Geology of the world-class Kiaka polyphase gold deposit, West African Craton, Burkina Faso

The Kiaka gold deposit is a major resource in West Africa, with measured and indicated resources of 124 Mt at 1.09 g/t Au (3.9 Moz) and inferred resources of 27 Mt at 0.83 g/t Au (0.8 Moz). Located within the Manga-Fada N'Gourma greenstone and plutonic belt in south of the Burlcina Faso, the deposit is hosted by a metamorphosed volcano-sedimentary sequence of lithic-, quartz-biotite metagreywackes, aluminosilicate-bearing metapelites and garnet-orthopyroxene-bearing schists and volcanic units. Structural observations indicate four local deformation events: DK1, DK2 and DK3 and DK4. Respectively, these events are linked to regional D-1 E-W compression, D-2 NW-SE compression and lastly, D-3 and D-4-related reactivations along D-2 shear zones. The S-2 foliation and D-2 shear zones are developed during lower amphibolite fades metamorphism whereas retrogression occurs during D3-4 reactivations along these shear zones at upper greenschist fades conditions. The emplacement of a dioritic intrusion, dated at 2140 +/- 7 Ma (Concordia U-Pb age on magmatic zircon), is interpreted to be contemporaneous with sinistral displacement along mineralized, NE-trending D-2 shear zones. The intersection of these shears zones and the Markoye shear zone (dextral-reverse D-1 and sinistral-reverse D2 reactivations) controlled the final geometry of the host rocks and the ore zones. Four subparallel elongated ore bodies are mainly hosted within D-2-related shear zones and some are developed in an apparent axial plane of a F-2 isoclinal fold. Detailed petrographic studies have identified two main types of hydrothermal alteration associated with two stages of gold mineralization. The stage (1) corresponds to replacement zones with biotite and clinozoisite during the D-2 event associated with pyrrhotite pyrite, chalcopyrite (disseminated gold stage). The stage (2) occurs during reactivations of the D-2-related auriferous shear zones (vein stage) and is characterized by diopside +/- actinolite D-3 veins and veinlets and D-4 pervasive muscovite, chlorite, calcite in quartz-carbonate vein selvages and associated with pyrrhotite arsenopyrite electrum, native gold and tellurobismuthite. The latter stage (2) could be divided into two sub-stages based on mineralogy and crosscutting relationship. A weighted average Re-Os pyrrhotite age at 2157 +/- 24 Ma (Re-Os age based on 3 replicates) constraints the timing of the disseminated gold stage and represents the first absolute age for gold mineralization in the Manga Fada N'Gourma area. The timing of gold at Kiaka may be also coeval with one of the two lode gold event at similar to ca. 2.16-2.15 Ga and occurred concomitant with tectono-thermal activity during Eo-Eburnean orogeny. The study of the Kiaka gold deposit emphasizes the importance of a multi-scale and multidisciplinary and geochronology) to decipher the approach (field observations, petrography geothermobarometry polyphase' character of some Paleoproterozoic gold deposits. (C) 2016 Elsevier Ltd. All rights reserved.