The geochemical characterization of Novokrivoyrog metavolcanics (2.2 Ga) and Krivoy Rog iron ores (1.8 Ga) in Ukraine represent an important tool for the understanding of their genesis and tectono-magmatic evolution. The petrological classification of the metavolcanics on SiO 2 /(Zr-TiO 2 ) and (Zr-TiO 2 )/(Nb/Y) Harker-type diagrams shows similarities to subalkaline andesitic basalts. An additional classification of the basalts on TAS (Na 2 O + K 2 O/SiO 2 ) and AFM (FeO-MgO-Na 2 O + K 2 O) diagrams exhibits a variable magmatic character from calc-alkaline to tholeiitic. The distribution of High Field Strength Elements, (HSFE: Ti, Zr, Y, Hf, Nb), V, Cr, and Rare Earth Elements (REE) in most of the rocks is close to calc-alkaline basalts (CAB) and can be compared to Precambrian mid-ocean ridge basalts (MORB) where high thermal (>250˚C) basaltic alteration is intensive under pH conditions between 2 and 4. These contributed to the deposition of the Krivoy Rog BIFs. Indeed REE distribution patterns of the BIFs suggest that they can be subdivided into shales and shaly BIFs (rich in LREEs since their detrital and clastic inputs are much higher) with (La/Yb)N > 1 as indication of clastic inputs; chert and cherty BIFs showing positive Eu anomaly with (La/Yb)N < 1 are similar to REE patterns of mixed hydrothermal fluids and seawater; alkaline altered BIFs whose (La/Yb)N ratio is >1 emphasizes post-depositional effects related to the enrichment of light REEs over heavy REEs with a positive Eu anomaly. The distribution of REE patterns of Krivoy Rog BIFs can finally be compared to Precambrian iron formations of mixed submarine hydrothermal fluids and seawater origin which correspond to the MORB signature of the Novokrivoyrog metavolcanics.
Sabga-Bamessing is a part of the Bamenda Mountains, an extinct volcanic center of the West Cameroon Highlands along the Cameroon Volcanic Line (CVL). The pristine volcanic rocks of the Sabga area are alkali mafic to felsic (basanites, phonolites, trachytes and rhyolites). Some weathered sections of a heterolithologic debris flow with a suppositious primary chemistry of the original volcanic rocks prior to weathering have shown significant calcium carbonate enrichment. CaO and LOI values of up 61.31% and 41.72% respectively show corresponding enrichment of 16.54 and 10.88, when compared with average fresh volcanic rocks. Na + normalized molar ratios computed from the chemistry of springs and rivers show carbonate dissolution signature which is contrary to silicate dissolution expected in acid volcanic rocks. Saturation indices (SI) calculated with PHREEQC reveal that brackish to saline springs are supersaturated with Calcite (CaCO 3), Aragonite (CaCO 3), Dolomite (CaMg(CO 3) 2 and Hydroxyl apatite (Ca 5 (PO 4) 3 OH). Recharging contributions to spring water chemistry deviate from those produced by rock weathering, precipitation and evaporation/crystallization. An enrichment process is therefore predicted as a recharging contributor to water chemistry.
The sedimentology and geochemistry (major and trace element compositions) of lignite and argillite (carbonaceous shale and claystone) sequences in a Basin in Bali Nyonga, west of the Bamenda Mountain have been investigated to determine their sequences and the prevailing environmental conditions which control their formation. Ten representative samples were obtained from trenches, pits, and river and stream valleys in the study area. These samples and their ashes were subsequently examined using X-ray fluorescence spectrometry (XRF), inductively coupled plasma spectrometry (ICP), and X-ray diffraction analysis (XRD). The geochemical results revealed that the lithophile, chalcophile and siderophile elements were dominantly epigenetic in origin, mainly from detrital sources supported by high silica and alumina concentrations in all the samples. The mineral phases identified were quartz, kaolinite, illite, pyrite, hematite, and minor phases of feldspars, pseudorutile. The relatively high silica (54.10 wt%) and alumina contents (27.77 wt%) in these samples can be explained by high detrital input during peat formation. The low contents of MgO and CaO in the analysed samples agree very much with the continental setting of the peat formating basin. A clayey microband derived from alkaline volcanic ashes was identified in the lignite and the dominant composition of these clayey microbands was mixed-layer clay minerals of illite and kaolinte, which were interlayered with organic bands. The modes of occurrence of ash bands indicated that the volcanic activities were characterized by multiple eruptions, short time interval and small scale for each eruption during peat accumulation. The ratios of redox-sensitive trace element (V/Cr versus Ni/Co and V/V + Ni versus Ni/Co), Sr/Ba, and major oxides ratio (CaO + MgO + Fe2O3)/(SiO2 + Al 2 O 3) from the analysed samples from Bali Nyonga indicate a terrestrial, reductive (oxic), littoral to brackish water environmental conditions which are characteristics of paludal-lacustrine basin that is filled by Tertiary volcanic materials.
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