| 1. |
- Bejgarn, Therese, et al.
(author)
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Geology, petrology and alteration geochemistry of the Palaeoproterozoic intrusive hosted Ägträsk Au deposit, Northern Sweden
- 2011
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In: Geological Society Special Publication. - 0305-8719 .- 2041-4927. ; :350, s. 105-132
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Journal article (peer-reviewed)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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| 2. |
- Bejgarn, Therese, et al.
(author)
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Intrusion-related mineralization in the Palaeo-proterozoic Jörn Granitoid Complex, northern Sweden
- 2009
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In: Smart science for exploration and mining. - : James Cook University of North Queensland. - 9780980558685 ; , s. 921-923
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Conference paper (peer-reviewed)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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| 3. |
- Bejgarn, Therese, et al.
(author)
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Tectonomagmatic aspects of intrusive hosted Cu-Au-Mo deposits in the Skellefte District, northern Sweden
- 2013
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In: Mineral deposit research for a high-tech world. - Uppsala : Sveriges Geologiska Undersökning. - 9789174032079 ; , s. 770-773
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Conference paper (peer-reviewed)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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| 4. |
- Bejgarn, Therese, et al.
(author)
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The Älgtrask intrusive-hosted Au (-Cu) deposit, Sweden
- 2008
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Conference paper (other academic/artistic)abstract
- The Algtrask gold deposit is located in the northern part of the Skellefte mining district, northern Sweden. It constitutes a major gold and copper exploration target for the mining company Boliden Mineral AB with an inferred mineral resource of 1.6 Mt grading 3 g/t Au. The deposit is situated in the southern margin of the Jorn Granitoid Complex (JGC), a composite, I-type, calc-alkaline batholith, which intruded into an island arc or continental margin arc volcanic succession in the early Proterozoic. The area has been affected by regional metamorphism of lower greenschist facies.Mineralization occurs as veins and disseminations in meter wide, steeply dipping, sub-parallel ENE-NE striking deformation zones within a coarse grained quartz-porphyritic granodiorite. The deposit has proximal silicic/phyllic and distal propylitic alteration. The altered zones commonly show ductile deformation, and where they are sulphide bearing, form IP-anomalies. Gabbro, equigranular tonalite, quartz-feldspar porphyritic dacitic dykes, basaltic dykes, aplitic dykes, quartz-calcite veins and episyenite have been recognized close to mineralization. The quartz-feldspar porphyritic dykes are in part altered and mineralized in a similar manner to the granodiorite.Two main mineralized zones have been distinguished at Algtrask; both contain pyrite, chalcopyrite, sphalerite and arsenopyrite and minor molybdenite, bornite, pyrrhotite, magnetite, gold and tellurides (e.g. petzite, hessite, altaite, coloradoite). Traces of native silver and bismuth have also been observed. The gold occurs as electrum (ca 80% Au) and calaverite closely associated with other tellurides. Gold and tellurides commonly occur as inclusions or in fractures in pyrite, within quartz-calcite veins or zones of phyllic-silicic alteration. Thicker bands of arsenopyrite are common in the southern zone, but do not occur in the northern zone, which suggests that the chemistry and sulphur fugacity of the ore forming fluids were different in the two mineralised zones.The Tallberg porphyry copper deposit is situated only 3 km west of Algtrask. Tallberg is characterized by quartz stockworks with disseminated pyrite, chalcopyrite, pyrrhotite and magnetite, hosted in propylitic and phyllic altered equigranular tonalite of the JGC. The similar settings, alteration and close spatial relationship, suggest a genetic link between the two deposits. The Algtrask deposit might represent a higher level epithermal system genetically linked to the Tallberg porphyry system. Ductile deformation took place during subsequent tectonic events, probably causing remobilization of sulphides and precious metals. Alternatively, a syntectonic model can be proposed in which the Algtrask deformation zones have overprinted an earlier porphyry copper system. In this model, syntectonic hydrothermal fluids may have "leached" gold from the earlier porphyry system during deformation and deposited gold in the deformation zones.
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