Magnetic Surveying Explained

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Magnetic SurveyMagnetic surveying is a geophysical method used in the mining industry to locate, calculate and determine quantities of minerals beneath the ground. It monitors spatial variations in the Earth's magnetic field, which allows specialists to detect and map artifacts, features and various other formations beneath the Earth's crust. These formations are often large deposits of minerals such as iron, steel, brick and other form of rock that are highly magnetic.
 
The tools used in magnetic surveying are called magnetometers. These scientific instruments are tuned to measure both the strength of the magnetic field as well as the direction. Currently, there are three different types of magnetometers used by the mining industry to be able to detect these anomalies, and they include:
  1. Gradiometers, which are pairs of meters separated at a fixed distance horizontally. The two values are then subtracted which provides an accurate measurement of the fields of gravity caused by anomalies.
  2. Fluxgate Magnetometers, typically consist of a ‘sense' coil and a ‘drive' coil that is wound around a core. An alternating current is applied to the drive coil which causes both plus and minus saturation. As there is an opposite polarity, when a magnetic field anomaly is applied, it will aid one polarity and oppose the other.
  3. Caesium Vapour Magnetometers, which consists of a photon emitter which contains a caesium lamp, an absorption chamber containing the vapour and a ‘buffer' gas, and also a photon detector. Complicated sounding, however in practice it's very simple, as a magnetic field comes into contact with this magnetometer, the polarization of the field will cause the caesium atoms to pass through and be measured by the photon detector.
Aeromagnetic surveying is another form of magnetometer. Rather than being placed on the ground, the magnetometer is onboard or is toed behind an aircraft. This allows much larger areas to be explored in less time. Aeromagnetic surveying is also typically more accurate because the plane moves at a uniform speed. The process of doing aeromagnetic surveying is similar to the small magnetometers listed above, but allows much larger areas of the earth's surface to be covered. In airborne magnetic surveys, the aircraft will typically fly in grid patterns as the magnetometer picks up slight differences in the magnetic field that are then expressed on maps as coloured imagery. This method of surveying is preferential in the mining industry because it provides a vast area of surveyed land in less time than traditional ground based surveying would take. Once the aeromagnetic survey is complete and the overall picture can be analyzed, in some cases a ground based survey is a logical step to target specific areas of interest.
 
The practice of airborne magnetic surveying is important to companies seeking magnetically active resources while ground based magnetic surveys are useful if the area is small or a specific area is the ideal target. Both play a role in the mining industry and act as an important tool to companies seeking the minerals entombed under the Earth's surface.
 
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