The Origin And Metallogenic Prediction Of The Xitieshan Lead-zinc Mine In Qinghai

Xitieshan lead-zinc deposit is a well-known super-large lead-zinc deposit on the northeastern of the northern edge of the Qaidam Basin tectonic belt of the Qinghai-Tibet Plateau.Since its exploitation in the 1950s,it has achieved a high degree of work,the ore reserves have exceeded 10 million tons,and the total amount of zinc and lead metals has exceeded 580,000 tons and 150,000 tons,respectively the mineral resources are abundant and it is easy to find minerals.However,due to the controversy over the specific genetic types of the deposit and the obscure metallogenic model,the next step is to restrict the prospecting work,in view of this situation,the author starts from the actual situation by comprehensively surveying the field and analyzing the samples taken the further study of the deposit was conducted in order to provide a more definite theoretical basis for the prospecting work of the Xitieshan lead-zinc deposit.The author finds out the basic geological characteristics of the Xitieshan lead-zinc deposit,and at the same time combines the isotope geochemical characteristics,fluid characteristics,and metallogenetic material characteristics of the deposit,and summarizes the sources of ore-forming materials and the specific metallogenic model.The nature of ore-forming fluids,etc.,further confirmed the genetic types of deposits and made predictions for the next exploration work.The ore-bearing rock series of the Xitieshan lead-zinc deposit is a set of green schist rocks that are metamorphosed by volcanic-sedimentary rocks.They consist of the following volcanic-sedimentary cycles?groups a and b?and the above volcanic-sedimentary cycles?groups c and d?.There are two ore-bearing strata in this deposit,in which the O₃tn^a-2 rock section is mainly a ore-bearing layer and O₃tn^b is a secondary-bearing ore-bearing stratum.Mineralized zoning was NW-SE spreading,and the ore body was composed of veinlet-dissolving pyrite-galena-sphalerite ore.The ore minerals of Xitieshan lead-zinc deposit mainly include galena,sphalerite,pyrite,chalcopyrite and pyrrhotite;gangue minerals mainly include quartz,calcite and albite.The ore structures are mainly semi-automorphic-self-shape crystal structure,solid solution structure,colloidal structure of pyrite,crushed structure,and anaphase erosion structure.The ore structures mainly include massive structures,vein-like and network-like structures,layered structures,and brecciated structures.Wall rock alterations mainly include sericitization,silicification,heavy-grained petrochemistry,carbonation,and sodium long petrochemicals.There are mainly three stages in the metallogenic process,which are divided into:pyrite-quartz stage?mineralization I stage?,polymetallic sulphide stage?mineralization stage II?,and carbonate quartz stage?mineralization stage III?.The fluid inclusions are mainly gas-liquid inclusions.The main metallogenic stage?mineralization stage II?fluids have medium-low temperature?190.3°C²78.6°C?,medium-low salinity?6.14wt%Nacl²2.09 wt%Nacl?,Low density?0.87 to 1.03 g/cm3?,The metallogenic pressure ranged from 18.62 to 37.52 MPa?average value 26.80 MPa?,and the metallogenic depth ranged from 1.86 to 3.75 Km?average value 2.68 Km?,from the early metallogenic stage to the late mineralization stage,with The law of temperature,salinity,and pressure in descending order.In the ore-forming stage I,the temperature of the ore-forming fluid is relatively high,under the oxidizing conditions,pyrite precipitates.In the ore-forming stage II,the ore-forming temperature and salinity decreased,and the source of the fluid was mainly magmatic water,With the fluid migration,the fluid temperature decreased,metal minerals precipitated,and minerals including galena and sphalerite were formed.In the ore-forming stage?,the temperature and the salinity further decreased,through the determination of C-O isotopes in calcite at this stage,it is believed that the original magmatic fluid is further mixed with a large amount of atmospheric precipitation,so that the fluid temperature becomes lower,and the metal mineral is very Little exists,the formation of calcite minerals such as calcite.Hydrogen,oxygen and carbon isotope test results show that the ore-forming fluids mainly come from magmatic hydrothermal fluids,with the progress of ore-forming processes,atmospheric precipitation is mixed in later stages.The sulphur isotope test results show that the source of sulphur in the ore-forming material is relatively simple,and there are few controlled factors,mainly from acid igneous magma.The lead isotope test results show that the lead of the ore-forming material originates from the upper crust,and at the same time,during the process of the subduction and orogenic reconstruction in the later period,there is a large amount of lead from the mantle,which has the characteristic of mixed lead.Comprehensive analysis shows that the main genetic type of the Xitieshan lead-zinc deposit is a massive sulphide deposit?SMS type-silver mine type?associated with sedimentary rocks;late development and O₃tn^b volcanic rocks of the Ordovician Upper Triassic Tanjianshan Group.The associated hot water jet deposition of a massive sulphide deposit?VMS type?is smaller.In terms of metallogenic prediction,the fault zone in the east of the ore belt is adjacent to the O₃tn^a-2 volcanic rock sandwiched by the O₃tn^a-2 volcanic rock and the O₃tn^b volcanic rock stratum in the east of the Xitieshan railway station.It is similar to and comparable to the strata in the mining area currently,there are only sporadic shallow drilling controls,which need further work.Taking into account that the area of gold in hot water jet flow lead-zinc ore averages0.58g/t,and the average silver is 36.20g/t,it is an advantageous surrounding rock of hydrothermal Au-Ag ore,and the medium-temperature thermal fluid type Au-Ag should be carried out,ore prospecting and evaluation work.