Characteristic mineral assemblage and special features of the composition of Au and Ag sulfides of gold-silver deposits have been established. The forms of the occurrence of Au and Ag in the minerals of the early and last stages have been analyzed. The conditions for the formation of uytenbogaardtite and petrovskaite in supergene and low-temperature hydrothermal processes have been considered. A thermodynamic model explaining their genesis in the oxidation zones is presented.