The Early Jurassic Jbel Bou Dahar reef-bearing carbonate platform in the eastern High Atlas, Morocco, contains numerous carbonate-hosted and fault-controlled Pb-Zn-Ba deposits, prospects, and showings. Combined field, petrographic and geochemical data, including REE + Y analyses, stable (C-O-S), radiogenic (SrPb) and noble gas (He, Ne, Ar) isotopic compositions, record two temporally distinct metallogenic events. Both events are related to post-rifting and inversion of the inherited Mesozoic Atlas paleorift. The ore deposits are thought to have been formed during large-scale episodes of transtensional basin evolution, which developed as a far-field effect of the drifting of the Central Atlantic Ocean and Maghrebian Tethys while the basin continued to invert in response to the ongoing convergence between the African and the Eurasian plates. The paragenetically earliest Zn-rich ore was generated in a transtensional setting coincident with the hyper-extension of Maghrebian Tethys and the initial stages of drifting and formation of the Central Atlantic passive margin. Crustal extension and high heat fluxes provided by the hot upwelling mantle would have triggered buoyancy-driven convection of deeply sourced fluids and maturation of organic matter dispersed within the host carbonates to produce hydrocarbons within an extensional basin setting. These relatively reduced Zn-rich ore-forming fluids acquired metals mainly through protracted interaction with the country rocks including the underlying Triassic siliciclastic series and the granitic basement rocks. Regional ENE- to E-W-trending major faults would have acted as conduits for upward fluid flow and traps for Zn-Pb-Ba mineralization. Conversely, the late Pb-rich mineralization stage II is broadly constrained to have occurred between ca. 70 Ma and 10 Ma and is thought to be related to the transition from orogenic shortening (late Eocene) to post-orogenic crustal extension and exhumation (early Miocene) following Alpine orogenic collapse. Mixing of down-ward percolating meteoric fluids and ascending rock-buffered hydrothermal brines that had previously equilibrated with the radiogenic basement rocks along with thermochemical sulfate reduction of transported sulfate and/or thermal cracking, would have been the main ore-forming processes that controlled ore deposition. Given these fluid characteristics and geodynamic settings, the Jbel Bou Dahar ore field is classified as a hybrid carbonate-hosted Pb-Zn-Ba district formed by the juxtaposition of two deposit types rather than one progressively evolving mineralizing system. From an exploration standpoint, new delineation here of the two metallogenic events provides valuable exploration tools for further targeting PbZn and barite resources in the Atlas system of North Africa and other areas where similar orogenic belts experienced post-rift subsidence and basin inversion.
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