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

Abstract

The present study deals with the petrographical, mineralogical and geochemical characteristics of thealteration 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 (microclineand 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 propyliticfacies 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 zoneis composed mainly of kaolinite with minor sericite, quartz, muscovite, chlorite and rare epidote as well aszircon, hematite, goethite, magnetite, ilmenite, ilmenorutile, rutile, titanite, apatite and garnet of spessartinetype as accessory minerals.The identified minerals in the studied two alteration facies zones can be grouped into three mineralgroups which are: the primary minerals (pyrite, magnetite, galena, columbite and gold), the secondaryminerals (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 tostrongly alkaline hydrothermal solutions at pH value of more than 7 with temperature varying between 350and 450ºC, while the advanced argillic alteration facies zone is essentially associated with strongly acidichydrothermal solutions at pH value less than 7 with temperature varying between 150 and 400ºC.