Aeromagnetic modeling of Precambrian subsurface structures of the Tasiast area, NW Mauritania : Mining consequence
Résumé
The NW sector of Mauritania represents the Archean province of the Reguibat Ridge. It is mainly
composed of the typical Archaean cratonic association of granitoid gneisses, greenstones 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 whose gold deposits
are hosted along a NS oriented shear zonewithasurfaceof70x15km2.
Themineral-bearing bodies of Tasiastare presented in both forms of (i) veins of quartz-carbonatewhite
feldspar-pyrrhotite-pyrite, vein lets of quartz-carbonated containing gold, and (ii) adjacent
gold disseminated and hosted within rocks from greens chistto amphibolite facies, banded iron
formations (BIF) withmagnetite-quartzite, and adjacent volcano-clasticrocks. The whole of the semineralizations follow a series of reactivated thrust faults, includingTasiast and Piment fracture
zones (Heronetal.,2016). Atthenorthernendofthe Chami Greenstone Belt, Piment mineralizations
are 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 clay
alteration and the high salinity of fluid inclusions indicate possible orogenetic gold deposits dated
between 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 subsurface
structural model. In fact, up ward continuations, apparent magnetic susceptibility, directional
derivatives, analyticalsignal, 3D Euler deconvolution and spectral analyses were investigated to
build this model (Thompson, 1982; Blakely and Simpson, 1986; Reid et al., 1990; Cowan and
Cowan, 1993; Blakely, 1996; Mushayandebvu et al., 2001; Roest et al., 1992). They helped decipher
the main evidenced structural features withthemain NNE-SSW, NW-SE and~N120° directions,
identified on most all computed maps combined within situ measurements. They probably
correspond 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 wards
the Neinagreement with the geological observations. In addition, the high values of magnetic
susceptibility (χm) measured in situ on BIF (25.7-35.10-3SI) southof Akjoujt could beat the origin of
metallotects sources associated with magnetic minerals for gold bearing and base metals
exploration.