Geological Characteristics And Genesis Of The Eulashankou Silver-lead-zinc Deposit,Qinghai Province

The Erlashankou silver-lead-zinc deposit in in Xinghai County,Qinghai Province.The geotectonic location is located in the southern part of the Jura Mountain orogenic belt.It is located at the southeastern end of the NNW Xiangquan-Wahongshan fault structural belt and is in the EW-oriented structure on the plane.The belt,the NNW tectonic belt and the NE-trending tectonic belt,the intersection of three large tectonic belts,the western part of the Jurashan magmatic rock belt,mainly distributed with acidic and acid intrusive rocks,the development of the Triassic continental volcanic rocks and the volcanic rocks.The Hekashan foreland thrust belt,which is constructed of stone and develops volcanic institutions,is located in the eastern part of the NNW-oriented hot spring fault.This formed the Erashan polymetallic metallogenic belt.The ore-forming stratum conditions in the study area are mainly a set of continental volcanic rocks,which are the ore-bearing surrounding rocks in the study area.The main lithologies are mountain rocks,Yingan rocks,rhyolite Yingan rocks,quartz andesite,Ying'an condensate Lava,rhyolite and rhyolite volcanic breccia blocks.The structure of the Elashankou mining area is dominated by the NW-NNW direction,the NE-trending fault structure and the SN-trending fault structure,and a small number of near EW fault structures and a series of radial faults developed in the vicinity of the Huda caldera.Construct a matching structure.The ore-forming age of the Elashankou silver-lead-zinc deposit is in the Middle-Late Triassic,which is basically the same as that of the ore-bearing strata.In this study,U-Pb geochronology geochemical tests were carried out on the Anshan IV tuff and granite porphyry of the Eulashan Formation in the Elashankou area.The results of Anshan tuff(255.2Ma)indicate that the main eruption age of the Eulashan Formation is the Late Triassic;while the test results of the granite porphyry(245.3Ma)define the sedimentary age of the lower part of the Eulashan Formation.Combined with the ages of the two,it is speculated that the ore-forming occurred after the Early Triassic,which may be similar to the formation of the Moorugou copper-gold deposit and the Shiduolong lead-zinc deposit in the area,which is the product of the Middle and Late Triassic magmatism.The main element characteristics of the two rock samples are characterized by high silicon and low aluminum,and the content of MgO and TiO2 are low,which reflects the characteristics of the potassium mysterious series;the rare earth trace elements of the two rocks have a relatively uniform trend.The main body has a small variation range and has the characteristics of trace elements of island arc magma.It exhibits the characteristics of light rare earth enrichment and heavy rare earth loss,and has a certain negative Eu anomaly.The sample is put into the tectonic background discrimination diagram,and most of the samples fall into the volcanic arc tectonic environment,suggesting that it forms with the ancient Tethys.Ocean subduction is related.The main research area of the Eulashankou silver-lead-zinc deposit is the H2-1 area.There are 32 ore bodies in the area,and the ore belt distribution is consistent with soil anomalies and IP anomalies.It is determined that the main ore body is M7 and M8 ore bodies,and the other 8 ore bodies are also relatively large.Among them,6 ore bodies such as M4,M5,M6,M8,M9 and M10 are associated with low grade ore,and their industrial mines are low.There is a natural gradual transition between the grades.The main form of the ore body is layered,lenticular,and vein-like;each ore body has different scales,and the length,width,thickness and grade vary greatly.The ore body goes north-northwest and tends to the southwest,except for the M7,M8,and M9 mines.The surface ground exploration trench is exposed,and the remaining ore bodies are concealed ore bodies.The ore-bearing lithology of the Eulashankou silver-lead-zinc deposit is Anshan-type tuff.The ore structure in the mining area is mainly a disseminated structure,a speckled structure,and a tuberculous structure.The ore structure is mainly composed of his crystal structure,self-crystal structure,twin crystal-mesh structure.The mineral types of ore include galena,sphalerite,chalcopyrite,pyrite,copper blue,etc.;gangue mineral quartz is the main,followed by calcite,containing a small amount of sericite,chlorite,kaolin.The alteration of ore is usually silicified,carbonated,green curtain petrochemical,a small amount of development of sericitization,chlorite and so on.The fluid inclusions of the Eulashankou silver-lead-zinc deposit are divided into gas-liquid two-phase inclusions and three-phase inclusions containing CO2.The uniform temperature of the gas-liquid two-phase fluid inclusions is between 120 °C and 250 °C.Between 1% and 11%(NaCl eqv);the uniform temperature of the CO2-containing three-phase fluid inclusions is between 190 °C and 260 °C,and the salinity is between 1% and 5%(NaCl eqv).The ore fluid has the characteristics of medium-low temperature and low salinity;the results of HO isotope test indicate that the source of ore-forming fluid is between atmospheric water and magma water,which may be a mixture of the two.Sulfur isotope shows that deep source magma sulfur is the main source,and the value of sulfur isotope is large.It is speculated that there may be multi-source sulfur incorporation.According to the geochemical,chronological,ore geological characteristics,metallogenic geological conditions and genesis of the Orashankou silver-lead-zinc deposit,the results show that the Eulashankou silver-lead-zinc deposit is controlled by fault structure.Low temperature and low salinity hydrothermal vein deposit.