ELECTRICAL RESISTIVITY TOMOGRAPHY (ERT) AND INDUCED POLARIZATION (IP) SURVEYS

Geoelectrical techniques are aimed at characterize the electrical properties of the Earth, such as resistivity and chargeability; chargeability can be thought as a measure of its capacitive response.

Electrical measurements are taken by a measurement dipole, after voltage is applied to the ground by means of a current dipole. The measured resistances are recorded and stored by a data logger. The resistances are then converted to apparent resistivity through a geometrical factor depending reciprocal position. At the same time, the voltage time decay is measured in order to evaluate the chargeability of the ground. The correction for telluric currents are automatically performed by the equipment, by periodically changing the voltage polarity.

The nowadays standard approach to get reliable 2D and 3D geoelectrical imaging, is based upon the multielectrode technique, by means of which it’s possible to simultaneously measure resistivity and chargeability by means of different dipoles.

Such method is called “Electrical Resistivity Tomography” (ERT), since it allows to depict “slices” of resistivity (and chargeability).

In an environmental prospect, resistivity and chargeability anomalies are often related to the presence of polluting fluids, like hydrocarbon-contaminated waters, or waste site leakage. The anomalies can also be used to identify metallic wastes, like steel drums.

 

IP Applications:

  • Detection of disseminated metallic luster minerals (veins or gold structures, etc.)
  • Detection of disseminated sulphides or veinlets surrounding a massive sulphide deposit
  • Discrimination between non-mineralized conductors (faults, shear zones, etc.)
  • Detection of low or non-conductive solid sulphides (rich in sphalerite, discontinuous mineralized strips, isolated sulphide grains, stockwork, etc.)
  • Mapping of alteration zones and structural elements controlling mineralization (porphyry copper systems)
  • Mapping of clay minerals associated with kimberlites
  • Polluting plumes delineation (contaminated waters, waste site leakages)
  • Identification of breaks in waste site geomembranes
  • Waste site investigations (metallic wastes)
  • Moist zones and water table identification
  • Subsoil layering and bedrock delineation
  • Landslide structure reconstruction
  • Cavity and Karst detection