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Based on the study of local volumes of minerals using the classical methods of isotope dilution and thermal ionization mass spectrometry (U–Pb ID TIMS), an isotopic study of pitchblende and galena is carried out at the Natali uranium ore occurrence (Northern Transbaikalia). For the first time, it was shown that the pitchblende mineralization at the ore occurrence has a Late Silurian (422 ± 4 Ma) age. Its formation is related to the Early–Middle Paleozoic collisional tectogenesis in the area of the Tonod uplift, accompanied by increased fluid activity. The Pb isotopic composition analysis in galena associated with pitchblende show that galena is enriched in radiogenic isotopes 206Pb and 207Pb, a source of which was ancient (Precambrian) concentrations of uranium. [ABSTRACT FROM AUTHOR]

Three groups of industrial uranium deposits that differ in the distribution of lanthanides in U oxides have been recognized. A dependence of the REE distribution type on the Yttrium content and Yttrium index YI = (La + Ce)/Y that controls the formation of REE phases capable of selective accumulation of lanthanides has been discovered. This indicates the important role of crystal-chemical fractionation in the distribution of lanthanides. Preferable accumulation of Sm-Gd by U oxides has been found to occur at relatively low contents of Y. In Proterozoic uranium deposits, the yttrium specialization of oxides predominates, while in most Phanerozoic deposits the lanthanum-cerium specialization is typical. These results extend the possibilities of using REEs in ores for purposes of study of the genesis of various uranium deposits. [ABSTRACT FROM AUTHOR]

The uneven character of the distribution of O/O and U/U values was established in the vertical cross section of the productive sequence of the Dybryn uranium deposit (Vitim uranium-ore region, Buryatia). Both a deficiency and an excess of U in relation to the equilibrium U/U ratio in the vertical sequence may provide evidence for the extremely low rate of the infiltration water flow. The behavior of oxygen isotope characteristics for different size fractions of terrigenous rocks provides evidence for active uranium redistribution and openness of the isotope system of this element during interaction of terrigenous-sedimentary rocks with infiltration waters. [ABSTRACT FROM AUTHOR]

The variations in U/U values accompanying mobilization of U by fracture waters from uranium-bearing rocks, in which U occurs as a fine impregnation of oxides and silicates, were studied by the high-precision (±0.07‰) MC-ICP-MS method. Transition of U into the aqueous phase in the oxidized state U(VI) is accompanied by its isotope fractionation with enrichment of dissolved U(VI) in the heavy isotope U up to 0.32‰ in relation to the composition of the solid phases. According to the sign, this effect is consistent with the tendency of the behavior of U and U upon interaction of river waters with rocks of the catchment areas [11] and with the effect observed during oxidation of uraninite by the oxygen-bearing NaHCO solution [12]. [ABSTRACT FROM AUTHOR]

Contrast variations in the type of REE distribution from a distinctly negative mode to a positive mode is revealed in zonal fluorites of Eastern Transbaikal, with a pronounced decrease in the Ce/Y ratios in successive zones of increasing Y accompanied by a gradual decrease in the temperature and salinity of fluid inclusions in the fluorites. It is assumed that these facts are caused by the appearance of nm-size phases of REE minerals characterized by various crystalline structures and demonstrating selective concentrations of lanthanides, i.e., exhibiting a crystal-chemical differentiation of REEs that is widespread in the processes of mineral formation. Based on this natural mechanism, the development of a procedure of selective REE extraction from the concentrates is proposed. The primary laboratory experiments resulted in the discovery of the difference in REE concentrations in the sediment and filtrate with the separation coefficient varying by a factor of 76. The results obtained allow one to expect a true separation possibility for Nd along with the medium and heavy REEs. In view of the data obtained, the crystalline-chemical separation of REEs has some advantages compared to the processes currently used, especially extraction. [ABSTRACT FROM AUTHOR]

This work presents the results of U-Pb geochronological studies of alkaline granites of the Aralaul complex of Northern Kazakhstan, which allow one to substantiate their Late Silurian (420 ± 4 Ma) age. Taking into consideration the previously obtained data, we propose a new development scheme of Paleozoic granitoid magmatism in Northern Kazakhstan, which includes Late Ordovician granite-granodiorite (Zerenda and Krykkuduk), Early Silurian granite-leucogranite (Borovoe and Karabulak), Late Silurian granosyenites-granite (Aralaul), and Early Devonian (Balkashino and Orlinogorsk) complexes. [ABSTRACT FROM AUTHOR]

The evolution of the geological structure in the Southern Argun' Region is studied in terms of changing geodynamic conditions of the Proterozoic, Caledonian, and Variscan Tectonomagmatic Cycles, which also under Mesozoic tectonomagmatic activation led to the formation of latite igneous rocks enriched in Au, Cu-Mo, Pb-Zn-Ag, volcanic and plutonic complexes of the caldera structures with Mo-U, Pb-Zn, and fluorite ores, and rare-metal granites with a Sn-W-Li-Ta spectrum. [ABSTRACT FROM AUTHOR]

This work presents the results of complex analysis of the field data and of mathematical modeling of the ice ring structure more than 4 km across, which was identified by the space images of South Baikal in April 2009. The measurements revealed that the ice thickness was 74 cm in the center of the structure, decreased to 43 cm at a distance of 2 km, and increased up to 70 cm and more beyond the ring. The ice water in the central part was warmer by 0.5°C and less saline (for 2 mg/kg) relative to the periphery of the structure. According to the tracer movements, the maximum velocities of the ice currents (3-4 cm/s) were observed at a distance of 2-3 km from the center of the structure with minimum ice thickness. The event was modeled using several mathematical models of various scales. The 3-D nonhydrostatic modeling of the large-scale processes on the basis of the temperature measured in the area of the structure showed the presence of local anticyclonic circulation, where the velocities of the currents increased up to the maximum (5-7 cm/s) at the distance of 2-3 km from the center and then decreased. The variations in the ice thickness in the area of the ring structure were modeled on the basis of these calculation results. The ice thicknesses determined in the context of the Stefan problem for the 2-D axis-symmetrical temperature distribution model are close to the measured ones. According to the model, the formation of the ring structure spans a period of 25-35 days. The origination of the dark ring on the satellite images is related to the lower ice thickness relative to the ambient areas and to the water level in microfractures closer to the ice surface. [ABSTRACT FROM AUTHOR]

The article discusses the geochemical and isotopic data on the formation of the Mesozoic volcanics caldara in the western part of the Argun tectonic block in Russia. Topics discussed include compositions of basalt and trachybasalt rocks, role of geochemical properties of basalts in magmatic process and concetration of silicon dioxide in trachyrhyodacites.

The article discusses rare earth elements (REE) analysis in snow samples which is used as a sensitive indicator of environment pollution. It mentions technique used including spectrometry with inductively coupled plasma (ICP-MS), quadrupole mass spectrometer, and filtration and precipitation. It informs that the influence of aerosol and the limits of biosphere persistence in relation to integral chemical pollution.