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

Abstract : 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.
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Submitted on : Tuesday, February 19, 2019 - 1:43:25 PM
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Tahar Aïfa, Bakary Savane, Khalidou Lo. Aeromagnetic modeling of Precambrian subsurface structures of the Tasiast area, NW Mauritania : Mining consequence. 3rd IGCP 638 International Conference, Oct 2018, Abidjan, Côte d’Ivoire. pp.2-3. ⟨insu-02024845⟩

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