Comment on “Petrogenesis of gem sapphire in a pegmatite-aplite vein from the Alvand batholith, Western Iran” (2020) by R. Sheikhi Gheshlaghi, M. Ghorbani, A. A. Sepahi, R. Deevsalar and R. Shinjo

Abstract

Corundum crystals of semi-gem quality (sapphire) formed in a syenitic dyke around the plutonic rocks in the Alvand igneous-metamorphic complex were studied by Sheikhi Gheshlaghi et al. (2020). These authors studied field relations and petrography of a corundum-bearing pegmatite, and proposed a genetic model for corundum formation. Although studies on whole rock chemistry of corundum-bearing pegmatites and oxygen isotope data for corundum by these authors are valuable, some of their reports and findings – such as the sharp contact between corundum-bearing pegmatite and Alvand syenite, the lack of tourmaline group minerals in corundum-bearing pegmatite, the presence of syngeneic quartz inclusion in corundum and the genesis of corundum as a result of kyanite break down – are in contrast with our own observations and findings. Neither the P-T conditions, nor the volatile-bearing minerals present, are in favour of formation of corundum from kyanite breakdown. Based on present authors’ studies, mineral chemistry of corundum in the Alvand area clearly indicates magmatic origin.