The Magnetic Induced Polarization (MIP) method measures the magnetic field associated with the induced polarization current rather than the electric field as is done with conventional (electrical) induced polarization (ElP). The inducing primary current is applied galvanically in the same manner as EIP, using a normal IP transmitter and two current electrodes. Instead of a pair of potential electrodes to measure the primary electrical voltage of the inducing current and the secondary voltage of the induced secondary current, the MIP method measures with a high sensitivity fluxgate vector magnetometer the associated primary and secondary magnetic fields due to the respective currents.

The primary magnetic field is used to calculate the magnetometric resistivity (MMR) and the secondary magnetic field gives the MIP parameter, which is the relative phase shift (RPS). The method uses Scintrex MFM-3 high sensitivity fluxgate magnetometers, Frequency Domain IP transmitters and a suitable frequency domain IP receiver.

• No direct contact with the ground or the currents is necessary.

With MIP/MMR measurements as magnetic fields due to currents can be measured at a distance from the current.

• Works best in conductive areas where it is normally difficult to measure voltages with ElP.

Conventional EIP measures voltages whereas MIP essentially measures current. This is an advantage in conductive areas where it is difficult to obtain measurable voltages, such as over salt lakes, areas of deep oxidation or thick clay or swamp cover.

• First order electromagnetic coupling is automatically removed with RPS MIP measurement.

In conductive areas inductive electromagnetic coupling can be a problem. The normal methods taken to minimise this with EIP also apply with MIP. These include: reducing the frequency with frequency domain, or increasing the time domain period and measuring a later decay slice, reducing the array size and applying multiple frequencies so the coupling effect can be stripped out. Uniquely the frequency IP parameter (Relative Phase Shift) has first order frequency coupling automatically removed in its derivation, making RPS the preferred IP parameter. The effect of coupling may be observed by a comparison with the Percent Frequency Effect (PFE). Also, assuming a conductive layer, this effect can be theoretically calculated and removed.

The Induced Polarization/resistivity method is the accepted and widely used geophysical technique for the detection of disseminated to semi-massive sulphides in mineral exploration. Dipole-dipole and gradient array are the normal arrays applied, but in certain geological areas these methods have geophysical problems and/or become more costly. The MIP/MMR method has special application in many areas, being more cost effective and solving the problem or minimizing the difficulties:

• Where relatively fresh rock is covered by a conductive layer, the MIP/MMR method has its prime application, as it penetrates the conductive layer and responds to sulphides in the fresh rock as well as mapping in terms of RPS and MMR the geological units at depth.

• Conductive Areas with deep oxidation and weathering, salt lakes or with thick clay, black soil, deep loam or swamp cover, where the currents are stronger, MIP measurements are easier.

• Highly resistive surface layer areas but with a conductive second layer and/or a relative conductive bedrock, where it is almost impossible to measure a potential field, such as over rocky scree, sand, caliche, calcrete, etc.

The standard MIP/MMR array is similar to gradient array, whereby two current electrodes are place widely apart, for example 1600m, and in the central square an area 800m x 800m is surveyed with stations typically every 25m, on lines 100m apart. With EIP, the current electrodes are placed normal to the geological strike and the lines are also surveyed across the strike. In contrast, with MIP the current electrodes are put along strike but MIP/MMR measurements are taken across strike. MIP is a current measuring method so by putting the electrodes along strike the current flows strongest within the conductive bodies and thus increases the magnetic field due to the current. (Simplistically, the linear body, either as a conductive MMR or MIP body acts as a line current source, whereas, if orthogonal, it appears as a short line element.) Thus MIP/MMR is more responsive to narrow conductive bodies due to current channelling and the method can be used instead of electromagnetic methods to detect conductive bodies and to detect resistive disseminated sulphide bodies at the same time.

Essentially both EIP and MIP measure the same geophysical phenomena: Current passes through material and produces an induced polarization response. However, one measures this with the magnetic effects of the current flow and the other with its electric field. With EIP, the apparent resistivity and chargeability are measured, from which the in-situ values can be calculated. In contrast and like gravity, MIP/MIP responds to the lateral variation of the in-situ values. The method does not respond or "see" any uniform horizontal layer, such as a conductive or resistive sheet, but responds strongly to vertical bodies. In this regard, the method is used as a mapping method and an anomaly hunting method, rather than to measure the physical values.

The results are usually presented as contour plans. From the shape and form of an anomaly, the depth, location, dip and size of the source is determined, with some assumptions as to the shape of the target source, (usually a dipping tabular body, as is normally done with magnetics or gradient array IP).

The MIP/MMR method for sulphide detection and geological mapping has been applied extensively throughout Australia. All states have had areas where MIP/MMR has been applied to overcome deep weathering, salt lakes, black soil plains, clays, rocky scree, and sand.

Internationally, its application has been less extensive and sporadic, but surveys have been done in caliche areas of Chile and Peru, and areas of conductive cover in the United States, Canada, Japan, China, Ireland, South Africa.