Alkaline Rocks and Carbonatites of the World

Setup during HiTech AlkCarb: an online database of alkaline rock and carbonatite occurrences

El Naga (Gabal El Naga)


Occurrence number: 
Longitude: 34.47, Latitude: 22.7

El Naga defines a horseshoe-shaped ridge some 4 km in diameter completely surrounded by wadi alluvium so that no outer contacts are exposed. However, on the outer side of the wadi in the northeast and southeast, beyond the area shown on Fig. ??, Precambrian gneisses are slightly fenitized with reddening of feldspars and development of amphibole. The outer part of the complex consists of coarse rocks described as umptekite consisting of perthite, a little nepheline and analcime, alkali pyroxene and amphibole, biotite and accessories. The central area is dominantly of nepheline syenite with 30% or more of nepheline, which may be replaced by zeolites and aegirine-augite. There are remnants of a volcanic cone in the central area which include trachybasalt, trachyte, phonolite and a range of pyroclastic rocks. They are cut by apophyses of the umptekite and nepheline syenite which have caused much alteration and the production of hybrid rocks. Numerous radial and ring-dykes up to 2 m thick consist of a range of microsyenites and phonolites. Modal and chemical data are given by El Ramly et al. (1969b and 1971) and trace element data by Abdel-Aziz and Hassan (1973) and Soliman (1987). M.S. Garson, in an unpublished report, refers to radially disposed, coarse-grained calcite veinlets on the north-eastern part of the central stock which contain up to 300 p.p.m. Nb. He also notes a record of a radial carbonatite dyke to the south-east of El Naga.

The complex has been investigated geochemically and radiometrically but no economically significant deposits were found at the surface (Abdel-Aziz and Hassan, 1973).
Five K-Ar determinations on umptekite and nepheline syenites ranged between 145 and 146 Ma (Serencsits et al., 1979) and Meneisy and Kreuzer (1974b) obtained 84±3 and 82±3 Ma on nepheline syenite. A Rb-Sr age of 146.1±6 was obtained by Hashad and El Reedy (1979). Fission-track dating of apatite from umptekite and nepheline syenite gave 72.0±4.6 to 77.2±2.9 Ma (Omar et al., 1987).

ABDEL-AZIZ, A.H. and HASSAN, M.A. 1973. Further contribution to geology and geochemistry of some Egyptian ring complexes. Annals of the Geological Survey of Egypt, 3: 167-75.EL RAMLY, M.F., BUDANOV, V.I., ARMANIOUS, L.K. and DERENIUK, N.E. 1969b. The three ring complexes of Gabal El Kahfa, Gabal Nigrub El Fogani and Gabal El Naga (South Eastern Desert of Egypt). Geological Survey of Egypt, Paper, 52: 1-39.EL RAMLY, M.F., BUDANOV, V.I. and HUSSEIN, A.A.A. 1971. The alkaline rocks of south-eastern Egypt. Geological Survey of Egypt, Paper, 53: 1-111.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.MENEISY, M.Y. and KREUZER, H. 1974b. Potassium-argon ages of nepheline syenite ring complexes in Egypt. Geologisches Jahrbuch, Hannover. D9: 33-9. SERENCSITS, C.M., FAUL, H., FOLAND, K.A., EL RAMLY, M.F. and HUSSEIN, A.A. 1979. Alkaline ring complexes in Egypt: their ages and relationship to tectonic development of the Red Sea. Annals of the Geological Survey of Egypt, 9: 102-16.SOLIMAN, M.M. 1987. The younger granites and ring complexes of the Southeastern desert of Egypt and their relation to mineralization. Journal of African Earth Sciences, 6: 745-54.

Fig. 3_58 El Naga (after Abdel-Aziz and Hassan, 1973, Plate 1).
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