| Abstrakt: |
Rare earth and trace element concentrations of Ngoma clay materials in the Douala sedimentary subbasin in Cameroon (Matanda-Wouri Miocene-Pliocene Formation) were studied in order to determine their provenance. X-ray diffraction and inductively coupled plasma mass spectrometry (ICP/MS) were performed to determine the mineralogical and chemical composition respectively of Ngoma clayey materials. Clayey materials consist mainly of kaolinite, smectite, quartz, l'ilmenite, goethite, l'hematite, anatase, minor amounts of K-feldspar, and occasionally muscovite, gypsum, corundum, and the pyrite. Total REE concentrations of these clay sediments reflect the variations in their grain-size fractions. The average value of Eu/Eu* (0.5), La/Sc (9.9), Th/Sc (3.4), La/Co (21.7), and Th/Co (7.2) ratios support essentially a felsic rock source. Moreover, Th and LREE abundances of Ngoma clay materials reflect those of felsic igneous rocks. Chondrite-normalized rare earth element (REE) patterns display LREE enrichment, flat HREE, and negative Eu anomaly, attributed to felsic rocks source main characteristic of Ngoma clay sediments. Immobile element canonical ratios (Nb/Y, Zr/Ti) indicate that the felsic rocks were syenite and monzodiorite or their metamorphic products. [ABSTRACT FROM AUTHOR] |
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