Abstract
The composition of groundwater has been determined in selected granitic, gabbroic and gneissic plutons in the Canadian Shield as part of the Canadian Nuclear Fuel Waste Management Program. A similar geochemical evolution of the groundwater is seen with increasing depth or with flow along the hydraulic gradient, irrespective of rock type. This pattern is comparable to that seen in mine groundwaters from throughout the Canadian Shield. Near-surface groundwaters are typically dilute, slightly alkaline and Ca-(Na)-HCO3 in composition. They evolve to higher pH, Na-(Ca)-HCO3 compositions along the flow path because of interaction with plagioclase, calcite precipitation and ion exchange on clay minerals. At greater depths (>≈200 m), groundwater salinity increases as a result of the dissolution of Cl-rich salts in the rock matrix and, in certain areas, mixing with Na-Cl brines from seawater or basinal formation water. Stable and radioactive isotopic data for the groundwaters help to interpret these characteristics and indicate high residence times for the deeper, saline groundwater.
Resume
évoluent du fait des interactions avec les plagioclases, de la précipitation de la calcite et des échanges d'ions avec les argiles. Aux plus grandes profondeurs (>≈200 m), l'accroissement de la salinité de l'eau souterraine est provoqué par la dissolution de chlorures de la matrice et, en certains endroits, par le mélange avec des saumures à Na et Cl d'eau de mer ou d'eau de formation de bassin. Les données des isotopes stables et radioactifs des eaux souterraines aident à interpréter leurs caractéristiques; elles indiquent des temps de séjour longs pour les eaux souterraines salées, les plus profondes.
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Gascoyne, M., Kamineni, D. The Hydrogeochemistry Of Fractured Plutonic Rocks In The Canadian Shield. HYJO 2, 43–49 (1994). https://doi.org/10.1007/s100400050044
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DOI: https://doi.org/10.1007/s100400050044