tuft' marker. The Sabine coal seams occur in a section up to 30 m thick consisting of predominantly grey to dark grey mudstone with very fine to fine labile sandstone and siltstone interbeds. In several localities light grey, labile, medium grained sandstone sequences up to 6 m thick occur fining upwards into mudstone. Carbonaceous detritus is common on bedding planes. Rock unit 5 (35 m thick) Interbeds of light grey fine to medium grained sandstone, siltstone and mudstone. Sandstone beds are labile with an argillaceous matrix and can occur up to 15 m in thickness in bodies of limited lateral extent. Rock unit 6 (30 m thick), Balgowan coal interval Predominantly an argillaceous sequence containing up to 7 thin coal seams less than I m thick four of which are split by high gamma ray emitting montmorillonitic claystone partings. Grey to dark grey mudstone dominates the section with minor very fine grained sandstone interbeds. Carbonaceous detritus is common on bedding planes. The coal seams, named BI to 87, have been previously described by Mengel ( 1963) from the Balgowan mine area located north of Acland . Rock unit 7 (80 m thick) , Marburg Formation Massive fining upward sandstone sequences from I to I O m in thickness. The sandstone beds have abrupt bases and grade upward from coarse sandstone, pebbly in places, to very fine sandstone, interbedded with grey to dark grey siltstone and mudstone.

Several very thin inferior coal seams of local extent have been intersected. This sequence is conformably overlain by Rock unit 6 of the Walloon Coal Measures and , following Meyers ( 1979), is assigned to the Marburg Formation. The boundary is taken to be at the uppermost of the coarse pebbly sandstone beds. COAL DEPOSITS AND STRUCTURE In the Oakey-Dalby region the location of shallow coal measures with potential for open cut mining is commonly related to the distribution of erosion remnants of Tertiary basalt. The more resistant volcanic rocks which form hill cappings have preserved the underlying coal measures in eievated positions above the surrounding flood plains where alluvial deposition has led to their deep burial. (Fig. 3). In some areas weathering has reduced the basalt cappings to floaters on tops of ridges leaving coal measures outcropping. Detailed wireline log correlation of the drillholes has shown that the coal intervals and the principal seams are remarkably persistent over long distances (Fig. 4). However, considerable variation occurs in thickness and quality of individual coal seams which deteriorate along strike by splitting, thinning and/or deterioration of individual component plies within the seams. Drilling to date has outlined in situ open-cut reserves of approximately 1200 million tonnes in a number of deposits along the crop line of the Acland-Sabine coal interval (Fig. I). Reserves have been calculated for a maximum ratio of overburden plus waste to total coal of 5: I (m:m), with a maximum depth to pit floor of60 m. The Sabine seams have been included in the total working seam section when the ratio of the inlerseam parting to the Sabine coal thickness is less than 1.5 to I. The principal economic deposit is at Glen Roslyn, ·although the contiguous deposits of Manning Vale and Sabine also contain large reserves of low over-burden ratio thermal coal, the aggregate mineable reserves amounting to 450 million tonnes at an average ratio of 2: I m 3/t. A typical analysis of coal from the Glen Roslyn deposit washed to 20% ash is given in Table I . The sample represents an average aggregate working seam thickness of 11 m from a total seam interval of up to 18 m. The coal is per-hydrous and commonly has a canneloid texture. It is classified as High

169

Table 1-Acland Washed Coal Qualit y

GAMMA

Proximate Analysis (air dried)

% % % %

Inhere nt Moisture Ash Content Volatile Matter Fixed Carbon Specific Energy

MJ / kg

RAY

., § ~

~ DENSITY u

4.0 20.0 39.5 36.5 26.30

% 0

% % %

COAL SEAM

!!: -;J CORRELATION (.)

=--

Ultimate Analysis (dry ash free) Carbon Hydrogen itrogen Oxygen Sulphur

ffi

ite

--=-

--~·-

-~-·-----

79.0 6.8 1.2 12.5 0.5

" - - - ·-

Macera/ Analysis Vitrinite Suberinite Exi nite lnertinite Mineral s

Vitrinite Reflectance - -- - -

% % % % %

65-70 10-20 3-5 trace 12-1 8

Ro Max

0.50-0.53

AI-A2 PortlnQ

Volatile Bituminous B (ASTM) with the Internationa l Classification of 7 11 (Australia n 711 , 3 to 5). There is a slight decrease in rank . from east to west represented by an inherent moisture variation from 4% to 6%. The overall structural dip in the coalfield is so uth to outhwest at less than 1.5 . Within coal depo it local variations in dip and strike occur due to local structural features, some re ulting from differential compaction of the edimentary pile. Faulting in the area of the mine workings follows two general directions, NE-SW and NW-SE (Mengel , 1963), the maximum observed displacement being about 80 m. Shell's drilling data indicates that the latter trend is the most developed with the most significant fa ult system cutting the Summers Hill, Box Ridge, Manning-Vale and Sabine deposits (Fig. I). Faulting in a similar direction is interpreted in the Glen Roslyn deposit.

SEDIMENTOLOGICAL STUDIES An obvio us characteristic observed in the Oakey-Dalby region is the cyclic nature of the coal mea ures sediment recognisable by colour, grain size variations, and distinctive wireline log respon es, especially on gamma ray a nd density logs. A cycle is taken to commence with (I) a whitish to light grey labile sandstone with a sharply defined base. The sandstone fines 170

Al Coal seam

A2 Cool seam Glt n Roslyn tuft marker A38A4 Seams S2 Cool seam

S3 +4 Cool stoms

s~ Cool stom

C • CHANNEL

O• OVER BANK

Fig. 5. Co mposi te log. boreholes Ac 135A/1 40A

upwards becoming (2) thinly interbedded with siltstone a nd mudstone which a re, in turn , overlain by (3) grey mud stone, with or without coal seams. This sequence is repeated throughout the section (Fig. 5). The light grey sa ndstone units, up to 12 m in thickness, are separated by between I to 40 m of the interbedded finer grained sediments, making up the remaining two members of the cycle. The three un its a re described from co res as follows. LITHOLOGY OF CYC LES

Sandstone units Several light grey fining upward sandstone units are present with abrupt, possibly erosio nal , bases aga inst the underlyin g mud-

tones. The bases of some units consist of medium grained sandstone containing intraformational angular mudstone and coaly fragments . Some low angle, planar crossbedding is evident; however, finely bedded cross laminations are the most common structures observed although a few units are poorly bedded and massive. The upper sections of the sandstone units grade over an interval of approximately 10 cm into mudstone or finely bedded fine grained sandstone, siltstone and mudstone. This interbedded sequence grades upwards into massive to well laminated mudstone. Petrologically, the sandstones are well sorted, tight , lithic containing about 50% quartz, 40% lithic fragments and 5% feldspar with small amounts of authigenic kaolinite and a carbonate mineral in the matrix. Quartz and feldspar grains are equant but angular and the quartz is of the plutonic variety. Both plagioclase and potassium feldspar are present and are relatively fresh. The lithic material forms heterogeneous, fine grained, granular aggregates probably derived from fine grained sediments or meta-sediments and as a result of diagenesis, the clasts possess ill-defined boundaries. The kaolinite, occurring as coarse grained aggregates, represents less than 3% of the total volume of rock.

Finely bedded sandstone, siltstone and mudstone units M udstone is the dominant lithology and the beds are massive to well laminated with mostly gradational contacts with siltstones and fine grained sandstones. The dip measured on laminations ranges from 0 ° to 13 ". Load casts and convolute bedding are present. In thin section the mudstones and siltstones are characterised by high muscovite contents, up to 20%. In some specimens the muscovite flakes are well oriented along the basal plane producing good bedding characteristics. The matrix is argillaceous (chiefly kaolinite) or carbonaceous. Thin layers of cone-in-cone limestone are inserted and are interpreted as syndepositional deposits. Siderite lenses are made up almost entirely of radial siderite spherules which completely obscure the original bedding. Coal intervals Coal intervals are characteristically interbanded with numerous mudstone partings.

Individual coal plies can attain thicknesses of up to 70 cm without being split by elastic parting but in places, coal plies contain numerous angular mudstone fragments and grade into inferior coal and carbonaceous shale. The coal i black, usually mid-lustrous with a homogeneous, massive or canneloid texture and only little bright and dull banding characteristic of normal humic coals. Although generally un-cleated , vertical closely spaced cleat patterns are well developed in some of the brighter coal plies in places and are usually infilled with calcite or, to a lesser extent, clay or pyrites. Vermicular white clay filled tubes resembling compacted burrows occur normal to the bedding in some partings, and also along the bedding planes of adjacent coal plies. M udstones range from grey to light brown in colour, the latter usually being mont morillonitic and puggy. Arenites rarely present, usually consist of angular mudstone fragments set in an argillaceous matrix. Occasional siderite bands and thin pyrite layers are present. DEPOSITIO AL E VIRO ME TS

Modern fluvial environments are represented by a spectrum of river channel patterns ranging from straight non-braided, through low-si nuosity, to meandering with high sinuosity. Studies of these fluvial environments by various authors (Allen, 1965; Hacquebard and Donaldson, 1969; Le Blanc, 1973) have enabled recognition of these sub-division s in ancient fluvial deposits and models have been proposed to account for deposits broadly similar to those of this section of the Walloon Coal Measures. Various depositional environments have been postulated for the Walloon Coal Measures by other workers in the Surat/ Moreton Basin, for example: Mond (1973), lacustrine, deltaic and pos ibly fluviatile; Swarbrick ( 1973), low energy swamp environment; Exon ( 1976), swamps and streams; Macdonald (1977) , tidal and fluvial channels with adjacent backswamps. As a result of the detailed sedimentological study undertaken as part of Shell's coal exploration programme in the Oakey-Dalby area it is possible to diagnose the depositional environments more precisely and it is considered that the lithologic, stratigraphic and palaeontological data for this section are best 171

attributable to fluvial deposition in a meandering stream environment. Amongst the points considered in making this interpretation were:-

( 1) Only fining-upward sa ndstone sequences a re present as opposed to both fi ning and coarsening-upward sequences tha t typify deltas and other coastal elastic deposits.

Table 2-Summary of Parameters of Fluvial Environments within Rock Units 3 to 5 of the Walloon Coal Measures Oakey-Dalby Region

Channel Facies: (point bar, channel lag, abandoned channel)

O verbank Facies: (levee flood basin elastics, crevasse splay, ponds)

LITHOLOGY

Light grey to grey, medium to fine grained labile sandstone. Contains abundant carbonaceous detritus. Basal section of sandstone body can contain intraformational angular mudstone pebbles, coal fragments and fossil wood. Thin grey mudstones so metimes present.

Light grey to grey fine to very fine grained sandstones, grey to dark brown siltstones and mudslones and carbonaceous shales. Siderite, limestone and iron oxide concretions.

Coal a nd ca rbonaceous shale with mudstone and rarely fine sa ndstone partings.

BED BASE TYPES

Abrupt or erosional base. Transitio nal upper boundary.

Mostly transitional boundaries together with abrupt and rarely erosional. Some convolute bedding.

Abrupt coal boundaries, some gradi ng thro ugh carbonaceous sha le to mud stones.

SEDIMENTARY STRUCTURES

Tabula r cross bedding in lower part of sandstone body. Massive sand stones, cross laminations very common. Thinl y bedded flat lying sandstone is sometimes present.

Beds less than I m thi nly bedded or laminated. Thin sandsto nes may be crosslaminated. Slump structures, load casts and slickensides developed in mudstones. Limestones show cone-in-cone structure.

Massive mudslonc partings, laminations, rootlet st ructure.

FOSSILS

Fossil wood.

Terrestrial plan t remains. Burrows sometimes present in carbonaceous mudslones.

Coalified plant material.

GEOMETRY

Basal contact truncates underlying strata with the upper contact gradational with overba nk or backswamp facies . Sandstone bodies pass laterally into overbank facies . Sand bodies are elongate and lenticular.

Basal contact may be in terbedded or laterall y gradational with channel facies. Upper contact may be erosion al o r abrupt against channel or backswa mp facies.

Occurs interbedded with overba nk facies and grades into ove rbank facies when coa l seams spli t and deteriorate. Bot h facies can have large lateral extent. Often has abrupt upper contact wi th channel facies.

GAMMA RAY LOG RESPONSE

Blocky to bell shaped curve. Degree of se rra tion depends o n the number of mud layers deposited during waning flood stages.

Relatively hi gh gamma cou nt rate. The degree of serration will depend on the extent of interbedding of thin sa nd stones and siltstones.

Low count rate si milar to sandstone bodies over coal seams. Carbonaceous shale wi ll be intermediate between coal and mudstone response.

DENSITY RESPONSE

Typica l baseline response of elastic sediments. High density kicks opposite silicified fossil wood.

Typical baseli ne response to elastic sediments. High density kicks opposite siderite, limestone and iron oxide concretions.

Easily recognisable low density response !'or coa l sea ms. Density response is decreased wit h increasing mineral mailer.

172

Backs1mmp Facies: (pea t swamp ponds)

Thicker sandstone units have abrupt basal contacts with repetition of fining upward sequences throughout the section. (2) Sandstone to shale ratios are low. (3) Terrestrial plant remains are commonly preserved throughout the sequence. Coaly fragments are preserved in the base of sandstone bodies together with fossil wool. Delicate fossil plant structures are perfectly preserved in laminated elastics. (4) Coal seams with rootlet structures in the coal seam floors indicate in situ growth and accumulation of terrestrial plant material. (5) Only terrestrial micro-fossils have been found in the Walloon Coal Measures. Marine micro-fossils have not been recorded. (6) Preservation of fossil plants and coal over a large area indicate low gradients. The three cyclic sedimentological units described in the previous section are interpreted broadly as being channel, overbank and backswamp facies of meandering stream and flood plain environments. The facies correspond respectively to the sa ndstone unit, the finely bedded sandtone/siltstone/mudstone unit, and the coal interval. The summary parameters defining these facies in the Oakey-Dalby region are listed in Table 2. It is recognised that individual characteristics are process specific not environment specific, however, the combination of parameters can be diagnostic for individual environments. FACIES A ALYSIS Two time-stratigraphic units, for which data over the entire coalfield are available, have been selected for facies analysis (Fig. 5): (I) The elastic parting between the A I and A2 coal earns within the Acland Sabine coal interval and (2) The interval from the top of the A I seam to the top of the Tarko tuft' marker. This sedimentary sequence, intersected in over 200 boreholes both cored and chip drilled , has been broadly subdivided into channel, overbank and backswamp facies by interpretation of the petrophysical logs (Fig. 6) . Because the gamma ray tool is essentially responsive to the natural radioactivity of the sediments, and because clay minerals usually give the highest readings, this log reflects the clay content of the sediments. A general

L.S.DENSITY CALIPER

LITHOLOGY

□ Thickly bedded sandstone

-D

Mudstone and interbedded sandstone

Coal

FACIES

Channel

Overbank Backswamp

Fig. 6. Facies interprelation . borehole Da 20

observation that clay content decreases with increasing grain size of sandstones means that lower count rates occur over the coarser sandstone units (Allen, 1965; Selley, 1978). Thus with chip samples from a drillhole together with the gamma ray, den ity a nd caliper log suite the following deductions can be made: (a) The recognition, accurate depth and thickness of: (a) coal seam (b) sandstone units (c) interbedded sandstones, siltstones and mudstones (d) mudstone units (e) sideritic, siliceous and calcareous bands. (2) Correlation of the above rock intervals. (3) The identification of specific gamma ray log motifs and their application to subsurface facies analysis when coupled to core data and parameters of environmental significance. The method employed for presentation of the facies data in map form was to determine for each drill hole the thickness of both of the selected time-rock units together with the percentage within each of the ch annel, overbank and backswamp facies. Facie percentages were plotted on ternary diagrams subdivided into a number of fields (Figs 7 & 8). The field in which each drillhole fell was recorded against that drillhole on a base map together with the thickness of relevant timerock interval. Palaeo-environmental facies maps were then obtained by outlining and shading the areas of equal facies percentages and super173

BACKSWAMP FACIES

'X,

CH ANNE L

OVE RBANK

Fig. 7. Ternary diagram. Al-A2 elastic parting

Fig. 8. Ternary diagram, A I to top Tarko tuff marker

imposing the isopachs of that interval (Figs 9 to 12). Interpretation of the resulting pairs of maps for two individual coal deposits is discussed below.

mudstone. Applying reduction factors of I 0: l for peat and 3:2 for interseam partings, the A2 coal seam would have an uncompacted thickness of about I 0.5 m. Thus for 20 m of elastic sediment to be accommodated in this section differential compaction of the underlying peat and elastic sediments must have occurred.

DEPOSITIO ALE VIRO ME TS

The Al-A2 elastic parting Generally it is observed throughout the coalfield that, where isopachs are less than 5 m thick , elastic sediments are amost totally overbank facies and conversely the thickest intersections of the parting correspond to areas of greater than 50% channel facies. Furthermore, there is an orderly arrangement in facies distribution on the map between the two extremes in sympathy with an increase in channel facies percentages as the thickness increases. lrvingdale-Tark o area

These points are well illustrated in this area (Fig. 9), where a dominant channel facies up to 20 m thick was developed in the west, while to the east only a thin veneer of overbank facie was deposited. A palaeo-environm ental cross section through the lrvingdale to Tarko deposits (Fig. 13), based on the Glen Rosyln tuft marker as a datum plane, clearly shows the relationship between the thickness of this interval and the facies distribution. Detailed correlation of coal seams from wireline logs in this section hows that the A2 coal seam is mostly absent beneath the channel facies and this is interpreted as due to erosion of the peat swamp during the development of the river channel. The A2 seam in this vicinity is about 1.55 m in thickness with 0.97 m of coal and 0.58 m of 174

Acland area

At Acland (Fig. I 0) thin overbank facies occurs over most of the area with a gradual thickening of the elastic wedge westward with an accompanying increase in channel facies percentages. The facies trends are elongate in a N W-SSE direction. The western boundary of the predominantly channel facies zone is not known at this stage due to lack of data.

Top of A 1 to Top of Tarko tu.If marker The distribution of facies data on the palaeo-environm ental maps shows a regular change in facies relationships throughout the coalfield . With a decrease in backswamp facies percentage below 60% there is a corresponding increase in overbank facies percentage. Within the 20 to 40% backswamp facies range there is a shift towards increased channel facies percentages and commensurate decrease in overbank facies. Acland area

A well defined facies trend is apparent through this area (Fig. 11 ). Where the interval is less than 25 m in thickness, it consists of predominantly backswamp facies with minor overbank facies . Virtually no channel facies is present in these areas. It appears that in these localities the peat forming environment was

_3___________ \

IRVINGOALE

GLEN ROSLYN

'; ./

•

• <:;:-. ... ·.·. ·. ·15

......

,..--.....__ 5 bopoch bote

Subaop

Al to top A2 cool seom

MANNING VALE

Acklrd cool ,earn,

Facies numbers refer to Fig. 7. Fig. 9. Facies map, A l-A2, Irvingdale to Tarko

..::.::.-.:..-.:::-,

'-',

GLEN ROSLYN

--:.:=-~

- ---- Subcrop base --top Aclond cool seams

3km

Facies numbers refer to Fig. 7. 11 Fig. 10. Facies map, Al-A2, Acland

MANNING VALE

IRVINGOALE

INE Subcrop

TARKO

baH

top

Acland cool seams

3km

lsopach top Al seam .......__,._ D fo top Torko tuff marker Subc:n>p

.... IOp

Aclond cool ,eoms

Facies numbers refer to Fig. 8. Facies numbers refer to Fig. 8. Fig. 11. Facies map, A 1-Tarko tuff marker, Acland

Fig. 12. Facies map, Al-Tarko tuffmarker, lrvingdale to Tarko

re-established continually during the entire time interval with regular interruptions by overbank facies deposition. The linear northeast trending facies contours indicate a zone of higher overbank and channel facies bordering the dominantly backswamp areas to the east. These variations reflect variations in the Sabine part of the coal interval as the A 1-A2 elastic parting is thin throughout the area. A thick, predominantly channel facies sequence occurs in the northwestern part of the Manning Vale deposit where the interval is at least 60 m in thickness. Channel facies generally becomes more prominent further westward.

parting (Fig. 12) and facies trends again follow thickness variations. A localised thinning of the interval occurs in the Summers Hill deposit producing an area of predominantly backswamp facies surrounded by an elongate area ofless than 10% channel facies. Adjacent and west of this area the interval rapidly thickens to 50 m with the addition of channel facies. The palaeo-environmental cross section (Fig. 13) shows that channel facies between the Sabine coal seams contributes to the overall thickening of the section as well as the A 1-A2 elastic parting. Thus this area shows repeated channel incursions through the peat swamp leaving adjacent areas as predominantly backswamps. Even though the section is exaggerated, it shows the difference in compactabilities of coal, fine grained sediments and sandstone bodies.

Irvingdale-Tarko area

In this area facies and isopach contours show similar trends to the A l-A2 elastic

175

IRVINGDALE

SUMMERS HILL RIDGE

20m.

3km .

Back swamp facies Overb an k

fac ies

F.)\·:)J Channel fac ies -

Tuff ma r ker

Fig. 13. Palaeo-environmental cross-section

CONCLUSIONS Drilling and detailed petrophysical logging have enabled the sub-surface stratigraphy of the lower portion of the Walloon Coal Measures to be divided into seven correlatable rock units, throughout which cyclic sedimentation is evident. Up to thirteen individual coal seams or sub-seams can be correlated between deposits in the principal economic coal interval which contains all the proven reserves. It is concl uded from facies analysis of selected time-stratigraphic units within this interval that the Walloon Coal Measures in the study area were deposited in a high si nuosity fluviatile environment dominated by meandering streams. The A I, A2, A3 and A4, S3 and S4, S8, and S9 coal seams developed within an extensive backswamp or flood basin. Individual seams (A2, A4, S3 and S4) can be locally absent because of(a) erosion by treams meandering across the backswamp, or (b) lateral gradation into carbonaceous shales, indicative of a change from a backswamp to a elastic overbank environment. Separate invasions by streams into the extensive peat swamps which existed at the time occurred between the A I and A2 coal 176

earns, the A4 and S3 coal seams and the S4 and S8 coal sea ms. Some erosion accompanied the migration of streams across the backswamp but differential compaction of the peat mass benea th the accumulating channel sands played an important role in accommodating the thickness of elastics deposited . The thinner Sabine coal seams (SI, S2, S5S7) probably represent backswamp facies associated with nearby channel facies, resulting in localised coal formation. The thin veneers of mudstone were probably deposited within the backswamp during the deposition of the A I-A2 elastic parting by suspended load during flood stages. The study of this pa rting provides a model to explain the numerous intercalcations of mudstone within the total coal seam which represent repeated periods of flooding of the peat swamp. This also explains the high inherent ash values present within coal seams. The high percentages of vitrinite and suberinite which make up over 75% of the coal macerals, and the thick banded nature of the coal intervals indicate rapid subsidence with early burial of peat swamps. The Myall , Irvingdale-Summers Hill, and western portions of the Manning Vale and Sabine areas were sites of repeated river

sedimentation throughout the Acland-Sabine time interval. Subsidence was greatest in these areas, assisted greatly by the ability of peat deposits to compact significantly under load.

The thickest coal deposits occur where peat development kept pace with subsidence in localised areas least affected by river sedimentation.

REFERENCES ALLEN , J. R. L., 1965: A review of the origin and characteristics of recent alluvial sediments. Sedimentology, 5, 91-191. ExoN , N. F. , I 976: Geology of the Surat Basin in Queensland. Bull. Bur. Miner. Resour. Geo/. Geophys. Aust., 166. HACQUERARD, P. A. and DONALDSON, J. R., 1969: Carboniferous coal deposition associated with flood-plain and limnic environments in Nova Scotia in Dapples, E. C. and Hopkins, M. E. (Eds), Environments of Coal Deposition. Spee. Pap. Geol. Soc. Am., 114. LE BLANC, R. J., 1972: Geometry of sandstone reservoirs. Mem. Am. Ass. Petrol. Geol. , 18, 133-177. MACDONA LD , L. , 1977: Paper presented at 2nd Aust. Geol. Conv. Melbourne (unpubl.). McLEA N-HODGSON, J ., 1978: Geological assessment A TP 205C Bowenville. The Shell Company of Australia Limited Company Report CEPR 4/78. MENGEL, D . C., 1963: Coal resources, Darling Downs (Oakey) Coalfield. Parts 1-4. Pubis. Geol. Sur11. Qd314-315. MEYERS, N. A. , 1970: Correlations and lithofacies of Jurassic sediments: Cecil Plains- Ipswich. Rep . Geol. Surv. Qd 40. Mo D, A. , 1973: Dalby, Qld I :250 000 geological series. Exp/an. Notes Bur. Miner. Resour. Geo/. Geophys. Aust., SG/56-13.

SELLEY, R . C., 1970: Ancient sedimentary e11vironme111s, Chapman and Hall Ltd , London. STEVESO , B., 1979: Examination of samples from Acland , Queensland. AMDEL service report 3.114/0-GS I 18/80 to Shell Company of Australia Ltd (unpubl.). SwARRRICK, C. F. J., 1973: Stratigraphy and economic potential of the lnjune Creek Group in the Surat Basin. Rep. Geol. Sur11. Qd 79. TAYLOR , D. A. and BRUNTON, J. S. , 1977: Geological report , Acland coal field, A TP I 29C, for period ended 27th May, 1977. Shell Development (Aust) Pty Ltd Company Report (unpubl.).

J. McLEAN-HODGSO N,* N. H. KEMPTON, The Shell Company of Australia Ltd, 155 William Street, Melbourne, Vic. , 3000.

*Present Address Marathon Petroleum Australia Ltd, I Ith Floor, AMP Place, I 0 Eagle Street, Brisbane, Qld., 4000.

177

OTES O

THE GEOLOGY OF THE TAROOM COAL DEPOSIT A D POSSIBLE UTILISATIO OF ITS COAL By B. A. Coxhead & B. A. Brandt ABSTRACT

The Taroom coal deposit is located on the eastern flank of the Mimosa Syncline in the northern Surat Basin, some 7 km south of Taroom township. The deposit occurs in the lower coal-bearing sequence of the Walloon Coal Measures and contains in excess of 150 million tonnes of strongly perhydrous high volatile bituminous coal within a 30 km 2 area of near-surface subcrop. This paper describes the geology of the deposit and gives details of some aspects of research into its potential utilisation as a feedstock for liquid synfuels and solvent refined coal. TRODUCTIO The Taroom coal deposit is the most northerly of the major Surat Basin coal deposit discovered to date. It is located on the eastern flank of the Mimosa Syncline, 7 km outheast of the town ofTaroom. Distance by road from Brisbane is 460 km and from Toowoomba, 330 km (Fig. I). Exploration title to the main body of the Taroom deposit is held by Mines Administration Pty Limited under Authority to Pros-

pect (AP) l 89C. A northeast lobe of the deposit, however, does extend into an adjoining Authority to Prospect, AP 152C, held by Brigalow Mines Limited and known as the Boxvale deposit. This paper describes both company deposits and refers collectively to them as the Taroom deposit. The development potential of the Taroom deposit is enhanced by its proximity to the town of Taroom , which has a population of 700, the Dawson River (4 km to the west) and the Leichhardt Highway, which crosses the central portion of the deposit (Fig. 2). EXPLORATION HISTORY

A study of seismic shot hole logs and water bore data by staff of Mines Administration Pty Limited in 1967 (Anderson, 1967) indicated that coal sea ms of possible economic significance were present in the Taroom area . An Authority to Prospect for coal (AP 41 C) was applied for on 28th April , 1967 and was granted to the company on 1st August , 1967. The first hole drilled by Mines Administration Pty Limited (Minad) was sited on the Leichhardt Highway just south of Back Creek. It intersected 4.5 m of clean coal at a depth of

!ii

Taroom Coal Deposit

100W00MIA 100'Scolo

Fig. I. Ta room Coal Deposit. Locality Map.

179

GSQ

Ta..-1 ,0

TR21

TR67

TR77 TR136 •·.· ...... :•..:.

. Ll i

A.P. 152 C

A. P. 256C 0

6km

Fig. 2. Taroom Coal Deposits. Tenement Map.

22.8 m. Follow-up drilling indicated the presence of at least 10 million tonnes of relatively low ash coal. Exploration drilling since that date by Minad has outlined 144 million tonnes of coal reserves in situ, of which 107 million are in the measured category. Brigalow Mines have outlined a further 10 million tonnes of reserves in the area covering their portion of the deposit. All reserves occur within 70 m of the surface and are considered to be amenable to su rface mining. Drilling statistics for the respective areas are: • 159 holes drilled , totalling 8242 m of rotary hole and 365 m of 52 mm core in AP I 89C (formerly AP 41C). • 9 holes drilled , totalling 664 m rotary hole a nd 70 m of 52 mm core in AP l 52C. GEOLOGY OF THE DEPOSIT

The regional stratigraphy of the Walloons in the northeastern Surat Basin and the geographic distribution of the major coal deposits in the subcrop zone of the lower and upper coal-bearing horizons are described by Jones and Patrick elsewhere in this volume. Stratigraphically, the Taroom deposit lies near the top of the lower coal-bearing horizon on the eastern flank of the Mimosa Syncline. It covers a surface area of approximately 30 km 2 . Drilling by Minad in the Taroom area has shown that the lower coal-bearing sequence (named the Taroom Coal Measures by Jones and Patrick) consists of 150 m of predominantly fine to medium grained grey labile sandstone with interbeds of grey siltsto ne and mudstone. 180

Fig. 3. Taroom Coal Deposit. Typical Drillhole Correlation Diagram.

Three coal seams, designated Seams I, 2 and 3 in descending order, occur within the section tested by drilling (Fig. 3). Seam I is present in the western portion of AP 189C, where it is generally less than I m thick. Drilling indicates that it has been washed out in part by the overlying Tangalooma Sandstone. No reserves have been outlined for the seam as it is not considered to be of any economic significance. Seam 2 lies a pproxima tely 40 m below Seam I. It consists of up to 7 m of relatively clean coal with an average thickness of 5 m, and is the main seam of economic interest at Taroom. The thickest development of clean coal occurs along an east-northeast axis as shown in Fig. 4. The seam shales out abruptly along the northern margin of the deposit but not quite so abruptly along the southern margin. Mudstone interbands in the seam are lenticular and are not continuous throughout the deposit. The seam, however, does split in the northeast into three partings, designated 2A, 2B and 2C. Structure contours drawn on the base of Seam 2 show that it dips gently west, generally at less than one degree. No faults of any significance occur in the deposit. Some 147 million tonnes of the total 153 million tonnes of measured and indicated class I coal so far outlined occur in this seam and its splits.

WASHABILITY TESTS

Ground Surface

'--V

VERTICAL EXAOGfltATION 10 : 1

Fig. 4. Taroom Coal Deposit. NE-SW Cross Section Seam 2.

Seam 3 consists of banded coal, mudstone and siltstone which may occur over a vertical interval ofup to 20 m. It lies about 35 m below Seam 2. Seam 3 contains an aggregate 2 to 3 m of coal. To date, one small area of potentially mineable reserves, around Back Creek, has been outlined by drilling. It contains 6 million tonnes of coal. COAL Q UALITY The average raw coal quality for the 153 million tonnes of measured and indicated class I coal reserves at Taroom is shown in Table I . Table 1-Taroom Coal Deposit. Raw Coal Quality. SEAM 2 SEAM 3 ::".;' ~

•MATE

ANAlYStS

14 • . - -1

MOISTURE I ASH I VCll.ATILE MATTER I FIXED CARBON I

TOTAL SULPHUR I PHOSPHORUS I SPEC IFIC ENERGY ( MJ / l,g ) HARDGROVE GRINMBI LITY CRUC IBLE

SWELL

7·8 22·9 37·8 31·5

7-2 33·2 32·2 27-4

7-8 23-5 37-4 31· 3

(}31 (}018 22-47 32 'h

(}25

0 ·30

1&50 3' 'h

22·22 32 'h

With regard to coal quality, three important properties of the Taroom deposit distinguish it from other Walloon deposits: (1) The relatively low raw coal ash of 22.9% for the 147 million tonnes of reserves outlined in Seam 2. This ash content is appreciably lower than for most of the other major deposits of Walloon coal of similar size. (2) The consistently low sulphur content of 0.3%. (3) The low H ardgrove Grindability Index.

Washability tests carried out on Taroom coal show that a low-ash product can be obtained using conventional wash plant technology. A 10% ash coal can readily be produced by washing a t 1.6 relative density (RD) giving average yield s in excess of 70% for Seam 2. The yield for Sea m 3 coal is va riable, and depends on the proportion of stone bands in the raw coal. The ultimate analysis of the coal shown in Table 2 demonstrates its perhydrous nature. The coal contains 6.3% hydrogen on a dryash-free (d.a.f.) basis. Table 2-Taroom Coal Deposit. Ultimate Analysis Seam 2.

CARBON I ( da.f.) HYDROGEN I ( da.f. ) NITROGEN I ( da.f.) SULPHUR I (d.a.f.) OXYGEN I ( da. f.) CARBO'-J DIOXIDE I l a.d.)

76·80 6·50 1• 10

0·50 15 · 10

0·40

Typical maceral analyses for Seams 2 a nd 3 appear in Table 3. They show the very high reactives to inerts ratio for the coal. Reflectance determinations show the coal to have a maximum mean oil reflectance (5290 °A) of0.47%. NOTES ON RESEARCH INTO UTI LISATION OF TA ROOM COAL A great deal of interest has been shown in recent years in the conversion potential of Australian coals to liquids and gases, mainly for transport fuels. It is necessary, therefore, in a paper such as this to summarise this work as related to the Taroom coal deposit. The first definitive testing of the conversion potential of Taroom coal was undertaken in 1975 by the Joint Coal Board as part of its survey on Australian black coals. This work confirmed that coal from the Taroom deposit was ideal as a potential feedstock for conversion to solvent refined coal (S RC) and/or synthetic liquid fuels. Details of the work are documented in a valuable publication by the Joint Coal Board and the Queensland Coal Board (Survey of Australian Black Coals of Conversion Potential, 1976).

181

During the first quarter of 1979, the Coal Group at CSR's Research Laboratories at Rosevi lle in Sydney carried out further testing of the properties of Taroom coal financed ational Energy Research Deunder the velopment and Demonstration Program ( ERDDC) of the Commonwealth Department of ational Development. This work was specifically directed towards catalytic hydrogenation of the coal to produce automotive fuels. The coals used were washed whole-of-seam composites of Seams 2 and 3 (Table 3).

Table 4-Batch Autoclave Hydrogenation Test Results on Taroom Coals.

E.p«iment

SU.Ml

SfAM2 COMIOSITE

aMQIIT(

HIA2

Hl35

H i.l

•oo

400 I

400 I I

96·6

97·2

96·7

97· 1

62-0 55-2

66·5

o.d. cool

68-2 56·9

73-8 62 ·0

do I cool

29·6

24·7

20·6

17-3

17·7

16·3

13-6

11· 8

1-030

1·040 A·92 0·93

1-056

1-064 9-01

15 · 1

22-4

6-8

7-2 5-6

8· 4 5·7

3·0

1·6

2·7

No .

·c

Temperotvr• Duration I hours) ¾ Coroly1t

SEAM2

SfAM 3

aMQIIT(

<DMIOStTE

Hl47

400 2 5

CONVflSH)N YIILD ¾ d.o. f. coo I

LIQUID YIIHO g/tOOg d.o f. cool g/ KX)g

56·3

GAS YIELD g /l00 0

li tr•• / IOOg d.o f cool CHAlACTUISTICS Of LIQUIDS •

Table 3---Analyses of Coal Samples used in NE RDDC Programme.

D.isity g/ on at 80'( Viscmity cST at H/C 11:otio

~o•c

Non di,tillablei at 470• C '-

SEAM 2

SEAM 3

c0M,Os1n

co1111,Os1n

""'HB>@l·610. -@~611>.

Heptane ln10luble1 o/. .tophaltene• ¾ Benune Insolubles •1.

4·03 0~6 13-8

9-8

6·86 0·96

0 ·89 23·0 13·9

8-8 5· 1

PIOXIMATE ANALYSIS '4 o.d. Inh ere nt M ou,ture

Ash

Volatil e Mo tt e, F,. e d Corboti

7·0 10· 0 U ·8 38 · 2

7·0 9·0 39 · 5 U ·5

78-0 6·3 l· I

• Properh.. of cool lqu.rh ON meawred on bulk

ore domtnot.d br the a,1g,nol

liquid sampl es ond

anthrocene oil .

Acca,d,ngly the prop•r•••• or• comporotiv• ond not r•p,.s•ntotiv. of thoM from cont1nuCMl'S operotiona.

ULTIMATE ANALYSIS '4 d.o . f .

O ■ yg e n

0 ·4 14 · 2

79·0 5· 8 1· 3 0·6 13 · 3

H/C RATIO

0 98

0· 89

VOLATILE MATTU '4 d.o.f.

53 ·9

47·0

Carbon Hydr<>Q en

Nitrog en

Sulphur

PETROGIIAPHIC AN ALYSI S '4 by Vol V1h1n1te

E•1n1te

73 21 tr a ce

Seffli - ,ner tinit e

trac e

l ne r t1n1te

M ine rals

The Seam 2 sample was prepared from six drill cores taken from the eastern side of the deposit. Recovery from float-sink separation at 1.6 RD was 70.5%. The Seam 3 composite was prepared from two drill cores. Yield at 1.6 RD was 56.7%the lower yield for this seam being due to a higher proportion of stone in the raw coal. In all, 9 hydrogenation tests were carried out on the Seam 2 samples under the following range of conditions: (I) Temperature- 375, 400 and 425 ° Celsius. (2) Concentration of Catalyst (Cobalt Molybdate)- 0, I and 5%. (3) Time- I or 2 hours. The more significant results of these tests are shown in Table 4. 182

The results obtained were: {I) In the pre ence of cobalt molybdate, conversion yields were between 94.3 and 97.2% under all conditions examined. Typically, conversion yields were 97 ± 0.5%. (2) In the absence of the catalyst, conversion was reduced to 73% using unhydrogenated anthracene oil. This was notably improved to 88% using a prehydrogenated anthracene oil. (3) Trends with variation in process conditions were similar to those observed with other coals, i. e. gas yields were increased at the expense of oil yields with increased temperature and time of hydrogenation. (4) Oil yields varied from 40.0 to 75 .9 g oil/ 100 g of d.a.f. coal depending upon process conditions and are comparable with results on Lemington coal (used as the reference coal) in the presence of cobalt molybdate. The ash contents of washed Taroom coal samples are slightly higher (at 10% for Seam 2 and 9% for Seam 3), so that oil yields for Seam 2 are generally about 5% lower on an air-dried basis. Oil yields for the two tests on Seam 3 coal are somewhat higher than for Seam 2. Without catalyst, oil yield was reduced more than for Lemington coal but oil yield

was improved when a prehydrogenated slurry oil was used. (5) Results on Seam 3 are, if anything, slightly better than those for Seam 2. Carbon balances for the reactants and the products for all tests were satisfactory, ranging from 98.2% to 101.4% and averaging 99. 1%. A large diameter (150 mm) core drilling programme has recently been completed at Taroom to extract a bulk sample of coal for shipment to the Federal Republic of Germany. The coal is to be tested in a 150 kg/day continuous catalytic hydrogenation reactor built by Saarbergwerke AG at Saarbriicken . The Saarberg process uses a cheap, disposable catalyst in a specially designed reactor which can operate at appreciably lower pressures than similar processes currently under development. The Saarbergwerke design simplifies the recovery of gaseous, liquid and solid products from the plant. Residue coke can be hydrocoked to produce the hydrogen used in the conversion process. The product oils can be cracked and refined using conventional refinery technology to produce transport fuels suitable for Australian needs. It is envisaged that the unit size of a commercial Saarbergwerke plant will be 40 000-50 000 barrels per day and will con-

sume approximately seven million tonnes of coal per annum. Should the technology and economies of operation be confirmed in pilot plant tests, the commercial development of the Saarbergwerke process will augur well for the development of medium-sized coal deposits such as Taroom because: (I) The capital cost of a conversion plant can be decreased to a more realistic figure (as compared with plant using other technology). (2) The volume of assured water supply needed to operate the plant is reduced appreciably- a very important consideration when selecting a site for a conversion plant. (3) The size of coal deposit needed to supply the plant during its expected operational life is reduced to 150-200 million tonnes. (4) There appears to be no economy of scale, i.e. a 50 000 barrel per day plant will operate just as efficiently as a I 00 000 barrel per day plant. In conclusion, it is considered that development of coal deposits such as Taroom will occur within the next 5 to I 0 years and that production of the Surat Basin coals could match that of the Permian Bowen Basin coals during the l 990's.

REFERE CES A NDERSO , J . C. , 1967: Coal prospects of the Injune Creek Beds in the T a room area. Mines Administration Pty Ltd Compa ny Report o. 5/1 967 (unpubl.). BRA NDT, B. A ., 1979: Third annual report Authority to Prospect 189C- Taroom. Mines Administration Pty Ltd Company Report No. Q/ 189C/643 (unpubl.). CoXHEAD, B. A. , 1976: Final relinquishment report on Authorities to Prospect 41C and 132C. Mines Administration Pty Ltd Company Report No . Q/41C-132Cf 584 (unpubl.). CoxHEAD, B. A., 1977: Progress report on geological investiga tion of Taroom coalfield. Mines Ad-

o. ministration Pty Ltd Company Report Q/ 189Cf602 (unpubl.). NATIONAL ENERGY RESEARCH DEVELOPMENT AND DEMONSTRATION COUNC IL, 1979: Progress report number I, catalytic coal hydrogenation for automotive fuel s (unpubl.).

B. A. COXHEAD, B. A. BRANDT, Mines Administration Pty Limited, 23rd Floor, AMP Place, 10 Eagle Street, Brisbane, Queensland, 4000.

183

THE AUSTI YALE COAL DEPOSIT- WA DOAN A PALAEOE YIRO MENTAL A ALYSIS By G. M . Leblang, P.A. Rayment & M. Smyth ABSTRACT

The Austinvale Deposit is typical of a series of shallow lying, thick, lenticular coal deposits which have been defined along the outcrop zone of the Jurassic Juandah Coal Measures near the township of Wandoan in the northeast Surat Basin. Exploratory drilling commenced in 1975 and to date some 59 drillholes have been completed within the potential economic boundaries of the deposit , which covers an area of about 7 square kilometres. A reconstruction of the conditions of deposition of the Austinvale deposit is presented. This reconstruction utilises detailed petrographic data to assess depositional cycles in the main coal seam horizons, and a study of sedimentary features, revealed from cored and non-cored drillhole data, for interpretation of facies variations in the elastic sediments. Expanded geological sections have been drawn to illustrate the role of differential compaction in controlling location and geometry of the coal deposits. Detailed petrographic profiles of the A and B seams at Austinvale are presented, and the distribution of macerals and microlithotypes is described . The environment of deposition of the Austinvale deposit is interpreted as lower fluvial. The coal sequence is preceded by migrating point bar sequences whose associated channels were stabilised during coal seam deposition, allowing thick peat accumulation in four episodes, with minor interruption by overbank type deposits. Coal deposition was interrupted finally by the onset of deposition of the Springbok Sandstone, characterised by migrating point bar-channel facies. I TRODUCTIO

This paper is based on the results of two studies of the Austinvale coal deposit. The first was a macroscopic study of the succession using data from close pattern drilling and the second was a microscopic study of the coal seams of economic interest. By considering

both sets of data in this paper, a reconstruction of the palaeoenvironment can be attempted . This work illustrates the benefit of techniques such as coal petrology and environmental reconstruction in the exploration of coal in the Surat Basin. LOCATIO

A D STRATIGRAPHIC SETTI G

The area studied lies in the northeast Surat Basin in southeast Queensland, 5 km north west of the township of Wandoan (Fig. I). The deposit contains three coal seam horizons, of which two are of economic interest. These coals occur within the Juandah Coal Measures (Jones and Patrick, this volume) and the top of the uppermost coal member marks the top of the formation. The Austinvale deposit is located in the thickest part of the coal-bearing sequence, which occupies the zone of greatest Jurassic subsidence. This zone, which is known as the Taroom _Tro_ugh , was strongly influenced by compact1on-1nduced subsidence in the underlying Permo-Triassic sediments of the Bowen Basin . The sequence thins away from the Taroom Trough on to the Roma Shelf to the west and into the Moreton Basin to the east. The coal seams were deposited when peat formation became a dominant facies at the close of major regressive sedimentary cycles in the Surat and Moreton Basins during the Jurassic. The compaction controlled subsidence in the Taroom Trough was comparatively steady and smooth and provided a suitable environment for continuous deposition of peat during the main coal-forming periods, whereas sharper adjustments in basement levels on the more stable environments of the Roma Shelf and Moreton Basin, which appear to have been tectonically controlled, caused frequent interruptions to peat deposition. Exploration has located an array of loci of thick coal deposition within the coal horizons at the top of the Juandah Coal Measures within the Taroom Trough, separated by 185

... ' . . . . _,_:_ ......... -:,.... , , ,,,.,,✓

•••

• •

· _· ---..;___l,----_

·~··l ,'

TR IAL

AUSTINVA COAL DEP

Fig. I. Loca ti on of the Austinvale Coal Deposi t.

deposition , although they were actually centres of low deposition. Each of the coal deposits shown in Figure 2 was formed in one of the e depocentres. The Austin vale deposit is adjacent to one of the large gaps defined on economic grounds, becau e of seam thinning, and the studies described in this paper were undertaken in an attempt to understand why such gaps occur. GEOLOGY OF THE AUSTI VALE DEPOSIT

GE ERAL

Ausbrwat•

Ar.a

J Fronk CIHk Ar•a YNbo9,JI 6

7 8 9 10 11

12 13

......_,__ J

Ar@IO

Tu b y Hil Areo Surrmet H,U Area Anchor Bar Ar• o Mud CrHk Area Bur ungo Area Gulugubo Area

Wo 1t ong1- Stanl ey Pork Area Glen Lau re l Area Paradise Downs Area

Fig. 2. Deposit Map, Wandoan Area.

gaps, where the seams are commonly too thin to be of economic significance; however, in one gap, between Anchor Bar and Woleebee, some coal members are discontinuous. The term coal depocentre is used in this paper to describe these loci of thick coal 186

The Au tin vale deposit is typical of the coal deposits in the uppermost part of the Juandah Coal Mea ure in the Taroom Trough area. Coal occurs in three recognisable horizons designated A, B and C in descending stratigraphic order. All the seams thin and split outward from their individual centres of deposition. As in most of the deposits nearby, the A and B seams are the only seams of economic importance, although C seam contributes minor reserves to the total in some areas. The geometry of the coal seams shown in Figure 3 is complex, but the elastic facies exhibit a much higher degree of complexity, and their geometry is difficult to interpret even with close spaced drilling. However, the geometry of the elastic facies , and correlation of elastic units is often critical in correlating coal seams.

COAL SEAMS

AF'PFIOX SCALE IN METRES

The A, 8 and C horizons consist of humic coal , which is macroscopically homogeneous, and " tonstein like" stone bands. Correlation of the seams is shown diagrammatically in Figures 4A and 48. Because the coal is relatively homogeneous in its macroscopic appearance, definite lithotype profiles are difficult to observe. Microscopically, however, good profiles can be obtained. Correlation on a macroscopic basis therefore relies to a large degree on stone bands. These bands in the Austinvale coals are persistent over distances of up to I km only and tend to change their character laterally, so th a t macroscopic correlation is very difficult in these areas. Hence assessment of coal reserves and mine planning at an early stage of exploration is subject to some risk. However, if the depositional processes involved are well understood , this risk can be minimised . Reconstruction of the environment of deposition is the key to this understanding.

CLASTIC SEDIMENTS

The elastic rocks in the sequence, while not diverse in lithology, exhibit complex geometry, so complex in fact that correlation of elastic facies between drill holes as close as 200 metres is often difficult if not ambiguous. For example, equally logical alternative interpretations to the correlations presented in Figure 3 could be proposed . In some areas of these sections it is possible that altern ative correlations of elastic facies can seriously alter the coal seam correlations derived by macroscopic interpretation. The solution to these ambiguities would appear difficult without more information provided by additional drilling and wireline logs. The authors believed that a reconstruction approach was required and that this should be done on both macro and micro scales. To this end, a macroscopic reconstruction was performed by expanding facies in geological section to approximate their original geometry prior to compaction, and detailed ply by ply analysis of a reference core of the A and 8 seams was made.

R101

SECTION

Fig. 3. Coal Seam Geometry (3 sections, non-expanded, 50: I)

PETROGRAPHIC ANALYSIS The A and 8 seams of the Austinvale deposit from drillhole C6748 have been

187

Cll.6

C223 C21B

C253

VERTIC AL

SCALE HOO

0 ·5 0

1·0 Metres

Fig. 4A . Coal Seam Correlation (lithoprofiles)

188

2·0

C 248

F11.7

C 11.9

C221

C J38

CIJ9

VERTICAL SCALE 1:100 0 -5 0 1-0 2-0 Metr es

Fig. 4B. Coal Sea m Co rrela tion (lith oprofi les)

189

WANDOAN ''A" SEAM

AU STINVALE

WANDOAN • 0· SEAM

AUSTINVALE

L M N

SHA L

~ -f

• COA

J SHALE.

uu +--_..,..,

X +----'',,I

V= z=::==;;==:= =:;;:::::=='.::==~I SHA L E = 11 11 1

:Jffi!~fil] ==~ AA-::-'.~==:::;;::---=::= 1-'--~ - - -~om - -:--::::::::;::' ~ -r--.88 ~l==,==~1~1-~p:=:_;: ,o 80 0 '/, VITRINITE

,o O ,o

VV +--,-~..---~,,.__~-1--'-,----....... 0r ,o O ,o O ,o 0 ,o 80 0 % VITRINITE

I % MINERALS "/, EXNITE I ¾NERTINITE

I % MINERALS % EXINITE I % INERTINITE

Fig. 5. Pet rographic Profiles a t Austin va le showin g maceral compositi o ns of plies A Wa nd oan ·A· Seam B Wa nd oan · B' Seam

anal ysed in detail for both maceral a nd microlithotype content (Figs. 5A, B and 6A, B). The majority of the subsections contain 80% or more vitrinite plus " resinous vitrinite" . Resinous vitrinite includes very low reflectivity vitrinite, resin impregnated vitrinite, and suberinitic tissue, and is 10-15% of the total vitrinite component. The exinite content of the subsections is I 0% and less: inertinite is as high as 44%, varying inversely to the vitrinite content. In high vitrinite subsections, resinite and semifusinite are the most abundant exinite and inertinite macerals, respectively (Fig. 7). Sporinite and inertodetrinite are dominant in the subsections richer in inertinite. Each of the latter subsections immediately precedes a dirt ba nd in the A seam . The B seam is petrographically much more uniform than the A seam, and does not show such marked variations. The components of the exinite and inertinite maceral groups are given in Figures 8 and 9, respectively. Figure 8 shows the overall 190

dominance of resinite. Cutinite, though not abundant, is usually very well preserved in the coal. Semifusinite is the dominant inertinite maceral (Fig. 9). The proportion of fusinite is unusually high and , in this low inertinite coal, a forest fire origin for it is likely. This hypothesis is supported by macroscopically visible, well preserved, charred twigs found in the coal. Most subsections of the seams are composed almost entirely of the microlithotypes vitrite plus clarite (Fig. I 0). The higher inertinite content of some plies is represented by an increase in the intermediates {duroclarite, clarodurite, vitrinertite) content or, rarely, as durite. Where durite is present, it underlies a dirt band which marks an horizon of major splitting. The increase in inertodetrinite, sporinite and du rite before the deposition of inorganic sediments of major significance may be due either to: (i) An increase in flowing water and thus water depth with greater oxidation of the plant debris; or

WANDOAN A SEAM

WANDOAN "s "' SEAM

AU STINVALE Sm

AUSTINVALE 6m

cc OD EE

slLE~

GG ~ ;- G_ J

HH 11

MM M

00 pp

D P = -.---,...---,-,..--,,..,--,r-"='r-'-=r~

R RR

uu vv

SHALE

V+C

y~z *=:::;:~=:;':==*=~=*

40 I

0 20 Du

0 20 Fu

0 20 0 20 Sh.C. M ¼

AA = BB

40 V+ C

40 I

0 20 Du

0 20 Fu

0 20 0 20 Sh_C. M

Fig. 6. Microlithotype Profiles at Austinvale A Wandoan ·A' Seam B Wandoan ·s' Sea m

(ii) A change in plant type, virtual absence of standing water with a resultant greater degree of oxidation of the plant debris. If (i) were the cause, the plants subjected to oxidation would be those which had been producing the vitrinite-rich layers. These plants would consist predominantly of woody tissue and the inertinite produced would most probably be rich in semifusinite. Also resinite should remain as the dominant exinite maceral. As inertodetrinite and sporinite characterise these durite-rich layers, cause (ii) is favoured . Inertodetrinite is derived from plants which are herbaceous rather than woody, and which grow in relatively dry conditions. Resinite is unlikely to occur in this environment as it is associated with woody tissue, whereas sporinite is commonly derived from herbaceous plants. Such durite-rich layers develop as an integral part of the coalforming cycle in Carboniferous coals (Smith, 1962). The durite-rich layers represent an equilibrium position for the swamp, and in a stable

environment can persist for much longer than the vitrite-rich layers. However, a fluvial environment, in terms of coal accumulation , is an unstable one, so that the equilibrium state is brief, and durite layers are very thin. MACROSCOPIC RECONSTRUCTION

This reconstruction is based largely on drill log information. All information on elastic '!'i.A.ti_Q_QAN

A+B

SEAMS:

AUS Tl NVALE

C6 7 4B

VITRINITE + RESINOUS VITRINITE • SPORNITE MOST ABUNDANT • CUTINITE ~ • AESINITE #

t INER TOOETR INITE {+H1CRINIT E) )0

HOST ABUNDANT ~

SEHIF US INtTE I + F USlNITE ) MOST ABUNDANT

70 )0

,o 10

EXINITE

INERT INITE

Fig. 7_ Macera! compositions of the plies of Wandoan A & B Seams at Au stinvale.

191

WANDOAN A•B -~EAMS: AUSIINYALE C674B SPORINITE

. •• . • .• .. . . . . • • ,=· . . .. • so

CUTINITE

RESINTE

Fig. 8. Components of the Exinite Macera! Group in the plies of the Wandoan A & B Seams at Austinvale.

sediments, apart from one full y cored hole, was derived from rotary drill cuttings. Most of the coal information has been derived from cored sections. A full eries of sections across the deposit was drawn, with 50: 1 vertical exaggeration employed to accentuate the geometry of the various facies. For this purpose a simplified set of three facies was devi sed . A full range of elastic sediments occurs in the sequence, ranging from coarse sandstones (minor) to medium to fine sandstones, through siltstone to shale (minor). The elastic rocks have been grouped into facies dominated ( > 90%) by sa nd s or dominated by silts and muds. The coal facies includes intraearn inorganic bands arbitrarily less than 0.30 m thick. Sections 3 a nd 4 (Fig. 3) are two repre entatives of the suite of sections drawn east-west and Section 7 is one representative WANDOAN A•B SEAMS: AUSTIN VALE C674B

of the north-south suite (Fig. 3). A number of important clues can be gained from these sections, even though, as mentioned previously, the correlations could be ambiguous: (i) The structure of the coal seams appears to be strongly controlled by differential compaction , influenced by the presence or absence of sand bodies. (ii) The main splits in the seams appear to be generated by elastic wedges which origin ated marginal to the deposit. (iii) The coal sea m splits which are separated by these cla tic wedges a re marked at their tops by the highest durite levels observed microscopically. Clastic wedges are well correlated with the inorganic subsectio ns, F, P. CC, HH in the core examined (Figs. SA, B and 6A, B). (iv) The sand and si lt sequences seem to fit a migrating point-bar facies model , especially those predating the main peat horizons; those sa nds postdating the peat horizons appear to be dominated by channel shaped bodies. (v) Section 7 (Fig. 3) appears to coincide with the axis of deposit ion exhibiting a southward shift in the centre of pea t deposition with time. To put these conventional interpretations to the test , each of the facies was expanded to approxi mate its estimated pre-compaction geometry. T he compaction ratios used were, sa nd 1:1, si lt-mud 2:1 , coal 10:1. The three sections in Figure 3 were expanded vertically with these ratios (Fig. 11 ). These sections were drawn by taking the top of the uppermost persistent seam, A seam, as a WANDOAN A•B S!:A.t,,1S: AUST NVA LE

6748

YITRtTE ♦ ClARITE

INERTOOETRINITE + HICRINITE

90 80 30 70 60

so 60

40 •G

30 BO

SEMIFUSINITE

FUSINITE

Fig. 9. Component s of the Inertini te Macera! Group in the plies of the Wandoan A & B Seams at Austinvale.

192

INTERMEDIATES

OURITE + INERTIT E

Fig. 10. Microlithotype compositions of the plies of the Wa ndoan A & B Seams at Aust invale.

3 LEGEND

Sandstone

Siltstone

Coal

RL36

HORIZONTAL

200

SCALE

300

LOO

Metres

SECTION I.

RJL9

R319

SECTION

Fig. 11. Expanded Sections.

193

horizontal datum, and as such approximate the section at the end of A seam deposition. Where A seam is known to be absent due to outcrop, the top of the lower seam, C seam, has been used as datum on a best fit basis. A number of conclusions can be drawn from these sections: (i) In general, the thicker peat accumulation occurred where the sa nd :silt ratio was low in the elastic fac ies deposited immediately before and during peat deposition . Th is condition appears to be a prerequisite for generation of localised peat accumulation. (ii) The sand:silt ratio increa es markedly to the ea t and we t (Section 3 and 4, Fig. 11 ). In the north-south Section 7 the sands are more irregularly distributed. In all the sections the locations of sand bodies can be seen to have a marked influence on the thickness of peat subsequently deposited . Section 7 also demonstrates that the centre of pea t deposition shifted so uthward with time, consistent with a regressive fluvial environment of deposition . (iii) The east-west sections suggest that the peat swamps were generally in equilibrium with the marginal elastic facies , and that all rock units are conformable. From

this we may concl ude that during peat accumulation the channels in the fluvial system were stable enough to obviate migration, and point bar sedimenta tion entered the pea t swamp area only in the majo r breaks in peat accumulation. This requires that peat growth was well bala nced with deposition in the elastic rich zones in the environment, apart from a few major elastic "overloads" which poured elastic wedges into the peat swamps either as overbank deposits, or by point bar encroachment. PALAEOE VIRONME TA L I TERPRETATIO

It is concluded from the foregoi ng observatio ns that the coals at Austinvale were deposited in a lower fluvial environment. The coals.occur at the top ofa regressive sequence of point ba r sedimentation . Point bar sedimentation was the dominant regime throughout Ju andah Coal Measures time, and at certain times the regime regressed to a stage where the point bars stabilised allowing swamp and flood plain depo ition to dominate. Th is situation is reached immediately up tream from the deltaic part of the fluvial system (Fig. 12). Delta Coa l

Swamps

YOUTH

MATURE

Fig. 12 . Deltaic Fluvial Systems Diagra m.

REFERENCES 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, o. 19. 423-474.

194

OLD

G. M. LEBLANG, P.A. RAYMENT, Thiess Bros Pty Ltd- Mining Division, Kerry Road , Archerfield, Qld , 4108. M. SMYTH , Fuel Geoscience Unit , CSIRO, Minerals Research Laboratories, P.O. Box 136, North Ryde, N .S.W., 2113.

Present Addresses: G . M. LEBLANG, Bond Corporation Pty Ltd, International Building, 26 St. Georges Terrace, Perth, W.A. , 6000. P. A. RAYMENT, Island Creek Coal Pty Ltd, 100 Miller Street, North Sydney, N.S.W. 2060.

195

PETROGRAPHIC STUDIES ON INSOLUBLE RESIDUES OF HYDROGENATED COALS By R. E. Guyot & C. F . K. Diessel ABSTRACT

Australian Coal Industry Research Laboratories Limited (ACIRL) commenced batch autoclave hydrogenation studies in 1965. These studies were accelerated by the petroleum shortages of 1973, and because of the need to find alternative fuels to both replace decreasing reserves of indigenous petroleum and counter ever increasing prices of imported crude. ACIRL's expanded activities have included the addition of batch autoclaves of various capacities and operating capabilities and the operation of a I kg per hour continuous reactor unit. Coal petrography has played an increasingly important role in coal hydrogenation. In order to understand more fully the hydrogenation history of the coal macerals, the feed coals and insoluble char residues were petrographically examined, both at ACIRL and the University of Newcastle. Special emphasis was placed on the influence of coal and maceral content on rank conversion/product yields, in addition to examining the petrographic entities in the insoluble char residue. Research has indicated that three groups of petrographic entities can be distinguished in the insoluble char residues, these being: 1. Undissolved material- apparently " inert" material such as inertinite and mineral matter; 2. Solvent affected material- partially dissolved carbonaceous material or polymerised/resolidified liquids. 3. Heat affected material- mesophase, semicoke, graphite. It was found in some coals that about half of the inertinite macerals had been converted by hydrogenation, especially if reflectance was below 1.4%. In addition, the amount of mesophase in the insoluble char residue was found to increase with an increase in the rank of the feed coal. As both the rank and proportion of "reactive" macerals associated with the feed coal were found to influence the degree of conversion and properties of the hydrogenation products, the term " petrofac-

tor" was devised to express the relationship between them. "Petrofactor" (P 1) is defined as: Mean Maximum Vitrinite Reflectance . 103 "Reactive" Macerals x with the " reactive" macerals comprising vitrinite plus exinite expressed on a mineral free basis. In the future it may be possible to include a portion of the inertinite in the " reactive" constituent of the coal. The data reported here were derived from some twenty coals varying in rank from brown to anthracite. These data indicate that increasing "petrofactor" relates to both decreasing coal conversion and yields of coal liquids and decreasing volatile matter and atomic H/C ratio of the feed coal. Increasing " petrofactor" was also found to relate to both increasing amounts of mesophase/semi-coke in the hydrogenation char residue. INTRODUCTION

Decreasing reserves of petroleum and increasing prices have catalysed world wide research into the conversion of coal into liquid hydrocarbons. Various processes have been devised to do this, one of which is direct hydrogenation. In direct hydrogenation a pulverised coal/solvent slurry is forced to react with hydrogen under elevated temperatures and pressures yielding gaseous and liquid conversion products as well as an insoluble char residue. The latter consists of both mineral and carbonaceous material, the carbonaceous material ranging from undissolved coal to solidified/polymerised coal liquids. Previous work by Guyot ( 1976), Guyot and Diessel ( 1979), Shibaoka and Ueda ( 1978), and Diessel and Guyot (in press), has shown that both the yields and properties of the liquids and insoluble char residues are dependent on a number of variables such as temperature-pressure-time conditions of hydrogenation, catalysts and the chemical and petrographic characteristics of the feed coal. In this paper relationships are explored between the effects of a combination of coal 197

rank and petrographic composition ("petrofactor" ) on both the non-catalytic conversion of coals into gases and liquids, as well as the cha racteristics of the coal liquids and petrography of the insoluble char residues. The term " petrofactor" was previously discussed by Guyot ( 1978 and 1979). PROCEDURE

HYDROGE ATIO

All coal conversion experiments discussed here were conducted by the general procedure outlined in Figure I. Specifically the procedure consists of reacting about 500 g of airdried coal, crushed to minus 75 µm, with three times its mass of tetralin solvent in a 4 litre batch autoclave. After sealing the autoclave the mixture is stirred and pressurised with hydrogen to give a "cold" initial pressure of 8.3 MPa (1200 psi) then heated to 400 cc over a I{ hour period and maintained at this temperature for a further 4 hours. At the end of the reaction period the autoclave a nd contents are allowed to cool down to 150 C a nd the gase , water vapour and lower boiling oils a re then vented , collected, weighed and a naly ed . After the autoclave and remaining HY DROGE N

COA L

contents have cooled to ambient temperature, the liquid and solid reaction products consisting of coal liquids, tetralin solvent and insoluble char residue are separated by vacuum filtra tion. The olids retained on the filter paper are washed with hot toluene until the washings are colourless, then dried under vacuum at 80 C until constant mass. Both the mass of the feed coal and dried solids are used in the calculation of the coal converted into liquids and gases, according to the formula: Conversion (%) = I00 x Mass coal (daf)- Mass insoluble residue (daf) Mass coal (daf) The toluene washings are added to the filtrate (coal solution) and then distilled at atmospheric pressure to recover the toluene and tetralin leaving the undistilled residue (total liquid product or coal extract) which is weighed to obtain yield data and anal ysed . A representa tive major portion of the coal extract is then vacuum distilled to obtain yield structure and analytical data for both the distillate oil a nd distilla tion residue, the latter being a pitch-like substance al so referred as solvent-refined-coal (S.R.C.).

SOLV EN T

RESULTS

GASES

AUTOCLAVE 1 - - - - - - - - - '

AUT OC LAV E PRODUCT

t F I LTRAT ION

t INSOLUBLE

M ATTE R

COAL

SOLU TION

t DISTILLATI ON 1 (AT MOS PHE RIC)

t t

COA L EXTRACT

RECO VERED

SOLVENT

DIS l'ILLATIO N 2 I VAC UUM )

OI STILL ATI ON - RESIDUE

DISTILLATE- Oil

f S . R.C. )

Figure I. Schematic flow diagram of hydrogenation procedure.

198

Twenty coals have been examined/analysed which consist of two brown coals, four subbituminous, four high-volatile bituminous, three medium-volatile bituminous, four low-volatile bituminous and three anthracitic coals. Their properties and classification are shown in Table I in which coals from the Surat Basin have been identified by an asterisk. In Table 2 some coal and conversion characteristics are compared whereas Table 3 shows the petrographic composition of the insoluble char residue. Figure 2 shows the general plot of the coals o n a Seyler diagram . The relationships between " petrofactor" and both the coal conversion and yields of total liquids are illustrated in Figure 3. Figure 4 shows the relationships between the rank parameters, volatile matter and atomic H /C and the " petrofactor". The relationships between " petrofactor" and both the relative density of the coal extract and the proportion of mesophase/semi-coke in the insoluble char residue are shown in Figure 5. Figures 6 to 12 inclusive are photomicrographs of some of the

100

-.. ~

6 0

:::

I A□ I M oisture (per 100BO OM F)

8910

J( S u b-Hydr ous

. s

I I I I I

., C

g3 u

100

Carbon Content

<% dry mineral matter lree

□

BROWN

•

SUB-BITUMINOUS

COALS (4)

HIGH- VOLATILE

BITUMINOUS

MEDIUM-VOLATILE

LOW-VOLATILE

ANTHRACITE

COALS (2)

BITUMINOUS

COALS

(4)

COALS (3)

COALS

(4)

(3)

Figure 2. Plot of feed coals on a Seyler diagram. Full circles and triangles refer to Surat Basin samples.

199

C "O

~ a:: 40

r~ ~

UJ 20

d ~

§2

....J

lJJ

PETR0FACT0R

u 20 0

0 --~-1----11----l,--l--- -, 60 40 20 0

1·0

PETR0FACT0R 0

100

~ 0·8

a:: El

~ :I:

•

~ 06

0 -0

~ ,2..

0·4

....J

PETR0FACT0R

w >0

Figure 4. The rel ationship between petrofactor and rank of feed coal. Circles in top diagram refer to volatile matter, squares in bottom diagram relate to atomic H/C. Full circles and squares indicate Su ra t Basi n sa mples.

=> 0

:J 20

petrographic entities identified in the insoluble char residues. DISCUSSIO

PETR0FACT0R Figure 3. The relationship between petrofactor and conversion (circles in top diagram), as well as liquid yield (sq uares in bottom diagram). Full squares and circles refer to Surat Basi n samples.

200

RELATIO SHIPS BETWEE COAL CHARACTERISTICS, CO VERSIO , YIELDS A D PROPERTIES OF HYD ROGENATION PRODUCTS Reference to Table 2 indicates that lower rank (R 0 max < 0.6%) and/or perhydrous

Table I-Analyses of Feed Coals Coal Sample

Coal Samples

Analysis B

Cl..l_ 4.3 10.8 7.7 2.7 16.8 l.3 8.5 47.3 42.5 85.5 42.0 40.6 41.3 l l.7 36.9 22.22 25.58 40.91 27.00 0 ½ ½

6.5 14.8 41.2 37.5 26.29 ½

H II

19,20

l.0 1.4 0.7 0.4 10.6 9.8 9.5 9.6 20.4 22.3 19.3 17.8 68.3 67.5 69.8 71.6 31.65 32.69 31.85 32.70 5 8 8 8½

l.4 13.2 13. l 72.3 29.86 0

2.8 5.0 2.7 6.9 8.6 16.7 25.0 35 .0 26.4 55.5 53. l 62.3 27.33 30.08 31.49 l 5 2½

0.8 25.9 21.0 52.3 25.65

p /8

PROXIMATE (As analysed) Moisture (%) Ash (%) Volatile Matter (%) Fixed Carbon (%) Specific Energy (MJ/ kg) Swelling Index

13.8 3.4 43 .8 39.0 22.97 0

ULTIMATE (dry-ash-free) Carbon {%) Hydrogen (%) Nitrogen (%) Sulphur (%) Oxygen (%) H/C Ratio Volati le Matter (%)

89.9 70.0 65.3 79.4 85.2 79.0 76.8 74.3 83.6 83.5 82.2 82.7 86.6 85.0 88.6 88.7 88.7 89.5 89.0 89. l 3.42 4.6 1 4.32 6.10 10.59 6.90 6.21 5.43 6.27 • 5.35 4.84 5.45 4.76 4.95 4.8 1 4.80 4.80 4.67 4. 16 4.0 0.62 0.55 l.00 0.95 l.29 l.06 l.46 l.95 l.80 l.40 2.05 l.96 l.69 l.62 l.90 l.98 2.08 l.66 l.69 l.80 l.51 0.40 0.46 0.53 0.68 0.48 0.36 0.58 0.57 0.72 0.57 0.58 0.56 0.52 0.32 0.31 0.69 0.72 0.47 0.55 24.25 29.51 13. 19 2.57 12.09 15.46 18.26 6.67 8.95 l l. l 0 9.27 6.00 7.88 4.61 4.02 3.95 3.03 4.61 4.63 4.32 0.79 0.80 0.92 l.49 l.06 0.97 0.88 0.90 0.77 . 0.71 0.78 0.66 0.70 0.65 0.65 0.65 0.63 0.56 0.54 0.46 52.9 53.8 50.7 88.l 53.2 52.4 39.5 44.5 38.3 31. l 39.7 29.8 28.8 23.0 24.8 21.7 19.9 15.4 13.8 l l.9

PETROGRAPHY Vitrinite (%) Exinite (%) l nertinite (%) Mineral Matter (%) Reflectance (R 0 max %) •'Petrofactor" ( Mineral -Free)

89 9 l l 0.24 2.4

*Surat Basin coals

N 0

90 7 2 l 0.32 3.3

79 3 ll 7 0.38 4.3

10 84 5 l 0.41 4.4

75 9 l 15 0.45 4.5

75 16

T 9 0.47 4.8

3.0 2.2 2.2 26.3 5.9 8.2 27.9 40.9 34.5 42.8 51.0 55. l 21.80 32.32 31.20 l 4

50 3 21 26 0.60 8.8

74 6 15 5 0.66 7.9

2.6 3.6 10.4 7.2 12.0 10.6 75.0 78.6 30.00 30.22 0 0

79 23 46 40 73 80 70 62 69 68 66 T l l T l l 5 54 30 20 16 19 33 18 65 22 29 38 ll 4 8 2 16 6 7 3 5 2 7 0.77 0.80 0.85 l.03 l.24 l.34 l.38 l.47 l.64 2.02 2.36 9.4 26.7 l l.2 14.7 22.5 31.2 20.3 18.8 19.8 25.6 36.4

52 48

T 2.64 50.8

coals have good hydrogenation potential, with the perhydrous types (H /C > 0.8) yielding a high proportion of coal liquids. Data in Table 2, illustrated in Figure 3, strongly suggest that increasing " petrofactor" relates to both decreasing coal conversion and yield of coal extract. This is understandable because an increase in the " petrofactor" means an increase in rank (vitrinite reflectance) and/or a decrease in the "reactive" constituent of the feed coal, both of which result in lower conversion/product yields. " Petrofactor" was found to relate to two other rank parameters, dry ash free volatile matter and atomic H/C ratio, these relationships being shown in Figure 4. The type of coal feed not only affects the yield structure of the coal hydrogenation products, but also their properties (Guyot, 1978, 1979). Thus the relative density, carbon content and specific energy of the coal liquids increase with an increase in the rank of the feed coal. An increase in coal rank also results in decreasing proportions of carbon oxides a nd increasing proportions of hydrocarbons C 1 - C 4 in the autoclave gases. Figure 5 illustrates the fact that increasing " petrofactor" results in an increase in the relative density of the coal extract. This reflects the

increasing molecular weight of the oils derived from coals of increasing rank (Guyot, 1978). Also Diessel and Guyot (in press) discussed the fact that increasing " petrofactor" (rank) resulted in an increase in the proportion of mesophase/semi-coke material in the soluble char residues. This is illustrated in Figure 5 and discussed more fully in the following section. RELATIONSHIPS BETWEEN COAL CHARACTERISTICS AND PROPERTIES OF THE INSOLUBLE CHAR RESIDUE In view of the relationship between both rank and type of the feed coal and its liquid conversion, it is not surprising to find also a relationship between the composition of the solid liquefaction residue and the coal properties mentioned above. An example of the influence of coal rank on the composition of the insoluble residues is demonstrated in Table 3. Mean maximum vitrinite (or huminite in lignite) reflectance has been used as a rank parameter based on I 00 readings in each case. In order to gain more insight into the conversion behaviour of the other maceral

Table 2-Coal and Conversion Data

freebasis)

Reflectance ( R., max '.1/J

"Petrofactor" ( Min eral free)

99 98 88 94 99 98 68 84 82 30 76 70 55 43 68 78 83 79 65 52

0.24 0.32 0.38 0.41 0.45 0.47 0.60 0.66 0.77 0.80 0.85 1.03 1.24 1.34 1.38 1.47 1.64 2.02 2.36 2.64

2.4 3.3 4.3 4.4 4.5 4.8 8.8 7.9 9.4 26.7 11.2 14.7 22.5 31.2 20.3 18 .8 19.8 25.6 36.4 50.8

"' Reactives'' (% Mineral-

COAL

A B

c• D E* F* G* H

I J K L M 0 p Q R

T *Su ra t Basin coals

202

( DAF)

YIELDS (% DA F)

Volatile Matter (o/J

A tomic H/ C

Conversion

CoalEx tract

52.9 53.8 50.7 88. 1 53.2 52.4 39.5 44.5 38.3 31.1 39.7 29.8 28.8 23.0 24.8 21.7 19.9 15 .4 13.8 11.9

0.79 0.80 0.92 1.49 1.06 0.97 0.88 0.90 0.77 0.71 0.78 0.66 0.70 0.65 0.65 0.65 0.63 0.58 0.54 0.46

93 87 86 96 90 93 73 82 76 45 65 64 45 30 63 48 53 23 15 9

68 57 63 90 80 84 69 77 66 38 59 60 42 27 60 45 50 19 13 6

Table 3-Petrographic composition of insoluble residues. The samples are identified by the vitrinite reflectance of the respective feed coals.

% R max (oil):

0.32

0.48

0.49

0.61

0.85

1.26

1.57

1.83

2.50

MINERALS VITRINITE/ H UM INITE EX IN ITE/ LIPTINITE IN ERTINITE

13.4

37.8

9.6

10.0 0.8

33.4

19.4 0.2 0.2 16.8

18.0

2.2 41.6

13.0 0.2 0.2 18.4

22.2

1.3 3.3

70.1 1.2 0.2 6.6

10.2

14.6

33.0

Components UN DISSOLV ED MATERIAL

SOLVENT AFFECTED MATERIAL

HEAT AFFECTED MATERIAL

N 0 \.;.)

PARTIALLY DISSOLVED COA L AMORPHOUS MATRIX (ASPHAL TENE) COAGU LANT/VITROPLAST

1.3

17.0

3.4

0.5

0.6

6.6

16.1 46.3

I. I 1.4

3.0 10.2

8.5 12.6

14.2 16.2

0.2 39.4

7.0 29.8

3.2 5.0

M ESOPHASE/SEM I CO KE CA RBON BLAC K/GRAPHITE

18. 1 0.2

1.2 1. 2

1.8

46.2 0.4

13.0 0.4

17.0 0.2

35.0

67.2 0.4

56.2

results of reflectance measurements carried out on unreacted macerals found in the insoluble residue of the respective coals after hydrogenation demonstrate that few macerals below 1.3% reflectivity remain unaffected by the hydrogenation process. There is the occasional vitrinite and exinite which has escaped liquefaction but, on the whole, most macerals, including inertinite, are quite reactive up to 1.4% reflectivity (Diessel and Guyot , in press). The observation of a partial reactivity of low reflecting inertinite is supported by the coal and conversion data listed in Table 2. They show that in ome low rank coals the conversion rates exceed their proportion of reactive macerals (vitrinite plus exinite). Mo t striking is the change in the relative proportion of liquefaction products. These can be classified into three categories which differ in the manner hydrogenation has affected them . The first group consists of undissolved material comprising components which appear to have remained inert during the reaction. The main representatives of this category are minerals, although the results obtained by Wakely et al. (1979) suggest that con iderable reactivity is shown by some minerals. Other undissolved matter consists of various coal macerals, particularly macerals of the inertinite group (Fig. 6). The second group of solid components compri e olvent affected material. This can take several forms , one of which is shown by partially dissolved coal. For example, residual

1·3

/e /4.~

I-

~ 1-2

0:: IX UJ _J

8 LI.. 0

d 0:

1·0

i 0

I •

0·9 60

PETROFACTOR 80 0

60 UJ 0:: <{ ~ :I: 0

UJ _J

40 l/) co

UJ 0 l/)

l/)

<{ z a.. ~ 20

:I: 0 l/) UJ

0/i

0 0

PETROFACTOR Figure 5. The relationship between petrofactor and characteristics of the hydrogenation products. Circles in top diagram refer to the relative density of coal extract, squares below indicate the amount of mesophase/semicoke in solid residue .

groups, additional reflectance measurements have been carried out on exinite and inertinite. The number of the additional readings taken varied proportionally to the percentages of exinite and inertinite as obtained from maceral group analyses. A comparison between the reflectivity spectra thus obtained and the 204

Figure 6. Undissolved inertin ite (white) and coagulant (grey) in solid residue of a subbituminous coal. Incident light ; oil immersion; width of field view = 0.22 mm , I polar.

Figure 7. Partly dissolved vitrinite in liquefaction residue. Incident light; oil immersion; width of field of view = 0.22 mm , I polar.

vitrinite may result from an incomplete reaction in which softening and dissolution was res~ricted to peripheral zones or along cracks wh1c~ commonly radiate from the grain margins towards the interior of coal particles. Large vesicles are also ubiquitous and occasionally only patches of vitrinite are left (Fig. 7). Other solvent affected material has lost all maceral characteristics. It consists of amorphous substances which either represent coal-derived asphaltenes which are formed as an intermediate step during coal liquefaction or they have been formed by repolymerisation of coal-derived liquids. The material is isotropic, :Without any distinct morphology and often displays somewhat concentric fractures (Fig. 8).

Figure 8. Amorphous re-polymerisation product (grey) containing undissolved inertinite fragments (white). Incident light; oil immersion; width of field of view = 0.22 mm , I polar.

Figure 9. Spherical coagulant (light grey) developing out of amorphous groundmass as in Figure 8. Incident light ; oil immersion; width of field of view = 0.22 mm , I polar.

In contact with the immersion oil and on exposure to light some of the amorphous material tarnishes quickly and displays brown and blue surface staining. Those portions of the substance which remain untarnished are comi_nonly spherical in shape (Fig. 9). They consist of more resi tant matter than the urrounding asphaltic matrix as is demonstr~ted by the fact that the spherical coagulattons separate from their matrix when the latter di solves under conditions of prolonged hydrogenation. In such ea e the spheres which have been referred to as coagulant in the analyses appear as isolated bodies or as fused clusters in the insoluble residue. The spheres appear to be identical to the vitroplasts of Mitchell et al. (1977). The third group of solid material consists of solvent affected substances which bear hallmarks of additional thermal influence in the form of strong optical anisotropy. This develops in various ways, one of which is the formation of numerous small mesophase spheres within the isotropic asphaltene (Figs. I O and I I)_. The spheres grow and coale ce, thus forming the anisotropic mosaic and domain structure of coke (Fig. 12). Whil t in this case the mesophase retains its spherical shape until the onset of coalescence, there are also many occurrences of i olated mesophase with irregular habits. It eems that in such cases mesophase has either been less mobile or its growth has been interfered with by the presence of solid impurities, such as minerals or small fragments of inertinite within the matrix. 205

Figure 10. Sperica l mesophase in amorph o us groundmass of re-polymerised coal liquid . T ransmitted light; width of fi eld view = 0.2 mm. I pola r.

graphite which , likewise, indicate temperature irregularities. Table 3 demonstrates that solvent affected material (i .e. partially dissolved coal, amorphous matrix, coagulant or vitroplast) is a common reaction product from low rank coals but its proportion decreases in low volatile bituminous coal such that none is left in anthracite. At the same time, the amount of mesophase increases so much that in semianthracite and anthracite hydrogenation seems to have a carbonising effect only. The influence of coal type is likewise marked. As can be expected, a change from low inertinite to high inertinite coal has an effect quite similar to an increase in rank on account of the high carbon and low hydrogen contents commonly found in macerals of the inertinite group. Likewise, the proportion of mesophase increases with increasing inertinite. CONCLUSIO S

Figure 11. As in Figure I 0, crossed pol ars.

I. The term " petrofactor" represents an inter-relationship between coal rank (vitrinite reflectance) and the petrographic (maceral) composition. 2. An increase in the ··petrofactor" can be related to the following: (a) Decreasing volatile matter and atomic H/C, (b) Decreasing coal conversion and yields of coal-liquids, (c) Increasing relative density, specific energy and carbon content of coalderived liquids, (d) Increasing content of mesophase/semicoke in the in soluble char residues. 3. Lower rank perhydrous coals, such as from the Surat Basin , have good potential for conversion to liquids.

ACKNOWLEDGEMENTS Figure 12. Semicoke (light grey) and coagulant (dark grey) in solid liquefaction residue of bituminous coal. Incident light; oil immersion; width of field of view = 0.22 mm , I polar.

Other material belonging in this group are small clusters of carbon black which might be sublimation products resulting from local overheating, as well as occasional laths of 206

The authors wish to thank the Director of the Australian Coal Industry Research Laboratories for permission to publish the paper. Technical and secretarial assistance has been received from members of both the Australian Coal Industry Research Laboratorie and the Department of Geology, The University of Newcastle, N.S.W. This is gratefully acknowledged .

REFERE CES C. F. K. and G UYOT, R. E .. (in press): Petrographic studies on solid residues derived from the hydrogena tion of so me Australian coals. 9th lnt . Congr. of Carboniferot1s Stratigraphy and Geol., Urbana, May 1979. G UYOT, R. E. , 1976: Production of synthetic oil and chemicals from coal - Part 3- Rel ationships between coal properties and hydro-liquefaction potential. A t1stra/ian Coal lndt1stry Research Laboratories Ltd., P.R . 76-8. G UYOT, R. E., I 978: Influence of coal characteristics o n the yield s and properties of hydrogenation pro<!ucts. At1stralian Coal Industry Research Laboratories Ltd., P.R. 78-8. GUYOT, R . E. , 1979: Rel a ti o nships between coa l properties a nd liquefaction potential. At1stralia11 Coal Industry Research Laboratories Ltd., P.R. 79-1 . G YOT, R. E. and D1ESSEL, C. F. K., 1979: The application of coal petrography to hydrogenation research . Australian Coal !ndt1str_r Research Laboratories Ltd., P.R . 79-3 . MITCHELL, G. D. , DAVIS, A . and SPA CKMAN, W ., 1977: A petrographic classification of solid residues derived from the hydrogenation of bituminous coals, in R . T. Ellington (Ed .). Liquidji,elsji-0111 coal, 255-270. Academic Press. London. DIESSEL ,

SHIBAOKA. K. and UEDA, S .• 1978: Form a tio n and stabilit y

of mesophase during coal hydroge na ti o n. Pa rts I and 2. Fuel, 57, 667-675. W AKELEY , L. D ., DAVIS, A .. JE NK INS, R. G .. MI TC HELL, G . D. a nd WALKER , P. L. , 1969: The nature of solids accumu lated during solvent refining of coal. Fuel, 58, 379-385.

R. E. GUYOT,* Australian Coal Industry Researc h Laboratories Limited, 22-30 Delhi Road , North Ryde, N .S. W. , 2113. C. F. K . DIESSEL, Department of Geology, The University of Newcastle, Newcastle, N.S.W., 2308. * Present address Robertso n Research (Australia) Pty Ltd, A.D .C. House, 77 Pacific Highway, North Sydney, N.S.W. , 2060.

207

SOME CHARACTERISTICS OF WA DOA COAL I HYDROGE ATIO

RELATION TO

By M. Shibaoka, A. J. R. Bennett & H. Echigo

ABSTRACT Coal reserves in the Surat Basin, Queensland, have been attracting increasing attention as a possible source of synthetic crude oil. This paper reports an assessment of two properties of Wandoan (Surat Basin) coal that are important to its possible use as a feedstock for liquefaction. (I) Multi-stage float-and-sink tests have shown that the separation of mineral matter from Wandoan coal is very easy, and that a satisfactory cumulative yield of coal with reduced ash yields can be obtained as floats . (2) Microscopic observation of the coal material remaining after hydrogenation with tetralin in the autoclave reveals that the vitrinite from the Wandoan coal behaves quite differently from that from Hunter Valley coals (N .S.W.)

INTRODUCTION Wandoan is located in the Surat Basin , an eastern lobe of the Great Artesian Basin in southern Queensland . Wandoan coal lies within the upper part of the Walloon Coal Measures which are of middle to late Jurassic age (Fig. 1). This coal differs from most of the Permian and Triassic coals in Australia in that it is of sub-bituminous rank and rich in vitrinite. Table I presents petrographic and chemical data for typical clean coal composites prepared from Wandoan coal. The CSIRO Division of Fossil Fuels, in collaboration with Thiess Bros Pty Ltd , has carried out an examination of Wandoan coal to assess some characteristics relevant to its utilisation in the production of solvent-refined coal (SRC) and synthetic liquid fuels . Two important aspects were studied: (I) The ease of removal of associated mineral matter from coal. Before coal undergoes any chemical treatment , it is desirable to remove (in an economical manner) as much mineral matter as possible, because the separation of solid residues from

viscous hydrogenation products is a most difficult and expensive process. It is possible that the ease with which mineral matter can be removed from a coal may be as important as the ease with which it can be hydrogenated . (2) The behaviour of various vitrinite macerals during coal hydrogenation . From a technical point of view it is important to realise that the vitrinite macerals of Wandoan coal, because of their unique properties {Leblang et al., 1981 ), may behave quite differently from those of ordinary bituminous coal.

SEPARATION OF MINERAL MATTER REMOVAL OF DIRT BANDS As is often the case with Surat Basin coal seams, Walloon coal in the Wandoan area contains many dirt bands of various thicknesses (Fig. 2). Prior to the wet tumbling test conducted as part of the float-and-sink separation programme, shale breakdown tests were carried out on samples from some typical Wandoan deposits using the Andreasen Pipette method . The purpose of such a test is to assess the dispersion behaviour of material from dirt bands within the seams and of roof and floor rock during treatment in a washery. The results of an Andreasen Pipette test on an Austinvale core of Wandoan coal showed that, in general, material from dirt bands broke down readily in water, producing particles finer than 0.5 mm in diameter (Table 2) . In a dense-medium coal washery plant, this dispersion of fine mineral particles* would cause operational problems. However, the results of breakdown tests suggest that if the run-of-mine coal is wet tumbled , or just soaked in water, and then screened at 0.5 mm before treatment in a dense-medium plant, most of the dirt bands could be removed as slimes by cyclones. The dense medium would then not be contaminated should any of the remaining material

*Usua ll y qu artz. kaolin ite and small a mounts of muscovitc. as shown by X-ra y powder di ffraction of the nom in a l - 101, m size fracti on.

209

NORTHERN TERRITORY

WESTERN AUSTRALIA

m Tertiary coals

fEJ Mesozoic coals ~

0 I I '

Permian coals

500km I

~OBART TASMANIA

Fig. I. Location of Wandoan area in the Surat Basi n, and loca tions of Tertia ry, Mesozoic and Permian coal deposits in Australia.

fail to be separated from the coal. The fact that the dirt bands in the Wandoan coal can be readily dispersed by wet tumbling is regarded as a desirable property (see below). FLOAT-AND-SINK TESTS Procedure

Two programmes of float-and-sink tests were carried out on a 100 mm diameter core from the Austinvale area to investigate the washability of Wandoan coal. Firstly, multistage float-and-sink tests were carried out on the sample from Seam A to investigate the effect of particle size. In this procedure, requiring a non-destructive test, the ash yields of coarse fractions were calculated from their apparent relative densities using an ash/ relative density correlation ob210

tained from determinations on the finer sized fractions. This allowed washability data to be calculated for the whole coal ( +0.5 mm) after it had been crushed to fractions of successively smaller top sizes. For this programme the core was crushed to - 26.5 mm . The first set of tests was conducted on material in the size ranges - 26.5 mm + 3.35 mm a nd - 3.35 mm +0.5 mm at relative densities of 1.25, 1.30, 1.35, 1.40, 1.60 and 1.80. The top size of 26.5 mm was selected to keep within the prescribed size limits specified for a 76 kg sa mple (AS I 66 I, I 979) . A final top size of 3.35 mm was chosen as a likely economic limit for dense-medium separation. All material in the - 26.5 mm +3.35 mm range was then crushed to - 13.2 mm and a second set of float-and-sink separations was

Table I-Chemical and Petrographic Analyses of Wandoan Clean-Coal Composites from Austinvale Bore C674B C HEMI CALA ALYSES (u 0 w w) Air-dried basis Mo isture Ash Vo la tile mailer Fixed carbon Specific energy (MJ /kg) Sulphur-total Carbon Hydrogen itrogen Sulphur Oxygen (differe nce)

Sea m A 6.7 14.0 40.8 38. 5 25.59 0.33 61.3 4.9 0.7 0.3 12. 1

Sea m B 6.5 18.0 38.8 36.7 23.89 0.27 58. 1 4.6 0.7 0.2 11.9

Dry ash-jree basis Volatile ma iler Fixed ca rbo n Specific e nergy (MJ/ kg) Carbon Hydroge n itrogen Sulphur Oxygen

5 1. 5 48. 5 32.30 77.4 6.2 0.9 0.3 15.2

51.4 48.6 31.62 76.8 6.1 0.9 0.3 15.9

PETROGRAPHIC A AL YSES (% v/v) Vitrinite Exinite lnertinite Mineral matter

73 6 8 13

(83) (6)

(II )

6 17

(87) (6) (7)

Values in pa rentheses a re o n a mineral maller free basis.

made on this new material in the size ranges - 13.2 mm + 3.35 mm and - 3.35 mm + 0.5 mm at the same relative densities as before. The procedure was repeated by crushing the coarser fractions to below 9.5 mm , 6.7 mm and 3.35 mm interspersed with the third , fourth and fifth set of float-and-sink separations. The apparent density of each fraction was determined at every stage by volume displacement. All the - 3.35 mm +0.5 mm fractions at each stage were subsequently crushed to - 212 µm for determination of true density and ash yield. Using values for ash yield and apparent density determined on the - 3.35 mm +0.5 mm fractions, a regression equation was calculated as follows: Ash % = 141.76 -

169.71 apparent relative density

From this formula it was possible to estimate, with an accuracy of ± 2.2% (2 x standard deviation), the ash yield of all the coarse floatand-sink fractions from measurements of their apparent relative density, and to compute washability curves for all coal

( +0.5 mm) assuming it to have been crushed to one of the fine top sizes selected. The second programme of float-and-sink tests was carried out on material from Seam B in the same Austin vale I 00 mm core in order to recognise the effect of wet tumbling. All material in the size range - 26.5 mm + 0.5 mm was tumbled for 30 min at 50 rev./min in a drum 380 mm long and 300 mm diameter using a 2: I water/coal ratio . The material was then wet screened at 0.5 mm . In this programme, only two sets of float-and-sink separations were carried out, the first on material below 26.5 mm and the second after crushing the coarser fractions to - 13.2 mm .

Results Values for cumulative yield of floats and ash yield for all samples above 0.5 mm after crushing to successively smaller top sizes are illustrated in Fig. 3. The figure shows that, because there is very little change in the degree of separation of mineral matter from a top size of 26.5 mm down to a top size as small as 3.35 mm, it is unnecessary to crush this 211

Table 2-Results of Breakdown Test for Di rt Bands wit hin Seam B from Austinvale Bore C674C Si=e dis1rib111ion ajier breakdown ( mass O O oj dry shale)

- 425 µ111

Thickness ( m)

M ois111re con/en/ ( mass O ..)

sie1 e si:e

- JO µm si=e ( nominal)

I• 2• 3 4 5 6 7 8* 9*

0.2 10 0.105 0.045 0.060 0.055 0.105 0.065 0. 120 0.325

4.0 3.6 5.1 6.7 3.3 5.4 4.4 4. 1 3.0

12. 7 33 .0 83.6 63 .3 1.6 40.6 98.0 98.5 75.4

8.7 25 .8 73.7 58.7 1. 5 24.1 82.0 85.8 61.4

10*

0.945

3.4

91.8

66.2

72.5

55.1

Tes/ No.

Roof

Floor

Weighted average • duplicate Total thickness tested total thickness of dirt bands = 2.035(m ) 2.305(m). The test nos. refer 10 Figure 2.

AS H PRO FILE

7· 58 m

BREAKDOWN TEST No. 1

2 - -:::::3 = -

--.....4

....--7

8 5·70 m

'-..

5 6

confirmed tha t gentle wet tumbling ca n reduce as much as I 1% of the 25% total shale content to - 0.5 mm material. Values for cumulative yield of floa ts and ash yield from the float a nd-sink tests on the - 26.5 mm + 0.5 mm material after wet tumbling are shown in Fig. 4. Calculated values for cumulative yield of floats in the ab ence of wet tumbling are also given. The cumulative yield of floats of about 62% at a rel a tive density of 1.35 with an ash yield of 6.8% would be expected to be increased by about 7% by wet tumbling, due to the remova l of sha le. Judging from the re ults of tests carried out on the Aust invale 100 mm core, the ability to obtain a high yield of low-ash coal, with a sharp separation of mineral matter from coal a t a relatively coarse size, is a distinct advantage when considering the utilisation of the Wand oan coal.

----- s

- ---..... 9 41 ·26 m

-,o 0 l

I , I , I I I ASH YIELD ( ¼)

Fig. 2. Ash profile of Sea ms A and B in a core from a Wandoan coal (Austinvale).

A ustinva le coal below a top size of 26.5 mm for preparation. The wet tumbling test using a sample of the B seam from the 100 mm Austinvale core has 212

BEHAVIO UR OF VITRI IT E MACE RALS DURI NG HYDROGENATION Microscopic examination of a coal sample gives informa tion on the yield of hydrogenation products from that particular coal (Given et al. , 1975; Guyot , 1978). However, microscopic techniques are rarely used in the selection of a raw coal for commerc ial production of synthetic fuels ; more detailed and

..,,

~ ....

..,,

JO~ ,c

~ 40 ....

"' "'

..... i

40 40 CD

... 60

• WITHOUT SHALE BREAKDOWN PRETREATMENT I CALCULATED I o WITH SHALE BREAKDOWN PRETREATMENT

..,, ;;:;

""'

"' 50 "'

... 60 >

B 70

g ~

~ 70

20 ~ ,c

... 2::

, 15 :% u

90 100

10 CUMULATIVE ASH YIELD 1% DRY BASIS)

10 CUMULATIVE ASH YIELD I¼ ORY BAS IS I

Fig. 3. Cumulative yield/ash curves from float-and-sink tests on a Wandoan coal (Austinvale, 100 mm core, Seam A).

Fig. 4. Cumulative yield/ash curves for - 26.5 mm +0.5 mm fractions from float-and-sink tests on a Wandoa n coal (Austinvale, 100 mm core, Seam B).

direct information is obtained from a simple autoclave test. In selecting a coal for the production of liquid fuel, various factors, in addition to its hydrogenation characteristics, should be taken into account, e.g. the size of coal reserves, mining costs and the market price of the coal. Hunter Valley coals and Victorian soft brown coals are the only large reserves of opencut-mineable non-coking coal in Australia. However, the Surat Basin coals could be considered for liquid fuel production because of their unique properties, even though the reserves are not large. It is important in using coals for liquefaction to select a process best suited to the coal, rather than to try to use the coal in a particular process. In selecting the process, it is desirable to know how the individual coal macerals behave during coal liquefaction so that appropriate decisions are made on operating details, such as optimum grain size, choice of vehicle solvent and method of separation of unreacted material. The Wandoan coal is rich in vitrinite which possesses unique optical properties (Leblang

et al., 1981). It is a sub-bituminous coal a nd therefore of lower rank than Hunter Valley ( .S.W.) coal, the hydrogenation behaviour of which has been investigated previously by one of the authors (Shibaoka, 1981 ). In this paper, Hunter Valley coa ls (Liddell and Bayswater) are briefly referred to for comparison with Wandoan coal.

EXPERIMENTAL In order to investigate the behaviour of coal particles during hydrogenation , autoclave experiments were interrupted at various stages during the reaction , and the solid material remaining was examined under the optical microscope and the scanning electron microscope (SEM) . As details of experimental techniques have been reported elsewhere (Shibaoka, 1979), only a brief description is given here. The reaction time used was I hour and the initial hydrogen pressure was 5 MPa. Tetralin ( I :2:3:4 tetrahydronaphthalene) was used as the hydrogen donor solvent. The ratio of coal to solvent was I to 4 by mass when a 300 ml capacity autoclave with a magnetic 213

Fig. 5. Changes in Bayswater (Hunter Valley) coal during hydrogenation in the temperature range 340-360 C using tetralin (a) 350 C: Cell cavity filling (corpocollinite) form globules hrinking away from the cell walls (telinite) which have remained relatively unchanged . (Incident light. oil immersion).

(b) 340 C: V1troplast sphere with smooth surface. (Part of the phere was damaged during specimen preparation .) (SEM).

tirrer was used, and I to 10 with an unstirred 50 ml autoclave. At the end of the reaction period, the solid residue was extracted with benzene (or in some in tance n-hexane) prior to preparation as a polished grain mount.

At 390 C, the cell walls had completely disintegrated. The solid material remaining was composed of inertinite particles, some exinite, and vitroplast spheres of various sizes (Fig. 7a). The surface of the vitroplast spheres

HU TER VALLEY COALS At a temperature of 340-350 C swelling of some telinite particles was observed and the corpocollinite (see Appendix), which filled cell cavities in the original coal, became plastic and formed spheres (Fig. Sa). These spheres can be called vitroplast (Mitchell et al., 1976). Where cell walls had been ruptured, the e pheres became isolated (Fig. Sb). At a temperature of 370 C, the cell walls became very thin. Rel atively large spheres were formed from lenses of telocollinite, and fine ones from de mocollinite (Fig. 6). Fewer changes were observed in inertinite particles.

Fig. 6. Changes in Bayswater coal hydrogenated at 370 C. lnertinite fragments (angular, white), cell wall remnants (thin films) and spheres exhibiting a range of reflectance a nd sizes. (Incident li gh t, oil immersion).

214

Fig. 7 Changes in 390-400 C range, during hydrogenation of Hunter Valley coals (a) Liddell coal, 390 C: Vitroplast spheres of various sizes, angular inertinite (whi te) and a long particle consisting of unaltered exinite and vitrinite (centre). (Incident light, oil immersion) (b) Bayswater coal, 390 C: Vitroplast sphere with dusty material, mainly mineral matter, on the surface (SEM).

Fig. 8. Changes in Wandoan coal hydrogenated in temperature range 360-380 C using tetralin. (Incident light, oil immersion) (a) 360 C: The microscopic texture of this coal shows only slight change. (Compare with Bayswa ter coal, Fig. Sa).

(b) 380 C: Bright pink and blue spec ks are visible (here appearing white).

derived from telocollinite at temperatures of 390 cc and above was covered with a dusty material (Fig. 7b), mainly mineral matter.

tained their original shape (Fig. 9a), although ome became porous. In some instances they were brownish in colour, due to the loss of organic material. Some relatively high reflectance telocollinite seemed to be less affected by tetralin, while some low reflectance desmocollinite particles became porous and adhered to other particles (Fig. 9b). In spite of the non -plasticity of vitrinite macerals of Wandoan coal, vitroplast occurs in various forms- spherical, botryoidal, irregular and massive- in the samples treated at temperatures higher than 380 cc. The tran sitional state from vitrinite to vitroplast, which is quite commonly recognised in Hunter Valley coal samples, was not observed in Wandoan coal samples, despite careful observation. After the tetralin treatment of Wandoan coal at 400 C, a thin layer of solid carbonaceous material was found along the internal

WA DOAN COAL Wandoan coal is quite different from Hunter Valley coal in its reaction with tetralin. In the lower temperature range of 360-380 cc, gelocollinite, which cemented remnants of cell walls in the original coal, was dissolved preferentially. Microscopic examination revealed the texture, previously unobservable, of some telocollinite, which bore a resemblance to chemically etched coal samples (Fig. 8a). In some particles, there were bright specks of pink and blue, probably due to internal reflections at the surface of fine vesicles and cracks produced in the particles by the treatment with tetralin (Fig. 8b). In the range 380-400 cC, many of the vitrinite particles of Wandoan coal still re-

Fig. 9. Changes in Wandoa n coal hydrogenated in temperature range 380-400 C using tetralin. (Incident light, oil immersion) (a) 400 C: The microscopic texture has altered only slightly.

(b) 380 C: Rela tively high-reflectance telocollinite (centre) has been little affected by tetralin. but lowreflect ance desmocollinite has become plastic.

215

Fig. 10. Material formed at 400-420 ' C during hydrogenation of Wandoa n coal using tetralin. (Incident light. oil immersion) , (a) 400 C: Vitroplast forms as a layer of carbo, naceous material alo ng inner su rface of au toclave,

(b) 420 ' C: Vitroplast cementing together pre-ex isting vitro plast spheres, inertinite particles, etc.

surface of the a utocl ave. This material is vitroplast (Fig. I Oa), which was probably formed from the di ssolved coaly material by thermal alteration along the hot internal su rface of the a utoclave. The vitroplast so formed appears to cement various other particles, such as pre-existing vitroplast spheres, partially dissolved vitrinite particles and inertinite particles (Fig. IOb).

Both the matrix vitroplast and vitroplast spheres have a wide range of reflectance values. Some agglomerates are loosely cemented by vitroplast, while others are quite compact. The proportion of aggloJ11erates in the residual material increases with increase in temperature. In the agglomerates from the 400 °C sa mple, vesicular vitroplast spheres were fre-

Fig. 11 . Material formed at 440 C during hydrogenation of Wandoan coal using tetralin. (Incident light, oil immersion) (a) Agglomerate cemented by low-reflectance, massive vitroplast. Reflectance of vitroplast spheres varies and some are vesicular.

(b) Agglomerate wit h porous matrix vi tropl ast

(c) Telocollinite particles, still retaining original shape, cemented into the agglomerate by lowreflectance, massive vitroplast.

(d) Onset of mesophase format ion in vitroplast

216

quently seen (Fig. 11 a). Vesiculation must have occurred before the agglomerates were formed . Agglomerates with a fairly porous matrix were also found in the same sample, probably as a result of partial redissolution of matrix vitroplast (Fig. 11 b). At 440 cc , some telocollinite particles of relatively high reflectance still retained their original shape, but some of lower reflectance became plastic and exhibited a vesicular texture (Fig. I le). If the temperature is maintained at 440 cc for several hours in the presence of sufficient hydrogen, both the remaining coal particles and the vitroplast would be expected to be gradually dissolved by tetralin. However, when the contents of the autoclave were not stirred during reaction, almost all the coaly material, except for inertinite particles, became anisotropic solid material within an hour (Fig. I Id). DlSCUSSIO Most vitrinite particles of Wandoan coal undergo only gradual dissolution in tetralin, showing no tendency to become highly plastic during hydrogenation . On the other hand, almost all vitrinite from Hunter Valley coal gives rise to vitroplast and is dissolved. Knowledge of this difference in behaviour is important in the commercial production of SRC and synthetic liquid fuels. For example, in a continuous coal hydrogenation plant, Hunter Valley vitrinite may be broken down at the preheating stage while, under the same conditions, much Wandoan vitrinite may survive this stage and enter the reactor as relatively large solid particles. Hunter Valley vitrinite forms vitroplast directly. Wandoan vitrinite may form a small quantity of vitroplast directly, but most vitrinite appears to be first dissolved by tetralin, part of the dissolved material then forming secondary vitroplast by thermal alteration . If there is insufficient hydrogen available, both Hunter Valley and Wandoan coals form mesophase mainly from vitroplast. Coking coal, which gives massive vitroplast, is likely to form larger quantities of mesophase than Wandoan coal. It is possible, however, that the change from dissolved coaly material to mesophase via secondary vitroplast is retarded or even reversed if sufficient hydrogen

HUNTER VALLEY

VITRINITE

VITROPLAST ~ MESOPHASE

~ WANDOAN

LIQUID

,f1 t! ,,, VITRINITE ~ , VITROPLASTj~ MESOPHASE

~ Fig. 12. Schematic representation of processes occurring during hydrogenation of vitrinite from Hunter Valley and Wandoan coals.

is available for transfer from solvent to vitroplast and mesophase (Fig. 12). SRC from Wandoan coal, when carbonised for use in the production of metallurgical coke, is likely to behave in a manner similar to SRC from a bituminous coal (Baltisberger et al. , 1978). CO CLUSIO Wandoan coal from the Surat Basin, Queensland, is regarded as a potential feedstock for the production ofSRC and oil-fromcoal. As a result of limited laboratory experiments, the following conclusions are drawn. (I) Most of the dirt bands are readily dispersed in water, and thus can be removed before the coal is treated in a washery plant. The separation of the remaining mineral matter from Wandoan coal is not difficult, and a relatively high yield of floats with fairly low ash yield are obtained. (2) The vitrinite macerals of Wandoan coal become only slightly plastic during tetralin treatment, which contrasts with the behaviour of vitrinite from Hunter Valley coal, most of which becomes very plastic prior to the major hydrogenation. The knowledge obtained using microscopic techniques should lead to a better understanding of the mechanism of coal hydrogenation. This, in turn , should lead to improvements in the design of industrial-scale processes. ACKNOWLEDGMENT The authors wish to express their thanks to Thiess Bros Pty Ltd for the supply of many 217

bore cores. Tha nks are also extended to Mr J. F. Stephens and Mr . J. Russell for their careful reading of the manu script and critical

discussions during the preparation of the paper.

REFERENCES AS 1661 , 1979: Float and sink testing o f hard coal. 8ALTISRERGER, R. J ., KARA , R. A. , KLARUN DE, K. J. , SAITO, K. , SUKALSKI , W. , STEN BERG, V. I. and WOOLSEY , N. F ., 1978: C o mparison ofsolventrefined lignite with solvent-refined bitumino us coals. Fuel. 57, 529-53 2. GIVEN , P. H ., CRONAUER, D . C., SPACKMA N, W. , LOVELL, H . L. , DAVIS , A . a nd 81SWAS, B. , 1975: Dependence o f co al liquefactio n behavio ur on coa l characte ristics. I. Vitrinite-rich sa mples. 2. Ro le of petrogra ph ic composition. Fuel. 54, 34--39 and 40-49. G UYOT. R. E., 1978: Prod uction of synthetic oil a nd chemicals fro m coal- Pa rt 3. Rela ti o nshi p between coa l properties a nd liquefactio n potential. Australian Coa l Industry Research Labora to ries Ltd . PR 79- 1. LEBLA:--IG, G . M., RAYME:--IT, P. A . a nd SM YTH , M., 198 1: The Austinva le coal deposit- -Wa ndoa n. A pa laeoenvironmenta l a na lysis. Coal Geology, I (4). M ITCHELL, G . D ., DAVIS. A . a nd SPACKMA N, W. , 1976: A petrogra ph ic classifica tion of solid resid ues

derived from the hydrogena tio n of bitumino us coal s. 172nd ACS Na t. Meet. , Sa n Francisco, Calif., Div. Fuel Chem ., Paper 42, 255-269 . SHIRAOKA, M ., 1981 : The beha vio ur o f vitrinite macerals in some organic solvents in the a utoclave. Fuel, 60, 240-246.

M. SHIBAOKA, A. J . R . BE ETT, H. ECHIGO,* CSIRO Division of Fossil Fuels, P.O. Box I 36, orth Ryde, .S.W., 2113. * Permanent address: No. I R & D Department, Sumitomo Metal Industries Ltd ., 5-15, Kitahama, Higashiku, Osa ka 541 , Japan

APPENDIX

(Definitions based on the recommendations of the I.C.C.P. in the Handbook of Coal Petrology, 1963, 1971). The vitrinite macerals Telinite shows more or less distinctly the cell structure of the original pl ant material. The cell cavities are either round/oval (T ype I) or the cells have been completely compressed and appear as lines (Type 2). In general , the cavities a re filled with other substances, e.g. corpocollinite. Telocollinite appears completely homogeneous and occurs in wide layers. It represents the end-stage of gelification of the preserved plant tissues (e.g. cell structure); the latter can be displayed by etching. Gelocollinite derives from a pure colloidal gel, and has a homogeneous and dense

2 18

appearance. Before hardening, the gel can permeate fissures and cell cavities. Gelocollinite has no distinct form and its boundaries are defined by the surfaces of the associated macerals. Desmocollinite is derived by coalification from brown coal humodetrinite which consists of the finest humic fragments with a finely distributed humic gel (gelocollinite) between them . Corpocollinite consists of homogeneous bodies which can be massive, round, oval or more or less angular. They may occur as cell fillings (Type I) or as isolated large oval bodies (Type 2). Vitrodetrinite consists of small fragments (finer than I Oµm) of gelified tissue (telinite and telocollinite) with more or less angular and irregular outlines.