Evaluation of Water Resources Quality in Sabodala Gold Mining Region and Its Surrounding Area (Senegal)

peer reviewedGeochemical and Geostatistical tools were used to assess: 1) the chemical quality and, geochemical processes in crystalline rock aquifers in Sabodala (Eastern Senegal) and its surroundings and 2) the impact of mining activities on their quality. A total of 26 water samples collected at boreholes, dug wells and stream, were analyzed to determine major and trace elements concentration focused on elements that represent more threats on human health. Boxplots define chemical characteristics of water for each aquifer formation compared to surface waters. Geostatistical analysis show two sources of water mineralization with regard to major elements: a first natural source characterized by Ca-Mg-HCO3 water type from boreholes and unpolluted surface water and a second group characterized by polluted water by nitrates with Na-NO3-Cl type mainly observed in upper weathered aquifers. However, considering trace element, geostatistical analysis showed three water groups: water with very low trace element concentrations encountered in boreholes and unpolluted surface waters, and waters with relatively high trace element concentrations such as Al observed in areas affected by gold mining activities and finally, polluted waters by Ni, Co, Mn and Cr observed at Sabodala. Results show that in eastern Senegal well waters are vulnerable and often affected by pollution

Contribution a l'etude de la serie birrimienne de Mako dans le secteur aurifere de Sabodala (Senegal oriental)

SIGLECNRS T 57885 / INIST-CNRS - Institut de l'Information Scientifique et TechniqueFRFranc

Tectonique et minéralisations aurifères dans les formations birimiennes de Frandi-Boboti, boutonnière de Kédougou-Kéniéba, Sénégal

Le secteur d étude comprend un ensemble sédimentaire de base (B1), recoupé par un complexe hypo-volcanique et volcanique (B2) puis par un complexe plutonique intrusif. Des sédiments détritiques et un volcanisme tardi- à post-birimien se mettent en place ultérieurement. Ces formations sont affectées par la tectonique éburnéenne comprenant trois phases: (1) D1 compressive affectant les sédiments du Birimien inférieur B1; (2) D2 comprenant trois stades: compression (D2a), transpression senestre (D2b) et chevauchement (D2c); (3) D3 transtensive dextre. La direction de contrainte principale de la déformation évolue en rotation anti-horaire entre les phases de déformation D1 et D3. Les différentes phases compressives sont séparées par des phases extensives avec émissions volcaniques et dépôts sédimentaires. Trois phases de minéralisations aurifères ont été identifiées. La première, ante-D1, souvent diffuse à stratiforme, est localisée dans les sédiments de l ensemble inférieur. La seconde, en relation avec l événement tectono-magmatique D2, donne un stockwerk silico-carbonaté et sulfuré localisé dans les fentes de tension, les veines V2 et les "shear zones". La troisième phase serait contrôlée par l événement tectono-magmatique D3 avec une paragenèse à quartz et pyrite dans les veines V3. Le fait que la minéralisation aurifère intervienne essentiellement dans les veines et les "shear zones" orientées ~N20 suggère qu une activité tectono-magmatique post-birimienne aurait exercé un rôle important dans la remobilisation de l or dans ces structures.The lithological setting of the study area consists of lower Birimian sedimentary rocks (B1), cross-cut both by a volcanic and subvolcanic complex (B2) and a plutonic intrusive complex. Late to post-Birimian silico-clastic sedimentary and volcanic rocks took place later. These Birimian rocks are affected by the Eburnean polyphased tectonics composed of the following phases: (1) D1 compression that affected the lower sedimentary formations B1; (2) D2 composed of three stages: D2a compression, D2b sinistral transpression and D2c thrusting; (3) D3 dextral transtension. An anti-clockwise rotation of the main stress direction is produced between D1 and D3 phases. These Eburnean tectonic phases are separated by extensional tectonic events associated with volcanic flows and sedimentary deposits. Three gold mineralization phases were identified. An ante-D1 primary phase, located in the sediments of the lower unit, is often disseminated and stratiform. The second phase, in relationship with D2 tectono-magmatic event, produces a silico-carbonated and sulphurized stockwerk, located in tension gashes, V2 veins and shear zones. The third phase would be associated to the late D3 tectono-magmatic event, with a paragenesis of quartz and pyrite, concentrated in the V3 veins. Mineralization is more frequent in the ~N20 oriented silico-carbonated veins and shear zones, suggesting that a post-Birimian tectono-magmatic event would have probably played an important role in the remobilisation of gold along these structures.RENNES1-BU Sciences Philo (352382102) / SudocSudocFranceF

Thrust to braiding transpression and transtension tectonics during the Paleoproterozoic evolution of the Birimian Greenstone Belt of Mako, Kédougou-Kéniéba Inlier, Eastern Senegal

International audienceThe structural cartography of the Birimian formations of the Mako area shows a polyphase deformation marked by variable structures such as imbricated shear zones, thrusts and reverse-shears, poly-foldings, “boudinages”, normal faults. The multiscale analysis of the various mapped structures combined with the satellite images allowed to distinguish three major phases of Eburnean deformations D1, D2 and D3. The D1 phase is compressive to thrust deformation due to SSE-NNW principal shortening direction which involves large overturned folds verging to the NW associated with minor thrust fault which are preserved in some lithologies (metabasalts, quartzites). The D2 phase is a sinistral transpressive deformation which comprises an early (D2a) stage followed by a late (D2b) stage. The early D2a stage is characterized by major NE-SW reverse-shears verging to the NW associated with NW-SE minor dextral shear zones. It is followed by D2b stage characterized by ENE-WSW shortening direction which creates major NNW-SSE sinistral reverse-shear zones. Interference between NE-SW and NNW-SSE major reverse-shear zone of D2a and D2b respectively creates an anatomizing pattern of the deformation. Shearing along D2 shear zone is associated with development of minor extensional zone which filled by varied magmatic products (mafic, intermediate and felsic). D3 phase is a transtension deformation associated with a dextral movement which creates conjugate normal faults with locally negative flower structures. D3 principal maximum stress is ENE-WSW oriented. The orientation of the main shortening direction of Eburnean phases D1, D3 and D3 is NNW-SSE, NW-SE and ENE-WSW, respectively. Such a pattern could be induced by an anticlockwise rotation of principal maximum stress in the Mako sector. The Eburnean granitoids emplaced before and during these three Eburnean orogenic phases

Thrust to braiding transpression and transtension tectonics during the Paleoproterozoic evolution of the Birimian Greenstone Belt of Mako, Kédougou-Kéniéba Inlier, Eastern Senegal

International audienceThe structural cartography of the Birimian formations of the Mako area shows a polyphase deformation marked by variable structures such as imbricated shear zones, thrusts and reverse-shears, poly-foldings, “boudinages”, normal faults. The multiscale analysis of the various mapped structures combined with the satellite images allowed to distinguish three major phases of Eburnean deformations D1, D2 and D3. The D1 phase is compressive to thrust deformation due to SSE-NNW principal shortening direction which involves large overturned folds verging to the NW associated with minor thrust fault which are preserved in some lithologies (metabasalts, quartzites). The D2 phase is a sinistral transpressive deformation which comprises an early (D2a) stage followed by a late (D2b) stage. The early D2a stage is characterized by major NE-SW reverse-shears verging to the NW associated with NW-SE minor dextral shear zones. It is followed by D2b stage characterized by ENE-WSW shortening direction which creates major NNW-SSE sinistral reverse-shear zones. Interference between NE-SW and NNW-SSE major reverse-shear zone of D2a and D2b respectively creates an anatomizing pattern of the deformation. Shearing along D2 shear zone is associated with development of minor extensional zone which filled by varied magmatic products (mafic, intermediate and felsic). D3 phase is a transtension deformation associated with a dextral movement which creates conjugate normal faults with locally negative flower structures. D3 principal maximum stress is ENE-WSW oriented. The orientation of the main shortening direction of Eburnean phases D1, D3 and D3 is NNW-SSE, NW-SE and ENE-WSW, respectively. Such a pattern could be induced by an anticlockwise rotation of principal maximum stress in the Mako sector. The Eburnean granitoids emplaced before and during these three Eburnean orogenic phases

Thrust to braiding transpression and transtension tectonics during the Paleoproterozoic evolution of the Birimian Greenstone Belt of Mako, Kédougou-Kéniéba Inlier, Eastern Senegal

International audienceThe structural cartography of the Birimian formations of the Mako area shows a polyphase deformation marked by variable structures such as imbricated shear zones, thrusts and reverse-shears, poly-foldings, “boudinages”, normal faults. The multiscale analysis of the various mapped structures combined with the satellite images allowed to distinguish three major phases of Eburnean deformations D1, D2 and D3. The D1 phase is compressive to thrust deformation due to SSE-NNW principal shortening direction which involves large overturned folds verging to the NW associated with minor thrust fault which are preserved in some lithologies (metabasalts, quartzites). The D2 phase is a sinistral transpressive deformation which comprises an early (D2a) stage followed by a late (D2b) stage. The early D2a stage is characterized by major NE-SW reverse-shears verging to the NW associated with NW-SE minor dextral shear zones. It is followed by D2b stage characterized by ENE-WSW shortening direction which creates major NNW-SSE sinistral reverse-shear zones. Interference between NE-SW and NNW-SSE major reverse-shear zone of D2a and D2b respectively creates an anatomizing pattern of the deformation. Shearing along D2 shear zone is associated with development of minor extensional zone which filled by varied magmatic products (mafic, intermediate and felsic). D3 phase is a transtension deformation associated with a dextral movement which creates conjugate normal faults with locally negative flower structures. D3 principal maximum stress is ENE-WSW oriented. The orientation of the main shortening direction of Eburnean phases D1, D3 and D3 is NNW-SSE, NW-SE and ENE-WSW, respectively. Such a pattern could be induced by an anticlockwise rotation of principal maximum stress in the Mako sector. The Eburnean granitoids emplaced before and during these three Eburnean orogenic phases

Lithological Architecture and Petrography of the Mako Birimian Greenstone Belt, Kédougou-Kéniéba Inlier, Eastern Senegal

International audienceThe new lithological and petrographic data obtained in the Mako sector are analyzed in the light of the geochemical data available in the literature. It consists of ultramaic, mafic rocks of tholeiitic affinities associated with intermediate and felsic rocks of calc-alkaline affinities and with intercalations of sedimentary rocks. The whole unit is intruded by Eburnean granitoids and affected by a greenschist to amphibolite facies metamorphism related to a high grade hydrothermalism. It consists of: (i) ultramafic rocks composed of a fractional crystallization succession of lherzolites, wehrlites and pyroxenites with mafic rock inclusions; (ii) layered, isotropic and pegmatitic metagabbros which gradually pass to metabasalts occur at the top; (iii) massive and in pillow metabasalts with locally tapered vesicles, completely or partially filled with quartzo-feldspathic minerals; (iv) quarzites locally overlying the mafic rocks and thus forming the top of the lower unit.This ultramafic-mafic lower unit presents a tholeiitic affinity near to the OIB or N-MORB. It represents the Mako Ophiolitic Complex (MOC), a lithospheric fragment of Birimian lithospheric crust.The upper unit is a mixed volcanic complex arranged in the tectonic corridors. From bottom to top it comprises the following: (i) andesitic, and (ii) rhyodacitic and rhyolitic lava flows and tuffs, respectively. They present a calc-alkaline affinity of the active margins.Three generations of Eburnean granitoids are recognized: (i) early (2215-2160 Ma); (ii) syn-tectonics (2150-2100 Ma) and post-tectonics (2090-2040 Ma). The lithological succession, geochemical and metamorphic characteristics of these units point to an ophiolitic supra-subduction zone

Diversity of the Palaeoproterozoic granitoids of the Kédougou inlier (eastern Sénégal): Petrographical and geochemical constraints

International audienceField, petrographical and geochemical studies of the Palaeoproterozoic granitoids of the Kédougou inlier (Eastern Sénégal) allow to define four compositional types: (i) the Layered Plutonic Complex consisting of sodic calc-alkaline granitoids defining a trend from Opx-, Cpx- and amphibole-bearing layered gabbros to amphibole-bearing tonalite; the latter shows similarities with adakite-like rocks; (ii) amphibole-bearing granitoids with TTG features occurring as composite batholiths and as isolated oval-shaped plutons cross cutting the entire Birimian metavolcanic and metasedimentary formations; (iii) potassic granitoids defining a trend from Opx-, Cpx-bearing gabbros to amphibole-bearing monzodiorite and preferentially emplaced within the calc-alkaline metavolcanites; (iv) peraluminous biotite-bearing granitoids emplaced within the metasediments of the upper part of the Birimian lithostratigraphical pile. The granitoid suites were emplaced within a time interval of about 80 Ma from about 2160 Ma (emplacement of the LPC) to 2080 Ma (emplacement of the youngest plutons such as the amphibole-bearing TTG granitoid or the pyroxene- and K-feldspar-bearing granitoids). The granitoid suites were emplaced in an immature arc environment [Dia, A., Van Schmus, W.R., Kröner, A., 1997. Isotopic constraints on the age and formation of a Palaeoproterozoic volcanic arc complex in the Kedougou inlier, eastern Senegal, West Africa. J. Afr. Earth Sci. 24 (3), 197 213]. Parental magmas were probably derived from the partial melting of a mantle wedge above a subduction zone. Tonalite magmas of distinctive composition were probably produced by partial melting of the subducting slab itself. They could characterize the early stage of the slab-melting, precursor of the TTG magmatism. The close association of calc-alkaline, trondhjemitic and peraluminous granitoids and the successive emplacement of granitoid groups more and more enriched in K2O recognized in the Kédougou inlier is typical of the Paleoproterozoic granitoid series from West Africa

Lithologie et contexte structural des formations néoprotérozoïques et paléozoïques des Mauritanides méridionales, région de Bakel, Sénégal oriental

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