The ferricrete deposit in Adi Kokeb district was investigated using field observations, petrographic studies and chemical analysis of samples for their geochemistry and mode of origin. Field observations confirmed the presence of kaolinites, thin iron bands and relict quartz veins. Petrographic studies of the samples revealed that quartz, sericite, muscovite, orthoclase feldspar and iron oxides/hydroxides are the dominant minerals. Geochemical determination of major, minor and trace elements of seventeen (17) samples were done using X-ray fluorescence (XRF). The results show a general increasing trend in Fe 2 O 3 (16.75-57.9 wt.%) and Al 2 O 3 (11.35-16.44 wt.%) values and decreasing trends in SiO 2 (57.05-22.01 wt.%) values from the Meta-sandstone to the ferricrete. The alkali and alkaline earth elements, notably K 2 O (0.142 wt.%), Na 2 O (<0.005 wt.%), CaO (0.075 wt.%) and MgO (0.098 wt.%), are highly depleted, confirming that iron precipitation with subsequent oxidation is major process in ferricrete formation. Similarly, the minor elements such as MnO (0.17 wt.%), TiO 2 (0.56 wt.%) and P 2 O 5 (0.154 wt.%) are highly depleted, implying their weak substitution for major elements in the ferricrete. The average value of trace elements such as Ba (669 ppm), Zr (348 ppm), Sr (215 ppm), Cu (125 ppm), Zn (55 ppm) and Pb (9.5 ppm) show a relative enrichment of the ferricrete compared to ferruginous sandstone and metasandstone. The relatively high concentrations of Zr, Ba and Sr in the ferricrete are attributed to their presence in detrital material during weathering (Zr) and their adsorption on neoformed kaolinite (Ba and Sr). Integration of field, petrographic and geochemical results suggest that the origin of this deposit is associated with weathering processes. Therefore, the deposit is likely to be a ferricrete.

Gold occurs as a native metal, usually containing silver, and in some cases mercury, copper, and palladium. It may also occur as inclusions within sulfur-rich minerals, such as pyrite and arsenopyrite. The style and variety of gold mineralization is influenced by the geological setting, chemistry of the ore fluids, and the nature of their interactions with rocks. Gold grains liberated from bedrock into surficial sediments during weathering and erosion are chemically stable and may be characterized according to their mineralogy: i.e the alloy composition and suite of mineral inclusions revealed within polished sections, characteristics faithful to gold from the hypogene source. This approach has been applied to placer gold grains from the Meyos-Essabikoula area, Cameroon, where the source of gold is not yet confirmed due to poor outcrop exposure. A total of 221 alluvial gold grains from 10 sites, tributaries of Sing and Bivele River over the Ntem Complex have been studied using Electron Probe Micro-Analysis (EMPA) to determine the concentration of minor alloying metals, (notably Au, Ag, Cu, and Hg) and Scanning Electron Microscopy (SEM) in order to evaluate the assemblage of mineral inclusions within the gold. Most of the grains are sub-rounded with pitted surfaces and inclusions of pyrrhotite, acanthite, and chalcopyrite were observed. The grains are Au-Ag alloys ranging from 54.4-99.8 wt% Au, 0.1-48.4 wt% Ag, 0.1-0.8 wt% Hg and 0-0.3 wt% Cu. The presence of Fe oxide (magnetite) inclusions containing Cr and V (to around 5 wt %) has not been reported elsewhere and suggests a strong interaction between hot reducing ore fluids and local mafic lithologies.

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Gold in Benin occurs as primary and alluvial forms in various deposits and occurrences. The mineralisation has a regional distribution covering, in particular, the Atacora area (Natitingou) and the regions of Bembèrèkè, Djougou and Dunkassa which are between the 9th and 11th parallel north. The data collected during previous work allow us to recognise the main style of primary gold as being quartz-vein hosted. This style occurs principally in quartzite, mica schist, schist and amphibolite lithologies, outcropping in the criss-crossing of the faults and the rugged relief. The mineralised veins are milky, deformed and gold is associated with sulphides and tourmaline. In these veins, gold exhibits three forms: free native metal, tellurides, and combined or included in sulphides. These gold-bearing quartz veins would proceed from hydrothermal solutions related to granitic mass. Classical characteristics available about the primary gold mineralisation in Bénin are inadequate to better clarify its geodynamic context. However, it has some similarities with deposits of the Precambrian terranes in adjacent countries (Pourra deposit in Burkina Faso and Kalana deposit in Mali) which are characterised by epigenetic gold deposits in Precambrian metamorphic terranes. Also, the vein gold of Bénin are mostly located in Precambrian metamorphosed sedimentary and volcanic formations ; these could also have the epigenetic disseminated gold style like in some West African deposits (Ashanti deposit).

The Fongo-Tongo's bauxites were investigated to characterise them. Their texture varies from massive, vesicular, alveolar, conglomeratic to nodular with dominantly red colour, reddishbrown and yellow. The main minerals identified by X-ray diffraction are gibbsite and goethite with subordinate quartz, anatase, hematite, magnetite, and traces of kaolinite. The abundance of gibbsite and goethite suggested intense weathering during the formation of the bauxite deposits. Chemical data of the bauxite showed high Al 2 O 3 (37.4-57.5 wt-%) with varied Fe 2 O 3 (3.97-29.5 wt-%), TiO 2 (0.57-7.5 wt-%) and SiO 2 (0.48-3.21 wt-%) contents, while other oxides are generally less than 0.6 wt-% indicating high bauxite quality with low impurities. The wide range of trace and REE concentrations of Zr, Nb, Sr, V, Ce, La, Nd and the presence of both positive and negative Eu anomalies suggested and acid igneous source with mafic input. These bauxites could serve as raw material for the aluminium industry.