Palladium, platinum, rhodium, ruthenium, and iridium in chromitites from the Massif du Sud and Tiebaghi Massif, New Caledonia

Abstract

Massive and disseminated podiform chromitite from 43 mines and other occurrences in the Massif du Sud and Tiebaghi Massif, both ophiolites, in New Caledonia contain up to 9 ppb Pd, up to 45 ppb Pt, up to 31 ppb Rh, up to 410 ppb Ir, and up to 1,130 ppb Ru. The chromitites are strongly depleted in Pt and Pd and mildly depleted in Ir and Ru with respect to an average chondrite composition, as are podiform chromitites from Oman, Turkey, Greece, and northern California. Stratiform chromitites from the Stillwater Complex, Montana, and the Bushveld Complex, South Africa, show inverse patterns of enrichment and depletion. These patterns suggest that either chromitite from ophiolites represents mantle rocks depleted in Pt and Pd or that the magmas that formed the ophiolites were depleted in Pt and Pd, or that the process of forming the chromitite involved the concentration of Os and Ir from a magma. The relatively high contents of Ir and Ru in the New Caledonian chromitite suggest the potential for the occurrence of placers that contain concentrations of Os-Ir alloys.