MINOR AND RARE ELEMENTS IN MANGANESE CRUSTS AND NODULES AND SEDIMENTSFROM THE MANIHIKI PLATEAU AND ADJACENT AREAS - RESULTS OF HMNZS TUI CRUISES

Six manganese crusts, 13 manganese nodules, and 16 sediments were anal yzed by instrumental neutron activation analysis. Data were generated on selected major and minor elements but geochemical evaluations are b ased only on Fe, Sc, U, Th, and the rare earth elements (REE). Mangane se dusts and manganese nodules have comparable trivalent REE contents and show a shale-like distribution pattern. Both crusts and nodules ar e characterized by a positive Ce anomaly but the anomaly is higher in nodules. REE contents in manganese nodules show a linear dependence on the Fe content, and it is concluded that these elements are incorpora ted in the Fe-rich (delta-MnO2) phase. In the crusts, the REE correlat e with Sc and ave therefore assumed to be associated with the clay min erals. Uranium contents are significantly higher in the crusts than in nodules whereas Th is slightly higher in the nodules. There is a clea r positive correlation between U and Th in nodules but there are too f ew data to make a similar conclusion for crusts. Compositional data su ggest a division of the sediments into two groups. The carbonate sedim ents have much lower REE contents and a more pronounced negative Ce an omaly than the clays, while both show a lithogenous component as indic ated by a slight negative Eu anomaly.