Mineral Resources Potential - Geothermal Resources

148 Mineral Resources Potential of Ethiopia
represents a phospho-genic period in which many phosphorites
have been discovered worldkide. Unfortunately, the Upper
Cretaceous sediments do not crop out at the surface.
Potential areas in Ethiopia with the greatest chance of
finding large quantities of sedimentary phosphates are in the
eastern part of the country, in Tertiary sedimentary sequences
associated with transgressions and regressions in the Somalia-
Ogaden embayment. The Auradu sequence in particular has the
potential of bearing phosphates as these sediments were deposited
under conditions favourable for phosphate accumulation. These
characteristics include a favourable palmgeographic setting, cyclic
transgressive-~gressive sequences, a typical chert-limestone-marl
association and deposition during a major phosphogenic time
interval, the Eocene. Other potential areas for finding phosphates
are the carbonatite-peralkaline ring structures of Cenozoic age.
To date, phosphate mineral resources in Ethiopia (Wollega,
= Bale, and Borena areas) are related to intrusive rocks. Layered
gabbro, gabbro-pyroxenite, and alkaline gabbro plutons host
apatite-ilmenite mineralization. The gabbroic intrusions of Bikilal
( Wollega) and gabbro-pyroxenite rocks emplaced in the basement
rocks of biotite-amphibole gneisses and quartzo-feldspathic
gneisses of Melka Arba are currently regarded as the most
promising potential phosphate resources. Apatite, ilmenite and
magnetite are the main minerals of economic interest in the area.
Apatite is mainly hosted by disseminated apatite-oxide-bearing
pyroxenite and gabbro pegmatites. The ore occurs as lenses and
interlayering with gabbro and have width ranging from stringers to
several meters. The average grade of P205 for Melka Arba area is
about 3.75% (Mengistu and Fentaw, 2000).
Small amounts of mitridatite, a very rare Ca-Fe-Mn
phosphate mineral with the formula c%(H~ 0) [(~e* 8.2
0.8)06(P04)9].3H20 has been found in lacustrine sediments in the
Shungura Formation near Kelem north of Lake Turkana, in