In an attempt to contribute to a better knowledge of phase relations, chemical trends and complex depositional history of the Co–Ni arsenide ores at Bou Azzer district, Morocco, (and by extension to the natural arsenides and sulfarsenides of the Ni–Co–Fe–As–S system), forty samples from the Aghbar mine have been studied. The Aghbar mine, located in the western central area of the Bou Azzer inlier, displays noticeable mineralogical variations depending on the type of mineralization: filling veins or replacing the host serpentinite. Nickel ores of vein type, Co–Fe ores of serpentinite-hosted type and late Cu ores are the assemblages that we identified. Although there is a good agreement with the general sequence established for the Bou Azzer district, meaningful differences in mineral chronology, composition and temperatures of formation are discussed on the basis of the experimental data. The crystallization sequence of Ni ores reveals a continuous increase in As fugacity up to the formation of Ni-rich skutterudite, with formation temperatures fitting well the field of solid solution experimentally established at 650°–625°C. In contrast, the Co–Fe ores seem to form at a somewhat lower temperature (from ~500° to 400°C), and especially at the lower part of this range, during the crystallization of arsenopyrite. These temperature differences between the two main ores of the deposit can be interpreted by assuming either different temperatures in the two ore-forming fluids or considering differences in the paths followed by similarly hot mineralizing fluids.

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