Ore-forming Characters And Tectonic Setting Of The Bulage Pb-Zn Deposit In Inner Mongolia

The Bulage Pb-Zn deposit is located in the middle part of the Erenhot-Dongwuqi metallogenic belt in the eastern part of the Central Asian metallogenic domain.It is a represenatative medium-low temperature hydrothermal vein type deposit controlled by fault.The ore body is mainly contained in the syenogranite and andesitic chip tuff of second lithologic Carboniferous-Permian Baoligaomiao formation.On the basis of the predecessors,the study of fluid inclusions,H-O isotopes,geochronology and geochemistry of the Pb-Zn deposit has been carried out.The hydrothermal mineralization is classified into three stages according to the mineral assemblage and the relationship of the veins:specularite-quartz phase???,polymetallic sulfide-quartz phase???,quartz-calcite-sulfide phase???.The area mainly developed Vapor-Liquid type inclusions?VL?and a small amount of pure liquid inclusions?L?.The homogeneous temperature of VL fluid inclusions at the early stage ranges from 156.4 to 261.2,and the salinity is 3.2%⁹.5%NaCleqv,and the homogeneous temperature of VL fluid inclusions at the middle stage is 143.2²30.6,2.6%to 8.3%NaCleqv,and the homogeneous temperature of VL fluid inclusions at the late stage is 111.9 to 172.4 C,and the salinity is 3.2%to6.6%NaCleqv.Generally speaking,it is medium-low temperature and low salinity NaCl-H₂O system.In the composition of stable isotopes of hydrogen and oxygen in fluid inclusions,?D value of the early stage is-95.9^-93‰,?¹⁸OH₂O is-4.5^-3.9,?D value of the middle stage is-110^-108.9‰,?¹⁸OH₂O is-7.9^-6.2‰,?D value of late stage is-117.8^-111.9‰,?¹⁸OH₂O is-8.9^-7.4‰.It indicates that the main source of metallogenic fluid is meteoric water.The LA-ICP-MS zircon U-Pb chronology shows that the age range of the quartz diorite,the syenite porphyry and the syenogranite in the mining area is 296³05Ma,which are products of the Late Carboniferous magmatic activity.The three magmatic rocks are closely related to ore bodies,providing ore-forming materials and hydrothermal fluids for mineralization.And the age of intrusive body can approximately represent the age of mineralization.Quartz diorite,monzonitic granite and syenogranite are I type granites.They are rich in Al,and poor in Ca and Mg.Also they enrich light rare earth elements?LREE?and high field-strength elements?HFSEs?,and lose large ion lithophile elements?LILEs?.They also have weak negative Eu anomalies,suggesting that magma comes from partial melting of crustal matter.The geochemical characteristics of the rocks indicate that they formed in the subduction environment of the Paleo-Asian Ocean.Combined with the regional tectonic background,this paper propose that the Bulage Pb-Zn deposit was formed in the Late Carboniferous Paleo-Asian Ocean subduction.