Menshikovite Pd3Ni2As3 and Associating Minerals of Sulfide Ores at the Eastern Flank of the Oktyabrsky Deposit (Norilsk Ore Field)

Abstract

Considerable amounts of menshikovite (the rare palladium–nickel arsenide Pd3Ni2As3) have been found at the eastern flank of the Oktyabrsky deposit (Norilsk ore field) near the contact of solid and impregnation sulfide Co–Ni–Cu ores within the magnetite–plagioclase–fassaite skarns. The sulfide material of the ores consists of aggregates of chalcopyrite, pentlandite, pyrrhotite, and cubanite produced by subsolidus transformations of high-temperature Iss3, Iss4 and subordinate Mss solid solutions, with ingrowth of later Se‑galena. Menshikovite associated to mertieite II, Ag-gold (756–706 fineness), Au-electrum (694–672 fineness), kotulskite, moncheite, rare altaite, hessite, naldrettite, and melonite consists of fine (30 μm or less) metasomatic ingrowths at the contact of silicate mass and aggregates of sulfides. The composition of menshikovite is close to the theoretical data: (Pd2.98Ru0.03)3.01(Ni1.89Fe0.08Co0.01)1.98 (As2.94Se0.04Bi0.02Sn0.01)3.01. Sperrylite metacrystals truncate the borders of menshikovite accretions along with other minerals of noble metals and contain their “corroded” inclusions. This association of pneumatolytic minerals of noble metals was formed under increased activity of As, Te, Sb, and Bi in fluids with low Sn activity. Menshikovite is characteristic for the Pd-richest Oktyabrsky deposit. Another palladium–nickel arsenide, that is, mayakite PdNiAs, is of quite wide occurrence in the Talnakh and Norilsk 1 deposits. The distribution of Pd and Ni arsenides is probably an element of the mineral zonality of the Norilsk ore field.