Gemstones-bearing sediments in the Mbiame floodplain, northwestern Cameroon
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ORIGINAL ARTICLE
Gemstones‑bearing sediments in the Mbiame floodplain, northwestern Cameroon Mary Ewokolo Molua Mbua Etutu1 · Cheo Emmanuel Suh1,2 · Akumbom Vishiti4 · Elisha M. Shemang3 · Christopher M. Agyingi1 · Julio C. Mendes5 Received: 4 August 2020 / Revised: 12 October 2020 / Accepted: 14 October 2020 / Published online: 3 November 2020 © Springer Nature Switzerland AG 2020
Abstract Sediment samples obtained from pits in the Mbiame floodplain gemstone prospect in the northwestern part of Cameroon were studied for their bulk geochemical properties together with the mineral composition of the gemstones found therein to decipher their provenance. Five main layers were isolated in each pit comprising an organic rich humus layer, muddy layer, unconsolidated and poorly sorted sandy layer, clay layer and gravel layer. The gravel layer is the most high-yielding in terms of gemstones content. The sediments have high rare earth element (REE) concentrations varying between 135 and 456 ppm with variable light/heavy rare earth element (LREE/HREE) ratio values (5.8–21.5). REE chondrite normalized patterns show similar high LREE enrichment and no Eu anomalies (Eu/Eu* = 0.9 − ~ 1) for all samples. The gemstones selected from the various horizons range in color from light gray, light blue/green, dark blue, pale brown and red. Some of the grains have zircon and ilmenite mineral inclusions while some of the zoned grains show simple core—rim zonation as well as oscillatory and sectorial zoning patterns. Bulk sediment geochemistry of sediments from the Mbiame gem prospect suggests an igneous provenance generally of felsic intermediate source input. The alluvial gemstones from the Mbiame gem prospect are the sapphire variety of corundum and the grains combined with zircon and ilmenite inclusions and megacrysts suggest a derivation from felsic to intermediate igneous rocks. Keywords Sediment provenance · Geochemistry · Gemstones · Inclusion · Mbiame gem prospect · Cameroon
Communicated by M. V. Alves Martins Electronic supplementary material The online version of this article (https://doi.org/10.1007/s43217-020-00033-4) contains supplementary material, which is available to authorized users. * Mary Ewokolo Molua Mbua Etutu [email protected] 1
Department of Geology, University of Buea, P.O. Box 63, Buea, South West Region, Cameroon
2
Department of Geology, Mining and Environmental Science, University of Bamenda, P.O. Box 39, Bamenda, North‑West Region, Cameroon
3
Department of Earth and Environmental Sciences, Botswana International University of Science and Technology, Private Bag 16, Palapye, Botswana
4
Department of Civil Engineering, University Institute of Technology, University of Douala, P.O. Box 8698, Douala, Cameroon
5
Departamento de Geologia, IGEO, Universidade Federal do Rio de Janeiro, Cidade Universitaria, Rio de Janeiro 21910‑949, Brazil
1 Introduction During the transport from source to sink, detrital materials are separated according to their grain size, shape and density, and
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