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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 δ18O 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.

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The Taezhny is a silver with gold (Au:Ag = 1:100) vein deposit with a pronounced mineralogical and geochemical selenium specializationof ores. The deposit is located in the eastern part of the Sikhote-Alin orogenic belt, 700 km north of Vladivostok. The regional position of the describable ore-bearing area, similar to the Mexican deposits of the Guanajuato area typical of the Pacific region, is determined by its relationto the Early Cretaceous island-arc terrane with a distinct geochemical enrichment in silver of its folded rock complex. Quartz vein bodies are located in submeridional fracturesfeathering NE-trending sinistral strike slip faults.The near-ore alteration is dominated bysericitization and silicification of host sandstones. The main silver minerals are freibergite, acanthite, and Se-containing pyrargyrite, polybasite, stephanite. Kustelite, electrum, aguilarite, allargentum, and discrasite are much less abundant. The mineralogical and geochemical zoning of ore bodies emphasized by a highly productive Ag-sulfosalt assemblage enriched in Sein the upper part of veins and the poor ores with predominant acanthite at depth is revealed.The veins were formed with the participation of sodium chloride solutions saturated with CO2 and CH4, at the temperature range from 400 to 150° C. The deposition of productive sulfosalt-bearingassemblages occurred with a suddendecrease in pressure under conditions of discharge of magmatic-meteoric fluids in circulation zones in the sandstones under the screen of volcanic rocks overlying the Kema terrane.