Geochemical Characteristics Of Nachatangbei's Skarn Pb-Zn Deposit In Tibet

The Nachatangbei Pb-Zn deposit,which is a skarn deposit in the eastern part of the Gangdise metallogenic belt and has low exploration and research in Tibet.Based on systematic geological records and field geological surveys,this paper based on the preliminary identification of the geological characteristics of the orebodies in Nachatangbei Pb-Zn deposit,focuses on the geochemical characteristics of the deposits,explores the genesis of the deposits,and then guides prospecting and exploration in the mining areas.Preliminary identification of the geological characteristics of the deposit.The ore-controlling strata of the the Nachatangbei skarn Pb-Zn deposit is the Upper Carboniferous-Lower Permian Laigu Formation?C₂P₁l?.The main ore-bearing rocks are skarn and hornfels,and the orebodies are mainly lamellar,cystic,irregularly thick plate-like and lenticular bodies are produced in the keratinite and marble contact zones,and some are produced in the biotite granite contact zone.There are two phases in the metallogenic process of the Nachatangbei Pb-Zn deposit:the magmatic hydrothermal filling and replacement period and the epigenetic period.The magmatic hydrothermal filling replacement period is related to mineralization and can be further divided into four stages:skarn stage,oxide stage,quartz sulphide stage,and carbonate stage.The system has carried out studies on the geochemical characteristics of surrounding rocks and ore-bearing rocks.The skarn in the mining area is formed by contact between the magmatic hydrothermal fluid and marble?limestone?and the occurrence of metasomatism and material exchange.The geochemical characteristics of skarn are constrained and influenced by marble?limestone?,biotite granite,and granodiorite porphyry,indicating that skarn is formed by contact metasomatism.Determine the origin of magmatic rocks in the mining area.The geochemical characteristics of the biotite granites and granodiorite porphyries in the Nachatangbei deposit shows that they have different geochemical characteristics from those in the collisional granites in the Gangdise area.The age of the magmatic rock in the mining area is Late Jurassic-Early Cretaceous,and the geochemical tectonic diagram also shows an island-arc granite environment.It is speculated that the magmatic rock in the mining area was caused by the late Jurassic-Early Cretaceous Neo-Tethys dipping into the north.The result of partial melting of the material.Sources of ore-forming materials were explored.Through the study of the S and Pb isotopic compositions of ores in the Nachatangbei Pb-Zn deposit,two peak phenomena appear in the frequency histogram of the S isotopic composition of the deposit,indicating that the source of sulfur is not completely homogeneous,indicating that the deposit S is not only derived from magma,but may be Because of the formation of sulfur in the ground,the characteristics of Pb isotope composition show that the ore-forming material is derived from the upper crust material?Nyenqingtangla crystal basement gneiss?.Therefore,the ore-forming material source has the dual role of magma and stratum.Through the above studies,it is believed that the Nachatangbei Pb-Zn deposit is an island-arc environment formed by the subduction of the Neo-Tethys,causing local melting of the crust and formation of a large amount of magmatic hydrothermal fluids.A skarn-type lead-zinc deposit that has been formed by precipitation of ore-forming material from the dripping formation.