Mineralogy and fluid inclusions evidence for the genesis of molybdenite mineralization at Gabal Gattar, North Eastern Desert, Egypt

摘要

Molybdenite mineralization is located at the northern periphery of Gabal Gattar granite. Molybdenite-bearing quartz veins are well developed within the granitic rocks in the northern part of the pluton. These veins are striking mainly NNE. Wall rock alteration represented by silicification, kaolinitization and serecitization. The study of ore mineral assemblage revealed the relative predominance of molybdenite, beside gold, silver and bismuth, whereas wulfenite, hubnerite, columbite, tantalite, goethite and jarosite are rare minerals. Ore bodies of sulphide phase are quite poor and represented by minor quantities of pyrite, chalcopyrite, galena and sphalerite. Fluid inclusion microthermometry confirmed the presence of two types of fluid inclusions. Primary two-phase aqueous inclusions (L + V) as type 1 and secondary two-phase aqueous inclusions (L + V) as type 2. The secondary inclusions are the most abundant type in quartz vein bearing molybdenite. They are arranged along healed fractures displaying oval, sphere or elongated shapes and up to 24 mu m in size. Fluid inclusion study indicates that fluids infiltrated in Gattar granite were generally low salinity from 1 to 6 wt.% NaCl eq. with a maximum peak at 1 wt.% NaCl eq. with temperatures from 149.7 to 272.3 degrees C with majorities at 220 degrees C and pressures between 35 and 100 bars. The decreasing of homogenization temperatures (Th) with salinity may indicate protracted mixing of two fluids that facilitated the attainment of thermal equilibrium as well as chemical homogeneity.