桂东南志留纪热水沉积成矿的碳氧同位素证据

Carbon and oxygen isotopic evidences of hydrothermal sedimentary mineralization in Silurian period in southeastern Guangxi

志留系地层是桂东南博白―岑溪地区铅锌矿床的主要赋矿层位,产出佛子冲和东桃等层状铅锌矿床,其直接赋矿围岩均为下志留统碎屑岩地层中的层状绿色岩和碳酸盐岩夹层。碳、氧同位素测试结果显示,赋矿层位中碳酸盐岩夹层的δ18 O值显著低于正常海相灰岩,在δ18 O-δ13 C图解上碳酸盐岩夹层和矿石中方解石样品投点均集中分布在基性-超基性岩浆岩和花岗岩区及附近。该碳酸盐岩夹层的形成与海底热水沉积作用有关,类似于现代海底烟囱中的低温喷口产物。桂东南志留纪热水沉积成矿作用可以概括为电解成矿机制。

Silurian stratum is the main ore-bearing horizon of Pb-Zn deposits in Bobai-Cenxi area of southeastern Guangxi, where occurs the stratified Pb-Zn deposits in Fozichong and Dongtao. Their directly ore-bearing wall rocks are stratified green rocks and carbonate rock interlayers in clastic rock strata of lower Silurian series. The results of carbon and oxygen isotope detection show that the δ^18O value of the carbonate rock interlayers inside the ore-bearing horizon is lower than that of normal marine limestone. The plotted points of calcite sampling in the carbonate rock interlayer and ores on the δ^18O-δ^13C diagram are intensively distributed along the basic-ultrabasic magmatite, granite and their peripheral area. The formation of the carbonate rock inter layer is closely related to submarine hydrothermal sedimentation, which is similar to the products of low temperature vents in modern submarine chimneys. The Silurian hydrothermal-sedimentary mineralization in southeastern Guangxi can be summarized as a kind of electrolytic bath metallogenic mechanism.