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Research subject. The paper presents data on the mineralogical, geochemical and fluid inclusion features of the Southern Ak-Dag gold-sulphide-quartz ore occurrence in Western Tuva.Methods. Mineral formation temperatures, salt composition and fluid salinity were examined using a Linkam TMS-600 cryostage and an Olympus BX 51 microscope. The chemical composition of samples was identified using a MIRA 3 LMU (Tescan Orsay Holding) scanning electron microscope equipped with INCA Energy 450+XMax 80 and INCA Wave 500 microanalysis systems; BSE photos were taken by Tescan Vega 3 and Hitachi ТМ-1000 SEM instruments.Results. The ores under study were found to contain both high-grade and medium-grade gold with an Ag content of up to 17.05 wt %. The average gold fineness comprised 904 ‰, ranging from 830 to 928 ‰. According to fluid inclusion data, gold-sulphide-quartz veins were formed at temperatures of 280–240 °C and pressures of 0.8–1.2 kbar from aqueous fluids having a salinity of 8.6–6.4 wt % NaCl eq. The narrow range of fluid salinity at decreasing temperatures and the prevalence of high-grade gold in sulphide-quartz veins indicate a relatively high rate of mineral formation in a narrow permeable zone without any significant interaction with host rocks or mixing with meteoric waters.Conclusions. Gold mineralization in the Southern Ak-Dag ore occurrence, which was formed within one ore substage, corresponds to the type of gold-galena-chalcopyrite with barite. The established similarity of native gold in the Southern Ak-Dag occurrence and other deposits in the Aldan-Maadyr ore cluster in terms of P-T parameters of ore formation and mineralogical and geochemical features, as well as association of the ore mineralization with beresites, indicate the possibility of discovering industrial ore deposits in the region and confirm its paragenetic relation with Devonian magmatic activity.

The paper shows new fluid inclusion and isotopic-geochemical data for minerals from sulphide-carbonate-quartz veins of Vosnesensky Cu-porphyry deposit. Fluid inclusions were analyzed by means Linkam TMS-600 cryostage equipped with Olympus BX 51 optical microscope; trace element amounts were performed used Agilent 7700x and ELAN 9000 mass-spectrometers; sulphur isotopic composition was analyzed on DeltaPLUS Advantagе mass-spectrometer. We determined that fluid inclusions in quartz were homogenized between 215 and 315 ºС, and in latest calcite, they are 230–280 ºС. Fluids are К-Na water chloride with salinity of 3–12 wt % NaCl-eq. Quartz contain high amounts of Al (184–5180 ppm), K (20.1–1040 ppm), Na (30.2–1570 ppm) and Ti (38.4–193 ppm). The REE distribution spectra of pyrite are characterized by light lanthanides accumulation (LaN/YbN = 3.6–6.44), and negative of Ce anomalies (0.7–0.92) and Eu (0.78–0.99). The Y/ Ho ratio in pyrite varies from 27.6 up to 36.8. The δ34S values in pyrite were –1.01…0.8 ‰, in chalcopyrite – 0.9 ‰. The data testify the Cu-porphyry mineralization of Vosnesensky deposit was formed due to magmatic acid high-aluminous К-Na chloride fluid enriched with light REE in mesothermal environment. We identified the geochemical markers of interaction between fluid and host rocks.

The relevance of the study is in the need to expand the mineral resource base of Russia. Eastern Transbaikalia is one of the oldest gold mining regions of the country. Nevertheless, even in such a well-studied region, the issue of search and discovery of new ore deposits is acute. For the successful completion of such a task, the data are needed from a detailed study of already known ore deposits, which can be used to develop scientifically based criteria for search for ore deposits and mineralization forecast. Such data include determination of sources of ore-bearing magmatic melts, age and conditions for gold mineralization formation of the Alexandrovskoegold deposit. The aim of the study was to prove participation in formation of several magma chambers with different characteristics, using the results of studying the distribution of rare-earth elements in igneous rocks and ores, the isotopic composition of oxygen of ore-bearing quartz and sulfur sulfide, as well physicochemical conditions for formation of mineralization by studying fluid inclusions in minerals. Objects of researches is igneous rocks and ores of the Alexandrovskoe gold deposit, located in the Eastern Transbaikalia. Methods.To determine the elemental composition of the rocks, we used the X-ray fluorescence method and standard chemical analysis, the concentrations of rare-earth elements were measured using the method of sorption-atomic emission analysis with inductively coupled plasma (GIN SB RAS, Ulan-Ude). The study of isotopic composition of sulfur sulfides, Au and Ag contents, and isotopic age (40Ar/39Ar) was carried out at the multicomponent and isotopic research center of the Siberian Branch of the Russian Academy of Sciences (Novosibirsk). Fluid inclusions in quartz of ore veins were studied by traditional methods of thermobarogeochemistry and Raman spectroscopy. Results. The age (40Ar/39Ar) of synrudic sericite (162 ±2,3 Ma) was determined, which corresponds to the age of intrusions of the Amujikan-Shakhtaminsky complex. It was established that variations in isotopic composition of oxygen in ore-bearing quartz and isotopes of sulfur sulfides correspond to a fluid of magmatic nature. An analysis of distribution of rare and rare earth elements indicates that the sources of mineralization were deep-seated, differentially differentiated magma chambers that functioned both in the upper and lower continental crust. According to the study of fluid inclusions in quartz of ore veins, crystallization of mineral paragenesis of ore deposits occurred in the temperature range from 150 to 402°C. A productive mineral association was formed at 402–360°C. The paper indicated the participation of ore-forming fluids that differ in salt compositionin ore formation. This indicates different conditions for generation and nature of ore-forming fluids. A distinctive feature of the deposit is ore formation due to various depthdifferent degrees differentiated ore-bearing magmatic sources.

In the paper, there are adduced the data of a thermobarogeochemistry investigation of fluid inclusions in apatite of magnetite-chlorite-carbonates rocks from ultrabasite Karabash massife. The rocks are carrying copper-bearing aurum (1.3-2.6 wt % Cu) and was formed at temperature in the range of 480-280°C and a pressure of about 2-3 kbar. The content of the inclusions corresponds to the salt system of H2O-NaCl and the salt concentration in the solution 3.7-8.8 wt % eq. NaCl. Fluids gas components, extraction by pirolysis up to temperature 450°C, are described by a system C-H-O with an insignificantly amount of nitrogen. In fluid composition presents a small amount of the reduced gasses - CO, H2, CH4, hard carbon-hydrates (C2H4, C2H6, C3H6, C3H8 etc.). Adduced comparative analysis of fluid composition and the degree of oxidation fluid gas component (Ofl = CO2/(CO2 + CO + H2 + CH4) during the forming magnetite-chlorite-carbonate rocks, the rodingites and the listwenites. It is established, that carbon acid part of mole in fluid (XCO2) grown from extremely low value by the forming of rodingites with copper-bearing aurum (

The Kara ore node is located within the Sretensk-Kara ore region of East Transbaikalia. The geological structure of this area is complex due to its location within the Mongol-Okhotsk suture, the zone wherein the Siberian and Mongolia-China continents collided into each other at the turn of the Early and Middle Jurassic. During the plate collision, intense magmatism was accompanied by the formation of focal-dome, dome-ring and other structures. The Kara ore node is controlled by the Ust-Kara focal dome-ring structure. The central part of latter is composed of Kara-Chacha granitoids from the Amudzhikan-Sretensk intrusive complex (J3-K1) with the system of subvolcanic and vein formations, including grorudites. It is suggested that gold mineralization in the study area is genetically related to grorudites; however, physical and chemical conditions for the formation of these alkaline rocks, their genesis and role in the hydrothermal gold-ore process still have not been sufficiently investigated. To this end, the authors of this paper have studied fluid inclusions (FI) in quartz from these rocks. It has been found that quartz porphyry phenocrysts in grorudite contain FI of diverse forms, the size of which ranges from 5 to 48 microns. Measured temperatures of ice melting (–2.5°C) and complete homogenization into liquid (350 °C) show that the concentration of salts in the fluid amounts to 4.2 wt % of eq. NaC, its density is 0.64 g/cm3, and the pressure is 1.6 kb. At LA-ICP-MS of individual FI, clear analytical signals were derived from Na and K. As, Mo, Sb, Cs, W, and Hg were traced in significant quantities. The Raman scanning showed the presence of N2 in the primary (substantially gaseous) FI, and CO2, N2, and CH4 in the primary-secondary FI.