Racetrack Gold Mine, Mount Pleasant, Black Flag Goldfield, Kalgoorlie-Boulder Shire, Western Australia, Australiai

Regional Level Types
Racetrack Gold Mine	Mine
Mount Pleasant	Mountain
Black Flag Goldfield	Ore Field
Kalgoorlie-Boulder Shire	Shire
Western Australia	State
Australia	Country

Racetrack is an abandoned water filled open pit towards the south end of the Mount Pleasant complex. It is the largest pit in the complex. The deposit was discovered in 1987. The mine produced 2.4 Mt at 2.9 g/t.

The deposit is hosted by the Victorious Basalt, with minor intrusions, felsic and intermediate porphyries and dolerite. The basalt is locally known as 'cat rock' due to its spotted nature. It is massive to pillowed, coarsely plagioclase-phyric tholeiitic basalt, within a coarse grained doleritic groundmass. The deposit is found on a splay fault between the Black Flag Fault to the west and Royal Standard Fault to the east.

Gold is found either in quartz breccia, or narrow shear zones with quartz veins. The breccia is hosted by a north-west dipping fault zone, and is related to brittle fault deformation. The shear zones strike
north-west, and display brittle-ductile deformation features. Gold grades and the type of reef vary depending on subtle changes in the strike and/or dip of the ore hosting zone. For example, the central area of the pit a 60 degree north-west fault, bends to 40 degrees, and changes from quartz breccia to narrow under 0.4 metres shear zone lacking quartz veins.

Most gold is found in the breccia, shear zones, breccia clasts and quartz matrix. Economic mineralisation dies out to the west where the shear zone flattens, and to the east is terminated by a horsetail splay.

Gold was formed as part of a two stage hydrothermal activity, and late quartz-carbonate veining. Gold formed in the first two stages and sulphides throughout. Stage 1 mineralisation developed in structures as zones of intense wall rock alteration, consisting of microcrystalline and crystalline quartz. This formed chlorite-carbonate-epidote fringing the mineralised ore of arsenopyrite, pyrite, chalcopyrite, Fe poor sphalerite, tetrahedrite, tennantite, fahlore, gold and electrum.

Stage 2 saw intense fracturing, veining and brecciation of stage 1 structures. The breccia matrix was cemented by hydrothermal minerals. Quartz crystals dominate, showing comb, rosette, plumrose and banded textures. Minerals desposited include freibergite, tetrahedrite, tennantite, galena, arsenopyrite, pyrite, chalcopyrite, sphalerite, gold, electrum and minor cassiterite.

Stage 3 was more intense fracturing, veining and brecciation in the western part of the mine, by fine grained carbonate. The carbonate has diluted gold grades in some areas. Some sulphides were deposited including pyrite, arsenopyrite and chalcopyrite.

Other Regions, Features and Areas containing this locality

References