Questions and Answers Ascribed to Chaves CO2-rich Thermal Waters Conceptual Model (N Portugal): A Review

Abstract

A review of the multidisciplinary approach, including geologic, tectonic, geochemical and isotopic (2H, 18O, 13C and 3H) techniques, attributed to the development of the Chaves CO2-rich thermal water's conceptual model, discharging in the N of Portugal, is presented. The Chaves thermal spring and borehole waters have discharge temperatures ranging from 48°C to 76°C, a dry residue of about 1600mg/L to 1850mg/L, and free CO2 between 350mg/L and 1100mg/L. The pH values are close to 7. Local/regional high altitude sites associated with highly fractured granitic rocks play an important role in conducting the infiltrated meteoric waters towards the discharge zones near the spas. The discharge zones are mainly related to the intersection of the main local/regional fault lineaments (and conjugate structures), responsible for promoting the thermal groundwaters’ ascent. The geochemical signatures of the Chaves CO2-rich thermal waters are mainly ascribed to water - upper mantle CO2 - granite interaction.