Silver Sulfides and Selenides in Ores from Au–Ag Epithermal Deposits of the Okhotsk—Chukotka Volcanic Belt

— Mineral associations and compositions of sulfoselenides and other silver chalcogenides from epithermal deposits of the Okhotsk–Chukotka volcanic belt (Northeast Russia)—Rogovik, Lunnoe, Julietta, Valunistoe, Corrida, and Pepenveem—have been studied. Different types of relationships between S–naumannite and Se-acanthite in the ores of the study deposits have been established. It is shown that the replacement of S–naumannite and Se-bearing minerals (Se–galena, Se–stephanite) of early parageneses by Se-acanthite or acanthite at later stages is a general pattern in the sequence of formation of silver chalcogenides. Based on the results of thermodynamic calculations and data on the composition of the main productive mineral associations, the physicochemical parameters (T, ƒS 2 , ƒSe 2 , ƒO 2 , pH) of ore formation at these deposits were reconstructed.