Mineralogical Facies and Metal Enrichment in the Shallow-Water Hydrothermal System of Panarea Island (Aeolian Volcanic Arc, Mediterranean Sea)

Shallow-water hydrothermal systems in active volcanic arcs serve as natural analogs for geothermal reservoir characterization and potential sources of Critical Raw Materials (CRMs). This study examines the Panarea hydrothermal system (Aeolian Islands, Tyrrhenian Sea, 37–207 m depth) to characterize its mineralogical facies and assess CRM enrichment patterns. Sixteen sediment samples collected during 2013–2015 research cruises were analyzed using SEM-EDS, XRPD with Rietveld refinement, and XRF. Four hydrothermal alteration facies were identified: (i) a low-temperature iron oxide facies dominated by nanocrystalline goethite with enrichments in As, V, and Mo; (ii) an argillic to propylitic facies containing smectite-group clays and high-temperature silica polymorphs, consistent with alteration at 200–350 °C; (iii) a phyllic to propylitic facies showing exceptional Ba enrichment (up to 46,976 ppm) and base-metal sulfide accumulations; and (iv) an advanced argillic facies including the first documented aluminophosphate–sulfate mineral at Panarea, a svanbergite–woodhouseite solid solution. Vanadium concentrations at Panarea exceed values reported across the Tyrrhenian–Aeolian domain, ranking this site among the highest-V shallow hydrothermal fields in the Mediterranean. These findings support a genetic model involving fault-controlled seawater circulation, magmatic CO2 input, and episodic redox fluctuations, providing baseline data for CRM cycling and geothermal evaluation in Mediterranean submarine volcanic systems.