| Qianjiadian sandstone-type uranium deposit is located in Yaojia Formation of the upper Cretaceous,southwest of the Songliao Basin.Based on the microscopy identification,electron microprobe analysis and geochemical tests,the paper did a deeper and more systematic study on the ore deposit geology.Compared the characteristics of geochemical changes in the samples of the ore bearing greywacke,mineralized greywacke and greywacke-type uranium ores,the regularity of uranium mineralization is explored and discussed.Electron microprobe analysis is used to determine the uranium occurrence in the area,finally,this paper expounded and summaried the genesis of ore deposits and metallogenic model.The composition of sand bodies in the target layer is complex.The content of fine ore-bearing debris is more than 50%,and the content of detritus is between 25% and 35%,mainly composed of uranium-rich materials,such as granite,siliceous rock,andesite,syenite and etc.The three types of samples' Si O2/Al2O3 were 6.19,7.78 and 7.53,which indicates that the maturity of the sandstone in the Yaojia Formation in this area was low,consistent with the microscopic identification results.It was determined that the ore-bearing host rock type was fine-medium grained feldspar lithic greywacke.The three types of samples' K2O/Na2 O were 1.64,1.66 and 1.68,with a significant potassium-rich feature,indicating that the source area developed weakly alkaline granitic rocks.Target sandbody mainly developd epigenetic hydrothermal carbonation,kaolinization,pyritization,epigenetic iron oxides,baritization,local hydrocarbon alteration and uranium mineralization.According to the relationship with uranium metallogenesis,the mineralization causes are divided into water-rock interaction,oil-gas reduction and alteration,and acid clay alteration.Based on the evolution sequence of mineralization alteration in the mineralization process,it was assumed that the mineralizing physical-chemical condition gradually changed from the acidic oxidation condition to the alkaline reduction condition in the process of repeated alternation.In the study of trace elements,uranium ore sample' U showed some correlation with Sc,Cr,Co,Ni,Cu,Ga,Rb,Y,Zr,Nb,Cs and Ba.The elements with relatively good correlation are Ba,Rb,Ga,and the correlation coefficient is greater than 0.5.Among these elements,the correlation between U and Ba is the best,and the correlation coefficient is as high as 0.842,the uranium ore samples of which are obviously higher than the samples of mineralized greywacke and ore bearing greywacke,associated with intense water-rock interactions.The elements with poor correlation are V,Zn,Sr,Pb,Th,and the correlation coefficient is less than 0.1.The three types of samples of the ore bearing greywacke,mineralized greywacke and greywacke-type uranium ores have significant differences in LREE and HREE in ore bearing sandstones.The average ?REE values are 120.73×10-6?116.44×10-6?153.44×10-6,the average LREE values are 104.78×10-6?105.89×10-6?137.56×10-6,and the average HREE values are 12.09×10-6?14.84×10-6?15.88×10-6,respectively.Microscope and electron probe analysis showed that most of the uranium in Qianjiadian sandstone-type uranium deposit existed in an adsorbed state,and independent minerals such as bituminous uranium ore and uranium ore were present occasionally.The adsorption state of uranium was often coexisted or symbiotic with pyrite,calcite,and clay,oil spots,etc.This paper summarized the deposit geology and geochemical characteristics of Qianjiadian sandstone-type uranium deposit and generalized the metallogenic model as a four-stage model of“sedimentary preconcentration-interlayer infiltration-mineralized transformation and enriched metallogeny-oil-gas reduction and ore protection.”... |
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