Uranium Isotope Variations (²³⁴U/²³⁸U and ²³⁸U/²³⁵U) and Behavior of U−Pb Isotope System in the Vershinnoe Sandstone-Type Uranium Deposit, Vitim Uranium Ore District, Russia

Abstract

The U-Pb isotope system and uranium isotope composition (²³⁵U/²³⁸U and ²³⁴U/²³⁸U) were studied in a number of samples from the vertical section of the uranium ore body at the Vershinnoe sandstone-type deposit, Vitim uranium ore district, Russia. These parameters were determined to broadly vary. Deviations of the ²³⁴U/²³⁸U ratio from the equilibrium value indicate that the uranium ore was not completely conserved during the postore stage, and uranium was determined to continue migrating at the deposit. Comparison of the U−Pb isotope age value and ²³⁴U/²³⁸U isotope ratio provides an insight into the migrate direction of uranium in the ore body. The broad variations (137.377–137.772) in the ²³⁸U/²³⁵U ratio over the vertical section of the ore body can be explained by the different settings of the samples relative to the ore deposition front and changes in the redox conditions when this front shifted. The fact that the δ²³⁸U and K_234/238 values are correlated indicates that the transfer of the ²³⁴U isotope into the aqueous phase may have been coupled with isotope fractionation in the ²³⁸U−²³⁵U system during the postformation uranium migration within the orebody.

Keywords

sandstone-type uranium deposit / U-Pb age / uranium isotope composition / ore deposit geology

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