Mineralogy and composition of the chromitites and their platinum-group minerals from Ortaca (Muğla-SW Turkey): evidence for ophiolitic chromitite genesis

A large number of podiform chromitite bodies of massive, disseminated and nodular type have been located in ultramafic units, composed of depleted mantle harzburgite and dunite of the Marmaris Peridotite from Ortaca (Muğla, SW Turkey). The chromite ore bodies are surrounded by dunite envelopes of variable thickness, exhibiting transitional boundaries to harzburgite host rocks. Chromitites, containing a large number of inclusions, i.e. silicates, base metal sulphides and alloys, and platinum-group minerals (PGM) have a wide range of chemical composition. The Cr# [Cr/(Cr + Al)] values of most chromitites are high (0.61–0.81) and Mg# [Mg/(Mg + Fe2 + )] values range between 0.65 and 0.71 with TiO2 content lower than 0.24 wt.%, which may reflect the crystallization of chromites from boninitic magmas in supra-subduction setting environment.