Mineralogy and formation conditions of Kholtoson tungsten deposit ores

The purpose of the research is to identify and study the features of mineral composition and formation conditions of ores of the Kholtoson tungsten deposit located within the Dzhida molybdenum-tungsten ore field (South-West Transbaikalia, Russia). The study employs a complex of mineralogical-petrographic and thermobarogeochemical methods. The molybdenum mineralization of the Dzhida ore field is confined to the apical part of the Pervomaisky stock (Pervomayskoye deposit), the tungsten mineralization is confined to numerous quartz veins in the western part of the ore field (Kholtoson vein deposit) as well as to the stockwork in the central part (Inkur stockwork deposit). The Kholtoson deposit occupies the western part of the ore field and is composed of numerous quartz veins localized mainly in the diorites of the Modonkul massif. Conducted works allowed to find out that the main gangue mineral is quartz; muscovite, potassium feldspar and carbonates are also present. Hubnerite is the main ore mineral of the Kholtoson deposit. In total, more than 20 mineral species have been identified including sulfides (pyrite, chalcopyrite, galena, sphalerite, bornite, etc.), sulfosalts (tetrahedrite, aikinite, stannite, etc.), oxides (scheelite, cassiterite), tellurides (hessite). According to the data of fluid inclusions study, calcium chlorides with an admixture of sodium and potassium chlorides predominate in the salt composition of oreforming fluids. The minimum temperatures of quartz deposition vary in the range of ~195–344 °С. Most of the homogenization temperatures determinations correspond to the range of ~250–300 °С. The presence of cogenetic fluid- and vapordominated inclusions in quartz from the ores of the Kholtoson deposit allows to estimate the fluid inclusion capture temperature range of 413–350 °C. The results of the studies carried out by the authors indicate that the main factors of hubnerite precipitation from hydrothermal solutions are changes in alkali-acid content and a temperature drop.