Mineralogical and Geochemical Constraints on the Genesis of the Carbonate-Hosted Jebel Ghozlane Pb-Zn Deposit (Nappe Zone, Northern Tunisia)

Abstract

The Pb-Zn deposit at Jebel Ghozlane, in the Nappe zone (northern Tunisia), is hosted by Triassic dolostones and Eocene limestones and is located along faults and a thrust-sheet boundary. The sulfide mineralization of the deposit consists mainly of galena and sphalerite and occurs as vein, stockwork, breccia, dissemination and replacement ores. Three hydrothermal stages are involved in the formation of the ores: stage I is dominated by celestite-barite, hydrothermal dolomite DII, colloform sphalerite, and galena I; stage II consist of galena II; and stage III contains calcite. Galena in the deposit yielded average 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb ratios of 18.705, 15.667 and 38.734, respectively, suggesting a single upper crustal source reservoir for metals. Trace element data indicate the presence of Zn- and As-free galena and As-rich galena (with 0.2-0.5% As). Sphalerite contains 0.4% As, 0.7-0.9% Cd and 0.1-1.5% Fe. Microthermometric analysis of fluid inclusions in celestite shows that the deposit formed from fluids composed of heterogeneous mixtures of saline (19.5 ± 1 wt% NaCl eq.) aqueous solutions sourced from basinal brines, and gaseous CO2-rich phases bearing low amounts of CH4, N2 and/or H2S, at temperatures of 172 ± 5°C. © 2012 The Authors; Resource Geology © 2012 The Society of Resource Geology.