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A melt and fluid inclusion assemblage in beryl from pegmatite in the Orlovka amazonite granite, East Transbaikalia, Russia: implications for pegmatite-forming melt systems

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Thomas, R and Davidson, P and Badanina, E (2009) A melt and fluid inclusion assemblage in beryl from pegmatite in the Orlovka amazonite granite, East Transbaikalia, Russia: implications for pegmatite-forming melt systems. Mineralogy and Petrology, 96 (3/4). pp. 129-140. ISSN 0930-0708

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Abstract

Beryl crystals from the stockscheider pegmatite in the apical portion of the Li-F granite of the Orlovka Massif in the Khangilay complex, a tantalum deposit, contain an assemblage of melt and fluid inclusions containing two different and mutually immiscible silicate melts, plus an aqueous CO2-rich supercritical fluid. Pure H2O and CO2 inclusions are subordinate. Using the terminology of Thomas et al. (2000) the melt inclusions can be classified as (i) water-poor type-A and (ii) water-rich type-B inclusions. Generally the primary trapped melt droplets have crystallized to several different mineral phases plus a vapor bubble. However, type-B melt inclusions which are not crystallized also occur, and at room temperature they contain four different phases: a silicate glass, a water-rich solution, and liquid and gaseous CO2. The primary fluid inclusions represent an aqueous CO2-rich supercritical fluid which contained elemental sulfur. Such fluids are extremely corrosive and reactive and were supersaturated with respect to Ta and Zn. From the phase compositions and relations we can show that the primary mineral-forming, volatile-rich melt had an extreme low density and viscosity and that melt-melt-fluid immiscibility was characteristic during the crystallization of beryl. The coexistence of different primary inclusion types in single growth zones underlines the existence of at least three mutually immiscible phases in the melt in which the large beryl crystals formed. Moreover, we show that the inclusions do not represent an anomalous boundary layer.

Item Type: Article
Keywords: beryl, pegmatite, melt-melt immiscibility, melt and fluid inclusions, columbite and sphalerite daughter minerals, native sulfur
Journal or Publication Title: Mineralogy and Petrology
Page Range: pp. 129-140
ISSN: 0930-0708
Identification Number - DOI: 10.1007/s00710-009-0053-6
Additional Information: The original publication is available at www.springerlink.com
Date Deposited: 24 Jun 2009 04:44
Last Modified: 18 Nov 2014 04:01
URI: http://eprints.utas.edu.au/id/eprint/8804
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