PLACER PGE MINERALS FROM THE FILIPPA CLINOPYROXENITE-DUNITE MASSIF (KAMCHATKA)

Abstract

Study is given to association of PGE minerals from the Maior Brook placer in the Filippa zoned massif of the Ural-Alaskan type. The massif rocks feeding placers (dunites, wehrlites, and clinopyroxenites) are seriously crushed and metasomatized. The PGE minerals are dominated by Ir-rich Pt-Fe alloys. The PGE mineral association involves native iridium grains (20%). The isoferroplatinum bears inclusions of PGE sulfides, arsenides, sulfoarsenides, and antimonides. There are also all varieties of PGE-thiospinels, including Pb- and Co-bearing ones, hollingworthite RhAsS with up to 15.7 wt.% Sb, and malanite-carrolite CuPt2S4-CuCo2S4 (up to 47 mol.%), kashinite-bowieite Ir2S3-Rh2S3, and, more seldom, laurite-erlichmanite RuS2-OsS2 isomorphous series. Their inclusions bear PGE-containing Mss and Iss solid solutions as well as rare minerals such as rhodarsenide (Rh,Pd,Pt)2As, polkanovite Rh12As7, genkinite (Pt,Pd)4Sb3, stumpflite PtSb, mertieite II (Pd,Pt)8Sb3, and unnamed phases IrAs(Sb,S), Pt(As,Sb,S), (Rh,Pt,Os,Fe)2(S,As)3, and (Fe,Cu)(Pd,Pt)3(S,Sb,As)3. The conclusion is drawn that the ore-forming system of the source-rock of the studied mineral association, namely, the Filippa massif, had mainly an iridium composition at the early magmatic stage and showed high activities of S and As during the postmagmatic transformations of Pt-Fe alloys. At the late evolution stage, the system became enriched in Pb and Co.