Mineralogy and chemistry over a cycle of oil shale deposition in the Brick Kiln Member, Rundle deposit, Queensland, Australia

Chemical Geology, 68 (1988) 207-219 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

207

[3]

MINERALOGY AND CHEMISTRY OVER A CYCLE OF OIL SHALE DEPOSITION IN THE BRICK KILN MEMBER, RUNDLE DEPOSIT, QUEENSLAND, AUSTRALIA J.H. P A T T E R S O N Lucas Heights Research Laboratories, Division of Fuel Technology, CSIRO, Menai, N.S. W. 2234 (Australia) (Received May 27, 1987; revised and accepted January 19, 1988)

Abstract Patterson, J.H., 1988. Mineralogy and chemistry over a cycle ofoil shale deposition in the Brick Kiln Member, Rundle deposit, Queensland, Australia. Chem. Geol., 68: 207-219. Chemical and semi-quantitative mineralogical analyses have been made for ore type samples over a typical cycle of oil shale deposition within the Brick Kiln Member, Rundle oil shale deposit. The geochemistry and mineralogy were similar throughout with differences mainly following oil shale grade rather than ore type. The main minerals included montmorillonite, quartz, feldspars, calcite, magnesian siderite and pyrite. Trace-element abundances were similar to those for an average shale. All samples were analyzed for a comprehensive range of major and trace elements. Correlation techniques, selective leaching procedures, X-ray diffractometry and electron microprobe analyses were used to establish geochemical associations and specific mineralogical residences for elements important in processing and waste disposal. S, As and Ni are mainly associated with pyrite and to a lesser extent with the kerogen. Mn occurs in the carbonate minerals calcite and magnesian siderite. The chemical composition of magnesian siderite differed in some samples and warrants more study as a possible indicator of depositional or diagenetic environments.

1. I n t r o d u c t i o n

The Tertiary oil shale deposits of eastern Queensland, Australia, comprise an important future source of alternative liquid fuels. In situ resources total 22.109 bbl* of oil in seven of these deposits (Moore et al., 1986). Condor, Rundle, Stuart, Nagoorin and Duaringa are the major deposits. Chemical and mineralogical characterization of these oil shales is important for selection of suitable processing technology and waste disposal methods. The present work "1 bbl= 1 barrel = 0.1590 m ~.

0009-2541/88/$03.50

on the Rundle deposit forms part of a series of mineralogical and trace-element characterization studies on the major Australian oil shale deposits. Results for oil shales from Julia Creek (Patterson et al., 1986) and Condor deposits (Patterson et al., 1988) have already been reported. The Rundle deposit occurs within The Narrows Graben ~ 15 km NW of Gladstone on the coast of Queensland, Australia. The geology, stratigraphy and extent of the resource have been described elsewhere (Lindner and Dixon, 1976; Henstridge and Missen, 1982; Henstridge and Coshell, 1984). The Rundle Formation

© 1988 Elsevier Science Publishers B.V.

208

comprises eight members: Kerosene Creek, Telegraph Creek, Munduran Creek, Humpy Creek, Brick Kiln, Ramsay Crossing, Teningie Creek and Monte Cristo, in order of increasing stratigraphic depth. The members, are part of a sequence of early Tertiary sediments and contain in excess of 5-109 bbl of shale oil (Henstridge and Coshell, 1984). The Brick Kiln Member, examined in the present work, is the thickest of the members and comprises up to 150 m of oil shale with minor interbeds of claystone and carbonaceous oil shale. It is one of the more favoured initial mining targets, especially for larger-scale operations. Rundle oil shales are considered to have been deposited in a freshwater lacustrine environment (Henstridge and Missen, 1982). All members, within the Rundle Formation show prominent cycles of oil shale deposition which can be correlated throughout the deposit and probably throughout The Narrows Graben itself. According to Coshell (1983), a typical depositional cycle in the Ramsay Crossing and Brick Kiln Members comprises an initial period when multiple transgressive and regressive events cause lake deposited sediments to be reworked by wave action and brecciated from subaerial exposure (ephemeral lacustrine or mud flat environment). The start of each transgressive event often shows a transported layer of coally plant material with gastropods. More permanent water is gradually established (very shallow lacustrine) with occasional regressive fluctuations until a deeper lake is fully established (shallow lacustrine conditions). This is abruptly followed by a long period of subaerial exposure (from transitional pedogenic to pedogenic environments) before again returning to the mud flat environment. Thus cycles are commonly observed which begin with brecciated oil shale (ore type 4), then grade into laminated oil shale (ore type 1 ) exhibiting syneresis cracks which are overlain by mottled clayey oil shale (ore type 5) grading upwards into claystone (ore type 6). One such cycle (see

Table II and Fig. 1 ) has been examined in the present study. Eight major ore types have been recognized throughout the deposit and described by Coshell (1983, 1984): Ore type

Lithology

1 2 3 4 5 6 7 8

laminated oil shale moderately laminated oil shale slightly laminated oil shale brecciated oil shale clayey oil shale claystone lignite dolomite

Individual ore types are often < 1 m thick and occur in different proportions in the various members. The four major ore types within the deposit are types 1, 4, 5 and 6 and the present work has concentrated on these major ore types. As the ore types are considered to be related to depositional environments (see Table I), the many changes in ore type, often in a cyclic pattern, reflect numerous changes in depositional environments over time. Each ore type is further subdivided on the basis of structural and sedimentological criteria (Coshell, 1984) but this is outside the scope of the present work. The general mineralogy of Rundle oil shales has been reported elsewhere (Henstridge and Missen, 1982; Coshell, 1983; Coshell and Loughnan, 1986). Montmorillonite-type clays and quartz predominate throughout and from a processing viewpoint, kaolinite, calcite, pyrite and siderite are the most important of the minor minerals. Lindner (1983) has compared the geology and geochemistry of the deposit with the other Tertiary oil shales in Queensland. Hutton (1985) has described the organic petrography of the deposit. Our earlier chemical analyses (Patterson et al., 1987) have established elemental abundance levels and indicated that As and Mn are the elements of greatest concern in processing. Abundance data for Rundle oil shale, including some elements not covered in this study, have been compared with those for other Australian oil shales ( Dale

209

and Fardy, 1986). The present work provides a more detailed study of the inorganic geochemistry over a typical cycle of oil shale deposition within the Brick Kiln Member.

2. E x p e r i m e n t a l The general procedures used for chemical analyses, inter-element correlations, selective leaching and scanning electron microprobe (SEM) studies were as previously described (Patterson et al., 1986, 1987). Further experimental aspects are given below.

2. I. Samples This work was carried out on four ore type composite samples from bore hole ERD 324 (Table I) and 15 core samples from bore hole ERD 325, 144.85-151.36 m (Table II). These samples cover the major ore types found throughout the Rundle deposit and cover one typical cycle of high-grade oil shale deposition at the base of the Brick Kiln Member. The more detailed sub-ore type classifications are given in Table II for reference.

2.2. Chemical analyses Organic carbon was obtained by difference between total carbon determined by the combustion method (LECO ® analyser) and inorganic carbon determined gravimetrically by reaction with hydrochloric acid [Australian Standard 1038 (1971)]. Total S was determined as described by Udaja et al. (1984). The dried shale samples were analyzed by instrumental neutron activation analysis for a comprehensive range of major and trace elements. Si was analyzed using inductively-coupled atomic emission spectrometry and Cu, Ni and Zn by X-ray fluorescence spectrometry on pressed powders. Analytical methods were checked for accuracy by analysis of the U.S. Geological Survey, Green River Shale SGR-1 and Cody Shale SCo-1 standard samples.

2.3. Correlation techniques The chemical and mineralogical data for the 15 core samples were evaluated statistically. Correlation coefficients were determined between all component pairs, and the matrix of these correlation coefficients was then used in

TABLE I Description of bulk ore type samples from the Brick Kiln Member, drill hole ERD

3 2 4 .1

Ore type

Oil yield ( l t - 1 ) .2

Lithology

Depositional environment

1

166

laminated oil shale

shallow lacustrine; fresh-water lake containing abundant algae and fine-grained clastic sediments

4

125

brecciated oil shale

ephemeral lacustrine (mud flat) ; transgressive and regressive movements of the lake edge cause desiccation and reworking of previously deposited lake sediments

5

84

clayey oil shale

ephemeral lacustrine to transitional pedogenic; prolonged periods of subaerial exposure with incipient pedogenesis of previously deposited lake sediments

6

31

claystone

transitional pedogenic; very prolonged periods of subaerial exposure with pedogenesis of previously deposited lake sediments

"~Descriptions from Coshell (1983) and Wilcock and McIver (1986). "~1 t = 1 metric tonne= 103 kg.

210 TABLE II Description of ore type samples from Brick Kiln Member, drill hole ERD 325 Sample No.

Depth (m)

Sub-ore type

Lithology

Organic C (%)

34988 34989 34990 34992 34993 34994 34995 34996 34997 34998 34999 35000 35041 35042 35044

144.85-145.03 145.03-145.37 145.37-146.00 146.00-146.52 146.52-146.72 146.72-147.70 147.70-148.14 148.14-148.32 148.32-148.72 148.72 - 149.19 149.19 - 149.70 149.70-149.98 149.98-150.37 150.37-150.98 150.98-151.36

4.2 4.2 4.2 4.2 6.3

brecciated oil shale brecciated oil shale brecciated oil shale brecciated oil shale claystone clayey oil shale claystone claystone clayey oil shale laminated oil shale brecciated oil shale brecciated oil shale brecciated oil shale brecciated oil shale moderately laminated oil shale

14.1 19.3 20.1 18.6 6.8 7.8 5.5 5.6 7.3 12.7 16.5 15.3 19.0 16.0 8.9

5.1 6.2 6.2 5.2

1.1 4.1 4.I 4.2 4.2 2.2

hierarchical cluster analysis programs in order to identify element and mineral associations.

2.4. Selective leaching procedures

The procedures described by Patterson et al. (1986) were adapted to suit the mineralogy of Rundle shales. The sequential leaching scheme included the following steps:

2.5. Scanning electron microprobe analyses A Cameca ® Camebax scanning electron microprobe equipped for both energy- and wavelength-dispersive analyses was used to identify trace minerals and to analyse the carbonate minerals and pyrite for trace elements. Chip samples from the four bulk ore type samples (Table I) were prepared as polished sections for analysis.

2.6. Mineralogical studies Step 1: Dissolution of calcite at 20°C in sodium acetate-acetic acid at pH 5. Step 2: Dissolution of siderite (and dolomite when present) in 1 M H C l a t 60°C. Step 3: Dissolution of sulphides using ascorbic acid in dilute H~02. Step 4: Dissolution of silicate minerals using HCI-HF.

Chemical analyses of the leached residues from each step allowed element distributions to be calculated between the geochemical groupings, carbonate-calcite, carbonate-siderite, sulphide, silicate and organics, respectively. A separate water leach at room temperature was used to determine water solubles which report to the carbonate-calcite group.

Minerals were identified using X-ray diffractometry (XRD). Diffraction peak heights, uncorrected for matrix effects, were used to make semi-quantitative measurements of the amounts of quartz, montmorillonite, magnesian siderite, calcite, feldspar and pyrite. Difw fraction peaks at 4.27, 4.5, 2.8, 3.03, 3.2 and 2.71 were used respectively. Mineralogical estimates were made for the bulk ore type samples using the chemical analyses, selective leaching and XRD results. Chemical compositions for Mg siderite and calcite were determined by microprobe analyses and that of montmorillonite was provided by Esso Australia Ltd. Because a

211

number of reasonable assumptions had to be made in allocation of silica and alumina to the various minerals, the final mineralogical compositions can only be considered as semi-quantitative and the accuracy is somewhat uncertain. The bulk ore type samples were then used to calibrate the XRD peak height data for the core samples. The results were confirmed by good correlations with the relevant major-element analyses and are useful for relative comparisons between the samples. 3. R e s u l t s a n d d i s c u s s i o n

3.1. Chemical analyses Chemical compositions of the ore type composites are given for both major and trace elements in Table III. The results are within expected concentration ranges for the deposit (Patterson et al., 1987). Several major inorganic elements tend to decrease as oil shale grade increases. Only a few elements follow organic C content including H, N, and S. As previously reported the S content is mainly comprised of pyritic S for Rundle oil shales ( Patterson et al., 1987) and tends to follow organic C content. There is also a tendency for CaO, C02 and associated trace elements Mn and Sr to remain constant or to increase slightly, with organic C content. This reflects the distribution of ostracodes within the sediments. Other trace elements are for practical purposes independent of ore type and their abundances are similar or less than those for an average shale (Turekian and Wedepohl, 1961 ) with the exception of S, reflecting pyrite contents, and C1 which reflects the salt content of formation and pore waters. S, As and Mn contents which can cause concern elsewhere in the deposit ( Patterson et al., 1987 ) are relatively low in the Brick Kiln Member. The chemical analyses for the 15 core samples are somewhat more variable, particularly in relation to CaO, MgO, FeO and C02, and associated trace elements Mn and Sr. Concentra-

tion depth profiles over the cycle of oil shale deposition are shown for selected minerals and associated elements in Fig. 1. Again, the generally inverse relationship is evident between organic C (and hence oil yield) and the silicate minerals and related elements. This could reflect either a variation in clastic input over the depositional cycle or a concentration effect due to oxidation and loss of organic material during prolonged periods of subaerial exposure ( Coshell, 1983; Wilcock and McIver, 1986). For the Rundle deposit, regular trends in montmorillonite, quartz and feldspar contents have been found with increasing stratigraphic depth, reflecting the provenance rather than diagenesis of the sediments (Coshell and Loughnan, 1986). Within an individual oil shale cycle, changes in the rate of clastic input are probably less likely and Coshell (1983) and Wilcock and McIver (1986) have suggested that most claystones have formed through prolonged desiccation, subaerial oxidation of organic material and pedogenesis of previously deposited oil shale sediments. Some claystones are considered to arise both from increased clastic input and pedogenic processes. The present mineralogical and chemical studies are insufficient to distinguish between such ore types. Coshell and Loughnan (1986) have examined many more samples and also found no consistent relationship between mineralogy and ore type. Trace elements can be important in oil refining and waste disposal. Associations of As and Ni with S, of Mn with FeO and CO2 and of Sr with CaO and CO2 (Fig. 1) are as previously reported for the deposit as a whole (Patterson et al., 1987). However, the tendency for S (mainly pyritic S) to follow organic C content was less evident, with several samples at the top and bottom clearly not following this trend ( Fig. 1). This probably arises from changes in S availability during diagenesis of the sediments. Variability in carbonate-related elements reflects on the environment during formation and diagenesis. Coshell and Loughnan (1986) have reported the general trend for carbonate min-

212

T A B L E III

Chemical and mineralogical analyses of ore types 1, 4, 5 and 6 from the Brick Kiln Member Major components (wt.%)

Trace elements ( mg kg- 1)

1

4

5

6

SiO2 A120:~ Fe* FeO MgO CaO Na20 KeO TiO~ PO4 CO2 S C,,~ H N

37.4 10.4 1.0 3.8 1.7 5.3 0.8 1.0 0.5 0.3 4.9 1.2 19.9 2.8 0.6

44.7 10.5 0.8 4.1 2.3 4.3 0.9 1.2 0.6 0.3 4.4 0.9 15.6 2.3 0.6

48.6 12.2 0.5 4.4 2.4 3.3 1.0 1.3 0.7 0.2 3.4 0.5 10.1 1.7 0.5

56.1 12.4 0.3 5.0 2.4 3.8 1.0 1.6 0.8 0.3 3.6 0.3 4.3 1.0 0.4

Ker Mon Qua Fel Kao Ill Cal Sid Pyr

25 30 15 5 5 5 5 5 2

22 30 20 5 5 5 5 5 1.5

15 40 20 5 5 5 2 5 1

5 45 25 5 2 10 3 5 0.5

C1 Sc V Cr Mn Co Ni Cu Zn Ga As Se Br Rb Sr Cs Ba La Ce Nd Sm Eu Tb Yb Lu Hf Ta Th U

1

4

5

6

1,300 11 80 45 830 18 35 20 65 9 9 1 10 60 300 3.5 290 15 28 10 3 0.8 0.5 2 0.3 2.5 0.5 4.4 1.8

1,280 12 80 48 865 19 55 15 65

1,080 12 90 65 550 19 45 30 75 15 10 1 5 70 270 3.9 280 17 32 13 3.3 0.7 0.4 1.8 0.3 2.9 0.5 5 2

1,120 13 85 68 600 15 35 30 80 13 5 1 5 95 220 3.8 280 18 34 15 3.5 0.8 0.5 2.2 0.4 2.9 0.4 5.3 1.5

10 1 7 70 250 3 275 15 29 3.5 0.7 0.5 1.9 0.3 2.4 0.3 4.3 2

Codes: Ker = kerogen; M o n = montmorillonite; Qua = quartz; Fel = feldspar; Kao = kaolinite; Ill = illite; Cal = calcite; Sid = magnesian siderite; Pyr = pyrite. *Fe calculated on the basis that total S occurs as pyrite and the remainder of total Fe should be expressed as FeO.

erals to increase progressively with increasing stratigraphic depth of the various oil shale members. The present results show weak tendencies for Mg-siderite and calcite to concentrate in the higher-grade sections, whereas dolomite was only detected in the lower-grade ore types 5 and 6 (Fig. 1). This suggests that sections of these sediments have been desiccated during diageneSis, as dolomite is commonly considered to be formed by crystallization from carbonate solutions during

periods of desiccation (Freytet, 1973). The relatively low pyrite contents in this zone ( Fig. 1 ) could also be explained by oxidation during desiccation and/or later subaerial exposure. Indeed, oxidation of sulphides may have yielded sulphuric acid for remobilization of calcite and Mg-siderite formed earlier in diagenesis. This could have provided suitable solutions for secondary crystallization of the observed thin and massive layers of essentially pure dolomite or ferroan dolomite.

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3.2. Mineralogical analyses The chemical variations discussed above reflect changes in distribution of the major mineral components identified by previous workers (Coshell, 1983; Coshell and Loughnan, 1986), i.e. montmorillonite, quartz, kerogen, calcite, siderite and pyrite. The present work reveals that the siderite should really be termed magnesian siderite (Section 3.5). Montmorillonite, quartz and even feldspar contents correlate well with A1203 content and are inversely related to kerogen content (Fig. 1 ). Variations in the carbonate minerals correlate well with

analyses for CaO, FeO and associated trace elements (Fig. 1 ). Minor minerals identified from our XRD results and those of the above-mentioned workers include illite, kaolinite, feldspars, dolomite, cristobalite, anatase, apatite, gypsum and halite.

3.3. Correlation studies and cluster analyses All samples from drill hole ERD 325 (Table II) were used in the statistical evaluations. The chemical data and the semi-quantitative mineralogical compositions were used to calculate linear correlation coefficients between all min-

214

eral-mineral, mineral-element and element-element pairs. None of the minerals or inorganic elements correlated significantly with organic C and hence the previously observed tendency for pyrite and related elements to follow oil shale grade (Patterson et al., 1987) was not maintained over this individual cycle of oil shale formation. This is not surprising and most probably reflects low S availability during diagenesis. Indeed the relatively low pyrite contents of the Brick Kiln Member relative to the stratigraphically younger members is somewhat of a processing advantage. The silicate minerals montmorillonite, quartz and feldspar correlate positively with themselves and negatively with organic C (Fig. 1). This is consistent with the detrital and provenance related origin reported for these minerals by Coshell and Loughnan (1986). Indeed, changes in the relative amounts of kerogen and clastic materials account for the observed variability of most of the major and trace elements. However, these elements are of little concern and from a processing and environmental viewpoint there is more interest in those elements which are related to the distribution of the minor carbonate minerals and pyrite. Significant correlations found for these minerals and trace elements are given in Table IV. The results are similar to those for the deposit as a whole (Patterson et al., 1987) excepting that correlations for As with S ( r = + 0 . 5 1 ) and pyrite (r= + 0.37) are not as strong as previously observed. The cluster diagram (Fig. 2) further illustrates the correlations discussed above and suggests the following geochemical associations for minor and trace elements: Sulphide Carbonate -siderite Carbonate-calcite Alumino-silicate Rare earths

Ni, As Fe, Mn, Mg Sr Na, K, Ti, V, Cu, Zn, Cs, Hf, Th La, Ce, Nd, Sm, Eu, Tb, Yb, Lu

Although the cluster diagram shows a clear distinction between the two carbonate groups,

this only reflects dominance of Mg-siderite and calcite over dolomite in the particular section. The elements involved can and do substitute in all of the carbonate minerals to some extent. The general geochemical association of many elements with alumino-silicates is enhanced by dilution of the clastic components with either kerogen and/or the carbonate minerals. Further studies would be needed to obtain more specific mineralogical residences.

3.4. Selective leaching Geochemical relationships between the elements were confirmed by the selective leaching results on the bulk samples. Results proved essentially similar for the higher-grade ore types 1 and 4 and differed only slightly for the other ore types. This further confirms the geochemical similarity of the major ore types. Semiquantitative estimates of the proportions of each element associated with the various geochemical groups are shown for ore type l in Table V. Ore types 5 and 6 contained increased proportions of Fe and Mg (55-60%) in the silicate group, reflecting the increased amounts of montmorillonite relative to Mg-siderite (Table III). Although XRD results on the leached residues confirmed complete dissolution it was difficult to be certain of selectivity between the carbonate minerals and during hydrochloric acid leaching (Patterson et al., 1987). Accordingly it is considered that most of the As, Ni and Co allocated to the carbonate groups should be allocated to the sulphide group (Table V). The residual kerogen contained 2.3% ash and it is uncertain if any trace elements other than As and Ni, are organically associated. Traces of anatase, residual minerals or fluorides precipitated during demineralization, most likely account for the Ti and Cr. Most of the Ca and Sr was associated with calcite, while Mg and Mn are rather equally associated with calcite and

215

T A B L E IV Positive correlation coefficients b e t w e e n m i n e r a l a n d e l e m e n t pairs (at 99% confidence level) Pyrite Pyrite S As Ni

S

As

Ni

0.87 -

0.37 .1 0.51 "1

0.68 0.74 0.53 *~ .

Calcite

.

Calcite CaO Sr

CaO

Sr

Siderite

FeO

-

-

.

. 0.67 0.82 -

l -

-~ 0.55 "~ -

l

0.81 -

0.77

Siderite FeO MgO COx Mn

MgO

COx

Mn

0.55 "~ 0.74

0.69 0.87 0.57 *~

0.56 *~ 0.75

0.77 0.81

0.75 0.83 0.93

0.84 0.88 0.93 0.96

-

*1At < 95% confidence level; *~at 95% confidence level.

Mg-siderite (Table V). Water solubles were as expected from dissolution of small amounts of halite arising from the saline formation and pore waters. Soxhlet extractions of ore type I with chloroform and then methanol extracted significant proportions of total As (3%), Ni (0.6%) and Co (1.4%), confirming some association with organics. The following chemical associations were indicated from the leaching results: W a t e r solubles Carbonatelcalcite Carbonate-siderite Sulphide Alumino-silicate Organics

Na, C1, B r Ca, Mg, Mn, Sr Fe, Mg, M n As, Ni, Co, Cu, Zn Na, Mg, A1, K, Ti, V, Cr, Fe, Cs As, Ni, Co?

Nickel porphyrins have been identified in solvent extracts from our Rundle ore type samples using UV-visible spectroscopy (C.J.R. Fookes, unpublished data, 1987). Organo-arsenic compounds have previously been reported in Green River oil shales (Fish et al., 1983) and nickel porphyrins have been previously identified in other Queensland oil shales from Julia Creek (Fookes, 1983) and the Condor deposit (A. Ekstrom, H.J. Loeh and C.J.R. Fookes, unpublished data, 1982 ).

3.5. Scanning electron microprobe (SEM) analyses The four composite samples were examined to identify trace minerals and to define the mineralogical residences of trace elements significant in processing. Trace minerals which were identified included K-feldspar, albite, biotite, apatite, anatase, zircon, ilmenite and galena. The latter four minerals can reasonably account for the P, Ti, Zr, and Pb present in the oil shale. However, attempts to find sphalerite and chalcopyrite to account for Zn and Cu contents proved unsuccessful. Wavelength-dispersive X-ray spectra were used to analyse pyrite and the carbonate minerals which are of particular environmental interest in processing and spent shale disposal. Pyrite was observed mainly in two forms, as framboids up to 20/~m in diameter and as euhedral grains up to 5-10 pm in size. The relative proportions of framboidal and euhedral forms is environmentally important ( Caruccio, 1975 ) but is difficult to judge from so few samples. Pyrite content ranged up to 2 wt.% in some samples (Table III; Fig. 1) and is relatively low in the Brick Kiln Member (Coshell and Loughnan, 1986). Microprobe analyses of framboids

216

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Fig. 2. Cluster diagram - Brick Kiln Member, Rundle deposit. H a t c h e d and euhedral pyrites showed variable concentrations of As and Ni. The euhedral pyrites were too small for good analyses but appeared similar to framboids. For framboids, As ranged up to 1500/2g g - 1 and averaged 400/2g g - z, whereas Ni ranged up to 1000/2g g-Z and averaged 300 /xg g-1. These results can account for ~ 75% of the As but < 20% of the Ni in the oil shales. The results are comparable to those for Condor oil shale (Patterson et al., 1988) except that Co, Cu and Zn were not detected. Kerogen typically occurs as thin laminae < 10

-0.4

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-0.6

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highlight significant clusters.

/xm in thickness and probe analyses were never fully free of Fe and matrix elements. However, S contents ( ~ 1% ) were well in excess of those which could be accounted for as pyritic S associated with the measured Fe contents. This confirms the presence of organic S as previously reported for demineralized kerogens (Lindner, 1983 ). Trace elements As, Ni and Co were not detected in kerogen areas but this is not surprizing since limits of detection were inadequate. Calcite in Rundle oil shales occurs mainly as

217 TABLE

V

Geochemical

distribution

Element

of elements from selective leaching experiments

% of element in geochemical group* water

carbonate-

carbonate-

solubles

calcite

siderite

Na

50

10

Mg A1

-

25

C1 K

90 -

10

Ca

-

90

Ti

-

V

sulphide

silicate

35 5 < 5 5

5

35

2

35 90

4 -

85

-

< 5 <3

organics

<3

-

2

85

14

5

5

90

Cr

-

5

15

70

9

Mn Fe

-

40 2

55 45

10

5 40

< 1 1

15

55

25

4

35

5

4O

18

20

60

Co Ni

-

Cu

-

Zn

-

10

As

-

< 5

Br Sr

75

Cs

100 5

55 35 -

15 -

25

3 -

15 -

20

-

20 -

70

7

*Figures for the organic group are from residual kerogen analyses, the others are by difference and the carbonate-siderite, sulphide and silicate groups are by successive differences.

ostracode fragments and microprobe analyses show only low levels of MgO (0.4-1.2%), MnO (0.3-0.4%), FeO (0.4-1.7%) and SrO (0.25%). Sr levels are sufficient to account for all the Sr in the oil shale and therefore confirm the results from cluster analyses and selective leaching. Small amounts of dolomite were identified over the low-grade section of bore hole ERD 325 (Fig. 1) but was not observed in the microprobe studies. Coshell (1983) has reported that dolomite occurs sporadically as hard tabular concentrations ranging in composition from dolomite to ferroan dolomite and ankerite. Grains of Mg-siderite were widely dispersed and mainly 5-10 pm in size. However, some sample chips were notably enriched in larger grains (20-50 ttm), reminiscent of those observed in Condor oil shale (Patterson et al., 1988). This may have a stratigraphic significance not detectable from bulk ore type sam-

ples. Microprobe analyses showed variable compositions for Fe, Mg, Ca and Mn. Most grains in ore type samples 1, 4 and 5 were of similar composition and averaged 29.8+_1.9% FeO, 16.6_+2.0% MgO, 5.3+_1.1% CaO and 0.7 +_0.15% MnO. However, grains in the ore type 6 sample were of different composition, averaging 37+_2.8% FeO, 11+_2% MgO, 7.0+_0.7% CaO and 1.1%_+0.3% MnO. Occasional grains in the ore type 1 sample contained notably more CaO (up to 12% ), less MgO (3%) and more MnO (3%). More investigations are needed on stratigraphically and lithologically selected samples before any clear pattern could be discerned. Several hand samples of ore types 1, 2, 5 and 6 were also examined from the slot cut, Ramsay Crossing Member. The Mg-siderite showed a consistent but different composition throughout and averaged 41.9 +_2.7% FeO, 7.7 _+1.3% MgO, 4.1 +_0.5% CaO and 2.0 +_1.6%

218 TABLE VI Mineralogical residences of minor and trace elements of Rundle oil shales Minerals identified Quartz Kaolinite Montmorillonite Illite K-feldspar Albite Calcite Magnesian siderite Kerogen Pyrite Galena Anatase Ilmenite Zircon Apatite Halite

Elements of the oil shale

point the Brick Kiln Member appears relatively favourable for development because trace metal and pyrite contents are low and carbonate minerals are more than sufficient to neutralize any sulphuric acid formed by oxidation in waste dumps.

4. C o n c l u s i o n s V, Ti, Sc, Cr, Cu, Zn, Cs, Hf, Th

Mg, Mn, Sr Mg, Ca, Mn organic S, As, Ni As, Ni Pb Ti Ti Zr P C1, Br

MnO. It appears likely that the chemical composition of Mg-siderite may reflect conditions during deposition or diagenesis as suggested for Condor oil shale (Patterson et al., 1988). Differences might be found between and within the other individual members of the Rundle deposit and this aspect will be pursued in future work (J.H. Patterson, in prep.).

(1) The geochemistry and mineralogy are similar in the major ore types of the Brick Kiln Member. Variations in chemical contents occur mainly through changes in the amounts of kerogen relative to clastic or carbonate minerals. (2) Pyrite content and trace-element abundances are relatively low in the Brick Kiln Member compared with other oil shales and other members of the Rundle deposit. (3) The mineralogical residences of the most important trace elements have been established. S, As and Ni are mainly associated with pyrite and to a lesser extent with the kerogen. Ni occurs partially as porphyrins. Mn is resident in both calcite and magnesian-siderite. (4) Mg-siderite grains have consistent compositions in most samples but Mg contents differ significantly between samples. This may well be significant in relation to depositional or diagenetic environments but the present data are insufficient for meaningful interpretation.

3.6. Mineralogical residence of trace elements Acknowledgements Minor and trace elements associated with groups of minerals and specific minerals are listed in Table VI. The results are very similar to those for other oil shales and especially to those for Condor oil shale, another of the Tertiary oil shales in Queensland (Patterson et al., 1988 ). Again most of the trace elements important in processing or in the environment are associated with pyrite, organic material or carbonate minerals. Rundle oil shales differ in that montmorillonite is the dominant clay mineral and the sulphide minerals sphalerite and chalcopyrite were not detected. From a chemical and mineralogical view-

The author gratefully acknowledges the assistance of the staff of the Analytical Chemistry Section, CSIRO Division of Fuel Technology and of the Accelerator Group of the Australian Nuclear Science & Technology Organisation. Thanks are also due to P. Udaja and K.M. Kinealy for their analytical work and to L. Coshell and Esso Australia Limited for providing the samples.

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