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 WE 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.

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.

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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 (d34S = –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.

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