What Is Induced Polarization?

Induced Polarization (IP) is a geophysical technique that measures the potential difference during and after an electrical current is injected directly in the ground or within boreholes, providing information about the chargeability and resistivity of the subsurface. This method reveals subtle variations in subsurface materials, driven by the electrochemical properties of rocks and soils.

Why is Induced Polarization important in mineral exploration?

Chargeability can help geologists identify zones of mineralization and alteration that might indicate valuable ore deposits by detecting the rock's ability to store and release electrical charge. Chargeability can reveal hidden features below the surface and enhance exploration strategies.

Why is Resistivity important?

Resistivity helps map geological structures and changes in rock types. Variations in resistivity can highlight features like fault zones, fractures, or changes in lithology, which are often associated with mineralization. By mapping these contrasts, resistivity data plays a vital role in guiding exploration efforts.

What rock properties influence IP and Resistivity signals?

• IP: Influenced by grain size, surface area, and the presence of metallic minerals or clays, which affect the rock's ability to temporarily hold and release an electrical charge.
• Resistivity: Controlled by factors such as mineral content, porosity, permeability, and the salinity of pore fluids, which together determine how easily electrical current flows through the rock.

Understanding these properties is key to accurately interpreting IP survey data.

How does an IP survey work?

During an IP survey, an electrical current is injected into the ground using at least two electrodes, placed in contact with the ground, to measure the resulting voltage. As the current is turned off, the decay of the voltage signal is recorded, providing insights into the subsurface’s electrical properties. Additionally, resistivity data is collected simultaneously, offering a complementary dataset for interpretation. Surveys are typically conducted on a grid (often with lines around 100 m apart and perpendicular to the geological strike) to ensure systematic coverage.

What IP survey types are available?

Induced Polarization (IP) and Resistivity surveys come in surface, borehole, and specialized deep exploration configurations. Each type varies in depth, geometry, and resolution.

Conventional 2D IP arrays provide data to about 250 m depth, ideal for shallow exploration. Abitibi Geophysics’ OreVision 2D & 3D IP system, designed for up to 30 electrodes, extends the depth of investigation to 600 m, while maintaining high data quality and resolution.

The DasVision 3D IP distributed array system minimizes the need for long cables, improving survey efficiency in challenging terrain. It provides detailed, high-density data for 3D models, enhancing exploration accuracy. The IRIS FullWaver system allows full waveform measurements for both deep and shallow exploration.

Borehole IP surveys directly measure rock properties, with Hole-To-Hole (H2H IP) surveys offering additional insights between and beneath boreholes.

Our geophysicists can recommend the best survey type for your goals and environment. Each survey configuration is selected based on the target deposit, survey area, and program goals, ensuring the optimal approach for accurate data collection and interpretation.

How do geologists interpret IP survey results?

Geologists integrate IP data with other geophysical measurements and geological observations. By correlating chargeability and resistivity data with known rock properties, previous exploration results, and geological mapping, they can build more refined subsurface models. This integrated approach aids in discriminating between mineralized targets and non-mineralized zones.

What kind of deposits can be found by an IP survey?

IP is particularly effective for mapping disseminated mineralization and sulphide mineralization, notably those associated with gold. It is also a proven tool for detecting: Volcanogenic massive sulfide (VMS) deposits, Porphyry copper, Kimberlite bodies, and Ni-Cu-PGE, lead-zinc, and uranium deposits.

Beyond mineral exploration, IP surveys can help distinguish between non-mineralized features, detect low or non-conductive sulphides, and map alteration zones. Resistivity can also be valuable for applications such as assessing bedrock depth, groundwater mapping, contamination studies, and leak detection.

Conclusion

Induced Polarization is a robust, science-based method grounded in fundamental physical principles. Through precise electrode placement, careful data acquisition, and integrated interpretation, Abitibi Geophysics provide detailed images of the subsurface. With advanced systems like OreVision, DasVision, and H2H, geologists are empowered to make informed exploration decisions, efficiently target mineral deposits, and demystify the complexities of the subsurface.