Induced & Spontaneous Polarization

Induced polarization, or IP, is a phenomenon discovered in the early days of resistivity surveying. It was found that certain bodies were “polarizable” or “chargeable” — that is, they could he caused to take an electric charge by passing a current through them. When the current was switched off, the charge did not disperse all at once, but drained away.

Resistivity and IP are normally conducted as a single survey. An electrical current is sent through the ground and the surfaces of minerals become charged. An overvoltage has to be applied to drive the current across these barriers. When the current is switched off, the overvoltage decays. In other words, there is a brief storage of energy that can be measured even after the current is switched off.The IP effect is particularly useful in detecting disseminated sulphide minerals, which may be economic in themselves or may serve as pathfinders to other mineral deposits.

Spontaneous Polarization

A conductive body extending both above and below the water table can act as a weak natural electric battery, creating an electric current in the rocks and soils surrounding it. Using a sensitive voltmeter, it is possible to detect the voltage difference along the flow of the current, which can indicate where the conductor is. SP, one of the first electrical techniques to be developed, is used only rarely now, as other methods are generally believed to be more sensitive.