Three-dimensional reflection seismic imaging of the iron oxide deposits in the Ludvika mining area, Sweden, using Fresnel volume migration

Abstract

Abstract. We present 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 the study is to directly image the ore-bearing horizons and to delineate their possible depth extension below depths known from existing boreholes. For this purpose, we applied a tailored pre-processing workflow and two different seismic imaging approaches, Kirchhoff pre-stack depth migration (KPSDM) 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 horizons, which are linked to known mineralization and provide insights on their possible lateral and depth extent. Comparison of the known mineralization with the final FVM reflection volume suggests a good agreement of the position and the shape of the imaged reflectors caused by the mineralization. Furthermore, the images show additional reflectors below the mineralization and reflectors with opposite dips. One of these reflectors is interpreted to be a fault intersecting the mineralization, which can be traced to the surface and linked to a fault trace in the geological map. The depth-imaging results can serve as the basis for further investigations, drilling, and follow-up mine planning at the Blötberget mining site..

Preface: State of the art in mineral exploration

“…In spite of the challenges related to the ground conditions and access, resulting in significant surface wave content, the processing applied allowed obtaining a good 3D image of the two main faults that determine the structural configuration of the Blötberget mining area. This work provides the first 3D image of the Blötberget mining area, and paves the way to other more advanced processing studies, also collected in this special issue (see Hloušek et al, 2022;Singh et al, 2022 below). This study highlights the potential of traditional active seismic methods to image subsurface structures in challenging crystalline environments.…”

“…In a following study, Hloušek et al (2022) apply two prestack depth migration approaches to the 3D seismic dataset acquired at the Blötberget iron oxide mining site described in Malehmir et al (2021). The authors apply a Kirchhoff pre-stack depth migration and Fresnel volume migration to the data, to produce a well-resolved 3D depth image of the deposit and its host rock.…”

High‐resolution 2.5D multifocusing imaging of a crooked seismic profile in a crystalline rock environment: Results from the Larder Lake area, Ontario, Canada

“…In regions with significant geologic complexity and lateral velocity variations, such as hard‐rock geological environments, seismic depth imaging methods are often preferred to time imaging methods (Bräunig et al., 2020; Hloušek et al., 2021; Yilmaz, 2001). However, the depth‐domain algorithms are computationally expensive and very sensitive to velocity–depth models.…”