No abstract

No abstract

Geochemical and isotopic studies have been undertaken to assess the origin of CO 2 -rich waters issuing in the northern part of Portugal. These solutions are hot (76°C) to cold (17°C) Na-HCO 3 mineral waters. The d 2 H and d 18 O signatures of the mineral waters reflect the influence of altitude on meteoric recharge. The lack of an 18 O-shift indicates there has been no high temperature water-rock interaction at depth, corroborating the results of several chemical geothermometers (reservoir temperature of about 120°C). The low 14 C activity (up to 9.9 pmC) measured in some of the cold CO 2 -rich mineral waters (total dissolved inorganic carbon) is incompatible with the presence of 3 H (from 1.7 to 4.1 TU) in those waters, which indicates relatively short subsurface circulation times. The d 13 C values of CO 2 gas and dissolved inorganic carbon range between )6& and )1& versus Vienna-Peedee Belemnite, indicating that the total carbon in the recharge waters is being diluted by larger quantities of CO 2 ( 14 C-free) introduced from deep-seated (upper mantle) sources, masking the 14 C-dating values. The differences in the 87 Sr/ 86 Sr ratios of the studied thermal and mineral waters seem to be caused by water-rock interaction with different granitic rocks. Chlorine isotope signatures ()0.4& < d 37 Cl < +0.4& versus standard mean ocean chloride) indicate that Cl in these waters could be derived from mixing of a small amount of igneous Cl from leaching of granitic rocks.

No abstract

No abstract