Global Marine Mineral Resources

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Researching mineral resources that occur within the U.S. Exclusive Economic Zone and areas beyond national jurisdictions.

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Research Overview

The Global Marine Mineral Resources project researches deep ocean minerals within the U.S. Exclusive Economic Zone and throughout the Earth’s oceans.  Our research concerns the setting, genesis, and metal enrichment processes of mineral deposits, the relationship between marine minerals related and deep-sea biota, and the potential geochemical footprint of any seafloor mining. We aim to provide stakeholders with the best available science regarding potential resources and environmental impacts associated with accessing those resources.

Map of Pacific Ocean with outlines of continents, United States, Alaska, and U.S. Pacific islands labeled, and EEZ outlined.

Dark blue areas on this map outline the Exclusive Economic Zone of the United States and affiliated islands, which combined are larger in area than the entire land area.

Courtesy of NOAA. Click the map to expand.

A collection of three photos showing people performing various operations on a ship.

Shipboard operations from various research expeditions. Top: A dredge is wrangled back on deck. Photo credit: Kira Mizell, USGS. Bottom left: Amy Gartman photographs freshly collected samples. Photo Credit: Kiana Frank, UH Manoa. Bottom right: Kira Mizell cuts ferromanganese crusts with a diamond-blade saw on the deck. Photo credit: James Hein, USGS.

Project objectives include:

  • Geochemical characterization of mineral samples, including mineralogy and metal concentrations, and their variability regionally and globally
  • Correlation of oceanographic and geographic parameters with mineralogy and metal content to elucidate the controls on mineral formation and element enrichment, and to map prospective mineral regions within the global ocean
  • Investigation of mineral stability and metal mobility with exposure to seawater over time through experimental geochemistry to constrain geochemical effects of mineral disturbance
  • Collaboration with biologists to determine associations between minerals and the biological communities which inhabit and surround them
Cross-section of rock with distinct layers of sand grains at core then mostly black, each layer dated back millions of years.

Cross section of one of the thickest ferromanganese crusts ever recovered, with the depositional ages labeled and many textural layers shown that reflect changes in oceanographic conditions over its 74 million-year growth. This crust sample was collected by dredge from the Marshall Islands at almost 2,000 meters depth on a USGS research expedition in 1989.

Our findings inform stakeholders, including the public, government, industry, academics and NGOs, about mineral wealth and its environmental setting within the vast offshore territory of the U.S. and helps them determine which regions and deposits may warrant further research.

Seafloor Mineral Deposits

There are a wide variety of deep-sea mineral categories; however, our team focuses on those marine mineral categories that have the greatest resource potential.

Seafloor pavements and encrusted rocks are known as ferromanganese crusts (also called cobalt-rich crusts). These crusts grow very slowly, at several millimeters per million years, and precipitate onto exposed rock surfaces throughout the global ocean—they do not form where sediment blankets the seafloor. In the oldest parts of the seafloor in the northwest Pacific Ocean, some crusts have been forming for over 70 million years and can be over 20 centimeters thick. Crusts act as a sponge of sorts, adsorbing metals and other elements from seawater over these long periods of time, and are especially enriched in cobalt, manganese, rare metals such as tellurium, precious metals such as platinum, and rare earth elements.

Flat underwater surface with many rocks tucked in close to each other; bright stripes of tape on rod that is touching bottom.

A bed of manganese nodules from deep offshore of the Cook Islands. Photo taken during a Japanese research cruise in the year 2000. Nodules range from about 2 to 10 centimeters across. See a photo of more manganese nodules.

Over millions of years, spheroidal rocks called manganese nodules (or polymetallic nodules) form atop sediment covering the abyssal plains of the global ocean. These nodules form by the accretion of iron and manganese oxides around a tiny nucleus, such as a large grain of sand, a shark tooth, or older nodule fragment. Manganese nodules are usually golf-ball to baseball size and grow very slowly like ferromanganese crusts if they acquire all their metals directly from seawater, or they grow faster if they also acquire their metals from the pore-waters of the sediment on which they sit. Nodules are currently of great interest for mining due to high concentrations of manganese, nickel, copper, and sometimes lithium, as well as the straightforward nature of quantifying their distribution and density.

Seafloor massive sulfides (also called polymetallic sulfides) form at hydrothermal vents when seawater penetrates the ocean’s crust and becomes heated and chemically modified through interaction with crustal rocks and, sometimes, by input of magmatic fluids. The hot hydrothermal fluids then rise back toward the seafloor and precipitate minerals as they cool along flow paths and upon mixing with seawater. A wide variety of minerals form through hydrothermal activity, but seafloor massive sulfides are formed from reduced sulfur and may be enriched in copper, zinc, iron, gold, and silver. Hydrothermal vents exist along mid-ocean ridge spreading centers, extensional systems associated with subduction zones, volcanoes, and intraplate hotspots. Yet, seafloor massive sulfides likely extend beyond these active hydrothermal zones. We know the minerals persist after removal from the heat source because of the presence of volcanogenic massive sulfide deposits on land.

Very crusty rock with tan outer layer, gray core, and bright yellow center. Man's booted foot is in background.

Cross section of a barite and silica chimney from East Diamante Caldera in the Mariana volcanic arc, west Pacific. The yellow center surrounds the conduit through which the hot fluids vented; the yellow color is due to a trace of iron in the silica. The chimney also contains moderate amounts of sphalerite and galena. Importantly, this illustrates that not all minerals formed at hydrothermal vents constitute seafloor massive sulfide.

Marine phosphorites primarily occur along continental margins where upwelling of cold, nutrient-rich, deep water is strong. These areas include the Peru-Chile margin, on plateaus such as Chatham Rise offshore New Zealand, and the Blake-Bahamas Plateau off the southeast United States; but they can also form on seamounts where ferromanganese crusts grow. Phosphorites form when abundant phosphate in seawater replaces carbonate in calcareous sediments or precipitates in situ as apatite to form hardgrounds, phosphatic nodules, or cements in breccias of multiple rock types. Marine phosphorites are sources of phosphate used as fertilizer for agriculture and phosphoric acid in the food industry. Phosphorites can also contain high concentrations of valuable, heavy, rare earth elements that may be economically recoverable and can contain up to 4% fluorine.

Mostly beige rock with lots of round orbs contained within its matrix.

Cross section of phosphorite rock formed on the seafloor offshore Southern California where a long history of high biological productivity has provided the necessary phosphorous to from extensive phosphorite deposits, including hardgrounds and phosphatic nodules. Photo credit: Amy West.

Marine Mining Context

The oceans cover nearly three quarters of the surface of the earth, and in the U.S., the area of seafloor comprising the Exclusive Economic Zone is greater than the land area on shore. This enormous ocean realm hosts many types of minerals that differ from those occurring terrestrially. Ferromanganese crusts, manganese nodules, phosphorites, and hydrothermal vent deposits, which occur from the Arctic to the Antarctic, are enriched in many metals including those currently deemed societally critical. It is therefore important to understand these minerals and the role they may play as future mineral resources.

People around the world demand metals and mineral resources for many uses, including technology, electronics, and green energy infrastructure such as wind turbines and electric cars. Critical minerals are defined as those that are essential to the economic and national security of a nation but that have a supply-chain vulnerable to disruption. In 2018, the Department of the Interior released a list of 54 critical minerals that was further refined to 35 based on Executive Order 13817, with the list to be reconsidered biannually. Across the USGS, research is underway to define and prioritize focus areas throughout the United States with resource potential for these 35 critical minerals. The Global Marine Mineral Resources project specifically informs the marine component.

To date, there is no mining of deep-sea minerals. In Areas Beyond National Jurisdiction, any marine mining is governed by the International Seabed Authority, which is currently drafting exploitation regulations. The Global Marine Mineral Resources project has provided scientific advice to the U.S. State Department and has served as a member of the U.S. delegation to the International Seabed Authority as an Observer Nation for the last 20 years. Japan completed equipment testing offshore of Okinawa in the fall of 2017, recovering 4 tons of metal sulfide. For comparison, it has been suggested that an economic seafloor massive sulfide (SMS) mine would recover on the order of 1 million tons of metal sulfide minerals. There is one permitted mine for copper, gold, and silver offshore Papua New Guinea, on 0.1 square kilometer of seafloor; and the Cook Islands are revising regulations for manganese nodules mining.

A woman stands at a lab table looking at a rock sample that she's holding.

In the Marine Minerals Laboratory at the Pacific Coastal and Marine Science Center in Santa Cruz, CA, USGS physical scientist Denise Payan catalogs ferromanganese crusts for future subsampling and geochemical analyses.

Woman stands near and prepares to open the doors of large apparatus; her smiling face is reflected in the glass of the doors.

USGS research oceanographer Amy Gartman waits for an X-ray diffractometer to analyze samples of hydrothermal sulfide minerals.