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Bounty - Southern Cross Belt |
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Western Australia, WA, Australia |
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Au
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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The Bounty gold deposit is located ~105 km SSE of Southern Cross, close to the southern limit of the belt of gold deposits of the Southern Cross Greenstone Belt, in the Southern Cross Domain of the Youanmi Terrane, in the Yilgarn Craton, Western Australia (#Location: 32° 5' 59"S, 119° 46' 13"E).
The deposit was discovered in 1985 by Aztec Exploration Limited while drilling for nickel. The mine operated from 1988 to 2002, from the Bounty, West Bounty and North Bounty pits. The mine closed when gold recovery rates were not to expectation. The mine produced ~40 t of gold, and at the time of closure had a remaining JORC compliant Mineral Resource of 3.3 Mt @ 3.69 g/t Au for a further 12 t of contained gold.
For more information on the Southern Cross Belt, its geological setting and deposits see also the Transvaal, Yilgarn Star, Marvel Loch, Nevoria, Fraser, and Copperhead records.
The Southern Cross Greenstone Belt is dominated by a sequence of greenstones that comprise tholeiitic basalts overlain by komatiitic volcanic rocks that have been altered to chlorite schist and serpentinised dunites, with lesser sandstone, siltstone and chert, unconformaby overlain by a succession of sedimentary rocks. Banded iron formation beds, which are equated with the regional Golconda Iron Formation, occur within the basalt-komatiite sequence. A series of east-west striking Palaeoproterozoic dolerite dykes also cut the belt.
Gold mineralisation at Bounty occurs in a narrow, semi-conformable, steeply dipping shear system, the Bounty Horizon, within a near vertical, west dipping unit that comprises almost equal amounts of banded amphibolite iron formation and chert. There is a strong association between gold and the banded iron formation and chert. The iron formation is composed of grunerite-ferroactinolite, magnetite-biotite, magnetite-grunerite-ferroactinolite and rarely magnetite-plagioclase. Thin iron rich pelitic interbeds are less common and contain biotite-almandine-hornblende-grunerite. The chert beds are composed of granoblastic quartz, with some magnetite, grunerite and ferroactinolite. Hedenbergite occurs as bedding parallel and cross cutting bands.
Pyrrhotite comprises up to 60% of the strongly deformed zones of the Bounty Horizon, occurring as disseminated replacement of magnetite rich bands, vein fillings, and as a matrix to breccia, while minor pyrite, marcasite, arsenopyrite, chalcopyrite and sphalerite is found in veins. Pyrite and marcasite are abundant in the upper oxidised zone but are only a minor constituent at depth.
Gold mainly occurs in the strongly deformed sections of the Bounty Horizon, mainly near the hanging wall, and in one area near the footwall and is accompanied by quartz-sulphide-carbonate alteration.
The hanging wall to the iron formation is composed of 40 to 60% fine to coarse grained subhedral hornblende after pyroxene, plagioclase, some actinolite and variable amounts of biotite. There is minor pyroxenitic and tremolite rich layers towards the lower contact with the deformed Bounty Horizon.
A smooth shiny black chlorite rock separates the hanging wall of the iron formation from the strongly deformed Bounty Horizon and contains some quartz aggregates that are rod shaped and steeply plunging with minor pyrite, and pyrrhotite, and graphite at the southern end of the deposit.
Within the Hanging Wall zone of the Bounty Horizon, in the iron formation, three vein types are recognised: i). quartz-calcite-hedenbergite-garnet; ii). pyrrhotite rich veins and matrix breccia; and iii). quartz with visible gold. The latter are 3 to 20 cm thick and extend from 1 to 10 m. Gold is associated with quartz, calcite and hedenbergite, with disseminated pyrrhotite, pentlandite, molybdenite and chalcopyrite. Veins containing quartz, actinolite, pyrrhotite, apatite, biotite and clinozoisite do not contain visible gold.
The Footwall gold zone comprises quartz veins with visible gold, and is associated with haloes of hedenbergite and pyrrhotite. Gold rich breccias contain clasts of hedenbergite, calcite, plagioclase, quartz, actinolite and blue-green hornblende, with minor biotite and apatite.
In the footwall of the iron formation, a zone of intense veining occurs adjacent to the Bounty Horizon. This zone ranges from 1 to several metres in width where veins form 50% of the rock. These veins are strongly deformed or are recrystallised and folded, and comprise quartz-pyrite-actinolite-pyrrhotite in variable proportions. Undeformed veins contain clinopyroxene with inclusions of calcite, euhedral epidote, and have an outer rim of clinozoisite and some quartz.
The deposit had at an average grade of 5 g/t Au over a 20 m width at surface. This grade persisted to a depth of 60 m, and was 8.9 g/t from 60 to 130 m.
The most recent source geological information used to prepare this decription was dated: 2004.
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.
Bounty
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Selected References:
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Coggon, J.H. and Rutherford, R.A., 1994 - Bounty Gold Deposit, Western Australia: Magnetic and Electromagnetic Responses: in Exploration Geophysics v.25, pp. 233-240.
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Doublier, M.P., Thebaud, N., Wingate, M.T.D., Romano, S.S., Kirkland, C.L., Gessnar, K., Mole, D.R. and Evans, N., 2014 - Structure and timing of Neoarchean gold mineralization in the Southern Cross district (Yilgarn Craton, Western Australia) suggest leading role of late Low-Ca I-type granite intrusions: in J. of Structural Geology v.67, pp. 205-221.
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Lintern, M.J., 2004 - Bounty gold deposit, Forrestania Greenstone Belt, Western Australia: in CRC LEME online, http://crcleme.org.au/RegExpOre/Bounty.pdf 3p.
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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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