NGT36-2-02
1956
Geology of the Storkollen - Blankenberg area, Kragerø, Norway.
36
2
89-140

The high-grade quartzites and schists of the pre-Cambrian Kongsberg-Bamle formation in the Storkollen-Blankenberg area, Kragerø, enclose small gabbroic stocks which were centripetally altered to amphibolite during the Sveco-fennide ( ?) metamorphism. Associated with the gabbros and probably derived from them are dikes and irregular bodies of granulose albitite containing varying amounts of other minerals, notable among which are quartz, microcline, rutile, and tourmaline. Certain areas of the large rutilealbitite body of Lindvikskollen (kragerøite) were found to contain corundum; this is a new locality for corundum in Norway. Euhedral tourmaline crystals in an albitite-amphibolite transition zone were found to be an Mg-rich variety; this is also a new locality. It is concluded that most if not all of the albitites were formed metasomatically from preexisting amphibolite.

Late in the orogeny, large, rare-earth bearing pegmatites were intruded in a highly liquid state, and cooled slowly with several stages of mineralization, including a partial replacement of microcline by cleavelandite.

Finally, after shearing stresses had locally faulted and brecciated the rocks, iron oxide mineralization took place along a small east-west fissure.