Abstract The Eglab shield is the easternmost part of the Reguibat rise, which belongs to the West African craton (WAC). It corresponds to the amalgamation of the Yetti and Eglab Palaeoproterozoic domains. These domains are separated by a mega-shear zone called the ‘Yetti–Eglab Junction’ where fieldwork has led to the discovery of kimberlite indicator minerals but no diamond. In the southwestern part of this zone, an outcrop of Archaean basement and a komatiitic–picritic dyke had been recognized. Within the Eglab shield, deep-seated lithospheric faults control emplacement of alkaline complexes, and of small circular structures made up of mafic, ultramafic and silica-undersaturated rocks. These structural zones are characterized by widespread development of dyke swarms and repeated reactivations of earlier Eburnean trends from the Neoproterozoic to Mesozoic. Accordingly, they are sites of high magmatic permeability and crustal weakness. In this study, we summarize all known earlier and newly obtained structural, geophysical, geological and geochemical data on this area. They indicate that the ‘Yetti–Eglab Junction’ has good possibilities for the finding of kimberlite or/and other diamondiferous rocks. The features of the Eglab shield provide a possible explanation for the enigmatic sources of the diamond-bearing Reggane placer deposit located at the boundary of the WAC.

Abstract From 1920 to 1990, these brave geologists travelled through the Sahara from Mauritania to Libya and from Algeria to Niger. During these hikes across thousands of kilometres, often in very difficult conditions, they were able to trace the main features of the geology of these desert regions, they established stratigraphical sections of the main sedimentary provinces, discovered volcanic and eruptive complexes and drew geological maps of large areas. Today, helicopters, four-wheel-drive vehicles, satellite observations and global positioning systems allow people to visit the most remote regions of the Sahara safely; however, geologists, naturalists and explorers like Chudeau, Kilian, De Lapparent, Monod made the most of their observations and discoveries thanks two essential auxiliaries: the camel and the goatskin bottle. The portraits and the principal contributions to the geology of the Sahara of these four pioneers are presented here with maps of their itineraries.

Abstract Théodore Monod (1902–2000), of the Muséum National d'Histoire Naturelle in Paris, was a natural scientist with an extraordinarily wide range of interests and expertise. His early researches were chiefly in marine zoology, which he continued to pursue throughout his career. However, in 1923 he began to work in the Sahara Desert and travelled through it for thousands of kilometres on foot and camel-back collecting samples for the museum and keeping detailed journals of the geology, palaeontology, flora, fauna, prehistoric artefacts, and the customs and cultures of the peoples he met. Monod published nearly 700 technical articles in scientific journals and numerous books for general readers. He won innumerable honours in France and internationally, but only one of his books, few of his articles, and no biographical accounts of Monod's activities have been published in English. This paper focuses on his search for the Fer de Dieu , an iron meteorite said to be 40 metres high and 100 metres long, lying in the desert of Mauritania. He found no trace of it, but the meteorite remains legendary in the history of meteoritics.

Abstract The NW sector of Mauritania represents the Archaean province of the Reguibat Shield. It is mainly composed of the typical Archaean cratonic association of granitoid gneisses, greenstone belts and granites. The greenstone belts contain high mineral potential, mainly gold. This is particularly the case of the Chami Greenstone Belt, which hosts the large Tasiast gold mine. The gold deposits are hosted along a NS oriented shear zone with a surface of 70 × 15 km 2 . In this study, a subsurface structural model is proposed based on the application of suitable computations on a high-resolution reduced-to-the-pole aeromagnetic anomaly map of the northern Chami area. Upward continuations, apparent magnetic susceptibility, directional derivatives, analytical signal, 3D Euler deconvolution and spectral analyses were performed to build this model. They were used to decipher the main evidenced structural features with the main NNE–SSW, NW–SE and ∼120° N directions, identified on most all computed maps combined with in situ measurements. They probably correspond to mafic dykes, faults and shears rooted up to 5 km in depth, particularly to the north, SW and NE, and southwards and westwards by spectral analyses and 3D Euler deconvolution, respectively. The basement is deeper towards the west and south and crops out towards the NE in agreement with the geological observations. In addition, the high values of magnetic susceptibility (χ m ) measured in situ on banded iron formations (25.7–35 × 10 −3 SI) SW of Akjoujt could be the origin of metallotect sources associated with magnetic minerals for exploration of gold-bearing and base metals.

Abstract The West African craton is fringed along its western side by a 3000 km long orogenic belt subdivided into three separate orogens: the Bassaride (Pan-African I orogeny), Rokelide (Pan-African II orogeny) and Mauritanide (Hercynian orogeny) thrust belts. The Bassarides are cut to the north by the Mauritanides and to the south by the Rokelides but parts of this Bassaride belt are incorporated in the other two younger belts. This review presents the main geological, geophysical and geochronological results from the western side of the West African craton, collected over the past 90 years, concentrating on those from the last 15 years. Former geological investigations underlined the thin-skinned structure model within these thrust belts, whereas the geophysical results gave prominence to the major importance of block faulting resulting from the Pan-African I orogeny and its strong influence on the subsequent orogenic belt features. The geochronological data allow us to distinguish major tectonothermal events related to the Pan-African I (660–650 Ma), Pan-African II (550–530 Ma) and Hercynian (330–300 Ma and 280–270 Ma) orogenies. However, they also reveal five other tectonothermal events (at 1200–1000, 750–700, 600–580, 510–480 and 450–380 Ma), which are still very poorly understood. The 1200–1000 Ma tectonothermal event recently revealed in the northern Mauritanides may correspond to a remanent orogenic belt segment that witnessed the Grenvillian orogeny.

Abstract Proven Infracambrian hydrocarbon plays occur in various parts of the world, including Oman, the former Soviet Union, India, Pakistan and Australia. Organic-rich strata also occur in NW Africa, and gas shows originating from Infracambrian hydrocarbon source rocks are known from well Abolag-1 in the Mauritanian part of the Taoudenni Basin. The distribution of Infracambrian source rocks in North Africa is patchy and deposition commonly occurred in half-graben and pull-apart basins. In these intra-shelf basins, marine, organic-rich shales and limestones were deposited beneath the turbulent wave zone, away from the coarse siliciclastic Pan-African molasse detritus. On the West African Craton (including the Taoudenni Basin) organic-rich horizons were also deposited earlier, in pre- and syn-Pan-African times between 0.5 and 2 Ga (Ga is 10 9 years). The long-lasting sedimentation history in this area contrasts with that of the Pan-African regions, such as Oman, which lies in the Pan-African province of the East African Orogen, where preserved sediments are rarely older than 640 Ma. Infracambrian black phyllites in the Anti-Atlas region of Morocco were deposited on a continental slope of a short-lived ocean lying to the north of the West African Craton. Hydrocarbons generated during Infracambrian times from these deposits, however, have a low preservation potential. Infracambrian organic-rich and/or black-pyritic deposits in North Africa are proven in the Taoudenni Basin, the Anti-Atlas and the Ahnet Basin. Thick carbonate successions exist in the Taoudenni Basin, indicating deposition in areas some distance from contaminating coarse siliciclastic hinterland influx. Infracambrian strata may also occur in the Tindouf Basin. However, their deep burial and consequent early maturation history may be unfavourable for the preservation of Infracambrian-sourced hydrocarbons in this area. Local development of Infracambrian source facies may also occur in the Reggane, Ahnet, Mouydir and Iullemeden basins, as indicated by black shales in wells MKRN-1 and MKRS-1 in the Ahnet Basin. Generally, however, these basins appear to be close to the active Pan-African orogenic belt and, consequently, probably received large quantities of coarse siliciclastic sediment, largely of continental facies, which may have diluted any significant hydrocarbon source potential.