Geology And Mineralization Of The Cu-Au Skarn System In Southeast Hubei Province And Northwest Jiangxi Province,Eastern China

There are many porphyry-related,skarn,and stratabound Cu-Fe-Au-Mo deposits in the Middle-Lower Yangtze River metallogenic belt(MLYRB)that associated with Late Mesozoic(Yanshanian)magmatism.Despite many years of research,considerable debate remains on the genesis of the carbonate-hosted vein-type Au deposits,and the stratabound massive sulfide orebodies that located peripheral to Cu-Au skarn deposits around the Yanshanian granodiorite intrusions.And the occurrence of dispersed metals remains obscure.In this study,different deposits/orebodies in the Fengshan and Chengmenshan areas were studied as examples for the debates mentioned above.In the Fengshan area,both the Cu-Au skarn and distal vein-type Au deposits have a complex Te-Au-Ag-(Tl)mineral assemblage,such as electrum,petzite,Au-Tl telluride.And the mineralogical Bi-Te signature characterizes the skarn assemblages,while the Te-Tl signature is typical of the distal vein-type Au mineralization.Magma-sourced Mn formed metal anomaly in the carbonate-replacement Pb-Zn and distal vein-type Au mineralization,with the decreasing Mn content in carbonate minerals over time.The C-O isotope compositions of carbonate display a tendency towards heavier isotopic compositions with time,which could be best interpreted as the effect of fluid-rock interaction between magmatic fluid and the Triassic carbonate host rocks.New S isotope data on sulfate minerals and C-O isotopic data suggest a common magmatic fluid source for both skarn and distal vein-type mineralization.In the Chengmenshan area,both skarn mineralization and peripheral stratabound massive sulfide mineralization share the same mineral assemblages with the same sequence,which is consistent with the paragenetic sequence of hydrothermal metasomatism rather than exhalative sedimentation.Analysis of trace elements illustrate that pyrite and sphalerite was deposited in the magmatic-hydrothermal system.Trace-element zoning in pyrite records fluid-rock interaction,and in response to the changing fluid composition with the increasing distance with the granodiorite intrusions.Most of pyrite S isotope data is distributed over a very small range(?34S=0?4‰),suggesting a magmatic sulfur source,whereas a slight increase of oxidation state and/or local disequilibrium may cause the enrichment of 32S(?34S?-30‰).Geological,paragenetic,stable isotopic studies and analysis of trace element are consistent with the model of a single magmatic-hydrothermal system for both Cu-Au skarn and carbonate-hosted vein-type Au mineralization in the Fengshan area,and support a magmatic-hydrothermal origin rather than a SEDEX system for the stratabound ores in Chengmenshan area.The C-O isotopic models between magmatic fluid and marine carbonate rocks and the diagram of Se/As-Co in pyrite could be used in the further research to deal with the similar debate in Jiurui district.Our study reveals the enrichment of dispersed metals in Fengshan and Chengmenshan areas.As for tellurium,there are plenty of tellurides in different types of mineralization(tetradymite,hessite,altaite).Thallium could occur as lorandite,Au-Tl telluride or be bounded in the anhedral pyrite during the late stages of the mineralization(up to 2400 ppm).Pyrite and sphalerite are important host minerals for selenium,and indium,gallium,cadmium,respectively.Fractures,faults,unconformities,or Te-Tl geochemical signature could be act as useful indicators for blind carbonate-hosted orebodies in the Fengshan and Chengmenshan area.