Hydrogeochemical Processes of Groundwater from Basement Complex Rocks in Keffi, Central Nigeria (Published)

Hydrochemical study of groundwater was done in a typical Basement Complex terrain to identify geochemical evolution of the resource and possible quality issues. In addition to water samples, overburden and fresh rock samples were analyzed for major ion concentration. Relative abundance of these ions in groundwater was compared to their concentrations in the weathered and fresh rock. Conventional graphical plots (Gibbs, Piper, and ionic ratio plots) of ionic concentrations in the groundwater were used to characterize water Facies and identify major processes responsible for the ionic assemblage. The study area is underlain by two main rock types, schist and gneiss. Relative abundance of major cations in groundwater is in the order: Ca²⁺> Mg²⁺ > Na⁺> K⁺ while relative abundance of major anions is in the order: Cl^–> HCO₃^–> CO₃^2- >SO₄^2-. In comparison, a depletion in the concentration of calcium, magnesium and sodium was observed in the weathered zone while being enriched in the fresh rock. This indicates the possibility of the ions being leached by infiltrating/percolating groundwater. Physical parameters indicate that pH of groundwater ranges from 5.6 to 13.1; TDS is also high ranging from 146.10mg/l and 9146.00mg/l. The main water type identified is mixed Ca-Mg-Cl type; others are Na-Cl, mixed Ca-Na-HCO₃, and Ca-HCO₃ types. Results of the analysis indicate that the main sources of ions into the groundwater are from water rock interaction i.e. dissolution and leaching from silicate minerals in the study area. Ground water is a mixture of the multiple processes involved in its evolution but especially that mineralogy of the aquifers plays an important role in determining the water chemistry. Most sampling points were hand dug wells and boreholes for domestic use; the high TDS and alkalinity of the water therefore presents some quality concerns.

Keywords: Basement Complex, Groundwater, Keffi, hydrogeochemical

Assessment of Groundwater Potential of Risha Part of Akwanga Sheet 209NE, North Central Nigeria (Published)

A geological traverse was undertaken in Risha, part of Akwanga Sheet 209NE North-Central Nigeria to appraise the rock types and their structural patterns that might enhance prospect for water. Three rock types; schistose-gneiss, granite-gneiss and pegmatite, with their main structural pattern were discovered, trending mostly NW-SE. Analysis of twenty-three Vertical Electrical Resistivity Soundings (VES) carried out in the area using the Campus Ohmega digital resistivity meter showed that the field curves were of H, KH, HK, A and K types. There were majorly four to five geoelectrical layers consisting of topsoil (sand/clay) with depth range of 0.3-2.4m and resistivity value of 66-2850Ωm. The second layer is lateritic clay with depth range of 0.4-5.7m and resistivity range of 222-3575Ωm. The third layer had a depth range of 1.2-8.6m with resistivity of 40-4591Ωm, while the fourth layer, weathered rocks or regolith, has a depth range of 3-33m and resistivity range of 49-23668Ωm. Two locations gave six lithological layers/units being partially fractured/fresh basement with resistivity values of 1028-4574Ωm and depth range of 11.4-24m. The water potential of the area may be classified as poor, moderate, good and very good and varied from location to location. The groundwater potential area varies with high potential around Risha, Tidde and Ridam compared to Ade-Katako, Ngazzu, AngwanDorowa, Ngakide and Adande. Based on the textures, structural pattern and well measurement interpretations, the granite gneiss was observed to have more water prospectivity than the schistose gneiss.

Keywords: Basement Complex, Groundwater, Resistivity, Rocks, potential

Assessment of Groundwater Potential of Risha Part of Akwanga Sheet 209NE, North Central Nigeria (Published)

A geological traverse was undertaken in Risha, part of Akwanga Sheet 209NE North-Central Nigeria to appraise the rock types and their structural patterns that might enhance prospect for water. Three rock types; schistose-gneiss, granite-gneiss and pegmatite, with their main structural pattern were discovered, trending mostly NW-SE. Analysis of twenty-three Vertical Electrical Resistivity Soundings (VES) carried out in the area using the Campus Ohmega digital resistivity meter showed that the field curves were of H, KH, HK, A and K types. There were majorly four to five geoelectrical layers consisting of topsoil (sand/clay) with depth range of 0.3-2.4m and resistivity value of 66-2850Ωm. The second layer is lateritic clay with depth range of 0.4-5.7m and resistivity range of 222-3575Ωm. The third layer had a depth range of 1.2-8.6m with resistivity of 40-4591Ωm, while the fourth layer, weathered rocks or regolith, has a depth range of 3-33m and resistivity range of 49-23668Ωm. Two locations gave six lithological layers/units being partially fractured/fresh basement with resistivity values of 1028-4574Ωm and depth range of 11.4-24m. The water potential of the area may be classified as poor, moderate, good and very good and varied from location to location. The groundwater potential area varies with high potential around Risha, Tidde and Ridam compared to Ade-Katako, Ngazzu, AngwanDorowa, Ngakide and Adande. Based on the textures, structural pattern and well measurement interpretations, the granite gneiss was observed to have more water prospectivity than the schistose gneiss.

Keywords: Basement Complex, Groundwater, Resistivity, Rocks, potential