Formation of serpentinite-hosted, Fe-rich arsenide ores at the latest stage of mineralization of the Bou-Azzer mining district (Morocco)

The Bou Azzer district in the central Anti-Atlas of Morocco is world’s unique mining where Co exploited from serpentinite-hosted hydrothermal Co-Ni-Fe arsenide ores. This paper provides first-ever mineralogical and geochemical characterization a suite Fe-rich orebodies found during recent Ait Ahmane area, district. These are lens-like massive disseminated ores fully hosted serpentinites (hereafter named as ores) that typically enveloped by arsenide-poor, carbonated serpentinite, evolving irregularly outwards to talc-rich serpentinite. part these mainly consists ore made up aggregates zoned spindle-like crystals löllingite whereas outer zone rosette-like löllingite. often contain accessory grains chromite display strong fracturation, zoning alteration. We propose general model for formation Bou-Azzer associated infiltration high-temperature (>400 °C) slightly alkaline, oxidized CaCl2-rich fluids through opening fault fractures. When channeled faults separating serpentinite quartz diorite (or other rocks) deposited Ni- Ni-Co-rich fault-related open spaces (here re-defined contact-type ores). Over course mineral deposition, generated Ni-poor tended migrate into first networks thin entwined veins progressively intergranular percolation, promoting dissolution infiltrated precipitation Co-Fe (the presence remnants included coexisting arsenides calcite sustains role played dissolution/precipitation, ore-forming process). Further circulation weak zones away serpentinite-quartz contact (intra faults), formed serpentinite-hosted, type represented F55 lens. most probably evolved at low temperature (~200 towards higher pH values oxidizing conditions increasing proportions CO2 CO32?, serpentine, increase magnetite component chromite, Cr Fe hydroxides, mobilization silica out reactive + arsenides.