NGU-BULL 436,2000 - PAGE 175

Building stone of central and southern : deposits and resource potential

HAILEYE SU SWALLE, SINTAYEHU ZEWDE& TOM HELDAL

Walle, H., Zewde, S. & Heldal, T. 2000: Buildin g stone of central and southern Ethiopi a: deposit s and resource pot ent ial. Norges geologiske undersekeise Bulletin 436, 175-182.

The bedrock geology of Eth iopia exhibits a variety of rock types th at can pote ntially be developed for bu ilding sto ne prod uction. The ETH IONOR project has so far includ ed investigation of such resources in t he southern and central part s of Ethi op ia. Wit hin t he Precamb rian, th ere are several deposits of pin k and grey granitoids, grey and w hite marble, soapstone and serpent inite; a number of these deposits are current ly exploite d by Ethiopian companies. Mesozoic and are fou nd at several places in the east-central and central part of the cou ntry, and in addition to t he small number of exist ing quarry opera tio ns, a potent ial existsfor the developme nt of new deposits. Basalt, tufts and igni mbrite are exte nsively used for local housing and construction in Ethiopia. Such resources represent a potential for low-cost supp ly of an excellent construction material. and could be developed furt her.

Hail eyesus Walle & Sintayehu Zewde, Eth iopian Institu te of Geological Surveys, Add isAbaba, Ethiopia. Tom Heldal, Norgesgeo /ogi ske undersekelse, N-749 7Trond heim, Nor way.

tance th at th e depo sit can give commercial-sized blocks Introduction (minimum 220 x 120 x 100 cm) and/o r slabs of uniform qual­ Durin g th e last 20 years, th e production and use of building ity, wit h produ ction costs matching th e market price (Shad­ stone1 hassteadily increased wo rldwide, and today stone has mon 1996). reached a positi on as one of th e world's most important min ­ Durin g th e last decades, and especially during t he 1990's, eral resour ces. For many count ries, expor t of stone has systematic prospecting for building stone in Ethiopi a has becom e a significant economic act ivity. For oth ers, th e rec­ been carried out by both th e EIG S and private companies, ognition of local sources of bu ilding sto ne has secured a and a number of bu ilding stone deposits throug ho ut the steady supply of cheap and durable const ruction materials count ry have been put int o producti on. This is reflected by for dom estic purposes. the extensive use of Ethiopi an sto ne in new buildi ngs in the Almo st any type of rock th at can be shaped and dressed capital and oth er cities. to blocksand slabs can be considered as a potential building Thu s, an imp ort ant goal wit hin th e ETHIONOR projecr' is sto ne source. Most comm onl y exploited are massive rocks to investigate and evaluate th e pot ential for locating build­ such as granite and other ign eous rocks, marble, lime ston e ing sto ne deposits in Ethiopia. So far, field work has been car­ and sandst one, and slab rockssuch asslate and flagstone . For ried out in th e cent ral and sout hern parts of th e count ry, and local housing and other construction, soft and/o r easily t he main result s are present ed in this paper. The north ern cleaved rocks are preferred, since th ey can be worked with regions of Gonder, Tigray and Amh ara will be covered in the simple tool s. On th e international market , however, th e aes­ remaining part of th e proj ect peri od (1999-2000). th eti c properties of th e rocks (colour and st ruct ure) are far more imp ortant, and generally th e pricing of buil ding stone depends on th e exclusiveness of th e rock. Rare colours such Geological background as blu e, pu re white, pure black, yellow and emerald green are The bedrock geology of Ethiop ia embraces a great variety of considerable higher priced th an th e more 'ordinary' colours. rock types within a w ide age range (Mo hr 1971, Kazmin 1972, For example, prices (delivered port) for blocks of th e low Meng esh et al. 1996; Fig. 1). Precamb rian metamorph ic and pric ed varietie s of Indi an siliceous sto ne are from 300 to 600 ign eous rocks cover 23% of th e country and include some of USD/cbm, depending on block size. Similarly, a middle pric e th e most interesting building stone sources, such as marbl es, range is from 600 to 1000 USD/cbm, and high-pr ice types granitoids and soapsto ne. Thick successions of Palaeozoic 2 from 1000 t o 1400 USD/ cbm . For Norwegian 'Blue Pearl' lar­ and Mesozoic sediments (25%) overlie th e Precambrian. vikite, th e price range is 1000 - 2000 USD/ cbm . For any indus­ These include building stone qu alit y lim estones and sand­ tri al scaled operation on bu ild ing sto ne, it is of vital impo r- stones. A large part of th e country is covered by Terti ary and Quaternary volcani c rocks (44%), and in th ese areas, basalts, 1. The term 'building sto ne' includes any type of rock, shaped and dressed to blocks or slabs, used for const ruction. Buildi ng stone is a 3. The ETHI ONOR project is an Ethi opian-Nor wegian co-opera tion more general term than th e term 'dimension stone; which is proj ect aimed at increasing th e knowledge of mine ral resources in restricted to cut-to-sizeslabsand blocks. Ethiopia. NGU is advising EIGS w it hin various fields regarding min ­ 2. http //www.chariot international.com/ priceListTiles.htm eral resources exploration and geologica l mapping. NGU -BUL L 436, 2000 - PAGE 176 HAILE YESUS WALLE, SIN TA YEHU ZEWDE & TOM HELDAL

DEP OSITS 1 Mora & Bapuri Marbles 2 Bulen ard GanzJ marbles 3 BanxJa (Moye, Gewi & Ekonte) marbles 4 Cehane Granite 5 Mankush Marble N ~ ~~~~~;~L~~~~e 8 Hamaresa Granite 9 Babile Grante 10 Melika Gran te 11 Kentich Serpentinite aro soapstone 12 Caleti Marble n~~ ~id~{;~te 15 Addis Ababa Ign mtxlte 16 Kombo lch Gran te 17 Wonchlt & ..lema Limestone 18 Zigl soapstone

GE NERAL~EDGEO LOG Y Quatern ary cove r (undifferentiated)

Quaternary-Tert iary rift sediments & volcanics Tertiary sedimentary rocks Tertiary volcanic rocks Mesozoic sed imentary rocks Palaeozoic sed imentary rocks Proterozoic metam orphic Rocks • Archaean rocks

Fig . 1. Simplified geological m ap of Et h io p ia with localities of bu ilding sto ne in the ce ntral and so uthern pa rts of t h e country.

tu ffs and ignimbrites are extensively used for local housing slight ly unconformably on locally developed Palaeozoic sed­ and construct ion. imentary rocks. The Adigrat sandstone varies in th ickness The Precambrian rocks of Ethiopia, upon which younger from a few to 800 m, and consists essentially of red to yellow, sedimentary and volcanic rocks were deposited, are exposed well-sorted qu artz sandsto ne. The up per part, however, is in in t he east-central (Harar), west-cent ral (Gojam and Wellega), places calcareous, particularly close to the transition to the north ern (Gondar and Tigray) and sout hern (Sidamo, Bale overlying of th e An talo Group. Thick limestone s and IIlibabo re) partsof th e cou nt ry. Most of th e exposures are are develop ed in the middle part of this grou p. These vary found in th e peripheral region s, w here younger rocks have from near-shore, oo lithic limestones, through fossiliferous, been removed by erosion. pale limeston e and marl to black limestones depos ited in The Precambrian rocks can be divided into a Lower, Mid­ deeper wate r. In the Harar area, a possible correlat ive to the dle and Upper Comp lex (Kazmin 1972). The Lower Complex Limeston e, t he Hamanlei Series, exhibits thick beds of comp rises possibly Archaean gneisses, migma tites and gran­ pale, calcitic to dolomitic limesto ne. ito ids, form ing a basement to th e volcanose dime ntary sue­ A large porti on of Central Et hiopia is covered by volcanic cession s of th e Middle and Upper Proterozoic Complexes. rocks, ranging from th e extensive plateau basalts within the These successions essent ially show polyph ase defo rmatio n Early to Middle Tertiary Trap Series, to Quaternary lavas, tuffs and low- to medium -grade metamorphism. However, th e and ignimbrite. Proterozoic rocks of nort hern Et hiopia, th ough stro ngly deformed, are only weakly metamorphosed. A variety of igneous rocks, predominantly granito ids of Massive stone - marble, Proterozoic to Early Palaeozoic age, occur as intrusive bodies limestone and granite within th e Precambrian metamo rphic units. Some of these In th e explo itatio n of massive stone (dimensional stone). have been emp laced prior to, or contemporaneous wit h, tee­ large, commercial blocks are ext racted in the quarry and tonom etamorph ic events; others postdate th ese events. transported to a processing plant for final shaping and fi nish­ The Late Palaeozoic(?) to Mesozoic sedimentary rocks of ing to slabs and t iles. The most homogeneous and attractive Eth iopia were deposited duri ng a regio nal transgression of types of rocks may be expo rted to other countries as rough th e Indian Ocean, fo llowed by Late Mesozoic upli ft and ero­ block s. Generally, deposits suitable for exploitation of mas­ sion (Kazmin 1972). In th e western-cent ral part of t he coun­ sive sto ne should be very hom ogeneous, both in colour and try, the lower portio n of t he Mesozoic succession is repre­ in st ructure. Furtherm ore, the occurrence of joints, veins and sented by t he Adigrat Sandstone of to age. ot her factors that contr ibute to a reducti on in the overall This rests unconform ably on t he Precambri an basement, or block yield, should be very small, except for extremely high - HAILEYESUSWALLE, SINTAYEHU ZEWDEs TOM HELDAL NGU-BULL 436,2000 - PAGE 177

priced (rare) rocks. The most obvio us resource potent ial within the investiga ted regio ns in Ethiopia lies in the huge marble formations in the weste rn part of the country, and in different varieties of granites and gneiss, limestone and ser­ pentinite/ soapstone. Market evaluation of such deposits is difficult. Firstly, th ere are no objective price lists available on the interna­ ti onal market, and prices can vary greatly due to changes of fashio n and personal taste of th e customers. Secondly, very few produce rs actually go public wi th th eir prices, and a pic­ ture of the market situation implies a need for experience among the professionals involved in the evaluation of stone deposits . Furthermore, the market for rough blocks is signifi­ cant ly different in com parison with finished products. In th e Fig. 2. The Daleti marble (Wellega) cladding t he facades of a mod ern former case, th e customers are stone-prod ucing companies buildi ng in Add is Ababa. around the wo rld, whilst th e custo mers of fini shed products are end-users (architects and constructo rs). The notable dif­ feren ce in raw material pricesfor different rock typ es may not it is within th at sector we would expect th e most significant be as obvio us for finished produ cts. Generally, however, th e growth in th e country's dimension-stone production in th e price difference between highl y att ractive and less attractive years to come. rock types is much high er for raw blocks th an for fin ished products. In this arti cle, we have used publ ished and non­ pub lished price lists for raw blocks of comparable types of Marble stone as a tool in market evaluatio n. Due to the subjective The most interesti ng deposits of marble are found in the character of such info rmation, price indications given below western part of Wellega (Daleti) and Gojam (Mora, Bulen, must be regarded as indicati ve only. Mankush and Baruda). The area is qui te remot e, and trans­ In Ethiop ia, the use and dom estic production of cut-to­ port distancesto Addi sAbaba vary between 550 and 800 km, size stone have increased du ring the last decades, contribut­ for the most part along non-paved roads. However, at th e ing positively in the development of a high -qu ality , dom estic present tim e, transport costsare still low enough for th e mar­ indu stry. For the major part, dimension stone used in Ethio­ ble-producing companies to find th e produ ction profitable. pia is derived from dom estic sourc es. Although limestone Most of th e marble deposits found in th ese areasform an and marble have been produc ed for a long tim e, th e produc­ elevated morphology, others have a flat, though well ti on and use of siliceous rocks has only recently started, and exposed, morphology. Predominant ly, the marbles are cal-

Fig. 3. Detailed geological map of the Ganzi marbl e deposit. Gojam (see Fig. 1 for location ). The map il­ lustrates the struct ural compl exity seen in som e of the marble depos­ its. s

Geological cross-sections

Grey. banded calcite marble, fine!mediwn-grained White calcite marble with grey bands, medium/coarse-grained White-grey, sulphide-bearing dolomitic(?) marble (outcrops sho wn darker in lithologies) ____ Lithological boundaries. observed

- Lithological boundaries. interpreted lOOm f i Strike!dip foliati on/! vertical foliation ..- Zones of Brecciation NGU-BULL 43 6, 2000 - PAGE 178 HAILEYESUSWALLE, SINTAYEHU ZEWDE& TOM HELDAL

exclusive types of marble, such as pure white and sky blue varieties. The latt er two may obtain very high prices on the internati onal market, but the depositsdiscovered to date are small and inhomogeneous.

Granitoids and gneiss Intrusive igneous rocks are common in the Precambrian of Ethiopia and range from granit ic bodies within the migma ­ tites of the Lower Complex, to pre-, syn and post-tectonic intr usions in the Middle and Upper Complexes (Kazmin 1972, Heldal et al. 1997). The former group is possibly of Archaean age, and,at present, the National Mining Company is exploit­ ing deposits in th e Harar area (Fig. 5). The deposits are situ­ Fig. 4. Fold ed pre-tectonic dykes (amphibolite) in calcite marble, ated closeto th e small town of Babile, and form massive boul ­ Manku sh, Gojam. ders and small hill s, giving good opportunities for the extracti on of large volumes of commercial-sized blocks.The citic, but white to grey dolom ite occur as layers withi n the Babile granite is a medi um-grained, pink to red 'schlieren'­ calcite marbles or as bordering units. The latt er has, until granite with a variegated, veined structure (Fig. 6), reflect ing now, not been of significant interest as building stone. its close relation ships with the surrounding migmatitic Several types of comm ercial marble occur in the area gneisses. By comparison with ot her commercial 'schlieren'­ (Malis & Dejen e 1983, Heldal et al. 1997). These include fin e­ granites on the international market, a low- to med ium-price to medium-grained, graphitic grey marble with white bands, level is estimated . The structure of the granite may vary medium- to coarse-grained white marble with grey bands within small areas between more or less gneissose (Fig 7), (Fig. 2) and several subordinate types such as pink, silicate­ rich marble, pure white , fine-grained marble and sky blue to green marble. The latter two typ es seem, both from field observatio ns and comparison with description of similar deposits in Norway, to be connected to contact -metamor­ phic aureoles surrounding gabbro intrusions. Grain size var­ ies from fine- to coarse-grained, and these variations are believed to be the result of local variations in metamorphic conditio ns, probably caused by heating related to syntec­ tonic intrusions, and grain-size reduction during later defor­ mation episodes, especially in high-strain zones. In the latter case, the marb leshave often a schisto se,'slabby' app earance, and are not suited for production of squared blocks.Fold pat­ tern s may be very comple x within some of the marble depos­ its, especially where com petent layers of dolomite are inter­ banded with less comp etent calcite marble. An example Fig. 5. Quarrying of a giant boul der in the Babile gran ite dep osit, Harar. from one of th e comp lexly folded Gojam deposits is shown in Fig. 3. Measurements of fold axes furthe r show that the folds are non-cylindrical, demanding care in estimating subsurface marble reserves. Pre-, syn- and post-tectonic dykes and veins of acid ic and basic composition are com mon in several of th e marble deposits (Fig. 4). Particularly, th e foliation-parallel, folded dykescause problemsfor th e extraction of marble, since th ey infiltrate a large part of the rock mass and are difficult to pre­ dict. Thus, in such areas, th e block yield and the possibilities of using sophisticated quarrying technology, such as dia­ mond -wire sawing, are reduced. Furth ermore, closely spaced jo ints cause similar problems in many cases. However, both the existing quarrying acti vity by several companies and recent investigations by the EIGS indicate a fairly good potent ial for increasing the prod uction of low- to medium­ Fig. 6. Polished surface of the variegat ed Babile granite (right) and priced, grey and white marble from the area. Furthermore, flamed and ho ned tiles of th e po rph yritic Anger Guten granite (left). investi gations suggest a possible development of high ly Hotel Sheraton, Add is Ababa. HAILEYESUSWALLE,SINTAYEHU ZEWDE& TOM HELDAL NGU-BULL 436,2000 - PAGE179

cantly, but some small hills show a spacing of more th an 1.5 m on average, w hich may be sufficient for large blo ck pro­ duct ion . Several other granite deposits may be of future intere st. These include th e Dehane granite, close to Mora in Gojam. This is a coarse-grained, pink granite, forming huge hill s and ridges of boulder deposits, which by reconnaissance appear to be very homogeneous in colou r and struct ure. Join ts are wi dely spaced, facilitati ng production of large blocks. In t he sout h, pilot quarrying of fine-grained , pinkish-grey granite has been carried out near Kibre Mengist in th e Sidamo area, where several small, syn-tecto nic(?) granite pluton s occur. However, th ese granit es are t ightly joi nted, and locally th ick kaolin zones are develop ed in th e weat hering profile. Thus, Fig.7. Gneissose layersin theBabilegranitedeposit. th ese granites are prob ably not of great interest as dim en­ sion-stone prospects. givi ng possibilitiesfor ext raction of several comm ercial stone ty pes, but also demanding care in the predi ction of uniform Limestone future reserves. Calcit ic lim estone of dim ension -stone quality is predomi ­ Pre- and syntectonic granitoids within th e Middle and nant ly found wit hin th e Jurassic Ant alo lim estone (central Upper Comp lexes comp rise med ium-grai ned, grey granodi ­ part of th e count ry) and the Hamanlei Series (east-central orites, fine-grained, pink to red granite, coarse-grained, pink part). The best exposures and th e most interesti ng deposits granite and porph yrit ic, pink to grey granites, all esti mate d to of th e Antalo Limestone are fo und in th e cent ral part of th e belong to a low- to medium-price level at the market. The Abay Valley, and side valleys such as the Jema, Wonchit and plutons may show a penetrativ e foliation th roug hout the ir Muger valleys. entire t hickness, or have a fo liated margin wit h a massive, The Jema and Wonchit limestone deposits occur in the non -fo liated core. The Anger Guti granite, Wellega (some­ bottoms of t he valleys of the same names. The lower part of times called th e Guten granit e), is presently exploited by t he limestone unit is by far th e most interest ing, since t his is National Mini ng Company. This is a foliated 'Augen'-granite, th e part wh ere the bed thickness reaches mo re t han one with large, pink phenocrysts of microclin e in a brownish-grey metre (Wondafresh et al. 1993). The lim estone is essential ly a groundmass of blotite, plagioclase, quartz and pota ssium calcareaou s, fossilifereous sandstone with poo rly developed feldsp ar (Figs. 6 and 8).Several deposits occur in the area, struct ure; colour varies from brown to off-w hite. Joint spac­ forming smoot h hills, wit h a steep foliation facilitating extrac­ ing varies considerabl y in the area, w here th e more massive tion by drilling, blasting and wedging. Variations in colour parts of the depos its form small hills and plat eaux. At th e and st ruct ure may occur, especially due to heterogeneous present time, the se limeston e dep osit s are not being distribution ofthe phenocrysts and a varying degree offolia­ exploited, due to difficult access (the access road is of poor tion development. The phenocrysts are commonly rounded qual ity) and locally closely spaced joints. and rot ated by st rain. Aplitic veins of several generations are Large limestone deposits are also found in th e eastern abundant, and may contribute to an increasing waste ratio in part of Ethiop ia, in th e Harar-Hak img ara areas. The Hakirn­ some of th e deposit s. Joint spacing in th e area varies signifi- gara lim estone has beds varying from some tens of centi me-

Fig. 8. Raw block surface of the Ange r Guten granite in the quarry (cut Fig. 9. Sawn limestone bed in a quarry within the Hakimgara limestone perpendiculartothefoliation).Drillholesareapproximately 25 mmwide. deposit, Harar. Note reduction fieldsin the upperpart of the bed. NG U-BU LL 436, 2000 - PAGE 180 HAILEYESUS WAL LE, SINTAYEHU ZEWDE s TOM HELDAL

tres to several metres in thickness (Schlede et al. 1990; Fig 9). Generally, extract ion of commercial-sized bloc ks is possibl e in th e thi cker beds, exceeding one metr e in thic kness, w here the spacing of vertical joi nts is wide. The lime ston e is partly fossiliferou s, and contains abund ant stylolites. The colour varies between yellow ish-brown and dark grey, the latt er occurring in irregularly distributed reductio n patt erns. Quar­ rying operat ions are carried out by both th e National Mining Company and the Ethiopian Marble Indu stry in the vicinity of Harar. The limestone form s hills and th e area is considered to have a large potent ial for easily accessible deposits.

Serpentinite and soapstone Fig. 11. Massive and homogeneous soapston e in the Metekel Zigi area, These rocks are found in the Upper Compl exes of both the Gojam. Sidamo and t he Gojam areas. Deposits in t he Sidamo­ Kent icha and in the Metekel-Zigi areas (Gojam) were visited dur ing the proj ect period (Heldal et al. 1997). They belong to ficial sampling has been carried out. Further knowledge on the Upper Proterozoi c Compl ex of th e Adol a and Birbir thi s is of vital importance both fo r investigations of potent ial groups respecti vely. soapston e and industrial talc deposits.The talc-rich rocks are Serpent inites (generally green wit h wh ite veins) are often essentially coarse-grained, flaky and have a green to grey col­ referred to as 'green marble' on the international market. ou r. Bot h massive and schistose zones are observed , the Such rocks have been used in Europe as decorative ston e former concentrated in fold hin ge zones along the margins since antiquity, and well-known types include several Italian of the serpentinites, as illustrated in Fig. 10.These fo ld hinges depo sits, such as the 'Verde Ant iqu e'. Serpent init es predom ­ are of special int erest, since the deposits are thickened in inantly belong to low - to med ium -pric e levels. Soapstones these areas, and th e soapsto nes have a more massive are geologically tightly linked to serpentinites, but are not appearan ce than in the th inned limbs. Detrital ultramafics are th at well established on the int ernational market. Howev er, also described from the Sidamo area, but these depos its have such rocks are increasingly used for fi replaces and even as not yet been investigated regarding building stone . bu ilding stone in northern Europe, and there mig ht be a The soapsto nes in the Metekel Zigi area in Gojam occur in fut ure market develop ment which would favou r the exp loi­ the t ransition zone between th e ultramafic parts of layered tation of such deposits in many places around th e world. int rusion s(Grenne et al. 1998) and the surrounding metased­ In Kent icha, Sout h Ethiopia, isolated, lens-shaped serpen­ iments. As in Kenticha, interchanging massive (Fig. 11) and ti nite bod ies occur within amph ibol ite units. The serpen­ schistose soapstone is found. Rusty weat hering seems, how­ tinites are fold ed and fo liated , and are enveloped by talc ever, to be lessintense than in Kenticha, and it should be pos­ schists. Talc-rich zones are also found in shear zones wi t hin sible to obtain fresh rock almost at the surface. In conclus ion, the serpenti nites. The green serpentinites apparentl y seem both areas have an interesti ng potential fo r soapsto ne highly fractu red at the surface, but fro m superfic ial investig a­ deposits, though further investigations are necessary, espe­ tions it is difficult to separate penetrative joints from selec­ cially concerning the depth of the weathering of magnes ite tive weat hering of carbonate veins. Thus, more detailed in Kenticha. invest igations by core drilling and sampling are necessary before any conclusions can be reached concerning sub-sur­ face qu ality of the serpent inite. Construction stone for local housing The talc zones ob served in Kenticha essentia lly conta in For local housing and construction, easy workable rocks are talc, chlorite and rusty spots that proba bly represent weath­ required in preference to rocks with attractive aesthet ic qua l­ ered, Fe-tich carbonate, such as magne site. The dept h of th is ities. The stone is shaped and worked to fin ished products stained weathering profile is yet not known , since only super- (hewn slabs and building blocks) in the quarry and/o r at the construction site. It is important that the rocks can be worked Talc schist and soapstone with simple technology to a low cost. In Ethiopia, t here are long traditions in using Mesozoic sandstone and tertiary vol­ I Scrpcntinitc canic rocks for such purposes. Also the aforementioned Harar limestone is widely used.

Sandstone Regarding building stone, the best potential of sandstone lies wit hin the thick, red bed series of the Adigrat Sandstone Fig. 10. Sketch showing the occurrence of talc-schist and soapstone en­ veloping deformed serpentinite bodies in the Kenticha area, Sidamo. along an axis from Ambo in the south , through the Abay val- HAILEYES USWALLE, SINTAYEHU ZEWDE& TOM HELDAL NGU-BULL 436 ,2000 - PAGE 181

Fig. 14. Wall constructio n with vesicular basalt near Debre Markos.

Basalt, tuff and ignimbrite Basa lt is widely used for local constr uction, both as building stone and aggrega te, in th ose part s of th e country where such rocks are fou nd (Fig. 14). A large number of small basalt quarries are fou nd t hroug hout the Cent ral Highlands, and crudely shaped pieces are worked with simple tools and manpower. In general, t he basalt deposi ts are not considered to be of specific intere st for more industrial-scaled building stone exploitati on, wit h t he possible exception of columna r and vesicular basalt (Fig. 15). The for mer coul d, with simple technology, represent a pot ent ial for th e production of split paving sto ne, w hile th e latt er, du e to it sexcellent workability, could be used for ashlar and brick. In and near th e Rift Valley, th ere are sizeable deposits of Fig. 12. Wedgin g sandsto ne beds in t he Ambo quarries. tu ffs (vitr ic tu ff, lith ic tuff and crystal tuff) and ign imbrites. These rocks are generally porous, soft to carve and easy to leys to Tigray in th e north. Exploitation mainly occurs in the split, and for a long time, ignimbrite and tuff have repre­ deposits near the town of Ambo (Figs. 12 and 13). Here, t he sente d the most important building stones of Addis Ababa cross-bedded, red and wh ite sandsto ne is worked to ashlars, (Karstaedt & Wondafrash 1986; Fig. 16). Due to the high split brick s and slabs mainly with t he help of simple tools poros ity, th ese rocks have excellent insulating properties. A such as sledge hammers, wedges and crow bars (Biazen number of small quarries are worked in th e vicinity of the 1962, Heldal et al. 1997). Products are distributed throughout capital (Fig. 17), mainly by hand, using simple tools. The ign­ most of Et hiopia, even though a major part of th e producti on imbrites are somew hat harder to wo rk t han th e tuffs, and is used in th e capital. th erefor e more com monly used for rubb le th an ashlars. Due

Fig. 13. Wall c1added wit h the Ambo sandstone, Hotel Sherato n, Addi s Fig. 15. Quarry in colum nar basalt near the town of Ambo. Ababa. NGU-BULL 436, 2000 - PAGE 182 HAILEYESUS WAL LE, SINTA YEHU ZEWDE & TOMHELDAL

ous marble depos its and for finding more exclusive types for the expo rt market. Extraction of granite is still in its early beginn ings in Ethi­ opia, but increasing knowledge of the resource potent ial com bined wi th improved extraction methods could benefit a posit ive development also in th is sector. However, the grani­ toid deposits localised unti l now in central and southern Ethi­ op ia are of such a type that will meet tough competition on the international market. Both limestone and sandstone are extensively used in the domestic market. With in both th e Adig rat sandstone and the Antalo and Hamanlei limestones there are still possibilit ies for exploration of new resources, thou gh these wi ll be lim ited to the relatively small areas where the se units are exposed. Fig. 16. Ignimbrite used for the construction of the Catholic church in The most important part of the Ethiopian building stone Add is Ababa. producti on, at least in terms of volum e, is the exploitat ion of volcanic rocks for local housing and, close to the capital, for industrial-scale construction work. Such resources represent a considerable potential for low-cost supply of an excellent construction material , and could be furt her developed.

Acknowledgements The aut hors wish to thank the National Mining Compan y and Ethiop ian Marble Industry for their help during fieldwork.The helpful commentsof Ingvar Lindahl (NGU) and Chris Spencer (BRGM, Orleans) are much appreciated.

References Biazen, B. 1962: Generalized report abou t the geological view of Ambo and Guder. Ministry ofMi nes and Sta te Domain, Addis Ababa, unpub­ lished report. Grenn e, T., Braathen, A., Selassie, M. G. & Worku, T. 1998: Results and Fig. 17.lgnimbrite quarry in Addis Ababa. models fro m fieldwork in the Meso-Neoproterozoic belt of western Et hiopia: t he Wombe ra-Baruda-Bulen-Kilaj transect of the Metekele zone. Norges geolagiske unde rsekelse Report 98.1 10, Heldal, T., Haileyesus W. & Sintayehu Z. 1997: Natural Sto ne in Ethiopia to th eir softn ess, such rocks are, however, not very suitabl e Visited in 1996/97, Norges geol ogiske undersekelse Report 98.040, . for use as paving stone and stairs. Karstaedt , H. & Wondafrash, M. 1986: Summarized Report on Building Raw Material in Eastern Addis Ababa (Bole). Ethiop ian Insti tu te of Tuffs and ignimbrite deposits are also exploi ted at several Geological Surveys, Report (unpublished). other places in the country. For instance, the famou s, rock­ Kazmin , V. 1972: Geology of Et hiopia, Explanatory note s to Geologic al hewn churches of Lalibela are carved in soft tuffs, and these Map of Ethiop ia 1:2,000,000, Ethiopian Insti tute o f Geo log ical Surveys. rocks have also been employed more recently for local con­ Malis, E.&Dejene,G. 1983: The Dalati marble dep osits.Ethiopian Insti tu te structi on in the area. ofGeological Surveys Report (unpublished). Mengesh, T., Tadiwos, C. & Workineh, H. 1996: Geological Map of Ethio­ pia; 1:2,000,000. Ethiopian Institu te ofGeological Surveys. Mohr, P.A. 1971: The Geolo gy of Ethiopia, Hailessilase I University Press, Conclusions Add is Ababa. Central and South ern Ethiopia exhibit a variety of rocks that Shadm on, A. 1996: Stone - an Introduction, Inte rmediate Technology already are either developed as, or can be in the future, Publication, London. Schlede, H., WaJle, H. & Ayalew, S. 1990: Preliminary evaluation of lime­ important building stone resources.The grey and white mar­ sto ne deposits at Delga Chebsi and Hakim Gara (Dire Dawa and East bles of th e western regions have already gained important Hararge adm.Region). Ethiopian Institu te ofGeolog ical Surveys Report indu strial developm ents, and contri bute to day in shaping (unpublished). the image of bui lding facades in Addis Ababa and other Ethi­ Wondafre sh, M., Haileyesus, W. & Hailu, B. 1993: Limeston e and gyp sum opian cities. There is stil l an interesting potential both for fur­ resou rcesat Wonchit and Jema Area Merhabete Northern Shoa. Ethi­ opian Institu te o f Geological Surveys Report (unpublished). th er develop ment of industrial-sized quarr ies in homogene-