Decadal-Scale Hydrothermal Alteration of Basalt: Implications for Long-Term Reactivity in Subsurface Technologies

Global demands to secure critical mineral supply chains, manage water resources, and store energy long-term require innovative resource management strategies. Subsurface basalt reservoirs potentially offer an unconventional dual-purpose approach to mining and energy storage, where compressed air energy storage can be coupled with water remediation strategies for the extraction of economically important and environmentally relevant elements. This study utilizes static batch experiments conducted on Columbia River Basalt Group samples to evaluate long-term fluid–rock interactions relevant to coupled subsurface applications. Samples were reacted under elevated temperature and pressure conditions, for 296 and 4061 days, providing a unique data set to assess geochemical evolution, element partitioning, and aqueous chemistry over decadal time scales. The alteration was dominated by silicate, aluminosilicate, and oxide phases. Progressive hydrothermal alteration increased the cation exchange capacity through the formation of secondary minerals (e.g., clays and zeolites), influencing solute retention, ion exchange behavior, and aqueous chemistry. Grain-scale and bulk analyses revealed selective cation release and retention patterns, establishing a mechanistic baseline for predicting element mobility. These geochemical constraints inform the prospective use of enhanced metal recovery for critical resources (e.g., Mn, Mg, Ti, and Fe) and associated water quality impacts, providing a foundation for the design and management of engineered fluid–rock systems in unconventional basalt reservoirs.