Study On The Mineralization Rule And Potential Evaluation Of Granite-type Ion-adsorption Rare Earth Ore

As an indispensable key element in the world’s cutting-edge technology and national defense construction,rare earth has long been an important strategic resource.In addition to the Baiyun Ebo ultra-large rare earth mine,the most remarkable is the ion adsorption rare earth ore in China.It has been half a century since the discovery of ion-adsorbed rare earth deposits.Chinese scholars have done a lot of research on this kind of deposits and accumulated a lot of data.It is expected to summarize the characteristics of ore-forming parent rock by using big data analysis technology.In recent years,the discovery of this deposits in the’high altitude’area of Yunnan has broken the tradition that it is difficult to find ion-adsorbed rare earth deposits above 1000m altitude,and has broken the previous external ore-forming law.Therefore,it is necessary to summarize the exogenic ore conditions of ion adsorption type rare earth ore.At present,the demand for rare earth ore is increasing rapidly,and the mining degree of ion adsorption rare earth ore resources in Yunnan is low,so it is necessary to evaluate the metallogenic potential of Yunnan.This paper summarizes the age,occurrence,lithology,mineral and rock geochemical data of 57 granite ion-adsorbed rare earth ore parent rocks in China,analyzes the characteristics of light（LREE）and heavy rare earth（HREE）parent rocks,and discusses the geochemical behavior of rare earth elements in granitic magma during diagenesis and its ore-indicating significance.Secondly,this paper uses GIS technology to quantitatively analyze the geomorphic feature of 22 rare earth deposits based on digital elevation model（DEM）,summarizes the geomorphological conditions of ion-adsorbed rare earth deposits in the’high altitude’area of Yunnan,then analyzes the geomorphological characteristics of typical deposits.Based on the metallogenic regularity of ion-adsorbed rare earth deposits summarized above,we predict the metallogenic potential of ion-adsorbed rare earth deposits in Yunnan by analytic hierarchy process and entropy method using the landform date,geochemistry date and distribution data of granite.The main results of this paper are as follows:（1）HREE type rock mass is formed in highly fractionated granite,while LREE type rock mass has relatively low differential degree;The alteration in the late magmatic hydrothermal stage played a key role in the enrichment of rare earth elements and the formation of weathering minerals in the parent rock of the deposit（especially HREE type）;The contents of 35 geochemical elements were analyzed by correlation analysis,cluster analysis and factor analysis.We find that Zr is closely related to light rare earth elements such as La,Ce,Pr,Nd and Eu,and K₂O,Mg O,Ta and Hf are closely related to rare earth elements such as Sm,Dy,Lu and Tm.It means that potassium metasomatism and chloritization are very important for the formation of heavy rare earth minerals,and the ratio of Zr/Hf is related to the ratio of LREE/HREE.（2）Favorable landforms for mineralization in Yunnan are medium-elevation slopes,steep slopes of hills and small undulating mountains.The deposits are mostly developed on the southern slopes without strong erosion.The deposits are distributed in the subtropical climate zone.Elevation is not the main controlling factor for the development of deposits.Slope is the basic topographic factor affecting the development of deposits.Ore are mostly form in the relatively flat terrain,low degree of surface erosion of the ridge,the mountainside.Due to the strong erosion of water,the foot of the mountain,especially in the longer gully,is not conducive to the enrichment of rare earth elements.（3）We predict the ore-forming potential of ion-adsorbed rare earth deposits in Yunnan based on analytic hierarchy process and entropy method.Validation of the model according to ROC curve shows that the prediction effect of entropy method is slightly higher than that of analytic hierarchy process.The prediction areas of ion-adsorption type rare earth deposits in Yunnan are mostly distributed around the known ore,but they also have ore-forming potential in Tengchong,Yingjiang,Longling,Ruili,Changning,Fengqing,Yunxian,Lvchun,Menghai,Jianshui and Zhenyuan Yi Hani Lahu Autonomous County,which are worthy of further exploration.