Metallogeny of a Pan-African oceanic arc: VHMS and gold deposits in the Ariab-Arbaat belt, Haya terrane, Red Sea Hills (Sudan)

International audienceIn the Neoproterozoic Arabo-Nubian Shield, the mined gold in the Ariab district (Red Sea Hills, Sudan) is in gossans reconcentrating primary gold overprinted over volcanogenic massive sulphide (VHMS) deposits, formed in the context of a Tonian ensimatic arc of the Haiya terrane. All the primary gold occurrences of the Ariab belt, whatever their style (VHMS-, quartz lode- or shear-zone-hosted), appear to have been syn-to late-kinematic, i.e., formed in the context of the final Pan-African collision leading to the Arabian-Nubian Shield (D3 event). Gold concentration occurs as native gold or electrum deposited in late (syn- to post-metamorphic) tectonic features, usually in sets of (micro)cracks, mostly within earlier pyrite or arsenopyrite. It is associated with either galena or bismuth tellurides. Gold deposition occurred in relation to an intense fluid circulation of metamorphic CO2-H2O rich fluids, which underwent significant strong decompression from lithostatic to hydrostatic pressures. Decompression and temperature decrease and dilution are probably at the origin of gold deposition, although no clear evidence of unmixing of the volatile was observed. The late-D3 gold event in the Ariab belt has all the makings of an orogenic gold system, notably similar to the Late Carboniferous gold event in the West European Variscan belt. Thus, it is possible to propose that, at the end of the collision events, fluids released from the newly formed terrane root were channelled towards the upper crust through the major D3 shear zones (the Oko shear zone for the Ariab belt). The fluids outpouring from these major drains were then conveyed through fault plays and damaged zones, up to specific chemical traps within massive sulphide ore bodies or quartz veins systems. Thus, the Ariab gold district could be classified as a representative of the class of orogenic gold deposits