内蒙古巴彦乌拉砂岩型铀矿床成因

通过对巴彦乌拉铀矿床含矿含水层水化学样品和氢氧同位素样品测试结果的分析得知,目的层段地下水分为Na HCO_3型水(高矿化度)和Na_2SO_4型水。两水型对应的自然环境为油田水环境和地表水环境,水化学特征和H-O同位素特征显示目的层段地下水为混合水,是深部油田水和地表溶滤水的混合。H-O同位素还显示目的层段地下水经历了水—岩作用,地下水的高矿化度主要由此产生,水文地球化学特征指示油田水所处的源区地层处于半封闭半开启状态,还原作用不彻底,有地表溶滤水的渗入,水交替迟缓。在差异隆升作用的影响下,被活化了的马尼特坳陷盆缘断裂和盆中深大断裂成为油田水上涌至目的层段的通道,油田水携带的CH_4、H_2S等还原剂一方面造成了目的层段的后生蚀变现象,另一方面与地表渗入的溶滤水中的碳酸铀酰反应,将碳酸铀酰中的六价铀还原成四价铀从水中沉淀析出堆积成矿。

Discussion on the genesis of Bayanula sandstone-type uranium deposit,Inner Mongolia

Based on the analysis of hydrochemical samples and hydrogen and oxygen isotope samples of ore-bearing aquifers in Bayanwula uranium deposit, the groundwater in the target zone can be divided into NaHCO3 type water (high salinity) and Na₂SO₄ type water. The natural environment corresponding to the two water types is oilfield water environment and surface water environment. The hydrochemical characteristics and hydrogen and oxygen isotope characteristics show that the groundwater in the target zone is mixed water, which is a mixture of deep oilfield water and surface dissolved water. Hydrogen and oxygen isotopes also show that the groundwater in the target interval undergoes water-rock interaction, and the high salinity of groundwater is mainly caused by it. Hydrogeochemical characteristics indicate that the source strata of oilfield water are in semi-closed and semi-open state, the reduction is not complete, the infiltration of surface leachate water is present, and the water alternation is slow. Under the influence of differential uplift, the activated basin margin faults and deep and large faults in Manite Depression become the channels for oil field water to flow to the target interval. On the one hand, the reductants such as CH₄ and H₂S carried by oil field water cause the epigenetic alteration of the target interval, on the other hand, they react with uranyl carbonate in leachate water infiltrated into the surface to reduce hexavalent uranium carbonate to tetravalent uranium. Uranium precipitates from water and accumulates to form minerals.