Location:

Kambalda, Yilgarn Block, Western Australia

Nickel deposits occur within ultramafic and mafic volcanic sequences in the Yilgarn Block, especially the Kambalda Sequence which comprises a hangingwall of basalts and minor metasediments overlying an ultramafic sequence of picrites, peridotites and komatiite flows above footwall basalts. Most of the nickel sulphides occur as high grade elongated bodies at the top of the footwall basalts. The primary assemblage is pyrrhotite, pentlandite, pyrite and magnetite, with minor chalcopyrite and iron-rich chromite. Post-crystallization polyphase deformation, low-grade amphibolite metamorphism and hydrothermal alteration have redistributed the ores. The redistributed ore types include gold-bearing quartz-carbonate veins and gold- and platinum bearing chalcopyrite stringers.

Major Minerals:

Monoclinic pyrrhotite, pentlandite, pyrite, chalcopyrite, magnetite, ironrich chromite; secondary violarite, ferritchromit

Minor Minerals:

Millerite, sphalerite

Trace Minerals:

Include native gold, sperrylite, sudburyite, merenskyite, moncheite, hessite, altaite, calaverite, breithauptite

Textures:

Spinels are euhedral to subhedral and are zoned from ferrochromite cores to magnetite rims. Pentlandite forms granular rims around, or flame-like exsolution bodies within, pyrrhotite. Pentlandite is altered to violarite along cleavage and grain boundaries. Pyrite and chalcopyrite have symplectite-like intergrowths and chalcopyrite carries rare exsolved sphalerite. Platinum group mineralsform discrete grains in association with iron-nickel arsenides and antimonides. Some gold and platinum group mineralization is associated with remobilized copper-rich ores.

References:

Ewers and Hudson, 1972; Marston andKay, 1980; Woolrich et al., 1981; Hudson and Donaldson, 1984; Lesher and Keays, 1984; Paterson et al., 1984