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Contrasting Depositional Environment of Iron Formation at Endengue Area, NW Congo Craton, Southern Cameroon: New Insights from Trace and Rare Earth Elements Geochemistry

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Document pages: 27 pages

Abstract: TheEndengue Banded Iron Formation (BIF) is located in the northwestern edge of theCongo craton in Cameroon. Here, wereport geochemical data of trace and rare earth elements (REE) of the EndengueBIF samples from the Archean Ntem complex and investigate their environmentalsetting. Two types of BIF occur at Endengue area, both containing minimalcontamination from terrestrial material. Total REE (ΣREE) contents in the Type 1 BIF are extremely low,ranging from 0.34 to 1.83 ppm, similarly to pure chemical sediments while Type2 BIF displays ΣREE contents ranging from 2.98 to 24.26 ppm. ThePAAS-normalized REE + Y patterns of the two BIFtypes display LREE enrichment relative to HREE and weak positive Eu anomaly,most likely suggesting that the source of iron and siliceous of the EndengueBIFs is mainly from the contribution of low-temperature hydrothermal alterationof the crust. Type 1 BIF shows very low Nd content (* and positive Ce anomalies which suggests suboxic or anoxic seawatersimilar to the depositional environment of Elom BIF in Archean Ntem complex. Incontrast, Type 2 BIF displays low to moderate Nd contents (1 and 100 ppm withthe exception of sample LBR65) with negative correlation between Nd and Ce Ce* and negative Ce anomalies.These features indicate precipatation of Type 2 BIF from oxic iron-rich solutionthat changed to oxidized surface by rapid precipitation of the hydrothermal Fe.The Endengue BIFs were deposited in the continental margin ocean in presence oflow-temperature hydrothermal fluids mixed with seawater, similar toPaleoproterozoic Kpwa-Atog BogaBIFs within the Nyong group and other Paleoproterozoic Superior-type BIFs worldwide.

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