The Geochemical Characteristics And Genesis Of Guangxi 375 Uranium Deposit

375 Uranium deposit is the largest uranium deposit which were found in Shiwandashan basin of Guangxi,also is the only uranium deposits that founded in Jurassic formation of uranium-productive basin in southern China.The ore-bearing layers are stability,and the grade of ore are higher.The study to Characteristics of the ore deposit and genesis of mineral deposit,not only have a great significance to the investigation and research on uranium resource of Shiwandashan basin,but also has very important theoretical and practical significance to the exploration of sandstone type uranium deposit in south China.In this paper,by studying the geological and geochemical characteristics of 375 uranium deposit which based on the basis of predecessors'information collection,field geological survey and data compilation and comprehensive study,to reveal the source of ore-forming materials,fluid source of ore deposits,and discuss the genesis of ore deposit.the result is as follows:?1?375 Uranium deposit is located in southeast side of northern section in Shiwandashan basin,the mining area by the south east to north west emerges Jurassic?J?and the strata of lower cretaceous?K₂x?in turn.There are two main uranium mineralization horizon inside the Deposit:in the upper of the Nadang group?J₂n³?and Dongli group?J₃d?.The ore-bearing bed mainly existed in the rock series of Jurassic that the color is light,and the roof and floor of the rock series that the color is light are purple-red mudstone;the occurrence between Ore body and sand body with light color are basic accordance.Be located in the axis of the fold which is in the upper of the"S"and its nearby upper and lower limb on the structure,mainly on the upper wing.Uranium mineralization is closely related to the formation and fold and fault in space.?2?By comparing the characteristics of constant element samples with different lithologic,showed that SiO₂ content is dominate in all the kinds of sample,Fe₂O₃/FeO numerical indication environmental form is partial oxidation;Through the analysis of the correlation element,Fe₂O₃ and MgO,TiO₂ has highly positive correlation,to a certain extent indicate matter source related to the magmatic rocks.?3?Through the microelement analysis,surrounding rock,ore and lean ore with the same change trend,the change of the enrichment coefficient and element enrichment and loss of different samples instructed that ore with the same source accompany with the later hydrothermal superimposition reformation at the same time.V/?V+Ni?ratio analysis showed that metallogenic environment is anaerobic.Analyses of rare earth elements,?REE of rich ore is lower than the surrounding rock and mineralization rocks,and?REE of the lean ore almost higher than the surrounding rock of the rare earth content,through Sm-Nd and La/Yb-REE geochemical discrimination diagram of rare earth elements,sedimentary clastic substance may be derived from granite.?4?The analysis of calcite shows that there are three periods of calcite?horizontal,vertical and inclined occurrence?at least,reflect the thermal fluid activity at least three times;the characteristics of carbon and oxygen isotope in calcite show that vein fluid of calcite part comes from the deep crust,also may come from the dissolution of carbonate rocks of marine sediment,shows that the diversity of the sources of ore-forming fluid.Through the sulfur isotope found that sulfur isotope is biogenic,and account for the organic matter plays a certain role to Uranium metallogenic.?5?Synthesize the former data,the metallogenic time of 375 uranium deposit respectively are 113,61,51,38Ma,indicated that the deposit is multi-stages mineralization,especially the later hydrothermal superimposition effect has important role.?6?Deposit genetic model is established.Through comprehensive study,considered that the ore-bearing stratum of 375 uranium deposit is sand mud interbedding lithologic combination that formed under the alternating effect of dry-semi-arid environment action,and enriched in the stages of sedimentary diagenesis;then under the action of redox in epigenesis stage,oxygen-enriched atmosphere precipitation leaching the uranium in stratum or rich uranium geological body into the sand body,in the process of fluid migration,the hexavalent uranium has been restored tetravalent uranium by reduction of components in the stratum,formed the uranium deposit of oxidation zone type in the redox transitional zone;In Himalayan period,under the influence of structure and fluid effect,deep fluid along the tectonic up constantly,and in the process of migration continuously extract uranium and superimposed on early ore body,form the industrial uranium deposit with high grade of ore.