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

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-forming 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-bearing 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.