Chronological And Geochemical Characteristics Of The Parent Rock Of The Huashan Ion Adsorption Ree Deposit,Guangxi

Granite is one of the most important ore-forming parent rocks of ion-adsorption type rare earth deposits.It is ubiquitous in various periods of the Earth’s evolution.However,not all granites in all periods have the metallogenic potential of ion-adsorbed rare earth deposits.Ionadsorbed rare earth deposits in South China are mainly related to Yanshanian granites.At present,the understanding of the relationship between the evolution of granitic magma and the formation of ion-adsorbed rare earth deposits is still unclear,which restricts our in-depth understanding of the metallogenic mechanism of ion-adsorbed rare earth deposits.In this paper,the parent rock of ion-adsorption type rare earth ore in Huashan area of northeastern Guangxi is selected as the research object,and the petrology,chronology,element geochemistry and rare earth mineralogy are studied.The main progress is as following.1.Zircon U-Pb geochronology study has shown that the formation age of Huashan granite in northeastern Guangxi is mainly 160 Ma ～ 159 Ma,which is the product of late Jurassic magmatic activity.2.The study of element geochemistry has shown that the ore-forming parent rock is characterized by high silicon,alkali,and potassium,and low phosphorus and calcium,belonging to high potassium calc-alkaline and peraluminous rock.They are enrichment in rare earth elements,and have high light rare earth element contents.They show obviously negative Eu anomalies,and generally have similar geochemical characteristics to those of highly differentiated A-type granite.These data indicate that the granite formed in a transitional tectonic environment of post-collision to intraplate extension.3.The study of rare earth mineralogy has shown that the samples are rich in rare earth minerals,especially bastnaesite and thorium,and the total amount of bastnaesite rare earth oxides is 73.8 % ～ 88.8 %;the total amount of rare earth oxides in thorite is 75.1 % ～ 78.8 %,which provide materials for the formation of ion-adsorption rare earth ore.4.The fractional crystallization of allanite,monazite,plagioclase and potassium feldspar during the evolution of granitic magma can affect the migration and enrichment of rare earth elements.High degree of fractional crystallization may be beneficial to the formation of ionadsorption rare earth ore.