Research On Clay Minerals And Uranium Mineralization Of Sandstone-type Uranium Deposits In The Northeast Of Ordos Basin

The sandstone-type uranium deposit in the northeastern Ordos Basin has strong clay alteration and is closely related to uranium mineralization.In this paper,by means of principal element analysis,x-diffraction analysis,scanning electron microscopy observation,high resolution transmission electron microscopy observation and other means,combined with field geological data and laboratory experimental research,taking the characteristics of clay minerals and the occurrence state of uranium as the main line,the role of clay minerals in the process of uranium mineralization was systematically discussed.The characteristics of clay minerals in different uranium deposit areas and the plane distribution characteristics of clay minerals in the study area have been identified.The types,composition,morphological characteristics,vertical distribution,evolution process and the migration and removal laws of the evolution process elements in the typical uranium deposits are clarified.The occurrence state of uranium in the study area,the optimum conditions for adsorption of uranium by clay minerals and the optimum experimental conditions for reduction of uranium by clay minerals after reduction by anaerobic bacteria were ascertained.The relationship between montmorillonite and kaolinite and uranium mineralization was discussed.The high-resolution transmission electron microscopy was used to find out the way of chlorite adsorption of uranium.The main results and understanding are:?1?By analyzing the characteristics of clay minerals in outcrops and typical uranium deposits,the plane distribution characteristics of clay minerals in the study area are summarized.The content of montmorillonite increases from Nalinggou uranium deposit to Daying uranium deposit to Bayingqinggli uranium deposit,but the content of kaolinite shows the opposite trend.The content of montmorillonite and kaolinite is highly correlated and consistent with the trend map of plane distribution.The content of montmorillonite increases while the content of kaolinite decreases.The clay minerals in the study area are mainly montmorillonite and kaolinite,which indicates that the two clay minerals are closely related to uranium mineralization.?2?The vertical distribution of clay minerals in single pore and typical profile is summarized.The clay minerals in the geochemical zones are mainly montmorillonite,followed by kaolinite,chlorite and illite.The total amount of clay minerals and chlorite content of sandstone in the green interlayer oxidation zone are the highest,which is also the main reason why the rocks are green.The content of kaolinite and illite is the highest in the uranium mineralization belt,and the content of montmorillonite is the lowest.?3?The microscopic characteristics of clay minerals and uranium minerals were identified.Montmorillonite is mainly produced in the form of honeycomb,honeycomb network,sheet mesh,flakes and a small amount of agglomerates.The kaolinite is in the form of a worm,and is partially produced in the form of a sheet of book and a plate-like aggregate.Chlorite is mainly produced in the form of needles,flowers,pompons and leaves.The uranium mineral particles are very small,and the uranium minerals are locally produced in large aggregates.The shapes are different,mainly showing intergranular grains,filaments,granules,granules,short rods and grains.Short columnar.It is often closely associated with organic matter,pyrite and clay minerals in the form of fine particles and aggregates.?4?The evolution law of clay minerals in the process of alteration and the migration and removal of elements during alteration are analyzed in detail.In the early stage of oxidative acidic alteration,feldspar was hydrolyzed to form kaolinite,which resulted in a significant increase in kaolinite content in sandstones of paleo-interlayer oxidation zone and uranium mineralization zone compared with sandstones of primary zone.In the weak alkaline alteration stage after oxidation stage,in the locally relatively acidic environment,montmorillonite transforms into kaolinite,resulting in a significant decrease in the content of montmorillonite and a significant increase in the content of kaolinite in the uranium mineralization zone.In the late stage of reducing weak alkaline alteration,Fe³⁺in sandstone of paleo-interlayer oxidation zone is reduced to Fe²⁺,and kaolinite can also be converted to chlorite in the presence of Fe²⁺.With titanium dioxide as inert element,compared with sandstone in primary zone,elements migrated from paleo-interlayer oxidation zone are Fe₂O₃,FeO,MgO and MnO,while elements migrated from paleo-interlayer oxidation zone are SiO₂,Al₂O₃,CaO,NaO,K₂O and P₂O₅;elements migrated from uranium mineralization zone are Fe₂O₃,FeO,CaO,Na₂O and MnO,while elements migrated from uranium mineralization zone are SiO₂,Al₂O₃,K₂O and MgO.?5?The optimum conditions for the adsorption of uranium by clay minerals and the optimal experimental conditions for the reduction of uranium by clay minerals after anaerobic reduction were discussed.With the prolongation of reaction time,the adsorption capacity of clay minerals will increase in a certain period of time,but eventually the adsorption equilibrium will be reached.Some clay minerals will also undergo desorption phenomenon,which will lead to the decrease of adsorption capacity.Too low or too high pH of the solution will affect the adsorption of uranium by clay minerals.In the solution with a certain concentration of initial uranium solution,increasing the amount of clay minerals can increase the total surface area and active sites of clay minerals,which is beneficial to the surface adsorption and ion exchange adsorption of uranyl ions by clay minerals,thereby increasing the clay minerals.Adsorption capacity.When the amount of clay minerals is constant,as the concentration of uranium solution increases,the adsorption of uranyl ions by clay minerals will gradually increase until saturation.As the temperature of the experimental group increases,the adsorption of uranyl ions by clay minerals increases.The montmorillonite content in the green interbedded oxidized zone is the highest,and the uranium concentration in the early strata is not high.The clay mineral plays an important role in the preconcentration of uranium.The clay reduced by anaerobic bacteria under weak acid conditions is more conducive to the process of reducing uranium.?6?The relationship between clay minerals and uranium mineralization has been explored.In the early stage of mineralization,namely the pre-enrichment stage,the concentration of uranium in acidic oxygen-bearing uranium-bearing water is not very high,and the pH condition is also conducive to the adsorption of uranium by montmorillonite.During the forward migration of oxygen-bearing uranium-bearing water,montmorillonite can adsorb uranyl ions in solution and play a preconcentration role for later uranium mineralization.In the uranium mineralization zone,the place with high uranium content is often the place with the highest kaolinite content,which can be used as a mineral to indicate the ore-bearing depth.At the same time,although the change of kaolinite content has limited influence on adsorption capacity,it can reflect the change of fluid environment.In the process of chloritization,not only the occurrence state of uranium in the original rock is changed,but also the uranium released from the process can be pre-enriched,which can provide some help for the later uranium mineralization.Chlorite is very easy to form organic clay complex with humic acid and other organic matter.During the process of fluid migration,with the change of physical and chemical properties of sand body,the external conditions of uranium hydrothermal solution change,and uranium precipitation is finally fixed by adsorption and reduction.