Alkaline Rocks and Carbonatites of the World

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Bir Um Hibal (Gebel Bir Um Hebal)

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Occurrence number: 
049-00-031
Country: 
Egypt
Location: 
Longitude: 33.23, Latitude: 23.72

The Bir Um Hibal complex is an elliptical intrusion covering 15x10 km which is overlain in places by Nubian sandstone. Most of the complex consists of peralkaline quartz syenite but in the south a broad band of peralkaline granite intrudes the syenite (Mohamed, 1996). The circular, 2 km diameter Agib complex comprises a core of leucocratic syenite surrounded by rhyolite lavas that cross-cut the quartz syenite. The quartz syenite is a coarse-grained rock of perthite, minor quartz, a calcic amphibole, aegirine, which is generally rimmed and replaced by arfvedsonite, prisms of arfvedsonite, relict fayalite and biotite. The granite is a medium-grained rock of perthite, albite, quartz, riebeckite and arfvedsonite, aenigmatite and biotite, which forms fringes around arfvedsonite. Eight rock analyses, including an extensive suite of trace elements, is given by Mohamed (1996).

Age: 
Rb-Sr on three syenites gave an isochron age of 223(9 Ma (Hashad and El Reedy, 1979).
References: 
HASHAD, A.H. and EL REEDY, M.W.M. 1979. Geochronology of the anorogenic alkalic rocks, South Eastern desert, Egypt. Annals of the Geological Survey of Egypt, 9: 81-101.MOHAMED, F.H. 1996. Geochemistry of Bir Um Hibal complex: alkaline syenites and granites from the Eastern Desert of Egypt. Chemie der Erd, 56: 45-64.
Location: 
Scratchpads developed and conceived by (alphabetical): Ed Baker, Katherine Bouton Alice Heaton Dimitris Koureas, Laurence Livermore, Dave Roberts, Simon Rycroft, Ben Scott, Vince Smith