V13C-3158
Fluid inclusion and stable isotopes studies of epithermal gold-bearing veins in the SE Afar Rift (Djibouti)
Monday, 14 December 2015
Poster Hall (Moscone South)
Nima Moussa, Centre d'Etude et de Recherche de Djibouti, Institut Science de la Terre, Djibouti, Djibouti, M.C Boiron, Laboratoire GeoRessources, G2R, CREGU, Vandœuvre lès Nancy, France, Nathalie Grassineau, Royal Holloway University of London, Department of Earth Sciences, EGHAM Surrey TW20 0EX, U.K, United Kingdom, Yves Fouquet, IFREMER, REM / Géosciences Marines, Plouzané, France and Bernard Le Gall, UMR 6538, Domaines océaniques, UBO-IUEM, Place Nicolas Copernic, 29280, Plouzané, France
Abstract:
The Afar rift results from the interaction of a number of actively-propagating tectono-magmatic axes. Recent field investigations in the SE Afar rift have emphasized the importance of hydrothermal system in rift-related volcanic complexes. Mineralization occur as gold-silver bearing veins and are associated with felsic volcanism. Late carbonate veins barren of sulfides and gold are common. The morphologies and textures of quartz show crustiform colloform banding, massive and breccias. Microthermometric measurements were made on quartz-hosted two phases (liquid + vapor) inclusions; mean homogenization temperature range from 150°C to 340°C and ice-melting temperatures range from -0.2° to 1.6°C indicating that inclusion solutions are dilute and contain 0.35 to 2.7 equivalent wt. % NaCl. Furthermore, δ18O and δ13C values from calcite range from 3.7 to 26.6 ‰ and -7.5 to 0.3‰, respectively. The presence of platy calcite and adularia indicate that boiling condition existed. This study shows that precious-metal deposition mainly occurred from hydrothermal fluids at 200°C at around 300 and 450 m below the present-day surface in a typical low-sulphidation epithermal environment.
