Why Employ Airborne Electromagnetic Surveys in Exploration?

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M Survey – Electromagnetic Surveys Electromagnetic surveys are a type of geophysical exploration used to detect metallic and non-metallic minerals. The mining industry uses this surveying method as an economical means of prospecting to acquire useful data for an exploration project.
While electromagnetic surveys can be done either by air or on the ground, airborne electromagnetic surveys (AEM) are comparably cost-efficient and faster to perform when compared with ground surveys.
Employing the principle of induction, airborne active electromagnetic surveys use man-made primary electromagnetic fields. This is done by establishing a magnetic field with the passing of a current through a coil. The magnetic field is then measured using a receiver that consists of a sensitive electronic amplifier.
If the area is near a conductive zone, an eddy current will be induced. The closer the coil is to the conductive area, the stronger the eddy current will become. As such, a comparison is drawn between the primary and secondary currents, indicating the conductive source.
There are several degrees of magnitude of subsurface conductivities that can be measured by an electromagnetic survey. For example, a survey will measure a strong response when it is carried out near massive sulphides. Graphite and clay, along with gravel and sand vary in their conductivity levels. Airborne electromagnetic surveys that are prospecting under bedrock will demonstrate that pyrite, graphite and pyrrhotite are commonplace.
The data quality of an airborne electromagnetic survey is strongly dependent upon the sophistication of the data acquisition system used. For this reason, mining companies source out geophysical survey companies that employ state-of-the-art data acquisition equipment.
While airborne electromagnetic surveys are cost-effective in comparison to ground surveys, it is crucial to ensure that the data quality meets industry standards and that it can be properly"leveled”, processed and interpreted by consulting geophysicists whose job it is to recommend areas for drilling and further exploration.
Data acquisition systems used in electromagnetic surveying should be able to respond accurately to variations in overburden conductivity, as well as to graphitic formational conductors and faults in shear zones.
When conducting an electromagnetic survey, it is important to keep in mind that certain conductive targets may be covered and their magnetic signatures disrupted by factors referred to as geological noise. The following factors act as barriers that affect electromagnetic survey data:
  • Faults in shear zones
  • Overburden conductivity and lateral variations
  • Zones in which there are high instances of clay and groundwater
  • Magnetite bands
Therefore, it is vital that the data acquisition system selected is capable of rendering accurate results while taking stock of the above variables that can potentially skew the results of an airborne electromagnetic survey.
In addition to using electromagnetic surveys as a means of mineral prospecting and geological mapping, these surveys are also employed as a way of detecting the presence of electromagnetic fields in populated communities, in order to ensure they are safe to live in. A community that has high levels of electromagnetic fields can be potentially harmful, especially to children, pregnant women and the elderly.  Airborne EM to the rescue, again!
Specialists in Airborne Geophysical Surveys
Terraquest was established in 1984 and since then, our dedicated team has flown over 1,500 airborne geophysical surveys using both fixed wing and helicopter platforms.  Our professional crews provide significant experience having carried out airborne magnetic surveys, airborne gravity surveys, airborne radiometric surveys, and airborne electromagnetic surveys on five continents.
Our quality data sets have been utilized in the exploration for base and precious metals, kimberlite, hydrocarbons, uranium, rare earth minerals and water.  The company has performed exemplary surveys for both small and large exploration groups as well as many government agencies.  References can be provided upon request. Visit www.terraquest.ca.




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