Preprints
https://doi.org/10.5194/se-2021-122
https://doi.org/10.5194/se-2021-122

  01 Oct 2021

01 Oct 2021

Review status: this preprint is currently under review for the journal SE.

3D high-resolution seismic imaging of the iron-oxide deposits in Ludvika (Sweden) using full-waveform inversion and reverse-time migration

Brij Singh1, Michał Malinowski1,2, Andrzej Górszczyk1,3, Alireza Malehmir4, Stefan Buske5, Łukasz Sito6, and Paul Marsden7 Brij Singh et al.
  • 1Institute of Geophysics, Polish Academy of Sciences Warsaw, 01-452, Warsaw, Poland
  • 2Geological Survey of Finland, FI-02151, Espoo, Finland
  • 3Institut des Sciences de la Terre (ISTerre), University Greoble Alpes, 38610, Grenoble, France
  • 4Department of Earth Sciences, Uppsala University, 75236, Uppsala, Sweden
  • 5Institute of Geophysics and Geoinformatics, TU Bergakademie Freiberg, D-09596, Freiberg, Germany
  • 6Geopartner Sp. z o. o., 30-383, Kraków, Poland
  • 7Nordic Iron Ore AB, 18291, Danderyd, Sweden

Abstract. A sparse 3D seismic survey was acquired over the Blötberget iron-oxide deposits of the Ludvika Mines in south-central Sweden. The main aim of the survey was to delineate the deeper extension of the mineralisation and to better understand its 3D nature and associated fault systems for mine planning purposes. To obtain a high-quality seismic image in depth, we applied time-domain 3D acoustic full-waveform inversion (FWI) to build a high-resolution P-wave velocity model. This model was subsequently used for pre-stack depth imaging with reverse time migration (RTM) to produce the complementary reflectivity section. We developed a data preprocessing workflow and inversion strategy for the successful implementation of FWI in the hardrock environment. We obtained a high-fidelity velocity model using FWI and assessed its robustness. We extensively tested and optimised the parameters associated with the RTM method for subsequent depth imaging using different velocity models: a constant velocity model, a model built using first-arrival traveltime tomography and a velocity model derived by FWI. We compare our RTM results with a priori data available in the area. We conclude that, from all tested velocity models, the FWI velocity model in combination with the subsequent RTM step, provided the most focussed image of the mineralisation and we successfully mapped its 3D geometrical nature. In particular, a major reflector interpreted as a cross-cutting fault, which is restricting the deeper extension of the mineralisation with depth, and several other fault structures which were earlier not imaged were also delineated. We believe that a thorough analysis of the depth images derived with the combined FWIRTM approach that we presented here can provide more details which will help with better estimation of areas with high mineralization, better mine planning and safety measures.

Brij Singh et al.

Status: open (until 12 Nov 2021)

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Brij Singh et al.

Brij Singh et al.

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Short summary
Fast depletion of shallower deposits is pushing the mining industry to look for cutting-edge technologies for deep mineral targeting. We demonstrated two new state-of-the-start technologies: full-waveform inversion and reverse time migration to produce earth images with high accuracy which can help with better estimation of areas with high mineralization, better mine planning and safety measures.