Research On The Geological, Geochemical Characteristics And Genesis Of Shenshuitan Gold Deposit In The Wulonggou Ore Concentration District In The Eastern Kunlun Orogenic Belt, Qinghai Province

Wulonggou ore concentration district is located at Dulan County,Qinghai Province.It is located tectonically at the north margin of middle East Kunlun orogenic belt.The area is rich in mineral resources and the geological ore-forming conditions in it are superior.Wulonggou ore concentration district includes 7 important gold deposits,i.e.Shihuigou,Shenshuitan,Hongqigou,Shuizhadonggou,Danshuigou,Zhongzhigou and Dachaigou.We focus on Shenshuitan golddeposit which was made a big breakthrough on ore prospecting in recent years,in order to determine its geological,geochemical characteristics and genesis.The exposed strata in this mining area are the Mesoproterozoic Changchengian Period Xiaomiao formation,the Neoproterozoic Qingbaikou Period Qiujidonggou formation,the early Paleozoic Ordovician volcanic rock formation within the Qimantage group and the Quatemary sediments.Ore bodies mainly occur in the contact zone between various granitic rocks and Qiujidonggou formation or volcanic rock formation within the Qimantage group.Faults are well-developed,and NW-striked faults mainly control and hold gold mineralizationin the area.Shenshuitan gold deposit is controlled mostly by fault No.XI.No.XI fault extents from Yingshigou to Shuizhadonggou.From the east to the west,there are three ore body concentration distributionsections,i.e.Heishigou,huanglonggou and Shuizhadonggou sections.120 ore bodies have been found in Shenshuitan gold district.The hydrothermal stages in Shenshuitan gold deposit can be divided into quartz sulfide epochs and calcite sulfide ones,and the former one contributes to major ore-forming mineralization.The metallic minerals are mostlyconsisted of pyrite,pyrrhotite and arsenopyrite,and a small amount of sphalerite,galena and chalcopyrite can be found in some ore sections.The gangue minerals are mostly consist of quartz,feldspar,hornblende,sericite and biotite.Calcite can be seen in some ore sections.The main textures of ores are cataclastic texture and metasomatic relict texture.The ore structure mainly consists of massive structure,disseminated structure and vein structure.The alteration of country rocks were composed of silicification,sericitization and calcitization etc.Studying on fluid inclusions in Shenshuitan gold districtshows that the homogenization temperatures of quartz sulfide epoch range from 146.8? to 393.7 ?,with the peak values ranging from 210? to 280?.The values of fluid salinity range from 1.56 wt%NaCl to 13.44wt%NaCl,with the peak values ranging from 7 wt%NaCl to13 wt%NaCl.The values of fluid density range from 0.59 g/cm3 to 0.99g/cm3.Then the result of laser Raman spectroscopy shows that the fluid inclusions is consisted of H2 O,with a small amount of CO2 and N2.It was concluded that the ore-forming fluid belongs to H2O-NaCl-CO2±N2 system which is characterized by medium-low temperature,medium-low salinity and low-density.H-O isotope analyses for quartzs within quartz sulfide ores indicates the measured?18O values for the gold-bearing quartz range from 9.7 to 15.9‰,and the estimated ?18O values for fluids range from 0.3 to 6.5‰.The ?D values for fluid inclusions of the gold-bearing quartz range from-117.3 to-87.4‰.It was suggested that the ore-forming fluid of Shenshuitan gold deposit is a mixture of metamorphic water and meteoricwater.As processing of mineralizations,meteoric water gradually occupiesa dominant position.Sulphurisotope test analyses of metal sulfides in quartz sulfide oresindicates the result of ?34SV-CDT varies from 0.4‰ to 8.5‰,with a mean value of 4.18‰,and the peak values between 3‰ and 6‰.It was shown that the sulfur is not simply sourced derived from magma but a mixed sulfur sourceture of among various crust-derived sulfurs ratherthan pure magmatic sourceand mantle.Analyses of lead isotope of them indicate that consist of206Pb/204 Pb ranging from 18.1516 to 18.4985,207Pb/204 Pb ranging from 15.4943 to 15.6320,and208Pb/204 Pb ranging from 38.3430 to 39.8076.It was concluded that Pb source is derived comes from host rocks which is controlled by orogenic settings.Finally,it was concluded that the metallogenic age of Shenshuitan gold deposit must be later than 215 Ma in the late Triassic era,and its genetic type belongs to the orogenic gold deposit.Following post-collision at late Indosinian,lots of large-scale regional thrust faults and secondary fauls were formed.The ore-forming fluids were migrated along these faults and mixed with meteoric water,resulting in gold mineralization within them by replacement and veinlet infilling.