Multistages mineralization and transformation of terrigenous rocks in the Vyun ore field, Yana-Kolyma metallogenic belt, Northeast Asia: insight from the sedimentary, diagenetic and hydrothermal sulfides and geochemistry of ore-hosting rocks

The article presents the results of studying the sulfidization zone of the Charky-Indigirka thrust fault within the Vyun ore field in the Upper Adycha sector of the Yana-Kolyma metallogenic belt. The purpose of the research is to study the composition and distribution of basic and trace elements in terrigenous rocks of the Upper Triassic and Middle Jurassic, as well as in distal metasomatites on the territory of the Vyun ore field. The petrochemical features of weakly altered terrigenous rocks, conditions of their formation and changes of composition during epigenetic processes were analyzed. Three generations of pyrite were identified: diagenetic Py1, metamorphogenic Py2 and metasomatic Py3. Typomorphic trace elements and variations of their distribution in pyrites were determined. Composition analyses of weakly altered sedimentary rocks of the Upper Triassic (V/(V+Ni)=0.5-0.8, V/Cr=0.1-2.9 and Ni/Co=2.5-10.3) and Middle Jurassic (V/(V+Ni)=0.7-0.9, V/Cr=0.2-2.0 and Ni/Co=1.3-8.8) yielded the conclusion that changes in oxygen conditions to disoxic and anoxic, as well as the enrichment of terrigenous material with ore elements, lead to the formation of authigenic sulfide mineralization at the early stages of the sedimentary strata formation. The subsequent multistage development of the territory was accompanied by an active migration of chemical elements, their input and redistribution.

Rapid Extraction Chemistry Using a Single Column for 230Th/U Dating of Quaternary Hydrothermal Sulfides

230Th/U dating can provide high-precision age constraints on Quaternary hydrothermal sulfides. However, low content of U and Th often involves extraction chemistry for the separation and enrichment of U and Th, but these chemical processes are very complex. We developed a simplified procedure consisting of total sample dissolution and single-column extraction chemistry, which can reduce the time and improve the accuracy of the dating. Concentrated HCl-HF followed by HNO3 was added to ensure complete dissolution. A single column filled with 0.4 mL of AG 1-X8 anion resin was used, then 8 M HNO3, 8 M HCl and 0.1 M HNO3 were used to elute most of the matrix metals, Th and U. This process provided more than 95% recoveries for U and Th, and negligible blanks. Meanwhile, Pb and Bi interferences were tested and showed no effect on the U and Th isotope ratio. The 230Th/238U activity of the Geological Survey of Japan geochemical reference material JZn-1 in secular equilibrium was determined and showed a radioactive equilibrium (1.00 ± 0.01, n = 5, all errors 2σ) and an in-house standard QS-1 was consistent to 0.0078 ± 0.0001 (n = 8, ±2σ) with an average age of 705 ± 10 yrs BP (n = 8, ±2σ). The technique greatly shortens the sample preparation time and allows more concise and effective analysis of U-Th isotopes. It is ideally suited for the high-precision 230Th/U dating of Quaternary submarine hydrothermal sulfides and sulfides from other settings.

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 (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.