Study On The Geological-geochemical Characteristics And Origin Of The Taiyangsi Gold Deposit,west Qinling,Gansu

The Qinling Mountains mountain ranges from east to west in Central China,a large structural belt formed by the North China plate,the Qinling micro block and the Yangtze plate.It is one of the most famous continental orogenic belts in the world.Its special geological structure,unique structural characteristics,complex evolution history and abundant mineral resources have attracted the attention of Chinese and foreign geologists.Among them,gold deposit is one of the most advantageous ore prospecting potential in the Qinling Mountains metallogenic belt.Western Qinling,which is an active accumulation area of metallogenic material and fluid and rich mineral resources,is also one of the key areas to study the complex orogenic belt metallogenic system.The TaiYangsi gold deposit is located in the North Qinling Mountains fold belt of the eastern part of the West Qinling Mountains orogenic belt,Its geological structure and metallogenic conditions are relatively complex.In addition,the research level of the predecessors is low,and the geological characteristics,geochemical characteristics,ore controlling factors and ore genesis of the gold deposit are not deeply understood,the classification of the type of deposit lacks the support of experimental data.Based on the existing research,this paper conducts a more thorough and comprehensive analysis.The main achievements and understanding are as follows:?1?The main formation of the mining area is the Dacaotan group of Devonian System and the Danfeng group of Sinian-Ordovician System,the main lithology is a set of terrigenous coarse clastic rock sedimentary formations and metamorphic basic volcanic rocks;The tectonic activity is strong and multiphase,the brittle-ductile fracture belt and its secondary faults are mainly distributed near the EW direction.In the region,the nearly NS direction fracture and the former structure formed"meter"shaped structure in the area.The fracture structures are all formed by north-south extrusion.?2?The acid rock in the mining area is more developed,The intrusive rocks are mainly the Tianzishan monzonitic granite rock mass on the west side,the Taibaixiang monzonitic granite rock mass and the late granite porphyry,diorite porphyry dikes,etc.The early gold deposits were mainly formed in the ductile shear zone,the late stage is mainly gold mineralization around diorite porphyry,and some diorite porphyry veins are both orebodies.?3?The main alteration of the surrounding rocks is brown iron mineralization?pyrite mineralization?silicification and sericite;Secondly,chlorinization and carbonation are more common in mining areas.The upper part is mainly performance ferritization,the distribution of banded along the two sides of the ore body and the fault zone,width of several meters-tens of meters,sericite is generally associated with it.Pyrite mineralization,silicification and carbonation are obvious below the oxidation zone,and chlorite and epidote are found locally.?4?The types of ore deposits in the mining area are mainly two types of altered rock type and quartz sulfide vein type.The ore structures are mainly granular,parcel,metasomatic and directional elongated structures.The main structures are disseminated structures,banded structures and broken breccia structures.?5?The mining area experienced epigenetic and two hydrothermal periods.The first stage hydrothermal period is related to the magmatic hydrothermal of the monzonitic granite and the hydrothermal fluids produced by ductile brittle shearing.It can be divided into two stages:the first stage is the pyrite quartz stage,and the second stage is the gold quartz pyrite stage.The second stage is the hydrothermal period related to diorite porphyrite,the two stages of mineralization are different in different positions.?6?The S isotopic range of the mining area is 1.0‰⁷.5‰,average 4.04‰,the S isotopic values of ores near diorite porphyrite are obviously lower,the characteristics of the sulfur source of magma;H-O isotopic characteristics show that the ore-forming fluid is mainly magmatic water,which is consistent with the sulfur isotope test results;the Pb isotopic characteristics show that the Pb is mixed with the crust and the mantle.?7?The analysis of fluid inclusions in the mining area shows that the ore-forming hydrothermal fluids are characterized by moderate low temperature and low salinity.The gas phase is mainly composed of CO₂,H₂S,CH₄,N₂ and H₂,and the possible fluid comes from the deep part.?8?In this study,the comprehensive analysis of various metallogenic factors suggests that there are two types of gold deposits in this area,which are ductile shear zone type gold deposits and porphyry type altered rock type gold deposits.