The paper is concerned with a geochemical study of apoultrabasic metasomatites of the Ospa-Kitoi, Parama, and Ust'-Kelyana ophiolite massifs located in the southern folded framing of the Siberian craton. The isotope (O, C, H, Sr, and Rb) systems of dunites, serpentinites, nephrites, listvenites, and talc-carbonate rocks are studied. The isotopic composition of oxygen in olivines from dunites is characterized by delta O-18 = 4.6-5.5 parts per thousand. The delta O-18 values of serpentinites (4.67-7.35 parts per thousand) point to the mantle genesis of fluids and might have been inherited from ultrabasic rocks. Nephrites are slightly enriched in heavy oxygen isotope (delta O-18 = 6.13-9.54 parts per thousand). This indicates that their fluid phase was transported from serpentinites and captured a small portion of the crustal component. The widest variations in delta O-18 values, from 8.12 to 17.46 parts per thousand, are observed in minerals from listvenites. Carbonates from these rocks show a highly heterogeneous isotopic composition of oxygen (delta O-18 = 12.9-18.8 parts per thousand) and carbon (delta C-13 = -2.8 to +2.8 parts per thousand). These rocks formed with the contribution of metamorphogenic fluids. According to the isotopic composition of hydrogen, the examined serpentinites are divided into two groups: with SD values specific to "magmatic water" (delta D = -73.50 to -85.00 parts per thousand) and those typical of meteoric fluids (delta D = -151.90 to -167.20 parts per thousand). The listvenites are characterized by low Rb and high Sr contents. Their Sr-87/Sr-86 values (0.70702-0.70971) indicate the contribution of a crustal source. The study of fluid inclusions in minerals from listvenites has shown that the rocks formed under relatively low-temperature conditions. The homogenization temperatures of fluid inclusions in quartz and magnesite from listvenites of the Ospa-Kitoi massif are 184-290 degrees C and 122-182 degrees C, respectively. In the Parama massif, the homogenization temperature of fluid inclusions in quartz is 130-170 degrees C. The solutions that formed listvenites of the Ospa-Kitoi massif were slightly saline (TDS = 2.9-8.4 wt.% NaCl eq.), with NaCl and Na2CO3 being the main salt components.

—We consider the isotope-geochemical features of epithermal fluorite deposits in Transbaikalia, including the REE compositions, Sr isotope ratios, Sm–Nd systems, and isotope compositions of oxygen, carbon, hydrogen, and sulfur. The 87Sr/86Sr ratios in fluorites are within 0.706–0.708, and the εNd values are negative. Oxygen in quartz, the main mineral of the deposits, has a light isotope composition (δ18O = –3.4 to +2.6‰), and the calculated isotope composition of oxygen in the fluid in equilibrium with quartz (δ18O = –9 to –16‰) indicates the presence of meteoric water. The latter is confirmed by analysis of the isotope compositions of oxygen and hydrogen in gas–liquid inclusions in fluorites from three deposits. These isotope compositions are due to recycling caused by the impact of shallow basic plutons. The isotope composition of sulfur indicates its deep source. During ascent, sulfur became enriched in its light isotope (δ34S = –1.8 to –7.7‰). We assess the association of fluorite ores with basaltoids widespread in the study area. The isotope and geochemical parameters suggest their spatial proximity. Probably, the basaltoids were responsible for the recycling of meteoric water. It is shown that the epithermal fluorite deposits formed by the same mechanism as fissure–vein thermal waters in western Transbaikalia.

Оценка масштабов участия метеорных вод в формировании эпитермальных флюоритовых месторождений (Забайкалье)

The paper presents the mineralogical and geochemical characteristics of two groups of hydrothermal rocks and their relation with subalkaline granites of the Ermakovskoe deposit. The first group includes fluorite-phenakite-bertrandite ore bodies, occurring outside the granite massif. The second group is presented by silicification bodies with sulfates, phosphates, kaolinite, muscovite and hematite. It bears REE (rare earth elements) mineralization (monazite, florencite, xenotime) and occurs within the massif. Our research included isotopic analyses of Sr, Nd and O, studies of trace, including rare-earth element compositions and age determination (U-Pb) of apatite from F-Be ores. Geochemical and isotopic studies are not according with relation between F-Be ores and granites. This is proven by the absence of Be-mineralization in granites and schlieren pegmatites, and a sharp difference in composition of their fluid phases. A reductive fluid specification forming F-Be ores (containing CH4, H2, N2, CO2 and H2S), contrasts sharply with fluid specification of granites. The granites are characterized by high oxygen fugacity, due to ferrous iron, sulfates and phosphates. Besides isotopic composition of oxygen in quartz (7.4 and 5.1‰ δ18О V-SMOW respectively), initial Sr ratios (0.7056-0.7065 and 0.707-0.709 respectively) and REE compositions are different.

This paper presents the results of geochronological (40Ar-39Ar, U–Pb SHRIMP II), petrological and geochemical studies of the Late Paleozoic complexes of alkaline rocks (Zimovechinsky, Tuchinsky and Koma) located within the Vitim Plateau (the western part of the Mongol-Okhotsk Orogenic Belt). The rocks were formed at 310–280 ​Ma. It is coeval with Late Paleozoic magmatism within the Central Asian Orogenic Belt. The εNd(T) values show large variations from −2.1 to +3.3 as well as the initial Sr(I) isotopic ratios from 0.7042 to 0.7138, that demonstrate strong isotopic heterogeneity of the magmatic source. The geochemical characteristics of the rocks show pronounced positive Pb and negative Ti, Zr–Hf anomalies that can be explained by involvement of the subducted component in primary melts. The rocks intruded in a setting of extension at the active continental margin of the Siberian Craton during subduction of Mongol-Okhotsk oceanic crust under the Siberian Craton.

isotope data of apocarbonate nephrites of the Vitim nephrite-bearing area are given.They haveonly meteoric-derived water source.Granites which concidered the source of water fluids produce only recycling of these waters.The oxygen in calciphyre was used from the altered matrix and formation water.

The aim of the study is to show evidence confirm the magmatic nature of the bastnaesite-fluorite rocks of the Ulan-Ude occurrence that represent a specific type of carbonatites. The minerals have been studied using electron microscopy, thermometry, and analysis of stable isotopes. In many cases, the content of both fluorite and bastnaesite in the studied rocks reaches 50%. The rocks formation time (134.2 ± 2.6 Ma) is close to that of the carbonatites in the Western Transbaikalia province. The temperature of bastnaesite and fluorite formation in the rocks exceeds 500 C. The studied rocks contain phenocrysts of fluorite, bastnaesite, and tetraferriflogopite. Their crystallization began in the intermediate focus. The fine-grain fluorite matrix with small bastnaesite scales was formed in near-to-the-surface conditions and fixed by the hardening of the rocks. The carbonatites feature melt “dryness”, which determines an extremely low occurrence of the hydrothermal processes, changes in the xenoliths and previously formed minerals. The low fluid saturation level is confirmed by the absence of phlogopite water in position A, filled with fluorine only. The carbonatites are characterized by a higher content of sulfates represented by tenardite, glauberite, plumbojarosite, and corkite that are present in the composition of the salt melts released at the later stage of the melt crystallization.

АННОТАЦИЯ: Жарчихинский рудный узел представляет собой уникальный объект.На его территории присутствуют несколько не типичных друг для друга типов минерализации.Это, помимо собственно молибденовой, на что и специализирована данная территория, флюорит-фенакит

Uakitite was observed in small troilite–daubréelite (±schreibersite) inclusions (up to 100 µm) and in large troilite–daubréelite nodules (up to 1 cm) in Fe-Ni-metal (kamacite) of the Uakit iron meteorite (IIAB), Republic of Buryatia, Russia. Such associations in the Uakit meteorite seemed to form due to high-temperature (>1000 °C) separation of Fe-Cr-rich sulfide liquid from Fe-metal melt. Most inclusions represent alternation of layers of troilite and daubréelite, which may be a result of solid decay of an initial Fe-Cr-sulfide. These inclusions are partially resorbed and mainly located in fissures of the meteorite, which is now filled with magnetite, and rarely other secondary minerals. Phase relations indicate that uakitite is one of the early minerals in these associations. It forms isometric (cubic) crystals (in daubréelite) or rounded grains (in schreibersite). The size of uakitite grains is usually less than 5 μm. It is associated with sulfides (daubréelite, troilite, grokhovskyite), schreibersite and magnetite. Carlsbergite CrN, a more abundant nitride in the Uakit meteorite, was not found in any assemblages with uakitite. Physical and optical properties of uakitite are quite similar to synthetic VN: yellow and transparent phase with metallic luster; Mohs hardness: 9–10; light gray color with a pinky tint in reflected light; density (calc.) = 6.128 g/cm3. Uakitite is structurally related to the osbornite group minerals: carlsbergite CrN and osbornite TiN. Structural data were obtained for three uakitite crystals using the electron backscatter diffraction (EBSD) technique. Fitting of the EBSD patterns for a synthetic VN model (cubic, Fm-3m, a = 4.1328(3) Å; V = 70.588(9) Å3; Z = 4) resulted in the parameter MAD = 0.14–0.37° (best-good fit). Analytical data for uakitite (n = 54, in wt. %) are: V, 71.33; Cr, 5.58; Fe, 1.56; N, 21.41; Ti, below detection limit (<0.005). The empirical formula (V0.91Cr0.07Fe0.02)1.00N1.00 indicates that chromium incorporates in the structure according to the scheme V3+ → Cr3+ (up to 7 mol. % of the carlsbergite end-member).

Research subject. The article presents results of mineralogical and geochemical investigation of albite-bearing granites with high concentrations of trace elements located in the Western Trans-Baikal region.Methods. The composition of rocks was determined by the methods of classical silicate analysis, X-ray fluorescence and ICP-MS analysis. Microstructural features, relationships and homogeneity of minerals were studied using an electron microscope LEO-1430 equipped with an energy dispersive spectrometer Inca Energy-300. Isotopic compositions of oxygen were carried out using a mass spectrometer Finigan MAT 253 in the mode of a constant helium flow.Results. Ore mineralization is specified by the presence of Nb-bearing and less REE-bearing minerals. The studied rocks were divided into two groups: albitized granites, and deep albitized granites and albitites. These groups differ in terms of the presence of accessory minerals. The deep albitized granites and albitites belong to alkaline riebeckite-albite granites containing Nb-, Zr-, Y- and REE-bearing minerals. These rocks contain Y-bearing minerals - thalenite and yttrialite, with an up to 4 wt % inclusion of Y2O3 in titanite, chevkinite, thorite and monazite. In contrast, the albitized granites contain fewer amounts of Y and HREE along with LREE-bearing minerals (monazite, allanite, fluocerite, samarskit).Conclusion. The selected groups of rocks have been analyzed in terms of their mineral and geochemical characteristics. The main Nb-bearing mineral in albitized granites is columbite. Minerals from albitites are rich in Y and HREE. The isotopic investigation has shown involvement of a magmatic-derived fluid in the rock formation process.

Within the city of Ulan-Ude, several sites of bastnaesite–fluorite rocks and calcite-containing rocks were found. They are confined to the exposures of Paleozoic schists and quartzites. The rocks have an age of 134.2 ± 2.6 Ma. They are brecciated lenticular and vein-like bodies cemented mainly with bastnaesite–fluorite aggregate. The content of fluorite in the rocks is several tens of percent, and the content of bastnaesite-(Ce) is 20–30%, often reaching 50%. Among the secondary minerals, there are monazite-(Ce), albite, and K-feldspar, and the accessory minerals are zircon, Nb-containing rutile, and manganilmenite. Light lanthanides are predominant among REE in the rocks. Bastnaesite and fluorite contain brine–melt fluid inclusions with homogenization temperatures of 490–520 °C. The salts of these inclusions are composed of predominant Na and Ca sulphates and subordinate Ca and REE carbonates, and the gas phase contains CO2. Gas inclusions and part of water–salt inclusions homogenized at 150–200, 290–350, and 430–450 °C. The salts of late fluids are composed of Ca and REE carbonates, K and/or Na chlorides, Ca, Mg, and Fe hydrosulphates, and Ca and Na hydrocarbonates, and the gas phase contains CO2 ± H2. The isotopic compositions of carbon (–5.9 to –8.3‰ δ13CV-PDB) and oxygen (4.3 to 8.3‰ δ18OV-SMOW) in bastnaesite and calcite fall in the PIC square specific to unaltered intrusive carbonatites. The primary strontium isotope ratios in fluorite and bastnaesite are equal to 0.70559–0.70568. The proximal location, close ages, and mineral and geochemical features indicate a genetic relationship of the studied rocks with the late Mesozoic carbonatites of southwestern Transbaikalia. The finding of this rock occurrence indicates a existence of one more carbonatite-bearing area and expands the distribution area of such rocks, which makes southwestern Transbaikalia promising for REE mineralization.

The purpose of the article is to date the ore formation process, study the composition and provide the description of mineral parageneses in rocks and ores of the Buluktai Mo-W deposit as well as to estimate the sources of matter and fluids. The Re-Os method (The Center for isotopic studies of A.P. Karpinsky Russian Geological Research Institute (VSEGEI)) is used for dating the molybdenum mineralization. The isotopic compositions of oxygen in silicates and carbon in carbonates is determined in the Geological Institute SB RAS. The isotopic composition of hydrogen of muscovite hydroxyl water is determined in the Center for isotopic studies of the Far Eastern Branch RAS. The isotopic analysis of sulfide sulfur is carried out in the Center for isotopic studies of the Far Eastern Branch RAS and partly at the Tbilisi State University. The age of the molybdenite phase (144±10 Ma) has been determined using the Re-Os method. The isotopic compositions of sulfide sulfur in both molybdenum and tungsten stages show a range of values close to the values of a mantle source. The isotopic compositions of oxygen in the minerals of Mo and W-stages are clearly divided into two groups. The deposit was formed with the participation of a mantle source. Its final stage is characterized with the increased influence of meteoric water as a part of fluids.

Object . The results of geochronological and isotope-geochemical studies of the Arsentyevsky titaniferous gabbro-syenite massif of the Western Transbaikalia, which previously referred to the gabbro-syenite series of a two-phase structure are presented. The rocks of the massif contain an increased concentration of titanomagnetite, ilmenite, magnetite and in some cases apatite and are considered as complex iron-titanium ores. Methods. The studies were performed by silicate analysis me­thods, XRF and ICP-MS; age determination for zircons was carried out by LA-ICP-MS and SHRIMP-II methods. The composition of minerals on the X-ray microarray analyzer MAP-3 and electron microscope LEO-1430 was studied. Results. In the basites, a standard trend is observed for the evolution of compositions from melanocratic to terminal leucocratic differen­ces with an increase in the content of silica, alumina, and sodium, and a decrease in magnesium and calcium. Syenites differ from anorthosites in the content of impurity elements including rubidium, niobium, strontium and REE The geochronological studies of rocks of Arsent’evsky gabbro-syenite massif, showed a significant time gap in the formation of gabbroids rela­tive to syenites. The U-Pb age of the gabbroids was 279.5 ± 2.0 Ma, alkali feldspar syenites have age 229.4 ± 2.8 Ma, and biotite syenites - 226 ± 2.4 Ma. Conclusion. The obtained results by age and data on the geochemical features of the rocks made it possible to conclude that there was no genetic relationship between basites and syenites. Petrochemical and geochemical features of biotite and alkali-feldspar syenites proved to be close to the rocks of the Mesozoic Kunaleisky complex.

We present results of geochronological (40Ar-39Ar, U-Pb SHRIMP-II, and LA-ICP-MS) and geochemical studies of alkaline rocks of the Amalat, Sirikta, Tsipa, Pravyi Uligli, and Verkhnii Uligli massifs in the Vitim plateau (western Transbaikalia). The formation of the alkaline rocks and the accompanying albitization are dated at 261-242 Ma. The isotope inhomogeneity (epsilon(Nd)(T)= +8.4 to -1.7) of the alkaline rocks indicates the heterogeneous composition of the source of their material, having a depleted component, an enriched juvenile metasomatic fluid, and a crustal substrate. (C) 2018, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.

The purpose of the publication is to estimate the fluid sources of the epithermal fluorite deposits of the Western Transbaikalia by analyzing the isotope composition of oxygen, carbon, hydrogen and sulfur. Methods. The isotopic compositions of oxygen in silicates as well as carbon in carbonates are determined by V.F. Posokhov in the Geological Institute SB RAS. Results. The isotopic composition of oxygen in quartz is characterized by low δ 18 O (-3.4 - + 2.6 ‰). Pyritic sulfer of these deposits is also enriched by the light isotope δ 34 S (from -1.8 to -7.7 ‰ δ 34 S). The value of δ 34 S varies from +0.4 to -9.7 ‰ and is -3.75 on the average for seven fields. Conclusions. The isotope studies indicate a deep source of sulfur, which underwent changes in the process of its rise from the magma pocket to the upper horizons. The composition of the fluid is indicative of the participation of water from the meteor source caused by recycling processes under the influence of shallow underlying basite pluton.

The Dzhida ore field includes Pervomaika (Mo), Inkur (W) and Kholtoson (W) deposits. This article presents stable and radiogenic isotopic data (O, C, D, S, Sr and Nd) in an attempt to better understand the petrogenetic processes and the problem concerning the sources of ore-forming fluids. Granites from the Pervomaika deposit, which includes Mo-ores, as well as the syenite dikes that precede W-mineralization, have low δ18O values (about 5‰ and 4‰ respectively), and low initial ratios 87Sr/86Sr (0.704–0.705). The εNd (T) values (+0.9–−1.1) in granites and syenites are close to the evolution trend of the mantle-derived source. It was determined that a mantle-derived source was involved in ore-forming processes. It was also confirmed that δ34S values in sulfide minerals (molybdenite, pyrite, sphalerite, galena, and chalcopyrite) were close to the meteoric standard (from −2‰ to +2‰). The δ13C and δ18O values in carbonate minerals (rhodochrosite and ankerite) of the Kholtoson deposit are located within the primary igneous carbonatite (PIC)-square, as a possible juvenile source of CO2. This was also confirmed by the δ18O and δD values in muscovite from greisens (4.2‰–6.5‰ δ18O, –78.8‰ … –84.0‰ δD). The δ18O values calculated in a fluid equilibrated with hydrothermal minerals indicated a meteoric origin.

Geochemical and U-Pb geochronological studies have shown that the alkali syenites of the China massif have an age of 311.4 +/- 1.8 Ma and potassic specialization in contrast to most massifs of the Vitim alkaline-magmatism zone. The rocks are similar in geochemistry to the nepheline syenites of the Synnyr massif, dated at 289.5 +/- 3.5 Ma. The alkali syenites of the China massif formed, most likely, from crustal protoliths. (C) 2017, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.

Our study of aplite dykes cross‐cutting the Oshurkov basite massif revealed drop‐shaped inclusions of the monzonite composition. These are crystallized drops of basite melts, which show traces of the interaction with the host acidic melt. The Ar‐Ar method was applied to determine the age of the aplites (114.9 Ma for biotite) and the monzonite inclusions (123.3 Ma for amphibole).