Total Field and Gradiometric Magnetics

Method

Total Field Magnetic surveys measure large changes in the local magnetic field. This can be useful in detecting large ore bodies or changes in bedrock geology. In a relatively homogeneous bedrock, the signal provides insight into depth of bedrock (useful in determining placer targets).

Gradiometric Magnetic surveys measure the difference in signal between two vertically aligned magnetometers (commonly referred to as the first vertical derivative). Overwhelming bedrock magnetic signatures thus become buffered while shallow anomalies are accentuated relative to the spacing between magnetometers. This has been most useful in tracking ferromagnetic minerals associated with certain placer deposits.

The shape and amplitude of an induced magnetic anomaly is generally a function of the orientation, geometry, size, depth, and magnetic susceptibility of the body. Intensity and inclination of the earth's magnetic field in the survey area will also affect the signature of a magnetic anomaly.

Instrumentation

We use a GEMSYS GSM-19 GW with differential GPS as a walking magnetometer, and a GEMSYS GSM-19 as a base station.

Application

In the mining sector Magnetics is mostly used for mineral exploration. Magnetics is a highly effective primary method for discovering dikes/veins/alteration zones, ore bodies, and kimberlite pipes. Size and shape of these targets can then be confirmed by 2D Resistivity / IP.

In some cases, Magnetics can be used as an auxiliary geophysical method for placer prospecting. If paleochannels, seen in a 2D Resistivity profile, have sufficient concentrations of magnetite they, can be effectively mapped with a magnetometer.

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