The effect of phosphatization on chemistry of marine cobalt -rich ferromanganese crusts was studied on a small scale. The interval of subsampleing from top to bottom for a 10-cm thick sample from a Magellan seamount, NW Pacific is 5 mm. The concentration profiles of ore-forming and rare earth elements show that obvious difference exists between the young unphosphatized crusts and old phosphatized crusts. Fe, Mn, Si, Al, Zn, Mg, Co, Ni, Cu elements are depleted and Ca, P, Sr, Ba, Pb elements are enriched in old crusts. The order of depletion and enrichment is Co > Ni > Mg > Al > Mn > Si> Cu > Zn > Fe and P > Ca > Ba > Pb > Sr separately. It is concluded that the phosphate mineral controls the concentration variation of ore-forming elements in crusts and causes the loss of Co, Ni etc. main ore-forming elements. The abundance of REEs and the content of Ce in old crusts are higher than those in young crusts, however, the pattern of REEs and their fractionation characteristic in new and old crusts are not changed fundamentally. Y positive anomaly in old crusts has no relation with the phosphatization. The research on phosphatization of co-rich crusts supplies useful information for the evaluation and comprehensive utilization of crust mineral resources.
Co-rich ferromanganese crusts occuring in submarine guyots have received much attention by many scientists since the begining of 1980's because they are enriched in Co, Mn, Pt, rare earth elements, and have large potential mineral resources, as well as occurring at shallow depths relative to polymetallic nodules in C-C zone (Halbach et al. 1982,1989, Hein et al. 1992,1999, Usui et al.1997, Yamazaki et al. 1998,2000, De Carlo et al.1987, Pan et al.1999, Wen et al.1997).