Two Distinct Geological Environments from Sedimentary to Diagenesis Stages: Examples from Sandstone-Type Uranium Deposits, Turpan-Hami Basin
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摘要: 砂岩型铀矿床的形成既需要适当的沉积环境做准备, 又与成岩环境关系密切.通过宏观沉积学和泥岩元素地球化学分析探讨了吐哈盆地西南缘水西沟群的沉积介质环境, 利用砂岩样品的流体包裹体及激光拉曼光谱分析阐明了成岩环境.研究发现, 从沉积期到成岩期研究区的水西沟群具有2种截然不同的地质环境: 沉积期泥岩矿物中Sr/Ba比值小于0.3, B平均值为46.35×10-6, 同时具有淡水动物化石组合, 显示为温暖潮湿的贫氧、淡水介质环境, 但到成岩期却演化为具有有机质参与的中低温(156.1℃)、超盐度(7.4%)成岩环境, 现今环境(地下水盐度为7.8%)恰好与成岩环境相似.值得注意的是, 研究区铀成矿的年龄(104± 1)Ma、(24± 1)Ma、(7± 0)Ma与成岩期基本吻合, 表明具有有机质参与的中低温、超盐度环境也可能是砂岩型铀矿的成矿环境.Abstract: The formation of sandstone-type uranium depositsis not only related to sedimentary environment, but also related to diagenesis environment. This paper illustrates the original sedimentary environment of the Shuixigou Group using sedimentology methods and analysis results of element geochemistry in mudstone, and discusses the diagenesis environment by means of fluid inclusions and Raman spectrum analysis in sandstone in the southwestern margin of the Turpan-Hami basin. The results show that two distinct geological environments from sedimentary to diagenesis stages are observed in the Shuixigou Group. In sedimentary stage, mudstones have the Sr/Ba value of less than 0.3 and the average B content of 46.35× 10-6, and the fresh water faunal fossils are observed, which indicates that in-situ sedimentary environment shows warm, wet, oxygen-deficient and fresh water.However, the diagenesis environment with middle-lower temperature(156.1 ℃)and supersalinity(about 7.4%)as evidenced from fluid inclusions is the same as that of the present formation water with a salinity of 7.8%. The research results indicate that the mineralization ages of uranium are basically coincident with the main diagenesis stages, which are(104± 1)Ma, (24± 1)Ma and (7± 0)Ma, respectively.So it is possible that supersaline hydrocarbon-bearing fluid with middle-lower temperature should be a favorable mineralization environment of uranium.
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图 1 研究区指示湖泊环境的淡水动物化石
a.鱼鳞; b.cf. Eosolimnadiopsis sp.; c.昆虫翅; d.昆虫尾甲; e.昆虫尾甲; f.昆虫尾甲
Fig. 1. Fresh water faunal fossils indicating the lacustrine environment, the southwestern margin of Turpan-Hami basin
图 2 研究区泥岩中B、Sr、Ba含量及Sr/Ba、K/Na值的垂向演化(36个样品统计)
Fig. 2. Vertical evolution charts of the content of B, Sr, Ba and Sr/Ba, K/Na values (36 samples counted)
图 3 相当硼含量换算曲线(Walker, 1968)
Fig. 3. The calculating curve of the corresponding boron
图 4 吐哈盆地西南缘铀成矿区成岩环境参数
Fig. 4. Parameters about diagenesis environment in uranium mineralization zone, the southwestern margin of Turpan-Hami basin
图 5 吐哈盆地西南缘铀成矿区典型包裹体的激光拉曼光谱测试
a.样品K-1-1, 钙质胶结物中的包裹体; b.样品K-3-2, 钙质胶结物中的包裹体; c.样品K-3-1, 石英裂隙中的包裹体
Fig. 5. Raman spectrum of typical inclusions in uranium mineralization zone, the southwestern margin of Turpan-Hami basin
图 6 研究区不同阶段地质环境的比较
图中铀成矿年龄据徐高中(2003)、周巧生和李占游(2003); 地下水信息据吴伯林等(2004); 艾丁湖信息据杨发相等(1996)、王亚俊和吴素芳(2003)
Fig. 6. Comparison of different geological environments
表 1 古氧相地球化学指标(Jones and Manning, 1994)
Table 1. Geochemical indices of palaeo-oxygenation facies
表 2 水西沟群泥岩中微量元素比值
Table 2. Microelement ratios in mudstone of Shuixigou Group, the southwestern margin of Turpan-Hami basin
表 3 吐哈盆地西南缘铀成矿区成岩包裹体基本特征
Table 3. Basic characteristics of fluid inclusions in uranium mineralization zone, the southwestern margin of Turpan-Hami basin
表 4 吐哈盆地西南缘铀成矿区成岩流体盐度计算参数与结果
Table 4. Calculated parameters and results in uranium mineralization zone, the southwestern margin of Turpan-Hami basin
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