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

Fontaine, Arnaud; Eglinger, Aurélien; Ada, Koumangdiwè; André-Mayer, Anne-Sylvie; Reisberg, Laurie; Siebenaller, Luc; Le Mignot, Elodie; Ganne, Jérôme; Poujol, Marc (2017). Geology of the world-class Kiaka polyphase gold deposit, West African Craton, Burkina Faso. Journal of African Earth Sciences , vol. 126 . p. 96-122. DOI: 10.1016/j.jafrearsci.2016.11.017.

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Résumé

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 Burkina 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 D₁ E-W compression, D₂ NW-SE compression and lastly, D₃- and D₄-related reactivations along D₂ shear zones. The S₂foliation and D₂ shear zones are developed during lower amphibolite facies metamorphism whereas retrogression occurs during D₃-₄ reactivations along these shear zones at upper greenschist facies 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 D₂shear 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 the ore zones. Four subparallel elongated ore bodies are mainly hosted within D₂-related shear zones and some are developed in an apparent axial plane of a F₂ 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 D₂ event associated with pyrrhotite ± pyrite, chalcopyrite (disseminated gold stage). The stage (2) occurs during reactivations of the D₂-related auriferous shear zones (vein stage) and is characterized by diopside ± actinolite D₃ veins and veinlets and D₄ 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 ∼ 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 approach (field observations, petrography geothermobarometry and geochronology) to decipher the polyphase character of some Paleoproterozoic gold deposits.

Type de document:
Mots-clés libres: orogenic gold deposit; Eburnean orogeny; metamorphism; magmatism; Birimian volcano-sedimentary belt; U-Pb and Re-Os geochronology
Centre: Centre Eau Terre Environnement
Date de dépôt: 16 juin 2017 18:51
Dernière modification: 16 juin 2017 18:51
URI: http://espace.inrs.ca/id/eprint/5168

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