MINERALOGICAL CHARACTERIZATION OF THE ALTERATION FACIES AT GABAL EL-MISSIKAT AREA, CENTRAL EASTERN DESERT, EGYPT

The present study deals with the petrographical, mineralogical and geochemical characteristics of the
alteration facies zones recognized around the shear zone at Gabal El-Missikat area, Central Eastern Desert,
Egypt.
Petrographically, the fresh granitic samples are composed mainly of quartz, K-feldspars (microcline
and microcline perthite), plagioclase, biotite. The secondary minerals are sericite, kaolinite, muscovite,
chlorite and epidote as well as zircon, apatite, fluorite, titanite and iron oxides as accessory minerals.
Two alteration facies zones are recognized and namely as propylitic and advanced argillic. The propylitic
facies zone is composed mainly of sericite with minor kaolinite, muscovite, quartz, relics of plagioclases,
chlorite and rare epidote as well as zircon, hematite, goethite, magnetite, ilmenite, ilmenorutile, rutile,
titanite, apatite, columbite and fluorite and secondary uranium minerals. the advanced argillic facies zone
is composed mainly of kaolinite with minor sericite, quartz, muscovite, chlorite and rare epidote as well as
zircon, hematite, goethite, magnetite, ilmenite, ilmenorutile, rutile, titanite, apatite and garnet of spessartine
type as accessory minerals.
The identified minerals in the studied two alteration facies zones can be grouped into three mineral
groups which are: the primary minerals (pyrite, magnetite, galena, columbite and gold), the secondary
minerals (uranophane, kasolite and wulfenite) and the gangue minerals (anhydrite, barite, celestine,
hematite, goethite and fluorite).
The identified mineral assemblage of the studied propylitic alteration facies zone may be attributed to
strongly alkaline hydrothermal solutions at pH value of more than 7 with temperature varying between 350
and 450ºC, while the advanced argillic alteration facies zone is essentially associated with strongly acidic
hydrothermal solutions at pH value less than 7 with temperature varying between 150 and 400ºC.