Africa is a continent with great assets for Astrophysics and Planetology (including astrobiology): skies unpolluted with anthropogenic light, meteorites and impact structures, and vast sedimentary-metamorphic-igneous records of early Earth’ geologic evolution. Aware of these assets, a community of scientists is involved in increasingly ambitious projects. Their original works notably highlight the African scientific heritage, alongside engagement in economic, cultural and societal development. One of the notable achievements of this group is the observation of three stellar occultations by asteroids in Senegal, in direct support of NASA missions of exploration of the Solar System. The first campaign was achieved in August 2018, in support of the flyby of Kuiper belt object Arrokoth by the New Horizons spacecraft. The second and third campaigns, in September 2020 and October 2021, in preparation for the upcoming flybys of Trojan asteroids Polymele and Orus by NASA’s Lucy mission, were led by Senegalese scientists, supported by a few European astronomers. Other notable achievements include fieldwork at potential or known impact structures (including search of tektites in Côte d’Ivoire), providing opportunities for student training and local education. Members of our group have also launched the first popular science magazine on astronomy (in French) (l’Astronomie Afrique). Last, founding the RISE 5A project (Astronomy and Astrophysics Arising Across Africa), with proposal intended to be resubmitted to the Horizon Europe program in 2022, together with some joint educational initiatives linking Egypt and Spain, will hopefully open new opportunities for staff and students exchanges between Europe and Africa. These achievements also impart an enduring engagement of the youth, while reinforcing the role of West African scientists in the scientific, cultural, and economic development of their countries and communities worldwide.

The univariate statistics of potassium (K) and thorium (Th) concentrations in the oceanic and continental crust of the Earth has been recently investigated from geochemical databases and airborne radiometric surveys [1]. This study demonstrates that the frequency distributions of these elements are scale-dependent. There are right-skewed for small-scale samples (typical volume of rocks analyzed for an individual sample in a dataset) but tend to be more symmetric for large-scale samples. The right-skewed behavior of K and Th is attributed to their incompatible behavior during partial melting or fractional crystallization. The scale-dependence and evolution toward normal distributions are a direct consequence of the central limit theorem applied to K and Th concentrations. The results of the results of this study may be applied to Mars, using the Mars Odyssey global maps of K and Th concentrations [2]. In light of available K, Th concentrations at the rock-scale (in-situ samples and martian meteorites), we infer that each “pixel” of these maps reflect a right-skewed distribution of K and Th concentrations at smaller-scales, where K and Th-poor rocks, such as basalts, are spatially dominant. In turn, K, and Th-rich rocks, such as those found by Curiosity at Gale crater [3], may occur globally, though their spatial extension must be limited to account for the values reported by Mars Odyssey. The global, but sparse occurrence of K, Th-rich rocks at the surface is consistent with a buried felsic crust, outcropping at the favor of tectonic or impact events. These conclusions will be discussed in the context of the inferred constraints about the structure of the martian crust from Insight data [4]. [1] Baratoux, et al., Earth and Space Science, in press. [2] Boynton et al. JRGP, doi:10.1029/2007JE002887. [3] Sautter et al. doi:10.1038/NGEO2474. [4] Knapmeyer-Endrun et al., Science, doi: 10.1126/science.abf8966

The univariate statistics of Potassium (K), Thorium (Th) and Uranium (U) concentrations, in the Earth’s oceanic and continental crust are examined by different techniques. The frequency distributions of the concentrations of these elements in the oceanic crust are derived from a global catalog of mid-ocean ridge basalts (MORB). Their frequency distributions of concentrations in the continental crust are illustrated by the North Pilbara Craton, and the West Africa Craton. For these two cratons, the distributions of K, Th and U derived from geochemical analyses of several thousand whole rock samples differ significantly from those derived from airborne radiometric surveys. The distributions from airborne surveys tends to be more symmetric with smaller standard deviations than the right-skewed distributions inferred from whole rock geochemical analyses. Hypothetic causes of these differences include (i) bias in rock sampling or in airborne surveys, (ii) the differences in the chemistry of superficial material, and (iii) the differences in scales of measurements. The scale factor, viewed as consequence of the central limit theorem applied to K, Th and U concentrations, appears to account for most of the observed differences in the distributions of K, Th and U. It suggests that the three scales of auto-correlation of K, Th and U concentrations are of the same order of magnitude as the resolution of the airborne radiometric surveys (50 – 200 m) and concentrations of K, Th, U are therefore generally heterogenous at smaller scales.

The International Research Laboratory MINERWA (Responsible Mining, West-Africa) has for objective to contribute to the comprehension of the distribution of mineral resources in Ivory Coast, and to their responsible exploration and exploitation, which implies a thorough understanding of environmental and societal impacts. It is co-funded by the French National Research Institute for Sustainable Development (IRD) and by the African Center of Excellence “Mines and Mining Environment” hosted by the INP-HB (Institut National Polytechnique Félix Houphouët-Boigny) in Yamoussoukro, Ivory Coast. It also involves the University Felix Houphouët-Boigny (UFHB, Abidjan), and 4 laboratories in France (Geosciences Environment Toulouse, PRODIG, Hydrosciences Montpellier and Espace-DEV). MINERWA is also part of the world-wide network AMEDEE (Activity of Mining, Environment, Development, Economy, Ethics, https://amedee-network.science/en/), which is an international collaborative R&D platform whose goal is to promote responsible mining in subtropical and intertropical areas in partnership. The approach is interdisciplinary and the research team is composed of specialists in social and environmental sciences and geologists. The focus is placed on a multi-scale analysis, from atomic/mineral to the crustal scale through the scale of territories. It aims to reinforce the analytical capabilities in Ivory coast, with a focus on free remote sensing data and software and low-coast portable instruments for geochemical analysis of rocks and contaminants in the field, including portable XRF, portable LIBS, portable gamma-ray spectrometers and portable visible/NIR spectrometers. The research laboratory shall be funded for 5 years and was initiated in 2019. The activities are divided into 5 work packages, including (1) a platform for continuous exchanges between the different actors, (2) capacity building, (3) geology of mineral ressources, (4) mines, environment and societies, (5) scale transfer. Several preliminary research outcomes in the framework of this laboratory will be presented in the session, in particular in relation to the environmental impact of artisanal mining in West Africa [1,2,3]. [1] Abass Saley, A. et al. , this session. [2] Ngome, M. et al., this session. [3] DAÏ, B.S.M. et al., this session.