Sitting on a gold mine: US eyes deep-sea mining in the CNMI

By Mar-Vic Cagurangan

The U.S. government is seeking to explore deep-sea mining in federally managed waters offshore the Northern Mariana Islands in line with the Trump administration's bid to facilitate domestic production of critical minerals, ensuring secure supply chains for U.S. defense, infrastructure and energy sectors.

The Bureau of Ocean Energy Management has issued a request for information to solicit industry interests, launching the initial steps that could potentially lead to leasing the seabed for mineral harvesting in the CNMI’s outer continental shelf.

The outer continental shelf, which lies beyond a state's territorial waters, is under U.S. federal jurisdiction. It extends from the seaward limit of state waters—typically 3 nautical miles—to the seaward limit of federal authority, often up to 200 nautical miles.

According to the bureau’s solicitation, the target area is located west of the Mariana Trench National Monument along the eastern edge of the U.S. exclusive economic zone.

The area is approximately 35,483,044 acres with an approximate water depth of 3,700-25,100 feet and lies entirely within the federal waters. The southern boundary area is roughly an equal distance between Guam and Rota. The closest distance from Saipan is about 128 statute miles.

The Northern Marianas is the second U.S. territory marked for potential deep-sea mining, following American Samoa, where the seabed mineral harvest plan has been met with resistance.

The U.S. Geological Survey's report profiling marine mineral resources in the Pacific Islands indicates that the CNMI sits on an unexplored wealth, such as cobalt-rich iron-manganese crusts, iron-manganese nodules, phosphorite, epithermal gold, hydrothermal manganese and iron oxide, hydrothermal polymetallic sulfides and phosphorite.

“This RFI is not a final decision to lease and does not prejudge any future secretarial decisions concerning leasing on the OCS offshore the CNMI,” the bureau states in the solicitation published Nov. 11 in the Federal Register.

Upon assuming office for his second term in January, President Trump issued a series of executive orders “unleashing” America’s offshore critical minerals to explore more energy resources and cut its dependence on China.

“The Trump administration recognizes that an overreliance on foreign critical minerals and their derivative products could jeopardize U.S. defense capabilities, infrastructure development and technological innovation,” the bureau said.

The emerging deep-sea mining industry is targeting polymetallic nodules critical for technologies that produce and store energy, such as batteries for electric vehicles and components for renewable energy systems like wind and solar power.

Trump has directed the Department of the Interior and attached bureaus to facilitate and expedite critical mineral permitting, leasing and development of critical minerals.

BOEM said it is taking immediate action to accelerate the development of mineral resources and associated extraction technologies.

 RFI: BOEM requests information and comments from Indigenous communities, territory, state, and local governments, federal agencies, environmental and other public interest organizations, the deep-sea mineral mining industry, other interested organizations and entities, and the public, for use in the consideration of whether to offer OCS minerals for lease offshore the CNMI. Read the BOEM's request for information here.

What lies beneath

According to USGS, the following minerals are likely present in the CNMI waters:

Cobalt-rich iron-manganese crusts occur on the sea­mounts located east of the Mariana Trench. Data for crusts from nearby seamounts indicate that crusts on sea­mounts within that sector of the CNMI EEZ have an excel­lent potential to be thick and have high contents of cobalt, nickel, and platinum. It is recommended that these sea­mounts be explored for their mineral potential. These crust deposits represent an intermediate-term resource potential for cobalt, nickel, platinum and perhaps other metals.

Iron-manganese nodules have seldom been recovered from the abyssal plain surface to the east of the Mariana Trench. Nodules have been recovered at depth in sediment cores, indicating that the current high rates of sedimentation do not favor nodule occurrence on the sea floor.

Phosphorite deposits occur on the Cretaceous sea­mounts with iron-manganese crusts, and their distribution and grade are also poorly known. These deposits are typi­cally either small, high-grade deposits or more widespread, low-grade deposits. This deposit type probably has a long-term resource potential.

Gold deposits: Epithermal gold has not been found in the CNMI EEZ, but geologic considerations indicate that it may occur along the Mariana Arc in submerged calderas (such as Maug and Esmeralda Bank) and in areas of back-arc spreading, such as the Mariana Trough. Recent work along the Mariana Arc supports these speculations. If high-grade gold deposits do occur offshore, they would offer a near- to intermediate-term resource.

Manganese oxides of hydrothermal origin are known to occur extensively along the Mariana, Yap, and Palau volca­nic arcs. From analysis of 26 samples from the Mariana Arc, manganese averages 47 percent and zinc 0.26 percent. Man­ganese oxides cement sandstone and form layers within the sediments. In some places, the manganese deposits have high con­tents of molybdenum, nickel, zinc, and/or chromium. How­ever, because large deposits of most of these metals occur on the continents, they offer only an intermediate- to long-term resource potential.

Polymetallic sulfides, sulfates and sulfur of hydro­thermal origin have been found within the CNMI EEZ at four submarine sites along the Mariana Arc and at three sites along the eastern margin of the Mariana Trough spreading center. There is a good potential to find large, high-grade polymetallic sulfide deposits along the active Mariana Arc and back-arc basin. If gold- and silver-rich polymetallic sulfides are found within the CNMI EEZ, they would have a short- to intermediate-term resource potential.

Insular phosphorites averaging 20 to 26 percent P2O5 occur on Saipan, Rota, Tinian and Aguijan Islands. During the Japanese occupation of the islands, phosphate mining began on Rota in 1937 and on Saipan in 1938 and continued until the United States took control of the islands in 1944. During those few years, 236,000 metric tons of ore were mined from Rota and 88,000 from Saipan. Rota may contain as much as 300,000 tons of reserves and Tinian hosts about 30,000 tons of reserves, both at about 23 percent P2O5.

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