22 • African Mining

Exploration

IntroductionEquatorial Guinea is located in the Gulf of Guinea,local to key markets in West Africa and Nigeria,and well-served by port infrastructure. The main-

land enclave of Rio Muni comprises the ArcheanCongo Craton granite-gneiss-greenstones, partlyreworked in the Paleoproterozoic (Eburnian) andin the Pan-African, all traversed by onshore struc-tures continuous with Atlantic transform faults.Recently, the entire area of Rio Muni has becomeavailable for minerals exploration, and togetherwith new Licensing Contract arrangements and anintegrated GIS database of exploration results,must qualify as an important greenfields explo-ration opportunity.

The CountryThe territory of Equatorial Guinea includes theislands of Bioko and Annobon, and the mainlandenclave of Rio Muni, which is bordered to the northby Cameroon and to the south and east by Gabon.The total surface area of the country is 28 051 km2,with mainland Rio Muni accounting for approxi-mately 26 000 km2. Rio Muni has a coastal plain anda mountainous interior, and the climate is tropicalwith four seasons (two wet and two dry). The popu-lation of the country is about 500 000 with an annualgrowth rate of 2,5 %. One third of the populationlives in the urban areas, mainly in the capital ofMalabo on the island of Bioko, and in Bata, thelargest town, port and administrative centre on themainland. Spanish is the official language butEnglish and French are widely spoken.

The economy is based mainly on forestry andhydrocarbon production, which together accountedfor around 97 % of total exports in 1997.Hydrocarbon production includes oil, natural gasand condensate, most of which is exported. Theexciting discovery of the Ceiba field in 1999 by UScompany Triton has now confirmed the Gulf ofGuinea as a major new petroleum province. Fasttrack-development of Ceiba, plus field expansion inthe Niger Delta province, is expected to increaseproduction rates to over 200 000 bbl/d during 2001.Revenues from hydrocarbons are already leading tomajor infrastructural improvements, including anew deep-water Freeport and processing facilitieson Bioko, and road improvement and electrificationprogrammes throughout the country.

Geological BackgroundRio Muni comprises the Archean terranes of theNtem Complex and the Monts de Cristal Massif,both of which were partly reworked during thePaleoproterozoic Eburnian orogeny, Figure 1.

New exploration opportunities inEquatorial Guinea

By Kevin Leahy*, Bob Foster*, Alexandra Harrison* and Jose Mba Mbeso†

Although Equatorial Guinea has virtually no mining industry, it does havepotential for gold, columbo-tantalite and diamond deposits and its Ministry ofMines and Energy is keen to encourage minerals exploration.

*Exploration Consultants Ltd, Highlands Farm, GreysRoad, Henley-on-Thames, UK. † Ministry of Mines and Energy, Calle 12 de Octubre,Malabo, Bioko Norte, Republic of Equatorial Guinea

Fig. 1: Regional tectonics map of Rio Muni (after Feybesse et al 1998).

African Mining • 23

Exploration

Exploration in Rio Muni has indicated the presenceof greenstone belts and major shear zones, includingEburnian terrane boundaries, which have a signifi-cant gold potential. Pan African transpressive struc-tures are common in the west and are associatedwith granitic intrusions and pegmatite bodies, andthese also occur across the interior. Low-metamor-phic-grade shales, dolomites and quartzites occur inthe south-west, representing the northernmostextension of the Niari foreland basin of the Pan-African-age West Congolian Orogeny. Higher-gradesedimentary packages, also attributed to the Pan-African, are found along the northern border of thecountry where they are associated with major strike-slip and thrust faults.

The coastal strip of Rio Muni comprisesCretaceous sands, shales and carbonates with basalconglomerates, developed in the early rifting phas-es of Atlantic opening. Significant transcurrentstructures (such as the Fang and Bata fracturezones) link to major onshore lineaments, at leastone of which shows evidence of Cainozoic rifting(the Benito Rift).

Exploration PotentialCurrent minerals production is negligible other thanfrom minor artisanal gold mining activities in RioMuni. Nevertheless, several studies have demon-strated the potential for gold, columbo-tantalite anddiamond deposits, with previous exploration high-lighting several areas of immediate interest. There isalso potential for platinoids, dimension stone, basemetals, and bauxite amongst other commodities.

Gold exploration has identified three mainareas – Coro, Aconibe and the Wele River basin onthe northern margins of the Monts de Cristal ter-rane, as well as several other occurrences. Theseare small alluvial prospects currently yielding gold,including several nuggets that occur with vein-quartz and lateritic minerals, attesting to nearbyprimary and secondary gold sources. The sourcesof the alluvial gold have yet to be delineated.South of Rio Muni in Gabon, the Monts de Cristal,Du Chaillu and Ogooué terranes have numerousalluvial workings and areas actively beingexplored by international gold mining companiesincluding the important prospects in the Etékégreenstone belt, Figure 2.

The diamond potential relates in part to post-Eburnian structural lineaments containing basicintrusives that extend along strike from the Mitzicdiamond mines in Gabon into the Nsork area of RioMuni, 50 km to the north and west. Heavy-mineralsampling results have identified zinc-rich chromitesfound in the Nsork area, similar to those found inthe meta-kimberlites at Mitzic. Recent exploration inGabon for both gold and diamonds has identifiedtrends right up to the southern borders of Rio Muni.

Columbo-tantalite mineralisation is known in atleast two areas (Aconibe and Ayamiken) defined byNb and Ta soil anomalies, and heavy minerals asso-ciated with Nb-Ta-rich pegmatites. Neither area hasbeen explored in great detail and thus they repre-sent early-stage exploration prospects for pegmatiteand/or skarn systems associated with Pan Africangranitic intrusions. The Aconibe occurrence com-prises discrete, laterally extensive pegmatites,

which are also overlain by eluvial and alluvialdeposits yielding grades of 3,0 to 7,5 kg/m3. Sampleassays have demonstrated niobium-rich columbo-tantalite (62,36 % Nb2O5) with subordinate tantalum(18,74 % Ta2O5).

Widespread lateritisation and indications ofbauxitic laterite, with grades up to 58,3 % Al2O3, and2,1 % to 5,3 % SiO2, indicate some potential for baux-ite, particularly in the Nzangayong, Ncoasas,Ayamiken and Churu areas. Anomalous values of U,Ni, Co, Pb, Zn, Cu, As, Ag, Mn and Mo have beendetected in laterite above black shales which occur inthe red-bed sequence near Cogo. The red-bedsequence is part of the West Congolian Niari forelandbasin, with known base metal deposits immediatelyto the south in Gabon, and is also equivalent in ageto the Katangan sequences of the DemocraticRepublic of Congo and Zambia. Serpentinised ultra-mafics and other basic intrusives along the footwallof the Benito Rift constitute an untested explorationprospect with some potential for base metals andplatinoid elements. Similar basic intrusives have alsobeen reported in southern Rio Muni, which may be anorthern extension of the Kinguélé ultrabasics trend.

Previous CampaignsBetween 1980 and 1986, BRGM and a Spanishexploration company undertook regional and fol-low-up stream-sediment surveys utilising heavymineral separates and sediment geochemistry.These highlighted the potential for gold productionfrom alluvial deposits at Coro, as well as the occur-rences of columbo-tantalite, diamond indicators,iron ore, radioactive minerals, rare earths and basemetals in other areas. Other activities included aside-looking radar survey and a 1970s vintage aero-

Fig. 2: Regional Goldtrends in Gabon andRio Muni (afterUMC/TerraView).

African Mining • 25

Exploration

magnetic survey of Rio Muni. In the late 90s the Exploration Licence for all of

Rio Muni was held by United Meridian Corp (laternamed Ocean Energy) and BoMc Holdings Inc.These companies undertook a wide range of explo-ration activities including regional and prospectgeological mapping, reconnaissance evaluation ofthe gold and bauxite potential of laterites, samplingand prospect evaluation of the artisanal workings,stream sediment sampling, interpretation of high-resolution radar imagery, and the generation of acomprehensive GIS database. At the end of 2000, theExploration Contract lapsed and the entirety of RioMuni became open for exploration.

Current Licensing Situation The Ministry of Mines and Energy is keen toencourage an exploration-friendly environment, andto this end the Mining Law is in the process of beingre-drafted. Exploration Licence Contracts are beingdrafted to permit large areas to be explored over aone to three year period. The explorer may also optfor registration of smaller Prospect Areas (up to100 ha) to permit detailed evaluation of individualprospects. Exploitation Licences will be grantedupon submission of a mining programme that mustinclude environmental management strategies.

Archived DataIn 2001 Exploration Consultants Ltd were appointedas Technical Advisers on minerals to the Ministry ofMines and Energy, having been Technical Advisersfor hydrocarbons for six years. ECL are now activelyinvolved in redrafting of exploration and miningregulations, as well as the promotion of explorationopportunities, contract negotiations, and compila-tion and sales of archive data.

Reports from previous exploration campaignsare available in hardcopy format. In addition, all theheavy mineral and geochemical sample data fromthe previous surveys, together with regional andprospect-scale maps, have been digitised and areavailable to be purchased from the Ministry in eitherhard-copy or GIS-file format. Regional geochemi-cal/heavy mineral maps (1:100 000 scale, 4 sheets)

and customised packages of all data will be avail-able in the near future, Figure 3. A full catalogueand price list will be available from ECL or theMinistry by mid-2001.

Contact DetailsFor further information, please contact either:Cristobal Manana Ela, Minister of Mines andEnergy, Calle 12 de Octubre, Malabo, Bioko Norte,Republic of Equatorial GuineaTel: +240-93567 Fax: +240-93353orDr Kevin Leahy, Exploration Consultants Ltd,Highlands Farm, Greys Road, Henley-on-Thames,Oxon, RG9 4PR, UKTel: +44 1491 415400 Fax: +44 1491 415415E-mail: k.leahy@ecqc.com

Fig. 3: Sample of GISdatabase – Coro goldarea, central Rio Muni,showing geochemicalanomalies.

Phelps Dodge Corp has joined BHP WorldExploration Inc in its option agreement with

Tenke Mining for the proposed development ofthe Tenke Fungurume copper/cobalt deposits inthe Democratic Republic of Congo.

The Tenke Fungurume concessions are locatedin Katanga province in the southernmost part ofthe country. The concessions, says Tenke Mining,host large, high-grade copper/cobalt deposits thatare world renowned and considered as one of thelargest and richest undeveloped copper/cobaltdeposits. BHP holds an option to acquire a con-trolling interest in Tenke Fungurume and to func-tion as the primary operator of the project.

Since the middle of 2000, Tenke has beenworking closely with BHP on the preparation oftechnical and economic studies related to poten-

tial future development of Tenke Fungurume.The agreement provides Phelps Dodge with theopportunity to earn up to 50 % of BHP’s positionin the project.

“Our strategy is to advance the project asquickly as possible and having Phelps Dodge joinwith BHP significantly strengthens our ability todo this,” says Adolf Lundin, president of TenkeMining. “This agreement will bring the resourcesof two of the world’s largest copper producers tobear on the development of this world-classdeposit.”

Discussions are continuing with Gecamines,the DRC state mining company, focused on thebest approach for future development of the pro-ject. These discussions are expected to continueover the next few months. ❑

Additional backing for Katangan project