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

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(2?, 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 com-parison 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.