Residence and fractionation of rare earth elements during kaolinization of alkaline peraluminous granites in NW Spain
| Autor: | M. G. Márquez, Patricia Aparicio, Emilio Galán, J.C. Fernández-Caliani, A. Miras |
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| Rok vydání: | 2007 |
| Předmět: |
Geochemistry
Mineralogy 020101 civil engineering Weathering 02 engineering and technology engineering.material 010502 geochemistry & geophysics Feldspar 01 natural sciences 0201 civil engineering Geochemistry and Petrology visual_art Monazite Illite engineering visual_art.visual_art_medium Kaolinite Clay minerals Geology Ilmenite 0105 earth and related environmental sciences Zircon |
| Zdroj: | Clay Minerals. 42:341-352 |
| ISSN: | 1471-8030 0009-8558 |
| Popis: | A geochemical and mineralogical study has allowed us to address the factors controlling distribution pattern, residence and behaviour of rare earth elements (REE) during kaolinization of Variscan granitoids in NW Spain. Mineral composition of the deeply weathered samples is dominated by kaolinite, with minor amounts of quartz, muscovite-illite, alkaline feldspar and traces of resistant minerals (rutile, ilmenite, zircon and monazite). Variable amounts of Si, Na, Ca, K, Rb, Cs, Ba, U and P were lost from the weathering profile, as a result of feldspars, mica and apatite breakdown, whereas Al, Fe, Ti, Zr, Th, Hf and REE were concentrated in the residual kaolin. Chondrite-normalized REE patterns of the kaolins show an overall enrichment of light REE (LaN/SmN = 1.22–2.53), heavy REE depletion (GdN/YbN = 2.42–15.10) and a strong negative Eu anomaly (Eu/Eu* = 0.11–0.25), probably inherited from the parent granite. Nevertheless, the normalization to the parent granite reveals some REE fractionation and increasing positive Eu anomalies with advancing weathering, in response to the breakdown of feldspars. Different grain-size fractions show similar REE distribution patterns, but differ in concentration levels. Although the fine fractions are the most important REE reservoir, there is no positive correlation with clay mineralogy. The correlative behaviour among P2O5, Th and REE in the REE budget in the weathering profile. |
| Databáze: | OpenAIRE |
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