Subhorizontal fractures in a granitic pluton: Their detection and implications for radioactive waste disposal

Abstract

Several countries are actively investigating the feasibility of using crystalline rock bodies for the ultimate disposal of radioactive nuclear waste. As part of the concept assessment phase in the Canadian nuclear fuel waste management program, a multidisciplinary research investigation is being conducted across the Lac du Bonnet batholith in southeastern Manitoba; no radioactive materials, other than sealed sources or tracers, are to be emplaced within this rock body. The results of a high‐resolution seismic reflection survey, together with information from a number of deep boreholes, demonstrates that major subhorizontal fractures occur at depths of up to 800 m within the batholith. An integrated interpretation of the seismic data with selected borehole logs shows that warm water is flowing up the major fractures from depth. A natural corollary of these results is that a three‐dimensional seismic reflection survey combined with an appropriate exploratory drilling program has the potential for delineating blocks of a rock body that may be relatively unfractured.