40Ar-39Ar isotopic dating of the Xianghualing Sn-polymetallic orefield in southern Hunan, China and its geological implications

The Xianghualing Sn-polymetallic orefield in Hunan Province, southern China, is a large-size tin orefield. Although numerous studies have been undertaken on this orefield, its genesis, mineralization age, and tectonic setting are still controversial, mainly because of the lack of reliable geochronological data on tin mineralization. The 40Ar/39Ar stepwise heating dating method was first employed on muscovite from different deposits in this orefield. The muscovite sample from the Xianghualing Sn-polymetallic deposit defines a plateau age of 154.4 +/- 1.1 Ma and an isochron age of 151.9 +/- 3.0 Ma; muscovite from the Xianghuapu W-polymetallic deposit yields a plateau age of 161.3 +/- 1.1 Ma and an isochron age of 160.0 +/- 3.2 Ma; muscovite from the Jianfengling greisen-type Sn-polymetallic deposit gives a plateau age of 158.7 +/- 1.2 Ma and an isochron age of 160.3 +/- 3.2 Ma. The tungsten-tin mineralization ages in the Xianghualing area are therefore restricted within 150-160 Ma. The tungsten -tin mineralization in Xianghualing occurred at the same time as the regional tin-tungsten mineralization including the Furong tin orefield, Shizhuyuan tungsten-tin polymetallic deposit and Yaogangxian tungsten-polymetallic deposit. Thus, the large-scale tungsten-tin metallogenesis in South China occurring at 160-150 Ma, probably is closely related to asthenospheric upwelling and crustmantle interaction under a geodynamic setting of crustal extension and lithosphere thinning during the transformation of tectonic regimes during the Mid-Late Jurassic.