Heavy Metals on the Deep-Sea Roor: Manganese Deposits 291
about the potential competition Many of them belong to the developing countries.
The resulting concept of the deposits as a "common heritage of mankind" has slowed
development of the resource, since venture capital is hesitant to take the risk both of
failure and of an unknown degree of taxation in case of success. Eventually, however,
the resource will probably be exploited. Mn, Co, Cu, and Ni are so-called strategic
minerals. For example, Co is used for dense and strong alloys in jet engine parts.
Because cobalt production is concentrated in a few African countries, the hostilities
between Angola and Zaire caused an increase in Co prices from US $ 3-6 per pound
during 1960--1977 to more than $ 22 in 1979. Cu, Mn, and Ni prices remained stable
- an illustration of difficulties in attempting to make economic forecasts in the mining industry.
10.4.2 Nature of Manganese Deposits. What are the ferro-manganese deposits like?
Where do they occur? How much of the valuable trace metals do they contain? How
did they originate?
The appearance of the manganese deposits varies. Nodules come in sizes of 1 to
10 cm and look much like small potatoes except for being black. The surface can be
smooth or rough. Not all deposits are nodules: some are crusts several centimeters
thick, others are pavements covering the sea floor in areas of active currents. The
nodules are rather porous. They are easily crushed, which should facilitate on-board
processing and chemical extraction of metals when the time comes. On cutting the
nodules, one notes a concentric structure. In the center there is commonly a core of
altered volcanic material. Fragments of older nodules, bones, or shark teeth can also
serve as core. From the age of such cores it is quite obvious that the deep-sea nodules
must grow very slowly, a few millimeters per million years, at most (Fig. 10.10 Bb).
The manganese nodules occur in areas of low sedimentation rate: because of their
slow growth they would soon be covered up in regions of high sediment supply (Fig.
10.11).
Calcareous ooze accumulates at about 10 m per million years, 1000 to 10 OOOx
faster than nodules; hence no nodules develop (excepting "micronodules" and
encrustations on shells of foraminifera in many areas). Ferromanganese is deposited
here also, but is greatly diluted with carbonate. Brown pelagic clay (Red Clay)
accumulates at less than 1 m, up to about 2.5 m, per million years, the higher values
applying in the Atlantic Ocean. Surprisingly, nodules have time to grow at the surface
under these conditions. Apparently they are moved about sufficiently, through the
activity of benthic organisms, to stay onm top of the clay. In fact, such movement
may be necessary to keep them round rather than mushroom-shaped, and to prevent
them from coalescing into a pavement. If we could mount a time-lapse camera on the
sea floor, taking a picture every 100 years for 10 000 or 100 000 years, what a
spectacle of dancing nodules we might see!
In places, bottom currents prevent clay deposition or even cause erosion over large
areas. Indeed, in sediment cores nodules can be seen to be concentrated at horizons
of Tertiary hiatuses.
The distribution of nodules is patchy (Fig. 10.10 A). For example, in the eastern
central Pacific, records were taken with bottom-near television cameras, for hundreds
about the potential competition Many of them belong to the developing countries.
The resulting concept of the deposits as a "common heritage of mankind" has slowed
development of the resource, since venture capital is hesitant to take the risk both of
failure and of an unknown degree of taxation in case of success. Eventually, however,
the resource will probably be exploited. Mn, Co, Cu, and Ni are so-called strategic
minerals. For example, Co is used for dense and strong alloys in jet engine parts.
Because cobalt production is concentrated in a few African countries, the hostilities
between Angola and Zaire caused an increase in Co prices from US $ 3-6 per pound
during 1960--1977 to more than $ 22 in 1979. Cu, Mn, and Ni prices remained stable
- an illustration of difficulties in attempting to make economic forecasts in the mining industry.
10.4.2 Nature of Manganese Deposits. What are the ferro-manganese deposits like?
Where do they occur? How much of the valuable trace metals do they contain? How
did they originate?
The appearance of the manganese deposits varies. Nodules come in sizes of 1 to
10 cm and look much like small potatoes except for being black. The surface can be
smooth or rough. Not all deposits are nodules: some are crusts several centimeters
thick, others are pavements covering the sea floor in areas of active currents. The
nodules are rather porous. They are easily crushed, which should facilitate on-board
processing and chemical extraction of metals when the time comes. On cutting the
nodules, one notes a concentric structure. In the center there is commonly a core of
altered volcanic material. Fragments of older nodules, bones, or shark teeth can also
serve as core. From the age of such cores it is quite obvious that the deep-sea nodules
must grow very slowly, a few millimeters per million years, at most (Fig. 10.10 Bb).
The manganese nodules occur in areas of low sedimentation rate: because of their
slow growth they would soon be covered up in regions of high sediment supply (Fig.
10.11).
Calcareous ooze accumulates at about 10 m per million years, 1000 to 10 OOOx
faster than nodules; hence no nodules develop (excepting "micronodules" and
encrustations on shells of foraminifera in many areas). Ferromanganese is deposited
here also, but is greatly diluted with carbonate. Brown pelagic clay (Red Clay)
accumulates at less than 1 m, up to about 2.5 m, per million years, the higher values
applying in the Atlantic Ocean. Surprisingly, nodules have time to grow at the surface
under these conditions. Apparently they are moved about sufficiently, through the
activity of benthic organisms, to stay onm top of the clay. In fact, such movement
may be necessary to keep them round rather than mushroom-shaped, and to prevent
them from coalescing into a pavement. If we could mount a time-lapse camera on the
sea floor, taking a picture every 100 years for 10 000 or 100 000 years, what a
spectacle of dancing nodules we might see!
In places, bottom currents prevent clay deposition or even cause erosion over large
areas. Indeed, in sediment cores nodules can be seen to be concentrated at horizons
of Tertiary hiatuses.
The distribution of nodules is patchy (Fig. 10.10 A). For example, in the eastern
central Pacific, records were taken with bottom-near television cameras, for hundreds