G. A. Travis, R. R. Keays, and R. M. Davison
Palladium and iridium in the evaluation of nickel gossans in Western Australia
Economic Geology and the Bulletin of the Society of Economic Geologists (November 1976), 71(7):1229-1243

Abstract:
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 non-nickeliferous sulfide assemblages permit distinction from true nickel gossans. Material with 15 to 30 ppb Pd and 5 to 10 ppb Ir indicates a possible minor original nickel sulfide component ([asymp]0.6% Ni), and at higher levels the former presence and approximate grade of nickel sulfides can be confidently predicted from the precious-metal values.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.