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Journal Articles Journal of African Earth Sciences Year : 2017

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 at1.09 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-FadaN’Gourma greenstone and plutonic belt in south of the Burkina Faso, the deposit is hosted by a metamorphosedvolcano-sedimentary sequence of lithic-, quartz-biotite metagreywacke, aluminosilicate-bearing metapelites andgarnet-orthopyroxene-bearing schists and volcanic units.Structural observations indicate four local deformation events: DK1, DK2 and DK3 and DK4. Respectively, theseevents are linked to regional D1 E-W compression, D2 NW-SE compression and lastly, D3- and D4-relatedreactivations along D2 shear zones. The S2 foliation and D2-related shear zones are developed during loweramphibolite facies metamorphism whereas retrogression occurs during D3-4 reactivations along these shear zonesat upper greenschist facies conditions. The emplacement of a dioritic intrusion, dated at 2140 ± 7 Ma (ConcordiaU-Pb age on magmatic zircon), is interpreted to be contemporaneous with sinistral displacement alongmineralized, NE-trending D2 shear zones. The intersection of these shears zones and the Markoye shear zone(dextral-reverse D1 and sinistral-reverse D2 reactivations) controlled the final geometry of the host rocks and theore zones.Four subparallel elongated ore bodies are mainly hosted within D2-related shear zones and some are developedin an apparent axial plane of a F2 isoclinal fold. Detailed petrographic studies have identified two main types ofhydrothermal alteration associated with two stages of gold mineralization. The stage (1) corresponds toreplacement zones with biotite and clinozoisite during the D2 event associated with pyrrhotite ± pyrite,chalcopyrite (disseminated gold stage). The stage (2) occurs during reactivations of the D2-related auriferousshear zones (vein stage) and are characterized by diopside ± actinolite D3 veins and veinlets and D4 pervasivemuscovite, ± 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 onmineralogy and crosscutting relationship. A weighted average Re-Os pyrrhotite age at 2157 ± 24 Ma (Re-Os agebased on 3 replicates) constraints the timing of the disseminated gold stage and represents the first absolute agefor gold mineralization in the Manga Fada N’Gourma area. The timing of gold at Kiaka may be also coeval withone of the two lode gold event at ~ca. 2.16-2.15 Ga and occurred concomitant with tectono-thermal activityduring Eo-Eburnean orogeny.The study of the Kiaka gold deposit emphasizes the importance of a multi-scale and multidisciplinary 59 approach(field observations, petrography geothermobarometry and geochronology) to decipher the polyphase character ofsome Paleoproterozoic gold deposits.
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insu-01397784 , version 1 (16-11-2016)



Arnaud Fontaine, Aurélien Eglinger, Koumangdiwè Ada, Anne-Sylvie André-Mayer, Laurie Reisberg, et al.. Geology of the world-class Kiaka polyphase gold deposit, West African Craton, Burkina Faso. Journal of African Earth Sciences, 2017, 126, pp.96-122. ⟨10.1016/j.jafrearsci.2016.11.017⟩. ⟨insu-01397784⟩
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