Co-Ni-arsenide mineralisation in the Bou Azzer district (Anti-Atlas, Morocco): Genetic model and tectonic implications

Abstract

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The World’s Highest-Grade Cobalt Mineralization at Bou Azzer Associated With Gondwana Supercontinent Breakup, Serpentinite and Kellwasser Hydrocarbon Source Rocks

“…an abiotic process of reduction of As(V) by Fe(II) as previously evidenced in sub-surface settings in studies dealing with environmental monitoring of groundwater quality (Bose & Sharma, 2002). Such a process taking place in deeper crustal settings at Bou Azzer would equally explain petrographic observations whereby magnetite in serpentinite is replaced by Ni-arsenides in particular (Tourneur et al, 2021); and 2. an additional pathway involving the abiotic thermal decarboxylation of hydrocarbon mentioned above. The oxidation of hydrocarbons would be accompa-…”

“…1C, 2B). The arsenide mineralization occurs also as localized and mineral-specific replacements (e.g., magnetite; Tourneur et al, 2021) in brecciated blocks of serpentinite cemented by calcite (fig. 2C).…”

“…The wider geodynamic environment of extensional tectonics in the Late Devonian on the northern edge of Gondwana is compatible with deposit-scale fault patterns and petrographic observations documenting mineralization at Bou Azzer as open-space filling, including within brecciated zones. Specifically, in this extensional context, low-angle detachment faulting led to the formation of open spaces between fragments of brecciated country rocks (e.g., serpentinite; Tourneur et al, 2021;figs. 2B, 2C).…”

“…Consequently, euhedral to subhedral minerals (e.g., arsenides and calcite; figs. 2B-D) could fill large-scale pockets in open spaces within an extensional environment (Tourneur et al, 2021). This tectonic setting would favor hydrothermal fluid flow and mineralization resulting from the involvement of two originally immiscible fluids (inset in fig.…”

“…1C, 2B), whereas Co-Ni-Fe arsenides vein systems occur within serpentinite and diorite (fig. 2C, 2D; Tourneur et al, 2021). Previous age estimates for the timing of arsenide mineralization have ranged from late Pan-African (~ 685-580 Ma; Leblanc, 1981) to late Variscan (ca.…”