Date of Award


Degree Type


Degree Name

Doctor of Philosophy


As part of the program for assessing the concept of disposing nuclear fuel waste in plutonic rocks, Atomic Energy Canada Limited (AECL) has chosen to investigate the East Bull Lake gabbro-anorthosite layered instrusion. This lopolith occupies an area of four by thirteen kilometres, in the Superior structural province, north of Lake Huron, Ontario, from which the continental ice sheet retreated less than 10,000 years ago. The lopolith is traversed by swarms of younger Proterozoic dykes, three major faults which have provoked periods of movement, and a myriad of cooling joints, cracks, and hydraulic fractures now occupied by comb textured calcite, prehnite, chlorite, quartz and feldspars, an average 6.7 mm wide and on average 8.3 cm apart. The relative abundance of isotopes of oxygen and carbon in calcite filling fractures indicates repeated deposition from mixed hydrous magmatic fluid and salt fluids at temperatures at or above 200{dollar}\sp\circ{dollar}C. Major and minor element abundances indicate a low K high Al tholeiitic character of the intrusion. A bimodal chemical trend, REE data and a rubble zone across the entire intrusion, suggest that multiple intrusion may have taken place in the layered complex. Vein and immediate wallrock composition indicates diffusion from fractures into the rock for a maximum 6.5 cm with major introduction of H{dollar}\sb2{dollar}O and CO{dollar}\sb2{dollar}.;Considering the evidence of present and past high horizontal stresses and the indications of high hydraulic conductivity in the past, it is inadvisable to select this area as a disposal site before better evaluation of fracturing, stress history, hydrology of the site, and their relationship to waste confinement.



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