Rare-earth element enrichment driven by fluid-mediated magma-carbonate interaction in volcanic-geothermal skarn...

Rare earth elements (REE) are essential for low-carbon and digital technologies, yet their primary sources remain geologically restricted and geopolitically vulnerable. This study shows that volcanic geothermal skarn systems can host substantial high REE concentration. Using core and cutting samples from a 2500 m deep geothermal borehole in the Sabatini volcanic district (central Italy), we reconstruct the chemical zonation and metasomatic evolution of calc-silicate reservoir formed by high-temperature fluid-mediated magma-carbonate interaction. Whole-rock and mineral chemistry indicate that light REE (LREE) are concentrated in an upper (ca. 400 m thick) vesuvianite-rich interval, whereas heavy REE (HREE) are preferentially incorporated in garnet at greater depths. Vesuvianite is identified as the dominant REE host (> 9000 ppm total REE), and accounting for most of the REE budget. Although the economic potential of the Sabatini skarn reservoir remains to be evaluated, geometry-based estimates indicate the Sabatini skarn as a potentially high-grade REE deposit at global scale. The widespread occurrence of similar skarn systems in Quaternary volcanic districts of Italy, coupled with extensive carbonate decarbonation in magmatic arcs, suggests that fluid-mediated magma-carbonate interaction in volcanic environments may represent an unexplored mechanism for REE enrichment and redistribution of metals within the continental crust.