Tomography of self-potential anomalies of electrochemical nature

Ore deposits and buried metals like pipelines behave as dipolar electrical geobatteries in which the source is due to (1) variation of the redox, potential with depth, (2) oxido-reduction reactions acting at the ore body/groundwater contact, and (3) migration of electrons in the ore body itself between the reducing and oxidizing zones. This polarization mechanism is responsible for an electrical field at the ground surface, the so-called self-potential anomaly. A new quick-look tomographic algorithm is developed to locate electrical dipolar sources in the subsurface of the Earth from the analysis of these self-potential signals. We applied this model to the self-potential anomaly discussed by Stoll et al. [1995] in the vicinity of the KTB-boreholes drilled during the Continental Deep Drilling Project in Germany. The source of this self-potontial signal is related to the presence of massive graphite veins associated with steeply inclined fault zones within the gneisses and observed in the KTB-boreholes.