Resistivity and induced polarization (IP) are two of the most common electrical methods. They measure parameters associated with voltages induced in the ground by direct application of current. Resistivity gives information on ground bulk resistivity while IP gives ground impedance or capacitance. Recent developments include Multi Pole-Dipole arrays for greater resolution.

1. Mineral exploration - detection of ore bodies by their resistivity and/or IP anomalies. Fugro also performs Downhole IP surveys in addition to standard surface methods.
2. Groundwater investigation - aquifers can be detected as resistivity anomalies.
3. Stratigraphy mapping - differing soil and/or rock types may have different inherent resistivity.
4. Geotechnical - soil or rock resistivity is important in many geotechnical projects.
5. Environmental - IP methods can assist in the assessment of the acid generating potential of waste rock and tailings from mine operations. Resistivity can be used to map contamination plumes.

1. Ideal for detecting disseminated sulfides, which often contain desired minerals.
2. Resistivity and IP data can be collected simultaneously using the same instrumentation.
3. Resistivity is equally effective at detecting resistive or conductive targets.
4. IP may be used for mineral discrimination.
5. A multitude of configurations are available depending on the survey target.

Fugro Ground operates both time and frequency domain IP equipment. A variety of transmitters and receivers (Scintrex, Zonge, Iris Instruments) are available to suit all operating requirements and environments.

Geophysicists are assigned to all field crews in order to ensure efficient field operations and to monitor data quality. In-field data products include contoured colour-image pseudo-section profiles and contoured shaded colour image plan maps of several parameters. Interpretation of the data is available using various computer modelling routines such as Interpex RESIXIP2DI using Zonge or Interpex algorithms.

The development of 3D IP Inversion software has lead to the requirement for more readings with depth. To increase the signal strength at greater n values, pole-dipole and 2 IPR-12 receivers are applied. Typically 16 receiver dipoles are set-up and 44 current electrodes are installed on a single 1.6 km long line. The line is surveyed in one day and 700 odd stations are recorded which gives the broad coverage and high resolution required for the 3D inversion. FGG has specialised in the operation and data acquisition of this newly designed and innovative IP exploration method. For further information, refer to the following Extended Abstract: A new survey design for 3D IP inversion modelling at Copper Hill

Logging of the resistivity and IP values down a drillhole is an important part of an exploration program involving surface IP. As these in-situ geoelectrical characteristics determine the surface IP responses, knowledge of them enables a fuller understanding of the surface data and guides any future exploration program.

When drilling an IP anomaly, it is necessary to determine if the source of the surface IP anomaly has been intersected. Further, by using wider electrode spacings, a near miss can be detected where the main IP body is a few or tens of metres away from the drill hole.

Downhole IP is widely applied in base-metal exploration, particularly for lead-zinc bodies and also for nickel and copper. For at-hole studies, the 25W or 200W Scintrex IPC-9 transmitters are used, while for wider electrode spacings to 'see' around a hole, a larger 3kW transmitter is used, measuring multiple dipoles simultaneously.