R. Johannes Giebel

R. Johannes Giebel
Technische Universität Berlin | TUB · Department of Applied Geochemistry

Dr. rer. nat.

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24
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Introduction
My research interests are interdisciplinary covering research fields of mineralogy, petrology, economic geology and geochemistry. Focus of my research is related to carbonatites and alkaline rocks and their related mineral deposits.

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Projects

Projects (9)
Project
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 of 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.
Project
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: (i) The behaviour of HFSE and REE in carbonatitic magmas is influenced by source contamination and silicate wall-rock interaction. (ii) 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. (iii) 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.
Project
Carbonatites are important sources of a number of critical raw materials, but the processability of these deposits is highly dependent on the nature of their mineralisation. This project aims to develop new innovative methods to make previously unprocessable carbonatite deposits economically viable.