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Modeling the spatial dependence structure of metal grades in the presence of soft boundaries between geological domains is challenging in any mineral resource estimation strategy. The aim of this work was to propose a structural model adapted to this type of geological boundary, based on a multivariate Matérn model that fits the observed direct (within domain) and cross (between domains) correlation structures of metal grades. The methodology was applied to a case study of an iron deposit located in southern Cameroon. Cross-validation scores show that accounting for the grade correlation across domain boundaries improved the traditional workflow, where the grade was estimated in each domain separately. The scores were significantly better when we also ensured that the mean grade was locally invariant from one domain to another to reflect the grade continuity across the domain boundary. [ABSTRACT FROM AUTHOR]

The Lom volcano-sedimentary formation belongs to the Adamawa-Yadé (AYD) domain of the Pan-African fold belt in Cameroon. It is a geological formation presenting mineral deposits of economic potential such as gold and diamonds. The area is under small-scale and many artisanal gold mines. A geophysical study was carried out in the village Yassa, a locality situated within this geological formation, close to an artisanal mining excavation in order to define and propose a model of potential mineralized targets. The geophysical study involved the combination of electrical resistivity tomography (ERT), induced polarization (IP), and self-potential (SP) methods. The acquisition of data consisted of 15 electrical tomography lines in Schlumberger arrangement and a collection of SP data along these profiles in the absence of injected current. The anomalies of possible sulfide mineralization were found at a depth of about 10–25 m with a major NE–SW trend by applying the Euler deconvolution to the SP data. The ERT and IP data allow the production of the 2D inversion which is interpolated to obtain pseudo-models of the isosurface of potential mineralization. The correlation of geological information and the 3D isosurface pseudo-models indicates the characterization of zones with sulfides, with high chargeability values (≥ 30 mV/V). A body exhibiting this high chargeability correlating with a low resistivity (≤ 60 Ω m) is observed south of the study area. This body linked to a sulfurized zone presents its roof at an average depth of 13 m with a lateral extension in depth and a NE–SW orientation in agreement with the overall orientation of the area's major tectonic lines. Another polarizable body, located in the near surface to the north of the study prospect over an average depth of about 10 m, correlates with high resistivity (4500 Ω m), thus characterizing a probable zone of silicification. [ABSTRACT FROM AUTHOR]

Resistivity method using seventy-sixth (976) Schlumberger vertical electrical soundings along forty-one (41) profiles are conducted in the Batouri and Ngoura subdivisions, East region of Cameroon, to investigate the subsurface layering, mineral potential, and groundwater resource characteristics. Results of quantitative and qualitative interpretation of data using Koefoed computation method reveal two to five layers having geometrical and electrical characteristics of geological layer models: topsoil (0.5 m < e p < 3 m ; 600 < ρ < 3000 Ω. m), lateritic soils (3 < e p < 20 m ; 1000 < ρ < 4000 Ω. m); conductive layer (5 < e p < 110 m ; 100 < ρ < 1000 Ω. m); fractured/weathered granite (20 < e p < 60 m ; 1000 / 5000 < ρ < 3000 / 9000 Ω. m); clayey layer (5 < e p < 20 m ; 600 / 1500 < ρ < 2000 / 3500 (dry) Ω.m); and fresh granites (ρ > 4000 Ω. m). From the qualitative interpretation of VES curves, the subsurface layering is depicted by nine (09) types of sounding curves (G, H, A, QH, KH, HK, HA, HKH, and KHK) characterizing the vertical changes and the typology of sounding curves in the East Cameroon crystalline basements. The lithology of the subsurface is dominated (more than 80%) by geoelectrical and lithological 1D models derived by the H, QH, KH, HK, HA, HKH, and KHK curve types. These models are characterized by the presence of conductive layers and fractured/weathered granites derived from tectonic activities of the region. Also, the resistivity method (VES) applied in this study bring information about variation of the resistivity with depth, geological structures, fractures, and rupture zones in the underground until 120 m depth. These abovementioned information reveal proper hydrogeological and mining conditions for an efficient evaluation of the mineral potential and groundwater resources. [ABSTRACT FROM AUTHOR]

The aim of this study was to map the transpressional and transtensional relay zones of the Central Cameroon Shear Zone in the Mbere Administrative Division of the Adamawa Region of Cameroon using, geological and geophysical data analysis. The central Cameroon Shear Zone (CCSZ) is characterised by several large strike-slip faults oriented between N030E and N070E. The geological and structural field data analysis revealed two deformation regimes (strike-slip and tensile) that exhibit characteristic deformation markers identified in the field. The dextral movements on the strike-slip faults of the CCSZ were associated with these markers, the two regimes were found to be associated with the D3 deformation along the CCSZ. The tensile regime generated transtensional structures and led to the formation of the Cretaceous Mbere and Djerem basins, whereas the transcurrent regime caused the transpressional tectonics. Structural analysis of the joints and veins of the D4 deformation shows that their directions describe those of the major axes of the CCSZ. As the D4 deformation is controlled by transcurrent tectonics, to show that the vein intrusions constitute transpressional relay zones and to derive different models, processing, and interpretation methods (spectral analysis, shaded relief analysis, magnetic signal filtering, upward continuation, horizontal gradient magnitude, analytical signal, and 2.5D inversion) have been applied to the geophysical data. Magnetic residual analysis shows that the transpressional relay zones are characterised by high-frequency rectilinear magnetic anomalies (207.12–305.809 nT) and interference along the strike-slip faults. Through the superimposition of the geophysical interpretations, a structural model integrating the two deformation regimes with relay and Cretaceous basin models was developed. [Display omitted] • The two interpreted deformation regimes are associated with transtensional and transpressional tectonics, respectively. • The first favored the development of cretaceous basins and the second the formation of transpressional relays. • Transpressional relays, rectilinear with high frequencies are associated with strike-slip faults. [ABSTRACT FROM AUTHOR]

The present study attempts to combine direct current and induced polarization methods for 3D geological modelling and preliminary volume estimation of gold mineralization targets in the Simi locality, Adamawa, Cameroon. To begin, resistivity and chargeability data were collected along seven profiles oriented in N150E using the electrical tomography technique. A geological investigation was also carried out and allowed in addition to the geological formations to highlight the existence of gold mineralization in the study area. The interpretation of the inversion results was done by taking into consideration the geological field data and the existing resistivity charts. The 3D distribution of the interpreted sections allowed us to make a horizontal correlation between the different sections and to elaborate the 3D geological model of the study area by using the deterministic inverse distance method. The estimated model indicates a volume of 621,130.625 m3 of the possible gold complex. The gold complex was then divided into two mineralization domains based on chargeability ranges (mV/V): A first domain is associated with a major mineralization zone (39–60 mV/V) with a volume of 10,842 m3, and a second domain is associated with secondary mineralization zone (18–39 mV/V) with a volume of 610,288 m3. This model allows to compartmentalize the gold complex and can be used as a base model for the gold investigation in the study area. [ABSTRACT FROM AUTHOR]

The Babouri-Figuil Basin (BFB) is a frontier basin for petroleum exploration in northern Cameroon that belongs to the series of Cretaceous rift basins of the West and Central Rift System (WCARS), and contiguous related WCARS rift basins in Niger, Chad, Sudan, and Nigeria have yielded commercial deposits. The recent discovery of Precambrian basement reservoirs in Chad (Bongor basin) highlights the existence of a new play for petroleum exploration in the region. A network of interconnected magmatic intrusions directly related to basement faults cross-cuts the BFB stratigraphy. This study aims to evaluate the interactions between magmatic intrusions and potential source rocks in the BFB and make comparisons with similar basins in the WCARS context. The results showed that magmatic intrusions are made up of dolerite and basalt, characterized by onion peel (ball-shape) or columnar joint structures, respectively, and a fine-grained microlithic-porphyritic texture. The analyzed samples are thermally immature except for the samples located close to magmatic intrusions, which are thermally mature. The SEM images revealed that organic matter was subrounded with a regular shape in the samples that are located away from magmatic intrusions, while it presented a characteristic pattern of thermally evolved organic matter in sample located closer to magmatic intrusions, characterized by a cloudy visual aspect that is filling small fractures and being disseminated over mineral grains. Contact metamorphism and hydrothermal processes led to the neoformation of mixed-layered illite/chlorite and illite/micas. This study shows that the interactions between sedimentary formations and magmatic intrusions are stronger when the distance toward magmatic intrusions decreases. The source rock maturation of outcrop samples was predominantly triggered by magmatic intrusions, so that the overall area would be immature without intrusions. The formation of secondary organic matter (solid bitumen) in source rocks provides a perspective into a working petroleum system in the BFB. The presence of magmatic intrusions in the Babouri-Figuil Basin may positively affect the thermal maturation history of source rocks and can activate petroleum generation at a shallow burial depth. Thus, the Babouri-Figuil Basin may host an atypical petroleum system. • The magmatic intrusions in the Babouri-Figuil Basin are made up of dolerite and basalt. • Contact metamorphism and hydrothermal processes led to the disappearance of detrital clay minerals and the neoformation of mixed-layered illite/chlorite and illite/micas. • The thermal maturity proxies of the analyzed samples revealed a systematic increase in thermal maturity indexes as the distance with magmatic intrusions decreases. • The formation of solid bitumen in source rocks provides a perspective on an atypical petroleum system in the Babouri-Figuil Basin. [ABSTRACT FROM AUTHOR]

In the Pitoa-Figuil area (Northern Cameroon), an interpretation of aeromagnetic data was conducted. The aim of this investigation was first to emphasize lineaments hidden under geological formations and secondly to propose two 2.75D models of the subsurface structures. Different magnetic data processing techniques were used, notably horizontal gradient magnitude, analytic signal, and Euler deconvolution. These techniques in combination with the 2.75D modelling to the aeromagnetic anomaly reduced to the equator permit to understand the stratification of the deep and near surface structures, which are sources of the observed anomalies. We managed to put in evidence and characterize 18 faults and some intrusive bodies. According to Euler's solutions, anomaly sources go up to a depth of 5.3 km. [ABSTRACT FROM AUTHOR]

The Babouri-Figuil Basin is an intracratonic basin (half-graben) in northern Cameroon that is genetically connected to the Benue Trough from Nigeria, and is an area of interest in terms of petroleum prospectivity. Recent studies highlighted the presence of organic-rich formations in the basin. However, none of these works have identified factors that governed the accumulation of organic matter (OM) in the sediments. The main objective of this work is the characterization of these formations through palynofacies and organic geochemical techniques (total organic carbon - TOC, total sulfur, insoluble residue and biomarkers), in order to determine the organic facies, their depositional environments and the main drivers for organic enrichment in the basin. The current study reveals that black shale and massive claystone lithologies constitute the main organic-rich formations in the basin, with TOC reaching up to 26.08 wt%, being characterized by a dominance of bacterially-derived amorphous OM. Palynofacies and biomarker data revealed that these formations are positively associated with anoxic conditions and a partly highly saline and stratified lake water column. The deposition of organic-rich formations in the Babouri-Figuil Basin was mainly controlled by restriction conditions which developed in connection with the regional tectonic framework. The Lower Cretaceous rifting episode in the West and Central African Rift System (WCARS) basins led to the formation of accommodation space, a reduction in water levels, and the development of anoxic conditions within the basin, facilitating the deposition of organic-rich formations. Therefore, the organic enrichment of the Babouri-Figuil Basin has been predominantly controlled by its tectonic evolution, particularly during the syn -rift phase. This phase created favorable conditions for the deposition and preservation of OM, including the establishment of anoxic conditions. Additionally, the paleoclimate (arid conditions), the development of bacterial biomass, and the basin's paleogeography all played a significant role in this process. The organic-rich formations of the Babouri-Figuil Basin show characteristics of prospective petroleum source rocks (high organic content, high proportion of oil-prone kerogen, significant thickness and lateral extension). The combination of organic-rich formations with sandstone deposits above and extensive claystone/shale deposits on top can indicate the presence of an oil play in the basin. A detailed study with broader sampling is needed to investigate thoroughly the variation of organic facies and the influence of paleoenvironmental factors that control the deposition of thick source rock intervals. • The black shale and massive claystone lithologies constitute the main organic-rich formations in the basin. • Organic-rich formations are positively associated with anoxic, highly saline and stratified bottom lake conditions. • Organic enrichment episodes in the basin were controlled by restriction conditions in connection with the regional tectonic coupled with paleoclimate, and the paleogeography. • These formations have characteristics of prospective petroleum source rocks. [ABSTRACT FROM AUTHOR]

The Babouri-Figuil Basin (BFB) is a frontier basin for petroleum in Cameroon. It belongs to the series of Cretaceous rift basins of the West and Central Rift System (WCARS), the origin of which is related to the opening of the South Atlantic. Within the same rift system, commercial hydrocarbon accumulations have been discovered in Chad, Sudan, Niger and, more recently, in Nigeria (Gongola Basin). The study of the geology of the BFB just recently received considerable attention, mainly because of its presumed hydrocarbon potential. In the pursuit of researching possible petroleum systems in the BFB, the current study provides a first look into the characterization of source and reservoir rock and its integration into a 2D lithostratigraphic model. The study was solely based on outcrop samples. Black shale and massive claystone are good to excellent hydrocarbon source rocks [e.g., up to 38 wt% total organic carbon (TOC), up to 943 mg/g hydrogen index, up to 85 m thickness, up to 20–30 km lateral extension], with moderate to high values of extractable organic matter (e.g., >10,000 ppm). Calcareous claystone, on the other hand, are poor source rocks [e.g., <0.20 wt% TOC]. The samples are thermally immature, except for those located close to volcanic intrusion at Golombe that have reached the threshold for oil generation (Tmax >435 °C, production index >0.1). The petrographic analysis of sandstone revealed that they are fine-grained to coarse-grained, poorly to moderately sorted, texturally and compositionally immature to submature, subarkosic to arkosic arenites. The main diagenetic processes that affected sandstones are as follows: moderate to intense compaction characterized by the development of long, concavo-convex, and sutured contacts between grains; cementation through calcite, iron oxide, and quartz cements; alteration of mica and feldspar grains; partial to complete dissolution of feldspar, mica, amphibole grains, and calcite cement; and the replacement of feldspar and mica grains by clay minerals. Alteration and dissolution increase the porosity of sandstone through the creation of secondary pores. However, mechanical compaction through the development of a pseudomatrix and cementation as pore-filling materials have significantly reduced the quality of sandstone beds as conventional petroleum reservoirs. Hence, the best reservoir-quality sandstones in the basin are generally located in the upper portion of the basin in terms of its lithostratigraphic model. They are the cleanest sandstones with the smallest amount of cement and the lowest ductile grain content (pseudomatrix), with a thickness that varies from 3 m to 120 m and a lateral extension of 20 km. The lithostratigraphic model of the basin is characterized by an extensive lacustrine environment that provided a thick sequence of organic-rich formations; sand deposited as extensive reservoirs sandwiched between shale/claystone beds; the development of stratigraphic traps through lateral facies change; and the widespread deposition of lacustrine and floodplain claystone that provide regional seals. The similarities between the Babouri-Figuil Basin and proven petroleum systems in other WCARS rift basins suggest that the basin may host at least one petroleum system where actively generating source rocks are present. [ABSTRACT FROM AUTHOR]

This study combines the finite element approach and the spectral analysis of Fourier's function, to investigate the eastern Cameroon and western Central African Republic. In this area, the signature of the gravity anomalies seems to correspond to the transition zone between the Congo Craton and the Panafrican Mobile Belt. Thus, a gravity interpretation based on the data obtained from four N-S profiles on the residual map is carried out using a 2.5D model. The residual anomaly map is obtained by using the finite element method (FEM) for data filtering. Spectral analysis is used to estimate the depth of the sources responsible of the observed anomalies. Our results demonstrated that the observed gravity anomalies in the region are associated with tectonic subsurface structures. This study suggests that the transition area, which comprises the northern margin of the Congo Craton (CC) and the southern border of the Mobile Zone of Central Africa (MZCA) known as the Pan-African Belt (area covering the geological Congo Craton limit (GCCL)), is a product of convergent collision. This collision has caused considerable over-thrusting of the Pan-African Belt (PAB) units onto the Congo Craton. The models suggest the intrusion of magmatic rocks during the continental collision, which were later metamorphosed into granulites along and around the northern margin of the Congo Craton. The presence of deep granulite structures in the northern margin of the CC expresses a continental collision. Some sediment formations appear in the Central African Republic with variable thicknesses. The granulites (deeper parts of PAB) observed might come from the uprising of some materials of the upper mantle probably during the opening of the Atlantic Ocean. The probable geophysical limit of the CC in the upper crust is suggested on this study. [ABSTRACT FROM AUTHOR]