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Xenotime-(Y) and Sn-rich thortveitite in miarolitic pegmatites from Baveno, Southern Alps, Italy

Published online by Cambridge University Press:  05 July 2018

A. Guastoni
Affiliation:
Department of Geosciences, University of Padova, Via Gradenigo 6, I-35131 Padova, Italy
F. Nestola*
Affiliation:
Department of Geosciences, University of Padova, Via Gradenigo 6, I-35131 Padova, Italy
C. Ferraris
Affiliation:
Laboratoire de Minéralogie et Cosmochimie Muséum National d’Histoire Naturelle, Rue Buffon 61, CP52, 75005 Paris, France
G. Parodi
Affiliation:
Laboratoire de Minéralogie et Cosmochimie Muséum National d’Histoire Naturelle, Rue Buffon 61, CP52, 75005 Paris, France

Abstract

Xenotime-(Y), (Y,REE)PO4, and thortveitite, (Sc, Y)2Si2O7, in a miarolitic cavity in a niobium, yttrium, fluorine (NYF) granitic pegmatite at Baveno, Verbania, Southern Alps, Italy, were investigated by electron microprobe analysis and single-crystal X-ray diffraction. Fluorine has an important role as a complexing agent for Y and REEs in supercritical pegmatitic fluids; annitesiderophyllite and chamosite are the most likely sources of the Y and REEs. The thortveitite from Baveno contains up to 3.20 wt.% SnO2, an unusually high Sn content. Xenotime-(Y) is enriched in Gd in comparison to other Alpine xenotimes. Quantitative chemical data and measurements of the lattice parameters show that a higher scandium content results in a smaller unit-cell volume in thortveitite. The substitution of REEs for Y up to ∼20 mol.% has little effect on the unit cell of xenotime-(Y). The textures of xenotime-(Y) and thortveitite provide information about the dissolution and crystallization processes in the miarolitic cavity.

Type
Research Article
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2016

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