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Tropicana, Havana, Boston Shaker

Western Australia, WA, Australia

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The Tropicanan, Havana and Boston Shaker gold deposits are located ~330 km east-northeast of Kalgoorlie, Western Australia, on the eastern margin of the Archaean Yilgarn Craton.
(#Location: 29° 14' 48"S, 124° 32' 18"E).

Together, these three deposits define a NE trending mineralised corridor, approximately 1.2 km wide and 5 km long, that has been tested to vertical depths of more than 1000 m. The Mineral Resource remains open down-dip for the Tropicana, Havana and Boston Shaker deposits and to the south of the Havana deposit. Neither the immediate metamorphic host rocks nor the mineralised zones are exposed at surface due to the presence of widespread cover sequences, which average between 0.5 and 15 m in thickness.

The Tropicana deposits are hosted within high-grade gneissic rocks that lie on the eastern edge of the Yilgarn craton, within its transition into the NE-SW oriented Albany Fraser orogen to the east. The Yilgarn craton is characterised by Meso to Neoarchaean granite greenstone terranes with widespread 2620 Ma granites. The Albany-Fraser orogen separates the Yilgarn and Mawson cratons. It is dominated by heterogeneous orthogneisses, and contains 1700 to 1600 Ma granitoids, followed by the deposition of <1500 Ma arenaceous sediments. Widespread intrusion of 1300 to 1190 Ma gabbro and 1190 to 1130 Ma granites followed.

The dominant lithotypes within a 5 x 4 km area surrounding the mineralised corridor comprise K feldspar dominated quartzo-feldspathic gneiss (the main host); garnet gneiss with lesser granulite-amphibolite adjacent to and interlayered with the quartzo-feldspathic gneisses; amphibole-dominated gneiss and granulite-amphibolite to the east and west of the previous two lithotypes. Zones of sericite-chlorite dominant schist/mylonite are found in the east, while quartzo-feldspathic gneiss, with subordinate amphibolite occur in the north. Narrow, structurally controlled NE and NNE trending biotite dominant schist/mylonite zones cut the sequence in the vicinity of the ore deposits.

Mineralisation at the Tropicana group of deposits is associated with late biotite and pyrite alteration. Towards the west, the deposit is dominated by Archaean and Proterozoic aged granitic, volcanic and metamorphic rocks of the Yilgarn Craton. Younger sedimentary rocks that unconformably overlie the Archaean and Proterozoic rocks dominate the geology of the deposit towards the east.

The Tropicana deposit comprises a main ore zone up to 63 m thick, dominantly hosted in quartzo-feldspathic gneiss, with subordinate 3 to 5 m thick, discontinuous mineralised lenses that typically grade >0.5 g/t Au, hosted within the garnet-gneiss dominated hanging wall package.

The Havana deposit comprises a lower, laterally continuous higher-grade lode up to 50 m thick that is overlain, in the central and southern parts of the proposed pit, by stacked, typically lower-grade and thinner (up to 25 m thick) ore zones dominantly hosted in quartzo-feldspathic gneiss. The ore zone occurs as one or two laterally extensive planar lenses with a moderate, 30 to 50°SE dip. The overlying sequence is largely composed os alternating quartz-feldspathic and garnet gneiss cut by steep-dipping basalt dykes.

Mineralisation within the ore zones is accompanied by 2 to 8% pyrite with accessory pyrrhotite, chalcopyrite, electrum and minor amounts of other sulphides and tellurides. The gold mineralisation is related to shear planes that postdate the main gneissic fabric developed during peak granulite-facies metamorphism.

Published JORC compliant ore reserves and mineral resources at 31 December, 2011 (AngloGold Ashanti, 2012) were:
    Measured + indicated + inferred resources, open pit - 52.15 Mt @ 1.99 g/t Au for 104.02 tonnes of contained gold.
    Measured + indicated + inferred resources, underground - 9.67 Mt @ 3.67 g/t Au for 35.50 t of contained gold.
    Measured + indicated + inferred resources, TOTAL - 61.82 Mt @ 2.26 g/t Au for 139.52 t of contained gold.
    Proved + probable reserves, open pit - 39.45 Mt @ 2.16 g/t Au for 85.21 t of contained gold.
Note: reserves are included within resources.

Main source: Anglogold Ashanti 2012 reserve statement.

The most recent source geological information used to prepare this summary was dated: 2011.    
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
 References to this deposit in the PGC Literature Collection:
Crawford, A.J. and Doyle, M.G.,  2016 - Granulite-Hosted Gold: Tectonic Setting and Lithogeochemistry of the Tropicana Deposit, Western Australia: in    Econ. Geol.   v.111 pp. 395-420


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