Chromitites Of Ultramafic Complexes Of The Valizhgen Peninsula, Koryakia, Ne Russia

Abstract

The paper presents the results of a study of ore and accessory chromite mineralization in the ultramafic rock complex of the Valizhgen Peninsula. The chromite mineralization belongs to the podiform type, is located in lens-shaped dunite bodies, and is represented by several structural-textural varieties. The ore and accessory chrome spinels have some specific compositional features that differ in the rocks of either series: chrome spinels of the cumulative dunite-orthopyroxenite-chromitite series have elevated Cr, Ti and Fe3+ contents, while spinels from residual harzburgites are typically low in Ti and Fe Fe3+ and variable in Cr and Mg contents. The specific location of chromitites in mafic-ultramafic massifs of the peninsula and the composition of ore and accessory chrome spinels from ultramafics can be accounted for by interaction of primitive mantle magmas with host harzburgites. The calculations using mineral thermobarometry indicate relatively low pressure and high temperature and oxygen fugacity during the formation of chromite mineralization. The chemical and Re-Os isotopic compositions are also studied for PGE minerals from placers of the Valizhgen Peninsula. We suggest that chromitites of the mafic-ultramafic massifs are sources of these placers.