Sapphire of the Naryn-Gol Creek Placer Deposit (Buryatia, Russia)

A new occurrence of gem corundum was discovered in the vicinity of Naryn-Gol Creek, on the Dzhida volcanic field, Russia. Sapphires were found in both alluvial deposits of the Naryn-Gol Creek and pyroclastic rocks of the nearby Cenozoic alkali basalt volcano Barun-Hobol Pravyi. These rocks contain, in addition to sapphire, large crystals of garnet, spinel, augite, olivine, enstatite, ilmenite, and feldspar. Chemical composition of the sapphires overall is typical for corundum from basalt: rich in Fe, low in Ti and Cr. The oxygen isotopic compositions of corundum and associated minerals show δ18Osmow values ranging between 4.6‰ and 6.8‰ that is attributed to magmatic rocks. Study of impurities reveals the great role of volatiles, CO2, in particular, during the formation process.