Invincible Gold Mine (LT-17), St. Ives gold camp, Kambalda, Coolgardie Shire, Western Australia, Australiai

Regional Level Types
Invincible Gold Mine (LT-17)	Mine
St. Ives gold camp	- not defined -
Kambalda	Town
Coolgardie Shire	Shire
Western Australia	State
Australia	Country

The Invincible gold mine was discovered in 2012, and is set to become the biggest gold mine in the St Ives area, with open pit production due to begin in 2015. The deposit is south-west of the Bahama-Santa Ana pits near the western shore of Lake Lefroy, and 8 kilometres north-west of the Lefroy Mill. A new causeway will be built across the lake bed to the mine. It is located on the Speedway Shear Zone, with potential for further deposits along the under-explored south south-east strike. The deposit has an estimated resource of 9.2 Mt at 4.5 g/t yielding 1.30 Moz. The area was formerly called LT-17 by the mining company (Goldfields Ltd).

The deposit occurs within the regional scale Speedway-Mount Morgan Shear Zones, which transect the western limb of the Kambalda-St Ives Anticline.

Gold mineralisation is found with the Black Flags Group, a steep south-west dipping package of rocks. There is a unit of mudstone/siltstone-sandstone-quartz-greywacke-conglomerate-volcaniclastic breccia. The mudstone/siltstone is 20 to 70 metres thick, which thins to the south. Overlying this is the other rocks mentioned as the Merougil Creek Beds. This contacts the west side of the Speedway Shear. The east contact is the Morgan Island Shear. There are also three un-mineralised, east-west trending, vertical dipping, Proterozoic dolerite dykes, which intrude the sedimentary package at the north and south ends of the ore body.

The Invincible ore body is truncated to the south by the north-east trending Alpha Island Fault. There is little supergene or halo development in the overlying regolith, due according to the geologists because of the absence largely of saprolite. These Tertiary sediments are 5 to 50 metres thick, and also contains a barren palaeochannel.

Gold is found in shear lodes, and extensional veins. The shear hosted deposits are confined to the mudstone/siltstone, consisting of hydrothermal quartz breccia veins, and intensely altered wallrock clasts of albite-pyrite-carbonate-biotite-pyrrhotite-chlorite-mica. Alteration zones are albite-pyrite. Gold is visible as under 1 mm irregular blebs within aggregates of biotite, as isolated grains within quartz veins, or within microfractures filled with pyrite-biotite-chlorite within the quartz breccia.

At the microscopic level, isolated gold grains are found within pyrrhotite grains, associated with pyrite, molybdenite and native tellurium.

The extensional vein hosted deposits are found within the sandstone/greywacke/conglomerate as less than 30 cm long veins, associated with albite-hematite-pyrite alteration. Visible gold is common as less than 1 mm isolated blebs within quartz veins, or associated with chlorite-biotite near the vein wall contacts.

Other Regions, Features and Areas containing this locality

References