The opportunities, challenges and advantages of deep-sea mining

Stef Kapusniak

  (1)Deep sea mining engineer


Mining in the sea is not a new activity. It has been done since the times of the Roman Empire, an example being with the mining of copper-bearing ores around parts of the coast of Cyprus. Mining underneath the seafloor is also not a new activity, with historic mining of coal underneath the seafloor having taken place off many coastlines across the world. The safety and environmental standards that society expects to be met have become tougher to meet over time and what was once deemed as socially acceptable is not necessarily acceptable today. Currently, dredging in relatively shallow coastal areas for aggregates, tin, titanium, gold, diamonds, salt and other minerals takes place at many places across the world and is considered by many as socially acceptable. Deep-sea mining, often classified as beyond 500m water depth, is not being carried out on an industrial scale, although there have been several prototypes and tests done at various ocean sites.

In recent times, advances in offshore exploration technology have enabled anallowed the increase in our knowledge and understanding of remote deep-sea mineral deposits. This increased knowledge has occurred not just in terms of mapping and measuring the physical characteristics of the mineral deposits and their potential value, but also in terms of mapping the presence and nature of any associated flora and fauna. The interactions and dependencies between sub-sea species is also being actively studied. Nevertheless, the deep-sea environment is still a relatively unexplored space compared to the earth’s land masses.

Mineral Opportunities

The main types of ore in the deep sea are ferro-manganese crusts, polymetallic nodules, and mineral rich sulphide deposits. There are some potentially attractive crusts on the top of submerged seamounts. These crusts are relatively thin, but potentially extractable and some areas have attractive concentrations of cobalt and other metals needed for electric vehicles and green energy applications. Nodules have been found to cover vast areas of the abyssal plains. Some of the more attractive resources from a metal content perspective are at a depth of up to 6000m. In addition to manganese and iron, the crusts and nodule resources in the deep sea are in some cases rich in cobalt, copper and nickel. Sulphide ores are often found adjacent to hydrothermal vents. These can be active or dormant subsea volcanic areas and the more attractive resources may typically contain good concentrations of copper and gold.

Some of the subsea areas have rare earth minerals, but to the author’s knowledge, heavier rare earth minerals have not, so far, been found in sufficiently desirable concentrations to justify exploitation, other than perhaps as a by-product or co-product.


Challenges remain from environmental, legal, technical and practical perspectives


Fundamentally, all types of mining activity - whether on land or at sea - have an environmental footprint and impact of some sort. Concerning deep-sea mining, the question remains as to whether the impact can be minimised to an extent that would prove to be environmentally and socially acceptable. Some areas of the seabed are more environmentally sensitive than others and some are relatively barren other than with respect to the micro-fauna and microbes found there. Also, some ore deposits are easier to mine than others and the process of extracting the ore can in some cases be more akin to “collection” than to digging - which could, in some cases, potentially minimise impact. This is particularly the case of polymetallic nodules.

Care needs to be taken with the design of the mining or collection machines to minimise plume generation. This is a particular challenge in deposits with fine sediments and slow currents, as any plume generated would tend to hang in the water column before settling. The generation of plumes can hamper visibility and may also influence the local environment in some areas.


Granting of licences and oversight of mining in international waters is governed by the International Seabed Authority. In the case of polymetallic or manganese nodules, exploration licences are typically awarded for quite large areas with some being the size of small countries. Approximately half of a licence area is typically reserved for the “benefit of mankind”. This is designed to ensure that larger developed countries do not dominate future extraction of the world’s shared resources. Significant areas around the licence area are also set aside, as what could be described as environmental impact monitoring zones. Obtaining a lease in international waters also requires the sponsorship of a state which must be signed up to UNCLOS (the United Nations Convention on the Law of the Sea).

Technical and practical

There are many technical challenges due to the depth of the operation – particularly if the wave-height is significant. A mining/collection machine needs power, which is generally supplied by a large vessel when working in remote offshore areas. Getting power to a mining or collection machine - which is between 0.5 and 6 km away vertically - is not easy in a submerged and remote environment. This is also challenging for electrical and hydraulic control systems. There can also be large energy requirements for lifting the ore to the surface vessel or platform in deep areas.

Any mining equipment needs to be maintained from time to time, so there are also energy and equipment requirements to lift the mining machine back to the surface vessel. And on-boarding large machines in high seas can be a difficult and risky task. The weight of any lifting wire/cable, even when submerged, can be very high due to its high suspended length. Some of the subsea equipment would typically need high-quality syntactic foam buoyancy blocks.

With depth comes pressure; so, key electrical and electronic equipment on the mining machine may need to be enclosed in a very strong pressure-resistant vessel.

Care also needs to be taken in limiting the amount of unwanted sediment taken on-board the mining machine, as this may dilute the product and potentially require separation circuits on the machine – making it bigger, heavier and in need of more power. And of course, any unwanted sediment taken onboard the mining machine, or the surface vessel, would need to be placed back carefully to the seabed in a manner which encourages rapid settlement.

As is the case on land, variability of ore grade can be a challenge. If this is anticipated as a problem, then the design of the mining equipment and overall system needs to be able to rapidly assess the ore grade and react in a timely manner. With very deep areas, transportation of the mined/collected material to the surface may take significant time, in which case it would be preferable to analyse the metal content at the seabed – either in advance of mining, or directly on the mining/collection machine to ensure that the receiving hoppers on the vessel at the surface do not fill up with silt or low grade ore (which is difficult or costly to treat and process to extract the final product).

Some subsea areas have very corrosive environments. Sulphides are formed during subsea volcanic activity. The ejecta/smoke streams from hydrothermal vents can also cause increased corrosivity nearby. Some of the prototype mining machines used have been equipped with cathodic protection. The deep sea is a dark place. Sound travels a long way in water, but light does not. The smoke streams can also cause visibility issues or indeed interference to navigation systems that use smart sonar or LIDAR systems.

Advantages of deep-sea mining

Deep-sea deposits of minerals are relatively untouched and many of them are shallow, laying with no requirement to remove substantial overburden material, whereas the stripping ratio (overburden material to ore) on land has gradually increased over time as the easy access deposits have been mined.

As the world’s population grows and the underdeveloped parts of the world modernise, new sources of high-grade minerals will be required. It is unlikely that we would be able to recycle sufficient metals to cater entirely for the demands of the future, particularly if the current trends in population and mineral requirements per capita persist. While recycling and re-purposing of metals and other materials is improving, the costs and environmental footprint of the recycling activities themselves can become cost prohibitive.

Our understanding of the oceans and the life in it is also increasing. Approximately 70% of the earth is covered by seas and oceans, and a lot of the higher quality easy-access minerals on land have already been found and mined out. So, moving to the oceans is in many ways logical. As time and technology advancement progresses and exploration continues, more and more viable mineral reserves will be found in the deep sea. Navigation, visualisation, and other perception system technologies are improving. Sub-sea vehicle design and prototype deep-sea mining systems are starting to mature and advancements in robotics continue.


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