Subsea mining as a commercial venture has been around since the 1960s, however it has been slow to gain traction. The greatest barrier to its widespread adoption is environmental in nature. The question many countries are asking, including New Zealand, is ‘Can subsea mining be sanctioned whilst maintaining a focus on environmental sustainability?’

Subsea mining involves the extraction of mineral resources from the seabed, with a diverse range of resources available, from aggregates through to high value mineral deposits. The latter resources   include Seafloor Massive Sulphides (SMS), poly-metallic or manganese nodules, rare earths, copper and even diamonds. Deposits are generally found around hydrothermal vents (typically between 1,400 – 3,700 m below the ocean’s surface) which form above cracks in the ocean floor. These cracks usually occur in volcanic areas, meaning countries located on or around areas of tectonic instability, such as New Zealand, Fiji, Tonga, or Papua New Guinea, are rich in these deposits.

The attempts at subsea mining were first recorded back in the 11th century BC, when the Phoenicians mined beds of seashells to extract a material they used to make purple dye. Probably the first recorded mineral extractions occurred in the third century BC when divers mined copper ore (from a depth of 4 m) near the island now known as Heybeli in the Bosporus. It wasn’t until the 1960s and 70s however, when a number of consortia began mapping hydrothermal vents and the resources they contained, that the true potential for subsea mining began to be realised.1

Why would we want to mine under the sea?

Like all mining activities, there are four key criteria that need to be met:

  1. Is it technically feasible?
  2. Is there a good economic case for it?
  3. Does it comply with all applicable regulations and law?
  4. Will the public find it environmentally acceptable?

Before even considering these questions, some may ask ‘Why attempt such risky endeavours in the deep, when there are deposits to be found on land?’ The answer is two-fold; quantity and quality.

There are numerous onshore mineral deposits found around the world, with approximately 30% of the earth’s total surface area being land, and the remainder water. Though not exact, the ratio for mineral deposits would be similar, with 30% onshore and 70% offshore. This means there is likely a great quantity of mineral reserves yet to be found subsea. The other factor is the quality of the deposit. In many mining operations on land we can see only 12% of resources recovered.2 In contrast to this is the quality of subsea minerals, with their composition being such that they are nearly 100% recoverable from the extracted ore body.3 This is why on quantity and quality criteria, subsea mining can provide a compelling case.

Where is it happening?

There have been a number of attempts around the world at subsea mining, with varying degrees of success. De Beers has been mining economic amounts of diamonds from subsea deposits since the 80s. Currently the best potential deep sea site, the Solwara 1 Project, found in the waters off Papua New Guinea, is a high-grade copper-gold resource, and the world’s first SMS resource. This development proposes sea floor mining at depths of up 2000m. At the depths envisaged conventional sea floor mining techniques such as suction dredges must be replaced by specialised sea floor mining tools such as autonomous underwater vehicles (AUV’s) which can operate independently of the surface production support vessel (PSV) or remotely operated vehicles (ROV’s) .

One country that potentially could benefit from subsea mineral deposits is New Zealand. Though a small country, it has an economic exclusion zone of some 4m km2, twice as large as China’s, and due to the geology and formation of the country it is rich in seabed minerals. With huge reserves available it is understandable why it could be an attractive proposition. For example, an investigation undertaken in 2012 for NZ Petroleum and Minerals (the Government agency responsible for mineral exploitation) on the potential for New Zealand Seafloor Mining in the Kermadec Arc region established that there was a strong case for further exploration and investigation of these territories (Transfield Worley New Zealand, 2012). Whilst some of this potential will be enclosed within the ocean sanctuary area recently announced by Government intended to protect the marine habitat, significant areas remain outside the sanctuary.

However in order for New Zealand to make use of these minerals they would need confidence that potential environmental impacts from the project could be properly mitigated.

Technical and economic feasibility

Given the right resources, both human and economic, anything is technically feasible . In the area of subsea mining, many industries have been doing it for quite some time.4 Each project will have its own challenges, whether it is extraction or processing, but it’s safe to say that there are no real technical reasons why commercial-scale operations aren’t possible.

From an economic perspective, most mines only become profitable once they’ve been in full production for a number of years. The same inputs into the business case for a mine onshore will be the same for one subsea. Even though there will be technical and financial challenges, the greatest hurdle to overcome is environmental, which will necessarily impact the business case with the management of environmental effects requiring specific attention. Regulatory oversight will be an important component of any risk mitigation strategy. Delineation and resolution of such issues and challenges is a major consideration in the front end development of any commercial investment of scale.

What are the environmental concerns?

Under NZ law, the disturbance or removal of material from the seabed and the deposit of tailings to the sea floor as a result of the mining activity are restricted activities and require a marine consent from the Environmental Protection Authority (EPA). Mining companies are required to submit detailed impact assessments as part of the marine consent process. This includes identifying any effects of undertaking the proposed activities on the environment or existing interests or other activities undertaken in the area. Measures taken to avoid, remedy or mitigate any adverse effects must be taken into consideration. One of the biggest issues around subsea mining is the plumes that mining activity will create and the extent of disturbances and impact on the local seabed ecology Including seabed habitats, marine mammals and fish stocks.

New Zealand has had two proposals (an iron sands project and a phosphate project) rejected in the past twelve months, with some groups calling for moratoriums on subsea mining. This was due in part to the outcomes of the Environmental Impact Assessment (EIA) submitted by the companies which set out to predict the size and extent of the impact on the environment or existing interests. Rightly these models looked at a worst case scenario, being a year of full production with continually turbulent sea conditions, but given the variabilities inherent in these two factors the outcomes did not provide the certainty (as is the nature of all models) that people needed to see around likely environmental effects.

The question that thus arises is whether it is then possible to conduct mining activities in a manner that will never see this worst case scenario occur and thus reduce the likelihood of environmental harm? The short answer is yes.

There are many case studies globally of how proactive adaptive monitoring provides an acceptable solution to the management of environmental impacts; be it dredging near sensitive coral reefs in the Pilbara, marine construction next to sensitive industrial pipe intakes, or reclaiming close to countries borders, Advisian has been involved with them all.

Advisian’s solution

The key to arriving at an acceptable solution is to understand these receptors and cut-off limits and then model backwards to work out acceptable limits (xm3 of spoil) that won’t come close to breaching the limits. This is possible in New Zealand. A similar matrix to a dive table can be produced combining the months of the year (to account for seasonality), with relevant metocean conditions (like a Beaufort scale). Teams can then analyse how much can be mined every day without breaching any receptors. Tonnages can be increased or decreased accordingly to daily metocean conditions, thus managing the potential for plumes, and thus environmental harm.

Controlling the mining operation in this manner is a relatively simple task, with matrix results used as inputs into the economic model to ensure viability, and also as part of operational contractual terms to ensure compliance. Advisian is currently doing exactly this for current reclamation in Singapore and elsewhere in the world. The hard part is gaining widespread acceptance that the approach is valid and relevant to New Zealand.

Table 1: Tonnes of material to be mined based on lookup table

Next Steps

With the quantity and quality of resources available, subsea mining will eventually become more common. Countries along the Pacific Rim, or indeed anywhere with good volcanic activity in adjacent oceans, stand to reap the rewards when operations commence. For New Zealand in particular, this will mean adopting a different approach to examining the potential effects on the environment form plumes and mining discharges. We suggest a preferred approach is to give a greater cognizance to understanding the desired limits for where environmental receptors are breached, rather than seeking to gain a perfect understanding through the simple modelling of effects.


  1. (page 260)
  2. Thanatia, the destiny of the Earth’s mineral resources: a thermodynamic cradle to cradle assessment, A. Valero Capilla, 2014, World Scientific Publishing Company (page 628)
  3. (page 39)