Eritrea has a long history of mining. Despite this modern mining began at the beginning of the 20th century following the Italian colonization of the country. After the Second World War, mining and related operations continued throughout the country, although intermittently. In the early seventies this resulted in the development of the short lived modern mine at Debarwa, before the independence struggle forced its closure.
Eritrea is now known to host significant VMS deposits as well as shear-hosted gold deposits. The first modern mine, Bisha VMS deposit, has started production. Koka project has completed feasibility work and there are other advanced projects and many exploration operations underway. Considering much of the country remains unexplored, these discoveries indicate the high mineral potential of the country. The potential for shear hosted gold deposits is also demonstrated from the recent, gold discovery in Zara, situated along a major shear zone that runs across the country. The country is not well explored. There are many prospective areas still to be discovered.
Eritrea possesses a geological setting that is favourable for both precious metals and base metal mineralization, as well as for industrial minerals. The range of identified potential deposits covers gold and other precious metals, polymetallic massive sulphide types and quartz vein and quartz stock work type of deposits. There is an indication for the occurrence of Nickel and chromite deposits associated to the ultrabasic rocks in the far north of the country.
Occurrences of minable potash and sulphur evaporates in the Danakil depression, has now become apparent, and a variety of construction materials, including marble, granite and others in several parts of the country is also well known.
Recent exploration activities have proved that gold occurrences are very widespread in many parts of Eritrea and the country has great potential for developing more gold deposits. In addition to the previously known areas of primary gold occurrence in the central highlands (which includes the so called Hamasien gold field), those of Shillalo (in southwestern lowlands) area, and those of southern Eritrea, exploration activity in the last decade has shown the presence of economic gold deposits in the western lowlands and also in the northern part of the country. The average head grades in most of the historic vein gold mines that were active during the Italian colonial time up to the late 1950s were reported to be as high as 25 – 45 g/t, with reasonably good recoveries. Eritrea’s gold mineralization is usually hosted in quartz veins and stock works, and in particular in shear zones associated with felsic volcanic rocks, dioritic intrusions and in various schists that are frequently sub-parallel to the strike of the pronounced cleavage of the host rocks.
Occurrences of gold within exhalative VMS deposits, and in the weathered and supergene zones overlying them, are becoming more evident with recent additional discoveries of gold in Debarwa and Adi Nefas (in the central highlands), and at Bisha and Harena (in the western lowlands).
Base Metal Deposits
NNW to NNE-trending belt of gossans, exhalative cherts and altered felsic rocks that are indicators of massive sulphide mineralization are recorded in many parts of Eritrea. The ores of these massive sulphide deposits are predominantly chalcocite, pyrite with minor amounts of sphalerite, chalcopyrite and bornite. A major belt of massive sulphide deposit with gold and base metal mineralization passes through Asmara and includes Debarwa, Adi Nefas, Embaderho and many other localities roughly within a 50 km wide belt over a strike length of 250 km, extending from, more than 50 km north of Asmara up to the Eritrean border to the south. The belt that includes the Bisha high-grade zinc-copper-gold VMS deposit and Harena VMS deposits in the Western Low lands has already proved the presence of world class deposits and is also being explored for additional discoveries. There are indications of similar VMS base metal deposits farther north of Kerkebet, Harabsuit and possibly surrounding areas. There is a belt of copper mineralization in Raba-Semait area, sulphide-rich gossanous rock in Mt Tullului (Bedeho) in Sahel, northern Eritrea and in Mt Seccar and Sheib areas in the Eastern Lowlands. At Bisha, a world class deposit of precious and base metal VMS deposit has been found. Exploration in Adi Nefas VMS shows 9.0 meters grading 11.91 g/t Au, 285 g/t Ag, 3.18% Cu and 11.05% Zn and in another test drill NG-043-D – 5.25 meters grading 10.81 g/t Au, 239.8 g/t Ag, 6.77 % Cu and 6.77% Zn has been obtained. Reserve estimation made recently has shown that minable zinc, copper and associated gold is present in Adi Nefas. Embaderho is now emerging as a large base metals (Cu-Zn) deposit with some associated gold. Resource estimation is still going on; however, at this stage it is confirmed that it is a big base metal deposit. Overall in terms of mineral potential assessment and geological work, much of the country remains unexplored, despite the several discoveries that are being made.
Potash, sylvite and gypsum-bearing evaporates occur at Colluli, south of Bada. South Boulder Mining Ltd, a company looking for Potash deposit in the southeastern margin of the evaporate deposits in Dankalia have shown their hope to discover Potash deposit in billions of tones. Substantial deposits of gypsum occur at Desset area, north-west of Massawa. Large deposits of common salt also occur at several places along the Red Sea coast. Considerable quantities of high quality silica are found at Merbet, which has been exploited for glass manufacturing. In addition, deposits of silica sand with feldspar occur at various wadis of Eritrea. High purity feldspars occur in pegmatites at Lahazen, 35 kms south of Massawa. Sub economic deposits of mica, which was once exported by the Italians, are found south east of Lahazien. Large deposits of kaolin occur in the lateritic horizon in parts of Teraimni, at Adi Koteio close to Adi Kwala, Adi Keih, Zeghib, Adi Hawusha, Adi Ahderom and west and southwest areas of Himbirti. Extensive deposits of the raw materials for cement manufacture are found at Adailo, close to Tio with all the constituents including limestone, marl, clay and gypsum close together. Barite occurrences have been identified around the Heneb, Meter and Gharsa wadis to the north west of Mersa Gulbub. Barite veins also occur associated with faults in the sediments of the Dogali and Desset Formations. Other barite deposits of economic significance, with reported grades of 95-97% are known to exist at Debarwa and Ketina.
Large deposits of marble occur as belts running north-northeast from Adi Ibrhim south to Gerenfi t areas. However, there are few quarries of Marble in Gogne and Goranda area which are situated at the middle of the belt. Similar belt also occurs further west and runs from Alebu southwards to Guluj. Far, in northern Eritrea, a belt of marble occurs in Adobha Valley area. Other significant marble deposits occur at Afhimbol, Amberbeb, and Mt. Kuruku (in the upper valley of Barka).
The Kertse-Komte and Debri black and gray marble deposits occur south of Decamhare and have been exploited for a long time. Recrystallised limestone deposits with variegated colours occur at Dichinema area, in the southwest of Eritrea. Granites of various colours and textures are exposed over large areas. Granites of dimension stone quality, which are currently being exploited, occur at Geleb (pink granite), and in the Arato, Korbaria, and Tukul areas (grey granite). The Mai-mine granite and Elabered granite are also suitable candidates for dimension stone. A narrow outcrop of coral limestone extends along the coast from the headland of Ras Kassar to the coastline of Tio. Immense deposits of limestone occur in the Adailo-Aitosh area south-west of Tio.
Economic exploitation of geothermal heat for power generation appears possible in rift-related volcanic rocks in the Red Sea Rift areas. Alid, Nabro, and Dubi areas are the main targets as geothermal activity in these areas is known to be intensive. Lower temperature activity also occurs at Mai Wuui, 30 kms west of Massawa. Geothermal activity, evidenced by fumaroles and hot springs with extensive alteration on the ground, is abundant in the Alid geothermal field. Studies carried out so far in this area indicate the presence of a possible subsurface high temperature reservoir. The geothermal manifestations at Nebro and Dubbi are also promising, but further study will be required to estimate the reservoir temperature.