Pb-zn Polymetallic Deposits Metallogenic Series And Prospecting Direction Of The West Slope Of Southern Great Xing'an Range

The Southern Great Xing'an Range is located in the eastern of Central Asian Orogenic Belt,which is also know as the south of the Hegenshan fracture,north of Xar Moron fracture and west of Nenjiang fracture region.It is an important Pb-Zn-W-Mo-Sn-Fe polymetallic mineral assemblage zone in north China.According to the geographical and topographical features Southern Great Xing'an Range can be divided into three NE trend extension area:west slope,the main peak and east slope.Xilinhot-Xilinguole Pb-Zn polymetallic belt formed in the west slope Southern Great Xing'an Range.The tectonic evolution history of study area can be divided into three stages: Paleo-Asian ocean tectonic system,Mongol-Okhotsk tectonic regime and Paleo-Pacific tectonic system.Zircon U-Pb dating and geochemistry have indicated that the study area influenced by the Paleo-Asian tectonic system before the Mesozoic,the magmatism and mineralization during Early permain formed in the setting of subduction under Paleo-Asian tectonic system.Trassic mineralization formed in the setting of synorogeny or post-orogeny after closure of the Paleo-Asian Ocean.Abundant magmatism and mineralization during Middle-Late Jurassic and early Early Cretaceous(170-135Ma)formed in a extensional environment,which related to the collapse or delamination of the thickened continental crust after the closure of Mongol-Okhotsk Ocean.The late Early Cretaceous magmatism and mineralization formed in a backarc extensional environment that was influenced by the Paleo-Pacific tectonic system.Based on the characteristics of ore deposit geology,we can be divided into two genetic types: high temperature vein type(Daolundaba W-Cu deposit),medium temperature vein type(Bairendaba Ag-Pb-Zn doposit,Weilasituo Cu polymetallic doposit,Hua'aobaote Pb-Zn polymetallic doposit and Bujinhei Pb-Zn polymetallic doposit).W-Sn and Cu mineralization stage of Daolundaba deposit all develop liquid-rich aqueous,CO2-H2O±CH4,daughter mineral contianed three-phase inclusions,laser Raman spectrum analysis results show that the CO2-H2O±CH4 inclusions in the gas bubble contains CO2,CH4 and N2.The stable isotope analyses indicate that ore-forming fluids were initially derived from the magmatic water and mixed with local meteoric water in the late stage.The early ore-forming fluids were high temperature and high salinity H2O-CO2-CH4-NaCl hydrothermal fluids under the fluid immiscibility,which became low-to medium temperature and low-to medium salinity of H2O-NaCl hydrothermal fluids in later stage.The study of stable isotopes indicate that the ore-forming fluids of medium temperature vein type deposits(eg: Bairendaba doposit,Weilasituo doposit and Bujinhei doposit)are initially derived from the magmatic water and mixed with local meteoric water in the late stage.These deposits develop liquid-rich aqueous and CO2-H2O±CH4 inclusions in early stage,laser Raman spectrum analysis results show that the gas bubble of CO2-H2O±CH4 inclusions contain CO2,CH4 and N2.The early ore-forming belong to medium-to high temperature and medium-to low salinity immiscible H2O-CO2-CH4-NaCl hydrothermal fluids,which became low-to medium temperature and low salinity of H2O-NaCl hydrothermal fluids in later stages.The ore fluids of Hua'aobaote and Shabulengshan deposit belong to medium temperature,medium-to low salinity H2O-NaCl hydrothermal fluids.Based on H and O isotope data,ore fluids mainly came from meteoric water in Hua'aobaote deposit.Ore sulfur of deposits in the west slope of SGXR are mainly sourced from magmatic hydrothermal fluids,but Bujinhei and Shabulengshan deposits derived from mixing source of magma and strata.Zircon U-Pb dating and Re-Os isotopic dating shown that mineralization in west slope of SGXR area can be divided three epoches,including Early Permain mineralization,Late Jurassic mineralization and Early Cretaceous mineralization.Daolundaba Cu-W deposit formed in Early Permain(about 292-278 Ma),Shabulengshan Cu-Zn deposit formed in Late Jurassic(153.2 Ma),Bairendaba Pb-Zn deposit,Weilasituo Cu polymetallic deposit and Hua'aobaote Pb-Zn deposit formed in early Early Cretaceous(about 133.4Ma-136Ma),while Bujinhei Pb-Zn polymetallic deposit formed in late Early Cretaceous(122.9 Ma).There are 3 metallogenic series developed in the weat slope SGXR,which the Cu-Zn-W polymetallic metallogenic series,Cu-Mo-Zn polymetallic metallogenic series and Pb-Zn-Cu-Ag polymetallic metallogenic series.The first is related to the Early Permain intermediate-acid intrusions.The second is related to the Late Jurassic intrusions.The last is related to the Early cretaceous acid igneous rocks,and it can be further divided into 2 sub-series: firstly,Pb-Zn-Cu-Ag sub-polymetallic metallogenic series which is related to the early Early cretaceous intermediate-acidic intrusions,secondly,Pb-Zn sub-polymetallic metallogenic series which is related to the late Early cretaceous intermediate-acidic igneous rocks.Many vein-type deposits are developed along the west slope of SGXR.The development and distribution of polymetallic deposits in west slope SGXR area is primarily controlled by structure.According the MRAS system,we dicover that Permian strata,Variscan and Yanshanian magmatite also are important prospecting marks.We analyzed the stream sediment geochenmistry data of study area,and found mineralized-element anomalistic places.Compared with already known mines,we summarized the relation of mineralization and anomalistic places.Finally,we extracted entropy of stratum assemblage,tectonic isodense anomalies,geophysical anomalies,geochemical etc.as evidence,using MRAS system.Based on evidence weight model,we marked out 8 prospecting target areas.