黔东南石英脉型金矿毒砂Re-Os同位素定年及其地质意义

Re-Os Isotope Dating of Arsenopyrite from the Quartz Vein-Type Gold Deposit,Southeastern Guizhou Province,and Its Geological Implications

黔东南石英脉型金矿床是雪峰多金属成矿带的重要组成部分,有较好的找矿前景,但对该区成矿理论的认识,特别是在成矿物质来源、成矿时代以及成矿动力学背景的认识上仍存在很大分歧。本次研究分别对该区两个主要金矿床(平秋、金井)的载金矿物——毒砂进行了Re-Os同位素定年研究。测试结果表明,平秋金矿蚀变岩型毒砂等时线年龄为400±24Ma,MSWD=0.96,初始187Os/188Os=1.24±0.57;金井金矿石英大脉型毒砂等时线年龄为174±15Ma,MSWD=1.07,初始187Os/188Os=8.04±0.45。前者属于加里东期,并与该区存在的东西向基底剪切断裂形成时期一致;后者属印支—燕山期,与雪峰地区存在的中酸性岩体以及黔东南地区广泛存在的隐伏岩体应属同期岩浆-构造活动产物。通过硫化物的Re-Os同位素定年研究,首次报道了该区至少存在加里东期、印支—燕山期两个重要的金成矿期。初始187Os/188Os值则反映该区金矿成矿物质来源于地壳。

The quartz vein-type gold deposit in southeastern Guizhou,being one of the important parts of the Xuefeng polymetallic ore belt,has showed the potential prospect for exploration.However,there still have been disputes on understanding of mineralized mechanism,especially the origin of metallogenetic materials,mineralization epoch,and geochronology and geodynamical setting of mineralization.The gold-bearing minerals（arsenopyrites） collected from two main gold deposits（Pingqiu and Jinjing） in the region were used to conduct Re-Os dating.The results show that the altered slate type arsenopyrites from the Pingqiu gold deposit yield an isochron age of 400±24 Ma,with an initial 187Os/188Os ratio of 1.24±0.57（MSWD=0.96）;while large quartz vein-type arsenopyrites from the Jinjing gold deposit yield an isochron age of 174±15 Ma,with an initial 187Os/188Os ratio of 8.04±0.45（MSWD=1.07）.The former age belongs to Caledonian period,and is consistent with the formation age of EW-trending shearing zone in the region;the latter belongs to Indosinian-Yanshanian period,and may be associated with the contemporaneous tectonic-magma activities as revealed by widely exposed intermediate-acid rocks in the Xuefeng area and the concealed intrusive bodies in southeast Guizhou Province.It is firstly reported using sulphide Re-Os isotopic dating that at least two important gold mineralizations occurred in Calidonian and Indosinian-Yanshanian periods.In addition,the initial 187Os/188Os ratios also suggest that the metallogenic materials derived from the crust rock.