ABSTRACT
Cabeço de Vide mineral waters have a distinct chemical composition (high pH; Na-Cl/Ca-OH type waters) and are associated with mafic/ultramafic rocks. Geochemical, isotopic and numerical approaches have contributed to increased knowledge of the nature of these mineral waters. Most of the local surface and shallow groundwater is of the Mg-HCO3 type. Since both the shallow Mg-HCO3 and the mineral waters have similar δ2H and δ18O signatures there may be an evolution from the HCO3-Mg waters towards the mineral waters. The reaction path simulations show that the progressive evolution of the Ca-HCO3 to Mg-HCO3 waters can be attributed to the interaction of meteoric water with serpentinite. The sequential dissolution in CO2(g) closed system conditions at depth leads to the precipitation of chrysotile, brucite and calcite, indicating that the water is responsible for the serpentinization of fresh ultramafic rocks (dunites) present at depth.
