Magnetotelluric measurements in the Skellefte ore district, northern Sweden

Broadband magnetotelluric (MT) data were acquired as part of the VINNOVA project "4D modelling of the Skellefte District" in one of the most important mining districts in Sweden. The project aims were to provide a better understanding of the local and regional processes that took place in the district, and in that way provide a framework for new exploration strategies to target deeper deposits. The MT data consist of about 100 stations along profiles that follow seismic reflection surveys. The dimensionality and quality of the data were carefully analysed and 2D and 3D inversions were carried out. The resulting models exhibit extreme resistivity values with several highly resistive and conductive features. With the help of geological observations, borehole data and the results from seismic reflection lines, it was possible to interpret the resistivity structures present in the models in geological terms. The most interesting outcomes are conductors that correspond with hydrothermally altered, ore-bearing volcanic rocks, and their relationship with faults inferred from the surface geology and co-located seismic surveys. These faults probably acted as conduits for the ore-forming hydrothermal fluids.