Characterisation and genesis of sapphires from the Yenya-U area, Thabeikkyin township, Mandalay region, Myanmar

The Yenya-U area in the Mandalay region of central Myanmar hosts two primary sapphire deposits, at Kyauk-tagar and Kyar-gaung. The sapphires form disseminated crystals within syenite pegmatite and nepheline syenite, respectively. Kyar-gaung is a source of relatively large crystals (up to 12 g) that are translucent to opaque, while Kyauk-tagar produces fine-quality vivid-blue sapphires in smaller sizes (up to 0.4 g). Alluvial deposits in the region yield high-quality sapphires of various colours (including colourless, yellow, purple, pink, greenish blue and blue), as well as quartz, topaz, spinel, garnet, zircon, tourmaline and fluorite. The studied Yenya-U sapphires contained solid inclusions of albite, biotite, graphite, melanophlogite and diaspore. In addition, pennantite is reported here for the first time as an inclusion in corundum. CO₂-rich fluid inclusions were commonly observed in most of the sapphires. Trace-element analyses of the sapphires are consistent with a metamorphic- metasomatic origin, mostly accompanied by desilicification processes.