Metallogenic Geological Characteristics And Genesis Of Gold Polymetallic Deposits In Bengbu Wuhe Area,Anhui Province

The gold deposits in the Wuhe area,Bengbu city,Anhui Province,are located in the adjacent area of the Bengbu Uplift and Wuhe syncline along the southeastern margin of the North China Craton.The systematic comparison research on the gold deposits have not been done in this area.Few studies have been carried on the precipitation mechanism of gold deposits.The genetic type of gold deposits in research area remain debated.In this paper,geological characteristic,fluid inclusion geochemistry,Re-Os isotopes and H-O-S isotopes of the typical gold deposits(Hekou,Rongdu and Tianjinghu gold deposit)were studied to determine the ore-formation age of the deposits and to explore the source of ore-forming materials and metallogenic processes of the deposits and preliminarily establish the ore-forming model.The main achievements of this study are as follows:The ore bodies in both deposits are composed of veinlet-disseminated type,veintype and reticulated vein-type ores hosted in the Paleo-Archaean Xigudui Formation.The ore-forming processes can be divided into four stages in the gold deposit:(1)quartz stage(early stage);(2)quartz pyrite stage(middle stage);(3)quartz polymetallic sulfide stage(middle stage);(4)the carbonate stage(late stage).The main gold mineralization occurred in the middle stage.and the mainly ore type is quartz vein type.The characteristic of the fluid inclusions shows that the ore-forming fluid in the area is medium temperature and low salinity fluid system.The salinity and temperature of the fluid decrease quickly from the early stage to the late stage.The temperature of the three gold deposits in the main ore-forming stage decrease from the Hekou gold deposit,the Rongdu gold deposit to the Tianjinghu gold deposit.The H-O isotopic characteristic of quartzs in the ore indicate that the ore-forming fluids of the Hekou gold deposit is the magmatic water+a few meteoric of water,those of Rongdu gold deposit is the magmatic water+the meteoric water,and those of the Tianjinghu gold deposit is mainly is the magmatic water+the organic water.The S-isotopic characteristic of ore and the surrounding rock indicates that the ore-forming materials of the three gold deposits are derived from magmatic rocks and strata.Based on the comparative study of the geological characteristic,fluid inclusion characteristic and H-O-S stable isotope characteristic of the three gold deposits,it is considered that the Hekou,Rongdu and Tianjinghu gold deposit belong to the same mineralization system and the Hekou gold deposit may be the mineralization hydrothermal center of the three gold deposits.The fracture gold,intergranular gold and inclusion gold have been discoved in pyrites and quartzs in the ore of the gold deposits.Combined with the study on the fluid inclusions and the LA-ICP-MS trace element mapping of pyrites of different generations,the gold precipitation was triggered by decompression boiling degassing and fluid mixing in multiple stages.Re-Os isochron dating of pyrites from the Rongdu gold deposit shows that the gold deposit was formed at 134±19Ma.Based on the previous magmatic dating in this area,It is inferred that the mineralization of the deposits may be closely related to the 130 Ma magmatism in the Wuhe area.In conclusion,it is considered that the gold deposits in Bengbu Wuhe area belong to mesothermal gold deposits which related to magmatic hydrothermal system,and a preliminary genetic model of the gold deposits in this area has been established.