Magnetic susceptibility is a measure of the ease of which a formation can be magnetised when subjected to an induced magnetic field. Geologically the magnetic susceptibility of a volume of rock is a function of the amount of magnetic minerals, (mainly magnetite and pyrrhotite), hosted within the rock. Magnetic susceptibility measurements can provide a rapid estimate of the ferromagnetism of the rock. These measurements can be interpreted to reflect lithological changes, degree of homogeneity and the presence of alteration zones in the rock mass. During the process of hydrothermal alteration, primary magnetic minerals (e.g. magnetite) may be altered (or oxidized) to weakly-magnetic or non-magnetic minerals (e.g. hematite). Anomalously low susceptibilities within an otherwise homogeneous high susceptibility (ferromagnetic) rock unit may be an indication of altered zones.

Applications:

The tool is a multi-parameter slim hole instrument primarily used for mineralogy logging of magnetically susceptible formations and is particularly useful for the determination of magnetite content and hard cap points of iron ore deposits. Similarly the tool provides signatory response to magnetically hosted mineralisation and also has an application for uranium where the log shows a negative correlation with uraniferous compounds. The tool can operate in dry or water filled holes as well as within PVC casing.

The most common applications are:

• Grade control (iron ore)
• Uranium exploration
• Horizon detection; particularly of altered sequences
• Mineralised zones
• Long term water well monitoring (salinity)

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