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Geological Socie rv Symposium (19BloMf Australia. V' Coal) Group. · elbourne C '~oal Resources. ISBN 0 909869 24 3.

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SYMPOSIUM COAL RESOURCES Origin Exploration and Utilization in Australia Proceedings

Edited by

C.W. MALLETT

Melbourne 15-19 November, 1982

AO<NOWLEDGEMENTS The production of this volume has been supported by Shel I Development Austral la and CSIRO, Division of Appl led Geomechanlcs, who provided ass i stance In manuscript preparation. Without the cooperation of the management and dedication of the staff of these organisations this volume would not have been available for the Symposium.

ISBN O 909869 24 3

CONTENTS -

PART 1

BROWN COAL SECTION GEOLOGICAL SETTING Smith, G.C.: A Review of the Tertiary-Cretaceous Tectonic History of the Gippsland Basin and its Control on Coal Measure Sedimentation. Thompson, B.R. and Walker, G.M.: The Geology of the Seaspray Depression: Gippsland Basin. Holgate, G.R.: Brown Coals and Facies Equivalents of the Alberton Area Gippsland, Victoria Greer, I.A. and Smith, G.C.: Geology of the Gelliondale Coalfield Partridge, A.O.: Palynological Evidence for Age and Environment of Deposition of Tertiary Coals in the Gippsland Basin. • Muir, A. and Kremor, A.: Tertiary Coal Deposits of the St Vincent Basin South Australia Meyer, G.M.: Geology of the Kingston Lignite deposit Elms, A.G., Matthews, R.D. and Chapman, D.G.: Notes on the Geology of the Lignite Resources - Esperance, Western Australia PROPERTIES OF BROWN COAL George, A.M.: Latrobe Valley Brown Coal - Lithotypes: Macerals: Coal Properties. Black, P.M.: Petrology and Inorganic Chemistry of South Island Lignites, New Zealand. Liu, S., Taylor, G.H. and Shibaoka, M.: Biochemical Gelification and the Nature of Some Huminite Macerals. Kiss, L.T.: Chemistry of Victorian Brown Coals. Kershaw, A.P. and Sluiter, I.A.: The Application of Pollen Analysis to the Elucidation of Latrobe Valley Brown Coal Depositional Environments and Stratigraphy. UTILIZATION OF BROWN COAL St Baker, T.C. and Juniper, L.A.: Combustion Utilization Assessment of Brown Coals and Lignites. Lindner, E.R.: Evaluation of South Australian Coals for Power Generation. Perry, G.J.: Liquefaction of Victorian Brown Coal. Philp, R.P., Gilbert, T.D. and Russell N.J.: Characterisation of Victorian Brown Coals by Pyrolysis Techniques Combined with Gas Chromatography and Gas Chromatography - Mass Spectrometry. OVERSEAS BROWN COAL FIELDS Chumroum, P. and Corsiri, R.: Thailand Lignite Development Ernst, H.: Rhineland Brown Coal Development. Isaac, M.: Geology of the Southland and .Otago Lignite Deposits, Southern New Zealand.

1 39 57 71 90 91 92 101

111 131 145 153 169

187 202 217 228

244 266 277

FOREWORD

The Coal Group of the Geological Society of Austral la Is one of Its most recently formed specialist groups and has experienced rapid and active growth. Its program has Included general symposia, regional and specific purpose workshops and technical sessions at geological society conventions. This growth has co Inc r ded wIth an upsurge In Interest In coa I as a major energy source. The group has attracted members from a wI de var I ety of geo Iog I ea I fields, Including coal petrography and chemistry, coal utilization, sedlmentology, exploration, geophysics and geomechanlcs. While workshops In specific topics are organised from time to time, the major symposia have been designed to appeal to a broad spectrum of the membership. This symposium Is concerned with three major areas of interest of members:Brown Coal - Australia has some of the most remarkable brown coal deposits in the world, to date exploited at only a few local !ties in Victoria. In recent years exploration has delineated substantial reserves In other areas, some of which are outlined. The geological controls of peat accumulation are described for the main lignite deposits and provide a framework for brown coal occurrence in southern Australia. The chemical and petrographic properties of coal are crucial to the assessment of Its utilization potential, and provide Insight Into the processes of formation of characteristics observed In black coals. Research Into potential utilization schemes for Australian lignite Is described. To provide a perspective on the Australian deposits, lignite fields In Germany, Thailand and New Zealand are discussed. Coal Deposit Evaluation - The symposium of the Group In 1980 was devoted primarily to this topic, and at this meeting, sessions are restricted to two main themes. These are geophysical field assessment of coal and coal measure properties, and geological data bank and processing systems. Geophysics Is continually being refined to Improve techniques, applications and Interpretation, and these sessions provide the opportunity for recent developments to be reported. The application of electronic data processing has been one of the most exciting recent developments for the exploration and mine geologist. The application of these systems Is Illustrated by case studies. Geotechnlcal - As coal prospects turn Into mines, an Increasing number of geologists are Involved In geotechnlcal aspects of mine development. Mine planners are becoming Increasingly aware that good geotechnlcal data and analyses are essential to successful mine operation. The geologist Is being appreciated as an lntergral part of a team and accorded appropriate respect and responslbll lty. Papers cover aspects of black coal underground and surface mines, and the unique problems of brown coal surface pits. It Is natural for a meeting of the Coal Group held In Victoria to place some emphasis on Brown Coals. Approximately half of the papers deal with some aspect of low rank coals, and the Symposium Field Excursion will examine the operating mines In the Latrobe Valley. This Is the most comprehensive review of the occurrence, propert I es and ut 111 zat I on of Austra I I an brown coa Is to date, and reflects the results of ·the greatly Increased exploration and reseach activities In recent years. C,W.Mal Jett

A review of the Tertiary-Cretaceous Tectonic History of the Gippsland Basin and its Control on Coal Measure Sedimentation G,C. SMITH ARCO Austral la Limited, 15-23 Adelaide St., Brisbane, 4001 Austral la KEY WORDS: Glppsland Basin, coal measures, coal petrography, Brown coal, contlnental margin. ABSTRACT The Lower Cretaceous to Tertiary sequences developed In the Glppsland Basin, Austral la, belong to a complex Atlantlc-type, tectonosedlmentary suite. The tectonic regime and variation with time of basin-wide subsidence rates and reglonal palaeocllmates largely control led the rates of sedimentation, the facles type and the occurrence of coals within the Glppsland Basin. Two rifting and drifting events are relevant: the first over the 130-100 Ma period associated with the opening of the Southern Ocean between Austral la and Antarctica; the second over the 100 - 55 Ma period associated with the opening of the Tasman Sea, FI ve tecton Ic phases are recogn I zab I e In the GI pps I and Basin: the Strzeleckl-Otway Rift phase (130 - 100 Ma); Tasman Sea Rift phase (100 - 80 Ma); Tasman Sea Drift phase (80 - 55 Ma); Glppsland Stable phase (55 - 20 Ma); Glppsland Shelf phase (20 - 0 Ma). The Strzeleckl-Otway and Tasman Sea Rift phases are characterised by tenslonal stress w Ith rap Id subs I dence and depos It I on at rates In excess of 150m/Ma. The rift-controlled structural trends In the Strzelecki-Otway Rift phase were orientated west-northwest to east-southeast but were overprinted by northeast to southwest structural trends of the Tasman Sea Rift phase. The sediments were deposited In al luvlal, fluvlal and restricted paludal environments In steep sided fault control led basins. Two lntracratonlc rift-valley clastlc suites developed: the volcanoclastlc Strzeleckl Group (at least 3km thick) and the second cycle Cenomanlan-Santonlan section of the Latrobe Group Cat least 2km thick). The coals form less than 5% of the sequences and are thin (< 3ml, lentlcular, prone to spl lttlng and deterioration. They have high lnertlnlte and mlneral matter contents and are thlnly banded (malnly claraln and duraln, minor vltraln and fusaln). The Strzeleckl and Tasman Rift phases are dlstlnctly separated by a Mlddle Cretaceous unconformity produced by upllft and erosion associated with Otway breakup and perhaps pre-Tasman rift doming. The Tasman Drift phase was characterised by the establlshment of marine conditions along the eastern edge of the offshore Glppsland Basin and moderation of tenslonal stresses, glv•lng subsidence and deposition rates < 100m/Ma. An aggradatlonal and progradatlonal fluvlo-deltalc to marglnal-marlne coal-bearing sequence developed. The coal seams are more numerous (5 - 10%), thin (typlcal ly < 5m but up to 20ml, prone to spl lttlng, wel I-banded (claraln, vltraln, duraln, fusaln) with high lnertlnlte and mlneral matter contents.

Austral Ian Coal Geology 4, part 1

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East-west cross section (top) through the offshore and onshore Gippsland Basin (details of faulting schematic). NE-SW cross section (bottom) through the offshore Gippsland Basin (based on James and Evans, 1971, Fi gure 4).

Austral Ian Coal Geology 4, part 1

G.C. Smith

The Glppsland Stable phase Is characterised by north-northwest to south-southeast compressional stress, minor right lateral shear and eustatic change. This resulted In renewed uplift of the Strzelecki Highlands, Initiation of the Latrobe Valley by downfaultlng, fold Ing In the offshore Glppsland Basin, and widespread development of erosional surfaces. Subsidence and deposition decreased (< 20m/Ma) and transgression occurred over the offshore Glppsland Basin. Coal measure sedimentation was confined to the Latrobe Valley, Lake Wellington, Seaspray and Alberton Depressions where thick and extensive sandstones, mudstones and coals (claralns, vltralns, minor duralns) were deposited with extremely thick coal seams being deposited In the western parts of the basin. The Glppsland Shelf phase saw renewed rapid subsidence and deposition In the offshore Glppsland Basin, probably resulting from the removal of regional compression, Increased right-lateral shearing, and Isostatic adjustment. A marine shelf-slope sequence developed offshore and the onshore coal measures built out over the marine beds to the present shoreline. INTRODUCTION The Glppsland Basin, located onshore and offshore In southeast Austral Ja (Figure I), Is one of the world's major coal and petroleum bearing basins. The baslnwlde stratigraphy and structure (Figures 2 and 3) are well known (for relevant I lterature refer Thompson l l l l , 1973; Douglas and Ferguson, 1976; Colman, 1976; Threlfal I n l l , 1976) but the regional relationships of tectonic history, structure and sedimentary facles, especially coal development, are not wel I documented. The GI pps I and Bas In Is an At I ant I c-marg In type bas In <Dewey and BI rd, 1970) and the major features of the stratigraphy and structure conform closely to the expected rifting and drifting events which have occurred during the Cretaceous and Tert I ary CF I gure 4). Severa I authors have attempted to exp Ia In these relationships (Carey, 1970; Griffiths, 1971; Elliot, 1972; Falvey, 1974; Boeuf and Doust, 1975; Gunn, 1975; Jones and Veevers, 1982). They have been confounded by some unreconcl I able mls-correlatlons between the stratigraphy and Interpreted plate tectonic history and the comp I !cations resulting from the effects of two rifting and drifting histories, one associated with the formation of Australia's southern margin and the other with the formation of Austra 11 a•s southeastern marg In. Recent re- I nterpretat Ion of the p Iate tecton Ic data may resolve these problems. Understand Ing the tectono-sed I mentary h I story of the Gi pps Iand Bas In Is of xconslderable Importance to coal geology because It represents a classic case of a young marginal basin and It well II lustrates the sedimentary evolution of coal-bearing seqeunces In such basins with tectonic development. Analysis of the Glppsland Basin offers useful models for coal exploration In other major coal-bearing basins. TECTONIC HISTORY The present ocean margins of Austral la result from the breakup of Ind la, Antarct I ea, Austra I I a and the area con ta In Ing Lord Howe RI se, New Zea I and, Chatham Rise and the Campbel I Plateau (for discussions refer Welssel l l l l , 1977; Falvey and Mutter, 1981; Veevers l l ll, 1982). Breakup began In the Late Jurassic on the northwest margin and progressed anticlockwise around

Austral Ian Coal Geology 4, part 1

G.C. Smith

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Austra 11 a to the northeast marg In where breakup occurred In the Pa Iaeocene. The breakup sequence Is Interpreted to be: 1. 2. 3, 4. 5.

Northwest - Late Jurassic, 155 Ma (Larson, 1975) Southwest - Early Cretaceous, 120 Ma (Larson .it± .lll, 1979) Southern - Middle Cretaceous, 100 Ma (Cande and Mutter, 1982) Southeast - Late Cretaceous, 80 Ma (Shaw, 1978) Northeast - Early Palaeocene, 65 Ma (Weisse! and Watts, 1979)

A series of Jurassic to Recent rift margin basins have developed which r~present classic examples of Atlantic margin type sedimentary basins. A qualitative tectonic model for Atlantic-type marginal basins Is now well established (Heeze, 1960; Dewey and BI rd, 1970; Bott, 1971; Burke and Dewey, 1973;

Austral Ian Coal Geology 4, part 1

G.C. Smith

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Falvey, 1974; Kinsman, 1975) though the exact mechanism Is arguable (compare Sleep, 1971; Burke and Whiteman, 1973; Falvey, 1974; McKenzie, 1978; Royden JU .al.. 1980; Falvey and Middleton, 1981; Veevers JU .al.. 1982). The tectonic model can be simplified Into two stages: B.l.f.t .S1ag.e

A rift-valley sedimentary basin system forms by crustal thinning and results In subsidence of continental crust along Incipient rift lines. High heat flow, associated alkal lne vu lean Ism, and rapid vertical foundering of large fault blocks occur along the rift system with rapid accumulation of Immature volcanoclastlcs. Commonly, major rift basins are located at rift line triple Junctions. A major erosion surface occurs at the base of the rift sequence which may result from a pre-rift period of extensive crustal uplift due to the effects of Initial I lthospherlc heating . .llt..l.f1 .S1ag.e

From 25-100 Ma after rift Initiation a spreading ridge begins to emerge along the axis of the rift basin. This causes a baslnwlde decrease In subsidence, relative uplift along the ridge margins and probably reverse-faulting of some earl fer formed rift fault blocks causing uplift In proximal areas. A distinct breakup unconformity forms In the main rift basins. A more restricted second cycle terrestrial sequence accumulates comprising Immature elastics although a shallow sea Incursion may occur. If this phase Is prolonged a distinct rim basin sequence can develop (Veevers JU .ll..L.. 1982). Subsequently, tholelltlc basalt extrusion occurs along the rift axis and results In continental separation away from the rift axis. In the case of a triple-Junction usually one arm degenerates (a failed-arm or aulacogen) which remains as a sedimentary trough (for examples see Burke and Dewey, 1973). Movement along the other two limbs Is not necessarily equal, rather one limb may be passive with most movement controlled by the other limb. Cooling of the oceanic plate causes It to subside with time (Sc later and Francheteau, 1970; Sclater JU .al.. 1971) and being coupled with the continental margin, the

Australian Coal Geology 4, part 1

G.C. Smith

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llo1tntl1raphlc r.on•tlon for the Cretaceous Period and C.inotolc En (1 - l l ow, 1969; ler11Ten, 1971. 2 - Taylor,

1'66, 1971, Palynolo1ical umation after Stover and Evans, 1973; Stover and Partridte, 1973; Partrld1e, 1976. Chronostn t i1raphy also after Yan Hinu, 1976; La lrecque n al , 1977) .

marginal basin also cools and subsides as model led In Figure 5 (Sleep, 1971; Watts and Ryan, 1976; Turcotte and Ahern, 1977; Royden Jtt .A.L. 1980). Continental separation and basin subsidence Initially give rise to shallow sea formation along the basin margin and later lead to a major dlachronous basinwide transgression (younglng away from the rift axis).

GJppslaod ~ formatJoo The Palaeozoic geology of southeastern Austral la Is dominated by rocks belonging to the north-south orientated Lachlan (Tasman) Geosyncllne (Brown .§1 .A.L. 1968). These rocks range from Ordovician (possibly Cambrian) to Lower Carboniferous. Some minor Permlan (mainly glaclgene, minor marine) and Triassic (terrestrial) sequences are known but no unequivocal Jurassic rocks have been found. Devonian granites form common lntruslves. The Palaeozoic sequences are unconformably overlain by a sequence of Cretaceous to Recent sed Imentary rocks depos Ited In approx I mate Iy east-west orientated basins. This first order east-west structural trend cuts across

Australian Coal Geology 4, part 1

G.C. Smith

LATE JURASSIC TO EARLY CRETACEOUS

80 Ma

Figure 7.

Late Jurassic - Early Cretaceous reconstruction (top) showing the approximate location of rift basins along the southern and south-eastern margins of Australia and Santonian reconstruction at 80 Ma (bottom). Figures 7 and 8 are polar stereographic projections showing : sea level and 1 km below sea level contours; active plate margins and transform faults; new ocean floor produced since previous reconstruction (shaded); arrows depicting vector movement of Australian plate relative to Pacific in the last SlMY. 8ased on Deighton et al (1976), Weissel et al. (1977), Crook and Belbin (1978), Shaw (1978), Cande and Mutter (1982).

Austral Ian Coal Geology 4, part 1

G.C. Smith

the earl ler north-south trends and the angular unconformity between the Jurassic and Cretaceous clearly marks a major tectonic event In the geologic history of southeastern Austral la. This tectonic event Is taken here to establ lsh the beginning of the Glppsland Basin and Is used to define the extent of the basin (Figure 1). In the Glppsland Basin this unconformity occurs at the base of the .C.... Stylosus palynologlcal zone which Is at least Neocomlan and possibly Berrlaslan (Figure 6).

StrzeleckJ-Otway R.Lf:t E.ha.s.e The first recognizable sedimentary sequence to develp In the Glppsland Basin Is the Strzelecki Group (Figure 4) comprising Lower Cretaceous lntracratonlc volcanoclastlcs (much of the literature prior to Medwell, 1954, refers to this sequence as being Jurassic). A similar Lower Cretaceous sedimentary sequence exists In the Otway Group. The Late Jurassic tectonic setting and location of Australia, Antarctica and the Lord Howe Rise group are shown In Figure 7. Given that 0tway breakup between Australia and Antarctica (110 - 90 Ma) began some 10 - 30 Ma prior to Tasman Sea break-up (about 80 Ma), the east-west rifting In southeast Australia during the Early Cretaceous Is probably 0tway rifting and the Glppsland and 0tway Basins probably formed a single east-west rift-basin (Carey, 1970; El I lot, 1972). This may have Included the Bass Basin or the Bass Basin may have been a major flanking graben (Dewey and Bird, 1970) elongated sub-para I lel to the Glppsland-0tway Basin. Al I three basins were connected through the KIng Is I and-Morn I ngton RI dge wh I eh d Id not beg In Its main phase of development until at least the end of the Early Cretaceous. The main structural trends would be east-west and Involved tensional downfaultlng. Initiation of Tasman Sea rifting could have begun during the Early Cretaceous or as late as the Middle Cretaceous. The east-west structural trends would have been overprinted by approximately northeast- southwest tensional downfaultlng. This would explain the dominance of both east-west and north eastto southwest structural trends which are pervasive through Strzelecki Group. The Strzelecki Group Is wel I known from outcrops and drl I I Ing In eastern Victoria where It Is at least 3 km thick (Jenkin, 1971). No definite marine Incursions have been found within the Strzelecki (or Otway) Group sediments. Edwards and Baker (1943), based upon extensive studies of the Strzelecki and Otway Groups, concluded that the Lower Cretaceous ("Jurassic") sediments In Victoria represented a single petrogenetlc rock-suite. Deposition occurred In large west-northwestto east-southeast oriented fault blocks (e.g. Knight, 1975, p. 334) In steep-sided flood plains (see examples In Edwards and Baker, 1943). Subsidence and deposition In the depocentres were rapid at rates of up to and over 150m/Ma. The Strzelecki Group Is undifferentiated and comprises arkoses, feldspathlc I ltharenltes, mudstones, conglomerates and thin subbituminous coals deposited In al luvlal, fluvlal and lacustrlne sedimentary environments. The arenltes and conglomerates comprise over 40% of the sequence. They are lenticular, commonly 30m thick but locally up to 150m thick. Petrographlcally they consist of 25-35% feldspar (ol lgoclase and alkal I), 15 - 40% rock fragments (volcanic andesltlc, tuffaceous, plutonlc) and a matrix of chlorlte, zo Is I te, ep I dote, fe I dspar, c I ays and carbonate. They are green-grey when fresh weathering to a buff brown. The mudstones are laterally more extensive, common I y 20m th I ck and rare I y greater than 60m th Ick. The coa I seams are thin, prone to spllttlng, heavily faulted and cleated. They are lenticular,

Austral Ian Coal Geology 4, part 1

G.C. Smith

Figure 8.

Reconstruction at SS Ma (late Palaeocene) and O Ma (Recent). See caption Figure 7 for explanation.

Australian Coal Geology 4, part 1

G.C. Smith

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up to three metres thick at their depocentre but thinning rapidly outwards and deteriorating over distances of 0.5 to 2 km. Edwards~ .Al... (1944) showed that In the South GI pps Iand Wonthagg I coa If Ie Ids the aggregate th Ickness of coal was related to subsidence control led by basement block faulting. The coals consist of minor vltraln with claraln and duraln bands predominating. Mudstone partings, detrltal quartz, clay mi neral matter and dlagenetlc slderlte are common. The source of the Strzelecki Group sediments Is not well-established and the direction of bas i n palaeoslope Is conjectural. Edwards and Baker (1943) Indicated that the coarse-grained sediments were deposited adjacent to the northern and southern areas of the main east-west trough while mudstones and coals accumulated In greater proportions along the axis. Palaeozoic sediments

Australian Coal Geology 4, part 1

G.C. Smith

and Igneous rocks form a substantial source and these could have been derived from the northern and southern margins of the rift basin (Edwards and Baker, 1943; Douglas, 1976). The volcanlc detritus may be derived from the extensive Jurassic and Early Cretaceous alkal 1-ollvlne basalts mainly remnant In south western Victoria (Ful larton and Tattam, 1976). Veevers n .al.... 11982) suggest that the volcanlc Input was derived from an andesltlc arc on the adjacent Lord Howe Rise to the east. This lmplles a palaeoslope from east to west which Is probable If 0tway rifting occurred prior to Tasman Sea rifting. Initiation of Tasman Sea rifting would have resulted In a west to east palaeoslope at least for most of the Glppsland Basin . .Ml..d.d..L.e Cretaceous Ull1f.1

Towards the end of the Ear I y Cretaceous the rate of subs I dance decreased In the Glppsland Basin and other basins along the southern margin of Austral la culmlnatlng In relatlve uplift and erosion represented by a Middle Cretaceous angular unconformity. Previous authors Inferred that this unconformity represented a rift unconformity or was related to a marine Incursion not associated with breakup (Griffiths, 1971; El I lot, 1972; Falvey, 1974; Boeuf and Doust, 1975; Gunn, 1975). Those Interpretations rel led upon 0tway breakup at about 55 Ma (Welssel and Hayes, 1972) whereas It Is now put at 110 - 90 Ma ICande and Mutter, 1982). The new Interpretation, If correct, means that the widespread Mlddle Cretaceous unconformity represents the 0tway breakup unconformity. This Interpretation fits the stratigraphic history and Is predicted by the slmple tectonic model of Atlantic marglnal type basins. If Otway breakup occurred at 55 Ma, more complex tectonic models are required lnvolvlng two-stage rifting, (Falvey, 1974; Falvey and Mlddleton, 1981), or the Mlddle Cretaceous unconformity could represent pre-rift doming associated with Otway rifting (Smith, 1981). The Middle Cretaceous uplift of Strzelecki Group rocks Initiated the onshore southeast Glppsland highlands (similar uplift of Otway Group sediments occurred In the Otway Basin). In the onshore Glppsland Basin this uplift was maintained at least during the Late Cretaceous and In parts up to the present with probably removal of over 11.5 km of Strzelecki Group sediments. The offshore Glppsland Basin also underwent structural movement. Stratigraphic Information from wells on the flanks of the Central Deep Indicates a Middle Cretaceous unconformity and seismic data Indicate the Strzelecki Group Is structurally deformed, relative to overlying sediments, with an angular unconformity along Its upper surface (Threlfal I n .aJ.... 1976). However, locally In the Central Deep the Upper and Lower Cretaceous rocks may be conformable. lsill Cretaceous Rl..ti .Eb.a..s.e ccenanan!an to Santon!an>

The configuration of Australia, Antarctica and the Lor d Howe Rise group at the beginning of the Late Cretaceous was essentlally that shown In Figure 7. The southern marg In of Austra 11 a a I ong the 0tway RI ft was beg Inn Ing the 0tway Drift phase with Initiation of ocean basalt extrusion and separation of Austral la and Antarctica. The Tasman Sea was stl 11 In Its rift phase and a second phase of rapid subsidence Is recognizable In the Gippsland Basin beg Inn Ing as ear I y as the Cenoman I an I.A, d I stocar I natus zone Is recorded In several offshore wel Is) and continuing to the Santoni an. Subsidence and deposition were confined to the Central Deep (Figures 2 and 3) and were greatest In the centre at over 150m/Ma being less along the rift axis and further Inshore (Smith, 1981). Subsidence was control led principally by downto-basin faulting along northeast-southwest I Ines with the basin margins

Australian Coal Geology 4, part 1

G.C. Smith confined by the earl ler east-west fault I Ines. This phase of rapid subsidence probab I y represents r I ft subs I dence In the GI pps I and arm of the Tasman Sea Rift although It can be Interpreted as a rim basin sequence developed behind an emerging Tasman Sea oceanic ridge (Veevers 1d lli 1982). The sedimentary rift sequence which developed In the offshore Glppsland Basin during the Cenomanlan to Santoni an Is poorly known. Only a smal I number of deep petroleum wel Is have penetrated the sequence (up to 1 km In Tuna-1) and knowledge of Its distribution Is based upon seismic Interpretation (Figure 3). The younger units progresslvely onlap onto the Strzeleckl Group. The sequence Is undifferentiated and at present Is Included In the Latrobe Group (Figure 4) defined by James and Evans (1971> as the major offshore I lthostratlgraphlc d Iv Is Ion encompass Ing Upper Cretaceous to Eocene coa I-bear Ing strata. The Cenomanlan to Santonlan sequence Is wholly non-marine and consists of poorly

Figure 10 Generalised Maastlchtlan to early Eocene sedimentary trends Large arrows denote Inferred upland source areas

Figure 11

SOKM

Generalised mlddle to late Eocene sedimentary trends. Large arrows denote Inferred upland source areas.

Austral Ian Coal Geology 4, part 1

G.C. Smith

Figure 12 Generalised Oligocene to early Miocene sedimentary trends (offshore channels developed at the end of the early Miocene). Large arrows denote inferred upland source areas. sorted arenltes, mudstones and bituminous coal seams of limited lateral extent, deposited In fluvlal, alluvial and lacustrlne sedimentary environment s. The arenltes are feldspathlc litharenltes and lltharenltes with high proportions of matrix and low porosity. The mudstones consist of fissile carbonaceous sl Its and shales. The coals are thin, high In mineral matter and wel I banded. The probable palaeoslope for the Cenomanlan to Santonian basin was from west to east which suggests the source rocks were mainly second cycle Strzeleckl Group, rift associated volcanlcs and Palaeozoic rocks. Any Influence from an easterly located arc would be minor. ll£Ilgil ~ .llr:..l.fi ~ ccampan Jan Il! ~ At approximate ly 80 Ma the Tasman Sea Rift System began the Drift Phase with initiation of oceanic material in the Tasman Sea Basin, recognisabl e by 76 Ma (Ring ls, 1972) and cessation of spreading soon after 55 Ma (Figure 8). This placed the offshore Gippsland Basin under tensional st ress and perhaps right lateral wrench faultlng (producing compression and associated reverse faulting and folding). A Camp an Ian to ear Iy Eocene sequence Is recogn Isab Ie In the GI pps Iand Bas In comprising I ithofacles which are distinct from the earlier formed rift sequences. A widespread breakup unconformity has not been recognized near the base of the Campanlan but this may reflect lack of data especially along the eastern edge of the basin. An unconformi ty is evident in some of the wel I sections located on the margins of the Central Deep (e.g. Emperor-1) where the section missing represents some or all of the .C.. triplex to H.. Senectus zones (figure 6). Within the Central Deep, sedimentat ion was continuous during breakup, at least locally. Subsidence and deposition were Initially rapid and confined to the Central Deep at rates of over 150m/Ma but by the Palaeocene, on lapping Into eastern Glppsland had occurred and baslnwlde deposition decreased to less than 100m/Ma (figure 9). The open Ing of the Tasman Sea a I Iowed a mar I ne transgress I on to come up the main north-south Tasman Sea rift from the south. A marine Incursion phase ls recognisabl e by the Maastrlchtl an CU.. .l1Lu.g.ll zone, L.. ~ zone, Partridge, 1976) and the eastern margin of the Glppsland Basin became a marine shoreline

Australian Coal Geology 4, part 1

G.C. Smith at least by the end of the Late Cretaceous (Figure 10). The shore I lne was orientated northeast-southwest along which marglnal marine sediments (unnamed) accumulated, lncludlng offshore, beach, barrier, estuarine and lagoonal facles. A thin sequence of shallow water marine sediments Cun-named) Is known to occur south-east of this shorellne. Landward of the shore I lne (to the northwest) a fluvlo-deltalc sequence of llthlc conglomerates, lltharentles and quartzose sandstones, mudstones and thin coal seams accumulated, characterised by rapid lateral I lthologlcal variation. This sequence Is referable to the Latrobe Group (James and Evans, 1971) and Is undifferentiated. Several progradatlonal sequences are recognlsable near the strand I lne probably representing minor eustatic cycles (Partridge, 1976), with each succeeding stacked sequence tending to occur further bas Inward (northwest). Burl al was greatest In the middle de I talc depositional areas between Klngflsh-1 and Barracouta-1 (Figure 9). The coals are generally less than 10m thick, prone to spllttlng and with numerous mudstone and fine sand partings. Seam thickness and frequency Increases towards the top of the Palaeocene section where several moderately thick seams (10 20m) were Intersected In some wells Including Barracouta-3, Bream-3, Marlln-1, Nannygal-1 and Turrum-1. The coals are wel I banded, comprising thin bands of claraln, vltraln, duraln and fusaln. Glppsland ~ ~ <Middle .w;.ene .1Q ~ Miocene>

Cessation of ocean formation In the Tasman Sea Basin by the early Eocene marked the end of rift-associated subsidence and removed the reglonal northeast-southwest tenslonal stresses due to spreading. This was replaced by a north-northwest to south-southwest compresslonal stress regime accompanied by wrench faultlng (Figure 13) due to Otway spreading south of the Tasman Sea and strike slip movement along Tasman Sea fracture zones (Weisse) and Hayes, 1972; We Isse I .e1 .al... 1977; Sm Ith, 1981). Onshore wIth In the Strze Ieck I Group rocks, high angle or reverse faultlng and wrench movement occurred along northeastsouthwest and east-west trends to form a series of asymmetric horsts and grabens generally tilted to the southeast. This movement has continued Intermittently through the Tertiary, rejuvenating the Southeast Victorian Highlands. Tertiary subsidence and sedimentation occurred In the downthrown blocks of the Latrobe Valley - Lake Wellington, Alberton and Seaspray DepressIons and the Moe Swamp Basin, at rates of less than 20m/Ma except adjacent to the overfaulted margins of downthrown blocks where thick sediment wedges have accumulated (e.g. on the downthrown side of the Rosedale Monocl lne In the Latrobe Valley Depression). In the offshore Glppsland Basin, development of the north-northwest to south-southeast compression and wrench faultlng caused structural upllft In the northeast offshore area, westerly tlltlng of Latrobe Group strata along the eastern margin and open en-echelon, approxlmately eastnortheast to west-southwest folds (Figure 13). Net deposition during the 51 20 Ma period was minor due to slow subsidence or uplift and erosion (Figure 9) and compared to the earlier burlal history of the Glppsland Basin this period represents a distinct stable phase of slow subsidence. This stable phase facllltated the development of several major eustatic cycles from the ear I y Eocene to the end of the ear I y O11 gocene. The Iow stands and non-deposition lead to the development of the Latrobe Unconformity surfaces on, and submarine channel llng of, the offshore Latrobe Group sediments. The fol lowing high sea level stands control led the westward migration of the mar I ne shore 11 ne from we 11 offshore In the ear I y Eocene w Ith the f Ina I sea level rise at the end of the early Ollgocene (foramlnlferal zone J, Figure 6), resultlng In a widespread transgression over the offshore Glppsland Basin

Austral Ian Coal Geology 4, part 1

G.C. Smith

l 0

, __ __

' II I \

100km \

Structural Map of the Glppsland Basin showing main fault and fold trends (Hocking n .al. 1976) and thei r relationship to the Inferred regional stress patterns.

Figure 13

Latrobe Group (Figures 3 and 12). The major eustatic changes correlate wel I with those In the Otway Basin, other Australian Tertiary basins and sequences on other continents (Glenle n .a.L. 1968; Rona, 1973; Val I n .aJ.... 1975; Partr I dge, 1976; Carter, 1978). Th Is suggests that they are re Iated to the effects of rapid ocean formation associated with the Otway drifting (Figure 8) and the onset of Antarctic glacial cycles. Worldwide climatic cooling occurred dur Ing the I ate Eocene and ear I y O11 gocene I ead Ing to the deve Iopment of Ice-sheets on Antarctica (Dorman, 1966; Devereaux, 1967; Margolis and Kennett, 1971). Intensified seafloor erosion resulted from activated bottom water circulation from Antarctica to lower latitudes, chemical dissolution and benthlc standing crop and activity (Kennett .e.:t .aJ.... 1972). In the Glppsland Basin shelf erosion and non-deposition of fine-grained sediments was effected by cold polar currents passing along the eastern seaboard of Austral la (Kennett n .a.J.... 1972). This ocean circulation pattern continued untl I the late 01 lgocene when drifting of Austral la from Antarctica was sufficient to establish the clrcum Antarctic ocean current (Deighton .lil .a.h. 1976). The eustatic and tectonic changes which occurred In the middle Eocene to Ollgocene period divided the Glppsland Basin Into offshore and onshore Basins s Im 11 ar to the present structura I d Iv Is I ons. The offshore GI pps Iand Bas In contains a middle and late Eocene fluvlo-deltalc/marglnal marine sequence unconformably overlain by a transgressive PI locene to Recent marine shelf sequence (Figures 3 and 4). The onshore Glppsland Basin contains a middle Eocene to Recent terrestrial sequence with the marginal marine facles boundary occurring In eastern Glppsland (Figures 3 and 4). The major environments of deposition In the offshore Glppsland Basin during

Austral tan Coal Geology 4, part 1

G.C. Smith

the middle and late Eocene are shown In Figure 11. Thin marine sediments occur along the eastern margin of the basin, comprising shallow open marine and submar I ne fan sed I ments depos I ted ma In I y dur Ing fa I 11 ng sea I eve Is and channel ff 11 sediments deposited mainly during rising sea levels (e.g. Flounder, Turrum and Gurnard Formations; James and Evans, 1971>. A fluvlodeltalc sequence referable to the Latrobe Group developed to the west. The units are of greater lateral persistence than older Latrobe Group fluvlodeltalc sequences and comprise quartzose sandstones, mudstones and some thick coal seams (10 - 30m thick In the Barracouta area). The coal seams are poorly to moderately wel I banded and consist of thick bands of claraln and vltraln with minor duraln. Thin mineral matter partings and major seam spl Its are common. Aggregate seam thickness exceeds that of the Upper Cretaceous to lower Eocene Latrobe Group. The transgression at the end of the early Ollgocene occurred over the offshore Glppsland Basin and the eastern parts of the onshore Glppsland Basin. A marginal marine barrier complex developed along the eastern Glppsland shoreline, while further east, shallow to deep water - marine shelf sedimentation began and has continued largely uninterrupted to the present day (Seaspray Group, Figure 4). The marine sediments Initially comprised green sands and mudstones but the formation of the clrcum Antarctic ocean current by the late Ollgocene diverted the main cold polar bottom currents away from the Glppsland coastline allowing deposition of fine-grained carbonates as water temperatures Increased.

w z w

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Figure 14 Lithostratlgraphlc units In the Latrobe Valley and their relationship (tentative) to the chronostratlgraphl c units.

Austral1an Coal Geology 4, part 1

G.C. Smith

The earl test systematic work on the onshore Glppsland Basin sequence was carr I ed out Iarge I y In the Latrobe Va I I ey, and the term Latrobe Va 11 ey Coa I Measures was Introduced by Thomas and Baragwanath (1949) for the middle Eocene to Miocene coal-bearing sequence (Figure 14). Carter (1964) extended the use of the term to the coal-bearing sediments which occurred In southeast Glppsland. The Latrobe Valley Coal Measures In their type area consist of a sequence of thick and laterally persistent I lthlc conglomerate s, quartzose sandstones, mudstones, coal and locally lnterbedded alkaline volcanlcs. Three main recognisable coal-forming episodes or fluvto-lacustr lne cycles are recognisable leading to the successive formation of the Traralgon, Morwel I and Ya 11 ourn Seams (In deta 11 each seam cons Ists of severa I sp 11 ts; GIoe, 1976). The Traralgon cycle was deposited In the middle Eocene to early Ollgocene and passed eastwards Into the fluvlo-deltatc coal-bearing sequences In the offshore Glpsland Basin. Thick coal seams (Traralgon and equivalents) developed over the flanks of the emerging Baragwanath Anticline and along the western margins of the Seaspray and Alberton Depressions (Figure 11). The succeeding Morwell cycle Is dominated by the extremely thick and laterally persistent Morwel I Seam and equivalents which developed during the early Ollgocene to ear I y MI ocene beh Ind a stab I e barr I er coast 11 ne CF Igure 12). Th I ck est peat development occurred on slowly subsiding structurally positive areas along the southern and western parts of the Latrobe Va 11 ey Depress Ion and around the Hedley Dome In the Gel llondale coalfield. The main fluvtal channels flowed to the east along the northern part of the Latrobe Valley - Lake Wei I tngton Depressions.

• M IOCENE o EOCENE • P'ALEOCENE t T. longua - T. lilli• i

• P'Rf:- T. lilli e i

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w 0

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Figure 15

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Plot of mean maximum vltrlnlte reflectance (~max%> versus depth (km) for coal samples from the Glppsland Basin. Samples Identified according to age.

Austral Ian Coal Geology 4, part 1

G.C. Smith

Lacustrlne muds and sands and thin coals were deposited to the east In back-barrier environments. The third and final Yal lourn cycle was deposited In the early to middle (upper?) Miocene. This cycle Is dominated by the thick Yallourn Seam and equivalents In the west passing Into a regressive sequence of thin coals, muds and sands In the east and Is related to the Miocene to Recent tectonic phase discussed below. G(pps(and SMl.f ~ CM(ocene to Recent>

At 20-18 Ma the offshore Glppsland Basin began a new period of extremely rapid burial and shelf-slope development which has lasted to the present day with rates of subsidence and deposition up to and over 150m/Ma (Figure 9). The cause of this rapid subsidence and deposition Is not clear but may result from removal of regional compression, Isostatic adjustment and re-activation of major right-lateral wrench movement on the Rosedale and possibly Foster Fault systems. This Is consistent with early Miocene structural development and channel ling and correlates well with the change from spreading between the Australian and Pacific plates to significant first-order right-lateral strikes 11 p movement (FI gure 8). Offshore th Is re-act I vated the east-northeast to west-southwest folds and associated northwest-southeast faults. Onshore, some macroscale folds developed In the Latrobe Valley Depression due to movements on the northeast-southwest high angle or reverse faults (Barton, 1979). The distribution of early to late Miocene sedimentation was slml lar to the Ollgocene patterns. However, Intensified lsostatlcal ly controlled hinterland up( 1ft (Wei Iman, 1974, 1979), Increased sedimentation rates, rapid subsidence offshore and a lowering of base level, resulted In progradatlon of the fluvlolacustrlne sediments over the marine sequences In eastern Glppsland and the development of several submarine channels on the continental shelf (Figures 3 and 12). Towards the end of the middle Miocene and during the late Miocene continued fold growth and lowering of base level resulted In widespread erosion throughout the Latrobe Valley but especially In those areas which corresponded to structural highs. Thin alluvlal and fluvlal sequences accumulated during the Pllocene to Recent period In the onshore part of the basin (Figure 14). These sediments are dlsconformable or paraconformable over the early Tertiary sequences In some areas but are unconformable In areas eroded In the late Miocene. A barrierbar system has developed along the present eastern Glppsland shore I lne and thick Pllocene and Quaternary marine sediments have accumulated offshore. COAL RANK VARIATION Coal rank Is a sensitive Indicator of low temperature-pressure burlal metamorphism (below greenschlst facles) In sedimentary sequences (HI It, 1973; Telchmul ler and Telchmul fer, 1954; Smith, 1981). Precise assessment of coal rank can be made using mean maximum reflectance values of coaly matter In most sedimentary rocks CTelchmul fer, 1950; Kantsler .e.1 .a.L. 1978; Bostick, 1979; Smith and Cook, 1980). Mean maximum vltrlnlte reflectance (Rvmax%> values have been obta I ned on a I arge number of we 11 samp I es In the GI pps I and Bas In and the results used to assess the level and history of burial metamorphism (Smith, 1981). Representative ~vmax% data are plotted In Figure 15 and lsoreflectance contours are shown on the east-west cross-section through the Glppsland Basin shown In Figure 16. The most obv Ious feature of the data Is the over a I I Increase In Rvmax% w Ith

Australian Coal Geology 4, part 1

G.C. Smith

20 w

SHO IULIH [

S.L.

! 2

MAftlNE

□

LATR08E GROUP

□ · ITRZELECKI GROUP •

2:0

Figure 16 East-west section through the Glppsland Basin showing estimated lsoreflectance contours. depth. Coal ranks range from onshore Tertiary soft brown coals with less than 0.3% Rvmax to Upper Cretaceous med I um-vo I at 11 e b I tum I nous coa Is w Ith Rvmax 1.2% and over at depth of 4 km or more. This Increase In Rvmax with depth Is statistically significant (r = 0.84 for the regression curve shown In Figure 15). Less obvious characteristics of the data Include the Increase In reflectance grad I ent w Ith depth (the best-f It regress I on shown In FI gure 15 Is a second degree equation for which the gradient Is dR/dX = -0.04 + 0.12X, where R Is R max% and X Is relative depth In metres). The gradient Is a function of ~ecreaslng thermal and burial gradients over the Upper Cretaceous to Ollgocene period (Smith, 1981). Figure 16 shows that the lsoreflectance contours dip eastwards across format Iona I boundar I es, the Latrobe Uncon form I ty and the offshore Glppsland Basin lsochrons. Samples from wells on the margins of the offshore Glppsland Basin tend to have higher Rymax values than samples from similar depths from wells within the Central ueep. Smith (1981) considered that this results primarily from the greater rates of burial within the Central Deep over the Upper Cretaceous and Calnozolc and t he related distribution of thermal gradients (Figure 17). Few Rvmax values for the Strzeleckl Group are aval I able but, as shown In Figure 16, the data Indicate a rank break between the onshore Eocene softbrown coa Is C Iess than 0.45% Rvmax) and the under I y Ing Lower Cretaceous subb I tum I nous coals (greater than 0.60% Rvmax). This Indicates a period of earlier burlal of the Strzelecki Group and subsequent uplift and erosion prior to deposition and burial of the onshore Tertiary sequence. The pre-Eocene coallflcatlon of the Strzelecki Group coals can be estimated using the Z scale on Karwell 1s nomogram (Figure 18) and Is about Z<Rvmax 0.65%) = 0.06 minus Z( Rvmax 0.43%) = 0.01 using the H reflectance scale which Is appropriate for "these young low rank coals (Smith, 1981). A Z value of 0.06 - 0.01 = 0.05 Indicates that the reflectance value of the Strzelecki Group coals attributable to pre-Eocene coal lflcatlon Is Rvmax = 0.60%. This rank In an Early Cretaceous coal Indicates conslderable and rapid pre-Tertiary coallflatlon which could only result from rapid and deep burial. The exact depths of burial prior to Late Cretaceous uplift are dlfflcult to estimate because coal

Austral Ian Coal Geology 4, part 1

G.C. Smith

21 141°

141°

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Figure 17

Fourth-order partial trend-surface to the geothermal gradients c°C/km) for data from 73 offshore wel Is (Smith 1981).

rank (and other burial metamorphic parameters) are dependent on the duration and rate of burial and the palaeothermal gradients. Assuming burial for 10 20 Ma an Rvmax value of 0.60% Indicates an Isothermal temperature (minimum) value of about 100° - 120°c. The burial model shown In Figure 5 suggests that heat f Iow Q after about 30 Ma C130 Ma to 100 Ma) of r I ft bas In deve Iopment should be 90mW/m 2. Assuming thermal conductivity for a fluvlal/al luvlal sequence between 1.5 - 2.5 W/m°K then the estimated range of geothermal gradients lies within 36 - 60°C/km (from Q = kT1 where k Is thermal conductivity and T' Is I lnear geothermal gradient). Using a surface temperature of T = 20°c the data suggest that a Rvmax value of 0.60% represents Early 0

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Figure 18 Karwell-Nomogram showing relationship of time (Ma), temperature 0 c and rank scales (after Bostlck,1973: flg.5). Scale A Karwell (1956), B - Telchmul ler & Telchmul ler (1968), - C Telchmuller (1971), D - Alpern & de Sousa (1970), E - estimated uncertalnlty In volatile matter - maslum reflectance conversion (Bostlck,1973) , H - qualltlve best flt relation (Bostick, 1973).

Australian Coal Geology 4, part 1

G.C. Smith

Cretaceous burial to between 1.3 km and 2.7 km. These results are consistent with the measured Rvmax and depth relationsh ips In the offshore Glppsland Basin (Figure 16) and the present offshore distributio n of geothermal gradients (Figure 17) both of which result largely from the post Eocene burial history. Thus the onshore Strzelecki Group has had an estimated 1.5 to 2.5 km of section removed prior to deposition of the onshore Tertiary sequence. COAL TYPE VARIATION Assessment Qf ,C,Qal l¥J2.e

Coal type variation between and within coal seams can be evaluated macroscopically In terms of llthotypes, or more precisely, by microscopic methods In terms of macerals. However, the current llthotype and maceral classlflcatl on systems of the Internation al Commission for Coal Petrology ( I.C.C.P., 1963, 1971, 1975) are restricted to either brown coals or hard coals. No single system Is applicable for the description of coals which range from soft brown to medium-vol atile bituminous coals. Smith (1981) was able to separate the effects of coal rank on coal macerals from those due to coal type and so develop a simple discriminat ing maceral system applicable to both brown and hard coals (given In Table 1). This system (Smith and Cook, In prep.) was based on examinatio n of over 250 coal samples and derived using numerical classificat ion techniques to objectively quantify preferred maceral relationships. The system recognises that the maceral groups vltrlnlte and humlnlte are synonyms as are exlnlte and llptlnlte. Superfluous maceral terms within the vltrlnlte group are discarded leaving three vltrlnlte maceral sub-groups termed televltrlnl te, detrovltrln lte and gelovltrlnl te. Teloy(tr(n (te (Figure 19) Is defined as Intact plant tissue phytoclast s, generally occurring as thin bands and larger than 10 microns In smallest dimension (width). Detroyltr[ n[te (Figure 19) Is defined as the vltrlnlte groundmass material which In soft brown coals consists of fine-grained (less than 10 microns diameter) fragmented attrltus, becoming optically less textured (compacted and gel I fled) at higher ranks. Geloy[tr[n [te (Figure 19) comprises those gellfled macerals which are greater than 10 microns In diameter and not clearly part of either telovltrlnl te or detrovltrln lte. Classification of the coals which occur In the Glppsland Basin based upon this system al lows recognition of at least three distinct major groups of coal seams (Table 2) which represent different geologic ages, tectonic and sedimentary settings:

(1) Lower Eastern View Type Coals (Cretaceous to early Eocene) (2) Upper Eastern View Type Coals (middle and late Eocene coals In the offshore Glppsland Basin). (3) Latrobe Valley Type Coals The f I rst two groups are named after the Eastern VI ew Coa I Measures In the Bass Basin (Brown, 1975) where these coal types were first discriminat ed and where a simple coal type sequence exists (Smith, 1981). ~

Eastern .'l.I.ll 1¥J2.e ~

The Cretaceous to lower Eocene coals In the Glppsland Basin form a petrographlcally distinct group of coals which Is strikingly dissimilar to the younger coa Is. The coa I seams form a mI nor proport Ion of the sequence and are typlca I ly thin being less than 20m thick and with a mode of 1 - 2m. Thin mineral

Austral Ian Coal Geology 4, part 1

G.C. Smith

TABLE

MACERAL

GROUP

PROPOSED COAL MACERAL CLASSIFICATION SYSTEM FOR HUMIC COALS.

MACERAL SUB-GROUP

MACERAL

Liptodetrinite Sporinite Cutinite Suberinite Resinite Fluorinite Exsudatinite Bituminite Alginite

EXINITE

Textinite Texto-ulminite Eu-ulminite Telocollinite

TELOVITRINITE

VITRINITE

Attrinite Densinite Desmocollinite

DETROVITRINITE

Corpovitrinite Porigelinite

GELOVITRINITE *

Eugelinite

Sclerotinite Semi-fusinite Fusinite Macrinite Micrinite Inertodetrinite

INERTINITE

Gelovitrinite is only recognized when not part of telovitrinite.

<10 microns diameter and when

Australian Coal Geology 4, part 1

G.C. Smith

Figure 19.

Reflected light photomicrograph of a Dark lithotype Latrobe Valley Type coal. Gelified detrovitrinite (DV) groundmass with inclusions and bands of telovitrinite (TV), gelovitrinite (GV), minor exinite (E), rare sclerotinite (I), and minor Morwell (Latrobe) Seam, R max = 0.32%, microporosity (P). v 0.60 mm. Field width

matter partings and major seam splits are common and the seams generally lens out over distances of 0.5 - 2 km. Macroscoplcal ly, the coals comprise distinct thin bands of claraln (30 - 50%), vltraln (20 - 40% ), duraln (10 - 30%) and fusaln (less than 5%). Seam thickness Increases and mineral matter content decreases vertlcally up through the sequence and more detailed sedlmentologlc and petrographic analysls of the older coals may al low separation of the rift phase coals (Strzelecki Group and Cenomanlan to Santonlan coals) from the drift phase coals (Campanlan to early Eocene). Mlcroscoplcally, the coals consist of thin bands of t elovltrlnlte lnterbedded with thicker bands mainly composed of detrovltrtnlte, lnertlnlte and minor mineral matter. The telovttrlnlte bands are gellfled even at low coal ranks. They commonly contain reslnlte, fluorlntte and suberlntsed cell walls and less commonly retain Intact cutlnlte. The cell lumens may contain mlcrlnlte, clay material or sulphides. Rare exsudatlnlte occurs, usually In cleats within telovltrlnlte and perpendlcular to the bedding. The detrovltrlnlte bands form the groundmass for Isolated telovltrlnltes, exlnltes, gelovltrlnltes, lnertlnltes and mineral matter. The exlnlte mainly comprises sporlnlte and llptodetrlnlte with minor reslnlte, fluorlnlte, suberlnlte or bltumlnlte. Gelovltrlnites, lncludlng corpovttrlnlte, are not com-

Australian Coal Geology 4, part 1

G.C. Smith TABLE

COAL PETROGRAPHIC DATA FOR THE MAIN LATE CRETACEOUS AND TERTIARY COAL MEASURE SEQUENCES IN THE BASS AND GIPPSLAND BASINS (INSUFFICIENT DATA FOR THE EARLY CRETACEOUS COALS).

AREA

SEAM AGE /TYPE

Onshore Gippsland Basin

P. asperopolous to

STATISTIC

-X S.E. Range

-X

Thin Seams

S.E. Range

Middle M. diversus X S.E. N. asperus Range Upper Cretaceous to Lower M diversus

KEY:

EX*

19.2 0.8 2-55

9.4 0.3 1-23

63.6 0.7 33-86

6.8 0.5 1-43

0.9 0.1 0-5

0.1 0.0 0-2

22.5 4.9 12-42

a.a

7.8

4-11

54.4 5.4 28-66

8.6 1.2 5-13

1.4 0.6 0. 7-2t

5.3 2.5 0-16

27.6 3.0 15-48

4.8 0.9 2-10

53.4 1.5 44-67

7.9 0.6 2-11

1.9 0.5 0.2-5

4.4 1.6 0.7-20

35.3 2.8 6-53

3.2 0.8 0-15

32.0 2.5 13-49

5.7 0.5 1-9

20.9 4.4 0.5-61

2.9 0.7 0.6-11

MM*

T. bellus Thick Seams

Offshore Gippsland Basin

-X S.E. Range

TV= telovitrinite, GV z gelovitrinite, DV = detrovitrinite, EX= exinite (liptinite), IN= inertinite, MM= mineral matter, X = mean, S.E. • ■ tandard error.

* No samples with>20% bituminite or mineral matter were used in the calculations.

One Sample, not included, contained 15% inertinite.

mon largely due to their Incorporation Into the detrovltrlnlte groundmass resulting from vltrlnlte dlagenesls and coallflcatlon. Exlnlte-rlch bands are minor though some thin detrovltrlnlte bands occur which contain high (up to 30%) proportions of sporlnlte and llptodetrlnlte. Thin claystone or mudstone bands occur In some coals and the coals typically contain framboldal pyrite and s lderlte. The most distinctive aspect of the Lower Eastern View Type coals Is the lnertlnlte population (Figure 20). All lnertlnlte macerals are common except sclerotlnlte which Is rare and each lnertlnlte maceral shows a wide range In morphology and reflectance within a given coal. Macrlnlte as found In Carbo-

Austral Ian Coal Geology 4, part 1

G.C. Smith

nlferous crasslduralns occurs In some coal bands often associated with exln Ite. These coa Is have re Iat Ive Iy Iow v I tr In Ite contents, an approx I mate I y equal ratio of telovltrlnlte and detrovltrlnlte, high lnertlnlte contents and the lowest exlnlte content (Table 2). The mineral matter content varies widely between coal seams but Is typically much higher than In the Latrobe Valley Type coals. ~

Eastern 'l..la ~ ,CQw

The offshore middle Eocene to late Eocene Latrobe Group sequence contains numerous thin seams typically 2-Sm thick and some well-developed coal seams up to 30m thick. Thickest aggregate seam development occurs In the western parts of the offshore Central Deep. The seams are laterally persistent over several kilometres but spilt and deteriorate over greater distances. Macroscoplcal ly, the coa Is are moderate I y we 11 banded and I arge I y cons I st of th Ick bands of claraln (vltrlnlte-rlch clarlte and vltrlte, dull to semi-bright lustre due to low rank) and vltraln, with minor duraln (vltrlnlte-rlch trlmacerlte and clarlte). Thin mineral matter partings are common.

Figure 20.

Reflected light photomicrograph of a Lower Eastern View Type coal. Inertinite (I, white-grey) and exinite (E, black) clasts in detrovitrinite groundmass (grey) with thin telovitrinite bands (TV, grey). Lower M. diversus age, R max = 0.55%, Field Width= 1.2 mm. V

Australian Coal Geology 4, part 1

G.C. Smith

Mlcroscoplc ally, the coals consist of relatlvely thick layers of poorly banded macerals. A detrovltrln lte groundmass generally comprises over 50% and tends to be less densely structured than the gellfled detrovltrln lte In the lower Eastern View Type coals, even at the same rank. This very fine granular groundmass Is the same as that described In Japanese Palaeogene coals by Asal and Tanno (1956} and termed degradlnlte . It contains Inclusions of telovltrlnlte, corpovltrln lte, exlnlte and mineral matter, with rare lnertlnlte (Figure 21}. Most of the exlnlte consists of llptodetrln lte or sporlnlte but In some bands reslnlte and fluorlnlte are usually abundan~ The lnertlnlte consists of sclerotlnl te with minor lnertodetr lnlte, mlcrlnlte and thick-walle d low reflectivity fuslnlte. Thin to thick telovltrlnl te bands may be lnterbedded with the detrovltrln lte. Reslnlte or fluorlnlte Inclusions In telovltrlnl te and telovltrlnl te with suberlnlsed cell walls and Intact cutlnlte are relatlvely common. Thin exlnlte-rlc h bands largely containing sporlnlte, llptodetrlnlte or bltumlnlte (generally with a clay matrix} are more common than In the lower Eastern View Type coals. The proportion of discrete mineral matter averages about 5% In the thicker seams with clays and slit mainly occurring along partings and cleat surfaces. Framboldal pyrite and slderlte (less common} are typical of the thinner seams whereas the thicker seams contain high organic sulphur levels but llttle sulphide or carbonate. Comparison of the three groups In Table 2 Indicates that the Upper Eastern View type coals have high total vltrlnlte contents (averaging 86%} and a moderately low ratio of telovltrln lte to detrovltrl nlte (near 1:2}. The average lnertlnlte content Is low whereas the exlnlte and mineral matter contents are sl lghtly high. Latrobe WJn I¥J2.8 .c.oa.l.s

The onshore Latrobe Valley Coal Measures and equivalents contain a number of very th lck seams (greater than 20m th lck) and numerous th Inner seams. The thick seams are laterally persistent over distances of several kilometres or more. Channel fl 11 sediments In the thick seams are rare and restricted to the top of seams or associated with seam spl Its. Discrete syndeposlt lonal mineral matter In the coals Is rare so that elastic fluvlal sedimentat ion within the coal swamps was almost non-existen t Indicating that at any one time the vegetated swamp-marsh facles were areally extensive. Thickest peat development occurred In slowly subsiding structurally positive areas In the Latrobe Valley, Seaspray and Alberton Depression s whereas the main easterly flowing fluvlal channels occurred along and to the north of the Latrobe Syncline and were mainly fed by the Eastern Victorian Highlands. Within the thick coal seams, paludal facles changes are recognisab le as a succession of I lthotype bands (Edwards, 1947; Kennedy, 1955; Baragwanat h, 1962; George, 1975}. The bands are from 2cm to 10m thick and range In areal extent from about 0.5-2 km, except for the Pa Ie bands wh I eh tend to be more restricted (usually 0.2-0.5 km}. Macroscoplcal ly, the coals consist of thick poorly-bedded llthotypes In which most of the llthotype boundaries are transitional though some boundaries are sharp. Edwards (1947} proposed classlflcatlon of the bulk of the coal Into I lgnltlc and earth bands. Baragwanat h (1962} referred to these as dark and llght bands respectively . These authors also noted thin fusaln bands and "pollen coals". George (1975} proposed a five-fold llthotype classlflcatl on comprising Dark and Medium-Dark (the llgnltlc coals}, Medium-Light and Light (the earthy coals} and Pale llthotypes (the pollen coals}. The thick seams are mainly comprised (Smith, 1980} of MediumDark (20 - 70%} and Medium-Light (10 - 50%} 1lthotypes with minor Light (3 37%> and Dark (2 - 25%} lithotypes and rare Pale llthotypes CO - 5%},

Austral Ian Coal Geology 4, part 1

G.C. Smith

Figure 21.

Reflected light photomicrograph of an Upper Eastern View Type coal. Detrovitrinite groundmass (DV , grey) with inclusions of inertinite (I), exinite (E) and telovitrinite bands (TV). P. asperopolus age, R max = 0.48%, Fi eld Width= 0.60 mm. V

The Dark and Medium-Dark I Jthotypes are moderately wel I-bedded and gel I fled. Mlcroscoplcally (Figure 19) they contain relatively high proportions of gellfled telovltrlnlte (usually 20 - 30%) and low proportions of exlnlte (about 3 - 5%) Jn a detrovltrlnlte groundmass of denslnlte and compact attrlnlte (50 60%). The telovltrlnlte contains corpovltrlnlte and porlgellnlte Inclusions but Intact cutlnlte or Inclusions of reslnlte or fluorlnlte are not common. Some telovltrlnlte has suberlnlsed cell walls. The exlnlte has a yellow-green fluorescence and consists of about equal proportions of sporlnlte and llptodetrlnlte. lnertlnlte Is rare but Includes sclerotlnlte, pyrofuslnlte (which can occur In very thin layers on bedding planes), seml-fuslnlte and fuslnlte (precursor) mater Ja I and I nertodetr Jn Jte. Petrograph lea 11 y, these I Jthotypes are analogous to the vltralns of hard coals.

Figure 22

Reflected light photomicrograph of Light l lthotype Latrobe Valley Valley Type coal (white light top, fluorescent light bottom). Ungellfled detrovltrlnlte groundmass with Inclusions of televltrlnlte (TV), common exlnlte (fluorescent material Jn lower frame), sclerotlnlte (I) and high mlcroporoslty (P). Morwel I Seam Rvmax=0.30%, Field width= 0.6rrm.

Australian Coal Geology 4, part 1

G.C. Smith

Figure 22.

Reflected light photomfcrograp h of a Light lithotype Latrobe Valley Type coal (white light top, fluorescent light bottom). Ungelified detrovitrinite groundmass with inclusions of telovitrinite (TV), common exinite (fluorescent material in lower frame), sclerotinite (I) and high microporosity (P). Morwell Seam, R max = 0.30%, Field Width= 0.60 mm. V Austral Ian Coal Geology 4, part 1

2'9

G.C. Smith

The Medium-Light and Light llthotypes are poorly bedded and ungellfled In the soft brown coals. Mlcroscoplcally they largely consist of an attrlnlte detrovltrlnlte groundmass (Figure 22) with I nclusions of corpovltrlnlte Cup to 40%), telovltrlnlte, exlnlte, sclerotlnlte and rare lnertodetrlnlte. Most contain minor amounts of telovltrlnlte (10-20%) occurring as texto-ulmlnlte and eu-ulmlnlte with minor textlnlte. The exlnlte (usually 5 - 15%) fluoresces green to yellow-green and consists largely of llptodetrlnlte with lesser amounts of sporlnlte,cutlnlte and reslnlte. Petrographlcally the Medium-Light llthotypes are analogous to the vltrlte-rlch claralns and the Light llthotypes are analogous to exlnlte-rlch claralns. The Pale I lthotypes are distinctive massive bands which mlcroscoplcal ly are composed of ungellfled detrovltrlnlte (attrlnlte) with very high proportions of exlnlte Cup to 50%). Llptodetrlnlte (with a green to green-yellow fluorescence) comprises by -f ar the major proportion of the exlnlte and sporlnlte (green-yellow fluoresence) makes up most the remainder. They contain minor amounts of telovltrlnlte, cutlnlte, suberlnlte, reslnlte, lnertodetrlnlte and characteristic sclerotlnlte. The mineral matter content Is low and mainly occurs as elemental lnorganlcs associated with chelate and functional groups or as dispersed submicroscopic su I ph I des I ess than 1 mIcron. Syndepos It Iona I arenaceous and arg 11 I aceous material Is rare as Is localised marcaslte which occur s as plant petrifactions or as massive crystal line epigenetic mineral matter (Edwards and Baker, 1951). Carbonates are not know from these low pH coals but euhedral grains of dlagenetlc quartz have been found In the Traralgon Seam In the Coolungoolun area (Smith, 1980). Table 2 Indicates that the Latrobe Valley Type coals are chiefly vltrlnlteexlnlte coals. They have very low telovltrlnlte to detrovltrlnlte ratios (1:3), high gelovltrlnlte contents (mainly recognisable due to their low rank), slightly high exlnlte contents and rare lnertlnlte and mineral matter and contents. DISCUSSION The d If ferences In tecton Ic sett Ing, pa Iaeoenv I ronment, 11 tho Iogy and petrog rap hy of the three main coal types detailed In this paper provide a basis from which their origin can be discussed. The rift and drift coal-bearing sequences contain the Lower Eastern View Type coal seams. These are relatively thin, contain significant proportions of adventitious mineral matter, and consist of vltrlnlte-exlnlte-lnertlnlte associations. Most represent localised eutrophlc peat swamps occurring adjacent to stream channels. The older rift val fey Cretaceous coals which were deposited on al luvlal and fluvlal plains are the thinnest and have the highest mineral matter contents. Those that belong to the Campanlan to early Eocene drift sequences were deposited In fluvlal and upper-delta le environments and In lower-deltalc and I lttoral env I ronments assoc I ated w Ith more para 11 c sed I men tat I on. For these coa Is rapid facles change over small Intervals of time did not allow the formation of thick seams nor the maintenance of highly acid peat swamp conditions. The high rates of elastic transportation and deposition and the rapid and Irregular subsidence associated with these deposltlonal areas probably lead to exposure (with consequent denudation), erosion, and spl lttlng or burial by elastic sedimentation of any developing peat. Proximity to marine environments would Increase the probability of alkaline and reducing brines mixing with the acid peat waters. Th Is part Iy exp Ia Ins the occurrence of frambo Ida I pyr I te, the

Australian Coal Geology 4, part 1

G.C. Smith

slderlte and the tendency for marked vltrlnlte dlagenesls In the Campanlan to Eocene coals. Vltrlte comprises much of the claraln and duraln and this Is reflected In the higher overall ratio of telovltrlnlte:detr ovltrlnlte suggestIng the dominance of woodland plant communities. The thinly banded nature of these coal seams Is consistent with rapid succession of plant communities occurring In response to changing swamp conditions. The Upper Eastern VI ew Type coa Is represent the wan Ing of the Tasman Dr I ft Phase. They Include moderately thick and thin coal seams. The thick seams tend to occur around the margins of the offshore Glppsland Basin In the more tectonlcal ly stable areas of slow subsidence and deposition. Petrographlcally they are similar In coal type and presumably origin to the Latrobe Valley Type coals except that they contain rare duraln bands (vltrlnertlte and trlmacerlte). The thin coals occur in the fluvlo-deltalc environments associated with the main channels of the palaeodralnage systems In the Central Deep where subsidence and deposition were rapid. Their situation Is similar to the Lower Eastern View Type coals. They contain a high proportion of adventitious mineral matter and are moderately banded, with bands of vltraln, claraln and less commonly durain and sapropelic bands. Though the Latrobe Valley Coal Measures Include numerous thin coal seams, volumetrlcal ly they are dominated by the extraordlnarlly thick Latrobe Valley Type seams. These th Ick seams are der I ved from ombrogenous, o 11 gotroph Ic peats (cf. Anderson, 1964) which accumulated In areas undergoing very slow tectonic subsidence (or relative upl 1ft) over long periods of time. This allowed the widespread development of stable plant communities In swamplands on extensive, flat-lying, marginal floodplain areas starved of Inorganic sediment. Their development was closely linked to the rate of Tertiary elastic accumulation In the onshore Glppsland Basin, being slow In relation to those regions of the offshore Glppsland Basin In which parallc, fluvlo-deltalc depositional environments dominated. In addit ion to the tectonic-sedimenta ry control on coal seam development and coal petrographic type, the prevailing climate and flora have exerted a considerable Influence. The Lower Eastern View Type coals were deposited at a time when the tropical belt was broad, under warm temperate conditions becoming near-tropical In the early Eocene (Partridge, 1976; Kemp, 1978). The associated flora was probably of a diverse temperate rainforest to neartropical rainforest type (Kemp, 1978). Worldwide climatic cooling began In the mI dd I e Eocene and peaked In the I ate Eocene and ear I y OI I gocene. SI nee then the climate In southeast Australia has essentially been cool-temperate or colder (Dorman, 1966; Devereaux, 1967; Addlcott, 1970; Frakes and Kemp, 1972). A major florlstlc change occurred In the middle Eocene (Partridge, 1976) resulting In the development of warm to cool-temperate mixed forests and this change Is associated with the formation of the Upper Eastern View Type coals. The Latrobe Valley Type thick seams, which first appear In the middle Eocene and dominate the coal measure sequences by the Ollgocene, are associated with the establishment of mixed forests with an Increasing sclerophyll component, marshland vegetation and cool climatic conditions. Peat temperatures are an Important factor In peat dlagenesls with low temperatures Inhibiting decay and this may In part explain the great thicknesses of well preserved vltrlnlte and lack of degradolnertlnlte. The pollen assemblages In the coals (Luly .§1 ~ 1980) record an Increase In open wood·I and, reed swamp and open marsh conditions (Composltae, Mllfordla types and monocotyledon sedges and rushes) which correlates well with a decreasing ratio of telovltrlnlte to detrovltrlnlte and an Increasing proportion of detrovltrlnlte-typ e clarlte.

Australian Coal Geology 4, part 1

G.C. Smith

The Morwel I Seam largely consists of Medium-Light and Light llthotypes Indicating the prevalence of open, mixed-woodland swamps and marshes. The drier and colder conditions which developed by the middle Miocene allowed the dom I nance of sc I erophy I I forests (BI ackburn, 1980) and the Ya I Iourn Seam largely consists of Medium-Dark and Dark llthotypes. The end of the Miocene Is marked by Increasing Acacia, Composltae and Gramlneae associated with a general decrease In rainfall, temperature and forest distribution In southeast Austral la (Kemp, 1978). This records the end of significant coal measure sedimentation and corresponds closely to the Messlnlan Stage. ACKNOWLEDGEMENTS The author's I nterpretat I ons g I ven In th Is paper have benef I ted from discussions with the geological staff and access to data and equipment at several organisations. These Include ESSO Austral la Ltd., Broken HII I Proprietary Ltd., State Electrlclty Commission of Victoria and The Department of Geology, University of Wollongong. REFERENCES Addlcott, W.O., 1970, Latitudinal gradients In Tert i ary molluscan faunas of the Pacific Coast. Palaeogqraphy, Palaeocliroatol, Pa1aeoecol,8, 287-312. Alpern, B. & Lemos de Sousa, M.J., 1970, Sur le pouvolr reflecteur de la v I rt In I te et de I a f us In I te des hou 11 I es. .c..R... ~ .s.c.L. Paris. [h. 21.L. 956959. Anderson, J.A~R., 1964, The structure and development of the peat swamps of Sarawak and Brunel . .J... Tropical~ .li4. 7-16. Asa I, K. & Tan no, H., 1956, Proposa I to t he nomenc I ature of coa I petro Iogy In the Tert I ary coa I of Japan. .P..r..o.c.... .2.n..d Meeting Intern, ,C.QmJlh. ~ Petro 1,. Bruxe l les, 77-80. Ba r agw anath, G.E., 1962, Some aspects of the format I on of brown coa I, and of the behaviour of brown coal ash In water tube boilers, with special reference to VI ctor Ian depos Its. fCQC.. Austra I as, J.n.s1.. M..I.n.. Meta I I, 202... 131-249. Barton, C.M., 1979, Analysis and prediction of geological structures In the Latrobe Valley. Y.1.c1.. .s.:t.a.:te .El.ecL. .comm.. f..u.e.l. .Q.ep_t.._ Exploration~ Geo!ogi~ Division Report, (unpubl.). Berggren, W.A., 1971, ~ Micropa!eonto!ogy Qf Oceans, 693 pp.

Cambridge Unlv. Press,

Blackburn, D.T., 1980, Florlstlc, environmental and llthotyplc correlations In the Yal lourn Formation, Victoria. Calnozoic Evo!utlon .of Continental~ Eastern Austra I i a~~ p. 9. Blow, W.H., 1969, Late Middle Eocene to Recent planktonlc foramlnlferal blostratlgraphy, l.n Bronnlmann, P. & Ren, H.H. (eds.), .P..r..o.c.... .l.li 1nternat, .GQn.L. PI ankton i c MI crofoss I Is, Geneva, 1967, 199-422.

Australian Coal Geology 4, part 1

G.C. Smith

Boeuf, M.G. & Doust, H., 1975, Structure and development of the southern marg In of Austra 11 a. .AE.EA .J...l..5.,33-43. Bost I ck, N.H., 1973, TI me as a factor In therm a I metamorph Ism of phytoc I asts Ccoa I y part I c I es). .c..R.. lih ~ I nternat. Strat I graph I c .e..t Gao I og I e c.a.ci2= onlfere, Kreteld, 1.91.L. 2.. 183-193. Bost I ck, N.H., 1979, MI croscop I c measurement of the I eve I of catagenes Is of sol Id organic matter In sedimentary rocks to aid exploration for petroleum and to determine former burl al temperatures - a review, ..Ln Schol le, P.A. and Sch I uger, P.R. Ceds.>, Aspects .o.f D[ agenes [ s. Spee. Pub. Soc. Econ. Pa I aeon, Min., 26, 17-43. Bott, M.H.P., 1971, Evolution of young contlnental margins and formation of shelf basins. Tectonophys[cs ~ 319-327. Brown, D.A., Campbel I, K.S.W. & Crook, K.A.W., 1968, .Iw Geolog[cal Evolutlon

.o.f Australia .arul ~ Zealand. Pergamon, Oxford, 409 pp. Brown, B.R., 1976, Bass Bas In, some aspects of the petro I eum geo I ogy ..Ln Leslle, R.B., Evans, H.G. & Knight, C.L., (eds.>, Economic Geology .o.f Austra.l.J..a. .arul fa.P.l,la ~ Gu I nea. ~ Petro I eum. Austra 11 a. Inst. MI n. Meta I I., pp. 6782. Burke, K. & Dewey, J.F., 1973, Plume generated triple Junctions: key Indicators In apply Ing plate tectonics to old rocks . .J.... ~ .B.L. 406-433. Burke, K. & Whiteman, A.J., 1973, Upl 1ft, rifting and the breakup of Africa, ..Ln Tari Ing, D.H. & Runcorn, S.K. (eds.>, Continental Drift, .5.e.a.EJ..o.o.r:. Spread~ .arul E.L.a:t.e Tectonics, Academic Press, London. Carey, S.W., 1970, Austral la, New Guinea and Melanesia In the current revolution In concepts of the evolution of the earth. ~ .h 178-189. Can, E.S.C., & Mutter, J.C., 1982, A rev I sed I dent If I cat I on of the o I dest seat I oor spread Ing anoma 11 es between Austra 11 a and Antarct I ea. .E.ar.:th .& PI anet, .sc..i... Letters ~ 151-160. Carter, A.N., 1964, Tert I ary Foram In I fera from GI pps I and, VI ctor I a, and the I r stratlgraphlcal significance. ~ ~ .S..W:.V... Yl.c.1.. .23.... Carter, A.N., 1978, Contrasts between ocean le and cont I nenta I 11 unconform It les" In the Ollgocene of the Austral Ian region. ~ 214a. 152-154. Colman, J.A.R., 1976, Glppsland Basin, on-shore, ..Ln Les I le, R.B., Evans, H.J. & Kn lght, C.L. (eds.>, Econom l_c Geology Q.f Austra I Ja .a.rul ~ ful.w. Gu I nea • .3.... Petro I eum, Austra I as. Inst. MI n. Meta 11., 34-41. Crook, K.A.W. & Bel bin, L., 1978, The southwest Pacific area during the last 90 m I I I I on years. .J.... ~ ~ .A.u..s.1... 24. 23-40, De I ghton, I., Fa Ivey, D.A. & Tay I or, D.J., 1976, Depos It Iona I env I ronments and geotecton I c framework: southern Austra I I an cont I nenta I marg In. .J.... .A.u..s.1... Petro I, Exp I or. Assoc. 16.... 25-36. Devereux, I., 1967, Oxygen Isotope pa I aeotemperatures on New Zea I and Tert I ary fossils . .N..L..J.....5.ck.li4. 988-1011,

Austral Ian Coal Geology 4, part 1

G.C. Smith

Dewey, J.F. & Bird, J.M., 1970, Mountai n belts and the new global tectonic s .

.J.... Geophys . Re.s..,_ 12.a. 2625-264 7.

Dorman, F.J., 1966, Austra 11 an Tertl ary pa I aeotemp eratures . 61.

J,Geol • .IA.. 49-

Douglas , J.G., 1976, Mesozoi c, 1.n Douglas , J.G. & Ferguso n, J.A., Geology .of VJctorJa , Spee. Publ. Geel. Soc. Aust., 5, 143-176 .

(eds.),

Douglas , J.G. & Ferguso n, J.A., (eds.), 1976, Geology Q.f Victoria Spee. Pub I. Geel. Soc. Viet., 5. Edwards , A.B., 1942, A dome- I Ike structur e In the J urass I c rocks of south G I p p s I a n d • f.c.Q.c.,_ .R... .S..0C... .tlc.1,_ .ll,.. 2 2 4- 2 2 8. Edwards, A.B., 1947, Coa I types In the Ya 11 ourn and Latrobe brown coa I seams. f.r:oc... Australa s • .l.JLtl.. .M..1Jl&. Metal 1, 146-147, 23-69. Ed w-ards, A.B., 1953, Fusaln In some Vi ctorian brown coals. l..n.il,_ .MJ..n., Meta I I, .1.1l4. 47-71.

Austral as

Edwards , A.B. & Baker, G., 1943, Jurassic arkose In southern Victoria

.R... .S..0C... .tlc.1,_ ..22... 19 5- 2 2 8.

f.c.Q.c.,_

Edwards, A.B. & Baker, G., 1951, Some occurren ces of supergen e Iron sulph i des In relation to their environm ents of depositio n . .J.... ~ Petrolog y .2L. 3446. Edwards , A.B., Baker, G. & Knight, J.L., 1944, The geology of the Wonthag gl coa If I e Id, VI ctor I a. f.r:oc... Austra I as, .l.JLtl.. .M..1Jl&. Meta I 1, "2a. 1-54. EI I I ot, J .L., 197 2, Cont I nenta I dr I ft and bas In deve I opment In south eastern Austral la . .AE.EA .J.....lk. 46-51. Falvey, D.A., 1974, The developm ent of continen tal mar gins In plate tectonic theory. .AE.EA .J....1..4.... 95-106. Falvey, D.A. & Middleto n, M.F., 1981, Passive contine ntal margins : evidence for a prebreak up deep crustal metamor phic subs i dence mechanis ms. Oceanolo gJca .Ac1.a .4.... 103-114. Falvey, D.A., & Mutter, J.C., 1981, Regiona l plate tectonic s and the evolutio n of Austral la's passive continen tal margins . .B.MR .J.... A.u.s.t... .G.eoL. Geophys, .f4. 129. Frakes, L.A. & Kemp, E., 1972, The Influence of continen tal position s on early Tert i ary climates . Na.1.uce 24.D... 97-100. Ful larton, D.J. & Tattam, C.M., 1976, Volcanlc s of the Dundas Tablelan d, 1.n Doug l as, J.G. & Ferguso n, J.A. (eds.), Geology Q.f Victoria Spee. Pub I. Geel. Soc. Aust. 5, 363-364. George, A.M., 1975, Brown coal I lthotype s In the Latrobe Valley deposits . .co.mm... Explor • .a.rul .G.e.o.L. .lli.Y.u.. Petrolog Jcal Report 1..L. Cunpubl .).

.tlc.1,_ ~ Elect •

Austral Ian Coal Geology 4, part 1

G.C. Smith

Glenle, R.C., Schofleld, J.C. & Ward, T.W., 1968, Tertiary sea levels In Austral la and New Zealand. Palaentr. Palaeocl lmatfcat. Palaeoecol, -2.. 141163. GI oe, C.S., 1960, The geo I ogy of the Latrobe Va I I ey coa If I e I d. E.cQc.. Austra1..2.4... 57-125.

~ J..n..s..t... .MJ...n... Meta 11.

Gloe, C.S., 1975, Latrobe Val fey coalfleld, .ln Traves, D.M. & King, D. (eds.), Economic Geol~y .of Austral Ia aru1 ,PaJ2.u.a N.e1t Guinea, .2... .coaJ... Austral la. Inst. MI n. Meta 11. 345-359. Gloe, C.S., 1976, Brown coal, .ln Douglas, J.G. & Ferguson, J.A. (eds.),~ Spee. Pub I. Geol. Soc. Aust. 5, 378-384.

.Qg.¥ .o.f Yictorfa,

Griffiths, J.R., 1971, Contlnental margin tectonics and the evolutlon of esoutheast Austral la. la. A.Y.s.t.. Petrol, Explor, ~ 1..L. 75-79. Gunn, P.J., 1975, Mesozoic - Calnozolc tectonics and Igneous activity: e a s t er n Au s t r a I I a. .J..a. .G..e.o.l.... .S.OC... A.u..s.:t... .22... 21 5 - 2 21 •

sout-

Hayes, D.E. & R Ing Is, J., 1973, Seaf I oor spread Ing In the Tasman Sea.

Nature

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Heezen, B.C., 1960, The r I ft In the ocean f I oor.

.s.c.L.. ~ 20..3... 98-11 O.

HIit, C., 1873, Die Bezlehurgen Zwlschen der Zusammensetzung und den technlschen Elgenschaflen der Stelnkohle. srtzber, Aachener Bezfrksyerelnlgung, VDI, H.4. Hocking, H.B., 1980, Definition and revision of Tertiary stratigraphic units, onshore Glppsland Basin • ..D.eirta. Minerals~ Energy • .Geo..1.,_ .5..u.a.. Bl2.L. 1976/], Hocking, J.B., Gloe, C.S. & Threlfall,, W.F., 1976, Glppsland Basin, .ln Douglas, J.G. & Ferguson, J,A., (eds.) Geology .o.f Victoria Spee. Pub I. Geol. Soc. Aust. 5, 248-273. lnternatlonal Commission for Coal Petrology, 1963, 1971, 1975, International Centre National de la Recherche Sclentlflque, Paris, 2nd ed. (1963), Supplement (1971), 2nd Supplement (1975).

Handbook.f.or:,CQa,.1 Petrol~¥•

James, E.A. & Evans, P.R. 1971, The stratigraphy of the offshore Glppsland Basin • .AP..£A .J..a..1.L. 71-74. Jenkin, J.J., 1971, Geologlcal history of the west Glppsland region.

~ &.

.S.0C... .Y.lc.±a. ~ 19- 2 8. Jones J.G. & Veevers, J.J., 1982, A calnozolc history of Austral la's southeast h I g h I a n d s. .J..a. .G..e.o.l.... .S.0C... A.u..s.:t... 29... 1 - 12. Kantsler, A.J., Smith, G.C. & Cook, A.C., 1978, Lateral and vertlcal rank variation: lmpllatlons for hydrocarbon exploratlon . .APf..A la. il._ 143-156. Karwell, J., 1956, Die metamorphose der Kohlen vom Standpunkt der physlckallschen Chemie. L. Deutsch . .Geo..l.,_ .G.e.s... .1fil 132-139.

Kennedy, G.L., 1955, A survey of the banded coa I types In VI ctor I an brown coa I seams. M.Sc. Thesis, Unlv. Melbourne, Aus., (unpubl.).

Austral Ian Coal Geology 4, part 1

G.C. Smith

Kennett, J.P., Burns, R.E., Andrews, J.E., Churkln, M., Davies, T.A., Dumltrlca, P., Edwards, A.R., Ga I ehouse, J. S., Pack ham, G.H. & Van Der LI ngen, G.J ., 1972, Australian-Antarctic continental drift, palaeoclrculatlon changes and 011 gocene deep-sea eros I on. .lia.:bu:§ ~ kl.a. 23.2.. 51-55. Kinsman, D.J.J., 1975, Rift vat ley basins and sedimentary history of tral I Ing continental margins, l.n Fischer, A.G. & Judson, S. (eds.), Petroleum ,gM .G.L.o.b.a.l. TectonJcs. Prlnceton University Press, Prlnceton, 83-126. Knight, J.L., 1975, Wonthaggl and other Cretaceous black coal-fields, Victoria, 1n Traves,D.M. & King, D. (eds.), Economic Geology su. Austral!a ~ ~ H.e..w. Guinea • .2...,C_o_al_._Australas. Inst. Min. Metal. 3-34-338. Labrecque, J .L., Kent, D. V. & Can de, S.C., 1977, Rev I sed magnet I c po I ar I ty time scale for Late Cretaceous and Cenozolc time. Geology~ 330-335. Larson, R.L., 1975, Late Jurassic sea-floor spreading In the eastern Ind Ian Ocean. Geology~ 69-71. Larson, R.L., Mutter, J.C., Diebold, J.B., Carpenter, G.E. & Symonds, P.A., 1979, Cuv I er Bas In. A product of ocean crust format I on by ear I y Cretaceous rifting of Western Australia • ..Ead:h ! Planet, kl.a. Letters A2,.. 105-114. Luly, J., Slulter, I.R. & Kershaw, A.P., 1980, Pollen studies of Tertiary brown coals: Pre I Im I nary analyses of Llthotypes within the Latrobe Valley, Victoria. MoMS.h .P.u.b..l.. l.n Geography. MoMS.h ~ Au.s... ~ 78. Mai lett, C.W., 1978, Sea level changes In the Neogene of southern Victoria.

A.QH .J.... 1..8.a. 64-69. Margo! Is, S.V. & Kennett, J.P., 1971, Cenozolc palaeoglaclal history of Antarctica recorded In Subantarctlc deep-sea cores . .Am.. .J... kl.a. 21.1.... 1-36. McKenz I e, D., 197 8, Some remarks on the deve I opment of sed I mentary bas Ins .

.E.a.r..:t.b. .& PI anet. ~ Letters 4.o. 25-32. Medwel I, L.M., 1954, Foss I I plants from Kl I Iara, near Casterton, Victoria • .P.J:.o.c... .R... .S.0.C.-. ll.c..:t... ~ 17 - 2 3.

Mutter, J.C. & Jongsma, D., 1978, The pattern of t he pre-Tasman sea rift system and the geometry of breakup. BJl.l..J..a.All..sL..S.O.C.-. Exp I or. Geophys. 2.... 7075. Parker, R.L. & Oldenburg, D.W., 1973, Thermal model of ocean ridges.

Nature

~ .stla. .2A4 13 7 -1 3 9.

Partridge, A.O., 1976, The geology expression of eustacy In the Early Tertiary of the Glppsland Basin. AP£A .J... ~ 73-79, R Ing Is, J., 1972, The structure and h I story of the Tasman Sea and southeast Austra 11 an marg In. Ph.D. Thes Is, Un Iv. New South Wa I es, 338 pp. (unpub I.). Royden, L., Sclater, J.G. & Von Herzen, R.P., 1980, Continental margin subdence and heat flow: Importance parameters In formation of petroleum hydrocarbons. BJl.l..J..a.Am.... Assoc. Petrol. G.e.o.l.....~ 173-187.

Australian Coal Geology 4, part 1

G.C. Smith

Rona, P.A., 1973, Relatlons between rates of sediment accumulatlon on continental shelves, sea-floor spreading and eustacy, Inferred from the Central North At I ant I c. .B..u..1J.... ~ ~ .AJD..§.C... ~ 2851-287 2. Sc later, J.G. & Francheteau, J., 1970, The lmpl !cation of terrestrial heat flow observations oncurrent tectonic and geochemical models of the crust and upper mant I e of the earth. Geophys, .J....~ Astron, ~.20... 509-542. Sc later, J.G., Anderson, R.N. & Bel I, M.L., 1971, Elevation of ridges and evolutlon of the central eastern Pacific . .J... Geophys, .Re.s... J.f4 7888-7915. Shaw, R.D., 1978, Sea floor spreading In the Tasman Sea: a Lord Howe Rise eastern Austral la reconstruction. aJLIJ.... AY.s.:ta. ~ Expror. Geophys.9. 75-81. SI eep, N.H., 1971, Therm a I ef facts of the format I on of At I ant I c cont I nenta I margins by contlnental breakup. Geophys • .J... ~ Astron. ~ 2A.. 325-350. Smith, G.C., 1980, Macropetrology, ln Higgins, R.S., Kiss, L.T., Al lard Ice, D.J., George, A.M. & King, T.N.W. Cads.). PropertJes .Q.f .B.c.ox.n ~ .f.c.o.m .1h.e Latrobe Ya I I ey. VI et. State EI act. Comm. Res. Dave I. Report, SC/80/ 17, 25-37, ( unpub I . ) . Sm Ith, G.C., 1981, Tart I ary and Upper Cretaceous coa Is and coa I measure sed1ments In the Bass and Glppsland Basins. Ph.D. Thesis, Unlv. Wollongong, 338 pp., (unpub I.). Sm Ith, G.C. & Cook, A.C., 1980, Coa I If I cat I on paths of ex In I te, v I tr In I te and lnertlnlte. ~ 2.9. 641-646. Stover, L.E. & Evans, P.R., 1973, Upper Cretaceous - Eocene spore po I I en zonatlon offshore Glppsland Basin, Austral la, ln Glover, J.E. & Playford, G. (eds.), Mesozoic and Calnozolc Palynology: Essays In Honour of Isobel Cookson. ~.P..u..b...1..,~~AJl.lla .A, 55-72. Stover, L.E. & Partr I dge, A.O., 1973, Tart I ary and Late Cretaceous spores and po I I en from the GI pps I and Bas In, south eastern Austra I I a. .fc.Q!;;_,_ B... ~ .Y.li;±._ li.4 237-286. Taylor, D.J., 1966, Esso Glppsland Shelf No. 1, the mid-Tertiary foramlnlferal sequence • .B..u..c.... MJner. Resour. ~ Geophys, AJl.lla. f.W2.l.... Petror. Search. ~ A.c.li.. 1f4. 31-46. Taylor, D.J., 1971, Foramlnlfera and the Cretaceous and Tertiary deposltlonal history In the Otway Basin In Vlctorlaln Wopfner, H. & Douglas, J.G. (eds.), .Irut ~ Blil.n .Q.f Southeastern Austral Ja. Spee. Bui I. Geol. Survs. s. Aust. and Viet., 217-233. Telchmul ler, M., 1950, Zum petrographlschen Aufbau und Werdegang der Welchbraunkohl e (mlt Beruckslchtlgung genetlscher Fragen der Stelnkohlenpetrographle), ~.J.J2.....6.h 429-488. Telchmuller, M., 1971, Anwendung kohlenpetrographlscher Methoden be! der Erdol - und Erdgasprospektlon . .Er..dQJ. .Ma. Koh.l..e 2A._ 69-76. Te I chmu 11 er, M. & R., 1954, DI e stoff 11 cha und strukture 11 e metamorphose der koh I e. ~ ~ A2,._ 265-296.

Austral Ian Coal Geology 4, part 1

G.C. Smith

Te I chmu I I er, M. & R., 1968, Geo I og I ea I aspects of coa I metamorph Ism, l.n Murchison, D.G. & Westol I, T.S., (eds.), .l:&.itl.a.ru l~ Bearing Strata, 01 Jver & Boyd, Edinburgh, 233-267. Thomas, D.E. & Baragwanath , W., 1949, Geo I ogy of the brown coa Is of VI ctor I a, Part 1. Ml.lh. ~ .J.... YJ..ct... .3.... 28-55. Thompson, B.R., Ripper, D.T., Bol lea, P.W. & Hocking, J.B., 1973, A geological bibliograph y of the Glppsland Sedimentary Basin • .8eJ2,.. .GmL.. .5un'... Y.lia.. 1... Threlfal I, W.F., Brown, B.R. & Griffith, B.R., 1976, Glppsland Basin, offshore, l.n :Les I le, R.B., Evans, H.G. & Knight, C.L. (eds.), Economic Geology .o..f Austral Ja .and~ N.e.w. Guinea, .1-. Petroleum, Australas. Inst. Min. Metal I. 41-67. Turcotte, D.L. & Ahern. J.L., 1977, On the therma I and subs I dence h I story of sedimentary basins . .J.... Geophys, ~ -8.4. 3762-3766. Val I, P.R., Mitchum, R.M., Sangree, J.B. & Thompson, S., 1975, Eustatic cycles from se Ism I c sequence ana I ys Is. ~ Ann... Meet Ing hln... Assoc, Petro I, ~ SeJsmJc .s±wa. ~ 1975, Cunpub I.). Van Hlnte, J.E., 1976, A Jurassic time-sca l e. fill.. 489-497.

B.JLll.a..AlL.Assoc, Petrol, ~

Watts, A.B. & Ryan, W.B.E., 1976, Flexure of the I Jthosphere and continenta l margin basins. Tectonophysfcs ~ 25-44. Veevers, J.J., Jones, J.G. & Powel I, C., McA., 1982, Tectonic framework of Austral la's sedimentary basins • .J.... Au..s.±.. Petrol, Explor, M.SOC.. 22.. 282-310. We I sse I, J.K. & Hayes, D.E., 1972, Magnet I c anoma I I es In the southeast Ind I an Ocean, l.n Hayes, D.E. (ed.), Antarctic Oceanology l i t .Ih..e Austral Jan-New Zea I and sector, Antarct I c Res. Ser., 19, 165-196. Weisse!, J.K., Hayes, D.E., & Kerron, E.M., 1977, Plate tectonics synthesis: the displacemen ts between Australia, New Zealand and Antarctica since the Late Cretaceous • .M.arllw Geology 25... 231-277. Weisse!, J.K. & Watts, A.B., 1979, Tectonic evolution of the Coral Sea .

Geophys, R.e..s..,_.8.A... 4572-82.

.J....

Wei Iman, P., 1974, Potassium- argon ages on the Calnozolc volcanic rocks of eastern Victoria, Austral Ja • .J....~~~ 2.L.359 -368. Wei Iman, P., 1979, On the Calnozolc upl 1ft of the southeaste rn Austral Ja highland . .J....~~ ~.2.6... 1-9.

The Geology of the Seaspray Depression: Gippsland Basin B.R. Thompson and G.M. Wa Iker Geological Survey Division, Department of Minerals and Energy, Melbourne. Victoria. 3000 Australia. Key Words:

Lignite, Glppsland Basin.

ABSTRACT The Seaspray Depression which forms the southwesterly extension of the Glppsland Basin hosts significant brown coal reserves; the main deposits are at Gelllondale and near Alberton where this recently completed survey outlined reserves of the order of 2000 mill Ion tonnes. A revised stratigraphy of the area Is presented which recognises a regional unconformity between the Latrobe Group - a predomlnantly non-marine sequence of upper Cretaceous to Eocene sediments that lnfl I led the central parts of the basin - and the Seaspray Group and Its lateral facles equivalent which were deposited as a result of a major marine transgression during the Late Ollgocene to Middle Miocene. A narrow barrier-bar complex of considerable thickness separates the marine and non-marine facles. The latter, called the Alberton Group, Includes a thick sequence of I Ignite rich beds - the Alberton Coal Measures - which deve Ioped beh Ind the barr Ier In response to r Is Ing sea Ieve Is, part Icu Iar Iy around slightly elevated 'basement' structures. The Gel I londale Coal Field consists of I Ignites belonging to the Latrobe Group which are Juxtaposed with the Alberton Coal Measures around the Hedley Dome. A major regression In the middle to late Miocene was followed by a short Jived transgression In the late Miocene to early Pllocene during which a thin sequence of sands and calcareous sediments, the Jemmys Point Formation, was deposited. The distribution and thickness of the various sand bodies within the format I ons have an Important bear Ing on the hydro Iogy of the area and hence w 11 I have an In fr uence on any p I ans to mI ne the 11 gn I te depos Its because of the dewaterlng problems Involved. INTRODUCTION In 1975 the Geological Survey Division of the Department of Minerals and Energy commenced an exploration program for lignite deposits along the western marg Ins of the GI pps I and Bas In; the ear I y resu Its of th Is program have been reported Thompson; (1977, 1978, 1980). By 1979 the search had moved to the Seaspray Depression, the southwesterly extension of the Glppsland Basin, where 2500 metres of drll llng and a program of geophysical logging of private water bores was undertaken. In 1980 the State Electrlclty Commission Joined the Investigation (Holdgate 1982). Australian Coal Geology 4, part, 1

B.R. Thompson and G.M. Walker

-,I

I GIPPSLAND / BASIN /

I I

-~1 :?

Figure 1 Location Map LOCATION The I Ignite deposit out I lned as a result of this study, called the Alberton Coalfield (Thompson & Walker, 1980). This Is to differentiate It from structura 11 y more comp Iex depos Its Iocated to t he west of AIberton near Ge I 11 onda I e. The sma I I sett I ement to the south of Yarram In southeast GI pps I and (Figure 1 ). GEOLOGY

structural Setting The Seaspray Depression Involves an area of 1700 square kl lometres which represents on I y four percent of the 41,000 square k I I ometres covered by the Glppsland Basin. The format I on of the GI pps I and Bas In can be traced to the deve Iopment of a pre-Gondwanaland break-up structure zone whi ch developed across the southern margin of the Australian block. This has been referred to as the Bassian Rift System by Carey (1956); the Gippsland extension of it being sometimes referred to as the Strze I eck I RI ft (Hock Ing, 1976). The comp I ex set of grabens wh I eh formed In the ear I y Mesozo I c were rap Id I y I nf 11 I ed by coarse gra I ned sed 1ments, a high proportion of which were derived from ac id volcanic sources and were deposited under predominantly non-marine conditions. The suture zone along which the Antarctic and Australian continents ultimately separated In the late Cretaceous does not correspond with the original zone of weakness, and a significant proportion of the older graben sedimentary sequence remains attached to the Austral Ian continent. The Otway and Strzelecki Ranges are formed of these sediments. After a period of uplift and erosion a new grab en began to deve Iop across the ear 11 er zone dur Ing the Iate Cretaceous, this eventually formed the Gippsland Basin, but Initially downfaultlng was restricted to a narrow zone which formed the Central Deep (Figure 3). The fault systems forming the Central Deep only approximately fol low the 11 mIts of the Lower Cretaceous r I ft. The northern I Im It, ea 11 ed the North Bounding Fault system, Is located some kilometres to the south of the earlier Australian Coal Geology 4, part, 1

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TABLE 1 Dr 1111 ng Summary Bass I an RI ft Boundary, termed the Lake We I I I ngton Fau It System by Thompson (1980). The Central Deep terminates against the Strzelecki Ranges to the west, the onshore part of the grab en forms the Seas pray Depress Ion. Sedimentation within It Is represented by limited thickness of late Cretaceous and early Tertiary sediments, and a suite of basaltlc volcanlcs underlain by sands and grave Is w h Ieh a I so outcrop on the ranges to the west. A younger suite of marine sediments covers much of the early Tertiary sequence within the depress I on. Block faulting of the lower Cretaceous (Strzelecki Group) sediments ln~olvlng differential movements across the main northeast-southwest and less dominant aast-w est structura I trends has resu I ted In the deve Iopment of a ser I es of minor horsts and grabens which have continued to Influence sedimentation to the present day; these features are expressed as folds or monocl Ines In the less competent overlying sediments. Australian Coal Geology 4, part,

B.R. Thompson and G.M. Walker ,.

•· ·••· ·•

·•

WOODH>E 4

DEVON - l'AlflSH NAIIES

I'\, ,~ut1SH 80U#DAltlES ♦

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YARRAM

□ lATlfO•E OIIOUI'

□ STIIZELECl<I OltOUI'

□ OLDElt VOLCANIC$

□ GIIA#ITE

Figure 2 Well Locations and Section Lines The major structural features of the basin are shown In Figure 5 and Include the easter I y un It of the Strze I eck I Ranges ea I Ied the Ba Iook BI ock, and Its main plunging easterly extension, the Baragwanath Anticline. To the south the Gel I londale Block also has a plungtng easterly extension called here the A I berton BI ock. Subs Id I ary features such as the Hed I ey Dome and the Nap I er Block are possibly back-tilted to the north. Some of these features have been described In earlier publications (Edwards, 1945, Thomas & Baragwanath, 1947), but additional structural features have been delineated by drll ling or have been Inferred from the geophysical surveys of the area during this study. The faults or monocl Ines bounding these structures, such as the Yarram Monocllne and Its continuation, the Won Wron Monocllne, form the boundary of the Ba look Block, while the Tora and Tap Tap Faul t s and the Gel I londale Monocl lne are associated with the Gel llondale Block. Slmllarly, the margin of the Napier Block Is formed by the Napier Monocllne. Other minor faults and monoc 11 nes w Ith In the Seaspray Depress I on have a I so been subject to Intermittent tectonic movements and have modified the pattern of sedimentation within the depression. The tectonic units out I lned by drl I I Ing and from Interpretation of the bouguer anomaly map of the area are shown In Figure 5.

Stratigraphy~ Sedimentation The stratigraphic sequence here reported for the area (Figure 6) closely follows the scheme proposed for the Lake Wellington Depression located to the north of the Balook Block (Thompson, 1980) and thus departs considerably from Austral Ian Coal Geology 4, part, 1

B.R. Thompson and G.M. Walker

Figure 3 Regional Structural Features other recent publ !cations (Hocking, 1976, 1980), which propose a depositional framework Involving a single massive transgressive event spanning the late Cretaceous to late PI locene. This, It was suggested, resulted In an onlapping time transgressive sequence consisting of the marine sediments of 01 lgocene to PI locene age, (the Seaspray Group) and a coal-rich fluvlatl le sequence, In part a facles equivalent, (Latrobe Valley Group). A younger mainly fluvlatlle sequence (the Sale Group) overlies both sequences. By contrast this study recognises a major dlsconformlty between the fluvlatlle Latrobe Group (as defined by James & Evans, 1971) and the Marine Seaspray Group and facles equivalents - redefined to exclude the PI locene marine and non-marine sequence. The facles equivalent Include a sandy barrier sequence, coal measures which are the main object of this study, and a number of associated terrestrial and regressive sequences deposited In response to the mid-Miocene marine regression. In the offshore areas the upper EoceneAustralian Coal Geology 4, part, 1

B.R. Thompson and G.M. Walker

□ LA TltO•E OltOUI' □ OL.DElt rOLCAHl'CS □ SntZELECKI OltOUfi'

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Figure 4 Bouguer Anomalies (after BMR) A 01 igocene hiatus is called the Latrobe Unconformity or Latrobe surface. disconformity is also recognised between the late Oilgocene to middle Miocene sequence and the over I y Ing PI I ocene mar I ne sed I me nts and the I r non-mar I ne facies equivalents. The latter has been designated the Jemmys Point Formation but has been redefined to Include two members, the Tarravll le Member and the Worango Member. A final sequence including the Haunted Hill Gravels, recent sediments and present day barrier sands, cover much of the present day coastal plain.

Thus post Lower Cretaceous sedimentation within the Seaspray Depression is envisaged as occurring in three main cycles - the wide-spread fluviati le deposition of the Latrobe Group during the late Cretaceous to late Eocene; a marine transgression resulting in on lapping deposition of marine and nonmarine sediments across a partly eroded surface during the late Oligocene to middle Miocene; finally after uplift fol lowed by erosion around some of the structural blocks, a short I ived marine transgression during the early Pliocene resulted in the deposition of another suite of marine and equivalent sediments across much of the Seaspray Depression. A DESCRIPTION OF MAIN SEDIMENTARY UNITS The lower Cretaceous Strzelecki Group deposited within the ancient Basslan RI ft system forms the 'basement' w Ith In the Sea spray Depress I on. Australian Coal Geology 4, part, 1

B.R. Thompson and G.M. Walker

•• ... .,

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Figure 5 Lower Cretaceous structural contours and structural features LATROBE GROUP (FIGURE 7) The thick delta le complex which consists predominantly of a fluvlo-deltalc sequence has been called the Latrobe Group by James and Evans (1971) from their study of the Glppsland offshore ol I province. It ranges In age from Upper Cretaceous to Upper Eocene and reaches th lcknesses of up to 3000 metres In the Central Deep. Only a few stratigraphic units within It have been form a 11 zed. These Inc I ude the Barracouta format Ion of Upper Cretaceous age <Tral I, 1968), Older Volcanlcs, and the Yarram Formation (Hocking, 1976) sub-basaltic sands wtlhln the Seaspray Depression - and I lmlted marine sequences Including the Gurnard, Turrum and Flounder Formations In the offshore parts of the Basin. The Latrobe Group sediments attain their thickest development within the Central Deep (Figure 7), where they were deposited by meandering streams distributing coarse-grained sediments derived from the highlands to the north and the Bass I an RI se to the south wh Ieh was e I evated above sea- I eve I dur Ing the ear Iy Tert Iary. The coarse angular nature of the quartz sands, the relatively higher gamma ray signal of the clayey horizons and . a higher heavy mineral content help distinguish this unit from similar overlying sandy sediments. Increasingly thicker I Ignite horizons occur towards the top of the sequence. These spread out across the confines of the Central Deep and probably once Australian Coal Geology 4, part, 1

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Figure 7 Structural contours - Latrobe Group covered the structural block that now forms the Strzelecki Ranges. Within the Lake Wei I lngton Depression the thickest I Ignite, which Is Included In the Trara lgon Formation (Gloe, 1960), subcrops on such elevated structures as the Loy Yang Dome and the Baragwanath Antic I lne. Lignites of this age occur on elevated structures at Won Wron and Boodyarn and probably subcrop beneath younger coals around the Hedley Dome ~Ith In the Gel llondale Coal Fleld. The distribution of basalts within the Latrobe Group In the Seaspray Depression outllne the trend of the Eocene palaeo-dralnage channel. The potassium/argon age of core samples taken from unweathered Intersections of this unit Indicate an age of 55± Ma BP. Evidence of marine Influence on sedimentation Is llmlted to the presence of sand barr I er fac I es near: the pr'esent-.day she If marg In (Partr I dge, 1976) and the presence of remnants of mid-Eocene marine channel deposits (the Gurnard Formation). An extensive part of the pro-delta sequence has probably been removed by marine channel erosion. Upllft and subsequent erosion of structurally e levated blocks occurred toward the close of the Eocene period - coinciding with a well recognised lowering of sea- I eve Is CF Igure 6). THE SEASPRAY GROUP CHOO<ING, 1976) Marine and marginal sediment deposited as a result of a marine tr~nsgfesslon consists of four units.

Austral Ian Coal Geology 4, part, 1

B.R. Thompson and G.M. Walker

:g:::;~E,C @ ~":ni.::NDS SEAS'1tAY OlfOU/1

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Figure 8 Palaeoenvlronment during the Lower and Middle Tertiary ~

Entrance Formation <Boutakoff, .12lli

A marine transgression occurred during the Ollgocene, associated with a eustatic sea-level change, but this had no expression In the on-shore Glppsland areas until the late Ollgocene when the glaucont lc sandy sediments of the Lakes Entrance Formation were depos lted {Thompson, 1981 ). The unconformab Ie contact between the Latrobe Group and the marine sediments Is easily recognisable In the offshore area where It forms an Important seismic horizon called the Latrobe Surface, but In the vicinity of the basin margins the nature of the contact Is less obvious.

Glppsland Limestone Formation <Crespin, 1.24n

.limU2Q R.cLe.c Formation

The Increasing dominance of marine conditions during the late 01 lgocene and early Miocene resulted In the deposition of marls and shelf carbonates which reach thicknesses of up to 1500 metres in the offshore areas. However, around the westerly margins of the basin the marine sediments on-lap such structures as the Baragwanath antic I ine which was already partly elevated above the deepening Lake Wei llngton and Seaspray Opresslons and thus were Isolated from the deposition of Lakes Entrance Formation sediments. Similarly the marginal areas were the first to reflect the effects of the regression during the middle to late Miocene which also coincided with a world wide sea-level drop Australian Coal Geology 4, part, 1

B.R. Thompson and G.M. Walker

CF Igure 6), with the resu It that progress I ve Iy younger mar I ne sed I ments are located towards the basin centre. This process of off-lapping resulted In the deposition of a sandy marl of upper Miocene age called the Tambe River Formation In areas some kl lometres seaward from the mid-Miocen e I Im Its of the transgressio n (Figure 8) .

.Ib.e _6gJ_QQk Formation <Thompson, .128.Ql The I Im Its of the early Tertiary transgress ion are marked by an unusually thick but narrowly distributed sequence of stacked quartose barrier sands f I rst descr I bed from the Lake We I 11 ngton Depress Ion, and ea I I ed the Ba Iook Formation. It consists of 400 metres of medium to fine sand with minor Intersperse d clayey and I Igneous horizons. No calcareous fossils have been recovered from the few bores that have fully penetrated the formation but a few arenaceous foram lnl fera were recovered In the Lake We l lington Depression. Any calcareous fossl Is were probably dissolved by acid groundwater s originating from the peat swamps behind the barrier. The barr I er sequence forms an a I most stra I ght 11 ne trend Ing NNE across the Sea spray and Lake We 11I ngton Depress Ions except for the I ntervent Ion of the Baragwanath Anticline and associated structures. Dlstrlbutar y mouth bars and other coasta I features probab I y ex I st In the northern I Im Its of each depression but remain to be outlined by drll ling (Figure 8). The general geometry of the barrier complex and Its great thickness Indicate a relative stll I-stand of the early Tertiary coastline In excess of 10 mll lion

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□ STRZELECKI QlfOUI' LJ 01tANfTE.

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Australian Coal Geology 4, part,

B.R. Thompson and G.M. Walker

across which In t:~nt~~ggarrl nt faulting ests that base::abl a hinge I lzed theformed oft11heneTerlary po sit Ion yteh:r~as In benea 1981 ). er which coast 11 ne (Thompson, NON-MARINE FACIES EQUIVALENTS

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Austra I Ian Coal Geology 4, part, 1

from Figure 2

B.R. Thompson and G.M. Walker

The lignites probably formed at about the same time as the Latrobe Valley Coal Measures, which Include the Ya) lourn and Morwel I Formations, In the Lake We I 11 ngton Depress Ion to the north, <Thompson, 1980). In both sub-bas Ins the Ba Iook Format Ion barr Ier comp Iex has been substant Ia I enough to a 11 ow th Ick peat swamps to deveop In Isolation from marine Invasion and form as lateral facles equivalent to the early Tertiary sedimentary sequence. A map Indicating the depth to the top of the lignites In the Seaspray Depression, called the Alberton Coal Measures, shows the lignites draped over the AI berton RI dge at depths of as I I tt I e as 30 metres but deepen Ing to the north and south to depths In excess of 100 metres In local synclinal depressions (Figure 9). The lignites become thinner and lnterflnger with the Balook Formation to the east and finally Jense out completely. While to the northwest they become thinner, shallow considerably and pass lateral Jy Into the fluvlatl le Bodman Creek Formation. The northern limit of economically significant deposits has not been fully determined. To the southwest towards the Gelllondale Coalfield the sequence appears to thicken. This area Is more structurally complex because the Latrobe Group sediments subcrop around the Hedley Dome In the centre of the field while the Alberton Coal Measures onlap around this structure In a way analogous to the Loy Yang Dome structure In the Latrobe Valley. Thus the Alberton Coal Measure lignites may directly overlie the Latrobe Group coals In some areas. Further deep stratigraphic drll ling and detal led palynology Is required to del lneate the relationship In this region. The thickest area of coal east of the Albert River occurs In a northsouth belt In the middle of the coalfield where It Is In excess of 40 metres thick at relatively shallow depths (Figure 9). A sl lght thinning over the Alberton Ridge crest Indicates some post-depositional erosion. The ma In upper seam has a we I ghted average mo I sture content of 61.0% an ash content of about 5% (dry bas Is) and a su I phur content of 1% or .1ess, (Holdgate, 1982) which Increases towards the eastern margins near the barrier sand complex. A potential resource of economically winnable coal of the order of 2000 mll lion tonnes Is Indicated by the combined results of the Department of Minerals and Energy and SECV drll ling programs. The location of the bores drll led and a tabulation of the data Is given In Figure 2 and Table 1. .Ihe .B.Qdman ~ .sl.illl Too I oonook .G.olYiu format Jon

The Alberton Coal Measures lnterflnger with a poorly sorted sequence of sands and clays to the north west of Alberton called the Bodman Creek Formation (Thompson & Walker, 1982) which In turn lnterflngers with and partly overlies a very coarse I Ignite rich gravelly unit - the Tooloonook Formation (op. clt.), a sequence of outwash gravels which are limited to width of about four kilometres around the Balook Block of the Strzelecki Ranges and were proba~ly formed by the reworking of older al luvlal deposits that once ca~ped the up 11 fted blocks . .Ihe ~ Wei I lngton formation

The mid-Miocene marine regression which Is an expression of a world wide eustatic event (Loult & Kennett, 1981) resulted In the deposition of Jacustrlne facles up to 90 metres thick In locally depressed areas and resulted In the reworking of some of the barrier sands across the calcareous sediments of the Seaspray Group. These were originally recognised as unconformably overlying the marine across the structurally elevated Baragwanath Antic) lne In the Lake Wei I lngton Depression (Boutakoff, 1955) and are described as fine uniform silty sand which exhibits rythmlc bedding. Such Australian Coal Geology 4, part, 1

B.R. Thompson and G.M. Walker

□ LA T1tO•E OltOU,,

□ OLDER voLcANICs □ STIUELECKI 0/tOU,.

[J OltANtTE

... LIIMT OF IIA/tlNE fi'llOCENE TltAN.$0/tESSION ' - DEl'TH TO TOI' OF JEIIIIYS l'OIN T FO/tllATION .... _. ISOl'ACH OF JIIIIIYS ,,OINT FO/tlilA TIO#

Figure 11

Pllocene marine thickness lsopachs

sediments have been observed ln cores from bores to the north of Yarram (Boodyarn 6, Won Wron 84, 85). Elsewhere this uni t may be represented by coarser non-calcareous sands formed by the reworking of the Ba look Formation, but they are llmlted to the Devon and Yarram Troughs and are not found across the structurally elevated blocks .

.Ihe .J..em.111¥-S fQJJl1 Form at I on The Jemmys Point Formation was deposited as the result of a relatlvely short llved marine transgression developed during the early Pllocene ln response to a eustatic sea-level rise, the dlsconformable nature of Its relatlonshlp with the underlying Seapsray Group being marked by phosphate nodules In the Lakes Entrance area and l n the Lake We 111 ngton Depress Ion (Carter, 1979, Thompson, 1980). Two new members are recognised ln the Seaspray Depression (Thompson & Walker, 1982). Within the Seaspray Depression the lnltlal transgression resulted In the deposltlon of dark lagoonal bloturbated muds and clays of the Tarravl I le Member up to 20 metres thick (Tarra Tarra 3 bore) which Is overlain by another un It of the Tarrav l I I e Member up to 100 metres of med I um to f l ne genera I I y non-fossl I lferous quartz sands Interpreted as redistributed beach, and dune sands deposited ahead of a trangresslng sea. These units are more fully developed In the Yarram Trough Structure. A sea-level maximum ln the late Pllocene resulted In the deposition of a flnal unit, the Woranga member, conslstlng of a thin marly limestone to shelly sand across the coast a I p I al ns, on I app Ing the Hed I ey Dome but not depos I ted over Australlan Coal Geology 4, part, 1

B.R. Thompson and G.M. Walker

the Napier Block or coastal plain between Woodside and Longford to the north Indicating I Jmlted tectonlsm prior to the transgression (Figure 10). The Jemmys Point Formation sediments reached further Into the basin than the early Tertiary marine sediments, a point Jn common with their distribution In the Lake Wei llngton Depression (Thompson, 1981). Foramlnlfera present Indicate an Early PI locene age for this event Jn the Globorotal la punctJculata zone of Mallett (1978). Towards the basin centre, offshore this unit progressively mar I ne.

Iar:r:a .R.u'..e.c FormatJoot Lateral non-marine factes equivalents to the west and north consist of fluvlatl le sands, clays and gravels and In places thin I Ignites called the Tarra River Formation (Thompson & Walker, 1982). These are limited In extent and thickness and dlfflcult to distinguish from the underlying Bodman Creek Formation; they are equivalent In age and lithology to non-marine units of the Bolsdale Beds of the Lake Wei llngton Depression.

Haunted Hlll. Gravels .a.ru:t PleJstocene Deposits The regress I on of the sea dur Ing the PI i ocene resu I ted In the depos It I on of river gravels and alluvium often referred to as the Haunted HIii Gravels; sea level changes during the Recent have modified sedimentation In the present day coasta I areas. AN OUTLINE OF THE AQUIFER SYSTEMS OF THE SEASPRAY DEPRESSION The most ex tens I ve aqu I fers formed by the coarse gra I ned sed I ments of the Latrobe Group, trend from the elevated Ba look Block where they subcrop, to the oil and gas field many kilometres offshore. Intake occurs around the margins of the Strzelecki Ranges particularly via the Older Volcantcs which outcrop In some of the stream beds such as Tarra River, Bruthen Creek and Jack River. This aquifer system Is artesian with plezometrlc levels of fifty metres or so above sea-level near the Intake areas. The main outflow zones are unknown but the location of the fresh water - salt water Interface some thirty kilometres offshore Is probably ·Indicative (Figure 12). Local zones of outflow occur at Dutson Springs on the Baragwanath anticline and around the Hedley Dome near Get I londale. To the east of this structure groundwater sal Jnltles are generally less than 500 parts per mllllon, total dissolved solids, but greater sal lnltes are recorded to the west of the Hedley Dome and sallnltles probably Increase gradua I Iy off shore. The groundwater temperatures can reach 30°C which Is a reflection of the genera I I y h I gh geotherma I grad I ant of the area as Ind I cated by bottom-ho I e well temperatures; the gradient within the Depression Is generally about 50°C per 1000 metres. The less extensive overlying Alberton Group aquifers generally contain waters of sl Jghtly greater sal lnlty but are stl 11 quite suitable for Irrigation. These aquifers exhibit sl lghtly lower artesian pressures than the deeper system and are probab I y part I y recharged by vert Iea I I eakage from It. The location of outflow zones Is unknown but vertical leakage via the Balook Formation Into the overly Ing Jemmys Point Formation probably occurs In a manner s Im I Iar to that suggested for the Lake We 11 I ngton Depress Ion aqu I fer systems <Thompson, 1981). Other overlying formations also contain aquifers Austral tan Coal Geology 4, part, 1

B.R. Thompson and G.M. Walker

38'

TUN-; -

. .

200

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2000

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~ BEDROCK OUTCIIOP •

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OIL FIELD

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Figure 12 Latrobe Group Aquifer Systems and Regional Pelzometrlc Levels which are mainly exploited for stock water suppl les. Of the fifteen or so Irr I gat Ion bores In the area about· ha If tap the AIf>erton Group aqu I fers and the others, mainly In the Parish of Devon, Intersect the Latrobe Group System. Any dewaterlng program undertaken to al low I Ignite mining would ultimately lower the plezometrlc levels In all aquifer systems.

ACKNOWLEDGEMENTS The authors wish to acknowledge the work of the Drll I Ing Branch and Chem lea I Branch .of the Department of Minerals and Energy for their assistance and the Staff of the State Electrlclty Commission who made the results of their survey aval I able. The authors thank the Acting Director of the Geological Survey Division of the DME In permitting this work to be publ ished. REFERENCES Abele, C., Gloe, C.S., Hocking, J.B., & Threfal I, W.F., 1976, In Geology .of Victoria. Editors J.G. Douglas & J.A. Ferguson. Spee. Pub I. Geol. Soc. Aust. 5, 198-229. Boutakoff, N., 1958, Lake We 111 ngton Format Ion - GI pps Iand. li.c.L. fil.21, 4 6-4 9.

MJ..n... .G.e.ol... .J.o.u.r....

Boutakof f, N., 1964, Lakes Entrance OI I and Cont I nen t a I She If. AfEA 2, 99100.

Austral Ian Coal Geology 4, part, 1

B.R. Thompson and G.M. Walker Carey, S.W., 1955, The orocllne concept In geotectonlcs. 255-288.

55 ~,S_Q.s;_._I.a..s...._&2,

Carter, A.N., 1964, Tertiary formlnlfera from Glppsland Victoria, and their stratigraphic significance. ~ ~ .5..u..o£.. ~ 23., Carter, A.N., 1972, Correlation of 01 lgocene unconformltles In Southern Austral la. ~ phys(caf scfence 231.. 12-13. • Carter, A.N., 1978, Contrasts between oceanic and continental unconformltles In the Ollgocene of the Australian Region, ~ ~ . 152-153. Carter, A.N . , 1978, The d I scovery of the phosphate nodu I e bed at the base of the Jemmys Point Formation In East Glppsland Victoria. ~ ~ 370-372. Carter, A.N., 1979, P 11 ocene eustasy and the onset of barr I er format I on In the Glppsland Basin. ~ 2.80., 131-132. Cresp In, I., 1943, The strat I graphy of the Tert I ary mar I ne rocks In GI pps I and v lctor I a. ~ .Qf ~ .& Sb I pp Ing Aull.. Pa I aeont, ~ A, Edwards, A.B., 1942, A dome-I Ike structure In the Jurassic rocks of south GI pp s I and. ~ ~ ,S_Q.s;_._ li.da. .llill, 5 9-7 ~Edwards, A.B., 1945, The composition of Victorian Brown Coals. Austra I I as .l.n.s1.. MJ..n.. Meta I I, llO., 205-280.

Evans, P.R., & Stover, L.E., 1971, Late Cretaceous to Eocene stratigraphic palynology of the offshore Glppsland Basin south-eastern Austral la. ANZAAS •

.con.t.. Abstract .1..211., Gloe,

C.S.,

1960,

The geology of the Latrobe Valley coalfield.

Austral fas .l.n.s1.. MJ..n.. Metal I, .12!, 57-125. Hocking, J.B., 1970, Geology of Lower Miocene calcareous deposits In the SaleYarram region, South Glppsland. MJ..n.. ~ ~ Y.l.d:.. .filfil., 80-90. Hocking, J.B., 1976, Glppsland Basin In Geology Q.f Y(ctorJa, Douglas, J.G., & Ferguson, J.A. (editors), Spee. Pub I. Geol. Soc. Aust. 5, 248-273. Hocking, J.B., 1980, Definition and revision of Tertiary Stratigraphic Units, Onshore ~lppsland Basin. ~ ~ .5..u..o£.. Y.l.d:.. 1.2I6L.1, Ho I dgate, G.R., 1982, Brown Coa Is and Fae I es equ Iva I ent of the A I berton Depression - Glppsland. Yfctor(an .S.:t.a.t.e Electr(c(ty Commfs( (on, Explorat(on .a.rul Geolog(cal D(v(s(on ~ 2A, Cunpubl.). • Ja mes, E.A., & Evans, P.R., 1971, The strat I graphy of the off shore GI pps I and l;las In. .A.P.E.A .J., 1971. Jenkin, J.J., 1968, The geomorphology and Upper Calnozolc geology of southeast Glppsland, Victoria. ~ .5..w::Y.. Y.l.d:.. .M.em, 27. Luolt, T.S., Kennett, J.P., 1981, New Zealand and Australian Cenozlc sed I mentary eye I es and g I oba I sea I eve I changes • .Am.. Assoc, Petro I, Geo I og, 1556-1601.

Australian Coal Geology 4, part, 1

B.R. Thompson and G.M. Walker

Ma I I ett, C. W., 1978, Sea I eve I changes In the Neogene of southern Victor I a. AE.fA 1... .Lli 6 4-6 9_._ Partridge. ~ .121.h Stratigraphic palynology .of .1he onshore Tertiary sediments .of~ Gfppsland .B..a.sl11 Yictorfa • .M...S.c... Thesis, N...5....l'L. Unfversfty CUnpub I,>, Partridge.~ l.21.6.,. I.b.e Geological expression .of eustacy 1.n .1he .EMJ..¥ Tertiary .of Gfppsland, APEA J. 16(1)_._ ~ Thomas, .D..Eu. .& Baragwanath, L. 1949-1951, 1w geology of l l i ..12.C:.ow..n ~ .of Yictorfa, ~l.-=-4... Min. Geol. J. Vlct._._.f.t....L. 3(6 ) :28-25, .Pi..~ 4(]l:362k .Pi.. .3..... 4(2);4]-63 • .Pi.. .4... 4(4):36-50, Thom pson, .B...R.... llI1.,._ .0..0 .1he .Ih.e.r:mfil waters .of .1he GI pp s I an d 6.a..sJ..D. .a.nJ1 .1he problems associated :«J-1:h l l i .s.1.u..d.¥ . o f ~ temperature aquifers, Annales lnstltutl. Geologic!. Publl. Huwgarlci 59_._ ~ 1-=4... Thompson, ~ il1J4. Geology .of l l i Stradbroke Coalfield= Gippsland, Surv. Rept. Viet. 61_._ Thompson.

~ .12.8.D...

Geol.

Lignite deposits of l l i western Gippsland ~ abstract BMR

= Cafnozofc Evolution .of Continental South-eastern Austral Ia Symposium, Record 1980/67_._

Thompson, .B...R.... .12.81.... I.b.e Gfppsland Sedimentary Basin, Un Ivers I ty .of Melbourne, <unp ub J, >,

f'.h.Jl... Thesis

Thompson, .B...Ra... .& Walker, .G...M.-... ~ A progress report .on .1he Alberton Geol. Surv. Viet. Unpubl. Rept. 1980/72.. Coalfield Jnvestlgatfon, Thompson, .B...Ra... .& wa Iker, .G...M.-... ~ I.b.e .G..e.Ql.Q~ .of .1he Al berton Coa If Iel d .iln press>, TraI J, L L 1.9..6.8.... ~ aspects .of .1he .LIJuuu" Cretaceous= J.Qw...e.r Tertfary section ln l l i Gippsland ~ Yictoria, APEA J. 8C2l_._ fil::1.l...,_ .Y.aJJ..... ~ llI1.,._ 1.n Seismic Stratigraphy, .E... Payton Cedftor>, Am. Assoc. Petrol. Geology_._ Spee fa I Pub I Icatfon, Walker, G.M- 1..9.8.2.. No:te.s .on~ Tertiary Stratigraphy of l l i Western Seaspray Depression .of l l i Gfppsland .B.a.s.1.n... Rep. Geol. Surv. Viet. 1982/71_._ <unpubl,>,

Brown Coals and Facies Equivalents of the Alberton Area - Gippsland, Victoria G.R. Holdgate

Exploration and Geological Division , Fuel Department, State Electricity Commission of Victoria, 15 William Street, Melbourne, Victoria, 3000 , Australia .

Key Words : Alberton Area, Equivalents

Brown

Coal,

Chemical

Constituents,

Facies

ABSTRACT An exploratory drilling project was begun in 1980 by the SECV to investigate the coa 1 potent i a 1 of the A1berton area to the east of the Ge 11 i onda 1e Coa 1 Initial bores were sited on previously defined positive gravity Field. residuals which were found to approximate to areas of minimum overburden. Two main brown coal seams of the P. tuberculatus spore-pollen zone age occur in a five kilometre wide belt trending southwards to Port Albert. They have a combined thickness of around 55 m. Termed the A and B seams of the Alberton Coal Measures, they comprise most of the brown coal resource potential of the area . They occur under an overburden varying between 40 and 90 m. The seams contain less than 5% ash, and have a moisture content of around 61%. Possible reserves whi eh meet economic criteria would amount to about two bi 11 ion tonnes. Lateral facies changes between inland fluvio-lacustrine sediments, and coastal barrier bar sands provide the main western and eastern limits to this economic reserve. An angular unconformity corre 1atab 1e to the offshore Latrobe Unconformity occurs in the Tertiary section below the B seam, and in the southwest towards Ge 11 i onda 1e brings together the A-B and a deeper C seam into one continuous coal sequence up to 100 m thick. At Alberton township the A seam grades laterally into exinite-rich laminated claystones similar to low grade oil shales.

Australian Coal Geology 4, part 1

G.R. Holdgate

INTRODUCTION AND METHODS In 1980 the geological section of the State Electricity Commission of Victoria began a drilling programme in the south-western part of the onshore Gippsland Basin to investigate coal potential . This programme is still in progress . The area examined lies to the east of the presently defined Gelliondale Coal Field out to the edge of the Victorian Government brown coal reserve area. Previous government and private water bo res indicated easterly extensions to the seams known at Gelliondale, although it was generally assumed these would for the most part be at depths in excess of those at Ge 11 ionda le, and in places beyond current economic cons i deration. Concurrently, coal exploratory drilling by the Department of Minerals and Energy (DMEV) in the same area also begc1.n. To date, some 32 SECV and DMEV ho l es have been drilled in this current exploration exploration phase, and in addition some 10 private water bores hc1.ve been relocated and wi re-1 i ne logged by . the DMEV. A11 SECV bores are drilled by private contractors using reverse circulati on methods which provide continuous core of all strata . DMEV bores (the programme of which is completed) were partially rotary cored and mostly flush drilled, the results of which are being independently assessed by Thomson & Walker (1982). All SECV and DMEV holes are wire-line logged . Both the SECV and DMEV programmes were co-ordinated jo i ntly to maximise the drilling coverage, with free exchange of the bore information. Hence , the results presented here include bore information from all sources available . The coal cores have been analysed by SECV and DMEV laboratories for their constituents . All the SECV coal samples are bulked over 3. 0 m intervals for moisture and ash, over 6.0 m for minerals and inorganics and over 12 . 0 m for proximates and ultimates. Bulked 2.0 m samples of fine ly laminated exinite-rich claystones were analysed by Fi scher Assay for their tar and oil yield. The petrography of these claystones are repo r ted on by Mackay (1981) and Hutton (1981). Numerous samples were also submitted to the DMEV paleontology section for foraminiferal and palynological zoning (C. Abele & V. Archer pers . comm . ). These, together with unpublished palynological results on older bores in this area (Partridge 1971) , provide the age control necessary for the facies reconstruction. GEOLOGY Regional Setting and Exploration Methods The Alberton Depression is situated at the south-west ern end of the Gippsland Basin in open, predominantly dairy farm i ng country, south and south-west of the township of Yarram. About half of the depression lies beneath the offshore islands and tidal channels of Corner Inlet. The steeply rising Strzelecki Hills comprising Early Cretaceous greywackes and arkoses of the Str zelecki Group occur to the west, and define the in l and edges of the onshore Alberton Depression. Sediments of the Str zelecki Group form an economic basement for brown coal exploration . At this western edge steeply rising monoclines and faults bring up the deepe r buried Early Tertiary sediments and volcanics to outcrop . These are known as the Yarram and Traralgon Formations . Thin coal seams of the Traralgon Formation can be found on the edges of the basin such as at Won Wron, northwest of Yarram. More gently folded Middle Tertiary strata referred to as the Alberton Coal Measures (Thompson & Walker 1982), are equivalents to the Morwell Formation in the Latrobe Valley, and

Australian Coal Geology 4, part 1

G.R. Holdgate

overlie these Early Tertiary sediments possibly unconformably. They comprise up to 250 m of non-marine coals, sands and clays which were deposited behind a sand barrier system which marks the point of maximum transgression from the Middle Tertiary marine Gippsland Limestone and Lakes Entrance Formations. Both marine and non-marine mid-Tertiary units are overlain in turn by Late Tertiary and Quaternary marine and non-marine sands, clays and mi nor limestones, which on the major anti cl inal structures truncate the mid-Tertiary units. Most of the sediments dip on a regional basis east and northeast basin-wards. Superimposed on this easterly dip are two major regional northeast trending anticlinal folds separated by an intervening synclinal area. These structures are complex and include subsidiary folding. • The trends of the major structures were first indicated from BMR gravity residuals contoured at one milligal intervals from the Alberton detailed gravity survey (1955) . The major positive gravity residual on this sheet coincides with the doma l structure complex located beneath the Ge 11 i onda le Coal Field and trends north-east towards Yarram. Against or on top of this structure, the coal seams are truncated by the later Tertiary overburden veneer. A second weaker but parallel positive residual gravity trend runs north-east from Alberton township through to Woodside. Earlier drilling immediately east of the Gelliondale Coal Field encountered the deeper buried coal seams in the intervening negative residual low which lies between these two major ' highs' . The SECV drilling was initially programmed to test whether the Gelliondale coal seams would be brought up again along the positive high between Alberton and Woodside. To a certain extent this proved to be the case particularly at Alberton, although much of the northern portions of the 'high' were found to coincide with a facies transition between the coaly sediments and the marine sediments to the east . Neve rt he less, the gravity picture provides a general guidance to the overall structural picture and is still used to help define future drilling targets. Detailed Stratigraphy and Quality of the Coal Seams and Interseams One of the initial bores in the current exploration phase was drilled through to basement to establish the complete Tertiary succession . Some 360 m of sediments were encountered near Alberton, and the bore finished in weathered volcanics at the base of the Tertiary sequence . This i ndicated the mid-Tertiary aged sediments in the upper 144 m (dated within the P. tuberculatus palynological zone) to be the most prospective for economic coal bearing seams (now defined as the Alberton Coal Measures) . The underlying Trara l gon Formati on sediments were found to be mostly sands and clays with one main coal seam about 19.0 m thick occurring at 293 m. Consequently, the SECV drilling programme was mainly orientated towards defining the lateral extent and quality of these P. tubercul atus zone coal seams. Most bores were drilled to depths not usually exceeding about 200 m. High pressure aquifers below these seams also mitigate further deeper dr i lling . Two more bores were completed in basement towards the south-west of the study area to elucidate the more complex stratigraphic relationships in this area . An east-west cross-section with time lines is drawn approximately normal to the strike of the Alberton- coal field area as shown in Fig . 1 and gives the general dispos i tion of the seams and their lateral facies changes. The Alberton Coal Measures comprise an upper A seam which at about 40 m to 55 m in thickness, occurs below an overburden varying between 40 m and 100 m. The thickness of overburden is shown by isopachs on Figure 4, which also shows

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G.R . Holdgate

the subcrop margins and bore hole locations. This thickness reduces at the coal field margins due to subsequent erosion and lateral facies changes. It is also partially eroded on the crest of the main structure between Alberton and Woodside . This structure affects the moisture content in the coal which tends to rise on the anticlines and fa 11 in the synclines. The A seam has a weighted average moisture content of 61 . 0% as arrived . A second seam B occurs about 12 m be l ow the base of the A seam and averages about 15 m in thickness. The B seam has a slightly lower weighted average moisture content of 59% a.r. Both seams have an ash content on a gross dry basis of between 2. 5% and 5. 5%. Mi nor seams between 1 m and 10 m thick occur within the 12 m i nterseam of mainly clays and minor sands . A typical example of the coal quality is given in Table 1. Towards the Gelliondale Coal Field, Traralgon Formation coal seam is brought up by structural movements to lie immediately below or separated by only a short interseam interval below the B seam. This is discussed in a subsequent section. Cross-sections are shown on Figures 1, 3 and 5. The coal seams occur over a strike length of between 15 and 18 kilometres opening to the south offshore, and swinging south-west to meet the Gelliondale Coal Field as shown in Figure 2. Average widths of the main seams very between 5 and 6 kilometres increasing towards the south. The total reserves of coal in this area remain to be estimated as the drilling continues but provisional figures based on rough approximations indicate about two billion tonnes of the total reserve would meet criteria defined for economi ea lly winnable coal (Brown Coal Resources Inter-Departmental Committee 1977). TABLE 1 ALBERTON COAL QUALITY - BORE NO. 5 ALBERTON EAST A SEAM (58 . 5 - 103.7m) (Weighted Average) Moisture % a. r . Ash (dry basis)% Volatiles (d . b. ) % Fixed carbon (d.b . ) % Carbon (d . b. ) % Hydrogen (d.b.) % Sulphur (d . b.) % Chlorine (d.b . ) % Sodium (d.b.) % Calorific value (MJ/kg) Gross dry Gross wet Net wet

B SEAM (134 . 2 - 154.6m) (Weighted Average)

63.5 3. 1 51. 5 45 . 5 65 . 3 4. 7 0. 4 0. 1 0.13

60.5 4. 4 50.6 44.9 65.8 4. 8 1.0 0.1 0.09

25 . 2 • 9. 2 7.4

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FACIES CHANGES The economic coal boundaries are defined in two major directions by facies changes. These are: (a) To the north-west and west of the main field area the A & 8 seams split and divide eventually wedging out and grading into clays, sands and minor thin coaly lenses of the Jack River Formation. This transition marks the interface between coal swamps and fluvial-lacustrine environments. There is an associated rise in total ash content in seams near this margin, including a rise in total sulphur content (Figure 6) . In one area at Alberton township the A seam grades into finely laminated varved-like exinite-rich claystones of probable lacustrine origin. These occur as a localised deposit within the main coal swamp area (Figure 2). Further analysis of these claystones is given in the following section. (b) To the east along the entire length of the deposit, the coals split and thin rapidly over a two kilometre wide distance through a sand and coaly sand interval into clean sands (the Balook Formation) and eventually into marine limestones and marls of the Gippsland Limestone Formation. The coaly sands are intimately associated with the coal seams, usually occurring immediately below the seams, grading up over a few metres through sandy coal to coal. They can persist over intervals up to 20 m thick, often overlying thicker intervals of coarse but cleaner sands. The coaly material partially coats the sands with a thin film of dark grey material, of wh i ch a small proportion is discrete particles with gel i ni te- 1i ke texture. The sands comprise mostly medium to fine quartz grains of well sorted and rounded appearance. The Balook Formation represents a complex of lagoonal and barrier bar environments similar to the present day Ninety Mile Beach, and the sands appear to be largely derived from this seaward margin. This transitional environment influences the moisture and sulphur content of the coals in the near vicinity as shown on Figures 5 and 6. In the A seam moisture decreases, and the total sulphur increases from 0.40% to 0.80% near this margin. The thin coal extensions of the A and B seams which interbed with the coaly sands contain high sulphur contents up to 4.0% before they wedge out completely as the limestones and marls are reached. These results indicate that the sulphur was brought into the depositional environment presumably by brackish or marine waters at the same time that the coal and i nterseams formed. Subsequent sulphur enrichment due to later Tertiary marine transgressions above ( the Jemmys Point Formation) probably contributes to the rise in sulphur values towards the top of the A seam. The tendency for the Band C seams to contain higher than A seam sulphur values is best explained by the marine influence extending further into the coal swamps during and subsequent to their formations, as shown by the greater landward penetration of the i nterseam sediments in the intervals between the A and B, and Band C coal seams (Figure 5). At the point where the interseams largely pinch out due to convergence of coal seams (e.g. at the Alberton West 176 bore), the sulphur values for all seams are at a minimum . Such positions probably represent the point of maximum landward advance for marine influenced waters, and marine derived sediments at this time. In the Latrobe Valley area later marine transgressions have similarly increased sulphur in ~nderlying coal seams as documented by Thompson (1979) and Holdgate (1980).

Australian Coal Geology 4, part 1

G.R. Holdgate

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Stratigraphy and Petrology of Exinite-Rich Claystones Laminated claystones which grade at the base and are a lateral facies equivalent to the A seam occur over a 15 m interval in the Alberton East 8 bore at Alberton township . The possible extent of this deposit as derived from similar gamma ray log characteristics in nearby flush-drilled bores is indicated on Figure 2, but it may also extend into the non-coaly areas north and west of the main coal field boundary. The sediment is a finely laminated claystone containing up to 35% coaly fragments . The remaining sediment includes clays, fine detrital particles of quartz and framboids of pyrite (rarely 20 m in diameter). Slight upward fining in each lamination occurs in a varve-like manner. Petrographic maceral counts of samples from this interval indicate about 11% are liptinite (exinite) derived mostly from higher plants (Mackay 1981; Hutton 1981). The remaining coaly fragments are mostly humotelinite and humodetrinite. In fluorescent light a small proportion of contained green fluorescing liptodetrinite appears to be discrete bodies derived from algal spores. If 5% exinite is taken as the cutoff for an oil shale then the samples examined are low grade oil shales, but the abundance of exinite derived from higher plants indicate they would be best termed cannel coals or canneloid claystones comparable with cannel coals from Freshford in New Zealand (Hutton op.cit.). The finely laminated texture and presence of huminite particles and liptinite suggest a lacustrine environment of deposition. Fischer assays of bulked 2.0 m samples from these claystones were made by the SECV laboratories to test their yield of tars and oils, and the results are presented in Table 2. FISCHER ASSAY OF SAMPLES FROM BORE ALBERTON EAST 8 (all results expressed as% dry basis) H20 OF TAR & OIL DEPTH (M) ASH% d. b. RESIDUE DECOMPOSITION YIELD

TABLE 2

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Stratigraphic Correlation Between Alberton and Gelliondale Coal Fields A series of east-west cross-sections running through both field areas were computer-drawn to establish their stratigraphic continuity. A generalised example of these cross-sections is shown by Figures 3 and 5. From the cross-sections it would appear the major seams in the Gelliondale Coal Field consist of the Band C seams from Alberton which have been combined on the domal area by an unconformity within the Tertiary sequence. The A seam appears to be present in the deeper more easterly portions of the Gelliondale lease area, but has been stripped by the younger Pliocene overburden unconformity from the domal areas. A thinner D seam is conformable with the C seam and occurs shortly above the Tertiary basement. Both and C and D seams are essentially conformable with this basement surface. Australian Coal Geology 4, part 1

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!,000

G.R. Holdgate

The unconformity within the Tertiary sequence, which juxtaposes different aged coal seams, is considered to be of the same age as the Latrobe Unconformity in the offshore part of the Gippsland Basin, where it is represented as a combined depositional hiatus and angular unconformity (Partridge 1976). The unconformity offshore is clearly marked at the lithological change between continental derived Palaeocene-Eocene sediments and marine 01 igocene-Miocene marls and limestones. In the Al berton area behind the barrier sand complex, the 01 i gocene-Mi ocene sediments are represented by the coa 1 seams A and B and their i nterseam sediments, which overlie Eocene aged coal seams C and D and their interseams. The unconfirmity is, therefore, lithologically indistinct as it brings together sediments of different ages but of similar continental origins. From limited palynological work it is surmised the unconformity occurs towards the top of the thick sand sequence which occurs between the Band C seams. This thesis remains to be fully substantiated by palynological dating of the coals within the Gelliondale lease area, but earlier work by Partridge (1971 and 1978) shows the presence of both N.asperus and P.tuberculatus age pollen zones within the Gelliondale coal measure sequence both 1n the lease area and immediately to the south . Seam corre 1at ion based on moisture content does not appear to be a re l i ab 1e index to seam identification as occurs in the Latrobe Valley. Structural location appears to play a significant part e.g. the weighted average moisture content for the B and C seams on the Ge 11 i onda le Dome is around 67% a. r. whereas for the younger A seam at Alberton where the overburden is greater the moisture is around 61.% a.r. The deeply buried thicker coal seams in the Port Albert Embayment (A, B & C) have the lowest weighted average moisture contents of around 56% a.r. (see Figure 5). CONCLUSIONS A stratigraphic and quality investigation of mid-Tertiary coal seams in the Al berton Depression has outlined some two bi 11 ion tonnes of economi ea l ly winnable brown coal occurring as two main seams in the Alberton township area. The extent and quality of these seams is closely related to the presence of a lateral lagoonal and barrier facies equivalent which lay between the peripheral-to-the-coast peat swamps and marine waters to the east. Structural warping and erosion that produced the early Tertiary Latrobe Unconformity has fortuitously brought together otherwise widely separated pre and post unconformity coal seams towards the south-west near Ge 11 i onda le producing a thicker economical coal sequence in this area. Some exinite-rich claystones occur as a localised facies of the youngest A seam beneath Alberton township and may be considered as low grade oil shales. The entire Tertiary stratigraphic sequence and deposition history is essentially similar to that of the Latrobe Valley, the main difference being the thickness and size of the deposit. In terms of scale, the coal resource of the combined Alberton and Gelliondale coal fields would rank second in Victoria to the Latrobe Valley.

Australian Coal Geology 4, part 1

G.R. Holdgate

ACKNOWLEDGEMENT The author wishes to acknowledge the assistance of the Pri nci pal Geologist, Dr . Colin Barton and all others of Exploration and Geological Division, SECV, and also for the co-operation and free exchange of information with Dr. B. R. Thompson, Dr. C. Abele, Miss V. Archer and Mr . G. Walker all of the DMEV. Th i s paper is published with Commission of Victoria.

the

permission of the State

Electricity

REFERENCEs Holdgate, G.R . , 1980. Geology of the Holey Plains - Coolungoolun Coal Fields and the Willung - Merrimans Creek area. SECV Exploration and Geological Division, Fuel Department, Report 1980/2. Hutton, A.C., 1981. Organic petrology of samples from Alberton 8. Department of Geology, University of Wollongong, unpublished report June 1981. Mackay, G. H., 1981. Bore core sample - Alberton East 8 (47.6 m) . Research & Development Department Laboratory Report No CS/81/18.

SECV

Partridge, A. D. , 1971. Stratigraphic palynolo9f of the onshore Tertiary sediments of the Gi ppsland Basin, Victoria . MSc hesis University of NSW, unpublished 1971. Partridge, A. D., 1976. The geological expression of eustacy in the Early Tertiary of the Gippsland Basin. APEA ~- 16, 73-79 . Partridge, A.D., 1978. Tertiary palynology of wells and bores in Corner Inlet sector onshore Gippsland Basin . Esso Australia Lt d. Palaeontology Report 1978/8 (unpublished). Thompson , B. R. , 1979. The Stradbroke Coalfield . Energy Geological Survey Report No . 61 .

Department of Minerals and

Thompson, B. R. , & Walker, G.M., 1982. Geology of the Western Margin of the Seaspray Depression - Gippsland Basin (paper in this symposium) .

Australian Coal Geology 4, part 1

Geology of the Gelliondale Coalfield I.R. Greer and G.C. Smith ARCO Austral la Limited 17th Floor, MLC Court, 15-23 Adelalde Street, BRISBANE, 4000, AUSTRALIA. Key Words:

Tertiary, Lignite, Coal resources, Victoria

ABSTRACT The Gelllondale Coalfield, Southeast Victoria, contains a very large resource of brown coal. The coalfleld occurs In the Alberton Depression within the Glppsland Basin and comprises a Calnozolc sequence of coal-bearing strata lying unconformably over the Lower Cretaceous Strzeleckl Group which forms economic basement for brown coal. The Strzelecki Group Is block faulted with east-west, northeast-southwest and minor northwest-southeast trends. Basement structural movements have been contemporaneous with Calnozolc sedimentation and have controlled their structural and deposltlonal development. The Calnozolc sequence Is drape folded over the fault blocks to produce a series of troughs and ridges dominated by the east-west Hedley Dome through the centre of the coalfleld, The Calnozolc sequence Includes a lower Tertiary fluvlal llthosome, a mlddle to upper Tertiary thick coal llthosome, an upper Tertiary marine llthosome and a Quaternary fluvlal llthosome. The thick coal llthosome Is dominated by the Gel I londale Seam which Is In places spl It to form the Gel I londale A and B Seams. A younger Alberton seam Is recognlzable In the east of the coalfield but It may be an upper spilt of the Gel llondale Seam. The Gel I londale Seam Is typically 50m or more thick. Its development Is related to the slow subsidence around the Hedley Dome and the area's location behind a stable barrier system which existed some 10km to the east during the middle and upper Tertiary. The Gel I londale Seam Is of soft brown coal rank with a low Minerals and lnorganlcs content of about 4 Wt%. INTRODUCTI ON The Gel I londale area Is located In the South Glppsland region of Victoria, approximately 200km by road southeast of Melbourne and 50km south of the main Latrobe Valley Coalflelds (Figure 1), It Iles on a relatlvely flat coastal plaln, In general about 5-15 metres above sea level, between the South Glppsland Hlghlands to the northwest and the Tasman Sea to the southeast (Figure 2). Much of the area Is used for farm Ing and Is part I a 11 y c I eared, a I though scattered stands of dense woodland and shrubs remain. Austral Ian Coal Geology 4, part 1

I.R. Greer & G.C. Smith

_ . Brown Coal Depo s it ■

- - - \{ -.J......_,\

I.. ,

.c::

......

.......

Cl)

100

200

........

.......

........

300

kilomet res

Figure 1 Map of Victoria showing the Gel I londale Coalfield, other Vict orian brown coal fields and Tertiary - Cretaceous sedimentary basins.

SEASPRAY DEPRESS ION

D -

Ter t l•ry/ Ouaternary

Bault -Tertiary

~ Strze l.ck l Group ~ Lower Cretaceous

[+++( L.!.!J Granlle-Uppar Devonian 10 JO'

Figure 2

kilometres

Claatlc lnllers - Lower Devonian

Map of the Alberton Depression showi ng the regional structure and exploration licence 583 (after 1:250,000 Alberton Sheet) Austra l Ian Coal Geology 4, part 1

I.R. Greer & G.C. Smith

•· u j

i5.,;

.. !I!

i;;~r

I~~

t; i

ul!

~§ at

iH ,---,.........,

4 000

3000

2000

1000

- ~ ~ ~

II:! 0

Victorian Min•• Department Drilling

SECV Drilling , llrown Coal Counc il

CRA/IOP Joi nt Venture

IOP

ARCO/IOP Joint Venture

l!!

Figure 3 Histograms of metres drl I led per year over the period 1902-1982. Redrll I and overburden pilot holes excluded. The region contains large resources of brown coal In several thick seams. In the Gel I londale area thick coal seams I le close to the surface producing an area of Iow overburden to coa I rat I os referred to as the Ge 111 onda I e coa If le Id. This area Is held within Exploration Licence 583 by International Oil Proprietary (Figure 2). The ex I stence of brown coa I In the area has been known s I nee the I ate 1800s. The Victorian Mines Department, partly In conjunction with the State Electricity Commission of Victoria (SECV}, drl I led 160 holes within the area of Exploration Licence 583 over a period since 1902 (Figure 3). Coal was first won In 1929 when the ICI company sunk a trial shaft near 5724100mN 451300mE extracting 230 tonnes of coal (Figure 6). Ful I scale mining began In 1934 when the Ge I I I onda I e Coa I and OI I Co. Ltd. operated an open cut mI ne over a ten year period and produced 41,000 tonnes, some of which was brlquetted. The pit was located near 5723400mN 462100mE (Figure 6} and Is presently flooded. International 01 I Explorations N.L. was granted portions of land over the Gelllondale coalfield In 1968 and carried out a limited exploration program. In August 1976 International 011 Limited (IOU, later re-named International 011 Proprietary (IOP}, was granted Explorat ion Licence 583. A joint venture agreement with Conzlnc Rio-Tinto Austral la Limited (CRA} was entered Into In September 1976 for exploration and development of the Gelllondale deposit with CRA as operator. Twenty-three holes were drl I led In the field programs of 1977 and 1978, most In 1977 (Figure 3). The CRA/IOP agreement was discontinued In 1979 leaving IOP solely responsible for exploration In 1979/8~ Austral Ian Coal Geology 4, part 1

I.R. Greer & G.C. Smith

In June 1980 a Joint effort began between ARCO Australia Limited and IOP with ARCO Australia Limited the operator. Since then ARCO and IOP have undertaken two exploration programs In 1980/81 and 1981/82 Involving a considerable amount of exploration drll ling and testwork (Figure 3).

1w -:--_._._._._._._ Eastern :-·

-----:-:_--149' -

141'

147' -

H i g h I an d s_

V i ctor i an :-

------ -

38°

L NM NM NM NM 51° 39• KI LOMETRES

146"

148'

149•

Figure 4 Major structural regions within the Glppsland Basin. BASIN SETTING

The Gel I londale coalfield Is located with i n the Glppsland Basin (Figure 1), a large Tertiary-Cretaceous sedimentary basin developed onshore and offshore In eastern Victoria (Douglas and Ferguson, 1976). The Glppsland Basin can be divided Into several distinct structural regions as shown In Figure 4. Major brown coal reserves occur In the Latrobe Valley Depression (e.g. Yal lourn, Morwel I and Loy Yang coalfields), the Seaspray Depression CStradbroke coalfield) and at Gelllondale In the Alberton Depression. Large reserves of oil and gas occur In the offshore Central Deep. The stratigraphy of the Glppsland Basin Is shown In Figure 5. sequences are recognizable:

Three major

(1) Upper Cretaceous to Tertiary sedimentary sequence comprising coal measures (Latrobe Group and equivalents) and marine facles (Seaspray Group). Quaternary to Recent sediments are known offshore and onshore. (2) Lower Cretaceous Strzelecki Group. (3) Palaeozoic basement rocks. Australian Coal Geology 4, part 1

I.R. Greer & G.C. Smith

Ma EPOCH

COALFIELD SE

UTR08~

GlfOUP

Q LATE a:

100

.... .. .... .. . ............. . ... . ... .....

w a:

125

PALAEOZO ERA

n LJ

NON-MARINE VOLCANOCLASTICS

□ COAL

MEASURES

□ COAL ~ SEAM

~ MARINE

[ill]

NOT PRESENT

Figure 5 Llthostratlgraphlc units Jn the Gel I Jondale Coalfleld and their tentative assignment to the time units. The basement rocks for the Glppsland Basin are of Ordovician to Devonian age and referab Ie to the Lach Ian Geosync I I ne (Doug Ias and Ferguson, 1976). Some minor Carboniferous and Permlan sediments are known (Douglas and Ferguson, 1976). Basement Is unconformably overlaln by the Lower Cretaceous Strzeleckl Group which typically consists of arkose, feldspathlc sandstone, mudstone, carbonaceous mudstones, and thin sub-bituminous coal seams (Douglas, 1976). In places these sedimentary rock units are overlaln by altered basalts. The Strzeleckl Group forms economic basement for brown coal at Gel llondale hence I Jttle data Is aval I able on detal Is of the Strzeleckl Group I Jthologles because most drlll-holes terminate Immediately It Is encountered. During at least the Mlddle and Late Cretaceous, upllft exposed the Strzeleckl Group and basal volcanlcs resultlng Jn the development of a weathering prof I le. Weathering of the Strzeleckl Group I Jthologles produces a mudstone un It, usua 11 y a b I ue grey s I I ty c I ay. Weather Ing of the basa Its produces a grey claystone from which quartz slit Is absent. In the Palaeocene and Austral Ian Coal Geology 4, part 1

I.R. Greer &G.C. Smith

Eocene, some onshore areas of uplifted Strzelecki Group rocks began to subside and form depressions which filled with Tertiary and Quaternary sediments (e.g. Alberton Depression, Latrobe Valley Depression). Consequently, the present-day Alberton Depression Is flanked to the north by uplifted Strzelecki Group rocks which largely form the South Glppsland Highlands, and within the Alberton Depression the Strzelecki Group Is unconformably overlain by a Palaeocene to Miocene sequence. At Gel llondale this sequence consists of Palaeocene to late Eocene clays, slits, sands and thin coals and late Eocene to Miocene thick brown coal seams with minor ligneous clays, slits and sands. This sequence Is analagous to the Latrobe Valley Coal Measures In the Latrobe Valley Depression. In the early Ollgocene a major transgression occurred over much of the Glppsland Basin. In the Alberton Depression the marine facles encroaches almost to Port Albert and a north-south orientated barrier facles system developed about 10 km east of Exploration Licence 583 with marine carbonate facles further east (Partridge, 1971). Thick coal seam facles continued to develop west of th Is barr Ier system (Ho Idgate, 1982). A further marine transgression In the late Tertiary pushed the shoreline back Into the Ge I 11 onda I e area dur Ing the P 11 ocene, from wh I eh It subsequent I y retreated to Its present-day position. Consequently, the upper coal Is dlsconformably to unconformably overlain by a transgressive-regressive sequence of Pllocene and Quaternary sediments consisting of marginal marine sediments passing Into weathered yellow-brown terrestrial clays, slits, sands and peats.

.. .... ~

Figure 6

-....

.... N

t k llom•tt••

Structure contours to top of economic basement (Strzelecki Group or volcanlcs) showing axes of Tertiary folding and section lines.

Australian Coal Geology 4, part 1

I .R. Greer & G._C. Smith

A.....,►•

,oo '50

BI RDS

S YNC LINE I C

·2u

rn (.)

,.o

.o~

II)

'l'

A ..,,.,,,.

'\'\'"'i •

,oo

'50

rn"

Figure 7 East - West cross-section through the Gelllondale Coalfield Figure 6).

CA-A on

STRUCTURE The regional structure of the Strzelecki Group Is dominated by block faulting orientated east-west and northeast-southeast with a minor northwest-southeast trend CF Igure 2). These three structura I trends are apparent In the Lower Cretaceous rocks at Gelllondale. Bounding the north of the deposit Is a large fault, part of the Toora Fault mapped by the Geological Survey of Victoria (Warragu I Sheet, 1:250,000; 1971 ). The western margin Is controlled by the Gell londale Monocllne (Hocking et al, 1976) which curves north to meet the Toora Fault.The structure of the deposit Is Indicated In Figure 6 and the cross sections given In Figures 7 and 8. The structure of the Strzelecki Group probably Is block-faulted with open folding as In the South Glppsland Highlands. The Tertiary sediments are drape folded over these fault blocks forming a series of antlcllnal ridges and synclinal trough features with each area possibly fault bounded (Figure 6). In the northern half of the l icence area dips within the Tertiary sediments mostly vary from 3°-9°. Dips up to 12° occur In small localised areas on the flanks of minor structural highs. In the southern half of the I lcence area Interpreted dips at the base of the Tertiary sequence are steeper being up to 20° over the monoc I Ines.

Austral Ian Coal Geology 4, part 1

I.R. Greer & G.C. Smith

,._,t\''~

,••

' 50

HEDLE Y

DOME

,so

l C:

.!!

VI I

I I I

.. ;

D•"'''

,00

,so

Figure 8 North - South cross-sections through the Gelllondale Coalfield CB-B, C-C and D-D on Figure 6). The major structures presently recognizable within the Gel I londale Licence area are detailed below. They are Interpreted from drill-hole data, gravity and resistivity survey data and hydrogeologlcal studies. Hedley Dome: A large antic I lnal structure known as the Hedley Dome runs approximately east-west through the centre of the exploration I lcence area (Glenle, 1977). This structural high forms the southern edge of a broad fault block tl lted to the north-northwest over much of t he northern half of the exploration licence area. This block contains several smaller scale structura I features a Iong Its northern marg Ins and Is bounded to the southeast and southwest by rapidly deepening basement (the southeastern boundary has been termed the AIberton Monoc 11 ne: GIen Ie, 1977 ). Australian Coal Geology 4, part 1

I.R. Greer & G.C. Smith

Gel llondale Trough: The northwest-southeast orientated sync I lnal structure was recognised by Glenle (1977) adjacent and to the north-east of the Hedley Dome. It p Itches to the south-east and runs Into the steep I y d I pp Ing south east area. The Gell londale Trough has had a marked effect on Tertiary sedimentation and contains high transmlsslvlty aquifers at Its eastern end. Lanes Dome: A 2.5 km east-west basement ridge termed Lanes Road High by Glen le (1977) Is recognizable north of the Gel llondale Trough. Jarvis Syncl lne: A broad shallow north-easterly trending synclinal structure has been Identified by recent drll ling In the north east of the licence area subjacent to Jarvis Road. Pearsons Antic I lne: A prominent northeast-southwest basement ridge termed Pearsons Road High by Glen le (1977) occurs north of the Hedley Dome. The ridge has affected Tertiary sedimentation Including coal seam formation and spl lttlng. Birds Dome and Birds Syncline: These adjacent northwest-southeast orientated structures I le near to Birds Road, north of and sub-para I lel to the western limb of the Hedley Dome. These three northwest-southwest orientated structures subdivide the area west of the Hedley Dome where Glenle (1977) had recognized a northeast-southwest orientated Hedley Trough. An east-west fault cutting Pearsons Anticline Is Inferred from drll I-hole data (as shown on Section C-C, Figure 8). The fault appears to have a component of right lateral strike-slip and Is downthrown to the south. TERTIARY AND QUATERNARY SEDIMENTATION The patterns of sedimentation within the Gelllondale coalfield can be related to the structural trends of the economic basement. The Tertiary sequence as a whole, and the Individual units within the sequence, are thickest In the sync I Ina I troughs over econom Ic basement Iow s and th In or are non-ex I stent over econom Ic basement h Ighs. I nterpretat Ion of the sed I mentat Ion trends Is complicated by exposure of the area In the late Tertiary leading to erosion of some upper Tert I ary un Its. The Tert I ary coa I measures and overburden sequences thicken and deepen considerably to the south and east where a greater rate of subsidence has accommodated thicker sedimentation. The sediments deposited In the area reflect the changing sea level conditions In the Glppsland Basin during the Tertiary and Quaternary periods. Four lithological units are recongnlsable (1) (2) (3) (4)

a lower Tertiary fluvlal sequence. middle to upper Tertiary thick coal measures. upper Tertiary marine beds. Quaternary surflclal deposits.

The detailed relationships of these rock units to blostratlgrahlc and chronostratlgraphlc units are not known. ihe ages are assigned on the basis of limited palynologlcal and foramlnlferal age determinations and are tentative designations.

Australian Coal Geology 4, part 1

I.R. Greer & G.C. Smith

t Figure 9 Sub-coal lsopach Map. ~

Tertiary fluvJal SeQuence

A Palaeocene to late Eocene sequence Is recognisable at the base of the section. It mainly comprises poorly consol ldated sands and muds with minor th in coals and Is Informally known as the subcoal sequence. Arenaceous sediments of both poorly and well-sorted unconsolidated grey sands predominate In basement trough areas and south of Hedley Dome. These are Interpreted as al luvlal and fluvlal sediments and they exhibit both coarsening and fining upwards unttsA Outwash and overbank floodplain argl I laceous sequences of s 11 ty c I ays and I Igneous c I ays occur on basement h Ighs and to the north and west of the coalfield near the coal subcrop. This distribution of sediments suggests that the basement structures observed today were active In the early Tertiary and control led deposition as I ndicated by the subcoal tsopach map (Figure 9). Rapid lateral facles change between the argll laceous and arenaceous sediments Is common particularly near and over basement highs. Palynologlcal dating (Cookson and Dettmann, 1959; Partridge, 1971) Indicate that a dlsconformlty or paraconformlty exists between the late Palaeocene and the middle Eocene north of the Hedley Dome. This probably represents the proximal Influence of the late Palaeocene baslnwlde decrease In subsidence and changes to base level occurring In the more distal areas of the Glppsland Basin In the early to mlddle Eocene (Partridge, 1976; Smith, 1981), At Yarram, the probable time equlvalents of this sequence are divided Into a Palaeocene Yarram Formation (Hocking n .al, 1976) commonly overlain by volcanlcs (Older Volcantcs) and unconformably by the lower part of the Traralgon Formation (Hocking n .al, 1976) However, at Gelllondale no obvious lithological break occurs which would allow distinction of Yarram and Traralgon Formation equivalents and In the absence of demonstrated lateral correlation of these llthostratlgraphlc units It Is premature to use these terms for parts of the Gelllondale sequence.

Australian Coal Geology 4, part 1

I .R. Greer & G.C. Smith

0 •5

Figure 10

lsopach of Gelllondale Seam plus Gelllondale A Seam and subcrop of Alberton Seam (top); lsopach of lntraseam parting (middle); lsopach of Gelllondale B Seam (bottom). Australian Coal Geology 4, part 1

I.R. Greer & G.C. Smith

82 Ih1.cis. ~ Measures

The late Eocene to late Miocene sequence Is dominated by the development of thick autochthonous coal seams with minor basal muds, thin partings or seam spllts and associated overlying ligneous muds and sands. Two major and persistent non-coal horizons occur within the thick coal seams over the llcence area and these allow recognition of three coal horizons (Figures 7 and 8). The Gel llondale Seam forms the main thick coal seam In the Gel llondale coalfleld occurring either as one unspllt seam or as two seam spllts separated by the Iower non-coa I hor I zon. The upper non-coa I hor I zon Is taken here as an lnterseam sediment separating the Gelllondale Seam from a younger seam referred to here as the Alberton seam. However, the upper non-coal horizon may be an Intra-seam parting In which case the Alberton seam would be an upper coal spilt of the Gelllondale Seam. The Gelllondale Seam occurs throughout most of the Gelllondale area and lies close to the surface around the Hedley Dome (Figures 10 and 11). The base of the Gelllondale Seam north and north west of the Hedley Dome Is characteris ed by a rapid vertlcal succession from sand or mud to carbonaceo us (I Igneous) clay, to an Inferior coal (defined as 30% - 10% ash, dry bas i s), to coal (defined as less than 10% ash, dry basis). The basal unit of Inferior coal Is typlcal ly 1-2m thick but can be much thicker especially In the trough areas where the base of the seam Is deteriorate d Into thin lnterbedded coal and noncoal bands. Some thin Inferior coal bands occur within the seam but these are generally not persistent throughout the coalfield. The top of the Gel llondale Seam Is characteris ed by slml lar transi t ions to Inferior coal and I Igneous c I ays and sands as occur at the base. In some areas, the seam top con ta Ins c I ay and sand-f 11 I ed Jo I nts. Some ev I dence ex I sts for Ioca I eros I on of the upper coal surface especlal ly to the east and south of the Hedley Dome.

kil ome tres

Figure 11

Overburden lsopach Map (PI locene and Quaternary Sediments) Austral Ian Coal Geology 4, part 1

I.R. Greer & G.C. Smith

The Gel llondale Seam Is free from major splitting In the areas adjacent and to the north of the Hedley Dome and adjacent and to the south of the Hedley Dome (Figure 10). The seam Is spl It Into an upper Gel I londale A and a lower Gelllondale B Seam to the southwest and northeast of the Hedley Dome. Correlation of this spilt between the two areas Is at present tentative although an Inferior coal band Is present at the appropriate level In some of the bores In the central northern area of the coalfield. The spilt In both the southeast and northeast areas occurs Just below the mid-point In the seam section and shows lateral facles change. In the west the seam split Is a I Igneous clay or mud about 1-2m thick which to the southeast thickens and further splits Into two c I ays separated by a th In coa I. In the north-east the sp I It beg Ins as a I Igneous clay typically 1-2m thick which further to the north and east thickens and Includes lnterbedded sands. Outs I de the 11 cence area and to the east the sp 11 t between the Ge 111 onda Ie A and B seams appears to correlate with a much thicker sequence of Inter-seam sediments. Holdgate (1982) suggests that the spilt contains an unconformity equivalent to the early Ollgocene Latrobe Unconformity. However, no evidence for an unconformity exists within the Gelllondale Seam (especially where It Is unspllt) although It Is possible that a dlsconformlty occurs. Development of the Gelllondale Seam around the Hedley Dome probably was continuous from the late Eocene (prior to the marine transgression) to at least the late Ollgocene and the splitting to the east and elsewhere Is Interpreted here as a result of facles change and greater rates of subsidence and deposition away from the Hed Iey Dome. Along the northern and northwestern margins the Gel llondale Seam deteriorates rapidly over distances of less than 100m. The seam along this margin Is split by lnterbedded sands and muds and the coal bands pinch out. The Gelllondale Seam wedges out rapidly onto the Hedley Dome from all directions although some localised thin bands of coal occur across the Hedley Dome. Some small deposltlonal troughs occur within the Hedley Dome but these mainly contain sands and muds w Ith some th In coa Is. The age of these sed I ments Is not c I ear but they appear to be facles equivalents of the subcoal and coal units and the sequence probably contains several dlsconformltles and unconformltles. In the east of the licence area another elastic horizon (mainly silty clays) occurs between coal towards the top of the coal measures. This has been taken here as an Inter-seam spilt and the upper (early Miocene) coal seam correlated with the similar age seam In the Alberton district to the east (Figures 7 and 8; also Holdgate, 1982). This younger seam Is referred to here as the Alberton seam and Inferred to subcrop due to erosion (Figure 10). However, It may be an upper sp I It of the Ge I 11 onda I e Seam, In wh I eh case the Inter-seam sediments pinch out and are facles equlvalents of coal deposited further west. This problem cannot be resolved without further Information Including detailed drllllng and palynologlcal studies. The latter view Is supported by the apparent convergence of the Alberton and Gel llondale Seams south of the Hedley Dome where one llthologlcally continuous seam Is recorded (Figure 10). ~ Jertfary .Ma.c..l..n.e .B.ild.s.

A major westward marine transgression occurred over much of the Alberton Depression In the Pllocene. In the Gel llondale area the transgression resulted In mar I ne sed I mentat Ion east and south of the Hed I ey Dome wIth marg Ina I marine, beach, lagoonal and brackish lacustrlne conditions reaching the Hedley Dome and overlying the coal measures to the north and west of the Hedley Dome

Austral Ian Coal Geology 4, part 1

I.R. Greer & G.C. Smith

(Figure 11). The marglnal marine sediments are paraconformable over the I Igneous sands and c I ays of the coa I measures and In p I aces I I e d I rect I y on Inferior coal. The relationship of the marine sediments to the coal measures south and east of the Hedley Dome Is largely paraconformable but Jn places Is probably unconformable, The marine beds are thickest towards the south and east and thin towards the northwest. Maximum marine deposition occurred Jn the ear I y PI I ocene w Ith gradua I sha I Iow Ing towards the end of the PI I ocene (Mai lett, 1977, 1978). The shallow marine sediments malnly comprise green-grey, poorly sorted sands, silts and marls with shell fragments and mica flakes common In the sands. The marg Ina I mar I ne sed I ments vary from we I I -sorted wh I te-grey beach sands to poorly sorted grey, mlcaceous sands and slits of Jagoonal and brackish marine facles.

Quaternary fluv[al/AI luv[al Depos[ts The gradual sea level shallowlng near the end of the Pllocene led to Quaternary regressive sedimentation In the Gel llondale area. The upper units of the marine I Jthosome are conformably overlaln by terrestrlal sediments. The latter comprise white, yellow and brown clays, sf lty sands and I Igneous muds represent Ing a I I uv I a I and f I uv I a I coasta I sed I men tat Ion. Th In peats occur around and over the Hedley Dome and to the south. The PI Jocene marine and Quaternary sequences together form the overburden to the Gelllondale coalfleld (Figure 11). The overburden Is typlcally less than 2Om thick north of the Hedley Dome but thickens to over 1OOm to the south and east. The PI I ocene mar I ne beds compr I ses the major part of the overburden sequence to the south and east whereas the Quaternary terrestrlal sediments comprise most of the overburden towards t he north and west. The detalled relatlonshlps of the units Jn the overburden sequence are complex and poorly understood. In the absence of systematic blostratlgraphlcal studies of these units, and detalled lateral correlatlon of the llthostratlgraphlc units with those In the Seaspray and Lake Wei I lngton Depressions, use of formatlonal names from these latter areas for the overburden units at Gelllondale Is not warranted at present. COAL SEAM COMPOSITION AND RESOURCES The composition of the thick coal seams at Gelllondale lies within the range of type and rank exhibited by the Latrobe Valley thick coals. The coal at Gelllondale Is of soft brown coal rank with bed-moisture values estimated at about 65 - 67% which are slmllar to the Yal lourn Seam. Average coal llthotype and coal maceral compositions are shown Jn Table 1. Detalled llthotype loggJng Is presently being undertaken. Prel Im I nary results Indicate that the Gelllondale Seam Is comprised mostly of Medium-Light to Light llthotypes and that th Is trend pers I sts I atera 11 y throughout most of the seam. However, a significant proportion of the seam consists of Medium-Dark llthotypes. Pale I Jthotypes (pollen bands) are rare or absent. The I Jthotype occurrence suggests that the peat env I ronments were dom I nated by open-marsh tac I es w Ith minor woodland swamps and few persistent open-water ponds.

Austral Ian Coal Geology 4, part 1

I.R. Greer & G.C. Smith TABLE 1:

AVERAGE COAL LITHOTYPE AND COAL MACERAL COMPOSITIONS FOR THE GELLIONDALE SEAM.

LITHOTYPEl DARK MEDIUM-DARK

SEAM\

MACERAL 2

SEAM\

HUMINITE (Vitrinite)

91½

(Humodetrinite)

(63)

(Humotelinite)

(20½)

(Humocollini te) MEDIUM-LIGHT

LIPTINITE (Exinite)

LIGHT

9½

INERTINITE

PALE

DISCRETE MINERALS

(7) 7 ½ 1

Brown coal llthotype classlflcatlon after George (1975)

Brown coal maceral classlflcatlon after I.C.C.P (1963,1971,1975)

The I Jthotype assessment Is supported by maceral analyses which Indicate a predom I nance of f I ne-gra I ned attr I ta I p I ant matter expected In open-marsh facles. The humotellnlte macerals largely occur Jn the Medium-Dark and Dark I Jthotypes consistent with derivation from the larger plants Jn woodland facles. Detal led chemical analyses have been undertaken on a large number of coal samples taken from cored drll I-holes at 3m and 6m Intervals and bulk samples. A typical coal analysis Is shown Jn Table 2. The Gel llondale Seam contains a low Minerals and Inorganic content relative to coals elsewhere In the world which Is typical of the Latrobe Valley type thick coal seams (Smith, 1981). Within seams vertical variation Jn seam composition Is minor. In the Gel llondale coalfield no major variations Jn chemical composition occur between the Gel llondale A and B Seams within the one bore-core. Increased Mlnerals and lnorganlcs content occurs near the base and top of the seam or adjacent to partings. Most of the sulphur occurs as organically bound sulphur, sulphates and carbonates are generally absent, and rare pyrite/ marcaslte occurs as smal I nodular secondary concretions with an apparent random distribution. The Gelllondale coalfield contains very large amounts of brown coal (Table 3). The Jn sltu Inferred Resources are Very Large while Jn sltu Indicated Resources are estimated presently as 1700 mll lion tonnes. The Recoverable Reserves of brown coal are defined as seams of coal with less than 10% ash, greater than 15m th I ck, where the depth to top of coa I Is Iess than 1OOm and to the base of coa I I ess than 200m, and the overburden to coa I ratio Is less than 0.5:1. Hydrological, geotechnlcal and socio-geographical constra I nts are a I so taken Into account. On th Is bas Is some 1050 m111 Jon tonnes presently are defined as Recoverable Reserves and these mainly lie to the north and around the margins of the Hedley Dome. Austral Ian Coal Geology 4, part 1

I.R. Greer & G.C. Smith

TABLE 2:

AVERAGE ANALYTICAL COMPOSITION OF THE GELLIONDALE SEAM. ANALYSIS

MOISTURE

MEAN

STANDARD DEVIATION

(Wt\)

As Received

65.9

2.16

Dry Basis

194.9

20.43

ASH (WU dry basis)

6.3

1.39

MINERALS AND INORGANICS

3.6

0.92

50.7

0.82

66.5

0.80

(WU dry basis)

VOLATILES YIELD (Wt\

ULTIMATES

dry basis)

(WU

d.m.i.f.)

CARBON HYDROGEN

4.6

0.18

NITROGEN

0.6

0.08 0.83

OXYGEN (difference)

27.4

ORGANIC SULPHUR

0.7

0.19

PYRITIC SULPHUR

0.2

0.05

GROSS DRY

25.52

0.42

GROSS WET

8.69

0.57

NET WET

6.81

0.68

1.14

0.02

SPECIFIC ENERGY (MJ/kg)

SPECIFIC DENSITY (g/cm3 )

d.m.i.f.

dry mineral and inorganic free.

Australian Coal Geology 4, part 1

I.R. Greer &G.C. Smith

TABLE 3:

COAL RESOURCES AND RESERVES WITHIN EXPLORATION LICENCE 583

CATEGORY

SEAM

INSITU RESOURCES RECOVERABLE

INDICATED (x106 tonnes)

INFERRED (X106 tonnesl

ALL SEAMS OVER 3m

1700

3500

Gelliondale Seam

347

Gelliondale A Seam

180

Gelliondale B Seam

102

Gelliondale Seam + Alberton Seam

421

RESERVES

TOTAL: -

1050

CONQUSIONS The development of the Gelllondale coalfield Is related to the tectonic history of the Alberton Depression and speclflcal ly to the Hedley Dome and Its associated structural features. Structural movements of the Strzelecki Group basement rocks allowed Initiation of Tertiary sedimentation and have controlled the rate of deposition and Influenced facles distribution throughout the Tertiary and Quaternary. The present I Im Its of the geological units In the Gel llondale coalfield approximately coincide with the original extent of the depositional environments. The Hedley Dome has acted as a structural high of low relief throughout the Tertiary and no significant thick coal seam developed over It later to be removed by erosion (this conclusion agrees with the original proposal of Thomas and Baragwanath, 1950). Rather, thick coal seams have developed around the flanks of the Hedley Dome which has been an area of very slow subsidence at rates of less than 5m/Ma. The almost continuous development of the thick Gel llondale Seam resulted from the slow subsidence of the Gelllondale coalf ield around the Hedley Dome and the area's d I sta I Iocat Ion beh Ind a stab I e barr I er system some 10 km to the east. Taken together, the low mineral matter content, absence of washouts and splits, and the thickness of the Gelllondale Seam, Indicate that plant matter accumulated over a wide area which was devoid of major stream channels and undergoing uniform slow subsidence over some 20 million years. This contrasts Australian Coal Geology 4, part 1

I.R. Greer & G.C. Smith

markedly with deltalc coal-forming environments where seams are thinner, prone to splitting and washouts, and high In mineral matter content. The origin and composition of the Gelllondale Seam are typical of thick Latrobe Valley type seams. Nevertheless, some significant differences In detail exist between t~e structural styles and sedimentation patterns of the Gel I londale and Latrobe Va I I ey coa Is. AO<NOWLEDGEMENTS This paper Is published with the permission of ARCO Australia Limited and International 011 Proprietary. C.E. Layden of International 011 Proprietary, C.R. Coxhead of Robertson Research (Australia) Pty. Ltd, and staff of Australian Groundwater Consultants Pty. Ltd. have assisted In data col lectlon and Interpretation. The manuscript was typed by R. Fitzgerald and drafted by C. Holmes. REFERENCES COOKSON, I.C. & DETTMANN, M.E, 1959, MI crof Ioras In bore cores from AIberton West, Victoria. ~R..~Y...l&.L.ll, 31-38. DOUGLAS, J.G., 1976, Glppsland Basin Mesozoic, l.n Douglas, J.G. & Ferguson, J.A., (eds.), Geology .o..f Victoria, Spee. Pub I, Geol. Soc. Aust. 5, 158-164. DOUGLAS, J.G. & FERGUSON, J.A. (eds.), 1976, Geology .o..f Victoria, Geol. Soc. Aust . .2.

Spee. Pub I.

GEORGE, A.M., 1975, ~~I ithotypes l.n .±h.§ Latrobe Val !ey deposits. Victorian State Electricity Commission, Exploration and Geological Division Petro Iog I ea I Report 17, (unpub I.). GLENIE, R.C., 1977, Gel I londa!e 6J::QB'.ll i&aJ Pro(ect Geo!oglcar ~ I, 11 and 111. Report to CRA Coal Group (unpubl.)

Volumes

HOCKING, J.B., GLOE, C.S. & THRELFALL, F.W., 1976, Glppsland Basin Tertiary, l.n Douglas, J.G. & Ferguson, J.A., (eds.), Geology .o..f Victoria. Spee. Publ. Geol. Soc. Aust. 5, 248-273. HOLDGATE, G.R,. 1982, ~ ~ .a.ru1 facies equivalents .o..t .±h.§ Alberton Depression - Gipps!and. Victoria. Victoria State Electricity Commission, Exploration and Geological Division Report 24 (unpubl.) INTERNATIONAL COMMISSION FOR COAL PETROLOGY, 1963, 1971, 1975: International Handbook .to.c .c.o.aJ. Petrology. Centre National de la Recherche Sclentlflque, Paris, 2nd edn (1963), Supplement (1971), Supplement (1975). MALLETT, c.w., 1977, ~ foraminiferar ~ l.n .:the Jemmys fQln.t Formation equivalent overlying .:the .c2ll measures. Gel lionda!e district. Mlcropalaeontologlcal Report to CRA Coal Group (unpubl.) MALLETT, C.W., 1978, Sealevel changes In the Neogene of Southern Victoria. AEEA .J., 1.a,64-69. PARTRIDGE, A.O., 1971, stratigraphic palynorogy .o..t .:the onshore Tertiary s.e.d..I..= YI ctor i a. M.Sc. Thes Is, Un Iv. New South Wa I es ( unpub I . ) .

m.§Ilil .o..f .±h.§ Gi pps I and Basin,

Australian Coal Geology 4, part 1

I.R. Greer & G.C. Smith

PARTRIDGE, A.O., 1976, The geological expression of eustacy In the Early Tertiary of the Glppsland Basin. N!£l, .J.JJi, 73-79. ~ .lli2J2.ec Cretaceous .cQaJ...s .a.rul .c.Q8J. measure ~ 1.n .1il S.8.ll .a.n..d G(pps(and Bas(ns, Ph.D. Thesis, Unlv. Wollongong

SMITH, G.C., 1981, Tertiary ~

(unpubl.).

THOMAS, D.E. & BARAGWANATH, W., 1959, Geology of the brown coals of Victoria. Part 2. HJ...n... G.82..L. Journ, l'...kL. A 36-52.

Palynological Evidence for Age and Environment of Deposition of Tertiary Coals in the Gippsland Basin A. D. PARTRIDGE

ESS0 Australia Ltd., G.P.0. Box 4047, Sydney, N.S.W., 2001 Austral la.

ABSTRACT Coal deposition occurred In the Glppsland Basin In the coarse facles of the wedge base (White, 1980) during a protracted period of marine transgression which started In the Late Cretaceous and ended Jn the Middle Miocene. Characteristic of the Glppsland Basin through this transgressive period has been discrete lateral and vertical separation of facles. The order of the facles sequence Jn the direction onshore to offshore (laterally) or stratlgraphlcally from older to younger rocks (vertically) Is as follows: 1. fluvlatlle sands, shales and thin coals; 2. coastal plain facles with t hick coals and sands but minor shales; 3. thick strand line sands with thin coals and shales; 4. marine greensands, shales or carbonates; 5. starved marine environments of nondeposition. It Is this discrete separation of facles that colours all the early literature on GI pps I and Bas In strat I graphy. The reason why th Is was so Is because the fossils Initially used for age dating and correlation are very much restricted to discrete facles. This problem has only been resolved by the application of palynology, In this case the analysis of the fossil spores and po) Jen produced by terrestrial plants. It Is by the use of these plant fossl Is which origI nate In the h Inter I and and on the coast a I p I a In and wh Ieh are subsequent I y distributed by agencies of both wind and water that It has been possible to break this historical facles barrier. Wh i te, D.A., 1980, Assessing ol I and gas plays In facles cycle wedges. .81Ll..1...M, 1158-1178.

~ ~ ~

Australian Coal Geology 4, part 1

Am...

Tertiary Coal Deposits of the St. Vincent Basin - South Australia

A. MUIR and A. KREMOR Coal Resources Branch, The Electricity Trust of South Austral la, 220 Greenhll I Road, Eastwood, South Austral ta, 5063. ABSTRACT The northern section of the St. Vincent Basin, South Australia, contains coalbearing sediments of Tertiary age. Indications of coal were orlglnal ly discovered by early water well drll ling with follow up Investigations by the South Austral Ian Department of Mines and Energy. Comparatively recent Investigations by the Electrlclty Trust of South Australla have delineated significant reserves of brown coal extending over a considerable area of the Basin. The base of the Tertiary sequence ls generally represented by coal and carbonaceous sand and clay, which ls overlain by sand, clay, I lmestone and a thin veneer of Quaternary sandy clay. Basement ls represented by Adelaldean and Cambrian quartzite, shale and calcareous sediments. The coal ls of low rank, high In moisture, sodium, chlorides and sulphur. Coal and carbonaceous sediments have formed In association within basement depressions, but the mechanism and environment of deposition Is not yet clearly understood. The coal occurs In seams up to 25m thick, but rapid thinning and splitting are characteristic . The Electricity Trust of South Austral la ls currently Investigating In detail the Bowmans Deposit as a source of coal for power generation.

Australian Coal Geology 4, part 1

Geology of the Kingston Lignite Deposit

G.M. MEYER Western Mining Corporation Limited 43-63 High Street, Preston, Victoria, 3072, Australia. KEY WORDS:

Lignite, Kingston, Coal reserves, Tertiary.

ABSTRACT The Kingston Lignite Deposit was discovered In 1979 by Western Mining Corporation. It contains a total resource of 985 ml I I Ion tonnes of I Ignite classified as type Band occurs on the northern margin of the Otway Basin In southeastern South Australia. Lignite occurs In one main series of seams with Individual seams up to 12 metres thick. The overburden, depending on topography, varies from 40 to 75m. The lignite ls similar In quality to other deposits of Tertiary age In South Australia. Ash content ls fairly uniform and averages 14.9% (dry basis) while sulphur and sodium/ash ratio are variable between 2.8 and 3.0% (dry basis), and 5.4 and 7.1 % respect I ve I y. The sod I um content Is I nf I uenced by groundwater salinity. Tertiary sediments exist In a north-south trough and overlie Cambrian Kanmantoo Group metasedlments. The trough ls bounded by shallow Ordovician felslc lntruslves. The lignite ls Middle Eocene In age and occurs In a transgressive sequence of Tertiary sediments which ls overlain by a regressive sequence of Quarternary sediments. INTRODUCTION The Kingston Lignite Deposit, discovered by Western Mining Corporation In 1979, occurs near the northern marg In of the Otway Bas In, 15 to 45 km north east of Kingston SE, on the east coast of South Australia (Figure 1). The deposit ls Middle Eocene In age, associated with other Tertiary and Quaternary sediments and Is of slml Jar age to I Ignites found In the Murray, Pirie-Torrens, Po Ida and St. Vincent basins In South Austral la. Western Mining Corporation also discovered a smal fer deposit, the Lochaber Lignite Deposit, 60 km to the east. Both deposits are classified as lignite type B. The Kingston Lignite Deposit ls lenticular In prof I le, extending over 50 kilometres. The main section occurs In two lobes 1 to 5 kilometres wide eastAustralian Coal Geology 4, part 1

G.M. MEYER

S.E. SOUTH AUSTRALIA

·,, .,,_.

LIGNITE OCCURRENCES I 0 Kilometres I \ Murray \ Basin 'li.: K EITH

.. :-,

Troubridge Basin

(· - -., •

', .

~El Boundary •

. .

•:::--1i,

A•

~ 0

-~c·: ~ ..•.{'t~ '"/• Tertiary Trough ~

, 70m depth to ) Dilwyn Fm.

KING DEP

Otwa y

• lignite Occurrence • Barren Hole € Palaeozoic Outcrop

Basin

FIGURE 1

i I

OVERBURDEN D > som

D 4o-som •

< 40m

KINGSTON LIGNITE DEPOSIT

LIGNITE AND OVERBURDEN THICKNESS 0

20 Kilometres FIGURE 2

Austral Ian Coal Geology 4, part 1

G.M. MEYER

[ Wm BRIDGEWATER FORMATION COOMANDOOK FORMATION ~ OIL WYN FORMATION ITill PRE-TERTIARY BASEMENT LIGNITE SEAM

100m

KINGSTON CROSS SECTION

A-A 2 km

NOTE. 20 : 1 VERTICAL SCALE EXAGGERATION FIGURE 3

EE] BRIDGEWATER FORMATION

ED PADTHAWAY FORMATION COOMANDOOK FORMATION t:;::;::;:1 GAMBIER LIMESTONE

KINGSTON CROSS-SECTION B-B

WN NARR A WA TURK MARL l2Zl DILWYN FORMATION f ,-;,1 PRE-TERTIARY BEDROCK

: ~ L.•.~Nl : E....: :•• •... ·.. =-

:,;.Lr--C..-C..-C..-C..- C..'E<.-£-+ + 4

2km

· •·· ·-:jY~~:::.

- -

NOTE-20:1 VERTICAL SCALE EXAGGERATION FIGURE 4

Austral Ian Coal Geology 4, part 1

G.M. MEYER

west over a combined length of 20 kilometres north-south (Figures 2, 3 and 4). The maximum lignite thickness Is approximately 12m In each lobe, joined by a narrow neck of lignite approximately 4m thick and 1 kilometre wide. Lignite thickens rapidly towards the central north-northeast/south-southwest axis of the deposit and splitting of the seam near the margin Is common.

Lignite occurs predominantly In one main series of seams. In the southern lobe, the seam Is usually continuous although thin partings may sometimes occur towards Its base. However In the northern lobe, a parting up to 4m thick Is developed. A series of upper seams rarely exceeding lm In thickness with parting thickness generally In excess of seam thickness occurs In portions of the deposit some 5 to 15m above the main seam. Overburden th I ckness var I es s I gn If Icant I y because of the I nf I uence of dune systems. A major part of the southern lobe occurs under dunes and within this area overburden ranges from 40 to 75m while on the flats It Is commonly between 40 and 50m. The northern lobe occurs mainly under flats and the overburden Is between 40 and 50m. The floor of the main seam forms an elongate trough with a maximum relief of 10 to 15m. Total measured, Indicated and Inferred reserves for the resource are estimated to be 985 Mt (April 1982). EXPLORATION METHODS The geological evaluation of the deposit was by drll I Ing with geophysical I ogg Ing used extens I ve I y. Over 460 ho I es were dr 11 I ed and 20% of the ho I es cored coal seams and 10% of the holes cored overburden sediments. In the exploration program, logs were routinely run for gamma, short and long spaced dens Ity, ea 11 per, se If-potent Ia I, po I nt res Istance, neutron and son Ic. The density and cal I per logs were used to define seam position, I Ignite ash content, specific energy and moisture while the gamma and neutron logs were used to define I lthology and correlate overburden units. The density and sonic logs were used to determine the position and relative strength of hard units. Bu I k samp I es were obta I ned by means of 210mm and 1.Orn d I a meter cores. 382 tonnes were recovered and most were despatched for combustion engineering In West Germany, and the USA. LIGNITE QUALITY LI ke other South Austra I I an I I gn I tes of s Im 11 ar age, they are soft and Iow rank. The In sltu ash content of the main seam series Is reasonably uniform over the depos It and averages 14.9% (dry bas Is). However, numerous part I ngs towards the margins produce an Increase In ash content. Volatile matter of In sltu I Ignite averages 46.9% (dry basis), fixed carbon 38.2% (dry basis), specific energy 10.6 megajoules per kl°logram (dry basis) and total moisture 55%. Sodium/ash ratio distributions are generally variable within the range 5.4% and 7.1% with highest sodium values In the central and northern sections of Australian Coal Geology 4, part 1

G.M. MEYER

96 Troubridge

•~,). '.>a

Otway Basin

FIGURE 5

I METASEDIMENTS

•. +

KINGSTON LIGNITE DEPOSIT

PRE-TERTIARY SUB-CROP 0

KIiometres

FIGURE 6

Australian Coal Geo logy 4, part 1

G.M. MEYER

the southern lobe. These correspond to areas where the aquifer lying directly below the lignite has a high salinity (up to 14,000mg/1) and the high sodium content In the lignite Is thought to be caused by upwards migration of these waters. Very Iow sod I um va I ues were recorded In the south, where the sub11 gn I te aquifer sal lnlty Is lowest, but were also low In the northern lobe where the aquifer sal lnlty Is high (over 14,000mg/1). In the latter case there may be no migration of fluids through the lignite or the migration may be In the downward direction from the low salinity overburden aquifer. Su I phur content Is norma 11 y between 2.8% and 3.0% (dry bas Is) wIth an Increase In average sulphur content In each lobe from south to north. However In detail the sulphur content Is erratic. The lignite has a high llptlnlte content w1th seam averages ranging from 12 to 19% and a low Jnertlnlte content with seam averages ranging from 1 to 3%. GEOLOGY

Stratigraphy The Kingston Lignite Deposit lies within formations of Tertiary overlying a basement of Cambrian Kanmantoo Group phyl I ltes and calc-sl I Jcates and Is overlain by a thick sequence of Quaternary sediments. The deposit occurs In a localized basement depression bounded to the west by Ordovician granites and to the east by Cambrian and Permlan rocks. The depression occurs within a regional basement high known as the Padthaway Ridge that separates the Otway, Troubr I dge and Murray bas Ins CF I gure 5). To the east of the deposit, aero-magnetic Intensity data suggests Ordovician felslc lntruslves I le close to the surface and are covered by a thin veneer of Cambrian and Permlan rocks (Figure 6). Minor, local felslc intruslves occur under the deposit where they form structural highs I lmiting I ignite occurrence. The Tertiary sediments were deposited during a major marine transgression from the south to the north during Eocene and O11 gocene t I mes. At KI ngston the three phases of sedimentation were as fol lows (Figure 7). 1) Middle Eocene, non-marine sediments of the Dilwyn Formation and marginal marine sediments of the Nirranda Sub-group. 2) Late Eocene, marginal marine, carbonate-rich clays and sands of the Nirranda Sub-group and non-marine sediments of the Dilwyn Formation. 3) Oligocene, open-marine, polyzoal limestones and minor, un-named carbonate rich clays and sands. The Di lwyn Formation, the basal sequence of the Tertiary section, Is the only lignite-bearing unit comprising interbedded carbonaceous sands, gravels, silts and clays. It can be divided Into two main units: a lower unit of relatively clean coarse feldspathlc sands and gravels; and an upper unit of interbedded I Ignite, carbonaceous c I ays, s I Its and sands. The Iow er unit of the Di I wyn Formation was deposited by braided streams with a local source from the Ordovician felsic intrusives. The unit is a major confined aquifer.

Australian Coal Geology 4, part 1

G.M.

MEYER

In the southern part of the depos It, the upper un It of the D11 wyn Format I on has been dated as Middle Eocene near the Early-Middle Eocene boundary. Sediments were deposited In fining upward sequences that pass from coarse quartzo-feldspathl c sands to clayey slits and then Into lignites and therefore probably represent sequences deposited under fluvlal conditions. The base of the I Ignite was usually a thin clay containing fossil roots. South and north of the deposit, I Ignite seams pass laterally Into a sequence of carbonaceous clayey slits and minor sands, while to the northeast and west, seams wedge out against a basement high. Along the southeastern margin, a prominent sand channel partly acted as a natural barrier to lignite deposition and the I Ignite was also partly eroded by washouts. Blostratlgraphlc analysis of the I Ignites Indicated deposition during the Proteac[d[tes confragosus spore-po I len zone of Harris (1971). A study of plant species Indicated deposition In a subtropical rainforest environment (Wood, 1981). In the northern part of the deposit, a hiatus during most of the Middle Eocene occurred above the main lignite seam. The younger sediments above the hiatus were dated as Late Eocene. These were deposited during the Tr[or[tes magn[f[cus spore-po I I en zone of Harris (1971) and were deposited In a tidal flat or lucustrlne environment as evident by the bloturbated, uniformly laminated silty clays and silty sands. Overlying the DI lwyn Formation In the southern part of the deposit, Is the Nlrranda Sub-group. This comprises the basal Mepunga Formation and the overlying Narrawaturk Marl. The Mepunga Formation Is of Late Eocene age and In the main I Ignite bearing area consists of dark brown, carbonaceous, clayey sand and slits, with glauconlte flecks and pet lets, abundant gastropod and bivalve fossl Is and pyrite. In this area the unit forms an aqultard but to the south near the town of KI ngston SE, the Mepunga Format Ion Is represented by I nterbedded quartzose, glauconltlc gravels, and sands that form a major aquifer. (Fennel .ft± .a..L. 1976, and W11 I Iams, 1977 ). The Narrawaturk Marl Is composed of green and brown glauconltlc marls which grade downwards Into calcarenltes and clays. The Gambler Limestone overlies the Nlrranda Sub-group In the southern part of the deposit. Calcareous sediments that occur In the northern part may be remnants of the Gambler Limestone. The Gambler Limestone Is represented by a light grey to white, bound, framework limestone composed of bryozoal skeletal fragments with occasional zone of glauconltlc mlcrltlc carbonates. There Is usually an Increase In glauconlte content with depth and often pellets of glauconltlc clay and pyrite nodu I es are present near the base. The I I mes tone was depos I ted under open marine conditions but three thin calcrete layers developed In the unit represent periods of emergence. There are three main Quaternary units represented at Kingston. These are the basal Coomandook Formation and the overlying Bridgewater and Padthaway Formations. The Quaternary sequence was deposited during a period of east to west marine regression and sediments represented grade from shallow marine units at the base through beach facles to sub-aerial aeolian or back-barrier lagoonal facles at the top.

Australian Coal Geology 4, part 1

G.M. MEYER

The Coomandook Formation consists of fine grained calcareous and glauconltlc sands and muddy sands usually containing abundant bivalve and gastropod fossl Is. The sequence was deposited under shallow marine conditions. The Coomandook Formation passes upwards, transitionally Into the Bridgewater and Padthaway Formations. During the marine regression, the Bridgewater Formation was deposited as a series of beach and dune ridges representing north-south strand 11 nes. The Padthaway Format Ion was depos lted In estuar I ne, Iagoona I and Iacustr I ne env I ronments beh Ind each dune r I dge. The base of the Bridgewater Formation consists of unconsol I dated, yellow quartzose sands deposited In near shore beach environments. These grade upwards Into yellow, var I ab Ie cemented ea Icar en I tes depos I ted In aeo 11 an dunes. The Padthaw ay Formation consists of white freshwater dolomitic limestones. They vary from soft, occasionally clay rich, mlcrltlc muds to tough sf I lceous I lmestones. Over Iy Ing the major Quaternary un Its Is a th In veneer of ea Icrete, reworked dune sands and topsolls.

Structure The Kingston Lignite Deposit occurs In a trough, which over most of the length of the deposit has a steeply dipping west margin and a less steeply dipping east margin. The trough Is also deeper to the south than the north and bifurcates at a point near the town of Kingston SE before Joining the deeper part of the Otway Basin. The trough appears to continue to the north east and Joins the Murray Basin (Figure 5). The trough was formed partly by faulting and partly by erosion. Faulting Is evident on both the east and west margins particularly near Ordovician Intrusive bodies. In most cases the faulting can be seen to have occurred after the I Ignite was deposited although they could represent re-activation of older faults. It Is thought that the trough existed as a major drainage channel during early Tert I ary depos It I on. The basa I Tert I ary sequences compr I se coarse gra I ned c I ast I cs that were depos I ted on softer, I ess res I stant, metased I ments, and were not deposited on the higher level, harder felslc lntruslves that form the margin of the trough. The shape of the trough appears to be controlled by the distribution of the softer metasedlments. Downwarp of the trough continued throughout most of the Eocene and Ollgocene as evident by the restricted lateral Incursion of Gambler Limestone Into the trough, and the trough shaped structure of the base and roof of the main lignite seam. CONQUSIONS The Kingston Lignite Deposit contains a total resource of 985 mllllon tonnes of I Ignite classified as type B. The lignite Is Middle Eocene In age and was deposited In an Eocene to Ollgocene marine transgressive sequene. Ash, volatl le matter and fixed carbon contents are uniform over the deposit but sodium and sulphur are relatively variable. Sodium concentration appears to be related to both aquifer salinity and permeability of sediments associated with the lignite. Sulphur content shows a general trend Increasing to the north away from the direction of marine transgression.

Australian Coal Geology 4, part 1

100

G.M. MEYER

NIRRANOA

SUB-GROUP

Base of ~aternary

OIL WYN FORMATION

-Orn •• : :-::: : ;_;:~;.:_:;_:_:___

MBIER LIMESTONE -,-....-::,,,...::....

- -0- - - -° i , - - - 0

..::...,.._

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- -

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.·.·.· O ·.

.. o

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KINGSTON LIGNITE DEPOSIT HIATUS

Cretaceous

CJ. SAND ~ GRAVEL

DIAGRAMMATIC SECTION 0

25Km Vertlcal exaggeration 250:1

CLAY

~ CALCAREOUS UNIT

FIGURE 7

The Kingston Lignite Deposit was deposited In a loca l depression formed on a regional structural high near the northern margin of the Otway Basin. The depression Is coincident with a belt of Cambrian Kanmantoo Group metasedlments and Is bordered to the east and west by Ordovician felslc lntruslves. The depression Is thought to be a partly erosional and partly a tectonic feature. REFERENCES Fennel, R.J., & WI I I lams, A.F., 1976, Completion report and wel I test, Kingston Town Water Suply, Bore NO. 10, S.A. Dept. of Mines and Energy RB 76/38 (unpublished). Harris, W.K., 1971, Tertiary stratigraphic palynology, Otway Basin, Ch. 4.ln The Otway Basin of South East Austral la. ~.B..u..ll.....G.il2.l..a..5..w:.Y...~~.arul Y.l.tl.. WIiiiams, A.F. 1977, Groundwater resources for South East Town Water Supplies, Review No. 1 - Kingston S.A. Dept. of Mines and Energy RB 77/23 (unpublished). Wood, G., 1981, Palynologlcal analysis of Eocene coals In the Gambler embayment near Kingston. Hons. Degree Thesis. Unlv. of Adelaide (unpubl !shed).

Australian Coal Geology 4, part 1

101

Notes on the Geology of the Lignite Resources - Esperance, Western Australia R.G. Elms, R.D. Matthews, D.G. Chapman

Western Colleries Limited, 29th Floor, City Centre Tower, 44 St. George ' s Terrace, Perth, W.A. 6000, Australia.

Keywords: Lignite, tertiary, Western Australia, coal resources, Bremer Basin, Esperance, Plantagenet, Werillup.

ABSTRACT The lignite resources of the Esperance region occur within the Bremer BasiQ in the Werillup Formation of the Eocene Plantagenet Group. The Werillup Formation is a paralic unit consisting, in the area, of varicoloured clays, carbonaceous sands and clays, silty sand and lignite, which was deposited on the irregular surface of the Precambrian Shield. Near the south coast the Werillup Formation is overlain, possibly conformably by the Pallinup Siltstone. In the recent phase of exp 1oration, severa 1 1ignite occurrences have been 1ocated, the 1argest of whi eh appears to occur in a buried pre-Upper Eocene drainage channe 1 whi eh has a north-south trend. The southern end of this deposit extends northerly for a known distance of 35 km, with a variable width of up to 7 km, an average thickness of 10m, and cover of 30m. The upper surface of the 1ignite exhibits gentle dips, while the base conforms in general terms to the basement topography . Drilling of this deposit has delineated shallow open-cut reserves in excess of 600 Mt in-situ. The lignite is a low energy fuel, with high ash and salt contents. Utilisation testing is being undertaken. INTRODUCTION The 1ignite deposits so far delineated by Western Collieries Ltd. 1ie within the Esperance 1:250,000 map sheet SI/51-6 . The deposits extend northerly from a point approximately 45 km north of Esperance. (Figure 1) Exploration title to the main deposit is held by Western Collieries Ltd. (WCL), while title elsewhere is held jointly by Western Collieries Ltd. and Makey Pty. Ltd .

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102

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The potential of these lignite deposits is enhanced by the proximity of the Norseman-Esperance road and standard gauge railway, which are both some 7 km to the west at the closest point (Figure 2) and the town of Esperance, which has a population of some 7,000 people. EXPLORATION HISTORY WCL interest in the possibility that economic lignite deposits might occur within the Tertiary sequence north of Esperance began in November 1979, when the Kumarl area, some 55 km north of Grass Patch was inspected as a result of very high ash, peaty lignite being found in Main Roads Department water bores drilled in 1977 (Loxton, 1978, p.36). In December 1979, Ministerial Temporary Reserve 7393H was created, excluding the region north of latitude 33 degrees South, including the Kumarl area, from exploration activity . However, subsequent study of available data, primarily geological literature and maps, air photos and sate 11 i te imagery, led to the Scaddan/Grass Patch area being selected for a scout drilling programme which was carried out in April, 1980. Ten of the sixteen holes drilled intersected carbonaceous sediments or lignite. Follow-up drilling was carried out in June and July 1980 and as the deposit began to be outlined, acquisition of coal mining leases (C.M.L. 's) began .

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Concurrently with these activities, joint venture discussions were held with Mokey Pty. Ltd. who had been granted large tenement areas to the east of Grass Patch . Once agreement was reached, a regional assessment was made, primarily utilising airborne geophysics (5,300 line km) and reconnaissance reverse circulation drilling (24,461m) . Some 1,340 km of access roads and drilling grids were bulldozed up to June 1982, when most of the original Mokey tenements were relinquished. Although lignite was found in a number of locations, the main find in this regional program occurred some 7 km east of the first deposit. Diamond drilling of the first deposit to date has outlined 607 million tonnes of lignite in-situ, of which 547 million are in the measured category. Overburden thickness averages about 30m and the lignite about 10m. Reserves should be amenable to surface mining. Drilling statistics to date on Temporary Reserves are 754 holes drilled, totalling 24,461m and on Coal Mining Leases 457 holes drilled, totalling 17,521m. REGIONAL GEOLOGY Away from the dissected coastal region, whi eh extends 20-40 km inland, the

land rises gently northward at a slope of less than 15 minutes. There are no we 11 defined va 11 eys, and a 11 drainage is internal into numerous east-west elongated salt lakes. On this plateau, the Ravensthorpe Ramp (Cope 1975, p. 40), there are rare outcrops of Precambrian granite, migmatite and gneiss. The physiographic lows between these basement highs have been infilled with Tertiary sediments. Unconformably overlying both the Tertiary and the Precambrian, is a thin bed of Pl ei stocene to Recent sediments that varies in thickness; it may locally exceed 10m but is typically 2-3m thick. These sediments are predominantly fine wind blown sands with subordinate clays, gypsiferous lake sediments, calcrete and silcrete. (Morgan and Peers, 1973). Within the Tertiary sequence, which is not exposed within the region, drilling has proven a series of facies types whose relative stratigraphic positions can be inferred (Figure 3). The basal unit, which varies in thickness from zero to more than 20m, is an unlithified, poorly sorted, medium to coarse, fluvial sand. Within this bed there are thin (0.5 - 20cm) clay horizons, abundant wood fragments and pyrite nodules. This basal sand may be overlain by any of the successive Tertiary units, depending on location . The lignite or equivalent carbonaceous clay which forms the next unit in the succession, is presumed to have been formed in a terrestrial environment . Palynological dates from the main lignite body give an age of Late Middle to Upper Eocene (B. Ingram and L. Milne, pers. comm.). This lignitic unit may be replaced in some localities by a dark green glauconitic, spiculitic (sponge) clay. The presence of glauconite and marine fossils clearly indicates a complex series of marine transgressions into the different areas of deposition. No dating has been concluded on these clays but they appear to be stratigraphically equivalent to the lignites although, in some instances, the glauconitic clay overlies the lignitic unit. The top unit in the Tertiary sequence is a fine, medium grained, moderately well sorted sand, alternating to silt and clay. It varies in thickness up to 40m. Australian Coal Geology 4, Part 1

104

R. G. Elms, R.D . Matthews, D. G. Chapman

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ESPE RANCE LIGNITE DEPOS IT s

Scale I=250000 ; Pion No 283

Australi an Coal Geology 4, Part 1

R.G. Elms, R.D . Matthews, D.G. Chapman

105

Fine grained multicoloured tand and clay

- Occaalonal 1pong•

+ +

fonll1

SIMPLIFIED SCHEMATIC GEOLOGICAL RELATIONSHIPS WITHIN THE TERTIARY SEO.UENCE 1 ESPERANCE REGION Figure 3

To the extreme east of the region between Mt. Ragged and Balladonia, large thicknesses, more than 60m, of bioclastic limestone are developed . In some areas this limestone overlies thin, poor quality lignites and basal sands. The total Tertiary sequence may be greater than 100m in certain localities. No age determinations have been carried out on these sediments, which are assumed to be equivalent to the Eocene Wilson's Bluff and Toolina Limestones of the Eucla Group. GEOLOGY The Tertiary sequence that contains the lignite deposit occupies a shallow north-south trending depression in the Precambri an basement . The sediments have a maximum recorded thickness of 60 to 70 metres although this is reduced locally within the depression by topographic highs in the basement. The Tertiary sequence, which can be divided into a lower unit, the Werillup Formation and an upper unit, the Pallinup Siltstone (Cockbain, 1968), rests directly on the Precambrian basement (Figure 4), the first 10 metres of which has decomposed to kaol initic clays. The sedimentary units are generally unconsolidated . The lower Tertiary unit is variably carbonaceous throughout and consists, in ascending horizons, of a basal sand, lignite, clay and sand/silt. Its maximum combined thickness is approximately 40 metres. The contained lignite layer has a maximum thickness of 17 metres (average 10m) but rapid lateral increases in clay content can cause deterioration through lignitic clay to carbonaceous

Australian Coal Geology 4, Part 1

106

906d

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,. 1

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R.G. Elms, R.D. Matthews, D.G. Chapman

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Australian Coal Geology 4, Part 1

►

Ill 0

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R.G. Elms, R. D. Matthews, D.G. Chapman

107

clay locally. The lignite can al so be split horizontally by discontinuous lenses of carbonaceous clay of variable thickness . The upper portion of the lignite layer can contain one or more discontinuous, thin (less than 10cm thick) layers of silicified lignite that are well lithified. The lignite occupies a constant stratigraphic position within the unit and as all the layers are approximately horizontal, topographic highs in the basement surface are a common cause of non-deposit ion and consequent di scont i nui ty in the lignite. The lignite is dull, earthy, chocolate brown in colour and contains wood fragments, pyrite and rare globules of resin. The ratios of overburden to lignite vary throughout the deposit, the most favourable approaching 1.6:1 for thicknesses of lignite exceeding 10 metres . The upper Tertiary unit, the Pallinup Siltstone, consists of cream to light grey clay with sandy silt. A weakly ferruginized zone can be present within. A surface capping of indurated calcareous material is occasionally present. HYDROGEOLOGY Essentially unconsolidated sand aquifers overlie and underlie the lignite at a proposed sample pit site where groundwater studies have been carried out . These aquifers are fully saturated with saline groundwater whi eh is under sub-artesian pressure. The aquifers do not appear to be in hydraulic connection . Studies indicate that unless the lower aquifer is depressurised the pit fl oar wi 11 heave. Dewateri ng of the upper aquifer may al so be a necessary pre-requisite for stability of the pit walls (Layton, 1982). Within the pit area, the lower aquifer varies in thickness from O - 10m, and has an average grain size of 1mm. It is of limited areal extent, occurring predominantly within basement lows. Locally it is inhomogeneous due to lateral facies change from unconsolidated sand to clay and clayey sand. It contains groundwater with a total dissolved solids content of 136,000 mg/1. Major components in order of abundance are chlorine (73,000 mg/1), sodium (42,000 mg/1), sulphate (10,900 mg/1) and magnesium (5,000 mg/1). The natural pi ezometri c surface occurs about 40m above the top of the aquifer (1 to 2m below natural surface). At the pit site the upper aquifer is about 15m thick and has an average grain size of 0. 5mm. Local inhomogeneity results where thin lenses of clay and siliceous cemented sand occur . The contained groundwater has a total dissolved sol i ds content of 105,000 mg/1 chlorine (57 ,200 mg/1) and sodium (32,600 mg/1) are the dominant components, with magnesium and sulphate next in importance . The natural piezometric surface occurs about 12m above the top of the aquifer (2 to 3m below natural surface). PALEOGEOGRAPHY AND PALEOENVIRONMENT Not withstanding the present day southerly regional slope of the land surface, a preliminary contour map of the basement topography, i.e . stripped of sediments, shows a number of linear depressions trending north-south . Using the 'fish hook' paleodrainage principle, ·the direction of flow in these channels is northward into the Lefroy Paleoriver (van de Graff et al . 1977, p.389). The reversal of the regional slope direction to its present southerly direction can be attributed to tilting about the Jarrahwood Axis in the Tertiary (Cope 1975) .

Australian Coal Geology 4, Part 1

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108

During these tilting and epeirogenic movements at certain stages, the ancient river beds would have become temporarily level having lost their catchments to the south, with the Harrahwood Axis forming a new drainage divide to the north . This would permit a low energy environment to develop and the lignites to form in swamps along the dislocated river channels. Differing amounts of uplift and downwarping as well as different original levels of the various channels could create the situation we see in the sediments today, that is , a mixture of marine and terrestrial facies in close assoc i at i on. To the east in the Mt. Ragged area there

environment on the edge of the Eucla Basin.

is a change to a fully marine

This hypothesis wi 11 be tested by further dating st udies in hand and more detailed interpretation of the pre-Tert iary topography as information is released from other exploration areas in the region . COAL QUALITY The coal, which consists mainly of woody material, is a fairly well gelified lignite with a high ash and salt content . (See Table 1) . TABLE 1 Typical Australian Lignite Analyses WAKEFIELD (S . A. )

KINGSTON (S . A.)

LOY YANG (VIC.)

11. 9 15.9 12 . 2 1. 9 7.6

4. 6 19 . 7 15 . 7 2. 1 10. 2

5. 2 19 . 3 15 . 4 1.4 9.4

0. 7 20.6 18.9 0.2 10 . 6

57 . 7 5.3

62.4 3. 6

58.8 4.5

68.0 4.8

6. 3

2. 4

1.0

0.2

ESPERANCE PROXIMATE (60% Mo i sture base) Ash% Volatile % Fixed Carbon% Total Sulphur% Specific Energy MJ/kg ULTIMATE (Dry Ash Free Basis) Carbon% Hydrogen% MISCELLANEOUS (60% Moisture Basis) NaCl%

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The huminite group macerals typically comprise approximately 80% of the organic matter present. Densinite and attrinite are most abundant with textinite, ulminite, gel inite and corpohuminite making up some 15% of that total . The l ipt i ni te macer al group may comprise up to 10% of the organic matter . Sporinite, cutinite, resinite and suberinite occur in proportions which vary from place to place . Suberinite may comprise up to 50% of the liptinite, elsewhere sporinite and cutinite are dominant . Inertinite macerals are common but not abundant, being present predominantly as sclerotinite to 5% of the organic matter . Macrinite and fusinite have been noted. Apart from quartz and pyrite, mineral matter is difficult to identify in polished section . This mineral matter, which is believed to be clay minerals and phyllosilicates, is intimately associated with organic matter, with which it is generally interstitial (Watson, 1982). Pyrite and quartz make up 5%+ of the coal. Quartz grains are generally well rounded, 0.3 to 0.5mm in diameter, and weakly bonded to organic matter. Pyrite is rarely present as discrete grains but is included in grains of organic matter. The grain size of the pyrite is generally less than 0.1mm. UTILISATION OF ESPERANCE COAL Ten tonnes of lignite were obtained from 200mm diamond drill cores for use in a variety of investigations . These include fluid bed combustion testwork, combustion testing, and pre-treatment studies. Initial testwork into fluid bed combustion is proceeding at CSIRO, North Ryde laboratories . Encouraging results have been achieved at reduced combustion temperatures, which have minimized the problems of high alkali compound content in the lignite. Preliminary test work using pulverised fuel combustion shows that the lignite possessed high fouling/slagging characteristics, and that further evaluation is necessary using lower combustion temperatures. Pre-treatment studies to reduce the salt content have been carried out by ACIRL and Westcoll Resea rch Laboratories using water washing and thermal dewatering . Precipitability test work to investigate the electrical characteristics of fly ash produced from the combustion of Esperance lignite has been carried out by ACIRL. ENVIRONMENTAL CONSIDERATIONS An environmental reconnaissance of -the region has been carried out . result of this, three main problems have been identified . (1)

As a

The problem of soil salts and the contained salts whi eh have formed a series of salt lakes in the region .

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R.G. Elms, R.D. Matthews, D.G. Chapman

110

(2)

There is potential for wind and water erosion in loose soils and as soon as the vegetation and topsoil are removed, sand blows occur in the area.

(3)

Because of nitrogen/moisture balances in restored lands, animals in the region tend to graze selectively on them, thus creating difficulties in regeneration.

ACKNOWLEDGEMENTS The authors thank Western Collieries Ltd . for permission to publish this paper, the various staff members and consultants who have contributed to the project, and those who helped with the typing and drafting of the manuscript. REFERENCES Cockbain, A. E., 1968. The Stratigraphy of the Plantagenet Group Western Australia. West Australia Geol. Surv. Ann . Report . 1967. Cope,

R.N., 1975 . Tertiary Epeirogeny in the Southern Part of Western Australia. West. Australia Geol. Surv. Ann. Rept. 1974.

Layton Groundwater Consultants, 1982. Groundwater Dewateri ng Investigation, Scaddan Bulk Sample Pit, for Western Collieries Ltd. (Unpubl.) Loxton, I. W., 1978. Kalgoorl ie Inspectorate. Mines Ann . Rept . 1977, 34-36 .

Peat.

West. Australia Dept.

Morgan, K.H. and Peers, R. , 1973. Esperance-Mondrain Island, W.A. Australia Geol. Surv. 1:250,000 Geol. Series Explan . Notes.

West.

van de Graaff, W.J . E., Crower, R.W.A., Bunting, J . A. , 1977, Jackson, M.J . Relict Early Cainozoic Drainages in Western Australia . Z. Geomorph. N.F., 21, 397-400. Watson, B., 1982. Analysis F 4208/82 (Unpubl).

Four Brown

Coals.

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111

Latrobe Valley Brown Coal - Lithotypes: Macerals: Coal Properties A.M. George

Exploration and Geological Division, Fuel Department, State Electricity Commission of Victoria, 15 William Street, Melbourne, Victoria, 3000, Australia

Key Words: Brown Coal, Latrobe Valley, Lithotypes, Macerals, Coal Properties

ABSTRACT Thi ck brown coa 1 seams are composed of bands or beds whose chemi ea 1 and physical properties show significant variations. The 1ithotypes of these bands originate at the time of coal formation and their characteristics are determined by the prevailing environment of deposition. A classification of Latrobe Valley lithotypes is presented. Macera 1 analysis describes the mi cropetro 1ogi ea 1 nature of these coa 1s and variation in maceral content is shown to be related to lithotype. Proximate and Ultimate chemical analysis show stratigraphic variation within a seam and those variations also correlate significantly with lithotype. INTRODUCTION The State El ectri city Commission of Victoria (SECV) has been winning soft brown coal from the State's Latrobe Valley deposits since the 1920s. At the present time three open cuts - Morwell, Yallourn and Yallourn North Extension -are being operated and produced about 35 mi 11 ion tonnes a year. A fourth open cut, Loy Yang, is being developed. The bulk of the 32 million tonnes of coal dug is burnt as pulverised raw brown coal in the Commission's power stations; nearly all the remainder of about 3 million tonnes is briquetted. Extensive investigations based on the examination and analysis of open cut and bore hole samples have demonstrated that coals from different seams or from different areas in the Latrobe Valley vary in their chemical and physical nature. In addition, at any location, within a relatively small vertical thickness of a seam, where the influence of rank is minimal, certain properties of the coal also show variation. This variation is due to changes in coal type. When the brown coa 1 seams of the Latrobe Va 11 ey were exposed by open cut operations, first at Yallourn North, then at Yallourn and Morwell, it became apparent that a stratigraphic banding or bedding occurred within the thick Australian Coal Geology 4, part 1

A.M . George

112

coal seams. In faces of fresh moist coal this banding is faint, but as the coal dries out differentiation in colour, texture and weathering pattern takes place and the variations in the character of the coal become more distinct. During the long period required for the accumulat i on of sufficient plant debris to form a thick coal seam the environment of deposition will show significant changes at any given 1oca 1i ty. Variations in the preva i1 i ng botani ea 1 community, in the depth and nature of the swamp water, and in the conditions of decay and decomposition of plant material, result in the formation of coals with different characteri stics, i .e . lithotypes. The changes in the basic nature of the coal between lithotypes are best demonstrated by micropetrographic methods. Variation in the maceral composition of the coal can, in general, be related to the characteristics shown by each 1ithotype . In the moist state, i.e. coal having its full bed moisture (50-70%) physical properties tend to be related to rank and are often reliable indicators of relatively small changes in physical rank. In the dry or air dried state physical properties generally show a relationship to lithotype while the influence of rank may be secondary . The organic chemical properties of the coal dete rmined by proximate and ultimate analysis are related to lithotype although rank has an overall influence on these properties . The content of i norgani cs in 1ow ash brown coal is related to neither type nor rank and their concentrations appear to be controlled by epigenetic processes . The occurrence of minerals such as quartz and kaolinite is generally dependent on the environment of deposition, but for the Latrobe Valley lithotype classification, only changes in the properties of low ash coal are considered . THE VICTORIAN LATROBE VALLEY COAL MEASURES The coal deposits at present being explo i ted by the SECV occur in the Latrobe Valley of Victoria, some 150 km southeast of Melbourne in the vicinity of the towns of Yallourn, Morwell and Traralgon. The coal measures are composed of a sequence of Tertiary clays, silts , sands , gravels and coal seams with basalt f1 ows in the 1ower section . This sequence, up to approximately 800 m in thickness occupies the Latrobe Valley Depress i on, which is located in the western or inland portion of the Gippsland Basin (Gloe, 1975) . The coa 1 measures rest unconformab ly on Cretaceous sediments whi eh outcrop extensively to the south and southwest of the Latrobe Valley Depression . To the north, beyond a narrow band of Cretaceous, outcrops of Paleozoic rocks of the Tasman Geosyncline rise. to over 1000 m in height. The Latrobe Valley Coal Measures (Latrobe Valley Group - Abele et al. 1976) are considered to range from Eocene to Miocene in age and the generalised sequence of the main seams in the Yallourn-Morwell and Loy Yang regions is as fol 1ows : Yallourn Formation Morwell Formation

Ya 11 ou r n Seam Morwel 1 lA Seam Morwe 11 1B Seam

Traralgon Formation

Morwe 11 2 Seam Trara 1gon Seam

50-80 m 40-80 m 70-130 m Latrobe Seam - 50- 80 m 30-60 m 50-70 m

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113

The range of thickness shown against each seam relates to typical thicknesses, where the seam is near the surface in open cut or potentially economic areas. The Latrobe seam at Yallourn North Extension is extensively eroded and typically 30-50 m thick in this area. The total coal resources in the Latrobe Valley fields are estimated to be about 100,000 million tonnes, of which some 11,000 million tonnes are considered readily recoverable (Gloe, 1975) . The Latrobe Va 11 ey coals are soft brown coals with moisture ranging from 50-70%. The ash content is between 1% and 5% (dry basis) for the greater part of the coal. The general range in dry basis values for volatile matter is 45-55%, for carbon 66-69%, and for hydrogen 4.5-5.5%. Gross dry heat values vary from 25.0-29 . 0 Mj/kg, while net wet heat values range from 6.5 to 12 . 0 Mj/kg. LITHOTYPE CLASSIFICATION IN THE FIELD The International Committee for Coal Petrology (ICCP) has not yet agreed on a lithotype classification for brown coal. However, there is general agreement that such a classification should be based on macroscopic characteristics, which can be determined in open-cut faces or from large hand specimens . This principle has been followed in classifying the Latrobe Valley lithotypes (George, 1975). Because of the unstable state of brown coals during their initial period of exposure to air, the characteristics of coals ranging from those with natural moisture content to those which are in the fully air-dried state are considered. The basic factors on which lithotypes are classified in this paper are colour and texture, with degree of gel ifi cation, weathering pattern, and physi ea l properties used as supplementary characteristics (Table 1). Because of the generally low ash content ( <5% dry basis) and a lack of substantial amounts of mineral matter, the lithotypes are defined in terms of organic material only, and mineral matter is treated as an inclusion. To date, no correlation has been shown between the presence of, for example, quartz sand or iron sulphides and the nature of the organic material (i.e. the lithotype) in which it occurs . This approach is not universal and the classification used in the German Democratic Republic by Suss and Sontag (1966, 1976) includes clay, sand, calcareous minerals, and iron sulphides as basic constituents of a lithotype which influence the classification. In freshly exposed coal, with full natural moisture content (50-70%), differentiation in colour is slight or not detectable . As the coal dries out differentiation in colour takes place, and when the coal is completely air dried the colours of the lithotypes generally show a significant range, from nearly black to brown-yellow, though predominantly some shade of brown (Figures 1 and 2) . In old weathered faces the surface may be greyish. Within a lithotype the colour is not necessarily uniform, differentiation in colour between the general groundmass of the coal and wood i nclusions or large plant structures being common. It is primarily the colour of the groundmass and of the smaller plant fragments which is considered in classification.

Australian Coal Geology 4, part 1

)> C

TABLE 1

LITHOTYPE CLASSIFICATION TYPICAL CHARACTERISTICS OF AIR-DRIED COAL

LITHOTYPE

ABBR.

COLOUR

TEXTURE

GELIFICATION

WEATHERING PATTERN

PHYSICAL PROPERTIES

DARK

Dark brown to black brown.

High wood content. Often small fragments .

Gelificat ion, partic. of woody material

Cracks wide and deep. Regular pattern.

Strong, hard, high density.

Cracks wide. Some regularity of pattern.

Strength variable, hardness and density above average.

<JI

r+ ""'l

"'_. "'::,

common.

r, 0

"' C)

MEDIUMDARK

M-d

Dark brown to medium brown.

rt> 0

High to medium wood content. Often large pieces.

Some gelificati on but not extensive

MEDIUMLIGHT

M-1

Medium brown to light brown.

High to low wood content. Often well preserved .

Gelificat ion uncommon. Confined mainly to wood.

Cracks shallow. Irregular pattern.

Intermedi ate physical propertie s.

LIGHT

Light brown.

Medium to low wood content.

Gelificat ion rare.

Cracks generally fine. Random orientatio n.

Generally soft, low density.

PALE

Pale brown to yellow brown.

Wood present but

Gelificat ion very rare.

Few extensive cracks.

Soft, crumbles readily, very low density.

-0

"'r+ ""'l

f--'

NOTE

Texture:

uncommon.

Wood content includes all tissue clearly distinguis hable from the groundmas

'?> :3: C)

rt> 0 ""'l

tC rt>

A.M . George

115

FIGURE 1

Lithotype bands in a coal face, Yallourn Seam, Yallourn Open Cut. A dark lithotype zone is near the top of the face and three pale l i thotype bands in the lower half .

FIGURE 2

Yallourn Open Cut . A section of a coal face about 15 m high. the base the white sand is washed from a sand-filled crack.

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It should also be noted that there is a detectable variation in colour between seams, and that, for example, a 'medium-light' lithotype from the Yallourn seam may be s i gni fi cant ly lighter than the same l i thotype from the Latrobe seam at the Yallourn North Extension. Within each seam at a specific locality, however, the sequence from 'dark' to 'pale' is preserved . This slight shift in lithotype colours is apparently due to changes in the physical rank of the coal which are generally indicated by difference in moisture content. Texture as a general term relates to the size and shape of component particles in the coal. Specifically it concerns the relative proportion of large pieces of wood or tissue to the fine groundmass of the coal. The concept of particles in brown coal should be qualified, as some of the structures which can be distinguished both macroscopically and microscopically cannot be separated out from the general mass of the coal by simple physical or chemical methods. In some cases well preserved wood fragments can be readily separated by physically breaking up the coal, but as coalification proceeds, tissue will tend to be digested into the body of the coal, although the original structure is still apparent. In some coals, therefore, the boundary between groundmass and tissue may be indeterminate. It is convenient to consider texture on three scales which may be called 'megatexture', 'macrotexture', and 'microtexture' respectively. Megatexture is seen in open cut faces only; the groundmass fragments are less than 1 cm, and the plant structures are from 1 cm to 5 m. Macrotexture is seen in hand specimens and dri 11 cores; the groundmass fragments are less than 1 mm and the plant structures are from 1 mm to 500 mm. Microtexture is seen under a microscope at magnifications of XlO to XlOOO; groundmass fragments are less than 10 µ, and plant structures range from 10 µ to over 1000 µ. Studies confined to macro and micro-structure may be misleading, as they take no account of the large plant remains evident in the megatexture of some l i thotypes . The process of gelification in brown coal appears to have a general association with lithotype, being most pronounced in the darker lithotypes. The exact nature of the gelification process in plant tissue is not fully understood, but it is related to a breakdown and swelling of the cell walls and the formation of a gel-like substance with little or no structure . This humic gel becomes relatively hard and black in air-dried coal and shows numerous shrinkage cracks. Gel ifi cation can al so occur in the groundmass, but tends to appear first in wood tissue, or as a filling of cracks or cavities in the coal. Pure gelinite filling such spaces in the coal (dopple r ite) is rare in the Latrobe Valley coals, but one large vein, extending for over 10 mat a width of about 5 cm, has been observed at Yallourn North Extension . Where dried wood fragments can be broken to show a shiny black structureless surface, a considerable degree of gelification has occurred. Observation of weathering patterns is possible only on open cut faces or natural outcrops of coal (Figures 3, 4 and 5) . The term weathering is used here to include all the processes which affect the exposed coal, of which the most significant is evaporation of part of the coal ' s moisture content. After a period of exposure the surface layer of coal shows different weathering characteristics related to lithotype. The identification of these patterns is based mainly on the width, depth and concentration of shrinkage cracks, and the presence or lack of any orientation or regularity. Australian Coal Geology 4, part 1

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FIGURE 3

Yallourn Open Cut. A coal face showing variation in weathering pattern due to lithotype.

FIGURE 4

Morwell Open Cut. Shrinkage crack pattern in a medium-dark coal.

FIGURE 5

Australian Coal Geology 4, part 1

Morwell Open Cut. Dark lithotype above and light lithotype below.

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The behaviour of the coal on drying out in open cut faces is affected by the rate of evaporation, the shrinkage characteristics, and the rate of diffusion of moisture which is itself related to the porosity and permeability of the coal. The weathered open cut face represents a relatively thin zone, which lies between the air and the body of the seam with its full natural moisture content. The rate of diffusion of moisture through the different l i thotypes is, therefore, of particular significance when considering the characteristics of the coal exposed in open cut faces. Based on a number of tests, Edwards (1947) concluded that the rate of diffusion in what he called 'earthy' coal (m-1 and Lt) was greater than in 'l i gnit i c' coal (dk and M-d). As the light coal dries on an exposed surface, some of the moisture is replaced by diffusion from the interior of the seam. This assists in reducing the rate of drying out and the consequent shrinkage. In the case of dark coal the rate of diffusion is less, and therefore the drying out is more rapid. Further, the greater development of cracks in this coal also assists drying, as a larger surface area is exposed to the air. However, tests on sma 11 blocks of coal carried out in the laboratory showed that, in addition, coals have different shrinkage characteristics, which are not influenced by the large-scale diffusion of water considered by Edwards. Simple physical properties which can be assessed in the field are the strength, hardness, and density of the partially dried coal. Strength is used here in its general sense and can be estimated by breaking up a specimen of coal by hand, or if necessary, with a geological hammer . Needle hardness and density are measured accurately on selected samples in the laboratory, but a useful estimation of hardness and density can be made in the field. Detailed work on brown coal lithotypes (Allardice et al. 1978 and Higgins et al. 1980) has demonstrated that the relatively simple and superficial characteristics which are discussed in the foregoing are in general satisfactory indicators of the variations in chemical composition, maceral content, and physical properties which are related to lithotypes occurring within brown coal seams. Some more specific comments on the parameters of Table 1 follow: COLOUR Dark Lithotype (Dk) From black to dark brown (dark brown-grey in old weathered faces); rarely an even black, but may contain highly gelified black wood fragments; very dark zones are usually associated with high gelification. Medium-dark Lithotype (Md) From dark brown to medium brown; greater differentiation between groundmass and wood than in Dk, the wood tending to be darker than the groundmass. Medium-Light Lithotype (M-1) Range relatively large - dark brown to light brown - but mostly medium brown; contrast between wood most marked of all lithotypes, the wood often standing out clearly from the lighter groundmass.

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Light Lithotype (Lt) . Typically light brown; more uniform than M-d or M-1 lithotypes. Pale Lithotype (Pa) Bands generally thin (10-50 cm, nowhere more than 100 cm); pale brown to yellow-brown (Yal lourn Open Cut and Morwel l Open Cut), pale to light brown (Yallourn North Extension Open Cut). TEXTURE Dark Lithotype (Dk) Wood content high; though mostly <25 cm, large pieces may be present; some localised tendency to parallel alignment of fragments leading to lamination detectable in dried coal. Medium-dark Lithotype (M-d) Wood content medium to high (rather less than in Dk) but larger pieces (>25 cm); parallel alignment lacking; wood more distinct from the groundmass than in Dk. Medium light Lithotype (M-1) Wood content very variable; present.

large pieces (>50 cm) or tree stumps may be

Light Lithotype (Lt) Wood content generally low. Pale Lithotype (Pa) Wood uncommon, and fragments generally <25 cm in length. Note that the term 'wood' in Table 1 and in this section includes all plant tissues and structures distinguishable from the groundmass and longer than 1 cm. The terms 'low' , 'medium' , and 'high' may be taken to indicate apparent percentages by volume of the following order: Low

0 - 10%

Medium

10 - 20%

High

20 - 30%

GELIFICATION Dark Lithotype (Dk) Advanced gelification commonly groundmass generally occurs .

found

in wood;

partial

Australian Coal Geology 4, part 1

gelification of

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120

Medium-dark Lithotype (M-d) Woods with low to high gelification common; may occur.

slight gelification of groundmass

Medium-light Lithotype (M-1) Light Lithotype (Lt) Pale Lithotype (Pa) Wood showing partial gelification may be present; groundmass rare.

significant gelification of

WEATHERING PATTERN Dark Lithotype (Dk) The most prominent pattern of shrinkage cracks; major cracks 25-40 cm apart, 0. 5-3.0 cm wide at surface, 30-45 cm deep, often forming a roughly rectangular or polygonal pattern; secondary cracks 5-10 cm apart; tertiary 1-3 cm apart; when surface is fully dried, small hard roughly cubic fragments bounded by cracks readily break away from the surface. Medium-dark Lithotype (M-d) Some deep cracks but generally irregular; depth and widt h very variable. Medium-light Lithotype (M-1) Cracking moderate; no deep cracks. Light Lithotype (Lt) Cracking slight; random orientation . Pale Lithotype (Pa) Little cracking; dried coal tends to crumble or flake rather than crack. NOTE:

At Yallourn North Extension deep regular cracking is less evident than at Yallourn Open Cut or Morwell Open Cut in spite of severe shrinkage in the Dk lithotype . This is believed to be related to the lower moisture content at Yallourn North Extension .

PHYSICAL PROPERTIES: IN THE FIELD Dark Lithotype (Dk) Strongest and hardest; difficult to break by hand or to dig from the face with the geological hammer; density highest. Pale Lithotype (Pa) Weakest; easily b~oken, often friable; density lowest. Other types intermediate. Australian Coal Geology 4, part 1

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PHYSICAL PROPERTIES - LABORATORY MEASUREMENTS In general, the identification and classification of lithotypes is necessary prior to the results of laboratory tests being available . Tests which allow for a more accurate determination of lithotype are Colour: Dry Coal (Colour Index) Brown coal colour is measured on a finely ground (<300 µ) sample of dry coal using a Hunter Lab Colourmeter. From this instrument three values are obtained, i.e . 'L' (white-black), 'a' (yellow-blue) and 'b' (red-green) and these are combined together numerically to produce a colour index which represents the relative colour of the sample. For coals of the same rank the higher the colour index the lighter the colour, i.e . light brown-yellow brown, while the lower the colour index the darker the colour, i.e. dark brown-black brown . The size distribution of the material tested is critical and only samples prepared by exactly the same method can be compared in absolute terms. Specific Gravity and Density : Dry Coal (g/cm 3 ) The specific gravity and density of dry brown coal is influenced by lithotype with dark lithotype coal having higher values than the light lithotype. Values for air dried specific gravity generally range from 0.70 to 1.00. Needle Hardness: Dry Coal (kg/mm 2 ) The needle hardness instrument employed is based on the principle of a fixed depth of penetration of a standard needle and variation in the weight or force required to achieve that penetration. For air dried coal needle hardness tends to have high values for dark l ithotype coal and relatively low values for light lithotype coal of the same rank. Shrinkage(% Volume) Soft brown coal shows a significant reduction in volume (20-60%) as it changes from the bed moist state to an air dried, or oven dried state. The amount of this shrinkage is related to l ithotype and dark l ithotype coal has a high shrinkage while light coal has a relatively low shrinkage . Shrinkage can be measured on a block of coal or on granular material. Porosity : Dry Coal (% Volume) Porosity is a fundamental structural property of brown coal . It is calculated from helium (true) and mercury (apparent) densities of dry granular coal. Porosity values are low for dark lithotype coal and relatively high for light l i thotype coal . MICROPETROLOGICAL ANALYSIS The changes in the nature of the coal related to lithotype can be demonstrated at the microscopic level . Examination of coal at magnifications ranging from X50 to X600 shows that its physical characteristics vary from one lithotype to another . In order to quantify this variation macer al analyses have been carried out following the brown coal maceral classification set up by the International Committee for Coal Petrology. Australian Coal Geology 4, part 1

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A.M . George

For maceral analysis the coal is air dried and crushed to pass through a sieve with 3. 7 mm mesh to provide material with a grain size range of 0.2 to 2.0 mm (60% being 0.6-1.0 mm). The coal grains are then mounted in a block of polyester resin about 25 x 25 x 20 mm in size and a vertical face of this block is ground and polished . Maceral analysis is carried out using the point count system. For the SECV's investigations 500 points are counted in reflected light and 500 points are counted in fluorescent light. In fluorescent light, the Lipt i ni te macer al s are counted, as only macera ls of this group fluoresce strongly, while in reflected light the Huminite and Inertinite group macerals are counted. The two counts are then combined to produce a composite analysis based on reflected and fluorescent light results . This method is not as satisfactory as counting only one set of 500 points and viewing each point in both reflected and fluorescent light but the time involved in changing from one light system to the other at each point is considered to be too great for this method to be practical when a large number of samples are to be analysed. Table 2 sets out the results of maceral analysis of five brown coal samples from the Yallourn Seam, Yallourn Open Cut, selected to demonstrate the range of l ithotypes present. The mac era ls shown in the table do not provide a comprehensive list for brown coal, but include all macerals which commonly occur in significant concentrations in the Latrobe Valley seams. The summary of the analysis results included in the table under the heading Maceral Groups gives some indication of the overall trends involved. In general , humodetri ni te tends to increase from the dark to light lit ho type. The pale lithotype is composed mainly of detrinitic material but a considerable proportion is formed of liptinite . The concentration of humotelinite is significant in determining the lithotype of the coal . Normally, humotelinite has high values for the dark and medium-dark coals, and these decrease through to the pale coal, which has low values . Humocollini t e also shows a similar trend, with higher values at the dark end of the series, but the concentration of this group is not always a satisfactory guide to lithotype. Liptinite values increase from the dark to the pale lithotype, and the concentration of liptinite macerals is important as their chemical composition varies significantly from that of the huminite macerals . Inertinite is unreliable as a guide to l i thotype, as the two main macer al s concerned are different in nature, and their occurrence is not related . When the inertinite is mainly composed of sclerotinite, which is common ly the case, the values will tend to increase slightly from the dark to the pale lithotype. The characteristics of the lithotypes, in terms of Maceral Groups, can be summarised as follows . The dark and medium dark lithotypes have high humotelinite and relatively high humocollinite concentrations, while their liptinite and humodetrinite values tend to be low. In contrast, the light and pale lithotypes have low concentrations of humotelinite and humocollinite, and they are characterised by high values for liptinite, and humodetrinite. The Huminite maceral grouping of the ICCP classification is, however, not satisfactory for lithotype determination by micropetrology. The degree of gelification in a coal is an important ind i cator of lithotype, and evidence of gelification is shown by macerals belonging to the three Huminite groups. A gelification index may be employed which i s based on the combined concentration of the most significant macerals, as follows: Densinite + Eu-Ulminite + Levigelinite + ~ Phlobaphinite (Pseudophlobaphinite)

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TABLE 2

123

MACERAL ANALYSIS YALLOURN SEAM, YALLOURN OPEN CUT

LITHOTYPE

M-d

M-1

53.5 32.0 9.5 2.6 2.4

59.7 23.6 11.9 3.7 1.1

65.7 16.8 8.1 7.8 1. 2 0.4

70.9 10.3 6.7 10.5 1. 6

63.5 7.3 1.9 23.7 2.9 0.7

100.0

MACERAL GROUPS 1 2 3 4 5 6

Humodetrin ite Humotelinit e Humocollin ite Liptinite Inertinite Minerals

MACERALS 1

Attrinite Densinite

32.2 21.3

51.1 8.6

64.5 1. 2

70.9

63.5

Textinite Texto-Ulmi nite Eu-Ulminite

1. 2 14.6 16.2

3.2 16.4 4.0

2.1 12.9 1.8

0.7 7.8 1.8

1.5 5.3 0.5

Telogelinit e Detrogelin ite Eugelinite Porigelinit e Phlobaphin ite

4.1 1.1

1.2

1.4 0.2

0.2

0.8 5.7

1.2 5.3

0.7 1.2

1. 7 1.1

2.0 0.4 1.6 1.8 2.0

3,3 1.0 0.2 3.2 2.8

7.8 0.3 2.1 12.1

0.7

0.6

1.0

2.4

0.2 0.2

0.6

0.5

4.3

Sporinite Cutinite Resinite Suberinite Liptodetrin ite

0.6 1.6 0.4

Sclerotinit e Fusinite Semifusinit e Inertodetri nite

1.3 0.7 0.4

0.2 1.0 9.5 0.4 0.5

Minerals

0.4 100.0

100.0

Australian Coal Geology 4, part 1

l.li

0.7 100.0

100.0

A.M. George

124

Using this combined figure as an index the values shown in Table 2 give the results Dk 44. 7%; M-d 18.7%; M-1 8.2%; Lt 4.6%; Pa 1.1%. This demonstrates a progression in gelification from the pale to the dark coal, which is significant for lithotype determination, and is also relevant to utilisation properties such as briquettability. In order to accurately determine the nature of the coal it is necessary to examine the individual maceral values. However, for an estimate of lithotype the maceral classes shown in Table 3 can be used. Here, eight macerals or maceral associations are listed, whose concentrations are related to the changes in the nature of the coal which are referred to lithotype. The macerals textinite, porigelinite and inertodetrinite are not included in Table 3 as their occurrence related to l i thotype is uncertain. The Humodetri ni te Group is separated into attrinite and ensinite. Densinite is gelified groundmass and indicates the degree of gelification of the coal. Significant concentrations of this maceral are generally confined to the dark and mediumdark coals. Ulminite, levigelinite and corpohuminite follow generally similar trends related to lithotype. However, sufficient variations occur to justify separation of these groups.

MACERALS AND MACERA!.. ASSOCIATIONS INFLUENCED BY LITHOTYPE : RANGE OF VALUES

TABLE 3

LITHOTYPE At;trinite

M-d

M-1

25-55

40-60

50-70

55-75

60-75

Densinite

5-40

1-15

0-5

0-3

0-2

Ulminite

20-35

15-30

10-25

5-20

3-10

Levigelinite

2-10

1-5

0-3

0-2

0-1

Corpohuminite

2-10

5-15

5-12

4-8

1-5

Liptinite

1-4

2-6

3-10

4-15

10-25

Sclerotinite

0-1

0-2

1-2

1-4

Fusinite

0-2

0-1

NOTE:

Ulminite Levigelinite Corpohuminite Liptinite Fusinite

Texto Ultimate+ EuUlminite Telogelinite + Detrogelinite + Eugelinite Phlobaphinite + Pseudophlobaphenite Liptinite Group Fusinite + Semifusinite

Inertinite is generally a minor constituent of Latrobe Valley coal (1-3%), but the macerals sclerotinite and fusinite are of value as indicators of lithotype. The concentration of these two macerals should be considered separately as they have different and unrelated or1g1ns. Sclerotinite is commonly present in all lithotypes, with maximum values in pale coal, while fusinite occurs sporadically in the coal, and its occurrence is mainly confined to the dark and medium-dark lithotypes. Australian Coal Geology 4, part 1

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125

In Table 3 the typical range of values is shown for each maceral or maceral association against coal lithotype . The range overlap, but the overall trends can be clearly seen. An exact definition of l ithotype based on maceral content is not proposed here, although there is sufficient data for a meaningful classification to be established . Rather than set up a microscopic classification which can only be verified at the laboratory stage, maceral analysis is used to provide detailed quantitative information which should confirm lithotype variation. If maceral analysis indicates that the initial determination of lithotype is incorrect, the macroscopic evidence is re-examined and a new lithotype may be allocated to the coal sampled. LITHOTYPE AND CHEMICAL COMPOSITION Li thotype influences certain chemi ea l properties of the coal. These can be grouped as the organic coal properties determined by proximate and ultimate analysis . The elements carbon, hydrogen and oxygen whi eh form the basis of the coal structure can be considered as immobile and therefore variations in their concentration at the time of deposition wi 11 be perpetuated in the developing coal seam . On the other hand, the elements termed inorganics such as iron, sodium, ea l ci um and magnesium tend to be mobile and it is probable that their distribution in the coal is governed by epigenetic processes. Minerals may be either primary (syngenetic) being incorporate with the plant material at the time of deposition, as is generally the case with quartz, or they may be secondary (epigenetic) being formed in the coal after the initial peat forming period as is the case with marcasite-pyrite. An extensive series of chemical analyses of lithotype samples has shown that variations in the organic coal properties - volatiles, carbon, hydrogen; oxygen and specific energy - are related to lithotype, while the concentration of the inorganics is generally independent of the lithotype sequence. Mineral occurrence also shows little relationship to lithotypes which are classfied on the basis of the organic material of the coal only . Table 4 sets out average lithotype values for organic coal properties derived from three suites of samples. These originate from the Yallourn and Morwell open cuts and from Bore LY1280 located in the Loy Yang open cut area. No typical dark lithotype was present in the sequence analysed from bore LY1280. Volatiles, carbon and hydrogen all show a trend increasing from the dark lithotype to the pale lithotype . For volatiles the range is about 10%, for carbon, some 2 to 3% and for hydrogen 1.5 to 2. 0%. For these properties the dark and medium-dark lithotypes show small differences for the Yallourn-Morwell open cut samples and this is due to a lack of very dark lithotype material which constitutes the dark end member of the lithotype sequence . Oxygen determined by difference generally decreases from the dark and medium-dark to the pale lithotype having a range of 3-5%. As ultimate analysis is a closed system with carbon, hydrogen, oxygen, organic sulphur, and nitrogen adding to 100, increases in carbon and hydrogen values tend to result in a decrease in oxygen values . Specific energy gross dry can be considered an organic coal property and follows a trend increasing from the dark to the pale lithotype through a range of 2.00 to 3.00 Mj/kg. For the Yallourn open cut samples tested, the values for the dark, medium-dark and medium-light lithotypes are virtually the _same but subsequent investigations show that this is not typical. Australian Coal Geology 4, part 1

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126

TABLE 4 LITHOTYPE

1 Dk

CHEMICAL COMPOSITION OF LITHOTYPES ASH DRY BASIS

ORGANIC COAL PROPERTIES DRY ASH FREE BASIS VOLATILES

CARBON

HYDROGEN

OXYGEN

SP ENERGY* MJ./kg

68.0

4.7

26.4

26.36

26.1

26.48 26.27

YALLOURN OPEN CUT (26 SAMPLES) 0.9

50.6

M-d

0.9

50.4

68 . 3

4.7

M-1

0.8

51.3

68.0

4.8

26.3

1. 2

56.6

69.3

5.5

24.2

27.78

70.7

6.5

21.9

29.26

1.1

63.4

MORWELL OPEN CUT (35 SAMPLES)

3.1

48.1

69.3

4.8

25.0

26.89

M-d

3.2

48.6

68.6

4. 7

25.8

26.50

24.2

27.45

M-1

3.7

51.0

69.8

5. 1

3.8

54.4

70.5

5. 4

23.2

28.08

4.4

57.4

70.9

6.0

22.2

29.03

BORE LY1280 (26 SAMPLES)

M-d M-1

1.9

49.3

66.9

4.5

27.4

25.50

0.6

52 . 6

68.9

4.8

25.5

26.52 27.45 28.54

1.0

55.0

69.5

5.3

24.5

1.0

58.5

70.7

5.8

22.7

* Specific Energy Gross Dry Table 5 shows the statistical relationship between lithotype and organic coal properties for 66 open cut samples and 60 bore hole samples . In general it can be seen that the correlation co-efficient is more than +0 . 6 and that significant correlation can be established in all cases . The relationship of colour to the organic coal properties is also shown in Table 5. Colour is a good indicator of lithotype and has the advantage that

Australian Coal Geology 4, part 1

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127

numerical values are obtained for each sample whereas lithotype classification requires a grouping which is to some extent arbitrary. Figures 6 and 7 depict this relationship graphically for a sequence from Bore LY1280. TABLE 5 : RELATIONSHIP OF CHEMICAL PROPERTIES TO LITHOTYPE AND COLOUR CORRELATION COEFFICIENTS Location

MOC

LY1280

LY1276

M2276

Seam

Depth m

0-94.5

77.0100.2

42.454.8

47.475.0

No Samples

Lithotype x Volatiles

-0. 725

-0. 748

r -0.865

r -0.759

x Hydrogen

-0.667

-0.760

-0.802

-0.734

Colour

x Oxygen

0.504

0.686

0.678

0.766

x Sp Energy GD

-0. 511

-0.700

-0.734

-0.753

x Volatiles

0.815

0.877

0.948

0.848

x Hydrogen

0.640

0.899

0.884

0.830

x Oxygen

-0.388

-0.836

-0.770

-0. 871

x Sp Energy GD

0.453

0.843

0.830

0.860

P < 0.05

0.242

0.388

0.514

0.497

P < 0.01

0.315

0.496

0.641

0.623

Significant Values

NOTE: MOC

Morwell Open Cut

Morwell I Seam

Yallourn Seam

Sp Energy GD= Specific Energy Gross Dry

In considering the relationship between coal type and the organic coal properties the influence of rank must also be taken into account. For type, it is the relative values for coals of similar rank which are significant, while to determine the influence of rank either the same lithotype or an average of a 11 l i thotypes must be compared. With increasing geochemi ea l rank carbon and specific energy tend to increase while volatiles and oxygen tend to decrease. Australian Coal Geology 4, part 1

N (X)

DtPTH METRES

DCPTH M(TRtS

)> C: 1/l

-s

"' ::, "'

ro 0 -s <O ro

M•I

••

~'"

M• I i uw

r,1Lt

~~ .'~

'< .l>, -c

"'-s r+

25 SPECIFIC

Cdm l f s

180

VOLATILE

160

11.0 120 INOEX--

MATTER (¼dmill

ENERGY

MJ / kg (gross dm ifl---

dt)' m1n~ral L lno,9anlu

tru}

,..,

:::;iin""s°"o,---t;,-=~:::---:1~2"0--1~4"'0--""160""'°--,1~eo INOEX-64

CARBON •;. ldmi ll - --

HYDROGEN ¼ (dmil J { d mlt • dry minual L lno,gon iu

,,~~ )

FIGURE 6 : Loy Yang Bore No 1280

FIGURE 7 : Loy Yang Bore No 1280

showing the relationship of colour,

volatiles and specific energy.

carbon and hydrogen.

A.M. George

129

CONCLUSION In order to understand the variation in the characteristics of soft brown coal within an extensive fie 1d or deposit such as the Latrobe Va 11 ey, it is necessary for the 1i thotypes present to be defined so that the influence of coal type can be isolated . When comparing coals which occur in basically different geo 1ogi ea 1 environments the effect of rank changes on the organic composition and character of the coal will tend to be dominant. However, when mining and utilising coal from a deposit with a narrow rank range, variations in the organic coal properti es are s i gnifica~tly influenced by coal type . Brown coal lithotypes can generally be identified by examination of extensive open cut faces or , with less certainty , by examination of large bore cores or large hand samples . Certain measured physical properties, particularly Microscopic examination and colour, give a valuable guide to lithotype. analysis is probably the most sati sfactory method for describing the physical changes in the coa 1 observed with 1 i thotype . The organic chemi ea 1 coa 1 properties are significantly influenced by lithotype and may in turn be used as coal type indicators . The practical implications of variation in the physical and organic chemical properties of the coal are important. The heat value of the coal both dry and moist is related to lithotype. The hardness and wood content of the coal is associated with lithotype and these factors influence the size of the milled product, which in turn affects the combustion efficiency of the coal . Briquette strength is influenced by lithotype and although all Yallourn Open Cut coa 1 wi 11 briquette the strength varies. The 1 i thotype of the coa 1 forming briquettes is critical for the quality of the char produced from them. ACKNOWLEDGEMENTS The author wishes to thank the State Electricity Commission of Victoria for permission to publish this paper. Some of the data presented in this paper were derived from the Victorian Brown Coa 1 Counci 1 study, No. P75/l; the approva 1 of the Counci 1 to present this information is gratefully acknowledged . Staff from the Exploration and Geological Division of Fuel Department and from the Coal Science Section of the Herman Laboratory of the SEC made significant contributions . REFERENCES Abe l e, C. et al., 1976. Gi pps l and Bas in , Tert i ary , Chapter 8; Geology of Victo r ra:--Ed. Douglas, J . G. and Ferguson, J.A . Geol . Soc . Aust. Special Publ i cation No . 5. Allardice, D. J ., George A. M. , King, T.N . W. and Kiss, L. T. , 1978. The Properties of Brown Coals f r om the Latrobe Valley . Victoria. State Electricity Commission . Research and Development Department Report No. 357. Edwards, A.M . , 1957. Coal types in the Yallourn and Latrobe Brown Coal Seams. Proc . Aust. I . M. M. , No . 147.

Australian Coal Geology 4, part 1

130

A.M. George

George, A.M., 1975. Brown coal lithotypes in the Latrobe Valley deposits. State Electricity Commission. Fuel Department. Petrological Report No. 17 . Gloe, C. S., 1975 . Latrobe Valley Coal Fields. Victoria. Economic Geology of Australia and Papua New Guinea. Vol 2, Coal. Aust. I.M. M. Monograph Series, No . 6. Higgins, R.S., Kiss, L.T., Allardice, D.J., George, A.M. and King, T.N.W., 1980 . Properties of Brown Coals from the Latrobe Valley - A basis for the Evaluation of Quality. State Electricity Commission of Victoria . Research and Development Department Report No. SC/80/17. Sontag, E. and Suss, M. , 1976. On the Macropetrographic Analysis of Soft Brown Coals. Part II : Recommendations for an International Classification System for Brown Coals. Zeitschrift fur angewandte geologie . 1976 22, (7) pp 313-319. Suss, M. and Sontag, E., 1966. On the Petrographic Nomenclature and Systematic Classification of Soft Brown Coals . Bergbautechnik, Vl6, No.4, pp 186-190, Leipzig.

Australian Coal Geology 4, part 1

131

Petrology and Inorganic Geochemistry Of South Island Lignites, New Zealand Philippa M. Black Department of Geology, University of Auckland, Private Bag, Auckland, New Zealand . Key Words:

Lignite, New Zealand, coal petrology, coal chemistry

ABSTRACT Seam composites from 17 cores drilled in the nine largest South Island lignite deposits have been analysed for organic and inorganic petrographic composition and inorganic chemical composition. Lignites from the three Central Otago fields (Miocene) were deposited in a limnic environment and tend to be petrographi ea lly more degraded having sma 11 amounts ( about 1%) of fus i ni te, and less humotelinite and xylite in comparison with the Eastern Southland lignite. The Eastern Southland lignite fields (Oligocene/Miocene), divided into a lower rank southern and a higher rank northern area, were deposited in a regressive paralic environment and therefore tend to be slightly higher in sulphur than Centra 1 Otago 1ignites. The clay mi nera 1 assemb 1age of the Centra 1 Otago lignites is dominated by kaolinite with minor illite, smectite and interlayer illite/smectite, while the Eastern Southland lignites contain a complex mixture of illite, smectite, chlorite, kaolinite and interlayer minerals. The exchangeable cation content of low ash 1ignites and clays are dominated by calcium and they have similar proportions of calcium, magnesium and sodium; clays have higher exchangeable potassium levels than lignites. The high temperature ash chemistry of lignites is determined mainly by the clay mineral assemblage except for very low ash lignites which have lime-rich ashes. INTRODUCTION An exploration programme carried out in southern New Zealand between November 1976 and May 1979 by Mines Division of the Ministry of Energy confirmed the presence of substantial lignite deposits. Mine areas with sufficient lignite at depths shallow enough for open cast mining were selected for more detailed study under the management of the Liquid Fuels Trust Board; three in Central Otago and the other six in Eastern Southland (Figure 1). This latter programme carried out during 1980-81 included seventeen fully cored holes, one in each of the three Central Otago deposits and at least two in each of the six Eastern Southland deposits; the numbers of the boreholes are also listed in Figure 1. Although the nine deposits have been shown to contain large amounts of lignite-in-ground (a range of 200-900 million tonnes in the individual deposits), the deposits are multi-seam and at this stage the amount of recoverable lignite is uncertain and little is known of the quality of the lignites. Australian Coal Geology 4, Part 1

P.M. Black

132

The samples used in this study originated from the Liquid Fuels Trust Board The samples provided were representative splits of Drilling Programme . crushed core sections (plies) and seam composites, taken after the core had been crushed to <4 mm for proximate analysis. This study investigates the petrology (organic and inorganic) of the lignites sampled by the seventeen boreholes, and the distribution of inorganic constituents between minerals and macerals. The data are believed to be r epresentative of the seams in the cores but not necessarily of the deposit as a whole .

EASTERN SOUTH LAND LIGNITE REGION

(:)

Figure 1.

•

Explorati on areas 0

E--i-3

Maj or depos i t 100 Km E----31

e-----1

Major lignite deposits in the southern part of the South Island showing the position of the mine deposits studied within the Central Otago and Eastern Southland lignite fields. Drill hole numbers are indicated together with average moisture and specific energy values for huminite-rich lignites. Australian Coal Geology 4, Part 1

P.M. Black

133

The geology of the South Island Lignite Fields is discussed by Isaac (this issue). The two major areas of interest are the Central Otago and the Eastern Southland Lignit'e Fields. CENTRAL OTAGO LIGNITES The Central Otago lignites are limnic in origin and are enclosed within fluviatile and lacustrine deposits of the Manuherikia Group (Miocene). The lignite measures were deposited and preserved in north to northeast trending block-faulted depressions. Present day contacts are in part sedimentary on basement metagreywackes or low grade schists, and in part fault contacted. At Roxburgh, the sma 11 est of the three Central Otago deposits, the lignite forms a single seam 19-79 m thick with 30-100 m cover and low in ash for the most part except near the base . To the east and southeast where the lignite measures thicken the single seam degenerates to an alternating sequence of low and high ash lignites. The single core was sited near the centre of the deposit. The two major Central Otago fields (Hawkdun and Home Hills) are both multi-seam deposits. At Hawkdun almost all the lignite is present within a 100 m interval as 8 closely spaced seams 2-18 m thick. In Home Hills there are 9 major seams, some of which are split. EASTERN SOUTHLAND LIGNITE FIELD The Gore Lignite Measures, the group of fluviodeltaic sediments which enclose the Eastern Southland lignites, were deposited during the Late Oligocene Early Miocene in a regressive paralic environment over a basement of Murihiku Group greywackes (Mesozoic). The Eastern Southland Lignite Field is bounded to the north, just north of Gore, by the Mataura River and extends south to Foveaux Strait. The Eastern Southland Lignite Field (Figure 1) can be divided into a northern area of lignite deposits of higher rank ( l ower moisture, higher specific energy) which includes Waimumu, Croydon and Mataura and a lower rank southern group of deposits (Waimatua, Ashers, Morton Mains). The reason for this rank difference is obscure as the northern and southern lignites are of a very similar age and no major fault has been detected between the two areas. In the northern higher rank area the Croydon (4 major seams) and Waimumu (8 major seams) deposits, on the northeast and southeast flanks respectively of an anticline, are bounded by major faults. The Mataura deposit contains 10 major seams in a westwards dipping sequence from an unconformable sedimentary contact with basement. No correlation has been possible with the Waimumu or Croydon seams across the faults. In the southern lower rank area the Ashers and Waimatua deposits both contain 5 major seams, show similar sequences and palynological evidence suggests they are laterally equivalent. The Morton Mains deposit, the most northern of the southern lower rank lignites contains 6 seams; to date l ithostratigraphic correlation with other deposits is not possible.

Australian Coal Geology 4, Part 1

P.M. Black

134

ORGANIC PETROLOGY Since the samples were received in a crushed state, lithotype analysis was not possible although individual grains in all composites showed a very substantial range in degree of gelification, degradation, xylite content and maceral composition. The Central Otago lignites are more degraded than the Eastern South land lignites, as evidenced by their generally higher liptinite (Figure 2) and lower humotelinite content (Figure 3), and contain notably more xylite (wood). The Central Otago lignites contain small amounts of rank fusinite, as well as semifusinite and schlerotinite, while in the Eastern Southland lignites the inertinite content is dominated by sclerotinite and semifusinite which has a lower reflectance than that of the Central Otago lignites. The reflectance of huminite is very variable ranging from 0.25% for the lower rank Eastern Southland lignites to 0.3% for the higher rank Eastern Southland and Central Otago lignites. EASTERN

0TAG0

CENTRAL

S0UTHLAN0

Hu min i te 100%

Hom• Hilts Hawkdun Ro•burg h

o b

•

Ashers

Wa imatua Morton Ma,ns Matouro Wa i mu mu Croydon

.. 8

Figure 2.

•

~ 80

· •." 0

Proportions of maceral Southland lignites.

groups

Central

Otago

and

Eastern

The Central Otago lignites show the greatest diversity in petrographic composition in particular in the Hawkdun and Home Hills cores - some sections being high in inertinite and others high in liptinite . The lower seams of the Home Hills core are extremely gelified but very porous and with open cell lumens . The Roxburgh deposit is notable for its degree of degradation and consequent high liptinite content which reflects in proximate analyses high volatile matter and specific energy values and in ultimate analyses as high hydrogen and low nitrogen (Table 1).

Australian Coal Geology 4, Part 1

P.M. Black

CENTRAL

OTAGO

EASTERN

135

SOUTH LAND

Humotelin ite

Humote li ni te 100% •

100%

• Hom• Hills o Hawkdun • Roxburgh

Ash•rs Wo i mo tuo Mo r ton Ma ins

.t.

Matoura

; ~~~;'ct~~u so

• 0

o.p ' •

·-·

•

♦

:,. o,, s o

• ♦

I\ 0

•

•o"x 0

) )0%

fi umodetrinite

Figure 3.

0 0 0

•

100o/e

Humocoll inite

Proportions of huminite group macerals in the Central Otago and Eastern Southland lignites.

The Eastern Southland lignites in general contain much more undegraded plant tissue and woody materials than the Central Otago lignites . Framboi ds and grains of pyrite are also more common and reflect the slightly higher sulphur levels of the marine-influenced Eastern Southland lignites ; silicification or pyritisation of wood also occurs. The southern lower rank Eastern Southland lignites contain slightly more wood than those in the higher rank area and megascopi ea lly they are earthy. The northern higher rank lignites are harder and microscopically more gelified but their detrital matrix is still composed of both gelified and ungelified material. INORGANIC PETROLOGY All composites and some 100 ash-rich lignite plies were examined using X-ray diffraction methods to determine the nature of the mineral matter in the lignites. The mineral assemblage of the Central Otago lignites was dominated by kaolinite with lesser amounts of illite, sm~tite, and interlayered illite/ smectHe (with a broad spacing at about 12 . 5A together with spacings in the 25-28A range) and quartz. The mineral matter i n the Eastern Southland lignites is much more diverse and assemblages are mixtures of illite, smectite , chlorite (sometimes swelling), kaolinite, interlayered illite/smectite and quartz. Calcite has been detected in some samples and feldspar (alkali plagioclase) of undoubted detrital origin has been detected in a few high-ash plies. Pyrite was the only sulphide observed in the lignites.

Australian Coal Geology 4, Part 1

P.M. Black

136

TABLE 1

COMPOSITIONS I

Oepos it

Roxburgh 24/481

SELECTED

LOW

Centra 1 Ota go Home Hills 24/569

LIGNITES

ASH

Eastern I

Hawkdun 24/649

WaioolllJ

53.2 2 .2

South 1and Ashers 24/869

Morton Mains

28/134

Croydon 28/258

49.1 3.6

40.0 3.3

40. 2 3.1

56. 5 3.1

61.0 2. 5

26.8 20 . 5 0 . 23

30 .8 25.9 0.34

31.9 24.8 0.29

22.9 17 . 5 0.30

21.4 15. 1 o. 16

24/784

Prox imate Anal,rsis* Moisture % Ash %

50.4

Volatile Matter % Fixed Carbon Sulphur

29 . 3 17.1 0 .24

25 .5

13.09

11. 73

12 .87

15.33

14 .60

10.49

9 .45

68.2 5 .9

68.6 4 .3 0.6 26. 5

68.9 5.1 0 .7 25.3

68.1 4.8 0. 7 26 .4

66 . 9 4.8 0.7 27 .6

66. 7 4.3 0. 7 28.3

66 .3 4 .2

85 11

85 12 3

86 13

92 6

86 10 3. 5

0.1 0.5 0.2 2

0.2

3 0.1 2

8 o. 5

3.2

19.1 0.18

S~ecific Energi•

MJ/Kgm Ultimate Analtsis* % Carbon % Hydrogen % Nitrogen

% Oxygen

0.6 25.3

0. 7 28.8

Petrograehic Com~sition Humini te

Liptinite Inertinite

81 17 2

Water soluble cations (lo-•gm/gm) Na

2 .5 5 0.1 0.2 0.6 o. 5 0.3 0.2 2 very low - in the 0.05 range

1 o. 5

I. 5 0.1 1.5

0.2 1.5 1

Exchangeable and Water Soluble Cations (10 •gm/gm) Na

10 1 45

90 10

Sa Sr Fe

43 65 14 15 at or below detection limit= 0.1 1.8 1.2 at or below detection 1 imit

1.5

below detection always

38.1 4.8 18.4 2.5 0.37

2 0.2 40

8 0. 5 70 16

6 0.4 70 11

0.8

0.9

I. 2

37 . 1 5. 5 17. 7 1.8 0.30 0.08

23.9 6. 7 9.1 3.8 0.66

28.9 3.8 20.2 2. 5 0.81

0.25 0.29 0.66

0.13 0. 16 0. 59

40 . 1 14.8

34 .2 5 .6

High Temeerature Ash Chemistrt* Cao MgO SiO, Al,0 3 Na,O K,O

no, ~o Fe,O, so,

(%)

23. 5 6.0 20 .8 21.1 1.3 0.59

35.3 5.3 5 .5 16.0 4. 2 0.22

19 .8 5. 7 28 . 4 19.6 I. 7 0.29

1.2 0 .2 5 11.5

0.05 0.25 14 .2

0.99 0. 29 12. 7

0.09 0 . 15 0.36 17 .4

0. 15 0.49 24.8

11.2

17. 7

7. 5

16.2

12. 9

* Data from N. Z. Coal Research Association

Australian Coal Geology 4, Part 1

137

P.M. Black

INORGANIC CHEMISTRY If one leaves aside trace elements which occur in the ppm-ppb range complexed to organic molecules in macerals or substituting for major element constituents in minerals, the inorganic constituents in lignite occur in three forms: (i)

as soluble salts and ions dissolved in pore waters

(ii)

as exchangeable cations substituting for hydrogens and oxygens of acid groups in organic materials, and

(iii)

as mineral matter dispersed through the lignite.

When the minerals in lignites are clay minerals then the inorganic constituents of the clays are both exchangeable and fixed in lattice sites. The cation exchange capacity of clays is very dependant on the nature of the clay mineral; smectites have notably high cation exchange capacities while illite and kaolinite have notably low cation exchange capacities . TABLE 2

CHEMICAL COMPOSITION OF REPRESENTATIVE CLAY-RICH LI GN !TES Eastern

Centra 1 Otago Home Hil 1s 24/519

Hawkdun 24/62 7

South land

Morton Ma i ns 24/ 739

Ashers 24/ 819

Matau ra 28/092

Croydon 28/285

59.6 1.3 25.4 5.7 0. 06 2. 3 0.6 0 .3 4.46 0.08

63.5 1. 3 24.6 4.4 0.04 1.6 0.6 0.8 2.9 0.08

63 .8 1. 1 21. l 6. 5 0 .08 1.8 1.3 1. 9 2. 7 0. 1

59 .6 1. 25 24.4 5.0 0.08 2. 1 1.3 0. 6 3.8 0. 6

2.3 2.0 3. 0 1. 8

1. 6 1. 2 1.2 0.9

1. 7 1.8 3 6.5

1. 6 1. 2 4 1.5

2 3. 5 13 8 0. 25

1. 7 2.2 25 7 0. 5

2. 8 3.8 28 6 0.8

Composition of high temperature ash (wt%) Si0 2 Ti0 2 A1 20 3 Fe 2 0 3 MnO MgO cao Na 2 0 K20 P20s

79.6 0.63 15 . l 1.8 0.04 0 .6 0.4 1. 3 1.4 0.04

61.4 1.3 27 .4 4.2 0. 05 1.6 0. 5 0. 3 3.2 0.1

Water soluble cations ( 1o-• gm/gm) Na K Ca Mg

2 1. 5 1 4

4 2.3 6 3.2

Exchangeable and Water Soluble cat i ons (10- 'gm/gm) Na K Ca Mg Sr

2.2 3. 2 10 4.3 0.25

4 6 17 6.5 0 .6

2.3 2.8 16 7.5 0.3

Australian Coal Geology 4, Part 1

138

P.M. Black

Exchangeable Cations In order to determine the nature and amount of exchangeable cations in lignites and clay bands within the lignites, 45 low ash (<6%) lignites and 20 high ash (>40%) shaley bands within the lignites were examined using the same exchange techniques . Two duplicate sets of each sample, 3 gm ground to <100 µm, were taken . One duplicate set was placed in 15 ml disti lled and deionized water and the other in 15 ml of lN ammonium acetate solution . The samples were dispersed in the solutions, redispersed every 12 hours and allowed to exchange for 48 hours. Samples were then washed out of the tubes on to thoro ughly rinsed filter paper (Watman 40) and rinsed at least 5 t i mes . The resulti ng solutions were made up to 50 ml (in case of 'water washed ' samples) and 100 ml (in case of ammonium The resulting solutions were analysed using Atomic exchanged samples). Absorption Spectrometry for sodium, potassium, calcium, magnesium, barium, strontium, iron, aluminium and the water washed samples for fluorine and chlorine using specific ion electrodes . The ammonium saturated sample which remained on the filter paper was dried at 50°C and then the whole sample plus filter paper shredded into a 100 ml beaker together with 50 ml s of deionized di st i 11 ed water and the sample-solution stirred continuously with a magnetic stirrer. 0.5 ml lOM sodium hydroxide was added and the amount of ammonium liberated measured with an ammonium selective ion electrode . The method is basically that of Busenberg and Clemency (1973). Because of the extreme solubility of sodium there is some difficulty in deciding how much of the 'water soluble' sodium in both the lignites and clays is truly from dissolved salts in pore waters and how much is being leached from exchange sites. However, the amount of eh l ori ne was low and much less than the sodium levels in the 'wash solutions' of both the clays and lignites, while in normal ground and ocean water the chlorine level is about the same as , or in excess of sodium (Drever, 1982) . This suggests that most of the sodium is being leached from the exchange sites and it was, therefore, regarded as exchangeable. The ratio and nature of the exchangeable cat ions are not the same in the lignites (Table 1) and clays (Table 2) although calc i um is the dominant cation in both . The nature and proportions of cations of sodium, potassium, calcium and magnesium vary, not only between clay and lignite but also with geographic location. In lignites, the major exchangeable cations are calcium, sodium and megnesium; potassium is minor and strontium, barium, iron and aluminium are in the ppm range or below detection (Table 1) . Plots of exchangeable cations (Figure 4) cluster into deposits. Lignites from Home Hills deposit are anomalous in their high sodium content while the othe r lignites show variations mainly in calcium/magnesium ratio wi th the Central Otago l igni t es having lower calcium/ magnesium ratios than most of the Easte r n Southland lig nites. The Eastern South land 1ignites show a genera 1 increase in ea lei um/magnesium ratio with progression up the Mataura Valley (see Figure 1). Since the clays a 1so show this trend it must be related to groundwater chemistry changes in the Mataura Valley rather than to changes in lignite rank.

Australian Coal Geology 4, Part 1

P. M. Black

CENTRAL OTAGO

139

EASTERN SOUTHLAND

½Co

•

• Hom• Hilts o Hawkdun • Rox burgh

o o •

Ashers Wo imotua Morton Ma ins Matauro Wa i mu mu Croydon

~Roxburgh

50 Hawkdun

No'----"---......__

Figure 4.

_.__

___,.~_5"""0---"-~~-~-~--50-~'---~---"----"------"Mg

Relative proportions of exchangeable calcium, sodium and magnesium in low ash lignites from Central Otago and Eastern Southland fields.

The clays have higher exchangeable potassium than the lignites, with the sodium/potassium ratio of clays usually less than unity but at most 2, while in lignites it is in excess of 5. The Central Otago clays have notably higher exchangeable sodium contents than clays from Eastern South land. In other respects the proportion of exchangeable sodium, calcium and magnesium in the clays closely coincides with that of the lignites plotted in Figure 4 except that the clays have a very slightly higher ea lei um/magnesium ratio than the lignites from the same deposit. The cation exchange capacity of the clays is generally similar to the sum of exchangeable cations but there is a substantial difference between the two values for the lignites . Although the higher cation exchange capacity for the lignites may be an indication of carboxylic acid content of the lignite, because our samples had been ground and stored in air for a period of several months before testing we would also expect oxidation effects to influence the data and we are unable to distinguish the relative proportions of primary and secondary effects on the data. High Temperature Ash Chemistry When lignite is ashed using the high temperature (>800°C) ashing procedure required by any of the standard Proximate Analysis methods a 11 exchangeable cat ions liberated when the lignite is combusted, together with any other inorganic constituents dissolved in, or precipitated from, pore solutions, are oxidised and if the coal is high in organic sulphur, may be converted to sulphate. Minerals are oxidised and dehydrated and in the process suffer a weight change . Australian Coal Geology 4, Part 1

P.M. Black

140

Major element compositions of high temperature ashes from approximately 90 lignites with less than 17% ash ,on a bed moisture basis, analysed by Coal Research Association of ijew Zealand were available as part of the Liquid Fuels Trust Board funded contract. In addition, we analysed 22 high ash (>40% ash on a bed moisture basis) lignites. All data are plotted in Figs. 6-8 and representative data for 1ow ash 1ignites and carbonaceous sha 1e bands are listed in Tables 1 and 2. The chemistry of low ash lignites is dominated by calcium oxide with minor amounts of silica and alumina . If we plot the ratios of those elements which are exchangeable in the proportions that they appear in the high temperature ashes for the 25 1ignites with 1ess than 4% ash and the 22 cl ay-ri eh bands (Figure 5) it can be seen that the calcium/magnesium ratios of the low ash 1ignites reflect the exchangeab 1e cation ratios ( cf. Figure 4) and the high sodium/potassium ratios are for Home Hills ligni t es which parallel the exchangeable sodium values . The calcium/magnesium and sodium/potassium ratios of clay bands are however dominated by non-exchangeable cations.

15 0

X O O

X ,;< xX

-l-

c lay s i•.

Figure 5.

No/K

Calcium/magnesium and sodium/potassium ratios of high temperature ashes of 25 low ash (<4%) lignites and 22 high ash (>40%) shaley lignites. Open circles are lignites from the higher rank northern Closed circles are 1 ignites from the Eastern South land fields. lower rank southern Eastern Southland field . Crosses are Central Otago lignites. Dots are clay rich lignites from all deposits . The four high sodium/potassium ratio Central Otago lignites are all from Home Hills deposit .

The "seam average" lignite ash chemistry is, however, dominated by the nature of the mineral matter . If we make the assumption t hat all alumina in the lignites occurs in clays, then there should be, and is, a linear relationship between the oxides of those elements (e. g. titanium oxide in Figure 6) whi eh occur in clays, and alumina. It is notable that whereas the line through the Australian Coal Geology 4 , Part 1

P. M. Black

141

plots of titanium oxide and alumina values in the Eastern Southland intersects the origin indicating all the titamium is held in clays, the plot of the Central Otago data reaches zero titanium oxide, at about 4% alumina.

•

•'•• •

•

X •~

xxx

=/"• X

~•

•

. •xxx

X X

xx X

! .,,,,,,,,_•• xX

,.if' o

X X

Figure 6.

Plot of titanium oxide versus alumina percentages in high temperature lignite ashes. Closed circles are lignites from Eastern Southland and crosses lignites from Central Otago deposits.

A plot of silica versus alumina (Figure 7) for all high temperature ashes shows that all Eastern Southland lignites have silica:alumina ratios of 2:1 or greater, while most Central Otago lignites have lower silica:alumina ratios. This is largely a reflection of clay mineral content as the mineral assemblage in the Central Otago lignites is dominated by kao l i ni te whi eh has a s il i ea: alumina ratio of 9:8 (in comparison with illite, 4:3; chlorite 3:2 and smectite 5:2). However, all low ash (<3. 5 ash) lignites from the Roxburgh and Home Hills cores have silica: alumina ratios below that of kaolinite (dashed line in Figure 7) indicating that some aluminium in the Central Otago lignites is present in some form other than as a silicate. Possibilities are that the aluminium could be complexed to humic material but not extractable with neutral ammonium acetate solution as has been suggested by Mi 11 er and Given (1979), or that it is present as a discrete phase - probably as a hydrated aluminate - although no lines corresponding to any aluminates were detected on X-ray diffractograms. Another element known to be able to be complexed with humic material but which does not respond to cation exchange extraction is iron. When iron occurs in silicates it occupies the same crystallographic sites as magnesium and these two elements should therefore show a regular distribution with minor variations due to differences in the proportions of clay species, when they are held dominantly in clays. The- ratio wi 11 be changed if iron occurs in another form such as pyrite or a hydroxide; the small amount of cation exchanged magnesium would not have a major effect on the ferric oxide/ magnesium oxide distribution .

Australian Coal Geology 4, Part 1

P.M. Black

142

¾ Si02 90

...

.. .: .

....

40 30 20

.. ... . .. X

Figure 7.

Plot of silica versus alumina content of high temperature lignite ashes. Closed circles are 1ignites from Eastern South land and crosses lignites from Central Otago fields. The solid line corresponding to a silica/alumina ratio of 2: 1 delimits the field of composition of Eastern Southland ashes. The dashed line represents the silica/alumina ratio of kaolinite.

Figure 8 shows a plot of ferric oxide versus magnesium oxide for high temperature ashes of lignites and ignited clay rich bands. The plot of the Central Otago samples shows a strong linear relat i onship which is to be expected since kaolinite does not contain ferric oxide or magnesium oxide and the other two clays illite and smectite have similar structures and ferric oxide and magnesium oxide levels. The Eastern Southland samples show more variation due to the more complicated clay mineral mixtures and to the presence of chlorite which when it occurs as a clay is usually iron-rich.

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¼ MgO

,,_/ 5

x, ./.'.o ~~ x

0 0

°' . 0

~ •

•

• •

~\o~ • ~-·r . ~-~

•

Figure 8.

Plot of magnesium oxide versus Fe2O3 percentages of high temperature lignite ashes. Open and closed circles are samples from the higher rank northern area and lower rank southern area respectively of the Eastern Southland lignite fields. Crosses are samples from Central Otago deposits. Dots distinguish data for high ash (>40%) clay ri eh lignite bands. Lines show trends for Central Otago and lower rank southern Eastern Southland lignites.

Some of the Eastern South land lignites have very high iron levels. Of the eleven samples with ferric oxide contents in excess of 20%, and which are all originally relatively low-ash (2.5 - 6.1% ash) lignites, only four have relatively high sulphur (>0.7%) suggesting the presence of pyrite. The other samples have low ash, low sulphur and low silica and alumina values. As examples, the two most iron-rich samples with 34% ferric oxide (from Morton Mains) were from a lignite with 2.5% ash and 0.16% s'ulphur and the ash contained 20.2% silica and 2.5% alumina while the sample with 40% alumina (from Ashers) was a lignite with 3.1% ash and 0.3% sulphur and the ash had 9% silica and 3.8% alumina . In samples such as these the iron can not exist in a silicate or sulphide structure and must occur organically bound or as a hydroxide. Since the high iron levels tend to be local and not characteristic of the seam or deposit, in contrast to aluminium, it seems more likely that the iron is present in the lignite as a hydroxide rather than complexed to the organic material. Of the other ash constituents, only oxides of phosphorus shows any noteworthy variation; it is consistently almost an order of magnitude higher in lignites from Roxburgh than it is in all the other lignite deposits. The high phosphorous in the Roxburgh deposit is, like its unusual ultimate analysis and petrographic composition, a reflection of its high level of degradation. SUMMARY It has been shown that there are fundamental differences in both organic and inorganic petrology and consequently in geochemi stry of the Eastern Southland and Central Otago lignites. These differences are a reflection of the different depositional environments, paralic versus limnic, experienced by the Eastern Southland and Central Otago lignites respectively.

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The inorganic chemistry of low ash lignites is dominated by their exchangeable cations; the nature of the exchangeab 1e cat ions is a reflection of local groundwater chemistry. The inorganic geochemistry of 'average', or what could be regarded as run-of-mine lignites, which contain some few percent or more of c 1ays, is dominated by the c 1ay mi nera 1 composition and the nature of the clays was determined by the depositional environment of the lignite. There is evidence from two of the Centra 1 Otago deposits (Roxburgh and Home Hills) that aluminium occurs either complexed to the humic material or as a discrete hydroxide phase in the lign i te as well as being held in clay minerals. Some few Eastern Southland lignites conta i n high ferric oxide which is not correlatable with high sulphur or with aluminium silicates (clays); in these lignites the iron seems most likely to occur as discrete hydroxides. ACKNOWLEDGEMENTS This study was funded by the New Zeal and Energy Research and Development Committee . Samples and some chemical data reported here originated and were I am indebted to both these provided by the Liquid Fuels Trust Board. organisations for permission to pub 1 i sh. The author has benefitted from discussions with Dr. Bruce Grigor, Chemistry Department, Auckland University and Dr. M. Isaac, New Zealand Geological Survey; both critically read an earlier draft report. REFERENCES Busenberg, E. & Clemency, C. V. , 1973. Determination of the Cat ion Exchange Capacity of Clays and Soils using an ammonia e 1ectrode. Clays and Clay Minerals, 21, 213-217 . 0rever, J. I., 1982. Jersey 388 pp .

The Geochemistry of Natural Waters .

Isaac, M., 1982 . Geology of the Southland and Otago Southern New Zealand. This volume.

Prentice Hall, New Lignite

Deposits,

Miller, R. N. & Given, P.H., 1979. A geochemical study of the inorganic constituents in some low-rank coals . E.R.D.A. Rept. FE 2494 TRI.

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Biochemical Gelification and the Nature of Some Huminite Macerals S. LI u, G.H. Tay Ior, Australian National University, Centre for Resource and Environmental Studies, P.O. Box 4, Canberra, 2600, Austra 11 a. M.

Sh I baoka,

CSIRO, Division of Fossil Fuels, P.O. Box 136, North Ryde, 2113, Austra 11 a. Key Words: Humlnlte, Biochemical gel lflcatlon, Col loldal particles, Porosity, Transmission electron microscopy. ABSTRACT BI ochem Iea I ge 11 f Icat Ion occurs dur Ing the peat and soft brown coa I stages. Transm I ss I on e I ectron mIcroscopy Is used In th Is study to reso I ve the f I ne structure and texture changes In association with biochemical gellflcatlon at the soft brown coal stage In samples from the Glppsland Basin, Victoria. The fine colloidal particles, the gels with particle sizes In the range of 50 nm to 150 nm, are found enclosed In the eel I lumens (as port gel lnlte) and cementing the detrltal humlnltlc and I lptlnltlc grains (as denslnlte). The cell walls of woody tissue show multi layered structure and frequently only the secondary and ter Iary Iayers are ge I If Ied. The ge Is f 1111 ng the ce 11 I umens are derived from enclosing eel I wal Is. The gels found In porlgel lnlte and humodetrlnlte are always associated with a large proportion of void spaces, whereas the gellfled cell walls In ulmlnlte do not exhibit obvious pore spaces with magnification up to 20,000. INTRODUCTION The two most Important processes In the format ion of humlnlte are humlflcatlon and gel lflcatton. Humtflcatlon Is usually regarded as a slow process of partial oxidation by which plant tissues are transformed Into hum le acids, aided by the activities of micro-organisms. Because oxygen Is necessary, humlflcatlon typically occurs at or near the peat surface. With the oxidative changes, Including the formation of the acidic carboxyl groups, the hum le material becomes capable of passing at least partially Into true or colloidal aqueous solution. The humlfled material may, other than for swelling, retain Its physical form or, depending on the environment and external constraints, be transported as a solution or suspension a short or long distance. Gel lflcatlon appears to be dependent upon prior humlflcatlon and the two processes are not ent I re Iy d I st I ngu Ishab Ie. Ge I If Icat Ion occurs through the desiccation of humlfled material, whether that humtfled material has remained Australian Coal Geology 4, part 1

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In sltu or whether there has been transport and red istribution of col loldal humlc matter. In the former case the gross morphology of the plant tissue Is preserved; In the latter case the gellfled material has a morphology unrelated to that of the plant material from which It derived. Thus, the transformation from textlnlte to ulmlnlte and subsequently to telocol llnlte has been ascribed to gellflcatlon of cell wall tissue In sltu. By contrast, The transformation from attrlnlte to deslnlte and subsequently to desmocol llnlte has been thought of as a process of cementing colloidal ge ls. Two stages of gel lflcatlon are recognised - biochemical and geochemical ge 11 f I cat Ion. The former occurs dur Ing the peat and soft brown coa I stages and Is governed by the original material, the facles, water and Ion supply, degree of alkal lnlty and oxidation conditions. The latter Is thought to affect al I the humlnltes at the boundary between dul I and brown coal and bright brown coal as a consequence of the raised temperature and pressure due to bur I a I. Current hypotheses on gellflcatlon are very largely based on observations made using light microscopy. Because the relevant textures and structures are only partly resolved In the light microscope, transmission electron microscopy has been used In these studies to provide the higher resolution needed to extend our understanding of the changes and the causative processes. The work reported here Is restricted to observations of soft brown coals and therefore of biochemical gellflcatlon only. We Intend to consider geochemical gel l flcatlon In a subsequent paper. TECHNIQUE AND MATERIALS The main technique used In this study was electron microscopic examination of ultra-thin section cut with diamond or glass knives, supported by reflected, transmitted and fluorescent light microscopy. All samples were of Tertiary brown coals from the Glppsland Basin, Victoria. Table 1 lists the origins and some Information on the samples. Al I specimens were air dried before Impregnation In epoxy resin; some were fixed In paraglutaraldehyde and osmium oxide prior to Impregnation to enhance the contrast and bring out fine structures, such as membranes. Many of the ultra-thin sections were stained with uranyl acetate (2% for 20 mln) or lead cl~rate (20 mln) at room temperature. All transmission electron microscopic examinations were made using a JEOL/100C Electron Microscope. OBSERVATIONS AND DISCUSSION The existence of amorphous material In peat Is well known. The formation of the amorphous material Is through humlflcatlon of plant tissue and biochemical gellflcatlon on humlfled material. In electron mlcrographs of brown coals the degradation of cell walls seems to have started with separation of walls Into fine lamellae followed by transformation Into col loldal particles with a more or less spherical outline. The col loldal particles occur In a wide range of sizes (Figure 1).

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TABLEl Sample Bore No.

Depth (m)

Llthotype

C( d.b. ) %

C(dmlf) %

Seam

69.6

Yal lourn Yel lourn Morwel I 18 Morwel I 18 Traralgon Traralgon Anglesea Field Anglesea Field

53 21 28 68 70 162

M2275 88.0-88.6 M2276 25.4-26.0 LY1278 25.4-26.0 LY1278 74.4-75.0 TB170 55.0-55.5 TB170 61.0-61.6 AN82 4.0-4.6

Light Dark Dark Light Light Dark Dark

68.6 63.4 68.1 67.8 67.1 64.7 67.7

68.3

165

AN82

12.7-13.3

Light

68.3

69.7

*M = Parish of Maryvale LY= Parish of Loy Yang TB= Parish of Tong Bong AN= Parish of Angahook

64.7

68.7 68.1 66.6 68.9

C(d.b.) = % carbon, dry bas Is C(dmlf) =%carbon, dry, mineral-free basis

(Samples and Information kindly provided by State Electricity Commission, Victoria). The porlgellnlte which fills some cell lumens (Figure 2) may have had the same origin. That Is, the porlgellnlte, rather than having been brought In solution was probably derived from the enclosing eel Is' wal Is. The finest particles which are present In porlgel lnlte, also seen In ettrlnlte and dens In I te, have s I zes rang Ing from 50 nm to 150 nm, w Ith an average s I ze of 100 nm. In denslnlte (Figure 4) which Is composed of closely cemented detr I ta I gra Ins and former ge I, there Is st 11 I a good dea I of poros I ty and fine gel particles are sometimes discernible. The biochemical gel lflcatlon of eel I wal Is, corresponding to the transformation of textlnlte to ulmlnlte, Is also well known among coal petrologists. In electron mlcrographs of brown coals the cell walls of some woody t Issue CF Igure 2) are composed of three I ayers, the compos I te mI dd I e lame I la (two primary wal Is and middle lame I la) and the two secondary eel I wal Is. The secondary eel I wal Is seen In Figure 3, which Is a high magnification view of the specimen seen also In Figure 2, ere loosened and swol fen; Figures 2 and 3 also show that the middle lame I lae retain sharp outlines and show no sign of being swollen. The middle lemellee of plant wood cells are usually most strongly llgnlfled and are therefore most resistant to degradation during humlflcatlon. Figure 5 shows how gel I fled material can either have become dispersed or remain In sltu, giving a swollen appearance of the eel I well structure. However, another textlnlte maceral examined under the transmission electron microscope (Figure 6) has thin and homogenized eel I wal Is without a mvltllayer structure. The reason for the loss of f i ne structure within cell wells Is possibly the thorough degradation of plant tissue during humlflcatlon.

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Figure 1 The degradation of cell walls seems to have started with separation of wal Is Into fine Jamel Jae fol lowed by transfor mation Into col loldal partlcles. Magnification x3300. Sample 53, Table 1. Figure 2 Porlgel llnlte and textlnlte. The porlgellnlte Is derived from the enclosing cell walls. Shown In picture are (a) composite middle lamellae (b) secondary eel I wal Is (cl areas where secondary eel I wal Is have been transformed Into galls. Magnification xl000. Holes are cutting artlfacts. Sample 53, Table 1.

Figure 3 The multi layered cell walls. The middle lamellae (a) retain sharp outlines whereas the secondary eel I wal Is (b) are loosened and swollen, part of the latter have been transformed Into porlgel lnlte. In the lower left area of the picture gels are rat her compacted and In the upper right area gels are dispersed. The paral lei I Ines are cutting artlfacts. Magnification xl0 000. Sample 53, Table 1.

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Figure 4 Denslnlte Is composed of (a) humlnltlc (b) llptlnltlc detrltal grains and Cc) cementing fine gel particles. Note the high porosity of the grain In the centre of the picture, and the fine gel particles which are discern Ible. Magnification xlO 000. Sample 28, Table 1.

Figure 5

The gel If led materlal can either have become dispersed (a) recognized as porlgelln lte or remain Jn sltu (b)glvlng a swollen appearance of the eel I wal I structure. In association there are ungellfled portions of cell walls Cc) Magnification x2000. Sample 23, Table 1.

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Figure 6 Textlnlte. The textlnlte has thin (not being swollen) and homogenized cell walls without multi-layered structure. Magnification x2000. Sample 21, Table 1.

Figure 7 Ulmlnlte with closed and partially closed cell lumens seems to have preserved partially the layered structure. The light layers could be gellfled Australian Coal Geology 4, part 1

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Sample 28, Table 1.

Figure 8 Texto-ulmlnlte and llpld rich substances fll llng cell lumens. The cell walls have swollen appearances. The cell lumens are fll led by heterogeneous, lipid rich aggregates which flouresce under blue Irradiation examined by light microscope. To the left of the picture Is a grain of eugellnlte. Magnification x3300. Sample 162, Table 1.

Figure 9 A higher magnification view of one cell lumen In Figure 8. It Is Austral Ian Coal Geology 4, part 1

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fll led by the remains and excretions of mic r o-organisms and their degradation products. Magnification x 13 000. Sample 162, Table 1. In one Instance very gel I fled ulmlnlte with partially closed and closed cell lumens (Figure 7Htwo swollen wal Is pushed together) seems to have preserved little of the layered structure. The thin light layers could be the gellfled mI dd Ie Iame I Iae. Figures 8 amd 9 are electron mlcrographs of texto-ulmlnlte which In the light microscope appeared to have gel I fled eel I walls and filled cell lumens. The ce I I I umens are f 11 I ed w Ith f I uoresc Ing I I pt In It Ic mater I a I. In e I ectron mlcrographs, such material can be seen to be extremely heterogeneous. It was probably formed by a process In which micro-organism s, such as fungi, bacteria and microscopic animals degrade cell contents and cell wal Is, In the process contributing lipid-rich substances. The remains of such organisms and their excretions, bacterial membranes and fungal hyphae, together with the degradation products are preserved as a heterogeneous aggregate. It Is clear that biochemical gel lflcatlon as Interpreted by transmission electron microscopic observation Is close ly bound up with the occurrence of fine col loldal particles - the gels. Those are found In macerals such as porlgellnlte, attrlnlte and denslnlte In both dispersed and coagulated forms. They are also found In association with swollen eel I wal Is, suggesting that the gel I fled, swollen structures observed and the f ine gel particles are products of two similar processes or even of the same process. The dispersed and coagulated gels found In porlgelln l te and humodetrlnlte are always associated with a large amount of void space, whereas the gellfled cell walls In ulmlnltes do not exhibit obvious pore spaces at least with magnifications up to 20,000. The Intl I I Ing of eel I lumens Is ascribed by coal pet rologists to chem I ea I gellflcatlon. Transmi ssion electron mi croscopic examination of brown coal macerals reveals that there are several ways In which the cell lumens of plant tissue can become Jnfllled by gels: The eel I lumen may be fl I led with material gel Jf led from surrounding 1. walls. The original eel I shape Is not changed slgnlflcantly. (Figure 2). The cell lumen may be closed when the opposite gellfled walls have been 2. pushed together. The original eel I shape Is then unrecognlzable . (Figure 7). There may have been Intl I I Ing of I lpt l nltlc material between gel I fled 3. cell walls (Figures 8 and 9). The llptlnltlc material seen under transmission electron microscope Is extremely heterogeneous. The existence of multi-layered and single-layered textlnltes Implies that the plant tissues have passed through different degrees of humlflcatlon. The highly hum I fled eel I wal Is show a homogenized structure without a swollen appearance. However the poss I b I I I ty that they are from d If ferent or I g Ina I materials should not be overlooked. ACKNOWLEDGEMENTS We are grateful to the State Electrici t y Commission of Victoria for the provision of samples and to the Research School of Biological Sciences, Australian National University fer the use of electron microscope facllltles. This work was supported In part by a grant from the National Energy Research Development and Demonstration Council. Austral Ian Coal Geology 4, part 1

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Chemistry of Victorian Brown Coals Louis T. Kiss

State Electricity Commission of Victoria, Herman Research Laboratory, Howard Street, Richmond, Victoria, 3121. Australia

ABSTRACT The methods used for the chemi ea l analysis of Victorian brown coals are reviewed and the application of special tests developed in Australia are stressed. The importance of sampling within a stratigraphic frame work is discussed. The influence of rank and type variations on the chemistry is indicated and the inter-relationships between some chemical properties are examined. The variation of chemical properties through a coal seam is i 11 ustrated and its importance in terms of evaluating the coal deposit for industrial purposes is discussed. The relevance of the chemical data for establishing meaningful coal property versus coal quality relationships is also examined. INTRODUCTION The chemical properties of Latrobe Valley brown coals have been extensively studied over the last twenty five years, indeed they are one of the best characterised coal deposits in the world. This was made possible by the development and adaptation of modern analytical methods to brown coal analysis in the 196O's pioneered jointly by the Commonwealth Scientific and Industrial Research Organisation (Durie, et al. 1963 and Sweatman et al. 1963) and the State Electricity Commission of Victoria, (Kiss, 1966)-:- As a result, the total coal analysis time was halved and the determination of the ash forming constituents directly on the coal took one sixth of the time of the conventional ash analysis. Most importantly brown coal analysis was put onto a rational basis, taking its unique properties into account and applying the newly available sensitivity of analysis methods emerging at the time. Thus a major and important advance was made from traditionally accepted methods of coal analysis which resulted in obtaining more pertinent information concerning the genesis, occurrence and use of brown coal. An understanding of the methodology used for brown coal analysis is therefore essential in understanding the chemistry of the coal. Over the last six years a concerted effort was made to extend further the knowledge of Victorian brown coals in a large project sponsored by the Victorian Brown Coal Council, VBCC (Allardice et al. 1978) and carried out by

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the SECV at their Herman Research Laboratory . The importance of this project is twofold. Firstly, by adopting a lithotype based sampling scheme it placed chemistry in a geological framework. Secondly, a wide range of chemical, physical and petrological properties were examined and related to each other. Thus a more balanced view emerged about the variability of Victorian brown coals and its implications for mining and utilisation . The understanding of the coal property - coal quality relationship has improved substantially as the result of the VBCC sponsored work. Because quality is a process dependent criterion the future utilisation of Victorian brown coals can now be based on sound coal property criteria. THE METHODOLOGY OF BROWN COAL ANALYSIS AND THE MEANING OF THE RESULTS Chemi ea l analysis is used for the characterisation of coals for utilisation purposes. Generally speaking two types of tests are applied. Empirical tests (e.g. proximate analysis) which have been derived from experience, and which can be interpreted in the light of that experience. The scientific tests have a definable meaning and the results are independent of the methods used to obtain them (e.g. ultimate analysis, specific energy, etc). Most coal analysis methods were developed for high rank (black) coals and have been adopted for low rank (brown) coals with some modification. This has the unfortunate effect that analytical techniques have not been optimised to the peculiarity of the material and this can have some serious consequences. For instance, Victorian brown coals are acidic, consequently they cannot readily contain carbonate minerals in their bed moist state. However, by applying an i nternat i ona l ly accepted test for carbonate determination one does obtain a positive result (Burns et al. 1962). Thus a totally meaningless chemical value can be obtained ingood faith by the inexperienced analyst, and may be taken seriously by the geologist/engineer interpreting the data. There are other unique characteristics of brown coal which have to be taken into account when designing meaningful analytical methods. Moisture The most important chemical measurement made on brown coals is the bed moisture content, which is also a good measure of physical rank. To geta meaningful result, the sampling and sample preparation have to be carried out simply and quickly to avoid water loss; the choice of the laboratory determination of moisture by weight loss, azeotropic distillation or direct absorption of the water evolved is of lesser importance. In this context it is important to realise that the bed moisture content of brown coal is significantly higher than its equilibrium moisture holding capacity, a This is parameter which is used to characterise higher rank coals. illustrated in Table 1 for a range of Victorian coals. Also note in the table, that for engineering purposes it is best to express moisture content on a dry coal basis. Therefore, whilst in terms of moisture, the economic value of high rank coals is best indicated by the moisture holding capacity, in the case of brown coals the bed moisture content is the critical value . Indeed, even upon exposure of brown coal seams in open cut mines, the coal retains its bed moisture content, except for a small surface layer. Ash The next important chemical parameter is the ash content of brown coal. This is an empirical test, historically based on the desire to assess the magnitude

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of the combustion residue, as the most common use for coal was (and is) in combustion processes . The ash content is also used to assess the so called "coal substance" (or organic coal) which allows the meaningful comparison of different coals. In this context the ash is used as an approximation of the mineral matter content of the coal. The tacit assumption is made of course, that the ash is derived solely from coal minerals; this is certainly not the case for brown coals where up to one third of the ash weight can be derived from organic sulphur present in the coal substance whi eh is "fixed" by the inorganic sodium, calcium and magnesium during ashing . In the case of brown coals the ash content obtained is also sensitive to the actual combustion conditions. Therefore the ash content should be regarded only as a result obtained in an empirical test and no other conclusions should be drawn from it. TABLE 1

BED MOISTURE VERSUS MOISTURE HOLDING CAPACITY FOR SELECTED VICTORIAN COALS

Coal Field (Selected Values)

Bed Moisture %

Moisture Holding Capacity % (Equilibrium Moisture) *

Dry Basis

As Received

Yallourn-Maryvale

182.4

64.2

38.4

Morwell-Narracan

154.0

60.5

38.2

Loy Yang

163.7

61.9

42 .1

Flynn

176.8

63.5

41. 2 41. 2

Yallourn North Ext

98.3

49.5

Coolungoolun

119.5

54.4

35.0

Gormandale

127.6

56.0

39.0 35.3

Gelliondale

183.3

64 .6

Stradbroke

141.4

58.4

37.1

Anglesea

87.5

46.6

32.9

Bacchus Marsh

152.9

60.4

31.2

* Determined at 97% humidity and 30°c.

Mineral and Inorganic Matter Content To explore further why the ash content is of limited value, one must consider the composition and analysis of the ash, and its relations hip to the ash forming constituents present in brown coal. In high rank coal technology, it was recognised that the ash content alone is insufficient when the use of coal is considered and the analysis and fusion temperatures of the ash were al so required to make sensible utilisation decisions. Coupled with this, the insensitivity of chemical methods available up to the mid 1950's required that the inorganic elements be "concentrated" in the ashing step so that an analysis could be performed . Thus looking at it pragmatically, the requirement for information was contained within the limitations of the tools available at the time to do the job. Australian Coal Geology 4, Part 1

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Taking into account the intent of the ash analysis the CSIRO-SECV initiative in the 1960' s recognised two things. Firstly what one really wanted to know was the chemi ea l composition of brown coal and not the composition of an ignition residue derived in an empirical test. The second point was that by judicious selection of newly emerging instrumental techniques of chemical analysis the mineral matter can be determined directly on the coal and ashing was not required to produce a concentrated sample for analysis. The combination of X-ray fluorescence and atomic absorption techniques was adopted for the task of direct elemental analysis of ash forming constituents in brown coal. This has solved the ana lyt i ea l problem, but because the analysis was carried out on the coal basis the problem of expressing results still remained. The expression of results of direct chemical analysis on Victorian brown coal was formalised by a scheme (Kiss and King, 1977 and 1979) based on dividing the mineral matter in brown coal into mineral (i.e. Minerals) and inorganic matter (i.e. Inorganics) fractions and expressing each in a way which reflects their occurrence in the coal. Mineral matter = Minerals and Inorganics The group named Minerals, which occurs as discrete particles principally of quartz, kaol inite and pyrite/marcasite is expressed in terms of chemical analysis as Minerals = Si0 2 + Ali 3 + Ti0 2 + Ki + FeS 2 This expression ignores the water of constitution of clays which is usually of negligible magnitude. The second group of ash forming elements was given the generic name Inorganics. These Inorganics are a group of dilute hydrochloric acid extractable and/or exchangeable cations and water soluble salts, expressed in terms of chemical analysis on a coal basis as Inorganics = Na+ Ca+ Mg+ Fe+ (Al) + (Si) + NaCl where Fe refers to the non-pyritic iron and (Al)(Si) to the acid soluble aluminium and silicon . This expression ignores the fact that some iron and aluminium can be present as hydroxide, which is usually of neglible magnitude. The total weight of Minerals and Inorgani cs expressed on a dry coal basis gives the best estimate of what is termed "mineral matter" in high rank coal technology. In the case of Latrobe Valley coals the Inorganics are far more important than Minerals from a utilisation point of view. Therefore a precedent was set in Victoria by analysing the ash forming material directly on the coal as one would analyse any other mineral. This information can then be used for a dual purpose. Knowing the mineral matter content allows the accurate assessment of the coal substance which is useful for comparing coals on a scientific basis. (The determination of the total weight of mineral matter using methods designed for high rank coals is not applicable to brown coals) . More importantly, through the knowledge of the chemical constitution of mineral matter it is possible to calculate and predict the composition of the ash or inorganic residue remaining under most techno l ogi ea l processes. Table 2 i 11 ustrates the comparison between mineral matter content and ash content and the successful calculation of ash content

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from mineral matter data for a number of Victorian brown coals. Table 3 illustrates the futility of predicting the quantities of ash produced in modern, pulverised fuel fired power stations from the empirical ash test results. It illustrates for Morwell and Yallourn coals the quantities of ash produced in a boil er as opposed to the ash test; and it compares the laboratory ash composition with the precipitator ash actually produced. The mineral matter composition is given as a guide; both the laboratory and precipitator ash compositions can be calculated from the composition of mineral matter by allowing for the difference in the degree of sulphation of By extending this approach the composition of inorganic the Inorgani cs. residue obtained in hydrogenation processes could also be calculated .

TABLE 2

COMPARISON OF ASH CONTENT AND MINERAL MATTER FOR SELECTED VICTORIAN COALS

Coal Field (Selected Values)

% Ash, Coal Dry Basis

% Mineral Matter,

Coal Dry Basis Determined

Calculated

Yallourn-Maryvale

2.3

2.4

1.7

Morwell-Narracan

2.4

2.6

1.5

Loy Yang

1.0

1. 1

0.8

Flynn

1.4

1.5

1.1

Yallourn North Ext

4.3

4.5

3.2

Coolungoolun

2.3

2.4

2.2

Gormandale

1. 6

1.6

1.3

Gelliondale

5.8

3.4

Stradbroke

3.9

3.6

2.0

Anglesea

3.9

3.4

2.2

Bacchus Marsh

7.4

3.5

Proximate Analysis Proximate analysis consisting of volatile matter, ash and fixed carbon (by difference) determination is an empirical test designed to classify higher rank coals according to their coking and gasifying characteristics. For low rank (brown) coals only the volatile matter has a useful meaning, because it relates to the organic coal properties, especially to the carbon and hydrogen contents of coals. Because of the high volatile matter of brown coals (often over 50%), modification is required to the test designed for examining black coals. An Australian Standard method is being drafted at present using the SECV's well established two-stage heating of brown coal as the basis for the test. The ash value obtained in this test (i.e. igniting the coal residue after devolatilisation) is always significantly lower than the ash produced from the whole brown coal (i. e. the standard empirical test). Consequently, neither the ash nor the fixed carbon value (or its ratio to volatile matter

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called 'fuel ratio') should be used as parameters for comparing brown coals. However, the volatile matter content is a very useful empirical parameter for comparing brown coals, particularly if expressed on a dry, mineral and inorganic free basis.

TABLE 3

COAL-ASH CHEMISTRY

Coal% Dry Basis

MORWELL OPEN CUT

Ash%

Laboratory

Boiler Precipitator

Minerals 0.13 0.19

6.2

8.0

0.04

1.3

1.7

Inorganics Fe

0.32

Fez03

17.6

22.7

o. 70

CaO

32.0

41.2

0.24

MgO

13.1

16.8

0.08

Na 2o

3. 6

4.6

0.04

26.1

5.0

3.1

2.6

Organic

0.25

Coal Dry Basis% - Ash

Ultimate Analysis Ultimate analysis is a scientific test and it expresses the composition of coal in percentages of carbon, hydrogen, nitrogen, sulphur, oxygen and ash (in lieu of mineral matter) regardless of their origin. After suitable corrections (e.g. forms of sulphur) have been applied, the composition of the organic carbon (i.e . corrected for carbonate, i f any), hydrogen (i.e. corrected for water), nitrogen, sulphur (i.e . corrected for sulphides and sulphates) and oxygen are obtained by difference . It should be noted that oxygen by difference can only be estimated if the mineral matter is known; using the ash va 1ue is not an acceptab 1e substitute. Carbon and hydrogen determination has changed 1itt 1e in the 1ast century, and the Liebig method

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possible to measure one of the most important coal substance dependent properties, the specific energy, rapidly, accurately and cheaply. For lower rank coals 24 MJ/kg bed moist, gross specific energy (ash free) is used as the upper boundary dividing it from higher rank coals. It should be noted that the gross dry specific energy is an excellent measure of the organic coal substance and its variation, whereas the net wet specific . energy is the best utilisation parameter for the comparison of coa 1s for industrial purposes. Trace Elements Australian low and high rank coals generally contain an order of magnitude lower concentration of trace elements than their European and American counterparts. The trace element (i . e. less than 0. 01% concentration) content of selected Latrobe Va 11 ey coals has been determined in an SECV survey and comprehensive reports are available (Bone and Schaap, 1981 a and b) on the occurrence of these elements and the methodology used for their determination, as well as their behaviour in combustion systems. CHEMICAL PROPERTIES Relationships There are a number of relationships between measured coal properties which can be used to simplify (and cheapen) the laboratory examination used in characterising brown coals. For instance, the specific energy (gross dry) of a coal can be calculated (King and Attwood, 1980) from its organic coal composition (i. e. carbon, hydrogen, etc). However, for each coal field or seam a different relationship has to be derived and the specific energy cannot be ea lcul ated with the same degree of accuracy as it can be determined by experiment. The other properties which correlate well with each other (at least in a localised situation) are volatile matter, hydrogen, carbon, oxygen and as mentioned previously, gross dry specific energy. Because the chemical properties of brown coals are influenced by both rank and type (lithotype) variations, it would be unreasonable to expect exact calculable relationships between properties when the data encompasses a range of lithotypes, several seams, different coal fields, etc. Therefore correlations between properties which are statistically significant at a high level of probability, are likely to be confined to a small sequence of adjacent samples in a seam; samples obtained from one seam in one area. However, some pairs of properties are significantly correlated in all seams and areas, and qualitative observations can be made as to how change in one property affects the other, e.g. "the higher the volatile matter the higher the hydrogen content" can be applied to a 11 brown coals without implying an exact, ea l culable relationship. Variation Within a Coal Seam The stratified layer sequence of brown coal seams has been observed for a long time. However, the understanding of the variability of the chemi ea l properties of coal has been much enhanced by the clear understanding of the dual influence of rank and type which manifests itself in a single coal property. The lithotype classification used by the SECV (George, 1982) to select samples demonstrates the variation in characteristics most strongly influenced by coal

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and its high temperat ure modifica tion (i.e. Sheffiel d method), where aonweighed (i. e. sample is burned in a closed system and the products of combusti intercarbon dioxide and water) fixed in an absorptio n train after removal ofation of fering substanc es, is used. The KJELDAHL method for the determin is method this of version updated an and 1883 in ed nitrogen was first introduc still used. The forms-of -sulphur determin ation requires separati on of mineral of and organic sulphur using well establish ed routes of selectiv e dissolut ion X-ray or y hotometr spectrop using iron compounds. Only the finishing steps fluoresc ence have been changed, replacin g the cl ass i ea l methods previous ly used.

TABLE 4

COAL-ASH CHEMISTRY

YALLOURN OPEN CUT

Coal% Dry Basis

Ash%

Laborato ry

Boiler Precipit ator

Minerals FeS2 Si02

0.19

Si02

13.8

14. 9

Al203

0.02

Al203

1.4

1.5

0.22

Fe203

22.S

24.2

0.08

CaO

8.0

8.6

0.21

MgO

24.9

26.8

0.08

Na20

7.7

8.3

0.09

S03

21. 4

17.4

1. 4

1.3

Inorgani cs

Organic

0.27

Coal Dry Basis% - Ash

Specific Energies , Gross and Net c The determin ation of gross and net specific energies (i.e. formerly calorifi nts Instrume years. few last the in change able consider e values) has undergon g designed to take advantage of microprocessors and rapid temperat ure measurin now is it Thus fold. four about analysis of rate the d increase have devices

Australi an Coal Geology 4, Part 1

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L.T. Kiss

type. The average, mixed samples taken over fixed depth interval s are useful to illustra te rank trends within a seam. DEPTH METRES 22

Lt M-1 Lt

M-1 Lt

M-1 Pa Lt Ok

M -d

76 Dk 78

M -1

M-d 80 Ok

84 M-dw 86

100 COLOUR

Fi gure 1.

25 SPECIFIC

160

140

VOLATILE 24

120 INDEX

55 MATTER (¾ dmif)

180

30 29 28 27 26 ENERGY MJ/kg (gross dmifl-- --

Variatio n with depth and 1i thotype of coa 1 properti es in Narracan Bore 3372.

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162

It is important that coal property variations are compared in a systematic fashion recognising three coherent groups of properties. Organic coal substance Bed moisture and wet specific energy Mineral and inorganic matter The variation of organic coal substance, a dry basis criterion, follows sedimentary layer sequences as established from the l ithotype logs. Thus the variations are not random but follow stratified layers of coal. Figures 1 and 2 i 11 ustrate the variation with depth and l ithotype of the organic coal substance related properties in two segments of a Narracan Bore 3372 (close to the Morwell Open Cut). The related properties are empirical tests

colour index, volatile matter

scientific tests - carbon, hydrogen, specific energy (gross dry) It is obvious that type variations affect all these property values and data available to date show that similar trends are observed in all Latrobe Valley coals (Hibbert et al. 1981) . The observation that many of the organic coal properties are 7nterdependent is of great importance when interpreting chemical results of coal analysis. It means that to establish the various organic coal layers, any one of these tests gives sufficient information and the other properties need only be determined if and when they are required for specific purposes. Of the other chemi ea l properties whi eh are part of the organic coal substance , oxygen concentration fo 11 ows an inverse pattern to carbon. Nitrogen is fairly constant in concentration and varies more with wood content than with l i thotype . The variation of organic sulphur al so appears to follow the sedimentary layer sequence, but it is not lithotype dependent (Kiss, 1981) . Considering the variation in the horizontal extent of the organic coal properties, satisfactory correlation was observed in layer sequences over a 1 km distance. This means that it is important to select natural boundaries for sampling intervals as one could observe and correlate stratigraphic sequences based on properly obtained chemical information . Thus selection of sampling interval can be just as importa nt a factor as consideration of the density of drilling in deciding exploration strategies . The variations of bed moisture and specific energy are discussed together because the dry basis specific energy is a good representation of the organic coal substance properties and the wet basis specific energy represents the as mined coal, thus allowing for an important nexus between dry and wet coal. Figure 3 shows the relationship between moisture, gross dry and net wet specific energies for a short l ithotype sequence in the Morwe 11 Open Cut (Hibbert el at. 1981). The importance of the moisture content is obvious, the net wet specTfi c energy is essentially its mirror image and the gross dry specific energy represents the variation in coal substance. It should be noted that the bed moisture content is not we 11 correlated to the l ithotype classification but a tendency for lighter coals to hol d less bed moisture than darker ones is apparent . Whatever the nat ure of the exact relationship, it is important to rea 1 i se that adjacent layers of coa 1 can have significantly different bed moisture contents; thus bed moisture, like the organic coal substance, is a layer dependent property.

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Kiss

163

DEPTH METRES

22 24

Lt M· l

M-1 Lt

M·l

Pa Lt Dk

r ,,,..,,)

M- d

I I

I {

....... 78

M -t M·d

80 Dk

82 lt w/Pa

84 M · dw

86 88

Dkw

M· d

'-- .......

.......

Coa l

Figure 2.

140

160

4·5

5·0

180

INDEX

70 68 CARBON % (dmif) - -

4. 1

120

00 COLOUR

5·5

6·0

6·3

HYDROGEN % (dmit ) - - ---

Variation with dept h and lithotype of coal properties in Narracan Bore 3372.

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164

In the discussion so far type variations were mostly considered. The superimposed gradua 1 change of rank with depth a 1so affects the organic coa 1 properties and more significantly the bed moisture content. In general, Hilt's 1aw app 1i es and organic coa 1 properties "improve" and the bed moisture content "decreases" with depth of coal. Thus the economic value of the coal increases markedly with depth. The rank effect may be observed from Figures 1 and 2 by contrasting the specific energy gross dry and carbon va 1ues in the upper and lower segments of the seam . The mineral and inorganic matter variations in the coal seam are considered together for hi stori ea 1 reasons because it is assumed that they are the material which forms the ash . However, there are good reasons why they should be separately considered· or at 1east their nature and occurrence sharply contrasted. Since minerals in brown coal occur as heterogeneous particles of quartz, pyrite and marcasite, clay, etc . , their concentration cannot be accurately inferred from bore samp 1e analysis except where "zones of i n-s i tu mineralisation" (usually silica or iron sulphide) are intercepted in the drilling. In most Victorian coals however, the bulk of the ash is not derived from the mi nera 1s present in the coa 1 , but it is "synthesised" from the Inorganics fraction and the organic sulphur present in the coal. The variation of the Inorganics constituents with lithotype is shown in Figure there is some variation in dry basis concentration of the magnesium, calcium and iron content, there are no evident concentration changes due to lithotype alone. This important conclusion, that the inorganic matter concentration is independent of lithotype, has been confirmed for all Thus for the determination of Victorian brown coals examined so far. Inorganics it is not necessary to use a l ithotype based sampling scheme . The important characteristics of the "Inorganics" group is their ability to diffuse through the water of bed moist coal and to form concentration profiles in a seam with depth. From the pract i ea 1 point of view they should be regarded as the "mobile fraction" of the ash forming constituents associated with the coa 1. As a consequence of the nature of their occurrence the Inorganics concentration can be accurately inferred from bore sample analysis. In general all coal fields can be precisely and predictably described in terms of Inorganics concentration, thus contrasting sharply the determination of Minerals. The distribution of Inorganics in brown coal strongly suggests that they are post-depositional in origin .

4 and a 1though

Variation with Coalfield Rank changes tend to dominate the variation of organic coal properties between coalfields, with lithotype sequences occurr ing in all Victorian coals . The organic sulphur content can vary significantly and up to 4% sulphur content on a dry basis can occur in some fie 1ds . Generally speaking, the hetero atoms oxygen and sulphur tend to substitute for one another and high sulphur coals have low oxygen values . As a consequence, one should not use the oxygen content alone as a guide to rank. Even slight differences in rank can give rise to significant reduction in the bed moisture content and improvement in the gross dry specific energy. As a consequence, the net wet specific energy can increase considerably and raise the commercial value of the coal.

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L. T. Kiss

LEVEL 5

M-d

Pa Lt M- 1

M-d

76 78

80 82

M-d

LEVEL 7

M-d

88 M-1

Lt M·I

M-d

LI 9

..-

Pa LEVEL 8

Figure 3.

--26--

MJ / kg GROSS

dmif

M J/kg

NET WET

MOISTURE % (a .rl

-----

Relationship between coal properties and lithotypes in a section of Morwell Open Cut .

However, the major differences between coal fields are in the magnitude and composition of Inorganics present. Although generally speaking Victorian coals are extremely low in Minerals and lnorganics content, particular combinations of inorganic elements can give rise to utilisation difficulties. For example, coal on the top layers of the Flynn field contains a high concentration of sodium chloride with virtually no other significant ash forming Australian Coal Geology 4, Part 1

L.T. Kiss

166

cations being present (e.g. calcium, magnesium, iron). Fortunately, the Inorganics concentration of the coal field can be readily and accurately determined from drilling, sampling and analysis, thus possible utilisation difficulties could be evaluated and anticipated. DEPTH MElRES

22 24

M-1

I I

I /

< ...,

M-I

', I

<'\

--'_l'

Pa Lt

-4- _ _ _

<._

Dk M· d

,, ,/

M-d

I Dk

(

( \

(....

M-dw

Dkw

M-d

LtW/ Pa

/ I

I I

M-I

(

/ /

M-d

76 78

Lt M-I

,---\

___' >

Inferior Cool Wood & S ilt Cloy . , lnf•r1or Coal Cloy

0·1

0·2

% db

0·3

0·4

0-5

SODIUM-CALCIUM - - - MAGNESIUM - IRON - - - - -

Figure 4.

Variation of Inorganic constituents with l i thotypes in Narracan Bore 3372. Australian Coal Geology 4, Part 1

L. T. Kiss

167

UTILISATION - COAL PROPERTY VERSUS QUALITY In the foregoing discussion it was shown that the chemical properties of brown coal can be accurately determined and the coal-in-the seam can be characterised in terms of properties which influence uti lisation. In the case of power generation, the essential coal property/quality factors can be divided into three groups of parameters Useable Energy Fouling and Corrosion Potential Pollution Potential Concerning the useable energy variation in the coal , all the important property variations are layer dependent (i.e. dry specific energy and moisture). Therefore major variations in useab 1e energy occur because of lithotypes and a gradual improvement with depth occurs simply because of a s 1i ght rank increase . Thus the knowledge of strati fi cation and the actua 1 position of the coal strata (in depth terms) is all important for describing the coal in useable energy terms . In the case of fouling and corrosion potential, the process of ash formation from Inorganics and organic sulphur dominates the quality parameters. Note, however, that the Inorganics are diffused through the bed moist coal and form concentration gradients with depth . The types of Inorganics are also influenced by the actual area or coalfield . On the other hand the organic sulphur is a layer dependent property. None the less the coal can be accurately described because we can distinguish between layer dependent properties and area or depth dependent properties. An accurate characterisation of the coal field allows the possibility of "time scheduling of coal qualities" during the life time of the open cut. This in turn allows the optimal design of the power station and open cut complex, taking into account the scheduled variability of coal delivered in sequence during the life time of a station. Therefore the extremely heavy capital financial burden for major power complex extensions can be optimised. None of this would be possible if the coal properties were treated as a random assemblage of chemical values, rather than chemistry viewed in its natural, geological setting . ACKNOWLEDGEMENTS The data in Tables 1 and 2 were reproduced by the permission of the VBCC. The author thanks the following friends and colleagues for their critical comments on the manuscript: R.W. Urie, R.S . Higgins, D. Allardice, D. Brockway, M. George, T. King , and D. Attwood.

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168

REFERENCES Allardice, D.J., George, A. M., King, T.N.W. and Kiss, L.T., 1978. The properties of Brown Coals from the Latrobe Valley . Results of Analysis and Tests, Victoria, State Electricity Commission, Report 357. Bone, K. and Schaap , H. A., 1981a. Trace Elements in Latrobe Valley Brown Coal State Environmental and Geochemical Implications, Victoria. Electricity Commission, Report S0/80/15 . Bone, K. and Schaap, H.A., 1981b. Elemental Mass Balance at Brown Coal-Fired Power Station, Victoria . State Electri city Commission, Report S0/81/37 . Burns, M.S., Durie, R. A. and Swaine , D.J . , 1962. The Significance of Chemical Evidence for the Presence of Carbonate Mi nera 1s in Brown Coa 1s and Lignites . Fuel 41, 373-379. Durie, R.A., Schafer, H.N.S. and Swaine, D. J . , 1963. Application of Atomic Absorption Spectrometry to Analysis of Inorgan i c Constituents in Victorian Brown Coals. CSIRO Aust., Division of Coal Research, Miscellaneous Report 178. Hibbert, W.D . , Smith, G.C. and Kiss, L.T., 1981. Variati on of Coal Properties with Lithotype - Part 1 : Morwell Ope n Cut, Victori a. State Electricity Commission, Report S0/81/32. George, A.M. , 1982. Latrobe Valley Brown Coals, Lithotypes; Properties. Aust. Coal Geol. 4 (this volume). King, T.N.W. and Attwood, D.H., 1980 . Coal Samples. Fuel 59, 602-603 .

Macerals;

Coal

Predicti ng Specifi c Energies for Brown

Kiss, L.T., 1966. X-Ray Fluorescence Determination of Brown Coal Inorganics. Analytical Chem. 38, 1931-1735. Kiss,

L. T. and King, T.N.W., 1977. The Expression of Results of Coal Analysis : The Case for Brown Coa 1s . Fue 1 56 , 340-341.

Kiss, L.T. and King, T.N.W., 1979. Report ing of Low Rank Coal Analysis - The Distinction Between Minerals and Inorganic. Fuel 58 , 547-549. Kiss,

L. T. , 1981. The Mode of Occurrence and Distribution of Inorganic Elements in Australian Brown Coals . Proc. International Conference on Coal Science E7,774-779, Dusseldorf , West Germany .

Sweatman, T.R., Norrish , K.and Durie, R. A. , 1963. An Assessment of X-Ray Fluorescence Spectrometry for the Determination of Inorganic Constituents CSIRO Aust. 1 Division of Coal Research, Miscellaneous in Brown Coals. Report 177.

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The Application of Pollen Analysis to The Elucidation of Latrobe Valley Brown Coal Depositional Environments and Stratigraphy A.P. Kershaw and I.R. Sluiter

Department of Geography, Monash University, Clayton, Victoria, 3168.

Key Words:

Australia

Pollen; tertiary; palaeoecology; stratigraphy; coal.

ABSTRACT Pollen analysis of 179 samples from two cores covering a large part of the Morwell 1B/lA coal seams revealed a great deal of variation in vegetation and envi ronmenta 1 conditions . The majority of 1 i ghter coa 1 1ithotype horizons were deposited under essentially unvegetated open water while darker 1 ithotypes formed under swamp communities containing a number of taxa re 1ated to The regional dryland present day rainforest and sclerophyll plants. vegetation was composed mainly of subtropical to cool temperate rainforest communities existing under high rainfall and probably ordered along a temperature controlled altitudinal gradient. Subtropical rainforest appears to have expanded over much of the Latrobe Valley at the beginning of deposition of the Morwe 11 1B seam and around the Morwe 11 lB/lA seam boundary though i nterseam samples from beneath the Morwell 1B seam suggest deposition within an extensive oligotrophic lake . Zonation of pollen diagrams constructed for the two cores provided the basis for detailed correlation between them and refinement of the position of the Morwell 1B/lA boundary. The position of the 01 i gocene/Miocene boundary was determined from the presence of a biostratigraphic marker species but no other indicator species began or ended their ranges within the core sequences to allow reliable estimates of coal accumulation rates . INTRODUCTION Pollen can make up a major component of the liptinite maceral group of brown coa 1s and therefore has an influence on the ut i 1i zat ion properties of this Examination of the contained pollen can also contribute to an resource. understanding of coa 1 formation and to detailing coal stratigraphy. Ecological pollen analysis seeks to determine botanical affinities for observed po 11 en taxa. From these are reconstructed vegetation communities which provide information on environmental conditions responsible for the deposition of the peat sediment precursors of coal. Stratigraphic pollen

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A.P. Kershaw and I.R. Sluiter

analysis separates pollen into distinct morphological types which can be used to establish biostratigraphies for intra-and interseam correlation. In the absence of marine organisms, pollen analysis is the only technique available for biostratigraphic studies on terrestrial sediments such as coal. This paper examines the potential of pollen analysis for the construction of stratigraphy and depositional environments of coals in the Latrobe Valley from an examination of cores taken from the Morwell lB/lA seams, approximately Late Oligocene to Early Miocene in age. Previous pollen stratigraphic study within the region has been restricted to the development of a broad pollen zonation scheme which could be correlated with that of the offshore sediments of the Gippsland Basin (Partridge, 1971; Stover and Partridge, 1973). Analyses were largely confined to the palynologically more diverse interseam sediments and l ittle attention was paid to the coal itself. Preliminary pal aeoenvi ronmenta l information has been derived from a study of the geologically younger Yallourn seam (Early to Mid-Miocene) and from some early samples prepared from the data set examined here. In the Yallourn seam ·samples, pollen variation could largely be related to coal lithotype (George, 1975) and it was suggested that the lighter coloured coals were originally deposited under open water and the darker coals under a variety of swamp communities (Luly et al. 1980) . More detailed interpretation or an assessment of the application of these reconstructions to the Latrobe Valley coals in general, was restricted by the small and stratigraphically restricted data base. The initial study of Morwell lB/lA coal considered pollen variation mainly in relation to lithotype (Sl uiter and Kershaw, 1982) and al though some support was given to the reconstructions derived from Yallourn coals, correlations between pollen and lithotype were not as strong. SAMPLING PROCEDURES AND LABORATORY METHODS The two cores for analysis were selected from those collected by the State Electricity Commission of Victoria (S.E . C.V.) and lai d out for inspection and sampling at the Ya 11 ourn North Extension core shed. Core LY 1275, 123m in length, was from the proposed Loy Yang open cut whi l e Core LY 1276, 104m in length, came from about 6 km to the east in the Flynn Field. Bulk samples of about 100 gm were taken from l ithotype horizons through the whole of the cores. 118 samples were co 11 ected from LY 1275 and 61 from LY 1276. Each sample was crushed; one cubic centimetre was extracted for pollen analysis and the remainder was used for quantitative calculation of colour value and determination of inorganic content. Colour values were calculated with the aid of a Hunter Laboratory colorimeter at the S. E. C. V. 's Herman Research Laboratory and these values are used for lithotype determination of all collected coal samples. The inorganic content of each sample is the percentage residue after igniti on of oven-dried coal in a furness at 600°C for 90 minutes. A11 samples for po 11 en analysis were treated with wet Shul tze solution and acetolysis to remove the bulk of lignin and cellulose respectively, and make the pollen clearly visible under the microscope (Luly et al. 1980). In addition, hydrofluoric acid was used to dissolve the silicainthose samples containing high proportions of inorganic matter. The residues were mounted in silicone oil (AK 2000) and pollen examined under an Olympus photomicroscope.

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171

Counts of 500 pollen grains and 200 fern spores were made on each LY 1276 and LY 1275 sample. A large number of different taxa were recorded but only a small selection are considered in this paper. CLASSIFICATION OF POLLEN SAMPLES Independent classifications of the two core sample sets were undertaken to determine pollen variation independent of stratigraphy and provide a basis for the determination of vegetation variation and its explanation . Only major taxa, which contain the bulk of variance within the data sets, are used in analysis. These taxa all have known botanical affinities so that realistic vegetation reconstructions and environmental inferences can be made from a knowledge of their present day ecology and aspects of their pollen production and dispersal. A list of these taxa, together with information on their identification status and ecology, is presented in Appendix 1, while details on the classification procedure are contained in Appendix 2. Results of Classification on Core LY 1276 Samples From the dendrogram (Figure 1) the samples are separated into two main groups. The left hand group is composed almost entirely of samples from the lighter lithotypes (pale, light and medium light) while the right hand group contains mainly darker samples (dark and medium dark, with some medium lights, but only one pale). Further subdivision, to the information level of 100, results in the formation of five clear groups. Details of these groups are shown on the pollen diagram (Figure 2). Nothofagus or Myrtaceae are the dominant pollen taxa although most other taxa are consistently represented. Nothofagus dominates the lighter lithotype groups 6-1 and 6-2 and other taxa, apart from Casuarinaceae and Myrtaceae in both groups, Lagarostrobus franklinii in 6-1, and Elaeocarpaceae in 6-2, have low values. Nothofagus is also dominant in the darkest group 6-3 but Myrtaceae increases relative to Nothofagus in 6-4 and 6-5. All darker groups have high but variable Gl ei cheni aceae and lower Casuari naceae than lighter groups. Restionaceae is high in 6-3, while Cunoniaceae (B) and Podocarpus have highest values in 6-3 and 6- 4. Most taxa vary independently through Quintinia and Cunoniaceae (A) appear to co-vary as do Myrtaceae and El aeocarpaceae except for 6-5. Average values for inorganic contents are similar and low in all groups with the exception of 6-3 which has a higher mean but contains a great deal of internal variation. Classification of Core LY 1275 Samples As in Core LY 1276, there is a high level division of samples into a left hand group dominated by the lighter lithotypes (pale to medium light) and a right hand group containing the bulk of medium dark and dark samples (Figure 3). Further subdivision results in the formation of six groups at the information content level of 100. Details of each group are shown in Figure 2. Nothofagus is by far the most abundant taxon in the groups from the left hand side of the hierarchy 5-1 to 5-3 and most other taxa, apart from Myrtaceae and Casuarinaceae, have low representation. Nothofagus decreases through 5-3 to 5-6 with concomitant increases in Myrtaceae. Group 5-4 is characterised by relatively high values of Elaeocarpaceae and Proteaceae, group 5-5 by high percentages of Casuari naceae, Proteaceae, Epacri daceae and especially Gleicheniaceae, and group 5-6 by high Elaeocarpaceae and Quintinia as well as

Australian Coal Geology 4, Part 1

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172

Myrtaceae . Again most taxa appear to vary independently except for Quintinia and Cunoni aceae (A), Dacrydi um and Phyll ocl adus, and within the first four groups, Myrtaceae and El aeocarpaceae. The di st i net ion between lighter and darker l i thotypes is not as apparent as in Core LY 1276 with the average colour value of group 5-6 being higher than that of group 5-3. All group mean inorganic contents, when basal interseam samples are excluded, fall between 1 and 2%. It is interesting that all interseam samples, which contain between 35 and 81.% inorganic matter, fall within group 5-3 which otherwise has the lowest inorganic content average. 400

350 250

....z ....zw

200

u z 0 .:::

~ 150 a:

2 ~

100

\GROUP 6 - 1~ - --

--GR0UP 6- 2 - - -- -~ -!duGHT

Figure 1.

Hierarchical classification and LY1276 samples .

t;ROUP 6- J.G.~~~fj

---<.,

!;]MEDIUM LIGHT

_I MEDIUM DARK

lithotype

Australian Coal Geology 4, Pa rt 1

l oARK

designation of

Core

A. P. Kershaw and I.R. Sluiter

tiJ

] Gleichen,aceae

] Cupressaceae

+ .. + * .. ] Phyllodadu.1 * + * +] Podocorpus + :I: l ] Dacry dium "'

~[ + :I: * ±

~[ * t + + ~[ *

:I:

♦

* •

] LagaroSlrobus franklin ii

:L,. ± f .. :I:

~[ * ~[ ±

•~ I ::

* ! ± i

± +

+ +

♦

:I:

] Quintinia

:E. + t

:~ +

t :r I

++ t t ++ t

Jt t t

++ t t ~ +

t t

+ + +

j t

J Epacridaceae :l ] Proteaceae

+ * t

•

t t

.. +~

t t

.., "' I J, w "' "' c. "' g- "'c. , ,c. a: g- ,

Figure 2.

___

t ·+ t t t 1~if !iJ

,~:r;anic content{%)

...J

Elaeocarpaceae

•E

(0 ,.._

I "'I

Casuarinaceae

'L_ PALE LI H MEDIUM LI HT MEDIUM DARK

![~ >-

Cunoniaceae (BI

J Cunoniaceae (A)

J Restionaceae

~[ ~[ ...

173

e e

" i5 " " i5

DARK Color value

"' ,.._ ~ >...J

I "'J,

e e

.., I

i "'I

"',c. g- "'g- "',c. "',c. "'ge e

" " i5 " " i5

Pollen diagram of groups derived from classification on samples from Cores LY 1276 and LY 1275. Group average percentage and one standard deviation are given for all 16 pollen taxa used in analyses where the mean exceeds 0. 3%. The means and standard deviations for group colour values and inorganic contents are also included.

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A.P. Kershaw and I . R. Sluiter

INFORMATION CONTENT

Figure 3.

Hierarchical classification and lithotype designation of Core LY 1275 samples .

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175

Comparison of Cores Apart from the presence of the interseam samples in core LY 1276, both cores cover a similar range of sediment types. Pale and light lithotypes are equally well represented, making up 21% and 25-27% of both cores respectively. However the dark l i thotype is poorly represented, forming only 2% of LY 1275 samples and 5% of LY 1276 samples. The major difference between the two cores is in the proportions of medium light and medium dark samples; LY 1275 contains 40% medium lights compared with 10% medium darks while LY 1275 has only 20% medium lights but 30% medium darks. After sample grouping, 8 of the 11 groups formed have an average col our value whi eh fa 11 s within the medium light to light lithotype range and there is no truly dark group. Group colour range is greatest in LY 1276 samples with the highest average of 154 (pale) in group 6-1 and the lowest average of 77 (medium dark) in group 6-3. Inorganic matter content of all coal samples is low, varying between 0.31% and 4.8% of dry weight. Core LY 1276 samples have a slightly higher mean than those of core LY 1275 but also contain a greater range of variation. All group averages fall between 1 and 2% except in group 6-3 which has a mean of 2.2%. Both cores contain all 16 taxa although few Cupressaceae are recorded in LY 1275. Nothofagus and Myrtaceae are clearly the most abundant taxa in both cores and show the inverse relationship expected with percentaged data. Nothofagus is dominant in those groups (6-1, 6-2, 5-1, 5-2, 5-3) which unite on the left hand side of each hierarchy, while Myrtaceae increases its representation from groups 6-3 to 6-5 and 5-4 to 5-6 on the right hand side of the hierarchies. Other taxa present within Nothofagus dominated groups tend not to vary greatly in their representation except for Lagarostrobus franklinii with its extremely high values in group 6-1. Marked variations in abundance between and within the other groups are expressed in Elaeocarpaceae, Casuarinaceae, Epacridaceae, Restionaceae, Cunoniaceae (B), and particularly Gleicheniaceae. The majority of taxa appear to vary independently but similar patterns of change do occur in Myrtaceae and Elaeocarpaceae for the most part, Quintinia and Cunoniaceae (A), and perhaps also Dacrydium and Phyllocladus. Taxa also vary in their representation between cores. Nothofagus and Casuarinaceae are generally higher in LY 1275, while Cunoniaceae (B), Lagarostrobus franklinii and Gleicheniaceae are clearly more abundant in samples from LY 1276. Intergroup Comparisons Each sample group pair was compared using the group mean abundance of the 16 taxa by option 1 of the program PERCINF (See Appendix 2). The resulting similarity matrix is shown in Figure 4. There is close correspondence between those groups (5-1, 5-2, 5-3 and 6-2) dominated by Nothofagus and containing mainly lighter coloured samples. The only lighter group excluded is group 6-1, presumably because of its very high percentage of Lagarostrobus franklinii. This group shows its greatest similarity, at a much higher information content, with group 5-2 which itself has a significant L. franklinii component. The great variability of taxon percentages between those groups on the right hand side of the hierarchies results in few close matches. Groups 5-4 and 6-4 are closest to each other and are the only ones which unite at an information content of less than 15. They both show some similarity to the 'lighter'

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groups with group 5-4 having closest correlation with group 6-2 . The relatively light l i thotype group 5-6 shows no s i mil ari ty with the lighter groups from the left hand side of the hie rarchies .

6- 1

Information Content

N -..J 0)

-<5

6- 3

lt'ttl 5- 10

6-4

ED 10- 15

6-5 5-1

~ N -..J

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(!)

..-

(!)

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LY 12 76

Figure 4.

LY 12 75

Numeri ea l comparison of groups derived from cl ass i fi cations on Cores LY 1276 and LY 1275.

CORE STRATIGRAPHY AND CORRELATION The pollen data were examined in relation to stratigraph y in order to attempt detailed correlation between the two cores and to provide stratigraph ic information which may help in the understanding of variation within the pollen data. Pollen variation within the cores is shown by fluctuation s in selected taxa on Figure 5. Nothofagus, Myrtaceae and El aeocarpaceae were chosen because they are the most common and consistentl y represented taxa and contribute greatly to pollen variations, and are re spons i ble for group formation at a high level in the classifiatio n dendrograms. The bulk of Nothofagus grains are from the form taxa N. emarcida and N. deminuta/va nsteensi i and it was decided to consider these separately . These taxa were not separated for classificati on as they cannot be related to distinct present day taxa and therefore they have no ecological significanc e . Also included on Fig. 5 are occurrences of two minor form taxa, Psilastepha nocolporite s micus and Proteacidit es stipplatus whose distribution s appear to have clear biostratigra phic value.

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A. P. Kershaw and I . R. Sluiter

1 OMSK>N

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177

10 PERCENT

CORE LY 1275

.s ~

l: 12

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11 10

9 8 7

•

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•

• 4

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Figure 5.

CORE LY 1276

Stratigraphic representation of selected taxa in cores LY 1275 and LY 1276 and correlation between the cores .

Pollen Diagram Zonation and Core Correlation The pollen diagrams from the two cores were zoned with the aid of results from the third option of PERCINF (see Appendix 2) . All 16 major taxa were used in this zonation procedure. From the best positions for zone boundaries suggested by PERCINF, those which related most closely to variations in taxa contained on the pollen diagram were selected . These resulted in the production of 11 zones in LY 1275, and 9 zones in LY 1276. These zones allowed cross-matching betwee n the two cores and a combined zonation is shown on Figure 5. Zone 1 contains the basal i nterseam samples of LY 1275 whi eh have low values for all four major taxa . Zone 2, from the base of the coal in LY 1275, is

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A.P . Kershaw and I.R. Sluiter

characterized by high El aeocarpaceae and Myrtaceae percentages and very low values of Nothofagus. The broad zone 3 is generally dominated by N. emarcida while zone 4 contains higher values of both Myrtaceae and Elaeocarpaceae and N. emarci da declines gradually through the zone. Zone 4 is the first one marked for LY 1276 though the basal few samples of this core may be more closely related to those of zone 3 in LY 1275. In zone 5 the two Nothofagus taxa are most important and have approximately equa l representation in both cores. Zone 6 contains peaks in Myrtaceae and Elaeocarpaceae and includes the last record of P. stipplatus in LY 1276. Nothofagus taxa are dominant in zone 7 which contains the last record of P. stipplatus in LY 1275 and the first appearance of P. micus in both cores . Zone 8 is clearly distinguished by high peaks of Myrtaceae and very low Nothofagus values. Zones 9 and 10 have low and high percentages of Myrtaceae respectively while zone 11, only part of which is recorded in LY 1275, achieves highest N. deminuta/ vansteenisii values in the diagram. Zone 12 has consistently high levels of N. emarcida. The Morwell 1B/lA Boundary Allardice et al. (1978) place this boundary at approximately 73m depth in LY 1276 and 45m depth in LY 1275. These depths occur in different pollen zones (zones 8 and 6 respectively) and therefore are probably not synchronous. The most likely position for this boundary from pollen evidence is between zones 7 and 8. This is just prior to a major peak in Myrtaceae, a situation mirrored at the zone 1-2 boundary. It could be that the high Myrtaceae values in subsequent zones 8 and 2 are a product of interseam influences on the coal seams. This proposed boundary is also close to the last appearance of P. stipplatus and first appearance of P. micus which give it added stratigraphic significance, and these taxa could provide a rapid and reliable means of seam identification and correlation in cores f r om other parts of the Latrobe Valley. Ages of the Core Sequences The Morwell 1B and lA seams fall within the broad Proteacidites tuberculatus pollen zone of Stover and Partridge (1973) dated from approximately 34 to 16 mi 11 ion years before present. Within this zone the first appearance of P. mi cus coincides with the 01 i gocene/Miocene boundary (about 22. 5 mi 11 ion years before present). This taxon was first recorded in the Hazelwood 1089 core just below the Morwell 1B/lA seam boundary by Partridge (1971), and this agrees closely with its first appearance in cores LY 1275 and LY 1276. The time span covered by the two cores cannot be reliably estimated as no other stratigraphic marker species begin or end their ranges within the recorded period. However, time estimates should be possible after the investigation of a third core, close to LY 1276, has been completed. This core extends from the Morwe 11 lA seam in the overlying Ya 11 ourn seam and transcends the P. tuberculatus/Triporopollenites bellus Zone boundary where a number of indicator species ranges begin or end. PALAEOGEOGRAPHIC RECONSTRUCTIONS We are now in a posit ion to try and reconstruct vegetation and environmental conditions existing during, and responsible for, the deposition of the Morwell 1B/lA coal seams.

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Vegetation/Lithotype Relationships In sample classifications (Figures 1 and 3), the major division in both cases was between lighter coals and samples containing the majority of medium darks and a 11 dark coals. Within the lighter coals the lack of great po 11 en variation within and between groups combined with low percentages for taxa such as Epacridaceae, Restionaceae and Gleicheniaceae, which have very limited pollen dispersal, suggests the absence of local vegetation and that sediment accumulated in open water. The contained pollen would have been derived from regional dry land and swamp sources. The dominance of Nothofagus in these groups, a taxon which produces large quantities of widely dispersed pollen and which tends not to occur within swamps, adds weight to this interpretation. Group 6-1 does differ from the other lighter groups in containing high levels of Lagarostrobus franklinii pollen . It is possible that this taxon did grow in otherwise open water as it is probably the most water tolerant of all 16 taxa examined, being largely restricted today to the regularly flooded river flats of south-western Tasmania. On the other hand, woody remains are seldom found in pale and light lithotypes which make up the samples of group 6-1 and it would be expected that the very durable timber of L. franklinii would have been preserved if it had been present. The very poor representation of the taxon in darker samples suggests that it was not a member of the swamp flora so that the only alternative explanation is that it became an extremely important component of the regional dry land vegetation at certain times when open water conditions prevailed in the Latrobe Valley basin. What these environmental conditions could have been is difficult to determine. Of the groups on the right-hand side of the hierarchies in Figs. 1 and 3 which contain the darker lithotype samples, only one - group 6-3 - is dominated by medium darks and darks, and can be directly compared with thelighter lithotype group to properly assess the significance of lithotype variation. The presence of local swamp vegetation is demonstrated by high values of Restionaceae and Gl ei cheni aceae and s i gni fi cant representation of Epacri daceae, a 11 of which have very restricted pollen dispersal. These taxa are not found in rainforest and indicate a s i gni fi cant scl erophyll component in the swamp vegetation. High values of Cunoniaceae (B) - a rainforest tree - suggest that this taxon al so occurred locally and that a rainforest component was al so present on the swamp . Stratigraphic Influences Groups other than group 6-3 from the right-hand side of the hierarchies vary greatly in their lithotype composition suggesting that factors other than the height of the water table are responsible for their pollen similarities. It is perhaps significant that four of these five groups (groups 6-4, 6-5, 5-5 and 5-6) have high values of Myrtaceae, considered in the previous section to be of stratigraphic importance. The majority of samples in groups 6-5, 5-5 and 5-6 are from either within or close to the 'interseam influence' zones 2 and 8 at the base of the Morwe 11 18 seam and between the Morwe 11 18 and lA seams respectively. During these phases, coal forming basins may not have been very extensive and the vegetation landscape from whi eh the po 11 en is derived could have been very different. Before further explanation can be attempted it is necessary to examine the likely composition of the catchment vegetation . Sluiter and Kershaw (1982), in their analyses on a smaller data set from the Morwell 18/lA seam, suggested the presence of three major dryland rainforest

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A.P. Kershaw and I.R. Sluiter

cool temperate, dominated by Notho f agus; warm temperate, communities: characterized by Cunoniaceae and Quintinia ; and sub-tropical dominated by Myrtaceae and Elaeocarpaceae. Such communities may have been ordered along a temperature controlled altitudinal gradient as they are today, broadly speaking, in the mountainous parts of northern New South Wales and Southern Queensland, in New Guinea and in New Zealand . Even today in Victoria, where rainforest has a very restricted distr i bution, Nothofagus is found at high altitudes to the north and south-west of the Latrobe Valley, while depauperate sub-tropical rainforest, dominated by the myrtaceous taxa Acemena and Tristania and often including Elaeocarpus, occurs relict to the south and south-east of the va 11 ey on Wilson I s Promontory and in east Gi pps land. The larger data base in this study increases support for this reconstruction. Myrtaceae and Elaeocarpaceae tend to co-vary on both the group and stratigraphic pollen diagrams (Figures 2 and 5) and in opposition to Nothofagus. Quintinia and Cunoniaceae (A) are also well correlat ed in the group diagram and their lack of variation within or between groups suggests a regional rather than a local presence . One reason for high Myrtaceae and El aeocarpaceae values during periods of restricted coal formation is that sub-tropical rainforest could expand across the floor of the Latrobe Valley and have a much greater and more local representation in the pollen rain . During times of more extensive coal formation, Nothofagus would dominate the regi ona 1 po 11 en rain because of its greater pollen production and dispersal capacity and because its occurrence at higher and presumably more exposed altitudes would facilitate wind dispersal . The high representation of some local taxa in lighter lithotypes dominated by Myrtaceae might also be explained by the restricted size of coal forming basins. Under these circumstances extensive areal development of individual 1i thotype horizons would be prevented and the closer proximity of areas of open water to swamp communities would result in great er representation within them of pollen dispersed short distances from swamp plants . Inorganic Matter Contents Swamp environments, divorced from an inorganic soil substrate, and where nutrients can be locked up in accumulating peat sediments , can have a very low nutrient status. The very low inorganic contents of all coal samples suggests that nutrients were in short supply thro ughout the period of formation of the Morwell 18 and lA coal seams at the co r e sites. It i s likely that the strong sclerophyll component within the swamp vegetati on developed in response to low nutrient levels rather than to any climatic factor. The importance of soil nutrient status in the development of sc l erophyll vegetation has been stressed elsewhere (e . g. Beadle, 1966; Specht , 1979) . Highest inorganic contents within the coal samples are concentrated in sample groups containing darker l i thotype samples. As these represent swamp rather than open water environments it is unlikely that t he inorganic material was washed in . A preferred explanation is that as sediment accumulated above the water table, the degree of decomposition of the organic component increased, effectively concentrating inorganic matter derived from atmospheric sources. The very high inorganic matter values of i nterseam sediment samples would have derived by stream flow from the surrounding catchment . This flow would be expected to have included a waterborne pollen component not represented significantly with the coals. The fact that the pollen composition of these samples differs little from the coal samples contained in the same sample

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group ( group 5- 3) is therefore somewhat confusing. A waterborne component usually contains a high proportion of spores from ferns and pollen from a number of taxa which are concentrated along stream banks . In their absence, the most likely depositional environment would have been a calm oligotrophic lake virtually devoid of living organisms to produce an organic sediment component and within which inorganic sediments have accumulated very slowly. Any waterborne pollen may have been deposited in more marginal lake environments. Climatic Considerations All taxa, with the exception of the sclerophyllous Restionaceae, Epacridaceae and Gl ei cheni aceae and perhaps a component of the Proteaceae, Myrtaceae and Casuarinaceae, which appear to be largely restricted to swamp environments, could have derived from rainforest. This suggests high regional precipitation, probably in excess of 1500mm per year. Evidence for the existence of sub-tropical to cool temperate rainforest within a catchment of probably no more than 1500m in relief indicates that temperatures need not have been very much higher than those of today with a similar lapse rate. It has been suggested that very high Myrtaceae and Elaeocarpaceae and very low Nothofagus values can be related to the proximity of lowland sub-tropical rainforest to coal forming basins, but the effect of temperature variations on changes in the extent of cool temperate and sub-tropical rainforest cannot be discounted. Within zones 3 to 7 of core LY 1275, which are outside the 'interseam influence' zones, the Myrtaceae and Elaeocarpaceae curves vary in a similar manner and in opposition to Nothofagus. These variations could be the result of temperature fluctuations, rather than changes in subsidence rate of the basin. Precipitation changes cannot be proposed from the pollen record as all taxa are capable of surviving under a wide range of moisture levels. CONCLUSIONS Pollen analysis has revealed a great deal of variation in vegetation and environmental conditions during the period of deposition of the Morwell 1B/lA The majority of lighter coloured coals were deposited in coal seams. open water, probably of great areal extent, although unvegetated essentially in places Lagarostrobus franklinii may have survived under these conditions. Darker coals are composed of the autochthonous remains of a mixture of sclerophyllous and rainforest plants. The presence of sclerophylls within a predominantly rainforest environment was probably due to the low nutrient status of the peat sediments, though the representation of sclerophyll plants was not as great as in the succeeding Yallourn seam (Luly et~- 1980). The clear pollen/colour lithotype relationships witnessed at Yallourn were complicated here by i nterseam influences at the base of the Morwe l l 1B seam and between the Morwe ll 1B and lA seams . It is suggested that with the decreased size of coal forming basins dryland vegetation encroached over much of the Latrobe Valley and contributed a greater pollen component to the peat sediments. In addition, the reduced lateral extent of open water in the smaller basins of accumulation resulted in a much greater pollen input from surrounding swamp sediments. The largely inorganic interseam sediments from the base of the Morwell 1B seam have a similar pollen composition to the coals which accumulated under open Australian Coal Geology 4, Part 1

182

A.P. Kershaw and I . R. Sluiter

water. It was inferred from this that these interseam sediments were deposited in a large oligotrophic lake containing few living organisms which could contribute an organic component of the sediment. Regional vegetation surrounding the Latrobe Va 11 ey depressions was composed largely of sub-tropical, warm temperate and cool temperate rainforest communities which are likely to have been ordered along an altitudinal gradient . Temperatures were probably a few degrees higher than those of today while precipitation would have exceeded 1500mm. There is some evidence for temperature variations within the recorded sequence, but the taxa used in analyses were not sufficiently sensitive to precipitation to allow the detection of moisture changes other than those which could be a result of tectonically controlled water level changes within the coal-forming basin. Stratigraphically it was possible to correlate closely the two cores examined, to refine the position of the Morwell lB/lA seam boundary, and to locate the 01 i gocene/Mi ocene boundary. An i nsuffi ci ent number of stratigraphic marker species were present to allow any reliable estimate of coal accumulation rates . ACKNOWLEDGEMENTS We are very grateful to the following : the Victorian Brown Coal Council for financial support for the study; staff of the S.E.C.V.'s Herman Research Laboratory for their encouragement and help with core collection and calculation of coal colour values; Dr . D.C. Mercer and Mr. M. Quinn for comments on the manuscript; Mr . A. N. Whittle for undertaking the computer programming; Ms . C. Battersby for typing the manuscript; and Mr . G.R.R . Swinton, Ms. S. Tomlins and Ms . V. Tipping for production of the figures. REFERENCES Allardice, D.J., George, A.M., Hausser, D., Neubert, K.H. & Smith, G.C . , 1977. The variation of Latrobe Valley brown coal properties and utilization parameters with lithotype. S. E. C. V. Brown Coal Research Division Scientific Report No . 342. Beadle, N.C.W., 1966. Soil phosphate and its role in moulding segments of the Australian flora and vegetation with special reference to xeromophy and sclerophylly. Ecology 47, 991-1022 . Blackburn, D. T. , 1981. Florist i c control on l i thotype banding within the Yallourn Coal Seam in the Yallourn Open Cut, Victoria: evidence from megafossil assemblages . S.E. C.V . Palaeobotany Project Report No. 2. Christophel, D. C., 1980 . Occurrence of Casuarina megafossils in the Tertiary of south-eastern Australia. Aust. J . Bot. 28, 249-59.

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Dale, N. B. & Albrecht, L., 1971. Comp. J. ~. 29-34.

Extension of information analysis.

Dale,

Information analysis of pollen di agrams.

N. B. & Walker, D., 1973. Pollen Spores 12, 21-37 .

Aust.

George, A. M., 1975. Brown coal lithotypes in the Latrobe Valley deposits. S.E.C. V. Exploration and Geological Division, Petrological Report No. 17. Numerical methods in Quaternary Gordon, A.D . & Birks, H.J . B., 1972. palaeoecology. I Zonat ion of po 11 en diagrams. New Phyto l . 71, 961-979. Kershaw, A. P. , 1973. Late Quaternary vegetation of the Atherton Tableland, north-east Queensland, Australia. Ph . D. Thesis, A.N.U. (Unpubl . ) Luly, J., Sluiter, I.R. & Kershaw, A.P . , 1980. Pollen studies of Tertiary brown coals: preliminary analyses of lithotypes within the Latrobe • Valley, Victoria. Monash Publications in Geography No. 23. Partridge, A.D. , 1971. Stratigraphic palynology of the onshore Tertiary sediments of the Gippsland Basin, Victoria. M. Sc . Thesis, Univ. N. S. W. (Unpubl.) Playford, G. & Dettmann , M. E. , 1978. Pollen of Dacrydium franklinii Hook. f. and comparable early Tertiary microfossils. Pollen Spores 20, 513-534. Quinn, C. J . , 1981. Taxonomy of Cacrydium Sol. (Podocarpaceae) . Aust. J . Bot. 30, 311-320.

ex Lamb . emend.

de Laub.

Raine, J.I., 1974. Pollen sedimentation in relation to the Quaternary vegetation history of the SnowY Mountains of New South Wales. Ph . D. Thesis, A.N.U. (Unpubl.) • Sluiter, I.R. & Kershaw, A.P., 1982. The nature of Late Tertiary vegetation in Australia. Alcheringa ~. (In press) . Specht , R. L., 1979. Heath lands and related shrub lands of the world; in Specht, R.L. (Ed.) Ecosystems of the World 9A, Heathlands and Related Shrublands of the World, Descriptive Studies, Elsevier, Amsterdam. Stover, L. E. & Partridge, A. D. , 1973. Tertiary and Late Cretaceous spores and pollen from the Gippsland Basin, southeast Australia. Proc. Roy. Soc . Viet. 85, 237-286.

Australian Coal Geology 4, Part 1

...... CX) ~

APPENDIX I Pollen taxon

Pollen production and dispersal characteristics

Generally a dominant canopy tree of cool temperate rainforest, existing under precipitation levels exceeding lS0Onnn per annum.

Wind pollinated with high production and wide dispersal.

Syzygium and Acmena are important A variety of forms, the majority canopy trees of tropical to warm of which fall within the morphological ranges of Syzygium, Acmena, temperate rainforests. Tristania is a rainforest margin to open forest Eucalyptus Tristania and Baeckea. tree while Baeckea species are -type pollen is extremely poorly sclerophyllous shrubs which frequently represented. grow on drier peat bogs.

Syzygium and Acmena are animal pollinated butdonave moderate production and dispersal. Baeckea can have high production but only There is little local dispersal. information available on Tristinia

Elaeocarpaceae

Elaeocarpus is an important canopy Includes the common genus El aeoca!Eus and other minor genera, tree of tropical to warm temperate rainforests. but excludes Sloanea.

Elaeoca~us has fairly high production and regional dispersal.

ll> :,

---

Wind pollinated with high Casuarina is widespread in Australian production and wide dispersal. sclerophyll vegetation but does not occur in rainforest. G~ostoma is generally associated witmoderately high rainfall rainforest environments in New Guinea and New Caledonia. Only one species, from the Cape York region, now exists in Australia.

Includes a number of taxa with affinities to genera such as Xylomelum,Helicia, Banksia, SY!!!£hionema and Beauprea.

Widespread trees and shrubs of a variety of rainforest and sclerophyll communities.

Epacridaceae

Largely Epacridaceae but could include pollen of Ericaceae.

Generally low production and very Epacrids are widespread shrubs of restricted dispersal. ~clerophyll woodlands, heath and peat bogs, but only occur in rainforests of the cool temperate type. Ericaceae have a similar but much more restricted distribution.

Restionaceae

Restionaceae and Centrolepidaceae

Herbs of sclerophyll communities which can have high cover abundance on swamps and peat bogs.

Wind pollinated - can have high

Quintinia

Morphologically distinctive

Trees or vines characteristically f,ound in warm temperate rainforests.

Fair production and wide dispersal.

Proteaceae "'O Qj

"'1

,"" tl)

From existing macrofossil informat ion (Christophel 1980), pollen is likely to be derived largely from the genus Gymnostoma rather than Casuarina

Casuarinaceae

r+ I--'

Known ecology and distribution esoeciall y in Australia.

Myrtaceae

):,

Taxonomic status

Includes all three pollen groups - 'brassii' which is dominant, 'menziesii' and 'fusca'.

("")

and ecological information on those taxa included in classifications.

Nothofa~s

"'1 ll>

Some taxonomic

Generally low production and very restricted dispersal.

=so, ~

..... V, C

r+ tl)

"'1

production but very limited dispersal.

Cunoniaceae (A)

Cunoniaceae with tricolpate or tricolporate pollen grains. Major Australian genera are Ackama and Pull ea.

Canopy trees most abundant in warm temperate rainforests.

Includes Cunoniaceae with dicolpate or dicolporate pollen and perhaps also Eucryphia (Eucryphiaceae)

Canopy trees of tropical to cool Moderate production and fairly .temperate rainforests, but most wide dispersal. abundant in warm temperate rainforests.

--Cunoniaceae (8)

"'c+

---

Laprostrobus Compares very closely with the franklinii extant species (Playford and formerly Dettman, 1978). Dacr)'.dium franklinii (See Quinn, 1982)

Long lived canopy tree now restricted to cool temperate rainforest patches largely along streams and on river flats in south -west Tasmania.

Dacr)'.dium

Includes a range of morphological types from Daccydium Section B (see Quinn 1982). Closely relatable to New Zealand's D. cuEressinum.

Predominantly tropical and sub-tropical Wind pollinated - fair production distribution. Q, cupressinum is the and dispersal. only species occurring at temperate latitudes.

Most likely Podocarpus species, but may include some species from Daccydium Section C (see Quinn, 1982).

Trees of tropical to cool temperate rainforest, excluding more complex forest types. In south-eastern Australia extends above the treeline as a dwarf al pine shrub.

Wind pollinated - fairly high production and wide dispersal.

Distinctive pollen.

Trees of cool temperate rainforest restricted within Australia to Tasmania.

Wind pollinated - moderate production but may achieve very wide dispersal.

May include a number of genera such as Callitris and Diselma within the Cupressaceae, and Arthrotaxis within the Taxodiaceae. £.alli.tris is most likely as its macro-remains have been identified from the coal (Blackburn, 1981).

Callitris dominates some open sclerophyll forests while the other genera are trees or shrubs of cool temperate rainforest extending into alpine heaths of Tasmania.

Difficulties of identification have led to different opinions on production and dispersal characteristics . Wind pollinated.

Spores compare well with Gleichenia.

Ground ferns found in diverse habitats including rainforest margins, swampy ground and peat bogs.

High spore production but limited wind dispersal.

""J

"' "':::,

Podocar1ms

"' C, t1)

0 tC

Moderate production and fairly wide dispersal.

Ph)'.l locladus

'< .:,.

Wind pollinated - fair production and dispersal.

;:,,; t1)

""J

:,-

"'c.:::, ...... V> C:

""' c+ ""J

Cupressaceae

I-'

Gleicheniaceae

c+ t1)

""J

..... CXl u,

186

A. P. Kershaw and I . R. Sluiter

APPENDIX 2 Numerical Methods The numerical analyses undertaken within this paper are options of the program PERCINF, computed by A.N. Whittle and based on a number of previously constructed programs to handle pollen data . All three options initially compare pairs of samples using as a similarity measure an extension of the information statistic devised for quantitative data i n percentage form (Dale and Albrecht, 1971). Option 1 constructs a similarity matrix of all sample pairs in the set. It essentially replaces POLLIN (Kershaw, 1973) which has been used previously on brown coal pollen data (Luly et!}_. 1980). Option 2 is an agglomerative hierarchical classifi cation procedure using It is essentially the same as the program centroid sorting. CENTPERC (Dale and Walker, 1970). Option 3 undertakes agglomerative hierarchical classification but with the stratigraphic constraint that only adjacent samples or derived samp 1e groups may fuse . Breaks between groups are used to 1ocate the best positions for zone boundaries on pollen diagrams . This option is based on the programs POLZONE and CONSLINK of Raine (1974) and Gordon and Birks (1972), respectively :

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Combustion Utilization Assessment of Brown Coals and Lignites T.C. St. Baker and L.A. Juniper

E.R.M. Consultants Pty . Ltd ., G.P.O. Box 2066, Brisbane, 4001, Australia

Key Words: Lignite, coal.

Combustion,

Coal

testing,

Power

generation,

Brown

ABSTRACT In all parts of the world, the increases in landed prices of imported fuel coals have improved the prospects of economic utilization of indigenous low grade energy resources for domestic power generation. The combustion utilization of lignites in large scale power utility boilers presents major imposts in power station capital and operating costs, and often severe boiler design difficulties to achieve reliable operation and satisfactory availability of power station plant. However the development of local resources for power generation has many attractions, as instanced by the Victorian brown coal development for power generation. From experience in the design and operation of power station combustfon facilities in most mainland Australian States involving a wide range of fuels, techniques have been developed for the utilization assessment of coal and lignite resources and for the optimisation of coal resource development and power generation utilization. This paper describes these procedures, identifying the extent of coal resource data necessary to establish the feasibility and cost of utilization and to ensure compatability of power station design and characteristics of nominated fuels, and identifying the order of utilization cost imports attributable to typical properties of lignites. INTRODUCTION The high cost of electric power generation based on fuel oil and the increased cost of imported steaming coals has increased the prospects for the economic utilization of indigenous low grade resources for domestic power generation. However, there are significant cost effects related to particular coal properties of low grade fuels, on capital and operating costs of power stations. Cost penalties also accrue from loss of performance and availability when a Australian Coal Geology 4, part 1

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power station is not properly designed for particular fuels it is required to accommodate. The design of boilers for these low grade fuels requires features in the plant to cater for their particular characteristics related to fuel handling, drying, pulverising, combustion, heat transfer, particulate collection and atmospheric emission control. The range of coal properties which affects the utilization assessment of low grade coal is more extensive than that for sub-bituminous steaming coal. Some of the fuel characteristics required are outside the normal analytical testing programs adopted for the assessment of sub-bituminous coals, and special consideration is required in the planning stages of a resource evaluation to ensure that full and adequate coal testing is undertaken and full benefit can be obtained from the overall exploration program. Before the design of power station plant for low grade fuels can be committed, detailed utilization assessment of the coal is required to establish design parameters on which detailed plant design can be based. This is particularly necessary for low grade fuels potentially subject to fouling. The design of plant for these fuels is difficult due to the complex nature of the coal chemistry, and plant operation is highly sensitive to changes in coal properties . Departures from design fuel specifications can lead to loss of performance or poor availability. Detailed utilization evaluation for such coals will include pilot-scale combustion testing to assess a coal's burn-out characteristics, propensity for fouling of heat transfer surfaces, sulphur absorption characteristics and precipitability characteristics. Other testing is required to assess grindability and wear characteristics, coal handling and storage characteristics, and ash solubility and the chemistry of leachates . The present paper sets out in some detail . -

general order cost comparisons between typical sub-bituminous coal fired power stations and lignite and brown coal fired power stations, showing the high relative capital costs and operating costs incurred in power stations burning low grade fuels;

the various fuel properties which contribute to increased capital and operating costs; and

special coal testing and evaluation necessary to ensure that a resource can be properly assessed for its utilization characteristics and economic feasibility against other high grade fuel alternatives.

POWER STATION COSTS Power generation costs are made up of capital charges on the total project capital costs, power station operation and maintenance costs, and the cost of ' ., the fuel to be burnt. The Zeidler report (1981) sets out power station capital and operating costs for a number of fuels including New South Wales black coal, South Australian lignite and Victorian brown coal, the latter two being low grade indigenous fuels. Capital costs for the design and construction of power stations burning these fuels are quoted by Zeidler at 1980 prices as:

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$595/kW for New South Wales black coal, $930/kW for South Australian lignite, and $1120/kW for Victorian brown coal. These costs include the cost of design and construction of all components of the power station, engineering and other overheads involved in the construction, all site and civil related works, interest on capital during construction and other allowances as appropriate. The differences · in the costs can be generally re 1ated to the differences in the design of coal dependent power station components. For example, because of high moisture content of lignites compared to typical black coals, boiler thermal efficiencies are much lower and the specific energy of the lignite is low and hence much larger tonnages of fuel need to be handled. Lignites being of 1ower rank have 1ower dry ash free specific energies further increasing tonnages . The high moisture content of lignites also causes lower temperatures within the combustion chamber and hence 1arger heat transfer surface areas are required in the furnace and superheater to transfer the required heat to the boiler water/steam circuit. An illustration of the range of boiler size for differing fuels is shown in Figure 1.

□

□ w

1-1W

r r r r 1-4H

1-SH

1-1H

lJ lJ Bituminous

Sub-Bituminous

Lignite

Brown Coal

Figure 1. Effect of Fuel on Furnace size Similar increases in annual operating and maintenance costs are incurred with low grade coals and Zeidler quotes the following for the three coals: $10/kW/a for New South Wales black coal, $19/kW/a for South Australian lignite, and $23/kW/a for Victorian brown coal.

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These costs include direct costs of wages and salaries for operating and maintenance personnel, materials, and indirect costs derived from administration and engineering support. The higher costs associated with low grade fuels can be attributed, firstly, to the much larger plant required for these fuels, and secondly to the direct effects of the fuels . Low grade fuels exhibit a higher propensity for ash deposit ion on heat transfer surfaces, requiri ng on-1 oad cleaning by soot-blowing. Maintenance of cleaning equipment represents a significant operating and maintenance cost, as well as a reduction in operation efficiencies due to the use of steam or water in this equipment and by loss of output during soot-blowing . In addition, unit availability is generally lower in power stations burning low grade fuels as boiler down time is longer and more frequent than black coal fired power stations due to the need for extensive off-load cleaning. Table 1 sets out the costs for 1400 MW power station developments based on the three fuels discussed above. Imported black coal is priced at a notional landed price in the other ~tates of $60 . 00/tonne . Capital charges are based on 10% per annum of the hi stori ea l cost, current ly the typi ea l ratio of capital charges to historical cost of plant in service in Australian State electricity systems. Capital, operation and maintenance charges, based on the Zeidler estimates, are added to the imported coal cost, resulting in a bulk energy cost of 3. 32 c/kWh sent out from the power station. TABLE 1 COMPARISONS OF A 1400 MW POWER DEVELOPMENT BASED ON IMPORTED BLACK COAL AND LOW GRADE INDIGENOUS FUELS AT 70% ANNUAL CAPACITY FACTOR Imported Black Coal

S.A. Lignite

Vic. Brown Coal

($/kW) ($M)

595 833

930 1303

1120 1568

($M p.a.)

83 . 3

103. 2

156.8

0 &M Charges*

($/kW/a) ($M p. a. )

10.0 14. 0

19.0 26.0

23.0 32.2

Coal Tonnage Coal GHV Coal Cost

(Mt/a) (Gj/t) ($/t)

2.9 27 . 0 60.0

6.3 13 . 6 21.18

11.1 9.1 6.64

Total Fuel Bill

($Mia)

174 . 0

133.5

74.7

Total Annual Charges

($Mia)

271. 3

262.7

272.7

Total Annual Energy Sent Out@ 70% ACF

(GWh/a)

8160

7900

Total Capital Cost* Capital Charges@ 10% per year on historical cost

3.32 3.32 Bulk Energy Cost (c/kWh) * Capital and operation and maintenance costs based on Zeidler (1981) . Australian Coal Geology 4, part 1

3.32

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191

Break even coal costs for South Australian lignite at 13. 6 Gj/tonne and Victorian brown coal at 9.1 Gj/t, are determined at $21.18/tonne and $6.64/ tonne to produce the same bulk energy costs from alternative power station developments based on local coals. The break-even coal costs of imported coal, and local South Australian and Victorian coals, expressed in $/gigajoule, are:

2.22 $/Gj for Imported black coal, 1.56 $/Gj for South Australian lignite, and 0. 73 $/Gj for Victorian brown coal.

This simplified example takes no account of coal effects on availability, coal transportation costs within the State or high voltage transmission costs to electrical load centres, or other benefits which accrue to the development of a local resource. Other factors which play an important role in determining an optimum power development strategy, include: -

employment of people for a local mining industry, government energy policies, and security of primary energy supplies.

The comparison is also very sensitive to the capital cost assumptions, interest rate assumptions and discount rates adopted for economical comparisons and to differential escalation rates for the alternative fuels. In a detailed study the break-even price comparisons for local fuels are likely to be increased by most of these factors. The comparisons quoted above represent base minimum order values for the indigenous fuels. POWER STATION DESIGN To make a proper assessment of a low grade coal's feasibility for a power station development, it is necessary to ensure that the properties of the fuel are within the range of 'state-of-the-art' design. In this respect, sufficient information is required about the coal to enable a conceptual design of the power station to be developed, and design parameters established. Table 2 illustrates the major items of plant in a power station and the coal properties which have an influence on the design of the equipment with regard to capacity ratings, size and the choice of type of plant. It can be seen that there is a wide range of coal properties whi eh have a bearing on the design of plant, some of which are not always available at the resource evaluation stage of a particular development. However, it is essential to recognise the effect of these properties so that the maximum benefit can be derived from the exploration and evaluation program for the resource to enable the effects on design and subsequent costs of variation in these parameters to be assessed. Boiler Efficiency Boiler efficiency is determined by the coal chemical composition and the final boiler flue gas exit temperature. Boiler efficiency is affected mainly by moisture content, as the latent heat . of evaporation of this moisture is lost during combustion. The efficiency of a black coal fired boiler can be as high as 90% based on the gross specific energy of the coal. For a lignite at 30% moisture content, the efficiency would be reduced to approximately 82% and for Victorian brown coal at 65% moisture content the efficiency could be below 70%. Australian Coal Geology 4, part 1

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192

TABLE 2

FUEL PROPERTIES AFFECTING THE DESIGN OF POWER STATION COMPONENTS

Plant Item

Coal Properties Affecting Design

Principal Design Criteria

Coal Handling Equipment - conveyors - bunkers - stockpiling

Coal Tonnage

Ash Content Mineral Matter Comp. Specific Energy Moisture Content Inherent Moisture Sulphur Content Volatile Content Fri ability

Pulverising Equipment - mi 11 s - feeders - PA fans - air heating - PF piping

Coal Tonnage Moisture Content Grindabilit y Raw Coal Sizing

Moisture Content Free Moisture Ash Content Mineral Matter comp. HG! Abrasiveness Grindabilit y

Boiler - burners - combustion chamber - convective passes - soot-blowers

Heat Transfer Combustion Gas Temps. Radiative and thermal properties of flue gases Fouling Properties

Specific Energy Ultimate Analysis Ash Content Sulphur Content Ash Fusion Temp. Moisture Content Ash Abrasiveness Reactivity

Precipitato rs

Particulate Density Ash Electrical Properties Statutory Regulations

Ash Content Sulphur Content Moisture Content Ash Dielectric Const. Mineral Matter Comp. Ash Particle Size

Ash Disposal System - ash collection - slurry disposal - ash water recovery - fly ash sales

Ash Disposal Quantities Soluble Compounds in Ash Ash Chemistry

Ash Content Chemical comp . of fly Ash product Ash Sulphur Absorption Ash Solubility Trace Elements

Emission Control - stacks - scrubbers - special combustion equipment

Sulphur Content Statutory Regulations Meteorological Conditions Nitrogen Content Ash Sulphur Absorption Nitrogen Chemistry Trade Elements Australian Coal Geology 4, part 1

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Final boiler flue gas exit temperature is dictated by the acid dewpoint of boiler flue gases, which is increased by greater sulphur oxides derived from high content fuels. For low sulphur coals a temperature of 130°C could be common, but for a high sulphur coal a temperature of 160°C might be adopted with a subsequent loss of boiler efficiency. The presence of large amounts of water vapour in the flue gas accentuates this effect. Loss of boiler efficiency directly affects the energy input of coal required to achieve the same electrical output from the power station . Fuel Handling Equipment Coal handling equipment may account for 5% - 7% of the total power station cost . Fuel handling equipment must be rated as a reasonable margin above the maximum demand coal rate, determined from the total heat demand required by the turbine, the boiler efficiency, and the fuel specific energy. The comparison of typical black coals and Victorian brown coal in Table 1 illustrated the much larger tonnages, nearly four times, required to be handled in Victorian power stations for the same electrical output . Low grade coals are also subject to handling difficulties if allowed to dry out excessively, due to a propensity for rapid size degradation as it dries. The moisture content of low grade coal can vary over a wide range, depending on atmospheric conditions, the amount of trans-handling and the extent of size degradation. There is a tendency towards extremes of 'sticky' consistency or excessive dustiness, if moisture levels are not controlled. These characteristics must be determined before a commitment can be made to the design of the fuel handling plant. Pulverising Equipment Pulverising equipment including mills, feeders , primary air fans, ductwork and burner systems accounts for 5 - 7% of the total power station capital costs. In addition operating and maintenance costs on pulverising equipment represents about 14% for a typical black coal fired power station, and up to 20% for a lignite fired boiler. The maximum demand fuel rate, the coal ash content, and its grindability and abrasiveness form the basis for the design of mills. For low grade fuels, the fuel rate is high due to their low specific energy, and the HGI is generally high . For Victorian brown coal of about 65% moisture content, mills are of the fan beater type. They are required to produce a pulverised coal sizing of not less than 98% minus 1 mm (1000 µm) . This sizing has been selected on the basis of SECV's previous experience with these mills and to suit the characteristics of these coals, as described by Sutherland (1979). Leigh Creek coal at about 30% moisture content, uses mills of vertical spindle design. In order to provide a dry product coal which will be readily combustible in the furnace, moisture must be removed from the coal. This is achieved by using pre-heated primary combustion air for coals up to 30% total moisture Above 30% moisture content, special facilities are necessary, content. involving furnace gas reci rcu l at ion to dry the coal during the pulverising process. For very high moisture contents, above about 65%, separation firing is required to maintain combustion stability at the low combustion temperatures within the furnace. These facilities are shown in Figure 2.

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T.C. St.Baker and L.A. Juniper

GAS Off TAKES GA S

REC IRCUL ATION DUCT

Figure 2. Separation Firing System for High Moisture Brown Coal Boiler Boilers, including superheaters, draft plant and auxiliary equipment accounts for 25% to 35% of total power station capital costs. As set out in Section 2, coal moisture content plays a key role in determining the size of a boiler as it has a dominant effect on the furnace combustion temperatures and therefore the potential for radiative and convective heat transfer. The other major determinant of boiler size is the design furnace exit gas temperature as this establishes the amount of heat required to be transferred by radiation in the furnace and the approach temperature available for superheating in the convective zones. Selection of the furnace exit gas temperature is mainly dependent on the slagging and fouling behaviour of coal ash, which is the deposition of ash on heat transfer surfaces due to the molten state of ash particles or chemical reaction of the ash canst i tuents producing a bonding agent. Low ash fusion coals require a lower furnace exit gas temperature to ensure that fly ash particles are in a solid phase before entering the convection zones to prevent possible ash deposition on the tubes. The size of the furnace is also determined by the radiation characteristics of 'the combustion gases and the suspended ash particles and the emissivity of the combustion flame envelope. Australian Coal Geology 4, part 1

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195

The fouling characteristics of the coal play a major role in the heat transfer obtained in the furnace as fouling of the furnace walls provides an insulating layer which restricts the flow of heat. Also, the emissivity of this layer is generally lower than the bare metal of the tubes, and at times can be very low, caused by particular elements, such as aluminium, as shown by Wall et al. -(1979). Fouling of low grade coals has been extensively investigated e.g. Kiss (1979), Kein (1977) and Hale et al. (1980), and the propensity for fouling can be related to the mineral composition of the coal ash. CSIR0 (1966) and (1971) have shown that the extent of fouling in a boiler burning Leigh Creek coal can be related to the sodium/ash ratio in the coal with a critical range of 0.35-0.40, above which operational problems have been experienced. The area requirements for the convective sections are determined from the gas temperatures through them and the required heat demands of the various sections. The design of the superheater sections is critically dependent on the design of the furnace as it is the selecti on of furnace exit temperature which is the precursor for the superheater design . The proper assessment of these critical cost factors and feasibility elements for low grade coals can only be gauged by pilot-scale combustion testing. Precipitators In Australia, precipitators account for approximately 4 - 8% of the total capital cost of a power station . The size of precipitators to achieve a collection efficiency commensurate with statutory regulations can be estimated from certain fuel characteristics as described by Paulson (1979) although some form of pilot-scale testing is generally required to establish final design parameters. The variables which affect the size of precipitators are the particulate and gas flows, the electrical properties of the ash, particularly dielectric constant and ash resistivity . The collection of fly ash is generally most cost effectively performed by electrostatic precipitators. They perform best on ashes of low electrical resistivity which is enhanced by hi gh moisture contents and certain conditioning by S03. The fly ash from low grade coals may be naturally conditioned for electrostatic prec i pitation by excess amounts of moisture and sulphur in the coal, and dust collection efficiencies greater than 99% can be anticipated without unduly high collection areas being required. Hart (1979) states that Victorian experience has shown that high levels of aluminium in the coal can produce ash that has a very low bulk density. This causes a problem of ash re-entrainment to the gas flow through the precipitator after it has collected on the discharge plates. SECV now design their precipitators with gas velocities below 1. 0 m/s which necessitates larger precipitators than would otherwise be required . With difficult precipitability coals, large electrostatic precipitators, and even bag filters, may be required, with up to 3% additional power station cost compared to more easily precipitated coal ashes. Ash Disposal System Ash disposal systems account for approximately 3% of the total power station cost . The design of the ash disposal system wi 11 vary according to the

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196

quantities of ash to be disposed of from the power station, al though local site factors may be a major factor in ash disposal costs. Various properties of ash affect the detailed design of ash disposal systems. These properties include the solubility of the ash and the chemistry of ash leachates in the ash sluicing water, if the disposal system is a wet system. Al so, the effect of trace elements wi 11 need to be assessed so that the ash disposal system will be environmentally acceptable. The establishment of these fuel properties is important in establishing design parameters and budget costs. Emissions Control The design of chimney stacks will vary according to the emission control requirements. Emphasis is placed on the ground level concentrations of sulphur dioxide. To reduce these to statutory requirements for high sulphur coals may require higher than normal stacks, with commensurate penalties in costs. In the extreme, flue gas conditioning may be required at high capital and operating cost. The propensity of the coal ash to absorb sulphur during combustion may alleviate problems of high sulphur emissions. SECV have developed empirical relationships, Deed (1973), for assessing the sulphur absorption characteristics of Victorian brown coals, involving elemental Although not constituents of calcium, magnesium, sodium and chlorine. quantitative, particularly for other coals, the equations give an indication of the likely sulphur absorption. However, proper assessment can only be made by pilot-scale testing . Australian coals are generally low in fuel Nitrogen which reduces the potential for emissions of NOx. In addition, the generally low combustion temperatures prevailing in furnaces burning low grade fuels further reduces the potential for NOx production. COAL AND COMBUSTION UTILIZATION TESTING The importance of coal testing and evaluation of combustion utilization aspects of low grade coals on the feasibility of a coal-fired power development concept, is i 11 ustrated by reference to Figure 3, from St. Baker and Juniper (1982). Coal Mining Studies The ability of a supplier of low grade coal to produce the proposed product coal and deliver it to the power station over its economical life has to be established beyond doubt before a commitment can be made for a new power station development based on that source. To satisfy the security of coal supply for a particular development, the following needs to be assessed: -

that proven mi neab le coal reserves exist whi eh can be dedicated to the long-term supply to meet the power station coal requirements from that source, that sufficient knowledge is available to provide confidence in the ability to recover the coal and to produce and deliver the coal of quality proposed, and that the proposed price of coal, reduced to an ex-mine cost, represents sufficient margin to a commercial miner to give confidence in his ability to profitably supply the coal over the life of the power station. Australian Coal Geology 4, part 1

T.C. St. Baker and L.A. Juniper

UTILIZATION

RE SOURCE OATA

I. COAL SOURCES

POW£R

ASPECTS

197

DEVELOPl'c:HT

CONCEPT

- - - - - - - - - - - - - - - - - - - - - - 7. SITING STUD IES - - - - - ,

- MINING STUDIES

8. H.V. TRANSMISSI.O N - - - -

- Co•L PI! I CEs

9, WATER S Y S T E M - - - - - - (

1. I N- $1 r u Co .a. L PROPERT I E S ~ ~ - C011ausr10N TesrtHG

10, WIOUNDHATER - - - - - - - - (

P RO DUCT COAL PR OPERTIES

4 , GRIHDA81LITY 1 WEAR TESTS

11 , METEOROLOGY - - - - - I

5. A.sH EucTAICAL (HARACTER1sr1cs { PILOT SCALE PRECIPITATOA TE STING)

6 , (OAL STORAGE

& HANDLING TESTS

12, 50

[MISSION/PLUME ntsPERSIO"

}3 , ASH

& WATER CHEMISTRY - - - - i

1~, [HVIRONNENTAL IMPACT STUDY

:: REFINE POWER REFJijE POi/ER STATION OES1Gtl PARAMETERS I - - - - - ' - - - - nEV.LOPMENT CONCEPT

Its. FEASISILITY REPORT!

Figure 3. Coal-fired Power Generation Feasibility Studies Coal Testing Testing of bore cores on a grid basis over the full extent of the in situ coal resource proposed to be committed to the development, should identify: average coal properties to a high level of confidence , and the variability of coal properties in the proposed mining sections and of the product coal proposed to be delivered to the power authority. Coal testing should identify coal properties for the in situ coal proposed to be mined as well as for the product coal, and should include: proximate analysis specific energy, relative density, total moisture content, total sulphur content, forms of sulphur, ultimate analysis, carbon dioxide, chlorine content, total sodium, ash and mineral analysis, trace element analysis, ash fusion temperatures, Hardgrove Grindability Index, ash abrasiveness (YGP), Australian Coal Geology 4, part 1

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198

Combustion Testing For a coal that has not been fired in fu 11-sca le pulverised fuel fired boilers, pilot-scale combustion tests should be undertaken before the final boiler designs are determined, to identify any peculiarities in the ignition, volatilisation, and char burn-out of the coal, and in ash deposition, fouling potential, and high temperature corrosion characteristics of the fly ash products of combustion, as well as to determine the sulphur absorption characteristics of the coal ash. For low grade coals combustion testing wi 11 generally be necessary in the feasibility stage to estublish reasonable confidence in the suitability of the coal and the capital and operating costs likely to be involved in its power generation utilization. The choice of combustion test rig necessary will depend on the indicated nature of the coal from laboratory testing. There are a number of suitable pilot-scale combustion rigs in various locations in USA, Europe and Japan, the SECV combustion test facility being the only one in Australia. Generally, the fuel is burnt in a small combustion chamber which simulates the time-temperature history of the combustion process in an operational boiler. Ash deposition is monitored on simulated furnace wall tubes and superheater tubes, and comparative assessments can be made relating to the amount and strength of the deposits which build up on these surfaces. A typical rig for this work is shown in Figure 4. Bulk sample quantities required for pilot-scale combustion testing varies between 500 kg and 50 tonnes, depending on the particular rig and the depth of testing involved. Burner

-"RIN

Radiant Furnace

Baghouse

Superhea ter Probe Banks

......___ _ ____,f.-~-

Slagging Probes

Tempera tu re/Gas Sampling

)

+ Particulate Sampling

Observation Ports

Figure 4. Typical pilot-scale combustion test facility. Australian Coal Geology 4, part 1

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199

Grindability and Wear Tests Direct measurement of gri ndabil i ty and mi 11 wear characteristics should be carried out before a commitment is made to a particular milling system. A number of manufacturers have test mills suitable for this purpose, requiring relatively small samples of product coal, of the order of 10 kg, which can be easily arranged during the course of the power station feas i bi 1ity studies. Such tests can serve to enhance the confidence with which power station design parameters can be identified in this area prior to deciding on a particular power station development based on particular coals. Ash Electrical Characteristics Low sulphur coals tend to exhibit ash electrical characteristi cs requiring large precipitator collection areas for efficient particulate collection and compliance with relevant statutory clean air requirements . Further, the variation in ash electrical characteristics of different low sulphur Austra 1i an coa 1s has been found to dictate precipitators of widely varying co 11 ect ion areas to achieve required effi ci enci es, with consequent varying capital costs to accommodate the coals. Standard testing of ash electrical properties should be undertaken in the power station feas ibi 1i ty study stage, and can provide an i ndi cation of any peculiarities in precipitator characteristics for a particular coal. It is generally also necessary for a new low grade coal to undergo pilot-scale precipitator tests to establish the actual precipitator characteristics for the coal and to identify the budget cost for power station planning purposes. Coal Storage and Handling Tests This is an area where power station difficulties can arise with facilities not tailored to a particular coal. The undertaking of a trial burn of a bulk sample, for combustion evaluation purposes , provides valuable data on the handling of the coal. However, in other cases appropriate testing will only be devised where certain doubts exist in re l ation to the size degradation or other problems in handling the coal. Testing of controlled stockpiles of crushed coal should, however, be undertaken to identify any problems in respect of size degradation or spontaneous combustion which require special control measures in the power station. REFERENCES CSIR0 1966, Coal Research in CSIR0 28, 11. CSIR0 1971, Coal Research in CSIR0 43, 2. Deed, R.G. 1973. State Electricity Commission of Victoria, Research and Development Deparfriient - Report No. 258. Hale, G.L., Levasseur, A.A . , Tyler, A.L. and Hensel , R. P. 1980. Coal Tech~ '80, 3rd International Coal Utilization Exhibition and Conference Houston-;-Texas. --Hart, J.A. 1979. Pulverised Coal Firing, Mineral Matter and its Effects. University of Newcastle .

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Kiss, L.J. and Morley, W.J. 1979. Pulverised Coal Firing, Mineral Matter and its Effects. University of Newcastle. Paulson, C.A.J., Kahane, Biennial Conference.

R.B.

Institute of Fuel

E.C. 1976.

and Potter,

Firing, Mineral

Sutherland, K.N. 1979 . Pulverised Coal Effects. University of Newcastle.

Matter and its

St.Baker, T.C., and Juniper, L. A. 1982. Conference of Electric Power Supply Industry of Asia and Pacific, Bangkok. Wall, T. F., Mai-Viet, T. , Becker, H. B. and Gupta, R. P. 1979. Pulverised Coal Firing, Mineral Matter and its Effects. University of Newcastle.

Zeidler 1981. Report of the Committee of Enquiry into Electricity Generation and the Sharing of Power Resources in South-East Australia. TABLE 1 COMPARISONS OF A 1400 MW POWER DEVELOPMENT BASED ON IMPORTED BLACK COAL AND LOW GRADE IND IGENOUS FUELS AT 70% ANNUAL CAPACITY FACTOR Imported Black Coal

S.A. Lignite

Vic. Brown Coal

(S/kW) ($M)

595 833

930 1303

1120 1568

($M p.a.)

83.3

103 . 2

156.8

0 & M Charges*

($/kW/a) ($M p.a.)

10 . 0 14.0

19.0 26.0

23 . 0 32.2

Coal Tonnage Coal GHV Coal Cost

(Mt/a) (Gj/t) ($/t)

2.9 27.0 60.0

6.3 13.6 21.18

11.1 9.1 6.64

Total Fuel Bi 11

($Mia)

174.0

133.5

74.7

Total Annual Charges

($Mia)

271. 3

262.7

272.7

Total Annual Energy Sent Out@ 70% ACF

(GWh/a)

8160

7900

Bulk Energy Cost

(c/kWh)

Total Capital Cost* Capital Charges@ 10% per annum on historical cost

3.32

* Capital and O & M costs based on Zeidler (1981). Australian Coal Geology 4, part 1

3.32

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201

TABLE 2 FUEL PROPERTIES AFFECTING THE DESIGN OF POWER STATION COMPONENTS Plant Item

Coal Properties Affecting Design

Principal Design Criteria

Coal Handling Equipment - conveyors - bunkers - stockpiling

Coal Tonnage

Ash Content Mineral Matter Comp. Specific Energy Moisture Content Inherent Moisture Sulphur Content Volatile Content Friability

Pulberising Equipment - mi 11 s - feeders - PA fans - air heating - PF piping

Coal Tonnage Moisture Content Grindability Raw Coal Sizing

Moisture Content Free Moisture Ash Content Mineral Matter comp . HGI Abrasiveness Grindability

Boiler - burners - combustion chamber - convective passes - sootblowers

Heat Transfer Combustion Gas Temps. Radiative and thermal properties of flue gases Fouling Properties

Specific Energy Ultimate Analysis Ash Content Sulphur Content Ash Fusion Temp. Moisture Content Ash Abrasiveness Reactivity

Precipitators

Particulare Density Ash Electrical Properties Statutory Regulations

Ash Content Sulphur Content Moisture Content Ash Dielectric Const. Mineral Matter Comp. Ash Particle Size

Ash Disposal System - ash collection - slurry disposal - ash water recovery - fly ash sales

Ash Disposal Quantities Soluble Compounds in .Ash Ash Chemistry

Ash Content Chemical comp. of fly Ash product Ash Sulphur Absorption Ash So 1ubil i ty Trace Elements

Emission Control - stacks - scrubbers - special combustion equipment

Sulphur Content Statutory Regulations Meteorological Conditions Nitrogen Content Ash Sulphur Absorption Nitrogen Chemistry Trade Elements Australian Coal Geology 4, part 1

202

Evaluation of South Australian Coals for Power Generation E.R. Lindner Electrlclty Trust of South Austral la, 220 Greenhill Road, Eastwood, South Austral la, 5063, Austra I la. Key Words: Lignite, Tertiary, South Austral la, Lignite combustion. ABSTRACT Amongst the supply options for the next stage of generation, the Electrlclty Trust of South Austral fa Is considering the use of South Austral Ian brown coal from e I ther the Wakef I e Id, KI ngston or Sedan depos Its. Due to the potent I a I dlfflcultles In utlllslng these coals ETSA In cooperation with the respective coal owners has carried out an extens i ve research program. This program concentrated on pulverised coal research but other develop Ing technologies were also Investigated. The pulverised coal combustion research was aimed at determining the effects of flame and flue gas temperatures and the addition of calcium based materials on slagging, fouling, high temperature corrosion and sulphur dioxide emission. This work was carried out on pi lot combustors of up to 1 MW thermal capacity. The research has provided a set of parameters which are now being used In feaslblllty, design and cost studies for boilers to burn Wakefield, Kingston and Sedan coa Is. INTRODUCTION Amongst the supply options for the next stage of generation, the Electrlclty Trust of South Australia (ETSA) Is cons idering the use of the large reserves of South Austral Ian brown coals, In particular coal from either the Wakefield, KIngston or Sedan depos Its. Normally prior to development for power generation, a new coal deposit Is examined In the following manner. Firstly, sufficient data Is collected so that the econom I cs of the coa I's extract I on, transportat Ion, and the subsequent power generation and distr i bution can be evaluated. This then enables, In most cases, a decision to be made whether to develop a particular coal deposit versus other deposits or alternative fuel sources. Much more detal I Is then required to enable the pl'ann l ng and design of the mine, the mining equipment, the coal hand I Ing plant, the bol ler and Its associated plant, the ash disposal system, and the provisions to protect against or minimize environmental changes. Australian Coal Geology 4, part 1

203

E.R. Llndner

The potential difficulties of utlllslng South Australian brown coals and the significant effect these have on the overall economics has meant that, before a decision can be made to develop any of these deposits, an Investigation Into their properties must be performed In much more detail than Is required normally.

Wakeffefd. Kingston .aru1 ~ ~ Coal reserves, ownership, location and coal quality are summarised In Tablet. A more detailed description of these coal deposits Is given In O'Brien (1982). TABLE 1

Wakeffefd

Kfnston

reserves

2000 ml I I Ion tonnes

1000 ml I I Ion tonnes

230 ml I I Ion tonnes

owner

ETSA

Western Mining Corp. Ltd.

CSR Ltd.

location

100km north of Adelaide

300km southeast of Adelaide

80km northeast of Adelaide

coal rank

Tert I ary brown coal coal

Moisture as mined

Tertiary brown

Tertiary brown coal

56%

54%

58%

HHV as mined MJ/Kg

10.6

9.4

Ash dry basis

11.6%

14.9%

19.5%

S dry basis

5.2%

2.9%

5.5%

1.6%

0.9%

0.65%

1.5%

0.2%

0.18%

Na/ash

13.8%

6.3%

3.3%

ADVERSE UTILISATION CHARACTERISTICS It can be seen above that the three coa Is have d If ferent concentrat Ions of sodium, chlorine and suplhur which can contribute to special problems when burnt In pulverised coal fired boilers. These problems are: slagging fou I Ing high temperature corrosion sulphur dioxide emission

Austral Ian Coal Geology 4, part 1

204

E.R. Lindner

Before cons I der Ing th Is 11 st In more deta I I, It Is necessary to have a bas Ic understanding of bol ler plant processes. Coal Is fed from the bunkers via feeders which control the coal flow rate to the pulveriser (Figure 1). The powdered coal Is then blown Into the furnace where It Ignites. The resultant combustion gases progress from the furnace to the stack via the convection section, the air heaters, the preclpltator and the sulphur dioxide scrubber, If required, In the furnace, heat for steam generation Is transferred pr I mar I I y by rad I at I on. In the convect I on sect I on, heat Is transferred by convection to superheat the steam and heat the Incoming water. The air heater preheats combust I on a I r and the pre I o I tators remove the ash from the f I ue gas.

Figure

Schematic arrangement of typical coal fired furnace showing path of combust ion gases

Sfagg[ng

Slagging Is the accumulation of fused ash deposits on surfaces predominantly exposed to radiant heat, I.e. the boiler furnace (Figure 2). Slag Impedes the heat transfer; also large slag accumulation dlslogdlng and falling from above may damage the tubes In the furnace hopper. The propensity for slagging depends on ash composition, and furnace and burner design. It Is difficult to predict the severity of slagging from coal analyses A crude Indication of the severity of slag formation Is given by ash fusion temperatures. The lower the ash fusion temperatures the higher the probabil lty that slagging wil I occur. South Australian brown coals have low ash fusion temperatures. fou I Ing Fouling Is the formation of ash deposits on tubes In the convection section of the bol ler, I.e. the superheater and reheater (Figure 2). The deposits grow In the shape of f Ins aga Inst the gas f Iow, adhere strong I y to the tubes and harden with time. If they are allowed to accumulate thay may force a boiler outage by restricting or, In extreme cases, blocking the gas passage by bridging across the tubes. If frequent costly shut downs are to be avoided then the boiler must be desgined appropriately for the particular fuel.

Australian Coal Geology 4, part 1

E.R. Lindner Figure 2

205 Slagging and Fouling Areas In coal fired Boilers

The tendency for a coal to cause fouling Is dependent on the Inorganic constituents In the coal. Because of the complexity of the fouling phenomenon, It Is difficult to predict foul Ing severity from coal analyses. However It Is wel I establ I shed that sod I um Is a major contr I butor to severe fouling and the ratio of sodium to ash Is a crude guide, I.e. the I arger th Is rat I o the greater the potential to cause severe fouling. Hlgh Temperature Corrosion High temperature corrosion occurs In the superheater and reheater when complex Inorganic salts react with the steel tubing. Coals with significant concentrations of sodium and sulphur, particularly In the presence of chlorine, have high potential to cause this type of corrosion. In recent years this form of corrosion has In the main been prevented by designing boilers to ensure the metal temperature does not exceed 590°C or by the use of corros Ion res I stant a I Ioy s.

Sulphur DJoxJde EmJssJon With Increasing levels of sulphur In coal, acceptable ground level concentrations may be achieved by Increasing the stack height. The level of sulphur and the stack height for which this type of solution Is still appropriate wll I be dependent on local atmospheric conditions. Alternatively, sulphur dioxide emission concentration can be reduced by adding ea I c I um based mater I a Is to the coa I pr tor to burn Ing to absorb the su I phur dioxide In the furnace. This method Is particularly applicable to brown coals where the combustion temperatures are low enough not to cause Inactivation of the ea I c I um by "dead burn Ing". Another method of reduc Ing su I phur d I ox I de emission concentration Is by wet scrubbing the flue gases. However, this Incurs very high capital and operating costs. Due to the potential problems of burning these coals In pulverised coal fired boilers, ETSA has carried out, In conjunction with the other coal owners for their respective coals, an extensive research program on the South Austral Ian coals. This program concentrated on pulverised coal firing research, but also for Wakefield coal Included less conventional technologies such as fluidised Australian Coal Geology 4, part 1

206

E.R. Lindner

bed combustion and coal pretreatement. All research was performed by outside organisations which enabled the extensive program to be set up qulckly. The plannlng and direction of the research was carried out by ETSA. Coal samples from the deposits were obtained by the respective deposit owners. The research for each coal was paid for by the respective deposit owners.

Pulverfsed CQaJ CqnbustJon Research The pulverlsed coal combutlon research was carried out In two stages, the first being on small scale combustion rigs with firing rates not exceeding 35 kg/hand the second on large scale combustors of approxlmately 1 MW thermal Input. The program concentrated on determining the effects of flame and flue gas temperatures and the addition of calclum based mater lals on slagglng, foul Ing, high temperature corrosion and sulphur dioxide emission. For high temperature corrosion the effect of metal temperature and type of alloy was also studied .

.smaJ.1. ~ Pulverfsed ,CoaJ. Canbustfon Research Smal I scale work was designed to give an Indication as to the I Ike I hood of successful utlllsatlon of the coals and provide guldellnes for the large scale tests. All coal samples for the small scale work were obtained from sllm bore core. Wakefleld coals was tested by: 1.

Brennstoff lnstltut Freiberg and the University of Dresden, East Germany.

Babcock and WIicox Company, USA.

State Electrlclty Conwnlsslon of Victoria (SECV).

Kingston and Sedan were tested only by SECV due to t he experience gained with Wakef lei d coa I. The University of Dresden tested Wakefleld coal In both their micro-furnace of 6 gm/hand a labroatory furnace of 10 kg/h. In the micro furnace test, coal was added to a hot gas stream and a disc Inserted downstream to collect a deposit. The deposit was weighed and studied under a microscope. This test had the advantage that a very small amount of coal was used. The laboratory sea I e furnace was used for rate depos It meas urements at vary Ing gas temperatures. An Important aspect of the East German test program was to compare their local salty coal with Wakefleld coal and learn of their experience with that coal. The East German salty coal Is the only coal outside South Austral la being utlllsed, with slmllar properties to Wakefleld coal. The Babcock & WIicox program consisted of ash slnterlng strength and corrosion tests. For these tests flyash, Intended to slmulate full scale boller flyash, was prepared In a laboratory scale combustor. The ash slnterlng strength test Is conducted by forming the flyash Into cyl lndrlcal pellets which are then heated to temperatures representative of boiler flue gas temperatures for 15 hours. When cooled the compressive Australlan Coal Geology 4, part 1

207

E.R. Lindner

strength of the cyl lnders Is measured In a standard metal lurglcal testing mach I ne. The Intent Ion of the test Is that the compress I ve strength of the cyllnder wlll be related to the strength of the boller deposit. Coal ash corrosion tests were conducted on candidate superheater materlals by embedding them In flyash and subjecting them to a slmulated flue gas for 100 hours. Corrosion was measured by weight loss. The SECV programme Involved firing the coals with and without additives of different concentrations and compositions In their experlmental furnace (furnace diagram Figure 3). The weight of ash deposited on a slmulated superheater bank was monitored for each two hour run. The gas temperature at the bank and the tube metal temperature were control led at pre-set values. This work highlighted the fact that the ash build up rate which has been used by some research organ I sat I ons Is not the so I e er I ter I on for assess Ing the touting severity of a coal. Some assessment of deposit strength and adherence Is a Iso necessary . .Latg,e ~ Pulyerfsed ,CQa.J. Cgnbustlon Research

The large scale work was carried out by the fol towing two organisations: - Rhelnlsch Westfaehllsches Elektrlzltaetswerk (RWE), the largest power utl I lty In the Federal Republ le of Germany which has more than 10,000 MW or 60% of Its Installed capacity fuelled by brown coal. - Combustion Engineering Inc CCE), a large bolter, nuclear and processing plant manufacturer In the USA. For this large scale work significant tonnages of coal were required: Wakefield

RWE CE

210 tonnes 400 tonnes

Kingston

RWE CE

20 tonnes 270 tonnes

Sedan

RWE

20 tonnes

These tonnages are as mined values. For Combustion Engineering the coal was predr I ed to between 30-40% mo I sture pr I or to send Ing, due to the I r m11 11 ng capabl I !ties. To obtain the Wakefield sample ETSA opened a small test mine, 300m In diameter and 60m deep, 13km east of Port Wakefield. The test mine also obtained geotechnlcal and hydrological data for the future open cut mine In a region of complex sal lne water hydrology. Most of the overburden Is below the water table. For Kingston and Sedan, WMC and CSR respectively obtained samples by drllllng lm diameter cores. This Is the first time to the authors knowledge that coal core of this diameter has been extracted. RWE - WAKEFIELD, KINGSTON AND SEDAN TESTS

RWE has a down-fired, U-shaped combustion rig (Figure 4) designed for a thermal Input of 0.5-1.0 MW. The furnace Is 1.05m In diameter and 6.6m long. Austral Ian Coal Geology 4, part 1

0 00

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State Electricity Commission or Victoria, Diagrammatic layout of 35 kg/hr experimental furnace

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INJE CTION ( A.DDITIONAL GA Sf S ) INJECTION ( ADDITIONAL SOLID S)

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A ES E A AC H RIG.

N I E DER A USS E M

210

E. R. LI ndner

The fuel Is ground In an In-I lne beater mlll with optional classifiers. Drying of high-moisture coals Is by flue gas recirculation. The combustion chamber Is cooled by cold reheat steam from a nearby brown coal boiler. The combustion air Is heated between room temperature and about 500 0 C by a 2stage preheat system. Propane Is used for preheating the rig at start-ups. primary

Figure 5

mi•l!Xe

RWE Research Rig Nlederaussem, Burner

The burner (Figure 5) Is axlsymmetrlc with central fuel Inlet. The annular air supply Incorporates a variable sw I r I generator. Exchangeab I e primary and secondary nozzles can be fitted to the burner exit to vary velocity and momentum of both flows. The r I g Is equ I pped w Ith feeders which allow the addition of solid additives directly to the coal, or at other positions. For additional contro l of flame temperature, flue gas recirculation at several positions of the rig Is simulated us Ing c I ean f I ue gas at var I ab I e temperature from a nearby boiler.

flue oos r.-circula tion (op lionol)

The gas temperature Is measured by a suction pyrometer with a doubly shielded Platlnum-Platlnlm Rhodium thermocouple. Gas and solid samples are taken by a probe with cooler/dryer and filter. Fouling and slagging material Is collected on the surface of a deposit probe (Figure 6). The Instrument Is divided Into two sections. Next to the water cooled extension there Is an air cooled metal tube which simulates a "clean bol ler tube". The surface temperature Is set by a thermocouple which controls the air flow. The extremity Is an uncooled ceramic tube simulating a "fouled boiler tube". The deposit probe Is normally Inserted Into the combustion chamber during continuous operation for a certain length of time. The last convective heat sink In the second pass of the rig Is slmllarly made of ceramic and Is uncooled. The last-but-one convective heat sink Is made and operated In the same way as the air cooled probe section. Further flame probing Instruments for the determination of velocity and convective end radiative heat transfers are avallable. Analytlcal back-up for the rig consists of X-ray flourescence, X-ray diffraction and scanning electron microscopy. For the three coals the test programs

had the followlng objectives:

- determine combustion and burn-out characteristics - detect and qua I lfy slagging and foul Ing properties under utility bollder conditions - determine emission levels of gaseous coumpounds and Investigate the possibility of control llng sulphur dioxide by the addition of dry calcium-based materials

Austral Ian Coal Geology 4, part 1

E.R. Lindner

211

38mm

WAT[N COOL(D

TH[NMOCOU~L[

UTENSION

I-------

~01[ H[AD - - - - - - - ' 1 1 - i

RWE Research Rig Nlederaussem, Deposit Probe Figure 6 The usual set of measurements for each change In running conditions were: - complete axial, and If necessary, radial temperature distribution on the radiative and convective section - gas and solid sampling, axial to the combustion system - sampling of deposits Inside the system and at several positions on heat transfer surfaces (radiative and convective sections) - burn-out analysis - gas analysis (oxygen, carbon dioxide, carbon monoxide, sulphur dioxide and oxides of nitrogen If necessary) - chemical analysis of deposits and flyash (sodium, potassium, calcium, magnesium, silicon, aluminium, Iron, sulphur, titanium) - deposit photographs - Input and output control measurements of the rig Wakefield coal was tested for ten weeks while Kingston and Sedan coals were tested for only one week due to rig aval labl I lty and experience gained with Wakefield. With all the coals the same trends were evident In that the addition of finely ground calcium based materials to the coal achieved significant reduction of sulphur dioxide In the flue gas and In general weakened deposits.

COMBUSTION ENGINEERING - WAKEFIELD AND KINGSTON TESTS The Combustion Engineering facility Is comprised of a separate coal handling and pulverisation system with air preheater and a test furnace. The fireside performance test furnace Is fed pneumatically with pulverised coal from the coa I system hopper. The furnace Is upward f I red, 0.92m I nterna I d I ameter, Australian Coal Geology 4, part 1

212

E.R. Lindner

5.6m high and lined with 15cm of refractory. Cooling Is by air drawn through the 4cm annulus between the refractory and the outer casing (Figure 7). The s Ing I e burner, at the bottom of the f Ires I de performance test furnace, has adjustable vanes to control the secondary air swirl. The maximum capacity of the furance Is 1.2 W. Firing In the fireside performance test furnace simulates commercial bol ler time-temperature history. In the radiant zone there Is a removable waterwal I test panel of 0.44m In three sections each coo Ied separate Iy. The pane I's meta I temperature Is contro 11 ed typ Iea 11 y at 370 oe to simulate the conditions In the lower furnace of a utility boiler for studying ash deposition and slagging of the test fuel. Heat absorption through the panel Is measured by monitoring the coolant flow. Flue gases leave the combustion zone at a right ang le through a horizontal water cooled superheater duct (Figure 8). The cross-sectional area of this duct Is 0.09m. A water-cooled transition section surrounds the entrance of the superheater.

WATER l AIR COil.ED

SECTION J

Alt C001.£0

SECTION I

4 cm -

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5.6 m - 18'-4',"

WATERWAU

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NR COOUD SECTION V

WATER COOUD

SECTION VI

Figure 7 Canbustlon Engineering, Fi reside Performance test furnace. 3.95m long. Four banks of 20cm long, 5cm diameter, air-cooled probes are used Austral Ian Coal Geology 4, part 1

E.R. Lindner

213

to slmulate superheater tubes. Each bank contains two rows of probes. Probe outer metal temperature Is typlcally controlled at 595°c. The probe banks are Inserted vertlcal ly Into the duct. The facl I lty Is Instrumented to monitor and record all fuel and air Inputs and cool Ing flows. A gas analysls system measures oxygen, carbon dioxide, carbon monoxide, sulphur dioxide and oxides of n I trogen In the f I ue gas. FI ame and gas temperatures are per Iod I ea 11 y measured with high veloclty suction pyrometers. Standardised tests have been developed to study the Influence of furnace operat Ing parameters on ash depos It I on and to compare resu Its from sever a I coals tested In the fireside performance test furnace. Superheater deposition Is stud I ed by measur Ing the t I me requ I red to reach a standard pressure drop across the leadlng probe bank caused by deposit bulld-up, by measuring the mass of deposits accumulated on the probes In a given period and by measuring the tenacity of the bond between the deposit and the heat transfer surface. A surface penetrometer measures the force required to push the deposit off the probe. Measurements of bonding strength are made In sltu whlle the faclllty Is operating and with the direction of the force applied perpendlcular to the deposit and tangent to the probe surface (Figure 9). High temperature corrosion Is characteristic during a standardised 300 hour fireside performance test furnace run with the superheater probes made of the alloys being tested. Afterward the probes are subjected to extensive metal lurglcal examination. The lower furnace deposits are characterised by monitoring the heat flow through the waterwall test panel. A large number of deposit samples from each test are ana I ysed In deta 11 by CE 1 s Kre Is Inger Deve I opment Laboratory, Windsor and their central metallurglcal laboratory In Chattanooga, Tennessee. The CE test with regard to foul Ing and sulphur dioxide emission confirmed the same trends as occurred with the RWE tests. The CE work was also able to quantify Important parameters such as the strength of convection section deposits, maximum flame temperature above which the onset of severe foul Ing occurred, and the reduction In heat transfer due to slagglng. The results of the SECV and RWE tests Indicated that the propensity for foullng In bollers can be substantlally reduced by the adoption of low flame temperatures. This was proven by the work at CE and to the author's knowledge this Is the first time this has been demonstrated. RESEARCH INTO UTILISATION OF WAKEFIELD COAL BY DEWATERING TECHNOLOGIES ,CQAl. Pretreatment

The Austral Jan Coal Industry Research Laboratories Ltd. CACIRU Investigated the posslblllty of removal of alkalal material from the coal by washing. It has been demonstrated that this can be done, but large quantities of fresh water are required and coal partlcle size degeneration occurs. Wakefleld coal has been tested by the Department of Chemlcal Engineering, University of Melbourne, for the removal of alkal Jes during the thermal dewaterlng process. In this process the coal Is extruded In a pressure reactor where water Is thermal l y expel led from It and then depressurlzed to achieve up to 80% water removal. With Wakefleld coal up to 60% sodium was removed with the water. This process consequently would be beneflclal but needs to be developed to a commerclal stage.

Austral Ian Coal Geology 4, part 1

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E.R. Lindner

215

Figure 9 Combustion Engineering Test Furnace, Super Heater Deposit Bonding Strength Measurement

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FLUIDISED BED COMBUSTION RESEAROf Fluidised bed combustion research was carried out by two organisations: - CSIRO whose combustor has a bed 0.3m x 0.3m - Verelnlgte Kesselwerke, West Germany whose bed has an Internal diameter of 0.6m and height of 1.2m. The aim of the test work was to Investigate the behaviour of the bed material, Its Interaction with In-bed tube material, sulphur retention and combustion of fines In the free board. The results were Inconclusive due to the availability of the rigs and hardware problems. It Is highly unlikely that reliable plant on this principle will be available for the next stage of generation. CONQUS ION The research undertaken by ETSA Into the utilisation of South Austrlalan brown coals has shown that: - the potent I a I to cause severe fou 11 ng can be reduced by temperature Australian Coal Geology 4, part 1

lowering flame

216

E.R. Lindner

- addition of calcium based material to the coal can significantly reduce sulphur dioxide emission and In general r educe fouling . potential This research also has provided a set of parameters which are now being used by two boiler manufacturers who have been contracted by ETSA to conduct feasibility, design and cost studies for boilers to burn Wakefie ld, Kingston and Sedan coa Is. REFERENCE 01Br Ien, M.D., 1982, A br Ief descr Ipt Ion of South Austra 11 an Coa If Ie Ids. Resources of South Australia Seminar AIE and RACI July 1982.

Coa I

217

Liquetaction of Victorian Brown Coal G.J . Perry

Victorian Brown Coal Council , 151 Flinders Street, Melbourne, Victoria, 3000, Australia.

Key Words :

liquefaction, Victorian brown coal, properties, synthetic fuels, pilot plant .

hydrogenation,

coal

ABSTRACT Extensive deposits of brown coal exist in Victoria, primarily in the Latrobe Valley . The total quantities of economically winnable coal in this region of Victoria and in other sma 11 er fie 1ds are 1arge enough to adequately assure Victoria's future e 1ectri city needs and a 1so provide 1arge quantities for alternative applications, including liquefaction. The unique properties of Victorian brown coal, together with the possibility of large scale open cut mining make it particularly attractive for a synthetic fuels industry. Local and overseas research programmes have demonstrated that Victorian brown coal can be hydrogenated to produce liquid fuels in high yields . The coal properties which show the strongest relationships to hydrogenation reactivity are those primarily associated with the hydrogen content of the coal. Various studies for major liquefaction projects proposed by Australian, German and Japanese interests are being undertaken with the co-operation of the Victorian A brown coal liquefaction pilot plant is under Brown Coal Council. construction at Morwell , in the Latrobe Valley, to confirm the suitability of a catalytic hydrogenation process for production of liquid fuels. INTRODUCTION The Latrobe Valley coalfields in Victoria comprise not only one of the largest single deposits of brown coal in the world but, in many locations, also the most favourable for mining . The overburden is frequently only 15-20 metres thick and there are many examp 1es of test bores having traversed continuous coal deposits exceeding 300m in thickness. The total demonstrated resources of this region of the State are over 100,000 million tonnes and by application of stringent criteria based on the mode of occurrence of these deposits, economic reserves of 36,000 million tonnes have been assessed. Outside the Latrobe Valley significant deposits of brown coal have been located at Gelliondale, Stradbroke, Anglesea, Bacchus Marsh and

Australian Coal Geology 4, part 1

G.J. Perry

218

Altona, tota 11 i ng in a 11 an additional 8,500 mi 11 ion tonnes of economi ea lly winnable coal.

Growth in the State's demand for e l ectri city wi 11 continue to be based on brown coal in the foreseeable future; however, despite the increased coal consumption required for this purpose the brown coal reserves of Victoria are large enough to also provide large quantities for other uses, for example the production of liquid fuels. The management of the State's research and development programme into potential uses for brown coal, (excluding the production of electricity and substitute natural gas but including the production of liquid fuels), is the responsibility of the Victorian Brown Coal Council (VBCC). This paper outlines some of the new potential uses for Victorian brown coal with particular emphasis on liquefaction processes leading to the production of synthetic fuels. The types of processes available for liquefaction of Victorian brown coals are discussed and the brown coal properties which significantly influence liquefaction behaviour are identified. The progress being made towards the implementation of coal conversion projects in Victoria is outlined.

NEW POTENTIAL USES FOR VICTORIAN BROWN COAL The major uses of Victorian brown coa ~ at present are power generation, briquette production and char manufacture with power generation being by far the most significant use . Victorian brown coal has a high moisture content (50-70%) and low calorific value compared to higher rank coals and consequently has traditionally been viewed as suitable only for power generation and gas production. However, it is now recognized that with suitable up-grading, primarily drying, Victorian brown coal has the potential to become the basis of the supply of energy in a vari ety of forms. Products whi eh can potentially be produced from brown coal can be roughly grouped into four categories (Perry, 1982). 1. 2. 3. 4.

Synthetic Fuels Direct Fuels Special Carbons Chemicals and Polymers

This paper will concentrate on Victorian brown coal .

the production of synthetic fuels

from

DEMAND FOR SYNTHETIC FUELS IN AUSTRALIA Currently Australia is approximately 70% self sufficient in petroleum products and oil recovered from the Bass Strait off-shore oil fields contributes about 65% of the total Australian crude oil requirements. The proportion of oil requirements provided from indigenous sources is expected to decline after the year 1985 and new discoveries, even if made at an optimistic rate, will only extend this time span a few years. This is illustrated in Figure 1.

Australian Coal Geology 4, part 1

G.J. Perry

219

►

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PRODUCTION FROM EXISTING DISCOVERIES

1965

Figure 1.

1970

1975

1980

1985

1990

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Australia's Oil Supply and Demand with New Discoveries. Esso, 1980).

2000

(After

Brown coal accounts for about 95% of Victoria's non-renewable energy reserves whilst crude oil accounts for only 2.6%, however, this meagre amount of oil is currently supplying 52% of Victoria's energy requirements. The transport sector consumes approximately 85% of this oil. Clearly an imbalance exists in Victoria's, and indeed Australia's, energy use pattern which opens up opportunities for synthetic fuels from coal, particularly in the transport fuels sector. With Australia's long transport distances separating population centres and mineral resources, an adequate supply of gasoline and diesel fuels is vital. Victorian brown coal is particularly attractive for a synthetic fuels industry due to its ready availability combined with the minimal residue problems (compared to shale oil) and relatively low land use requirements (compared to synthetic fuel from biomass) . Synthetic fuels from brown coal have the ability to relieve our dependence on imported crude oil . COAL LIQUEFACTION PROCESSES The fundamental objective of all coal liquefaction processes is to change the chemi ea l composition of the coal , essentially by increasing its hydrogen to carbon ratio. This ratio which is typically 0. 8 to 1.0 in coal (approximately 0.9 in Victorian brown coal) should ideally be increased to within the range 1.6 to 2.0 for liquid fuels of acceptable quality .

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There are a variety of processes for producing synthetic fuels from coal and most of these can be grouped into four broad categories (Nowacki, 1979): pyrolysis, sol vent extraction, catalytic liquefaction and gas ifi cation plus synthesis. This latter process is an indirect route to coal liquefaction whilst the first three are termed direct liquefaction processes . A schematic flow diagram illustrating the major processes is shown in Figure 2 and these are briefly described below.

LIQUID PRODUCT

Oil HYOROTRfATING

PYROLYSIS

CHAR

SOLVENT EXTRACTION

SOLID OR LIQUID PRODUCT

SOLIDS SEPARATION

COAL HIHIHG AND PREPARATION

LIQUID PRODUCT

CATALYTIC HYDROGENATION CATALYTIC LIQUEFACTION

SOLIDS SEPARATION

SYNTHESIS GAS PRODUCTION

SHIFT CONVERSION

LIQUID PRODUCT LIQUID PRODUCT

HzS, COz REMOVAL HETHAHOL SYNTHESIS

IUHANOL

Figure 2. Major Coal Liquefaction Processes Pyrolysis or destructive distillation of coal involves heating the coal in the absence of oxygen to yield a heavy oil ( or tar), light liquids, gases and char. Generally more than 50% of the original coal remains as a char by-product and the heavy oil yield is usually only 10-30% of the feed coal. This heavy oil requires hydrogenation to produce liquid fuels of acceptable quality. Pyrolysis liquid yields can be maxi mi zed by very rapid heating of small coal particles at short residence times. The Commonwealth Scientific and Industrial Research Organization (CS I RO) is working on developing a flash pyrolysis process for Australian coals . Solvent extraction involves contacting coal at temperatures up to 550°C with a hydrogen donor solvent to maximize the f r action of coal which is solubilized. Examp 1es of this process are the Sol vent Refined Coal processes SRC I and SRC II. The National Coal Board (UK) is pioneering a supercritical extraction process by treating coal with selected solvents above their critical points. Under supercritical conditions the solvent in vapour form extracts some of the coal substance and carries it from the reactor . Reduction of pressure then causes the liquid extract to precipitate. Australian Coal Geology 4, part 1

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Catalytic coa 1 1i quefact ion i nvo 1ves hydrogenation of a coa 1/oil -s 1urry at temperatures between 400-500°C in the presence of a catalyst. The slurrying oil is usually a distillation ·traction of the product · liquids which is recycled. Liquefaction processes in this category are direct descendants of the classic Bergius hydrogenation technology. The H-Coal Process (Hydrocarbon Research Inc.) and the Exxon Corporation's EDS (Exxon Donor Solvent) Process are examples of catalytic coal liquefaction processes. The carbon monoxide steam process is a second gene rat ion coa 1 1i quefact ion technology which uses carbon monoxide or · synthesis gas (carbon monoxide plus hydrogen) i.n p 1ace of pure hydrogen. l;lydrogen _, is produced from the , carbon monoxide and water via the Water Gas Shift Reaction .

usually in the presen.ce of a catalyst-. .The, carbon monoxide steam· process is particularly attract·ive for low rank coals as they show high reactivitY and part of their inherent moisture can be utilized for hydrogen production via the shift reaction thereby reducing drying costs. • At present there is no generally accepted mechanism to adequately explain the -effectiveness of the carbon monoxide steam process for 1i quefact ion of ·low rank coa 1s and the importance of direct• interaction of carbon monoxide with the coal and the role of hydrogen produced by the shift reaction is .not fully understood. Indirect 1i quefact ion ofi coa 1 commences with the gas ifi cation of coa 1 with steam and oxygen to produce synthesis gas ( carbon monoxide p1us hydrogen) which is then converted to liquid hydrocarbons by using suitable catalysts and processing conditions · in the Fischer-Tropsch synthesis. The process is used by the only commerci a 1 sea 1e coa 1 1i quefact.i on p 1ant currently operating. This plant is being operated by SASOL in South Africa, where it is, politically, important to have a measure. of independence from imported, oil. Methanol · can a 1so be produced from synthesis gas and by .reaction of the methano-1 over zeo 1ite catalysts using the MTG process deve 1oped by Mobil , gaso 1i ne can be obtained (Le Blanc et al 1981) . • Each of the process types described above have their own particular technical advantages and disadvantages whi eh form , the , bas is for determining the economics of a process. The choice of a particular liqueJaction process is a complex one depending . not only on end -product requirements but .on the nature of the feed coal available, whilst bearing in mind economic considerations . Generally· speaking yields of oil from , pyrolysis processes are lower .than for the other direct liquefaction pro.c esses . and this is p~rticularly true for Victorian brown coal,. The solvent extraction and catalytic 1iquefaction processes are potentially. the most efficient methods .of producing ' oil from coa 1. • Howe·v er, one of the most difficult operations in these processes is ·the separation of the oil from the coal mineral matter and unreacted coal. Coals with high reactivity and a low mineral matter content -make 'the most desirable feeds tocks for these . processes. Fortunately ,Victorian brown coa 1 • possesses both of these features ~ . . The gasification and synthesis route to liquids has a lower thermal efficiency and higher capita 1 costs then the direct processes but has the di st i net advantage of employing proven technology and is far more tolerant of coals with a range of properties. In Victoria, to date, the majority of research and development activity has centred around the direct liquefaction processes. However, we should not lose Australian Coal Geology 4, part 1

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sight of the fact that brown coal may also be converted to synthesis gas, and, with the subsequent use of various catalytic reactions, be synthesized to a range of fuels including methanol and a variety of industrial feedstocks. RESEARCH PROGRAMMES Research into the liquefaction of Victorian brown coal is not new and it is interesting to note that in the 1930's following the demonstration in Germany that the process of direct hydrogenation of brown coal could produce synthetic transport fuels, an extensive and successful research programme was conducted in England on liquefaction of Victorian brown coal (Sinnet and Baragwanath, 1938). This research was conducted by Mr. George Baragwanath and staff of the Fuel Research Station, Greenwich, England on Yallourn, Yallourn North and Road trials of motor vehicles using gasoline Gelliondale brown coals. produced as a result of this research programme established the technical feasibility of converting Victorian brown coals to liquid fuels. Brown Coal Evaluation Programme In 1973 the Victorian Government initiated research and development activities aimed at evaluating the brown coal resource for conversion to liquid fuels. The Government invited private participation and eleven major companies or groups joined with the Government in financing the research. Since 1979 the Victorian Brown Coal Council has been responsible for these research activities. A Brown Coal Evaluation Programme was undertaken by the SECV's Herman Research Laboratory on the Counci 1 's beha 1f to acquire comp re hens i ve data on the characteristics of Victorian brown coa 1 such that tentative or firm coa 1 quality requirements for proposed conversion processes can be assessed and related to location and availability of coal supplies. To achieve this objective a sampling philosophy was adopted that would high1i ght the natura 1 variability of the coa 1 and indicate the range of coa 1 qua 1 it i es whi eh may be encountered during mining and ut i 1 i zat ion of the deposits. The programme commenced in the Latrobe Valley coal fields by sampling open cut faces and 220 mm diameter bore cores and was later extended to include major coal deposits outside the Latrobe Valley. To date in this study a tota 1 of 20 bores have been dri 11 ed in the major

Victorian coal fields and selected samples within each bore have been analysed for a variety of physical, chemical and petrographic characteristics and utilization parameters; 144 parameters in all. A complete correlation matrix and a cluster analysis have been produced from this data to enable relationships between coal properties to be determined. Analysis of this data has revea 1ed significant differences in coa 1 qua 1i ty between the different coa 1 fields enabling the identification of coal with specific properties for particular applications. In addition, the important factors governing the qua 1i ty of coa 1 for conversion have been i dent i fi ed (Perry and Kiss, 1982). Coal properties associated with the hydrogen content of the coal (e.g. hydrogen/carbon ratio, liptinite content, volatile matter) have shown the strongest relationships to hydrogenation reactiv i ty. The dependence of conversion on volatile matter content is illustrated in Figure 3. The vo 1 ume of data generated from this research programme represents one of the most comprehensive coal resource surveys in the world, and the data base of coal quality information will be drawn upon for many years to come. Australian Coal Geology 4, part 1

223

G. J. Perry

.•

•

,86

.. . .•• .... . .. .. 82 .............. "' 78 .... . . .. . 74 • . • . . ..-. • • •

I••

•

• I

9:'.:S •

r • 0.59

•

!,..

Cl)

Volatile Matter (% dmif) Figure 3.

Dependence of Conversion on Volatile Matter (151 Coal Samples)

Brown Coal Conversion Research Brown Coal Conversion Research is conducted by the Council with two principal objectives (a) To establish the hydrogenation reactivity characteristics of Victorian brown coals under a range of conditions selected where possible to parallel the operating conditions in liquefaction processes under development, and (b) To evaluate the relative hydrogenation performance of Victorian brown coal from various fields and relate this information to coal properties. Victorian brown coals have been found to be highly reactive under hydrogenation conditions often exhibiting conversion to liquid and gaseous products of over 90% (dmif, coal basis). This high hydrogenation reactivity is a consequence of the low levels of inertinite and, in many cases, the catalytic effects of inherent mineral and inorganic matter. If a hydrogen donor solvent is used heavy oil yields of approximately 50% (dmif, coal basis) are typical even without the addition of a catalyst. Oil yields can be increased significantly with the addition of a catalyst and this has the added advantage of improving the quality of the oil product. Significant differences have been observed in the hydrogenation performance of coal samples from different coal fields (Camier and Perry, 1981) and the optimum reaction conditions for maximum oil yield have been found to be clearly coal dependent.

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G. J. Perry

In addition to the Council's own research efforts in this area, research projects of a fundamental and applied nature are sponsored at a number of tertiary institutions in Victoria. DEVELOPMENT PROJECTS The Victorian' Brown Coal Council has received proposals from a number of companies and groups of companies who wish to develop the brown coal resource for a variety of uses including liquefaction. Major research and development projects and feasibility ; studies are now proceeding, through co-operation between these companies and the Council. Some of these projects will be briefly described . The Brown Coal Liquefaction (Victoria) Co . Ltd. (BCLV) Project This project was originally proposed by the KOMINIC group of Japanese companies (Kobe Steel Ltd. , Mitsubishi Chemical Industries Ltd., Nissho Iwai Co. Ltd.) to produce solid Solvent Refined Coal for use in coke-making for the Japanese ste~ l industry. It has now been redirected to the production of liquid fuels. As such, it has become attractive to the Japanese Government, and has been adopted by them as a "national project". A feasibility study has been conducted leading to a decision to start constr uction of a 50 tonne of dried coal/day pilot plant in Victoria in 1981, followed eventually by a demonstration plant and a commercial plant if satisfactory results are obtained from the research and development programme. A commercial plant would require the supply of about 30 million tonnes of coal per year - this is, equal to the present combined production of brown coal from the two· large open cuts supplying the State Electricity Commission's Latrobe Valley power stations. The pilot plant is now under construction on a 17 hectare site at Morwell and is expected to be operational during 1983. It will operate initially with coal from the Morwell open cut using a two stage process . The first stage of the process is a Catalysed Solvent Refined Coal process (C-SRC) using a disposable i ran-based catalyst. The SRC produced from Stage I wi 11 then be deashed and cata lyt i ea lly hydrogenated to liquid fuels in Stage I I. In addition to confirming the suitability of this process for Victorian brown coal the primary objective of the pilot plant wi 11 be to derive design and operating data necessary for scale-up. Funding of $200 million for the construction and operation of the pilot plant is being provided by the Japanese Government. The Victorian Government, through the Council, is contributing towards the cost by making land available for rental and by the provision of coal and services . The Mitsui SRC Development Co . Ltd./CSR Project This project is being pursued by the Mitsui SRC Development Co. Ltd. of Japan and the Australian company CSR Ltd., and is directed primarily to the production of solid SRC. This could be used in the Japanese steel industry ~s a component of coal blends for coke-making or as a feedstock for other processes producing, for example, electrode carbon or carbon fibre. The Mitsui ' process ·has been developed using· a pilot plant in Ohmuta, Japan; this plant has run extensively on Yallourn briquettes, and it ran exclusively on raw Morwel l brown coal for a period of approximately six months from Australian Coal Geology 4, part 1

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225

November 1980. To deal with the high moisture content of the coal a special dewatering section has been constructed ahead of the conversion stage. Arrangements have been made between the Mitsui Company and CSR Ltd. to provide for the management and conduct of a substantial feasibility study into the commercial application of the process. The preliminary evaluation phase of the study was completed in March this year and work is now concentrating on marketing investigations, refinement of technology in Japan, and some coal field studies in the Latrobe Valley. This project is based on a plant with a proposed capacity to process approximately 8 million tonnes of raw brown coal per year which could produce 800,000 tonnes of solid SRC and 300,000 tonnes of liquid products. The Rheinbraun Project The German company Rhei ni sche Braunkoh 1enwerke AG ( Rhei nbraun) has proposed that a study be conducted, based on process concepts deriving from German techno 1ogi ea 1 deve 1opments. The new study is to examine arrangements for producing brown coal as well as for constructing and operating the conversion plant itself. Rhei nbraun have successfully operated a sma 11 pi 1ot p1ant in Germany on Victorian brown coa 1 using a modification of the sump-phase hydrogenation process developed by Bergius and Pier in the 1920's. This process is a direct liquefaction process followed by product up-grading to liquid transport fuels (Brocker et al. 1980) . A commercial scale operation in Victoria would require approximately 30 million tonnes of brown coal per year. The BP Project BP Australia, in co-operation with the Council, i s carrying out an evaluation programme relating to the potential development of part of the Victorian brown coal resource for liquid transportation fuels. The study will identify economi ea lly and techni ea lly preferred conversion routes and wi 11 include an evaluation of the impact on local refining and marketing of · petroleum products . In support of this study, laboratory work is underway at the BP Australia Coal Research Laboratory in Melbourne on novel methods of brown coal dewatering . A co 11 aborat i ve research project with Monash University on brown coa 1 1i quefact ion using synthesis gas is also underway . The APM Project In December 1981 Austral i an Paper Manufacturers Ltd. proposed a staged development of the Rosedale coal field. The mine development stages involve geological assessment, then a trial open cut, followed by two mine expansion stages achieving full development in the late 1990 ' s . Technologies under consideration inc l ude:(i)

drying and pulverizing to produce "Drikol" - a process developed to pilot plant stage by APM at Maddingley in 1981;

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G. J. Perry

(ii)

coal-in-oil mixtures primarily for export;

(iii)

activated carbon - which is the subject of a separate feasibility study by APM, and ultimately

(iv)

SRC and/or coal liquefaction.

THE JOINT AUSTRALIA/FRG COAL-TO-OIL FEASIBILITY STUDY This comprehensive study is the result of an arrangement between the West German, Austra 1i an, Victorian, New South Wa 1es and Queens 1and Governments which began in 1979 and was reported late last year. The feasibility study examined in detail the processes, plant, infrastructure and economic factors i nvo 1ved in setting up coa 1 conversion p1ants designed for production of liquid fuels at sites in Victoria, New South Wales and Queensland. For the purposes of the study, Victoria specified that the nominal plant output be 3 million tonnes per year of transport fuels consisting of gasoline and automotive diesel oil in a 2: 1 ratio. The results of this study using Victorian brown coal have been very encouraging and the German partners have concluded that a plant in Victoria is economically and commercially justified. Discounted cash flow analyses of plant economics showed that for the Victorian case, depending on financing and commodity escalation assumptions, real returns on investment in the range of 7-29% per annum could be expected depending on debt/equity composition. Development strategies Many factors need to be considered to determine the preferred strategy for coal conversion development in Victoria . The Victorian Brown Coal Council has, and is, conducting studies designed to evaluate the factors that bear on the allocation of coal to the range of end uses, the selection of coal fields for development and the preferred approach to coal extraction, supply and conversion. The availability of brown coal is not considered a constraint. However, the availability of finance, labour and infrastructure and the influence of environmental factors will govern the rate at which coal conversion operations can be established . A major study, the Victorian Brown Coal Resource Development Study, has been commissioned by the Council to determine how the best use of the total Victorian brown coal resource can be achieved taking into account the factors mentioned above. The results of this study will be valuable in determining the best way to develop our brown coal resources for new applications, including the production of liquid fuels .

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REFERENCES Camier , R.J . and Perry, G. J . , 1981. Brown Coal Liquefaction: Batch autoclave hydrogenation of Victorian brown coals . State Electricity Commission of Victoria. Brown Coal Research Division . Scientific Report No. SC/81/26. Le Blanc, J.R. , Moore , D. 0. and Cover, A.E. , 1981. Hydrocarbon Processing, June 1981, 133-138. Nowacki , P. , 1979. Jersey, 13-21.

Coal Liquefaction Processes

Coal can be gasoline.

Noyes Data Corporation, New

Perry, G. J., 1982. New developments in the use of Victorian brown coal. Proc. Aust. Inst. Min. Metall. Annual Conference 1982, 59-73. -Perry, G.J. and Kiss L.T., 1982 . Relationships between Victorian brown coal characteristics and its liquefaction behaviour. Presented at Symposium on Characteristics of Australian Coals and their Consequences for Utilization. North Ryde, New South Wales, May 1982. Sinnet , F.S . and Baragwanath, G.E, 1938. The Hydrogenation of Victorian Brown Coals . Vol . 1-3.

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228

Characterisation of Victorian Brown Coals by Pyrolysis Techniques Combined with Gas Chromatography and Gas Chromatography - Mass Spectrometry R.P. Philp, T.D, Gilbert and N.J. Russell

CSIRO Division of Fossil Fuels, P.O. Box 136, North Ryde, N.S.W. 2113, Australia

Keywords:

Pyrolysis, soft brown coals, lignin structure, coal gelification, gas chromatography - mass spectrometry.

ABSTRACT The pyrolysis products of lignins from angiosperm and gymosperm plants, soft brown coal woods that have undergone varying degrees of gel ifi cation, and various soft brown coal l i thotypes were examined by gas chromatography-mass spectrometry. The soft brown coal samples were co 11 ected from the Latrobe Valley, Victoria. Comparison of pyrograms from lign i ns and soft brown coals supports a predominantly gymnosperm origin for the coals, as suggested by previous microscopic studies. Poorly gelified soft brown coal woods (xylites) contained significant amounts of furan-type products that were not found in the gelified soft brown coal wood samples. No systematic variation in the distribution of methoxy compounds with increase in the degree of gelification was observed in the soft brown coal woods . Although the qualitative distribution of characteristic compounds was similar for all lithotypes of each deposit, changes in their relative concentrations were observed with decrease in the colour index (i.e. with darkening) of the soft brown coal Pyrolysis-gas chromatography-mass spectrometry (Py-GC-MS) of lithotypes. cuticle and resin produced characteristic pyrograms that allowed contributions from each of these components to be identified in the pyrograms of the soft brown coal lithotypes. INTRODUCTION Characterization of the organic matter in coals is complicated by the fact that the bulk of this material is insoluble in most common organic solvents at normal temperatures and pressures (Francis, 1961). Although the soluble material can be readily characterized by analytical techniques such as gas chromatography (GC) and gas chromatography-mass spectrometry (GC-MS) (Philp, 1982), alternative approaches have to be used to examine the insoluble fraction. In recent years, non-deSfi:uctive techniques such as Fourier transC cross polarized, magic angle sample form infra-red spectroscopy and spinning, nuclear magnetic resonance spectroscopy have been used to obtain structural information on whole coals (Zilm et al. 1979). An alternative Australian Coal Geology 4, Part 1

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229

approach is to degrade the coal prior to analysis, analyse one or more soluble fractions, identify the degradation products and attempt to reassemble these compounds into a ·representative structure for the coals. Much of this work has centred on the use of various oxidizing reagents to partially or completely degrade the coal followed by GC and GC-MS to identify ·the products (Hayatsu et al . 1978). Another degradation-typ~ approach used for coal characterization is that of microscale pyrolysis (Py) techniques combined directly with GC or GC-MS ( Larter and Douglas, 1978). A variety of other geochemical samples such as algal mats (Philp, 1980), oil shales (Van De Meent et al. 1980) and oil source rocks- (Whelan et al. 1980) have al so been characterized in this manner . Information obtained by this technique has been used for structural determinations, oil-source identifications and thermal maturity measurements. This paper presents results obtained from a Py-GC and Py-GC-MS study of Victorian soft brown coal woods and lithotypes, including · resin and cuticular tissue samples. A more detailed account of the results · for prese·nt day " lignins and soft brown coal woods appears in Philp et al. (1982). The major aims of the study can be summarized as follows: (1)

To · evaluate the use of -pyrolysis for the characterization of soft · brown • coal woods and lithotypes.

(.2)

To determine the relative contribution of specific components -s.uch as lignins, cuticular material, , resi·ns and .soft brown coal woods to the various l ithotypes by comparison of pyrolysis products. (This approach is analogous to the 'biological marker' technique used to identify specific sources of organic matter ,in geochemi"cal samples (Eglinton, 1973)).

(3) .fo examine the relationship between the distribution of the pyrolysis prdducts and the colour of the soft brown lithotypes that results from variations in the degree of gelification, geochemical coa]ification and maceral composition. In addition, pyrolysis products from soft brown coal woods were compared with those obtained from present-day gymnosper.m and angiosperm l i gni ns. Several accounts of the microscopic characterization of present~day -and fossil Australian coniferous woods can be found in the literature (Nobes, •1922; Phillips, 1941; Patton, 1958), although some examples of angiosperm wood have been identified (Patton, 1958) . This does not necessarily reflect the paucity of angiosperms in the original flora, rather it reflects the lower resistance to degradation of the angiosperms compared with the gymnosperms (Teichmuller and Teichmuller, 1968). The present study provides chemical confirmation of the microscopic observations and should assist in the determination of the gymnosperm or angiosperm origin of gelified soft brown coal wood that ~annot be clearly identified under the microscope (See Philp et al. 1982 for further -details) . EXPERIMENTAL The l i thotype samples were selected as being representative of the . five principal soft brown coal l i thotypes present in the Vall ourn and Morwe 11 opencut mines, Latrobe Va 11 ey. The soft brown coal woods were selected to represent various degrees of gelification, ranging from ungelified , soft ' brown

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R.P. Philp, T.D. Gilbert and N.J. Russell

coal wood (Xylite) to gelified soft brown coal wood, for discrete woody material present in these opencut mines. The resin and cuticular tissue samples were hand picked in the field. The resin is uncontaminated, but the cuticular tissue sample may be contaminated with a small amount of woody material with which it was associated. The maceral composition of the samples was checked by examination under incident white light and fluorescence microscopy. Prior to pyrolysis the samples were exhaustively extracted with Ch 2 Cl,MeOH (1:1) for 40 hours. The extracted samples were pyrolysed using a chemical Data Systems pyroprobe at a rate of 20°C/ms with a final pyrolysis temperature of 610°C. The pyroprobe was interfaced to either a gas chromatograph or a gas chromatograph-mass spectrometer system. For the Py-GC analysis a HP 5700 gas chromatograph was used and the pyrolysis products were analysed directly on a OVlOl SCOT column (25m x 0.3mm i.d.) operated at 10°C for 4 min. and then temperature programmed to 270°C at 4°C/min. Helium was used as carrier gas at 2.5 ml/min. For the Py-GC-MS analyses, a Finnigan 4023 system was used with a Carbowax 20M WCOT silica column (25m x 0.18mm i.d.) for the soft brown coal woods or a Se-30 WCOT silica column to analyse the products from the soft brown coa 1 1i thotypes. The oven temperature of the gas chromatograph was initially held at 10°C for 2 min . and then programmed at 4°C/min. to 200°C for the Carbowax 20M column and 280°C for the Se-30 column. Operating conditions for the MS were: ionization vo 1tage 50-70 eV, filament current 300 A and ion source temperature 260°C. Mass spectral data were acquired using an INCOS data system. Tentative identification of compounds was achieved by comparison of mass spectra with EPA/NIH/NBS mass spectral data base and interpretation of individual mass spectra. Subs amp 1es of the soft brown coa 1 woods and 1i thotypes were prepared as polished particulate grain mounts suitable for petrographic analysis by incident 1 i ght, oi 1 immersion microscopy. Humi nite reflectance measurements and macera 1 analyses were carried out on the soft brown coa 1 woods in accordance with the recommendations of the Internat i ona 1 Committee for Coa 1 Petrology (Stach, 1975; ICCP, 1963, 1971, 1975). The samples were also examined by incident blue-light excitation microscopy in order to observe the huminite maceral autofluorescence (Philp et al. 1982). The Hunter, L., a, b System for quantitative colour measurement is briefly described by Hunter (1979). The co 1our index va 1ues supp 1i ed by the State Electricity Commission of Victoria (SECV) are calculated from the L, a, b values using "in house" equations; indices of 20-200 cover the dark to pale soft brown lithotype range found in the Yallourn and Morwell opencut mines. RESULTS AND DISCUSSION Petrography and Ultimate Analyses The sample descriptions (macroscopic appearance in hand specimen) and ultimate analyses for selected soft brown coal woods and soft brown coal lithotypes, and wood-derived material used in this study are presented in Table 1. In hand specimen the Victorian soft brown coal woods can be classified as ungelified (xylite), partially gelified or gelified. Increasing gelification is accompanied by a decrease in the atomic H/C ratio and a less well-defined decrease in the atomic 0/C. There is an overall increase in the huminite reflectance wi,th decrease in the atomic H/C ratio, i.e. increase in the degree of gelification.

Australian ·Coal Geology 4, Part 1

Till.I I 01-1.cal analy••• of preeent-day wood-d.erh·ed aaterlal. 5-ple deacrlption

Coloui lndez

day 1100d-derlved •terlal P. rM.iata Lipln fraction I. r!i!!!!!• Llgulo fraction llolocelluloae fraction

Pre ■ent

> C:

Ill ,.+ -s Ill

Tertiary ■oft brovn coal IIOOd• YaIIourn •••7taIIourn o7c lylita Partially gellfled xyllte Gellfled. ■ oft brown coal wood

Ill :,

0 Ill

llorwll ae•/llorwll 0/C Xylito Gellfled ■ oft brown coal wod

■ oft

brown coal wr,ode and llthot:,pee froa the Latrobe Valley, Victoria

lleigbt loaa (%)

Aah (% d.b.)

Ultiaate analy ■ la (% d.a.f .) s ~ II H C

Atoaic ratio 0/C H/C

3.6 4.S

1.10 o.so

56.08 56.98

6.15 6.09

0.12 0.20

37.35 36.33

0.30 0.40

1.31 1.21

o.so 0.42

:::tl

7. 7

1.90

43.23

6.21

0.20

S0.06

0.30

1. 71

0.87

:,,

.,, =r

180.0 117 .4

9.1 9.1

0.65 0.46

59.38 62.07

s.so S.16

0.09 0.09

34.91 32.SS

0.12 0.13

1.10 0.99

o.44 0.39

64.S

14.6

1.06

61.68

4.25

0.39

33.29

0.39

0.82

0.41

65.8

8.S 12.3

o. 73 1.s2

60.01 67.07

S.29 4.99

0.12 0.39

34.33 27 .37

0.25 0.18

I.OS 0.89

0.43 0.31

Ill -s ,.+

....

:--4 C>

..... c-

U.ptlnltea

.,,

ID 0

.....

Pale yellOlfi ■ h brown cuticular tl•aue Yellow, poroua, realn aa ■oclated with xyllte in -di'"" light brovn lithotype

7.3

0.12

66.66

6.04

0.66

3.2

0.10

77.44

8.35

0.35

26 .64 ♦

1.08

-0.3

ID -s ,.+

1.29

o.13

c..

Ill :, 326.0

13.57

0.29

L1tbotype•

Yalloura •••/Tallouro 0/C Pale litbotype Pale/l11ht brown lithotype lledi1a H1ht brovn lithotype Mad.h• dark brown/dark brown lithotype llorwll ae•/llorwll 0/C Pale lithotype Light brown lithotype lledi1a H1ht brown lithotype lledi1a dark brown Uthotype

183.7 138.6 109.8

7.S 12.4 12.1

1.08 69.SO 1.47 66.24 1.53 66.14

6.97 S.39 S.14

0.33 0.41 0.54

22. 75 27 .81 27.72

0.45 0.1s 0.46

1.20 0.97 0.93

0.2s 0.32 0.32

69.1

14.6

1.38

64.84

4. 78

0.53

29.SO

0.35

0.88

0.34

174. I 126.7 109.1 83.8

9.2 14.4 13. 7 13.8

2.25 2.51 2.62 2.36

70.Sl 65.59 66.87 65.72

6. IS 4.60 4. 70 4.51

0.58 o.84 0.84 0.85

22.53 28.73 27.31 28.63

0.23 0.24 0.28 o.29

1.04 0.84 0.84 0.82

0.24 0.33 0.31 0.33

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R.P. Philp, T.D. Gilbert anq N.J. Russell

232

Viewed under the microscope, an increase in the degree of gelification of the soft brown coal wood produces the following changes. (1)

Loss of detailed structure, e.g. bordering pits, and swelling of the cell wall tissue resulting in the ultimate closure of the cell lumen, i . e. the gelification series textinite - texto-ultimate - eu-ulminite.

(2)

Elimination of highly fluorescent cell wall tissue, which in part is equated with the removal of residual cellulosic material.

(3)

An overall increase in reflectance and a tendency towards homogenization of the huminite as it approaches low rank vitrinite in appearance.

It is generally accepted that the reflectance of wood-derived material increases with the degree of gelification (Teichmuller and Teichmuller, 1968; ICCP, 1975). This assumes that all woody material undergoes gelification during the brown coal stage of coal ifi cation and that the degree of gel i ficat ion reflects edaphic conditions (e . g. pH, Eh) in the peat and soft brown coal stages of coalification. However, it has been suggested that the differences in the reflectance of wood-deri v-ed material are due to differences in the structure of the original material (Ting, 1977). Thus differences in huminite refl~ctance may reflect resistanr.e to gelification and not the level of gelification, and hence the latter may not be directly correlated with the edaphic conditions . Py-GC and Py-GC-MS Lignins Pyrolysis of the lignins from P. radiata and E. regnans (Figures l(a) and (b)) produced specific compounds that permitted differentiation between the gymnosperm ( P. radiata) and the angiosperm ( E. regnans). Significant peaks are indicated on the pyrograms. The E. regnans pyrogram (Figure l(b)) is dominated by 3,4-dimethoxyphenol, 1,2,3-trimethoxybenzene, 3-methoxy-4-hydroxybenzaldehyde and 3,4-dimethoxyphenylethanone. In addition, three sy.ringyl derivatives previously shown to be characteristic of angiosperm lignin oxidation products (Hedges and Parker, 1976) are also present. By comparison, the P. radiata pyrogram (Figure l(a)) contains several vanillyl stuctures of the type generally thought to be associated with gymnosperm lignins (Birner et al. 1978). The major products in the P. radiata pyrogram are 1-methoxyphenol, 2-methoxy-4-methylphenol, 1,3,4-trimethyl-2-methoxybenzene, 1,2,3-trimethoxybenzene and another compound which has been tentatively identified as l-ethoxy-4-methoxybenzene. No syringyl-type structures were found in the P. radiata lignin pyrogram and hence the presence or absence of syri ngyl structures enables angiosperm and gymnosperm l i gni ns to be differentiated in these particular examples. Py-GC or Py-GC-MS provides a far more rapid analytical scheme for distinguishing between angiosperm and !'jymnosperm lignins than more classi-cal techniques such as oxidation. The presence of furan derivatives in the early portion of the P. radiata pyrogram probably indicates the incomplete removal of cellulose from this l1gnin fraction rather than their presence as an integral part of the lignin structure.

Australian Coal Geology 4, Part 1

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234

R.P. Philp, T. D. Gilbert and N. J . Russell

Resin The sample of Yallourn resin produced a pyrogram dominated by tetrasubstituted benzenes, substituted naphtha 1enes and i ndenes and a number of substituted phenanthrene carboxylic acids. In view of 'the fact that diterpenoid acids are known to be common constituents of brown coal resins, it is proposed that the phenanthrene carboxylic acids are formed from these diterpenoid acids. Cuticle Py-GC of a piece of hand-picked cuticle taken from the Loy Yang 1276 borehole (Flynn Field) produced the pyrogram shown in Figure 2. In addition to a small number of pheno 1i c components with short retention times, the dominant and characteristic feature of this pyrogram is the even/odd predominance of the alkenes in the c20 -C 7 q region . It is proposed that these compounds are formed by pyrolysis or wax esters present in the cuticular material. Such a pronounced distribution permits the cuticular material to be readily recognised amongst the pyrolysis products of the lithotypes. The presence of phenolic components in this pyrogram may, in part, represent minor contamination of the sample by woody constituents .

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Pyrogram obtained from Py-GC analysis of cuticular tissue . Each doub 1et is an a 1kene(*)/a 1kane pair and the carbon numbers of various components are indicated . Australian Coal Geology 4, Part 1

R.P. Philp, T.D. Gilbert and N.J. Russell

235

Soft brown coal woods Py-GC-MS of the soft brown coal woods listed in Table 1 resulted in qualitatively similar pyrograms. Figure 2 shows pyrograms typical of those obtained by Py-GC-MS of ungelified (Figure 3(a)) and gelified (Figure 3(b)) soft brown coal woods. The pyrograms are similar to that for P. radiata lignin and are dominated by the presence of 1-methoxypheno 1 and 2-methoxy-4-methyl pheno 1. Fu rans and vani llyl-type compounds are a 1so present in concentrations whi eh vary between samples. It is generally assumed that the furan derivatives are derived from the ce 11 ul ose fraction of the wood, and that the more rapidly biodegraded cellulose fraction is eliminated with increasing gelification. The presence of furan derivatives in the less gelified samples and their absence in the more highly gelified samples is consistent with this assumption. The four principal components in the pyrograms are 1-methoxyphenol, 2-methoxy-4-methylphenol, 3,4-dimethoxyphenol, 1,2,3-trimethoxybenzene, and two important observations can be made on the relative distributions of these components. First, 1-methoxypheno 1 and 2-methoxy-4-methyl pheno 1 , whi eh are the dominant components in almost all the soft brown coal woods, are also the dominant components in the milled wood (Philp et al. 1982) and lignin fraction of P. radiata. In the milled wood and l1gn1n fraction of E. regnans, 3 ,4-dimethoxypheno 1 and 1, 2, 3-trimethoxybenzene predominate. Hence, in addition to the presence or absence of syringyl derivatives, it appears that the relative concentrations of these four components is another useful parameter in determining the angiosperm and gymnosperm contribution to the brown coals. The majority of compounds produced by pyrolysis of the soft brown coal woods appear to reflect closely the structure of the original lignin . Although many structures have been proposed for lignin, that postulated by Freudenberg and Neish (1968) appears to be a useful model for illustrating the origin of many of the pyrolysis products observed in this study. The cleavage of one or two bonds within this lignin structure on pyrolysis could readily give rise to the substituted aromatic products identified in the pyrograms. The current study indicates that there is no systematic variation in the proportions of the different types of methoxyl-bearing components with increase in the degree of ge 1 ifi cation of the soft brown coa 1 wood. This observation, combined with the findings of solid state n.m.r. studies (Barron et al. 1980), suggests that all methoxy groups exhibit the same resistance to degradation during gel ification. Slight variations in the proportions of methoxy groups presumably reflect variations in the composition of the original plant lignin. The elimination of furan derivatives, indicative of the presence of cellulose, with increasing degree of gelification of the soft brown coal wood is the major clear trend of coalification observed in the pyrograms produced in this study. Soft brown coal lithotypes Soft brown coal lithotypes are composed of a variety of macerals, i.e. huminite (soft brown coal macerals derived from woods), resins, cuticular material and other liptinite macerals, sclerotinite, etc. (ICCP, 1975). The macroscopic co 1our of the Victorian soft brown coa 1 1 i thotypes varies with changes in their maceral composition (George, 1975). The dominant maceral in the lithotypes is humodetrinite, which represents a fine-grained, woody attri tus, the re 1at i ve abundance of whi eh decreases with decrease in the colour index. Decrease in the colour index of the soft brown coal lithotypes

Australian Coal Geology 4, Part 1

236

R.P. Philp, T.D. Gilbert and N.J. Russell

is associated with a decrease in the liptinite content and an increase in the humotelinite and humocollinite contents (George, 1975). Since the decrease in the colour index, i.e. darkening, of the lithotypes is also associated with an increase in the degree of gel ification of the huminite component, similar trends in the distribution of aromatic products might be expected in the l i thotypes as were observed with increasing gel i fi cation of the soft brown coal woods. In a previous study, Chaffee et al. (1982) examined a series of lithotypes from the Flynn field in the Loy Yang region of the Latrobe Valley and observed a number of changes within the pyrolysis products that could be correlated with variations in the colour of the lithotype. The proportion of components in the triterpenoid region decreased with decrease in the colour index of the lithotype whereas the proportion of phenolic components generally increased. Although it is not possible to make a direct comparison of the pyrolysis results for the Yallourn and Morwell samples (pre-extracted coals) with those from Loy Yang (whole coals) (Chaffee et al. 1982), certain similarities were observed. Figure 4 is a comparison of the pyrolysis products from pale and medium dark lithotypes from Yallourn. The 'medium dark' pyrogram is dominated by phenolic components similar in nature to those described above for the soft brown coal woods. By comparison, the pyrogram for the pale l ithotype is characterized by a relatively high concentration of prist-1-ene, prist-2-ene, aliphatic hydrocarbons above the C?n region and a relatively complex mixture The phenolic of predominantly pentacyc l i c unsaturated tri terpenoi ds. components are also present, although in relatively lower concentrations than in the medium dark lithotype. Within each group of compounds (i.e. aromatics, isoprenoids, aliphatics and triterpenoids), the relative distribution of individual components is the same in all the Yallourn lithotypes. Variations in the relative proportions of the groups of compounds probably reflect changes in niaceral composition . For example, in the darker l ithotypes, the increase in the relative concentration of aromatic products and decrease in the concentration of the other components by comparison with the paler lithotypes may be due to an increase in the concentration of soft brown coal wood material and decrease in the proportion of liptinite . Pyrograms from two of the Morwell lithotypes (Figure 5) illustrate some of the changes observed within these l i thotypes. There are only slight differences in the distribution of pyrolysis products for the Yallourn and Morwell lithotypes which is consistent with their similarity in rank. As mentioned above there are four major classes of pyrolysis products in each of the Yallourn and Morwell pyrograms (see Figure 4). The aromatic components, predominantly substituted phenols, are derived from the soft brown coal woods. The unsaturated isoprenoids, prist-1-ene and prist-2-ene, are found in the pyrolysis products of a large variety of geochemi ea l samples and have been postulated as being derived from th~ phytyl side chain of chlorophyll (Larter et al. 1979). The triterpenoids, which have been shown by GC-MS to be predominantly pentacyclic triterpenes with one or two double bonds, are present as a fairly complex mixture wi th similar distributions in all the lithotypes from each deposit. Chaffee et al. (1982) mentioned that the identification of the fully saturated hopane-type triterpanes, particularly those with greater than 30 carbon atoms, provided good chemical evidence for th~ presence and presumed action of bacteria in the early stages of diagenesis of these lithotypes, since these compounds are known to be derived by degradation of molecules presently known in some living bacteria and blue green algal species.

Australian Coal Geology 4, Part 1

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240

R.P . Philp, T.D. Gilbert and N.J. Russell

In the present study, only relatively small quantities of the fully saturated triterpenoids were observed. The majority of the components contained one or two double bonds suggesting that either the precursor molecules were linked to the residues by ether or ester linkages, or they were present as relatively high molecular weight and polar derivatives in the coals and not removed during the extraction procedure. In either case, pyrolysis would lead to removal of the functional group or cleavage of the ester linkage to produce an unsaturated triterpenoid. The distribution could be useful in partially differentiating source variations between the deposits . A final comment should be made on the distribution of the aliphatic hydrocarbons in the C to C O region . As described above, pyrolysis of a pure sample of cuticul1~ matef1al produced a pyrogram dominated by al kenes with a marked even/odd preference in the C2 ? to C30 region and a maximum at C?h· It was proposed that the alkenes are cre~ived from the long chain wax esters. It is therefore suggested that the very marked even/odd alkene distribution in the C?fl-c 30 region of the lithotype pyrograms originates from the presence of cuticcrrar or similar liptinitic material in the soft brown coal itself. Pyrolysis of the long chain wax esters, which may be an integral part of the insoluble portion of the coal, will preferentially form the alkenes rather This distribution is far more evident in the Yallourn than alkanes. lithotypes than the Morwell lithotypes and possibly reflects a difference in relative amounts of cuticular (or similar l iptinitic) material in the two deposits. The even/odd al kane distribution over the C20 -c 10 region of the Yallourn lithotype pyrograms is slightly more difficurt tb explain. If a cracking mechanism was responsible for the distribution of the n-alkanes, this would imply a predominance of even numbered alkane precursors Tn the coals as well as even numbered alkene precursors. The situation is slightly different in the Morwe 11 samples where the al kenes are no longer dominant over the al kanes in t~e C:i 0-c 1 0. region, al though a slight even/odd predominance is observed in this rtrgio~\Figure 5), especially in the darker lithotypes. CONCLUSIONS Pyrolysis combined with gas chromatography and gas chromatography-mass spectrometry has been used to characterize l i gni n, resinous and cut i cul ar material , soft brown coal woods and various soft brown coal l i thotypes from the Yallourn and Morwell brown coal deposits in Victoria. From a purely qualitative point of view, the distributions of the various classes of pyrolysis products from lithotypes from one deposit are similar to each other, al though they are different from the corresponding lit ho types of the other deposit. In particular, significant differences i n the pentacyclic triterpenoids and alkene/alkanes were observed in the lithotypes from the two deposits . Darkening (i.e. decrease in the colour index) of the Yallourn and Morwell soft brown coal lithotypes is associated with a relative increase in concentration of the phenolic components over that of the aliphatic and alicyclic components, a fact previously observed by Chaffee et al. (1982) for the Loy Yang soft brown coal l i thotypes. The GC-MS results are consistent with the hypothesis that this decrease in the colour index of the lithotypes is due to the combined effects of an increase in the concentration and degree of gel ification of the woody constitutents and a decrease in the content of l ipti nite.

Australian Coal Geology 4, Part 1

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241

Examination of the pyrolysis products from specific components of the soft brown coal l i thotypes such as resin, cuticle and soft brown coal woods has permitted certain products to be i dent ifi ed that can be used as marker compounds to indicate the presence or absence of particular components in the soft brown coal lithotypes. An extension of this approach to other components (e.g. suberinite) in the lithotypes should prove valuable in obtaining a further insight into lithotype composition and provide information that can be readily correlated with microscopic observations. ACKNOWLEDGEMENTS The authors wish to thank Mr. E. Murray for preparation of the polished specimens for microscopic examination; Mrs . J . Friedrich for assistance with the solvent extraction and column chromatography of the soft brown coals prior to GC-MS analysis; the Victorian Brown Coal Council and State Electricity Commission of Victoria (SECV) for their assistance to N.J. Russell in the collection of the samples; and t1r. L.T. Kiss, Mr. A.M. George and Mr. C. Murdoch (SECV) for providing the quantitative colour measurements for the soft brown coal samples. Support was provided under the National Energy Research, Development and Demonstration Program administered by the Commonwealth Department of National Development and Energy. REFERENCES Barron, P. F. , Russell, N.J. and Albert, S., 1980 . Gelification of woody brown relationship between petrographic properties and gross chemical coal: composition determined by solid state n.m.r. In 5th Austrlian Workshop on Coal Hydrogenation, Sydney, 7.3-7.7 Birner, J., Given, P.J . and Raj, S. , 1978. Phenols as chemical fossils in coals. In Organic chemistry of coal (Larsen, J . W. , ed. )A.C.S. Symposium Series No . 71, 86-99. Chaffee, A.L., Perry, G.J. and Johns, B.R., 1982. Pyrolysis-gas chromatography of Australian coals. I. Victorian brown coal lithotypes. Fuel (in press). Eglinton, G. , 1973. Chemical fossils. A combined organic geochemical and environmental approach . Pure Appl. Chem. 34, 611-632. Francis, W. , London.

1961.

Coal - its formation and composition,

Edward

Arnold,

Freudenberg, K. and Neish, A.C . , 1968. In Constitution and biosynthesis of lignin, Springer-Verlag, New York, 103 . George, A. M. , 1975. Brown coal l i thotypes in the Latrobe Va 11 ey deposits. State Electricity Commission of Victoria, Exploration and Geological Division, Petrological report no . 17, August 1975 (unpublished) . Hayatsu, R., Winans, R.E., Scott, R.G .·, Moore, L.P.and Studier, M.H., 1978. Trapped organic compounds and aromatic units in coals . Fuel 57, 541-548. Hedges, J.I . and Parker, D. L., 1976 . Land-derived organic matter in surface sediments from the Gulf of Mexico . Geochim. Cosmochim. Acta 40, 1019-1031

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Hunter, P.S., 1979. 218), 68-72.

How does it look to you? Industr ial Research/Development

International Committee for Coal Petrology, 1963. Coal Petrography, CNRS, Paris, Second Edition.

International Handbook of

International Committee for Coal Petrology, 1971. International Handbook of Coal Petrography, CNRS, Paris . Supplement to Second Edition. International Committee for Coal Petrology, 1975. International Handbook of Coal Petrography, CNRS, Paris, Second supplement to the Second Ed1t1on . Larter, S.R. and Douglas, A.G., 1978. Low molecular weight aromatic hydrocarbons in coal maceral pyrolysates as indicators of diagenesis and organic matter type. In Environmental biogeochemistry and geomicrobiology (Krumbein, W.E., ed), Ann Arbor, Micigan, 373-386. Larter, S.R., Solli, H., Douglas, A.G., De Lange F., and De Leeuw, J.W., 1979. Occurrence and significance of prist-1-ene in ke rogen pyrolysates . Nature -279, 405-408 . Nobes, E.D., 1922 . A preliminary note on the fossil woods from some Australian brown coal deposits. R. Soc. S. Aust . trans. 46, 528-536. Patton, R.T., 1927. Anatomy of Australian coniferous timbers. Vic. 40(NS), Part L, 1-16. Patton, R. T., 1958. 70, 129-143.

Proc . R. Soc.

Fossil wood from Victorian brown coal . Proc . R. Soc. Vic .

Phillips, E.W.J., 1941. The identification of coniferous woods by their microscopic structure. Linn. Soc. Lond. ~- 52, 259-314 . Philp, R. P. , 1980. Comparative organic geochemical studies of recent algal mats and sediments of algal mats and sediments of algal origin. In Bio eochemistr of ancient and modern environments (Trudinger, P.A., Walter, M. R. and Ralph, B. J., eds , Australian Academy of Sciences, Canberra, 173-185. Philp, R. P., 1982 . Application of computerized gas chromatography-mass spectrometry to fossil fuel research . Spectra (in press). Philp, R. P. , Russell, N.J., Gilbert , T.D . and Friedrich, J.M. (1982) Characterization of Victorian soft brown coal wood by microscopic techniques and Curie point pyrolysis combined with gas chromatography-mass spectrometry. J. Anal . Appl. Pyrol. i (in press) . Stach, E. , 1975 . Textbook of coal petrology, Gebruder Borntraeger, Berlin, Second completely revised edition (English translation). Teichmuller, M. and Teichmuller, R., 1968. Cainozoic and Mesozoic coal deposits of Germany. In Coal and coal bearing strata (Murchison, D.G. and Westall, T. S., eds) . , Oliver and Boyd, Edinburgh, 347-379. Ting,

F.T.C., 1977. Microscopic investigation of the transformation (diagenesis) from peat to lignite. J. Microsc. 109, 75-83.

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Van de Meent, D., Brown, S. C. , Philp, R.P. and Simoneit, B.R., 1980. Pyrolysis-high resolution gas chromatography and pyrolysis gas chromatography-mass spectrometry of kerogens and kerogen precursors. Geochim. Cosmochim. Acta 44(7), 999-1013. Whelan, J.K., Hunt, J.M . and Jue, A.Y . , 1980. Applications pf thermal distillation-pyrolysis to petroleum source rock studies and marine pollution. J. Anal . APpl. Pyrol . ~. 79-96 . Ailm, K.W., Pugmire, R.J., Grant, D.M., Wood, R.E. and Wiser, W. H., 1979. A comparison of the carbon-13 NMR spectra of solid coal and their liquids obtained by catalytic hydrogenation. Fuel 58, 11-16.

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244

Thailand Lignite Development P. Chumroum and

R. Corslrl

Electricity Generation Authority of Thailand KEY WORDS:

Lignite, Tertiary, coal resources, Thailand, surface mining.

ABSTRACT Cenozolc basins In Thailand are located In many small Jntermontane areas. The sma 11 er bas Ins are ma In Iy fau It-bounded grabens formed by react I vat I on of basement structures. Coal deposits have been found mostly Jn Tertiary strata. About 80% of occurrences are Jn smal I structural basins. Thal land has at least 57 localities of coal occurrence most of which await further geological Investigation and development. Exploration and mining for I Ignite Jn the country are mainly conducted by Electricity Generating Authority of Thailand CEGAT> for power generation purposes. EGAT, Jn co-operation wIth Department of Mineral Resources CDMR) of Thailand has been conducting preliminary geological Investigations In many Tertiary basins since 1979. These will be extended to assess the coal resource potential for long-term planning. Exploration by private companies Is also underway, and although presently very limited, Is expected to Increase. At present only six coal areas are being mined by two governmental agencies and three pr I vate f I rms. A11 of these are opencast mInes. The two Iargest mines belong to EGAT and produce more than 90% of the nation's I Ignite production. EGAT plans to expand production within the next ten years to 12 mill Ion tonne/year at Mae Moh, to fuel the adjacent power stations. Coal from smal I private mines has been used as fuel Jn the tobacco Industry and In cement production. Although Thal land has a long history of coal mining, Its fu I I potent I a I has not been deve Ioped. SI nee the mI d-1970 1 s the demand for coa I has been I ncreas Ing rap Id I y and th Is trend Is expected to cont I nue, as the cost of using coal Is still very low compared with other sources energy.

INTRODUCTION The first explorer and miner of I Ignite In Thal land was Mr. Robert Young, an Engl Jsh resident of Penang, who In 1889 operated at a local Jty near Krabl town. In 1917, after King Rama the sixth Introduced the Forest Conservation Poilcy, the Royal State Railways of Thailand had to f ind an alternative fuel to replace fire logs. As a result of this search large quantities of I Ignite were discovered Jn Mae Moh, Krabl and Klansa basins. The further exploration and development, however was very limited due to the economic and technological difficulties. From 1950 to 1952, under the Colombo Plan, the U.S. and Australian Governments assisted by sending equipment and geologists for exp Iorat Ion programs at Mae Moh and Krab I. In th Is per I od, Mr. C.S. GIoe, a geologlst from the State Electricity Commission of Victoria, spent more than one year In Thailand. As a result of this exploration, two open-cut I Ignite Australian Coal Geology 4, part 1

P. Chumroum & R. Corslrl

245

mines were developed In the following year. A !Ignite fired power station of 12.5 MW was operated from 1960 to 1979 at Mae Moh and another of 60 MW from 1965 to the present at Krabl. Following the oll crisis In 1973, the exploration and development of I Ignite has Increased. In Mae Moh, the I Ignite production has gone from less than 100,000 tons to 1.8 ml I I Ion tons per year, to fuel three 75 MW units which have been operating since 1981. An additional four units of 150 MW each are present Iy under construction. Our Ing 1980-1981 I ntens lve geo log lea I exp Ioration was carried out In the rest of the basin. Lignite reserves are estimated at 451.6 mllllon tonnes that can be mined at the current economic costs, and there are enough reserves to accommodate 2,000 MW total capacity for the life of the power stations. In Krabl, I Ignite production of 300,000 tonnes per year suppl Jes the existing powerplant. Large scale exploration which Included surface geophysical methods, has been completed. The pref lmlnary drl I I Ing results show that the I Ignite resource could be large. The on-going exploration programs wl I I assess the feaslblllty of mining In the near future. Throughout the country, activity In Thailand I Ignite development has Increased rapidly, both by the private sector and by government departments. A countrywide exploration plan Is being set up by OMR and EGAT In order to explore and develop alternative domestic sources of energy. About 57 Cenozolc basins have been mapped In Thailand and most contain coal In the Tertiary strata. Further exploration by EGAT using systematic modern techniques Is Increasing, and the rate of accumulation of geological data has dramatically Increased. This paper contains a summary of Thailand regional Cenozolc basins and their coal occurrences, some preliminary results of exploration In various basins, detal Is of exploration techniques being used by EGAT, mining activity of Thal land coal, domestic coal utl I lzatlon and a discussion of future activities. REGIONAL CENOZOIC BASIN GEOLOGY OF THAILAND LIGNITE OCCURRENCES Cenozotc deposits (see Figures 1A, 1B, 2) occur In several regions, both on land and offshore. In northern and southern Thal land, they occur In smal I lntermontane basins, whereas In the central region they form a large regional depression. Offshore they occupy part of the Gulf of Thailand. In the northern region there are 49 I lsted basins whose surface areas range from 30 to 1,400 sq. km. In the centra I reg I on the I argest bas In Is about 60,200 sq. km., covers the depression of the Chao Phraya river basin. Only eight smal I basins are reported In the southern region. The present day surface elevations of the basins vary from 86m below mean sea level In the Pattanl Trough In the Gu If to 820m above mean sea Ieve I at Ban Hauy Dua, Mae Hong Son prov I nee In the northern reg I on. The bas Ins, pr Inc I pa I I y fau It-bounded grabens and ha If grabens, were formed by the react I vat I on of basement structures. The Intermittent major movements In the Tertiary orogeny which formed the present physlographlc features probably ended In the Wallachlan (Late Pllocene). The subsidence In the central region was formed simultaneously with emerging fault blocks associated with basalt In the northern region.

Austral Ian Coal Geology 4, part 1

P. Chumroum & R. Corslrl

246

LL.

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Austral Ian Coal Geology 4, part 1

247

P. Chumroum & R. Corslrl

QUATERNARY

LOWER QUATERNARY

TERTIARY

MIDDLE TERTIARY

LOWER TERTIARY

Recent flood plain,alluvial sand silt, back swamp deposits, beach sand Terrace gravel, sand, silt laterite and lateritic soil Semi- and consolidated conglomerate, sandstone, shale, coal with fossils, limestone Sandstone brick red, fine medium grained, fairly well sorted, massive, with very large scale cross-beds Siltstone,shale,sandstone, brick or purplish red, weathered white to grey, thin to thick bedded, rock salt, potash, gypsum and anhydrite LIHITE 111111 O~t:N CUT

CENOZOIC

BASINS

OF THAILAND SCALE 0

100 km.

FIG.18

Australian Coal Geology 4, part 1

P. Chumroum & R. Corslrl

248

102

106

BANGKOK @

,, 0

: 0

·,

BASIN 0

100

200

SCALE IN

300

400

500

KILOMETRES

LOCATION MAP THAILAND

LIGNITE

MINES

Australian Coal Geology 4, part 1

FIG.2

P. Chumroum & R. Corslrl

249

Fine terrlgenous association: sediment types In approximate order of abundance are sandstone, mudstone, coal, oil shale, carbonate, dlatomlte and gypsum. Strata Inc I ude mass Ive, f Iss 11 e, ea Icareous, and toss 11 Iferous sequences. Fossil beds mostly contain plant remains associated with coal laminae. Fish and Insect fragments, arthropods, and gastropods are common. These all suggest a shallow lacustrlne envlronmentwlth a variety of associated fluvlal, coastal swamp and subllttoral facles. Fine terrlgenous-carbonate association: sediment types In approximate order of abundance are mudstone, sandstone, ol I sha I e, carbonate and gypsum. The coarse-grained sediment Is pebbly, and the fine-grained sediment Is calcareous or carbonaceous. Mass I ve, f I ss 11 e, and we I I strat If I e.d beds are common. A lacustrlne environment of moderate depth Is suggested .

.CW occurrences .arul pcOJ;>ertfes Coal measures occur as deposits of coal and I Igneous claystone. The measures are generally under I a In and lntebedded with claystone. Thlcknesses vary laterally and quallty varies both vertlcally and horlzontally. Coal seams are malnly banded, consisting of flnely Inter layered vltraln, and attrltal. Impurities Include clay lenses and layers, pyrite, calcareous nodules and gastropod shel Is. Phys lea I properties In general are concholdal to platy fractures; vitreous to earthy luster; 1.2 to 1.5 specific gravity; and 9.7 to 32.5Mj/kg In heat Ing va I ue. MI croscop Ic exam I nat Ion of Mae Moh coa I shows that flnely detrltal hum le components form more than 95% of the material; sclerotlnlte and reslnlte are rare, pollen and fungal spores occur In smal I amounts. The coal was described as the decomposition product of stems, leaves, and roots of herbaceous plants. Apparent rank of coals as Indicated by Its heating value, ranges from !Ignite to bituminous class. Proximate analyses of coal from various places Indicate that constituents vary considerably. The composltlonal proportion Is considered by weight percent. Fixed carbon values can be as high as 60% whl le the mIn I mum content of vo I at 11 es Is as I ow as a few percent. Mo I sture content varies and Is generally below 35%. Mlneral matter and sulphur content Is high. The maximum ash yleld Is 45.39%, and the sulphur content average for 68 samples Is 3.7% (Ratanasthlen, 1980). EXPLORATION ACTIVITIES Although the major exploration Is carried out by government departments, Interest from the private sector Is Increasing. There are three major goverment departments responslble for coal exploratlon activity which are:DMR - Control and regulate exploration NEA - Exp Iore In the 11 censed area, approved by DMR and seek sma I I er sea I e coal supplles for Industries. EGAT - Explore In the licensed and/or co-project area with DMR. on large scale deposits for power generation.

Emphasis Is

Among these three organisations, EGAT Is the largest exploratlon (and mining) organisation In the country.

Austral Ian Coal Geology 4, part 1

N I.TI

IYITUI

S.,,n

Or E-h

PUttOD

HOIITH(IIIN

h.,.....: ~

,,N. I WAtSOOk

-+ DI

tt••>

Plots-.

l; -

Ploocono

0 DI

,DI

!fldPoolhaiofld:,

Miocene ►

,. ii

Cinwol

Ci<o...

Gnwtl-loulder

Sand/Clay

Sood/ Cloy

Clor 11,ooo ft. I

l(OOfll

A,--

M - Cool

011 Sood

CloJ/Sftalt

CHAI ,,,_AKAftM

~,.o,o, OU ShcNe ColeartOUI Sand Ma,I

t+1,2oofU

-.,c:aic..-, Qf'Nftlth (+10011.I

-.---

, TNo , . . . , _ Llffltttonl

O,ISGncl

NOT

REACHED

Softdapebbll

-··

,111111

·8"llokaaW111

F~~!! .. '

"tl

-s-(")

-::r

=-~

No-, 1cwlo Sq

1 :§

J;8 1 + M

8 "-

iii=

·-

tft Cotl ( Lq.1•)

j j

i§ i l f -.! ♦

i. i.

;L,t -~

►

,:: ,::

....5

-~"'°_,.. EMO s.--ToaodNIR ll'IO..,. ..

s ~ ...- c . . c .. p1_1? IS,

__..1, _ _

------L-------

1.Eocen1 to.Ii ( f 1 hM

ean Non1J v.. , c ~ I K•U .. ,G E.Jt74 ,....anot COl'nfflWfttCOflOfl)

(c 1 PropoMd

t.-~-

SoliM

Sond,,N

I bi .ia,,,_.1,J. 119691

Cloya5-

..........

' - - ' E d.

IHI" I IIOnN,efflbeddN

1•500ft.)

·--

ANO fLOIIAL

olld~,IIU

>.-·-OD-1""'-",IHII .......... Sq, S-,,-.Sq,

s-.. -1..

lal llunMll,Col.Somakll9691

(81,111'1ftOQ,1Hland ,

,!ii

J- 4 MottodOft - ~

~-'.!.~!,!.)_

Cl:NTltAL

IANaKOIC 7

P1ont·0.,-,1,_

'E.

011 Shol• Majo,'Cool

Lelerite

I Fie•- C1'f-

- - • S q.

IAIIN -

c,.,

◄ . Pttrili••

----

6 -~ ,;;

PHRAYA

AY!JOH'tAI

AlhMwM

SIU

~fillllnlfllty

CHAO

PootMi,11•1)

Clay

1.Ccirboftii• Wood

►

SaftdySNlo

,...,,u

Ptlleocene

1+40011.1

t.u.C SOON

Eocena

------ ----

.,._ Coot

::;

!(>Oft.I

Major Cool

Mif'IOf' Cool

Clr9Clf'OCSholo

Mift•OII Sha ..

-- - ---~ ------

Sholl

"'...

---l<>0fll

.....,

l Tol&oyo,t9•1)

... 11,o..,;,,.., AUwh••

.,__ __(,!_~•:!._

011gocene

l .......,_, ,AIMA AM) ,u.M. )

£ndo ,I M ◄ allM

Allw...,_

Sand/Cloy

er <l

;::

Ml DATNM ,_,.. "'HLI

Allwk,•

c:aic..---

-·· ,

.,__ - ~-!..~~-! .-

I.Cl

CINC"-a,1174)

Atkolilc SoM

Si....,., •• ,.,

G"l

(Gk>e,IISS ,~.1111

L1 4 18-,IHI

lll ------ - - ---- - - ---- -----Allwwto

IASIN

INTUIMONTAN(

--1

•NO CHIAHGlll~I

( Bwo.o.,Col. S,

Recent

WAI IOT 1

lty 1M writer hi !hit pap9f' .

Table 1. Stratigraphic Correlation of Major Tertiary Basins in Thailand.

NOT

REACHED

"";:o

251

P. Chumroum & R. Corslrl SYS TEii

Seri•

P[RIOO

Epodl

OFFSHORE

GULF

F"LORAL

ZONE

" ~

Recent

Pleistocene

s lll f

- Plioc-

Miocene

iii

C CIC

►

<l j::

Cloy

KIIAllt

n.0t1AL

Alluvlu111

Solly Cloy

F'bdocorpu1

Sand

Gro.. 1 and Sand

<=-10011)

Sand- Sond•t-

1"'

Cool il\ll<Mdl

...., i

Cloya,Sllole,IIQhiqrwy Sondtlonl wilh Coal

Oocrydium

Flor-.chuetrlo

me, khono Mt

Sholft, vori9oted SondtlON

Floo,chuetrio 11,lpoll

a: w

--...

.e C

.2 w

•"B 0

Sholft ,dar• 9"1Y

:::;

Cloya

I-

Ollqocene

BASIN - WEST

( Hedlund ,1tn)

COASTAL

Flonclluetrio -

Sandal-

trlloboto ( ) 12,000 It. )

Eocene

Paleocene

-------- -------Mudt-,Ql'IY Fo11i lifen,u1

NOT

REAOiED

Sholl Major Cool Shol1,lime1ton1 (+HOii.)

C I

• J ~ c .j JI

i gl 0

Table 1 (cont.) Correlation of the Major Tertiary Basins of Thal land Cenozolc strata lie unconformably on Mesozoic and older rocks. Inclination of strata Is generally low but Is locally steeper adjacent to faults. The stratigraphic sequences are mostly slml Jar but the thlcknesses vary. Maximum thlcknesses recorded from oll company drll Jing Is greater than 3,846 m shore and 3,609m Inland. The sequences are assigned to at least six formations, Chao Phraya, Mae Fang, Mae Sot, Mae Moh, LI and Nam Pat (see Table 1). The depositional facles range from fluvlal to offshore-shelf, related to factors such as de I ta prograd Ing, sh I ft Ing of r I ver channe I~. subs I dence of basins, and fluctuation of sea level In the Terti ary. Glbllng (1980) examined many Cenozolc basins In northern Thal land, and grouped their llthologlc successions as follows. Coarse terrlgenous association: sediment types In approximate order of abundance are conglomerate, sandstone, mudstone and coal. Strata show horizontal lamination, cross-stratification, cross-cutting erosional surfaces, and graded bedding. These collectlvely suggest a fluvlal origin. Austral Ian Coal Geology 4, part 1

252

P. Chumroum & R. Corslrl

ExploratJon program .of .EGA! Since 1975, thirteen basins have been investigated to some extent by NEA and by EGAT. Considerable additional reserves have beeb del lneated by this program. EGAT's exploratory drll ling ls presently concentrated at Mae Moh and Krabl, but exploration has been done in other areas. In 1981, EGAT set up the ''Lignite Exploration for Power Generation Project" to be responsible for geological exploration of I ignite In Thal land for use in power generation. A systematic exploration program has been formulated in conjunction with DMR and involves overseas consultants.

ExploratJon tecboIQues ~ .12¥ .EGA! In 1970, conventional fully cored sampling was introduced to improve on chip sampl Ing previously employed. This improved sampl Ing, but was very time consuming. In 1979 consultants initiated and trained EGAT staff in a coord I nated Invest I gat Ion program. Th Is I nvo I ved project p Iann Ing, open and cored hole drll ling, digitised geophysica l logging, a geological data base and processing, geotechnlcal logging and testing, and chemical analyses. Geological, geophysical and goetechnlcal interpretations were then made. This work Is now continued by EGAT staff. Drl I I Ing equipment owned by EGAT includes 2 rotary drl I I units with 150m capacity, 1 of 300m capacity, 3 with 500m capacity and 2 diamond coring units with 300m capacity. Two computerised bore hole logging units have capabilities for cal lper, density, gamma, resistivity, spontaneous potential and neutron logs to a depth of I000m. Further purchases of drl I I Ing and logging equipment are proposed. Geological database software Is also being implemented to ass Ist l.nterpretat Ion.

Progress

~ .to ~

EGAT has done preliminary geological exploration In many Tertiary basins over the last five years. This involved mainly surface geological mapping and some exploratory scout drll llngs. Six basins namely Mae Ramat, Chae Hom, Wang Nua, Ngao, Lampang and Kantang have been reported (see Figures 1A, 1B). Mae Ramat Basin: Surface geological mapping was fol lowed up by thirteen ge~phys Iea I I y Iogged ho I es 250m to 850m deep, over an area of more than 80 km. It was concluded that no commercial deposit occurred in this area and no further exploration ls planned. Chae Hom Basin: Surface geological mapping was supplemented with 39 geophys2 Total lcal ly logged bore holes at depths of 150-300m over an area of 224m. estimated lnferrej Reserves ls 22.56 ml I I ion tonnes within two sub-baslnal areas of 1 to 3 km. As the strip ratio ls very high (1:26), the resources cannot be developed in the near future, and exploration ceased. Wang Nua Basin: lmmedlatly north of Chae Hom basin, Wang Nua Is very similar. Lignite was found In five sub-baslnal areas with total Inferred reserves of 25 mI I I Ion tonnes and 1:38.7 str Ip ratio. Ngao Bas In: An area of 30 km 2 on the eastern edge o f the bas In was Investlgated. Sixteen holes were drilled but no geophysical logging done. A total of 24.5 ml I I ion tonnes inferred reserves were calculated with strip ratio of Austral Ian Coal Geology 4, part 1

253

P. Chumroum & R. Corslrl

• Sandstone

5!!i Limestone

O Greywacke

•

Shale

Quartzite or alllclfled Mudatone

T Tertiary Rocke •

Plelatocene Basalt

1•

¥;'.

,~.J' •

2030000

PM R

I I

---;

/ -----

I I I /

-'-

li2

2020000

' --R 2

Pha Kan Fm,

PMR Tuff agglomerate Permotrlaaalc

SCAL! IN KILOMETER8

MAE MOH BASIN GEOLOGICAL MAP

Australian Coal Geology 4, part 1

FIG. 3

Gp i > C

-+ -,

. ....

-0

~--=;-:;:.:=--=.. - - - -~

. ...

(")

:::r

::,

.,3

(")

SECTION

N21

"'"

:x,

~ ;

"-,

;

•

;

~\/

' ...

••

SECTION

...

MAE GEOLOGICAL

MOH CROSS

SECTION

FIG.4

b'-, u, .,

P. Chumroum & R. Corslrl

255

1:2.6. The I Ignite seam Is rather shallow (0-70 metres) and further InvestIgat Ions are p Ianned. La~pang Basin: This Is a large area of Irregular shape covering more than 800 km . It con ta Ins many sub-bas Ins e.g. Mae Th a-Koh Kha, Serm Ngarm, etc. Some geological reconnaissance Is being done and the Mae Tha-Koh Kha area will be explored by drll ling In late 1982. Kan tang Bas In: It Is the on I y bas In In the southern part of Tha I I and, apart from the Krabl basin, which was explored. Seventeen fore holes were drilled to average depth of 150m covering approxlm~tely 15 km around outcrop and old mine workings. The basin Is about 150 km In area, The geological lnformeatlon and the drilling results Indicate this area should have good prospects, Although the I Ignite Intersections from drl I I Ing were thin (1-3 m), deeper, thicker coal Is expected to be encountered In subsequent Investigations . MINING DEVELOPMENTS

The Mae Moh deposit Is contained within a generally flat rolling valley. The val fey Is oval shaped, elongated In a north-north-ea st direction, with dimensions about 18 km by 8 km. It has an average elevation about 320 metres above sea I eve I. (see F lgure 3).

Geological i □ vestJgatJon The data from the gravity survey, mlnl-SOSIE* high-resolutio n seismic Investigation, cal lbratlon drl I I Ing with electronic bore hole logging, and field mapping were used, It was shown that the area contained three separate basins, separated by basement structural highs, with a main basin, and others to the north and west. The only occurrences of commercially attractive lignite were recorded within the main basin, (Figure 4)where the stratigraphic sequence Is: Superficial gravels and al luvlum. Red Beds (weathered c I aystones: - very weak to weak rock with zones of very stiff to hard clays), 0 - 300m thick. Grey Claystones, typically 10 - 150m thick. Upper Lignite Seam "K", 15 - 30m thick. lnterburden - grey claystones, 10 - 30m thick. Lower LI gn I te Seam "Q", genera I Iy 10 - 30m th Ick. Grey Claystones, 250 - 450m thick. The maximum thickness reached by the Tertiary sequence has been estimated at about l,OOOm.

LI go ite reserves Lignite QYallty dJstrJbutlon In the north and south of the main basin, the partings within both I Ignite seams Increase greatly In thickness. In addition, I Ignite qual lty deteriorates, so the area of recoverable resources must of necessity be defined by Australian Coal Geology 4, part 1

N u, O't

> C:

...

,.,,

OltUJINAL G..OUNO SU"P'ACI ( AV. + llO .... )

'. ~~~

-+ -,

~ -

Ill Ill :,

s Ill

G> (!)

- - -r.,--c,"J \'. _,.,.. . I .Im.

"'O

-:7" C

WIN INe DU'TH

150ffl

IIIN[ CROSS SECTION

""::0

(.Q

EXISTING

b' -,

~W(lt 1'1..ANT 11 W . EACH

"O Ill

LIGNITE

HANOLIN8 SYSTEM

HOffl.

lfLT CONVEYOR l,000 MIil.

CAPAQTY 500 TONI / Ht

r - - - - -- - - - - - - - - - - - - - ,oom .- - - - - - - - - - - - - - ---1 SCHEMATIC MAE MOH MINING SYSTEM I EXISTING )

FIG. 5

257

P. Chumroum & R. Corslrl

a "grade cut-off" In the north and south. On the east and west marg Ins of the basin the seams are of higher quality with far fewer splits. Typical lignite analysis results are summarised In Table 2. The tota I I I gn I te reserves In Mae Moh ma In bas In can be summarised as follows:K + Q Seams Mt Measured Indicated

Llgn lte Geological Seam 65% Ash Cut-off 45% Ash Cut-off 35% Ash Cut-off

1047.6 802.6 661.0 555.3

296.8 185.1 153.2 122.8

Vertical Average Strip In sltu Ratio BCM/t Ash% DB

Total 1317.4 987.7 814.2 678.1

4.1 5.7 7.1 8.7

26.1 % 22.9 % 21.7 %

.Ma.e .M2h ~

Mae Moh Mine started operation In 1954 and subsequently Increased production capability In 1960 to supply lignite to a 12.5 MW thermal plant and later to a nearby fertilizer plant before Its closure In 1978. The mine has slgnlflcantly Increased Its production since May 1978 as the first 75 MW I Ignite-fired power unit started to tie In with the EGAT system. In January 1979 the second unit was commissioned and the third of the same capacity was completed In Aprl .l 1981.

NAME OF BAS IN

c. v. *

PROXIMATE ANALYSIS /AS RECEIVED BASIS)

PROVINCE NAME

F.C. (% }

5(%}

MOIST(%) LAMPANG

2,700

3,500

MAE TA

LAMPANG

4.6

6,000 3,000

(M)

MAE MOH

V.M. (%}

c.v_.

ASH (% }

(CAL/GM.)

CHAE HOM

LAMPANG

2,300

2. 0

WANG NUG

LAMPANG

1. 3

3,000

NGAO

LAMPANG

6.5

6,000

1 1 4.3 4.8 1.8 1. 9 4 1.1 1. 5

7,000

TAK

MAE RAMAT

TAK

THA SONG YANG

TAK

5 11

HOD

CHIANG MAI

MAE CHEAM

CHIANG MAI

CHIANG DAO

CH IANG MAI

LAMPOON

MAE HONG SON

KRABI

3,000

(M)

MAE TUEN

(M)

PAI KRABI

(Ml TABLE

7,000 6,000 5,000 5,500 5,000 6,000 5,500 4,000

SOME ANALYSIS RESULT OF COAL IN THAILAND (APPROXIMATED MEAN VALUE)

= Vo la tile Matter = Fixed Ca,,bon s = Sulphur (Total) c.v. = Calorifia Value (Cal/Gm . ) V.M.

F.C. (M} = Aative Mine CS}

'Moist, Mineral Matter Free Basis

The mining method Is open-cut using trucks and shovels together with crusher and belt conveying system (see Figure 5). Overburden Is excavated by five P&H Austral Ian Coal Geology 4, part 1

258

P. Chumroum & R. Corslrl

Figure 6. General layout of the Mae Moh proposed mine and dumping area.

TOTAL WASTE

1,707 1 10' m

TOTAL L IGNITE

33~.16 a tcf TOno .

70,o

'°"'

◄ Op

30p

20p

10,0

1010

II ii 1114 II It If It It 1010

Figure 7. Diagram of proposed production schedule of Mae Moh Mine from 1985 to 2020. Note: The production schedule has been developed upon the basis of:6,500 operating hours per annum of each unit; 2,600 KCal/Kwh specific power consumption of each unit; 2,705 KCal/Kg mean calorific value of lignite. Av. lignite production: 12 Mt. per year; Av. 0/B: 50 Mio. M3 /year. Meanwhl le preparation and studies for future expansion of the project are being carried out. Since the planning, operation and management of large open cut mInes are new to Tha 11 and, I nternat Iona I consu It Ing serv Ices are be Ing ut 111 sed. Many stud I es have been performed by German and Austra 11 an f I rms Inc I ud Ing some government a I d. These Inc I ude an exp Iorat I on program us Ing modern electronic field measurements, geological data storage and evaluation by means of computer, mine planning, mine equipment selection, coal handling

Australian Coal Geology 4, part 1

P. Chumroum & R. Corslrl

259

engineering, feaslblllty studies and environmental studies. EGAT currently have contracts to manage and Implement var ious programs In technical training, detailed geotechnlcal studies, computer data base for geology and mining p I ann Ing of Mae Moh. EGAT staff are I nvo I ved In these programs, and fu 11 y trained In their operation. The present development of Mae Moh Mine has been financed by the IBRD and local financing firms. f.u.±.J.u:§ development

The future development of Mae Moh mining project has been outl lned In a recently reported Feast bi I lty Study (Rhelnbraun-Consultlng, 1982). Extensive geological exploration was completed In 1981, and the assessment of larger reserves was followed by a Feasibility Report In 1982. The report covers the mine expansion period from 1985 - 2020 (Figure 7) and Is based on an Increase of generating capacity from 225 MW at present to 1,725 MW In 1989. lignite reserves are assessed at 345 million tonnes, with average calorific vilue of 11.27Mj/kg, average ash 20%, and mining field energy value of 3.87 x 10 Gj. The Mae Moh Mine will be expanded up to a tota l output of 12 ml I lion tonnes of lignite and 68 mill Ion cubic meters of overburden per year. The overall waste to I Ignite ratio Is 5.1 : 1 CBCM : t). An open pit method Incorporating Integrated electric shovel, rear dump truck, semlmoblle crusher and conveyor operations has been selected for mining Mae Moh. De atls of major equipment are not yet decided, but will probably be twelve 23 m dipper electric shovels In conjunction with thirty 170 ton trucks.

The pit wll I be expanded northward (Figure 6). The face wll I be developed f u I I wI dth to I I ow Ing the eastern f I ank of the sync 11 ne. The p It w11 I then turn ant I c Iockw I se a I ong the northern subcrop to the western f I ank of syncl t ne. The pit will be about 1,800m wide, 9.5 kllometers long and 280m depth from the surface. In an early stage, about 600 mill Ion BCM of waste have to be dumped east of the mine. In the next stage, the waste wt I I be dumped Ins I de the p It as back f 11 I. The env I ronmenta I Impact has been stud I ed, and plans prepared to prevent a i r and water pol lutlon. Land reclamations wt 11 to I Iow deve Iopment. The Feaslbl I lty Study placed the basic cost of Mae Moh Project at 3,969.926 ml I I Ion US dollars. The mine operating cost per ton of I Ignite Is US $ 20.5. It Is estimated that, In full production, the Mae Moh Mine would employ about 2,000 people directly. KRABI Geology

The bas In topography Is typ I ea I I y f I at and feature I ess, and con ta Ins I arge areas of mangrove In the southern portion. Tertiary strata were Identified by the presence of thin beds of I Ignite or ligneous clay, although In some cases Insect and she 11 toss 11 s s Im 11 ar to those at Krab I and Mae Moh MI nes were found. Limestone, claystone, oll shale and fine sandstone were also recorded (Figure 8).

Fol lowing a geological reconnaissance survey during October 1980, surface geophysical work was carried out. Within the central part of the deeper basin Australian Coal Geology 4, part 1

P. Chumroum & R. Corslrl

260

1100,000

Basin boundary

- - - Seismic line ,,,,,,,,,,,,, Slrotem traverse

( :·'!~/!!;r_:-"!J Prospective llgnlte1,-L----'L----~....a..-_.__----r_ _ _ _ ___...___---t ;.;.·-~ .-, ..,

area

0123-4667 Scale

km.

GENERAL LAYOUT OF KRABI BASIN

Austral Ian Coal Geology 4, part 1

FIG. 8

P. Chumroum & R. Corslrl

261

area there Is a good posslbl I lty (based on Information extrapolated from previous boreholes) that the "Wal-Lek Type" I Ignite seam Is present. In addition, seismic and Slrotem results Indicate an up-faulting and decrease In dip of the Wal-Lek deposit to the east of the present mine. There Is a good potential to considerably upgrade reserves In this area provided certain surface drainage and diversion works are carr ied out.

Reserves <:llli1 QYalJty The reserves have been known only along the subcrop of lignite near the three existing mine-site areas, to the maximum depth of not greater than 100 metres. The tota I proven reserve now Is 13.5 mI I 11 on tonnes and about 9.8 tonnes Is recoverab Ie (Inc I ud Ing the mI ned-out of 4.0 m1111 on tonnes from Bang Pu Oum). The quality of all Krabl existing mine-sites are generally consistent as shown In Tab I e 2. ~ .mJ..n.e.s

Krabl Mine started Its production In 1965. The mine Is a small open pit truck and shovel operation which provides I Ignite to fuel three units of 20 MW at the power station nearby. Small expansions have been undertaken, through the development of two adjacent new mining operations in 1978, at Klong Wal Lek and Klong Bang Mark. The lignite from these new mines have been available for use by the Krabl power station since 1980. The last power unit at Krabl was commissioned In 1967 and no further power expansion Is presently planned. The deposit Is nevertheless being further Investigated by EGAT to delineate more reserves. 3 Overburden Is currently excavated by three 2.4 m3 61 RB shovels and two 1.8 m 54 RB shovels loaded Into 10 ton rear dump trucks, and carried to the overburden dump outside the pit (Wal Lek) and Into an old pit (Bang Pu Oum). Average overburden removed Is about 2.0 ml I I Ion m per year. Lignite Is excavated by a 51-8 shovel with combination of Traxcavator Cat 955 H (2 un Its) and Ioaded to Euc 11 d 15 to 17 tonnes and HI no KR 6 tons rear dump trucks and carried to the power station coal shed. Its I Ignite production averages 360,000 tonnes per year. The production cost Is about 300 Baht/t. At the final stage the size of existing pits will be about 2.5 kllometers long and 300 - 1,300m w Ide and 60 - 70m deep. The average strip ratio range from 3.6 to 6.3 BCM/t of I Ignite. The major mining problems are the heavy ralnfal I (average 3,500 mll llmeters/year) and slope stabll lty, due to the geological cond It Ions and, In part I cu I ar, the very steep d Ip ang I e of the I I gn I te seam (30°). ~ .luls.lJ1

develqpment

As there Is limited power generating sources In the south of Thailand the EGAT power development plan makes Krabl exploration work a top priority. From early 1982, following gravity, resistivity (Dodds and Haigh, 1982) and seismic Investigations, a drilling programme to explore the whole area of the basin has been undertaken. To date some 80 geophys I ea 11 y Iogged dr 111 ho I es have been completed and the preliminary evaluations and Interpretations carried out. It Is reported that significant lignite could ocurr east of the existing subcrop mining area towards the deeper central part of the basin. The lignite seam occurs In a sync I I ne d I pp Ing east at up to 25° to a depth greater than Australian Coal Geology 4, part 1

P. Chumroum &R. Corslrl

262

RESERVED (MIO. TONS)

LOCATION

RANK

PROPRIETOR

UTILITY

OVER ALL

MEASURED

ASTM STANDARD

HAE MOH

1,300.00

802.00

LIGNITE B SUB8ITUM!NOUS C

EGAT

POWER GENERATING

KRABI

13.5

LIGNITE B-LIGNITE A

EGAT

POWER GENERATING

MAE TIP

10.00

1.00

SUBBITUMINOUS A-HIGH VOLATILE C BITUMINOUS

PHRAE LIGNITE CO., LTD

TOBACCO AND CEMENT INDUSTRY

LI (PAKHA)

10.00

6.00

SUBBITUMINOUS A-HIGH VOLATILE C BITUMINOUS

TOBACCO AND CEMENT INDUSTRY

LI (BAN PU)

5.00

2.00

HIGH VOLATILE C BITUMINOUS

NATIONAL ENERGY ADMINISTRATION (NEAl NEA. AND l«:IRLD FUEL CO., LTD.

HIGH VOLATILE C-HIGH VOLATILE A BITUMINOUS

THAI LIGNITE CO., LTD.

CEMENT INDUSTRY

HAE TUEN

1.23

TOTAL

1,325.00

898. 23

TABLE 3

PROPRIETOR

LOCATION

1. EGAT

TOBACCO INDUSTRY

ACTIVE COAL MINES (FROM EGAT & OMR., 1981)

1976

1977

1978

1979

1980

1981

KRABI

445,978.2

250,000.0

275,000.0

304,000.0

385,000.0

338,000.0

MAE MOH

209,925.0

136,600.0

275,362.0

941,458.0

935,408.5 1,204,465.0

2. NEA

LI : ( BAN PAKHA)

23,770.0

48,000.0

83,000.0

94,000.0

75,800.0

41,300.0

3. PHRAE LIGNITE

NGAO: (HAE TIP)

670.0

3,970.0

5,580.0

10,900.0

11,900.0

37,585.0

LI : ( BAN PU)

6,110.0

18,390.0

62,100.0

HAE TUEN

67.5

2,592.0

680,343.2

438,570.0

CO .l TO

4. WORLD

FUEL CO.,LTO 5. THAI LIGNITE CO. ,L TO

TOTAL TABLE 4

638,942.0 11,356,468.0 ,426,566.0 1,686,043.0

DOMESTIC COAL PRODUCTION 1976-1981 (IN TONNES) (from Economic and Infol'ITlation Division: DMR. 1982)

Austral Ian Coal Geology 4, part 1

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263

500m. It possibly shallows further to the east on the other side of the sync 11 ne. It Is poss Ib Ie that the 11 gn Ite resources at Krab I are rough Iy 180 ml I I Ion tonnes of which 30 ml I I Ion tonnes can probably be mined by open cut methods. The average thickness of the seam Is 20m. Further drilling In this area Is underway. EGAT hopes that the exploration wl I I locate sufficient resources to allow an expansion of power generation capacity. OTHER MINES Besides the Mae Moh and Krabl Mines, there are four other smal I open cuts current I y In operat I on. They produce genera I I y h Igher qua I I ty I I gn I te and supply domestic Industries (Table 3). The mines are all located In the Tertiary basins In the northern part of Thal land (see Fig. 1A, 1B and Fig. 2). Geology

The I Ignite deposits are situated In small basins and sub-basins. of each basin can be described as fol lows:-

The geology

LI Bas In: The ma In LI bas In boundary covers I arge area of 700 ~m 2 and contains m~ny sub-basins. The sub-basins named Ban Pa Kha Is 2.5 km and Ban Pu Is I km In area. The geological section consists of mudstone, carbonaceous claystone, I Ignite and ol I shale wIth 10° dips and 5 to 7m I Ignite thickness at a depth range from Oto 150 meters. Mae Tip Basin: The mine opened In the outcfop zone on the western edge of the basin. The basin covers the area of 30 km In a north-south elongated shape. Coal and shale are lnterbedded. Overlying formations consists of 4 - 10m of grave I and sand over 30m o 11 sha I e and coa I 8 - 12m th Ick. The bedrock Is limestone. Coal seams dip 20° to 40° to the central part of the basin. Mae Tuen Basin: It Is an Isolated basin, north of Mae Sod - Mae Ramat basin, and Is 10 km long and 1 km wide. It Is enclosed by high mountains of Cambrian metamorphic rock. The overburden consists of conglomerate, sandstone, clay, shale, and oil shale. A average coal thickness Is 1.2 - 10m.

Reserves .a.ru1 qua!Jty None of these basins have been adequately drll led. The total reserves are not known. Drll ling has been done mainly around the outcrops. They are generally less than 150m deep, and provide a poor basis for estimating resources. The known reserves are shown In Table 3. The qua I lty of I Ignite Is generally better than those found at Mae Moh and Krabl as summarised In Table 2. ~

The mines started their operation only a few years ago, except Ban Pakha which NEA has operated since 1969. Mines are generally operated using ordinary smal I trucks and front-end Ioaders together w Ith sma 11 Ioca 11 y made conveyor and crusher systems. The run-of-m I ne 11 gn I te Is crushed and sorted by hand to Improve quality. Blasting of overburden Is common.The main customers of those mines are tobacco curing plants, cement factories and other Industries. Commercial dealings are done by short term contract between the seller and buyer. The annual production of each mine Is summarised In Table 4.

Austral Ian Coal Geology 4, part 1

264

P. Chumroum & R. Corslrl

The actual cost of production of each mine was not reported. The only Information Is the posted price from DMR used for royalty calculatlon, which tends to Increase every year, for example:1976 - 1979 The posted price was 80.00 Baht/ton 1980 The posted price was 122.20 Baht/ton 1981 The posted price was s 163.0 Baht/ton Private companies are now very active In exploration, partlcularly In the north of the country, and have taken up concessional areas. There Is however a shortage of trained and experienced profess Iona ls from which the companies can draw.

CONCLUSION Although Thal land has a long history In coal mining, development Is far short of Its potential level. Both mining and utl I lzatlon of coal can be significantly Increased. Since the energy crisis of the mld-1970 1s petroleum has been scarce and costly within the country. The demand for coal has been escalating gradually, and this trend should continue. Among 57 basins In the country only a few have been explored In detail. Most deposits are awaiting development; only six deposits are being mined by two government agenc I es and three pr I vate comp an I es. EGAT Is the I argest coa I explorer and miner Jn this country but alms to develop the lignite potential area for power geneatlon only. The demand of coal In other Industries also prov I des opportun It Ies for sma 11 er mIn Ing operat Ions. Coa I Is pred Icted to play a greater role In Thal land's economy In future years. AO<NOWLEDGEMENTS The authors to acknowledge the permission of Mr. Kasame Chatlkavanlj, the Genera I Manager of EGAT, to prepare and present th Is paper. Deep thanks are also extended to the geologists and mining engineers, as well as office staff, of the Lignite Mine Department for their Information and help. REFERENCES Anon, 1982, Coal activities In Thal land. Coal Working Group, Mineral Fuel DI v Is Ion, DMR., November 1982. Corslrl, R., 1982, Lignite development project, USA-Thal land Llgnlte/ol I shale Symposium, Bangkok, February, 1982. Dodds, A.R. and Ha Igh, J.E., 1982, The use of trans I ent e I ectromagnet I c methods for resistivity sounding and mapping with particular reference to coal basin studies. ~~~A (this volume). Dravo Eng I neers and Constructors, 1982, Tha I I and dr 111 Ing ass I stance and guidance, U.S. Trade Development Program, EGAT. Glbllng, M. & Ratanasathlen, B., 1980, Cenozolc basins of Thailand and their coal deposits. A preliminary report no. 8009-2: Chiang Mai University. Austral Ian Coal Geology 4, part 1

P. Chumroum & R. Corslrl

265

Glbllng, M., Ukaklmaphan, Y. Srlsuk, S., 1981, Facles changes of coal and oll shale strata In the Cenozolc Mae tip basin, Northern Thailand, Department of Geological Sciences, Chiang Mai University Penflle Report 8105-2. Lignite Mine Department, 1980, generation, EGAT, March 1980.

Coal and I Ignite exploration project for power

Longworth-CMPS Engineers, Australia, 1980, of Krabl Basin for EGAT, December 1980.

Preliminary geological assessment

Longworth-CMPS Engineers, Australia, 1981, the Mae Moh Basin for EGAT, June 1981.

Assessment of lignite reserves In

Longworth-CMPS Englneeers, Austral ia, 1981, A further assessment of lignite reserves, Krabl Basin for EGAT, Draft report, June 1980. Longworth-CMPS Engineers, Austral la, 1981b, A prellmlnary assessment of lignite reserves Krabl basin for EGAT, August 1981. Ratanasthlen, B,. 1980, Upgrading coal/lignite for household use, Part I, the coal qua I lty In the north of Thal land, Thesis report, for National Research Committee Cln Thal). Ratanasth Ien, B., GIb 11 ng, M., 1981, Pa Ieogene toss 11 assemb Iages In the Ban Pa Kha Basin, LI district northern Thal land. Departm!ll± .Q.f

Geologfcal Sc fences, Chfang M.al Unfyersfty, ~~report

.8.1..QH.

Rhelnbraun-Consultlng GMBH, F.R. Germany, 1981, Report of the feaslbl I tty study on the Mae Moh I Ignite Mine project with 1725 MW, December 1981. Sol Id-fuel Geology Division, EGAT, 1982, 1981, Report No. 421-2510.

Annual exploration program report

Ukaklmaphan, Y. Suprutpanlch, S, 1982, The report of exploration and drll ling of Mae Tuen Lignite Deposit, Tak Province, January and May, 1982. Ukaklmaphan, Ruankaew, N. & Srlbuntham, B., 1981, Report of exploratory dr 1111 ng of coa I depos Its at Tambon Mae TI p, Amp hoe Ngao, Lam pang· Prov I nee. ~ .Q.f Mfneraf .E.wtl. Pfvfsfon, ~ Mfneraf Resources, Cln Thal>.

266

Rhineland Brown Coal Development H. Ernst 606 St. Kilda Road, Rheinbraun Consulting Australia Pty . Ltd . , St. Kilda Road, Melbourne, 3004, Australia.

ABSTRACT The development of the Rhenish Brown Coal Area is an example of how low rank brown coal can be mined economically in an environment of complicated geology, dense population and highly developed industrial and agricultural infrastructure . 35 billion tonnes of brown coal out of in place resources of 56 bill ion tonnes are regarded as economi ea lly recoverab 1e under present energy price levels. This will include opencut mining of reserves at depths of 600m and stripping ratios of 10:1 (m 3 :t). Todays production level is 120 million tonnes of coal and 420 million m3 of overburden per year. Brown coal represents some 20% of the primary energy generation in West Germany and some 30% of its total power generation. Economic mining under these conditions requires large scale operations (mine capacities up to 50 million tonnes per year), high capacity equipment (bucketwheel excavator/conveyor/stacker systems of up to 240,000 m3 /d) and a most accurate control of the geological, hydrological, geotechnical and environmental conditions. INTRODUCTION The deve 1opment of the brown coa 1 industry in the Rhine 1and of West Germany has already been described on many occasions . However, it is appreciated that this session of the symposium related to the brown coal development in various countries should include mention of the Rhine Valley , since this deposit has significant geo 1ogi ea 1 , techni ea 1 , economi ea 1 and envi ronmenta 1 differences from other major brown coal deposits, for example of the Latrobe Valley or the Gulf Coast lignite belt of the U. S. A. But in some ways it is also more similar in its geological setting to the brown coal deposits in other European countries, Thailand, China and perhaps South Australia. I would like to divide this paper into a brief description of -

the geological situation of the Rhineland Brown Coal District its current energy-economic role in Germany its historical development its technical development and some concluding remarks related to the constraints of its future development.

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267

GEOLOGY OF THE RHINELAND BROWN COAL AREA Germany is not noted for the wea 1th of its mi nera 1 deposits. The only minerals which occur in abundance are black coal and brown coal. Besides the large deposits in the central and eastern parts of Germany brown coal is found in several deposits in Lower Saxony, Hesse, Bavaria and finally the Rhineland. With some 56 billion tonnes the Rhineland deposit comprises more than 95% of West Germany's brown coa 1 resources . It represents the 1argest combined European brown coal deposit. It consists of 3 main seam groups with a total thickness of 70 to 100m. Normally they are embedded within layers of unconsolidated materials, primarily sand, gravel and clay and include up to five independent aquifers; four of them above and in the coal and one aquifer below the coal seam. Tectonic movements divided the deposit in several provinces. There are tectonic faults with throws of up to several hundred metres . Correspondingly the depth of the coa 1 and the thickness of the overburden (Figure 1) varies between nil and more than 500m . The quality of the raw coal depends primarily on lithotype and depth: net spec . energy

density

6.5

12.0 Mj/kg

1.12

1.23 t/m 3

moisture

62%

ash

10%

In some areas clay and sand are valuable commercial by-products . The coal was formed during the Miocene and Pliocene, that means about 10 to 25 million years ago. The climate at that time was still primarily sub-tropical, and the general profile of the European continent and the North Sea had been established when the Rhineland trough began to sink and the formation of the brown coa 1 started. The "Ni ederrhei ni sche Bucht" was then fi 11 ed up by sediments which were in several phases delivered both by the North Sea and rivers which originated in the mountainous area in the South . It took some 30,000 to 50,000 years to form a coal seam of some 10m thickness. Also in Germany this period was followed by heavy volcanic activity which produced large amounts of basalt . Fortunately, it did not cover the brown coal deposit, but was restricted to the neighbouring Eifel Mountains to the west of the area . TODAY'S ECONOMIC ROLE The consumption of primary energy in the FRG amounted in 1981 to some 11,000 PJ or 375 million tonnes of black coal equivalent . This consumption had dropped by some 4. 4% each in 1981 and 1980 and last year was at the same level as in 1972 before the first so called "oil crisis". More than 50% of the primary energy has to be imported in the form of oil and gas. In light of this scenario you wi 11 recognize that it is in the interest of the country to make as much use as possible of its brown coal resources which provide a safe supply and is the cheapest fuel available in Germany.

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268

RHENISH BROWN COAL FIELDS

LEGEND

Excavation

Mining Area

Dumping

llllii! Agricultural Reclamation

OMONCHENGLADBA CH

~ Reafforestation -

Water Reaevolra Rivera

Brown Coal Power Station

Brlquettlng Plant

FIG.

Figure 1. Opencuts of the Rhineland Brown Coal Area

s.w

Rur-block Zukunft

m • 200

Erft-block Hambach

lnden

Eschweiler Rur

Leverkusen

VilleErft Rucken

· 400

- 800 Quaternary

- 800 -1000

NE.

Cologne-block Fortuna

and aand ~ Gravel Sand and gravel

CJ Sand

km.o Vertical Exaggeratk>n

Tertiary

Clay Brown Coal

Carboniferous { !,......... ! Upper Carboniferous ~ Lower Carboniferous Devonian ~

Figure 2. Geological Cross-section of the Rhineland Brown Coal Area Australian Coal Geology, 4, part 1

269

H. Ernst

With some 120 mi 11 ion tonnes per year the Rhineland provides roughly 90% of the brown coal production of the FRG. Approximately 15% is being used for the production of briquettes, pulverised dried fuel, coke, fertilizer and soil improver, while about 85% is used for generation of power. With an installed capacity of some 11,400 MW the brown coal power plants of RWE, the parent company of Rhei ni sche Braunkoh l enwerke AG (Rhei nbraun) produced about 27% of the total electricity generated in Germany or about 90% of the total Australian power production. In absolute figures this means some 82,000 GWh or an utilisation at full load of 81.6% respectively 7.150 operating hours per year. Rhei nbraun is active in the research and development of gas ifi cation and liquefaction of brown coal. We still believe that in the medium and long term gas and liquids from brown coal will play an important role as chemical feedstock and substitute for crude oil. Earlier gasification and liquefaction plants built in the 1930's and 1940's were only closed in the middle of the 1960's. We are going to put into operation the first line of our new commercial gasification plant based on advanced technology in 1984. Larger quantities of brown coal, however, will only be available for such purposes in the Rhineland if a considerably larger amount of electricity generation is taken over by nuclear power. HISTORICAL DEVELOPMENT The following table shows a few figures about the historical development of brown coal mining in Germany and particularly in the Rhineland: 1700

initial commercial use

1822

92 pits;

1885

foundation of German Brown Coal Industry Association (DEBRIV); 15.5 million tonnes, 75% underground

1902

43 million tonnes; 10% of primary energy consumption (PEC), stripping ratio 0 . 3:1 (m 3 :t)

total production of 70,000 t/a;

1927

150 million tonnes;

1943

254 million tonnes

20% of PEC

1950

64 million tonnes in Rhineland only

1960

80 million tonnes in Rhineland only

1970

92 million tonnes in Rhineland only

1980

117

million

tonnes

600 workers

in Rhineland only,

stripping

(m 3 : t)

ratio

3.6:1

Si mi l ar to the hi story of the brown coal development here in Victoria as described by E. D. J. Stewart in a paper at the AIMM conference earlier this year, the development of the brown coal industry in Germany was strongly influenced by the relevant political events and in particular the availability of black coal of much higher energy content. Its current role, however, has resulted from the rapid progress of its mining and utilization technologies.

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H. Ernst

Although handmade briquettes were already made in the 18th century mechanized production began with the invention of the excentre-presses in 1859. The maximum briquette production in the Rhineland was reached in 1956, when 47 mi 11 ion tonnes of raw coal were converted into some 17 mi 11 ion tonnes of briquettes . Although the briquette production has declined since then to some 4 . 2 mi 11 ion tonnes per year much of the coal drying, screening and handling facilities are still in use for the production of new brown coal products such as pulverised dried fuel or coke. The use of brown coal for the generation of power started around 1900 . The use was accelerated by the introduction of high voltage and long di stance transmission of power. In 1939 50% of the electricity generation in Germany was based on brown coal. The recent decades saw a regular doubling of the capacities of the generating sets with 150 MW units during the 50's; 300 MW units during the 60' s; and the first 600 MW unit being commissioned in the Rhineland (Weissweiler power plant) about 9 year s ago in February 1974. I mentioned earlier the use of brown coal for conversion to chemi ea l feedstocks, gas or gasoline. After the basic processes had been developed by Fischer-Tropsch, Berguis-Pier and others during the 20's, several conversion plants had been built in East Germany based on brown coals rich in bitumen . The low bituminous brown coals of the Rhineland could only be uti l i sect for these purposes when high pressure processes (around 700 bar) had been developed. The first plant at UK Wesseling, a subsidiary of RHEINBRAUN, was commissioned in 1941. In 1944 40% of the German gasoline consumption was produced from brown coal . The high production rates of the 1930 ' s and 1940 ' s had made extensive use of the productive mining areas in the geologically favourable southern parts of the Rheni sh Brown Coal Di stri et. Many of these mi nes were worked out. New mining areas needed to be developed in the central and northern areas where the coal seams are located far below the groundwater table and where the seam. groups are split and covered by much greater thickness of overburden . Many studies and tests had proven that the exploitation of these resources by underground methods is uneconomic ; and the application of ins i tu mining processes under the given circumstances is still a dream of the future . A prerequisite for economic mining of the deep brown coal reserves was:

to consolidate the mining leases and to concentrate on the production in a few open cut5 to dewater the unconsolidated sediments and to monitor and reassess the significance of all geotechnical factors to advance the existing open cut technology in view of large scale overburden and coal winning and to incorporate the most effective surface reclamation procedures. Today, at a production level of some 120 million tonnes of coal per year, there are 7 operating opencuts in the Rhineland . They are Fri mmersdorf Ville; Frechen; Fortuna-Garsdorf; Neurath; South and West; Zukunft-Inden and Hambach (Figure 2) . In some 20 years ' time, with a similar annual production rate , there will only be 3 mines left: Hambach Frimmersdorf/Garzweiler Inden

45 - 50 million tonnes/a II II 45 - 50 20 - 25

Australian Coal Geology , 4, part 1

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271

Some highlights of the development of the brown coal industry in the Rhineland during the last 30 years are compiled in the following table: -

the merger of 12 formerly independent mining companies and

the reduction of operating opencuts from 23 to 6, while

the coal production was doubled from 64 to 120 million tonnes and

the overburden removal was increased 8 times from 50 to more than 400 million m3

from number of employees during this period of time was reduced from 23,000 to 17,000

and the productivity in the mines has been increased 5 times from about 20 to an average of some 100 tonnes of coal per man and shift, which means - keeping the stripping ratio in mind - some 400 (m3 + t) per man and shift. TECHNICAL DEVELOPMENT The results as described earlier could only be achieved by a systematical and continuous improvement in all fields of technology, such as geological exploration, coal quality evaluation, groundwater and geotechnical investigations, mine planning and scheduling. Of utmost importance, however, was the selection and design of the most efficient mining systems and equipment for the excavation, transportation and dumping of the various materi a 1s, which needed to reflect the existing geo 1ogi ea 1 conditions, the need for perfect reclamation of the surfaces and, of course, the need to compete with other energy sources . Three factors in particular determined the selection of the bucketwheel excavator/conveyor/stacker technology which is today nearly exclusively in use in the Rhineland : -

the application of direct casting or crosspit conveying systems is impossible or at least uneconomical due to the depth and the width of the pits. In recognition of the principal economic advantages of such systems a lot of efforts have been made to investigate the application of such systems for the Rhineland conditions;

optimum selective mining characteristics are required due to the heavy faulting of the deposit, the large number of individual coal seams, the need to contro 1 the coa 1 qua 1i ty, to estab 1i sh safe and economic dump slopes and proper reclamation of land; and

finally, truck or rail transportation at least within the pit are uncompetitive due to the need for 1arge sea 1e production, making the combination of bucketwheel excavators with conveyors and stackers technically and economically the most suited technology for the Rhineland conditions .

The first systems with capacities of some 10,000 m3 per day had been put into operation during the 1930' s. Unt i 1 today there have been deve 1oped 25,000; 40,000; 60,000; 100,000; 200,000 and most recently 240,000 m3 per day

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H. Ernst

machines (Figure 3). Systematic research and consequent improvement of detailed design not only of the indiv i dual machines but the whole mining system lead to the result that the biggest units today achieve output rates of more than 50 mi 11 ion bm 3 per year. Tab 1e 1 shows some techni ea 1 data of dredgers, conveyors and stackers compari ng 60,000; 100,000 and 240,000 m3 I d-machines, whereas the 60,000 m3 /d units represent the order of magnitude of the dredgers being used in the Loy Yang opencut .

Figure 3. 240,000 m3 /d Bucketwheel Excavator

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273

TABLE 1 DETAILS OF MINING EQUIPMENT

Capacity

bm 3 /d

60,000

110,000

240,000

Eff . Output

bm 3 /h

3,100

5,700

12,500

bucketwheel ~

12,25

17,50

21,60

bucketwheel-drive power

750

1,290

3,360

high cut

deep cut

total digging height

100

av. ground pressure

N/cm 2

8,0

14,8

17,0

service weight

3,600

7,900

13,000

BW-Excavator

Stacker discharge boom

100

belt width

2,400

3,200

av. ground pressure

N/cm 3

12,3

18,4

service weight

2,500

5,000

Belt Conveyors belt width

1,800

2,200

2,800

belt speed

m/s

5,2

7,5

max. drive power

6.430

6.630

6 . 2000

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H. Ernst

A mining system of 24,000 ml/d capacity as described above and consisting of excavator, say 10 km of belt conveyors and stacker today costs significantly more than 100 million dollars. The Hambach opencut will employ eight of these systems and requirements include coal handling, mainter,ance and administration facilities as well as the cost for five years development until initial coal production; a capital expenditure of some 2,500 million dollars. To justify such an investment it is, of course, important to negotiate sustainable coal sales agreements. It is, however, at least of equal importance to obtain maximum confidence in the accuracy and reliability of all geological, hydrological, geotechnical and environmental data and implications of such a project. About 25,000 boreholes have been dri 11 ed within the 2,500 km 2 triangle of Cologne, Aachen and Dusseldorf. About 15,000 of them have been geophysically logged . The existing opencuts themselves are of course of particular value for the detailed understanding of the geo l ogi ea l setting of the Rhineland. They provide the detailed information about the tectonic patterns as well as the location, nature, thickness and dip of the individual layers, which again is required, e.g. for the detailed design and scheduling of the mines or the forecast and mi nimi sat ion of a 11 kinds of mining problems. An accurate knowledge of the distribution of the coal quality gets more and more important in view of advanced coal utilisation processes and environmental demands. The available geophysical methods, unfortunately, are in our opinion still unsatisfactory in this respect. As far as the hydrology is concerned we of course want to restrict the groundwater withdrawal for economic and environmental reasons to the extent that the stability of our pit slopes is assured. Furthermore we must at all times be in a position to assess accurately the implications of the groundwater withdrawal for the subside nee and utilisation of the surface, replacement of present water supplies as well as the consequences of the regeneration of the water table in the dumping areas. One or two dimensional models are used to determine the optimum dewatering method as well as the numbers and size of the wells . Due to the highly permeable aquifers the optimum dewateri ng system in the Rhineland is in most cases a combination of dewatering wells within the mining fields and galleries along the rims of the mines. In view of time and capacity required, the optimum dewatering period is four to five years. Between 1955 and 1981 roughly 30,000 mi 11 ion ml of groundwater have been pumped; this is at a rate of 1,100 mi 11 ion ml per year, 3 mi 11 ion ml /per calendar day or 40 ml/s. For this purpose about 1,000 wells and pumps with an installed capacity of some 170 MW are in use. The deeper the opencut the more important is the amount of "unproductive" batter overburden, and the more important it is to design the slopes as steep as possible without jeopardising the safety of people, production and equipment. To determine the optimum construction of the mine and dump slopes we also use the internationally standardised formulas according to Jambu, Neuber, Bishop, Bureau of Reclamation and others . However, with unconsolidated materials and slopes of 350m and more as in the Rhineland, you wi 11 accept that this is no longer just a mathematical processing of data. Extensive experience is essential to check the plausibility of all individual data, to determine the shape and location of eventual slip j oints, to evaluate the impact of length and lifetime of the slopes and to assess the importance of the subjects to be protected as well as the economic consequences. A slope failure in this sense must not always be regarded as a disaster as long as the

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risks remain within forecasted limits and the design of the mine and the selection of the equipment provide sufficient operational flexibility. I will briefly describe the environmental impact of this large scale opencut mining in the last paragraph. But let me conclude this section by saying that all geological and technical aspects have been developed to the extent that opencut-mining of the Rhineland brown coal resources up to their maximum depth of 600m is no longer restricted by technical factors. Mining at this depth is al so not restricted by economic reasons under present German energy price levels as long as the stripping ratio does not significantly exceed the figure of 10: 1. CONSTRAINTS OF FUTURE DEVELOPMENT While mining even at depths of 600m is generally not restricted by economic reasons it has, however, to be taken into account that economic grounds can only be achieved by large seal e operation as practised today. Furthermore, the planning of the mines, the specification and commissioning of equipment as well as the initial overburden removal also in the Rhineland require periods of up to twelve years. Financing of such large scale projects may be a burden for a single company too. The major constraint for the simultaneous operation of a larger number of opencuts, results, however, from the fact that the Rhineland with some 420 people per km 2 is one of the most densely populated areas of Europe with a highly developed industrial infrastructure and very fertile soils which are intensively used for farming of grain, sugar beets and vegetables, and this in the immediate vicinity of a number of large cities. Pollution of air, water or soil caused by the opencuts and coal utilisation plants is not a major problem. Reasonable regulations and technology to minimize this kind of pollution is available. The main constraints are in fact related to people, the need for their resettlement, the relocation of vi 11 ages, the rerouti ng of highways, rivers and rail roads and the partially necessary changes of the landscape. Many costly measures are undertaken to minimize such disadvantages: exhausted mines are normally fully backfilled with overburden from other mines under development; the areas (Figure 4) are landscaped with lakes and forests and extensive popular recreation areas have been established; the reclaimed farming areas, after some five years of recultivation by specially experienced agricultural engineers of the company, normally achieve equal or even better harvest results than the "unspoiled" areas; the new vi 11 ages or suburbs are a much more modern and efficient standard, and social problems are reduced to a minimum by other individual measures . For more than thirty years now environmental responsibility and planning have been an integrated and major part of all planning considerations for the future development of the Rhenish Brown Coal area. By realistic and thoughful planning for the future plus extensive communication with the public, approval has al ready been received by the relevant governmental, municipal and also private bodies to continue the mining of brown coal in the Rhineland with its present high production levels . for the next fifty years. In this context it perhaps should be mentioned too that the existing governmental regulations are drawn up to provide flexibility to cater for future production levels and eventual changes in the technological, political or economical environments .

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Figure 4. Restored Recreation Area South of Cologne

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Geology of the Southland and Otago Lignite Deposits, Southern New Zealand Michael Isaac New Zealand Geological Survey, D.S.I.R . , P. 0. Box 61012, Otara, Auckland, New Zealand.

Key Words : Lignites, paralic, limnic, mining feasibility.

ABSTRACT Extensive Late 01 igocene to Miocene 1ignite measures of the southern South Island include New Zealand's largest coal deposits. State-funded exploration begun in late 1976 outlined 9 areas with sufficient lignite at depths shallow enough to warrant more detailed investigation . In Southland, the Gore Lignite Measures overlie Paleozoic and Mesozoic greywackes over an area of 2700 km 2 . Basal marine and estuarine beds are overlain by paralic measures with multiple thin (average 4-6m) but laterally persistent seams, succeeded by barren measures dominated by thick upward-fining fluviatile cycles; Gore Lignite Measures are interpreted as a prograding deltaic to fluviatile sequence. The limnic Manuherikia Group of Cental Otago overlies Paleozoic and Mesozoic greywacke and schist in a series of elongate fault angle depressions formed during the Late Cenozoic Kaikoura Orogeny . Typically, basal Manuherikia quartz gravels and sands are succeeded by lignite-bearing fluvio-lacustrine beds , in turn overlain by 1acustri ne muds and silts. Seams are up to 90m thick, but laterally variable . The deposits are geologically dissimilar, and differences in structural setting, elastic geology and seam geometry will have an important bearing on further prospecting and eventual mining. Preliminary reports on mining feasibility are at present under study. INTRODUCTION New Zea 1and ' s known 1i quid hydrocarbon resources are sma 11. The synthetic petrol plant under construction in Taranaki, North Island will utilise natural gas from the large offshore Maui Field, but in the future it is hoped to further reduce re 1i ance on imported crude oi 1 by producing transport fue 1s from coal . Two areas of New Zealand have coal deposits large enough to be considered as sources of feedstock for a coal conversion plant. Although the Eocene sub-bituminous coalfields of northern North Island are extensive, much of the coal could only be worked by relatively expensive underground mining,

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and a significant proportion is committed to supplying existing and planned industrial users and thermal power stations. The Late 01 i gocene to Miocene lignites of southern South Island, however, are New Zeal and' s largest coal deposits; they are uncommitted, and are s.uitable for large scale open pit mining . State-funded investigation drilling between late 1976 and mid 1979 outlined 9 areas in Southland and Otago with sufficient lignite at shallow enough depths to warrant further consideration (Figure 1). Subsequently a limited programme of core drilling has been carried out to improve electric log calibration, provide preliminary geotechnical data, and recover lignite for analysis. Ori gi na l depositional environments and subsequent tectonic hi story of the Southland and Otago lignite deposits differ and have resulted in different structural settings, seam geometries, cl ast i c geology and probably different lignite types and chemistry. The latter aspect is dealt with separately (Black, this issue); this paper describes the geology of the South land and Otago deposits, and outlines some of the consequent effects on mining feasibility. N

t ~ CENTRAL OTAGO •

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~ ~ J

~ SOUTHLAND

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Figure 1.

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tit

Southland and Central Otago Lignite Fields, Southern South Island, New Zealand. Cross hatching shows areas explored 1976-1981, solid areas are the major deposits. Australian Coal Geology 4, part 1

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S0UTHLAND LIGNITES Geology Late 0ligocene to Early Miocene Gore Lignite Measures (Wood, 1956) are present over 2700 km 2 , generally unconformab ly overlying Permi an to Jurassic basement, and locally up to 1 km thick. Carbonate-dominated marine shelf sediments are intercalated with Gore Lignite Measures in the west, but elsewhere associated marine and estuarine beds are discontinuous, and virtually restricted to the base of the sequence (Figure 2). The lower measures comprise predominantly clean, well sorted upward-fining sand units, with lesser finely laminated silts and muds and minor lignite in seams which show rapid lateral variation. The geology is not well known, as drilling was concentrated on the stratigraphically higher lignites of economic potential; they were probably deposited in a range of delta front and lower delta plain environments (model and terminology after Horne et al. 1978).

] ]

l J

Figure 2.

UPPER LIGNITE MEASURES . ':,IPWard • _fining gravel,sond,silt cycles with th ick intervening mudston•s. Thtn ,discontinuous lig-iites

MAIN LIGNITE-BEARING INTERVAL : multiple persistent ..ans, including the WAIMUMU SEAM 9-18m thick . Seams interbedded with carbonaceous muds, laminated silts and muds, and persistent fine sands

LOWER LIGNITE MEASURES : up¥rtard7" coorsen i~ and . up~ard-fining sand, silt, mud units with minor thin , discontinuous lignites .

CHATTON MARINE . shelly 9\ouconitic sands. muds .minor limestone PERMIAN -JURASSIC GREYWACKE

Schematic stratigraphic column for the Gore Lignite Measures at Waimumu, Southland, New Zealand. Sequences elsewhere in Southland are similar except at Mataura, where the lower member is absent and the lignite-bearing interval atypically thick. (After J.K. Lindquist).

Productive measures overlying (or locally equivalent to) the lower measures are 50 - 300m thick, with multiple lignites averaging 4 - 6m thick but locally as thick as 18m. Seams are laterally persistent and although usually partly removed by erosion can in a number of areas be traced over 50 km 2 between the outcrop and the limit of the drilling. The nature and proportion of the elastic sediments between seams varies, locally comprising mostly silts, carbonaceous and non-carbonaceous muds, but e 1sewhere 1atera l ly persistent upward-fining and upward-coarsening sands 10 -40m thick predominate, with lesser finely laminated silts and muds. Lignites succeed both "seat earths" Australian Coal Geology 4, part 1

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with well developed root horizons and subaquatic highly carbonaceous muds, but peat accumulation was generally halted by inundation, as seams are typically overlain by either carbonaceous mud or channel sands . The productive measures are interpreted as point bar, channel and washover splay sands, flood plain silts and muds, l acustri ne muds and swamp peats accumulated in a lower to middle delta plain (the transitional lower delta plain of Horne et al. 1978) setting. -Repetitive upward-fining gravel , sand , sil t cycles 20 - 50m thick separated by equally thick slightly or non-carbonaceo us muds tones overl i e the productive measures. These upper measures contain l ittle lignite, and are interpreted as "stacked" point bar and flood basin sedi ments deposited in upper delta to fluvial plain environments. The Gore Lignite Measures of Eastern South land are thus interpreted as a paralic prograding deltaic to fluviatile sequence , deposited after the extensive Late 0ligocene marine transgress i on of the New Zealand landmass.

% BED MOISTURE

Figure 3.

¾ASH

Summary diagram showing bed moisture vs ash content for Southland and Central 0tago lignites . Analyses by Coal Research Association of New Zeal and . (After J. K. Lindquist).

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Major Deposits The three northen deposits at Croydon, Waimumu and Mataura are of higher rank (i.e. lower moisture) than those to the south at Morton Mains, Wai matua and Ashers (Figure 3), the difference being attributed to different depths of burial (Lindquist, 1982). Pollen/spore zonation indicates the main seams in all areas are about the same age (Pocknall and Mildenhall in press). Croydon and Waimumu deposits include the same seams on the northeast and southwest limbs of a northwest trending anticline respectively. Both are bounded partly by seam outcrop, and partly by major reverse faults with at least 300m of post-Miocene vertical displacement. In both areas the principal seam is up to 18m thick, but nearly 50% of the total lignite-in-ground is in thinner seams above and below it . Thick laterally persistent aquifer sands are present between seams and in the overburden. The deposits ~re comparatively sma 11 , with an aggregate of slightly less than 800 x 10 tonnes of lignite-in-ground. Best part:t of the Croydon and Wai mumu deposits are estimated to contain 410 x 10 tonnes and 205 x 10 6 tonnes respectively; overburden to lignite ratios of between 5:1 and 8:1 are likely (Bowen, 1980). At Mataura the productive measures are atypically thick, with 10 major seams normally 4-6m but locally up to llm thick present within a 250 - 300m interval which overlies basement or marine beds directly . Extent and thickness of the lower 6 seams have been largely contra 11 ed by basement pal eotopography, the lignites being thin or absent over three major buried ridges (Figure 4). Thick laterally persistent aquifer sands separate the seams, and considerable aquifer recharge is likely from the nearby Mataura River along the eastern margin of the deposit, as the sequence dips west at 3-5°. In the west the lignite-bearing sequence is overlain by up to 200m of barren upper measures, which also include major aquifers. Mat'.\}'ra is the largest of the South Island lignite deposits, with about 3000 x 10 tonnes of l i gni te-i n-ground at less than 300 metres of cover. The area of greatestg>otential covers 32 km 2 west of the outcrop of the lowest seam, with 750 x 10 tonnes present at less than 200 metres depth, at an overburden to lignite ratio between 5:1 and 6:1. The Morton Mains deposit comprises a major seam up to 15m thick with up to 5 minor seams; the major seam includes 50% of the total lignite-in-ground. The 4 minor seams stratigraphically above the major seam split and thin rapidly. Structure of the deposit is not well known, but differences in seam elevations between drillholes are easily accounted for if open folding about north-south axes is assumed, with dips of between 2° and 5° . Seam interbeds are predominantly silts and muds, with mi nor sands; groundwater problems would be less severe than in other areas . Tota lignite-in-ground at less than 200m depth is estimated at about 1000 x 10 tonnes; tha part of the deposit most favourable for mining probably contains 550 x 10 5 tonnes at an overburden to lignite ratio of about 4:1 .

Most of the lignite at Waimatua is in three seams, typically 4-8m but locally up to 12m thick, flat-lying or dipping very gently to the northwest over 40 km 2 immediately southeast of Invercargill city. Local variation is apparent in the nature and proportion of interseam elastic sediments, which range from silts and muds to fine sands elsewhere . Total lignite-in-ground at less than 150 metres depth is close to 1000 x £1-0 6 tonnes; the most prospective area covers 36 km 2 and includes 590 x 10 tonnes at less than 100m depth, with an overburden to lignite ratio of better than 3:1.

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At Ashers, the lowest seam is up to 14m thick, but it splits and thins rapidly westward downdi p from the outcrop (Figure 4). The four over-lying seams are more persistent, and are normally 2-Sm thick. Extensive thick aquifer sands overlie, underlie and separate the major. seams, and considerable aquifer recharge is likely along strike from the sea. Splitting and thinning of the lowest seam is caused by a series of north-south trending sand units; higher seams are thin over the area of maximum sand thickness presumably as a consequence of differential post-depositional compactioC. Total lignite-in-ground at less than 150m depth is estimated at 1300 x 10 tonnes; the mgst favourable parts of the deposit cover 44 km 2 , and include about 700 x 10 tonnes of lignite-in-ground at less than 150m depth, at an overburden to lignite ratio of about 4: 1. In summary, Southland lignite deposits comprise multiple relatively thin but laterally persistent low ash seams, typically with equally persistent aquifer sands between the seams and overlying them. Except at Croydon and Waimumu, structure is likely to be relatively favourable for large scale mining, with gentle dips and possibly no major and few minor faults. The major obstacles to mining include expected groundwater problems, the large number of seams and splits to be worked, comparatively low aggregate seam thicknesses, and in some cases, the high value of the land for agriculture. OTAGO LIGNITES Geology Central Otago lignites are part of the Early-Mid Miocene Manuherikia Group, (Hector, 1884) an extensive thick unit of fluviatile and lacustrine sediments now preserved in a series of north to northeast trending fault angle depressions formed during the Late Miocene-Recent Kaikoura 0rogeny. Typically, western margins of the depressions are high angle reverse fault contacts between basement schists or greywacke and steeply tilted Manuherikia strata, whilst in the east Manuherikia beds are in unconformable sedimentary contact with the basement. At its maxi mum the Late 01 i gocene marine transgress ion reached only part way across the eastern-most (maniototo) basin; Central 0tago coals are limnic in character, formed in environments associated with a major intermontane lake basin. In many areas Manuherikia strata can be divided into three units (Figure 5). Auriferous quartz gravels and sands in thick cross-stratified units often overlying basement are 0 - 200m thick, and have in the past been worked extensively for gold. They include minor finer grained flood plain sediments and rare thin discontinuous lignites, and were probably deposited in fluviatile and lacustrine deltaic distributary channels . Thick lignites, carbonaceous and non-carbonaceous muds, silts and minor fine sands overlying or laterally equivalent to the basal gravels and sands were deposited in 1ake margin and 1ake delta p1ai n settings. The carbonaceous sequence is usually 0 - 100m thick, and in places consists almost entirely of 1ignite. Non-carbonaceous de 1ta front and 1ake bas i n s i 1ts and muds overlie the 1 ignites in many p1aces. Detailed studies at the University of Otago (Douglas, 1980), have resulted in recognition of a number of specific coal-forming environments within the Manuherikia Group.

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I I

ASH ERS west

--== ~ ~ i;:::::..-1--

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(upper) Cross section through part of the Ashers deposit, Southland, illustrating rapid thinning of the lowest seam and lateral persistence of higher seams. (lower) Cross section parallel to the regional strike at Mataura, Southland. Note the lateral persistence of the thin multiple seams and the effects of paleotopography. Four stratigraphically higher seams outcrop west of the line of section . Vertical exaggeration x 10; compare with Figure 6, which is at natural scale. Left hand trace natural gamma, right hand trace LSD density; logs by B. P.B. Australian Coal Geology 4, part 1

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UPPE R MANU HERIKI A GROUP inter bedded muds, silts and minor so nds wit h minor thin lignites

MAIN LIGNITE -BEARING INTERVA t~ick bu t latera lly vari able seam (or seams) plus minor seems, separated by car bona ceous muds • laminated silt s.and m1nor sands LOWER MANUHER IKIA GROUP quartz gravels and sa nds undulying or laterally equ iva lent to the maj or li gn ites PERM IAN - JUR AS S IC

Figure 5.

SCHIST & GRE YWACKE

Schematic stratigraphic column for the Manuherikia Group in the Hawkdun/Home Hi 11 s area, Centr al 0tago, New Zeal and (partly after Douglas 1980).

Major Depos i ts At Roxburgh, · 2oom of Manuherikia strata are preserved in a north-south ori ented elliptical inlier bounded in the west by a major reverse fault . Locally up to 20m of quartz gravels and sands overlie the basement, but el sewhere the Roxburgh Seam (30-70m) overlies deep ly weathered schist with little or no intervening strata . The seam typically comprises 32 - 45m of low ash lignite with an additional several metres of high ash lignite near the base, but in the south and west the seam deteriorates to include high ash bands and mudstone partings (Figure 6). The particularly rapid westward deterioration apparent from electric logs may be due largely to crushing close to the western boundary fault . Roxburgh Seam is overlain by up to 50m of non-carbonaceous Manuheri ki a Group silty muds and 50m of terrace gravel s6 Geology of the deposit is not well known; it may contain as much as 245 x 10 tonnes of lignite at an overburden to lignite ratio of between 2:1 and 3:1. Manuherikia beds at Hawkdun are in high angle normal or reverse fault contact with basement in the north, east and west. The lignite bearing interval comprises the major Hawkdun Seam , up to 90m thic k wi th 10-15 mudstone partings and a discrete 2-4m seam several metres above it (Figure 6). Individual splits of Hawkdun Seam are up to 16m t hi ck, and all splits are thickest about an area near the centre of the deposit, south of which thickness and proportion of the elastic partings increase . Where thickest, Hawkdun Seam is only 5-15m above basement , but in the so uth thick f l uviatile gravels and sands are present at or near the base of the sequence. Seams are overlain by at least 70m of silts and muds with littl e lignite. Hawkdun is t~ largest of the Central 0tago deposits, estimated to incl ude 812 x 10 tonnes of lignite-in-ground with less than 200m cover at an overburden to lignite ratio of between 2:1 and 3:1.

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RO XBURGH north

south

HAWK OUN southwest

•600m basement

........,......~--

Figure 6.

2km

(upper) Cross-section through the most favourable part of the Roxburgh deposit, Central Otago. (lower) Cross-section through the Hawkdun deposit, Central Otago. Note the persistent nature of the relatively thin carbonaceous mudstone partings. Based partly on seismic surveys. Vertical exaggeration x 10; compare with Figure 4, which is at natural scale. Left hand trace natural gamma, right hand trace LSD density; logs by B.P.B.

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At Home Hills 12 km southeast of Hawkdun 200m of Manuherikia beds are preserved in an open assymetric syncline plugning northeast at 2° towards the major Hawkdun Fault System. Extent of fl uvi at i le gravels and sands locally present above basement is limited by pal eotopography, and the two lowermost lignites are similarly restricted. Higher seams are widespread; the principal Home Hills Seam is up to at least 23m thick, and it and two others overlying it include 90% of the total lignite-in-ground. The lignites are separated by fine sands, silts and muds, the proportion of coar ser elastics being higher in the extreme north of the deposit. Silts and muds overlying the major seams include carbonaceous intervals but l i tt l~ or no workable l yini te. Total lignite-in-ground is estimated at 346 x 10 tonnes, but 50 x 10 tonnes is in a 1 km wide strip between seam outcrop and the Hawkdun Fault, and it may n~t be economically recoverable. The remainder is present at an overburden to lignite ratio of the order of 3:1. In summary, the limnic Central 0tago deposits typically comprise a thick single seam or relatively few thick seams, and the seams are characterised by rapid lateral variation in thickness, ash content, and number of elastic partings. Seams are generally overlain and separated by relatively fine grained sediments, and thick gravel and sand aquifers are generally present only between the seams and basement. Structure may present problems to mining, as all three deposits are adjacent to one or more major high angle reverse faults . Much smaller scale fau l ting is likely to be present at both Roxburgh and Hawkdun, but a recent mini-SOSIE* seismic reflection survey trial suggested the Home Hills deposit may not be greatly disturbed. Although seams dip at low to moderate angles over large areas dips up to 15° have been demonstrated elsewhere (e.g. Home Hills, northwest limb of the syncline) . Aspects favourable to mining include the low number of seams to be worked, high aggregate thi cknesses of lignite, fewer di ffi cult i es with groundwater, low value of the land for agriculture, and the possibility of recovering alluvial gold ·as a by-product. Mining may be hindered by, among other things, unfavourable geological structure. MINING FEASIBILITY

In 1980 the N. Z. Liquid Fuels Trust Board engaged consultants to conduct a preliminary mining feasibility assessment of the South Island lignites, the work to include estimation of recoverable lignite quantities, evaluation of mining costs, sensitivity of costs to production levels, and recommendations for future work. The consultants considered quantitative and qualitative factors such as likely capital costs, operating costs, hydrological and geotechnical considerations, existing infrastructure, environmental impact, size of the deposits, and likelihood of further lignite in the vicinity, and ranked the deposits according to amenability for mining. A major cone l us ion of the study was that whilst no deposit presented insurmountable obstacles to mining, it is likely mining wi 11 only be economic ~ ing bucket wheel excavators at a minimum production rate of about 10 x 10 tonnes per year. Estimated mining costs for the better deposits are similar to other planned or working lignite opencast mines elsewhere in the world . In considering lignite mining in 0tago and Southland it needs to be taken into account that average mining losses in the Rhine brown coal district have increased with the mining of less favourable deposits; average lasses for open pit mines worked to date have been estimated at 26% (Hannak in Fettweis, 1979) . Assuming similar or greater losses are likely for open pit mines working the comparatively deep multiple seam New Zeal and deposits, then the deposits at Roxburgh, Home Hills, Croydon and Waimumu could well be too small Australian Coal Geology 4, part 1

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to sustain production of 10 x 106 tonnes per year for a reasonable period of time and working two smaller pits would probably be uneconomic because of the considerable capital cost of additional machinery required. At present not one of the five larger deposits stands out as clear favourite, and in some cases differences are small enough that the final overall ranking could be altered by further exploration and assessment . FUTURE WORK Additional investigations are necessary for the deposits regarded as most favourable for mining, the work to include: 1.

2. 3. 4.

dri 11 i ng to improve quantity estimates, 1 i ke ly mine boundaries, overburden to lignite ratios, structure, and possible seam washout zones; investigation of lignite quality and chemistry; a mining-oriented study of geotechnical factors; and hydrological investigations, including pump testing.

Such work is likely to require a budget of at least several million dollars. ACKNOWLEDGEMENTS Those parts of this paper dea 1 i ng with the geo 1ogy of the 1 ignites draw heavily on work by J . K. Lindquist, N.Z. Geological Survey, and B.J . Douglas, University of Otago. The paper has been significantly improved following comments and criticism by R.P. Suggart, J . K. Lindquist, A.M. Sherwood and F.E. Bowen. *Mini-SOSIE is a Registered Trade Mark, Societe Nationale Elf Aquitaine (Production). REFERENCES Black, P.M. 1982. Petrology and Inorganic Geochemistry of South Lignites, New Zealand (this issue).

Island

Bowen, F. E. 1980. Effects of Variations in Mining Parameters on Recovery Percentages and Overburden: Coal Ratios, Croydon and Mataura Sectors, Eastern Southland Coalfield. N.Z. Geological Sruvey Report M84. Douglas, B.J. 1980. The St. Bathans Delta, Central Otago: A Potential Coal Resource in Geological Society of New Zealand, Christchurch Conference Program and Abstracts. Fettweis, G.B . 1979.

World Coal Resources.

Verlag Gluckauf GmbH, Essen 416

Hector, J. 1984. Genera 1 tab 1e of r~ference to the sedimentary rocks of New Zealand. N.Z. Geological Survey Reports of Geological exploration 1883-4. Horne, J.C., Ferm, J.C., Caruccio, F.T. and Baganz, B.P . , 1978. Depositional models in coal exploration and mine planning in the Appalachian Region. Am . Assoc. Petrol. Geology. Bull. 62, 2379-2411 .

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Lindquist, J.K. 1982 . The Dependence of Specific Energy and Density on Moisture and Ash Content, south 1and and Centra 1 Otago Lignites, New Zealand: a Key to Burial History. N. Z. Geological Survey Report M88. Pocknall, D. T. & Mildenhall, D. C. (in press). Late Oligocene-Early Miocene N.Z. Geological Survey Spores and Pollen, Southland, New Zealand. Paleontological Bulletin. Wood, B.L. , 1958. 53.

The geology of the Gore Subdivision, N.Z. Geol . Surv. Bull.

Australian Coal Geology 4, part 1

CONTENTS -

PART 2

KEYNOTE ADDRESS Gluskoter, H.J.: Applications of Geology in Coal Exploration and Production COAL DEPOSIT EVALUATION GENERAL METHODS AND REGIONAL STUDIES Barton, C.M.: A Review of Investigations of Brown Coal Geology by the State Electricity Commission of Victoria Jones, G.D.: CSR's Brown Coal Exploration Ward, C.R.: Exploration and Development of Black Coal in Australia - an Historical Perspective Park, W.J.: The Geology of the Muja Sub-Basin; a Model for the Collie Basin, Western Australia GEOPHYSICAL TECHNIQUES Peck, W. and S.M. Yu: Seismic Refraction Studies for Mine Planning and Design Weber, M.: Well Log Geophysics for Coal Measures Haigh, J.E. and Edwards, I.H.: Computer Processing of Geophysical Logging Data in Coal Deposits Dodds, J.E. and Haigh, J.E.: The Use of Transient Electromagnetic Methods for Resistivity Sounding and Mapping with Particular Reference to Coal Basin Studies Rosengren, K.J., Williams, C.C.D., Grimstone, L.R. and Gorman, J.M.: Geotechnical Analysis of Coal Measures Strata by Downhole Sonic Logging Henderson, R., Lilly, I. and Pippett, T.: High Resolution Magnetics for the Delineation of Coal Seam Structure Murdoch, R.B.: Exploration of Black Coal Subcrop Zones using Electrical Geophysical Techniques GEOLOGICAL DATA BASE AND PROCESSING Mallett, C.W. and Ward, C.R.: Standardisation of Geological Data in Coal-Bearing Sequences Barton, C.M., Dubrovich, A.P. and Webster, R.: Geostatistical Applications in Brown Coal Resource Investigation Dubrovich, A.P.: Computer Applications in Brown Coal Investigations Gill, B.F.: Data Processing of Bore Records Grimstone, LR., Hodgson, W., McTaggart, S. and Peterson, M.S.: Computer Aided Geological Modelling for a New Queensland Coal Mine Pauncz, I. and Holt, G.E.: Computer Based Geotechnical Data Management System for Coal Exploration and Mine Planning HARD COAL PROPERTIES Diessel, C.F.K.: An Appraisal of Coal Facies Based on Maceral Characteristics Hunt, J.W.: Relationship Between Microlithotype and Maceral Composition of Coals and Geological Setting of Coal Measures in the Permian Basins of Eastern Australia Beeston, J.W.: Coal Sedimentation in the Reids Dome Beds, Bowen Basin: A Depositional Model

289

290 304 305 319

341 354 364 381 391 392 393

400 413 429 440 451 464

474 484 503

MINE DEVELOPMENT SECTION Gaulton, R.J.: The Role of the Mine Geologist in Brown Coal Winning Miller, R.: Prediction of Coal Mining Conditions and their Areal Variations using Exploration Geotechnical Data Wooltorton, B.A.: Predevelopment Data Techniques: Note on Recent Developments in Instrumented Drilling and Hydraulic Fracturing Mallett, C.W., Seedsman, R.S. and Emerson, W.W.: The Significance of Plastic Clay Horizons in Coal Measures of the Bowen Basin, Queensland Boyd, G.L: The Geotechnical Assessment of the Theodore Prospect Brumley, J.C. and Reid, M.A.: An Investigation of the Groundwater Resources of the Latrobe Valley, Victoria Sullivan, T.: The Origin and Characteristics of Defects in Oil Shale Rawlings, C.D. and Gale, W.J.: Prediction of Roof Deformation Mechanisms in Underground Coal Mines Rawlings, C.D., Gale, W.J., Stone, I. and Cook, C.: Geotechnical Investigations of Roof Conditions at Tahmoor Colliery.

505 513 529

531 542 562 582 596 597

289

Applications of Geology in Coal Exploration and Production Harold J. Gluskoter Exxon Production Research Company Houston, P.O. Box 2189, Houston, Texas. ABSTRACT Geology Is often referred to as an Impure science relative to pristine fields such as chemistry, physics, and mathematics and comments concerning the heterogeneous Interdisciplinary nature of the geosclences are common. Somewhere among the least pure of the subsets of this heterosclence Is coal geo Iogy, an a I I encompass Ing and rather amb I guous term. Geosc I ent I sts who have found themselves label led •coal geologist• Include stratlgraphers, sedlmentologlsts, geophysicists, mineralogists, geochemlsts, petrographers, environmental geologists, paleobotanlsts, engineering geologists, and economic geologists. Fortunately for all concerned, all these disciplines have Important contributions to make to coal geology. In most of the world, coal mining historically has proceeded with very little assistance from geologists of any Ilk. However, higher prices from competing fuels have provided an Impetus to coal geology as well as to coal mining and the application of modern techniques of geoslences to the exploration, evaluation, and production of coal Is now taking place. Coal exploration has been greatly Improved by the appl !cation of geophysical methods, such as high resolution seismic surveys and Jogging techniques: applications that owe their origins to earl fer developments In the petroleum Industry. Coals can be evaluated for uses other than direct combustion by modern analytical chemistry and by coal petrography. The latter has had Its greatest success In the prediction of coking character of coals. The abl I lty to extrapolate coal quality beyond the narrow confines of a drill hole requires a geological model and the sedlmentologlst, paleobatonlst, and coal petrographer are among those that contribute to the development of this model. Geotechnlcal Investigations now precede mine development and the engineering geologist Is, at times, being heeded. The world coal demand Is projected to Increase by approximately 85-90 percent during the 1980-2000 time period. The Increase wll I be principally In electric power generation and In synfuels. Estimating the exact time In the future at which the demand for coal will be Impacted significantly by synfuels and estimating the time at which the world's production wl I I exceed 5000 ml I I Ion tonnes (ft was approximately 2800 ml I I Ion tonnes In 1980) are both difficu lt to do. However, there Is general agreement as to the trend. This Increased demand for caol wil l carry with It Increased demand for the application of geosclences to coa l exploration, evaluat ion, and production.

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A Review of Investigations of Brown Coal Geology by the State Electricity Commission of Victoria C.M. Barton

Exp~oration and Geological Division, Fuel Department, State Electricity Commission of Victoria, 15 William Street, Melbourne, Victoria, 3000, Australia

Key Words: Geology, Coal, Lignite

ABSTRACT The organisation of the brown coal geological i nvestigations, within the State Electricity Commission of Victoria, is described and the system of drilling and samp 1i ng is out 1i ned . The techniques used in the dri 11 i ng, the data management and the associated investigations re 1ated to stratigraphy, structure, geohydro 1ogy, petro 1ogy, geophysics and engineering geo 1ogy are documented. Systems have been estab 1i shed to cater for exchanges of i nformati on between Government authorities and private companies and to ensure that the centra 1 data bank i s kept up to date . INTRODUCTION Some 35 mi 11 ion tonnes per annum of brown coa 1 are produced by the State Electricity Commission of Victoria (SECV) from the Latrobe Valley coal deposits. The coal is used primarily for the generation of electricity and, to a lesser extent, for the production of briquettes and char and as a source of fuel for local paper making and cement i ndustries. From 1916 until the mid-1920 period, the Victorian Department of Mines conducted drilling in the Latrobe Valley and identified sufficient brown coal to warrant the establishment of the SECV. Since that time, the Commission has undertaken extensive studies of the brown coal areas of the State. In addition to these major investigations , the Victorian Department of Mi nera 1s and Energy has conducted brown coal exploration work; notably in the Stradbroke and Gelliondale areas (Thompson, 1979). Other brown coal resources investigations have been carried out by private companies at Ge 11 i onda 1e in South Gippsland and at Anglesea and Bacchus Marsh . In recent times, exploration work has been undertaken by various companies in peri phera 1 areas of the Latrobe Valley and elsewhere in the State.

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The SECV investigations have been undertaken in many areas of the State, but have been heavily concentrated in the Latrobe Va 11 ey region, where over 100 thousand million tonnes of brown coal have been defined (Gloe, 1979). A brief account is now presented covering the investigational procedures and technical aspects of this work. The paper should be read in conjunction with other papers (Barton et al. Brumley and Reid, Dubrovich, Gaulton, George, Gill, Holdgate, and Kiss in this symposium) in whi eh details of various aspects of the work are described. Reference should be made to papers by Gloe (1960 and 1976) for descriptions of the geology of the brown coal areas of Victoria; a 'concealed outcrop' map of the Latrobe Valley brown coalfields is presented for reference purposes (Figure 1). ORGANISATION OF COAL GEOLOGY INVESTIGATIONS WITHIN THE STATE ELECTRICITY COMMISSION OF VICTORIA Coal geology i nvesti gat ions are centred in the Exploration and Geo l ogi ea l Division of the Fuel Department of the SECV. The division is sub-divided into three sections covering Basin Structures (Stratigraphy and Coal Petrology, etc. ) , Engineering Geology ( i ncl udi ng geohydro l ogy and computing) and Cartography. The work embraces the specification of dri 11 i ng and the conduct of investigations to determine the location, extent, nature and constitution of potentially exploitable brown coal resources. Investigations are sustained by the establishment and maintenance of a data bank on the brown coal resources of the State. Coal resource dri 11 i ng is carried out by the Latrobe Va 11 ey organisation of the SECV. DRILLING AND SAMPLING Exploration dri 11 i ng by the SECV in the Latrobe Va 11 ey region has been on a variable spacing of around 1 to 2 km . Coal exploration drilling in the main part of the Valley is largely complete, but private drilling is continuing in peripheral areas which are covered by exploration licences. Proving drilling by the SECV has been on a general 400 m bore grid. Programs are underway to complete the 400 m spaced drilling of open cut areas. Associated stratigraphic exploration, geohydrological, geotechnical, operational and special investigation drilling is variably spaced to suit the particular project needs . Approximately 20,000 m of coal resource and associated drilling, is being conducted by the State Electricity Commission of Victoria in the current 1982/83 year. A11 coal resource bores are geophys i ea lly logged and all coal is sampled. Drilling is carried out to average depths of around 250 m (maximum depths are around 800 m) by private contract and SECV rigs. Both rotary and percussion methods are used and routine samples are obtained by standard coring, continuous coring and ,earth socket . Bulk samples are taken by bucket auger. Samples from thick seams are composited over 3 m intervals and tested for moisture and ash . Two 3 m intervals are combined into a 6 m sample, at the Herman Research

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Laboratory of the SECV and are analysed for a comprehensive range of mineral and inorganic constituents . Two 6 m samples are then combined into a 12 m sample and are analysed for coal properties and specific energy characteristics. An example of the output format of the results of the tests is demonstrated by Gill (1982, paper in this symposium). Kiss (1982; paper in this symposium) enters into further discussions related to this topic. The standardised test procedures, outlined above, have been found to be compatible with general operational requirements. The standard sampling and testing methods are varied for thin seams and for petrological and other special evaluation purposes. PRIMARY ANALYSIS OF DATA Strata and geophysical logging of bores are carried out mainly by the geologists and technicians based in the Latrobe Va 11 ey. Geophysi ea l logging covers multiple resi sti vi ty, gamma, temperature, ea l iper and occasionally, density and neutron methods. Primary data are obtained through the use of an SIE 750 logger recording onto charts and a digital recorder. Petrological specialist.

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The results of the sample analyses are transmitted to the Exploration and Geological Division where the information is combined with the strata logs and the bore master details and is checked and entered into the data bank (Gill, 1982; paper in this symposium). Physical and maceral analyses of the coal are effected in the Richmond petrolological laboratories of the Exploration and Geological Division and, as part of spe~ific project investigations, in the Coal Science of the Herman Research Laboratory (George, 1982 and Kiss, 1982; papers in this symposium). Clay mineralogy and clay cation-exchange determinations are undertaken at the Herman Research Laboratories whilst sand-size analyses are carried out at various other SECV laboratories; results are entered into the central data bank (Barton, 1971). Soil (sediment and coal) testing laboratories in the SECV's General Engineer; ng and Construction Department provide primary geotechni ea l testing facilities. TECHNIQUES A variety of techniques have been developed to process the base data and to service the investigations . The central SECV brown coal resource data bank holds records of approximately 15,000 bores. Manipulation and maintenance of these records forms a major part of the investigational work (Dubrovich and Gill, 1982; papers in this symposium). Pictorial logs can be drawn directly from the central data records and bores can be plotted onto cross sections for subsequent manual construction of the stratigraphic interconnections. A series of 400 m spaced, approximately north-south and east-west cross sections, have been drawn in this manner, across pratically the whole of the coal bearing strata of the Latrobe Valley and South Gippsland. Australian Coal Geology 4, part 2

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294

Extensive use is made of a computerised drafting system (Figure 2). The system (Autotrol CC80) has an input digitiser and offers the facility of placing a single map on several layers. Updated information can be changed on one layer, leaving the base map intact. Changes of scale on plans and cross sections can be made almost instantly. 0 0

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Numerous contoured strata and other surfaces, are al so prepared from the centralised base data. In many instances, the contours are machine drawn using a Calcomp plotting routine. In all cases, careful manual checking is necessary to ensure contour accuracy; linear, quadratic, cubic and quartic trend surfaces and any combination of residual contours can be automatically drafted as required (Dubrovich, 1982; paper in this symposium). The calculation of coal quantities and qualities obviously forms a major part of the invest i gat i ona l work. A variety of methods are used ranging from computer and hand calculation of coal areas, on cross sections and contoured thickness plans, to both two and three dimensional geostatistics (Barton, Dubrovich and Webster, 1982; paper in this symposium) . The most commonly used system is based on polygons which are constructed around representative bores by computer and manual methods. Programs have been developed (Dubrovic, 1982; paper in this symposium) to calculate weighted averages of properties for each polygonal block. Almost the entire Latrobe Valley coalfields have been analysed in this manner and statements of general quantities and properties, in many separate areas, have been issued (Gloe, 1979). The statistics are supplemented by the computer production of cumulative probability plots (Figure 3) and of property histograms (i.e. flag plans) down boreholes (Figure 4) . Pioneering studies of the structure of the coal mass, embracing the interrelated maceral constitution and lithotype characteristics of the coal, have led to the production of a manual of brown coal petrology (George, 1982; a paper in this symposium). Many of the coal properties relate to lithotype; a relationship which has led to the requirement to map lithotype distributions on open cut faces (Gaulton, 1982; paper in this symposium). The relationship between the lithotype and the environment of deposition has been recognised and has led to the provision of funds by the SECV, to the University of Adelaide, for Mr. D. Blackburn to conduct applied research into plant macrofossils . Monash University is conducting parallel investigations on plant macrofossils . It is necessary to extract underground water to maintain the stability of the open cuts; approximately 800 litres/sec . is currently extracted from a main dewatering centre beneath Morwell Open Cut. In connection with this operation, the aquifer systems and the geohydrology have been studied by the SECV and the Victorian Department of Minerals and Energy in order to provide data for predicting the effects of water extraction (Brumley and Reid, 1982; paper in this symposium) . A mathematical finite element model is used to help in predicting the effects of dewatering. As part of these studies, procedures have been developed to produce moments of particle-size distributions from curve fits to laboratory data. In the Morwe 11 Open Cut area, these parameters have been related to aquifer transmi ss i vit i es (Barton, 1971, Figure 5). Investigations into the stability of the open cuts require the adoption of a range of techniques (Gloe, James and Barton, 1971). Joints and other structures are measured in the open cuts and are manually and computer plotted as stereo-nets (Barton, 1969 - Figure 6) and other pictorial representations (Figure 6). The program produces pole plots and contoured pole plots on equal area and equal angle nets and includes the facility to produce Kamb plots and joint intensity plots which are corrected for traverse bias. Predictions of structural conditions at future open cut sites have been made through

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structural analyses to determine present in situ stress regions (Barton, 1981, Figure 7) . The stress regions re 1ate to the occurrence and predi et ion of seismic events . In this context, the SECV provides a grant to the Phi 11 ip Institute of Technology to maintain a seismic station in the Latrobe Valley and to provide information on the return period statistics and potential characteristics of ground acceleration related to seismic events (Gibson, Wesson and Cuthbertson , 1981). Movements around open cuts ar e monitored by the survey groups and are plotted by the Drafting Section of the Exploration and Geological Division (Figure 8) . Engineering analyses are conducted by an SECV geotechni ea 1 group in the Development Division of the Fuel Department.

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In order that the field geologists and engineers are able to make speedy decisions on batter stability, programs have been developed whereby a comprehensive range of block wedge and arcuate failures (Figure 9) can be numerically analysed in a hand-held Tl59 calculator (Foxall and Barton, 1981). The programs can be operated without the need for any specialised knowledge of the algebraic methods. It is appropriate to conclude the techn i cal review by covering some procedures which are used to provide stratigraphi c input to the design of open cuts. Raw stratigraphic data is often unsu i table for open cut design and the design engineers are loath to make the necessary prior stratigraphic amendments. The matter has been resolved by the preparat i on, by the design engineers, of detailed requirements for stratigraphic amendments which are suitable for incorporation in open cut design. A computer program has been created to amend bore strata in accordance with open cut design rules and to present the amended levels for top and bottom of "diggable" coal (Dubrovich, 1982; paper in this symposium). The system involves multiple checks to ensure that data is reliable.

Australian Coal Geology 4, part 2

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Figure 9.

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Some examples of batter failures which can be numerically analysed using a Tl59 hand-held calculator.

TECHNICAL INTERCHANGES The geo l ogi ea l mapping and survey work of the Department of Minerals and Energy complements the brown coal resource investigations of the SECV. Regular meetings are held with the technical staff of the Department of Minerals and Energy to ensure that regional programs dovetail together and that no duplication of effort occurs. Integrated studies are undertaken as appropriate (Brumley and Reid, 1982; paper in this symposium).

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A11 computerised strata and coal analysis logs, processed by the SECV, are supplied to the Department of Minerals and Energy and to the Victorian Brown Coal Council. The Department, in return, freely supplies all Departmental and non-restricted company data for inclusion within the computer data bank. Practically all companies, which have been involved in drilling for brown coal throughout the State, have forwarded data for the central data bank. Such information is helpful to the overall investigations and ensures that the data bank is complete. In return, the SECV is able to pr ovide base data, computer output and, where appropriate, technical advice to the various companies. Individuals and many authorities periodi cally ask for and are provided with, bore and coal quality information. In all cases, rules which have been established, in conjunction with the Department of Minerals and Energy, apply to ensure the confidentiality of information . CONCLUSIONS Brown coal investigations by the SECV, have led to the definition of over 100 thousand million tonnes of brown coal in the Latrobe Valley area of Victoria. Coal exploration drilling in the Latrobe Valley, at bore spacings of more than 1 km, is largely complete; proving drilling, in areas of specific interest, is generally on a 400 m to 800 m bore grid . A major computer data bank, containing strata and coal quality records from approximately 15,000 bores, is held and maintained by the SECV. The brown coal investigations, conducted by the Exploration and Geo l ogi ea l Division of the SECV, involve the application of manual, computer and computerized drafting techniques to produce numerous contour and trend surface plots . Coal qualities and coal property statistics are obtained through the application of a variety of techniques; including complex two- and three-dimensional geostatistical analyses. Pioneering work, on the physical structure of the coal, has been carried out at the Commission's Richmond Laboratories, whilst the associated plant macrofossil studies have been undertaken at the University of Adelaide . Underground water, which must be extracted to ensure open cut stability, has been studied as a joint geohydrological project with the Department of Minerals and Energy. In connection with this work, programs have been developed or modified to analyse the particle-size characteristics of sand and to conduct finite element modelling of groundwater systems. Joints and other structures are measured in the open cuts and automat i ea l ly plotted onto stereo-nets. Structural and stress analyses are effected to predict conditions ahead of operations . The structural work is related to the seismicity of the region through the provision of a grant from the SECV to the Phillip Institute Seismology Centre for the maintenance and operation of a seismic station in the Latrobe Valley . As part of the provision of geological data for geotechni ea l analyses, techniques have been developed to enable comprehensive numerical analyses of block, wedge and some arcuate failures, to be carried out under field conditions . Brown coal geologists, with the SECV, provide stratigraphic and coal property data in forms which are suitable for the subsequent design of open cuts and power station plant .

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Subject to estab 1 i shed confident i a 1 ity restri et ions, coa 1 resource data is freely exchanged between Governmental authorities and private companies. Such interchanges prevent unnecessary dup 1i cation of effort and ensure that the central data bank continues to contain comprehensive records. ACKNOWLEDGEMENTS The author wishes to thank the State Electricity Commission of Victoria for permission to publish this paper. The work of the late Dr. A. B. Edwards and of Mr . C. S. Gloe, the former Pri nci pa 1 Geo 1ogi st of the SECV has contributed si gni fi cant ly to the SECV investigations. All members of the Exploration and Geological Division of the Fuel Department of the SECV helped in formulating this review. Acknowledgements are due to Mr. J.M. Alexander, Chief Engineer, Fuel Department, SECV, for his encouragement and advice. REFERENCES Barton, C. M., 1969. Graphical Analysis of Fracture Plans. and AIMM Symposium on Rock Mechanics, Sydney 58-60. Barton, C.M., 1971. 191-204.

The Morwell Interseam Sands.

Proc. Aust. Eng.

Jour. Geol. Soc. Aust. 17,

Barton, C.M. 1981. Regional Stress and Structure in Relation to Brown Coal Open Cuts of the Latrobe Valley, Victoria. Jour. Geol. Soc. Aust. 28, 333-339 . Fosall, K.W. & Barton, C.J.K., 1981. Tl59 Calculator Programs and Procedures for On-Site Analysis of Slope Stability. State Electricity Commission of Victoria Report (unpubl.) Gibson, G., Wesson, V. & Cuthbertson, R., 1981. 1980 - Jour. Geol. Soc. Aust. 28, 341-356. Gloe,

Seismicity of Victoria to

C. S., 1960. The Geology of the Latrobe Valley Coalfields - Proc. Austral . Inst. Min. Metall . 194, 59-125.

Gloe, C:S., 1976. ~rown Coal - in Douglas, J.G. & Ferguson, J.A . (ed) Geology of Victoria, Sp. Pub. Geol. Soc. Aust. 5, 378-89. Gloe, C. S., 1979. The Brown Coal Reserves of Victoria . Proc. Austral . Inst. Min. Metall . S~mposium on Estimation and Statement of Mineral Reserves, Sydney 1979, 4 -61 . Gloe, C.S., James, J.P. & Barton, C.M.~ 1971. Geotechnical Investigations for Slope Stability Studies in Brown Coal Open Cuts, Proc. Inst. Aust. N.Z. Conference on Geomechanics, Australian Geomechanic Society, Melbourne, 1971, 1, 329-336. Thompson, B.R., 1979. The Stradbroke Coalfield. Minerals and Energy Report 61 .

Victorian Department of

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CSR's Brown Coal Exploration G.D. Jones CSR Coal Division, GPO Box 650, Brisbane, 4001

ABSTRACT CSR Limited and Its subsidiaries, Thless Bros. Pty Limited and Western Collieries Limited have been actively Involved In brown coal exploration since 1978, when attention was directed towards the Murray Basin In South Australia. Since that date, exploration for brown coa l has been conducted In the Longford Basin In Tasmania, the Glppsland Basin In Victoria, the Murray Basin In South Australia and the Bremer Basin In Western Australia. Exploration has been directed at defining coal resources where there Is either a Ioca I I nterna I energy shortage, for examp I e, In South Austra I I a and Tasmania, or where a large source can be Identifiably used In the production of synfuels, for example, at Esperance, and In the Latr obe Valley. Exploration techniques have largely been Influenced by the local geological conditions, such as the depth and thickness of coal, or the continuity and distribution of coal. These techniques have Included surface mapping and photogeology, ground geophysics, exploratory drll ling and geophysical logging, and they have been modified depending on the difficulties associated with exploration In each area. For example, brown coal occurs In pre-Tertiary basement lows In the Mannum area, and Is overlain by the cavernous Mannum Limestone. Magnetic, gravity and resistivity surveys were conducted to help delineate the basement "topography". The follow-up exploratory drilling then had to cope with the Mannum Limestone, In which drl I I Ing fluids and hence drl 11 samples, were often completely or partially Jost. In these Instances, the llthologlcal Interpretation was based on drll I penetration and geophysical Iog responses. By using these techniques, CSR has Identified In sltu reserves of open-cut brown coal exceeding 250 ml I I Ion tonnes In South Austral la, which detal led analytical testing has shown to be suitable for combustion In conventional thermal power stations. Exploration Is continuing In Tasmania, Victoria and Western Austral la and has outlined significant resources of brown coal.

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Exploration and Development of Black Coal in Australia - An Historical Perspective C.R. WARD Department of Applied Geology New South Wales Institute of Technology P.O. Box 123, Broadway, N.S.W. 2007 Key Words:

Coal geology, coal Industry, coal resources, Australia

ABSTRACT The last thirty years have seen progressive growth In the contribution made by geologists to the Austral Ian black coal Industry. Technological changes In exploration methods, such as drll ling and geophysical techniques, have enables the acquisition of more rel fable data for coal seam mapping and reserves estimation, while advances In coal petrology and other laboratory techniques have greately Increased the amount of Information that can be obtained on coal quality. Computer-based data processing systems have also been developed to allow efficient storage, manipulation and retrelval of these data In coalfield exploration programs. With the advent of large-scale, capital-Intensive mines, designed for high productivity and maximum recovery of coal resources, the geologist has become a special 1st member of a multl-dlsclpllnary technical team, rather than an Independent geological prospector. Geological work Is essential at all stages In the planning and operation of these mines, and thus the geologist needs to be aware of the relevance of his activities to other aspects of the overal I project. Coal geology has also come to embrace the fields of engineering geology and geomechanlcs, as wel I as making use of specialized techniques such as the various geophysical methods. Together with the development and application of sedimentary models to coal seams and coalbearing sequences, these aspects have the greatest potential for growth In the next phase of the Industry's development. INTRODUCTION Exploration and mining of the black coal resources of Austral la has a history almost as long as that of the nation Itself. The site of the first settlement was chosen at the centre of the Sydney Basin, and coastal outcrops of coal In both the lllawarra and Hunter districts were discovered within a few years of 1788. Organized mining commenced In 1801, and, spurred on by the development of ral I ways, town gas suppl les and the early steel ndustry, a total of 100 coal mines were In operation In N.S.W. by 1900. .These produced a total of 5.5 mll lion tonnes of coal In that year, of which 3.4 mllllon tonnes was exported to other states or overseas. Although coal was also discovered In the other States as they became establ I shed, the degree of mine development outside N.S.W. was almo~t negligible at that time, with Queensland, the only other significant producer, contributing a total of 500,000 tonnes. The black coal Industry, In many ways, changed llttle In character until after World War II. Total production grew steadily, reaching 16.8 million tonnes Austral Ian Coal Geology 4, part 2

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per year by 1950, but the markets aval I able and the mining methods In use still followed many of the traditional patterns of earlier years. A review of the geology of the principal Austral Ian coalfields, as It was known In the early fifties, and a discussion of various aspects of the mining Industry at that time Is given In a compilation for the 5th Empire Mining and Metallurgical Congress by McKeown (1953). During the early sixties, avallablllty of export markets, lnltlally for coking products, changed the character of the Austral Ian coal Industry considerably. Coupled with advances In mining technology, access to these markets al lowed development of the large resources In the Bowen Basin of Queensland, and the resulting exploration activities In this area are summarized by King (1975) and Trengrove (1979). These benefits also flowed on to New South Wales, however, and supplying coal for export now takes up around 50% of that State's total saleable production. The developments In Queensland called for a different approach to coal exploration than had previously been customary In N.S. W., and for some time geologists on either side of the border almost operated In different worlds. However, as large-scale open cut operations became more common In the Hunter Valley, and the underground operations e lsewhere In the Sydney Basin began to require more detailed geological knowledge for efficient planning, N.S.W. geologists also began to revise their techniques considerably. The "ol I crisis" of the early seventies stimulated world-wide Interest Jn coal exploration techniques (e.g. Muir, 1976, Argal I, 1979), and, as a result of al I these factors, a wide range of experience has now been gained by Austral Ian geologists In a variety of situations. Some of the techniques that have been applied were reviewed at the previous Coal Geology Group symposium In 1980. This paper Is an attempt to Indicate the nature of the changes that have taken place In the work of the Austral Ian coal geologist since the early 1960 1s. It Is unashamedly biased towards the Industry In New South Wales, partly because of the author's greater famlllarlty with that State, and partly because, with both underground and open-cut developments, the changes In these have probably been more pronounced. In the context of these changes, It Is hoped the significance of the developments discussed at the present symposium will be more fully appreciated. GEOLOGY IN THE COAL INDUSTRY Traditionally, the mining Industry has viewed t he geologist as one who describes how the ore (or coal) came to be there, but only after It has been mined out. Although this was not true even then, this opinion certainly seems to have preva 11 ed more strong I y In the past than It does today. Hard facts show Ing the I ncreas Ing ro I e of the geo Iog I st In the coa I Industry are difficult to obtain, but Table 1, comp I led from data released by the Austra I I an Bureau of Stat I st Ics, shows the great Increases In pr I vate expend I ture on coa I exp Iorat Ion that have taken p I ace s I nee 197 4. Tab I e 2, complied from data published by the Joint Coal Board, further shows the level of expenditure on "proving reserves and prospecting" In N.S.W., where an Increase by nearly forty times has been experienced In the 17 year period between 1962-63 and 1978-79. Much of th Is Increase, of course, represents Inflation and general growth over that period, but Table 2 also shows how the actual proportion of the Industry's total capital expenditure that was devoted to exp Iorat I on has, In fact, r I sen by near I y four t I mes, from 2% to 7 .5%, In the period under review.

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In part this Increase In expenditure on geologlcal studies Is undoubtedly due to the need for greater amounts of data as mines are being forced to work In Increasingly more complex settings, and to the more detailed studies generally required for open-cut developments than for underground mines. In part, however, It also represents the fact that, for modern, high-productivity extract Ion methods of an type, the des I gn of the mI ne, the se I ect I on of the mining equipment and the day-to-day production scheduling of the operation at the site requires a very detailed knowledge of the geology of the area to be worked. The geologist has become, In this context, a speclallst member of a multl-dlsclpllnary design team, with the responslbll lty of ensuring that al I pert I nent geo Iog Iea I factors are f u I I y eva I uated and taken Into account by those concerned with other aspects of the project. Another measure of the level of Involvement of geologlsts In the coal Industry Is the extent of exploratory drllllng In coalfield areas. As shown In Table 3, the total number of holes drl I led In NSW Increased by over five times In the 13 year period between 1966-67 and 1978-79 while the total length drll led Increased by a little over four times. The average I ength of each ho I e Increased In the ear I y part of th Is per I od, but then decreased during the 1970 1s, probably as open-cut developments became a more significant part of the Industry In N.S.W. The overal I proportion of non-cored ho I es has r I sen over th Is per Iod, part I y for the same reasons and partly because greater knowledge of reg Iona I gelogy has al lowed even deep holes for underground mines to be drl I led to a depth close to that of the target seam before core recovery commenced. SI m11 ar trends are a I so shown for dr 11 11 ng by the Queens I and Department of Mines In the period between 1972-73 and 1980-81 (Table 4). With the exception of the unusually large number In 1977-78, which reflected extensive work on one particular project, the total number of holes drl I led has risen by over five times In the period under review. The average length per hole has decreased and the proportion of non-cored drll ling Increased over this period, the latter reflecting, In part, greater use of down-hole geophysical logging techniques. LEGISLATIVE FRAMEWORK As Is still the case with the search for most other mineral commodities, black coal exploration up until the early 1970 1s was based largely, If not entirely, on titles that could be gained at the Initiative of the various lndlvlduals or organizations that might be Interested. This situation stll I prevails, to a great extent, In Tasman Ia, South Austra I Ia, Western Austra 11 a and VI ctor Ia, but In New South Wales and In the prlnclpal coalfield areas of Queensland, t It I e to exp I ore and deve Iop new depos Its Is now contro I I ed very c Iose Iy by the State Government (e.g. Rose, 1976). Much of the lnltlal exploration for coal In these latter two States Is, In fact, carr I ed out by the re I evant Department of MI nes or MI nera I Resources. Areas exp Iored by the Government from th Is "grass roots" I eve I, as we 11 as areas ref lnqulshed, for various reasons, after lnltlal or fol low-up exploration by private title holders, may be made available In several ways to the Industry for further evaluation and/or mine development. The procedure by which this Is accompl I shed Includes a system of competitive tendering, but

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Individual companies may also be granted titles directly for a variety of reasons, Inc I ud Ing the prov Is Ion of resources to a I Iow rep Iacement of a mIne that Is nearing the end of Its working life. It Is now now uncommon for a large amount of geological work to have been carried out on an area before any title passes Into the hands of a mining company. In such cases, the work of the company geologist represents a special 1st contribution to a multl-dlsclpl I nary study of the technical and economic feaslblllty of mining In the area, rather than the more traditional task of exploring for coal In previously uncharted terrain. The geologist therefore needs to be familiar with the relevance of the various geological features of the depos It to other aspects of the project, so that they can be fully taken Into account by the other specialists Involved In this study. SURFACE STUDIES The coal-bearing strata In many of Austral la's coalfields are either deeply weathered or concealed from the surface by thick accumulations of other mater I a I. A I though reg Iona I stud I es In these areas may be based I arge Iy on field mapping, details of the distribution, thickness and quality of the seams present can, In general, only be otalned from the results of a subsurface dr 1111 ng program. In some areas, however, such as In the escarpments o·f the Southern and Western Coalfields of New South Wales, exposures may exist that can provide valuable stratigraphic and structural data (e.g. Goldbery, 1969) that may be used to supplement, and therefore reduce the cost of, these drllllng operations. Structural studies of a different type can also be carried out by Interpretation of aerial photographs and sate I I lte Imagery. Shepherd et al (1981), for example, have used such data, together with surface and underground studies and statistical techniques, to Investigate the regional structure of major coalfield areas and hence draw conclusions on the problems likely to be encountered In underground mining of coal from the seams beneath. Geophysical exploration methods have been appl led to Austral Ian coalfield studies for some time (e.g. Price, 1978), but with recent advances In techno1ogy, Inc I ud Ing both data gather Ing and data process Ing systems, these techniques have begun to play a more significant role over the past few years. Gravity surveys have been applied, chiefly by the Bureau of Mineral Resources, to coalfields In several states (e.g. Chamberlain, 1948; Duffin, 1970), giving valuable data on basin structure and, In some cases, the distribution of coal seams. Aerial and ground-based magnetic surveys have llkewlse been used at various scales (e.g. Henderson, 1967) not only to del lneate the reg Iona I structure but also to outline any masses of Igneous material that may conceal, Interrupt or even destroy substantial quantities of coal reserves. Seismic reflection studies have also been used from time to time to help solve particular problems. Such techniques may be used for Investigations, at a regional scale, of the structure of coalfield areas (e.g. Rlngls et al., 1967) or on a smaller scale at lndlvldual mine sites (e.g. Taylor, 1965). Because even relatively smal I strucutes can have a great effect on the cost and eff Ic Iency of a mIn Ing operat Ion, a h Igher degree of reso I ut Ion Is genera I Iy needed In such studies than for a comparable Investigation In the petrleum Industry. Harman (1982) gives details of the techniques used to obtain this resolution, citing examples drawn mainly from areas suitable for underground mining, whl le King (1979) and King and Greenhalgh (1982) describe a costAustral Ian Coal Geology 4, part 2

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effective technique, with a moderate degree of resolutlon, that has been found to be successful for many coal seams at depths where open-cut mining Is envisaged. DRILLING PROGRAMS Dr 1111 ng to test subsurface coa I resources has been conducted In Austra 11 a since at least the latter part of the 19th Century, but the recovery of samples from these early holes was mostly too poor, and the llthologlc descriptions too generalized for the results to be of much relevance to modern mine developments. The Introduction of the triple tube core barrel, described by Mosher Jl1 .Ah. ( 1957), he Iped great Iy to Improve the re 11 ab 111 ty of bore ho Ie studies through Improved sample recoveries, while greater use of geologists by the Industry at large helped to Increase the amount of useful data extracted from the drilling program. Systematic analysls of coal seams from drlll cores and mine exposures has been carried out since the early 1950 1s by organizations such as CSIRO, ACIRL and the Jo I nt Coa I Board. The petro I og I c stud I es of CS I RO, In part Icu I ar, have made that organization an lnternatlonally recognized authority on the nature and or I g In of Gondwana coa Is, and have a I so done much to re I ate the petrographic properties of Australian black coals to their utilization characteristics (e.g. Benenett and Taylor, 1970). On a hand-spec Imen sea Ie, the techn Ique of macropetrograph Ic (or 11br Ightness") logging, on a ply-by-ply basis has been applied to an Increasing extent since the early 1960 1 s. Coupled with the Introduction of standards for graphic representation of different coal types (Standards Association of Austral la, 1970), this has enabled Improvements, among other things, In seam correlatlon and qua I lty control for mining operations. X-radlography of drl I I cores, using techniques such as those described by Jones (1970), Is al so being used to progresslvely greater extent, partly as a means of determining the distribution of mlneral matter In a seam and partly to provide a record of the core In question before It Is broken up for the analysts program. The degree of sophistication In analysls programs for exploratlon cores has also Increased conslderably since the 1960 1s. Comprehensive float-and-sink testing, for example, Is now a part of most laboratory studies, replaclng the assessment of clean coal quallty from a seam composite, excludlng any brands of non-coa I mater I a I. The va 11 d I ty of such tests has a I so been Improved by the development of preconditioning techniques (Proudfoot, 1977), prlnclpal ly based on 150 to 200 mm cores, that are Intended to reproduce the effects of the various mining and hand I Ing processes on the different coal products. Indeed, Austral Ian expertise In this fleld has resulted In the publlcatlon by the Standards Assoc I at Ion of Austra 118 ( 1981) of the wor Id's f I rst "Gu Ide to the Evaluatlon of Hard Coal Deposits by Borehole Technqlues". Coal seam analyses, as wel I as I lthologlc studies of non-coal strata, have also benefited greatly from the Introduction of down-hole geophyslcal logglng to the coal Industry. Although trials of equipment used In the petroleum Industry were conducted In the early sixties, the development of techniques speclflcally for coal and coal-bearing strata Is a relatively recent advance, and Is described more fully by authors such as Reeves (1976), Renwick (1982) and Groves and Bowen (1982).

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As well as being an Invaluable aid In non-core drl I ling, down-hole geophysical logs In many cases provide a more objective and reproducible record of the strata penetrated by the borehole than Is commonly obtained from visual Iogg Ing of cores. The use of these Iogs often enab I es more re 11 ab I e correlations of marker beds or other characteristic stratigraphic sequences to be carried out. The logs can be used with cored holes to fix the positions of llthologlc changes more precisely, as they are not affected by core losses or by slippage In the core barrel. With the aid of results from logs run where coal qua I lty data have been collected from the same hole, they can also be used, In many areas, to Indicate parameters such as the coal's ash content, on a ply-by-ply or full-seam basis, In seams where no core has been taken at all. Although not as relalble as actual analytical results, this can be used to produce more reasonable Interpolations between analysed holes when preparing coa I qua II ty maps. Although significant development In borehole studies has been the systematic extraction of geotechnlcal data from the drill cores. Using techniques such as point load strength Index determination (Broch & Frankl In, 1972) and an lndlctlon of the spacing of fractures In the core (e.g. Deere et al, 1976), object I ve data can be gathered that are often of great s I gn If I ea nee to the mine design operation. Geohydrologlc studies may also be carried out on appropriate boreholes to assist these aspects of the project. At present, most studies of this type are carried out by a specialist team or contractor at a relatively late stage In the drll ling program but In the future more of this type of work Is likely to be carried out by exploration and mine geologists at al I stages from preliminary evaluation of new areas to detailed studies of lndlvldual mine sites and their operatlnal problems.

DATA PROCESSING AND RESERVES EVALUATION The results of a black coal exploration program are generally summarized by presentation of graphic and written borelogs, geological cross-sections, lsopachs, structure contours and an appropriate series of coal qua I lty maps. These have traditionally been prepared by manual methods, using support staff such as typ I sts, tracers, cartographers and draftsmen, but, s I nee the ear I y 1970 1 s, Increasing use has also been made of computer-based systems for storage, retrieval, Interpretation and presentation of the data Involved. Amoung the first attempts to make use of the computer for processing geological data from Australian coalfields were the t r end-surface studies of Cook (1969) and Johnson (1974). Since that time, a wide range of techniques has become available, Including the Input of borelogs directly In a computercompatible format (e.g. Thomson, 1979), the preparation of graphic logs and cross-sections In a form suitable directly for publlcatlon and the contouring of variables, such as thlckenss, reduced level or coal qual lty parameters, by a wide range of methods. Some of the techniques available are summarized by Moore (1978), while their Integration Into the exploratln program Is discussed In a case study by Wootton C In press). Once all the data are brought together, using either manual or computer-based techniques, the geologist Is generally In a position to calculate coal reserves. Representing, as they do, the coal that Is actually known to be present, known to be of economic value and known to be recoverable by mining, these "reserves" must take Into account the legal, technical, environmental

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and f I nanc I a I constra I nts on extract I on that ex I st In the area In quest Ion. Coa I that cannot be extracted, for var lous reasons, Is c I assed on I y as "resources". It Is trad It Iona I to eva I uate and descr I be the "In s I tu", "recoverab I e" and "marketable" reserves of black coal separately, with reference to the degree of geologic cetalnty (I.e. "measured" or "Indicated") being noted In each case. In New South Wales, the terminology used for calculatlng and reporting these reserves Is based 9n the work of the Stand Ing Comm I ttee on Coa If I e Id Geology of NSW, a body set up In 1961 under the aegis of the (then) Department of Mines, with the objects (Inter al la) of bringing together detal led knowledge of the various coalflelds In the State and of Improving methods of coa I reserves assessment. The "Code for Ca Ic u I at I on and Report Ing of Coa I Reserves", first published by the Standing Committee In 1969 and currently In Its fourth edition (Standing Committee of Coalfleld Geology of NSW, 1979), Includes a pro-forma statement that gives a clear and unamblgulos account of the coal quantities and qualities under discussion. A s Im 11 ar document has been drawn up by the Queens I and Department of MI nes

(1968), outl In Ing the parameters for calculatlng and reporting coal reserves In that State, and this was subsequently revised, principally through a change over to metric units, by Mengel (1977). Federal authorities, however, In a recent assessment of national coal and other energy resources, (National Energy Committee, 1977) have made use of the somewhat different and more widely ranging terminology of McKelvey (1976). The Joint Coal Board, on the other hand, gives a comprehensive account of the black coal resources of New South Wales (Joint Coal Board, 1979) based on the Standing Committee's reserves Code. The reserves available for each Individual mining project depend, to a great extent, on the methods of extraction and preparation, as well as the marketing factors that w 11 I be app I I ed, and thus cannot, In many cases, be f u I Iy established until the project has advanced beyond Its feasibility study. Even If no new geological data are gathered, revision may also need to be made to the estimates after production commences, to allow for changes on mining and preparation technology or for changes In the various marketing and utlllzatlon parameters. The use of computer-based data storage, processing and retrieval systems generally al lows these adjustments to be made more read I ly than do manual methods, and, Indeed, slmulatlons of several different options may be Introduced, In the planning stages, to find the optimum combination of reserves and extraction techniques. The geologist Is again part of a mulfldlsclpllnary team In these circumstances. The use of geostatlstlcal methods In reserves estimation has been attempted by authors such as Pauncz and Nixon (1980), but has not yet become widely establ !shed In the Austral Ian coal Industry. Such techniques, although originally developed for metal I Jc ores, do offer significant potential If used In the right way, partlcularly as they allow better estimation of confidence limits for the values given. MINE GEOLOGY

Provided economic conditions are favourable, a successful program of coal epxloratlon ultimately leads to the development and operation of an open-cut or underground coal mine. On-going geologlcal studies are an essential part of the mine design process, and of the day-to-day or long-term planning of the Austral Ian Coal Geology 4, part 2

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mine. Geologic data are used to al low better delineation of coal thickness, qua I I ty and work Ing cond It I ons and to detect, In advance, any major Interruptions to seam continuity. They are also significant, however, In the solution of problems such as roof fal Is or pit-slope fat lures, and In the amel !oration of unfavourable environmental Impact from the mining and coal preparation process. Geologic studies have long been a part of underground coal mining operations, with special emphasis on the solution of problems relating to roof conditions CDlessel & Moel le, 1967; Williams and Wilson, 1976; Shepherd and Gale, 1982). Underground and surface studies of roof lithology and structure are an essential part of this process (e.g. Connelly, 1970) aided In more recent times by air photo Interpretation and satellite Imagery (Shepherd .id .al.a. 1981). However, both geomecharilcal studies (e.g. Blackwood .id .AL. 1976) and geological observation (Shepherd and Huntington, 19811; WII I lams and Turner, In press) show that high horizontal compressive stresses may also have to be taken Into account In many areas. Experience In parts of central Queensland has also shown that plt-wal I and spoll-plle lnstabll lty can seriously affect the efficiency and safety of opencut mining operations (Sutherland and Eldridge, 1974; Boyd .id .al.a. 1978). Such problems are best addressed by Integration of detailed engineering geology assessments with exploration and mine geology studies (Boyd, In press), thus opening up a further field of study to the coal geologist. Another aspect of mine geology that has b&come Increasingly significant In the Australian coal Industry Is the Introduction of geologic studies relating to outbursts of coa I, rock and gas In underground mInes (e.g. Shepherd and Creasey, 1979; Hanes and Shepherd, 1981). In addition, the need for better del I neat Ion of any features, such as faults or dykes, that may I le ahead of the mine workings has led to the Introduction of In-seam seismic techniques to Austral la (Asten .id .al.a. 1982). These and other techniques are I lkely to become more widely used In the Industry over the next decade. COAL MEASURE SEDIMENTATION The large amount of geologic data that Is potentially avallale from these various techniques may, In appropriate circumstances, be brought together to produce a three-dimensional picture of the distribution of the various coal seams and other strata In the project area. If the processes that gave rise to these rock units are fully understood, they may be used to derive a sedimentary model for the sequence, from which predictions can be made regarding details of the geology In other parts of t he study area. An ear Iy study of th Is type, summar Ized by Br I tten .id .al.a. ( 197 5), presented an explanation for the development of zlg-zag splits In the coal seams of the Slngletn area, N.S.W., whl le another CDlessel and Moel le, 1970) put forward an explanation for the formation of floor rolls In the seams of the 11 lawarra district. Other studies (e.g. McLean-Hodgson and Kempton, 1981; Leblang .id .a.L. 1981) have derived depositional models to explain the nature of Individual coal deposits, while others, as yet unpublished, have used such depositional mode Is In mI ne geo Iogy, such as In stud I es concerned w Ith the eva I uat I on of slope stability In open-cut operations. The depositional environment and metamorphic history of the coal seams themse Ives have a I so been stud I es by numerous authors (e.g. Smyth, 1970; Austral Ian Coal Geology 4, part 2

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March Ion I, 1980), but detal led discussion of the results Is beyond the scope of the present paper. Nevertheless, In view of the relatlonshlps between coal rank, coal composition and the various coal utl I lzatlon parameters, these studies have an undoubted significance to the dellneatlon of coal quallty In geologlcal exploratlon and mine geology studies. CONQUS IONS The geologlst has played a steadl ly Increasing role In the Austral Ian black coal Industry over the past twenty years, and Is now an lndlspenslble member of a multl-dlsclpl I nary team with the task of del lneatlng, developing and extracting the nation's coal resources In the most effective way possible. In the process, he has had to sacrifice much of the Independence enjoyed by the prospector, and at the same time acquire a considerable degree of familiarity with other aspects of coal mining, preparation and utilization technology. New techniques In the fields of drll ling, geophysics and data processing have made the acquisition and Interpretation of geologic data easier, and at the same time have allowed the Integration of more diverse types of Information Into exploration and mine geology programs. Geomechanlcal studies have also begun to be Incorporated Into the geological activities connected with a mIn Ing project. One area, how ever, that has not yet been deve Ioped to Its f u I I extent Is the use of depositional models of coal-bearing sequences to understand and predict the d I str I but Ion of coa I seams or other beds In exp Iorat Ion and mI ne development areas. Experience overseas (e.g. Horne et al. 1978) has shown that much useful Information can be achieved from such studies, and It Is to be anticipated that they will become more widespread In Australia In the very near future. REFERENCES Argal I, G.O. Jr. Ced> 1979, ~ explorotion = Yol.wn§ r...o.:. Proceedings .o..t ..:l:rul lnternational .coA.1 Exploration Symposium, Denyer, Colorado. Ml Iler Freeman Pub 11 cat Ions Inc., San Franc Isco, 560 pp.

As ten, M. W., Greze I, K.J ., & Leung, L., 1982, In-seam se Ism Ic techn I q ues for coal exploration. ~~Geology 3(1), 21-29. Bennett, A.J.R. & Taylor, G.H. 1970. A petrographic basis for classifying Austral Ian coals. ~A.u..s.i...LJl.ila..MlJl. Metal 1, lli, 1-6. Blackwood, R.L., Hargraves, A.J. & McKay, J, 1976, Absolute stress Investigations In coal at Appln Colliery, New South Wales, ISRM Symposium on Investigation of stress In rock - Advances In stress measurement, Aust. Geomechanlcs Society Cont. Publ. 76/4. Boyd, G.L., Coa I measure geo Iogy and the p I ann Ing of open str Ip coa I mInes.

A.u..s..t.. .CW. .G.e.o..l.. .3. ( 2 ) , I r. p re s s.

Boyd, G.L., Komdeur, W. & RIchards, B.G., 1978, Open str Ip p ltwa I I I nstab 11 lty at Goonye 11 a mI ne - causes and effects. ~ Ann.-. ,CQnL_ A.u..s..t.. .LJl.ila. .M.l..o.,_ Metal 1.. No.r:th Queensland, 1329-157.

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Br ttten, R.A., Smythe, M., Bennett, A.J.R. & Sh I baoka, M., 1975, Env I ronmenta I Interpretations of Gondwana coal measure seqeunces In the Sydney Basin of New South Wates, In Gondwana Geol~y, Ced, K.S.W. Campbel I), Austral tan National University Press, Canberra, 233-247. Brock, E. & Frank I In, J.A., 1792, The po I nt I oad strength test, .J.... ~ ~ Ml.na. ~ .2 669-698. Chamber I a In, N.G., 1948, Pre 11 mI nary report on the geophys I ea I survey of the Co I I I e Coa I Bas In, .B..w:.. Ml.na. ~ A.u..s.:t.... ~ 1.... Conne I I y, M.A., 1970, A geo I og I ea I structura I assessment at App In co I I I ery with reference to roof failure and directional mining,~ Au.ila. .lM:t.. .M.l.n,. Metal!, 23..4 17-26. Cook, A.C., 1969, Trend-surface ana I ys Is of the structure of the Bu I I I seam, Sydney Basin, New South Wales, .Ma.1b.. GeQl.a. 1.... 53-78. Deere, D.U., Hendron, A.J ., Patton, F.D. & Cord Ing, E.J ., 1967, Des I gn of Proc. 8th Symp. on Rock surface and near-surface construction In rock. Meehan lcs, MI nnesota, pp. 237-302. Dlessel, C.F.K. & Moel le, K.H.R., 1967, The appl teat Ion of analysts of the sedimentary and structural features of a coal seam and Its surrounding strata to the operations of mining. General, 8th Common. Min. Metal I. Cong. 837-860. Dlessel, C.F.K. & Moel le, K.H.R., 1970, On the occurrence and origin of stonerol ls In the Bui II seam of the Southern Coalfield In New South Wales, Austral la. Compte Rendu de Congres Intern. Strat. Geol. Carbonlf., Sheffield, Vol 11, pp. 619-630. Duffin, R.H., 1970, Bouguer anomal les In the Muswel I brook one-ml le sheet. 1970/429 Cunpubl.>.

~ ~ .G.e.Q..L..~ N,s,w., Ru,..G....S.,

Gol dbery, R., 1969, Geo I ogy of the Western BI ue Moun ta Ins. .B..u..lJ... ~ 17 2 pp.

GeQl.a. ~ ~

Groves, B. & Bowen, E., 1982, The appllcatlon of geophysical borehole logging to coa I exp I orat I on. Aystca 11 an ,CQa,.l Geo I ogy rn 51-59. Hanes, J. & Shepherd, J., 1981, Mining Induced cleavage, cleats and Instantaneous outbursts In the Gemini seam at Lelchhardt Colliery, Blackwater, Queens I and. ~ Aystra I, ..I.M1-. M..l.n.. Meta I I, 2ll.., 17-26. Harman, P., 1982, High resolution seismic reflection technqlues In the coal Industry. Aystcal!an ~ Geol~y .1U.l. 3-14. Henderson, R.J., 1967, Surface and underground magnet I c Invest I gat Jons In the Southern Coa If I e Ids of New South Wa I es. ~ A.u..s.:t.... .l.n.s.L. Ml.na. Meta 11, .22.4 27-36. Horne, J.C., Ferm, J.C., Carucclo, F.T. & Baganz, B.P., 1978, Depositional models In coal exploration and mine planning Jn the Appalachian region • .B..u.1l,_ Am... Assoc. Petco I- .G.e.Q..L.. .fi.2 237 9-2411.

Australian Coal Geology 4, part 2

315

C.R. Ward

Johnson, K.R., 1974, The relation of the structural evolution of the Macquarie Syncline to sedlmentalton In the Moon Island Baach Sub-group, New South Wales . .J... ~ ~ A1Lila. .2.1(2) 157-172. Joint Coal Board, 1979, .I.b..e a.!..ad .l&a..l Resources .of~ .,SQ__u_1h ~ . Joint Coa I Board, Sydney, 70pp. • Jones, R.H.,

1970, A bore core radiography unit.

Journal .of Pbyslcs, .E .l

screntitic Instruments,~ 363-366. King, D.,

1975, History of exploration and development.

In Economic Geola:gy

.of Austral la~~~ Gulnea, 2 .c.o.aJ. Ced D.M. Traves and D. King), Monograph 6, Austra I as,

Inst. MI n. Meta 11., 5-24.

King, D., 1979, Mlnl-SOSIE seismic prof I I Ing for coal In the Gloucester Basin of New South Wa I es. .6..Y1..L. A1Lila. ~ Exp I or. Geop bys, l...Q12l 156-163. King, D. & Greenhalgh, S., 1982, Mlnl-SOSIE seismic profiling of coal deposits In Australia. Australian Coll Geology .31.U 15-19. Leb I ang, G.M., Rayment, P.A. & Smyth, M., 1981, The Aust I nva I e coa I depos It, Wandoan, a palaeoenvlronmental analysis . .coal. .GeoL. .llAl. 185-195. McKelvey, V.E., 1976, Principles of mineral resource classification system of the US Bureau of MI nes and the US Geo I og I ea I Survey. .l.l.,_S_,_ ~ ~ .6..Y1..L.

.1A2.Q=.A. McKeown, M.R. (ed), 1953, ~ l1l Austral la, metallurgical congress, Melbourne, 832pp.

5th Emprle mining and

McLean Hodgson, J. & Kempton, N.H., 1981, The Oakey - Da I by reg Ion, Dar 11 ng Downs Coalfield: stratigraphy and depositional environments • .coal. .G.eol i<4> 165-177. Marchlonl, D.L., 1980, Petrography and depositional environment of the Liddell seam, Upper Hunter Valley, New South Wales. lntern. J.... .CW. .GeoL. L. 35-61. Menge I, D.C., 1977, The ro I e of the Geo I og I ea I survey of Queens I and In exploratory coal drll I Ing. Proc. Symp. on Coal Borehole Evaluation, Brisbane. Australas. Inst. Min. Metal I, 21-35. Moore, I.G., 1978, Appl I cation of computer graphics to mineral exploration .

.Q.lJ1.. .G.o.rl... Ml..na. .J... .JJu1.e .121.a. Mosher, K.G., Vltnel I, B.W. & Lees, M.G., 1957, Core recovery and presentation In coalfield diamond drll ling - a new spilt Inner tube and core barrel • .Pr:.oc... A1Lila. .l..n.ila. Ml.n, Meta I I l...8k. 3 7 - 5 4. W.L.G. Ced>, 1976, .c.o.aJ. exploration: proceedings 1g .1.b.e .fJ..r..s.1 lnternatlonal .c.oaJ. exploration symposlum, London, Tll ler Freeman Publications

Muir, Inc.,

San Franc I sco, 664pp.

Nat Iona I Energy Adv I sory Comm I ttee, 1977, Austra I I an Energy Resources: .an assessment, Canberra lia.t... Energy ~.G1.e.... ~N.o....2a.

Australian Coal Geology 4, part 2

316

C.R. Ward

Pauncz, I. & Nixon, T.R., 1980, Appl !cation of geostatlstlcs for a more prec I se statement of coa I reserves. ~ ~ .l.ru1a. ~ LAJ2.. ~ ~ .8.0.= .4 76pp. Price, G.P., 1978, A survey Into the appl !cation of geophysls In the Austral Ian coal mining Industry . .cs..l.RQ ~.ll..u'... A,QJu.. Geomech. Geomech. ~ .M.1.n... ~ ~ 45pp. Proudfoot, B.W., 1977, The treatment of bore cores to prov I de re 11 ab I e data for coal preparation plant deslng. Proc. Symp. on coal borehole evaluatlon, Brisbane. Aust. Inst. Min. Metall. 102-113. Queensland Department of Mines, 1968, Parameters for the calculatlon and report Ing of coa I reserves In Queens I and. .Q..1.da. ~ M..l.n.l.ng .J... .62 400-402. Reeves, D.R., 1976, App I I cat I on of w I re I I ne I ogg Ing techn I ques to coa I In ,C.g..QJ. Exp[orat[on (ed W.L.G. Muir). Mll ler Freeman exploration. Pub 11 cat I ons, San Franc I sco, pp. 112-128. Renwick, R.I., 1982, The uses and benefits of down-hole geophys1cal logglng In coal exploratlon programs. Austral Jan ,CoA,1 Geo[~y. ~(1), 37-50. RIng Is, J., Hawk Ins, L.V. & Seedsman, K., 1970. Offshore se Ism le and magnet I c surveys of the Southern Coalfields off Stanwell Park. ~ ~ .l.o.s.:t.. .M.Illa. Metal r• .2ll 7-16. Rose, G., 1976, The Department of MI nes 1 programme of exp I orat I on and deve I opment of the States coa I resources. ~ Anlla. ~ Austra I as. Inst. MIn. Meta I I, Wo I I on gong, 87-98. Shepherd, J. & Creasey, J.W., 1979, Forewarn Ing of fau Its and outbursts of Co[[Jery Guard[an ~ coal and gas at Westcl lff col llery, Austral la. rntecootionol, 221<40>, 13-22. Sh~pherd, J. & Gale, W., 1982, Col I lery roof stability and the role of geology: a review. .A.u.s±.. .J... ,CQo.1 M..l.n.l.ng Technol~y Research l.. 47-67. Shepherd, J. & Huntington, J.F., 1981, Geologlcal fracture mapping In coalflelds and the stress fields of the Sydney Basin . .J... .G.eo.L. .S.OC.. ~ .28. 299-309. Shepherd, J., Hunt! ngton, J. & Creasey, J.W., 1981, Surface and underground geologlcal prediction of bad roof conditions In col I lerles of the Western Coa If I e Id, New South Wa I es, Austra I I a. Icons, I nstn, M.Ln... Meta I I , ~ J3J. Appl Jed .Ea.d:h Science> .2-'k 1-13. Symth, M., 1970, Type seam sequences for some Permlan Austral Ian coals.

~ l..n.s..t.. .Ml.n.e. Meto I I , -U.4 7 -1 5.

Sutherland, R.F. & Eldrldge, B.J., 1974, Stab! I lty problems associated with strip mining In central Queensland, Proc. Ann. Conf. Aust. Inst. Min. Metal I., Brisbane, pp. 275-281. Standards Assoc I at I on of Austra 11 a, 1970, Sympo Is for 8pp. representation of coal seams. Austral Jan Standard

Austral Ian Coal Geology 4, part 2

the graph I ea I

C.R. Ward

317

Standards Association of Austral la, 1982, Gulde to the evaluatlon of hard coal deposits using borehole techniques. Aystral(an Standard 2519-1982. 60pp. Standing Committee on Coalfield Geology of NSW, 1979, Code for calculating and reporting coal reserves (Fourth edition). ~.Ge.oL.~.M..S.-..Ll..9(2) 273278. Tay Ior• C.P., 1965, Determ I nat Ion of the structure of the Bu 111 Seam at App In Col I lery, N.S.W. by the seismic reflection method. f.r:..Q.c... A.u..s..1.. l.n.s±a. .Ml.na. Meta 11, ZIA.. 103-112. Thomson, J., 1979, COALBOR coding manual, 3rd edition . .NSW .JleR,t.. .M.1J1es... 1zeQL. ~R.u..a..5.. ]979/067 32pp (unpubl). Trengrove, A., 1979, D(scovery; stor(es .o.f modern m(neral exp(orat(on. Stockwell Press, Melbourne, 276pp. WI I I lams, R.J. & Turner, R.I., 1982, An Interpretation of the mining conditions at Stockton borehole colliery by geological analysis. AYs:t.. ~ Geo Iogy .3.(2) In press. W11 I Iams, W.A. & W11 son, R.G., 1976, Geo Iog I ea I aspects of coa I seam roof conditions In the Southern Coal field of New South Wales. Proc. Ann. Cont. Aus. Inst. Min. Metal I., Wollongong, 65-76.

Wootton, P.P., 1982, Computer appl !cation In exploration and planning of Hunter Valley No. 1 mine. A.u..s..1...c.oa..L...Ge.oL. .3.(2).

TABLE 1.

PRIVATE COAL EXPLORATION EXPENDITURE IN AUSTRALIA (from Austral Ian Bureau of Statistics Data) 1973-74 to 1980-81 Flnanclal Year

Current Prices S mll llon

Constant Prices* S mll I Ion

1973-74 1974-75 1975-76 1976-77 1977-78 1978-79 1979-80 1980-81

4 6 6

13 24 23 47 74

10 17 15 28 40

5 5

* Calculated using the Implicit price deflator for Gross National Expenditure (1974-75 base year).

Austral Ian Coal Geology 4, part 2

318

C.R. Ward TABLE 2.

CAPITAL EXPENDITURE BY THE NEW SOUTH WALES COAL INDUSTRY (FROM JOINT COAL BOARD DATA)

Year

Capital Expenditure on Total Capital Raw Coal Proving Reserves and Expenditure Production $M %of Total $M Mt

1962-63 1966-67 1971-72 1975-76 1978-79 1979-80

18.725 26.206 36.380 40.590 50.517 48.710 TABLE 3.

15.838 20.268 50.820 101.492 163.519 197 .987

0.318 0.567 2.784 5.208 12.460 14.682

2.01 2.80 5.49 5.13 7.62 7.42

EXPLORATORY DRILLING IN NEW SOUTH WALES (from Joint Coal Board Data)

Year

Average Tota I Total Length drll led Length per Number of Hole (m) Ho Ies dr I I Ied Cm)

1966-67 1971-72 1975-76 1978-79 1979-80

359 452 826 1928 1736 TABLE 4.

Year

1972-73 1974-75 1975-76 1976-77 1978-79 1980-81

33,231 68,144 79,920 147,417 184,856

n.d. 37.9 25.3 50.9 52.6

COAL DRILLING BY QUEENSLAND DEPT. OF MINES (from Queensland Coal Board)

No. of Holes Completed 99 132 116 309 524 520

92.6 150.8 96.8 76.1 106.5

Proportion of length non-cored

Total Length Dr! I led Cm)

Average Length per hole Cm)

Proportion of length

22,875 22,286 18,416 22,215 44,010 47,873

231.1 168.8 158.8 71.9 84.0 92.0

20.6 32.8 37.6 68.3 70.7 84.1

Australian Coal Geology 4, part 2

<%>

319

The Geology of the Muja Sub-Basin a Model for the Collie Basin, Westem Australia W.J. Park

Consultant Geologist, 33 Hensman Road, Subiaco, Western Australia, 6008, Australia

Key Words:

Structural Origin, Muja Fault, Contemporaneous Braided River System, Collie Basin Model.

Deposition,

ABSTRACT Si nee the discovery of coal at Co 11 i e a number of theories have prevailed concerning the origin of the Collie Basin, an intracratonic Permian coal basin within the Archaean Yilgarn Block of Western Australia . Recent mine development work and related geological studies at Griffin Coal's Muja Open Cut and adjacent mining lease areas have confirmed that the basin is of structural origin. The Muja Fault, a fault exceeding 1000m in displacement, forms the western margin of the Muja sub-Basin of the Collie Basin. The fault has been extensively drilled and is now exposed in the western wall of the Muja Open Cut . Sedimentological evidence suggests that the fault was active during the deposit ion of the Upper Permi an part of the Co 11 i e Coal Measures . It is believed that sporadic movement on the fault produced a regular alternation between high energy braided river facies sediments and low energy lacustrine-swamp facies sediments within a partially enclosed graben valley. The structural and sedimentary pattern of the Muja sub-Basin is similar to that of the Cardiff sub-Basin whi eh forms the larger, western half of the Collie Basin, therefore it is suggested that the geological model raised for the Muja sub-Basin can be applied to the Collie Basin as a whole. REGIONAL SETTING The Collie Basin is situated approximqtely 150 kilometres south of Perth and 27 kilometres east of the Darling Fault which forms the western margin of the Yil garn Block (Figure 1 - Locality Plan, Regional Geology). The Basin has dimensions of 26 kilometres by 15 kilometres and is elongate in a northwest-southeas t direction, parallel to the strike of the major basinal faults.

Australian Coal Geology 4, Part 2

320

W.J . Park

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Australian Coal Geology 4, Part 2

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The basin is divided into two unequal lobes by a fault controlled basement high , the Stockton Ridge, whi eh is exposed over the southern half of its extent (Figure 2) . The Stockton Ridge strikes northwest, southeast and separates the larger Cardiff sub-Basin, situated to the south of the ridge from the smaller Shotts and Muja sub-Basins. The Cardiff sub-Basin contains up to 1,500 metres thickness of Permian sediments, the Shotts sub-Basin 600 metres and the Muja sub-Basin 800 metres . The sedimentary history of both parts of the basin is similar. The earliest Permian unit is the Stockton Formation, a unit of irregular thickness which occurs over the entire basin. The sequence is considered to be partially of glacigene origin (Lord, op. cit) . This unit is conformably overlain by the Collie Coal Measures which includes three major coal bearing Members in both parts of the basin. The coal seams of the lowermost Ewi ngton Member can be broadly correlated over the entire basin, whereas the seams of the upper two coal members, the Collieburn and Cardiff Members of the Cardiff sub-Basin and the Premier and Muja Members of the Shotts and Muja sub-Basins are believed to be contemporaneous but cannot be correlated. The Co 11 i e Coal Measures are overlain unconformably over the entire basin by thin Tertiary deposits of the Nakina Formation. The relationship between the units named above is shown in Figure 3.

CARDIFF SUB - BASIN

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Australian Coal Geology 4, Part 2

W.J. Park

323

MUJA SUB-BASIN STRATIGRAPHY The content of the paper concentrates on the sedi mento 1ogy and structure of the Muja sub-Basin, from which a geological model of the sub-basin is raised. The geology of the sub-basin is shown in plan in Figure 4 and in section in Figures 5 and 6. A composite stratigraphic column is presented in Figure 7. Stockton Formation The Muja sub-Basin commenced in the early Permi an as a part of a bas i nwi de topographic depression, possibly of glacial origin, in which sediments of the Stockton Formation were carried. Within the sub-basin, this Formation is known to be locally absent and varies in thickness up to a maximum of 50m, indicating deposition on a irregular basement surface. A number of deep, government cored ho 1es penetrated a thin, bas a 1 t i 11 i te immediately overlying glacially striated basement (Low, 1958). The tillite consists primarily of massive, dark grey argillites with variable proportions of irregular clasts of basement origin up to 20mm in size. The glacigene sediments are overlain by similar massive, argillaceous sediments which are of lacustrine origin . Whether the depression was of glacial origin or whether it represented early downward movement on the major controlling faults is uncertain . However, at this point it should be made clear that while glacial influences are recognised in early Permian history of the Collie Basin, they played no part in the sequence of events which led to the deposition and preservation of the sediments of the overlying Collie Coal Measures. Ewington Member The argi 11 aceous sequence of the Stockton Formation grades rapidly upwards into the dominantly fluvial Collie Coal Measures. The earliest sandstone units are fine-grained with the proportion of coarser grained beds increasing upwards in the sequence. Approximately 50m of fluvial sandstones were laid down prior to the earliest coal measure deposition within the Ewington Member. The Ewi ngton Member varies from 60m to 80m in thickness and i nc 1 udes three major coal horizons, in descending stratigraphic order, the Achilles, Ajax and Ares Seams. The Ewington seams can be broadly correlated over the entire Collie Basin, indicating that the Muja Fault was most likely inactive at this time or at least was not a dominating factor. This is further supported by the pattern of sedimentation following deposition of the Ewington Member and preceding the overlying Premier Member. The interval between the Achilles and Centaur Seams averages 170m in thickness and shows no pattern of thickening towards the Muja Fault . It is probable that the sequence predating deposition of the Premier Member represents a locally preserved part of a more extensive fluvial system . It is thought that this sequence may be equivalent to the sequence preserved in the Wilga Basin and possibly equivalent to the lowermost part of the Permian Sue Coal Measures in the Perth Basin (P l ayford et al . 1975). Premier Member Evidence suggests that the Muja Fault became active about the time that deposition of the Premier Member commenced. The depositional pattern of the member exhibits a di st i net pattern of thickening towards the Muja Fault. A

Australian Coal Geology 4, Part 2

324

W.J. Park

study of individual interseam intervals shows that this pattern first developed following the deposition of the Centaur Seam, the lowermost seam of the Premier Member. Isopachs of the Centaur-Chiron interval and the member as a whole are shown in Figures 8 and 9. It is believed that the pattern of downward fault displacement and predominantly fl uvi al deposition continued throughout the remainder of the Permi an period. Sedimentary facies interpretations and the proposed depositional model for the Upper Permi an sequence are discussed in Sections 4 and 5, respectively. The Premier Member includes nine named seams, in descending stratigraphic order - Api s, Uraeus, Uni corn, Pegasus, Hydra, Briare us, Gryps, Chiron and Centaur. The Centaur Seam is currently being mined in the Chicken Creek Open Cut . Muja Member The Muja Member is separated from the underlying Premier Member by up to 1OOm of predominantly fluvial sediments . Within its limited present day extent, the member thickens westwards from 12Om to 155m. The sequence includes nine seams, in descending stratigraphic order - Ate, Be 11 ona, Ceres, Diana, Eos, Flora, Galatea, Hebe and Iona. Several thinner seams of limited distribution are recognised but have not been forma 11 y named. The nine major seams are currently being mined in the Muja Open Cut . A maximum of 8Om of sediments overlie the Muja Member sediments. No geological record exists between the late Permian and the Tertiary Nakina Formation. The depositional history of the Muja Member is discussed later. Nakina Formation The Naki na Formation is a sequence of i nterbedded sands and clays whi eh unconformab ly overlie the Permi an sequence over the entire sub-basin. The unit was laid down over a gently undulating post-Permian erosion surface which in places is marked by the development of a minor lateritic horizon. The Formation ranges in thickness from 4m in the vicinity of the Chicken Creek Open Cut to a maxi mum of 3Om within the Muja Open Cut. The unit has been partially removed by erosion and the thickness is primarily a product of present-day topography. A thin but vari ab 1e cover of resistant, sandy and pisolitic laterite and recent surface sands obscure the formation over much of the sub-basin. SEDIMENTARY FACIES The determination of the primary faci es types within the Upper Permi an is based largely on examination of the sequence exposed within the Muja Open Cut in addition to the study of a limited number of Mines Department cores . The large number of geophysically logged boreholes within the Muja Member and the lower part of the Premier Member has allowed these lithological studies to be translated into an analysis of facies distribution from which the depositional model for the Upper Permian has been raised. The following major depositional facies are recognised.

Australian Coal Geology 4, Part 2

W.J . Park

325

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Australian Coal Geology 4, Part 2

{ k m)

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FIGURE 6

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W.J. Park

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Australian Coal Geology 4, Part 2

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W.J. Park

328

Braided River Facies The major sandstone units of the Muja Member exhibit sedimentological features associated with high-energy deposition within a braided river system, as described by Walker and Cant (1977). The sandstones are typically thick and laterally continuous . Argillaceous deposits constitute a relatively small proportion of the sequence and occur as discrete beds ranging from 0.3 to 3 metres in thickness, which are not generally persistent over wide areas . The sandstones are poorly consolidated due to relatively shallow burial. They are primarily quartzose and are extremely variable in composition. Grain sizes vary from fine-grained to very coarse and granular, with grain sizes towards the larger end of the scale predominating . Rounded pebble beds commonly occur as channel lag deposits. The sandstones are typically poorly sorted and exhibit variable rounding which would indi cate multiple sources of material. It can be assumed tht material has been transported from points distant from the sub-basin as we 11 as from local sources, notably from the rapid weathering of the fault scarp. The sandstones generally contain high proportions of clayey material which is thought to have been produced by the alteration of feldspars and in cases feldspar pseudomorphs have been recognized. The relatively high proportion of original feldspar content is again indicative of the limited transport of much of the material carried into the sub-basin. Trough and tabular cross-bedding, varying in scale from 0.1 to 0.5 metres are commonly observed . It is believed that the former results from sinuous crested dune bedforms which occur in deeper channels whereas the latter form as straight-crested sandwaves of very long wavelength in sha 11 ower channels and on bar tops. Scour and fill structures often mark the base of the sandstone units. It is postulated that deposition was in longtitudi nal and transverse bars which coalesced as the numerous stream channels migrated over the width of the river system, that is, the sandstone accumulated through the processes of lateral accretion. Argillaceous, vertical accretion beds were formed as island and channel bank deposits. This system is in marked contrast to the more usual coal measure depositional modes within meandering or mature river systems in which sandstone units exhibit high sinuosity and argillaceous sediments are relatively common . Floodplain and Lacustrine Facies The lithologies included within floodplain facies are those which conform to the facies definition proposed by Reineck and Singh (1973) for fluvial systems in which active lateral migration occurs. Floodplain deposits include all sediment deposited during overbank flow. In such systems, classical levee and crevasse splay deposits are rarely developed due to the absence of levee banks and the floodplain sediments are typically spread as an irregular sheet . Within the Muja Member, floodplain sandstones up to several metres in thickness occur. The sandstones are generally fine to medium-grained with a relatively minor coarse fraction . Horizontally-bedde d, argillaceous interbeds ranging from millimetre to decimetre scale are common and are often predominant. Small-scale cross-bedding, convolute bedding and upward fining are commonly observed sedimentary features.

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Argillaceous beds up to several metres thick, but usually less than one metre tend to predominate within the fl oodp lain faci es. These units generally consist of horizontally-bedded, dark grey, silty shales. Abundant leaf fossils have been found within a number of horizons. It is thought that the argillaceous beds represent flood basin deposition and with prolonged wet humid conditions deposition took place within large shallow lakes. Such conditions favour dense vegetation and the development of backswamps . Consequently mi nor coal seams are frequent ly associated with floodplain facies. The development of shallow lacustrine conditions over much of the sub-basin is thought to have preceded the development of all major coal seams within the Upper Permian sequence. Lacustrine deposition is thought to have also produced a number of argillaceous horizons up to ten metres in thickness within the Upper Permian sequence. One such unit, the Hebe Shale, is exposed within the Muja Open Cut. The sequence consists of finely laminated, dark grey, silty shale with variable development of millimetre scale siltstone and fine sandstone intercalations . The proportion, scale and grain size of the sandstone intercalations increase towards the top of the unit and this is thought to represent a transition to floodplain deposition. DEPOSITIONAL MODEL Following activation of the Muja Fault the Muja sub-Basin became a closed depositional system as opposed to the open system which existed previously. The irregular but continuing downward movement on the fault was the controlling factor on sedimentation and produced a cyclic depositional pattern with alternating high and low energy regimes. The proposed depositional model is shown in Figure 10. During periods of active downwarp, the sub-basin formed a partially enclosed, graben-like valley. The Muja Fault scarp on the west was the dominant topographic feature. High energy river tributaries flowed in a north-northeasterly direction off the scarp and formed a major, braided river system trending northwards. Palaeocurrent studies by Wilde and Walker (1977) within the Muja Open Cut suggested a dominant north-northeasterly current direction . The braided river system produced th i ck sandstone units which generally increase in thickness towards the Muja Fault. Minor argillaceous beds representing channel bank and island deposits occur within the braided river The latter deposits are generally lenticular but in cases are facies. relatively continuous in extent and represent temporary periods of lower flow regime. At times the river system dominated the entire valley and during other periods was restricted to the western portion of the sub-basin, adjacent to the fault scarp . Areas adjacent to the main, braided river channel, that is, areas generally in the southern and eastern portions of the fluvial valley system, received Such higher proportions of argillaceous vertical accretion sediments. sequences are significantly thinner than the adjacent fluvial sequences and represent floodplain facies deposition. Minor discontinuous coal horizons formed within this environment .

Australian Coal Geology 4, Part 2

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A. SUNKLAND - Lacustrine Swamp ( major coal deposition)

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Australian Coal Geology 4, Part 2

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To summarize, the deposition pattern duri ng periods of active downwarp was one in which the sequence thickened to the west with an i ncrease in the proportion of braided river faci es deposits. In the flanking regions, the sequence is significantly thinner and includes a proportionally higher fraction of lower energy facies sediments. Minor coal seams tend to diminish in frequency and disappear westwards. At the close of the period of active downwarp the high energy fluvial sequences typically grade upward into fine sandstones, siltstones and mudstones which represent a gradual return to an equilibrium base level. At this stage the fluvial valley system has been replaced by a lacustrine-swamp, sunkland environment and prolonged quiet conditions allowed the accumulation of considerable thicknesses of peat over much of the sub-basin. Often only a single major coal seam was laid down between periods of tectonic activity. Whereas during prolonged periods of relative tectonic inactivity, alternating peat swamp, lacustrine and floodplain environments resulted in the deposition of a number of seams. Conditions favouring peat accumulation existed on a cyclical basis throughout two major coal-forming periods during which the coal seams of the Premier and Muja Members were laid down. The Premier and Muja seams are typically regular in thickness and continuous in extent which supports the supposition that the seams were deposited within a single, extensive sunkland swamp. The present day distribution of these seams, particularly the Muja seams are limited by erosional boundaries and it is therefore difficult to predict whether the swamps once covered the entire area of the sub-basin. Reactivation of movement on the Muja Fault brought a close of each major coal forming period and marked the commencement of a new cycle of deposition. In some areas, particularly adjacent to the fault, high energy stream activity scoured out · recently deposited coal seams resulting in localized seam washouts. MUJA MEMBER The Muja Member is the upper coal-bearing unit in the Muja sub-Basin. At the time of deposition the unit probably extended over much of the Muja sub-Basin and possibly into the continuous Shotts sub-Basin to the north. However, the unit has been largely removed by erosion and today is restricted in distribution to an elongate, fully enclosed basinal structure, four kilometres by one kilometre. For the purposes of the paper, this structure is informally referred to as the Muja Syncline. The axis of the syncline trends northwest, parallel to the Muja Fault . To aid mine planning a northwest oriented mine grid has been superimposed over the mine area with the origin at the southern end of the Muja Syncline. The mine area has been grid drilled at 100 metre centres from 700 NW to 2200 NW and geophysical logs are available for most holes. In addition, within the open cut, exce 11 ent exposures of the entire sequence have been examined. A detailed picture of the depositional history of the Muja Member can therefore be built up over this area. A generalised section of the member with dominant lithologies and proposed depositional environments is shown on Figure 11.

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Despositional History The Muja Member exhibits the depositional characteristics outlined in the previous section . The preserved sequence is close to the Muja Fault and is therefore dominated by westward thickening, high energy, braided river facies sandstones. The sequence can be resolved into a number of di st i net depositional cycles which reflect periods of major movement on the Muja Fault, as outlined below: The lowermost Iona-Hebe-Hebe Shale interval is dominated by low energy peat accumulation and the deposition of floodplain and lacustrine facies sediments. However, to the north of 1800 NW localized fault movement has produced a westward thickening sandstone unit up to 10m thick between Iona and Hebe adjacent to the fault. The unit broadens northwards. The overlying Hebe Shale-Galatea interval was a period of major fault activity during which a braided river sequence up to 42m in thickness was deposited. The Hebe-Galatea interval typifies the depositional system proposed for the Upper Permi an sequence of the Muja sub-Basin and is discussed in greater detail in the following sub-section. Deposition of the Galatea seam was followed by further reactivation of the fault, a~though movement was less significant . The Galatea-Flora sandstone unit is of relatively constant thickness and has a maximum thickness of 12m. During this period the river system was of greater lateral extent than during its previous phase of activity and extended beyond the present day distribution of the unit. A period of quiescence followed, during which the Flora, Eos, Diana and Diana Upper seams were laid down. The i nterseam sediments are dominated by low energy lacusttine and floodplain facies sediments . However, small scale local i sect fault movement has produced wedge-shaped higher energy sandstone units up to several metres in thickness adjacent to fault within the Eos-Diana and Diana-Diana Upper intervals. The Diana Upper-Ceres interval represents a second phase of major downwarp . A sandstone unit of 36m maximum thickness was deposited in a braided river system which extended beyond the present day distribution of the unit. The sequence does not exhibit any regular pattern of thickening. Further movement on the fault followed deposition of the Ceres Seam. Fault movement was on a lesser scale and the maximum thickness of fluvial sediments was 10 metres along the western margin of the sub-Basin. The unit thins gradually eastwards. The Bellona-Ate interval reflects a return to quieter depositional conditions. The sequence consists predominantly of lower energy lacustrine and floodplain facies sediments and includes a number of minor coal seams of limited distribution. A period of major fault reactivation followed the deposition of the Ate Seam. A maximum thickness of 80 metres of above Ate sediments are preserved today in the axis of the Muja Syncline. The remnant sequence consists primarily of high energy fluvial sediments with only minor argillaceous deposition and occasional development of thin, discontinuous coal seams.

Australian Coal Geology 4, Part 2

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Australian Coal Geology 4, Part 2

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Hebe-Galatea Interval The Hebe-Galatea depositional system is illustrated in Figure 12. shows the facies distribution and main channel sandstone isopachs . is shown in section in Figure 13.

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Quiet conditions prevailed for a prolonged period during which the Hebe Seam and Hebe Shale were deposited. The Hebe Seam is continuous in extent and has an average thickness of 12m of clean coal. Two and sometimes three thin, shale interbands up to 1 metre thick develop along the western margin but these rapidly thin and disappear into the sub-basin. The bands suggest that s 1 i ght ly deeper water conditions existed temporarily adjacent to the fault. The presence of lenticular canneloid coal within the seam further indicates water level fluctuations along the western margin of the Hebe swamp. Fo 11 owing deposition of the Hebe Seam, a predominantly sha 1e sequence of lacustrine origin, the Hebe Shale, was laid down. The actual shale unit is relatively thin and varies from 1 to 5 metres in thickness. The overlying sequence whi eh consists of i nterbanded sha 1e and fine-grained sandstones is generally included within the Hebe Shale unit. This transitional unit can vary up to 10 metres in thickness and is thought to represent higher energy floodplain facies deposition. A major period of reactivation of the Muja Fault followed and the first large scale braided river sandstone unit of the Muja Member was laid down. The geometry of this unit typifies the depositional pattern proposed for the Muja sub-Basin. The unit has a maximum thickness of 42 metres in the region of maximum displacement on the fault, and thins eastwards to less than 5 metres. The unit broadens northwards in the direction of river flow. Near the eastern margin of t~e main channel system a number of vertical accretion island deposits up to 3 metres in thickness can be i dent ifi ed. One such deposit exceeds 2 metres in thickness over a significant area and is elongate in the direction of flow of the river system. Towards the end of the depositional cycle a temporary period of inactivity resulted in the widespread deposition of argillaceous vertical accretion sediments in assocation with a thin, discontinuous coal and carbonaceous sha 1e unit, informally known as Gal a tea Lower . During this latter phase, the river channel was restricted to the western margin of the sub-basin. Subsequent reactivation saw a temporary return to fluvial deposition. Quieter conditions prevailed in the flanking area to the southeast and a considerably thinner sequence of predominantly argillaceous sediments of lacustrine and floodplain facies was depos i ted over this area. The period of depositional activity closed with an upward fining sequence of fine sandstone, siltstone and shale up to lm in thickness . The Galatea Seam which averages 3.5 metres in thickness was deposited during the following period of lacustrine swamp deposition. This period was terminated by reactivation of the Muja Fault which resulted in extensive scouring and washing out of the recently deposited Galatea Seam. A new cycle of depositional activity had commenced. Seam Washouts Coal seam washouts and irregularly scoured upper seam surfaces are commonly observed in face exposures within the Muja Open Cut and have a 1so been recognised in boreholes intersecting the Muja Member . Washouts are known to

Australian Coal Geology 4, Part 2

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337

occur within the Ate, Ceres, Diana Upper, Eos and Galatea Seams . The distribution of known seam washouts within the Galatea seam are shown on Figure 12. The deposition of these seams immediately preceded the deposition of major braided river sandstone units. Furthermore, all washout sizes with the exception of minor washouts in the Ceres and Galatea Seams have been found to occur adjacent to the Muja Fault which strongly suggests that they result from erosion by high energy stream flow off the Muja Fault scarp following reactivation of the fault. Coarse channel lag deposits generally occur at the base of washout infill deposits . MUJA SUB-BASIN, STRUCTURE The sediments of the Muja sub-Basin are preserved within a north-northwest trending downfaulted block. The downfaulting was the product of major tensional forces acting on the sub-basin. It is considered possible that the movement may have been associated with that which initiated movement on the Darling Fault to the west, however, such discussion is beyond the scope of this paper . The major controlling faults were active throughout much of the depositional history of the sub-basin and continued for a considerable time afterwards. Movement may have commenced prior to deposition, however, there is no strong evidence to support this . The downward movement of the graben block was dominated by the Muja Fault which forms the western margin of the graben. The sedimentary sequence preserved within the fault block exceeds 800 metres adjacent to the fault and Lowry (op.cit) has estimated that of the order of 300 metres has been subsequently removed from the sedimentary pile through erosion. Displacement on the Muja Fault is therefore known to exceed 1000m. Movement on the eastern margin was substantially less but still of the order of several hundred metres. Along much of the eastern margin the Ewington seams do not subcrop but are faulted out at depth against the eastern fault zone. The eastern faulting is less we 11 known than the Muja Fault due to the low density of drilling in this region. However, it appears that unlike the Muja Fault there is no single major fault but a series of faulted blocks which have acted as a hinge zone. Within the sub-basin a series of large scale faults downthrown to the west and sub-parallel to the Muja Fault are known. It is thought that this faulting represents major block faulting of the Archaean basement which was contemporaneous with and accommodated the movement on the Muja Fault. Several such faults, namely the Main Fault, Eastern Fault, Chicken Creek Fault, Centaur Fault and Buckingham Fault have been identified (see Figures 4, 5 and 6). Displacement is of the order of 50 metres to 150 metres with movement tending to increase towards the region of greatest displacement on the Muja Fault, the axial region of the Muja Syncline. The Main Fault which lies within the Muja Open Cut is a good example of this. The fault extends over 1.8 kilometres, is hinged at both ends and has a maximum displacement of 50 metres. This general pattern of displacement parallels that of the Muja Fault. Fault intersections in boreholes and exposures within the Muja Open Cut indicate that all faults including the major, boundary faults are high angle, normal faults. In addition to the major faults, a number of smaller scale faults up to 3 metres in throw, have been exposed within the open cut. Minor faulting is generally restricted to the western margin, adjacent to the Muja Fault.

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While large-scale faulting is common throughout the sub-basin, the only known large-scale folding is that observed within the Muja Member adjacent to the Muja Fault. The regional dip within the sub-basin is to the east-southeast towards the fault and the dip increases from 6° along the eastern margin up to 180° close to the axis of the Muja Syncline . Adjacent to the Muja Fault large scale drag on the fault has produced a reversal of dip. Recent drilling along the western margin of the syncline has shown that dips exceeding 40° are common. The manner in whi eh the beds have been folded rather than faulted suggests that fault displacement was contemporaneous with deposition and the recently deposited sediments and peat horizons were readily contorted. The downward drag has al so produced a significant degree of thinning of beds in the vicinity of the fault. Minor scale isoclinal faulting has been observed within the open cut in the hinge regions of the Main Fault . Muja Fault Within the past two years, the western margin of the Muja sub-Basin has been extensively drilled in conjunction with mine development work within the Muja Open Cut. Preliminary drilling strongly suggested the existence of a large scale, near vertical, normal fault forming the boundary between the Permian coal measures of the sub-basin and the Archaean basement of the Stockton Ridge. The contact region was subsequently exposed in the western wall of the open cut, providing the first direct evidence of a faulted basin boundary within the Collie Basin . The fault is herein named the Muja Fault. Examination of the fault within the open cut, subsequent close space drilling, including angled core holes, and seismic work has revealed more of the nature of the fault (Peck and Mou 1982). The Muja Fault is a normal fault dipping at an average angle of 80° to the north-northeast into the sub-basin. Adjacent to the fault plane is a zone of highly sheared basement rock consisting of "mylonitic", chloritic schists and foliated gneisses . Beyond the heavily sheared zone moderately jointed gneiss is exposed. It is likely that the shear zone represents an Archaean fault zone whi eh was a zone of weakness along which the Muja Fault subsequently acted. Precise determination of the commencement of movement on the Muja Fault is difficult. Lowry (op. cit.) has suggested that deposition of the Lower Permian Stockton Formation may have taken place within a broad depression resulting from early movement along the western margin fault of the Collie Basin, although there is no strong evidence to suggest this. Depositional patterns do indicate that the fault was active during the deposition of the Premier and Muja Members in the Upper Permian. Movement on the fault continued well after the deposition of the Muja Member resulting in the structural configuration evident in the sub-basin today . However, it is known that movement had ceased prior to deposition of the Tertiary Nakina Formation as this unit is undisturbed by the basinal faulting. CONCLUSIONS The foregoing discussion has concentrated exclusively on the depositional and structural hi story of the Muja sub-Basin. There are however many obvious similarities between the two lobes of the Collie Basin. The structural configuration of the Cardiff sub-basin is similar to that of the Muja sub-Basin. The sub-Basin is bounded on the west by a major lineament sub-parallel to the Muja Fault and it is considered that this boundary will prove to be a major basement fault. Similarly, displacement has been far less Australian Coal Geology 4, Part 2

340

W.J. Park

significant along the eastern margin of the sub-Basin and within the sub-Basin the sequence has been downfaul ted westwards into a series of sub-para 11 e l blocks reflecting basement faulting. Downward displacement has been significantly greater in the Cardiff sub-Basin and consequently the sedimentary pile is proportionally thicker. However, the depositional pattern is very similar to that of the Muja sub-Basin and therefore probably reflects identical cycles of sedimentary and tectonic activity. It is therefore concluded that the geological history of the Cardiff sub-Basin parallels that of the adjacent Muja sub-Basin and that the latter provides a model for the formation of the Collie Basin as a whole. ACKNOWLEDGEMENTS I would like to thank the management of The Griffin Coal Mining Company Limited for permission to use the data which forms the basis for much of the paper. I would al so like to thank friends and co 11 eagues within Jaci a Mine Managment & Consulting Services and the University of Western Australia for their helpful advice and assistance during the preparation of this paper. The author was Senior Geologist to The Griffin Coal Mining Company Limited from April 1980 to June 1982. BIBLIOGRAPHY Lord, J. H., 1952 . Collie Mineral Field . 105, (1), 247 .

West Australian geol. Survei'. Bull.

Low, G.H., 1958. Co 11 i e Mineral Field . 105, (2), 135.

West Australian geol. Survei'. Bull.

Lowry, D.C., 1976. Tectonic History of the Collie Basin, Western Australia. J. geol. Soc. Aust. 23, 95-104. Peck, W., and Mou, Y.S., 1982. Seismic refraction studies for mine planning and design. Aust . Coal Geology 4, (this volume). Playford, P.E., Cope, R.N., Cockbain, A.E., Low, G.H . , and Lowry, D.C., 1975 . Collie and Wilga Basins, in Geological of Western Australia. West Australian geol . Survei'. Mem. 2, 420-428. Reineck, H. E. and Singh, I. B., 1973 . Springer-Verlag, Berlin, 439 .

Depositional Sedimentari'. Environments.

Walker, R.G., and Cant, D. J., 1979 . Sandy Fluvial systems in Facies Models ed R.G. Walker. Wilde, S. A. and Walker, I. W. , 1978. Pal aeocurrent directions in the Permi an Collie Coal Measures, Collie, Western Australia, West Australian geol. Survei'. Ann . Report 1977, 41-43.

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Seismic Refraction Studies for Mine Planning and Design W. Peck and S. M. Yu

Golder Associates Pty. Ltd., Consulting Geotechnical and Mining Engineers, 466 Malvern Road, Prahran, Vic. 3181, Australia.

Key Words:

Coal m1n1ng, seismic refraction, rippability, predevelopment data, mine planning.

ABSTRACT Seismic refraction surveys run in Australian Permian and Triassic Coal fields for mine planning and design have generally produced useful results despite some difficulties in data acquisition and interpretation. These difficulties are discussed and remedies described which the authors have found effective. Caution should be exercised in making rippability assessments from seismic data, since seismic velocity of itself is not conclusive as to strata excavation characteristics, and other factors must be considered. Examples are given where faults have been identified from refraction data. A comparison is made of the effectiveness of two different reciprocal interpretation techniques. It is concluded that useful additional data about major geological discontinuities can be acquired for little extra cost while refraction traverses are being run for overburden assessment purposes, and that the status is confirmed of the refraction method in studies for mine planning and design. INTRODUCTION Seismic refraction techniques for mine planning and design have been used in Australian Permian and Triassic Coal fields for at least the past six years. Prior to this, seismic studies have been used almost routinely within investigations for engineering structures for more than two decades. Although mainly used to assess overburden excavation characteristics for open pit mines, seismic refraction surveys have also successfully located faults in a number of coal fields. In some cases the refraction survey was run specifically to find the faults, while in others the survey was devoted to excavation characteristics' and the faults were interpreted during the data processing stage. High resolution seismic reflection and mini-SOSIE* techniques are widely used to locate coal fields faults, with varying degrees of success, both in Australia and overseas. These reflection techniques are essentially seeking Australian Coal Geology 4, Part 2

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faults by detecting strata offsets and fault drag. The refraction technique sees the fracturing and/or weathering that frequently occurs in the vicinity of faults as zones of anomalous seismic velocity. With a few refinements in field procedures and data processing, a routine refraction survey for assessing excavation characteristics can locate geological discontinuities for very little additional cost. Although the geological conditions in many Australian Permian and Triassic Coal fields are not ideal for seismic refraction traversing, the equipment and analytical techniques currently available permit good results to be achieved. Problems frequently encountered but generally surmountable include: poor transmission of seismic waves; complex layering; abrupt lateral changes; and masking of refractors by high velocity lateritic cappings. Unfortunately it is not widely understood , amongst those involved in studies for mine planning and design, that seismic velocity alone is not conclusive as to rippability . In the assessment of excavation characteristics, seismic data should be considered in conjunction with other data and not in isolation . Quite accurate seismic profi 1es can st i 11 be grossly misinterpreted by the inexperienced, as to excavation characteri stics, and unfortunately the blame is often (unfairly) laid on the seismic refraction technique itself. REFRACTION SURVEYS FOR RIPPABILITY ASSESSMENTS Most seismic refraction surveys run in Australian Pe rmian and Triassic Coal fields have been for the purpose of assessing excavation characteristics. While they have generally produced good results and have been of value in mine planning, the author is are aware of a number of problems and difficulties that have been encountered, and these are discussed below. A portion of the results obtained in a rippability survey run on the Wittingham Coal Measures (Permian) of the Northern Coal field of N. S.W. is presented as Figure 1. Relevant geological information obtained from drilling has been superimposed on the seismic prof i le (Figure l(a)), which consists of three layers - soil, weathered rock, and fresh rock as the bottom seismic layer . Lateral changes in refractor velocity occur in both the intermediate layer and the bottom layer, whi eh al so contains a 6m wide anomalous low velocity zone (1560 m/s) . Available drilling data indicated this low velocity zone corresponded with a normal fault with a throw of 75m, and the lateral ve l ocity changes to be the result of the juxtaposition of sandstone , on the downthrown block, against siltstone and shale on the upthrown block . The seismic velocity of each layer, as measured by surface refraction traverses, is the velocity at the top of the layer and in rippability surveys it should not be assumed that the entire layer has this same velocity . Unless there is good evidence to the contrary, it should be assumed that the velocity of the layer steadily increases with depth . However, the allthors have encountered some thick sandstones where the seismic velocity falls with increasing depth. Reference to drill core or to the sonic log of the borehole is needed to determine the extent of possible variations of velocity with depth within a seismic layer.

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LEGEND -X-XX 2600 3200! 1~0

SEISMIC REFRACTOR CALCULATED DEPTH SEISMIC VELOCITY ( metres per Hcond) LATERAL CHANGE IN REFRACTOR VELOCITY GEOLOGICAL BOUNDARY INFERRED GEOLOGICAL BOUNDARY GROUND SOIL

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

x-x--X -

-x-

1280 WEATHERED SANDSTONE

SURFACE

x----x--x-x-X·

380

780

WEATHERED

SHALE 10

I I

_ _x_x __ 3200

I EDD

FRESH SANDSTONE

metrN

/560/_X_X--.::::.

RToN SE,4M /

FRESH SILTSTONE

2600

i' /

PIERCEFIELD / ~<I:'// SEAM /~~ ,._/

/V~,,_., / ,._ .... / ~v / ~'II'-/

20motrH

/ / / /

( A) SEISMIC

AND

GEOLOGICAL

PROFILE

GROUND

SURFACE

RIPPABLE

20 rnetrH

20metr•

( B) INFERRED EXCAVATION CHARACTERISTICS ( CAT D9H)

Figure 1.

Results of seismic Measures, N.S.W.

refraction survey on the Wittingham Coal

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The inferred excavation characteristics indicated (Figure l(b)) are for a Caterpillar 09H dozer with · single tyne ripper. It has been conservatively assumed that the velocity of the intermediate layer increases linearly with depth although in actual practice the rate of increase would accelerate as the underlying retractor is approached. Based' on ripping trials, the marginal ripping zone was assessed as 2,000 m/s to 2,200 m/s, and the economic ripping limit as 2,200 m/s. Field Techniques Coal measure strata have very inconsistent seismic energy transmission characteristics. Areas that produce severe attenuation of seismic energy can alternate with areas that have excellent transmission where a hammer seismograph could successfully profile to depths of 20m. Coal subcrop zones usually have very poor transmission . Transmission is also poor through inhomogeneous materials such as gravels, weathered conglomerates, and decomposed rocks containing numerous corestones of sound rock. In areas with reasonable seismic energy transmission characteristics and low background noise levels, good results can be obtained with a modern signal-enhancement single channel seismograph using a 5 kg sledgehammer as the seismic source. The advantages of a hammer seismograph are its easy portability in uncl eared bush, and a cost advantage under favourable conditions compared with multi-channel seismograph surveys using explosives or a drop-weight. Typi ea l i ndi vi dual traverses are 60m in 1ength with readings taken with the geophone not only at each end of the traverse but also offset up to 60m off each end of the traverses. Usual practice is to abut the 60m traverses to make up a continuous traverse of the desired length, although a greater coverage can be obtained for the same cost by, for example, leaving a gap of 40m - 100m between adjacent traverses . However the moment contact is lost with fresh rock (this is usually the bottom seismic layer with a velocity in the range of 2,000 m/s - 3,500 m/s), a high energy source such as explosives must be used, and this involves changing over to a multi-channel seismograph. In zones of poor seismic transmission, competent strata, such as an unrippable conglomerate with a seismic velocity of 2600 m/s, have not been detected by some hammer seismograph surveys at the comparatively shallow depth of Sm -8m . Significant improvements have been made in recent years in the capabilities of multi-channel refraction seismographs. Instruments are now available with timing lines at 1 m/s and 0. 5 m/s spacings, with signal-enhancement, filtering of the input signal as required, and contra ls for optimising trace size and position on playback. The signal-enhancement capability makes it feasible to use a drop-weight source in lieu of explosives . The authors have successfully used a 50 kg weight dropped from a height of 3m by a powered-winch mounted on a four wheel drive vehicle, to profile refractors to depths of 30m in zones of poor seismic transmission. The slight loss in timing resolution due to the lower frequency content of drop-weight sources can be offset against the cost and time savings in not requiring shot holes to be drilled for the explosives . The significant advantages of having acti ve signal filters in the amplifier of each channel of a multi-channel seismograph was demonstrated recently at the Muja Open Cut at Collie, W.A., where refraction traverses were run alongside the pit during working hours . A strong 50 hz interference from the adjacent Muja Power Station and overhead power lines was largely eliminated by switch; ng in the 50 hz notch filter . A strong 1ow frequency rumble below 20 hz

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emanated from the coal grinders alongside the boilers of the power station . Passing traffic on the pit's haul roads generated both low frequency (40 hz-8 hz) and high frequency (generally above 190 hz) noise. By using T.N.T. explosives, refracted waves were produced with frequencies mainly in the 60 hz-30 hz range. The instrument's bandpass filters were set to pass the refracted waves and to discriminate against both the high and low frequency noise. On other occasions the instrument's low pass filters have been valuable in minimising high frequency wind no i se . Limitations For refraction of seismic waves to occur at an interface between two different rock materials, it is necessary for the seismic velocity of the l ower material to be greater than that of the overlying material. The typi ea l Australian deeply weathered profile normally satisfies this requirement but it should be noted that the seismic refraction technique cannot detect a velocity inversion such as a soft near-horizontal layer underlying a hard layer . Similarly, hard, continuous near-surface bands such as laterite and calcrete can effectively "blanket" underlying soft weathered layers, which would then not normally be detected . Since the technique does not detect the underside of hard bands, it is necessary to use other investigation methods to determine the thickness of hard bands that are underlain by soft bands . Lateritic gravels and caprocks occur in a number of Australian Coal fields. In the authors' experience some laterites are not good transmitters of seismic energy and, with the adoption of appropriate field techniques, it is possible to overcome the blanket effect of the velocity inversion. These techniques simply limit the amount of energy coupled into the laterite, for example, by placing the shots well into the weathered layer that underlies the laterite. Where the late rite is not a massive homogeneous sheet, the first seismic arrival via the laterite is generally attenuated over a distance of 25m - 50m down to such a low level that the second seismic arrival via the slower weathered layer becomes clearly visible on the records . Laterites can be quite variable in their properties and distribution across a site, and seismic refraction profiling may be feasible in some parts of a site but not in others. Data Analysis Australian coal measure strata of Permian and Triassic age are frequently deeply weathered with complex seismic profiles, often with three or four seismic layers, and sometimes even five layers. Fresh rock is frequently at depths between 20m and 50m. Due to local variations in the depth of weathering, the seismic interfaces undulate giving a scatter of points on time-distance plots making it difficult for the interpreter to establish the exact number of layers present . Large depth errors, of the order of 50 per cent, result from either missing an entire layer from a seismic profile, or inserting a fictitious layer . In one case from the Bowen Basin, a coal seam was overlain by fresh rock (2200 m/s - 2900 m/s) that was in turn overlain by two intermediate layers (900 m/s overlying 1450 m/s) and a few metres of soil (350 m/s - 400 m/s). Proceeding up-dip into the coal subcrop zone, the strata constituting the 900 m/s intermediate layer move up into the soil layer where they lose their identity leaving only one intermediate layer (1300 m/s). This change from four layers to three layers up-dip is not immediately obvious, although careful analysis of the data did detect the change in layering . Assuming a four

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layer profile in the subcrop zones gives typical depths of 46m to fresh rock and 33m to the top of the marginal ripping zone, both of whi eh depths are below the coal seam. The correct three layer profile at the same point gives depths of 35m to fresh rock and 16m to the top of the marginal ripping zone which in this case is above the coal seam. Thus while the shape of a seismic interface might be accurate, it could be at the wrong depth. Comparison of arrival times along a spread for shots fired at different offset distances is valuable in establishing the number of refractors. The Generalised Reciprocal Method of Palmer (1981) provides a means for checking whether undetected layers are indicated, including velocity inversions and hidden layers (Soske, 1959) whi eh occur where energy from a retractor of higher seismic velocity arrives at the surface before energy from an overlying retractor. Correlation with the available borings, test pits and exposures readily establishes how many layers are present and, in effect, provides "control" for the seismic profile. For this reason the seismic refraction technique is most effective when used to extend from the known (e.g . a borehole) to the unknown. Depths to important refractors and an analysis of the velocities in those refractors can be calculated, using simple numerical computation, by recourse to one of the reciprocal methods. The Reciprocal Method of Hawkins (1961) is widely accepted but increasing use is being made of Palmer's Generalised Reciprocal Method (1981). Figure 2 compares the two methods. The Generalised Reciprocal Method uses the travel times at two geophones, separated by a di stance XY such that the upward trave 11 i ng segments of the rays to each geophone emerge from near the same point on the re fr actor. In contrast, Hawkins Reciprocal Method, which effectively has XY equal to zero, tends to smooth irregular retractor topography. As i 11 ustrated below, the Generalised Reciprocal Method can detect narrow anomalies in retractor velocity not clearly defined by Hawkins Reciprocal Method. Care must be taken with both methods that anomalies due to near-surface and retractor irregular; ties are not incorrectly interpreted as being due to retractor velocity changes. Assessment of Excavation Characteristics Correlation of seismic profiles is needed, not only to verify the layering but also to identify what material constitutes each layer, since numerous different materials can have the same seismic velocity. For example a velocity of 2000 m/s could correspond to a fresh siltstone in the Hunter Valley, or to a moderately weathered sandstone in the Bowen Basin, or to an overconsolidated clay below the water-table in the Latrobe Valley . This range of materials with different excavation characteristics but with the same seismic velocity illustrates the fact that seismic velocity of itself is not conclusive as to rippability. Other geological factors must be considered such as rock type, the thickness of individual beds, the spacing of natural weakness planes such as joints and bedding, and the variability of each layer over the site. Consequently the correct use of seismic data in assessing excavation characteristics requires that seismic data be considered in conjunction with other data and not in isolation. Seismic velocity is only one of several parameters to be used when comparing a bed of known excavation characteristics with another bed whose ri ppabi l i ty is as yet unknown, hence seismic ri ppability charts that only specify rock type represent an over-simplification.

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(I l l

( I I HAWKINS RECIPROCAL METHOD

PALMERS G.R .M.

: s ~ A :t ! I:"· z Shot Point

•

Shot

~lnt

•

BEDROCK

I . DETERMINE MIGRATED DISTANCE XY

2 . OBTAIN END TO END TIME AB

2 . OBTAIN TRAVEL TIMES AY AND BX

3. TIME DEPTH (z l AT C

3. OBTAIN END TO END TIME AB 4 . TIME DEPTH (zl ATM:

AY + BX-(AB+XY/Vll 2

5. DEPTH (OJ 'Z .I,.

4. DEPTH (DJ =zk 5. WHERE k IS VERTICAL VELOCITY FACTOR ; k "

BEDROCK

I . OBTAIN TRAVEL TIMES AC AND BC

: AC+ BC-AB

Figure 2.

•

:'"

v1 v2 -T- ✓ vl- vF

Comparison of two different refraction interpretati on.

WHERE

/t IS VERTICAL VELOCITY FACTOR ;

v.2 k -- VI v.-'-/v.2I 2 2'

reciprocal

methods

seismic

Probably the best known seismic velocity ripping charts are those published by the Caterpillar Tractor Company. The latest Caterpillar Performance Handbook (Edition 12, October 1981) states, "Considering the extreme variations among materials and even among rocks of a specific classificat ion, the charts must be recognized as being at best only one i ndi ea tor of ri ppabil i ty". The applicabili ty of many seismic ripping charts is seriously limited due to the lack of precise geological data about the materials ripped in field trials used to develop the charts. In the authors' experience, economic ripping limits are often at lower seismic velocities than those given on the Caterpillar charts, and by far the most reliable technique for establishin g excavation characteris tics is an onsite trial . A seismic survey combined with geological mapping and drilling then provides the basis for extrapolatin g from the trial slots to the whole site. If it is i mpract i ea l to conduct on~ site trials ( and this is the case for drag-lines and bucket-wheel excavators) , the next best thing is to compare the materials on the new site with materials at other sites whose excavation characteris tics are well established . Again seismic velocity is an important parameter, but not the only parameter that should be considered in making the comparison.

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LOCATION OF GEOLOGICAL DISCONTINUITIES In addition to providing information about the excavation characteristics of overburden, seismic refraction surveys can locate geo l ogi ea l di scant i nuit i es such as weathered dykes, faults, zones of fractured bedrock, and buried former river channels, although not all discontinuities produce detectable velocity contrasts. Where conditions have been favourable, seismic surveys have al so differentiated between oxidised coal and unaltered coal in subcrop areas. The Triassic coal seams at Tarong (Qld) can have velocities in the range 2000 m/s 2900 m/s when unaltered, which can constitute significant refractors. Approaching the subcrop areas there is a distinct lateral velocity change down to 1200 m/s - 1700 m/s representing the oxidised coal. The location of faults and zones of fractured rock is of considerable value in mine planning and design. Two field examples of fault location by seismic refraction survey are given below; in one case the survey was run specifically to locate a known fault whose strike was not linear, and in the other case re-analysis of the field data from a rippability survey, using the Generalised Reciprocal Method, disclosed a fault that had not previously been detected when the data was first analysed by Hawkins Method.

Muja Fault, Collie, W.A. The Muja Fault is a high angle normal fault which separates the Permian coal measures from the Pre-Cambrian Basement. The strike of the fault meanders and in places it appears that the Hebe Seam - the thickest seam in the Muja Pit abuts the fault and assumes dips as steep as 60 degrees due to fault drag. This varying geometry complicates the design of the pit's west wall . A series of seismic refraction traverses were run normal to the strike of the fault to locate it and the Hebe Seam, so that drillholes to investigate the extension of the pit's west wall could be sited in optimum locations. A portion of the refractor velocity ana lysis plot for one of the traverses is presented as Figure 3, contrasting the plots for Palmer's Method with Hawkins Method. The ea l cul ated optimum XY spacing for the Generalised Reciprocal Method is 15 metres . The geology as established by drilling is superimposed on the seismic profile (Figure 4). Seismic velocities established on an exposure in the pit's north wall have been superimposed on the mapped geology and are presented on Figure 5 for correlation purposes. The refractor velocity plot (Figure 3) for the Hawkins Method shows the transition from granite (2100 m/s) to Permian sediments (800 m/s), but not the fault zone itself. The Generalised Reciprocal Method, (Palmer's Method) sees in addition the Sm wide fault zone (650 m/s) and the higher velocity wedge of Permian (1450 m/s). The detailed refractor velocity data on the seismic profile (Figure 4) was derived from the plot with XY equal to the optimum spacing of 15 metres. These velocities correlate well with the directly measured velocities in the existing pit (Figure 5). Northern Coal Field, N.S.W. The refractor velocity plot, seismic profile, and available geo l ogi ea l data are presented as Figure 6. The optimum XY spacing for the Generalised Reciprocal Method is 10 metres . The Generalised Reciprocal Method (Palmer's Method) sees a 10m wide low velocity zone (1400 m/s) on the site of a known reverse fault, which is not delineated on the Hawkins plot. Unlike the traverse across the Muja Fault which used explosives as the seismic source, this survey used a 50 kg weight drop. Australian Coal Geology 4, Part 2

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BOREHOLE CORRELATION BORE MUG 821 IN GRANITE DATA (see fig .4)

349

BORE MUG 1113 IN PERMIAN INCL . LOWER PORTION HEIIE SEAM.

-0

.. C 0

.,u

·e

-:::E

I-

LEGEND

l·M'""'"'

Figure 3.

800

SEISMIC VELOCITY ( metres per second )

PALMERS METHOD ( XY : 20 metres )

PALMERS METHOD ( XY : 15 metres)

HAWKINS METHOD

20metres

Refractor velocity analysis plot for traverse crossing the Muja Fault, W.A.

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Profile containing seismic data obtained from Figure 3 onto which has been superimposed geological data obtained by drilling, Muja Fault, W.A.

Figure 4.

LEGEND

-X/450 1450

SEISMIC REFRACTOR (depths Interpolated from end polntl) SEISMIC REFRACTOR (depths d1t1rmlntd at ~metre lntervol1) SEISMIC VELOCITY ( motrH per tocond)

JeoO LATERAL CHANGE IN SEISMIC VELOCITY

MUO 621

GROUND SURFACE

MUG 613

330

LOOSE

MUO 820

- -

HIGHLY WEATHERED GRANITE

MUG 618

SAND

HIGH\-Y WEATHERED PERMIAN SEDIMENTS

LEGEND 2600

SEISMIC VELOCITY ( motrH per second)

2sol7BO LATERAL CHANGE IN SEISMIC VELOCITY

BASE OF

Figure 5.

Geological profile obtained from face mapping in the Muja Open Cut, W.A., showing measured seismic velocities.

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CORRELATION BORING PASSED THROUGH FAULT

LEGEND

1400

SEISMIC VELOCIT Y ( metres per second)

- - X - - PALMERS METHOD

- - 0 - - HAWKINS METHOD LEGEND

□

E'.Zl

CLAY EXTREMELY WEATHERED CLAYSTONE FRESH CLAYSTONE COAL

/4CX)

SEISMIC VELOCITY ( metrH per tecond J

- X - SEISMIC REFRACTOR

zo,.,,,..

- X - LATERAL CHANGE IN SEISMIC VELOCITY /~00 LOW VELOCITY ZONE ~

CORRELATION BORING

r.: -x-x---x

[

20motru

3200

20metrH

Figure 6.

Refractor velocity plot, seismic profile and geological data obtained during refraction survey of a proposed strip mine in the Northern Coal field, N.S.W. For simplicity the intermediate and soil layers have been omitted from the profile.

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DISCUSSION The senior author (W.P.) has extensively used Hawkins Method for over a decade to analyse seismic refraction traverses, and has found it successful in locating discontinuities such as faults, weathered dykes, zones of fractured rock, buried former river channe 1s, etc. The authors' recent experience suggests that the Genera 1i sed Reciproca 1 Method can detect di scant i nui ties that are not wide enough to be seen when the same data is analysed using Hawkins Method. However, there is a cost penalty for the increased resolution offered by the Genera 1 i sed Reci proca 1 Method because of the need for more accurate arrival times and closer geophone spacings than have been used by many geophysicists in the past. The refinements discussed be 1ow do i nvo 1ve some increase in cost for routine refraction surveys. It is considered that the necessary accuracy in arrival times for high resolution is somewhere between ±0 . 5 and ±0.2 of a millisecond. While the instrumentation is available with this order of timing resolution, the accurate picking of the arrival times or "breaks" requires the incoming waveform to have a rapid rise time . The authors have confirmed the frequently stated contention that explosive sources provide sharper breaks than do weight-drops. While the authors do not use geophone spacings wider t han 10m, many refraction surveys are run with geophone spacings up to 30m, which can be analysed by Hawkins Method but not by the Generalised Reciprocal Method, since such wide geophone spacings exceed the optimum XY values, and Palmer (1981) reports loss of resolution if non-optimum XY values are used . In order to perform the full Generalised Reciprocal Method analysis, Palmer suggests at least three geophone intervals per optimum XY spacing are required, which in many cases would require _a geophone spacing of 4m - 7m. With correlation borings available to identify hidden layers and velocity reversals, should they occur, it is possible to calculate the optimum XY spacing without the need to check it by inspection of the velocity analysis and time-depth functions calculated for a range of XY values. This approach has permitted the authors to use geophone spacings of between 5m and 10m. COSTS Assuming a refraction survey is commissioned to determine excavation characteristics involving several kilometres of traversing at a 10m geophone spacing, the approximate order of cost per line kilometre is currently (1982) around $3,600 - $4,000, i ncl udi ng exp 1os i ves and shot-ho 1e dri 11 i ng but not line clearing if it is required. The additional costs for a detailed analysis for faults and other discontinuities is estimated around $500 per line kilometre, or about 13%. Although it is unlikely that all faults within the boundaries of potential strip-mines will produce detectable anomalies in refraction traversing, this is still a very modest cost as an extra on a rippability survey for detecting just some of the faults . By comparison, Mini-SOSIE reflection surveys were quoted at $3,000 - $4,000 per line kilometre and high resolution seismic reflection at $5,000 per line kilometre in 1980 by Harman (1981). Hence if a rippability seismic refraction survey is planned, it would seem a sound investment to pay the additional cost for detailed fault analysis.

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CONCLUSIONS Seismic refraction surveys provide data for pit and infrastructure design, which includes the assessment of overburden excavation characteristics. The seismic refraction technique should be used with some caution in Australian Permian and Triassic coal measure strata, since the interpretation of the data is rarely straightforward and the ease of data acquisition can vary rapidly over a coal lease. While refraction traverses are being run for overburden assessment purposes, useful additional geological data can frequently be acquired for little extra cost. Faults and other discontinuities have been detected when refraction data has been analysed by Hawkins Reciprocal Method, but Palmer's Generalised Reciproca 1 Method · is able to detect faults with narrower velocity anomalies that cannot be delineated on refractor ve 1oci ty p1ots generated by Hawkins Method . A1though it is not suggested that seismic refraction surveys can 1ocate a 11 major discontinuities within the boundaries of potential and operating open pits, the ability of refraction techniques to profile overburden and to locate geological discontinuities confirms the status of the seismic refraction method as a valuable geophysical technique for mine planning and design. ACKNOWLEDGEMENT The detailed data from the Muja Open Cut is published with the permission of the Griffin Coal Mining Company. The valuable assistance of Mr. Albert Brantly, Chief Geologist/Hydrologist, and Mr. Ian Clarke, Chief Mining Engineer, during the seismic refraction survey at Muja is gratefully acknowledged. Mini-SOSIE is a Registered Trade Mark of Societe Nationale Elf Aquitaine (Production). REFERENCES Harman, P. , 1981. High resolution seismic reflection techniques in the coal industry, Australian Coal Geology~ (1), 3-14. Hawkins, L.V., 1961. The reciprocal method of routine shallow seismic refraction investigations, Geophysics 26, 806-819 . Pa 1mer, D. , 1981. An introduction to the genera 1 i sed reci proca 1 method of seismic refract·ion interpretation, Geophysics 46, 1508-1518. Soske, J.L., 1959. The blind zone Geophysics 24, 359-365.

problem

in engineering

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Well-Log Geophysics for Coal Measures M. Weber Century Geophyslcal Corporation of Austral la, P.O. Box 95, Brighton, S.A., 5048. Key Words: Fully digital system, multi function probes, callbratton, format presentation and Interpretation. ABSTRACT A number of parameters can be run In borehole logging, to determine the presence of coal measures, coal seam thlcknesses and a coal quallty analysts. For coal exploration a single probe can be run to measure Natural Gamma, Callper, Focused Resistivity and Gamma-Gamma Density. Century Geophyslcal Is an International mineral logging company with an United States division that Investigates coal, of I and gas and uranium properties, which has recently expanded Into logging, and an Austral Ian division which does complete mineral logging. The Instrument package on the vehicles uses an on-board digital computer that stores raw data, processes and computes It and d I sp Iays parameters used by geo Iog I sts and Iog ana Iysts. The Compulog system of down-hole probes and surface Instrumentation Is fully digital. HISTORY Century Geophysical Corporation began In the early 1950 1s as a developer and service contractor In the seismic field for of I and gas exploration. By the 1960 1s the company had evolved Into the world's largest supplier of electronic The U.S. division of Century Instruments for the seismic business. Geophysical Is unique In that ft staffs an engineering department that designs, develops, produces and uttlzes Its own logging and evaluation equipment. In the mid 1960 1s, Century began to uttl tze digital technology In Its logging. Surface Instrumentation was employed that would record the gamma ray and depth information, so ft could be processed on a computer. It was Century's first effort, and probably the first In the Industry by a service company, In developing Instrumentation spectftcal ly to satisfy the needs of the mineral logging customers.

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In coa I Iogg Ing, Century now has un Its work Ing In severa I Iocat Ions throughout the world. Century's coal qua I lty evaluation techniques provide a quantitative coal qua I lty analysis. They al low Century to operate In the thin-seam lignite areas where other techniques cannot be used, as wel I as In the thick-seam, high rank deposits. Century's coal analysts gives Information of heat yield In Megajoules per kilogram and ash content In percent by weight within a 5% accuracy In one of two conditions: either moisture-free or In sltu. In the In sltu analysls, percent moisture by weight Is given. The measured parameters are Density, Natural Gamma-ray, Resistivity, Callper and various other physical parameters of coal. COMPLETE DIGITAL SYSTEM The Century vehicle fleet Is composed of approximately 150 units; many are four-wheel drive trucks and swamp buggies, but the heart of Century's service capablllty Is the Instrument package on the vehicles. The Compu-Log on-board computer system Is the Industry's only proven truck-borne dlgltal computer used In the mlnerals Industry that stores raw data, processes, computes the data and dlsplays parameters used by geologlst and log analysts. The CompuLog system Is the only one In mineral logging In which the complete computer analysis can be run In the vehicle at the same time that the logs are being prepared. The use of the digital computer, Its Interactive Input, Its multiple output devices, and advanced software give a level of performance not possible In analog systems. The signals from a sonde are stored on magnetic tape In raw form with only one pass through the hole. This stored data Is processed by the computer for plotting In conventional chart form, for printout by the I lne printer, and for presentation of results such as ore grade calculations and deviation Information. Compu-Log completes the work In the hole and presents the data before an analog system could complete the log acquisition. Scale changes can be made and data plotted at wit I. The logging of data occurs as the sonde Is be Ing retracted from the ho I e at rates of 5 to 18m per mI nute. A sc I nt 11 I at I on crysta I Cover f I ve t I mes the vo I ume of 'standard' mI nera Is Industry crystals) makes possible Improved stattstlcal results. Skewing or distortion problems that arise In analog systems due to lag or time constant effects do not exist In the Compu-Log system. In coal exploration, Gamma-Gamma density measurements are available In combination with Cal I per, Focused-Current Resistivity and Gamma-ray. The geologlst In the fleld can have refined and plotted data available at the same time as the logging results are avallable. The system e I Im I nates many of the prob I ems caused by operator dependence, while Increasing data qua I lty and logglng speeds. Century's trucks are capable of logglng holes to depths of 200m under a variety of field conditions. Units In Austral la Include DA-115 Toyota Trucks (Figure 1) and Mercedes Benz Unlmagos (Figure 2). Before togging, the computer (Figure 3) prompts the operator for probe cal I brat Ion Information, log heading Information such as cl lent, hole number, date, ho I e s I ze, too I I dent If I cat I on, magnet I c dee 11 nat Ion, etc. Th Is Information Is stored permanently on magnetic tape and automatically printed out on the log.

Austral Ian Coal Geology 4, part 2

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Mark Weber

Figure 1 Toyota DA-115 Compulog System

Figure 2 Mercedes-Benz Unlmog Australian Coal Geology 4, part 2

357

Mark Weber

Figure 3 Compulog Computer

Figure 4 Multlfunctlon Probes 9055 on left 9032 on right

Figure 5 Focussed Resistivity Section of a 9032 Probe Australian Coal Geology 4, part 2

Mark Weber

358 MULTIFUNCTION PROBES

In some areas of coal exploratlon the drlll hole does not stay open very long; It Is deslrable to have multlple sensors In the sonde to gain as much Information as Is needed In a slngle pass of the hole (Figure 4). In coal exploratlon , various single density spacings of 40cm, 20cm and 9.7cm are avallable as a long, medium and short or bed Boundary Defining probe. The density spacings are In combination with a slngle arm callper, natural gamma, and focused resistivity . The probe Is 6.0cm In diameter and 2.65m long. The cal I per section Is located between the source and detector of the density section, to ensure the decentral I zing of the density section. The density section Is col llmated by using a Mai lory metal section with machined 'windows' to direct gamma rays Into the formation and Into the detector. The natural gamma Iog crysta I Is 28mm by 112mm and Is Iocated near the top of the probe, being large enough to gain statlstlcal quality from the gamma ray flux. The Focused Resistivity section Is located In the centr e of the probe (Figure 5) with the guards on either side of the electrode array. The beam of the guard array Is 2.5cm, and focused outwards, horlzontall y has approxlmate ly 2m radius of Investigatio n. The advantages to the guard log are 1) 2) 3) 4)

bed boundary resolutlon Is good pick clay partings works In areas of sallnlty qua I lfles high resistivity areas.

The 9055A Probe has f I ve parameters measur Ing Natura I Gamma, Se I f Potent Ia I CSP), SI ng Ie Po I nt Res I stance, Neutron-Neutron, and Dev Iat Ion In one pass of the hole. Orlglnally designed for uranium exploration , this tool has become popular for Its deviation and neutron-neu tron logs In coal. The natural gamma section Is located at the top of the probe using a 2.2cm diameter by 10cm long crystal. The deviation section comprises three fluxgates for the magnetics, with two accelerome ters for the vertlcal angle. The deviation section Is located In the centre of the probe. Data presentation Is In a plotted plan view or as a printed slant angle-slant bearing. (Figure 6). Further down the probe Is located the slngle point resistance and selfpotentlal electrode. At the bottom of the probe Is located the neutronneutron section. The source to detector spacing Is 40cm, usl~ a 1 curie AmBe 214 source, and a detector for thermal neutrons using a He detector. The dimensions of the probe are 4.6cm diameter by 2.97m long, with a logglng speed of 18m per mI nute. The sonic probe central lzed In the borehole consists of two receivers below the transmitter . The probe measures the P-Waves which are compresslon al In nature and are transmitted both through flulds and sol Ids. The P-Wave response Is of use In coal as an addltlonal Independent parameter for petrophyslc al analysls, and In general to give porosity Information . When combined with a density log, the sonic log wll I give Information on a rock 'strength Index•. The probe wll I The f I rst rece I ver Is Iocated 0.9m be Iow the f It Into a 8.9cm ho I e. transmitter and the second receiver Is located 30m below the first receiver, giving the abll lty to determine a Delta T In microseconds per metre and using an analysis program the borehole compensate d veloclty In kl lometres per second can be determined.

Austral Ian Coal Geology 4, part 2

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359

. i._. ~_ " _, _

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CALIBRATIONS Presentation by most service companies In the coal exploration field are In counts per second. Century has gone one step further and presented a llnearlzed density In apparent grams per cubic centimetre. The probes were run In standard facl I I ties of water, dry sand, wet sand and an alumlnlum block. Depending upon the probe type a water cal I brat Ion standard was assigned, A second water car I brat Ion was run In the fleld to determine the probe bias from the standard number. Different parameters such as water temperature, mlneral content, sallnlty, source used, will affect the cal lbratlon run. The computer automatlcally makes an adjustment when plotting In apparent grams per cubic centimetre. SI mI I ar I y for the neutron-neutron probe a water standard Is used, A car I brat Ion run Is made In the fleld, and the log Is normal I zed against the known water standard.

Australian Coal Geology 4, part 2

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360

FORMAT PRESENTATION The down hole data Is collected as the probe moves up the hole In a digital format. The sampl Ing rate Is every 1/10 second and the data Is stored on magnetic tape cartridges with respect to depth, to an accuracy of 1cm. A real-time plot can be made while logging as wel I as store data on tape, a read after write check of the data. Once the data Is stored on tape, zones of Interest can be played back at different depth scales as wel I as d I fferent f unct Ion sea Ies. The program format tape can present combinations of data, on the Houston Instrument DP-11 Plotter, listed below: 1) Natura I Gamma, ea 11 per, apparent gm/cc, Resistivity (Figure 7). 2) Expanded natura I gamma, ea I I per, apparent gm/cc, Reslsltlvlty Figure 8 3) Ca 11 per, counts per second, resistivity (Figure 9). 4) Natura I gamma, SP, S.P.R., Neutron-Neutron (Figure 10). 5) Natural gamma, Neutron-Neutron (Figure 11) and other combinations.

The system can analysis work Including 1)

2) 3)

Plan view of Vertical Deviation. Coal Quality Analysis. Borehole compensated Velocity Survey.

Figure 7 Showing records from left to right Natural Gamma, Callper Apparent gm/cc, Resistivity

INTERPRETATION Geology always has surprises and generalities may not be true In all cases. Coal geologist can Identify basic I lthology In terms of sedimentary, Igneous and metamorphic rocks. Sub-divisions such as coal, sandstone, sha I es, limestones, granites and basalts are Identifiable. Geologists with experience In special llthologles and restricted areas can subdivide much further - Into shale bands, differences between sl ltstones, and mudstones.

GAMMA RAY LOG Potassium or Isotope K40 Is the source of activity. The potassium Is present In most shales and Is usually an evaluation of shale content. In the coal environment, In a typical sequence of logs, a Shale Line can be drawn. This Australian Coal Geology 4, part 2

Mark Weber

361

Figure 8 Expanded section from 10 to 20m from f i gure 9

Figure 9 Callper, Gamma-Gamma (cps) Resistivi ty

line Is an estimatio n of 100% shallness. A Sand Line can be drawn to Indicate a typ lea I 1c I ean 1 sandstone . Be I ow the Sand LI ne may represen t coa I 11 mestone. Between the Sand and Shale Line Indicatio n of graduatio n between sandstone s and shales, usually slltstones and mudstones .

DENSITY LOG nFrom a wlrellne tool, the gamma-gamma density tool, has a response proportio al to the formation electron density, which relates to the number of protons, Ic Z In the format I on. How ever, the b u I k or mass dens I ty Is re I ated to atom of weight, A, of the material. In most common elements found In formation or Interest, Z/A = 0.5, with hydrogen Z/A = 1.0, an exception . When hydrogen Is ratio the arises; Z/A 2 of ratio heavy elements are Involved, a correction I e, 2 Z/ A because the system Is ea 11 brated to a reference of 0.5. For examp water hav Ing a true dens I ty of 1.00 gm/cc, has an apparent dens I ty of 1.11 since Z/A for water Is 0.55, 2 Z/A Is 1.11. For some coals the values gm/cc: from 0.51 to 0.53 w Ith 2 Z/ A va I ues rang Ing from 1.02 to 1.06. range A of Z/ Norr Is, 1980). WI th the var I ous source to detector spac I ngs ava 11 ab I e, seam I ut I on dens I · th I ckness measureme nts can be determ I ned from 20cm to 40cm. The bed reso bed coal for result ltatlve I qua a p.rovldes ch i wh spacing, 9.7cm a section has boundarie s. Seams thinner than the source to detector spacing would require a thickness derived amplitude correction .

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Mark Weber

Figure 10 Natural Gamma, S.P., Resistance Neutron-Neutron Porosity

Figure 11 Natural Gamma and Neutron-Neutron Log

CALIPER LOG The callper tool measures the diameter of the borehole. It can be a three arm dev i ce, with arms at 120 degrees of each other mechanically connected and driven. The single arm type Is used In sldewall tools to push the face against the borehole wal I for purposes of density measurement. RESISTIVITY LOG The three electrode guard resistivity sonde utll lzes a system Including a short measure electrode (2.5cm) on a 9032 probe and a medium measure electrode (15cm) on a 9030 with a long 1guard 1 electrode on each side, as Indicated In Figure 5. This results In a current flow pattern similar to a f lat disc volume, with the guard electrodes constralnlng the current flow horizontally outwards, A characteristic of the three electrode guard log Is that the measuring disc Is deflected or 'bends' as a result of significant changes In resistivity at sharp boundaries. This log has been used for correlation and Identification but must be treated with caution as Its diagnostic properties may vary for a number of reasons. Usually shales wl 11 read low and everything else wl 11 read higher. But sometimes, the coal and sandstone wll I read low, ca using serious Interpretive Austral Ian Coal Geology 4, part 2

Mark Weber

363

errors. Coa Is In the form of I I gn I te and anthrac I te have ·very I ow resfstfvftfes, whf lst bituminous and sub-bituminous coal can vary from low to high. Bed boundar ies, ff horfzontal with a clean coal Interface present, ft . may be possfble to use the fnflexfon point of the focused guard resistivity response as a bed boundary Indicator. NEUTRON-NEUTRON LOG This log responds to the hydrogen and to a lesser extent carbon content, and Is bas Iea 11 y a cont I rmat Ion of the gamma ray Iog. DEVIATION The presentation Is a plan view of the drf I lhofe. It can be used to position the borehole path with respect to underground mining activities. It Is useful for determining vertfcal I fty of boreholes when encountering steeply dipping formations and faults. SUMMARY The Compu-Log system Is a fuf fy Integrated digital system. In coa I exp Iorat Ion, the Gamma-Gamma dens Ity measurements are ava I Iab Ie In combination with cal !per, Focused-Current Resistivity and Gamma-ray. The geologfst In the fie Id can have refined and plotted data avaf fable at. the same time as the fogging results are avaflable. With the quicker loggfng speeds up to 18m per minute, due to the dlgital transmission system, there Is a saving In drf 11 standby charges to the money conscious geologfst.

Australian Coal Geology 4, part 2

364

Computer Processing of GeophY.sical Logging Data in Coal Deposits J.E. HAIGH and I.H. EDWARDS GEOEX Pty. Ltd. P.O. Box 42, Unley, 5061 Australia

Key Words: analysis.

Geophys I ea I Iogg Ing, crossp I ots, computer process Ing,

Iog

ABSTRACT The recording of digital geophysical borehole logs Is now commonplace In coal exploration programs. In-truck computers enable data to be recorded directly onto nine track tape and also to be displayed as ful ly-cal lbrated logs, or processed readings. A typical calibrated digital recording system Is first described. In the of I Industry statistical methods have long been employed, and no analysis Is complete without such aids as histograms and crossplots. In coal exploration I lttle has been done with these techniques apart from regression analyses and correlations. Examples from a borehole Illustrate how additional Information and a greater understanding of geophysical logging can be extracted from statistical processing of digital log data. INTRODUCTION Near Iy every coa I exp Iorat Ion program now I nvo Ives rout Ine Iogg Ing of boreho Ies by either geophysical wlrellne logging contractors or the exploration company's own logging system. The degree of sophlstlctlon varies from project to project; this Is not only different for the type of equipment used to record the Iogs, but a Iso In the treatment of resu I tant data, e I ther In Its processing or Its Interpretation. Recent work by Groves and Bowen (1980), Renwick (1982) and Jackson (1981) has discussed In detal I borehole tool specifications, cal I brat Ions, processing and quan t ltlve Interpretation of logs, and each article contains a thorough bibliography or list of references. 011 well log analysts have used statistical methods for formation evaluation for many years, and logging company publications outline the standard use of these methods; Schlumberger (1972), Dresser Atlas (1975). In addition other workers such as Nelnast and Knox (1973), Mc Fadzea n (1973), Connolly (1974) and Hes Iop ( 197 4) have shown how stat I st I ea I treatment of Iogs can extract Information not read I ly apparent from a casual observation of field logs. Furthermore they have shown how several errors may be recognized In field recording and easily adjusted to produce fully Interpreted results without In any way compromising the validity of the results. Australian Coal Geology 4, part 2

J.E. HAIGH and I.H. EDWARDS

365

Although some of these methods have been used In coal log Interpretation, they have largely been I lmlted to regression analysls with core data or for parameter selectlon for further processing as outllned by Reeves {1978). With the advent of cheap computing systems, either In the office or In-truck, treatment of logglng data Is now easlly accompllshed, and this paper outllnes how statlstlcal methods, by use of computers, can enhance straight Interpretation of analogue fleld data, after It has already undergone a certain amount of callbratlon and presentation processing. STANDARD TREATMENT OF DATA Data are collected In a totally raw dlgltal state by the logglng system, and var Ious degrees of process Ing can be app I I ed to make resu Its more usab Ie or I nterpretab Ie as descr I bed by Ha Igh and Henderson {1979) and Edwards {1982). In the simplest case callbratlons are applled, for example, to the count rate of the cal I per log and the result Is a measurement, In centimetres, of the hole size. As this log Is recorded by a purely electrlcal-mechanlcal system, no fl lters are appl led, whereas In the case of radiation logs, different I ength f 11 ters need to be utl 11 zed depend Ing on factors such as count rate, logging speed and vertical resolution required. Thus for a fixed logglng speed (say 5 metres per minute) a natural gamma ray log with a low count rate would need a longer fllter compared to a neutron log with count rates an order of magnitude higher. A short spaced density log, however, which Is used pr I mar 11 y for coa I seam th Ickness and boundary reso I ut Ion, does not requ Ire the statistics to be smoothed as much, and hence generally has a short filter applied. As mentioned previously, since the data Is recorded In a raw state, any I ength or type of f 11 ter can be chosen and app I I ed at the t I me of p Iott1ng. A I I Iogs undergo ea 11 brat Ion to a greater or Iesser extent.

The ea 11 per Is straightforward as the end result Is a fixed quantity that can easl ly be checked, namely distance. The sonic tool, however, measures the reciprocal of veloclty, I.e. transit time, In microseconds per metre. This Is done by recording two full waveforms received from a 25 KHz transmitter and comparing the arrival time. Knowing the tool receiver configuration, a comparison of waveforms by the In-truck computer yields a "lag" In the crosscorrelatlon which Is equivalent to the transit time of the P-waves. Calibrations for this too I (apart from frequency checks) can be effected In the bore ho I e by examination of areas of known velocity such as steel casing, large fluid fll led cavities, or pure minerals such as evaporltes. Radiation logs are calibrated by secondary devices which relate to actual rock properties. The neutron tool has a series of piastre calibrators which give different count rates at known tool posit i ons. These In turn can be references to true rock porosity. The gamma tool Is cal lbrated by a Jig which, when located In a fixed position, gives radiation Intensity (above background level) equal to 200 API units - a measurement derived from the America! Petroleum Institute test pit at the University of Houston. Density I ogs are ea 11 brated on grooved s I abs of d I fferent mater I a I; a I um In I um (2.7 gm/cc), magnesium (1.74 gm/cc) and acryl le (1.2 gm/cc). Any number of these can be used to cal lbrate the tool directly to bulk density, although generally, preference Is given to callbrators with similar values to the rocks I lkely to be encountered.

Austral Ian Coal Geology 4, part 2

J.E. HAIGH and l , H. EDWARDS

366

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PLATE 1 TypicaJ suite of logs from a coal basin Austral Ian Coal Geology 4, part 2

J.E. HAIGH and I.H. EDWARDS

367

ANALYSIS OF LOGS BY COMPUTER PI ate 1 I I I ustrates a typ Iea I su I te of Iogs recorded In an Austra I I an coa I basin. Various cal ibratlons and ff lters have been appl led and these are plotted on the header section as well as on nine track tape. Each calibrated and filtered log was transferred to disk for easier manipulation. Figure 1 Is a histogram of the long spaced density log for the section of the ho Ie from 120 to 70 metres. The p Iot Is se If sea 11 ng and uses va I ues at a digitized Interval of 10 cm. From this plot several points emerge: (a) The minimum density of coal Is around 1.32 gm/cc and the median value Iles around 1.4 gm/cc. (b) The majority of rocks have densities between 2.2 and 2.6; a loglcal conclusion as sandstones and shales typically show this variation with differing porosities. Cc) There are possibly at least two sets of rocks In this range as maxima lle at 7.36 and 2.56 gm/cc. (d) There Is a zone of rock densities between 1.68 and 1.9 gm/cc. Examination of the log shows that this Is the probable density range of dirty coal. (e) A smal I range of points Iles between 2 and 2,2 gm/cc. carbonaceous material or posslbly caving of the borehole wal I.

This could be

The above features are quickly dlscernable from a casual look at the histogram whereas they are not read I I y apparent from a q u I ck observat I on of the Iogs. Therefore, whl 1st not adding anything to the data, a different presentation, In some cases, al lows us a more rapid assessment of certain features. Apart from this use of the histogram, Its major role In wel I log analysis has been the recognition of mlscalculatlons of logs. This can be accompllshed In two ways. Firstly If a diagnostic or unique mater la I Is known to exist, a quick look at this histogram wll I determine whether the log reading Is correct. A slmple case could be a cal I per log recorded In 76 mm casing or a density log In a known anhydrite bed of 2.96 gm/cc. Secondly, where histograms have been run over a whole exploration project, a 'master' h I stogram can be bu 11 t up from every hole, or a known zone of every hole, and comparison by overlay of subsequent results can show whether cal I brat Ions are eeeesatlsfactory. Care must be taken however that true geological features are not Interpreted as mlscallbratlons. Different histograms for different logs should decide whether a geological anomaly or trend Is present. Apart from plottlng histograms, a comparison of two logs, or a crossplot, can often yleld Information not read I ly apparent from the logs. Figure 2 Is a crossplot of depth on the y-axis versus density along the x-axis. Each number Is the frequency at which a pair of values occurs at that particular matrix point. This example Is therefore exactly equivalent to a density log at a reduced scale and coal seams can be easl ly seen In the lower half. A useful feature of the crossplot Is the "drop-option" as shown In Figure 3. This Is often Austral Ian Coal Geology 4, part 2

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J.E. HAIGH and I.H. EDWARDS

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Figure 3 Depth versus Density Cross Plot with Drop-Option

Austral Ian Coal Geology 4, part 2

370

J.E. HAIGH and I.H. EDWARDS

used to hlghllght certain features or trends within the crossplot Itself. In this case al I occurrences of less than 4 have been dropped to reveal the major trend. Here can be seen two obvious features: (al A trend In density with depth from average 2.2 gm/cc at shallow depths to 2.5 gm/cc at the bottom of the hole. This Is no doubt due to compaction. (b) The coal seams are stlll apparent, although a lower drop option may have given us posslly more Information about the coal seams themselves. Log data bases can be quickly and easily bullt on smal I minicomputers either In-truck or In the office and I lne printer crossplots such as Figures 1 - 3 If a plotter Is aval I able, the can be easl ly produced at I lttle cost. restrictions Imposed by the necessary printer matrix are overcome and crossplots may be produced that show the true density of features rather than a frequency number. Figure 4 shows such a crossplot (or scattergram as they are known In statistSeveral ics) of I lnearlsed and cal lbrated short versus long density. features, some of whi eh cannot be seen from actua I Iogs, are read 11 y apparent. (al The cal I brat Ion of both densities has been reasonably 'successful'. Since both measurements are Independent, we would expect a straight I lne through the origin. This Is nearly the case al low Ing for the fol low Ing: (I) Statistics and the subsequent use of different fl lter lengths causes a scatter about the straight llne. (I I) Depth of Investigation Is proportional to source detector spacings. DI screpanc Ies ex Ist therefore where h Igh Iy d I pp Ing beds occur or cav Ing Inf I uences both readings to a different extent. In this case points can be seen where the short density reads lower than the long; an Indication of either cav Ing or mudcake bu 11 d up on the boreho I e wa 11. Apart from the 11 near density algorithms, a combination of the two densities can be used to compensate, to some extent, for these dlvergencles caused by caving. The effect Is to 1 mI grate' the po I nt back to the stra I ght 11 ne and thus eva I uate the true compensated density. The nature of this compensation Is normally a very simple equation, such as: T

2L - S

where T Is true density In gm/cc. L Is long density In gm/cc. S Is short density In gm/cc.

Because of the shape of the plot, It Is often known as a 'spine and ribs' p I ot. Even a 11 ow Ing for the above d I screpanc I es caused by adverse ho I e effects, the correlation coefficient between the two logs Is around 0.8. This shows that callbratlon has been achieved with both the density equation used and the actual physical method of calibration, an Important point If logs are to be used quantltatlvely. (b) Trends shown In the histograms for one density are again out I lned In this crossplot e.g. two high densities, coal, etc. Figure 5 Is Density versus Gamma Ray Crossplots. As the gamma ray log Is often a very good Indicator of the presence of shale, an Indication of rock Australian Coal Geology 4, part 2

J.E. HA IGH and I.H. EDWARDS

371

CRCISS PLCIT NELL NO , A.. EA I 120. 00 - 20. 00 a. OE~TH , DATE ~~0Cf55EO , 9/23 / 82 NO . OF ~OJNTS OUT OF BOUNDS • 0. NO . OF ~OJNTS noT TEO • 100 1. L ONG OEN5JTT

• •,...•- ~ , . ~·-· - ~ , ._••- - ·~· ·-• .J1s

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Long v. Short Density Cross plot

Figure 4.

types can often be obtained by examination of crossplots In wh ich one axis Is the gamma ray. As the density log Is probably most affected by coal, the comb ination of these two logs gives a good representation of coal, shale and sandtone (or l imestone). In Figure 5 th i s becomes readily apparent with the cleanest coal being lowest density and gamma count. Away from this 1 pure 1 coal point, there can be seen to exist two trends. Different Interpretations can be put on each trend, for examp I e trend 1 to the mI dd I e/ I ow gamma rock area could Indicate one of three posslbl I !ties: Cl) Coal/sandstone boundaries. (Ill Progressive Increase In low gamma mineral matter. (lll)Contamlnatlon by a high density material, e.g. pyrite. Australian Coal Geology 4, part 2

372

J.E. HAIGH and I.H. EDWARDS

and the coal area, there Is a wide scatter of points which supports previous Interpretations of at least two other rock types other than coal.

CROSS PLOT

NO.

NELL NO • AftEA , OVTH , 120. 00 - 70 . 00 L DATE ,ftOCE55EO , 9 / 23 / 82 OF ,01NTS 'LOTTEO • SO I. NO. OF ,otNTS O~T OF 80UNOS • 0 .

SO, ISO ~

. 00

IG. 00

'10. 00

I0. 00

IG . 00

100. 00

11 0 . DO

120 . 00

110.00

140. 00

150 . 00

... a

. a

.... a

Gamma Ray v. Density Cross plot

Figure 5.

Figure 7 shows a neutron density crossplot. Once again, coal Is read I ly ldentlflable, but this time the trend In other rocks has less scatter. As mentioned previously, count rate variation In coal Is not particularly large with the neutron - about 250 cps - whereas variations In density exist between 1.3 and 2 gm/cc - presumab Iy a major effect of mI nera I matter. In the rock region, the pattern again suggests several rock types, but a definite high or low In either neutron or density does not Indicate one particular rock. Using broad rock types, rather than three percentages from simultaneous equations, and a I so from exper I ence In the prev I ous presentat I ons, four d Iv Is I ons are Austral Ian Coal Geology 4, part 2

J.E. HAIGH and I.H. EDWARDS suggested as shown. 1. 2. 3. 4.

373

Working from the bottom these could be labelled:

High porosity shale Low porosity shale Low porosity sandstone/limestone High porosity sandstone/I lmestone

Within the arcuate nature of these I lthotypes, there appear to be a few unaccounted-for points. These are probably distinct bed boundaries (as aga Inst gradat Ions).

CROSS PLOT Cll ENT N[LL NO AMA I D[nH , NO.

- 00

IG. 00

DENONSTNAT I ON

12D. DD - 70. DO -.

OAH ~NOCESS[D 1 8/23/12 NO . Of ~OINTS OUT Of BOUNDS • o . Of ~OINTS noTHO • 501.

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.....

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lOO. 00

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120. 00

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Gamma Ray v. Neutron Neutron Cross plot ~

Figure 6

Australian Coal Geology 4, part 2

J.E. HAIGH and I.H. EDWARDS

374

PL □ T

CR □ SS

NO.

.Jl. 00

I 0. 00

, OEMONST~ATION CLIENT NELL NO , A~EA • l20. 00 - 70 . 00 a. OH'TH I 9/23/12 DATE ,MCE5SEO , NO . Of ,oJNT5 OUT Of BOUNDS • 0. Of ,01NTS 'LOTTEO • SOI.

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Neutron Neutron v. Density Cross plot Figure 7.

The neutron log In this example was converted to porosity by using three points; namely the tightest I lmestone/sandston e or highest neutron reading being assigned as 5% porosity, shale assigned as 40% porosity and coal as 60% apparent porosity. These values are obtained from the llterature (Dresser, 1974) and previous experience, and produce a log regression with correlation coefficient of over 0.95. Secondary calibrators can thus be assigned porosity values If required, and the neutron log converted to a porosity scale. Figure 12 II lustrates a plot of density versus neutron porosity with gamma In the Z axis. The results summarise previous concluslons thus: Coal ls In the region of high apparent porosity, low density and low a) gamma va I ues.

Austral Ian Coal Geology 4, part 2

J.E. HAIGH and I.H. EDWARDS

375

FI gure 8 Is a son I c gamma crossp Iot. Once aga In there Is a Iarge scatter of points II lustratlng a diversity of rock types. Coal again Is obvious and also a high velocity low gamma rock; probably a tight sandstone or llmestone. No direct trend between these two regions supports previous conclusions of shaletype mlneral matter. As the sonic log often gives an Indication of rock strength, th Is crossp Iot 111 ustrates that s I nee t Ight rock and coa I show no trend between each other, contact between hard rock and coal Is uni lkely; an Important point when roof and floor conditions or rlppablllty are considered. The variation of the sonic log In the coal seam would Indicate that this log shows more va I ue In coa I assessment than d Id the neutron. Coa I type classlflcatlon either by area definition or by simultaneous equations can be performed In a slml lar fashion to the previous suggestions for rocks. This variation Is borne out by examination of the sonic and neutron logs at 112.5 metres and 84.5 metres. Figure 9 similarly shows scatter In coal type Indicating that mineral matter alone may not be responslble for the variation of density and sonic redlngs through coa I. A crossp Iot of these two Iogs produces on I y one broad dense region, however, which although possibly appearing Inconsistent with previous results, may Indicate the majority of rock types present cause slml lar responses to sonic and density logs. Figure 10 Illustrates the remaining crossplot, between sonic and neutron. As can be seen from the Iog a broad curved trend ex I sts that appears to 1 sp I It' at the slow sonic and low neutron count region. Previous crossplot data show that the lower neutron count rate trend Is the coal region whereas the higher count rate Is sha I e. From Iogs, determ I nat Ion of rock type, even coa I, can sometimes be misleading. For example, by Just taking the neutron and sonic from 103 to 110 metres and hav Ing no know I edge of deta I I ed Iog responses, a mIs I nterpretat I on of 7 metres of coa I cou Id ar I se rather than 3.5 metres of coal and 3.5 metres of shale. This misinterpretation of logs could also posslbly occur If the analyst were not aware of the previously observed consistency of the neutron log response In coal. A method using three logs Is aval lable whereby a third dimension Is Introduced to the crossplot and Is known as a Z plot. To II lustrate this, Figure 11 was run over this zone from 116 to 110 metres. The neutron and sonic were again crossp Iotted, but the numbers p Iotted now 111 ustrate dens lty va I ues from 1.3 to 2.6 gm/cc, I .e. 1.3 or I ess w111 be a zero, 2.5 or greater an aster I sk, and values In between are graded accordingly. It can now be easily seen that even without prior knowledge of neutron or sonic coal values, the divergence seen In the stra I ght neutron son Ic crossp Iot of FI g ure 10 Is great I y enhanced by the response of coal which gives low Z numbers. The neutron log Is often expressed In terms of I lmestone or sandstone porosity. To date no primary cat lbrators are aval I able In Austral la but cal I brat Ions In these units can be easl ly obtained In two ways. Firstly, a crossplot of sonic porosity (derived from standard equations lnvolvlng the transit times of water, rock and the reading) can be run against neutron and a regression applled to obtain the neutron porosity. Figure 10 shows the smal I divergence between trends and hence the valldlty of this approach (excluding coal areas). Alternatively porosity values can be assigned to known formations and neutron counts again regressed to give a conversion algorlthm. In either case, a logarlthmlc flt Is generally emplrlally satisfied as ls borne out by most porosity studies In the literature such as the Dresser Atlas C1974).

Austral Ian Coal Geology 4, part 2

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Sonic v . Gamma Ray Cross plot

Figure 8.

J.E. HAIGH and I.H. EDWARDS

377

CROSS PLOT CLIENT , OEMONSTAATION NELL HO t AAEA

NO .

~00 . 00

260. 00

OE~TH , 120. 00 - 70. 00 L DATE ~AOCE55EO , 9/23 / 82 Of ~OINT5 nOTTEO • 501. NO . Of ~OINTS OUT Of 80UN05 • 0.

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Figure 10.

b) In the coal region high Z values can be Interpreted as carbonaceous shale. c) There Is a strong density trend with little variation In neutron porosity - at this stage It Is not clear exactly what causes this but Is worth further Investigation. d)

The remaining area Is of varlabl~-poroslty shale and low gamma material.

From this recognition It Is possible to Isolate several rock types and correct, If required, for chemically bound water which Is seen by the neutron log. By means of simultaneous equations and parameter cut-offs a total computer Interpretation can then be produced. Australian Coal Geology 4, part 2

J.E. HAIGH and I.H. EDWARDS

378 _\

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Austral Ian Coal Geology 4, part 2

379

J.E. HAIGH and I.H. EDWARDS CONCLUSIONS

It may be noted from the previous discussion that al I Interpretations and conclusions were based on geophysical logs alone, and that no core or chip data were utilised. Furthermore use of the actual logs was minimized to underline the extra amount of data that can be extracted by these statistical methods. This was del I berate to I I lustrate the use of post-logging data processing. What has been achieved with some level of confidence are several usefu I factors. These Inc I ude: al The cal lbratlon of several tools, from primary cal lbratlons right through to totally compensated and corrected readings. bl The cross checking of several cal Jbratlons ensuring precision not only Jn one hole but throughout a logging project. c)

A geological

(d)

An understanding of tool responses Jn different geological settings.

Interpretation.

e) Parameter selection - either at cut off level or 100% 'pure' mineral point - for machine Interpretation. When actual core data and logs are used along with a Judicious selection of computer processing, geological Interpretation becomes much more complete. REFERENCES Connolly, E.T., 1974, Digital log analysis: recognition and treatment of field recording errors. SPWLA Fifteenth Annual Logging Symposium, Paper S. Dresser Atlas, 1974,

~ ~

Dresser Atlas, 1975,

Edwards,

loterpretatJon Fundamentals.

I.H., 1982,

Computer Ised boreho Ie Iogg Ing for mI nera Is 1.n MI nera I Austral Ian Development Assistance Bureau, Department of Foreign Affairs. Managed by WAIT-AID Ltd. (In preparation). Exp I orat I on, An I nternat Iona I Ira In Ing Course,

Groves, B. and Bowen, E.A., 1980, The appl I cation of geophysical borehole logging to coal exploration. Geological Society of Austral la. Coal Group Symposium, Sydney. Ha Igh, J.E. & Henderson R.J., 1979, Computer Ised process Ing and presentat Ion of borehore data . .B..u..U......A.ll.ila.~ Explor, GeophysJcJsts .1.U (3). Hes Iop, A., 197 4, Gamma-ray response of sha Iey sandstones. Annual Logging Symposium, Paper M. Jackson, L.J., 1981,

SPWLA FI fteenth

Geophysical examination of coal deposits .

Research, .8§J2.t.. ICIIS/TR

.l.fA ~

McFadzean, T.B., 1973, Crossplottlng - A Neglected Technique Jn Log Analysis. SPWLA Fourteenth Annual Logging Symposium, Paper Y. Nelnast, G.S. & Knox, C.C., 1973,

Normal lzatlon of wel I log data.

Austral Ian Coal Geology 4, part 2

SPWLA

380

J.E. HAIGH and I.H. EDWARDS

Fourteenth Annual Logging Symposium, Paper I. Renwick, R.I., 1982, A study of the uses and benefits of down-hole geophyslcal logglng In coal exploratlon programs. A.u.s.:ta. .!&a.I. .G.i!Q..l.. J, 37-50. Reeves, D.R., 1978, Some Improvements and develpments In coal wlrel lne logglng techniques. 1.n .!&a.I. Exp[oratfon, ~ 2. Proceedings of the Second lnternatlonal Coal Exploratlon Symposium, Denver, MIiier Freeman Publlcatlons Inc. Schlumberger, 1972,

.Log [nterpretatfon, ~ I - Pc[ncfpfes.

Australian Coal Geol_cgy 4, part 2

381

The Use of Transient Electroma~netic Methods for Resistivity Sounding and Mappmg with Particular Reference to Coal Basin Studies A.R. Dodds and J.E. Haigh Geoex Pty. Ltd., P.O. Box 42, Unley. South Australia. 5061 Austral la.

Key Words: Resistivity, Coal exploration, Transient electromagentlc method. ABSTRACT A study of ground resistivity can assist the coal geologist In mapping lateral and vertlcal llmlts of a coal basin, the presence or otherwise of coal within the coal basin, and structures such as faults, within the coal bearing strata. Although not the only geophyslcal method that can achieve these objectives, resistivity Is frequently the most cost effective. The Transient Electromagnetic method CTEM) of determining resistivity, has clear advantages over ga I van I c methods. The typ Iea I Iow res I st Iv It I es of coa I bear Ing sed I ments result In high signal to noise ratios for TEM methods and low signal to noise ratios for galvanic methods. Depth soundings are performed quickly and easily, without recourse to large electrode arrays. Electrical contacts with the ground are not necessary. These advantages are demonstrated by examples of surveys In Austral la and Thailand. INTRODUCTION The use of resistivity methods In coal exp Ioration Is by no means new. We will show that the addition of the Transient EM techlque to the older galvanlc method has Increased the efficiency, sensitivity and usefulness of resistivity surveys. GROUND RESISTIVITIES IN THE COAL ENVIRONMENT The effectiveness of any resistivity method rel les on a contrast In resistivity between two or more elements of the subsurface, but not necessarily between coal and Its host rocks. A brief overview of characteristic resistivity patterns In a coal environment Is useful for understanding the full range of posslbl I !ties. (Figure 1 ). There Is normally a resistivity contrast between the basement and the strata f 11 I Ing the coa I bas In. Basement genera I Iy compr I ses crysta I 11 ne rocks or more compacted sediments, whlle the coal host Is sedimentary with perhaps some Austral Ian Coal Geology 4, part 2

382

A.R.Dodds & J.E.Halgh FAULT

Figure 1

FAULT

Model Coal Basin.

lntruslves. Thus basement can be expected to show higher reslstlvltles and the basement contours can normally be mapped by resistivity methods unless It Is partlcularly deep. The I lthologles Involved In coal measure sequences are by their nature conductive. In Austral la these sedimentary sequences are often saturated by hlghly saline waters which lower the reslstlvltles to less than 1 ohm-metre. Coal may be more conductive or more resistive than the host sediments, dependIng partly on rank. Lignites are generally conductive, whlle black coal tends to be resistive. There may also be other resistivity variations within the sedimentary sequence, due to the layered structure. Fau Its have a var r ety of res I st Iv I ty express Ions, t he s Imp Iest be r ng an open and saturated zone of higher conductivity or a more resistive sll lclfled zone. Such a zone, If steeply dipping, would generally show a marked contrast with Its surrounds, being a sub-vertlcal feature In a generally horlzontal ly layered sequence. Fau Its can a Iso cause an offset In the Iayer Ing pattern, where there Is some vertlcal movement on the fault. For t h is to be observable there must, of course, be a stratification In resistivity, but such a contrast does not have to be between coal and other sediments. METHODS AND RESISTIVITY MEASUREMENT The galvanlc method of resistivity measurement, which has been used for many years, uses an array of four grounded electrodes, two of which are used to Inject current on to the ground and the other two to measure the voltage d I fference Induced by the current f Iow. CF Igure 2). The depth penetration Is a function of t he total separation of the electrodes and a resistivity sounding Is achieved by taking a series of measurements with vary Ing d I stances between the e Iectrodes. In very genera I terms the depth penetration Is about one quarter of jhe total electrode separation giving 25m penetration for a 100m electrode spread. The transient EM method uses a loop of wire lald out on the ground, an Inducing current being passed through the loop for a short period of time and then the response measured on the same loop (Figure 3). The response, which Is a direct function of the apparent resistivity of the ground, Is measured concurrently at a sequence of delay times after the cut off of the energising Austral Ian Coal Geology 4, part 2

A.R.Dodds & J.E.Halgh

383

current, these t I mes contro I I Ing the depth penetrat I on of the measurement. Thus a comp Iete sound Ing to a depth of 100 to 200 metres Is measured at one time without moving the loop, in about 3 minutes. The size of the loop can vary from 50 to 200 metres square, and determines the maximum depth penetration, which ls roughly equal to the size of the loop.

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Transient Electromagnetic Loop Configuration.

ADVANTAGES OF THE TRANSIENT EM METHOD The signal strength ls, to some extent, a measure of the sensitivity of the survey. With a Transient EM system, the greater the conductivity, the stronger the s I gna I and thus the more sens It I ve the survey becomes. This can be important, as resistivity features are sometimes very subtle. With a galvanic resistivity system the opposite applies, with a signal strength decreasing in more conductive areas, and a consequent loss of sensitivity. The need for Austral Ian Coal Geology 4, part 2

384

A.R.Dodds & J.E.Halgh .

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Figure 4 Slrotem Resistivity - Time Plot Line H1700 Leigh Creek Coal Basin, South Australia. Australian Coal Geology 4, part 2

A.R.Dodds & J.E.Halgh

385

electrlcal contact with the ground brings In other potential sources of noise to the galvanic method. Every Trans I ent EM measurement compr I ses a fu I I depth sound Ing, and can be achieved In about 3 minutes. Thus a TEM traverse yields a data set that shows al I resistivity variations In both horizontal and vertical directions. By contrast, a galvanic survey traverse, for similar speed, would yield only one proflle of data at a selected depth penetration, which puts severe I Imitations on the Interpretation of the data and Increases the I lkel !hood of missing features of Interest. The Interpretation of stratification Is well establlshed In the galvanic mode, with computer Inversion routines readlly available. While TEM Interpretation techniques are rather less wel I developed, direct Interpretation of two layer cases and model I Ing programs for the multl-layer ones are aval I able. An Inversion program Is expected to be available soon. However, TEM data Is at present llmlted In resolution to three layer cases, and It wlll require some extension of the Instrumentation facilities to allow more complex models to be resolved. The detection of faults, particularly where the fault zone Is conductive, Is a strong point of TEM resistivity surveying. Such features produce clear anomal Jes because of the flow of eddy currents In the fault zone Itself, thus providing an excel lent mapping tool for these structures. Even where the fault zone has no resistivity expression In It's own right the continuous sounding capablllty of TEM wll I Indicate an offset In horozontal resistivity features (whether coal or other sediments) to mark the presence of the fault. The resolution of a TEM resistivity survey Is control led largely by the size of the I oops used as Is that of ga I van Ic methods by the I ength of the array. The TEM loop size Is approximately, equal to the depth of the penetration expected, but the array I ength for a ga I van I c survey Is some four t I mes the depth of penetration. Thus the TEM survey should give better resolution by a factor of about four. Also the size of the TEM loop acts as a spatial averaging fl lter, which tends to remove noise genetrated by local, near surface features. This tends to Improve the survey resolution by Improving the signal to noise ratio. CASE STUDIES .Le.l.gh ~ ,SQJdb

Austra 11 a

Figure 4 shows the results of a survey llne CH1700) over the Leigh Creek coal basin In South Austral la. (This survey was conducted by Geoex Pty. Ltd. for the Electricity Trust of South Austral la, ETSA). At the top are the resistivity values obtained with Slrotem at Intervals of 50 metres. Below this resistivity time-distance section are the Interpreted coal horizons from a high resoltulon seismic survey conducted by the South Australian Department of Mines and Energy. The Slrotem reslstlvltles show the edges of the coal basin clearly by the sharp gradients at either end of the llne and the coal subcrop Is Indicated, at the southern end, by a smal I but consistent change In resistivity from about 4 ohm-metres to 6 ohm-metres, and at the northern end, In this generally more conductive area, by a much more subtle change In resistivity of only 0.3 ohm-metres above background.

Austral Ian Coal Geology 4, part 2

A.R.Dodds & J.E.Haigh

386

The cleanness of these data at the sout hern end is apparent. Figure 5 is a profile taken from Just one of the time-delay channels of Sirotem showing the consistency of the readings. North from 4000S the value is 4.4 ohm-metres for 6 consecutive stations when it only then changes by 0.1 ohm-metres. The conventional resistivity results In this area had a noise level around 2 ohmmetres. (Co I eman, pres. comm.).

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At the northern end of I ine H1700, the faults interpreted from the high resolution seismic survey are all clearly shown on the Sirotem resistivity results as lowL In some cases, the values of resistivity here are less than 1.0 ohmmetres and would generally be "no reading" areas for galvanic resistivity. At the only low zone (1750S), it is possible to Infer another fault from the se Ism Ic resu Its upon re-exam I nat Ion. (Ne Ison, pers. comm.). Thus the absence of resistivity lows such as the case at the southern end of the I lne can generally be taken as Indication of the absence of faults . ~ .6.a.slD

Coalfield, Queensland

Figure 6 is one I ine from a survey in the Bowen Basin of Queensland where a fault Is indicated In the coal seam by the low resistivity at station 125, and In fact, the coa I seam I tse If Is qu I te ev I dent by the depth- I Im I ted zone of high resistivity on either side of the fault. Also it is qualitatively apparent that the coal seam had been down-thrown on the eastern side and an interpretation of the depth to the top of the coal seam on either side of the fault verifies this and suggests a throw of 2 metres. Australian Coal Geology 4, part 2

387

A.R.Dodds & J.E.Halgh

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Figure 7 II lustrates one line of results from a Slrotem survey performed at Krabl, Thal land by Geoex Pty. Ltd. for the Electrlclty Generating Authority of Thal land (Chumroum and Corslrl,th l s volume). In this case the coal ls llgnlte and produces low reslstlvltles. Fault ing ln a higher resist ivity sequence ls also Indicated by vary i ng dept h to top to this formation as well as by marked vertical zones of low reslstlvltles at 500 Wand 740 W.

Bowmans CQa.1 Deposit, .5..Qu.tb. Austral Ja Figure 8 Is a geologlcal section across the Bowmans deposit near Pt. Wakefield, South Australia (courtesy of ETSA), showing the portion surveyed with Slrotem by Geoex Pty. Ltd. for ETSA. The Slrotem reslstlvltles (Figure 9) show a baslcal ly three layer situation with very low values In the middle layer corresponding to the sal i ne water-saturated coal measure sequence with the higher values Indicating basement beneath. The deepening of the basin to the west of th i s section Is evident. A quantitative Interpretation of the results by model I Ing three layers al lows the depth to basement to be wel I defined. Figure 10 shows the results of this analysis from three specific stations 1350E, 2050E and 2350E.

Austral Ian Coal Geology 4, part 2

A.R.Dodds & J.E.Halgh

388

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The closeness of flt to the measured values Is very good (note the large resistivity scale). Also the depths agree wel I with drl I I results. For example, at 1350E, where model I Ing gives 120m, the act ual depth Is 115m. As these evaluations can be made at every 50m station Interval, reserve estimates can be better defined than from the dr ll ling which has an average spacing of 500m. It Is also Interesting to see that boundaries deeper than 100m can be detected with a 100m x 100m transmitter loop In such a low resistivity medium. To define this Interface with conventional resistivity depth sounding would require a Schlumberger current dipo le of over 500m In length and would take at least one hour to complete. CONQ.USIONS In summary, resistivity mapping by Slrotem In coal environments has the necessary precision resulting from high signals to detect the often subtle variations which reflect subcrop and lnterformatlonal faulting. The data are also free from electrode contact noise and Improved by the spatial averaging of the large receiver loop configuration. As compared with the galvanic method, Slrotem depth Information can be obtained more quickly, Is freer from lateral effects nad has better penetration for a slml lar equipment weight. Australian Coal Geology 4, part 2

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391

Geotechnical Analysis of Coal Measures Strata by Downhole Sonic Logging K.J. Rosengren*, C.C.D. WI I I lams**, L.R. Grlmstone*** and J.M.

Gorman*****

* Golder Associates Pty. Ltd., Brisbane ** BPB Instruments (Austral la) Pty. Ltd., Brisbane *** Curragh Queensland Mining Limited, Brisbane **** Curragh Queensland Mining Limited, Blackwater ABSTRACT The paper desrlbes the appl Ication of high resolution sonic logging In the geotechnlcal evaluation of coal measures strata, with particular reference to the Curragh coal project, located In the Rangal Coal Measures In Central Queensland. Sonic velocity can be related to material hardness, In a slml lar fashion to seismic velocity, which has been used for many years In the evaluation of material excavation charaterlstlcs. The recently developed BPB multi-channel sonic sonde permits continuous high resolution sonic profiles to be obtained from small diameter boreholes, The technical specifications and performance of this equipment Is discussed. An essential requirement of sonic logging Is a f I u Id f I I I ed bore ho I e so that the son I c pu I ses can be transm I tted from the transmitter to the borehole wal Is back to the receivers. When logging above the natural water table, the borehole must be artlflclal ly ff I led and field problems associated with this requirement are discussed. A major program of sonic logging has been undertaken to obtain a broad picture of geotechnlcal conditions In the developing Curragh strip coal mine. This program ut 11 I sed an ex I st Ing program of open ho I e dr 11 I Ing on a 400m gr Id, carried out primarily for coal quality and reserve purposes. Drll I Ing costs for the geotechnlcal program were therefore minimal. Magnetic tapes from the geophysical logging were fed directly Into the Curragh computer data base and geophysical profiles, together with llthologlcal profiles from the data base, plotted by computer. The plots were produced as a series of longitudinal projections representing different stages of mining of the deposit. Geotechnlcal conditions at each stage of mining are therefore readily available for planning purposes. The sonic profiles were used to determine geotechnlcal data Including: definition of zones where blasting Is not required definition of powder factors where blasting Is required definition of soft floor zones which may Influence spoil stability or traflcabll lty. The program has demonstrated that geophysical logging Is a rapid and economical method for obtaining geotechnlcal characteristics over large areas and for defining areas where more specific geotechnlcal studies are warranted.

Australian Coal Geology 4, part 2

392

High Resolution Magnetics for the Delineation of Coal Seam Structure

R. Henderson, I. LII ly and T. Plppett

geoMetrlcs International Corporation, 18 Gertrude Street, Arne I lffe, Sydney, 2205

ABSTRACT The deployment of a high sensitivity geoMetrlcs magnetometer In a helicopter capable of flying slowly at close line spacings and at such low altitudes as 30 metres, enab I es very deta I I ed magnet I c da.ta to be obta I ned over coa I f I e Ids. The resu Its In the form of prof I I es and contour maps rev ea I subt I e expressions due to faulting and Intrusive dykes, as well as the more obvious features of I ntrus I ve s 11 Is and necks. Examp I es from the Hunter Va 11 ey and the Western Coal Fields of New South Wales Illustrate these points. The very high density of Intrusions In one area and the consequent extensive disruption of the coal seams are clearly demonstrated.

Australian Coal Geology 4, part 2

393

Exploration of Black Coal Subcrop Zones using Electrical Geophysical Techniques R.B. Murdoch Murdoch Geophysics (Austral la) 203 Main Road, Maroochydore, 4558 Austral la. Key Words: subcrop.

Geophysics, resistivity, SI Ingram electromagnetlc, black coal,

ABSTRACT Resistivity and electromagnetlc surveys over subcrop zones of black coal seams are capable of defining the extent of oxidation of the coal. Fleld examples are presented of both these types of electrical geophyslcal surveys In the Bowen Basin, Queensland and In the Hunter Valley of N.S.W. Results obtained by the SI Ingram type frequency electromagnetlc system using a Geonlcs EM 34-3 are similar to those obtained by resistivity proflllng, but are considered not as diagnostic as resistivity profiling. However successful Identification of deeper anoma 11 es requ Ires measurement and assessment of var I at Ions In the resistivity of near-surface layers. INTRODUCTION Since 1975 Murdoch Geophysics (Austral la) has been researching and refining the use of electrical geophysical methods, In particular resistivity methods, In coal exploration. In the past two to three years It appears that the method has become a very re I I ab I e gu I de to Iocat Ing coa I depos Its, mapp Ing coal seam structure and seam subcrop. With help from the Department of Natlonal Development, through a provision of a research grant, Murdoch Geophysics has now been able to complete a program of research In the method and copies of the ful I report are available. This report ff I Is a long felt need as project geologists have had a need for a working reference In the method, that they can study and understand. The resistivity technique has provided valuable data during the exploration and assessment of over ten Austral Ian black coal deposits, and the author Is not aware of Instances where It has missed a major fault or a seam subcrop. However, because of the need to meet specific budgets, problems can arise where there Is a lack of clear, precise survey objectives and/or subsequent feedback. The resistivity technique Is far too broad to cover In one paper. The purpose of this paper Is to solely discuss the use of the technique In coal seam subcrop mapping, as related to mine development plannlng. It Is assumed that the reader Is faml I far with the methods of resistivity data col lectlon, and with the basic theory of the method. TECHNIQUE Black coal Is a resistor, which under many circumstances can be mapped from the surface, provided other resistors not associated with the coal seams can

Austral Ian Coal Geology 4, part 2

R.B. MURDOCH

394

be filtered out. The apparent reslstlvltles recorded at the surface rise as either the total thlcknesses of coal Increases and/or the seam comes closer to the surface. A short three to four day feaslbl I lty study Is generally sufficient for an assessment to be made as to what coal seam and other geological parameters are likely to be mappable In a given area. COAL SUBCROP MAPPING Whilst fresh black coal Is very resistive, weathered coal on the other hand Is much more conductive. Across a coal seam subcrop apparent reslstlvltles are a maximum where the coal seam Is totally fresh. As the seam weathers, so values drop to reach a minimum where the seam Is totally weathered. A typical subcrop resistivity prof! le anomaly Is shown on Figure 1. The position on this profile, where the values are a maximum, Is called the "totally fresh coal position", and the position where the values are a minimum Is the "totally weathered coal posit ion". These are the two positions normally Interpreted from a subcrop proflle. The shape of the proflle grad I ent between these two po I nts Is genera I I y a ref I ect Ion of the shape of the weathering profile. Where the gradient Is smooth, the depth of weathering Is fairly uniform, but where It varies considerably, the depth of weathering Is usually variable.

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Australian Coal Geology 4, part 2

R.B. MURDOCH

395

weathering prof! le, and on the location of such features as oxidization windows Into the coal seam. Overal I, resistivity Is cheaper and faster for this type of work than Slrotem, and hence most of our work In subcrop mapping Is with that technique. At times, the author has used the very fast portable SI Ingram type frequency electromagnetic system (Geonlcs EM 34-3) to define subcrop. For the partlcular case history I I lustrated on Figure 1, the results obtained are slml lar to those obtained by resistivity prof! I Ing. However, overal I, It Is considered that this Instrument Is not as diagnostic as resistivity proflllng, and Its results can be misleading where stray anomalles due to near-surface conductivity variations Interfere with the anomal Jes from deeper sources. However, once the actual subcrop has been Initially located on a series of I Ines (say some 200 metres or so apart) using resistivity prof Iles, then the Geonlcs EM system can be used to map the subcrop Jn the detal I required, between the reference I Ines. To accurately measure subcrop using resistivity methods, we commonly use relatlvely small current electrode separations (50-100 metres), and a reading Interval of 20 metres or less. For transient electromagnetic methods, we suggest coincident 50 metre loops and readings at 25 metre Intervals. For the Geonlcs system a 40m separation between transmitter and receiver and a reading Interval of 10m has been used by the author. FIELD EXAMPLES Figure 1 Is an example of a typical fleld prof! le obtained over a subcropplng coal seam near Slngleton. The correlatlon between the resistivity and electromagnetic prof! les, and the drl I I Ing results Is plus/minus 20m Jn this case. This Is fairly typlcal of the type of results that might be expected In most s Jtuatlons. Figure 2 Illustrates examples of subcrop responses obtained over two separate coal deposits In the northern Bowen Basin of Queensland. Example (al shows the typically sharp weathering gradient that Is commonly associated with the subcrop of thick seams. The 100% fresh coal position Is at 180E, and the 0% fresh coal position Is at SOE. Examp I e (b) Is typ Iea I of the type of prof 11 e recorded over a coa I subcrop, where there Is conslderable variation Jn the weathering prof! le. Ori I !hole 01, for Instance, Intersected 2 metres of fresh coa I at 40m. Both the extent of the sma r I b Iock of fresh coa I Intersected In Dr I I I ho I e O1, and the approxlm~te shape of the weathering profile between Holes DH03 and DH05, can be seen from the profile drawn. In areas of fairly complex subcrop, electrlcal geophysical methods become a very attractive method of defining whether smal I blocks of fresher coal, or oxidization w Jndows occur. They can be used to extrapolate between drll I holes, and help Improve the positioning of the box-cuts for an open-cut mine. Figure 3 Is a typical resistivity contour map which Illustrates the effect of a large oxidization window on the subcrop response recorded on several I Ines. The example Is from an area In Central Queensland.

Austral Ian Coal Geology 4, part 2

396

R.B. MURDOCH

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Australian Coal Geology 4, part 2

397

R.B. MURDOCH UNe

UNE

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Figure 3 Contoured resistivity plan showing oxidation window and subcrop response. In a multi-seam situation, where several seams occur very close together, the subcrop response of thinner seams can sometimes be suppressed by the effects of deeper, thicker, more predominant seams. Figure 4 Is an example of a resistivity and an EM 34-3 electromagnetic profile conducted over a series of subcropping seams occurring either side of an anticline near Muswellbrook In the Hunter Va I I ey. The ax Is of an ant I c I I ne occurs near the centre of the traverse I Ines. In this particular case, the electromagnetic profile has been used to define subcrop. The res I sti v Ity prof I Ie, wIth a wI de (r) separat Ion of 200 metres, was used to map structure. Therefore, only the electromagnetic prof lie wll I be discussed in detail. The central high resistivity area of the electromagnetic profile is a reflection of the presence of the thick Bayswater seam at shallow depth, over the axis of the anticline. The gradually lower apparent resistlvitles either s I de of the ant I c I I ne bas I ea I I y ref I ect the gradua I deepen Ing of that seam. Three thinner seams are known to subcrop on each I lmb of the antic I ine. On the left hand side, seams B, C, and D, al I close together, tend to form the one resistive anomaly from K3 to halfway between K4 and K5. The subcrop of the very thin Seam A ls not evident. On the right hand side dips are flatter, and Seams A1 and B1 are man I tested by changes or f I atten Ing of the grad I ent

Australian Coal Geology 4, part 2

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associated with the gradually deepening, dominant Bayswater Seam. Seam C1 1s subcrop causes another change In shape, but overal I Its response Is much clearer, not because the seam Is any thicker, but because the dominant Bayswabter Seam Is deeper. Basically In any multi-seam situation, the subcrop of the major seam Is easier to locate than the subcrop of the minor seams. In areas where the subcrops of several seams occur close together (I.e. say within 20ml, the subcrop of each lndlvldual seam may not be separately resolvable. They may, In fact, be Integrated Into one subcrop anomaly. CONQUSIONS It Is possible to use very detailed narrow current electrode separation resistivity and electromagnetic prof II Ing to Initially locate, and then fol low, black coal seam subcrop zones. It Is possible to approximately determine the 100% fresh and 0% fresh coal positions to an accuracy of plus/minus 20% In most cases, for final planning of open-cut mines. It Is also possible to locate either Isolated blocks of fresh coal, or areas of locally deeper weathering (oxidization windows) within the subcrop zone. Subcrop mapping by electrical methods requires some caution with respect to the following two factors. The successful Identification of deeper anomalies requires measurement of variations In the resistivity of near-surface layers and assessment of their effects on the Interpreted profile. In a multi-seam situation, the subcrop of smal I seams can be either partially or totally suppressed by large anomalies generated by the subcrop of major seams. Where several seams subcrop close together, they may In fact, be lntergrated Into a single subcrop anomaly.

Australian Coal Geology 4, part 2

400

Standardisation of Geological Data in Coal Measures C.W. Mallett* and C.R. Ward** * CSIRO, Division of Appl led Geomechanlcs PO Box 54, Mount Waverley, Victoria 3149 Austral la ** New South Wales Institute of Technology PO Box 123, Broadway, Sydney, 2007, Austra 11 a Key Words:

Bore logging, Coal Measures, Standardised llthologles

ABSTRACT The Increase In e Iectron Ic storage and man I pu I at I on of geo Iog Iea I data has highlighted the necessity for standardisation of rock descriptions. The current procedures for geological bore logging are reviewed and the case put for standard reference manuals for Austral Ian coal measure sequences. The appl lcatlon of these In coal measure studies Is discussed. INTRODUCTION The co I I ect I on and I nterpretat Ion of a w I de range of geo Iog Iea I data Is the starting point for the discovery, delineation and evaluation of a coal resource. Once the resource Is proven adequate, however, such data are also used as the basic framework for mine design and operation. Terminology and classifications used to describe rock types and structures can be based on genetic or other Interpreted concepts rather than descriptive features. Each geologist generally has personal preferences In the use of classifications and descriptive terms. Where several geologists are Involved In col lectlng data In a single program, Inconsistencies usually develop. Disagreement between geologists on fundamental questions such as the names of rocks, creates confusion among other professionals with whom the geologists are associated. This paper reviews the methods available to coal geologists to record basic geological data, with emphasis on those methods that reduce ambiguity In sedimentary terminology. It describes a systematic approach to the problem of establishing consistent terminology for sedimentary materials In field studies, Involving the comp! latlon of photograph lea I ly 11lustrated catalogues of representative rock specimens. STYLES OF DESCRIPTION Geologlcal descriptions may be recorded as free prose or In a systematic format. The free prose form has been trad rt Iona I I y used for record Ing bore logs. Detar Is of each stratum are recorded using words or abbreviations. This Austral ran Coal Geology 4, part 2

C.W. MALLETT & C.R.WARD

401

method offers great flexlbl I lty, and al lows a precise description of al I features. Usua I I y the geo Iog I st wr I tes out the Iog on s I te w Ith subsequent transcr I pt I on by a typ I st for reports. A tape recorder Is somet I mes used to record the orig Ina I descriptions. The flexlbl I lty of free prose Is both Its greatest potential strength and weakness. The geologist Is free to range broadly or be as specific as he likes. Guldellnes may be given Indicating the mIn I mum data to be recorded, but the qua 11 ty of data depends on the geo Iog I st 1 s judgement, enthusiasm and competence. Common deflclences In this recording style are: Oversights of Important features Undue emphasis on Irrelevant characteristics Omission of commonly occurring characteristics which are only recorded occasionally to avoid repetition In practice, some formatting of descriptions Is always used, even If the geologlst has a free hand, as logging a repetetlve sequence such as coal measures, generates an I nterna I framework of prompts, around wh I eh descr I pt I ons are based. Vlrtual ly all coal measure fogging today uses formatted check llsts. These are des I gned to cover the s I gn If I cant features expected to be encountered or to record specific characteristics. The formats vary from slmple prompt lists to detalled tabulated forms with comprehensive mnemonic descriptors, or sheets w Ith opt I on boxes. In the acq u Is It I on of genera I purpose data, a great many detalls must be recorded. For example, coal exploration borehole data must be adequate to assess the quantity and qua I lty of coal resources, for basin analysis to assess exploratlon targets, and to provide the basis for mine planning and geotechnlcal analysls (Figure 1). The fll led In tables and sheets may constitute the log In their own right, or In a decoded prose form. Data are genera 11 y entered Into a data bank by a computer encoder. It can be done automatlcal ly by machine-readable forms, or by the geologlst using portable recording devices which interface to large computer systems. ELECTRONIC DATA STORAGE The advantages of machine processing geologlcal borehole data has led to Its widespread adoption by the Industry. Many systems have been developed, based on the needs of the user, computer hardware avallable, and the priorities of system designers. They range from specific purpose developments (Barton, this volume) to addendums to mine planning packages where geological data for each depth Interval are forced Into three digits. This has provided an Impetus for the formatting and standardisation of descriptions In a form appropriate to the aval I able computer technology. The constraints placed on formats are related to the capacity of the central processing unit, and the trade off between processing efficiency and friendliness to the user. Large computers can easily cope with free prose formats and such a system Is In use by the State Electrlclty Commission of Victoria. These systems require large I lbrarles of acceptable geological descriptors, to encompass al I I lthologles. In the case mentioned, approximately 10,000 descriptive phrases are used. For reasons of economy, more efficient processing systems that require pre-structured data are generally favoured, which can be supported on minicomputers. Most systems use a tabulated format with a I lmlted variety of

Austral Ian Coal Geology 4, part 2

C.W. MALLETT & C.R.WARD

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LN11NATED 60 40 . SANDSTONE : LIOHT OREY BROWN, FINE AND l'tEDIUt'I QRAINED , l'IICACEOUS, LtTl-0-FELDSPATMIC, SPARSE OBLICtUE JOINTS, SHARP OBLICtUE BASE1 LOW ANOLE CROSS BEDDIN0 1 DISTURBED BEDDIN01 COtV10N THIN COALY LAl'IINAE , CAR BONACEOUS REMINS1 SECONDARY QYPSUN1 ON JOINTS. SILTSTONE : DARK QREY1 THINLY LAl'll~TED 1 ADDITIONM... FEATURES INCLUDE : l't lC RO FAU..TJ,.,0, ROOT TRACES,

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Fi gure 1 Typical coding sheets with decoded log utl I I sing tabulated columns and mnemonics (courtesy Earth Science Computer Services Pty Ltd Austral Ian Coal Geology 4, part 2

C.W. MALLETT & C.R.WARD

403

mnemonic responses for particular characteristics. The range of choices given In such forms as Figure 1 cover most logging requirements. Small microcomputers are now capable of handling all the processing required by a mine geology group, as wel I as mine planning and stab I I lty analysis programs. The low cost of these machines allow them to be entirely dedicated to a single purpose, and although much slower than big machines, perform at a satisfactory rate for most working situations. Mai lett and Bonner (1981) reported a microcomputer based bore coding system capable of Incorporating data from free prose or formatted logs. SYNTHETIC LITHOLOGIES Many coal programs aim to maximise exploration coverage by reducing expensive cor Ing and subst I tut Ing geophys I ea I Iogg Ing In cheaper open ho I es. To some this Is a welcome slmpl lflcatlon which gives the critical data on I lthologlcal distributions, without al I the comp I !cations of detal led geologlcal logs. Synthetic I lthologles can be generated from geophysical logs by rule of thumb comparison of a number of different logs. The process Involves a few manipulations on a I lmlted data set, with a smal I group of end point I lthology options. It can be performed by machine, to obtain an apparently unbiased I lthologlcal description. The llthologles obtained are only as good as the conceptual models upon which the ana I ys Is Is based, but In pract Ice the I nterpretat Ion prov Ides adequate qua I I ty of data for exp Iorat I on purposes. Its great v I rtue Is that It Is standardised for particular geophysical rock responses and provides a basis for correlation between boreholes. It Is clear that standardisation of description of rock Is necessary If maximum benefit Is to be gained from the processing and analysing facilities now available. Operators are prepared to accept a much lower level of Information to achieve standardisation. In many appllcat I ons, the cons I stency of data makes It more usef u I than convent Iona I core Iogg Ing. The synthet Ic 11 tho Iog Ies Interpreted are, however, on Iy approx Imat Ions based on Idealised models selected from the enormous range of naturally occurring rock characteristics. STANDARDS FOR LITHOLOGICAL DESCRIPTIONS Logg Ing of dr 11 I cores by e I ther free prose or a formatted techn I que st 11 I depends heavily on the concepts and criteria used by each geologist for ldentlflng and naming the various rock types, textures and structural features. Because of the diversity of materials and geological needs, no uniform code of llthologlcal usage has been practical within sedimentary rocks. Within Austral la however, the need for standards has resulted In active discussion and attempts to have guidelines for operating geologists and engineers. Attempts have been made by the Standards Association of Austral la (1970) and the standIng committee on Coalfleld Geology of New South Wales (1969) to deal with this problem. Cr I ter I a for descr I b Ing rock strata from a geomechan I ea I po I nt of v I ew are discussed by the Geologlcal Society Engineering Group (1970), International Society of Rock Mechanics (1980) and the Austral Ian Geomechanlcs Society (1982). Although these have the advantage of Incorporating quantitative aspects such as rock strength and fracture spac Ing, they are very genera I In scope. A more specific set of geotechnlcal criteria, relevant at least to Austral Ian Coal Geology 4, part 2

404

C.W. MALLETT & C.R.WARD

much of the New South Wales coal Industry, Is given by McMahon .et .aJ.. (1975), but this does not address the basic problem of ldentlflng and describing visible features of the rock Itself.

CONSISTENCY IN LITHOLOGICAL TERMINOLOGY In order to assess the variation In terminology used In describing coal measure rocks, an examination of drll I core was conducted In December 1980 by the Standing Committee- on Coalfield Geology of New South Wales. Coal geologists Involved were experienced personnel from both private and government organisations. They were asked to describe a series of core specimens In the same manner as If the material had been encountered In a borehole. They were given no prompts as to which features were to be described or the level of detail to use. Seven llthologles were represented and each participant described at least one spec I men from each I I tho I ogy. The results are summarised In Figure 2, which gives an Indication of the number of geologists who would normally note any particular feature, and the number of different terms which might be used to describe the features observed. Further details of the range of terms used Is given and some of the specimens are Illustrated In Figure 3. Trends In description for various characteristics are discussed.

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The rock type, or In some cases the mixtures of rock types, Is the only feature noted by all participants for all samples. However the only specimens on which unanimous agreement Figure 2 Bargraphs of the percentage was achieved were sandstones. Al I of participants describing each featother materials were described by a ure In each lithology and the ratio diversity of I lthologlcal terms, with of the number of terms used for each the degree of diversity greatest In feature to the number referring to the lnterbedded arenlte/lutlte that feature In descriptions samples. Terms such as mudstone, siltstone and claystone appear to be used lndlscrlmlnately, despite the fact that clear definitions of these terms are laid down by the Standing Committee. The colour was noted by almost all participants. Colour Interpretation Is very subjective, but differences can be minimised by use of the rock colour chart prepared by the Geological Society of America (1948) or the Munsel I Sol I Colour Chart (1975). These are Incorporated Into the formatted prompting systems described by Goscombe .et .al. (1977). Austral Ian Coal Geology 4, part 2

C.W. MALLETT & C.R.WARD

40:5

Particle size was noted by almost al I when describing sandstones, but by few In finer grained rocks. The degree of diversity In grain size description Is relatively low for sandstones, and high In other materials, but this reflects the small number of participants that noted particle size at all in llthologles other than sandstone. Llthologlca l adjectives chiefly noting petrographic composition were commonly used with respect to sandstones, but were also used to describe unusual features In finer grained rocks. The diversity of terms used to describe rock mater I a Is Is h I gh In a 11 cases. It Is I ow est In the sandstones, but even In these the one specimen was described with such confl lctlng terms as 1 1lthlc' and quartzose or 'calcareous' and mlcaceous 1

•

A wide diversity of terms were used to describe sedimentary structures, especlal ly In the lnterbedded materials. Terms such as 'slumping', 'Irregular bedding' and 'disturbed bedding' were used Interchangeably, despite each hav Ing a c Iear Iy d I fferent mean Ing. Very few made spec If Ic reference to bed th I ckness, wh 11 e none commented on the presence of b I oturbat I on such as In specimen C, Figure 3. Except for mudstones where 60% of participants commented on the strength or fracture character I st Ics, I ess than ha If of the part I c I pants ment Ioned the mechanical properties of the rocks. PHOTOGRAPHIC REFERENCE MANUALS Photographs of dr 11 I cores have been used In the Austra 11 an coa I Industry for many years as a means of I I lustrating the descriptive geological records. Normally the opened core boxes are photographed with scale and bore location details clearly Identified. The photographs are attached to reports and used by geologists, engineers and other specialists to assess the descriptive logs with respect to their particular Interests (Pauncz and Holt, this volume). Photographs of particular rock specimens, representative of lithologies in the sequence being Investigated, can also be used as an aid to the actual logging process. If the cat a Iogue Is based on a comprehens I ve survey of the strat !graphic sequence in the area concerned, each unit In the hole can be checked against a corresponding photograph to obtain a standardised I lthological designation. The use of such photographic catalogues In the coal Industry was first described by Melton and Ferm (1978), and several such comp I latlons for American coalfields have been published In book form since (Ferm and Melton, 1977; Ruby .!rt _gj_. 1981). Others have been comp! led In a more I lmlted way for In-house use by Individual coal exploration companies (Lehmann, 1978). One of the initial objectives of such catalogues In the U.S.A. was to assist in obtaining reliable geological descriptions by drillers, engineers and field ass I stants. The cata Iogues were set up to Inc I ude a s Imp Ie numer I ea I code that enabled easy computer data processing. The eye is remarkably precise as a comparative tool, and Is much more rel lab le than subjective verbal descriptions. Interpretations by one lndlvidual of the words used by another to describe his concepts of what he thought he saw is a tenuous I ine of communication. Photographs short circuit this process, and exploit the geologist's visual comparative skills. Australian Coal Geology 4, part 2

406

C.W. MALLETT & C.R.WARD

ROCK TYPE

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Grey

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1 Muds tone/ conglomerate 1 Breccia

Figure 3 Summary of Survey Responses and I I lustratlons of some specimens Australian Coal Geology 4, part 2

C.W. MALLETT & C.R.WARD

3 Medium 3 Medium

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407

STRUCTURES

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Figure 3 -continued Austral fan Coal Geology 4, part 2

Massive

C.W. MALLETT & C.R.WARD

408

Standard lltbologles For this process to be effective the standard set of llthologles for comparison must satisfy stringent conditions. Be representative of the total I lthologlcal variation In the area of Interest. 2 Represent the naturally occurring ldentlflable llthologles rather than adhering to some conventional llthologlcal classification which may be Irrelevant to a particular sequence. If this Is not done users are frustrated by having to choose between a number of unsatisfactory options. 3 Reflect the current concepts of professlonal geologists that govern the way they differentiate llthologles. 4 Be slmple enough to be usable and acceptable. 5 Be complex enough to support the variety of purposes for which geologlcal records are needed. Thus the process by which the reference set Is estab l ished Is crltlcal to Its effect Iveness. There are a number of groups In Austral la curre ntly Involved In In the construction of reference I lthology manuals, and they are al I baslcal ly fol lowing the procedures used by the American workers. After an area of Interest has been delineated, complete cored holes distributed throughout the area are sampled at each change of llthology. As not everyone agrees on points of I lthology change, sampl Ing Is conservative, and done for doubtful Intervals also. Enough bores are examined to ensure complete coverage of llthologlcal types, that Is, untll no new I lthologles appear In boreholes. While sampllng Is proceeding, specimens are continually grouped Into slmllar llthologles and resorted until there Is a consensus view that the best llthologlcal groupings have been obtained. This process del lneates some distinctive groups and others where there Is a gradation between distinctive end members. The process of sampling Is painstaking, t ime consuming and not very exciting, but Is essentlal If comprehensively representative groups are to be obtained. The divisions are based entlrely on observed slml rarities and differences between specimens and not on preconceived rock classlflcatlons. These groups represent a consensus view of the recognlsably different llthologles present, reflect current geologlcal practice, and thus conform In a broad way to the tradltlonal I lthologlcal breaks.

Two pi lot areas have been chosen to compare the llthologlcal variations within and between different coal measure sequences of the basin. They are the Bara I aba Coa I Measures between Theodore and Bara Iaba and the Moran bah Coa I Measures between Goonyella and Norwich Park. The Baralaba exercise was conducted by CSIRO, Division of Appl led Geomechanlcs, and utll lsed sixteen fully cored ho I es a Iong the str Ike I ength of 80km. Each con ta Ins at Ieast 300m of coal measures, with varying lengths of overlying and underlying sequences In addition. These resulted In approximately 5000 specimens which have been sorted and representative samples photographed. Sampling from cores within the Moranbah Coal Measures Is continuing, concentrating on sections near the present surface mining developments. This Is being done by the Utah Development Company and CSIRO, and to date about 2500 samples have been sorted. These Austral Ian Coal Geology 4, part 2

C.W. MALLETT & C.R.WARD

409

surveys are being conducted with the cooperation of the Queensland Geological Survey, who provide facl I ltles for core storage, Jogging, and logistic help .

.5.¥.dn.e.¥ .6a.s1ll Two projects are underway In the Sydney Basin, with sl lghtly different emphases. A Department of National Development fu nded project at the New South

Wales Institute of Techno logy Is lnltlally concentrating on the Western Coalfleld. It Is utl llslng fully cored holes of the New South Wales Department of Mineral Resources, at relatively close spacing. This project wlll later extend Into laboratory studies of the geomechanlcal properties of the Individual llthologles. To date about 2000 samples have been collected from eleven boreholes, located from Bel I In the southeast to Kelgoola and Nandoura In the northwest. The samples cover the entire sequence of the II lawarra Coal Measures at each locallty, and as much of the ad j acent Narrabeen and Shoalhaven Groups as have been recovered In the cores. A classification of the llthologles based on work to date Is given in Figure 4. CLASSIFICATION and DESCRIPTION of SEDIMENT ARY ROCKS in the WESTERN COALFIELD ROCK TYPE

STRATIFIED

I .QISTINGUISHING CHARACTERISTICS

MASSIVE

RUDITES

Bedded Conglomerate

Massive Conglaaerate

MIXED RUDITES

Conglomerate with Sandy Bands

Conglomerate, Sandy

and ARENITES

Particles > 2am in diameter provide > 25\ of the structural framework of the rock Textural Descriptors Boulder > 256 mt Cobble : 64 - 256 m Pebble 4-64-mm Granule : 2 4 mm Minera l ogical Descr iptions Dominantly (?uartzose Dominantly Lithic

Particles > 0.06 1r1r1 in diameter provide > 25\

Sandstone with Pebbly Bands

Sandst one , Pebbly

of the structu r al framework of the r ock Textur a l Descriptors Very Coarse Coarse Medium

Sandstone ,

MIXED ARENITES

and LUTITES

~-- - - ---- -------- --- ~---------- ------~ Bedded and/or Cross Bedded

ARENITES

) F

) Gra..1;ewor Dominantly Feldspathic ) ra n•

1.0 - 2.0 ffll!'I O.S - 1.0 mm 0.25- 0 . 5 11'111

0.12 - 0.2Srrn 0.06- 0 . 12nn

Fine

t-- - - - - - - - - Sandstone, Minor Shaley/ Sil ty/Coaly, Bands/I,&minae/ Clasts/Lenticles

Very Fine

Massive Sandstone

Mineralogical Descriptors Framework Grain s:

Dominantly nuartzose/Li thic/Feldspathic !tatrix: Argillaceous/Ferruginous/Sider itic/Calcareous/

Interstratified Sandstone/ Shale

Siliceous/Micaceous/Carbonaceou s/Tuffaceous (?)

~~~ kd!liPg_C~~~ InterstratHied Shale/ Sandstone Regular Bedding Contorted

: :

- Silt~,;;-) ~~~;:::e

~ Sandy

IIP-a r_ti_c _le-, -, - o-. 0-. -..,, - in_ d_ i_ame _ t_e_r -pr-ov - i-de_ a_ p-pr-ox--1. 75\ of the structur a l framework of the rock Textural Descriptors Silt Sir:ed Clay Sized

Siltstone

LUTITES

0.06 - 0.04 m <O . 04 11'111

Mineralogical Descriptions

Shale

Regular

Contorted

Bedding

Hudstone

General Appearance:

Cherty, Pyritic Claystone Matrix:

l======-➔--------,...--+--=====--=-=-=-fl ~!~!~~:°;:~:~~:~°'::~:!:::1~;~/Calcareous/ Shale with Coaly)

COALY LUTITES

MIXED LUTITES

and RUDITES

Siltstone )

) Bands/ ) )

Shale with

)

Carbonaceous

)

Laminae/ Lenticles

)

Mudstone

)Carbonaceous )

Claystone )

Pebbly (Gritty) Mud.stone; including P~roclastic(?) Muds tone with Pebbly Bands

~e~i ~ _ _ _ _ _ Conglomerate with abundant Silty or Clayey Matrix

Regular - Cross-Bedded and Rippled- Roo t ed - Burrowed-Churned-Slumped-Conto rted

Austral Ian Coal Geology 4, part 2

410

C.W. MALLETT & C.R.WARD

The second project ls being conducted by the Earth Resources Foundation, University of Sydney and the Coal Strategy Group of the Department of Mineral Resources. They are conducting a basin-wide reconnaissance using widely separated boreholes In al I the coal measures to assess the degree of variation of llthologles throughout the basin. The Immediate roof and floor of coal seams are not usually available for the Sydney Basin cores. APPLICATION There a number of potential uses for these manuals In coal measure studies . .QQil logging

Cons I derab Ie core I ogg Ing Is st 11 I be Ing done desp I te the Increased use of geophysical logging In exploration programs. The major purpose of the exercise Is to provide a means of standardising the descriptions of similar rocks. The explosion In electronic data storage and manipulation demands consistency In terminology, or much of the benefits of this facl I lty are lost. As II lustrated earlier, three men's siltstone ls another's lnterbedded claystone/sandsto ne. It ls only when the data In the computer systems ls consistent that It can be fully exploited. As It ls quicker and easier to make rel fable comparisons rather than numerous descr I pt I ons, the data obta I ned by Iogg Ing wIth these booklets Is not only better, but ls obtained much faster. There are only a limited number of llthologlcal variations, and only simple codes are needed to describe the complete variation observed In a coalfield. They can be Incorporated very easily Into any existing core coding system, as It suits each user. A three or four digit code has been developed for some of the Austral Ian manuals, along the same lines as the American booklets. Geomechanlcal assesslllfillI Intact rock strength properties and dlscontlnultles control the overall rock mass properties needed for mine planning. After establ lshlng the range of Intact rock properties within each I lthology, composite values for potential mine sequences can be developed from coded logs. Geophysical callbratJons The I nterpretat Ion of synthet Ic I Itho Iog Ies from geophys Iea I Iogs Is a gross slmpllflcatlon of the potential causes for a particular set of responses. If the I Imitations on the varieties of rock that wll I be found are known, and the characteristic responses already documented, It wl II be possible to refine the Interpretation and generate more reliable synthetic rock sections.

B.as.I1l Analyses Analyses of trends within basins wll I be simplified when workers are confident that the data they are processing Is consistent. This opens the way for regional studies to predict I lkely economic coal occurrences, environmental analyses to assist mine planning (Boyd, this volume), and basin syntheses of characteristics such as geochemical trends, provenance and thermal effects.

Austral Ian Coal Geology 4, part 2

C.W. MALLETT & C.R.WARD

411

ACKNOWLEDGEMENTS Many geologists have contributed to the core logging work described In this paper, and particular reference ls made to Dick Britten and Jenny Thompson for assistance with the survey, and Harry Bowman and Graham Holt for subsequent review of the results obtained. The work has been stimulated by Professor John Ferm of the University of Kentucky, during his visit to Austral la. The projects have been partially supported by the National Energy Research, Development and Demonstration program of the Department of National Development. John Comlno and Michele Tosatto have worked on the classlflcatlon of rocks In the Western Coa If I e Id where cores have been prov I ded by Austen and Butta Ltd., CI utha Deve Iopment Ltd., Coa Iex Pty Ltd., the EI ectr Ic Ity Comm Iss l on of N.S.W. and the N.S.W. Department of Mineral Resources. Cores from the Bowen Basin have been made available by the Geological Survey of Queensland and Utah Development Company. Dr V.V. Nguyen, N. Lindsay, A. Davies N. Godfrey and students from the Queensland Institute of Technology have been Involved In the sampling and sorting. REFERENCES Austral Ian Geomechanlcs Society, Victoria Group, 1982, Workshop on geotechnlcal logging of boreholes Proceedings, Aprl I 21st,1982, Institute of Engineers Austra I Ia, Parkv I I Ie. Ferm, J.C. & Melton, R.A., 1977, A Gulde to cored rocks In the Pocahontas Basin, Department of Geology, University of South Carol Ina, Columbia, 90 pp. Geological Society Engineering Group Working Party, 1970, The logging of rock cores for engineering purposes, .Q... .J.... Engineer . .G.i!Qh .3., 1-24. Geological Society of America, 1948, Rock Color Chart, Geological Society of America, Boulder, Colorado. Goscombe, P.W., Coxhead, B.A. & Brandt, B.A., 1977, A computer based GEOLOG/ ASSAYLOG system for coa I exp Iorat Ion and eva I uat Ion. Proc. Austra Ias. lnstlt. Min. Metal I. Symp. Coal Borehole evaluation, Brisbane, pp48-62. Horne, J.C., Ferm, J.C., Carucclo, F.T. & Baganz, B.P., 1978, Deposltlonal models In coal exploration and mine planning In the Appalachian region. lliilL. .Am...~ Petrol, Geol~ . .6.2,2379-2411. International Society for Rock Mechanics, 1980, Basic geotechnlcal description of rock masses. Intern, .J.... RQ.d M ~ .Ml.lh. k.L. .G..e.om.e.c.h.a..n.... Abstracts .1.8,85-110. Lehmann, R.J., 1978, Appl !cation of core logging technique for standardising descriptions and slmpl lfylng computerisation of data. Proc. 2nd Symp. Geology of Rocky Mountain Coal, Colorado Geol. Survey, 149-152. Mai lett, C.W., & Bonner, G.W., 1981, A basic program for bore log coding of coal measure sequences using microcomputers . .c.sJRQ A.u..s.1.. .lll.Y.,_ ~ Geomechan,, Geomech. ,CQ,aJ. .MJ..n.... .88.lh .3.1, 1-16. McMahon, B.K., Douglas, D.J., & Burgess, P.J. 1975, Engineering classlflcatlon of rocks In the Sydney Area . .A.u..s:t.a. Geomechan, ~- pp 51-53. Austral Ian Coal Geology 4, part 2

412

C.W. MALLETT & C.R.WARD

Me Iton, R.A. & Ferm, J.C., 1978, Photo-book construct Ion and computer ass Isted procedures for asslmllatlo n and preparat ion of core data. Proc. 2nd Symp. on Geology of Rocky Mountain Coal, Colorado Geol. Survey, 143-148. Munsel I Color Co., 1975, Munsel I sol I colour charts, Macbeth Dlv., Kol lmorgan Corp., Baltimore, Maryland. Ruby, C.H., Horne, J.C., & Reinhart, P.J ., 1981, Cretaceous rocks of western North America: A guide to terrlgenous elastic rock Identificat ion. Research Planning Institute, Columbia, South Carolina, 100 pp . Shelton, J.W., 1963, Measured sections of sandstones and shales . .B..u..l..L. hm.... ~ Petrol, Georog. A1C12l, 2047-50. Standards Assoc I at I on of Austra I I a, 1970, Symbo Is for the graph Iea I representat ion of coal seams. Austral Ian Standard K183, 8pp. Standing Committee on Coalfield geo l ogy of N.S.W., 1969, Report of the Subcomm I ttee on Sed I mentary Term I no Iogy. ~ .G.e.oL. ~ N...S..~ .UC2), 109114.

Thomson, J., 1979, COALBOR coding manual, 3rd edition, .G.e.oL. ~ ~ .M..Ln.e.s. .D..eil.1 ~ GS]979/067,32pp., Cunpubl.l.

Australian Coal Geology 4, part 2

413

Geostatistical Applications in Brown Coal Resource Investigation C.M. Barton, A. Dubrovich and R. Webster

Exploration and Geological Division, Fuel Department, State Electricity Commission of Victoria, 15 William Street, Melbourne, Victoria, 3000 Australia.

Key Words: Geostatistics, Brown Coal, Sodium Percentage

ABSTRACT Geostatistical methods are being tested and applied by the State Electricity Commission of Victoria in brown coal resource investigations of the Latrobe Valley coalfield. An outline of the background, the adopted procedures and some results of the preliminary studies are described . Initial studies of the Flynn brown coal show that the sodium content of the brown coal increases upwards at distinctive rates which differ in different seams . A comparison is made of the reliability of the kriged estimates of the sodium content and the net wet specific energy of brown coal samples derived from 400 metre and 1200 metre spaced bores; the 400 metre grid is shown to produce much more reliable estimates . INTRODUCTION The Exploration and Geological Di vision of the Fuel Department of the State Electricity Commission of Victoria (SECV) conducts brown coal resource investigations for electricity generation and other purposes. In recent times attention has been directed towards the development of geostatistical methods for application in the brown coal resource studies. The stage has now been reached where two- and three-dimensional geostatistical kriging programs have been prepared for operation on the SECV Amdahl 470/V78 main frame computer . The geostatistical techniques have been applied to provide input data to a study into the quality of salty brown coals, in the Flynn area of the western Latrobe Valley, where extremely thick readily accessible coal deposits have been defined (Gloe, 1979).

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414

THE NEED FOR GEOSTATISTICS IN THE BROWN COAL RESOURCE INVESTIGATIONS Brown coal is a low grade fuel which is very sensitive to minor variations in properties . As a consequence, it is necessary to define the variability and spatial dispositions of the significant properties in order to assess the behaviour of the coal during utilisation. The application of geostatistics can provide important information on both coal property parameters and sampling adequacies . Raw data on Victorian brown coal is derived, almost exclusively, from drilling. In the first instance, drilling is on a spacing of around one-two kilometres to define the broad stratigraphy and the general extent and properties of the brown coal. Drilling on a much closer spacing is necessary to quantify the characteristics of the brown coal to a level which is satisfactory for utilisation purposes . Up to the present time, only comparatively uniform quality coal has been used in the major power stations and any feedback from actual utilisation behaviour, in relation to adequacy of prior quality definition, has been restricted by these limitations . Despite the great effort and care which have been given to the laboratory testing and associated predictions of coal utilisation behaviour it is apparent that, prio r to the availability of geostatistical methods, assessment of drilling information for quantification of coal quality in future open cuts, has been necessarily dependent upon In order to improve the quality empiricism, judgement and experience. predictions, initial studies in applied geostatistics have been undertaken. An outline of the background procedures and some results of these preliminary studies are described in this paper . BASIC THEORY Only the very basic theory will be discussed here. For detailed mathematical derivation and proof of the underlying theory the references listed in the bibliography should be consulted. The essential aim of geostatistics, as applied to coal resource studies, is by taking into account spatial distribution characteristics to estimate: (a) (b)

the most likely values of coal-block characteristics; the errors of such estimates.

The main tool used in geostatistics is the semi-variogram, consisting of the average of squared difference between values for given spacing. This is used because ordinary statistics are inadequate to describe a coal body fully. For example, the drawing of histograms ignores spatial characteristics. The importance of the spatial arrangement can be seen from the following example presented by Royle: Suppose we had the following group of values for coal thickness in bores 200 m apart 3, 5, 7, 9, 8, 4, 2 and 9, 3, 8, 2, 6, 5, 7, 4 Clearly, they both have the same mean and variance; however, their spatial di stri but ions are not the same . This is shown by the difference between adjacent pairs (regardless of sign), i.e. -

Australian Coal Geology 4, part 2

C.M. Barton, A. Dubrovich, R. Webster

2, 2, 2, 1, 2, 2, 2

and

415

6, 5, 6, 4, 1, 2, 3

The position of the sample becomes of even greater importance when we assume samples have a zone of influence. Samples, therefore, lying within each other's zone of influence should exhibit smaller differences than those outside the zone . The greater the di stance between samples, then usually the greater would be the expected difference between their values. is a graphical representation of the correlation

The semi-variogram y (h) between samples . It is defined as a plot of -

y (h) Vs Lag 2

where

y (h) = l:[f(x) - f(x + h)] 2n X

(x + h)

n Lag

= = = =

in %

sample value at point x sample value at a distance h from x number of pairs distance between point x and (x + h)

It is calculated by taking the difference between pairs at the same spacing, squaring the value, then dividing it by twice the number of pairs as shown in Figure 1. The variogram is calculated in many ' directions to test for anisotropy in the deposit . The ideal shape of the variogram is shown in Figure 2. This example, called the spherical model, is one of the most common of the many shapes found. It is mathematically defined as 3

y (h) = Co + C (3~ - -h3 2a 2a = C + C 0 where

for h ~ a for h ~ a

C is the sill value a is the range C0 is the nugget effect

The sill is approximately equal to the normal sample variance. The nugget effect is equal to the sampling error and the range is the distance for the zone of influence. The second main tool of the geostatistician is estimation of block values using Kriging . Kri gi ng can be defined as an estimation technique whi eh provides a set of weights to data that minimises the extension variance giving a linear unbiased estimation . Wi th the extension variance cr ~ being the variance of the error in extending a sample value of volume v to the ~olume of a block V.

Australian Coal Geology 4, part 2

416

C.M. Barton, A. Dubrovich, R. Webster

Figure 1 Semi-variogram calculation

Kriging gives an unbiased estimation, as the mean erro r of estimation is zero, i. e. where

E(Z - Z*) k = 0 E = expectation z = actual value Z*k = kriged estimate

and the sum of the weights produced equals 1, i.e. Weights Al+ A2 . .. An = 1 The requirements for kriging are that blocks to be estimated lie within the neighbourhood for which the semi-variogram has been calculated. Enough samples need to be included to allow the semi-variogram to provide a reliable picture of the variability. The kriging procedure, in estimating block values of a coal constituent from drill hole sample data, is as follows (David, 1977) : The vari ogram is drawn from the sample data, then for each block to be estimated (a)

samples influencing the block are located;

(b)

covariances function;

between

samples

are

computed

from

Australian Coal Geology 4, part 2

the

semi-variogram

C.M . Barton, A. Dubrovich, R. Webster

417

(c)

covariances between samples and the blocks are calculated from the semi-variogram function;

(d)

the covariances are arranged in a linear system;

(e)

the equations are solved for the weights;

(f)

block values are obtained by multiplying sample values by the corresponding weight;

(g)

the extension variance is calculated.

The kriging system can be expressed in matrix form with (n + 1) linear equations for (n + 1) unknowns (then weights A and the Lagrange multiplierµ). The linear equations can be expressed as -

r A c (vv) - µ = c (vV) where

c (vv) µ

c (vV)

= weights = mean covariance value between samples = Lagrange multiplier = mean covariance value between the samples and the block to be estimated .

The kriging variance cr { depends on three factors (a)

the basic geometry of the sample and blocks;

(b)

the semi-variogram;

(c)

the weights.

It can be written as cr { = c (VV) + µ - r A c (vV)

where c (VV) = mean covariance function within the block. PROGRAMS USED FOR THE STUDY The following programs were adapted for use on the computer for the study : (a) (b) (c) (d) (e)

semi-variogram determination; point kriging ; 2-D block kriging ; reserve calculation ; 3-D kriging.

The first four programs were obtained from the Joint Coal Board who had acquired them from Rayl es (1979) . The 3-D kri gi ng program was adapted from the program of Journel and Huijbregts (1978). Australian Coal Geology 4, part 2

C.M. Barton, A. Dubrovich , R. Webster

418

The following is a brief description of the above programs: Semi-variogram Determination This program produces p1ots for the histogram and semi-vari ogram of samp 1e data located on an approximate grid system . The necessary input data required is (a) (b) (c) (d)

position and value of the samples; direction for the variogram to be calculated; lag interval (usually mean spacing between samples); number of lags required .

Point Kriging This program is used to test the reliability and accuracy of the semi-variogram model proposed. This is achieved by systematically removing each sample value and using the semi-variogram function to predict the value of the sample removed using the surrounding data. The input to this program consists of the same samp 1e data as for the semi-variogram program plus the semi-variogram function . The output is a list of sample values with their kriged estimate and squared error of estimate. To further test the reliability of one set of semi-vari ogram parameters against another the following values are also calculated (a)

the mean algebraic difference between the estimates and the true value;

(b)

mean absolute difference;

(c)

mean squared difference;

(d)

mean kriging variance .

This program at present only applies to the spherical semi-variogram. 2-D Block Kriging This program estimates panel values and their kriging estimates using a spherical semi-variogram function taking into account the geometrical anisotropy of the variable. The variables used may be coal thickness, overburden thickness, ash or moisture percentage, etc. The input data required is the same sample data as for the semi-vari ogram, plus panel dimensions and semi-variogram function. The output from the program consists of the estimated values for the panels, their kriging variance and the co-ordinates of the panels . Plotting routines have been added to produce contoured plans for the estimated panel data and its kriged standard deviation within a predetermined boundary.

Australian Coal Geology 4, part 2

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419

Reserves Calculation This program uses the output from the 2-D kriging program to calculate volumes of coal or overburden based on the esti mated value . The volumes for the panels are sorted from highest to lowest and from highest to lowest kriging variance in the output .

NUGGET EFFECT 0

Figure 2.

RANGE

LAG IMETRESI FIG . 2

Ideal shape for spherical semi-variogram

3-D Kriging This program produces kriged estimates of parallelepipedic network of blocks, using drill hole data . It can use either the spheri ea l or exponential semi-variogram models obtained for both horizontal and vertical directions . Blocks are kriged and the kriging variance is calculated level-by-level using sample information located above and below as well as within the same level. The results from this program will eventually be plotted as a contoured surface for each level and profile independently. Almost any size , shape or location of rectangular blocks can be selected. APPLICATIONS Introduction The sodium content and the net wet specific energy of the brown coal are important indicators of coal quality. In the Flynn/Loy Yang coalfield (Figure 3) both of these properties have been subjected to a preliminary geostatistical analysis . Prior to the start of the analysis, it was evident that sodium content varied rapidly, and apparently irregularly, with depth. The first part of the geostatistical study was therefore directed to resolution of the vertical variation of sodium . The second part of the study extended the work into an examination of the lateral variations in both sodium and net wet specific energy and of the adequacy of the adopted 400 m bore spacing . Some preliminary results of the work are now discussed.

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420

C.M. Barton, A. Dubrovich, R. Webster

Morwell e

~ LOY YANG - FLYNN F IEL D

eBoolar ro

Figure 3. Loy Yang - Flynn Field Locality Plan Procedures and Results Vertical Var1at1on in Sodium As a means to find the general vertical variation in sodium percentage within the coal seams at Flynn and Loy Yang areas, semi-variograms were produced from boreho l e sample data. As the coal is usually analysed on 6 m sample lengths this length was used for the semi-variogram spacing. The results as shown in Figure 4 clearly indicate a trend with a linear relationship between ){h) and Lag h, i.e .

This trend was found for each seam with the Yallourn seam having the greatest increase whilst the Morwell 2 seam showed only a nugget effect (Figure 4) indicating that any variation within this seam is due mainly to sampling error .

Australian Coal Geology 4, part 2

C.M. Barton, A. Dubrovich, R. Webster

421

0 . 009

a.cos M1A P:~ 60

= o. 0001et¼12/m :

0 . 001

0 ,0131.¼

0, 006

o.oos .c

Q.004 M18

o.oos-:. ,.-,-,-

Q.003

0.000016(¼)2/,n

0,0087¼

0.002

l(h ): ph "' o

0.001

Yollourn MlA M l8

. .

S poc,ng; n mitlt on

Log (h)

LOY YANG & FLYNN FIELOS

Figure 4.

Vertical semi-variogram for sodium% within coal seams at Loy Yang and Flynn field .

Adequacy of Bore Spacing for Characterisation

of Sodium and Net Wet

Specific

A preliminary investigation into the effect of borehole spacing and estimation of lateral coal seam characteristics was carried out using geostatistics. Net wet specific energy and sodium% values obtained from bore samples located at the base of Morwell lB seam at Loy Yang and Flynn, were used in the investigation . The bottom 6 m of the seam was used to avoid vertical variation with the seam confusing the results. Both variables gave very similar spherical semi-variograms as shown in Figures 5 and 6. The sodium percentage gave a sill value of 0.008% 2 , a high nugget effect of 0.006% 2 and a range of 3200 m. The net wet specific energy semi-vari ogram had a s i 11 of 0. 47 (Mj/kg)2, a high nugget effect of 0. 32 (Mj/kg) 2 and a range of 3200m.

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422

C. M. Barton, A. 0ubrovich, R. Webs t er

Using the semi-variogram, data values for 200 x 200 m panels were estimated using the 2-dimensional kriging program . Both variables had the panel values predicted using firstly, 211 bores based on a 400 m grid, and then using 25 bores consistent with 1200 m grid . Contour plots of the estimated panel values and their kri ged standard deviation were produced and are shown in Figures. 7 to 14. From these plots the following results were obtained.

r::::,

0-008

X X

SILL

C\I

Q.006

L.J 1,-.j

NUGGET EFFECT

- Q.004 .c

0.002

400 800 1200

2000

AANGE

4000

6000

LAG. h ( m I

Figure 5 Horizontal semi-variogram for sodium% for the bottom 6m of MlB coal seam at Loy Yang and Flynn field. Sodium Percentage From Figures . 7 and 8, it can be seen that the general trend is an increase in sodium % from 0. 05% in the west to a high approximately 0. 30% to the southeast. The difference between the kriged values, using the two different grids, was approximately 0.01% except in the high percentage area in the southeastern area. Here the 1200 m gr i d produced values up to 0.14% higher than the 400 m grid. The anomalous high values produced by the 1200 m grid are due to the influence of only one bore . If coal quality was predicted in this area, using only bores on the 1200 m grid, serious inaccuracies could be encountered. Contoured plans of the kriged standard deviation (Figures . 9 & 10) were vastly different for the two grids. The 400 m grid gave values between 0. 03 and 0. 06% whilst the 1200 m grid gave values between 0.06 and 0.11%. In contrast to the standard deviation plot for the 400 m grid, the 1200 m grid (Figure 10) gave a very irregular pattern. Blocks intersected by boreholes gave the lowest values, with an aureole effect around these blocks as the standard deviation values increased rapidly away from the borehole. The patterns reflect the poorer reliability of estimation from the 1200 m grid.

Australian Coal Geology 4, part 2

C.M. Barton, A. Dubrovich, R. Webster

o.s

SILL

o. 4

0::::, ,:;

)(

423

(\J

0.3

)(

L..J

......

,:;

NUGGET EFFECT

0.2

O. l

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Figure 6.

Horizontal semi-vari ogram fo r net wet specific energy for the bottom 6m of MlB coal seam at Loy Yang and Flynn field .

Figure 7

Sodium% Loy Yang and Flynn areas. Kriged estimates using bores on a 400m grid . Bottom 6 metres of MlB seam.

Australian Coal Geology 4, part 2

C.M . Barton, A. Dubrovich, R. Webster

424

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Figure 8

Sodium% Loy Yang and Flynn Areas. Kriged estimates using bores on a 1200m grid. Bottom 6 metres of MlB seam.

Net Wet Specific Energy Contoured p 1ots of the pane 1 estimates of the net wet specific energy are shown in Figures 11 and 12. Both grids gave similar results with an increase towards the north. This is consistent with direction of dip for the coal seam, with the net wet specific energy increasing as the seam becomes deeper . The values ranged from approximately 8.2 Mj/kg in south to 9. 80 Mj/kg in the Values estimated by the two grids had a general difference of north. 0. 2 Mj/kg in the south and 0. 4 Mj/kg in the north. There were a number of locations which had much greater differences with a maximum of 0.87 Mj/kg. For this block, the 400 m grid had a value of 8.67 Mj/kg whilst the 1200 m grid gave a value of 9.53 Mj/kg . The plot of the standard deviation for the 1200 m grid (Figure 14) again showed an aureo 1e effect around bore ho 1es although not as pronounced as for the sodium%. The standard deviation values for this grid ranged from 0.44 to 0. 63 Mj/kg whilst the 400 m grid (Figure 13) had values from 0.26 to 0. 55 Mj/kg. The values reflect the greater reliability of estimation gained by using the 400 m grid .

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C. M. Barton, A. Dubrovich, R. Webster

CONCLUSIONS Geostatisti cal methods are being used by the State Electricity Commission to help in the quantificat ion of the properties of the brown coals of the Latrobe Valley . The need for geostatisti s is related to the sensitivity of brown coal utilisation behaviour to minor variations in mineral and inorganic properties. Programs covering semi-variogram determinati on, two- and three-dimensional kriging, point kriging and reserve calculation have been developed for operation on an Amdahl 470/V7 main frame computer. Initial geostatisti cal studies of brown coal in the Flynn area show that sodium content is constant in the Morwell No . 2 seam but increased upwards at di st i net i ve rates in the younger seams . Average sodium content is shown to increase from 0. 05% in the northwest to 0. 30% in t he southeast of the study area. Standard deviations on these estimates, derived from a 400 m spaced bore grid, ranged between 0. 03 and 0. 06% whilst the equivalent values for a 1200 mm bore grid were generally poor and ranged between 0. 06 and 0. 11%. The net wet specific energy was shown to increase as the seam depth increased, from approximately 8. 60 Mj/kg in the south to approximately 9. 80 Mj/kg in the north of the study area. Standard deviations on these estimates, derived from a 400 m spaced bore grid, ranged between 0. 26 and 0. 55 Mj/kg whilst the equivalent values for a 1200 m bore grid were generally poor and ranged between 0. 44 and 0. 63 Mj/kg. The results show that, in both instances, the 400 m bore spacing gave significant ly greater reliability in the estimates. ACKNOWLEDGEMENTS The authors wish to thank the State Electricity Commission of Victoria for permission to publish this paper. The authors also express their appreciatio n to Professor · Marechal of the Centre de Geostatistiq ue Fontainebleau, France, for very helpful discussions and the provision of standard test data for checking the 3-D program . REFERENCES Armstrong, A., 1981. Geostatisti cs and Coal. Earth Resources Foundation, University of Sydney, Course Notes. February 1981. Clark, I., 1979. England .

Practical Geostatisti cs.

Applied Science Publishers Ltd.,

David, M. , 1977 . Geostatisti cal Ore Reserve Estimation. Publishing Company, New York .

Elsevier Scientific

The Brown Coal Reserves of Victoria.

Austral. Instit.Min.

Gloe, C. , 1979. Metal l .

Journel, A. and Huijbregts, Press, London .

C. H., 1978.

Mining Geostatisti cs.

Royle, A. , 1979. A Practical Introduction to Geostatisti cs. Mining and Mineral Science, Un1vers1ty of Leeds .

Australian Coal Geology 4, part 2

Academic

Department of

429

Computer Applications in Brown Coal Investigations A.P. Dubrovich Exploration and Geological Division, Fuel Department, State Electricity Commission of Victoria, 15 William Street, Melbourne, Victoria 3000, Australia.

Key Words: Geology, Computer, Programs, Data processing

ABSTRACT A short description of the extent to which the SECV staff are able to utilise the information collected in the Bore Data Bank is given. The main programs are enumerated and briefly described. INTRODUCTION Today, if the management of an organisation makes the decision to start collecting information on a future mining project, it can choose from a plethora of available data base management packages . Very careful evaluation of their capabilities is, of course, needed before deciding which package is the most suited to the needs of the project. The situation was very different in the late fifties when the State Electricity Commission of Victoria (SECV) decided to computerise their geological records. Nothing was available; nothing was even on the horizon . The most pressing need was for a program which would produce listings of bore strata and sample analysis. Due mainly to the efforts of the late Mr. H. Beer (1960), the beginnings of a rudimentary data base were laid down and the first in a 1ong 1i ne of app 1i cation programs was written. The ori gi na 1 concepts (Gill, 1982; paper in this symposium) were further developed but their limitations, which became more and more evident as the years passed, remained as the limiting factor on future development. To change this framework would need man-decades of work - clearly not practicable . Apart from the data base 1 imitations, the other constraint was always the state of computer technology availabl.e to SECV computer programmers. Until the advent of computer p1otters and graphic termi na 1s, any graphic app 1i cations were unthinkable. Until the advent of TSO (Time Sharing Option) it ~as not poss i b1e to deve 1op interactive programs, etc. Each of these quantum jumps occasioned much rewriting of o1d programs as we 11 as creation of new programs to exploit the new possibilities.

Australian Coal Geology 4, Part 2

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Descriptions are given of the programs currently available within the SECV . I wi 11 limit myself to programs in constant use without mentioning some scores of ad hoe programs. PRESENTATION GROUP Into this category are those programs which present available information essentially unchanged, but with headings and other aids added for easier interpretation . Listing of Bore Master Records Each bore on the base has as first record, the master which contains the "vital statistics", position in three co-ordinates, depth , date of drilling, etc. It was found convenient to maintain a separate file of all such records and list it periodically. It affords a quick overview of all bores available in any parish. Strata Listing Program A listing of strata of any number of bores is produced. If the bores intersect coal and the coal was sampled, then the moisture and ash are shown at sampled intervals in the corresponding seam . Coal Analysis Program Presents coal analysis in three parts : (a)

coal minerals and inorganics;

(b)

organic analysis on dry basis;

(c)

organic analysis on mineral and inorganic free basis .

The format of the output was designed to make it organically compatible with the strata listings and therefore the total available information on any one bore can be filed together in a binder. COMPUTATION GROUP Daily, Monthly and Yearly Dredger Samples The sum total of all data produced by drilling enables the geologists to make predi et ions as to quantity and quality of coal to be found in a certain locality (e•.g . projected open cut). To see how close to the mark this prediction is, we continually sample coal at the coal winning faces and analyse part of the sample immediately with regard to moisture and ash content. A summary of these analyses is prepared every month to enable the mine management to monitor the quality of coal delivered to the power stations. The second part of the sample goes into the making up of a composite sample for the month . These composite samples are then completely analysed with regard to all parameters which figure in the usual bore sample analysis . The monthly and yearly averages reflect very well the changes in coal quality as the coal faces move.

Australian Coal Geology 4, Part 2

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431

Percentage Distribution, Mass and Weighted Averages of Coal Parameters This group of programs produces abovementioned statistics for any grouping of data - be it an area, a seam or group of seams, an open cut level or bench, separately or in any combination . These programs are in the process of being replaced by more modern geostat i st i ea l programs whi eh wi 11 permit much more detailed insight into spatial distribution of coal parameters. GROUP OF UTILITY PROGRAMS The function of these programs is to disburden the geologists and the draftsmen of time-consuming searches for information .

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Australian Coal Geology 4, Part 2

4 05200

432

A.P. Dubrovich

Bore Location Program Extracts a 11 bores in an area defined by a boundary of co-ordinated points. The bores found are listed and/or plotted. The shape of the area is immaterial as the program can deal with any defined area, even an annulus or up to six inner areas. The plot is done to a pre-selected scale. (See Figure 1) . Extraction of Tops and Bottoms of Coal Seams Tops and bottoms of all seams encountered in a group of bores are listed bore by bore in tabular form. At the same time, for each top or bottom, an entry is made in a disk data set in a form which is directly compatible with the Ca lcomp General Purpose Contouring Package . When the run is finished, this data set can be sorted, equipped with control cards and contour plots of seam tops and bottoms produced. (See Figures 2 & 2A) . A variant of this program produces tops and bottoms of seams already adjusted for prospective mining losses. T4335GS.AR4.CATA C~lTL

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A.P . Dubrovich

TOP

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Program to Evaluation.

Compute Areas

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Computes areas of influence inside a co-ordinated boundary . As successive depth levels are nominated, the areas on the boundary are adjusted for preselected batter slopes. (See Figure 3) .

Australian Coal Geology 4, Part 2

434

A.P. Dubrovich

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Selection of Nominated Materials from Coded Strata Records As explained in Gill (this symposium) each bore strata record is coded with regard to type of material, seam and geological age. A geologist, looking for e. g. kao 1in, specifies the code for kao 1in as we 11 as another three codes under which this material could possibly appear, e.g. white clay, pipe clay, etc. The program searches the specified group of bores for presence of selected material . Australian Coal Geology 4, Part 2

A. P. Dubrovich

435

GROUP OF GRAPHIC UTILITIES The purpose of this group of programs is to produce plotter output which can be used directly as such or else, by reprographic means, form the basis for production of transparencies, preparation of overlays and transfers, etc. Production of Geological Cross-sections Skeletal cross-sections are produced, i.e. the bore information is plotted but the resolution of stratigraphy is left to the geologist. While in some 70% of cases the computer could undoubtedly produce acceptable strata connections, this is not attempted due to the internal complexity of Latrobe Valley stratigraphy in the remaining 30% of cases. The only strata highlighted are coal and inferior coal - the two ingredients of main interest. (See Figure 4).

Figure 4.

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Portion of several sect ions. (Inferior coal shown as hatched boxes; good coal as blank boxes).

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Australian Coal Geology 4, Part 2

436

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Australian Coal Geo l ogy 4, Part 2

A. P. Dubrovich

437

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A.P. Dubrovich

438

Pictorial Logs of Bore Strata To overcome the limitations of the previous program (i . e. complete concentration on coal/non-coal) a further program was developed which plots the lithology in the bores and represents the materials encountered with graphic symbols. So far this program was mainly used for positioning of the screens in dewatering bores. (See Figure 5). Contouring Package The package used is the Ca lcomp Genera 1 Purpose Contouring Program. The author had to write a rep 1acement subroutine for b1anki ng of comp 1i cated eros i ona 1 areas and a1so a separate trend surfaces program as the ori gi na 1 supp 1i ed was found unsatisfactory . The package performed exceptionally we 11 but is saddled with the limitation of tape input/output for saving and restoring of contoured areas. A disk oriented upgrading is indicated. Flag Plotting Programs As the title indicates, these programs plot the specified variable in the shape of a flag . The variables may be chemical constituents of ash, specific energy or any other derived quantity . The original plot is used to prepare transfers which the draftsmen stick to the drawing, thus decreasing the eyestrain and improving the productivity significantly. (See Figure 6) . DISCUSSION The main purpose of this paper has been to describe the functions of the various computer programs which have been developed for use in the SECV brown coal resource investigations . The way in which the programs fit in with the over a11 scope of the investigations is not covered and, in order to gain an appreciation of this aspect of the work, reference should be made to Barton, 1982 (paper in this symposium) . Listings and examples of various computer outputs are held in the Exploration and Geological Division of the SECV. There are new developments in the pipeline; notably, changes in the system to provide easier general access to the programs and to speed up the production of output to meet the ever-changing requirements . In relation to the purely technical work, the geostatistical program developments show a promise of great possibility for the future (Barton, Dubrovich &Webster, 1982 - paper in this symposium) . In conclusion, it is pointed out that this application paper should be read in conjunction with the paper by Gill, 1982 (in this symposium). Taken together, the two papers illustrate the sizable and essential contribution that a small computer group can make towards a speedier and easier utilisation of geological data.

Australian Coal Geology 4, Part 2

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439

CONCLUSIONS In the late 1950' s, when the SECV began to computerise geo l ogi ea l data, no suitable commercial computer packages were available . A series of in-house programs were developed to perform various functions related to the storage, retrieval and management of bore and coal property data. Basic presentation programs cover the production of bore strata listings and the presentation of mineral, inorganic and coal property details. Computer programs provide for the calculation of property statistics from dredger and bore samples. Utility programs provide bore location listings, top and bottom contours of coal seams (either directly or fo 11 owing adjustments for mine losses) and computation of polygonal areas of influence around boreholes. A group of graphic utility programs produce cross-sections, pictorial logs, various contouring plots, and down-hole property histograms for marking "flag plans". Listings of all programs are held in the Exploration and Geological Division New developments are leading to of the Fuel Department of the SECV. increasingly easy access to the applications programs, to speedier production of output and to the utilisation of 2- and 3-dimensional geostatistical analyses. ACKNOWLEDGEMENTS I express my gratitude to the State Electricity Commission of Victoria for permission to publish this paper and to C.M. Barton, B.F. Gill , C.S. Gloe, R.L. Webster and other members of the SECV Exploration and Geological Division for their helpful advice. REFERENCE Beer, H.E., 1960. Development of methods for the use of punched cards in the recording of drill logs in the exploration for brown coal. Austral. Instit. Min. Metall. Proc. 194.

Australian Coal Geology 4, Part 2

440

Data Processing of Bore Records B. F. Gill

Exploration and Geological Division, Fuel Department, State Electricity Commission of Victoria, 15 William Street, Melbourne, Victoria, 3000, Australia .

Key Words: Computer, Data Bank, Brown Coal, Bores

ABSTRACT The State Electricity Commission of Victoria (SECV) maintains a computer data bank covering approximately 15,000 bores wh i ch relate to brown coal investigations in the State of Victoria . The deve 1opment of the computer system since its introduction in 1957 is described. Primary records are sub-divided into four data categories. Flow charts are presented to show how the categories interrelate and how the output data is presented . INTRODUCTION A computerised boredata bank has been operated by the SECV over the past 25 years, and has been developed into a comprehensive and convenient system. Some 22 years have elapsed without any published report on the development of the system. An attempt is now made to fi l l this gap . THE DEVELOPMENT OF THE SYSTEM Information from bores drilled in the Latrobe Valley has accumulated since the late 1880°s. By the middle 1950's, the accumulation of information in large In 1957, quantities prohibited efficient data extraction and analysis. punched card equipment was acquired by the SECV for accounting purposes . By July 1957, a computer punched card system for bore records was designed (Beer 1960). With the introduction of more modern electronic computers in 1965, the whole record base was updated so that each bore had a sequence deck of cards. In 1969 the records, whi eh contained over 700,000 cards, were copied onto magnetic tapes. In 1973, upon the introduction of metrication , the author converted all records back to their basic input fo rm and to metric standards. At this time there were two record systems, one containing strata information and the other coal analysis records. These two systems were merged into one data bank in 1977. By 1980, the loading of magnetic tapes became time consuming and in 1981 the ever expanding data bank was placed on a permanently

Australian Coal Geology 4, part 2

B.F. Gill

441

mounted disk pack. The data bank now contains records for approximately 15,000 bores and over 1,000,000 metres of drilling are recorded in approximately 400 , 000 card images.

RE CORDING

BORE

FIG . INFORMATION

"MASTER"

(Re fer appendix for abbreviations) BORE

REQUEST

E.S.O. M.S.S. ALLOCATES UNIQUE BORE NUMBER a PEGS POSITION IN THE FIELD

BORE

SURVEYOR a LEVEL

PROGRESS

M.S.S. SURVEYS LOCATION OF BORE COLLAR

C.P.D. M.S.S. D.S.M. L.V. CO-ORDINATES S 1---.....,;~ B.R.C. ADDS TOTAL DEPTH A.H.D. R.L. CALCULATED a DATE OF COMPLETION C.S.D. KEYS DATA a TRANSFERS TO MAINFRAME COMPUTER

PROCEDURE SORT BORES INTO PARISH CODE S BORE NUMBER

PROGRAM CALCULATES A .M.G. CO-OROS. S PRINTS 5 LISTINGS I M.S.S. 2 D.S.M. 3 G.E.S C. 4 D.M.E. 5 E a G

E D.P.O.

FUEL

D.P.O. RECORDS S OBTAINS ADDITIONAL T .D.S. FOR G.E.S C. REQUESTED BORES

M.S.S. CHECKS LISTING

a G

D.P.O. ISSUE S LISTINGS

AMENDS

DATA

D.P.O. ADDS NEW DAT A TO BORE MASTER FILE VIA A N A UTOMATIC PROCEDURE

PROCEDURE ADDS NEW AT A TO THE END OF MASTER FILE, SORTS BORES INTO CORRECT ORDER, REPLACES OLD FILE WITH NEW, BACKS UP ENTIRE DAT A BANK a PRINTS LISTING OF BORE MASTER FILE

Australian Coal Geology 4, part 2

B.F. Gill

442

DATA BANK RECORDS OF A BORE The data bank records of a bore basically consist of four types of records 1.

2. 3. 4.

"Master" Information "Comments" Strata Descriptions Coal Analysis Records

All records are of fixed length of 80 characters, i . e. card image. There is no set limit to the number of records in each bore and most application programs allow for up to 300 records each for Strata and Analysis. The Master Information is contained in one record and comments a 11 ow for up to 10 records. DETAILED DESCRIPTION OF RECORDS 1.

The Master Information record contains the Parish code, bore number, Australian Map Grid co-ordinates, the date of completion, Australian Height Datum reduced 1eve l of the co 11 ar, the total depth of the bore, SECV Latrobe Valley Grid co-ordinates (where applicable), a "drilled by" identifier and an identifier if the co-ordinates and/or reduced level is approximate.

The Comment records contain the type of bore, e.g. Exploratory, Proving, Operational, etc., and can contain up to 10 records of 60 characters of free-formatted information. The first six characters of each record are the Parish Code and bore number which is a unique number for every record in the bore.

Strata records consist of the same unique number (Parish Code and bore number) in the first six characters, then up to 51 characters for the description of the material, the depth "from" and the depth "to" and a seven character numeric field for the coding of the material. The first two columns are a numeric field for seam coding and geological age identification.

Coal analysis records (when coal samples have been analysed) are of three different types. The first six characters are again the unique number in each record. Type ( a)

contains depth "FROM", depth "TO" and the moisture and ash determinations . It may also contain an identifier to indicate the start of a composite sample (usually three metres).

Type (b)

contains the same as type (a) and also the Proximate and Ultimate analysis of a composite sample from preceding samples (usually 12 metres). This is commonly referred to as the Organic analysis record.

Type (c)

contains depth "FROM", depth "TO" corresponding to portion or all of the invervals in Type (a) and (b), an ash determination, the coal minerals analysis and the inorganic analyses (usually six metres). This is commonly referred to as the Coal Minerals and Inorganics record. Australian Coal Geology 4, part 2

B. F. Gill

RECORDING

BORE • "STRATA"

443

FIG . 2 INFORMATION

(Refer appendix tor obbreviot10ns)

BORE

DRILLERS F IELD LOG

D.S.M. B.R.C. REWRITES LOG FROM DRILLERS FIELD LOG

GEOPHYSICAL LOGS

D.S.M.

B.R.C. FORWARDS OGS TO 0 .P.0.IE.6.GI

E 6 G GEOLOGIST

CHECKS

SEE FIGURE

C.S.D. KEYED a, TRANSFERRED TO MAINFRAME COMPUTER

NEW ST RAT A SORTED INTO ALPHABETICAL ORDER a, CHECKED AGAINST STRATA COOING LIBRARY THIS PROGRAM PRODUCES 3 FILES ,---31'1. I CODED STRATA DATA 2 UNCOOED STRATA DATA

THE

UNIQUE

CONTAINED STRATA

□ .P.O.

E 6 G MAY AMEND

DESCRIPTIONS IN UNCOOED

UNCODED

ST RAT A OR CODE UNIQUE DESCRIPTIONS TO ADD TO LIBRARY

STRATA

PROCEDURE SORTS NEW STRATA INTO ASCENDING BORE ORDER a DESCENDING DEPTHS WlTHlN BORE, ADDS NEW DAT A TO THE CURRENT ST RAT A FILE, SORTS INTO

ORDER

WITHIN

FILE.

REPLACES NEW FILE, BACKS UP THE DATA BANK 8 PRINTS A LISTING OF THE CURRENT STRATA FILE

Australian Coal Geology 4, part 2

B.F. Gill

444

FIG.3 RECORDING

BORE

(Refer

FROM FIGURE 2

"COMMENTS"

appendix

for

INFORMATION

abbreviations)

E B G D.P.O. RECEIVES COPIES OF BORE REQUESTS, AND STRATA LOGS FROM B.R.C., D.S.M.

\ I

D.P.O. KEYS PARISH CODE, BORE NUMBER, BORE CATEGORY B ANY RELEVANT COMMENTS. le LOGGED BY, GEOPHYSICAL LOGS, DETAILED DESCRIPTIONS OF SAMPLES ETC. THIS IS ADDED TO THE DATA BANK AT ANYTIME PRIOR TO FINAL ISSUE AND IS KNOWN AS THE COMMENTS FILE

Australian Coal Geology 4, part 2

B.F. Gill

RECORDING BORE

BORE

445

FIG.4 INFORMATION

"ANALYSIS"

fRefer appendnt' tor obbrev101lons)

PROGRESS

DRILLER TAKES SAMPLES OF EVERY 3 METRES OF COAL a PLACES IN A SEALED ORUM

c.s.s.

C.P.O. 0.$.M,

SAMPLER COLLECTS DRUMS FROM THE FIELD & RETURNS TO MORWELL COAL STORE

O.S.M. SAMPLER CRUSHES COAL . QUARTERS EACH SAMPLE ANO PACKS IN A PLASTIC BAG INSIDE A SAMPLE TN UKql

STORES REST OF COMPOSITE SAMPLES

BRIQUETTE MADE FOR X-RAY ANALYSIS

c.s.s.

R & D A .C.S. X-RAY ANALYSIS PERFORMED TD DETERMINE INORGANIC CONSTITUENT PERCENT AGES IN COAL \ORY BASISI

DETERMINES ORGANICS 6 COAL MINERALS

c.s.s. D.S.M. GEOLOGIST CHECKS SAMPLE DEPTHS AGAINST GEOPHYSICAL LOGS ANO MAKES ANY NECESSARY ADJUSTMENTS TO SAMPLE DEPTHS.

FINAL

THIS

A.C.S PRODUCES

TAPE

WHICH

IDENTIFICATION

TINS FORWARDED TO H.R.L. COPIES OF SAMPLE LISTS SENT TO 0 .P.0. IE & GI & C.S.S.IH.R.L.I

c.s.s.

CHECKED

PAPER E 6 G D.P.O. RECORDS RECIEVAL OF DATA

HAS

ADDED

C.S.D. KEYS PAPER TAPE DATA 6 TRANSFERS TD MAINFRAME COMPUTER

SAMPLE

RESULTS

C.S.D. KEYS COAL ANALYSIS DAT A 6 TRANSFERS TO MAINFRAME

PROCEDURE SORTS BORES BY PARISH CODE BORE NUMBER. DESCENDING DEPTHS \ORGANICS FIRST. INDRGANICS 6 COAL MINERALS SECOND\

PROGRAM CALCULATES % D.B. VALUES OF INORGANICS 6 PRINTS LISTINGS OF RESULTS

DETERMINES % MOISTURE % ASH !ORY 8AS1S1 STORES OR?EO SAMPLES

A .C.S. LISTINGS CHECKED 6 PASSED ON TO C.S.S.

E 6 G O.P.O. NOTIFIED

LISTS OF DEPTHS, M 6 A FIGURES FOR ENTIRE BORE

E 6 G GEOLOGIST GROUPS CONTINUOUS SAMPLES FOR COMPOSITING 8 TYPE OF ANALYSIS 8 THIS IS CHECKED BY THE O.P.O.

E & G D.P.0. USES PROCEDURE WHICH ADDS NEW DAT A TO CURRENT ANALYSIS FILE; SORTS ENTIRE FILE. "REPLACES SORTED FILE ON DATA BANK. BACKS UP DATA . BANK 6 PRINTS LISTING OF CURRENT ANAL Y5IS FILE

c.s.s. COMPOSITE SAMPLES MADE UP FROM UST

Australian Coal Geology 4, part 2

E 6 G D.P.D. DOES AMENDMENTS ON A V.D.U.

B. F. Gill

446

DAT A

TRANSFER

PERMAJIENT

TI-£

FIG. 5 DAT A BAI\K

(Refer appendix for obbrevtohons) CURRENT STRATA FILE

COMMENTS FILE

MASTER FILE

CURRENT ANALYSIS FILE

E 6 G 0.P.O. SELECTS BORES BY KEYNG PARISH CODES 8 BORE NUMBERS ON V.D.U.

PROCEDURE SORTS SELECTED BORES I\ITO PARISH 8 BORE NUMBER ORDER, THEN SELECTS THE AVAn...ABLE DATA FOR THE SELECTED BORES AND CREATES A NEW FILE CONT AiNJNG THIS OAT A FR..E. Fft....E IS SORTED INTO THE ORDER-MASTER. COMMENTS, STRATA 8 ANALYSIS

ERROR CHECKING PROGRAM SCANS NEW FILE FOR ANY MISSING OR INCORRECT RECORDS

E 6 G O.P.O. CORRECTS SELECTED OAT A FILE VI~ V.O.U.

E 6 G 0.P.O. VIA V.0.U. REQUESTS PRELIMINARY ST RAT A LOG LISTING

PROGRAM READS SELECTED DAT A FILE 8 PRODUCES LISTING

E 6 G GEOLOGIST CHECKS LOG, ADDS COAL SEAM IDENTIFICATION, GEOLOGICAL AGE, 8 ANY FURTHER COMMENTS

E 6 G O.P .0. KEYS GEOLOGIST'S ADDITIONS OR AMENDMENTS VIA V.0.U. 8 REQUESTS FINAL LISTINGS

INTERACTIVE PROGRAMMING DETERMINES THE NUMBER OF COPIES 8 WHETHER OUTPUT IS TO BE ON PAPER OR ON MICROFICHE STRAT A LOG L - - - - - - ~ - - - - - - ~ COAL ANALYSIS LISTINGS LIST INGS I E S G 1 E & G PROGRAMS PRODUCE FINAL 2 O.S.M. 2 O.S .M. ST RA T A LOG LISTINGS 8

; g:~·.: .

COAL

ANALYSIS

E S

LISTINGS

g:~:t

AFTER FINAL CHECK D.P.0. THEN UPDATES THE DAT A BANK BY A COMMAND ON THE V .D.U.

PROCEDURE PLACES NEW BORES IN T HEIR COR RE CT SEQUENCE WITHIN THE BANK. BACKUP THE ENTIRE OAT A BANK. THEN DELETES SELECTED BORE OAT A FROM THE COMMENTS, CURRENT STRA TA 8 CUR RENT ANALYSIS FILES 8 DELET ES T HE SEL ECTE D OA T A FlL E

Australian Coal Geology 4 , part 2

B.F . Gill

447

PROCESSING OF BORE DATA For a bore to be placed on the data base, it must contain Master Record Information, Comment and at least one strata i nterval (i . e. from the top to the bottom of the hole). Because of the complexity of the sources, personnel involved and the interchange of data, flow charts showing the sources of data and the steps needed to place such data on the permanent data bank are presented (Figures 1-5). It may be seen, from the figures that information is supplied from surveyors, drilling personnel, chemists, and geologists and is eventually merged into the data bank system . DATA OUTPUT Basic data output consists of a strata log and a coal analysis listing. Both listings contain the bore number, Parish Name, Australian Map Grid Co-ordinates, Australian Height Datum reduced level of the bore collar, the total depth of the bore, its date of completion and where applicable the SEC Latrobe Valley co-ordinates and their relevant SEC map sheet breakdown. Strata lists the category of the bore, any relevant comments, prints the description of each interval , the interval 's reduced levels and thickness and where applicable, moisture and ash intervals for analysed coal samples. Coal Analysis listing is of three parts, the first part lists the coal minerals and inorganic percentages, the second lists the coal properties on a dry basis and the third lists the coal properties on a dry mineral and inorganic free basis . Sample listings of both are presented (Figures 6 and 7). SYSTEM UPGRADING At the moment the system is being further upgraded for more automatic process; ng of coal analysis data. and the use of interactive programming for the automatic use of computer applications which use the data bank records . All records on the bore data bank are available to any computer terminal user within the SECV. CONCLUSIONS A computer punched card system was initiated by H. Beer of the SECV in 1957 to cater for the large quantities of bore data which had accumulated since the foundation of the SECV. The data bank has been deve l aped into a coherent system containing data from approximately 15,000 bores. Bore records are held in four categories; namely master information, comments, strata descriptions and coal analysis records . The flow of information leading to the comprehensive storage and presentation of data is complex. Information is fed into the system from the field survey and dri 11 i ng groups, the Herman Research Laboratory and the Exploration and Geological Division. Details of the data flow are presented in flow charts and examples of data display are featured on copies of computer output listings .

Australian Coal Geology 4, part 2

.I>, .I>,

B O R E

8 0 1

L O Y

Y A N

AUST . IIAP GRID CO·ORD'S •6059•.• PI EAST 5768952.2 11 NORTH •• TOTAL DEPTH

391 . 7 PI•• RL

SECV L . V. GRID CO· ORD ' S •1•058 . 9 PI EAST 26 23 77 . 3 PI NORTH •• SEC MAP SHEET A•C3 LO ~ YANG PROVING BORE . SEAM SPLIT AT DEPTH 189.0 11 15 ARBITRARY. · • ·· DEPTH AND THICKNESS IN PIETRES ·· •COAL SEAPI• ·· · · · · · · · · DESCRIPTION or STRATA · · · · · · ···· • rRQII TO RLTOP RLBOT THICK CODE lOR PERCENTAGE or IIOISTURE AND ASH)

)> C

"'c+ "'5 ~

("")

C'l (D

0 0 tC

'< .I>,

"C ~

"'5

c+ N

0.0 0.3 12 . 8 12 . 8 13 . 15 . 5 15 . 5 18 . 0 18 . 0 19. 2 19 . 2 19 . 8 20 . 7 20.7 22 . 3 22.3 23 . 8 23 . 8 25 . 3 28 . 0 29 . 6 35 . 1 35 . 7 35 . 7 36 . 0 31, , 0 36.6 39 . 6 •2 . 7 •5 . 7 ~8 . 8 '51 .8 s• . 9 '57 . 9 61 .o 6•.o 67. 1

•

0.3 12 . 8 13 . • 13 . • 15 . 5 18 . 0 18 . 0 19 . 2 19 . 2 20 . 7 19 . 8 20 . 7 22 . 3 22·. 3 23 . 8 2J . 8 25 . 3 25 . 3 28 . 0 29 . 6 35 . 1 35 . 7 36 . 0 36 . 0 75 . 3 36 . 6 39 . 6 •2 . 7 •5 . 7 •8 . 8 51 . 8 5• . 9 57 . 9 61 . 0 6• . o 67 . 1 70. 1

72.2 71 . 9 59 . • 59 . • 58.8 56.7 56 . 7 5•.2 5• . 2 53 . 0 53·, 0 52.• 51 . 5 5 1 . '5 •9 . 9 •9 . 9 •8.• •8 . • •6 . 9

71 . 9 59 . • 58 . B 58 . 8 56 . 7 5• . 2 5• . 2 53 . 0 53.0 51 . 5 52 . • 51 . 5 •9.9 •9 . 9 •8 . •

....... . 2

•2 . 6 37 . 1 36 . 5 36 . ?. 36 . 2 .3.1 35.6 32. 6 29 . 5 26 . 5 23 . • 20 . • ' 7. J 1• . J 11 . 2 8.2 '5 . 1 2. 1

•2 . 6 37 . 1 36 . 5 ' 36 . 5 36 . 2 36 . 2 35 . 6 32 . 6 2 9 . '5 26 . 5 23 . • 20 . • 17 . 3 1• . 3 11 . 2 8.2 '5 . 1

"i8 . ....

0,3 12 . 5 0 .,6 2.1 2.5 1. 2 y

1. 5 y

1. 6

1 . '5

....... . 2

2.7 1. 6 '5.'5 0.6 0.3

ASH ASH ASH ASH ASH

... ASH

' .5

•6 . 9 •6 . 9

SANDY SOIL CLAYEY SAND LIGNEOUS CLAY 0 . 6 PI NOT ANALYSED BROUN CLAY LIGNEOUS CLAY 2 . '5 II •8.8 11015 •• . 8 INrERIOR COAL 1·, 2 PI 6•.9 11015 10 . 2 COAL BROIJN 0 . 6 PI 65 . 7 M IS 5.0 0.9 II 56.8 11015 3.• INrERIOR COAL 1 . 6 II 60 . 6 110 IS 10 . 7 CO AL BROUN 1 . '5 II 63 . 7 110 IS JNrERJOR COAL 1 . 5 II 62 . 3 1101 5 10 . 2 BROIJN CLAY GREY CL AY BROIJN SILTY CL AY SAND JNrERIOR COAL UET 0 . 3 II NOT ANAL YSE D CO AL BROIJN 0 . 6 II 62 . 9 11015 6.0 3 . 0 II 61. 9 11015 J . '5 3 . 1 II 60 . 2 11015 2.6 3.0 PI 62 . 0 "01 5 2.2 3. 1 II 61 . 0 '1015 2.2 J . O II 61. 9 PIO IS 2.2 3 . 1 II 65.0 11015 1 . '5 3 . 0 II 63 . 9 11015 1.• 3 . 1 P1 6 3 , 9 11015 1. 2 1.• 3 . 0 II 63.8 1101 S 3 . 1 II 62 . 6 11015 1. 9 3 . 0 PI 62 . 9 · 1101s 2.0

39 . 3 y y y y y

y y

y y y y y

AS H

ASH ASH ASH AS H ASH ASH ASH ASH ASH ASH ASH ASH

?=' .,, C'l

B O R E "T1 (C C

-s (t) -..J

U'I

-s

l)J

AUST .

- - - - --- DEPTH

J> ::, (t)

l)J

-0 (t)

l)J

::, ('")

0 ..... l)J

l)J ~

c;') (t)

0 0 (C

'< ~

-0 l)J

-s

('")

0 l)J ~

FROM

0.0 36 . 0 '15 . 7 51 . 8 57 . 9 6'1.0

36 . 0 '15 . 7 51 . 8 57 . 9 6'1 . 0 70 . 1

- - - -- - - DEPTH FROl'I

0.0 36 . 0 '15 . 7 57 . 9

36 . 0 '15 . 7 5 7 .9 70 . 1

l)J ~

'< U'I U'I

• ------- DEPTH

U'I

THICKNESS

- - ---- - - - ----- COAL MINERALS

RLBOT

THK

72 . 2 36.2 26 . 5 20 . 'I 1'1 . 3 8.2

36 . 2 26 . 5 20 . 'I 1 .. . 3 8.2 2.1

36 . 0 9.7 6.1 6.1 6.1 6.1

THICKNESS

-------

RLTOP

RLBOT

THK

72 . 2 36 . 2 26.5 1 .. . 3

36 . 2 26 . 5 1 '1 . 3 2. 1

36 . 0 9.7 12 . 2 12 . 2

<+ ~ -

72 . 2 N AHO•• CONPLETED 18 . 0'1 . ~7

G~ID CO-ORO ' S '11'1058 . 9 N EAST 262377 . 3 N NORTH •• SEC NAP SHEET A'IC3 LOY YANG

.•

THICKNESS

RLTOP

RLIOT

THK

36 . 0 '15.7 57 . 9 70 . 1

72 . 2 36 . 2 26 . 5 1'1.3

36 . 2 26 . 5 1'1 . 3 2.1

36 . 0 9.7 12 . 2 12 . 2

::,

------- ------------- INORGANICS - - - - -- - - - - - - 5 FE FE CA FES2• • "'I • ASH "'' NA CL TOT • • • NP TOT

• 5102

AL203

K20

TIOZ

o·. 51

0. 1 5 0 . 02 0 . 02 0 . 11 0 . 17

0 . 01'1 0 . 013 0 . 011 0 . 010 0. 011

0 . 017 0 . 007 0 . 005 0 . 005 0 . 007

0 . 09 0 . 17 0.02 0 . 06

.• •

COAL NINERALS, !NORGAHICS

FOUL . INDEX

GAP

NOISTURE PERCENT . AR DB

::,

391. 7 M •• RL

SECV L.V .

RLTOP

FIG. 7

' LOY YANG

801

MAP GRID CO - ORD ' S '16059'1 . 'I M EAST 5768952 . 2 M NORTH oo TOTAL DEPTH

.•

0 . 0'1 0.09 0 . 09 0.0 0 . 02

0 . '18 0 . 53 0 . 37 0 . '11 0 . '13

0 . 1 'I 0. 1 'I 0 . 08 0 . 11 0 . 13

0 . 50 0 . 57 0 . '11 0 . '11 0 . 'l'I

o . 32 0 . 19 0 . 12 0 . 22 0 . 29 0 . 19 o. 12 o. 18 0. 16 o . 16 0 . 12 o . 16 0 . 20 0 . 16 0 . 1'1 o. 15· 0 . .!'1

COAL PROPERTIES : TYPE 1

0 . 16 0 . 1 'I 0 . 19

.•

1 . 98 1 . '19 1 . 18 1 . 16 1 . 3'1

3. 1 2.2 1.6 1.5 1.9

0.235 0 . 219 0 . 121 0 . 1 37 O . 1 'IS

-- - - - - PERCENTAGE - - - - DRY ---- BASIS ------- •SPECIFIC ENERGY MJ , KG0 • PROXINATE •-- - - - ULTINATE - - - - - GROSS GROSS NET •

• ASH • ,.,, I •• VOL F . C . •

5 ORG

DRY

MET

• GAP

61 . 'I 159 . 'I 63.0 169 . 9 63 . 3 172 . 5

3.0 1 . 98 52 . 9 '1'1 . 0 6'1 . 1 '1 . 8 0 . 60 0.20 7.85 25 . 0J 9 . 65 1. 8 1 . 33 51 . 7 '16.'I 65 . 3 '1 . 5 0.60 o. 12 25 . 07 9 . 29 7 . 50 6'1 . 7 '1 . 6 0 . 60 0. 16 1.6 9 . 17 '15 . 8 2'1 . 98 1 . 25 52 . 5 7 . 36 COAL PROPERTIES : TYPE 2 MOISTURE• PERCENTAGE• ---- DRY N!NERAL AND INORGANIC FREE ----- • • PERCEN~ . • DRY IAS!S • PROX . • -- - ULTINATE ANALYSIS -- -• SPEC . ENERGY • AR DB •ASH• N'I • VOL • C H N S O •GROSS• NET • • • • ORG DIFF • • MET

•

0.0 36 . 0 '15.7 57 . 9

GAP 61 . 'I 159 . 'I 63 . 0 169.9 63 . 3 172 . 5

3.0 1.B 1.6

1 . 98 1 . 33

1. 25

5'1. 0 52 . 'I 53 . 2

65 . 'I '1 . 9 0 . 61 66 . 2 '1 . 6 0 . 61 65.5 .. . 7 0 . 61

0 . 20 28 . 9 0 . 13 28 . 5 0 . 17 29.0

25 . 5'1 25 . '11 25.30

7 . 85 7 . 50 7 . 36

B. F. Gill

450

A11 basic records can be accessed on any termi na 1 whi eh is connected to the SECV computer mainframe. The basic data is used in a large variety of applications (Dubrovic 1982 this volume). ACKNOWLEDGEMENTS The author wishes to thank the State Electricity Commission of Victoria for its permission to present this Paper and, in particular, Dr. C. Barton, Principal Geologist, and Mr. A.P. Dubrovic of the Exploration and Geological Division. REFERENCES Beer, H.E., 1960. Development of Methods for the Use of Punched Cards in the recording of Drill Logs in the exploration for Brown Coal. Austral. Instit. Min. Metall. Proc. 194. Dubrovic, A.P., 1982. Computer applications in Brown Coal investigations of the State Electricity Commission of Victoria . (This volume). APPENDIX LIST OF ABBREVIATIONS TO BE USED IN CONJUNCTION WITH BORE RECORDS FLOW CHARTS SECV DME ESD Fuel CSD CPD R&D GE&C HRL CSS ACS MSS DSM E&G

State Electricity Commission of Victoria Department of Minerals and Energy, Victoria Engineering Services Department, SECV, Morwell Fuel Department, SECV, and Melbourne Computer Services Department, SECV, Melbourne Coal Production Department, SECV, Morwell Research & Development Department, SECV, Richmond General Engineering & Construction Department, SECV, Melbourne Herman Research Laboratory, R&D Department, Richmond Coal Science Section, HRL, Richmond Analytical Chemistry Section, HRL, Richmond Morwell ·Survey Section, ESD, Morwell Drilling Section, CPD, Morwell Exploration & Geological Division, Fuel Department, Melbourne

BRC

Bore Records Clerk, DSM, Morwell

DPO LV AMG AHO RL TD VDU

Data Processing Officer, E&G, Melbourne Latrobe Valley Grid Co-ordinates Australian Map Grid Co-ordinates, Zone 55 Australian Height Datum Reduced Level Total Depth Visual Display Computer Terminal

Australian Coal Geology 4, part 2

451

Computer Aided Geological Modelling for a New Queensland Coal Mine L.R. Grlmstone*, W. Hodgson**, S. McTaggart** & M.S. Peterson* * Curragh Queensland Mining Limited, 390 Queen Street, Brisbane, 4000 Austral la. ** Mlncom Pty. Ltd., 12 Floor, AMP Place, 10 Eagle St., Brisbane, 4000 Austral la. Key Words:

Coal mining, geological data processing, mine planning.

ABSTRACT: A multi-seam mine Is being developed as a conventional dragllne operation In the Rang a I Coa I Measures at Curragh near BI ackwater In Centra I Queens I and. Saleable coal wl l I comprise a high qual lty coking coal product and a steaming coal blend of raw coal and middlings steaming coal by-product. The geologlcal setting Is typical of the Rangal Coal Measures, showing lenticular sedimentation and variable seam structure and I lthotype composition. To achieve consistent run of mine coal qua I lty, accurate mine schedul Ing Is required. The complexity and volume of raw data to be assessed demands the extensive use of computers. The key element In such a system Is access by operating personnel to a geological database and model which can constantly evolve as mining proceeds. Excel lent communication between geologlst and systems designer Is necessary to build such a system, especially when the time Is short, with the volume of data large and growing constantly. This paper out I Ines how the system was developed by a team of geologists and computer geosclentlsts. In the 14 months since construction of the database commenced, some 1400 boreho Ie I ogs and 200 sets of deta I I ed coa I ana I yses have been encoded, 200 suites of geophysical logs digitised, and 150 suites of geophysical logs taken from n I ne track tapes. A geo Iog I ea I mode I has been created from th Is data, together with coal quality Information. Contour plans and sections of the required stratigraphy have been generated and In sltu reserves computed. INTRODUCTION In December 1979, the State Electricity Commission of Queensland CSECQ) called tenders for the development of the Curragh deposit to produce steaming coal for domestic power generation CSECQ, 1979). The cok Ing coa I fraction was to be d I sposed of separate I y by the successfu I tenderer. The tender· c I osed In July 1980, was awarded In Nobember 1980 CARCO-ACI-R.W. Ml I ler-Mltsul CoVenture, 1980), and a coal supply agreement signed In January 1981, with coal sales scheduled to commence In October 1983. The operator, Curragh Queensland Mining Limited (CQMU, Immediately commenced detal led mine planning studies. Australian Coal Geology 4, part 2

452

L.R. Grlmstone, W.Hodgson, S. McTaggart & M.S. Peterson

SCALE .,

3040

Kilometres

s:::

~ <(

\~ >

0~~ ~

... • -~

~ ~ ~ ~

~ \

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A large amount of geological data had been Inherited· from the SECQ (Staines, 1975, 1977, 1978; Gal I lgan, 1977, 1978 a, b, c, 1979; Hogan & Reeves 1977; Hot I lngsworth & Pigott 1978; LePage & Proudfoot, 1978; LePage & Gal I Jgan, 1979; Mui fer & Hair, 1980; Phi Ip, 1978 a, b, R.W. Ml Iler 1979). In the exploration program by the SECQ, approximately 1000 holes had been drilled In the mine area, of which approximately 700 were chip holes, most of which had been geophysically logged.

Austral tan Coat Geology 4, part 2

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453

For CQML to handle and process the existing data and new data yet to be collected, In a form readlly accesslble for constant review, rapid lmplementatlon of the most practlcal computer based data storage and manlpulatlon system was necessary. Thus It was decided to work with a computer service bureau which could offer (a) an extensive range of software readlly avallable. (b) software which most closely slmulated what a geologlst would do manually, Cc) a system which Is user oriented, I.e. the cl lent provides most of the labour and so can put In as much or as I lttle effort as necessary, and there Is less chance of misunderstanding between the programmer and the scientist, (d) ready access for consultatlon, (e) compatlblllty with other onslte computer needs. CQML and Mlncom Pty Limited conjolntly began the task of constructing the database and Its associated software In mld-1981.

-ARIES

CASTOR POLLUX ORION - - - - -

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full

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rono•

Variation of Quallty along strike

GEOLOGY The Curragh coal resources occur north of Blackwater In the Upper Perm Ian Rangal Coal Measures on the western llmb of the Central Bowen Basin and along strike from other large open-cut operations. The coal occurs In a series of gently easterly dipping seams up to 8 metres In aggregate thickness (Figure 1). The area Is located near broad zones of baslnal deformation and several faults have been dellneated In the mine area. Small scale structural lrregularltles resultlng from lentlcular sedimentation or minor faultlng are anticipated. These remain dlfflcult to accurately define, but should not slgnlflcantly affect mining. On a reg Iona I scale spl lttlng and coalescence of seams Is typical (Staines, 1972), but the general character of a correlatable seam Is lateral persistent. In the Curragh mine area four seams, each with a distinctive llthotype proflle and qua I lty characteristics, are lndlvldual ly mlneable. There Is local qua I lty variation along strike (Figure 2). Each seam's contribution to coal production (Figure 3) Is therefore governed by Its ablllty to provide a treatment of a selected size range) together with a mlddllngs steaming coal by-product; fraction). All oxidised coal wll I be utlllzed as raw steaming coal.

Austral Ian Coal Geology 4, part 2

L.R. Grlmstone, W.Hodgson, S. McTaggart & M.S. Peterson

454

Oxidised coal _

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wash

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Figure 3

Constitution of Saleable Coal Products

Therefore, each data point can possess a series of concurrently val Id yet mutually exclusive quallty values for each seam (e.g. raw coal, raw coarse bypass coal, washed coking coal, by-product mlddl Jngs coal). Analytlcal computer fifes have to be able to handle such a comprehensive range of data. SYSTEMS OVERVIEW The avallable Mlncom software Is llsted In Table 1. This paper deals with the GEODAS, GEOLOG and MINER I I software systems. GEODAS (geologlcal data acquisition system) provides a computerised geolog ical database system for entry, va I ldatlon, storage and reporting of drl 11 hole Information. L ltholog lca I logs are dlrectly encoded on to forms In the field. Survey and ana I yt I ea I data are genera I I y encoded at a I ater date In the off Ice. After valldatlon of the data, llthologlcal and analytlcal reports In plain English can be produced when required. Geophysical logs are Integrated with I lthololcal logs and sampllng and testing Information through GEOLOG, a system for the d I sp I ay and ana I ys Is of a geo Iog I ea I mode I for strat I form depos Its. It performs mine model I Ing through calculatlon of overburden, lnterburden and reserves In discrete mlneable units, together with preparation plant slmulatfon based on laboratory qual lty data. EXPLORATION Geobase Geodraft GEODAS GEOLOG Geomap Geoplot

EVALUATION

PRODUCTION

MINER 11

Ore Control Plant Maintenance Inventory Payrol I Costing Accounting

Mlnesched Fiscal

M. I .S.

TABLE 1.

Avallable Mlncom Integrated systems (Highlighting Software discussed herein)

Australian Coal Geology 4, part 2

455

L.R. Grlmstone, W.Hodgson, S. McTaggart & M.S. Peterson

~ ~

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Australian Coal Geology 4, part 2

456

L.R. Grlmstone, W.Hodgson, S. McTaggart & M.S. Peterson

DATA ENTRY AND GRAPHICAL DISPLAY SYSTEMS The SECQ exploration program was based on a series of east-west traverses perpendicular to the strike, spaced 300-400 m apart. This traverse system was used by CQML as the basis for a regularly spaced grid of cored and tested holes. Drll llng on this grid commenced In October 1981, and a complete grid coverage at 400 m spacing was achieved by July 1982. From July to September 1982 the drlll hole separation was closed to 250 m In the area to be mined In the first five years. Future drilling wl l I extend the 250 m grid throughout the mine. The survey, I lthology and analytical database Is maintained by the GEODAS system. Since construction of the database commenced, some 1400 lithological logs and 200 sets of detailed coal analyses have been entered, for both SECQ and CQML drl 11 holes. Extensive use of geophysical logs was made for accurate depth control, especially at sites where multiple holes had been drl I led to provide data for different seams at different times. Approximately 200 suites of geophysical logs run for the SECQ were digitised Into the computer from hard copy, and 150 suites of logs run for CQML have been provided on nine track tape. Multi-seam strip mining Involves a succession of passes through any strip, with the continuous generation of Information to be recorded and processed. Thus basic data has to be read I ly and continua I ly Input, stored, updated, retr Ieved, eva I uated and, If necessary, manua 11 y ad j usted. The geophys Iea I, 1lthologlcal and analytical Information Is visually displayed on reproducible computer plotted worksheets through the GEOLOG system {Figure 4, after Reeves, 1976). Al I Interpretations affecting this data are recorded on these sheets, which represent the building blocks of the model I Ing to follow. Following any Interpretative adjustments to the Information from GEODAS as a result of the GEOLOG display, val !dated drll I hole data Is added Into the MINER II modelling system. The ability to visually d isplay basic llthologlcal and ana I yt I ea I data In contoured, sect Iona I or pr I nted form was cons I de red essential for validation or editing by the user before model llng. During operations, geological data wlll be acquired In a variety of forms such as extraction surveys, production statistics, mapped exposures etc .• most of wh Ieh do not or I g I nate from a po I nt source of data. For th Is data, d I g I ta I either by tape, from another Instrument or In a entry Is required, different clerlcal form. MODELLING AND RESERVE CALCULATION Model I Ing geology by computer Is as effective as the mathematical ground rules It Is able to utilise and the degree of stratigraphic logic which controls It {Davis, 1973; Henley, 1981). The system used for the MINER II model employs a totally data honouring algorithm as Its surface fitting technique. Sectional, plan and graphic displays al low ready verification of the model led data {Figures 5 and 6), which, once approved by the user, forms the numeric base from which mining models may be constructed. Once other surfaces such as topography, base of weathering etc. are digitised, the physical relationship of modelled seam surfaces to these surfaces can be quantified within any defined area, such as a proposed mining block. Austral Ian Coal Geology 4, part 2

L.R. Grlmstone, W.Hodgson, S. McTaggart & M.S. Peterson

CUR400 PROJECT

SHEET PAPER

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b) ISOMETRIC PROJECTION OF PFLOOR VIEWED FROM SOUTHEAST.

Figure 5

Pollux Seam Structure

Australian Coal Geology 4, part 2

457

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L.R. Grlmstone, W.Hodgson, S. McTaggart & M.S. Peterson

459

Whtie at present faults are not accepted directly Into the database, manlpulat l on of the mode I can be read 11 y accomp 11shed as necessary to ref I ect tau 1tlng. The calculation of tonneage and quality for mine development and production planning needs to be more deflnltlve and precise than that required ln exploration to determine feaslbl I lty. During the exploration stage, statistical averages of quantities ln large blocks may suffice, but ln mine development, these detal Is are required for block sizes of the order of 250 metres x 60 metres. Moreover, for the adequate schedu I l ng of var Ious Input tonneages of different qua I !ties, the statistical assignment of both seam thickness and qua I lty needs to be made on the same basis. Production schedul Ing wl 11 be more easily achieved with a regular grid of llthologlcal and analytlcal Information. This spatial distribution must be ref lected by the surface fitting technique which must adequately represent the pattern of thickness and qua I lty variance as determined by the geologist. Careful attention to the mathematical distance weighting parameters which model the data lnt9 a surface are required (Barnes, 1980). An example of the effect of different distance weighting methods on model I Ing techn i ques Is shown by the shape of the contours In Figure 7. CURRAGH. PROJECT

CURRAGH PROJECT

ij 0

POLLUX SEAM

POLLUX SEAM SMOD.TH CONTOURS OF

Figure 7

YLUI AT 2,5 X INTERVALS

SMOUTH . C::l'I TOURS OF

YLU! AT 2 ,5 X. INTERVALS

Effect of Variation In Distance Weighting Parameters

Analytical data Is adjusted to take mining dilution and processing efficiencies Into account, and Is also modelled as a set of surfaces. Reserves can be calculated and qual !ties assigned to those reserves on numerous bases, depending upon the boundary cond itions Input Into the model. These bounding conditions are automatlcal ly quoted ln reserve printouts to remind the user of the degree of control he has placed over the data mantpulatlon.

Austral tan Coal Geology 4, part 2

460

L.R. Grlmstone, W.Hodgson, S. McTaggart & M.S. Peterson

POLLUX SEAM

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Austra 11 an Coa I Geology 4, part 2

32.75 -0 . 7066

L.R. Grlmstone, W.Hodgson, S. McTaggart & M.S. Peterson

461

Once the geologist Is confident of all of the modelled surfaces, they can be used by the mining engineer. Early versions of the model may lead to queries and feedback from the engineers, and manual adjustment of the data may be required to resolve local structural or oxidation zone problems. Planned strip designs are digitised Into the database and superimposed upon the model. Mine scheduling software can then be utilized to caclulate quantities and assign qua I I ties to the various 250 x 60 metre blocks of coal from each mlneable seam. Once coal quality and tonnes and overburden/lnterbu rden quantities have been assigned to these blocks they can be recalled In any order which does not vlolate stratigraphic logic, to reflect different mining sequences. Again queries may arise and feedback obtained from the engineers. Where such feedback requires reinterpretation of the geology, new data acquisition may be necessary. Manual adjustment Is based on local knowledge and professlonal experience essential to an effective geological model. Once mining commences, model led predictions have to be measured against production statistics to develop a series of relationships of performance to exploration predictions. Most producing mines derive such basic statistics of contract specifications for hlndcastlng. However, access to a computer database and mode I a I Iows the use of these re I at I onsh I ps to be expanded dramatically. For example two-dimensional cross-plotting Is the obvious first step (Figure 8, Kloosterman et al, 1977; Renwick, 1980). CONQUSIONS A case history of the software development to effectively and continually model the geology of a large and complex coal mine has been outlined. It was necessary that operating staff rapidly develop a famlllarlty with and appreciation of the software. Equally Important was the maintenance of an objective overview of the development to ensure It was proceeding along the right path. It Is unllkely that an equivalent total number of CQML and Mlncom staff would have been able to manually Interpret the Information and derive a geologlcal model lncludlng reserves In the required time. In any case, those staff would need to be retained to repeat the task when necessary, whereas now model ling can be readily repeated with a smal I staff of 3 or 4. In addition, the flexlbl I lty of the database wl I I encourage the geologist and engineer to tackle the more difficult conceptual problems that would otherwise have been beyond them because of daunting clerical problems. Such freedom for Innovative thinking places the company In a much better position to meet unexpected challenges In Its operations and Increase Its productivity and competitiveness In the market p Iace. AO< NOWL EDGEMENTS The authors wish to thank Curragh Queensland Mining Limited for permission to pub I lsh this paper. The opinions expressed herein are those of the authors and are not necessarily endorsed by C<;/ML.

Australian Coal Geology 4, part 2

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L.R. Grlmstone, W.Hodgson, S. McTaggart & M.S. Peterson

REFERENCES Tender to the State Electricity Comm 1ss 1on of Queens I and, Spee I f I cat 1on No. CN/2, for the supp I y of steam Ing coal from an Initial development of the Curragh Coal Deposits, Vols. I - IX (Unpubl.).

ARCO-ACI-R.W. Mll I er-Mitsui Co-Venture, 1980,

Computer ass I sted mI nera I appra Isa I and teas I b 11 I ty.

Barnes, M.P., 1980,

Am..

l.n.s.i.. Ml.n... M.e..t.. .& ~ ~ Davis, J.C., 1973, I nternat Iona I .

.5.iail~iil~ .Q.f O~li A.a.al.,¥~~ ln fi~QJ..Q~,

WIiey

An eva I uat I on of Sha I I ow Coa I Resources 1n the Curragh Ga 11 I gan, A.G., 1977, Area 56D. ~ .5..un'.... .Ql.d.... ~ I 977/73, Henley, S., 1981,

Non-parametric sieostatfstfcs, Appl led Science Pub I lshers.

Hogan, G.C. & Reeves, A.S., 1977, A pre 11 m I nary rev I ew of the m In Ing of open cut coa I reserves In the Curragh Area, South Centra I Bow en Bas In. Departmenta I Area 56D, SECQ Br I sbane. CUnpub I.). Kloosterman, R.A., Broom, R.W.C. & Lonfat, F., 1977, Appl !cation of wire I lne I ogg Ing techn 1ques In the assessment of open p It mI neab I e coa I, presented at symposium The lndoneslan Mining Industry, Its present and future, Jakarta. Curragh coal aquifer testing report on Mui ler, P.J. & Hair, I.D., 1980, hydrologlcal Investigations. ~.5..u.c.Y.,_.Q.lJ1..Rec.,_ ]980/39 CUnpubl.). Curragh project, Authority to prospect 217C, prel lmlnary Phi Ip, M.G., 1978, geotechnlcal study, supplementary core f ogging, Coffey and Partners Pty. Ltd., Brisbane. CUnpubl.). Application of wlrellne logging techniques to coal Reeves, D.R., 1976, exploration In Muir, W.L.C. Ced) Coal Exp!oratfon, Ml Iler Freeman. Renwick, R.I., 1980, A study of the uses and benefits of downhole logging In coal exploration programs.~ ~ ~ l , 37-50. Report on the evaluation and lnltlal surface mine Ml I fer, R.W., 1979, development of the coal reserves In authority to prospect 217C Curragh, Clermont Mining District, Central Queensland, Vols. I - IX CUnpubl.). Staines, H.R.E., 1972, Ranga I Coa I Measures. 1.0., CUnpub I.).

Blackwater coalfleld: Correlation of seams In the McKenz I e R I ver to SI r 1us Creek. ~ .5.Jla.. .Q.lJ1.. ~

Coal exploration, South central Bowen Basin Staines, H.R.E., 1975, departmenta I area 56D, ~ .5..u.c.Y.,_ .Q.lJ1.. Rec.,_ 1975/89 CUnpub I.). Sta Ines, H.R.E., 1977, Jel I lnbah-Caledonla area.

Coa I

exp I orat 1on,

~ .5..u.c.Y.,_

South

centra I

Bow en

Bas In,

.Q.lJ1.. Ree-. ]977/]0 CUnpubl.).

Coal exploration, South central Bowen Staines, H.R.E., 1978, Jel I lnbah-Caledonla area . .G..eol.-. .5..u.CTa. .Q.lJ1.. Ree-. 1978/44, CUnpubl.).

Austral Ian Coal Geology 4, part 2

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L.R. Grlmstone, W.Hodgson, S. McTaggart & M.S. Peterson

463

State Electricity Commission of Queensland, 1979, An evaluation of the coal resources In Author lty to prospect 217C, Curragh, Vo Is. I - X (Un pub I.). State Electrlclty Commission of Queensland, 1979, Invitation to tenderers Specification No. CN/2 for the supply of steaming coal from an lnltlal development of the Curragh coal deposits (Unpubl.)

Australian Coal Geology 4, part 2

464

Computer Based Geotechnical Data Management System for Coal Exploration and Mine Planning I. PAUNCZ and G.E. HOLT Austra 11 an Coa I Industry Research Laborator Ies Ltd., P.O. Box 83, NORTH RYDE. N.S.W. 2113 KEY WORDS: graphics.

Geotechnlcal, logglng, exp loration, mine design, computers,

ABSTRACT The geotechnlcal assessment of core materlal retrieved from boreholes Is an Integral part of a wel I planned appralsal of a rock mass under lnvestlgtlon for coal mine development. The key parameters In bore core evaluation are the mechan I ea I propert I es of the 'I ntact 1 core, the degree of fractur Ing of the core and the susceptlbllltles of the various rock types to strength loss with time. In order to manage and process the large quantities of data acquired by fleld Iogg Ing and Iaboratory test Ing, the Geotechn lea I Logg Ing System of computer programs has been Imp I emented by Austra 11 an Coa I Industry Research Laborator Ies Ltd. This Geotechnlcal Logging System has facl I ltles for converting abbreviated coding Information Into grammatlcally correct geological description, decoding and reporting fleld point load test resul t s, fracture logglng data and laboratory determinations of rock mechanlcal properties and then presenting al I this Information slmultaneously on a continuous log produced on a computer control led plotter. Space Is allocated on this fina l log for affixing scaled colour photographs of the bore core, Apart from the usual advantages associated with computer processing, this system rel I eves fie Id and laboratory personnel of repetitive and at times Involved calcualtlons and fleld log drawing which usually requires re-drafting, INTRODUCTION Current expansion of existing coal mines and the development of new open cut and underground operations are occurring at greater depths and under more difficult geotechnlcal codltlons than previously experienced, In response to Industry requests for Improved prediction of I lkely mining conditions a research program was commenced In 1977 by Austral Ian Coal Industry Research Laboratories Ltd. CACIRL) to develop systematic procedures for recording and Interpreting geotechnlcal Information. emphasis was placed on maximum utlllsatlon of bore core retrieved from coal exploration drll llng programs for two prlnclpal reasons: Ca)

to assess llkely mining conditions as early as possible In an exploration program,

Austra 11 an Coa I Geo Iogy 4, part 2

I.Pauncz & G.E.Holt (b)

465

to reduce the need for speclal geotechnlcal drll llng programs.

The motivation was clearly economic, considering the high cost of mine development and the often marglnal economic nature of mine operations. Data acquisition procedures and Interpretation systems were selected and tested at a number of col llerles Jn New South Wales (Richmond and Smith 1979, Richmond rl .sl..l... 1979). It became evident that data processing would be necessary to handle the large volume geotechnlcal data generated from studies for new operations and Jn late 1980 the fracture logglng program (CINDEX) was developed. All programs were Implemented by mld-1981 on a bureau's mainframe computer. With the Jnstallatlon of ACIRL's VZX 11/750 mini-computer In November 1981, the full system of geotechnlcal logglng programs was converted to run In-house. The most recent deve Iopment has been the I nsta I I at I on of an automated data acquisition system Jn ACIRL 1s geomechanlcal laboratory at Be I Iamb I, New South Wa I es. As we I I as contro I I Ing the I aboratory test Ing, this system logs and processes data at the time of the test and updates the geotechnlcal data repository with the results. DATA ACQUISITION Geotechnlcal logglng and testing procedures which are unlversal In nature can be partlcularly useful Jn coal exploratlon and mining assessment programs. Such procedures can be undertaken Jn early drl 11 Ing programs by exp Ioration personnel, providing valuable quantitative Information on llkely mining conditions. Mine design engineers can then be Jn a position to advise reallstlcal ly on mining methods at the time coal qual Jty and quantity assessments are being presented. As projects move progresslvely to mine plannlng stages the same geotechnlcal procedures are utlllsed to provide detalled design Informat Ion, I ncorporat Ing data from the f Irst programs, and us Ing the same boreholes drllled for coal assessment purposes. The system desr I bed here a I I ow s Iogg Ing to be sp I It between geo Iog I sts and technicians If required and reduces logglng time to a minimum. It ellmlnates the office time required by geologlsts and technicians re-drafting data for reporting, al lows speclal Jsed Interpretation of Information, Is modular, adaptable and economic. It has been proven on several hundred boreholes since Inception Jn a wide variety of conditions Jn Queensland, New South Wales and Western Australla. Much of the logglng has been carried out by coal company personnel after Jnltlal Introduction to procedures. The geotechn Iea I propert I es of bore core that can be read I I y determ I ned as part of a coal exploratlon program Include: (al

the degree to which core Is fractured,

(b)

the mechanlcal properties of 'Intact' core,

Cc)

the susceptlblllty to strength loss with time .

.Elill GeotechnJcal Logging

There are two stages In the acq u Is It Ion of comprehens I ve geotechn Iea I data from bore core. The first (non-destructive) stage consists of detalled geotechnlcal logglng and photography of the bore core. The second stage consists

Austral Ian Coal Geology 4, part 2

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I.Pauncz & G.E.Holt

of an essentially destructive geotechnlcal laboratory testing program on the bore core. Where posslble, ACIRL uses procedures recommended by the International Society of Rock Mechanics for both the logglng and testing of bore core. In addition, ACIRL has developed standard procedures for the logglng and photography of the core In order to maximise the efficiency of data gathering. The s It Ing of dr 11 I ho I es, amount of core to be Iogged and deta 11 of Iogg Ing requ I red for a geotechn Iea I Invest I gat I on are dependent I arge I y on var Ious reglonal, structural and geologlcal factors, and on the purpose of subsequent design work. As a qulde at least ten metres of roof strata, the seam section and three metres of floor strata are usually logged for underground mines. In open cut areas the core Is usually logged from the surface to the anticipated pit bottom. At times variations to these generallsatlons become necessary. Geotechnlcal data requirements wl I I be different for designing a shaft or drift from subsidence Investigations where llmlted data are required from the seam to the surface. Wherever poss I b I e fresh core Is Iogged, on s I te, to 11 mIt deter I orat I on and fracturing Induced by storage and transport. This appl Jes whether the core Is obtained during a surface exploration program or from specific underground lnvestlgtlons and partlcularly when labortory testing Is to be undertaken. As In conventlonal logging, core recovery Is assessed, Depth levels and Intervals with consistent density of fractures are marked on the core to aid Iogg Ing and photography. The I lthologlcal log Is an essential part of geotechnlcal logging and ful I descriptions are Incorporated. These are partlcularly Important - for example In assessing the llkely goat behaviour, or blastlng and ripping charaterlstlcs of massive strata. Variation In the degree of fracturing of the core Is recorded on a separate form. The fracture logglng coding sheets al low for measurement of core losses, the number of natural breaks In the core, and the length of every piece of core greater than the core diameter. This data permits the calculation of core recovery, Rock Qua I lty Designation (Deere 1964P), C Factor (Han sag I 197 4) and fractures per metre. All three Indices are recorded to help overcome deficiencies In these fracture Iogg Ing methods. None were spec If I ea I I y des I gned for use In sed I mentary strata, and anomalies can occur. The C Factor Is considered more useful than RQD because It can allow for different core sizes and core fragments of length equa I to d Ia meter, thus exc I ud Ing Iess core from cons Iderat Ion. It has a Iso proved useful In reducing laboratory determined strength properties to those more closely reflecting rock mass properties (Hebblewhlte 1982). Core Is photographed using a speclal llghtwelght, demountable core photographic frame to enable accurately scaled, high quallty prints of bore core to be obtained (see Figure 1). Scaled photographs are affixed to the final geotechnlcal log sheets and enlargements attached to report. With fleld-logged bore core for which detalled laboratory testing Is not to be undertaken, point load testing with a portable testing machine Is done on site. Another coding sheet Is used for this operation. After photography, any core to be tested Is transported to an appropriately equipped laboratory. Prior to lnstal I at Ion of the automated data acquisition system, separate sheets were designed to enable the various operations to be undertaken Independently and also accept the coding system used by other laboratorles.

Austral Ian Coal Geology 4, part 2

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467

Figure 1 Borehole photographic frame

Laboratory Testing An In-house standard set of laboratory tests was developed to provide an Indication of strata characteristics as well as quantitative values for design purposes. The se lectlon of tests was dictated by ACIRL's emphasis on mathematical and physical model llng techniques for mine design rather than emplrlcal or llmlt equll lbr l um methods. There Is a I lmlt on the number of samples wh ich can be prepared from a seam Intersection, yet a maximum number of test results Is needed to al low for natural variation In rock strengths and Inhomogeneity of sedimentary strata. Usually al I aval Iable sol Id core Is utl I lsed for testing and often test cyllnders of rock are reduced In length to twice the diameter rather than the recommended 2.5 to 3.0 height-to-diameter ratio recommended In ISRM Suggested Methods (ISRM 1981). The fol !owing tests and their approximate numbers for ten metres of roof and three metres of floor strata are:

Austral Ian Coal Geology 4, part 2

I.Pauncz & G.E.Holt

468 (a)

Unlaxlal compressive strength, elastic modulus, Polssons Ratio and density 20 each

Cb)

Indirect tensile strength

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DATA PROCESSING AND PRESENTATION ACIRL 1s Geotechnlcal Logging System contains a suite of computer programs for processing the raw data acquired In the field and the laboratory and the presentation of results. It optionally Interfaces with the Geotechnlcal Data Management System for long term storage and easy retrieval of borehole Information. The complete system Is Illustrated schematically by Figure 2. The Geotechnlcal Logging System can be subdivided Into five modules, each des Igned to be capab I e of stand-a Ione operat Ion. Eac h modu Ie cons I sts of a number of programs and performs spec If Ic tasks. In It Ia I subd Iv Is Ion can be made on a module's position In the processing hierarchy . .D.a1il ..en..tr-¥ .a1lll process! ng

The three modules for these tasks are CINDEX, STONES and STRATA for handling fracture, rock property and geological logging data respectively. Each has a multlstage operation to perform three basic functions. Stage one reads the header Information and date encoded by field or laboratory personne I on purpose des Igned cod Ing forms. Extens Ive error check Ing Is carr led out to trap any encoding mistakes which may have been made during logging. In CINDEX and STONES calculations necessary to produce the results are performed. A report Is produced echoing thelnput data with error message where appropriate detailing Intermediate and fina l results of calculations. STONES produces Mohr Circle plots such as Figures 3 from trlaxlal test data to aid the testing engineer In the construction of the Mohr Envelope. STRATA performs no mathematical manipulations but contains more extensive error checking. Encoded mnemonics are checked for val idity and positional Integrity. Stage two consists of the optional Geotechnlcal Data Management System CGDMS) routines. These handle permanent storage of the logging results for later use by other moules of the Geotechnlcal Logging System. Basically the routines are of two types: Cl)

the storage of data after the successful completion of stage one,

(Ill the retrieval of stored Information for a specific borehole In preparation for further processing.

Australian Coal Geology 4, part 2

469

I.Pauncz & G.E.Holt

STRATA

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Figure 2 The Geotechnlcal Logging System Stage three produces fully formatted output taking the form of results calculated by CINDEX and STONES or expanded Engl lsh description produced by STRAT. Depending upon the packaging of the system, this report wl I I either be for only the Intervals for which Input data are suppl led, If Implemented as a stand-a Ione vers I on, or for an ent I re boreho I e for a GDMS vers I on. In th Is latter Implementation, this stage Is usually run Independently after all data for a borehole have been checked and loaded to avoid unnecessary duplication of resu Its.

Graphic presentat)on Q.f results The two modules for these tasks are TEKLIS and TEKLOG which combine selected geotechn I ea I deta for a bore ho I e and present resu Its as A4 s I ze co I umnated tables or continuous strip charts respectively (see Figures 4 and 5). Each module has a two stage operation.

Australian Coal Geology 4, part 2

I.Pauncz & G.E.Holt

47 0

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In the assessment of coal bearing areas, mine designers seek early Information on I lkely mining conditions, often at the time exploration personnel are fully committed to delineating the extent and natue of coal seams. Operating coal mines planning extensions to workings In previously drl I led, and commonly deeper areas, require detal led Information on roof and floor conditions. Geotechnlcal assessment of coal measures strata Is proving crltlcal for longwa I I mIn Ing In many areas of Eastern Austra I Ia. Remed Ia I Invest Igat Ions In operat Ing mInes have been ass Isted by deta 11 ed geotechn Iea I Iogg Ing and test1ng of core retrieved from underground drllllng. Subsidence Investigations also benefit from careful geotechnlcal studies. In the system described, emphasis was placed on slmpl I city of use, modular des ign and photographlcal ly supplemented computer graphic data presentation. Th i s has proved most acceptable to non-geologlcal personnel whlle retaining geological Information.

Austral Ian Coal Geology 4, part 2

.AUSTR.AllAH COAL INOUSTRT RESEARCH l AB OR.AT OR I ES LTO ROCK PROPERTT TEST RESULTS c.,t,d1•1••' s11,,, 55 . oo. t, 7J . oo. {V,r t t c, I Sul,

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AUSTRALIAN COAL INDU STRY RESEARCH LABORATORIES LTD GEOTECHNICAL LOG

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Australian Coal Geology 4, part 2

I.Pauncz & G.E.Holt

473

AO<N0WLEDGEMENTS Permission of Australian Coal Industry Research Laboratories Ltd. to publish this material, and In particular, col leagues In the Mining Division who · participated In the development of the system, are acknowledged. REFERENCES Deere, D.U., 1964, Technical description of rock cores for engineering purposes. .8..Qd ~ .a.rul Eng Jnear. ~ .l, 16-22. Han sag I,

I.,

1973, A method of determ In Ing the degree of f I ssurat I on In rock.

Intern, .J.....8..Qd ~ .MJ..n..~.& Geomech, Abstracts, l l , 379-388.

Hebb I ew h I te, B.K., 1982, The use of mode I I Ing techn I q ues for mI ne des I gn.

~ .J..a. .co.al. .Ml.n... .Iecila. ~ Ho... .1.

I .S.R.M., 1982, .Rock Character Jzat Jon Test Jng .a.ru1 Mon Jtor Jng. (Ed. E.T. Brown> Pergamon Press. Richmond, A. and Smith, K., 1979, Prediction of mining conditions from bore core Information. ~ .Coal .1rula. ~.Lab....~ 1.2-li Richmond, A., Levers, R. and Smith, K., 1979, Prediction of mining conditions from bore core Information. ~ .GoA,J. .1rula. ~.Lab....~ 1.2-11.

474

An Appraisal of Coal Facies Based on Maceral Characteristics C. F. K. Diessel

Department of Geology, University of Newcastle, New South Wales, 2308, Australia

Key Words: Coal facies, Macerals, Facies Triangle, ratio, Gelification Index .

Palaeoenvironment, Wood

ABSTRACT The paper discusses a method of coal f aci es analysis wh i eh makes use of conventional macer al counts. Diagnostic macer al s are related to each other and contrasted with non-diagnostic macerals. Two indices, a wood ratio and a gel i fi cation index have proved to be a useful base for the construction of facies maps. INTRODUCTION It has been known for a long time that coal type, i.e. the composition of coal in terms of its petrographic components, is a function of the depositional environment prevailing at the time of peat accretion. Both the kind of peat forming vegetab l e matter and its biochemical coalification are influenced by the position of the groundwater table relative to the peat surface. Tasch (1960) was among the first who related the various coal lithotypes to a range of wet and dry conditions whi eh were thought to r eflect different rates of subsidence . Fusain (fibrous coal) having been formed under dry conditions was taken to represent slow subsidence whereas durain (dull coal) indicated wet, i.e. rapid conditions of subside nee with the other coal l i thotypes taking an intermediate position. Whilst this system is simple and valid, as far as the bright components are concerned the genetic position of dura in cannot be ascertained from its macroscopic appearance alone. The dullness of a coal is merely an indication of its heterogeneous composition which may be brought about by a combination of such "wet" components as sporinite, inertodetrinite, alginite, and syngenetic minerals or by "dry" constituents such as fusinite, In both cases the fr acture would be uneven semi fus i ni te and macri ni te. resulting in a diffuse reflection of light, i.e. dullness. Hacquebard et al. (1967), Hacquebard and Donaldson (1969) refined petrography based coal facies analyses by emphasising the palaeoenvironmental significance Following the lead of Osvald (1937) and Teichmuller of microlithotypes.

Australian Coal Geology 4, Part 2

C.F.K. Diessel

475

(1962) four peat forming environments have been di st i ngui shed ranging from the relatively dry terrestrial forest moor through wet forest moor, limno-telmatic reed moor to open moor lakes. These environments are illustrated on a double triangle the apices of which are occupied by facies identifiers. The latter consist of conventional microlithotypes which have been further sub-divided in order to highlight their environmental significance. For example, vitrinertite has been split into vitrinite-rich "vitrinertite V" (wet formation) and inertinite-rich "vitrinertite I" (dry formation) . In applying the system to the Permian coals of the Hunter Valley, N. S. W. successive adjustments have been made by Marchoni (1976) and Marchioni (1980), Fay (1980), Bailey (1981) and Warbrooke (1981). To date the modified microlithotype analysis has been the most successful petrographic approach to palaeoenvironmental reconstruction, particularly when supplemented by chemical, botanical and mineralogical information. However, this method is cumbersome and very time consuming whi eh has prevented its application in conventional exploration programs although a thorough knowledge of vertical and lateral facies changes would be of great benefit to the planning of drill tiole distribution. The following paper describes how on the basis of simple ratios between some key components with more than average diagnostic significance conventional maceral analysis, too, might be suitable for coal facies studies .

MACERALS AS PALAEOENVIRONMENTAL IDENTIFIERS Coal macerals are the result of both depositional conditions in the peat bog and post-depositional coalification . Some macerals are the products of specific plants or parts of plants, others may result from a wide range of source materials but differ in response to changing biochemical environments of peatification. Coal facies analysis can be based on both plant-specific macerals, as well as those which develop in the peat . An example of the first kind may be alginite the presence of which indicates limnic or lacustrine conditions because algal growth requires the presence of water. On the other hand, most inertinite macerals are influenced by at least partial oxidation of a wide range of vegetable tissues which suggests relative dryness during the formation of such components . However, the latter case is not without ambiguity because the place at which a maceral is formed does not necessarily become its place of burial. Wind and water transportation cause considerable movement of materials within a swamp. As in other environments the preferred direction of movement is from high to low ground which can result in the coexistence of, for instance, fusinite and alginite in the same sample. Obviously, the latter is more likely to represent depositional facies than the former. Table 1 gives a list of the macerals commonly distinguished in black coals although for commercial purposes more general groupings are frequently used . Vitrinite, for example, is rarely separated into the individual components but often a dinstinction is made between vitrinite A and B after Brown et al. (1964). Of the two, vitrinite A appears to have higher diagnostic value.1t consists of telinite and telocollinite both of which have been derived mainly from incompletely gelified xylem and cortex tissues thus indicating an origin from wood producing plants under rather moist conditions. Most vitrinite B consists of desmocollinite which represents a thoroughly decomposed and gelified attritus of a variety of source materials among which soft tissues seem to have dominated. Leaves, grasses, shrubs and reed-like plants may have been the main contributors but the diagnostic value of desmocollinite is in

Australian Coal Geology 4, Part 2

C.F . K. Diessel

476

some doubt. Even less i ndi cati ve are gel oco 11 i nite and corpoco 11 i nite but their proportion in the coal usually is quite insignificant. Likewise, vitrodetrinite is a maceral which attracts little attention on account of its rarity in most coals. TABLE 1.

The Macerals and Maceral Groups of Black Coal

Vitrinite

Exinite

Inertinite

Telinite Telocollinite Gelocollinite Corpocollinite Oesmocollinite Vitrodetrinite

Sporinite Cutinite Resinite Alginite Suberinite (secondary exinite) Liptodetrinite

Fusinite Semifusinite Macrinite Micrinite Sclerotinite Inertodetrinite

Minerals

Most macerals of the exinite group can be related to specific source materials whi eh may have considerable pal aeo-envi ronmenta l s i gni fi cance . Spores and pollen may be produced in many parts of the swamp but most of them find their final resting place amongst the "reeds" of the l i mnotelmatic zone or on the bottom of ponds and lakes. High concentrations of sporinite reveal therefore sub-aqueous deposition, particularly when dealing with post-Carboniferous coals which, for reason of plant evolution, commonly contain fewer spores than earlier coals. It should also be noted that alkaline conditions (i . e. marine environment) tend to affect adversely the preservation of spores whi eh, for instance, is shown by bleaching and chemical corrosion of sporinite in the Greta Seam of the Hunter Valley, N.S .W. The palaeo-environmental significance of alginite has been mentioned above. It consists of remnants of algae which flourish in ponds, lakes, lagoons, estuaries and other aqueous environments ranging from fresh-water to hypersa line. Most alginite in coal has been derived from body algae (Alginite A of Hutton et al., 1980) of planktonic habit which, after death, accumulate on the depositional interface. The remaining exinite macerals are not very speci fi c in terms of depositional facies. Cutinite, a coalification product of mostly leaf cuticles is often associated with wood derived vitrinite which would place it into the forest moor . However, many non-woody plants also carry leaves and cuticles and all may be widely dispersed by wind and water, particularly those of the deciduous Gondwana forests. Resi ni te is the product of a variety of pl ant resins and waxes. When associated with telinite and still situated in the resin ducts of former xylem tissue the presence of appreciable quantities of resinite may be quite indicative of a forest moor environment. However, this resinite of high diagnostic value in most coals is supplemented by several other varieties of no specific association. Since the aim of the paper is to utilise conventional macerals only without further sub-dividing macerals or introducing new Australian Coal Geology 4, Part 2

C.F.K. Diessel

477

ones, resinite in its present definition is not quite suitable as a facies indicator. The situation is similar with suberinite which resembles cutinite in composition but originates from suberin-impregnated cork tissues. When in situ, suberinite might indicate forest growth but it too can be found in other environments as a residual allogenic component . Secondary exinite, such as exsudatinite, fluorinite, bituminite and others are of no concern here because they are products of coal ifi cation. Li ptodetri ni te is i ndi cat i ve of transportation and, usually, subaqueous deposition but in quantitative terms it is of little importance in black coal and therefore not counted separately in a conventional maceral analysis. Of the inertinite group only micrinite is of no interest because it is a dissociation product of exinite formed during coalification. Fusinite and semifusinite are commonly regarded as the products of terrestrial forest moors either by way of charcoal formation (pyrofusinite) or as a result of attack of wood by fungi and bacteria under slightly oxidising conditions ( degradofus i ni te). In most commercially oriented maceral analyses sclerotinite is combined with either fusinite or semifusinite which does not make any difference as far as the environmental significance is concerned but it does raise the amount of alleged wood-derived matter. Indeed, the latter is increased further by the occurrence of fusinitised leaf cuticles and mesophyll tissue (Di esse l , 1982). The presence in coal of i nertodetri ni te has two aspects. Consisting essentially of fragmented cell walls of fusinite and semifusinite somewhat dry and slightly oxidising conditions are required for its formation, presumably, in a terrestrial forest moor. The latter, however, is not the place of burial for most of the inertodetrinite which is indicated by its frequent coexistence with sporinite, alginite and framboidal pyrite. The notion of transportation and sub-aqueous deposition indicated by its association is supported further by the sedimentary structures displayed by inertinite concentrations, such as graded bedding (Figure 1) and particle imbrication. This means that inertodetrinite, although initially formed in a relatively dry forest moor is the result of transportation and redeposition in a sub-aqueous environment. In some respect the situation is similar with macrinite, except that macrinite initially begins its development under reducing conditions resulting in the destruction of cell tissues and homogenisation similar to the formation of vitrinite. This trend is subsequently interrupted by oxidation which can be brought about by one of two processes, namely transportation or a drop in groundwater table . The first case leads to the formation of flocks of macrinite which frequently coexist with inertodetrinite . They have been formed from humic colloids picked up by flash-floods and oxidised before final burial. The diagnostic value of this kind of macrinite is similar to that of inertodetrinite, but only if it is analysed separately from the "ground-mass macri nite" whi eh occurs in continuous layers as a result of a lowering of the ground water table and oxidation of the peat surface. Minerals, particularly those of authigenic origin may be of considerable diagnostic value . Yet they are not considered here because many macer al analyses are carried out on washed coal in which the minerals retained in the "floats" do not represent the full spectrum of the inorganic matter that is present in the raw coal. To a lesser extent this may be true al so for the maceral distribution because the "sinks" contain some coal as well. However, the variation introduced by washing is minor and not likely to result in constrasting facies between raw and washed coal.

Australian Coal Geology 4, Part 2

C. F.K. Di esse l

478

Figure 1.

Photomicrograph Incident light,

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0. 24 x 0. 36mm.

Australian Coal Geology 4, Part 2

inertodetrinite . Field of view =

C.F.K. Diessel

479

COAL FACIES ANALYSIS The analytica l procedure is based on the so-ca l led f acies triangle which is a graph i c device widely used in sedimentology for the purpose of illustrating lithofacies trends with the use of sand/shale ratios , elastic ratios and othe r indices. For the purpose of coal facies analysis the two triangular diagrams illustrated in Figure 2 are used. In the D-W-R triangle the macerals considered to be facies diagnostic are contrasted with the remaining ones. The essentially wood derived macerals fusinite, semifusinite, telinite and telocollinite occupy apex Won the left-hand side of the base line whereas the opposite apex D contains the dispersed macerals inertodetrinite and sporinite plus alginite . The remaining macerals occupy apex R at the top of the triangle which is divided into two portions at the horizontal 50% line. Coals which plot in the upper field contain less than 50% diagnostic macerals which, in some cases, could indicate a rather thorough decomposition of the vegetable More matter , usually leading to a high proport i on of desmocollinite. frequently , it seems that a low proportion of diagnostic macerals has resulted from a rather mi xed coal forming environment without a strong tendency towards either forest moor or limnic conditions. For this reason the upper field is not sub-divided any further but appears as "mixed facies" in both triangle and facies map. The coal s which plot in the lower field contain a sufficiently large number of diagnostic macerals to warrant further analysis which requires construction of a second triangle in which the wood derived macerals are divided into gelified (telinite and telocollinite at apex T) and fusinitised (fusinite and semifusinite at apex F) components . The former signify relatively wet and the latter relative ly dry forest moors . Both are contrasted with the open moor conditions symbol i sed by the □ -components which are the same as in the W-D-R triangle . In order to facilitate construction of coal facies maps the T-F-D triangle is sub-divided on the basis of component ratios . The TF / D ratio may be called wood ratio because it is a measure of the amount of wood derived macer al s present in the coal . If it is less than 1 no further sub-division is necessary because the coal was formed mainly under limnotelmatic reed moor or limnic conditions with little input from forests. At a TF/0 ratio greater than 1 more than 50% of the diagnostic macerals can be assumed to have been formed from wood tissues in a forest moor. The relative wetness or dryness of the latter is given by the T/ F ratio. High moisture conditions are indicated by a T/F ratio above 1 whereas a ratio of less than 1 suggests a somewhat drier environment. However, the amount of □ -components may st i 11 be high enough to suggest incomplete cover by forests and substant i al contributions to the peat f r om open moor environments. When the TF/0 ratio exceeds 4 (i.e . 80%), wood derived matter is so dominant that the T/ F ratio whi eh can be regarded as a gel i fi cation index is divided into additional sections at 4 and ¼ respectively. The result is a fourfold separation of wood-derivatives ranging from highly gelified material at +4 to highly fusinitised matter at-¼. It is suggested that these contrasting T/ F ratios reflect a change from wet, limnotelmatic forest moors at high ratios to relatively dry, terrestrial forests at low ratios .

Australian Coal Geology 4, Part 2

C.F.K. Diessel

480

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1 I.

The facies triangles which form the basis for the construction of co,1 facies maps. W = fusinite + semi fusinite + telinite + telocollinite; D = alginite + sporinite + inertodetrinite; R = remaining macerals; T = telin i te + telocollinite; F = fusinite + semifusinite.

COAL FACIES MAPS Figure 3 gives an example of a coal fac i es map based on the analysis results displayed in Figure 4. They have been obtained from the Braymont Seam and its upper split in the Maules Creek area of the Gunnedah Basin. The map shows a central area of high wood ratio, probably representing telmatic forest growth . To the east the forest apparently was wetter as shown by pockets of high gel i fi cation index flanked by mixed faci es. To the western outcrop boundary both wood ratio and gelification index drop which probably is the result of intermittent flooding of otherwise relatively dry conditions near the Boggabri Ridge. The reason for the drop in the wood ratio is an increase in intertodetrinite which may have been washed down from the adjacent highland. In this context it is of interest to have a closer look at the relationship between fusinite plus semifusinite and inertodetrinite. The respective proportions of each are plotted in Figure 5 which is based on several hundred analyses of different Australian coals . It is obvious that the quantitative relationships between the two are influenced by two principles : (a)

A coal with a high content of autochthonous fusinite and semifusinite will always carry a small proportion of likewise insitu inertodetrinite as a result of some mechanical disintegration . In this case the (semi-) fusinite/inertodetrinite ratio is quite high ranging between 4 and 8.

Australian Coal Geology 4, Part 2

C.F.K . Diessel

•

481

•

f •

• 1Km

Figure 3. (b)

An example of a coal facies map . near Boggabri, N.S.W .

Braymont and Braymont "A" Seam

A coal with a high content of hypautochthonous or allochthonous inertodetrinite always is associated with an appreciable amount of transported and redeposited fusinite and semifusinite . In this case the (semi-) fusinite/inertodetrinite ratio ranges between 2 and¼ with smaller values occurring only rarely.

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482

Figure 4.

The coal facies triangles from which the map displayed in Figure 3 has been constructed . Circles= full Braymont Seam ; Dots= Braymont "A" seam .

CONCLUSIONS It has been shown that the value of macerals as coal facies indicators varies. Those which are highly diagnostic can be grouped into facies triangles from which various ratios are obtained such as the wood ratio and the gelification index . These form the basis for the construction of facies maps from which palaeogeographical interpretations can be made . ACKNOWLEDGEMENTS The analysis results have been published with permiss i on of Kembla Coal & Coke Pty . Limited for which the author wishes to express his appreciation. The manuscript was typed by Mrs . M. Shilcock, photog r aphy and drafting were carried out by Mrs. J . Walker and Mr. W. Crebert . Mr. E. Krupic was responsib l e for sample preparation, all of which is gratefully acknowledged . REFERENCES 1981. The geology of the Broke-Mt . Thorley area . J. , Bailey, Newcastle, N.S . W. (Unpubl. B. Sc.)

Univ.of

Brown, H. R., Cook, A. C. and Taylor, G. H. , 1964. Va r iations in the properties of vitrinite in isometamorphic coal. Fuel 43, 111-124.

Australian Coal Geology 4, Part 2

483

C.F.K. Diessel Fay,

G.M., 1980. The geology of the Minmi-East Maitland Area. Newcastle, N.S.W. (Unpubl. B.Sc.)

Uni.

Hacquebard, P.A. , Birmingham, T. F. and Donaldson, J. R. , 1967. Petrography of Canadian coals in relation to environment of deposition. Dept. of Energy Mines and Resources, Symposium on Science and technology of coal, 84-97. Hacquebard, P.A. and Donaldson, J. R., 1969. Carboniferous coal deposition associated with flood-plain and limnic environments in Nova Scotia, in E.C. Dapples and M.E. Hopkins (Ed.), Environments of coal deposition"-:Geol. Soc. of America, Spee. Paper 114, 143-191. Hutton, A.C., Kantsler, A.J., Cook, A.C. and McKirdy, D.M., 1980. matter in oil shales. APEA. ~ - 20, 44-67.

Organic

Marchoni, D. L., 1976 . Investigations into the Palaeoenvironment of the Fo brook Formation in the Hebden-Ravensworth Area Hunter Valle New South Wales. Ph.D. Thesis, Univ . of Newcastle. (Unpubl. PH.D. Thesis Marchioni, D. L., 1980. Petrography and depositional environment of the Liddell Seam, Upper Hunter Valley, New South Wales . Intern. Journal of Coal Geology l, 35-61. Osvald , H., 1937. Myrar och myrodling. Stockholm, Sweden.

Kooperative Forbundels Bikflorlag,

Tasch, K. H., 1960. Di e Mogl ichkeiten Zuhilfenahme von Flozbildungsdiagrammen.

der Flozgleichstellung unter Bergbau- Rundschau 12, 153-157.

Teichmuller, M., 1962. Die Genese der Kohle . Stratigraphy and Geol., f.:.B.. }_, 699-722.

4th Int. Congr. Carboniferous

Warbrooke, P.R ., 1981. Depositional environments of the Upper Tomago and Lower Newcastle Coal Measures, New South Wales. Univ. of Newcastle, N. S.W. (Unpubl. Ph . D. Thesis)

.... :

IJJ

JJ UJ

,-.

~20 j:

IJJ

o/, INERTOOETRINITE

Figure 5.

Diagram showing correlation between inertodetrinite and fusinite plus semifusinite in Australian black coals . Australian Coal Geology 4, Part 2

484

Relationship between Microlithotype and Maceral Composition of Coals and Geological Setting of Coal Measures in the Permian Basins of Eastern Australia J.W. Hunt

CSIRO Division of Fossil Fuels, P. 0. Box 136 , North Ryde, N.S.W., 2113, Australia.

Key Words: Australian Permian Coals, Microlithotype Analysis, Maceral Analysis, Sydney Basin, Bowen Basin, Gunnedah Basin, Cooper Basin, Galilee Basin, Oaklands Basin.

ABSTRACT Microlithotype analysis has been carried out on Permian coals from the marginal Sydney, Gunnedah and Bowen Basins, and the i ntracratoni c Galilee, Cooper, Pedirka, Arckaringa, Blair Athol, Wolfang and Oaklands Basins. Significant differences in the average composition and variability of microlithotype composition are ascribed to the age and tectonic setting of the coal measures. Vitrinite content of the coal is related to variations in the composition and level of groundwater during deposition of plant material in the peat swamp. Coals deposited in the marginal basins are more finely banded in the Early Permi an than the Late Permi an, and are more coarsely banded in the troughs The marginal basins are characterised by thick than on the shelves. fluvio-deltaic sequences, deposited in rapidly subsiding troughs in the eastern part and thin fl uvi o-de l tai c sequences lapping onto the continental margin in the western part. Coals deposited in lower delta facies are usually vitrinite-rich, and coals developed in the upper delta-fluvial facies are vitrinite-poor. Coals deposited in the i ntracratoni c basins are finely banded in both the Early Permian and the Late Permian. The intracratonic basins are characterised by thin sequences of mainly fluvial sediments deposited in slowly subsiding downwarps within the continental crust. Vitrinite-poor coals are associated with overbank facies while medium virtinite coals were deposited in the channel facies. INTRODUCTION The majority of Australia's hard coal deposits are found within the Permi an successions of eastern Australia (Figure 1). Coals within the Sydney, Gunnedah and Bowen Basins are widely exploited, and non-commercial coals are Australian Coal Geology 4, Part 2

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J . W. Hunt

present, generally at depth, within the adjoining Cooper and Galilee Basins. The coa 1s di sp 1ay a wide range of petrographic type compared with coa 1s of other ages and locations, and may be characterised by their variability. The variation is, however, systematically distributed in time and space and may be related to the complex interactions of geographical, geological and biological factors operating during the formation of the seams.

CI) MARG INAL BASINS

~ INTRA(RATONI( BASIMS

- >\.

-~r

PE~AR(~

-,- _ _

BR ISBANE

r I AO

NEY

250

500 km

HOBART

Figure 1. Location of the major Permian coal basins of eastern Australia . In this paper the relationship between coal type, measured by microlithotype analysis in particular, and geological factors, mainly the tectonic setting and depositional environment of the coal-bearing sequences, is examined . The depositional environments of the coal-bearing strata are, however, difficult to assess because of lack of uniform regional syntheses and conflicting interpretations presented by various authors in smaller area studies . Coal Type Coal type is discussed in terms of mircoscopic petrographic analyses, including both maceral and microlithotype analyses. The petrographic analyses are reported on a mi nera 1 matter free basis (mmf) because the genesis and distribution of mineral matter generally bear no simple relationship to the organic components in which they are found. Maceral analysis measures the proportion by volume of the organically derived, microscopically recognisable components of coal, which are defined by their morphology. At the simplest level they are divided into three main groups -

Australian Coal Geology 4, Part 2

B AGE

)> C:

ARCKAR PEOIRKA INGA

N SYDNEY

BO WEN COOPER

Toolachee Fm .

LA TE PERMIAN

GALILEE

west

Bandanna Fm .

c+ ""'!

llJ llJ ::,

central

north

Rangal C.M. Burngrove Fort Fm . Cooper Fair Hill C.M . Fm . German Moranbah C.M Creek Fm.

east

north east

~orth

Bara laba C.M. Newcastle Woll ombi C.M . C. M. Kaloola Member

south

west

lllawarra C.M

Toma go WittingC.M. ham C.M.

NEW GIJNNEOAH ENG LANO OAKLANOS BLOCK

Black Jack C.M.

Bayswater WoonCJ10 Ulan Littw:p,11 Hoskissons seam seam seam seam seam

Corrabin C.M.

n 0

c....

llJ

Blair Athol C.M.

C) It)

0 0 (0

'< ~

llJ ""'!

c+ N

EARY PERMIAN Ml loondina Fm .

Purn, Fm.

Collins vIlle C.M.

:I: C:

::,

Greta C.M.

Patchawarra Fm .

CI yd e C. M. Reids Oome Beds

Maules Creek Fm .

Ashford C.M .

C.M. -Co al Measures Fm . - Formation Note , Age relationships shown on this chart are approximate

TABLE 1 Simplified correlation chart for eastern Australian Permian coals based on Thornton (1979) and Dickens (1967)

J . W. Hunt

487

vitrinite, inertinite and exinite . Vitrinite (Figure 2) originates mainly from humified "woody" plant remains. Inertinite, which represents oxidised and degraded plant remains, can have the same origin as vitrinite, and is divided principally into semifusinite (Figure 2), showing botanical structure (cell lumens), and inertodetrinite (Figure 2) , broken and detrital inertinite showing no botanical structure. Exinite (Figure 2), which is mainly composed of plant spores, cuticles, resin, or occasionally algae, is usually only a minor (5% mmf) component of Australian Permian coals.

Figure 2.

Semifusinite (sf), inertodetrinite (i), vitrinite (v) and sporinite (s) in vitrite (V), duroclarite (DC), and vitrinertite (VI), in a coal from the Newcastle Coal Measures in the Sydney Basin.

Individual microlithotypes are defined in terms of maceral assemblages. The microlithotype compositions of Australian Permian coals are presented herein using the following groupings . (1)

"vitrite + clarite" - 50 µm bands composed mainly( > 95%) of vitrinite or vitrinite + exinite (both > 5%),

(2)

"vitrinertite + duroclarite + clarodurite" - 50 µm bands composed of vitrinite + inertinite ± exinite (all > 5%), and

(3)

"inertite + durite" - 50 µm bands of inertinite ( > 95%) or inertinite + exinite (both > 5%), and have been determined by the "selon-la-ligne" method (ICCP, 1963).

Because Australian Permian coals are generally low in exinite ( < 5%), microlithotype analyses when presented as described above, in fact approximate to a two component system, with vitrite ( > 95% vitrinite) and inertite ( > 95% inertinite) as the end members. The degree of mixing (measured microscopically at the 50 µm level) of the two components varies in coals of different ages and locations, and on Figure 3 is shown as coarse, medium, fine and very

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488

finely banded, using banding coefficients defined by curves of height (h) 1-9, each enclosing 10% of the area of the diagram. The curves were derived from data used in this study (Cameron and Hunt, in prep.), and Bennett (1974) observed similar trends in macroscopic data that describe coal lithotypes in terms of their bright and dull components at a 5mm minimum band width. The approximate vitrinite content of a coal may be calculated from a microlithotype analysis using the formula "vitrinite = vitrite + clarite + 0.5 (vitrinertite + duroclarite + clarodurite)" (Smyth, 1974).

. .

VITRINERTIH OUROCLARITE CLAROOURITE 100

100 ll!:.~:::::::;:::...1......____.__j_-.,___._..1.._,.::::~~ 100

INERTITE v, v,,,..,. .£,,•'"" 2 01 OURITE @' c,,-,, ••-,•' l •J

VITRITE CLARITE

MICROLITHOTYPE ANALYSIS Figure 3.

Separation of micro l i thotype composition into areas of coarse, medium, fine and very fine banding.

Most of the microlithotype analyses made at CSIRO to date have been for clean coal composites, i.e. excluding subsections with [ 35% ash by weight. Recently, with the interest in washability of coals, analyses have been made on 1.60 relative density float fractions. Preliminary indications are that for low ash coals the difference in petrographic composition between the 1.60 float fraction and clean coal composites is not signficant. TECTONIC SETTING The economic coal basins of eastern Australia, the Sydney, Gunnedah and Bowen Basins (Figure 1), were developed on the eastern margin of Australia during the Permian, although the exact nature of the basins, i.e. foredeep, forearc, overthrust, rift, thermal or strike-slip is debatable (Harrington, 1982). The important aspect of these basins for coal formation was the presence of deep troughs with high subsidence and sedimentation rates in which thick, coalbearing sequences were deposited. The marginal basins al so include "shelf areas" subject to low subsidence and sedimentation rates, containing thin, coal-bearing sequences, lapping onto the western craton.

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The more westerly Permi an basins - Galilee, Cooper, Pedi rka and Arckari nga -represent large, sometimes interconnected basins , formed on broad, sometimes fault bounded downwarps in the crust. Most workers have considered that these basins overlie a Precambrian craton, and are therefore intracratonic . Harrington (1974) considered that they might be parts of the infilling of a marginal sea formed by rifting of the craton in the late Proterozoic or Early Cambrian . Intracratonic basins are characterised by low subsidence and sedimentation rates. These basins were al so sites of coal deposition during the Permian, although the coal seams developed are economically less important in quality and quantity compared with those in the marginal basins. The Oaklands Basin to the southwest of the Sydney Basin, the Ashford Basin in the New England Block to the north, and perhaps the Blair Athol and Wolfang Basins west of the Bowen are grabens or half grabens that represent smaller intracratonic or intramontaine basins subject to very low subsidence and sedimentation rates . Several of these were probably connected intermittently and genetically related to adjacent basins . GEOGRAPHIC SETTING AND THE PERMIAN FLORA Several Early Permian coal-bearing sequences overlie glacially-deri ved diamictites. The commencement of coal formation in the Sydney Basin generally coincided with the waning of cold climatic cond i tions and the establishment of a Gangamopteris dominated flora (Retallack, 1980). Glacial influence was least in the Bowen Basin which was some 10° further north in palaeolatitude than the Sydney and Gunnedah Basins. The extent of marine influence on coals was least in the intracratonic basins, reaching a maximum where the Sydney, Gunnedah, Bowen and Arckaringa Basins were more directly connected to the sea. Marine conditions were established throughout most of the basins between late in the Early Permian and early in the Late Permian. Following regression of the sea in the Late Permian, and further climatic amelioration, coal measures composed of a Glossopteris dominated flora were formed throughout the Sydney, Gunnedah, Bowen, Galilee and Cooper Basins. Depositional environments in the marginal basins tend to be deltaic at the base becoming fluvial upwards. "Marine" intercalations are a feature of the lower part of the sequence, and coarse , braided fluviatile deposits occur intermittently throughout, probably due to local tectonic controls . Braided fl uvi at i le deposits are often a major component at the top of the coal measures, and they grade laterally into transitional facies towards the basin centre. Other more local depositional environments discussed in the following section have been reported in area studies, although some interpretation s are contentious . The intracratonic basins are characterised by meandering fluvial systems whi eh, in the Cooper and Galilee Basins, have probably reworked initially deltaic deposits, with overbank, lacustrine and paludal elements in the associated flood basins . The continental basins could be expected to grade laterally into transitional (deltaic or shoreline) facies where they join the marginal basins . COAL TYPE AND DEPOSITIONAL ENVIRONMENT The microlithotype compositions for various coal basins in the Early Permian are summarised in Figures 4 to 6 and in Figures 7 and 8 for the Late Permian. Fineness of banding and vitrinite content may be estimated from these data by Australian Coal Geology 4, Part 2

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J.W. Hunt

reference to Figure 3. Table 1 shows a highly simplified correlation of coal-bearing units discussed in the following sections which contain a summary of interpretation s of the depositional systems of the coal basins, and comments on vert i ea l and 1atera l trends in vi tri ni te content where appropriate. Early Permian Bowen Basin The Bowen Basin contains Early Permi an coal measures at two horizons. The lower coal-bearing sequence in the Reids Dome Beds was deposited early in the Early Permian and the upper coal-bearing sequence, which includes the Collinsville and Blair Athol Coal Measures, was deposited late in the Early Permian. Vitrinite-poor seams in the Reids Dome Beds (Figure 4) accumulated in a swamp-dominated alluvial plain crossed by moderate sinuosity meandering streams, while those with a higher vitrinite content developed in a similar environment crossed by high sinuosity meandering streams (Fleming, 1982). A restricted deltaic depositional environment has been postulated for the Collinsville Coal Measures (Figure 4) by Mengel (1975), and the basal seam is vitrinite-poor . The depositional setting of the Blair Athol Coal Measures (Figure 4) has been described as an isolated topographic basin by Witcher and others (1960) and Osman (1970). The thick basal seam at Blair Athol and Wo lfang is vi tri ni te-poor but the thin upper seams at Wolf ang are vitrinite-rich . Sydney Basin Petrographic data are available for the later Early Permian Greta Coal Measures at Cessnock, Muswellbrook and Glendonbrook in the north of the Sydney Basin and the Clyde Coa 1 Measures in the south. The Greta Coa 1 Measures at Cessnock (Figure 5) were probably deposited in peat swamps associated with fluvial fan delta systems building out into open water. Postulated depositional environments for the Greta Coal Measures at Muswel lbrook (Figure 5) include deltaic and fluvial elements probably down dip from alluvial fans, suggested by an increasing amount of coarse elastics towards the bounding Hunter Thrust System. Vitri nite tends to increase up the sequence and a low vitrinite basal seam is sometimes present. The Clyde Coal Measures (Figure 5) were developed within a palaeodrainage system incised into the Upper Carboniferous basement (Gast in and Herbert, 1973). Gunnedah Basin Limited petrographic data are available for later Early Permian coals in the The rapid Maules Creek Formation (Figure 5) of the Gunnedah Basin. north-easterly thickening of the Maules Creek Formation, predominance of coarse elastics (Brownlow, 1980), presence of both fining and coarsening up sequences with the abrupt appearance of coal seams are indicative of braided stream deposition with intermittent peat formation during times of low sedimentation. Coals within the thick sequence to the northeast are vitrinite-rich while those in the thin sequence in the south are vitrinite -poor . New England Block The Ashford Coal Measures (Figure 5) are located within the orogenic New Engl and Fo 1d Belt east of the Gunnedah Basin and north of the Sydney Basin Australian Coal Geology 4, Part 2

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491

Figure 1). Sedimentation was probably fluvial and the sequence is underlain by conglomerate, which is sometimes coal-bearing (Britten , 1975a). VITRINERTITE

VITRINERTITE ♦

♦

DURO(LARITE

♦

(LARODURITE

(L ARODURITE 100

100

100 """'=----'.....__,._,_---'.___ .__,.___,_--'----,.___,_~1 00 50

100 -==-__,.....__,._,_---'.___.__,.___,_....1......._....:,::::::a 1oo

INERT ITE

VI TRITE

INE~TITE

DU RITE

(LARITE

DURITE

MICROLITHOTYPE ANALYSIS

VI TRITE (LARITE

MICROLITHOTYPE ANALYSIS EARLY PERMIAN- SYDNEY BASIN

EARLY PERMIAN- BOWE N BASIN

COLU N SVILLE WOLFAN G

BLAIR

CO AL MEA SURE S

BA SI N

.\THOL

REIDS

DOM E

EN C L OS E S

BEOS

POINT

FALLING

111

Figure 4.

COAL IIIUSUN:S CESSNOCK (C)

CIIANICY CORN(R aAS IN (C)

EARLY PERIIIAN- GUNNEOAH MEA SURES

(CJ

-♦

{C ♦ S)

AWA Y

BASIN

(EAST)

MAUL.CS C"fEK FOftMATION (C)

EARLY P£RIIIAN - NEW ENGLAND BLOCK

MA JO RIT Y

FROM

DATA

ASHF0"0 COAL MEA SUIIES

MAJORITY

• OF

GlltfTA

(')

( CJ

CO AL

LI N E

'• ··•

- -4 G"[U COAL IIIIUSUIUS IIIIUSWELLBROOK (C) • CLYOt: COAL MU.SUMS (C)

COOK

ANO

READ

( 18911)

DATA

(

COMPOSITE

SUB SECTIO N

Microlithotype analysis of Early Permian coals from the Bowen Basin.

Figure 5.

Microlithotype analysis of Early Permian coals from the Sydney and Gunnedah Basins and the New England Block. See Fig . 4 for explanations .

Cooper Basin Early Permian coal measures in the Cooper Basin are found within the Patchawarra Formation (Figure 6), which was deposited in a fluvial depositional setting consisting of high sinuosity meandering streams (Grund, 1966; Thorton, 1979) . Smyth (1982) has shown a good correlation between vitrinite-poor coals and overbank facies, and between medium-vitrinite coals and channel facies in the Patchawarra Formation. Arckaringa Basin The Arckari nga Basin is an i ntracratoni c Permi an basin composed of deep marginal grabens or half grabens and a large central area of shallow basement (Devine and Youngs, 1975). The depositional environment for a seam in the Mt . Toondina Formation (Figure 6) was probably fluvial.

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492

Pedirka Basin The coal-bearing Purni Formation (Figure 6) in the Pedirka Basin consists of terrestri a 1 sediments deposited fo 11 owing a southwest erly retreat of the sea through the Arckaringa Basin (Devine and Youngs, 1975). Microlithotype compositions of cuttings from three wells in the basin are shown on Figure 6. Late Permian Bowen Basin Economic coal facies were developed in the Bowen Bas i n both early and late in the Late Permi an, and a 1though the intervening strata are coa 1-beari ng, the frequency and thickness of tuff bands throughout has precluded the coals from consideration as economic deposits to date . The early Late Permian German Creek Formation is overlain by the marine MacMillan Formation, which interfingers with the partly laterally equivalent Moranbah Coal Measures . They are overlain by the uneconomically coal-bearing Fair Hill and Burngrove Formations or Fort Cooper Coa 1 Measures through most of the basin. Later in the Late Permian, economic coal facies were developed throughout most of the basin. They are the Ranga 1 Coa 1 Measures in the north and south, the Bara 1aba Coa 1 Measures in the east, and the Bandanna Formation in the west (See Table 1) . VIT RINERTITE +

OUROCL AR ITE +

VIT RINE RTIT E

(L AROO URITE

DU R0CL AA ITE

100

CL AR0DU RITE 100

100 .__,__....___'-'---'---"--'---''--'-'--L ..::as 100

INER TI TE

♦

VITRITE CLARITE

DUR ITE

(LARITE

OU RITE

100

100 IN[RT ITE

VIT RITE

MICR0LITH0TYPE ANALYSIS

LATE PERMIAN -

-•

UNCOftRELATED SEAM (C • $)

BOWEN BASIN

I AHDANNA .. - , o,u uTION (Cl

lltAHGAL ·· - coAL MEASURES 1,1 FORMATION

.. · · ·•

PUftNI

• . . . fAlR HILL

FORMATtON (C +$)

fOfltMATION

PATCHAWARR A

FORMAT ION (C•Sl

•-

Figure 7.

COOPER

BAS I N

TOOLaCM[E FOftMATI0N

LATE PERM I AN -

Microlithotype analysis of Early Permian coals from the Arckaringa, Pedirka and Cooper Basins . See Fig. 4 for explanations.

(CJ

IC)

MOIUNBAH CO AL ME.I.SURES t.)

LATE P[RM IA N -

Figure 6.

lol[MICR

(C)

_ _ GCIUUN CR[fK F0IUOTION ( C I

EAR LY PERMIAN • COOPER BASIN -

8ARALAIA ·· - cOAL M(ASURES (C)

. . . . ICALOOLA

• • . • BIJANGROVE

EAR LY PERMIAN - PEDIRKA BASI N

Eosl

NDflh ond Ctnlrol

Wtsl

EARLY PERM IAN - ARCKAR INGA BASIN

GAL I LEE

IAHOANIU

FOftMaTION

IC •S )

BASIN (C)

Microlithotype analysis of Late Permian coals from the Bowen, Cooper and Galilee Basins . See Fig.4 for explanations.

Australian Coal Geology 4, Part 2

J.W. Hunt

493

The German Creek Formation (Figure 7) overlies the marine Maria Formation and was deposited in a deltaic environment, which prograded from a westerly, quartz-rich province (Dickens and Malone, 1973), probably in an estuarine or i nterdi stri butory bay setting, evi de need by frequent burrows. The Moranbah Coal Measures (Figure 7) have been described as fluvial/upper delta plain sediments (Archi ba 1d, 1982) deposited in a south f1 owing drainage system, carrying volcanolithic sediments from a northern source . Depositional environments in the Fair Hill Formation are poorly documented and probably range from fluvial to deltaic. Microlithotype analyses for several seams in the Fair Hill Formation in Emerald NS2 are shown in Figure 7. The seams are coarse to medium banded with high vitrinite contents. The samples analysed had high ash contents, and the organic composition of the seams probably is not comparable to low-ash seams formed in a similar environment. Burrowed sections in the Burngrove Formation (Figure 7) suggest intermittent estuarine or interdistributary bay conditions . The Rangal Coal Measures (Figure 7) have also been attributed to a fluvial depositional system (Jensen, 1971), although given the preponderance of peat formation, the fluvial facies can be regarded as a subordinate e 1ement of an essentially pa 1uda 1 system (Mallett, 1982) . Vitrinite content varies from low to medium for the thinner sequence in the north and 1ow to high in the east. The deposit i ona 1 system for the Baralaba Coal Measures (Figure 7) has been described as fluviodeltaic (Mallett and others, 1980) with fluvial elements encroaching on extensive paludal systems in the south, and deltaic components in the north . Seams in the basal Kaloola Member tend to be vitrinite-rich, and vitrinite content is medium to high in the remainder of the sequence. The depositional environment for the Bandanna Formation in the west (Figure 7) has been described as continental to fluvial (Hawthorne, 1975). Sydney Basin Coal-bearing facies were deposited in the Sydney Basin throughout the whole of the Late Permian . In the northeast, around Newcastle, the Tomago and overlying Newcastle Coal Measures contain mainly economic coal throughout, with the exception of a barren i nterva 1 in the middle of the former and the tuff-banded coals in the middle of the latter. Their equivalents in the Upper Hunter Valley to the north are the Wittingham and overlying Wol lombi Coal Measures, and the latter are often highly tuff-banded and uneconomic. In the south and west of the Sydney Basin, the I 11 awarra Coa 1 Measures contain equivalents of the northern sequences of the basin (Table 1). The sequence in the northeast represents a transition from burrowed estuarine and lower deltaic depositional environments containing vitrinite-rich seams in the Tomago and basal Newcastle Coal Measures (Figure 8) (Connolly and Ferm, 1971; Diessel, 1980) to terrestrial alluvial fan deposits comprising coarse elastics which contain vitrinite-poor seams in the upper sub-groups of the Newcastle Coal Measures . The Whittingham Coal Measures (Figure 8) are transitional with underlying marine rocks, and postulated depositional environments include burrowed deltaic, fluvial meandering (Britten, 1975b; Marchioni, 1982) and alluvial piedmonts (Cameron and others, 1982). Conaghan (1982) proposed a deep water lacustrine origin for some coals in the region . Vitrinite content is usually high except for the Bayswater seam, which contains 25-40% (mmf) vitrinite. Britten and Smyth (1973) proposed a shallow lagoonal/lacustrine depositional environment for the formation of the Bayswater seam.

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494

KEY

VITRIN[RTIH

(OA L

DUR0CLARIH

SILT

CL AR0DUR IH 100

SANO

(ONGLOHERATE

h:3-52 GUNNEOAH

BANDIN G OF

HICROUTHOTYPES very l ine h = 6-10 h=4-6 l ine

med ium h = 2- 4 coarse h= 0 - 2 (see F1gJ also )

h:3L7! 100

IH[R TITE

HUSWELLBROOK

100 VITRIH

CLARITE

OUR ITE

HIC RO LITHOTYPE ANALYSIS LATE

PER MI AN -

ILL. Wt. RFU. • • • COAL MEA SU RE S (C} - -

SYDNEY BAS I N North

North eosl

South ond Wu t

NEW C ASTLE COAL lo'[A SURES (Cl -

WITTI NGMAM CO AL M[.t, SURES (C)

:~:of;, LITHGO W SE AM

(Cl

L ATE

P ERM l AN -

GU NN[ OAH

BASIN

Sou th coo ~~:~ll wt:;~RES H

CC )

HOSlllSSONS ICI SEU.I

L ATE P[R MI AN -OAKL AN OS BASIN

Figure 8.

L ANE S SHAFT

S(A ""

IC)

Microlithotype analysis of Late Permian coals from the Sydney, Gunnedah and Oaklands Basins. See Fig. 4 for explanations.

24m

Figure 9.

110m

217m

3BO m

Correlation between microlithotype banding and tectonic setting for early Permian coals of the Sydney and Gunnedah Basins.

The depositional setting for the main coal-bearing sequence in the Illawarra Coal Measures to the south of the basin (Figure 8) has been described as lower delta pla i n (Bowman, 1980). The basal seams are associated with burrowed pro-delta and lower delta facies while the upper seams have been attributed to an upper delta plain environment (Connolly and Ferm, 1971). The basal seam (Woonona) is vitrinite-poor_ The main coal-bearing sequence of the Illawarra Coal Measures in the west (Figure 8) comprises braided fluvial sediments (containing the low-vitrinite Lithgow seam) overlain by pro-delta/lower delta sediments and finally by fluvial sediments (Bembrick, 1981). The Ul an seam to the northwest (Figure 8) in a similar stratigraphic position to the Lithgow seam is also low in vitrinite . Gunnedah Basin The B1ack Jack Formation whi eh contains Late Permi an coa 1 measures in the Gunnedah Basin is currently the subject of a major basin-wide drilling programme, and a limited amount of petrographic data is available (Figure 8) . The lower seams tend to be vitrinite-rich and the upper seams, vitrinite-poor . The Hoskissons seam which is worked in the bas i n is a correlative of the Australian Coal Geology 4, Part 2

J.W . Hunt

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Bayswater seam to the south. It is vi tri nite-poor overa 11 ( 40% mmf) . The sequence is transitional with underlying marine sediments and was deposited in a deltaic setting (Weber and others, 1982). Galilee Basin A thin sequence of Late Permi an coa 1 measures in the Bandanna Formation is exposed only along the eastern margin of the Galilee Basin, and microlithotype data are available for the Degulla area to the south (Figure 7). The depositional environment of the sequence has been described in terms of a southwards prograding deltaic sequence (Hawkins, 1976) . Vitrinite content is higher for the basal seams in the Degulla area and the overall vitrinite content is lower in the north of the basin and increases to the south. Cooper Basin Late Permian coal measures in the Toolachee Formation of the Cooper Basin are kn_own only from petroleum drilling, and petrographic data are available from the Patchawarra and Nappamerri e Troughs in the South Australian half of the basin (Figure 7) . A depositional setting of extensive floodplains traversed by northerly flowing channels during a tectonically quiescent period has been proposed for the Toolachee Formation (Thornton, 1979) . 0aklands Basin The Corrabi n Coal Measures (Figure 8) at the top of the sequence in the 0aklands Basin contain only a few seams (Driver, 1975), and the depositional environment was probably fluvial . DISCUSSION Coal type is determined principally by the kind of flora which initially formed the peat, and the e·xtent of its alteration by aerial oxidation or biochemical agents during · deposition and early in diagenesis. The Permian succession of floras was climatically controlled and gradational in the Sydney Basin (Retallack, 1980) and, given the meridional orientation of the basins, probably significantly diachronous (Brakel, 1982). Following the waning of glacial conditions early in the Permian, a generally cool temperate climate has been postulated for the remainder of the Permian period. The Permian (and Triassic)flora consist of a low diversity pteridosperm dominated assemblage, with the few elements often represented by innumerable individuals (Gould and Shibaoka, 1980). A few representatives of the lycopods, equisitaleans and ferns are present (Gould, 1975). An important implication of this situation is that the peat-forming components of the flora may be regarded as a more or less homogeneous input to the Permian coal swamps, although given the productivity of floating macrophytes and reeds in present day swamp successions (Moore and Bellamy, 1974) combined with their low preservation potential as macrofossils, it is possible that the contribution of Permian analogues has been underestimated. The extent of alteration of the peat-forming material is dependent on several interrelated factors including rate of subsidence, climatic conditions, geographical position, depositional environment, the composition of the peat-forming flora and most importantly the level and composition of swamp water and fluctuations of the groundwater table. Given a cool temperate climate, microbial degradation of peat would have proceeded at a slow rate, and subaerial oxidative decomposition was probably a significant factor in the formation of inertinite-rich peats. The interaction of the several factors Australian Coal Geology 4, Part 2

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outlined above to form coal deposits is examined in the following section, in the context of the depositional systems of the basins. Microlithotype Composition Microlithotype classification was initially proposed in Germany because of differences in the techno l ogi ea l behaviour of coals related to different maceral associations. A variety of genetic interpretations based on the Carboniferous coals of Europe and America, many of which place emphasis on the kind and proportion of exinites present in the microlithotypes has also been developed (e . g. Hacquebard and others, 1967). Because of the small amount (5% average) of exinite and the dominance of sporinite in Australian Gondwana coals, the microlithotype analyses presented in this paper have been essentially reduced to a two-component system measuring vitrinite (vitrite + clarite) and inertinite (inertite + durite), with all possible mixtures of vitrinite and inertinite (vitrinertite, duroclarite and clarodurite) . Microlithotype analysis at the two-component level measures the proportion of components which have attained an observed thickness (50 µm) without a significant change taking place in the redox conditions effective in the _vicinity of the sampling site . The thickness attained in any one cycle of oxidation or reduction is a function of biological productivity and preservation, versus the periodicity of changes in the redox conditions at the site, both of which are determined by the complex interact ions of flora and swamp dynamics with climatic, geographical and geological conditions. Changes in redox conditions at the 50 µm band width level probably reflect fluctuations in water table with a seasonal peri odi city, given an accumulation rate of lm of peat/1000 years and a compaction factor of 10 : 1. Examination of data in this study shows t hat the coal s from a particular area and age form a di st i net i ve suite, with a characteri stic degree of banding across the whole range of vitrinite content. The curves in Figure 3, which show equivalence of banding were calculated from the data in Figure 8. An hypothesis that Early Permi an coals are more finely banded than Late Permian coals is supported by data in this paper, in that no Early Permian coal is as coarsely banded as the most coarsely banded Late Permi an coal. However, the overlap of banding is considerable, wi th early Permian coals ranging between banding coefficients (h) 3 and 9 (most results) and Late Permian coals ranging between h = 2 and 8. Within t he Late Permian, coarsening of band width with decreasing age is apparent for trough sequences, e.g. the Tomago-Newcastle Coal Measure sequence (Figure 8) in the Sydney Basin and German Creek/Moranbah-Rangal Coal Measure sequence (Figure 7) in the Bowen Basin. Shelf sequences are more unpredictable, the I 11 awarra Coal Measures (Figure 8) in the southern Sydney Basin becoming more finely banded upwards, possibly reflecting subtle changes in subsidence and sedimentation rates. Coals of the intracratonic Cooper Basin (Figures 6 and 7) are finely banded in both the Early and Late Permian. Lateral variations in the degree of microscopic banding with tectonic setting are illustrated by the Early Permian coals of the Sydney and Gunnedah Basins. Total thickness of representative sections for the above coal measures, the aggregate thickness of various l i tho l ogi es and the range of banding of the microlithotypes are shown in Figure 9. All the above coals are vitrinite-rich across a range of depositional environments .

Australian Coal Geology 4, Part 2

J.W. Hunt 497 The summary of microlithotype composition, depositional environment and tectonic setting for Early Permian coals in Figure 10 shows a good correlation between microl ithotype composition and tectonic setting but no correlation with depositional environment that can be applied to all basins. Lateral variation in microlithotype composition with tectonic setting in the Late Permi an is demonstrated by a vi tri ni te-poor horizon within the Sydney Basin (the Bayswater-Ulan-Lithgow-Woonona seam horizon in Table 1) which was formed following a basin-wide cycle of transgression and regression. The Bayswater seam in a thick fluvio-deltaic sequence (Marchioni, 1982); Cameron and others , 1982); Britten, 1975b) is finely banded (h = 4-5), the Woonona seam, in a thin pro-delta sequence (Bowman, 1980) is finely banded (h = 6) and the Lithgow seam in a thin braided fluvial piedmont sequence (Bembrick, 1981) is fine to very finely banded (h = 5\ - 8). Figure 11 shows the relationship between microlithotype composition, depositional environment and tectonic setting for Late Permian coals . There is good correlation between microlithotype composition and tectonic setting and a poor correlation between microlithotype composition and depositional environments .

. .

VITRINERTITE

0UR0CLARITE

CLAR00URITE 100

100 -,:;:,____._....J.....,__...>-___._

_,__......._..J.....1_->--==-100

INERT ITE

VI TRITE

100 _,:::,;___._....J......,.__.....____.'--..,___._....l.....l.__..=,-100 INERTITE SO VI TRITE

DURITE

CLARITE

0URITE

MICR0LITH0TYPE ANALYSIS @ · Shell

CJ @ ~

Figure 10. Relationship between microlithotype composition, depositional environment and tectonic setting in the Early Permian of eastern Australia.

CLARITE

MICR0LITH0TYPE ANALYSIS

(!) · Trough

Upper Delh Pl• in • Fluvial Lower Oelh Pl• in Bnided Fluvi•l Piedmont Mundering Fluv ial • Flood Basin

@ · Shell

(!) ·Trough

EJ Oelhic -und ilhronli.ted 12] F•n Delh . Fluvio Delhic ~ Br, idtd Fluvi1l Pied,nont Munduing Fluvi•l • flood Buin

Figure 11. Relationship between microlithotype composition, depositional environment and tectonic setting in the Late Permian of eastern Australia.

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The trend to coarser banding in younger coals of the Sydney Basin has been attributed by Cook (1981) to differences between the Early and Late Permian flora, which is supported by Retallack (1980). This trend in Australia culminates in coarse to medium banded (h = 1½ - 4) Triassic coals formed from a Dicroidium dominated pteridosperm flora. Vertical trends in microlithotype composition are not as well marked in the Bowen Basin as in the Sydney Basin. This may reflect a smaller variation in the coal-forming flora which may have been s i gni fi cant ly di achronous because of the warmer pal aeo latitudes to the north (Brakel, 1982). The relationship between microlithotype composition and tectonic setting may to some extent reflect higher organic productivity in the troughs due to better nutrient supply (Moore and Bellamy, 1974, p.50), with the reverse situation applying on the shelf areas and in the intracratonic basins. Variations in microscopic banding between trough and shelf sequences are usually paralleled by variations of several other geological parameters, including the total thickness of the coal measure sediments and the geometry and total and individual thickness of coal seams (Diessel, 1970; Shibaoka and Smyth, 1975; Bless and others, 1981) . The correlation of depositional environment with vitri ni te content in the Early Permian is not good because although the fluvial coals are usually vitrinite-poor, vitrinite-rich coals are found in fluvio-deltaic (including fan deltas), deltaic and braided fluvial environments. Smyth (1982) has shown a good correlation between vitrinite-poor coals and overbank (flood basin-paludal) facies, and between medium-vitrinite coals and channel facies in the intracratonic Cooper Basin . Vitrinite-rich coals in the Late Permian are characte r istic of the lower delta plain environment, reflecting higher groundwater levels; while vitrinite-poor coals are characteristic of upper delta plain, meandering and braided fluvial environments, reflecting lower and fluctuating groundwater table levels. CONCLUSIONS The major controls of microlithotype composition (i.e. the degree of mixing of vitrinite and inertinite at the 50 µm band width level) for Australian Permian coals were the composition of the peat-forming flora (low diversity pteridosperm assemblage) and the tectonic setting of the coal basins. Coals from a particular area and age form a distinctive suite with a characteristic degree of microscopic banding for the whole range of vitrinite content. Early Permian coals are more finely banded on average than Late Permian coals, probably reflecting climatically controlled compositional changes in the peat-forfuing flora. Fine to very finely banded coals were formed in the i ntracratoni c and i ntramontai ne basins both in the Early and Late Permi an, reflecting slow subsidence rates, and low biological productivity due to low nutrient supply. In the marginal basins lateral variation in the degree of microscopic banding may be correlated with tectonic setting in both the Early and Late Permi an. More coarsely banded coals are associated with thick trough sequences, and more finely banded coals with thin shelf sequences, probably reflecting higher preservation and higher rates of organic productivity because of enhanced nutrient supply.

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Vitrinite-rich coals are most often associated with lower delta sediments, while vitrinite-poor coals are most often associated with upper delta meandering fluvial and braided fluvial sediments. Several notable exceptions to the above generalisation suggest that local variations in the composition and 1eve 1 of groundwater may be the major determinant of the overa 11 vi tri ni te/ inertinite ratio. ACKNOWLEDGEMENTS This paper summarises data collated for the j oint CSIRO-BMR "Permian Coals of Eastern Australia" project funded unde r the National Energy Research, Development and Demonstration Prog r am admin i stered by the Department of Nati ona 1 Deve 1opment and Energy . Many of the analyses presented herein were made by M. Smyth of the CSIRO Di vision of Fossil Fuels, and more recent analyses have been made by myself with guidance from M. Smyth . The author wishes to thank H.J . Harrington and A. Brakel of the Bureau of Mineral Resources , and M. Smyth and A. J.R . Bennett of this Div i sion for critically r eading the manuscript and for their useful comments . T. Latter of the BMR drafting section prepared some of the diagrams. Grateful acknowledgement is made to the many companies and government bodies that provided samples from newl y explored areas, in part i cular to AMAX, BHP , Cl utha and Utah Dev . Co. , the Geo l ogi ea 1 Survey of Queensland and the N. S. W. Dept. of Mineral Resou r ces . REFERENCES Archibald, D., 1982 . Sedimentary environments of the Peak Downs Coal Mine, Central Queensland. Abstracts of the Permian Geology of Queensland Symposium , Brisbane,~. 129 . Bembrick, C., 1981. Stratigraphic subdivision and sedimentary environment of the Illawarra Coal Measures, Western Coalfield . Abstracts of Symposium on Geology and Colliery Development in the Western Coalfield, NSW, 5-6. Bennett, A.J.R., 1974. Coal petrology and its application to seam evaluation . In Geology and geophysics in coal exploration and mining, Australian Mineral Foundation Inc., Adelaide, 139-169 . Bless, M. J . M., Paproth, E and Wolf, M., 1981. Interdependence of basin development and coal formation in the West European Carboniferous . Soc. Nat . Elf-Aguitaine (Production), BCREDP 5 , 535-553. Bowman, H. N., 1980. Southern Coalfield, Upper Shoal haven Group and Illawarra Coa 1 Measures . In A guide to the Sydney Basin (Herbert , C. and He 1by , R. , eds.) N.S.W . Geol . Surv . Bull . 26, 117-132 . Brakel , A. T. , 1982. Stratig r aphic correlation of the upper coal measures of the Sydney Basin with their equivalents in the Bowen Basin. Abstracts for the Sixteenth Symposium on "Advances in the Study of the Sydney Basin", 32-34 . Britten, R.A., 1975a. Ashford Coal Field, NSW . In Economic geology of Australia and Papua New Guinea. 2. Coal (Traves, D. M. and King, D., eds), Australasian Institute of Mining and Metallurgy, Melbourne 258-260.

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Britten, R.A., 1975b. Singleton-Muswellbrook District. In Economic geology of Australia and Papua New Guinea. 2. Coal. (Traves, D. M. and King, D., eds.), Australasian Institute of Mining and Metallurgy, Melbourne, 191-205. Britten, R.A. and Smyth, M., 1973. The Bayswater coa l member of the Singleton Coal Measures of New South Wales . Austral. Inst. Min. Metal 1., Proc. 248, 37-47. Brownlow, J . , 1980. Early Permian sediments in the Maules Creek District, New South Wales . Coal Geol. ~ (3, 4), 126-160. Cameron, R. G. , Conaghan, P.J. and Parbury, C.F.R., 1981. Piedmont depositional regimes within the Ravensworth al l uvial embayment, Wittingham Coal Measures, northern Sydney Basin. Abstracts for the Sixteenth Symposium on "Advances in the Study of the Sydney Basin", 32-34. Conaghan, P. J . , 1981. Lacustrine (Gilbert) deltas in the Permian coal measures of eastern Australia and India; implications for the widespread hydroponic origin and deep-water diagenesis of Gondwanan coals . Abstracts for the Sixteenth Symposium on "Advances in the Study of the Sydney Basin", 6. Connolly, J.R . and Ferm, J.C., 1971. Permo-Triassic sedimentation patterns, Sydney Basin Australia. Am. Assoc. Pet. Geol. Bu l l . 55, 2018-2032 . Cook, A. C., 1981. Temporal variation of the type in Australian coal seams. Soc . Nat. Elf-Aguitaine (Production), BCREDP, 5(2), 443-459 . Cook, A. C. and Read, H. W. , 1968. Clyde River Coal Measures, J . Proc. 101, 109-118.

The petrography of a coal seam from the Clyde River Gorge NSW. R. Soc . N.S.W.,

Devine, S. B. and Youngs, B. C. , 1975. Review of the Palaeozoic stratigraphy and petroleum potential of northern South Australia. APEA J. 15(1), 45-54. Dickens, J.M., 1967. Correlation chart for the Permian system in Australia. In Gondwana stratigraphy, IUGS Symposium, UNESCO, Buenos Aires. Dickens, J.M. and Malone, E. J., 1973. Geology of the Bowen Basin, Queensland. Aust. Bur. Miner. Resour. Geol. Geophys. Bull. 130. Diessel, C.F.K., 1970 . Paralic coal seam formation. Australian Membership, 8th Conference, Brisbane.

In Inst . of Fuel,

Diessel, C.F.K., 1980 . Newcastle and Tomago Coal Measures . In A guide to the Sydney Basin (Herbert, C. and He 1by R. , eds. ) NSW Geo 1. Surv. Bull. 26, 101-114. Driver, R.D., 1975. Oakland-Coorabin Coal Field, NSW. In Economic geology of Australia and Papua New Guinea. 2. Coal (Traves, D.M., and King, D., eds) Australasian Institute of Mining and Metallurgy, Melbourne, 260-263. Fleming, P. J . G. , 1982. Coal-forming and associated environments, Permian Denison Trough, Queensland. Queensl. Gov . Min. J. 83 (968), 284-292.

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Gostin, V. A. and Herbert, C., 1973 . Stratigraphy of the Upper Carboniferous and Lower Permian sequence southern Sydney Basin . Geol. Soc . Aust. J. 20(1), 49-70 . Gould, R. , 1975. The succession of Australian pre-Tertiary megafossil floras . Bot. Rev. 41(4), 453-483. Gould, R. and Shibaoka, M., 1980. Some aspects of the formation and petrographic features of coal members in Australia, with specific reference to the Tasmanian orogenic zone. Coal Geol. ~(1), 1-29 . Grund, R., 1966. The Glaci ene sediments of the Coo ers Creek Basin. University of Adelaide B.Sc. Hons thesis unpub . . Hacquebard, P.A., Birmingham, T.F. and Donaldson, J.R., 1967. Petrography of Canadian coals in relation to environment of deposition. In Symposium on Science and Technology of Coal, Ottawa, 84-97 . Harrington, H. J., 1974. The Tasman Geosyncline in Australia. In The Tasman Geosyncline - A symposium (Denmead, A. K. , Tweedale, G.W. and Wilson, A.F., eds) Geol . Soc . Aust . , Qld. Div., Brisbane, 383-407. Harrington, H. J., 1982. Tectonics and the Sydney Basin. Keynote Address. In Abstracts for the Sixteenth Symposium on "Advances in the Study of the Sydney Basin", 15-19 . '

Hawkins, P.J . , 1976 . Facies analyses and economic significance of Later Permian strata in the northern Galilee Basin. Queensl . Gov . Min. J . 77, 15-32. Hawthorne, W.L . , 1975. Permian Coal Measures - other basins - An Introduction. In Economic Geology of Australia and Papua New Guinea. 2. Coal (Traves, D. M. and King, D., ed), Australasian Institute of Mining and Metallurgy, Melbourne 246-247. International Committee for Coal Petrology (ICCP), 1963. book of Coal Petrography, CNRS, Paris, 2nd Edition .

International Hand-

Jansen, A.R., 1971. Regional aspects of the Upper Permian regression in the northern Part of the Bowen Basin Queensland. In Proceedings of the second Bowen Basin symposium (Davis, A. , ed), Queens 1. Geo 1. Surv . 1 Rep . 62, 7-17. Mallett, C.W., 1982 . Depositional environments in the Rangal Coal Measures, southern Bowen Basin . Abstracts of the Permian Geology of Queensland Symposium, Brisbane,~. 30. Mallett, C.W., Flood, P.G . , Nguyen, V.V. and Ledger, P. , 1980. Depositional environments in the Baral aba Coal Measures Moura Queens 1and. Aust., CSIRO, Div. Appl. Geomech. 1 Geomechanics of Coal Mining Rep. 19, 1-29. Marchioni, D., 1982 . Fluvial sedimentation in the Foybrook Formation, Wittingham Coal Measures . Abstracts for the Sixteenth Symposium "Advances in the Study of the Sydney Basin", 13 .

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In Economic geology of Collinsville Coal Measures. Mengal, D. C., 1975. Australia and Papua New Guinea. 2. Coal (Traves, D.M. and King D., eds.), Australasian Institute of Mining and Metallurgy, Melbourne, 83-89. Moore, P.O. and Bellany, D.J., 1974. Ltd. London.

Peat lands, Paul Elek (Scientific Books)

Osman, A.H., 1970. The Blair Athol Coalfield. In Proceedings of the second Bowen Basin symposium, Queens l. Geo l. Surv. Rep. , 62. Retallack, G., 1980. Late Carboniferous to middle Triassic megafossil floras In A guide to Sydney Basin (Herbert, C. and from the Sydney Basin. Helby, R. eds) N.S.W. Geol. Surv. Bull . 26, 385-430. Shibaoka, M. and Smyth, M., 1975. Coal petrology and the formation of coal seams in some Australian sedimentary basins. Econ. Geol. 70, 1463-1473. Smyth, M., 1974. The relationship between coal macerals and microlithotypes Aust., CSIRO, Miner. Res. Lab., Invest. Rep. 105. Smyth, M. , 1982. Coal microlithotypes related to sedimentary environments in Paper presented at International the Cooper Basin, Australia . Congress on Sedimentology, Hamilton, Ontario. Regional stratigraphic ana l ysis of the Gidgealpa Thornton, R.N.C., 1979. S. Aust. Geol. Surv. Bull 49, Group, Southern Cooper Basin Australia. 1-140. Weber, C.R., Becket, J. and Hamilton, D., 1982 . Recent exploration in the Gunnedah Basin by the Department of Mineral Resources. Abstracts for the Sixteenth Symposium on "Advances in the Study of the Sydney Basin", 36-37. Witcher, I.G., Mciver, F. and Knight C. L., 1960. Report on Blair Athol Coal Field. Consolidated Zinc Pty. Ltd. Report (unpub).

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Coal Sedimentation in the Reids Dome Beds, Bowen Basin: A depositional Model J. W. Bees ton

Geological Survey of Queensland Mineral House, George Street, Brisbane, 4000 Austral la. ABSTRACT Coal accumulations In the Relds Dome beds, Bowen Basin, Queensland, range from phyteral size to seams greater than 12 metres In thickness, and occur within sandstones, sl ltstones and carbonaceous mudstones associated mainly with permanent swamp I lthofacles. Some 190 Intact spot coal samples, augmented where necessary by Intact tota I seam samp Ies and representat I ve part Icu Iate samples, were selected from 8 boreholes. GSQ Sprlngsure 9, 14, 15 GSQ Taroom 11/llA GSQ Eddystone 1, 4 GSQ Emerald 1 GSQ Denison NS 29 Samples were analysed qua I ltatlvely and quantitatively using white I lght Incident and autofluorescence microscopical techniques. Results Include detailed maceral analysis, and palaeobotanlcal Identifications where elements were recognisable. Variations In maceral type and floral content were correlated with llthologlcal, palaeobotanical and palynologlcal characteristics. A resultant model Incorporating five major coal facles was prepared. These facles were termed the wood facles, leaf facles, detrltal facles, articulate facles and gel facles. Various combinations of these facles, termed coal facles assemb I ages, can be recogn I sed In the boreho I es, and can be corre I ated w Ith the llthodeposltlonal system In the Relds Dome beds. Although most maceral types can be distinguished In each I lthodeposltlonal system, various key macerals characterise the various coal facles present. Differences between coal facles are due chiefly to variations In floral type and mode of deposition. The floras contributing to coal accumulation Included a swamp-dwel llng sporophyte flora dominated by articulates, and a riparian flora dominated by the gymnospermous glossopterlds. Peat accumulation took place In free-standing water, ranging from shallow water swamps to deep water ponds and lake margins. Where these supported plant growth, accumulation was either totally autochthonous or mixed autochthonous/al lochthonous. In the absence of In sltu plant growth, accumulation was al lochthonous only. The sites aval I able for plant growth and for peat accumulation were a direct function of the presence and permanence of the various llthofacles within the system. Some Gondwanan coal characteristics can be explained In terms of the model out I lned above. The presence of a riparian Glossopterls flora providing Austral Ian Coal Geology 4, part 2

504

J.W. Beaston

allochthonous material to the peat Is compatible with the apparent allochthonous nature of many coals, this Interpretation being supported by the lack of major rootbeds beneath seams, the lack of stump horizons and upright stems within the above seams, and the horizontal layering of major coal llthotypes. The common but Inconspicuous presence of fine roots within the floors of many seams can then be attributed to the swamp-dwelling articulates, which characteristically developed fine root hairs from a surface rhizome system. The presence of free-standing water with in the peat accumulating environment provided a medium for the deposit ion of the horizontally layered coal llthotypes and the often laterally extensive, thin laminated mudstones which occur In many seams. It also provided a mechanism whereby oxygenated water cou Id a Id In the degradat Ion of Inert In I te macer a Is, such as macr In I te and Jnertodetrlnlte, which commonly form a high proportion of Gondwanan coals. The commonly observed upward Increase In dull coal components through many seam prof! les can be Interpreted as fol lows. An Increase In water Influx caused the peats to become dominated by oxidised al lochthonous mater I al deposited In deep water, and culminated In the deposition of lacustrlne and associated sediments above the submerged peat. (Th is summary Is adapted from a review of the geology and palaeoenvlronment of the Relds Dome beds, Bowen Basin, Queensland, being prepared by J.J. Draper, J.W. Beaston, J.F. Rigby and C.B. Foster, for pub I Ication by the Geological Survey of Queens I and. It Is pub 11 shed w Ith the perm I ss I on of the DI rectorGenera I of MI nes, Queens Iand).

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The Role of the Mine Geologist in Brown Coal Winning R. J . Gaulton

State Electricity Commission of Victoria, Post Office Box 195, Morwell. Victoria . 3840 . Australia

Key Words:

Mine Geology, Geotechnical .

Brown

Coal ,

Surface

Mining,

Coal

Quality,

ABSTRACT Until recently, brown coal in Australia has received relatively little recognition as a potentially valuable resource other than as a fuel for power stations in the state of Victoria. Consequently, a few geologists have been closely involved with brown coal and only a handful have ever practised as brown coal mine geologists. In view of the current expansion of interest in brown coal, this has caused a knowledge gap wi th regard to the contribution geology can and should make at all stages in the development and operation of a brown coal mine . Although it may be useful to examine the role of the black coal mine geologist in this context, it must also be recognised that it is not possible to apply the same criteria for geological input to both black and brown coal mining. This is due largely to the fact that what might be of prime importance in one field is in many cases of only secondary importance in the other. The pecul i ari ties of brown coal and its usual geo l ogi ea l setting must also be both appreciated and understood by the brown coal mine geologist, whose role is thereby sufficiently different from that normally fulfilled by the black coal mine geologist as to canst i tute a quite separate field of endeavour . INTRODUCTION Most economically viable deposits of brown coal in Australia are likely to share a number of fundamental similarities in terms of their general geological setting and age. It can therefore be anticipated that the mining of brown coal at various locations will be subject to a reasonably predictable array of geo l ogi ea l influences, al though these wi 11 vary in severity and relative importance from one operation to another . This means that future mine geologists employed in the brown coal industry will to some degree share a common core of basic duties . The aim of this paper is to present, in simple terms, a listing of the main areas of responsibility likely to .be required of any brown coal mine geologist or mine geology group. A number of hypothetical examples will be referred to in order to more fully explain the significance of some aspects. Australian Coal Geology 4, Part 2

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In discussing the role of the mine geologist, it will be necessary to briefly describe the usual situation in which he or she is likely to work. For the . purpose of presenting this paper then, it can be assumed that : (a)

Coal winning is taking place by large scale surface mining.

(b)

The exploratory phase has yielded adequate reliable information to permit a reasonable degree of proper mine planning.

( c)

The nature and quality of the coa l is sufficientl y we 11 described to accurately assess its general suitability for the utilisation process envisaged.

(d)

Analytical geologist.

and coal

petrographi c services are available to the mine

Methods of data acquisition and interpretati on which can or should be employed by the brown coal mine geologists will not be discussed, as these are dictated preference, available technology and corporate largely by personal . s requirement AREAS OF RESPONSIBILITY For convenience, the practice of brown coal mine geology can be regarded as embracing four broad spheres of activity which often interrelate and sometimes overlap. These are: 1.

2. 3. 4.

Conventional Mine Geology Coal Quality and Coal Lithotype Investigatio ns Geotechnical Control and Hydrogeology Technical and Scientific Liaison

These areas are not listed in any specific order of priority and are likely to vary in relative importance both from one mine or region to another and with time at any one mining operation . CONVENTIONAL MINE GEOLOGY This sphere of activity is probably the least specialised in terms of brown coal mining as it employs standard techniques of geological investigatio n used elsewhere in the mining industry . Conventional geo l ogy in brown coal mining is likely to involve periodicall y updating, enhancing or amending the existing geological model as required by the mining operation. In short, this means that when the geological situation differs or threatens to differ significant ly from that which has been predicted, the mine geologist is called upon to provide some answers. Alterations to the planned development of the mine may also require that extra geological information be obtained at short notice, and here as well the mine geologist has a vital role to play. Ideally the mine geologist will always be in a position to identify and evaluate irregularit ies before problems develop and will be involved in deciding the best remedial action to be taken. Australian Coal Geology 4, Part 2

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Identification of Structures The basic geometry of the strata to be mined will have been defined during the exploratory phase and further refined prior to deve 1opment . This wi 11 have involved drilling and geophysical investigations , and a folio of plans and sections detailing vital information such as top and bottom of coal contours, coa 1 i sopachs, major i nfl uenci ng structures and deve 1opment 1i mi ts wi 11 be available . No matter how good this information i s however, it is obvious that it can never be entirely comp 1ete and numerous surprises, both 1arge and small, await the development of any mine. With brown coal, the most commonly encountered aberrations are likely to be caused by undetected minor structures such as small scale faults, erosional irregularities and burn craters . Having escaped detection prior to mining , such structu r es will be small relative to overall seam thickness, but this does not diminish their importance or effect. The high rate of excavation possible with brown coal mining can quickly result in the inadvertent inclusion of unacceptably high levels of inorganic contaminant, especially where freshly exposed adjacent sediments are of a similar texture consistency and colour to the coal . From the above, i t should be appa r ent that one important aspect of the mine geologist's duties will be the speedy identification and evaluation of· previously undetected structural irregularities. To illustrate this, it would obviously be vital to know whether the sudden appearance of a shallow clay fi 11 ed depression extending downwards into the coa 1 from beneath the overburden is part of an early burn crater or whether it is a cross section through a stream channel, the likely lateral persistence of each being very different. In some cases, it may be necessary for the geologist to probe ahead using drilling, trenching, geophysics or some other investigatory technique, complementing such measures with an informed appreciation of the geological nature of the target. Lithology Again, the geological model constructed prior to development will yield, to varying degrees, a genera 1 but i ncomp 1ete record of the 1itho 1ogi es to be encountered by, or which will influence , the mining operation . Workable seams of brown coal are likely to occur within relat i vely soft, semi consolidated sedimentary sequences which may, at least potentially, be subject to abrupt local changes in nature where for instance epigenetic cementation takes place in otherwise 1oose sands or grave 1s . In extreme cases, this can have an immediate drastic and highly damaging effect on machines such as bucket wheel excavators: Should such an incident occur, the mine geologist can anticipate being called on to answer the following questions (usually put in rapid succession): (a) What is it? (b) How much of it is there? (c) What can we do about it? and (d) Why didn't we know about it? The fourth question can be given diplomatic consideration at a later date, but the first two questions need to be answered quickly so that the third can be resolved. Past experience may well equip the mine geologist to provide a rapid assessment, but sometimes extra information will be required. This may be provided by drilling, geophysics or simple exploratory excavation, all of which will be directed by the geologist. Australian Coal Geology 4, Part 2

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The coal itself may also be subject to unexpected changes in lithology where substantial deposits of massive silica, iron sulphide or other chemically redeposited minerals occur as layers and pockets, within porous woody material, or as joint infillings. Here again the mine geologist will be called upon to provide an assessment of these problems and should keep a detailed record of a 11 such incidents in the event that some pattern of occurrence or association can be delineated. Reserve and Volume Calculations Where it becomes obvious that due to an unforeseen geological influence some revision of existing reserve or volumetric estimates is necessary, it is essential that the mine geologist be involed. This ties in closely with the identification of structure, and it is only when the anticipated shape or extent of whatever it is that has perhaps penetrated or displaced coal is appreciated in terms of its geological genesis that meaningful computations can be carried out. It is of course unlikely that large adjustments will need to be made to the overall estimates of coal reserves, volumes of overburden or interseam sediments. Commonly, however, revisions will need to be made regarding the amount of coal available from one particular level over a given period of time, or in a similar context the amount of waste material which needs to be removed from a development block or other defined area. COAL QUALITY AND COAL LITHOTYPE INVESTIGATIONS Any deposit of brown coal will almost certainly display significant variations in chemistry, petrology and physical properties of the coal . In general, such variations will be reasonably predictable and can therefore be at least partly compensated for . This might be achieved by engineering an appropriate degree of flexibility into the utilisation process or by the implementation of mine oriented measures such as blending and/or selective mining. In either case coal quality can be adversely affected where localised variations well outside the norm arise during mining, and such instances must be properly identified, described and dealt with. Sampling One responsibility of the mine geologist must be to ensure that all sampling, whether at the face, on stream, or by drilling, is both properly implemented and appropriate. The potential for bad sampling practices in brown coal tends to be high, as personnel unaware of the many factors governing the way in which, for instance inorganic constituents are distributed within the coal, are liable to adopt inappropriate sampling procedures . Further inaccuracies can arise where it is not fully appreciated that fresh coal is subject to rapid desiccation on exposure to the atmosphere or that errant lumps of ligneous clay can sometimes easily be mistaken for brown coal when moist. Sampling with regard to petrol ogi ea l , l ithotype or pal aeobotani ea l considerations is also of course heavily dependent on appropriate geological direction. Chemical Properties The non-organic constituents of brown coal will always occur in a variety of forms differing both in mode of distribution and genesis. A typical situation

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faced by the mine geologist is likely to be a complaint from the user or quality controller concerning sudden "high ash" or some related problem. The geologist is then required to quickly determine the nature and source of the offending material and decide whether it is for example due to : (a)

inclusion of mineral matter, and if so, whether epigenetic or syngenetic;

(b)

an anomalously high content of soluble inorganics bonded to the organic coal structure ;

(c)

inadvertent inclusion of adjacent sediments ;

(d)

a combination of some or all of these possibilities.

Obviously, the geologist must have a good appreciation of the way in which non-organic constituents both occur in the coal and can be identified. It is al so desirable that the geologist be aware of the si gnifi ea nee certain coal constituents or combinations of constituents might have in regard to their effect, negative or otherwise, on coal utilisation processes . For instance, sodium and ea lei um may create different degrees of boil er fouling in thermal power stations depending on whether the content of sulphur is high or low. Similarly, a high content of aluminium can cause ash handling and stack emission problems if the percentage of silica present is very small . The organic chemistry of brown coal is potentially even more complex and the mine geologist wi ll probably not be in a position to evaluate organic variations in terms of pure chemistry . With brown coal, however, the organic chemistry is related to both petrology and coal lithotype, and here the mine geologi st can play a vital role in identifying coals which are able to be classified into groupings with similar organic composition and/or behavioural characteristics. One such example might be the close relationship between exi ni te content, l i thotype, hydrogen to carbon ratio and apparent conversion reactivity. Lithotype Investigations Where coal lithotype is considered to be of sufficient importance to warrant some degr ee of selective excavation or feedstream blending, it will be necessary for the mine geologist to furnish details on the location and di st r i but ion of coal l ithotypes within the seam to be mined. This can be achieved through intensive coring ahead of the working faces, or at a less extravagant level by simply mapping the working face visually. The latter method is both subjective and difficult as coal lithotypes are unlikely to be easily identified in freshly exposed coal, and for this reason visual mapping should be backed up by hand sampling or coring . The samples thus obtai~ed can then be dried, examined and subjected to labo ratory determinations such as maceral counts or numerical colour index measurements. These the mine geologist can use to validate his own field interpretations as based on vis i ble colour, textural, physical and botanical differences in the coal which can be related t o lithotype. (It should be noted here that brown coal lithotypes are often metres thick and can be traced laterally for many hundreds of metres) . Physical Properties Although different brown coal lithotypes will give rise to different physical properties of the coal in the dried state, fresh, bed-moist brown coal in situ

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is likely to be relatively uniform in physical properties. Where some degree of weathering, oxidation, reworking or gross permeation of the coal has taken place, however, its physical nature is liable to be affected. This will usually become apparent during excavation, transport or usage of the coal, most commonly as an abnormally high rate of adhesion to equipment or as difficulties in utilisation. Here the mine geologist must investigate the cause and nature of abnormal physical properties and submit a useful evaluation in much the same way as for chemical properties. GEOTECHNICAL CONTROL AND HYDROGEOLOGY The mining of brown coal by surface methods is very much subject to the successful maintenance of pit stability and dewatering. The designer of the opening will have taken into account these considerations , but a good deal of at tent ion a 1so needs to be paid to these matters on a day to day basis. The mine geologist will be required to be involved in the continuous monitoring of stabi 1i ty and in groundwater management, and must be ab 1e to recognise in advance warning signs and recommend appropriate remedial action. Jointing Jointing within the coal or adjacent lithologies exerts a major influence on slope stability and therefore requires careful recording, analysis and evaluation. A limited amount of data regarding patterns of jointing can be obtained through oriented core recovery or exploratory trenching prior to development, but only extensive exposure will yield a clear picture of the situation. The mine geologist should therefore implement surveys which record the orientation, intensity, mode of occurrence and salient features of the jointing. From this information can be predicted such effects as the potential for development of joint controlled face instability or large scale block movements in batter systems. Typical examples of joint controlled failure in coal are planar and wedge slides and toppling failure, all of which are dependent on the geometry of certain joint intersections coupled with the orientation and slope of the face. The disposition of the general joint population also controls to a large degree the ingress and drainage of groundwater, and for this reason also the jointing should be studied from a geological viewpoint. Earth Movements and Failures The mine geologist is one person among many who should be alert to the appearance of any signs warning of the development of instability. This will frequently take the form of tension cracking or opening along joint planes, and it must be determined without delay whether such cracking is the result of normal stress release or indicative of a potentially hazardous situation. If there is a possibility of the latter, it then becomes necessary to investigate the cause, which may be related to jointing, groundwater, slippage along interseam sediments, circular failure or some combination of these or other effects. Appropriate remedial action such as modifying drainage, active dewatering, flattening the slope of the working face or altering the geometry of the excavation can then be recommended by the geologist in consultation with whatever other geotechnical expertise is available. Degrees of risk can often be quantified where a factor of safety is able to be computed, and here it is absolutely essential to take into account all

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geological factors likely to influence the situation. Back analysis of failures which do occur is also valuable for future reference, but it is obviously desirable that the mine geologist try to avoid this necessity. Groundwater It is almost certain that any brown coal mine will be affected in some way by groundwater, present either as a free standing water table or within confined or semi-confined aquifers . The presence of groundwater is often detrimental to both stability and working conditions, and it is usually desirable if not essential to dewater in the immediate vicinity of the mine. This is normally achieved using pumping bores or by employing gravitationally assisted drainage via horizontal or inclined boreholes, but alternative methods such as electroosmosis may be used in some circumstances. For drainage of the coal seam, geological direction is required concerning the placement, orientation and depth of drainage bores with regard to patterns of jointing or other influences governing gross seam permeability. The dewatering or de-pressurization of interseam sediments and overburden usually demands a knowledge of aquifer characteristics and sedimentology, and the geologist is able to advise on the location, spacing and design of dewatering installations such as pumping of free flow bores. This also requires a working knowledge of groundwater hydrology, but need not of course be the sole preserve of the mine geologist if other suitably trained personnel are available. The predi et ion, monitoring and contra l of the various common effects of dewatering is an art very much dependent on the recognition of geological variables. Subsidence for instance, an almost inevitable result of aquifer depressurization, can be quite substantial in the vicinity of the mine where thick sequences of semi-consolidated material are involved. Whether the resulting subsidence contours are smooth and concentric or show abrupt distortions indicative of localised differential settlement is determined largely by the local geology and should be observed closely by the mine geologist, particularly where surface structures are likely to be involved. Other responsibilities which might be required of the geologist are to monitor the effect of mine dewatering on the local groundwater regime and to ensure that undesirable consequences such as the inadvertent hydraulic connection of previously separate aquifers or aquifer systems are avoided during drilling or mining. TECHNICAL AND SCIENTIFIC LIAISON Although the topic may sound vague, this aspect of the mine geologist's service is likely to be of genuine importance to the overa 11 success of the mining operation. When viewed objectively, the position of mine geologist is one which places the incumbent squarely between the worlds of science and practical mining . Idealistic concepts of these two broad areas of enterprise being interdependent and mutually supportive are rarely fully realised and the mine geologist therefore becomes part of a semi-permeable interface between two different worlds. Armed with some forethought and a little diplomacy however, the geologist is in a key position to play a role in promoting dialogue and comprehension between many of the different groups which can or do contribute to the mining operation. Most commonly, this will involve those areas related to geological activities but which are specialised and express results using some degree of

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parochial jargon. Foremost among these are coal petrology and coal chemistry, both of which are likely to be vital considerations but are perhaps difficult to fully comprehend by those whose speciality or contribution lies in other areas. Conversely, the geologist may, with an intimate knowledge of the mining operation, play a useful role in advising researchers of the potential practicality of proposals which might otherwise lack pragmatic input during their evolution. GENERAL CONSIDERATIONS From the discussion so far, it will be apparent that the brown coal mine geologist will give service in a number of different areas. This does not mean that he or she needs to be an expert in each of the fields mentioned this is clearly impossible. What the mine geolog i st does need to develop however, is some degree of farni l i ari ty with a 11 aspects of brown coal mining in order to be capable of providing a wide range of sound geological advice both promptly and efficiently. In this regard, the mine geologist is essentially an earth science general practitioner providing an on site geological service to the brown coal mining operation. Ideally, the option of calling in specialised assistance if and when required will be available, and the mine geo 1ogi st need not be concerned about having to exceed his own expertise in giving advice on various aspects. A tendency will exist, both now and in the future, for some people to regard the surface mining of brown coal as being less dependent on regular geological input than, say, the underground mining of black coal. This probably sterns from the observation that most workable seams of brown coal will be relatively thick, fairly shallow and generally less affected by structure than most black coals. Two initial tasks of the brown coal mine geologist will therefore be to achieve credi bi 1i ty and to establish the need for an on site geo l ogi ea l service. The latter wi 11 become obvious soon after mining is commenced in earnest and is therefore easy, while the former will be made less difficult if the geologist puts into practice the simple art of effective communication. The mine geologist is and must always be a realist who simply cannot afford the luxury of couching practical advice in traditional geological terminology when the recipients and users of this advice are unfamiliar with such terminology or the concepts it is meant to describe . CONCLUSIONS 1.

The ro 1e of the brown coal mine geologist is a complex one ernbraci ng a wide range of activities.

The on site services of a mine geologist are essential to attaining optimum efficiency in any substantial brown coal mining operation.

The brown coal mine geologist should be a practical person capable of developing the skills of effective communication and able to bring science and mining practice together in a constructive way.

Brown coal mine geologists will in general, share a common list of basic duties related to the inherent geo l ogi ea l s i mi l ari ties of brown coal mining operations.

ACKNOWLEDGEMENT The author wishes to thank the SECV for permission to publish. Australian Coal Geology 4, Part 2

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Prediction of Coal Mining Conditions and their Areal Variations using Exploration Geotechnical Data Robin Miller

The Shell Company of Australia Ltd., Coal Division, 155 William Street, Melbourne, Victoria, 3000

Key Wo r ds:

Geotechnical data, prediction, exploration, planning .

mini ng

conditions,

computers,

ABSTRACT The importance of making the best possible prediction of mining conditions is argued as a way of reducing some of the risks in planning new mining projects. Existing methods of making these predictions are briefly reviewed. A methodology for extension and improvement of these techniques is outlined. This concept takes advantage of the ease of data manipulation afforded by modern computerised geological/geotech nical data management systems. Geotechnical data is combined in many ways to provide plans of the variation of many different mining conditions . This involves such a quantity of work that it is only possible with computing facilities . A case study is given and some suggested combinations of critical factors quoted for a variety of conditions. INTRODUCTION Today's new mines are being designed in times when economic margins are becoming progressively narrower . Ways of reducing the "fat" in new operations, i.e. reducing inefficiency and contingent allowances , are eagerly sought in order that profitability can be maintained during hard times. This is a continuing process ; in the future the "lean" projects of today wi 11 tomorrow seem fat as the industry learns to apply tighter methods of planning and contra l. One implication of this is that it becomes desirable to allow smaller contingencies for dealing with the unexpected. Thus, reducing the chance of the unexpected will provide a major financial benefi t to any mining operation. One major area in which these risks may be reduced lies in the prediction of the mining conditions . An ever increasing amount of time and money is being devoted to this aspect of mine planning. This is in line with the modern trend ; companies are now prepared to spend mo re money on investigations and studies and furthermore, spend this money at an early stage when this cash outflow is relatively more expensive, in order to reduce the risks and increase the chance of a favourable long term outcome .

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Most mining conditions fall into two broad categories: those which relate to the stability of workings and those which control machine performance. The information needed to predict these matters is largely geological and geotechnical and, in Australia, this is most often obtained from exploration boreholes because outcrops are few, seams usually subcrop beneath highly weathered surface materials, and many projects are in new areas where mining experience is not available. Even in structurally simple areas, lithology can vary widely in short di stances, and the assumption that a neighbour's conditions will be similar to your own can often be invalid. In any case, such an assumption, even if valid, needs verification by some geotechnical work. Experience shows that even small structural or depositional variations can lead to very significant variations in conditions. With fluvio-deltaic depositional environments, wide variations in very short horizontal distances wi 11 be experienced. Many authors have related the effects of the depositional environment on the stability of underground workings and to a lesser extent surface mines. Papers by Shepherd & Gale (1982), Moebs (1977) and Iannacchione et al. (1981) provide useful accounts. The accurate location of channel, delta front, overbank, swamp deposits and so forth will be of major use in predicting the mining conditions . The construction of a credible model of the depositional environment is an area in which the sedimentologis t can be of the greatest use for mine planning. The paper firstly reviews the methods used until now and discusses their relative advantages and limitations. The paper then goes on to outline some ways in which these methods can be enhanced. To an extent this paper is somewhat idealistic, as in many instances the required density or range of data is not available and its collection is not financially justified (especially in the case of small scale operations). However, the author considers that an idealistic approach is necessary, practical limitations will ensure that such an approach will be moderated to an acceptable compromise. If a lower target is set, the final work will inevitably be less than acceptable. Some of the techniques outlined have been utilised, others are, as yet merely advocated. They are, however, in the author's opinion, the direction of progress. The paper is intended to stimulate interest and discussion as much as anything else. The need for progress in this field cannot be in doubt. Over the past decade or so the techniques of better data collection and the application of improved geotechnical tests have become more common. In many instances this has been prompted by the wider use of small computers for data storage and manipulation. That (but there are still many notable exceptions) better forms of data are collected and recorded than ten years ago is a laudable achievement in itself and is a prerequisite for further developments. However, it is the author's impression that there must be many hard working mining geologists sitting by computers stuffed to the gunwales with geotechnical data, obtained at great expense, and wondering at its relevance. It is no wonder that these geologists grow cynical about the purpose of such data. The mining company has paid good money to be advised as to what data to collect and how, but it is only partly or poorly used. This information is often handed to consultants who using their skilled expertise interpret the data in some mysterious manner. While there is a continuing need for the development of better methods of collecting geotechnical data, particularly field data, probably the biggest need is in learning how best to use the data we already have. WHAT ARE "MINING CONDITIONS"? Many engineers have different interpretation s of this expression. Underground, it probably first gives rise to thoughts concerning roof stability, on the Australian Coal Geology 4, Part 2

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surface it may bring to mind slope stability, machine performance or blasting requirements. I classify mining conditions in the manner shown in Table 1. TABLE 1 Underground Stability

Roof Floor Pillars Caving Characteristics

Stability Surface Stability

Low Walls High Walls Spoil Dumps

Machine Performance Underground/Surface

Drillabili ty Cuttability Abrasiveness Trafficability Diggabili ty Rippabil i ty

Other s

Blastability

Some of these conditions can be calculated from data using deterministic or probabilistic methods because the constitutive relationship between the input parameters is known (more correctly; known to a degree that enables reasonably accurate engineering estimates to be derived). In most cases though, particularly machine performance, we have a good idea of what the input parameters are, but little or no idea of their precise interaction i.e. there is no proven canst itut i ve relationship between the parameters. Note that these types of mine conditions are usually suffixed II ability" and are usually ill-defined, complex and poorly researched . For example, we know that the main factors influencing diggability are:(a)

Degree of fragmentation of the rock mass (especially by discontinuities)

(b)

Rock strength

(c)

Bulk factor

(d)

Abrasiveness

(e)

Density

(f)

Clay content (stickiness)

(g)

Moisture content and stickiness

(h)

Location of digging horizon (penetration by bucket into major discontinuities).

There are doubtless other contributory factors. Despite knowing these factors have an effect, it has not been possible to produce an equation relating these factors to machine performance. There is no accepted quantitative measure of diggability. One can qualitatively predict machine performance from experiments in trial pits or excavations. Alternatively, design can be based on the results of indirect measurements such as seismic velocities. These indirect Australian Coal Geology 4, Part 2

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methods are representative of the rock mass in that they depend on the same factors that control diggability; rock density, discontinuities, fabric and structure. It is relatively easy to measure and apply such indirect methods but there is never a direct relationship between the property measured and that of fundamental interest. An example of the application of the indirect approach is the use of seismic refraction measurements by the Caterpillar Co. (Anon. 1978, Weaver 1975) for the prediction of ripping machine requirements. Circumstances where we have proven constitutive relationships (for example slope stability calculations) pose far less of a problem than where these relationships are unknown. However, in the field, conditions vary and the mine must be divided into domains of consistent conditions. For many mines, such domains are not clear cut, especially where characteristics are defined by gradational deposition changes rather than the relatively sharp structural or 1i tho 1ogi ea 1 transitions such as those caused by the presence of channe 1 structures. In these circumstances the processing of the data becomes more akin to the problem involving non-constitutive relationships. For this case, we know or can reasonably guess which are the controlling parameters and even predict which are the more important, but we cannot plug these numbers into equations in order to drop out an answer such as a safety factor, a probability of failure or a machine requirement. Techniques to manipulate this data are not complicated (at least in principle), and are discussed in the following sections . A systematic approach, whether performed manually or by computer, is vital when assessing the influence of more than a few parameters. Non-systematic mental appraisals will only work for combinations of two or three factors at the most. Even then consistency is hard to achieve especially if different personnel work on or interpret the appraisal. Such methods are often described as using an expert's II lengthy experience in interpretation of data" or some such phrase. For most mining conditions, the number of factors is too great for such mental juggling acts and either some data has to be made redundant or a systematic approach adopted . ROCK MASS CLASSIFICATION SYSTEMS From the time of the earliest classification systems, notably the development of the Rock Quality Designation (RQD) by Deere (1964), engineers have sought to correlate these classifications to mining conditions, especially support requirements. The two best developed and most often used systems are the Geomechanics Classification which provides a Rock Mass Rating or RMR, developed by Bieniawski (1976, 1980) and the Norwegian Geotechnical Institute's NGI Classification which provides a Rock Mass Quality or Q rating (Barton, Lien and Lunde 1974, Barton 1976). Both systems have been shown to work well for the prediction of support requirements for large civil structures, particularly tunnels, in which a wide variety of domains may be traversed. These systems do not depend upon constitutive relationsh ips being known . However, such systems are first order only and are used to go from a state of no knowledge to one in whi eh the main support systems may be predicted, for example, whether an excavation will require high density bolting, meshing and shotcrete or merely spot bolting . The systems work best in ground of one predominant character. For example, whilst a tunnel may traverse several widely ranging domains, within each domain the rock mass properties inside the zone of influence of the excavation are broadly si mi 1ar. This is not generally the case for coal mining where the mining horizon is predetermined by the nature of the deposit . For underground mining to be economic in average seam Australian Coal Geology 4, Part 2

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thicknesses in Australia, then roof support should be provided by bolting at densities down to about one bolt per square metre , supplemented perhaps by W straps and props. More intensive support systems , for example, the use of steel arches as is common in the European industry, are not economic. Hence we do not require a rock mass classification system to tell us what general form of support is required unless it is to predict that conditions exist which substantially differ from the broad average . Also in coal measures the rock mass properties may also vary substantially within short distances of the seam. For example , a seam may have an associated thin , weak, clay rich stratum lying inconveniently near to the intended roof horizon but which does not intersect the workings . Such a layer may have little effect on the RMR or Q number because of its relative dimension . Yet this layer may cause major problems of bolt anchorage or delamination . RMR's are not really capable of dealing with the influence of highly localised variations from the surrounding rock mass properties. Hence RMR's have rather less application to coal mining than say tunne 11 i ng or cavern excavation, al though subsequent modi fi cations and application may alter this favourably . The two main classification systems agree closely on the critical input parameters . These are : (a)

RQD

(b)

Spacing of joints

(c)

Joint conditions (roughness, -degree of alteration)

(d)

Ground water conditions

Bieniawski's system also includes compressive strength and joint orientation whilst Barton's puts more emphasis on joint conditions and uses a "stress reduction factor" to account for stress conditions. It is worth noting that a tolerably consistent correlation has been shown between the two systems. These systems are in increasing use in the civil tunnelling industry in particular, with even their incorporation into contract conditions in Australia. Laubscher and Taylor (1976) are notable for having modified the RMR systems for use in hard rock mining although there are significant problems with application of the systems to most stratified deposits. THE AMERICAN "OVERLAY" TECHNIQUE In recent years the main systematic alternative to Rock Mass Classification systems is what is best described as the American overlay technique. This has been applied in a number of cases and examples are given by Overby et al. (1973), Benedict and Thompson (1973), Campbell et al. (1975) and ETTiscin (1978). The method is essentially simple and depends upon the identification of several critical factors whose influence upon stability far outweigh other contributory factors. The areal variation of these factors is each plotted on separate mine plans in the form of contours, zones or limit lines . The data is obtained primarily from cored boreholes and the effectiveness of the technique will thus depend upon the density of boreholes. Each plan can then be overlain so that areas in which the least favourable combination of factors can be identified. For example, the four most crucial factors might be considered to be: the extent of a weak shale roof horizon, the presence of

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groundwater in the roof, sudden changes in depth of cover causing local stress imbalance, areas having a high frequency of jointing, faulting and other discontinuities. Obviously a combination of all four of these factors will provide the worst conditions, whilst areas with only one will give rise to conditions only slightly worse than normal. Generally, up to four contributory factors have been used but there is no real reason, apart from the increasing labour involved in the task, why greater numbers cannot be considered. The technique has mainly been used for predicting immediate roof conditions but there is no reason why it cannot be modified to cover other forms of mining conditions. The method depends upon a pre-knowledge of the significant factors. When these are not known one has to play safe and incorporate all factors considered to be influential and in doing so the technique may lose Furthermore, the quantity of work i nvo 1ved may much of its s imp 1 i city . require the use of computing facilities as manual methods would become exorbitantly expensive. Figure 1 shows an example of a hazard prediction map drawn up by Overby (11).

0 ·:·. ·.=.:·· FRACTURE TRACE DENSIT Y U04llf: '"""'" I '"-AC fUAIS

'1:"' •ooo so n

UNSTABLE ROOF ROCK F ACIES

STREAM UNLO ADING

lO W t( Hk.l StllE...aT"' --.C,STO-.:S SttALU AJC> S,uc,-, SHAU: I

OVl ... Ufl0OI 0, 100 rT o,t WON. ll(.,.::,•1u A80YC COAL

BLACKSVILLE QUADRANGLE

1/1

OSAGE QUADRANGLE

DEGREE OF POTENTIAL HAZARD ONE OF 3 GEOLOGIC FACTORS OPERATING TWO OF 3 GEOLOGIC FACTORS OPERATING All 3 GEOLOGIC FACTORS OPERATING

~ □ □ k] l!llID

■

Figure 1. Potential hazard map showing location and degree of hazard (after Overby et~ - 1973).

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IMPROVED METHODS When more than four or five facto rs a r e conside r ed to be critical, then not only does a physical overlay approach become cumbe r some, but the larger quantity of data necessitates computer storage in some form . It is logical to have the computer manipulate the data and directly produce p 1ans of the variation of mining conditions. The same range of data can be processed by its se 1ect i ve use and modification to produce p 1ans for a wide range of purposes. Most data obtained from bore ho 1es is presented and interpreted in the same sense as the borehole orientation, i.e . usually vertically. This is the most useful presentation for most geological purposes, allowing correlations to be seen and cross sections to be plotted . For most mine planning purposes though, the data is best presented in a p 1ane para 11 e 1 to the seam ( the exception being for steep seams where the mining developments are not in the p 1ane of the seam, but rather intersect the seam by 1eve 1s or benches) . Because of this, bore ho 1e data has to be reprocessed, from the vert i ea 1, to (usually) the plane of the seam. Spatial variations of the data on an areal rather than sectional basis can be more readily related to mine layouts. Many mine areas can be affected by the same critical facto r s but the way in which they interact may be different . A big influence on the way in which these factors are summed is in the thickness of layer chosen. For example, compare the vertical intervals influencing the support requirements for roadways and for caving characteristics. Both conditions are controlled by much the same properties but for the former, a vertical interval of two to three metres may suffice whereas ten or tens of metres is required to assess the latter . As with a 11 other systematic approaches, a 11 parameters are required in the form of numeri ea 1 va 1ues . At this stage it may be worth considering the use of weightings for certain of the data and whether or not the scale of values should be linear or otherwise. For example, RQD is a strictly linearly scaled property since it is merely the percentage of stick lengths greater than 100mm in any chosen run of core. Many would fee 1 that direct use of this figure does not realistically reflect the increasing influence of low RQD's on rock mass properties . A non-1 i near sea 1e may be used to correct this . Either the class intervals or the value assigned may be varied to achieve this. An example is shown in Table 2 (where worsening of properties is indicated by an increase in assigned value); TABLE 2 RQD

Assigned Value

80 - 100 60 - 80

RQD

Assigned Value

1 2

80 - 100 55 - 80

1 2

40 -

33 -

20 -

21 -

0 -

14 10 -

21 14

8 10

6 -

0 -

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In either case, if the RQD interval average is plotted against the assigned value the points will all be found to be approximately on the same (arbitrarily chosen) curve. Where certain input parameters are considered to be of much greater importance the effect of these on the mining condition may be emphasised by applying suitable weightings . Hence we can allow for the significant effects of one critical factor or the cumulative effects of several non-critical factors . To produce a plot of the areal variation of a specific mining condition, the weighted numerical values of each contributory factor are summed over the relevant vertical interval at each point (usually a borehole). These summated values are then plotted out at suitable scale and contoured.

This plan enables the variation of the condition to be readily appreciated but it is as yet uncorrelated to the actual field condition of stability or machine performance . This can be done by correlating the extreme numerical values to actual field performance. The correlations should be checked at every opportunity and an adjustment made to the interpretation of the index if necessary. DATA COLLECTION Th i s subject alone could justify several papers, but for now a few pertinent comments are worth making. Rock Strength vs Discontinuity Data Where rock mass is closely jointed, bedded or faulted, the rock's strength properties become increasingly irrelevant since the rock mass behaviour becomes progressively contra 11 ed by movement a 1ong the existing di scont inui ties and 1ess by the creation and propagation of new ones. The geo 1ogi st must use his judgement to decide where field or laboratory testing of rock strengths becomes redundant. In a 11 cases the discontinuity or fracture 1og is of greater importance than the strength log, although there will tend to be a degree of correlation between the two . This is why a detailed fracture log, from whi eh other fracture indices may l ater be ea lcul ated, is recommended rather than recording such indices (e.g . RQD) directly, even though this is a slower process. In this area there is much potential for using quick, indirect in situ methods of assessing both strength and fracture density simultaneously (but not separately) such as downhole sonic velocity logging . As experience is gained with the interpretation of these 1ogs, in combination with the other estab 1i shed geophys i ea 1 1ogs, this method wi 11 come to provide va 1uab 1e addi t i ona 1 or poss i bly alternative data . In situ methods have t he obvious advantage of reducing the possible mis-recording of dr i lling and stress-relief fractures. Angled Holes It is desirable that, unless representative outcrops exist, some angled holes be drilled in every exploration area to obtain data on vertical or subvertical joints. The use of angled holes will also ensure better core recovery in thinly bedded or high stressed deposits since disking on bedded surfaces or by

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stress relief may be minimised. Angled holes provide an opportunity for core orientation which should not be missed since multiple sets of near vertical joints can then be distinguishe d. In many cases, this may be done by reference to the bedding and the dip direction of the hole, where this is regular and known. Alternative ly, a core orientation device may be used . A simple and effective core orientation device was described by Ca 11 et.£! (1981) . Fracture Logs These should record fractures by groups according to the similarity of frequency rather than by lithology, although the two may sometimes correlate . Notes must be made to identify known or suspected drilling fractures, washed out joint fillings etc. Thin layers of clays and the like may be convenientl y recorded as bedding breaks that are infilled whether this is the case or not, s i nee structurall y they have the same effect. Fractures occurring within a fracture unit but which are different in character to the others in that unit must be separately recorded and flagged in the log. Class Divisions The definitions used for dividing measured or estimated parameters should always be clearly defined. There are many such divisions in existence and there is much potential for confusion especially if the divisions are denoted adjectively , e. g. strong, very strong, extremely strong etc. There is a very great need for the use of standard methods of rock mass classificati on and the potential user is faced with a bewildering array of alternative s, many of them "Standards" . Great care is needed when comparing these methods as many of them are similar but not identical . Strength Properties In most cases the most important strength property is the tensile strength. Because the point load strength method causes tensile failure, this test is best suited for obtaining this data. It is obviously more accurate than a geologist's field estimate and much cheaper than laboratory tests. However, it must be done sufficientl y often to provide a statistical ly valid mean result. This can be checked by quickly plotting out the frequency distribution of the results for any class of material tested. Meaningful results will produce a reasonably normal distributio n . Non-normal distribution s indicate that either more than one class of rock has been measured, poor technique or insufficien t data. Discretion must be used when combining results from similar strata in other boreholes in order to derive sensible averages. Basic Geotechnical Description It wi 11 be seen that certain factors are considered cri t i ea l to a 11 assessments of mining conditions. These common factors are the discontinui ty description , which includes information on spacing, orientation and joint fillings etc . , and the strength. A most useful reference for suggested methods and classificati ons is the ISRM publication "Rock Characteris ation Testing and Monitoring" (Brown 1981) . This publication also provides references to many other sources of relevant information .

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SUGGESTED CRITICAL FACTORS AND VERTICAL INTERVALS FOR ASSESSING VARIOUS MINING CONDITIONS The following lists contain examples of the facto r s which are suggested as being most important when making an assessment of conditions. The vertical interval over which these factors should be summed is also included. Roof Bolting Requirements Critical factors include: Discontinuity frequency, discontinuity description, durability (Slaking potential), strength (field estimate , point load or laboratory UCS), clay content (plasticity), groundwater 1.

Boltable Interval Sufficiently Competent for Point Anchored Bolts? By examining the entire vertical interval of the bolt length, the combined factors should highlight ar eas where roof material is insufficiently competent for the use of point anchored bolts, regardless of whether a suitable anchorage horizon exists. An unfavourable index would indicate the need for a full column anchored bolt . Vertical interval - from O to 2 or 2. 5 metres above planned roof horizon (depends upon maximum possible bolt length which in turn depends on extracted seam thickness) .

Suitable Horizon Available for Point Anchored Bolts? It is presumed that point anchored bolts are bonded by either resin or cementitious cartridge . An unfavourable index would indicate the need for a full column anchored bolt . Vertical interval - from 1.5 to 2. 0 or 2. 0 to 2. 5 metres above planned roof horizon (assumes that the end 0.5m of roof bolt is the potential length for "point" anchoring).

Bolt Head Bearing Arrangement Relatively favourable indices will indicate that spot bolting with 200m x 200mm bearing plates will be sufficient. Les s favourable indices will indicate the use of W straps then, progressively, W straps with supplementary spot bolts with large bearing plates (butterfly bolts). Very unfavourable indices will also require meshing between all fixtures. Vertical interval - immediate 500mm of roof .

Bolt Density Unfavourable indices will indicate high bolting densities (1 bolt/m 2 and higher) with l½ times this density at intersections . Stress field and orientation or workings must also be considered . Vert i ea 1 interval - from O to 3 t i mes the extracted section above the proposed roof horizon.

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Longwall Workings Critical factors include : Discontinuity frequency and description, strength. 1.

Immediate Roof Quality This highlights the potential for roof slabbing and falling into face workings, and also fretting, guttering and flushing of roof ahead of and between powered supports . Vertical interval - from Oto 500mm above proposed roof horizon.

Caving Properties - Intermediate Roof This examines the caving properties of the intermediate roof and high1i ghts the presence or absence of massive, strong rocks that wi 11 tend not to cave. in a regular fashion and may cause overloading of power supports and/ or pillar edges. Conversely, a very weak and thinly bedded roof may cave too readily and tend to encroach on the face-line. Moderate figures therefore indicate optimum conditions. Vert i ea 1 i nterva 1 - from O to 3 times the extracted height above the proposed roof horizon. (this index probably also relevant to caving with workings).

room and pillar

Caving Properties - Upper Roof This includes the properties of the upper roof and highlights the presence of massive strong rocks that can bend without excessive fracturing to promote early bridging of largely intact strata from over the face to the waste . Moderate values are again desirable as over strong rocks will not bend sufficiently to allow bridging nor will weak rocks allow bridging . Vert i ea 1 i nterva 1 - from 3 times the extracted section up to 50m above the proposed roof horizon.

Room and Pillar Workings Critical factors include: Discontinuity frequency (cleat) and description, strength 1.

Pillar Stability This examines the coal properties to determine whether pillars are liable to excessive spalling and possible progressive failure. Vertical interval - the extracted section proposed.

Caving As for longwall mining.

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Floor Quality Critical factors include: frequency Discontinuity plasticity, groundwater

and

description,

durability,

strength,

This examines floor materials for the possibility of heaving caused by swelling and/or insufficient bearing strength. Vertical interval - first metre of floor. Blastability Critical factors include: Discontinuity frequency and description, strength, groundwater This describes the ease with which materials may be blasted. It is relatable to powder factors and blasting practice as well as rock conditions . Vertical interval - to suit overburden or interburden thickness drilled as one unit. Ori 11 ability Critical factors are: groundwater, strength, Discontinuity frequency and description, abrasiveness (Taber Abraser, Los Angeles Test etc), drillability indices (Goodrich Drillability, Morris drillability), plasticity, durability Describes how easily overburden may be penetrated by bl asthole drills. Vertical interval - to suit overburden or interburden thickness drilled as one unit. Trafficability Critical factors are: Discontinuity frequency and description, durabi l ity, plasticity. This is the ability of mining machinery, especially wheeled vehicles, to be able to move on surfaces as mined. Diggability Critical factors are: Discontinuity frequency and description, strength, plasticity, density, bulk factor, moisture content .

abrasiveness,

This describes not only how easily materials are broken out but how effi ci ent ly they can be loaded out.

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Ri ppabi 1ity Critical factors are: Discontinuity frequency and description, strength, hardness, abrasiveness This describes how easily floor material may be ripped (and dozed) by bulldozers equipped with ripping tines. Vertical interval - to suit proposed ripped interval APPLICATION An example of the principle to predict roof conditions in a planned underground mine is given. Detailed geotechnical logs comprising both field logs and the results of laboratory tests were available from fully cored boreholes at 5OOm spacing over most of the proposed mine area. Only roof and floor conditions were considered but the exercise will be repeated for other conditions, with the inclusion of data from infill drilling, at a later date. The data available from logs that were considered critical to roof and floor stability were: RQD, Strength (geologist's field estimates, point load tests and laboratory UCS), Durability (field estimate of the slaking characteristics), Plasticity (field estimate of the clay content), Bedding and joints . These factors, amongst others, had been recorded onto She 11 's COGEO System which has extensive exploration data filing capacity. The variations of these critical parameters were recorded in accordance with the natural groupings of similar characteristics and were not delineated by lithology. These parameters along with a lithological column and vertical scale could be plotted out vertically as shown in Figure 2. These property indices were summed and the result also plotted and contoured. In this instance no weightings or other modifications were applied. For the purpose of predicting roadway support requirements it was considered that only the immediate two metres of roof material were relevant (the roof horizon having been established by a natura 1 parting and coa 1 qua 1i ty cons i de rations). This examp 1e, shown in Figure 3, was expected to primarily relate to the efficacy of the roof bolts and not to other conditions such as caving characteristics . Unfortunately, it wi 11 be severa 1 years before these predi et ions may be confirmed in their consistency or the index correlated by experience to the support required . However, the work as it stands has proved to be of value in furthering the mine planning, particularly with regard to estimating the cost of support for the different planned areas of extraction.

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ROD

DOH 13

100

L..___.J

BEDDING DURABILITY PLASTICITY STRENGTH 100 0 ,oo O 100 0 O L____J

COMBINED INDEX JOINTS

r RL 349 0

RL 350 0

Figure 2. Borehole lithology and vertical variation in mechanical properties. CONCLUSIONS This paper has been written in very general terms . It is a methodology being advocated and not a specified set of tried and tested instructions. Detailed procedures wi 11 vary from site to site, as wi 11 cri t i ea l factors. Many companies have geological and geotechnical data handling systems and the existing software will delineate the direction of future processing systems. One of the ·most important advantages of setting up a flexible geotechnical data handling system is that it becomes relatively simple to experiment with the data. Exploiting this ease of experimentation the geotechni ea l engineer will be able to expose trends that would otherwise be overlooked. Some factors critical to mining conditions cannot be included in this approach. Perhaps the best example of this is the effect of the orientation of the stress fields and the consequent implications of directional mining upon stability. However, the fact that most of the critical factors have been assessed makes the consideration of those that cannot be incorporated easier .

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Ol)()Ht2

Figure 3. The mechanical properties of the first two metres of roof. The paper has dealt primarily with underground mining and stability aspects. This is because it is the area in whi eh these ana lyt i ea l methods have been most developed so far and because it is the author's own area of experience. In principle the system is applicable to surface mines; particularly for machine pe r formance . The machine manufacturer can provide encouragement in learning to use geotechnical data and encourage its collection . ACKNOWLEDGEMENTS I would l ike to express my thanks to the Coal Division of The Shell Company of Australia Limited for permission to publ i sh t his paper . My thanks are also due to Ian Wollff , Geologist with Shell ' s Coal Division, fo r the stimulus which his work gave me . REFERENCES Anon,

1978 . Handbook of Ripping, Illinois.

6th Ed .

Caterpillar Tractor Co., Peoria,

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Barton, N. , Lien, R. & Lunde, J. 1974. Engineering Classification of Rock Masses for the Design of Tunnel Support . Norwegian Geotechnical Institute Pub. 106, Oslo. Barton, N., 1976. Recent Experience with the Q System of Tunnel Support Design. Proc. Symp. Exploration for Rock Engineering, Johannesburg, Nov. 1976 pp 107-116. Benedict, L.G. and Thompson, R.R., 1973. The Use of Geological Information to describe Coal Mine Roof Conditions. Paper presented to the American Chemical Society, Chicago, Illinois, August 1973. Bieniawski, Z. T., 1976. Rock Mass Classifications in Rock Engineering. Proc. Symp. Exploration for Rock Engineering, Johannesburg, Nov. 1976, 97-1~ Bieniawski, Z.T., 1980 . Rock Classification : State of the Art and Prospects for Standardisation. Transportation Research Record 783, pp. 2-9. Brown, E.T . (Editor) . Rock Characterisation, Testing I.S . R. M. Suggested Methods, Pergamon Press, 1981.

and

Monitoring.

Call, R. L.D., Savely, J.P. and Pakalnis, R., 1981. A Simple Core Orientation Device . Proc . 3rd Int . Conf . Stability in Surface Mining, Vancouver, 1981, pp.465-481. Campbell, J.A. L., Petrovic, L.J . , Mallia, W.J . and Schulties, C.W . , 1975. How to Predict Coal Mine Roof Conditions Before Mining. Mining Engineering, October 1975, pp . 37-46 . Deere, D.U., 1964. Technical Description of Rock Cores for Engineering Purposes. Rock Mech. Eng . Geol. 1, (1), pp . 17-22. Ellison, R.D., 1978 . Underground Mine Hazard Analysis Technique. Stability in Coal Mining, Proc . 1st Int . Symp . Stability in Coal Mining, Vancouver, B.C . , 1978, pp.299-318 . Iannacchione, A. T., Ulery, J.P . , Hyman, D.M. and Chase, F.E., 1981. Geologic Factors in Predicting Coal Mine Roof Rock Stability in the Upper Kittanning Coal Bed, Somerset County, Pa. U.S. Bureau of Mines, Report of Investigations 8575. Laubscher, D.H. and Taylor, H.W. 1976 . The Importance of Geomechanics Classification of Jointed Rock Masses in Mining Operations. Proc. Symp . Exploration for Rock Engineering, Johannesburg, Nov . 1976, pp . 119-128. Moebs, N.N., 1977 . Roof Rock Structures and Related Roof Support Problems in the Pittsburgh Coal Bed of Southwestern Pennsylvania. U.S . Bureau of Mines, Report of Investigations 8230 . Overby, W.K. Komar, C. A. and Pasini, J . 1973. Predicting Probable Roof Fall Areas in Advance of Mining by Geological Analysis. U.S. Bureau of Mines, Technical Progress Report 70 . Shepherd, J. , and Ga 1e, W. , 1982. Co 11 i ery Roof Stability and The Role of Geology: A Review. Australian J. Coal Mining Tech. & Research l, 47-67. Weaver, J.M . , 1975. Geological Factors Significant in the Assessment of Rippability. The Civil Engineer in South Africa, December, 1975, 313-316 . Australian Coal Geology 4, Part 2

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Predevelopment Data Techniques: Note on Recent Developments in Instrumented Drilling and Hydraulic Fracturing B.A. WOOLTORTON CSIRO, Division of Applied Geomechanlcs, P.O. Box 54, Mount Waverley, 3149, Australia. Key Words: fracturing.

Coal mining, predevelopme nt data, drl I labl I lty, hydraul le

ABSTRACT In the fleld of aqulsltlon of 1Predevelopment Data', CSIRO Division of Applied Geomechan Ics Is engaged In work on sever a I non-geophys Iea I boreho Ie techn 1ques. Two such techniques are Instrumented Drilling and Hydraulic Fracture. Predevelopment and exploration Investigations Invariably Involve large drilling programs. Holes are drl I led In order to assess material properties by testing core or by running borehole probes In open holes. The drilling process Itself Is one of the most fundamental In sltu tests and potentially one of the most efficient and comprehensive If a reliable relationship between drlllablllty and rock strength parameters can be establlshed. Initial drlllablllty studies conducted by the Division have demonstrated that changes In penetration rate can be shown to correspond with changes In llthology, and also that an estimate of the unconfined compressive strength of a particular rock type can be made from the drll llng record. In the I ast year, work has been concentrated on the deve Iopment of hardware associated with the on-going drlllablllty program. A small diamond drilling rig has been extensively modified and Instrumented to automatlcal ly record penetration rate, thrust at the drlll bit, torque and rotatlonal speed. Thrust and penetration rate are two crltlcal drill Ing parameters which have been considered by many other workers to be proportional to rock strength parameters under certain conditions. The CSIRO rig has been fitted with a constant thrust system to elucidate the relatlonshlp between penetration rate and rock strength. This relationship Is however Influenced by other parameters such as bit type. Diamond bits or tungsten carbide chip bits, employing a 'point attack' cutting action, have been favoured In the studies to date. However, the efficiency of this type of cutting action Is very dependent upon bit wear and efficient cuttings removal. In order to minimize the effect of these two unquantlflable parameters, future work wll I be directed towards the use of highly wear-resistan t shearing action bits with greater emphasis on drill stem torque. A knowledge of the In sltu stress regime Is of vital Importance In the plann-

ing stage of the development of an underground or deep surface mine. Convent Iona I stress measurement techn I ques, based on deformat I on pr Inc Ip I es (overcorlng for example), are obvlously not suited to predevelopment Investigations where measurements must be made at depth from the ground surface. For th Is reason, the DI v Is I on has for some years been deve I op Ing the Hydrau I Ic Austral Ian Coal Geology 4, part 2

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B.A. WOOLTORTON

Fracture technique of stress measurement and an extensive experience base has now been established. Documented trials have proven the valldlty of fracture results In comparisons with the accepted conventlonal techniques. The Hydraul le Fracture technique Involves seal Ing a section of borehole between a straddle packer arrangement, and pressurizing that section with fluid untll a fracture Is Initiated . If the resultlng crack ls vertlcal, It wlll have formed a Iong a p I ane para I I e I to the major pr Inc I pa I stress, and at a borehole pressure which can be related to the In sltu stress. Thus the magni tude and direction of the secondary prlnclpal stresses In the horlzontal plane can be determined. Restrictions placed on the appllcabll lty of the technique by rock type may be severe. Idea I I y, the techn I q ue Is su I ted to mass I ve f I ne gra I ned sandstone which Is free from any planar discontinuiti es or defects. Hlghly lamlnated material (partlcularly If there Is a gross anisotropy of tensile strength In the planes perpendicular and parallel to bedding) may sometimes yield a successful test but Is generally avoided If possible. Jo inted or otherwise fractured material cannot be tested. The Hydraul le Fracture equipment currently being used ls the culmination of a number of years development, and possesses some unique design features. There are two options for hand I Ing the fracture tools and positioning them In the boreholes. The first method utl llzes specially machined drl I I rods In the dual role of placement rods and a high pressure hydraul le conduit for supply of f I u Id to the test sect I on. Th Is method Is used for sha I Iow work (to 200 metres) or when site access ls restricted. When site access Is favourable and the requ I red test hor I zons re Iat I ve Iy deep (to 1000 metres), a Iarge tra I Ier mounted Endless Tubing Unit ls used for fracture tool placement. The Endless Tub Ing Un It bas Iea I I y cons I sts of a cont I nuous stee I tube wound on a 2. 4m diameter drum but also

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531

The Significance of Plastic Clay Horizons in Coal Measures of the Bowen Basin C.W.Mal lett*,

R.W.Seedsman**, & W.W.Emerson**

* CSIRO, Division of Appl led Geomechanlcs PO Box 54, Mt Waverley, 3149, Austral la. ** CSIRO, Division of Solis, Private Bag 2, Glen Osmond, 5064, Austral la

ABSTRACT Large foundation fal lures occur within the surface coal mines of the Bowen Basin. In strip mines failures Initiate on thin soft clay bands which dip Into the pit at the base of the spoil or hlghwalls. These soft clays originate from a variety of processes. Such processes may Include deposition of potentially weak material such as tuff or carbonaceous units, structural deformations through geological time, Tertiary weathering, presentday near surface processes and the effects of mIn Ing . The soft c Iays have s Im I Iar mI nera Iogy to surrounding beds, from which they differ consistently only In their higher moisture content and softness. The abll lty of the clays to swell and take up water ls Identified as the cause of their loss of strength. The relative roles of exchangeable sodium cations, Included organic matter, carbonate cementatlon, and mechanical reworking In control I Ing water uptake at particular mine sites are discussed. Techniques for field Identification of the soft bands are assessed. INTRODUCTION In surface coal mines, mining methods and equipment dictate the combination of pit shape, slopes, and spoil-excavation procedure. Within the Bowen Basin and most other Australian Permlan surface coal mining areas, dragllnes have been used In shallow strip operations. Although many other mining designs are possible (Chiron ls 1978), factors In favour of drag I Ines have been low dips, sha 11 ow coa I, and genera 11 y s Ing I e seam operat Ions. Drag 11 nes however have limitations In that spoil and excavation slopes are located adjacent to exposed coal and haul roads. Any lnstabll lty In these slopes can Interrupt the extraction of coal and add significantly to cost. More flexible systems which allow lower pit slopes and outside dumps for spoil have not been used because of the high operating costs of truck and shovel, and scrapper operations. The hardness of overburden limits the appl !cation of continuous mining systems such as bucket wheels. Stab II lty within the surface coal mines of the Bowen Basin ls primarily related to the occurrence of thin plastic clay bands within either the coal measure sequence or the rehandled overburden spoil. The location, orientation, and formation of these bands ls the result of specific sedlmentologlcal, structural, and chemical events In the history of the basin. Terrlgenous Australian Coal Geology 4, part 2

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C.W. Mai lett, R.W. Seedsman, & W.W. Emerson

sediment was predominantly derived from a volcanic source. It has been largely altered to clay during transport and deposition, or during dlagen- • esls. The result has been to produce a,,_ remarkably consistent mineralogical assemblage, Independent of depositional history, onto which Is superImposed of other geologlcal and mining effects.

• Colllnavllle

100km.

Goonyella /

GEOMECHANICAL FACTORS The configuration of a typical surface \ i<ockhampton • coal mine In the Bowen Basin Is a ,..... Emera lfl • strip excavation, bounded on one side •Blac kwater\/ '✓ by a hlghwall of Intact coal measures ,......, at the maximum angle of stab II lty, \:, approximately 45° to 70° (figure 1). • Baralaba On the other side Is spoiled overburMoura, den at the ang Ie of repose for r I I Ied material, ranging from 30° to 40°. do This sits on the seam floor which ~ _:;.,o ~ dips at 0° to 10° towards the high-••~ covER ~ MEsozoic wal I. Given the distribution of stress ,~ ,1 within this excavation and the : strength va I ues measured for coa I measure rocks and spoil, Richards C .al. 1981) have demonstrated the stabl- Figure 1 Locality Map for Mines Bowen Basin I lty of this configuration with results from numerical models. Spoil failures were shown to develop only when a low strength layer at the base of the spoil was Introduced Into the finite element model. In hlghwall failures It was shown that the shear strength of the basa I fa I I ure p Iane Is the most significant parameter for determining hlghwal I stabll lty.

•

There are a number of natural discontinuities which allow the development of fal lures by shearing on particular planes. Such planes are bedding planes, unconformltles and faults within the unmlned section and near the spoil floor contact. In addition weak zones may develop during the mining operation, which, even though they are not In the area of maximum stress concentration, suffer sufficient strength loss to allow movement to take place along them. To affect stab I I lty these planes must usually be dipping Into the pit. Where a weak planar discontinuity Is present near the base of a spoil plle, a spreadIng type fal lure occurs, whereby the moving section of the spot I Is broken Into two wedges. (Gonano 1980) The upper wedge Is cons I dared to prov I de the driving force to shift the lower wedge laterally Into the pit (figure 1). Hlghwall failures generate on preexlstlng planes such as bedding, Joints or unconformltles. Within the surface mines of the Bowen Basin, circular sl Ip fa I lures through the body of the spot I are not significant, and are restricted to minor surface sl lps shortly after the spot I has been dumped (Dunbavan 1981).

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JOINT / PLANE

I FAILURE

Figure 2 Cross-section of a Surface Mine Pit with Failure Surfaces Examples are given of the types of large fal lures found by CSIRO In strip mines In Queensland (figure 2). Fa[ lure .QQ ~ J.n .b..a.s..e .l2.f. .s.J2Qli. - Goonyel la

After the overburden has been spoiled, weak planes are developed at the base of spot I as materials lose strength as a result of the mining process and uptake of water(Boyd .e:t .Al. 1978). Spoil from Goonyella shows dramatic reduction In shear strength when tested In saturated conditions compared to values at natura I mol sture content. Dunbavan C1982) reported for undra I ned conditions with natural moisture content average values of coheslon(C) = 105-137 kPa, Internal friction 0 = 5-15°,and for saturated conditions C = 100-150 kPa, 0= 0. This loss of strength Is related to the uptake of water In the predominantly clayey spot I. Godfrey (1979) and Seedsman and Emerson (1981) have Investigated the slaking and dispersion of this clayey spoil which was shown to be particularly sensitive to the Ingress of water. As groundwater or rainwater lnfl ltrates to the base of the spot I, a zone of soft highly plastic clays with high water content and low shear strength can form. Deterioration of the spoil base can be extreme, with a layer of llqulfled mud formed, which, when encountered In drl 11 Ing, has flowed Into and up bore casing. This weak planar discontinuity provides the basal plane al lowing the development of a two wedge fa I I ure. A character I st Ic of th Is type of fa 11 ure Is the I ack of significant coal buckling and coal heave . .5J2Q.lJ. ta I I ure ~ I o-t I oor J2,.L.an.e.s .5l2.u1h BI ackwater .a.rul ~

Large spot I fal lures have been reported from Terang Pit, South Blackwater (Dunbavan & Welsh 1981) and Moura Pit 18 (0 1Regan .e1 al.. 1981). Both these examples are of large fallures which were repeated In successive strips. In the case of the Terang Pit, virtually the whole pit failed for several strips. There are similar mechanisms of failure In both pits. The spoil failures were associated with considerable coal buck I Ing and overthrustlng In the pit floor. Shear strips Inserted In the floors showed planes of movement within the first few metres below the pit floor. Excavations In the pit floor, and overthrust sheets, have shown that movement takes place on a thin pug or plastic clay band. This band Is only a few centimetres thick and lies parallel to the bedding In the floor, and thus dips toward the hlghwal I at a low angle. The distribution of failures along the pits and down dip Indicates the extensive occurrence of the soft clay In the floor. It Is the presence of the thin clay band which allows the development of the two wedge failure mechanism. Austral Ian Coal Geology 4, part 2

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C.W. Mai Jett, R.W. Seedsman, & W.W. Emerson

Hlghwal I fa( lures .Qil bedding ~

Goonyel la

SI gn If I cant h I ghwa I I fa I I ures have occurred at Goon ye I I a where beds In the highwall overburden dip back Into the pit In the opposite sense to that of the coa I (Barton & McKean 1978). The overburden s 11 des on bedd Ing p Iane surfaces referred to as 'black clay planes'. When the highwal I Is excavated, stress relaxation around the opening, and blast vibrations, cause some moveout of beds Into the pit. The amount of movement varies up the wall, and takes place along existing discontinuities In the rock mass, with shearing along subhorlzonta I bedd Ing and the open Ing and shear Ing of vert I ea I Jo I nts. Movement on these planes reduces their shear strength. Stab I I lty Is further decreased by the effects of water seeping down the opened discontinuities, and hydrostatic pressure adds to the stress factors. As movement continues the effects cumu1ate to g I ve a dramat I c drop In the strength on the p I anes of movement. At many areas In Goonyel la mine, the bedding planes In the overburden curve and steepen their dip Into the pit, above the top of the coal seam. Such a bedding surface can join to a near vertical Joint and thus bound a large wedge of potentially unstable material. If the shear strength of the planes Is sufficiently reduced, fal lures can be generated . Where the strike of the beds strictly parallels the pit direction, the failures can be propagated for long distances along the strip. Hlghwal I £al lures - ..silJ2 .Qil unconformitles

.SQJrth Blackwater

Failure mechanisms similar to those described above occur on other discontinuities In the hlghwal I such as unconformltles. At the Togara Pit at South Blackwater, toppl Ing of blocks of fairly competent Tertiary sands and basalts occurs after moveout along a dipping unconformity. Basal moveout may be associated with bearing capacity failure of rock columns founded on the soft clayey materials on the unconformity. GEOLOGICAL FACTORS Sedlmentologlcal controls

The plastic clay bands In the examples above, are found parallel to bedding In three cases. The fourth Is associated with weathered Permlan on the Permlan Tertiary unconformity. There are two situations where problems are caused by soft clay~ occurring within the Permlan section. The first Is where the clay Is extensive, parallel to and located within a few metres of the floor of the seam, and the second where the clay over I Jes the coal but Is dipping at a significant angle to the seam. lnt!oor ~ para! lel . t o ~

Both failure sites studied have an lnterseam sequence below the coal composed mainly of strong sandstone, with only a few metres of siltstone and claystone at the top, directly underlying the coal. They represent a two storeyed lnterseam unit of Mai lett (1982). The first storey of steeply dipping channel sands was subsequently overlain by a thin sheet of extensive horizontal lacustrlne and marsh sl Its. The first storey was deposited by an active, but narrow channel migrating laterally Into a peat swamp (figure 3). Warping down of the peat during deposition generates the steep sandstone dips. After the sandy channel moves away, very slow compression of the peat continues, and allows the deve I opment of an ex tens I ve I ake over the channe I sands. As there Is an evenly distributed load on the peat by this time, the lacustrlne beds of the second storey are deposited, and remain, horizontal. Vegetation eventually Austral Ian Coal Geology 4, part 2

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re-establ lshes Itself on the shallow lacustrlne deposits, and the accumulation of the next coal seam begins. MAIN DISTRIBUT ARY CHANNEL

SPLAY CHANNEL

Figure 3 Depositional model showing the development of lacustrlne pit floor sediments at Moura Pit 18.

Figure 4 Depositional model showing the environment In which the Black clays planes were formed at Goonyel la

Characteristics of the lacustrlne beds at the two sites differ In details. At Moura, they cons I st of carbonaceous coa I I y s 11 tstone, w Ith rare th In c I aystones and laminated sandstones.The soft clay Is continuous, Is associated with a breccla, and Immediately under I Jes a cemented calcareous siltstone, stronger than the rest of the beds. At Terang, South Blackwater, the sequence Is finely laminated grey and dark grey slltstones, rooted and slicked Immediately beneath coal. The soft clay Is distinctly I lghter In colour. Although It has been altered, Its colour and texture suggest a possible tuffaceous origin. This soft light clay Is found In what otherwise Is a fairly uniform sequence. It Is commonly found In the floor but Is discontinuous, related presumably to the original distribution of the tuffaceous sediment. ~

d1pp 1ng iQ ~

Soft thin black clays occur within steeply dipping beds In the overburden at Goonyella. In the northern mine section the hlghwal I consists mainly of Interbedded slltstones and sandstones. Llthologles are light coloured In greys and browns, with the lower section of the hlghwal I more sf lty and flnely lnterbedded (McKean 1977, Godfrey 1979). Occasionally thin 1-5cm black claystone beds are conformab I e In these sequences. These beds are d I st I net from the th lck carbonaceous claystones that are associated with the rider seam to the Goonyel la Mlddle Seam In the southern section of the mine. The flnely lnterbedded I lthologles represent splays emanating from a major dlstrlbutary, not generally found In the hlghwall sections (figure 4). Loading and compression of the peat as out I lned for the sand channels above, formed the steeply dipping beds now seen In the hlghwal I. As the thin dark clays are found In the lower section of the hlghwal I, they were therefore deposited on the side of the sediment belt, and adjacent to the peat, over which the belt was migrating. The silty nature of this side suggests that the main sediment axis with the coarse sediment, was separated from the peat by a shallow area receiving fine suspension sedimentation. The dark soft beds contain a higher organic content than other sediments In the area. The rapid variation and recurrence of flnely lnterbedded I lthologles reflect rapid changes In depositional conditions. This shows In the gralnslze, colour and cementatlon of the Australian Coal Geology 4, part 2

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sediments. The black clays are commonly associated with thin hard dolomitic slltstones. These variations produce an extremely In-homogeneous hlghwal I.

Structural geol~y The sediments have had a long history of deformations since their deposition. It began even before any I lthlflcatlon, as the pea t compressed during the depos It I on of the terr I genous c I ast I cs. After some d I agenes Is, s I gn If Icant penecontemporaneous faulting occurred at South Blackwater. This occurred particularly around the time of deposition of B seam (pers comm P.Cottam). Subsequently the basin was deformed, with a major tectonic zone traversing the basin northwest southeast (Dickens & Malone 1973 ). During the Tertiary, basa Its were erupted in many areas, and severa I phases of assoc I ated steep normal and reversed faulting have been Identified (Devey 1982). Although new fault systems were developed In this period, movement probably occurred on reactivated older faults as well. Although coal measures are relatively fla t lying over much of the Bowen Basin, severe east west compression has resulted In common low angle thrusting and bedding plane faulting. These structures are difficult to observe In vertical cores, but can be seen In surface and underground workings. Where this faulting affects distinctly stratified sequences such as coal measures, dislocations are local lsed In the weakest beds, commonly sf ltstones adjacent to coal. At Moura and Terang the soft clay horizons are associated with bedding plane faults. These are thought to have selectively fol lowed originally weak beds such as tuffs or carbonaceous layers. Deformation of clays and the Ingress of water along the faults have created a very weak fault gouge material. This phenomena has a ~so been reported from the european coal measures where It has been referred to as 'clay mylonlte 1 (Stimpson & Walton 1970). Deformation Is not necessarl ly confined to the weakest layer. At Terang P i t, In areas where the tuffaceous bed Is locally absent, normal sf ltstones have been sheared, and a network of weak c I ay 11ned Jo I nts deve Ioped (Ma I Iett il li• 1982). In other areas of the pit, the fault zone Is confined to a few centimetres thickness, with enclosing rocks unaffected. The Moura sequence Is harder and more ea Icareous, wIth s lgn If Icant brecc la zones often assoc Iated with the deformation zones. Low angle faulting does not seem to be s ignificant In the development of weak b Iack c Iay bands at Goonye I Ia. Movement on these re Iat I ve Iy steep Iy d Ipp Ing planes Is compatable with the high angle tensional faulting associated with the Tertiary faulting In the area.

Tertiary weathering Tertiary weathering has been directly re lated to the production of weak clay horizons both on the Tertiary/Perm Ian unconformity and within the Perm Ian sequence, where groundwater Inflow has modified the original sediments (Ma 11 ett .ei .al. 1982). Over much of the Bowen Basin there Is evidence of a laterltlc weathering profile. This has severely leached the surface of the Permlan sediments, and weak water-sensitive clays have been produced. At Goonyel la, sandstones near the unconformity have been altered such that they now have greater potential for dispersion than almost any other rock In the mine. At Terang Pit, the material associated with the low angle faults Is considerably softer In the area of the surface mine than equivalent materials at depth Australian Coal Geology 4, part 2

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In the underground mine, or In the Utah Development Company's Blackwater Mine to the north. There appears to be a relations hip between the weakness of the floor materials and associated overlying Tertiary lake sediments. Where there are thick Tertiary sediments, It Is more likely that very weak floor material wll I be found. It seems probable then that the clays within the Perm Ian sect I on have been affected by weather Ing processes In the Tert I ary. The reduced amount of carbonate, and the presence of kaolin In the weathered material, Indicate that the clays have been exposed to attack by acid water. There are several possible sources of this water, but It may have entered as groundwater Inflow from overlying Tertiary lakes. Fossil leaf Impressions Indicate red uc Ing cond It Ions In the Iakes. By ana Iogy wIth modern env Ironments, such lakes would also have been acidic. PHYSICAL PROPERTIES OF PLASTIC CLAYS It has been shown above that there are two major requirement s for large scale hlghwal I or spol I pi le fal lures. Firstly there must be a surface which dips Into the pit, and secondly there should be clayey material of low shear strength on th Is surface, The fa 11 ures are not s 11 ps a Iong smooth Inc 11 ned planes, but Involve the shearing through of materials. The shear strength of a soft rock or sol I Is derived from frictional resistance between the constituent particles. For clay-rich materials associated with the failures described above, the magnitude of this resistance Is most Influenced by groundwate r conditions and the presence of mineral cements (Mitchell 1976). Potential low shear strength of clayey material Is Indicated by an ability to swel I and take up large amounts of water at low suctions. Table 1 gives the water content at lkPa suction for several of the low strength materials Involved In slope failures, along with typical values for surrounding sediments. Site Water content Dispersion Index South BI ackwater lnfloor failure plane 45-46% 2M mudstones 13-17% 3M Goonyel la potential base of spoil 38-42% 1M Intact spo I I 17% 3M dolomitic siltstone 6-8% 8M Goonyel la black clay plane 22-42% 1M hlghwall mudstones 17% 3M TABLE 1 The uptake of water at lkPa suction of failure materials and surrounding sediments. The dispersion Index Is that of Emerson & Seedsman 1982. For those mater I a Is w Ith h I gh water content, the swe I 11 ng of the con ta I ned clay Is so great that It Is only the appl led suction that Is holding the material together. If the suction Is reduced to zero by Immersion of the material In water of low salinity, osmotic stress will be sufficient to cause the Individual clay particles to diffuse out Into solution. Such materials come within the class 1M (complete dispersion) or 2M (partial dispersion) of the Modified Emerson Crumb Test (Emerson & Seedsman 1982). In the context of the materials discussed here, where an Increase In osmotic pressure Is sufficient to cause dispersion, a proportion of the negative charge of the clays Is balanced by monovalent cations such as sodium Ions. However clays with only divalent exchangeable cations such as calcium and magnesium Ions can be made Australian Coal Geology 4, part 2

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C.W. Mai lett, R.W. Seedsman, & W.W. Emerson

to disperse In water by osmotic stress, If they are mechan I ea 11 y worked first In the presence of water (Emerson & Smith 1970). Materials that disperse In water after being worked at a water content corresponding to Its plastic limit fall within class 3M of the above test. If they do not disperse they are assigned to class 4M. Clays that are too strongly cemented to be reworked are placed In class 8M. The exchangeable sodium potential (ESP) required for a clay to be In any given class depends on the attractive 100 80 forces between the clay particles. The 60 0 40 20 stronger they are the greater the ESP Exchangeable sodium percentage required. Conversely for clay of given composition and ESP, lack of disper- Figure 5 The effect of reworking on the dispersion of Goonyel la hlghwal I sion can be used to Indicate the presmaterial, caused by Increasing ence of bonding materials. The bonding osmotic pressure. agents Important In the Bowen Basin are organic matter and carbonate, the latter commonly In the form of dolomite or ferroan dolomite. Mixed-layer mlca/montmorll I lnlte Is the dominant clay mineral present throughout the Bowen Baslon, accounting for 80% of the clay fraction. Kao( In, 111 lte and quartz are the minor clay size minerals present. The proportion of mlcaceous Iayers In the mI xed I ayer c I ay Is est I mated to be about 70 to 80%, and both random and Intermixed ordering has been detected. The relatively uniform assemblage al lows comparison of the various effects of bonding agents at different mine sites. The type of ordering In the mixed layers Is not considered significant. lot Joor~

Seedsman and Emerson (1981) have shown that for a carbonaceous clayey sf Itstone from Goonyel la, the ESP must exceed 40 before significant dispersion wl I I occur from an air dried state (Figure 5). If t he bonds that hold this rock together are broken by working with a spatula In the presence of water, then an ESP of about 5 Is sufficient to cause dispersion. The fal lure material, from Terang Pit, South Blackwater C Table 1 ) can be I lkened to such reworked mater I a I as It has neg I I g I b I e carbonate cement or organ I c matter present. In the abscence of any bonding agent, a low ESP value of 5.6 Is sufficient to al low dispersion from an air dried state (class 2M). The enclosing grey slltstones have similar ESP values, but organic matter Is preventing dispersion. These slltstones disperse after reworking (class 3M) .

.B.a.s..e .Qf .,SSl.Q.U As mentioned above, clay-rich rocks can be made to d isperse by reworking them In the presence of sufficient water. The amount of water needed depends In part on the composition of the exchangeable cations (Figure 5), and may not be much more than the maximum water uptake of the material (Emerson 1967). For carbonaceous slltstones that can be reworked, usually with a carbonate content less than 10% expressed as CaC03, the maximum water uptake Is 15 to 20%. With Austral Ian Coal Geology 4, part 2

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water content of 20%, significa nt dispersion can occur with an ESP as low as 5 (Figure 5). Note that the relations hip between ESP and dispersio n Is not linear, and that an ESP greater than 10 wlll result In ~early as much dispersion as one of 50. For material with no exchangeable sodium present, a water content at remoulding of 50% Is required before dispersion occurs (Seedsman & Emerson 1981). During mining, reworking occurs during b I ast r ng, excavat I on, spo J I Ing, settl Ing of spol I, and Incipient fal lure. At Goonyel la, the clayey siltstone near the coa I has an Ins I tu water content of about 17%. If this material Is reworked by spol I Ing operation s, the water content of the excavated mater I a I cou Id r I se to 35% If Iow sallnlty water Is allowed access (Figure 6). Further reworking at this higher water content could cause a further Increase to 55%.

100 •

Goonyefl a Siltstone ESP= 22

-.,o

::,

'.j

a, C:

g 20

There are two Important Imp I Icat Ions cii of this mechanism . Flrst,the whole OI spol I need not break down to affect 3: 0 20 40 60 80 100 stab I I lty, as the formation of weak clay zones on the outside of blocks Water content at remoulding ('11,) may be sufficien t. Second, the level of reworking that occurs during mining Figure 6 Relationsh ip between water Is probably not sufficien t to release uptake and water content of the c I ays w Ith Iow ESP, such as South sample at reworking for Goonyel la Blackwate r mudstones (class 3M, ESP hlghwall material. about 5), or high levels of cement such as Moura (ESP about 50 and> 10% carbonate ). It Is hoped that further development of the crumb dispersion test wl 11 al low correlatio n with shear strengths of clayey rocks .

.B.l..a.ck ct.a.¥ ~

The black clay planes at Goonyel la and their associated uncemented mudstones are very similar, both being silty claystone s with 50 to 60% ctay, having an ESP of 22 to 28. Despite this, note the large differenc e In swel I Ing and dispersion behaviour Indicated In Table 1. Carbonate does not appear to act as a bonding agent at levels less than about 10%. Some results suggest that the black clay planes contain more carbonate than surroundi ng rocks, although va I ues are st I I I Iow. Organ I c matter Is more concentra ted In the b Iack c Iay planes and this Is thought to be responsib le for the observed dispersion . Note that this Is In contrast to South Blackwate r where organic matter Is thought to reduce dispersio n. Organic matter can hold clay particles together In unsheared aggregate s, but wll I Increase the repluslve force between the particles If the organic bonds are mechanica lly broken by shearing (Emerson 1977). At Goonyel la there has been considera ble shearing along the black clay planes, and this may have altered the role organic matter plays. It Is possible that the more organic beds with greater than 2% carbon, may have been sl lghtly weaker and so have localised the strain. Such movements wil I have broken the clay/orga nic bonding, and arranged the clays In such a way that they wl I I disperse In water. The black clay planes with lower water contents around 20%, have organic contents of 5%, and in these this extra organic matter sti I I Australian Coal Geology 4, part 2

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C.W. Mai lett, R.W. Seedsman, & W.W. Emerson

binds the clay together. It Is not known what Is the relative shear strength of such material. IDENTIFICATION The modified Emerson Crumb Test (Emerson & Seedsman 1982) Identifies material that may take up dangerous levels of water, and hence lose Its strength during mining. In the test, spoil Ing and other mining operations are model led by reworking In the presence of water. The test also al lows potent I al fal lure zones In hlghwalls and pit floors to be located, as they fall Into classes 1M and 2M. Only smal I chip samples are required for the test, but a drawback to the test Is that the materlals of most Interest ar e often lost during the drll llng process. Invest Igat I ons to date Ind Icate that d I spers I on propert I es of the var I ous I lthologles remain falrly constant within each mine lease. The examination of a re I at I ve I y sma 11 number of dr 111 cores shou Id estab 11 sh the presence of overburden materlals that may weaken when spoiled. Bands of weak material within the coal measure sequence may be only a matter of a few centimetres thick, and their detection by downhole geophysical logging Is dlfflcult. The only characteris tics In which they conslstentl y differ from the surrounding rocks are their softness and high water content. Water content may be up to three times background. A high resolutlon neutron probe for their detection Is currently being evaluated by the Division of Appl led Geomechanlcs. Other posslble tools that may offer help Include a dlelectrlc meter, borehole camera, penetromete r or callpers. REFERENCES Barton,C.M.& McKean,R.M. 1978 Review of engineerin g geology aspects of an Investigati on of slope stab I I lty In strip coal mining at Goonyel la, Queensland • .cs..l.BQ Austral ta, P1vtston Appl led Geomechanlcs, Technical .Rei2.Pc.1 .!8. Boyd,G.L., Komdeur,W. & Richards B.G., 1978 Open strip pltwal I stab I I lty at Goonyel la mine - causes and effects. Australasia n Institute Mining and Metallurgy, Conference, North Queensland 1978, 139-157. Chrlonls,N .P., 1978. ~~oper ating handbook .of .c..12.a..l surface mining~ reclamation . McGrawHII I, New York, 1-442. Devey ,D.M., 1982. The I nf I uence of structure on the deve Iopment of underground mInes In the western Bowen Bas In. Geo Iog Iea I Soc I ety Austra 11 a, Queens I and Division Symposlum,Permlan Geology of Queensland, In press. Dickens J.M., & Malone E.J., 1973. Geology of the Bowen Basin, Queensland . .B..!.lr:..ea.u MI nera I Resources Austra I I a, .B..u.l.1.... ~ 130p. Dunbavan,M., 1981. Spoll plle lnstablllty with reference to the Goonyella mine, Queensland . Australasia n Institute Mining & Meta l lurgy Central Queensland Branch,Symposlum, Strip mining 45 metres and beyond 1981,119-130. Dunbavan,M., 1982. Laboratory testing of spol I materlal. CSIRO Austral la, Division Appl led Geomechanlcs, Progress report on col laboratlve studies with Utah Development Company No 2, June 1982,3-17 (unpubllshed).

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& W.W. Emerson

541

Dunbavan,M. & Welsh,T.C., 1981. Spol I pi le lnstabl I lty South Blackwater mine, Queensland • .c..s.J.B.Q Austral la, Division Appl led Geomechanlcs, Geomechanlcs Qf . c o a l ~ ~ ~1-34. Emerson, W.W., 1967. A classlflcatlon of sol I aggregates based on their coherence In water. Austral Ian Journal .so.IJ. Research .2,47-57. Emerson, W.W. & Seedsman R.W., 1982. A mod If I ed em er son crumb test .c..s.J.B.Q Austral la Division Appl led Geomechanlcs,Tec hnlcal Memorandum 1..2. Emerson W.W. & Sm Ith B.H.,

.tia1.Yc..e .228.,453-454.

1970. Magnes I um, organ I c matter and so 11 structure .

Godfrey,N.H.H., 1979. Clay and I lthology stud i es at Goonyel la for pltwal I lnstabl I lty research. Utah Development Company, Technical Services Division Report (unpub 11 shed) Gonano,L.P., 1980. An lntergrated report on slope fal lure at Goonyel la - November 1976 • .c..s..IB.Q Austral la, Division Appl led Geomechanlcs, Technical Report

.l,li.

Mai lett,C.W., 1982.Deposltlonal environments In the Rangal Coal Measures, southern Bowen Basin. Geologlcal Society Australla, Queensland Division Sympos I um, Perm I an Geology of Queens I and, In press. Mallett,C.W., Dunbavan,M., & Seedsman,R.W., 1982. Geotechnlcal Investigation of Terang Pit, South Blackwater. CSIRO Austral la Division Appl led Geomechanlcs, Internal Report 44 (unpubllshed). McKean,R.M., 1977. Notes on stratigraphic types In the lacustrlne overclays at the Goonyel la strip mine. CSIRO Austral la Division Appl led Geomechanlcs, Stab I I lty problems In open pit excavations and spot I piles Project Report 29, 10p (unpub 11 shed). Mltchell,J.K., 1976. Fundamentals.Qf.s. ol.J behaviour. John WIiey & Sons, New York. 0 1 Regan,G.J., Dunbavan,M. & Mallett,C.W., 1981. An Investigation Into spoil stability at Moura. Australaslan Institute Mining Metallurgy Central Queensland Branch, Symposium, Strip mining 45 metres and beyond. 145-154. Rlchards,B.G., Coulthard,M.A., & Toh,C.T., 1981, Analysts of slope stab I I lty at Goonyella mine. Canadian Geotechnlcal Journal 1..8,179-194. Runge, I .C., 1981. MI n Ing des I gn for deep opencut mInes. Austra I as I an Inst I tute Min Ing Meta I I urgy Centra I Queens I and Branch, Sympos I um, Str Ip m In Ing - 45 metres and beyond, 37-42. Seedsman,R.W. & Emerson,W.W., 1981. Dispersion tests and spoil plle stability • .c..s.J.B.Q Austral la, Division Appl led Geomechanlcs, Geomechanlcs CQaJ. Mining Report~Stlmpson,B. & Walton,G., 1970. Clay niylonftes In opencast slope stability. Proceedings 1st International congress, International Association engineering Geology, Paris 1970, vol. 2,1388-93.

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The Geotechnical Assessment of the Theodore Prospect G.L. Boyd CSR, Energy Division, National Mutual Centre, 144 Edward Street, Brlsbane,4000 Austra 11 a Key Words: Surface coal mining, Bowen Basin, Mine planning ABSTRACT Proposals to mine the Theodore North steaming coal prospect In the Bowen Basin, Queensland, cal I for an open pit shovel/truck terrace mining operation extracting coal to a depth of 170 to 200m. Geotechnlcal and hydrogeologlcal Investigations Identified a number of constraints to mine plannlng, chlefly In the area of footwal I stab I I lty, and lnterburden fragmentation requirements. To quantify the spatlal distribution of these constraints, sedlmentologlcal analysls of lnterburden sediments was undertaken to the level of Identifying mappable depositional units, and their related llthofacles. The vlabll lty of this approach relied on the assignment of Important geotechnlcal constraints to the different I lthofacles, the mapping of which thus provided mine planners with lnterburden properties on a mine-wide basis. Mapping techniques, prlnclpal ly the preparation of three-dlmenslonal sections and sediment ratio plans proved useful methods for data reduction and presentation. Wlrellne geophysical tools, partlcularly close spaced neutron and dlpmeter sondes, were Invaluable aids to Identifying llthofacles composition, bedforms, sedimentary and tectonic structures. INTRODUCTION The Theodore prospect 11 es 120km Southwest of GI adstone w Ith In the fert 11 e valley of the Dawson River. Moura and Klanga open cut and underground coal mines lie 40km to the north, extracting from equivalent seams of the Baralaba (Rangal) Coal Measures of late Permlan age. Current mln)ng proposals cal I for a 4 Mta open pit terrace mining operation at Theodore North using shovel/trucks for overburden stripping and the mining of eleven prlnclpal seams and associated spl Its. Mining Is to occur over a 9km x 2km pit area to a depth of 170m. The coal Is destined for the export steaming market, currently being sought by Theodore Coal Pty. Ltd., a CSR/Shel I Joint venture. Figure 1 provides an ob'I lque view of perceived operations, and defines pltwal I nomenclature referred to throughout this paper. Coal won from 15m thick benches wl 11 be transported to the surface via a footwal I ramp. Each alternate bench left In the hlghwal I wll I allow haulage of waste rock to In-pit dumps. Haulage of waste to an external dump wl I I occur lnltlal ly untl I strike I lne advance commences fol lowing boxcut excavation to the ful I pit depth.

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·--·. . - - - ··•-· ~

Figure 1 Obi lque View of Mining Proposal This paper presents an account of geotechnlcal constraints to mine planning, with particular emphasis on quantifying the Impact of such constraints. Described also are the field and analytical techniques used to marry sedlmentologlcal data with geotechnlcal criteria as Input to mine design. Finally, some specific results of the geotechnlcal appraisal are described to provide a context for the approach taken. INTERBURDEN GEOLOGY

Geological .and DeposJtJooal Setting The Theodore Prospect Iles In Upper Permlan Baralaba Coal Measures In a south eastern extens I on of the Bowen Bas In. The coa I measures are brought to the subsurface on the eastern limb of the Mimosa Syncline, a regional structural feature of the southern Bowen Basin. Our Ing the I ate Perm I an, depos It I on of terr I genous sed I ments under f I uv I a I conditions {Svenson, 1975) al lowed repetetlve and extensive coal swamp development over broad flood plains. Regional stratigraphy Indicates the sediment provenance lay to the south as northerly flowing dra inage developed behind a major marine regression resulting In {Bowen) basin wide coal development <Bara I aba/Ranga I Coa I Measures). In Theodore North area a tota I of 12 coa I seams were laid down. Depos It Iona I contro Is ev I dent from exp Iorat Ion data and from exam I nat Ion of exposures at Moura, clearly relate to channel forming processes developed within depositional environments ranging from:

Austral Ian Coal Geology 4, part 2

544

G.L. Boyd I)

High energy fluvlal environments resulting In wide-spread fine to coarse sandstone deposition;

Ill

Relatively low energy depositional environments, typical of an upper and lower delta plain comprising laminated to thinly bedded fine grained sediments.

Depositional environments are represented by clear transitions In the vertical sequence with separation by coal seams, as Indicated In the type llthocolumn presented In Figure 2. Lithological changes within lnterburden sequences were evidence for lateral transition In depositional environments between coal form Ing ep I sodes.

GNII

Sediment Composition .aruf Ciassification Petrographic analysis by thin section was employed to determine elastic sediment composition, while X-ray diffract I on of coarse and f I ne gra I ned sed 1ments was undertaken to determine fine silt to clay size material composition.

F_,ioft

Findings from the analyses relative to material composition were: Sandstones analysed from all lnterb urden sequences c I ass I fy on a QRF diagram as I ttharenltes (see Figure 4).

b) Llthlc components In sandstone and coarse s I I tstones are dom I nated by volcanic rock fragments Cup to 54%) and clay pseudomorphs/lnterstltlal clay Cup to 50%), with minor quartz and feldspar and variable carbonate.

Clay

Sandstone

Sha le

S11fstont

Coo l

Boralabo

Coal

Meaaurn

cl Clay composition for al I sediment types Is dominated by smectlte or mixed layer 111 lte - smectlte clay mlneral. These clay types are moderately expans I ve. On I y mI nor amounts of smect I te clay are thought to Include pure montmor I I Ion I te.

rn rn

Sandstone / S1tt1tone lnterbedd1d

Sandstone /Shale tnt1rb1dd1CI

Shale / S1ltlt0M lnterbeddtd

Sholt / Coa

lnterbeddlCI

Siltstone / Sha .. lnterbedd1d

8oM of weotherino

d) Sandstone classification does not appear to vary noticeably with depth. e) No preferred occurrence of clay minerals with particular sedlmenttypes was observed.

GN 11 - o fu ll y - ccred 1trot1;raphlc holt drilled by tM Queen1land Dlportment of Minn c., hne 5 1OOON

Figure 2 Representative section Theodore North

Over a I I, It was cone I uded that var I at I on In sed I ment character I st I cs throughout the depos It was a funct I on of mater I a I texture (gra In s I ze), not composition. Thus characterisation of lnterburden strata was possible by mapping grain-size variation alone, since geotechnlcal ly, strata properties would not be slgnlflcantly Influenced by compositional variations.

Australian Coal Geology 4, part 2

545

G.L. Boyd fu:l!;;.k

.Mass Structures

Defects

Engineering logging of cored roof and floor Intervals to al I target coal seams resulted In the repetetlve Identification of the following defect types: al Partings - A defect para! Jel to a layered arrangement of mineral grains or mlcrofractures which have caused planar anisotropy Jn the rock substance. b) .J..Qln.t - A defect across which the rock substance has llttle or no tensI le strength but that Is not related to textural features Jn the rock substance. c l ~ .5M.UI ZQn.e - Zone of very low strength, h I gh s Iak Ing, sha I e and claystone.

llP't M

-••··

_14 ·0

_1 5·0

_16·0

gl Broken ZQn.e - Zone known to or considered to have been crushed and disturbed by the drll ling process. hl .E.a..u..J..t - Defects or an Individual defect known to have Involved differential movement across the plane of the defect.

-. . : ... •: • --· . ••• -· • -· • -· •• ., I I

•

I I I

dl ~ .5.e.aln - Seam of cohes I ve so 11 materlal. el Clayey _s_u_t ..$.e.am - Seam of soil mater I a I cont a In Ing a mI xture of cohes lve and non-cohesive materials.

....

_17·0

•

I I I I I I I

_18·0

I I I I I

I I

...

Figure 3 ENGLOG of Geotechnlcal Data

Spacing, orientation, attitude, planarity and surface roughness as we) I as surface composition were logged directly onto an engineering geological data base system (ENGLOG). The defects were rated Into three categories according to the I r pers Istance; ass Igned c Iass If Icat Ion of defects (I.e. rat Ing 1, 2 or 3) was computer plotted as shown Jn Figure 3 . .J.ctl1lll

Orientations of Joints was obtained from an angled, fully cored borehole, mapping the wal Is of the trlal excavation, and from wire I lne (dlpmeterl results. Two types of Joints were observed In the trlal excavation:

Formation Joints, usually normal to bedding surfaces and confined Jn extent to discrete beds such that the extent of the Joint trace reflects thickness of the bed. Australian Coal Geology 4, part 2

■

G.L. Boyd

546 2.

Tectonic Joints, penetrating bedding, usually wel I spaced (5-10m) which may extend over the complete lnterburden.

In general the Joints strike diagonally to the direction of dip of the measures and are normal to subnormal to the dip of bedding. Major Joint set orientations are as follows:

DIP DIRECTION (0 )

SET A

060

130

With the above orientations, Joints wl 11 strike ob l l quely to major pltwal I orientations . .Ea.u.lis

A major fault was discovered during the resource evaluation drll !Ing program

and later confirmed by detal led drl I I Ing about the known areas of displacement. The true dip and dip direction of the fault was determined as being 36° to 337°. This corresponds to a 17° component of dip Into the hlghwal I, but a 10° to 12° component of dip out of the footwall. The material In the faulted zone Is thought to be Intensely Jointed and sheared with most defect surfaces being sllckenslded. Smal I local lsed faults were observed In a trial excavation exposing the lowermost seam to be mined. These faults are probably associated with post deposltlonal compaction of the soft sediments and their lateral and vertical extent was no more the 150m and 10m respectively.

Geotechnlcal Constraints .o..f .M.l.n.e De..s.l.gn It was concluded from the geotechnlcal appraisal that constraints to the mIn Ing proposa I were assoc I ated w Ith the fo 11 ow Ing, In order of I ncreas Ing concern: sediment composition sediment bedform faults seepage pressures rock mass defects stratigraphic dip The potent I a I Impact of each feature Is sum mar I sed In Tab I e 1. Prov Is I ons were made In the feaslblllty study for control measures to accommodate these constraints. A description of each of the features fol lows. ~

Description aru1 Properties

Rock mass defects, pr Inc I pa I Iy bedd Ing p Iane part I ngs, c Iay seams or softened shale bands In conjunction with the stratigraphic dip and face seepage For slml lar provide the potential for lnstabl I lty of the footwal I. Austral Ian Coal Geology 4, part 2

G.L. Boyd

547

TABLE 1 Geotechnlcal Constraints on Mining Proposal FEATURE

NATURE OF CONCERN

IMPACT ON MINING PROPOSAL

1. Sediment composition

High slake potential mudstones, shales, some slltstones . Sources of natural construction materials

Deterioration of spoil jeopardising stab I I lty of lnplt dumps . Erosion of footwal I pavement for excessive siltation of pit base . Lower operating costs

2. Sediment bedforms

. Massive hard material deposits hinder fragmentat Ion . Well bedded strata likely to contain weak planes . Local dip reversals

. Blasting costs Increase or loading /haulage efflclences decrease

Fau Its

. Attitude, orientation and low strength _affect pltwal I stab II lty

Affects batter slope angle and hence overburden stripping ratio

4 Seepage

. High exit seepage gradients may destaballse pltwal Is

. lnstabl I lty of lower portions of highwal I and footwal I, and may require flatter slopes and higher strip ratios

5 Rock mass defects

. Low strength defect and potential for footwal I lnstabl I lty

. Disruptive to production and pit safety; affects design of footwal I ramp for coal haulage

. Promotes gravitational . Footwal I lnstabi I lty sl ldlng If excessive for a given defect . Limits equipment access I b I I Ity

Stratlgtaphlc dip

. Pltwal I lnstabi I lty; fragmentation (shape) Local pltwal I lnstabi I lty

oL-----+----+---+----->o o

100

lllCK FRAGMENT$

Figure 4 QRF Classlflcatlon of Sandstones Austral Ian Coal Geology 4, part 2

G.L. Boyd

548

TABLE 2 Design Strength Grouping of Rock Mass Defects Group

Angle of Friction Design Range Value

Type of Defect Included

General Defect Rat Ing

14.5-20

.CLAY SEAMS consisting of medium to high plasticity silty clay In contact with any rock type .CLAYEY S ILT bands .SOFT SHALE zones

17-21

.SHALE/ MUDSTONE PARTINGS and JOINTS which are either polished or smooth or sl lckenslded . COAL PARTINGS which are polished or sl lckenslded

1&2

21-27

.SILTSTONE PARTING and JOINTS which are planar, pol lshed or sllckenslded .SHALE and MUDSTONE PARTINGS and JOINTS which are rough, undulose or stepped . . COAL PARTINGS and JOINTS which are smooth to rough .SILTY SAND SEAMS

27.5

27-33

.SILTSTONE PARTINGS and JOINTS which are smooth to rough

2&3

<33

.SILTSTONE JOINTS rough, undulose or stepped .SANDSTONE PARTINGS and JOINTS

operations In the U.K., footwal I lnstabl I lty causes significant Increases In mining costs through the need to over-excavate down Into more stable strata, and/or employment of anchoring and bolting techniques, or placement of toe burden embankments (Wa Iton .irt .al. 1980). A total of 27 direct shear strength tests were conducted on defects, as wel I as clayey sl It bands and a soft shale band. Results Indicated a neg I lglble cohesive strength component under drained, residual conditions. Thus available shear strength along any defect was expressed by a single parameter I.e. the effective angle of friction. For design purposes, the various rock mass defects were grouped according to shear strength, as sum mar I sed In Tab I e 2. Defect rat I ngs der I ved from the ENGLOG (Figure 3) are shown opposite corresponding strength groupings. For the hlghwall and north endwall It was shown that high seepage pressures computed from packer pump tests and flow net analyses would cause movement of Joint bounded blocks. Other than local Influences of faults, no other rock mass structures were of concern to pltwalls stability. Australian Coal Geology 4, part 2

G.L. Boyd

549

Geotechnlcal Properties Related TI> Composition/Textures Geotechnlcal tests on the various sediment types represented In the coal measures sequence Included: a) b) c) d) e) f)

density porosity slake potential point load strength unconfined compressive strength rock substance modul I

Results complied In Table 3 confirm the Influence of rock texture rather than composition on geotechnlcal properties of the various I lthofacles. This Is part Icu Iar Iy ev I dent In the var Iat Ion of poros I ty wIth sed I ment type, be Ing lowest for sandstone (due to dlagenetlc mineral deposition) and Increasing the finer the sediment type. Slaking potential, which Is a function of material composition, lump size and surface porosity, Is lowest for the low porosity material, and higher for sediments with an Increased porosity. Again the higher strength and moduli results for sandstones compared to finer grained strata represent a division In sediment properties recognisable by the textural variation between materials.

Bed form er Iter Ia The shape of deposit Iona I units Impacts on mine design In a number of ways. Thick massive tabular, lentlcular to wedge shaped sandstone present fragmentation problems unless blasts are adequately designed. Poor fragmentation leading to excessive oversized material reduces shovel ff I I factors and truck haul-loads. Lenticular to thin tabular deposits of fine grained laminated sediments are the probable location of defects affecting footwal I stability. I nterna I bed form structures, such as cross-bedd Ing, a I so present potent I a I surfaces along which failure may take place, due more to their characteristic steepness than strength criteria. In a broad sense, seam sp 11 tt Ing Is another bed form feature. The sp 11 tt Ing and coalescence of seams represents compaction phenomena (Boyd 1980; Mallett n .al. 1980) typical of Bowen Basin Coal Measures, the effect of which may lead to abnormal reversal of dip. However, on analysing top of seam structure contours for each seam, It was concluded that dip reversals associated with seam splits presented no constraints to the mine plan. SEDIMENTOLOGICAL ANALYSIS FOR 1GEOTECHNICAL 1 MAPPING

Requirements .foe lnterburden Characterisation From the foregoing description of the major constraints to mine planning, a scheme was required to define In summary form the distribution of rock mass features of geotechnlcal Importance to mine design. Such a scheme was requ I red to a) b)

define the distribution of the various categories of weak defects relative to the pltwal I slopes; define the distribution of bedforms for which separate provisions relating to excavatlbll lty, spot I dump composition and pltwal I stabll lty were required In the mine plan. Australian Coal Geology 4, part 2

550

G.L. Boyd

Since It was shown that compositional effects were of minor concern, and that features of greatest Importance could be represented by textural properties of the sed I ments, a scheme to map group I ngs of sed I ment types (or 11 thofac Ies) was adopted. Llthofacles chosen were selected on the basis of their al

association with the crltlcal geotechnlcal features to be mapped; and

their abll lty to represent depositional units within the sedlmentologlcal character of each lnterburden.

Item (b) was fundamental to the scheme, since mapping ref ied on the Interpretation of drll I and borehole geophysics logs. As an aid to accurate Interpretation sedlmentologlcal principles relevant to the (known) depositional environment were applied to maximise the accuracy of the mapping.

Environment .o.t Deposition The sect Ion, Geo Iog Iea I and Depos It Iona I Sett Ing, descr I bes the depos It Ion of the Bara I aba Coa I Measures as a resu It of f I uv I a I sed I mentat I on w Ith Intermittent back swamp development where thick peat deposits were laid down. Figure 2 shows the high proportion of sandstone and lnterbedded sandstone/ siltstone forming thick beds In the various lnterburdens. The distribution of sandstone strata per lnterburden reveals lateral as wel I as vertical variations within each lnterburden, and within the overall vertical succession. Using the form, character and ext ent of channel development as a guide, three basic subdlvlslsons of the succession were possible. a)

Below Seam 6-7 (see Fig. 2), laterally and vertically extensive fine to coarse sandstone dominates lnterburden strata, representing a high energy depositional environment, characteristic of a fluvlal (channel) and backswamp depositional environment.

Between Seam 6-7 and base of seam 3, dominant but discrete channel forms are recognisable together with associated overbank and floodplain deposits representative of a moderate to high energy depositional environment as typified by an upper delta plain - fluvlal depositional environment.

Above Seam 3, channel development (hence fluvlal/processes) are much localised, and associated overbank and floodplain/swamp deposits dominate, typical of a transitional lower delta plain depositional environment.

The three stages of coarse to f I ne sed I ment depos It I on as descr I bed, corres pond to a change In sedimentation pattern from progradatlonal (lateral accretion) to aggradatlonal (vertical accretion) growth of the sediment stack. Sedimentation patterns were thus examined (for mapping the lnterburden llthologles) by recognising appropriate deposltlonal units. On the basis of the above diagnostic characteristics, a depositional model largely control led by fluvlo-deltalc processes was adopted to describe coal measure sedimentation at Theodore North.

Austral Ian Coal Geology 4, part 2

G.L. Boyd

551

Deposltlonal .l.ln..1.1s. Channel development Is the key to understanding sedimentation patterns In a fluvlo-deltalc environment, since sediment Introduction and distribution rely on fluvlal processes, particularly during cycles of flood-breaching of channel embankments or levees and Inundation of associated flood plains. Deposltlonal un r ts typ rea I I y found assoc I ated w r th f I uv ro-de r tar c env r ronments Inc I ude channe Is, Ievees, crevasse sp Iays and over bank f Ioodp I a In depos Its. In high energy deposltlonal settings, channel deposits form thick units with a well defined base (erosion surface), a high width to height ratio, and moderate I y steep f I anks across wh I eh channe I sed I ments gradua I I y merge or lnterdlgltate with adjacent sediments. During flood cycles, levee embankments develop adjacent to the channel In response to the lnltlal reduction of current velocities beyond the channel. Fine gra I ned sed r ment and organ I c debr Is Is usua I I y carr red we I I beyond the levee. However, floral growth of the levee may result In retention of some carbonaceous bedding surfaces. Crevasse splays result from the breaching of a levee and local Inundation/ sedimentation over the adjacent floodplaln. Such deposits usually comprise coarsen Ing up sequences of I nterbedded sandstone and s I I tstone, agar n generally devoid of fine grained sediment or organic debris lylng In bedding surfaces. Floodplaln deposition Is synomonous with overbank deposition, where during flood cycles, the finer grained sediments are carried beyond the I Im Its of the channel and channel levee deposits. Characteristics of overbank sedimentation Include: a)

Finely layered texture of deposits due to flood pulsatlon plus deposition of suspended sol Ids and col loldal minerals.

Sediment grain size decreases with distance from the channel.

Frequency with which bedding surfaces are left coated with clay minerals or organic debris Increases with distance from the channel.

Thus criteria exist for recognising proxlmal and dlstal overbank deposits, I.e. very thin to thin bedded units In which bedding surfaces are coated with clays or organic debris/fossils are more likely to represent distal overbank deposits. Proximal deposits wlll largely be free of such coatings on bedding surfaces or slml lar spacing. Where swamps prevalled over the delta or floodplaln, paludal deposits comprising laminated to very thinly bedded mudstones and claystones occur with organic debris and col loldal precipitates. Deposits formed by vertical stacking of sheet-I Ike layers may extend over the source channel thus marking the commencement of a period of quiescent, coal-forming conditions. Similarly, where channel activity ceased but the depth of water posslbly exceeded 2m, lacustrlne sediments accumulated over large areas. Sediments comprise clay or fine sl It rich lnterbeds with col loldal precipitates, again forming a laminated to very thlnly lnterbedded sediment stack.

Austral Ian Coal Geology 4, part 2

552

G.L. Boyd

r-i

Rating 1 D•f•cla

I I I

.. . .. . . . • .!a i ~ I~ I" i I., " I

•

LITHCWACIU

'ii

" -· "'-· ---· ._____..,

...

Rating J Defacta

I• I

.. .. .. . . . •

Frequency of Occurrence of Defect Rating• 1, 2 & 3 Within Principal LlthofaclH

L"'HOt'AC1rt

Figure 5 Defect Class Distribution with Llthofacles

GeotechnJcal SJgnJfJcance Qf LJthofacJes Llthofacles selected to represent depositional units were also found to discriminate the critical geotechnlcal features Important to mine design. WI th respect to the var Ious defect categor I es, a survey of the d I str I but I on throughout the proposed pit area using ENGLOG records (Figure 4) determined their frequency of occurrence within each llthofac les. Results are shown In Figure 5 from which It was concluded that al

Defects with the least resistance to shear stresses Crating 1 defects) are predom I nant In pa I uda I sed I ments I .e. carbonaceous shales, mudstones, and soft clay shale band, which usually form roof and/or floor deposits.

Rating 2 defects display a wider distribution but clearly favour an occurrence In distal overbank deposits.

Rating 3 defects, representing defects likely to generate the greatest resistance to shear stress, channel and flank deposits.

With respect to sediment composition, there was a need to map the distribution of mud stones, sha I es and carbonaceous s 11 tstones to comp I y w Ith spo 11 dump stability criteria and dump rehabllltat lon due to adverse slaking properties (see Table 3) and effect on surface sol I composition and nutrient levels. These rock types could be readily discriminated by mapping distal overbank and paludal/lacustrlne deposits. Austral Ian Coal Geology 4, part 2

G.L. Boyd

553

Mapping the distribution and thickness of channel fill deposits provided data for mine planners to cater for variable blast i ng and excavation requirements due to the massive nature of the strata.

LOG RESPONSE I!

CASE

"~ ~ ""

~ ~~

Reduceid porosity with reduction in radiometric minaral content . PONibilitiN:

{i) Inc,.... in carbonate content (ii) lncrNNd KM>linit• content (iii) Reduced m ineral -clay transformetiona (iv) P ~ of evaporit• (unlilla,ly}

As for 1(a) with d lac•nible inc,.... in deneity rNpOnN. O~rved aNOCiatioM: ( i) Pr. .nce of • i~•rite band• ( ii) Pr-..nce of ironatone bands

Aa for 1 ( ■) with R•st■ nce offNt ObeenMd cau._: (i) Calcite filled joint, and for (ii) Zone of , ..atiVl9ty high carbonate content.

Strong offMt from low to normal neutron and reaistivity raponN leveh. Poaib ilitiN: (i) P■ INOeOI horizon (obMrved ■ uoci ■tion) (ii) Tr■ naition from highly carbonaceous strata (iii) WNth•inv effect

CASE

Rectuc.d • and r ~. Obaerved neociation.: (i) fractured nodular ironstone banda (ii) Sih:atone interbtda in maui v■ Nnd9ton,e

r·

Reduced pNb for ■ . Rt and Mlop. Obaer"9d aeeoc i ■t ione: (ii) Hole enl ■,..,,.,.. due to .aH ■ prone walls

O.....,,_. aeeociati~ ■r ■ for coa,_ Nndstone paieet,. in cong~et• band carrying acid volcanic peblMee teeving higtt. compoeite deneity. 1.1:•1-

g -1 1 - ... Rt.....___ 'l.....,..._

Figure 6 Typical Wlrellne Tool Response Theodore North

LJthofacJes Mapping The suite of sondes used during wlrellne logging successfully Improved upon the accuracy of strata I dent If I cat Ion from rotary eh Ip ho I es. In add It I on, the vertical relationship between strata (I.e. I lthofacles), was read I ly Australian Coal Geology 4, part 2

G. L. Boyd

5S4

Neutron log: Coarsening up sequence - crevasse splay channel encroachment and aggradatlon phase

Neutron Log: Fining up sequence - waning flood cycle

Neutron Log: Depositional dlsconformlty - erosion surface associated with downward cutting channel

Neutron Log: lnterbedded sandstone/silt stone representing levee phase or channel abandonment Figure 7 Depositional lndlcat9rs from Wire! lne Logs Interpretable and this greatly assisted the understanding of depositional processes. The dlpmeter provided data on planar rock fabrics (bedding, layering and In some Instances, Joints) whereas the multi-channel sonic log provided quantitative data of direct relevance to blast design. Before the wlrellne log results were accepted as reflecting true changes In rock type and texture, the log response was compared to results of a fully cored borehole, which was sampled for detal led petrological and X-ray In recognising that each llthofacles had a unique set Diffraction analysis. of physical (and textural) properties, the ability of each sonde to determine these properties as determined from core comparison was assessed, with results summarised In Figure 6. Important depositional Indicators were also revealed with some clarity In the neutron log response, examples of which are shown In Figure 7. Particular Indicators Included fining up and coarsening up units, lnterbedded strata Intervals, and boundaries and I lthologlcal associations of flood and waning f I ood eye Ies. Apart from the neutron and sonic tools, the three point resistance dlpmeter was found extremely useful In providing accurate data relevant to pit geomechanlcs, as wel I as sedimentation patterns. Comparisons of dlpmeter Australian Coal Geology 4, part 2

G.L. Boyd read-outs for dip and dip orientation were made within core from a fut ly cored borehole. The comparison gave a correlation coefficient of 0.88, which was taken as s I g n I f I c-a n t. The dlpmeter was subsequently run In noncored bore ho I es, and resu Its used to define layering and Joint orientation data, as wel I as assist In the Interpretation of sediment bedforms, as shown In Figure 8.

555 TN 529 C

er- DeddiN CNrN . . . . . . . . . lfl ball w,ttl ~

. .....,

1:,•. 2,..diPt W...tiofl 10

,.,,. . . . . , . . ~ ~ . ;

cr..Ndctillldipeof~'-3e-

c- Hwi.lOMIJI •

. ... '

.,......,a-.- ...........

c,.. ~...,..........,. • ....,. . .,...

Presentation .Qf .D..a1.a

(10'-14-,(IIC>-4)

HonMMOI .......

To slmpl lfy the mapping of the llthofacles yet comply with supplying adequate Information for mine planning, the fol low Ing scheme was adopted

H o r i . . . , . . . . C l " o a ~ ~-

, . ,.

al for each lnterburden/pl ot sandstone :tot a I sed I ment rat I os perta In Ing to that lnterburden

---......

Seom 6 - T (14-?Hl!l3•e)

~ , ,__,._ Cur, ... , be4d l"t

b) for each lnterburden , plot mudstone/sha Ie: total sediment values c) for each I nterburden, p I ot thickness contours of carbonaceous mudstone/clay stone associated with each coal seam(l.e. paludal/lacust rlne sediments). d) express s 11 tstone ( d I sta I and proximal varieties) as a function of sandstone ratios. This scheme worked wet I, as rock groupings (I) and (Ill) retained a consistent and easily Interpreted distribution within lnterburden sequences. SI ltstone rich beds were, In comparison, much more Irregular.

..... ,.

.. ,' . . . ·1 ~

....

. "

TDD 202·!111111

LITHOLOGY REFERENCE SOI.

~ §

SHAU

SI. TST-

IUIST-

WIJST-

C-

LEGEND

' o.

TOTAL DEPTH Of BORE HOLE

1_Qj)_

lOTAL DEPTH Of OPNCTEA AlSll.TS

11·-...

t1• DIP Of BEDS TO NORTH W£.Sl INOIITH I-" PAc;[l

- l· IOEA5UIIEIOEJIT

□

To quantify the distribution of slitFigure 8 Bedform Discrimination stone rlch . llthofacles as found In from wlrellne logs. I evee, crevasse sp I ay and prox I ma I overbank deposits, addltlonal analysts of sediment ratio data was performe~ Figure 9 summarises the proportion of non-sandstone sediment comprising slltstones lying within the >0.9, 0.9-0.75, 0.75-0.50, 0.50-0.25, <0.25 sandstone to total sediment ratio. At high sandstone ratios (>0.75), siltstone dominates the remaining llthologles, but becomes less prevalent with decreasing sandstone ratio relative to finer grained I lthologles. This result Is In accord with fluvlal deposltlonal processes; In the proximity of the channel, grain size Is coarsest and with Increasing distance the proportion of fine grained sediment Increases.

Austral Ian Coal Geology 4, part 2

556

G.L. Boyd :i

i 10095 !

1 i i I ~

,.t ~

80 75 65

50 45

zo 10

CloM

SANOSlONE

lllTIO r90

·,0--75

·75- -50

·S>-25

c -Z5 -

INCREASING DISTANCE , , _ CHANNEL

Figure 9 Lithological Associations Theodore North Class I Sandstone rich lnterburden overlain by waning flood slits, muds (paludal/lacus trlne) Class II lnterbedded sandstone/silt stone deposits with Increasing slit away from channels Class 111-V Increasing mudstone/shale with distance from channel The reporting of results of sedlmentologlc al studies for geotechnlcal mapping ls described through the following steps Involving data reduction, processing and presentation a)

Preparation of three dimensional borehole array (fence) diagrams produced at scales of 1:1000 (vertical and lateral) and 1:2000 (longitudinal) using llthocolumns computer plotted from the GEOLOG data base and corrected against cal lbrated wire I lne geophysical logs.

Preparation of a longitudinal section along the 150m cover line to Seam 7 or 6-7 drawn to describe hlghwal I sedlmentology.

Determination of Incremental (by lnterburden) sediment ratios plotted In plan and contoured at a scale of 1:10 000.

The Information presented In ( I ll) was recomputed and contoured to express llthofacles distribution per Individual mining bench at a scale of 1: 10 000.

Analysis of structure contours to the top of seams to determine variations In attitude and orientation of t he stratigraphic dip.

Analysis of the spatial distribution of re levant seams In areas of seam splitting to check for dip abnorma l ities.

FOOTWALL GEOMECHANICS As an example of the application of sedlmentologlc al studies to mine planning at Theodore, the problems surrounding anticipated footwal I performance are described. The example also al lows a summary description of the major constraints to the proposed mine design determined from geoiechnlcal and hydrogeological studies. Australian Coal Geology 4, part 2

G.L. Boyd

557

The footwal I Is left after the lower-most seam (seams 6-7) Is mined and Is bounded by the mining face and the In-put spoil dump (see Figure 1). For a pit 170m deep In which the average footwal I dip Is 13°, the footwal I slope length Is 755m and crest width 2500m. Results of stabi l ity analyses suggested that unstable conditions could occur as a result of a) b) cl

the presence of low strength bedding partings underlying the pavement the dip of the footwal I, and the presence of high seepage forces In the footwal I.

Since the footwal I pavement represents base of coal strata, fine grained paludal/lacust rlne to distal overbank sediments are represented. From Table 2 these are known to contain Rating 1 and 2 defects Cl.~ Group A, B, C defects). The presence of these potential surfaces of sliding were confirmed from Individual ENGLOG records. However, since the angle of Internal friction of defects (see Table 2) exceeds the range of footwall (hence defect) dips of 9 to 16°, stab i I ty cond It I ons were thus dependent on the effect of seepage Issuing from the portion of the footwal I slope lying below the phreatlc surface. As part of hydrogeologlc al Investigation s, a total of 27 single packer pump tests were conducted to determine drainage properties and pit Inflow rates. Results Indicated that coal seams were about 10 times more conductive than roe~ strata, with average permeabllltles estimated at 3 x 10-5cm/sec and 3 x 10- cm/sec respectively. Flow net analysis by computer model I Ing Indicated the fol lowing Interaction between the footwall and groundwater. a)

The distance of groundwater lowering behind the crest of the footwal I was about 300m.

Drawdown due to self drainage through the footwal I would leave the bottom 280m (slope length) carrying seepage.

Exit seepage gradients varied between O and 1.45 over the wetted slope area.

Pit Inflows of 0.26Ml/day/m of footwall advance can be expected.

With the effect of footwal I seepage Included In stab! llty analyses, unstable conditions were predicted as summarised In Figure lO(a). The coefficient 1r 1, when positive, Is a measure of the degree of lnstabll lty, and this varies from the toe of the footw a I I ups Iope In response to changes In the va I ue of the exit seepage gradient. In simpler terms, Figure lO(b) describes the friction angle along defects required for stability (limit equll lbrlum conditions) for footwall dips varying between 11° and 15°. Also annotated on Figure 10(b) Is the available friction angles for Class A to D defects, and thus we can summarise a)

In the bottom 85m of the s Iope·, downs Iope forces exceed the frictional resistance offered by all defects;

Australian Coal Geology 4, part 2

G. L. Boyd

558 b)

In the bottom 200m of the slope, defect Class A, Band C are Incapable of restraining the slope for dips up to 15°, with defect Classes A and B only affecting the lower 100m of slope for dips of 13°;

the bottom 100m of footwal I slopes dipping 11° are unstable for al I defect classes.

---

/f z ,.,.....,._,.-,,t r

,..,_._.........

,,-300 -

-1

,,.

l-· ..tl#/

•

,_,_.,/I,

10 ' - - - - - - ~ - - - - ~ - - - - - - - , x /#/ 100

200

Figure 10 Results of Footwal I Stability Analysis A simple measure to control seepage pressures Is to drl 11 pressure ref lef ho I es norm a I to the footw a I I. Prov Is I on for th Is has been Incorporated In mine planning, but due to the magnitude of out of balance forces In the bottom 85m of the slope, stripping of the pavement to remove strata containing Class A, Band C defects will be undertaken. The scale of potential lnstabll lty Is of concern when estimating the risk to personnel and disruption to operations. Experience In the U.K. with open cast mIn Ing suggests that buck 11 ng fa 11 ~es generate the Iargest fa 11 ure vo I umes, with failures Involving up to 2000m of materlal recorded. The potential for Austral Ian Coal Geology 4, part 2

559

G.L. Boyd

Sur foe • of separar1on ~7uol to non- PK1n•d top O

W'= Wsin,Q

ooiJmn

..-\\-

tW d -Joni under comoresSIOfl and so or,entatec:J to oc• ,,, slab ,e JOlf'II fakes no wt of s/OM SM()r

Frr c.olumn.

w = Tf EI

I =!i_J

•2

CR-yz-

For d= Im, W'~.G' =".2 £ • OOBJ

NCR

!....

12 7 96 • 103 f

N ,;R (slob).: sino

or O = /__,

?10

150

25· 7

87 2

75 4

660 5

7604

23716

Hf:R (s la b ) =

1·94, 10

168,rf

5 4 ,10

tog WCR =

225

200

150 100 50 Faif,d slab »"'}lh I N ) Cau,ng Wc R

Figure 11

X= L , _x_,

coso

for sq.xve secron

E= 3 ·5 GPa (from test oo,a for nudstone / shqJe }

285

~ res 755

46 41.() 5

85556

5 7 7113

276, 105 7 5, 10 5

224, 10

metres rnerr es 4

N/m 2

Buck I Ing Resistance of Footwal I Slabs

buckling failure was modelled by assuming analogous conditions to (thin) columns. Eulers Theory was adopted to compute crit ical buck I Ing stresses (purely elastic) for a column fixed at one end and with frictionless restraint at the other, as shown In Figure 11. For a given portion of a footwal I slab subject to buck I Ing CU, the magnitude of the critical buck I Ing stress CWcR> can be computed as graphed In Figure 11 (Curve A). Downslope forces CR) associated with various lengths of fal led slab (N) are shown for two dip angles of the footwal I (Curves Band CJ; It can be seen these forces stay wel I Austral Ian Coal Geology 4, part 2

G.L. Boyd

560

below critical buck I Ing stress levels by a fair margin. Thus the conclusion was reached that buck I Ing fal lure was an uni lkely mechanism for footwal I lnstabl I lty.

To quantify the amount of footwall stripping to remove defect Classes A, Band C, th Ickness Isopachs of host depos It Iona I un Its were computed and ver If Ied against ENGLOG records to ensure accuracy. Given mine scheduling Information, the amount of str I pp Ing was annua 11 sed and Incorporated Into a year by year stripping schedule. CONCLUSIONS Due to the lack of outcrop In the Theodore North Prospect, the Impact of adverse geotechnlcal properties of sediments to mining proposals were quantified by Interpretation of subsurface data records. This was achieved by simple sedlmentologlcal analysis of borehole and wlrellne geophysical records taken to the level of defining llthofacles representing principal desposltlonal units, which In turn defined discrete geotechnlcal constraints to mine planning. Conclusions arising from this approach were as follows: 1.

Use of sedlmentologlcal analysis as a basis for engineering geological (geotechnlcal) mapping was confirmed by al

ability to define depositional units In terms of sediment type(sl

abll lty to map the depositional units In three-dimensional section given the field data

ability to characterise llthofacles representing depositional units by geotechnlcal properties of Importance to design.

Since much of the data was computerised, the method allows spatial distribution of reduced data Into any configurati on demanded by changes to the mine plan.

Wlrellne geophysics confirmed as an Invaluable aid to sedlmentologlcal as well as structural analysis, particularly the neutron-neutron (close spaced) and dlpmeter tools: high radiometric counts of the consistent composition across al I lithofacles serverely limited the usefulness of natural gamma logs.

Use of three-dimensional sections (fence diagrams) to plot spatial distribution of I lthofacles provided dist i nct advantages particularly for ensuring accuracy of unit correlation by achieving satisfactory closure about the 3-D section al lowing recognition of sedimentation patterns In three-dimensions. The achievement of satisfactory closure was particularly Important for seam and seam split correlation.

Open hole drl I I Ing of lnterburden In conjunction with running a suite of wlrellne geophysical tools Is a cost-effective (and expedient) form of data gathering which lends Itself to reduction and presentation by computer methods.

Australian Coal Geology 4, part 2

G.L. Boyd

561

REFERENCES Svenson D., .id .al. 1975 Perm Ian Coal Measures - Bowen Basin, Queensland: Theodore - Baralaba District. li.Qlli2ID~ Geology Q.f Austral Ja llJI ~ ~ ~ .coal (Eds. Traves D.M, King D.) Australas. lnstlt. Min. Metal I. Monogr, No. 6. Wa I ton G., and Coates H., 1980 Some Footwa 11 Fa 11 ure Modes In South Wa I es Opencast Workings. Second Conference on Ground Movement and Structures, Cardiff. Boyd G.L., 1980 Structural Dlagenesls of CoaJ Measure Sediments. Thesis, James Cook University of North Queensland (unpublished)

MSc.

Ma I I ett C. W., .e.± _aJ_ 1980 Depos It Iona I Env I ronments In the Bara I aba Coa I Measures, Moura, Queensland. CSIRO, PJvJsJon .o..f Appl Jed .G..eQmechanJcs, Geomechan Jcs ln .Goal M.1..nl.og fte.g__orj: J!l.

Australian Coal Geology 4, part 2

562

An Investigation of the Groundwater Resources of the Latrobe Valley, Victoria John Brum 1ey

Exploration and Geological Division, Fuel Department, State Electricity Commission of Victoria, 15 William Street, Melbourne, Victoria, 3000. Australia

Mark Reid

Geological Survey Division, Department of Minerals and Energy, Victoria, 140 Bourke Street, Melbourne, Victoria, 3000. Australia

Key Words :

Latrobe Valley, Groundwater Resources, Aquifers

ABSTRACT A study of the Latrobe Valley groundwater resources has been carried out by the State Electricity Commission of Victoria (SECV) and the Department of Minerals and Energy, Victoria (DMEV) from 1976 to 1981). The main purpose of the study was to gain an overa 11 view of the groundwater resources of the Latrobe Valley Group strata which contain the major aquifers within the Latrobe Valley Depression. An extensive drilling and testing program was conducted by SECV and DMEV from 1977 and 1979 to determine the stratigraphy and hydrogeological properties of the Latrobe Va 11 ey Group aquifers and to estab 1i sh a series of groundwater observation bores. The water 1eve 1s in these bores have been regularly monitored since drilling was completed in mid-1979. The response of the aquifer systems to the dewateri ng operations at Morwe 11 Open Cut is evaluated by examining the regional potentiometric decline and the The study indicates the existence of two major consequent subsidence. co9fined Latrobe Valley Group aquifer systems which contain at least 20 300 x 10 litres of high quality groundwater. The evidence from the study indicates that most aquifer recharge currently occurs in the hills west of Morwell Open Cut. Australian Coal Geology 4, Part 2

J. Brumley and M. Reid

563

INTRODUCTION The Latrobe Valley Depression lies between the Eastern Highlands to the north and the South Gippsland Highlands to the south and south-west. To the west it is separated from the Moe Swamp Basin by the Haunted Hills and near Sale it opens to the east into the main part of the Gippsland Basin (Figure 1). The Latrobe Valley Depression is known to contain up to at least 770 m of Tertiary continental Latrobe Valley Group strata, which include numerous i nterbedded and interconnected confined sand and gravel aquifers within the Morwell and Traralgon Formations. Some zones of relatively unweathered volcanics within the Traralgon Formation also act as confined aquifers . Relatively minor unconfined aquifers occur within the overlying Haunted Hill Gravels and in the Recent a 11 uvi al s. The general sequence of geo l ogi ea l formations in the Latrobe Valley Depression is shown in Figure 1).

EASTERN

HIGHLANDS

/ SOUTH

GIPPSLAND

•• /

,c,' )'

HIGHLANDS

(

• YA RRAH

•!.-) ~o\l";)!.11-"!,.-_.

SC ALE OF KILOHE TR[S

'-0

Figure 1. Latrobe Valley Depression locality plan. Prior to 1976, the State Electricity Commission of Victoria and the Department of Minerals and Energy, Victoria, conducted only local or reconnaissance investigations into the hydrogeology of the Latrobe Valley Depression . In March 1976, a more comprehensive study of the groundwater resources commenced Australian Coal Geology 4, Part 2

564

J. Brumley and M. Reid

as a joint project between SECV and DMEV. The main objectives of this joint study were to assess the hydrogeological characteristics of the Latrobe Valley Group aquifer system and to evaluate the quantity and quality of the groundwater in the system. The study concentrated on investigating the little known Traralgon Formation aquifers. A total of 22 bores were drilled, screened and developed at 15 separate sites, mainly in the Traralgon Formation, at a cost of approximately $1,100,000. All bores were geophysically logged and samples of the aquifer sands were taken for grain size analysis . Pumping tests were performed at 11 sites . Bore locations are shown in Figure 3. The study also incorporates information from Morwell Open Cut and from regional bores established both prior to and after the joint SECV/DMEV investigation. Water levels are regularly monitored in all bores. A detailed report on the investigation is presented by Brumley, Barton, Holdgate and Reid (1981). Methods of drilling and bore construction are described by Galimberti (1979) . GENERAL STRATIGRAPHICAL CONSIDERATIONS The general geology and stratigraphical correlation in the main part of the Latrobe Valley Depression and in the Merrimans Creek Sub-Basin is described by Abele et al. (1976) and Gloe (1976a) and is shown in Figure 2. Figure 2 also shows the correlation proposed by Thompson (1980) for the eastern portion of the Latrobe Valley Depression and its relationship to the stratigraphy of the Lake Wellington Depression .

LATROBE VALLEY DEPRESSION

---LAKE WELLINGTON DEPRESSION I

SEA LEVEL

WEST

NQT TQ S CALE

Figure 2. Diagrammatic geological section from Thorpdale to Lake Wellington .

Australian Coal Geology 4, Part 2

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565

The evidence obtained so fa r supports the existence of two major confined aquifer systems in the Latrobe Valley Gr oup; namely the Morwell Formation and the Trara l gon Formation Aquifer Systems. The Ml and the M2 Aquifers at Morwell Open Cut occur in the Morwell Formation and the Traralgon Formation Aquifer Systems respectively. Throughout the main part of the Latrobe Valley Depression, the aquifers are confined by clay, silt and coal strata of variable vertical hydraulic conductivity . Because these confining layers allow vertical leakage from the aquifers, they are referred to as aquitards . The base of the Latrobe Valley Depression consists mainly of lower Cretaceous sandstones and mudstones which are considered to be relatively impermeable. The LPG sands and gravels, which comprise the most important aquifers, reach their maximum depth and thickness along the Traralgon-Latrobe Syncline which is the main synclinal axis of the Latrobe Valley Depression. Towards the eastern end of the Latrobe Valley Depression, a direct hydraulic connection occurs between the Morwe 11 Formation and the Bal ook Formation (Formation name pr oposed by Thompson 1980) . The Balook Formation also connects with the overlying Boisdale and Lake Wellington Formations. The Trara l gon Formation aquifers are effectively separated from the overlying Balook Formation and the Lakes Entrance Formation by the Traralgon Coal Seam (Figure 2). Along the northern , southern and western margins of the Latrobe Valley Depression, the aquifers generally thin and rise and are occasionally exposed in the va 11 eys along the western margin . To the southeast, the Baragwanath Anticline forms a structural high which impedes hydraulic connection between the main Latrobe Va 11 ey Depression and the Merri mans Creek Sub-Basin . The geology of this Anticline and Sub-Basin has been described by Holdgate (1980). The nature of the hydrogeological boundary between the Latrobe Valley Depression and the Moe Swamp Basin is currently being investigated . The major structures in the Latrobe Valley Depression are shown in Figure 3. These structures influence the thickness and elevation of the aquifers . The major geo l ogi ea l structures occur predominantly in the southern part of the Latrobe Valley Depression where the intensity of folding increases. The major fold axes are generally oriented northeast/southwest . The Thorpdale Volcanics form a significant but minor part of the Traralgon Formation Aquifer System. The weathering of the Thorpdale Volcanics varies from residual soil (clay), to almost fresh jointed basalt of relatively high hydraulic conductivity and storage capacity . Analyses of typi ea l sand samples from the Trara l gon Formation aquifers show that poorly sorted, coarse to very coarse sand predominates. Analyses of samples from the Morwell Formation aquifer sands at Morwell Open Cut (Ml Aquifer) show the average particle size to be finer, but otherwise the samples are similar. The characteristics of the Morwell interseam sands (Ml and M2 aquifers) are described i n detail by Barton (1971). Despite the overall similarities , the Latrobe Valley Group aquifer sediments can exhibit extreme local variability and are known to range from very fine sand to coarse gravel. For instance, a fine grained faci es occurs near the southern boundary of the Latrobe Va 11 ey in the Loy Yang area and fine to medium silty sands are characteristics of the Balook Formation (Thompson 1980) .

Australian Coal Geology 4, Part 2

J. Brumley and M. Reid

566

Figure 3.

Bore locations and main geological structures.

GROUNDWATER EXTRACTION The Morwell and Loy Yang Open Cut areas overlie Latrobe Valley Group aquifers As open cut development proceeds, in which high artesian pressures exist. these hydrostatic pressures must be reduced to maintain stability of the Artesian pressures also exist beneath the Yallourn Open Cuts, excavations. however, an aquifer dewateri ng program has not been required because the weight of the strata overlying the aquifers has been sufficient to keep floor The artesian pressures are due to the heave within acceptable limits. relatively high elevation of the recharge areas in the surrounding hills. At Morwell Open Cut, equilibrium between the combined uplift of the aquifer pressures and the weight of the overlying sediments has been maintained by pumping from both the Ml and the M2 aquifers . Pumping from the Ml Aquifer Figure 4 shows the commenced in 1960 and from the M2 Aquifer in 1969 . variation in flow rate for each aquifer since pumping commenced . Figure 4 a1so shows the corresponding dee 1i ne in the potent i ometri c 1eve 1 of each aquifer. Both aquifers have been lowered by approximately 130 mover the area The maximum combined extraction rate was 1350 1/s of the open cut . (litres/second) in 1973 . Stable artesian pressures were not achieved until Currently approximately 90 1/S is pumped from the Ml Aquifer and 1975. approximately 740 1/s from the M2 Aqui er. The total volume extracted from It is also noted that the 1960 to 1980 is approximately 354 x 10 litres. potentiometric level of the M2 Aquifer was lowered approximately 38 m by increased vert i ea 1 1eakage into the Ml Aquifer over the period from 1960 to 1969, when groundwater was extracted only from the Ml Aquifer.

Australian Coal Geology 4, Part 2

J. Brumley and M. Reid

I N ITI U

567

11 2 L['lt~ .

1200

35 000

' ' ---

-' ,

1000 ]0000 \

Co•• •ncont of . d1rHt tO rut,on - - \, from P12 AQu , hr \

\ ,

' c:i

..... ,,

'7•'> ,..."\~

.;_ 0

--' u.r20

....--'

X" 20 000

•••

600 "-...

3 0

15000

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'f.,J

--'

3 a

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400 i

10000

~-40

10 0

....:I:>-

5000

M 1 FLOW

~ - 60

-- --- -=-----""'-=--=-=::::~"' ---""

....>-z

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1970

---r-------- -~---~ 1975

1910

YEAR

Figure 4.

Potentiometric levels and flows

Morwell Open Cut.

The water is used for fire prevention purposes and power station requirements. Excess pumping is avoided because of the high cost of establishing and maintaining pumping bores and to minimise the decline in the regional potentiometri c surfaces and the consequent regional subsidence . A more detailed account of the artesian pressure relief at Morwell Open Cut is given by Fraser and Pitt (1979). Aquifer depressuri sat ion will not be required at Loy Yang Open Cut until after 1985. In addition to the groundwater extracted from Morwell Open Cut, State Rivers and Water Supply Commission records show that an average of approximately 700 l/s is extracted from the Latrobe Valley region for other purposes . A large proportion (approximately 590 l/s) of this water is extracted from shallow unconfined aquifers and most of the remainder is extracted from the Boisdale Formation confined aquifers in the Sale area . The highest average extraction rate from the Boisdale Formation is about 88 l/s for the Sale town water supply. Relatively small quantities of deep artesian groundwater were extracted by Australian Paper Manufacturers from two bores at Maryva le between 1966 and 1975. No other industrial users of the Latrobe Valley Group aquifers are known and only a few private extraction bores exist around the margins of the Latrobe Valley Depression .

Australian Coal Geology 4, Part 2

J. Brumley and M. Reid

568

WATER LEVELS Regional Potentiometric Surfaces Contours of the potentiometric surface of the Traralgon Formation aquifers are plotted on Figure 5 to show the change in the potentiometric surface from June/ July 1979 to April/May 1982. On a regional scale, sufficient hydraulic connection appears to exist between the aquifers of the Traralgon Formation to realistically represent the potentiometri c surfaces shown in Figure 5. An approximation of the 1960 potentiometric surface of the Traralgon Formation aquifers is shown in Figure 6. A regional potentiometric map has also been drawn for the Morwell Formation aquifers (Figure 7) using data from monitoring bores established in 1981/82 and from several older bores . The potentiometric levels have been corrected to a standard temperature of 15°C according to the method described by Nahm and Reid (1979) .

JO K m

Figure 5.

Potentiometric surface of the Traralgon Formation Aquifer System: 1979 to 1982. The contours are in metres (AHO) and indicate the change in the potent i ometri c surface from 1979 (solid lines) to 1982 (dashed lines).

Comparison of the 1979-82 series of Traralgon Formation potentiometric contours (Figure 5) with those in 1960 (Figure 6), shows that the artesian drawdown in these aquifers extends throughout the Latrobe Valley Depression with a maximum drawdown at Morwell Open Cut of approximately 130 m. Figure 5 also shows that the highest rates of drawdown are currently occurring immediately around the Open Cut, along the southern limb of the Latrobe Australian Coal Geology 4, Part 2

569

J. Brumley and M. Reid

Syncline extending eastwards about 33 km to Rosedale and in the area between Morwell and Loy Yang. Elsewhere the recent changes are relatively sma 11 , i ndi cat i ng either that effective recharge is occurring or that the area is at least partially hydrogeologically separated from the influence of drawdown. For instance, only small changes have recently occurred in the potentiometric levels south of the Baragwanath Anticline which indicates an effective separation of the Latrobe Valley Depression aquifers from the aquifers in the Merrimans Creek Sub-Basin. Further evidence of this is provided by isotope studies (Airey 1980 and Brumley et al. 1981).

Figure 6.

20 Km

Potentiometric surface of the Traralgon Formation Aquifer System in 1960. Contours in metres (AHO).

The potentiometric map for the Morwell Formation aquifers (Figure 7) shows that the influence of the drawdown at Morwell Open Cut extends to Loy Yang . East of Loy Yang, the artesian pressures in the Morwell Formation and in the Balook Formation aquifers are not affected by groundwater extraction at Morwe 11 Open Cut . These aquifers recharge the overlying Boi sda le Formation aquifers by upward vertical leakage (Thompson, 1980) . The potentiometric surface of the Morwell Formation aquifers has a hydraulic gradient of approximately 1:1000 from Loy Yang towards Lake Wellington. This gradient is similar to that estimated for the Traralgon Formation aquifers in 1960 prior to aquifer dewatering at Morwell Open Cut (Figure 6) when equilibrium conditions existed in the Latrobe Valley Depression groundwater regime . Australian Coal Geology 4, Part 2

J. Brumley and M. Reid

570

The effect of aquifer dewatering at Morwe l l Open Cut is far more widespread in the Traralgon Formation aquifers than in the Morwell Formation aquifers. This observation supports the geological evidence for the existence of two discrete major confined aquifer systems in the Latrobe Valley Group strata, although the presence of some vertical leakage between t he aquifer systems is recognised. The data also suggests that significant recharge of the Morwell Formation aquifers occurs at the eastern end of the Latrobe Valley Depression, probably from the area of the Baragwanath Anticline .

l I \ \

Figure 7.

JO Km

Potent i ometri c surface of the Morwe 11 Formation Aquifer System in 1982. Contours in metres (AHO) .

Hydrographs Selected hydrographs of four Traralgon Formation bores are shown in Figure 8. The graphs indicate a relatively steady, linear decline in water level over the period of observation and show that the rate of drawdown decreases away from Morwell Open Cut . Monitoring Water levels in the regional bores are monitored by DEMV and SECV at regular monthly or three-monthly intervals . A total of 75 regional observation bores are currently used to monitor the water levels in the Latrobe Valley Depression and the Merrimans Creek Sub-Basin.

Australian Coal Geology 4, Part 2

571

J . Brumley and M. Reid

,oo

I I I I t r I TTTT"Tr T ~

r 1

r 1 ,

. . 1

•

,, 0

no no

lOV V AN G 16 T ~

7'""T:rr.:1'7rrr:rr:,t--.r.:rr.:r,-,--,-,-,.:,-tl

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,. 0

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'-rr.;r..:r.-r f ., J ! .. I I I 1.. 1 J., J I r--r:T7'::'1 I f f ..l r.;r '

198 0

Regional observation bore hydrographs.

Subsidence A consequence of lowering the potentiometric surfaces in the Latrobe Valley Depression is regional subsidence. Subsidence occurs in response to the increase in the vertical effective stress on the sediments which occurs as the pressures in the aquifers are reduced. Contours of the regional subsidence which has occurred up to 1980 are shown in Figure 9. The subsidence extends around Morwell Open Cut and to the east along the south limb of the Latrobe Syncline for approximately 20 km east of Morwe 11 Open Cut to Flynns Creek. The subsidence contours are similar to the patterns of potentiometric drawdown shown in Figures 5 and 7. Most of the subsidence is accounted for by consolidation of the aquitards . Subsidence can, therefore, be used to estimate the volume of water derived from drainage of the aquitards. This aspect is discussed further in the section on groundwater quantities. The magnitude and rate of subsidence are related to the changes in effective stress due to the potentiometric head decline and to the thickness, compressibility and vertical hydraulic conductivity of the sediments. The magnitude of subsidence is also significantly affected by the geological history of the sediments. Further details on the regional subsidence associated with groundwater withdrawal from Morwell Open Cut are given by Gloe (1976b); Hutchings, Fajdiga and Raisbeck (1977); and Raisbeck (1980 and 1981). Detailed monitoring of the regional subsidence has been carried out by SECV for the past eleven years.

Australian Coal Geology 4, Part 2

572

J . Brumley and M. Reid

,ci

10 Km

Figure 9. Latrobe Valley subsidence. Contour interval is 100mm. AQUIFER RECHARGE/DISCHARGE Geological mapping (Brumley 1981) and monitoring of the potentiometric surfaces (Figures 5 and 7), indicate that most aquifer recharge currently occurs in the hi 11 s west of Morwe 11 Open Cut. Recharge al so occurs by infiltration into aquifer subcrops within the Latrobe Valley Depression and by direct intake in areas near the northern and southern margins of the Latrobe Va 11 ey Depression, such as the area of the Baragwanath Anticline (Ho l dgate 1979). However, the rate of recharge from the southern margin is apparently too low to prevent the relatively large drawdown that is occurring in the Traralgon Formation potentiometric surface between Morwel 1 and Loy Yang and along the Latrobe Syncline towards Rosedale. Groundwater in the Traralgon Formation aquifers ultimately flows beneath the Lakes Entrance Formation into the Gippsland Basin . The groundwater in the Morwell Formation aquifers flows through the Balook Formation into the Boisdale, Lake Wellington and Lakes Entrance Formations (refer Figure 2), ultimately discharging into Bass Strait . The Boisdale Formation aquifers may also discharge groundwater into Lake Wellington. Mathematical model studies by Fraser (1980) indicate that the total regional recharge is about 170 l /s, and that the rate may ultimately increase to approximately 400 1/s with future open cut development . Fraser (1980) estimates the outflow at the eastern end of the Latrobe Valley Depression to be about 140 1/s . Thompson (1980) estimates an average outflow of approximately 60 1/s .

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J . Brumley and M. Reid

573

It is worth noting that future changes in the respectiv e potentio metric surfaces , especial ly if new centres of groundwater extractio n are located towards the east of the Latrobe Valley, could signific antly change the recharge pattern by intersec ting new hydrogeological boundaries. PUMPING TEST RESULTS The pumping tests consiste d mainly of constant rate and multi-ra te as describe d by Nahm (1980). The constant rate tests were analysed usingtests Jacob's straight line method for the test bore data and various type curve methods for the observat ion bore data. The multi-ra te tests were analysed using a numerical method derived by Nahm (1980). Interpre tation of the pumping tests is hampered by the complex nature of the stratigra phy and the attendan t difficul ty in estimati ng the overall thicknes of the test interval s . The full effect of the unavoidable partial screenin gs of the aquifers is also difficul t to estimate . Aquifer parameters derived from the pumping tests are listed in Table 1. In the Morwe 11 Open Cut area, the Ml Aquifer has an average hydrauli c conductivity -o.J approximately 22 m/day and a storage co-effic ient of approximately 1 x 10 at aquifer conditio ns. -~qui va lent values for the M2 Aquifer are approximately 57 m/day and 3 x 10 . At Loy Yang, thin fine sand aquifers occur in the Morwell Formation . Values of hydrauli c conducti vity these aquifers rangEt from a~911t 2 to 7 m/day and the storage co-effic ientin ranges 3 from about 10 to 10 at aquifer conditio ns. Fine grained sand with similar values of hydrauli c conducti vity also occur in theaquifers Balook Formation and the Lakes Entrance Formation. Regional values of the hydrauli conducti vity of the Traralgon Formation aquifers vary from about 5 m/day toc 88 m/day_s<at aquifer_ conditio ns), and the storage co-effic ient 7.ranges from 2.5 x 10 to 4 x 10 4 (at aquifer conditio ns). Although aquifer parameters for the Morwell Formation aquifers have only been determined at Morwell, Loy Yang and near Heyfield , it would appear that the Traralgon Formation aquifers are generall y more permeable than the Morwell Formation aquifers . Consiste ntly high values of hydrauli c conducti vity were obtained for the Traralgon Formation aquifers along the Latrobe Syncline between Morwell and Rosedale. These high values correspond with the presence of coarse sands and high groundwater temperat ures. East of Roseda le, the hydrauli c conducti vity of the Traralgon Formation aquifers decrease s signific antly in accordance with the presence of finer sands and lower groundwater temperatures . similar decrease in hydrauli c conducti vity would be expected in the Morwell A Formation sands where they merge into the fine grained and silty sands of the Bal ook Formation . The Latrobe Valley Group aquifers are confined by aquitard s of variable vertical hydrauli c conducti vity. Some aquitard s allow negligib le vertical leakage (confine d aquifer conditio ns), while in other cases consider able vertical leakage occurs (semi-co nfined aquifer conditio ns). Calculat ions using methods describe d by Hazel (1975), indicate that the Traralgon Formation aquifers are confined by strata with veDIJ low hydraul_i:f conducti For instance , values in the order of 0.2 x 10 to 1.7 x 10 m/day werevity. obtained for Latrobe Va 11 ey Depression bores 1333H and 1338H. Effectiv e c separatio n of the Morwell Formation and the Traralgon Formationhydrauli aquifer systems is also demonstrated by the signific antly higher (up to 40 m) potentio metric level of the Morwell Formation aquifers between Traralgo n and Rosedale . Australi an Coal Geology 4, Part 2

J. Brumley and M. Reid

574

ed consider able quantity of groundwater wh i ch is also present in the unconfinons shallow aquifers and in the Latrobe Valley Group aquitard s . Major assumpti . concerning the groundwater system are incorpor ated in the calculat ions scale regional the on defined well not Aquifer dimensions and parameters are has been and an artifici al eastern boundary for the Latrobe Valley Depression Basin Swamp Moe the and n Sub-Basi Creek s Merriman The . assumed at Rosedale are excluded from the estimate s. Total Storage Capacity of the Confined Aquifer System three Water stored in a confined aquifer can be consider ed as consistin g cof yield" components which are referred to as "potenti ometric yield", "specifivolume of and "specifi c retention ". The "potenti ometric yield" refers to the hydrowater which can be extracte d by depressu rising the aquifer. When the decline) , static pressure is fully dissipate d (i.e . full potentio metric head which the the confined aquifer can be considered as an unconfined aquifer from ts represen water of volume This pumped. or water in the voids can be drained the total the "specifi c yield" of the aquifer. It is usually about 20% of the volume volume of a confined sand aquifer and is substant ially greater than involvin g water artesian of n Extractio availabl e from "potenti ometric yield". dewatereither "potenti ometric yield" or "specifi c yield" i s referred to as remains a ing. When complete dewatering of the aquifer has occurred , there and surface "specifi c retention " component of water which is held by molecular coarse sand tension forces. This component is relative ly low for medium to aquifers sand fine for ant signific becomes but , aquifers and gravel aquifers and aquitard s. It is not considered in the following estimate s. i§ The component of storage currentl y availabl e from "potenti ometric yield" 1750 10 all Latrobe Valley Group aquifers is estimate d at approximately of litres. Full potentio metric head decline has occur r ed only in a small area storage the Ml Aquifer beneath Morwell Open Cut . The 9 "specifi c yield" component is estimate d at approximately 18,500 x 10 litres. The estimate s of stored groundwater quantiti es are summarised in Table 2. TABLE 2 : ESTIMATES OF AQUIFER STORAGE CAPACITY Quantity (10

9 litres)

Morwel l Formation Aquifers

Traralgon Formation Aquifers

Total

200

1 , 550

1,750

Specific Yield

3,100

15,450

18,550

Total Aquifer Storage (excludin g specific retentio n component)

3,300

17,000

20,300

Groundwater Source

Potentio metric Yield

Components of Confined Groundwater Extracte d from Morwell Open Cut Open The total volume of groundwater extracte ~ from aquifers beneath Morwell from Cut up to 1981 is approximately 354 x 10 litres. This water is derived drainage , aquifers the of yield metric potentio ng three major sources, comprisi Australi an Coal Geology 4, Part 2

J. Brumley and M. Reid TABLE I

575

LATROBE VALLEY GROUP AQUIFER PUMPING TEST RESULTS

~.-~

~ 0

". W C

!!~~ ~ g.~

•

"~~

~~u

~ ~ ~

.., g ,-. • u

00 CU o.J i,..

Ill

i,..

.,... I.I

Q.I

(I)

I,., cu .... Cl) ::, f-<' ..... " u , 4-1 v .... c:r

i;-

C<~ ~

",-. ,-."~

(m)

(m/d)

2000?

1600?

ll20

145?

60?

1333

1010

375

4xlo-s

5~2 - 593 . 5

do.

1348

725

305

I.SxI0- 6

542-557.5

do.

HP 185

140

881 -92 6

Lakes

74?

Traralgon

Formation -

10. 5

14?

423-433.5

do.

Entrance Formation **HP 189

410

335

13 . 5

183-21)

Traralgon

130

805-818

do.

Formation R

301

307

1100

440

563-587

do.

286

2100

620

553-595

do.

*TB 183

190

140

7. 5

418-431 and 455-46 7

do.

lxlO - s

+I/WL 168

520

370

43 . 5

162-174

do.

H:wt 197

580

29 . 5

415

15 . 5

318-342 and 345- 358

do.

32?

658-6 77

do .

6 . Sxlo- s ·

l], 5

7. Sxl0 - 6

242 -25 5

Harwell Formation?

6.5xl0- s (145-160)

Harwell Formation

OWN 44

600?

l 75?

IWN 45

175

110

Morwell Open Cut (Ml Sand)

325

150

(22)

1700

675

(57)

lxl0-1;

Morwell Open Cut

(H2 Sand)

1,10- s

(220-250)

Traralgon Formation

Denotes one observation hare av.1il.1.hlc> .'.l.t sire. Denotes two observation bores ;ivail,1,bJe at site.

Denotes sites tested before the implementat ion of the present joint project. (15) Brackets denote approximate average . + Denotes bores in the Merriman s Creek Suh-Basin.

The high rate of vertica l leakage at Morwell Open Cut, which occurred from the M2 Aquifer into the Ml Aquifer (Figure 4) when groundwater was extract ed only from the Ml Aquifer, is accounted for by the opening of joints in the confinin g strata as the open cut developed. ESTIMATES OF GROUNDWATER QUANTITIES Basis of Estimates The estimat es re 1ate only to groundwater stored in the confined aquifer s of the Morwell and Traralgon Formation in the Latrobe Valley Depression, and the rate of recharge to these aquifer s. The estimat es do not include to the Austral ian Coal Geology 4, Part 2

576

J . Brumley and M. Reid

of the aquitards (clay, silt and coalg and aquifer recharge . It is estimated that a total of approximately 227 x 10 litres has been derived from potentiometri c yi e 1d of the aquifer. The estimated vo 1ume of wat~ derived from drainage of the aquitards is calculated to be about 93 x 10 litres. This volume is estimated from the subsidence contours (Figure 9) with the assumption that approximately 90% of the subsidenc§ comprises consolidation of The remainder, namely 34 x 10 li tres is attributed to the aquitards. replenishment of the aquifers from recharge. This suggests a current average "recharge" component of approximately 80 - 100 1/s in the present total extraction rate of approximately 830 1/s. This rate of recharge to Morwell Open Cut is consistent with the estimate by Fraser (1980) of 170 1/s for the current tota 1 regi ona 1 recharge to the Lat rob~ Va 11 ey Group aquifers. The component derived from consolidation of the aquitards represents approximately 26% of the total volume extracted. Yield from the aquitards will continue for many years until subsidence due to the new stress regime ceases. GROUNDWATER QUALITY Hydrochemistry Comments on the regional hydrochemistry are restricted mainly to the Traralgon Formation aquifers because there is very little regional data on the Morwell Formation aquifers. The regional hydrochemistry of both aquifer systems is probably similar, although studies of the Ml and M2 Aquifers at Morwell Open Cut (Brumley et al. 1981) indicate that the Morwell Formation aquifers have a slightly higher salinity on average. Table 3 summarises the chemical analyses of samples taken from 19 regional observation bores and from bores at Loy Yang and Morwell Open Cut. Except for some relatively high TDS (total dissolved solids) values at Loy Yang, the groundwater is of potable quality. At Loy Yang , the concentration of TDS in the Morwell Formation aquifers ranges from 163 mg/1 (1156 LY) to 3067 mg/1 (1177 LY). Elsewhere within the Latrobe Valley Depression, the TDS values range from 104 mg/1 at 183TB to 724 mg/1 at 2390M and average about 400 mg/1. In the Merriman's Creek Sub-Basin, the TDS values range from as little as 73 mg/1 at 197WL to only 121 mg/1 at 189HP . The water of the Traralgon Formation aquifers is basically a sodium chloride type water. However, downdi p from the intake areas the bi carbonate content becomes proportionally high, tending to yield water which is slightly hard. The increase in bicarbonate is probably mainly due to the dissolution of carbonates . Although there are also significant downdip increases in sodium, magnesium, calcium and chlorine, the greatest increase occurs in the bicarbonate concentration . Sulphate concentration is generally less than 10 mg/1 and pH ranges from 5. 4 to 8.4. Aquifer Temperature Geothermal artesian groundwater in the Latrobe Valley Depression was initially recorded in a bore drilled by Australian Paper Manuf acturers at Maryvale in 1945. The bore encountered numerous sand aquifers down to approximately 510m and ori gi na lly had a free flow of 70 1/s . The temperature of the flowing water reached 70°C which indicates a geothermal gradient significantly higher than the normal gradient of 1°C per 30m. Gloe (1960), and Jenkins (1962), consider that the anomalous heat in the Latrobe Valley Group aquifers results from partial oxidation of the coal seams . This concept is discounted by Thompson (1980) on the basis that significant depletion of the coal deposits Australian Coal Geology 4, Part 2

J. Brumley and M. Reid

577

would occur within a short period of geological time if the heat was generated by oxidation of coal (and i ron oxides) alone. Thompson (1980) suggests that the main source of heat is from high geothermal fluxes along major fault zones. In either case, the retention of heat would be enhanced by the insulating properties of the coal.

TABLE 3 : REGIONAL CHEMICAL ANALYSES (mg/1)

Bore

Sample

Number

Date

Sample Interval

Stratigraphic Total DisOccurrence

of Sample Interval /s

solved Solids

co 3

HC0

so4 N03

S10

Nil

<0 . 1

(m)

ft: Total pi! Sol- Total Har duable ness as

CaC03

10/5/79

177-204

Traralgon Formation

44 Nil

6. 20

ON 53

22/9/74

357-3&8

Harwell

332

97 Nil

108

Nil Nil

6.54

ON 54

12/2/75

278-292 & 312-332

do.

58&

215 Nil

168

1 Nil

131

Nil

132

6,89

1320 10/7/79

423-433. 5

Traralgon Formation

407

153 Nil

8 Nil

<0 .1

7 .45

1333 31/7/79

582-593 . 5

do.

482

192 Nil

106

2 Nil

118

0.1

105

7 .45

1348 11/6/79

Formation (?)

542-557.5

do.

455

188 Nil

3 Nil

116

<O .l

7. 20

HP 185

7/2/79

881-926

Lakes Entrance Formation

328

64 Nil

154

l Nil

<0 .1

7. 76

HP 189

12/4/79

183-213

Traralgon

121

49 Nil

9 Nil

0.1

6.15

do .

724

128 17

325

l Nil

137

0.3

< l

173

8.22 8 .00

Formation M

2390 22/11/79 556-561

3294 2/7 /73

28,-296

do.

487

117

224

Nil Nil

n.d. n.d. n.d. Nil

159

301

27/6/78

805-818

do.

149

55 Nil

20 Nil

0.3

< 1

5.61

307

24/8/78

563-587

do .

257

87 Nil

2 Nil

<0. 1

< 1

7.12

286

25/9/78

553-595

do .

442

138 Nil

156

1 Nil

<0 .l

104

7 .99

TB 183

2/3/79

418-431 & 455-467

do.

104

49 Nil

3 Nil

<0.1

n . d.

6.42

WL 168

8/8/72

162-174

do.

38 Nil

8 Nil

Nil

0.1

5 . 40

Wt 197

12/2/79

318-342 & 345-358

do .

31 Nil

3 Nil

0.1

6.47

WN 44 {abandoned)

18/4/74

658-677

do .

250

73 Nil

7 Nil

<0 .1

6 . 47

WN 45

24/7 /74

242-254

Morwell Formation (?)

682

251 Nil

186

5 Nil

166

0.2

136

7 .35

WU 10 (abc'.ndoned)

16 /12/74 567-588.5

Traralgon Formation

402

171

Nil Nil

<0.1

8.43

MOR\.IELL OPEN CUT (Average values: Brumley et al, 1981)

194 2-81 1960-81

Ml Aquifer

793

224 n . d. 185

n.d. n .d.

118

n.d. n.d. n.d.

n.d .

· 6.2

123 n . d. 200

n.d. n. d .

103

n.d . n.d. n.d.

n . d.

n.d.

•6 .6

4.96

504

LY 1177 1975

171.6-17:s.8 Harvell Formation

3067

1633 n . d.

74 n . d. n.d. n.d. n.d. n.d. n.d. 40

n . d.

LY 1151 1975

157.3-159, 7 do.

1147

517 n.d.

51 n.d . n.d. n.d. n . d. n.d . n.d. 16

n.d.

5.31

LY 1156 1975

144.6-146.2 do.

163

66 n.d .

< 1 n.d. n.d . n.d. n.d. n.d. n.d.

n.d.

5. 75

M2 Aquifer

LOY YANG (Average values, Thatcher 1976)

NOTES :

n.d. • not determined

* Donates bores in the Merriman s Creek Sub-Basin. Total dissolved solids comprise the sum of all ions tabulated from Cl to Fe solu~le.

Australian Coal Geology 4, Part 2

J. Brumley and M. Reid

578

Regionally, the Trara l gon Formation aquifer tempratures vary from approximately 20°C around the margins of the Latrobe Valley Depression, to over 60°C along the Latrobe Syncline. Currently, the highest recorded temperatures are 68°C in bore 1675 LY and 70°C in bore 2661 M. These high temperatures suggest that no significant regional cooling of the aquifers has occurred due to groundwater extraction from Morwell Open Cut, although a drop of about 3°C to 7°C in the average annual temperature of the M2 Aquifer at Morwell Open Cut has been detected over the past decade (Brumley et al . 1981). This is probably due to the increased intake of water from the nearby western recharge areas . CONCLUSIONS The study has defined the general characteristics of the Latrobe Valley Group confined aquifers in the Latrobe Valley Depression and provided an initial estimate of the groundwater resources in these aquifers. It has al so high1i ghted areas where more specific data would be an advantage. In particular, more data is required on the Morwell Formation aquifers in areas remote from the open cuts, on the recharge areas and on the reg i onal hydrochemistry . The study also illustrated the value of maintaining comprehensive programs to regularly monitor water levels, water temperatures, hydrochemistry and subsidence. The following specific conclusions are drawn from the study: (1)

Hydraulic connection exists between the Morwell Formation and the Balook Formation . The Balook Formation is considered to recharge the overlying Boisdale and Lake Wellington Formations by vert i cal leakage .

(2)

Stratigraphical, hydrogeological and isotope data indicate that the Baragwanath Anticline forms a hydraulic . boundary between the main Latrobe Valley Depression and the Merrimans Creek Sub-Basin. 9 In maintaining the stability of Morwell Open Cut, approximately 354 x 10 1i tres of groundwater have been extracted from the confined aquifers beneath the open cut since extraction commenced in 1960 . This has caused a regional decline in the potentiometric surface of each aquifer system and produced minor regional subsidence over a large area of the Latrobe Valley Depression.

(3)

(4)

The regional potentiometric contours substantiate the geological evidence that most recharge is currently occurring from the western margin of the Latrobe Valley Depression and confirms the existence of two major aquifer systems in the main part of the Latrobe Valley Depression; namely the Morwell Formation and the Traralgon Formation Aquifer Systems.

(5)

It is difficult to draw conclusions from the relatively few aquifer parameter values obtained. However, it is clear that the Traralgon Formation aquifers generally have a relatively high hydraulic conductivity, and that they form an extensive interconnected aquifer system over a large part of the Latrobe Valley Depression. Th i s is substantiated by the large areal extent of the potentiometric decline around Morwell Open Cut. The information obtained so far indicates that the Morwell Formation aquifers are also extensive but that the hydraulic conductivity is generally less than that of the Traralgon Formation aquifers .

Australian Coal Geology 4, Part 2

579

J. Brumley and M. Reid

(6)

Estimates of groundwater quantities indicate a total ~oundwater resource in the Latrobe Valley Group of at least 20 300 x 10 litres within the This quantity includes approximately Latrobe valley Depression. 1750 x 10 9 litres which is stored in the confined aquifers by virtue of the confining pressure. The total regional recharge to the Latrobe Valley Group aquifers is estimated to be about 170 1/s .

(7)

Temperature monitoring indicates that no significant regional cooling of the aquifers has occurred due to groundwater extraction from Morwell Open Cut, al though the temperature of the M2 Aquifer at the open cut has apparently dropped by several degrees since dewatering commenced, probably due to the increased intake of water from the nearby western recharge areas.

(8)

The groundwater is generally of potable quality when cooled and allowed to settle .

ACKNOWLEDGEMENTS Contributions from the following organisations and people are acknowledged: Department of Minerals and R. Williamson, and Messrs . A. Paskevicius);

Energy, Victoria - (Drs. C. Leonard , D. Nahm, J. Y.

Lawrence and McGrath and

(Dr. C. Barton, Messrs. State Electricity Commission of Victoria J . Alexander, C. Gloe, G. Holdgate, T. McKinley, S. Newcomb, J. Washusen, R. Webster, D. Dodds, A. Galimberti and A. Scott); and State Rivers and Water Supply Commission - (Messrs. D. Currey and D. Dole). The authors wish to thank the State Electricity Commission of Victoria and the Department of Minerals and Energy, Victoria for permission to publish this paper . REFERENCES Abele et al., 1976. In, Geology of Victoria, Tertiary Section, Douglas, J.G. and Ferguson, J.A., (Eds). Geol. Soc. Aust. Spee. Publ. ~. 177-273. Airey, P. , 1980. Australian Atomic Energy Commission. Geologist, SECV, 16.4.80.

Letter to Principal

Barton, C.M., 1971. The Morwell Interseam Sands. J. Geol. Soc. Aust. 17, (2). Brumley, J.C., 1981. General Hydrogeology of the Latrobe Valley Depression and the Effects of Aquifer Dewatering at Morwell Open Cut, Victoria. Proc. Seminar on Groundwater A ril 8 Aust. Geomechanics Societ Vic.

Brumley, J . C. , Barton, C.M . , Holdgate, G. R. and Reid, M.A . , 1981. Regional Groundwater Investigation of the Latrobe Valley 1976-1981. Joint SECV/ DMEV report . Unpubl .

Australian Coal Geology 4, Part 2

580

J. Brumley and M. Reid

Fraser, C.J., 1980 . Latrobe Valley Regional Groundwater Investigation. Initial Mathematical Modelling Studies. Vol. 1 & 2. SECV Fuel Dept . Report 1980/3, Unpubl. Fraser, C.A. and Pitt, H.A., 1979. Artesian Dewatering Operations at Morwell Open Cut. Proc 1st Intern . Mine Drainage Symp. Denver Colorado May 1979. Galimberti, A.G., 1979. Regional Groundwater Investigation of the Latrobe Valley . Details of the Drilling and Installation of the SECV Bores. SECV Fuel Department Exploration and Geological Division Report, Unpubl. Gloe,

C.S., 1960. The Geology of the Latrobe Valley Coalfield, Australas. Inst . Min. Metall, 194, 57-125.

Proc.

Gloe, C. S. , 1976a. The Latrobe Valley Coal Measures, Geology of Victoria, Douglas, J . G. and Ferguson, J . A. (eds). Geol . Soc. Aust. Spee. Publ . , ~. 378-386. Gloe, C.S . , 1976b. Land Subsidence Related to Brown Coal Open Cut Operations, Latrobe Valley, Victoria, Australia. Proc. 2nd Intern. Symposium on Land Subsidence, Anaheim, California, pp 399-408. Hazel , C. P. , 1975. Groundwater Hydraulics. Australian Water Resources Council's Groundwater School, Adelaide (1975). Holdgate, G.R., 1979. Latrobe Valley Regional Groundwater Bore Cross-sections SECV, Fuel Department, Exploration and Geological Division Report, unpubl. Holdgate, G. R., 1980 . Geology of the Holey Plains - Coolungoolun Coalfields and the Wi 11 ung-Merri man's Creek Area. SECV, Fuel Department, Exp l oration and Geological Division Report 1980/2, unpubl. Hutchings, R. , Fajdiga, M. and Raisbeck, D. , 1977. The Effect of Large Ground Movements Resulting from Brown Coal Open Cut Excavations in the Latrobe Valley, Victoria . Proc . Conf . on Large Ground Movements and Structures, Cardiff Wales, Session 2. Jenkins, J.J., 1962. Underground Water in East Gipps l and. Underground Water Investigation Report No 6.

Dept. Mines Vic.,

Nahm, G. Y. , 1980. Estimating Transmissivity and Well Loss Constant Using Multirate Test Data from a Pumped Well . Groundwate r 18, No 3 (1980). Nahm,

G. Y. and Reid, M. A. , ' 1979 . The Potentiometric Contour Map and Equi geo-therma l Gradient Contour Map of the Latrobe Va 11 ey Group Basal Aquifers. Victorian Govt. 1 Dept. Min. & Energy Geol. Survey Unpubl. Report No 1979/102.

Raisbeck , D. , 1980. Settlement of Power Station Structures in the Latrobe Valley, Victoria, Proc. of 3rd Aust.-N.Z. Conf. on Geomechanics, Wellington, N.Z., Vol 1, pp 3 -3 . Raisbeck, D. , 1981. Subsidence Related to the Withdrawal of Groundwater. Proc. Seminar on Groundwater, April 8, Aust. Geomechanics Society, Vic. Group.

Australian Coal Geology 4, Part 2

J. Brumley and M. Reid

581

Thatcher, R. C., 1976, Loy Yang Project : Aquifer Characte ristics from Pump Tests conducted during 1975 . SECV Fuel Dept . Dev . Div . Report 111, unpubl. Thompson, B. R. , onshore area .

1980. The Gippsland Sedimenta ry Basin - a study of the Ph.D . Thesis, Melbourne Universit y, unpubl .

Australian Coal Geology 4, Part 2

582

The Origin and Characteristics of Defects in Oil Shale T. Sul I Ivan Coffey & Partners Pty. Ltd. P.O. Box 125, North Ryde, N.S.W. 2113, Austra I la KEY WORDS:

011 shale, clay structure, fissure, engineering geology, mining.

ABSTRACT It Is generally accepted that It Is the structural features that dominate the engineering behaviour of heavily overconsoll dated clays and clay shale~ As the Tertiary oil shales of eastern Australia generally belong to this category of soil-rocks, the structure of the deposits Is a crit ical aspect of any mine design study. This paper covers this aspect of one of these deposits. The deta I Ied structure of the bas In Is d Iscussed, f I rst Iy In re Iat Ion to the geology and secondly In relation to the fundamental engineering properties and composition of the soil-rocks. A tentative model Is formulated which relates the observed distribution and characteris tics of the structural defects to the geological and electrochem ical conditions prevailing at the time of deposition and to the subsequent history of stressing of the soil during partial dlagenes Is. A c Iass If Icat I on system Is presented for record Ing the geotechn I ea I aspects of each defect type for later analysis and evaluation. INTRODUCTION Recent developmen ts In the petroleum Industry have focussed attention on alternative energy sources such as Austral Ian 011 Shales. However, little Is known of their formation, structure and engineering properties. The Tertiary oil shales of Australia were formed In sma l l semi-Isolat ed lacustrlne environments with similar llthologles to many coal deposits, however, beause of their origin, engineering properties, relatively low strengths and structure they have markedly different properties. This paper presents some of the results of a geotechnlca l study for a proposed mine In the Yaamba 011 Shale deposit. The Yaamba Basin Is completely covered, and hence In the early stages of eva I uat Ion and mI ne des Ign there were no exposures. Study of the o 11 sha I e sequence In the basin was limited to HQ sized core. Initial Inspection showed that the sequence was Intersected by Joints and fissures and the fissures occurred both as Isolated defects and In discrete zones. SI nee It Is genera I Iy accepted that the structura I defects dom Inate the engineerin g behaviour of these sol I/rock types, determinat ion of the occurrence, geometry, orientation and continuity of the defects was a crltlcal aspect of mine design. An essential part of this was an understandin g of the origin and mode of formation of the ' defects.

Australian Coal Geology 4, part 2

583

T. Sul I Ivan A defect classlflcatto n

system was developed to provide an adequate descr I pt Ion of each defect wh Ieh cou Id be used Iater· to eva I uate the strength test results and assess the relative effect on the mass strength. A brief description of the relevant aspects of geology Is presented, together with the material properties of the oil shales, and a detailed description of the structure of the oil shale sequence. A postulated origin for each of the · rock mass defects Is presented together with a description of the defect classlflcatlon system. GEOLOGICAL HISTORY The Yaamba Basin Is one of a series of coastal Tertiary Basins which extend In a northwest trend from Lowmead In the south, to Proserplne In the north (Figure 1). Other Tertiary basins In the area are Rundle, Stuart, Casuarlna and Water Park Creek. These basins are generally elongated In~ northwesterly direction and, In the Yaamba-Glads tone area, al lgned along major regional faults. 150°

151 •

--1.,..,..,., YAAMBA~ • ROCK HAMPTON

UART BASIN

SCALE

Kl L01o1£Tll£S

GLADSTONE

~, 0

· -: 'i

Figure 1 Location plan showing distribution of the major faults and associated Tertiary oil shale basins. Block faulting and subsidence associated with tension In the Palaeozoic basement rocks during the late Cretaceous and early Tertiary, resulted In reactlvat Ion of the reg Iona I fau Its and the format I on of a number of sma I I, sem 11sol ated terrestrial basins. Lacustrlne systems developed In these basins and resulted In deposition of an lnterbedded series of of I shales, I Ignites and Australian Coal Geology 4, part 2

T. Sul I Ivan

584

c I aystones w Ith mI nor s 11 tstone and sandstone. In the Rund Ie-Stuart bas In, the thickness of sediments are estimated to be greater than 1000m (Henstrldge and Mlssen, 1981). Movement along these faults was probably both contemporaneous and post-depositional. The bas Ins genera I Iy take the form of truncated sync 11 nes wIth bedd Ing d I ps flatternlng towards the centre. Typlcal dips range from 7° to 20° at the subcrop to 4° to 5° towards the basin centre. The present physiography of the area appears to be related to the block faultlng, and because of It, and the erodabl I lty of the Tertiary sediments, the majority of the basins are covered by thick Quaternary al luvlal deposits.

Stratigraphy The stratigraphy of the oll shale sequence Is complex with major formations and smaller seams and lnterbeds (Henstrldge and Mlssen, 1982). In general the formations may be easlly correlated across the basin. Because of the complex stratigraphy, and the fact that the rock characterlst I cs rem a In re I at I ve I y constant between format I ons, the eng I neer Ing character I st Ics of the depos It are best d I scussed and understood In re I at I on to the major component rock types:oll shale llgnltlc oll shale claystone (brown) claystone (green) - lncludlng minor slltstone and sandstone minor components consisting of llmestone, marly beds and Irregular concretions The relatlonshlps of the rocks (excludlng llgnltlc oll shale) and their main components are shown on Figure 2. Co Co~/ FERROAN CALCITE 100 MARLS 0nd } LIMESTONES

STONE BANOS

CLAYSTONE ( green) KEROGEN

L-----....faC~CLL,f.d..L..t.~ OIL SHALE

CLAY, OUARTZ ETC.

CLAYSTONE (brown)

Figure 2 Diagrammatic representation of rock compositions and relatlonshlps (after Gal lols and Hartan, 1981 ). The oll shale consists of brown to black shale with well developed bedding; It occurs throughout the sequence In thick beds. The llgnltlc oll shale Is black, with very well developed bedding. The brown claystone occurs malnly In the Austral Ian Coal Geology 4, part 2

585

T. Su I I Ivan

upper sections and ls gradatlo nal to the oil shale but with poorly develope d bedding ; It general ly occurs In thin beds and sometim es as very thin beds within the thicker oil shale seams. The green c I aystone occurs through out the sequenc e, genera 11 y In th In beds less than 2m thick. Similar lnterbed s of green clayston e have been by Henstr Idge and MI ssen ( 1982) from the Rund Ie/ Stuart bas Ins. It Increported I udes complete series of rock types from clayston e to sandston e with some associat a limeston e and marl. It ls graded/bedded. lndlvldu al beds sometimes start ed as clayston e grade up to llthlc sandston e In the centre then to clayston e at the top. The stone bands consist of I lmestone beds, carbona te recemen ted layers, Irregula r carbona te concret ions and thin sandston e beds. Bed thickne ss ls generall y less than 1m with an average of 0.15m. MATERIAL PROPERTIES ~

Testing

Enginee ring Index testing, Includin g Atterber g Limits, particle determi nations and hydrome ter analyse s, was carried out on samples of size the major rock types to categori se the likely engineer ing behaviou r and evaluate the shear strength test results. The summary results for each rock type are presente d on Figure 4.

. z

80 1---+----, ,f'-+----+ ----tl------ -H

~ w 60 +-----+------ - - + , ~ - - -- ---H ILN

I!:

0001

100

l!! in 40 r.<-- 4 - ~ . : . . + - - 1 - - - + - --+I :! i:i 20 i---- - - - 1 , , L - - + - - l - - , ' - + - --+1

150

)(

►

....

;::

"' 0

100

150

200

LIQUID LIMIT WL

CLAY I SILT PARj'CLE.JQZE - )mmGRAVEL LEGEND

CLAYS TONE (GrHn)

Figure 3

Index Properti es of major rock types

CLAYSTONE (GrHn) SANDY CLAYSTONE ( B<own ) OIL SHALE

In genera I, the green c Iaystones c Iass If Ied as s 11 ty c Iays and c Iays of h I gh plastic ity, whl le the ol I shale classifi ed as a sl It, sandy sl It of high liquid limit. As expected , the brown clayston es were Intermed iate between the two with a silty clay grading, and slit Atterber g limits. The organic content and bonding In the oil shales have consider ably reduced the plastici ty Index va I ues and th Is behav I our Is s Im I I ar to that reported for "b I tum I nous c I ay shales" from the United Kingdom (Jackson and Fookes, 1974). Mlneral~ y

X-ray diffracti on analyses were carried out on represen tative samples and summary ls presente d In Table 1. The results Indicate that the main minerala compone nts are montmor l I lonlte and kaol lnlte with minor quartz, slderlte , pyrite, crlstoba llte and calclte. Australi an Coal Geology 4, part 2

586

T. Su I I Ivan TABLE 1 MINERALOGY RANGE

Cl)

ROCK TYPE

-rl

t::

-rl .-i 0

AVERAGE ()

AND

-rl Cl)

u -rl .-i .-i

0 -rl

-rl

u 0 t:: .-i

M ::,

-0

0 .-i

"' O' A-25

7-25 (13)

e i::

::c

Cl)

M u

M Cl)

-rl

Cl)

u -rl

M >, p..

Cl)

u u

(I) -rl -rl .-i

-rl <.)

.-i

M ol

u ,lJ

A-8

Cl)

Oil Shale* 20-40 (25)

30-80

Clay stone (brown)

25-50 (40)

30-65 (40)

8-25

A-12

Clay stone (green)

10-50 (25)

30-90 (60)

A-25

A-20

A-10

A-20

(SO)

A = Absent * Note these percentages are of the total crystalline phases with no allowance for kerogen or volatiles

l.nTili;1 .8QJ;,k Strength

The rock substance strengths for each of the main rock types are shown on Figure 4. The mean strength range for Permlan coal measure rocks In Australia Is Included for comparison. The oil shale and I lgnltlc oil shale are generally of very low strength and markedly stronger than the green claystone which has a mean strength on the soil/rock boundary. Based on observatio ns at Yaamba and experience from slml lar Plelstocen e deposits In Botany Bay and Newcastle Harbour (New South Wales), It Is considered that due to the bonding of the organic matter, these relative strength differences developed at an early stage In the deposltlona l history of the deposit. STRUCTURE It Is genera 11 y accepted <Barden, 1972) that structura I defects dom I nate the engineering behaviour of overconsoll dated clays and clay/shales . Consequently It Is Important to define the types of defects present and their orientation , and geometry so that their effect on the strength of samples and the rock mass can be evaluated.

Inspection and logging of aval Iable exploration cores showed the ol I shale sequence contained a number of structural defects. These were:- Joints, f I ssures, f Issured zones. There were two ma In Jo I nt types, shear and tens Ion Joints and these were differentia ted In the core on the basis of their surface character I st Ics, or Ien tat Ion re Iat I ve to bedd Ing and occurrence. The or Ientat Ic and dlagrammatrcal ly on Figure 5.

Australian Coal Geology 4, part 2

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587

Tension .J..o.ln.:t.s.

These joints have been termed "tens I on" on the bas Is of the I r probable mode of formation. The Joints were generally planar/step ped, rough, subvertlca l and discontinuo us. They occurred ma Inly In the I lgnltlc ol I shale and to a lesser extent In the of I shale. The surface of a typlcal tension Joint from Yaamba Is shown on Figure 6. The surface displays the plume markings, steps and fringe Joints normally associated with jo I nts formed In tens Ion (Hodgson,

ROCK TYPE

OIL SHALE LIGNITE CLAYSTONE CLAYSTONE (GREEN)

0 -1 EL

1961).

The tension Joints generally formed two sets, striking normal and parallel to bedding. The results of orientat I on/measure ment from one bore ho I e are presented on Figure 7 as a scatter diagram of the lndlvldual points, and a contoured Schmidt projection with the Terzaghl correction. These orientations relative to bedding are bel levedto be maintained around the basin.

(BROWN)

2.4 VL

7 L

24 M

70 H

UNCONFINED COMPRESS IVE STRENGTH Ou LEGEND

E -

EXTREMLY

V - VERY

L -

LOW M _ MODERATELY H _ HIGH

I • . . . . ____, RANGE r

MEAN APPROX I MATE MEAN STRENGTH OF PERMIAN COAL MEASURE ROCKS IN AUSTRALIA .

Figure 4 Unconfined Compressiv e Strengths of Major Rock Types.

OIL SHALE

CLAYSTONE OIL SHALE

Fissured Zone Shear Joint Tension Joint Fissure

Figure 5 Diagrammatic

MPo

sketch of major structural effects.

Austral Ian Coal Geology 4, part 2

588

T. Sullivan

( a)

( b)

SHEAR JOINTS B

N: 71

·:::./: it/

.. ..

fT),@ • Y::.:J'

:;.•.

;.t'.:;.

··{.;(

0= 4% 411): B% •= 12% 0= 16%

. ,

TENSION JOINTS B

N : 47

•

41) : 10%

8 =15o/o 0= 20%

...

B N a 3 18

.. .. ..

® = 4%

•= 8% •= 12% ®= 16%

• = N = No . of measurements

Figure 8 Stereograms of shear and tension Joints and fissures Cal scatter diagrams (b) contoured Schmidt projetlons with Terzaghl corrections applied. Australian Coal Geolog y 4, pa r t 2

T. Sullivan

589

..s.he.ar: .J.o..illll These Joints have been termed "shear" on the basis of their probable mode of formation. These joints were generally planar, slickenslded and polished and formed discrete planes cutting across the bedding. They did not appear to extend across the boundaries between different rock types. The shear Joints often truncate and cut across the f I ssures and hence are cons I dered to have post-dated the f I ssures. They occurred ma In I y In the o 11 sha I e w Ith mI nor occurrences In the I Ign It Ic o 11 sha Ies and c Iaystones. The surface character l st l cs of a typical shear Joint are shown on Figure 8. The shear Joints generally formed two sets both striking para I lel to bedding, but with dips opposite to and In the same direction as bedding, essentially

Figure 7 Tension Joint In I Ignite - core diameter 63mm

Figure 9 Shear Joint In oil shale - core diameter 63mm

Figure 10 Fissure In oil shale - core diameter 63mm

Figure 11 Fissure zone In brown claystone - core diameter 63mm

Australian Coal Geology 4, part 2

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T.Sulllvan

forming a conjugate set. The results of orientation measurements from one borehole are presented on Figure 7 as a scatter diagram and contoured projection. It Is considered that the shear Joints maintain their orientations relative to bedding around the basin, In a similar manner to the tension Joints.

Fissures Fissures are defined as smal I fractures existing In beds but not crossing the boundary of a bed or horizons within the bed (Fookes and WI Ison, 1966). At Yaamba they were generally undulose/lrregular with rough, striated or sf lckenslded surfaces. A photograph of a typical sl lckenslded fissure Is presented on Figure 10. The fissures were best developed In the brown and green claystones with minor ocurrences In the of I shales. The shape and surface characteristics of the fissures appeared to be dependent on rock type, with subvertlcal rough fissures In the slltstones and Irregular sl lckenslded fissures In the of I shales and brown mudstones. Al I fissures appeared to be discontinuous, and were generally either truncated by other fissures or bedding, or graded to rough Irregular surfaces within the width of the HQ s I zed core. The resu Its of or I en tat I on measurements from one boreho I e are presented on Figure 7 as a scatter diagram and contoured project ion. They have a slmllar distribution to the shear Joints but with a wider scatter. This preferred orientation does not agree with other reported occurrences from slmllar rocks (Fookes and WIison, 1966) where the fissures were generally random.

Fissure~ Zones of fissuring occurred throughout the sequence; however, they were always wIth In the brown and green c Iaystones and genera I Iy sub para I I e I to bedd Ing. The locatlon of the zones relative to the other defects are shown dlagrammatlcal ly on Figure 5. The zones covered a complete range with the two end members belng:(a)

zones of closely to moderately spaced (less than 40mm) Irregular, smooth to rough, Interconnecting fissures

(b)

zones of closely spaced (generally less than 5mm) flattened rhomb-shaped discs of polished and sllckenslded Interconnecting fissures (Figure 10).

Type (a) zones tended to occur throughout the green claystones, while type (b) occurred occasionally In the brown claystones, and usually within the green claystones mainly at the boundaries between major rock types. The thickness of these zones ranged from less than 5mm to a zone greater than 10m which was located at the base of the oil shale sequence. POSTULATED ORIGIN OF STRUCTURE

Fissure ZQn.es. Tertiary of I shale sequences developed In a fresh-water lacustrlne environment under quiet lagoonal conditions with a supply of fine grained detritus (Noon, Consequently the of I shales produced a 1981; Henstrldge and Mlssen, 1982). Austral Ian Coal Geology 4, part 2

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591

non-f I occu I ated, I am I nated para I I e I a I I gnment of part I c I es. Th Is Is cons Istent wIth the we I I deve I oped bedd Ing and f I ss I I I ty ev I dent In the cores. In addition, except for the Isolated sl lckenslded fissures, the ol lshales are generally unflssured. However, the green claystones are generally massive and fissured and consequently a different electro-chemical environment was probably operative during their deposition. Previously It has been thought that flocculation of clays only occurred under marine conditions, however, Barden (1972) has shown that flocculation can result from deposition In brackish water with a salt content well below that of marine conditions. Furthermore, experiments by White (1961) Indicated that changes In the salt concentration, type of salt present, or In the stream load would cause flocculation of the clay particles, even though the overal I salt concentration remained constant. Hence, If dur Ing f I ood stages the source supp 11 es a more concentrated I oaq, the c I ays would flocculate In the basin and result In deposition of the massive green claystones. Jungst (1934) found that fissures developed In flocculated suspensions as a result of synaeresis, which Is the expulsion of part of the I !quid phase In a I !quid/sol Id suspension when the Internal forces of attraction are greater than the Internal forces of repulsion between the particles of the sol Id phase. This Is supported by experiments carried out by White (1961), which showed that clays sedlmented under non-flocculatlng conditions, produced horizontal lam I nations due to the para I lel al lgnment of clay particles with a general absence of f I ssures. However, under f I occu I at Ing cond It I ons the c I ays were randomly oriented and fissured (Figure 11). The spacing of the fissures was a function of the mineralogy, partlcle size and the concentrations and kind of cations present. The open flocculated structure also resulted In a conslderab I y I arger sett I ed vo I ume CF I g ure 11 ). Therefore It Is cons I dered that the type Cal fissure zone In the green claystones developed during lnltlal deposition of the sediment.

CONDITIONS

SEDIMENTATION

NON-

FLOCCULATING

INDIVIDUAL PA[CLES ~

♦

LAY~

♦ ~ • f FISSURES _,---

OIL SHALE

Figure 12 Diagrammatic representation of formation of oll shale and green claystone

-----

GREEN CLAYSTONE

Australian Coal Geology 4, part 2

592

T. Sul I Ivan

These fissure zones would be zones of lower strength within the sol I/rock mass. In addition, it ls considered that organic bonding in the of I shales and lignites resulted in higher relative strengths (and modulus of elasticity) ear Iy In the sed I mentary h Istory of the bas In. Consequent Iy, fo Id Ing of the beds during basin subsidence would tend to concentrate shear stresses at the boundaries between the stronger ol I shales/1 Ignites and the fissured green claystones, and result in partlal or complete transformation of type (a) fissures to type (b). Col lapse of the open structure during consol ldatlon would assist In real lgnment and hence pol lshlng of fissure surfaces. The settling rate of kaol lnlte Is approximately an order of magnitude faster than montmor I 11 on I te (Shaw, 1981), and this wou Id tend to concentrate these minerals at the upper surface of the beds. This may also affect the degree and nature of fissuring and the resultant shear strength. fissures

The fissures are considered to have two origins, firstly, synaeresis cracking and, secondly, as a result of differential compaction of underlying sediments. In the o 11 sha I e, the f I ssures are undu I ose and s 11 ckens I ded, and probab I y formed as a result of dlfferentlal compaction of underlying beds In a slml lar manner to the numerous s 11 ckens I des encountered In f I ne gra I ned rocks above coal seams. The higher lnltlal void ratio associated with the flocculated structure In the green claystones could a lso result In larger settlements and hence a greater opportun Ity for the occurrence of compact Ion f Issures. The concentration of fissures towards the base of major oil shale beds supports these theories. The orientation of the fissures relative to bedding lmpl les that basin subsidence during early consolldatlon may also have affected their characteristics and formation . .J.Q..l.nll

As discussed earl ler,

the ol I shales and I lgnltlc of I shale probably develop relatively high early strengths, and the same subsidence which produces shear strains in the fissure zones, results in tensile strains in the more competent beds leading to development of tension Joints.

The surface characteristics of the shear Joints, their orientation relative to bedding, and their occurrence within the sequence, al I imply a mode of formation related to folding due to basin subsidence, and the development of shear stresses In the more competent beds C I rgn It Ic o I I sha Ie and o 11 sha Ie). Similar shear Joints have been reported from other clay/shales which have undergone slml lar broad scale folding (Fookes and WI Ison, 1966). Based on their postulated origin and the experience from other clay shales, it ls considered that these Joints are at least continuous across a particular bed. FISSURE AND JOINT LOGGING SYSTEM After the In It I a I Inspect I ons of the exp I orat I on core, It was ev I dent that a defect classification system was required to:provlde an adequate description of the individual defect or zone assist in sampling those defects with expected lower bound strengths analyse the strength test results assess the relative effects of these defects on mass strength Australian Coal Geology 4, part 2

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593

The system adopted was developed lnltlal ly for logglng the fissured clays of Newcastle and Botany Bay (New South Wales) and was modified substantlal ly to take account of the requirement s at Yaamba. The system was designed to accommodate description of:the slngle defect the: discrete rock unit, for example, an ol I shale or I Ignite bed which has a partlcular defect pervasively through It specific fissure zones The defects were described In terms of their orientatio n, shape, surface characteri stics, continuity and spacing, and these features were given a numerical weighting ranging from 1 to 5 depending on their estimated effect on the mass strength. The classlflcatl on system Is presented on Table 2. An example would be classlflcatl on of the shear Joint In Figure 9 which would have a classifica tion number of 3, 1, 1, 1, 4, whereas the fissure zone In Figure 11 would have a classificati on number of 1, 2/3, 1, 2, 2. Because of the wel I defined bedding In the ol I shale and I Ignite and the uniform correlation of beds across the site, It was considered adequate to orient al I defects relative to bedding.

TABLE II FISSURE CLASSIFICATION Class Rating No.

Orientation (deg.) 1.

Surface Shape

Surface Characteris tics

Continuity

0 - 20

planar

s lickensided

continuous across the core

20 - 35

curved

polished

truncated by other joints

5-10

35 - SS

undulose

striated

discontinuo us

10-40

SS - 70

irregular

smooth

isolated

70 - 90

stepped

rough

unfissured

(mm)

Example: Joint in lignite, 90°, planar, rough, discontinuo us Rating: S, l, S, 3, 4 = 18 1.

Relative to horizontal.

Austral Ian Coal Geology 4, part 2

Spacing

T. Sul I Ivan

594 CONQUSIONS

The fol low Ing tentative conclusions apply to the Yaamba Basin. Obviously, the appllcablllty of this work should be assessed In relation to the results from other oil shale basins: (a)

The Tertiary oil shale sequence compr i ses rocks which are In the low strength to extremely low strength Csoll) range.

(b)

The physlo-chemlca l environment of deposition has a marked effect on the development of structure In the unconsol !dated sediments.

Cc)

Stress developed In the sol I-rocks due to partial dlagenesls and basin subsidence can modify the lnltlal structure.

(d)

The folding associated with basin subsidence resu lts In the formation of Joints within the sequence. These Joints comprise essentially two typesshear and tension Joints. Orientation and continuity of the Joints may be related to the orientation and thickness of the beds In which they occur.

AO<NOWLEDGEMENTS This work was undertaken as part of a feaslbl I lty stage geotechnlcal and hydrogeologlca l study for a proposed open pit mine In the Yaamba deposit. The author w I shes to record h Is thanks to Mr. G. Johnson (Peabody Austra 11 a Pty. Ltd.) for permission to pub! lsh the paper and Dr. J. Dear (Peabody Austral la Pty. Ltd.) for many Informative discussions, and correction of my misconceptions regarding the geology of the deposit. REFERENCES Barden, L., 1972, The relation of sol I structure to the engineering geology of clay sol I. Quart.J. Engineer, .G.e..QJ......2.,.. 85-102. Cripps, J.C. & Horton, A., 1981, Field Investigation of British Mesozoic and Tertiary mudstones. ~ .J... Engineer, G.eQL. 1.4&. 311-324. Fookes, P.G., 1965, Orientation of fissures In stiff overconsol ldated clay of the Slwal lk clay. GeotechniQue ~ 195-206. Fookes, P.G. & WI Ison, D.D., 1966, The geometry of discontinuous and slope failures In Slwallk clay. Geotechn(Que J._Q,._ 305-320. Gallols, R.W. & Horton, A., 1981, Field Investigation of British Mesozoic and Tertiary mudstones. ~ .J.... Engineer, G.eQL. 1.4&. 311-324. Henstrldge D.A. & Mlssen, D.D., 1981, The geology of the Narrows Graben near GIadstone, QI d., Austra 11 a. 51 st ANSAAS Congress, Br Isbane, Austra I I a. Henstr I dge, D.A. & MI ssen, D.D., 1982, Geo I ogy of o 11 sha I e depos Its w Ith In the Narrows Graben, Qld., Austral la. B.lLLL. ilIIl.a. ~ Petrol, Geo!og, -~ 719-731.

Austral Ian Coal Geology 4, part 2

T. Sul I Ivan Hodgson, R.A.,

595

1961, Classlflcatlon of structures on Joint surfaces.

~ 22.9..,_ 4 9 3- 5 0 2.

Am.er:.._ ..L..

Hutton, A.C., 1982, Or I g In of organ r c matter In Austra I I an Tert I ary o I I shales. Bass Becking Symp. on 01 I Shales and Black Shales. Jackson, J.O. & Fookes, P.G., 1974, The relatlonshlp of the estimated former burl al depth of the Lower Oxford clay to some sol I properties. Quart . ..L.. Engineer, ~ L . 137-179. Jungst,

H.,

Rundschau,

1934, Geologlcal 321-325.

significance of

synaeresis.

GeoJogJsche

Noon, T.A., 1981, Stratigraphic drl I I Ing report - GSQ Rockhampton 2 and 3. Qua rt, Goy em, MJ.n.... ..L.. .J..u..1.¥_ .19..8..2... 31 o- 31 6. Shaw, H.F., 1981, Mlnerology and Petrology of the argl I laceous sedimentary rocks of the U.K. ~ .J.... Eng I neer, .G..e.Q.L. lA.... 277-290. Tay I or,

R.K.

& Spears,

D.A.,

1981,

Quart, .J... Eng I neer, ~ lA.... 290-31 o. Wh I te,

W.A.,

1961,

Laboratory Invest I gat I on of mudrock.

Co II o Id Phenomena In sed I men tat I on of arg 111 aceous rocks .

.J... .5.e.d..lm.en:t, Petro 1, lL. 56o- 57o.

Austral Ian Coal Geology 4, part 2

596

Prediction of Roof Deformation Mechanisms in Underground Coal Mines C.D. Rawlings* & W.J. Gale** * CSR, Coal Division 144 Edward St., Brisbane, 4000,Australla ** CSIRO, P.O. Box 2083, Wollongong, N.S.W. 2500, Austra 11 a. ABSTRACT Underground coal mines In Australia experience a large variety of development roadway conditions. The type and severity of roof and floor fat lure varies both within and between col I lerles. The distribution of roof fal lure ls largely determined by the sedlmentologlcal and structural configuration of the rocks forming the working and main roof together with regional and local variations In the deforming stress fields. Such variations In the stress fields can be caused by regional geological structures, surface topogrphic features and localised extraction procedures. The mechanisms of roof deformat Ion are determ I ned by a re I at Ionsh i p between the rock mass strength, the frequency of structural defects within the rock mass, the magnitude and orientation of the deforming stress field, the geometry of the roadway and the type and Installation time of the support system. Stab I I lty In roadways, which are deformed by vertically oriented maximum principal stress fields, Is predominantly determined by the frequency and orientation of steeply dipping Joints and the relative partablllty of bedding planes within 1.5 seam heights of the working roof. Roof failure often occurs by bed separat Ion Iead Ing to roof sag and u It I mate Iy to "beam-type" roof fa I I. Failures In Jointed rock can be largely controlled by correct roadway orientation. Major Joint traces In the working roof should not Intersect the roadway at angles less than 25°. Fal lures by separation of a roof plate along weakly cohesive bedding planes can be minimised by reducing the width of the roof span. The use of sma I I head Ing mach Ines and sem 1-c I rcu Iar or obround roadway profiles can achieve smaller roof spans. The mechanisms of roof deformation In roadways, which are dominated by high or an I sotrop I c hor I zonta I stress f I e Ids, can be pred Icted w Ith respect to the angle between the maximum stress axis and the roadway orientation. Roof deformation generally fol lows a series of prescribed fal lure paths up to ultimate roof col lapse. Thinly bedded llthologles In the Immediate roof are Initially deformed by dilation and subsequently shear, when the angle between the maximum stress axis and the roadway ranges from 55° to 90°. These I lthologles deform by preferential shearing and buckling on one side of the roadway with total coll'Wse resulting from cant I lever beam fal lures when the angle ranges from 35 to 55°. Minor roof slabbing wl I I occur In the 25° to 35° angular range. Extremes of stress magnitude and the presence of joint zones wll I cause these critical angles to be reduced. More massive Immediate roofs wll I only deform at high stress magnitudes when the critical angle Is greater than 75°. Australian Coal Geology 4, part 2

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Geotechnical Investigations of Roof Conditions at Tahmoor Colliery C.D. Rawllngs*, W.J. Gale**, I. Stone*** & C. Cook*** * CSR, Coal Division, PO Box 281, Brlsbane,Aust ralla ** CSIRO, PO Box 2083,Wollongong, Austral la *** C I utha Deve Iopment, PO Box 12, Nare I I en, Austra I I a **** BHP, Whyal la, South Australia. Australia ABSTRACT A study

of roof rock strength, In s I tu stress, roof rock fa I I ure and roof support deformation has been undertaken In the Perm Ian Bui II Seam at Tahmoor Coll lery, N.S.W. The seam varies In thickness from 1.6 to 2.4m and workings are currently located at depths of 400 to 430m. The sediments of the Immediate roof consist of lnterbedded lamlnltes, sandstones, slltstones and mudstones, from 3 to 11m In thickness. Overlying these units are the massive sandstones of the Narrabeen Group. Difficult roof conditions, caused by high horizontal stress fields, have been experienced at the col I lery. Difficult roof conditions beneath laminated roof occur commonly In the mines of the Southern Coalfields. Unconfined and trlaxlal strength testing of the lamlnltes showed that strength was Inversely proportional to the development of bedding. Lamlnltes were tested with differing angles between the axis of compression and the planes. Three modes offal lure, which depended on this angle, were observed. A series of direct shear tests on lamlnlte beddln~ planes gave an Intact cohesion of 10 MPa with an angle of friction 0 = 29. Preparted bedding planes gave a cohesion of 1 MPa with 0 = 26°, Implying that once dilation of a roof rockmass had occurred progressive deformation could continue at reduced stress levels. Examination of underground roof deformation enables a four-fold classlflcatlon of roof fa 11 ure to be made. MI n I ng-1 nduced conjugate shear fractures, wh Ieh occurred at the working face, were observed at various spatial orientations. The attitude of the fractures gave an Indication of the al lgnment of the maximum principal horizontal stress axis. In sltu stress measurements using the CSIRO soft Inclusion eel I were used to confirm the orientation of the stress field at four locations. Particular classes of roof fal lure were observed to occur at certain ranges of angles between the maximum stress d I rect I on and the roadway or I en tat Ion. The amount of roof deformat Ion was observed to decrease In sequentially driven roadways Indicating a partial degree of mining-Induced stress relief. Observed roof bolt loads correlate closely with the class of roof failure and consequently with the angle between the maximum horizontal stress axis and the roadway. Predictions of Impending types and amounts of road deformation can be made using the methods Investigated at Tahmoor Colliery.

Austral Ian Coal Geology 4, part 2