Minerals Report - International Seabed Authority

discovery of the new hydrothermal sulphide fields, Logachev–1 and
Logachev–2.
5. Cobalt-rich ferromanganese crusts: Global distribution,composition,
origin and research activities
Dr James R. Hein, Senior Geologist at the United States Geological
Survey made a presentation to the workshop on the origin, composition of
and distribution of cobalt-rich ferromanganese crusts deposits in the world’s
oceans.
He informed the workshop that cobalt-rich ferromanganese crusts
occur throughout the world’s oceans on the seafloor and on the flanks and
summits of seamounts, ridges, plateaus, and abyssal hills where the substrate
rocks have been swept clean of sediments, at least intermittently, for millions
of years. Ferromanganese crusts form at water depths of about 400 – 4,000
meters, with the thickest and most cobalt-rich crusts occurring at depths of
about 800 – 2,500 meters. Formed by the precipitation of the elements of
interest from cold ambient bottom waters of the oceans, crusts accumulate as
pavements of mineral deposits up to 250mm thick on hard-rock surfaces to be
found in the areas described above, and contain iron, manganese (generally in
equal amounts), cobalt, nickel, platinum, titanium, and the rare earth
elements, tellurium, thallium, phosphorus and others. Cobalt is the metal of
greatest commercial interest in crusts and ranges in concentration from 0.19 to
0.74 % in various parts of the world’s oceans. Nickel (1.1%) and platinum
(1.9%) to be found in some crusts deposits are also of commercial interest.
Compared with polymetallic nodules that are found in the abyssal plains, Dr.
Hein pointed out that while elements such as iron, cobalt, platinum, lead,
arsenic, bismuth, bromine, vanadium, phosphorous, calcium, titanium,
strontium and the rare earth metals are more strongly enriched in crusts
deposits, polymetallic nodules are more enriched in copper, nickel, zinc,
lithium, aluminium, potassium and cadmium.
Dr. Hein informed participants that interest in deep-sea
ferromanganese crusts deposits following their discovery during the
Challenger Expeditions of 1873 – 1876 occurred during the various campaigns
in the 1960s and 1970s for polymetallic nodule deposits. Although up until the
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