Geochemistry of palaeofluids circulation in the Franceville basin and around Oklo natural nuclear reaction zones (Gabon)

The geochemical characteristics of five palaeofluids in the Franceville bas in (Gabon) have been studied using a multi-disciplinary investigation of fl uid inclusions: (1) a low saline meteoric water firstly migrating through t he basement and injected into the basin, (2) high chlorine brines equilibra ted with carbonate and evaporitic layers in sandstones, (3) hydrocarbon-ric h fluid derived from organic matter maturation in the pelites, (4) a minera lising fluid (Lw(mix)) originating from the mixing of (1) and (2), (5) a ho t fluid related to the nuclear reactors functioning. The interaction of flu ids (3) and (4) is responsible for the U-mineralisation at the redox bounda ry developed between sandstones and pelites. (C) 2000 Elsevier Science B.V. All rights reserved.