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- Bark, Glenn, et al.
(författare)
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Fluid chemistry of the hypozonal Fäboliden orogenic gold deposit, northern Sweden
- 2006
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Ingår i: The 27th Nordic Geological Winter Meeting, January 9-12, 2006, Oulu, Finland. ; , s. 13-
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Southwest of the well-known Skellefte District in northern Sweden a new ore province is presently being explored, the so called Gold Line. Today the largest known gold deposit in the Gold Line is the Fäboliden orogenic gold deposit.The gold mineralization is commonly hosted in quartz veins, which parallel the steep main foliation, within a shear zone in the metagreywacke host rocks. The fine-grained (2-40 μm) gold is closely associated with arsenopyrite in the quartz veins.Two main groups of fluid inclusions are present in the Fäboliden quartz veins. 1) Primary inclusions with a CO2-CH4 or a H2S (±CH4) composition (the latter recognized for the first time in a Swedish ore deposit). 2) Secondary fluid inclusions composed of pure CH4 and low-salinity aqueous fluids. The primary fluid inclusions are associated with arsenopyrite (+gold) and the CO2-CH4 fluid was also involved in precipitation of graphite. The graphite-forming reactions should generate a H2O phase as well. However, the presence of a H2O phase was not detected in any of the primary fluid inclusions and is suggested to have been consumed by wall rock reactions, generating hydrated alteration minerals such as Ca-amphibole, biotite, and minor tourmaline. Fluid inclusion data indicate arsenopyrite and graphite deposition at a pressure condition of ~4 kbars. Graphite is useful as an indicator of the metamorphic grade because the graphitization process is irreversible with no effects on the graphite structure during retrogression (Beyssac et al., 2002). Graphite in the mineralized quartz veins at Fäboliden indicates maximum temperatures of 520-560°C for the hydrothermal alteration system.Pyrrhotite was deposited after a subsequent pressure decrease and a later input of pure CH4 and low-salinity aqueous fluids, as suggested by the secondary fluid inclusions. These later fluids were trapped at a substantially lower pressure of ~0.3 kbars and a temperature of ~400°C.
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| 2. |
- Bark, Glenn, et al.
(författare)
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Fluid chemistry of the Palaeoproterozoic Fäboliden hypozonal orogenic gold deposit, northern Sweden : evidence from fluid inclusions
- 2007
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Ingår i: GFF. - : Informa UK Limited. - 1103-5897 .- 2000-0863. ; 129:3, s. 197-210
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Tidskriftsartikel (refereegranskat)abstract
- A new ore province, the Gold Line, southwest of the Skellefte District, northern Sweden, is currently under exploration. The largest known deposit in the Gold Line is the hypozonal Fäboliden orogenic gold deposit. The mineralization is hosted by arsenopyrite-bearing quartz veins, within a steep shear zone in amphibolite facies metagreywacke host rocks. Gold occur in fractures and as intergrowths in arsenopyrite-löllingite, and as free grains in the silicate matrix of the host rock. The hydrothermal mineral assemblage in the proximal alteration zone is diopside, calcic amphibole, biotite, and minor andalusite and tourmaline. Primary fluid inclusions in the Fäboliden quartz veins show a CO2-CH4 or a H2S (±CH4) composition (the latter recognized for the first time in a Swedish ore deposit). The primary fluid inclusions are associated with arsenopyrite-löllingite (+gold) and the CO2-CH4 fluid was also involved in precipitation of graphite. A prevalence of carbonic over aqueous fluid inclusions is characteristic for a number of hypozonal high-temperature orogenic gold deposits. The Fäboliden deposit, thus, shows fluid compositions similar to other hypozonal orogenic gold deposits. The proposed main mechanism for precipitation of gold from the fluids, is a mixing between H2S-rich and H2O?-CO2±CH4 fluids. Fluid inclusion data indicate arsenopyrite-löllingite and graphite deposition at a pressure condition of about 4 kbar. Graphite thermometry indicates maximum temperatures of 520-560°C for the hydrothermal alteration at Fäboliden, suggesting that at least the late stages of the mineralizing event took place shortly after peak-metamorphism in the area, i.e. at c. 1.80 Ga.
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| 3. |
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| 4. |
- Bark, Glenn, et al.
(författare)
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Orogenic gold in the new Lycksele-Storuman ore province, northern Sweden : the Palaeoproterozoic Fäboliden deposit
- 2007
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Ingår i: Ore Geology Reviews. - : Elsevier BV. - 0169-1368 .- 1872-7360. ; 32:1-2, s. 431-451
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Tidskriftsartikel (refereegranskat)abstract
- Southwest of the well-known Skellefte District, northern Sweden, a new gold ore province, the so called Gold Line, is presently being explored. During the past decade a number of gold occurrences have been discovered in this area. The largest known gold occurrence is the Fäboliden deposit. Late-to post-orogenic, ca. 1.81 to 1.77 Ga, Revsund granite constitutes the main rock type in the Fäboliden area and surrounds a narrow belt of mineralized metagreywackes and metavolcanic rocks. The supracrustal rocks are strongly deformed within a roughly N-S trending subvertical shear zone. The mineralization constitutes a 30 to 50 m wide, N-S striking, steeply dipping zone. The mineralization is commonly hosted by arsenopyrite-bearing quartz-veins within the supracrustal rocks. The quartz veins parallel the main foliation in the shear zone. Gold is closely associated with arsenopyrite-löllingite and stibnite and found in fractures and as intergrowths in the arsenopyrite-löllingite. Gold is also seen as free grains in the silicate matrix of the host rock. The proximal alteration zone displays positive correlation with Ca, S, As, Ag, Sb, Sn, W, Pb, Bi, Cd, Se, and Hg, whereas K and Na show a slightly negative correlation. The hydrothermal mineral assemblage in the proximal alteration zone is diopside, calcic amphibole, biotite, and minor andalusite and tourmaline. This type of assemblage is commonly recognized in hypozonal orogenic gold deposits worldwide. Garnet-biotite geothermometry indicates amphibolite facies in the Fäboliden area. The ductile fabric that hosts the mineralization is also found in the margin of the surrounding Revsund granitoid. It is therefore suggested that at least the final stages of the gold mineralization are syn- to late-kinematic, and the minimum age for the mineralization is thus constrained at ca. 1.80 Ga (Revsund age).
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| 5. |
- 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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| 6. |
- 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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| 7. |
- Bejgarn, Therese, et al.
(författare)
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The Älgtrask intrusive-hosted Au (-Cu) deposit, Sweden
- 2008
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)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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| 8. |
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| 9. |
- Dehghannejad, M., et al.
(författare)
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High-resolution reflection seismic imaging in the Skellefte ore district : a contribution to 4D geologic modeling
- 2009
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Ingår i: Geophysical Research Abstracts.
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The Kristineberg VHMS (volcanic-hosted massive sulfide) mining area is located in the western part of the Skellefte Ore District, the most important metallogenic zone in northern Sweden. The area has been the subject of several geological and geophysical studies with the aim of understanding the contact relationships between the ore bearing volcanic and volcanosedimentary formations and the surrounding rocks. To establish the structural geologic framework at depth, two new reflection seismic profiles, a N-S directed high resolution one with a length of about 6.3 km and an E-W directed one perpendicular to the high-resolution profile with a length of about 13 km were acquired in 2008. Although the structural geology is complex, a preliminary stacked section of the high-resolution profile reveals a series of steeply dipping to sub-horizontal reflections in the southern and northern parts of the profile, many of which can be traced to the surface for correlation with surface geology. Several reflections appear to be consistent with reflections observed in two previously acquired profiles in the study area. The new reflection seismic results will be integrated with the previous reflection seismic results, potential field modeling, magnetotelluric data and geological observations to improve earlier geological interpretations that led to a pilot 3D geologic model of the study area.
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| 10. |
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