I am interested in all kinds of fluids responsible for ore-formation in magmatic, metamorphic, sedimentary, and hydrothermal settings. My major research focus is to decipher processes leading to ore formation in carbonatites, alkaline rocks and hydrothermal vein-type deposits. My current projects are:

Alkaline silicate rocks and carbonatites

• Thermodynamics of carbonatitic fluids
• Magma evolution in space and time along the Kuboos-Bremen Line, Namibia
• The role of cumulate formation on HFSE enrichments in alkaline and carbonatitic systems
• The influence of crustal contamination on late-stage REE-mineralizations in carbonatites
• The role of late-stage fluids in carbonatite and alkaline silicate rocks
• The mineralogical control of geophysical exploration signatures
• New geomodels for exploring carbonatites and alkaline silicate rocks
• The genesis of the South African and Namibian alkaline provinces
• Petrology and age constraints of the southern Central European Volcanic Province
• Shallow plumbing systems in alkaline and carbonatite complexes

Hydrothermal vein type deposits

• Fluorite-baryte-quartz veins with base metal mineralization in Namibia, Morocco, the USA, and Nigeria
• Mass balance calculations in hydrothermal systems
• Basement leaching as source for metals in continental basement brines
• The genesis of the vein-type graphite deposit at Aukam, Namibia
• Trace element systematics of hematite-hosted fluid inclusions
• Mineralogical changes within a single vein and the relation to superregional events
• Deciphering fluid migration pathways
• The geochemistry of native arsenic and arsenides in hydrothermal vein-type deposits 
• The genesis of ore shoots in hydrothermal veins
• Kinetics of ore precipitation in hydrothermal systems 

Metamorphic and structural geology projects

• Metamorphism of carbonatites
• Release of refractory gold in pyrite and arsenopyrite during metamorphism
• Formation of the Black Angel mineralization in Greenland by deformation
• Pathway generation and devolatilization in Finland and related atypical and typical orogenic gold deposits

Environmental projects and projects related to domestic raw materials

• Metal inventory of medieval mining tailings in SW Germany
• Transport of elements in acid mining drainage
• Metal inventory of geothermal brines in the Upper Rhine Graben
• Effect of flash floods in arid environments on the water protection in mining districts
• Anthropology: Dating and climate reconstruction during calcrete formation including related human relicts in Namibia
• Climate reconstruction, Quaternary neotectonics and “laterite” formation in the 40 Ma old Namib desert

Other projects

• Dolomitization in oil reservoirs 
• How to bring hydrocarbons into crystalline basement rocks? 
• Testing the resilience of ancient early diagenetic dolomites as archives of their paleo-environment

DFG single projects

WA 3116/22-1: “The weakly eroded Kruidfontein phonolite-carbonatite volcano – a proxy sound into the interior of the Laacher See volcano”

Carbonatites are relatively rare rocks (~610 occurrences world-wide). About 80 % of all carbonatite occurrences are spatially associated with diverse silicate rocks, whereby the genetic relationship between carbonatites and these silicate rocks is debated with different models. Only a minor proportion of carbonatites (50 occurrences) are extrusive; the associated silicate rocks are mostly nephelinites and phonolites, whereby phonolitic melts are assumed to evolve from parental nephelinitic melts. However, their specific genetic relation to carbonatites is not clear. A good example for this controversity is the Quaternary Laacher See phonolitic volcano, which is part of the Eastern Eifel (Germany). Carbonatites at Laacher See are only known from xenoliths, which indicate a phonolite-carbonatite association at depth. In general, only surface pyroclastic deposits are exposed, while the feeding system, which may show a direct relationship between carbonatites and phonolites, remains unexposed. A better understanding of the holistic structure of Laacher See (as a representative for carbonatite-phonolite complexes) would require a comparison with similar but shallow intrusions and feeding systems that are only slightly eroded to deeper intrusion levels. An ideal candidate for such a comparative study represents the so far poorly studied Kruidfontein Proterozoic phonolite–carbonatite volcano (South Africa).
This project will investigate the Kruidfontein carbonatite-phonolite complex, which preserves surface pyroclastic phonolitic facies that are penetrated by later phonolitic and carbonatitic intrusions at a subsurface level. The carbonatites at Kruidfontain, furthermore, reflect a highly evolved composition represented by fluorite-rich calcite carbonatites and pure fluorite veins. Our study will focus on (1) the eruption mechanism of the Kruidfontein volcano in comparison to the Laacher See volcano, (2) the age determination of Kruidfontein and its temporal assignment into regional magmatic events, and (3) the origin and role of fluorine in the carbonatites. For this purpose, the different lithologies of the Kruidfontein complex will be investigated by means of petrography (microscopy, µXRF, SEM), whole rock analyses (XRF, ICP-MS, CSA), mineral chemistry (EMPA), stable and radiogenic isotopy (IRMS, ICP-MS), and detailed fluid inclusion studies (micro-thermometry, Micro-Raman spectroscopy). Results will be compared with the information available from the Laacher See volcano, which will allow a better understanding of phonolite-carbonatite associations in general.

WA 3116/20-1: “HFSE enrichment in carbonatites and associated peridotite-melilitolite-foidolite complexes: the role of fractionation versus metasomatism in ore-forming processes”

Carbonatites associated with ultramafic rocks, melilitolites and foidolites contain economic HFSE mineralizations in some cases but are barren in others. In that sense, the Kovdor (Russia) and Gardiner (E Greenland) complexes, which will be studied and compared in this project, represent key examples for such opposite cases: carbonatites at Kovdor are HFSE-mineralized, with only minor HFSE-phases in the associated silicate rocks. In contrast, melilitolites from Gardiner show ore-grade enrichment of perovskite, while the associated carbonatites are barren. Our previous study (DOME 1) suggests that ultramafics and melilitolites from Gardiner are cumulates of a mantle-derived, primitive and Ti-rich silicate melt. In contrast, ultramafic rocks from Kovdor are calcite- and biotite-rich, lack cumulate textures and are strongly depleted in compatible elements (e.g., Ni and Cr), which contradicts a cumulate, but rather supports a metasomatic origin. We hypothesize, that these rocks formed by a reaction between mantle-derived carbonatitic melts and silicic host rocks. This project aims at comparing these two complexes in detail to decipher the processes leading to the HFSE-enrichment in early cumulates (Gardiner) and late-stage carbonatites (Kovdor), respectively. If silicate rocks in such complexes can form by reaction of mantle-derived carbonatites with silicic wall rocks, enrichment of HFSE in such cases would be controlled by carbonatitic melts, and not by fractionation processes in evolving silicate magmas. This probably leads to completely different enrichment and fractionation patterns (e.g., Zr/Hf, Nb/Ta, La/Lu). To test this hypothesis, we will follow two complementary analytical strategies: (1) melt and fluid inclusions in all major rock units will be investigated by a state-of-the-art analytical approach (re-homogenization, microthermometry, confocal Raman spectroscopy, high-resolution X-ray computed tomography, EPMA, LA-ICP-MS), and (2) radiogenic isotope compositions (Sr-Nd-Pb) will be obtained for major minerals using both in-situ methods (LA-MC-ICP-MS) and high-precision analysis by ID-TIMS. The expected results will allow to constrain the nature and composition of the host melt/fluid at variable evolutionary stages and associated element enrichment processes. Combined with radiogenic isotope tracers which resolve isotopic differences from complex-scale to individual grains, this will clarify if silicate rocks associated with carbonatites indeed represent products of variable stages of metasomatism between carbonatite and crustal host rocks. This finding would have major implications for ore-forming processes of HFSE in carbonatite-alkaline silicate rock complexes, which differ strongly in style and timing depending on whether magmatic or metasomatic processes dominate.

WA 3116/21-1: “The formation of atypical orogenic Au deposits: insight from Finland greenstone belts”

Orogenic gold deposits are an important source of gold and occur worldwide. They are hydrothermal deposits associated with the formation of mountain ranges and are very common in the Finnish Archean and Precambrian orogenic belts. Finland contains orogenic gold-only deposits and atypical deposits enriched not only in gold but also in other metals, such as Co, Cu, Ni, Ag and U. The occurrence of other metals beside gold in such an environment is not well understood, and new studies will help to improve the genetic model of orogenic deposits and the exploration vectors in Europe for critical metals such as Co. The exploration of critical metals in Europe is relevant for production of alternative energy and the low-carbon economy. Cobalt, for example, is needed for electric vehicle batteries and copper for the solar photovoltaics.
Four deposits hosted in the same host rocks and structures were chosen from the Precambrian Pohjanmaan Belt in order to study their genesis. These are the typical orogenic gold Laivakangas and Huhta, and atypical Kurula and Jouhineva deposits formed during the Svecofennian orogeny (1.92–1.79 Ga). The main objective of this project is to understand why some deposits are polymetallic and others are gold-only. We intend to determine the age of the four deposits and compare with other regional events, such as magmatism and metamorphism, to understand the main precipitation mechanisms, the fluid and metal sources, and the interaction between rock and fluid during the fluid percolation from the source to the host rocks. For this investigation, petrography, in-situ mineral analysis, dating and further geochemical analysis will be held.

WA 3116/18-1: “The behavior of high field-strength elements (HFSE) in F-rich peralkaline systems”

Peralkaline igneous rocks (rocks with a molar (Na+K)/Al ratio > 1) are strongly enriched in halogens, rare earth elements (REE), and high field strength elements (HFSE; Zr, Hf, Nb, Ta) and represent some of the most promising sources for future HFSE and REE supply. This project investigates the behaviour of halogens and HFSE/REE-bearing phases in the texturally and compositionally zoned peralkaline plutonic Monchique complex (Portugal) that evolved from gabbroic to foid syenitic compositions. The special role of sodalite, fluorite and various F-rich Na-Ca-HFSE disilicates (FDC) for the retention of halogens in peralkaline magmas will be investigated and the variable effects of fractional crystallization, fluid exsolution/degassing and fluid-wall rock interaction on halogen systematics and HFSE/REE mobility will be distinguished from each other. The following three working hypotheses will be guiding the workflow of the anticipated project:
• Halogen abundances and halogen systematics (F/Cl, Cl/Br ratios) in the Monchique rocks reflect the effects of fractional crystallization during magmatic stages and redistribution of halogens caused by fluid exsolution and accompanied (autometasomatic) hydrothermal alteration.
• The Monchique complex shows vertical and horizontal zonation with respect to the relative abundance of sodalite-FDS assemblages, which may or may not correlate with the HFSE distribution in this tabular body.
• Locally developed fenites around the Monchique complex are Cl-rich but F-poor and therefore devoid of FDS but zircon- and titanite-bearing, which is mainly controlled by the low F/Cl ratio of the fenitizing fluids.
To test these hypotheses, we will combine detailed petrography, whole-rock analysis (XRF, ICP-MC, CIC), mineral chemistry (EPMA, CIC, LA-ICP-MS), thermodynamic modelling, and fluid inclusion investigations (microthermometry, LA-ICP-MS). The expected results of this project will not only decipher halogen and HFSE behaviour in such a peralkaline system but will certainly have general implications on the formation and migration of halogen-bearing fluids that are capable of HFSE transport within a shallow-level plutonic complex. Geochemical monitors (e.g., whole rock halogen data, HFSE data) will be combined with mineralogical observations (e.g., FDS, sodalite, fluorite distribution) and will allow for a detailed view on fluid exsolution/degassing processes in tabular magma bodies.

WA 3116/16-1: “Towards an improved understanding of open- versus closed-system diagenesis in carbonate research”

Carbonate-archive data record, at the time of their deposition, a brief snapshot of the ambient Earth’s surface conditions. All carbonate archives are susceptible to post-depositional alteration. The challenge is to separate a meaningful environmental signal from one that is modified by later diagenetic or metamorphic alteration, and hence to reliably assess the integrity and robustness of the extracted proxy data as indicators of their paleo-environment. In the context of early- to late-diagenetic pathways, carbonate phases may undergo rock-buffered (= preserving environmental signals) or fluid-buffered (overprinting environmental signals) diagenesis. In many cases, the difficulty lies in recognizing fluid- versus rock-buffered diagenesis, particularly in the definition of generally applicable criteria to separate these fundamentally different environments and in cases where fluid-buffered alteration is later overprinted under rock-buffered conditions. Additional complexity arises from the observation that a carbonate rock may display fluid-buffered behavior for one element (i.e., oxygen) and rock-buffered behavior for another (i.e., carbon, magnesium, calcium, or strontium).
This project will investigate if the combination of petrographic and geochemical analysis with microthermometrical data derived from fluid inclusions can serve as a fingerprint for either of the two (fluid- versus rock-buffered) alteration modes. The study will be performed in the Steltenberg quarry in the northern Rhenish Massif in western Germany, where a complex set of Devonian carbonates that has undergone burial- and meteoric diagenesis will be investigated as a litmus test for the above considerations. This Devonian `natural laboratory’ is ideal in the sense that it allows comparing fundamentally different types of diagenetic and tectonic overprint of fluid-buffered and overprinted rocks, and such that seem to evidence rock-buffered diagenesis and preserved environmental data. 
To test our hypothesis, we will build on a detailed preliminary petrographic assessment to reconstruct fluid paleo-temperatures and fluid chemistry using carbon and oxygen isotope values, radiogenic strontium, calcium, and magnesium isotope values, and microthermometry, and place these data into a stratigraphic/temporal context employing U-Pb carbonate dating. This work will allow us to place all this petrographical and geochemical data in a fluid property context and to establish criteria for diagenesis for the open (fluid-buffered) and the closed (rock-buffered) system end-members and their corresponding intermediate stages.

WA 3116/14-1: “Mechanism of Paleoproterozoic hydrothermal Zn-Pb-Ag-rare metals mineralization in the Black Angel district, central West Greenland”

In this project, we intend to investigate the mineralogy, geochemistry and structures of Paleoproterozoic Zn-Pb-Ag-rare metals ores in the Black Angel District of central West Greenland. Black Angel represents one of the oldest carbonate-hosted Pb-Zn deposits on Earth, having produced 11.2 Mt Zn-Pb-Ag ore between 1973 and 1990. In a preliminary study, we were able to identify the Ge mineral briartite, which is only known from 11 other deposits worldwide. Our preliminary data indicate that the formation of briartite is controlled by deformation of the ore and redistribution of Ge.
In this project, we aim at investigating the absolute age, processes of hydrothermal mineralization and the distribution of important trace elements (e.g., Cd, Ge, Ga, In) in the orebodies related to different structural features of the ore. The data will provide important constraints on (1) the temperature, pH and redox state during hydrothermal mineralization, and (2) the potential source for metals and hydrothermal fluid. The aim of the project is to develop a detailed model of the evolution of hydrothermal mineralization from the source of fluids and metals to the site of metal precipitation. We expect important results from trace element combined with microstructural analysis of sulfides with respect to deformation- and fluid- controlled element distribution.

WA 3116/15-1: “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 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:
• The behaviour of HFSE and REE in carbonatitic magmas is influenced by source contamination and silicate wall-rock interaction.
• 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.
• 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.

MA 2563/19-1: “Petrology and age of foidites in SW Germany”

Foidites are mantle-derived and strongly SiO2-undersaturated volcanic rocks, with primitive olivine melilitites possibly representing primary magma compositions. Among the Palaeogene volcanic rocks in SW Germany, foidite occurrences are concentrated in seven areas (Kaiserstuhl, Upper Rhine Graben, Bonndorf Graben including Vosges, Hegau, Urach, Lower Neckar). Mineralogically, they range between olivine melilitites, nephelinites and haüynites, with clear differences between those areas. However, except for the Kaiserstuhl, their petrology has not been systematically investigated, and their ages are not reliably constrained. 
The proposed study will test the following hypotheses: (i) Mineralogical differences of the melilitite-nephelinite-haüynite series at the locations to be investigated relate to variable degrees and courses of magmatic differentiation of parental olivine melilititic magmas. (ii) The intrusion ages for these rocks relate to transient geodynamic settings that cause distinct melting events in the mantle manifested in distinct ages for the different areas to be studied.
To test these hypotheses, detailed petrographic and mineral chemical data (EMPA and LA-ICP-MS on minerals) will be combined with petrological modeling (T-aSiO₂-fO₂ conditions and differentiation paths) and geochronological data (LA-ICP-MS dating). The expected results will enable us to characterize the crystallization conditions and differentiation paths for the foidites at the different localities. Their comparison with each other will help to decipher potential genetic relations between the foidite types of each locality and will show if the courses of differentiation at the different localities are similar or different from each other. Such a comparative study has never been performed so far, and the results are expected to have major implications on our understanding on the potential heterogeneity of the mantle domains below SW Germany. The results of this study will be integrated in recent models on the post-Variscan tectonic evolution in SW Germany.

WA 3116/4-1: “Effect and significance of contamination-related compositional melt variations of the Tweerivier and Bulhoekkop carbonatites, South Africa, with special reference to their REE mineralization”

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.

MA 2135/26-1: “Influence of crustal contamination on REE-enrichment in carbonatites of the Kalkfeld group (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.

DFG priority programme DOME Dynamics of Ore Metal Enrichment

MA 2563/18-1: “The role of early cumulate formation for HFSE enrichment in foidolitic systems”

Foidolites are mantle-derived and strongly SiO2-undersaturated plutonic cumulate rocks. Studies on economically interesting HFSE deposits associated with foidolitic rocks are generally rare, but the Gardiner Complex in E Greenland and the Kovdor Complex in Russia were studied in some detail. The various lithologies of both complexes are believed to derive from a mela-nephelinitic parental magma. In both complexes a suite of peridotitic rocks (dunite & clinopyroxenite), melteigitic to urtitic rocks, foidolitic rocks (melilitolite) and carbonatite occur. Although the parental magma compositions are melanephelinitic for the Kovdor and Gardiner complexes, the mineralogical composition of melilitolite and carbonatite of these two complexes show clear differences: Melilitolite of the Gardiner Complex shows ore grade enrichment of perovskite in cumulates, whereas melilitolite at Kovdor contains only accessory perovskite. In contrast, Kovdor carbonatite is HFSE-mineralized, but at Gardiner these rocks are barren in HFSE. This project aims at comparing these two similar complexes in detail and to decipher the processes leading to the HFSE-enrichment in early cumulates at Gardiner and the late-stage HFSE-enrichment in the Kovdor carbonatite. 
The proposed study will be guided by the following two working hypotheses: (i) the mineralogical differences between the peridotitic rocks (minor chromite versus minor Ti-magnetite) and melilitolite (presence or absence of massive perovskite cumulates) at the Gardiner and Kovdor complexes relate to differences in their parental magma composition, which influenced the timing of perovskite saturation; (ii) the concentration of HFSE in carbonatite of Gardiner (low) and Kovdor (enriched) relate to the intensity of previous perovskite fractionation. To test these hypotheses, detailed petrographic, mineral chemical and petrological data for the different rock types of the two complexes will be gathered and thoroughly compared. Special focus will be given to the distribution of REE + HFSE (Zr, Hf, Nb, Ta) between apatite, clinopyroxene, olivine, perovskite, and melilitite. The project further aims at developing exploration indicators that will help to search for the different enrichment types within a complex (early cumulate versus late stage magmatic versus hydrothermal overprint).

• Petrology of the Kaiserstuhl 
• Recontruction of fluid evolution of continental basement brines using microthermometry and crush-leach analyses
• Ore-forming processes in hydrothermal vein-type deposits, Schwarzwald, Germany
• Stable isotope chemistry of hydrothermal vein-type deposits
• Mg-isotope systematics of hydrothermal carbonates (cooperation with A. Immenhauser, RUB Bochum, Germany)
• Ore petrography and ore chemistry of hydrothermal vein-type deposits
• Ore fluid evolution in the continental crystalline basement
• Ore precipitation processes by LA-ICP-MS analyses of single fluid inclusions (cooperation with C. Heinrich & M. Wälle ETH Zürich, Switzerland)
• U-Pb age dating of hydrothermal gangue and ore minerals (cooperation with A. Gerdes, Frankfurt, Germany)
• Evolution of fluid pathways in crystalline basement (cooperation with C. Heinrich & M. Wälle ETH Zürich, Switzerland)
• Multi-aquifer fluid mixing processes as first order processes for ore precipitation
 

Dipl.-Mineraloge, Post-Doc, lab manager for microthermometry and cathodoluminescence microscopy

Since 04/2020: Associated editor The Depositional Record

Victor-Moritz-Goldschmidt Award 2023

2026

Kemmler, L., Giebel, R. J., Walter, B. F., Marks, M. A. W., Macey, P. H. & Markl, G. (2026): Revisiting the Alnöitic Tuffisite Diatremes in the Kainab Alkaline Province, Southern Namibia. Communications of the Geological Survey of Namibia 29, 1–42.

2025

Steffann, R., Walter, B. F., Giebel, R. J., Marks, M. A. W., Ladisic, A., Kemmler, L., Schlosser, N., Binder, T., Reinhard, F., Mössinger, L., Löschner, P., Dück, S. & Markl, G. (2025): Phengite formation at the contact between carbonatites and muscovite-kyanite schists: Kwaggaspan, northwestern Namibia. Communications of the Geological Survey of Namibia, 29 (2025), 71–88.

Rddad, L., Jinari, A., Walter, B. F., Raza, M., Benaouda, R. & Mouguina, E. M. (2025): Fluid evolution and ore genesis of the Amensif ZnCu (Pb-Ag-Au) distal skarn deposit (western High Atlas, Morocco): Constraints from fluid inclusions, crush-leach analysis, REY geochemistry, and Pb isotopes. Geochemistry 85, 126353 (18 p.).

Walter, B. F., Giebel, R. J., Marks, M. A. W. & Markl, G. (2025): A global review of the architecture of carbonatite complexes and its implications for melt ascent. Communications of the Geological Survey of Namibia 29, 43–70.

Reinhard, F., Walter, B. F., Giebel, R. J., Zeh, A., Marks, M. A. W. & Markl, G. (2025): Carbonatitic metasomatism in ultramafic rocks at the Blue Hill, Namibia. Lithos 518–519, 108317 (19 p.).

de Araujo Silva, A., Hector, S., Patten, C., Beranoaguirre, A., Eiche, E., Walter, B. F. & Kolb, J. (2025): Hydrothermal co enrichment of Au, As, Co, and Cu in orogenic deposits: insights from the Pohjanmaa belt. Mineralium Deposita (25 p.).

Binder, T., Marks, M. A. W., Fusswinkel, T., Walter, B. F. & Markl, G. (2025): Variable onset of magma segregation controls contrasting geochemical patterns of mineral assemblages in fractionating alkaline volcanic systems. Lithos 514–515, 108185 (22 p.).

Andrić-Tomašević, N., Walter, B. F., Simić, V., Raza, M., Životić, D., Novković, Ž., Kolb, J., Gerdes, A. & Beranoaguirre, A. (2025): Contributions of arid climate and hydrothermal fluid flow on sedimentation in saline-alkaline lakes: Insight from the Ibar intramontane basin (Southern Serbia). The Depositional Record (34 p.).

Ladisic, A., Marks, M. A. W., Walter, B. F., Giebel, R. J., Beranoaguirre, A. & Markl, G. (2025): Permo-Triassic magmatism in the Damaraland Igneous Province, NW Namibia: The Ondurakorume alkaline‑carbonatite complex. Geochemistry 85 (3), 126287 (20 p.).

Rddad, L., Cherai, M., Walter, B. F. & Talbi, F. (2025): Multistage ore-forming processes in the genesis of the fluorite-baryte Merguechoum ore deposit (Moroccan eastern Meseta) in relation to Pangea rifting. Journal of Geochemical Exploration 275, 107766 (20 p.).

Raza, M., Giebel, R. J., Staude, S., Beranoaguirre, A., Kolb, J., Markl, G. & Walter, B. F. (2025): The post-magmatic evolution of the Nooitgedacht Carbonatite Complex, South Africa. Geochemistry, 126249 (26 p.).

2024

Schmitt, F., Marks, M. A. W., Siegel, M., Henzler, M., Zaitsev, A. N., Markl, G. (2024): Nephelinites from Burko volcano (Tanzania) record the phase relations among perovskite, magnetite, titanite and andradite in evolved alkaline and silica-undersaturated systems. Geochemistry 84 (4), 126211 (24 p.).

Jungmann, M., Walter, B. F., Eiche, E., Giebel, R. J. & Kolb, J. (2024): The source of lithium in connate fluids: Evidence from the geothermal reservoir at Soultz-sous-Forêts, Upper Rhine Graben, France. Journal of Geochemical Exploration, 107641.

Kluge, T., Eiche, E., Walter, B. F., Kramer, U., Göttlicher, J., Gudelius, D., Giebel, R. J. & Kolb, J. (2024): The influence of fluid pressure, redox potential and crystal growth characteristics in Mississippi-Valley-Type (MVT) ore formation – lessons from a modern geothermal scale. Mineralium Deposita (21 p.).

Rddad, L., Cherai, M., Walter, B. F., Talbi, F., Kraemer, D. & Billström, K. (2024): Geochemistry and fluid inclusion study of the Jbel Tirremi fluorite-baryte deposit, Morocco: New insights into the genetic model in relation to Mesozoic tectonics. Geochemistry, 126162.

Binder, T., Marks, M. A. W., Walter, B. F., Wenzel, T. & Markl, G. (2024): Two Distinct Metasomatized Mantle Sources Produced Two Groups of Alkaline SiO₂-undersaturated Rocks in the Southern Central European Volcanic Province. Journal of Petrology 65 (7), egae070.

Kasay, G. M., Borst, A. M., Giebel, R. J., Bolarinwa, A. T., Beranoaguirre, A., Kluge, T., Aromolaran, O. K., Raza, M., Eiche, E., Kolb, J., Nzolang, C. & Walter, B. F. (2024): Petrogenesis and geodynamic setting of the Bingo alkaline-carbonatite complex, DRC: Constraints from petrography, geochemistry, C-O isotopes and U-Pb geochronology. Precambrian Research 408, 107421.

Walter, B. F., Giebel, R. J., Arthuzzi, J. C. L., Kemmler, L. & Kolb, J. (2024): Diatreme-hosted fluorite mineralization in S-Namibia – A tale of cryogenic brine formation and fluid mixing below an unconformity in the context of Pangea rifting. Journal of African Earth Sciences 210, 105154.

Rapprich, V., Walter, B. F., Kopačková-Strnadová, V., Kluge, T. M., Čejková, B., Pour, O., Hora, J., M., Kynický, J. & Magna, T. (2024): Gravitational collapse of a volcano edifice as a trigger for explosive carbonatite eruption? The Geological Society of America Bulletin 136, 2291–2304.

Mueller, M., Walter, B. F., Giebel, R. J., Beranoaguirre, A., Swart, P. K., Lu, C., Riechelmann, S. & Immenhauser, A. (2024): Towards a better understanding of the geochemical proxy record of complex carbonate archives. Geochimica et Cosmochimica Acta 376, 68–99.

Binder, T., Marks, M. A. W., Friedrichsen, B.-E., Walter, B. F., Wenzel, T. & Markl, G. (2024): Bimodal volcanism in the Hegau region (SW Germany): Differentiation of primitive melilititic to nephelinitic rocks produces evolved nosean phonolites. Lithos 472–473, 107565.

2023

Walter, B. F. & Kolb, J. (2023): The raw material potential of SW-Germany – A brief overview. SGA news 53, 1–4.

Walter, B. F., Giebel, R. J., Siegfried, P. R., Gudelius, D. & Kolb, J. (2023): The eruption interface between carbonatitic dykes and diatremes – The Gross Brukkaros volcanic field Namibia. Chemical Geology 621, 121344.

Walter, B. F., Giebel, R. J., Siegfried, P., Doggart, S., Macey, P., Schiebel, D. & Kolb, J. (2023): The genesis of hydrothermal veins in the Aukam valley SW Namibia– A far field consequence of Pangean rifting? Journal of Geochemical Exploration 250, 107229.

Peng, E., Kolb, J., Walter, B. F., Frenzel, M., Patten, C. G. C., Xu, D., Wang, Y., Gan, J., Beranoaguirre, A. & Wang, Z. (2023): New Insights on the formation of the Jingchong Cu-Co-Pb-Zn deposit, South China: Evidence from sphalerite mineralogy and muscovite ⁴⁰Ar-³⁹Ar dating. Ore Geology Reviews 162, 105667.

Hector, S., G. C. Patten, C., Kolb, J., de Araujo Silva, A., Walter, B. F. & Molnár, F. (2023): Orogenic Au deposits with atypical metal association (Cu, Co, Ni): insights from the Pohjanmaa Belt, western Finland. Ore Geology Reviews 154, 105326.

Gudelius, D., Marks, M. W., Markl, G., Nielsen, T. F. D., Kolb, J. & Walter, B. (2023): The Origin of Ultramafic Complexes with Melilitolites and Carbonatites: A Petrological Comparison of the Gardiner (E Greenland) and Kovdor (Russia) Intrusions. Journal of Petrology 64 (6), 1–26.

Cherai, M., Rddad, L., Talbi, F. & Walter, B. F. (2023): Trace-element geochemistry and S–O isotopes in the fluorite-barite mineralization of Merguechoum, Moroccan eastern Meseta: insights into ore genesis to the Pangea rifting. Acta Geochimica 42, 435–452.

Binder, T., Marks, M. A. W., Gerdes, A., Walter, B. F., Grimmer, J., Beranoaguirre, A., Wenzel, T. & Markl, G. (2023): Two distinct age groups of melilitites, foidites, and basanites from the southern Central European Volcanic Province reflect lithospheric heterogeneity. International Journal of Earth Sciences 112 (3), 881–905.

Beard, C. D., Goodenough, K. M., Borst, A. M., Wall, F., Siegfried, P. R., Deady, E. A., Pohl, C., Hutchison, W., Finch, A. A., Walter, B. F., Elliott, H. A. L. & Brauch, K. (2023): Alkaline-Silicate REE-HFSE Systems. Economic Geology 118 (1), 177–208.

2022

Walter, B. F., Giebel, R. J., Marlow, A. G., Siegfried, P. R., Marks, M., Markl, G., Palmer, M. & Kolb, J. (2022): The Kieshöhe carbonatites of southwestern Namibia – the post-magmatic role of silicate xenoliths on REE mobilisation. Communications of the Geological Survey Namibia 25, 1–31.

Scharrer, M., Epp, T., Walter, B., Pfaff, K., Vennemann, T. & Markl, G. (2022): The formation of (Ni-Co-Sb)-Ag-As ore shoots in hydrothermal galena-sphalerite-fluorite veins. Mineralium Deposita 57, 853–885.

Rddad, L., Kraemer, D., Walter, B. F., Darling, R. & Cousens, B. (2022): Unravelling the fluid flow evolution and precipitation mechanisms recorded in calcite veins in relation to Pangea rifting–Newark Basin, USA. Geochemistry 82 (4), 125918.

Ngounouno, F. Y., Negue, E. N., Kolb, J., Walter, B., Teda Soh, A. C., Patten, C. & Ngounouno, I. (2022): Tectonic setting, fluid inclusion and gold mineralization of the southwest Poli region (northern Cameroon Domain). Journal of African Earth Sciences 194, 104579.

Müller, M., Walter, B. F., Swart, P. K., Jöns, N., Jacquemyn, C., Igbokwe, O. A. & Immenhauser, A. (2022): A tale of three fluids: fluid-inclusion and carbonate clumped-isotope paleothermometry reveals complex dolomitization and dedolomitization history of the latemare platform. Journal of Sedimentary Research 92 (12), 1141–1168.

Mueller, M., Jacquemyn, C., Walter, B. F., Pederson, C. L., Schurr, S. L., Igbokwe, O. A., Jöns, N., Riechelmann, S., Dietzel, M., Strauss, H. & Immenhauser, A. (2022): Constraints on the preservation of proxy data in carbonate archives – lessons from a marine limestone to marble transect, Latemar, Italy. Sedimentology 69 (2), 423–460.

2021

Walter, B. F., Giebel, R. J., Steele-MacInnis, M., Marks, M. A. W., Kolb, J. & Markl, G. (2021): Fluids associated with carbonatitic magmatism: A critical review and implications for carbonatite magma ascent. Earth-Science Reviews 215, 103509.

Scharrer, M., Reich, R., Fusswinkel, T., Walter, B. F. & Markl, G. (2021): Basement aquifer evolution and the formation of unconformity-related hydrothermal vein deposits: LA-ICP-MS analyses of single fluid inclusions in fluorite from SW Germany. Chemical Geology 575, 120260.

2020

Walter, B. F., Jensen, J. L., Coutinho, P., Laurent, O., Markl, G. & Steele-MacInnis, M. (2020): Formation of hydrothermal fluorite-hematite veins by mixing of continental basement brine and redbed-derived fluid: Schwarzwald mining district, SW-Germany. Journal of Geochemical Exploration 212, 106512.

Walter, B. F., Scharrer, M., Burisch, M., Apukthina, O. & Markl, G. (2020): Limited availability of sulfur promotes copper-rich mineralization in hydrothermal Pb-Zn veins: A case study from the Schwarzwald, SW Germany. Chemical Geology 532, 119358.

Walter, B., Steele-MacInnis, M., Giebel, R. J., Marks, M. A. W. & Markl, G. (2020): Complex carbonate-sulfate brines in fluid inclusions from carbonatites: Estimating compositions in the system H₂O-Na-K-CO₃-SO₄-Cl. Geochimica et Cosmochimica Acta 277, 224–242.

Scharrer, M., Sandritter, K., Walter, B. F., Neumann, U. & Markl, G. (2020): Formation of native arsenic in hydrothermal base metal deposits and related supergene U⁶⁺ enrichment: The Michael vein near Lahr, SW Germany. American Mineralogist 105 (5), 727–744.

Mueller, M., Igbokwe, O. A., Walter, B., Pederson, C. L., Riechelmann, S., Richter, D. K., Albert, R., Gerdes, A., Buhl, D., Neuser, R. D., Bertotti, G. & Immenhauser, A. (2020): Testing the preservation potential of early diagenetic dolomites as geochemical archives. Sedimentology 67 (2), 849–881.

Ladenburger, S., Walter, B. F., Marks, M. A. W. & Markl, G. (2020): Combining Ion Chromatography and Total Reflection X-ray Fluorescence for Detection of Major, Minor and Trace Elements in Quartz-hosted Fluid Inclusions. Journal of Analytical Chemistry 75 (11), 1477–1485.

Kolchugin, A., Immenhauser, A., Morozov, V., Walter, B., Eskin, A., Korolev, E. & Neuser, R. (2020): A comparative study of two Mississippian dolostone reservoirs in the Volga-Ural Basin, Russia. Journal of Asian Earth Sciences, 199, 104465.

2019

Walter, B. F., Kortenbruck, P., Scharrer, M., Zeitvogel, C., Wälle, M., Mertz-Kraus, R. & Markl, G. (2019): Chemical evolution of ore-forming brines – Basement leaching, metal provenance, and the redox link between barren and ore-bearing hydrothermal veins. A case study from the Schwarzwald mining district in SW-Germany. Chemical Geology 506, 126–148.

Giebel, R. J., Parsapoor, A., Walter, B. F., Braunger, S., Marks, M. A. W., Wenzel, T. & Markl, G. (2019): Evidence for Magma–Wall Rock Interaction in Carbonatites from the Kaiserstuhl Volcanic Complex (Southwest Germany). Journal of Petrology 60 (6), 1163–1194.

Banks, G. J., Walter, B. F., Marks, M. A. W. & Siegfried, P. R. (2019): A Workflow to Define, Map and Name A Carbonatite- or Alkaline Igneous-Associated REE-HFSE Mineral System: A Case Study from SW Germany. Minerals 9 (2), 97.

Keim, M. F., Walter, B. F., Neumann, U., Kreissl, S., Bayerl, R. & Markl, G. (2019): Polyphase enrichment and redistribution processes in silver-rich mineral associations of the hydrothermal fluorite-barite-(Ag-Cu) Clara deposit, SW Germany. Mineralium Deposita 54, 155–174.

2018

Epp, T., Walter, B. F., Scharrer, M., Lehmann, G., Henze, K., Heimgärtner, C., Bach, W. & Markl, G. (2018): Quartz veins with associated Sb-Pb-Ag±Au mineralization in the Schwarzwald, SW Germany: a record of metamorphic cooling, tectonic rifting and element remobilization processes in the Variscan belt. Mineralium Deposita. Mineralium Deposita 54, 281–306.

Braunger, S., Marks, M. A. W., Walter, B. F., Neubauer, R., Reich, R., Wenzel, T., Parsapoor A. & Markl, G. (2018). The Petrology of the Kaiserstuhl Volcanic Complex, SW Germany: The Importance of Metasomatized and Oxidized Lithospheric Mantle for Carbonatite Generation. Journal of Petrology. Journal of Petrology 59 (9), 1731–1762.

Walter, B. F., Gerdes, A., Kleinhanns, I. C., Dunkl, I., von Eynatten, H., Kreissl, S. & Markl, G. (2018): The connection between hydrothermal fluids, mineralization, tectonics and magmatism in a continental rift setting: fluorite Sm-Nd and hematite and carbonates U-Pb geochronology from the Rhinegraben in SW Germany. Geochimica et Cosmochimica Acta 240, 11–42.

Walter B.F., Parsapoor A., Braunger S., Marks M.A.W., Wenzel T., Martin M., Markl G. (2018): Pyrochlore as a monitor for magmatic and hydrothermal processes in carbonatites from the Kaiserstuhl volcanic complex (SW Germany). Chemical Geology 498, 1–16.

Kreissl, S., Gerdes, A., Walter, B. F., Neumann, U., Wenzel, T. & Markl, G. (2018): Reconstruction of a >200 Ma multi-stage “five element” Bi-Co-Ni-Fe-As-S system in the Penninic Alps, Switzerland. Ore Geology Reviews 95, 746–788.

Walter, B. F., Burisch, M., Fusswinkel, T., Marks, M. A. W., Steele-MacInnis, M., Wälle, M., Apukhtina, O. & Markl, G. (2018): Multi-reservoir fluid mixing processes in rift-related hydrothermal veins, Schwarzwald, SW-Germany. Journal of Geochemical Exploration 186, 158–186.

Burisch, M., Walter, B. F., Gerdes, A., Lanz, M. & Markl, G. (2018): Late-stage anhydrite-gypsum-siderite-dolomite-calcite assemblages record the transition from a deep to a shallow hydrothermal system in the Schwarzwald mining district, SW Germany. Geochimica and Cosmochimica Acta 223, 259–278.

2017

Walter, B. F., Steele-MacInnis, M. & Markl, G. (2017): Sulfate brines in fluid inclusions of hydrothermal veins: Compositional determinations in the system H₂O-Na-Ca-Cl-SO₄. Geochimica et Cosmochimica Acta 209, 184–203.

Burisch, M., Walter, B. F. & Markl, G. (2017): Silification of hydrothermal gangue minerals in Pb-Zn-Cu-fluorite-quartz-baryte veins. The Canadian Mineralogist 55, 501–514.

Walter, B. F., Burisch, M., Marks, M. A. W. & Markl, G. (2017): Major element composition of fluid inclusions from hydrothermal vein-type deposits record eroded sedimentary Units in the Schwarzwald district, SW Germany. Mineralium Deposita 52 (8), 1191–1204.

Burisch, M., Gerdes, A., Walter, B. F., Neumann, U., Fettel, M. & Markl, G. (2016): Methane and the origin of five-element veins: Mineralogy, age, fluid inclusion chemistry and ore forming processes in the Odenwald, SW Germany. Ore Geology Reviews 81 (1), 42–61.

2016

Walter, B. F., Burisch, M. & Markl, G. (2016): Long-term chemical Evolution and modification of Continental Basement brines - a field study from the Schwarzwald, SW Germany. Geofluids 16, 604–623.

Burisch, M., Walter, B. F., Wälle, M. & Markl, G. (2016): Tracing fluid migration pathways in root zone below unconformity-related hydrothermal veins: Insights from trace element systematics of individual fluid inclusions. Chemical Geology 429, 44–50.

Kolchugin, A., Immenhauser, A., Walter, B. & Morozov, V. P. (2016): Diagenesis of the palaeo-oil-water transition zone in a Lower Pennsylvanian carbonate reservoir: Constraints from cathodoluminescence microscopy, microthermometry, and isotope geochemistry. Marine and Petroleum Geology 72, 45–61.

2015

Walter, B. F., Immenhauser, A., Geske, A. & Markl, G. (2015): Exploration of hydrothermal Carbonate Magnesium isotop signatures as Tracers for Continental fluid aquifers, Schwarzwald mining district, SW Germany. Chemical Geology 400, 87–105.

2014

Bons, P., Fusswinkel, T., Gomez-Rivas, E., Markl, G., Wagner, T. & Walter, B. (2014): Fluid mixing from below in unconformity-related hydrothermal ore deposits. Geology 42 (12), 1035–1038.