Experiment of audio-magnetotelluric and dual-frequency induced polarization joint inversion in a Pb-Zn ore deposit in inner Mongolia, China

In the present study, we evaluated a method of joint inversion in which audio-magnetotelluric (AMT) and dual frequency induced polarization (DFIP) data sets are inverted simultaneously to produce a consistent 2D resistivity model to show a clear image of subsurface structures. To achieve the objectives, we conducted AMT and DFIP surveys first on the same survey line within the Dongjun lead-zinc deposit in inner Mongolia by developing 31 AMT survey sites with an interstation separation of 40 m on a 1440 m survey track and operated in fifty-three frequencies in the range 1–10,400 Hz to record the resistivity distribution of subsurface to depths exceeding 800 m. The same survey setup up was applied to the DFIP method by utilizing the SQ-3C model instrument. The two-dimensional (2D) resistivity model obtained from AMT data revealed distinct low resistivity anomalies (C2, C3) in the middle of the 2D inversion model. In contrast, the DFIP inversion model showed a high resistive body (R2) with resistivity > 7000 Ωm in the same region. In response to the discrepancies observed in the 2D inversion models, we implemented a joint approach by subjecting the AMT data to inversion in conjunction with a DFIP dataset. The joint inversion resistivity model shows surficial conducting bodies (C1, C2), highly resistive bodies (R1), and resolve area of interest high conductive body (C3) along the profile. The final joint inversion resistivity model clearly images the large silica alteration zone and area of lead and zinc sulfide mineralization corresponding to the overlap between the obtained resistivity model and geological section, resistivity signature and high percent frequency effect (PFE) value. Collectively, this study demonstrates the feasibility of a joint inversion methodology and highlights the value of integrating geophysical methods through joint inversion for enhanced characterization and exploration targeting in future research.