الفهرس 
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Abstract
The Um Naggat Late Neoproterozoic pluton, ” ” " ~ " ” ” 66 km southwest of Qusier city, Central Eastern Desert, Egypt, is an example of a post- to anorogenic granite that hosts rare-metals mineralization. In order to study and decipher the types of alteration across the pluton, 220 representative samples were collected and prepared for thin-polished and thin sectioning for the detailed conventional petrographic investigation, and for the Scanning Electron Microscope-Energy Dispersive Spectroscopy (SEM-EDS) analytical technique. Integration of comprehensive fieldwork and petrographic investigations reveals that the Um Naggat pluton is differentiated into three granite types: southern biotite; central alkali-feldspar; and northern albite granites. Texturally, the three varieties are separated by gradational rather than sharp contacts. The pluton has a semi-rectangular shape, and intrudes ophiolitic metavolcanics to the north and northwest, and meta-pelitic rocks to the east. Whitish, greenish and reddish colorations increase significantly towards the granite-metavolcanic contact. The magmatic phases of the three granite varieties have been pervasively subjected to a series of autometamorphic alterations and subsequent hydrothermal metasomatism. Subsolidus reactions have motivated a sequence of alternating alkaline- and acidic-based alterations that account for albitization and greisenization, respectively. Subordinate microclinization is autometamorphic, whereas the pervasive silicification and hematitization as well as chloritization are characteristic of the hydrothermal event. Among the three granite types, the albite granite is the highly altered variety. Concentration of fluorite and a significant increase in alteration towards the granite-metavolcanic contact imply that the albite-rich granitic melt might have represented the apical part of the magma chamber. The texture of the three granite varieties, and the types and intensity of the alterations they accommodate suggest that the granite rocks of the Um Naggat pluton are genetically related.