Critical Minerals Repositories Discovered in Northern Maine

“It’s a perfect example of the science working just as intended and the importance of scientific collaboration. Having all of us involved meant as soon as we identified the feature, Professor Wang was onsite within a day to do the recon work,” said Maine Geological Survey scientist Amber Whittaker, project lead for the MGS. “It shows how much there is still to discover about Maine’s geology.”

Geological exploration would be required to know whether this discovery might be an economically significant deposit. “If mining is eventually considered, a rezoning application would need to be submitted to DACF’s Land Use Planning Commission,” said Maine Land Use Planning Commission Acting Director Stacie Beyer. “It would need to meet Maine’s stringent environmental standards, including at least two years of baseline environmental monitoring before a mining permit application could then be submitted to the Maine Department of Environmental Protection.”

“This discovery shows the importance of new evaluations for potential critical mineral resources based on integrated studies involving geophysics, geology, and geochemistry,” said USGS scientist emeritus John Slack of Farmington, Maine, who participated in the project and coauthored the new publication.

“Northern Maine was geologically ignored for many decades until recently, when MGS received funding to conduct a multi-year bedrock mapping project with the support of the USGS STATEMAP program,” said Wang. “The MGS geologic maps helped narrow down the locations where more information could make a difference.”

The geologic feature was revealed by surveys flown by aircraft in 2021. The flights collected geophysical data, such as variations in Earth’s magnetic field and natural low-level radiation. These variations are created by different rock types beneath the trees and up to several miles beneath the surface. Because each rock type has its own signature, like a fingerprint, the data can give a better idea of what lies beneath the ground surface.

Once USGS scientists noticed the unusual feature in the data, they sent the results to Wang, who quickly went to Pennington Mountain to collect rock samples and then sent them to a laboratory for geochemical analysis.

“I was astonished when seeing the analytical results that the rocks were so significantly enriched in rare earth elements and several trace metals,” Wang explained. “Northern Maine is full of amazing geologic wonders. You never know what is next to discover.”

Analyses of these samples show that they chemically match similar rocks in eastern Australia and central China that are known to be enriched in rare earth elements, niobium, and zirconium. Rare earth elements are important components in electronics like smartphones, as well as renewable-energy applications like wind energy and battery components. Niobium, meanwhile, is an essential element in steelmaking, and in superalloys used for things like jet engines. Zirconium is primarily used in ceramics, as well as some superalloys.

Mapping and other geological work is continuing in the Pennington Mountain area. Future research aims to identify the depth of the geologic deposit, as well as how it formed, and which specific minerals contain the rare earth elements identified to date. The publication also suggests that similar deposits may exist in other areas of northern Maine, and that scientists hope to apply the lessons learned in Maine elsewhere in the country and in the world.

The study is entitled “A Recently Discovered Trachyte-Hosted Rare Earth Element-Niobium-Zirconium Occurrence in Northern Maine, USA” and is published in the scientific journal Economic Geology.