Granitoids of the Ergelyakh Intrusion-Related Gold–Bismuth Deposit (Kular-Nera Slate Belt, Northeast Russia): Petrology, Physicochemical Parameters of Formation, and Ore Potential

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

Disseminated Gold–Sulfide Mineralization in Metasomatites of the Khangalas Deposit, Yana–Kolyma Metallogenic Belt (Northeast Russia): Analysis of the Texture, Geochemistry, and S Isotopic Composition of Pyrite and Arsenopyrite

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

Geodynamic Emplacement Setting of Late Jurassic Dikes of the Yana–Kolyma Gold Belt, NE Folded Framing of the Siberian Craton: Geochemical, Petrologic, and U–Pb Zircon Data

We present the results of geostructural, mineralogic–petrographic, geochemical, and U–Pb geochronological investigations of mafic, intermediate, and felsic igneous rocks from dikes in the Yana–Kolyma gold belt of the Verkhoyansk–Kolyma folded area (northeastern Asia). The dikes of the Vyun deposit and the Shumniy occurrence intruding Mesozoic terrigenous rocks of the Kular–Nera and Polousniy–Debin terranes were examined in detail. The dikes had diverse mineralogical and petrographic compositions including trachybasalts, andesites, trachyandesites, dacites, and granodiorites. The rocks showed significant similarities in distributions of REE, and their concentrations of most HFSEs were close to the intermediate ones between ocean islands basalts and enriched middle ocean ridge basalts. We propose that the subduction that was ongoing during the collision of the Kolyma–Omolon superterrane with Siberia led to melting in the asthenospheric wedge and in the lithosphere, which formed a mixed source for the dike systems from both an enriched and a depleted mantle source. The U–Pb SHRIMP-II dates obtained for the dikes corresponded to the Late Jurassic interval of 151–145 Ma. We present a geodynamic model for the northeastern margin of the Siberian Craton for the Tithonian age of the Late Jurassic