Genesis of Zn-Pb-(Ba-Sr) mineralization in the peridiapiric cover of Jebel El Akhouat, Ech Chehid salt dome, Northern Tunisia

The Jebel El Akhouat Zn-Pb-(Ba-Sr) ore deposit, located in the Tunisian Dome zone, is hosted mainly in the organic matter-rich Albian and Cenomanian-Turonian rocks. The orebodies occur mainly as open-space fillings and are structurally-controlled. The paragenetic sequence consists of three stages, which reflect three ore events. Three discrete stages of Zn-Pb sulfide and/or Zn-Pb-Ba-Sr sulfide-sulfate ores are identified. Fluid inclusion study carried out on selected minerals of different stages reveals that sphalerite, galena, marcasite, celestine, barite, and fluorite precipitated as a result of mixing between a hydrothermal, saline, metal-rich basinal fluid and a low-temperature, less saline, metal-depleted, sulfur- or sulfate-rich fluid with the intermittent involvement of hydrocarbons. Based on sulfur isotope data, sulfur of sulfides was derived from the reduction of the dissolved Triassic sulfates primary through thermochemical sulfate reduction with a contribution of bacterial sulfate reduction. The Pb isotopic composition of galena samples and trace elements data of the host carbonate rocks suggest that metals were derived primarily from the Paleozoic siliciclastic rocks with a contribution of the organic matter-rich Albian and Cenomanian-Turonian rocks. The Alpine orogeny triggered the migration of the metalliferous fluids from the deep parts of the basin towards the peridiapiric paleohigh of Ech Chehid diapir through major faults towards the loci of deposition.