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The Piteiras emerald mine, Minas Gerais, Brazil; fluid-inclusion and gemmological perspectives

E. P. Lynch, A. Costanzo, M. Feely, N. J. F. Blamey, J. Pironon and P. Lavin
The Piteiras emerald mine, Minas Gerais, Brazil; fluid-inclusion and gemmological perspectives
Mineralogical Magazine (December 2014) 78 (7): 1571-1587

Abstract

New fluid inclusion analyses using a range of analytical techniques including quadropole mass spectrometric analyses coupled with gemmological investigations were conducted on rough and gem-quality faceted emeralds from the Piteiras Mine, Minas Gerais, Brazil. These data complement those of Rondeau et al. (2003) who also presented analyses of the Piteiras emeralds. Emeralds are found typically as euhedral-to-anhedral crystals disseminated in biotite-phlogopite schist and range from 0.5 to 50 mm long. Emerald mineralization is associated closely with alkaline metasomatized pegmatite bodies, quartz boudin and veins, and talc-chlorite bands. Four types of fluid inclusions are recognized in the emeralds. These include aqueous brine and aqueous carbonic varieties containing one or two liquid phases, along with gas bubbles and/or solid crystals (e.g. carbonates). Primary fluid inclusions in emeralds record salinities of approximately 4-24 eq. wt.% NaCl and minimum trapping temperatures from approximately 350 to 480 degrees C. Combined microthermometry, Raman spectroscopy and crush-leach gas analyses indicate that the mineralizing fluid was an aqueous carbonic brine enriched in reduced volatile species such as CH (sub 4) , N (sub 2) , H (sub 2) S and alkanes. With respect to their optical properties (RI epsilon = 1.573 1.580; RI omega = 1.580-1.588; birefringence = 0.006-0.008) and specific gravity (2.65-2.78), the Piteiras emeralds fall within the expected range for metasomatic, schist-hosted emeralds.


ISSN: 0026-461X
EISSN: 1471-8022
Coden: MNLMBB
Serial Title: Mineralogical Magazine
Serial Volume: 78
Serial Issue: 7
Title: The Piteiras emerald mine, Minas Gerais, Brazil; fluid-inclusion and gemmological perspectives
Affiliation: National University of Ireland Galway, School of Natural Sciences, Galway, Ireland
Pages: 1571-1587
Published: 201412
Text Language: English
Publisher: Mineralogical Society, London, United Kingdom
References: 48
Accession Number: 2015-024192
Categories: Mineralogy of silicatesEconomic geology, geology of nonmetal deposits
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 3 tables
S23°30'00" - S14°00'00", W51°00'00" - W39°45'00"
Secondary Affiliation: New Mexico Institute of Mining and Technology, USA, United StatesUniversite Nancy I, FRA, FranceJewellery Valuations Ireland, IRL, Ireland
Country of Publication: United Kingdom
Secondary Affiliation: GeoRef, Copyright 2017, American Geosciences Institute. Abstract, Copyright, Mineralogical Society of Great Britain and Ireland. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201512
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