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The Ekomedion two-mica granite, southwestern Cameroon, has potential for uranium and molybdenum mineralization. Here, we present LA-ICP-MS U–Pb ages, Lu–Hf isotope characteristics, trace element concentrations and Ti-geothermometry of zircon from this granite hosting U–Mo mineralization in pegmatitic pods. The majority of zircon are CL-dark though some CL-bright cores were also identified. U–Pb zircon age data range from 121 ± 3 to 743 ± 11 Ma with only 5 of 34 ages being near concordant. The concordant mean age of 603 ± 12 Ma is similar to ages of granitic intrusions along the Central African Shear Zone in Cameroon. Apparent ages with mean of 261 ± 6 Ma reveal open system behavior with respect to Pb and/or U. Zircon eHfi values range from − 20.3 to − 0.3. This implies that U–Mo was remobilized during partial melting of the surrounding gneiss. Zircon Th/U > 0.1 as well as an increasing Hf with decreasing Th/U indicates that fractional crystallization was the main factor that controlled U–Mo mineralization in pegmatitic pods. Y and Y/Ho ratios cluster from 29 to 33 close to the chondritic ratio of 28 and indicate fractionation of Y and Ho with low F contents during the earliest stages of crystallization. Late stage accumulation of F-rich magmatic-hydrothermal fluids impacted U–Mo mineralization as a ligand. Zircon contains a prominent negative Eu anomaly pointing to a fractionating system rich in plagioclase. Calculated Ti-in-zircon temperatures span 672 °C to 1232 °C with the temperatures at the high end reflecting interference from mineral inclusions in the zircon grains while the lower temperature values are linked to crystallization.

The study of changes in rocks due to interaction with hydrothermal fluids at active volcanoes provides insights into wall rock alteration associated with ore deposits formed in the geological past. Therefore, the nature of mineral alteration and chemical changes experienced by wall rocks can be investigated at eruptive sites on active volcanoes and the results used to better constrain ore-forming processes. In this study, we investigated the alteration at eruptive sites at Mount Cameroon volcano. These eruptive vents lie along NE-SW-trending fissures that define the Mount Cameroon rift. The vents are surrounded by cones composed largely of pyroclastic materials and to a lesser extent lava. Fumaroles (volcanic gases) rising through the vents during and after the 1999 eruption have resulted in the alteration of the pyroclastic robble along the fissures and the inner walls of the cones. Consequently, altered basaltic materials are covered with thin films of reddish, yellowish to whitish secondary minerals. These coatings result from an interaction between the surfaces of the basaltic glass with volcanically-derived acidic fluids. Petrographic investigations and XRD analysis of the basalts have identified primary mineral phases, such as olivine, pyroxene (mainly augite) and feldspars. Alteration products revealed include ubiquitous silica as well as gypsum, magnetite, feldspar, alunite and jarosite. Jarosite occurrence indicates that SO2 is the primary volcanically-derived acid source involved in coating formation. High contents of sulfur identified in the basalts indicate that melts at Mount Cameroon can be sulfur saturated as backed by previous melt inclusion data. Whole rock geochemical analysis shows a gain in silica in the altered samples and this ties with the mass balance calculations although minor gains of Al2O3, , MgO, MnO, CaO and K2O are shown by some samples.

This study presents the ore texture, mineralogy and whole rock geochemistry of iron occurrence from the Edea North area located at the upper limit of the Nyong Unit, part of the Congo craton. This iron mineralization is of magnetite quartzite type enclosed by metamorphic rocks of the granulite facies. Two main facies have been identified over the study area including the banded and the massive facies. The mineralogical set of these facies is in majority represented by magnetite, quartz and pyroxene martite in addition to minor biotite, apatite, and amphibole. Magnetite presents as irregular and elongated minerals which can contain quartz inclusions of various shapes and sizes, as blasts clustering, around pyroxenes and isolated xenomorphic magnetite minerals in the silicate phases. Quartz varies from fine to coarse-grained and ribbon quartz. This indicates re-crystallization and deformation during metamorphism. Electron microprobe analysis on magnetite and martite show Fe2O3 contents that vary between 96.11 and 99.76. Whole rock chemical data showed that Fe-contents are as high as 62.9 wt%. The SiO2 content varies between 33.8 wt% and 51.2 wt%. Iron oxides and SiO2 are negatively correlated. Moreover, the low positive correlations between Al2O3 and HFSE, and LILE suggest a contribution of clastic materials in the protolith of studied materials. The samples show low contents of V, Cr, Ba, Zr with respect to igneous rocks. This may infer a sedimentary origin for the studied rocks; furthermore, these materials may have undergone hydrothermal alteration. The REE patterns reveal enrichment in LREE compared to HREE. Some samples show positive Eu (1.82) and other negative anomalies Eu (0.54 to 0.97). The lack of Ce anomalies suggests that the depositional environment of the Edea North iron occurrence was anoxic or suboxic. Overall, the Edea North iron occurrence may have undergone significant input from hydrothermal sources with imprints of the clastic during its deposition.

Major and trace element composition of iron duricrusts including clayey material samples and biostratigraphy of the Missole I outcrop from the Paleocene–Eocene N’Kapa Formation in the Douala sub-basin of Cameroon were used to infer the palaeoenvironment and relative age of the iron duricrusts. Iron duricrusts and clayey materials are essentially kaolinitic and smectitic and are generally siliceous and ferruginous (iron duricrusts) or siliceous and aluminous (clayey materials). These materials have high Chemical Indices of Alteration (CIA = 86.6–99.33%). The negative Eu anomalies with high (La/Yb) N shown by iron duricrusts and clayey sediments are essentially derived from silicic or felsic parent rocks when fractionated chondrite-normalized REE patterns also indicate felsic or silicic parent rocks. The Missole I iron duricrusts have a post-Thanetian age according to the relative age of claystones (Thanetian) and were formed after the deposition of sedimentary materials in an anoxic low-depth marine environment with eutrophication of surface water, and may have been exhumed and oxidized under arid climate.

Major and trace element concentrations of clay deposits of the Missole II and Bomkoul respectively from the Paleocene-Eocene N’Kapa Formation and the Miocene-Pliocene-Matanda-Wouri Formation in the eastern part of the Wouri River in the Douala sub-basin of Cameroon have been investigated to identify the parent rocks. To carry out this study, X-ray diffraction, inductively coupled plasma–atomic emission spectrometry (ICP/AES) and inductively coupled plasma–mass spectrometry (ICP/MS) were performed to determine respectively the mineralogical and chemical data of Missole II and Bomkoul clayey materials. Clay sediments are essentially kaolinitic and illitic, and kaolinitic and smectitic respectively in both sites. They are generally siliceous, aluminous with small iron and bases (MgO, CaO, Na 2 O, and K 2 O) contents. Samples of Missole II profiles are more siliceous than those from the Bomkoul grey and dark grey clayey materials. Clayey materials have high Chemical Index of Alteration (CIA = 80–99.34) which suggests that they are strongly weathered under humid tropical climate before and after their deposition in the coastal plain. The value of Eu/Eu * (0.48–0.61), La/Sc (2.15–20.50), Th/Sc (0.74–2.25), Th/Co (1.08–8.33), and Cr/Th (5.24–13.55) ratios support essentially a silicic or felsic parent rocks. Total REE concentrations reflect the variations in their grain-size fractions. Chondrite-normalised REE patterns with LREE enrichment, flat HREE, and negative Eu anomaly are attributed essentially to silicic or felsic parent rocks like those from weathered materials developed from the gneisses around the coastal plain in the littoral part of Cameroon ( Noa Tang et al., 2012 ), main characteristic of Paleocene-Eocene and Miocene-Pliocene clay sediments of Missole II and Bomkoul areas.

Fresh nephelinitic rocks and hydrothermally altered rocks at Mount Etinde (Cameroon Volcanic Line, West Africa) have been studied by combined whole rock geochemistry (ICP-MS), mineralogy and mineral chemistry (SEM-EDS, WDS, XRD) techniques. The nephelinites have feldspathoids, clinopyroxene, perovskite and titanomagnetite as the principal minerals in the mode with subsidiary apatite and sphene. The mineralogy of their hydrothermally altered counterparts includes phillipsite, calcite and analcime which are secondary phases developed in response to hydrothermal fluid events. Correspondingly, the bulk rock geochemical data show elevated SiO 2 , CaO, Na 2 O and K 2 O concentrations with increasing alteration and Al 2 O 3 and Fe 2 O 3 depletion while MgO, MnO and TiO 2 concentrations are largely unaffected. The nephelinites also have high concentrations of LILLE, HFSE and REE and upon hydrothermal alteration they show an enrichment of LREE and MREE over HREE. Phillipsite is the principal alteration mineral in the rocks and it occurs along cracks, vesicles and also forms alteromorphs after feldspathoids. The Ce content of these categories of phillipsite varies. Phillipsite along cracks is richer in Ce while phillipsite associated with calcite has lower Ce concentration and the phillipsite alteromorphs very little or no Ce. Various stages of fluid circulation are proposed hereby to explain the variations in phillipsite generation and composition.

The progressive weathering of 0.65 Ma nephelinites from Mount Etinde (South Western Cameroon) in a humid tropical setting has resulted in the formation of a 150 cm thick weathering crust. The soil profiles consist of three horizons: Ah/Bw/C. A major differentiation of the chemical and mineralogical parameters is related to the complexity of the saprolites, some of which were hydrothermally altered. Bulk geochemical and microgeochemical analyses were performed on selected minerals from the different horizons of two reference profiles, of which one (E 4 ) was developed from unaltered nephelinite (nephelinite U ) while the other (BO 1 ) formed from hydrothermally altered nephelinite (nephelinite H ). The results show that the primary minerals (clinopyroxene, nepheline, leucite, hauyne, titanomagnetite, perovskite, apatite and sphene) experienced differential weathering rates with primary minerals rich in rare earth elements (titanomagnetite, perovskite, apatite and sphene) surviving in the saprolite and the Bw horizons. The weathering of the primary minerals is reflected in the leaching of alkaline and alkaline-earth elements, except for Ba and Rb in the hydrothermalised nephelinite soil. The order of mobility is influenced by hydrothermal processes: Na > K > Rb > Ca > Cs > Sr in nephelinite U soil , Na > K > Sr > Ca > Mg in nephelinite H soil; Rb/Sr and Sr/Mg can be used as indicators of the kinetic of the weathering on nephelinite U and on nephelinite H . Barium enrichment is related to variable concentrations in the nephelinites, to the formation of crandallites and the leaching of surface horizons. The content of metallic elements is higher in nephelinite H soil than in the nephelinite U soil. Results show that hydrothermal alteration leads to an enrichment of light (La, Ce, Nd) and intermediate (Sm, Eu, Dy) rare earth elements. The enrichment in Cr and Pb in the surface horizons is discussed in relation to organic matter activity, the dissolution of magnetites, and the impact of hydrothermal processes as well as atmospheric pollution in the case of lead.

Mt. Cameroon erupted simultaneously in March–April 1999 in two distinct places on its southwestern flank. A hawaiite (with An 83-76 plagioclase phenocrysts) and an alkali basalt (with Fo 84-80 olivine phenocrysts) have been simultaneously emitted respectively at 1 400 and 2 650 m of altitude a.s.l. The eruption of these co-magmatic lavas attests to the occurrence of a unique magmatic reservoir inside which the magma differentiation took place by crystal setting of denser mineral phases.

Mt Etinde eruptions are dated at 0.65 Ma. It is located on the SW oceanic border of Mt Cameroon, and is composed essentially of nephenilitic rocks. The weathering of nephelinites has resulted in the formation of a 150 cm deep Andic Cambisol (Humic) consisting of three horizons: Ah/Bw/C. Mineral weathering was studied in detail in two profiles: one (P 1 ) developed from unaltered nephelinite (nephelinite U ) and the other (P 2 ) formed from hydrothermally altered nephelinite (nephelinite H ). Emphasis was on the impact of hydrothermal alterations on weathering profiles, to characterise the signature of halloysite in nephelinitic regoliths and to discuss the evolution of Mt Etinde soils on the Quaternary nephelinitic parent rocks. The mineralogy of nephelinite U consists predominantly of clinopyroxene, nepheline, leucite, hauyne, titanomagnetite, perovskite, apatite and sphene. Nephelinite H differs from nephelinite U by phillipsite–calcite occurrence. The main weathering products are halloysites (1-nm and 0.7-nm) and minor occurrence of gibbsite and hematite. SEM micromorphological examination coupled with microprobe analyses showed halloysites resulting from in situ alterations of feldspathoids, phillipsites and clinopyroxenes. 1-nm hydrated halloysite neoformation characterises the alteromorphs of the saprolite while 1-nm and 0.7-nm halloysite coexist in the Bw and the Ah horizons of both soils. During weathering, these halloysites had a chemical dependence with parent mineral as follows: Ce-rich halloysite characterises alteromorph after phillipsite; Fe-rich halloysite, alteromorph after clinopyroxene; Ca-rich halloysite alteromorph, after hauyne; and K-rich halloysite, alteromorph after leucite. Ce-rich halloysite is a tracer of the hydrothermal impact in soils profile. The Si/Al ratio is also characteristic of the parent mineral. Therefore, the availability of Si is the only factor that controlled the formation of 1-nm halloysite at the base of the saprolite while the presence of 1-nm and 0.7 halloysite in the upper part of the saprolite, the Bw horizon and the Ah horizon suggesting only time controls of the evolution of the profiles by both kinetic (wet–dry seasons) and thermodynamic (Si-bearing) factors. Gibbsite occurs only in the nephelinite H soil. Its presence is due to the hydrothermal alteration which favoured the development of an intense microporosity allowing the elimination of silica. The study highlighted the influence of past hydrothermal activity on the recent weathering process in the humid tropical area.