Mineral Resources Potential - Geothermal Resources

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western Asfa and continues along the eastern side of Mica. ThG ;, &'
system already includes sectors that represent evolving
basins (the Gulf of Aden and the Rsd Sea), but mostly it comptises
sub-aerial intracratonic rifb, including the Ethiopian Rift Valley.
Sub-aerial volcanism h the Ethiopian Rift Valley %has caused
hydrothermal activity, which is still active in s v d sites being
investigated for geothed energy. Extinct geothd fields are
also quite common. The possibility that these gmthermd systems,
related to the contined rifling, have been .and may be oreforming
systems cannot be discarded a priori.
An epithermal gold deposit is one in which the gold
minerdidon occurs within 1 tp 2 km of surface and is deposited
from hot fluids, The fluids are estimated to range in tempemhm
from less than lOOC to hut 300C and, during the hdon of a
&posit, can appear at the surface as hot springs, similar to those
found in Yellowstone National Park (in northwestern Wyoming,
muthem Montana and e&m Idaho). The deposits are mast often
fomd in areas of active volcanism around the margins of
continents.
EpiEhermal gold mineralization can be formed from two
types of chemical1 y distinct fluids -"low sulphidation' (LS) fluids,
which are qduced and have a na-neu-tral pH (the measure of tb
concentration of hydrogen ions) atld "high sdphidation" (HS)
fluids, which are more oxidhd and acidic. LS fluids are a mixture
of rainwater that has percolated into the subsurface and magmatic
water (derived from a molten m k source deeper in the earth) that
has risen toward the mfke. Gold is carried in ailution and; for LS
waters, is deposited when the water approaches the surface and
boils, HS fluids are mainly derived from a magmatic some a d
deposit gold near the surface when the solution c ds or is diluted
by mixing with rainwater. The gold in solution may come either