Relations between groundwater composition and fracture filling mineralogy in swedisk deep rocks

Groundwater flowing through the rock will undergo a continuous change in composition along the flowpath due to chemical reactions with the surrounding minerals. The surfaces in contact with the water do not have the same composition as the rock matrix, but fracture filling minerals of different origin are present. Here recent data from the SKB investigations of deep groundwater and fracture filling mineralogy have been reviewed and equilibrium calculations using the PHREEQE code performed. Most waters seem to be close to equilibrium with respect to calcite. For other minerals the saturation state is more varying. If this is due to the real conditions or to inaccurate modeling is not quite clear. Although investigations have been performed at a number of sites during the years, relevant chemical data are few, and it is difficult to couple water chemistry data and fracture filling mineralogy from the same fracture. This is due to the difficulty in sampling deep waters without disturbing the composition. However, ranges of probable composition of major ions and redox potentials in deep granitic groundwaters may be defined. 2 figs., 2 tabs., 17 refs