陕西华阳川铀-多金属矿床晶质铀矿电子探针U-Th-Pb化学定年及其地质意义

EPMA chemical U-Th-Pb dating of uraninite in Huayangchuan U-polymetallic deposit of Shaanxi Province and its geological significance

华阳川铀-多金属矿床位于小秦岭陆内造山带内,以铀铌铅为主,并伴生稀有、稀土元素矿化,含矿脉岩主要有伟晶岩和碳酸岩。文章利用电子探针U-Th-Pb化学定年技术对华阳川铀-多金属矿床中晶质铀矿开展了定年工作,并获得了2组U-Th-Pb年龄。第一组晶质铀矿加权平均年龄为(221.9±5.1)Ma(MSWD=0.36,n=18),该区印支期老牛山岩体及邻近的黄龙铺钼矿床、黄水庵钼矿床年龄均集中在220 Ma左右,说明晚三叠世是东秦岭地区一个重要的成岩成矿时代,华阳川铀-多金属矿床在220 Ma左右也发育一期铀-铌成矿作用。第二组晶质铀矿加权平均年龄为(137.1±2.0)Ma (MSWD=1.06,n=47),指示了华阳川铀-多金属矿床存在白垩纪的一期铀-铌活化-沉淀事件。测定的2组晶质铀矿化学年龄可能分别记录了该区自晚三叠世开始的后碰撞伸展环境和早白垩世的造山后伸展环境。

The Huayangchuan U-polymetallic deposit is located in the Xiaoqinling intracontinental orogenic belt,dominated by uranium-niobium-lead elements and associated with REE mineralization.The ore-bearing vein rocks are mainly pegmatite and carbonate.In this paper,U-Th-Pb EPMA chemical dating was carried out on the uraninite in the Huayangchuan deposit,and two groups of results were obtained.The first group of age is(221.9±5.1)Ma(MSWD=0.36,n=18),which is closer to the ages of the Indosinian Laoniushan intrusion and the adjacent Huanglongpu molybdenum deposit and Huangshuian molybdenum deposit(220 Ma),indicating that the Late Triassic period is an important petrogenic and metallogenic epoch in the East Qinling.The Huayangchuan deposit also developed a stage of uranium-niobium mineralization around 220 Ma.The second group of age is(137.1±2.0)Ma(MSWD=1.06,n=47),which indicates the second-stage uranium-niobium activation-precipitation of the Cretaceous in the Huayangchuan deposit.These two groups of ages of uraninite in the Huayangchuan deposit may record the post-collisional extensional environment in the late Triassic period and the post-orogenic extensional environment in the early Cretaceous period,respectively.