The mining industry has seen an increasing interest in the mineral potential of oceans with rock formations on the seafloor, including ferromanganese crusts, manganese nodules, marine phosphorites, and seafloor massive sulphides, among others.
Since the 1970s, the US Geological Survey (USGS) has been investigating marine mineral potential, focused on the US’ exclusive economic zone (EEZ), which extends 200 miles from the country’s shoreline and allows control over the exploration and exploitation of marine resources in the area.
While the USGS’s main focus has changed over the years, in 2018, President Trump’s Federal Strategy on Critical Minerals issued a list of 35 mineral commodities deemed critical to the economy and security of the country.
This strategy, in turn, gave new directions to the USGS’s work. Analysis of the US’s potential mineral wealth helps the industry determine which regions and deposits are worth exploring, while also assisting stakeholders to understand the effects of mining on the marine environment.
As the US EEZ is larger than the land area of the country, the map demonstrates where the USGS performs scientific tests and conducts marine mineral formation studies. This research is focused on the means by which specific elements concentrate in these minerals and their global distribution and environmental setting. The agency also conducts research into the potential environmental impacts of extracting these deposits.
The team is currently continuing work on the intersection of ocean chemistry and marine mineral enrichment of specific elements; the geologic processes; the distribution of marine minerals, and the conditions under which marine minerals dissolve into ocean water.
USGS research oceanographer and leader of the company’s Global Marine Minerals project Amy Gartman explains more about the nature of marine minerals: “Typically, when discussing ‘marine’ minerals, we are talking about deep-ocean minerals, of which the three most widely discussed categories are seafloor massive sulphides, ferromanganese crusts, and manganese nodules. Each of these categories is totally distinct from the others, in terms of composition, rate of formation, and location within the oceans. There is currently no mining of any of these mineral types anywhere in the oceans.”
Gartman explains that their ‘ocean-hosted’ origin is a major reason why deep-ocean minerals differ from terrestrial minerals: “Since oceanic crust is much younger than continental crust, marine minerals are typically much younger than terrestrial minerals, and are much less removed from their conditions of formation.
“The oldest seafloor massive sulphide minerals we know about are only a couple of hundred thousand years old. Ferromanganese crusts and nodules may be tens of millions years old, and can provide a window into ocean history. The oceans and marine sediments are also the source of many of the elements in ferromanganese crusts and manganese nodules, and result in their particular enrichment patterns, for instance for cobalt, manganese, nickel, and copper.”
As well as deep-ocean marine minerals, there are a range of distinct coastal marine minerals, which are now being mined in some locations.
“These exist in offshore extensions of continental crust, or in the case of placer deposits, they are terrestrial minerals that have weathered offshore. While environmental impacts of mining coastal minerals occur in the coastal zone of the oceans, coastal deposits have much more in common with terrestrial deposits than deep-ocean deposits,” Gartman says.
Similar to terrestrial mining, marine minerals are also mined by different techniques, and have individual environmental hazards distinct from one another. For this reason, the potential of one marine mineral should be considered on its own merit rather than lumping them into a single category.
When asked about the most exciting marine discoveries, Gartman says: “Every sample we get back is interesting! For instance, in 2017, our team published a paper about ferromanganese crusts in the Arctic that had some enrichment in the element scandium, which was a clear illustration of the way that ocean basin chemistry influences mineral composition.
“Another paper from our group, [which came] out this year, explored the ocean chemistry-mineral relationship for the Pacific Ocean and found the oxygen concentration of seawater is a critical determining factor in element enrichment.”
Considering the huge size of the US EEZ, big areas are still left unresearched in terms of the extent and composition of minerals, and potential co-located living resources.
“Based on our research, we have predicted that there are broad regions of the US EEZ where such minerals may occur,’ says Gartman.
“The predictions are important working hypotheses, but it will take further observation, sampling, and experiments to be able to provide clear information on resource potential and environmental impacts,” she concludes.