Induced Polarization – discovered in the early days of resistivity surveying (i.e. shooting electrical charges through the ground and mapping the varying levels of conducivity). IP is based on the finding that certain types of mineral deposits can be “charged” and will hold an electrical charge passed through them. When the charge is turned off, it does not “switch off” but instead drains off over time. Resistivity and IP are usually done at the same time. This is particularly useful in detecting sulphide minerals which may be economic in themselves, or which can serve as pathfinders to other mineral deposits.