Effect of mineralogy on physico-chemical and some geotechnical properties of soils developed over granite, schist, and migmatite gneiss: a case study of Minna, Central Nigeria

Results of influence of mineralogy on physico-chemical and some geotechnical properties of soils developed over granite, schist, and migmatite gneiss around Minna in central Nigeria are presented. A region around Minna was studied to obtain the structure and petrography of the rocks. Three trial pits taken to depths of 5.0, 3.5, and 4.0m were dogged within region of granites, schists, and migmatite gneiss rocks, respectively, all of which belong to Basement Complex of northern Nigeria, to study the mineralogical, physico-chemical, and some geotechnical properties of overburden soils over these rocks. In each of the trial pits, soil samples were collected at interval of 0.5m depths to terminal depths of the pits. X-ray diffraction, index properties, and compaction tests were carried out the samples, and the results were analyzed to determine the influence of mineralogy on physico-chemical and some geotechnical properties of the soils. The result showed that rate of weathering is higher in granite rocks, where primary minerals altered to secondary minerals including smectite minerals. This is followed by overburden over schists, which was observed to alter to secondary minerals like illite and kaolinite. Overburden soil over migmatite gneiss did not showed alteration to secondary minerals but conversion of the carbon element to sodium carbonate salt. Higher fines content, cation exchange capacity, and Atterberg limits, recorded from soils developed over granite rocks, probably resulted from the smectite minerals recorded within this profile. The non-plastic nature of soils, on schist rocks, despite presence of secondary minerals, and judging from the low natural moisture content observed within this profile, indicated that the minerals developed under poor drainage condition. It was therefore concluded that mineralogy of overburden soils over basement complexes and the drainage condition during formation affect their geotechnical properties.