Geological Characteristics And Genesis Of The Dachaigou Gold Deposit In Wulonggou Area,East Kunlun Orogenic Belt

East Kunlun orogenic belt in Qinghai province is located in the northern margin of Qinghai-Tibet Plateau and the western section of the central orogenic belt,which is an important mineral resource area in China.Wulonggou gold concentration area is located in the middle part of east Kunlun orogenic belt.So far,The Dachaigou,Hongqigou,Baishenggou,Xintuo-Haxiwa and Yanjingou gold deposits have been discovered,which has important gold metallogenic potential.The newly discovered Dachaigou gold deposit,with verified gold and metal content of 13476.7294kg and average grade of5.43g/t,still shows great metallogenic potential.The research degree of this deposit is very low,the occurrence state of gold,tectonic ore-control law,fluid geology are not involved,the type of deposit is not clear.Route of the study in the hope that through detailed field geological survey and indoor test analysis method(light slice,rock geochemical analysis,fluid inclusions microscopic measuring temperature,H-O isotopes and S isotope,scanning electron microscopy and energy spectrum analysis),the nature of its geological characteristics,ore-forming fluid,metallogenic material source and genesis are studied systematically,It can improve the comprehensive research level of the deposit and provide new ideas for further prospecting in the deep mining area and Wulonggou gold concentration area.The deposit is mainly controlled by the secondary EW trending faults of the NW trending large ductile shear zone.The ore bodies are distributed nearly EW trending.The occurrence of the NO.III mineralized alteration zone is 20°?40°?45°?58°,about 1km long and 2?5m wide,and the occurrence of the No.IV mineralized alteration zone is 330°?35°?70°,about 0.5km long and 1-3m wide.The ore type is mainly altered rock type,with disseminated and brecciated structure,semiidiomorphic granular and metasomatic structure.The mineralization is mainly pyritization,and the alteration of surrounding rock is mainly silicification,sericitization and carbonation.According to the vein of puncture and mineral metasomatic relations between think playing facies,there are two main gold metallogenic period,respectively,the hydrothermal mineralization period and supergene oxidation period,which is given priority to with the hydrothermal mineralization period ore-forming period,the mineralization period can be divided into:(1)stage of arsenopyrite-pyrite-quartz,(2)stage of quartz-polymetallic sulfide and(3)stage of quartz-carbonate.The orebody of Dachaigou gold deposit is mainly controlled by the secondary faults of nearly EW trending.The fault structure of nearly EW trending shows the characteristics of right-rotation and reverse faults.The mineralization is partially opened and enriched in the place where the occurrence becomes slow in vertical direction and the west-west-north trending direction in strike direction,and the thickness and grade of the orebody become larger and richer,and the orebody tends to fall toward east.The mineralization enrichment of the two parallel veins has the characteristics of transverse corresponding relationship and subsection enrichment,and the two veins can be the prospecting mark of each other.Fluid inclusion characteristics and test results of the three stages of hydrothermal mineralization are as follows:I arsenopyrite-pyrite-quartz stage mainly consists of L type(gas-liquid two-phase inclusions)and C type(CO₂ three-phase inclusions),is a CO₂-Na Cl-H₂O system with medium temperature(273?338?),low salinity(4.9?6.7wt.%Na Cl)and low density(0.7?0.8 g/cm³);II.The quartz-polymetallic sulfide stage is a Na Cl-H₂O system with L-type inclusions which is medium temperature(219?262?),low salinity(4.0?7.0wt.%Na Cl)and low density(0.8-0.9g/cm³).III.The quartz-carbonate stage mainly contains L-type inclusions,and is a Na Cl-H₂O system with low temperature(182?202?),low salinity(4.0?6.0wt.%Na Cl),and low density(0.9?1.0 g/cm³).The metallogenic pressure and depth are 70?107MPa and 6.77?8.56km,respectively.The?D values of quartz range from-71.5‰to-60.6‰and?¹⁸O_H2O range from 5.6‰to 6.0‰,indicating that the ore-forming fluid is mainly derived from primary mantle water.In situ S isotope test results of pyrite show that the?³⁴S values range from 1.55‰to 12.38‰.There are four?³⁴S values ranging from1.55‰to 4.53‰and two?³⁴S values ranging from 11.91‰to 12.38‰.Previous studies show that gold deposits in Wulonggou and other areas of east Kunlun orogenic belt are genetically related to middle-basic dikes,reflecting the participation of mantle-derived materials in mineralization.The?³⁴S values of 1.55?4.53‰and11.91?12.38‰are derived from mantle sources,and S is probably derived from the diorite of the main host ore with relatively high gold abundance.The genetic type of the deposit is medium-temperature hydrothermal vein type gold deposit,which belongs to orogenic gold deposit according to the geological background and fluid characteristics of its formation.In this study,it is concluded that the metallogenic model of Dachaigou gold deposit is as follows:When the East Kunlun Orogenic Belt developed to the late Indosinian period,the asthenosphere mantle upwelled due to the debasement of lithospheric mantle,and the mantle-derived C-H-O fluid extracted Au from the Au-rich upper mantle source area and upwelled along deep faults.Early fluid immiscibility,late temperature drop,magmatic water mixed with atmospheric water lead to changes in physical and chemical conditions,making the complex unstable,resulting in Au unloading precipitation,and finally forming Dachaigou gold deposit.