Metallogenic Tectonic Background Of Indosinian Ion Adsorption Type REE Deposits

The South China plate has experienced multiple tectonism,magmatism and mineralization events such as the Caledonian movement,the Indosinian movement,and the Yanshanian movement,forming a number of metallogenic belts and large-scale granites.Among them,the formation of ion adsorption-type REE deposit is mostly related to Yanshanian granite,whereas the Indosinian ion adsorption-type REE deposit has been rarely reported so far.In recent years,the prospecting work of ion adsorption-type REE deposit has delineated some prospecting target area of Indosinian ion adsorption-type REE deposit in southeastern Guangxi.In this paper,mineral petrology,zircon U-Pb geochronology,element geochemistry and rare earth mineral composition of Indosinian granite exposed in Qinfang area,southeastern Guangxi were studied.Combined with the previous data of ion adsorptiontype REE deposit,the metallogenic tectonic background of Indosinian ion adsorption-type REE deposit was discussed.This paper has made the following main research progress.1.The formation age of Indosinian granite in Qinfang area of southeastern Guangxi is concentrated at ～ 250 Ma,which is the product of Early Triassic magmatic activity.2.The Indosinian granite in southeastern Guangxi belongs to high-potassium calcalkaline peraluminous S-type granite,which shows the characteristics of high silicon potassium,poor magnesium calcium and low phosphorus titanium.The granite is rich in rare earth minerals such as sphene,apatite,monazite and yttrium phosphate.The rare earth elements show LREE enrichment,HREY relative loss,and Eu negative anomaly.It is relatively enriched in Th,Zr,Hf,U and Rb,and depleted in Ba,Nb,Ta,Sr,P and Ti.In general,it shows similar geochemical characteristics to the ore-forming parent rock of Yanshanian ion adsorption-type REE deposits in South China.3.The Indosinian granite in the Qinfang area of southeastern Guangxi is a product of partial melting of metamorphic argillaceous source rocks which heated by mantle sources.They had undergone fractional crystallization during the process of magma evolution.Their formation is likely related to the subduction of the Paleo-Tethyan Ocean.4.During the process of subduction between oceanic and continental crust,the addition of juvenile crustal materials and subduction sediments facilitates the formation of rare earth minerals in the parent rock,which in turn facilitates the formation of ion adsorption-type REE deposit.However,the granite formed by intracontinental orogeny may not be conducive to the formation of ion adsorption-type REE deposit due to the absence of subduction sediments and juvenile crustal materials.