Partition of Some Metal Elements in Pacific Pelagic Sediments

Abstract

Pelagic surface sediments and their coarse fraction from the Central Pacific Basin were under extraction by hydroxylamine hydrochloride and acetic acid. Both the parts extracted and residual were analyzed for Fe, Mn, Co, Ni, Cu and Zn, and mineral composition of the residual parts were studied by means of X-ray diffraction.
The most refractory element among the six is Fe, while Mn is the most soluble. It is noteworthy that about a half amount of Cu stay in the residual part while only about 20% of Ni does.
The chemical composition of the extracted part from the coarse fraction of sediment are grouped into two trends in Mn/Fe-Cu/Ni diagram. One of the trends is characterized by a reverse correlation between Mn/Fe and Cu/Ni ratios and represents the expected characteristics of residual matter after preferential removing of Mn versus Fe, and Ni versus Cu from metal oxide and/or oxyhydroxide during early diagenesis. Another trend is characterized by rather positive correlation between Mn/Fe and Cu/Ni ratios, representing primary precipitates from sea water, secondary reprecipitates through early diagenesis, and/or mixture of them just like nodule composing minerals.
It is clarified that Fe, Cu and Zn in the residual part is dominantly localized in smectite and that a part of the smectite is captured or cemented in recrystallized radiolarian tests. Whereas dominant amount of Mn, Co and Ni all in the residual phase may be localized in ferro-manganese oxide and/or oxyhydroxide captured or cemented in recrystallized radiolarian tests. We infer authigenic origin of the smectite, though the mineral species is not disignated. In the area studied, biogenic silica, iron and aluminum of various origins may form smectite with together, uptaking more than a half of total Cu and Zn during early diagenesis.