含辉钼矿全岩样品Re-Os同位素定年研究:在北京大庄科钼矿床中的应用

采用硝酸在比色管中对辉钼矿样品中Re含量进行初测的方法,测得辉钼矿标准样品JDC Re含量与推荐值在误差范围内基本一致,与传统的Carius管法相比,该方法具有简便快速的特点。传统的辉钼矿Re-Os同位素定年分析对象为辉钼矿单矿物,根据所测得的187Re/187Os值获得辉钼矿的Re-Os年龄,Re、Os在辉钼矿中大量富集,而在硅酸盐矿物中几乎没有,探索性地对含有辉钼矿的全岩样品进行Re-Os同位素定年,虽然所得Re、Os含量偏低,但187Re/187Os值不会变。该方法省去了选样过程花费的大量时间,避免了选样过程中可能造成的交叉污染。采用同位素稀释Carius管逆王水法探索性地对北京大庄科钼矿床中含辉钼矿全岩样品进行Re-Os同位素年龄测定,获得了(137.6±3.7)Ma精确的等时线年龄,与挑选出辉钼矿单矿物样品的Re-Os同位素等时线年龄(136.8±2.6)Ma吻合较好,直接厘定了大庄科钼矿的成矿时代。该年龄与矿区汉家川石英二长岩锆石U-Pb年龄一致,表明大庄科钼矿的形成与汉家川石英二长岩关系较为密切,为中国东部第二期大规模成矿作用的产物,形成于中国东部岩石圈伸展环境。

Re-Os Dating for Molybdenite-bearing Rock Samples: Application in Dazhuangke Molybdenum Deposit in Beijing

A simple and rapid method for preliminary determination of rhenium using nitric acid in colorimetric tube was described,the method was identified by analyzing the standard reference molybdenite sample and the results were in good with the certified value.The object of the traditional Re-Os isotope dating for molybdenite was pure mineral,and the Re-Os age was obtained due to the values 187Re/187Os.Molybdenite were rich in Re and radiogenic 187Os.In contrast,silicate mineral incorporates essentially was not involving Re and Os.Therefore,molybdenite-bearing rock samples were tried for Re-Os dating,and the molybdenite testing process of this method reducing the molybdenite processing can save a lot of time and avoid the cross contamination.Re-Os model ages for molybdenite-bearing whole rock samples collected from the Dazhuangke deposit range from(135.7±2.2) to(137.7±2.1) Ma,and the isochrone age was(137.6±3.7) Ma.The Re-Os age of molybdenite-bearing whole rock samples were nearly same to the Re-Os age of pure molybdenite mineral samples.The molybdenite Re-Os age was identical to the U-Pb zircon age for the quartz-monzonite,showing that the Mo mineralization of the Dazhuangke molybdenum deposit has a close relationship with the intrusion of quartz-monzonite.The age of the Dazhuangke molybdenum deposit was consistent with the second period of large scale mineralization in East China,indicating that Mo mineralization was driven by lithosphere extension in East China.