PLATINUM GROUP MINERALS AND TYPES OF THEIR ASSOCIATIONS IN GOLD PLACERS OF THE SAYAN-BAIKAL FOLDED AREA (Buryatia)
D.A. Orsoev, Yu.Ch. Ochirov, A.G. Mironov, B.B. Damdinov, and S.M. Zhmodik*
Geological Institute, Siberian Branch of the RAS, 6 ul. Sakh'yanovoi, Ulan Ude, 670047, Russia
* Institute of Geology, Siberian Branch of the RAS, 3 prosp. Koptyuga, Novosibirsk, 630090, Russia
Keywords: PGE minerals, types of associations, alluvial placers, ultrabasic rocks, ophiolites
Pages: 312-324
Abstract
Minerals of platinum group elements (PGE) from gold placers were studied in various regions of the Sayan-Baikal Folded Area (Buryatia). Four types of mineral associations have first been recognized: Ru-Ir-Os, Os-Ir, Pt-Fe, and sperrylite, which differ from each other in a set of platinoids. Primary minerals are dominated by Os-Ir-Ru alloys; Pt-Os-Ir-Ru and Pt-Fe solid solutions are less common; and sperrylite is scarce. Secondary PGE minerals are sulfides, arsenides, sulfoarsenides, sulfoantimonides, and Pt-Cu alloys. Based on the mineral compositions and our own and literature data, conclusions about the source rocks for PGE minerals have been drawn. The Ru-Ir-Os association is supposed to have formed in chromitites of dunite-harzburgite complexes of ophiolite belts; the sperrylite one, in layered gabbro-peridotite massifs with Cu-Ni sulfide mineralization; and the Os-Ir association, in zones of hydrothermal processes in ultrabasic rocks and their metamorphic varieties. The source rock for Pt-Fe association has not been established yet. This association might be genetically related to zonal basic-ultrabasic massifs of the Uralian-Alaskan type. Its occurrences in the Muya zone suggest the existence of commercial gold placers in northern Buryatia.
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