PALLADIUM AND IRIDIUM IN THE EVALUATION OF NICKEL GOSSANS IN WESTERN AUSTRALIA.

Palladium and iridium show a strong positive correlation with nickel in Western Australian nickel sulfide deposits, and their inertness during weathering, combined with depletion of the more mobile components, usually results in retention or enhancement of the primary values in gossans and other oxidized derivatives. Precious-metal enrichment from background levels occurs in some lateritized barren ultramafic rocks, but the low values in most lateritic products and gossans derived from nonnickeliferous sulfide assemblages permit distinction from true nickel gossans. Pd-Ir analysis has particular application to the recognition of an original nickel sulfide component in highly leached gossans with low Ni-Cu values, to the evaluation of ferruginous, siliceous, and clay-rich lateritized ultramafic products enriched in Ni and Cu, and to the estimation of the nickel content in the parent sulfide assemblage.