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| 2. |
- Andersson, Stefan S., et al.
(author)
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Origin of the high-temperature Olserum-Djupedal REE-phosphate mineralisation, SE Sweden : A unique contact metamorphic-hydrothermal system
- 2018
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In: Ore Geology Reviews. - : Elsevier BV. - 0169-1368 .- 1872-7360. ; 101, s. 740-764
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Journal article (peer-reviewed)abstract
- The Swedish part of the Fennoscandian Shield hosts a variety of rare earth element (REE) deposits, including magmatic to magmatic-hydrothermal types. This paper focuses on the origin of the Olserum-Djupedal REEphosphate mineralisation located in the sparsely studied Vastervik region, SE Sweden. Here, mineralisation occurs in three main areas, Olserum, Djupedal and Bersummen. Primary hydrothermal REE mineralisation formed at high temperatures (about 600 degrees C), leading to precipitation of monazite-(Ce), xenotime-(Y), fluor apatite and minor (Y,REE,U,Fe)-(Nb,Ta)-oxides in veins and vein zones dominated by biotite, amphibole, magnetite and quartz. The veins are hosted primarily by metasedimentary rocks present close to, or within, the contact aureole of a local 1.8 Ga ferroan alkali feldspar granite pluton, but also occur within in the chemically most primitive granite in the outermost part of that pluton. In the Djupedal area, REE-mineralised metasedimentary bodies are extensively migmatised, with migmatisation post-dating the main stage of mineralisation. In the Olserum and Bersummen areas, the REE-bearing veins are cross-cut by abundant pegmatitic to granitic dykes. The field-relationships demonstrate a-protracted magmatic evolution of the granitic,pluton and a clear spatial and temporal relationship of the REE mineralisation to the granite. The major and trace element chemistry of ore-associated biotite and magnetite support genetic links between all mineralised areas. Biotite mineral chemistry data further demonstrate a distinct chemical trend from meta sediment-hosted ore-associated biotite distal to the major contact of the granite to the biotite in the granite hosted veins. This trend is characterised by a systematic decrease in Mg and Na and a coupled increase in Fe and Ti with proximity to the granite-hosted veins. The halogen compositions of ore-associated biotite indicate elevated contents of HCl and HF in the primary REE mineralising fluid. Calculated log(f(HF)/f(HCL)) values in the Olserum area suggest a constant ratio of about -1 at temperatures of 650-550 degrees C during the evolution of the primary hydrothermal system. In the Djupedal and Bersummen areas, the fluid locally equilibrated at lower log (f(HF)/f(HCl)) values down to -2. High Na contents in ore-associated biotite and amphibole, and the abundance of primary ore-associated biotite indicate a K- and Na-rich character of the primary REE mineralising fluid and suggest initial high-temperature K-Na metasomatism. With subsequent cooling of the system, the fluid evolved locally to more Ca-rich compositions as indicated by the presence of the Ca-rich minerals allanite-(Ce) and uvitic tourmaline and by the significant calcic alteration of monazite-(Ce). The later Ca-rich stages were probably coeval with low to medium-high temperature (200-500 degrees C) Na-Ca metasomatism variably affecting the granite and the wall rocks, producing distinct white quartz-plagioclase rocks. All observations and data lead us to discard the prevailing model that the REE mineralisation in the Olserum-Djupedal district represents assimilated and remobilised former heavy mineral-rich beds. Instead, we propose that the primary REE mineralisation formed by granite-derived fluids enriched in REE and P that were expelled early during the evolution of a local granitic pluton. The REE mineralisation developed primarily in the contact aureole of this granite and represents the product of a high temperature contact metamorphic-hydrothermal mineralising system. The REE mineralisation probably formed synchronously with K-Na and subsequent Na-Ca metasomatism affecting the granite and the wall rocks. The later Na-Ca metasomatic stage is probably related to a regional Na +/- Ca metasomatic and associated U +/- REE mineralising system operating concurrently with granitic magmatism at c. 1.8 Ga in the Vastervik region. This highlights the potential for discovering hitherto unknown REE deposits and for the reappraisal of already known deposits in this part of the Fennoscandian Shield.
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- Sjöqvist, Axel S.L. 1990, et al.
(author)
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Geochronology of the Norra Kärr alkaline complex, southern Sweden
- 2014
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In: 31st Nordic Geological Winter Meeting.
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Conference paper (other academic/artistic)abstract
- The Norra Kärr alkaline complex is a small intrusion of agpaitic nepheline syenite, located approximately 10 km north of Grän- na, southern Sweden, that is being explored for REE and Zr. Agpaitic nepheline syenites per definition do not contain simple Zr minerals like zircon and baddeleyite, despite generally high Zr contents (up to 1–2 wt.% ZrO2). Instead, Zr is mainly hosted in rock-forming complex Na-Ca-Zr silicate minerals such as members of the catapleiite, eudialyte, rosenbuschite, and wöhlerite groups. U-Pb zircon geochronology is thus highly impeded by the agpaitic nature. We established a new, reliable igneous age for the Norra Kärr alkaline complex at 1489±8 Ma (MSWD = 0.95) by dating zircons (U-Pb) in the country rocks that were affected by the magmatism-related alkaline alteration (fenitisation) by LA-MC-ICP-MS. Zircons from a satellite body of non-agpaitic syenite gave intercept ages within error of the age of fenitisation. This is an improvement upon an imprecise whole-rock Rb-Sr age of 1545±61 Ma (Blaxland 1977; Welin 1980). The non-fenitised country granite itself is dated at 1781±8 Ma (MSWD = 0.59), and thus belongs to the TIB1 (1.81–1.76 Ga) episode of the Transscandinavian Igneous Belt (TIB). Rare zircon xenocrysts extracted from the nepheline syenite show ages corresponding to 1.5 Ga lower crustal intrusives (rapakivi?), TIB, Svecofennian, and one Archaean zircon, which suggests the possibility for a remnant of Archaean basement below the TIB. There has historically been a vivid discussion about wheth- er or not Norra Kärr has been deformed and metamorphosed. New Ar-Ar step heating ages on sodic amphibole from Norra Kärr and muscovite and biotite from the country rocks give plateau ages at 1.1 Ga and 0.94 Ga, which correspond to ages derived for Sveconorwegian shear zones in the area. Together with textural and crystal chemical evidence, these ages make a compelling argument for some form of Sveconorwegian overprint of the Norra Kärr alkaline complex.
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| 4. |
- Sjöqvist, Axel S.L. 1990, et al.
(author)
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The Norra Kärr REE-Zr Project
- 2013
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In: Excursion Guidebook SWE3, SWE6 & SWE7. - Uppsala : Elanders Sverige AB. - 9789174032130 ; , s. 36-48
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Book chapter (peer-reviewed)
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| 5. |
- Sjöqvist, Axel S.L. 1990, et al.
(author)
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Three Compositional Varieties of Rare-Earth Element Ore: Eudialyte-Group Minerals from the Norra Kärr Alkaline Complex, Southern Sweden
- 2013
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In: Minerals. - : MDPI AG. - 2075-163X. ; 3:1, s. 94-120
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Journal article (peer-reviewed)abstract
- Agpaitic nepheline syenites at the Norra Kärr Alkaline Complex, southern Sweden, are rich in zirconium and rare-earth elements (REE), which are mainly accommodated in eudialyte-group minerals (EGM). Norra Kärr hosts three compositionally distinct groups of EGM, which are complex zirconosilicates. Analyses of EGM by electron beam energy-dispersive (SEM-EDS) and wavelength-dispersive (WDS-EMP) X-ray microanalysis are presented and compared, complemented by whole-rock analyses. The SEM-EDS and WDS-EMP methods produce comparable results for most elements. Considering that most SEM instruments have a user-friendly EDS system, it is a useful tool for reconnaissance work in research and especially in exploration-related studies. The EGM evolved markedly from an initial Fe-rich and REE-poor, but HREE-dominated variety, to an intermediate Fe-Mn and HREE-rich one, and to a final Mn- and LREE-rich variety, which occur in rocks classified as lakarpite and grennaite. Based on the Mn/(Fe+Mn) ratios of the EGM, this trend is interpreted as a result of magmatic evolution. The threefold diversity of EGM presented in this work is much broader than has previously been documented.
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