Over the next year, you might notice what looks like a low-flying plane on a lollipop stick flying back and forth. Those flights are part of a federal geological survey of rare earth minerals over the Carolinas and Virginia that begins this month. And that lollipop stick is a passive sensor
U.S. Geological Survey geophysicist Anji Shah oversees an initiative to map critical mineral resources like cobalt and lithium in the Carolinas and Virginia. She said the data will provide a rough sketch of what lies miles beneath our feet.
“Industry might say, ‘Oh, there’s something there. Maybe I’ll explore this area in more detail,’” Shah said.
What are critical earth minerals?
Critical mineral resources are the elements that we use to manufacture the items we use day to day. Some of them like lithium and cobalt are used in electric vehicles. The Earth Mapping Resource Initiative was a response to an executive order issued by former President Donald Trump in 2017. The federal government identified 35 critical minerals, 14 of which the U.S. exclusively imports.
When I interviewed Shah, we were talking over Zoom.
“Right now, you and I are looking at a computer screen,” Shah said. “Our computer screen has all kinds of rare earth elements in it.”
The magnets inside my laptop speakers might contain the element neodymium. Our touch screens use the electrically conductive element indium to relay your touch input to your phone’s processor. Although rare earth minerals make up less than one percent of the weight of your phone, they are essential for everything we see and hear through our phones and computers.
What else is the plane looking for?
Shah said that there are other applications of the data, such as mapping earthquake hazards, geothermal energy resources and groundwater reserves. Past surveys of the Charleston area mapped a poorly understood seismic zone that produced a magnitude 7 earthquake in 1886. Understanding underground faults and folds can help geologists predict future seismic activity.
One of the plane’s sensors will pick up radioactivity, which can help geologists identify natural hazards such as radon gas. In North Carolina, 450 people die from radon-induced lung cancer every year. It is the leading cause of lung cancer among non-smokers across the nation, according to the U.S. Environmental Protection Agency.
The USGS will spend about a year processing the data once the survey is finished. Those maps and datasets will be made available here, on the Earth MRI website, where you can view the results of past surveys.
How does it work?
The magnetic sensor, or magnetometer, sticks out behind the plane on a boom, away from the magnetic interference of the plane’s engine. The plane will fly during the day at an altitude of 400-1,000 ft., depending on where it’s flying — it’ll fly higher over cities and lower in the countryside.
One sensor measures subtle variations in Earth’s magnetic field. Another sensor measures radioactivity. This sensor can detect elements like potassium, uranium and thorium.
The magnetic sensor collects data about what’s going on miles below the surface. Researchers will then be able to trace faultlines that extend deep underground. This would help scientists predict future earthquake hazards.
“Both methods map out geology underneath trees and vegetation,” Shah said. “This is a way of passively seeing under the skin of the Earth.”
Many rocks have a unique magnetic signature. For example, iron interacts differently with Earth’s magnetic field than, say, quartz.
Alkali metals, like lithium, aren’t magnetic, so the new maps won’t read like a battery-material treasure map. However, Shah said by mapping out the faults, folds and tectonic history surrounding a known lithium deposit — like Kings Mountain, North Carolina — scientists can learn more about the geologic “context of the lithium.”
“That can help geologists better understand perhaps where lithium is likely to occur,” Shah said.
Some elements do show up directly on the sensor. For example, thorium is a radioactive metal that suggests the presence of sand containing titanium and rare earth elements. This is something that geologists have observed along the border of the coastal plains and the Piedmont, along the route that I-95 runs. By flying over that land and looking for thorium, geologists can mark areas of interest for future mining operations.
