Fen Carbonatite Complex

Image: Illustration imagining how the Fen Volcano looked 580 million years ago.

The story of Fen in Nome tells us about a very special volcano, an intense scholarly debate spanning from the 1920s until today, and a variety of rare rocks and uncommon minerals.

The continent of Baltika, which ''Norway'' was part of 580 million years ago, was at this time a worn steppelandscape called 'The Subcambrian Peneplain'. We can find this landscape several places in Norway, such as Hardangervidda. But as often happens throughout Earth's history, the conditions changed, and the ocean flooded the plains. This change happened due to hot streams underneath the Earth's crust at one of Baltika's collision zones. The rise of temperature smelted what is today's Ulefoss, perhaps in relation with a hotspot, and the result became the Fen volcano.

But what is so special about this volcano? The rocks found here today is very atypical for volcanoes. Already in 1921, one of Norway's great geologists, W.C. Brøgger, suggested the calcareous rocks had a volcanic origins. He called these rocks carbonatites, but his theory was widely disregarded, as everyone knew these rocks were created through deposition in the oceans, or rarely in relation to hot springs. Volcanic rocks were suppsed to be basalts, porphyry, and similar rocks. It wasn't until the 1960s that english geologists could prove calcareous lava in volcanoes in the African Rift. So Brøgger was proved right! The rocks he described from Nome was named after farms in the area, such as sovite, melteigite, vipetoite, fenite and rauhaugite. All the rocks was described in detail, and the Fens Field became an important type- and reference locality for volcanic calcaerous rocks. Carbonatites is still the scientific term for this group.

The carbonatites of Fen, is therefore of magmatic origin, meaning it comes from molten masses. Damkjernite has surfaced from great depths, in relation with exlosive volcanism. You can find long dikes of this rock far outside the Fens Field itself. Fenite is the result of a morphingprocess (Fenitization). The molten carbonatitepushed through the older basement rocks, and the result became a rock characterized by its composition of alkali feldspar, sodium rich amphibol, nefeline, aegirine and phlogopite. Other minerals such as titanite and apatite can also occur.

The volcanic activity led to cracks in the crust, in which hot aquatic solutions sirculated. This process led to oxidation of the iron in the carbonatites, leading to the intense red color of the rocks containing iron. This color led to the name Rødberg, or Red Hill in english, which is the area where iron was mined from the 1650s. The ore from Fen was delivered to Ulefos Iron Work. Other unusual chemical substances also exist in the carbonatites. After the Second World War, the area was mined for the rare metal niobium, and the amount of thorium has made the Fens Field well known in Norway.

A new industry is about to emerge in Ulefoss. New findings suggest the Fen Field might contain Europes largest occurence of rare earth minerals, a group of elements essential to modern technology production. Among other things, these elements are used in the production of magnets for electric motors, renewable energy technology and medical equipment. In the Fens Field these elements are bound in the rock rauhaugite, one of the carbonatites created by the calcareous magma. Today, the majority of rare earth elements is mined and refined in China, making the Fens Field geopolitically important for European technology production.