Chemical and boron isotope composition of tourmaline from the Kiaka orogenic gold deposit (Burkina Faso, West African Craton) as a proxy for ore-forming processes

Abstract

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Tourmaline occurrence and gold mineralization at a granitoid-metasediment contact in the Upper Lom Basin, east Cameroon

“…The dominant Mg +1 Fe -1 and □Al +1 (Na,Mg) -1 exchange vectors (Fig. 7c and d), may be suggesting tourmaline precipitation from reduced hydrothermal fluids [15,67]. The Mg-Fe 2+ substitution is indicative of an insufficient proportion of Fe 3+ in the tourmaline composition [66].…”

“…As an incompatible element, B is readily transported by granitic melts and hydrous fluids derived therefrom [74]. Granitic rocks emplaced along gold-bearing shear zones associated with significant hydrothermal alteration is proposed as a major source of [33], Bétaré Oya vein Au [50], Lom and Nyong alluvial gold [29], Primary gold East region, Cameroon [45], Betare Oya alluvial Au [23], Gamba district Au [26] boron-rich magmatic fluid [15]. Magmatic-hydrothermal fluids enriched in isotopically heavy boron probably dominated the formation of tourmaline [75].…”

“…The relative abundance of δ 11 B in nature [~ 60%; 5] makes the boron isotope system a valuable tracer of boron source in magmatic-hydrothermal and metamorphic systems [14]. There is a plexus of views on the source of fluid and metals in hydrothermal and orogenic gold deposits based on the interpretation of δ 11 B isotopic data and the geologic setting of such gold deposits in the world [15]. A metamorphic source of fluid associated with boron metasomatism is now widely considered to be the major source of mineralizing fluids in orogenic gold deposit systems, derived from prograde to peak metamorphic devolatilization of metasedimentary basement units [16,17].…”

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

“…At Kiaka, ~4.5 Moz of gold are hosted by amphibolitefacies biotite-kyanite-garnet-amphibole-bearing schists within the Tenkodogo-Fada N'Gourma Domain in southern Burkina Faso (Fontaine et al 2017;Gauriau et al 2020). The early disseminated gold event at Kiaka occurred during sinistralreverse displacement along the NNE-striking Markoye shear zone at 2157 ± 24 Ma (Fontaine et al 2017), broadly coeval with region-wide lower amphibolite-facies metamorphism and intrusion of a syn-kinematic diorite at 2140 ± 7 Ma (Fontaine et al 2017).…”