甘肃省龙首山成矿带青山堡岩体闪长岩特征及与铀成矿关系北大核心CSCD

青山堡花岗岩体位于龙首山成矿带东段,为探讨该岩体细粒闪长岩与铀成矿的关系,对其进行了岩石地球化学、同位素年代学等研究。分析结果表明,随着U含量的增加,SiO_(2)、Al_(2)O_(3)、Fe_(2)O_(3)、Na_(2)O、K_(2)O、MgO的含量增加,FeO、CaO的含量减少,这与成矿期发育的碱交代蚀变关系有关;同时岩石具Rb、Ta、U、Hf等元素相对富集,Nb、Zr、Ti等元素相对亏损及轻稀土右倾分馏明显的地球化学特征。区内沿断裂分布的细粒闪长岩是铀成矿的有利赋矿岩石之一,而其与花岗(闪长)岩的接触面为铀矿富集提供了物理化学环境突变的成矿结构面;含矿蚀变闪长岩矿石中发现有网脉状、细脉状的沥青铀矿脉。结合区域资料表明,志留纪龙首山地区广泛发育的碱交代铀成矿作用在青山堡岩体中亦有发育。后期龙首山东段抬升剥蚀速度较中段要强烈,潜水氧化作用发育,前期区域性碱交代热液成矿作用所形成的含矿构造蚀变带是后生潜水氧化改造叠加形成浅部淋积型工业富铀矿体的关键。

Characteristics of diorite from the Qingshanbao pluton and their relationship with uranium mineralization in the Longshoushan metallogenic belt, Gansu Province

The Qinshanbu granite body is located in the eastern part of the Longshoushan metallogenic belt. In order to discuss the relationship between the diorite and the uranium mineralization of this granite body, this work conducted lithogeochemical and isotopic geochronological research on the granite body. Results show that with the increase of U content, the contents of SiO2, Al2O3, Fe2O3, Na2O, K2O and MgO increase, while the contents of FeO and CaO decrease, which is closely related to the alkali metasomatic alteration developed in metallogenic period. In addition, the rocks display the enrichment of Rb, Ta, U and Hf, depletion of Nb, Zr and Ti, and right-inclined fractionation of LREE. The fine-grained diorite distributed along the faults in the area is favorable host rock for uranium mineralization, and the interface between the fine-grained diorite and the granite (diorite) provides ore-forming structural plane with abrupt physicochemical environments for uranium enrichment. Network type veins and vein-like pitchblende veins are observed in ore-bearing altered diorite ores. In combination with regional data, it is indicated that the widely distributed Silurian alkali-metasomatic uranium mineralization in the Longshoushan area is commonly developed in the Qingshanbao pluton. In later stage, the uplift and denudation rate of the eastern part of Longshoushan was stronger than that of the middle part, with well-developed phreatic oxidation. The ore-bearing structural alteration zone formed by the regional alkali metasomatic hydrothermal mineralization in early stage is critical for the formation of shallow leached uranium-rich ore bodies.