Reflection seismic imaging to unravel subsurface geological structures of the Zinkgruvan mining area, central Sweden

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.EIT-RawMaterials is gratefully thanked for funding this up-scaling project 17024.Peer reviewe

3D reflection seismic imaging of the Zinkgruvan mineral-bearing structures in the south-eastern Bergslagen mineral district (Sweden)

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

SIT4ME project: Up-scaling seismic methods for mineral exploration in the Zinkgruvan mining area, Sweden

EGU2020: Sharing science Online, 4-8 may 2020Mineral resources are used in large quantities than ever before because they are fundamental to our modern society. To this front and facing an up-scaling challenge, the EIT Raw-Materials funded project SIT4ME (Seismic Imaging Techniques for Mineral Exploration) was launched involving several European institutions. As part of the project, a dense multi-method seismic dataset was acquired in the Zinkgruvan mining area at the Bergslagen mineral district of Sweden, which hosts one of the largest volcanic-hosted massive sulphide (VMS) deposits in the country. In November 2018, a dense multi-method seismic dataset was acquired in the Zinkgruvan mining area, in a joint collaborative approach among Swedish, Spanish and German partners. A combination of sparse 3D grid and dense 2D profiles in an area of approximately 6 km2 was acquired using a 32t seismic vibrator (10-150 Hz) of TU Bergakademie Freiberg, enabling reasonable pseudo-3D sub-surface illumination. For the data acquisition, a total of approximately 1300 receiver positions (10-20 m apart), using different recorders, and 950 source positions were surveyed. All receivers were active during the data acquisition allowing a combination of 2D and semi-3D data to be obtained for various imaging and comparative studies. The main objective of the study, apart from its commercial-realization approach, was also to provide information useful for deep-targeting and structural imaging in this complex geological setting. The main massive-sulphide bearing horizon, Zinkgruvan formation, is strongly reflective as correlated with the existing boreholes in the mine. Careful analysis of the seismic sections suggests a dominant northeast-dipping structure, consistent with the general plunge of the main Zinkgruvan fold that has been suggested in the area.EIT-RawMaterials is gratefully thanked for funding this up-scaling project 17024

Active and passive-source seismic imaging for exploration of deep-seated massive sulphide mineralization in the Zinkgruvan mine, south-central Sweden

EGU General Assembly in Vienna, Austria, 7–12 April 2019Population growth, together with overall improvement of life standards, greater level of environmental awareness and energy transition towards green technologies, result in globally increasing demand for mineral resources on a yearly basis. Considering that most of the shallow large-scale deposits have likely already been explored and mined out (or are being mined), there is a great interest to explore for deeper-seated deposits. For this purpose, the SIT4ME project, through EIT Raw Material Program was established, aiming to promote, improve and further establish seismic methods for mineral exploration in hard rock environments. In November 2018, a multi-method seismic dataset was acquired in the Zinkgruvan mining area in the Bergslagen mineral province of Sweden. Both active (32t seismic vibrator truck as source) and passive data were acquired using a combination of sparse 3D grid and dense 2D profiles in an area of approximately 6 km2 enabling reasonable 3D subsurface illumination. For the data acquisition, a total of 1300 receivers were used across the study area, distributed along ten 2D-crooked-seismic lines and in a 3D mesh. This provided us with a comprehensive dataset, which would be used for a multitude of processing and imaging approaches. The objectives are to image any deep (> 500 m depth) massive sulphide mineralization and structures hosting them within this complex three-dimensionally deformed hard rock setting. Here, we present the acquisition setup, preliminary reflection seismic processing results obtained from active part of the dataset