辉钼矿Re-Os同位素定年方法的改进与应用

公认的Re-Os同位素定年代表物辉钼矿,目前已在金属硫化物矿床年代学研究领域获得了广泛的应用。本研究采用浓HNO₃分解辉钼矿样品,大大地简化了Re和Os的化学制备过程,并根据辉钼矿中正常Os含量水平相对放射成因¹⁸⁷Os可以忽略的特点,以正常Os标准为稀释剂,实现了仪器测量过程中Os同位素质量分馏的在线校正,改善了分析数据的质量。该方法经辉钼矿国家标准物质进行验证,获得了满意的Re、Os含量及Re-Os年龄数据,并且在南岭地区与连阳复式岩体相关的姓坪夕卡岩型钼矿床成矿年龄研究中获得了成功应用。在实际应用中,为了获得有意义的能反映真实地质事件的年龄数据,辉钼矿样品不仅要有足够的取样量,而且还要保证粒度细、混合均匀。

The improved molybdenite Re-Os dating method and its application

As a robust proxy, molybdenite has been widely applied to determination of Re-Os age. This study simplified the chemical separation of Re and Os using concentrated HNO₃ for digestion of molybdenite. Based on the negligible level of common Os relative to radiogenetic ¹⁸⁷Os in molybdenite, a common Os standard was used as spike, and as a result, Os isotopic mass fractionation during ICP-MS measurements could be on-line corrected, improving the quality of analytical data. This method was validated using national certified molybdenite standards, and the results were well consistent with the certified values. Using this method for determination of molybdenite sampled from Xingping skarn-type Mo deposit, Liangyang granite composite, reasonable Re-Os age data have been obtained. In practice, it is suggested to use enough amounts of molybdenite, which should be homogenized fine-grain in order to obtain representative Re-Os age.