『Abstract
　Mineralogy and geochemistry of the ferromanganese oxides collected from two seamounts in the Andaman Sea have been investigated with special reference to the solid phase partitioning behaviour of rare earth elements (REEs). Bulk elemental compositions indicate that the oxides from a volcanic cratered seamount, CSM, are hydrothermal while those from another seamount, SM2, are hydrogenous in origin. The distributions of REEs and yttrium in four geochemical phases (viz. easily exchangeable, Mn-oxide, Fe-oxyhydroxide and residual) of CSM-oxides were distinctly different from that of SM2-oxides. In CSM-oxides, the REEs and yttrium are mainly associated with Fe-oxyhydroxide phase while in SM2-oxides, both Mn-oxide and Fe-oxyhydroxide phases contain the major fraction of these elements. The exchangeable and residual phases of both hydrothermal and hydrogenous oxides have extremely low REE-content. The shale normalized negative Ce-anomalies and relative enrichment of heavy REE, characteristic of hydrothermal oxides, are retained in Fe-oxyhydroxide phase. In hydrogenous oxides, the positive Ce-anomalies occurred in both Fe and Mn^oxide phases while negative Y-anomalies were found only in Fe-oxyhydroxide phase. The phase distribution of REEs and yttrium in hydrothermal oxides is described in terms of co-precipitation and adsorption of their halide complexes and available free ions in hydrothermal solutions. Instead, adsorption of major carbonate species from seawater primarily regulates the partitioning of REEs among the coexisting phases of hydrogenous oxides.

Keywords: Ferromanganese oxide; Hydrothermal; Hydrogenous; Yttrium; Rare earth elements; Elemental speciation』

1. Introduction
2. Sampling locations and sample description
3. Analytical techniques
　3.1. Mineralogical analysis
　3.2. Bulk geochemical analysis
　3.3. Iron isotope analysis
　3.4. Sequential leaching and chemical analysis of leachates
4. Results and discussion
　4.1. Mineralogy, bulk geochemistry and growth rates of ferromanganese oxides: The genetic perspective
　4.2. Geochemistry of REEs and yttrium in ferromanganese oxides: processes involved in hydrogenous and hydrothermal precipitation
　　4.2.1. Bulk REEs and yttrium composition
　　4.2.2. Relative abundance of REEs and yttrium in sequential leachates
　　4.2.3. Shale normalized REE-yttrium-patterns of sequential leachates
5. Conclusion
Acknowledgment
References