The Distribution of PGE and the Role of Arsenic as a Collector of PGE in the Spotted Quoll Nickel Ore Deposit in the Forrestania Greenstone Belt, Western Australia

Abstract

The Spotted Quoll PGE-bearing Ni deposit in the Forrestania greenstone belt in the Archean Yilgarn block in Western Australia is a komatiite-associated massive sulfide orebody tectonically displaced from its original host. The brecciated ore contains clasts of quartz and garnet schist and is located along a shear zone overlain by banded iron formation (BIF) and underlain by BIF and quartz-biotite metasediments. The deformation of the ore has destroyed its magmatic textures and it has been sheared and recrystallized at amphibolite facies. Then the deformed ore has been subjected to a hydrothermal event that concentrated the PGE with Au and As, often at the edge of the Ni ore. The PGE are distributed between PGM and in solid solution in Ni sulfarsenides, and Pd also occurs in pentlandite. The PGM include sudburyite (PdSb), sperrylite (PtAs2), and irarsite (IrAsS). All six PGE and minor Au are hosted in gersdorffite (NiAsS). Two generations of gersdorffite have been recognized. A higher temperature magmatic euhedral Co-rich gersdorffite encloses Ir-, Pt- and Rh-bearing PGM surrounded by halos of Rh-, Ir-, and Os-rich gersdorffite. A lower temperature Ni-rich gersdorffite forms anhedral grains and rims on grains of nickeline (NiAs). In this low-temperature gersdorffite PGE are concentrated toward the mineral edges. Sudburyite and gold occur associated predominantly with nickeline. The PGE and gold are now predominantly associated with sulfarsenides that are the controlling factor for their distribution.