Platinum-group minerals in podiform chromitites of the Oman Ophiolite

Chromitite lenses rich in PGE occur in the deeper part of the mantle section of the N part of the Oman ophiolite; stratigraphically, there are two types of chromitites - Moho transition zone (MTZ) and mantle types. PGM are mainly found in the PGE-rich mantle chromitite, and comprise four main categories in order of abundance: 1) sulphides (Os-rich laurite, erlichmanite and unnamed (Ir,Rh)(Ni,Cu,Fe) (sub 2) S (sub 3) ), 2) sulpharsenides and arsenides (irarsite-hollingworthite series, palladoarsenide), 3) alloys and native metals and 4) PGE oxide (Re-Os-Ir oxide). Base-metal sulphides and base-metal alloys are also found, as inclusions in chromian spinel and interstitial matrix. The common abundance of PGE sulphides, e.g. Os-rich laurite, is ascribed to the sulphide-undersaturated nature of the magma. The presence of PGE oxides commonly associated with fractured chromian spinel indicates that the PGE distribution in rocks can easily be modified at an early stage of serpentinization. Numerous EPMA results are given.