HANDBOOK ON THE PHYSICS AND CHEMISTRY OF RARE EARTHS

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HANDBOOK ON THE PHYSICS AND CHEMISTRY OF RARE EARTHS ( handbook-onphysics-and-chemistry-rare-earths )

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196 Handbook on the Physics and Chemistry of Rare Earths 1500–2500 tons of REO have been produced as by-product of niobium from loparite annually (Zaitsev and Kogarko, 2012). Nevertheless, many of the deposits of this group are enriched in more valuable HREEs (Fig. 30), inher- iting from the composition of the REEs of alkaline magmas, and hence a number of projects aim to produce HREEs in the world (Fig. 29). The deposits associated with nepheline syenites are further classified into the deposits formed by the magmatic process and hydrothermal pro- cess. The deposits formed by plutonic process are represented by those (Kvanefjeld, Zone 3, Sørensen, and Tanbreez) associated with the Il ́ımaussaq complex in Greenland, Kipawa in Quebec State of Canada, Norra Kärr in Sweden, in addition to the Lovozero deposit. The major REE minerals of these deposits are loparite (Lovozero), steenstrupine [Na14Ce6Mn2Fe2(Zr,Th,U) (PO4)7Si12O36(OH)23H2O] (Il ́ımaussaq) and eudialyte [Na15Ca6(Fe2+,Mn2+)3Zr3 (Si,Nb)(Si25O73)(O,OH,H2O)3(Cl,OH)2] (Il ́ımaussaq, Norra Kärr, Kipawa), and mosandrite [(H3O+,Na,Ca)3Ca3REE(Ti,Zr)(Si2O7)(O,OH,F)4 (Kipawa) which are unconventional for the production of REEs except loparite. Accumulation of these REE minerals in the magma chambers is an important mechanism for mineral concentration at Lovozero and a part of Il ́ımaussaq complexes. Among these, the REE reserves of the deposits in the Il ́ımaussaq complex amounts to 38.3 Mt REO, which exceeds the total reserves of the Bayan Obo deposit in China. The deposits formed by hydrothermal process are represented by the Nechalacho deposit in Northwest Territories of Canada, which hosts 4.2 Mt REO with an average grade of 1.37 wt.% REO. The rare earth mineralization of the Nechalacho deposit is hosted in the metasomatized zone situated at the uppermost part of the 2.1 Ga Thor Lake syenite intruding in the 2.2 Ga Grace Lake granite (Sheard et al., 2012). The metasomatized zone includes lower and upper mineralized zones, with intercalation of magnetite and sodic– potassic altered syenite layers (Hoshino et al., 2013). These lower and upper mineralized zones possibly represent original eudialyte cumulate layers and zircon cumulate layers, which are completely metasomatized with secondary zircons and fergusonite-(Y) in addition to REE fluorocarbonates such as bastnäsite-(Ce), parisite-(Ce), and synchysite-(Ce) (Hoshino et al., 2013; Sheard et al., 2012). The major REE ore minerals at Nechalacho are zircon and fergusontite-(Y), both of which are enriched in HREEs. The deposits associated with alkaline granites are represented by Strange Lake in Canada, Bokan in the United States, Khaldzan Buregtey in Mongolia, Pitinga in Brazil, and Jabal Tawlah in Saudi Arabia. The mineralization of all these deposits is related to the metasomatism and subsequent hydro- thermal activities. The major REE minerals of these deposits are xenotime- (Y) (Bokan, Pitinga, Jabal Tawlah), zirconium silicates (zircon, elipdite) (Khaldzan Buregtey), and waimirite-(Y) and Nb-oxides (Jabal Tawlah). Those of the Strange Lake deposit are more complex: pyrochlore, monazite-(Ce), bastnäsite-(Ce), gadolinite-(Y) [Y2Fe2+Be2Si2O10], gerenite-(Y) [(Ca,Na)2

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