Mineral Resources Potential - Geothermal Resources

54 Mineral Resources Potential of Ethiopia
directly from the magma source or it may be leached out of the
host volcanic rocks as the fluids travel through them.
In both LS and HS models, fluids travel toward the s ace
via fractures in the rock, and mineralization often occurs 4within
these conduits. LS fluids usually form large cavity-filling veins, or
a series of finer veins, called stockworks, that host the gold. The
hotter, more acidic HS fluids penetrate Wer into the host rock,
creating mineralization that may include veins but which is mostly
scattered throughout the rock. LS deposits can also contain
economic quantities of silver, and minor amounts of lead, zinc and
copper, whereas HS systems often produce economic quantities of
copper and some silver. Other minerals associated with LS systems
are quartz (including chalcedony), carbonate, pyrite, sphalerite a h
galena, whereas an HS system contains quartz, alunite, pyrite and
copper sulphides such as erwgite. Geochemical exploration for
these deposits can result in different chemical anomalies,
depending on the type of mineralization involved, LS systems tend
to be higher in zinc and lead, and lower in copper, with a high
silver-to-gold ratio. HS systems can be higher in arsenic and
copper with a lower silver-to-gold ratio.
Epithermal gold occurrences in Ethiopia
The Ethiopian Rift Valley in general held little more than an
academic interest in scientific circles for a long period of time.
Detailed geological studies and regional mapping of the rift valley
have been conducted since the last 25 years. These have helped
delineate specific industrial resources (e, g,, diatomite, bentonite,
soda ash and geothermal steam), mainly through the work of the
EGS. A new metallogenic province characterized by epithermal-
type gold mineralization has been recently identified in Ethiopia
(Solomon Tadesse, 200 1 ). Low sulphidation (adularia-sericite
type) occ~cces have been found within Quaternary volcanoclastic
rocks of the MER.