Geochemical characteristics of seamount ferromanganese nodules from mid-Pacific Ocean

Nine seamount ferromanganese nodules fromsix seamounts in the mid-Pacific Ocean have been sampled,the obtained sixteen sub-samples were used to analyze theirmain elements, trace elements and rare earth elements by thechemical method and ICP-MS, platinum group elementshave also been analyzed for some subsamples, using themethods of Te co-precipitation pre-concentration and isotopedilution. All subsamples have been analyzed by X-ray dif-fraction for their mineral composition. It is shown from theanalysis results that the mineral composition, chemicalcharacteristics and the occurrence of main components ofseamount nodules from mid-Pacific Ocean are similar tothose of hydrogenous cobalt-rich crust on seamounts, whichindicates that seamount nodules were hydrogenous. Com-pared with the ferromanganese nodules occurring on thesurface of deep-sea sediments, seamounl nodules have higherFe and Co but lower Cu and Ni, so the seamount nodulesfrom mid-Pacific Ocean might be formed on the surface ofsediments on seamounts in weak acidic but strong oxidationenvironment. Because of their similar occurring depth andredox conditions, seamount nodules are very similar to co-balt-rich crust in their chemical composition, minerals andoccurrence of main compositions. However, having beenfound on the sediment-seawater interface, seamount nodulesexperienced the influence of early-diagenesis of sediments, sothe typical seamount crust has some characteristics of tran-sition to ferromanganese nodules.