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2.2.5 Geophysical Surveys
Geologists and prospectors may only access outcropping rock to determine the presence of valuable minerals and metals. However, they would undoubtedly like to have the equivalent of a divining rod to know where exactly in the subsoil the much sought-after gold, copper and iron are located.
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Many geologists and prospectors have observed that in the presence of magnetic iron (magnetite), their compass spins. They have also observed that uranium causes a reaction in the first Geiger counters brought out in the 1930s.
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As of the mid 1920s in the Abitibi region, geologists and prospectors started to use magnetometers to locate and delineat areas of metal mineralization.
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Referred to as "electric prospecting" at the time, this technique made up for the dearth of outcrops in marshy regions covered with peat moss.
With the development of more sophisticated magnetometers in the 1940s, capable of measuring the magnetic forces of different types of terrain and mostly used in airborne surveys as of 1946, the Geological Survey of Canada was able to undertake and produce a general geophysical map of Canada.
For 20 years, from 1962 to 1982, the Government of Quebec participated in and was even the architect of the federal program to make more detailed aeromagnetic surveys of the entire territory of Quebec. This cartography, quickly made public, was used by private exploration companies when preparing their own surveys.
In the 1950s, individual prospectors also used battery-powered metal detectors to locate metals near the surface.
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