Radiolytic (H2, O2) and other trace gases (CO2, CH4, C2H6, N2) in fluid inclusions from unconformity-related U deposits

Fluid inclusions from quartz and dolomite veins from five unconformity-related uranium deposits (Athabasca basin, Canada) have been analyzed by Raman spectrometry in order to identify trace gases in their vapor phase at room temperature. About 80% of fluid inclusions have detectable gases. The most common gases are H-2, O-2, CO2, CH4, C2H6 and N-2. So-called "NaCl-rich" and "CaCl2-rich" brine inclusions have similar gas contents. U-bearing fluid inclusions have similar gas compositions when compared to U-absent fluid inclusions. Radiolysis (i.e. production of H-2 and O-2 from H2O when fluids have been in contact with previously deposited UO2) and fluid-rock interactions are the most probable origins for H-2, O-2 and CO2, CH4, C2H6 and N-2 respectively. The relative abundance of radiolytic O-2 is related to distance to ore and could be used as vectors towards mineralization. Other trace gases may be indicative of ore-forming processes, specifically of fluid-rock interaction and UO2 deposition. (C) 2017 The Authors. Published by Elsevier B. V.