The Kambalda nickel deposits are located 56km SSE of Kalgoorlie in the Archean Yilgarn Block, a complex cratonic unit. The rocks of the Yilgarn Block can be classified into two categories: (1) low grade metamorphic, located within “greenstone belts”, derived from ultrabasic, basic and acid volcanics and associated sedimentary deposits; (2) intrusive granites, gneisses and other high grade metamorphic rocks surrounding the greenstone belts. Overlying the craton is a deep weathered zone.
The general stratigraphy of Kambalda consists of a conformable succession of meta-igneous rocks. The succession exceeds 3000m in thickness and consists of a footwall basalt, the ultramafic sequence, lower hanging wall basalts, shale and upper hanging wall basalts. The footwall basalt is 2000+m in thick and makes up the bulk of the sequence.
The footwall basalt primarily consists of fine grained, massive meta-basalts. Pillowed and flow breccia horizons are common. The ultramafic sequence consists of magnesium rich ultramafic rocks with nickel sulfide concentrations and conformable sedimentary horizons. Individual lithological horizons rarely exceed 30m in thickness and many contain spinifex textures and breccia structures in the upper portion. All the known nickel concentrations occur within this unit or at the base of it. The contact nickel sulfide mineralization occurs in lenses along the contact of the ultramafic sequence and footwall basalt. The contact mineralization grades into disseminated mineralization, which extends upto 100m above the contact.
A typical shoot lies along the meta-basalt/ultra-basic contact and is composed of a disseminated zone, which increases in sulfide content to a massively banded zone. The banded zone usually consists of 90-95% pyrrhotite/pentlandite with minor chalcopyrite and cobalt rich pyrite. The pentlandite in the massive banded layer exists as thin bands 1-3mm thick and 8mm apart.
During intrusion of the ultra-basic, gravity settling caused the heavier sulfides to settle at the bottom of the intrusion, where the current shoots are located.
The primary economic mineral is pentlandite which is processed to extract nickel.
