Some controls on the geochemical variability of manganese nodules with particular reference to the tropical South Pacific

Abstract

Superimposed on traditional controls on manganese nodule compositional variability, such as metal source and nodule mineralogy, are additional controls related to biological productivity, water depth, the depth of the calcite compensation depth (CCD) and the nature of the associated sediments. Fluxes of Mn, Ni, and Cu to the nodules increase in equatorial regions of high biological productivity but high values of these metals in south equatorial Pacific nodules appear to occur only within about 200 m of the CCD. This is thought to result from the concentration of labile organic matter there, the decay of which fuels the diagenetic reactions leading to Mn, Ni, and Cu enrichment in the nodules. However, this process appears to be at its most intense on the flanks of the South Pacific equatorial high productivity zone. Under the most highly productive waters, Mn, Ni, and Cu rich nodules do not occur at any depth nor are nodules abundant there. This is thought to be due to the presence of biogenic silica, the concentration of which is not depth dependent, as the main diluent of the labile organic material at depths near and below the CCD under the most highly productive waters.

Submarine hydrothermal manganese deposits in the Izu–Bonin – Mariana arc: An overview

“…Manganese and ferromanganese oxides form various types of deposits in the world oceans. Genetically, they are categorized as hydrogenetic, early diagenetic, and hydrothermal deposits (Cronan 1997; Hein et al 1997; Usui & Someya 1997). Of the three types, the hydrothermal manganese deposits show characteristics quite different from the other two types in the mode of occurrence and chemical, mineralogical and structural features.…”

Ni-Cu-Co-rich hydrothermal manganese mineralization in the Wallis and Futuna back-arc environment (SW Pacific)

“…1) and high concentrations of Co, Ni, Cu, REE (Rare Earth Elements), HFSE (High Field Strength Elements), Te and Pt, ferromanganese crusts are presently regarded as a potential mineral resource (Hein et al, 2013). Polymetallic nodules exhibit a wide range of Fe/Mn ratio (1 to 15) and metals contents (Cronan, 1997;Dymond et al, 1984) and may be of economic interest for Cu and Ni in specific environments (e.g. Clarion and…”

The effect of environmental controls on the metal content in ferromanganese crusts and nodules from the Mozambique Ridge and in the Mozambique Basin, southwestern Indian Ocean

“…The availability of metals in seawater for incorporation into ferromanganese nodules and crusts is a function of three principal environmental controls: 1) primary productivity in the surface waters, which influences diagenetic enrichment through its effect on the supply of labile organic matter to the sediments (plankton can concentrate metals in their tissues and then transport them, on death, to the sea floor) and hydrogenetic enrichment through its effect on the export of metals from surfaces waters; 2) the CCD, which influences diagenetic enrichment through its effect on the concentration of labile organic matter versus carbonate remains in the sediments; and 3) the O 2 min layer, which influences hydrogenetic enrichment through its effect on the availability of metals in the water column (Cronan, 1997;Hein et al, 2000;Verlaan et al, 2004).…”

“…Hydrothermal deposits, as suggested by the name, form as a result of metal precipitation from circulating hydrothermal fluids. The concentration of metals such as Mn, Fe, Co, Ni and Cu in ferromanganese deposits as a result of these mineralisation mechanisms can be highly variable and environmental factors, including primary productivity in the surface waters, the oxygen minimum layer (O 2 min layer) and the calcium carbonate compensation depth (CCD), are frequently identified as potential drivers of these variations (Cronan, 1997;Hein et al, 2000;Verlaan et al, 2004). This paper presents the results of a systematic study of the nature of the relationships between the mineralisation mechanism, environmental parameters and compositional variations of Mn, Fe, Co, Ni and Cu in the ferromanganese nodules and crusts from the Mozambique Ridge and Mozambique Basin.…”