New Discriminant Functions and Geochemistry of the Mamfe Cretaceous Formations (South West Cameroon)

Major and trace element geochemistry have been used to unravel the tectonic setting, source rock composition, and depositional environment of sedimentary rocks in the Mamfe formation. Field studies reveal both sub tabular and tabular outcrops indicating a post tectonic sedimentary activity for the subtabualar outcrops. Major element geochemistry reveals a moderate to high proportion (50-75wt %) of silica for the analyzed samples. New discriminant diagrams constructed for usage of adjusted major elements shows samples plotting on collision, arc and rift. Another discriminant plot for adjusted major element combined with trace elements shows samples plotting on active and passive tectonic setting.  Ratios of highly immobile trace elements such as Cr/Th, Th/Sc, Th/Co, and La/Sc conclude a felsic source rock for the studied rocks of the Mamfe formation. Trace elements ratios for redox conditions and marine-continental discrimination such as Ni/Co, U/Th, V/Cr, Th/U, and Y/Ho show that the sedimentary rocks of the   formation were deposited in a shallow oxygenated continental fluvio-lacustrine environment

Compositions and mobility of major, dD, d18O, trace, and REEs patterns in water sources at Benue River Basin-Cameroon: Implications for recharge mechanisms, geoenvironmental

Hydrogeochemical data are required for understanding of water quality, provenance and chemical composition for the 2117700 km2 Niger River Basin. This study presents hydrogeochemical analysis of the Benue River Basin, a major tributary of the Niger River. The distribution of, major ions, Si, δD and δ18O, Trace and Rare Earth Elements (TE and REEs, respectively) composition in 86 random water samples, revealed mixing of, groundwater with surface water to recharge shallow aquifers by July and September rains. Equilibration of groundwater with kaolinite, and montmorillonites by, incongruent dissolution imprints hydrochemical signatures that vary from Ca+Mg-NO3 in shallow wells to Na+K-HCO3 in boreholes and surface waters, with undesirable concentrations of fluoride identified as major source of fluorosis in the local population. Our results further indicate nonisochemical dissolution of local rocks by water, with springs, wells and borehole waters exhibiting surface watergaining, weakest water-rock interaction, and strongest water-rock interaction processes, respectively. Poorly mobile elements (Al, Th and Fe) are preferentially retained in the solid residue of incongruent dissolution, while alkalis, alkaline earth and oxo-anion-forming elements (U, Mo, Na, K, Rb, Ca, Li, Sr, Ba, Zn, Pb) are more mobile and enriched in the aqueous phase, whereas transition metals display an intermediate behaviour. Trace elements vary in the order of Ba > Sr > Zn > Li > V > Cu > Ni > Co > As > Cr > Sc > Ti > Be > Pb > Cd, with Potentially Harmful Elements such as Cd, As, and Pb mobilized in acidic media attaining near undesirable levels in populated localities. With the exception of Y, REEs distribution in groundwater in the order of Eu > Sm > Ce >Nd > La > Gd > Pr > Dy > Er > Yb > Ho > Tb > Tm, differ slightly with surface water composition. Post-Archean Average Australian Shale normalized REEs patterns ranging from 1.08-199, point to the dissolution of silicates as key sources of trace elements to groundwater, coupled to deposition by eolian dust

Trace Element and U–Pb Core Age for Zircons from Western Meiganga Gold Placer, Cameroon: Their Genesis and Archean-Proterozoic Sources

Trace element concentrations and U–Pb ages were obtained using Laser Ablation Split Stream Method from the core of 115 zircon grains from the western Meiganga gold placer deposit. The data was used to characterize zircon, to understand the history of crystallization and to locate source rocks within the local and regional geological settings. Zircon trace element geochemistry was used to distinguish between magmatic and metamorphic affinity. The magmatic zircons have characteristics compatible with their probable origin from granitoid, syenite, tonalite, charnockite and mafic to ultramafic rocks. The metamorphic zircons composition is compatible with growth from anatectic melts and by sub-solidus crystallization in equilibrium with garnet. The zircon ages reveal Archean, Paleoproterozoic, Mesoproterozic, and Neoproterozoic events with the principal source could mainly belong to Paleoproterozoic magmatic lineage. Some of the Paleoproterozoic magmatic zircons were probably sourced from two mica granite found within the local geology, whereas the remaining zircons have features indicating source rocks within the Congo Craton. We suggest that the geologic history of these zircons is related to crustal-scale magmatic and/or tectono-metamorphic events, possibly linked to Eburnean and Pan-African orogeny

Provenance of clastic sediments: A case study from Cameroon, Central Africa

The provenance of clastic sediments in stream beds, river terraces, rivers, swamps, lakes and beaches from different geological settings was investigated based on their compositional and geochemical variations. The geochemistry data of 622 sediment samples from 22 sites in the Cameroon were compiled to infer the provenance. The results suggest that, their mineralogy is dominated by quartz, low amount of feldspars, clay minerals, heavy minerals, ferric minerals, and rock fragments. The SiO2/Al2O3 ratio indicate that the sediments of Cameroonian region are mostly rich in quartz and clay-minerals. The enrichment of K2O/Na2O ratio implies plagioclase disintegration as K-feldspar during weathering and/or K-reintroduction in the system during diagenesis. The sediments are rich in light rare earth elements (LREE) and classified as shale, Fe-shale, Fe-sand, wacke, arkose, litharenite, sublitharenite, and quartzarenite. The sediments are composed of detritus derived from felsic igneous rocks, which correspond to the geology of the source areas. Weathering indices such as chemical index of alteration (CIA), chemical index of weathering (CIW), plagioclase index of alteration (PIA) and, A–CN–K (A=Al2O3, CN=CaO∗ + Na2O, K=K2O) plot indicated that the source rocks are subjected to low, moderate and intense weathering

Provenance, paleoclimate and diagenetic signatures of sandstones in the Mamfe Basin (West Africa)

Petrography, heavy mineral and trace element geochemistry have been used to unravel the tectonic setting, source area lithology, diagenesis and paleoclimate conditions of the Mamfe sandstones. Quartz exists as monocrystalline (79%), and polycrystalline grains (21%). Orthoclase and microcline are the most dominant feldspars in the rocks. Heavy minerals such as zircon, tourmaline, kyanite, augite, garnets, hornblende, epidotes, diopside, muscovites, biotites, and opaque minerals were disclosed by the samples after bromoform separation. These sandstones are mineralogically and texturally immature and have been classified as arkose on the basis of the QFR diagram. QtFL plot indicates derivation mainly from a transitional continental region of continental block provenance with trace elements geochemical data pointing to a felsic source. The felsic sources are related to the Precambrian granitic/gneissic rocks which formed the basement and margins of the basin. The bivariant log-log Qt/F+R and Qp/F+R plot and the nature of quartz grains of the studied sandstone specimens indicate a semi-humid climatic condition prevailed at the time of deposition in a fluvial environment. The sandstones display deformation of mica, cementation, replacement, and albitization with some having an imprinted reddish brown color indicating a redoxmorphic, locomorphic and phyllomorphic diagenetic stages associated to early, burial and uplift diagenetic processes