LAUSR

Abstract The Mississippi Valley-type Pb-Zn ore deposit of the Tigrinine-Taabast ore district, located in the southern border of the Moroccan Central High Atlas, is hosted in hydrothermally dolomitized Hettangian-Sinumerian carbonates. The mineralogical paragenetic sequence is simple: Quartz-dolomite-pyrite-galena-sphalerite. Fluid inclusions carried out on sphalerite reveal that sulfide ore precipitated from a NaCl-CaCl2-MgCl2 basin-derived warm (78° - 168°C) and saline (21 - 36 wt.% NaCl equiv.) brine. The carbon and oxygen isotopes of the ore-related calcite (Cal-1) suggests an equilibrium between the calcite-forming fluid and carbonates. The late post-ore calcite (Cal-2) reveals the influx of isotopically light meteoric fluid during the precipitation of this calcite. The δ34S values range from 6.6 to 9.4‰ and from 12.7 to 13.0‰ for galena and sphalerite, respectively. Sulfur derived from dissolved Triassic-Jurassic sulfates and/or coeval seawater pore sulfates primarily through thermochemical sulfate reduction and possibly bacterial sulfate reduction. Galena samples have a homogeneous Pb isotopic composition with 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios ranging from 18.229 to 18.236, 15.643 to 15.655, and 38.448 to 38.527, respectively. This uniform Pb isotope composition suggests that Pb and by inference other metals derived primarily from the Paleozoic rocks. During the African-European Cenozoic collision, the metal-bearing fluid was remobilized and migrated through the major faults and mixed with a shallow, diluted, cooler fluid, leading to the precipitation of ore sulfides.