Contribution of Major, Trace and Rare Earth elements in the determination of sandstone and pelite source rocks in Bangue (Cameroon).

Résumé

The Ngola Series (upper part of low Dja Series) is mainly composed of fine grained rocks commonly called pelites, associated with sandstones. The qualitative and semi-quantitative measurements of clay abundance with Macdiff software were carried out by Brucker X-ray diffractometer. These measurements were done on normal sample, heated sample, and sample with glycerol. The major element geochemical analysis was performed by X-ray fluorescence spectrometry; whereas trace and rare earth elements abundance were analyzed by Iductively coupled Plasma Mass Spectrometry (ICP-MS)

The mineralogical suites in bangué sandstones and pelites include: argillaceous minerals (Illite and Kaolinite) and non argillaceous minerals (goethite, gibbsite...). Elementary grouping based on their correlation suggests a slightly dominance of mafic minerals (biotite, amphibole, and a titanium mineral), apatite, and Ce enriced mineral (zircon).

Various elementary ratios and the high value of the chimemical weathering index (CWI > or = 90%) is typical of harsh weathering activities within the lithified sediments source area. The use of La-Th-Sc ternary diagram, and samples distribution pattern in Co/th versus La/Sc and K2O, show that the distributed elements found in the lithified clasts were sorted from mafic to intermediate source rocks.

Key word: Chemical composition, source rock, pelites, sandstones