赣南大埠花岗岩体重稀土预富集机制OA

The Dabu granite pluton is located in the eastern section of the nearly E-W trending tectonic-magmatic belt in the Nanling Range.A world-class ion-adsorption type heavy rare earth element(HREE)deposit is developed in the pluton.At present,there is still controversy about the age of the main body of the Dabu pluton,and there is al-so a lack of systematic understanding of the initial enrichment mechanism of heavy rare earths.In this paper,the zircon U-Pb geochronology and whole rock geochemistry of the Dabu pluton were studied.The formation age of the main body of the Dabu pluton(biotite monzogranite)was(154.7±0.6)Ma,and the age of the complement(two-mica monzogranite)was(152.3±0.5)Ma,both of which were the products of early Yanshanian magmatic ac-tivity.Geochemical results show that the Dabu pluton is characterized by high silicon,rich alkali,poor iron and magnesium,relatively enriched Rb,Th,U,Ta,Pb elements and depleted Ba,Sr,P,Ti,Nb and other elements.The Zr/Hf(average 19.76)and Nb/Ta(average 5.23)ratios of the pluton are low,which belongs to the highly differ-entiated granite.With the crystallization and differentiation of magma,the Dabu pluton experienced the fractional crystallization of monazite,allanite and apatite,and the magmatic melt-fluid interaction gradually strengthened.HREE is increasingly enriched in the late two-mica monzogranite,which may be related to the fractional crystalli-zation of phosphorus-containing rare earth accessory minerals and the metasomatism of late F-rich fluids.The ear-ly-phase biotite granite(LREE/HREE ratio is low and rich in Y)and the late-phase two-mica granite or musco-vite granite of the highly fractionated granite are easy to form heavy rare earth ore after weathering.