Origin and genesis of the Oklo uranium ore deposits (Gabon): results from a basin scale fluid flow modelling

Abstract

Hydrologic processes that have contributed to the mineralogenesis of uranium ore deposits in the Franceville basin at Oklo (Gabon) are still uncertain. Based on stratigraphic, sedimentological and petrophysical data available from the outcrops at the Oklo area, we have performed a series of simulation experiments in order to constrain hypothetical paleoflow systems at the basin scale. Two-dimensional (2D) models have been applied to test hypotheses concerning convective flow systems in the Franceville basin and its transport capacity, the possible location of recharge and discharge areas and the existence of tectonosedimentary drains. Modelling results show that 2D flow models are insufficient to describe a system flux that is compatible with the location and distribution of the uraninite bodies in the Franceville basin. A 3D model has therefore been developed that successfully represents possible paleoflow systems with sufficient system flux in those parts of the basin, where the mineralisation is observed.