BLOCK 68-A
The Block 68-A is located north of Wadi Onib in the state of Red Sea, spread over an area of 75 Sq.km after
two levels of Relinquishment as per the licence norms. Approximate Central coordinates 21° 33’ 45" N ; 35°
19’ 40" E.
The Block is accessible from Al Abedia or Muhammad Qol (north of Port Sudan) through wadis and desert
sandy paths. It is located at the about 230 km from Muhammad Qol or about 670 km from Atbara via Nauraya
and Jabel Nimar Markets. Port Sudan city is the nearest Seaport, Railway terminus and the Airport.
Regional Geology and Structure
The Arabian-Nubian Shield (ANS) represents the
northern part of the East African Orogeny.
Deformation, metamorphism, and accretion
occurred between ~ 850 Ma and 550 Ma. The ANS is
composed of intra-oceanic island arc/back-arc basin
complexes and micro-continents, welded together
along north to east trending sutures.
The Basement complex (Kashebib Series) towards
the Red Sea comprises migmatites and granitoids,
minor grabbroic rocks, amphibolites and meta-
sedimentary sequences viz., mica schists, quartzites
and marbles.
Block 68-A Geology and Structure
The area forms the NE strike contiguity of the
ancient Onib gold mining area. The Onib ophiolite
complex defines that of the Onib - Sol Hamed suture
in the Nubian Shield.
The Onib complex forms a 60 km long belt flanked
by volcano-sedimentary sequences of the Gebeit
and the Gerf terranes. The complex is in tectonic
contact with the volcano-sedimentary sequences
that are apparently younger than the ophiolite.
Gold Mineralization in Block 68-A
Two styles of Gold mineralization have been observed based on the geological, structural and exploration
data.
This is along the WNW-ESE trending fracture and is
associated with extensive wall rock alterations and
flanking thick veins of smoky and milky quartz. Host
rock in this case is diorite. Several intersections of this
WNW-ESE fracture are observed with NE-SW and a few
NW-SE faults. The mineralized highly altered host rock
and the associated quartz veins can be traced along the
WNW-ESE strike for over 1500 m, though faulted in NE-
SW trends at several places. Intense ferruginous/sericitic
alteration and associated gold mineralization in higher
grades are noticed in the zone of intersection between
WNW-ESE, NE-SW and NW-SE structural elements.
This, with a regional NE-SW shear trend, is along the
contact of altered metasediments (phyllites) and
metavolcanics, with pervasive quartz (smoky and
milky) stringers. These formations are tightly folded.
NW-SE trend of the fold axis is common with plunge
gently to moderately due NW. Deformation in two
phases is observed, i.e., NW-SE trending folds that
are re-folded in E-W direction. Gold mineralization
is recorded in association with the altered wall
rocks of the quartz veins along the fold axes.
Abundance of cubic disseminated pyrite is observed
all over in the phyllite.
The overlying greenschist complex or the ophiolite-volcanic-sedimentary greenschist assemblage
(Nafirdeib Series) contains ophiolitic rocks, andesites, rhyolites and meta-sediments, occurring as narrow
elongated belts. Mafic to felsic plutons and ring complexes intruded the Proterozoic rocks during and after
the Pan-African Orogeny.
Structural evolution of the northern Red Sea Hills is summarized in three or more phases of deformation
(Miller and Dixon, 1992).
Older pre-orogenic sheared granitioids and associated Metasedimentary rocks, ophiolitic mafic -ultramafic
rocks, low grade arc volcano-sedimentary sequences syn-orogenic granitioids complexes, late orogenic
alkaline complexes and micro granite dykes and sills are exposed in the Block. Locally, complete ophiolitic
sequences can be observed including peridotites, gabbros, sheeted dykes, pillow lavas and sedimentary
rocks that reflect a deep-sea environment.
Regional strike of the formations in this complex is NE-SW. A secondary major fracture is manifested by
significant mylonitization and alteration in WNE-ESE direction.
Most common lineations noticed are the mineral lineation, micro-fold axis lineation and boudins. Intensive
shearing is observed mainly in NE-SW direction parallel to the dominant foliation trend.
