Mineral Resources Potential - Geothermal Resources

60 Mineral Rrsources Potential of Ethiopia
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numerous active faults which as a whole define the sites of active
spreading.
The fissures and faults are evidence of active and fossil
hydrothermal deposits which extend for several kms along strike.
In fact, the most interesting feature of this area is the extensive
hydrothermal activity which is controlled by N W -SE trending
normal faulting. h the Tmdaho rift, the hydrothermal activity in
the area extends for several krns according to a general NW-SE
trend and consists mainly of steaming grounds. Several veins
preferably cut the rocks undergoing potassic altersttion. These
veins, with variable strike mund NW-SE, range from veinlets a
few meters long and a few cehheters thick to bodies several
hundreds of meters long. The quartz forming in these veins may be
chalcedony near the walls, but commonly the central part of the
veins is drusy and colourless mmcrystalline quartz. The
alteration is manifested by the presence of mined assemblages
a including chlorite, smectite, vermiculite, epidote, adularia and
1 . quartz. The sulphide minerals include pyrite, galena, chalcopyrite,
stibnite and covelitt. Sarnples h m drill cores recovered for the
purpose of exploratory geothermal energy have been analyzed for
gold. Analysis of a few samples hrn a core in Tendaho (TDI)
range in value fiom tens of pbb to 400 pbb Au.
I
PetPobgicrrl notes
The volcanic rocks of the above described formations range in
composition from alkali olivine basalts to peralkali rhyolite and
have the following genevpl petrographic features. Ignimbrites:
these rocks show a remarkable uniformity of composition over
large areas. They are porphyritic pdkdine rhyolites with
abundant glassy matrix usually constituted by a very fine glassy
dust. The common phenacrysts are an orthoclase, acmite and
faydite. Xenoliths of foreign rocks are abundant in the ignimbrites.