Sluzhenikinite, Pd15(Sb7-xSnx) 3 ≤ x ≤ 4, a new platinum group mineral (PGM) from the Oktyabrsk deposit, the Noril`sk deposits, Russia

Abstract

AbstractSluzhenikinite, Pd15(Sb7–xSnx) with 3 ≤ x ≤ 4, is a new mineral discovered in the pegmatoidal galena–chalcopyrite massive ore from the Oktyabrsk mine, Oktyabrsk deposit of the Noril`sk deposits, Russia. Sluzhenikinite forms euhedral elongate lamellar crystals (100–150 μm long and 10–50 μm wide) associated with Au–Ag alloy, insizwaite and myrmekitic intergrowths of Pt–Pd minerals (stibiopalladinite, maslovite and sobolevskite), in close association of sperrylite and base-metal sulfides (galena, chalcopyrite, cubanite and pentlandite). In plane-polarised light, sluzhenikinite is pale brown with weak bireflectance, imperceptible pleochroism, and weak anisotropy with straw yellow to deep blue rotation tints; it exhibits no internal reflections. Reflectance values for sluzhenikinite in air (R1,R2 in %) are: 46.2, 46.5 at 470nm; 52.1, 52.2 at 546nm; 54.7, 55.1 at 589nm; and 57.8, 59.0 at 650nm. Thirteen electron-microprobe analyses of sluzhenikinite gave an average composition: Pd 65.06, Sn 15.60 and Sb 19.58, total 100.24 wt.%, corresponding to the formula Pd14.88(Sb3.92Sn3.20)Σ7.12 based on 22 atoms; the average of twenty-one energy dispersive spectroscopy analyses on co-type material gave: Pd 63.36, Pt 1.15, Sn 16.28 and Sb 19.21, total 100.00 wt.%, corresponding to the formula (Pd14.62Pt0.14)Σ14.76(Sb3.87Sn3.37)Σ7.24. The density, calculated on the basis of the empirical formula, is 11.22 g/cm3. The mineral is monoclinic, space group P21/m, with a = 7.5558(1), b = 29.2967(3), c = 7.5713(1) Å, β = 119.931(2)°, V = 1452.44(4) Å3 and Z = 4. The crystal structure was determined using data from single-crystal X-ray diffraction and demonstrates conclusively that the correct stoichiometry is Pd15(Sb,Sn)7, rather than Pd2(Sb,Sn); R1 = 0.035, wR2 = 0.073, GoF = 1.118 for 209 refined parameters and 4738 unique reflections. The mineral is named after Sergey Fedorovich Sluzhenikin, an expert on platinum-group minerals, particularly from the area of the type locality.