Petrogenesis of gem sapphire in a pegmatite-aplite vein from the Alvand batholith, Western Iran
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ORIGINAL PAPER
Petrogenesis of gem sapphire in a pegmatite-aplite vein from the Alvand batholith, Western Iran Rasoul Sheikhi Gheshlaghi 1 & Mansour Ghorbani 1
&
Ali Asghar Sepahi 2 & Reza Deevsalar 3 & Ryuichi Shinjo 3
Received: 25 November 2019 / Accepted: 2 July 2020 # Springer-Verlag GmbH Austria, part of Springer Nature 2020
Abstract In the Hamadan region, Sanandaj-Sirjan Zone (SaSiZ), W Iran, a pegmatite-aplite vein occurs that contains up to 15 vol% sapphire. The Hamadan sapphire is black to blue, and translucent to opaque, which reveals its semi-gem and gem quality. On the basis of petrographic studies, the Hamadan sapphire-bearing pegmatite-aplite vein represents alkali syenitic to syenitic composition and its adjacent granitoids have a range of composition from syenitic to quartz monzonite and granodiorite. New petrographic, whole-rock geochemical data and δ18O values [9.30–12.45‰VSMOW (Vienna Standard Mean Ocean Water)] suggest crustal origin for the peraluminous, S-type and alkaline sapphire-bearing pegmatite-aplite vein. The presence of syngenetic quartz inclusions in the sapphire, and some similar physical-gemological signatures (e.g., parting patterns and angles) of the Hamadan sapphire and kyanite support the generation of the sapphire at the expense of kyanite. In addition, a secondary metasomatic stage may have played a minor role in formation of the sapphire grains. The results indicate an important role for the mafic magmas in triggering crustal anatexis and gem crystallization in continental subduction zone settings. Keywords Sapphire . Pegmatite . Subduction zone . Gem quality . Oxygen isotope . Geochemistry
Introduction Presently, the economic importance of gem corundum has encouraged many researchers to study genesis and origin of corundum-bearing rocks (e.g., Yui et al. 2003; Graham et al. 2008; Vysotskiy et al. 2014; Palke et al. 2016; Sorokina et al. 2017). Sapphire is a gem variety of corundum (α-Al2O3) which occurs in various colors (Wong and Verdel 2017), and is hosted in some places by pegmatites (e.g., Giuliani et al. 2014;
Editorial handling: L. Nasdala Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00710-020-00716-w) contains supplementary material, which is available to authorized users. * Mansour Ghorbani [email protected] 1
Department of Minerals & Groundwater Resources, School of Earth Sciences, Shahid Beheshti University, Tehran 1983969411, Iran
2
Department of Geology, Bu Ali Sina University, Hamadan 65174-33391, Iran
3
Department of Physics and Earth Sciences, University of the Ryukyus, Okinawa 903-0213, Japan
Voudouris et al. 2019). These pegmatites commonly have a syenitic composition, and are found in the South Urals (Russia; e.g., Sorokina et al. 2017), Ontario (Canada; e.g., Field 1951), Garba Tula (central Kenya; Simonet et al. 2004), and other places. The study of sapphire-bearing pegmatites provides a framework for further exploration of this mineral and even other gemstones associated with pegmatites,
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