Unconstrained 2D and 3D magnetotelluric inversion - Detection of a Ni-Cu-PGE ore zone and carbonaceous phyllites - Kevitsa

Abstract

The large Kevitsa Ni-Cu-PGE (platinum group elements) deposit in Finland is part of a complex geoelectrical setting. The ore zone is electrically conductive compared to the high resistivity olivine pyroxenite host rock. The ore body and host are surrounded by thin sheet like high electrical conductive carbonaceous phyllites. Unconstrained 2D and 3D inversion of magnetotelluric (MT) data was performed using seven densely sampled MT transverses ranging in length from 2500m to 7000m. Two dimensional inversions included a total of 312 MT stations along the seven transverses, while 3D inversion was completed on a subset of 270 MT stations focused around the ore zone. The inversions were conducted on the Pawsey Centre, Magnus Cray XC30 supercomputer. The challenge for this site was to resolve the ore body in the presence of the carbonaceous phyllites using sparse transverses. We compare the outcome of 2D and 3D MT inversion and find that 3D inversion appears to provide superior definition of the ore zone. This research and the resulting electrical conductivity distributions will inform our future work on full 3D cooperative inversion of seismic and MT data over the Kevitsa site.