Abstract
This research investigated the influence of the local geology on the groundwater potential of the two kunike chiefdoms (Sanda and Barina) in the Tonkolili District, Northern Sierra Leone. The local geology is made up of rocks typical of the West African Archean greenstone belt. The stratigraphic sequence is marked by the basic ultramafics followed by mafics (metavolcanics) and a metasedimentary unit i.e., quartzite and banded iron formations in a greenstone belt lying on or beside granitic basement rocks. The basement relationship of the granites to the supracrustals has been obliterated by intrusion of Late-Kinematic granites and by deformation and metamorphism during the Liberian tectonothermal event (=2700 Ma) which produced the dominant N-S to NNE-SSW trend. Because of the geology, aquifers in the studied area are located in two different lithologies-granitic terrain and schist belt. Aquifer characteristics such as transmissivity and yield were measured and compared for the different lithologies. Comparison results show that the yield is greater (0.03%) in the granitic terrain than in the schist belt. And this is because of the presence of clays in the schist belt. The research also revealed that groundwater is readily available in the area.
Highlights
Sierra Leone forms parts of the West African Craton
Field observations during the mapping helped to unravel the geology of the area
Stream channels helped in unraveling of the geology of the area
Summary
Sierra Leone forms parts of the West African Craton. About 70% of the outcrops are older than 2.1 G.a. About 70% of the outcrops are older than 2.1 G.a These rocks have been affected by many tectonic events and the structures produced have been used to unravel the geological history of the country. The country consists mainly of an Archaean granite greenstone terrain bounded in the West by a West ward dipping zone of intense high grade rocks, this forms the Kasila group and it has been interpreted as suture. East wards the granite-greenstone terrain is bounded by low grade metamorphic rocks of the Marampa group where the project area is found. The water output of the boreholes in the area is largely dependent on the surrounding geology
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