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

Geological, mineralogical, geochemical and fluid inclusion studies were car ried out on both the granitic rocks at the Gabal El-Ineigi Pluton and assoc iated fluorite veins in order to examine their genetic relations. Gabal El-Ineigi rocks range from adamellite to granite composition. They or ginated from metaluminus calc-alkaline magma having strong alkaline tendenc ies. They have similar characteristics to I-type granites and were probably generated within an extensional environment due to crustal relaxation duri ng a post-collision episode (< 600 Ma). Studies of fluid inclusions from vein fluorite and quartz show that they ar e aqueous with phases (L+V) and that secondary inclusions predominate. The fluorite mineralisation probably took place at temperatures of > 250 degree sC; the fluid salinities ranged up to 21.4 equiv, wt% NaCl. The quartz vein s were formed at lower temperatures (similar to 120 degreesC) and fluid sal inites ranging up to 10.36 equiv. wt% NaCl. Rare earth element abundances in fluorite are variable and the relation bet ween Tb/Ca versus Tb/La confirms a hydrothermal origin for fluorite. The ne gative Ce anamolies indicate high O fugacities at the source of the hydroth ermal fluids. The negative Eu anomalies suggest equilibration of the hydrot hermal fluids with the host granites. (C) 2001 Elsevier Science Limited. Al l rights reserved.