Precise molybdenite Re-Os and mica Ar-Ar dating of the Mesozoic Yaogangxian tungsten deposit, central Nanling district, South China

The Yaogangxian deposit in the central Nanling region, South China consists of vein-type ore bodies hosted in Cambrian to Jurassic strata and Mesozoic granitic intrusions. Wolframite and molybdenite are the dominant ore minerals intergrown with gangue minerals of quartz, feldspar, phlogopite, and muscovite. We have carried out molybdenite Re - Os and phlogopite and muscovite 40Ar/39Ar dating to better understand the timing and genesis of mineralization. Re - Os dating of eight molybdenite samples yielded model ages ranging from 152.0 +/- 3.5 to 161.1 +/- 4.5 Ma, with an average of 156.0 Ma. The Re - Os analyses give a well-defined Re-187/Os-187 isochron with an age of 154.9 +/- 2.6 Ma (MSWD= 2.4). Hydrothermal phlogopite and muscovite display extremely flat 40Ar/39Ar age spectra. Phlogopite yields a 40Ar/39Ar plateau age of 153.0 +/- 1.1 Ma, whereas muscovite yields a plateau age of 155.1 +/- 1.1 Ma. Both 40Ar/39Ar ages are in good agreement with the Re - Os ages, placing the timing of tungsten mineralization at about 154 Ma. This age is consistent with the field relationships. Our new data, when combined with published geochronological results from other major deposits in this region, suggest that large scale W - Sn mineralization occurred throughout the central Nanling region in the Late Jurassic.