Normative mineral composition of high-temperature coal ashes from the Sydney basin coalfields, Australia

International Journal o f Coal Geology, 4 (1984) 2 4 9 - 2 6 2

249

Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands

NORMATIVE MINERAL COMPOSITION OF HIGH-TEMPERATURE COAL ASHES FROM THE SYDNEY BASIN COALFIELDS, AUSTRALIA

J.M. SLANSKY

Joint Coal Board, 1 Chifley Square, G.P.O. Box 3842, Sydney, N.S.W. 2001 (Australia) (Received December 5, 1983; revised and accepted July 6, 1984)

ABSTRACT Slansky, J.M., 1984. Normative mineral composition of high-temperature coal ashes from the Sydney Basin Coalfields, Australia. Int. J. Coal Geol., 4: 249--262. Chemical differences in the composition of high-temperature coal ashes of major economic seams o f the Sydney Basin were studied using a normative analysis. All chemical data were recalculated to normative mineral assemblages consisting of: quartz, kaolinite and iUite. Quartz and clay minerals, the principal constituents o f mineral matter occurring in coals, account for most of the variations found in the chemical composition of high-temperature coal ashes between seams of various stratigraphic levels and/or geographic locations. Ternary diagrams based on the quantitative relation of quartz, kaolinite and illite were used to demonstrate these differences.

INTRODUCTION

Differences in chemical composition of high-temperature (HT) coal ashes of the major economic seams from the Sydney Basin have been investigated and their gross chemistry compared using a normative analysis. A normative mineral analysis consists of a recalculation of chemical analyses to normative minerals which might or might not have a direct relationship to actual mineral assemblages occurring in the samples. Various modifications of this method are used for comparative chemical studies of a variety of sedimentary rocks (Imbrie and Poldervaart, 1959; Nicholls, 1962; Miesch, 1962; Pearson, 1978). The use of normative analysis as a method for study of the distribution of minerals in coals was advocated by Pollack (1979). Given et al. (1981) compared the results of mineralogical analyses (based on X-ray diffraction and IR spectrometry of low temperature ashes) with the normative mineral composition calculated from chemical analyses of HT coal ashes for a range of American coals and found that the normative analysis gave a reasonably good estimate of the composition of mineral assemblages in coal samples.

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250 DATA SOURCES AND GEOLOGICAL BACKGROUND The data base for the current study consists of chemical records and reports of the Joint Coal Board* and of chemical analyses reported by Brown et al. (1959). The data have been acquired during various surveys of coking properties, conversion and fuel potential of Australian Black Coals over a period longer than 25 years. Most of the older data represent typical sections of the seams as mined in different collieries. The most recent data relate mainly to prospective working seam sections taken from boreholes sunk during exploration programs. Most of the chemical analyses were carried out on HT ashes of clean composite seam samples (excluding bands) except for the Balmoral seam which is represented by raw coal. A reasonable compatibility between the data sets is assumed, because sampling techniques and laboratory tests met procedures recommended by the British and/or Australian Standard Associations. Stratigraphic relationship of the Coal Measures and their seams with the number of analyses available for each seam are given in Table 1. The Sydney Basin Coalfields are situated at the margin of the Basin (Fig. 1). In the Permian, the coal-forming sedimentation took place in two widely different depositional environments, a shelf and a trough, which each in its own way influenced the character of the sediments and coals as well. The Coal Measures of the Western and the Southern Coalfields axe associated with the shelf environment. The Upper and Lower Hunter Valley and Newcastle Coalfields were deposited in a trough environment. The influence of the tectonic environment on the formation of coal seams in the S y d n e y Basin was discussed by Diessel (1970). PROCEDURE The normative analysis used in the present study is similar to Niggli's Molecular Norm applied to classification of rocks in igneous and metamorphic petrology. The procedure involves normalisation of the data by conversion of oxides to cationic proportions and to base 100. These data are then recalculated to normative mineral assemblages consisting of: kaolinite, illite, quartz, calcite, magnesite, hematite, anhydrite, apatite, and anatase. This set of mineral is deemed to be realistic, although not necessarily the most representative of the actual mineral assemblages present in coals. The results of geochemical studies of the major and minor elements in NSW coals suggest (Slansky, 1983) t h a t they are predominantly associated with their inorganic component, although a minor contribution *A part of the original chemical records of the Joint Coal Board has already been published (see references).

251 TABLE 1 Stratigraphic relationship of the Permian Coal Measures in Eastern Australia, N.S.W. (selected seams only)

Upper Permian

Illawarra Coal Measures

Newcastle Coal Measures

Coalfield, Area

Seam

Southern

Bulli (43)* Balgownie (4) Wongawilli (23) Tongarra (5)

Western

K a t o o m b a (13) Middle River (1) Irondale/Wolgan (4) Lidsdale/Lithgow (22)

Northern-western

Ulan(15)

Northern

Wallarah (8) Great Northern (17) Fassifern (8) Victoria Tunnell (11) Young Wallsend (9) Dudley (3) Borehole (15)

Lower Upper Permian

Hunter Valley, Wittingham Coal Measures, Undifferentiated seams (48)

Lower Permian

Greta Coal Measures

Muswellbrook

Brougham (4) Grasstrees (4) Thiess (10) Puxtrees (13) Balmoral (raw, 47)

Cessnoek

Greta (23) Homeville (4)

* Number of anal ~ses available.

from the original plant material cannot be ruled out. The distribution of these elements in various mineral phases occurring in coals is given in Table 2. The major steps in the normative procedure involve allocation of corresponding amounts of elements to each mineral norm as expressed by its chemical composition. An average composition o f Fithian illite (type illite, Grim et al., 1937) and an average kaolinite (both as anhydrous forms) as well as theoretical chemical formulae for the rest of the minerals were used in the calculations. The amounts o f silicon and aluminium in each coal sample were divided between illite, kaolinite and quartz, and illite and kaolinite, respectively. Both potassium and sodium contents were assigned to illite. Calcium was partitioned between apatite, anhydrite and

252

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Wollongong

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Western

I|

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Lower

Hunter

Area

IV

Upper

Hunter

Area

& Newcastle

Fig. 1. General location of the major Sydney Basin Coalfields.

Coalfield

253 TABLE 2 Distribution of major chemical components among various minerals occurring in coals Mineral

Chemical Constituents

Quartz Feldspars Mica

Si Si,A1,K,Na,Ca Si,AI,K,Fe,Mn,Mg,(Na)

Kaolinite Illite Mixed-layer mica-smectite Smectite

Si,A1 Si,A1,K,(Na,Mg,Fe) Si,A1,K,Mg,(Ca,Na,Fe) Si,A1,Mg,(Na,Ca,Fe)

Calcite Siderite Dolomite Dawsonite

Ca,CO2 Fe,CO 2 Ca,Mg,CO2 Na,A1,CO2

Apatite Crandallite series Anatase Gypsum Pyrite

Ca,P A1,Ca,P Ti Ca,S Fe,S

(Na) = minor component(s).

calcite. Magnesium and iron were taken as magnesite and hematite, respectively, and the c o n t e n t o f titanium was made equal to anatase. The m e t h o d does not estimate the amount of smectite or mixed-layer clay minerals; they are represented by the iUite norm. The calculations were handled on a programmable calculator. RELATION

BETWEEN NORMATIVE AND ACTUAL MINERAL COMPOSITION

Direct determinations of mineral assemblages in coal samples were n o t available. Consequently, all inferences concerning the relationship between mineral matter and chemical phases present in New South Wales coal seams are based on previously published sources. An account of minerals found in Australian coals and their m o d e of occurrence is given by Marshall and Tompkins (1964) and by Keme~ys and Taylor (1964). Ward (1978} studied the character and variety of mineral assemblages in a range o f Australian commercially exploited coal seams with a particular emphasis on a more detailed investigation of their clay mineral content. According to the present knowledge the most c o m m o n minerals associated with Permian coals of the S y d n e y Basin are: quartz, feldspar, calcite, dolomite, ankerite, siderite, pyrite and clay minerals. Other, seemingly rare, mineral species in New South Wales coals are: phosphates of the apatite and crandallite group, anatase, sulphates (e.g. gyp-

254

sum) and sulphides (such as chalcopyrite, sphalerite, millerite, galena). In the Greta coals and coals of the Singleton Coal Measures from the Hunter Valley, Loughnan and See (1967) and Loughnan and Goldbery (1972) reported an occurrence of dawsonite (a hydrated carbonate of sodium and aluminium). The composition of clay mineral assemblages in the coal seams studied by Ward (1978) is rather variable (see Table 3). Kaolinite is the dominant component in general. IUite never occurs in significant quantities with few exceptions (e.g. Greta, Homeville seams). However, the mixed-layer clay minerals and smectite have been recorded fairly often (Grim, cit. in Booker, 1961; Ward, 1978). In some seams, e.g. the Tongarra, Balgownie, Dudley, Victoria Tunnel and Lithgow, they form a significant proportion of the clay mineral fraction.

TABLE 3 Common minerals present in New South Wales coal seams (after Ward, 1978"; data on carbonates after Taylor, 1969) Seam

Constituents Dominant

Subordinate

Accessory

Greta

Kaolinite

Illite, quartz

Homeville

Kaolinite, quartz

Illite

Feldspars, dolomite, siderite, calcite, g y p s u m , pyrite Dolomite, siderite, calcite

Lithgow

Mixed-layer I-M ~, quartz

Kaolinite

Feldspar, anatase

Bulli

Kaolinite

Balgownie

Mixed-layer I-M

Mixed-layer I-M, quartz Kaolinite, quartz

Wongawilli Tongarra

Kaolinite, quartz Mixed-layer I-M or kaolinite

Mixed-layer I-M Mixed-layer I-M or kaolinite

Apatite, crandallite, calcite, siderite Dolomite, siderite, calcite, anatase Siderite Siderite

Wallarah Great Northern Victoria Tunnel

Kaolinite Kaolinite Mixed-layer or smectite Mixed-layer I-M or smectite Kaolinite

Quartz Mixed-layer I-M Kaolinite

Calcite Calcite, siderite Siderite

Kaolinite, illite

Feldspar, siderite

Mixed-layer I-M, quartz

Feldspar, dolomite, siderite

Dudley Borehole

*Determined in clay fraction < 2um. 1Illite-montmorillonite.

255

The degree to which norms represent the actual minerals in coals will vary with respect to the complexity of mineral associations. This variation is due chiefly to the variability in the composition of clay minerals and carbonates. Also, the allocation o f the total sodium to illite could be a source of discrepancy between the normative and actual mineral composition, especially in seams with higher sodium contents. Thus, it is conceivable that in seams with high amounts of alkalies, quartz and kaolinite may be underestimated. When the apportion of alkalies, as well as other minor components, in minerals is exactly known, the mineral norms can be easily modified and the accuracy o f the normative analysis improved. DISCUSSION

It is assumed that quartz and clay minerals, as the principal constituents of coal mineral matter, account for most of the variations in the chemical composition of HT coal ashes. So the quantitative relation between the three major normative c o m p o n e n t s viz. quartz, kaolinite and illite, was used to demonstrate differences in the chemical composition of the mineral matter in seams o f various stratigraphic positions and/or geographic areas. The results are presented in triangular diagrams (Figs. 2--7). F o r most seams the proportions o f normative quartz, kaolinite and illite are c o m m o n l y identical in each seam regardless of the proportion of other mineral phases present (e.g. carbonates).

Greta Coal Measures (Lower Permian) The difference in quartz, kaolinite, illite composition b e t w e e n the seams of the Greta Coal Measures from the t w o different areas, the Cessnock and the Muswellbrook area, is illustrated in Fig. 2. The Greta coals, generally, contain a very small a m o u n t of normative quartz and for nearly half of the samples even negative quartz values are obtained. The samples with the negative quartz values greater than 2% are n o t included in the diagram. The depletion of silicon in respect to the aluminium c o n t e n t of coal samples m a y indicate that a part o f the aluminium is present in some other form than sheet silicates. The seams of the Greta Coal Measures from the Muswellbrook area are richer in quartz in comparison to the seams from the stratigraphically higher seams of the same sequence; this is in spite of the fact that the Balmoral seam is represented b y raw coal samples.

Wittingham

Coal Measures (Lower Upper Permian; Muswellbrook area)

Variability in the normative composition o f seams o f the Wittingham Coal Measures o f the U p p e r H u n t e r Valley is rather large for all seams

256 QTZ. I00% A '0/ ~ 9° "=0 / \ ~0

ao/

~.~o

oo/O/}?:a:_ KAOL.

I0

20

30

SEAMS : • GRETA • HOMEVILLE I"1 BROUGHAM a GRASSTREES A PUXTREES a THIESS 0 BALMORAL

40

50

• • ?°0o% 60

70

80

90

ILL.

Fig. 2. Variation in normative composition of mineral matter in the Lower Permian coal seams. OTZ. 10o% A /o/ ~ 9o

~o /

~o/

V

~ ~o

.

so/

SEAMS : A MALABAR FORM X MT. 0GILVIE FORM • B U R N ~ W O O O FORM

o FO~BROOKFO"M

\• Z× \.°

~.

Z'x°"

100%

,

,

,

KAOL.

~

20

30

°

,

40

50

60

70

80

90

I00% ILL.

Fig. 3. Variation in normative composition of mineral matter in seams of the Wittingham Coal Measures, Hunter Valley. (Fig. 3). D i f f e r e n c e s in the c o m p o s i t i o n b e t w e e n seams o f various stratigraphic levels are subtle, suggesting t h a t the original c o m p o s i t i o n o f mineral m a t t e r in coals o f t h e w h o l e s e q u e n c e is s o m e w h a t m o n o t o n o u s .

Illawarra and Newcastle Coal Measures (Upper Permian) T h e m o s t effective separation o f the seams, based o n n o r m a t i v e mineral analyses, is o b t a i n e d f o r t h e seams o f t h e Western Coalfield. T h e

257

K a t o o m b a , Lithgow, and the Ulan seams plot in different parts of the triangular diagram (Fig. 4). This points to rather significant differences in the composition of original mineral matter assemblages occurring in these coals. Unfortunately, other seams developed within the stratigraphic sequence in this Coalfield, the Wolgan and the Middle River seams, are not sufficiently represented by data; however, their isolated plots indicate that the mineral matter is quartz- and illite-rich. QTZ.

SEAMS

100%

O r] • ~ (I

A /o , , / ~ , . e o / \ _ ~-o / ~ t'~

~o/

.

:

KATOOMBA MIDDLE RIVER WOLGAN UTHGOW ULAN

~,Io

.

.

-

•

iOO% KAOL

I

, I0

, 20

, 50

, 40

, 50

, 60

, 70

, 80

, .'* 90

i00O/o ILL.

Fig. 4. Variation in normative composition of mineral matter in the Illawarra Coal Measures coals, Western Coalfield.

The seams of the Southern Coalfield also show a good separation with some overlap (Fig. 5). Whereas the samples of the Bulli coals plot in an area close to the kaolinite apex and along the kaolinite-illite tie line, the samples of the Wongawilli seam cluster in the area adjacent to the midpoint o f the kaolinite-quartz tie line. A small number of the Bulli seam samples gave negative quartz values, some larger than 2% and these, as in the case of the Greta coals, are n o t plotted in the diagram. The composition of mineral matter in the Tongarra seam lies somewhat between that of the Bulli and the Wongawilli seams. The plots of the Balgownie coal samples suggest that the dominant constituent in these coals are clay minerals represented b y normative illite. The normative composition of HT coal ashes of the Newcastle Coal Measures is demonstrated in Figs. 6 and 7. The data points, representing the lower part o f the Newcastle sequence, cluster in an area limited by the kaolinite and illite apices and b y a line drawn from the kaolinite apex to the mid-point of the quartz-illite tie line (Fig. 6).

258

OTZ.

SEAMS :

~00%

0

~o!

\~°

•o / ~ % , ~

iooo/o KAOL.

~

,,,~--,~:----,-,-, I0 20 30 40

F i g . 5. V a r i a t i o n Coalfield.

\.o

~o/

KAOL

V "

,

I0

20

~ iooO/o ILL

90

OTZ.

SEAMS:

I00%

& DUDLEY 0 YOUNG W A L L S E N D

~°

• BOREHOLE

~° ~° o oo

":'; ,

,

30

40

~o

--

_ o..:

,

. 80

in normative composition o f m i n e r a l matter in seams of the Southern

~o/ ~o/

100%

. . . 60 70

50

/o 7 / / ~

,o/

BULLI

~ 50

\,°

\°

,

,

,

,

60

70

80

90

~ 100% ILL.

Fig. 6. Variation in normative c o m p o s i t i o n o f mineral matter in coal seams from the basal part of t h e N e w c a s t l e Coal Measures sequence.

The plot area for the stratigraphically higher seams in this sequence is similar, but, there is a greater dispersion o f data above the kaolinite apex and quartz-illite mid-point tie line (Fig. 7). The general trend of the plotted data for the Newcastle Coalfield indicates stratigraphically significant changes in the composition of mineral matter. The same conclusion is valid for the Illawarra Coal Measures in both the Western and the Southern Coalfiels. In the Newcastle Coalfield

259

these changes are gradual in the vertical direction, at least for the part of the stratigraphic sequence which is represented by the data; however, in seams deposited in the shelf environment (Western and Southern Coalfields), they axe relatively abrupt. In the Newcastle Coalfield the composition of clay minerals changes upward, from assemblages which are kaolinite-rich (Borehole Seam) to kaolinite-poor and expandable mineral-rich (Victoria Tunnel Seam) and again to kalinite-rich (Wallarah Seam) at the top of the sequence. QTZ. ioo% A IO , / ~ ojO eO/ '~t, 0

~'o/ ,'o/

SEAMS ; 0 WALLARAH , GREAT NORTHERN E] FASSIFERN A VICTORIA TUNNEL

,~o ',k~o

•o / o A ' ~ " Z _ ' ^ ~

\ ~o

O/o 100% L... KAOL.

,

,

,

I0

20

30

,

40

,

,

,

50

60

70

\,o

,

80

a

~'

90

100% ILL.

7. Variation in normative composition of mineral matter in seams from the middle and the upper part of the Newcastle Coal Measures sequence.

Fig.

SEAMS :

SEAMS :

A KATOOMBA 13 WOLGAN o LITHGOW

X Si 13 I00% • Z~

Si I00%

SEAMS:

BULLI BALGOWNIE Si WONGAWILLI Io0% TONGARRA

~o

eo/

~ ~o

~ ° / 2 ~_

.o.~ I0

,

,

20

30

• o O &

WALLARAH GREAT NORTHERN FASSlFERN VICTORIA TUNNEL

+

BOREHOLE

~o

"C/

°

. . . . . . . . I0

20

30

I0

20

30

~o 40

50

60

7% ~ ( Ti, Fe, etc. )

% F i g ° 8. Variation in chemical composition of mineral matter in seams of the Upper Permian Coal Measures. Based on cationic proportions ( % ) .

260 The results obtained suggest that the normative analysis has more discriminative power than the direct plots of oxides or cationic proportions. To compare both methods, variation diagrams based on the three-component system of Si, A1 and the sum of the rest of the elements are given in Fig. 8. CONCLUSIONS The normative analysis seems to be a suitable m e t h o d for the comparison of bulk - chemical composition of mineral matter in coal seams. In ideal cases it may be also a reasonably good semi-quantitative measure of actual mineral assemblages present in coals. There are a lot o f assumptions, however. The nature of clay mineral content in coals is believed to be a major reason for chemical dissimilarities found between seams of various stratigraphic levels and/or geographic areas. The occurrence of kaolinite and/or mixed-layer mica-smectite and/or smectite-rich clay-mineral assemblages previously identified in the Permian coal seams of the Sydney Basin is also suggested by the results of the normative analysis. Each seam shows a characteristic composition of clay minerals, i.e., in some seams kaolinite, in others expandable clay minerals may be dominant. The vertical distribution of these constituents has stratigraphic significance. Within the Upper Permian Illawarra and the Newcastle Coal Measures sequence a trend from kaolinite-rich to kaolinite-poor and expandable clay-minerals-rich and again to kaolinite-rich assemblages can be observed from the b o t t o m to the top. In the Newcastle Coalfield these upward changes in clay mineral composition are gradual. This may indicate that in the late Permian the sedimentation in the trough environment was continuous whereas in the shelf area it was more episodic in nature. The vertical trends in clay mineral composition of the Upper Permian coal seams are interpreted to reflect the changes in geochemical conditions of the coal-forming environment which occurred as the sedimentation in the basin progressed with time. All significant variations in the clay-mineral assemblages could relate to long-term changes in provenance and/or weathering and/or physiographic conditions. Superimposed on these was a general, and in the trough, rather rapid subsidence followed by an uplift. This was accompanied by a strong volcanic activity which is demonstrated by thick accumulations of volcanoclastic debris in the Newcastle Coal Measures sequence. There, the occurrence of expandable clay minerals is associated with volcanic material which under rapid subsidence did not undergo intensive leaching. On the other hand, the formation of kaolinite, even if the same source is considered, is promoted by slow subsidence or relative tectonic stability, along with intensive leaching which may be enhanced by climate conditions.

261 ACKNOWLEDGEMENTS

The author appreciates the assistance of the Joint Coal Board with the preparation of the paper. Thanks are due to Miss D. Peters w h o drew the pictures and to Mrs. L. Ciantar w h o typed the manuscript. I am grateful to one of the anonymous reviewers for constructive comments on the manuscript.

REFERENCES Australian Black Coals, 1979 (Rev. ed.). Joint Coal Board and Queensland Coal Board, Sydney, N.S.W., 48 pp. Australian Black Coals, Survey of Conversion Potential, 1981 (Rev. ed.). Joint Coal Board and Queensland Coal Board, Sydney, N.S.W., 32 pp. Booker, F.W., 1961. Studies in Permian Sedimentation in the Sydney Basin. Dept. of Mines, N.S.W., 53 pp. Brown, H.R., Clark, M.C. and Durie, R.A., 1959. Characteristics of the ashes from Australian Coals. Coal Research, C.S.I.R.O., N.S.W. Australia. Ref. T.C., 33: 1--10. Brown, H.R., Durie, R.A. and Schafer, H.N.S., 1960. The Inorganic Constituents in Australian Coals. If. Combined acid-digestion--low-temperature Oxidation Procedure for Determination of Total Mineral Matter Content, Water of Hydratation of Siliacte Minerals and Composition of Carbonate Minerals. Fuel (London), 39: 59--70. Diessel, C.F.K., 1970. Paralic coal seams formation. Inst. of Fuel, Aust. M e m b . Conference, Brisbane, Paper, 14: 1--21. Given, P.H., Weldon, D. and Suhr, N., 1981. Investigation of the distribution of minerals in coals by normative analysis. Pennsylvania State University Technical Rep. 2L (Coal Research Scn., Dept. Mater. Sci. Eng.), 27 pp. Grim, Q.E., Bray, R.H. and Bradley, W.F., 1937. The mica in argillaceous sediments. A m . Mineral., 22: 813--829. Imbrie, J. and Poldervaart, A., 1959. Mineral composition calculated from chemical analyses of sedimentary rocks. J. Sediment. Petrol., 29: 588--595. Keme~ys, M. and Taylor, G.H., 1964. Occurrence and distribution of minerals in some Australian coals. Fuel (London), 27(284): 389--397. Loughnan, F.C. and Goldbery, R., 1972. Dawsonite and analcite in the Singleton Coal Measures of the Sydney Basin. A m . Mineral., 57: 1437--1447. Loughnan, F.C. and See, G.T., 1967. Dawsonite in the Greta Coal Measures at Muswellbrook, N e w South Wales. Am. Mineral., 52: 1216--1219. Marshall, C.E. and Tompkins, D.K., 1964. Mineral Matter in Permian Coal Seams. Inorganic Constituents in Fuel, Symposium, Melbourne, Paper No. 4, pp. 57--69. Mietseh, A.T., 1962. Computing mineral composition of sedimentary rocks from chemical analyses. J. Sediment. Petrol., 32: 217--225. Nicholls, G.D., 1962. A scheme for recalculating the chemical analyses of argillaceous rocks for comparative purposes. A m . Mineral., 47: 34--46. Pearson, M.J., 1978. Quantitative clay mineralogical analyses from the bulk chemistry of sedimentary rocks. Clays Clay Miner., 26: 423--433. Pollack, S., 1979. Estimating mineral matter in coals from its major inorganic elements. Fuel, 58: 76--78. Slansky, J.M., 1983. Distribution of inorganic chemical elements in coals seams of the Sydney Basin, N e w South Wales, Australia: A statistical study. Xth International Congress of Carboniferous Stratigraphy and Geology, Madrid, 12--17 September, 1983 (Abstr.).

262 Taylor, F.G., 1969. Dolomite identified in some N.S.W. coals. Coal Res. in CSIRO, 38: 2--3. Ward, C.R., 1978. Mineral Matter in Australian Bituminous Coals. Proc. Australas. Inst. Min. MetaU., 267: 7--25. Weaver, C.E. and Pollard, L.D., 1973. The chemistry of Clay Minerals. Elsevier, Amsterdam.