Quarries producing clay materials are extensively used because of the physico-chemical and mineralogical properties of their geomaterials [1] [2]. In Niger, the majority of applications for clay geomaterials are in the construction of houses and in pottery or ceramics in the broadest sense. The Zinder region—and more specifically the Korama Valley, given its geology—is an area with significant potential for clay materials. The pottery of Mirriah, a commune in the Zinder region, is well known beyond our borders. However, to make better use of these materials, it is important to understand them through their characterisation. The clay geomaterials exploited in Niger, and in Zinder in particular, remain scientifically poorly understood. Only a few publications [3]-[6] are available. The objectives of this study are to characterise (physico-chemically and mineralogically) the clay geomaterials and to propose a typology of the quarries operated in the Korama Valley, specifically at the Kolleram 1, Garaké, Kolleram 2, Menari and Yaouri quarries.

The Korama Valley, the study area, covers an area of approximately 12,000 km² and occupies the southern part of the Zinder Region; it covers the whole of the Kantché and Magaria departments and the southern part of the Mirriah and Gouré departments [7]. It is a vast alluvial plain, oriented north-west to south-east, situated on the edges of the western Niger basin (Iullemeden Basin) and the eastern Niger basin (Lake Chad Basin). With a population of over 1,320,788 in 2009, distributed across twenty-six (26) municipalities—23 rural and three (3) urban—the Korama Valley is also the most densely populated area in the Zinder Region.

Its climate varies from the Northern Sudanese type in the south to the Sahelian type in the north, and is characterised by two distinct seasons: a short four-month rainy season (from June to September), followed by a longer dry season lasting around eight months. In parts of the area, rainfall exceeds 600 mm per year. It receives the highest rainfall in the Zinder Region. In this part of the Zinder Region, floods are recurrent and devastating. The people of the Korama Valley use several types of banco, mainly black and red banco, to build their homes. These building materials are vulnerable to flooding. This explains the significant collapses of habitations and the resulting loss of life [8].

The lithological analysis of the 10 lithological sections from the five quarries selected for this study reveals two types of horizons: superficial sedimentary horizons and deeper alterite horizons. Superficial sedimentary horizons are characteristic of depositional environments. In the study area, these environments correspond to the valley itself, the floodplains and the basins [9]. The decreasing grain size observed at the Kolleram 1 and Garaké quarries demonstrates that this is a fluvial system characterised by a gradual loss of energy. This confirms that the environment is more of a valley than a basin or a shallow water area [10]. Thus, the superficial position and sedimentary nature of these horizons explain their low degree of consolidation. This low degree of consolidation is mainly due to the fact that these recent sediments have not yet undergone prolonged diagenesis, the geological process that transforms loose sediment into solid rock under the influence of pressure and temperature [11]. As for the deep alterite horizons, their degree of consolidation is explained by their position and the alteration process. In a complete alteration profile, hardening does not occur uniformly; instead, vertical zoning is observed from top to bottom, due to greater pressure and also temperature. The weathering process, in this case by hydrolysis, increases the cohesion of the particles through cementation. This cementation results from the transformation of the primary minerals of the protolith (feldspars and micas) into secondary clay minerals. The characteristics of these secondary minerals act as a cementing agent for the disintegrated particles [12]. The geochemistry of the 30 samples collected shows that they are all composed predominantly of SiO₂ and Al₂O₃. This confirms that they are alumina silicates, like any clay material. However, the proportions of these two elements and the other major oxides varied from one sample to another and from one site to another. Indeed, these proportions of the various oxides are good indicators that enable the differentiation of these different geomaterials [1]-[13]. Thus, two groups emerge: one characterised by high levels of SiO₂ and alkaline and alkaline earth elements containing montmorillonite and being dark in colour; and another group relatively low in silica and alkaline and alkaline earth elements, containing TiO₂ and kaolinite, and being red in colour. For the first group, the high levels of these elements can be explained by the transport process. Indeed, at these quarries, Figure 11 shows a strong correlation (angle 40˚, Figure 11) between these high proportions of alkaline and alkaline earth elements and the high proportions of quartz (SiO₂). This confirms that this is an environment where alkaline earth elements and silica accumulate. These clay deposits are classified as secondary or reworked deposits (Yven B., 2007). Remobilized clays are clay-based geomaterials whose natural structure has been destroyed or altered by transport or mechanical actions, such as mixing. Upon deposition, these clays lose a significant proportion of their cohesion and shear strength compared with intact clays. They are also referred to as loose clays with low consolidation pressures [14] [15]. However, in quarries that are relatively poor in alkaline and alkaline earth elements and silica, strong correlations emerge between Al₂O₃ and Fe₂O₃, as well as with TiO₂. The presence of TiO₂ indicates that no transport has taken place and that the material was therefore formed in situ, consistent with a weathering profile. The proportions of Fe₂O₃ account for the reddish colour of the material. It is well known that during the hydrolysis of rock formations, water leaches out silica (SiO₂) and alkaline earth elements. It breaks down the original mineral, and the aluminium (Al) combines to form clays. The leaching of silica is called desiallitisation; it is a gradual process and can lead to complete leaching, in which case the term allitisation is used [16]. The montmorillonite found in the silica-rich samples (Figure 11) is a key indicator of climatic conditions, the depositional environment and the origin of the sediments. Montmorillonite forms in an environment characterised by poor or slow drainage—or even confined drainage—and an alkaline environment resulting from moderate chemical alteration of the parent rocks. This explains their high content of alkaline and alkaline earth elements (Mg²⁺, K⁺, Na⁺). In the case of our study area, the formation environment would correspond well to lowland pools [5]. The kaolinite found in the second category of geomaterials indicates that this is an environment that has undergone strong, if not total, hydrolysis. Kaolinite is a mineral that has lost a proportion of its silica and many other elements, a sign of very extensive leaching of the parent rock. The residual alumina hydrates and silica react to form kaolinitic clays. This reaction is known as siallitisation. When this formation occurs in situ due to meteoric and/or hydrothermal fluids, it is referred to as a primary deposit. This is the case for the geomaterials from the Kolleram 2, Menari and Yaouri quarries in the Korama Valley. Kaolinite is thought to result from the alteration of feldspars in a sufficiently well-drained environment, whilst micas—ferromagnesian minerals—release a significant amount of iron in the form of ferric oxide. This is consistent with the high percentage of iron oxide in the materials from these quarries. This particularly high Fe₂O₃ content accounts for the reddish colour observed in these samples [17]. All these results have made it possible to determine a typology of the quarries sampled. The Kollerem 1 and Garaké quarries are classified as surface quarries. These are quarries containing montmorillonite-rich clay geomaterials, which are rich in silica and alkaline and alkaline earth elements, dark in colour and not very consolidated. The Kolleram 2, Menari and Yaouri quarries are classified as deep quarries. These consist of kaolinite-rich clay geomaterials, which are relatively low in silica and alkaline and alkaline earth elements, more consolidated and red in colour.

The results of this study indicate that the 30 samples from five (05) quarries—Kolleram 1, Garaké, Kolleram 2, Menari and Yaouri—are aluminosilicates, with varying proportions of major oxides, and are blackish in colour (Kolleram 1, Garaké) and red in colour (Kolleram 2, Menari and Yaouri). Two types of horizons are observed in the lithology of these quarries: shallow, slightly compacted sedimentary horizons and deeper, more compacted alterite horizons. The geochemistry of the major oxides and clay minerals in the various samples from the five quarries has enabled a typology of these quarries to be established. Two types of quarry emerge: the surface quarries—Kolleram 1 and Garaké—which contain montmorillonite-rich clay geomaterials, high in silica and alkaline and alkaline earth elements, dark in colour and relatively unconsolidated; and the deep quarries—Kolleram 2, Menari and Yaouri, which are quarries containing kaolinite-based clay geomaterials, relatively low in silica and alkaline and alkaline earth elements, more compacted and reddish in colour. These results make it possible to identify suitable clay geomaterials for various forms of utilisation.

We would like to express our gratitude to the Ministry of Research and Technological Innovation for its support, in particular through the Fund for Research and Technological Innovation (FARSIT), which is funding this research; and to André Salifou University in Zinder for providing the field vehicle.

Conceptualization, Abdoul Moumouni Adamou Laouali Malam and Abdoulkader Moussa Issaka; methodology, Abdoulkader Moussa Issaka, Bouba Hassane and Dia Hantchi Karimou; software, Oumarou Faroukou Habibou Maman and Nana Mariama Habibou Maman; validation, Abdoulkader Moussa Issaka, Souley Harouna; formal analysis, Abdoul Moumouni Adamou Laouali Malam and Abdoulkader Moussa Issaka; investigation, Abdoul Moumouni Adamou Laouali Malam and Abdoulkader Moussa Issaka; resources, Research and Technological Innovation Support Fund of the Ministry of Research and Technological Innovation; data curation, Oumarou Faroukou Habibou Maman and Nana Mariama Habibou Maman; writing—original draft preparation, Abdoulkader Moussa Issaka; writing—review and editing, Bouba Hassane; visualization, Abdoul Moumouni Adamou Laouali Malam; supervision, Abdoulkader Moussa Issaka; project administration, Ministry of Research and Technological Innovation; funding acquisition, Research and Technological Innovation Support Fund of the Ministry of Research and Technological Innovation. All authors have read and agreed to the published version of the manuscript.