Platinum-group minerals from the Kambalda nickel deposits, Western Australia

Abstract

The relative abundance, compositional variability, and geologic occurrence of platinum-group minerals have been determined by a study of samples from a number of geologic environments in the Kambalda nickel deposits. These results have been integrated with findings from a previous study by Hudson and Donaldson (1984) of platinum-group minerals in amalgamation residues from the gold recovery circuit of the Kambalda nickel mill, to give an overall picture of the nature and distribution of platinum-group minerals at Kambalda.The major platinum minerals are sperrylite and moncheite, and the major palladium minerals are sudburyite, merenskyite, stibiopalladinite, palladoarsenide, michenerite, and testibiopalladite; palladium also occurs in solid solution in palladian melonite. Irarsite is the only iridium mineral recognized, and no discrete phases have been observed for the other platinum-group elements. Sperrylite occurs within massive pyrrhotite-pentlandite ores and is particularly abundant in ores that are rich in chalcopyrite. A high proportion of the Pt in the Kambalda nickel deposits is believed to occur as sperrylite, but not all sperrylite is sufficiently coarse in grain size to enable gravity concentration. Nevertheless, sperrylite is the dominant platinum-group mineral recovered in gravity concentrates.Discrete palladium minerals are most abundant in stringers of sulfide in the footwall to the ore, in crosscutting sulfide veins, or in reaction zones associated with hydrothermal veins and porphyries. Within the massive and matrix ores, coarse discrete palladium minerals are rare, and it is concluded that palladium occurs in solid solution or as finely dispersed submicroscopic grains in sulfide minerals, predominantly pentlandite. The occurrence, within the ore zones, of Pt as sperrylite and Pd dispersed in pentlandite is believed to reflect a primary magmatic distribution. However, the presence of sudburyite, moncheite, merenskyite, michenerite, testibiopalladite, and palladian melonite in stringers and reaction zones indicates that their formation may be related to postmagmatic processes, in particular metamorphic segregation of sulfides and the interaction of ore sulfides with younger hydrothermal fluids.