『Abstract
Manganese nodules are concretions of manganese and other transition
metal oxides which form in marine and freshwater sedimentary environments
worldwide. The Clarion-Clipperton zone (CCZ) deposits are on the
surficial sediments of the deep seabed in the northeastern tropical
Pacific Ocean. In general, manganese nodules are believed to form
in aqueous, unconsolidated sedimentary environments which include
a flux of disslved or chemically adsorbed manganese and iron through
a gradient between relatively reducing conditions where Mn(II)
is stable in solution (or as an adsorbed species on particles)
and oxidizing conditions where the manganese will precipitate
as basically tetravalent oxides.
Two sources have been proposed for the metals in the CCZ deposits:
hydrothermal sources from seabed volcanoes, and terrestrial sources
from North and Central American rivers and airborne particles.
Active vulcanism is significant only in the extreme eastern part
of the CCZ, so the metals in almost all of the CCZ deposits must
involve some sort of lateral transport from the east for either
primary sources. Research completed to date suggests that metals
in the CCZ surface waters consist mostly of adsorbed species on
fine particles concentrated at the top of the thermocline, moving
with the surface currents to the west. Plankton concentrate these
adsorbed and fine-grained particulate metals into body parts and
fecal pellets which are large enough to settle through the water
column to the seabed. Thus accumulations of manganese nodules
can be expected to be proportional to the productivity of the
overlying surface waters. Growth rates of the nodules appear to
vary between about 3 to perhaps 20 mm/My. Deposits are patchy,
exhibiting wide variations of sbundance in apparent response to
local geographic and oceanographic factors.
Available data for the CCZ cover an interpolated area of 9 million
km2, which hold 34 billion metric tons of manganese
nodules. Specific estimates of metal resources include the following
(units, millions of metric tons): Mn - 7500, Ni - 340, Cu - 265,
C0 - 78.』
6.1 Inrtroduction
6.2 Formation processes
6.2.1 Chemical and mineralogical factors
6.2.2 Metal sources and oathways
6.2.2.1 Lateral transport in surface waters
6.2.2.2 Vertical transport
6.3 Nodule growth rates
6.4 Local factors
6.5 Resource assessment
6.5.1 Kriging
6.5.2 General results
6.5.3 Resource assessment results
6.6 Environmental implications
6.7 Conclusion
Acknowledgments
References