沽源-红山子铀成矿带核桃坝铀矿床矿相学和成矿年代学研究

核桃坝矿床是著名的沽源-红山子铀成矿带上新近勘查突破的重要铀矿床之一。为恢复成矿过程、划分成矿阶段和探讨矿床成因,本文开展了系统的矿相学和成矿年代学研究,以期为区内铀矿勘查和找矿突破提供理论支持。矿相学研究表明,矿床矿石矿物以铀石为主,成矿作用可划分为早期钠长石化交代阶段、早期热液成矿阶段、晚期热液成矿阶段和成矿后阶段四个阶段。核桃坝矿床属于碱交代型(钠交代)热液铀矿床。沥青铀矿U-Pb同位素表观年龄、电子探针化学年龄以及等时线年龄综合研究显示,矿床形成时代应在99. 1Ma左右,是晚白垩世成矿作用的产物。核桃坝矿床可能是富铀岩体在碱交代作用后形成流体(富铀含硅酸成矿流体)在外部条件改变的情况下沉淀成矿。因此,矿体的定位与富铀岩体关系密切,富铀岩体附近的开放空间(断裂构造、层间破碎带等)是重要的找矿方向。

Study on the mineragraphy and geochronology of Hetaoba uranium deposit in Guyuan-Hongshanzi uranium metallogenic belt

Hetaoba uranium deposit is one of the most important uranium deposits on the Guyuan-Hongshanzi uranium metallogenic belt. In this paper, systematic study on the mineralogy and geochronology of the deposit were carried out to restore its metallogenic and genetic process, and to divide its ore-forming stages, so as to provide theoretical support for the exploration and prospecting of uranium deposits in this area. According to its mineralogical properties, the main ore-bearing mineral of the deposit is coffinite, and the ore-forming mineralization of this depsoit can be divided into four stages:the early stages of sodium petrification, the early hydrothermal mineralization, the late hydrothermal mineralization, and the post-mineralization. Hetaoba deposit is a sodium metasomatic hydrothermal uranium deposit. U-Pb isotopic ages, isochron ages, and electron-probe chemical ages of the uranium minerals indicate that the ore-forming age should be around 99.1Ma, so the deposit was possibly formed by the Late Cretaceous mineralization. The formation of the Hetaoba uranium deposit may be resulted from the U-enriched silicic acid bearing fluids which was formed after the alkaline metasomatism of the uranium-enriched rocks and these fluids precipitated to form a deposit as the external conditions changed. Therefore, the deposit may be closely related to the uranium-rich rocks, and the open spaces in the vicinity of the uranium-rich rocks are important prospecting areas, including fractured structures, interlaminar fracture zones, etc.