SELF POTENTIAL MEASUREMENTS: these are "passive geoelectric measurements" obtained with the help of two non-polarizable electrodes, measuring the "natural" variations of the electric potential of the soil without introducing current in the same. When different portions of a mineralisation come into contact with fluids of different composition, the resulting chemical reactions generate different solution pressures in the respective contact areas, increasing the potential difference and determining a flow current in the soil itself. This method is mainly used for surface mining above the water table (e.g. sulphites or graphite).