Prospecting
in Low Magnetic Latitudes?
How Can You 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.
