Rare earths refer to the lanthanide elements plus scandium and yttrium, two elements of the third transition metal group in the periodic table, making a total of 17 elements. Among them, the first eight elements of the lanthanide series are commonly referred to as light rare earths, including lanthanum, cerium, praseodymium, neodymium, bismuth, samarium, europium, and gadolinium; scandium and yttrium, together with the last seven elements of the lanthanide series, are called heavy rare earths, including terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium. Rare earths are widely used in all aspects of modern society, such as neodymium in magnets (often the king of permanent magnets) in mobile phones, cerium and neodymium added to automotive UV-blocking glass, and neodymium, yttrium, and ytterbium used to manufacture solid lasers, while barium lanthanum copper and strontium lanthanum copper oxides have high-temperature superconductivity characteristics.
China is the country with the largest rare earth reserves in the world, mainly due to the super-large carbonate-type rare earth mines in Bayan Obo, Inner Mongolia Autonomous Region, and the weathered crust rare earth mines in highly evolved granites in South China. Bayan Obo has the largest rare earth mine in the world. The latest data shows that the rare earth reserves in Bayan Obo exceed 50 million tons. It is believed that its light rare earth content accounts for more than half of the globally proven reserves. The origin of these rare earths is still a subject of great controversy. There are two mainstream views: one believes that it is the result of igneous carbonate formation; the other believes that it is the product of the chemical reaction between aqueous fluids and igneous rocks, followed by the reaction with sedimentary carbonates. Bayan Obo is located on the northern edge of the North China Craton, close to the Central Asian Orogenic Belt. Recent studies suggest that its mineralization may be the result of the superposition of multiple geological events. South China, on the other hand, has a globally unique mineralization belt. It contains 60% of the world's tungsten, 60% of antimony, and 20% of tin, and is also a well-known heavy rare earth production area. Among them, tungsten, tin, and heavy rare earths are mainly distributed in the Nanling region, where the highly evolved granites form weathered crusts enriched in rare earths. Most of the world's heavy rare earths currently mined come from here. The large-scale mineralization in Nanling is also related to the superposition of multiple geological events.