| 1. |
- Gil de la Iglesia, Alba, et al.
(författare)
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3D reflection seismic imaging of the Zinkgruvan mineral-bearing structures in the south-eastern Bergslagen mineral district (Sweden)
- 2023
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Ingår i: Geophysical Prospecting. - : John Wiley & Sons. - 0016-8025 .- 1365-2478. ; 71:7, s. 1132-1151
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Tidskriftsartikel (refereegranskat)abstract
- Mineral exploration is facing greater challenges nowadays because of the increasing demand for raw materials and the lesser chance of finding large deposits at shallow depths. To be efficient and address new exploration challenges, high-resolution and sensitive methods that are cost-effective and environmentally friendly are required. In this work, we present the results of a sparse 3D seismic survey that was conducted in the Zinkgruvan mining area, in the Bergslagen mineral district of central Sweden. The survey covers an area of 10.5 km2 for deep targeting of massive sulphides in a polyphasic tectonic setting. A total of 1311 receivers and 950 shot points in a fixed 3D geometry setup were employed for the survey. Nine 2D profiles and a smaller 3D mesh were used. Shots were generated at every 10 m, and receivers were placed at every 10-20 m, along the 2D profiles, and 40-80 m in the mesh area. An analysis of the seismic fold coverage at depth was used to determine the potential resolving power of this sparse 3D setup. The data processing had to account for cultural noise from the operating mine and strong source-generated surface waves, which were attenuated during both pre- and post-stack processing steps. The processing workflow employed a combination of 2D and 3D refraction static corrections, and post-stack FK filters along inlines and crosslines. The resulting 3D seismic volume is correlated with downhole data (density and P-wave, acoustic impedance, reflection coefficient), synthetic seismograms, surface geology and a 3D model of mineral-bearing horizons in order to suggest new exploration targets at depth. The overall geological architecture at Zinkgruvan is interpreted as two EW overturn folds, an antiform and a synform, affected by later NS-trending folding. Two strong sets of shallow reflections, associated with the Zn-Pb mineralization, are located at the hinge of an EW-trending antiform, while a strong set of reflections, associated with the main mineralization, is located at the overturned apex of the EW synform. The NS Knalla fault that crosses the study area terminates the continuation of the mineral-bearing deposits at depth towards the west, a conclusion solely based on the reflectivity character of the seismic volume. This study illustrates that sparse 3D data acquisition, while it has its own challenges, can be a suitable replacement for 2D profiles while line cutting, and environmental footprints can totally be avoided.
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| 2. |
- Gil de la Iglesia, Alba, et al.
(författare)
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Reflection seismic imaging to unravel subsurface geological structures of the Zinkgruvan mining area, central Sweden
- 2021
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Ingår i: Ore Geology Reviews. - : Elsevier. - 0169-1368 .- 1872-7360. ; 137
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Tidskriftsartikel (refereegranskat)abstract
- The Zinkgruvan mining area is located on the south-eastern part of the Bergslagen district, one of the three major mineral producing regions in Sweden. In this study, we present the results from three (P1, P2 and P8) reflection seismic profiles each approximately 3000 m-long crossing the Zinkgruvan Zn-Pb-Ag-(Cu) mining area. P1 was acquired using cabled geophones with 10 m receiver and source interval and crossed major geological features. The other two profiles (P2 and P8) were acquired by wireless recorders with 20 m receiver and 10 m source interval and ran perpendicular to P1. Through a special data processing workflow adapted to this dataset, good quality seismic sections were obtained along these profiles, although a high noise level due to high voltage electric power lines was present. The interpretations were constrained by (1) seismic P-wave velocity and density data from a series of downhole logging measurements, (2) 3D forward reflection traveltime modelling in both pre- and post-stack domains, and (3) other geophysical and geological observations available from the site. Despite the notably complex geology, the processed seismic sections clearly reveal a series of horizontal to gently dipping reflections associated with known geological formations. Results indicate that most structures and lithological contacts dip or plunge to the northeast, including the targeted Zinkgruvan Formation. The results from this seismic survey are encouraging regarding the potential of the seismic method for base-metal exploration in Sweden and in particular in the Bergslagen district. It shows the high resolving power of the reflection seismic methods for imaging complex geological structures in a cost-effective and environmentally-friendly way.
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| 3. |
- Malehmir, Alireza, 1977-, et al.
(författare)
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Sparse 3D reflection seismic survey for deep-targeting iron oxide deposits and their host rocks, Ludvika Mines, Sweden
- 2021
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Ingår i: Solid Earth. - : Copernicus Publications. - 1869-9510 .- 1869-9529. ; 12:2, s. 483-502
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Tidskriftsartikel (refereegranskat)abstract
- Many metallic mineral deposits have sufficient physical property contrasts, particularly density, to be detectable using seismic methods. These deposits are sometimes significant for our society and 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 Blotberget mine, in central Sweden, covering an area of approximately 6 km(2) 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 32 t vibrator, generating 1056 shot points in a fixed geometry setup. Shots were fired at every 10 m where possible, and receivers were placed at every 10-20 m. Notable quality data were acquired despite the area being dominated by swampy places as well as by built-up roads and historical tailings The data processing had to overcome these challenges for the static corrections and strong surface waves in particular. A tailored for hardrock setting and processing workflow was developed for handling such a dataset, where the use of mixed 2D and 3D refraction static corrections was relevant. The resulting seismic volume is rich in terms of reflectivity, with clear southeast-dipping reflections originating from the iron oxide deposits extending vertically and laterally at least 300 m beyond what was known from available boreholes. As a result, we estimate potential additional resources from the 3D reflection seismic experiment on the order of 10 Mt to be worth drilling for detailed assessments. The mineralization is crosscut by at least two major sets of northwest-dipping reflections interpreted to dominantly be normal faults and to be responsible for much of the lowland in the Blotberget 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 are so valuable for both mineral exploration and mine planning applications.
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| 4. |
- Murton, Bramley J., et al.
(författare)
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Geological fate of seafloor massive sulphides at the TAG hydrothermal field (Mid-Atlantic Ridge)
- 2019
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Ingår i: Ore Geology Reviews. - : Elsevier. - 0169-1368 .- 1872-7360. ; 107, s. 903-925
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Forskningsöversikt (refereegranskat)abstract
- Deep-sea mineral deposits potentially represent vast metal resources that could make a major contribution to future global raw material supply. Increasing demand for these metals, many of which are required to enable a low-carbon and high-technology society and to relieve pressure on land-based resources, may result in deep sea mining within the next decade. Seafloor massive sulphide (SMS) deposits, containing abundant copper, zinc, gold and silver, have been the subject of recent and ongoing commercial interest. Although many seafloor hydrothermally systems have been studied, inactive SMS deposits are likely more accessible to future mining and far more abundant, but are often obscured by pelagic sediment and hence difficult tolocate. Furthermore, SMS deposits are three dimensional. Yet, to date, very few have been explored or sampled below the seafloor. Here, we describe the most comprehensive study to date of hydrothermally extinct seafloor massive sulphide (eSMS) deposits formed at a slow spreading ridge. Our approach involved two research cruises in the summer of 2016 to the Trans-Atlantic Geotraverse (TAG) hydrothermal field at 26 N on the Mid-Atlantic Ridge. These expeditions mapped a number of hydrothermally extinct SMS deposits using an autonomous underwater vehicle and remotely operated vehicle, acquired a combination of geophysical data including sub-seafloor seismic reflection and refraction data from 25 ocean bottom instruments, and recovered core using a robotic lander-type seafloor drilling rig. Together, these results that have allowed us to construct a new generic model for extinct seafloor massive sulphide deposits indicate the presence of up to five times more massive sulphide at and below the seafloor than was previously thought.
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