Timeline for the Fen Complex

Trygve Johansen (t.h.) med driftsbestyrer Tormod Johnsen og ingeniør Thorvald Mellingen antagelig i 1957. Foto: Bergverks-Nytt
Trygve Johansen (left) with operations manager Tormod Johnsen and engineer Thorvald Mellingen presumably in the old Søve mines, 1957. Photo: Bergverks-Nytt

Author: Tor Espen Simonsen

Published: 10 Nov, 2023


Updated: 10 Dec, 2023

foto Asmund Tunning - Illustrasjon Johannes Fredriksen

580 million years ago

A limestone volcano was active in the area which today lies just outside Ulefoss in Telemark. The remaining remnants of the volcano are what is called the Fen Complex. Note that the image above is only an illustration.

Photo: Asmund Tunning/illustration Johannes Fredriksen

Bildet viser Ulefos Jernværk som ligger ved Telemarkskanalen.

1657 –

Holden Jernværk (later Ulefos Jernværk) was established on the basis of the iron mines at Fen.

The ironworks in Fossum, Moss and Bolvig also had their own mines at Fen. In certain periods, iron ore was mined for export abroad.

Bilde av jerngruve i Gruveåsen på Fen.

1881 -

A longer break in mining operations marked the end of the first historical phase for Fen's iron mines.

kammerherre Diderik Cappelen

1898 –

Owner of Ulefos Jernværk and the iron mines, Diderik Cappelen (1856-1935), restarted the mining operations.

Krigsskip fra 1. verdenskrig

1914 –

World War I led to mineral shortages and high demand. Several countries worked to improve their self-sufficiency and in Norway the Raw Materials Committee was established in 1917. An important part of the committee's work was mapping the Fen Complex.

Geolog Waldemar Christofer Brøgger

1920 –

Geologist Waldemar Christofer Brøgger maps the Fen Complex on behalf of the Raw Materials Committee, and publishes the book Das Fengebiet. His research results caused a stir and were heavily debated.

Brøgger had for the first time demonstrated and described limestones of magmatic origin (that is, origin from a volcanic eruption). The discovery has made the Fen Complex a reference point for limestone volcanism.


Vaskeriet ved Fensgruvene

1927 –

The iron mines are closed for good.

The picture shows parts of the processing plant for the iron mines, where the ore-containing gravel from the Fens mines was washed before further transport.


Bildet viser en tysk V2-rakket fra 2. verdenskrig.


During the Second World War, several projects were started to utilize the minerals in the Fen Complex. There was a desire to mine apatite as a raw material for the production of agricultural fertilizer.

It is best known that the German occupying power started sampling of niobium for military purposes. Niobium was to be used in V1 and V2-rockets. which was launched over England.


Bergarten søvitt som inneholder niob.

1953 -

State-owned AS Norsk Bergverk arranged for new mineral operations in the Fen Complex, but this time in the Søve part of the area. AS Norsk Bergverk mined the metal niobium and produced ferroniobium as an alloy to give steel a better ability to withstand high temperatures.

The Cold War was the trigger for the start-up, and the Americans were the only customer.

The rocktype søvitt*, containing niobium, was the starting point for the business (see picture).

AS Norsk Bergverk's metallurgical production of ferroniob resulted in slag with elevated radioactive values. You can read more about the issues here.

Bilder viser AS Norsk Bergverks anlegg ved Søve gruver.

1965 –

Norsk Bergverk shuts down its operations after the contract with the Americans is not extended. This marks the provisional end to commercial mining in the Fen complex.

Last shift out of the old Søve mine in 1965. Photo: Gerhard Hedlund.

1967-71 –

Research group for rare earths (FSJ) carried out the first systematic survey of rare earths in the Fen Complex, mainly in Gruveåsen where the old iron mines were located.

This was one of several periods of mapping and exploration activity in the Fen Complex during the Cold War. None of the campaigns ended with new mining, but contributed with research and increased knowledge of the field, which has become important later.

the 1980s -

A new wave of exploration activity and renewed interest in the Fen Complex started in 1980. The activity took place under the auspices of the company Fenco AS, where Cappelen, ELKEM and others. The aim was to map thorium and rare earths (REE).

1985 -

In the mid-1980s, plans for new mining operations were put on hold by Fenco.

Foto av rødberg.

2000 -

At the beginning of the new millennium, great attention was again paid to the Fen Complex. This time it concerned the rich deposits of thorium, including in the red rock near the old iron mines. The picture shows a sample of the red rock, which contains relatively high values ​​of thorium.

Red rock is an iron ore-bearing carbonatite rock. It was geologist Brøgger who coined the name.

Faksimile av forsiden til Thoriumutvalgets rapport fra 2008

2008 -

The government presents the report «Thorium som energikilde – muligheter for Norge» ("Thorium as an energy source – opportunities for Norway"). At this time, there was a lack of political will in Norway to invest in nuclear power and to develop expertise on thorium.

Kart over land som produserer kritiske mineraler i verden.


As a result of rising prices, interest gradually shifted from thorium to rare earths.

China had emerged as the dominant player for these technology minerals worldwide, and several Western countries were concerned about the supply situation.

En borerigg som brukes til undersøkelser i Fensfeltet.

2011 -

REE Minerals AS carried out trial drilling for rare earths in areas of the Fen Complex that were previously seen as less relevant. The results were encouraging, and the core samples showed high values of rare earths and relatively little thorium.

The EU published its first list of critical raw materials, in which rare earths were listed together with 13 other raw materials. Read the EU's list here (document in English)

Fen og Fensfeltet sett fra Holla kirkeruin.

2011-14 –

REE Minerals AS carried out several systematic test drillings, which confirmed the first findings of a interesting deposit of REE.

Illustrasjon av thorium

2013 –

For the first time was thorium used as fuel in the research reactor in Halden. This was part of the company Thor Energy AS' research into developing products from thorium from the Fen Complex. The reactor in Halden was shut down in 2018.


Bildet viser kjerneprøver fra Fensfeltet.

2018 -

The Storting allocated money for deep drillings maping the deposit of rare earthss down to 1,000 metres. Two deep drillings were carried out in 2018.

Bilde av regiongeolog Sven Dahlgren under Fensdagene 2023.

2019 -

Regional geological advisor, Sven Dahlgren, presented his scientific analyzes based on the deep drillings and extensive work on creating a new geological map of the Fen Complex. IN rapporten Dahlgren states that the Fen Complex is a world-class exploration target for the Hi-Tech and “Green-shift” Industry, and that it may contain Europe's largest deposit of rare earths.

Fylkesordfører Sven Tore Løkslid og Finn Tore Sylte fra Norsk Mineral AS i 2019.

2017-2019 -

All previous mining rights* held by the the Norwegian state was transferred to Telemark County Municipality in 2017. To a large extent, the state's area of ​​jurisdiction overlapped important parts of the complex where there are believed to be large deposits of rare earths. In 2019, the county council sold its rights to Norsk Mineral AS. Today, the rights lie with Rare Earths Norway AS, which is owned by Hustadlitt AS and Cappelen.

2023 -

There are now two companies involved extraction rights* for rare earths in the Fen Complex. Extraction right means that the companies are in a position to apply for an operating license when the minerals in their area has been sufficiently mapped and documented. The relevant companies are REE Minerals AS and Rare Earths Norway AS.

In 2023, Norway's mineral strategy was also put forward by the government and the EU's new mineral law (CRMA) was adopted. In 2024, it is also expected that a new mineral law will be adopted in Norway.