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Polymetal JSC has identified several new gold deposits in the Turinsko-Auerbachovsky ore region of the Middle Urals in recent years. The study of geological and geochemical materials on these objects allowed us to substantiate their polygenic and polychronous nature. The gold mineralization took a long time to form during the concedimentary and conflict epochs of the region's development. During sedimentation, volcanogenic-sedimentary formations were enriched with ore elements due to underwater fluid flow during volcanic and subvolcanic processes, up to the formation of pyrites, including goldbearing ores. In the collisional epoch, three stages of gold accumulation were established, associated with linear folding and final granitoid magmatism, each of which was accompanied by the manifestation of goldbearing hydrothermal-metasomatic processes of the berezitoid type. The first two stages were ore preparation and led to the formation of gold-bearing mineralized zones of berezites, within which, during the third ore stage, ore zones were formed during their activation with the manifestation of shale, crushing, veining, and sulfidization. The analysis of materials from the well-known Vorontsovskoye deposit also confirmed the polygenic and polychronous nature of ore formation, previously noted by a number of researchers.

The origin of rare-metal deposits in granites is considered with regard for experimental data, which place constraints onto interpretations of geological materials and the genetic models. The role of both magmatic and hydrothermal–metasomatic factors in the formation of various types of rare-metal deposits is discussed. The saturation concentrations of Ta and Nb in granite melt significantly depend on the melt composition and vary from ~2–5 to ~0.1 wt %. These concentrations depend much less significantly on temperature and pressure. In granite melt in equilibrium with fluorine-bearing fluid, Ta and Nb are strongly partitioned into the melt. The paper demonstrates principal difference in the partitioning of W and Ta, Nb, Sn in melt granite–salt systems. The fluoride water–salt phase is a very effective extractant of W, while Ta, Nb, and Sn are completely retained in the aluminosilicate melt. The model magmatic fluid in equilibrium with Li–F granite melt is multiphase and contains significant amounts of SiO2 and Na, Al, Li and K fluorides. The solubility of ore minerals in this fluid is insignificant, with the concentration of Nb much higher than that of Ta. The HF concentrations in high-temperature magmatic fluids were estimated at ~0.5–1 M HF. The experimentally determined solidus temperatures of Li–F granites are ~570–630°C at a pressure of 100–200 MPa. At T = 300–550°С and P = 50–100 MPa, the actual hydrothermal transfer of Ta and Nb is possible only with sufficiently concentrated HF and, possibly, KF solutions (fluids). In sodium alkaline solutions, hydrothermal transport is quite probable for Nb but difficult for Ta, and the pyrochlore solubility is thereby higher than that of columbite. [ABSTRACT FROM AUTHOR]