Data set for COMMSENV-26-1226-T

Rare earth elements (REE) are essential for low-carbon and digital technologies, yet their primary sources remain geologically restricted and geopolitically vulnerable. Here we show that volcanic geothermal skarn systems can host substantial 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 calcsilicate reservoir formed by high-temperature fluid-mediated magma–carbonate interaction. Whole-rock and mineral chemistry indicate that LREE are concentrated in an upper (ca. 400 m thick) vesuvianite-rich interval, whereas HREE are preferentially incorporated in garnet at greater depths. Vesuvianite is identified as the dominant REE host, reaching >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 comparable skarn systems in Quaternary volcanic districts of Italy and, more generally, the diffuse decarbonation processes in magmatic arcs, indicates that fluid-mediated magma–carbonate interaction in volcanic settings is an underexplored pathway for REE enrichment and a promising target for unconventional critical mineral exploration.