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Ce anomalies and trace element distribution in Sardinian lithiophorite-rich Mn concretions

Mongelli, Giovanni and Sinisi, Rosa and Mameli, Paola and Oggiano, Giacomo (2015) Ce anomalies and trace element distribution in Sardinian lithiophorite-rich Mn concretions. Journal of Geochemical Exploration, Vol. 153 , p. 88-96. ISSN 0375-6742. Article.

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DOI: 10.1016/j.gexplo.2015.03.004


Supergene concentrations of lithiophorite found in alluvial conglomerates and residual sandy clay deposits of Messinian age in northern Sardinia, were investigated for minero-chemical composition and fractionation processes. The Mn concentration occurs as cement in conglomerate, coatings on pebbles and as concretions in clays. In the mineralisation, some transition metals including Ni, Cu, and Zn along with Ba, U, Pb, and REEs, are enriched relative to the composition of the upper continental crust. Zn and Ni co-vary with Mn, suggesting that they are hosted in lithiophorite. Also the REEs, with the exception of Ce, co-vary with Mn. Ce, due to its redox chemistry, fractionates relative to the other REEs and precipitates as cerianite during Mn4+ reduction. Mn mineralisation has a different Ce signature as expressed by the Ce anomaly, which varies between 0.22 and 11.75. A two-stage model was proposed for explaining the Ce anomaly fluctuations. Precipitation of the samples with positive Ce anomalies occurred in the first stage from organic matter-free fluids which favored the oxidation of cerium on the Mn phase surface; in the second stage, instead, Ce-depleted solutions, resulting from the first stage, were responsible for the precipitation of samples with negative Ce anomalies.

Item Type:Article
ID Code:11001
Uncontrolled Keywords:Mn mineralisation, lithiophorite, REEs fractionation, sediments, Sardinia, Italy
Subjects:Area 04 - Scienze della terra > GEO/09 Georisorse minerarie e applicazioni mineralogico- petrografiche per l'ambiente ed i beni culturali
Area 04 - Scienze della terra > GEO/03 Geologia strutturale
Divisions:001 Università di Sassari > 01-a Nuovi Dipartimenti dal 2012 > Scienze della Natura e del Territorio
Deposited On:11 Jun 2015 11:05

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