Geology of the Sir Samuel 1:250 000 sheet area, Western ... · PDF file1:250 000 sheet area,...

S.F. Liu, D.C. Champion and K.F. Cassidy

S P A T I A L I N F O R M A T I O N F O R T H E N A T I O N

Geology of the Sir Samuel1:250 000 sheet area,Western Australia

A U S T R A L I AGEOSCIENCE

Record 2002/14

Geology of the Sir Samuel 1:250 000sheet area, Western Australia

Geoscience AustraliaRecord 2002/14

S.F. Liu, D.C. Champion and K.F. Cassidy

Geoscience Australia

Chief Executive Officer: Neil Williams

Department of Industry, Tourism and Resources

Minister for Industry, Tourism and Resources: The Hon. Ian Macfarlane, MPParliamentary Secretary: The Hon. Warren Entsch, MP

© Commonwealth of Australia 2002

This work is copyright. Apart from any fair dealings for the purposes of study, research, criticism orreview, as permitted under the Copyright Act, no part may be reproduced by any process withoutwritten permission. Inquiries should be directed to the Communications Unit, Geoscience Australia,GPO Box 378, Canberra ACT 2601.

ISSN: 1039 0073ISBN: 0 642 46743 9

The recommended reference for this publication is:LIU, S.F., CHAMPION, D.C., & CASSIDY, K.F., 2002, Geology of the Sir Samuel 1:250 000 sheet

area, Western Australia: Geoscience Australia, Record 2002/14, 57p.

Geoscience Australia has tried to make the information in this product as accurate as possible. How-ever, it does not guarantee that the information is totally accurate or complete. THEREFORE, YOUSHOULD NOT RELY SOLELY ON THIS INFORMATION WHEN MAKING A COMMERCIALDECISION.

iii

Contents

Abstract 1Introduction 2

Previous investigations 2Physiography and access 4

Archaean Geology 5Geological framework 5Archaean rock units 8

Metamorphosed ultramafic rocks (Au, Auc, Auk, Aul, Aup, Aur, Aus, Aut, Aux) 8Metamorphosed mafic extrusive rocks (Ab, Abam, Abb, Abc, Abf, Abi, Abm,Abp, Abs) 10

Mount Goode Basalt (AbMG, AbMGp) 12Interleaved greenstone and granitoid (Abg) 12

Metamorphosed mafic intrusive rocks (Ao, Aod, Aog, AoKV, AoKVa, AoKVg,AoKVx) 13

Kathleen Valley Gabbro (AoKV, AoKVa, AoKVg, AoKVx) 13Metamorphosed felsic volcanic and volcaniclastic rocks (Af, Afpf, Afs, Aft,Afv, Afx) 16

Spring Well felsic volcanic complex 16Metasedimentary rocks (As, Asc, Ascf, Ascq, Ash, Ashd, AsJC, AsJCa, AsJCb,Asq, Ass, Ac, Aci, Acis) 17

Jones Creek Conglomerate (AsJC, AsJCa, AsJCb) 18Conglomerate with granitic matrix (AsJC) and arkose (AsJCa) 18Conglomerate with mafic matrix (AsJCb) 19Depositional environment 20Age of the Conglomerate 20Hydraulic breccia 20

Low- to medium-grade metamorphic rocks (Ala, Alb, Ald, Alf, Alfq, All,Alm, Alqm) 20Granitoids (Ag, Agb, Agc, Agd, Agdq, Age, Agf, Agfo, Agg, Agm, Agmp, Agn,Agp, Ags, Agt, Agu, AgWA, AgWE, AgWEf) 22

Classification 24Petrogenesis and implications 25

Veins and dykes (a, d, e, g, p, po, q) 25Greenstone belts and major faults 26

Yakabindie greenstone belt 26Miranda and Emu Faults 27Waroonga Shear Zones 27

Agnew greenstone belt 28Mount Keith–Perseverance greenstone belt 29

Perseverance and Erawalla Faults 29Mount Keith–Six Mile Well section 30Perseverance–McDonough Lookout section 31

Yandal greenstone belt 32Mount McClure Fault 33Cocks–Satisfaction Zone 34Ockerburry Fault Zone 34Ninnis Fault 36

Ninnis Well area 36Woorana Soak area 36Mount Grey Fault 36Rosewood Fault 37

The Yandal compressional jog 37Dingo Range greenstone belt 37Stratigraphic correlation with the Kalgoorlie and Leonora–Laverton areas 40

iv

Deformation history 41First deformation event (D

1) 41

Second deformation event (D2) 41

Third deformation event (D3) 42

Post-D3 deformations 42

Metamorphism 43Proterozoic geology 43Palaeozoic geology 44

Permian sedimentary rocks (PAf, PAg, PAl) 44Cainozoic geology 44Economic geology 45

Gold 45Bronzewing gold deposits 46Mount McClure gold mining centre 47Darlot – Centenary mining centre 48Bellevue gold deposit 48Genesis and New Holland gold deposits 48

Nickel 49Mount Keith nickel deposit 49Perseverance and Rocky’s Reward nickel deposits 50

Copper 50Corundum 50Tin 51Uranium 51

Acknowledgments 51References 51

Appendix

Gazetteer of localities on SIR SAMUEL 1:250 000 sheet area 57

Figures

1. Location of the SIR SAMUEL 1:250 000 sheet area 32. Main cultural and physiographic features in the SIR SAMUEL 1:250 000 sheet area 53. Simplified geology of the SIR SAMUEL and northern part of the LEONORA

1:250 000 sheet areas 74. Greyscale first vertical derivative of total magnetic intensity image of the SIR

SAMUEL and northern part of the LEONORA 1:250 000 sheet areas 95. A. Solid geology of the Six Mile Well – Lawlers area 10

B. Solid geology of the Honeymoon Well – Six Mile Well area 116. Solid geology of the southern Yandal greenstone belt 147. Solid geology of the Dingo Range greenstone belt 158. Photograph of deformed chert-pebble conglomerate, Mount Harold area 199. Photograph of granitic hydraulic breccia, Yellow Aster area 2110. Photographs of D

1 structures in the Ockerburry Hill area 35

11. Photograph of isoclinal D1 fold in cherty rocks in the Dingo Range 38

12. Photograph of folded intersection lineation in cherty rocks in the Dingo Range 3913. Photograph of sub-vertical fractural cleavages in cherty rocks in the Dingo Range 40

Tables

1. Summary of geological, petrographic, and age data for granite groups of thenorth Eastern Goldfields Province 24

2. Structural and metamorphic history of the Archaean granite–greenstones onthe SIR SAMUEL 1:250 000 sheet area 42

3. Mineral commodity statistics for the SIR SAMUEL 1:250 000 sheet area 46

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Geoscience Australia Record 2002/14 Geology of the Sir Samuel 1:250 000 sheet area

Abstract

Archaean granite–greenstones in the SIR SAMUEL 1:250 000 sheet area can be divided into three north- tonorth-northwest-trending major greenstone belts separated by large areas of granitoid. From west to east,these are the Agnew–Wiluna, Yandal and Dingo Range greenstone belts. The western Agnew–Wilunagreenstone belt varies in width from 2 to 17 km, and can be divided into three domains namely the Yakabindie,Agnew and Mount Keith–Perseverance greenstone belts.

The Yakabindie greenstone belt comprises a layered sequence of the Kathleen Valley Gabbro overlain bythe massive tholeiitic Mount Goode Basalt. The Agnew greenstone belt comprises a lower sequence ofmetamorphosed ultramafic, mafic, felsic volcanic, and sedimentary rocks, which is exposed in the Lawlersand Leinster Anticlines. The upper sequence, as exposed in the Mount White Syncline area, consists ofmetabasalt, metagabbro and metasedimentary rocks. Metamorphosed ultramafic, mafic, felsic volcanic andsedimentary rocks in the Perseverance area extend farther north to west of Mount Pasco. From Six Mile Well,ultramafic, sedimentary, and felsic volcanic/volcaniclastic rocks correlate with the greenstone sequencesfrom Mount Keith to Wiluna. The Jones Creek Conglomerate represents a late clastic sequence and is restrictedto a narrow, fault-bounded zone between the Yakabindie greenstone belt and granitoid in the west and theMount Keith–Perseverance and Agnew greenstone belts to the east.

The southern Yandal greenstone belt consists of two major packages of greenstones, i.e. mafic and someultramafic rocks in the Bronzewing–Mount McClure, Hartwell, Yandal Well and Darlot areas, and felsicrocks along the Ockerburry Fault Zone and Spring Well area. In the Dingo Range greenstone belt, the DingoRange antiform is interpreted to be a refolded earlier fold of banded iron formation/chert, ultramafic andmafic rocks. Felsic volcanic/volcaniclastic rocks are present in the Mount Harold area. The Stirling Peaksarea is largely undeformed metabasalt.

The western part of the sheet is largely granitoid, with an arcuate belt up to 18 km wide of highlydeformed and gneissic granitoid west of the Waroonga Shear Zone. The southern Yandal greenstone belt isseparated from the Agnew–Wiluna greenstone belt by a 20–40 km-wide interval of granitoid and gneiss,including the sigmoidal Koonoonooka monzogranite, and a highly deformed zone, up to 12 km wide, ofinterleaved granitoid and greenstone west of the Mount McClure Fault. A large area of variably deformedgranitoid and gneiss separates the Yandal and Dingo Range belts. The granitoids are primarily monzogranitewith minor granodiorite, syenogranite and quartz syenite, and can be divided petrographically andgeochemically into two main groups, high–Ca (>60% of total granitoids) and low–Ca (>20–25%), and threeminor groups, mafic (<5–10%), syenitic (<5%) and high–HFSE (high–field strength element, <5%).

Three major deformation events are recognised in the granite–greenstones in the SIR SAMUEL area. Thefirst deformation, although poorly understood, produced bedding-parallel foliation including flattened pillowstructures in basalt, and some tight to isoclinal folds. Major orogenic compression during D2 produced thenorth-northwest greenstone belt trends and linear structures including faults, shear zones and folds. DuringD3, deformation appears to have been largely concentrated along major shear zones. Some north- to north-northeast-trending structures were probably produced, or reoriented into their current positions, during D3,which shaped the current structural architecture. Post-D3 deformation is represented by normal faults, fractures,and sub-horizontal crenulations. A major phase of regional metamorphism was initiated during D2 and peakedlate during or after D2. Granitoid intrusion occurred throughout the deformation and metamorphic history inthe SIR SAMUEL area.

The SIR SAMUEL area contains significant gold and nickel mineralisation. Gold mineralisation is structurallycontrolled and associated with brittle-ductile shear zones and quartz veins. Mineralisation is hosted by a

Geology of the Sir Samuel 1:250 000 sheet area,Western Australia

by S.F. Liu, D.C. Champion and K.F. Cassidy

2

Liu et al.

IntroductionThe SIR SAMUEL1 1:250 000 map sheet area (SG51–13) is bounded by latitudes 27º00’S and 28º00’Sand longitudes 120º00’E to 121º30’E (Fig. 1). Thesheet is situated between LEONORA and WILUNA inthe eastern Yilgarn Craton and bounds the westernpart of the Eastern Goldfields Province and theeastern part of the Southern Cross Province.

The first edition of the SIR SAMUEL 1:250 000geological map (Bunting & Williams 1977) wasprepared and published during the extensive nickelexploration in the 1970s but before the extensivegold exploration in the 1980s. Gold and nickelexploration and mining have resulted in a largeamount of geological data, much of which is in theform of company reports in the WAMEX open-file system housed in the Geological Survey ofWestern Australia (GSWA).

Second generation mapping was carried out bygeologists from the Geoscience Australia (GA;formerly Australian Geological SurveyOrganisation) and GSWA on the six 1:100 000sheets in the SIR SAMUEL area between 1994 and1997 as part of the joint National GeoscienceMapping Accord (NGMA) project. YEELIRRIE(Champion & Stewart 1998), MOUNT KEITH(Jagodzinski et al. 1997), and WANGGANNOO(Lyons et al. 1996) have been published by GA,and DEPOT SPRINGS (Wyche & Griffin 1998),SIR SAMUEL (Liu et al. 1996) and DARLOT(Wyche & Westaway 1996) by GSWA. Mostadjacent 1:100 000 geological maps have also beenreleased – WILUNA (Langford & Liu 1997),LAKE VIOLET (Stewart & Bastrakova 1997),SANDALWOOD (Blake & Whitaker 1996), TATE(Champion 1996), BANJAWARN (Farrell &Griffin 1997), WEEBO (Oversby et al. 1996a),WILDARA (Oversby et al. 1996b) and

MUNJEROO (Duggan et al. 1996). The geologicalmaps in the SIR SAMUEL area have recently beencollated as geospatially referenced digitalinformation in Phase 2 of the East YilgarnGeoscience Database project by GSWA(Groenewald et al. 2001).

The mapping was carried out using 1:25 000colour aerial photographs (taken in March 1994)for MOUNT KEITH, WANGGANNOO, SIRSAMUEL, and DARLOT, and 1:50 000 black andwhite aerial photographs (taken in May 1989) forYEELIRRIE and DEPOT SPRINGS. This workwas assisted by Landsat Thematic Mapper imagery.The aerial photographs and Landsat images areavailable from the Department of LandAdministration (DOLA) of Western Australia andthe National Mapping Division of GeoscienceAustralia (formerly AUSLIG) in Canberra.Interpretation of 400 m line spacing aeromagneticdata, together with images of airborne g-rayspectrometric data and regional gravity data(available through GA and GSWA), andinformation from mining and exploration companyreports (WAMEX), were used extensively duringthis work. Discussions with mining and explorationcompanies working in the SIR SAMUEL area by themapping geologists also contributed to theunderstanding of the geology of the area.Topographic and cultural data are modified fromthe digital data supplied by DOLA and GA withinformation from the 1994 colour aerialphotographs.

Previous investigations

The first edition of the SIR SAMUEL geological mapand explanatory notes were by Bunting & Williams(1977, 1979). The second edition of the map (Liu2000) was largely compiled from the new1:100 000 maps, plus some additional fieldworkby the author for consistency checking and problemsolving in 1997. A solid geology map of the SIR

SAMUEL area (Liu et al. 2000a) is also based on thepublished 1:100 000 geological maps plus

1 1:250 000 map sheet names are printed in small capitals toavoid confusion with identical place names. Similarly 1:100000 map sheet names are printed in large capitals.

variety of lithologies, principally metamorphosed basalt and gabbro, metasedimentary rocks and locally ingranitoids. Significant deposits include the Bronzewing and Darlot–Centenary gold deposits in the Yandalgreenstone belt, and New Holland, Genesis and Bellevue deposits in Agnew–Wiluna greenstone belt. Nickeldeposits include Perseverance and Rockys Reward at Leinster, and Mount Keith. Other mineralisation includesminor copper mineralisation in the Kathleen Valley area, and calcrete uranium prospects (e.g. Lake Maitland)and tin southwest of the Kathleen Valley town-site.

KEYWORDS:Archaean geology, greenstones, granitoids, Eastern Goldfields, Sir Samuel, Agnew–Wiluna,Yandal, Dingo Range, mineral resources, gold nickel.

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interpretation of the 400 m line spacingaeromagnetic data acquired by GA under theNGMA program and additional geologicalinformation from exploration companies. Thecurrent SIR SAMUEL explanatory notes drawextensively on published explanatory notes forthree 1:100 000 sheets, i.e. DARLOT (Westaway

& Wyche 1998), MOUNT KEITH (Jagodzinski etal. 1999) and SIR SAMUEL (Liu et al. 1998).Additional information is derived from synthesiswork by Liu & Chen (1998a & b), Chen et al. (1998,2001) and the published literature.

Naldrett & Turner (1977) recognised two

16/G51/13

120°00' 123°00'

27°00'

28°00'

Leinster

Bronzewing

Wiluna

JundeeMillrose

Duketon

Laverton

Leonora29°00'

26°00'121°00' 122°00'

? ??

?

Kilkenny

Fault

Mt G

eorgeS

hear Z

on

eFault

Ninnis

Fault

Granitoid, undividedGreenstone, undivided

Geological boundary

Fault

Fault (inferred)

Fault (concealed)Archaean

Proterozoic

?

Sir Samuel1:250 000 sheet area

Ballard

0 100 km

Mt Celia

Ida F

ault

?

Conglomerate& sandstone

Granitic gneiss& foliated graniteEaraheedy Group

Earaheedy Group(banded iron formation)

Granitoid, foliated

Figure 1. Location of the SIR SAMUEL 1:250 000 sheet area in the north Eastern Goldfields

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Liu et al.

greenstone sequences in the Mount Keith–Lawlersarea, a lower sequence to the west dominated (over90%) by mafic rocks and an upper sequence to theeast, with approximately one-third mafic and two-thirds felsic rocks. These two sequences areseparated by an unconformity and associatedconglomerate. Dowling & Hill (1990) and Hill etal. (1990, 1995) described the physical features ofkomatiite flows at Mount Keith, and Dowling &Hill (1992) documented the Mount Keith nickeldeposit. The volcanology of komatiite in theAgnew–Mount Keith area was studied in detail byHill et al. (1995, 1996) as part of their study of theNorseman–Wiluna belt (see also Hill et al. 1996).Giles (1980, 1982) and Messenger (2000) havedocumented the Spring Well felsic volcaniccomplex. These reports include mapping,petrography and geochemistry. Recently Barley etal. (1998) studied the complex as part of theirresearch on the felsic volcanic and sedimentarysuccessions in the Eastern Goldfields. Discussionof the Yandal greenstone belt is presented inMessenger (2000) and Vearncombe et al. (2000).

Durney (1972) studied the conglomerate in theJones Creek area in the Mount Keith–Perseverancegreenstone belt, and recognised a majorunconformity within the Archaean greenstones.Marston & Travis (1976), in a study of the JonesCreek Conglomerate, concluded that the structuralcomplexity makes regional stratigraphicrelationships, particularly Durney’s (1972)suggestion that the Jones Creek Conglomerateseparates two major mafic dominated greenstonesequences, difficult to justify. Results ofgeochronological dating of the Jones CreekConglomerate and some other rocks in the SIR

SAMUEL area are reported in Nelson (1997a, 1998,2000) and Krapez et al. (2000).

Platt et al. (1978) presented the first detailedstructural study in the north Eastern Goldfields forthe Lawlers Anticline area, a small part of which isin the SIR SAMUEL area. Eisenlohr (1987, 1989,1992) carried out a detailed mapping and structuralstudy of the Kathleen Valley–Lawlers (Agnew) areawith emphasis on the northern part. He recognisedcontrasting deformation styles between eastern andwestern greenstone sequences in the Mount Keith–Agnew area. A structural synthesis by Hammond& Nisbet (1992) for the Norseman–Wiluna beltcovered the SIR SAMUEL area. Bongers (1994)studied in detail the structures of the Mount Keithnickel mine area. Overprinting evidence waspresented to outline a structural history of fourdeformations in Liu & Griffin (1996) and Liu et al.(1998) for the Yakabindie–Leinster area.

Jagodzinski et al. (1999) discussed structures inthe MOUNT KEITH sheet area. Vearncombe et al.(2000) synthesises the regional, structural andexploration geology of the Yandal greenstone belt.Syntheses of structural work from the currentNGMA mapping in the north Eastern Goldfieldsare presented in Farrell (1997), Liu & Chen (1998a& b), Chen et al. (1998, 2001) and Wyche & Farrell(2000). Late transpression is discussed in Chen et

al. (1998, 2001).

Several recent studies of the nickel and golddeposits on SIR SAMUEL have been published. Theseinclude studies on the Mount Keith nickel deposit(Burt & Sheppy 1975, Hopf & Head 1998), thePerseverance and Rocky’s Reward nickel deposits(Libby et al. 1997, 1998, De-Vitry et al. 1998), theBellevue gold deposit (Brotherton & Wilson 1990),the Bronzewing gold deposit (Eshuys et al. 1995,Dugdale 1997, Phillips et al. 1998a), the Darlot–Centenary gold deposit (Bucknell 1997, Krcmarovet al. 2000), the Mount McClure gold deposits(Otterman & Miguel 1995, Harris 1998), and theNew Holland and Genesis gold deposits (Inwood1998).

Physiography and access

The SIR SAMUEL area is about 700 km northeast ofPerth, and about 400 km north of Kalgoorlie. TheMeekatharra–Wiluna–Kalgoorlie road, whichbypasses Leinster, is sealed from Wiluna toKalgoorlie and being sealed from Wiluna toMeekatharra at the time of writing. The road fromthe Perseverance nickel mine, via Leinster, is sealedto the Meekatharra–Wiluna–Kalgoorlie road. Theroad from Leinster to north of Agnew is also sealed,where a gravel road links, via Sandstone, to theGreat Northern Highway to Perth.

Gravel roads provide access to the MountMcClure and Bronzewing gold mining operationsto the northeast, Darlot gold mine in the southeastand all homesteads (Fig. 2). The low relief andnumerous station and exploration tracks enablegood access by 4WD to all parts of greenstones inthe SIR SAMUEL area.

Leinster is a major town in the south of the SIR

SAMUEL area. It was established in 1989 to supportthe Perseverance (formerly Agnew) nickel mine,11 km to the north. The townsite of Agnew, 1 kmoutside the sheet area in the south, is the centre forthe New Holland and Genesis gold mines on SIR

SAMUEL, and Emu and Redeemer gold mines, onLEONORA. Pastoral leases on SIR SAMUEL includeAlbion Downs, Depot Springs, Leinster Downs,

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Melrose, Wonganoo, Yakabindie, Yandal andYeelirrie (Fig. 2).

The SIR SAMUEL area has subdued topographyranging from flat to undulating (Fig. 2). The hillsare 500–540 m above sea level and rise above theplains at 460–500 m above sea level. The hillscorrespond to areas of outcrop of greenstones thattrend approximately north to north-northwest. Theyare separated by large areas of sandplain containingsome low breakaways above outcrops of granitoid.The Agnew–Mount Keith–Perseverance andYandal greenstone belts are cut by the east-trendingLake Miranda and Lake Darlot playa systemsrespectively. The area from a few km to 20 kmnorth of Lake Miranda has the highest relief andthe best exposure.

The hilly areas over greenstone generally havea dense cover of Acacia (mulga mainly) and Cassiashrubs. Both narrow and broad ephemeral drainagecourses are characterised by dense vegetation thatincludes Acacia, Eucalyptus, and sandalwood.Bluebush, saltbush and samphire grow around theplaya lake systems. Sandplains largely overlie areasof sheetwash and granitoid and are dominated byspinifex and Acacia woodland. The vegetationassemblages in the Eastern Goldfields have beendescribed by Burbidge (1943) and Beard (1990).

The SIR SAMUEL area is in a semi-arid area.According to the Commonwealth Bureau ofMeteorology (www.bom.gov.au), annual rainfall atLawlers (just south of the map sheet area) is about210 mm. This includes winter showers andsignificant rainfalls that result from tropical stormsand cyclones in the summer. Temperaturesregularly exceed 40ºC in the summer months fromDecember to February (average daily maximumtemperature 35ºC to 36ºC). There are occasionalfrosts in the winter months between June andAugust (average daily minimum temperature 6ºCto 7ºC).

Archaean Geology

Geological framework

The western part of SIR SAMUEL covers theboundary area between the Southern Cross andEastern Goldfields provinces in the Yilgarn Craton,although the boundary in this region has not beenwell defined (see section on ‘Greenstone Belts andMajor Faults’ for more discussion).

The Archaean geology in the SIR SAMUEL areacan be divided into seven parts: four north-northwest-trending areas of granitoid that are

120°00' 120°30' 121°00' 121°30'27°00'

27°30'

28°00'16/G51/14

LEINSTER

Wonganoo

Melrose

Yandal

Albion Downs

Yakabindie

Genesis AuNew Holland Au

Perseverance Ni

Rocky's Reward Ni

Bellevue Au

Cosmos Ni

Yellow Aster Au

Yakabindie Ni

Mt Keith Ni

Mt Keith

Cockburn Au

Bronzewing AuLotus Au

Mt McCluremines office

Success Au

Parmelia Au

Dragon Au

Centenary AuDarlot Au

Lake Darlot

LeinsterDowns

Creek

Road

Town

Homestead

Locality

Mine

Yeelirrie

LakeMaitland

0 40 km

Lake Miranda

Figure 2. Main cultural and physiographic features in the SIR SAMUEL 1:250 000 sheet area

http://www.bom.gov.au/

6

Liu et al.

separated by three north-northwest-trendinggreenstone belts (Figs 1, 3–4). The greenstone beltin the west is part of the Agnew–Wiluna greenstonebelt that extends southwards to LEONORA andnorthwards to WILUNA. The central belt is part ofthe Yandal greenstone belt that extends northwardsto WILUNA, and the belt in the east is part of theDingo Range greenstone belt.

The Agnew–Wiluna greenstone belt was furtherdivided into the Agnew, Coles Find, Mount Keith–Perseverance, and Wiluna greenstone belts byGriffin (1990), based on structural and greenstoneoutcrop continuity, for the convenience ofdiscussion. The boundaries of these greenstonebelts are not always well defined. The Yakabindiegreenstone belt west of Miranda Fault wassubdivided from the Agnew–Wiluna greenstone byLiu et al. (1998, Figs 3, 5). In the Wiluna area, theErawalla Fault separates the Coles Find greenstonebelt from the Wiluna belt (Griffin 1990, Liu et al.1995). In this Record, greenstones in the MountKeith–Perseverance area are discussed as onegreenstone domain, which is faulted along the SirSamuel Fault against the Agnew belt.

Large areas of granitoid and gneiss separate thegreenstone belts (Figs 3–7). Although parts of thegranite–greenstone contacts are intrusive, in mostcases, the contacts are faulted or sheared. East ofthe Perseverance Fault and west of the MountMcClure Fault are strongly foliated granitoids thatinclude some interleaved amphibolite. West of theWaroonga Shear Zone there is an arcuatenorth-trending zone, a few kilometres to 18 kmwide, of strongly deformed granitic gneiss.

The granite–greenstone terrain experiencedthree major deformation events (Farrell 1997, Liu& Chen 1998b, Wyche & Farrell 2000, Chen et al.2001). The nature of the first deformation event(D1) is not well understood, but it producedbedding-parallel foliation (S1) and some tight toisoclinal folds. The second event (D2) waseast-northeast–west-southwest-directed orogeniccompression that resulted in the shaping ofnorth-northwest-trending regional structuresincluding shear zones, faults, folds and the lineardistribution of greenstone belts. A prominent sub-vertical to steeply dipping foliation was producedin appropriate rock types. This event progressedinto a third event (D3) of transpression during whichdeformation was largely concentrated along majorshear zones. Some north- to north-northeast-trending faults and shear zones are considered tohave developed, or further developed, during thisevent. Post-D3 deformation is difficult to correlatebecause of the lack of overprinting evidence, but

includes east-, northeast- and northwest-trendingfaults and fractures, and sub-horizontalcrenulations. Some east-trending fractures andfaults are filled with Proterozoic mafic dykes thatare not exposed but readily interpreted fromaeromagnetic data.

Regional fault/shear zones and linear greenstonebelts are prominent features in the SIR SAMUEL areaas in the surrounding areas of the EasternGoldfields. Some of these structures had along-lived history, which may have lasted fromgreenstone formation to the last major tectonicevent, D3, that shaped the structural architecture ofthe area and the entire Eastern Goldfields. It shouldbe noted that the term ‘fault’ is used in a generalsense, partly because of historical reasons. Manyregional faults are actually ductile shear zones 1km or wider. For convenience of presentation,however, single lines of fault are shown on maps.In most cases, the fault lines mark only the mostextensively deformed part of the shear zones orthe boundaries between different rock types. Largeareas of highly deformed rocks are marked by asymbol for ‘highly deformed rocks’ in the solidgeology map (Liu et al. 2000a). In most cases, thehistorical usage of the terms ‘fault’ or ‘shear zone’are followed. The context makes it clear what ismeant in most cases.

Regional faults/shear zones broadly fall intothree groups: (1) north-northwest- to northwest-trending faults including the Perseverance andNinnis Faults; (2) approximately north- tonorth-northeast-trending faults including theMiranda, Emu and Mount McClure faults and theOckerburry Fault Zone; and (3) the arcuateWaroonga Shear Zones (Fig. 3).

The prominent north-northwest-trendingPerseverance and Ninnis Faults are parts of twomajor lineaments, the Keith–Kilkenny and CeliaLineaments, respectively. Both lineaments areapparently ‘crustal-scale’ structures, whichprobably predated, but were active during, theformation of greenstones in the region. At the earlystages the Perseverance Fault may have linked withthe Kilkenny Fault Zone along the north-northwest-trending Keith–Kilkenny lineament, but in thecurrent structural configuration, the PerseveranceFault links with the Mount George Shear Zonenorth-northwest and south-southwest of Leonora(Fig. 1, Liu & Chen 1998b). Most regional faults/shear zones appear to be fairly steep or nearlyvertical at surface.

Metamorphism in the area is generally low,mostly in the greenschist facies away from the

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120°00'27°00'

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28°30'

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16/G51/15

Granitoid, undivided

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Fault

Fault (inferred)

FaultFault

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LT

D1 fold

D2 fold

D3 fold

Trend

Perseverance

Bundarra

Koonoonooka m

onzogranite

YA

ND

AL

GR

EE

NS

TO

NE

BE

LT

0 40 km

Leinster monzogranite

Bronzewing

Mt Clifford

Conglomerate and sandstone

Granitic gneiss and foliated granite

Sir S

amuel F

Cocks -

Zo

ne

Satisfactio

n

1

2 3

4

5

Weebo Granodiorite

Wadarrah Quartz Monzonite

Granitoid, foliated

DIN

GO

RA

NG

E G

RE

EN

STO

NE

BE

LT

Figure 3. Simplified geology of the SIR SAMUEL and northern part of the LEONORA 1:250 000 sheetareas. Numbers refer to localities mentioned in the text: 1 – Lawlers Anticline, 2 – MountWhite Syncline, 3 – Leinster Anticline, 4 – Bronzewing Anticline, 5 – Dingo Range antiform

granite–greenstone contacts. Near the contacts, thegreenstones are commonly metamorphosed toamphibolite facies (Binns et al. 1976).

The geochronology of the greenstone sequencesin the SIR SAMUEL area is poorly constrained. Atonalitic sample from the Kathleen Valley Gabbrosequence, which is part of the Yakabindiegreenstone belt (Fig. 3), has a Sensitive HighResolution Ion Microprobe (SHRIMP) U–Pbzircon age of 2736 ± 3 Ma (Black L.P., 2000,

written comm.). This suggests that at least some ofthe greenstone sequences are older than the 2705–2675 Ma old greenstones that predominate in mostof the Eastern Goldfields (Nelson 1997b, Krapezet al. 2000). A deformed felsic volcanic rock fromthe Rockys Reward mine near Leinster has aSHRIMP U–Pb zircon age of 2720 ± 14 Ma(Nelson, 1997b). Felsic volcanic rocks from theSpring Well Complex in the southern Yandalgreenstone belt have ages of ca. 2700–2690 Ma(Nelson 1997b). Basement to the greenstones is

8

Liu et al.

not exposed in the SIR SAMUEL area. Granitic rocksare generally younger than the greenstones andhave ages ranging from 2685 to 2640 Ma(Champion & Sheraton 1997, Nelson 1997a,Wyche & Farrell 2000, Geoscience Australia,unpublished data). A gneissic granite sample(strongly deformed granitoid) from west of theMount McClure Fault was dated to be 2738 ± 6Ma by Nelson (1997a) and represents an earlyphase of granitoid magmatism.

Archaean rock units

Metamorphosed ultramafic rocks(Au, Auc, Auk, Aul, Aup, Aur, Aus, Aut,Aux)

Ultramafic rocks are a common component of thegreenstone sequences on SIR SAMUEL, particularlyin the Mount Keith–Perseverance and Agnewgreenstone belts. They also occur in the DingoRange greenstone belt and in the west part of thesouthern Yandal greenstone belt. In most cases theyare deeply weathered and rarely crop out exceptwhere silicified. Better outcrop occurs around theMount Keith nickel mine, 5–6 km south-southeastand just northwest of Six Mile Well, in the areaeast and north of McDonough Lookout, aroundMount Sir Samuel, around the Perseverance Nickelmine (Fig. 5) and at Dingo Range (Fig. 3). Theycommonly correspond to prominent anomaly highsin images of aeromagnetic data (Fig. 4). In someareas of no outcrop but where ultramafic rocks areinferred from aeromagnetic data, their presence hasbeen confirmed by shallow drilling, e.g. along thesouthwestern margin of the Yandal greenstone belt(Fig. 6). Exposed ultramafic rocks are commonlyserpentinized, silicified and/or schistose, but theoriginal igneous textures (cumulate textures andspinifex textures) are preserved in places. Whereultramafic rocks are inferred to underlie silicacaprock, the map unit Czu has been used.

Undivided ultramafic rocks are mapped as Au,mostly in the area between Six Mile Well toPerseverance and about 1 km west of MountRoberts. Metamorphosed komatiite (Auk) isrecognised by the presence of platy olivine-spinifextextures in hand specimen. Only two units aremapped in the SIR SAMUEL area, one southwest ofthe Mount Keith nickel mine and the other about 7km north-northwest of Six Mile Well. They are alsofound in association with other ultramafic rocks,e.g. peridotite around Six Mile Well. It forms smallexposures in ‘Spinifex Park’, 2 km southwest ofthe Mount Keith nickel mine (Jagodzinski et al.

1999). Metamorphosed pyroxenite (Aux), occurringnortheast of McDonough Lookout, has a medium-to fine-grained texture that is dominated in thinsection by a mixture of tremolite and actinolite,and includes minor talc and chlorite.

Serpentinized peridotite, commonly with adistinctive olivine cumulate texture, is mapped asAup, e.g. 4 km north of Mount Sir Samuel, 2.5 kmsouth of Six Mile Well and 5 km west of MountKeith in the Mount Keith–Perseverance belt, 5 kmsouth of Mount Roberts in the Agnew belt, 3 kmeast-southeast of Mount McClure and 2.5 kmnorthwest of Desperation Well in the Yandal belt.These rocks are commonly silicified. Relictcumulate olivine grains, up to 2 mm across, arepseudomorphed by radiating serpentine. Magnetitefills cracks in the olivine grains. The intercumulusmaterial consists of serpentine, talc, carbonate, andin places, actinolite.

Ultramafic cumulates in the Mount Keith–Perseverance and Agnew greenstone belts havepreviously been interpreted as dyke-like intrusions(Burt & Sheppy 1976, Groves & Keays 1979,Groves & Hudson 1981, Marston et al. 1981), assubvolcanic sill-like feeder chambers for overlyingspinifex-textured komatiites (Lesher & Groves1986, Naldrett & Turner 1977), or as extrusivecumulate bodies formed in lava lakes (Donaldsonet al. 1986). Hill et al. (1990) showed that theseadcumulate bodies have gradational contacts withthe overlying and/or underlying strata. It isconsidered that they accumulated in major flowchannels, formed by thermal erosion of underlyingrocks, during ultramafic eruptions (Hill et al. 1995).

A linear belt of talc-carbonate rock (Auc), 1.4km long and ranging from 100 to 200 m wide, islocated about 1 km south-southeast of MirandaWell. The rocks are yellow-brown and containsmall red-brown spots (<3 mm) of hydrated ironoxides after magnetite (or carbonate). South ofMiranda Well (AMG 661332), there is a low, rockyhill where the rocks above ground are stronglysilicified and massive, whereas the rocks close toground level are less silicified and have a strongfoliation. Carbonates are commonly leached out,leaving small holes filled with hydrated iron oxides.Talc–carbonate rock (Auc) is also mappednorthwest and south-southwest of Vivien Well.

Two units of chlorite schist (Aul) are mapped,one about 2 km northeast of Mount Keith and theother at the east edge of Dingo Range. The rock isgrey or green, less commonly brown or yellow,fine- to medium-grained, and consists largely ofchlorite with minor talc or quartz (Jagodzinski etal. 1999).

9


Tremolite–chlorite schist (Aur) crops out a fewkm south of Six Mile Well, 3 km north-northwestof Perseverance, 2 km west-southwest ofDesperation Well, east of Mount McClure, and westof Boundary Well. It is commonly green, acicularor fibrous, and composed of fine tremolite needles(<1mm, but up to 8 mm) and varying amounts ofchlorite, magnetite, talc and calcite. Like talc-schist(Aut), it represents zones of high strain through thegreenstones, and is highly schistose (Jagodzinskiet al. 1999).

Serpentinite (Aus) after dunite is present in

rotary air-blast (RAB) drillholes 1–6 km north-northwest of Mount Keith mine and boulders areexposed in a ditch at AMG 546862 (Jagodzinski etal. 1999). Serpentinite is also mapped about 2 kmsoutheast of Mount Grey Well and a few kmnorthwest of Dingo Range.

Several units of talc schist (Aut) are mapped,mostly in the area south-southeast of MountRoberts. Jagodzinski et al. (1999) described a unit4 km north-northwest of Six Mile Well. The rockis commonly yellowish green, pale green, or white,but in places grey, buff, or brown, fine-grained, and

16/G51/16

120°00'27°00'

27°30'

28°00'

28°30'

121°30'121°00'120°30'

0 40 km

Figure 4. Greyscale first vertical derivative of total magnetic intensity image of the SIR SAMUEL andnorthern part of the LEONORA 1:250 000 sheet areas

10

Liu et al.

composed largely of talc with lesser chlorite.

Metamorphosed mafic extrusive rocks(Ab, Abam, Abb, Abc, Abf, Abi, Abm, Abp,Abs)

Basaltic rocks are a major component of thegreenstones on SIR SAMUEL. They have beenmetamorphosed under greenschist to loweramphibolite facies conditions. They are mappedas undivided (Ab) where they are deeply weatheredand mostly fine-grained, and where they cannot beassigned to a specific category described below.

Metabasalt (Abb) is widespread in the

greenstone belts, e.g. it is well exposed south ofMount Sir Samuel, west of the Perseverance mine,in the Mount White area, and in the Stirling Peaksof the Dingo Range greenstone belt. In these areas,it generally occurs as thin flows associated with,and probably interbedded with, metasedimentaryrocks and/or gabbro. It commonly forms low hills.Most of the metabasalt designated as Abb is fine-grained to aphyric and massive, and probably hasa tholeiitic rather than a high–Mg composition(Naldrett & Turner 1977). The tholeiitic metabasaltthat crops out as thick, massive flows over a largearea, 3 km wide and 14 km long, east of Yakabindieis named the Mount Goode Basalt (AbMG, AbMGp,Liu et al. 1998).


Greenstone, undivided

Metasedimentary rocks

Metamorphosed felsic volcanic and/orvolcaniclastic rocks, undivided

Metamorphosed ultramafic rocks

Geological boundary

Fault

Granitoid interleaved withminor greenstone

Metadolerite/gabbro

Greenstone interleavedwith minor granitoid

Magnetic trend

Trend

D2 syncline/synform

D2 fold

D2 anticline/antiform

120°30'

27°30'

28°00'

Perseveran

ce

Fault

Six Mile Well

MT

KE

ITH

- PE

RS

EV

ER

AN

CE

GR

EE

NS

TO

NE

BE

LT

Meredith Well

Highw

ay

Fault

YA

KA

BIN

DIE

G

RE

EN

ST

ON

E

BE

LT

McDonough Lookout

Perseverance

Leinster

Fault

Vivien

Faul

t

Em

u

Em

uF

ault

16/G51/17

Fau

lt

Hal

fway

Granitoid, foliated

Yakabindie

Fault

Yakabindie

Miran

da

Fau

ltW

aroo

ng

aS

hear Zone

Fault

Samuel

Sir

Lawlers

Agnew

0 20 km

Fault

Six

Mile

AG

NE

W

GR

EE

NS

TO

NE

BE

LT



A)

11


Metabasalt with plagioclase phenocrysts is adistinctive local variant (Abp) and is commonlyreferred to as ‘cat rock’ where phenocrysts areabundant. The plagioclase phenocrysts are locallyup to 1.5 cm, and can constitute up to 15% of themetabasalt. This rock is commonly found in patcheswithin metabasalt, but rarely can be mapped as aseparate unit. On SIR SAMUEL it is only mappedabout 7 km east of Barwidgee. The most distinctiveoutcrop of metamorphosed porphyritic basalt formsthe southeastern part of the Mount Goode Basalt(AbMGp), and is discussed separately below.

Metamorphosed high–Mg basalt (Abm) ischaracterised by Mg-rich metamorphic mineralssuch as tremolite, secondary carbonate, and

variolitic, and/or pyroxene spinifex textures (Liuet al. 1998). The variolitic texture consists of palespheres, 2–10 mm in diameter, usually randomlydistributed throughout the rock. Weathering canaccentuate the texture, either preferentially erodingthe spheres to create small depressions or thespheres may resist erosion to form scattered lumpson the surface. The pyroxene spinifex textureconsists of randomly oriented needles, 5–15 mmlong, of tremolite that have replaced primarypyroxene. High–Mg basalt (Abm) is shown in theAgnew and Mount Keith–Perseverance greenstonebelts in the current map, although it was alsomapped in the DARLOT 1:100 000 sheet area byWyche & Westaway (1998). The largest units are

120°30'




Metamorphosed chert and/orbanded-iron-formation



Geological boundary

Fault


Metadolerite/gabbro


27°00'

27°30'16/G51/18

Trend

High-Mg metabasalt

Fault

Honeymoon Well

Cork TreeFlat Well

CharlieWell

Erawalla

Mt Keith

Mt Keith Ni

Perseveran

ceF

ault

Six Mile Well

0 20 km



Granitoid, foliated

Figure 5. A) Solid geology of the Six Mile Well – Lawlers area. Numbers refer to localities mentionedin the text: 1 – Lawlers Anticline, 2 – Mount White Syncline, 3 – Leinster Anticline; B) Solidgeology of the Honeymoon Well – Six Mile Well area

B)

12

Liu et al.

mapped south of Six Mile Well, east of YellowAster, and south of Mount Roberts.

Intermediate volcanic and high-level intrusiverocks (Abi) are only mapped as part of the Springgreenstone belt. They are associated with morefelsic rocks and range in composition from basalticandesite to andesite (Westaway & Wyche 1998,Messenger 2000). The rocks are generallyfine-grained, but locally porphyritic and glomero-porphyritic, with phenocrysts of plagioclase and/or clinopyroxene, in places up to 5 mm across.

Strongly carbonated mafic rock (Abc) is onlymapped in a group of low hills about 4 km north-northeast of Yandal Well, around AMG 201395, inthe southern Yandal greenstone belt (Westaway &Wyche 1998). The rocks are generally fine-grained,with pale-green metamorphic amphibole as themajor constituent and contain abundant calcite,both as porphyroblasts up to about 1 mm, and asvery fine-grained interstitial material. They arelocally amygdaloidal with small quartz- and calcite-filled amygdales up to about 1 cm.

Strongly foliated fine-grained mafic rocks aremapped as Abf, or Abs where a schistosity isdeveloped. The high degree of recrystallisationobscures evidence of the protolith for these rocks.Abf and Abs are most common in areas of shearing,such as the contacts with granitoids, and fault zones.Abf is mapped east of Mount McClure, west ofBoundary Well, around Woorana Soak, and westof Mount Harold. Abs is mapped west of the NewHolland gold mine in the SIR SAMUEL area.

Amphibolite (Abam) crops out close to, or incontact with, granitic rocks, e.g. west of MeredithWell and along the western margin of the Yandalgreenstone belt. Amphibolitic metabasalt ischaracterised by destruction of primary igneoustextures and by a strong penetrative foliation (andcommonly lineation). The foliation is commonlyweakly crenulated at granitoid margins. It is mostcommon at greenstone margins and in maficinclusions in the adjacent granitic rocks.Amphibolite is recrystallised, and slightly coarser-grained and darker than the metabasalt (Abb). Felsicporphyry dykes, which are usually strongly foliatedand quartz veined, commonly intrude amphiboliteclose to granitoid contacts (Jagodzinski et al. 1999).

Mount Goode Basalt (AbMG, AbMGp)

The Mount Goode Basalt was formally named byLiu et al. (1998) for the extensive suite of basaltnorth of Lake Miranda and west of the MirandaFault. Typical Mount Goode Basalt (AbMG) is

massive, fine-grained tholeiitic metabasalt andforms the lower part of the Basalt. The upper partof the Mount Goode Basalt (AbMGp) is commonlyporphyritic with plagioclase phenocrystscomprising up to 15%, and occasionally 30%, ofthe rock (Liu et al. 1998: fig. 6). Pillow lavastructures are preserved locally. Pillow basalt, withplagioclase phenocrysts up to 20 cm in diameter,is well exposed at the southeastern end of an islandin Lake Miranda (AMG 594376) about 3 km southof the Bellevue Gold Mine (Liu et al. 1998: figs 6–7).

Interleaved greenstone and granitoid (Abg)

Interleaved layers of moderately to steeply dipping,foliated greenstone and granitoid (Abg) formbanded units up to 1.5 km wide west of the northsector of the Mount McClure Fault, which marksthe west boundary of the southern Yandalgreenstone belt. Individual lenses of greenstone orgranitoid vary in width from less than 1 m to about50 m and form north-northwest-trending lownarrow ridges. This unit, as a whole, has adistinctive striped pattern on aerial photographs andsatellite and aeromagnetic images (Liu et al. 1998,Jagodzinski et al. 1999). It is also mapped north ofCharlie Well near the northern edge of the mapsheet in the Mount Keith–Perseverance greenstonebelt.

Most greenstones in the interleaved granite–greenstone Cocks–Satisfaction Zone attainedamphibolite facies metamorphic assemblages, incontrast to greenschist facies assemblages in theadjacent greenstone sequence to the east. Theamphibolite is fine-grained and displays a strongfoliation defined by alignment of elongate quartz,plagioclase, and hornblende grains. They locallydisplay thin gneissic banding formed bysegregation of mafic and felsic minerals (e.g. AMG910614, AMG 904632). Despite the highmetamorphic grade, some greenstones in theinterleaved zone retain their primary textures inplaces. All rock types in Abg, and especially thegranitoids, exhibit a strong sub-horizontal minerallineation trending 340º (Jagodzinski et al. 1999).In granitoid, the lineation is defined byrecrystallised quartz and aggregates ofrecrystallised biotite, commonly 1–2 mm wide andup to 4 cm long. West of Mount McClure, thislineation has a shallow plunge to the southeast.

The interleaved units designated as Abg westof the Gardiner Fault (Fig. 3) are interpreted fromimages aeromagnetic data.

13


Metamorphosed mafic intrusive rocks(Ao, Aod, Aog, AoKV, AoKVa, AoKVg,AoKVx)

Medium- to coarse-grained mafic rock with aknown or implied intrusive origin is a common rocktype and mapped in all greenstone belts in the SIR

SAMUEL area. Undivided metamorphosed maficintrusive rocks (Ao) crop out in the LawlersAnticline, Leinster Anticline, east of MountMcClure Fault and in the area between StirlingPeaks and Dingo Range. These gabbroic rocks arecommonly deeply weathered and the interpretationof an intrusive origin is based primarily on amedium to coarse grain size.

Fine- to medium-grained, mafic intrusive rocksare mapped as Aod, for example, north of CharlesWell, Mount Keith, in the Leinster Anticline, andnorth of Kens Bore. They commonly occur asconcordant layers in basalt (Jagodzinski et al.1999). They are massive and largely resistant todeformation. In high strain zones, the surroundingfiner grained basalts tend to be strongly foliated,whereas the dolerite is only weakly foliated. Therocks mapped as Aod are smaller in grain size thanthose mapped as Aog, although the distinction isnot well defined. Good exposures of Aod occur inhills 3 km north of the Agnew–Leinster roadbetween Vivien Well and Old Brilliant Well. Heremafic rocks with both ophitic and granular texturesare interlayered with metabasalt. Metadolerite alsocrops out as a small, north-northwest-trendingdyke, less than 3 m wide and 20 m long, thatintruded the Kathleen Valley Gabbro about 600 mnorth of an abandoned open pit (AMG 585529).Pyroxene is completely replaced by metamorphicamphibole but the rock retains an ophitic texture.Its strongly recrystallised nature suggests that it islate Archaean, rather than a Proterozoic dyke.Jagodzinski et al. (1999) consider that someintrusive dolerites can be distinguished fromextrusive dolerites (medium-grained interiors ofbasalt flows) by its slightly coarser grain, darkercolour, and occurrence as resistant ridges in thefield.

Metagabbro (Aog) occurs as medium- to coarse-grained mafic rocks within the greenstonesequences in the Agnew, Mount Keith–Perseverance and Yandal belts. They areparticularly well exposed in the Kathleen ValleyGabbro, where they are part of an extensive layeredmafic sequence. Where relationships can beobserved, they are generally concordant withsurrounding units, suggesting that they are sill-likebodies.

Other than in the Kathleen Valley Gabbro,Westaway & Wyche (1998) also note crystaldifferentiation for a metagabbro outcrop 3 km westof Paul Well (AMG 032414). This unit is about120 m thick and its composition varies, from westto east, from pyroxenitic gabbro at the base, througha series of thin units of leucogabbro, pyroxene-phyric gabbro and microgabbro up into coarse,quartz-bearing gabbro and microgabbro (Westaway& Wyche 1998). These authors also report gabbrobodies that show compositional and grainsizelayering south-southeast of Boundary Well (AMG073245) and north of Mica Mica Waterhole (AMG177209). Similar zoned gabbro bodies occur on thesoutheastern extension of the Dingo Rangegreenstone belt in the DUKETON area.

Metagabbros are mapped as part of folds in thearea south of Six Mile Well, Yandal Well and inthe Mount White Syncline. In the Mount WhiteSyncline they occur as sills between fine-grainedmetasediments and metabasalts. South of Six MileWell, a metagabbro (Aog) sill is part of folded maficand ultramafic rocks (Jagodzinski et al. 1999).

Kathleen Valley Gabbro (AoKV, AoKVa,AoKVg, AoKVx)

The Kathleen Valley Gabbro crops out in a lowhilly area in the area south of Jones Creek.Previously known as Kathleen Valley gabbro(Bunting & Williams 1979), and Kathleen ValleyGabbro and Granophyre (Cooper et al. 1978), theformal name ‘Kathleen Valley Gabbro’ was firstused in Gee et al. (1981). Kathleen Valley Gabbrowas also used in Liu et al. (1996, 1998), where itwas described in detail.

The Kathleen Valley Gabbro is a differentiatedlayered mafic intrusion consisting mainly ofgabbro, but ranging in composition to anorthositeand (amphibolitized) pyroxenite end members. Thesuite also includes tonalite and quartz gabbro. Therocks are metamorphosed to greenschist facies,with original clinopyroxene altered to blue-greenacicular to fibrous amphibole. Original igneoustextures and zoned plagioclase are preserved. Thegabbro forms a fault-bounded block in theYakabindie greenstone belt, and is in fault contactwith metabasalt, and locally with the Jones CreekConglomerate, to the east. It is overlain by theMount Goode Basalt.

Primary igneous layering in the Kathleen ValleyGabbro dips steeply northwest. The compositionallayering indicates that the gabbro youngs to thesoutheast, and is overturned. The strike of themetagabbros changes from northeast to north-

14

Liu et al.

northwest towards the Yakabindie shear zone tothe west.

Sinistral strike-slip movement along north-northwest-striking faults disrupts the intrusionaround Kathleen, forming fault blocks withsignificant displacement. Deformation within theintrusion is confined to narrow shear zones. Smaller

normal faults slightly offset compositional layeringwest of these larger shears in the main part of thegabbro sequences. Undeformed granitic pegmatitedykes trending dominantly northwest (parallel tothe shear zones and normal faults) intrude thegabbros and crosscut a north-trending foliationwithin them. The components of the intrusion aredescribed below, from stratigraphically lowest to

28°00'

27°30'

121°00'

16/G51/19

Beale Well

Lotus

Parmelia

Mt McClure

Kens Bore

Mt Joel

Mt Grey

Woorana Soak

YandalNinnis Well

Ockerburry Hill

Spring Well

Rosewood Well

Darlot

Ock

erb

urr

yF

ault

Zo

ne Rosew

ood

Fault

Nin

nis

Fault

Fau

lt

Mt G

rey

Fau

lt

Mt M

cClu

re

Lotus

Fault

Mt

McC

lure

Fau

lt

Perseverance

Fault

Fau

lt

Gar

din

er

Wes

tG

ard

iner

Fau

lt

HartwellWell

YandalWell

Bronzewing

Faul

t

Gar

dine

r

0 20 km

Figure 6. Solid geology of the southern Yandal greenstone belt. See Figure 7 for legend

15


highest.

The exposed lowest, and northernmost, unit ofthe Kathleen Valley Gabbro is a layered gabbro(AoKV), at least 1100 m thick, with 2–10 mcompositional rhythmic layering clearly visible onaerial photographs, and centimetre-scale layeringin hand specimen (Jagodzinski et al. 1999: fig. 4).The layering is due to varying proportions ofamphibole and plagioclase. Some anorthosite andpyroxenite layers are also present.

Overlying the layered gabbro unit (AoKV) is aunit, up to 1700 m thick, of metamorphosed,generally coarse-grained, anorthositic gabbro andanorthosite (AoKVa). Plagioclase varies from 60%to >95% in anorthosite (Jagodzinski et al. 1999:fig. 5), and occurs as both phenocryst andgroundmass phases. Plagioclase phenocrysts,

mostly less than 2 cm but up to 5–10 cm across,are commonly milky, and rounded to tabular(euhedral). Although generally pervasive, theytypically only constitute a few percent of the totalrock.

Some plagioclase-rich metagabbro has apoikilitic texture with euhedral plagioclase crystalswithin large (up to 15 cm) pyroxene (nowamphibole) oikocrysts (e.g. AMG 580557).Amphibole has pseudomorphed the originalpyroxene during metamorphism, occurring asreplacing single oikocryst or multiple crystals withthe same orientation.

Medium-grained metagabbro (AoKV), up to1500 m thick, overlies anorthositic metagabbro(AoKVa), west of a north-northwest-trending shearzone west of Kathleen. Three layers can be

27°00'

27°30'

121°30'

16/G51/20

Dingo

Range

Mt Harold

StirlingPeaks




Metamorphosed chert and/orbanded-iron-formation



D1 fold

Geological boundary

Fault


D2 syncline/synform


D3 syncline/synform

Granodiorite

Syenite

Tonalite

Quartz monzonite

Wadarrah Quartz Monzonite


Weebo Granodiorite

Metadolerite/gabbro

Magnetic trend


Granitoid, foliated

0 20 km


Figure 7. Solid geology of the southern Dingo Range greenstone belt

16

Liu et al.

recognised on aerial photographs in this unit, withthe central layer being slightly darker due to ahigher amphibole content.

Metamorphosed pyroxenitic gabbro (AoKVx)occurs in a layer about 100 m wide south of themedium-grained metagabbro unit (AoKV). It has asmooth pattern on aerial photographs. The rocksare dark, almost black, and fine- to medium-grained, with most grains ranging in size from 0.5to 2 mm. The rocks contain more than 80%amphibole (derived from pyroxene), 10%plagioclase and less than 3% quartz. In thin section,the amphibole is blue-green and is probablyactinolite or actinolitic hornblende.

Immediately south of the metamorphosedpyroxenitic gabbro (AoKVx) is a unit of quartzgabbro and tonalite (AoKVg) which constitutes oneof the uppermost units of the Kathleen ValleyGabbro (Liu et al. 1996). The metamorphosedquartz gabbro and tonalite are best exposed in a500 m wide zone 1 km north of an open pit east ofthe old Wiluna–Leinster road (AMG 583533). Atonalite sample from this unit has a SHRIMP U–Pb zircon age of 2736 ± 3 Ma (GA sample97965402, Black L.P., 2000, written comm.). Thisage is younger than an earlier publishedconventional U–Pb zircon age of 2795 ± 38 Ma byCooper & Dong (1983). Farther to the south thereis a 200 m wide zone of metamorphosed quartz-bearing gabbro, and a 100 m zone of coarse-grainedmetagabbro.

Metamorphosed felsic volcanic andvolcaniclastic rocks(Af, Afpf, Afs, Aft, Afv, Afx)

Metamorphosed felsic volcanic and volcaniclasticrocks are a common rock type in the Agnew, MountKeith–Perseverance, Yandal and Dingo Rangegreenstone belts. With exceptions in the SpringWell felsic volcanic complex, in which rocks aregenerally fresh and little deformed, most felsicvolcanic/volcaniclastic outcrops are foliated anddeeply weathered. It is thus often difficult todetermine the protolith. These outcrops generallycontain relict small euhedral or embayed quartzphenocrysts, which probably imply a volcanic orvolcaniclastic origin in many cases. Undividedfelsic volcanic and/or volcaniclastic rocks aremapped as Af. Porphyritic rocks are mapped as Afpf,e.g. in the Spring Well felsic volcanic complex.Where the foliation and recrystallisation in thesepoorly exposed felsic rocks is intense and aschistosity is developed, the outcrop is labelled Afs(felsic schist). It is commonly found along major

fault or shear zones, e.g. Mount McClure Fault,Ockerburry Fault Zone. The schistosity is definedby white mica, and oriented feldspar and quartz.Quartz–feldspar schist of uncertain protolith isdescribed below with the low-grade metamorphicrocks (Al section).

Felsic tuff (Aft) is a widespread rock type, butmost outcrops are small; only two units are largeenough to be shown in the current map, i.e. in thearea east of Yellow Aster (Liu et al. 1998). Theyare relatively fresh, massive, felsic lithic tuff. Theclasts are poorly sorted, dominated by crystal-richfelsic volcanic/volcaniclastic rocks, some of whichalso have fragmental texture (Liu et al. 1998: fig.9). Clasts of fine-grained mafic schist andmetasedimentary rocks are a minor component.

Rocks mapped as Afv (felsic volcanic and/orvolcaniclastic rocks) indicates that a volcanic andvolcaniclastic origin is clear. Rocks mapped in theundivided unit Af may include some weatheredsedimentary rocks, which are difficult to distinguishfrom felsic volcanic and volcaniclastic rocks. Afvunits are mapped southeast of Vivien Well in theAgnew greenstone belt, between Ninnis Well andYandal Well, and around Spring Well in the Yandalgreenstone belt. Descriptions of examples can befound in Westaway & Wyche (1998) and Liu et al.(1998).

Felsic volcanic breccia (Afx) is mapped in theSpring Well felsic volcanic complex, as well as oneunit southeast of Yandal Well. Felsic volcanicbreccias are generally poorly sorted and matrix-supported, with a range of volcanic clast types(Westaway & Wyche 1998: fig. 8). Outcropsgenerally show no internal stratification or bedding,although there is an overall grainsize reduction andlocally bedding that is consistent with a westwardyounging of the complex.

Spring Well felsic volcanic complex

The Spring Well felsic volcanic complex wasstudied in detail by Giles (1980, 1982). It consistsof felsic volcanic and volcaniclastic rocks and highlevel intrusive rocks, in the area up to 10 or morekm around Spring Well. Compositions vary fromrhyolite to basaltic andesite. Mapped units on SIR

SAMUEL include metamorphosed felsic volcanic/volcaniclastic rocks (Afv), rhyolitic and rhyodacitictuff and/or breccias (Afx), felsic porphyry (Afpf),and andesitic metabasalt (Abi). For more details,the reader is referred to Wyche and Westaway(1996), Giles (1980, 1982), Barley et al. (1998)and Messenger (2000).

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The rocks have some systematic variation inrelation to the distance away from the volcaniccentre (Giles 1980, 1982, Westaway & Wyche1998). Away from the volcanic centre, rocks havea more limited range of volcanic textures with finergrained pyroclastic and volcaniclastic sedimentaryrocks dominating. Westaway & Wyche (1998)consider that the lateral lithological andcompositional changes, high proportion ofpyroclastic rocks, and large volume of volcanicbreccias near the volcanic centre suggest that theSpring Well complex represent a continentalstratavolcano.

Barley et al. (1998) mapped four distinct faciesassociations. The lowermost association (Unit 1)is dominated by massive andesite and basalticandesite lavas and sills, with subordinate epiclasticsandstones and conglomerates. Unit 2 records thedeposition of proximal autoclastic and debris-flowbreccia associated with shallow subaqueous tosubaerial andesite to dacite lava flows, probably ina shoreline setting. Unit 3 comprises thick lobatedacite and rhyolite lava flows with associatedautobreccia, possible welded ignimbrite, andpolymictic conglomerates with fluvially reworkedclasts. This unit reflects a transition into distinctlymore felsic phase of volcanism, erosion, and fluvialdeposition. The uppermost unit (4) comprises thickandesite conglomerates and breccias. All units wereintruded by bifurcating microdioritic sills.

Facies associations vary markedly in thicknessalong strike (Barley et al. 1998). The coarseandesite breccia units thicken from 150m north ofSpring Well to more than 600m, south of SpringWell. Thick rhyolite and dacite lava flows andmonomict breccias pinch out over short distances(hundreds of metres or less) along strike, and eitherrepresent fault contacts or indicate that lava flowswere dome-like in geometry with associated thickaprons of autoclastic debris.

The Spring Well complex contrasts with otherintermediate calc-alkaline volcanic complexes inthe Eastern Goldfields (e.g. Edjudina, Melita,Teutonic Bore, and the Black Flag Group of theKalgoorlie area) in its high proportion ofvolcaniclastic breccias, conglomerates, andsandstones (Barley et al. 1998). The inferred originfor these volcaniclastic facies ranges fromautoclastic and fluvial for the coarse andesite anddacite breccias, to alluvial fan or debris-flowdeposits with fluvially derived material for theconglomerates.

A SHRIMP U–Pb zircon age of 2690 ± 6 Mahas been obtained on a sample of crystal-rich

porphyritic rhyolite from about 1 km southwest ofSpring Well (AMG 183124, GSWA sample118953; Nelson 1997a). The rhyolite is interpretedas a rheomorphic ignimbrite, and the age, therefore,represents that of explosive rhyolite volcanism atthe Spring Well complex (Barley et al. 1998).

Metasedimentary rocks(As, Asc, Ascf, Ascq, Ash, Ashd, AsJC,AsJCa, AsJCb, Asq, Ass, Ac, Aci, Acis)

Metasedimentary rocks are a minor but widespreadrock type on SIR SAMUEL. They are mapped in allbut the Yakabindie greenstone belt and areparticularly common in the Mount Keith–Perseverance and Agnew greenstone belts. Mostrocks are poorly exposed and deeply weathered.Undivided units are mapped as As, and occurmostly in the McDonough Lookout to Perseverancearea and in the Mount White Syncline. Fine-grainedmetasedimentary rocks, mostly phyllite, aremapped as Ash. Many, particularly the finer grainedvarieties, have a well-developed foliation and someoutcrops are silicified. The protolith for most ofthese rocks is assumed to be fine-grained sandstone,siltstone, and mudstone, but may include felsicvolcanic rocks, particularly in finely interbeddedsequences. Although not well exposed, forexample, metasedimentary rocks are mapped in theMount White Syncline based on clear trend patternson aerial photographs. These rocks and gabbroicunits define the macroscopic fold.

Metamorphosed pelitic, shaly, or phylliticsedimentary rocks (Ash) occur mainly as thin bedswithin metamorphosed mafic, ultramafic and felsicvolcanic rocks. The fine-grained metasedimentaryrocks, where well exposed, can provide evidenceof multiple deformation, e.g. 3 km north-northeastof McDonough Lookout at AMG 647450, as thepelitic rocks contain an early cleavage that has beencrenulated. They include minor quartz-mica schistand locally contain andalusite and cordieriteporphyroblasts. One unit of phyllite with abundantandalusite porphyroblasts (Ashd) occurs as a north-northwest-trending unit about 3.5 km northeast ofMount Goode. The best exposures can be seen in asmall creek at AMG 628503 where the rockscontain scattered andalusite porphyroblasts (1–3mm) constituting 15–20% of the rock.

Metamorphosed sandstones (Ass) are mostlymapped between Letter Box Well and Cork TreeFlat Well east of the Erawalla Fault near the northedge of map sheet. Another unit is mapped in thearea north of McDonough Lookout. One quartziteunit crops out about 2 km northeast of Mount Keith

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Liu et al.

as a discontinuous ridge 2 km long (Jagodzinski etal. 1999). The rock is blue-grey, fine-grained,recrystallised, foliated and lineated.

Conglomerate occurs in several parts on SIR

SAMUEL, with the most prominent being the JonesCreek Conglomerate (AsJC, AsJCa, AsJCb) andits equivalent, Scotty Creek conglomerate. One unitof undivided conglomerate (Asc) was mappedabout 3 km north-northeast of Yellow Aster.

Oligmictic conglomeratic (Ascf) of dominantlyfelsic volcanic clasts is mapped 4 km south ofNinnis Well (Westaway & Wyche 1998). It isassociated with felsic volcaniclastic rocks, is poorlysorted and made up of mostly felsic volcanic clasts,some of which are vesicular, in a quartzofeldspathicmatrix. The size of the clasts increases towards theeastern side of the outcrop, with some up to 15 cmin diameter. The conglomerate is deformed, withflattened clasts aligned with the regional foliation.

Pebbly cherty conglomerate with dominantlyquartz or chert clasts (Ascq) occurs in the northeastof Mount Harold in the Dingo Range greenstonebelt (AMG 476693, Fig. 8). Clasts vary from 1 mmto 3 cm in width and 5 mm to 20 cm in length andare mostly chert or banded chert. They are similarto rock types forming the ridges nearby, which areconsidered to be source rocks for the pebblyconglomerate. All clasts are strongly deformed.Length/width ratios vary from 3 to 7 and commonlygreater than 5. S2 foliation as defined by theflattening of pebbles was measured as 331º/68ºSW.Long axes of pebbles plunges 52º towards 297º,which is considered to be sub-parallel to the axisof the macroscopic antiform at Mount Harold.

Metamorphosed fine-grained, siliceous and/orferruginous metasedimentary rocks (Ac, Aci, Acis)are mapped in many locations, particularly in theMcDonough Lookout–Yellow Aster area, east andnortheast of Mount Keith, north of Charles Well,Dingo Range, Mount Harold, and east of StirlingPeaks.

Metamorphosed siliceous metasedimentaryrocks (Ac) are prominent in the area betweenMcDonough Lookout and the Perseverance nickelmine, and in the Yandal greenstone belt along theeastern margin of the sheet area where they arewell exposed as discontinuous ridges that runparallel to the north-northwest regional trend. Therocks are fine to very fine-grained and quartz-rich,with most quartz recrystallised duringmetamorphism. They are typically grey-and-whitebanded, locally pyritic and, at the surface, locallyvery ferruginous. These rocks are often referred to

as ‘chert’, but a chemical sedimentary origin is notalways clear. In the Mount Harold area, chertdefines the macroscopic fold.

Banded iron-formation (BIF) (Aci), thatweathers to prominent, narrow, ironstone ridges,crops out northeast of Charlie Well, east of MountKeith, and between the Rocky’s Reward and thePerseverance open pits. Metamorphosed fine-grained siliceous and iron-rich sedimentary rocksare rarely more than a few metres thick, are highlymagnetised, and are commonly associated withshale and quartz-mica schist. They can be goodmarker horizons preserving complex foldstructures.

Jones Creek Conglomerate (AsJC, AsJCa,AsJCb) AsJCb)

Metamorphosed conglomerate, the Jones CreekConglomerate (Durney 1972), is a significantcomponent of the Six Mile Well–Lawlers area (Figs3, 5). Metamorphosed conglomerates 3–4 km west-northwest of Vivien have been informally calledthe Scotty Creek conglomerate, but are consideredto be part of the same formation as that in the JonesCreek area. Much of the Jones Creek Conglomerateis a conglomerate with granitic clasts and matrix(AsJC) with interbedded arkose (AsJCa). In the eastpart of the unit there is conglomerate with maficmatrix (AsJCb). Durney (1972), Marston & Travis(1976), Liu (1997), Liu et al. (1998) andJagodzinski et al. (1999) give detailed descriptionsof the conglomerates.

Conglomerate with granitic matrix (AsJC)and arkose (AsJCa)

A 1000 m thick cross section of the unit crops outwest of Jones Creek. Here the conglomerateunconformably overlies monzogranite to the west(Liu 1997: fig. 24). The sandstone beds are thinnerover the granite ridge, suggesting a sedimentarycontact between the granitoid and the sandstones.North of the granite ridge at this outcrop, a foliation(cleavage) cuts through the boundary between thesandstone and the granitoid. The unconformity,graded beds and cross-beds in arkose to the east ofthe contact, consistently indicates younging to theeast. South of Jones Creek, however, theunconformity is deformed, sheared or faulted.

Towards the base of the conglomeratic sequencein the area north of the Jones Creek, there are threechannel-like embayments in the underlyingmonzogranite. Clasts are large, up to 3 m across,angular, and tightly packed. The very immaturenature of most of the clasts within the lower part

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of the conglomerate indicates that they were locallyderived. Below the conglomerate there is atransitional zone of fragmented monzogranitepassing through to unbroken monzogranite. It isthus difficult to precisely locate the unconformityin most cases. Away from the contact, theconglomerate is better sorted, with predominantlywell-rounded, 8–20 cm cobbles of mainly massivemedium- to coarse-grained monzogranite (AsJC),although the granitoid clasts range from 1 cm to 1m in some beds (Jagodzinski et al. 1999). A minoramount of other clast types, e.g. foliated granitoid,felsic porphyry, and rare mafic rocks, are alsopresent, particularly in places away from theunconformity. Metamorphosed arkose (AsJCa) isinterbedded with the conglomerate. Themeta-arkose and matrix of the conglomerate consistof quartz, plagioclase, microcline, biotite, andmuscovite. They have been recrystallised andcontain a fabric defined by the preferred alignmentof mica, quartz, and feldspars (Marston & Travis1976, Nelson 1997a). In the conglomerate,boundaries between clasts and matrix are generallysharp, but locally gradational due to partialrecrystallisation (Jagodzinski et al. 1999).

Felsic conglomerate is also well exposed alongthe SIR SAMUEL–MOUNT KEITH 1:100 000map sheet boundary. In the area west andimmediately east of the old road to Wiluna, theconglomerate contains clasts of dominantlymedium- to coarse-grained massive granitoid rock,

with subordinate felsic porphyry and mafic rock.Clasts range in size up to 40 cm, but most aresmaller than 20 cm. They are rounded to sub-rounded and closely packed. The conglomerate hasbeen partially recrystallised and boundariesbetween clasts and matrix are generally sharp, butlocally gradational. A few fractures less than 1 cmwide in massive outcrop are the only evidence ofdeformation within the conglomerate, but contactswith the adjacent rock units are strongly sheared.Arkosic beds within the formation, about 300 meast of the old road to Wiluna around AMG 597558in the north, strike north-northwest and dip steeplyto the west.

Unlike the felsic conglomerate described above,clasts in conglomerate in drill core from 2 km southof Yellow Aster are mostly felsic porphyry withonly minor granitoid, mafic and sedimentary rock.Some of these conglomerates contain gold.

Conglomerate with mafic matrix (AsJCb)

The mafic conglomerate component comprisesrounded felsic clasts in a mafic matrix, which isoften strongly deformed in the form of chlorite-rich schist (Durney 1972, Jagodzinski et al. 1997,Liu et al. 1996). Conglomerate with mafic matrix(AsJCb) is mapped from west of Six Mile Well tosoutheast of Kathleen over a distance of more than10 km. It is also mapped in the Scotty Creekconglomerate in the Agnew area. They occur in

Figure 8. Photograph of deformed chert-pebble conglomerate, 1 km northeast of Mount Harold (AMG476693, hammer is 26 cm in length)

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Liu et al.

close proximity to greenstones in the east, i.e. theMt Keith–Perseverance greenstone belt in the northand the Agnew greenstone belt in the south, andthe greenstones possibly sourced the mafic matrix.

Compared with conglomerate with graniticmatrix, clasts in the conglomerate with maficmatrix are more variable, ranging frommedium-grained granitoid, granitic porphyry,aplite, and vein quartz. Thus, these conglomeratesare polymictic. In contrast to the relativelyundeformed felsic conglomerate, the matrix of themafic conglomerate typically is strongly foliatedparallel to the regional north-northwest trend(Jagodzinski et al. 1999). The best exposure ofconglomerate with mafic matrix are found along acreek at AMG 596636 (GA site 97965429). Thematrix is largely chlorite schist with a significantcomponent of quartz and perhaps altered feldspar.An S2 cleavage is well developed in the maficmatrix. Thin layers of sandy quartz-feldspar matrixare also present, but they have been boudinagedduring strong compressional deformation.

The mafic-matrix conglomerate becomes moredominant farther south, i.e. in the area east andsouth-southeast of Yellow Aster where a larger areaof conglomerate with mafic matrix is mapped.Exposures extend for about 5 km. The aerialphotograph pattern for these rocks is similar to thatof areas of metabasalt. However, the maficconglomerate does not outcrop as well as the felsicconglomerate but forms low, rubble-covered hillswhere granitoid clasts (mostly pebbles andboulders) stand out due to differential weatheringor occur as rounded to semi-rounded float.

Depositional environment

Durney (1972), Marston & Travis (1976) andBunting & Williams (1979) discussed thedepositional environment of the Jones CreekConglomerate. The nature of the poorly sortedangular clasts and transitional zone of fragmentedmonzogranite in the unconformity embaymentssuggest a local source for the conglomerate froman eroding upland area comprising themonzogranite in the west. Thus Durney (1972)interpreted the basal conglomerate as valley-filltalus. Away from the unconformity, the well-rounded, closely packed clasts in the conglomerateindicate a high-energy environment (Jagodzinskiet al. 1999). Bunting & Williams (1979) suggestedthe conglomerate sourced a rapidly eroding uplandarea. The erosion materials were transported overa very short distance via talus slopes and smallalluvial fans to a high-energy shoreline of a rapidlysubsiding, fault bounded, elongate trough. The

more distal conglomerate probably representedriver and beach gravel (Jagodzinski et al. 1999).

Age of the Conglomerate

A sandstone sample (GSWA sample 118937) of theJones Creek Conglomerate sequence at AMG590620 was analysed by SHRIMP U–Pb zircondating in 1996 and 1999 (Nelson 1997a & 2000).Nelson (2000) interpreted a 2667 ± 6 Ma age asthe maximum depositional age of the sandstone.This interpretation is consistent with the age of2665 ± 5 Ma for the conglomerate reported byKrapez et al. (2000), and with the geologicalcontext of the area.

Hydraulic breccia

In the felsic component of the Jones CreekConglomerate, hydraulic breccias are present in alow and flat outcrop at AMG 592563 (GA site97965023), about 3 km north-northwest of YellowAster, and in diamond drillcore from about 1.2 kmsouth-southeast of Yellow Aster (AMG 601529).

At AMG 592563 there are fragmentedmedium-grained granitic rocks. The clasts areessentially of granitic composition, in aquartzofeldspathic matrix with some biotite. Thejigsaw-fit fractures shown in Figure 9 are diagnosticof hydraulic breccia. The planar fracturing in thewest part of outcrop is also typical of hydraulicbreccia. Some of the biotite in the quartzo-feldspathic matrix may be of hydrothermal origin.

Hydraulic breccia also occurs in diamonddrillcore from about 1.2 km south-southeast ofYellow Aster (AMG 601529). At this locality, theclasts are predominantly porphyritic granitoid withsome fine-grained sedimentary and basaltic rocks.The matrix is biotite rich and of possiblehydrothermal origin. A hydraulic fracturing originfor the breccias has been suggested (Pirajno F.,1995, pers. comm.). The drillhole also intersectedgold mineralisation. The host rocks, including theapparent hydraulic breccias, were mapped as partof the Jones Creek Conglomerate (Bunting &Williams 1977, Liu et al. 1996). It is not clearwhether the hydraulic fracturing occurred beforeor after the sedimentation although a likely timingis that the hydraulic fracturing post-dated thesedimentation.

Low- to medium-grade metamorphic rocks(Ala, Alb, Ald, Alf, Alfq, All, Alm, Alqm)

Where the protolith of some low- to medium-grademetamorphic rocks cannot be recognised due to

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the high degree of deformation and recrystallis-ation, the prefix Al is used with a suffix indicatingthe characteristic mineralogy. Many of these rocksare identified from rock chips obtained fromshallow drilling. Where the rocks are almost whollyclay, and either massive or schistose, they aremapped as Alb. Quartz is absent or minor. Five outof the six Alb units were mapped in theWANGGANNOO area, including northeast ofBronzewing gold mine, southeast of Mount Greyand east of the massive basalt (Abb) unit at StirlingPeaks.

Amphibolite of probable metasedimentaryorigin (Ala) is mapped east of Mount McClure,north of Beale Well, and northwest of Ninnis Well.The north-trending unit east of Mount McClure wasdescribed in Liu et al. (1998). It is a layeredplagioclase–hornblende–clinopyroxene–quartz-rich rock. This unit is markedly more leucocraticthan the deformed mafic rocks that bound it to theeast and west. It shows a pronounced layering,streaky or discontinuous, which is defined by bothvariations in composition and grain size. It has beenextensively recrystallised and is mainly fine- tovery fine-grained with thin (up to 5 mm wide)coarser layers containing various combinations ofplagioclase, quartz, amphibole and clinopyroxene.Jagodzinski et al. (1999) reported quartz-richamphibolite (Ala) that forms three outcropsnorthwest and north of Beale Well.

Figure 9. Photograph showing jigsaw fit of clasts in a granitic hydraulic breccia, 3 km north-northeastof Yellow Aster (AMG 592563, pencil is 14 cm in length)

About 2.5 km north of Mount Goode, at AMG599503, pelitic schist (Ald), which is associatedwith quartzofeldspathic schist, contains alteredandalusite and cordierite porphyroblasts (Liu et al.1998: fig. 11). Pale blue andalusite porphyroblastsare mostly a few millimetres wide, up to 1–2 cmlong, and randomly oriented. Cordieriteporphyroblasts appear as round brown patches ofalteration products 1–2 cm in diameter.

Quartz–feldspar schist (Alf) occurs at severalplaces in the Mount Keith–Six Mile Well area inthe Mount Keith greenstone belt, and aroundWoorana Soak in the Yandal greenstone belt. Inoutcrop, the schist is heavily weathered to a yellow,fine- to very fine-grained quartz–clay rock withrelict schistosity. Fresh rock in a RAB drillhole atAMG 578782 consists of small phenocrysts ofsaussuritized plagioclase and broken and partlyrecrystallised quartz in a very fine-grainedgroundmass of chlorite, quartz, plagioclase,epidote, and muscovite. The rock is a deformedand metamorphosed dacitic or tonalitic porphyry;the considerable extent of the exposures suggeststhat the precursor was a felsic volcanic.

Heavily weathered quartz–feldspar schist in theform of schistose clay rock with clear quartz eyesis mapped as Alfq east of the north sector of theMount McClure Fault. Two such units are near thegranite–greenstone contact south-southwest of

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Mount McClure mining centre and one is north ofBeale Well. The quartz eyes are interpreted as relictquartz phenocrysts, consistent with a felsic volcanicorigin.

It should be noted that the unit terms Alf andAlfq were not used in the GSWA’s 1:100 000geological maps (DARLOT, SIR SAMUEL andDEPOT SPRINGS), in which rocks with thedefinitions of Alf and Alfq were probably mappedas felsic schist (Afs). No attempt was made torationalise these rock units in the compilation ofthe SIR SAMUEL 1:250 000 geology map.

Chlorite schist (All) occurs west of Vivien Wellnear the southern map boundary in the Agnewgreenstone belt and identified from drill holessouth-southeast of Mount White. Muscovite schist(Alm) occurs in the Mount Keith – Six Mile Wellarea of the Mount Keith greenstone belt and westof Woorana Soak in the Yandal greenstone belt.Quartz–muscovite schist (Alqm) occurs south ofMount Keith and 5 km west-northwest of VivienWell. It has also been identified from drill holes inmetasedimentary rocks south-southeast of MountWhite.

Granitoids(Ag, Agb, Agc, Agd, Agdq, Age, Agf, Agfo,Agg, Agm, Agmp, Agn, Agp, Ags, Agt, Agu,AgWA, AgWE, AgWEf)

Archaean granitic rocks, mostly biotitemonzogranite, dominate the granite–greenstonegeology on SIR SAMUEL, but are in general eitherpoorly exposed or strongly kaolinised. Outcropsare mostly limited to low-lying, variably weatheredpatches in areas of granitoid-derived sand tovariably kaolinised outcrops in breakaway countrybelow eroded silcrete duricrust surfaces, and toisolated, relatively fresh, pavements and tors.Significant areas of excellent outcrop do occur,however, including the majority of the Barr SmithRange, and the area around Mt Blackburn.

Undivided and/or unassigned granitic rocks(Ag) commonly comprise deeply weathered, mostlykaolinised and locally silicified, granitoid, typicallyassociated with breakaways, but also includeregions of poor exposure and some unvisitedoutcrops. On GA’s 1:100 000 maps, i.e.YEELIRRIE, MOUNT KEITH, WANGGANNOO,areas of outcrop of strongly kaolinised graniticrocks of indeterminate lithology have beensubdivided on the basis of dominant grainsize ortexture, using both quartz grains and relict textures,into either fine- (Agf), medium- (Age), coarse-

grained (Agc), mixed fine- to coarse-grained (Agu),or porphyritic (Agp) varieties.

Other, non-lithological classifications ofgranitoids (for strongly weathered to fresh outcrop)are based on structural characteristics, in particularthe degree of structural and metamorphic overprintof mostly granitoid precursors. These structuralunits are largely confined to DEPOT SPRINGS andSIR SAMUEL. They include undivided foliatedgranitoids (Agfo; only used on GSWA’s 1:100 000maps), strongly foliated granitoids with locallydeveloped gneissic textures or incipient banding(Agn), strongly foliated and locally gneissicgranitoids with interleaved greenstone rocks (Agb),and areas of banded gneiss and/or gneissic granitoid(An). Banding developed in these rocks, indicatedby variations in grains size, phenocryst content,and/or mineral content, reflect original lithologicalvariation (e.g. granitoid dykes, enclaves,pegmatites, aplites, igneous layering and schlieren)and, in areas of higher grade and/or strain,metamorphic & structural effects (e.g. metamorphicsegregation).

The foliated to gneissic granitic units typicallyoccur along the margins of granitoid masses. Oneexample is the large arcuate north-south zone (7–15 km wide), of strongly deformed granitoid, westof the Waroonga Shear Zone in the southwesternpart of SIR SAMUEL, clearly visible on aeromagneticimages. Although mostly poorly exposed, relativelygood outcrop occurs in the region west of the NewHolland openpit, comprising strongly deformedgneissic and/or foliated granodiorite and granite,which contain thin discontinuous zones ofamphibolite (either remnant mafic dykes orgreenstone rocks), and both concordant anddiscordant granitoid dykes and pegmatites. Anotherexample includes the strongly foliated andgreenstone-intercalated zones (Agb) that occuralong both the eastern and western margins of thegranitoid mass separating the Agnew–Wiluna andYandal greenstone belts, described in detail by Liuet al. (1998). Here, foliated and/or lineatedgreenstone, mostly of amphibolite-facies, occursas lenses within strongly deformed granitoid. Asample of gneissic granitoid from one such outcropwest of the Parmelia openpit has a SHRIMP U–Pbzircon age of 2738 ± 6 Ma (Nelson 1998). This isone of the oldest recorded granitoid ages found inthe Eastern Goldfields Province. Availablegeochemistry (Geoscience Australia, unpublisheddata) suggests that the dated sample is part of theHigh–HFSE group of Champion & Sheraton(1997). Granitoids of this group have a strongspatial relationship with contemporaneous (and in

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part co-genetic) felsic volcanic rocks, raising thepossibility of volcanics (and, hence, greenstone)of similar age in the region. Interestingly, Nelson(1997a) reports an age of 2720 ± 14 from adeformed felsic volcanic rock from the Rocky’sReward nickel mine, which although younger iswithin experimental error of the age for the gneissnear the Parmelia openpit. Similarly, a tonaliticphase of the Kathleen Valley Gabbro has aSHRIMP U–Pb zircon age of 2736 ± 3 Ma (BlackL.P., 2000, written comm.), all suggesting thepresence of older greenstone (to 2750 Ma) withinthe region.

The dominant lithology on SIR SAMUEL ismonzogranite (Agm). These are typicallyundeformed to variably foliated and/or lineated,biotite-bearing (<5–10%) granitoids, which,locally, may have minor amphibole (up to a fewpercent). Minor muscovite and accessory fluoritemay also be present, e.g. at Mt Blackburn – thelatter relatively common in the Low–Ca groupgranitoids (see below). Textures vary fromequigranular to porphyritic, and include adistinctive moderately to strongly K-feldsparporphyritic (Agmp) variety, best seen in the BarrSmith Range area. Grainsize varies from fine- tocoarse-grained, with many of the monzogranitescomprising larger medium-coarse grained unitscontaining sparse to locally common pods anddykes of variably porphyritic fine and fine-mediummonzogranite. Good examples of theserelationships can be seen in the Hannans Boreregion (south-central MOUNT KEITH area), andin many of the outcrops in the south-central part ofthe DEPOT SPRINGS 1:100 000 sheet. Anotherfeature of these granitoids (and many of the lessdeformed granitoids in the Eastern Goldfields), bestseen in the excellent outcrop of the Barr SmithRange, are the manifestations of igneous flowlayering. These include good phenocryst alignment,cryptic banding (defined by changes in grain sizeand biotite-content), and the presence of biotiteschlieren. The latter comprise typically elongate(to several metres) but thin (<5 cm) wispy layerslargely of biotite and accessory phases. They mayoccur sparsely throughout a unit or be locallyconcentrated. Their origins are equivocal; they mayrepresent either disrupted (strung-out) enclaves, orsome forms of cumulate.

SHRIMP U–Pb zircon ages for monzograniteunits include 2685 ± 7 for the High–Ca granitoid(Agmp) west of Jones Creek Conglomerate (westof Six Mile Well) (Nelson 1997a), and a ca. 2652Ma age (Black L.P., 2000, written comm.) for theLow–Ca granitoid (Agmp) 2.5 km southeast of

Hannans Bore.

Less common, more mafic granitic units in theSIR SAMUEL area include hornblende–biotite andbiotite granodiorite (to monzogranite) (Agg) andbiotite tonalite (Agt), the majority intrusive intogreenstones. These units include the stronglyweathered granodiorite body, readily visible onaeromagnetic images, in the Kens Bore region(Agg; description in Nelson 1997a), the biotitegranodiorite (shown on the map as Ag) 5 km westof the Kens Bore body, and the biotite tonalite (Agt)10 km north-east of the Kens Bore body. The firsttwo have similar SHRIMP U–Pb zircon ages of2669 ± 6 (Nelson 1997a) and ca. 2666 Ma (BlackL.P., 2000, written comm.). The WeeboGranodiorite, comprising a coarse-grained titanite–biotite–hornblende granodiorite phase (AgWE), anda fine-grained marginal variant of similarmineralogy (AgWEf), both described in detail byWestaway & Wyche (1998), also intrudesgreenstones of the Yandal belt but has a slightlyyounger SHRIMP U–Pb zircon age of 2658 ± 7Ma (Nelson 1997a). Granodiorite marginal togreenstones or intrusive into other granitoidsincludes the titanite–hornblende–biotitegranodiorite (Agg), east of Melrose Homestead(Westaway & Wyche 1998), with a SHRIMP U–Pb zircon age of 2666 ± 6 Ma (Nelson 1997a), andthe strongly foliated to banded titanite–hornblende–biotite granodiorite (Agg) occurring in the westernpart of the Barr Smith Range.

Alkaline granitoids on SIR SAMUEL, includetitanite–hornblende–pyroxene and titanite–pyroxene syenite to quartz syenite (Ags), whichoutcrop in the Woorana Soak and Red Hill regions,on WANGGANNOO (Johnson 1991, Lyons et al.1996, Smithies & Champion 1999), and theWadarrah Quartz Monzonite (AgWA) – a titanite–biotite–hornblende quartz monzonite on DARLOT(Johnson 1991, Westaway & Wyche 1998). Boththe syenitic rocks and the quartz monzonite exhibitsome textural variation, a common feature ofsyenitic rocks in the Eastern Goldfields (Johnson1991, Smithies & Champion 1999). Variationsinclude the amount and type of phenocrysts,different mineral proportions, especially amountof feldspar, and grainsize variations. Goodexamples include outcrops of the Woorana Soakbody (e.g. AMG 228593, east of thetelecommunications tower) and in the Red Hillbody. Similarly, Johnson (1991), who mapped theoutcrops of the Red Hill body in great detail,describes multiple units of pyroxene syenite,syenodiorite, quartz syenite, and alkali granite. TheWoorana Soak body and the Wadarrah Quartz

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Liu et al.

Monzonite have similar SHRIMP U–Pb zircon agesof 2644 ± 13 and 2643 ± 6 Ma, respectively (Nelson1997a). Westaway & Wyche (1998) also report asmall clinopyroxene quartz monzonite outcrop onDARLOT (AMG 368450, not shown on the map).

Other small outcrops include diorite tomonzodiorite (Agd), porphyritic microdiorite(AMG 401081, not shown on map), both onDARLOT, and a number of quartz monzodioriteto quartz diorite (Agdq) outcrops around and southof Yellow Aster on SIR SAMUEL 1:100 000(mostly not shown on the map).

Classification

Champion & Sheraton (1997) subdivided thegranitoids in the northern Eastern GoldfieldsProvince, on the basis of petrography andgeochemistry, into 5 groups, namely, High–Ca(>60% by area of total granitoids), Low–Ca (>20–25%), Mafic (<5–10%), High–HFSE (<5–10%),and Syenitic groups (<5%). Geochemical andpetrographic features of each group are listed inTable 1. This scheme ignores previous structuralclassifications, in particular the use of pre- and post-folding terminology (e.g. Bettenay 1977,

Champion & Sheraton 1993, Witt & Davy 1997)that has been demonstrated by subsequentgeochronology to have many inconsistencies(Champion 1997), largely reflecting the inherentdifficulties in interpreting structural histories ofgranitoids in poorly outcropping terranes.

High–Ca group granitoids on SIR SAMUEL aremostly (hornblende–) biotite monzogranite andlesser hornblende–biotite granodiorite. Theyinclude the majority of the granitoids immediatelywest of the Agnew–Wiluna greenstone belt,including the belt of strongly foliated granitoidsthat extend north from west of the Genesis and NewHolland gold deposits (Agb, Agfo), the stronglylineated granitoids in the Nuendah area (Agmp),and less deformed to undeformed granitoids alongthe Barr Smith range (Agmp, Agg). Other High–Ca granitoids include around Mt Pasco (Agf), eastof Melrose homestead (Agg, Agm), and east andnortheast of Wonganoo homestead (Agmp, Agg).

Low–Ca group granitoids are relativelyabundant on SIR SAMUEL, occupying the westernhalf of the YEELIRRIE 1:100 000 sheet, most ofthe central region of granitoid between the Agnew–Wiluna and Yandal greenstone belts, the majority

Group Lithologies Fabric & textures Characteristic features Age (Ga) Examples

High–Ca biotite ± minor gneissic (locally sodic compositions (i.e. high mostly granitoid along Barramphibole, titanite; migmatitic); foliated Na

2O); low to moderate 2.72–2.655 Smith Range; strongly

granodiorite, and/or lineated to radiometric response; foliated granitoidstrondhjemite & non-foliated; strongly common irregularly-zoned west of the Genesismonzogranite feldspar-phyric to plagioclase in thin section and New Holland gold

equigranular deposits

High– biotite ± amphibole, foliated to non-foliated; mostly high silica (74–77 wt% 2.685–2.66 Weebo granodiorite;HFSE pyroxene, titanite; rare gneiss; feldspar- SiO

2); often amphibole- (and/or west of the Mt Joel

monzogranite & phyric to seriate pyroxene-) bearing despite silica- and Greenstone Hillsyenogranite, rich compositions; often spatially areasminor granodiorite associated with felsic volcanics

Mafic amphibole, biotite foliated to non-foliated; mafic compositions (<60–70 wt% mostly granodiorite at Kens± pyroxene; amphibole-feldspar- SiO

2); common to abundant 2.69–2.66 Bore, and south of

diorite, tonalite, phyric to equigranular amphibole (5–20%) with pyroxene Anxiety Boretrondhjemite, and/or biotite; common well-granodiorite zoned plagioclase in thin section

Low–Ca biotite, ± allanite, non-foliated to locally potassic compositions (high K2O, mostly granitoids in the Mt

titanite, fluorite, strongly foliated and/or K2O/Na

2O), with high Rb, La, Ce, 2.655–2.63 Blackburn region;

muscovite; lineated; feldspar- Zr; high radiometric response; granitoid nearmonzogranite, phyric to equigranular common accessory fluorite, titanite Leinster; stronglyminor granodiorite, and allanite, best seen in thin section; foliated granitoid atsyenogranite general lack of zoning in plagioclase. Ryans Well

Syenite titanite, amphibole, foliated to non-foliated; common to abundant pink to grey mostly Wadarrah Quartzgreen pyroxene; locally gneissic; K-feldspar, common green pyroxene 2.655–2.64 Monzonite; quartzsyenite, alkali feldspar ± and/or hornblende, minor quartz syenite at Red Hill, andquartz syenite, amphibole-phyric to (<10–15%) near Woorana Soakquartz monzonite equigranular

Table 1. Summary of geological, petrographic and age data for granitoid groups of the northernEastern Goldfields Province. Modified from Champion (1997)

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of granitoids between Mt Blackburn and west ofWonganoo homestead, and the granitoid nearLeinster. Most units are biotite monzogranite andlesser biotite (± fluorite) syenogranite. Low–Cagranitoids are mostly non-foliated, but do includesome strongly foliated members (e.g. themonzogranite at Ryans Well in the Yandalgreenstone belt).

Members of the High–HFSE group within thenorthern Eastern Goldfields Province arecommonly found associated with felsic volcanicrocks of similar geochemistry (Champion 1997).This is also the case for the Weebo Granodiorite(Westaway & Wyche 1998), in the Spring Wellarea. Other High–HFSE members include thegranitoid along the western margin of the YandalGreenstone Belt, in the area west of the Mt Joel toGreenstone Hill area, and as part of the gneissic tostrongly foliated granitoids (Agb), west of theDragon to Cockburn gold deposits.

Syenitic group members on SIR SAMUEL, includethe syenite and quartz syenite at Woorana Soak andRed Hill, as well as the Wadarrah Quartz Monzonite(Westaway & Wyche 1998). Members of the MaficGroup, include the hornblende–biotite granodioriteat Kens Bore and south of Anxiety Bore (Ag onmap), and numerous porphyries (intersected indiamond drillcore), all within the YandalGreenstone Belt, and an unexposed granodioriteintersected in diamond drillcore from the HurleysReward area in the southern part of the DingoRange greenstone belt.

Petrogenesis and implications

Detailed petrogenetic models for these granitoidgroups are discussed in Champion & Sheraton(1993, 1997), Champion (1997), and Smithies &Champion (1999); Witt & Davy (1997) also presentbroadly similar models for granitoids of thesouthern Eastern Goldfields Province. In brief, themajority of granitoids appear to be largely crustal-derived, especially the Low–Ca and High–HFSEgroups. The origin of the High–Ca group granitoids,although not as unequivocal, requires theirderivation by partial melting at high pressures, e.g.at middle to lower crustal depths in thickened crust(Champion & Sheraton 1997). More importantly,the available Sm–Nd isotopic data (Champion &Sheraton 1997) requires that the source rocks forthe Low–Ca and High–Ca groups were distinctlydifferent, i.e. not only were the Low– and High–Ca granitoids derived at different pressures but alsofrom largely different protolith. The fullsignificance of this is realised when coupled withthe recognition that the granitoid groups themselves

form a largely coherent chronology (see Table 1),from early (2720 to 2655 Ma) High–Ca granitoids,and localised Mafic and High–HFSE granitoid, tolater (2660 and younger) Low–Ca and Syeniticgranitoids. This sequence is interpreted to largelyreflect the ‘post-tectonic’, i.e. post the main-orogenic shortening deformation event, nature ofthe syenitic and Low–Ca granitoids. This isinterpreted to a fundamental change in tectonicenvironment post 2660–2655 Ma, from crustalthickening (shortening) and voluminous High–Cagranitoids, to a tensional environment favouringLow–Ca and syenitic magmatism (see alsoSmithies & Champion 1999). Smithies &Champion (1999) suggested that this post-2660 Mamagmatism, extending down to 2630 Ma andyounger, represented an additional tectonothermalevent in the eastern Yilgarn Craton,contemporaneous with lower-middle crustal high-grade metamorphism and regional goldmineralisation (e.g. Kent et al. 1996). Smithies &Champion (1999) further postulated that thisthermal event might have resulted from lower-crustal delamination following crustal thickeningduring the main-orogenic shortening deformationevent.

Veins and dykes(a, d, e, g, p, po, q)

Several aplite (a) dykes are mapped in the northeastpart of the map sheet area, around Red Hill andeast of Wonganoo. Small veins and dykes ofgranitoid (g) are generally most abundant neargranite–greenstone contacts. Most are deeplyweathered but they appear to be mainly biotitemonzogranite. Mapped units can be found in theBarr Smith Range and east of Barwidgee. Dioriteveins are mapped as d, e.g. at Stirling Peaks. Veinsrich in epidosite/epidote are mapped as e south ofMount Joel and southeast of Red Hill in theWANGGANNOO area.

Pegmatite veins (p) are a common but minorphase in granitoid areas, e.g. at Mount Pasco, butthey also occur in greenstones. About 2 kmsouthwest of Mount Goode, they intrudemetabasalt. In granitoid areas, they occur as bothdiffuse phases in the granitoid and late crosscuttingveins.

Felsic porphyry dyke (po) is also a common butminor rock type. In most cases they are too smallto be shown on the current map. Mapped largerdykes can be found 7–9 km north of Mount Keith,and near the north shore of Lake Miranda. In thelatter locality, the dyke is about 3 m wide on a small

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Liu et al.

hill. It contains both quartz and plagioclasephenocrysts. Although most of the dyke is littledeformed, it is strongly foliated along its margins.

Quartz veins (q) are a minor componentthroughout the SIR SAMUEL area in both greenstonesand granitoids. They are generally short anddiscontinuous outcrops, varying from a fewcentimetres to several metres wide. Larger veinsoccur in the Wild Cat Hills in the southwest part ofthe map area. Liu et al. (1998) considered that thequartz veins are mainly late Archaean in age asthey are not observed to cut the large Proterozoicdykes in greenstones elsewhere in the EasternGoldfields. Many of the larger veins are associatedwith sheared contacts between granitoids andgreenstones. Gold mineralisation is often associatedwith quartz veins that were a major target for earlyprospectors.

Greenstone belts and majorfaults

Greenstones in the Eastern Goldfields Provincewere subdivided into separate greenstone beltsduring the 1970’s and summarised in Griffin (1990)based on their distribution, differences in thedominant rock types, and structural complexity.The belts were named primarily for ease ofdiscussion, and boundaries are not everywhere welldefined.

On SIR SAMUEL greenstone belts include theYakabindie, Mount Keith–Perseverance, Agnew,Yandal, and Dingo Range greenstone belts (Figs3, 5). The Yakabindie greenstone belt refers to thegreenstone sequence west of the Miranda Fault(Fig. 3, Liu et al. 1998). Griffin (1990) interpretedthe Agnew belt to be faulted against the MountKeith–Perseverance belt, and the boundary faultwas shown as the Sir Samuel Fault in Liu et al.(1998). The Jones Creek Conglomerate lies in afault-bounded zone between the Yakabindiegreenstone belt and the Agnew and Mount Keith–Perseverance greenstone belts (Fig. 3).

Much of the SIR SAMUEL area belongs to theEastern Goldfields Province, with the western part(granitic, gneissic rocks, and perhaps theYakabindie greenstone belt) probably belonging tothe Southern Cross Province (see discussionsbelow).

Yakabindie greenstone belt

The Yakabindie greenstone belt consists of thelayered Kathleen Valley Gabbro and the overlying,massive Mount Goode Basalt (Fig. 5a, Liu et al.1998). Both units young towards the south and havea mainly steep to nearly vertical dip to thenorthwest. Rocks are little deformed except alongthe faults and shear zones that are a prominentfeature in the Kathleen Valley Gabbro. Thesequence is bounded by the north-trending MirandaFault, and intruded by granitoid in the west.

The Kathleen Valley Gabbro is a layeredsequence, varying from anorthosite in the north(lower part), to gabbro in the middle, to quartz-bearing gabbro and tonalite in the south (upperpart). The upper part of the Mount Goode Basalt ischaracterised by patchy development of aplagioclase-phyric phase while its lower part ismassive tholeiitic basalt. A tonalitic sample fromAMG 583530 (GA site 97965402) from thedifferentiated upper part of the layered KathleenValley Gabbro has a SHRIMP U–Pb zircon age of2736 ± 3 Ma (Black L.P., 2000, written comm.).This age for the Yakabindie greenstone beltsuggests that the belt is older than much of otheradjacent greenstone belts, which are inferred to beabout 2705 Ma old or younger. The greenstonesequence of the Yakabindie belt appears to beunique in the area and does not appear to haveequivalent sequences in the other greenstone beltsin the area.

Two prominent faults, the Yakabindie Fault andthe Highway Fault, both trending about 330º, cutthe Mount Goode Basalt and the Kathleen ValleyGabbro (Fig. 5). In the Kathleen Valley Gabbrothere are several small north-northwest-trendingshear zones with apparent sinistral movementsense. Eisenlohr (1987, p.88) stated that these shearzones cut a locally developed northeast-trendingfoliation (S1) parallel to the compositional layeringof the gabbro. The Yakabindie Fault (Fig. 5) isdefined by a 50–100 m wide shear zone in theMount Goode Basalt, resulting in a well-developed,steep, northwest-trending mineral foliation at AMG589448. The shear zone can be clearly seen onaerial photos. Basaltic rocks in the shear zonecontain a pronounced foliation (334º/84ºNE2) anda steep, northwest-plunging mineral lineation(64º→335º 3). In some outcrops the lineation isdefined by elongate plagioclase aggregates afterplagioclase phenocrysts. Basalt away from theshear zone is relatively undeformed.

Layering in the Kathleen Valley Gabbro changesfrom an overall east-northeast trend to a more north-

2 334º/84ºNE means ‘strike = 334º, dip = 84ºNE’.

3 64º→335º means ‘plunge = 64º to 335º’.

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northeast trend in the vicinity of the YakabindieFault (Fig. 5). This suggests sinistral movementfor the Yakabindie Fault during D2–3, and isconsistent with observations at Lake Miranda(AMG 593375), small-scale structures in theHighway Fault (AMG 589390), and the sigmoidalshape of the Koonoonooka monzogranite east ofthe Perseverance Fault (Figs 3–4). In thin section,an overprinting relationship between the prominentS2 cleavage and earlier amphibole porphyroblastsalso suggests sinistral movement (Liu et al. 1998:fig. 15).

Liu et al. (1998) presented evidence for threeductile deformation events from beach and low cliffoutcrops on the southeastern end of the elongateisland 3 km south of Bellevue gold mine (AMG593375). Pillow structures in metabasalt (Liu etal. 1998: fig. 7) were flattened in earliestrecognisable deformation (D1). S1 is steep tovertical and trends to the north-northeast. Theflattened pillows are overprinted by the strongregional deformation (D2) that produced theprominent steep, north-trending cleavage (S2).Sinistral shear sense is indicated by the asymmetricshape of pressure shadows around plagioclasephenocrysts (Liu et al. 1998: fig. 13). Foldingduring D3 resulted in formation of upright folds(e.g. felsic porphyry dyke exposed in thenortheastern part of the island, Liu et al. 1998: fig.12), and a spaced axial planar S3 crenulationcleavage, which overprints the earlier S2 cleavageformed by mineral segregation (Liu et al. 1998:fig. 14).

North of Mount Goode at AMG 599502, thesequence includes strongly foliated metabasalticrocks and quartzofeldspathic schist with roundedcordierite porphyroblasts and randomly orientedandalusite porphyroblasts (Liu et al. 1998: fig. 11).The foliation in the mafic and quartzofeldspathicschists dips steeply west and trends northeast. Themetamorphic grade is upper greenschist to loweramphibolite facies. Immediately to the west, acrossa fault parallel to the Miranda Fault, however, grey,fine-grained metabasalt (Mount Goode Basalt) isonly slightly deformed with a lower (greenschistfacies) grade of metamorphism. To the east, theMiranda Fault contact between metamorphosedbasaltic rock and the metamorphosed felsicconglomerate is not exposed, but can be located towithin 10 m in places. Rocks adjacent to theMiranda Fault are strongly foliated.

Miranda and Emu Faults

The zone between the Emu and Miranda Faults is1–5 km wide and houses the Jones Creek and Scotty

Creek conglomerates that extend north-south forat least 80 km from west of Six Mile Well to westof Lawlers. The faults are poorly exposed, and aremainly inferred from geological and geophysicaldiscontinuities (Fig. 5). The Miranda Fault joinsthe Waroonga Shear Zone in the south, whichserves as the west boundary of the Scotty CreekConglomerate.

Waroonga Shear Zones

The Waroonga Shear Zone was named by Platt etal. (1978) and recognised as the contact betweenthe granitic gneiss to the west and the Scotty Creekconglomerate to the east. In fact, there appear tobe at least three major sub-parallel shear zones (Fig.5a, Liu & Chen 1998a), including the originalWaroonga Shear Zone mapped by Platt et al.(1978). As shown in Figure 5a, the Waroonga ShearZone links with the Miranda Fault and serves asthe west boundary of the Jones Creek and ScottyCreek conglomerates. In detail, the MiddleWaroonga Shear Zone appears to link with theBallard Fault extending from the Menzies–Kalgoorlie area in the south (Liu et al. 2000a, b).The West Waroonga Shear Zone extends north-south for at least 100 km.

In the area of the Waroonga Shear Zone, theWest Waroonga Shear Zone, and to the west, thereis a large corridor, up to 20 km wide, of highlydeformed granitic rocks. The rocks contain anextensively developed foliation (schistosity S1) andextend farther north of the shear zones, where theS1 foliation was folded by D2.

The West Waroonga Shear Zone has an arcuategeometry convex to the east (Fig. 5a, Liu et al.2000b). Along its northern arm, the geometricalrelationship between the shear zone and foliationindicates a sinistral movement. Along its southernarm, however, dextral movement has been reported(Platt et al. 1978). A gravity anomaly high extendsfrom the greenstone in the east, across theWaroonga Shear Zone and West Waroonga ShearZone, to the area of gneissic granitoid in the west,and is interpreted to indicate abundant greenstonebelow the granitoid. This and the convex-to-the-east trace of the shear zones suggest that it dips tothe west. The opposite movement senses along itsnorthern and southern arms indicate an eastwarddifferential thrusting. Interpreted thrust duplexessuggest westward thrusting along the Eleven MileFault (Liu et al. 1996). The opposite movementalong the Waroonga Shear Zone and the ElevenMile Fault is considered to be due to east–west-directed compressional deformation duringD2.

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Liu et al.

Farther south, the Waroonga Shear Zone appearsto join the Ballard Fault (parallel to the Ida Fault)from the Menzies–Kalgoorlie region (Fig. 1, Liu& Chen 1998b). The Ida Fault has been consideredto be a major tectonic boundary between theSouthern Cross and the Eastern Goldfieldsprovinces (Swager et al. 1995). Taking this intoconsideration, the Waroonga Shear Zone, and theMiranda, Emu, and Erawalla faults may be theboundary between the two provinces in the SIR

SAMUEL and WILUNA areas. The Yakabindiegreenstone belt, therefore, may belong to theSouthern Cross Province, with the Jones CreekConglomerate deposited along province boundaryfaults. Farther north in the WILUNA area, theErawalla Fault separates the Coles Find greenstonebelt in the west from the Wiluna greenstone belt inthe east.

Alternatively, the boundary of the SouthernCross and Eastern Goldfields provinces may extendnorthward along the Ida Fault in the MENZIES area,to along the west boundary of the Coles Findgreenstone belt on WILUNA (e.g. Myers 1997). Thisis not evident, however, in the 400 m line-spacingaeromagnetic data housed in GA. If the boundaryis along this zone, it has been disrupted andconcealed by granitic plutons.

Agnew greenstone belt

The Agnew greenstone belt is faulted against theMount Keith–Perseverance greenstone belt alongthe Sir Samuel Fault. It is characterised by severalmacroscopic folds including the Lawlers Anticline,Mount White Syncline, and Leinster Anticline (Fig.5a). These folds are separated by faults. In thewestern part, greenstones are interleaved with theJones Creek Conglomerate and granitoid in a fault-bounded zone adjacent to the Waroonga ShearZone.

The Lawlers Anticline is clearly evident onimages of aeromagnetic data for LEONORA and SIR

SAMUEL. The greenstone sequence is dominated bymetamorphosed mafic and ultramafic rocks andcontains minor interbedded, fine-grainedmetasedimentary rocks. Foliation is steep to verticaland trends north-northwest with a consistent north-plunging stretching lineation (Liu 1997). In the SIR

SAMUEL area, however, the anticline is poorlyexposed beneath lateritic duricrust in the area westof Vivien Well.

The Mount White Syncline is a tight, uprightsyncline, consisting of metabasalt, medium-grainedmetagabbro and thin layers of metamorphosed fine-grained sedimentary rocks (Fig. 5a). The

metasedimentary rocks are poorly exposed but theirdistribution is reasonably well established frompatterns on aerial photographs and images ofaeromagnetic data. The best exposures of thesequence are around Mount White. The MountWhite Syncline is structurally higher than theLawlers and Leinster anticlines. A similarrelationship is interpreted for the greenstonesequences.

The Plonkys Well area, west of the Sir SamuelFault and east of Plonkys Fault (Fig. 5a, Liu et al.2000a), contrasts with the Perseverance area in thatit comprises mainly metabasalt, with subordinatemetagabbro and some thin layers of fine-grainedmetasedimentary rocks that define macroscopicfolds. There are few ultramafic rocks in this area,and the overall range of rock types and thestructural style are similar to the Mount WhiteSyncline area.

The Leinster Anticline (Fig. 5a) plungesshallowly to north-northwest. The greenstonesequence here is dominated by metamorphosedhigh–Mg and tholeiitic basalt, komatiite, doleriteand gabbro, and is well exposed in the western limbof the fold. The Halfway Fault separates these rocksfrom the Lawlers Anticline and Mount WhiteSyncline. Foliation (S2–3) on the western limb issteep to vertical and trends north-northwest. Amoderate to steep north-northwest plunging L2

mineral elongation lineation is developed in thearea south-southeast of Leinster Downs.Greenstones on the eastern limb have been intrudedby the Leinster monzogranite. The foliation trendson the eastern limb are to the west-northwest,suggesting that they have been folded by and sopredate the formation of the Leinster Anticline. Ashallow to moderate south-plunging mineralelongation lineation in the western limb of the foldprobably relates to D3 strike-slip movement alongthe Halfway Fault.

The mafic and ultramafic-dominated sequencein the core of the Lawlers Anticline is interpretedas continuing through the Mount White Synclineinto the Leinster Anticline across the Vivien andHalfway Faults (Bunting & Williams 1979,Marston 1984). Thus, the greenstone sequence inthe Agnew greenstone belt is interpreted to consistof (1) a mafic (basalt and gabbro) and ultramaficsequence in the lower part, (2) a package of poorlyexposed felsic volcanic/volcaniclastic andsedimentary rocks in the middle, and (3) a sequenceof basalt and thin sedimentary units with minorgabbro in the upper part.

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Mount Keith–Perseverance greenstonebelt

The Mount Keith–Perseverance greenstone beltextends for more than 150 km from Perseverancein the SIR SAMUEL area to north of Wiluna in theWILUNA area. In the SIR SAMUEL area, it is boundedby the Perseverance Fault against granitic rocks tothe east. Its west boundary is faulted against graniticrocks along the Erawalla Fault to the north, theJones Creek Conglomerate along the Emu Faultfrom west of Six Mile Well to west of McDonoughLookout, and the Agnew belt along the Sir SamuelFault in the south (Fig. 5).

This belt trends north-northwest, parallel tomost of the faults and foliation within the belt.Many rocks are strongly deformed and contain awell-defined foliation. Almost all contacts betweendifferent rock types are faulted or sheared.Eisenlohr (1992) described the contrastingdeformation between the western (Yakabindie) beltand eastern (Mount Keith–Perseverance) belt, i.e.most rocks in the east belt are highly deformedwhile most rocks in the west belt are little deformed.Locally, however, there are less-deformed areaswhere primary textures and relationships arepreserved as a result of strain partitioning.

The Mount Keith–Perseverance greenstone beltcan be divided into two sections along the Six MileFault based on greenstone associations andstructure. The northern section, from north ofWiluna through Mount Keith to Six Mile Well, hasa relatively simple structure and greenstonesequence. Macroscopic folds are largely absent inthis section, particularly from Charles Well to SixMile Well. In the southern section between theEmu–Sir Samuel Faults and Six Mile–PerseveranceFaults, however, there are a number of macroscopicfolds (Fig. 5a).

Perseverance and Erawalla Faults

The north-northwest-trending Perseverance Faultcan be mapped geologically and interpreted fromaeromagnetic data for at least 200 km (Figs 1, 3).It is interpreted to constitute part of the Keith–Kilkenny lineament that continues further southwith a total length of more than 400 km. Theposition of the Perseverance Fault in Figure 3follows Liu & Chen (1998a). This position differsfrom Martin & Allchurch (1976) and Bunting &Williams (1979), who placed the PerseveranceFault running across the Mount Keith–Perseverance greenstone belt from east ofMcDonough Lookout to west of Six Mile Well,and continuing further north along the west

boundary of the greenstone belt to the WILUNAarea.

Liu et al. (1995) named the west boundary faultof the Wiluna greenstone belt as the Erawalla Fault.It continues south to west of Six Mile Well, whereit joins with the Emu Fault as the east boundary ofthe Jones Creek Conglomerate and the newlynamed Six Mile Fault. The Six Mile Fault continuesacross the Mount Keith–Perseverance greenstonebelt to join the Perseverance Fault east ofMcDonough Lookout (Fig. 5a, Liu et al. 2000a).The Six Mile Fault has an outcrop expression ofquartz veins, and is considered to be a relativelylater structural feature than the greenstoneboundary faults, such as the Erawalla andPerseverance Faults.

On SIR SAMUEL, the Erawalla Fault appears todip steeply to the east, as inferred from foliationeast of Cork Tree Flat Well. A shallowly (2–15º)plunging mineral lineation is present in suitablerock types. The greenstone belt in the Mount Keith–Six Mile Well area is very narrow, only about 2 kmwide. The gravity data are consistent with thesuggestion that the greenstone belt dies out at depth.Considering the structures along, and the oppositedips of the east-dipping Erawalla Fault and thewest-dipping Perseverance Fault in the Cork TreeFlat Well–Mount Keith–Six Mile Well area, it issuggested that these two faults underwentsignificant sinistral strike-slip movement during D3

transpression.

The Perseverance Fault is better termed a shearzone. For example, east of the mappedPerseverance Fault on SIR SAMUEL, there is a zoneof highly deformed granitic rocks varying from 1to 6 km wide. The zone is a mixture of highlydeformed granitoid and granitic gneiss withinterleaved amphibolite. Gneissic granitoid ismapped towards the southern boundary of the mapsheet. There are also small outcrops of gneissicgranitoid east of the Perseverance nickel mine.

In the greenstones west of the PerseveranceFault, a zone up to 1 km wide of amphibolite, whichis interleaved with abundant lenses of highlydeformed granitic rocks, is commonly developed.West of Mount Pasco foliated and lineatedamphibolite (Abam), which includes lenses ofstrongly deformed granitoids (granitic bodies andapllite dykes), has been mapped. Foliation is steepto sub-vertical along the Perseverance Fault.

Several northwest- to north-northwest-trendingfaults join the Perseverance Fault in the Six MileWell–Perseverance area. South of Perseverance, for

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example, are the Sir Samuel, Plonkys, and ElevenMile Faults. A thrust duplex was interpretedbetween the Plonkys and Eleven Mile faults andsuggests westward thrusting (Liu et al. 1998a), i.e.greenstones were thrusted over granitoids.

Eisenlohr (1992) described two minerallineations, one plunging steeply to the south-southeast and the other plunging shallowly to thenorth, in the Mount Keith–Perseverance greenstonebelt. The steeply south-southeast-plunging lineationis observed only adjacent (less than 0.5–1 km) tothe granite–greenstone boundary, is developed bothin greenstones and granitoids, and is a mineralelongation lineation. Rocks near the granite–greenstone contact are characterised by an intensefoliation. S–C fabrics and pressure shadows suggestsinistral displacement. Outside the area ofintensively deformed rocks along the PerseveranceFault, Eisenlohr (1992) reported a shallow north-plunging lineation, and a sub-vertical north-trending foliation that is present in all but the mostcompetent rock types.

The fault-bounded greenstone area, between theSix Mile Fault and Perseverance Fault, west ofMeredith Well (Fig. 5a) consists of stronglydeformed amphibolite and fine-grainedmetasedimentary rocks interleaved with deformedlenses of granitoid, some of which are porphyritic.Fine-grained amphibolite at AMG 634557developed a strong foliation (S2: 347º/70º SW) witha steep south-plunging L2 mineral lineation(66º→196º). Immediately to the north-northwest(AMG 633560) are S2 foliated amphibolites thatwere folded into D3 open upright folds with a nearlyvertical axial planes and fold hinges plunging 12ºto the south-southeast.

In the area ~1.5 km west of Mount Pasco is anorth-northwest-trending strip (0.5 km wide and3–4 km long) of amphibolite (Abam) in contact withfine-grained metasedimentary rocks (Ash). In thearea around AMG 623604 dark grey, fine-grainedamphibolite is strongly foliated and often lineated.The foliation is probably a composite S2–3 in theform of a closely spaced (<1 mm) cleavage orschistosity. On the foliation is a common steeplynorth- or south-plunging L2 mineral lineationdefined by alignment of fine-grained amphiboliteand plagioclase (all < 0.5 – 1 mm). Folded smallquartz veins have fold hinges parallel to this steeplineation in amphibolite. At several locations a sub-horizontal crenulation overprints the steepcomposite S2–3 foliation and steep L2 minerallineation, and is interpreted to have developedduring post-D3 deformation.

Mount Keith–Six Mile Well section

This area is generally very poorly exposed withregional geological interpretation and stratigraphiccorrelation dependent on aeromagnetic data andinformation from drilling. Previous studies suggestthat the ultramafic rocks can be correlated fromSix Mile Well, through Mount Keith, to theHoneymoon Well ultramafic complex (Dowling &Hill 1990, 1992, Hill et al. 1995, Gole et al. 1996).

Dowling & Hill (1990, 1992) recognised threepackages of ultramafic rocks, Eastern, Central andWestern Ultramafic Units, at the Mount Keithnickel mine area. Distinctly different volcanicfacies are present within the three major ultramaficunits. The Eastern Ultramafic Unit consists of verythick cumulate flow units of dominantly olivineorthocumulates, and is characterised by lenticularbodies of olivine adcumulate-mesocumulateshowing similar relationships to those at Six MileWell (Hill et al. 1995). The Central Ultramafic Unitcontains thick cumulate flow units and thindifferentiated flow units, and the WesternUltramafic Unit consists primarily of thindifferentiated flow units. The major ultramafic unitsvary in thickness and continuity along strike, dipsteeply to the west and young in the same direction.Easterly younging directions have been determinedin the Western Ultramafic Unit, to the west ofMount Keith, indicating the presence of a synclinalaxis running up the belt. In places, the major unitsare juxtaposed as a result of faulting (Hill et al.1995).

The Mount Keith ultramafic complex isunderlain by a series of discontinuous thinultramafic flow units, separated from the maincomplex of felsic tuffs. The detailed stratigraphyof this part of the section is suggestive of virtuallysimultaneous bimodal felsic–ultramafic volcanism,with these basal komatiite units representingprecursor episodes to the major eruptive event thatproduced the Mount Keith complex (Hill et al.1995).

At Six Mile Well there are also three similarkomatiite packages separated by volcaniclasticmetasediments. The three packages at Six MileWell can be correlated north through Mount Keithto Honeymoon Well (Dowling & Hill 1990, Goleet al. 1996). The lowermost Unit, the EasternUltramafic Unit, contains several mineralisedolivine adcumulate lenses. The complex isconcordant with the west-facing stratigraphy andhas a steep southeasterly plunge (Hill et al. 1995).

The highly magnetised ultramafic units can beused as a stratigraphic marker from the Six Mile

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Well area to the Honeymoon Well ultramaficcomplex and probably further north to the area westof Wiluna. A high–Mg basalt unit, also readilyinterpreted from the aeromagnetic data, can be usedas a second stratigraphic marker from the Wilunaarea to the area a few kilometres west of CharlieWell near the north map boundary of SIR SAMUEL

(Liu et al. 1995). Using these markers, and aidedby interpretation from outcrop mapping, drillholeinformation and aeromagnetic data, from west toeast, five packages of rocks can be depicted fromSix Mile Well, through Mount Keith nickel mine,to Charlie Well on SIR SAMUEL.

1. Sedimentary rocks, with some sandstone andconglomerate, that occur along Erawalla Faultthat continues to west of Wiluna (Liu et al.1995).

2. Metamorphosed ultramafic rocks that are moreor less continuous to the Honeymoon Wellcomplex and further north to west of Wiluna.

3. Metamorphosed felsic volcanic/volcaniclasticrocks, that may be conformable to ultramaficrocks to the west and high–Mg metabasalt tothe east in the area west of Honeymoon Welland Charlie Well (Fig. 5b), although the contactsare not exposed and may have been deformed.The felsic rocks are interpreted to be faultedagainst the Perseverance Fault in the area fromMount Keith to Six Mile Well.

4. High–Mg metabasalt (Fig. 5b) that does not cropout on SIR SAMUEL but is readily interpreted fromaeromagnetic data about 4 km west of CharlieWell and continues onto WILUNA. East of thehigh–Mg metabasalt are outcrops of tholeiiticmetabasalt that is intruded by an oval shapemonzogranite pluton south of Charlie Well (Fig.5b).

5. East of the fault from southeast of HoneymoonWell and west of Charlie Well (Fig. 5b) is amixed package of metamorphosed basalt andgabbro, foliated basaltic rocks, interleavedfoliated granitic rocks and amphibolite. BIFrafts occur in granitic rocks near thePerseverance Fault about 2–3 km northeast ofCharlie Well.

The five packages of rocks on SIR SAMUEL arecorrelated with the Wiluna sequence recognised byLiu et al. (1995) from Wiluna to Mount Way. TheWiluna sequence is overall west-younging. Localeast-younging is due to minor folding, probablyassociated with faults.

Although there is evidence for multiple

deformation events in the Mount Keith–Six Milearea (Liu et al. 1995, Gole et al. 1996, Jagodzinskiet al. 1999) geological relationships indicate arelatively simple greenstone sequence.

In the Mount Keith nickel mine area, Bongers(1994) reported some D1 structures that includegently southerly dipping chloritic cleavage andfolded but originally east-striking veins inultramafic rocks. Later structures in the MountKeith–Six Mile area are characterised by a steepnorth-northwest-trending S2 foliation and a gentlyplunging lineation in the foliation (Jagodzinski etal. 1999). Shear bands, C–planes, boudins, andvergence of small folds indicate a consistentsinistral sense of shear. Folds in rafts of BIF in thegranitoid east of the Perseverance Fault east ofMount Keith are gently plunging, and show avergence indicating west-block-up, i.e. greenstone(to west) up and over granitoid (to east). In contrast,Eisenlohr (1992) suggested that the easterngranitoid is upthrust over the greenstones to thewest. The granite–greenstone contact dippingtowards the greenstone belt along the PerseveranceFault as inferred from foliation measurements alongthe fault is consistent with Jagodzinski et al. (1999).Post-D2 structures include small-scale, steeply-plunging open to isoclinal folds and kink bands(Jagodzinski et al. 1999).

Perseverance–McDonough Lookout section

The geology of the Perseverance–McDonoughLookout area, and for some 15 km further to thenorth, is different from the Six Mile Well–MountKeith–Wiluna area. The differences include lessmetamorphosed felsic volcanic/volcaniclasticrocks, and the presence of prominent ‘cherty’ ridgesof fine-grained siliceous metasedimentary rocks,which define macroscopic folds.

Between the Emu and Six Mile Faults south ofSix Mile Well is a syncline defined by metagabbro,tholeiitic and high–Mg metabasalt, andmetamorphosed ultramafic rocks includingperidotite, komatiite and tremolite schist. Naldrett& Turner (1977) called the structure the ‘Serp Hillsyncline’. It plunges shallowly to the north-northwest and has a wavelength of about 1.5 km.About 12 km north-northwest of the Perseverancenickel mine around Mount Sir Samuel is an uprightregional tight to isoclinal antiform developed incherty units. The fold axis plunges shallowly (~30º) to the north-northwest. It crops out over anarea about 1.5 km east-west and nearly 5 km north-south. It is considered to be a D2 fold because onits east limb are earlier small (metre-scale)recumbent D1 folds with east-plunging fold axes

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(Liu et al. 1996, 1998).

Felsic volcanic/volcaniclastic rocks appear tobe a minor component in the Perseverance–McDonough Lookout area in general, although theyare mapped and may be a significant part of thesequence in the area around the Perseverance andRocky’s Reward nickel mines. The greenstonesequence and structural styles correlate well fromPerseverance to the area around McDonoughLookout (see also Naldrett & Turner 1977; Bunting& Williams 1979; Marston 1984), and further northto the area between the Six Mile Fault and EmuFault south of Six Mile Well.

The Perseverance ultramafic complex is a bodyof amphibolite-facies metamorphosed ultramaficrocks of komatiitic affinity consisting of spinifex-textured flows, layered olivine orthocumulate andmesocumulate and a central body of coarse-grainedolivine adcumulate (Barnes et al. 1995). Thecomplex overlies a sequence of thin cumulate flowunits that host the Perseverance and Rocky’sReward nickel deposits (Barnes et al. 1988a, Goleet al. 1989). It is overlain by a mixed sequence ofhighly deformed komatiite, high–Mg basalt, andfelsic volcanic rocks, truncated by the PerseveranceFault. The entire sequence is overturned, faces tothe east, and dips 70–80º to the west.

Ultramafic rocks in the Perseverance area aredated at ca. 2702–2707 Ma (Hill & Campbell,unpublished data, cited in Libby et al. 1998).Nelson (1997a) reported a 2720 ± 14 Ma age for adeformed felsic volcanic rock 200 mstratigraphically below the ultramafic rocks. Theultramafic rocks in the Perseverance area arecorrelated with those in the Mount Keith–Six MileWell section of the greenstone belt, those in theAgnew greenstone belt, and the major ultramaficunits dated to be around 2705 Ma in the southernpart of the Eastern Goldfields (Nelson 1997b).

Rocks in the Perseverance area have undergonethree major deformations (Libby et al. 1997, 1998).D1 produced thrusting and isoclinal and recumbentfolding that resulted in top-to-the-north stackingof the greenstone sequence and intercalation ofrocks units. D2 marked a change to a regime ofeast-northeast to west-southwest bulkinhomogenous shortening, and resulted in thedevelopment of regional-scale upright folds andintensely deformed zones in which primarylithological layering was transposed. D3 isexpressed by the development of laterally extensivenorth-northwest- and north-northeast-trendingstrike-slip shear zones and associated folds andthrusts. Despite of the multiple deformation history

in the Perseverance area, however, the greenstonesequence there is overall east facing (Hill et al.1995, Libby et al. 1998).

Yandal greenstone belt

The north- to northwest-trending Yandal greenstonebelt extends for more than 200 km from the southedge of SIR SAMUEL to the WILUNA area. During thepast decade the Yandal belt has emerged as asignificant gold-rich mineral province with its goldendowment increasing from ~1 Moz in 1990 to over14 Moz in 2000 (Phillips et al. 1998b, Phillips &Anand 2000).

The greenstone sequence is difficult to establishfor the Yandal greenstone belt because of very poorexposure in most parts of the belt. However,Phillips et al. (1998b) proposed a three-partgreenstone sequence for the northern Yandal beltfrom Jundee to Bronzewing. Their lower sequencerefers to the BIF unit along the west margin of thebelt in the Jundee–Lake Violet area. A middlesequence refers to the mafic–dominatedmafic-ultramafic association, including the locallynamed “Bronzewing Komatiite”, while their uppersequence refers to the dacite-dominated felsicvolcanic/volcaniclastic package in the Lake Violetarea.

On SIR SAMUEL, the southern Yandal greenstonebelt can be broadly divided into three zones,separated by major north-south faults (Figs 3, 6).The western zone, between the Mount McClureFault and the Ockerburry Fault Zone, includes aregional north-northwest-trending antiform, theBronzewing antiform with a wavelength of about10–15 km east-west and a curved axial trace in thearea east of Bronzewing, and Kens Boregranodiorite (Fig. 3). Locally a few hundred metresnortheast of Bronzewing, a smaller scalesouth-plunging ‘Hook antiform’ forms part of themore complex Bronzewing antiform. Liu & Chen(1998a) interpreted the Bronzewing antiform as aD2 structure, based on regional interpretation andstructural observation east of Kens Bore. About 1.8km east-northeast of Kens Bore (AMG 090589)are some silica cap rocks and fine-grained siliceousand ferruginous metasedimentary rocks near thehinge of the Bronzewing antiform. Themetasedimentary rocks are interbedded shale andsiltstone and clearly show bedding. Within about30 m, bedding changes from 063º/75ºSE in the eastto 279º/75ºSW in the west. In places an earlycleavage (S1) is sub-parallel to the bedding. Inothers, S1 is vertical at a small angle (< 15º)clockwise from the bedding. Both bedding and S1

are folded by the antiform. The S1 cleavage has also

33


been crenulated probably during D3 (axial plane ofcrenulations 035º/65ºSE and hinge of crenulations72º→155º).

The western zone appear to consist of threepackages of greenstone:

1. Immediately east of the Mount McClure Fault,in the area north-northwest of Mount McClure,is a 0.5–1.0 km wide zone of dominantly felsicschists. At Mount McClure, and to the southalong the Mount McClure Fault, is a mixedsequence of chert units (fine-grained siliceousmetasedimentary rocks), and foliatedmetamorphosed felsic volcanic/volcaniclastic,sedimentary and basaltic rocks.

2. The above sequence is overlain by a large areaof mafic-dominated mafic–ultramafic rocksbetween Mount McClure and the Kens Boregranodiorite. The sequence is east-younging,based on sedimentary structures anddifferentiation layering in a gabbroic sill.Relationships between sedimentary and maficrocks displayed in drill core from the MountMcClure gold mines also indicate younging tothe east (Westaway & Wyche 1998).

3. A package of felsic volcanic/volcaniclasticrocks in the area between the Paul Well–TonyWell area and Ockerburry Fault Zone, based onlimited drill core data and interpretation ofaeromagnetic data.

These three packages appear to correlate withthose proposed by Phillips et al. (1998b). In thiscorrelation, the Bronzewing komatiite correlateswith the komatiitic ultramafic rocks in the Lotusand Cockburn gold deposits, and south of the KensBore granodiorite. If this is correct, the Bronzewingto Lotus–Cockburn area may be, structurally, a D2

fold (i.e. the Bronzewing antiform) which refoldeda D1 fold. The D1 fold axial trace would besomewhere between Bronzewing and Lotus andCockburn gold deposits. Alternatively, structuralcontinuity in the Bronzewing to Lotus–Cockburnarea may have been disrupted by a major fault, suchas the Lotus Fault.

The central zone, the Ockerburry Fault Zone,consists of mostly highly deformed felsic volcanic/volcaniclastic rocks, with some mafic rocks in thesouth and minor ultramafic rocks in the area about6 km west of Woorana Soak. This fault zone has aclear linear expression in the magnetic data (Figs3–4). It appears to die out towards the northboundary of the SIR SAMUEL map sheet boundary,thus, the eastern and western zones merge.

The eastern zone, between the Ockerburry FaultZone and the Ninnis and Rosewood Faults,comprises 30–40% of felsic volcanic/volcaniclasticrocks and 60–70% basaltic and doleritic rocks.Based on younging evidence, and structuralinterpretation, in the Spring Well–Darlot area, itappears that in the east zone is a broad north-northeast-trending D3 synform which overprintednorth-northwest-trending D2 folds such as the onesin the Darlot area.

Hill et al. (1990) suggested that the thickkomatiite units in the Eastern Goldfields Provincerepresent one short period of extrusive activity.Komatiite is suggested to have formed in a singleevent around 2705 Ma in the Eastern Goldfields,and can be used as a stratigraphic marker inmapping (Nelson 1997b). If this is true for thekomatiitic ultramafic rocks in the Bronzewing toLotus–Cockburn area, then greenstones in this areamay correlate with those in the Darlot area, wherea porphyritic rhyolite sample was dated at 2702 ±5 Ma (Nelson 1997a). Furthermore, if the highlydeformed felsic volcanic/volcaniclastic rocks in theOckerburry Fault Zone correlate with those felsicrocks in the Spring Well–Darlot zone, then theentire southern Yandal greenstone belt may be acomplex synclinorium.

Mount McClure Fault

The Mount McClure Fault trends approximatelynorth-south along the western boundary of thesouthern Yandal greenstone belt. It separatesinterleaved, deformed granitoid and greenstone ofmostly amphibolite facies to the west anddominantly greenschist facies greenstones to theeast. Hammond & Nisbet (1992) suggested normalfaulting during early extension along the fault thatuplifted amphibolite facies rocks into contact withgreenschist facies rocks. This view is consistentwith observation of a S–C fabric in graniticmylonite west of the Mount McClure Fault thatindicates granitoid (west block) upward andgreenstone (east block) downward movement.

East of Bogada Bore, a poorly preservednorthwest-trending greenstone sequence thatincludes recrystallised ferruginous and siliceousmetasedimentary rocks (“chert”), a thin ultramaficunit and strongly deformed metabasalt mayrepresent the western limb of a shallow southeast-plunging ?D2 antiform (Wyche S., 1995, pers.comm.). The core of the structure is occupied bystrongly deformed granitoid rock with a shallowsoutheast-plunging mineral lineation. At AMG994286, a shallow southeast dipping S1 foliation(044º/13ºSE) is observed in highly deformed

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Liu et al.

granitoid. The eastern limb may have been shearedout by an interpreted fault west of the MountMcClure Fault. Outcrop through this area is verypatchy and a faulted contact between the antiformand the main north trending greenstone belt maybe concealed beneath the extensive regolith cover.

In the area north and south of Hartwell Well, anapproximately north-south strike, moderate to steep(40–80º) easterly dipping foliation/schistosity(S2–3) is commonly developed in several rocks, withor without a steeply south-plunging minerallineation (L3?). The moderate to steep south-plunging mineral lineation along the fault isconsistent with reverse movement along the faultduring local compressional deformation (Chen etal. 2001).

Cocks–Satisfaction Zone

The Cocks–Satisfaction Zone, west of the MountMcClure Fault, is a 5–12 km wide zone of highlydeformed interleaved granitoid and lenses ofgreenstone. Deformed granitoid containing lensesof foliated mafic rocks (Agb) and interleavedfoliated mafic rocks with lenses of felsic rocks(Abg) are best exposed west of the northern sectionof the Mount McClure Fault. These rocks have adistinct north-northwest-trending pattern on aerialphotographs and images of aeromagnetic data. Thegranitic rocks are dominated by medium-grainedfoliated to strongly foliated and lineatedmonzogranite, with mylonite developed in places.The greenstones in these interleaved units (Agb,Abg) are mostly strongly foliated amphibolite. Inthe south, the zone is poorly exposed and theinterpreted geology is almost entirely based onaeromagnetic data (Figs 3–4).

Foliation in both granitoid and greenstone dipsmoderately to steeply east. However, in places, thefoliation is gently dipping (mainly to the south),probably parallel to the original granite–greenstonecontact. The foliation is defined by the alignmentof biotite and feldspar, and contains a prominentmineral lineation plunging gently to the south andsouth-southeast. The contact-parallel foliation waslocally folded into open, upright folds with hingesplunging 15–20º to the south and south-southeast.

The foliated granitoids in this zone have beenmapped as gneiss in previous studies. Bunting &Williams (1979) considered them as orthogneiss.The current study, however, suggests that they aredeformed granitoid. A sample from west of theParmelia open pit indicates a crystallisation age of2738 ± 6 Ma (Nelson 1998), which probablyrepresent a phase of granitic magmatism earlier

than the greenstone formation in the region.

Ockerburry Fault Zone

The Ockerburry Fault Zone is the most prominentamong several north- and north-northeast-trendingfaults in the southern Yandal greenstone belt. It is2–8 km wide, and about 150 km long, with a Z-sigmoidal pattern clearly indicated in images ofaeromagnetic data (Figs 3–4). The rock associationin the fault zone appears to be dominantly felsicvolcanic/volcaniclastic. At its southern end, itmerges with the Perseverance Fault–Mount GeorgeShear Zone in a highly deformed zone a fewkilometres wide (Fig. 1). To the north, the faultzone dies out near the map sheet boundary (Fig.3).

Both sinistral and dextral movement senses havebeen observed along the Ockerburry Fault Zone(Vearncombe 1998, Chen et al. 2001, this study).The most prominent movement sense indicator isthe magnetic pattern of granitoids northwest ofBundarra, east of the southern end of the fault zone(Figs 3–4, Liu & Chen 1998a). Here, an earlyfoliation (S1) has been folded into a north-northwest-trending D2 fold. The S1 foliation on thewest limb was dragged into the Ockerburry FaultZone, indicating dextral shear. However, the overallarchitecture of the fault zone shows a Z-sigmoidalpattern, which was probably shaped by sinistralmovement during D3 transpression. This isconsistent with the shallowly plunging minerallineation and slickenline on a steeply dippingcleavage, together with steeply plunging S-asymmetric folds, suggesting a sinistral strike-slipmovement in the Ockerburry Hill area (Chen et al.2001).

West of Ockerburry Hill, banded chert horizonsare interbedded with shale and siltstone (Ash). Agently south-dipping, bedding-parallel, slatycleavage (S1) in shale and siltstone is well preservedaround the hinges of upright, north-trending D2–3

folds, that have wavelengths ranging from a fewcentimetres to tens of metres (Fig. 10, Chen et al.2001). The rocks locally contain a mineral lineationplunging 5–25º to the south and south-southeast.Gently south-dipping thrust surfaces, parallel to thebedding of banded chert, are accompanied bynumerous south-plunging slickenlines, and minornormal faults dipping 20º to the north, whichindicate a northerly transport direction. This issupported by locally preserved north-vergingrecumbent folds defined by bedding.

East of the Ockerburry Fault Zone are severalnorth-northeast-trending folds. Three larger ones

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Figure 10. Photographs of D1 structures in the Ockerburry Hill area: A) Gently dipping S

1 slaty cleavage

folded by an open D2 fold. Intersection lineation between S1 and S2 plunges 5° to south-southeast.Siltstone interbedded with shale. 4 km northeast of Ockerburry Well. Scale bar is 10 cm(Photograph by S.F. Chen); B) S

1 foliation in siltstone folded by an open D

2 fold plunging

gently (5°) to south-southeast. North of Ockerburry Hill. Diameter of coin is 3 cm (Photographby S.F. Chen)

A)

B)

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Liu et al.

are shown in Figures 3 and 6. The axial traces ofthese folds are at a large angle (40–50°) to andappear to post-date those of the large scale north-west-trending D2 folds at Bronzewing and Darlot,and are considered to be D3 folds. Chen et al. (2001)relate these folds and the north-northeast-trendingfaults including the Ockerburry Fault Zone to thedevelopment of the Yandal compressional jogduring D3 transpression.

Ninnis Fault

The north-northwest-trending Ninnis Fault marksthe eastern boundary of the Yandal greenstone belt,and is part of the Celia lineament. In the SIR SAMUEL

area, it splays into several faults in the areas aroundMount Grey, Woorana Soak, and Ninnis Well (Fig.6). The deflection pattern of these faults againstthe Ninnis Fault suggests significant sinistraldisplacement along the Ninnis Fault.

Ninnis Well area

Rocks around Ninnis Well are strongly deformed.In a 1.5 km-wide high-strain zone, adjacent to theNinnis Fault, amphibolite is interleaved withvarious schists derived from felsic volcanic,sedimentary and granitoid rocks (Chen et al. 2001).They contain a pervasive foliation (S2–3) trendingnorth-northwest (332–345°) and dipping steeply(82–88°) to the west-southwest, parallel to the fault.A steeply plunging L2 mineral lineation (60–85° toSSE) is also present, mainly in amphibolite closeto the granite–greenstone contact. A shallowlyplunging L3 mineral lineation (25–28° to SSE) isprominent throughout various rock types within thehigh–strain zone. A pervasive schistosity in anarrow zone of mylonitic monzogranite adjacentto the contact contains a mineral lineation pitching30° to the south-southeast. The fault pattern anddeflection of structural trends in the greenstones,adjacent to the Ninnis Fault, is consistent withsinistral strike-slip displacement (Figs 4, 6).Locally, the shallow L3 lineation overprints thesteep L2 lineation.

Woorana Soak area

In the vicinity of Woorana Soak, the Ninnis Faultis a zone, nearly 1 km wide, of highly deformedrocks including quartz–feldspar schist (Alf),amphibolite (Abam) and deformed granitic rocks.The quartz–feldspar schist is mostly deeplyweathered, often in the form of quartz–clay rockinterleaved with some grey shale or quartz–sericiteschist. A strong foliation in the form of a schistositytrends north-northwest and dips steeply to northeastto sub-vertical, parallel to the granite–greenstone

contact. Schistosity is best developed in the lightgrey quartz–muscovite schist.

About 200 m west of Woorana Soak, lowoutcrops of strongly foliated fine-grained maficrocks contain an intense layering 0.5–2 cm wide(339°/87°NE). About 250 m south of WooranaSoak, in a small north-northwest creek, are outcropsof intensively deformed granitic rocks with a strongfoliation (S2: 335°/78°SW) and a stretchinglineation (L2: 53°→184°). In the hilly area to theeast are rocky outcrops of little or weakly deformedmonzogranite. This monzogranite is considered tobe the protolith for the intensively deformedgranitic rocks in the creek described above.

In the area about 2–3 km north, northeast to eastof Woorana Soak, there are several units mappedas syenite (Ags), one of which has been dated at2644 ± 13 Ma (Nelson 1998), consistent with manysyenite ages in the Eastern Goldfields.

Mount Grey Fault

The Mount Grey Fault links the Ninnis Fault andOckerburry Fault Zone (Fig. 6). Along the granite–greenstone boundary west of Mount Grey is a zoneof thinly banded tonalitic, gneissic granitoid thatcrops out discontinuously for 10 km in a north-northwest-trending zone as part of the OckerburryFault Zone. The gneissic rock is very similar to theadjoining granitoid to the east, and is, therefore,considered to be the deformed parts of those units(Stewart A.J., 1999, pers. comm.). In the gneissicgranitoid there is a shallow (15–20°), south-plunging mineral lineation. This shallow lineationis probably related to the strike-slip movement ofthe Ockerburry Fault Zone.

The Ockerburry Fault Zone is around 2 km widein the area west of Mount Grey, as deduced fromthe highly deformed rocks in scattered outcrops andas interpreted from aeromagnetic data. In thesouthern section of Tom’s Gossan (silica cap rockafter ultramafic rocks, Lyons et al. 1996) at AMG152586 (GA site 94968954), the hinge of a smallfold plunges 18º south. The ‘S’ vergence of thisfold indicates sinistral movement in the fault zone.However, in foliated basaltic rocks about 1 km tothe south-southwest at AMG 149576 (GA site94968951), S–C fabric in schistosity (005º/60ºNW)indicates dextral shearing. At AMG 172619 (GAsite 94967732), there are a small exposure and adrillhole into felsic schist with a schistosity of 020º/67ºSE. The rocks here contain a strong stretchinglineation (35º→187º). S–C fabric in the schistindicates dextral shearing, which is consistent withthe S-vergence of a cm-scale small fold in quartz-

37


rich layer. The hinge of this fold measures45º→177º (Stewart A.J., 1999, pers. comm.).

It is difficult to comment on these oppositemovement senses (sinistral and dextral) becauseof the lack of timing evidence on these structuresin the deformation history of the area. It is possiblethat the Ockerburry Fault Zone moved in oppositedirections during different stages of the history. Onthe other hand, the wedge-shape greenstone blockbetween the north-northeast-trending Mount GreyFault and the north-northwest-trending Ninnis Fault(Fig. 6) may have moved southward as an ‘escape’block during D3 transpression. This would haveresulted in dextral movement along the Mount GreyFault (see above) and sinistral movement along theNinnis Fault (Chen et al. 2001). A similarexplanation may apply to the opposite movementdirections in the Ockerburry Fault Zone describedabove.

Rosewood Fault

The Rosewood Fault splays off Ninnis Fault andtrends south-southeast. The granite–greenstonecontact is mapped in the Rosewood Well area (Fig.6). At this locality, Wyche & Westaway (1996)mapped a prominent fault 200–300 m west of thecontact. Along the fault is an approximately 300m-wide, high-strain zone. Amphibolite isinterleaved with intensely foliated monzograniteand later, undeformed granitoid dykes. A prominentfoliation (S2–3) trends 315–328º and dips 65–84º tothe southwest, with a locally preserved L2 minerallineation pitching 72º to the northwest (Chen et al.2001). About 50 m northeast of the contact, mediumto coarse-grained quartz monzonite is relativelyundeformed.

The Yandal compressional jog

Chen (1998) and Chen et al. (1998, 2001) discussedcompressional jogs in the north Eastern Goldfields,a structural pattern not previously recognised.According to these authors, a compressional jog isa configuration of stepover strike-slip faults, witha transfer fault that runs diagonally to link theboundary strike-slip faults. One of these jogs is theYandal compressional jog in the southern Yandalgreenstone belt (Figs 3, 6). The other two are theLaverton and Duketon jogs. The compressionaljogs are considered to have been finally shapedduring D3 transpression (Chen et al. 2001).

The Yandal compressional jog is defined by thenorth-northwest-trending Perseverance Fault andNinnis Fault, with the north–south-trendingOckerburry Fault Zone running diagonally within

the rhombic southern Yandal greenstone belt (Chenet al. 1998, 2001). East and west of the fault zonethere are several approximately north–south-trending faults including the Mount McClure andGardiner Faults, which are probably also shearzones. The jog is approximately 60 km wide, andcan be subdivided into three parts as discussedbefore. Internal structures within the jog aredominated by north- to north-northeast-trendingfolds and reverse faults, accompanied by awidespread axial planar foliation.

Both dextral and sinistral movement is apparenton the Ockerburry Fault Zone as discussed earlier.Dextral movement might be associated with D2

compression, while sinistral movement is attributedto strike-slip movement during D3 transpressionChen et al. (2001). The Mount McClure Fault isinterpreted to dip moderately to steeply the east.Reverse movement is inferred from the moderatelyto steeply south-plunging lineation in east dippingfoliation.

Three macroscopic folds east of the OckerburryShear Zone (Figs 3, 6), are representative of morewidespread mesoscopic upright folds in the area(Westaway & Wyche 1998). They are part of acomplex north-northeast-trending synclinoriumthat overprints north-northwest-trending D2 foldswithin the southern Yandal greenstone belt (Figs3, 6). Internal arcuate reverse faults are interpretedfrom aeromagnetic data, parallel to the fold axialtraces and main foliation surfaces in the areabetween the Rosewood Fault and Ockerburry FaultZone. The deflection pattern of these faults againstthe boundary Ninnis Fault and the Gardiner andMount McClure faults against the boundaryPerseverance Fault implies that their developmentis closely related to the sinistral strike-slip on theboundary faults (Figs 3, 6).

Dingo Range greenstone belt

The Dingo Range greenstone belt has an arcuategeometry convex to the west. North of DingoRange on SIR SAMUEL it trends approximately north-northeast onto WILUNA and KINGSTON. In the DingoRange area and to the south, it trends approximatelysouth-southeast onto DUKETON (Fig. 7).

Contacts between the greenstone belt andgranitoids are partly intrusive and partly faulted,with the majority of intrusive contacts shearedduring the major deformation events. For example,the eastern contact of the belt north of MountHarold near the east margin of the SIR SAMUEL areaappears to be intrusive (from aeromagnetic data),however, rocks at AMG 443794 near the contact

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Liu et al.

are strongly deformed, and mapped as chloriteschist derived from ultramafic rocks (Aul).

The Dingo Range consists of two prominentridges of siliceous metasediments (chert and BIF,mapped as Ac). The prominent structure here is theDingo Range antiform, which extends from theDingo Range to the Mount Harold area. Bunting& Williams (1979) considered this structure as ananticline, based on the ‘northerly dip of beddingaround the fold closure in the Dingo Range,parasitic folds in chert bands, northerly plungingmineral elongation lineation associated with axialplane foliation, and facing from pillows and gradedbedding in the vicinity of Wonganoo’. However,based on structural data and interpretation of the400 m line-spacing aeromagnetic data (Fig. 7), Liu& Chen (1998a) interpret this structure as a D2

antiform that folded an earlier recumbent fold (D1).This is consistent with structural observations onthe eastern limb of the antiform. Considering thenortherly younging evidence in the vicinity ofWonganoo of Bunting & Williams (1979), thecurrent interpretation means that rocks south-southeast of the Dingo Range young to south-southeast towards Mount Harold.

At the eastern end of Dingo Range, in the areaaround AMG 432811, there is a mesoscopicsynform mapped by Lyons et al. (1996). It is about200 m wide northeasterly and 500 m northwesterly.

It plunges shallowly to the northwest. A smallisoclinal D1 fold is observed at the southern part ofthe mesoscopic synform’s hinge area (Fig. 11). Itis about 10 cm across (S0: 310º/80ºSW, S1: 310º/80ºSW, hinge: 76º→143º) with S2 fracturalcleavage nearby, trending north-northwest. AtAMG 433809, an L1 intersection lineation (S1/S0)has been folded around a D2 antiform (S2 axialplane: 321°/85°SW, hinge: 80°→322°; Fig. 12).Small D3 folds (wavelength 10–20 cm) have nearvertical axial planes trending about 343º. An L3

intersection lineation (S3/S0), parallel to D3 foldhinges, plunges at 64°→162°. At several locations,S2 fracture cleavages (sub-vertical, trending north-northwest) crosscut both limbs of the mesoscopicsynform (Fig. 13).

The Dingo Range antiform is sheared againstthe granitoid to the west. In the area between DingoRange and Red Hill, are several outcrops of felsicgneiss (An), sheared granitic rocks (Ag) andultramafic rocks (Aus, Czu). They develop a nearlyvertical, strong foliation trending north-northwest,parallel to the greenstone belt boundary. Part ofthe eastern boundary of the antiform is also thoughtto be sheared against granitic rocks. At AMG442793 are some small outcrops of chlorite schist(Aul) after ultramafic rocks in a small creek. Theserocks have a well developed schistosity S2 (347º/66ºSW). Fine-grained basaltic rocks (Ab), some

Figure 11. Photograph of isoclinal D1 fold in cherty rocks in the Dingo Range (AMG 433808, coin is 2 cm

in diameter)

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200 m to the west, are also foliated. The shearedgranite–greenstone boundary is thought to beimmediately east of the mapped unit of chloriteschist (Aul).

The prominent ridges in the Mount Harold areaare mainly light coloured chert (Ac) and some BIF.These rocks clearly define a northwesterly plungingantiform. The two limbs appear to have beensheared close to the position of axial plane asrevealed from images of aeromagnetic data andexploration drilling. Parasitic folds are mapped onboth limbs and plunge steeply northwest (see alsoLyons et al. 1996).

At AMG 475678 there is a mesoscopic, D2

parasitic fold of banded chert (Ac), with awavelength about 10 m in outcrop. The axial plane(S2) measures about 326º/64ºSW, however the folddoes not develop an axial planar cleavage probably

due to the very competent cherty lithology. Anarrow-spaced (1–2 mm) fracture cleavage (S3:352º/80ºNE) crosscuts the fold close to the hingearea.

Felsic schist (Afs) occurs between the foldedchert unit (Ac) immediately north and about 1.1km northeast of Mount Harold. It appears that therocks between the folded chert unit are mainlydeformed and metamorphosed felsic volcanic and/or volcaniclastic rocks, apart from some chertpebble conglomerates about 1 km northeast ofMount Harold (Fig. 8).

If the structural interpretation for the DingoRange antiform to be a D2 antiform refoldedrecumbent D1 fold is correct, then a simplestratigraphic sequence can be speculated. The lowerpart in the Dingo Range consists of mainly basaltand ultramafic rocks, and some chert and BIF

Figure 12. Photograph of folded intersection lineation in cherty rocks in the Dingo Range (AMG 433809,pencil is 14 cm in length)

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Liu et al.

among the lower-most part of the sequence. Theupper part of the sequence, in the Mount Haroldarea, consists of felsic volcanic/volcaniclastic rocksabove a chert/BIF layer and minor chert-pebbleconglomerate. The felsic volcanic/volcaniclasticand sedimentary in the area north-northwest ofWonganoo may correlate with the felsic volcanic/volcaniclastic rocks in the Mount Harold area.

Stratigraphic correlation with theKalgoorlie and Leonora–Laverton areas

In the Kalgoorlie area, some 400 km to the south,a simple stratigraphy has been described, consistingof (1) a lower basalt unit overlain by (2) a komatiiteunit followed by (3) an upper basalt unit and then(4) a felsic volcanic and sedimentary rock unit,which are (5) all unconformably overlain by aclastic sedimentary unit (Swager et al. 1995).

Hallberg (1985) presented a synthesis of thegeology in the Leonora–Laverton area immediatelyto the south and southeast of the SIR SAMUEL area.Although he did not produce a regionalstratigraphy, Hallberg (1985) divided rocks in theLeonora–Laverton area into a lower sequence(Association 1) with abundant ultramafic rocks andrare felsic volcanic rocks, and an upper sequence(Association 2) with only rare ultramafic rocks andabundant felsic volcanic rocks.

In the Agnew–Wiluna, Yandal, and DingoRange greenstone belts, it appears that there is ageneral trend of (1) predominantly mafic andultramafic rocks in the lower part of the greenstonesequence, while (2) the upper part is dominantlyfelsic volcanic/volcaniclastic and sedimentaryrocks. This trend is broadly comparable with thosein the Kalgoorlie and Leonora–Laverton areas,

Figure 13. Photograph of sub-vertical fractural cleavages in cherty rocks in the Dingo Range (AMG432809, pencil is 14 cm in length)

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although in detail, the greenstone sequences aredifferent.

Polymictic conglomerate is present in theAgnew–Wiluna greenstone belt and comparablewith similar rocks in the Leonora–Laverton area(e.g. Yilgangi conglomerate) and the Kalgoorliearea (e.g. Penny Dam conglomerate). Suchconglomerate is absent in the Yandal and DingoRange greenstone belts.

Deformation history

Below is a synthesis of deformation history for theSIR SAMUEL area (Fig. 3, Table 2), mainly after Liuet al. (1998), Liu & Chen (1998a, b) and Chen etal. (2001).

First deformation event (D1)

The earliest recognisable structures (D1) includebedding-parallel foliation, tight to isoclinal folds,and faults. They are typically recognised in areaswhere they are at high angles (e.g. east-northeast-trending) to the regional north-northwest-trendingD2 structures, and are often overprinted by the latter.Elsewhere they are difficult to distinguish unlessoverprinting relationships are available.

Examples of regional D1 structures in the SIR

SAMUEL area include

(a) flattening of basalt pillows near the north shoreof Lake Miranda;

(b) east plunging isoclinal fold in chert about 13km NW of Perseverance (Liu et al. 1996, 1998);

(c) bedding-parallel foliation in shale in theOckerburry Hill area (Fig. 10);

(d) bedding-parallel S1 foliation and associatedtight to isoclinal D1 folds refolded by the D2

Lawlers Anticline (Platt et al. 1978); and,

(e) isoclinal fold refolded by the north-northwest-trending D2 antiform at Dingo Range (Fig. 7).

These D1 structures are similar to those reportedelsewhere in the northern Eastern Goldfields,including southwest of Melita (Witt 1994), andrecently recognised as D1 structures in the BenallaHill area (Stewart 1998).

Second deformation event (D2)

Regional east-northeast–west-southwest–directedorogenic shortening during D2 resulted in thedevelopment of prominent north-northwest-

trending folds, faults and greenstone belts. Somenorth-northeast-trending shear zones/faults may beearlier structures reactivated during D2. RegionalD2 folds have wavelengths of 5–30 km and areaccompanied by upright, axial planar foliation (S2).The steeply dipping S2 foliation is sometimesassociated with a steeply plunging L2 lineation(Chen et al. 2001).

The deformation intensity is heterogenousbecause of rock type differences and strainpartitioning. Overprinting relationships between D2

structures and D1 and/or D3 structures are locallypreserved. For example, near the north shore ofLake Miranda at the southeastern end of an island3 km south of Bellevue gold mine, pillows inmetabasalt were strongly flattened and aligned ina north-northeast direction (parallel to S1). Theflattened pillows were transected by a strong, north-trending and nearly vertical cleavage (S2), whichwas in turn overprinted by D3 upright folds and S3

spaced axial planar crenulation cleavage trendingabout 330º.

In some cases a steeply plunging lineation (L2)is developed, which is sometimes locallyoverprinted by a shallowly plunging L3 minerallineation, for example along the Ninnis Fault (Chenet al. 2001).

Regional D2 folds and associated S2 axial planarfoliation can be correlated across SIR SAMUEL, aswell as the entire north Eastern Goldfields Provincein terms of their style, scale, orientation, and timingof associated granitoid emplacement. Using D2

folds, and particularly S2 foliation, as referencestructures, earlier or later structures in differentareas can be identified, but with difficulties due tothe lack of overprinting relationships in some cases.Correlation of earlier and later structures indifferent areas may be problematic as it is notknown if they developed at the same times.

Some D2 faults and shear zones show evidenceof reverse movement, for example, along thePerseverance and Ninnis faults. Some dextralmovement observed along the north-northeastsector of the Ockerburry Fault Zone might haveoccurred during D2, which was responsible fordragging S1 foliation into the fault zone east of itssouthern termination.

The Jones Creek Conglomerate formed post-D1 and probably early syn-D2. The conglomerateswere deformed in late D2 and contain the regionalS2 foliation.

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Liu et al.

Third deformation event (D3)

D3 is a transpressional deformation event,apparently progressive from the orogeniccompression during D2. It resulted in thedevelopment of regional north- to northeast-trending folds, faults, and shear zones. Some north-to northeast-trending structures were initiated inD3, but others may be reoriented earlier structures(Chen et al. 2001). The north- to northeast-trendingD3 structures were predominantly situated in localcompressional areas, including

(a) within newly recognised compressional jogs(e.g. Yandal compressional jog) defined bynorth-northwest-trending, sinistral strike-slipfaults or shear zones (Chen 1998, Chen et al.2001), and

(b) wedge-shape areas defined by north- to north-northeast-trending and north-northwest-trending regional faults, e.g. in the area southof Mt Grey, and in the Melita area (Witt 1994,Liu & Chen 1998a).

Similar north- to northeast-trending structuresdeveloped in D3 are also reported in faulttermination areas of regional north-northwest-trending faults, e.g. in the Kilkenny area (Chen1998, Chen et al. 1998, 2001). In some cases the

upright foliation may be a composite S2–3 foliation,but locally preserved overprinting evidence (e.g.near north shore of Lake Miranda) suggests thatD3 was a separate deformation event.

The north-northeast-trending Ockerburry FaultZone merges with the north-northwest-trendingPerseverance and Ninnis Faults. East and west ofthe Ockerburry Fault Zone are several north- tonorth-northeast-trending faults, the currentgeometry of which were also shaped during D3.Several north-northeast-trending folds withwavelengths of 0.5–1 km east of the OckerburryFault Zone were probably developed during D3.The sigmoidal geometry of the Koonoonookamonzogranite between the Perseverance andGardiner faults and the Z-sigmoidal pattern of theseveral regional faults between the Perseveranceand Ninnis Faults were finally shaped by the D3

transpression.

Post-D3 deformation

Post-D3 structures are dominated by east-trendingnormal faults and fractures. Some of the faultsdisplace north-northwest- to north-northeast-trending D2 and D3 structures, greenstone belts andgold-bearing veins. Some structures are filled withmafic–ultramafic dykes of probable Proterozoicage. Kink folds and sub-horizontal crenulations that

Major features Metamorphism Comments

Post-D3 East-trending normal faulting and Some faults and fractures filled Small granitoid bodiesfracturing; with quartz veins and metasomatic intruded post-D3

Subhorizontal crenulations alteration involving growth ofamphibole

D3 Regional transpression resulted in Greenschist facies recrystallization Shaped crustal architectureN-, NNE- to NE- trending folds, mainly in shear zones, local of granite–greenstones;faults and shear zones predominantly retrogression 2640 ± 5 Mawithin local compressional areasdefined by NNW- trending sinistralstrike-slip regional faults

D2 Regional ENE-directed compression Peak metamorphism late during ENE-directed compressionproduced dominant NNW-trending or post-D2; produced much of thefolds, wide-spread axial planar Randomly oriented andalusite crustal architecture of thefoliation, and regional scale reverse porphyroblasts; granite–greenstones;faults associated with deposition Major regional greenschist Major phase of granitoidof polymictic conglomerates in facies, local amphibolite facies intrusion pre- to syn-D2;compressional basins, and 2660–2670 Maemplacement of granitoids

D1 Tight to isoclinal folds, bedding ? low- to medium grade regional Intrusion of granitoidssub-parallel foliations and faults, comagmatic to late stagescommonly recognised at high angles of felsic volcanism;to regional D2 NNW-trending structures ~ 2685 Ma

pre-D1 Deposition of main greenstone Volcanic-associated Nisuccession mineralization

Table 2. Structural and metamorphic history of the Archaean granite-greenstones on theSIR SAMUEL 1:250 000 sheet area

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post-date D3 structures occur in many locations.However, their relationship with the post-D3 faultsis not clear.

Metamorphism

There is evidence for three phases of regionalmetamorphism in the SIR SAMUEL area. The earliestrecognisable metamorphic event is that associatedwith the development of D1 fabrics (foliation andlineation). Evidence for this event is only locallypreserved, so it is not possible to estimate the extentof this event. The metamorphic grade during thisevent is in the range of greenschist to amphibolitefaces as deduced from the relict fabric in shalesand relict amphibole crystals of an early fabric thatwere overprinted by S2 foliation.

The most prominent metamorphic event is theregional metamorphism associated with D2

orogenic compression and emplacement ofvoluminous granitoids (mostly monzogranite). Thisis evident in the low- to medium-grade (greenschistto amphibolite facies) metamorphism in allgreenstones that accompanied the development ofcleavages (S2) axial planar to D2 folds and theschistose rocks along shear zones. Amphibolitefacies metamorphism is mostly restricted to near(up to 1–2 km) granite–greenstone contacts whereamphibolite commonly develops a foliation andmineral lineation. Further away from the contact,the metamorphic grade is commonly low grade, togreenschist facies assemblages.

Cordierite porphyroblasts and randomlyoriented andalusite porphyroblasts from north ofMount Goode suggest that the highest temperatures(peak metamorphism) were reached afterdevelopment of the prominent cleavage, some timeeither late during or after D2, but prior to D3. D3

caused some retrogression and the development ofstrong fabrics in regional-scale ductile faults suchas the Waroonga Shear Zone, Perseverance Faultand Mount McClure Fault.

Peak metamorphic conditions were about 550ºCand 3 kb in the Perseverance mine area (Gole et al.1987). Komatiites have been metamorphosed toolivine–tremolite–chlorite–cummingtoniteassemblages, with enstatite, anthophyllite, talc, andprograde antigorite in the more magnesian rocks,depending upon metamorphic fluid composition.Retrogression of metamorphic olivine to serpentineis common.

Regional metamorphism, particularly thatduring D2 orogenic compression, is largely acontact metamorphism on a regional scale, with

the highest metamorphic grade (amphibolite facies)almost always along granite–greenstoneboundaries. This suggests that granitic magmascontributed much to the heat budget of regionalmetamorphism in the region. Metamorphic eventsduring D1 and D3 may also be related to granitoidemplacement. The close association of regionalmetamorphism and granitoid emplacement isconsistent with the suggestion that granitoids werethe heat sources for regional metamorphism (Binnset al. 1976, Archibald et al. 1981, Hill & Campbell1993).

Proterozoic geologyProterozoic rocks, other than dykes, only crop outin the southwest part of the SIR SAMUEL area, i.e. inthe DEPOT SPRINGS sheet area. In the area northof the Langford Well, there are Proterozoic flat-lying polymictic conglomerate and arkosicsandstone and mudstone of the KaluweerieConglomerate (PKc and PKs). Some thin, linearmostly east-west features that cut across theregional geological trends in the aeromagnetic datahave been interpreted as Proterozoic mafic dykes(Pdy) because of their similarity to theaeromagnetic patterns of Proterozoic dykes in otherparts of the Eastern Goldfields. Although locallyexposed as ridges, such as in the granodiorite unitsouth of Daylight Well in the southeast corner ofSIR SAMUEL, the majority of dykes are covered bysurficial deposits. The dykes are mainly fine- tomedium-grained dolerite and gabbro, althoughrange in composition from pyroxenite, throughgabbro norite, to granophyre.

Present exposure of the KaluweerieConglomerate forms an east-trending belt 15 kmlong by 1.5 km wide, and is described in detail byAllchurch & Bunting (1976). The maximumexposed thickness is 25 m (Bunting & Williams1979), although in drillholes 10 km west ofKaluweerie Hill the conglomerate is 35 m thick.Two lithological units are mapped, polymicticconglomerate (PKc) and arkosic sandstone andmudstone (PKs). The conglomerate generally formsa lower unit, whereas the mudstone is dominant inthe upper unit. Important features are the highproportion of mechanically unstable clastic grains(e.g. carbonate, epidote, chlorite, amphibole, andfelsic lava) in the sand fraction, and the variety ofigneous and metamorphic rock types in theconglomerate. Bedding structures in both theconglomerate and mudstone are poorly developed.Allchurch & Bunting (1976) consider the sequenceto be locally derived from the west, possibly in a

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Liu et al.

partly confined channel or as a valley-fill deposit.

Palaeozoic geology

Permian sedimentary rocks(PAf, PAg, PAl)

Three areas of clastic sedimentary rocks interpretedas Permian in age occur on SIR SAMUEL: in the BarrSmith Range in the northwest, ~6 km northeast ofYandal in the central east, and in the area aroundOckerburry Hill in the southeast. These rocks havebeen correlated with the Paterson Formation of theOfficer Basin (MacLeod 1969, Lowry et al. 1972,Bunting & Williams 1979).

The most extensive exposures are aroundOckerburry Hill where a Permian sequence islocally well-exposed (Westaway & Wyche 1998).Away from the Ockerburry Hill, the Permian istypically represented by float of mainly granitoidboulders, which are probably erosional remnantsof a tillite unit. Recent mineral exploration drillingin the southwest suggests that there may be moreextensive Permian sequence under Cainozoic coverin the vicinity of the Ockerburry Fault.

Polymictic conglomerate (PAg) occurs mainlyas a boulder float on low, rounded hills. Clasts canbe more than a metre across, and are commonlyfaceted. Most are composed of granitoid andinclude foliated, massive, porphyritic and non-porphyritic varieties. Other clasts are composed offelsic and mafic volcanic rock, metasedimentaryrock including BIF and chert, and vein quartz. Theconglomerate appears to overlie a fine- to medium-grained, poorly sorted, medium-bedded, immature,quartz-rich sandstone but the relationship is notclear in outcrop (Westaway & Wyche 1998). Thereis a disconformity between the conglomerate andthe overlying, thinlybedded claystone and siltstoneunit. The poor sorting, faceting of the clasts, andwide variety of clast types, none of which are foundin outcrop in the surrounding region, suggest thatthe source for the conglomerate is remote and theconglomerate is probably a glacial deposit.

Claystone and siltstone (PAl) disconformablyoverlie the conglomerate and have been describedby MacLeod (1969). The succession consists ofthinly bedded to laminated siltstone overlain bywell-bedded sandy claystone, mudstone, andsiltstone. The total thickness is about 50 m. Anoutcrop 2.5 km east-southeast of Ockerburry Hill(AMG 116168) contains well-developed, ribbon-

like, sinuous trace fossils in bedding planes;scattered, monaxon-type sponge spifules; andfragments of an organism with regular rows of veryfine nodules (10 rows to 1 mm). These fragmentsmay represent decalcified moulds of a thin, sheet-like bryozoan. This fossil assemblage suggests thatthe rock is younger than early Ordovician, and isconsistent with a Permian age (Webby B.D., 1996,pers. comm., cited in Westaway & Wyche 1998).The lower part of this unit contains distinctive andspectacular Liesegang banding and is known as‘Weebo Stone’ (MacLeod 1969).

Loose, rounded cobbles of mainly undeformedfine- and coarse-grained granitoid, together withlesser amounts of vein quartz and metasedimentaryrocks overlie Archaean rocks 7–8 km north-northwest of Mount McClure (AMG 977466). Thecobbles range in size from 4 to 30 cm, but aregenerally 5–10 cm across. Some of the cobbles haveflat surfaces that have been interpreted as glacigenefacets. Bunting & Williams (1977, 1979) correlatedthese isolated sedimentary rocks and screeoutcrops, along with more substantial, essentiallyflat-lying, sequences elsewhere in the SIR SAMUEL

area, with Early Permian fluvioglacial rocks of thePaterson Formation of the Officer Basin.

Sandstone, pebbly to boulderly siltstone, andconglomerate (PAf), also of the Paterson Formation,occur in northwest on the YEELIRRIE 1:100 000sheet (Champion & Stewart 1998). These rockslargely comprise mostly strongly kaolinised, andlocally silicified, fine to granular quartz sandstones,with local quartz pebbles from 1 to 5 cm wide. Thesandstones are crudely horizontally laminated, andare mostly poorly sorted, becoming better sortedhigher in the sequence. Grains are sub-angular tosub-rounded. Beds non-conformably overlieArchaean granitoids, with irregular contacts andinfilling of original granitoid topography. Thesandstones generally form thin (1–5 m) sequencesthat are topographically expressed as flat,commonly treeless, ‘terraces’. These have beeninterpreted as Permian, although may, indeed, beyounger.

Cainozoic geologyThe SIR SAMUEL area is dominated by a relativelystable, ancient landscape, developed on deeplyweathered rocks, mostly Archaean. Consolidatedand unconsolidated Cainozoic regolith units arewidespread. Most of these units have beendeveloping since the Tertiary, and include a veneerof unconsolidated Quaternary material. The type

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of Cainozoic unit, including its distribution andthickness are closely related to the landform andthe source material. For example, ferruginous unitsare common in areas of greenstone. The Cainozoicunits in the SIR SAMUEL area can be broadlyclassified into four categories: residual, proximal,distal, and active alluvial systems.

Residual varieties developed on pre-existingweathered rock and include ferruginous lateriticduricrust (Czl), silica caprock developed overultramafic rocks (Czu) and silcrete over granitoid(Czz). Duricrust units over mafic greenstones (Czl)are commonly ferruginous with a reddish-brownto black colour, while those on granitoid (Czz) areusually silica-rich and paler in colour. The lattervaries substantially in thickness, often occurringwith kaolinised granitoid (Czzg).

Proximal units include colluvial depositsdeveloped on slopes and low hills and regionsaround these features. They include degradedlateritic duricrust and massive ironstone rubble(Czf) in iron-rich source areas; areas of deeplyweathered granitoid (Czg); quartz vein rubble anddebris (Czq); and colluvial deposits of gravel andsands as sheetwash and talus (Czc).

The more distal colluvial deposits containsignificant clay and fine sand and can formextensive sheetwash fans (Cza). Extensivesandplains (Czs) are dominated by unconsolidatedred, quartz-rich sand and typically overlie granitoidrocks. Where dunes are present, they are stable andwell vegetated with spinifex and a variety of smalltrees and shrubs. A degraded duricrust surfaceformed on deeply weathered granitoid rocks hasbeen observed beneath the sandplain in severalareas, e.g. at Leinster townsite.

Deposits of saline and gypsiferous evaporites,clay and sand (Czp) occur in Lake Miranda andLake Darlot. Sand, silt, clay and gypsum (Czd) formstabilised dunes in and around the lakes. Calcrete(Czk) crops out around Lake Miranda, in the lakesystem southeast of Yeelirrie, and in the northeastpart of Lake Darlot in the SIR SAMUEL area. It alsodeveloped in the alluvial valley east of LakeMiranda, and in the broad drainage valley south ofMount McClure. Silt, sand and gravel in halophyteflats adjacent to playas (Czh) are mapped in LakeMaitland in the northwest. Kopi (Czy) – lithifiedgypsum and clay in mounds and dunes – aremapped in the lake area northeast of Yakabindie. Alarge area of sand plain (Czsv) occupies an alluvialvalley adjacent to and east of Lake Miranda. Thismaterial and the associated lake deposits define thechannel of the Carey Palaeoriver (Hocking &

Cockbain 1990).

The drainage basin associated with the Darlotlake system contains areas of calcrete (Czk), andeolian and alluvial sheets and dunes made up ofsand, silt, and clay (Czb). These deposits are cutby both ancient and present drainage channelsresulting in a strongly reticulated land surface,leaving a series of mounds, typically only a fewmetres high, covered in dense vegetation. Theseremnant mounds produce a distinctive pattern thatis clearly visible on aerial photographs and satelliteimages. This pattern has a west-northwesterlytrend, and is most evident in the area south of LakeDarlot. Scattered throughout the Czb units arenumerous small claypans of which only the largerbodies have been delineated.

Alluvial deposits (Qa) occur along active fluvialchannels and on floodplains. Small claypans (Qac)may be part of the active system.

Economic geologySIR SAMUEL is a major mining centre in thenortheastern Yilgarn Craton. Resources in the areainclude nickel, gold, silver, copper, corundum, andtin (Table 3). Gold and nickel are the major miningactivities in the area, principally from severalmining centres: gold – Bronzewing, MountMcClure, Darlot–Centenary, Bellevue, NewHolland–Genesis; nickel – Mount Keith, Leinster(includes Perseverance and Rocky’s Reward) andCosmos. Several uranium prospects associated withvalley-fill sediments of the palaeodrainage systemare reported on SIR SAMUEL. Minor base metalprospects have been identified in the Agnew–Wiluna greenstone belt.

Gold

Gold has been mined from the SIR SAMUEL areasince the 1890’s from centres within the Agnewand Mount Keith–Perseverance greenstone beltsand, more recently, from the Yandal greenstone belt,e.g. Bronzewing, Mount McClure and Darlot–Centenary. The combined identified resources atpublication date are estimated at about 400 t of gold(GA’s OZMIN database, Table 3).

Prior to the late 1980s, the Yandal greenstonebelt was largely neglected for gold explorationprobably due to the limited exposure and poorunderstanding of the geology of the belt. In 1986,Minsaco Resources recognised the Yandal belt tobe closely akin to gold-prospective greenstone belts

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elsewhere in the Eastern Goldfields Province. Inthe following few years, there was acceleratedexploration in the Yandal belt, resulting in thediscovery of several major gold deposits includingJundee–Nimary, Bronzewing, the Mount McCluredeposits (including Lotus, Cockburn, Success,Parmelia, Challenger, and Dragon), and Centenary.

All greenstone sequences host goldmineralisation, with only minor gold reported fromthe granitoid-gneiss domains between thegreenstone belts. Gold is found in a range of hostrocks, including Fe-rich tholeiitic basalt,differentiated dolerite, metasedimentary rocks andconglomerate, and felsic porphyry dykes. Goldmineralisation is structurally controlled andprobably introduced late in the evolution of theArchaean granite–greenstone terrains (Phillips etal. 1998b, Vearncombe 1998, Phillips & Anand2000). The majority of deposits show similarfeatures to gold deposits elsewhere in the EasternGoldfields Province and have collectively beendescribed as ‘late-orogenic structurally controlled’(Witt & Vanderhor 1998) or ‘orogenic’ (Groves etal. 1998) gold deposits. Many of the deposits haveexploitable lateritic gold mineralisation in regolithabove primary mineralisation (e.g. Bronzewing).The discovery of some deposits, particularly in theYandal greenstone belt, is largely the result ofadvances in remote sensing and regolith samplingand analysis (Phillips & Anand 2000). Placer gold

deposits are rare on SIR SAMUEL and, whererecognised, are closely associated with knownlateritic or primary mineralisation.

Bronzewing gold deposits

The Bronzewing gold deposits occur west of thenorth-northwest-trending Bronzewing antiform(Fig. 6), were discovered by RAB drilling in 1992and include three zones: Western, Central andDiscovery (Phillips et al. 1998a). Locally thedeposits lie several hundred metres southwest ofthe Bronzewing komatiite-defined, north trendingHook antiform. Structurally, the deposits are innorth- or north-northeast-trending shear zones. TheWestern zone is in a north-northeast-trending shearzone just west of the Bapinmarra dolerite sill. TheCentral and Discovery zones are within 100–300m east of the sill in north-trending shear zoneslinked by subsidiary shears. Locally, however,anastomosing pattern of shear zones resulted inintra-shear pods of less deformed rocks. Greenstonein the mine area is dominated by west-youngingtholeiitic basalt with sporadic pillow structures andthin sills (Phillips et al. 1998a). In the Bronzewingarea, the mineral assemblage (i.e. actinolite–plagioclase) indicates peak metamorphicconditions below the amphibolite–greenschistfacies boundary.

A broad, well-defined, alteration halo surrounds

Deposit 1:100k Easting Northing Status Production to Remaining resource Grade Totalsheet (t) (t) (g/t***) (t)

Bellevue Au 3042 258 900 6940 200 Closed 25.360 Mar 1997 25.360Bronzewing Au 3143 302 300 6969 000 Operating 27.149 Dec 1998 23 280 000 3.9 117.941Centenary Au 3142 330 500 6923 100 Operating 8 400 000 7.7 64.680Cosmos Co 3042 260 500 6944 500 Deposit 401 000 measured .12% 480Cosmos Cu 3042 260 500 6944 500 Deposit 401 000 measured .36% 14440Cosmos Ni 3042 260 500 6944 500 Deposit 401 000 measured 8.2% 32880Darlot Au 3142 329 400 6914 000 Operating 18.546 Dec 1998 11 852 000 combined 4.56 72.591Genesis Au 2942 253 700 6902 400 Closed 1.358 Jan 1998 668 000 measured 2.6 3.095

& indicatedLake Maitland U 3143 310 100 6993 700 Deposit 11 600 000 estimated .05% 5800Leinster* Ni 3042 273 800 6920 600 Operating 327791 Dec 1998 246 300 000 measured, .73% 2125781

indicated& inferred

Mt Keith Ni 3043 256 700 6985 600 Operating 147094 Dec 1998 516 800 000 combined .56% 3041174Mt McClure** Au 3043 295 100 6965 400 Operating 18.682 Dec 1998 17 138 000 combined 1.84 50.216NewHolland Au 2942 253 700 6901 700 Closed 3.116 Jan 1997 8 454 400 measured 7.12 63.311

& indicatedYakabindie Ni 3043 260 300 6963 800 Deposit 214 700 000 measured .51% 1094970

& indicatedYellow Aster Au 3042 259 800 6954 500 Closed 1.700 Jan 1997 1.700

NOTES: * Leinster includes Perseverance & Rocky’s Reward Ni mines; ** Mt McClure includes Lotus, Cockburn, Success, Permelia,Challenger & Dragon Au deposits; *** Grade unit is g/t unless indicated otherwise

Table 3. Mineral commodity statistics for the SIR SAMUEL 1:250 000 sheet area (from GA’s OZMINdatabase as of April 2000)

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the Bronzewing gold deposit (Phillips et al. 1998a).Unaltered rocks have an actinolite–plagioclaseassemblage. The halo comprises an outer zone ofchlorite–calcite alteration, followed inwards by azone of ankerite–biotite alteration and a zone ofmuscovite–pyrite alteration proximal tomineralisation. Gold occurs in quartz veins in maficschist where the shear zones converge and diverge(Phillips et al. 1998a).

There appear to be multiple phases of goldmineralisation at Bronzewing. Isoclinal folding ofthe mineralised quartz vein of the Western zonesuggests ductile deformation after mineralisation.However, Phillips et al. (1998a) consider that themajor mineralisation in the Bronzewing area issuperimposed upon north-trending ductile shearzones. Orebody outlines and boundaries areinfluenced by brittle northeast- andeast-southeast-trending cross faults and fractures.

Mount McClure gold mining centre

The Mount McClure mining centre consists of sixdeposits localised along a zone of about 25 km,i.e. Lotus and Cockburn localised along a faultpassing north of Anxiety Bore, and Success,Parmelia, Challenger, and Dragon localised westof the Mount McClure Fault. The deposits werediscovered between 1987 and 1990, withproduction from 1992 to 2001. The geology of thesedeposits is summarised in Otterman & Miguel(1995) and Harris (1998).

Lotus and Cockburn deposits occur along amajor north-northwest-trending shear zone, theLotus Fault (Liu et al. 2000a). The fault consists ofseveral step-over faults that tend to follow particularrock units and contacts. The greenstone sequencecomprises an overturned, east-younging,metamorphosed rock package from basalultramafic rocks, through tholeiitic basalt andbasaltic tuff, to andesitic and dacitic tuff and lava.These rocks are interbedded with sulphidic chertytuff and some clastic sedimentary units (Harris1998).

Gold mineralisation occurs in a variety of rocktypes in the Lotus and Cockburn deposits. In thesouthwest part of the Cockburn deposit, higher-grade gold mineralisation is associated with amassive sulphide-chert horizon and withinmetakomatiite. In the northeastern part ofCockburn, however, significant gold mineralisationis found in metamorphosed dolerite and felsicrocks. At Lotus, gold mineralisation is hosted bydolerite, mafic and felsic volcanic rocks. Goldoccurs in quartz–carbonate–chlorite veins, which

are commonly tightly folded but sub-parallel tofoliation. At Cockburn, however, gold is associatedwith a stockwork of irregular quartz–carbonate ±chlorite veins. Bismuth minerals, galena,molybdenite, and scheelite occur in the veins withhighest gold grades. Pervasive chlorite–biotite–carbonate alteration is common in stronglymineralisation zones. At both Lotus and Cockburn,zones of epidote veins, accompanied by pervasivehematite alteration, occur in all rock types and areinterpreted to be unrelated to gold mineralisation.Late-stage quartz–calcite–chlorite–sulphide veinsare associated with strong carbonate–chloritealteration.

The other four deposits (Success, Parmelia,Challenger, and Dragon) lie about 2–3 km east ofthe Mount McClure Fault. Success, Parmelia andChallenger are at the same stratigraphic horizon ofstrongly foliated, weakly- to moderately-graphiticfelsic cherty tuff, which is overlain by a foliated,fine-grained, chloritic metasedimentary rocks(Harris 1998). Metabasalt units and thinmetadolerite intrusions are also present. Thefootwall is a strongly foliated, metamorphoseddacitic felsic volcanic/volcaniclastic rock. Goldmineralisation is associated with numerous quartz(with minor carbonate–chlorite) veins to 10 cmthick, sub-parallel to the foliation. The veins arecommonly boudinaged and/or folded.Disseminated pyrite–arsenopyrite (<10%) and traceto minor chalcopyrite–sphalerite are associatedwith the mineralisation zone, which showsmoderate to strong biotite–chlorite–carbonate–sericite metasomatic alteration.

The Dragon deposit is hosted by rocks slightlyhigher in the east-facing stratigraphic succession(Harris 1998). Upper greenschist to amphibolitefacies metamorphism and strongly developedfoliation have largely destroyed the primary rocktextures. The structurally and inferred stratigraphicfootwall unit is a tholeiitic basalt. Breccias andcarbonate alteration are common in the southernpart of the deposit. In the north of the deposit, thebasalt unit has been mylonitised, then annealed toform a crudely laminated, coarse-grained rock withabundant diopside. Overlying the footwall unit isa coarse-grained, ultramafic schist (interleaved withbands of graphitic schist) comprising talc, chlorite,carbonate, anthophyllite and phlogopite, to 25 mthick, that is the main host for gold mineralisation.The hangingwall sequence comprises basalt anddolerite. Gold mineralisation is mainly confinedto the lower half of the ultramafic unit, includingits graphitic zones, and associated with thin quartzveins, generally sub-parallel to the foliation, with

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minor to 5% disseminated pyrite and arsenopyrite.Prominent north-striking white quartz veins, whichdo not contain significant gold values, cut themineralised zone.

Darlot–Centenary mining centre

In the Darlot district, gold mineralisation was firstmined in 1894 and included quartz veins, placersand alluvials (Bunting & Williams 1976). Historicalrecords indicate that between 1894 and 1910, thearea was one of the richest alluvial goldfields inthe Yilgarn. Recorded historical production from1898 to 1913 of approximately 30 000 t at 15.8 g/t gold was from high-grade, quartz vein-hosteddeposits; alluvial production is unknown (Bucknell,1997). Modern exploration began in the area in theearly 1980’s, with open pit mining commencing atDarlot in 1988, and underground mining in 1995.The Centenary deposit was discovered 1.2 km eastof Darlot mine in 1996, and underground miningcommenced in 1998. The geology of the depositsis summarised by Bucknell (1997) and Krcmarovet al. (2000).

The Darlot–Centenary area is part of the easternDarlot domain in the southern Yandal greenstonebelt (Krcmarov et al. 2000). Stratigraphy comprisesa lower basaltic package with minor interflowmetasedimentary units, overlain bymetamorphosed intermediate to felsic volcanic andmetasedimentary rocks. A series of dolerite sillsand dyke-like bodies intrude the sequence. The areais characterised by early thrust repetition of thestratigraphy, subsequent north- the north-northwest-trending folds and later shearing alongnorth-northwest to northwest-trending faults. East-west and northeast-trending faults crosscut thedominant north-northwest fabric and, in places,younger intermediate dykes and lamprophyresintrude along these faults (Krcmarov et al. 2000).All rocks were metamorphosed to greenschistfacies assemblages.

The Darlot–Centenary deposit is localised in themoderately dipping western limb of the shallowlynorth-northwest plunging, Darlot syncline. Goldmineralisation is contained in late-tectonic, brittle-to brittle-ductile structures in two sub-parallelsystems – the Darlot and Centenary orebodies(Krcmarov et al. 2000). The Darlot orebody ishosed in mafic and felsic volcanic rocks, whereasCentenary is hosted by the 600 m thick,differentiated Mount Pickering dolerite sill. TheDarlot orebody consists of laminar, sheeted quartzveins and en echelon arrays of shallowly southwest-dipping quartz veins, and the Centenary orebodyis an en echelon array of shallowly west-southwest-

dipping quartz veins. In both orebodies, goldmineralisation occurs in 1–3 m thick, albite–ankerite–sericite–pyrite alteration selvedges aroundquartz–carbonate–chlorite–sulphide (pyrite–pyrrhotite–galena) veins, as well as sited withinthe veins.

Bellevue gold deposit

The Bellevue gold deposit, situated in theYakabindie domain of the Agnew–Wilunagreenstone belt, commenced as an undergroundmining operation in 1987 after some shallow opencut mining (Brotherton & Wilson 1990). It issituated towards the southern end of the MountGoode Basalt, west of the Miranda Fault-boundedJones Creek Conglomerate unit. Tholeiiticmetasbasalts, in part plagioclase-phyric, of theMount Goode Basalt is the host to goldmineralisation. Gold mineralisation occurs in north-to northwest-trending, west-dipping, shear zonesand associated quartz veins and breccias. Gold isassociated with massive and disseminatedsulphides, principally pyrrhotite with minor pyriteand chalcopyrite. Free gold is rarely observed.Sulphides occur in both quartz breccias andsurrounding mylonitic metabasalt. In the lattersituation the sulphides are associated with the shearfoliation, or disseminated within the matrix. Thinquartz veins are present within the shear zones.

New Holland and Genesis gold deposits

The New Holland and Genesis deposits arelocalised in the Scotty Creek conglomerate in theAgnew domain of the Agnew–Wiluna greenstonebelt. Gold was discovered in 1894 in the Agnewarea, with historic production from the NewHolland deposit from 1989 to 1946. Explorationin the late 1980s and early 1990s led to discoveryof Genesis deposit and additional resources in theHew Holland area (Inwood, 1998). Goldproduction from the Genesis, New Holland andNew Holland South ore bodies is from acombination of open pit and undergroundsmethods.

The Scotty Creek conglomerate is a 1500 mthick sequence that trends north to north-northwestand contains bedding that dips steeply and faceswest. The conglomerate comprises of fine- tocoarse-grained sedimentary rocks, metamorphosedto greenschist facies assemblages, and displayscyclic graded beds from very coarse grained pebblysandstones and conglomerates, through fine- tomedium-grained sandstones to fine-grainedsandstones and siltstones (Inwood 1998). Clasts

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range from predominantly ultramafic-derived in thebasal part of the conglomerate to arkose andgranitoid-clast conglomerate. Mineralisation in theNew Holland and Genesis deposits is hosted bymedium- to coarse-grained sandstone unitscomposed of detrital quartz, feldspar and minorpebbles of granitoid, with little or subeconomicmineralisation in finer-grained units.

Gold mineralisation is closely associated withquartz veining in the medium- to coarse-grainedsandstone units. Mineralisation is associated withhigh-grade, shallow northeast-dipping quartz veinsand low-grade, steeply south-dipping veins(Inwood 1998). High-grade, shallow northeast-dipping quartz veins are grouped into two vein-sets: quartz–calcite and feldspar–quartz veins(D’Ercole 1992). Quartz–calcite veins comprise ofquartz, calcite and biotite with minor microcline,albite, arsenopyrite and chlorite. Quartz forms>60% of the veins. Feldspar–quartz veins comprisemicrocline, quartz, albite and minor biotite,arsenopyrite and chlorite, with feldspar formingover 50%. High-grade quartz veins at New Hollandcontain up to 3% galena. The steeply south-dippingveins at Genesis are characterised by a lack ofarsenopyrite and lower gold grades (Inwood 1998).

Wallrock alteration associated with the twotypes of mineralisation at New Holland and Genesisis poorly developed. Biotite, quartz, calcite andarsenpyrite are characteristic alteration minerals,with muscovite and chlorite associated in zones ofhigh-grade, sheared quartz veins at New Hollandand strong shearing and lower grades at Genesis(D’Ercole 1992, Inwood 1998).

Nickel

Nickel sulphide mineralisation in the SIR SAMUEL

area is restricted to ultramafic rocks in the Agnew–Wiluna greenstone belt. Mineral exploration hasresulted in many significant nickel deposits,including Six Mile Well at Yakabindie and Cosmos,as well as the currently exploited Mouth Keithdeposit in the north of the SIR SAMUEL area, and thePerseverance and Rocky’s Reward deposits atLeinster.

Hill et al. (1996) described two types of nickelmineralisation. Type I deposits comprise orebodiesof massive and/or matrix sulphide ore hosted bykomatiite, and include Perseverance and Rocky’sReward. Matrix ore refers to ore with olivinecrystals in a continuous matrix of sulphide. Nickelgrade is generally higher (2–20% Ni) in massivesulphide ore, with matrix ore containing about 1–5% Ni (average 2.3%). Type II deposits are larger,

lower grade orebodies comprising accumulationsof disseminated sulphide in the central zone of largeolivine cumulate bodies, and include Mount Keithand the Six Mile Well prospect at Yakabindie.Sulphide is fine-grained and grades are generally<1% Ni and consistently average 0.6% Ni.

Mount Keith nickel deposit

The Mount Keith nickel deposit is a large tonnage,low grade (0.5–1.5% Ni) disseminated nickelsulphide deposit hosted by layered adcumulate–mesocumulate ultramafic body. Mount Keith wasdiscovered in 1968, and openpit mining began in1994. Mineralisation extends for over 2 km alongstrike and continues to a depth of at least 500 m,and contains in excess of 450 Mt of ore at a gradeof 0.60% Ni (Hopf & Head 1998). The deposit wasdescribed in detail by Burt & Sheppy (1975),Marston (1984), Dowling & Hill (1993) and Hopf& Head (1998).

The mineralisation occurs in the easternmostof three komatiite units, the Eastern ultramafic unitof Dowling & Hill (1990), in an overall west-facinggreenstone sequence, which was metamorphosedto mid-greenschist facies. The host komatiite unithas a minimum thickness of about 650 m and iscompletely serpentinised. The unit can be dividedinto three lithologically distinct zones: (1) a basalolivine orthocumulate; (2) a central zone ofunmineralised, coarse-grained olivine adcumulatewhich grades upwards to a layered olivine-sulphideadcumulate–mesocumulate which hosts the MountKeith orebody; and (3) an upper orthocumulatewhich contains zones of differentiated gabbroicrocks (Hopf & Head 1998).

There are two distinct nickel-bearingassemblages: (a) pentlandite–pyrrhotite ±magnetite, and (b) pentlandite–millerite ±heazlewoodite ± magnetite. The pentlandite–pyrrhotite ± magnetite assemblage is dominant andrepresents the primary magmatic assemblage.Primary nickel-bearing sulphides occur in lobateaggregates in the interstices between former olivinegrains (Hopf & Head 1998).

At Mount Keith, nickel mineralisation isinterpreted to have developed within a large activekomatiite lava channel (Dowling & Hill 1990, Hillet al. 1996). The nickel ore formed whencrystallisation of olivine led to sulphur saturationin the melt and exsolution of sulphide melt. A largeproportion of total nickel may have been originallycontained in igneous olivine. Subsequent reactionsinvolving olivine after initial crystallisation isconsidered to be an important factor in upgrading

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the nickel content of ore. Further enrichment ofnickel occurred during serpentinisation andcarbonation during which nickel was released fromolivine (Hopf & Head 1998).

Perseverance and Rocky’s Reward nickeldeposits

The Perseverance deposit (formerly Agnewdeposit) is the world’s largest Type I nickel deposit,as well as the largest known occurrence in theYilgarn Craton where significant volumes of bothhigh-grade Type I (massive and disseminated) andlow-grade Type II (weakly disseminated) nickelsulphide mineralisation coexist (Hill et al. 1996,Libby et al. 1998). The deposit was discovered in1971 and underground mining commenced in 1976.The Rocky’s Reward deposit is located 2 km northof Perseverance and was discovered in 1984 (De-Vitry et al. 1998). Production at these deposits toJune 1996 yielded 13.8 Mt of ore at a grade of2.27% Ni, and Proved and Probable Reserves areover 37 Mt at a grade of 1.75% Ni (De-Vitry et al.1998, Libby et al. 1998). The deposits have beendescribed by Martin & Allchurch (1975), Marston(1984), Barnes et al. (1988b), De-Vitry et al. (1998)and Libby et al. (1998).

The greenstone sequence in the Perseverance–Rocky’s Reward area includes komatiite, high–Mgbasalt and felsic volcanic/volcaniclastic rocks, allmetamorphosed to amphibolite facies. Thesequence is overall east-younging, although localwest-facing indicators are recorded (Libby et al.1998).

A prominent geological feature in thePerseverance area is the Perseverance ultramaficcomplex west of the Perseverance Fault. Thecomplex is a zone of thickening in the regionallyextensive ultramafic horizon and consists of a thickaccummulation of olivine-rich ultramafic rocks(mesocumulate to adcumulate), flanked byorthocumulate-dominant, spinifex-texturedkomatiite. The complex is 700 m thick (east–west),2 km north-south, and at least 1100 m and probablymuch more in vertical extent (Barnes et al. 1988a).

The Perseverance orebody is at a perturbationin the western contact of the ultramafic complexin an area that has undergone significant structuralmodification (Libby et al. 1998). The orebody is azone of high-grade massive and disseminatedmineralisation situated within an extensive sheetof weakly disseminated mineralisation. The sheetof weak mineralisation is confined to thestratigraphic base of the ultramafic complex. ThePerseverance deposit occupies a structurally

complex position within the weakly mineralisedsheet, in which deformation has resulted in foldingof the orebody, remobilisation of mineralisationinto fault bounded lodes and fold hinges anddismemberment of the main disseminatedmineralisation. Within the mine environment, thedisseminated mineralisation forms a distinct shootthat plunges 70º to the south. In contrast, themassive sulphide mineralisation occurs in a seriesof individual, fault-bounded sheets that generallydip steeply to the west and strike north (Libby etal. 1998). The ultramafic body hosting the Rocky’sReward massive sulphide ore is correlated with andinterpreted to be tectonic slice of that atPerseverance (De-Vitry et al. 1998). Sulphideminerals at Perseverance and Rocky’s Rewardinclude pyrrhotite, pentlandite, minor chalcopyriteand pyrite, and trace gersdorffite. Pentlandite andpyrite increase in relative abundance in thedisseminated ores (Barnes et al. 1988a).

The thick Perseverance ultramafic complex isinterpreted as the product of a large komatiite lavachannel complex, and important for the formationof massive sulphide ores (Barnes et al. 1988b) in asimilar way to that at Kambalda (Groves et al.1986). Ore grade mineralisation formed during thesame volcaninc event as the sheet of weaklydisseminated mineralisation (Libby et al. 1998),with the orebody representing a subchannel lavachannel complex. Variations in the primary rocktypes of the ultramafic complex are interpreted toreflect changes in the processes and conditionswithin the channel during lava flow (Libby et al.1998). Subsequent deformation resulted in faulting,folding and imbrication of the orebody andremobilisation of massive sulphide mineralisation,including tectonic displacement of a large fragmentof the orebody to form the Rocky’s Reward deposit.

Copper

Some 420 t of copper was mined from the KathleenValley area between 1909 and 1967 (Liu et al.1998). The copper mineralisation, commonly withgold and silver, is in pyrite–chalcopyrite–quartzveins within mafic hosts spatially related to north-northwest-trending shear zones in Kathleen ValleyGabbro and Mount Goode Basalt (Bunting &Williams 1979). Copper also occurs in the MountKeith nickel deposit, but has not been exploited.

Corundum

Corundum has been mined from aluminousmetasedimentary rocks interlayered with maficrocks at AMG 586571 (Carter 1976). The mine

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produced 55 t of ore in 1952 (only recordedproduction).

Tin

Two minor occurrences of tin were noted byBunting & Williams (1979). A cassiterite-bearinglepidolite–albite pegmatite 3 km south-southwestof Kathleen Valley and another small deposit 400m southwest of the Sir Samuel townsite wereworked between 1945 and 1953 and produced 8 tof ore containing 0.2 t of tin.

Uranium

Several calcrete-hosted uranium prospectslocalised in palaeodrainage systems are present onSIR SAMUEL. The Lake Maitland deposit, locatedon WANGGANNOO, contains over 11 Mt at agrade of 0.05% U and has been described byLorimer (1973) and Bunting & Williams (1979).The Yeelirrie deposit, just west of the SIR SAMUEL

area, has been described by Dall’Aglio et al. (1974),Langford (1974), Mann (1974) and Bunting &Williams (1979), and contains an estimated 30 Mtof ore at an average grade of 0.15% (46 kt of U3O8).

AcknowledgmentsThis work benefited greatly from numerous discussionswith GA–GSWA geologists in the Eastern GoldfieldsNGMA project and exploration geologists, particularlyShe Fa Chen, Alastair Stewart, Terry Farrell, Tim Griffin,Steve Wyche, Jane Westaway, Patrick Lyons, MartinGole, Neil Phillips and Kevin Tomlinson. AlastairStewart, Patrick Lyons, Alan Whitaker and Steve Wychereviewed and improved the manuscript.

Dominion Mining are thanked for permission to use theYakabindie Homestead as a base for field work in theYakabindie–Perseverance area and Aaron Sedgmen forhis assistance during field work in 1997. WMCResources Ltd allowed access to their 1:10 000 scalegeological maps of part of the Perseverance–MountKeith greenstone belt. David Milton of DominionMining; Peter Langworthy, David Sharp and John Libbyof WMC; Kevin Shugg of the Bellevue Gold Project;Jeff Harris and the other Arimco Mining Pty Ltdgeologists at the Mount McClure gold mine; geologistsof Plutonic Resources Ltd at the Darlot gold mine; andexploration staff of Dominion Mining Ltd are thankedfor their time, support and discussions at various stagesof this mapping project. Lana Murray is thanked fordrafting the figures.

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Locality AMG (E) AMG (N) Locality AMG (E) AMG (N)

Albion Downs 241 700 6978 700 Mount Grey 317 700 6966 400Alf Well 297 900 6981 000 Mount Harold 346 900 6968 700Barr Smith Range northwest Mount Joel 306 500 6987 100Barwidgee 293 800 7008 000 Mount Keith 256 300 6991 900Beale Well 291 800 6974 200 Mount Keith Ni mine 256 700 6985 600Bellevue Au mine 258 900 6940 200 Mount Mann 258 300 6958 000Bogada Bore 296 800 6928 200 Mount McClure 301 600 6939 900Boundary Well 306 500 6927 400 Mount McClure office 295 100 6965 400Bronzewing Au mine 302 300 6969 000 Mount Mundy 347 400 6955 900Centenary Au mine 330 500 6923 100 Mount Pasco 264 100 6960 400Challenger Au mine 299 300 6949 200 Mount Roberts 265 400 6915 300Charlie Well 253 300 7006 600 Mount Sir Samuel 268 000 6932 300Chooweelarra Rock 273 300 6951 200 Mount White 261 300 6914 400Cockburn Au mine 296 200 6965 100 New Holland Au mine 253 700 6901 700Cork Tree Flat Well 242 200 7009 300 Ninnis Well 324 700 6948 000Cosmos Ni deposit 260 500 6944 500 Ockerburry Hill 309 800 6917 700Darlot Au mine 329 400 6914 000 Old Brilliant Well 270 800 6906 600Dayling Well 340 200 6912 800 Overland Well 311 900 6912 100Desperation Well 305 200 6946 500 Parmelia Au mine 297 400 6952 800Dragon Au mine 302 700 6942 600 Paul Well 306 200 6941 300Dingo Range northeast Perseverance Ni mine 273 800 6920 600Express Bore 296 500 6972 800 Plonkys Well 263 500 6928 300Genesis Au mine 253 700 6902 400 Rocky’s Reward mine 273 000 6923 600Ginnabooka Well 298 600 6939 000 Rosewood Well 335 900 6917 600Kens Bore 306 900 6958 100 Satisfaction Bore 292 400 6955 100Hartwell Well 303 900 6918 400 Success Au mine 296 500 6954 800Hope Bore 315 700 6929 700 Six Mile Well 260 500 6963 400Kathleen 259 400 6954 500 Spring Well 318 800 6912 900Katherine Well 317 000 6941 400 Spinifex Well 303 000 6991 400Leinster 273 400 6909 700 Stirling Peaks eastLeinster Downs 264 200 6917 300 Top Mile Well 303 500 6990 200Letter Box Well 248 200 6999 500 Vivien Well 260 900 6903 100Lotus Au mine 295 300 6966 700 Wadarrah Rocks 335 100 6918 900McArthurs Bore 272 300 6928 800 Wonganoo 335 300 6996 900McDonough Lookout 265 200 6942 000 William Well 261 100 6944 900Meredith Well 265 300 6953 000 Woorana Soak 321 400 6957 400Melrose 333 100 6909 400 Yakabindie 256 200 6947 200Mica Mica Waterhole 318 000 6919 000 Yakabindie Ni deposit 260 300 6963 800Miranda Well 265 700 6934 200 Yandal 317 100 6949 800Mount Blackburn 335 400 6947 500 Yandal Lagoon 319 000 6936 500Mount Doolette 315 600 6916 200 Yandal Well 318 000 6936 500Mount Goode 260 000 6947 800 Yellow Aster 259 800 6954 500

Appendix

Gazetteer of localities on SIR SAMUEL

Geology of the Sir Samuel 1:250 000 sheet area, Western ... · PDF file1:250 000 sheet area,...

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