Mineralization Styles and Alteration Paragenesis of Metasomatic Zones in the Highly Fractionated Granite of Gabal Gattar, Northern Eastern Desert, Egypt

Abstract

The Gattar-II uranium occurrence is one of the major seven granite-related uranium localities in Gabal Gattar area, northern Eastern Desert of Egypt. It is the most significant occurrence in the area, where many uranium showing were delineated within a metasomatized granitic body, accompanied by many alteration features. This occurrence was selected in this study with the aim to determine the geological, structural and mineralogical characteristics of the uranium mineralization related to metasomatized
rocks and construct a paragenetic sequence for the alteration assemblage. The granite at this locality is alkali feldspar granite that belongs to uranium-bearing granite with highly evolved characteristics. The richest uranium ore bodies are distributed along a nearly E–W striking shear zone that transected by mineralized NS, NNE to NE and NW trending fractures. A metasomatic zone is developed along intersections of these fractures with the major shear zone. Main uranium mineralization, predominantly, consisting of uranophane with lesser amounts of pitchblende. Mineralogical and petrographical observations for mineralized samples from G-II suggested at least three stages for alteration and uranium minerals generation in the granite. The earliest pre-ore stage is characterized by partial to complete chloritization of biotite and precipitation of calcite in vugs as well as partial dissolution of
primary quartz. This stage is followed by main ore stage, which characterized by local crystallization of pitchblende-pyrite-magnetite assemblage and accumulation of uranophane-fluorite-calcite mineral phases. The last stage of alteration is marked by limited alteration of magnetite to hematite and limonite as well as kaolinitization and precipitation of Mn-oxides.