MINERAL ASSOCIATIONS OF PLATINUM AND PALLADIUM IN LATERITIC REGOLITH,ORA-BANDA SILL, WESTERN-AUSTRALIA

Investigation of the mineral phases hosting the platinum group element s (PGE) has been undertaken at Mt Carnage on the PGE-rich Ora Panda si ll, Western Australia. The regolith is 40-60 m thick and PGE contents increase steadily towards the surface, with a total enrichment of thre e- to five-fold in the lateritic, ferruginous zone, giving maximum con centrations up to 2000 ppb total PGE in clay-rich duricrusts. The accu mulations appear to be residual and are of the same order as other ele ments, such as Cr, Zr and Cu, that also appear to be immobile. Scannin g electron microscope and electron microprobe investigations were, wit h minor exceptions, unable to distinguish separate mineral phases enri ched in PGE. Particle size analysis indicated that most Pt and Pd are in the < 2 mu m fraction. Selective extraction investigations show tha t most of the Pt, and a small proportion of the Pd, are associated wit h secondary Fe oxides. Magnetic separation suggests that Pt tends to b e associated with hematite, whereas that component of the Pd associate d with Fe oxides appears to be hosted by Al-rich goethite. These diffe rences may reflect initial differences in the locations of Pt and Pd. It is inferred that Pt is in an easily weatherable phase, leading to e arly release and incorporation into hematite, whereas Pd is in a more stable phase and is only slowly released during weathering, becoming i ncorporated into later-formed Fe oxides such as Al-rich goethite. The location of Pt and Pd in secondary Fe oxides or resistate primary phas es is consistent with their accumulation bring residual.