PT-PD TETRAAURICUPRIDE AND ASSOCIATED MINERALS IN ORES OF THE NORILSK-I DEPOSIT

Abstract

A specific assemblage of precious-metal minerals including majakite, Pb stannopalladinite, Pt-Pd tetraauricupride, plumbopalladinite, Sn plumbopalladinite, polarite, tetraferroplatinum, kuestelite, and electrum is described in magmatic galena-magnetite-pentlandite-chalcopyrite ores of the Norilsk-I deposit. The composition of stannopalladinite varies from [(Pd4.5Pt0.5)Cu(Sn1.7Pb0.3)] (generation 1) to [Pd3(Pb1.0Sn0.8Bi0.1Sb0. 1)]. Majakite was formed by replacement of pentlandite. Its composition changes from (Pd0.98Ni1.02As) to (Pd1.01Ni0.99Co0.01As0.99). Polarite was formed generally by replacement of plumbopalladinite and consequently has a high proportion of Pb [Pd(Pb0.8-0.7Bi0.2-0.3)]. Tetraferroplatinum contains 3-4 wt % Ni and 1.5-2 wt % Cu, tetraauricupride (CuAu) has 4-5 wt % Pd and 3-7 wt % Pt, and kuestelite and electrum include Pt and Pd traces. Fineness is 399-309‰ for electrum and 282-168‰ for kuestelite. Precious-metal mineral aggregates originated by replacement of galena (and, locally, of magnetite, chalcopyrite, and pentlandite) under strongly reducing conditions. Fluids transported Pd, Pt, Ag, Au, As, Sn, Bi, and Sb, while Pb, Ni, Cu, Fe, and Co were derived from replaced minerals of sulfide ores. The occurrence of tetraauricupride indicates that the Pd, Pt, Ag, and Au mineral assemblage crystallized at temperatures below 410°C. This assemblage is rich in Pd arsenide. Its minerals have high Pb contents, are almost free of Te, and include only small amounts of Sb. Most of the other precious-metal mineral assemblages of the Norilsk ore field contain sperrylite (PtAs2), paolovite [Pd2(Sn,Sb)], geversite [Pt(Sb,Bi)2], maslovite (PtTeBi), and michenerite (PdTeBi), together with altaite (PbTe) and hessite (Ag2Te).