Three-dimensional forward modelling and inversion of magnetic anomaly using finite-infinite element coupling method with Comsol: A case study of Pingchuan iron-ore deposit, Southwest China

We implemented the finite-infinite element coupling method in Comsol for three-dimensional magnetic forward modelling in geophysics exploration. The finite-infinite element coupling method optimizes boundary conditions by combining finite and infinite elements, and its boundary and mesh convergence were validated against analytical solutions. For non-ellipsoidal magnetic bodies without analytical solutions, we compared the forward magnetic anomaly solutions of a cube using the finite-infinite element coupling method and finite volume method with hexahedral meshes. The finite-infinite element coupling method demonstrated higher accuracy compared to the finite volume method under the presence of remanent magnetization, highlighting the impact of spatial discretization on solution quality. Simulation results from the rectangular prism and composite models showed that the finite-infinite element coupling method, through unstructured meshes, enables precise modelling of complex geometries and non-uniform magnetic field distributions. Using Comsol Multiphysics, we successfully applied the finite-infinite element coupling method for the three-dimensional inversion of ore body models and analysed data from the Pingchuan iron ore deposit in Southwest China. This study illustrates the applicability of the finite-infinite element coupling method in advancing magnetic modelling and the effectiveness of Comsol as a tool for characterizing complex geological structures.