Regolith-hosted rare earth element deposits (also known as ion-adsorption deposits) are rare-earth element (REE) ores in decomposed rocks that are formed by intense weathering of REE-rich parental rocks (e.g. granite, tuff etc.) in subtropical areas. In these areas, rocks are intensely broken and decomposed. Then, REEs infiltrate downward with rain water and they are concentrated along a deeper weathered layer beneath the ground surface. Extraction technology of the deposits has been evolving over the last 50 years. In the past, REEs were primarily extracted in small amount as by-products in mines of other metals or granitic sands at the beach. However, in recent decades, the development of the high-tech industries (e.g. aerospace engineering, telecommunication etc.) leads to high demand for REEs. Hence, regolith-hosted rare earth element deposits were recognised and extraction technologies have been rapidly developed since the 1980s. Currently, China dominates more than 95% of the global REE production. Regolith-hosted rare earth element deposits, which contributes 35% of China's REE production, are mainly found in South China. Global distribution Regoliths are unconsolidated deposits of fragmented and decomposed rocks and may include dust, soil, broken rock, and other related materials. They are the source of minerals and construction materials and if they contain much biological material are known as soils. Most of the regolith-hosted rare earth mineral deposits are found in South China, which currently dominates more than 95% of global REE production. There are two major types of deposit, namely "light" rare earth elements (LREE) (i.e. La, Ce, Pr and Nd) deposit and middle and heavy rare earth elements (HREE) (i.e. Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb and Lu) deposit. Both of these types are mainly found in Jiangxi, Hunan, Guangdong and Fujian province. The Zudong deposit in Jiangxi, the Datian and the Xiawentian deposits are the major HREE-mines in South China. Meanwhile, LREE is dominated by the Heling deposit and the Dingnan deposit in Jiangxi Province. Meanwhile, exploration for this kind of deposit are actively taking place across the world. Currently, some potential deposits have been discovered in the US, Southeast Asia, Malawi, Brazil and Madagascar. Geological overview Regolith-hosted rare earth element deposits are found along ridges in low-lying granitic hills in South China. The ore deposit can be profiled into four layers based on its extent of weathering while the orebody lies at lower layer of weathered soil. Geomorphology The morphology of the deposits in