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The Miri Hills form the largest alkaline complex, of about 800 km2, in the Nuba Mountains. Basement rocks on the southeastern side of the complex are granitic gneisses, while in the north graphitic schists are transected. The main mass of the hills is a peralkaline quartz syenite but with some subalkaline areas. It is variable in compositon with one minor facies of aegirine, albite and fluorite which was interpreted by Curtis and Brinkmann (1985) as being metasomatic. Areas of peralkaline granite and microgranite have been mapped in various parts of the complex and some are dyke-like bodies. A vent breccia within a set of ring-dykes has been identified as have small areas of peralkaline rhyolitic breccia and porphyritic trachyte. An area of approximately 9x1 km has been delineated by anomalously high gamma-ray counts which appear to be caused by veins up to 20 cm thick of ferruginous quartz-rich rock usually containing aegirine and sodic amphibole. Trace element data for samples of the veins are given by Curtis and Brinkmann (1985) and bastnasite was identified in some specimens.
CURTIS, P. and BRINKMANN, K. 1985. The geology of younger intrusive alkali complexes in the southwestern Nuba Mountains, Sudan. Geologisches Jahrbuch, 63: 3-41.EL NADI, A.H. 1980. The geology of the Kheig El Kheil, Damik and Umm Dugo igneous complexes, Nuba Mountains, Sudan. M.Sc. thesis, University of Khartoum. (unpublished)
