| 1. |
- Andersson, Stefan S., et al.
(författare)
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Mineral paragenesis and sulphide trace element distribution in the metamorphosed Lovisa Zn-Pb deposit, Bergslagen (Sweden), as revealed by 3D X-ray tomography, ore petrography and LA-ICP-MS analysis
- 2022
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Ingår i: Ore Geology Reviews. - : Elsevier BV. - 0169-1368 .- 1872-7360. ; 140
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Tidskriftsartikel (refereegranskat)abstract
- This study encompasses the ore mineralogy, textures and sulphide trace element chemistry of the Palaeoproterozoic Lovisa stratiform Zn-Pb deposit and the stratigraphically underlying Lovisa Fe Formation in the Bergslagen ore province (Sweden). We investigate the relative timing of formation and subsequent modifications of its ores in relation to the c. 1.87-1.80 Ga Svecokarelian orogeny. The Lovisa Zn-Pb deposit consists of several different ore types. The massive sphalerite-galena ore is distinctly deformed, exhibiting a multiple-scale "ball ore" texture with rounded silicate clasts within a deformed, fine-grained sulphide matrix. Underlying the massive ore is a locally folded, sphalerite-rich laminated ore, interpreted to represent a metamorphosed relict primary lamination. Several generations of sphalerite-galena fracture fillings and veins occur adjacent to the main ore zones and they cross-cut early ductile structures and metamorphic features. The trace element signatures of the sphalerite-galena infillings generally mimic those of the two main ore zones, thus supporting an origin by localised remobilisation of the primary sulphide ore and demonstrating limited trace element redistribution during this process. In contrast, discrete sulphosalt-rich fracture fillings cross-cutting earlier galena-chalcopyriterich fracture fillings and veinlets in the Lovisa Fe Formation suggest a significant but still relatively localised redistribution of metals. Trace element mapping of sulphides from the Lovisa Zn-Pb deposit reveals that inclusion-free overgrowths on pyrite crystals are locally Co-enriched compared to the cores, which resulted from the redistribution of Co during late metamorphic processes. Combined textural and geochemical evidence suggest that the originally syngenetic exhalative sulphide ore at Lovisa was locally strongly affected by polyphase deformation and remobilisation. This was initiated during the first stage of amphibolite facies grade regional metamorphism and deformation (D1, c. 1.87-1.85 Ga) but is mostly evident from the later stages (D2) and the evolution to retrograde and brittle conditions (c. 1.83-1.80 Ga and later).
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| 2. |
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| 3. |
- Bergman, S., et al.
(författare)
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Timing of Palaeoproterozoic intra-orogenic sedimentation in the central Fennoscandian Shield; evidence from detrital zircon in metasandstone
- 2008
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Ingår i: Precambrian Research. - : Elsevier BV. - 0301-9268 .- 1872-7433. ; 161:3-4, s. 231-249
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Tidskriftsartikel (refereegranskat)abstract
- Detrital zircon U-Pb SIMS data on quartz-rich metasandstone units presumed to belong to the upper part of the Svecofennian stratigraphy in southeastern Finland and east-central Sweden suggest the existence of clastic sedimentary basins between the two main orogenic phases at 1.89-1.86 Ga and 1.83-1.79 Ga, during a period referred to as the intra-orogenic phase (1.86-1.83 Ga). Stratigraphically below the metasandstone at Hamrange, east-central Sweden, is a metadacite with an U-Pb zircon TIMS age of 1888 +/- 6 Ma, which indicates the maximum age of sedimentation. It also indicates that an earlier proposed correlation of Hamrange metavolcanic rocks and 1.86Ga equivalents at Los to the northwest must be rejected. Instead, there is a temporal affinity to the metavolcanic rocks in the Bergslagen Province to the south or Southern Finland to the east. Quartz-rich metasandstone samples from four localities, Luukkola, Pyhantaka and Tiirismaa in Finland and Hamrange in Sweden, yield multimodal detrital zircon age distributions with main populations at 2.95-2.60 Ga, 2.10-1.95 Ga and 1.92-1.85 Ga. The groups are similar in all four samples, and they are comparable to previously reported detrital ages in this part of the Fennoscandian Shield. The oldest zircon analysed gave an age of 3.32 Ga (Tiirismaa). The maximum ages of sedimentation (and of subsequent deformation and metamorphism), indicated by the youngest detrital zircon, from the four localities are 1842 10 Ma (Luukkola), 1865 +/- 11 Ma (Pyhantaka), 1848 +/- 13 Ma (Tiirismaa), and 1855 10 Ma (Hamrange), respectively. Possible source rocks for these zircon grains are found within and around the vast Ljusdal Batholith in Sweden, and in the Arc Complexes of Western and Southern Finland. It is concluded that several intra-orogenic sedimentary basins existed during the time interval 1.86-1.83 Ga ago, between two major orogenic events in the Fermoscandian Shield.
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| 4. |
- Högdahl, Karin, et al.
(författare)
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Geological relations and U-Pb geochronology of Hyttsjo granites in the Langban-Nordmark area, western Bergslagen, Sweden
- 2007
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Ingår i: GFF. - : Informa UK Limited. - 1103-5897 .- 2000-0863. ; 129:1, s. 43-54
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Tidskriftsartikel (refereegranskat)abstract
- The Hyttsjo granites occur in the extensively mineralised Langban-Nordmark area in the westernmost part of the Bergslagen ore province. They have been classified as late Svecokarelian granites due to their homogeneous and generally isotropic appearance in addition to a WR Rb/Sr age. Moreover, they have been considered as possible candidates for supplying essential metals to epigenetic mineralisation in this classic ore district. Two Hyttsjo granites yield U-Pb zircon data ages of 1791 2 and 1793 3 Ma, respectively, which overlap with emplacement ages of the adjacent 1.80-1.78 Ga Filipstad suite belonging to the Transscandinavian Igneous Belt (TIB). Mafic rocks occur quite abundantly associated with the Filipstad-type granite (sensu lato) and various types of mafic enclaves as well as hybrid rocks are present, suggesting a co-magmatic origin. Such mafic intrusives are also exposed in the vicinity of most known Hyttsjo-type plutons. Not least our observations that the former exhibit back-veining by granitic melts suggest intimate causal and temporal relationships between granite formation and mafic TIB rocks. The Hyttsjo granites were probably produced through partial melting related to the intrusion of hot, mafic magmas in and along the border between the TIB and the Svecofennian supracrustal and subvolcanic rocks. Thus, all available observations and data suggest that the Hyttsjo granites are intimately related to and most probable a product of TIB magmatism. Also, they do not lend any support for the hypothesis that the formation of the Hyttsjo granites represent a temporally separate intrusive episode. The Hyttsjo granites are therefore unlikely to be discernibly responsible for specific mineralisation in this area.
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| 5. |
- Troll, Valentin R., et al.
(författare)
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Global Fe–O isotope correlation reveals magmatic origin of Kiruna-type apatite-iron-oxide ores
- 2019
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 10:1
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Tidskriftsartikel (refereegranskat)abstract
- Kiruna-type apatite-iron-oxide ores are key iron sources for modern industry, yet their origin remains controversial. Diverse ore-forming processes have been discussed, comprising low-temperature hydrothermal processes versus a high-temperature origin from magma or magmatic fluids. We present an extensive set of new and combined iron and oxygen isotope data from magnetite of Kiruna-type ores from Sweden, Chile and Iran, and compare them with new global reference data from layered intrusions, active volcanic provinces, and established low-temperature and hydrothermal iron ores. We show that approximately 80% of the magnetite from the investigated Kiruna-type ores exhibit δ56Fe and δ18O ratios that overlap with the volcanic and plutonic reference materials (> 800 °C), whereas ~20%, mainly vein-hosted and disseminated magnetite, match the low-temperature reference samples (≤400 °C). Thus, Kiruna-type ores are dominantly magmatic in origin, but may contain late-stage hydrothermal magnetite populations that can locally overprint primary high-temperature magmatic signatures.
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| 6. |
- Buntin, Sebastian, et al.
(författare)
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Emplacement and 3D geometry of crustal-scale saucer-shaped intrusions in the Fennoscandian Shield
- 2019
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Saucer-shaped intrusions of tens of meters to tens of kilometres across have been observed both from surface geological mapping and geophysical observations. However, there is only one location where they have been reported to extend c. 100 km laterally, and emplaced both in a sedimentary basin and the crystalline basement down to 12 km depth. The legacy BABEL offshore seismic data, acquired over the central Fennoscandian Shield in 1989, have been recovered and reprocessed with the main goal of focusing on this series of globally unique crustal-scale saucer-shaped intrusions present onshore and offshore below the Bothnian Sea. The intrusions (c. 1.25 Ga), emplaced in an extensional setting, are observed within both sedimentary rocks (<1.5 Ga) and in the crystalline basement (>1.5 Ga). They have oval shapes with diameters ranging 30-100 km. The reprocessed seismic data provide evidence of up-doming of the lower crust (representing the melt reservoir) below the intrusions that, in turn, are observed at different depths in addition to a steep seismically transparent zone interpreted to be a discordant feeder dyke system. Relative age constraints and correlation with onshore saucer-shaped intrusions of different size suggest that they are internally connected and fed by each other from deeper to shallower levels. We argue for a nested emplacement mechanism and against a controlling role by the overlying sedimentary basin as the saucer-shaped intrusions are emplaced in both the sedimentary rocks as well as in the underlying crystalline basement. The interplay between magma pressure and overburden pressure, as well as the, at the time, ambient stress regime, are responsible for their extensive extent and rather constant thicknesses (c. 100-300 m). Saucer-shaped intrusions may therefore be present elsewhere in the crystalline basement to the same extent as observed in this study some of which are a significant source of raw materials.
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| 7. |
- Buntin, Sebastian, et al.
(författare)
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Long-lived Paleoproterozoic eclogitic lower crust
- 2021
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Ingår i: Nature Communications. - : Springer Nature. - 2041-1723. ; 12
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Tidskriftsartikel (refereegranskat)abstract
- The nature of the lower crust and the crust-mantle transition is fundamental to Earth sciences. Transformation of lower crustal rocks into eclogite facies is usually expected to result in lower crustal delamination. Here we provide compelling evidence for long-lasting presence of lower crustal eclogite below the seismic Moho. Our new wide-angle seismic data from the Paleoproterozoic Fennoscandian Shield identify a 6–8 km thick body with extremely high velocity (Vp ~ 8.5–8.6 km/s) and high density (>3.4 g/cm3) immediately beneath equally thinned high-velocity (Vp ~ 7.3–7.4 km/s) lowermost crust, which extends over >350 km distance. We relate this observed structure to partial (50–70%) transformation of part of the mafic lowermost crustal layer into eclogite facies during Paleoproterozoic orogeny without later delamination. Our findings challenge conventional models for the role of lower crustal eclogitization and delamination in lithosphere evolution and for the long-term stability of cratonic crust.
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| 8. |
- Jonsson, Erik, et al.
(författare)
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Roquesite and associated Indium-bearing sulphides from a Palaeoproterozoic carbonate-hosted mineralisation : Lindbom’s prospect, Bergslagen, Sweden
- 2013
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Ingår i: Canadian Mineralogist. - : Mineralogical Association of Canada. - 0008-4476 .- 1499-1276. ; 51:4, s. 629-641
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Tidskriftsartikel (refereegranskat)abstract
- The present study describes a new discovery of the copper-indium sulfide mineral roquesite (nominally CuInS2) together with indium-bearing sulfides associated with magnetite in a carbonate-hosted, polymetallic sulfide mineralization. This occurrence, Lindbom’s Prospect, is located in the western part of the Paleoproterozoic Bergslagen ore province, Sweden. Here, roquesite occurs in indium-bearing bornite, characteristically associated with indium and copper-bearing sphalerite, as well as chalcopyrite, cuproan galena, late-stage chalcocite-digenite and covellite, variable amounts of bismuth minerals, abundant magnetite, and locally cassiterite. The indium-bearing ore mineral assemblages were studied by a combination of optical and field emission scanning electron microscopy and field emission electron probe microanalyzer (FE-EPMA) techniques. FE-EPMA analyses of roquesite yield an average composition corresponding to Cu0.93Fe0.02Zn0.06In1.00S2. It occurs as ca. 4–30 micron-sized subhedral to anhedral, often angular crystals in bornite, typically in direct contact, or in close association with, indium-bearing sphalerite. The latter has variable indium content, ranging from below detection limit to at least 1.5 wt.% In, and exhibits an average of 0.03 wt.% In. Notably, sphalerite grains show a slight enrichment of indium towards the rims and the adjacent bornite, where roquesite occurs. The associated bornite, as well as minor chalcopyrite, mostly exhibit low to very low indium contents. These are mostly below detection limit, but locally higher in bornite; average 0.01 wt.% In and maximum 0.2 wt.% In. The highest indium content observed in chalcopyrite is 0.02 wt.% In. Combining textural evidence and high-resolution mineral chemical data, we suggest that roquesite formed as a consequence of reactions between diffusion-driven indium from sphalerite, and the surrounding bornite, during regional metamorphism. Based on available evidence, it is most likely that the studied assemblages represent part of a metamorphically overprinted, in part remobilized ca. 1.89–1.88 Ga volcanic-subvolcanic hydrothermal mineralization.
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| 9. |
- Malehmir, Alireza, et al.
(författare)
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Reflection seismic investigations in the Dannemora area, central Sweden : insights into the geometry of polyphase deformation zones and magnetite-skarn deposits
- 2011
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Ingår i: Journal of Geophysical Research. - 0148-0227 .- 2156-2202 .- 2169-9313 .- 2169-9356. ; 116, s. B11307-
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Tidskriftsartikel (refereegranskat)abstract
- The Bergslagen region is one of the most ore prospective districts in Sweden. Presented here are results from two nearly 25 km long reflection seismic profiles crossing this region in the Dannemora mining area. The interpretations are constrained by seismic wave velocity measurements on a series of rock samples, cross-dip analysis, prestack time migration, and swath 3-D imaging, as well as by other available geophysical and geological observations. A series of major fault zones is imaged by the seismic data, as is a large mafic intrusion. However, the most prominent feature is a package of east-dipping reflectors found east of the Dannemora area that extend down to at least 3 km depth. This package is associated with a polyphase, ductile-brittle deformation zone with the latest ductile movement showing east-side-up or reverse kinematics. Its total vertical displacement is estimated to be in the order of 2.5 km. Also clearly imaged in the seismic data is a steeply dipping reflector near the Dannemora mine that extends down to a depth of at least 2.2 km. The geological nature of this reflector is not known, but it could represent either a fluid-bearing fault zone or a deep-seated iron deposit, making it an important target for further detailed geophysical and geological investigations.
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| 10. |
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