Abstract: The mineral composition and the contents of the oreforming and rare earth elements in different spherical layers of Co-rich nodules, collected from the YJB Sea Mount in the MARCUS Ridge in the central Pacific ocean, were determined using ICP-AES,ICP-MS,XRD,FT-IR and JSM. The results show that the spherical nodules consist of a basalt core and four surrounding spherical layers. In the nodules, the ore minerals include vernadite and a small amount of todorokite, gangue minerals are apatite quartz and plagioclase and minor minerals are montmorillonite, kaolinite, natrolite, cristobalite, pyroxene, stibite and others. TMn, Cu, Ca and P are relativily enriched in the old nodules while TFe, Co, Ni, Si and Al are enriched in new nodules. In both the old and new nodules, the contents of TMn, Co, Ni, Cu, Ba, Zn, Pb and Mo are gradually decreased from the underlying layers outwards and that of TFe is increased. The core basalts belong to WPB. Their total REE contents are measured to be 1 924.07×10^-6 with distinctively positive Ce anomalies. In different spherical layers of both the old and new nodules the varying tendency of Ce is similar to that of TMn while varying tendency of other REE to that of Fe.

Key words: Pacific ocean, Co-rich nodule, mineral composition, element geochemistry