Genetic Model for Beryl/Emerald-Related Schist in Egypt: Clues of Metasomatism

Um Solimate emerald deposit is a unique example for the well-known beryl-related schist type. Where, the Be-mineralization is restricted to NNE-trending quartz veins/lenses and as disseminated emerald grains within the altered-metasomatic zones of phlogopite- and graphite-schists. The study of fluid inclusions for the mineralized quartz vein revealed three major groups: (i) aqueous (H2O-NaCl), (ii) aqueous-carbonic (H2O-CO2-[CH4]-NaCl), and (iii) aqueous-hydrocarbonic (H2O-CH4) FIs. They have been further classified into five types (namely: types 1, 2, 3, 4 and 5) according to number of phases at the room temperature (20 degrees C) as well as microthermometric measurements. Based upon the study of fluid inclusions, the initial-ore forming fluid was supposed to be of magmatic nature, characterized by a relatively high temperature of homogenization (Th, tot: 269-485 degrees C) and higher salinity (8.4 wt.%-9.6 wt.% NaCl equiv.), followed by development of aqueous-carbonic inclusions at lower temperature (Th, tot: 241-355 degrees C) and lower salinity (3.3 wt.%-4.9 wt.% NaCl equiv.) through metamorphic dehydration/decarbonation. Methane-rich FIs were suggested to be formed as a result of local re-equilibration of graphite in reduced environment at the contact aureole of the felsic intrusion. The P-T conditions of ore formation were estimated as modal temperature between (330-370 degrees C) and fluid pressures of about 200 MPa, corresponding to an estimated depth ranges from 7 to 10 km. The formation of emerald is closely associated with multiple events through the ore evolution, the deposition is ascribed to destabilization process of continuous metasomatic interactions and elemental substitutions between felsic-derived Be-bearing fluids with the adjacent mafic-ultramafic rocks at the zone of mineralization.