2012:61 Geochemical Constraints on Buffer Pore Water Evolution and Implications for Erosion

Mineralogical data from the Forsmark Site show that smectite and calcite occur at all depths in Forsmark fractures, with no evidence for removal/dissolution by previous glacial episodes.  This natural analogue information implies that these minerals may not have been eroded/dissolved during previous glacial episodes.

Available thermodynamic data suggest that repository-depth Forsmark groundwaters are in equilibrium (steady-state) with montmorillonite and saponite and these minerals may control pH, PCO2, SiO2(aq) and Na/Ca in groundwaters (and any future intruding glacial meltwaters) in the near-field at the site. This conclusion would not be evident from modelling approaches using mixing only.

Modelling of the reaction of montmorillonite in the buffer with Forsmark groundwater shows a trend towards conversion of montmorillonite to saponite, suggesting that the buffer may be partially altered prior to glacial meltwater intrusion.