Integrated strato-tectonic, U-Pb geochronology and metallogenic studies of the Oudalan-Gorouol volcano-sedimentary Belt ( OGB) and the Gorom-Gorom granitoid terrane (GGGT), Burkina Faso and Niger, West Africa

A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg, 2015.The Palaeoproterozoic Baoulé-Mossi domain of the West African Craton in northeastern Burkina Faso hosts numerous gold deposits such as Essakane and Tarpako. Integrated strato-tectonic, geophysical, geochemical, geochronological, regional stratigraphic framework and metallogenic studies of the Oudalan-Gorouol volcano-sedimentary Belt and the Gorom-Gorom Granitoid Terrane have provided new insight into the geotectonic evolution of the northeastern part of Burkina Faso. This work outlines the structural context and architecture necessary for forming these deposits. In this work, a new strato-tectonic model is proposed for the area by integrating field data and geophysical, geochemical, and geochronological data. The integrated data highlights and characterizes the setting of the Essakane gold mine and gold camp relative to the location of other regional gold deposits, metamorphosed Birimian Supergroup, intrusive rocks and shear zones. Structural, geochemical and geochronological analyses have helped to clarify the geological evolution of the Oudalan-Gorouol volcano-sedimentary Belt and the Gorom-Gorom Granitoid Terrane during the Tangaean (D1) and Eburnean (D2) orogenies through to the Wabo Tampelse Event (D3). Further to these, zircon U-Pb geochronology data have demonstrated that the Oudalan-Gorouol volcano-sedimentary Belt and the Gorom-Gorom Granitoid Terrane represent some of the oldest outcropping geology in the Palaeoproterozoic Baoulé-Mossi domain recognised to date. The geochronology and geology suggest that the basement or a pre- Birimian crust to the Birimian Supergroup may be found in the northeast of Burkina Faso. The Eburnean Orogeny in northeastern Burkina Faso is preceded by two phases of deformation (D1-x and D1), and two phases of magmatism. The first, D1-x, is associated with the emplacement of the Dori Batholith at the onset of D1 (2164 – 2141 Ma). D1 ductile-brittle deformation formed F1 folds and discrete high-strain mylonite zones that deformed the Oudalan- Gorouol volcano-sedimentary Belt and the Gorom-Gorom Granitoid Terrane during a southwestdirected palaeo-principal compressive stress. The pre-Birimian to Birimian supracrustal rocks and intrusions were regionally metamorphosed during D1 to greenschist to amphibolite facies with development of mineral assemblage of quartz-chlorite-muscovite ± chloritoid to biotite-potash feldspar ± hornblende. D1 is also associated with volcanic arc type calc-alkaline magmatism, producing TTGs enriched in heavy rare earth elements. The Eburnean Orogeny (2130 – 1980 Ma) is characterised by northwest-southeast shortening; it was followed by north-northwest - south-southeast shortening with development of northeast trending sinistral strike-slip faults and shears. D2 brittle-(ductile) deformation is manifested by refolding of F1 by northeast-trending F2, and development of a pervasive northeast-trending S2 to S2-C foliation. Metamorphic grade attained greenschist facies during D2, with development of mineral assemblage of quartz-chlorite-muscovite ± actinolite. The Wabo Tampelse (D3) deformation event is brittle in character and does not significantly affect the regional geological architecture in the study area

Palaeotectonic setting of the south-eastern Kédougou-Kéniéba Inlier, West Africa: new insights from igneous trace element geochemistry and U-Pb zircon ages

New U-Pb zircon ages and geochemistry from the eastern Kédougou-Kéniéba Inlier are presented and integrated with published data to generate a revised tectonic framework for the westernmost Birimian terranes. The Falémé Volcanic Belt and Kofi Series are highly prospective, hosting several multi-million ounce gold deposits and a significant iron ore resource, but remain under-researched. It is therefore important to constrain the fundamental geological setting. The igneous rocks of the eastern Kédougou-Kéniéba Inlier are dominantly of high-K calc-alkaline affinity, with fractionated REE patterns and negative Nb-Ta anomalies. The plutonic rocks in the Falémé Belt are dioritic to granodioritic in composition, with moderately fractionated REE patterns and metaluminous A/CNK signatures. Felsic, peraluminous granite stocks, dykes and plutons with fractionated REE patterns and negative Eu, Ti and P anomalies intruded both the Falémé Belt and Kofi Series. Albitisation masks the affinity of some units, although use of the Th-Co diagram shows that prior to albitisation, all igneous units belonged to the high-K calc-alkaline series. New U-Pb age data for the Boboti and Balangouma plutons indicate crystallisation at 2088.5 ± 8.5 Ma and at 2112 ± 13 Ma, respectively. Inherited zircons in the Boboti pluton indicate magmatic activity in the Falémé Belt at 2218 ± 83 Ma coincided with the oldest dated units in the Mako Belt to the West. Systematic changes in Dy/Yb, Sm/La, Nb/Zr, Rb concentration, Eu-anomaly and ɛNdt over ∼200 Ma reveal that the tectonic setting in the KKI evolved from a volcanic island arc environment to an active continental margin. Crustal thickening, as a result of a shift to collisional tectonic setting, combined with magmatic differentiation, led to the generation of peraluminous, granitic melts with a significant crustal component. A small suite of more basic intrusive and extrusive rocks on the eastern margin of the Dialé-Daléma basin are highly metaluminous and display limited LILE enrichment, with normalised HREE values close to unity. The Daléma igneous rocks may have formed in an extensional back arc, related to the arc system

Paleoproterozoic gold events in the southern West African Craton: review and synopsis

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