内蒙古北大山新井地区热液型铀矿化特征及成因探讨

Discussion on the Mineralization Characteristics and Genisis of Hydrothermal Uranium Deposit in Xinjing Area of Beidashan in Inner Mongolia

热液型铀矿是内蒙古北大山地区重要的铀矿类型。文章以北大山中部新井铀矿点为研究对象,详细阐述了新井地区地质特征和铀矿化特征,认为铀成矿受断裂构造、斜长角闪片岩、伟晶状花岗岩脉及热液蚀变控制,F_(1)断裂为铀矿化提供了运移通道和赋存空间,构造变异部位控制铀矿床的定位;古元古界变质岩为有利的含铀建造,作为矿源层和储矿层为热液型铀矿化的形成发挥着重要作用;海西晚期侵入的伟晶状花岗岩为钙碱性铝过饱和系列富铀花岗岩,该岩脉控制铀矿体的产出部位;蚀变是矿化的先导和基础,铀矿体与富矿体一般出现在多期次热液蚀变叠加部位,热液蚀变是铀矿叠加富集的必要条件。综合分析认为新井地区热液型铀矿的形成经历了含矿建造形成阶段、预富集阶段、成矿阶段及矿体叠加富集阶段,下一步勘查工作的重点是F_(1)断裂带及其走向发生变异的部位,受F_(1)断裂带控制的热液蚀变带是找矿的重点区段,伟晶状花岗岩与斜长角闪片岩的接触面是产矿的最佳界面,伟晶状花岗岩脉密集分布区是铀成矿的有利部位。

Hydrothermal uranium deposit is an important type in Beidashan area of Inner Mongolia.In this paper,Xinjing uranium occurrence in the middle of Beidashan was studied to elaborates the geology and uranium mineralization characteristics of Xinjing area.The uranium mineralization was believed to be controlled by fault structure,oblique amphibolite,pegmatoid granite veins and hydrothermal alteration.The F_(1) fault provided a transportation channel and storage space for uranium mineralization,and the variation part controled the positioning of uranium deposits.Paleoproterozoic metamorphic rocks were the host uranous rock and played an important role in the formation of hydrothermal uranium mineralization both as source layers and reservoirs.The pegmatoid granite intruded in the later Hercynian Period is a uranium-rich calciumalkaline peraluminous granite,which controlled the poisoning of uranium ore bodies.Alteration was the precursor and basis for the mineralization,uranium ore bodies and rich ore bodies generally occurred in superposition site of multi-stage hydrothermal alteration.Comprehensive analysis showed that the formation of hydrothermal uranium deposit in Xinjing area experienced the formation stages of uranous host rock,preenrichment,mineralization and superposition enrichment of ore body.Therefore,the next exploration should orients along the F_(1) fault zone,focuses on the change part of its strike,the hydrothermal alteration controlled by the F_(1) fault zone,especially the contact interface between pegmatoid granite and oblique amphibolite,and the dense distribution area of pegmatoid granite veins will be the best.