This paper presents the results of a quantitative analysis of impurity elements present in the structural form and composition of mineral and fluid inclusions in the quartz of the Kuznechikhinskoe deposit. The studies have been carried out using ICP–OES and FT–IR spectroscopy, electron paramagnetic resonance (EPR), and gas chromatography. It has been shown that the concentrations of mineral and fluid inclusions are low due to the deposit formation conditions, which positively affects the purity of quartz concentrates obtained. The main impurity is Al, present in the composition of mineral and fluid inclusions and in the crystal lattice of quartz itself. Spectroscopic studies allowed localizing impurities in the quartz and selecting an effective staged concentration process. The quartz samples are first crushed to the fraction of 0.1 to 0.4 mm, then subjected to electromagnetic separation, agglomeration treatment, and microwave decrepitation, and, at the final stage, undergo acid treatment in a combination of hydrofluoric and hydrochloric acids. The finishing deionized water washing and drying complete the deep concentration process to produce high-purity concentrates.

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The paper considers the conditions of quartz formation of hydrothermal-metamorphogenic-metasomatic and hydrothermal-metamorphogenic genesis of deposits and manifestations of the Middle and Southern Urals based on the study of fluid inclusions by methods of thermobarogeochemistry, ion and gas chromatography. It is established that the studied quartz objects are formed in a wide temperature range, against the background of insignificant differences in pressure values. It is shown that the temperatures of mineral formation in deposits of hydrothermal-metamorphogenic-metasomatic genesis vary from 440-230 ° C at a pressure of 1.2-1.4 kbar. The formation of these veins occurred with the participation of K-Mg-Fe-chloride fluid with a salinity of 1.2-8.7 wt. % NaCl-eq., depleted Mg and Fe due to the deposition of magnesia-ferruginous carbonates. A typomorphic feature of hydrothermal-metamorphogenic-metasomatic quartz is the high values of boron associated with the placement of quartz veins among pegmatoids and the presence of boron-containing mineral inclusions on quartz-vein objects. Veins of hydrothermal-metamorphogenic genesis were formed when the crack system was filled with quartz with the participation of a substantially K-Na chloride fluid (0.2-15.5 wt. % NaCl-eq.), at homogenization temperatures of 435-335 ° C and a pressure of 1.3-2.3 kbar. In the composition of fluid inclusions of hydrothermal-metamorphogenic-metasomatic quartz, the sum of "harmful" components (H2O, CO2, CH4, Cl, B, Na, K, Mg and Li) is less than in hydrothermal-metamorphogenic quartz. The studied quartz deposits and veins were formed in the range of temperatures and pressures not higher than the green shale stage during several successive stages: the formation of quartz veins – in a more high-temperature hydrothermal stage, while subsequent changes in quartz veins occurred under the influence of metamorphism processes, with a decrease in temperature. Subsequent changes are associated with the appearance of fracturing, cataclysm and recrystallization of quartz bodies with a decrease in grain size.

Research subject. Quartz veins of the Svetlorechenskoye, Karayan, Gora Khrustalnaya and Tolstikha quartz deposits in the Southern Urals.Methods. An optical study of quartz was performed using an Olympus BX51 optical microscope. A fluid inclusion study was performed using a thermostage TMS-600 (Linkam) equipped with the LinkSys V-2.39 software and an Olympus BX51 optical microscope (South Urals State University, Miass). The fluid composition in the inclusions was estimated from eutectic temperatures. Fluid salinity was calculated based on the melting temperatures of crystalline pha ses. Registration of infrared spectra was carried out using an infrared Fourier spectrometer Nicolet-6700 Thermo Scientific (SU FRC MG UB RAS, Miass). The spectra were processed using the OMNIC Thermo Nicolet software package and the Peakfit program. The extinction coefficients for calculating the concentration of molecular water and OH-groups were used from.Results. The veins are composed of coarse-grained milky-white quartz. The fluid inclusion data shows that the quartz veins were deposited from similar in composition NaCl-H2O fluids with salinities of 3–9 wt % NaCl eq. and at temperatures ranging from 100 to 280°C. Quartz in the Tolstikha deposit was deposited at the highest temperatures. According to IR spectroscopy data, quartz in the studied deposits is characterized by high contents of molecular water and average concentrations of Al-OH groups. According to the content of OH-groups, quartz in the Tolstikha deposit approaches industrial granulated quartz used in the production of high-purity quartz concentrates.Conclusions. Quartz veins in the studied deposits formed at temperatures ranging from 100 to 280°C. The salinity of inclusions in quartz ranged from 10 to 3.5 wt % NaCl eq. Mineral-forming fluids were of Na-chloride or Na-K-chloride composition, which indicates quartz crystallization during the post-diagenetic (metamorphic) transformation of rocks. Quartz in the studied deposits is characterized by a specific ratio of water and Al-OH, which is associated with the conditions of deposit formation and incompleteness of quartz metamorphism processes therein.

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