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Vol 67, No 4 (2025)
Gold deposits of Northeast Asia - dedicated to the memory of G. N. Gamyanin
Delyankir local gold ore-magmatic system (Yana-Kolyma belt, North-East Russia)
Abstract
The local gold ore-magmatic system of the granitoid related type is characterized. The data on geochemistry of ore-bearing granitoids, mineralogy and geochemistry of ores are presented. Gold mineralization is attributed to the gold-bismuth type. The signs of the genetic relationship of granitoids and ore mineralization have been established, which consist in the mineralogical-geochemical and isotope-geochemical characteristics of the constituent parts of the Delyankir ore-magmatic cluster. The evolution of fluid composition from quartz deposition to arsenopyrite and ore minerals deposition is shown.
Geologiâ rudnyh mestoroždenij. 2025;67(4):397-415
397-415
Near-ore alterations and mineralization of terrigenous rocks of the Khangalas gold deposit, North-East Russia
Abstract
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.
Geologiâ rudnyh mestoroždenij. 2025;67(4):416-438
416-438
Khokhoy deposit is a new Carlin-type gold-bearing object (Aldan shield)
Abstract
To the west of the unique gold-mining Central Aldan ore district at the Khokhoy deposit of Verkhneamginskaya area, gold mineralization has been identified for the first time in terms of regional position, structural, morphological, and mineralogical-geochemical parameters comparable to its global analogue, the Carlin type. The deposit is located on the northern margin of the Precambrian Aldan shield in the deep Amga fault zone at the junction of two large structural units: the Olekminsky granite-greenstone region (Olekminsky craton) and the Aldan granulite-gneiss region (mobile belt). The mineralization is represented by sandy loam-clay-clastic karst formations developed on the tectonized contact of Lower Cambrian carbonate and Lower Jurassic terrigenous sedimentary rocks. Ore-bearing sublongitudinal steeply falling discontinuous faults are accompanied by Cretaceous dikes of sub-alkaline rocks. The friable supergenic formations consist of quartz, muscovite, clay minerals (illite, clinochlore, Fe-clinochlore, kaolinite), lepidocrocite, carbonates, barite, fluorite, goethite, jarosite, and hematite. The primary ores were preserved in the form of fragments/relics of jasperoids – pyrite-adularia-quartz metasomatites formed as a result of silicic-potassic metasomatism of carbonate rocks. Jasperoids carry low-temperature mineralization, represented by fine-grained quartz, chalcedony, adularia, sericite, calcite, barite, fluorite, illite, hollandite, pyrite, minerals of thallium, antimony, arsenic, tellurium and mercury. Geochemical association of elements – Au-As-Sb-Tl-Te-Hg. Finely dispersed native gold of primary ores with a size of no more than 0.005 mm is found in oxidized pyrite enriched with Sb, As and Hg, as well as in association with minerals of thallium and mercury. In friable karst formations, the residual gold was released and enlarged to 0.1–0.5 mm. High-grade supergenic gold is characterized by a spongy structure and an admixture of Hg. A new mineral, thallium tellurate Tl2TeO6 – amgaite, has been discovered in the ores. The substantiation of the highly productive Carlin type of gold mineralization of the Khokhoy deposit will serve as the basis for the revision and revaluation of the Kuranakh type in the area of the Aldan shield.
Geologiâ rudnyh mestoroždenij. 2025;67(4):439-460
439-460
The Kirovskoe gold deposit in talc-carbonate rocks (S. Urals): mineralogy, geochemistry, physicochemical conditions of formation and genesis
Abstract
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.
Geologiâ rudnyh mestoroždenij. 2025;67(4):461-483
461-483
The sequence and mechanisms of crystallization of precious metal minerals in veins of graphic galena-chalcopyrite ores in the central part of Oktyabr’sky Cu-Ni-PGE deposits
Abstract
The paper presents original results of studying platinum group minerals (PGM) in graphic galena-chalcopyrite ores of the central part of the Oktyabr’sky Cu-Ni-PGE deposit. Three successive mechanisms of PGE aggregate formation are proposed: growth from melt, subsolidus transformations and metasomatic processes. They can be divided into 7 stages: (1) accumulation of a critical amount of PGE and TABS in the residual (Cu-Pb-sulfide) melt due to fractional crystallization of sulfide melt; (2) crystallization of graphic intergrowths with distillation and concentration of incompatible elements in the form of "drops" along the sulfide-silicate boundary; (3) crystallization of platinum group minerals from this melt: sperrylite, altaite, cabriite-I, paolovite-I and hessite-containing solid solution (hessite-ss); (4) growth of maslovite-I crystals on early nucleation grains; (5) completion of melt crystallization with formation of maichnerite, sobolevskite-containing solid solution (sobolevskite-ss), frudite-I and gold-silver alloys; (6) subsolidus transformations with decomposition of sobolevskite-ss – sobolevskite+cabriite-II+paolovite-II; hessite-ss – hessite+maslovite-II, as well as additional growth of frudite-II; (7) growth of sperrylite metacrystals and formation of gold-silver alloys. The dominant role of sulfide melt fractionation in formation of large PGM aggregates is confirmed. A new variety of sobolevskite – Cu-Ni-Sb-sobolevskite – is described for the first time.
Geologiâ rudnyh mestoroždenij. 2025;67(4):484-506
484-506