By Warren Day, U.S. Geological Survey
The Alaska Range, east-central Alaska, looking south. Photo: W. Day, USGS.
What it is
The Earth Mapping Resources Initiative (Earth MRI) is the USGS response to a federal directive to address weaknesses in the Nation's supply of critical minerals. It gathers new basic geologic data on the United States and its territories to find areas that may hold critical minerals — and makes the data public through the Earth MRI portal.
A critical mineral is "(i) a non-fuel mineral or mineral material essential to the economic and national security of the United States, (ii) the supply chain of which is vulnerable to disruption, and (iii) that serves an essential function in the manufacturing of a product, the absence of which would have significant consequences for our economy or our national security." — Executive Order 13817
How it started
| Date | |
|---|---|
| December 20, 2017 | Executive Order 13817 directs agencies, the USGS among them, to develop "a Federal strategy to ensure secure and reliable supplies of critical minerals" |
| December 21, 2017 | Interior Secretarial Order 3359 directs the USGS to plan better topographic, geologic and geophysical mapping, with the data made electronically accessible to support private-sector exploration |
| May 18, 2018 | the list of critical minerals, prepared by the USGS with other agencies, is published in the Federal Register — "final," but meant to be updated as supply, demand, production and policy change |
| June 4, 2019 | the Department of Commerce releases "A Federal Strategy to Ensure Secure and Reliable Supplies of Critical Minerals"; Earth MRI grows from it and Order 3359 |
Why it matters
Earth MRI is a national effort across all 50 States and the territories, run with the State Geological Surveys. More domestic minerals mean less reliance on foreign sources and less exposure to supply disruptions. The new data also help with:
- groundwater, geothermal and petroleum resources;
- natural hazards — landslides, flooding, earthquakes;
- sand and gravel for repairing infrastructure — roads, bridges and rail lines.
In Charleston, South Carolina, for example, a new aeromagnetic survey flown for geology and mineral potential is also revealing buried earthquake faults. Some data can even reveal archaeological and cultural sites.
Three kinds of data
1. Airborne geophysical surveys
The USGS contracts with specialist firms flying small aircraft from local airports — helicopters over rugged ground, airplanes over flat land — usually 300 to 500 feet (90 to 150 meters) up.
A helicopter carrying a magnetometer on a forward "stinger" for surveying rugged terrain. Photo: Benjamin Drenth, USGS.
- Aeromagnetic surveys detect tiny anomalies in Earth's magnetic field caused by the magnetism of soil and rock near and below the surface. Specialists turn the maps into 2D or 3D models of buried rocks. The method is passive — nothing is transmitted — and far cheaper than ground surveys over large areas.
- Radiometric surveys map natural gamma rays from potassium, thorium and uranium at the surface, usually flown with the magnetic surveys. Potassium-rich readings can trace granite under vegetation, or mark rock altered by hot water — often near mineral deposits. Also passive: they measure only natural radiation.
Aeromagnetic data as of April 2020: every part of the country has some coverage, but only the red areas have public data detailed enough for subsurface and 3D mapping; most surveys are old, of poor quality, or not designed for local geology. USGS.
2. Geologic mapping
New surface and bedrock mapping is carried out mostly by State Geological Surveys and universities: examining outcrops, mapping faults and folds, and collecting rock samples for chemistry and dating, which the USGS analyzes. The USGS is also building a database of drill-hole information with the States, to archive it and eventually make it public.
Bedrock geologic mapping at detailed (1:24,000) and intermediate (1:48,000 to 1:63,360) scales, as of February 2020; yellow areas are mapped too coarsely to assess critical-mineral potential. USGS.
3. Lidar elevation data
Earth MRI adds funding to the 3D Elevation Program (3DEP), which aims to finish nationwide lidar (and IfSAR in Alaska) by 2023 — the first national baseline of consistent high-resolution elevation. A laser on a high-flying plane sends pulses to the ground; the reflections form a point cloud and bare-earth elevation models, unobscured by vegetation (though lidar can't see below the surface). Lidar is critical for:
- mapping young deposits and landforms;
- underpinning geologic maps that guide mineral, energy and groundwater development;
- engineering studies;
- making geologic mapping faster and more precise — in some cases doubling the units that can be mapped.
Lidar (and IfSAR in Alaska) meeting 3DEP standards, available or under way, as of September 2020. USGS.
Getting the data
Everything Earth MRI collects — aeromagnetic data, interpretive maps, new geologic maps and lidar — is public, free and without use restrictions, through the Earth MRI website and The National Map. Users range from federal, State and Tribal governments to industry, universities and the public.
Contact: Earth MRI Science Coordinator, USGS Mineral Resources Program — minerals@usgs.gov.
Sources
Based on Technical Overview of the U.S. Geological Survey Earth Mapping Resources Initiative (Earth MRI), by Warren Day, USGS Fact Sheet 2020–3055, U.S. Geological Survey; a work of the United States government in the public domain. The maps and USGS photographs are taken from the fact sheet's PDF, which the import had left out; its photograph of a survey airplane, courtesy of EON Geosciences, is not reproduced.
Licence: CC0 1.0 (public domain) · Adapted from pubs.usgs.gov
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