Mineralogy and geochemistry of Gabal El-Ineigi Granite and associated fluorite veins, Central Eastern Desert, Egypt: application of fluid inclusions to fluorite genesis

Abstract

Geological, mineralogical, geochemical and fluid inclusion studies were carried out on both the granitic rocks at the Gabal El-Ineigi Pluton and associated fluorite veins in order to examine their genetic relations. Gabal El-Ineigi rocks range from adamellite to granite composition. They originated from metaluminus calc-alkaline magma having strong alkaline tendencies. They have similar characteristics to I-type granites and were probably generated within an extensional environment due to crustal relaxation during a post-collision episode (< 600 Ma). Studies of fluid inclusions from vein fluorite and quartz show that they are aqueous with phases (L + V) and that secondary inclusions predominate. The fluorite mineralisation probably took place at temperatures of > 250°C; the fluid salinites ranged up to 21.4 equiv. wt% NaCl. The quartz veins were formed at lower temperatures (∼ 120°C) and fluid salinites ranging up to 10.36 equiv. wt% NaCl. Rare earth element abundances in fluorite are variable and the relation between Tb/Ca versus Tb/La confirms a hydrothermal origin for fluorite. The negative Ce anamolies indicate high O fugacities at the source of the hydrothermal fluids. The negative Eu anomalies suggest equilibration of the hydrothermal fluids with the host granites.