| Danfeng area is located in Caledonian fold belt in Southern margin of North China Platform, belongs to the northern Qinling uraninium belt of Qinling-Dabie uraninium metallogenic province of Qinling-Qilian-Kulun uranium metallogenic domain, which is the most important pegmatite-type uraninium deposit producing area in China. Based on the previous studies, microscope, scanning electron microscopy(SEM) and electron probe microanalyser(EPMA) had been employed to study the characteristics of ore bodies,uranium metallogenic dating, genesis of ore-bearing pegmatite vein etc in this study..The main understanding been made as fellows:Ore bodies are mainly occur as veins and strongly controlled by pegmatite veins.Forthmore some pegmatite veins itself are ore bodies. Biotite pegmatite is the main host-rock, gangue minerals are potassium feldspar, quartz and biorite et al. The ore minerals constract by idiomorphic or hypidiomorphic granular uraninite, coffinite,uranotile and other secondary uranium minerals. Uranium-bearing accessory minerals include zircon, apatite, monazite, pyrite, chalcopyrite, hematite, etc.Uraninite is mainly consisted of the oxides of U, Th, and Pb. Elements of Y, Ca, Si,Na, Fe, Mg, Hf, Zr, P and Mn are subordinate. The content of UO2 of Uraninite from Guangshigou uranium deposit and Chenjiazhuang uranium deposit is high and variable in82.39~89.40wt%(average value for 86.65wt%) and 84.02~90.47wt%(average value for87.58wt%), and the average content of ThO2 is 2.37wt% and 2.71wt%, respectively. The oxides of Si, Ca, Al, Mg and Fe are generally below 0.5wt%. The radios of U/Th is mainly variable in 27.69~41.91(average value for 36.4) and 24.94~34.30(average value for 28.74),respectively, but some radios of U/Th of uraninite in Chenjiazhuang uranium deposit is variable in 63.34~66.82, which indicates that the deposit experienced two mineralization stages, or a longer metallogenic process happened in the deposit.The ore is characterized by disseminated structure and massive structure;idiomorphic or hypidiomorphic granular texture, coterminal texture, inclusion texture,poikilitic texture and heterogranular texture. Secondly structures contain vienlet structure,metasomatic dissolution texture, reaction rim texture metasomatic texture etc.Alteration halos most commonly occur around uraninite, which is primarily consisted of pyrite, chlorite and clay minerals, secondly(Mg,Fe)-oxides, carbonates(calcite) and other minerals in Guangshigou uranium deposit.And pyrite or chlorite rim often surrounds the uraninite. But Fe-oxides, Ti-oxides,(Mg,Fe)-oxides, and clay minerals mainly consist the alteration halos, secondly xenomorphic granular hematite, magnetite, rutile, calcite, d pyrite and chalcopyrite. Besides, chalcopyrite and calcite rim is visible.This paper has studied the metallogenic age of uraninite in Chenjiazhuag uranium deposit with electron microprobe dating method. The ore-forming age is 401.0±10Ma and377.6±7.6Ma, respectively, which is perfectly identical to the previous zircon U-Pb isochron age and indicates that the deposit had experienced a longer mineralization process.The study of this paper shows that the uranium mineraliztion is controlled by primitive magma crystallization differentiation in Guangshigou and Chenjiazhuang uranium ore-field, furthermore slightly experienced superimposition and alteration mineralization for the affects of the later tectonic stress, hydro-thermal action and supergene oxidation. |
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