Abstract
Highly PGE-enriched podiform chromitite in the N Oman ophiolite has Sigma PGE of < or = 1.5 ppm, and is Ir-, Os- and Ru-enriched, and Rh-, Pt- and Pd-depleted. Its PGM in order of abundance are: 1) sulphides (Os-rich laurite, laurite-earlichmanite solid solution and an unnamed Ir sulphide); 2) alloys (Os-Ir and Ir-Rh alloys) and 3 sulpharsenides (irarsite and hollingworthite). All the high PGE contents occur in a mantle-section discordant chromitite with high Cr (> 0.7) spinel and an olivine matrix. Other chromitite-types are PGE-poor and have spinels with lower Cr (< or = 0.6). These differences imply that two distinct magmatic episodes formed these chromitites. One, residual from low-degree partial melting of peridotite, produced low Cr, PGE-poor chromitites at the Moho transition zone, and in the mantle possibly beneath a fast-spreading MOR. The other, from higher-degree partial melting produced high Cr, PGE-rich discordant chromitite in the upper mantle, possibly in a supra-subduction zone setting.