The Perevalnoe Silver-Polymetallic Deposit in the Dukat Ore Field (Balygychan—Sugoi Volcano Depression, Northeast Russia)

This study is the first examination of the geological structural and mineralogical-geochemical features of the Perevalnoe silver-polymetallic deposit, Northeast Russia. The deposit lies in the northeastern flank of the Dukat ore field in the middle of the Balygychan–Sugoi riftogenic volcanic depression which was formed synchronously with the structures of the Okhotsk–Chukchi volcanogenic belt (OChVB). The deposit lies along the periphery of a volcanic dome rise and is localized in a large subvolcanic dike consisting of Late Cretaceous porphyritic rhyolites (nevadites) at a depth of 140–160 m beneath the ground surface. The richest mineralization is controlled by geniculate bends in the dike. The bulk of silver in the ores is mostly related to Ag-tetrahedrite and freibergite. As well, a substantial amount of silver is due to pyrargyrite, native silver, acanthite, and the sulfurous analogue of geffroyite ((Ag, Cu, Fe)₉(Se, S)₈). A small fraction of silver is related to rare (for these ores) minerals, namely, proustite, argentopyrite, and minerals of the isomorphous series lenaite (AgFeS₂)—chalcopyrite. The chief mineralogical peculiarity of these ores consists in a wide occurrence of coarse-flake muscovite and rutile, the presence of rhodonite, anatase, zirconium, and leucoxene. The carbonates are dominated by siderite and rhodochrosite. The Perevalnoe deposit was found to involve a two-phase mineralization, namely, telescoped superposition of high-temperature greisens (those of the later phase) upon silver-polymetallic ores (those of the earlier phase) with distinct signs of thermal metamorphism of the latter and the associated natural enrichment in Ag. Greisenization and the arrival of high-temperature brine seem to be related to the emplacement of the later phase of an unexposed intrusive massif. The results of mineralogical studies enable us to classify the Ag-polymetallic Perevalnoe deposit, similarly to the other mineral deposits in the Omsukchan metallogenic zone, as the intermediate sulfidation epithermal class of deposits.