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GEOLOGY AND MINERALISATION OF THE FIFIELD PLATINUM PROVINCE, NEW SOUTH WALES Sixth International Platinum Symposium Guidebook for the Pre-Symposium Field Excursion

Edited by

S.J. Elliott and A.R. Martin

Produced by: CSIRO, Division of Exploration Geoscience, Private Bag, Wembley, WA 6014.

This book is copyright. Apart from any fair dealing for the purpose of private study, research, criticism or review, as permitted under the Copyright Act, no part may be reproduced by any process without prior written permission of the copyright owner.

ISBN O909 86980 4

Printed by Vanguard Press 26 John St., PERTH Western Australia 6000

Front cover illustration: Platinum nuggets from Fifield, field of view 15 mm wide. Photograph courtesy of Helix Resources NL.

CONTRIBUTORS S. J. Elliott and A. R. Martin Helix Resources NL, PO Box 825, West Perth, Western Australia

Gary J.Jones Lachlan Resources NL, PO Box 580, Milsons Point, N.S.W., Australia.

G .M. Derrick G.M. Derrick and Associates Pty. Ltd., P.O. Box 184, Corinda, QLD. 4075

Front cover illustration: Platinum nuggets from Fifield, field of view 15 mm wide. Photograph courtesy of Helix Resources NL.

CONTENTS

FOREWORD

PREFACE

CHAPTER 1- ALASKAN-TYPE INTRUSIVE COMPLEXES OF THE FIFIELD BELT, CENTRAL NEW SOUTH WALES 4 1.1. INTRODUCTION 1.2. REGIONAL GEOLOGY 1.3. THE ALASK.AN-TYPE INTRUSIVE COMPLEXES 1.4. PGE MINERALISATION 1.5. SUMMARY AND CONCLUSIONS

4 4 6 8 11

CHAPTER 2 - THE OWENDALE ALASKAN-TYPE INTRUSIVE COMPLEX AND ASSOCIATED PGE MINERALISATION FIFIELD BELT, NEW SOUTH WALES

2.1. INTRODUCTION 2.2. GEOLOGY 2.3. PGE MINERALISATION 2.4. PETROGENESIS and METALLOGENESIS 2.5. SUMMARY AND CONCLUSIONS

12 12 15 20 22

CHAPTER 3 - GEOLOGY AND ECONOMIC POTENTIAL OF THE TOUT COMPLEX, NSW 24 3.1. INTRODUCTION AND TECTONIC SETTING 3.2. GEOPHYSICS AND GEOLOGY 3.3. LATERITISATION AND YOUNGER GEOLOGY 3.4. GEOCHEMISTRY 3.5. ECONOMIC POTENTIAL, TOUT COMPLEX 3.6. SUMMARY AND CONCLUSIONS

24 24 29 30 32 33

CHAPTER 4 - THE KARS AND GILGAI INTRUSIVE COMPLEXES AND ASSOCIATED PGM MINERALISATION, FIFIELD N.S.W

4.1. INTRODUCTION 4.2. KARS PROSPECT 4.3. GILGAI PROSPECT

REFERENCES

35 35 39

FOREWORD This volume is an official Excursion Guide Book for the 6th International Platinum Symposium, Perth Western Australia, July 1991. The International Platinum Symposium is held under the auspices of the International Association for the Genesis of Ore Deposits (IAGOD) by the Commission on Ore Deposits in Mafic and Ultramafic Rocks (CODMUR). The purpose of the symposium is to bring together international scientists working on aspects of the genesis, exploration, exploitation and beneficiation of platinum group metal deposits, to discuss current research and present new concepts relevant to the field. Of specific importance is the opportunity for delegates to visit locations of important platinum mines and prospects in the host nation in conjunction with the symposium. These symposia foster good will and collaboration, between scientists and institutes from different participating countries. They not only enhance international co-operation, but provide the continuity necessary for long-term research success. The Organizing Committee for the 6th International Platinum Symposium appreciate the financial support given by the Federal Committee of the Geological Society of Australia, to print this publication. Acknowledgements are extended to the authors whose papers are included in this guide and to the numerous individuals from industry and academia who have provided information used in these papers. Special acknowledgements are also due to Helix Resources NL, Platsearch NL and Poseidon Exploration Ltd, all of whom have provided invaluable financial and technical assistance. Thanks are also extended to the Organising Committee of the Sixth International Platinum Symposium, in particular Ms Sarah Dowling for editorial comment and logistical support and to Dr. Caroline Perring of CSIRO for editorial comment.

ROBIN E T IITLL Chairman 6th International Platinum Symposium SJ.ELLIOTT Excursion Co-ordinator

PREFACE S.J. Elliott Since their discovery in 1887, the placer platinum deposits of the Fifield area, central New South Wales, have been Australia's only significant producers of platinum metal as a primary product. Over 630 kilograms of platinum was produced from this area. Exploration activities completed by various companies up until the mid-1980's failed to prove any additional placer deposits or to locate the original source/s of the platinum. A resurgence in platinum exploration in Australia in the mid-1980's prompted a number of exploration and mining companies to reassess the Fifield area with the resultant discovery of residual and primary Platinum Group Metals (PGM) mineralisation associated with Alaskan-type intrusive complexes. The Fifield Platinum Province which covers the original placer deposits and a number of

intrusive complexes with associated PGM mineralisation has now been shown to extend over an area 180 kilometres by 80 kilometres, the same area which defines the Fifield Belt of Alaskan-type intrusive complexes. No economic PGM deposits have yet been proved in the Fifield Platinum Province although exploration is continuing as is academic interest in the area. This excursion guide comprises a brief summary of the geology and mineralisation of the Fifield Platinum Province in addition to detailed descriptions of the PGM-mineralised Owendale, Tout and Kars Intrusive Complexes. These complexes, in addition to the original placer platinum deposits, are the subject of a three day field excursion conducted in conjunction with the Sixth International Platinum Symposium.

FIELD EXCURSION LOCALITIES Field excursion localities for the Fifield area of the Fifield Platinum Province are indicated in Plate 1 (next page) and are described briefly below: Locality 1: Abandoned workings of the Platina, Gillenbine Tank and Fifield Deep Lead platinum/gold placer deposits. Platinum may be panned from mullock from some of the old workings. Locality 2: Owendale Intrusive Complex. This complex does not outcrop although trench exposures of Ultramafic Series and Marginal Series lithologies can be seen in the Kelvin Grove Area. Diamond drill core from the Kelvin Grove and North Owendale areas of the complex can be viewed at the core shed at Kelvin Grove farm. Rotary Air Blast (RAB) drill chips from all areas of the complex can also be viewed onsite.

Locality 3: Tout Intrusive Complex. This is the best exposed of the Alaskan-type intrusive complexes of the Fifield Belt with fair outcrop and subcrop of most igneous lithologies or their weathered derivatives. RAB drill chips of these lithologies and the overlying laterite profile may be viewed on-site. Good exposures of the laterite profile can also be seen in the abandoned open-cut workings of the Fifield magnesite mine. Locality 4: Kars Intrusive Complex. This complex does not outcrop although diamond drill core from the complex may be viewed at the Kelvin Grove core shed. Locality 5: Gobondery Granite. Good outcrop of the granite and mafic xenoliths can be viewed in this area. The Gobondery Granite is possibly genetically related to the Alaskan-type intrusive complexes.

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Fifield Area-Field Excursion Localities

CHAPTER 1- ALASKAN-TYPE INTRUSIVE COMPLEXES OF THE FIFIELD BELT, CENTRAL NEW SOUTH WALES S.J. Elliott and A.R. Martin Helix Resources NL, PO Box 825, West Perth, Western Australia

1.1. INTRODUCTION A number of Alaskan-type intrusive complexes with associated Platinum Group Elements (PGE) mineralisation occur in a northerly trending belt in excess of 180 km long and 80 km wide in central New South Wales (Fig. 1.1). This belt has been termed the Fifield Belt after the small hamlet of Fifield situated near its southern end. Although significantly larger dimensions have been used to define this belt by other authors (eg. Johan et al, 1989), the term Fifield Belt as used here refers only to that area which contains intrusions with proven Alaskan-type characteristics. Most of the Alaskan-type intrusive complexes in the Fifield Belt outcrop poorly or not at all, many having been only recently discovered by drilling of aeromagnetic anomalies. Prior to 1985 only a few intrusions had been recognised and it was only during the latter half of the decade that the Fifield belt of

Alaskan-type intrusive complexes was formally recognised and several of the intrusions described in detail, largely as a result of extensive exploration by various companies for PGE mineralisation in the region. Much data are now available on most of the intrusions, largely in the form of unpublished company reports. The locations of the known Alaskan-type intrusive complexes are shown on Figure 1.1. The majority of the Alaskan-type intrusive complexes identified in the Fifield Belt have been shown to contain platinum-group element concentrations of geochemical significance and several of the complexes have been shown to host PGE mineralisation of economic significance. Furthermore, placer (alluvial) PGE mineralisation of economic significance is spatially associated with several of the complexes in the Fifield area.

1.2. REGIONAL GEOLOGY The Alaskan-type intrusive complexes of the Fifield Belt are located within the Girilambone-Wagga Anticlinorial Zone, one of the earliest tectono-stratigraphic provinces of the Tasman Geosyncline. The Tasman Geosyncline represents a Palaeozoic, eastwardly-migrating zone of accretion of continental material along a convergent plate margin in eastern continental Australia. The Girilambone-Wagga Anticlinorial Zone is composed of a north-south trending metamorphosed flysch sedimentary sequence • (Bowman et al, 1982). Metasediments comprising the Girilambone Group consist of slate, schist, phyllite, quartz greywacke and quartzite with minor basaltic amphibolite and calcsilicate amphibolite. The Girilambone

Group sediments were deposited during the Late Cambrian to Early Ordovician and are bounded to the east and west by Late Silurian to Early Devonian acid volcanics and sediments and Middle Devonian sediments of the Tullamore and Murga Synclines respectively. Girilambone Group sediments span a 500 km long by 80 km wide north-south trending belt of gravity highs known as the Parkes Terrace. A discontinuous series of thin, arcuate serpentinites within the Parkes Terrace are believed to marlc the locus of a subduction zone active during the Ordovician. This zone, regarded as a zone of structural weakness and site for potential tapping and de-gassing of the upper mantle, re-opened during the Devonian as a result of crustal thinning which produced the

REFERENCE Alluvium overlaying Mesozoic sediments 0

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Parkes Terrace gravity high. Johan et al (1989) suggest that the Alaskan-type intrusive complexes were emplaced during the Devonian near this palaeosuture in the western half of the Parkes Terrace. These intrusions are believed to represent exposed conduits for andesitic volcanism of the same age (Agnew, 1987). Potassic granites of Devonian age appear to be spatially associated with centres of emplacement of Alaskan-type intrusive complexes. The Gobondery granite outcrops to the east of the Owendale Intrusive Complex and granite is known from drillhole data to occur east of the Honeybugle Intrusive Complex and is interpreted from aeromagnetic data to occur east of the Bulbodney Creek Intrusive Complex. It is possible that these granite intrusions are genetically related to the Alaskan-type complexes as they are of similar age and in some cases contain xenoliths of mafic rocks possibly

derived from the complexes. The late Palaeozoic in the Fifield region was dominated by deep erosion to expose the intrusive complexes. The Mesozoic saw continued erosion and, during the Tertiary, a period of intense weathering which resulted in the development of a thick laterite profile over many of the complexes. The laterite generally has a well developed ferruginous zone underlain by partially developed mottled, pallid and saprolite zones. The present-day thickness of the laterite profile varies from 10 m to 80 m. The present topography of the Fifield Belt is flat to gently undulating with slight depressions over many of the intrusive complexes. Outcrop is rare. Soils, eluvium and sheet wash and buried drainage channels containing gravel, sand and clay overly most lithologies.

1.3. THE ALASKAN-TYPE INTRUSIVE COMPLEXES Alaskan-type intrusive complexes of the Fifield Belt have been described in varying degrees of detail depending upon the amount of exploratory drilling completed on individual complexes. Probably the best known is the Owendale Intrusive Complex which was first classified by Bowman et al (1982) as an Alaskan-type intrusion and which has subsequently been used as a standard for classification of the other bodies in the Fifield Belt. The Owendale Intrusive Complex is classified as an Alaskan-type intrusion as it has several features in common with typical Alaskan-type intrusions as defined by Taylor (1967). Raedeke (1988) summarised the following diagnostic features of the Owendale Intrusive Complex as being consistent with an Alaskan-type classification:1. The complex shows a crude zonation pattern in plan view.

olivine is forsteritic, and magnetite occurs as a primary crystallising phase with modes of 1520% in magnetite-clinopyroxenites. 4. Hornblendite or hornblende-rich rocks and biotite-rich rocks occur near the margin. 5. The complex is part of a belt of intrusions similar to belts of Alaskan-type mafic-ultramafic complexes in Alaska, USA, and the Urals, USSR. Despite these consistencies, it should be noted that the Owendale Complex and other complexes in the Fifield Belt show several features which are dissimilar to "typical" Alaskan-type intrusions: 1) Biotite and K-feldspar are far more abundant that in "typical" Alaskan-type intrusions indicating a more potassium-rich magma,

2. Principal lithologies include clinopyroxenite, olivine-clinopyroxenite, magnetiteclinopyroxenite, biotite-clinopyroxenite, wehrlite and dunite.

2) "Typical" Alaskan-type ultramafic intrusions are totally surrounded by gabbro or diorite whereas ultramafic rocks of the Owendale Complex are often more or less in direct contact with country rock, and

3. Mineralogy: Diopsidic augite (clinopyroxene) is the dominant mineral in the ultramafic rocks, orthopyroxene is rare or absent in the ultramafics (significant orthopyroxene contents are reported from mafic and ultramafic rocks of the Tout Complex - G.M. Derrick, this volume),

3) Contacts of mafic with ultramafic lithologies are sharp and intrusive in Alaskan-type intrusions whereas at Owendale, contacts appear to be both intrusive and gradational crystallisation or assimilation contacts (Raedeke, 1988).

In addition to the diagnostic features described above, the Owendale Intrusive Complex shares a feature with many "typical" Alaskan-type intrusions. It has associated alluvial PGE mineralisation and the ultramafic lithologies, in addition to hosting PGE mineralisation of economic significance, have high average background PGE contents compared with other types of ultramafic intrusions. Background contents of PGE commonly exceed 30ppb platinum plus palladium, in ultramafic lithologies of the Fifield Belt complexes. The other intrusive complexes of the Fifield Belt have been classified as Alaskan-type because they are broadly similar to the Owendale Complex. Many additional similar intrusions of possible Alaskan-type affinity are known, or suspected from aeromagnetic data, to occur in the Fifield Belt. These intrusions have not been designated as Alaskan-type on Figure 1.1 as they are either too poorly described or have very small or non-existent ultramafic components. Alaskan-type complexes of the Fifield Belt are pipe-like bodies with steeply dipping internal contacts. Many of the complexes are approximately circular or elliptical in plan view although more irregular shapes do occur. Surface areas of the complexes vary in size, the smallest being only a few square kilometres in area whilst the largest occupies an area of approximately 120 sq km. Some of the complexes occur in groups and possibly share a common magma chamber at depth. Age determinations for the complexes vary depending upon the method used. Ages range from late Ordovician to late Devonian (L. Barron - pers. comm.). The reason for this large range in ages has not been determined. Earlier work produced K-Ar ages of 397 16 Ma for the Tout Complex and 397 12 Ma for the Hylea Complex. Preliminary SHRIMP U-Pb ages obtained by R. I. Hill of ANU for zircons from two intrusions are 445 6 Ma (95% CL) for Honeybugle, and 448 4 Ma (95% CL) for Bulbodney Creek (R.1. Hill - pers. comm.). Both intrusions apparently were emplaced during Late Ordovician (Eastonian/Bolindian) time. Bulbodney Creek also contains inherited zircon of Late Proterozoic (1050-1100 Ma) age. This latter age appears to be the most reliable obtained to date although it is not consistent with the model for emplacement of the intrusions into the Parkes Terrace outlined in the preceding section. More work is therefore required before a definite age can be placed on the complexes. Igneous rocks of the Alaskan-type

complexes of the Fifield Belt can be broadly subdivided into Ultramafic, Mafic-Felsic and Marginal Series lithologies as based on the work completed by Raedeke (1988) on the Owendale Complex. These Series may be more or less well developed and vary in proportion between complexes. The spatial relationships of the Ultramafic Series and Mafic-Felsic Series lithologies also vary between complexes. In some cases the Ultramafic Series appears to be entirely enclosed within the Mafic-Felsic Series (eg. Honeybugle Intrusive Complex) whilst in others it is peripheral or adjacent to the MaficFelsic Series and in direct contact with the Marginal Series or country rock (eg. Owendale Intrusive Complex). The Marginal Series nearly always occurs at the contact of the two other Series with the country rock although there is an instance in the Owendale Complex where Marginal Series lithologies occur between the Ultramafic Series and Mafic-Felsic Series.

1.3.1. Ultramafic Series The Ultramafic Series is comprised of dunite, wehrlite, olivine-clinopyroxenite, biotiteclinopyroxenite, magnetite-clinopyroxenite and clinopyroxenite. The clinopyroxene is augite. Individual complexes may contain all or some of these lithologies. Ultramafic Series lithologies often, but not always, exhibit a concentric zonation with an outer zone rich in clinopyroxene and an inner zone rich in olivine This zonation is exhibited in its simplest form in the Tout Intrusive Complex. Other complexes, notably the Owendale Intrusive Complex, have several apparently discordant serpentinised wehrlite-dunite bodies enclosed within biotite-clinopyroxenite and magnetite-clinopyroxenite. Olivine-rich ultramafics are nowhere in direct contact with rocks of the Mafic-Felsic Series, the Marginal Series or country rock. Dunite-wehrlite bodies at Owendale are often wholly or partly rimmed by biotite-rich clinopyroxenite. Although olivine-bearing lithologies are known from most of the complexes, dunite bodies of appreciable size have only been shown to be present in the Tout and Owendale complexes. Whereas the dunite body in the Tout Complex appears to be "primary" and to be approximately concordant with the other ultramafic lithologies, several of the dunite (wehrlite) bodies at Owendale appear to be "secondary" and discordant with the enclosing pyroxenites. It has been suggested that these "secondary" dunites may be due to the metasomatic replacement of pyroxene by olivine

under conditions of increased water fugacity (Raedeke, 1988; Turvey, 1989b). These dunite bodies are analogous to similar bodies seen in other intrusions including the Bushveld and Stillwater layered intrusions (Raedeke, 1988). Dunite and wehrlite lithologies in the Fifield Belt Alaskan-type complexes exhibit almost complete serpentinisation of olivine.

1.3.2. Mafic-Felsic Series Principal constituent minerals of the Mafic-Felsic Series include plagioclase, augite and K-feldspar with most rocks also having magnetite and biotite and some rocks having hornblende. and hypersthene quartz, Hypersthene and hornblende rarely occur in the same rock, at least in the Owendale Complex (Raedeke, 1988). Lithologies of this series include diorite, monzonite and syenite and variations on this basic theme dependent on the amount of accessory pyroxene, hornblende and quartz (eg. quartz diorite). Internal zonation of the Mafic-Felsic Series lithologies is apparent in the Owendale Complex where there is an outer plagioclase-rich zone (diorite) enveloping an inner K-feldsparrich zone (monzonite). Quartz-bearing rocks of the Mafic-Felsic series in the same complex are generally restricted to the margin of the intrusion. Zonation characteristics of the MaficFelsic Series in other complexes of the Fifield Belt are not as apparent as in the Owendale and Tout Complexes, largely as a result of insufficient outcrop or drillhole data. Contact relationships between rocks of the Mafic-Felsic Series and those of the Ultrarnafic Series have only been defined in any detail in the Owendale and Kars Intrusive Complexes. Contacts observed in drill core from the Owendale Complex are in some cases sheared intrusive contacts or are crystallisation

contacts related to either assimilation or normal fractionation. Mafic-Felsic Series rocks in the Kars Complex clearly intrude the Ultramafic Series in a wide breccia zone.

1.3.3. Marginal Series Hornblende-rich Marginal Series rocks occur at the margins of the Mafic-Felsic Series and the Ultramafic Series, most commonly adjacent to the contact of the intrusive complex with the enclosing country rock. The width of the Marginal Series varies between complexes and within individual complexes. In places it is absent or of negligible extent Hornblende-rich rocks at the margin of the Owendale Complex can be observed in drill core interlayered with hornfelsed country rock. Hornblende in the Marginal Series rocks was probably formed as a result of assimilation of country rock. Hornblende-rich clinopyroxenites near the margin of some complexes are included in the Marginal Series rather than the Ultramafic Series because of their location and because the hornblende is probably the result of interaction with the country rock. None of the intrusive Complexes in the Fifield Belt exhibit deformation features other than the minor shear zones observable in drill core. Major fault systems are interpreted from aeromagnetic data to transgress several intrusions, notably the Owendale, Bulbodney Creek and Honeybugle Complexes, but no direct evidence of such large scale features has yet been located. effects metamorphic Thermal associated with the intrusive complexes appear to be minor although hornfelsed country rock is associated with the Owendale Complex. There is some evidence to suggest that at least some of the complexes, notably the Kars Complex, were tectonically emplaced.

1.4. PGE MINERALISATION Many of the Alaskan-type intrusive complexes in the Fifield Belt host PGE mineralisation of economic significance and most contain PGE in above average concentrations for ultramafic rocks. All PGE mineralisation is confined to Ultrarnafic Series lithologies and their weathered derivatives and, more specifically, shows a strong spatial association with olivine-rich rocks. The majority of analyses for PGE in the Fifield Belt Complexes have been derived from exploratory work completed by mining

companies. The data have been derived using a number of analytical techniques and are therefore inherently inconsistent with respect to accuracy. However, check-assaying completed by the various companies and independent academic and government institutions is sufficient to ensure that the data are reliable and sufficiently accurate to establish mineralisation trends. Three types of PGE mineralisation are present in the Fifield region:

1. Placer (alluvial). PGE mineralisation in palaeo-drainage systems spatially associated with the intrusive complexes. 2. Residual. PGE mineralisation in laterite profiles overlying ultramafic rocks of the intrusive complexes. 3. Primary. PGE mineralisation associated with pegmatitic clinopyroxenites and dunite/wehrlite bodies.

1.4.1. Placer Deposits The Fifield Platinum Field, situated near the small hamlet of Fifield, was Australia's first significant producer of platinum, and remains the only area from which platinum has been produced as a primary product. Discovered in 1887 and worked intermittently until the mid1960s, the Fifield Platinum Field has produced 639.5 kg of platinum, the majority of which has been . obtained from buried palaeo-channels known as deep leads. In addition, 179 kg of gold have been recovered from the same The Fifield Platinum Field sources. encompasses several placer deposits, the most productive of these being the Platina Lead (478 kg platinum and 53 kg gold) followed by the Fifield Lead (145 kg platinum and 53 kg gold) and the Girilambone Tank Lead (6.5 kg Platinum and 1 kg gold). The locations of these deep leads are shown on the map at the front of this volume. Some 10 kg of platinum and 1 kg of gold were also produced from Tertiary conglomerate at Jacks Lookout. Platinum and gold mineralisation in the deep leads is generally contained within thin gravel units less than 1 m thick at the base of the deep lead palaeo-channels. The leads are all less than 30 m wide, up to 3 km long and were worked via numerous shafts up to 30 m deep. Reported grades varied from 6 to 18.4 g/t platinum and 1 to 4.5 g/t gold, with the average being close to the lower end of the range (Bowman et al, 1982). PGE distribution in the deep leads was approximately 90% platinum, 8% osmium, J % iridium and 1% rhodium. Approximately 90% of the platinum in the deep leads occurs as isoferroplatinum and platinum alloyed with iridium, osmium, iron and copper. The remaining 10% occurs as platinum group minerals (PGM) found as inclusions within the platinum alloys. These PGM include osmiridium, laurite (RuS2) and an Ir-Rh sulphide. Most nuggets are less than 1mm in diameter and consist of single crystals or agglomerates of several nuggets. Most nuggets

are rounded although some nuggets panned from alluvial material overlying the Owendale Complex have well-defined crystal faces and only minor bevelling of edges. The principal platinum-bearing palaeochannels of the Fifield Platinum Field, although spatially associated with the Owendale, Tout and Murga Complexes, do not appear to have been sourced directly from them. This implies that the alluvial platinum was either not derived from these complexes or was subjected to two or more periods of erosion and transportation. The latter explanation is the most likely as there is ample evidence to suggest that the Fifield Region has been subjected to numerous periods of erosion and deposition, possibly commencing as early as the Permian (Horwitz, 1988). No alluvial platinum mineralisation is known from the Fifield Region outside of the Fifield Platinum Field,other than minor platinum associated with cassiterite and gold in the Burra Deep Lead between the Tresylva and Owendale Complexes (Bowman et al, 1982) and in sheet wash overlying and adjacent to the Owendale Complex (Elliott, 1989).

1.4.2. Residual PGE Mineralisation Residual PGE mineralisation is associated with a number of the Complexes which have been subjected to deep lateritic weathering. This type of mineralisation is invariably found within laterite profiles, or vestiges of these profiles, overlying olivine-rich ultramafic rocks. Residual mineralisation is best developed in the Owendale, Tout and Bulbodney Creek Complexes although several of the other complexes including Honeybugle and Gilgai also host residual concentrations of PGE. Grades of residual PGE mineralisation associated with the various complexes vary up to 1.0 g/t platinum with isolated concentrations over small intervals as high as 14 g/t platinum. The best intersection recorded to-date from exploratory drilling is 16 m of 4.3 g/t platinum from a vertical rotary air blast (RAB) drillhole in the Bulbodney Creek Complex (Martin and The remaining PGE MacDonald, 1990). rhodium, iridium, osmium, (palladium, ruthenium) are subordinate to platinum. They comprise less than 10% of the total PGE content. Palladium comprises the substantial proportion of this remainder. The association of PGE mineralisation with olivine-rich lithologies is particularly evident in the Owendale Complex where broad zones of low grade residual mineralisation (commonly 0.1 to 0.3 g/t platinum) overlie

dunite/wehrlite bodies. Narrower, higher grade zones (0.5 to 1.5 g/t platinum) closely parallel the axes of these bodies. Studies of PGE mineralised laterite profiles in the Bulbodney Creek Complex completed by Brill and Keays (1988, 1989a, 1989b, 1990) have indicated that the PGE mineralisation is the result of concentration of pre-existing, primary PGE by mass-loss incurred during the lateritisation process. No direct evidence for low-temperature mobilisation of PGE in the laterite profile was found. Much of the data used to reach this conclusion was from detailed geochemical analysis of chips from RAB drillhole BCR-5 from - the Bulbodney Creek Complex. It should be noted that this drillhole intersected higher average platinum grades (16 m at 4.3 g/t platinum) than are considered typical of Fifield belt residual PGE mineralisation. The data are therefore not typical of this type of mineralisation. Platinum-iron alloys, principally isoferroplatinum, appear to be the dominant PGM species present in the residual mineralisation. Most of the PGM are very fine (less than 25um) although metallurgical test work at Owendale has indicated that a significant proportion of the PGM (30% to 40%) are recoverable by conventional gravity techniques. This re-inforces the proposition that a significant proportion of the PGM occur as "coarse" grains (>25um).

1.4.3. Primary PGE Mineralisation Primary PGE mineralisation of economic significance has to date only been recognised within the Owendale Intrusive Complex, although minor, low grade concentrations have also been reported from the Honeybugle Complex (up to 0.3 g/t platinum), the Bulbodney Creek Complex (up to 0.2 g/t platinum) and the Kars Complex (up to 2.0 g/t platinum) and the Gilgai Complex (up to 2.0 g/t platinum). Primary PGE mineralisation in the Owendale Complex and similar but lower grade concentrations in the Bulbodney Creek, Honeybugle and Kars Complexes, invariably exhibit a close spatial association with olivinerich lithologies. Two distinct, but probably related types of primary mineralisation have been identified in the Owendale Complex; PGEmineralised pegmatitic clinopyroxenites known as P-Units (Suppel et al, 1986), and dunite/wehrlite PGE mineralisation. A genetic model linking both types of mineralisation to formation of secondary dunite/wehrlite bodies

has been proposed by Raedeke (1988) and Turvey (1990) and is summarised by Elliott and Martin (1991, this volume). In brief, the proposed genetic model involves scavenging of PGE during formation of the secondary dunite/wehrlite bodies and subsequent deposition of the PGE in and adjacent to these bodies. The P-units were formed as a result of "streaming" of PGE-bearing volatile fluids away from the secondary dunite/wehrlite bodies. P-units range from coarse-grained to pegmatitic, monomineralic clinopyroxenites and are only known in the southern part of the Ultramafic Series of the Owendale Complex. PGE mineralisation to 13.6 g/t platinum drilled over a 1.4 m interval is associated with these units which range in thickness from a few centimetres to 1.4 m. P-units appear to be discontinuous and lens-shaped bodies. They are usually totally enclosed within biotite-pyroxenite and some are edged by a biotite selvage. PGE are present in the P-units as platinum-iron alloys and alloys, sulphides, antimonides and arsenides of Pt, Pd, Os, Ir and Rh. Platinum is by far the dominant PGE comprising approximately 90% of total, with palladium forming the bulk of the remainder. PGM in the P-units are found as inclusions within magnetite and augite. Chalcopyrite, pyrrhotite, cobaltopentlandite, cobaltite, galena and sphalerite as well as magnetite and ilmenite are sometimes associated with the PGM. The total sulphide content of the P-units is however very low (<0.5%). Dunite/wehrlite-associated PGE mineralisation is less well defined than the Punit mineralisation and has only been positively identified in the Owendale and Kars Complexes. Mineralisation of this type appears to occur at, and adjacent to, contacts of dunite with enclosing wehrlite. PGE grades as high as 2.4 g/t platinum are present associated with dunite/wehrlite bodies of the Owendale Complex and grades as high as 2.0 g/t platinum· are reported from similar litholgies in the Kars Complex. The various PGE are present in similar proportions to that found in the P-unit mineralisation. The total sulphide content of this type of mineralisation is very low (<0.5%). In addition to the types of mineralisation described above, minor hydrothermal PGE mineralisation is associated with probable fracture zones in pyroxenites and diorites of the Tout Complex. This type of mineralisation is known from two localities, both of which appear to be of very limited extent. Hydrothermal PGE mineralisation of this type is palladium-dominant with minor platinum

associated with secondary copper minerals, gold and silver. Typical grades are 1.0 g/t palladium,

0.2 g/t platinum, 2.0 g/t gold, 8.0 g/t silver and 1.5 wt% copper.

1.5. SUMMARY AND CONCLUSIONS The Fifield Belt of central New South Wales comprises a number of complex, zoned igneous intrusions of Early Palaeozoic age which bear many similarities to Alaskan-type intrusions of Alaska and the Urals, USSR. The igneous complexes of the Fifield Belt vary in size, shape, zonation characteristics and proportions of constituent lithologies, but all are sufficiently similar to "typical" Alaskan-type intrusions to be collectively placed within that class. Intrusions in the belt which do not contain ultramafic lithologies, but are similar to the Alaskan-type intrusive complexes in all other aspects, have not been included in this category. Lithologies comprising the Alaskantype complexes can be grouped in three series; Ultramafic, Mafic-Felsic and Marginal. Rocks of these series are present, or presumed to be present in varying proportions, in all of the complexes. Although the zonation and contact relationships between these three series vary from complex to complex, an "ideal" complex would have a core comprised of Ultramafic Series lithologies enclosed within an envelope of Mafic-Felsic Series rocks which would in turn be rimmed by Marginal Series rocks at the contact of the complex with the enclosing country rock. Three principal types of PGE mineralisation are associated with the Alaskan-

type complexes:]. Placer (alluvial) PGE mineralisation. 2. Residual PGE mineralisation associated with lateritisation of ultramafic rocks. 3. Primary PGE mineralisation associated with dunite/wehrlite bodies and pegmatitic clinopyroxenites. All residual and primary PGE mineralisation is invariably associated with Ultramafic Series rocks and, more specifically with olivine-rich variants. Placer PGE mineralisation is presumed to have been derived from erosion of the residual and primary mineralisation. Although some of the Fifield Belt complexes have been relatively well described, many of the complexes have been defined only from aeromagnetic data and a few drillholes. Many additional aeromagnetic anomalies may also prove to be Alaskan-type complexes. Much additional work is required on all of the complexes to fully describe their mode of emplacement and petrogenesis and the genesis of associated PGE mineralisation. Although some work has been completed in this area our knowledge of the ongm of the PGE mineralisation is still largely hypothetical. Additional work on this theme will be invaluable to the mining companies exploring for PGE mineralisation in the region.

CHAPTER 2 - THE OWENDALE ALASKAN-TYPE INTRUSIVE COMPLEX AND ASSOCIATED PGE MINERALISATION FIFIELD BELT, NEW SOUTH WALES S J Elliott and A R Martin

2.1. INTRODUCTION The Owendale Alaskan-type Intrusive Complex (Owendale Complex) is one of a number of similar complexes which comprise the Fifield Belt of Alaskan-type complexes situated in central New South Wales. This belt of Alaskan-type complexes has been previously described by Elliott and Martin (1991, this volume). The Owendale Complex has been the subject of intensive exploration for economic Platinum Group Element (PGE) mineralisation since 1985. In the six year period since commencement of exploration activities the complex has been investigated by over 31,000 m of rotary air blast (RAB), reverse circulation and diamond drilling and 6,000 m of trenching. As the complex does not outcrop, almost all lithological and geochemical data have been

derived from this work. Exploration of the Owendale Complex has, in addition to defining its lithological and geochemical characteristics, led to the discovery of PGE mineralisation in various settings. Placer, residual and primary mineralisation have been defined associated with the complex. Of these, only placer (alluvial) mineralisation, which is spatially associated with the complex but not necessarily derived from it, has been commercially exploited, albeit on a small scale. Discovery of residual and primary PGE mineralisation directly associated with the complex has subsequently provided impetus for further detailed study of the complex and for the discovery of similar types of mineralisation in other complexes of the Fifield Belt.

2.2. GEOLOGY The Owendale Complex (Fig. 2.1) is one of several Alaskan-type complexes situated near the small hamlet of Fifield, central New South Wales. Interpretation of aeromagnetic data, in combination with drilling, has shown that the complex is approximately circular in plan view with a surface area of 26 sq kms. The complex is pipe-like in form with steeply dipping external contacts and is emplaced within metasediments, predominantly quartz-mica schists, of the Cambra-Ordovician Girilambone Group. No extrusive equivalents of the Owendale Complex lithologies have been positively identified although it has been suggested by Bowman et al (1982) that the andesitic Raggatt Volcanics of probable SiluroDevonian age, which outcrop to the east of the

complex, may have their ultimate derivation from this and similar complexes. The lithologies which comprise the Owendale Complex can be broadly subdivided into an Ultramafic Series, a Mafic-Felsic Series and a Marginal Series (Raedeke, 1988). Ultramafic Series lithologies comprise approximately one-third of the surface area of the complex and, apart from an isolated body near the centre of the complex, form a continuous zone in the east and south (Fig. 2.1). This zone has been further subdivided for easy reference into the Kelvin Grove (south), Cincinatti (east) and North Owendale (northeast) areas, this subdivision being on the basis of geography rather than lithological variation. Mafic-Felsic Series lithologies comprise the bulk of the remainder of the complex with

Metapelites

N Metapelites 1km

I: X

Ultramaf ic series

Dunite-wehrlite

Mafic-felsic series

Marginal series

Figure 2.1. Geological Interpretation of the Owendale Complex

Marginal Series lithologies confined to the outer margins of the complex and, to a lesser extent, to contacts between the other two series. It should be noted that the contacts of the various lithologies shown on Figure 2.1 have been defined largely by extrapolation from vertical RAB drillholes and therefore cannot be

considered to be definitive.

2.2.1. Ultramafic Series Rocks of the Ultramafic Series comprise clinopyroxenite, biotiteclinopyroxenite, magnetite-clinopyroxenite,

olivine-clinopyroxenite, wehrlite and dunite. Hornblende-clinopyroxenites occur interlayered with Ultramafic Series lithologies but are generally restricted to the margins of the complex and are therefore included in the Marginal Series. Clinopyroxene-rich lithologies of the Ultramafic Series comprise diopsidic augite with varying amounts of biotite, magnetite and olivine. Clinopyroxenites which contain more than 10% and less than 40% modal biotite, magnetite or olivine are termed, respectively, biotite-clinopyroxenite, magnetiteclinopyroxenite or olivine-clinopyroxenite. Wehrlite comprises 40%-85% olivine and dunite greater than 85% olivine. Other accessory minerals (less than 10%) in the clinopyroxenites include minor hornblende and to a lesser degree plagioclase and rare K-feldspar (orthoclase) (Martin and MacDonald, 1990). No orthopyroxene is present in the ultramafic rocks. Biotite is present in the ultramafic rocks in amounts up to 50% and occurs as two distinct textural types; as discrete crystals evenly distributed throughout the rock and as coarse grained segregations up to 15mm across. Some biotite segregations have cores of olivine. Biotite occurs in clinopyroxenites throughout the ultramafic zone but appears to be concentrated in broad zones surrounding dunite-wehrlite bodies and near the margins of the complex. Primary magnetite occurs in most ultramafic rocks but seldom exceeds 10%, except in the Kelvin Grove area where magnetite-clinopyroxenite forms a large proportion of the Ultramafic Series. Secondary magnetite, a product of serpenumsation, is present in olivineclinopyroxenites, wehrlite and dunite. Some clinopyroxenites observed in drill core exhibit wispy, hair-like black lines which comprise magnetite with serpentine minerals. This texture appears to be the result of serpentinisation of olivine along grain boundaries and the cleavage fractures of clinopyroxene (Turvey, 1990). Olivine in the ultrarnafic rocks forms discrete crystals in the clinopyroxenites but occurs increasingly as amaeboidal-shaped segregations in wehrlite. Accessory hornblende in the clinopyroxenites occurs as pseudomorphs replacing clinopyroxene. Where replacement of clinopyroxene by hornblende has exceeded 10% (hornblende-clinopyroxenite) the rocks are usually grouped as part of the Marginal Series. Monominerallic clinopyroxenite is rare although small lenses of coarse-grained to pegmatitic clinopyroxenite largely devoid of accessory minerals, have been observed in drill core from the Kelvin Grove area. These units

have been termed 'P-units' by Suppel and Barron (1986) and are related to PGE metallogenesis in the Owendale Complex. Ultramafic Series lithologies are, with the exceptions of the olivine and biotite segregations described previously, commonly medium-to coarse-grained and exhibit cumulate textures. Pegmatitic textures have been observed in P-units and in some wehrlites adjacent to dunite bodies in the North Owendale area. Textures indicating the resorption of clinopyroxene by olivine have also been observed at the latter location. Crude layering observed in drill core from the Kelvin Grove area indicates the presence of steeply-dipping units which appear to parallel the external contact of the complex. Cyclical layering on a scale of several metres to tens of metres has been identified by Raedeke (1988). These poorly developed cycles show a general increase in olivine from clinopyroxenite to wehrlite towards the centre of the complex. Whilst the Ultramafic Series as a whole is approximately concordant with the walls of the intrusion,there are several dunite-wehrlite bodies which are apparently discordant to this overall concentricity and also, by association, with the internal layering described above. These bodies are generally of the order of several hundred metres wide and up to 1000 m long with the long axes orientated semi-parallel to oblique to the external contact of the complex. Elongate dunite bodies occur near the centre of these bodies with a linear decrease in olivine content through wehrlite to olivine- and biotiterich clinopyroxenite at the margins. Dunite contains greater than 95% olivine, largely converted to serpentine and secondary magnetite, with minor enclaves of coarse clinopyroxene grains and equigranular clinopyroxenite (Turvey, 1990). Wehrlite adjacent to the dunites is often pegmatitic. The dunite-wehrlite bodies, although discordant, do not appear to be intrusive into other rocks of the Ultramafic Series but are interpreted to be replacement bodies with olivine replacing pre-existing clinopyroxene (Raedeke, 1988; Turvey, 1990). Similar secondary dunite bodies are known from other intrusions including other Alaskan-type intrusions and the Bushveld Layered Intrusion.

2.2.2. Mafic-Felsic Series Rocks of this series can be broadly subdivided into a central core of monzonite and an outer zone of diorite which is in contact with rocks of the Ultramafic Series to the south and

east and with rocks of the Marginal Series and enclosing metasediments to the north and west It has been suggested by L. Barron (pers. comm.) that these broad subdivisions can be further subdivided into concentrically zoned units depending on the proportions of primary and accessory constituent minerals. The principal rock-forming minerals of the Mafic-Felsic Series are plagioclase, augite and K-feldspar (orthoclase) and most rocks also contain minor magnetite and biotite. Some rocks also contain either hypersthene or hornblende, but rarely both. Quartz is generally restricted to rocks adjacent to the margins of the complex. Mafic-Felsic Series rocks are generally medium-to coarse-grained. Plagioclase occurs as zoned subhedral phenocrysts, augite is subhedral to anhedral and orthoclase is usually interstitial. Diorite of the Mafic-Felsic Series can be seen in direct contact with Ultramafic Series lithologies in drill core from the Kelvin Grove area. These contacts are in some cases sheared, which may be related to either faulting or intrusion, or are crystallisation contacts related to either assimilation or normal fractionation (Raedeke, 1988). The presence of Marginal Series rocks between the Ultramafic Series and the Mafic-Felsic Series west of Cincinatti suggests an intrusive relationship between the two series.

2.2.3. Marginal Series Marginal Series lithologies are, as the name suggests, confined to the margins of the complex and, to a lesser extent, between MaficFelsic and Ultramafic Series rocks. A small outlier of Marginal Series rocks also occurs within metasediments immediately to the south of the complex. Marginal Series rocks are interlayered with, and to some extent gradational to, rocks of the other two Series. Marginal Series rocks are characteristically hornblenderich with hornblende content being used as a discriminator between rocks of this Series and those of the Ultramafic and Mafic-Felsic Series. Marginal Series rocks comprise hornblendite, pyroxene-hornblendite/hornblende-

clinopyroxenite and hornblende-gabbro. Hornfels are also interlayered with rocks of the Marginal Series. Rocks of the Marginal Series are usually medium-to coarse-grained and are occasionally porphyritic. A porphyritic rock containing large (up to 15 mm) phenocrysts of hornblende has been noted in thin zones a few metres wide in trenches in the Kelvin Grove area. This characteristic rock has been unofficially termed the Honeybugle Hornblendite after the type locality in the Honeybugle Complex which is situated in the Fifield Belt approximately 100 km north of Owendale. The Owendale Complex exhibits no significant deformation features, the last significant period of deformation in the Fifield Region being the Delamerian Orogeny which was responsible for deformation and metamorphism of the enclosing Girilambone Group metasediments prior to emplacement of the complex. Major dislocation structures, notably a fault zone which transgresses the complex and enclosing metasediments in a northwesterly direction, have been interpreted from aeromagnetic data. This interpreted fault has not been confirmed by subsequent drilling and there is no apparent significant dislocation of the major lithological Series. Numerous small shear zones, rarely in excess of a few centimetreswide, have been noted in drill core from the Kelvin Grove area. These shear zones appear to be most predominant in, and adjacent to, Marginal Series rocks and are possibly related to the emplacement of the complex into its present position. All rocks of the Owendale Complex are weathered to depths from a few metres to 80 m and are covered by a thin veneer of soil and clay/sand/gravel alluvium up to 40 m deep. Rocks of the Ultramafic Series have been particularly susceptible to weathering. A laterite profile, comprising an upper iron-rich zone overlying mottled and saprolite zones has developed over most ultramafic rocks. The thickness and completeness of the laterite profile varies depending upon the topography prevalent during weathering and the depth of subsequent erosion.

2.3. PGE MINERALISATION PGE mineralisation associated with the Owendale Complex occurs in three basic settings:]. Placer (alluvial) mineralisation in

palaeochannels overlying or adjacent to the complex. 2. Residual mineralisation associated with deep lateritic weathering of Ultramafic Series

lithologies. 3. Primary mineralisation associated with Ultramafic Series lithologies.

2.3.1. Placer PGE Mineralisation Placer (alluvial) PGE mineralisation has previously been mined from palaeochannels in the Fifield Platinum Field, the northern extent of which is situated approximately 8 km south of the Owendale Complex. This mineralisation has previously been described by Bowman et al (1982) and Elliott and Martin (1991, this volume). The PGE in these palaeochannels were almost certainly derived from Alaskan-type complexes which outcrop in the area, including the Owendale Complex, but due to a complex history of erosion and transportation cannot be definitely linked to any specific complex or complexes. Small amounts of PGE have also been shown by assay and by microscopic examination of heavy mineral concentrates to be associated with alluvium overlying and immediately adjacent to the Owendale Complex. This alluvium occurs in two broad northeasterly trending palaeochannels known as the Owendale and Milverton Leads. These palaeochannels would have had their headwaters in, or near, the adjacent Tout Complex and it is therefore possible that at least some of the PGE were derived by erosion of this complex. Sediments of the palaeochannels comprise clay and sand with minor thin, poorlysorted gravel horizons which contain clasts of subrounded to angular vein quartz, lesser goethite (presumably derived from erosion of laterite), and rare clasts of igneous lithologies derived from the complex. Clasts rarely exceed 10 cm in diameter and are more commonly 1-2 cm. PGE are concentrated in gravel horizons overlying erosional unconformities at the base of the channels or within the channels where a period of deposition has been followed by a period of erosion and subsequent redeposition. Bulle sampling of near-surface gravels of the Milverton Lead near the southeastem margin of the complex has indicated platinum grades as high as 0.14 g/loose cubic metre platinum. Assay of alluvial material obtained from RAB drillholes in the Owendale Lead in the North Owendale area has indicated grades as high as 0.4 g/t platinum. Platinum is the principal PGE in the Milverton Lead and probably accounts for more than 90% of the total PGE present. Platinum occurs as small (up to 3 mm), irregularly shaped

nuggets of isoferroplatinum (Pt3Fe). Johan et al (1990) have also identified Os-Ir-Pt alloys, cuprorhodsite, Bowieite - kashinite (Rh, lr, Pt, Cu, Fe, Os, S, As bearing minerals) and Pd and Rh-Pd arsenides occurring as inclusions in the larger isoferroplatinum nuggets. Gold occurs as irregular nuggets up to 5mm long and generally comprises less than one third of the total precious metals content of the Milverton Lead. Most of this gold is probably derived from quartz veins in the Girilambone Group schists.

2.3.2. Residual PGE Mineralisation Residual PGE mineralisation in the Owendale Complex is associated exclusively with deep lateritisation of Ultramafic Series rocks (Fig. 2.2) and, more specifically, with olivine-rich lithologies, particularly the discordant dunite-wehrlite bodies. Drilling has shown that zones of residual mineralisation broadly parallel these bodies and usually have a high grade, elongate central zone some tens of metres wide and hundreds of metres long surrounded by a broad halo of low-grade mineralisation. Mineralisation of this type is present in all areas of the Ultramafic Series but is best developed in the Cincinatti and North Owendale areas. Residual mineralisation PGE grades are commonly between 0.1 and l.5g/t platinum with lesser palladium and minor osmium, iridium and rhodium. The platinum to palladium ratio is similar to that for most other forms of PGE mineralisation associated with the Owendale Complex being usually greater than 10: 1. Higher PGE grades do occur in the laterite profile with grades up to 8g/t platinum over a 1 m vertical interval recorded from the Cincinatti area. The laterite profile containing the residual PGE mineralisation at Owendale is a typical laterite profile exhibiting enrichment in iron due to the loss of magnesium and silica during weathering. Manganese, nickel, cobalt, copper and chrome are also enriched in the profile to varying degrees. The profile typically has an upper, iron-rich zone below which there is a mottled zone and saprolite. Platinum is concentrated in the profile over thicknesses from a few metres to 40 m with peak values usually occurring at the base of, or immediately below, the ferricrete zone (Fig. 2.3). Peak platinum values are sometimes observed at, or near, the top of the ferricrete, a situation which is probably due to physical concentration of resistate platinum-bearing minerals by reworking of the upper parts of the laterite

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N -------+~==Horizontal Scale 1:7,000 Histogram Scale 1cm=1,000ppb Pt (200ppb cut off)

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DOH collar and number (Prefixed by FKD)

Figure 2.2. Owendale Intrusive Complex, Kelvin Grove area. Costeans showing Pt assays over 2 m intervals

profile or by these minerals working their way down into the top portions of the laterite from overlying alluvium. Detailed investigations by Brill et al (1989a/b) of PGE mineralisation in a RAB drillhole (FIR-375) from the North Owendale

area have shown that platinum is enriched by a factor of 27 over the underlying, unweathered bedrock. This high enrichment factor indicates that the platinum was originally very erratically distributed in the rock prior to weathering and that the high grades now observed in the laterite

ALLUVIUM FERRUGINOUS ZONE:Dark brow to black and grey clay with ,60¼ iron oxides. Minor chalcedony at base. SAPROLITE: Green and brown

:=-_-- clays. Minor biotite and -

_ _ __ -

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clinopyroxene towards base. Minor chalcedony WEATHERED BEDROCK : Green and brown weathered peridotite. Upper contact gradational.

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I 100 200 300 400 ppb

;., ....... /:

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: I

wt¼

20,000

40,000

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Figure 2.3. RAB drill hole FIR-375, Geochemical profiles, North Owendale Area. Modified from Brill and Keays, 1989

profile reflect a primary protore which has subsequently been entirely weathered. There is no direct evidence to suggest large scale supergene remobilisation of PGE in the lateritic environment although a supergene origin for at least some of the lateritic PGE has been proposed by Turvey (1990) and Bowles (1989). Results of investigations completed by Brill et al (1989a/b) on similar lateritic mineralisation associated with the Bulbodney Creek Complex, another Alaskan-type intrusive complex of the Fifield Belt, indicated that the mineralisation is probably the result of residual concentration during weathering, although there were some ambiguities which might be explained in terms of contributing supergene processes. Additional detailed investigations are required in this area before a definite genetic model can be established. Metallurgical work completed to date has shown that the platinum group minerals (PGM) which comprise the residual mineralisation are much finer grained than those observed in placer mineralisation with few grains exceeding 100 microns and most being less than 50 microns. Work completed by Bowles (1989) and Brill et at (1990) has indicated that the dominant mineral species is platinum-iron alloy. One grain of this alloy was observed to have a small inclusion of

osmiridium.

2.3.3. Primary PGE Mineralisation Two types of primary PGE mineralisation are known to be associated with the Owendale Complex: 1. P-Unit mineralisation (Coarse grained to pegmatitic, monominerallic clinopyroxenite). 2. Mineralisation associated with dunite-wehrlite bodies. P-Unit Mineralisation. P-units have been defined by Suppel and Barron (1986) as coarse-grained to pegmattllc, monominerallic clinopyroxenite which sometimes contain high concentrations of PGE, predominantly platinum. These units have only been positively identified in drillcore from the Kelvin Grove area. The majority of platinum intersections shown on Figure 2.4 correspond to the location of P-units. The fact that they have not been identified elsewhere in the Ultramafic Series of the Owendale Complex, or in any of the other Fifield Belt complexes, may be an artifact of the manner in which exploration has been conducted. P-units vary in width from a few millimetres to 2 m and appear to be discontinuous, lens shaped bodies probably not

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Figure 2.4 Owendale Intrusive Complex - Kelvin Grove Area Diamond Drillhole Section 11,000E showing best platinum intersections.

more than a few tens of metres in length. They are invariably enclosed within biotite-magnetiteclinopyroxenites with which they have contacts varying from apparently conformable to crosscutting and sharp to gradational. The contact is also often marked by a significant increase of accessory minerals, principally biotite, in the host clinopyroxenite. Some P-units have a centre line which is defined either by a fracture or by a cavity now filled with coarse biotite. Punits often occur in 'swarms' with a single mineralised interval defined by assay containing several, apparently separate, units. PGE mineralisation associated with Punits is variable in tenor but is invariably platinum-dominant. Platinum usually comprises in excess of 90% of the total PGE content with lesser palladium and minor osmium, iridium and rhodium. The most significant mineralisation located to-date was intersected in vertical diamond drillhole FKD-1 in the Kelvin Grove area. A P-unit was intersected over an interval of 2.08 m, a 1.57 m sub-section of which assayed 13.19 gram/tonne platinum and 0.9 gram/tonne palladium. There is no definitive relationship between PGE content and grain size, or position of the P-units. Many P-units contain only background concentrations of PGE. PGE in the P-units are present as discrete minerals and as inclusions in other PGM. PGM occur as inclusions in clinopyroxene, on grain boundaries and within fractures in chrome-bearing magnetite. All PGM are fine grained, rarely exceeding 30 microns in maximum dimension. PGM associated with P-unit mineralisation include cooperite, isoferroplatinum, tetraferroplatinum, erlichman-

ite, cuprorhodsite, malanite, geversite, sperrylite, stumpflite and several unidentified palladium antimonides (Johan et at, 1989). Base metal sulphides are present only in trace amounts and are not enriched above the levels observed in the surrounding, unmineralised biotite-magnetiteclinopyroxenites. Du.nite/Wehrlite Mineralisation

PGE mineralisation associated with the discordant dunite-wehrlite bodies described previously has only recently been discovered and as such is only poorly defined. This type of mineralisation has only been observed in reverse circulation and diamond drillholes from the North Owendale area. Significant intersections from this area include drilled intervals of 4 m at 1.6 g/t platinum and 4 m at 1.1 g/t platinum in diamond drillhole FKD-13, 26 m at 0.79 g/t platinum in reverse circulation drillhole FRC-46, and 32 m at 0.4 g/t platinum in reverse circulation drillhole FRC-55 (Martin and MacDonald, 1990). PGE mineralisation associated with the dunite-wehrlite bodies appears to occur over broad intervals in both lithologies but appears to reach highest levels in serpentinised dunite. Nothing is known of the mineralogy of the mineralisation although it is probable that the PGE exists as discrete minerals disseminated throughout the rock. Base metal sulphides are present in only trace amounts, if at all. Turvey (1990) has suggested that the PGM might be associated with chrome-bearing magnetite in the wehrlite. Higher grades of residual PGE mineralisation described previously are interpreted to be largely the result of weathering of dunite-wehrlite associated mineralisation.

2.4. PETROGENESIS AND METALLOGENESIS Both multiple intrusion (Taylor, 1967) and fractional crystallisation have been advocated as mechanisms for emplacement of Alaskan-type intrusions. A model encompassing both of these mechanisms has been proposed by Raedeke (1988) and Turvey (1990) for emplacement of the Owendale Complex. The following petrogenetic sequence is summarised from their work: 1) The first magma to intrude the metasediments along a deep, mantle-tapping structure formed the Marginal Series rocks and the thermal metamorphic aureole (Fig. 2.5). Hornblende and biotite of the Marginal Series rocks were formed by assimilation of the country rock.

2) The magma which formed the Ultramafic Series rocks was a potassium-rich alkali olivine basalt. Crystal settling in the basal magma chamber and loss of crystals during ascent resulted in a differentiated magma being emplaced to form the Ultramafic Series. During quiescent periods between tnJections, crystallisation of the in situ magma proceeded from the cooler walls inward and further fractionated the magma. Crude layering evident in drill core from the Kelvin Grove area is consistent with constant disruption of crystallisation by new injections of magma. 3) The magma eventually reached plagioclase saturation by continued crystallisation within the pipe or in the underlying magma chamber.

Episodic pulses of the more fractionated magma formed the diorites of the Mafic-Felsic Series. At about the same time as the dioritic magma

was being emplaced, a more differentiated, siliceous magma was intruded to form the monzonitic core of the Mafic-Felsic Series.

Clinopyroxenite I

. . ..

"P-Units" \

Distal Alteration

. . X

hrlite (::i

Wehrlite

R:i~c,

c()

Clinopyroxenite I I

X X

I I

X X

I I

X X

I X

Diorite X X

X X

+ +

+ + Monzonite + + +

X X

condary Dunite

X X X

Figure 2.5. Schematic diagram showing primary platinum mineralization styles of the Owendale Complex (Modified from Turvey, 1990)

4) The discordant dunite-wehrlite bodies in the Ultramafic Series are interpreted to be the result of late-stage magmatic alteration produced as a result of the addition of water to the melt With this increase in water fugacity, clinopyroxene is resorbed to form olivine, thus producing the olivine-rich bodies. The formation of the secondary dunite-wehrlite bodies by this mechanism is probably related to the intrusion of the differentiated, monzonitic magma (Fig. 2.5). PGE mineralisation associated with the Owendale Complex has been interpreted by Raedeke (1988) and Turvey (1990) as being directly related to the episode of late-stage magmatic alteration which was responsible for formation of the secondary dunite-wehrlite bodies. Various styles of alteration in the Ultramafic Series rocks, with or without associated PGE mineralisation, stem from, and are interpreted to be spatially related to the secondary dunite-wehrlite bodies. This association of alteration styles is illustrated in Figure 2.5. The end members of this alteration series are the secondary dunite bodies and the pegmatitic clinopyroxenites (P-units), with the intervening alteration styles being characterised by pseudomorph and incipient replacement of clinopyroxene by olivine, biotite and, to a lesser extent, hornblende. PGE mineralisation has been observed associated with the secondary dunite-(wehrlite) and with the P-units, as described previously. PGE associated with these alteration styles were presumably transported to their present position by the fluids which were responsible for the alteration with subsequent deposition being dependent upon the prevailing physio-chemical conditions prevailing at the deposition site. The alteration and associated PGE mineralisation is interpreted by Turvey (1990) to be vertically zoned and to favour units with the highest contents of magmatic olivine.

The alteration and mineralisation is therefore believed to roughly parallel the sub-vertical magmatic stratigraphy, although the dunitewehrlite bodies may themselves be markedly discordant. Although the model proposed by Turvey (1990) and Raedeke (1988) readily accounts for the observed location of PGE mineralisation in the Ultramafic Series, the ultimate source of the PGE is still open to conjecture. No likely 'protore' such as a sulphide-rich layer has been located, although all evidence of such a protore may have been destroyed by the alteration, and no particular units or area of the Ultramafic Series appears to be unduly depleted with respect to PGE. Notwithstanding this, there are three possible sources from which the PGE might have been derived: 1) The PGE may have been evenly (or relatively so) distributed throughout the ultramafic rocks,having been pre-concentrated into these rocks by differentiation in the underlying magma chamber. Pervasive alteration fluids subsequently leached some, but not all, of the PGE from these rocks to be re-deposited and concentrated in specific locations. 2) The PGE may have been concentrated by magmatic processes into specific horizons with subsequent selective leaching by the alteration fluids and redeposition into the settings described previously. 3) The PGE may have been introduced along with the alteration fluids from an unknown source. No conclusion has been reached regarding which of the above mechanisms is the most likely. Further work is required before any definite conclusions can be reached regarding PGE metallogenesis in the Owendale Complex.

2.5. SUMMARY AND CONCLUSIONS The Owendale Intrusive Complex is a pipe-like, Alaskan-type intrusion situated in the Fifield Belt of Alaskan-type intrusions in central New South Wales. The complex comprises three distinct lithological groupings based on mineralogy and stratigraphic position: An Ultramafic Series which comprises the eastern and southern area of the complex, a Mafic-Felsic Series which comprises the north, west and centre of the complex, and a Marginal Series which for the most part occurs adjacent to the external contacts of the complex. Rocks of the Ultramafic Series comprise biotite-, magnetite-,

and olivine-bearing clino-pyroxenites, dunite and wehrlite. The dunites and surrounding envelopes of wehrlite are the product of latestage magmatic alteration. Rocks of the MaficFelsic Series comprise principally diorite and monzonite whilst those of the Marginal Series are characterised by an abundance of hornblende. Primary PGE mineralisation in the Owendale Complex is associated with the secondary dunite-wehrlite bodies of the Ultramafic Series and with coarse grained to pegmatitic, monominerallic clinopyroxenite (P-

units). Both types of mineralisation are interpreted to be directly related to the late-stage magmatic alteration event which produced the secondary dunite-wehrlite bodies. Platinum is by far the dominant PGE in the primary mineralisation, usually comprising in excess of 90% of the total PGE. The remaining PGE comprise lesser amounts of palladium and minor osmium, iridium and rhodium. PGM appear to occur as discrete minerals with no accompanying base metals mineralisation. Disseminated chrome-bearing magnetite may be associated with the PGE in the dunite-wehrlite mineralisation. PGM in the P-unit mineralisation are predominantly cooperite and Pt-Fe alloys with lesser amounts of erlichmanite, sperrylite-geversite and minor alloys, sulphides, arsenides and antirnonides of the PGE. The mineralogy of the dunite-wehrlite mineralisation is unknown but is expected to be dominated by Pt-Fe alloys. In addition to the primary mineralisation, residual PGE mineralisation occurs associated with a laterite profile developed over much of the Ultramafic Series rocks. This mineralisation is associated with the dunite-wehrlite bodies and probably reflects reconcentration of the primary dunite-wehrlite mineralisation in addition to concentration of low-grade, background contents of PGE disseminated throughout the underlying rocks. Platinum is once again by far the dominant PGE

comprising in excess of 90% with lesser palladium and minor osmium, iridium, rhodium and gold. Platinum-iron alloys appear to be the dominant PGM. Minor low-grade placer platinum (and gold) mineralisation has been observed in poorly sorted gravels in palaeochannels overlying and immediately adjacent to the Owendale Complex. This mineralisation is presumably derived from erosion of PGM from the residual PGE mineralisation overlying the complex. Almost all of the platinum occurs as small nuggets of platinum-iron alloy with small inclusions of otherPGM. The Owendale Intrusive Complex and the other Alaskan-type complexes of the Fifield Belt are unique, albeit that they share many similarities with other Alaskan-type complexes described in the literature. These complexes are still relatively poorly described and much work needs to be completed before the hypothetical petrogenetic history summarised in the preceding text can be substantiated. PGE mineralisation associated with these complexes is similarly poorly understood, particularly with respect to genesis of the mineralisation. Exploration for economic PGE mineralisation in the Fifield Belt is however continuing, results of which will undoubtedly, in time, establish a definitive model for PGE mineralisation in Alaskan-type intrusions in general and in the Fifield Belt complexes in particular.

CHAPTER 3 - GEOLOGY AND ECONOMIC POTENTIAL OF THE TOUT COMPLEX, NSW G .M. Derrick

3.1. INTRODUCTION AND TECTONIC SETTING The Tout Complex is one of the many mafic to ultramafic Alaskan-type complexes which intrude Cambro-Ordovician Girilambone Group metasediments in central western New South Wales. These intrusions occur along the Parkes Terrace, a 500 km long x 80 km wide NNE-trending gravity high. The Parkes Terrace represents a zone of crustal thinning, possibly containing deep crustal structures (sutures, detachments etc) which have focussed emplacement of the Alaskan complexes into mid-crustal levels from source areas in upwelling lithospheric mantle. The age of the Tout complex is uncertain; it, like most of the other complexes in the region, has previously been assigned to the early Devonian (405 Ma. Pogson and Hilyard, 1981), but more recent U-Pb zircon work indicates a late Ordovician age (445 Ma., Helix Resources, pers. comm. 1990 ) is more likely. The Tout Complex has recently been categorised as part of an extensive belt of Ordovician shoshonitic volcanic and associated intrusive

rocks in central NSW (Wybom and Cameron 1990; Agnew et al 1987) (Figure 3.1). The Alaskan-type complexes show trace element compositions similar to those of Ordovician volcanic rocks (Figure 3.2), and modem shoshonites (Figure 3.2). Some tholeiitic association may also be Present. The shoshonitic association is characterised by high K, Sr, Ba and P, and low Ti, Zr, Y, and Nb, and appears to be derived from metasomatically-altered subcontinental lithosphere rather than from subducted oceanic crust. The presence of many gold deposits and Pt-bearing Alaskan intrusives in the Ordovician magmatic suite in central NSW suggests that the shoshonitic magmas were derived from S-undersaturated and Au and PGEenriched lithosphere. These enriched shoshinitic magmas underwent further fractional crystallisation in the crust. Some gold deposits (e.g. Goonumbla porphyry system) and Ptbearing ultramafic units (e.g. Owendale Complex) are typically S-poor (Wybom and Cameron, 1990).

3.2. GEOPHYSICS AND GEOLOGY The Tout Complex, like many other Alaskan intrusives in the Lachlan Fold Belt, is anomalously magnetic, and appears as distinctive, strongly magnetic "flotsam" floating in a magnetically quiet sea of Girilambone Group metasediments (Figure 3.3). The strong magnetic signature of the Tout Complex, in particular, reflects an abundance of magnetitebearing pyroxenite and gabbro, particularly in the eastern half of the complex. A simplified geological interpretation of the Tout Complex (formerly known as the Flemington Intrusion) is shown in Figure 3.4. The complex is poorly exposed, with less than 1% of rock units outcropping. Geology is based

on the work of Emerson et al (1979), Suppel and Barron (1986), Agnew (1987), Agnew et al (1987), and exploration by Noble Resources and Poseidon Ltd (Derrick, 1989). The Tout intrusion is 16 km long, elongate in a WNW direction and is up to 6.5 km wide. Agnew et al (1987) recognised six igneous "Series" in the intrusion, each petrologically and geochemically distinct, and each with sufficient magnetic contrast to characterise the various Series in the subsurface. Agnew et al (1987) suggest that each Series represents a separate intrusive event, with intermediate magma intruded first, followed by pulses of successively more mafic to ultramafic magma.

~147° 00 ' ~ Honeybugle Complex

148 °30'

□ DUBBO

150°00 '

32 °00'

Hylea t; Complex

.'\'e st VVyalo ny

35 °00 '

D CANBERRA

50 km

Gold deposit

38°00 '

Platinum-rich intrusive co,nplex 16/ N/39

Figure 3 .1. Distribution of Ordovician volcanic rocks and Alaskan-type intrusions in the Lachlan Fold Belt, NSW (from BMR Research Newsletter). Shaded areas are subcrop inferred from magnetics

3.2.1 The Igneous Rock Series The following six igneous rock series are recognised in the Tout Complex. 1. Hornblende Quartz Monzonite Series 2. Hornblende Melamonzonite - Meladiorite Series 3. Hornblende Pyroxenite Series 4. Clinopyroxene Quartz Monzonite - Diorite Series 5. Pyroxenite-Gabbro Series 6. Dunite Series

Inferred distribution of these Series is shown in Figure 3.4. The order of Series 1 to 6 is possibly a sequence of intrusion, from oldest to youngest, and also a spatial distribution from west to east The Series were formalised by Agnew (1987), but Series 5 and 6 in particular have been extensively revised by Derrick (1989), based on detailed exploration work by Poseidon Ltd and Noble Resources. 1. Hornblende Quartz-Monzonite Series This Series comprises mainly quartz monzonite, locally grading into quartz syenite

•KLI\NJRA (16)"

.+ORANGE-WEJ.1.INGTON (24

500

Lihir Island ----- Fiji -- - Western USA (Meen&Eggler 1987) f\ ··· ·· · Mount Hag en. • \ New Guinea

aFFELD-NYNGAN ( 4)

:g0 200 ~

100

~ 50 0 E

r~__/ \ \

'-- 10

\•

.,,_

u 0 a::

. /, ~

A ORDOVICIAN VOLCANIC S Pb

Bo Rb

Nb K

Ce Lo

Nd Sr

Zr P

Y Ti

MODERN SHOSHONITES

Pb Rb Ba Th U K Nb La Ce Sr Nd P Zr Ti Y Na

Fig . 3.2. Average trace element content of (a) Ordovician volcanic rocks of the Lach/an Fold Belt and (b) Modern shoshonites (from BMR Research Letter 811988)

•

'· +·

r..-

•

( +

~ , ',\•\

•!

,,_,...

~--..--."tl ()~

•

OSEDALE ANOMALY • '

J I

~ --. "'1 0

•

HILL ANOMALY

,,t

l ,..... I

\ \ ,\ \ '· \ . \\\\~~:.

\\'\•~'-<

· .,'='

GLEN IRIS ANOMALY '11

\'-,,_",,> \ '°' --<-~_ .', '.-·.:.-- ·1•_.~•~,''._.-··

--·

+·

I I j.,

__=3., - .,{>~~lh ·_-;-,~ •• ~,,,,1 ,

~ ·.

~ YOES ANO~Y

•lJ ~

• : \,· -

•

1/,

/ ~ - +,

Figure 3.3. Airborne magnetic response of various maficlultramafic intrusions, Fifield area

KELVIN GROVE •

,.,,. - "' Unit boundaries (..-__.-~

(INFERRED)

..-·······,'.::·:- Laterite \

....•·-·-·

., Mg

Magnesite workings G

Outcrop, float IGNEOUS ROCK SERIES - late ORDOVICIAN(?)

Hornblende quartz monzonite series

Hornblende melamonzonite-meladiorite series 2a Quartz syenite

3 4

INTERPRETED GEOLOGY OF THE TOUT COMPLEX

Gabbro Pyroxenite Olivine pyroxenite

Serpentinised dunite

Girilambone metasediments (Cambre-Ordovician)

Sa Sb

(We.tern hell after AGNEW 1987;

Ee.tern hell after DERRICK 1989)

Hornblende pyroxenite series Cpx quartz monzonite-<liorite series

and diorite. Hornblende (28%-37%) is the main mafic mineral, with pyroxene and magnetite as accessory phases. Low magnetite content results in a moderate to low aeromagnetic response. Layering generally parallels the outer margin of the complex and dips between 60° and 85° towards the centre of the intrusion. 2. Hornblende Melamonzorute-Meladiorite Series This Series occurs only as cobble and boulder float, but is inferred to constitute most of the westernmost lobe of the Tout intrusion and part of the northern contact zone with metasedimentary country rock. This Series is distinguished from the quartz monzonite Series by being more mafic, with 50% - 60% fine- to medium-grained hornblende and 5% - 12% clinopyroxene. Magnetite is generally less than 1%, resulting in a correspondingly low aeromagnetic response (Agnew, 1987). A small intrusion of quartz syenite (unit 2a, Figure 3.4) may be a late differentiate of the melamonzonite, or younger mafic rocks. 3. Hornblende Pyroxenite Series

Hornblende, clinopyroxene and K feldspar are the principal rock-forming minerals in the Series: variation in modal content of

FIGURE 3_4

hornblende and clinopyroxene results in lithologies ranging from hornblende pyroxenite to pyroxene hornblendite. K-feldspar varies from 5% to 16%, and quartz is interstitial and generally not visible in hand specimen. These hornblende-rich rocks are closely associated with the melamonzonites of Series 2 (e.g. around the eastern and western margins of the complex) but are separated from them •on the basis of textural differences: the Series 3 hornblendes are invariably coarser grained (5 mm - 30 mm) and occur as euhedral to subhedral phenocrysts. are homblendites porphyritic Coarsely characteristic of marginal rock suites throughout the Fifield-Nyngan belt, and are commonly referred to as "Honeybugle Hornblendite" - type, from their common occurrence around the Honeybugle intrusion 100 km to the north. with veinlets, rich K-feldspar hornblende-rich margins, locally cut rocks of this series (Agnew 1987). The common spatial association of hornblende-rich rocks (e.g Series 1,2 and 3) with marginal zones of the Tout and other complexes may reflect interaction of crystalising magma with Ca and H 2O-rich crustal material during emplacement. 4. Clinopyroxene Monzonite-Diorite Series

This

Series

forms

subcircular

intrusion, 3 km in diameter, near the middle of the Tout Complex. It contains fine- to mediumgrained lithologies, mainly gabbroic diorite, diorite quartz monzonite and minor anorthosite. The principal mafic mineral is diopsidic augite (18% - 57%) with some accessory olivine and 6% to 8% magnetite. The latter provides a strong magnetic signature, indistinguishable from that of the Pyroxene Series. Rhythmic centimetre-scale layering is present, defined by feldspar-clinopyroxene alternation. The strike of the layering varies from NW to NE and dips range from 45° to 60° inwards. Zones of epidote-actinolite rock may be alteration zones within the clinopyroxene monzonites (epidote and actinolite being derived from plagioclase and clinopyroxene, respectively). Other possible late-stage veining/alteration includes K feldspar-epidote rock and plagioclase-K feldspar-quartzhornblende rock (Agnew 1987). 5. Pyroxenite Series This Series crops out sporadically in the eastern half of the complex. Three subdivisions are recognised (Derrick, 1989), as shown in Figure 3.4. Series Sa is a coarse-grained gabbro, with abundant clinopyroxene (diopsidic augite), plagioclase and magnetite, and accessory Kfeldspar, biotite, olivine, apatite and epidote. The gabbroic Series forms a semicircular outer zone along the west, south and southeastern margin of the pyroxenite Series. Hypersthene gabbro (plagioclase 45%, cpx 35%, opx 16%, magnetite 3%) is present in the west of the subdivision. Series Sb comprises coarse-grained cumulate-textured pyroxenite, which forms a 0.3 to 1 km-wide annulus internal to the gabbro and external to the dunite "plug". Grain size is commonly 2-5 mm and a typical modal assemblage is 50 to 90% granoblastic clinopyroxene, 5 to 20% magnetite , with smaller amounts of phlogopite, hornblende, olivine and green spinel, the latter associated with magnetite. Layered magnetite (80%) clinopyroxene (20%) rock occurs locally in the northern margin of the subdivision. Series Sc is composed of olivine pyroxenite, generally similar to the pyroxenites of subdivision Sb, but containing 5% - 20% olivine which is altered to red-brown iddingsite.

Olivine pyroxenites tend to fom1 irregular layers or zones within the pyroxenites, and immediately adjacent to the olivine-rich dunite plug. Late hydrothermal alteration of pyroxenites Sb and Sc is associated with minor Cu-Au-Pd mineralisation, and some epidoteprehnite veining. A prominent zone of phlogopite- biotite-K feldspar alteration is localised along the southeastern margin, where the pyroxenites are cut by NE-trending shear zones. The phlogopite(biotite) forms coarse 110 mm aggregates; some of this material may be vermiculite . 6. Dunite Series This term describes a poorly-exposed sub-circular "plug" of serpentinised dunite, about 3 km by 1.5 km and elongate in an eastwest direction, located near the eastern end of the Tout Complex, and identified mainly on the basis of RAB drilling. In outcrop the dunite is pale grey-green, commonly displaying a 0.5 - 2 mm "spheroidal" texture derived from weathered olivine-rich aggregates. Outcrop occurs at the northern and southeastern margins of the plug, where it shows progressive lateritisation, in particular silicification and the development of a skeletal mesh texture comprising chalcedonic quartz vein replacement of goethitic clay (see later section on laterite). The dunite plug includes olivine-rich (+90%) varieties, wehrlite and lherzolite. The latter is a clay-altered olivine peridotite containing olivine pseudomorphs (55% - 60%), 1 mm grains of clinopyroxene (20%), orthopyroxene (23%) and magnetite (2%). Grains of altered olivine are veined by trails of fine magnetite. Orthopyroxene is identified on the basis of bastite alteration zones in the serpentine and relict crystal outlines. Rare, partly- chloritised phlogopite crystals are present in some samples. Although slightly magnetic, the dunite plQg is marked by a central magnetic low within the highly magnetic pyroxenite annulus. The northern and north-western margins of the dunite are characterised by lobate projections of dunite into pyroxenite, and/or a series of small discrete intrusions (plugs, dykes, tectonic slices ?) into pyroxenite. The southeastem contact with pyroxenite appears sharp and steep-dipping or vertical.

3.3. LATERITISATION AND YOUNGER GEOLOGY Parts of the Tout Complex are overlain by a thick, early Tertiary laterite profile which is manifested locally by outcrops of red-brown pisolitic laterite and massive to cavernous brown limonitic and siliceous laterite (Figure 3.4). The profile is best developed over the ultramafic (eastern) part of the complex and attains maximum development (+30 m) over the more easily weathered dunite plug. The profile over dunite is characterised

by an upper and lower siliceous zone and an intervening thick development of goethitic orange-brown clay, which is enriched in Cr, Ni, Co and, locally, Pt (Table 1; Figure 3.5). The profile over pyroxenite is thinner (5-10 m), less siliceous, and characteristically rich in purple, red and buff-coloured mottled ferruginous clays, with a 1-2 m zone of apple green to grey nontronitic clay developed immediately above pyroxenite bed-rock.

TABLE 1: TYPICAL LATERITE ZONATION OVER DUNITE BEDROCK, TOUT COMPLEX THICKNESS

LITHOLOGY

1-Sm

Red brown pisolitic laterite (hematite, maghemite).

1-Sm

Brown siliceous clayey ironstone UPPER SILICEOUS ZONE

10-25m

Tan-brown friable clayey limonitic laterite with zones of brittle skeletal quartz/chalcedony meshwork

10m

Brown siliceous laterite, increasingly jasperoidal and massive, relict dunite texture. -LOWER SILICEOUS ZONE

l-2m

Deep brown "expanding" clays

ZONE

Brown-grey clayey/ serpentinised duni te, with some Si veining and carbonate alteration. SAPROLITE/BEDROCK

Drilling shows the ferruginous laterite profile to be gently folded or warped, with the pisolitic laterite to siliceous laterite zones being upturned around the margins of the dunite. This profile is overlain unconformably by grey-white calcareous and magnesitic clays, clayey

sandstone and gravels of fluvial and lacustrine ongm which occupy a NE-trending palaeochannel across the ultramafic complex. These sediments are probably of late Tertiary to Recent age and are locally platiniferous (" deep leads").

Tertiary Clay/sst/gravel

Pisolitic ironstone (hematitic) 1

• • ..

Siliceous ironstone -=-= I _--_- \

--- \ :-=•

. °!

·.....

20 -::- I Tan-brown goethitic clay -- .: 1 Co =-=I ---- I\

'Pt

·.

----- \ =---= '

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

30 Siliceous goethitic clay, silica meshwork L L - L ~ ~ - - 1 L -_ _2 L - _ - J a L - - _ - J 4 . __

0·5

1·5

~ Ni, Co %

•- ............,.__._, o._•s_ _

_,5c~/4

Pt ppm

Figure 3.5. Typical down-lwle assay variation in laterite overlying dunite, Tout Complex

3.4. GEOCHEMISTRY Agnew (1987) described bulk geochemical characteristics of the Tout Complex - high total alkalies (>5% in non-cumulate lithologies), high K2O/Na2O (>0.66% at 50 weight % SiO2, > 1% at 55 weight % SiO2 ), high Ba and Sr, low TiO 2 (<1%), and high Fe2Oy'FeO (>0.5) - which suggest a shoshonitic affiliation. Harker variation diagrams for rocks of all Series show linear trends (e.g. increasing Total Fe, MnO, MgO, Cao with decreasing SiOi), and plots of Mg Number and Solidification Index also give linear correlations, suggesting the Tout Complex Series (and possibly the Owendale Complex Series) were derived from the same source.

Agnew (1987) suggested felsic melt fractions were intruded first, followed by successively more basic pulses. Agnew also noted Sr concentrations of up to 2500 ppm in clinopyroxene diorite (Series 4) containing 25% modal plagioclase, suggesting that these rocks crystallize from a liquid which had undergone protracted olivine and clinopyroxene fractionation which enriched the residual melt in Sr. Wybom and Cameron (1990) report that four samples from the Fifield belt may be classified as shoshonites, with low S content (<200 ppm S), and were probably derived by

partial melting of an upper mantle source undersaturated in S and also enriched in PGE and Au (up to 10 to 20 times higher than in the tholeiitic rocks from the Lachlan Fold Belt). Further fractionation of these S-undersaturated partial melts at mid-crustal levels would lead to further enrichment of Pt, particularly in Mg-rich olivine cumulates, which contain 20 to 50 ppb Pt in the dunite core-zone of the Tout Complex (Derrick, 1989). It is notable also that the Tout (and Owendale) Complexes contain olivine-rich cumulates which show high Pt/[Pt+Pd] ratios,

compared with associated non-cumulate Ordovician volcanic rocks in the Lachlan Fold Belt. Wybom and Cameron (1990) suggest this is due to possible decoupling of Pt and Pd, the former compatible with chrome spinet as a Pdpoor isoferroplatinum alloy. In contrast to a totally shoshonitic classification , Yu Xueyuan (1990) suggests that some of the Series of the Tout Complex - the Pyroxenite-Gabbro Series and Hornblende Diorite Series - are better classified as tholeiitic, on the basis of AFM geochemistry (Figure 3.6).

Cale-alkaline series

FIGURE 3.6 AFM DIAGRAM , TOUT COMPLEX A = (Na20 + K20), F = total Fe as FeO, M = MgO, all in Wt % O

ll. □

pyraxenite - gabbro series homblendite - diorite series melamonzaonite - melasyenite series

The Melamonzonite-Melasyenite Series (Series 2, Figure 3.4) is more truly calc-alkaline or shoshonitic in character, and Agnew (1987) reports that this particular unit in the Tout Complex may represent a late-stage differentiate from some later intrusive pulse. This is possibly analogous to the Owendale and Kars Complexes, where late monzonitic units intrude more mafic and ultramafic units. Alternatively, the vanations from tholeiitic to shoshonitic geochemistry may be a function of: a) some sampling bias, b) insufficient sampling, and/or c) slight variation in the nature of the upper mantle source rock (e.g. from a 15% partial melt of spine! lherzolite, to a low degree partial melt of phlogopite-bearing lherzolite, respectively: Yu Xueyuan, 1990). Most recently, Barron et al. (1991)

report that the Fifield platinum province source rocks may be extension-related tholeiitic to shoshonitic high-temperature felsic magmas which subsequently assimilated Alpine peridotite at moderate crustal levels (12-18 km) to produce large volumes of uniform ultramafic reaction cumulates set within an intrusive complex of mainly felsic material. These rocks are locally modified by high-T fluids to produce pegmatoidal bodies of clinopyroxene and olivine, K-feldspar etc, which locally may be enriched in PGE. The dunite core of the Tout Complex is poorly exposed and sampled, and it is not yet known whether it contains ultramafic to felsic pegmatoids, and other evidence of highT hydrothermal alteration, as is evident in the adjacent Owendale Complex.

3.5. ECONOMIC POTENTIAL, TOUT COMPLEX Most economic potential resides in the Pt-Cr-Ni content of high-mg lithologies of the Tout Complex - the dunite-peridotite plug and olivine pyroxenites forming the eastern one-third of the complex. Past exploration effort has focussed on Pt-bearing placers and their hardrock source areas, and on magnesite occurrences within and adjacent to Mg- rich lithologies.

Pt Cr Ni

More recently, attention has been drawn to a ferruginous laterite which is preferentially developed over high-mg rocks. This profile (Table 1) contains significant volumes of brownish ferruginous clay which are enriched in Pt, Cr and Ni, and, to a lesser extent, Co (Figure 3.5). Some typical grades are as follows:-

Parent dunite grade

Overlying laterite grade

20-50ppb 300-800 ppm 500-IOOOppm

0.8 ppm; up to 16 ppm 2%; upto 10% 0.8% ; up to 2%

The enriched zones of lateritic clay form semi-circular arcuate belts 100-300 m wide, 1-2 km long and up to 10 m thick in the eastern and northern areas of the dunite plug. The zones are overlapping, and are Cr-rich towards the middle of the dunite, Ni-rich towards the margin of the dunite, and Ptenriched in a zone overlapping Cr and Ni.

3.5.1. Vertical Geochemical Variation Generalised but typical down hole element variation for Cr, Ni, Co and Pt , relative to laterite zonation, is shown in Figure 3.5. Depth of hole is 36 metres. Chromium shows typical bimodal concentration, the upper peak commonly being greater than the lower peak; grade is 30 m @ 1.64% (6-36 m); peak values correlate with

zones of silica enrichment (zones 2,4), and zones of orange-brown goethitic clay. Nickel consistently shows an asymptotic profile down hole, with peak values towards the base of zone 3 goethitic clays, and upper parts of the lower siliceous zone, zone 4. Grade is 14 m @ 0.62% Ni (20-34 m). Cobalt distribution tends to parallel that of nickel, and is related to dark brown, Mn-enriched clay (?asbolitic) developed immediately above the lower siliceous zone. Platinum distribution overlaps that of Cr and Ni, but tends to be concentrated in friable goethitic clay (zone 3), where it is commonly present as very fine to sporadically coarse (0.05 mm to 1 mm) grains of Fe-Pt alloy. Grade is 28 m @ 0.47 g/t Pt (6-34 m). Some grains of Pt alloy to 1.5 mm occur locally in ferruginous laterite, and show distinctive lamellar striation

due to osmiridium intergrowth in the isoferroplatinum. Weakly rounded grains of similar morphology occur in adjacent deep leads overlying the laterite profile.

3.5.2. Development of Enriched Laterite Profile Chromium, Ni and Pt enrichment in lateritic clay possibly represents in situ concentration from parental zones in the dunite which are enriched in these elements, such as high-Cr dunite and/or chromitite layers. Lateritic processes of mass wastage, plus element redistribution by ground waters, may explain most distribution patterns. Two periods of lateritisation are proposed. During an earlier moist period (? Early Tertiary), a hematite-rich pisolitic zone developed above a high-level water table, and secondary silicification occurred at or about the water table. Goethitic clays developed in a fossil mottled zone. With the onset of aridity during a younger period of weathering(? Late Tertiary), and a falling water table, Cr remained moderately immobile high in the profile, but was taken into solution from lower in the profile and re-concentrated at and above the new palaeo- watertable and associated lower siliceous zone. These processes account

for the observed bimodal Cr distribution (See Figure 3.5). Ni is inferred to have been taken into solution from high in the older profile, and redistributed downwards during the younger lateritisation, accompanied in part by Co. Pt appears NOT to have been redistributed during the younger lateritisation; rather, Pt is concentrated uniformly through the profile by residual enrichment and mass wastage from a Ptrich chromite-bearing dunite precursor. Local enrichment peaks (to 16 ppm) are probably due to a nugget effect rather than to any significant supergene process, since Pt grains in the laterite show high temperature exsolution textures.

3.5.3. Magnesite Occurrence Magnesite is associated with high-Mg lithologies of the Tout Complex. It forms part of the laterite profile and occurs as nodular masses invading goethitic clays of zone 3. More commonly, economic magnesite occurs as nodules and layers in Girilambone Group metasediments, and in clayey, sandy and silty lacustrine and fluviatile sediments of TertiaryQuaternary age. Magnesite probably forms by decarbonation of Mg- and C02- charged ground waters draining from Mg-rich dunite and pyroxenite.

3.6. SUMMARY AND CONCLUSIONS The Tout Complex is an elongate funnel-shaped late-Ordovician ultrarnafic to intermediate Alaskan-type body intruding the Cambro-Ordovician Girilambone Group in central NSW. It is one of many such intrusions possibly derived by partial melting of a Sundersaturated, PGE-rich, upper-mantle spinel and phlogopite-bearing lherzolite; the resultant tholeiitic to shoshinitic magma possibly underwent further fractionation in mid- crustal Interaction of highmagma chambers. temperature felsic magma with Alpine-type peridotites may also have produced much of the ultramafic cumulate material. Earliest (and marginal) intrusive phases were hornblende-rich diorite, quartz monzonite, melamonzonite and meladiorite: these form the western half of the complex. Younger gabbro, intruded were dunite and pyroxenite successively in the eastern part of the complex,

with dunite forming a near-vertical plug or corezone rimmed by pyroxenite and gabbro. Platinum is associated with high-Mg lithologies, mainly serpentinised dunite, wehrlite and olivine pyroxenite, some of which may also be chromerich; chromitites may also be present. At least two periods of lateritisation, best preserved over dunite, have resulted in residual enrichment of lateritic clays in Cr, Ni, Co, and Pt, the latter as Pt-Fe alloy (Figure 3.7). Magnesite is present to economic levels in the laterite profile, and in Tertiary-Quaternary stream channels and basins adjacent to dunitepyroxenite. Some younger placers above the Tout Complex contain alluvial Pt derived from weathering and erosion of the laterite profile. Future exploration and research will focus on the extractive metallurgy of Cr, Ni and Pt in ferruginous laterite, and the nature of Pt, Cr, and Ni in primary zones within the dunite plug.

EAST

m Zone 1: PRIMARY ZONE: dunites of varying olivine content and degrees of serpentinisation; olivine-rich zones, with possible chromitite seams or schlieren, contain most of the Pt alloy; zones of Ni-anomalous dunite occur on the outer margin of the Crrich zone. Zone 2: LATERITE ZONE: Thick ?Tertiary ferruginous laterite profile developed preferentially over dunite (shallow laterite profile developed over pyroxenite). Dispersal and widening of Cr- and Pt-anomalous zones with further concentration possible by mass-wastage in profile. Figure 3. 7. Interpretation of laterite and subsurface geology, Tout Complex, Dunite/Pyroxenite Series

CHAPTER 4 - THE KARS AND GILGAI INTRUSIVE COMPLEXES AND ASSOCIATED PGM MINERALISATION, FIFIELD N.S.W Gary J. Jones

4.1. INTRODUCTION Platinum Search N.L. became involved in platinum exploration in Central New South Wales (N.S.W.) soon after the discovery of high grade platinum in drill core from the Owendale complex at Fifield by Government geologists (Suppel and Barron, 1986). At this time Lachlan Resources N.L., the parent company of Platinum Search, moved quickly to secure tenure over ground recognised by the company geophysicist as having potential to host ultramafic complexes similar to those present at Fifield. Following a programme of literature research and field reconnaissance in mid-1986,

the author confirmed the presence of ultramafic rocks in six of the Platinum Search N.L. tenements. It was postulated that all the intrusions, including those at Fifield, were contained within a 35 km wide corridor located between Derriwong in the south and Gerar in the north (Fig. 4.1), a distance in excess of 230 km (Jones, 1986/90 and Rangott, 1987). Subsequent detailed exploration on these tenements has led to the discovery of two significant new platinum occurrences at the Kars and Gilgai prospects.

4.2. KARS PROSPECT The Kars complex is situated 20 km south of Fifield and is the smaller of two ultramafic intrusions, the other being the Mount Derriwong complex known from Exploration Licence No. 2653. The Kars and Mt Derriwong complexes intrude Middle Ordovician sediments of the Girilambone Group and are unconformably overlain to the south and east by Lower Devonian sediments of the Derriwong Beds. The region is mostly under seasonal cultivation, and outcrop of the older rocks is sparse. In contrast, the younger overlying sandstones and conglomerates of the Derriwong Beds commonly form small areas of elevated, rugged terrain. The Kars and Mt Derriwong complexes are well defined by high level Bureau of Mineral Resources (BMR) aeromagnetic data, and are similar in this respect to other intrusions in the southern part of the ultramafic corridor. The sharp anomaly definition is due to the contrast in magnetite content between the dunite pyroxenite - monzonite of the complexes and the non-magnetic Girilambone sediments.

Initial exploration of the Kars prospect comprised gridding and detailed ground magnetic surveys. Results of this work clearly outlined the intrusive complex in plan view as a semi-elliptical body with a 700 m-long major axis, striking approximately 300 degrees magnetic. The western end of the intrusion is sharply truncated by a NE- trending structure believed to be a fault. The magnetic data indicated the presence of a zone of lower intensity in the centre of the complex, now known to coincide with the main platiniferous lithologies. Soil and rotary air blast (RAB) geochemical surveys were conducted over the complex and outlined a strong platinum anomaly 50 m wide and 500 m long, as depicted in Figure 4.2. Ten backhoe costeans were subsequently excavated across the anomaly and sampling of these confirmed the presence of widespread low grade platinum mineralisation (0.1 to 2.0 gm/t Pt in weathered rock). (Rangott, 1987). Bed-rock exposed in the costeans is

LOCATION MAP

_______ .,,-·"'-·'· a Bourke

Cobar o

□PROJECT FIFIELD

NS.W.

•

SYDNEY

l__ '----,

CANBERRA 0

'v·--........,.\_

GILGAI 500m x 800m platinum anomaly defined by RAB drilling Values uo to 3m @ 2. tglt Pt

::::::, <:::::::-

HONEYBUGLE

::::::, <:::::::-

Derriwong - Nyngan Ultramafic corridor

32°00'S

Anomalous platinum in costeans. Up to 2m @ 17.8glt Pt

Ultramafic Intrusive Complex

c::J Platinum Search tenements BULBODNEY CREEK Anomalous platinum In RAB drllling. Up to Bm @ 5.2glt Pt

Tottenham~

-□ "

HYLEA Anomalous platinum in RAB drilling & laterite float.

EL2652

\ ',..

30km

..-------------..'n a.

Tullamore

Widespread anomalous platinum in costeans & RAB dril.ling.

•-=:::"'------------~ " OWENDALE

TOUT

□

\\~ - - ' \\ ,.

DEVEX LEASES T

Fifield •

EL2653..

33°00'S Lach/an

Widespread anomalous platinum in core. RAB drilling & costeans. Up to 1.4m @ 13.8glt Pt

~ □ Trundle

KARS Near surface platinum mineralization 500m x 50m zone averaging 0.42glt Pt

River

FIFIELD PLATINUM PROVINCE Ultramafic Intrusions and Tenure coverage

148°00'E

Figure 4.1

5200E

5000E

5400E

5600E

eoooe

5800E

D Trench

• RAB Hole ~~

Trench interval with ave. Platinum grade 0.20--0.65 git.

Diamond drill hole with Platinum Intersection

•-

oc=======i200metr~

Approx. out/Ina of main Kars Ultramaflc Complex Ground magnetic contours reflect m,1gnetlc phases of ultramafic complex.

KARS PROSPECT Composite Map showing significant results Figure 4.2

5000E

5200E

5400E

5600E

6000E

5800E

~ Pyroxenite Olivine pyroxenlte ~

~ Wehrllte - Dunite

F=====~ Monzonite

Olivine pyroxenite with dunlte dykes & pods

[)J Sediments oc:::==== = =200m=aelres

KARS PROSPECT Geological Interpretation Figure 4.3

predominantly olivine - pyroxenite (Fig. 4.3). Broad units are recognisable, varying from fineto medium-grained through to coarse pegmatitic vaneues. Contacts are frequently gradational and serpentinisation is prominent in many areas. The very coarse grained varieties tend to be more olivine-rich, grading into wehrlite and, locally, dunite. Narrow dykes of aplite, hornblende monzonite and diorite intrude the pyroxenite. Two inclined diamond drill holes, each

150 m deep, were drilled from north to south to test the platinum anomaly at depth (Fig. 4.2). DDH-Kl, drilled on section 5525 east, intersected a 42.3 m zone, between down-hole depths of 20.7 and 63.0 m, which averaged 0.43 gm/t Pt (Fig. 4.4). This intersection included a higher grade zone of 5.7 m between 45.1 and 50.8 m which averaged 1.18 gm/t Pt. DDH-K2, drilled on section 5600 east, intersected a 23 .2 m zone between down-hole depths of 59.1 and 82.3 m which averaged 0.24 gm/t Pt.

[!:-\~·~:] Wehrllte - Ounlte ~ Pyroxenlte

1.25

"'i

=====50metres

1.00

0.75

::,

! 0.50 :5

a.. 0.25 0

=~'::::'::=::':!::::::'::::::'::'::~~~~~~~~~~~~::::'::~C::::::~:l:'::'::':':======rRENCHKT2

arbonste veining & alteration

42.28m @ 0.43

m @ 1.18 g/1 Pt.

~d~~ HIGHER GRADE PLATINUM ZotE

KARS PROSPECT

Geological Section 5525E Figure 4.4

Both holes intersected a sequence of coarse- to very-coarse grained olivine pyroxenites, intermixed with zones of wehrlite and dunite, before passing into fine- to mediumto coarse-grained pyroxenites at depth. Olivine bearing lithologies from the upper weathered part of the hole have been serpentinised with olivine altered to a black magnetite - smectite talc mixture. Irregular fine fractures within pyroxene are frequently coated with green antigorite, talc, and chlorite. • Rotary air blast drilling has defined a 70-100 m wide zone of hornblende monzonite draped around the southern periphery of the Kars intrusion (Fig. 4.3). The southern end of costean

KT-3 exposed the contact zone between the monzonite and the main body of olivine pyroxenite. Contact features include thin monzonite dykes enclosing scattered pyroxenite fragments and a massive monzonite breccia with coarse angular pyroxenite xenoliths. These larger pyroxenite fragments commonly exhibit a 1-2 mm wide reaction rim, comprising dark hornblende, and frequently show a corresponding depletion of hornblende in the enclosing monzonite. Clearly the more acid rocks have intruded at the southern margin subsequent to the crystallisation of the pyroxenite. Assaying of lithologies from both the

costeans and the drill core has shown the platinum mineralisation to be associated with the more olivine-rich wehrlite - dunite phases and olivine pyroxenites which are cut by numerous dunite dykes and pods. In the core from DDHKl, carbonate alteration is present in the form of fine veinlets and disseminations and is most pronounced in a zone coincident with the highest platinum concentrations. However the carbonate also shows a tendency to be more strongly developed in the olivine-rich rocks so any genetic association between platinum and of carbonate alteration may only be apparent. Only very minor amounts of this style of alteration were noted in the costeans where it appears to have been destroyed or redistributed by the nearsurface weathering processes. Scanning electron microprobe analysis has shown that the majority of platinum at Kars is in the form of either polyxene (6-11% Fe) or ferroplatinum (16-21 % Fe) (Creelman, 1988). Ferroplatinum grains show a strong association

with magnetite particles, occurring on grain boundaries or within the magnetite grains. However, not all magnetite is platinum bearing. Of the other elements analysed, both gold and palladium are generally very low. Nickel values show a good correlation with platinum, reaching peaks of between 500 and 700 ppm but more generally in the range 300400 ppm. A moderate correlation exists between cobalt and platinum while copper and chromium both show a poor correlation with platinum. Some preliminary metallurgical test work has been completed on samples collected from the Kars costeans. Results have shown that a high grade platinum concentrate can be produced using conventional gravity concentration techniques however overall recoveries are only in the range of 30-40 %. Most of the platinum appears to have a very fine grain size and grinding to 100 microns would be required to achieve acceptable recoveries.

4.3. GILGAI PROSPECT The other main focus of exploration for Platinum Search N.L. has been at the Gilgai prospect situated 25 km west of Nyngan at the northern extremity of the ultramafic corridor (Fig. 4.1) (Jones, 1990). In contrast to the Kars prospect the platiniferous zone discovered at Gilgai comprises only a small part of a much larger complex, which at this time •is poorly understood due to the total lack of outcrop. The prospect has been evaluated by ground magnetic surveying and systematic RAB drilling. A buried laterite cap, in places reaching thicknesses of up to 45 m is present over the dunite and olivine pyroxenite, in the central part of the prospect. Continuous 3 m sampling of RAB holes has shown the laterite to contain platinum grades of up to 2 gm/t. Nickel and chromium are also enriched but do not attain economic grades. Palladium is generally low. The platinum geochemical anomaly at Gilgai covers an area of 350 by 250 m and has been tested by two inclined diamond drill holes each to a depth of 250 m (Fig. 4.5). Both holes

intersected zones of dunite and olivine pyroxenite containing widespread low-grade platinum mineralisation commonly in the range 0.1 to 0.4 gm/t but reaching peaks of between 1 and 2 gm/t Pt over isolated 1 m intervals. Palladium levels are insignificant and neutron activation scans on core samples have failed to detect other significant Platinum Group Metals PGMs. No visible platinum minerals were identified and sulphide contents are extremely low. It is assumed that the principal platinum mineral is isoferroplatinum as present at Fifield andKars. Interpretation of the geology suggests that the Gilgai complex is zoned about an olivine-rich dunite core in a similar fashion to the Owendale and Kars intrusions, and other known Alaskan-type complexes. Good macrolithological correlation exists between the two drill holes and as might be expected, the dunite is the more strongly mineralised of the two platinum bearing rock types.

5200E

5100E

C:J

O. 1 _ 0_4 ppm Platinum

(fil[]

0 _4 _ 1_0 ppm Platinum

l:J

>1.0 ppm Platinum RABdrlllhole

5300E

5700E

590CE

3200N

REFERENCES Agnew, P.D., 1987. The Petrology and Geochemistry of the Tout and Owendale Complexes, Fifield, NSW. University of NSW, Dept. of Applied Geology - Unpublished Honours Thesis. Agnew P.D, Hensen, BJ. and Dunlop, A.C., 1987. The petrology and geochemistry of the Tout and Owendale Complexes, Fifield, NSW. in Platiniferous Horizons in Layered Intrusions Symposium in conjunction with the J.J.Frankel Memorial Lecture, Univ. of NSW. (abs.) Barron, L., Suppel, D., Slansky, E., Joban, Z., Obnenstetter, M. & Spencer, R., 1991. The Fifield Platinum Province (abs.), in Geol.Soc.Aust. Abstracts and Field Trip guide No. 29, Tectonics and Metallogenesis of the Lachlan Fold Belt. Bowles, J.T.W., 1989. Mineralogical Study of Platinum-Rich Nuggets from the Fifield Area; Initial Examination OctoberDecember, 1989. Mineral Sciences Ltd - Unpublished Report. Bowman, H.N., Richardson, SJ. Dolanski, J., 1982. Narromine 1:250,000 Metallogenic Map SISS-3: Mine Data Sheets and Metallogenic Study, NSW Geological Survey.

Brill, B.A. and Keays, R.R., 1988. Fifield Project Report: June-November, 1988. Uni. of Melbourne. Dept. of Geology Unpublished Research Report. Brill, B.A. and Keays R.R., 1989a. Fifield Project Report: January-March, 1989. Uni. of Melbourne. Dept of Geology Unpublished Research Report. Brill, B.A. and Keays R.R., 1989b. Fifield Project Report: May-August, 1989. Uni. of Melbourne. Dept. of Geology Unpublished Research Report.

Brill, B.A. and Keays R.R., 1990. Fifield Project Report: May, 1990. Uni. of Melbourne. Dept. of Geology Unpublished Research Report. Creelman, R.A. (1988) Electron Microprobe Analysis of Platinum Bearing Concentrates from the Kars Prospect N.S.W (unpubl. report for Lachlan Resources N.L) Derrick, G.M., 1989. Fifield Project, NSW: Reports for the period 23.3.88 - 22.3.89 on behalf of the Noble Resources/Poseidon Ltd joint venture, EL 2663, 2664. NSW Mines Dept Company Reports. Elliott, SJ., 1989. Fifield Project - Exploration Licence 2521: Alluvial Platinum/Gold Programme - Report on Activities for Period July, 1989 to November, 1989. Helix Resources NL - Unpublished Report. Emerson, D.W., Embleton, BJ.J., & Clark, D., 1979 The Flemington intrusion, Fifield, NSW - petrophysical and petrological notes. Aust. Soc. of Explor. Geophysicists, Bulletin 10 (1), 67-78 Horwitz, R.C., 1988. The Buried Alluvial Channels of the Fifield, Tullamore, Tottenham and Honeybugle Areas of New South Wales; Notes to Accompany Generalised Geological Maps. Helix Resources NL Unpublished Report. Joban, Z., Obenstetter, M., Slansky, E., Barron, L.M., and Suppel, D., 1989. Platinum Mineralisation in the AlaskanType Intrusive Complexes near Fifield, New South Wales, Australia. Part 1: Platinum-Group Minerals in Clinopyroxenites of the Kelvin Grove Prospe£t, Owendale Intrusion. Geological Survey of NSW Unpublished Report No 89/14. Jones, GJ., (1986). Introductory Report on N.S.W Platinum Areas. (Unpubl. report for Lachlan Resources N.L).

Jones, GJ., (1990). EL 2654 Miandetta Progress Report on the Gilgai Prospect (unpubl. report for Platinum Search N.L). Martin, A.R. and MacDonald, C., 1990. Fifield Region Report, Project Summary - November, 1990. Helix Resources NL - Unpublished Report. Pogson, DJ., & Hilyard, D., 1981 Results of isotopic age dating related to GSNSW investigations, 1974 -1978. NSW Geol. Survey Records 20 (2), 251-273 Raedeke, L.D., 1988. Owendale Complex, Fifield Platinum Prospect, New South Wales, Australia. Chevron Oil Field Research Company - Unpublished Report. Rangott, M.F., 1990. Six Monthly Progress Reports on EL 2653 Derriwong. (Unpubl. reports for Platinum Search N.L).

Suppel, D.W. and Barron L.M., 1986. Platinum in Basic to Ultrabasic Intrusive Complexes at Fifield: A Preliminary Report. New South Wales Geological Survey - Quarterly Notes 65 (1-8). Taylor, H.P., 1967. The Zoned Ultramafic Complexes of Southeast Alaska: in Wylie, P.J., ed. 1967. Ultramafic and Related Rocks: Wilie, New York (47121). Turvey,

DJ., 1989. Primary Platinum Mineralisation Review; Owendale Intrusion. Resource Services Group Unpublished Report

Wyborn ,D. & Cameron, W. 1990. Ordovician magmatism in the central Lachlan fold belt and precious metal potential. in Geol. Soc. Australia Abstracts, 10th Geol. Convention, Hobart Xueyuan, Y., 1990 The petrology of the Tout Complex NSW Dept of Mines, unpublished report.

SPONSORS The Organizing Committee of the Sixth International Platinum Symposium expresses sincere appreciation to the following sponsors: Ansett Airlines of Australia Australian Federal Government, Dept. of Industry, Trade and Commerce

CSIRO Delta Gold N.L. Geological Society of Australia, Federal Committee and W .A. Branch Gold Corporation Helix Resources N.L. Hendry Rae and Court Hunter Resources Ltd. Jane Brook Estate Wines Johnson Mathey Lachlan Resources N.L. Ord Partners Parker and Parker Pancontinental Mining Ltd. QANTAS

Society of Economic Geologists