Minerals Report - International Seabed Authority

economic potential in hydrogenetic ferromanganese crusts and ranges in
value in individual bulk crusts from about 0.05 – 1.7 per cent. The average
metal value in known crust bearing areas, he also said is between 0.19 and
0.74 per cent for various parts of the world’s oceans.
Dr Hein said that ferromanganese crusts are found in all ocean basins
that contain hard, sediment- free rocks. Crusts occur on seamounts, ridges
and plateaus where currents have kept the rocks swept clean of sediments for
millions of years. According to Dr Hein, in the areas where ferromanganese
crust formation occurs in part, as a result of hydrothermal precipitation,
associated hydrothermal activity tends to dilute the interesting elements that
are sought from crusts. With regard to cobalt-rich crusts, Dr Hein said that the
best environments are those far removed from areas of hydrothermal venting
such as the central equatorial Pacific Ocean. Dr Hein stated that
ferromanganese crusts have been discovered in environments that encircle the
centre of the Atlantic, the Indian and the eastern part of the Pacific Ocean.
However, since these areas are also environments of hydrothermal activity,
Dr Hein said that the crusts were not enriched in cobalt. He also said that the
same is true of the island arcs of the west Pacific Ocean, the Philippines,
Japan, Vanuatu and Tonga. As concerns the mid Atlantic ridge as a whole, Dr
Hein told participants that on a regional basis, less than 30% of the crusts that
have been found here are the products of hydrothermal precipitation.
In respect of the Atlantic, Indian and Pacific Oceans, Dr Hein pointed
out that both the Indian and Atlantic Oceans are dominated by spreading
centres and not seamounts like in many parts of the Pacific Ocean that could
be described as cobalt-rich crust areas. Additionally, the crusts to be found in
these two oceans are also diluted by the amount of detrital material that is
brought into their basins from the continents by major rivers. Dr Hein further
pointed out that the Atlantic Ocean basin, for example, is much smaller than
the Pacific Ocean basin. With the added effect of huge rivers such as the
Amazon and Congo discharging detritus containing effluents into the Atlantic
Ocean and huge deserts that contribute eolian material into the oceans, a lot of
material is introduced into this ocean to dilute the grade of the crusts. Dr
Hein observed that the same conditions apply in the continental margins of
the Pacific Ocean, which have very similar crust compositions to the crusts in
the Atlantic and Indian Oceans. Dr Hein stated that based on this very simple
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