Investigation géophysique par la méthode aeromagnétique : implication tectonique et minière dans la zone de Djadom-eta au Sud-Est Cameroun

Abstract

Geophysical methods are used to measure the contrast of physical properties within the earth that represents a variation in structural geology. In this perspective, magnetic survey work is strongly suggested. The data from this work is particularly effective in supplementing and improving known information. In this case, the data used in this work was collected by the Compagnie Minière du Cameroun 2012 in Djadom-Eta, Southeast Cameroon. The objective of this study is to improve the structural mapand target potential iron ore zones and other minerals. Beyond this, the methodology of data processing and interpretation is based on the use of adequate filtering techniques (Tilt angle methods, horizontal gradients, Euler deconvolution and the analytic signal). The latter will make it possible to propose a structural map then, inverse models (2.75D and 3D) in order to analyze the magnetic susceptibility contrast distribution of the study area. Moreover, the methods of the tilt angle (tilt derivative) and the maxima of the amplitude of the horizontal gradient, the large structural features WSW–ENE, WNW–ESE and W–E are highlighted. In particular the Djadom faults (WSW–ENE), the Dja faults of (S–N) and the Eta faults of (WNW–ESE), respectively corresponding to the geological formations of Panafrican and Craton and the E - W structural features are mostly minor lineaments. The dips of the maxima of the amplitude of the horizontal gradient thus some correlate with those of the geological map are also highlighted. In view of this, the Euler deconvolution has made it possible to obtain these geological structures and to estimate their depths and the geometry from the bodies buried while the contact reveals that the depths of the tilt angle are included in those of the solutions. Euler and that the set of applied filters shows a network of faults and the 2.75D inversions show models of the subsoil affected by the tectonic activities. From this point of view, 2.75D and 3D inversions models are essential in mining. The application of these on the potential data makes it possible to identify and locate the ores as they make it possible to obtain the depth, the geometry, the extensions and the nature of the mineral sources. The 2.75D model therefore identifies the quality of the source, its geometry, its extension and its depth. Thus, Banded Iron Formation (BIF) and Banded Iron Quartzite (BIQ), Amphibole (AM), Gneiss, Schist and Green Rock, Quartz, Quartz-Micaschist (QMS), Sandstone are identified. The 3D inversion model applied to the residual grid, in addition to the information given by 2.75D gives the size of the deposit. By this 3D inversion model, the strongly (susceptibilities greater than 0.02 cgs) and weakly (susceptibilities less than 0.02 cgs) magnetized deposits are highlighted. The latter highlights the supposed faults of Djadom, Eta, and Dja. These highly magnetized zones are responsible for the magnetic responses marked by positive anomalies. According to the 2.75D models these are reactions of the magnetic bodies such as the BIF and BIQ whose content is important in the aera. These two models of coupled inversion make it possible to estimate the potential zones of some drilling. Thus, the deposit and the geometry of the bodies of strong and weak magnetizations are realistic then validated by the geological data and the works carried out around this zone of study. This study proves that the 2.75D and 3D inversions of magnetic data are valuable tools for geophysicists and geologists in the exploration of ore deposits.