The Nimba and Simandou greenstone belts are significant structures within the Archaean basement in the Guinea-Liberia border area (Thiéblemont et al., 2004). The Nimba greenstone belt is a 1400 m-thick sequence of metavolcanic and metasedimentary rocks which extends for a total length of 45 km, with 25 km in Liberia and the remainder to the northeast along the border zone of Guinea and Côte d’Ivoire (Berge, 1974). Dating of detrital zircons in quartzite has placed the Nimba greenstone belt as latest Archaean to early Palaeoproterozoic (Billa et al., 1999), the same age as the Simandou belt in Guinea.

Historically iron ore has been exploited from both the Liberian and the Guinean sectors of the Nimba greenstone belt. In Liberia, the main Nimba ore body, now mined out, was located in one of two parallel bands of Archaean BIF with a north-east strike (Berge et al., 1977). The rocks in the Nimba belt are divided into two major units, the Yekepa Supergroup, comprising gneisses and orthoamphibolites with a dominant north–south structural trend, and the younger Nimba Supergroup, which consists of a basal conglomerate overlain by amphibole schists of volcanic origin, succeeded by metasedimentary formations comprising phyllites, the Nimba itabirite and the iron ores (Berge, 1974). The contact between the Nimba Supergroup and the underlying Yekepa Supergroup was interpreted as a regional unconformity, similar to that observed in the Simandou area of Guinea, located about 100 km to the north (Berge, 1972).

Before mining the ore body was 250–300 m thick, 800 m long and known to a depth of 670 m. The ore was formed as a result of alteration of the enclosing grey itabirite during metamorphism, although the role of post-metamorphic meteoric fluids is unclear.

The proposed Nimba Iron Ore Project is located in the Guinean Nimba Mountains, in south-eastern Guinea, adjacent to the Liberian and Ivoirian borders. It involves mining high-grade haematite from two open pits at high elevations in a mining concession of 6.25 square kilometres, at the northern end of the mountain range. The ore is extremely high-grade and friable with almost no impurities (e.g. silica, phosphorus, aluminium oxides), little to no overburden covering the ore, and minimal waste-rock throughout the life of the mine. No tailings dam is required.

The mining process is not technically complicated: ore would be extracted from the surface of the pit.

After primary crushing, ore would be loaded onto a largely suspended conveyor belt to transport it to a facility in the surrounding lowlands, generating electricity as the ore descends. The ore would proceed through secondary crushers and screens, and then be stockpiled. From there, it would be loaded onto trains and sent to port. The project seeks to mine approximately 450 million tonnes of ore across 15-25 years, depending on the rate of production. The ore needs no treatment other than simple dry-crushing and screening. Processing of the ore requires no wetprocessing or treatment with chemicals. There would be no tailings dam and very little waste-rock.

Production of high–quality lump and fines products.

Ore would be exported via the existing railway in Liberia, which is operational to within 25 km of the Guinean border.