In Cameroon, topomorphic vertisols are widespread in the Sudano-sahelian zone above latitude 9ºN. With a depth of about 2 to 2.5 m above the water table, these soils show four main horizons from bottom to top: a dark grey horizon with hydromorphic patches (B 3g), dark grey horizon (B 21), dark grey horizon with slickensides (B 1) and a surficial grey humiferous horizon (A 1) with desiccation cracks. Also, they show a heavy clayey texture, very massive structure, high bulk density, very low porosity and a high compacity. The microfabric of the soils is marked by abundant plasmas, isotic at the surface but birefringent at depth, with numerous stress cutans. The microscopic analysis of heavy minerals reveals the presence of magmatic and metamorphic minerals from the upper part of the watershed. Quartz grains are mainly angular to sub-angular revealing short fluvial transport distance. The vertisols are thus formed from recent alluvial deposits from weathering, erosion and deposition of rocks from upper parts of the watershed. Physico-chemically, the studied soils are characterized by high cation exchange capacity (26-42 meq/100g), high sum of bases (74.30-94.23 meq/100g), high base saturation, low organic carbon and a very high C/N ratio. Geochemically, Si and Al are the dominant elements, characterised by a Si/Al ratio range of 2.27 and 2.94. According to this rate, 2/1 clay minerals, namely smectite, are predominant and their presence confirms the shrink-swell behaviour of the soils. Total base concentrations are high and could be related to the contrasted climate and the low landscape position. Mechanical analyses revealed very high liquid limits (36-46%), low plastic limits (10-17%), high plasticity indices and high shrinkage limits that permit to classify those soils as medium to high plasticity inorganic clays. Those soils could be potentially useful in many domains like the chemical industry, pharmaceutics, petroleum industry, agronomy or environmental protection.

Vertisols occupy approximately 1,200,000 ha in Northern Cameroon. Their richness in smectites allows for the production of “bleaching earths” necessary for refining palm oil, and their effluent is used for leachate treatment. In the present work, two mineral acids (HCl and H2SO4) were compared, and the most efficient acid with the lowest cost was determined for use in industrial applications. Under similar experimental conditions (ratio of acid solution/clay mass = 5/1, temperature = 97 °C, stirring time = 4 h), the quantity of cations (Fe2+, Fe3+, Al3+) solubilised during acid activation, palm oil discolouration rate by each activated sample and the financial cost of 5 L of acid solution that is required for the acid activation of one kilogram of smectite clay were compared. It was found that 2N H2SO4 was more efficient than 1N HCl and 1N H2SO4, considering palm oil bleaching efficiency and cost. The filtrate collected after the acid activation of vertisols was rich in H+ (2.04.10−1M), Fe2+ (2.8.10−3M), Fe3+ (4.2.10−2M) and Al3+ (9.2.10−2M) ions. One gram of smectite clay material produced 9 mL of this filtrate that was used for the treatment of leachate from a controlled landfill. The leachate colour decreased from 4262 to 285 PtCo units, while the corresponding chemical oxygen demand (COD) decreased from 802 to 128 mg/L. Thus, the most effective acid for industrial bleaching earth production from vertisol is 2N H2SO4 acid.

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The morphology and quantitative chemical analyses of fifty alluvial gold grains from fourteen studied sites were used to constraint gold deposit type and its implications to exploration in the Abiete-Toko Gold District in South Cameroon. The main results revealed that the gold grains show a core-rim zonation marked by Ag depleted rims as a result of leaching during transportation. The fineness of grains ranges from 826 to 1000 and their composition is almost binary gold-silver. Gold fineness refers to the relative amounts of Ag and Au present, given as a number out of 1000 and defined by Au/(Ag þ Au)*1000. The chemical composition of the gold grains are range as thus: 83.40-100 wt.% Au, 0.07-17.45 wt.% Ag, 0-0.96 wt.% Cu, 0-0.01 wt.% As, 0-0.02 wt.% Ni, 0-0.02 wt.% Co, 0-0.01 wt.% Se, 0-0.08 wt.% Hg and 0.003-0.03 wt.% S. The high sulphur concentrations of the gold grains probably imply primary deposition of gold by sulphidation; The ranges of Ni and Co concentrations suggest an interaction with greenstones. Such findings indicate that the Abiete-Toko area hosts a mesothermal-orogenic gold deposit. Exploration operations must target fractures and contact zones between ironstones, felsic gneiss and greenstones. Soil sampling is not recommended in this orogenic gold district due to the very thick and transported nature of the weathering mantle. Detailed mapping coupled to geophysical surveys are the recommended key exploration methods prior to drilling program.

Up to date, tropical mountainous ecosystems still lack in depth information on soil and environmental characteristics which are major factors limiting optimum crop production. The objective of this work was to study soil characteristics and to evaluate the land capability level for the production of some common tropical crops in mountainous ecosystem soils of North West Cameroon. Soil sampling was done following a randomized complete block design (RCBD) with four replications for three topographic positions (upslope, midslope and footslope) and at two depths (0 -20 cm and 20 -100 cm). It was completed by standard laboratory analyses. The fertility capability classification (FCC) system enabled to identify soil limitations and to classify soils into FCC units. Land and climate were evaluated by simple limitation and parametric methods. Globally, the soils were dark-colored, sandy clayey to clayey, compact and very acidic (pHH 2 O = 4.3 -5.8). The organic matter (3.7% -5.1% dry matter), total nitrogen (0.08% -0.56%) and available phosphorus (22.1 to 30.9 mg·kg −1 ) recorded for the 0 -20 cm depth then reduced with depth but midslope values were also lower. The C/N ratio varied between 9 and 45. Low C/N values appeared mostly in 0 -20 cm depth at the upslope and downslope soils and subsurface soils of midslope position. Exchangeable Ca was very low to low (1.43 -3.6 cmol + kg DOI: 10.4236/gep.2018.67002 16 Journal of Geoscience and Environment Protection was the most relatively concentrated base in all the soils. There was a clear variation of most of the soil properties along the slope and with depth. The soils were classified in the FCC system as aek for the upslope soils, Caek for the midslope soils and Cagk for the footslope soils. The principal limitations to production of huckleberry, beans, maize and potatoes were heavy rainfall, wetness, steep slope, soil texture/structure and low soil fertility. These constraints might be overcome by farming at the end of the raining season, contour ploughing, terracing, fertilization and liming.

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