湖北凹子岗锌矿床Rb-Sr同位素测年及其地质意义

Rb-Sr dating of sphalerites from the Aozigang zinc deposit in Hubei Province and its geological significance

凹子岗锌矿床位于黄陵背斜东部,是近年来在湘西鄂西地区发现的代表性矿床。锌矿体呈似层状-透镜状产出,赋存于灯影组二段,含矿岩性为一套角砾状泥粉晶云岩,严格受地层层位及岩性控制。文章运用闪锌矿Rb-Sr同位素测年方法,测得凹子岗锌矿床成矿年龄为431-434 Ma,相当于早志留世,代表了矿床的主成矿阶段年龄。闪锌矿具有较高的Sr同位素初始比值（0.71119-0.71136）,反映成矿物质或成矿流体由基底岩石和震旦系碳酸盐岩地层共同提供。凹子岗锌矿床早期成矿作用与早志留世的裂谷盆地伸展运动关系密切,晚期成矿作用与加里东运动关系密切,是伸展环境盆地流体运移的产物。加里期运动与黄陵周缘铅锌矿的成矿作用关系密切。凹子岗锌矿床成因类型为热液喀斯特成因,可分为深埋藏成岩成矿阶段和热液喀斯特化成矿阶段。

The Aozigang zinc deposit lies in eastern Huangling anticline. It is a representative lead zinc deposit recently discovered in western Hubei and Hunan area. The zinc orebodies are strictly controlled by the stratigraphic horizon and lithology, and are mainly hosted in the second member of the Sinian Dengying Formation. The ore-bearing rocks occur in stratoid and lenticular forms, being a suite of brecciform micritic crystal powder dolomites. The Rb-Sr dating of sphalerite separates yielded isochron ages of 431-434 Ma for the deposit, suggesting that the deposit was formed in the early Silurian, which represents the main ore-forming epoch of the deposit. Based on a study of the source of the ore-forming material and the geological significance, the authors hold that higher initial ratios of Sr isotope （0.71119-0.71136） suggest that the metallogenic substances or ore-forming fluids came from relatively high basement rocks and relatively low Sinian carbonate layers. The early mineralization of the Aozigang zinc deposit wasclosely related to the Early Silurian stretching rift basin, whereas the late mineralization was closely associated with the Caledonian movement and was the product of fluid migration in a stretching basin. The mineralization of the lead-zinc deposits around the Huangling faulted dome was closely related to Caledonian movement. The Aozigang zinc deposit is genetically of hydrothermal karst type, and its formation can be divided into deep burial diagenetic ore-forming stage and hydrothermal karst metallogenic stage.