Fracture water/fracture mineral interaction at Palmottu study site

Fracture mineralogy and the chemical composition of fracture waters at the U-Th mineralization Palmottu, a natural analogue study site for radionuclide migration in Nummi-Pusula, southern Finland, were studied. Water/rock interaction processes were interpreted by means of equilibrium thermodynamic calculations. Results from one of the drill holes indicate dissolution of calcite and pyrite, while in other two holes, calcite had equilibrated with the water. Kaolinite is a typical fracture mineral, but the concentrations of aluminium and silica in waters is evidently derived from pyrite, which is also an abundant fracture mineral. Pyrite is not equilibrium with sulphate at the measured Eh-pH conditions. However, calculations indicate that pyrite and thiosulphate are more close to equilibrium