The Roc Blanc orogenic Pb-Zn-Ag-Au deposit (Morocco). A product of metamorphic dehydration and CO2 devolatilization during exhumation of the Variscan Jebilet massif

The Roc Blanc Pb-Zn-Ag ± Au vein system in the Variscan Central Jebilet massif, Morocco, is confined within the contactmetamorphic aureole of S- and I-type calc-alkaline granitic stocks (327 ± 4 to 295 ± 15 Ma) along the Marrakech ShearZone. Host rocks consist of a succession of greenschist- to amphibolite-facies metasedimentary and metavolcaniclasticrocks of Carboniferous age. The ore mineralogy is predominantly base metal and Ag-bearing sulfides and sulfosalts,intergrown with quartz and carbonates. Late-stage gold mineralization is commonly present as electrum in intimateassociation with all major generations of sulfide and sulfosalt minerals. Ore-related hydrothermal alteration includessilicification, sericitization, chloritization, and carbonatization. Chlorite and arsenopyrite geothermometry suggest meantemperatures of 364 and 350 °C; respectively. Calculatedδ18Ofluidvalues of 15 to 18‰are consistent with metamorphicfluid sources, by which the mineralizing fluids were produced during the emplacement of granitic intrusions and subse-quent devolatilization of graphitic black shale and interlayered carbonate beds. Lead and strontium isotope data constrainthe source of the ore-forming components (i.e., metals and sulfur) to the enclosing host rocks. A decrease in temperatureduring fluid ascent and subsequent alteration-associated fluid-rock interaction resulted in the deposition of the Pb-Zn-Ag ±Au mineralization in a post-collisional extensional setting