We are just back from Tsehay Mewcha after our scientific expedition with the Universities of Nantes and Addis Ababa.

Article issued in the AFG magazine (French Association of Gemology) December 2010 N° 174

Purchase the magazine :
AFG 7, rue Cadet 75009 Paris
tel : +331 42 46 78 46 fax : +33 1 40 22 09 77
Lysiane Borioli Cette adresse e-mail est protégée contre les robots spammeurs. Vous devez activer le JavaScript pour la visualiser.


welo wollo opal ethiopia AFG cover

Authors :
Francesco Mazzero1, Christian Désagulier 2, Benjamin Rondeau3, Dereje Ayalew4, Genet Ezezew5, Thomas Cenki6, Eyassu Bekele 7


Noble opal (fig.1) has been mined since March 2008 in several deposits near Wegel Tena (fig.2) in the province of Wollo (also written as Welo or Wello) in Ethiopia. A first article, describing the deposit, its mining conditions and the opals found there, was published in the Revue de l’Association Française de Gemmologie ( French Gemology Association Journal) (N° 167 – Mazzero et al
.2009). Since then, several publications have detailed the physicochemical properties of these opals (Rondeau et al., 2009, 2010a, b).Others will come out (Rondeau et al. 2011). The present article gives an account of a scientific expedition to this deposit organized and financed both by Opalinda/Eyaopal companies and Nantes University. The objectives were : providing information about the exploitation of this deposit, which seems very promising, and understanding the geological formation of opals.

November 4th to 7th 2010 : PREPARATION

Such an expedition cannot be prepared in just any way. In order to go to the places we intended to reach, from Addis Ababa to Wegel Tena in Wollo province, distances have to be measured in time units rather than kilometres. The camp will be only set up after 2 days and 5 hours’ driving on chaotic tracks with a 4x4 and we’ll be sleeping in a tent, with a nice crescent moon shaping the filament of a bedside lamp for sole lighting. A minutely detailed inventory of our logistical needs is necessary. FM spends October in Addis Ababa to gather the essentials and prepare the permits with DA and EB.

So nothing vital should miss, from a nail to the electric generator, from sleeping bags to jumper, saw, pickaxe, non-perishable food for 10 days, olive oil, kilos of oranges and folding chairs, blue and green jerrycans… to make the difference between water and petrol, plastic funnels, ropes and thin cords, water and gas for heating food. At a height of 3200m, even near the equator, 12- hour nights are cold. An advantage however: water boils quickly not at 100°C but, according to Clapeyron law, at about 85°C. We’ll also have to load the roof racks with eucalyptus wood, stakes and poles necessary for framing the mess, a large shelter covered with tightened tarpaulin, designed by FM.

November 8th to 10th : SETTING OFF

Our route is given by Google Maps : from Bole International airport, we have to take Equatorial Guinea Street due north through the former road to Asmara (Erythrea). We leave Addis Ababa (New Flower) to Tsehay Mewcha (Sun Gate) with Genet (Paradise) in two overloaded Landcruisers. Journey : 530 kms. With us, two experienced multi-skilled drivers: Tesfaye and Dereje. We drive past Mezezo, the first opal deposit in Ethiopia, exploited since the 90’s (see e.g. Mazzerro et al. 2003); then we stop in Robit, a town with marabouts and toads. As usual, the group has injera for dinner, a traditional dish with berbere spices in the shape of a grey, slightly acid spongy pancake, which serves both for meal and plate. This dish, both container and content, is prepared with tef flour, a grass from the poaceae family, extensively cultivated in Ethiopian mountains. Its composition is rich in proteins and it contains a large proportion of calcium and vitamins. Associated to different vegetables and a small quantity of meat (mutton, beef, chicken, goat) it is enough to meet the needs of each member of the expedition for five days out of seven. The week counts two non-meat days carefully respected by those Christians from the very beginning who miss no prayer.

Due to some diversions, we reach Dessié two days later. Purchasing some additional material made us stay there another night before overloading our 4x4 roof racks with eucalyptus poles, mineral water, and above all, Saint George endemic beer. In the Woreda , equivalent to a French canton, everything which is local prevails over what is federal. The permits allowing access to the deposits are difficult to obtain. Ethiopian owners have decided not to admit foreigners lest they should be plundered , which is justified by different recent examples. We have to repeat our objectives endlessly, explaining they are purely scientific and in no way commercial. Dessié at last, where each of us buys a gabi on the market, a long scarf with indecipherable color codes, which will be so useful in the burning coolness of the Tsehay Mewcha high plateau awaiting us (fig. 3).

November 11th to 15th : FIELDWORK

The engines fall silent in the welcoming shade of Weys Maryam orthodox church. We set up our camp here (fig.4), less than one kilometre from Tsehay Mewcha. This hamlet, with only a few shelters 2 years ago, has now become a big village with 250 permanent houses (sheet-metal roofs, wood and cob walls, stone foundations) and an important primary school and a health centre.The youths wearing fashionable clothes, with wrist-watches and mobile phones, drive their crossmopeds, a striking evidence of the economic transformation Wollo opal has

brought about locally .

On the arrival day, geologists devoted their afternoon to a preliminary exploration of Tsehay Mewcha site (fig.2 points 1 to 3), whereas the rest of the group was setting up the camp , occasionally greeting and exchanging with the village chief : our thanks to our driver Dereje whom we knew was a good translator but revealed himself also a diplomat.

Our camp has an impressive bird’s-eye view, breathtaking for ones already short of breath for lack of oxygen at an altitude of 3200 meters. In front of us, in the bottom of a clear narrow line, half-way up the cliff, men have dug tunnels climbing through ignimbrite, looking for precious opal. And silence… a silence sometimes broken by family quarrels between gelada monkeys which have settled in the canyon cavities.

As often happens, discussions with local miners prove to be very useful. We learn that opal is not only mined on the sites visited by FM and TC in April 2009 (fig.5) but that dozens of other areas are exploited, sometimes more than ten kilometres away. As days go by, we can establish that all the deposits are located in a line on the same stratigraphic level in the volcano-sedimentary sequence: so Wollo opal corresponds to a single geological formation episode.

On November 12th a 7 kilometer track leads us to Borena Mikael deposit (fig.2,point8) (fig.6,7,8,9,10,11,12). It is the only fieldwork day gathering all the members of the expedition. From a geological point of view, we note down an obvious similarity between Borena Mikael and Tsehay Mewcha deposits, observed the previous day. With binoculars we can also see another deposit located near Kisat Gebrel (fig.2 point 9), here again at the same stratigraphic level.

So, the opalized level stretches over dozens of square kilometres, but discontinuously. We think that there may still exist numerous deposits to discover, some of which outcrop… while others are totally under the plateau !

November 13th left its mark because of an accident which disturbed our programme. CD fell several meters and found himself lying on his back unable to move. We were very worried: we had to organize transportation to hospital. The nearest one is in Dessié, five hours on bumpy tracks; the injured man is first transported on a stretcher carried by mountain peasants on their shoulders. Superficial injuries are treated by the male nurse of Tsehay Mewcha health center, who advises us to drive CD to Dessié in order to receive proper treatment for more serious injuries. Transported by Dereje Driver, the injured man is then taken to the capital city, still accompanied by FM. After following a hazardous route, fraught with administrative and medical pitfalls, CD got treatment in Dessié, then Addis and eventually Paris. Fortunately the writer is now convalescing.

Our geological adventure went on for a few more days with a reduced team, visiting among others Zelehon Myriam deposits which quite similar to the other ones (fig. 2 points 4 to 7).

November 16th to 19th : COMING BACK

Apart from an unavoidable feeling of nostalgia, returning from an expedition is emotionally less charged. This was exactly the case, above all because we knew our injured companion was out of danger. We left the settlement after having distributed the working material to miners. We had taken the initiative in bringing some basic tools in order to improve their working conditions as it is mentioned at a later point. The camping material was given to the inhabitants of near villages, the electric generator and lighting equipment to Weys Maryam parish.

The samples arrived in Nantes without a hitch. Field observations will soon be enriched with laboratory data and complete the geological history, still very limited, of this exceptional deposit.


The opal deposit of Tsehay Mewcha consists of a series of very thin lenticular layers stretching out – from a few dozens to a few hundred meters in length – all of them are displayed on the same stratigraphic level of the thick oligocene ignimbritic series. The mineralized rock consists of a very thin edge which underwent particularly strong meteoric alteration after depositing. Bioturbations (like holes, root marks) are very numerous, such as other sedimentary processes like ferruginous oolites which show a certain local modification of the impaired rock. One finds opal scattered about one to two meters thick without any possibility of spotting a precise lower or upper limit: from top to bottom, mineralization appears and then disappears progressively. Some opals contain spectacular plant fossils (fig. 13&14) whose taxonomy is not precisely defined. The fact that these plants, still containing carbon, are very well preserved shows that they were trapped during solidification of silica gel opal is made of. Consequently, opal formed at the surface of the terrestrial crust when water was present : probably in a lake or a swamp. The development of plant life and the presence of a swamp which has allowed ignimbrite alteration implies that during a rather long period (1000 years ? 10000 years ?) volcanic eruptions had stopped. This period of time is very short compared to geological time scale and goes almost unnoticed in the thick series of volcanic rocks (about 3 kms thick, 350 meters of which cover the opal-rich level). We have observed that the opalized layer shows a high opal-gem content : several percent of the rock to several decimetres in thickness. The mining potential of this deposit has a fine future of several decades ahead : it is a deposit of worldwide importance which could become the opal deposit of the 21st century…provided mining gets organized in a rational way.


It is important to underline that mining conditions are extremely dangerous because miners have no knowledge of mining techniques : they are former farmers recycled for the occasion. Fatal accidents are very numerous (out of one thousand miners, 80 died in two years) mainly caused by collapsing rocks or falls from cliffs. Non-fatal accidents are due to lack of equipment limited to hammers, chisels, shovels and pickaxes. Although tunnels are dozens of meters long, there is no shoring up nor ventilation (fig. 16). Many workers hurt themselves with tools and some of them work bare-footed. During our stay there, we took the opportunity of giving miners some basics in safety rules (fig.17) while giving them material bought in Dessié, Addis Ababa and in France : protected chisels (to avoid smashing one’s fingers with a hammer), clubhammers, jumpers, helmets and goggles. We insisted on the reasonable price of these tools which miners could easily afford since selling opal has considerably increased their income.


We express our thanks to the Ethiopian Authorities, who have permitted access to the site normally forbidden to foreigners, in order to carry out this scientific study. Thank you also to the Ministry of Mines and Energy (Mr Tamrat Mojo, Mr Gebre Zabher) who allowed exportation of samples intended for scientific research about this deposit. Thanks to Melku Tadesse, male nurse of Tsehay Mewcha who gave first-aid treatment to our injured colleague and to the French embassy services who sorted out the administrative imbroglio thus making his return to France easier.


welo wollo ethiopia opal
Cover : Opal and sunset at Tsehay Mewcha, 20 MM and 6 49 PM local time. The srong blue is due to light scattering in the stone body such as nice blue diffractions.

welo wollo opal rough ethiopia
1 -
Rough opal from Wegel Tena 35 mm large. This specimen may be called « snow flakes » for aesthetic reasons

2 - Map of the Tsehay Mewcha area, north-east of Wegel Tena. The several opalized deposits are indicated in red. Numbers are used in the textand figures caption.

3 - View over the Kisat Mikael and Borena Mikael area, eastward. Photo by Thomas Cenki

4 - The field camp is established between the Weys Maryam church and the canyon, at an elevation of 3130 m. The blue tent is the mess. Photo by Rondeau

5 - Since 2009, when FM and TC visited the site, the opal minig site at Weys Maryam has changed : now, tunnels have been digged, some are 20 to 40 m long. Thick unmined areas sustain the ovelying rocks. Point 1 on the map. Photo by Rondeau

6 - Opal deposit # 8 on the map, at Borena Mikael. It is currently mined by about 30 miners. Photo Mazzero

7 - Group of miners on the site of Borena Mikael (deposit # 8 on the map). Waste stones and natural erosion products constitute the tones accumulations. Photo by Mazzero

8 - A common opal in situ, 20 x 20 cm. On every mined place, the presence of opal is clearly visible : the deposit is very rich in opal, several percent of the rock. Photo by Cenki.

9 - Miner at work in a tunnel at Borena Mikael (deposit # 8 on the map). Working tools

are very simple, danger is everywhere, and the work is exhausting. Photo by Mazzero.

10 - Wonderful rough, play-of-color opals just extracted at Borena Mikael (deposit # 8 on the map) in the hands of their finder

11 - Miners and geologists at Borena Mikael (deposit # 8 on the map). DA and BR investigate the opalized layer, while TC takes notes. Photo by Mazzero

12 - Genet Ezezew, geologist at the Ethiopian Ministry of Mines, is advised by two local miners, among which Desalew Gedefie (center). Photo by Mazzero.

wollo welo ethiopia opalized wood
13 - This cylinder is an opalized fossil wood with red play-of-color, 25 mm long. Such wood fossils are sporadically found on the several deposits of the Wegel Tena area. Photo by Mazzero.

14 - Plant fossil included in and opal. Picture 21 x 15 mm. Plants fossils and wood opal indicate that the opal formed in a sedimentary (lacustrian ?) environment, most probably at the occasion of a pause during the volcanic event. Photo by Mazzero.

15 - Intensive during the first year of mining the opalized layers induced rock collapsing such as this one, responsible for many dead miners (here, and example at the deposit # 2). Such accident do not occur any more because mining is organized in tunnels, also dangerous but for other reasons. Miners idicate the scale. Photo by Rondeau.

16 - Young miner from Wegel Tena at the entrance of a tunnel. This deposit is very promising. However the working conditions are very dangerous and need to revisit the conditions of exploitation. Photo by Mazzero.

17 - Security tools such as protected hats, ans safety googles are given as demonstration samples to the miners. Hoping that this will demonstrate the necessity of protecting theirselves… Photo by Rondeau


1 - Chef d’expédition. Opalinda / Gemoa 59 rue Sainte Anne 75002 Paris.

2 - Ingénieur-écrivain envoyé par J.N.A. Rimbaud (lettre de mission celle datée du 6 mai 1883).

3 - Géologue et gemmologue. Université de Nantes, LPGN, CNUR-UMR 6112, 2 rue de la Houssinière, BP92208, 44322 Nantes Cedex 3.

4 - Géologue au Département des Sciences de la Terre de l’université D’Addis Ababa, Ethiopie.

5 - Géologue envoyée en observatrice par le Service des Mines du Ministère des Mines et de l’Energie d’Ethiopie.

6 - Logisticien puis chef d’expédition par intérim. Opalinda.

7 - Eyaopal, Addis Ababa .


Mazzero F. (2003) A la découverte des gisements d’opale du Shewa, relation de voyage en Ethiopie. Revue de Gemmologie a.f.g., vol. 148, pp. 27-31.

Mazzero F., Gauthier J.-P., Rondeau B. , Fritsch E., Bekele E. (2009) Nouveau gisement d'opales d'Ethiopie dans la Province du Welo : premières informations. Revue de Gemmologie a.f.g., vol. 167, pp 4-5.

Rondeau B., Mazzero F., Bekele E., Gauthier J.-P., Fritsch E. (2009) Gem News International: New play-of-color opal from Welo, Ethiopia. Gems & Gemology, Vol. 45, No. 1, pp. 59-60.

Rondeau B., Fritsch E., Cenki-Tok B., Mazzero F. (2010a) New opals from Wollo, Ethiopia: geochemical characterization. Geochimica et Cosmochimica Acta, vol. .74, n°12, p. A880.

Rondeau B., Fritsch E., Gauthier J.-P., Mazzero F., Cenki-Tok B., Bekele E., Gaillou E. (2010b) A new source of play-of-color opal at Wegel Tena, Wollo, Ethiopia. Gems & Gemology, vol. 46, n°2, 90-102.

Rondeau B., Cenki-Tok B., Fritsch E., Mazzero F., Gauthier J.-P., Bodeur Y., Bekele E., Gaillou E. (2011) Trace-element geochemical characterization of opals from Wegel Tena, Wollo, Ethiopia. Geochemistry, Exploration, Environment, Analysis , soumis en octobre 2010.


  • Vues: 12492