南秦岭旬阳盆地下古生界热水沉积成矿地球化学

Geochemistry of hydrothermal sedimentary mineralization in the Lower Paleozoic of the Xunyang basin,South Qinling,China.

新近在南秦岭旬阳盆地志留系中发现重要铅锌矿化,含矿岩系主要是下、中志留统弱变质含炭细碎屑岩和新发现识别出的热水沉积炭硅质岩、钠长石岩等;矿体呈层状与志留系整合产出,含矿层中有热水沉积硅质岩和铁碳酸盐岩。矿床REE地球化学反映铅锌矿石、硅质岩和钠长石岩的形成物质可能来自盆下源深处,成岩成矿作用具有热水沉积性质;岩矿石稳定同位素组成指示成矿流体为深部来源,成矿流体中富含CO2(18.656～35.063mol%),成矿温度135～297℃;矿石S和Pb同位素组成反映S来源于深部,Pb来自盆地基底和沉积地层。受地幔热点控制的扬子北缘古生代伸展海盆中,热水沉积是旬阳盆地志留系铅锌成矿的基本方式。

Recently, important Zn-Pb deposits have been discovered in the Silurian of the Xunyang basin in the South Qinling. The ore-bearing sedimentary sequence consists of predominantly of Lower-Mid Silurian weakly metamorphosed carbonaceous fine-clastic rocks and hydrothermal sedimentary carbonaceous-siliceous rocks and albite rock and siliceous rock recognized recently. The stratiform orebodies are concordant with the Silurian strata, and the ore horizon contains hydrothermal sedimentary siliceous rocks and iron carbonate rocks. The REE geochemistry of Zn-Pb ores, albite rock and siliceous rocks shows that their material may have come from the depths below the basins. The ore-forming fluids are rich in CO2（18.656-35.063 mol%）with ore-forming temperatures ranging from 135℃ to 297℃, and the stable isotopic composition of the rocks and ores indicates a deep origin of ore-fornfing fluids. The sulfur and lead isotopic compositions of ores indicates that ore sulfur was derived from the depths, while lead from the lower Paleozoic basement and sediments below the ore-beating strata. In the mantle hot spot-controlled Paleozoic extensional sea basin on the northern margin of the Yangtze block, Silurian hydrothermal sedimentation is the basic manner of lead-zinc mineralization in the Xunyang basin.