Geochronology and lithostratigraphy of the Siguiri district: Implications for gold mineralisation in the Siguiri Basin (Guinea, West Africa)

Erwann Lebrun, Nicolas Thebaud, J Miller, S. Ulrich, Julien Bourget, O. Terblanche

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    Abstract

    © 2015 Elsevier B.V. Geochronology and lithostratigraphic characterisation of the Siguiri district in the Palaeoproterozoic Birimian terrane of West Africa has provided a reappraisal of the Siguiri Basin stratigraphy. This new insight into the evolution of the central part of the basin further highlights first order controls on the location of the world class Siguiri orogenic gold district. Three metasedimentary formations occur in the Siguiri district: the Balato, Fatoya and Kintinian formations. These formations consist of fine-grained organic-rich shales, mudstone and siltstone/greywacke/limestone interbeds, decimetre- to metre-thick graded greywacke beds and debris flow deposits. The Balato Formation displays low-energy, hemipelagic marine or lake sediments, whereas the Fatoya Formation consists of distal turbidite deposits (thin-bedded turbidites and channel-fill deposits). Altogether they form a basal regressive sequence. The overlying Kintinian Formation is shale-rich, and contains a stack of polymict conglomeratic interbeds (up to 100 m in thickness) around the base of the Formation in the Siguiri district. This conglomerate unit transects the whole Siguiri Basin and is interpreted to be the product of repeated subaqueous debris flow deposits and represent olistostromes (or mélanges of sedimentary origin) with various autochthonous and allochthonous clasts. The youngest detrital zircon age population for each of the Balato, Fatoya and Kintinian formations yields ages of 2113 ± 10 Ma, 2113 ± 5 Ma and 2124 ± 7 Ma respectively, thus constraining the maximum age of deposition for each of these formations. The minimum age of deposition of these sedimentary rocks is constrained by a crosscutting volcanic breccia dated at 2092 ± 5 Ma, and by the Maléa monzogranite intrusion dated at 2089 ± 12 Ma. Comparison of the sedimentary facies and geochronology of the Siguiri sedimentary rocks with other sedimentary basins in the West African Craton, suggests that the Kintinian Formation is part of the Lower Tarkwa Group,
    Original languageEnglish
    Pages (from-to)136-160
    Number of pages25
    JournalPrecambrian Research
    Volume274
    DOIs
    Publication statusPublished - 2016

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