| The Zhashui-Shanyang ore district in the South Qinling is one of the important ore districts in the Qinling orogenic belt.There is a strong tectonic magmatic activity in the area,and a large number of micro disseminated gold deposits occur in the clastic turbidite or carbonate formation.The key scientific issues such as the metallogenic geological background,the metallogenic age,the relationship between magmatic activity and mineralization,the metallogenic mechanism and the metallogenic dynamic background of the gold deposits in the ore concentration area need further study,which restricts the further exploration and development of the gold deposits in the ore concentration area.In this paper,four typical gold deposits of Xiajiadian,Longtougou,Wangjiaping and Qinglingou are taken as the main research objects.On the basis of previous studies,through detailed regional geological survey,geophysical and geochemical exploration,remote sensing and mineralogy research,and systematic experimental test and analysis,the occurrence state and metallogenic age of gold in the gold deposits of Zha-Shan ore concentration area are discussed,the relationship between gold mineralization and magmatic activity,metallogenic process and metallogenic tectonic background are studied.The following major achievements are obtained:(1)The gold deposits(points)exposed in Zha-Shan ore concentration area are mainly concentrated in Ertaizi-Fengzhen-Xiajiadian gold belt and Qinglingou-Wangjiagou-Miaoliang gold belt.The host rock of the deposit is a set of carbonate rock or clastic rock sedimentary formation.The ore body is obviously controlled by the fracture structure,closely associated with Au,as,Sb and other ore-forming elements.It has the characteristics of silicification,carbonation,pyritization,sericitization,kaolinization and other wall rock alteration.Its host rock,gold occurrence state and other basic characteristics are the same or the same as the Carlin type gold deposit in Nevada,USA Similarly,the ore grade and fluid properties are different.(2)According to the geological background characteristics and detailed mineralogical study of Xiajiadian,Longtougou,Wangjiaping and Qinglingou deposits,the metallogenic stage can be divided into quartz pyrite(±sericite),quartz sulfide(±a small amount of calcite)and quartz calcite;Pyrite,arsenopyrite and arsenopyrite are the main gold bearing minerals,and the distribution types of gold include fissure gold,intergranular gold and inclusion gold.(3)Based on the study of fluid inclusions,it is considered that the ore-forming fluid of gold deposits in Zha-Shan ore concentration area is characterized by medium low temperature and low salinity,and the gold deposits are formed in neutral or weak alkaline and reductive environments;Gold mainly migrates in the form of Au(HS)~0 in the hydrothermal solution,and the fluid rock interaction is the most critical role of Au rich integrated ore in Carlin-like Carlin type gold deposits in Zuoshan ore concentration area.(4)Based on the study of C-H-O-S isotopes and sulfide trace elements,it is considered that the ore-forming fluid in the middle early stage of the gold deposit has the characteristics of magmatic water,and the meteoric water is added in the later stage of the mineralization.the ore-forming material is formed by mixing the deep mantle magma with the crust in different proportions.(5)Based on the comprehensive comparative analysis,it is considered that there are two stages of gold mineralization events in Zha-Shan ore concentration area,i.e.Indosinian and Yanshanian.The gold deposits are controlled by fault structures,and the mineralization is related to the activities of high potassium calc alkaline quasi aluminous I-type granites in Indosinian and Yanshanian.Qinglingou was formed in the late Indosinian epoch.The ore-forming materials were all mixed by mantle magma and crust.The event was formed in the tectonic background of lithospheric stress transition from compression to extension.The Sm-Nd isochron age of calcite and fluorite in Xiajiadian gold deposit is 139.6±0.98 Ma,and the SM nd isochron age of bedsheet mineral in longtougou gold deposit is 141±3.6Ma.The metallogenic age of Xiajiadian gold deposit and longtougou gold deposit can represent the main age of regional Carlin type gold deposit,and wangjiaping gold deposit is also formed around 140 Ma;The Yanshanian metallogenic environment is the tectonic environment of lithospheric extension and thinning.Because the Qinling orogenic belt entered the stage of extension and rifting,the thickness of the crust decreased.Under the condition of mantle heat and tectonic decompression,the upwelling of mantle material and thermal fluid brought a lot of gold and other metallogenic elements.At the same time,it induced strong crust mantle interaction,extracted and activated gold in some strata,resulting in a large amount of gold precipitation aggregation mineralization,the gold deposit and the porphyry skarn Cu Mo deposit are the same metallogenic system. |
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