A Geochemical and Isotopic Study of Crystalline Rock at Chalk River, Ontario, Canada☆

Abstract Crystalline rock is one of several proposed long term storage sites for accumulated nuclear waste. The primary concern during long residence times (>100 Ka) is the transportation of hazardous materials by groundwater migration. The main pathways for fluid flow and material transport in crystalline rock tend to be porosity due to fractures caused by the tectonic stresses after initial deposition. Investigation and understanding of existing fractures and the precipitated minerals within them offer powerful tools to understand and predict the future stability of a site. Several methods were utilized to assist in investigating the hydrogeological history of the crystalline bedrock below the Chalk River site. These were chiefly focused on the fracture mineral, chemistry, and isotopes and their relationship to associated groundwaters. Multiple generations were identified within the fracture filling minerals themselves consisting primarily of calcite precipitated from several fluids under variable hydraulic conditions. The overall objective of this investigation was to identify if evidence exists for recent low temperature mineral formation, none of which were found despite a varied depositional history.