Journal
JOURNAL OF ASIAN EARTH SCIENCES
Volume 34, Issue 1, Pages 1-9Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.jseaes.2008.03.010
Keywords
Hong Kong; Fe, Mn, Ce; Oxyhydroxides; Rare earth elements; Weathering
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Funding
- Research Grants Council of the Hong Kong Special Administrative Region, China [HKU 7002/03P]
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Variation in type and abundance of oxyhydroxide phases and the fractionation of rare earth elements (REE) within a weathered felsic pyroclastic profile in Hong Kong were investigated in order to assess the key factors and micro-environmental conditions controlling their distribution during weathering at rock and mineral scales. Three types of oxyhydroxide phases (Fe-, Mn- and Ce-rich) were recognized based on their most abundant elements. The Fe-rich types appeared in all samples at different stages of weathering. The Mn-rich types, however, were limited to samples at advanced stages of weathering, while the Ce-rich types were found solely in samples from oxyhydroxide-rich zones. Fractionation of REE likely started at the early stages of weathering, but became evident only at the advanced stages. Characteristics of REE patterns, especially the direction (negative or positive) and extent of Ce-anomalies, correlated very well with the appearance and abundance of Mn-oxyhydroxides, and were attributed to the co-existence of distinct micro-environmental conditions within the profile. These conditions resulted from two major competing processes, leaching and fixation and oxidation (precipitation) and reduction (dissolution), which operated simultaneously within the profile at any given stage of weathering. (C) 2008 Elsevier Ltd. All rights reserved.
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