Metallogenesis Of Huangtan Au-Cu Deposit In Kalatag Ore Concentration Area,East Tianshan

The Eastern Tianshan Terrane occupies an important position on the southern margin of the Central Asian Orogenic Belt(CAOB).A large amount of Cu polymetallic deposits have been discoverd in this terrane.The Huangtan deposit is located in the north of Dananhu-Tou Suquan Paleozoic accretionary arc zone,it was the recently discovery of the VMS deposit in the Eastern Tianshan.According to previous studies,based on detailed analysis of the gelogical setting and deposit characteristics,this thesis investigated the petrography,mineralogy,microthermometric measurement of fluid inclusions,and Re-Os isotopes dating of the Huangtan deposit in the Kalatag district.The metallogenic stages are determined,the occurrence mechanism of gold is analyzed,and the genetic types of the deposits are discussed.The mineralization process of the Huangtan deposit can be divided into VMS period,hydrothermal period and supergene period.The VMS period can be further subdivided into pyrite stage and chalcopyrite-sphalerite stage.The hydrothermal period includes the quartz-sulfide stage and quartz-calcite stage.The visible gold mainly occurs as inclusions in massive sulfide from the VMS period,filling microfractures in pyrite or on the margins of the sulfide grains.The petzite occurs on the margins of the chalcopyrite grains,which enrich during the same period,it is the origin of submarine exhalative-sedimentation.In contrast,the electrum and native gold mainly occur in the hydrothermal period,distributed in quartz sulfide veins.It is round and irregular,with larger particles and higher content of gold and silver,which enrich as a result of late hydrothermal superposition.The chalcopyrite-sphalerite stage have higher homogenization temperature(247.6?-357.6?)and salinities(6.6-16.1 wt.%)during the VMS period.However,fluid inclusions in quartz-sulfide stage have lower homogenization temperature(143??215?)and salinities(0.4?7.3wt.%)during the hydrothermal period.From the VMS period to the hydrothermal period,with the decrease of salinity,ore-forming fluids from medium high temperature to medium low temperature,the main component of fluid is water,it also contains a small amount of reducing gases such as CH4 and CO2.Pyrite Re-Os geochronology provides a accurately tool for computing the age of sulphide mineralization.Our Re-Os isotopic data for pyrite provide reliable constraints on the timing of ore formation of the Huangtan deposit:the Re-Os isochron age of 436.2±7.5 Ma is interpreted to represent the age of the Cu mineralization in the VMS period,and the Re-Os isochron age of hydrothermal period is 436.3±7.6 Ma to represent the age of Au-Cu mineralization,respectively.Comprehensive research shows that Huangtan VMS deposit formed under marine environment at early Silurian,superimposed by late hydrothermal.As the sub-volcanic rock invades continuously,the temperature of the hydrothermal fluid rises continuously.The mixing of hydrothermal fluid and seawater and the conduction cooling of the nozzle fluid cause changes in physical and chemical conditions such as temperature,pressure,pH and oxygen fugacity of the ore-containing hydrothermal fluid.The Au element is activated from the substrate by the recrystallization of sulfides in the form of[Au(HS)2]-,with large-scale gold-silver precipitation mineralization occurs in the hot liquid rich in precious metal elements in the late low temperature and low pressure environment.