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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.

The uneven character of the distribution of 18O/16O and 234U/238U 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 234U in relation to the equilibrium 234U/238U 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.

The variations in 238U/235U 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 238U 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 238U and 235U 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 NaHCO3 solution [12].

Isotopic analysis of hydrogen and oxygen was performed using the DeltaPlus mass spectrometer (ThermoQuest, Finnigan). Gaseous hydrogen from water samples was obtained by the decomposition of water on hot powder of metallic chrome at 800 ° C. Determination of the oxygen isotopic composition was based on the method of isotopic balance of water with ee 2 [5]. The δ D and δ 18 e values were determined accurate to 0.3 and 0.2 ‰, respectively. We used the following MAGATE reference samples: OH-1, OH-2, OH-3, and OH-4. All results presented in Figs. 1 and 2 are shown relative to the international standard V-SMOW.