REDISTRIBUTION OF IRON AT BOUNDARIES OF GRAINS OF FE-PT ALLOYS WITH OLIVINE AND CHROMITE

Abstract

The authors in a previous work showed that Fe-Pt alloys in ultramafic rocks are secondary, and proposed a fluid metasomatic model for their genesis, i.e., formation from primary solid solutions of Pt, Ir, Ru and Os via loss of rare platinum group elements from the system and reduction of iron in host-rock minerals by derived reducing fluid. That model was based chiefly on observations of relationships between platinum-metal minerals in rocks of different ultramafic associations and on analysis of chemical compositions of the same minerals. Here we shall discuss the new finding of redistribution of iron at the boundaries of grains of Fe-Pt alloy with their host minerals, olivine and chromite in dunite. The authors have established that deposition of Fe-Pt mineralization in rocks of the ultramafic associations was accompanied by solid-phase reactions, in which iron was redistributed between host-rock minerals and accessory platinum alloys.