Determination of Reserve Estimate of Quartzite Deposit using Geoelectric Sounding and Laboratory Measurement - A Case Study of Ipinsa area, near Akure, Southwestern Nigeria

A total of 36 Vertical Electrical Sounding data and laboratory analysis was carried out at southern part of Ipinsa, near Akure, Southwestern Nigeria with the aim of determining the reserve estimate of a portion of the quartzite deposit in the area. The Vertical Electrical Sounding (VES) method adopted Schlumberger configuration with half current electrode spacing varying from minimum of 1 to maximum of 40 to 150 m. The VES results delineated three to six geoelectric layers which correspond to the top soil, weathered layer, weathered basement, fractured basement and the presumed fresh basement. At the top soil, the resistivity varies from 38 to 878 ohm-m, while the thickness value ranges from 0.1 to 6.8 m. At the weathered layer, resistivity varies from 17 to 9749 ohm-m, while the thickness value ranges from 0.1 m to infinity. The weathered basement resistivity ranges from 24 to 18088 ohm-m, while the thickness values range from 0.6 m to infinity. The partially fractured basement resistivity varies from 62 to 1331ohm-m and its thickness range from 4.0 to 5.1 m. The quartzite layer resistivity value in the study area is generally greater than 150 ohm-m, with average thickness of 8.86 m. From the 14 quartzite samples collected across the study area, the average density value was determined to be 2.51 g/cm3 (2510 kg/m2). The area extent of the quartzite deposit was calculated to be 1,024,729 m2, while the volume of the quartzite deposit is 9,079,098 m3. The mass of the quartzite deposit was estimated to be 22,788,538 tonnes. Keywords: Vertical electrical sounding, laboratory measurement, density, thickness, area, volume and tonnage

Geoelectrical and Geotechnical Investigations of Subsurface Corrosivity in Ondo State Industrial Layout, Akure, Southwestern Nigeria

Fifty two vertical electrical sounding (VES) data and six subsurface soil samples were collected at Ondo State Industrial Layout, Akure, south-western Nigeria in order to determine the subsurface corrosivity. The VES results delineated 3 to 5 geoelectric layers across the area, which correspond to topsoil, weathered layer, weathered basement, weathered/fractured basement and the presumed fresh bedrock. The layer resistivity values range from 22 to 602 ohm-m, 7 to 2468 ohm-m, 17 to 436 ohm-m, 25 to 39 ohm-m and 203 to 10023 ohm-m in the topsoil, weathered layer, weathered basement, weathered/fractured basement and the presumed fresh bedrock respectively. The iso-resistivity maps at depth slices of 1 and 2 m show that the northeastern, southeastern and the upper central part of the area are non-corrosive (above 350 ohm-m) to slightly corrosive (250 - 350 ohm-m), while the lower central, northwestern and southwestern parts of the area are moderately (150 - 250 ohm-m) to strongly corrosive (60 - 150 ohm-m).  Soil sample analysis shows liquid limit results that  vary from 37.6 to 59.7, while the plasticity limit results vary from 29.3 to 42.5 and all the plasticity index plots were below the A line indicating presence of non-plastic clay. The natural moisture content values vary from 21.4 to 35.5 %. The 2 m depth slice isoresistivity map and clay plasticity factor were synthesized using additive model to generate subsurface CR-index corrosivity model map which indicates that the northwestern, north-eastern and southern parts of the area are moderately (0.4 - 0.6) to strongly corrosive (0.6 - 0.8), while the upper central area and the flanks are slightly corrosive. The moderately and strongly corrosive zones correspond to the low elevation and water logged zones of the study area. The corrosivity model map was validated by the pH and corrosivity data. Keywords: Geotechnical, Liquid Limit, Plastic Limit, Plasticity Index, Clay Plasticit