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Les ressources minérales profondes en Polynésie française / Deep-sea mineral resources in French Polynesia

 | 
Pierre-Yves Le Meur
, 
Pierre Cochonat
, 
Carine David
, 
et al.

III. Summary report

4. Technological research and development campaigns

Texte intégral

1More than anywhere else, deep-sea scientific expertise relies on the development of advanced technologies and access to heavy equipment that is fundamental to the ability to work on the seafloor. This is an area where technological advances have a direct impact on knowledge acquisition. Deep-sea research could also generate a new industry with the market for deep-sea technologies, and not just the conventional and operational offshore oil sector, as the backdrop.

2Underwater mineral resources are found in the ocean depths, except aggregates, phosphates and placers (particularly diamonds in Namibia), which can be found on the continental shelf (at depths of < 200 m). The techniques for investigating the shelf and the deep-sea often apply the same principles, based on a geophysical approach, but differ significantly in scale (acoustic frequency, power and penetration). They require heavy equipment capable of working in the deep-sea (to 6,000 m). It is on the seafloor that deep-sea mineral resources are found: mud with rare earth elements and polymetallic nodules (5,000-6,000 m), massive sulphide deposits (1,000-5,000 m) and polymetallic crusts (800-4,000 m) such as those reported in the French Polynesian EEZ.

Strategies of the countries and stakeholders involved

3Some countries, such as France, have developed the expertise and tools necessary for ocean exploration. After a few attempts focused on nodules in the 1970s, we are now witnessing the first signs of renewed interest for deep-sea mineral resources (excluding oil) from the industry (see III-2). However, the means used for investigation still mainly come through public oceanographic research. Indeed, exploration conducted in these extreme environments relies on scientific and technological expertise developed over nearly half a century in research programmes carried out by national institutions. As a result, the various stakeholders involved in exploring deep-sea mineral resources are oceanographers, geologists, biologists, technology developers and so on. They work in the public domain (research organisations) or, more rarely, in private companies. When it comes to developing marine mining, this research community is called on to verify whether the mineral occurrences discovered by geological exploration can be used to identify deposits with economic potential. Their activities often take place in the context of exploration and research permits issued by the International Seabed Authority (ISA) for international waters and by sovereign nations for their EEZ.

4Until recently, national stakeholders in the onshore mining industry paid little attention to the marine environment and have learned little about its particular characteristics. France was a pioneer in exploring the seafloor, especially deep basins (nodules) and ocean ridges (hydrothermal), through multi-agency research programs (CNRS, IFREMER, IRD, BRGM, etc.) (Fouquet and Lacroix, 2012), and in upholding licenses in international waters through IFREMER (permit signed for nodules in 2001 and for massive sulphide deposits in 2012). Today, some countries have a strong strategic vision for marine resource exploitation (Australia, Brazil, China, Germany, India, Japan, Russia, South Korea, the United States, etc.) and are very active in this field, judging by the quantity and quality of their publications and their participation in ISA activities.

5In France, the government signalled its ambitions with its Grenelle of the Sea recommendations (2009), which were followed by the launch of the Wallis and Futuna project. In June 2011, the Interdepartmental Committee of the Sea (CIMER) decided to launch “a national strategy for deep-sea mineral resources that will set the guidelines for sustainable exploitation of these resources in waters under national jurisdiction and in international waters”. Meanwhile, IFREMER, with the participation of representatives of many French institutions, conducted a prospective study on marine mineral resources (Fouquet and Lacroix, 2012), while the MEDDE commissioned the joint scientific appraisal of the environmental impact of exploiting deep-sea mineral resources (carried out by CNRS and IFREMER; Dyment et al., 2014.).

6The French Maritime Cluster, backed by several manufacturers including Eramet and Technip and recently joined by other companies such as Fayat Travaux Sous-marins, DCNS, Louis-Dreyfus Armateurs and Creocean, is endeavouring to develop a national deep-sea mining industry. At the current time, the activities that are subject to public policy decisions and require considerable budgets for campaigns at sea are primarily the maintaining of nodule permits issued by the International Seabed Authority in the Clarion-Clipperton zone.

7In Europe, the European Innovation Partnership for Raw Materials (EIP) brings together representatives of various stakeholders: industries, public services, academia and NGOs. Eighty Raw Material Commitments (RMCs) were launched under the EIP, of which four involved projects for marine mineral resources. In the end, only one project was chosen for the H2020 programme (a Belgian project on nodules). It should be noted, however, that the Secretariat of the Pacific Community (SPC), comprising 15 member countries from the Pacific Islands, has launched the Deep-Sea Mineral Project in collaboration with the European Union.

8In the international context, many organisations, government agencies or groups of countries (listed above) are active in the field of marine mineral resources. The exploration of deep-sea mineral resources mainly takes place in the International “zone”, under the auspices of the ISA, which has approved 26 exploration contracts. Of these, fourteen were issued to Asian Pacific countries, seven to Western European nations, four to Eastern European nations and one to a Latin American-Caribbean group (the US has not ratified the 1982 Convention of the United Nations on the Law of the Sea and so attends meetings of the ISA as an observer).

9From the viewpoint of French national strategy, the request for this expert group review from French Polynesia and the French government could lead to a revival of a programme for research on and access to marine mineral resources. The panel of expert recommends an innovative programme on polymetallic crusts, fitting with a local (country), regional (SPC), or national context, to be specified.

Knowledge of polymetallic crusts

10The analysis of the state of geological knowledge shows that, as deep-sea mineral resources, polymetallic crusts may hold considerable potential in French Polynesia. They are located in favourable areas in terms of geomorphology – at depths from 800 to 2,500 m – particularly in the Tuamotu sector where they are deposited on carbonate substrates, which could be important for their mineability.

11For this type of resources, major exploration efforts will first have to be conducted in Polynesia, as was the case for other regions that were initially promising: to date, only three permits for exploring polymetallic crusts have been awarded by the ISA (to Russia, Japan and China, all for sites in the Pacific Ocean). A request from Brazil for the South Atlantic is under consideration.

12Currently, the majority of publications on the physical environment and the characteristics of polymetallic crusts are found in academic research and journals. At this early stage in exploration, it is clear that there are few, if any, activities specifically involving mining crusts and even less technical and economic data to serve as the basis for economic calculations. There is a large gap between the current state of knowledge, which is intermittent and fragmentary, and the creation of the databases needed to describe reserves and perform economic calculations. Many questions remain as to the nature of the resource and its mineability. There is a need for additional accurate field data and calculations if we are to access this potential resource: geological surveys of mineral-rich areas, the exploitable volume (crust thicknesses), the morphology and roughness of the seafloor, the lateral extent and continuity of zones with crusts, the geotechnical properties of the crust and the substrate, continuous monitoring of crust thickness, the influence of the substrate on dilution during collection, and the impact of mining on ecosystems.

Overview of exploration technology

13Ocean exploration to discover mineable deposits involves a nested approach using special technologies. The objective is to establish a geological model for crust formation, to qualitatively and quantitatively evaluate the mineralisation, and to describe the environment and biodiversity. Besides ships, the technology that currently exists (or under development) for locating and studying potential resources can be analysed at three levels with a multi-scale and multidisciplinary strategy. These three levels are: regional exploration technology, technology for surveying sites and assessing resources and biodiversity, and technology for monitoring and protecting the environment (see III-1 and III-3).

Regional exploration technology

14This is primarily for mapping, utilising geophysical surveys and samples to perform initial physico-chemical and metallogenic analyses. This is an essential step for identifying sites before resources can be assessed. To identify areas of potential interest, it is necessary to conduct large-scale surface surveys using indirect methods such as acoustic (bathymetry or sonar reflectivity), potential (gravimetry, magnetism or gammametry) or seismic approaches. Current mapping tools make it possible to create regional bathymetric maps at resolutions of about one hundred metres, for example. No site survey can be started without this general knowledge that furthers understanding of the geological and morphological context. Aside from low-resolution satellite data (at kilometeric level, compared to bathymetric data acquired by multibeam sounders at decametric level) and not including Extraplac data, regional bathymetric maps created using modern means are virtually non-existent for the Polynesian EEZ. At this stage, rock samples (by rock dredging) are also required to determine the nature of the seafloor and identify areas that could potentially present relative enrichments of cobalt and platinum. Biological sampling must also be performed from the outset, to understand the regional aspects of the spatial distribution of biodiversity in deep-sea environments. This dimension is vital if the connections and interactions among ecosystems at different scales are to be incorporated. Polymetallic crusts are structures which form over long periods of time in highly specific ocean conditions. The seamounts where they develop are open environments, due to the connections between the different compartments of the water column and beyond – to neighbouring and distant marine areas via trophic (food chains) and ontogenetic (life cycles) links.

Technology for surveying sites and assessing resources and biodiversity

  • 32 ROV: Remotely Operated Vehicle.
  • 33 AUV: Autonomous Underwater Vehicle.

15Once sites have been identified (continuous areas measuring 100 sq. km are sought), acquiring scientific understanding of geological, geochemical and biological processes involves work near the seafloor using submersibles (ROV32, AUV33 or manned vehicles). This equipment can provide more detail to local explorations (bathymetry and imagery at resolutions of a few dozen centimetres) and enable precise sampling at sites near the seafloor to study the composition and geometry of potential deposits. When studying crusts, core drilling as well as conventional rock dredging will be vital for measuring their metal content and thickness. A key point for technological innovation will be sampling by micro-drilling, something that remains to be developed or adapted from existing systems for use by a ROV. The question of taking in situ measurements while drilling (logging), and development for micro-drilling may be raised. This robotic equipment could, for example, combine core drilling (sampling) and destructive drilling (with the attendant in situ measurements) into a single tool to collect samples and take measurements in the same place. This is a very interesting perspective that emphasises the importance of developing a ground-breaking tool.

16On the other hand, it could be very worthwhile to develop mobile in situ analysis capabilities near the seafloor, including Raman techniques for in situ non-destructive analysis of solids. This equipment must be suitable for ROV and AUV vectors. Raman spectroscopy is an analysis technique widely used in the field of solids that requires no sample preparation or reagent. The objective is to develop a method of operational spectroscopic detection capable of identifying solids on the seafloor. Spectral data are provided in real time, allowing for immediate chemical identification. The targeted compounds are solid compounds, regardless of whether they are inorganic, organic or even biological. This tool (under development as part of a European project) will constitute a significant technological breakthrough for both geological and biological research (Fouquet, 2013).

17Further exploration techniques might use ICP-AES (Inductively Coupled Plasma -Atomic Emission Spectroscopy) or micro x-ray fluorescence coupled with a micro-drilling system.

18Regarding biodiversity, the habitats associated with polymetallic crusts are poorly understood but it is known that the conditions of their formation (long-term oceanic conditions) determine the type of organisms that develop there. These conditions favour stationary (or less mobile) organisms with long lifespans that form, as with trees in forests or coral in reefs, biogenic habitats for a diverse group of species. The functioning of the benthic ecosystem usually involves significant interactions with the rest of the water column (vertical interactions) over great geographic distances (horizontal interactions). An understanding of the habitats in the areas chosen for mining operations must be incorporated into a research plan that takes these various scales into account. The knowledge currently available and the specific bio-geographic situation of French Polynesia raise the possibility of, if not a high percentage of endemic benthic fauna, at least the presence of specialised benthic fauna.

Technology for monitoring and protecting the environment

19Preparations must also be made for monitoring the spatio-temporal evolution of these sites for environmental surveillance and protection. To minimise the impact of deep-sea resource exploitation, specific tools are needed to establish baseline conditions, especially in biological terms. This means developing tools to monitor temporal variability, bearing in mind that the environments in question were formed over long periods of time and that their resilience to disturbances (turbidity and changes in physico-chemical factors for the entire water column, depending on surface and deep ocean currents) is almost certainly quite low and slow to recover. Vertical and horizontal connections with other habitats must be taken into account in these approaches.

20Seafloor observatories will monitor changes to the site environment at different stages: baseline state prior to exploitation, assessing the impact of mining activities on ecosystems and post-operational monitoring. Remote observatories will be set up to evaluate the impact on interconnected marine compartments.

Current situation of mining technology

21The development of equipment and techniques for deep-sea mining is one of the major scientific and technological undertakings of the past 50 years. Developments for deep-sea offshore oilfields have seen the greatest progress. Moreover, protecting the environment is now a major challenge for an industry that does not have the best track record in this area. We need to find a way for mineral resource access and environmental aspects to coexist (see III-1 and III-4).

22Advances in drilling capacity, trenching and production for deep-sea oil have significantly expanded the range of technology available, but this will require significant modifications -or innovation -to suit the more selective extraction processes required for deposits of harder and more superficial minerals, as will be the case for the crusts that interest us in the French Polynesian EEZ.

23The recovery of nodules is relatively easy because they lie on a soft sediment substrate; this same cannot be said of crusts that may be more or less firmly attached to the substrate (they are easier to “detach” in the case of a carbonate substrate). For successful exploitation, it is crucial that the crusts are recovered without removing the substrate, which can significantly dilute the ore content, except where the substrate contains phosphorite (Pichocki and Hoffert, 1987) that would be worth exploiting as well. In their simulations, Dyment et al. (2014) thus describe a series of operations: fragmentation, grinding, removal, separation and recovery by airlift (air injection pump system). Self-propelled vehicles would travel at a speed of about 20 cm/s on the seafloor (which seems high) and would be attached to a ship or a mining platform at the surface by means of a hydraulic removal system and an electric cable. Rough estimates put production volume at around one million tonnes per year. Other methods are available for separating the crust from the substrate, such as water jet stripping, in situ leaching techniques and detachment using an acoustic method. Another possibility would take inspiration from the collection system (crawlers, cutters and riser) used to mine diamonds trapped in consolidated particles (by De Beers Marine for the Nautilus Solwara programme, see V).

24According to findings from the deep-sea Synergie working group of the French Maritime Cluster, the area of collection systems and support vehicles are the least mature in terms of technology.

Accessible resources and technological needs

Exploration (access to ships and machinery)

25Research infrastructure and sea vessels suitable for exploring marine mineral resources have been developed and are managed by large public, and occasionally private (United States), research organisations; they are normally accessed through research-oriented calls for tender. To use this highly specialised equipment and process the resulting data, it is necessary to have solid scientific expertise in creating and leading exploration projects.

Photo 2. The vessel Alis, from the French oceanographic fleet, docked at Papeete. © IRD/S. Petek

  • 34 TGIR: Very large research infrastructure. FOF: French oceanographic fleet.

26The offshore division of the French oceanographic fleet (TGIR FOF34), used to explore the deep ocean, mainly consists of seven ships operated by IFREMER (the Suroit, the Thalassa, the Atalante and the Pourquoi Pas?), IRD (the Alis and the Antea) and the Paul Émile Victor French Polar Institute (IPEV; the Marion Dufresne). The fleet is used primarily for scientific research. It can also be used for public service operations (such as Extraplac) or research-industry contracts, such as those conducted with Total, ExxonMobil, Technip and Eramet.

27The schedule of oceanographic campaigns results from a multi-year process for scientific research campaigns, including the response to the call for tenders from evaluation boards and the evaluation of tender files by those boards. They are scheduled jointly at the “Fleet” Joint Service Unit by fleet operators, who bear the cost in their institutional budgets. In some cases, scheduling may proceed more quickly, logistics permitting, for co-funded campaigns such as public service campaigns, public-private partnerships (research-industry contracts) or charters.

28Private companies – service companies, particularly those that conduct oil explorations – have yet to fully develop real skills for exploring mineral resources, but they will certainly do so once the market further matures.

29There is therefore a significant variety of vessels and machinery available for underwater exploration; however, we have identified gaps or new technology needs still to be covered, especially when it comes to exploring polymetallic crusts.

30Acquiring new data is essential for establishing a geological model of crust formation (structural geology, age of the substrate, geomorphology, ocean currents, sea water/bedrock exchanges, microbiology, etc.). This will serve as a guide for exploration when it comes to profiling promising areas and their spatial dimensions in view of future exploitation.

31The physical and mineral characteristics of the crusts should be further clarified with regard to:

  • measurements of crust thickness, which can vary from a few centimetres to 25 cm, leading to very large differences in the assessment of resources;
  • crucial metal content measurements (analysis of core samples);
  • precise knowledge of microtopography to determine the extent of the deposits and the roughness of their surface.

32Finally, there are large gaps in information about the ecosystems likely to be disturbed by exploitation (environment baseline situation, understanding of the spatial distribution of biodiversity, changes to the physico-chemical characteristics of the water, currentology, pollution plume, resilience of habitats in the event of destruction, etc.).

Mining

33As we have seen, there is little existing or available information on industry strategy. The first technological developments concerning the possible exploitation of deep-water mineral resources (massive sulphide deposits or nodules) were carried out independently and with the utmost secrecy by each of the consortia involved. The developments that have been put forward recently generally combine the experience of offshore deep-sea oil and gas service companies with the expertise of manufacturers of mining industry machines and tools. Figure 5 is a schematic drawing showing a futuristic vision of deep-sea mining. Ongoing research and development for exploiting nodules and massive sulphide deposits could be partially adapted to crusts (seafloor/surface connections, removal of ore after grinding, and robotics), but the system for grinding and sampling the ore will be specific to the crusts.

34On the other hand, proposing an exemplary extraction model in terms of environmental impact means drawing on very thorough knowledge of the habitat and of innovative technologies. From a strictly technological point of view, a prototype of a collection system specifically adapted to the crusts will need to be developed. It seems that detaching the “crusts” is easier on a carbonate substrate, as has been observed during the NODCO and ZEPOLYF campaigns. This is a major point, requiring confirmation. Recovery of a phosphate substrate may add value to the mined product. To determine dimensions, it is necessary to define the geotechnical properties of the crust to ensure suitability of the grinding systems and provide tools to measure crust thickness and proceed with the development of the collection system. Then there is the question of whether surface processing will take place on barges or after transporting the ore onshore. Ultimately, given the innovative nature of this type of production, it should be tested through a pilot operation, bearing in mind that initial efforts should be focused on exploration.

Figure 5. Futuristic vision of how could be “deep-sea mining” in French Polynesia. On this schematic drawing: 1/ surface structure such as a mining vessel, receiving ore, providing energy to the seabed gears, and transporting ore to a port or a nearby platform; 2/ riser: flexible pipe used to transfer ore from the seabed to the surface facilities and cables for energy; 3/ pump: propulsion of the divided materials in the riser (air lift); 4/ self-propelled mining gear: extraction, fragmentation and collection of materials (polymetallic crusts).
© IRD/L. Corsini

35Finally, any future impact studies into crust mining projects will need to take into account the presence of ecotoxic elements in polymetallic crusts, among other considerations. A solution must be developed to manage very fine mud (tailings), especially, but not exclusively, if processing takes place at sea. Indeed, high levels of arsenic, lead and thallium were detected in samples from the Polydrag campaign (Martel-Jeantin et al., 2001). These three ecotoxic metals could pose waste management problems when processing the ore.

Specific issues and roadmap

36Many uncertainties subsist with regard to the issue of technological developments in the deep-sea environment. This situation forces us to make many assumptions about the morphological, geometric, metallogenic and environmental characteristics of potential deposits. In addition, the technology for deep-sea machinery will be different from that considered or designed for other resources. With regard to the possible in situ pyrometallurgical or (bio) hydrometallurgical processing that could be theoretically suitable, the limited amount of reference material on the processing of an ore comparable to these crusts raises issues (see, however, Goto et al., 2010; and the work of Agarwal et al., 2012, on nodules). Nonetheless, the crusts in French Polynesia could be presented as a representative case study.

37For French Polynesia, everything began 30 years ago with a small amount of data acquired during the ZEPOLYF and NODCO campaigns. Given the above remarks, the urgency lies in confirming these previous data, especially the metal content of the polymetallic crusts, and in obtaining better morpho-bathymetric information on the sites of potential interest. Existing methods (hull-mounted multibeam sounders and rock dredging) must be used to perform a bathymetric survey and to take samples of large quantities of crust, as well as samples of the associated fauna. Following a solid sample analysis programme, it could be possible to verify, and maybe even confirm, the geological potential of the sector. Moreover, the existence and extent of certain targets of potential interest could be confirmed with a view to subsequent explorations using tools specially adapted to acquiring high-resolution data of the seafloor. A study of the spatial distribution of the biodiversity will also begin with these initial samples. It will have a profound effect on the direction of future geological and biological exploration and the evaluation of the resources. This campaign is the top priority.

38It could then be followed by research on the geological and biological exploration of other regions in the EEZ. Exploration techniques could be improved, especially using micro-drilling and in situ measurements of thicknesses and metal content and, in the longer term, suitable collection systems need to be developed for a pilot operation that could be the first step toward exploiting crusts on a global scale. Industrial exploitation would be conceived through extrapolation, involving choices between different industrial technology options, both in terms of reliability and efficiency and in terms of environmental impact.

39Environmental (e.g. impact on ecosystems and waste management) and societal (e.g. social acceptability and concurrent uses) aspects must be integral parts of this research from the start. As a whole, this would be a vast programme that could be incorporated into a European framework or in a “national strategy on deep-sea resources” in accordance with the measures announced during the Interdepartmental Committee of the Sea (CIMER) on 22 October 2015 with regard to “medium- to long-term planning for the exploitation of the ocean floor”, or a more regional framework, with other islands that are highly active in this area, or even with a partner such as Japan that may have an interest in the subject.

Notes

32 ROV: Remotely Operated Vehicle.

33 AUV: Autonomous Underwater Vehicle.

34 TGIR: Very large research infrastructure. FOF: French oceanographic fleet.

Table des illustrations

Légende Photo 2. The vessel Alis, from the French oceanographic fleet, docked at Papeete. © IRD/S. Petek
URL http://books.openedition.org/irdeditions/docannexe/image/9592/img-1.jpg
Fichier image/jpeg, 150k
Légende Figure 5. Futuristic vision of how could be “deep-sea mining” in French Polynesia. On this schematic drawing: 1/ surface structure such as a mining vessel, receiving ore, providing energy to the seabed gears, and transporting ore to a port or a nearby platform; 2/ riser: flexible pipe used to transfer ore from the seabed to the surface facilities and cables for energy; 3/ pump: propulsion of the divided materials in the riser (air lift); 4/ self-propelled mining gear: extraction, fragmentation and collection of materials (polymetallic crusts).© IRD/L. Corsini
URL http://books.openedition.org/irdeditions/docannexe/image/9592/img-2.jpg
Fichier image/jpeg, 256k

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