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A fluid inclusion study was performed in the vicinity of the McArthur River unconformity-type uranium deposit,Saskatchewan, Canada. Euhedral quartz veins and breccias were sampled from the contact of the uranium orebody to a distance of 50 m from it. Raman analyses of the fluid inclusions vapor phase indicated the presence of H2 and O2 with various proportions. Fluids located at the immediate vicinity of the uranium ore contain nearly exclusively O2. At 1 m from the ore, the oxygen proportion relative to other gases rapidly decreases, whereas H2 increases and occasional traces of CH4 occur. Additional C2H6 as well as CO2 appear at about 10 m from mineralization, in the basement. Finally, only occasional traces of H2 were detected in fluid inclusions located at 50 m from the mineralization, in the sandstones. Thus, fluids that circulated at the contact of the orebody became oxidizing, whereas fluids circulating at distance from it were more reduced, due to the combination of water radiolysis and differential migration of H2 and O2. This repartition of gases probably induced indirectly significant modifications in the host rock after the ore formation, such as hematization or graphite alteration and subsequent gas production. In addition, the migration of H2 at long distance from the orebody should represent an potential prospecting tool. |
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