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Tropicana Gold Mine, Plumridge Lakes Nature Reserve, Menzies Shire, Western Australia, Australiai

Regional Level Types
Tropicana Gold Mine	Mine
Plumridge Lakes Nature Reserve	Nature Reserve
Menzies Shire	Shire
Western Australia	State
Australia	Country

The Tropicana Gold Mine is 330 kilometres east north-east of Kalgoorlie in the Great Victoria Desert. The name invokes palm trees and white sandy beaches, and is in keeping with gold miners in Western Australia naming sites totally at odds with sand-dunes, desert vegetation and 45 degree heat. The mine is west of the Plumridge Lakes Nature Reserve, being the nearest geographical feature, in the otherwise largely featureless Great Victoria Desert.

The nearest civilisation is the Pinjin Station, about 70 kilometres to the west. No roads exist and the mining company had to build one to link-up with the access road to the station.

Tropicana was discovered in 2005, and is jointly owned by AngloGold Ashanti and Independence Group NL. Its late discovery is due to the remoteness of the region, and that the resource lay hidden under 0.5-15 metres of overburden. Mining is due to commence in late 2013. It is the latest gold discovery in Australia, and opened up a major new gold province. The companies mentioned above control 12 000 square kilometres of tenements around the mine. Eventually the pit will be 6 kilometres long, 1.5 kilometres wide, and up to 400 metres deep. Underground mining is possible in the future as mineralisation has been tested to 1000 metres deep and is open ended.

Four deposits are planned to be mined (from the north), Boston Shaker, Tropicana, Havana, and Havana South, trending north north-east, and within a few kilometres of each other. The mine life is expected to be 15 years. http://www.igo.com.au/irm/content/tropicana-gold-mine-jv1.aspx?RID=303 (accessed Oct. 2015) mentions four open pits. In 2011, a JORC resource estimate was produced of 56.4 Mt of ore at 2.16 g/t yielding 3.9 million ounces of gold.

The Tropicana Gold Mine sits at the far north-east edge of the Albany-Fraser Orogen. The deposit does not outcrop, hidden by sand-dunes up to 12 metres high. Under this is siltstone, sandstone and pebbly conglomerate units. The host rocks below this include granite gneiss, quartzofeldspathic gneiss, amphibole, granulite, metasedimentary rocks and pegmatites.

Structurally, the northern margin of the Tropicana Domain is defined by the east north-east trending Boston Shaker Shear Zone. The Tropicana and Havana deposits are separated by the north-east to east striking Muddler, Swizzler and Cobbler shear zones.

Mineralisation occurs along a corridor 5 kilometres long, by 1.2 kilometres wide. The main host is K-feldspar dominated quartzo-feldspathic gneiss. Further there is garnet gneiss, with lesser granulite-amphibolite adjacent to and interlayered with the quartzo-feldpathic gneisses; amphibole dominated gneiss; and granulite amphibole to the east and west.

Sericite-chlorite dominated schist is seen to the east, and quartz-feldspathic gneiss with sub-ordinate amphibole in the north. Biotite dominant schist zones cut the sequence near the ore deposits.

There are two forms of gold deposits. The first is gold associated with biotite-sericite-pyrite, disseminated, banded, and crackle mosaic breccia units, and veins with altered quartzo-feldspathic gneiss, and rarely in garnet gneiss.

The second is sub-economic patchy and vein style pyrite-pyrrhotite, incompletely replacing shear zones, calaclastic rocks(angular clasts in a fine grained matrix formed by faulting and fracturing), thin metasedimentary intervals, interleaved with and at the base of the Hanging Wall garnet gneiss.

Mineralisation is accompanied by 2-8% volume pyrite, with lesser pyrrhotite, chalcopyrite, electrum, and minor other sulphides and tellurides, and trace sphalerite, galena and bornite. Free gold is mostly seen as fine grained inclusions in pyrite, and less commonly along biotite-sericite fractures cutting silicate minerals. Quartz veins are largely and notably absent.

The pyritic ores are enveloped by disseminated pyrrhotite-pyrite haloes, in variable states of oxidation. The alteration envelopes are zoned, nearest the ore body being biotite-sericite-calcite-siderite. The next outward zone is sericite-biotite-chlorite-calcite. Then at the margins sericite-chlorite-biotite-calcite.

Outside of these zones the metamorphic minerals have been variably altered to an assemblage of chlorite, sericite, epidote, calcite and hematite

Gold is related to the shears, which post date the gneissic fabric. Fluids passed outwards from the controlling thrusts, into a receptive K feldspar rich gneissic package.

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