Induced polarization effects in transient electromagnetic data: A case study from the Hawiah volcanogenic massive sulfide deposit in Saudi Arabia

In exploring volcanogenic massive sulfide (VMS) deposits, the transient electromagnetic (TEM) method is highly effective due to its sensitivity to metallic conductors such as sulfide minerals. A recent TEM survey over the Hawiah VMS deposit in Saudi Arabia utilized ten stations to investigate the distribution of VMS targets. Several stations exhibited anomalous fast decay curves attributed to induced polarization (IP) effects, a common characteristic of VMS minerals. Spectral IP (SIP) measurements of local VMS core samples indicated large IP effects, aligning with results from a previous time domain IP (TDIP) survey in the area. IP effects can distort TEM measurements, causing as fast decay followed by sign reversals, complicating interpretation when using conventional resistivity-only (RO) workflows. These distortions can result in unreliable interpretations, especially in regions with complex subsurface conditions. In this paper, we present a synthetic model analysis based on geological setting information, demonstrating that in scenarios with moderately resistive backgrounds and deeply buried high-polarizable bodies, TEM curves can exhibit anomalous fast decay in the middle to late time, aligning with the observed field data. Thus, this behavior serves as a key indicator of IP effects in the survey area. Through RO and IP-incorporated inversions, along with an uncertainty analysis of the resulting resistivity models, our findings show that the data is better fitted using an IP-incorporated inversion approach. This highlights the importance of analyzing anomalous decay in TEM data and supports adopting refined methodologies that account for IP effects. Such approaches are crucial for achieving accurate and reliable evaluations in areas with highly conductive and polarizable materials, like VMS deposits.