Aeromagnetic modeling of Precambrian subsurface structures of the Tasiast area, NW Mauritania : Mining consequence

Abstract

International audienceThe NW sector of Mauritania represents the Archean province of the Reguibat Ridge. It is mainlycomposed of the typical Archaean cratonic association of granitoid gneisses, greenstones belts andgranites. The greenstone belts contain high mineral potential, mainly gold. This is particularly thecase of the Chami Greenstone Belt, which hosts the large Tasiast gold mine whose gold depositsare hosted along a NS oriented shear zonewithasurfaceof70x15km2.Themineral-bearing bodies of Tasiastare presented in both forms of (i) veins of quartz-carbonatewhitefeldspar-pyrrhotite-pyrite, vein lets of quartz-carbonated containing gold, and (ii) adjacentgold disseminated and hosted within rocks from greens chistto amphibolite facies, banded ironformations (BIF) withmagnetite-quartzite, and adjacent volcano-clasticrocks. The whole of the semineralizations follow a series of reactivated thrust faults, includingTasiast and Piment fracturezones (Heronetal.,2016). Atthenorthernendofthe Chami Greenstone Belt, Piment mineralizationsare hosted within BIF, felsicvolcanic rocks, and associated clastic rocks, whilein its western branch,they are hosted within mafic rocks (Sedore and Masterman, 2012; Heron et al., 2016). The clayalteration and the high salinity of fluid inclusions indicate possible orogenetic gold deposits datedbetween 1.85 Ga and 1. 5 Ga(Higashihara et al.,2004; Marutani et al.,2005).Thanks to the available aeromagnetic data recorded at 100 m elevation northern Chamiarea,suitable computations on the anomalyma preduced to the pole were used to propose a subsurfacestructural model. In fact, up ward continuations, apparent magnetic susceptibility, directionalderivatives, analyticalsignal, 3D Euler deconvolution and spectral analyses were investigated tobuild this model (Thompson, 1982; Blakely and Simpson, 1986; Reid et al., 1990; Cowan andCowan, 1993; Blakely, 1996; Mushayandebvu et al., 2001; Roest et al., 1992). They helped decipherthe main evidenced structural features withthemain NNE-SSW, NW-SE and~N120° directions,identified on most all computed maps combined within situ measurements. They probablycorrespond to mafic dykes, fault sands hears rooted up to 5 km depth, particularly to the North,SW and NE, and southwards and west wards by spectral analyses and 3D Euler deconvolution,respectively (Fig. 1). The base mentis deeper to wards the West and South and out crops to wardsthe Neinagreement with the geological observations. In addition, the high values of magneticsusceptibility (χm) measured in situ on BIF (25.7-35.10-3SI) southof Akjoujt could beat the origin ofmetallotects sources associated with magnetic minerals for gold bearing and base metalsexploration