## 4 Results and Discussion
### Geochemistry  
The results of the XRF chemical analyses expressed as mass percentages of the oxides of the selected samples from different sites of the study area are presented in Table 2. The geochemical analysis of clay materials gives a precise idea of their origin and the processes that contributed to their formation, but also provides the information necessary to understand their technological properties [54]. The observation of the geochemical composition presented shows that the studied samples mainly consisted of silica (SiO\({}_{2}\)), alumina (Al\({}_{2}\)O\({}_{3}\)), iron oxide (Fe\({}_{2}\)O\({}_{3}\)) and traces of TiO\({}_{2}\), CaO, MgO, Na\({}_{2}\)O, K\({}_{2}\)O and SO\({}_{3}\). The samples from Yansoki basically contained 38.23-51.18% of silica, 13.01-16.45% of alumina and 4.9-17.76% of iron oxide. The samples from Japoma contained both the highest (58.03%) and lowest (38.18%) fraction of silica. The alumina content was 19.92-22.94% and 3.86-6.43% of iron oxide. The contents of the oxides in the samples from Ndogpassi were constituted with 22.21-55.62% of silica, 12.84-19.37% of alumina and 1.07-17.92% of iron oxide. These oxides were in preponderant proportions in several studied samples of Cameroon coastal basins [25; 48; 55]. The occurrence of CaO, MgO, Na\({}_{2}\)O and K\({}_{2}\)O was low, which indicates the unlikely presence of high swelling clay minerals such as montmorillonite, except for the N1C4 sample which had 11.7% of K\({}_{2}\)O [55; 56]. The high percentage of SiO\({}_{2}\) (22.21-58.03%) demonstrates the abundance of quartz in the samples. Al\({}_{2}\)O\({}_{3}\) (12.84-22.94%) may be linked to the presence of kaolinite. The iron oxide content (1.07-17.92%) explains the existence of hematite and goethite in the clays and consequently are at the origin of the reddish brown or reddish yellow coloring (Y1C2 and N1C4) [45; 55]. In view of these analyses, the geochemical composition is in agreement with the mineralogical data and effectively confirms the presence of the different mineral phases that have crystallized, such as quartz and kaolinite. The ratio of SiO\({}_{2}\)/Al\({}_{2}\)O\({}_{3}\) varied between one and three, except for samples such as Y1C1 (3.11), N1C3 (4.33) and N1C1 (3.22) (Table 3). According to [57; 58], the low SiO\({}_{2}\)/Al\({}_{2}\)O\({}_{3}\) ratios close to two in the material demonstrates the predominance of type 1:1 clays. Thus, the SiO\({}_{2}\)/Al\({}_{2}\)O\({}_{3}\) ratios of most of the samples studied were close to two, which would indicate the presence of minerals of the kaolinite family (type 1:1). The N1C3, N1C1 and Y1C1 samples had ratios that were greater than two, suggesting the presence of free forms of silica and clay minerals type 2/1, such as illite in the materials as well as a chemical maturity of the studied clay materials [57; 58]. Low levels of the exchangeable cations CaO, Na\({}_{2}\)O and K\({}_{2}\)O observed in all the samples confirm the low content of the 2:1 type mineral [56]. Therefore, the clay materials in the study area had significant proportions of type 1:1 clay minerals compared to type 2:1 clay minerals. A representation of the SiO\({}_{2}\)-Al\({}_{2}\)O\({}_{3}\)-Fe\({}_{2}\)O\({}_{3}\) triangular diagram (Figure 7) showed that all samples were located towards the SiO\({}_{2}\) pole and along the SiO\({}_{2}\)-Al\({}_{2}\)O\({}_{3}\) axis, which is in agreement with a SiO\({}_{2}\)/Al\({}_{2}\)O\({}_{3}\) ratio. This indicates excesses of SiO\({}_{2}\) and Al\({}_{2}\)O\({}_{3}\) and effectively confirms the presence of quartz and kaolinite in the studied samples [57; 58]. For most selected samples from different studied sites, the variation of LOI (between 8.19 and 16.11%) reveals the presence of mainly hydrated minerals such as clay and goethite [59]. These results would indicate the presence of minerals as halloysite with a high hydration capacity. The Chemical Index of Alteration (CIA) varied from 61.59-97.76%, suggesting that the studied clays underwent an intense alteration (Table 2).