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- Dehghannejad, Mahdieh, et al.
(författare)
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Crustal geometry of the central Skellefte district, northern Sweden : constraints from reflection seismic investigations
- 2012
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Ingår i: Tectonophysics. - : Elsevier BV. - 0040-1951 .- 1879-3266. ; 524-525, s. 87-99
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Tidskriftsartikel (refereegranskat)abstract
- The Palaeoproterozoic Skellefte mining district in Sweden is one of the most important mining districts in Europe. As a part of a 4D geologic modeling project, three new sub-parallel reflection seismic profiles, with a total length of about 95 km, were acquired in the central part of the district. Processed seismic data reveal a series of gentle- to steeply- dipping reflections and a series of diffraction packages. The majority of reflections that extend to the surface can be correlated with geological features either observed in the field or interpreted from the aeromagnetic map. A set of south-dipping reflections represent inferred syn-extensional listric extensional faults that were inverted during subsequent crustal-shortening. Cross-cutting north-dipping reflections are correlated to late-compressional break-back faults. Flat-lying reflections in the central parts of the study area could represent lithological contacts within the Skellefte Group, or the contact between Skellefte Group rocks and their unknown basement. Flat-lying reflections occurring further north are inferred to originate from the top of the Jörn intrusive complex or an intrusive contact within it. So far unknown south- and north-dipping faults have been identified in the vicinity of the Maurliden deposit. Based on the seismic results, a preliminary 3D-model has been created in order to visualize the fault pattern and to provide a base for future 3D/4D modeling in the Skellefte district.
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| 2. |
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| 3. |
- Dehghannejad, Mahdieh, et al.
(författare)
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Reflection seismic imaging of the upper crust in the Kristineberg mining area, northern Sweden
- 2010
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Ingår i: Journal of Applied Geophysics. - : Elsevier BV. - 0926-9851 .- 1879-1859. ; 71:4, s. 125-136
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Tidskriftsartikel (refereegranskat)abstract
- The Kristineberg mining area is located in the western part of the Palaeoproterozoic Skellefte Ore District, one of the most important mining districts in Europe. As a part of a 3D geologic modeling project, two new reflection seismic profiles were acquired with a total length of about 20 km. One profile (HR), parallel to previous seismic profiles, was acquired using a 10 m receiver and source interval and crosses the steeply dipping structures of the Kristineberg mine. The other profile (Profile 2) runs perpendicular to all existing profiles in the area. Although the structural geology is complex, the processed seismic data reveal a series of steeply dipping to sub-horizontal reflections, some of which reach the surface and allow correlation with surface geology. Our general interpretation of the seismic images is that the Kristineberg mine and associated mineral horizon are located in the northern part of a series of steeply south dipping structures. Overall, main structures plunge to the west at about 30 degrees-40 degrees. Cross-dip analysis and reflection modeling were carried out to obtain the 3D orientation of the main reflections and to provide insight into the possible contribution of out-of-the-plane reflections. This helped, for example, to obtain the 3D geometry of a deep reflection that was previously interpreted as structural basement to volcanic rocks. The new reflection seismic profiles have improved our understanding of shallow geological structures in the area and in conjunction with recently acquired potential field data, magnetotelluric data and geological observations will help to refine previous 3D geologic modeling interpretations that were aimed at larger scale structures.
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| 4. |
- Malehmir, Alireza, et al.
(författare)
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Regional structural profiles in the western part of the Palaeoproterozoic Skellefte Ore District, northern Sweden
- 2007
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Ingår i: Precambrian Research. - : Elsevier BV. - 0301-9268 .- 1872-7433. ; 159:1-2, s. 1-18
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Tidskriftsartikel (refereegranskat)abstract
- The Kristineberg mining area is situated in the western part of the Palaeoproterozoic Skellefte Ore District, northern Sweden, and is well known for its VHMS base-metal and gold deposits. This paper presents five upper crustal geological cross sections that have been constructed and mainly constrained by seismic reflection data, potential field modeling as well as geological field observations. These profiles are visualized in 3D to highlight the three dimensionality and internal consistency of structures across the region. The resulting structural model for the Skellefte volcanics and overlying metasediments comprises two thrust-sheets that expose the Skellefte volcanics in the cores of hanging-wall anticlinal structures. A shear-zone is imaged as a band of seismic reflectivity terminated by the southern Revsund granite unit. Another shear-zone, possibly a continuation of the Skellefte Shear Zone (SSZ) runs through the centre of the region and accounts for some of the structural complexity and shearing observed between the two anticlinal exposures of the volcanics. Additional smaller scale shear-zones have been identified from geological and geophysical mapping within the main structural blocks of the Skellefte volcanics. The Mala volcanic rocks in the north are separated from the Skellefte volcanics by a fault that cuts discordant to the strike of the Mala volcanics. A structural basement has been proposed to the Skellefte volcanics, constrained by seismic reflection data. Exposures of Bothnian Basin rocks south of the Revsund granite outcrops, suggest that the domain beneath the north dipping reflectivity is associated with Bothnian Basin stratigraphy. The preferred interpretation for the contact between the Skellefte volcanics and the Bothnian Basin rocks is a thrust fault that brings the felsic volcanic rocks over the metasedimentary domain. The Revsund granites are divided into two major groups based on their present day thickness and shapes. Although parts of the Viterliden intrusion are almost undeformed, it is cut by a series of shear-zones, causing the magnetic lineations seen within these rocks. The structural profiles presented demonstrate that the Kristineberg ore is situated in the northern limb of a local synformal structure. The new crustal-scale structural model demonstrates the potential of integrating geophysical and geological data when modelling structures hosting mineralization in a complex region like the Skellefte District. The structural profiles presented in this paper, have greatly improved our understanding of the 3D tectonostratigraphy and architecture of the poly-deformed ca. 1.9 Ga the Skellefte Ore District.
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| 5. |
- Malehmir, Alireza, et al.
(författare)
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Seismic imaging and potential field modeling to delineate structures hosting VHMS deposits in the Skellefte Ore District, northern Sweden
- 2006
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Ingår i: Tectonophysics. - : Elsevier BV. - 0040-1951 .- 1879-3266. ; 426:3-4, s. 319-334
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 6. |
- Tryggvason, Ari, et al.
(författare)
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Reflection seismic investigations in the western part of the paleoproterozoic VHMS-bearing Skellefte district, northern Sweden
- 2006
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Ingår i: Economic geology and the bulletin of the Society of Economic Geologists. - : Society of Economic Geologists. - 0361-0128 .- 1554-0774. ; 101:5, s. 1039-1054
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Tidskriftsartikel (refereegranskat)abstract
- The Skellefte district forms part of the Svecofennian ca. 1.90 to 1.80 Ga, snpracrustal sequence and associated intrusive rocks in the northern part of Sweden. The western part of the Skellefte district, which is the most important metallogenic province in northern Sweden today, hosts major volcanic-hosted massive Sulfide (VHMS) deposits (e.g., the 23 million metric tons (Mt) Kristineberg Cu-Zn-Pb-Ag-Au deposit). In order to obtain a better understanding of the VHMS ore potential at depth, new seismic reflection data were acquired along two parallel and 25-km-long profiles in the Kristineberg area in 2003. The data were collected with the purpose of obtaining high-resolution images of the top 10 kin of the crust and are presented here for the first time. Although the structural setting is very complex, the stacked sections reveal numerous reflections that can be correlated with surface geology. Visible on both profiles is a pronounced north-dipping hand of reflections marking a boundary between relatively transparent crust above and significantly more reflective crust beneath it. We interpret this reflective crust to represent a structural basement to the ore-bearing Skellefte Group, possibly constituting Bothnian basin metasedimentary rocks bordering the Skellefte district to the south. This new interpretation is important for the understanding of the tectonic evolution of the Skellefte district and for defining exploration strategies in the area. The seismic results suggest that the Kristineberg and Ravliden deposits occur on the northern limb of a kilometer-scale local second-order syncline within the hinge zone of a major antiform. Results from a profile located approximately 8 kin to the west of the Kristineberg mine indicate that the Revsund granitoid has a thickness of about 3 to 3.5 km. Ultramafic rocks are also imaged clearly Diffraction patterns and bright-spot reflectivity is interpreted as originating from either mafic to ultramafic intrusions ora mineralization zone at 3- to 5-km depth. These results help to identify new prospective areas and mineral potential, both downplunge from known ores and on the same stratigraphic horizon on the southern limb of the ore-bearing syncline. The seismic reflection profiling has been effective in imaging the major structures around the Kristineberg orebody, demonstrating that this technique can be used for delineating complex structures significant for mineral exploration.
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