Gas coring and lava flow through a small vent, followed by hydrothermal activity has produced a calcite-baryte-fluorite-anatase-bearing syenite and types of metagabbro which intersect Precambrian gneiss. A pegmatite dike, also of Precambrian age, is cut by diabase dikes. Breccia with xenoliths of diabase and gneiss and a matrix of syenite is locally developed along the rim of the syenite body. Permian or late Precambrian age of the syenite is discussed. The feldspars of the syenite: low temperature al bite and highly ordered submicroscopically twinned microcline is assumed to be the result of alteration or original alkali-feldspar mixed crystals by low temperature and high water pressure.
The precambrian rocks of the Telemark area in South Central Norway. IV. Calcite syenite with marginal breccia at Fjone.