Rare earth and other chemical element contents and partitions in bottom sediments, micronodules, and nodules from the bioproductive zone of the Pacific Ocean@en

Concentrations and compositions of rare earth elements (REE) in three micronodule fractions (50-250, 250-500, and >500 ?m), coexisting macronodules, and host sediments were studied. Samples were collected at three sites (Guatemala Basin, Peru Basin, and northern equatorial Pacific) located in elevated bioproductivity zones of surface waters. Influence of micronodule size is dominant for REE compositions and subordinate for REE concentrations. For example, Ce concentration inversely correlates with micronodule size and drops to the lowest value in macronodules and host sediments. Decrease of Ce concentration is generally accompanied by Mn/Fe increase in micro- and macronodules. Hence, the role of diagenetic source of material directly correlates with micronodule sizes. Contribution of the diagenetic source is maximal for macronodules. REE composition distinctions for micronodules and macronodules can be attributed to variations of hydrogenic iron oxyhydroxides and diagenetic (hydrothermal) iron hydroxophosphates that are the major REE carriers in ferromanganese ore deposits. Relationship and general trend in chemistry of coexisting macronodules suggest that they can represent products of the initial stage of nodule formation.本研究对三个粒级微结核（50-250、250-500及>500微米）、伴生大结核以及宿主沉积物中的稀土元素（rare earth elements, REE）浓度与组成特征展开了分析。样本采集于三处位于表层水体高生物生产力区的站位：危地马拉海盆、秘鲁海盆与北赤道太平洋海域。微结核粒径对稀土元素组成的影响占据主导地位，而对稀土元素浓度的影响则相对次要。例如，铈（Ce）浓度与微结核粒径呈负相关关系，并在大结核及宿主沉积物中降至最低值。通常而言，微结核与大结核内铈浓度的降低往往伴随锰铁比（Mn/Fe）的升高。由此可见，物质成岩来源的作用与微结核粒径直接相关，其中大结核的成岩来源贡献最大。微结核与大结核之间的稀土元素组成差异，可归因于铁锰矿床中作为稀土元素主要载体的水成铁氢氧化物与成岩（热液）羟基磷酸铁的变化。伴生大结核的化学特征及其整体变化趋势表明，其可代表结核形成初始阶段的产物。