The platinum group element mineralisation examined in this study is found in the extensive ultramafic massif located in the south of New Caledonia, at the estuary of Rivière des Pirogues. The exogenic processes acting on exposed rocks in the inter-tropical belt have resulted in deep metal-rich lateritic mantles developing at the expense of the New Caledonia peridotite nappe. The purpose of this study was to characterise the chemical and mineralogical changes affecting the carrier-phases of platinum group elements (PGE) in this lateritic environment. Petrographic and petrological analysis of three weathering profiles in the anomalous platinum-palladium bearing zone has highlighted the key role played by hydrothermal serpentine alteration in the evolution of platinum group element mineralisation. This pre meteoric weathering process has resulted in the neoformation and formation of platinum group minerals by desulfurisation of PGM sulfide precursors and precipitation of new minerals. Contact with the atmosphere and hydrosphere causes PGMs to evolve differently depending on their chemical composition. Isoferroplatinum type phases that are very rich in platinum (Pt3Fe) are stable in the weathering mantle, while phases with a higher iron, copper and palladium content such as tetraferroplatinum (PtFe), tulameenite (Pt2FeCu) and Pt-Fe oxides undergo incongruent dissolution, with selective leaching of their chemical components. Geochemical characterisation of weathering rinds using electron microprobe analysis shows the following element mobility in the lateritic weathering of PGMs: S > Cu > Pd > Fe > Pt. Regardless of the precursor mineral, the neoformed phase shows relative upgrading of the Pt contents and a tendency to acquire the chemical composition of isoferroplatinum (Fe3Pt).
