Geoscience Reference
In-Depth Information
The Schist Belts group of which Ilesa area is part have been variously termed“ Newer
Metasediments” (Oyawoye, 1964), “Younger metasediments” (McCurry, 1976); “Schist
belts” (Ajibade, 1976) and“ Slightly migmatized to non-migmatized metasedimentary and
meta-igneous rocks” (Rahaman, 1988). The Nigerian Schist belts occur as prominent N-S
trending features in the Nigerian Basement Complex. Lithologically, the schist belt consists
of metamorphosed pelitic to semi-pelitic rocks, quartzites, calc-silicates rocks,
metaconglomerates and pebbly schists; amphibolites and metavolcanic rocks. On the basis
of lithology, metamorphism, structure, geochemical characteristics such as the tholeitic
affinities of the amphibolites, and economic potentials, the schist belts show similarities to
typical Archaean greenstone belts of the world (Wright and McCurry, 1970; Hubbard, 1975;
Elueze, 1977; Klemm et al, 1979, 1984).
However, certain differences exist between these schist belts and typical greenstone belts.
Though the schist belts of Nigeria have the sedimentary and ultramafic rock groups as
defined by Anhaeusser et al, (1969), the so-called, “greenstone group” comprising
serpentinites, crystalline limestones, rhyolites, banded ironstones of chemical origin and
massive carbonated “greenstones” are either absent or less conspicuous. Also the ratio of
metasediments to metavolcanics is much higher in the Schists belts of Nigeria than in the
typical Archaean greenstone belts (Wright and McCurry, 1970). Mineralization is also not
strongly developed in the schist's belts as in well known greenstone belts of the Canadian,
Indian, Australian, and South African Precambrian shield areas.
3. Location, geomorphology and relief of study area
The area of study is located in the southern part of Ilesa and is geographically enclosed
within Latitude 7 0 30`N to 7 0 36` N and Longitude 4 0 38`E to 4 0 50`E. It covers an area of
about 1200 square kilometers. There are a good number of major and minor roads that link
up the towns and villages in the study area. There are also main paths and footpaths linking
the communities. These make the entire study area fairly accessible. The landscape of the
area of study can be generally described as undulating, rising gently to steeply, but in some
areas is punctuated by hilly ridges. The ridges are formed by quartz-schist or quartzite that
rises abruptly from the enveloping basins and trend in the North to South direction. On the
other hand, hills which are probably products of fragments of coarse-grained batholitic
granite or resistance gneisses have a positive relief and are covered up by vegetation.
Dissected topography also develops over the easily eroded basic rocks which according to
De Swardt (1953) reflect the erosion cycles that separately occur in the area.
4. Research methodology
Preliminary work in the survey area took the form of a reconnaissance geological mapping
followed by the statistical analysis of geochemical data to delineate areas with geochemical
anomalies indicative of possible mineralization (Ariyibi et. al. 2010). This was aimed at
studying the geology and selecting geophysical traverses approximately normal to the strike
of the geochemical anomaly. In some cases however, the dense vegetation necessitated the
cutting of traverses, although most of the traverses used were along existing roads and
footpaths. The field data acquisition involved ground magnetic, electrical resistivity and
VLF - EM survey methods. Essentially, the magnetic and VLF - EM measurements were
carried out simultaneously on the chosen traverses located on the delineated area using
topographical and geochemical anomaly maps.
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