| The northern Ordos Basin have discovered a series of large sandstone-type uranium deposits,and it is also an important place of production of in-situ leachable sandstone-type uranium deposits in China.From east to west,there are Nalinggou uranium deposit,Dongsheng uranium deposit,Hangjinqi uranium deposit and Daying uranium deposit in the northern Ordos Basin.With the researching of uranium exploration in Ordos Basin,new prospective areas are discovered constantly,meanwhile,people have found the ideal metallogenic horizons and uranium mineralization of sandstone-type uranium in bottom member of middle jurassic Zhiluo formation located in Bayin Qinggeli region of western Daying uranium deposit in The northern Ordos Basin,which shows favorable prospecting potential in the Bayin Qinggeli region.This paper is guided by Petrology,Mineralogy and metallogenic theory of sandstone-type uranium deposits,using a variety of analytical and testing methods such as light microscopy,LA-MC-ICPMS,radiography and electron probe,systematically studying Petrology,provenance,diagenetic and metallogenic sequence,detrital zircon,U-Pb isotope dating,alpha etching tracks and occurrence state of uranium minerals,combined with characteristics of interlayer oxidation zone and thermal fluid revamping to discuss uranium metallogenic mechanism in Bayin Qinggeli region in order to provide a certain foundation for further ore prospecting.This paper has studied types and occurrence state of uranium minerals in uranium mineralization by means of analyses of alpha etching tracks and electron probe,which indicates the main provenances of sandstones in bottom member of Zhiluo formation located in Bayin Qinggeli region may come from TTG gneiss and granulite from Daqingshan-Wula mountain and Jining area in the northern Bayingqingli region,in addition,the northern mixtite and mafic dyke swarms in the Central orogenic belt of the North China craton and the Yinshan Block formed in the Paleozoic Era magmatic rock.The types and occurrence state of uranium minerals in uranium mineralization have been studied by means of alpha etching track and electron probe,and the result reveals uranium minerals are mainly in the forms of adsorbed state and independent uranium minerals,it is mainly coffinites,a little of brannerites and uranothorites,which are closely related to biotites,pyrites and titanium-bearing ores.The uranium enrichment in the study area was mainly formed in sufficient reducing environment,having a bearing on abundant reducer such as the organic matter and pyrite.The results of electron probe show that the content of Y and Th is higher in some coffinite minerals,which shoulid be formed in hydrothermal solution,meanwhile,the area also found brannerites with high Ti containing,which reveals enrichment of uranium and metallogenesis in the study area are related to later hydrothermal activity.According to observation under a microscope for standstone from Zhiluo formation,result indicates sandstone from target stratum has not been deeply buried,only experiencing stage A and stage B of early diagenesis in diagenetic stage,meanwhile,without going through the late diagenetic stage,it directly entered the stage of exodiagenesis and supergene metallogenesis,and also suffered effect of superposition and transformation from thermal fluid.Referring to other previous research,it is concluded that sandstone-type uranium deposits in Bayin Qinggeli region are controlled by the paleo-interlayer oxidation zone,and then affected by the effect of superposition and transformation from thermal fluid formed tabular(stratoid)orebody in the late stage.The metallogenic model mainly includes the stage of uranium preenrichment in sedimentary period,the metallogenic stage of paleo-interlayer oxidation zone and the metallogentic stage of superposition and transformation from thermal fluid. |
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