Mineralogy and geochemistry of some Proterozoic Banded Iron Formations from the Eastern Desert of Egypt

Citation

Taman ZI, Scott PW, Osman A & Hilmy ME (2002) Mineralogy and geochemistry of some Proterozoic Banded Iron Formations from the Eastern Desert of Egypt. 18th International Mineralogical Association Congress, Edinburgh, 01.2002.

Abstract
Proterozoic Banded Iron Formations (BIFs) are found in the central part of the Eastern Desert of Egypt between lats 25° 15´ & 26° 31´ N and longs 33° 22´& 34° 20´ E. Other occurrences have been reported recently in the southwestern corner of Egypt (Oweinat area). The current study has involved two areas Semna and Abu Marawat. They are the most northern occurrences of the BIFs in Egypt. The BIFs are made up mainly of magnetite, martite, specular hematite, quartz, calcite, ferroan dolomite, chlorite and apatile. Goethite, pyrite, chalcopyrite and pyrrhotitte are minor minerals. The ores show various sedimentary features including oolitic texture, fine laminations, lensoidal laminae, and contemporaneous deformation (slumping, meso- and micro-faulting). The BlF occur in successions of volcaniclastics and intercalated lavas of calc- alkaline affinity. These igneous rocks are slightly metamorphosed to lower greenschist facies. The volcanic succession is predominantly made up of fine tuffs, lapilli tuff, agglomerate and volcanic sheets. They are characterized by andesitic and basaltic compositions. Porphyritic and amygdaloidal textures are common. Pillow lava is found in some horizons. Within basin reworking occurs in the volcaniclastics and the BIFs. The BIFs are characterized by high but variable contents of iron oxides and silica. Fe2O3 usually predominates over FeO which is partially a result of the surface oxidation of the rocks. The Abu Marawal BIFs have more Fe2O3 than that of Semna area. In general, the ores are characterized by high P2O5 and low Al2O3 and alkalis. Both BIFs and volcanogenic sequence in the two areas show great similarities, in mineralogy, textures, structures and geological setting. These criteria may indicate a common origin.