Vymazalovaite, Pd3Bi2S2, a new mineral from the Noril'sk-Talnakh deposit, Krasnoyarskiy region, Russia

摘要

Vymazalovaite, Pd3Bi2S2 is a new platinum-group mineral discovered in the Komsomolsky mine of the Talnalch deposit, Noril'sk district, Russia. It forms small (from a few pm to 20-35 mu m) inclusions or euhedral grains in intergrowths of polarite, sobolevskite, acanthite and unnamed (Pd,Ag)(5)BiS2 in aggregates (up to similar to 200 mu m) in galena and rarely in chalcopyrite. It occurs with telargpalite, cooperite, braggite, vysotskite, sopcheite, stibiopalladinite, sobolevskite, moncheite, kotulskite, malyshevite, insizwaite, Au-bearing silver and the newly described mineral kravtsovite (PdAg2S) in association with pyrite, chalcopyrite and galena in vein-disseminated mineralization in skarn rocks. Synthetic vymazalovaite is brittle; it has a metallic lustre and a grey streak. In plane-polarized reflected light, vymazalovaite is creamy grey and appears slightly brownish against galena in the assemblage with chalcopyrite. It exhibits no internal reflections. Average reflectance values in air for natural and synthetic vymazalovaite are (R natural, R synthetic in %) are: 46.35, 45.7 at 470 nm, 47.65, 47.45 at 546 nm, 48.5, 48.2 at 589 nm and 49.5, 49.0 at 650 nm. Seven electron probe micro-analyses of vymazalovaite give an average composition: Pd 40.42, Bi 49.15, Ag 0.55, Pb 1.02, S 7.77 and Se 0.26, total 99.17 wt.%, corresponding to the empirical formula Pd-3.05 (Bi1.89Ag0.04Pb0.04)(Sigma 1.97)(S1.95Se0.03)(Sigma 1.98) based on a total of 7 atoms per formula unit. The simplified formula is Pd3Bi2S2. The mineral is cubic, space group I2(1)3, with a = 8.3097(9) , V = 573.79(1) (3) and Z = 4. The density calculated on the basis of the empirical formula and cell dimensions of synthetic vymazalovaite is 9.25 g/cm(3). The strongest lines in the powder X-ray diffraction pattern of synthetic vymamlovaite [d in (I) (hkl)] are: 4.15(32)(200), 2.93(78)(220), 2.40(100)(220), 2.08(53)(400), 1.695(34)(422), 1.468(35)(440) and 1.252(31)(622). The structural identity of natural vyrnazalovaite with synthetic Pd3Bi2S2 was confirmed by electron back-scatter diffraction measurements on the natural sample. This new mineral honours Dr Anna Vymazalova of the Czech Geological Survey, Prague.