Imaging Deep Crustal Structures and Mineralised Zones by 3D Modeling of Potential Field and Magnetotelluric Data - Example

The Geological Survey of Sweden (SGU) conducted a few geophysical measurements in the frame of Barents bedrock mapping project to better understand the bedrock geology as well as study some key mineralisation zones in northern Norrbotten area. In this context magnetotelluric (MT), reflection seismic and ground gravity data were collected. The gravity, airborne magnetic and MT data were inverted in 3D and the resulting models were used for a combined interpretation. Most of the high resistivity features coincide with the crystalline intrusive rocks such as granites and basalts where the high susceptibility and high density zones coincide with the basaltic intrusions. The moderately low resistivity zones occur at locations mapped as meta-sedimentary rocks hosting known conductive mineralisations for example graphite. Most of these low resistivity zones show very low magnetic susceptibilities and at some locations low densities. To the east of the study area a very distinct low resistivity zone matches the occurrence of copper sulphide and graphite mineralisations. The zone becomes very conductive (< 10 Ohmm) and non magnetic. Compared to the other models the MT resistivity models lack resolution at the surface suggesting more detailed study using electromagnetic methods such as controlled source MT or time domain EM.