1.State Key Laboratory of Nuclear Resources and Environment，East China University of Technology;2.School of Earth Sciences，East China University of Technology
陕西省华阳川矿床位于华北克拉通与秦岭造山带接触的小秦岭成矿带内，是一个与碳酸岩有关的世界级铀铌多金属矿床，铌和铀主要赋存于烧绿石矿物中。前人对华阳川成矿机理进行了详细的研究，但关于矿床岩浆-热液演化过程及其与成矿的关系均较薄弱，因此本论文运用电子探针对华阳川发育的2种原生烧绿石（pcl Ⅰ, pcl Ⅱ）和3种蚀变烧绿石（pcl Ⅰ alt1, pcl Ⅰ alt2和pcl Ⅱ alt）开展详细的矿物学和化学组成及其演化特征研究。结果显示华阳川碳酸岩体中U-Nb富集过程与晚三叠世岩浆作用关系密切，地幔部分熔融形成原始的富铀铌碳酸岩浆，再通过结晶分异等过程形成原生（岩浆）烧绿石pcl Ⅰ、原生（岩浆）烧绿石pcl Ⅱ和原生晶质铀矿Ur1。早白垩世，华阳川碳酸岩体受到高温热液蚀变作用，高温富氟流体交代早期原生烧绿石pcl Ⅰ，从烧绿石pcl Ⅰ中释放出的部分Nb和U被溶解、再活化，从而形成原生晶质铀矿Ur2、蚀变烧绿石pcl Ⅰ alt1和次生榍石Ttn2。此外，华阳川矿床还受到成矿后低温热液蚀变作用，原生烧绿石pcl Ⅰ和原生烧绿石pcl Ⅱ被交代形成蚀变烧绿石pcl Ⅰ alt2和蚀变烧绿石pcl Ⅱ alt。由此表明华阳川矿床在晚三叠世-早白垩世发生了两次岩浆-热液铀铌矿化及一次成矿后低温热液蚀变作用。
Abstract: The Huayangchuan deposit in Shaanxi Province is located in the Xiaoqinling metallogenic belt in contact between the North China Craton and the Qinling orogenic belt. It is a world-class uranium and niobium polymetallic deposit related to carbonatite, in which pyrochlore is the major U and Nb-bearing mineral. Although the Huayangchuan metallogenic mechanism has been well studied, the magmatic-hydrothermal evolution process of the deposit and its relationship with mineralization were poorly understood. Hereby, this paper study mineralogy, chemical composition and evolution characteristics of two types of primary pyrochlore (pcl Ⅰ and pcl Ⅱ) and three types of altered pyrochlore (pcl Ⅰ alt1, pcl Ⅰ alt2 and pcl Ⅱ alt) in the Huayangchuan deposit. The results show uranium and niobium mineralization in Huayangchuan carbonatite is closely related to the Late Triassic magmatism. It was related to a mantle-derived, initially U-rich carbonatitic magma, which has been further enriched in U by crystallization differentiation and formed the primary (magmatic) pyrochlore (pcl I), primary pyrochlore (pcl Ⅱ) and primary uraninite (Ur1) through partial melting from the mantle. In the early Cretaceous, the carbonatite in Huayangchuan were subjected to high-temperature hydrothermal alteration, and part of Nb and U released from the early pyrochlore (pcl Ⅰ) were dissolved and reactivated by the high temperature high-F fluid, which formed the primary uranite (Ur2), the altered pyrochlore (pcl Ⅰ alt1) and the secondary titanite (Ttn2). The primary pyrochlore (pcl Ⅰ) and primary pyrochlore (pcl Ⅱ) can be replaced by the altered pyrochlore pcl Ⅰ alt2 and altered pyrochlore pcl Ⅱ alt in the post ore low-temperature alteration. These results indicate that two magmatic-hydrothermal uranium-niobium mineralization and one post-mineralization low-temperature hydrothermal alteration occurred in Huayangchuan deposit during late Triassic and early Cretaceous.