Silver-polymetallic deposit Perevalnoye of the Ducatsky ore field (Balygychano-Sugoysky volcanic trough, North-East of Russia)

The geological, structural, mineralogical, and geochemical features of the silver polymetallic deposit Perevalnoye (Northeastern Russia) are considered for the first time. The deposit is located on the northeastern flank of the Dukat ore field in the central part of the Balygychan-Sugoysky riftogenic volcanic trough, which formed synchronously with the structures of the Okhotsk-Chukchi volcanic belt. The deposit lies on the periphery of a volcanic dome uplift and is localized in a large subvolcanic dike of Late Cretaceous porphyritic rhyolites (nevadites) at a depth of 140‒160 m from the surface. The richest mineralization is controlled by the knee-shaped bends of the dyke. The main amount of silver in the ores is mainly associated with Ag-tetrahedrite and freibergite. In addition, a significant proportion of silver is due to pyrargyrite, native silver, acanthite, and geffroite ((Ag, Cu, Fe)₉(Se, S)₈). A small part of the silver is associated with rare (for these ores) minerals – proustite, argentopyrite, and minerals of the lenaite (AgFeS₂) – chalcopyrite isomorphic series. The main mineralogical feature of the ores is the widespread development of coarse–scaled muscovite and rutile, the presence of rhodonite, anatase, zircon and leucoxene. Siderite and rhodochrosite predominate among carbonates. A two-stage ore formation has been established for the Perevalny deposit – the telescoped superposition of high-temperature greysens (late stage) on silver-polymetallic ores (early stage) with distinct signs of thermometamorphism of the latter and the associated natural Ag enrichment. Greisenization and the influx of high-temperature solutions seem to be associated with the introduction of a late phase of an undiscovered intrusive massif. The results of mineralogical studies allow us to classify the Ag–polymetallic deposit Perevalnoye, as well as other deposits of the Omsukchan metallogenic zone, to the intermediate sulfidized class of epithermal deposits.