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Coolgardie - Kundana Goldfield - Geko, Greenfields, Tindals, Gibraltar, Bayleys, Three Mile Hill, Rubicon, Hornet, Pegasus, Raleigh
Western Australia, WA, Australia
Main commodities: Au

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The Coolgardie - Kundana Goldfield is located 35 km to the southwest of Kalgoorlie, Western Australia, some 560 km east of Perth.   It lies towards the western margin of the Kalgoorlie Terrane, the westernmost element of the Eastern Goldfields Supeterrane, of the Archaean Yilgarn Craton.   It include deposits such as Geko, Greenfields, Tindals, Gibraltar, Bullabulling, Bayleys, Three Mile Hill, Rubicon, Hornet, Pegasus and Raleigh that are distributed over a semi-circular arcuate, NW concave, area with a radius of ~25 km. Some authors (e.g., Lea, 1998) regard Kundana as part of the Coolgardie GoldField, while others (e.g., Cooke et al., 2017) suggest it is a separate goldfield. The western wing of the Coolgardie Goldfield that includes the Gibraltar and Bullabulling deposits, 25 km west of Coolgardie, has also been regarded as part of a separate Bullabulling Goldfield (e.g., Partington et al., 2017). A number of these deposits and more recent discoveries, are exploited by the Mungari mining operation via a central mill.

The Coolgardie Goldfield comprises an arcuate belt of mafic to ultramafic volcanic and intrusive rocks overlain by felsic volcanic and sedimentary rocks which have been metamorphosed to amphibolite facies and are bounded and intruded by granitoid bodies.   The greenstone belt sequence commences with 500 to 600 m of high-Mg basalt intruded by a 500 m thick Fe rich differentiated gabbro sill, and overlain by around 2000 m of massive spinifex textured mafic rocks with interflow black shales and cherts.   These are in turn overlain by 2500 m of felsic volcanics and volcaniclastics.   All of these rocks are cut by a series of felsic and mafic porphyries, with compositions including dacite, rhyolite to diorite, dolerite and hornblende lamprophyre.   Dating of correlates in the region suggest ages of between 2702± 4 Ma near the base to 2684 to 2673 Ma near the top of the sequence. This sequence belongs to the Kambalda and Kalgoorlie sequences as described in more detail in the Kalgoorlie and Yilgarn Craton records.

The greenstone belt rocks are intruded by a number of granitoid bodies which form composite batholiths and include monzogranites, tonalites, porphyritic granodiorites and granites with ages ranging from 2682 to 2702 Ma.

The majority of deposits in the goldfield appear to be zoned in relation to the contact of one of these granitoids, the Calooli Monzogranite.   Goldfield scale variations in the distribution and style of mineralisation, gangue and ore mineralogy, zoned wall rock alteration assemblages around the lodes and the ore geochemistry are all correlated with plan view distance from the contact between the greenstone hosts and the Calooli Monzogranite (Knight et al., 2000).

Gold deposits in the goldfield are hosted by all greenstone lithotypes and some granitoids, are spatially associated with sets of late structures and are of three types, namely:
i). replacement orebodies up to 10 to 15 m wide in ductile-brittle shear zones with disseminated mineralisation and associated quartz-amphibole-sulphide veinlets,
ii). shear zone hosted quartz (with sulphides and gangue silicates) reefs (with numerous parallel subsidiary quartz veinlets) in 10 to 15 m wide shears with strike lengths of up to 1 km and
iii). brittle vein sets (mainly quartz extension veins) within particular competent mafic rock units.

Gold was first discovered at Coolgardie in 1892.   Since then to 2000, some 75 tonnes of gold, plus 2 tonnes of silver, have been extracted from numerous, moderate tonnage, structurally controlled deposits within the goldfield. Including resources known in 2016 (but excluding Kundana, the total endowment of the goldfield is estimated to be ~140 t of contained gold (Goodz et al., 2017).

In 2019, the main remaining operation is the Kundana cluster of deposits that are ~22 km NNE of Coolgardie. Mineralisation is distributed over a NNW trending interval of ~10 km and includes from north to North Arctic, Millenium, Barker's North, Barker's/21 Mile, South/Centenary, Strzelecki, Pope John, Moonbeam, Raleigh, Pegasus, Rubicon, Kurrawang, Hornet, Frog's Leg and White Foil.
  Prospecting and small-scale mining in the area began in ~1895, with 30 small mining operations, which had virtually all ceased by 1897. Systematic modern exploration began in ~1987 and mining commenced in 1988 in the original Kundana South, Kundana North and Strzelecki open pits. Mineralisation was discovered along the K2 mineralised trend in 1999, including the separate deposits of Rubicon, Hornet and Pegasus. The Raleigh deposit, located 2 km to the NW on the Strzelecki trend in 2000. Open pit mining commenced at Rubicon and Raleigh in 2002. Underground production from Raleigh was began in 2006 and from Rubicon-Hornet in 2011 (Northern Star Resources website, 2019).

  The Kundana line of deposits is located in close proximity to the regional 150 km long Zuleika Shear Zone which separates the Ora Banda and Coolgardie domains of the Kalgoorlie Terrane. The structural disruption associated with the broader shear zone at Kundana is typically >1 km. Two successions, divided into the Coolgardie and Ora Banda sequences are recognised in the district, is as follows, from the base (Cooke et al., 2017):
Coolgardie Domain, west of the Zuleika Shear Zone,
Hampton Ultramafic - spinifex textured komatiitic flows;
High Magnesian Basalt - pillowed basalt;
Lower White Flag Formation - sandstone, siltstone and shale;
Powder Sill - differentiated mafic intrusion; Barker's, Strzelecki and White Foil are hosted within or on the contact of this sill;
Strzelecki Shear
White Flag Formation - intermediate volcaniclastic suite with coherent andesite and crystal tuff; Host to Raleigh;
Ora Banda Domain, east of the Zuleika Shear Zone,
Bent Tree Basalt - mafic pillowed basalt; The K2a mineralisation is within the Zuleika Shear at the base and the K2b mineralisation at the top of this unit;
Victorious Basalt - coarse plagioclase porphyritic basalt;
• The K2 Shear is transgressive from the base of the Centenary Shale to the base of the White Flag Formation and hosts the K2 and K2HW mineralisation;
Centenary Shale - carbonaceous pyritic shale;
White Flag Formation - intermediate volcaniclastic suite with andesitic crystal tuff and andesite;
Quartz Porphyry Intrusion - locally developed, hosting the Kurrawang mineralisation;
Gibson Honman Formation - felsic dacitic volcanic and sedimentary rocks;
Navajo Formation - quartz-rich crossbedded sandstone;
Kurrawang Formation - late clastic basin conglomerate and crossbedded sandstone.

  Numerous styles of gold mineralisation are evident in the field reflecting temporal, structural, lithological and geochemical influences. The bulk of the historic production and current resources are hosted by narrow crack-seal veins within structures at lithological contacts, particularly from the K2, Strzelecki and Barker's lines. Stockwork style brittle vein arrays are found in rheologically competent and structurally prepared rocks, the most notabel of which is the White Foil deposit which is hosted in the Powder Sill Gabbro (Cooke et al., 2017).
  The main K2 host structure at Rubicon, Hornet and Pegasus is a steeply west-dipping laminated shear vein that generally varies from 0.3 and 0.8 m in thickness. The ore zone is typically wider than the vein structure (up to 5 m) due to the presence of mineralised footwall stockwork veins and breccia zones. The vein typically contains coarse-grained disseminated galena, sphalerite, scheelite and gold (Northern Star Resources website, 2019). Gold mineralisation at the Raleigh deposit is associated with a steeply west-dipping laminated quartz vein system of the Strzelecki structure, developed at the contact between andesitic volcanics and a sedimentary unit in the immediate footwall of the thick, differentiated gabbroi Powder Sill. Vein infill mineralogy is similar to that described above for the K2 structure (Northern Star Resources website, 2019).

Four stages of alteration are recognised: i). Stage 1 - calcic or sodic; ii). Stage 2 - potassic-calcic-sodic that accompanied the mineralisation; followed by iii). Stages 3 and 4 - both of which were calcic. The calcic assemblages including calcic amphibole, calcite, plagioclase, clinozoisite, epidote and/or titanite; overprinted by early sodic albite alteration and during mineralisation by a pulse of potassic alteration, including K feldspar or biotite. Mineralisation has been protracted influenced by deformation, and is indicated to have involved at least four temporally distinct mineralising events during D4a to D5 ( Cooke et al., 2017; deformation stages as per Blewett et al., 2010).

Remaining Measured + Indicated + Inferred Mineral Resources at Kundana at 30 June 2016 were 32.23 Mt @ 4.28 g/t Au for 138 t of contained gold (Cooke et al., 2017).

For detail consult the reference(s) listed below.

The most recent source geological information used to prepare this decription was dated: 2017.     Record last updated: 5/9/2019
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd.   Unauthorised copying, reproduction, storage or dissemination prohibited.

  References & Additional Information
   Selected References:
Cooke, D.P., Ramsey, T., Miller, J.M. and Bath, A.B.,  2017 - Kundana goldfield: in Phillips, G.N., (Ed.), 2017 Australian Ore Deposits, The AusIMM, Melbourne,   Mono 32, pp. 199-205.
Hemming G R  1998 - Geko gold deposit: in Berkman D A, Mackenzie D H (Ed.s), 1998 Geology of Australian & Papua New Guinean Mineral Deposits The AusIMM, Melbourne   Mono 22 pp 211-214
Keele R A, Shelton M C  1990 - Greenfields Gold deposit, Coolgardie: in Hughes F E (Ed.), 1990 Geology of the Mineral Deposits of Australia & Papua New Guinea The AusIMM, Melbourne   Mono 14, v1 pp 463-466
Knight J T, Ridley J R, Groves D I  2000 - The Archean Amphibolite facies Coolgardie Goldfield, Yilgarn Craton, Western Australia: nature, controls, and Gold field-scale patterns of hydrothermal wall-rock alteration: in    Econ. Geol.   v95 pp 49-84
Lea J R  1998 - Kundana gold deposits: in Berkman D A, Mackenzie D H (Ed.s), 1998 Geology of Australian & Papua New Guinean Mineral Deposits The AusIMM, Melbourne   Mono 22 pp 207-210
McCormick C, Hanna J P  1990 - Tindals Gold deposits, Coolgardie: in Hughes F E (Ed.), 1990 Geology of the Mineral Deposits of Australia & Papua New Guinea The AusIMM, Melbourne   Mono 14, v1 pp 467-473
Middleton T W  1990 - Three Mile Hill Gold deposit, Coolgardie: in Hughes F E (Ed.), 1990 Geology of the Mineral Deposits of Australia & Papua New Guinea The AusIMM, Melbourne   Mono 14, v1 pp 459-462
Pyke D  1990 - Gibraltar Gold deposit: in Hughes F E (Ed.), 1990 Geology of the Mineral Deposits of Australia & Papua New Guinea The AusIMM, Melbourne   Mono 14, v1 pp 475-477
Swager N  1990 - Bayleys Gold deposit, Coolgardie: in Hughes F E (Ed.), 1990 Geology of the Mineral Deposits of Australia & Papua New Guinea The AusIMM, Melbourne   Mono 14, v1 pp 455-457

Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge.   It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published.   While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants:   i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and   ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.

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