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The REE minerals of the bastnas-type deposits, south-central Sweden

Dan Holtstam and Ulf B. Andersson
The REE minerals of the bastnas-type deposits, south-central Sweden
The Canadian Mineralogist (October 2007) 45 (5): 1073-1114


On the basis of characteristic assemblages, the Bastnas-type Fe-(Cu-)REE skarn deposits in the Bergslagen mining region of south-central Sweden can be divided into two subtypes: one almost exclusively with LREE enrichment (subtype 1, mainly in the Riddarhyttan-Bastnas area), and another showing enrichment of both LREE and Y+HREE subtype 2, Norberg District). New data have been collected on twenty REE species including three unnamed ones, using electron-microprobe analysis, X-ray diffraction and Mossbauer spectroscopy. Cerite-(Ce) is, together with ferriallanite-(Ce), the most important REE mineral at Bastnas, but less common at the subtype-2 deposits. Compared to other occurrences worldwide, the present samples of cerite-(Ce) are poor in Ca and enriched in Mg and F. Calcium and (REE+Y) in the samples are negatively correlated, and the upper limit for Ca is close to 1 apfu. Iron ranges from 0.01 to 0.30 apfu, and is mainly in the trivalent state. Cerite-(Ce) is a major carrier of Y (up to 3.5 wt.% Y (sub 2) O (sub 3) ). Fluorbritholite is found only in the subtype-2 deposits, and is low in P, Na and the actinides compared to other major occurrences in the world. Significant inter- and intrasample variations in REE and Y occur, ranging from fluorbritholite-(Ce) to the unaccredited member "fluorbritholite-(Y)". Fluorbritholite is non-stoichiometric, with Ca<2 and (REE+Y)>3 apfu. Vastmanlandite-(Ce) is another important host for the REE in subtype 2. By means of the substitutions Mg (super 2+) +F (super -) -->Fe (super 3+) +O (super 2-) and Mg (super 2+) -->Fe (super 2+) , it forms solid solutions with an unnamed Fe-dominant member that is found in the subtype-1 deposits. Dollaseite-(Ce), which forms a partial solid-solution series with dissakisite-(Ce), is restricted to subtype 2. Gadolinite is very rare at the subtype-1 deposits, and more widespread in the Norberg District. All samples have a significant hingganite component in solid solution (0.10-0.35 molar fraction). Single crystals are commonly zoned with respect to REE and Y, with compositions corresponding to gadolinite-(Ce), gadolinite-(Y) and an Nd-dominant member. The substantial fractionation of REE and Y on a local scale within the Bastnas-type deposits is dependent both on crystal-chemical factors and on fluctuations in fluid composition during crystallization. The initial precipitation of REE silicates in type-1 and type-2 deposits (mainly cerite and fluorbritholite, respectively) was a reaction between relatively acidic solutions carrying major amounts of REE complexed mainly by ligands of F and Si, and dolomitic host-rocks.

ISSN: 0008-4476
EISSN: 1499-1276
Coden: CAMIA6
Serial Title: The Canadian Mineralogist
Serial Volume: 45
Serial Issue: 5
Title: The REE minerals of the bastnas-type deposits, south-central Sweden
Affiliation: Swedish Museum of Natural History, Department of Mineralogy, Stockholm, Sweden
Pages: 1073-1114
Published: 200710
Text Language: English
Publisher: Mineralogical Association of Canada, Ottawa, ON, Canada
References: 91
Accession Number: 2008-063113
Categories: Mineralogy of non-silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 11 tables, sketch map
N55°15'00" - N69°15'00", E11°00'00" - E24°15'00"
Secondary Affiliation: GeoforschungsZentrum Potsdam, DEU, Federal Republic of Germany
Country of Publication: Canada
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, copyright, Mineralogical Association of Canada. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 200814
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