Podiform Chromitites from the Bou Azzer Ophiolites: An Overview of Mineralogy of Platinum-Group Minerals and PGE Contents

The Bou Azzer ophiolite complex is located in the central part of the Anti-Atlas Mountains. It corresponds to a part of Upper Proterozoic oceanic crust obducted onto the northern margin of the West African craton during the Pan-African orogeny. The Bou Azzer ophiolite comprises in itslower part about 2000 m of serpentinite rocks which correspond to mantle peridotites, harzburgites and dunites, including a few chromitite pods and a sulphide-bearing horizon. The Neoproterozoic Bou Azzer ophiolite complex is host to small lenticular bodies of massive and disseminated chromite. Cores of metallurgical-grade high-Mg and high-Cr spine! (48-62 wt% Cr2O3) reveal complex alteration patterns resulting in successive Cr enrichment and loss of Al while Mg# remains almost constant. Concentration patterns of platinum-group elements are typical for ophiolitic chromitite poor in sulphides, with predominance of the IPGE, variable Rh, and low Pt and Pd. Laurite [RuS2], [Os-Ir-Ru] alloy and kashinite occur either included in spine! or in silicate matrix, accompanied by Ni/Co sulphides, arsenides and sulpharsenides. [Ni-Co-Fe] sulfides, arsenides and sulfarsenides devoid of PGE are associated with the alteration of chromite. Alteration of primary PGM encompasses formation of Ru-rich alloy from laurite, and Ir-rich phases found in Ni arsenide.