Abstract: A geophysical prospecting detector device and method of measuring potentials existing in the air in the area of the lower atmosphere between about one and ten meters above the surface of the earth in order to detect petroleum accumulations and mineral deposits below the surface of the earth. A detector device is mounted on the front bumper of an off-the-road vehicle and the vehicle is moved across the surface of a given area of earth in a more or less continuous fashion. Changes in the electron flow through the ion field at the surface of the earth to increased and decreased resistivity values in the crust of the earth are recorded.