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Depositional age and tectonic environment of the Gouap banded iron formations from the Nyong group,SW Cameroon:Insights from isotopic,geochemical and geochronological studies of drillcore samples

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Geoscience Frontiers 2021年第2期12卷 549-572页

作者： Landry Soh Tamehe Chongtao Wei Sylvestre Ganno Carlos Alberto Rosiere Jean Paul Nzenti chesther gatse ebotehouna Guanwen Lu Key Laboratory of CBM Resources and Reservoir Formation Process Chinese Ministry of EducationChina University of Mining and TechnologyXuzhouJiangsu221116China Department of Earth Sciences University of Yaounde IP.O.Box 812YaoundeCameroon Department of Geology Universidade Federal de Minas Gerais31270-901Belo HorizonteMinas GeraisBrazil School of Civil and Environmental Engineering University of Science and Technology BeijingBeijing 100083China

The discovery of the Gouap banded iron formations(BIFs)-hosted iron mineralization in the northwestern of the Nyong Group(Ntem Complex)in southwestern Cameroon provides unique insights into the geology of this *** this contribution,we firstly report detailed study of geochemistry,isotopic and geochronology of well preserved samples of the Gouap BIFs collected from diamond *** Gouap BIFs consist mainly of amphibole BIFs and amphibole-pyrite BIFs characterized by dominant Fe_(2)O_(3)+SiO_(2)contents and variable contents of CaO,MgO and SO_(3),consistent with the presence of amphibole,chlorite,epidote and pyrite,formed during amphibolite facies metamorphism and overprinted hydrothermal *** amphibole–pyrite BIFs are typically enriched in trace and rare earth elements(REE)compared to the amphibole BIFs,suggesting the influence of detrital materials as well as secondary hydrothermal *** Post Archean Australian Shale(PAAS)-normalized REE–Y profiles of the Gouap BIFs display positive La,Eu anomalies,weak negative Ce anomalies,indicating a mixture of low-temperature hydrothermal fluids and relatively oxic conditions probably under relative shallow *** present here the first isotopic data of BIFs within the Ntem ***δ^(30)Si_(NBS28)values of the quartz from the Gouap BIFs vary from-1.5‰to-0.3‰and from-0.8‰to-0.9‰for the amphibole BIFs and amphibole–pyrite BIFs,*** quartz hasδ^(18)OV-SMOW values of 6.8‰–9.5‰(amphibole BIFs)and 9.2‰–10.6‰(amphibole–pyrite BIFs).The magnetite from the Gouap BIFs showsδ^(18)O values ranging from-3.5‰to-1.8‰and from-3‰to-1.7‰for the amphibole BIFs and amphibole–pyrite BIFs,***,the pyrite grains in the amphibole–pyrite BIFs displayδ34S values of 1.1‰–1.8‰.All isotopic data of the Gouap BIFs confirm that they might have precipitated from low-temperature hydrothermal fluids with detrital input distant from the volcanic *** to their geochemical and isotop

关键词： Gouap Banded iron formations Isotope geochemistry Zircon geochronology Ryacian period Brasiliano-Congo orogeny

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Hydrogeological Characterization and Approach to a Conceptual Model of the Aquifer of the Cuvette Basin, Republic of Congo

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International Journal of Geosciences 2022年第11期13卷 997-1023页

作者： Noida Janesia Lebela Mouakoumbat Urbain Mbilou Gampio Guy Moukandi Nkaya chesther Gatsé ebotehouna Armel Obami Ondon Romain Richard Niere National Polythecnic School Marien Ngouabi University Brazzaville Congo Department of Geology Faculties of Science and Technology Marien Ngouabi University Brazzaville Congo

The continuous aquifers of the Congolese Cuvette basin constitute the seat of significant water tables reversibly supplying the Congo River basin as well as the water tables they drain. Consisting mainly of sandy-clayey-sandstone formations, these aquifers contain groundwater which is the main source of drinking water supply for communities in this sector of the departments Cuvette and Cuvette-Ouest. The need for water being more and more acute, these aquifers have been subjected to drilling operations in order to supply drinking water to these populations. The information obtained from these operations is data which made it possible to obtain information relating to the lithology, the hydrogeological parameters of these aquifers and information on the depth and on the lateral variations of the water table. The purpose of this present work is to contribute to the hydrogeological characterization of the aquifer of the Cuvette basin in the departments of Cuvette and Cuvette-Ouest via data from the analysis of the technical sheets of drillings carried out by the ASPERBRAS Company, collected at the Ministry of Major Works and territory planning. This characterization was made using Visual MODFLOW Flex 2015.1 software coupled with Surfer 10 software and Rock Works 17 software. The hydrogeological interpretation of the data shows that this aquifer, whose constitution is essentially made up of sands, clayey sands and clay, is continuous, porous and free. This composition gives the aquifer of Cuvette basin a heterogeneous character. In addition, a piezometric map was produced in order to indicate the direction of the water flows which turned out to be from west to east towards the lowest areas occupied by the valleys of the rivers and rivers. The conceptual model shows that the depth of the aquifer deceases considerably from the Cuvette-Ouest towards the Cuvette.

关键词： Cuvette Basin Hydrogeology Aquifer Piezometric Map Conceptual Model

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