At the orogenic gold deposits of the Yana–Kolyma metallogenic belt (northeast Russia) both Au–quartz-sulfide mineralization with native gold and disseminated sulfide mineralization with invisible Au developed. The textural and mineralogical-geochemical features, isotope-geochemical characteristics of gold-bearing sulfides from proximal metasomatites, and possible forms of Au occurrence in pyrite and arsenopyrite have been studied using electron microprobe, atomic absorption, LA-ICP-MS trace element, isotope analysis, and computed microtomography. Four generations of pyrite (Py1, diagenetic; Py2, metamorphic; Py3, metasomatic; Py4, veined) and two generations of arsenopyrite (Apy1, metasomatic; Apy2, veined) have been identified at the Khangalas deposit. In the proximal metasomatites, the most common are Py3 and Apy1. Studying their chemical composition makes it possible to identify the features of the distribution patterns of typochemical trace elements in pyrite and arsenopyrite, and to establish the nature of the relationship between Au and these elements. In Py3 and Apy1, structurally bound (solid solution) Au⁺ prevails, isomorphically entering the crystal lattice or its defects. Isotope characteristics of hydrothermal sulfides (δ³⁴S = −2.0 to −0.6‰) indicate that mantle/magmatic sulfur was involved in the formation of the deposit, though the participation of sulfur from the host rocks of the Verkhoyansk clastic complex cannot be ruled out. The Khangalas deposit has much in common with other gold deposits of the Yana–Kolyma metallogenic belt, and from this point of view, the results obtained will help to better reveal their gold potential and understand their origin.

This work presents results of structural analysis of the orogenic Bazovskoe gold-ore deposit, the structure of which is controlled by an imbricate fan with frontal succession of ore-controlling thrust faults and conjugated thrust ramps. It was established that linear and stratified stockworks and their combinations are formed by several systems of quartz veins and veinlets, regularly related to thrusting along the ore-controlling zones and interlayer shears. In addition, superimposed shear deformations are widely distributed. The features revealed of the geological structure of the Bazovskoe gold-ore deposit allow us to refine the prospecting and searching pattern developed for gold-ore deposits of the Verkhoyansk–Kolyma fold belt.

The Yana–Kolyma metallogenic belt, NE Russia, is a world-class gold belt with resources numbering ~8300 tons of gold. The belt is localized in the central part of the Verkhoyansk–Kolyma orogen, formed by a collage of diverse terranes. The Tithonian-to-Early-Cretaceous orogenic gold deposits are hosted in a sequence of Permian–Triassic and Jurassic clastic rocks and altered Late Jurassic andesite, dacite, granodiorite, trachyandesite, and trachybasalt dykes. High-fineness gold (800–900‰) in quartz veins and invisible gold in disseminated arsenian pyrite-3 (Py3) and arsenopyrite-1 (Apy1) are present in ores. Here, we present new data about microtextures; the chemical composition and stable sulfur isotopes of auriferous pyrite-3 and arsenopyrite-1 from proximal alterations in sediment-hosted (Malo–Taryn, Badran, Khangalas); and intrusion-hosted (V’yun, Shumniy) orogenic Au deposits in the central sector of the Yana–Kolyma metallogenic belt to better constrain the ore-forming process and tracking their evolution. Detailed petrography defined the following generations of pyrite: syn-sedimentary/diagenetic Py1, metamorphic Py2 and hydrothermal Py3, and Apy1. Hydrothermal Py3 and Apy1 are localized in the proximal pyrite–arsenopyrite–sericite–carbonate–quartz alteration in ore zones and make a major contribution to the economic value of the veinlet-disseminated mineralization with “invisible” gold in the orogenic deposits of the Yana–Kolyma metallogenic belt. Electron microprobe analysis (EMPA) of Py3 in both types of deposits shows concentrations of As (up to 3.16 wt%), Co, Ni, Cu, Sb, and Pb. Py3 in intrusion-hosted orogenic gold deposits reveals elevated concentrations of Co (up to 0.87 wt%), Ni (up to 3.52 wt%), and Cu (up to 2.31 wt%). The identified negative correlation between S and As indicates an isomorphic substitution of sulfur by As¹⁻. Py3 from igneous rocks is characterized by a high degree of correlation for the pairs Fe²⁺→ Co²⁺ and Fe²⁺→ Ni²⁺. For hydrothermal Apy1, Co (up to 0.27 wt%), Ni (up to 0.30 wt%), Cu (up to 0.04 wt%), and Sb (up to 0.76 wt%) are typomorphic. According to atomic absorption spectrometry, the concentration of Au in Py3 reaches 159.5 ppm; in Apy1, it reaches 168.5 ppm. The determination of the precise site of the invisible gold within Py3 and Apy1 showed the predominance of solid-solution Au⁺ in the crystal lattice. The values of δ³⁴S in Py3 and Apy1 (from −6.4 to +5.6‰, mean value of about +0.6‰), both from sediment-hosted and from intrusion-hosted deposits, display a relatively narrow range and are characteristic of the hydrothermal ore stage. Our analytical results showed no systematic differences between the chemical and stable sulfur isotope compositions of both auriferous pyrite-3 and arsenopyrite-1 from the proximal alteration in sediment-hosted (Malo–Taryn, Badran, Khangalas) and intrusion-hosted (V’yun, Shumniy) orogenic Au deposits, indicating that the primary source of sulfur, gold, and mineralizing fluids was likely from subcrustal and metamorphic systems in the Late-Jurassic-to-Early-Cretaceous Verkhoyansk–Kolyma orogen.

This paper describes features of petrographic and chemical compositions and isotopic dating of the Ergelyakh and Sokh plutons, located within the Kular-Nera slate belt, Verkhoyansk-Kolyma folded region (VKFR), Northeast Russia. Intrusion of the massifs took place approximately 145–150 million years ago. Different isotopic systems on the whole rock samples and mineral separates record at least two stages of later tectono-magmatic activity 130–120 and 110–100 million years ago. Granitoid magmas for the Ergelyakh and Sokh plutons were formed at high temperatures (950–1060 °C) within the amphibolitic lower crust of an island arc setting. The ages of crustal protoliths for granitoids of the Ergelyakh intrusion-related gold–bismuth deposit, calculated on Rb–Sr and Sm–Nd two-stage models, are 1109–1383 and 1199–1322 million years, respectively. Formation of the Ergelyakh and Sokh plutons took place within a significant temperature interval (<450 to 901 °C) and, with regard to the superposition of later events, lasted for a long time. During the cooling process of granitoid melts, at the time of biotite crystallization in both massifs, a significant increase of oxygen fugacity was registered. The ore potential of granitoids of both massifs seems to be similar, but due to some differences in the physicochemical parameters of their formation (redox conditions), it was partially realized only within the Ergelyakh massif with the generation of several minor intrusion-related gold–bismuth deposits. Granitoid melts of the Ergelyakh massif were formed in relatively heterogeneous and oxidizing conditions (∆Ni–NiO = +3.26 to –3.60). Granitoid melts for the Sokh massif (∆Ni–NiO = –2.88 to –9.27) were formed in reducing conditions.

This study reports the results of the analysis of multi-stage deformation structures of the Khangalas gold ore cluster, northeast Russia. Four Late Mesozoic-Early Eocene deformation stages were identified. The first deformation event (D1) was characterized by the development of NW-striking tight to isoclinal folds of the first generation (F1) and interstratal detachment thrusts. Major folds, extensive thrusts, boudinage, cleavage, auriferous mineralized fault zones and quartz-vein gold mineralization were formed in the reverse and thrust fault stress field during the progressive deformation stage (D1), with NE-SW-oriented σ1. Post-ore deformation is widely manifested in the region. Structures D2 and D3 are coaxial. Sinistral strike-slip motions (D2 and D3) occurred along NW-trending faults under prevailing W-E compression. They were accompanied by the formation of NS- and NE-striking F2–3 folds with steep hinges and by bending of the earlier formed structures, among them ore-controlling ones. The last deformation event (D4) was represented by normal-dextral strike-slip faulting, refolding of rocks, pre-existing structures and ore bodies and by the development of folds with steep hinges. Key structural elements of varying age are described, the chronology of deformation events and mineralization reconstructed and their relation to geodynamic events in northeast Asia established.

The Khangalas orogenic gold deposit is located in the central part of the Yana–Kolyma metallogenic belt. The structure of the deposit is defined by several mineralized fracturing zones up to 70 m thick and up to 1400 m long in the arch and the southwestern limb of a NW-trending anticline. The Upper Permian terrigenous rocks host ore bodies with massive, banded, veinlet, disseminated, and brecciated textures. The major gangue minerals include quartz, carbonates, and rare sericite. The major ore minerals are pyrite and arsenopyrite, the subordinate minerals are galena, sphalerite, chalcopyrite, and native gold, and Fe-gersdorffite, tetrahedrite, and argentotennantite are rare minerals. Supergene minerals (sulfates, phosphates, arsenates, and hydrooxides) are abundant in a linear oxidation zone. The mineral formation occurred in two stages: gold–sulfide–quartz and silver–quartz. Quartz veins with visible native gold formed from low-saline (~5.0 wt % NaCl-equiv.) CO₂-bearing hydrocarbonate fluids at a temperature of 330–280°C and a pressure of ~0.8 kbar. Disseminated Au-bearing pyrite-3 (up to 39.3 ppm Au) and arsenopyrite-1 (up to 23.8 ppm Au) from sericite–carbonate–quartz metasomatites are characterized by nonstoichiometric composition, a Fe excess, and a deficit of S (in addition to As in Apy), and Fe/(S + As) ratios of 0.47–0.52 (Py2) and 0.47–0.50 (Apy 1). Structurally bound Au⁺ is the dominant mode of occurrence of invisible gold in Py3 and Apy1. The isotopic composition of oxygen of quartz (+15.2 to +16.1‰ δ¹⁸O) and fluid (+8.4 to +9.2‰ δ¹⁸O_H2O), as well as sulfur of sulfides (–2.1 to 0.6‰ δ³⁴S), in addition to the ¹⁸⁷Os/¹⁸⁸Os ratios (0.2212–0.2338) of native gold and Pb of galena (²⁰⁶Pb/²⁰⁴Pb = 18.0214, ²⁰⁷Pb/²⁰⁴Pb = 15.5356, and ²⁰⁸Pb/²⁰⁴Pb = 38.2216) and geochemical features of Py3 and Apy1, allow us to suggest that sources are involved in ore formation that are mainly from the subcontinental lithospheric mantle and, to a lesser extent, crustal reservoirs. The formation of gold-bearing ore bodies of the deposit is related to the final progressive reverse-thrust deformations of stage D1 of the Valanginian period of the Early Cretaceous (~137 Ma), which occurred during postorogenic processes in the Yana–Kolyma belt upon regional southwestern transportation of rocks. Our results are important for forecasting metallogenic and prospecting works directed for the discovery of large-volume gold mineralization of orogenic belts.