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http://dx.doi.org/10.9719/EEG.2013.46.3.267

Occurrences of Hot Spring and Potential for Epithermal Type Mineralization in Main Ethiopian Rift Valley  

Moon, Dong-Hyeok (Korea Institute of Geoscience and Mineral Resources)
Kim, Eui-Jun (Korea Institute of Geoscience and Mineral Resources)
Koh, Sang-Mo (Korea Institute of Geoscience and Mineral Resources)
Publication Information
Economic and Environmental Geology / v.46, no.3, 2013 , pp. 267-278 More about this Journal
Abstract
The East African Rift System(EARS) is known to be hosted epithermal Au-Ag deposits, and the best-known example is Main Ethiopian Rift Valley(MER) related to Quaternary bimodal volcanism. Large horst-graben system during rifting provides open space for emplacement of bimodal magmas and flow channel of geothermal fluids. In recent, large hydrothermally altered zones(Shala, Langano, and Allalobeda) and hot spring related to deeply circulating geothermal water have been increasing their importance due to new discoveries in MER and Danakil depression. The hot springs in Shala and Allalobeda occur as boiling pool and geyser on the surface, whereas some areas didn't observe them due to decreasing ground water table. The host rocks are altered to quartz, kaolinite, illite, smectite, and chlorite due to interaction with rising geothermal water. The hot springs in MER are neutral to slightly alkaline pH(7.88~8.83) and mostly classified into $HCO_3{^-}$ type geothermal water. They are strongly depleted in Au, and Ag, but show a higher Se concentration of up to 26.7 ppm. In contrast, siliceous altered rocks around hot springs are strongly enriched in Pb(up to 33 ppm, Shala), Zn(up to 313 ppm, Shala), Cu(up to 53.1 ppm, Demaegona), and Mn(up to 0.18 wt%t, Shala). In conclusion, anomalous Se in hot spring water, Pb, Zn, Cu, and Mn in siliceous altered rocks, and new discoveries in MER have been increasing potential for epithermal gold mineralization.
Keywords
epithermal Au-Ag deposits; Main Ethiopian Rift Valley; geothermal fluids; hydrothermally altered zone; hot spring;
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