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Geoquimica dos fluidos e da interaccao agua-rocha Os casos das aguas mineralizadas quentes e frias de Chaves, Vilarelho da Raia, Vidago e Pedras Salgadas

By Jose Manuel Vaz Velho Barbosa Marques

Abstract

Isotopic and geochemical studies have been carried out on hot and cold HCO_3 / Na / CO_2-rich mineral waters discharging in northern Portugal. The #delta#D and #delta#"1"8O values show the meteoric origin of these waters. SiO_2 and K"2/Mg geothermometers suggest that reservoir temperature of Chaves hot waters (76degC) is of about 120 deg.C. The higher "3H activity found in Vidago and Pedras Salgadas cold (17 deg.C) mineral indicates that these cold mineral waters should be mainly related to shallow underground flowpaths. #delta#"1"3C_(_T_I_D_C_) values observed in hot and cold mineral waters indicate a deep-seated (mantle) origin for part of the CO_2. Nevertheless, the dissolution of carbonate rock levels at depth cannot be excluded. Mineropetrografic characterization of drill-cores from an exploration well (Vilarelho da Raia AC2) indicates a vein alteration stage along natural fracture zones where the granite is altered into a quartz and muscovite mineral paragenesis. The low water/rock ratios, along natural fracture zones, suggest the presence of a rock-dominated environment. The #delta#D values of the water in equilibrium with muscovites (at 150degC and 230degC) are close to those of the present day meteoric waters of the region, indicating that hydrothermal fluids can be interpreted as having a predominated meteoric originAvailable from Fundacao para a Ciencia e a Tecnologia, Servico de Informacao e Documentacao, Av. D. Carlos I, 126, 1200 Lisboa / FCT - Fundação para o Ciência e a TecnologiaSIGLEPTPortuga

Topics: 08B - Hydrology, limnology, 08E - Geology, mineralogy, sedimentology, GEOCHEMISTRY, HOT AND COLD CO_2-RICH MINERAL WATERS, UNDERGROUND FLOW PATHS, WATER/ROCK INTERACTION, CHAVES GEOTHERMAL AREA, PORTUGAL
Year: 1999
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Provided by: OpenGrey Repository
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