The Role of Metamorphic Devolatilization in Building Orogenic Gold Deposits within Paleoproterozoic Organic-Rich Sediments: P-T-X Thermobarometric and Carbon Isotopic Constraints from the Chertovo Koryto Deposit (Eastern Siberia)

• Published in: Russian journal of Pacific geology 2022-08, Vol.16 (4), p.387-404
• Main Authors: Tarasova, Yu, Budyak, A., Goryachev, N., Skuzovatov, S., Reutsky, V., Gareev, B., Batalin, G., Nizamova, A.
• Format: Article
• Language: English
• Subjects: Analytical methods; Carbon; Carbon dioxide; Chemical composition; Earth and Environmental Science; Earth Sciences; Fluids; Geology; Gold; Heavy metals; Isotopes; Juveniles; Low temperature; Metamorphic water; Mineralization; Organic matter; Oxidation; Precipitation; Pressure; Quartz; Sediment; Sedimentary rocks; Sediments; Shale; Spectroscopy; Spectrum analysis; Terrigenous sediments
• ISSN: 1819-7140; 1819-7159
• DOI: 10.1134/S1819714022040078

Orogenic gold deposits hosted by terrigenous sediments rich in organic matter as well as the role of host sediments and their metamorphic modification in making up such deposits remain highly debatable. So far, the origin of gold deposits in the Lena gold province (Eastern Siberia) mainly hosted by folded and deformed Neoproterozoic complexes of passive-margin sediments, including the giant Sukhoi Log teposit, has been regarded to as postmagmatic (juvenile) or metamorphic, primarily driven by metamorphic devolatilization and redistribution of metals with carbon-rich fluids. Yet, the origin of similar but smaller-scale deposits hosted by the underlying Paleoproterozoic metasediments in the same area is poorly known. The aim of this work was to establish the key processes, which contributed to the formation of gold and associated mineralization of the Chertovo Koryto deposit, through fluid inclusion thermobarometry, spectroscopy and carbon isotopic composition. Fluid inclusions in different types of quartz from the deposit were studied by Raman spectroscopy and cryothermometry. The high P – T parameters (2.8 kbar; 440°C) indicate the initial stage of the ore process. The interaction of metamorphic water-rich fluid with organic matter of the host sediments led to oxidation of water with the release of CO 2 . The ore precipitation was associated with a sharp pressure decrease (0.3–0.6 kbar) and cooling of the system (320–200°C), which, according to the model, occurred as a result of tectonic deformations and open cavities within the zone of maximum tectonic stress. This pressure reduction zone was the most suitable for the deposition of gold-containing liquid. The overprinting ore-barren stage was characterized by even lower temperatures to (154–87°C) but a wider pressure range (0.1–0.6 kbar). Similar carbon isotopic composition of fluid inclusions in quartz from the early ore stage (δ 13 C within –16.9 to –17.8%) and the gold precipitation stage (from –16.6 to –17.9%) resembling that of the host Neoproterozoic sediments and previously reported isotopic data for other deposits (Sukhoi Log, Krasniy) suggest the uniform inheritance of metal-bearing C–N–H–S-rich fluid fluid from the host black-shale sediments. Overall, the results suggest that the whole process of sedimentary preconditioning to metamorphic redistribution of gold and other metals in carbon-rich fluids in the Chertovo Koryto deposit was governed primarily by host sediments without any contribution