蒙古国阿林诺尔钼矿床辉钼矿Re-Os同位素年龄及地质意义

Re-Os Isotopic Dating of Molybdenite from the Aryn nuur Mo Deposit in Mongolia and Its Geological Implications

通过对蒙古国苏赫巴托尔省阿林诺尔钼矿7件辉钼矿样品进行Re-Os同位素分析,获得的同位素模式年龄介于(225.7±3.5)Ma^(227.5±3.4)Ma之间以及一个相关性很好的等时线年龄(227.7±3.1)Ma(2σ,MSWD=0.066)。模式年龄和等时线年龄结果集中一致,为研究阿林诺尔钼矿床的形成时代提供了一个准确的时限。该矿床的成矿年龄与阿林诺尔黑云母花岗岩的形成时代比较一致。据此可以推断阿林诺尔钼矿床与含矿围岩黑云母花岗岩体的形成时间均为中三叠世末,属印支期构造-岩浆活动的产物。阿林诺尔钼矿床辉钼矿样品的Re含量为26.00×10-6~66.40×10-6,表明其成矿物质来源为壳幔混合来源。

Located in central Sühbaatar Province of southeast Mongolia,the Aryn nuur Mo deposit is a prophyry-type Mo deposit with an average Mo grade of 0.096 wt.%.The ore deposit is temporally and spatially associated with the biotite granite.Mo mineralization is mainly present as stockworks,lenses and layers hosted by the biotite granite.Seven samples of molybdenite for Re-Os isotopic dating were analyzed,which yielded model ages from（225.7±3.5） Ma to（227.5±3.4） Ma,averaging（226.4±3.4） Ma,and a good isochronic age of（227.7±3.1） Ma（2σ,MSWD=0.066）.The consistency of the above dating data indicates an accurate time limit of the formation of the Aryn nuur Mo deposit.The ore-forming age is consistent with the age of the Aryn nuur biotite granite.It is thus held that the Aryn nuur Mo deposit was formed at the end of Triassic and related to the Indosinian acid and intermediate-acid magmatic activities.The Re content of the molybdenite varies in the range of 26.00×10^-6 to 66.40×10^-6,with an average of 49.42×10^-6.According to the content of Re in the Aryn nuur Mo deposit in comparison with the data obtained from other molybdenite-bearing deposits,the Aryn nuur Mo deposit is considered to have derived its ore-forming materials from the crust and the upper mantle.