Mineralogy of Lateritic Weathering Profiles Developed on the Rocks under a Sub-equatorial Monsoon Climate: Case of the Bambouto Mountains

Abstract

The main objective of this work is to make a comparative assessment of the mineralogy on weathering profiles resulting from the alteration of the different rocks in an equatorial microclimate of altitude. This was carried out in the lower flank of the southern slope of the Bambouto Mountains. Mineralogical analysis and normative restructuring have given very interesting results on the profiles, between the basement rocks and the surface/cover rocks. Given that the alteration pathways of the basement rocks are different, they are similar within the zone of containment and potential leaching. Meanwhile, the cover rocks vary from one domain to another: virtual weathering, potential confinement, potential and virtual weathering, and induration. The alterological activity is very intense in the profile on trachybasalt. The predominant weathering processes in all cases are allitization and monosialitization, which are marked by a singular phenomenon of ferrolysis. The characteristic minerals of this profile are kaolinite and diopside. The weathering profile on biotite and hornblende granitoid is not very differentiated and is particularly rich in quartz (max: 40 weight-%) and microcline (max: 40 weight-%). The soils developed on granitoid, adopt elastic-fragile deformation to elastoplastics with sharp break in relation to the load applied. The alteration profile on orthogneiss is poorly differentiated, and thin, with a low degree of alteration. Hydrolytic alteration by monosiallitization marked this profile. This is particularly rich in quartz (max: 100 weight-%) and kaolinite (max: 57 weight-%). The profile on anatexite is particularly rich in quartz (max: 66 weight-%) and kaolinite (max: 40 weight-%). The normative restructuring confirmed over 98 weight-% of the various minerals obtained and thus made it possible to better characterize the alteration and its application in geotechnics. These soils constitute potential deposits of chromatogenic minerals: kaolinite, hematite, goethite, gibbsite, magnetite, biotite.