Study Of Pb-Zn Polymetallic Mineralization In The Southern Section Of The Tianshan-tuquan Metallogenic Subzone Of The Great Xing’an Range

The southern Great Xing’an range is located in the eastern part of the Central Asian orogenic belt,which is bounded by the Hegengshan Fault in the north and the Xing’an Massif,the Xilamulun Fault in the south and the northern margin of The North China Craton,and the Nengjiang Fault in the east and the western margin of the Songliao Basin.Since the Phanerozoic,the area has experienced a series of major geological events such as the evolution and closure of the Paleo Asian Ocean,the closure of the Mongolian-Okhotsk Ocean and the westward subduction of the Paleo Pacific Ocean,resulting in the occurrence of several phases of magmatic-hydrothermal mineralization events.In recent years,with the discovery of a series of large and ultra-large Pb-Zn polymetallic deposits such as Weilasituo,Bairendaba,Bianjiadayuan and Shuangjianzishan,it has become one of the most important Pb-Zn metallogenic provinces in China.A lot of research work has been carried out on copper polymetallic deposits developed in the Xilinhot-Xilingole Pb-Zn,Huanggangliang-Ganzurmiao Fe-Sn polymetallic,and Tuquan area,which belongs to the northern part of the Tianshan-Tuquan Cu-polymetallic metallogenic subzone.However,there is a lack of systematic research work on the southern section of the Tianshan-Tuquan Cu-polymetallic metallogenic subzone,resulting in no significant breakthrough in the exploration and search of non-ferrous mineral resources in the region for a long time.At the same time,the research on the hydrothermal Pb-Zn polymetallic deposits in the Paleozoic stratigraphy of the region has achieved a deeper understanding,but there is no systematic research on the Pb-Zn polymetallic deposits in the Mesozoic volcanic-subvolcanic rocks,which greatly limits the understanding of the Pb-Zn polymetallic mineralization in the southern Great Xing’an range and restricts the further mineralization search in the region.Therefore,this paper selects the Panjiaduan Cu-Pb-Zn（Ag）,Lamahanshan Ag-Pb-Zn,and Bianbianshan Cu-polymetallic deposits in the southern section of the Tianshan-Tuquan metallogenic subzone of the Great Xing’an range as the research objects,and carries out studies on the geological characteristics of the deposits,fluid inclusions,isotope geochemistry,geochronology,and geochemistry to explore the genesis of each typical Pb-Zn polymetallic deposit and the regional Pb-Zn polymetallic mineralization,and establish regional mineralization model.Through field geological investigation and data summarization,it was found that the Panjiaduan Cu-Pb-Zn（Ag）deposit is hosted in the tectonic fracture zone between andesitic breccias of the Upper Jurassic Manitu Formation and granodiorite,with a small amount produced in the contact zone of both.The Cu-Pb-Zn（Ag）deposit is divided into four stages:quartz-pyrite-arsenopyrite,quartz-polymetallic sulfide,quartz-galena-sphalerite-argentite,quartz-calcite-barren sulfide.The Lamahanshan Ag-Pb-Zn deposit is hosted in the tectonic alteration/fracture zone of gneissic plagioclase granite,granite porphyry and quartz porphyry,and a small amount is produced in the Upper Jurassic Manketouebo Formation,and the ore body is mainly in lenticular and vein-like.The Ag-Pb-Zn mineralization is divided into four stages:quartz-magnetite,quartz-pyrite-chalcopyrite,quartz-polymetallic sulfide,and quartz-sphalerite.The Bianbianshan Cu-polymetallic deposit is mainly hosted in the volcanic rocks or volcanic clastic rocks of the Upper Jurassic Manketouebo Formation,and the ore body is mainly in vein form.The Cu-polymetallic mineralization can be divided into four stages:quartz-pyrite-arsenopyrite,quartz-pyrite-chalcopyrite,quartz-polymetallic sulfide,quartz-calcite-barren sulfide.The nature,origin,evolution and source of ore-forming fluids and metal source of each typical deposit are constrained by fluid inclusion petrography,microthermometry,laser Raman analysis,and H-O-He-Ar isotope studies.Among them,both the Panjiaduan Cu-Pb-Zn（Ag）and Lamahanshan Ag-Pb-Zn deposits develop rich gas phase（LV）,gas liquid two phase（VL）and daughter mineral three phase（SL）inclusions,and the laser Raman analysis results show that the fluids in the early stages of mineralization all contain trace CO₂ components,and the early stages of mineralization are all medium-high temperature,high salinity Na Cl-H₂O±CO₂ systems,and the late stages evolve into medium-low temperature,low salinity Na Cl-H₂O±CO₂ systems.In the process of mineral precipitation,fluid boiling and mixing with meteoric water occurred.The rich gas phase（LV）,gas liquid two phase（VL）and CO₂-bearing three-phase（LC）inclusions are developed in the Bianbianshan Cu-polymetallic deposit,and the laser Raman analysis results show that the CO₂ content in the fluid is significantly higher.The early stages of mineralization is medium-high temperature,medium-low salinity CO₂-H₂O-Na Cl systems,and the late stages evolve into medium-low temperature,low salinity H₂O-Na Cl systems.The H-O isotope show that the initial fluids of all three deposits originated from magmatic water and were mixed with meteoric water at a later stage.The S-Pb isotope reveal that all three typical deposits are characterized by deep magmatic sulfur and also show the mixed crust-mantle source of Pb,suggesting a close genetic connection between their mineralization and deep magma.Based on the temperature parameters in different stages of the Panjiaduan,Lamahanshan and Bianbianshan deposits obtained by microthermometry of fluid inclusions,combined with the characteristics of mineral symbiosis association observed by minerals and the thermodynamic data in SUPCRT92 database,the thermodynamic calculation and simulation of the main ore-forming stages of the three deposits were carried out.The results show that the environment of Pb-Zn polymetallic mineralization is characterized by changes in the oxygen fugacity,p H,∑S and a Cl-in the hydrothermal fluid,which leads to the precipitation of ore in the form of metallic sulfides.However,the metallogenic mechanisms differ significantly,with the early stages of the Panjiaduan and Lamahanshan deposits being characterized by fluid boiling,which leads to the precipitation of metal sulfides,and the later stages being characterized by mixing with meteoric water.In contrast,fluid immiscibility occurred in the early stage of the Bianbianshan deposit,resulting in the precipitation of metal sulfides,and meteoric water was mixed in the late stage.Based on LA-ICP-MS zircon U-Pb dating and sphalerite Rb-Sr dating,three phases of magmatism were identified:（a）Early Triassic（252.6-250 Ma）,（b）Late Triassic（236.1-233.9 Ma）,and（c）Early Cretaceous（～140 Ma）,with Pb-Zn polymetallic mineralization mainly occurring in the Early Cretaceous（138.5-137.5 Ma）.There may be hidden ore-forming rock mass in the depth of these three deposits,resulting in the formation of intermediate and distant hydrothermal deposits in the vertical direction.Combined with the regional geotectonic evolution,it is believed that the Early Triassic magmatism was formed during the collisional orogeny after the closure of the Paleo-Asian Ocean,and the Late Triassic magmatism was formed in the post-collisional extensional setting after the closure of the Paleo-Asian Ocean,while the Early Cretaceous magmatism and Pb-Zn polymetallic mineralization were formed under the joint influence of the post-collisional extensional after the closure of the Mongolian-Okhotsk Ocean and westward subduction of the Paleo pacific plate.It is directly related to the deep geological processes such as regional extension,asthenosphere upwelling and lithosphere thinning.