Geochemical Characteristics Of Rare Earth Elements In Yijiang-sidu Quartz Diorite And Its Weathered Crust In Southern Hunan

Rare earth is an important strategic resource,Scandium?Sc?,as one of rare earth,has important applications in the fields of metallurgy,new materials and new energy.In recent years,the United States,Japan,Russia,and the European Union have listed Sc as a key mineral.Sc is also classified as a strategic metal by the National Mineral Resources Planning?2016²020?in China.There are Sidu and Leigongxian Sc mine in Hunan,Yijiang Sc deposit was discovered in 1987.In order to find out the rare earth of quartz diorite during the weathering process,especially,the migration and enrichment characteristics of Sc,this paper selected Yijiang and Sidu bodies,and studied quartz diorite and weathering crust by petrology and geochemistry characteristic,using identification of rock and minerals,scanning electron microscopy-energy dispersive spectrum analysis,X-ray diffraction?XRD?,X-ray fluorescence spectroscopy and Inductively compled plasma mass spectrometry?ICP-MS?and so on,supplemented by rare earth leaching experiment.The main minerals of Yijiang and Sidu quartz diorite are plagioclase?60⁷0%?,quartz?5-15%?,biotite?8-12%?,hornblende?5-12%?and Pyroxene?5⁷%?,the secondary minerals are magnetite,zircon,pyrite,monazite,apatite,etc.The main components of weathering crust are kaolinite?15.1⁸1%?,quartz?12.5⁶4.5%?,muscovite?0¹6%?,oblique chlorite?0⁸.7%?and goethite?0³.8%?.During the weathering process,the main elements such as TFe₂O₃,Al₂O₃,TiO₂ content increased,SiO₂,MnO,MgO,CaO,Na₂O,K₂O and P₂O₅ content decreased;the enrichment of rare earth increased,especially heavy rare earth,the rare earth distribution curve is nearly horizontal in the completely weathered layer;the content of Sc increases with the increase of the degree of weathering from the weathering crust profile is top-down,but compared with quartz diorite,there is no obvious enrichment.Combined with the geological characteristics of the mining area,it is believed that:?1?The ionic phase rare earth in the weathering crust of quartz diorite account for 68%⁹2%of the total,and the rest of the rare earth mostly occur in rare earth minerals;the Sc account for 11²7%,the others are exist in goethite by isomorphism;?2?In the weathering crust of quartz diorite from the surface soil layer to the completely weathered layer,The leaching rate of the ionic phase of the rare earth increases,and the leaching rate of the rare earth in the lower part of the completely weathered layer is?70-94%?.The leaching rate of the ionic phase scandium of the weathering crust is?11-28%?,as the degree of weathering increases,there is no obvious regular change in the ionic phase of the Sc.?3?During the weathering process,with the weathering of rock-forming minerals and accessory minerals,the rare earth changed from the mineral phase and the isomorphism to the ionic phase,and the ionic phase of the rare earth were adsorbed on the surface of the clay mineral to be enriched;Sc changed from the isomorphism to the Sc³⁺and Sc³⁺replace Fe³⁺in goethite to forming a solid solution of the Fe³⁺and Sc³⁺,and Sc is enriched.