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 compo- sition and its adjacent granitoids have a range of composition from syenitic to quartz monzonite and granodiorite. New petro- graphic, whole-rock geochemical data and δ 18 O 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 en- couraged 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-Al 2 O 3 ) which occurs in various colors (Wong and Verdel 2017), and is hosted in some places by pegmatites (e.g., Giuliani et al. 2014; Voudouris et al. 2019). These pegmatites commonly have a sy- enitic 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, elsewhere. Pegmatites are found in various geological settings with igne- ous (e.g., Burnham and Nekvasil 1986; Cerny 1982), meta- morphic (e.g., Winkler 1965; Von platen 1965), and metaso- matic (e.g., Kozlowski 2002) origins. In addition, sapphires can be divided into two groups: metamorphic (e.g., Simonet et al., 2004; Stern et al., 2013; Peucat et al., 2007; Giuliani et al., 2005), and igneous (e.g., Simonet et al., 2004; Peucat et al., 2007). Metamorphic sapphire is subdivided into meta- morphic, anatectic and metasomatic (Simonet et al. 2008). Also, pegmatite and sapphire may be formed by combination of several origins. For example, corundum pegmatite can be caused by a magmatic stage and a later metasomatism stage (Rose 1957; Sorokina et al. 2017). In addition, corundum in the Mazan pegmatitic field occurs during two stages: 1. Anatectic melting of Al-rich metasedimentary rocks and for- mation of andalusite pegmatite 2. Alteration of andalusite to form corundum (Sardi et al. 2009). 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 m_ghorbani@hotmail.com 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 Mineralogy and Petrology https://doi.org/10.1007/s00710-020-00716-w