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RESTON, Va. — Low-level helicopter flights are planned over areas of Upper Michigan and northern Wisconsin to image geology using airborne geophysical technology. Data collection for this survey area will be conducted beginning in April for approximately 4 months, weather and flight restriction permitting. Surveying is expected to be completed by the fall.

The Michigan and Wisconsin flights are part of a national effort to map critical mineral resources needed to drive the U.S. economy and national security, searching below ground and in tailings from old mines. As directed by the Energy Act of 2020, the U.S. Geological Survey has identified 50 critical minerals essential to the U.S. economy and national security, with a supply chain vulnerable to disruption. The USGS partners on this effort with the Michigan Geological Survey, the Wisconsin Geological and Natural History Survey, and many other state geological surveys.

Flights will cover areas within Alger, Baraga, Chippewa, Delta, Dickinson, Gogebic, Houghton, Iron, Keweenaw, Luce, Mackinac, Marquette, Menominee, Ontonagon, and Schoolcraft Counties in Upper Michigan as well as Florence, Forest, Marinette, and Vilas County in Wisconsin.

The flights will be based out of various Michigan airports. Flights and landing areas could shift with little warning to other parts of the survey area as necessary to minimize ferrying distances and avoid adverse flying conditions.

The purpose of the airborne electromagnetic (AEM) survey is to provide images of subsurface electrical resistivity that expand the fundamental knowledge of geology underpinning an area covering parts of the Penokean orogen and the Midcontinent Rift System in Michigan’s Upper Peninsula into Wisconsin. These flights are a part of a two-year airborne data collection project, expected to finish in 2025. The survey is funded by the USGS Earth Mapping Resources Initiative and is designed to meet needs related to mineral resource assessments, regional geologic framework and mapping studies, as well as water resource investigations and surficial mapping studies. The AEM survey is focused on characterizing several major mineral systems, including critical minerals associated with mafic magmatic, volcanogenic seafloor, and porphyry systems.

The new geophysical data will be processed to develop high-resolution three-dimensional representations of near-surface geology from the surface to depths up to 1500 ft (roughly 500 meters) below the surface. The 3D models and maps derived from this project are important for improving our understanding of critical mineral resource potential, water resources, groundwater pathways near legacy mining areas, parameters for infrastructure and land use planning.

The helicopter will fly along pre-planned fight paths relatively low to the ground at about 100 – 200 feet (30-60 meters) above the land surface. The ground clearance will be increased as needed and will comply with Federal Aviation Administration (FAA) regulations. Flight lines will be flown along lines of variable orientation and spacing with approximate typical spacings ranging from 5000 ft (1500 m) to 6.2 miles (10 km).

A sensor that resembles a large hula-hoop will be towed beneath the helicopter to measure small electromagnetic signals that can be used to map geologic features.

None of the instruments carried beneath or on the aircraft pose a health risk to people, animals, or plant life. No photography or video data will be collected. The data collected will be made freely available to the public on ScienceBase, typically within one year of flight completion. The aircraft will be flown by experienced pilots that are specially trained and approved for low-level flying. The survey company works with the FAA to ensure flights are safe and in accordance with U.S. law. The surveys will be conducted during daylight hours only. Surveys do not occur over densely populated areas and the helicopter will not directly overfly buildings at low altitude.

The survey fits into a broader effort by the USGS, the Michigan Geological Survey, the Wisconsin Geological and Natural History Survey, and other partners, including private companies, academics and state and federal agencies to modernize our understanding of the Nation’s fundamental geologic framework and knowledge of mineral resources. This effort is known as the Earth Mapping Resources Initiative, and it includes airborne geophysical surveys like this one, geochemical reconnaissance surveys, topographic mapping using LiDAR technology, hyperspectral surveys, and geologic mapping projects.