Mineral Resources Potential - Geothermal Resources

Metallic Minerals 59
with tempratures up to 95%- steaming grounds, silica sinter and
travertine deposits. The hydrothermal deposit temperatures
measured in the deq cxploratdry wells range from 88 b 335'C
(Solomon Kebede, 1 986).
The alteration observed in the studied samples froin Aluto
includes an upper facies characterized by intermediate 'and
propylitic assemblages. Intermediate argillic facies are typidy
represented by smectite-group clay minerals; alteration intensity is
variable, hm incipient groundmass argillification to almost
pervasive metasomatism. The latter is best developed in rack units
originally very rich in glass. Propylitic alteration includes the
chmcteristic minerals, calcite, chlorite, quartz and epidote. The
metallic minerals found in the studied samples mostly include
oxides and sulphides. The oxides consist of magnetite, ilmenite,
hematite and Ti-oxide. The sulphide minerals are pyrite,
chalcopyrite, and sulphosalts possibly of Pb. Pyrite is the most
abundant. Gold value ranges from few ppb to 100 ppb,
The emd dab graben
This graben is found further north in the Afar depression. It is a
NW-SE trending graben about 50 lun wide and is the southern
extension of the Afar active spreading zones where the active Erta
Ale-Manda Harm volcanic ranges are situated. The A h axial
: ranges are considered to be the exposed equivalents on land of the
Red Sea oceanic spreading ridges (Barberi and Varet, 19771,
The Tendaha graben exposes a thick succession of basalt
flows of Pliocene age (known as the Afar Stratoid Series) at its
borders. The graben is filled with thick lacustrine and alluvial
1 deposits consisting of siltstone and sandstone. Very young basaltic
flows and scoria cones (the Afar Axial Ranges) have be~n
emplaced on top of the graben volcani-cIastic sediments. The axial.
zone is also characterized by the ~resence of open fissms and