In recent years,the close relationship between uranium and Ti-Fe oxides in the sandstonetype uranium deposits has been extensively recognized.However,the altered characteristics of ilmenite and its relationship with u...In recent years,the close relationship between uranium and Ti-Fe oxides in the sandstonetype uranium deposits has been extensively recognized.However,the altered characteristics of ilmenite and its relationship with uranium enrichment still remain unclear.With this paper based on heavymineral sorting of uranium ore selected from the Tarangaole-Nalinggou deposit in the northeastern Ordos Basin,electron probe,backscattering image,energy spectrum and scanning electron microscopy were systematically performed.The ilmenite in the sandstone can be divided into four groups,including unaltered,weakly altered,moderately altered,and strongly altered ilmenite.The alteration of ilmenite in uranium ores is notably more intense than that of the surrounding rocks.In addition,weakly,moderately,and strongly altered ilmenite associated with uranium minerals in uranium ores demonstrate that the more intensity ilmenite altered,the closer its relationship with uranium minerals is.The ilmenite has likely been somewhat altered before mineralization,and the alteration intensifies by later exposure related to an oxygencontaining fluid.The alteration mechanism comprises a process of competitive diffusion between Fe^(2+)and O_(2)-ions.In the early stage,Fe ions was mainly diffused on the particle surface.Subsequently,diffusion of O ions into the particles began to be dominate.Most of the leached iron is stripped or carried away by fluid.In an alkaline and reductive environment,the remaining iron is reduced to form the surrounding pyrite,and TiO_(2)in a form of titanium sol recrystallizes(i.e.,anatase).Backscattering images show that uranium and altered ilmenite are close in space.Coffinite is often distributed along the edges of altered ilmenite as burrs in shape.Colloidal or knitted coffinite associated with anatase is formed in the voids of altered ilmenite.The chemical composition of altered ilmenite varies considerably from the core to edge,and the mineral assemblage sequence is from girdle with ilmenite,to leucosphenite,to anatase,and to coffinite.There is no brannerite that is symbiotic with altered ilmenite.It is considered to be a uranium-containing titanium mineral aggregate caused by the reduction and adsorption of uranium.As the altered product of ilmenite,TiO_(2)is an aggregation agent,increasing the concentration of uranium by adsorption.Together with Fe^(2+)and S_(2)-in secondary pyrite,this aggregate creates a uranium-rich environment in the microzone for the formation of coffinite.Therefore,the alteration of ilmenite plays a geochemical role in the processes of sedimentary,diagenesis and mineralization,in which Fe is removed,Ti is enriched,and U is adsorbed and reduced.展开更多
Carbonaceous debris(CD) is widely disseminated within sandstones in the Shuanglong uranium deposit,southern Ordos Basin,and is the dominant enrichment agent for uranium precipitation.The occurrence and chemical compos...Carbonaceous debris(CD) is widely disseminated within sandstones in the Shuanglong uranium deposit,southern Ordos Basin,and is the dominant enrichment agent for uranium precipitation.The occurrence and chemical composition of uranium minerals within CD were investigated by using scanning electron microscope and electron microprobe analyses.The results show that uranium minerals mostly occur in cell pores in the forms of fructus aurantia and concentric band structure.Pitchblende and coffinite are the main uranium minerals,and the former is dominant.According to the crystal morphology and composition of trace elements of uranium minerals,uranium precipitation on the pores is grouped into two periods,orderly Ⅰ,Ⅱ.Moreover,the Ⅰ period is further divided into two sub-period,orderly Ⅰ_(1),Ⅰ_(2).Moreover,askew sphere uranium minerals could indicate fluid migration.Under certain geological environment condition,uranium is unevenly adsorbed on the surface of the pore by the Van der Waals(i.e.,Ⅰ_(1) period),and then is precipitated towards to the center of the pore until the whole pore is filled up with uranium minerals by complicated process such as microorganism activities(i.e.,Ⅰ_(2),Ⅱ period).It will provide some guidance for studying the metallogenic environment and genesis of sandstone-type uranium deposit.展开更多
基金financially supported by projects under the National Key Research and Development Program of China(No.2018YFC0604200)the Open Fund Project of State Key Laboratory of Nuclear Resources and Environment (No.2020NRE10)+3 种基金the National Key Infrastructure Development Plan (No.2015CB453006)the China Geological Survey (Nos.DD20190119,DD20221678)the International Geoscience Programme (No.IGCP-675)the National Nature Science Foundation of China (No.92162212)
文摘In recent years,the close relationship between uranium and Ti-Fe oxides in the sandstonetype uranium deposits has been extensively recognized.However,the altered characteristics of ilmenite and its relationship with uranium enrichment still remain unclear.With this paper based on heavymineral sorting of uranium ore selected from the Tarangaole-Nalinggou deposit in the northeastern Ordos Basin,electron probe,backscattering image,energy spectrum and scanning electron microscopy were systematically performed.The ilmenite in the sandstone can be divided into four groups,including unaltered,weakly altered,moderately altered,and strongly altered ilmenite.The alteration of ilmenite in uranium ores is notably more intense than that of the surrounding rocks.In addition,weakly,moderately,and strongly altered ilmenite associated with uranium minerals in uranium ores demonstrate that the more intensity ilmenite altered,the closer its relationship with uranium minerals is.The ilmenite has likely been somewhat altered before mineralization,and the alteration intensifies by later exposure related to an oxygencontaining fluid.The alteration mechanism comprises a process of competitive diffusion between Fe^(2+)and O_(2)-ions.In the early stage,Fe ions was mainly diffused on the particle surface.Subsequently,diffusion of O ions into the particles began to be dominate.Most of the leached iron is stripped or carried away by fluid.In an alkaline and reductive environment,the remaining iron is reduced to form the surrounding pyrite,and TiO_(2)in a form of titanium sol recrystallizes(i.e.,anatase).Backscattering images show that uranium and altered ilmenite are close in space.Coffinite is often distributed along the edges of altered ilmenite as burrs in shape.Colloidal or knitted coffinite associated with anatase is formed in the voids of altered ilmenite.The chemical composition of altered ilmenite varies considerably from the core to edge,and the mineral assemblage sequence is from girdle with ilmenite,to leucosphenite,to anatase,and to coffinite.There is no brannerite that is symbiotic with altered ilmenite.It is considered to be a uranium-containing titanium mineral aggregate caused by the reduction and adsorption of uranium.As the altered product of ilmenite,TiO_(2)is an aggregation agent,increasing the concentration of uranium by adsorption.Together with Fe^(2+)and S_(2)-in secondary pyrite,this aggregate creates a uranium-rich environment in the microzone for the formation of coffinite.Therefore,the alteration of ilmenite plays a geochemical role in the processes of sedimentary,diagenesis and mineralization,in which Fe is removed,Ti is enriched,and U is adsorbed and reduced.
基金supported by the China Postdoctoral Science Foundation (No.2021M703001)Fundamental Research Funds for the Central Universities,China University of Geosciences (Wuhan) (No.G1323521101)+3 种基金open fund of State Key Laboratory of Nuclear Resources and Environment (East China University of Technology) (No.2022NRE02)open fund of Key Laboratory of Tectonics and Petroleum Resources (China University of Geosciences (Wuhan)),Ministry of Education (No.TPR2019-08)Fund of Outstanding Talents in Discipline of China University of Geosciences (Wuhan) (No.102162301192664)support from SINO Shaanxi Industry Group in this study。
文摘Carbonaceous debris(CD) is widely disseminated within sandstones in the Shuanglong uranium deposit,southern Ordos Basin,and is the dominant enrichment agent for uranium precipitation.The occurrence and chemical composition of uranium minerals within CD were investigated by using scanning electron microscope and electron microprobe analyses.The results show that uranium minerals mostly occur in cell pores in the forms of fructus aurantia and concentric band structure.Pitchblende and coffinite are the main uranium minerals,and the former is dominant.According to the crystal morphology and composition of trace elements of uranium minerals,uranium precipitation on the pores is grouped into two periods,orderly Ⅰ,Ⅱ.Moreover,the Ⅰ period is further divided into two sub-period,orderly Ⅰ_(1),Ⅰ_(2).Moreover,askew sphere uranium minerals could indicate fluid migration.Under certain geological environment condition,uranium is unevenly adsorbed on the surface of the pore by the Van der Waals(i.e.,Ⅰ_(1) period),and then is precipitated towards to the center of the pore until the whole pore is filled up with uranium minerals by complicated process such as microorganism activities(i.e.,Ⅰ_(2),Ⅱ period).It will provide some guidance for studying the metallogenic environment and genesis of sandstone-type uranium deposit.
