661铀矿床矿石U-Pb等时线年龄及其成矿构造背景

Ore U-Pb isochron ages and metallogenic tectonic setting of No.661 uranium deposit

661铀矿床位于赣杭构造火山岩铀成矿带东段大洲铀矿田内,矿体赋存于磨石山群九里坪组流纹岩之中,矿床定位于岩石圈伸展断陷盆地附近,明显受断裂带的控制。利用矿石U-Pb等时线法确定了该矿床两个矿体的成矿时代,分别为(107.0±2.3)Ma和(110.0±3.5)Ma。这些年龄值与断陷红盆底部发育的玄武岩的成岩年龄一致,也与东南沿海地区明显存在的110 Ma基性脉岩拉张活动的时间一致,表明岩石圈伸展与铀成矿之间具有良好的对应关系,为岩石圈伸展期与铀成矿关系研究提供了年代学证据。岩石圈伸展控制着富CO2热液形成的时间,因而也大致控制了铀成矿的时代。

The No.661 uranium deposit of the Dazhou uranium orefield is located in the Gan-Hang tectonic volcanics-hosted uranium belt,with the ore bodies existent in Jiuliping Formation rhyolite of Moshishan Group.Two U-Pb isochron ages obtained for ores from two ore bodies are（107.4±2.3） Ma and（110.0±3.5） Ma,respectively.These ages are consistent with ore-forming ages of the other uranium deposits in the Gan-Hang metallogenic belt and the ages of basalts or dikes at the bottom of the basins that host the ore deposits,indicating the existence of good correlation between the lithospheric extension and the uranium mineralization.This paper provides chronologic evidence for uranium metallogenesis during the lithospheric extension.Lithospheric extension controlled the injection of mantle-derived components into hydrothermal fluids and the formation of CO2-rich hydrothermal fluids,and hence basically controlled the uranium mineralization age.