Geological Characteristics And Ore-forming Processes Of Erdaohezi Lead-zinc Deposit,Inner Mongolia

Erdaohezi Pb-Zn deposit,situated 40km northeast of Derbuer townlet,Inner Mongolia,is located in the Derbugan metallogenetic zone and is a typical Pb-Zn deposit within the area.Pb-Zn ore bodies mainly occur in the Volcanic rock of Jurassic Tamulangou Formation(J2tm).Wall-rock are andesite and lithic crystal tuff.It's alterations are silicifi cation sericitization,kaolinitizatin pyritization,carbonatation and chloritization which are closely related to mineralization.Ore structure are dominated by vein.According to the studies on isotopic geochronology,the zircon U-Pb ages of the ore-bearing lithic crystal tuff is 164.2±2.3 and ore-bearing andesite is 163.4±1.1 Ma.The accurate dating results indicate that the rock-forming process occurred in Middle Jurassic and the ore-forming process occurred later than it.In combination with the regional Mesozoic epithermal deposits metallogenic epoch,It is supposed that the ore-forming process occurred in late jurassic to early cretaceousThe results of geochemical characteristics show that all of ore-bearing volcanic rocks have wide range SiO2(40.32%?73.68%),K2O+Na2O(4.61%-9.74%),and wide range shand index(A/GNK?0.51?2.84).They are enriched in light rare earth elements,depleted in heavy rare earth elements(LREE/HREE=8.92?21.63,(La/Yb)N=9.68?33.33)with a medium negative Eu anomaly(?Eu=0.57?0.99).They are also enriched in Rb,K,La,and Nd,depleted in Nb,Ta,Sr,and Ti.The analytical results of major and trace elements show that these volcanicl rocks belong to high K(HK)series.The whole rock Sr,Nd,Pb isotopic results show that the ore-forming materials may originate from the mantle and there are the earth's crust material contamination.Fluid inclusion studies indicate that the inclusions in each mineralization stage are all gas-liquid two-phase aqueous inclusions.From early stage to late stage,along the decrease of mineralization temperature,the fluid's salinity changed slightly.The temperature range of Pb-Zn mineralization stage is between 118.3? and 325.1?,with the peak of 200??240?;the salinity varies from 1.000%to 18.72%NaCleqv,with the peak of 7.0%?9.0%NaCleqv.Combined with the analysis of Laser Raman Probe,the Pb-Zn-forming fluid is a NaCl-H2O system with meso-low temperature and low salinity.The H-O isotopic features suggest that the ore fluids is a mixture of magmatic water and meteoric water.The Pb isotopic composition of the volcanic rocks and sulphides from the ore and the ?34S values of the sulphides indicate that the ore-forming materials may originate from the mantle and there are the earth's crust material contamination.Erdaohezi Pb-Zn deposit and the volcanical rocks are controlled by the regional tectonic evolution.In late jurassic to early Cretaceous,after the closure of Mongol-Okhotian marine trough,the region became to post-collisional extension setting,lithosphere delamination lead to the asthenosphere upwelling.The Erdaohezi deposit and the volcanical rocks are the puoduct of the crust-mantle interaction.