THE EFFECTS OF PHOSPHATIZATION ON THE REY OF CO-RICH FE-MN CRUSTS

Rare earth elements and yttrium (REY) are extremely coherent in the nature. The relative abundances of them can be used to deduce their sources or subsequent geological processes. Major elements and REY of the Co-rich Fe-Mn Crusts from Marcus-Wake Seamounts and Mid-Pacific seamounts are analyzed by XRF and ICP-MS. Combined with previous studies, REY characteristic of phosphatized and non-phosphatized Fe-Mn Crusts are emphasized respectively. Fe-Mn Crusts with low P have low ΣREY and notably positive Ce anomaly, as well as negative yttrium anomaly, after normalized by the North American shale composite(NASC). While Fe-Mn Crusts with high P have relatively high ΣREY, positive Ce anomaly and notably positive yttrium anomaly normalized by NASC. There must exist REY-rich phosphate components in the phosphatized Co-rich Fe-Mn Crusts, which are especially rich in yttrium. The issue of phosphatized crusts could be regarded as a mixed model of phosphate components and Fe-Mn crust components. Mixed model simulating result indicates that REY-rich phosphate components in Fe-Mn Crusts have the same REY pattern as seamount phosphate rock, but the content could be more than 10 times over that of seamount phosphate rock. Besides REY³⁺ and Ca²⁺, other alkali-earth metal ions can also be bound to PO₄^3- in water column, and there are numerous calcareous sediments in ocean, PO₄^3- can replace CO₃^2- in carbonate sediments to form REY-poor phosphate. However, the growth of the Fe-Mn Crust is so slow that REY has a better environment to compete with Ca at the time of PO₄^3- input, forming dissemination REY-rich phosphate. Although PO₄^3- is still mainly bound with Ca²⁺ in REY-rich phosphate, ΣREY/Ca ratio increases remarkably. This REY enrichment model may be a common geological process in non-calcium sediments in deep sea.