الفهرس 
Title : Metasomatic alterations and economic potentialities of Neoproterozoic ophiolite rocks at the Um RashidHagar Dungash area, central Eastern Desert, Egypt
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Abstract
Ophiolitic rocks at the Um Rashid{u2013}Hagar Dungash (URHD) area are located at the southern part of the central Eastern Desert of Egypt, the northwestern corner of the Arabian- Nubian Shield (ANS). They represent the southern extension of El-Barramiya ophiolite sequence. They are dismembered, strongly deformed, metamorphosed, and show various degrees of alterations. Serpentinites form the main component of the URHD ophiolite with less common metagabbro that are found as blocks of various sizes within the ophiolitic mélange. The serpentinized ultramafic rocks are divided into partly serpentinized peridotite, massive serpentinite, sheared serpentinite and carbonated serpentinite. They host chromitite pods that occur as lenticular bodies exhibiting variation in size representing massive and nodular types. Alteration of the ophiolitic mafic-ultramafic rocks in the area of study led to the development of talc-carbonate, magnesite, rodingite and listvenite. The ultramafic rocks of the URHD ophiolites are generally highly altered and metamorphosed leading to change in the mineralogical composition of these rocks to some extent, although original igneous minerals and textures are preserved occasionally. Fresh relics of primary Cr-spinel, olivine and pyroxenes are preserved in the serpentinites. Fresh cores of Crspinel are always surrounded by ferritchromite and Cr-magnetite rims. Fresh Cr-spinel crystals have high Cr# (0.64-0.84) and low TiO2 (<0.02 wt%). Both primary and secondary olivines are recorded in the URHD serpentinites. The latter resulted from recrystallization of olivine in serpentinite due the thermal effect of adjacent granitic intrusions. Fresh olivine relics have high Fo content (0.91-0.92) similar to primary mantle olivine, while the metamorphic olivine shows wide range of Fo content (0.75 to 0.96). Fresh relics of pyroxenes include orthopyroxene and clinopyroxene