Geological And Geochemical Characteristics And Genesis Of The Angeer Yinwula Deposit,Inner Mongolia

The Angeer Yinwula Pb-Zn deposit discovered in recent years is located in the eastern part of the Dongwuzhumuqin Banner,Inner Mongolia,in the eastern part of the Paleozoic orogenic belt of central Asia,and in the famous Erlianhot-Dongwuqi polymetallic metallogenic belt of China,with superior metallogenic conditions.This paper summarizes the geological characteristics of the Angeer Yinwula Pb-Zn deposit on the basis of previous studies.Based on the tests of fluid inclusions,C-H-O-S-Pb isotopes,zircons and geochemistry of the deposit,this paper systematically discussed the characteristics,origin and evolution of the ore-forming fluids,the source and evolution of the ore-forming materials,the preliminary prediction of the ore-forming age and the evolution of the tectonic background,and further summarized the genesis of the deposit.The strata in the study area only expose the Upper Devonian Angeer Yinwula Formation and the Quaternary.There are two main groups of fault structures in the study area,which are NW-trending and nearly EW-trending.Among them,the NW-trending faults strike 290-305°,incline to NW and dip about 55°,which are the main ore-controlling and ore-hosting structures in the area.Coarse-grained syenite occurs in the mining area,mostly located in the southern part of the area,and generally distributes in the East-West direction.Quartz diorite can be seen in some deep drills.According to the characteristics of mineral association and vein cutting,the hydrothermal metallogenic system can be divided into three stages:(I)arsenopyrite-pyrrhotite-chalcopyrite-pyrite-quartz stage;(II)chalcopyrite-pyrrhotite-pyrite-galena-sphalerite-quartz stage;(III)galena-sphalerite-quartz-pyrite-calcite stage.The main types of wall rock alteration are carbonation,chloritization,epidote,silicification,sericitization and kaolinization,among which silicification and mineralization are most closely related.The study of fluid inclusions shows that there are three types of inclusions in the Angeer Yinwula Pb-Zn deposit: three-phase inclusions containing NaCl sub-minerals,gas-liquid two-phase inclusions and gas-rich inclusions.The mineralizing fluid of the Angeer Yinwula Pb-Zn deposit has gradually changed from NaCl-H2 O system hydrothermal solution of medium temperature and medium-high salinity to NaCl-H2 O system of medium-low temperature and low salinity hydrothermal system.The peak homogenization temperatures of inclusions in stage I are 300-360 ? and salinity is0.58-51.65 wt.% NaCl eqv;the peak homogenization temperatures of inclusions in stage II are 240-280? and salinity is 2.40-5.99 wt.% NaCl eqv;the peak homogenization temperatures of inclusions in stage III are 160-200? and salinity is 0.87%-3.85 wt.% NaCl eqv.The main sulfur source of the Angeer Yinwula deposit is the upper mantle and the deep crust,and the source of lead has obvious mixed source characteristics,which can be used to determine that the mineralizing materials are involved in the mantle and accompanied by the contamination of crustal materials.Quartz diorite is the ore-forming rock of the deposit(the crystallization age is 152.0±1.5 Ma),which can be approximately regarded as the ore-forming age of the deposit,which is the Late Jurassic of Mesozoic.The early Cretaceous syenogranite(136.1±0.9 Ma)are similar to I-type granites in the background of island arc or active continental margin.Therefore,it is presumed that the formation of syenogranite in the area is closely related to the subduction of the Pacific plate.Based on the tectonic evolution history of the Erlianhot-Dongwuqi polymetallic metallogenic belt from 120 to 170 Ma,this paper holds that under the subduction environment of the Paleo-Pacific Ocean,the magmatic hydrothermal fluid in the deep crust carries a large amount of ore-forming materials,and the ore-bearing hydrothermal fluid rises to the near surface along the tectonic fracture zone,accompanied by it and itsparts.With the occurrence of metasomatic alteration of ore-bearing hydrothermal fluid in the tectonic cataclastic zone and the continuous mixing of atmospheric precipitation,the abrupt decrease of temperature and pressure in the metallogenic system leads to the imbalance of the hydrothermal system,and the ore-forming material precipitates from the hydrothermal solution,filling and forming the ore body at the favorable position.