Carbonatite metasomatism: More than meets the eye

Date & time

4–5pm 5 June 2018

Location

Jaeger 1 Seminar Room, RSES

Speakers

Mr Michael Anenburg (RSES)

Event series

Contacts

 Antony Burnham

Carbonatites are unusual igneous rocks that primarily contain carbonate minerals such as calcite or dolomite. Metasomatism is the process by which solid rocks are chemically transformed to different rocks by the action of fluids or melts. As carbonatites are melts, they are also capable of metasomatising rocks. Nolans Bore in the Northern Territory is a rare earth element (REE) ore deposit that consists of fluorapatite veins rimmed by diopside selvages. Nolans Bore was hypothesised to form by aqueous hydrothermal fluids, and a carbonatitic origin was rejected due to the lack of carbonates. I performed experiments demonstrating that Nolans Bore could have formed via carbonatite metasomatism. Carbonatitic melt reacts with the host rock forming REE-fluorapatite and diopside, and then migrates to form a proper carbonatite rock elsewhere.

Other than showing a carbonatitic origin for Nolans Bore, these experiments show a variety of reactions that can occur by reaction of solid silicate rocks with carbonatitic melts. As these melts have high wetting capabilities and low viscosities, they are efficient metasomatic agents, modifying rocks but leaving no carbonate behind. Thus, the carbonatitic origin is often obscured. These metasomatic reactions generate carbon dioxide and may have an effect on Earth's long term climate. Finally, I will present preliminary observations from experiments that carbonatites are efficient transporters of not only REE, but also highly siderophile elements (HSE).

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