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Minerals 2013, 3(1), 94-120; doi:10.3390/min3010094
Article

Three Compositional Varieties of Rare-Earth Element Ore: Eudialyte-Group Minerals from the Norra Kärr Alkaline Complex, Southern Sweden

1,* , 1
,
2
,
2
,
1
 and
3
1 Department of Earth Sciences, University of Gothenburg, PO Box 460, SE-405 30 Göteborg, Sweden 2 Department of Geosciences, University of Oslo, PO Box 1047 Blindern, N-0316 Oslo, Norway 3 Tasman Metals Ltd., Skiftesvägen 14, SE-563 31 Gränna, Sweden
* Author to whom correspondence should be addressed.
Received: 8 December 2012 / Revised: 18 January 2013 / Accepted: 25 February 2013 / Published: 20 March 2013
(This article belongs to the Special Issue Advances in Economic Minerals)
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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.
Keywords: eudialyte-group minerals; agpaitic rocks; nepheline syenite; rare-earth elements; Norra Kärr Alkaline Complex; SEM-EDS; WDS-EMP eudialyte-group minerals; agpaitic rocks; nepheline syenite; rare-earth elements; Norra Kärr Alkaline Complex; SEM-EDS; WDS-EMP
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Sjöqvist, A.S.; Cornell, D.H.; Andersen, T.; Erambert, M.; Ek, M.; Leijd, M. Three Compositional Varieties of Rare-Earth Element Ore: Eudialyte-Group Minerals from the Norra Kärr Alkaline Complex, Southern Sweden. Minerals 2013, 3, 94-120.

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