The Pan-African Province (PAP) of south Maradi (Niger) corresponds to the northeastern part of the Benin-Nigerian Shield, which is part of the Pan-African Mobile Belt, located to the East of the West African Craton. This study focuses on the microstructural study supported by geochronological data of the South Maradi Pan-African shear zones. The structural analysis of the Pan-African shear bands, combined with the previous radiometric data allowed to highlight a polyphase history of this northeastern part of the Benin-Nigerian Shield. Two major tectonic periods are highlighted: A ductile to brittle Pan-African deformation stage (D1) relayed by a brittle post-Pan-African deformation stage (D2). The first phase D1 consists of two episodes noted D1a and D1b: (1) the D1a episode was a ductile pan-African deformation stage with a strong coaxial component, which favoured the development of symmetric fabrics of foliation. The tectonic regime was characterized, first by a NW-SE (~N140°) trending pure-shear-dominated shortening episode, which prevailed between 617.9 ± 2.8 to 589 ± 1.9 Ma. Then during episode D1a, the shortening direction evolved gradually from NW-SE to ~E-W (N90°-N70°). This change of direction is due to the constraint coming from the Pan-African orogeny. The deformation had progressively a rotational component and this is how D1b episode began. This latter was characterized by a brittle-ductile deformation, associated with the formation of mylonitic gneiss and micaschist. So, the counter clockwise sinistral rotation of the shortening axis Z (from N140° to N90°- N70°) reveals a Pan-African continuum of deformation between D1a and D1b episode. (2). Subsequently, a stage of brittle deformation D2 affected all the previous structures. This D2 stage is marked by a continental-scale system of conjugated strike-slip faults, NE-SW and NW-SE trending. This investigation contribute to knowledge of Pan-African kinematic evolution of Benin-Nigerian Shield, particularly its northeastern part (South Maradi).

Le socle du Sud Maradi (Sud Niger) correspond à l’extrémité Nord du bouclier Bénino-Nigérian, appartenant à la zone mobile panafricaine à l’Est du Craton Ouest-Africain. Cette étude apporte une modeste contribution dans la caractérisation géochimique des minéralisations aurifères de cette province métallogénique panafricaine. A cet effet, l’approche méthodologique mise en oeuvre associe le dosage géochimique de l’or par absorption atomique (Au Fire Assay/AA) pour les roches saines, et la séparation des pépites d’or par l’utilisation de la table à secousse pour les altérites du socle et les sédiments (placers et paléoplacers). Les analyses géochimiques ont mis en évidence l’existence de deux types de minéralisations: primaires et secondaires. Les minéralisations primaires de l’or sont à l’état disséminé (faibles teneurs de 0.005 à 0.017 g/t) mais des teneurs relativement plus élevées (0.006 à 0.017 g/t) ont été enregistrées au voisinage des zones de cisaillement du socle. Tandis que la minéralisation secondaire, mise en évidence dans les altérites du socle, dans les alluvions (placers) et dans les grès du Crétacé (paléoplacers) présentent des teneurs en or plus élevées (5 à 30 g/t), dépassant largement les teneurs des minéralisations primaires observées dans les roches saines du socle. Ce grand écart de teneurs s’explique par un fort lessivage du socle, qui aurait permis une reconcentration de l’or dans les sédiments. The South Maradi (South Niger) basement corresponds to the northeastern part of the Benin-Nigerian Shield, belonging to the Pan-African mobile zone, which is located to the east of the West African Craton. This study brings a modest contribution to the geochemical characterization of gold mineralization in this Pan-African metallogenic province. For this purpose, the methodological approach implemented combines the geochemical determination of gold contents by atomic absorption (Au Fire Assay/AA) for basement rocks and physical separation of gold specks by using the vibrating table process for basement alterites and sediments (placers and paleoplacers). The obtained results showed two types of gold mineralization: primary and secondary. Primary gold mineralization is in a disseminated state (low contents of 0.005 to 0.017 g / t) but relatively the higher values (0.006 to 0.017 g / t) were recorded near the basement shear zones. While the secondary gold mineralization, highlighted in basement alterites, alluvium (placers) and Cretaceous sandstones (paleoplacers) present higher gold contents (5 to 30 g / t) than primary gold contents observed in basement rocks. This large difference in values can be explained by a strong alteration of the basement, which would have allowed a reconcentration of the gold in the sediments.

The survey zone corresponds to the Sirba greenstone belt, one of Liptako Birimian Formations (LBF) of Niger. Previous aeromagnetic and geochemical works reveal the significant gold occurrences. The present study integrates geophysical mapping of these occurrences by electromagnetic induction on field. A multi-frequencies system of 10 frequencies was used for depth and subsurface investigation of resistive anomalies. The interpretation of obtained results shown two types of resistive anomalies, corresponding to the conductive units: deep anomalies obtained with low frequencies and subsurface anomalies detected with high frequencies. The subsurface anomalies were detected around the 15 meters and the deep anomalies were recorded beyond 80 meters. All of the detected resistive anomalies are in a lenticulars shapes oriented N-S or E-W. The analysis of combined resistivity map from all frequencies shown three zones of resistive anomaly presenting a high potential in conductive metals: The first zone Z1 (most important), located in Eastern studied zone covering, covering a surface of 3.5 Km2, the second zone Z2 is located in West and covers an area of 2.9 Km2 and the third anomaly zone Z3 is located in South with a surface of 0.96 Km2. On field, these conductive units correspond to auriferous quartz veins and/or highly altered manganese schists, exploited by using the artisanal mining wells, up to 20 meters in depth.