Geological and geochemical constrains on the genesis of the sedimentary-hosted Bou Arfa Mn(-Fe) deposit (Eastern High Atlas, Morocco)

Carbonate-hosted Mn deposits are widespread in North Africa with most of the ores being hosted by Mesozoic dolomitic formations Moroccan Atlasic system. The Bou Arfa Mn(-Fe) deposit described herein is located eastern High Atlas, close to Front, and has accounted for production ~2 Mt ore grading from 33 82% Mn. mineralization occurs within Sinemurian flat-lying dolostones as stratabound karst-filling (veins, lenses, pockets). This characterized extensive presence pyrolusite, minor concentrations manganite, hausmannite, goethite hematite. Previous studies suggested that Mn-bearing a strictly synsedimentary origin, but intense dolomitization occurrence oxides instead carbonates question this model. New petrographical, mineralogical geochemical data show three phases accompanied formation. early was not responsible strong enrichments, whereas second took place formation hausmannite manganite during diagenesis. precipitation mechanism involves circulation dissolved Mn2+ pore waters, then under diagenetic suboxic alkaline conditions. scarcity likely due competitiveness species have favored dolomite stage. Presence saddle subsequent alteration stage, crystallography Fe oxides, evolution δ13C δ18O reflect burial diagenesis fluid mixing carbonate host rock. These conditions enabled transformation primary into when diagenetically-derived hydrothermal fluids generated vein-filling ore. position site above paleohigh formed Atlas rifting, faulted zone series delimited extension deposit, which some points similar MVT Africa. Weathering poorly recorded stability ore-forming minerals subaerial relation recent periods exposure building.