Magnetotelluric survey in the Kuusamo Schist Belt, Northeastern Finland

Abstract

New broadband magnetotelluric (MT) data were acquired within the BATCircle2.0 project (WP1) in the Kuusamo Schist Belt (KuSB), northeastern Finland. The MT measurements aim to outline the regional geological structures of the belt together with potential field and petrophysical data. The new knowledge on the large-scale structures of the KuSB helps to understand its evolution and holds clues to mineralization processes of the area. A 20 km wide and 70 km long window crossing the KuSB in the NW–SE direction was selected as the survey area from which new MT and gravity data were collected. Here, we present the first results from the MT part of the study.The survey area is located in the KuSB that is a southern extension of the Central Lapland Greenstone Belt (CLGB). The CLGB is one of the largest Proterozoic greenstone belts in the world. It consists of a Palaeoproterozoic (2.5–1.97 Ga) volcanic and sedimentary cover that was deposited on the Archaean (> 2.5 Ga) basement. Rifting, magmatism, deposition of sedimentary sequences occurred 2.44–2.0 Ga. Deformation and metamorphism were related to Svecofennian orogenic events 1.92–1.79 Ga. The KuSB area is particularly prospective for Co-Cu-Au-U-REE deposits and several such mineralizations are known in the area.The collected MT dataset consists of ca. 150 sites with site spacing of 1–5 km. A profile with denser site spacing (1 km) was supported by sparse (5 km) off-profile sites. From time series processing high quality transfer functions were obtained in the period range 0.003–256 s. Phase tensor analysis shows that the regional electrical dimensionality is mainly 3D. First 3D inversions of the MT data set using the ModEM code (Kelbert et al., 2014) indicate the existence of a crustal conductor at several kilometers depth in the northern part of the study area.