U-Pb systems and U isotopic composition of the sandstone-hosted paleovalley Dybryn uranium deposit, Vitim uranium district, Russia |
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Authors: | V N Golubev I V Chernyshev A V Chugaev A V Eremina A N Baranova V V Krupskaya |
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Institution: | 1. Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, Russian Academy of Sciences, Staromonetnyi per. 35, Moscow, 119017, Russia
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Abstract: | The isotopic (U-Pb, 238U-235U, 234U-238U) and chemical study of whole-rock samples and finegrained fractions of rocks in a vertical section of the terrigenous sequence at the Dybryn uranium deposit in the Khiagda ore field shows that a wide U-Pb isotopic age range (26.9-6.5 Ma) is caused by oxidation and disturbance of the U-Pb isotopic system in combination with protracted uranium ore deposition. The oxidation of rocks resulted in the loss of uranium relative to lead and eventually to an overestimated 206Pb/238U age at sites with a low U content. The 238U/235U ratios in the studied samples are within the range of 137.74–137.88. Samples with a high uranium content are characterized by a decreasing 238U/235U ratio with a decrease in 207Pb/235U and 206Pb/238U ages. A nonequilibrium 234U/238U ratio in most studied samples furnishes evidence for young (<1.5 Ma) transformation of the Miocene uranium ore, which is responsible for uranium migration and its redeposition. |
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