Very Low Frequency (VLF) measurements are typically used in mineral exploration to determine the location, thickness and dip of conductive ores. The same properties can also be determined for contusion zones or faults. Other applications include permafrost mapping and mapping the distribution of electrically conductive contaminants.
The absence of a separate transmitter loop simplifies the measurement. The measurement can be performed by one person. There is extensive experience in using the methods and the processing and interpretation of the data is typically clear. Since it is an electromagnetic method, the conductor does not necessarily have to be massive.
The measurement is performed with a mobile receiver. The measurement is performed point by point and the distance between the points on the line is typically about ten meters. At each point, the secondary field caused by the VLF transmitters is detected.
We use the Geonics EM-16/EM-16R device for VLF and VLF-R measurements, which is the world's most widely used electromagnetic geophysics measuring device.
In VLF measurements, only international general base stations can be used or a TX27 mobile VLF transmitter can be used to amplify the signal. Using a mobile base station also allows for more versatile line geometry planning than using international VLF stations.
The result is the real and imaginary components of the secondary field at each point. Typically, the results are presented as a line profile. The conductivity distribution (classification of conductivity based on the Re/Im ratio), as well as the thickness of the conductive object (in the line direction) and the slope can be interpreted.
