GEOLOGICAL CHARACTERISTICS OF ION ADSORPTION TYPE RARE EARTH DEPOSITS IN THE HUOXIEMA PLUTON,NINGDU,SOUTHERN JIANGXI
The parent rocks of ion adsorption type rare earth deposits in the graniteweathering crust inHuoxiema area,Ningdu County,are mainly porphyritic biotite diorite and biotite diorite granite of different grain sizes,belonging to strongly peraluminous and highlyfractionated shoshonite-high-K calc-alkaline granite.The rare earth element distribution curve of which are inclined to the right in a"V"shape,enriched in large ion incompatible elements such as Rb,Th and K,and deficient in high field strength elements such as Ba,Sr,P,Ti,Nb and Ta.They were formed in an extensional tectonic background,similar to post-collisional granite.The source area of them was metamorphic mudstone,which went through magma self-metasomatism,hydrothermal alteration,and other endogenous mineralization,and formed easily oxidizable and decomposable rare earth minerals.After surface weathering and enrichment,the weathering crust ion adsorption type rare earth deposits were formed.