ODDS ‘N’SODS — Airplanes and prospecting (2)

Airplanes and prospectors were to form an interesting new bond following the Second World War. The U.S. had developed an airborne system for finding submerged German U-boats, which detected the magnetic quality of the submarines metal. First used in 1943, this was, in effect, the first airborne magnetometer (mag). Mining people were quick to adapt it for finding magnetic ore, such as nickel or iron ore, beneath the Earths surface.

The International Nickel Company (Inco), with large nickel mines in Sudbury, Ont., contracted one of the very first airborne mag surveys in peacetime. It began in January, 1947, and covered the whole Sudbury Basin. The early mags were held in bomb-shaped units which were dragged beneath the aircraft on a cable. The crew consisted of a pilot, a navigator and an operator sitting in the back of the plane. The operator watched for anomalous readings which would indicate that the plane was flying over a magnetic source.

The results of the survey were so good that Inco began an airborne mag survey in northern Manitoba in June of the same year, which would ultimately result in the discovery of the Thompson nickel orebody.

Consulting geologist Charles Pegg tells of an episode in the early days of aero-mag surveys. He was flying a survey in the Ungava Peninsula of northern Quebec. As navigator, Pegg was seated beside the pilot. Because of the crude instrumentation the operator in the back of the plane with a hand-held magnetometer the pilot had to fly low, just over the tree tops. The flight path was directed toward a mountain in the distance. Pegg noticed the mountain getting closer and closer. Finally it was so close that he turned to the pilot and saw, to his horror, that he was asleep. The pilot woke up just in time to raise the nose of the craft, almost vertically, and thereby avoid disaster.

In the mid-1950s, Selco Mining & Development was so interested in airborne surveying that it began its own airborne geophysics division which would be renamed Questor in 1967. It financed its work by doing airborne surveys on contract for other mining companies.

Selco was one of several groups working in the 1950s on a new system electro-magnetic (EM) induction which could be used on aerial surveys. It was able to detect material which conducted electro-magnetism, such as base metals, sulphides, graphite and clays.

If a region were surveyed for mag and EM, the superimposed plots of the two surveys would give a lot more information than either of the two systems alone could do. Mag and EM are still the two main survey systems used in the search for base metal deposits; the former is used to locate a favorable area, the latter to pinpoint potential deposits. They can also be used to find gold deposits and kimberlite pipes.

Airborne surveys were in their heyday in Canada in the 1950s and 1960s when virtually the whole country was flown over. The Geological Survey of Canada began its mag surveys in 1948 and systematically produced and published data from across the country. Many areas were reflown for mag and EM in the 1970s, when aviation companies were replacing Second World War-vintage planes with modern equipment.

Airborne geophysics was responsible for the discovery of some of Ontarios newer mines, including Kidd Creek in Timmins, Detour Lake north of Kirkland Lake, Mattabi near Ignace, Thiery near Pickle Lake, Marmora near Peterborough and the Adams mine near Kirkland Lake. Many deposits found by airborne surveys may someday become mines if metal prices rise.

In the past decade, airborne surveys have improved in terms of instrumentation, the volume of data that can be collected, and the speed at which data can be handled. The latter two improvements are the result of better computer systems on the planes and at mine camps.

The preceding is the conclusion of a 2-part series from Energy, Mines & Resources Canada.