陕西华阳川铀铌矿床中铀矿物的年代学与矿物化学研究及其对铀成矿的启示

本文在详细的野外地质工作基础上，利用场发射扫描电镜(FE SEM)结合能谱分析(EDS)与电子探针分析(EMPA)等手段对华阳川铀铌矿床中主要铀矿物的种类、共生组合关系及铀矿物的矿物化学与年代学开展了详细的研究工作。研究成果显示，铀主要以铌钛铀矿的形式产出，其次为晶质铀矿。晶质铀矿的矿物学研究和电子探针年代学研究结果显示，矿床中存在两期晶质铀矿年龄，早期晶质铀矿的化学年龄为~201 Ma(印支期 燕山期之交)，形成于岩浆 高温热液体系，并伴随大量早期蚀变的铌钛铀矿产出，为矿床形成的主要成矿期；晚期晶质铀矿的化学年龄为~129 Ma(燕山期)，形成于高温热液体系，与少量未蚀变的铌钛铀矿产出，仅占次要地位，可能是区域内强烈的燕山期岩浆热液交代早期铌钛铀矿后，淋滤出的铀再次沉淀的结果。结合区域地质关系，认为早期的铀成矿可能主要与(霓辉石)黑云母方解石碳酸岩脉有成因联系，是矿床形成的重要时期；晚期的铀矿物可能只是区域内燕山期的岩浆热液交代早期铌钛铀矿后，铀被淋滤带出后再次在有利部位沉淀的结果。因此，华阳川铀铌矿床可能是一个主要形成于印支期 燕山期之交，并被燕山期岩浆活动(叠加)改造的与碳酸岩脉有关的铀铌矿床。

Chronology and mineral chemistry of the uranium minerals in Huayangchuan uranium- niobium deposit, Shaanxi Province and its implications for uranium mineralization

The Huayangchuan uranium- niobium polymetallic deposit which is located on the southern margin of the North China Craton, is a large carbonatite- related uranium deposit.Based on detailed field geological work, this paper focus on the petrography, mineral chemistry and chronology of the uranium minerals, using field emission scanning electron microscopy (FE- SEM) combined with energy Disperse spectrum (EDS) and electron microprobe analysis (EMPA). The results show that primary uranium mineral is betafite, followed by uraninite. Uraninite chemical U- Th- Pb geochronology and mineralogical evidences provide the timing constraints and insights into the formation of the Huayangchuan uranium- niobium deposit. Two types of mineralization are identified and documented here: magmatic uranites and betafites related to (aegirine- augite) biotite calcite carbonatitic and syenite pegmatitic veins, formed during the peak (~201 Ma) associated with a large number of altered betafites, and high- temperature vein- hosted uraninites and betafites related to granitic gneiss, formed during the peak (~129 Ma) with few unaltered betafite grains. Minerology and mineral chemistry study indicate that the uraninite and betafite formed at the late stage may precipitate from the Yanshanian magmatic hydrothermal fluid which leached the uranium element from the early betafites. It is demonstrated that the early uranium mineralization related to the (Aegirine- augite) biotite calcite carbonatitic veins, is the primary stage for the deposit, while the late uranium mineralization may be only the altered produced due to the Yanshanian magmatic activity. In summary, the Huayangchuan uranium- niobium deposit show the genetic relationship with the Indosinian- Yanshanian carbonatitic veins but superimposed by the Yanshanian magmatism activity.