Relationship Between Yanshanian Intermediate-acid Magmatic Activity And Au-Cu Polymetallic Mineralization

The Yanshanian magmatism was an important magmatism in eastern China,and its genetic relationship with gold and copper deposits was one of the most important research contents.Gold is a mineral resource with important economic value.It can be used as precious jewelry and also has currency attributes.Now it is widely used in aviation,medical and electronic technology,etc.However,in recent years,Chinese gold reserves are still in short supply.It is extremely important to increase the exploration of gold deposits and to study the genesis of gold polymetallic deposits.Tongling ore-cluster region,Bengbu area and Chuzhou-Machang area are important gold and copper resources in Anhui Province,and they have also been key areas for domestic and foreign research for many years.The Yanshanian magmatic rocks are also extremely developed in the area,but there are still many controversies about the genetic relationship between Yanshanian magmatic activities and gold and copper deposits.In particular,the relationship between a series of new deposits discoveredand the Yanshanian magmatic rocks is still unclear,and relevant research work is still needed.This work focuses on selecting Au,Cu deposits newly discovered in the above areas in recent years such as Yangchongli Au deposit,Hucunnan Cu-Mo deposit,Jiangshan Au deposit and Damiaoshan Au deposit,etc.as typical deposits.We will carry out relevant diagenetic-metallogenic geochemical research to solve the main problems of the time-space relationship of diagenesis and mineralization,the source of diagenetic minerals and the genesis of regional deposits.The research of Yangchongli Au deposit shows that the ore-forming hydrothermal fluidmainly came from magma.The Yangchongli deposit was the same ore-forming system as Shujiadian porphyry Au deposit.The different ore-forming assemblages were related tothe change of the composition ratio of ore-forming fluid.There may be a period of epithermal hydrothermal mineralization event in the shallow part.The research of Hucunnan Cu-Mo deposit showed that the mineralization wass related to the Yanshanian granodiorite in the area.The diagenetic and metallogenic ages were basically the same.The magmatic rocks had the attributes of subducting oceanic crust adakitic rocks.The metallogenic materials of porphyry stage and skam stage were basically the same,but slightly different.The stratigraphic materials of skarn stage participate more,and the metallogenic model of the deposit was established.The research of Jiangshan Au deposit showed that the diagenesis and mineralization mainly occurred in the late Early Cretaceous,which corresponded to the third Mesozoic magmatic activity in the area.Trace elements such as Sr,Y and Hf isotope indicated that it had the crust-derived properties and had mantle origin.The magma had the characteristics of high oxygen fugacity,which was conducive to Au mineralization.The surrounding rock was an ancient metamorphic basement with high Au element abundance.The micro regional geochemical characteristics of sulfide and in-situ S isotope also indicated that the joint action of magma and strata was the main genesis of gold deposits in the area.The complex fracture zone structure provided a different storage space from other gold deposits in the area,formed a unique ore body shape.The study of Damiaoshan Au depositshowed that the magmatic rocks in the area were formed at about 130 Ma.In the past,because of the small scale of the rock mass,the relationship between the magmatic rocks and mineralization was often ignored.Most of the predecessors thought that the deposit was Carlin-like.However,the trace elements of zircon showed that the magma had high oxygen fugacity,which was beneficial to Au mineralization.The in-situ S isotope of sulfide indicated a multi-element metallogenic feature,which indicated that both strata and magmawere involved in Au mineralization.The micro regional geochemical characteristics of sulfide showed that magma playeda vital role in the metallogenic process.Based on the study of typical deposits,the research work of regional diagenesis and metallogenesis was systematically summarized,combined with previous research work,the relationship between Yanshanian magmatic activity and Au-Cu mineralization in the three regions was summarized as well as the genesis of regional deposits.It was considered that the Yanshanian magmatic rocks in the three areas were all adakitic rocks with high oxygen fugacity,and the Au-Cu polymetallic deposits in the area were mainly related to these Yanshanian adakitic rocks.The magma source areas of the three areas were slightly different.Tongling and Chuzhou-Machang area originated from partial melting of subducted oceanic crust.The Yanshanian magmatic rocks in Tongling,especially pyroxene diorite,had more mantle source materials.The Yanshanian magmatic rocks in Chuzhou-Machang area were contaminated with more crust source materials.The reason may be related to the deep faults developed in Tongling ore concentration area.The Bengbu area originated from the partial melting of the lower crust and the enrichment of mantle derived materials.Due to the differences of basement properties,different metallogenic types and ore bearing horizons weare formed in the three areas.The basement in Bengbu area had certain mantle source materials added during the formation,the element abundance of basement Au was higher(5 times of the average value of the crust),and the basement wall rock also provided a lot of metallogenic materials in the metallogenic process.Therefore,most of the gold deposits in this area developed in the Archean metamorphic basement,and the ore-forming type is mainly the orogenic type controlled by the structure(Quartz vein type,tectonic altered rock type)gold deposits.The basement of the Tongling ore concentration area and Chuzhou-Machang area were mainly crust-derived material,and the magma with mantle-derived material provides the main formation for Au-Cu deposits in the area.So ore bodies were mostly developed in carbonate strata with more active geochemical properties,and most of the ore-forming types were porphyry-skarn and magmatic hydrothermal deposits.