A Chinese research team has discovered that an orange lichen could help locate rare earth deposits in different parts of the world. The organism, identified as Xanthoria elegans, preferentially colonizes carbonatite rocks enriched with these elements, according to findings published on July 27 in the journal Economic Geology.
The discovery is only the second time Chinese scientists have identified a biological indicator for mineral exploration, following the use of copper grass for the same purpose in the 1950s. Rare earth elements are a group of metals used in magnets, batteries, wind turbines and electronics, and are considered critical for the energy transition.
Professor Li Yang, of Peking University and the Chinese Academy of Sciences, said the lichen's coloring comes from the organism itself rather than from the minerals it absorbs. He said that is what makes it such a reliable indicator, because it can be spotted from a distance.
Concentrated at the world's largest rare earth mine
Researchers detected the lichen on 57 of 67 mapped carbonatite rocks in the Bayan Obo mining zone in northern China, the largest rare earth deposit on the planet. By contrast, the lichen's presence on granite, sandstone or quartzite was found in fewer than 1% of cases.
Chemical analysis confirmed that Xanthoria elegans contains between 3,500 and 17,000 parts per million of rare earth elements. That concentration rose in direct proportion to the mineral richness of the rock it grew on, with lichens attached to more heavily mineralized carbonatites showing higher levels than those growing on barren or altered substrates.
The lichen's orange-brown crust stands out clearly against the duller color of the surrounding rock, making it possible to spot visually and quickly.
Drones and remote sensing to scan large areas
Researchers said this visual contrast could be paired with unmanned aerial vehicles and hyperspectral remote sensing to survey large stretches of terrain. Cameras mounted on drones would be able to track the lichen's distinctive color signature from the air, letting prospecting teams focus on specific sites instead of searching blindly across wide areas.
Li said that once the lichen is found, teams can prioritize sampling there, which significantly raises the odds of finding deposits compared with random searching.
Scientists have already reported similar sightings of the organism in the high mountains of Western Kunlun, suggesting the pattern is not limited to the Bayan Obo deposit.
Why the lichen prefers these rocks remains unclear
It is not yet known with certainty why Xanthoria elegans favors carbonatite rocks, though early data suggests the behavior could hold true globally. If that is confirmed, the search for critical minerals needed for the energy transition could become faster, cheaper and less invasive for the environment, according to the researchers.
