Study On Geological And Geochemical Characteristics And Metallization Of The Xiaojianshan Gold Deposit,Eastern Tianshan Mountain

The Xiaojianshan gold deposit is located in the Kanggurtag gold belt in the Eastern Tianshan,and its tectonic position is the northern edge of Yamansu island arc belt.The ore bearing stratum is a set of intermediate acid volcaniclastic rocks.The gold deposit is composed of three alteration-type orebodies,with the tectonic line of NWW direction.Based on the study of ore deposit geology and ore geochemistry,following understanding were obtainted by research:(1)Metal minerals of the Xiaojianshan gold deposit are mainly pyrite and chalcopyrite,nonmetal minerals are mainly quartz,sericite and chlorite;gold is occurred in quartz and pyrite in the form of intergranular gold,fissure-filling gold and inclusion gold;The rock alteration types are sericitization,chloritization,silicification and carbonation.(2)Zircon U-Pb age of the granite is 257±2.3Ma,which means the magmatic activity in this mining area,is in the Late Permian,The age of granite vein formation is the same with metallogenic epoch of gold belt,and may be closely related to the formation of the Xiaojianshan gold deposit;Geochemical studies show that granite veins are peraluminous calc alkaline series,with the characteristics of volcanic arc magmatic rock,and might be related to the inheritance of magmatic activity and the crust formed in volcano arc background.(3)The quartz veins mainly develop gas-liquid inclusions and CO₂ bearing three-phase inclusions and the fluid homogenization temperature ranged from 145?to 396?,with the salinity from 1.4%Na Cleqv to 11.2%Na Cleqv.The medium-low temperature and low salinity fluid are consistent with the typical orogenic gold deposit;from the early stage to the late stage of mineralization,the trend of fluid temperature,salinity,metallogenic pressure and corresponding depth are decreased while the fluid density increased.(4)H-O isotope studies indicate that ore-forming fluids are mainly derived from the metamorphic water produced during the post collision evolution stage of orogenic process.The ore-forming process may be mixed with a small amount of magmatic water and meteoric water,and may be related to the magma invasion and deep circulation of atmospheric precipitation.The ³⁴S value between 2.12‰?3.48‰and shows that the ore-forming material has the characteristics of mantle derived sulfur,the sulfur isotopic characteristics are consistent with the volcano rock strata of wall rocks of the gold belt,indicating the source of ore-forming materials is wall rocks,its mantle features may be related to the deep source of volcanic and volcano clastic rock.The source of fluid and metallogenic material is the same as that of the typical orogenic gold deposits.Combining field and laboratory research results with the evolution of the regional tectonics,summarize the following mineralization of the Xiaojianshan gold deposit:in Late Carboniferous and Permian,metamorphic fluids produced in the process of shear deformation extract metallogenic material from the ore source rocks that formed in Carboniferous in the migration process,and forming ore-forming fluids.The crystallization in the mylonite foliation leading to preliminary enrichment of gold.Tectonic evolution makes the geological bodies transform from ductile deformation to brittle deformation in the late Hercynian(Late Permian)with granite intrusiving.Metamorphic fluid formed ore-forming fluids through the leaching extraction of gold and other metallogenic material from the wall rock in the migration process.The mixing of meteoric water and magmatic water with the change of physical and chemical conditions make the ore bearing fluid unload and precipitate in the favorable area and form gold deposits finally.