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

The Fedj Hassène 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 Hassène, 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/cm3 and 1.11 g/cm3 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°C. These inclusions homogenized to the liquid phase between 156°C and 210°C and salinities values ranging from 22 to 28 wt% NaCl and an average around 23% wt NaCl. The δ34S (VCDT) values of sphalerite are in the range of + 4,6‰ to 6,4‰ (average=5,6‰). Thermochemical reduction of Triassic sulfate by reaction with hydro-carbons is the most probable source for the heavy and the narrow range of the ?34S values. Mineralogical, geochemical of trace elements, fluid inclusions and sulfur isotopes studies allow to include the vein-type ore field of Fedj Hassène in the polymetallic (Pb-Zn-As-Hg) vein mineralization of the nappe zone in northern Tunisia and north eastern Algeria. Le district minier de Fedj Hassène est situé à proximité de la frontière algéro-tunisienne, à 10 Km au sud de la ville de Ghardimaou. Il regroupe plusieurs filons à Pb-Zn, localement accompagnés par des sulfures de Cu, d’As et d’Hg. Les réserves sont estimées à 370.000 t à 10% de Zn et 0,2% de Pb. Les minéralisations remplissent des fractures subparallèles à la faille d’Ain Kohla de direction ESEWNW et des fentes d’extension qui recoupent les calcaires marneux du Turonien moyen. Le filon principal est formé par de la sphalérite massive brune et accessoirement par de la galène et de la barytine. Le minerai peut se présenter sous forme massive ou sous la forme de ciment d