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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 (CC BY 3.0).

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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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