Minerals Report - International Seabed Authority

J. Mero had evaluated the total amount of polymetallic nodules lying
on the sea floor to more than 1.5 x 10 12 tonnes in 1965 [5]. This estimation was
reduced to 5 x 10 11 tonnes by A. Archer in 1981 [6]. However, not all nodule
fields are eligible for potential mining. Several attempts were made to
calculate the probable resources for (near!) future development. The approach
was to determine the number of “mining sites” that the World Ocean could
accommodate. A mining site was defined as a portion of the seabed where a
commercial operation could be maintained during 20-25 years with a
production of 1.5 to 4 x 10 6 tonnes per year of “good nodules”. Good nodules
were those containing an average of 1.25-1.5% nickel and 1-1.4% copper, in
addition to 27-30% manganese and 0.2- 0.25% cobalt. The estimate of the
number of sites varied from 8 to 225, which corresponds to a total amount of
inferred resources between 480 x 10 6 to 13,500 x 10 6 tonnes [6-10]. Further
considerations, on the capacity of the world metal markets to absorb
production from this source in the first 20 years of operation along with and
more severe mining requirements, reduced this range to 3-10 mining sites
with a tonnage of 100-600 10 6 tonnes [11]. These are estimates of “speculative
inferred resources”.
From 1984 to 1989, the French group Afernod 1 /Gemonod 2 carried out
an extensive pre-feasibility study, whose results have been published. It
constitutes the basis for the following assumptions on a polymetallic nodule
deposit that might be suitable for a possible commercial operation [12-14]:
• The depth of the ocean floor in the area varies from 4,800 m to 5,200 m.
The topography is formed of long dissymmetric hills. Their crests are
orientated north-south, spaced by 2-5 km, and dominate the lower
parts by 100-300 m. Slopes are less than 10% in more than 70% of the
area, but vertical cliffs, sometimes 40 m high, have been identified on
the flanks of the hills. In some places, potholes 100 to 1,000 m wide and
40 m deep have been observed.
1/ Association Française pour l’Etude et la Recherche des Nodules (AFERNOD).
2/ Groupement d'intérêt Public formed in 1983 by IFREMER, Commissariat à
l'Energie Atomique and Technicatome. A parent organisation of AFERNOD.
INTERNATIONAL SEABED AUTHORITY 427