The Geochemical Characteristics Of Phosphorus And Its Significance To Uranium Mineralization In Xiangshan Uranium Ore-Field

In Xiangshan uranium orefield,it is found that the phosphorus content in large uranium rich ore body is obviously increases,and P₂O₅is positively correlated with U,Th and REE.The geochemical characteristics,mineralogy and simulation experiments of P and apatite in different plastids in Xiangshan ore field were studied in this paper,the influences of P on the precipitation,migration and enrichment of U,Th and REE elements are analyed,and the characteristics of phosphorus in uranium ore and its significance for uranium mineralization were also explored.Firstly,the contents of P,U,Th and REE in various background rocks,weakly altered wall rocks,strongly altered near ore wall rocks,different grade ores,main rock forming minerals and their corresponded altered minerals were measured,by analysis and comparison,we can understand the characteristics and variation rules of these components in various geological bodies,and discuss the influence of P on the enrichment of U,Th,REE and other components in the process of diagenesis,alteration and mineralization.Secondly,the types,occurrence characteristics,structural morphology and geochemical characteristics of apatite associated with uranium in large uranium rich ore bodies were tested by electron microprobe and scanning electron microscope,studied the mineralogical characteristics of phosphorus and uranium in large uranium rich ore bodies and their relationship were studied.Finally,based on the previous research,the simulation experiments of P and U activation and apatite adsorption uranium precipitation were carried out,the migration law of P with U,Th,REE and other elements was studied to verify that apatite can adsorb U,REE and other precipitation enrichment;Combined with the previous results of mineralization temperature and age,the significance of phosphorus to mineralization in Xiangshan uranium deposit is analyzed.The results are as follows:(1)There is no significant difference in phosphorus content among all kinds of background rocks,but there is a great difference in U,Th and REE content.The average content of P₂O₅is 0.13%in metamorphic rocks,0.03%in porphyry lava and 0.11%in granite porphyry.The content of P₂O₅in the background is low as a whole,which is similar to that in metamorphic rocks and granite porphyry,and slightly higher than that in porphyry lava.The average content of U is 2.7×10^-6in metamorphic rocks,8.46×10^-6in porphyry lava and 5.85×10^-6in granite porphyry.The content of U all kinds of background rocks varies about three times,and the distribution of U content is porphyry lava>granite>metamorphic rock.During the evolution of porphyry lava and granite porphyry formed by the remelting of metamorphic rocks,U,Th and REE are obviously enriched,but the change of P₂O₅is not obvious.It is speculated that only U,Th and REE are obviously enriched during diagenesis in Xiangshan ore field,and no P₂O₅is enriched.(2)During mineralization,there is a nonlinear positive correlation between P₂O₅and U,Th,REE in the U mineralization.(1)Ore-containing section,From no alteration to near ore altered wall rock to ore body,P₂O₅and U,Th,REE increased gradually.(2)P₂O₅is positively correlated with U,Th,?REE,LREE and HREE,the higher the content of U,the more obvious the correlation between P₂O₅and these elements.In the ultra rich ore(uranium grade is higher than 1%),P₂O₅is obviously enriched with Th,?REE and HREE,which belongs to HREE enriched type,P₂O₅is positively correlated with U and other elements.(3)In porphyry and lava deposits,P₂O₅is positively correlated with U,Th,?REE,LREE and HREE.The content of P₂O₅in lava type deposit is higher than that in porphyry type deposit,so is the content of U.In Xiangshan ore field,the content of P₂O₅in uranium ore,rich or poor,is significantly higher than that in background rocks,and positively correlated with U,Th and REE,which is a good indicator of uranium mineralization and prospecting.(3)During the alteration,P₂O₅increases synchronously with U,Th and REE.It shows that P₂O₅can promote the activation and migration of these ore-forming components.The EPMA analysis of the alteration process of feldspar and mica in Xiangshan ore field shows that,generally,there is a nonlinear positive correlation between P₂O₅and U,Th in feldspar of different alteration degrees;in the process of feldspar alteration from sericite to chlorite,the content of U and Th increases,while the content of P₂O₅decreases.There is a nonlinear positive correlation between biotite P₂O₅with different alteration degrees and elements such as U and Th.The higher the REE content is,the more obvious the correlation is;during the alteration of biotite into chlorite,the content of U and Th increases,while the content of P₂O₅decreases.The activation and migration experiments show that P₂O₅,U,Th,?REE,LREE and HREE enter the liquid state from solid state under acidic conditions,The stronger the acidity is,the higher the proportion of entering the liquid state is.The proportion of phosphorus and uranium entering the liquid state increases again after superposition of oxidation conditions.The alteration process and activation migration experiment results all above show that phosphorus can promote the migration of U,Th and REE from solid to liquid in acidic hydrothermal environment..(4)P₂O₅is of great significance for uranium precipitation and enrichment in Xiangshan ore field to form large rich ore bodies,it is an indispensable factor for the formation of large uranium rich ore bodies in Xiangshan uranium orefield.(1)The apatite in Xiangshan uranium ore field is mainly fluorapatite,it can be roughly divided into two types:euhedral subhedral apatite and xenomorphic apatite.The former does not contain uranium minerals.Its grain size is generally large,the inclusions appear in groups,and the homogenization temperature is concentrated in 165-288?.Uranium minerals are mainly distributed in the surrounding or fractures in the form of stars or veinlets.It is composed of microcrystalline apatite with rough surface.The inclusions are small and few.The homogenization temperature is 233?,373?and 383?.Generally,there are granular or tiny star like uranium minerals in apatite.(2)Apatite can adsorb uranium in acidic condition,and the reaction can be spontaneous.No new mineral phases of U and P are formed after apatite adsorbs uranium.Uranium is amorphous adsorbed on apatite surface,mainly chemical adsorption,accompanied by physical adsorption.(3)Combined with the previous understanding that there are early and late metallogenic stages in Xiangshan,the significance of P₂O₅in the two stages of uranium precipitation metallogenesis is different.Combined with the previous understanding that there are early and late metallogenic stages in Xiangshan,the significance of P₂O₅in the two stages of uranium precipitation metallogenesis is different.The early metallogenic stage is(115±0.5)Ma,which is mainly in the late stage of porphyry formation.P₂O₅activates uranium and other metallogenic elements in acidic volcanic rocks and porphyry,resulting in low grade U ore and high hydrothermal temperature.The metallogenic temperature is about 310?,which is similar to the homogenization temperature of microcrystalline apatite inclusions 233?,373?and 383?,it is speculated that microcrystalline apatite was mainly formed in the early metallogenic stage.The late metallogenic stage is(98±8)Ma,which is also the formation stage of the red basin.It is mainly controlled by NE trending faults.The hydrothermal solution mainly comes from the basin water heated by deep faults after dehydration.P₂O₅can promote the activation and migration of uranium and other ore-forming components from the solid phase into the hydrothermal solution.The controlled Basin fault has a large amount of hydrothermal solution and a long time of action.The ore-forming temperature is about 220?,which is close to the homogenization temperature of medium and coarse-grained euhedral subhedral apatite inclusions from165?to 288?.The two mineralization periods can be formed separately,for example that,the characteristics of uranium mineralization in the early stage of Yunji deposit are obvious,rich in apatite and low grade of U.Two stage superimposed mineralization is a necessary condition for the formation of large and rich deposits in Xiangshan orefield,such as Shannan and Zoujiashan deposits.The main innovations of this paper are as follows:P₂O₅is positively correlated with U,Th and REE in uranium mineralization in Xiangshan orefield,P₂O₅is an important indicator for the mineralization and prospecting of rich uranium deposits.P₂O₅can promote U,Th and REE from solid phase to liquid phase in hydrothermal environment,P₂O₅plays an important role in promoting the activation and migration of uranium in the two stages of hydrothermal mineralization in Xiangshan,but there was no obvious correlation between P₂O₅and uranium in the diagenetic stage of metamorphic rock remelting.The adsorption and precipitation of apatite on uranium during the mineralization of Xiangshan uranium deposit also is results in the uranium enrichment.