Petrographic and structural characteristics of the pozzolanic formations and associated rocks in the Brobo area, northern part of the Fêtêkro belt, central Côte d'Ivoire: Implications for potential pozzolan exploitation

 Corresponding author: Koffi alexis N’dri Copyright © 2025 Author(s) retain the copyright of this article. This article is published under the terms of the Creative Commons Attribution License 4.0. Petrographic and structural characteristics of the pozzolanic formations and associated rocks in the Brobo area, northern part of the Fêtêkro belt, central Côte d’Ivoire: Implications for potential pozzolan exploitation Koffi Alexis N’dri 1, *, Koffi Raoul Teha 2, Ziandjêdé Hervé Siagné 1 and Bekan Kouakou 3 1 Institut National Polytechnique Félix Houphouët-Boigny, Laboratoire des Sciences Géographiques, du Génie Civil et des Géosciences, Ecole Supérieure des Mines et de Géologie, BP 1093 Yamoussoukro, Côte d’Ivoire. 2 Université Félix Houphouët-Boigny, Laboratoire de Géologie, Ressources Minérales et Energétiques, 22 BP 582 Abidjan, Côte d’Ivoire. 3 Ecole Spéciale du Bâtiment et des Travaux Publics, Abidjan, Côte d’Ivoire. World Journal of Advanced Research and Reviews, 2025, 28(02), 2107-2119 Publication history: Received 13 October 2025; revised on 22 November 2025; accepted on 24 November 2025 Article DOI: https://doi.org/10.30574/wjarr.2025.28.2.3928 Abstract The Brobo area, located in the northern Fêtêkro Belt within the Baoulé–Mossi domain of the West African Craton, offers significant potential for understanding crustal evolution and developing natural pozzolanic resources. Despite growing industrial interest, the geological and structural controls of pozzolan occurrences in this region remain poorly constrained. This study combines petrographic and structural analyses to characterize the volcanic, plutonic, and metamorphic rocks associated with pozzolanic materials and to assess their exploration significance. Field and microscopic investigations reveal that the area is dominated by acid to intermediate volcanic rocks—rhyolites, rhyodacites, and pyroclastic formations—spatially associated with granitoid intrusions (granite, granodiorite, tonalite) and minor quartzites. The pyroclastic facies display microlitic to porphyritic textures and mineral assemblages (quartz, feldspar, sericite, epidote) comparable to recognized natural pozzolans. Structurally, two deformation regimes are identified: ductile (N010°–N040° foliations and shear bands under NE–SW compression) and brittle (N070°–N110° faults and en-echelon quartz veins). These features correspond to the regional Birimian tectonic pattern, indicating synto late-Eburnean emplacement. The mineralogical and textural characteristics of the pyroclastic formations suggest favorable pozzolanic reactivity, highlighting the Brobo area as a promising target for expanding Côte d’Ivoire’s pozzolan exploitation. Keywords: Brobo; Fêtêkro Belt; Pozzolan; Petrography; Côte d’Ivoire; West African Craton 1. Introduction As part of efforts to revitalize its mining sector—long focused on gold and diamonds [1]—and to expand into quarry materials such as aggregates and pozzolan, Côte d’Ivoire has, over the past decade, undertaken an extensive campaign to explore these resources [2]. According to data provided by the Ministry of Mines, Petroleum and Energy through the DGMG, pozzolan production in Côte d’Ivoire, which began in 2019, increased from 126,577 tonnes to 394,880 tonnes in 2023—an average annual growth rate of 32.9% [2]. Pozzolan plays an essential role in the cement industry as an additive that enhances the mechanical properties and durability of hydraulic binders. It is mainly associated with acid and intermediate volcanic formations (rhyolites, rhyodacites) and their pyroclastic derivatives [3, 4]. Natural pozzolans are typically characterized by silica contents of 42–55%, alumina of 12–24%, and iron oxide of 8–20%. To optimize cement production, reduce import-related costs, and promote local resource autonomy, it is essential to valorize locally available materials such as pozzolan. Although pozzolan production has recently expanded in Côte d’Ivoire, the geological and structural controls governing its occurrence in the Brobo area remain poorly documented. This study World Journal of Advanced Research and Reviews, 2025, 28(02), 2107-2119 2108 aims to improve geological and structural knowledge of the rocks associated with pozzolan in the Brobo area. A combined petrostructural approach was adopted to (i) describe and identify the geological formations associated with pozzolan, (ii) analyze the structures and deformations of the rocks to determine their genetic mechanisms, and (iii) propose a possible relationship between rock type, structure, and pozzolan occurrence to serve as a guide for future exploration. 2. Geological setting The West African Craton (WAC) comprises two major geological domains: the Reguibat Ridge in the north and the Leo Ridge in the south [5–7]. Both are composed of Paleoproterozoic and Archean terranes (Figure 1). The WAC was shaped through three major orogenic cycles: the Leonian (3200–2900 Ma), the Liberian (2900–2800 Ma), and the Eburnean megacycle (2500–1600 Ma) [8, 9]. The Man Ridge, which hosts the study area, is divided by the north–south Sassandra Fault into an Archean Kenema–Man domain to the west and a Paleoproterozoic Baoulé–Mossi domain to the east, with a transitional zone between them [9]. Figure 1 Geological map of the southern West African Craton (sWAC), including the Paleoproterozoic Baoulé-Mossi Domain and Kédougou-Kénieba Inlier, Archean Kénéma-Man Domain, SASCA Domain, and study area (modified after [10, 11]) The Brobo area lies in central Côte d’Ivoire, in the northern part of the Fêtêkro Belt. Its geological formations can be subdivided into three main groups (Figure 2; [12]): (i) a granito-gneissic complex occupying the western part; (ii) a median Belt formed by lavas, breccias, and volcano-sedimentary rocks interlayered with schists and quartzites; (iii) sedimentary and volcano-sedimentary formations in the eastern part. These units are intruded by granitic, granodioritic, and mafic bodies. Structurally, the area is dominated by a major north–south Brobo Fault, expressed as a deformation zone mainly affecting the granitoids [13]. World Journal of Advanced Research and Reviews, 2025, 28(02), 2107-2119 2109 Figure 2 Simplified geological map of study area (modified after [12]). The inserts (a and b) show the location of the study area 3. Material and methods It began with a field phase, during which rock samples were collected and described macroscopically. Each sampling site was systematically recorded using GPS for precise location. These samples were subsequently used to prepare fourteen thin sections at the Geology Laboratory of Félix Houphouët-Boigny University, Abidjan-Cocody. The thin sections were examined under a polarizing optical microscope to refine the petrographic study, emphasizing the identification of mineral parageneses and lithological facies. The structural framework of the area was established by describing the deformation structures affecting the various lithologies, specifying their orientation and dip where possible. Special attention was given to their spatial relationships and to the relative chronology of the successive deformation events. The structural measurements obtained were then used to construct directional rose diagrams, allowing the identification of the predominant structural trends. 4. Results 4.1. Petrography of plutonic rocks 4.1.1. Granodiorite The granodiorite occurs as slab-like bodies. It is a mediumto coarse-grained, locally oriented, mesocratic rock. The orientation observed in certain facies in the field may reflect variations in the temperature and pressure conditions of the parent magma during emplacement or crystallization. Mineralogically, it is composed mainly of quartz, feldspar, amphibole, and biotite. Quartz crystals vary from medium to coarse and commonly display well-developed undulatory extinction. Feldspars include both plagioclase and orthoclase. Plagioclase, recognized by its polysynthetic twin, appears as coarse xenomorphic to sub-idiomorphic grains with cores and rims variably altered to sericite. In the oriented facies, plagioclase occurs as rounded and slightly bent crystals molded by a cataclastic matrix rich in sericite (Figures 3a–c). Orthoclase, less abundant than plagioclase, is identified by Carlsbad twin and shows strong alteration along its borders to sericite and amphibole (Figures 3a–c). Perthitic intergrowths between orthoclase and plagioclase are also common. Amphibole occurs as greenish, sub-idiomorphic crystals with distinct cleavage in basal sections; it is generally fresh and locally marks the dark foliation bands (Figures 3d–f). Biotite is sparse (~1%), brown in color, and forms thin colored layers in thin section. World Journal of Advanced Research and Reviews, 2025, 28(02), 2107-2119 2110 4.1.2. Granite and metagranite Granite and metagranite crop out as elongated slabs. Both belong to the group of felsic magmatic rocks. Fresh granite contains about 60% quartz and displays a pinkish hue, with orthoclase generally dominating over plagioclase. Under the microscope, granite exhibits a typical coarse-grained, whereas metagranite shows a lepidoblastic texture. Locally, metagranite is coarse-grained and displays a poorly defined foliation marked by alternating dark, ferromagnesian-rich bands and light-colored (white, gray, or pink) quartz–feldspar bands. Both rocks have a similar mineral assemblage composed mainly of: (i) Quartz, locally forming small, recrystallized grains (Figures 3g–i); and (ii) Plagioclase, commonly showing cores and rims altered to sericite. 4.1.3. Tonalite Tonalite occurs as enclaves within the granites and granodiorites (Figure 3j). These enclaves are subrounded to rounded and display a melanocratic appearance. Under the microscope, tonalite has a granitic texture and is mainly composed of abundant, medium-grained plagioclase. Perthitic feldspars rimmed by sericite are also present. Biotite crystals occur either individually or clustered with other minerals (Figures 3k-l); they are brown to reddish-brown and show bright pleochroic colors. Quartz is xenomorphic and fine-grained, while amphibole is less abundant and typically associated with sericite. 4.2. Petrography of volcanic rocks 4.2.1. Rhyolite and rhyodacite Acid lavas occur either as dome-shaped bodies or elongated (Figure 4a). Rhyolites and rhyodacites are typically homogeneous, massive, and often aphanitic, occasionally containing scattered quartz phenocrysts (“quartz eyes”). Under the microscope, these rocks display microlithic to microlithic-porphyritic textures. The principal minerals include quartz and plagioclase, the latter being extensively altered to sericite and epidote. Quartz crystals, which are abundant (> 50%), commonly form small aggregates (< 0.3 mm) within the matrix (Figures 4a–c). In porphyritic rhyolites, subhedral to euhedral quartz porphyroblasts exhibit pronounced undulatory extinction and recrystallization, producing subgrains (neoblasts) and small polygonal textures (Figure 4b). Most clasts consist of feldspar (plagioclase and orthoclase), which may reach centimeter size and display cores and rims altered to sericite (Figure4b). These feldspars, generally subhedral to euhedral, locally deflect the schistosity. Sericite, derived from feldspar alteration, forms fine ribbons that define the foliation in metarhyolites (Figure 4c) and occasionally occurs as coronas around quartz phenocrysts. Accessory minerals are mainly opaque phases. 4.2.2. Pyroclastite Pyroclastic lavas occur widely and display variable facies—tuffaceous with fine particles, conglomeratic with subrounded clasts, or brecciated with angular fragments. The volcanic breccias, abundant in the study area, are predominantly pyroclastic in origin (Figures 4d-f). These rocks exhibit a microlithic-porphyritic texture. Their angular fragments are cemented by a grayish-white to greenish matrix. The grayish cement results from quartz–feldspar recrystallization, while the greenish color indicates a higher content of epidote and chlorite (Figure 4f). 4.2.3. Basic lava The basic lavas consist mainly of volcanic rocks of basaltic to andesitic composition (Figures 4g-h). They are massive and dark-colored. Basalt, the predominant basic lava described here, typically forms large domes or blocks, though some occurrences display pillow-like structures known as pillow lavas. Under the microscope, basalt exhibits a microlithic texture, composed largely of volcanic glass, pyroxenes, and microlith, some of which are partially altered. World Journal of Advanced Research and Reviews, 2025, 28(02), 2107-2119 2111 Figure 3 Photographs showing petrography of plutonic rocks. (a-c) granodiorite; (g-i) orientated granodiorite; (j-l) Tonalite enclave within orientated granodiorite; (m-o) aplite dyke within orientated granodiorite. Qz=quartz, Pl=plagioclase, Fd=felspar, Amp=amphibole, Ser= sericite, Or=orthoclase, Bt=Biotite, Per=perthite World Journal of Advanced Research and Reviews, 2025, 28(02), 2107-2119 2112 Figure 4 Photographs showing petrography of volcanic rocks. (a-c) rhyolite and rhyodacite; (d-f) pyroclastite; (g-h) basic lava. Qz=quartz, Pl=plagioclase, Kfs=K-felspar, Ser= sericite, Ep=epidote, Chl=chlorite, Mop=Oxide 4.3. Petrography of metamorphic rocks 4.3.1. Quartzite Quartzites are relatively rare formations occurring as intercalations between the granitic zone and the volcanosedimentary units, or within the volcano-sedimentary complex. They are gray to black, very fine-grained, and typically massive, though some show distinct banding (Figure 5a). The quartzites consist predominantly of quartz (Figures 5b– c). The quartz crystals are abundant, with grain sizes ranging from medium to coarse. The quartz porphyroblasts display pronounced undulatory extinction. World Journal of Advanced Research and Reviews, 2025, 28(02), 2107-2119 2113 Figure 5 Photographs showing petrography of Quartzite, with quartz porphyroblasts display pronounced undulatory extinction. Qz=quartz 4.4. Structural characteristics of the Brobo area 4.4.1. Foliation Planar fabric constitutes the dominant structural feature within the rocks of the study area, expressed through pervasive foliation (Figure 6). In the granitoids, the planar fabric is defined by an N020° foliation characterized by the alternation of millimeterto centimeter-scale quartzofeldspathic layers and ferromagnesian bands composed mainly of biotite and amphibole (Figure 6a). This foliation reflects a flattening fabric associated with ductile deformation under regional compressive stress. The foliation is represented by a penetrative, generally subvertical foliation. Two main types are recognized: spaced and slaty cleavage (Figures 6b–c). The spaced cleavage, oriented N120°, occurs mainly within quartzitic units and consists of thin, open fractures lacking evidence of recrystallization (Figure 6b), suggesting deformation under brittle–ductile transitional conditions. The slaty cleavage, striking N010°–N040°, is defined by the preferred orientation and stretching of phyllitic minerals within the metarhyolites (Figure 6c). A structural rose diagram indicates a dominant NE–SW trend for the main foliation. The dip of the foliation is variable—locally directed toward the NW but predominantly toward the SE. In quartzitic formations, the foliation dips toward the SW. World Journal of Advanced Research and Reviews, 2025, 28(02), 2107-2119 2114 Figure 6 Photographs of planar structures observed in outcrop. (a) Alternating light quartz–feldspar bands and dark ferromagnesian bands (foliation); (b) Spaced cleavage developed in quartzites; (c) Slaty cleavage in acid lavas. Stereograms of planar structures World Journal of Advanced Research and Reviews, 2025, 28(02), 2107-2119 2115 4.4.2. Shear zones, boudinage, and tension veins Shearing is locally well developed and characterized by zones of high finite strain, evidenced by the displacement of passive markers. Shear zones striking N160° offset quartz veins trending N030° and exhibit a sinistral sense (Figure 7a). These structures likely correspond to localized ductile shear zones within the regional stress field. Boudinage structures are common and reflect extensional deformation of competent lithologies under differential stress parallel to the layering. Quartz-vein boudins trend N010° and indicate layer-parallel extension synchronous with ductile flattening (Figure 7b). En echelon tension veins are observed within foliated granodiorite and trend N100° (Figure 7c). Their geometry and orientation suggest formation under ductile shear conditions, consistent with progressive noncoaxial deformation within the same stress regime responsible for the shear zones. Figure 7 Photographs illustrating shear deformation: (a) sinistral shear; (b) boudinage structure; (c) dextral enechelon tension veins