贵州杉树林铅锌矿床中闪锌矿Rb-Sr定年及其意义

The geological significance of Rb-Sr isotopic dating of sphalerite in Shanshulin Pb-Zn deposit in Guizhou

杉树林铅锌矿位于扬子板块西部,川滇黔成矿省的东南部,其主要赋存在石炭系白云质灰岩、白云岩中。根据脉次间切割关系及矿物组合的不同,可将杉树林矿床成矿期次划分为沉积阶段(Ⅰ)、热液阶段(Ⅱ)和表生阶段(Ⅲ)。其中,阶段Ⅰ矿化呈层状,赋存于石炭系中,可能形成于石炭纪;阶段Ⅱ矿化呈脉状,切割阶段Ⅰ层状矿体及地层。通过闪锌矿Rb-Sr同位素测试,得出阶段Ⅱ中闪锌矿Sr的(87Sr/86Sr)200Ma比值为0.7126~0.7127,成矿年龄为(212.7±9.5)Ma。结合前人S-Pb同位素研究成果可知,杉树林矿床中硫主要来自于沉积盖层,而成矿物质主要来自于前寒武系基底与沉积盖层的混合,峨眉山玄武岩为阶段Ⅱ提供了少量的成矿物质。

The Shanshulin Pb-Zn deposit is located in the western Yangtze Block and Southeastern SYG(Sichuan-Yunnan-Guizhou)metallogenic province.The orebodies of the deposit are hosted in the Carboniferous dolomitic limestone and dolomite.According to the interspersed relationship between veins and different mineral assemblages,the metallogenic phase of the Shanshulin deposit can be divided into three stages,the sedimentation stage(Ⅰ),the hydrothermal stage(Ⅱ)and the supergene stage(Ⅲ).Among them,the Pb-Zn mineralization of stage Ⅰ is layered and occurs in Carboniferous strata,which may be formed in Carboniferous.The Pb-Zn mineralization of stage Ⅱ is vein-like,and cuts the layered ore bodies and strata of stage Ⅰ.Sphalerite Rb-Sr isotopic analysis indicates that(87Sr/86Sr)200 Ma ratios of the stage Ⅱ are 0.7126–0.7127,and Rb-Sr isochron age is(212.7±9.5)Ma.Integrating with the previous studies,S in the Shanshulin deposit is provided by the sedimentary rocks.The metallogenic materials mainly come from the mixing of the basement rocks of Precambrian system and the sedimentary rocks.The Emeishan basalts provided a little of metallogenic material in the stage Ⅱ.