GEOCHEMISTRY AND ISOTOPE HYDROLOGY OF GROUNDWATERS IN THE STRIPA GRANITE RESULTS AND PRELIMINARY INTERPRETATION

Abstract

This paper presents the results of geochemical and isotopic analyses on water samples from the granite at St ri pa, Sweden. Grou ndwater samples co11 ected from shallow, private wells; su boreholes; and boreholes drilled from the 330 m and 410 m mine levels were analyzed for their major ion chemistry, dissolved gases, and environmental isotope conterits. The principal change in the chemical load with depth is typified by chloride concentration, which increases from less than 5 mg/liter to about 300 my/liter. There is a parallel increase in pH, which changes from about 6.5 to over 9.75. It is important to notice that calcite saturation is maintained and that, because of rising pH, dissolved inorganic carbon is lost. The total carbonate content thus decreases from about 70 mg/liter to less than 7 mg/liter. The 180 and deuterium analyses demonstrate that different fracture systems contain different water masses, whose age increases with depth. Groundwater age determinations with 14C and isotopes of the uranium decay series strongly indicate that water ages exceed 25,000 years. The 13C contents of the aqueous carbonate in these groundwaters indicate groundwater recharge through vegetated soil--presumably during an interglacial period. The 13C and 180 determinations show that most fracture calcites have formed in a wide variety of depositional environments~ and not in the waters circulating today.