Study On The Characteristics Of Uraninite And Its Radiohalo In The Uranium Deposits Of Danfeng Area

The Guangshigou pegmatite-type uranium deposit and the Chenjiazhuang pegmatitetype uranium deposit are typical pegmatite-type uranium deposits in the Danfeng area of China.The deposist are located in the eastern section of the North Qinling orogenic belt,between the Caichuan fault and the Shang-Dan fault.On the basis of previous research work,this paper focuses on the work of the uraninite,its co-occurring radioactive alteration halo,host minerals(biotite,feldspar),which are in the bearin-uraninite pluton.Polarized light microscopy,SEM,and EMPA were used to be on systems of mineralogical characteristics and analysis of chemical composition.Based on this,the characters of radioactive alteration halos and their formation processes were analyzed preliminarily.This paper presents the mineralogical characteristics of uraninite,radioactive alteration halo and their host minerals(feldspars and biotite)in the Guangshigou granite pegmatitetype uranium deposit and the Chenjiazhuang granite pegmatite-type uranium deposit in Danfeng.After conducting a comprehensive study,we obtained the following understanding:(1)The most abundant sites of uraninite are in primary quartz of the Guangshigou uranium deposit,and the quartz can preserve uraninite well.Uraninites in the uraniumproducing rocks are generally large and have the largest grain size for 1500 ?m in diameter;the most abundant sites of uraninite are in biotite of the Chenjiazhuang uranium deposit,where the uraninite occurs primarily.There contains more large-grained in the uraniumbearing rock.The maximum size is 500 ?m.(2)The uraninites in the Guangshigou uranium deposit symbiotically combine with quartz during the late diagenesis;the uraninites in Chenjiazhuang uranium deposit are biased towards the symbiotic association of diagenesis with biotite in the early diagenesis.(3)The alteration halos of uraninite in the uranium rock of Guangshigou are complex,with many minerals,such as chlorite,pyrite,hematite,zircon,uranium silicite,yttrium,uranyl thorium,apatite,etc.Chlorite which is in alterations halo is common;the composition of alteration halo in uranium deposits of Chenjiazhuang is complex with much mineral components,such as calcadian,rutile,ilmenite,brannerite,uranophane,pyrite,limonite,hematite,calcite,chlorite,monazite,zircon etc.Hematite in the alteration halo is common.The uranium deposits all have undergone retrofitting with fluids which cotains S and C.(4)The formation of alteration halos around uraninites mainly depends on the ?-decay of uraninites with destroying the structure of surrounding minerals,and the formed amorphous material is transformed by the later-stage fluid.