Crustal geometry of the central Skellefte district, northern Sweden – constraints from reflection seismic investigations

The Palaeoproterozoic Skellefte mining district in Sweden is one of the most important mining districts in Europe. As a part of a 4D geologic modeling project, three new sub-parallel reflection seismic profiles, with a total length of about 95 km, were acquired in the central part of the district. Processed seismic data reveal a series of gentle- to steeply- dipping reflections and a series of diffraction packages. The majority of reflections that extend to the surface can be correlated with geological features either observed in the field or interpreted from the aeromagnetic map. A set of south-dipping reflections represent inferred syn-extensional listric extensional faults that were inverted during subsequent crustal-shortening. Cross-cutting north-dipping reflections are correlated to late-compressional break-back faults. Flat-lying reflections in the central parts of the study area could represent lithological contacts within the Skellefte Group, or the contact between Skellefte Group rocks and their unknown basement. Flat-lying reflections occurring further north are inferred to originate from the top of the Jörn intrusive complex or an intrusive contact within it. So far unknown south- and north-dipping faults have been identified in the vicinity of the Maurliden deposit. Based on the seismic results, a preliminary 3D-model has been created in order to visualize the fault pattern and to provide a base for future 3D/4D modeling in the Skellefte district.

► To constrain 3D geological models of the central Skellefte district, three new seismic reflection profiles were acquired.
► A mechanical hammer was used to generate seismic signals and allowed imaging of reflections down to 6 km depth.
► Results suggest the presence of a synformal structure near the Maurliden massive sulphide deposits that extends down to depths of about 3 km.
► A series of major shear-zones are also observed that can be correlated with surface geology.
► A preliminary 3D geologic model of the major faults and shear zones is also presented.