68
Y. Fouquet
Deep-Sea Mineral Deposits
Manganese Nodules
The positions of the main nodule fields and hydrothermal mineral deposits are indicated on the world map in Fig. 4.2. Manganese nodules are considered to be potential
mineral resources. Exploitable metal concentrations (copper + nickel + cobalt) are
around 1.3 % in the Pacific. Concentrations in the richest areas (up to 2.4 %) are greater than or equal to those of land-based deposits. Growing awareness of the potential
economic importance of nodules caused President Johnson in 1966 to call for the
seabed to be declared “common heritage of mankind”. This proposal was made into
a resolution in 1970 by the United Nations General Assembly. As copper resources,
nodules represent around 10 % of continental reserves and underwent many investigations in the 1970s and 1980s. These investigations did not lead to their exploitation
for various reasons: poor estimation of the resource, high cost of metal processing,
political issues related to the law of the sea and drop in metal prices. These nodules constitute however a major potential reserve of nickel, copper and cobalt, which
would help to diversify supply sources in case of tension over continental resources.
Their exploitation would require high resolution maps to be produced, the formation processes for the richest nodules to be understood and the biodiversity and
functioning of related ecosystems to be well known, in order to minimise the environmental impact of their possible exploitation. With this in mind, France has
obtained two mining licenses in the North Pacific.
Location The first nodules were discovered in shallow waters in the Kara Sea in
1868. Then, between 1873 and 1876, the British vessel Challenger showed that
nodules were common in the deep sea. Their mining potential has been highlighted
since the 1950s due to nickel contents greater than or equal to those of laterite
deposits, copper contents greater than or equal to those of major land-based copper
deposits (0.5 % copper) and cobalt concentrations similar to those of land-based
deposits. Currently, nodules are known to exist in all the oceans, at all latitudes and
even in some lakes. Nevertheless, metal abundance and wealth on the seabed vary
tremendously. From 1973, particularly rich fields with a high density of nodules
were found along an east-west belt in the North Pacific in the Clarion-Clipperton
Zone (Fig. 4.2).
The sediment environment of nodules is composed of deep-sea red clay, siliceous radiolarian ooze, or carbonate foraminiferal ooze. These sediments are always heavily water-saturated. In the Clarion-Clipperton Zone, ooze is composed
of radiolarians (30 %) and iron and manganese hydroxide. These sediments lie on
a volcanic crust formed on the axis of the East Pacific Rise some 30 to 40 million
years ago. The mountainous features, 100 to 300 m high and spreading north-south
over several dozen kilometres, were inherited from the East Pacific Rise. The faults
affecting the sediments are located in line with the faults of the basaltic basement.
The topography in parallel ridges and valleys inherited from the rise is essential
for nodule formation. It enables secondary displacement of sediment particles by
Y. Fouquet
Deep-Sea Mineral Deposits
Manganese Nodules
The positions of the main nodule fields and hydrothermal mineral deposits are indicated on the world map in Fig. 4.2. Manganese nodules are considered to be potential
mineral resources. Exploitable metal concentrations (copper + nickel + cobalt) are
around 1.3 % in the Pacific. Concentrations in the richest areas (up to 2.4 %) are greater than or equal to those of land-based deposits. Growing awareness of the potential
economic importance of nodules caused President Johnson in 1966 to call for the
seabed to be declared “common heritage of mankind”. This proposal was made into
a resolution in 1970 by the United Nations General Assembly. As copper resources,
nodules represent around 10 % of continental reserves and underwent many investigations in the 1970s and 1980s. These investigations did not lead to their exploitation
for various reasons: poor estimation of the resource, high cost of metal processing,
political issues related to the law of the sea and drop in metal prices. These nodules constitute however a major potential reserve of nickel, copper and cobalt, which
would help to diversify supply sources in case of tension over continental resources.
Their exploitation would require high resolution maps to be produced, the formation processes for the richest nodules to be understood and the biodiversity and
functioning of related ecosystems to be well known, in order to minimise the environmental impact of their possible exploitation. With this in mind, France has
obtained two mining licenses in the North Pacific.
Location The first nodules were discovered in shallow waters in the Kara Sea in
1868. Then, between 1873 and 1876, the British vessel Challenger showed that
nodules were common in the deep sea. Their mining potential has been highlighted
since the 1950s due to nickel contents greater than or equal to those of laterite
deposits, copper contents greater than or equal to those of major land-based copper
deposits (0.5 % copper) and cobalt concentrations similar to those of land-based
deposits. Currently, nodules are known to exist in all the oceans, at all latitudes and
even in some lakes. Nevertheless, metal abundance and wealth on the seabed vary
tremendously. From 1973, particularly rich fields with a high density of nodules
were found along an east-west belt in the North Pacific in the Clarion-Clipperton
Zone (Fig. 4.2).
The sediment environment of nodules is composed of deep-sea red clay, siliceous radiolarian ooze, or carbonate foraminiferal ooze. These sediments are always heavily water-saturated. In the Clarion-Clipperton Zone, ooze is composed
of radiolarians (30 %) and iron and manganese hydroxide. These sediments lie on
a volcanic crust formed on the axis of the East Pacific Rise some 30 to 40 million
years ago. The mountainous features, 100 to 300 m high and spreading north-south
over several dozen kilometres, were inherited from the East Pacific Rise. The faults
affecting the sediments are located in line with the faults of the basaltic basement.
The topography in parallel ridges and valleys inherited from the rise is essential
for nodule formation. It enables secondary displacement of sediment particles by