Elemental Variations Induced by Phosphatization and Controlling Factors of REY in Phosphatized Crusts from the Lemkein Seamount, Western Pacific

Abstract

Phosphatized crusts from the Lemkein seamount were analyzed to confirm effects of phosphatization on elemental composition. Major phases of the ferromanganese crusts were observed with their compositions using SEM and it was verified by XRD. Ten samples of specific depth in a phosphatized ferromanganese crust CD 5-5 were collected by drilling, and measured by ICP-AES for major and minor elements and ICP-MS for trace elements. Thin section faced with drilled sites were analyzed by EPMA and LA-ICP-MS. Elements such as Co, Al, Ti, Fe, As, and Mn are depleted, otherwise, other elements like Zn, Ni, and Cu are enriched compared to non-phosphatized crusts. These major trends of elemental variation between non-phosphatized crusts and phosphatized crusts are coincident with previous study. Elemental variations are induced by recrystallization of Mn oxides, loss of Fe phases, and formation of carbonate fluorapatite (CFA). Ce enrichment is observed in discrimination diagram using REY, and Ce and Mn are strongly related based on correlation coefficients number tables (CC # tables). It suggests that Ce is enriched in one of Mn oxide phases rather than CFA. Positive correlation between REE and Ca/P ratios with increasing correlation coefficients as increasing atomic number is observed. It indicates that REE contents are controlled by anion composition of CFA at similar P concentrations in phosphatized crusts. Y also displays analogous correlations, but is less remarkable than REE. LA-ICP-MS displays distinct differences between the phases composing phosphatized crusts, and respective phases have typical REY pattern depending on major phases of ablated area. Total REE contents except Ce are enriched in CFA aggregates and are depleted in todorokite. REY contents and patterns are controlled by loss of primary ferromanganese phases and compensation by secondary phosphatized phases.