The Study Of Mineralization And Genesis Of Au-Pb-Zn Polymetallic Deposit In Bengbu Area Of Anhui Province

The Wuhe-Fengyang area of Bengbu city,Anhui province, is located in the Tancheng-Lujiang fault zone and west of it in eastern China.This area belongs to the Bengbu anticline and Wuhe syncline in the southern margin of North China Craton,which was treated as a secondary tectonic unit,the North China Platform—Bengbu-Qixia anticlinorum corresponding with the northern of Jiongdong peninsula.Current tectonic pattern is the result of sinistral strike-slip of Tan-Lu fault zone. It was inferred that the gold deposits around Bengbu uplift be supposed to be the counterpart of the Zhaoyuan-Yexian gold belt of Jiaodong Peninsula in the west of Tan-Lu fault zone.Intensive tectonic deformation and magmatism have been recognized around Bengbu area such as ductile and brittle-ductile shear zones. Many gold and silver mineralization have been found in last two decades.It is believed that this area has a good mineralization conditions.Many small and medium-sized Au,Ag,Au-Ag-Pb-Zn deposits was found in the research area. Limited by lack of exploration extense,the genesis of the deposits of this area is remain unclear,limited the further prospecting work in the region.This study based on the study of previous work, carried out a detailed survey and experimental test, and make clear the minerogenetic condition, and also have a new understanding of the genesis of the deposit.The gold deposit type of Bengbu area are quartz veins and structure altered rock type, most ore bodies are in the near north-south ductile-brittle shear zone （fracture） .Existing major gold deposits are located in the junction of the east-west folds and the Tan-Lu fault zone ,and also the area around it.The ductile （brittle） shear zone widely developed in the research area, with the development of various types of tectonite, mostl mylonite belongs to the blastomylonite series, through post-structural superimposed deformation. The deformation environment analysis of Ductile shear zone showed that the formation environment of ductile shear zone is difference from the conditions in temperature and pressure obtained by fluid inclusions, so the Bengbu area gold deposit should be post-ductile shear zone type gold deposit, no gold mineralization in the syn- ductile sheering.Stable isotope analysis shows that the ore-forming materials of gold deposits in this region have the crust-mantle mixed characteristics,the ore-forming fluids is magmatic water and metamorphic water, may also be mixed with meteoric water. Fluid inclusions in auriferous quartz veins are rich in CO₂, and low salinity.In the metallogenic stage ,the ore-forming temperature were 329-345℃, pressure was 150-180MPa.Compared with the Jiaodong,Xiaoqinling gold deposits where also belong to the southern margin of North China plate,the Begnbu gold deposits may be Mesozoic Orogenic-type gold deposits, formed in the background of the Yangtze plate subduction to North China plate , were closely related to lithosphere thinning process in eastern China,crust-mantle interaction, magmatic activities and the activities of the Tan-Lu fault zone at the same period.