Formation of Placer Gold Content of the Gonam River Basin, Yursky Object (Aldan-Stanovoy Shield)

The placer gold content of the Yursky creek (right tributary of the Gonam river) has been studied. It was revealed that the Cretaceous conglomerates and the producing layer of the alluvial placer are composed of pebbles and boulders of the same petrographic composition. The petrographic composition of pebbles and boulders is as follows: leucogranites, granite-gneisses, metagabbro, diafluorinated shales of sericite-chlorite-epidote-quartz composition and quartzites. Gold from alluvial deposits and conglomerates of the Cretaceous age also has the same typomorphic features and is represented mainly by flake and lamellar forms, measuring 0.1-0.25 mm, sometimes there are larger gold particles, with a shagreen surface and casts of impressing of minerals of the host deposits, often with through holes. The gold fineness has a wide range from 720 to 1000‰. Inclusion minerals represented by pyrite, chalcopyrite, galena, presumably chamosite and difficult-to-diagnose aluminosilicates were found in native gold from conglomerates. A similar set of mineral inclusions was also identified in native gold from the alluvial deposits of the Yursky creek. The common character of mineralogical and geochemical features of alluvial gold from alluvium and conglomerates, as well as the same petrographic composition of pebbles in conglomerates and the producing horizon allows us to conclude that the placer of the Yursky object was formed due to the supply of gold from the Cretaceous conglomerates. superimposed late ore mineralization.