Results from a preliminary seismic program in the Abitibi area have caught the interest of the mining industry (see June issue, TNMM). Both Minnova Ltd. and Falconbridge Inc. are contributing financial support to continue the pilot project and Inco Ltd. is interested in extending the project across the Sudbury area.
Since the inception of Lithoprobe in 1981, representatives from the mining and petroleum industries have contributed their time and expertise to the project; now companies such as bp Selco, Chevron Canada Resources, Cambior Inc., Pan Canadian Petroleum and Gulf Canada are actively involved, through direct contributions and participation, in data interpretation and planning.
Lithoprobe is a tightly co-ordinated but highly decentralized research project investigating the fundamental nature and evolution of the Canadian lithosphere. The project name derives from the phrase “probing the lithosphere” — the rigid, outermost 100 km of the earth, the dynamics of which control the geological development of the Earth’s crust.
To unravel the mysteries surrounding the present structure and past evolution of the continent requires the application of indirect methods of exploration. By bringing together geophysicists, geologists and geochemists, and focusing their knowledge and energy on major technical problems, scientific study can go beyond individual contributions.
Seismic reflection surveys are especially important to Lithoprobe because this geophysical technique produces the best resolution of structures and boundaries in the subsurface. In its simplest form, the method is an echo technique based on the same principles as sonar, i.e. bouncing sound waves off the boundaries between different types of material — in the case of crustal studies, rock layers. Lithoprobe uses large truck-mounted mechanical vibrators as sources (the “Vibroseis” method) because they are logistically appropriate and environmentally safe for the hard rock areas in which they work. A central Seismic Processing Facility is in Calgary while the central office is at the University of British Columbia in Vancouver.
Although Lithoprobe is not prospecting for minerals or oil, it addresses such problems as the structure and origin of the rocks that contain metallic minerals and the development of oil- and gas-bearing sedimentary basins. The principal scientific and operational aspects are built around a number of transects or corridors which cross major geological structures. Each transect addresses one or more fundamental problem concerning the deep structure and evolution of part of the lithosphere.
Five active transects span the country: Southern Cordillera (British Columbia), Great Lakes International Multidisciplinary Program on Crustal Evolution (GLIMPCE), Kapuskasing Structure Zone (northern Ontario), Abitibi-Grenville straddling Quebec and Ontario and Lithoprobe East (Newfoundland). Three new transects have been recommended for the program: Trans-Hudson Orogen (northern Saskatchewan and Manitoba), Eastern Canadian Shield Onshore-Offshore (eastern Labrador) and Alberta Basement.
The Abitibi-Grenville transect includes the Archean greenstone belt (Abitibi) and the Grenville Front. Because much of the Canadian Shield mineral wealth is in the Abitibi greenstone belt, a pilot seismic reflection study was carried out in the base metal (copper/zinc) mining region of Noranda, Que., and the gold district of Kirkland Lake, in the winter of 1988.
The pilot project was supported by significant financial contributions from both the Quebec and Ontario provincial geological surveys and some financial and logistic support from Minnova and Cambior Inc. It was designed to tackle some fundamental regional geological problems. A specific aspect of the transect project was to target upper crustal structures in these economically important areas, with a view to defining a 3-dimensional geological framework for future mineral exploration and understanding the migration of fluids in the crust during ore deposition.
The surveys were designed to test different seismic acquisition parameters in the complex upper crust and deep crustal levels of the Abitibi; to image shear zones related to gold mineralization; and to define volcanic and plutonic assemblages within the upper crust of the Abitibi belt. Preliminary seismic reflection studies were carried out across the Blake River Group (BRG) volcanics and into the surrounding Kinojevis volcanics and the Pontiac metasediments. Both regional and high resolution parameters were used along adjacent lines for line 12 in Ontario and along the same section for line 14 in Quebec.
The data obtained in the high resolution mode are of excellent quality. Prominent subhorizontal reflections, representing intrusions and/or thrust faults, can be seen to be significantly offset by steep (up to 15-km-deep) faults which are traced to the surface as the major gold-mineralized fault zones, such as the Cadillac-Larder Lake Fault of Quebec and Ontario.
Gravity and electro-magnetic data have been collected in this transect and will be used with the regional geology to generate a more accurate 3-dimensional structure for the BRG and surrounding geological formations. A series of high resolution lines is planned for the Noranda area.
The original Lithoprobe concept was developed in 1981 at a meeting of university earth scientists sponsored by the Natural Sciences and Engineering Research Council (NSERC) of Canada. A steering committee was formed and, in 1984, NSERC and Energy, Mines and Resources Canada (EMR) were approached to fund trial experiments in the Vancouver Island and Kapuskasing areas.
This trial, known as Lithoprobe Phase I, was necessary because some methods, particularly reflection seismology, although extensively tested in other parts of the continent, had not been used under conditions of rugged terrain and complex surface geology. Phase I was funded and scientific results of outstanding quality were obtained.
The five transects of Phase II were chosen in 1986 for their scientific merit, with a view to distributing efforts across Canada and in areas of interest to the mining and petroleum industries. During the early stages of Phase II special emphasis was placed on the imaging of key features in the lithosphere to depths of tens of kilometres below the earth’s surface. This involved adapting and extending the seismic reflection technology used by the petroleum exploration industry, both onshore and offshore, and required more extensive and innovative seismic refraction and electromagnetic surveys.
Lithoprobe is the largest earth science research program ever undertaken in Canada and is funded by grants from NSERC, by contracts, capital equipment and direct participation from EMR, and by contributions in various forms from Canadian industry. The program involves representatives from almost every university department of earth science, geology and geophysics in Canada, all scientific divisions of the Geological Survey of Canada, most provincial geological surveys, and many mining exploration and petroleum companies.
The U.S., the U.S.S.R., the United Kingdom, France, the Federal Republic of Germany, Australia and the European Economic Community support their own, though somewhat different, national and international programs for the deep investigation of the earth.
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