In this investigation, the level of toxic metals (Cd, Pb, Hg, Cu, Ni, Al, Zn and U) was determined in sediment samples from two watersheds (Kienké and Tchangué) in the Abiete-Toko gold district, southern Cameroon. The potential contamination and toxicity of studied metals was determined by evaluating enrichment factor (EF), geo-accumulation index (Igeo) and ecological risk assessment (ERA). Considering the spatial distribution patterns, metal concentrations were lower than the average shale values, except for Cu and Ni of site 4 in the Kienké watershed and only Ni in the Tchangué watershed. In this study, the EF and Igeo values revealed that sediments were moderately polluted by Ni and Cu and unpolluted by other metals. The evaluation of the ERA based on ecological risk index (RI), ecological risk factor (Er), contamination factor (CF) and pollution load index (PLI) revealed that the sediments from the Abiete-Toko watersheds have significant to very high ecological risk assessment and are generally unpolluted by trace metals and U, except for Ni and Cu. Little quantities of heavy metals with low U levels and distribution were found at the sites close to the vicinity of artisanal mining and peri-urban areas. This proximity reveals that artisanal gold mining activities, agricultural runoff, and other anthropogenic inputs in the study area are probable sources of slight metal contamination. However, the non-use of toxic effluents for gold mining and pesticides for agriculture can be an advantage of the unpolluted status of the watersheds. The physical degradation of the ecosystem through excavations, wells and other stream diversion methods is expanding in the zone. Appropriate measures should be taken by artisans to rehabilitate the gold mining sites, to ensure appropriate treatment of wastewater and non-use of toxic effluents into nearby tributaries.

The geology of the Abiete-Toko gold district in South Cameroon is investigated using a combination of Landsat 7 ETM+/SRTM image processing techniques, conventional geologic field mapping and geostatistical analysis. The satellite images were treated using Principal Component Analysis and Sobel filters to separate the background noise from lithotectonic structures which were matched with field data. The results show that this area has been affected by a polyphase deformation represented by S 1 foliation, S c1 schistosity, L 1 lineation, S 2 foliation, F 2 folds, and F 3 shear zones and faults. A detailed analysis of all the structures led to the identification of two major networks of dextral and sinistral shear zones oriented WNW-ESE and NE-SW, respectively. These results may serve in mining prospection, especially in the search for tectonically controlled primary mineralization and so may significantly guide the exploration of primary gold mineralization in the Abiete-Toko area subjected to years of artisanal gold mining.

Problem: Latosols of Liberia are marked by intense surface leaching, strong acidity, low soil organic matter (SOM) content, and low nutrients status, caused by low aggregate stability, which are limiting factors to crop production. Aim: to evaluate the effect of soil organic carbon (SOC) different forms of Fe and Al on the aggregate stability of latosols. Methodology: Composite surface (0-20 cm depth) samples of four latosols at different localities in Liberia (Lat1, Phebe; Lat2, Felela; Lat3, Salala; Lat4, Todee) were collected and analyzed for aggregate stability parameters and factors by standard laboratory methods. Results: the studied soils are sandy clayey, very acidic and poor in SOC. The cation exchange capacity (CEC) ranges from 10.28 to 14.80 mmol.kg−1. Dominant forms of Al and Fe are free Fe (Fed) and Al [1], followed by amorphous Fe (Feo) and Al (Alo) and chelated Fe (Fep) and Al (Alp). The highest levels of water dispersible clay (WDC) and clay dispersible index (CDI) in Lat1 and Lat2 implied that these two soils are less stable compared to Lat3 and Lat4. The Fe and Al in all forms seem to contribute to soil aggregate stability. The SOC, although very low, also contributes to soil aggregate stability. SOC correlated positively with WDC, CDI and ASC, indicating the impact of SOC both as an aggregating agent and as a dispersing agent, in contrast to previous studies. Conclusion: The study reveals that Fe, Al and SOC are cementing materials which impact the aggregate stability in Latosols.