Joint 3D resistivity inversion of ground-based MT and CSEM data to improve resolution for deep mineral exploration

Abstract

The growing demand for critical raw materials to support carbon-neutral energy and transportation systems motivates the exploration of deep-seated (500–4000 m) mineral deposits. While electrical resistivity is a key parameter for identifying mineralization, imaging these depths remains challenging due to limitations in resolution and non-uniqueness of individual electromagnetic inversions. This study evaluates the potential of joint three-dimensional (3D) inversion of magnetotelluric (MT) and controlled-source electromagnetic (CSEM) data to improve subsurface resistivity models. A joint inversion framework is implemented using open-source codes, balancing MT and CSEM sensitivities via a relative weight defined by the ratio of the Frobenius norms of their weighted Jacobian matrices. The methodology is applied to a large-scale field data set from northeastern Finland, targeting a deep mafic-ultramafic intrusion at depths exceeding 1.5 km, with regional potential for copper, nickel, platinum-group elements, vanadium, titanium, and iron. Results demonstrate that joint inversion improves model resolution and consistency with known geology and legacy geophysical data compared to individual inversions. These findings highlight the feasibility and promise of combined large-scale 3D MT–CSEM surveys for deep mineral exploration and provide a scalable framework for both future research and commercial applications.