The paper presents new isotope geochronological data for several mineral deposits, ore occurrences, and related igneous bodies (plutons and dikes) in the Verkhoyansk–Kolyma folded area, eastern Yakutia. Twenty-one 40Ar/39Ar mica and four U–Pb zircon dates provide the first age constraints on key metallogenic units in the area. The dating results allow correlation between tectonic, magmatic, and metallogenic events. The sampled mineral deposits within the Adycha–Taryn fault zone in the southeastern Verkhoyansk–Chersky orogen apparently formed at the Jurassic–Cretaceous boundary during the final phase of the collision between the Siberian (North Asian) craton and the Kolyma–Omolon microcontinent (Kupol’noe deposit and the early metallogenic pulse of the Malotarynskoe deposit, ~ 143–144 Ma) and in the latest Early Cretaceous, in the beginning of the orogen collapse (Tallalakh and Dora-Pil’ deposits and the Malotarynskoe late metallogenic pulse, ~ 126 Ma). According to the suggested new classification of metallogenic units, these deposits belong to the Late Jurassic–Early Cretaceous Yana–Kolyma metallogenic belt. The Kyuchus deposit (~ 106 Ma), the Deputatsky ore cluster (~ 106–113 Ma), and the Khotoidokh deposit (~ 116 Ma) in the northern Verkhoyansk–Kolyma folded area belong to the North Verkhoyansk metallogenic belt. Their origin was associated with accretional and collisional processes that produced the Novosibirsk–Chukotka orogen in the middle Cretaceous. The Mangazeya ore cluster (~ 100 Ma, Early–Late Cretaceous boundary) in the southwestern end of the North Tirekhtyakh magmatic transverse belt belongs to the West Verkhoyansk metallogenic belt. The Nezhdaninskoe, Zaderzhnoe, Kurum, and Kuta deposits of the South Verkhoyansk area (~ 125–120 and ~ 100–95 Ma) can be joined into a single Verkhoyansk–Okhotsk metallogenic belt. The belt resulted from accretion and collision along the East Asian active continental margin and the related formation of the South Verkhoyansk orogen in the Early Cretaceous.
Typomorphic features of supergene gold in karst cavities were studied in the recently discovered Au–Te–Sb–Tl deposit within the Khokhoy gold ore field of the Aldan-Stanovoy auriferous province (Aldan shield, East Russia). Two morphological types of supergene gold, massive and porous, are recognized there. The first type is represented by gold crystals and irregular mass, with the fineness ranging from 835 to 1000‰. They are closely associated with goethite, siderite, unnamed Fe, Te, and Tl carbonates, Tl tellurites/tellurates and antimonates, as well as avicennite with a Te impurity. The second type is represented by mustard gold of two types with different internal structure: microporous and dendritic. The supergene gold is characterized by persistently high fineness. Along with Ag, it invariably contains Hg (up to 5.78 wt%) and Bi, and, rarely, Pb, Cu, and Fe. The supergene gold is chemically homogeneous, and its particles are all marked by high fineness, without any rims or margins. The obtained characteristics made it possible to prove the existence of two genetic types of supergene gold. Mustard microporous gold is the result of the decomposition of the associated minerals—goethite, Tl oxides, tellurium, Fe, Mn and Tl carbonates and antimonates, containing microinclusions of gold. Massive gold and dendrites are newly formed. The decomposition, remobilization, and reprecipitation of residual gold nanoparticles and their aggregation led to the formation of dendrites, and with further crystal growth and filling of pores, to gold of massive morphology. In terms of morphology, internal structure, fineness, and trace element composition, supergene gold of the Khokhoy gold ore field is comparable to gold from the Kuranakh deposit (Russia) and the Carlin-type gold deposits. It also is similar to spungy and mustard gold from Au–Te and Au–Sb deposits, weathering crusts, and placers. Its main characteristic feature is a close paragenesis with Tl minerals.
This study presents the typomorphic features of native gold grains from three different geological-industrial types (GIT) of gold deposits in the North-East of Russia: (1) gold–arsenic-sulfide in black shale strata (Natalka, Degdekan, Karalveem, Maldyak deposits), (2) gold–quartz veins in granitoids (Dorozhnoye, Butarnoye, Shkolnoye, Maltan deposits), and (3) gold–silver adularia in volcanogenic strata (Kupol, Olcha, Kubaka, Burgali, Primorskoe, Dalnee deposits). The reliability of the geological interpretation is directly related to mineral associations, fineness variations, its internal structure and the content of microimpurities. Native gold is a reliable indicator for identifying various GIT of gold deposits at the early geological-prospecting stages of studying gold-bearing areas. Typomorphic features of native gold for each of the considered GIT are stable and do not depend on the age and scale of mineralization. It is shown that using an integrated approach obtains genetic information about a particular ore object, which makes it possible to predict the vertical range of mineralization and outline the technology for processing ores. The information obtained can also be effectively used in the search for placer deposits in nearby watercourses. Identification of typomorphic features of ore and placer native gold opens up wide opportunities for delineating the distribution areas of placer deposits.
The physicochemical modeling of mineral formation processes at the Badran subthrust gold-quartz deposit was performed, based on a study of fluid inclusions in quartz by Raman spectroscopy, gas chromatography, thermometry, and freezing. The results show that at stage I, highly productive gold-bearing quartz veins (gray quartz) of the deposit formed from heterogeneous fluid at <320 ºC and 2.0–0.1 kbar with the active participation of CO2, N2, and CH4; the salinity of this solution reached 10 wt.% NaCl-equiv. At stage II (Au-productive), milky-white quartz was produced from the homogeneous medium-chloride-sulfide solution which remained after the heterogenization of the initial fluid, at 300–100 ºC and 0.1 kbar. At stage III (with low Au production), clear quartz formed from homogeneous chloride solutions with salinity of <4.5 wt.% NaCl-equiv. at <200 ºC and <0.1 kbar. The physicochemical conditions of Au concentration within the complex geochemical system Au–Fe–Cu–Pb–Zn–As–Sb–Hg–Ag–H2O–Cl–H2S–CO2 at the Badran deposit was modeled using the Chiller software. The following models were used: (1) solution–rock interaction and (2) condensation of gas phase (for stage I); (3) simple cooling of medium-chloride-sulfide solution (for stage II); (4) simple cooling and (5) mixing of low-chloride-sulfide solution with acid meteoric waters (for stage III). The models show the sequence of vein formation in the ore-producing system and the host-rock metasomatism in the deep horizons of the deposit.
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