DOI: 10.5593/sgem2017/11/S01.005


V.I. Mamedov, M.A. Makarova, E.S. Shipilova
Saturday 9 September 2017 by Libadmin2017

References: 17th International Multidisciplinary Scientific GeoConference SGEM 2017, www.sgem.org, SGEM2017 Conference Proceedings, ISBN 978-619-7105-98-8 / ISSN 1314-2704, 29 June - 5 July, 2017, Vol. 17, Issue 11, 35-48 pp, DOI: 10.5593/sgem2017/11/S01.005


The paper concerns the geochemical trends (loss and accumulation) of trace elements studied in the lateritic weathering profile of Futa Jallon-Mandingo Province and related to weathering of silty mudstones and dolerites.
Whatever their composition, structure, texture, strike, and dip the bauxite-bearing weathering mantles usually show a zoned profile consisting of two generic horizons. The lower horizon mainly consists of clays grading in the mineralogical composition from polymineralic, with fragments of slightly weathered parent rocks, in the lower part (the saprolite) to essentially kaolinitic, with increasing iron, in the upper part (the lithomarge). The upper horizon is mainly composed of iron and aluminum oxides and hydroxides and includes the laterites of transition zone, the bauxite horizon, and the cuirass. This horizon can be considered as the properly lateritic mantle.
The zoning of lateritic weathering profile has originated from the infiltration metasomatism and the physicochemical environment varying over the profile. Therefore, each subjacent horizon should be considered as the protolith of each superjacent horizon. Samples of each horizon have been analyzed for trace elements by inductively coupled plasma mass spectrometry (ICP-MS). The analyses were made by a device ELEMENT 2 produced by Thermo Finnigan, at laboratories of the Lomonosov Moscow State University. Comparison between the weathering profile zones in the trace element composition calculated on isovolumetric base (as absolute abundances) allows better understanding the behavior of trace elements, their loss and accumulation from zone to zone. Such a comparative analysis was made with each of the 55 trace elements measured, using its concentration ratio (Rc) calculated as its absolute abundance ratio of superjacent to subjacent horizon. Rc > 1 is a case of the element absolute accumulation, whereas Rc < 1 is a case of the element loss. Absolute value of Rc is a function of loss/accumulation intensity in the horizon.

Keywords: bauxite, lateritic weathering profile, migration, trace elements, concentration factor

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