Kambalda Type Komatiitic Nickel Ore Deposits - Supergene Modification

Supergene Modification

Kambalda style komatiitic nickel mineralisation was initially discovered by gossan searching in ~1965, which discovered the Long, Victor, Otter-Juan and other shoots within the Kambalda Dome. The Redross, Widgie Townsite, Mariners, Wannaway, Dordie North and Miitel nickel gossans were identified generally at or around the time of drilling of the Widgiemoltha area beginning in 1985, and continuing till today.

Gossans of nickel mineralisation, especially massive sulfides, are dominated in the arid Yilgarn Craton by boxworks of goethite, hematite, maghemite and ocher clays. Non-sulfide nickel minerals are typically soluble, and preserved rarely at surface as carbonates, although often can be preserved as nickel arsenates (nickeline) within gossans. Within subtropical and Arctic regions, it is unlikely gossans would be preserved or, if they are, would not contain carbonate minerals.

Minerals such as gaspeite, hellyerite, otwayite, widgiemoolthalite and related hydrous nickel carbonates are diagnostic of nickel gossans, but are exceedingly rare. More usually, malachite, azurite, chalcocite and cobalt compounds are more persistent in boxworks and may provide diagnostic information.

Nickel mineralisation in the regolith, in the upper saprolite typically exists as goethite, hematite, limonite and is often associated with polydymite and violarite, nickel sulfides which are of supergene association. Within the lower saprolite, violarite is transitional with unaltered pentlandite-pyrite-pyrrhotite ore.