Characterization and origin of clays in the Bou Arhous (Morocco) non-sulfide Zn ore deposit

International audienceSupergene non-sulfide Zn deposits offer high mineralogical diversity including clayminerals that can incorporate significant amounts of Zn like sauconite. Although clayeymaterial is commonly observed in such ore deposits, its nature and origin have beenrarely studied, especially in carbonate-hosting environments. However the role of clayminerals is essential for mineral processing because they usually have a negative impacton zinc recovery.In this work, we focus on the Bou Arhous Zn-Pb ore deposit in Eastern High Atlas,Morocco. This deposit is located in an anticline formed by Lower Jurassic limestoneand marl, with Upper Triassic shale in the core of the anticline. Zn-rich clayey materialfills karstic cavities and two types of clay rich deposits have been identified field: 1)white to ochre granular clay (kaolinite/smectite (K/S) irregular mixed layers, smectiteand illite) and 2) red smooth clay (kaolinite, chlorite, illite). The white to ochre granularclays are closely associated with supergene willemite (zinc silicate), one of the main Znbearing mineral phases of the Bou Arhous deposit. The red smooth clays fillkarst-related cavities cutting across the non-sulfide mineralized bodies. The red smoothclays present evidence of stratification that reflects internal sedimentation processesduring karst evolution. Bulk chemical analyses reveal that the Zn content is highlyvariable in all clayey samples and even can reach several percent. This enrichment maybe due to fine inclusions of zinc silicate or carbonate in the clayey material, or to theoccurrence of Zn clay minerals (i.e. sauconite).The mineralogy of clays and associated minerals in bulk powders and separated