Genetic implications of pyrite chemistry from the Palaeoproterozoic Olary Domain and overlying Neoproterozoic Adelaidean sequences, northeastern South Australia

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Ore Geology Reviews 25 (2004) 237–257

Genetic implications of pyrite chemistry from the

Palaeoproterozoic Olary Domain and overlying Neoproterozoic

Adelaidean sequences, northeastern South Australia

Chris Clarka,*, Ben Grguricb, Andreas Schmidt Mummc

aContinental Evolution Research Group, School of Earth and Environmental Sciences, University of Adelaide, Adelaide, S.A. 5005, AustraliabWMC Resources, Belmont, W.A. 6984, Australia

cSchool of Earth and Environmental Science, University of Adelaide, S.A. 5005, Australia

Received 13 August 2003; accepted 2 April 2004

Available online 2 July 2004

Abstract

Sulphide mineralisation associated with rocks from the Palaeoproterozoic Olary Domain (OD) and overlying Neoproterozoic

Adelaidean sequences has undergone a complex history of metamorphism and remobilisation. In this study, new trace element

and sulphur isotopic analyses of pyrites from a large number of deposits and paragenetic generations are combined with an

existing data set to build up a sequence of mineralising events linked to the tectonometamorphic evolution of the region. The

typically high Co/Ni ratios (>10) indicate that early strata-bound pyrite precipitated from a volcanic-related fluid, which had

fluctuating activities of the two metals during the early stages of the evolution of the Willyama basin. This period of

mineralisation was followed by a diagenetic concentration of sulphide mineralisation at the horizon known as the Bimba

Formation, which occurred as a result of the differing redox conditions between the upper and lower sequences in the Willyama

Supergroup. During the Mesoproterozoic (f1600 to 1500 Ma) Olarian Orogeny, metamorphic remobilisation of strata-bound

pyrite resulted in an epigenetic signature; the trace element concentrations of this generation were controlled primarily by the

proximity of mineralisation to the mafic intrusive bodies found throughout the terrane. Further reworking of existing sulphides

during the Delamerian Orogeny and associated granitoid-intrusive rocks led to the formation of a new generation of epigenetic

pyrite that occurs in quartz veins in the Adelaidean sequences and veins that crosscut Olarian fabrics in the Olary Domain. y34Sresults range from 16x to 11x, but most data fall between 2x and 4x. This association is suggestive of an initial uniform

deep-seated crustal reservoir of sulphur, which has been repeatedly tapped throughout the metallogenic history of the region. The

isotopic outliers can be explained by the input of biogenic sulphur or sulphur derived from oxidised, possibly evaporitic,

sediments, respectively. Previous workers have invoked the Kupferschiefer and the Zambian Copperbelt as analogues to

mineralisation processes in the Olary Domain. This study shows that y34S and trace element data are suggestive of some affinities

with the aforementioned analogues, but a more likely link can be made between epigenetic remobilisation in the Olary region and

the iron oxide copper gold (IOCG) style of mineralisation found at the nearby Olympic Dam deposit.

D 2004 Elsevier B.V. All rights reserved.

Keywords: Pyrite; Sulphur isotopes; Olary Domain; Metallogeny; Ni; Co

0169-1368/$ - see front matter D 2004 Elsevier B.V. All rights reserved.

doi:10.1016/j.oregeorev.2004.04.003

* Corresponding author. Tel.: +61-8-83033174; fax: +61-8-830-34811.

E-mail address: [email protected] (C. Clark).

C. Clark et al. / Ore Geology Reviews 25 (2004) 237–257238

1. Introduction

Sedimentary basins are host to some of the largest

metallic resources throughout the world (e.g., Kyser,

2000). Constraining the nature of sulphide minerali-

sation related to basin evolution and subsequent

inversion and metamorphism forms a fundamental

component in the understanding of the processes of

ore formation. In turn, this couples the ore system to

the broader evolution of the host terrane. In discussing

the various styles of mineralisation and mineralising

processes contained within the Olary Domain (OD) of

southeastern central Australia (Fig. 1), it is emphas-

ised that there are broad similarities between it and

other mineralised terranes. Previous workers have

attempted to equate sulphide mineralisation in the

Olary Domain with those found in the Kupferschiefer,

Zambian Copperbelt (Cook and Ashley, 1992), and

Palaeoproterozoic iron oxide copper gold deposits,

such as the nearby Olympic Dam deposit (Skirrow

and Ashley, 2000; Williams and Skirrow, 2002).

The aim of this paper is firstly to outline the general

styles of mineralisation in the Olary Domain, the trace

Fig. 1. Location map of the Olary Domain and Curnamona Province.

element and stable isotopic characteristics of pyrite in

those ores, and the associated ore textures. Previous

studies of sulphide mineralisation in the Domain (Cook

and Ashley, 1992; Bierlein et al., 1995; Skirrow and

Ashley, 2000; Kent et al., 2000) have focussed primar-

ily on mineralising systems in the Palaeoproterozoic

Willyama Supergroup and their relationships with

regional alteration systems. These studies have high-

lighted the episodic nature of regional alteration and

ore fluid generation, the limited remobilisation of

stratiform deposits and the mineralogically diverse

alteration assemblages associated with mineralisation.

The aim of this study is to combine the results of

previous studies with new trace element and sulphur

isotope data obtained during this study and present a

regional framework for metallogenesis in the Olary

Domain. We also examine deposits hosted by the

overlying Adelaidean metasediments and determine

their trace element and S-isotope characteristics with

the goal of identifying possible overprinting Adelai-

dean-style mineralisation in the rocks of the Willyama

Supergroup.

The overarching goal of this paper is to link the

mineralising systems occurring in the Olary Domain

with the broader scale tectonic evolution of other

Australian mineralised terranes of Proterozoic age

(Mt Isa, Georgetown Inlier, and the Gawler Craton).

This paper will also assess the validity of previous

analogues drawn between the styles of sulphide min-

eralisation found within the Olary Domain and other

mineralised provinces, such as the Kupferschiefer and

Zambian Copperbelt.

2. Geological background

2.1. Stratigraphy and tectonic evolution

The Olary Domain is an inlier of the Curnamona

Province, a major Proterozoic terrain located within

eastern South Australia and western New South Wales

(Fig. 1). Previous studies of the geology have been

summarised by Clarke et al. (1986, 1987), Cook and

Ashley (1992), Flint and Parker (1993), Robertson et

al. (1998), and Conor (2000). The stratigraphic se-

quence of the Olary Domain (Fig. 2) displays broad

regional correlations with the Willyama Supergroup in

the adjacent Broken Hill Domain (Page et al., 1998;

Fig. 2. Olary Domain lithostratigraphic sequence (modified after Conor, 2000).

C. Clark et al. / Ore Geology Reviews 25 (2004) 237–257 239

Cook and Ashley, 1992). Unconformably overlying

the rocks of the Willyama Supergroup are Neoproter-

ozoic Adelaidean metasedimentary rocks. The depo-

sition of these rocks is associated with sedimentation

during the opening of the Adelaide Geosyncline

beginning f830 Ma (Preiss, 2000).

The Willyama Supergroup rocks have been subject

to at least five deformation and metamorphic events

(Clarke et al., 1986). Flint and Parker (1993) attribute

the first three deformation events in the Olary Domain

to the Olarian Orogeny (OD1–OD3), a major episode

of deformation and metamorphism that occurred be-

tween f1600 and 1500 Ma (Robertson et al., 1998).

Ashley et al. (1998), on the basis of more recent field

and geochronological studies, suggest that a deforma-

tion event occurred prior to f1640 Ma. The younger

two deformation events (DD1, DD2) are related to the

Delamerian Orogeny (f500–450 Ma; Kent et al.,

2000).

OD1 and OD2 are the result of a major episode of

compressional deformation and regional metamor-

phism reaching amphibolite facies in rocks exposed

in the Olary Domain at f1600 Ma (Clarke et al.,

1986). Peak regional metamorphic conditions were

achieved during this period. Studies of pelitic rocks

by Clarke et al. (1987) estimated upper amphibolite

facies metamorphic conditions with maximum pres-

sures of 400–600 MPa and temperatures of 550–650

jC in the central and southern portions of the Olary

Domain (Flint and Parker, 1993).

Several igneous suites have intruded the rocks of

the Willyama Supergroup. A-type (Basso) granitoids

intruded f1700 Ma and comagmatic rhyolitic volca-

nic rocks erupted at f1710–1700 Ma during depo-

sition of the Willyama Supergroup sequence (Fig. 2;

Ashley et al., 1996). Ashley et al. (1998) suggest that

the Willyama Supergroup was then deformed prior to

the intrusion of several mafic igneous masses and

small I-type granitoid (Poodla and Antro suite) bodies

into the central part of the Olary Domain at f1640–

1630 Ma. Following peak metamorphic conditions,

voluminous S-type (Bimbowrie) granitoids and asso-

ciated pegmatites intruded the sequence. These are

interpreted to be late syntectonic granites, which

Fig. 3. Locality map showing the distribution of the upper and lower sequences of the Willyama Supergroup and occurrences of sulphide mineralisation.

C.Clark

etal./Ore

GeologyReview

s25(2004)237–257

240


intruded at the end of the OD2 event (Kent et al.,

2000).

Retrograde metamorphism and alteration, including

a retrograde deformation event, OD3, continued epi-

sodically betweenf1580 andf1500 Ma (Kent et al.,

2000). OD3 is mostly restricted to discrete shear zones

where retrograde mineral assemblages overprint earlier

assemblages (Clarke et al., 1987). Further minor ther-

mal perturbations occurred during the Musgravian

Orogeny (f1200 to 1100 Ma; Lu et al., 1996), mafic

dyke emplacement during the development of the

Adelaide Geosyncline (f820 Ma), and finally two

low-grade metamorphic events (DD1 and DD2) attrib-

uted to the Delamerian Orogeny (f500 Ma; Flint and

Parker, 1993). The Delamerian Orogeny also affected

the Neoproterozoic Adelaidean sediments overlying

the Willyama Supergroup rocks. Paul et al. (2000)

Table 1

Summary of the mineralisation style, age, host lithology, and alteration st

Name of deposit Mineralisation style Age (Ma)

Ethiudna Pyrite–chalcopyrite–pyrrhotite

strata-bound concentrated

around regional redox boundary

Na

White Dam Chalcopyrite–pyrite–molybdenite

epigenetic quartz veins and

strata-bound pyrite–

magnetite–chalcopyrite

1612–1631a

490F 4b

Green and

Gold/Wilkins

Chalcopyrite–pyrite–pyrrhotite–

arsenopyrite–magnetite–

sphalerite–Au veins associated

with retrograde shear zones

474F 4c

Majorie Mine Pyrite–chalcopyrite–hematite

in OD3 quartz veins

Na

North Portia Cu–Au(–Mo) strata-bound

mineralisation in veins,

stockworks, replacement

along compositional layering,

disseminations

1605–1630a

1614–1616d

Luxemburg Chalcopyrite–pyrite–magnetite

in epigenetic quartz veins

Na

Anabama Pyrite–magnetite– ilmentite–

molybdenite–pyrrhotite–

chalcopyrite–borniten

greisen-style mineralisation

485F 4e

a Skirrow and Ashley (2000).b Cordon (1998).c Green (1996).d Teale and Fanning (2000).e Richards (1981).

suggest that during the Delamerian Orogeny, defor-

mation of the Willyama Supergroup was controlled by

reactivation of preexisting structural features.

2.2. Alteration and mineralisation

Metasomatism has affected all parts of theWillyama

Supergroup with variable intensity, with the effects

heterogeneously distributed (Ashley et al., 1998).

Skirrow and Ashley (2000) condense alteration into

two dominant regional styles. Sodic alteration that

resulted in albitisation is interpreted to be early (i.e.,

pre- or syntectonic) and is generally strata-bound.

Regional sodic alteration postdates the Basso suite

magmatic event but is known to continue through to

OD3 (Ashley et al., 1998). This was then followed by

possible syntectonic Na–Ca –Fe metasomatism

yle present at sulphide deposits in the Olary region

Host sequence Alteration style Reference

Bimba Formation Diagenetic Grguric (1992)

Ethiudna and

Wiperaminga

gneisses and

calc– silicates

Na–Ca metasomatism

and retrograde

metamorphism

Cordon (1998)

Delamerian retrograde

shear zone

schists and associated

quartz veins

Mn–Fe-rich at

GG Ca–Fe-rich

at Wilkins

Green (1996)

This study

Quartz veins in

Strathearn

psammo–pelites

not observed Penhall (2001)

This study

Palaeoproterozoic

sediments

Albitisation at 1630 Teale (2000)

This study

Quartz veins

associated

with amphibolite

not observed This study

Delamerian

granodiorite

Greisenisation and

seriticisation

This study


f1588 to 1583Ma (Skirrow and Ashley, 2000), which

has affected the OD3 retrograde shear zones. Skirrow

and Ashley (2000) observed that regional- and local-

scale hydrothermal alteration in the Curnamona Prov-

ince is consistent with that observed in iron oxide

copper–gold systems globally.

Mineralisation in the Olary Domain (OD) consists

predominantly of U and Cu–Au deposits (minor Th,

REE, W, Co, Au, and Ba), but few deposits of

significant economic importance have been located

(Fig. 3). The major deposits are Radium Hill, Crock-

ers Well, Beverly and Honeymoon uranium mines and

the White Dam, Green and Gold, Waukaloo, Kalka-

roo, and Portia copper–gold deposits. The region

shows strong potential for economic deposits, but

such deposits, at this stage, remain elusive.

Mineralisation occurring in the Olary Domain and

overlying Adelaidean sequences has been classified

by Ashley et al. (1998); the main styles being

stratiform, strata-bound, and epigenetic (Table 1).

Stratiform deposits are disseminated to massive,

generally sediment-hosted, with local evidence of

felsic volcanism, possible redox boundary control

and have an association with evaporitic facies. They

are mainly Fe-dominated sulphide occurrences with

minor amounts of base metals, as well as localised

Fe and Cu sulphide occurrences associated with iron

formations at certain stratigraphic levels. Strata-

bound deposits comprise disseminated sediment-

hosted Fe–Cu–Zn (FCo–W–U–F) mineralisation,

which is possibly syngenetic. The latter may be

controlled by redox boundaries, although mineralisa-

tion shows some structural control and displays

variable degrees of remobilisation (Bierlein et al.,

1996a). Epigenetic vein and replacement mineralisa-

tion is episodic and represents structurally and lith-

ologically controlled deposition of hydrothermally

(re-)mobilised sulphides. Mobilisation of the sul-

phides is associated with fluids generated during

the Olarian orogenic event and also with (re-)mobi-

lisation during the Delamerian Orogeny (Bierlein et

al., 1996b).

3. Controls on pyrite chemistry

Pyrite may crystallise initially in forms as diverse

as framboids or cubes depending on various intrinsic

parameters (e.g., temperature and pressure) and other

environmental factors. Fluid-rich diagenesis or low-

grade metamorphism results in thorough recrystalli-

sation and the common formation of pyrite cubes

(e.g., Craig et al., 1998). Once these have formed,

the pyrite becomes much more refractory and retains

many textural characteristics even in deposits that

have undergone penetrative deformation (e.g., Craig

and Vokes, 1993). This is in strong contrast to the

behaviour of most of the accompanying sulphides,

which often undergo ductile deformation, solid state,

or chemical remobilisation and annealing. Pyrite

deforms sparingly until there is brittle failure. How-

ever, there may be significant corrosion and regrowth

of pyrite during metamorphism as a result of sulphur

exchange with other minerals, especially pyrrhotite

(Cook, 1996). Optical microscopic examination and

electron microprobe chemical mapping of pyrites

from a variety of mineral deposits, including several

high-grade metamorphosed ores, reveals that the

pyrites frequently contain both physical and chemical

textures that may be interpreted in terms of the

depositional and the postdepositional history of the

deposits (Cox, 1987; Cook et al., 1994; Cook, 1996).

Inclusions of sulphides or other minerals reveal

information on the timing of crystallisation or recrys-

tallisation, whereas chemical analysis of trace ele-

ments such as nickel, cobalt, and arsenic reveals

information on the source of the fluids and relative

timing of the transport of these elements in the

fluids.

Cobalt and nickel are the most common trace

elements found in pyrite (e.g., Loftus-Hills and Sol-

omon, 1967). Up to 9 wt.% cobalt can be included in

pyrite at temperatures of 400 jC, and at elevated

temperatures (>700 jC) complete FeS2–CoS2 solid

solution can occur (Moh, 1980). At lower temper-

atures, cobalt and nickel, both strongly chalcophile

elements, exhibit isomorphous solid solution with iron

in pyrite. The Co/Ni ratio in pyrite has been used by

many authors as an empirical indicator of the envi-

ronment of deposition (Loftus-Hills and Solomon,

1967; Bralia et al., 1979; Roberts, 1982; Campbell

and Ethier, 1984; Meyer et al., 1990; Raymond, 1996;

Craig et al., 1998). In some cases, the ratio reflects the

temperature of initial formation, independently of

metamorphic grade (Walshe and Solomon, 1981;

Huston et al., 1995; Cook, 1996). Cobalt content in


pyrite is also suggested to be higher in copper-rich

ores formed at higher temperatures within feeder

zones to massive deposits (Cook, 1996). Co/Ni ratios

of less than one with a low standard deviation are

generally accepted to represent pyrite of sedimentary

origin. Low Co and Ni concentrations are also char-

acteristic of such pyrite. Conversely, highly variable

Co/Ni ratios, usually greater than one, are thought to

be the result of hydrothermal mineralisation (e.g.,

Bralia et al., 1979).

Sulphur isotopic investigations can also be used to

provide evidence on the source of sulphur and can be

used to interpret the conditions under which pyrite

forms (e.g., Ohmoto, 1972). Previous studies of the

sulphur isotopic signatures of metamorphosed sul-

phide deposits (von Gehlen et al., 1983; Seccombe

et al., 1985, Bierlein et al., 1996a; Cook and Hoefs,

1997) indicate that there may be localised reequili-

bration of sulphur isotopic signatures between ore

minerals, but little evidence of homogenisation at a

deposit, let alone regional scale. von Gehlen et al.

(1983) found that, in the polymetallic sulphide depos-

its at Aggeneys-Gamsberg (South Africa), the original

sulphur isotopic patterns remain intact, although the

deposits experienced peak metamorphic conditions in

the order of f670 jC and 500 MPa. Cook and Hoefs

(1997) state that modification by hydrothermal pro-

cesses associated with metamorphism is limited, and

the sulphur isotopic systematics of sulphide deposits

effectively behave as a closed system during meta-

morphism. Other studies (Willan and Coleman, 1983;

Skauli et al., 1992) have shown that significant

changes have taken place within restricted parts of

the deposit as a result of local processes controlled by

tectonic processes, fluid flow regimes, and other

factors (Cook and Hoefs, 1997). Zheng (1990)

reviewed the behaviour of sulphur isotopes during

regional metamorphism and found that a large num-

ber of factors, such as thermodynamic and kinetic

fractionation between sulphur-bearing minerals under

metamorphic conditions, interactions with metamor-

phic fluids, and homogenisation, influence the isoto-

pic signature of sulphides. Zheng (1990) proposes

that interpretation of the isotopic signatures occurring

in metamorphosed rocks and ores should be

approached with caution, because the observed dis-

tributions can almost always be explained in a num-

ber of different ways.

4. Analytical methods

Over 450 trace element analyses of pyrite were

determined for Co, Ni, Cu, As, Zn, and Se on a

CAMECA SX-51 electron microprobe at the Univer-

sity of Adelaide. An acceleration voltage of 15 kV

and a beam current of 20 nA were used. Operating

conditions were as follows: Cu metal (Ka), FeS2 (Fe

Ka, S Ka), Co metal (Ka), and Ni metal (Ka).

Count times were either 20 or 30 s depending on

the element. Optimum detection limits on the micro-

probe were 100 ppm for Co, Ni, and Cu, and 150

ppm for As, Zn, and Se. A total of 135 pyrite samples

were analysed for their sulphur isotopic composition.

Sulphide-bearing samples were crushed to < 500 Amusing a minijaw crusher and washed, and sulphides

subsequently hand picked. The sulphide separates

were then checked for impurities using X-ray diffrac-

tion. Analysis of results using the X-Plot program

indicated monomineralic sulphide species were pres-

ent in each sample to within acceptable limits ( < 5%

multiple sulphide species). Sulphur isotope ratios

were determined at the Department of Geology and

Geophysics, University of Adelaide. Methods de-

scribed by Robinson and Kusakabe (1975) were

implemented in extracting and purifying SO2 gas

from sulphide separates. Sulphur isotope ratios of

the extracted SO2 gas were measured using a Micro-

mass VG 602E Stable Isotope Mass Spectrometer.

Results are reported as y34S in parts per mil (x)

relative to Canyon Diablo Troilite (CDT). Replicate

analysis was conducted to within F 0.2x on each

sample and to within F 0.2x on substandards (Bro-

ken Hill lode No. 7).

5. Results

5.1. Pyrite textures and trace element composition

The trace element geochemical and textural char-

acteristics of the different generations of pyrite from

the Olary Domain pyrites permits assessment of

depositional conditions and the effects of any subse-

quent deformation. In the Olary Domain, pyrite is by

far the most abundant sulphide. Unlike most other

sulphides, which may recrystallise after peak meta-

morphism and associated deformation, pyrite textures

C. Clark et al. / Ore Geology R244

reflect the entire metamorphic and deformational

history undergone by the mineral (Craig et al.,

1998). Textures vary considerably and commonly

reflect changes in metamorphic grade between local-

ities and differences in the rheological behaviour of

pyrite relative to the matrix minerals during deforma-

tion. Pyrite deformation in both the brittle and ductile

fields is recorded in the textures of pyrites from the

Olary Domain.

Six main stages of pyrite growth in Willyama and

Adelaidean sulphide occurrences have been identified

on the basis of textural and geochemical differences

in this study. Most of the deposits examined in this

paper exhibit more than one generation of pyrite

growth, and care has been taken to identify which

generation was analysed. The results of the analyses

and the average Co/Ni ratio of the dominant gener-

ation of pyrite present at each locality are shown in

Fig. 4. These stages of pyrite growth are in general

agreement with those identified by Bierlein et al.

(1995); their main textural and geochemical proper-

ties are discussed below.

Fig. 4. Plot of cobalt versus nickel for pyrite groupe

5.2. Pyrite I

Pyrite I occurs most commonly in the strata-bound/

stratiform sulphide deposits (Lady Louise, Cathedral

Rock, Ethiudna and Wilkins) and is characterised by

relatively low cobalt contents (100–5000 ppm), high

Co/Ni ratios (7–110), and growth zoning defined by

variation in cobalt content (Fig. 5). Petrographic and

textural relationships of Pyrite I (Fig. 6A) suggest that it

has a premetamorphic origin and grew during sedi-

mentation/diagenesis.

5.3. Pyrite II

Pyrite II occurs as euhedral to subhedral dissem-

inated grains associated with chalcopyrite, pyrrho-

tite, and cobalt- and arsenic-rich minerals such as

skutterudite, cobaltite, and arsenopyrite. It is char-

acterised by high cobalt contents (>10000 ppm) and

lack of any discernable zoning. Inclusions of pro-

grade metamorphic silicates in Pyrite II are indica-

tive of coeval crystallisation with these phases (Fig.

eviews 25 (2004) 237–257

d by deposit location and mineralisation style.

Fig. 5. Backscattered electron image of a premetamorpic pyrite (Pyrite I) crystal from the Wiperaminga Subgroup, Ethiudna mine, showing

well-defined zoning. A chemical profile across the crystal (below) indicates zoning is defined by variations in cobalt (Grguric, 1992).


6B). Pyrite II occurs both in stratiform/strata-bound

deposits as overgrowths on Pyrite I and in epige-

netic sulphide occurrences as euhedral to subhedral

grains.

5.4. Pyrite III

At the Ethiudna mine, small weakly Co-bearing,

euhedral pyrite crystals are commonly observed in

pyrrhotite grains. The lack of zoning and frequent

alignment of the crystals within the host pyrrhotite

suggest that they are an inclusion or coexisting phase.

This type of pyrite is also observed at the Wilkins

prospect, where it characteristically occurs as subhe-

dral, corroded grains with a dull reflectance, which are

also interpreted to be inclusions of pyrite within

pyrrhotite (Fig. 6C). Bierlein et al. (1995) also noted

the occurrence of this type of pyrite and its occurrence

in both strata-bound and epigenetic-style deposits.

Pyrite III exhibits low contents of cobalt ( < 5000

ppm) but has moderate to high Co/Ni ratios (1–10).

5.5. Pyrite IV

Pyrite IV occurs as fine veinlets penetrating cleav-

ages of muscovite (Fig. 6C), both in epigenetic-style

deposits (e.g., the Green and Gold deposit) and also

some strata-bound deposits, such as Ethiudna. Pyrite

IV coexists with clusters of epidote indicating forma-

tion during the retrograde stage of metamorphism.

Kinking of the muscovite/pyrite lamellae suggests that

the pyrite was formed early during the retrograde OD3

event. Pyrite IV generally has low contents of cobalt

(0–2500 ppm) and low Co/Ni ratios ( < 1).

Fig. 6. (A) Pyrite I-layer-parallel sulphides in Wiperaminga Subgroup, Ethiudna mine. Euhedral premetamorphic pyrite (py) is bordered by

chalcopyrite (ccp) and pyrrhotite (po). Marked compositional zoning of the pyrite is not observable in reflected light. (B) Pyrite II-sulphide

mineralisation, Ethiudna mine. Euhedral to subhedral high-Co pyrite associated with chalcopyrite and prograde andradite (and). Coeval

crystallisation is indicated by the distribution of inclusions. (C) Pyrite III-inclusions of low-Co pyrite in pyrrhotite host, Wilkins prospect. (D)

Pyrite IV-pyrite-penetrating muscovite along cleavage planes. Both pyrite and muscovite are kinked by OD3 folds, Green and Gold prospect. (E)

Pyrite V-euhedral pyrite with chalcopyrite inclusion associated with chalcopyrite and magnetite (mt) in a quartz vein, which cuts the Olarian

fabric from the Luxemburg mine, this pyrite is high in Co. (F) Pyrite VI-euhedral Adelaidean pyrite crystal with inclusion of chalcopyrite,


5.6. Pyrite V

Pyrite V is found in association with chalcopyrite

in epigenetic quartz veins cutting Olarian-age fabrics.

At White Dam, Pyrite V has been analysed by the

electron microprobe and found to have elevated con-

tents of nickel relative to cobalt, resulting in low Co/

Anabama mine.

Ni ratios ( < 1). This is in contrast to pyrite occurring

in quartz veins at Luxemburg, where Co contents can

reach 37100 ppm with Co/Ni ratios up to 700. The

timing of Pyrite V formation is unclear, but due to the

crosscutting nature of the host quartz veins, it is

assumed to postdate Olarian orogenesis and is possi-

bly formed during the Delamerian Orogeny.

Table 2

Results of sulphur isotope analyses from mineralised localities in the Olary region

Locality Classification y34S Locality Classification y34S

White Dam Epigenetic � 6.3 Mt Howden Strata-bound � 0.8


White Dam Epigenetic � 4 Mt Howden Strata-bound � 2.6



White Dam Epigenetic � 2.5 Mt Howden Strata-bound � 3


Luxemburg Epigenetic � 3.9 Mutooroo Strata-bound 6.5



Luxemburg Epigenetic 0 Mutooroo Strata-bound 6.6

Luxemburg Epigenetic 0.1 Mutooroo Strata-bound 6.7




Luxemburg Epigenetic 1.1 Anabama Adelaidean 2.7

Luxemburg Epigenetic 1.1 Anabama Adelaidean 2.6

Green and Gold Epigenetic � 6.1 Anabama Adelaidean 2

Wilkins Epigenetic � 0.5 Anabama Adelaidean 2

Wilkins Epigenetic � 0.1 Anabama Adelaidean 1.5

Wilkins Epigenetic 5.9 Anabama Adelaidean 1.7

Wilkins Epigenetic 6.2 Anabama Adelaidean 1.8

Ethiudna Strata-bound 1.7 Anabama Adelaidean 1.8

Ethiudna Strata-bound 4.2 Cathedral Rock Strata-bound 3.1






Ethiudna Strata-bound 1.2 Cathedral Rock Strata-bound 3

Ethiudna Strata-bound � 0.3 Cathedral Rock Strata-bound 3

Ethiudna Strata-bound � 0.5 Lady Louise Strata-bound � 1.5


Ethiudna Strata-bound 3.8 Lady Louise Strata-bound � 4.5






Ethiudna Strata-bound 0.5 Radium Hill Epigenetic � 1.8







Ethiudna Strata-bound 1.3 Radium Hill Epigenetic � 2

Ethiudna Strata-bound 1.1 Wadnaminga Adelaidean 3.2





East Doughboy Strata-bound 2.4 Wadnaminga Adelaidean 3.4

(continued on next page)



Table 2 (continued)

Locality Classification y34S Locality Classification y34S

East Doughboy Strata-bound 2.4 Wadnaminga Adelaidean 4.1

East Doughboy Strata-bound 2.4 Wadnaminga Adelaidean 4

East Doughboy Strata-bound 2.4 Waukaringa Adelaidean 0.2

East Doughboy Strata-bound 2.6 Waukaringa Adelaidean 0.1

East Doughboy Strata-bound 2.4 Waukaringa Adelaidean 11

East Doughboy Strata-bound 1.9 Waukaringa Adelaidean 11

East Doughboy Strata-bound 2.4 Waukaringa Adelaidean � 0.4

Majorie Mine Strata-bound 1.1 Waukaringa Adelaidean 0

Majorie Mine Strata-bound 1.2 Waukaringa Adelaidean 0

Fig. 7. Histogram of y34S of pyrites in the studied deposits, grouped

by style of mineralisation.

5.7. Pyrite VI

Pyrite VI is restricted to mineralisation hosted by

the Adelaidean sequences and Delamerian granitoids

(Fig. 6F). Pyrite VI formation is associated with fluids

generated by the emplacement of Delamerian gran-

itoids, such as the Anabama Granite, into the Adelai-

dean sequences. It is also associated with chalcopyrite,

gold and quartz veining in deposits, such as Wadna-

minga and Waukaringa. Pyrite VI is characterised by

relatively low levels of Co (500 to 1400 ppm) and

moderate to high Co/Ni ratios (0.8 to 103). Pyrite V

and Pyrite VI exhibit many textural similarities, the

main difference is the hosting of Pyrite V by Willyama

Supergroup sequences and Pyrite VI by Adelaidean

sequences or Delamerian granitoids.

5.8. Sulphur isotope ratios of Olarian pyrites

A total of 105 sulphide samples from 15 occur-

rences were analysed for y34S. Results are given in

Table 2 and shown on the histograms in Fig. 7. Also

included in Table 2 are data from 30 Ethiudna samples

collected by Grguric (1992) using identical instru-

mentation and methods as in this study. The histo-

grams also incorporate y34S data for pyrite presented

in Bierlein et al. (1996a). The deposits and occurren-

ces are arranged in the histograms according to the

style of mineralisation, and where there is more than

one style of sulphide mineralisation present at anyone

location, care was taken to ensure that only a single

generation of pyrite was analysed.

The overall spread in y34S range from � 16x to

11x. Most analyses yield values between 0x and 4

x. These results are consistent with those obtained by

Bierlein et al. (1996a), and support the conclusion of

those authors that the sulphur source involved in

sulphide mineralisation is of a crustal origin. Table 3

presents a summary of the trace element y34S and

textural characteristics of each individual generation

of pyrite. From this table, it can be observed that there

Table 3

Summary of trace element, isotopic, and textural characteristics of the various pyrite generations


is no systematic variation in y34S as a function of trace

element content of pyrite.

6. Discussion

6.1. Factors controlling sulphide mineralisation in

the Olary region

In the Olary region, cobalt and nickel are by far the

most abundant and useful trace elements for differen-

tiating the chemically distinct generations of pyrite.

The concentration of these elements in pyrite is

controlled by a number of factors, and these factors

can explain some of the variations in petrographically

similar but chemically different pyrites. Factors such

as associated sulphide phases, variations in the trace

element concentration of host lithologies, fO2, and pH

of the mineralising fluids and fluid-host lithology

interactions will all have a bearing in the final trace

element composition of pyrite (Velikoborets, 1987).

Pyrite I, which forms the cores of many composite

pyrite grains, is interpreted to be premetamorphic due

to the lack of inclusion of surrounding sulphide

phases and the presence of growth zoning defined

by variation in cobalt content (Fig. 5). Such zoning is

common in hydrothermally deposited pyrites (e.g.,

Ramdohr, 1969) and may reflect fluctuations in tem-

perature, pH, or precipitation of pyrite from an aque-

ous solution under conditions of varying Co/Ni

activity. Bogush (1983) states that compositional

zoning in pyrite is unlikely to occur in pyrite of a

metamorphic origin, because fluctuating fluid param-

eters are not expected from a regional metamorphic

fluid which evolved in equilibrium with the surround-

ing host lithologies, unless the equilibrium conditions

are close to a stability boundary. Consequently, given

the presence of chemical zoning and the lack of

inclusions, Pyrite I most likely formed during the

early stages of the evolution of the Willyama Basin

and prior to the Olarian orogenic event.

The second stage of pyrite deposition (pyrite II)

refers to a temporally coincident domain-wide pyrite

mineralisation event during OD3 metamorphism and

the associated fluid flow. Bierlein et al. (1995)

proposed that epigenetic sulphide mineralisation re-

lated to OD3 was a consequence of the generation of

metal-bearing metamorphic brines travelling through

fluid conduits to shallower crustal levels and precip-

itating epigenetic sulphides along the way. The source

of metals and sulphur for Pyrite II is inferred to be the

felsic volcaniclastic rocks deposited during the tec-


tonically active period of the rift system, this is the

same source invoked for the earlier Pyrite I, and this

is borne out in the uniform sulphur isotopic compo-

sitions for Pyrite I and II. Pyrite II forms overgrowths

on Pyrite I in some localities or as disseminated to

subhedral grains in association with other sulphides

and silicates. The association of Pyrite II with other

Co-rich sulphide phases, such as cobaltite, skutteru-

dite, and arsenopyrite indicates that precipitation

occurred from a Co-rich fluid and low sulphur

activity (Fig. 6E). Coeval crystallization of peak

metamorphic silicates with pyrite and other sulphide

minerals (Fig. 6B) demonstrates that precipitation of

sulphides occurred during peak metamorphism. The

lack of chemical zoning observed in Pyrite II suggests

that the mineralising fluid had a relatively homoge-

nous chemical composition. This further evidence

that Pyrite II crystallisation is related to a metamor-

phic fluid which evolved in equilibrium with the host

lithologies as the fluid would not be expected to vary

in its chemical composition. The range of cobalt

concentrations measured in Pyrite II is a function of

the host lithologies. Deposits with high Co values

(e.g., Ethiudna, Meningie Well, Dome Rock) are

generally spatially associated with amphibolite bod-

ies. Host lithology will have a major impact on the

trace element and y34S composition of the fluid

(Table 4). Mafic rocks, such as the Lady Louise suite,

have higher concentrations of Co and Ni than typical

metasedimentary rocks, and therefore trace element

content of the sulphide mineralisation reflects the

content of a fluid that has interacted with a mafic

body. The preferential partitioning of Co into pyrite

and Ni into other sulphides, such as pyrrhotite, leads

to the elevated Co/Ni ratios of Pyrite II, although Co

and Ni contents of mafic rocks are similar (Craig and

Vaughan, 1994).

Table 4

Trace element composition of representative lithologies in the Olary

Domain

Rock type Co (ppm) Ni (ppm)

Basso suite 40–85 0–12

Poodla I-type 50–55 4–30

Bimbowrie granite 32–110 0–18

Lady Louise suite 49–130 48–126

Metasediments 25–48 9–30

The association of Pyrite III with pyrrhotite and the

low Co concentrations but high Co/Ni ratios measured

in Pyrite III are interpreted to result from the replace-

ment of pyrrhotite. Pyrrhotite, found in association

with Pyrite III at Ethiudna mine, was found to have

considerably lower Co/Ni ratios of f2 and Co

compositions of f2000 ppm as compared to that of

Pyrite II, which has an average Co/Ni ratio of 26.3

and Co contents up to 70000 ppm. Textural evidence

for this relationship can be found at Ethiudna, where

late-stage retrograde alteration of pyrrhotite to pyrite

and marcasite occurs along grain boundaries and

adjacent to fractures (Fig. 6C). Bierlein et al. (1995)

report subhedral pyrite with a dull reflectance that

displays low Co concentrations but moderate to high

Co/Ni ratios. The moderate to high Co/Ni ratios are a

function of the preferential partitioning of cobalt in

pyrite relative to nickel during the replacement of the

host pyrrhotite (Craig and Vaughan, 1994).

Pyrite IV may be temporally equivalent to Pyrite

III but formed as a result of the remobilisation of

existing sulphides rather than by replacement of

pyrrhotite. The intergrowth of Pyrite IV and musco-

vite and the association with epidote indicates that

Pyrite IV crystallised during a retrograde event, and

the kinking of the muscovite and pyrite lamellae

suggests that crystallisation took place early during

the event. The 474F 4 Ma ages obtained by K–Ar

dating of coexisting biotite and muscovite at the

Green and Gold prospect (Green, 1996), whilst con-

sistent with ages obtained by Bierlein et al. (1996b)

from other prospects, may not represent the actual age

of mineralisation but rather reflect the thermal reset-

ting of the system during a subsequent Delamerian

metamorphic event.

Pyrite V and VI are most likely related to fluid

generation associated with the Delamerian Orogeny,

and typically contains low cobalt (generally < 1000

ppm) reflecting the composition of the host rocks. At

White Dam, where both older strata-bound and later-

epigenetic sulphides are present, the younger pyrite

has very low Co/Ni ratios. These low values are

controlled by the compositions of the host rocks

(Wipermaninga psammites and Ethiudna albitites),

which have low trace element concentrations. This

is in contrast to the case at Luxemburg, where

sulphide mineralisation occurs in quartz veins cutting

the Olarian fabric, and pyrite has high Co (>10000


ppm). The high values measured at Luxemburg can

be explained by the presence of a large amphibolite

body within 100 m of the mineralised quartz veins.

Mineralisation hosted by the Adelaidean metasedi-

mentary rocks has high Co/Ni ratios and low Co

( < 1400 ppm), once again reflecting the concentra-

tion of these elements in the host lithologies. An

additional control on the trace element contents is

the lower temperatures of the mineralising fluids

(120 to 250 jC) that precipitated the Adelaidean

pyrite (Richards, 1981), which do not allow the fluid

to transport elevated concentrations of trace ele-

ments, such as Co and Ni (Moh, 1980). The higher

Co/Ni ratios observed for pyrite mineralisation at

Anabama are a function of the relative partitioning of

Co into pyrite and Ni into pyrrhotite (Vaughn and

Craig, 1978).

6.2. Evidence from sulphur isotope ratios

In accordance with the new sulphur isotope anal-

yses in Table 2, further weight can be added to the

argument that the sulphur source involved in sulphide

mineralisation can be best characterised as a deep-

seated crustal reservoir of sulphur. This source has

been repeatedly tapped to provide a continuous supply

of hydrothermal sulphur-bearing fluids (Bierlein et al.,

1995). The combination of a crustal sulphur source

and the prolonged metamorphic history experienced

by the terrane has lead to the homogenisation of the

sulphur isotopic values to a mean around 0x to 4x.

Local scale mixing at some localities (e.g., Hunters

Dam) with oxidizing, possibly evaporite-related, flu-

ids has lead to some of the heavier values observed.

Lower values can be attributed to a possible influx of

isotopically lighter biogenic sulphur. There was no

systematic variation in the sulphur isotopic ratios as a

function of the Co/Ni ratio observed in the deposits.

This indicates that factors other than the sulphur

concentration in the fluid source controlled the trace

element content of pyrite.

6.3. An Olarian/Adelaidean mineralisation scenario

The different generations of pyrite in the Olary

Domain, and their petrographic relationships, allow

the evolution of the Olarian/Adelaidean mineralising

system to be placed into a temporal and tectonic

context. The evolution of the basin into which the

Willyama Supergroup sediments were deposited in is

still the subject of much debate. Similarities in the

geochronological and tectonic evolution have been

documented between the Curnamona Province, Mac-

arthur Basin, and the Mt Isa inliers, and it has been

suggested that these basins were once linked (Betts et

al., 2002; Page et al., 2000). The evolution of these

basins can be linked temporally with accretionary

processes long the continental margin, suggesting a

paired evolution of the terranes (Betts et al., 2002).

Giles et al. (2002) suggest that the Mt Isa, Macarthur,

and Willyama basins formed as continental back-arc

basins as a consequence of the extensional stress

regime created by the rollback of a subducting slab

(Fig. 8a). During this period of extension and basin

formation, exhalative mineralisation styles such as the

stratiform Cu–Pb–Zn deposits at Polygonum and

North Portia developed (Teale, 2000). The metals

for Pyrite I are considered to be sourced from the

terrigenous sediments and volcaniclastic rocks depos-

ited during the tectonically active period of the rift

system (Cook and Ashley, 1992). Cobalt and Ni

contents of these materials are relatively low, but

sulphide mineralisation still retains the high Co/Ni

of the volcanic source ratios, and as a consequence,

Pyrite I can be linked to early sulphide mineralisation

during the opening of the Willyama Basin. As the

basin deepened, more reduced sediments belonging to

the Strathearn Group were deposited on top of the

oxidised volcaniclastic rocks and quartzose sediments

of the Curnamona Group (Leyh and Conor, 2000).

This contact became a horizon in which redox-style

concentration of sulphides occurred (Fig. 8b). The

resulting sulphide-rich horizon is known in the region

as the Bimba Formation, host to many mineralised

occurrences (e.g., Ethiudna, Mt Howden, and Lady

Louise). Interaction of mineralising fluid, created by

the dewatering of the sedimentary pile, with previ-

ously emplaced mafic rocks, such as the Woman-in-

White amphibolite, would have produced a fluid with

elevated Co concentrations. This leads to the forma-

tion of the Co-bearing pyrite and other Co-rich

minerals associated with strata-bound mineralisation

throughout the Olary Domain. The source of sulphur

for this style of mineralisation is thought to be the

remobilisation of sulphide ore constituents deposited

during sedimentation as opposed to existing sul-

Fig. 8. Interpretative tectonic and metallogenic evolution of the Olary region. (a) Formation of the Willyama basin due to extensional forces

caused by rollback on a subducting slab (after Betts et al., 2002). (b) Redox style mineralisation at the interface between the oxidised

Curnamona Group sediments and the reduced Strathearn sediments. (c) Basin inversion during the Olarian Orogeny remobilising existing

sulphides associated with the emplacement of I-type granitoids. (d) Delamerian Orogeny and associated plutonism causes minor remobilisation

in the Willyama Supergroup and quartz vein style mineralisation in the Adelaidean sequences.


phides, remobilisation of existing sulphides during

this period is thought to be restricted to less than a

few centimeters (Bierlein et al., 1995).

Subsequent to the formation of the Willyama basin,

a period of compressive deformation and metamor-

phism occurred (Fig. 8c). This orogenic event can be

traced through the Mt Isa and Georgetown Inliers and

also in the Curnamona Province, where it is known as

the Olarian Orogeny (Page et al., 1998). The major

style of mineralisation associated with the Olarian

Orogeny is vein-style epigenetic Cu–Au mineralisa-

tion (Skirrow and Ashley, 2000). Examples of this

style of mineralisation are found at Portia, Kalkaroo,

White Dam, and Waukaloo prospects. Skirrow et al.

(1999) have dated molybdenite associated with epi-

genetic Cu–Au mineralisation at f1632 to f1612

Ma using the Re–Os technique, consistent with U–Pb

SHRIMP ages of f1605 Ma for hydrothermal mon-

azite from the Portia prospect (Teale and Fanning,

2000). Stable isotopic and fluid inclusion studies of


the fluids associated with epigenetic Cu–Au mineral-

isation have demonstrated that they are chemically

and isotopically distinct from the fluids associated

with regional Na–Ca–Fe alteration (Skirrow et al.,

1999). The latter authors propose a hybrid magmatic-

metamorphic source for the fluids, whereby the high-

temperature Cu–Au-bearing fluids were generated by

a combination of leaching of metasedimentary Will-

yama Supergroup rocks and a magmatic contribution.

The most likely source of the magmatic component of

these fluids is the Poodla and Antro I-type granitoids,

which have been dated at 1629F 29 (Cook et al.,

1994) and 1641F 8 Ma (Freeman, 1995), respective-

ly. Fluids generated during this event flowed outward

along thrusts from the higher grade core at the centre

of the orogen towards the lower grade foreland (Fig.

8c), transporting mineralising constituents in the pro-

cess (Davies, 2000). Oxygen isotopic signatures of the

fluids associated with OD3 deformation indicate that

the fluids were sourced primarily from the Willyama

Supergroup metasediments, and equilibrium temper-

atures derived from isotope pairs yield temperatures

around 400 to 450 jC and associated pressure esti-

mates of 400 to 500 MPa, suggesting that alteration

and fluid generation took place at depths of around 10

to 15 km (Clark et al., 2004).

The final style of mineralisation in the Olary

Domain is associated with the emplacement of gran-

ites and resulting fluid generation during the Delam-

erian Orogeny at f480 Ma (Fig. 8d). Examples of

this style are Cu–Au (Mo) greisen and minor skarn

developed around the Anabama Granite, Au-bearing

quartz veins in the Adelaidean sequences, such as at

Wadnaminga and Waukaringa, and minor quartz–

sulphide veining in Willyama Supergroup rocks at

Luxemburg and White Dam. Types V and VI pyrite

are associated with veining, and their trace element

content appears to be entirely dependent on the host

lithologies. At Luxemburg, high Co contents and Co/

Ni ratios in pyrite are explained by the presence of a

large amphibolite body, and the low values observed

at White Dam, where sulphide-bearing quartz veins

cut the Olarian schistosity, result from the lack of any

Co- or Ni-enriched lithologies in the vicinity. Bierlein

et al. (1996a) propose that the sulphur source of the

sulphide-bearing fluids during the Delamerian was

the same as that which provided sulphur for the

earlier Olarian mineralising systems. This hypothesis

is borne out in the isotopic data obtained during this

study (Fig. 7), which shows near identical systemat-

ics for pyrite formed in Delamerian and Olarian

times.

6.4. Comparison with other mineralised provinces

Trace element and isotopic data are effective dis-

criminators for styles of mineralisation in terranes

similar to the Olary Domain. Previous workers (Cook

and Ashley, 1992; Leyh and Conor, 2000) have

suggested that a regional redox boundary style of

mineralisation analogous to that defined for the Kup-

ferchiefer and the Zambian Copperbelt exists in the

Olary Region.

There are a number of differences between sulphide

mineralisation in the Olary Region and in the Kupfer-

schiefer of Europe. The most striking difference is that

observed in the range of sulphur isotopic values in the

two regions. y34S of sulphides from the Kupferschiefer

vary between � 44.7x and � 35.2x (CDT) with

higher values of up to � 8.4x at the base of the

mineralised strata (Bechtel et al., 2001). These strong-

ly negative isotopic values can be interpreted to be the

result of significant contribution of biogenic sulphur

during the mineralisation process (Bechtel et al.,

2002). Coupled with the fact that the Kupferschiefer

formed at end of the Permian, a period of isotopically

light sulphate–sulphur, involvement of biogenic sul-

phur would also contribute to their more negative

isotopic values (Cortecci et al., 1981). This is in

contrast to the Olary region, where y34S values for

strata-bound mineralisation range between � 16xand 11x, where most range between 0x and 4xand are thought to reflect a deep-seated crustal source

of sulphur (Bierlein et al., 1996a). Whereas the sul-

phide deposits in Olary have undergone a significant

degree of metamorphism, if compared to those of the

Kupferschiefer, there is little evidence that isotopic

signatures can be affected by metamorphism on a

regional scale (e.g., Cook and Hoefs, 1997). Both Co

and Ni are enriched in the copper zones within the

Kupferschiefer (Kucha, 1990), and Co-minerals such

as cobaltite have been reported (Bechtel et al., 2002).

Cobalt concentrations in the Kupferschiefer (up to 500

ppm) are significantly lower than those observed in the

Olary region (up to 70000 ppm). This can be attributed

to the different mechanisms, most likely related to the


differing fluid compositions, acting in the different

environments. In the Kupferschiefer, Co enrichment is

thought to be a result of organic matter fixing the

chalcophile elements (Oszczepalski, 1999). Whereas

in the Olary Domain, Co enrichment is most marked

where deposits are proximal to mafic rocks (Radium

Hill, Luxemburg, and Ethiudna), y34S data from the

sulphides suggest that biogenic activity did not play

part in the fixing of Co, and the relatively low Co

content of the Willyama Supergroup rocks preclude

their ability to have acted as a source of enrichment

(Table 4). It can therefore be concluded that the mafic

rocks (Lady Louise suite) act as the primary source of

Co and Ni enrichment in sulphide mineralisation in the

Olary Domain.

Annels and Simmonds (1984), in their consider-

ation of the Zambian Copperbelt, proposed interaction

between a hydrothermal fluid and a mafic magma,

emplaced during crustal rifting, as the mechanism for

the observed Co enrichment in the copper mineralisa-

tion. This mechanism is similar to that proposed in

this paper as the origin of the anomalously high Co

observed in Olarian pyrites. When comparing the y34Svalues for the regions, it is once again apparent that

the sulphur sources differ. McGowan et al. (2003)

report that the range of y34S for copper–cobalt ore

sulphides (� 1x to 18x) does not have the same

source as diagenetic pyrite (� 17x to � 1x). They

suggest an epigenetic model for the formation of the

orebodies that involves the introduction of metal- and

sulphate-bearing hydrothermal fluids into quartzo-

feldspathic units during basin inversion, with sulphide

derived from thermochemical reduction of sulphate

near the site of deposition. This is in contrast to the

Olary Domain, where the source of sulphur for

epigenetic sulphide mineralisation is the same as the

source for the earlier strata-bound sulphide minerali-

sation and has resulted in the y34S for both gener-

ations being similar (Bierlein et al., 1996a).

Recent work by Skirrow and Ashley (2000) and

Williams and Skirrow (2002) has compared epigenetic

mineralisation in the Olary region to the Palaeoproter-

ozoic iron oxide copper–gold styles of mineralisation

such as that occurring at the Olympic Dam deposit in

the Gawler Craton of South Australia. This compar-

ison is based on the temporal coincidence of magma-

tism, alteration, and mineralisation in the Olary region

and at Olympic Dam, although it is stressed that

further age characterisation is needed to fully resolve

this relationship (Skirrow et al., 1999). Reeve et al.

(1990) observed elevated Co contents of chalcopyrite

and pyrite from Olympic Dam, and related this to a

mafic source of metals involved in ore formation in

the deposit. One hypothesised source for metals at

Olympic Dam is the hydrothermal alteration of Mid-

dle Proterozoic basalts on the nearby Stuart Shelf

(Knutson et al., 1992).

The source of sulphur at Olympic Dam is thought

to be different than in Olary. Lower y34S values,

� 4.6x to � 10.8x, are reported which has been

interpreted to be mixing of a magmatic sulphur source

with moderately oxidised fluids (Roberts and Hudson,

1984). The similarity in trace element characteristics,

the coincident timing of magmatism and mineralisa-

tion and the similarities in the proposed mafic source

of metals in the Olary Domain and the Olympic Dam

deposit present a compelling argument that there may

be iron oxide copper–gold style mineralisation pres-

ent in the Olary region, but further work must be done

to further explore this possibility.

7. Summary

Variations in the trace element geochemistry of

petrographically distinct generations of pyrite, indi-

cating different mechanisms of pyrite formation, sup-

port the presence of four distinct metallogenic styles

within the Olary region. The initial stage of pyrite

deposition is associated with extension and the open-

ing of the Willyama Basin. Sulphide mineralisation

during this period is predominantly strata-bound in

style, and the source of the mineralising constituents

are the felsic volcaniclastic material being deposited

during the tectonically active period of the rift system.

Pyrite I is the dominant pyrite type deposited during

this period, and the characteristic zoning exhibited by

the pyrite is controlled by the fluctuating Co content

of the mineralising fluid. The second stage of sulphide

mineralisation is related to the formation of a regional

redox boundary at the interface of the oxidised Cur-

namona Group sediments and the overlying reduced

Strathearn Group sediments. A change in redox con-

ditions could result from either the deepening of the

basin or the onset of anoxia due to stagnation

(Schultz, 1991). The dominant generation of pyrite


growth during this stage is pyrite II, which forms both

overgrowths on Pyrite I and discrete subhedral to

euhedral crystal, both of which are chemically unz-

oned. The lack of zoning indicates that the mineralis-

ing fluid, which is primarily metamorphic in origin,

evolved in chemical equilibrium with the surrounding

host lithologies and precipitated pyrite with a uniform

trace element content reflecting that of the source

rocks. The trace element content of this stage of pyrite

mineralisation is controlled by the immediate host

lithologies, and where pyrite formation occurs prox-

imal to mafic units, such as the Lady Louise suite, the

resulting pyrite will have a high content of cobalt.

Pyrite generations III and IV are related to sulphide

mineralisation occurring during the OD3 event asso-

ciated with basin inversion. Again, trace element

content of the pyrite is controlled largely by the host

lithologies, with minor inputs from magmatic fluids

associated with the emplacement of syntectonic gran-

ites. The final major stage of sulphide mineralisation

is related to the Delamerian Orogeny and associated

emplacement of granites such as the Anabama Gran-

ite. This remobilises some basement sulphides into

veins that cut the dominant Olarian fabric and quartz

vein-related Cu–Au mineralisation hosted in the

Adelaidean metasedimentary rocks.

The sulphur isotope geochemistry of the Olarian

pyrites suggests that the sulphur source was relative-

ly uniform throughout the history of mineralisation.

Repeated tapping of a crustal source by hydrother-

mal fluids can be invoked to explain the relatively

uniform distribution of the analysed pyrites. Local

scale mixing with biogenic and oxidised sulphur has

lead to the higher and lower values observed in some

deposits.

Acknowledgements

This work is the result of a PIRSA-sponsored grant

and is part of work towards a PhD by CC. Thorough

and careful reviews by Geordie Mark and Phil

Seccombe greatly improved the quality of this paper.

We gratefully acknowledge discussions with Colin

Conor, Wolfgang Preiss, and Alistair Crooks about

mineralising processes in the Curnamona Province.

We also thank Frank Bierlein for providing editorial

advice and data from his doctoral work, as well as the

many University of Adelaide honour students who

have worked on various aspects of the Olarian

geology.

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Documents

Genetic implications of pyrite chemistry from the Palaeoproterozoic Olary Domain and overlying Neoproterozoic Adelaidean sequences, northeastern South Australia