江南造山带西南缘石英脉型金矿中毒砂Re-Os同位素定年研究

江南造山带西南缘的贵州东南部地区石英脉型金矿产于低绿片岩相的板溪群浅变质岩中,具有典型的造山型金矿特征。与江南造山带其他造山型金矿一样,其成矿时代具有较大的争议,金矿的形成与造山运动的关系还不清楚,制约了对本区金矿成矿作用的深入研究。本文采集了平秋和八克两个石英脉型金矿中与金成矿作用密切相关的含金石英脉中毒砂样品进行高精度的Re-Os同位素分析,分别得到235±3.4 Ma和410±52 Ma两个Re-Os同位素等时线年龄,八克金矿毒砂样品的年龄误差较大的原因是毒砂中Re含量较低所致,但其中低含量高射性样品计算得到的Re-Os同位素模式年龄仍然与其等时线年龄一致。两个矿床的毒砂Re-Os同位素年龄揭示了江南造山带石英脉型金矿与加里东期和印支期两次陆内造山运动有关,是华南显生宙陆内造山运动的产物。

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.