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2.5D Modelling of Aeromagnetic Data and Their Mining Implications Over the Ngaoundere Area (Adamawa Province, Cameroon)

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2.5D Modelling of Aeromagnetic Data and Their Mining Implications Over the Ngaoundere Area (Adamawa Province, Cameroon) International Journal of Geosciences, 2019, 10, 173-192 http://www.scirp.org/journal/ijg ISSN Online: 2156-8367 ISSN Print: 2156-8359 2.5D Modelling of Aeromagnetic Data and their Mining Implications over the Ngaoundere Area (Adamawa Province, Cameroon) Meying Arsène1*, Gouet Daniel Hervé2, Ndougsa Mbarga Theophile3,4, Ndam Njikam Mouhamed1, Owono Amougou Olivier Ulrich Igor3 1School of Geology and Mining Engineering, University of Ngaoundere, Meiganga, Cameroon 2Department of Petroleum, Mining & Groundwater Resources Exploration, Faculty of Mines and Petroleum Industries, University of Maroua, Maroua, Cameroun 3Department of Physics, Advanced Teacher’s Training College, University of Yaoundé I, Yaoundé, Cameroon 4Postgraduate School of Science, Technologies & Geosciences, University of Yaoundé I, Yaoundé, Cameroon How to cite this paper: Arsène, M., Hervé, Abstract G.D., Theophile, N.M., Mouhamed, N.N. and Igor, O.A.O.U. (2019) 2.5D Modelling This study is based on the analysis and interpretation of aeromagnetic data of Aeromagnetic Data and their Mining Im- using version 8.4 of the Geosoft Oasis Montaj Software, to map the subsur- plications over the Ngaoundere Area (Ada- face or deep geological structures that affected the geological formations of mawa Province, Cameroon). International the Ngaoundere area. The use of the standard aeromagnetic methods made it Journal of Geosciences, 10, 173-192. https://doi.org/10.4236/ijg.2019.102011 possible to draw up the maps of the residual magnetic field reduced to the equator (RTE), the horizontal gradient (HG), the analytical signal (AS) and Received: December 17, 2018 that of the Euler solutions (ED) to find the main magnetic facies correspond- Accepted: February 17, 2019 ing to these structures. The geological formations of the studied area thus ap- Published: February 20, 2019 pear to be intensely fractured by a NE-SW (N45˚E) and ENE-WSW (N70˚E) Copyright © 2019 by author(s) and main orientation fault system, the depth of which has been estimated by Scientific Research Publishing Inc. combining the three-analytical methods HG, AS and ED. Advanced magmat- This work is licensed under the Creative ic map analysis revealed dikes associated with vertical faults in the studied Commons Attribution International area. The development of an interpretative geological map taking into ac- License (CC BY 4.0). http://creativecommons.org/licenses/by/4.0/ count the basic geology, the deep faults, the identified dikes and the minera- Open Access lization index made it possible to extract a correlation between geological structures and mineralization of the studied area. The 2.5D modelling of two magnetic profiles plotted on the reduced residual map at the equator was performed to approximate the geometry and depth of the dikes sector, which are potential sources of mineralization here. Keywords Aeromagnetic Data, Analytical Methods, Faults, Mineralization, 2.5D Modelling DOI: 10.4236/ijg.2019.102011 Feb. 20, 2019 173 International Journal of Geosciences M. Arsène et al. 1. Introduction Since 1970, the Adamawa plateau in general and the studied area has been the subject of several geological studies by several authors, such as the studies con- ducted by Eno Belinga [1], Dumont [2], Ngounouno [3], roughly covering pe- trography, geochemistry and tectonics in the study area. The results of these stu- dies show that, on one hand, the basement of the studied area consisted mainly of gneiss and granite, the latter being crossed by granitoids and on the other hand, the major structures of the area had WSW-ENE (N70˚E), NE-SW (N45˚E) and NNE-SSW (N30˚E) orientations. Nevertheless, all these studies are superfi- cial and do not therefore give sufficient information on the structures of the subsoil of the studied area. In addition to these studies, few geophysical studies, focused on gravimetric studies [4]-[9] were conducted in the Adamawa region. They consisted of processing and interpreting the gravity data acquired during various gravity campaigns carried out in the sixties over the Cameroonian terri- tory. They aimed to provide additional information on the structuration and geodynamic evolution of the Adamawa plateau. The results from these gravime- tric investigations show a fairly good correlation with the surface geology and the directions of the major structures identified here remained similar to the previous ones. Although the information obtained so far is already quite inter- esting, the scale of the data used in these studies (from 1/3,000,000 to 1/500,000) does not allow to have a little more detailed knowledge on geology and the mi- neralization of the study area as required by mineral exploration. Some addi- tional information that could be derived from aeromagnetic data at scales, like the 1:50,000, would allow to have a much more detailed study. Based on the ex- istence of aeromagnetic data coverage over the studied area, which comprises longitudes 12˚30' - 13˚30'E and latitudes 6˚45' - 7˚15'N, the present study is in- itiated to enhance the level of structural knowledge. Aeromagnetic data have very often been used in the mining sector to detect areas of magnetic anomalies that may correspond to mineral concentration. They are currently widely used for geological land reconnaissance, especially in large areas where land or plant cover is important. The magnetic susceptibility technique from airborne data is therefore used to specify geological interpreta- tions at regional scales. In the case of this study, the main objective is to produce a structural mapping from the aeromagnetic data of the studied area to highlight a correlation between the geological structures (faults, geological contacts) and the possible mineralization of the studied zone. This study will therefore be unique in that research studies in the study area have so far consisted either of studying the general geology or measuring the av- erage thickness of the earth’s crust. They therefore did not provide information on the potential sources of near surface anomalies that are generally important for mineral research. All the results that will come from this study will provide a basic document on the very solid study area to base further investigations in mineral research. DOI: 10.4236/ijg.2019.102011 174 International Journal of Geosciences M. Arsène et al. 2. Geologic and Tectonic Setting of Studied Area The studied area covers an area of approximately 4647 Km2. It is limited by lon- gitudes 12˚30' - 13˚30'East and latitudes 6˚45' - 7˚15'North. It’s a plateau area of altitudes between 875 m and 1325 m. The Adamawa plateau is largely covered by large basaltic and basalto-andesitic volcanic effusions of essentially Tertiary age, which extend into the middle part of the southern moat [10] [11] [12] [13]. The basement of the study area is composed of granito-gneissic (Figure 1) intersected by granitoids between 652 and 612million years old [3]. According to Lasserre [14], the region of Adamawa was the seat of intense volcanic activity in the Tertiary and Quaternary, favored by a major fracturing-orientated NW-SE and secondary accidents E-W affecting the basement around Ngaoundere. The Pan-African gneiss and granite units are crossed by mylonitic bands, the largest of which, with a general ENE-WSW orientation, marks out the southern edge of the Adamawa. This myloniticb and corresponds to an important zone of sub-vertical faults having played in the Pan-African [15] [16]. The Adamawa represents an axial mass consisting of Precambrian basement, raised during the Upper Cretaceous and Tertiary and in which, the Adamawa plateau is likened to a horst. This asymmetrical horst lo- cated in the Mobile Zone of Central Africa, is limited to the north by the Ngaoundere cliff and to the south by the Mbéré-Djérem moat, both oriented N70˚E (ENE-WSW) corresponding to the general direction of the Plateau [16]. It is located on the route of large-scale mylonitic accidents. After the Pan-African event, the basement was traversed by magmatic comets corresponding to the tertiary magmatic activity of the “Cameroon Line”. This alkaline magmatism is reflected on the Adamawa plateau by the establishment of felsic domes, and ba- saltic flows. According to some authors [3] [18] [19] [20], the basement tectonics having played several times is responsible for its horst and graben structure. Figure 1. Geological map of the study area (Reproduced and modified after Guiraudie & Lasserre [17]). DOI: 10.4236/ijg.2019.102011 175 International Journal of Geosciences M. Arsène et al. This plateau has an altitude of 1100 m above sea level, with large basaltic flows accompanied by trachytes and trachyphonolites [3] [11] [12]. A thematic map of the mineral resources of Cameroon published in 2001 by the Ministry of Mines, Water and Energy (MINMEE) shows several indices of mineralization (Gold, Aluminum, Germanium, Tin, Thermal springs) in the studied area (Figure 2). Part of the bauxite plateau of MinimMartap is perfectly superimposed on the Aluminum indices found in the south of the studied area (Figure 2). 3. Materials and Methods 3.1. Origin of Aeromagnetic Data The data set used in the present study was obtained an aeromagnetic survey covering some parts of the Cameroon territory [21]. This aeromagnetic survey was conducted in 1970 by Survair Limited (Ottawa) as part of a co-operative agreement between the Canadian and the Cameroon government. The flying height was 235 Meters, flight lines had a N135˚E direction with 750 meters inter- lines space and the recording sensitivity of the magnetometer used was than 0.5 nT [21]. After correction of the measurements due to the temporary variation of the magnetic field, the final report of Paterson et al. [21] was accompanied by magnetic maps. The digitization of these maps made it possible to have a data base of 1,396,268 measuring points for the entire studied area (4647 Km2).
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