Fluorite recognized as the principal source mineral for regolith-hosted HREE deposits

Abstract Regolith-hosted rare earth element (REE) deposits in South China supply most of the world’s heavy REE (HREE), but the parent minerals that liberate HREE during weathering remain uncertain because commonly invoked accessory phases are refractory. Here we recognize that fluorite is the dominant HREE host in the granitic bedrock of the world’s largest deposit (Shitouping; ~174,000 t HREE oxides). Fluorite occurs in the Early Cretaceous syenogranite at a concentration of ~0.8 wt.% and contains 4.7 wt.% REE with a LREE/HREE ratio of 0.3, accounting for 82% of the bulk-rock HREE budget. During supergene weathering, fluorite dissolves almost completely (> 99%), releasing HREE that adsorb onto clay minerals in the overlying saprolite, whereas refractory phases such as xenotime persist. Mass-balance modelling confirms that HREE ions liberated from primary magmatic fluorite constitute the principal source of the economic ore. Extreme magmatic fractionation enriches residual melts in fluorine and HREE, driving fluorite crystallization and preferential HREE incorporation. Our results imply that regolith-hosted HREE deposits require bedrocks enriched in easily weathered HREE phases (notably fluorite) and depleted in refractory HREE hosts (e.g., xenotime and titanite), guiding exploration to F-rich, highly fractionated granites low in P and Ti.