3D modelling of controlled-source electromagnetic fields adopted to mineral prospecting

Time period: 2020-04-01 to 2020-09-30

Project leader: Thomas Kalscheuer

Funder: Vinnova

Type of award: Project grant

Total fundning: 330 000 SEK

Purpose and goal: The project aimed at a simplified but accurate geometric description of ore bodies and host rock in modelling electromagnetic geophysical measurements and an improved description of the phase distribution of the current along the transmitter cable. We used the open-source program gmsh to generated computational meshes starting from geometric descriptions of ore bodies and modified an existing spectral-element code to read in such unstructured meshes, to adjust the computations for deformed hexahedra, and allow for the phase distribution of the transmitter current. Expected results and effects: The computational accuracy of the modified spectral-element code was verified using a finite-element code and is significantly better than that of commercially available codes based on descriptions of ore bodies as thin sheets. Hence, we assume that this combination of a simplified geometric description and improved computational accuracy can contribute to improved and more readily accessible models of ore deposits, reduced costs of prospecting, more efficient drilling programs and sustainable mineral extraction. Approach and implementation: We started with an analysis of available meshing programs requiring the possibility of defining geometric structures (ore bodies, hostrock, topography) in a graphical user interface. After selecting gmsh, we modified our spectral-element code to read in such meshes and to allow for the phase distribution of the current along the transmitter cable. To deal with complicated geometries, the meshes are unstructured. Hence, the computations became more advanced, and some improvements were made to the code to deal with deformed hexahedral elements.