The South Sopchinsky massif (SSM): PGM descriptions.
ClausthalitePbSe - the mineral is relatively rare (Fig. 4 a). It may occur as an inclusion in silicate minerals, on the grain boundaries between chalcopyrite and bornite and as dispersed drop-like inclusions along the periphery of chalcopyrite. Grains are rounded in shape with a size of 1-7 microns. The mineral occurs in association with silver, covellite and geerite. The chemical composition is: Pb 75.39-76.21, Se 22.12-23.79 (wt. %).
Vincentite Pd3As – this is one of the most common minerals. It occurs within silicate minerals and along the periphery of millerite grains and also forms intergrowths at the grain boundaries of silicates with chalcopyrite and bornite(Fig. 4 b, f). Most frequent are accretions with kotulskite and silver. The grains are usually irregular and angular in shape and also form drop-like inclusions in chalcopyrite. The mineral occurs in association with hollingworthite, chalcocite and covellite. The chemical composition is: Pd 72.14-79.74, As 17.92-21.38 (wt. %). In addition, there is up to 2.10 wt% Te, 0.61 wt% Sb, 2.64 wt% Fe, 2.74 wt% Ni, and 5.62 wt. % Hg).
Sopcheite Ag4Pd3Te4 – this is a rare mineral observed in silicate minerals (Fig. 4 c). The grain size is up to 20 microns, and grains are irregular in shape. The mineral occurs associated with palladoarsenide, sperrylite, kotulskite, bornite and magnetite. The chemical composition is: Ag 34.10, Pd 25.19, Te 40.71 (wt. %).
Palladoarsenide Pd2As – this forms isolated grains with sizes of up to 20 microns (Fig. 4 c). Grains of irregular shape occur in association with sopcheite, sperrylite, kotulskite and bornite in silicate minerals. The chemical composition is: Pd 74.25, As 22.50 (wt. %) with the admixture of 3.25 wt. % Hg.
Braggite (Pt, Pd, Ni) S - Grains are rounded in shape with sizes of about 4 microns, located in silicate minerals. The mineral occurs in association with chalcopyrite, bornite, sperrylite and stillwaterite(Fig. 4 d). The chemical composition is: Pt 84.80, Pd 1.99, Ni 1.04, S 12.17 (wt. %).
Stillwaterite Pd8As3 - single occurrenceintergrown with sperrylite in silicate mineral (Fig. 4 d). The grain is irregular in shape with a size of 5 microns. The mineral occurs in association with braggite, chalcopyrite and bornite. The chemical composition is: Pd 77.97, As 21.90 (wt. %). The mineral also contains a small amount of Ni (0.13 wt. %).
Hollingworthite (Rh, Pt, Pd) AsS - this rare mineral forms individual grains in silicate minerals and simple accretions with sperrylite(Fig. 4 e, f). The grain size is 4-6 microns. The mineral occurs in association with covellite, magnetite and ilmenite. The chemical composition is: Rh 20.62-46.26, Pt 3.87-17.09, Pd 0.85-1.71, As 30.27-32.34, S 12.78-15.88 (wt. %). In some cases significant amounts of Ir may occur (1.95-18.10 wt. %).
Kotulskite Pd (Te, Bi) 1-2 – together with vincentite this is one of the most frequently encountered minerals. It forms drop-like inclusions in chalcopyrite, but it is more often intergrown with vincentite and silver along the periphery of bornite or chalcopyrite grains (Fig. 4 f). Rarely, kotulskite occurs in silicate minerals. Complex intergrowths with sopcheite, palladoarsenide, sperrylite and bornite were also observed (Fig. 4 c). The grain shape of kotulskite is irregular, and grain size varies from 2 to 20 microns. The chemical composition is: Pd 40.08-42.25, Te 31.09-33.45, Bi 24.91-26.64 (wt. %).
Sperrylite PtAs2 – the mineral was observed in a few cases in various positions (Fig. 4 c, d, f). Grains are irregular and angular in shape. The grain sizes range from 2 to 25 microns. The mineral occurs in association with chalcopyrite, bornite, stillwaterite, braggite, hollingworthite, sopcheite, palladoarsenide and kotulskite. The chemical composition is: Pt 54.77-55.11, As 44.89-45.10 (wt. %). The mineral may contain 0.31 wt. % Pd.