Том 67, № 4 (2025)

The results of complex mineralogical and geochemical studies of Upper Permian terrigenous rocks of the orogenic Khangalas gold deposit in the Yana-Kolyma belt are presented. The petrographic and lithochemical characteristics of the rocks are typical for polymictic sandstones (graywacke), oligomictic graywackle siltstones and mudstones. The terrigenous component of the Upper Permian sediments is a product of erosion of rocks with a predominant acidic and less basic composition, as well as graywacke. The presence of volcanogenic material is characteristic. Formation of thick units of polymictic sandstones (graywacke) with interlayers of oligomictic siltstones and mudstones is due to the high rates of sedimentation in delta complexes and periodic sea-level fluctuations. The changing redox conditions of the bottom water were a favorable factor for mobilization of ore elements and formation of diagenetic sulfide mineralization of rocks. The processes of regional and dislocational metamorphism are characterized by the removal of Si⁴⁺, Al³⁺, Ca²⁺, Fe²⁺, Mg²⁺ into the pore space and by enriching the interporous expelled water with these elements. Hydrothermal changes involved supply of Al³⁺, Ca²⁺, Fe²⁺, Mg²⁺, Sb, Au, Ag, Co, Ni, Cd, Te and the formation of geochemical associations of Au with chalcophylic (As, Sb, S, Cd) and lithophylic (Na, Ca, P, Mn, Be, Mg, W) elements. The connection of Au with a group of newly formed minerals (pyrite, arsenopyrite, siderite, and sericite) is emphasized. The increased concentration of W and Mo indicates their entry in the composition of the high-temperature fluid, related to magmatic source characteristic of superimposed Ag-Sb mineralization. Lithogenesis processes contribute to the formation of the mineralogical and geochemical specialization of the host rocks, favorable for the occurrence of a disseminated type of mineralization with isomorphically bound gold at the Khangalas deposit. The results obtained are important for a proper understanding of the influence of the environment on the conditions of ore formation in slightly metamorphosed complexes of collisional terranes and forecasting of orogenic gold deposits.

The deposit belongs to the type of aposerpentinite gold-bearing "serpentine veins" and is localized in the thrust zone of NW dipping, separating the Dzhabyk-Karagay anticlinorium and the Sukhtelinsky synclinorium. Mineralization is controlled by the thrust zone of NW dipping and tension cracks mainly of SEE dipping, caused by the dynamic influence of this Dzhabyk granitoid massif during its formation. Ores are represented by poor sulfide sheared and brecciated talc-carbonate rocks. Ore talc-carbonate metasomatism is manifested in the sequential replacement of serpentinites by talc and carbonates (breunnerite, magnesite) and ends with the formation of veinlet dolomite, talc and antigorite. Ore minerals are represented by disseminated small particles of native gold, sulfides and sulfoarsenides of Cu, Fe, Ni, Co (pentlandite, chalcopyrite, violarite, ulmanite, millerite, gersdorffite-cobaltite), as well as sulfoarsenides of Ir (irarsite) and Pt (platarsite). The sulfur content in the ores does not exceed 0.02 wt.%. Grains of native gold (Au-Ag solid solution with a fineness of more than 910‰) are enclosed in serpentine, chlorite, talc, and less often carbonate; they are often confined to shear cracks in metasomatites. Serpentinites at a distance from the deposit are specialized in Ni, Co and Cr. In addition, talc-carbonate rocks are recorded to have higher contents of granitophile elements (W, Sn, Rb, Cs, U) compared to serpentinites. Antigorite veinlets contain Ni, Sb and Ta, talc – Ag, dolomite – Mn, Sr, Ba, REE, Pb, Mo, Bi and Cd. Thermocryometric study of fluid inclusions in carbonates has established that talc-carbonate metasomatites were formed in the temperature range of 400–200°С from fluids belonging to the salt systems H₂O–NaCl, H₂O–NaCl–NaHCO₃ and H₂O–NaCl (MgCl₂) of low salinity (2.6–5.3 wt.% equiv. NaCl). Interpretation of the results of the oxygen and carbon isotope composition of carbonates (δ¹⁸O and δ¹³C, respectively, 19.2–24.2‰ and -7.3–8.5‰), as well as oxygen and hydrogen of serpentine, talc and chlorite (δ¹⁸O = 12.5…18.2‰, δD = -50.6…-68.0‰) indicates a metamorphic origin of the fluid. This fluid was formed as a result of the interaction of juvenile water with volcanogenic-sedimentary rocks enclosing the ultramafic massif. Participation of water released during the replacement of serpentine and talc by carbonates, as well as magmatic fluid genetically related to the Dzhabyk granitoid massif, is allowed. It is assumed that Cu, Fe, Ni, Co, Au, Pt, Ir in the ores were extracted by carbon dioxide fluid from ultrabasic rocks, and the increased contents of granitophile elements (W, Sn, Rb, Cs, U, etc.) are associated with the influx of magmatic fluid.