Mineral Associations In The Boussouma Post Birimian Mafic Dyke And Their Petrogenetic Significance (Burkina Faso, West-African Craton)

A systematic electron microprobe analysis, was carried out on constituent mineral phases (olivine, pyroxene, amphibole, plagioclase, micas, opaques) in dolerite, gabbro and pegmatitic suite associated with a mafic dyke of the Boussouma area in Burkina Faso, in order to characterize the magmatic and tectonic affinity of this intrusion. The compositions and microtextures of minerals and their paragenesis led the re- examination of the magmatic origin of this dyke. The mineralogical sequence made up of ferriferous olivine, calcic- plagioclase, orthopyroxene, augite, quartz/ micropegmatite and titano-magnetite, indicates a tholeiitic composition of the parent magma of the dyke. The composition of clinopyroxenes is in agreement with tholeiitic character of this mafic dyke and typical of rocks formed by anorogenic processes in a crustal distension zone. Enrichment in quartz/ micropegmatite and in ferro- titanic oxides from the edge to the centre of the dyke and the corresponding impoverishment of olivine, are compatible with a magmatic fractionation process. The temperature of the magma during crystallization using coexistent augite and orthopyroxene geothermometry, is estimated between 1000 and 1150°C and it progressively decreased to about 600 to 800°C, during the late crystallization stages as revealed by biotite thermometry. The post magmatic evolution of the dyke is marked by the neoformation hydrothermal minerals of dominantly low temperature hydrous phases Keywords: Dolerite, micro-analysis, minerals, tholeiite, distension, geothermometry.Global Journal of Geological Sciences Vol. 6 (2) 2008: pp. 157-17

Origine du complex gneissique Paleoproterozoique du domiane Baoule Mossi de la region de Kaya, Burkina Faso

(Origin of the Paleoproterozoic gneiss complex of the Baoule Mossi shield, Kaya region, Burkina Faso

Geochemical Affinity And Geotectonic Setting Of Palaeoproterozoic Amphibolites Within Granitic -Gneissic Basement Of The South Central Area Of Burkina Faso, West- Africa

The south central part of the basement of Burkina Faso which lies within the west African craton, comprises of granitic- gneissic complex in close association with lenticular masses of amphibolites possibly of Archaean age. Petrographic analysis indicates that these rocks were products of contact metamorphism of early basic volcanic rocks induced by surrounding Eburnean granite intrusions. Their geochemical features are consistent with oceanic low K tholeiite, emplaced within a back- arc basin basalts (BABB) setting during Eburnean orogeny (2200-2000 Ma). Field and radiometric data (Pb/Pb, Rb/Sr) suggest that amphibolites (2180+- 90 Ma) are older than calc-alkaline granitic plutons and dykes (2007+-39, 1935+-27 Ma), both units being of Palaeoproterozoic age. Keywords: Burkina Faso, amphibolites, tholeiite, Back- arc basin basalts, PalaeoproterozoicGlobal Journal of Geological Sciences Vol. 6 (1) 2008: pp. 9-2

Les anomalies geochimique (Pb-Zn-Cu) du district metallogenique de la Region de Gaoua, ceinture Birimienne de poura, Burkina Faso

(Geochemical anomalies of lead-zinc-copper (Pb-Zn-Cu) in the metallogenetic district of Gaoua region, Birimian Poura greenstone belt, Burkina Faso

Distribution des filons de dolérite d’après les interprétations géologiques de données aéromagnétiques et leur signification géodynamique (Burkina Faso, Craton ouest africain)

Les fractures et filons de dolérite forment au Burkina Faso d’après leurs signatures aéromagnétiques, un réseau tectonique dense affectant les ceintures de roches vertes birimiennes et les granitoïdes paléoprotérozoïques associés ainsi que leur couverture sédimentaire néoprotérozoïque à paléozoïque. L’analyse statistique de ces signatures met en évidence à travers les diagrammes de rose, trois directions majeures, WNW-ESE, ENE- WSW, NE-SW pour les filons de dolérite, les deux dernières coincidant avec les principales orientations des fractures. Les filons méridiens sont moins fréquents que les fractures d’orientation équivalente. Les orientations NE-SW sont majoritairement associées aux filons de la couverture sédimentaire et marquent la déformation régionale des ceintures birimiennes, ce qui suppose un possible remplissage de magma doléritique des fractures post éburnéennes probablement réactivées au cours d’épisodes tectoniques ultérieurs. Les rares données radiométriques (K/Ar) de sills de la couverture sédimentaire (250 ± 13Ma) et de dykes injectés dans le socle birimien (1814 Ma), suggèrent leur mise en place au cours de deux venues doléritiques majeures en relation d’une part, avec les distensions tardi à post- éburnéennes et d’autre part avec le pré- rifting océanique atlantique. Les corrélations pétrologiques avec les systèmes filoniens de la sous région Ouest africaine, n’excluent pas que les événements distensifs kibariens au mésoprotérozoïque et éventuellement néoprotérozoïque ou pré-panafricain soient marqués par des émissions doléritiques au Burkina Faso, à l’instar du Craton Ouest-Africai

Permeability to water of sintered clay ceramics

International audienceThe microstructural characteristics of sintered clay ceramics depend mainly on the clay type and thermal transformations. Different pore morphology and connectivity change the liquid water flow process through the material, as in the case of roof tiles which are progressively saturated with water during rain. In this study, 2 clays mined in Burkina Faso are used for manufacturing roof tiles. The major phases detected by X-ray diffraction in the two clays are kaolinite, illite, smectite, quartz and feldspar. The thermal behavior of clays by DTA and TG between 25 °C and 1100 °C is mainly related to individual roles of clay minerals. During sintering, dilatometry curves show successive densification stages in variable temperature ranges, as a function of clay mineral fractions in compositions. It explains differences in microstrutural characteristics and pore structure. The simulation of the capillary absorption of water uses the Sharp Front model. The interesting feature of this approach is that measurement of the data for the model requires no complex equipment. Only the Darcy permeability of the material and the steady state capillary pressure are necessary. Results evidence the strong difference of water absorption rates in the 2 clay ceramics, whereas they present similar porosity. It confirms the importance of pore morphology and connectivity in ceramics, induced mostly by the clay type and the sintering process

Permeability to water of sintered clay ceramics

International audienceThe microstructural characteristics of sintered clay ceramics depend mainly on the clay type and thermal transformations. Different pore morphology and connectivity change the liquid water flow process through the material, as in the case of roof tiles which are progressively saturated with water during rain. In this study, 2 clays mined in Burkina Faso are used for manufacturing roof tiles. The major phases detected by X-ray diffraction in the two clays are kaolinite, illite, smectite, quartz and feldspar. The thermal behavior of clays by DTA and TG between 25 °C and 1100 °C is mainly related to individual roles of clay minerals. During sintering, dilatometry curves show successive densification stages in variable temperature ranges, as a function of clay mineral fractions in compositions. It explains differences in microstrutural characteristics and pore structure. The simulation of the capillary absorption of water uses the Sharp Front model. The interesting feature of this approach is that measurement of the data for the model requires no complex equipment. Only the Darcy permeability of the material and the steady state capillary pressure are necessary. Results evidence the strong difference of water absorption rates in the 2 clay ceramics, whereas they present similar porosity. It confirms the importance of pore morphology and connectivity in ceramics, induced mostly by the clay type and the sintering process