Le champ filonien à Zn-(Pb, Cu, As, Hg) du district minier de Fedj Hassène (Nord Ouest de la Tunisie): Minéralogie, Eléments en traces, Isotopes du Soufre et Inclusions Fluides

J. Bejaoui; S. Bouhlel; D. Barca; A. Braham

doi:10.3989/egeol.40214.118

Authors

J. Bejaoui Centre National des Sciences et Technologies Nucléaires, Sidi Thabet; U.R. de Minéralogie et Géochimie Appliquées, Département de Géologie, Faculté des Sciences de Tunis, Université de Tunis
S. Bouhlel U.R. de Minéralogie et Géochimie Appliquées, Département de Géologie, Faculté des Sciences de Tunis, Université de Tunis
D. Barca Department of Earth Sciences -University of Calabria, Arcavacata, Rende
A. Braham Direction Inventaire et Exploration Minérale, Office National des Mines, Tunis

DOI:

https://doi.org/10.3989/egeol.40214.118

Keywords:

Vein-type Zn-Pb ore deposit, mineralogy, trace elements, sulfur isotope, fluid inclusions, Fedj Hassène, Tunisia

Abstract

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.

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