Induced Polarization

Induced polarization is a phenomenon which was discovered when resistivity surveying was still in its early days. It was noticed that certain bodies were changeable or polarizable, in other words, they could be caused to take an electric charge by passing a current through them. The charge did not disperse all at once, but instead it drained away when the current was switched off.

Induced polarization and resistivity are for the most part conducted as a single survey. An electrical current is sent through the ground and the surfaces of metallic minerals get charged. One has to apply an overvoltage to drive the current through the barriers that can be found there. Once the current is switched off, the overvoltage decays. To express it in other words, there is a small storage of energy that can be measured even after the current has been switched off.

The induced polarization effect is useful particularly when detecting disseminated sulphide minerals, which can be economic in themselves or may also be useful as pathfinders to other deposits of minerals.

Spontaneous Polarization
A conductive body which extends both below and above the water table can act as a weak natural electric battery, which creates an electric current in the soils and rocks that surround it. It is possible to detect the difference in voltage along the flow of the current by using a sensitive voltmeter; this can also indicate where you can find the conductor. Spontaneous polarization is one of the first electrical techniques that was developed, now it is used only rarely because other methods are most of the time believed to be much more sensitive.