Case Study - Chatham Rise phosphate mining

Chatham Rock Phosphate Limited (CRP) proposes to mine phosphorite nodules from the crest of Chatham Rise, about halfway between Banks Peninsula and Chatham Islands. The crest of the Rise is characterised by low sedimentation rates (because of the distance from land and prevailing currents) and high productivity which makes it favourable for both nodule formation as well as fish production.

CRP has a mining permit for 820 km2. It also holds two prospecting licences for surrounding areas. In June 2014, CRP applied for a marine consent under the EEZ Act. The application was declined in 2015. 4594 Initially consent was sought for a 35 year operation over an area of 10,192 km2. On 1 August 2014 the area for which consent was sought was reduced to 5,207 km2 by the withdrawal of the application’s eastern mining block. CRP proposed to undertake the mining in stages, restricting the first five years of the operation to the 820 km2 mining permit area (MPL 55549). Over the full 35 year period for which consent was sought, a total of some 1,050 km2 was to be mined.  

The mining was to be carried out by a specially built or modified vessel using a mining system designed by Royal Boskalis Westminster  (Boskalis). Phosphorite-bearing material was to be retrieved from the seabed by means of a trailing suction drag-head and mechanically processed on board the vessel. Phosphorite nodules greater than 2 mm would be separated from other material using sieves and logwashers and stored on the vessel. Waste material would then be released close to the seabed, using a discharge (sinker) pipe with a diffuser.

CRP proposed to mine three of its 10 km2 mining blocks each year, giving an estimated annual production of some 1.5 million tonnes. The mining would be at depths of up to 450 m. The applicant’s outline mining plan included provision for establishing mining exclusion areas aimed at protecting areas of particular scientific or conservation sensitivity and values as identified through a marine spatial planning exercise. The applicant stated that it intended to undertake a range of monitoring and environmental surveys, including seabed sampling and habitat creation trials.

 The potential effects of the proposal on the marine environment, which have been identified in the CRP application but are yet to be tested through the assessment process, are outlined in the table below:

Potential effect

Benthic environment

The mining operations will completely remove the upper layer of the seabed, including resident benthic fauna. Fauna directly above the seafloor – hyperbenthos – will also be removed/killed. There will be a long-term change in habitat from mixed nodule/soft sediment habitat to soft sediment habitat. Benthic fauna which live in soft sediments are likely to recover, taking at least 10 years to attain community complexity. Benthic fauna which depend on hard substrate are unlikely to recover due to the removal of the hard material. This fauna includes cold-water coral species and associated organisms. 

After the phosphoric material is extracted, the non-phosphoric material (approximately 85 per cent of the material extracted) will be returned to the seabed using a pipe. These tailings will be discharged approximately 10 metres above the seabed in the area that is being mined. The sediment will form a plume of suspended sediment. Depending on currents, the sediment plume will be transportedfrom the site of discharge (with distance depending on the sediment particle size) and sediment will subsequently settle on the seabed. The suspended sediment plume will have sedimentation effects on the benthic environment adjacent to the mining site (deposition of one to two centimetres could extend three kilometres from the mining blocks). CRP states that the suspended sediment concentration is predicted to be near background levels (around one milligram per litre) within about 15 kilometres of the mining site.

Approximately half of the marine consent area overlaps with approximately 60 per cent of a Benthic Protection Area (the overlap is 5,236 km2). These are areas which are closed to bottom trawling in order to protect seabed habitat. CRP states that it has identified mining exclusion areas (1,822 kilometres2) for protection from seabed disturbance which better recognise the values associated with the central crest of Chatham Rise. 

Water quality

The mining activity will result in the formation of a suspended sediment plume reducing water clarity. The disturbance of sediment will result in the release of chemical elements (nutrients such as nitrogen and phosphorus and trace elements such as arsenic, nickel and uranium) found in the sediments into the water column. CRP states that the elements released are likely to result in the 99 per cent ANZEEC trigger value being exceeded, but that following dilution, concentrations will not exceed the trigger value. In the case of uranium, there will be a near field concentration increase of 10 per cent.

Sediment quality

There will be discharge of organic matter after mining due to the incorporation of benthic biota in the mined sediment. This discharge is likely to increase oxygen demand.

If organic enrichment occurs, then the oxygen demand and consumption by bacteria decomposing the organic matter will increase, possibly leading to hypoxia or anoxia. CRP states that it will not result in anoxia at the water-sediment interface.

Food web

CRP has commissioned the development of a trophic model of the food web on the Chatham Rise. CRP states that the model indicates that much of the Chatham Rise fisheries resource is reliant on primary production through phytoplankton and the build-up of mesopelagic (200-1000 metres deep) food resource. It suggests that there is limited food dependency between fisheries and benthic fauna because the proposed mining is below the photic zone. CRP concludes that the trophic impacts of removing benthic fauna in the mining area will be minor in the broader context.


More than 200 species of fish have been identified on Chatham Rise. Key commercial species include hoki, hake, and ling. Fish may be impacted by increased suspended sediment, changes in water quality and noise. 

Marine mammals

Based on datasets of opportunistic sightings, CRP states that 12 species of whales or dolphin and one species group (beaked whales) have been observed in Chatham Rise waters between 1981 and 2007. These sightings include two threatened species (killer whale and the southern right whale) and three International Union for Conservation of Nature endangered species (sei, blue and humpback whales). Marine mammals may be impacted by noise created by mining activities, interactions with the mining vessel (e.g., ship strike), disruption of food sources, and introduction of pollutants into the environment.

CRP states that noise effects may occur within two kilometres of the vessel for some marine mammal species. It states that the sound levels produced by an operating dredger (similar to the equipment to be used on the mining vessel) are comparable to the sound levels produced by a similar sized ship transiting across Chatham Rise. It proposes consent conditions to avoid any impacts of noise on marine mammals.


Chatham Rise is one of the most important areas for seabirds in New Zealand, with the majority of seabirds being present over the course of a year. The high marine productivity in this area attracts foraging birds. CRP has identified that approximately 28 species are “key members of the Chatham Rise avifauna”, most of which are threatened or at risk. Seabirds may be impacted by interaction with the mining vessel (particularly lighting impacts), disruption of food sources, and the introduction of pollutants into the environment. 

Cumulative impacts

Currently, the only human use of natural resources on the Chatham Rise is fishing, which results in damage to benthic environments and by-catch of marine mammals, seabirds, and other non-target species. CRP has identified that approximately 92,000 km2 of the Chatham Rise (under 1000m depth) was trawled between 1989 and 2011. CRP states that the impacts of mining on the crest of the Chatham Rise (450 km2 over 15 years) will be proportionally very small compared to the area on the flanks of the Chatham Rise that has been and continues to be impacted by commercial fishing.

The cumulative impacts of trawling and mining have been addressed by CRP in response to a further information request. 3579  CRP proposes to mine 30 kmper year for 15 + years and after 15 years 450 km2 will have been directly affected (a larger area will be indirectly affected by the sediment plume) which is about 0.2% of the Chatham Rise shallower than 1000m. Bottom trawling activities directly impacted about 18,000 kmof the Chatham Rise in the 2012/13 fishing year. However, fishing activities often repeatedly trawl the seabed so the total trawling effort in the 2012/13 fishing year is estimated to be about 35,000 km and since 1989/90 it is estimated to be approximately 1,106,000 km2, which is about six times the area shallower than 1000m. There is discussion about the effects themselves in the additional information provided, including removal of benthic habitat, increase in suspended sediment, sound, etc.

CRP proposed an environmental compensation package to address effects which could not be avoided, remedied or mitigated. This is not strictly speaking biodiversity offsetting, as that requires the compensatory works to be closely related to the biodiversity impacts of the project. CRP’s proposal would involve the establishment of a trust that will receive $200,000 per annum (inflation adjusted) from CRP while mining operations are occurring. The trust’s funds would be expended in the following areas:

  • Scientific research of the Chatham Rise of relevance to CRP’s mining activities (e.g., research into the creation of hard substrate habitat for recolonisation);
  • Biodiversity and other environmental initiatives on the Chatham Islands (e.g., establishment of a second breeding colony for the Chatham Island albatross);
  • Research into and development of technological improvements in seabed mining methods which reduce adverse impacts on the marine environment; and
  • Other environmental initiatives related to the adverse impacts of CRP’s mining activities

CRP proposed an adaptive management approach. This approach restricted mining to the 820 square kilometre area of the Chatham Rise for the first five years of mining operations. Mining would be able to commence in the additional mining area only if:

  • The applicant has investigated the bathymetry, physical characteristics of the seabed, and benthic ecology of the additional mining area;
  • The plume modelling results have been confirmed based on current data for the additional mining area;
  • The applicant has identified mining exclusion areas in the additional mining area;
  • The Environmental Reference Group (made up of representatives of key stakeholders and scientists) has reviewed information gathered;
  • The applicant has been granted a mining permit under the Crown Minerals Act 1991; and
  • If total suspended solids concentrations exceed 50 milligrams per litre at a point five kilometres or greater away from the mining operations or at a point 50 metres or greater above the seabed the applicant must:
    -   Undertake additional monitoring to confirm that the threshold is exceeded;
    -   If the threshold is exceeded, advise the EPA;
    -   Undertake investigations to identify the point at which total suspended solids reach 50 milligrams per litre and the point at which they reach ‘background’ levels;
    -   Within three months of advising the EPA, complete an assessment of responses which will avoid, remedy, or minimise total suspended solid levels. If a solution is identified, identify timeframes for implementation.
    -   If an adaptive management approach is to be implemented, implement it in accordance with the timeframe identified.

CRP’s adaptive management approach also provided for the following response where an “unexpected adverse impact” is identified:

  • Advise the EPA of the unexpected adverse impact, which has not been defined;
  • Within three months of advising the EPA, complete an assessment of responses which will avoid, remedy, or minimise total suspended solid levels. If a solution is identified, identify timeframes for implementation; and
  • If an adaptive management approach is to be implemented, implement in accordance with the timeframe identified.

A decision to decline the application for consent was made in February 2015. In general, the Decision-Making Committee found that changes to the benthic environment were undisputed by any party to the application, and the physical and biological changes would be inevitable as a result of the proposed mining and sediment disposal methods. A key consideration for the Decision-Making Committee was determining how significant these changes would be, and in particular, the likely short and long term effects on benthic communities, and how they may be avoided, remedied or mitigated.

The destructive impact of the drag-head on the seabed and on the benthic fauna in and on the seabed was a major concern, given that:

(a) these effects could not be avoided, remedied or mitigated;

(b) the mining would largely be occurring in an area where the seabed is currently protected from trawling and dredging by the Mid Chatham Rise Benthic Protection Area;

(c) the effects would include the destruction of communities dominated by protected stony corals which are potentially unique to the Chatham Rise and which the Decision-Making Committee concluded are rare and vulnerable ecosystems; and

(d) the habitat would not return to its present form but rather would be transformed wholly into soft sediment habitat. 

Moreover, the return of waste material to the seabed stood to have adverse effects on the benthic habitat in and around the mining blocks and across the wider marine environment. 

Notwithstanding the efforts of the applicant to research, document and substantiate its case, the Decision-Making Committee was left with a lack of certainty about both the receiving environment and the adverse effects of the project on that environment and existing interests. Partly this is explained by the current state of scientific knowledge about the Chatham Rise marine environment, albeit well researched in some dimensions. But there were other uncertainties stemming from the fact that this would be the first seabed mining project ever undertaken at such depths anywhere in the world, and from the heavy reliance placed on insufficiently validated modelling to predict the impacts of the project.  

The Decision-Making Committee gave consideration to the likely economic benefit to New Zealand of the proposal. It was not persuaded that the proposal’s economic benefit to New Zealand would be of the significance argued by the applicant, or that reliance could be placed on economic benefits as a potential offsetting factor.

The Decision-Making Committee gave careful consideration to whether an adaptive management approach would allow the activity to be undertaken. It also, as required by Section 59(2)(j) of the EEZ Act, considered the extent to which imposing conditions under Section 63 of the EEZ Act might avoid, remedy or mitigate the adverse effects of the activity. 

The Decision-Making Committee's finding was that the destructive effects of the extractive activity, coupled with the potentially significant impact of the deposition of sediment on the areas adjacent to the mining blocks and on the wider marine environment, could not be mitigated by any set of conditions or adaptive management regime that might reasonably be imposed. The conditions proposed by the applicant, although they went some way towards addressing some of the risks associated with the proposal, did not allay the Decision-Making Committee’s basic concern about the adverse effects of the proposal on a distinctive and important marine environment. The various proposals made by the applicant for environmental compensation did not in the Decision-Making Committee’s view amount to mitigation. After weighing all the information and evidence, and taking into account the matters listed in Section 59 of the EEZ Act, the Decision-Making Committee concluded that the application could not be approved either in part or in whole. The Decision-Making Committee’s decision therefore was to refuse consent.


Last updated at 12:46PM on January 10, 2018