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https://doi.org/10.5194/se-2020-141
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/se-2020-141
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  25 Aug 2020

25 Aug 2020

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This preprint is currently under review for the journal SE.

Sparse 3D reflection seismic survey for deep-targeting iron-oxide deposits and their host rocks, Ludvika Mines-Sweden

Alireza Malehmir1, Magdalena Markovic1, Paul Marsden2, Alba Gil1, Stefan Buske3, Lukasz Sito4, Emma Bäckström2, Martiya Sadeghi5, and Stefan Luth5 Alireza Malehmir et al.
  • 1Department of Earth Sciences, Uppsala University, SE 75236, Uppsala, Sweden
  • 2Nordic Iron Ore AB, Sweden
  • 3TU Bergakademie Freiberg, Germany
  • 4Geopartner, Poland
  • 5Geological Survey of Sweden, Uppsala, Sweden

Abstract. Many metallic mineral deposits have sufficient contrasts, particularly density, to be detectable using seismic methods. These deposits are sometimes significant for our society, economic growth and can help to accelerate the energy transition towards decarbonization. However, their exploration at depth requires high-resolution and sensitive methods. Following a series of 2D seismic trials, a sparse, narrow source-receiver azimuth, 3D seismic survey was conducted in the Blötberget mine, in central Sweden, covering an area of approximately 6 km2 for deep targeting iron-oxide deposits and their host rock structures. The survey benefited from a collaborative work by putting together 1266 seismic recorders and a 32t vibrator generating 1056 shot points in a fixed geometry setup. A linear sweep ranging from 10–160 Hz and 20 s long was generated three times per shot point. Shots were fired at every 10 m where possible and receivers placed at every 10–20 m. Notable quality data were acquired although the area is dominated by swampy places as well as by built-up roads and historical tailings. The data processing had to overcome these challenges in particular for the static corrections and strong surface-waves. A tailored for hardrock-setting-processing workflow was developed for handling such a dataset, where the use of mixed 2D and 3D refraction static corrections were relevant. The resulting seismic volume is rich in terms of reflectivity with clear southeast dipping reflections originated from iron-oxide deposits extending vertically and laterally at least 300 m beyond what was known from boreholes. We estimate potential additional resources from the 3D reflection seismic experiment on the order of 10 Mt worth drilling for detailed assessments. The mineralization is crosscut by at least two major sets of northwest dipping reflections interpreted to be dominantly normal faults and responsible for much of the lowland in the Blötberget area. Moreover, these post-mineralization faults likely control the current 3D geometry of the deposits. Curved and submerged reflections interpreted from folds or later intrusions are also observed showing the geological complexity of the study area. The seismic survey also delineates the near-surface expression of a historical tailing as a by-product of refraction static corrections demonstrating why 3D seismic data. The sparse 3D survey illustrates that performing cost-effective reflection surveys for mineral exploration is achievable if they are conducted and planned carefully, systematically and based on earlier experiences.

Alireza Malehmir et al.

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Alireza Malehmir et al.

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Short summary
A smooth transition toward decarbonization demands access to more minerals of critical importance. Europe has a good geology for many of these mineral deposits but at depth requiring sensitive, environmentally-friendly and cost-effective methods for their exploration. In this context, we present a sparse 3D seismic dataset that allowed identification of potential iron-oxide resources at depth and helped to characterise key geological structures as well as a historical tailing in central Sweden.
A smooth transition toward decarbonization demands access to more minerals of critical...
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