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Lancefield |
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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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All papers now Open Access.
Available as Full Text for direct download or on request. |
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The Lancefield Archaean gold deposit is located 8 km north of Laverton in the Margaret segment of the Laverton greenstone belt. It is situated near the eastern margin of the Kurnalpi Terrane, which is within the Eastern Golfdfields Superterrane of the Archaean Yilgarn Craton of Western Australia.
Gold was discovered at Lancefield in 1897, with production commencing in 1899. The mine operated until 1940 with some interruptions and changes of ownership. In 1979, Western Mining Corporation re-opened the mine from four open pits distributed over a 2 km strike length. It was then developed as an underground operation, renamed the Summit Mine, and reaching a depth of 950 m making it one of the deepest in Western Australia. The mine closed in 1994.
The greenstone belt in the Lancefield area is bounded by the Laverton and Celia tectonic lineaments and comprises three major cycles of ultramafic to mafic volcanics separated by thin heterogeneous units of one or more of banded iron formation, chert and carbonaceous shale. The third cycle is overlain by conglomerate along the western margin of the Laverton tectonic lineament. These greenstones are bounded by a variety of granitoids with intrusive contacts.
The Lancefield deposits are found towards the top of the third cycle in a sequence of komatiites, Mg basalts, massive pillowed mafic volcanics, carbonaceous shale, iron formation and chert. It includes three (or more) sulphidic beds separated by mafic volcanic units. The lowest, W6, is a black shale and chert with 0 to 5% sulphide which also contains ore grade gold as the West Lode. The next, W10 is a 1 to 2 m thick unit of sulphidic chert and/or black shale, with chlorite and mainly pyrite and/or pyrrhotite-magnetite. The highest in the sequence, M1, has around 15% pyrite + pyrrhotite and lesser arsenopyrite and is the host to gold mineralisation in the Main Lode. The sulphides occur as irregular, wispy, anastomosing aggregates, generally parallel to, but not conformable to bedding. These sulphidic units are laterally persistent and grade out to graphitic shale units.
The host sequence, including the stratabound mineralised sulphide W6, W10 and M1 beds, strikes at 15 to 20° and dips at 30 to 45° E. These sulphidic bands were explored and worked at three localities over a strike length of over 2 km. The old Lancefield mine was developed on a high grade shoot in the Main Lode (which is in the M1 bed). This shoot was 2 to 7 m thick, 300 m in strike length at surface,tapering to 70 m some 340 m down dip, before expanding again to 200 m in length to at least 500 m below surface. &nbp; The best grade is mostly in the centre of the M1 sulphide bed, generally in association with the contained sulphides, although laterally it transgresses into the overlying basalt and next shale unit above. The West Lode consists of a number ofstyles from free gold bearing quartz veins, cherts, carbonatised and silicified komatiites and hydrothermally altered sediments, particularly W6. Similar size shoots to those described in M1 are also found in W6. Alteration occurs as a 2 to 8 m selvage to the sulphidic units.
The total endowment in 1987, as estimated by Woodall (1990) was - 6.376 Mt @ 8.17 g/t Au for 52.08 t of gold; comprising,
Historic production to 1987 - 9.167 Mt @ 8.24 g/t Au;
Remaining reserves at June 1987 - 3.3 Mt @ 8.1 g/t Au.
For detail consult the reference(s) listed below.
The most recent source geological information used to prepare this decription was dated: 1990.
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.
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Hronksy J M A, Perriam R P A, Schmulian M L 1990 - Lancefield Gold Deposit, Laverton: in Hughes F E (Ed.), 1990 Geology of the Mineral Deposits of Australia & Papua New Guinea The AusIMM, Melbourne Mono 14, v1 pp 511-517
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