New Criteria of the Genesis of Platinum Group Minerals in Intergrowths with Pyroxenes from Zonal Gabbro-Pyroxenite-Dunite Massifs in the South Koryak Highland (Russia)

摘要

The mineralogy of platinum group minerals (PGM) from placer deposits, transitional reservoirs, and primary sources of multiphase zonal gabbro-pyroxenite-dunite massifs has been characterized in the South Koryak Highland rather completely [1-3]. Nevertheless, examination of platinum heavy concentrates allowed us to reveal previously unstudied clinopyroxene (Cpx) + PGM intergrowths, which undoubtedly are of interest with respect to identification of their primary source. Taking into account the previous experience in PGM study [3, 4], several tons of pyroxenite should be reworked to gather a collection of (Cpx + PGM) grains. As is known, geochemistry of clinopyroxenes is very informative for the petrogenetic reconstructions of the origin of ultrama-fic rocks [5]. Therefore, the examination of clinopyroxenes from (Cpx + PGM) grains will obviously provide insight into their typomorphic genetic features and make it possible to specify new PGM sources in zonal gabbro-pyroxenite-dunite massifs. To solve the problem, the pyroxenes from a random selection of 110 (Cpx + PGM) grains were studied. Their major element compositions were determined on a Camebax Microbeam microprobe at the Institute of Geochemistry and Analytical Chemistry, Moscow (N.N. Kononkova, analyst). Among 148 analyzed clinopyroxenes, we selected 11 samples of (Cpx + PGM) grains for determining trace elements with secondary-ion mass spectroscopy (SIMS).