ГЕОЛОГИЧЕСКАЯ КАРТА ЮГО-ВОСТОЧНОЙ ФЕННОСКАНДИИ МАСШТАБА 1:750 000: НОВЫЕ ПОДХОДЫ К СОСТАВЛЕНИЮ

The results of the study of rare-metal (Bi, Te, Se. Be, In) mineralization of skarn deposits (Sn, Zn) in the Pitkäranta Mining District, genetically related to the Salmi anorthosite-rapakivi granite batholiths of Early Riphean age are reported. Minerals and their chemical composition were identified on the base of optical microscopy as well as electron microanalysis. The diversity of rare-metal ore mineralization (native metals, oxides, and hydroxides, carbonates, tellurides, selenides, sulfides, sulphosalts, borates, and silicates) in Pitkäranta Mining District ores is indicative of considerable variations in the physicochemical conditions of their formation controlled by the discrete-pulse-like supply of fluids. Bismuth, wittichenite, and matildite are the most common rare-metal minerals. Sulfosalts of the bismuthinite-aikinite series are represented only by its end-members. The absence of solid solution exsolution structures in sulfobismuthides suggests that they crystallized from hydrothermal solutions at low temperatures. Be (>10 minerals) and In (roquesite) minerals occur mainly in aposkarn greisens. Roquesite in Pitkäranta Mining District ores formed upon greisen alteration of skarns with In released upon the alteration of In-bearing solid sphalerite (Cu¹⁺ In³⁺) ↔ (Zn²⁺, Fe²⁺) and chalcopyrite In³⁺ ↔ Fe³⁺ and 2Fe³⁺ ↔ (Fe²⁺, Zn²⁺) Sn⁴⁺ solutions. Sphalerite with an average In concentration of 2001 ppm, is a major In-bearing mineral in the ores.

A wide application of modern precision research techniques to the studies of Pitkyaranta ores allowed us to find increased contents of indium (to 0.33%), silver (447 g/t), gold (0.2–0.4 g/t), and...

The paper reports the results of studies on critical metal mineralization genetically related to the late-stage intrusions of Salmi anorthosite-rapakivi granite batholith (SARGB) in the Riphean age. In, Bi, and Be mineralization in skarn-greisen deposits and occurrences at the SARGB endocontact, as well as REE and Nb-Ta mineralization in Li-F granites, understood as the late intrusive phases of the batholith, were studied. It is the first report on columbite-group minerals, as well as REE-Ta-Nb and REE mineralization in SARGB granites. Optical and scanning electron microscopy, EDS and LA ICP MS microanalysis, X-ray fluorescence spectrometry, Raman spectroscopy, and inductively coupled plasma mass spectrometry (ICP-MS) were used. The data obtained show that roquesite formation was mainly triggered by the decay of In-bearing solid sphalerite and chalcopyrite solutions. Zavaritskite, associated with unoxidized sulphides, was derived hypogenically and seldom occurs in ores. A helvine-group mineral association with zinc-enriched spinel (ZnO 22%–25%) seems to have been one of the factors preventing genthelvite formation. The Muzilampi, Hepaoja and Avtodor ore occurrences in Li-F granites display similar REE and Nb-Ta mineralization. They are associated with Y-fluorite and Li-siderophyllite, which contain exceptionally high Nb concentrations (0.25%–0.78%) in Muzilampi granites. Additionally, fluorite-1 is commonly overfilled (to >50%) with micron-sized synchisite and parisite inclusions. Columbite-tantalite-group minerals, present at all the occurrences studied, occur solely as ferricolumbites with a dominant Mn/(Mn + Fe) ratio of 0.9 approaching the maximum values (~1.0) in the most differentiated granites.

The Rajkonkoski ore occurrence is located within the region of the Karelian craton (AR₂) and the Svecofennian folded belt (PR₁) conjugation. It is presented by quartz-carbonate veins in metadoleriles and a zone of brecciation, crumple, and silification of carbonaceous shales within the volcanites of the Soanlakhtinsky suite (PR₁). Ore mineralization in black shales and quartz veins has features of genetic similarity presenting different levels of the ore system controlled by different range strike-slip fault dislocations. At the Rajkonkoski ore occurrence, 41 ore minerals have been identified: 12 tellurides (native tellurium, hedleyite, pilsenite, tsumoite, tellurobismuthite, hessite, stuetzite, radclidzhite, joseite-B, altaite, volynskite, petzite); 4 bismuth-tellurides of the following compositions Bi₃Te, Bi₃Te₂, BiTe₄, PbBiTe; 3 selenides (clausthalite, tellurolaitakarite, native selenium); and 12 native metals (gold, silver, electrum, copper, iron, lead, tin, bismuth, osmiridium). The contents of the main ore minerals in places exceed 10%, and the concentrations of elements reach as follows: Cu and Pb, 5%; Zn, Bi, 1%; Se, 219 ppm; Te, 171 ppm; Sb, 3 ppm; As, 5 ppm; Ag, >0.1%; Au, 35.28 ppm. Ore mineralization is formed during the temperature interval from 550°C up to 300°C) complete miscibilities galenite-clausthalite and galenite-altaite are observed. In aggregate with a wide temperature interval (>400°C) of ore process evolution and mineral specia variety of telluride and native metal mineralizations, the original “torsion” of different temperature mineralizations makes it possible to determine the affiliation of the Rajkonkoski ore occurrence to the xenothermal type deposits or epithermal “alkaline,” gold-telluride A-type characterized by a close connection with magmatism of increased alkalinity and the original geochemical (Te-V-F) and mineral (tellurides of gold, silver and other metals, fluorite, roscoelite, vanadium-containing sulfides) associations. Taking into consideration that many of the xenothermal and epithermal A-type gold and silver deposits are large commercial objects, the prospects of the Rajkonkoski ore occurrence and the region of the Karelian craton and Svecofennian folded belt conjugation seem to be significant for noble metal mineralization.

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⁺ + In³⁺ ↔ 2Zn²⁺, 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).