Gold mineralization in siliceous-carbonate rocks of southeastern East Sayan

Complex study and comparative analysis were carried out for two gold deposits, Vodorazdel’noe and Ondol’toi, localized among carbonate and siliceous-carbonate rocks of the Il’chir Formation in southeastern East Sayan. The Vodorazdel’noe deposit is of gold-quartz-sulfide type; it formed at 275–300 °C with the participation of highly concentrated chloride fluids and bears low-fineness gold associated with quartz-sulfide mineralization. In sulfur isotope composition (δ³⁴S) the deposit ores are similar to sulfides of hydrothermal structures of slow-spreading ridges.The Ondol’toi deposit is formed by low-sulfide carbonate breccias and hematitized jasperoids. This deposit is localized in the frontal zone of a large thrust and bears gold-sulfide mineralization (fine-grained sulfides and submicron gold in siliceous-carbonate rocks and jasperoids). It is characterized by the presence of brecciated rocks and high contents of Hg, Sb, Ba, and Fe both in ores and in the host rocks. The established geologic, mineralogical, and geochemical features of the deposit permit it to be assigned to the Carlin type.