In order to update the geohydrologic characterisation of Chaves geothermal area, coupled isotopic and chemical studies have been carried out on hot and cold CO2-rich mineral waters discharging, in northern Portugal, along one of the major regional NNE-trending faults (the so-called "Verin-Chaves-Penacova Depression"). Based upon their location, and chemical and isotopic composition, the analysed waters can be divided into two groups. The northern group belongs to the HCO3/Na/CO2-rich type, and consists of the hot spring waters of Chaves and the cold spring waters of Vilarelho da Raia. The delta D and delta(18)O values show that these waters are of meteoric origin. The lack of an O-18 shift indicates that there is no evidence of water/rock interaction at high temperatures. The southern group includes the cold spring waters of Campilho/Vidago and Sabroso/Pedras Salgadas. Their chemistry is similar to that of the northern group but their heavier delta D and delta(18)O values could be attributed to different recharge altitudes. Mixing between deep mineralised waters and dilute superficial waters of meteoric origin might explain the higher H-3 activity found in the Vidago and Pedras Salgadas mineral waters. Alternatively, they could be mainly related to shallow underground flowpaths. The delta(13)C values support a deep-seated origin for the CO2. The delta(37)Cl is comparable in all the mineral waters of the study area, indicating a common origin of Cl. The Sr-87/Sr-86 ratios in waters seem to be dominated by the dissolution of plagioclases of granitic rocks.