Brines at the Origin of the Silver Mineralization at the Koudia El Hamra Deposit, Central Jebilet, Morocco

The Koudia El Hamra Ag deposit corresponds to mineralized quartz-carbonates veins crosscutting Hercynian schists (Jebilet, Morocco). Two major deposition stages are recognized: (i) pre-ore stage dominated by quartz constituting the main vein infilling, with pyrrhotite, arsenopyrite, pyrite and tourmaline, followed by chlorite and siderite. (ii) ore stage starting by the deposition of sphalerite-calcite-dolomite followed by Ag paragenesis: Ag sulfides and sulfosalts, native Ag, Ag-Sb, galena and chalcopyrite. Calcite-dolomite-sphalerite are related to high salinity brine (with halite crystal), salinity > 26 to 35 wt. % eq. NaCl and Th from 100 to 150 degrees C. Ag mineralizing fluid is a brine with salinity from 20.1 to slightly > 23.2 wt. % eq. NaCl and Th from 152 to 307 degrees C. The previous model relating the Koudia El Hamra Ag- ores to the Hercynian orogeny is reviewed. Ag paragenesis is rather a later event associated with the circulation of brines in fractures postdating quartz and dolomite-calcite-sphalerite assemblages. The latter are related at least to the effects in Jebilet of first stages of Atlantic opening (late Permian-Triassic rifting). Thus, Ag deposition event is at least post-Permian-Triassic likely due to the circulation of brines derived from Moroccan Atlasic basins subsequent to Atlantic rifting.