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GEOREF RECORD

Sapphire megacrysts in syenite pegmatites from the Ilmen Mountains, south Urals, Russia; new mineralogical data

Elena S. Sorokina, Stefanos Karampelas, Tursun P. Nishanbaev, Sergey N. Nikandrov and Boris S. Semiannikov
Sapphire megacrysts in syenite pegmatites from the Ilmen Mountains, south Urals, Russia; new mineralogical data
The Canadian Mineralogist (September 2017) 55 (5): 823-843

Abstract

Sapphires in the Ilmen Mountains of Russia's South Urals are found in syenite pegmatites where the mineral forms blue transparent to translucent megacrysts up to 6 cm in length. The corundum crystallized during the magmatic stage in equilibrium with columbite-(Fe), K-Na-feldspar, and + or - perthite. There was a later metasomatic stage in which muscovite formed by the reaction corundum + orthoclase + H (sub 2) O <--> muscovite and diaspore precipitated. Highly distributed syn- and post-tectonic brittle deformation of the host rocks is responsible for the polysynthetic twinning and parting of blue sapphires along the r face, which decreases the gem quality of the raw material. The formation of the corundum syenite pegmatites is associated with the intrusion of miascites in the Ilmenogorsky complex of alkaline rocks. Columbite-(Fe), zircon, and minerals from the alkali feldspar group were identified as syngenetic inclusions within the blue sapphire. Monazite-(Ce), sub-micron grains of uraninite, muscovite and diaspore, and exsolved micron-sized needles of ilmenite were also found. The chemical composition of the sapphires fits well with those of magmatic sapphires from the literature with 10,000Ga/Al above 2.7, Ga/Mg > 29, Fe/Mg > 429, Cr/Ga < 0.074, and Fe/Ti > 19.Solid inclusions within the sapphires of the Ilmen syenite pegmatites, as well as their chemistry, provide possible genetic linkages with sapphires from alluvial and eluvial deposits of alkali basaltic terrains in Houai Sai (northern Laos) and several mines in Chantaburi province (Thailand).


ISSN: 0008-4476
EISSN: 1499-1276
Coden: CAMIA6
Serial Title: The Canadian Mineralogist
Serial Volume: 55
Serial Issue: 5
Title: Sapphire megacrysts in syenite pegmatites from the Ilmen Mountains, south Urals, Russia; new mineralogical data
Affiliation: Russian Academy of Sciences, Vernadskiy Institute of Geochemistry and Analytical Chemistry, Moscow, Russian Federation
Pages: 823-843
Published: 201709
Text Language: English
Publisher: Mineralogical Association of Canada, Ottawa, ON, Canada
References: 57
Accession Number: 2017-087878
Categories: Mineralogy of non-silicatesIgneous and metamorphic petrology
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 5 tables, sketch map
N54°47'60" - N55°46'60", E60°00'00" - E60°28'00"
Secondary Affiliation: Bahrain Institute for Pearls & Gemstones, BHR, BahrainIlmen State Reserve, RUS, Russian Federation
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: 201746
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