Water–rock interactions fundamentally control the mobilization, transport, partitioning, and precipitation of critical minerals across diverse subsurface environments. This session invites contributions that examine the geochemical behavior of critical elements, including rare earth elements (REE), lithium, and related trace metals, in natural and engineered systems such as hydrothermal ore deposits, geothermal reservoirs, produced water and sedimentary brines, mineral scale, mine drainage, waste streams, and carbon sequestration settings. We welcome field, experimental, analytical, and modeling studies, including hydrothermal experiments and reactive transport approaches (i.e., PHREEQC, GWB, GEM-Selektor, Reaktoro, etc.) that collectively constrain how fluid chemistry, temperature, pressure, redox conditions, and mineral dissolution–precipitation reactions influence critical mineral mobility, solubility, enrichment, and recovery. Contributions addressing trace and REE partitioning in gangue and reactive minerals, including carbonates, sulfates, and fluorite, are especially encouraged, as these phases provide key insight into ore-forming fluids and element partitioning.