Description and chemical composition of manganese nodules during R/V "Tyro" cruise APNAP 1 to the Madeira Abyssal Plain in 1986

The porewater and sediment composition of two boxcores and of a small gravity core, taken on a manganese-nodule-covered hill and in the Madeira Abyssal Plain proper respectively, are compared. The pore-water study of the two boxcores indicates that oxic conditions prevail in both cores. In addition, it indicates that no detectable fluxes of Mn or Fe occur from the porewater to the ocean bottom water. Variations in the geochemical composition of the sediments can be explained by fluctuations in the amount of carbonate, which acts as a diluting agent. A clear carbonate minimum is observed at 20-22 cm depth in the two cores. This minimum is likely to be associated with the last glacial period (10-20 kyr B.P.). This association is supported by the sediment accumulation rate of 15 mm/kyr as found by extrapolation from the rate for pelagic sediments in the Madeira Abyssal Plain. The bulk composition of the manganese nodules recovered from the submarine hill is chemically almost identical to the average composition of Atlantic nodules. The trace metal and Rare Earth Elements composition indicate a hydrogenous origin for the manganese nodules of this study. On the basis of the chemical composition, and that of nodules relative to that of the adjacent sediments, an average nodule accretian rate of 2.8-3.3 mm/myr has been calculated. Although the analyses of the entire ferromanganese nodules that have been studied seem to indicate a homogenous composition, internal structures of the nodules reveal great inhomogeneity, both visually and chemically. These fluctuations may be related to variations in the fluxes of Mn and Fe, which in turn could be climate-related.

(Table 3) Contents of phosphorus, iron, and manganese in various zones of Fe-Mn nodules from the Pacific radiolarian belt

Phosphorus content in the surface layer of bottom sediments varies from 0.07% to 0.73%. Clayey radiolarian and radiolarian clayey oozes contain 0.12% P, miopelagic clays 0.21% P, and sediments with high iron and manganese concentrations 0.46% P (average contents). Phosphorus content of iron-manganese nodules varies from 0.14% to 0.39%, average 0.19%. Correlation between phosphorus contents in nodules and surrounding sediments is indicated indirectly by P/Fe ratio. Phosphorus is non-uniformly distributed in some nodules and sometimes correlates with iron. Accumulation of phosphorus in iron-manganese nodules is governed by a degree of manganese predominance in ore components.

Heavy metal contents in bottom sediments and Fe-Mn nodules and their states in bottom and interstitial waters from the Clarion-Clipperton province

Ultrafiltration with tagged atoms was used to study physicochemical states (dissolved, colloidal, suspended) of Mn, Co, Ni, Zn, and Ce in bottom and interstitial waters collected in two areas of the Pacific Ocean with Fe-Mn nodules of different size, shape, structure and origin in different abundances. Use of filters with pore diameter of 0.05 ?m allowed to identify colloidal forms of the metals in bottom sediments and interstitial waters. It was demonstrated experimentally that differences in physicochemical situation in the studied areas could result in formation of nodules by different mechanisms, producing characteristic differences that were observed.

Abundance of nodules, chemical and mineral compositions of nodules and sediments from the Central Pacific

The monograph considers facial conditions of ore-formation in the Central Equatorial Pacific, as well as lithostratigraphy and local variability of bottom sediments. Mineral composition of nodules, forms of occurrence of chemical elements in sediments and nodules, composition of interstitial waters, age of nodules, regularities and processes of ore formation in the radiolarian belt of the Pacific Ocean zone are also under consideration.

Composition of Fe-Mn nodules and crusts from the Southwest Pacific

A study of samples dredged within areas of tectonic arc-trench systems (Kermadec and New Hebrides) allows to distinguish three types of ferromanganese mineralization. Relationship between mineral and geochemical specialization is established. A conclusion is made that ferromanganese mineralization is a permanent genetic series of matter supply: from endogenic (hydrothermal solution is a dominant source at deposition of chemical elements from mixture seawater plus hydrothermal solutions) to hydrogenic (seawater is a dominant source at element deposition). This results in geochemical and mineralogical variety of ferromanganese mineralization within this part of the Pacific Ocean.

Description and chemical composition of ferromanganese nodules from Station 123, Oneida Lake, New York

226Ra is used to document the growth histories of six manganese nodules from Oneida Lake, New York. Detailed sectioning and analysis reveal that there are discontinuous gradients in 226Ra content in these samples. These gradients result from periods of rapid growth (>1 mm/100 years) separated by periods of no growth of erosion. Although the 226Ra 'age' of the nodules approximates the age of Oneida Lake, the nodules are not sediment-covered because they occur only in areas of the lake where fine-grained sediments are not accumulating.

Rare earth elements in bottom sediments and Fe-Mn nodules of the Black Sea

Distributions of rare earth element contents in surface layer bottom sediments, in vertical sediment section, and in Fe-Mn nodules of the Black Sea have been studied. An inverse relationship of rare earth element contents and CaCO3 contents has been found in the studied sediments. Fe-Mn nodules of the Black Sea do not concentrate rare earth elements, and their rare earth element composition differs from one of host sediments. It is concluded that rare earth elements are bound with clay minerals of bottom sediments.

Composition of Fe-Mn nodules from the radiolarian belt of the Pacific Ocean

Typomorphic features of the main morphogenetic types of Fe-Mn nodules from the radiolarian belt have been considered on materials from polygons in the Clarion-Clipperton ore province and in the Central Basin of the Pacific Ocean. By character of surfaces, features of internal structure, mineral and chemical compositions, behavior of trace elements at selective leaching three genetic types of nodules have been divided: predominantly sedimentary, diagenetic, and sedimentary diagenetic. Their formation results from mechanism of growth.

Geochemistry on ferromanganese crusts and nodules from Green Bay, Lake Michigan

The differential solubility of ferromanganese oxides can lead to stratigraphic separation of iron and manganese. Results of chemical analysis of a sequence of ferromanganese nodules overlying iron-rich crusts in northern Green Bay show that selec¬tive ion transport is important in concentrating manganese and associated trace elements near the oxygenated water-sediment interface. Manganese carbonate, which cements ferromanganese nodules, occurs in dark-gray silty sands that are located adjacent to the organic-rich muds of southern Green Bay. These muds contain an average of approximately 3.5 ppm (6x10-5M) interstitial Mn with 2.8 meq/l carbonate alkalinity. Thermodynamic calculation shows that interstitial water approaches equilibrium with MnCO3 in the upper 10 cm of sediment. This carbonate has a composition (Mn73Ca22Fe5)CO3 and has been identified as rhodochrosite.