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Bounty Gold Mine, Forrestania Goldfield (Mount Holland), Yilgarn Shire, Western Australia, Australia

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Latitude & Longitude (WGS84): 32° 6' 14'' South , 119° 46' 51'' East
Latitude & Longitude (decimal): -32.10394,119.78110
GeoHash:G#: qdm1metuv
Locality type:Mine
Köppen climate type:BSk : Cold semi-arid (steppe) climate


The Bounty gold anomalies were discovered in 1985 by Aztec Exploration Limited after re-studying drill cores taken searching for nickel. The mine operated from 1988 to 2002, with Bounty, West Bounty and North Bounty pits which were developed over the strongest anomalies. The mine is 115 kilometres south south-east of Southern Cross. The mine closed when Aztec hit financial difficulties, when gold recovery rates were not to expectation.

The mine is located in a southern extension of the Archaean Southern Cross Greenstone Belt. This belt is dominated by tholeiitic basalt, with lesser sandstone, siltstone and chert. Ultramafic rocks include komatiite altered to chlorite schist and serpentinized dunites. There are also some banded iron formations. A series of east striking lower Proterozoic gabbroic dykes cut the belt.

At Bounty, gold is found in a narrow belt called the Bounty Horizon. This is composed of banded iron formation related Fe rich amphibolites, and some associated siliceous and pelitic rocks. Dolerite flanks the zone to the west, and high Mg basalt to the east.

Weathering at Bounty reaches 40 metres. It consists of variable Fe rich clays, lateritic fragments, black Fe rich nodules, pale grey sandy clays, bleached saprolite and yellow-brown loose sands.

Gold mineralization is found in a steeply dipping shear system, with near vertically west dipping banded iron formation and chert. There is a strong association between the gold and the underlying banded iron formation and chert. Gold occurs in zones of quartz-sulphide-carbonate alterations, at an average grade of 5 g/t over a 20 metre wide near surface zone.

The sources here give far more information than will fit on Mindat. They focus on economic mineralisation, and a visit to the waste dumps at the mine by the writer would indicate there are more species than listed here.

JORC confirmed resources for the Bounty Main mine is 3.3 Mt of ore at 3.69 g/t yielding 319 000 ounces of gold. The mine produced 1.3 million ounces of gold during its 12 year life.

The Bounty Horizon is a sheared amphibolite iron formation and chert rich beds (50% each) 15 to 30 metres thick, dipping steeply west. The iron rich beds contain grunerite-ferroactinolite, magnetite-biotite, magnetite-grunerite-ferroactinolite or rarely magnetite-plagioclase. Thin iron rich pelitic interbeds are less common and contain biotite-almandine-hornblende-grunerite. The chert rich beds contain granoblastic quartz, and some magnetite, grunerite and ferroactinolite. Hedenbergite forms parallel bedding bands and cross cutting bands.

Pyrrhotite dominates the Bounty Horizon, with up to 60% of rock in the strongly deformed zones. It forms disseminated replacement to magnetite rich bands, vein fillings, and as a matrix to breccia. In addition there is minor pyrite, marcasite, arsenopyrite, chalcopyrite and sphalerite in the veins. Pyrite and marcasite are abundant in the upper oxidised levels but minor at depth.

Spodumene and muscovite rich pegmatites intrude the Bounty Horizon. The regionally major Binneringie Dyke cuts the Bounty Deposit, and has oxidised pyrrhotite to magnetite within 100 metres of it.

Gold is mainly found in the strongly deformed areas of the Bounty Horizon near the Hanging Wall, and in one area near the Footwall. Three types of veins occur in the former (1) quartz-calcite-hedenbergite-garnet (2) pyrrhotite rich veins and matrix breccia (3) quartz with visible gold. The quartz-gold veins are 3 to 20 cms thick and extend from 1 to 10 metres. The gold is found 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 area of Footwall with gold shows quartz veins with visible gold, and associated with haloes of hedenbergite and pyrrhotite. Gold rich breccias contain mineral clasts of hedenbergite, calcite, plagioclase, quartz, actinolite, and blue-green hornblende, with minor biotite and apatite.

Between the Hanging Wall and strongly deformed areas of the Bounty Horizon is a chlorite zone, showing as smooth shiny black rock. Some quartz is found in this as aggregates, rod shaped and steep plunging with minor pyrite, and pyrrhotite, (and graphite at the southern end of the deposit).

The Hanging Wall is fine to coarse grained subhedral hornblende after pyroxene (40-60%), plagioclase, some actinolite and variable amounts of biotite. There is minor pyroxenitic and tremolite rich layers towards the lower contact with the Bounty Horizon.

A zone of intense veining occurs within the Footwall rocks, adjacent to the Bounty Horizon, ranging from 1 to several metres with veins forming 50% of the rocks. The veins are quartz-pyrite-actinolite-pyrrhotite in variable proportions, strongly deformed or recrystallised and folded. Undeformed veins contain clinopyroxene with inclusions of calcite, euhedral epidote, and an outer rim of clinozoisite and some quartz.


Commodity List

This is a list of exploitable or exploited mineral commodities recorded at this locality.


Mineral List


24 valid minerals.

Rock Types Recorded

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Regional Geology

This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.

Click on geological units on the map for more information. Click here to view full-screen map on Macrostrat.org

Archean
2500 - 4000 Ma



ID: 902548
metamorphosed ultramafic rocks 74286

Age: Archean (2500 - 4000 Ma)

Description: Metamorphosed komatiite, pyroxenite, chlorite-tremolite schist, talc-chlorite schist, anthophyllite-tremolite-talc rock; olivine-cummingtonite schist; talc-carbonate-tremolite-chlorite rock, serpentinite; amphibole schist after pyroxenite

Comments: igneous ultramafic volcanic; meta-igneous ultramafic intrusive; synthesis of multiple published descriptions

Lithology: Igneous ultramafic volcanic; meta-igneous ultramafic intrusive

Reference: Raymond, O.L., Liu, S., Gallagher, R., Zhang, W., Highet, L.M. Surface Geology of Australia 1:1 million scale dataset 2012 edition. Commonwealth of Australia (Geoscience Australia). [5]

Neoarchean - Mesoarchean
2500 - 3200 Ma



ID: 3193082
Archean crystalline metamorphic rocks

Age: Archean (2500 - 3200 Ma)

Comments: Yilgarn Craton

Lithology: Gneiss

Reference: Chorlton, L.B. Generalized geology of the world: bedrock domains and major faults in GIS format: a small-scale world geology map with an extended geological attribute database. doi: 10.4095/223767. Geological Survey of Canada, Open File 5529. [154]

Data and map coding provided by Macrostrat.org, used under Creative Commons Attribution 4.0 License



This page contains all mineral locality references listed on mindat.org. This does not claim to be a complete list. If you know of more minerals from this site, please register so you can add to our database. This locality information is for reference purposes only. You should never attempt to visit any sites listed in mindat.org without first ensuring that you have the permission of the land and/or mineral rights holders for access and that you are aware of all safety precautions necessary.

References

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Economic Geology (1997) 92:181-209.
Lintern, M.J. (2004) Bounty Gold Deposit, Forrestania Greenstone Belt, Western Australia, Cooperative Research Centre for Landscape Environments and Mineral Exploration (CRCLEME).
Rutherford, R.A., Coggon, J.H. (1994) Gold: Bounty Gold Deposit Western Australia: Magnetic and Electromagnetic Responses, 1994.
Rutherford, R.A. (1992) Bounty Gold Mine: Deformation History and the Development of Ore Fluid Pathways Within an Iron Formation Host Western Australia, Masters Thesis, University of Tasmania, 1992.

 
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