Altermark talc mine, located about 20 km west of Mo i Rana, the center of the municipality of Rana, is about 800m in length going from NE to SW. It is operated in 5 different levels (status in 2000). The mine is driven on talc zones in the Annabergan ultramafite belonging to the Rödingsfjället Nappe Complex of the Norwegian Caledonides.
The central body consisting of serpentinite stands out as a very narrow and barren cliff in a valley. The mineralization is zoned with un-altered ultramafic rocks in the centre (dunite, pyroxenite and rodingite)surrounded by a serpentinite(mainly antigorite). The talc has been formed by SiO 2 enriched hydrothermal action on the outskirts of the serpentinite, forming a talc/carbonate rock that is mined for talc. The main mineralization is in the contact area between the serpintinite and the surronding rocks, and two different assemblages are described: 1) actinolite/chlorite/biotite/mica shist and 2) actinolite/chlorite-epidote/epidote/ marble or amphibolite. in this transition zone, a 0-1m with pure talc may be found.
Between the mine and the old dump pile is another outcrop where it is possible to study the weathered surface of the serpentinite. It is called "elephant skin", which is a very good description of how it looks.
References:
- Birtel, S. (2002): Fluid-rock interaction on alpine- type ultramafic rocks from the Norwegian Caledonides. Dissertation zur Erlangung des Doktorgrades der Geowissenschaftlichen Fakultät der Albert-Ludwigs Universität Freiburg i.Br.
Mineral List:18 entries listed. 12 valid minerals.
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