Where the U.S. Might Find Critical Minerals: A National Map of Focus Areas

Focus areas for 23 mineral systems that could host critical mineral resources in the United States and Puerto Rico; the number of focus areas for each system is in parentheses. USGS map, from Dicken and others (2022).

Earth MRI

The U.S. Geological Survey launched the Earth Mapping Resources Initiative (Earth MRI) to modernize surface and subsurface geologic mapping of the United States, with a focus on areas that may hold critical mineral resources. It can inform strategies for secure and reliable domestic supplies of critical minerals, as required by Executive Order 13817 and the Infrastructure and Jobs Act of 2021.

Earth MRI is a collaboration between the USGS and the state geological surveys, represented by the Association of American State Geologists, to identify, prioritize and acquire new geoscience data for focus areas — places across the country with potential to host critical minerals.

How the focus areas were drawn

• A framework: mapping follows a framework of mineral systems and the deposit types associated with them that could host critical minerals. It defines a hierarchy of the geologic factors that control how mineral deposits form and are preserved; a mineral system hosts deposits that are related in both time and space.
• Workshops: using available geologic, geophysical, geochemical and mineral deposit data, teams of USGS scientists and state geological survey representatives outlined areas with evidence of the key features of one or more mineral systems.
• Alaska: its focus areas drew on statewide geological, geochemical, geophysical and mineral occurrence data and on earlier prospectivity analyses.
• Other evidence: known mining districts and mineral belts, areas of historical mining of critical minerals, recent exploration, and sometimes the mapped extent of rocks that may contain critical minerals — such as phosphorites or clays with known or potentially high concentrations of rare earth elements.

The focus areas are a first, broad screening tool for choosing where Earth MRI should gather new geologic, geochemical, topographic and geophysical data.

The first national map

More than 800 focus areas were identified for 23 mineral system types in Alaska, the conterminous United States, Hawaii and Puerto Rico — and the map above is the first national map to show them all. By choosing subsets of the underlying data, users can map focus areas for some or all of the 23 systems. The systems with the most focus areas are porphyry Cu-Mo-Au (109), basin brine path (85), mafic magmatic (77), Climax-type (70) and magmatic REE (68).

One system in detail: the mafic magmatic system forms in large igneous provinces related to mantle plumes or meteorite impacts.

PGE: platinum-group elements.

Lithium

Giant white spodumene crystals in a pegmatite in New England. Spodumene is an important source of lithium for electric vehicle batteries. Photograph by John Mars, U.S. Geological Survey.

Lithium is an important critical mineral, used widely in the growing market for rechargeable batteries and in the green economy — yet in 2021 the country had only one domestic lithium producer. The focus areas show places in the U.S. with lithium potential that, if developed, could increase domestic supply.

Three mineral systems could host it:

1. Porphyry tin: as the mineral spodumene, in pegmatites associated with granites — such as those along the Appalachians in North Carolina and Maine.
2. Lacustrine evaporite: in clays and evaporites in dried lake beds (salars) in the western United States.
3. Basin brine path: dissolved in brines, such as those of the Smackover Formation in Texas, Arkansas and Mississippi.

New data from Earth MRI could be combined with existing data to evaluate the lithium potential of these areas.

Three mineral systems that could host lithium, and known lithium deposits, in the conterminous United States and Alaska. USGS map, from Dicken and others (2022) and Karl and others (2019).

The data

• Focus area extents: Dicken and others (2022), a USGS data release.
• Known lithium deposits: Karl and others (2019).
• More about the initiative: Earth MRI.

Sources

Based on Jane M. Hammarstrom, Douglas C. Kreiner, Connie L. Dicken and Laurel G. Woodruff, "National Map of Focus Areas for Potential Critical Mineral Resources in the United States," Fact Sheet 2023–3007, February 2023, U.S. Geological Survey; a work of the United States government in the public domain. The import had kept only fragments of the fact sheet's text; its text and figures are taken from the fact sheet's PDF.