Abundance & Distribution
Despite their name, the REE are in fact not especially rare. Each is more common in the earth's crust than silver, gold or platinum, while cerium, yttrium, neodymium and anthanum are more common than lead. The light REE (La through Eu) are more abundant than the heavy REE (Gd through Lu), and furthermore, the elements of even atomic number are more abundant than their neighbours of odd atomic number, because of the greater relative stability of nuclei with even atomic number compared to those with odd atomic number. REE are never found as free metals in the earth's crust and all their naturally occurring minerals consist of mixtures of various REE and nonmetals. Bastnaesite [(Ce,La)(CO3)F], monazite[(Ce,La,Nd,Th)(PO4)] [(REE)PO4] and xenotime [YPO4] are the three most economically significant minerals of the more than 200 minerals known to contain essential or significant REE. Bastnaesite and monazite are sources of the light REE and account for about 95% of the REE currently utilised. Monazite is also the principal ore of thorium, containing up to 30% Th, which together with smaller (up to ~1%) quantities of U imparts radioactive properties to the monazite. Xenotime and minerals such as allanite are a source of the heavy REE and yttrium.
Bastnaesite occurs predominantly in calc-silicate rich rocks related to alkaline intrusive igneous complexes, and to a lesser extent, in quartz veins, epithermal fluorite-bearing veins and breccia fillings. Monazite and xenotime occur as accessory minerals in low-Ca granitoid rocks and pegmatites. Following weathering of these rock types, monazite and xenotime are concentrated in heavy mineral placer deposits because of their resistance to chemical attack and high specific gravity. Xenotime is commonly associated with zircon, being isostructural and often found enclosing zircon.
Other commercial sources of rare earth elements are apatite [(Ca,Na,Ce,Th)5(P,Si,S,Bi)3O12(F,OH,Cl,O)] (Russia), REE-bearing clays ("Longnan clay", Jiangxi Province, China), and various minerals such as allanite [CaCe(Fe2+Al2)(SiO4)3(OH) or CaY(Fe2+Al2)(SiO4)3(OH)] that are produced as a by-product of uranium mining (Canada). Of lesser importance are allanite (containing Ce and Y), zircon (Th, Y and Ce), euxenite and loparite. The main commercial source of scandium is as a by-product from the processing of uranium and tungsten.
There is large amount of reserves of rare earth minerals in the world. The largest proved reserves are located in China. Other important reserves of rare earths are located in Australia, Russian Federation, United States, Brazil, Canada and India. In Vietnam. In addition, some deposits of rare earths was found in South Africa, Malaysia, Indonesia, Sri Lanka, Mongolia, North Korea, Afghanistan, Saudi Arabia, Turkey, Norway, Greece and Nigeria, Kenya, Tanzania, Burundi, Madagascar, Mozambique and Egypt.
Table 51 - World reserves of Rare Earths (Mt,REO)*