Two-dimensional regularization inversion of magnetotelluric data for deeper mineral exploration: An example from the Sanjiang River copper deposit

Abstract

As near-surface ore bodies are depleted, the exploration for economic minerals requires information from deeper depths. The magnetotelluric method has the necessary depth capability, unlike many of the controlled-source electromagnetic prospecting techniques traditionally used. The geological setting of ore deposits is usually complex, requiring two-dimensional or three-dimensional Earth models for their representation. An example of the applicability of two-dimensional inversion of magnetotelluric data to mineral exploration is presented here. The magnetotelluric inverse problem is ill-posed and the inverse results are unstable and non-unique. It means that different geo-electrical model could fit the observed data with the same accuracy. A stable solution of the ill-posed inverse problem can be obtained by utilizing the regularization methods in the objective function. Solving large scale linear equation of inverse problem, the damped Gauss-Newton algorithm was adopted, which can improve local convergence of Gauss-Newton method. On the one hand, inversion of TE-mode data is more sensitive for the low abnormal body and has poor resolution for the high abnormal body. On the other hand, inversion of TM-mode data has better resolution for the high abnormal body. Jointed two-mode data inversion is able to achieve better model and stack quality in considerably fewer iterations. In order to better inversion results, TE- and TM-mode magnetotelluric data are jointed. Through two-dimensional regularization inversion of the field data, the Sanjiang River copper deposit is located.