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The Terraquest XDS VLF System:
Discussion of the 3-component passive VLF EM system and exploration case
studies
By Peter Walker1 and Jeremy S. Brett2
1 Geophysical Algorithms
2 MPH Consulting Limited
VLF-EM is a passive electromagnetic method that
employs energy in the 3-30 KHz band, typically broadcast by naval
transmitters. Under good conditions, VLF-EM can be sensitive to
conductivity variation to a depth of 100 meters.
Standard VLF measurements are typically made by tuning the system to a
particular transmitter. Provided the transmitter is on, and
provided the strike of the conductivity variation is in-line with the
direction to the transmitter, useful data can be acquired.
Unfortunately, these conditions are not always met, and VLF data must
often be discarded.
The XDS-VLF system has been developed by Terraquest to overcome these
difficulties. While it can acquire data in the standard mode,
tuned to a particular VLF transmitter, it also has a broadband mode
spanning from 12 to 35 KHz. Thus, XDS is not sensitive to
geological strike and the foibles of a particular transmitter.
This increases the reliability of the XDS measurement in comparison to
the standard method. The XDS receiver consists of three orthogonal
coils and so is sensitive to geological variation independent of the
strike to the transmitter and the orientation of the aircraft.
VLF data can be of great utility, particularly when interpreted in
conjunction with magnetic and radiometric data to confirm or identify
new structures. Results from a number of case histories will be
presented. It will be shown how VLF conductors and associated probable
structures can be identified in the Athabasca Basin, how structures
associated with uranium mineralization in the Otish Basin can be traced,
and how VLF data can be employed in gold, nickel-copper/chromite and
diamond exploration.
XDS/VLF – EM
| VLF / EM |
| Model |
XDS |
| Manufacturer |
Terraquest Ltd. |
| Primary Source |
Magnetic field component
radiated from government VLF radio transmitter |
| Parameters Measured |
X, Y, Z components, absolute
field |
| Broadband |
12 to 35 KHz |
| Gain |
Constant Gain Setting |
Examples
The Terraquest XDS VLF System; Discussion
of the 3-Component Passive VLF EM System and Case Studies.
By:
Peter Walker, Geophysical Algorithms
Jeremy S. Brett, MPH Consulting Limited
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