Naryn-Gol Creek Sapphire Placer Deposit, Buryatia, Russia

A new gem corundum occurrence has been discovered in the Naryn-Gol Creek placer of the
Dzhida volcanic field (Russia). In this placer deposit, sapphire associates with large crystals of garnet,
spinel, augite, olivine, enstatite, ilmenite, Ti-magnetite, and alkali feldspar. Such a combination
of minerals is typical for the placer deposits associated with alkali basalts widely distributed in
Southeastern Asia and Australia. We have also found sapphire crystals in phonotephrites of the
nearby Cenozoic alkali-basalt paleovolcano Barun Khobol Pravyi, and in basalt sample and trachybasalt
from the valley flood basalts. The chemical composition of sapphire is generally typical for
‘basalt’ corundum: it is rich in Fe, and depleted in Ti and Cr. The 18O SMOW values of corundum
and related megacrysts range from 4.6 to 6.8 ‰, thus corresponding to the isotopic signature of
igneous rocks. Etched and corroded surfaces of sapphire and other megacrysts indicate that they are
in non-equilibrium with their host alkali basalts. Volatile components, CO2 in particular, played a
significant role during sapphire formation as gas inclusions reveal.

Evgeniy V. Kislov, Anna V. Aseeva, Vladislav V. Vanteev, Anton Yurievich Sinyov and Olga A. Eliseeva

Minerals 2022, 12, 509.