内蒙古苏尼特左旗准苏吉花钼矿床成岩成矿年代学及其地质意义

Geochronology of Zhunsujihua molybdenum deposit in Sonid Left Banner,Inner Mongolia,and its geological significance

通过辉钼矿Re-Os及锆石SHRIMP U-Pb同位素年代学的研究,测得辉钼矿的Re-Os等时线年龄为(298.1±3.6)Ma,赋矿似斑状花岗岩中锆石SHRIMP U-Pb年龄为(298.2±3.1)Ma,确定准苏吉花斑岩型钼矿床成岩成矿时代为早二叠世。辉钼矿中Re的含量指示成矿物质可能为壳幔混合来源。结合区域内其他斑岩型矿床的成矿年代,可以将区内斑岩型矿化时代划分为4个阶段,即晚泥盆世成矿阶段、早二叠世成矿阶段、三叠纪成矿阶段及白垩纪成矿阶段。根据这些斑岩型矿床矿化形式在不同地质历史时期的演化,可以将其划分为2期,即晚泥盆世时期以铜为主的斑岩型矿化和早二叠世及其后的以钼为主的斑岩型矿化,早二叠世斑岩型钼矿化可能与板块俯冲过程中弧后伸展作用岩浆作用有关,而三叠纪及白垩纪期间斑岩型钼矿化则是西伯利亚板块与华北板块拼接后多期伸展作用的产物。中蒙边境中东部地区的这些斑岩型矿床矿化形式上的差异是该区域内成矿环境变化的反映。

A precise Early Permian Re-Os isochron age of（298.1±3.6） Ma for the molybdenite and a zircon SHRIMP U-Pb age of（298.2±3.1） Ma for the ore-bearing granite from the Zhunsujihua porphyry molybdenum deposit in Sonid Left Banner of Inner Mongolia provide new information for the ore-forming epoch of the Zhunsujihua porphyry molybdenum deposit.The rhenium content of molybdenite suggests a crust-mantle mixed source for the ore-forming substance.Combined with the mineralization ages of the porphyry deposits in northern central Inner Mongolia and the adjacent Mongolia from the literature,the authors recognized four metallogenic episodes,i.e.,Late Devonian,Early Permian,Triassic and Cretaceous.On the basis of the metallogenic evolution,the porphyry mineralization type is divided into the Late Devonian copper ore-forming stage in an arc tectonic setting and the Early Permian and subsequent molybdenum ore-forming stage in an extensional tectonic setting.The difference and evolution of mineralization types in geohistory indicate variation of tectonic setting,which gradually changed from the subduction accretion related tectonic setting through the subduction related back arc spreading tectonic setting to the continental extensional setting.These data also provide great potential for exploration of molybdenum deposits hosted in the extensional setting.