Formation of giant carbonatite rare earth deposits controlled by deep-seated magma chambers

Carbonatite-associated rare earth element (REE) deposits are currently the primary source of REE resources. Their formation requires REE enrichment during prolonged magma evolution, achieved by suppressing REE-rich mineral crystallization and promoting REE-enriched brine melt formation. Our experiments on the fractional crystallization of carbonatitic magmas indicate that pressure (emplacement depth) is the primary factor controlling REE enrichment. High-pressure ( >0.3 GPa) promotes early olivine crystallization, depleting silica and suppressing REE-rich apatite formation. Deep emplacement also delays aqueous fluid exsolution, thereby stabilizing brine melts that enhance phosphate dissolution and prevent REE dispersion into apatite. In contrast, low-pressure conditions (