Manganese nodule project was quite fashionable during the seventies. The drop in metal prices led to almost a complete reduction of the activities on the subject at the beginning of the '80. But the Law of the Sea incited the countries that signed it to build a strategy for this ocean resource.
GEMONOD was created in France in 1984 with a 4-year mission. This paper presents the results of its program devoted to the technical and economic studies of nodule exploitation.
A commercial mining system is presented. The nodules would be collected by a self propelled miner and lifted hydraulically through a rigid pipestring.
A complete optimized scenario has been built taking into account offshore mining, ore transfer at sea, transportation and processing to analyse the profitability of the project.
Considering an average conservative basis for metal prices, after a deep analysis of the market, the return rate of investment of the project appears fairly interesting.
These results are new and are explained in comparison with previous foreign studies. These results must not hide the innovative nature of the project nor the associated risks. This is the reason why a mining pilot is required and has been specified by GEMONOD.
Though they lay at very great depths, the polymetallic nodules are the most well known submarine hard mineral resource.
This probably results from the great deal of work that has been performed during the last 20 years by the counties and consortiums involved in the project.
Meanwhile, the level of activities has followed variations since the preliminary studies of 1970.
1970–1978: The nodule rush From 1970 to 1978, the economic growth incited the participants to explore this potential resource so as to locate and quantify it. This prospection led to focus on the Clarion Clipperton zone located in the NorthEastern Tropical Pacific Ocean, where nodules were found to be abundant and rich in metals. During this phase, consortiums studied two means for nodule mining :
The C.L.B. (Continuous Line Bucket) which is a passive system. It presents the advantage of being simple and cheap but leads to a random collecting which is not compatible with the variability of the seabed topography (obstacles) and nodule abundance.
The hydraulic system which has been preferred and tested during 3 operations carried out in 1978–79, using converted ships and 5000-m long vertical pipestrings.
These tests were more or less successful and showed the necessity to perform an important development work to enable an industrial collecting of this marine ore.
1978–1983: The slackening of the project The world economic crisis, particularly on raw materials, the long term development of the project and the uncertainties on the legal status of the mining sites have led to a slowing down of the nodule activity.
Consortiums have performed exploration work so as to be in a position to claim a mining area. However, only a minor deal of work, regarding mining engineering, has been completed.
