甘肃龙首山青井地区花岗质砾岩中钍、铀混合型矿化特征及成因探讨

青井是位于龙首山成矿带西段的一个钍、铀混合型异常点,通过钻孔查证在青井盆地的花岗质砾岩中发现了较好的矿化线索,矿石具有热液型矿化的特征,发育钾长石化、赤铁矿化、碳酸盐化和绿泥石化为主的钾交代蚀变组合。通过对含矿花岗质砾岩的岩矿鉴定、电子探针测试、地球化学分析和钍矿物U-Pb同位素年龄测定进行综合研究,认为花岗质砾岩中发育的是产于挤压-俯冲构造环境下受断裂构造和辉绿岩脉共同控制的热液成因钍、铀混合型矿化,含钍、含铀矿物主要为钍石、沥青铀矿和铀石,成矿期应为新生代中晚期。热液成矿过程中带来了大量的外来组分,矿石中的Al_2O_3、Fe_2O_3和K_2O等主量元素和轻、重稀土元素以及Rb、Nb、Nd、Zr、Hf、Ta、W、Sb等微量元素均随着Th、U含量的增加而增加。

Mineralization characteristics and genesis of thorium-uranium in granitic conglomerates of the Qingjing area, Longshoushan, Gansu Province

The Qingjing area is a thorium-uranium mixed anomaly in the western part of the Longshoushan metallogenic belt, Gansu Province. Borehole verification found mineralization in the granitic conglomerate of this area. The ore is characterized by characteristics of hydrothermal mineralization, with potassium metasomatic alteration assemblages dominated by potassium feldspar, hematite, carbonate and chlorite. Combination of ore identification, electron probe testing, geochemical analysis and U-Pb isotope dating of thorite minerals in ore-bearing granitic conglomerates suggests that the hydrothermal thorium-uranium mixed type mineralization formed in the granitic conglomerates, controlled by fault structures and diabase in a compression-subduction tectonic environment. The minerals bearing thorite and uranium are mainly thorite, pitchblende and uranite, which formed in Middle to Late Cenozoic. During hydrothermal mineralization, a large number of exotic components were brought. The main elements such as Al2O3, Fe2O3 and K2O, light and heavy rare earth elements, and trace elements such as Rb, Nb, Nd, Zr, Hf, Ta, W and Sb in ores increase with growing Th and U content.