Aeromagnetic modelling of Precambrian subsurface structures of the Tasiast area, NW Mauritania
Résumé
The NW sector of Mauritania represents the Archaean province of the Reguibat Shield. It is mainly composed of the typical Archaean cratonic association of granitoid gneisses, greenstone belts and granites. The greenstone belts contain high mineral potential, mainly gold. This is particularly the case of the Chami Greenstone Belt, which hosts the large Tasiast gold mine. The gold deposits are hosted along a NS oriented shear zone with a surface of 70 × 15 km2.
In this study, a subsurface structural model is proposed based on the application of suitable computations on a high-resolution reduced-to-the-pole aeromagnetic anomaly map of the northern Chami area. Upward continuations, apparent magnetic susceptibility, directional derivatives, analytical signal, 3D Euler deconvolution and spectral analyses were performed to build this model. They were used to decipher the main evidenced structural features with the main NNE–SSW, NW–SE and ∼120° N directions, identified on most all computed maps combined with in situ measurements. They probably correspond to mafic dykes, faults and shears rooted up to 5 km in depth, particularly to the north, SW and NE, and southwards and westwards by spectral analyses and 3D Euler deconvolution, respectively. The basement is deeper towards the west and south and crops out towards the NE in agreement with the geological observations. In addition, the high values of magnetic susceptibility (χm) measured in situ on banded iron formations (25.7–35 × 10−3 SI) SW of Akjoujt could be the origin of metallotect sources associated with magnetic minerals for exploration of gold-bearing and base metals.