Genesis of small chromitite bodies at the later stages of melt/rock interaction in the Ojen ultramafic massif, South Spain

摘要

Small chromitite bodies occur in the Ojen ultramafic massif as irregular pods, schlierens and entwined veins within clinopyroxenites, orthopyroxenites and dunites. The chemical ocmposition of chromite expands in a compositional field that mostly overlaps that of the different podiform chromitites described in the literature from Al- and Ti-rich to Cr-rich and Ti-poor compositions. Chromite crystals contain abundant solid inclusions that show complex mineral assemblages comosed of anhydrous and hydrous silicates, base-metal sulfides, Ni arsenides and sulfarsenides and a great variety of PGM (specially laurite and irarsite). The genesis of these chromitites can be related with the later stages of melt percolation in porous flow channels. Chromite formed at expenses of teh percolated silicates from differentiated, volatile-rich melts at variably but high oxygen fugacity.