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Seismic investigations and physical property studies of natural resources in Finland and Sweden: Efficient exploration of groundwater and mineral resources
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.ORCID iD: 0000-0002-6843-3924
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Natural resources, such as mineral deposits and groundwater in particular, are crucial for our society, as the world prepares itself for a smooth transition towards green technologies and decarbonization. Apart from extraction and use, innovative mineral exploration solutions are needed to complete the full value chain and to achieve the sustainable development goals.  

The application of seismic methods for both near-surface environmental and deep mineral exploration investigations is known, but high costs are associated with data acquisition and processing. In order to illustrate the potential of the seismic methods for efficient exploration of groundwater and mineral resources, cost-effective seismic surveys were acquired within two locations in Finland and Sweden, for aquifer delineation and imaging of iron-oxide mineralization in a hardrock environment, respectively. Physical properties, obtained from geophysical downhole logging and laboratory measurements, were analyzed for a complete characterization of the mineralization and its host rocks. 3D ray-tracing and 2D finite-difference forward modeling were carried out for better assessing the seismic response of the mineralization.

The effectiveness of these seismic surveys was revealed by the quality seismic data acquired using a low-cost, easily operated seismic source and different sensors, including a broadband seismic landstreamer. In particular, the seismic source provided adequate penetration in two different and challenging environments, namely soft glacial sediments at Virttaankangas, southwest Finland, and swampy glacial cover at Blötberget, south central Sweden. The large-scale units of the Virttaankangas aquifer were successfully delineated and integrated with the hydrogeological units of the groundwater flow model. The mineralization at Blötberget was interpreted to further extend 300-400 m downdip, below the currently known depth from borehole observations. 3D processing of the 2D seismic profiles revealed a lateral extent of least 300 m, providing encouraging results for improved assessments of the mineral resources. The reflection pattern validated through forward modeling, suggested a possible new mineralized horizon below the known deposits. Physical property studies helped characterize the mineralization and its host rocks in terms of seismic attenuation and rock quality. Fracture zones detected through sonic full-waveform logging were associated with high seismic attenuation, suggesting low mechanical competence of the mineralized rocks despite good rock quality designation, providing thus important information for mine planning and exploration.   

The studies presented in this thesis illustrate the potential of seismic methods and physical property studies for efficient natural resources exploration in crystalline rocks and in overlying glacial sediments.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2020. , p. 84
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1936
Keywords [en]
Seismic reflection, seismic refraction, esker, glacial sediments, iron-oxide, hardrock, efficient exploration, physical property, forward modeling, seismic quality factor, Finland, Sweden, Bergslagen
National Category
Geophysics
Identifiers
URN: urn:nbn:se:uu:diva-408712ISBN: 978-91-513-0953-8 (print)OAI: oai:DiVA.org:uu-408712DiVA, id: diva2:1423815
Public defence
2020-06-05, Ekmansalen, Entré 14, Evolutionsbiologiskt centrum (EBC), Norbyvägen 14-18, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2020-05-14 Created: 2020-04-15 Last updated: 2020-05-17
List of papers
1. Interlobate esker architecture and related hydrogeological features derived from a combination of high-resolution reflection seismics and refraction tomography, Virttaankangas, southwest Finland
Open this publication in new window or tab >>Interlobate esker architecture and related hydrogeological features derived from a combination of high-resolution reflection seismics and refraction tomography, Virttaankangas, southwest Finland
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2017 (English)In: Hydrogeology Journal, ISSN 1431-2174, E-ISSN 1435-0157, Vol. 25, no 3, p. 829-845Article in journal (Refereed) Published
Abstract [en]

A novel high-resolution (2-4 m source and receiver spacing) reflection and refraction seismic survey was carried out for aquifer characterization and to confirm the existing depositional model of the interlobate esker of Virttaankangas, which is part of the Sakylanharju-Virttaankangas glaciofluvial esker-chain complex in southwest Finland. The interlobate esker complex hosting the managed aquifer recharge (MAR) plant is the source of the entire water supply for the city of Turku and its surrounding municipalities. An accurate delineation of the aquifer is therefore critical for long-term MAR planning and sustainable use of the esker resources. Moreover, an additional target was to resolve the poorly known stratigraphy of the 70-100-m-thick glacial deposits overlying a zone of fractured bedrock. Bedrock surface as well as fracture zones were confirmed through combined reflection seismic and refraction tomography results and further validated against existing borehole information. The high-resolution seismic data proved successful in accurately delineating the esker cores and revealing complex stratigraphy from fan lobes to kettle holes, providing valuable information for potential new pumping wells. This study illustrates the potential of geophysical methods for fast and cost-effective esker studies, in particular the digital-based landstreamer and its combination with geophone-based wireless recorders, where the cover sediments are reasonably thick.

Place, publisher, year, edition, pages
SPRINGER, 2017
Keywords
Esker architecture, Landstreamer, Unconsolidated sediments, Geophysical methods, Finland
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:uu:diva-324625 (URN)10.1007/s10040-016-1513-9 (DOI)000400755400015 ()
Funder
Swedish Research Council Formas, 252-2012-1907
Available from: 2017-06-22 Created: 2017-06-22 Last updated: 2020-04-15Bibliographically approved
2. Downhole physical property logging for iron-oxide exploration, rock quality, and mining: An example from central Sweden
Open this publication in new window or tab >>Downhole physical property logging for iron-oxide exploration, rock quality, and mining: An example from central Sweden
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2017 (English)In: Ore Geology Reviews, ISSN 0169-1368, E-ISSN 1872-7360, Vol. 90, p. 1-13Article in journal (Refereed) Published
Abstract [en]

Several physical properties obtained from geophysical logging and laboratory measurements were analyzed in order to characterize iron-oxide mineralization and host rocks in the Blotberget mining area of central Sweden. Seven boreholes intersecting the mineralization between 300 and 600 m depth in a volcano-sedimentary setting were downhole logged for this purpose. The downhole logging included full-waveform triple sonic, natural gamma, magnetic susceptibility, formation resistivity, fluid temperature and conductivity while laboratory measurements consisted of density, rock quality designation and magnetite content measurements. Full-waveform sonic data were used for rock quality assessments of the mineralized zones and their host rocks and proved their potential to be used for mine planning purposes. The ore-bearing rocks are primarily distinguished by increased density and dynamic elastic moduli estimated from the full-waveform sonic logging. Although seismic velocities do not follow a linear increase with the density for the mineralized rocks, as expected for igneous rocks, it is observed that a strong seismic signal from the mineralization can be expected primarily due to their high density. In addition, the full-waveform sonic data could be used as a proxy for fracture delineations and in situ rock quality assessment. For example, zones of washed-up amplitudes in these data correlate well with zones of poor quality rocks, identified by core logging. Based on the full-waveform sonic data, seismic attenuation and its reciprocal, the seismic quality factor, were calculated. A decrease in the seismic quality factor was observed at zones with low rock quality designation, but also correlated with the mineralized zones suggesting several fracture zones in the mineralization and that the ore-bearing rocks might be less competent than the surrounding host rocks. Eventual rock support and reinforcement might be required for future mining operations. Full-waveform sonic data have the potential to improve rock quality assessments for mine planning and exploration purposes.

Place, publisher, year, edition, pages
Elsevier, 2017
Keywords
Downhole physical property logging, Iron oxide deposits, Elastic constants, Seismic quality factor, Sweden
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-345223 (URN)10.1016/j.oregeorev.2017.10.012 (DOI)000423248600001 ()
Available from: 2018-03-14 Created: 2018-03-14 Last updated: 2020-04-15Bibliographically approved
3. Deep reflection seismic imaging of iron-oxide deposits in the Ludvika mining area of central Sweden
Open this publication in new window or tab >>Deep reflection seismic imaging of iron-oxide deposits in the Ludvika mining area of central Sweden
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2020 (English)In: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478, Vol. 68, no 1, p. 7-23Article in journal (Refereed) Published
Abstract [en]

Reflection seismic data were acquired within two field campaigns in the Blötberget, Ludvika mining area of central Sweden, for deep imaging of iron-oxide mineralization that were known to extend down to 800-850 m depth. The two surveys conducted in years 2015 and 2016, one employing a seismic landstreamer and geophones connected to wireless recorders, and another one using cabled geophones and wireless recorders, aimed to delineate the geometry and depth extent of the iron-oxide mineralization for when mining commences in the area. Even with minimal and conventional processing approaches, the merged datasets provide encouraging information about the depth continuation of the mineralized horizons and the geological setting of the study area. Multiple sets of strong reflections represent a possible continuation of the known deposits that extend approximately 300 m further down-dip than the known 850 m depth obtained from historical drilling. They show excellent correlation in shape and strength with those of the Blötberget deposits. Furthermore, several reflections in the footwall of the known mineralization can potentially be additional resources underlying the known ones. The results from these seismic surveys are encouraging for mineral exploration purposes given the good quality of the final section and fast seismic surveys employing a simple cost-effective and easily available impact-type seismic source.

Keywords
Data processing, Imaging, Seismic
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-408710 (URN)10.1111/1365-2478.12855 (DOI)000482451500001 ()
Funder
VinnovaEU, Horizon 2020, 775971
Available from: 2020-04-12 Created: 2020-04-12 Last updated: 2020-04-15Bibliographically approved
4. Cross-profile seismic data acquisition, imaging and modeling of iron-oxide deposits: A case study from Blötberget, south central Sweden
Open this publication in new window or tab >>Cross-profile seismic data acquisition, imaging and modeling of iron-oxide deposits: A case study from Blötberget, south central Sweden
(English)Manuscript (preprint) (Other academic)
Keywords
case history, imaging, mining, modeling, reflection
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-408711 (URN)
Available from: 2020-04-12 Created: 2020-04-12 Last updated: 2020-04-15

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