by Joel Simon Mbai, Akumbom Vishiti, Bravo Martin Mbang Bonda, Gilbert François NGON NGON, Elie Constantin Bayiga, Martine Gérard and Jacques Etamè
Original Research
The lolodorf syenite axis is known for its radiometric indices. In the Ngombas area the migration and retention of uranium in the regolith developed on syenite is studied using a combination of mineralogy and geochemistry in a bid to understand the processes involved in the dissolution and redistribution of uranium in the secondary environment. A trench dug in the area shows three horizons from the bottom to the top. They include the saprolite, B and Ah horizons. Petrographic and XRD investigations of the syenites reveals minerals such as plagioclase, potassic feldspar, amphibole, pyroxene, biotite, quartz, hematite, zircon coupled with uraninite, U-monazite. The regolith developed on the syenite shows relics of plagioclase, amphibole, quartz, hematite, goethite, chlorite, vermiculite, kaolinite. This is associated with U-bearing minerals such as uranothorite, U-monazite, U-zircon, U-florencite and U-rhadophane. The chemical alteration index (CIA), and gain and loss diagrams indicate that the horizons are more weathered from the top to the bottom. The presence of uranium bearing phases such as uranothorite indicates that U-minerals were dissolved, migrated and sorbed on thorite. The occurrences of U-florencite and U-rhabdophane in the weathering blanket indicate that uranyl is stabilized by phosphate minerals. Under oxidizing conditions the stability of hexavalent uranium is favored by the presence of clay minerals and Fe/Mn-oxyhydroxides. Thus, the migration of uranium in Ngombas is sequestrated by clay blended on Fe-oxides through the process of sorption. The U-bearing phases in the regolith that survived weathering include monazite and zircon. The presence of accessories minerals (U-zircon, U-monazite), sorption of uranium by phosphates, by Fe/Mn-oxyhydroxides, and clays minerals play important roles to reduce the U migration in environmental impact of Ngombas region.
Journal of Geosciences and Geomatics. 2022, 10(2), 99-111. DOI: 10.12691/jgg-10-2-4
Pub. Date: May 23, 2022
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by Michèle Vanessa Bomolomo, Ivan Emmanuel Fotsing Mouafo, Christian Bouba Mana, Boris Gouott Bekonga Secke, Prisca-Gaëlle Bien à Nwos and François Ndong Bidzang
Original Research
The samples used in this study were collected in the Mayo Kebbi region (western Chad). From a geological point of view, the Mayo Kebbi is a region with great potential. A lot of work has been done in this part of Chad. The aim of this study is to determine the proportions and types of minerals present in the <2µm fraction of the study area, their physico-chemio-mineralogical properties, their origin and the paleoenvironmental conditions that prevailed during their formation. Mineralogical analyses carried out on bulk rock and the positive hydrochloric acid test revealed that the fresh rocks of the two profiles studied are limestones. X-ray diffractometric analysis combined with ethylene glycol treatments and heating performed on the <2µm fraction of the collected materials, reveal the presence of smectitic type clay. The results obtained from these analyses reveal that smectite is the major mineral in these materials, with contents varying between 63 and 98%. It is associated with very low proportions of kaolinite (1 to 30%), illite (1 to 2%), and chlorite (1 to 5%). Quartz is the only non-clay accessory mineral identified. Geochemistry of these samples revealed that they consist primarily of SiO2 (1.3-78.67 wt. %), CaO (50.81-0.3 wt. %), Al2O3 (18.25-0.37 wt. %), and Fe2O3 (0.09-6.52 wt. %). The pH is slightly alkaline for these materials. The CEC (Cation Exchange Capacity) and exchangeable bases oscillate between 9.23-13.95 and 6.4-10.53 meq/100 respectively. The saturation indice is between 6 and 24 and the residual moisture values between 1.94 and 10.99%. These mineralogical and physico-chemical properties of these clay-rich Mayo Kebbi’s materials indicate that they can be used in many conventional clay applications. Furthermore, the findings of the geochemistry, the mineralogy of the bulk and <2µm fractions, added to the consideration of some geological parameters suggest that the smectites of the Mayo Kebbi's area, in Western Chad, have a dual origin. One part of these smectites is formed during partial hydrolysis and erosion of the formations located on the slopes near the mayo. The second part is formed in situ. Moreover, the results also suggested that the smectites in the study area were formed in an area with low topography and in which the dominant alteration is bisiallitization.
Journal of Geosciences and Geomatics. 2022, 10(2), 89-98. DOI: 10.12691/jgg-10-2-3
Pub. Date: May 12, 2022
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by Mana Bouba Christian, Ismaïla Ahmadou, Ipan Antoinette Solange, Issac Bertrand Gbambie Mbowou, Yingyang Wanbitching Raoul, Sep Nlonngan Jean Paul, Dili-Rake Jacques, Bomolomo Michel Vanessa, Safianou Ousmanou and Bello Bienvenue
Original Research
A petrographic and a structural study of the Gounbela region (Adamawa-Yadé) basement have been made. This included a macroscopic and a microscopic approach. The lithology is made up of biotite-amphibole gneisses and amphibolites (belonging to the amphibolite facies); of biotite-muscovite and pink granites with a porphiryc granular texture showing a syn-to late tectonic character of rocks. The Gounbela tectonic present four deformational phases; D1, D2, D3, D4. D1 is materialized by the S1 foliation; D2 is marked by the S2 schistosity resulting from the tranposition of S1 foliation. D3 is charasterized by F3 folds and C3 shear planes. The D4 deformational phase is made up of veins and faults. The major faults directions N130-N140 are similar to those belonging to the Lamé cretaceous Serie in Tchad, suggesting that they may have been occurred during the Atlantic opening.
Journal of Geosciences and Geomatics. 2022, 10(2), 81-88. DOI: 10.12691/jgg-10-2-2
Pub. Date: May 08, 2022
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by Ismaila Ahmadou, Mana Bouba Christian, Ipan Antoinette Solange, Aboubakar Abdoulaye Sahabo, Sep Nlonngan Jean Paul, Yinyang Wanbitching Raoul, Mohamadou Sali and Tchameni Rigobert
Original Research
The Biboko locality is located eastward in the central domain of the Pan-African Fold Belt of Central Africa. The task consisted in the cartography of the various types of rocks, to do their petrographic and structural studies with the aim of understanding the geological context of gold which is be exploited in the locality. Weal so brought out the study of environmental impact generated by this exploitation. The main types of rock identified in the locality could be grouped in to two: the metamorphic and plutonic rocks and their associate intrusion. The metamorphic rocks are represented by amphibole-biotite orthogneisses and amphibolites. Their main blade texture is granonematoblastic. The primary assemblage is made up of amphibole, biotite, plagioclase, quartz, zircon and apatite which are in equilibrium in the amphibolite facies. The secondary assemblage is made up of quartz, biotite, chlorite, pyrite, sericites derived from either the alteration or the recristallization of the primary assemblage. The plutonic rocks are slightly deformed and are represented by biotite bearing tonalite, microcline bearing granite, biotite bearing granite, biotite-epidote granite. These rocks have grained-oriented texture made up of quartz + microcline + orthose + plagioclase +/- biotite + accessory minerals. Concerning the structural study of the area, we have four deformationals phases. The first phase D1 is caracterized by subhorizontal shistosity/ foliation. The second phase D2, caracterised by open folds P2, shistosity S2, subvertical to vertical and slightly plonge lineation L2. It is a transpressive deformation with senestral sheared plans. The migmatisation which is the origin of certain plutonic rocks is syn-D1 to syn-D2. The third phase which is not penetrative, is made of folds P3 with straight axes and crenulation S3. The fourth phase is brittle-like and characterized by fractures. The abondances in secondary minerals (microcline, pyrite, chlorite, sericite) in certain facies (microcline bearing granite) is a proof for hydrothermalism. Part of gold found at Biboko could have been derive from altered rocks in the region. This is proved by the presence quartz in intrusion slightly mineralised in pyrite which is associate mineral of gold.
Journal of Geosciences and Geomatics. 2022, 10(2), 74-80. DOI: 10.12691/jgg-10-2-1
Pub. Date: April 26, 2022
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