Résumé
3D induced polarization (IP) method is a very promising tool to image the geological/mineralogical distribution and to estimate the volume of potential ore deposits. However, exploring in 3D using the conventional cable system to cover more than a kilometre by kilometre could be limited logistically and physically. Recent technological advancements, particularly the adoption of nodal geophysical recording systems commonly used in seismic, electromagnetic (EM), and electrical resistivity tomography (ERT) surveys, have revolutionized data acquisition. These nodal systems enable the deployment of independent receiving and injecting dipoles across the surface without geometric constraints, eliminating the need for extensive cabling and reducing cross-talk that can compromise ERT-IP performance. With continuous full time-series recording of both voltage and current, nodal systems facilitate flexible, adaptive stacking and advanced signal processing. This study outlines the requirements for conducting 3D IP surveys, demonstrating the complete workflow through case studies at actual mineral deposit sites. Although we adopt a nodal system using data loggers, designing 3D IP targeting from mid-range (> 100 m) to deep (500 m – 1 km) depths presents several technical and logistical challenges that must be carefully considered in survey planning: limited resources (geophysical logistics, budget, and time), DC assumption, sufficient signal-to-noise ratio, ensuring sensitivity and spatial resolution for the targeted zone. To address these challenges, we evaluated key strategies, including survey planning, high-power current injection, unconventional electrode configurations and advanced signal processing techniques. We applied this workflow at two different exploration targets in northeastern sites in Finland: 1) Deep (> 1 km) 3D surveys over the Koillismaa deep intrusion and 2) high-resolution 3D survey over the Juomasuo Au-Co deposit. For the first case, we explored approximately 16×6 km² apertures with 114 nodal electric receivers and 25 TX dipoles (Fig 1). We successfully obtained 3D inversion images for resistivity and IP using 0.125 Hz data, which corresponds to the expected mafic-ultramafic model from magnetic data. The second case employed 99 receiver stations and 66 transmitter dipoles in 2.5×2.5 km² apertures to target less than 500 m depths obtaining high-resolution data (Fig 2). The anomalous zone of resistivity and IP corresponds to the anomaly of the preliminary airborne EM survey. This study demonstrates the capability of 3D SIP utilizing a nodal system, but at the same time, emphasizes that 3D SIP surveys require careful and quantitative planning to overcome both technical and logistical challenges. This comprehensive approach is broadly applicable not only in mineral exploration but also for other deep-depth investigations, such as hydrogeological and geothermal studies. Future work will aim to integrate these geoelectrical models with laboratory-scale data, including borehole data and laboratory measurements.