Magnetotelluric Inversion, Carbonaceous Phyllites and an Ore Zone: Kevitsa, Finland

Abstract

We invert seven densely sampled magnetotelluric transects at the Kevitsa Ni-Cu-PGE (platinum group elements) deposit in Finland. The geology at the deposit presents at least two high electrical conductivity rock types within a resistive host. We consider the extent to which highly conductive phyllite and an ore zone can be separated through inversion of magnetotelluric data. Multiple inversions were completed with 312 magnetotelluric (MT) stations. It was possible to generate a three-dimensional conductivity volume from the 2D MT derived conductivities sections via volumetric interpolation. We compare the resulting 3D conductivity volume with co-located 2D and 3D seismic data. Comparisons show that an impression of the Ni-Cu-PGE ore-body could be observed in both seismic reflection and conductivity volumes. We discuss methods for constraining MT inversions and the impact they may have in separating proximal but highly conductive units. The inversions were complete as a precursor to full 3D cooperative inversion of the seismic and magnetotelluric data at this site.