Geochemistry of Rare Earth Element Deposits

Rare earth element (REE) deposits are formed through a spectrum of geological processes that concentrate lanthanides and yttrium into economically exploitable ore bodies. Primary magmatic systems, particularly carbonatite complexes and peralkaline intrusions, account for the bulk of global REE resources. In these settings, CO₂- and fluorine-rich magmas evolve by fractional crystallisation, generating residual melts or “brine-melts” from which primary REE-bearing carbonates and fluorocarbonates precipitate. Subsequent hydrothermal activity and metasomatic alteration mobilise REE, redistributing them into minerals such as bastnäsite, monazite and fluocerite. Stable isotope and trace-element data demonstrate that fluids derived from recycled marine sediments or metasomatised mantle play a central role in fertilising subcontinental lithospheric sources. Recent advances in high-precision geochronology and geophysical imaging have refined the timing of multi-stage mineralisation and shed light on lithospheric controls on magma ascent. A holistic understanding of mantle source evolution, magmatic differentiation and fluid–rock interaction is essential for guiding exploration of new REE resources critical to renewable energy and advanced electronic applications.

Research from Nature Portfolio

Recent seismic tomography integrated with geochemical mapping has shown that a thick continental lithospheric root, prior metasomatic fertilisation and trans-lithospheric weaknesses are prerequisites for generating giant carbonatite-associated REE systems in southwestern China. Isotopic investigations of Cenozoic carbonatite-hosted REE deposits have demonstrated that melting of a mantle source enriched by fluids from recycled marine sediments yields highly fertile magmas, with Sr–Nd–Pb–O signatures highlighting the importance of ancient convergent margins and strike-slip fault networks in focusing magma ascent. Studies of Late Triassic carbonatites in the Qinling orogen have identified rare heavy REE- and molybdenum-rich end-members formed by melting of subducted carbonate-bearing slabs and subsequent metasomatism of a thickened lower crust, thereby broadening the geochemical spectrum of ore-forming carbonatites beyond conventional light REE enrichment.

Geochemistry of Rare Earth Element Deposits publication trend

The graph below shows the total number of articles in geochemistry of rare earth element deposits across all publications each year (not limited to Nature Index journals).

Technical terms

Carbonatite: A carbonate-rich igneous rock often associated with mantle-derived magmas that host rare earth element deposits.

Metasomatism: The chemical alteration of a rock by hydrothermal fluids that introduce or remove chemical components.

Bastnäsite: A primary REE-bearing carbonate mineral (REECO₃F) commonly found in carbonatite and hydrothermal deposits.

Fluocerite: A rare earth fluoride mineral (REEF₃) that can act as a precursor to other REE minerals in magmatic-hydrothermal systems.

References

1. Three-stage niobium mineralization at Bayan Obo, China. National Science Review (2024).
2. Refertilized continental root controls the formation of the Mianning–Dechang carbonatite-associated rare-earth-element ore system. Communications Earth & Environment (2023).
3. The role of fluocerite in the genesis of bastnäsite: mechanistic insights and transformation pathways. Nanoscale (2024).
4. Formation of carbonatite-related giant rare-earth-element deposits by the recycling of marine sediments. Scientific Reports (2015).
5. Formation of Rare Earth Deposits in Carbonatites. Elements (2021).
6. Origin of unusual HREE-Mo-rich carbonatites in the Qinling orogen, China. Scientific Reports (2016).