Geology

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Engineering Geological Mapping and Land Slide Assessment of Dessie Town
(Addis Ababa University, 2001-06) Terefe, Kefyalew; Ayenew, Tenalem (Prof.)
In order to understand the geotechnical properties of soils and rocks and the slope stability in Dessie, field traverses, digging of test pits, drilling of bore hole, vertical electrical sounding test, standard penetration test, point load test, Schmidt hammer test and various type of laboratory tests have been carried out. The purpose of this work is to ensure those geological factors affecting planning, design, construction of engineering structures related to soils and rocks and to assesses the landslides to give a mitigation and control methods related to slope gradient classification map, Geomorphological map, Engineering geological map, landslide hazard classification map, land use and land cover map have been performed. Dessie is situated in a graben formed by successive parallel faults that run in the north south direction. The geomorphology of Desire is governed by, the geology, the regional tectonic activity, erosion and depositional process. The study area is covered with alternate layers of basalt and quaternary deposits of colluvial, alluviall and residual soils. Alternate layers of stratoid and degreaded basalt separated by thin palleosoil are typical layers along the escarpments of Tosse and Azewa Gedel. The centeral part of the town is characterised by scattered hills of vesicular basalt. The thickness of colluvial and alluvial deposits vary according to the palemorphology of the garben. Three borehole were drilled during the field work in selected areas and show that the thickness of these colluvial - alluvial soils reaches about 40m. Landslides, especially induced by gully erosion and rockfalls down the slope is nowadays a common phenomena in Desire Town. About 20 landslides including rock fall prone areas have been recognised. Most of them are resulted from the lack of proper surface drainage system on the thick colluvial - alluvial sediment and rockfalls toppleing from the steep cliffs. The landslides are aggravated by natural and man made activities, such as rainfall, change in the slope gradient, human intervention, gullies and streambed erosion.
Evaluation of Cement Raw Materials in Wayou ( New Mugher ) Area
(Addis Ababa University, 1980-07) Lakew, Tesfaye; Asssefa, Getaneh (PhD)
The raw mater i als used in the manu f acture of P ortland cement were s tudied in the Wayu locality (New Mughe r). The study showed th. t there is lime s tone of a good quality in large aMount which justifies exploitation. The c l ay ~ate ri a l studied was fou nd ou t t o be de f icient in silica and neens a si l ica modulus correc t or . Conse quently , a sandstone body which is found b e neath the basalt was investi~ated and the investigation showed that there is enough san stone tha t can be used as a cor r ector . The study of the gyps um deposi t also revealed that sufficient amount of gypsum e x ists . A conclusion was reached to the effect that the installation of a cement p l ant is justifiedo
The Geology and Geochemistry of the Banded Iron Formation in Chago-werekalu, Wellega Province
(Addis Ababa University, 1985-10) Getahun, Abera; Valera, Roberto (Prof.)
The r ocks of the stulied area form nart of the ~ o llepa Birbir proup of the uppe r c08plex and consist of a series of me t ased i me ntary and plutonic proterozoic rocks. The winiera lo~ical assembl age indicate tha t t he metamorphism is of the r r eenshist facies. The variation diagram cons tructed for the va rious plut onic re e ks stronpl y supvest coma pmatic oripin by crysta l f rac ti ona ti on . Major and trace element ana lyses of re ore sentative samples of the Chago iron formation ? t he plutonic ann. YOllnp:er e f f us i ve rocks are presented . The Chago iron f ormation can be c las s i f i ed as nre cambrian banded iron for mation and is in J11any r espects siJrii l ar to the oxide fa cies iron format i on of Lake Superior t ype. The Cha go iron fo r mation consis t s only of Iron oxides and mi nor amoun t of sil i ca with total absence of iron silica t e, s ulfide and carbonate minerals. Trace element pe ochemis try sUPRests that t he iron f orma ti on was chemic ally prec i pitated as ox ida t e s ediments in which the principal i ron mineral, ma gne tite 1 was formed at low te mpera ture in a s ~lallow nea r shore environment .
Geology and Geochemistry of the Negash Pluton and their Metallogenic Significance, Central Tigrai
(Addis Ababa University, 1997-01) Asrat, Asfawossen; Peccerillo, Angelo (Prof.)
The Negash area is located in Central Tigrai, Northern Ethiopia. The area consists of metamorphic rocks th at are cut by some granitoid intrusions. The present investigation was directed to one of such intrusions, the Negash granitoid stock. Geological mapping at a scale of I: 50 000, and geochemical studies led to the assessment of the petro logy, geochemistry and tectonic setting of both the intrusion and the country rocks and the economic potential of the area. The meramorphic rocks are mainly low - grade metavolcanic rocks with a wide compositional variation from tholeiitic to calc - alkaline mafic to felsic composition formed in an island arc environment. There are also minor intercalations of metased imentary rocks. Hornblende - hornfels facies rocks are found in proximi ty to the intrusion. The Negash granitoid body is unde fo rmed, discordant, circular stock that consists of diorites, quartz diorites, tonalites, monzonites and granodiorites with minor aplitic, grani tic and pegmatitic dikes. Its western boundary lies along a fault line (the Suluh Fault) that forms the Suluh River valley. The intrusion is dominantly of mafic and intermediate composition rocks, even though the felsic rocks crop out extensively at the top most part of the intrusion. Geochemical and petrological data suggest that the intrusive rocks were diffe rentiated from a mafic magma by fract ional crystallization and assimilation with fractional crystallization (AFC). Hornblende was the main fractionating mineral phase. This process resulted in relatively dry residual magma, as can be evidenced from the scarc ity of pegmatites and related mineralization. Preliminary geochemical survey of the Negash granitoid stock show no significant anomalies except for Zn and Sn. The country rocks show anomalies for several elements including Au, Zn, U, Sb, As and Ba. This indicates that the intrusive magma did not play an important role in generating mineralization in the area but it furnished the heat which triggered fluid circulation in the country rocks. The geochemical anomalies for most of the elements are concentrated along the western boundary of the , intrusion, the Suluh fault line. The fault presumably provided the ease through which the metasomatic fluids enriched the area with metals. Further geological and geochemical investigations should be directed to this zone.
The Geology Geochemistry and Origin of Supplied Mineralization in Katta,Wollega Province
(Addis Ababa University, 1980-07) Mammo, Telahun; Valera, Roberto (Prof.)
The Katta rocks form part of the Birbir group of the upper compl ex s i tuated in the paleo- cal c-alkaline arc that runs northsouth across the country and which compri ses thick sequences of metavolcanic and metasedimen tary r ocks 0 The rocks are intensel y folded and faulted o Their minera l ogy and texture indicate that metamorphism is o f the greenschist facies o Logging of five bore ho l es , their correlation and subs equerr petrographic s tudies on selected samples are conducted and depth variation i n miner a logy i s presented o Geochemical studies on stre am sedime nt s , bed r ock and f l oat samples, soil and core samples , and statistical tr eatment, of the results show that there is lateral and vertical variati ons in the copper and zinc mineralizations . The geochemical s oil maps show that Cu , Zn , Pb , Ni , and Co mineralizations are concentr ated along fo liation and bedding p laneso There is low litho logical c ontro l of mi neralization o Moda l ana l ysis on the core samples s how that main mineralization is a s sociated to carbonate o Ore microscopic studies show that pyrite , chalco pyrite , magnetite , bornite , cubanite) bournonite , cuprite and sphal e r ite are the ore minerals found occuring in bands , as d i ss eminati ons and in veins o Two types of mineralization are recognized syngenetic stratabound and e pigene t ic vein and dissemina t ed types . It was the syn~enetic type that gave rise to epigenetic types as a resul t of later met a morphi(: and supergene remobilization. 'r'he epigenetic type is considered to be the main mineralization in the area o
The influence of Geology , and other Soil Forming Factors in the Inherent Fertility of Soils in the Assela Area, Arssi, Ethiopia
(Addis Ababa University, 1982-02) Abebe, Bekele; Cinque, Ardol (Prof.)
The geology of the Asela area has been studied In de t a ~ l and the fertility status of the soils in relation t o the f actors of soil formation (parent material, climate, top ogr aphy , organisms and time) examined qualitatively and semiquant itatiVielyo The area is associated with Pliocene and younger volcanics (central and fissur al) and is intensively aff e cted by different episodes of faultingo Basal t s, Trachybasalts , trachytes and acidic pyroclastics are the rocks oc curing in the areao The major soils are the dark-dark brown and the reddish brown soils of the plate au and the dark-browndark ye llowish brown soils of the rifto In general, the rif t s oils have higher plant nutrient s t atus than the plateau soil s o Removal of materials is important on the plate au and addition in the rifto Parts of the plateau and mo s t of t he r i f t f l oor are affected by poor drainageo The abundance of surf ace hindrances on the surface of the rift soils might be attr i buted to t he young age of the rocks in the lattero In te r ms of physical limit ations of the land, both t he lowland and t he plateau have their drawbacks o The cumulative influence of the topography and the climate is found to be dominantly r e s p ons ible for the lateral and vertical variations of the inherent fe rtility of the soilso
The Sedimentology of the Diatomite Bearing Lacustrine D_posits of Adami Tulu Area
(Addis Ababa University, 1996-06) Amare, Ketema

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