Abstract Paleoproterozoic (Rhyacian) gold deposits of the Loulo district in western Mali contain >17 million ounces (Moz) Au and form part of the second most highly endowed region within West Africa. The deposits are located within siliciclastic, marble, and evaporitic rocks of the ca. 2110 Ma greenschist facies Kofi series, which were folded and inverted between ca. 2100 and 2070 Ma, prior to gold mineralization. Deposits at Yalea and Gounkoto are located along discontinuous, low-displacement, albite- and carbonate-altered shear zones, whereas Gara is confined to a tourmaline-altered quartz sandstone unit. Lodes typically plunge gently to moderately, reflecting the attitude of folds in the adjacent rocks and bends in the host shear zones, both of which influenced their location. Gold mineralization in the Loulo district was broadly synchronous with emplacement of the Falémé batholith and associated Fe skarn mineralization, which intrude and overprint the western margin of the Kofi series, respectively. However, hydrothermal fluids generated during metamorphic devolatilization of the Kofi series rocks appear responsible for gold mineralization, albeit within a district-wide thermal gradient associated with emplacement of the Falémé batholith. The regional-scale Senegal-Mali shear zone, commonly cited as an important control on the location of gold deposits in western Mali, is absent in the Loulo district.

Abstract The Taoudenni Basin, North Africa's largest sedimentary basin, is located in western Mauritania, northern Mali and southwestern Algeria. Of the four petroleum wildcat wells drilled to date, the Abolag-1 well, Mauritania, yielded gas shows in Infracambrian (Neoproterozoic) stromatolitic carbonates. We present details of the different plays of the basin from the Chenachène region in Algeria. The Infracambrian is generally composed of three sedimentary packages: a basal sandstone (a unit of the Douik Group), overlain by carbonates (the Hank Group), sandstones and shales (the Dar Echeikh Group). The play is sourced by Infracambrian organic-rich black shales. In neighbouring Mauritania these were penetrated by water wells and shallow boreholes, containing in places >20% TOC. In the Hank Group the best reservoirs are associated with fractured intervals. The Dar Echeikh Group includes several potential reservoir units with porosities of up to 26%. Potential petroleum trap types in the Algerian part of the Taoudenni Basin are associated with folds, the basal Palaeozoic unconformity, and Infracambrian and Triassic–Jurassic half-graben.

Abstract This paper presents a reconstruction of the palaeodrainage evolution of the Niger River in West Africa in order to contribute to the understanding of sediment supply to the Niger Delta. It has been covered extensively in literature that the Niger River has undergone changes along its course in the Holocene, as implied by the large bend it makes in Mali. However, other enigmatic bends further downstream are indicative of an older and more complicated history that has yet to be understood, and is the focus of this paper. Until now, sediment supply from the Niger River has been considered as being negligible compared to that of the Benue River. The results of this study imply that the contribution from the Niger River was more important than previously thought. The Niger River obtained its present-day geometry in three phases: a Bida Basin phase (Maastrichtian–Miocene); a Iullemmeden Basin phase (Miocene–Pleistocene); and a present-day Niger River phase (Holocene). In the Miocene, an important capture event occurred, increasing the incipient drainage basin by 10 6 km 2 , thereby changing the provenance of the sediment supplied to the Niger Delta from mainly crystalline basement to mixed lithologies including sandstone, shale, limestone and volcanic outcrops.