Uranium Element Occurrence State And Provenance Analysis Of Bayanwula Uranium Deposit In Erlian Basin

This article takes the sandstone of the Saihan Formation in Bayanwula uranium deposit,Inner Mongolia,as the research object.Through observation using hand specimens,optical microscope,scanning electron microscope,etc.,it investigated the lithofacies and structural characteristics of the Saihan Formation sandstone.Based on this,through major and trace element geochemical analysis,it revealed the material sources of the Saihan Formation sandstone and the structural characteristics of the material sources area,and discussed the paleoclimatic characteristics during diagenesis and mineralization.By means of detrital zircon U-Pb dating,the time of mineralization and the possible provenance area were determined.Meanwhile,combined with the regional geological background,it explored the mineralization environment and process of Bayanwula uranium deposit.Through the above research,the following conclusions can be drawn:（1）Uranium is mostly produced in the form of irregular nuggets or adsorbates,growing in the internal cavities of minerals such as quartz,feldspar,and mica or along the interstitial cracks between minerals.It commonly occurs in association with pyrite,clay minerals,and organic matter.The types of uranium ores are mainly uranium-quartz and uranium-titanium oxides.Uranium in ores exists in the form of adsorbates or independent uranium minerals.（2）The mineralized sandstones in the study area are mainly rich in quartz content feldspar sandstones,which have poor rock sorting and low component and structural maturity,indicating that the clasts have not undergone long-distance transportation and suggesting that the mineralized sandstones were formed by near-source accumulation.The Chemical Index of Alteration（CIA）value for rock alteration ranges from 60.13 to 79.40,averaging at 65.19.This suggests that the Sandstone in study area has undergone a low degree of weathering,indicating that the geochemical composition of the research area’s sandstone is mainly controlled by its source region,which meets the conditions for the provenance discussion.（3）The F₁-F₂ major element discriminant function diagram,La/Th-Hf diagram,and Rb-K₂O diagram show that the data points for the Saihan Formation sandstone are all within the range of the source area for felsic igneous rock and neutral volcanic rocks,suggesting that its source rock is of intermediate-acidic igneous rocks.The U-Pb age of detrital zircons in the Saihan Formation sandstone shows two peak value,one at 294-320Ma and the other at209-230Ma.Combining previous studies of the exposed rock masses at the north and south boundaries of the study area,it can be inferred that the main sources of the study area are the diorite of the Caiyuanchao blocks,Ashaha blocks,Baoerhan lamasery blocks and other areas in the Sunite uplift,as well as the intermediate-acidic igneous rocks in the Bayinwula,Bayinbaolige group volcano-sedimentary strata,Baiyinlaogao group,Chaganaobao-Honggeer-Alatanbaolage and Hadatu Temple areas.（4）Analysis of the B content of microelements in the Sahain Formation sandstone of the Bayanwula Uranium Deposit and the n（Sr）/n（Ba）value indicate that the early sedimentary environment was a freshwater environment with a warm and humid climate,conducive to the Formation of pyrite and organic matter,providing a good environment for the pre-uranium enrichment of the stratum.Analysis of the n（V）/n（V+Ni）andδU as well as the enrichment analysis of the redox sensitive elements U and Mo,indicate that the water at the time of sandstone deposition had low oxygen content and was in a reducing environment.The comprehensive indicators of n（Sr）/n（Cu）and w（Si O₂）/w（Al₂O₃）that it was in a dry and hot climate during the late stage of sedimentation,which is conducive to the activation and migration of uranium in the source area and the Formation of oxygen-and uranium-bearing fluids,providing important conditions for the mineralization of the Bayanwula Uranium Deposit.Based on the comprehensive research of this article,the source area of the Bayanwula Uranium Deposit is believed to be composed of acidic igneous rocks such as Bayanwula and Bayinbaolige Group volcanics and sediments,Baiyinlaogao group,Chaganaobao-Honggeer-Alatanbaolage and Hadatu Temple areas.,etc.in Bayinbaolige uplift and Caiyuanchao blocks,Asaha blocks,and Baoerhan Lama temple rock setle rock series in Sunite Uplift.The early warm and humid sedimentary environment provided a good environment for the pre-uranium enrichment of the stratigraphy,while the later arid-semiarid environment was conducive to the activation and migration of uranium in the source area and the Formation of oxygen-and uranium-bearing fluids,providing necessary conditions for the Formation of uranium deposits.