| 31. |
- 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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| 32. |
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| 33. |
- 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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| 34. |
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| 35. |
- 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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| 36. |
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| 37. |
- Bejgarn, Therese, et al.
(författare)
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Geology, petrology and alteration geochemistry of the Palaeoproterozoic intrusive hosted Ägträsk Au deposit, Northern Sweden
- 2011
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Ingår i: Geological Society Special Publication. - 0305-8719 .- 2041-4927. ; :350, s. 105-132
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Tidskriftsartikel (refereegranskat)abstract
- The Ägträsk intrusive hosted Au deposit, Skellefte district, northern Sweden, is situated in the oldest, most heterogeneous part of the c. 1.89-1.86 Ga Jörn granitoid complex, which intruded a complex volcano-sedimentary succession in an island arc or continental margin arc environment. The Tallberg porphyry Cu deposit, situated only 3 km west of Ägträsk, is associated with quartz feldspar porphyritic dykes. These dykes are suggested to be genetically related to similar porphyry dykes in Älgträsk and the tonalitic host rock in Tallberg. The granodiorite hosting the Ägträsk Au-deposit does not appear to be genetically related to the tonalite or the porphyry dykes.
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| 38. |
- Bejgarn, Therese, et al.
(författare)
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Intrusion-related mineralization in the Palaeo-proterozoic Jörn Granitoid Complex, northern Sweden
- 2009
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Ingår i: Smart science for exploration and mining. - : James Cook University of North Queensland. - 9780980558685 ; , s. 921-923
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Konferensbidrag (refereegranskat)abstract
- Immediately north of the Skellefte mining district, northern Sweden, the early orogenicsynvolcanic Jörn granitoid complex hosts several mineral deposits. The Jörn granitoid batholith intruded into a continental margin arc or island arc volcanic succession during the early Proterozoic, and comprises a composite, I-type, calc-alkaline batholith, ranging from granite to gabbro in composition. Several mineral deposits occur in the heterogeneous margin of the complex, i.e. the Tallberg porphyry Cu-Au-Mo, the Älgträsk Au and the Älgliden Ni-Cu-Au deposits in the south and the Näsberg Fe±PGE and Granberg porphyry Cu mineralization in the north. The known deposits indicate that the intrusion is fertile for further exploration activities and that Palaeoproterozioc synvolcanic intrusions close to VMS districts should be studied more closely to further develop genetic models which can be used to reconstruct the ore forming environments and tectonic evolution. This knowledge might be used as guidelines when exploring for new districts with economic potential in Palaeoproterozoic terrains.
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| 39. |
- Bejgarn, Therese, et al.
(författare)
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Palaeoproterozoic porphyry Cu-Au, intrusion-hosted Au and ultramafic Cu-Ni deposits in the Fennoscandian Shield: Temporal constraints using U-Pb geochronology
- 2013
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Ingår i: Lithos. - : Elsevier BV. - 0024-4937 .- 1872-6143. ; 174, s. 236-254
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Tidskriftsartikel (refereegranskat)abstract
- The Skellefte district, northern Sweden, is known for the occurrence of 1.89 Ga Palaeoproterozoic volcanogenic massive sulphide (VMS) deposits. The deposits are hosted by the older part of a volcanosedimentary succession, which was intruded at 1.88-1.86 Ga by multiple phases of the syn-volcanic, early orogenic Jorn intrusive complex (JIC). The oldest phase of the JIC hosts different styles of mineralisation, among them porphyry Cu-Mo-Au, intrusion-related Au, and mafic-hosted Fe and Cu-Ni deposits. To discriminate between the different intrusive and ore related events, U-Pb ages of zircons have been obtained for nine intrusive phases and from Na-Ca alteration spatially related to mineralisation, while U-Pb ages of baddeleyite (ZrO2) have been used to constrain intrusive ages of three mineralised and barren mafic-ultramafic intrusive rocks. The two main JIC intrusive phases of a granodioritic-tonalitic composition in the southern study area intruded at 1887 +/- 3 Ma and 1886 +/- 3 Ma, respectively, and were succeeded by the intrusion of layered mafic-ultramafic intrusive rocks in the northern and southern study area at 1879 +/- 1 Ma and 1884 +/- 2 Ma, respectively. Emplacement of porphyry dykes took place at ca. 1877 Ma in the southern, western and northern JIC. The dykes are spatially and temporally associated with formation of porphyry style mineralisation, alteration and Au-mineralisation, as inferred from 1879 +/- 5 Ma zircons in adjacent Na-Ca alteration zones. High SiO2 and Al2O3 contents together with high Sr/Y ratios, mingling structures, mafic xenoliths and hornblende phenocrysts in the porphyry dykes suggest that the magma originated from hydrated partial melts, possibly from the base of the crust at a mature stage of subduction. Local extension resulted in intrusion of mafic-ultramafic rocks around 1.88 Ga prior to and after, the porphyry dykes and associated mineralisation, approximately 10 Ma after the formation of the spatially related 1.89 Ga VMS deposits in the Skellefte district. This 1.88 Ga event correlates with other 1.88 Ga mafic-ultramafic units widespread around the world, and could possibly be interpreted as a large scale response to supercontinent formation. (C) 2012 Elsevier B.V. All rights reserved.
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| 40. |
- Bejgarn, Therese, et al.
(författare)
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Tectonomagmatic aspects of intrusive hosted Cu-Au-Mo deposits in the Skellefte District, northern Sweden
- 2013
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Ingår i: Mineral deposit research for a high-tech world. - Uppsala : Sveriges Geologiska Undersökning. - 9789174032079 ; , s. 770-773
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Konferensbidrag (refereegranskat)abstract
- The Algtrask gold deposit and several low grade base metal deposits, e.g. the Tallberg porphyry deposit, are hosted by the Jam intrusive complex in the northern part of the Skellefte District, northern Sweden. The intrusive complex was emplaced at 1.89-1.86 Ga in a continental margin volcanic arc setting, and the oldest 1.89 Ga phase is coeval with volcanic rocks within the Skellefte Group, a complex volcano-sedimentary succession hosting numerous VMS deposits. The intrusive hosted deposits are associated with 1.88 Ga quartz-feldspar porphyritic intrusive rocks, which formed from 1.89 Ga recycled crust. Hence, it is interpreted that the intrusive hosted deposits formed when the arc was under transpression-compression, 10 Myr after the spatially related VMS deposits, which formed when the arc was under extension.
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