Regional-scale geometry of the central Skellefte district, northern Sweden—results from 2.5D potential field modeling along three previously acquired seismic profiles

Abstract

The Skellefte district in northern Sweden is one of the most important mining districts in Europe hosting approximately 80 volcanic massive sulfide (VMS) deposits. Due to its economical importance, geological and geophysical studies were carried out in order to create an image of the geometry of the upper crustal structure and integral geological elements and to evaluate their relationship to mineral deposits . Consequently, seismic reflection data along three sub-parallel profiles were acquired during 2009–2010 to map the spatial relationships between the geological structures down to a depth of ~ 4.5 km. Although these seismic studies helped researchers understand the regional relationship between geologic units in the central Skellefte district (CSD), the seismic reflection data did not succeed entirely in mapping the lithological contacts in the area. In this study, the model derived from the seismic reflection data was examined by using 2.5D modeling of potential field data (down to a 5 km depth) constrained by physical properties of the rocks and surface geology. Moreover, we modeled gravity and magnetic data along the non-reflective or poorly reflective parts of the seismic profiles to identify major lithological contacts and shear zones in the CSD, which could not be modeled on the basis of the seismic reflection data. Gravity and magnetic data helped reveal the spatial relationship between the Skellefte volcanic rocks, Vargfors group meta-sedimentary rocks and two meta­intrusive complexes. Results suggest a maximum depth extent of 2.1 km for the tectonic contact at the southern border of the Jörn granitoid . Furthermore, this north-dipping Skellefte–Jörn contact coincides closely with magnetic lows and gravity highs, which implies that the Jörn intrusive rocks have a greater thickness than the underlying basalt . Further to the NW, gravity and magnetic data suggest a depth extent of 2 km for the Gallejaur complex, which coincides with a set of gently dipping reflectors. In addition, this study supports previous concepts of fault geometries and fault patterns as a result of upper-crustal extension and subsequent inversion during crustal shortening . In the final model interpretations of the IP data were included, thus relating indications of mineralization to the geological structures. ► Potential field modeling along seismic profiles has successfully been applied. ► Model based on potential field data coincide with several of the seismic reflectors. ► IP results from the upper 0.43 km of the crust, highlights possible VMS deposits. ► Major granite intrusions, Jörn and Gallejaur, were modeled down to 1–2 km depth. ► Forward and inverse modeling of joint geophysical/geological data proved successful.