rst,

The survey being completed is commonly refered to as IP or induced polerization. I am not a geophysists but basically the readings obtained after the current between 2 electrodes has been shut off is what is being measured. For example, electrodes placed in the ground and connected by wire through which a charge, voltage, from a battery can be introduced. Now after the curent is disconnected the meter will still show some residiual voltage, i.e., the voltage will not go to zero immediately. The decay of this charge varies depending on the rock and mineral content. The IP survey technique has been used successfully on gold exploration projects for years. You can google "Induced polerization" to read more. This, based on my limited knowledge of the IP survey. Hope this helps a little.