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Bronzewing
Western Australia, WA, Australia
Main commodities: Au


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The Bronzewing Archaean gold deposit is located within the Yandal greenstone belt of the northern Yilgarn Craton, 400 km north of Kalgoorlie, Western Australia.

After a reconnaissance RAB drilling program that commenced in 1992, the deposit was discovered by Great Central Mines in the same year. Mining at Jundee commenced in November 1994 at the Laterite, Central and Discovery open pits. The Central pit became the access to the portal supporting underground mining from mid 1995. Between 1991 and 2004 the treatment plant at Bronzewing produced ~100 t of gold from eleven open cuts and two underground operations over an area extending some 30 km south of the Bronzewing mine. The mine was acquired by View Resources in 2004, and was initially placed under care and maintenance, before being re-opened in 2007. Ore was mined from two open pits, Success and Central, and two underground declines, Discovery and Calista. By 2008 gold recoveries were below expectations, the mine was closed, and View Resources went into liquidation.

The Yandal belt, which lies on the eastern margin of the northern Kalgoorlie Terrane, contains five significant gold deposits, all found within the 1990s. The sequence in the belt varies along strike, containing interlayered tholeiitic and high Mg basalts, Fe rich shales, ultramafic rocks and internal granites, with felsic rocks to the south and ironstones to the north. Major shear zones trend parallel to the greenstone belt for tens of kilometres, and there are cross faults at a high angle to the belt that persist across the greenstone belt and surrounding granite. Metamorphic grade is upper greenschist, with some amphibolite facies domains such as near Mt Joel 20 km NE.

Tholeiitic basalt is the main gold host rock for the Central and Discovery shoots at Bronzewing (Phillips et al, 1998). There is the differentiated Bapinmarra Dolerite sill and komatiite units in the mine area, but these are poorly mineralised. The basalt is relatively uniform in hand specimen but has been subdivided on the basis of higher Fe, Ti, Zr, Y and V, and lower Al, Mg, Ni and Cr in the east (Kohler et al, 2003). Gold-related hydrothermal alteration of the tholeiitic basalt forms an envelope up to 100 m wide around the Central and Discovery shoots. The regional metamorphic assemblage of actinolite and epidote is initially transformed to distal calcitechlorite assemblages, and then more proximal ankerite-mica

The main structure, which comprises anastomosing highly strained rocks enclosing lenses of lower strain material, is 100 to 500 m wide at Bronzewing.

Gold mineralisation at Bronzewing is contained within quartz veins and foliated basalt. The Central and Discovery shoots are major east–west elongated auriferous quartz vein systems of 100–200 m length in plan view, and continuous to 600 m depth (Kohler et al, 2003). The quartz veins contain albite, ankerite and minor pyrite and pyrrhotite; gold predominantly occurs within, and to a lesser degree is marginal to, the quartz veins.

Hydrothermal alteration related gold mineralisation within the tholeiitic basalt forms an envelope up to 100 m wide around the Central and Discovery shoots. The regional metamorphic assemblage of actinolite and epidote is initially transformed to distal calcitechlorite assemblages, and then more proximal ankerite-mica rocks that are commonly foliated. Ratios of muscovite to biotite and pyrite to pyrrhotite increase with depth.

Shear zones of several tens of metres width are a major feature of the Central and Discovery areas, trending approximately north-east, but with numerous interconnecting splays. Between the splays are boudins of low-strain dolerite and ultramafic rocks. Chlorite, actinolite and mica define the fabric in the mafic schists and talc in ultramafic rocks. A broad north-trending antiform that plunges south dictates rock unit distribution in the mine area. The minor Western Lode system is characterised by isoclinally folded quartz veins within a shear zone. Later NE-trending cross faults are an important influence on gold distribution.

Alteration associated with gold mineralisation includes calcite and ankerite in mafic rocks, and talc with dolomite-magnesite in ultramafic lithologies. Gold is hosted in 1 to 2 m thick laminated quartz veins and stockwork quartz veins and altered basalt wallrock, with the better grade in the veins. Pyrite is the predominant sulphide.

The orebodies are covered by up to 50 m of young transported material and a thick lateritic profile. Economic grades of gold were associated with ferruginous pisolites in the lateritic profile and were exploited early in the mine life, although not a major contributor to overall production. Their main contribution has been as an exploration indicator.

The total resource in 1996 was 38.3 Mt @ 2.9 g/t Au, with total production to that date having been 12.6 Mt.

The approximate endowment of Bronzewing is 150 t of contained gold (Phillips in Porter 2017).

Sections of this description are drawn from a section contributed by Neil Phillips to Porter, 2017 - Other significant deposits; Phillips, G.N., (Ed.); Australian Ore Deposits, The AusIMM, Melbourne, Monograph 32, pp. 857-864,

The most recent source geological information used to prepare this decription was dated: 2001.    
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.


Bronzewing

  References & Additional Information
   Selected References:
Anonymous  1998 - Bronzewing (GCM): in    Register of Australian Mining 1997/98    pp 80-81
Eilu T, Mikucki E J and Dugdale A L  2001 - Alteration zoning and primary geochemical dispersion at the Bronzewing lode-gold deposit, Western Australia: in    Mineralium Deposita   v36 pp 13-31
Elmer F L, Powell R, White R W and Phillips G N,  2007 - Timing of Gold Mineralization Relative to the Peak of Metamorphism at Bronzewing, Western Australia: in    Econ. Geol.   v102 pp 379-392
Eshuys E, Herbison I, Wright J  1995 - Discovery of Bronzewing gold mine: in   New Generation Gold Mines: Case Histories of Discovery, Conf. Proc., Perth, 27-28 Nov., 1995 AMF Adelaide    pp 2.1-2.15
Phillips G N, Vearncombe J R, Blucher I, Rak D  1998 - Bronzewing gold deposit: in Berkman D A, Mackenzie D H (Eds),  Geology of Australian and Papua New Guinean Mineral Deposits The AusIMM, Melbourne    pp 127-136
Phillips G N, Vearncombe J R, Eshuys E  1998 - Yandal Greenstone Belt, Western Australia: 12 million ounces of gold in the 1990 s: in    Mineralium Deposita   v33 pp 310-316
Ryan D  1997 - Bronzewing and Jundee Gold Mines: Five Years after Discovery: in   World Gold 97 Conference, Singapore, Sept. 1997, Papers AusIMM, Melbourne    pp 227-231


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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