Телегинский массив сложен преимущественно габброидами и пироксенитами. В породах массива были изучены такие амфиболы как гастингсит, эденит, роговая обманка, тремолит и актинолит. Гастингсит, эденит и роговая обманка являются первичными амфиболами габброидов, тремолит и актинолит, образованы позднее в результате постмагматических процессов.

—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)

В пределах г. Улан-Удэ обнаружено несколько участков существенно бастнезит-флюоритовых и кальцитсодержащих пород. Они приурочены к выходам палеозойских кристаллических сланцев, кварцитов, имеют возраст 134.2±2.6 млн. лет. Породы представлены брекчированными линзои жилообразными телами, сцементированными преимущественно бастнезит-флюоритовым агрегатом. Содержание флюорита в породах составляет несколько десятков процентов, бастнезита(Се) – 20-30 %, нередко достигая 50 %. В числе второстепенных присутствуют монацит-(Се), альбит, калиевый полевой шпат, в качестве акцессорных – циркон, ниобий-содержащий рутил, манганильменит. Редкоземельные элементы в породах специализированы на легкие лантаноиды. В бастнезите и флюорите установлены солевые рассол-расплавные включения с температурами гомогенизациии 490-520 °С. Солевой состав таких включений представлен преимущественно сульфатами Na и Ca (50-60 об. %), в подчиненном количестве присутствуют карбонаты Ca и REE (20-30 об. %), газовая фаза включений содержит углекислоту. Газовые и часть водно-солевых включений (до 30-50 об. % солевых фаз) гомогенизировались при температурах 150-200, 290-350 и 430-450 °С. Солевой состав поздних флюидов отвечает карбонатам Ca, REE, хлоридами K и/или Na, гидросульфатам Ca, Mg и Fe и гидрокарбонатам Ca и Na, а газовая фаза включений содержит CO2±H2. Изотопные составы углерода (-5.9 ....-8.3 ‰ 13С V-PDB) и кислорода (4.3...8.3 ‰ 18О V-SMOW) в бастнезитах и кальцитах ложатся в контур квадрата PIC, характерный для неизмененных интрузивных карбонатитов. Первичные изотопные стронциевые отношения во флюорите и бастнезите равны 0.70559-0.70568. Пространственная сопряженность, близкий возраст и минералого-геохимические особенности указывают на их генетическую связь с позднемезозойскими карбонатитами Юго-Западного Забайкалья. Обнаружение этого проявления свидетельствует о существовании еще одной карбнатитоносной площади и расширяет ареал распространения таких пород, увеличивая перспективы территории Юго-Западного Забайкалья на редкоземельное оруденение.

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.

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.

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).

The paper gives a mineralogical and geochemical characterization of the North Gurvunur deposit, which was discovered in the Eravna ore district. The ore is composed of apatite–magnetite paragenesis. Apatite is distinguished by elevated LREE concentrations; some of them are contained in emulsion-type impregnation of monazite. Hematitization, carbonate, quartz, and pyrite veinlets formed at the postore stage, and gypsum–anhydrite mineralization is widespread in the supraore sequence. Two groups of endogenic minerals are distinguished by oxygen isotopic composition. One of them comprises magnetite and apatite, which are characterized by a homogeneous composition throughout the section of the ore lode and are close to the mantle source. The oxygen–isotope temperature calculated for the apatite–magnetite couple (620–800°C) provides evidence for magmatic origin of ore. The δ18O of fluid in equilibrium with hematite is 8.0–8.5‰ and shows a certain enrichment in crustal component; carbonates of postore veinlets reveal participation of meteoric water. The study has made it possible to refer the North Gurvunur deposit to the Kiruna type.

We present results of isotope-geochemical study of the Ermakovka F-Be deposit, including data on the oxygen and carbon isotope compositions in dolomite and calcite marbles and in carbonates accompanying skarns, of early and late stages of ore formation and of post-ore parageneses. To elucidate the sources of fluids participated in the ore formation, we calculated the oxygen isotope composition in water and the hydrogen isotope composition in hydroxyl-containing minerals. Phlogopite in marbleized dolomites, vesuvianite and amphibole in skarns, eudidimite and bertrandite in ore parageneses, and bavenite formed during post-ore processes are analyzed. Most of the ore-stage minerals are depleted in heavy oxygen. Their delta O-18 values are lower than 5-6 parts per thousand (SMOW). Oxygen in carbonate minerals of the initial stage (dolomite and bastnaesite) is heavier (1.3-4.9 parts per thousand) than that in calcite (+2 to -3.7 parts per thousand). The delta O-18 values of water in equilibrium both with carbonate and with silicate minerals (-4 to -14 parts per thousand) suggest the contribution of meteoric water to the mineral formation. A magmatic fluid (delta O-18 from +6 to +9 parts per thousand) participated in the skarn formation at the initial stage, and a meteoric fluid, at the final stage (delta O-18 from -1 to -9 parts per thousand). A meteoric source is confirmed by the depleted hydrogen isotope composition in minerals (dD from -119 to -192 parts per thousand). (C) 2016, V.S. Sobolev IGM, Siberian Branch of the RAS. Published by Elsevier B.V. All rights reserved.

Isotope-geochemical study of the Ermakovskoe fluorine–beryllium deposit was carried out to estimate the ore sources and role of host carbonate rocks in its formation. We analyzed oxygen and carbon isotope compositions in marbles, skarn carbonates, ore and post-ore parageneses; oxygen isotope compositions in oxides, silicates, apatite; and sulfur isotope composition in sulfides and sulfates. Sources of fluids participating in the rock and ore formation were determined using hydrogen and oxygen isotope compositions in hydroxyl-bearing minerals: phlogopite from marbles, vesuvian from skarns, eudidymite and bertrandite from ore parageneses, and bavenite of the post-ore stage. Isotopic studies suggest crustal source of sulfur, oxygen, and carbon dioxide, while oxygen and hydrogen isotope compositions in the hydroxyl-bearing minerals points to the contribution of meteoric waters in the formation of the fluorine-beryllium ores.

We present the results of a study on gabbroic rocks, syenites, pegmatites, carbonatites, and hydrothermal products of the Oshurkovo apatite-bearing massif. The results include Nd and Sr isotope ratios; the isotope compositions of carbon and oxygen in calcite; oxygen in apatite, magnetite, and silicate minerals (phlogopite, titanite, diopside, amphibole, K-feldspar, and quartz); sulfur in barite; and hydrogen in mica. The isotopic data are close to the EM-1 enriched mantle values and confirm a comagmatic relationship between the gabbros and carbonatites. The binary plot ɛNd vs. 87Sr/86Sr demonstrates strong differentiation between silicate rocks and carbonatites, as is the case with the other Late Mesozoic carbonatite occurrences of southwestern Transbaikalia. The oxygen isotope composition of all comagmatic phases also falls within the range of mantle values. A clear trend toward heavier oxygen and lighter carbon isotope compositions is observed in all successively emplaced phases, which is consistent with a trend defined by hydrothermal products formed under the influence of the parent magma chamber. Carbonates formed during the greenstone alteration of gabbroic rocks are enriched in the light oxygen isotope (δ18O from −2.8 to −7.3‰), suggesting a contribution of vadose water.

This paper reports the results of Rb-Sr, 40 Ar- 39 Ar, and U-Pb geochronological investigations for igneous and metamorphic rocks from the regions of the Oshurkovo basic massif. It was shown that the gabbro-syenite-granite complex that was formed there is similar to the bimodal basalt-rhyolite series of volcanic associations. Three major stages of magmatic activity were recognized: syenite-granite (132–127 Ma), basic (126–117 Ma), and granite (121–112 Ma). The silicic igneous rocks were formed owing to anatexis under the influence of heat released from the parent chamber of alkaline gabbroids.

На примере проявления Веселое рассмотрены процессы метаморфического изменения карбонатитов. По имеющимся данным, возраст карбонатитов составляет 596 ± 3.5 млн. лет, а время метаморфических процессов оценивается в 550 ± 14 млн. лет. Породы на проявлении Веселое были метаморфизованы в условиях зеленосланцевой фации (эпидот-мусковит-хлоритовая субфация) при повышенных давлениях. Термометрическое изучение газо-жидких включений в минералах показало, что температура метаморфического преобразования – 377–450°С, а давление по фенгитовому барометру – 6–8 кбар. Низкоградиентные параметры процессов метаморфизма карбонатитов обусловили частичную рекристаллизацию карбонатов и апатита, их очищение от элементов-примесей. С этим процессом связано изменение изотопного состава кислорода изученных минералов. Метаморфизм сопровождался образованием таких не характерных для карбонатитов минералов как тальк, фенгит, хлорит, кварц, тремолит-актинолит, антофиллит. Полученные данные показывают, что метаморфические процессы оказывают влияние на петрохимические, минеральные, изотопно-геохимические особенности и технологические свойства карбонатитов. Влияние метаморфических процессов необходимо учитывать при определении природы рудной минерализации и оценке перспективности карбонатитовых проявлений и качества руд.

Metamorphism of carbonatite is exemplified in the Vesely occurrence. According to available data, the age of the carbonatite is 596 ± 3.5Ma, whereas metamorphism is dated at 550 ± 14 Ma. The rocks at the Vesely occurrence were metamorphosed under conditions of greenschist facies (epidote-muscovite-chlorite subfacies) under elevated pressure. Microthermometry of fluid inclusions in minerals indicates that the temperature of metamorphism is 377−450°C and the pressure estimated from phengite geobarometer is 6−8 kbar. The low-grade metamorphism led to the partial recrystallization of carbonates and apatite with removal of trace elements. This process resulted in a change of the oxygen isotopic composition of the studied minerals. Metamorphism was accompanied by formation of talc, phengite, chlorite, quartz, tremolite-actinolite, and anthophyllite, which are not typical of carbonatite. The data obtained show that the metamorphism exerted an effect on the mineralogical, isotopic, geochemical, and technological properties of the carbonatite. The effect of metamorphism should be taken into account in determination of the nature of ore mineralization and estimation of ore quality and perspective of the occurrence.