Research on Topographic Effects of the Time-Domain Induced Polarization Method in Mineral Exploration

Time-domain induced polarization (TDIP) is a widely adopted geophysical technique for metallic mineral exploration. Field surveys are frequently carried out under complex topographic conditions such as slopes and valleys. Topographic undulation distorts TDIP responses and may bias the interpretation of ore-related subsurface anomalies. In this work, an unstructured finite-element forward modeling framework for TDIP is constructed using tetrahedral meshes generated by TetGen1.5.1, and the preconditioned conjugate gradient (PCG) solver is employed to solve large sparse linear systems. A spherical model with an analytical solution is adopted to verify the reliability of the algorithm. Numerical experiments are designed for flat, slope and valley terrain conditions to quantitatively evaluate mesh performance and topographic effects. Numerical results indicate that mesh quality acts as a dominant factor controlling simulation accuracy. Local adaptive mesh refinement can effectively reduce relative numerical errors and achieve a good balance between computational accuracy and cost. This study reproduces topographic effects that have been documented in the existing literature: the apparent chargeability exhibits asymmetric distribution over slopes, with attenuated anomaly amplitude and shifted anomaly position as the dip angle increases; current convergence in valleys amplifies secondary IP signals and alters anomaly patterns. Synthetic inversion tests demonstrate that neglecting topographic relief can induce inversion artifacts and misposition the target geological bodies. A field TDIP dataset from a mountainous polymetallic deposit further shows that terrain-constrained inversion facilitates the identification and discrimination of anomalies. The core advancement of this study lies in the establishment of an adaptive meshing workflow for TDIP forward modeling under complex terrain and its systematic quantitative evaluation. The proposed framework provides reliable technical support for high-precision TDIP data interpretation in mountainous mining areas.