| Summary: | The AOC Granite 7-32-89-10 hole, drilled to search for oil in the Precambrian basement below the Alberta bituminous (tar) sands near Fort McMurray, Canada, penetrates layered biotite-hypersthene quartz diorite-gabbro sills that occur between 543 and 2363.3 meters depth. Three episodes of fracturing and cataclasis affected these sills. The first allowed K- and Si-metasomatism to change many parts of the sills into myrmekite-bearing granite and granodiorite. Recrystallization, accompanying this metasomatism, eliminated any porosity. A second episode of fracturing, barren of oil and methane, allowed minor magnetite to fill tiny fractures, cutting both granite and quartz diorite. A third, Tertiary period of deformation caused faulting and fracturing of the sills to produce an anticlinal-shaped cataclastic zone in which oil and methane were trapped. Repeated showings of oil and methane occur throughout the 1820-meter-thick series of sills, but insufficient for production. Lessons learned from this study suggest that the search for oil in myrmekite-bearing Precambrian granitic rocks will likely be unsuccessful unless such rocks have been fractured during a time later than any fracturing that permitted the K- and Si-metasomatism. Non-myrmekite-bearing, fractured, primary granitic rocks would not have this problem. Myrmekite and Metasomatic Granite 47. (2003) 1526-5757
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