1 Historical Perspective

Although the first known discovery of deep-sea minerals (Fig. 1.1) was made during the expedition of H.M.S. Challenger (21 December 1872–24 May 1876) when the expedition leader C.W. Thomson described the dredge haul of polymetallic nodules on 7 March 1873 as ‘peculiar black oval bodies about 1 inch long’ and the chemist J.Y. Buchanan revealed that they were ‘almost pure manganese oxide’ (en.wikipedi.org/wiki/HMSChallenger), it was Mero (1965) who unravelled the economic potential of these deposits and predicted that deep-sea mining would commence in 20 years time that steered the world attention towards developing these resources as an alternative source of metals for the future.

Fig. 1.1
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Artist’s impression of association of deep-sea minerals with seafloor features

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A global effort during the conference on ‘Ferro-manganese deposits on the ocean floor’ at Lamont Doherty Geological Observatory in January 1972 to collate existing data on nodules was followed by studies dealing with distribution, geochemistry, and mineralogy of the deposits in different parts of the Pacific Ocean (Hein et al. 1979; Thijssen et al. 1981; Glasby 1982; Usui and Moritani 1992), as well as Indian Ocean (Glasby 1972; Siddiquie et al. 1978; Frazer and Wilson 1980; Cronan and Moorby 1981). Many of the studies also deciphered the formation process, geological factors as well as their relationship with sedimentary environment (Cronan 1980; Frazer and Fisk 1981; Glasby et al. 1982; Rao and Nath 1988; Martin-Barajas et al. 1991). Simultaneously, hydrothermal sulphides (Rona 1988; Plueger et al. 1990) and cobalt-rich ferromanganese crusts (Halbach et al. 1989; Hein et al. 1997) were also identified as potential resources.

Following the initial studies, extensive exploration programs ensued leading to several entities laying claims over large tracts of seafloor with potential resources in the international waters for gaining exclusive rights under the United Nations Convention on Law of the Sea, which led to the establishment of International Seabed Authority with its headquarters in Jamaica in 1994 for regulating the activities in the ‘Area’, i.e. in the international waters beyond the national jurisdiction of any country. Whereas until 2010, there were eight Registered Pioneer Investors subsequently called the ‘Contractors’ (France, Russia, Japan, China, Korea, Germany and InterOceanMetal Joint Orgnisation —a consortium of East European countries—in the Pacific Ocean and India in the Indian Ocean), all of them for polymetallic nodules only; a sudden spurt of applications was witnessed raising the number to 25 by 2015 for nodules, crusts, and sulfides (Table 1.1, Fig. 1.2a–d) (www.isa.org.jm (2016)).

Table 1.1 Contractors for exploration for (a) polymetallic nodules, (b) ferromanganese crusts, (c) hydrothermal sulphides
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Fig. 1.2
figure 2figure 2figure 2figure 2

(a) Map of exploration areas for polymetallic nodules in Pacific Ocean (www.isa.org.jm). (b) Map of exploration areas for ferromanganese crusts in Pacific Ocean (www.isa.org.jm). (c) Map of exploration areas for hydrothermal sulphides in Atlantic Ocean (www.isa.org.jm). (d) Map of exploration areas for polymetallic nodules and hydrothermal sulphides in Indian Ocean (www.isa.org.jm)

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Persistent interest in exploring these mineral resources, coupled with continued research and development for new technologies for prospecting as well as mining and extracting the metals from these ores, has led to numerous publications in several journals, symposia proceedings, and reports. The objective of this book is to synthesize all the information and make it available in a concise form so as to make it available for future generations. This chapter provides an overview of the hypothetical estimation of potential of one of the mineral resources in a typical area and introduces economic, technical , environmental, and policy issues related to deep-sea mining. The subsequent chapters deal with each of these issues in detail on the basis of actual experimentation and analysis.

2 Economic Issues

Periodical evaluation of information on distribution and potential of deep-sea minerals as well as techniques for resource estimation and mining (Pearson 1975; Glasby 1977; Cronan 1980, 2000; UNOET 1982, 1987; Dick 1985; Kunzendorf 1986; Rona 2003) has kept the world’s interest in these deposits alive, even leading to the preparation of a geological model for polymetallic nodules in the Clarion-Clipperton Fracture Zone of the Pacific Ocean (ISA 2009). Reports of Fe-Mn deposits from the Christmas island region and Afanasiy-Nikitin seamounts of the Indian Ocean (Exon et al. 2002; Banakar et al. 2007) as well as the Marshall island area of the Pacific Ocean (Usui et al. 2003) and the granting of licences to private entrepreneurs for exploration of seafloor massive sulphides off Papua New Guinea and New Zealand (Gleason 2008) reaffirm the continuing interest of researchers and mining companies in exploring and exploiting the deep sea mineral deposits, indicating the possibility of gradually developing technologies for mining of marine minerals from relatively shallower deposits such as the crusts and sulphides (1000–2500 m) towards the deeper ferro-manganese nodules (4000–6000 m).

Fluctuating metal prices as well as factors such as recycling, new onshore deposits, and technological developments have stalled the commercial exploitation of these deposits, although these are considered important in the overall metal budget of the earth and constitute a substantial resource that would cover the twenty-first century demand for metals such as Mn, Fe, NI, Co, Cu, Mo, and many others including Rare Earth Elements (Kotlinski 2001). According to Lenoble (2000), the commercial viability of deep-sea deposits lies in their concentration compared to the currently mined deposits on land and also in their estimated magnitude. As per one estimate (Glumov et al. 2000), considering the present trends of mining ores with low metal grades, mean metal contents in deep-sea manganese oxide ores will be higher than those in the terrestrial deposits by factors between 1.1 for Ni and >5 for Co in about 2020.

The decision to commence mining of any deep-sea mineral will depend on the availability of metals from terrestrial sources and their price in the world market, as well as the techno-economic analysis based on capital and operating costs of the deep-sea mining system. With each of the Contractors being allotted areas averaging several thousand square kilometers in international waters (ISA 1998), considering the resource potential in a typical area of 75,000 km2. for polymetallic nodules and their cut off abundance (5 kg/m2) as specified by UNOET (1987), the total resource available in the area could be 375 Mt (wet) or 281.25 Mt (dry) with a total metal equal to 67.081 Mt (Table 1.2), at a conservative value of concentration of metals (Mn = 22%, Ni = 1.0%, Cu = 0.78%, Co = 0.1%). Out of the 281.25 Mt, only 10.6–21.2% (i.e. 30–60 million tonnes) of the resource will be used at the proposed mining rate of either 1.5 million tonnes/year (ISA 2008a) or 3 million tonnes/year (UNOET 1987) over duration of 20 years, with a large balance (78.8–89.4%) to be mined in future.

Table 1.2 Resource potential and metal production estimates—a hypothetical case study
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The total annual production of metals would range from 0.358 Mt/year (for 1.5 Mt/year) to 0.716 Mt/year (for 3 Mt/year). Considering average metal prices for a given period (www.metalprices.com (2011)), the value of total metals produced annually will be $936.5 million, with a total yield of about $18.73 billion in 20 years from a single mine-site at 1.5 Mt/year mining rate. The same would be double (i.e. $1873 million/year, or ~$37.46 billion in 20 years) for a mining rate of 3 Mt/year (Table 1.2). Here it must be noted that these estimates are based on minimum value of metals and also lowest value of abundance and so the actual returns could be much higher as the in-situ average abundances are normally expected to be higher than the cut off (i.e. 5 kg/m2) and also the concentrations of metals could be higher in the potential mine-sites than that considered here as have been reported in the Pacific Ocean (Herrouin et al. 1991).

In spite of such a potential, most of the deep-sea mineral deposits can only be termed as ‘resources’ (and not ‘reserves’) as they cannot be economically recovered under prevailing economic conditions, but may be exploitable in the foreseeable future and such resources could become economic when price and market conditions or new technologies increase the profit margin to acceptable levels (UNOET 1987). According to estimates, the cost of different types of collectors, power generation, and risers, as proposed by different Contractors that are involved in developing technology for mining at 1.5 Mt of nodules annually, shows a capital expenditure of $372–562 million and an operating cost of $69–96 million/year. Added to this would be the capital expenditure for purchasing three vessels for ore transfer estimated at $495–600 million, with an annual operating cost of $93–132 million and a capital expenditure of $750 million for the processing plant with an annual operating cost of $250 million (ISA 2008a). Even if we consider the highest values (rounded to the nearest 50), the total estimated cost of a single deep-sea mining venture works out to $11.90 billion (Table 1.3), which when compared with the total yield of metals worth $18.73 billion (Table 1.2) may seem promising.

Table 1.3 Estimated capital and operating expenditures for polymetallic nodules mining [figures in brackets show the range for different systems as proposed by different Contractors (ISA 2008a)]
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However, in order to ‘fix’ the timing for commencement of deep-sea mining, a detailed economic study looking at the CAPEX and OPEX with respect to production rates and metal values is required to arrive at an optimum mining rate. Most of the earlier studies conducted in 1970s and 1980s based on conditions existing at that time suggested that processing of 3 Mt/year could be less costly per tonne of nodules (UNOET 1987). Calculations had also shown that mining of 3 Mt/year using a single ship was not viable, except in case of higher nodule abundances, higher ship speed, or larger dredge head (Glasby 1983). Earlier estimates for a 2 Mt/year operation, when the capital investment was estimated at $250 m and metal prices were significantly lower than considered here, showed the expected rate of return at 13% per year (Mero 1977). Alternative scenarios of mining operations from 1.2 to 3 million tonnes per year for a 20 year mine-life produced internal rates of return ranging from 14.9 to 37.8% (ISA 2008a). This scenario could undergo a change taking into consideration the techno-economic feasibility as well as metal markets.

3 Technical Issues

3.1 Delineation of Mine-Site and Estimation of Area for Mining

A ‘mine site’ is defined as an ocean bottom area where, under specific geological, technical, and economic conditions, a single mining operation can be carried out for a period of time. For example, the following criteria have been suggested for polymetallic nodules (UNOET 1987):

  • Cut off grade = 1.8% Cu + Ni

  • Cut off abundance = 5 kg/m2

  • Topography = acceptable

  • Duration (D) = 20 years

  • Annual recovery (A r) = 3 million dry tonnes, which has been subsequently proposed as 1.5 million tonnes by ISA (2008a).

Using this information, the total mineable area (M) can be estimated as follows:

$$ M={A}_{\mathrm{t}} - \left({A}_{\mathrm{u}}+{A}_{\mathrm{g}}+{A}_{\mathrm{a}}\right) $$
(1.1)

where, A t = total area,

  • A u = area un-mineable due to the topography,

  • A g = area below cut-off grade;

  • A a = area below cut-off abundance.

Furthermore, the size of mine site (As) can be calculated as:

$$ {A}_{\mathrm{s}}=\frac{\left({A}_{\mathrm{r}}\right)(D)}{\left({A}_{\mathrm{n}}\right)(E)(M)} $$
(1.2)

where,

  • A s = size of mine-site (km2),

  • A r = annual nodule recovery rate (dry tonnes/year),

  • D = duration of mining operation (years),

  • A n = average nodule abundance in the mineable area,

  • E = overall efficiency of the mining device (%),

  • M = proportion of mineable area.

Higher the average abundance, smaller would be the size of the mine-site with respect to the allotted area that augers well with the concept of restricting the mining activities to a smaller area, especially from the point of environmental impacts.

3.2 Mining System Development

The overall efficiency (E) of a mining system would largely depend upon the collection efficiency of the dredge head that would sweep the seafloor to collect the minerals which is calculated as (UNOET 1987):

$$ E={e}_{\mathrm{d}}\times {e}_{\mathrm{s}}, $$
(1.3)

where,

  • e d = dredge efficiency, which is the ratio of minerals effectively gathered by the dredge head, versus the minerals on the seabed before dredging,

  • e s = sweep efficiency, which is the percentage of the bottom actually swept by the area dredged.

The efficiency of deep-sea mining would also depend on the system for lifting the minerals to the surface, such as, the air-lift, which has 2–5 times higher energy consumption, but is easier to maintain as the compressors are above the water surface as compared to the hydraulic lift, which requires less power, allows higher transport densities, and hence needs smaller pipes for lifting the minerals, but is difficult to maintain due to under water pump system (Amann 1982). Given the high investment–high risk nature of the operations, future technology could consider deployment of a number of autonomous vehicles operating from the mining platform that would provide better operational and maintenance options, even from environmental point of view due to limited area of contact of these devices with the water column and the seafloor; and also in recovery or abandoning them in case of a mishap, as the mining platform and collection devices would be independent of one another (Sharma 2011).

Information available in public domain suggests that development of mining technology has been in different stages, including model studies and a few at-sea tests of crawlers and lifting mechanisms by the Contractors (Table 1.4). However, once these designs and prototypes are tested, the real challenge lies in up-scaling and integrating different subsystems and making them work on a sustained basis continuously for ~300 days/year under variable conditions, including extreme weather (rainfall, winds, and cyclones), hydrographical conditions (high pressure, low temperature, currents, and lack of natural light), and seafloor environment (undulating topography, sediment thickness, and heterogeneous distribution of deposits).

Table 1.4 Status of mining and processing technologies for deep-sea polymetallic nodules
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Application of new technology for exploration as well as mining, such as 3D sensing, autonomous navigation, robotic manipulators, and vehicles for the extreme environment adopted from space missions, could provide some of the solutions (Jasiobedzki et al. 2007). Similarly, advances in floating oil platforms, availability of riser hardware for deep-water and harsh environments, sub-sea power systems and pumps required for mining (Halkyard 2008), as well as the advantages of flexible risers in connecting pumps and power cables, reduced top tension for surface vessel, ability to retrieve and reinstall, and easy handling in severe weather conditions could provide the much required technological support for development of sub-sea mining systems (Hill 2008).

Major research efforts have been concentrated on the development of collector and riser systems (Chung 2003), whereas very few studies have been conducted on the mining platform and ore handling or transfer at sea (Amann 1982; Ford et al. 1987; Herrouin et al. 1991) that have proposed possible designs, dimensions, and infrastructure required to support a deep-sea mining activity. This sector (mining platform and ore transfer) may have to depend on existing infrastructure available for offshore oil and gas production and bulk carriers to be modified into mining platforms and transport vessels.

3.3 Processing Technology and Waste Management

Different Contractors are pursuing different approaches or processing routes mainly depending on the number of metals to be extracted (Table 1.4). According to a study ‘the incremental capital requirement of manganese recovery (in addition to Cu, Ni, Co) in a four metal route over a three metal route was small enough to make a 1.5 Mt/year capacity plant economically viable’ (ISA 2008b). Further, it has also been suggested that ‘a three metal recovery system needed to operate at higher annual capacities, with 3 million dry tonnes per year; whereas, four metal systems with additional costs and revenues from manganese production can operate at half the capacity’. Finally, the decision of extracting three or four metals will depend on the metal prices, available technology, investment potential, and the returns expected from such investments. In terms of post-processing scenario, probably the least attention has been given to the disposal of material that will remain after extraction of metals. In case of polymetallic nodules, it amounts to large quantities of material (as high as 76% in case of four metals and 97.5% in case of three metals) for which due consideration is required for either disposing them or using them for any ‘constructive’ purpose (see Wiltshire 2000; Wiltshire, this issue).

4 Environmental Issues

4.1 Impact of Environment on Mining

Generally in case of any developmental activity, the issue of the impact of the activity on the environment occupies higher significance not realising that the component of ‘environment’ has a two-way implication. As in case of deep-sea mining, the activity in most likelihood would have an impact on the marine environment; the reverse, i.e. impact of environment on mining activity, is equally important because the prevailing conditions such as atmospheric, hydrographic, seafloor topography, mineral characteristics, and associated substrates at the mine-site would play a major role in the design and performance of different sub-systems of the mining system (Table 1.5). Hence, collection of environmental data would not only help in impact assessment after mining activity, but also play a key role in designing of the mining system as well as planning of the mining operation (Sharma 2011).

Table 1.5 Influence of environmental conditions on mining system design and operation
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4.2 Impact of Mining on Environment

It is known that the areas likely to be affected by deep-sea mining would range from the surface and water column due to particles discharged (accidently or otherwise) during lifting, at-sea processing, and transportation (Pearson 1975; Amos et al. 1977) to the seafloor where the mineral will be separated from the associated substrate either due to scooping or drilling, leading to resuspension and redistribution of debris in the bottom water along the path of the collector device as well as in the vicinity of the mining tracks (Foell et al. 1990; Trueblood 1993; Fukushima 1995; Tkatchenko et al. 1996; Sharma and Nath 2000; Theil 2001; Sharma 2001, 2005) and the land due to metal extraction and tailing disposal (Fig. 1.3).

Fig. 1.3
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Areas likely to be affected due to different activities of deep-sea mining

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The first impact assessment study for deep-sea mining was during two of the pilot mining tests under the Deep Ocean Mining Environment Study (DOMES , 1972–1981) conducted by Ocean mining Inc. (OMI) and Ocean mining Associates (OMA) in the Pacific Ocean (Ozturgut et al. 1980). Subsequently, several experiments have been conducted by Contractors for assessing the potential impacts using devices such as the plough-harrow as well as a hydraulic sediment re-suspension system in the Pacific and Indian Oceans (Table 1.6). Their results have shown that the scale of these experiments was significantly smaller than that expected during commercial mining (Yamazaki and Sharma 2001). Syntheses of the results of these experiments have revealed the need for several improvements for conducting similar experiments in future (Morgan et al. 1999). An engineering and environmental assessment of deep-sea mining has suggested to ‘test benthic disturbance in scale and system large enough to represent the commercial mining scale’ (Chung et al. 2001).

Table 1.6 Basic data of Benthic Impact Experiments (BIEs) for assessing potential environmental impact of nodule mining
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5 Policy Issues

A deep-sea mining venture requires the implementation of several components starting with ‘Exploration and resource estimation’ followed by ‘Technology development’ for mining and metallurgical processing, and ‘Environmental’ component so as to establish baseline conditions, undertake impact assessment and monitoring, leading to development of environmental management plan. The final execution of the project would depend on a ‘Techno-economic assessment’ as well as ‘Legal’ framework in order to guide the decisions and actions for implementation on the basis of inputs received from other components. Activities under each of these components could initially be independent of each other, but a close networking among these is required to execute the project.

In view of many of the deep-sea mineral deposits occurring in the international waters, any commercial activity related to them could have global implications for which the Preparatory Commission for the International Seabed Authority (ISA) initiated the ‘Draft regulations on prospecting, exploration and exploitation of polymetallic nodules in the Area’ (UN 1990). With increasing awareness for the need to regulate such activities in the international waters, it was also suggested that the ‘UN and ISA should draw up a concrete plan for keeping abreast of scientific progress and at regular intervals assess the need for revising regulations’ (Markussen 1994).

Since the formation of the ISA in 1994 (by article 156 of 1982 United Nations Convention on Law of the Sea), it has served as the regulating agency for all activities related to the resources in the Area (i.e. defined as the seabed and subsoil beyond the limits of national jurisdiction); beginning with the notification of the plan of work for exploration of the Pioneer Investors and the area allotted to them (ISA 1998) to the establishment of a comprehensive set of rules, regulations, and procedures for prospecting and exploration for polymetallic nodules in the international seabed Area (ISA 2000). Through a series of international workshops, ISA has also issued the recommendations for assessment of possible environmental impacts from exploration of nodules (ISA 2001) and for establishment of environmental baselines and associated monitoring program for exploration of polymetallic sulphides and cobalt crusts (ISA 2005). The International Marine Minerals Society has also prepared a code for environmental management for marine mining, which provides a framework for development and implementation of an environmental program for a marine exploration and extraction site by marine mining companies and for other stakeholders in evaluating such programs (www.immsoc.org/IMMS_code.htm (2011)).

Deep-sea mining is in an advantageous position due to the substantial lead time available to the regulatory agencies to put in place the policies required for exploration and exploitation of the seabed resources as well as the Contractors to adopt such guidelines and gear themselves up for a sustained development of this common heritage of mankind.