『Abstract
　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.

Keywords: Hong Kong; Fe, Mn, Ce; Oxyhydroxides; Rare earth elements; Weathering』

1. Introduction
2. Materials and methods
3. Results and discussion
　3.1. Early stages of weathering
　　3.1.1. Mn-free Fe-rich oxyhydroxides
　3.2. Advanced stages of weathering
　　3.2.1. Co-existing Mn- and Fe-rich oxyhydroxides
　　3.2.2. Co-existing Fe-, Mn- and Ce-rich oxyhydroxides
　3.3. Distribution of REE
4. Summary and conclusions
Acknowledgments
References