UMaine geologist helps identify critical minerals in northern Maine

In his career as a University of Maine geologist, Martin Yates has been recruited to help investigate geologic anomalies, but none like the one found last year on Pennington Mountain in Aroostook County. His work contributed to a major discovery of critical mineral resources of rare earth elements and trace metals that was the first of its kind in the eastern half of the U.S.

Chunzeng Wang, a professor at the University of Maine at Presque Isle, and John Slack, a U.S. Geological Survey scientist emeritus from Farmington, met with Yates at his microprobe lab in the Bryand Global Science Center in early June 2022 to identify minerals in rock samples Wang collected from Pennington Mountain. In 2021, USGS found the first signs of the anomaly during an airborne survey, and Wang traveled to the site to examine the rocks and collect samples for geochemical analysis.

For two, nine-hour days, Yates, Wang and Slack examined thin, polished rock samples the size of dominos using an electron microprobe. They also used the electron beams to measure various X-rays emitted from the rocks, the types and concentrations of which serve as signatures for identifying minerals.

At the culmination of their analysis, the three geologists found 15–20 identifiable minerals, including the highly desirable metals niobium and zirconium. According to the USGS, niobium is a crucial component in steelmaking and superalloys for jets. Zirconium is another rare metal used for manufacturing ceramics and some superalloys.

Following the mineral identification research at UMaine and other analyses conducted by the University of New Brunswick and ALS Laboratories, Yates joined Wang; Slack; and Anjana Shah, a USGS research geophysicist; and other scientists for an additional survey of the Pennington Mountain anomaly in late June 2022. Their trek, combined with more than a year of evidence, confirmed that it contained a unique combination of rare earth elements, niobium and zirconium all contained in trachyte, an igneous rock with feldspar crystals.

Rare earth elements are used to make smartphones and other electronics and renewable energy technology, according to USGS. A commercial mining operation in Mountain Pass, California, is the only one in the U.S. that harvests rare earth elements.

Yates says the team found that the rare earth elements and trace metal deposits in the mountain were created through hydrothermal mineralization. There has been no other evidence of mineralized trachyte in Maine that has been formed this way, Yates says, and it also confirms that the geologic anomaly was not man-made.

This trachyte-hosted rare earth element-niobium-zirconium occurrence is similar to others found across the world in China and Australia, according to researchers. Based on the similarities to these other occurrences and a lack of detailed mapping conducted in and around Pennington Mountain, researchers say it’s possible northern Maine may contain other notable quantities of rare and critical minerals.

Researchers published their findings in the journal Economic Geology. Wang is first author, with Yates, and other researchers from the USGS, Maine Geological Survey and the University of New Brunswick serving as co-authors.

“The discovery itself of this occurrence is of scientific interest. It’s something that’s not been described east of the Mississippi River before, so it’s exciting that we found this. Is this of economic significance? It only has potential,” Yates says. “I think that it will inspire some mining companies that are forward thinking and entrepreneurial to start looking at other possible occurrences in Maine.”

The initial survey that kick-started the Pennington Mountain investigation was part of the USGS Earth Mapping Resources Initiative. The effort aims to uncover more information about the nation’s geological framework and possible critical mineral deposits that could support the economy by creating new geologic maps, and by conducting new geophysical and topographic surveys and geochemical sampling.

Yates says little is known about the possible rare metals and other critical minerals present in Maine because the state has extensive forest cover, water, swampland and glacial till that typically block out signals from radiological survey drones used to uncover these resources.

“So the fact that we happened to find this and it happened to be confirmed by doing the legwork after finding it with the survey, suggests that there may be more deposits of this type in the state,” he says, “we have this — what I consider — a major success that has directly come out of the federal government’s mapping with these surveys.”

Yates says he was not surprised when Wang contacted him for help with the investigation. Yates is the only university geologist with a microprobe in Maine, and his ability to use it and expertise in mineral identification with it is also unique. The two geologists also have known each other for more than 20 years, and have worked together on many projects and co-advised several students.

“He is a powerhouse,” Yates says about Wang. “I have never seen anyone so energetic. I think he puts more days in the field than any other geologist that I know in the state right now. From the first moment that the snow is off the outcrops of northern Maine, he is out collecting samples.”

Yates says he also has collaborated with other geologists from the University of Maine at Farmington (UMF) over the years. Maine geologists are “a tight-knit group,” Yates says, particularly because they go to meetings and on trips together.

Inter-university collaboration between geologists from different institutions within the University of Maine System (UMS), including UMaine, UMPI and UMF, bolsters research efforts and generates more comprehensive findings, Yates says.

Partnerships between UMS geologists also benefits students by giving them access to expertise and resources not available at their home institutions, Yates says. For example, Yates offers unique equipment and instruction in mineral identification and analytical instrumentation not found outside of UMaine. Wang is one of the researchers in the state who conducts in-depth geological mapping.

“This is my role,” Yates says. “I feel I have a real responsibility to offer service and expertise and the analytical abilities our labs have to other campuses and colleges.”

Contact: Marcus Wolf, 207.581.3721; marcus.wolf@maine.edu