Insoluble carbonaceous substance (ICS) at the Sukhoi Log gold deposit has been studied following the scheme: source shales — concentrates — residual substance of rocks. Examination by electron microscopy, transmission electron microscopy with electron microdiffraction, thermography, and mass spectrometry revealed several morphogenetic ICS varieties: dot-drop-like, honeycomb, single graphite crystals, and spherical graphite crystals.
Study of source shales and concentrates has shown their similar carbon isotope compositions (δ13Cav = 18.03–17.54‰). Residual carbonaceous substance is characterized by a heavy carbon isotope composition (δ13Cav = 10‰). Its enrichment with heavy carbon isotope, as compared with the source rocks, calls for special geochemical studies. The ICS heterogeneity in the Sukhoi Log shales points to variations in the physicochemical settings of ore formation at the deposit.