Past event

In Person SEES Seminar --- Dr Robert Johannes Giebel, Researcher, Berlin Institute of Technology A short story of carbonatites: Processes involved in magma ascent and related effects on mineralization

Carbonatites are relatively rare magmatic rocks originating from the Earth's mantle, defined by a modal content of 50 vol.% carbonates.Despite their relative rarity, with only about 600 occurrences worldwide, they represent an important economic resource.Sixty out of 600 occurrences represent world-class deposits of LREE, Nb, F, P and/or Fe, with further economic concentrations of Zr and Cu (only one deposit) mined or under exploration.In particular rare earth elements have attracted interest in carbonatites in recent decades, while their mineralisation and enrichment are not yet fully understood.To understand mineralisation in carbonatites, it is of utmost importance to understand their formation, their ascent through the crust and their emplacement in the upper crustal levels.Carbonatites cannot be grouped into a single type of rock, as their mineralogy renders them a variety of rocks.The most important types are classified as calcio-carbonatites, magnesio-carbonatites, ferro-carbonatites and natro-carbonatites, whereby carbonatites with a silicate content of more than 20 vol.% are referred to as silico-carbonatites.The abundance of major non-carbonate minerals such as apatite, magnetite or baryte may result in sub-grouping.Certain groups and subgroups of carbonatites are particularly associated with specific commodities.Calcio-carbonatites are often enriched in P and Fe, highly developed calcium carbonatites also in F. Magnesio- and ferro-carbonatites often show a higher enrichment in REE.But not only their types and economic importance make carbonatites a potential target for science.Carbonatitic melts formed directly or indirectly from metasomatised mantle and possess very different physical properties compared to silicate melts.They have an extremely low viscosity, which is more comparable to water than to a basaltic melt.They show a very strong density contrast to the much denser silicate melts.And they are highly reactive due to their large chemical contrast to most crustal rocks and their high content of volatile phases such as water, fluorine and alkalis.These properties lead to very rapid and reactive carbonatite ascent, and high potential for contamination.Combined with their low silica and aluminium solubility (and activity) and their immiscibility with other melts (silicate, iron oxide and sulfide melts), ascending carbonatite melts may produce a large variety of mineralisations and even rock variations.Even surrounding crustal lithologies experience strong metasomatic overprinting, which can form a completely new type of rocks.