Abstract

To assess the nature of the post-ore behaviour of uranium in the Namaru deposit (Khiagda ore field), U–Pb isotope systems and the isotopic composition of uranium (²³⁴U/²³⁸U and ²³⁸U/²³⁵U) were studied. The studied samples represent different ore zones of the deposit and were collected along cross-sections both vertically and horizontally. Wide variations in the isotopic composition of uranium and U–Pb isotopic age have been established. Deviations of the ²³⁴U/²³⁸U ratio from equilibrium values, which for some samples exceed 50%, along with significant variations in the isotopic age, indicate that permafrost layer, which covered the catchment areas of paleovalleys with meteoric oxygen-containing waters ca. 2.5 Ma ago, did not lead to preserving uranium ores at the deposit. Uranium migration took place during the Quaternary period. The effective combining the U–Pb dating and ²³⁴U/²³⁸U data in assessing the post-ore redistribution of uranium made it possible to recognize: removal of uranium from some zones of the ore body and its accompanying redeposition in others. Wide variations in the ²³⁸U/²³⁵U (137.484–137.851) ratios throughout the entire studied cross-sections can be explained by the different locations of samples relatively to the ore deposition front and change in redox conditions as this front advanced. Depletion of the light isotope ²³⁵U in the lower zone of the ore body may be associated with the influence of ascending carbonic waters established in the regional basement. The effect of such waters on uranium-bearing rocks causes predominant leaching of light ²³⁵U.

中文翻译：

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砂岩赋存型矿床中铀迁移的矿后过程：234U/238U、238U/235U 和 U-Pb 外贝加尔北部 Vitim 区 Namaru 矿床矿石的系统学

摘要

为了评估 Namaru 矿床（Khiagda 矿场）中铀的矿后行为的性质，研究了 U-Pb 同位素系统和铀的同位素组成（²³⁴ U/ ²³⁸ U 和²³⁸ U/ ²³⁵ U）。研究的样品代表矿床的不同矿区，并沿垂直和水平横截面收集。已经确定铀的同位素组成和 U-Pb 同位素年龄存在很大差异。²³⁴ U/ ^{238 的}偏差来自平衡值的 U 比，对于一些样品超过 50%，以及同位素年龄的显着变化，表明永久冻土层，其覆盖了具有大气含氧水的古河谷的集水区。2.5 Ma前，未导致在矿床保存铀矿。铀迁移发生在第四纪。将 U-Pb 测年和²³⁴ U/ ²³⁸ U 数据有效地结合起来评估铀的矿后再分布，可以认识到：从矿体的某些区域去除铀及其在其他区域的伴随再沉积。²³⁸ U/ ^{235 的}广泛变化U (137.484–137.851) 比率在整个研究横截面中可以通过样品相对于矿石沉积前沿的不同位置以及随着该前沿前进而氧化还原条件的变化来解释。矿体下部带轻同位素²³⁵ U 的枯竭可能与区域基底中形成的上升碳酸水的影响有关。这种水对含铀岩石的影响导致主要的光²³⁵ U浸出。