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Seismic imaging and potential field modeling to delineate structures hosting VHMS deposits in the Skellefte Ore District, northern Sweden
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics. (Geophysics)
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
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2006 (English)In: Tectonophysics, ISSN 0040-1951, E-ISSN 1879-3266, Vol. 426, no 3-4, 319-334 p.Article in journal (Refereed) Published
Description
Abstract [en]

The Skellefte District in northern Sweden is a roughly 150 by 50 km2 large early Proterozoic massive sulphide belt. Based on high-resolution reflection seismic data along two parallel seismic profiles, potential field modeling has been carried out and two geologic cross sections have been constructed that are consistent with the available geophysical data as well as surface geologic observations. The combined modelling suggests that the Kristineberg deposit occurs on the northern limb of a regional E–W striking syncline. The interpretations help to identify new prospective areas, both down-plunge from known ores, and on the ore-bearing horizon on the southern limb of the syncline. The new results suggest that the post-orogenic Revsund granites can be divided into two major types of intrusives, those which are intruded as domes/stokes with a maximum present day thickness of about 3–3.5 km and those which are intruded as thin sheets, with a maximum thickness of a few hundred meters. The margins of the intrusions are generally inclined inwards, suggesting that the current erosion level is near the middle, or toward the base, of the granites. The contact between the Skellefte volcanic rocks and the Bothnian Basin has been interpreted as a thrust fault. We also suggest that crustal thickening predates the Skellefte volcanism and that the interpreted Bothnian Basin rocks are either a structural basement or a separate terrane to the Skellefte volcanism. Diffraction patterns in the reflection seismic data can be interpreted as originating from either a mafic–ultramafic intrusion or a mineralization zone, similar to observations elsewhere in the world. The results obtained in this study have greatly improved our understanding of the tectonostratigraphic framework and architecture of the poly-deformed c. 1.9 Ga Skellefte VHMS belt and is a key step towards building a 3D geological model in the area.

Place, publisher, year, edition, pages
2006. Vol. 426, no 3-4, 319-334 p.
Keyword [en]
Seismic imaging, Potential field modelling, VHMS deposits, Skellefte
National Category
Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:uu:diva-96159DOI: 10.1016/j.tecto.2006.08.006ISI: 000242010200005OAI: oai:DiVA.org:uu-96159DiVA: diva2:170638
Available from: 2007-09-03 Created: 2007-09-03 Last updated: 2017-12-14Bibliographically approved
In thesis
1. 3D Geophysical and Geological Modeling in the Skellefte District: Implications for Targeting Ore Deposits
Open this publication in new window or tab >>3D Geophysical and Geological Modeling in the Skellefte District: Implications for Targeting Ore Deposits
2007 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

With the advancements in acquisition and processing of seismic reflection data recorded over crystalline rocks, building three-dimensional geologic models becomes increasingly favorable. Because of little available petrophysical data, interpretations of seismic reflection data in hardrock terrains are often speculative. Potential field data modeling are sometimes performed in order to reduce the ambiguity of seismic reflection interpretations. The Kristineberg mining area in the western part of the Paleoproterozoic Skellefte Ore District was chosen to construct a pilot three-dimensional geologic model in an attempt to understand the crustal architecture in the region and how the major mineral systems operated in this architecture. To contribute to this aim, two parallel seismic reflection profiles were acquired in 2003 and processed to 20 sec with special attention to the top 4 sec of data. Several reflections were imaged and interpreted by the aid of reflector modeling, borehole data, 2.5D and 3D potential field modeling, and geological observations. Interpretations are informative at the crustal scale and help to construct a three-dimensional geologic model of the Kristineberg mining area. The three-dimensional geologic model covers an area of 30×30 km2 down to a depth of 12 km. The integrations help to interpret a structural basement to the Skellefte volcanic rocks, possibly with Bothnian Basin metasedimentary affinity. The contact is a shear-zone that separates the two units, generating large fold structures, which can be observed in the region. The interpretations help to divide the Revsund granitic rocks into two major groups based on their present shape and thickness. A large gravity low in the south is best represented by the intrusion of thick dome of Revsund granite. In the north, the low-gravity corresponds to the intrusion of sheet-like Revsund granites. In general, the structure associated with the Skellefte volcanics and the overlying metasedimentary rocks are two thrusts exposing the Skellefte volcanic rocks in the cores of hanging wall anticlinal structures. Lack of coherent reflectivity in the seismic reflection data may be due to complex faulting and folding systems observed in the Skellefte volcanics. Ultramafic sills within the metasedimentary rocks are interpreted to extend down to depths of about 5-6 km. The interpretations are helpful for targeting new VHMS deposits and areas with gold potential. For VHMS deposits, these are situated in the southern limb of a local synformal structure south of the Kristineberg mine, on the contact between the Revsund granite and the Skellefte volcanic rocks. A combination of metasedimentary and mafic-ultramafic rocks are highly gold prospective in the west, similar to observations elsewhere in the region. There are still questions that remain unanswered and need more work. New data in the study area will help to answer questions related to e.g., an enigmatic diffraction seismic signal in Profile 5 and the structural relationship between the Skellefte volcanic rocks and the Malå volcanics. Although the derived 3D geologic model is preliminary and constructed at the crustal scale, it provides useful information to better understand the tectonic evolution of the Kristineberg mining area.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2007. 84 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 337
Keyword
Geophysics, Seismic reflection, Hardrock, VHMS deposits, Potential field, 3D geologic model, Skellefte District, Geofysik
National Category
Geophysics
Identifiers
urn:nbn:se:uu:diva-8188 (URN)978-91-554-6957-3 (ISBN)
Public defence
2007-09-27, Axel Hambergsalen, Geocentrum, Villavägen 16, Uppsala, 10:00
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Available from: 2007-09-03 Created: 2007-09-03 Last updated: 2016-05-13Bibliographically approved

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Malehmir, AlirezaTryggvason, AriJuhlin, Christopher

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