Mineralogy and ore fluid chemistry of the Roc Blanc Ag deposit, Jebilet Hercynian massif, Morocco

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

“…In combination with observations and data reported by previous studies (Huvelin 1977;Chouhaïdi 1986;Essarraj et al 2017), our new mineralogy, chemical, and isotopic data are used to (1) characterize the Ag-and Au-bearing mineral phases; (2) document the mineral and chemical evolution of the mineralizing fluids; (3) provide an indication of fluid source and constraints on fluid-rock interaction; and (4) evaluate the role of different fluids and ore depositional processes that operated during mineralization in the central Jebilet metallogenic province, as a framework for constructing a new genetic model.…”

“…EPMA analyses (ESM 3) show homogenous ripidolitic compositions (MgO = 4-10 wt%; Fe/[Fe + Mg] = 0.63-0.84; Al IV = 2.68-2.86 atoms per formula unit) according to Hey (1954) (ESM 4A). Chlorite geothermometry, using the approach of Cathelineau and Nieva (1985) and Kranidiotis and MaClean (1987), indicates formation temperatures between 352 and 382°C and averaging 364°C (ESM 4B), which are consistently higher than the temperatures inferred from fluid inclusion data (Essarraj et al 2017).…”

“…Insights into probable source(s) of the mineralizing fluids that formed the Roc Blanc deposit are provided by trace element geochemistry including REYs, fluid inclusion data (Essarraj et al 2017), and stable (C, O, H) isotopes of ore-related hydrothermal Ca-Fe-Mg carbonates. Together, the data suggest that diverse fluids were involved in the genesis and evolution of the mineralizing system.…”

“…Despite its economic significance, the origin of the Roc Blanc base metal Ag-Au-rich mineralization remains controversial with regard to the source of both fluids and metals (e.g., Huvelin et al 1978;Essarraj et al 2017). The disagreement stems from the absence of precise constraints on the age of mineralization.…”

“…Indeed, possible links between base metal Ag-Au-rich mineralization, magmatism, metamorphism, and regional tectonics remain unresolved at the district scale; importantly, the question of such genetic relationships is fundamental to successful explorations models. In this context, several conflicting hypotheses have been proposed for the genesis of Roc Blanc mineralization, with recent studies suggesting large-scale, hydrothermal circulation of basinal brines as the main oreforming process, with the fluid system being likely related to Triassic opening of the Central Atlantic Ocean (Essarraj et al 2017). Conversely, Huvelin (1977) suggested a Variscan age for the Roc Blanc mineralization, genetically related to emplacement of Late Variscan granitoids.…”