A comparison of REE geochemistry between polymetallic nodules and cobalt-rich crusts in the Pacific Ocean

Abstract： Polymetallic nodules and cobalt-rich crusts are two types of ferro-manganese deposits in the ocean. In order to probe into their REE geochemical characteristics in different oceanic areas of the Pacific Ocean, the authors collected samples from eastern Pacific basin, central Pacific Ocean and western Pacific Ocean and examined REE characteristics by means of ICP-AES. There are obvious positive Ce anomalies, rich LREE (light REE) and high total REE (∑REE) in the crusts. In contrast, there are rich HREE (heave REE) and relatively low ∑REE in the nodules, Ce anomalies have different styles, such as positive, negative and indistinct anomalies caused by different genetic types of nodules. The “M” type tetrad effects of nodules indicate that the nodules have suffered diagenesis, while the crusts have not been subjected to this effect. There exist different modes of occurrence of REE in nodules and crusts in different oceanic areas. REE in the crusts from central Pacific Ocean and in the nodules from eastern Pacific Ocean probably exist in the Fe-mineral phase, whereas REE in the crusts from western Pacific Ocean might exist in the Mn-mineral phase. REE in the nodules and crusts might have been mainly derived from seawater and seamount altered basalt respectively, with limited hydrothermal contribution.