The redox control of groundwater around the Okelobondo uranium deposit (Gabon): 1D reactive transport modelling

The Okelobondo uraninite massive body is located in the Oklo district at a depth of about 300 m. Groundwater samples from boreholes located at shallow er depths (100-200 m) show neutral to basic pH and reducing conditions, and they are saturated with respect to uraninite. In contrast, deeper samples collected in the vicinity of the ore body are oxidising and slightly basic. Under these conditions, the solution is subsaturated with respect to urani nite and dissolves. These oxidising conditions at depth are unique, and the ir origin deserves investigation as they affect the chemical stability of u ranium oxide under repository conditions. The feasibility of the processes leading to this situation are analysed by simulating water flow and the che mical reactions through three 1D columns. (C) 2000 Elsevier Science B.V. Al l rights reserved.