Minerals Report - International Seabed Authority

The tonnage indications provided in the last column are very
speculative. Some come from the literature [19-35], and others have been
calculated by the author on very hypothetical and unproven assumptions.
They only provide an order of magnitude.
2.3. Mining and processing technologies
2.3.1. Polymetallic nodules
Many systems have been proposed for mining deep seabed
polymetallic nodule deposits. From the Afernod prefeasibility study, one can
assume that the following assemblage 5/ will be appropriate to mine the French
site described above [12];
- A self propelled dredge, crawling on the bottom collects the
nodules, crushes them and introduces crushed nodules to a 600 mlong
flexible hose connected to a rigid pipe;
- The crushed nodules are lifted to the semi-submersible surface
platform in a 4 800 m rigid-steel pipe by airlift or pumps,
- The transfer of the nodules from the platform to the ore carrier is
done by pumping them through a flexible hose as a thick pulp;
- The production rate will be 1.5 10 6/ tonnes of dry nodules per year.
During the operations from harvesting on the bottom to delivery at the
processing plant on land, it has been assumed by Afernod that 30% of the
nodules will be lost. Consequently one can calculate that the total area, that
will be mined during the 20 years of operation, is in the range of 4 500 km 2 .
The corresponding mine-able fields (approximately 100) could be embodied
in a total area of 15 000 km 2 , but as the most promising parts of the pioneer
area are not likely contiguous, a more important surface should be envisaged.
It must be pointed out that these results are based on statistical assumptions.
5/ Comparable mining systems have been tested at the end of the seventies at pilot
scale level (1/10) by several consortia. In 1997, Japan tested a similar assemblage, with
a towed collector, on the top of a seamount at a depth of 2 200 m.
INTERNATIONAL SEABED AUTHORITY 435