Relation entre les sols de la région manganésifère de Moanda (Gabon, Afrique de l'Ouest) et les terrils pisolitiques issus de l'activité minière

National audienc

Multicellular Consortia Preserved in Biogenic Ductile-Plastic Nodules of Okondja Basin (Gabon) by 2.1 Ga

International audienc

Application of in situ-produced cosmogenic 10 Be and 26 Al to the study of lateritic soil development in tropical forest : theory and examples from Cameroon and Gabon

Depth profiles of in situ-produced cosmogenic nuclides, including 10 Be (T1/2 = 1.5X10(exp 6) years) and 26 Al (T1/2 = 0.73X10(exp 6) years), in the upper few meters of the Earth's crust may be used to study surficial processes, quantifying denudation and burial rates and elucidating mechanisms involved in landform evolution and soil formations. In this paper, we discuss the fundamentals of the method and apply it to two lateritic sequences located in African tropical forests. (Résumé d'auteur

An Akouemma hemisphaeria Organic Macrofossils Colony Hosting Biodiversity Assemblage on the Seafloor of Okondja Basin (Gabon) dated at 2.2 Ga

International audienc

Petrogenesis of the ~2.77 Ga Monts de Cristal Complex, Gabon: Evidence for Direct Precipitation of Pt-arsenides from Basaltic Magma

The Monts de Cristal Complex of Gabon consists of several igneous bodies interpreted to be remnants of a tectonically dismembered, >100 km long and 1–3 km wide, ultramafic–mafic intrusion emplaced at 2765–2775 Ma. It is the most significant mafic–ultramafic layered complex yet identified on the Congo Craton. The complex consists largely of orthopyroxenite cumulates, with less abundant olivine-orthopyroxenite and norite, and rare harzburgite and dunite. Mineral compositions (Fo ol 84, Mg# Opx 85, An plag 60–68, Cr/Fe chromite 1–1·45) and whole-rock data suggest that the parent magma was a low-Ti basalt containing approximately 10% MgO and 0·5% TiO2. Trace element and Rb–Sr and Sm–Nd isotope data indicate the presence of an enriched component, possibly derived from crustal contamination of a magma generated in the sub-lithospheric mantle. Most rocks show a highly unusual pattern of strong Pt enrichment (10–150 ppb) at low concentrations of Pd (1–15 ppb), Au (1–2 ppb), Cu (1–20 ppm), and S (<500 ppm), suggesting that unlike in most other PGE-rich intrusions globally, platinum in the Monts de Cristal Complex is not hosted in magmatic sulfides. Synchrotron X-ray fluorescence mapping has revealed the location of buried small Pt particles, most of which are associated with As. We propose that this constitutes some of the strongest evidence yet in support of magmatic crystallization of a Pt–As phase from S-undersaturated magma