Geochemistry of cold CO₂-rich springs of the Scuol-Tarasp region, Lower Engadine, Swiss Alps

A study of CO₂-rich (up to 3000 mg l⁻¹) mineral (up to 460 meq l⁻¹ total dissolved ions) and cold (2°–9°C) springs of the Lower Engadine region in the Swiss Alps, indicate the existence of three distinct geochemical groups: Ca-HCO₃ water, Na-HCO₃, Cl water and Na, Mg-HCO₃, SO₄ water. In each water group local mixing is observed between a mineral endmember of a pre-1953 age and a fresh, post-1953, endmember. All the spring waters appear to be of shallow origin and derived from local precipitation. The chemical composition is reached by local water-rock interactions, induced by CO₂, which ascends as a gaseous phase that emerges in mofettes and gets locally dissolved in shallow groundwater. The CO₂ is of crustal origin, as indicated by accompanying ³He/⁴He values of 0.1 of the atmospheric value, and δ ¹³C of around - 4‰ (PDB) (decomposition of marine carbonates and/or carbonates associated with rocks belonging to an ophiolitic suite)