Paper Published: Origin and evolution of Cl in CO2-rich thermal and mineral waters from Northern Portugal

The paper  'Origin and evolution of Cl in CO2-rich thermal and mineral waters from Northern Portugal' by José M. Marques, Hans G. M. Eggenkamp, Paula M. Carreira and Manuel Antunes da Silva was published in Applied Geochemistry .



The aim of this study is to enhance the use of coupled geochemical and isotope signatures of chlorine as important tools to give new insights on the source of Cl in the studied CO2-rich thermal and mineral waters that discharge from (relatively chlorine poor) granitic rocks along the Verin-Régua-Penacova fault in Northern Portugal between the Spanish border (Vilarelho da Raia and Chaves) in the north and Vidago and Pedras Salgadas in the south. For this purpose we used geochemical (major ion composition), stable (δ2H, δ13C, δ18O and δ37Cl) and radioactive (3H and 14C) isotopic data obtained during two field work campaigns (Winter-February and Summer-July). The present study focuses on variations in the stable chlorine isotope ratios, using Cl chemical and isotopic signatures of local / regional shallow cold dilute groundwaters for comparison. The main challenge in this study is to determine whether the source of Cl is related to the local/regional granitic rocks or not. We link previous trends found for Cl with trends observed in other data of possible geochemical significance to find evidence for i) previous hypotheses on the nature of such complex CO2-rich thermal and mineral waters, ii) spatial/temporal variations (from recharge to discharge), and iii) water-rock interaction processes occurring at depth. In the Vilarelho da Raia - Pedras Salgadas region, the Chaves, Vidago and Pedras Salgadas CO2-rich thermal and mineral waters are used for spa treatments (e.g., Chaves Spa and Pedras Salgadas Spa & Nature Park) and as bottled sparkling water (e.g., Água de Vidago and Água das Pedras Salgadas) amongst others. The results obtained indicate that the possible origins of the chloride are i) locally and regionally recharged meteoric waters, ii) water-rock interactions during shallow and deep underground flow paths and iii) possible very deep (upper mantle?) originated chloride. 37Cl/35Cl ratios and Cl- concentrations in the studied CO2-rich thermal and mineral waters do not appear to be independent from other geochemical parameters (e.g., the water-rock interaction related to different underground flow paths, the age of the groundwaters and temperature dependence of the CO2 dissolution in water, respectively). 


José M. Marques, Hans G.M. Eggenkamp, Paula M. Carreira, Manuel Antunes da Silva (2020). Origin and evolution of Cl in CO2-rich thermal and mineral waters from northern Portugal, Applied Geochemistry, Volume 116, 104569, DOI: 10.1016/j.apgeochem.2020.104569