The topic of raw materials plays a central role for the African continent: it holds approximately 30 percent of the world’s mineral and critical raw material reserves and is also home to enormous deposits of oil, natural gas, cobalt, lithium, and rare earth elements. At the Karlsruhe Institute of Technology, scientists are conducting numerous projects focused on raw materials in Africa. These include both ongoing and already completed research initiatives.
KBL - Magma evolution in space and time along the Kuboos-Bremen Line in Namibia
The genesis of carbonatites is typically explained by a combination of factors, including low-degree partial melting of an enriched mantle source, crystal fractionation and carbonate-silicate liquid immiscibility. Previous work by the applicants indicate that carbonatite magmas can be significantly modified by crustal contamination. The relation between emplacement depth, multiple reuse of pathways and carbonatite generation was, however, given only limited attention. In an ideal case study, we would investigate spatially related intrusions covering broad range of igneous silicate rocks and carbonatites. In such an ideal natural laboratory we could 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. Such an ideal system with an excellent outcrop situation can be found at the Namibian- South African border at the Kuboos-Bremen Line (KBL). 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 be guided by the following hypotheses:
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The behaviour of HFSE and REE in carbonatitic magmas is influenced by source contamination and silicate wall-rock interaction.
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The crosscutting relationships of the individual complexes and available age data suggest progressive evolution of the province from SW to NE evolving from granitic to foid-syenitic/carbonatitic compositions with time and location.
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The rock associations represent two magma suites derived from variable sources that used the same zone of weakness for ascent and emplacement.
To test these alternative scenarios, textural, mineral chemical, isotopic and geochronological data will be gathered and compared for the representative intrusions of the Kuboos-Bremen Line. 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.
Contact: Dr. Benjamin Walter, Jorge Corrêia Leite Arthuzzi
Duration: 2022 - 2025
Influence of crustal contamination on REE-enrichment in carbonatites of the Kalkfeld group (Namibia)
This is a joint project of the Geochemistry & Economic Geology of KIT and the Petrology Group at the University of Tuebingen. 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
Duration: 2025 completed
Contact: Prof. Dr. Jochen Kolb, Dr. Benjamin Walter
Effect and significance of contamination-related compositional melt variations of the Tweerivier and Bulhoekkop carbonatites, South Africa, with special reference to their REE mineralization
This is a joint project of the Geochemistry & Economic Geology of KIT and the
Mineralogical museum at the Technical University of Berlin. REE enrichment in carbonatitic melts are generally explained by a combination of parameters, including low-degree melting of geochemically enriched mantle sources, carbonate-silicate melt immiscibility, crystal fractionation, melt-aqueous brine immiscibility and hydrothermal alteration. However, the effect of crustal contamination, as a potential first order process 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.
Duration: 2025 completed
Contact: Prof. Dr. Jochen Kolb, Dr. Benjamin Walter