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GEOREF RECORD

Metasomatism at a granitic pegmatite-dunite contact in Galicia; the Franqueira occurrence of chrysoberyl (alexandrite), emerald, and phenakite

Agustin Martin Izard, Andres Paniagua, Damaso Moreiras, R. D. Acevedo and C. Marcos Pascual
Metasomatism at a granitic pegmatite-dunite contact in Galicia; the Franqueira occurrence of chrysoberyl (alexandrite), emerald, and phenakite
The Canadian Mineralogist (August 1995) 33, Part 4: 775-792

Abstract

This deposit of gem-quality chrysoberyl, emerald and phenakite in NW Spain occurs in the Galicia-Tras os Montes zone. At Franqueira, a pegmatite related to the heterogeneous two-mica granites cuts an ultramafic body, and at the contact a metasomatic zone developed in which the dunite is almost completely altered to phlogopite (with an anthophyllite-rich rim); distal to the pegmatite, the dunite is altered to tremolite. The phlogopite-rich metasomatic rocks contain the chrysoberyl, emerald and phenakite, together with apatite. All the metasomatic rocks are relatively enriched in Mg and Cr from the dunite, and in Al, K, Be and Si from the pegmatite. Two discontinuous hydrothermal stages are distinguished, the first stage being characterized by the trapping of two types of aqueous fluid inclusions with T (sub h) 318-381 degrees C; a third type of inclusion suggests an independent episode of fluid circulation during later tectonic events. The formation of chrysoberyl may be due to its structural similarity with olivine, allowing epitactic nucleation on olivine relics. Emerald is the latest Be mineral to form; it partially replaces chrysoberyl and phenakite and may have formed by the reaction chrysoberyl + phenakite + quartz ->> emerald until the quartz was used up.


ISSN: 0008-4476
EISSN: 1499-1276
Coden: CAMIA6
Serial Title: The Canadian Mineralogist
Serial Volume: 33, Part 4
Title: Metasomatism at a granitic pegmatite-dunite contact in Galicia; the Franqueira occurrence of chrysoberyl (alexandrite), emerald, and phenakite
Affiliation: Universidad de Oviedo, Departmento de Geologia, Asturias, Spain
Pages: 775-792
Published: 199508
Text Language: English
Publisher: Mineralogical Association of Canada, Ottawa, ON, Canada
References: 38
Accession Number: 1999-051751
Categories: Economic geology, geology of nonmetal depositsGeneral mineralogy
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 3 tables, geol. sketch map
N41°47'60" - N43°47'60", W09°19'60" - W06°45'00"
Secondary Affiliation: Cirgeo, ARG, Argentina
Country of Publication: Canada
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United KingdomTwickenhamUKUnited Kingdom
Update Code: 199918
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