Relationship Between Mineralogical And Geochemical Characteristics Of Pyrite And Uranium Mineralization In The Datian Uranium Deposit On The Kandian Axis

The Datian uranium deposit is located in the south-central part of the Kangdian axis.It is famous for its unique deposit type and giant grained uranium deposit(>0.1 cm).Up to now,there has been half a century of exploration and research,but the source and origin of the fluid in this deposit are still controversial,which has affected the prospecting and exploration in this area.In this paper,on the basis of the data collection system,combined with the field geological survey,system to collect the related samples,the rich uranium ore was carried out by petrography,ore microscopy observation,using advanced instruments such as Scanning electron microscopy,Electron probe,Laser ablation-plasma mass spectrometer further analysis of geochemical characteristics of pyrite,aims to elucidate uranium ore-forming geological characteristics of uranium deposits in open field.The source of ore-forming fluid and the genesis of the deposit are also discussed.The main understanding obtained in this paper is as follows:(1)The host rocks of the Datian uranium deposit are migmatite and mylonite,which have undergone intense metamorphism deformation anatexis.There are three uranium ore belts in the mining area,and their strike is nearly east-west,which is consistent with the gneiss strike in the mining area.The ore is disseminated or lenticular in distribution.The ore minerals are mainly uranite,but also contain secondary uranium minerals such as uranite and calcium uranite.Gangue minerals include pyrite,pyrrhotite,chalcopyrite,ilmenite and a small amount of molybdenite and galena.(2)Pyrite is closely related to uranite in space.According to the morphological characteristics of pyrite,pyrite can be divided into two stages.One is the mineralization stage of pyrite(Py?),which is granular and disseminated in the ore or around uranite.The second is the pyrite(Py?)after the mineralization period,which is vein-like and surrounds the uranite or the perforated ore.(3)pyrite in situ LA–ICP-MS trace element analysis results showed that Py?enrich-ment of LREE and Co,Cu and zinc,Pb iron,copper,Loss high field strength elements,Co/Ni ratio between 0.56?9.16,the vast majority of the value near 1,an average of 1.6.Combined with the mineral assemblage characteristics of the ore,it is indicated that the ore-forming fluids in the ore-forming period have the characteristics of medium-high temperature,which may be derived from metamorphic fluids.Late ore-forming pyrite(Py?)enrichment of Cu,Co,Zn,Pb.Py?with similar characteristics.But the Co and Ni content significantly lower than the Py?,Co/Ni ratio between 0.06?0.73,the average was 0.35,showing sedimentary origin,combined with its output position and attitude,it is considered that it was formed in medium-low temperature environment.(4)In situ sulfur isotope analysis of metal sulfides(pyrite,pyrrhotite,molybdenite and chalcopyrite)in Ores by FE-MC-LA-ICP-MS was carried out that the metallogenic period of granular pyrite(Py?)delta?³⁴S value range between 1.7‰?9.2‰,with an average of 4.9‰The?³⁴S value of chalcopyrite ranges from 4.3‰to 6.2‰,with an average of 5.1‰.Molybdenite?³⁴S values range from 10.3‰to 10.5‰,with an average of 10.4‰.The?³⁴S value of pyrrhotite is 10.3‰;Vein pyrite mineralization period(Py?)delta?³⁴S value range between2‰?10.6‰,with an average of 4.4‰.The?³⁴S value of pyrite in metamorphic rocks is 13.5‰.Most of the sulfide?³⁴S values in the deposit are positive,and the sulfur isotope values are similar to those of metamorphic rocks,suggesting that the fluid may undergo metamorphism.(5)The study indicates that the field uranium deposit is Neoproterozoic plate subduction orogenic activity,causes the continental crust thickening,lower crust material upwelling,resulting in the original kangding group of partial melting of the basement,lava,and cause U elements in base formation activation,with rich in halogen elements(F^-,Cl^-)dissolved ore-forming fluid migration.With the continuous migration of ore-forming hydrothermal solution,in group exposed to kangding group of bamboo cold shut(Pt₁lz)graphite piece of rock,ore fluid in contact with a large number of external reductant,Combined with the reduction ions such as Fe²⁺,Cu⁺in the fluid,uranium elements are enriched in the surface texture of ductile shear zone(high grade disseminated granular uranium deposit)and lower concentration of graphite layer.