Fen Complex, Nome, Telemark, Norwayi

Regional Level Types
Fen Complex	Complex
Nome	Municipality
Telemark	County
Norway	Country

Note: The borders in the map above are approximate.

The Fen carbonatite complex, a peralkaline-carbonatitic ring complex, is situated near lake Norsjø in the Nome municipality in Telemark county, southeast Norway.

It consists of a circular 5 km² core with various carbonatites and alkaline igneous rocks (mainly of the melteigite-ijolite-urtite series), intruded 583 +/- 10 Ma ago into Mesoproterozoic granitic Telemark Gneiss (ca. 1105 Ma old). The intrusion was followed by intense faulting and brecciation, producing several phases through metasomatic alteration and fenitization of the country rock (Brøgger, 1921, Sæther, 1957, Andersen, 1989, Verschure & Maijer, 2005).

The original minerals of the gneiss, quartz, biotite, and amphibole (hornblende), were altered or replaced by aegirine-augite and sodium amphiboles. Microcline and oligoclase were also replaced by mesoperthite and chessboard albite (Verschure & Maijer, 2005). A fenite aureole surrounds the western and southern parts of the complex, as well as metasomatic alteration of the fenite at the contact with the carbonatite (Kresten & Morogan, 1986, Andersen 1989).

It became famous after publication of the classic monograph of Brøgger in 1921. Brøgger called the Fen carbonate rocks “Karbonatite” (carbonatites) and he named the metasomatism of the country “fenitisierung” (fenitization). The Fen complex is famous for its rare volcanic/meta-volcanic rocks, many first described by Brøgger (1921):

Carbonatites:
søvite (coarse-grained calcite carbonatite),
rødberg (altered carbonatite with hematite stained granular calcite, dolomite and sometimes ankerite),
rauhaugite (dolomite carbonatite),
ringite (coarse-grained carbonatite containing aegirine and alkali-feldspar).

Lamprophyres:
damkjernite (melanocratic nepheline lamprophyre).

Ijolites:
melteigite (melanocratic nepheline ijolite),
hollaite (calcite-melteigite, consisting of pyroxene (55%), calcite and nepheline).

Other rocks:
fenite (metasomatic rock composed of alkali feldspar, sodic pyroxene and/or alkali amphibole, sometimes monomineralic alkali feldspar rock),
vibetoite (pyroxenite containing abundant Ti-augite and hornblende with biotite, primary calcite, and occasional albite and nepheline).

Most areas of the complex are now protected because of its value to science, and collecting is prohibited!

Iron ores associated with the ferrocarbonatites were worked in the Fen Iron Mines in the eastern part of the Fen Complex between 1657 and 1927, in the so-called “Rødberg area”.

Hematite was mined from 1956 to 1925 with production estimated at ca 10⁶ t (Bjørlykke & Svinndal 1960; Andersen 1983).

The iron ores are typically lenses, veins and dike-like bodies within carbonatites and carbonated gneisses.

Pyrochlore was produced from sövite in the Søve Mines from 1953 to 1964 and pioneered the production and use of this mineral (Deans, 1978).

Geochronology

Mineralization age: Neoproterozoic : 568 Ma

Important note: This table is based only on rock and mineral ages recorded on mindat.org for this locality and is not necessarily a complete representation of the geochronology, but does give an indication of possible mineralization events relevant to this locality. As more age information is added this table may expand in the future. A break in the table simply indicates a lack of data entered here, not necessarily a break in the geologic sequence. Grey background entries are from different, related, localities.

Geologic Time				Rocks, Minerals and Events
Precambrian
	Proterozoic
		Neoproterozoic
			Ediacaran	ⓘ Biotite 568 Ma

Fossils

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References