Geomorphology: The topographical characteristics of the area within Enyigba comprises of undulating plain with irregular ridges and gentle sloping hills (low hills). The main relief is an elongate ridge of 200m above sea level, trending northeast-southwest incurving toward the east at its northern end. These topographical features were seen to be controlled by the bedrock geology; defined by the highly weathered shales, which occupy the area capped by the low lands. The weathered rusty brown to reddish brown shales were mainly exposed by road cuts and erosion surfaces, while the dark grey or black shales were mainly exposed by operational lead-zinc mines and occasionally by river channels and emplaced almost horizontally.
The flow patterns recorded in the research area are that of the irregular dendritic patterns which consist mainly a number of small ephemeral streams. The parent course is the Ebonyi River (Figure 4). Other drainage courses include the Akpara River, Iyinu stream, Ikpete stream, Obelebe stream, Mgbuchi stream.
Generally, the water course flows eastward to join the Cross River, somewhere outside the research area.
The vegetation of the area is Parkland, which is derived savannah. This is characterized by stunted trees and pockets of derelict woodland and secondary forests consisting of few shrubs with dispersed large trees and climbers.
Soil type and Land use
The area within Enyigba is characterized by reddish brown gravely and pale brown and clayey soils formed from shales, and shallow pale brown soils derived from sandy shales. The clayey swamp (flood plain) is suitable for rice farming.
Vein ridges and low-lying mineralization terrains where mining activities take place occupy about 10% of the research area. Land for inhabitation occupies about 20%, whereas the rest of the land is used for agriculture and vegetation.
Literature Review ON Geomorphology
Several geologic survey works have been conducted in the area within Enyigba, but were mainly on regional scales. Going by the fact that the Benue Trough has not been fully investigated, Enyigba and its environs were no exception.
The economic importance (the occurrence of lead-zinc) in the research area has attracted much attention of various geologists in a quest to gain full descriptive knowledge of the general geology and geologic characteristics of the area, towards evaluating its potential.
One of the earliest survey projects were the geologic survey of Southern Nigeria, under the Imperial Institute between 1903 and 1913; and that on the Southern region by the Geological Survey of Nigeria, from 1922.
Shell D’ Arcy geologists in their survey reports on the geological nature and characteristics of Southeastern Nigeria established the facts on the Cretaceous successions of the Southern Benue Trough. These successions they said form the Western limb of the Okigwe-Abakaliki Anticlinorium, which towards its axis, the highest formation begins to experience variation in lithology with the shally units grading to sandstones. On these, they established three basic stratigraphical successions underlying the Cross River Plain to include: the oldest Asu River Group named after Esu River in Okposi-Uburu area, the Eze-Aku Formation and the youngest Awgu Ndiabor Shale Formation.
The rock units in Enyigba and its environs were seen to be of Lower-Cretaceous- middle Albian age, and the Albian sediments of Asu River Group were known to consist of rather poorly bedded sandy shales known as Abakaliki Shales, with sandstones and sandy limestone lenses (Kogbe, 1989).
Gravity surveys (Cratchley and Jones, 1965) prove some features aligned in a Northeast-Southwest direction in the Benue Trough.
The mode of mineralization of Enyigba lode according to Orazulike (1994) was largely by open space filling. According to Uzuakpunwa (1974), the tectonic history of the Abakaliki district shows that there was extensive faulting, folding with igneous activities and mineralization.
Field observation (Orazulike, 1976) and structural analysis (Ezepue, 1984) support this view. Macro textures on the minerals according to Orazulike (1994) include incompletely filled vugs and cavities in mineralized zone and combstructures in which well-formed quartz crystals are observed projecting towards the centre vugs.
On the origin, the Abakaliki Shale of the Asu River Group hosts the galena and sphalerite. This is the Albian carbonaceous shales (Reyment, 1965). These sediments were intruded by the Santonian tectonic extent alongside with the Cenomenian-Turonian sediments (Orazulike, 1994).
Igneous related hydrothermal fluids injected into the fractures to effect mineralization (Uzuakpunwa, 1974) the volcanic/pyroclastic rocks and their genetic relations to Enyigba lead-zinc mineralization are provided and described by Reyment, 1965.