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Prospecting in Low Magnetic Latitudes? How to Get the Best Data Possible

Countries along the equator (i.e. in low magnetic latitudes between the tropics of Cancer and Capricorn) today provide some of the most exciting exploration potential in the world.

BHP-Billiton is one example of a major company that has achieved many successes in South America and Africa and that continues to have a strong focus in these regions. As noted by BHP Billiton chief executive Brian Gilbertson recently, “If you want to hunt elephants, you must go to elephant country.” In addition, juniors are active in these areas – drawn by the economic potential of smaller, yet still rewarding, exploration targets.

Challenges in Obtaining High Quality Data

From the perspective of explorationists using magnetics in low magnetic latitudes, there are unique challenges to obtaining high quality magnetic data. These affect most modern methods.

  • Optically pumped methods encounter problems that are related to the horizontal field and sensor orientation requirements. Depending on the direction of travel, sensors must be oriented carefully to minimize orientation effects. This process is prone to operator error and is complicated as optimal orientations must be determined and maintained to obtain reliable data.
  • Proton precession methods generate lower signals in low latitudes due to lower precession frequency and low coil signal-quality factor. These two effects result in higher noise and correspondingly poorer reading quality).

The most reliable alternative is to use Overhauser methods. The benefits of Overhauser methods relate to generation of auxiliary fields while polarizing and omni-directional sensors.

Understanding the Overhauser Effect

The Overhauser effect is produced by saturating the electron spin resonance (ESR) line of a free radical, unpaired electron. The radical produces two ESR lines that are under the influence of its nucleus and the lines are separated in proportion to the strength of the earth’s magnetic field.

In stronger fields, the lines are separated by a Gauss — meaning that it is effective to saturate only one line for measurement. However, in weaker equatorial fields, the spectral lines come close together and saturation of a single line is less effective — reducing gain and signal quality.

To counter this effect, GEM introduced a proprietary technology that generates auxiliary magnetic fields during Overhauser polarization. This results in an artificial separation of the two ESR lines in low magnetic latitudes — boosting the gain. As a result, Overhauser magnetometers will produce the same quality readings regardless of the intensity of the measured field (i.e. from 10,000 to 120,00 nT).

In addition, use of fully omni-directional sensors makes surveys anywhere on the Earth easy and reliable.

Whether you are hunting “elephants” or smaller, yet, still economically attractive exploration targets in some of today’s most exciting frontiers, magnetic technologies are a fundamental and effective prospecting tool. And with technologies, such as Overhauser methods, you can help ensure that your results deliver the data quality needed to maximize success — regardless of magnetic latitude.

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