COARSE-GRAINED CABRIITE FROM NORIL'SK, RUSSIA

Abstract

Cabriite, ideally Pd 2SnCu, has been reported from five localities worldwide, and was first described in the Noril'sk-Talnakh mining district of northwestern Russia. We summarize previous research on cabriite and provide an additional description. A relatively coarse (0.50 * 0.35 mm) roundish oval grain of cabriite was found in a sulfide-PGM (platinum-group mineral) concentrate from the Noril'sk district. It is surrounded by cubanite and chalcopyrite, which are cut by minor veinlets of galen a and flanked by coarse (mm-scale) crystals of sperrylite. The cabriite itself is rather homogeneous, 10 analyses revealing Pt and Sb as the only significant minor elements. It contains on average 4.87 wt.% Pt and 0.82% Sb, and its formula is (Pd 1.92Pt0.10) (Sn0.95Sb0.03)Cu0.99. The Pt apparently substitutes for Pd, and Sb to a lesser extent for Sn. The cabriite contains minute (1-6 μm) rounded blebs of a Pt-Sb-Bi phase, bismuthian geversite, Pt(Sb,As,Bi) 2, with Sb > Bi and minimal As. Associated phases (cubanite, chalcopyrite, sperrylite) are also rather pure and homogeneous, with the exceptions of talnakhite and cubanite exsol ved from chalcopyrite and the compositional diversity of abundant Au-Ag alloy. Thus the cabriite has a partial rim of native silver (<1 wt.% Au), indistinguishable from silver that infills a brittle fracture in the margin of adjacent coarse sperrylite, yet quite distinct from nearby coarse zoned aurian silver (1.5–24 wt.% Au). Textural features of the sample are compared to published data, affirming a late-stage origin for cabriite and associated Au–Ag alloy.