New findings on sought-after lithium

Lithium is a key metal for battery production, and demand within the EU for domestic deposits is rising sharply as part of the green transition. If researchers can understand how this rare metal was once formed, future needs can be secured more effectively. Ore geologists at Luleå University of Technology have therefore carried out an extensive study of the Varuträsk area in Västerbotten, renowned worldwide for its rich occurrence of pegmatite rocks, which often contain the much sought-after lithium.

“Our study now provides, for the first time, a more detailed and nuanced picture of how lithium-rich pegmatites were actually formed in northern Sweden. This knowledge is crucial for developing smarter methods for future lithium exploration in Sweden and northern Finland,” says Joel Andersson, researcher in ore geology at Luleå University of Technology and project leader of the new study Exploration Information System (EIS).

Seeking to Solve the Lithium Puzzle

Lithium, caesium and tantalum are critical metals often found in pegmatite rocks. At Varuträsk in Västerbotten, lithium and caesium were mined on a small scale during the 1930s and 1940s. The deposit is not currently economically viable, but it is geologically important for research into pegmatite formation and thus for solving the puzzle of how and where lithium was formed 1,780 million years ago.

"Lithium is incredibly difficult to locate because the geophysical contrasts with the surrounding rock where it is found are often very weak. This means that these rock types blend geophysically into their surroundings. In this way, they differ from iron ore, which stands out very clearly due to its magnetic properties. Our results in this new study provide us with a better understanding of the geological environment in which lithium can be found. This now offers a solid scientific basis for those wishing to prospect for this sought-after metal", says Joel Andersson.

The current research by ore geologists in Varuträsk, funded by Horizon Europe, has employed new methods and a broader perspective to understand how these rocks originated. The researchers have sought answers to where the molten rock came from, how it moved through the bedrock, and finally where and how it solidified.

Their focus has been on investigating when the pegmatites in Varuträsk formed and how they relate to other rocks in the area, particularly different types of granite. Previously, it was believed that the pegmatites arose directly as a result of the formation of the large granite bodies in the region. New datings by the researchers now show that the pegmatites are about 15 million years younger. This means they formed during a separate geological event, which changes the understanding of how and where lithium was created and where it is best to search for it.

Although the granite plutons and pegmatites appear to have originated from the same ancient surface rocks of the Bothnian Basin, a geological area in eastern Sweden where thick layers of sedimentary rocks formed on an ancient seabed, the researchers’ results now show that they formed at different times and probably under different temperature conditions. This implies that pegmatites do not necessarily need to occur near larger granite bodies. It opens up for more potential areas for future lithium exploration in Sweden.

"Already now, our results may prove significant for lithium prospecting, as they show that the potential is not necessarily tied to granite bodies but also to structural features within the bedrock", says Joel Andersson.

Lithium Often Found in Shallow Structures

To understand how pegmatite melts moved through the bedrock, the researchers combined field studies, microscopic analyses and 3D modelling. They observed that the melts exploited pre-existing fractures and faults in the rock as transport pathways. How the pegmatites then intruded into the rock depended greatly on the mechanical properties of the host rocks. Harder rocks produced shallower intrusion angles, while softer rocks allowed more vertical veins. This is particularly interesting since the world’s largest lithium-rich pegmatites are often found in shallow structures.

These new results mean that researchers can more easily predict which host rocks are more favourable for lithium-rich pegmatites, and thus where lithium deposits may be discovered.

“Our research is fundamentally about understanding how Sweden’s lithium-rich pegmatites were formed, knowledge that is vital for future exploration and for strengthening Europe’s access to critical metals. At the same time, many questions remain unresolved, not least concerning the influence of geological structures on pegmatite formation. We will therefore continue our work in Varuträsk but also broaden our studies to more environments to build a more comprehensive picture of how these unique rocks have developed,” says Joel Andersson.

The research has been carried out in collaboration with the Geological Survey of Sweden (SGU) and the Swedish Museum of Natural History.

The results of the study are published in Mineralium Deposita, which is issued by Springer, one of the highest-ranked journals in ore geology:

• Lithium-caesium-tantalum pegmatites in the Varuträsk area, Sweden: geological setting, timing, and source-transport-trap characteristics