Indium Distribution in Sphalerites from Pitkäranta Mining District (South Karelia, Russia)

The high-precision analytical study of sphalerites from Pitkäranta ore deposits used microprobe and La-ICP-MS analyses. Average concentrations of minor (Fe, Cu, Mn, Cd) and trace elements (In, Сo, Ni, Ga, Ge, As, Ag, Sn, Sb, Te, Au, Tl, Pb, Bi) in sphalerite were calculated from 169 analyses. It is shown that most analyzed elements are present in sphalerite as isomorphic components. The average content of In in sphalerite is 1927 ppm, and its maximum content is 1.5 wt %. The In-enriched sphalerite displays medium concentrations of Fe (3–6 wt % Fe), low Mn (300–400 ppm), and high Co (0.1–0.2 wt %). Parameters of the “indium window,” favorable for indium penetration into the sphalerite crystalline lattice, according to the scheme Cu + + In 3+ ↔ 2Zn 2+ , correspond to 0.6–1.2% Cd. The highest In content in sphalerite is characteristic of chalcopyrite-free ore-bearing mineral assemblages. The sphalerite-chalcopyrite association is, however, typical of the proper indium mineral, roquesite. Sphalerite in this association is distinguished by a low indium content (260–657 ppm). Ratio of indium contents in sphalerite and chalcopyrite (In Zn /In Cu ) in roquesite-bearing assemblages varies from 2 to 4, while in roquesite-free assemblages it is much higher (from 10 to 215). Indium distribution in the sphalerite samples, having also elevated contents of Cd, Ag, and Au, indicates that roquesite-free propylitized skarns with Sn–Zn–Fe mineralization in sites with relatively abrupt (40°–50°) dipping of the Salmi rapakivi massif roof, and without Li–F granites, are most perspective for indium and those other metals (Kitelä deposit, Kulismajoki and Hopunlampi ore occurrences).