鄂尔多斯盆地纳岭沟铀矿床绿泥石特征及地质意义

纳岭沟铀矿床位于鄂尔多斯盆地北部,具有明显的后期热液作用的特征,矿体空间展布主要受控于绿色-灰色砂岩的过渡界面,与绿泥石化的蚀变砂岩关系密切。通过对纳岭沟铀矿床不同颜色砂岩中的绿泥石进行详细的岩相学研究和电子探针化学成分分析,依据绿泥石的成因与共生矿物的关系,识别出绿泥石主要的3种类型:填隙物型绿泥石,片状与黄铁矿共生型绿泥石以及黑云母蚀变型绿泥石;同时通过绿泥石的Fe-Si图解确定了纳岭沟铀矿床不同颜色砂岩中的绿泥石主要为铁镁绿泥石和密绿泥石。根据Al/(Fe+Mg+Al)-Mg/(Fe+Mg)的关系图解确定出不同颜色砂岩中的绿泥石具有铁镁质流体和泥质两种来源,通过绿泥石中主要阳离子与镁的关系图解和计算得出的绿泥石形成温度共同确定出绿泥石是多期次的中低温热液流体作用的产物。综合研究表明,纳岭沟铀矿床的绿泥石形成至少经历了温度稍高的还原性流体和温度稍低的氧化性流体等两个期次的流体作用,稍高温的还原性流体与成矿关系更为重要。与绿泥石形成有关的热液流体作用不仅带入了部分铀,还促进了铀的活化和运移。

Characteristics of Chlorite from the Nalinggou Uranium Deposit in the Ordos Basin and Its Geological Significance

The Nalinggou uranium deposit in the northern Ordos Basin has obvious late hydrothermal features. Spatial distribution of the ore bodies is mainly controlled by the green gray sandstone transition interface, and closely associated with chloritization of alteration sandstone. Detailed petrographic and electron microprobe chemical analysis was conducted to chlorite from the Nalinggou uranium deposit. Based on the relationship between chlorite genesis and paragenetic minerals, three types of chlorite have been identified: filling type chlorite, flakes chlorite intergrowth with pyrite and chlorite altered from biotite. Fe Si diagram of chlorite also determines that chlorite in different color sandstones can be divided into two types: brunsvigite and pycnochlorite. The diagram of Al/(Fe+Mg+Al) Mg/(Fe+Mg) shows that chlorite in different color sandstone is of two origins: femic constituents fluid and pelitopsammite. On the basis of the relation between major cations and magnesium in chlorite, our calculation suggests that chlorite resulted from multiple medium to low temperature hydrothermal fluid effect. Comprehensive studies have shown that chlorite in the Nalinggou uranium deposits experienced at least two fluid activities, a slightly high temperature reducing fluid activity and a slightly low temperature oxidizing fluids activity. It can be concluded that the former played an important role in mineralization. The hydrothermal fluid that associated with chlorite formation not only brought part of uranium but also promoted the activation and migration of uranium.