Mining exploration is a strange but very fascinating activity; its methodology evolves as science and technology are progressing. I was either adapting the way of exploration with newer types of sensing instruments or developing new ones. During the 1970s, reconnaissance exploration was done with a surveying aircraft equipped with a specific set of sensors for finding local zone of interest. These located zones, usually of about 200-meter radius, were then explored, on foot, by geologists and other technicians with portable set of sensors. Electrically conductive formations (ECM) are usually interesting for those looking for mineral deposits, but they are usually buried under the surface of the ground; the most common sensor for detecting such spots are known as electro-magnetometers (EM) : instruments similar to those used for detecting metallic bombs or mines during WW2. There are airborne EM sensors (usually very heavy), and portable EM sensors. This photo is showing two aircraft, each one was carrying a specific type of airborne EM sensor. As you can see, these aircraft are huge. The one at the forefront is a De Havilland Canada DHC-3 Otter The one further away is a PBY Canso; it is even bigger. You can get more details about these aircraft on the Internet.