Mineralization and fluid inclusion studies of the Aptian carbonate-hosted PbZnBa ore deposits at Jebel Hamra, Central Tunisia

The Jebel Hamra, which is hosted in the Graben Zone of central Tunisia, is an epigenetic dolomite-hosted PbZnBa deposit that replaces platform carbonates of Lower Cretaceous age (Upper Aptian). Mineralization occurs as stratiform lenses, and breccia- and paleokarst-fillings. Ore reserves are around 0.5Mt and grades are 7% Zn and 3% Pb. Sulphide mineralization occurs as local replacement of dolomitized and silicified carbonate strata. Primary inclusion fluids in sphalerite have homogenization temperatures ranging from 110 to 152°C with a mode at 137°C. Final ice-melting temperatures range from -15 to -10°C, corresponding to salinities of 13.5-18.5wt.% NaCl equiv. Fluid inclusions in saddle dolomite homogenize to the liquid phase between 175°C and 193°C, with a mode at 187°C. Final ice-melting temperatures range from -23 to -15°C corresponding to salinities between 18 and 24wt.% NaCl equiv. δ34S values of sphalerite and galena vary between -3 and +6.3‰, compatible with a thermochemical reduction of sulfate from Triassic evaporites (δ34S=+15‰). PbZnBa mineralization is spatially and possibly genetically related to E-W-trending fractures, which acted as conduits and/or depositional sites for circulating hydrothermal fluids. Fluid inclusion and sulfur isotope data suggest the contribution of basinal brines in ore formation. Combined field, sedimentological, mineralogical, isotopic and geochemical data of the Lower Cretaceous mineralization in Jebel Hamra is compatible with Mississippi-Valley-type mineralization. © 2013.