Abstract:

The Co-rich Fe-Mn crust sample, MKD23B-3, was dredged from Seamount MK of Magellan Seamount cluster at a water depth of about 2 170 m. Major elements, rare earth elements (REE) as well as Y compositions along the section of this sample are analyzed by ICP-OES and ICP-MS. The existing phases of REE and Y are investigated based on linear correlation analysis. The section of this sample can be divided into 5 layers from substrate to surface, the layers Ⅰ-Ⅱ of this Co-rich Fe-Mn crust are phosphatized and the layers Ⅲ, Ⅳ and Ⅴ are non-phosphatized. In nonphosphatized layers, REE and Y are mainly distributed in the phase of δ-MnO₂. In phosphatized layers, besides in the phase of δ-MnO₂ and Fe oxyhydroxides, REE  and Y are mainly consisted in the phase (probably REE phosphate) independent from carbonate fluorapatite. A new method for calculation of secondary REE in phosphatized Fe-Mn crusts is proposed, and the secondary rare earth elements in the phosphatized layers Ⅰ and Ⅱ of Corich Fe-Mn crust MKD23B-3 are calculated. In the phosphatized layers, the secondary rare earth elements are 42%-88% of total rare earth elements, which indicates nearly more than half of total REE in phosphatized Fe-Mn crustal layers are secondary, and the effect of phosphatization is significant during the enrichment of secondary REE. It’s concluded that the contamination of secondary rare earth elements should be excluded from the paleoceanographic record of REE (especially Nd) in phosphatized Fe-Mn crusts.

Key words: Co-rich Fe-Mn crusts, rare earth elements, existing phase, Magellan Seamount cluster