Formation of Supergene Zinc Silicates in Carbonates: New Advances from the Bou Arhous Deposit (Morocco)

Willemite, a zinc silicate usually reported in hypogene non-sulfide deposit has been observed in the supergene Bou Arhous deposit. Based on a set of microscopic observation and microanalyses, it is possible to establish that willemite replaces sphalerite and is coeval with other oxidation-related species, like cerussite. The formation of the High Atlas Belt during the Tertiary has contributed to the exhumation of sulphides and the developpement of vertical conduits for percolation of meteoric waters. Several generation of willemite can be distinguished, with evidence of dissolution-reprecipitation under surface conditions. Dissolution of willemite leads to releasing Zn and Si in the meteoric water. These solutions may interact with residual clays filling the karstic cavities, resulting in the neogenesis of zinc clays.