Study On Trace Element Composition And Fluid Inclusion Characteristics Of Tectonic Alteration Zone In Hongqigou Mining Area,Wulonggou Gold Field,East Kunlun

The Wulonggou gold ore field is located in the north-central part of Qinghai Province,and the tectonic position is in the central tectonic belt of the East Kunlun orogenic belt.The Hongqigou mining area is located in the eastern part of the Wulonggou gold field.There is strong tectonic-magmatism in the area,which is conducive to gold polymetallic mineralization.Through summarizing the relevant scientific research achievements of predecessors and carrying out the field geological survey of the mining area,this paper comprehensively uses the theoretical methods of petrography,mineralography and rock geochemistry,and combines the analysis of fluid inclusions and electron probe analysis.The gold and its related trace element composition,the formation environment of gold-bearing minerals and the characteristics of ore-forming fluids in the Hongqigou mining area were systematically analyzed.The exposed strata in the Hongqigou mining area are mainly Proterozoic Jinshuikou Group,Xiaomiao Formation and Qiujidonggou Formation.The surface rocks in the mining area are highly fragmented,the cataclastic rock is strong,the joints and fissures are well developed,and the types of magmatic rocks in the area are diverse.Various types of granites and diorites produced by intermediate-acidic magma intrusion are widely distributed.125 gold(mineralized)bodies have been delineated in the mining area and surrounding areas,and the scale of the deposit has reached large gold deposits.The metal minerals in the ore are mainly pyrite,chalcopyrite,galenite and sphalerite.The non-metallic minerals are mainly graphite,garnet,quartz and other minerals.The structure is mainly semi-automorphic-allomorphic granular structure,granular fibrous crystal structure,etc.,and the structure is mainly sparse disseminated structure.There are various types of surrounding rock lithology,mainly plagioclase granite,biotite quartz schist and tuffaceous slate.The alteration of surrounding rock is common in the mining area.Pyritization,silicification and other phenomena play an important role in finding the formation of gold ore bodies.According to the trace element spider diagram,the gold and related elements in the structural alteration zone and the surrounding rock in the Hongqigou mining area are generally characterized by rich Hg,medium Au,Ba,As,and low Ba,Co,and W.This synchronous change relationship indicates that the structural alteration zone is involved in the alteration process from the later surrounding rock material,according to the correlation of gold and related elements in the alteration zone and R-type cluster analysis,combined with previous studies,it is considered that the elements closely related to Au in the area are Cu,Sn,W,Ni,Zn and Mn.The temperature measurement of fluid inclusions shows that the homogenization temperature of ore-forming fluid is between 226～301°C,the salinity is between1.81～14.04wt%Na Cl,the calculated density of ore-forming fluid is between0.7292～0.9416g/cm~3,themetallogenicpressureisbetween154.1305×10~5～341.9194×10~5Pa,and the metallogenic depth is between 1.54～3.42km.Combined with the test results of fluid inclusions,the characteristics of gold-bearing minerals such as pyrrhotite,pyrite and sphalerite indicate that the gold deposits in the mining area are formed in the medium-temperature and medium-deep environment.The main and trace element characteristics of pyrite and sphalerite indicate that the mineralization of gold is related to granitic magmatism,showing magmatic hydrothermal genesis.Combined with the characteristics of fluid inclusions,gold-bearing minerals and geochemical characteristics of the deposit,it is considered that the gold deposit in the Hongqigou mining area is formed in a medium-temperature and medium-shallow environment,and the genetic type should be an orogenic gold deposit related to hydrothermal fluid.The Au-As-Sb-Hg-W-Sn-Cu-Ni-Mn-Zn element combination characteristics have a good indication for gold polymetallic prospecting in the East Kunlun area.