T1: Comprehensive understanding of the crustal evolution and resource exploration in Asia (Symposium)

[T1-06] Ion adsorption-type REE deposits: the source of HREE

「招待講演」

*Yasushi Watanabe¹ (1. Akita Univ. Int. Res. Sci.)

Keywords:ion adsorption-type deposit, heavy rare earth elements, weathering, magnet

Ion adsorption rare earth deposits were confirmed in southern China including Jiangxi province in late 1970's. This unique deposit type forms by adsorption of rare earth ions on clay minerals represented by kaolinite and halloysite due to weathering of granitic rocks. Although the ore grades of this deposit type is extremely lower (<0.2 wt%) than the other rare earth deposits such as carbonatite, extraction of rare earths from the clay ores is easy and inexpensive. The development of this deposit type has been accelerating since 2000 as the source of heavy rare earths. This is due to the invention of neodymium magnet in 1983, followed by commercialization in 1985, and production of hybrid vehicle (Prius) in 1997. Because major rare earth deposits such as carbonatite and placer deposits are enriched in LREE but poor in HREE, the ion adsorption type deposits became the important HREE supply source. Although exploration of HREE prospects has been conducted worldwide and a few HREE enriched alkaline-rock related deposits were discovered, no deposit is better than the ion adsorption deposits in terms of production cost and easiness in processing. The ion adsorption type deposits are distributed not only in southern China but also in southeast Asia. This type of deposits also present in suthern Africa including Malawi and Madagascar and South America such as Brazil and Chile. Presently Myanmar has become the major country that produces ionic ores. For the formation of ion adsorption HREE deposits needs the following three conditions; 1) presence of HREE enriched host rocks, 2) formation of thick (>10 m) weathering crust, and 3) presence of REE minerals in the host rocks that easily dissolve during weathering.