The Vein-type Zn-(Pb, Cu, As, Hg) mineralization at Fedj Hassene orefield, North-Western Tunisia: Mineralogy, Trace Elements, Sulfur Isotopes and Fluid Inclusions

The Fedj Hassene district is localized at the edge of the Tuniso-Algerian border 10 km of Ghardimaou area. It consists of a Zn-Pb vein type with minor amounts of Cu-As-Hg. The total Zn reserves are about 370.000t. The mineralization occurs within subparallel fractures to the Ain El Kohla ESE-WNW fault. Host rocks consist of limestones and marly limestones of the Middle Turonian. In the principal lode of Fedj Hassene, the mineralization occurs as vein filling of massive and brecciated brown sphalerite and minor galena ore with gangue. Other trace minerals are pyrite, chalcopyrite, orpiment, realgar, smithsonite and cerussite. LA-ICP-MS analyses in sphalerites show mean contents of 0,84 wt% Fe, 0,14 wt% Cd and 0,02 wt% Mn Ore. Fluid inclusions study in calcite and sphalerite reveals one mineralizing fluid characterized by an average salinity 23% wt NaCl with decreasing homogenisation temperature. In fact the temperature shows decrease from sphalerite to calcite. The fluid density that corresponds to trapping pressure ranges between 1.00 g/cm(3) and 1.11 g/cm(3) and pressure close to 200 bars. Microthermometric data in fluid inclusion hosted by gangue mineral presented by calcite show an average temperature of formation around 194 degrees C. These inclusions homogenized to the liquid phase between 156 degrees C and 210 degrees C and salinities values ranging from 22 to 28 wt% NaCl and an average around 23% wt NaCl. The delta(34)S (VCDT) values of sphalerite are in the range of + 4,6 parts per thousand to 6,4 parts per thousand (average=5,6 parts per thousand). Thermo-chemical reduction of Triassic sulfate by reaction with hydro-carbons is the most probable source for the heavy and the narrow range of the delta(34)S values. Mineralogical, geochemical of trace elements, fluid inclusions and sulfur isotopes studies allow to include the vein-type ore field of Fedj Hassene in the polymetallic (Pb-Zn-As-Hg) vein mineralization of the nappe zone in northern Tunisia and north eastern Algeria.