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Uranium accumulation in modern and ancient Fe-oxide sediments: Examples from the Ashadze-2 hydrothermal sulfide field (Mid-Atlantic Ridge) and Yubileynoe massive sulfide deposit (South Urals, Russia)
- Ayupova, N.R., Melekestseva, I.Yu., Maslennikov, V.V., Tseluyko, A.S., Blinov, I.A., Beltenev, V.E.
- Sedimentary geology 2018 v.367 pp. 164-174
- apatite, iron oxides, iron oxyhydroxides, oxidation, rocks, seawater, sediments, sepiolite, sulfide minerals, sulfides, uranium, Russia
- Fe-oxyhydroxide sediments (gossans) from the Ashadze-2 hydrothermal sulfide field (Mid-Atlantic Ridge) and hematite–carbonate–quartz rocks (gossanites) from the Yubileynoe Cu-Zn VHMS deposit (South Urals) are characterized by anomalously high U contents (up to 352 ppm and 73 ppm, respectively). In gossans from the Ashadze-2 hydrothermal sulfide field, rare isometric anhedral uraninite grains (up to 2 μm) with outer P- and Ca-rich rims, and numerous smaller (<1 μm) grains, occur in Fe-oxyhydroxides and sepiolite, associated with pyrite, isocubanite, chalcopyrite, galena, atacamite and halite. In gossanites from the Yubileynoe deposit, numerous uraninite particles (<3 μm) are associated with apatite, V-rich Mg-chlorite, micro-nodules of pyrite, Se-bearing galena, hessite and acanthite in a hematite–carbonate–quartz matrix. Small (1–3 μm) round grains of uraninite, which locally coalesce to large grains up to 10 μm in size, are associated with authigenic chalcopyrite. The similar diagenetic processes of U accumulation in modern and ancient Fe-oxyhydroxide sediments were the result of U fixation from seawater during the oxidation of sulfide minerals. Uraninite in gossanites was mainly deposited from diagenetic pore fluids, which circulated in the sulfide–hyaloclast–carbonate sediments.