Carbonatite

As a carbonatite igneous rock is called in geology that contains more than 50 % carbonate minerals.

Composition

In general, the proportion of carbonate is 70 to 90%, which are represented mainly as calcium and CO2 in the empirical formula. Main minerals are usually calcite, dolomite, ankerite and siderite. In addition, silicate minerals ( forsterite, melilite, diopside, aegirine, wollastonite, alkali amphibole, phlogopite, titanite, zircon, alkali feldspars, oxides (magnetite, ilmenite, rutile, perovskite, pyrochlore ) and apatite occur.

History

The carbonatites were Waldemar Christopher Brøgger ( German: Brögger ) in 1920 first described in the publication series Videnskaps Skrifter the Norske Akademi Videnskaps - scientific. Its description is based on the outcrops of the Fengebiets in the southern Norwegian Telemark.

Karbonatitvarietäten

Differences are:

• Calcitkarbonatit: coarse to medium grain Sövit and small-and fine-grained Alvikit with mostly distinct flow texture
• Ferrokarbonatit: with ankerite or siderite as the main mineral
• Natrokarbonatit: Main minerals are sodium, potassium, calcium, carbonatites, eg in the Oldoinyo Lengai complex in Tanzania
• Dolomitkarbonatit: main mineral is dolomite

Geological environment and occurrence

Carbonatites are mainly associated with alkalinem magmatism, mostly as subvolcanic or shallow plutonic complexes, and store lavas and pyroclastics nephelinitische.

Carbonatites represent one of the least common types of rock, about 500 complexes are barely documented worldwide. They come usually strictly localized in only a few square kilometers large areas before. Their occurrence is mainly associated with hot-spot volcanism and the associated continental Riftsystemen. Therefore, Africa, with its East African grave breach, the continent with the world's only active Karbonatitvulkan. The Ol Doinyo Lengai is the only active volcano erupted directly, the Karbonatitlava. But there are also carbonatite complexes in the St. Lawrence River Trench (Canada), on the Cycladic island of Anafi and the Upper Rhine Graben (Kaiser chair).

The largest known accumulation of rare earth minerals in the world is bound to carbonatite -course and kalireiche intrusions, and is found in the Sulphide Queen deposit at Mountain Pass District ( California). The name of the deposit is actually somewhat misleading because it is not named after any sulfide minerals, but according to the Sulphide Queen mountains. The main ore minerals are Bastnäsit and Parisit.

Another unusual feature is the open pit at the Paleoproterozoic carbonatite from Phalaborwa in South Africa. There is a serpentinite magnetite rock apatite is degraded at a Karbonatitkern carrying the local and commercial name Phoscorite. By-products are, inter alia, Magnetite, apatite, gold, silver, platinum group elements, and uranium. Within the same alkaline rock complex is also the world's largest igneous phosphate deposit. There also apatite- rich pyroxenite is degraded. Similar carbonatite - alkaline rock complexes are also found on the Kola Peninsula. Also there is the most important phosphate mineral apatite.