2D Seismic Imaging of the Koillismaa Layered Igneous Complex, North-Eastern Finland

Abstract. The Seismic and Electromagnetics Methods for Deep mineral exploration (SEEMS DEEP) project is associated with the Koillismaa Layered Igneous Complex (KLIC) in north-eastern Finland. The KLIC is characterized by a Bouguer positive gravity and magnetic anomaly zone connecting the two exposed ends of the KLIC i.e. the Koillismaa intrusion and the Näränkävaara intrusion. The KLIC has the potential to host several critical raw minerals, like nickel and cobalt which are included in the European Union’s critical raw material list. For this purpose, two regional seismic profiles were acquired to map the regional reflectivity in the area, constraining the large-scale information about the geological architecture of KLIC. Seismic imaging delineated reflectivity up to a depth of ~5–6 km with several reflective packages at various depths which may be representative of the presence of dykes, faults, and major lithological contacts present in the area. Several regional faults were also imaged. The top of the magma conduit associated with KLIC was successfully mapped with hints of fault-like events cross-cutting the intrusion revealing a more complex internal structure that was earlier assumed of as a single lithological unit. It was interpreted that a second magma conduit might exist between the Koillismaa intrusion and the Näränkävaara Intrusion. Results were compared against the available petrophysical data and a preliminary available geological model based on the density model of the gravity inversion with constraints from the drillhole data.