Mining of Deep-Sea Seafloor Massive Sulfides: A Review of the Deposits, their Benthic Communities, Impacts from Mining, Regulatory Frameworks and Management Strategies

Mining & Minerals - Evaluations / Deep Sea Mining

Boschen, and three co-authors, reported in 2013 that seafloor massive sulfide (SMS) deposits form in a suite of hydrothermal settings across a range of depths. Many deposits are of a tonnage and mineral grade comparable to land deposits and are attractive to mining companies. Economically viable deposits can be either active or inactive, with different biological communities present at each. These benthic communities may include specially adapted and endemic fauna that could be severely impacted by mining activity. Although there is currently no active SMS mining, recent research from Industry and scientific investigations is able to inform decisions on the
management of SMS deposits, including appropriate mitigation strategies to minimize the impact of mining activities. Mitigation strategies will likely focus on facilitating recolonization of areas impacted by mining, spatial management with open and closed areas and reducing the effects of sediment plumes from mining activity. Regulation of mining activity at SMS deposits can be complex, falling under national and international legislation alongside codes of practice issued by industry and other stakeholders.

Despite decades of research effort, there are still many unknowns about the ecology of SMS deposits, in particular for inactive SMS sites and the genetic and demographic connectivity of populations among deposits. With considerable industry interest in the exploitation of SMS deposits in the Western South Pacific Ocean, there is an urgent need to assess the potential impact of SMS mining, particularly on the benthic fauna, so that appropriate management strategies can be designed and implemented.

Although SMS mining is still at the prospecting and exploratory phase, exploitation of SMS deposits will probably occur in the next few years in the Western Pacific. Globally, numerous deposits have been identified from a suite of hydrothermal environments and depths, with a range in deposit size and mineral content. SMS deposits can either be hydrothermally active or inactive, although the distinction between these is not always clear. As well as commercially viable ore, deposits are also host to complex biological communities. These include a chemosynthetic community of hydrothermal vent specialists adapted to active deposits and a community of background fauna inhabiting inactive deposits. There is also the potential for another community to exist at inactive deposits adapted to the weathered sulfide habitat. Benthic communities
demonstrate complex distributions at deposits, with the vent communities also exhibiting particularly constrained biogeographic patterns. The connectivity, recolonization and potential recovery of populations at SMS deposits have not been studied in detail; vent populations have been investigated at various locations
but the ecology of populations at inactive deposits is largely unknown.

As there is no precedent for SMS mining, predicting the impacts is challenging. However, impacts are predicted to occur across all marine environments ranging from site to regional scale over short and of prolonged duration. The nature of these impacts will vary between deposit locations and with the equipment and methods used. Regulation of SMS mining falls under different legislation according to the jurisdiction under which the proposed project falls. Within the EEZ or legal continental shelf of a country, SMS mining is regulated by national legislation; outside of this, projects are regulated by international legislation implemented by the International Seabed Authority. There are also various codes issued by stakeholders to encourage best practice in mitigation strategies. Management of SMS mining should include the development of clear management objectives, a comprehensive environmental impact assessment, implementation of suitable mitigation strategies, establishment of a long-term monitoring program, and clear decision rules associated with changes.

It should be acknowledged that alongside the negative impacts of SMS mining on the communities at deposits, there is also an opportunity for improved understanding of deposit ecology through involvement with industry surveys and assessments and that there is a global need for the minerals found in SMS deposits.