Angewandte Geochemie

Calkroc – Carbonatite and ALKaline Rock OCcurrences

Die unterschiedlichen Projekte der Calkroc-Forschungsgruppe, einem Forschungsverbund der Technischen Universität Berlin (TUB), dem Karlsruher Institut für Technologie (KIT) und der Eberhard Karls Universität Tübingen (EKU), beschäftigen sich mit der Genese, Entwicklung und Modifikation von Karbonatiten und ihren assoziierten Gesteinen, sowie alkalinen Silikatgesteinen.

Laufende Projekte

Wirkung und Bedeutung von kontaminations-bedingten Variationen der Schmelzzusammensetzung der Tweerivier und Bulhoekkop Karbonatite, Südafrika, unter besonderer Berücksichtigung ihrer SEE-Mineralisierung

REE enrichment in carbonatitic melts are generally explained by a combination of parameters, including melt generation from an enriched mantle source, magma evolution by crystal fractionation, melt-aqueous brine immiscibility, hydrothermal alteration etc. However, the effect of crustal contamination is only weakly constrained. Nevertheless, our recent study of Kaiserstuhl carbonatites clearly provided evidence that the interaction of carbonatite magma with silicate wall rocks can enable strong REE enrichment in apatite via the britholite substitution mechanism involving Si. Based on the results from the Kaiserstuhl, the role of variable contaminants needs to be tested in detail to show if this process is of general importance in carbonatitic systems.

This project will investigate the impact of carbonatite-country rock interaction on REE enrichment in carbonatites. The study will be performed using field examples from the Tweerivier and Bulhoekkop carbonatites in the Republic of South Africa which are known to bear a large variability of crustal xenoliths and xenoliths of associated silicate rocks and contain variable amounts of silicate minerals (amphibole, clinopyroxene, mica, tremolite) that may indicate crustal contamination.

To test this hypothesis, whole rock data (XRF and ICP-MS), textural, mineral chemical and isotopic data (microscopy, EMPA, C and O-isotope systematics) will be carried out for the different carbonatites samples to study the effect of contamination by Fe, Mg, Al and Si-rich lithologies. The expected results will allow for (1) Identification of the influence of contamination on the REE pattern of the residual melt. (2) Identification of mineralogical and compositional variation of major mineral phases.

Projektträger: DFG

Projektleitung: Dr. Johannes Giebel (TUB), Dr. Benjamin Walter (KIT)

Projektbearbeiter: BSc. Ole Schröder(MSc. Arbeit)

Magmen-Entwicklung in Zeit und Raum entlang der Kuboos-Bremen Linie in Namibia

The genesis of carbonatites is typically attributed to a combination of factors, including low-degree partial melting of a carbonated mantle source, crystal fractionation and carbonate-silicate liquid immiscibility. The relation between emplacement depth, multiple reuse of pathways and carbonatite generation was, however, given only limited attention. In an ideal natural laboratory, namely the Kuboos-Bremen Line (KBL, located at the Namibian-South African border) we investigate spatially related intrusions covering broad ranges of igneous silicate rocks and carbonatites. This enable us to study the effect of emplacement depth-related variations and the multiple reuse of pathways which can be evaluated against crustal contamination in a carbonatitic-alkaline igneous province. The Kuboos-Bremen-Line complexes show highly variable rock associations, some of them include carbonatites.

Two important observations lead to research questions of scientific and economic significance:

  1. While the carbonatites of the Marinkas Quellen complex are strongly enriched in HFSE, the eastern carbonatites are barren.
  2. Many of the silicate rocks associated with the carbonatites are granites and syenites, but their genetic relations towards each other are not clear.

The proposed study will therefore investigate the genetic relationships between granites, quartz syenites, syenites, foid syenites and carbonatites and will include textural, mineral chemical, isotopic and geochronological analyses. The expected results will allow to characterize the magmatic to hydrothermal evolution of the whole system in great detail and to reconstruct the genesis of carbonatites in alkaline silicate dominated igneous provinces.

Projektträger: DAAD

Projektleitung: Dr. Benjamin Walter (KIT), Dr. Johannes Giebel (TUB), PD Dr. Michael Marks (EKU)

Projektbearbeiter: MSc. Jorge Arthuzzi(Promotion)

Die Bedeutung karbonatitischer Fluide für die HFSE-REE-Mineralisierung

Rare Earth Elements (REE) are essential and strategic metals, with growing demand in high-tech applications like electric and hybrid cars, LED lights, and wind turbines. REEs can be found in various rocks, but carbonatites are the ideal host rocks and important discovery targets due to their high enrichments in REEs, size, and partly extraction-friendly mineralogy. Carbonatites are magmatic mantle-derived intrusive and extrusive rocks having more than 50% carbonate minerals. The evolution of carbonatites and associated alkaline rocks is caused by magmatic and metasomatic processes. These processes are also responsible for the transportation and accumulation of economic elements. However, details of these ore-forming processes including fluid composition, fluid transportation capability, precipitation mechanisms and metasomatic reactions are not fully understood yet. Due to the poor understanding of these processes, it is fundamental and economic interest to shed light on the reasons why ten percent of the carbonatites are highly mineralized and therefore economic while others remain barren.

The main aim of this research work is to improve the knowledge of fluids systems in carbonatites and associated alkaline igneous rocks in terms of geology and genesis. For this purpose, carbonatites samples from different localities will be studied in terms of fluid chemistry, homogenization temperatures and physical properties (fluid inclusion petrography, microthermometry, Raman spectroscopy, and major and trace element composition). Based on these studies a genetic model for the carbonatites will be developed. The completion of this research project will help to improve the state-of-the-art knowledge of fluid exsolution in carbonatites and related ore forming processes.

This project is funded by Higher Education Commission, Pakistan and German Academic Exchange Service (DAAD), Germany.

Projektträger: DAAD

Projektleitung: Dr. Benjamin Walter (KIT), PD Dr. Michael Marks (EKU)

Projektbearbeiter: MSc. Mohsin Raza(Promotion)

Projektpartner: Dr. Johannes Giebel (TUB)

Einflüsse krustaler Kontaminationen auf SEE-Anreicherung in Karbonatiten der Kalkfeld-Gruppe (Namibia)

High levels of REE in carbonatites are generally explained by a combination of factors, including low-degree melting of geochemically enriched mantle sources, crystal fractionation, carbonate-silicate melt immiscibility, melt-aqueous brine immiscibility and hydrothermal alteration. Crustal contamination, however, is a process that is typically not considered to play an important role during carbonatite magmatism. Nevertheless, a recent study of the applicants demonstrated that the interaction of carbonatite magma with silicate wall rocks can enable strong REE enrichment in apatite via a coupled substitution mechanism involving Si. Having shown this for the Kaiserstuhl, the applicants suggest that such processes may be of general importance in carbonatitic systems.

This project will investigate the impact of carbonatite-wall rock interaction on REE enrichment in carbonatites. The study will be performed using field examples from the Damaraland Province (Namibia), because these carbonatites show variable REE enrichment and REE mineralogy and contain variable amounts of silicate minerals (amphibole, clinopyroxene, quartz, feldspar) that may indicate crustal contamination.

To test this hypothesis, textural, mineral chemical and geochronological data (microscopy, EMPA, LA-ICP-MS) as well as fluid inclusion data (microthermometry including numerical liquidus-surface modeling for quantification, Raman spectroscopy) for the different carbonatites which are probably genetic related will be gathered and compared with each other.

The expected results will allow for

  1. characterizing the magmatic to hydrothermal evolution of the carbonatites in great detail and
  2. reconstructing the genesis of the REE mineralizations including the potential influence of wall-rock interaction and hydrothermal overprint.

Projektträger: DFG

Projektleitung: Dr. Benjamin Walter (KIT), PD Dr. Michael Marks (EKU)

Projektbearbeiter: N.N.

Projektpartner: Dr. Johannes Giebel (TUB)

Die Mineralogie und Petrologie der Syenite des Palabora Komplexes: Eine Charakterisierung von Karbonatit-assoziierten Syenit Intrusionen

Projektart: Lehrbegleitendes Studienprojekt

Projektleitung: Dr. Johannes Giebel (TUB)

Projektbearbeiter: Jonas Hegner (TUB)

Projektpartner: Dr. Benjamin Walter (KIT)

Glimmer in Karbonatiten: Ein Review zum Potenzial der Interpretation von magmatischen Vorgängen in karbonatitischen Systemen durch Glimmer

Projektart: BSc. Arbeit

Projektleitung: Dr. Johannes Giebel (TUB)

Projektbearbeiter: Laura Schulz (TUB)

Projektpartner: Dr. Benjamin Walter (KIT)

Karbonatit-Karbonatit Interaktionen: Sövitische Mega-Xenolithe in den Alvikiten des Dicker Willem Komplexes (Namibia)

Projektart: BSc. Arbeit

Projektleitung: Dr. Johannes Giebel (TUB)

Projektbearbeiter: Lorenz Kemmler (TUB)

Projektpartner: Dr. Benjamin Walter (KIT)

Der Eureka Karbonatit (Namibia) und seine massive Monazit-Mineralisation: Die Bedeutung von Fluiden für die Vererzung von Karbonatiten

Projektart: Exploration/Research project

Projektbearbeiter: Dr. Benjamin Walter (KIT), Dr. Johannes Giebel (TUB)

Abgeschlossene Projekte

Krustale Multi-Komponenten-Kontamination der alvikitischen Karbonatit-Gänge des Gross Brukkaros (Namibia): Petrologie und Geochemie (BSc. Projekt)

Die Selten-Erd-Element Mineralisationen des Palabora Karbonatit Komplexes (Südafrika) (DFG Projekt)