Magnetic Surveys

Magnetic intensity measurements are taken along survey traverses (normally on a regular
grid) and are used to identify metallic mineralization that is related to magnetic materials
(normally magnetite and/or pyrrhotite). Magnetic data are also used as a mapping tool to
distinguish rock types, identify faults, bedding, structure and alteration zones. Line and
station intervals are usually determined by the size and depth of the exploration targets.
The magnetic field has both an amplitude and a direction and instrumentation is available
to measure both components. The most common technique used in mineral exploration is
to measure just the amplitude component using a proton precession magnetometer. The
instrument digitally records the survey line, station, total magnetic field and time of day
at each station. This information is typically downloaded to a computer at the end of each
day for archiving and further processing.
The earth’s magnetic field is continually changing (diurnal variations) and field
measurements must be adjusted for these variations. The most accurate technique is to
establish a stationary base station magnetometer that continually monitors and records the
magnetic field for the duration of the survey. The base station and field magnetometers
are synchronized on the basis of time and computer software is used to correct the field
data for the diurnal variations.