Research

Ongoing research of the petrology group at Tübingen University focusses on the mineralogical, petrological, and geochemical evolution of magmatic and hydrothermal systems relevant to rock formation and ore deposition.

Our projects typically combine field work with microscopic investigations and state-of-the-art geochemical analytics such as XRF and ICP-MS (whole-rock major and trace elements), SEM, EPMA and LA ICP-MS (spaced-resolved mineral analysis), fluid inclusion analysis, liquid ion chromatography (cations and anions in liquids), combustion ion chromatography (halogens and sulfur in solids) and stable and radiogenic isotope analysis.

Our current projects involve field work in Germany (e.g., Schwarzwald, Hegau, Bayerischer Wald, Lausitz), other European countries (e.g., Sweden, Greenland), Africa (e.g., Namibia, Tanzania, South Africa) and Australia. All projects aim at the integration of field data, mineral assemblages and macro- and microtextures with compositional data to develop detailed petrogenetic models for various geologic processes related to magmatism and ore formation.

Magmatic petrology and geochemistry

One research focus of our group concerns the mineralogical, petrological, and geochemical evolution of magmatic to hydrothermal systems, with a special emphasis on alkaline rocks and carbonatites. Such rocks are typically associated with crustal-scale lineaments and continental rifting zones. Key examples, where we study rift-related magmatism are the Proterozoic Gardar Province (Greenland), the Palaeogene Central European Volcanic Province, and the recent East African Rift system. Other ongoing projects are related to alkaline rocks and carbonatites in Namibia, South Africa and elsewhere.

These projects are generally based on field observations combined with micro-textural investigations, compositional data on key minerals as well as computer-based modelling of crystallization or reaction processes to discern magmatic and hydrothermal processes, such as fractional crystallization, magma mixing, origin of magmatic layering, assimilation, fluid exsolution, and rare element enrichment processes during differentiation of melts and during hydrothermal alteration of magmatic bodies.

The Tübingen petrology group was also part of an EU-funded collaborative research project on alkaline rocks and carbonatites called HiTech AlkCarb. The project brought together industry partners involved in exploration, geophysics, and environmental assessment in a team with geological surveys and university academics. This project resulted in a step-change in exploration models for alkaline and carbonatite provinces, establishing methodologies by which mineralogy, petrology, geochemistry, and geophysics are combined. This included the state-of-the-art interpretation of high-resolution geophysics and downhole measurement tools that can be used to make robust predictions about mineral prospection at depth. The project conducted field studies at seven key natural laboratories (Germany, Italy, Greenland, Malawi, Mongolia, Namibia, South Africa). The outcomes where integrated into new geomodels on multiple scales and comprised a world catalogue as well as deposit models.

Ore-forming processes

Increasing demand of raw materials necessitates a better understanding of the processes involved in ore formation of all kinds of ore deposits. The Tübingen petrology group focusses on three types: liquid-magmatic sulfide deposits, skarn deposits and vein-type hydrothermal deposits.

Massive sulfides (golden) infiltrating and melting older basalt (black), forming an emulsion. Kambalda, Western Australia. Field of view: 30 cm.

Due to their metal content needed for the increasing battery demand, processes involved in ore formation are investigated in magmatic Ni-Co-Cu-(PGE) sulfide deposits of the Lausitz area (Saxony) and from Western Australia. Metamorphosed SEDEX-type sulfides are comparatively investigated in the Bavarian Forest of Southeast Germany. In all massive sulfide occurrences, the mineralogy, petrology, and geochemistry of sulfide- and sulfide-silicate textures are studied. These textures are the key to understand sulfide infiltration, sulfide crystallization and fractionation, as well as upgrading processes to change subeconomic sulfide melts into an ore deposit. Methods involved are detailed transmitted and reflected light microscopy, stable and radiogenic isotope analyses, microprobe and scanning electron microscopy investigations as well as micro-XRD studies.

Massive sulfides (light colours) infiltrating older granodiorite (dark colours), Sora quarry, Lausitz, Saxony. Field of view: 17 cm.

Skarn and greisen deposits in the Erzgebirge (Saxony, Germany) are the focus of Sn, W, and Li exploration activity, again for industrial metal demand. The aim of this study is to understand how tin and other elements like iron, fluorine and aluminium are distributed during late-magmatic cooling and fluid evolution between silicate minerals (malayaite, titanite and others), oxide minerals (cassiterite), skarn-forming and greisen-forming fluids. Methods involved are detailed transmitted and reflected light microscopy, fluid inclusion studies, and microprobe and scanning electron microscopy investigations.

Hand specimen in short-wave ultraviolet light highlighting the Sn-baring skarn-hosted malayaite (green) and the greisen-hosted scheelite (blue). Ehrenfriedersdorf, Saxony. Field of view: 25 cm.

Hydrothermal deposits in central Europe (Schwarzwald) and Western Australia are investigated with regards to their mineralogy, petrology, and geochemistry. Detailed research questions concern the nature of the fluids involved in their genesis, the source of the metals and other elements (e. g., F, S, C) present in the deposits, the role of fluid mixing during mineralization and the details of element redistribution during weathering. Methods involved are detailed transmitted and reflected light microscopy, followed by fluid inclusions studies, stable and radiogenic isotope analyses, microprobe and scanning electron microscopy investigations and micro-XRD studies.

Hydrothermal fluorite-barite vein in the Schwarzwald.

Hydrothermal scheelite- (blue in short-wave ultraviolet light) and pentlandite-bearing mineralization. Kambalda, Western Australia. Field of view: 20 cm.

Chemical map of different hydrothermal arsenide minerals. Green: Ni; blue: Co; red: Fe.

Halogen in Earth materials

An additional focus of our group lies in the investigation of halogens (F, Cl, Br and I) in various Earth’s materials. Halogens are important tracers for a large variety of geological processes such as magmatic differentiation, metasomatism, subduction, hydrothermal vein formation or magmatic degassing.

Projects focusing on halogens include the investigation of halogen contents of mantle rocks and minerals, halogen budgets in various magmatic systems, halogen systematics in various magmatic and hydrothermal minerals, as well as the role of halogens during the surface weathering of ore deposits and halogen cycling in soils.

The methods used to determine halogen contents in various materials are electron microprobe, Total Reflexion X-Ray Fluorescence (TXRF), Ion Chromatography for liquids and Combustion Ion Chromatography (CIC) for solids. In some of the projects we combine this with Secondary Ion Mass Spectrometry (collaboration with the University of Heidelberg) and stable Cl and Br isotope systematics (collaboration with CNRS, Paris).