Geological Characteristics And Genesis Of The Yangjiao Uranium Deposit In Hunan Province

Yangjiaonao uranium deposit is located on the border between Rucheng County of Hunan Province and Chongyi County of Jiangxi Province.It is tectonically located in the middle range of Zhuguangshan complex massif in the Wugong-Zhuguang lifted block region of South China.Yangjiaonao uranium deposit is one of deposits of Lujing uranium ore field which has low geological research degree.In this paper,the main ore controlling factors of Yangjiaonao uranium deposit are identified by field observations.Rock-mineral identification,fluid inclusions testing and isotope analyzing are carried out.The main achievements are listed as below:Yangjiaonao uranium deposit is located in the southwest of Lujing uranium ore field which is a typical siliceous vein type uranium deposit.The ore bodies are mainly hosted within fault fracture zones of granite massif.Uranium-microcrystalline quartz(pyrite)and uranium-clay types are the major ore types.The pitchblende is the main ore mineral.The autunite,chalcolite and other secondary uranium minerals are observed in the shallow crust.The wall rock alteration is extensively developed in the ore district,including the silication,hematitization,albitization,sericitization,chloritization,carbonatation,pyritization and argillation.The hematitization,albitization,carbonatation,chloritization and argillation are most closely correlated with the uranium mineralization.The NE trending fault structure zone(QFv)is the main ore conducting structure.The NNE and NE trending secondary fractures are main ore-hosting structures.Homogenization temperature of early-stage ore-forming fluid of Yangjiaonao uranium deposit is 149-317?.The average temperature is 228.5 ?.The salinity of ore-forming fluid is from 6.6 to 12.8wt%NaCl with 9.4wt%in average.Homogenization temperature of ore-forming fluid within the principal metallogenic epoch is from 169 to 230? with 196?in average,and the salinity of this period is from 6.3 to 9.9wt%NaCl with 7.5wt%NaCl in average.During the late metallogenic stage,the temperature is from 119 to 215? with 183.6? in average,and the salinity is from 5.9 to 9.9wt%NaCl with 7.2wt%NaCl in average.Homogenization temperature and salinity of ore-forming fluid are trending down from the early to principal to late metallogenic stage.The ore-forming fluid is of medium-low temperature and low salinity.During the early metallogenic stage,the 8 13CPDB of calcite is from-5.0‰ to-6.4‰with-5.8‰ in average,and the 81 Osmow is from 9.5‰ to 10.2‰ with 9.9‰ in average.During the principal metallogenic stage,the ?1 CPDB is from-7.3‰ to-8.2‰ with-7.7‰ in average,and the ?18OSMOW is from 10.6‰ to 12.0‰ with 12.4‰ in average.At the late metallogenic stage,the ?13CPDB is from-9.1‰ to-9.5‰with-9.3‰ in average,and the?18OSMOW is from 10.6‰ to 12.0‰ with 11.5‰ in average.The carbon and oxygen isotope composition of calcite indicates that the CO2,mineralizer of the deposit,is from the mantle degassing due to the crustal and lithospheric extension.The metallogenic model is established in this paper.The formation of the Yangjiaonao uranium deposit has been divided into three stages:? Emplacement of granitic magma:The main bodies of granite were formed after the emplacement of granitic magma during the middle of Indo-Chinese epoch,which are also the main source rocks of the deposit.? Pre-enrichment of uranium:Pre-enrichment of uranium occurred when the granitic magma was emplaced again into the early rock bodies during the early Yanshanian epoch.? Uranium mineralization:The uranium is continuously extracted from source rocks such as granites during migration of ore-bearing hydrothermal solution through the structural fissures.The deposition and enrichment of uranium proceeded when physicochemical conditions(e.g.temperature and pressure)changed and geochemical barriers formed.