Basically, geological mapping involves the study of rocks; in situ, that is, in their natural environment and the representation of such rocks on a geological map. Furthermore, rocks of the Igarra area constitute part of the Basement Complex of southwestern Nigeria. On the basis of field relationships and petrological studies, these rocks can be grouped into gneissic rocks, meta-sedimentary assemblages, intrusive igneous rock bodies and sedimentary rocks (formations).
The gneissic rocks comprise of calc-gneiss and migmatite-gneiss, and the metasedimentary assemblages chiefly; metapelites are found as quartzites and pelitic schist. The intrusive rocks consist essentially of Pan-African granitic units. The minor rocks include; pegmatite and quartz vein.
Field and petrographic studies have confirmed that the rocks in this area have undergone at least three episodes of deformation, D1, D2 and D3. The first and second episodes of deformation produced F1 and F2 along with the foliations S1 and S2 respectively. Associated with the three episodes of deformations D1, D2 and D3 are the M1, M2 and M3 episodes of metamorphism. The entire study area belongs to low to middle metamorphic grade (that is, greenschist facies to amphibolite facies).
This comprehensive report consist of two section A and B. Although section A is also the basement complex of Nigeria consists of the migmatite gneissic complex, the metasediment, schist belt, the granitoids and the minor rocks. The granitiods consist of mainly of syenite and aplites (microgranite) while the minor rocks are quartz veins, aplites and dolerites dykes. The region has undergone multiple deformations, evidence of which are folds, faults, cross-cutting relationship and various types of metamorphism. The contact point of all rocks and structural features were established. The region is also of great economic interest because of mable, quartzite and granite which are quarried for industrial purposes.