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One primary area of interest for researchers on the Escanaba Trough expedition is to expand knowledge of the mineral resources found at seafloor spreading centers such as Escanaba Trough. Among these seafloor resources are potential deposits of minerals, deemed “critical” to national security and commerce, which have supply chains vulnerable to disruption.

Map of Pacific Ocean with outlines of continents, United States, Alaska, and U.S. Pacific islands labeled, and EEZ outlined.
Dark blue areas outline the Exclusive Economic Zone (EEZ) of the United States and affiliated islands.

Critical minerals are essential to the production of high-tech equipment in a wide variety of sectors including energy production, national defense, battery technology, information technology, and health care. Large quantities of critical minerals such as nickel, cobalt, and rare earth elements are fundamental components needed for a transition to renewable energy sources. Identifying domestic sources of these critical minerals contributes to strengthening supply chains and represents a potential revenue source for the U.S.

Escanaba Trough is the only seafloor spreading center within the U.S. Exclusive Economic Zone (EEZ). EEZs extend 200 nautical miles from the shores of coastal nations, granting them control of energy or mineral resources located therein, from surface waters to the seafloor. The U.S EEZ, at 4.4 million square miles, is larger than the country’s entire land area.

Map showing location of Escanaba Trough
Escanaba Trough.
 

At seafloor spreading areas such as the Escanaba Trough, which is part of the larger Gorda Ridge system, diverging tectonic plates allow heat from the earth’s mantle to interact with seawater, creating hydrothermal fluids rich with minerals. As these fluids heat up and rise back to the seafloor surface, they are cooled by seawater, forming mineral deposits known as seafloor massive sulfides. At Escanaba Trough, thick layers of sediment—up to 500 meters deep in places—serve to trap heat emitted by the tectonic boundary, allowing elements and minerals to gradually precipitate near active heat sources. While most of the hydrothermal systems at Escanaba Trough are no longer active, the mineral deposits they left behind are largely unexplored and poorly understood.

 

A metal mechanical arm grabs a rock from off the seafloor.
ROV Jason gathers a mineral sample from the seafloor.
 
Two metal mechanical arms each hold a piece of rock from the seafloor with the silty ocean bottom below it.
ROV Jason collects two mineral samples from the seafloor.
 

Of particular interest to the Global Marine Mineral Resources group is how hydrothermal systems change over time. Because most of the hydrothermal activity at Escanaba Trough either ceased long ago or is gradually cooling down, researchers want to know how mineral deposits there may be altered over time as they interact with seawater and move further from active heat sources.

 

A woman peers at a rock using a hand lens.
Amy Gartman, USGS Research Oceanographer and chief scientist for the Escanaba Trough expedition, examines a mineral sample with a hand lens.
 
A man shines a small light on some rock samples.
Tom Lorensen, USGS Physical Scientist, uses an ultraviolet light to examine mineral samples.

Previous studies of this area suggest that large quantities of sulfide minerals may be present in the sediments at Escanaba Trough. The Bureau of Ocean Energy Management (BOEM) and USGS work together to identify the location and extent of mineral resources within the EEZ, as well as to better understand the biology and ecology of the deep-sea environments where they are located. This combined inventory provides valuable information to ensure responsible stewardship over the submerged lands of the U.S.

 

Close-up photo of rocks that are orange in color with a thin middle section that is shiny metallic.
Iron-oxyhydroxide gossan, formed by weathering of massive sulfide. Dominantly porous orange goethite, with a compact darker to metallic layer of dense goethite.
 
Photo of a shiny, wet-looking gray rock with yellowish coating in spots.
Close-up of fine-grained pyrrhotite-rich massive sulfide.
A cracked piece of rocky crist from the seafloor that reveals the differences between the outside of the crust and its inside
Partially weathered hydrothermal chimney, composed mostly of barite (BaSO4). The white material is the outer weathered rind, where the disseminated sulfide minerals have been leached out by oxidation, leaving an orange iron oxide stain.
 

USGS partners with BOEM to characterize the U.S. EEZ with modern remote sensing systems to find areas favorable for critical minerals. The inventory of hard mineral resources will include identification of offshore areas where these minerals are likely to occur. These areas can be further characterized to help understand the broader environment, including the roles that these minerals play as part of the habitat and ecology of the deep sea.

Watch three short videos about this expedition, read other deep-dive stories to learn more about the hydrothermal systems and marine geology of Escanaba Trough, and read about why the USGS goes to such depths.

 

Photograph of three rocks arranged side-by-side with a plain background.
Close up of fine-grained seafloor massive sulfide containing the primary minerals pyrrhotite, sphalerite, and barite. Weathering has produced secondary minerals, including iron oxide and possibly jarosite.
Photograph of three rocks arranged side-by-side with a plain background.
Close up of fine-grained seafloor massive sulfide under an ultraviolet light source, revealing the minerals that fluoresce under the light.

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