Sidi M'Barek: a representative example of the Moroccan massive sulfide deposits

In addition to a Zn-rich lens representing the northern prolongation of the Draa Sfar volcanogenic massive sulfide deposit, the Sidi M'Barek deposit includes Cu-rich lenses in which gold is being recovered profitably as a by-product. The Cu-rich mineralization is composed of numerous structurally controlled veins whose morphology suits that of a lode rather than that of a stratiform orebody. Although the Cu-rich and Zn-rich orebodies are dominated by pyrrhotite, pyrrhotite is coarser grained in the Cu-rich lenses and mineralization is polyphase. Pyrrhotite is deformed and recrystallized; it is cross-cut and replaced by pyrite infilling veins. Pyrite also crystallizes along the S1 cleavage and in pressure shadows around bioclasts in the disseminated ore. Chalcopyrite veins postdate both the pyrrhotite and pyrite phases. The concentration of Co and Au is higher in the Cu-rich lenses relative to the Zn-rich lenses, which have higher concentrations of Pb, Ag and As. Pyrite and pyrrhotite have distinct sulfur and lead isotopic signatures. We propose a polygenetic model in which a pre-existing syngenetic pyrrhotite-rich mineralization is remobilized in shear zones during a major ductile deformation event allowing deposition of pyrite. The shear zones were reopened during a late ductile–brittle deformation event allowing deposition of chalcopyrite.