The Geology and the Iron Mineralisation in the Northeastern Nuba Mountains, Kordofan Province, Sudan.

Abstract

The area occupies the northeastern portion of the Nuba Mountains – a distinctive physiographic feature from central Kordofan – and is bounded by latitudes 11˚45'N and 12˚15'N and longitudes 31˚15'E and it is about 2,700sq km in area. The lithology belongs to the basement comlex which is generally assigned as being of Precambrian age. The succession includes major lithologies recognized elsewhere in the Nuba Mountains and consisting of the acid gneiss group at the base of the succession followed by a metasedimentary sequence of which grey marbles and graphitic schists are most significant for wider correlation. Both groups have suffered an early history of intense isoclinal folding (F1) and relatively high grade regional metamorphism (M1), a history which is considered to be unique for the two groups. A wide volcanic activity followed these events and resulted in the formation of basic and acid rocks – now the metavolcanics – lying disconformably on the pre – existing deformed and highly metamorphosed rocks. This is followed by a second deformation (F2) and metamorphism (M2) of the greenschist facies. The present concordant relation between the older groups and the metavolcanics is considered to be dominantly a structural one due to the F2 deformation. F2 folding was accompanied by major thrusting which is believed to be responsible for the juxtaposition of the older gneisses and the relatively younger metasediments. Rejuvenation of movement along the F2 thrusts during the F2 deformation represents a significant event resulting in the formation of regional cataclysis (M2) and wrench faulting post – dating the granitic intrusions in the area as well as the first post – F2 and pre – F3 hydrothermal iron mineralisation (Jebel El – Ahmar type) and represent the channel for the second iron mineralization (Jebel Agbash type). Jebel El – Ahmar types and ebel Agbash type are mainly magnetite and deposits respectively. Each type of iron mineralization is accompanied by wall rock alterations preceding and succeeding the iron ore deposition. The hydrothermal origin of these iron ores is reached from field observations, mineralogical, textural, structural and wall rock alteration criteria together with chemical and spectral analyses results. Estimates of ore quantity for the exposed parts of the two type of iron ores have been made. An attempt is made to correlate the geology and iron ore mineralisations of the present area with that of Jebel Abu Tulu and other parts of the Nuba Mountains. A brief account of the general history of the mapped area as well