扬子陆块东南缘升天坪锌矿床地质特征、闪锌矿Rb-Sr定年及其地质意义

Geological Characteristics and Rb-Sr Dating of Sphalerites from the Shengtianping Zinc Deposit in Southeastern Yangtze Block and Its Geological Significance

升天坪锌矿床位于扬子陆块东南缘雪峰山地区,是湘西地区产于陡山沱组的中型锌矿床。采用同位素稀释法对主成矿期闪锌矿进行Rb-Sr同位素组成分析,获得等时线年龄为490 Ma,初始锶同位素组成^(87)Sr/^(86)Sr为0.71235。该等时线年龄代表了该矿床的主成矿阶段年龄,说明矿床形成的地质时代为晚寒武世,成矿作用发生于加里东中期。成矿作用时代与闪锌矿初始锶同位素比值特征反映成矿物质或成矿流体由基底岩石(板溪群)和震旦系碳酸盐岩地层共同提供。结合矿床地质特征与区内铅锌矿成矿地质背景,认为周边板块碰撞的远程效应为热液成矿提供了构造驱动力,加里东期的构造运动对升天坪锌矿床的形成起着重要作用。升天坪锌矿床严格受地层控制,矿床类型为沉积-改造型层控矿床。

Shengtianping zinc deposit is located in Xuefengshan region,which is at the southeastern part of Yangtze Block.It is a medium-size zinc deposit that occurs in the Doushantuo Formation in western Hunan Province.In this study,Rb,Sr isotope analysis were carried out on the main metallogenic period of sphalerite using the isotopic dilution method.Rb-Sr analyses yield an isochron age of 490 Ma and the initial strontium isotopic composition of 87Sr/86Sr is 0.71235.The isochron age represents the timing of the main mineralization stage of the deposit,indicating that the deposit was formed in the late Cambrian and the mineralization occurred in the middle Caledonian.The characteristics of the sphalerite initial strontium isotope ratios reflect the far-field effect of the collisions of surrounding blocks,which provided a driving force for the hydrothermal mineralization,and the Caledonian tectonism plays an important role in the formation of the Shengtianping zinc deposit.The Shengtianping zinc deposit is strictly strata-bound,and the deposit belongs to the sedimentary-transformation type of strata-bound ore deposit.