Geophysical Exploration is Commonly Employed as the Prospecting Stage in Mineral Exploration

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geophysical prospectingA mineral exploration is conducted in several stages, and the prospecting stage is arguably one of the most important. Mineral prospecting can be done in various different ways and geophysical surveys are enabling mining companies to acquire highly accurate results with regards to the mineral concentrations in the Earth's crust. There are two specific types of airborne surveys that can be employed in a prospecting project: detailed and regional.
 
There are two methods of prospecting that a detailed survey is completed for: direct and indirect. Surveys conducted as a direct prospecting method are employed to gain a detailed perspective on the concentrations of magnetic ores such as magnetic iron ores, chrome and kimberlites. Aeromagnetic surveys will uncover high concentrations of commodities that are highly sought after by the mining industry. Concentration levels of these minable commodities are reflected in the magnetic fields in the space directly above the land.
 
The other method is called indirect prospecting, used as a means of discovering the structural body, depth and geometry of a specific area. Indirect prospecting assists in the task of mapping out weak magnetic fields as well as successfully discriminating between conductors that are both metallic and non-metallic.
 
Detailed aeromagnetic surveys offer data at a higher resolution using a traverse line spacing of under 250 meters. As such, these surveys are able to act as sufficient mineral prospecting tools for magnetic iron ores and kimberlites. A detailed survey is capable of helping to assess the body and depth of the land that will be explored, and can locate specific basement targets in hydrocarbon exploration.
 
Regional aeromagnetic surveys assess a large terrain of usually more than 5000 square kilometers, with a traverse line spacing of up to 500 meters. These surveys are employed to look for commodities such as coal and petroleum. Mining companies prospect for these as well as use regional surveying as a means of prospecting for other non-metallic valuable substances that can be found in the basement surface.
 
While there are several different ways of conducting a geophysical survey as a means of mineral prospecting, airborne magnetic surveys are the most commonly used surveys for this purpose. Airborne magnetic surveys work by employing the use of a magnetometer, either attached to the aircraft or towed behind, and work by detecting ambient magnetic fields that are caused by minerals in the subsurface of the Earth.
 
Similar to handheld magnetic surveys, airborne magnetic surveys enable a vast space to be assessed at one time. While the aircraft is in flight, the magnetometer will test the magnetic fields over the land including the spatial variations that are a result of the regional magnetic field and the concentrations of the minerals under the surface of the Earth. Minerals that can be detected are uranium, titanium, base and precious metals, kimberlites, and minable magnetic ores.
 
While aeromagnetic surveys are highly useful in mineral prospecting, there are certain areas that are covered by heavy bedrock and other factors that can obstruct the presence of ambient magnetic fields. In such cases, mining companies will use airborne electromagnetic surveys as a prospecting tool.
 
Using the concept of induction, electromagnetic surveys induce an electric current through a coal that is passed underground. When the coil is underground, an eddy current develops.
 
The eddy current will begin to circulate and become stronger the closer it gets to a conductive zone and, in turn, a secondary current will develop.
 
Electromagnetic surveys are cost-efficient ways of mineral prospecting. However, it is important to remember that there will be certain factors that can interfere with the acquiring of accurate data. These factors are labeled geological noise and can disrupt electromagnetic currents.
 
Geophysical surveys are an extremely helpful tool in the mineral prospecting stage of an exploration and mining companies depend heavily upon their results in order to render profitable expeditions.
 
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