Sweden
has been called the "home of the rare earth elements", due
to the fact that both the first light and the first heavy rare earth
elements (LREE and HREE, respectively) were discovered here during
the late 18th and early 19th centuries. Yttrium (Y), ytterbium (Yb),
terbium (Tb) and erbium (Er) were discovered in gadolinite from the
Ytterby mine north of Stockholm, and named for their original
locality. Additional HREE (such as holmium (Ho), named after
Stockholm) were also subsequently discovered at Ytterby. In the
Bastnäs mines near Riddarhyttan in the Bergslagen province, cerium
(Ce) was discovered and described in 1804, followed by several other
LREE. Sweden is now known to host a large number of REE occurrences
of different genetic types, and numerous REE-bearing minerals were
originally discovered in this country.
REE in alkaline intrusives
Other
alkaline intrusives with potential for REE are the Särna
intrusives
in western central Sweden, consisting of partly cancrinite-bearing
nepheline syenites, and the Almunge
nepheline
syenite complex east of Uppsala, which consists of several types of
syenitic rocks surrounded by a fenite aureole.
REE in carbonatitic intrusives
Some
of the highest concentrations of REE as a whole in Sweden, and some
of the most LREE-enriched compositions, have been identified in
sövite from the Alnö
alkaline
complex in Sweden, which includes both silicic (syenitic) and
carbonatitic rocks, with higher potential for REE enrichment in the
carbonatitic rocks. REE minerals within the Alnö complex include
apatite, monazite, synchysite, aeschynite, fersmite, brockite,
(perovskite, pyrochlore), titanite, zirkonolite, wöhlerite and
Ti-andradite. North of Alnö, further carbonatite intrusions north of
Söråker locally show elevated REE concentrations. Small carbonatite
dykes also occur in the Kalix area, close to the Finnish border in
north easternmost Sweden. They contain leucoxene, apatite and
perovskite.
REE in apatite-iron oxide ores
The
magnetite-(haematite)-apatite ores of Kiruna type generally exhibit
anomalously high concentrations of REE. These are hosted by primary
fluorapatite and later-formed phases, mainly monazite-(Ce) and
allanite-(Ce). Total REE contents in the fluorapatite may reach up to
weight-percent levels. Important examples of this deposit type
include Kirunavaara
and
Malmberget in
northernmost Sweden, and Grängesberg-Blötberget-Idkerberget in
Bergslagen, south-central Sweden.
REE in iron skarn (Bastnäs-type) deposits
The Bastnäs-type
deposits are located in the Bergslagen ore province of south central
Sweden, where they form a discontinuous, narrow belt of approximately
100 km length, the so-called REE-line. These types of deposits
occur in skarn-altered carbonate interbedded with felsic,
calc-alkaline volcanic units of Palaeoproterozoic age. LREE-enriched
deposits are located mainly in the Riddarhyttan-Bastnäs area,
whereas those in the Norberg district may also have HREE enrichment.
Typical host minerals comprise cerite-(Ce), törnebohmite-(Ce) and
allanite, as well as REE-fluorocarbonates such as bastnäsite-(Ce).
REE-U in phosphorites
There
are some occurrences associated with phosphorites in Sweden,
particularly the Tåsjö
U-REE
mineralization. This is hosted by Palaeozoic calcareous sandstone and
shales with phosphorite layers, within the lower allochthon units of
the Caledonian front, and contains 0.03–0.07 percent U3O8 and
0.11–0.24 percent total REE (Gustafsson, 1979).
REE in granitic pegmatites and granites
Several
granite intrusions and granitic pegmatite fields in the Swedish
crystalline bedrock contain primary magmatic REE-bearing oxides,
phosphates and/or silicates, and in some instances also
late-magmatic/hydrothermal carbonates. Generally, these deposits are
either too small or too low in grade to be commercially exploited
today. REE could represent by-products from pegmatites mined for
other minerals, such as feldspar or mica. The highest contents of REE
are found in some pegmatite-hosted oxides, phosphates, and silicates.
Allanite-bearing pegmatites are common and generally have high
LREE/HREE ratios.
The
Näverån
Th-(U)-REE-prospect,
in west-central Sweden, is a fracture or breccia-type mineralization
hosted by weakly foliated granite to granodiorite. Here, REE-bearing
minerals include uraninite, xenotime-(Y), monazite-(Ce), "allanite"
and an Y-bearing phosphate.
REE in quartzite-hosted palaeoplacer-type deposits
In
the Västervik region in southeastern Sweden, several occurrences of
U-rich, REE-bearing minerals have been identified in
quartzite-dominated Palaeoproterozoic metasedimentary successions
(e.g., the Klockartorpet and Trostad mineralisations). These are
interpreted to represent palaeoplacer-type original concentrations of
heavy mineral sands.
REE in apatite-magnetite vein mineralisations
Key References
Andersson,
U B (ed.). 2004. The Bastnäs-type REE mineralisations in
north-western Bergslagen, Sweden. SGU
Rapporter and Meddelanden. 119:
34 pp.
Gustafsson,
B. 1979. Uranuppslag inom Norrbotten och Västerbotten 1979. SGU,
PRAP 79056.
Unpublished prospecting report. 58 pp. (in Swedish).
Gustafsson,
B. 1992. Sällsynta jordartsmetaller. Regional fältkontroll 1991 av
arkivuppslag. Sveriges
Geologiska AB PRAP 91047. Unpublished
prospecting report. 22 pp. (in Swedish.)
Jonsson,
E. (ed.) 2013.The Norra Kärr REE-Zr project and the birthplace of
the light REEs. SGA
excursion guidebook SWE3, SWE6 & SWE7. 36–51.
Jonsson,
E and Högdahl, K. 2013. New evidence for the timing of formation of
Bastnäs-type REE mineralisation in Bergslagen, Sweden. In: E.
Jonsson et al. (eds.), Mineral deposit research for a high-tech
world. Proceedings
of the 12th biennial SGA meeting. 1724–1727.
Sadeghi,
M, Morris, G A, Carranza, E J M, Ladenberger, A, and Andersson, M.
2013. Rare earth element distribution and mineralization in Sweden:
An application of principal component analysis to FOREGS soil
geochemistry. Journal
of Geochemical Exploration,
133, 160–175.
