铁锰结核的矿物相变和其它次生变化

MINERAL FACIES CHANGES AND SECONDARY CHANGES IN FERRO-MANGANESE NODULES

本文通过对太平洋中部61个铁锰结核的研究,发现在结核形成后,发生了渐近相变、退化相变和Mn、Ni、Cu的次生富集作用。渐近相变是,随着结核成岩作用的增强(伴随着氧化还原电位由高到低的变化),锰矿物发生了由原生δ-MnO_2→环带状、薄层状钠水锰矿和钡镁锰矿→块状磷片状钡镁锰矿集合体的相变。在这一相变系统中钠水锰矿是相变的过渡阶段,钡镁锰矿是相变的高级阶段。退化相变:具层纹构造的原生δ-MnO_2在底层水(可能贫Mn、Ni、Cu而富Fe)的作用下,其中一部分Mn、Ni、Cu等被水带走而沉淀下Fe,形成新的富Fe、δ-MnO_2或非晶质水合铁锰氧化物。Mn、Ni、Cu的次生富集作用。结核在重结晶作用或由结核成岩作用到成岩后生作用过程中均发生了Mn、Ni、Cu的次生富集作用。它不仅表现在由原生δ-MnO_2→环带状钠水锰矿和钡镁锰矿→块状钡镁锰矿过程中,而且还表现在由早期到后期形成的δ-MnO_2成分上。

Studies of 61 ferro-manganese nodule samples from the central Pacific Ocean have shown that manganese minerals underwent progressive and degenerative facies changes and secondary enrichment of Mn, Ni, Cu. Progressive facies changes mean that with intensifying diagenesis (following Eh changes from high to low) the nodules underwent such facies changes as from primary δ-MnO_2 to zoned and laminated birnessite and todorokite to massive and scaly aggregates of todorokite. In this system birnessite is the transition member involved in facies changes and todorokite is the product of facies change at higher stage. Degenerative facies change: under the action of sea floor water (poor in Mn, Ni, Cu but rich in Fe), Mn, Ni and Cu in the primary δ-MnO_2 were partly carried out by water, followed by precipitation of Fe, thereby forming feruginous δ-MnO_2 or amorphous ferro-manganese hydrates. Secondary enrichment of Mn, Ni and Cu: in the process of recrystallization or in the time period from diagenesis to de uterogenesls of nodules. It is not only reflected in changes from the primary δ-MnO_2 to zoned and laminated birnessite and todorokite to masslye scaly aggregates of todorokite, but also in the chemical composition of δ-MnO_2 formed at early to late stages.