The manganese vein of Mount Brandnuten, Botnedal, South Norway.

Abstract

The manganese deposit on the NE. slope of Mt. Brandnuten near the head-waters of Botnedalen in western Telemark has the shape of a massive vein of vertical attitude. It is conformably intercalated between arkoses of the Precambrian Telemark suite of metamorphic supracrustal rocks. Granite invades the wall rocks in the immediate neighbourhood of the deposit. The manganese vein strikes N30-35 degr. E across Botne brook, has been traced over a distance of more than 300 m, and has a thickness between zero and 2.10 m. There are a few parallel veins of minor importance and also some smaller veins striking obliquely or perpendiculary to the bedding of the arkoses, which latter show intercalations of amphibolite. The main ore body mainly consists of coarsely crystalline rhodonite and spessartite carrying lenses of Mn-oxides to a quantity of about 15%. Braunite is the main Mn-ore and is associated with some hausmannite and jacobsite. There are, in addition, a few subordinate and secondary Mn-silicates of unknown composition replacing rhodonite, small quantities of metasomatic fluorspar and rhodochrosite; furthermore small amounts of, respectively, a mineral of the psilomelane group, an unknown Mn-oxide, pyrite, hematite, and native copper. Rhodonite replaces braunite, which is also earlier than hausmannite and jacobsite. Spessartite seems to be partly earlier and partly later than rhodonite.