Geophysical Survey for Identifying Sand and Gravel Deposits in Ogun State

This study applies electrical resistivity methods to identify and characterise sand and gravel deposits suitable for construction aggregate production in Ogun State, South West Nigeria. Ogun State is the primary supplier of aggregates for the Lagos metropolitan construction industry, but indiscriminate sand mining from river channels has created environmental degradation and regulatory challenges. Systematic geophysical investigation of upland sand and gravel deposits can identify alternative sources that reduce pressure on river systems. This study deploys a combination of Wenner constant separation traversing and Schlumberger VES data acquisition along 15 profiles and 18 sounding stations in Sagamu, Ijebu North, and Odogbolu local government areas. Profiles are positioned to intersect river terrace and valley-fill deposits identified in SRTM topographic analysis. Data are inverted and interpreted with reference to trial pits dug to 3 metres depth at 12 control points. Sieve analysis and Atterberg limits from trial pit samples validate geophysical interpretations. Findings reveal resistivity values of 120 to 600 ohm-metres associated with clean sand and gravel deposits of adequate grading for concrete aggregate, distinguishable from silty or clayey sands (15 to 80 ohm-metres) and laterite (above 800 ohm-metres). Three commercially significant sand and gravel bodies are delineated with thicknesses of 3 to 8 metres and lateral extents of 0.8 to 2.4 kilometres, estimated total volumes of 2.4 to 8.6 million cubic metres. The study concludes that resistivity surveying provides a cost-effective tool for rational aggregate resource evaluation and recommends its mandatory use before sand mining licence applications in Ogun State.

Keywords: resistivity survey, sand and gravel, aggregate resources, Ogun State, construction materials.