ORIGIN OF INCLUSIONS OF HYDROUS SILICATES IN PLATINUM MINERALS AND CHROMIAN SPINELS FROM ULTRAMAFIC ROCKS

Abstract

The authors describe silicate inclusions in chromian spinels and syngenetic platinum minerals from the alpinotype ultramafic rocks of the Koryak Highlands and the alkalic-ultramafic plutons of the Aldan Shield. Both of these ultramafic associations are platiniferous and occur together with placers of platinum minerals. However, the mineralogical and chemical biases of the places differ. Thus, placers of hexagonal solid solutions of osmium, iridium and ruthenium are mainly associated with plutons of alpinotype ultramafics, while isoferroplatinum placers occur near alkalic-ultramafic plutons. A stable paragenetic relationship of the platinum minerals and chromian spinels to hydrous silicates is typical of both associational types of platinum-bearing ultramafic rocks. The syngenetic origin of the minerals of this paragenesis is indicated by finds of two-phase inclusions.