The conditions of existence and typomorphism of native gold in ores of the Degdekanskoe deposit (northeastern Russia) in black-shale strata

We studied the typomorphic features of native gold in orebodies with veinlet-disseminated quartz-sulfide mineralization at the Degdekanskoe deposit localized in Permian black-shale strata of the Ayan–Yuryakh anticlinorium in the upper-Yana–Chukchi folded area. With a successive HF and HNO3 dissolution of samples, the abundance of native gold intimately intergrown with sulfides (on the average, 42.1%) and carbonaceous substance was revealed. It is shown that most of its grains are small and fine (the <0.25 mm fraction averages 90.2%) and are accumulated mainly in interstices. Two gold generations have been revealed: low-medium-grade (751–840‰) (main) and high-grade (885–931‰). The zonal structure of mineralization has been established. The upper, most enriched horizons bear coarser-grained gold of the two generations, which are localized in both sulfide and silicate minerals. With depth, the total content of gold decreases, the share of sulfide gold increases, and the grain size and grade also diminish, with the low-medium-grade generation prevailing.