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Abstract

The Koillismaa-Näränkävaara complex in North-eastern Finland is currently studied with a variety of geophysical and geochemical investigations to better understand its geological history and assess its mineral potential. The area is characterized by an East-West oriented deeply seated ultramafic intrusion within the granitoid bedrock which has been indicated by gravity and magnetic anomalies as well as 2D inversion of sparse magnetotelluric (MT) data. It was successfully drilled at a depth of 1.5 km by the Koillismaa Deep Hole. The aim of this study is to better delineate the geological structure around the Koillismaa Deep Hole area. We collected 70 MT sites along an approximately 40 km long profile across the intrusion. In addition, we also tested our newly acquired EM transmitter and collected a densely sampled controlled source AMT (CSAMT) profile across the Koillismaa Deep Hole at the centre of the MT profile. Data analysis of the MT data shows prominent geoelectrical strike direction perpendicular to the intrusion. However, it also shows a change of strike direction with depth by 20^◦. We will discuss possible causes of observed anisotropy and show inversion results of the MT data and compare it with latest results from our CSAMT survey. Our EM results will be further compared to other existing geophysical data such as borehole logs, gravity, and magnetic modelling as well as petrophysical measurements of the drill core.