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- Bauer, Tobias, et al.
(författare)
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3D-modelling of the Central Skellefte District, Sweden
- 2009
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Ingår i: Smart science for exploration and mining. - : James Cook University of North Queensland. - 9780980558685
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Konferensbidrag (refereegranskat)abstract
- The central part of the Palaeoproterozoic Skellefte District in northern Sweden is host to several VMS deposits. This area is dominated by upright folds with axial surfaces trending WNW - ESE. Northeast - SW trending faults crosscut WNW - ESE trending faults and impart a distinct fault pattern. Subvertical stretching as expressed by subvertical mineral lineations as well as gently W-plunging mineral lineations parallel to the F2 fold axes indicate not only significant vertical movement, but also pronounced lateral movement. The faults formed in an extensional stage and were reactivated during a compressional stage oblique to the earlier phase. This crustal shortening caused folding and development of the main foliation. Overturned, tight to isoclinal folds within the Vargfors meta-sediments coincide with 1st and 2nd order faults and are considered to be related to reactivation of the early normal and transfer faults. A three dimensional model taking into account the structures was constructed using the GoCAD 3D-modelling software.
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| 3. |
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| 4. |
- Bauer, Tobias, et al.
(författare)
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Correlation between distribution and shape of VMS deposits, and regional deformation patterns, Skellefte district, northern Sweden
- 2014
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Ingår i: Mineralium Deposita. - : Springer Science and Business Media LLC. - 0026-4598 .- 1432-1866. ; 49:5, s. 555-573
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Tidskriftsartikel (refereegranskat)abstract
- The Skellefte district in northern Sweden is host to abundant volcanogenic massive sulphide (VMS) deposits comprising pyritic, massive, semi-massive and disseminated Zn–Cu–Au ± Pb ores surrounded by disseminated pyrite and with or without stockwork mineralisation. The VMS deposits are associated with Palaeoproterozoic upper crustal extension (D1) that resulted in the development of normal faults and related transfer faults. The VMS ores formed as sub-seafloor replacement in both felsic volcaniclastic and sedimentary rocks and partly as exhalative deposits within the uppermost part of the volcanic stratigraphy. Subsequently, the district was subjected to deformation (D2) during crustal shortening. Comparing the distribution of VMS deposits with the regional fault pattern reveals a close spatial relationship of VMS deposits to the faults that formed during crustal extension (D1) utilising the syn-extensional faults as fluid conduits. Analysing the shape and orientation of VMS ore bodies shows how their deformation pattern mimics those of the hosting structures and results from the overprinting D2 deformation. Furthermore, regional structural transitions are imitated in the deformation patterns of the ore bodies. Plotting the aspect ratios of VMS ore bodies and the comparison with undeformed equivalents in the Hokuroko district, Japan allow an estimation of apparent strain and show correlation with the D2 deformation intensity of the certain structural domains. A comparison of the size of VMS deposits with their location shows that the smallest deposits are not related to known high-strain zones and the largest deposits are associated with regional-scale high-strain zones. The comparison of distribution and size with the pattern of high-strain zones provides an important tool for regional-scale mineral exploration in the Skellefte district, whereas the analysis of ore body shape and orientation can aid near-mine exploration activities.
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| 5. |
- Bauer, Tobias, et al.
(författare)
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Crustal Scale Shear Zones Controlling Grade and Tonnage of VMS Deposits in the Skellefte District, Northern Sweden
- 2015
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Ingår i: Mineral Resources in a Sustainable World. - 9782855550664 ; , s. 45-48
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Konferensbidrag (refereegranskat)abstract
- The Skellefte district in northern Sweden hosts abundant Paleoproterozoic, volcanic-hosted massive sulfide (VMS) deposits. The deposits formed due to pull apart basin formation in a volcanic arc setting and utilized the syn-extensional faults as fluid conduits. By comparing the structural setting in distinct structural domains with the tonnage and Cu, Au, and Ag grades a clear coupling between VMS deposits and the size of structures becomes evident. This shows how major crustal fault zones acted as fluid conduits for the ore forming hydrothermal fluids during an extensional phase. The same structures were subsequently re-activated as shear zones and possibly enhanced secondary enrichment processes.
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| 6. |
- Bauer, Tobias, et al.
(författare)
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Fault-controlled sedimentation in a progressively opening extensional basin : the Palaeoproterozoic Vargfors basin, Skellefte mining district, Sweden.
- 2013
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Ingår i: International journal of earth sciences. - : Springer Science and Business Media LLC. - 1437-3254 .- 1437-3262. ; 102:2, s. 385-400
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Tidskriftsartikel (refereegranskat)abstract
- The Vargfors basin in the central part of the Skellefte mining district is an inverted sedimentary basin within a Palaeoproterozoic (1. 89 Ga) marine volcanic arc. The fault-segmented basin formed from upper-crustal extension and subsequent compression, following a period of intense sub-marine volcanism and VMS ore formation. New detailed mapping reveals variations in stratigraphy attributed to syn-extensional sedimentation, as well as provenance of conglomerate clasts associated with tectonic activity at the transition from extension to compression. The onset of fan delta to alluvial fan sedimentation associated with basin subsidence indicates that significant dip-slip displacement accommodating rapid uplift of the intrusive complex and/or subsidence of the adjacent volcano-sedimentary domain took place along a major fault zone at the southern margin of the intrusive complex. Subsidence of the Jörn intrusive complex and/or its burial by sedimentary units caused a break in erosion of the intrusion and favoured the deposition of a tonalite clast-barren conglomerate. Clast compositions of conglomerates show that the syn-extensional deposits become younger in the south-eastern parts of the basin, indicating that opening of the basin progressed from north-west to south-east. Subsequent basin inversion, associated with the accretion to the Karelian margin, involved reverse activation of the normal faults and development of related upright synclines. Progressive crustal shortening caused the formation of break-back faults accompanied by mafic volcanic activity that particularly affected the southern contact of the Jörn intrusive complex and the northern contact of the Vargfors basin
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| 8. |
- Bauer, Tobias, et al.
(författare)
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Geological multi-scale modelling as a tool for modern ore exploration in the Skellefte mining district, Sweden
- 2011
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Ingår i: Proceedings IAMG 2011 Salzburg. - : cogeo@oeaw-giscience. ; , s. 759-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The Palaeoproterozoic Skellefte Mining District is host to abundant ore deposits. Geological 3Dmodelling was performed using the gOcad software platform. Geological methods such as field mapping, structural analysis and facies analysis combined with geophysical techniques such as reflection seismic investigations, resistivity, magnetic, electromagnetic and gravimetric studies and analysis of potential field data provide a framework for the reconstruction of the crustal geometry and geological history of the district as a tool for modern ore exploration. Results will be furthermore utilized for kinematic 4-dimensional modelling
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| 10. |
- Bauer, Tobias, et al.
(författare)
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Syn-extensional faulting controlling structural inversion : Insights from the Palaeoproterozoic Vargfors syncline, Skellefte mining district, Sweden
- 2011
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Ingår i: Precambrian Research. - : Elsevier BV. - 0301-9268 .- 1872-7433. ; 191:3-4, s. 166-183
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Tidskriftsartikel (refereegranskat)abstract
- The Vargfors basin in the central Skellefte district, Sweden, is an inverted sedimentary sub-basin within a Palaeoproterozoic (1.89 Ga) marine volcanic arc. The sub-basin formed from upper-crustal extension and subsequent compression, following a period of intense marine volcanism and VMS ore formation. Detailed mapping and structural analysis reveals a pattern of SE–NW-striking normal faults and interlinked NE–SW-striking transfer faults, which define distinct fault-bound compartments, each with an individual structural geometry and stratigraphy. Constraints on the deformation style and mechanisms achieved by 2D forward modelling are in agreement with the previously inferred inversion of the early normal faults during a regional crustal shortening event. A rheologically weak carbonate-rich layer at the base of the sedimentary sequence favoured the fault inversion over more distributed shortening as the controlling deformation mechanism. Transposition of sedimentary strata into the approximately SE–NW faults led to formation of asymmetric synclines that were tightened during progressive shortening. Structural analysis infers a progressive opening of the basin towards SE and NW with time. Furthermore, it is inferred that a displacement gradient was developed along the main structural grain, with decreasing dip-slip displacements towards SE and NW, both during the extension and the structural inversion.VMS deposits in the vicinity of the contact between the volcanic and the overlying sedimentary rocks were formed along early normal faults, which reacted as fluid conduits. Subsequently, the deposits were transposed into the inverted faults during crustal shortening. Consequently, the inverted faults provide a useful tool for mineral exploration in the district.
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