Electrical resistivity studies are the oldest electro-prospecting methods. Direct current (DC) running through the ground allows obtaining information about rocks resistivity distribution. The using of DC itself is not very common now and in the most modern tools it is replaced by very low frequency alternating current (from first Hz to first hundred Hz). For several ratios of measurement array size and rock resistivities, electromagnetic signals at such frequencies, from the one hand, still can be discussed as DC from the point of view of physics. From the other hand, their application can decrease the influence of electric noise at the measurement data, and they also allow us to realize measurements without use of grounded electrodes.
In general case, the measurement array includes both current and potential electrodes, their mutual position and measurement technique determine the variety of DC resistivity methods.
DC resistivity methods can be roughly divided onto three branches:
Electrical horizontal profiling using different types of arrays (Dipole-Dipole, Wenner, Pole-Pole etc).;
Vertical electric soundings (VES) and its variations;
Electrical resistivity tomography or electrical resistivity imaging is a modern DC resistivity technique which combines both profiling and soundings. It makes possible 2D and 3D electrical imaging of geological structure.
DC resistivity methods are preferable for the detection of non-conducting rocks in low-resistive media because the measured voltage is directly proportional to the rock resistivity. These kind of methods are not very suitable for the study of conductive rocks since the signal can be lower than a noise level.
Resistivity methods are widely used in various geological studies from the specification of general geological structure of survey area to mineral deposit prospecting. They are often good for the specification and mapping of overlaid auriferous quarz-veins.