Zoned REE-enriched dravite from a granitic pegmatite in Forshammar, Bergslagen province, Sweden: an EMPA, XRD and LA-ICP-MS study
- Author(s)
- Peter Bacik, Pavel Uher, Andreas Ertl, Erik Jonsson, Per Nysten, Viktor Kanicky, Tomas Vaculovic
- Abstract
Green to grayish green tourmaline crystals (up to 10 cm across), with distinct optical zoning, occurs with quartz, blocky albite and muscovite in the Forshammar granitic pegmatite, central Bergslagen province, Sweden. Tourmaline contains inclusions of zircon and xenotime-(Y), and it is cut by veinlets of muscovite and hydroxylbastnasite-(Ce). Microanal. and structural data (from the rim) indicate that the tourmaline can be classified as a dravite with moderate Al-Mg disorder at the Y and Z sites. Tourmaline displays chem. zoning that reflects the distribution of Fe, Mg, Al, Ca and Na. The Mg/(Mg + Fe) value is high; it decreases from core (~0.85) to intermediate zone (0.76-0.79), but increases in the rim and vein dravite (0.93). The core has the highest proportion of X-site vacancy and Al content, whereas the intermediate zone is the most enriched in Fe and Na. The rim is slightly depleted in Al and has the highest Na compared to inner zones. Tourmaline veins crosscut the pre-existing tourmaline and are relatively more enriched in Na and Ca. The main compositional variations are driven by AlX?Mg-1Na-1 and AlOMg-1(OH)-1 substitutions. The Forshammar dravite shows the highest known concns. of REE from pegmatite tourmaline, =1200 ppm REE, =210 ppm La, =670 ppm Ce; the chondrite-normalized patterns reveal high LaN/YbN (32 to 464) values and strongly neg. Eu anomalies (Eu/Eu* = 0.005 to 0.05). The contents of Ti, Mn, Y and REE generally increase at the boundary of the intermediate zone and rim, whereas the contents of Zn, Ga and Sn decrease from the core to the rim. The core is likely a product of an early magmatic process during the late Svecofennian pegmatite formation (~1.8 Ga) as suggested by oscillatory zoning of trace elements. The intermediate zone, rim and tourmaline veins originated during the late magmatic to hydrothermal stage. Hydroxylbastnasite-(Ce) and muscovite are apparently the final products of the hydrothermal process.
- Organisation(s)
- Department of Mineralogy and Crystallography
- External organisation(s)
- Comenius University Bratislava, Geological Survey of Sweden, Masaryk University
- Journal
- The Canadian Mineralogist
- Volume
- 50
- Pages
- 825-841
- No. of pages
- 17
- ISSN
- 0008-4476
- Publication date
- 2012
- Peer reviewed
- Yes
- Austrian Fields of Science 2012
- 105113 Crystallography, 105116 Mineralogy
- Portal url
- https://ucrisportal.univie.ac.at/en/publications/6705c3a9-4d51-4ce5-a47d-76b494293c07