Re-Os Isotopic Dating of Arsenopyrite from Auriferous Quartz Vein-type Gold Deposits in the Southwestern Margin of Jiangnan Orogen

Quartz vein-type gold deposits of Southeastern Guizhou Province in the southwestern margin of Jiangnan Orogen, which are typical orogenic gold deposits, are hosted in Neoproterozoic Banxi Group sub-greenschist facies metamorphic rocks. However, similar to other gold deposits in Jiangnan Orogen, mineralization ages of these deposits is a controversial issue and its relationship with Indosinian and Caledonian intra-continental orogenies remains unresolved, which limits the further study of ore-forming mechanisms. In this study, highly precise Re-Os isotopic analyses for arsenopyrites from bedding-concordant veins in Pingqiu and Bake Deposits were performed, and the isochron Re-Os ages of 235±3.4 Ma and 410±52 Ma, respectively were obtained. Low Re in arsenopyrite samples is responsible for the large uncertainty of Bake Re-Os isochron age. Nonetheless, the lack of common Os in one arsenopyrite sample from the Bake permit calculation of a single mineral model age, which is consistent with those determined using the isochron method. The Re-Os ages of arsenopyrite indicate that there were two distinct periods of gold deposition in Jiangnan Orogen coinciding with Caledonian and Indo-Sinian intra-continental orogenies.