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Monazite-(Ce) and xenotime-(Y) from an LCT, NYF Tertiary pegmatite field; evidence from a regional study in the Central Alps (Italy and Switzerland)

Alessandro Guastoni, Giacomo Pozzi, Luciano Secco, Mariangela Schiazza, Giorgio Pennacchioni, Anna Maria Fioretti and Fabrizio Nestola
Monazite-(Ce) and xenotime-(Y) from an LCT, NYF Tertiary pegmatite field; evidence from a regional study in the Central Alps (Italy and Switzerland) (in Mineralogy, crystallography, petrology, economic geology, geochemistry; pegmatite special issue dedicated to Drs. William B. (Skip) Simmons and Karen L. Webber, Alexander U. Falster (prefacer) and Pietro Vignola (prefacer))
The Canadian Mineralogist (July 2016) 54 (4): 863-877

Abstract

Monazite-(Ce) and xenotime-(Y) from tertiary pegmatites of the central Alps (Italy and Switzerland) were studied by EMPA and SCXRD analytical methods. The REE-phosphate minerals analyzed are from LCT and NYF pegmatite dikes of the Central Alps, which includes three main areas: Vigezzo (LCT and NYF from the Vigezzo valley), Bodengo (NYF from the Leggia valley and LCT from the Cama valley), and Codera (LCT from Codera and Chiavenna valleys and Alpe Rossaccio). SEM-BSE images of monazite-(Ce) show primary growth zoning, sector zoning, and patchy zoning. SEM-BSE images of xenotime-(Y) show faint patchy-type zoning and spongiform texture. Both REE-phosphates evidence secondary mineral replacements that include thorianite, thorite, and uraninite. EMPA compositions show that the monazite-(Ce) is characterized by variable amounts of huttonite (ThSiO (sub 4) ) and cheralite [Ca(Th,U)(PO (sub 4) )] molecules. SCXRD analyses shows that the unit-cell volume of monazite-(Ce) correlates with its chemical composition; the b cell parameter shows an evident relationship with the huttonite molecule. The unit-cell volume of xenotime-(Y) is well correlated to its chemical composition. Xenotime-(Y) related to the NYF family shows a significant increase in yttrium and a lower U + HREE content.The Tertiary pegmatite field of the central Alps is related to the Masino-Bregaglia intrusion, the San Fedelino granite, and younger magmatic pulses generated by the migration of the metamorphic thermal Lepontine Dome towards the west. The presence of poikiloblastic thorite, thorianite, and uraninite in monazite and xenotime can be induced to form from alkali-bearing fluids via coupled dissolution-reprecipitation, under moderate to high-grade and post-peak Alpine metamorphic conditions.


ISSN: 0008-4476
EISSN: 1499-1276
Coden: CAMIA6
Serial Title: The Canadian Mineralogist
Serial Volume: 54
Serial Issue: 4
Title: Monazite-(Ce) and xenotime-(Y) from an LCT, NYF Tertiary pegmatite field; evidence from a regional study in the Central Alps (Italy and Switzerland)
Title: Mineralogy, crystallography, petrology, economic geology, geochemistry; pegmatite special issue dedicated to Drs. William B. (Skip) Simmons and Karen L. Webber
Author(s): Guastoni, AlessandroPozzi, GiacomoSecco, LucianoSchiazza, MariangelaPennacchioni, GiorgioFioretti, Anna MariaNestola, Fabrizio
Author(s): Falster, Alexander U.prefacer
Author(s): Vignola, Pietroprefacer
Affiliation: Padova University, Department of Geosciences, Padua, Italy
Affiliation: Maine Gem and Mineral Museum, Bethel, ME, United States
Pages: 863-877
Published: 201607
Text Language: English
Publisher: Mineralogical Association of Canada, Ottawa, ON, Canada
References: 42
Accession Number: 2017-080335
Categories: Mineralogy of non-silicates
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 4 tables, sketch map
N46°00'00" - N47°00'00", E09°00'00" - E11°30'00"
Secondary Affiliation: Durham University, GBR, United KingdomChieti University "G. d'Annunzio", ITA, ItalyCNR, Institute of Geosciences and Earth Resources, ITA, Italy
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: 201742
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