A wide range of the temperatures of hydrothermal fluid regime (430-103 °C) has been revealed in the result of microthermometric study of the fluid inclusions in the minerals of pre-ore and post-ore stages developed at the Elkon deposit. Average temperatures, as well as the temperature variation are similar for both pre-ore and post-ore stages. It allows sure determination of temperatures of uranium ore formation as 400-120 °C. Fluids possessed Na-chloride, rarely Na-chloride-carbonate composition and moderate salinity (6-16 wt. % · NaCl equiv.). The wide range of tem-peratures confirms an assumption made before that various temperatures were the reason of formation of uranium mineralization both in the form of predominantly amorphous phase (U-Ti-metagel), as well as the rarely crystalline form (brannerite). Abrupt temperature decrease was apparently the main factor of the ore precipitation.

The Bystrinskoe skarn-porphyry Cu–Au–Fe deposit (Eastern Trans-Baikal Region) is confined to skarn zones, which were formed along the contact of granitoids referred to the Shakhtama intrusive complex (J2–3), with terrigenous–carbonate sedimentary rocks. Commercial (Cu–Au–Fe ± W, Mo) mineralization was formed due to the regional postcollision development involving the intrusion of porphyritic granitoids, the derivatives of oxidized adakite highly magnesian magmas enriched in water, sulfur, and metals, which could develop under melting of garnet-bearing amphibolite in the mafic lower crustal arc.

The paper considers for the first time the morphology, composition, and conditions of formation of the greisens of the Solnechnoe deposit (Komsomol’sk ore district), a typical cassiterite–silicate assemblage. The greisens are localized in the root parts of the deposit and represent a system of veins and veinlets formed in the contraction fractures of the metasomatically altered roof of the monzogranite intrusion (age of 94–92 Ma). The cassiterite–chlorite–carbonate–muscovite–quartz composition of the greisens with admixture of topaz, fluorite, and apatite reflects the composition of the monzogranites. The greisens are close in age (85.3 Ma on muscovite) to the granitic aplites (80–85 Ma on the whole-rock and biotite) of the final phase of the intrusive magmatism. The fluid regime of their formation differs from that of the economic ores in higher temperature, pressure, and salinity. One distinguishing feature of the greisens is elevated contents of LREE, U, and Th, which are incorporated in the REE fluorcarbonates, thorite, and uranothorite crystallizing together with cassiterite.

Special methodology was used to study the distribution of REE and some other elements in zoned fluorites from the different deposits of Eastern Transbaikalia. Fluorites from the uranium and polymetallic ore fields sharply differ in their REE distribution pattern and the composition of fluid inclusions, which reflects the geochemical specifics and indicates the possible sources of parental solutions. A gradual change in REE distribution patterns established in the successive growth zones of fluorites clearly coincides with the gradual decrease of temperature and mineralization of fluid inclusions. It is suggested that a change in the REE distribution pattern was provoked by the crystallochemical differentiation related to the formation of nano-sized mineral admixtures of REE phosphates and/or fluorcarbonates, which possess an ability to the selective accumulation of different REE groups. It was found that the zoned fluorites from the Streltsovka and Garsonui deposits show an opposite trends in the change of REE pattern with zonation. With a general decrease in total REE contents, fluorite from the Streltsovka deposit shows a change from positive parabolic to subchondritic pattern, while that from the Garsonui deposit, varies from the negative via subchondritic to the positive patterns.

С использованием специальной методологии изучено распределение РЗЭ и ряда других элементов в зональных флюоритах различных месторождений Восточного Забайкалья. Для флюоритов из урановых и полиметаллических рудных полей выявлены существенные отличия в типе распределения РЗЭ и характере флюидных включений, отражающие геохимическую специфику и указывающие на вероятные источники сформировавших их растворов. В последовательных зонах роста флюоритов установлена постепенная смена распределения лантаноидов, отчетливо совпадающая с постепенным снижением температуры и минерализации флюидных включений. Предполагается, что смена типа распределения лантаноидов связана с кристаллохимической дифференциацией, которая обусловлена образованием наноразмерных минеральных примесей фосфатов и/или фторкарбонатов РЗЭ, обладавших селективной концентрацией разных групп лантаноидов. При этом выявлена противоположная направленность изменения типа распределения лантаноидов в зональных флюоритах Стрельцовского и Гарсонуйского месторождений. Так, в первом при общем снижении суммарной концентрации лантаноидов наблюдается смена положительного параболического типа на субхондритовый, а во втором – отрицательного через субхондритовый до положительного.

Изучены условия формирования рудных тел и условия отложения вольфрамита на вольфрамовом месторождении Дегана (Раджастан, Индия) и олово-вольфрамовом месторождении Тигриное (Дальний Восток, Россия). При изучении флюидных включений (ФВ) методом микротермометрии и на основании детального петрографического анализа ФВ установлены различия в составе и состоянии флюидных систем. На месторождении Дегана формирование рудных жил в гранитах происходило при температурах от >420 до 120°С, давлении до 1550 бар из К-Na-Ca-( Mg, Fe и др.)-хлоридных флюидов с концентрацией до 36 мас.%-экв. NaCl. На этом же месторождении при формировании рудных тел в брекчиях температуры достигали 450°С, давление не превышало 400 бар, флюиды имели преимущественно Na-хлоридный состав и концентрацию не более 18 мас. %. На месторождении Тигриное при отложении кварц-вольфрамит-касситеритовых жил температуры варьировали от 420 до 240°С, давление не превышало 300 бар, флюиды имели Na-хлоридный состав и концентрацию 7–3 мас. %. Вольфрамит кристаллизовался в начальный период рудообразующего процесса. Рассмотрены вероятные источники флюидов. Высказано предположение о том, что даже на одном месторождении факторы, вызывающие отложение вольфрамита, могли быть различны.

Formation conditions of orebodies and conditions of wolframite deposition at the Degana tungsten deposits in Rajasthan, India and the Tigrinoe tin-tungsten deposit in the Russian Far East were studied. Differences in the composition and state of fluid systems were established by microthermometric study of fluid inclusions (FI) and thorough petrographic examination of FI. At the Degana deposit, the ore veins in granite were formed from K-Na-Ca-(Mg, Fe, etc.) chloride solutions with a salinity up to 36 wt % NaCl equiv at a temperature of >420 to 120°C and under a pressure reaching 1550 bar. The formation temperature of the orebodies hosted in breccia reached 450°C and pressure was below 400 bar. The salinity of mainly Nachloride aqueous solutions was no higher than 18 wt % NaCl equiv. At the Tigrinoe deposit, the temperature during formation of quartz-wolframite-cassiterite veins varied from 420 to 240°C and the pressure was no higher than 300 bar. The salt concentration of Na-chloride solutions was 7-3 wt %. Wolframite crystallized at the very beginning of ore deposition. Probable sources of fluids are discussed. It is suggested that the factors controlling wolframite deposition could have been different even at the same deposit.

Бугдаинское золотоносное W-Mo-месторождение (Восточное Забайкалье) приурочено к центральной части вулкано-купольной структуры в пределах крупного плутона варисских гранитоидов. По своим характеристикам оно соответствует месторождениям типа Клаймакс или риолитовому субклассу Mo-порфировых месторождений. Его повышенная золотоносность обусловлена относительно широким распространением жильного и жильно-прожилкового золото-полиметаллического оруденения. В штокверковых и жильных рудах сейчас диагностировано более 70 минералов, включая самородные элементы, сульфиды, сульфосоли, теллуриды, оксиды, молибдаты, вольфраматы, карбонаты и сульфаты, в том числе впервые установленные здесь джалиндит, гринокит, молибденсодержащий штольцит, амальгамы серебра и золота, штромейерит, сервеллеит, берриит и др. Выделено четыре стадии минералообразующего процесса. Наиболее ранняя дорудная стадия проявилась после внедрения субвулканического штока риолит(гранит)-порфиров в виде калишпатизации и интенсивного окварцевания. Вслед за ними сформировалась штокверковая и жильно-прожилковая W-Mo-минерализация кварц-молибденитовой стадии. Серицитизация, пиритизация и последующее образование кварц-сульфидных жил и прожилков с самородным золотом, сульфидами полиметаллов и разнообразными Ag-Cu-Pb-Bi-Sb-сульфосолями золото-полиметаллической стадии происходили после изменения регионального плана тектонических деформаций. Завершался гидротермальный процесс отложением аргиллизитовой (каолинит-смектитовой) ассоциации послерудной стадии.

The Bugdaya Au-bearing W-Mo porphyry deposit, Eastern Transbaikal Region, Russia, is located in the central part of volcanic dome and hosted in the large Variscan granitic pluton. In its characteristics, this is a Climax-type deposit, or an Mo porphyry deposit of rhyolitic subclass. The enrichment in gold is related to the relatively widespread vein and veinlet gold-base-metal mineralization. More than 70 minerals (native metals, sulfides, sulfosalts, tellurides, oxides, molybdates, wolframates, carbonates, and sulfates) have been identified in stockwork and vein ores, including dzhalindite, greenockite, Mo-bearing stolzite, Ag and Au amalgams, stromeyerite, cervelleite, and berryite identified here for the first time. Four stages of mineral formation are recognized. The earliest preore stage in form of potassic alteration and intense silicification developed after emplacement of subvolcanic rhyolite (granite) porphyry stock. The stockwork and vein W-Mo mineralization of the quartz-molybdenite stage was the next. Sericite alteration, pyritization, and the subsequent quartz-sulfide veins and veinlets with native gold, base-metal sulfides, and various Ag-Cu-Pb-Bi-Sb sulfosalts of the gold-base-metal stage were formed after the rearrangement of regional pattern of tectonic deformation. The hydrothermal process was completed by argillic (kaolinite-smectite) assemblage of the postore stage. The fluid inclusion study (microthermometry and Raman spectroscopy) allowed us to establish that the stockwork W-Mo mineralization was formed at 550–380°C from both the highly concentrated Mg-Na chloride solution (brine) and the low-density gas with significant N2 and H2S contents. The Pb-Zn vein ore of the gold-base-metal stage enriched in Au, Ag, Bi, and other rare metals was deposited at 360–140°C from a homogeneous Na-K chloride (hydrocarbonate, sulfate) hydrothermal solution of medium salinity.

Specific features of the fluid regime in ore-magmatic systems located in the southwestern part of the Kavalerovo ore district (Primorye) are considered. One system is accompanied by mineralization of the porphyry copper type (Lazurnoe deposit); the other system, by tin (copper-tin) mineralization of the hydrothermal type (Iskra deposit). It is shown that the magmatic stages of these systems are distinguished mainly by the chlorophile nature of the copper-gold system and the fluorophile nature of the copper-tin system. The well-known distinction of these systems in terms of the redox parameter is confirmed, and its different evolution scenarios in the systems are shown. The results of the study of fluid inclusions in quartz of postmagmatic associations show that the processes of ore formation at the Lazurnoe deposit were characterized by a wide temperature range and the heterogeneity of the mineral-forming environment. The early period was marked by the coexistence of aqueous-saline brines (mainly of Na-Ca-Mg-chloride composition) and low-density fluid inclusions. The late period was dominated by ordinary hydrothermal solutions. The Iskra deposit formed in a relatively narrow temperature range from homogeneous fluids of essentially Na-chloride composition characterized by moderate and low salinity.

The ambiguity of genetic interpretations of uranium ore formation at Mo-U deposits of the Strel’tsovka ore field led us to perform additional geochemical, mineralogical, and thermobarogeochemical studies. As a result, it has been established that closely related U and F were progressively gained in the Late Mesozoic volcanic rocks from the older basic volcanics (170 Ma) to the younger silicic igneous rocks (140 Ma). The Early Cretaceous postmagmatic hydrothermal epoch (140–125 Ma) is subdivided into preore, uranium ore, and first and second postore stages. The primary brannerite-pitchblende ore was formed in association with fluorite. At the first postore stage, this assemblage was replaced by a U-Si metagel, which was previously identified as coffinite. The metagel shows a wide compositional variation; its fine structure has been studied. The preore metasomatic alteration and related veined mineralization were formed under the effect of sodium (bicarbonate)-chloride solution at a temperature of 250–200°C. The uranium ore formation began with albitization and hematitization of rocks affected by supercritical fluid at 530–500°C; brannerite and pitchblende precipitated at 350–300°C. The chondrite-normalized REE patterns of pitchblende hosted in trachybasalt, trachydacite, and granite demonstrate a pronounced Sm-Nd discontinuity and a statistically significant tetrad effect of W type. These attributes were not established in REE patterns of rhyolites derived from the upper crustal magma chamber. This circumstance and a chronological gap of 5 Ma between silicic volcanism and ore formation do not allow us to suggest that uranium was derived from this magma chamber. According to the proposed model, the evolved silicic Li-F magma was a source of uranium. U4+, together with REE, was fractionated into the fluid phase as complex fluoride compounds. The uranium mineralization was deposited at a temperature barrier. It is suggested that hydromica alteration and the formation of molybdenum mineralization were genetically unrelated to the uranium ore formation.

The goeochemistry of ore-forming fluids from typical tin-bearing ore-magmatic systems of Sikhote Alin has been studied. Fluid inclusions and stable isotopes (O, H, and S) were analyzed in minerals of different megastages at the Arsen'evsk, Vysokogorsk, and Solnechnoe deposits, which formed in different geodynamic settings. Tin deposits of the Sikhote Alin accretionary fold system are related to continental paleomargins, where superposition of subduction and transform settings led to the spatial juxtaposition of magmatism and ores of different types and age. Two megastages of mineral formation, molybdenum and tin, were distinguished at the deposits studied. Fluid inclusions in quartz and fluorite of different generations; in tourmaline and apatite of the molybdenum megastage; and in quartz, cassiterite, and calcite of the tin megastage, are described in detail. The homogenization temperatures, composition, and salinity of solutions and the gas phase of fluid inclusions were determined by microthermometry, Raman spectroscopy, and gas chromatography. It was established that molybdenum mineralization formed at 540-160 degrees C from essentially aqueous Mg/Ca/Na(K) chloride fluids in the presence of CH4, N-2, CO, and CO2. At temperatures more than 480 degrees C, minerals formed from a heterogeneous system consisting of high-density (65-50 wt % NaCl equiv.) aqueous-salt and gas fluids; at lower temperatures, minerals formed from homogeneous fluids with a salinity from 40 to 5 wt % NaCl equiv. Mineral assemblages of the tin megastage precipitated at 390-180 degrees C mainly from aqueous Na chloride fluids with a salinity of 16-0.7 wt % NaCl equiv. and variable amounts of CO2, CH4, N-2, CO, and H2S in a pulsation regime. A gas fluid with subordinate Mg-Ca-Na-chloride brines similar to those of the molybdenum megastage participated in the mineral formation. Stable isotope compositions (O, H, and S) were studied in minerals of different megastages from the Arsen'evsk, Vysokogorsk, and Solnechnoe deposits. It was shown that fluids of the molybdenum megastage were magmatic in origin since calculated delta O-18 and delta D of fluid water vary from +6.8 to +10.1 parts per thousand and from -102 to -46.4 parts per thousand, respectively, and delta S-34-H2S vary from -1.3 to +1.5 parts per thousand. Most values of delta O-18(H2O) obtained for the tin stage of the Solnechnoe, Vysoko-orsk, and Arsen'evsk deposits occur in the field of magmatic waters (delta O-18 from +3 to +9.5 parts per thousand). However, light oxygen isotope signatures in some samples (delta O-18 from -1.3 to +1.5 parts per thousand) suggest involvement of heated meteoric waters. Sulfur isotope values of H2S in the mineral-forming fluid fall into two intervals: from -3.7 to +1.5 parts per thousand (magmatic sulfur) and from +43 to +8.2 parts per thousand (sulfate S). Our investigations showed the following: (1) ore-forming fluids related to different settings (trans-, form margin and suprasubduction zone) differ in composition, physicochemical parameters, and sources and (2) the studied deposits formed from fluids of different composition, properties, and origin.

Mineral assemblages, stages, and the evolution of metasomatic processes were examined in the ore field of the Maiskoe gold-quartz deposit. The metasomatic processes affected the Lower Proterozoic volcano-sedimentary sequence of the Salla-Kuolajarvi graben-synclinorium in northern Karelia and proceeded in two stages. The first of them involved propylitization and magnesian metasomatism, and the second stage was marked by gumbeitization and the deposition of gold-sulfide ore mineralization. The paper presents a detailed characterization of the gumbeites, which were the first rocks of this type found in the Precambrian of the Baltic Shield. They consist of Kfs + Cal + Qtz and sometimes also contain Ms, Ccp, and Bn.(1)A prograde evolutionary trend of the propylites and magnesian metasomatites with an increase in the X-Mg of the minerals with time is identified based on the chemistry of minerals and data on fluid inclusions. The gumbeitization and ore deposition differed from the earlier processes by an increase in the CO2 fugacity and the activities of K2O and BaO in the solution. The temperature of these processes, which was determined by fluid inclusions and chlorite geo-thermometers was 330-380 degrees C for the early propylitization, 470-490 degrees C for younger veinlets in the propylites, 250-300 degrees C for the onset of magnesian metasomatism (actinolite veinlets), similar to 400 degrees C for the late magnesian metasomatism (Hbl + Bt assemblage), 350-370 degrees C for gumbeitization, and 180-250 degrees C for ore deposition. The metasomatic processes were dated (Rb-Sr and K-Ar ages of minerals) at 1800 Ma for the propylitization, 17001600 Ma for the magnesian metasomatism, and approximately 1400 Ma for the gumbeitization and ore deposition. The propylitization and magnesian metasomatism are thought to have been genetically related to (and roughly coeval with) the strike-slip faulting, shearing, and mafic magmatism. The gumbeitization and the development of ore mineralization could be linked with the origin of a chamber of a crustal granodiorite (or monzonite) magma. According to the Sr isotopic composition, it could have had two sources: the country rocks and the fluid. All of the metasomatic processes were related to the same tectonic style, which was controlled by strike-slip fault zones and the tectonic and magmatic evolution.

The localization and formation conditions of uranium mineralization in the Karku deposit (northern Ladoga region) are discussed based on the results of complex studies. It is shown that most of the orebodies are localized in the lower part of a Riphean subplatform volcano-sedimentary sequence and are controlled by the surface of structural-stratigraphic unconformity between the Riphean rocks and the crystalline basement. The succession and mode of Riphean catagenetic transformations and metasomatic pre- and synore alterations in the sedimentary-volcanogenic sequence and the basement are described. The main uranium and associated minerals are presented in detail. It is established that high-grade ores are dominated by uranium oxides of three generations associated with Fe-Mg chlorite, calcite, and pyrrhotite. Uranium silicates are the main uranium minerals of average- and low-grade ores. Using microthermometry and Raman spectrometry of liquid-vapor inclusions in minerals, physicochemical formation conditions of uranium ores are estimated. In distinction from deposits of the hydrothermal type, the Karku deposit is characterized by highly variable temperature, composition, and concentration of solutions, as well as composition and density of the vapor component in inclusions of minerals deposited at the ore-formation stage. Simultaneously, physicochemical parameters of fluid systems that formed the Karku deposit are close to their counterparts in unconformity-type uranium deposits occurring in the Athabasca basin. The complex studies performed suggest that the Karku deposit is similar to the unique unconformity-type Athabasca deposits in several geological, mineralogical-geochemical, and physicochemical features. A possible mechanism responsible for the formation of uranium ores of the deposit is considered.