In the far north of Sweden, enormous deposits of valuable metals lie underground. They promise economic independence for Europe's high-tech and environmental industries. The find is the result of geoscientific exploration work in which Cologne scientists were also involved.

By Jan Voelkel

Kiruna, the country's northernmost city, does not have much to do with a Bullerby image of Sweden. Instead of picturesque red wooden houses à la Astrid Lindgren, mining dominates the landscape here, just 200 kilometres from the Arctic Circle. Iron ore has been mined in what is now the world's largest underground mine since 1898. A huge ore mine on the outskirts of Kiruna is visible from afar and looks a bit like a gigantic cruise ship lying in front of the town.

So you would think there would not be much left here in the way of mining that would come as a big surprise. In January, however, something else was found besides iron ore that is being treated as a sensation: rare-earth elements. The exact extent is not yet known, but it is certain that this is the largest deposit of rare-earth elements found in Europe so far.

Rare-earth elements — Rare-earth elements are actually metals. And they are not really rare. Lanthanum occurs in the earth's crust more than 10,000 times as much as gold. However, rare-earth elements are not found in pure form, but only in ores. There, the concentration is often very low, which makes mining uneconomical.

These metals are at the top of the list of sought-after raw materials and are needed to manufacture electric car motors or to produce wind turbines; they are found in fibreglass or LEDs. They are therefore very much in demand in terms of future technologies. According to the mining company LKAB, the deposit now found could cover most of Europe's needs. So far, according to the German Institute for Economic Research, China is the largest supplier for Europe and Germany, with around 90 per cent. The new find, which could make Europe more independent on the world market, is the result of extensive geoscientific exploration work. The University of Cologne also contributed to the exploration of the deposit.

Kilometre-long power cables for the measurements

Dr Pritam Yogeshwar and Dr Wiebke Mörbe from the Institute of Geophysics and Meteorology from Cologne are involved in the joint project DESMEX (Deep Electromagnetic Sounding for Mineral Exploration) and the two follow-up projects DESMEX-II and DESMEX-Real. Yogeshwar and his team took over validation work for new electromagnetic measurement methods and were responsible for the work on the ground. The best way to imagine it is that Yogeshwar and his colleagues were exploring and investigating what the subsurface is like by means of a current signal that is conducted into the ground. For this purpose, the Cologne team installed long cables that serve as power sources. The measuring area ‘Per Geijer’ in Kiruna was about eight by eight kilometres, the longest cable in the measuring area was about five kilometres long.

“The current is pulsed – that is, switched on and off again and again. During this pulsing process, an electromagnetic signal is created. And that creates an interaction with the stratifications in the ground,” Yogeshwar explains. The electrical currents are concentrated where there is good conductive material such as iron ore in the soil. Measurements of the signal therefore provide important clues about the composition of the soil.

A combination of ground-based techniques and novel airborne methods were utilized in Kiruna to explore the area. The ground-based transmitters provide a strong source signal that reaches up to one kilometre into the subsurface. This signal is recorded by magnetic field sensors in a towed body attached to a helicopter. At a flight speed of 90 km/h, data can thus be continuously collected from the air and the entire area can be 'scanned' in a few hours of flight. “The combination provides excellent data in a short time and a high data density that we can evaluate,” says the geophysicist.

Boreholes en masse

The scientists use the data to create a conductivity model of the soil: Where does the soil conduct electricity particularly well and where not? But as good as the data is, it does not provide precise information about what is going on in the soil. There is no signal that indicates exactly whether there are rare-earth elements or other specific minerals. “Besides iron ore, where rare-earth elements are usually found, a clay layer would also generate a good conductive signal, or a water-bearing layer with a contaminated aquifer that is salinated,” Yogeshwar explains. “Therefore, preliminary geological investigations and drilling are always necessary to clarify in advance whether certain deposits are present, and if they are even worth exploiting.”

In Kiruna, there were many years of preliminary work, and the area around the mine is riddled with boreholes. It was therefore probable that rare-earth elements existed there. The new measurement data now confirmed that it is of a magnitude that is unique in Europe.

However, it will be some time before large-scale European raw material production begins. Even at the time of the announcement at the beginning of the year, the mining company LKAB was expecting production to begin in ten to fifteen years. In addition to licensing procedures, a low concentration of rare-earth elements in the iron ore could also make mining difficult. Critics also point out that although rare-earth elements are associated with green technologies, their production is often associated with high environmental pollution. So here, too, it is important to break away from Bullerby stereotyping. Nevertheless, most experts agree that the site in Kiruna can become an important element in Europe's security of supply.

In DESMEX and the currently running follow-up projects DESMEX-II and DESMEX-Real, airborne geophysical measuring methods are being developed with which, among other things, ore bodies can be detected underground. DESMEX is a German consortium of universities, research institutes and industrial partners funded by the Federal Ministry of Education and Research (BMBF). The universities of Cologne, Münster and Freiberg, the Federal Institute for Geosciences and Natural Resources, the Leibniz Institutes for Applied Geophysics and for Photonic Technologies and the companies Supracon AG and Metronix GmbH were involved in the work in Kiruna.