3D reflection seismic imaging of the iron-oxide deposits in the Ludvika mining area (Sweden) using a focusing pre-stack depth migration approach

Abstract. We present the pre-stack depth imaging results for a case study of 3D reflection seismic exploration at the Blötberget iron-oxide mining site belonging to the Bergslagen mineral district in central Sweden. The goal of this case study is to directly image the ore-bearing units and to map its possible extension down to greater depths than known from existing boreholes. Therefore, we applied a tailored pre-processing workflow as well as two different seismic imaging approaches, Kirchhoff pre-stack depth migration and Fresnel Volume Migration (FVM). Both imaging techniques deliver a well resolved 3D image of the deposit and its host rock, where the FVM image yields a significantly better image quality compared to the KPSDM image. We were able to unravel distinct reflection horizons, which are linked to known mineralisation and provide insights on lateral and depth extent of the deposits beyond their known extension from borehole data. A comparison of the known mineralization and the image show a good agreement of the position and the shape of the imaged reflectors caused by the mineralization. Furthermore, the images show a reflector, which is interpreted to be a fault intersecting the mineralisation and which can be linked to the surface geology. The depth imaging results can serve as the basis for further investigations, drillings and follow-up mine planning at the Blötberget mining site.