Alexis Ndongo PhD thesis

canyon Sedimentological and tectonic setting of paleoproterozic Franceville basin (Gabon) : fluid pressure structures, bitumen and uranium deposits

Funding: Areva and Gabon government

Supervisors: Michel Guiraud, laboratoire Biogéosciences; Jean-Louis Feybesse, Areva NC Géoscience Groupe Technique  

Beginning of the thesis: november 2010

 

Abstract

série francevillienne Metallogenic deposits within paleproterozoic basins depend on generation and migration of fluids. The aim of this study is to provide a better understanding of tectonic, sedimentological and diagenetic setting of the uranium deposits in the Franceville basin and to characterize hydraulic fracturing impact on fluid migration processes in sandstone reservoirs.

Tectonic study define the N180-170° transfer faults, associated with Archean tectonic and the N110-120° longitudinal normal faults. These two fault directions split the Franceville basin into small sub-basins. The longitudinal normal faults are associated with footwall anticlines and hanging wall synclines. The uranium deposits of Franceville basin are located in footwall anticlines of longitudinal normal faults.

carte géologique Franceville Sedimentological analysis allows to describe four depositional environments: Fluvial (lower FA), deltaic (middle FA), tidal (upper FA), and open marine environments (FB). Facies distribution in the FA-FB transition promotes the establishment of permeability barriers. These latter are responsible of the increase in fluid pressure and of the formation of fluid pressure structures (dykes, stylolites, quartz veins), in footwall anticlines of longitudinal normal faults. Increase in fluid pressure allows the migration of uranium-fluids, and hydrocarbon from the deep basin to the footwall anticline. Hydraulic fracturing processes lead the precipitation of uranium mineralization, associated with bitumen, in microfractures.

 

affleurement stratigraphique Keywords

Franceville basin, paleoproterozoic, transfer faults, longitudinal normal faults, footwall anticlines, permeability barriers, fluid pressure structures, hydraulic fracturing, bitumen, uranium mineralization

 

PhD commitee

Michel Mbina, université des sciences du Gabon

Michel Guiraud, laboratoire Biogéosciences

Roger Soliva, université de Montpellier 2

Emmanuelle Vennin, laboratoire Biogéosciences