PLATINOIDS IN WEBSTERITES FROM THE NARUN MASSIF OF MAFIC AND ULTRAMAFIC ROCKS (WESTERN MONGOLIA)

Finely-dispersed grains of PGE metals were recognized for the first ti me in websterites from a banded complex of the Naran Massif of mafic a nd ultramafic rocks. The massif lies among Caledonian structures and i s part of the ophiolite association of Western Mongolia. The PGE miner als have the Pt-Pd-Fe-Ni-Cu composition and are doped with Rh and S. F erronickelplatinum is diagnosed among them; the rest of the compounds have no their own names. The platinoid mineralization in websterites o f the massif significantly differs from that in the chromites, with dr astically predominant minerals of the Os-Ir-Ru composition. Along with PGE minerals, grains of cupriferous awaruite with finest inclusions o f native silver and argentite have been found in websterites. It is su pposed that websterites are genetically related to the origin of a gab broid body intruded along the southern tectonic contact of an ultramaf ic protrusion with metamorphosed volcano-terrigenous rocks of its fram ing.