Larvikite, Coldwell Complex, Marathon, Ontario. Larvikite is an alkali-syenite rock composed mainly of anorthoclase feldspar.
The Coldwell Complex is a large circular gabbro and syenite intrusion within the Earth’s crust. It is near Marathon, on the north shore of Lake Superior. The Coldwell Complex is the largest alkaline intrusion in North America. The intrusion is 25 kilometers in diameter. The complex was formed in three cycles during the eruption which included caldera. Platinum and Palladium may prove to be found here in deposits rich enough to mine.
Map of the Coldwell Complex and cross section of the caldera of a volcano where the land collapses into the magma chamber after an eruption. The name caldera comes from the latin caldaria which means cooking pot.
Cross section of caldera collapse into magma chamber after eruption