Download The area occupies the northeastern portion of the Nuba Mountains

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Transcript
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 (M 2) 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 w