Re-Os dating of molybdenite from the Xintianling giant tungsten-molybdenum deposit in southern Hunan Province,China and its geological implications

The Xintianling tungsten deposit is a large-sized skarn and vein-type tungsten-molybdenum polymetallic deposit located in southern Hunan Province,which is genetically associated with the early stage hornblende-biotite monzonitic granite of Qitianling pluton. Direct Re-Os dating on molybdenites collected from the skarn and quartz-vein type ore in the Xintianling deposit have been carried out, to better understand the age of mineralization.The results show that the Re-Os dating of one molybdenite sample collected from skarn-type ore yields a 187 Re-187 Os model age of 159.1±1.9Ma,and six molybdenite samples collected from quartz-vein-type ore yield 187 Re- 187 Os model ages ranging from 159.1±1.9Ma to 160.2±2.9Ma,with an average of 159.4±1.3Ma,and give an isochron age of 161.7±9.3Ma(2σ),with an initial 187 Os of 0.6±2.3(MSWD=0.051).Comparison of the Re-Os ages with published Ar-Ar date(157.1±0.3Ma)on iron mica and Rb-Sr date(157.4±3.2Ma)on quartz indicates that the timing of skarnization and tungsten-molybdenum mineralization are identical within error.Therefore,we can constrain the absolute age of tungsten-molybdenum mineralization in the Xintianling deposit at ca.161.7～157.1Ma.These ages are consistent with the SHRIMP zircon U-Pb ages(163～160Ma)of the early stage hornblende-biotite monzonitic granite.Based on previous studies,it is suggested that the mineralization of the Xintianling W-Mo deposit is spatially and temporally related to the early stage hornblende-biotite monzonitic granite of Qitianling pluton. While the Furong tin deposit located in southern part of Qitianling pluton may be closely related to the late stage biotite monzonitic granite.The emplacement of the Qitianling A-type granite and associated tungsten-tin polymetallic mineralization is a continuous evolution process,which are the products of large-scale mineralization of the Nanling in Middle-Late Jurassic(150～160Ma).Under the tectonic setting of Mesozoic lithospheric extension,asthenosphere upwelling along deep fault,intensive mantle-crust interaction processes probablyprovide not only the high heat flow,but also part mantle-derived material for large-scale W-Sn-polymetallic mineralization in this area.