Gold-Rare-Metal Mineralization of the Mokrundya Placer Deposit in Arctic Siberia, Republic of Sakha (Yakutia)

The Mokrundya alluvial-placer gold deposit is located in the Verkhoyansk-Kolyma folded region, within the Tuguchak ore-placer cluster. The authors used ore and scanning electron microscopy and chemical-analytical methods to study the typomorphic and mineralogic-geochemical features of gold, minerals of the heavy fraction of the placer, and ore mineralization of the dolerite dike complex stripped in the placer bedrock. Stages of development of the ore-forming system in dolerites have been established. The main productive periods with native gold are associated with the postmagmatic stages: (a) early arsenopyrite-polysulfide stage and (b) gold-bismuth-tellu-ride stage. The latter is composed of bismuth tellurides and sulfotellurides, native gold, bismuth, maldonite AuBi2, and complex Au and Bi intermetallic compounds. The authors hypothesize the sources of placer gold in the alluvial deposits. One of them is the ore mineralization of the dolerite dike complex, and the other is associated with mineralized zones of the Gematitovoe skarn-hydrothermal ore occurrence in the upper reaches of the Mokrundya Stream.