Origin of Podiform Chromitites in the Sebuku Island Ophiolite (South Kalimantan, Indonesia): Constraints from Chromite Composition and PGE Mineralogy

The presence of PGM associated with the podiform chromitites in Jurassic–Cretaceous ophiolite Sebuku Island (South Kalimantan, Indonesia) is reported for first time. Two types chromitite have been recognized; one high-Cr composition (Cr/(Cr + Al) > 0.7) occurs deep mantle, other, high-Al < 0.6), located close to Moho transition zone. TiO2-Al2O3 relations indicate affinity IAT and MORB, chromitites, respectively. However, both are believed formed by mantle/melt reaction differentiation a magma characterized an initial related SSZ. Primary magmatic inclusions (<10 ?m) laurite Ru/Os chondritic ratio only found indicating crystallization from undifferentiated magma, at low fS2 mantle. In contrast, chondrite, suggesting increase evolved melt. Besides laurite, contains complex assemblage secondary (Pt-Fe, garutiite, iridium, ruthenium–magnetite aggregates, zaccariniite unnamed Ru Mn oxides). These irregular shape occur exclusively chlorite matrix sometimes Mn-Ni-Fe-Cr hydroxides. They interpreted desulfuration primary interstitial sulfides or precipitated fluids during T alteration. relative abundance PPGE as result PGE fractionation parent melt chromitites.