NGU-BULL 436,2000 - PAGE 175 Building stone of central and southern Ethiopia: 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 sandstone and limestone 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 limestones 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 Antalo 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.