U. Geymond1, V. Roche2&3 and I. Moretti2
1 IPGP, Paris, France
2 LFCR, UPPA, Pau, France
3 LPG, Le Mans Université, Le Mans, France
Recent works in Australia and Brazil showed that the Archean-Paleoproterozoic Banded Iron Formations (BIFs) could be one source of H2. Although the reaction is similar to the serpentinization (Fe2+ oxidation - H2O reduction process), the iron content may be higher than in mafic lithologies, thus generating more H2. Here, we present structural evidence that the Neoproterozoic BIFs – the Ghaub and Chuos Formations – underlie the Waterberg basin of Namibia where H2 emissions are reported (Moretti et al., 2022). The fairy circles are numerous in this basin. Density could be calculated and they could be highlighted by Vegetation Index anomalies. This remote sensing approach allows us to discriminate the H2 related features from other types of depressions such as Salt Pan.
We study in detail the Chuos Fm. and show that magnetite, a known H2 generating mineral (Geymond et al., 2023), is ubiquitous. Within the Chuos Formation, magnetite appears as pervasive coherent microbands in foliation and fractures planes and/or diffusely disseminated, independently of the metamorphism grade, thus implying that metamorphism does not affect negatively the Fe2+content required to generate hydrogen. H2 seepages in the Waterberg basin suggest that an active H2 generating system may exist at depth. Potential traps could be the compressive structures of the Damara belt and reservoirs of the carbonate between the two BIFs but subsurface data has to be acquired to confirm this hypothesis.
Cited biblio :
Geymond, U., T. Briolet, V. Combaudon, O. Sissmann, I. Martinez, M. Duttine, I. Moretti. 2023. Reassessing the role of magnetite during natural hydrogen generation. Frontiers in Earth Science. DOI 10.3389/feart.2023.1169356
Moretti, I., Geymond, U., Pasquet, G., Aimar, L., & Rabaute, A. (2022). Natural hydrogen emanations in Namibia: Field acquisition and vegetation indexes from multispectral satellite image analysis. International Journal of Hydrogen Energy, 47(84), 35588-35607. https://doi.org/10.1016/j.ijhydene.2022.08.135