The application of finely ground silicate minerals to croplands and forests, with the aim of enhancing the rate of natural CO₂ consuming weathering reactions, is receiving attention as a part of climate change mitigation strategies. Yet considerable uncertainty surrounds the quantification of CO₂ removal associated with Enhanced Weathering, and its potential efficacy remains undemonstrated outside of the laboratory. Here, I discuss how the geochemical insights garnered from decades of natural weathering studies provide a pathway towards a strategy for ‘Monitoring, Reporting and Verification’ of CO₂ sequestration. These natural weathering studies have also produced an understanding of what limits silicate weathering in different settings, which can be used to shed light on how deployment strategies, and specifically application sites, can be optimised.

In this work we study critical questions which determine the scale and viability of ocean alkalinity enhancement (OAE): Which coastal locations are able to sustain a large flux of alkalinity at minimal pH and aragonite saturation changes? What is the interference distance between adjacent OAE projects? How much CO₂ is absorbed per unit of alkalinity added? How quickly does the induced CO₂ deficiency equilibrate with the atmosphere?
Using the LLC270 (0.3deg) ECCO global circulation model we find that the steady-state OAE rate varies over 1–2 orders of magnitude between different coasts and exhibits complex patterns and non-local dependencies which vary from region to region. Neighboring OAE sites can exhibit dependencies as far as 400 km or more. We show that near-coastal OAE has the potential to scale globally to several GtCO₂/yr of drawdown with conservative pH constraints, but only if the effort is spread over the majority of available coastlines.
Depending on the location, we find a diverse set of equilibration kinetics, determined by the interplay of gas exchange and surface residence time. Most locations reach an uptake-efficiency plateau of 0.6–0.8mol CO₂ per mol of alkalinity after 3–4 years, after which there is little further CO₂ uptake. Some locations (e.g. Hawaii) take significantly longer to equilibrate (up to 8–10 years), but can still eventually achieve high uptake. If the alkalinity released advects into regions of significant downwelling (e.g. around Iceland) up to half of the OAE potential can be lost to bottom waters.

The seafloor functions as a substantial long-term (>100 yr) carbon sink and reservoir in the form of sedimentary organic particles. Human activities can modify the seafloor's natural carbon sequestration capacity by disturbing the upper sediment layers and thereby altering biogeochemical processes and releasing previously trapped carbon. Yet, the overall magnitudes of the changes in sedimentary carbon pools induced by these processes are not well known and could not be adequately considered in environmental impact assessments so far.

In this study, we quantify anthropogenic disturbances of sedimentary carbon sequestration in the North Sea using a combination of measurement data and numerical modeling. In particular, we examine the effects of bottom-contacting fisheries, sediment extraction, and material dumping. By resolving spatial and temporal patterns of both natural and anthropogenic drivers, we identify areas particularly vulnerable to degradation, representing the most detailed large-scale estimates of human impacts on North Sea sediments to date. Our results indicate that while the impacts of human activities on sedimentary carbon sequestration are comparable in magnitude to natural sedimentation processes, the resulting carbon benefits are considerably lower than previously estimated.

Although remaining uncertainties need to be further confined and missing processes such as ecosystem feedbacks considered, our findings can serve as a useful basis for the consideration of sedimentary carbon disturbance in the context of marine spatial management plans.

The tropics have the potential to capture large amounts of CO2 through enhanced weathering of mafic rocks. This negative emissions technology can be articulated with the needs of the agricultural sector, in particular the large irrigated tropical cropland in the tropics. High-yield agricultural soils in the tropics are acidic. Their acidity is traditionally controlled with lime, which in turn emits CO2. Crushed mafic rocks can be used instead of lime, with the added benefit of not only avoiding the lime emissions, but also capturing CO2. In tropical Colombia, there are extensive plantations of African oil palm, sugar cane, rice, banana, and corn. Nearby, there are large open-cast mining operations that produce massive volumes of mafic and ultramafic rocks as waste product. We are characterizing mafic and ultramafic rocks closest to the potential application sites, as well as the products of their weathering under natural conditions. We are also conducting field experiments with natural soils from areas of active afforestation, as well as in soils degraded by cattle ranching. Both were previously covered by rain forests. In these experiments we are evaluating the reaction rates and efficiencies of mafic and ultramafic rocks under tropical conditions in natural soils. We aim to establish the technical and scientific basis for a process by which the forestry, mining, agricultural, and energy industries in the tropics can reduce their operational carbon footprint, and eventually offer carbon capture bonds in the international market.

It is now well known that limiting the warming of the planet to 1,5°C by the end of the century will require some degree of carbon dioxide removal (CDR) and marine CDR technologies have emerged as a potential solution to mitigate climate change. While marine CDR can be piloted domestically, its maximum efficiency requires international coordination due to transboundary effects. However, the current international legal framework, including the UNFCCC and its descendants, lacks a dedicated regime for CDR, resulting in a plethora of potentially applicable sources of law with different answers on the legality of CDR. Emphasizing the challenges and necessities of coordinating CDR activities on a global level, this presentation addresses the unrealistic optimism of current law to over-rely on clear cut answers from natural sciences. It will explain how the traditional approach of the law needs to be revised to adapt to the scientific realities of climate action. This analysis should provide a reflection on the need for a wider societal debate to solve “trade-offs” issues that lawyers alone are not in a position to solve.

The Andean region possess a wealth of mineral resources, such as copper and lithium, which are increasingly in demand by various industries and sectors, including renewable energy, electronics, and transportation. The mining industry has the potential to contribute significantly to its growth and social development, desirably in line with the Sustainable Development Goals (SDGs) of the UN Agenda 2030. At the same time, the sector also creates complex socio-economic and environmental challenges in the region.
In this context, the German Federal Ministry for Economic Cooperation and Development (BMZ) has commissioned the Federal Institute for Geoscience and Natural Resources (BGR) to carry out the MinSus project in cooperation with its regional counterpart, the United Nations Economic Commission for Latin America and the Caribbean (ECLAC).
The presentation will showcase how the MinSus project has promoted responsible and sustainable mining in the Andean countries over the past seven years, highlighting how the project has worked through building capacity for sustainable mining practices, improving governance frameworks, and fostering partnerships between stakeholders.
The presentation will also feature examples of dealing with abandoned mining sites. It will be illustrated how the investigation of these sites with regard to environmental and health hazards can be carried out, as well as how the potential for tailings reprocessing can be determined (“secondary mining”), demonstrating concrete approaches and applied geoscientific methodologies to managing mining legacies in a responsible and sustainable way.

For 60 years, Germany’s National Metrology Institute Physikalisch-Technische Bundesanstalt (PTB) has been promoting the improvement of metrology systems and quality infrastructure within its partner countries in the Global South. Metrology and quality infrastructure are fundamental for the reliable measurement of all environmental parameters. Thus, geoscientific research heavily relies on them as a basis for comparable and accurate data.

Quality infrastructure includes metrology, standardization, testing, quality management, certification, and accreditation. PTB endeavours to strengthen all these components in its technical cooperation projects. For example, PTB works with its partner institutions in the Global South on the adaptation and development of environmental standards. These include, among others, standards concerning soil and water quality. Furthermore, PTB supports the process of accreditation of analytical test laboratories to increase credibility of environmental data on water, air, and soil.
All environmental data relies on the conformity of units. Accredited laboratories need to proof the traceability of their measurements up to the highest metrological authorities. PTB therefore strengthens National Metrology Institutes in its partner countries with regards to environmental services.

In the presentation, the components of quality infrastructure and their importance for geosciences will be introduced. Highlights from PTB projects in India and Guatemala will showcase success stories of improved quality infrastructure in the context of international cooperation for geoscientific applications.

Mongolia is a sparsely populated, resource-rich country with a wide range of different mineral deposits and mining activities in size and quality of operation, distributed over a vast area of the territory. The wealth of mineral resources already being mined or developed for future exploitation, provide the country with a huge opportunity for its economic progress but also present challenges for a sustainable and effective state management of the mining sector.

Since the political change in Germany and Mongolia in the 1990s, the BGR (Federal Institute for Geosciences and Natural Resources) has carried out various projects within the framework of the German-Mongolian development cooperation, together with different Mongolian government institutions responsible for the mineral resources sector. To support a transparent and efficient governance of a responsible and sustainable mining sector, the BGR-projects focused mainly on capacity development and elaboration of professional information and data at the geology and mining authorities. In recent years, the focus has been increasingly on supporting digital transformation processes in connection with more efficient mining inspection and supervision works, digital mining cadastre, the digital management of geological maps, as well as enhancing the digital data exchange between institutions. These digital instruments support a more transparent and efficient state management of the mining sector and, during the Covid-pandemic, enabled the continuation of administrative processes (licensing, permits, reporting). Yet, the continuous need for further refinement and maintenance of these digital systems presents a challenge for human and financial capacities of state authorities in developing countries

Honduras, located in Central America at the convergence of the North American tectonic plate with the Caribbean plate in the northwestern part and the Cocos plate with the Caribbean plate in the southern part, has geothermal potential not only related to power production but also for direct use application. A special strategic approach in the Central America is the geoscientific exploration of the over 1500 hot springs in the region. Only in Honduras, there are over 200 hot springs identified, from which over 40% have a superficial temperature of over 50°C and over 10% have temperatures of even more then 80°C.

This abstract presents the case of geochemical investigation in in Namasigüe and El Triunfo districts, located near the border to Nicaragua, in order to proceed in the identification of a deep geothermal reservoir but also identify the opportunity to delineate the potential of geothermal direct use for the community. Important elements of the geoscientific exploration in this socially conflictive area is the preparation of geoscientific information to raise awareness regarding the thermal waters among the local community but also to enhance the acceptance for the geothermal exploration taken out by the National Electric Power Company (ENEE).

The activities are part of Yacimientos II project, implemented by the Federal Institute for Geosciences and Natural Resources (BGR) from Germany and are supported by the National Secretary of Energy (SEN), who has an operative involvement with local communication concepts to prepare geoscientific findings for the community.

BGR and the Zambian government jointly develop and protect the groundwater resources in the country’s capital Lusaka. As one of the fastest growing cities in southern Africa, Lusaka has been facing a sharp increase in the demand for water in recent years.

Sustainable abstraction of groundwater and the protection of the vulnerable karst aquifer supplying Lusaka are two key elements for future urban planning in the face of population growth, annual outbreaks of waterborne diseases and climate change. Geoscientific experts have to ensure that decisions are based on scientific results and technical recommendations and that the importance of protecting the natural resource is being communicated as a priority to the government, industries and society.

Potential new well fields were identified and one objective of the BGR project is the delineation of groundwater protection zones as a case study for Zambia. The development of statutory instruments to make groundwater protection an integral part of the Zambian law secures the resources for the future. The delineation of the zones is based on the approach from Botswana, as the various Western approaches cannot simply be transferred to southern Africa as soil structure, geology, climate and urban areas are often drastically different.

Protecting a karst aquifer with a thin soil cover is scientifically challenging. The population growth and limited urban planning structures combined with insufficient data increase the risk of groundwater contamination in Lusaka. A high level of cooperation between geoscientists, decision-makers, environmental regulators and the society is required to face the various challenges.

Given the increasing challenges posed by climate change, especially more frequent and severe droughts experienced globally, effective exploration and management of groundwater resources is essential to ensure a sustainable and resilient society. As part of this effort, it is necessary to acquire comprehensive knowledge of the distribution of significant and readily accessible freshwater reservoirs on continents. This outlines the critical need for an efficient and cost-effective imaging method to assess this vital resource. In response, we propose a novel imaging method that utilizes observations of air-pressure-induced seismic velocity changes. We utilize findings of our study (Kramer et al., 2023) which shows atmospheric tides and their interaction with the groundwater body are the primary cause of sub-daily seismic velocity changes. Analyzing these velocity changes can reveal valuable information on the hydro-geophysical properties of the underlying groundwater body. Building on this knowledge, we introduce this imaging method and apply it to the seismic data collected across South and Central Europe. For this purpose, we use coda-wave-interferometry to investigate four years of continuous data from AlpArray and other locations throughout Europe.

Kramer, R., Lu, Y., & Bokelmann, G. (2023). Interaction of air pressure and groundwater as main cause of sub-daily relative seismic velocity changes. Geophysical Research Letters, 50, e2022GL101298. https://doi.org/10.1029/2022GL101298

The Mekong Delta, including Ca Mau province in the south, faces severe land subsidence, attributed in part to the excessive groundwater extraction. Addressing this issue requires finding alternative water sources while considering technical, environmental and social challenges. This study aims to understand the significance of groundwater to the people of Ca Mau, their water usage habits and awareness with environmental issues. Supported by local Provincial People's Committees, a comprehensive survey and group interviews were conducted across 9 districts of Ca Mau province. The research aimed to identify the spatial distribution of the required water management solutions and acceptance levels of alternative water resources. Water samples were collected and analyzed to establish the connection between water quality and people's water usage habits. Groundwater plays a vital role in people’s life, serving various purposes such as washing, cooking, drinking, and other activities. Groundwater usage depends on people's perceptions of its quality. For activities requiring higher levels of hygiene, additional water treatment or alternative water sources are preferred. The analytical approach from general viewpoints to details in this study investigates deeper into the story behind their water usage habits. It emphasizes the need to inform people about environmental challenges and raise awareness of cause-effect relationships. Evaluating alternative water resources and designing new water utilization concepts is based on local demands and willingness to change water-related habits. This research sheds light on people's awareness and concern while providing valuable insights for sustainable water management strategies in the Mekong Delta, specifically in Ca Mau province.

With escalating global freshwater scarcity, the Mekong Delta basin has emerged as one of the most socially and ecologically vulnerable regions, experiencing severe freshwater stress and storage loss. This vulnerability is primarily driven by the progressive "loss of land and freshwater" phenomenon, which encompasses a range of interconnected environmental issues, including land subsidence and seawater intrusion. The exponential growth in population, urbanization, climate change and rapid industrial and agricultural development has significantly increased the demand for freshwater, placing already limited supplies under immense pressure. In the coastal zones of the Mekong Delta, groundwater has become the primary and increasingly overexploited source of freshwater. Consequently, a decline in hydraulic heads and the threat of saline intrusion have become pressing concerns. To gain a comprehensive understanding of the hydrogeochemical processes at play, a meticulous investigation was conducted in the coastal province of Ca Mau, Vietnam. Through extensive sampling campaigns and rigorous hydrogeochemical analysis, this study sheds light on the intricate dynamics of groundwater chemistry in the region. The results reveal that ion-exchange processes and the decomposition of organic matter play dominant roles in shaping the groundwater chemistry. These findings hold significant implications for the sustainable management of water resources in the Mekong Delta. By unraveling the past and current hydrogeochemical groundwater dynamics, stakeholders can develop effective strategies to mitigate freshwater scarcity. The knowledge gained from this research contributes to the scientific understanding of hydrological systems and aids in the formulation of integrated water management policies for the region's long-term sustainability.

The transboundary Cuvelai-Etosha Basin (CEB), located in Southern Angola and Northern Namibia, is part of the Kalahari Basin, one of the world´s largest intracontinental basins. It contains mostly unconsolidated sandy sediments, often deposited by so-called megafans. The most prominent one in the CEB is the Cubango Megafan (CM). Megafans can contain large aquifers and thus have huge potential for water supply, especially in semi-arid regions. The CM hosts three aquifers: a locally present, perched aquifer, a regional mostly unconfined and a deep confined aquifer.

The regional climate is semi-arid, with very high evapotranspiration (> 2000 mm/yr) that far exceeds the highly seasonal and variable precipitation (400-800 mm/yr). The widespread salinity in the contemporary groundwater of the CM can be attributed to both sub-recent and co-sedimentary evaporative processes.

In the lower parts of the CEB, specifically at the southwestern rim of the megafan towards the Etosha Pan, saline groundwater predominates. Hydrochemical data indicate large-scale and long-term ion exchange processes. Together with environmental tracers, this shows that younger groundwater infiltrating to the north of the basin is slowly displacing the originally brackish-saline pore water. ⁸¹Kr ages range between 40 to 170 ka indicating the fossil nature of this resource. Analysis of stable isotopes and noble gases reveals that climatic conditions during recharge of the confined aquifer were approximately 3 – 5°C colder than today.

Considering the population growth and predicted impact of climate change on water availability, careful management of this vulnerable and only partially replenishable resource is advisable.

Higher temperatures and increasing droughts are likely to lead to a reduction in available water resources in the Berlin-Brandenburg region. Concurrently, there is an increasing demand for water due to the population and economic development in the region. This results in serious water management challenges. To mitigate this water scarcity, in 2021, work began on setting up a coordinated joint groundwater management system based on a transboundary groundwater flow model for the capital region (approx. 2800 km², from which Berlin covers 892 km²). The central component is the modelling of the reciprocal effects of the groundwater abstraction by the water suppliers in the region with regard to sustainable management of the common groundwater body. In the first step, the hydrogeological structural model (HSM) for the region is created. In doing so, up-to-date geological sections from the Berlin and Brandenburg Geological Surveys as well as stratigraphical settings from existing calibrated groundwater models are brought together. The groundwater models of the Berliner Wasserbetriebe are also incorporated in this process. These models have been developed since approximately 20 years and are regularly updated. They are used both in approval processes and in daily operation. In the second step, the HSM is converted into a flow model. This flow model is calibrated and compared with the existing models. In the end, a model for the entire capital region will be available for the first time. At the conference, the current status of the project will be presented and the challenges will be highlighted.

In vielen Regionen zeigt die Auswertung der Grundwasserstandsentwicklung, dass ein Rückgang der Grundwasserstände zu verzeichnen ist (z.B. NLWKN, 2020). Jedoch steigen gleichzeitig der Wasserbedarf und die Anzahl der Wasserrechtsanträge, vor allem in landwirtschaftlich geprägten Regionen. Vor diesem Hintergrund, wird auch in der Forderung des Deutschen Vereins des Gas- und Wasserfaches e.V. (DVGW Wasser-Impuls: Zukunftsbilder 2030 bis 2100) beschrieben, dass bei der Entwicklung und Umsetzung langfristiger Zukunftskonzepte im Bereich Wassermanagement digitale Lösungen eine erhebliche Unterstützung sein sollen. Dazu werden u.a. Prognose- und Managementmodelle für ganze Einzugsgebiete vorgeschlagen.

In diesem Sinne wurde für den Landkreis Vechta ein Grundwassermodell in FEFLOW erstellt, um bei der Bearbeitung von Wasserrechtsanträgen zu unterstützen (Flechtner et al., 2022). Grundwassermodelle sind jedoch oft teuer und nur von Experten nutzbar. Das bedeutet, dass die Modellierung von weiteren Szenarien (z.B. erhöhte Pumpraten oder zusätzliche Brunnenstandorte), an denen der Kunde oder die Behörde interessiert ist, sprich die Weiterverwendung des Modells, meist von externen Experten durchgeführt werden muss. Um der Behörde ein wie vom DVGW beschriebenes Prognose- und Managementmodell bereitzustellen, welches von dieser selbstständig im täglichen Geschäft verwendet werden kann, wurde von DHI WASY das Grundwassermodell zu einem interaktiven Modell erweitert. Dieses kann die Behörde in Ihrem täglichen Geschäft über eine Benutzeroberfläche selbst, mit wenigen, einfachen Arbeitsschritten, bedienen, ohne auf externe Experten angewiesen zu sein. Die Modellergebnisse der von der Behörde erstellten Szenarien werden automatisch exportiert und in einem interaktiven HTML-Format angezeigt, so dass der Kunde alle relevanten Daten und Ergebnisse schnell und auf einen Blick für weitere Entscheidungen zur Hand hat.

Climate projections indicate that extreme weather events have increased in frequency and intensity in the past and will affect sensitive Germany in the near future. Our study site, the catchment of the lower Spree, is located in Brandenburg. The region is affected by water stress showing a water deficit of 80 Mio. m³ on an area of 3500 km² with many competing water users. Our goal is to investigate the impact of shifts in climate, land use and vegetation on recharge and available groundwater resources. In four different catchments with different characteristics we monitor groundwater und lake levels, stream discharge, and depth dependent soil moisture. Isotopic composition of precipitation, groundwater, and surface water is investigated to calculate water fluxes between different compartments. Electrical conductivity down to a depth of 200m below surface is recorded. Measured NaCl concentrations reach up to 10 – 15 g/kg. Employing the hydrological model SWAT evapotranspiration, discharge and soil moisture are calibrated to calculate long-term groundwater ranges pattern, which ranges in average at 77 mm/a. The M-K test shows decreasing recharge from May to August, an increase from December to February, and almost no change from September to November leading to an overall decreasing trend over the last 20 years. We are planning to derive concepts for areas with highest economic or ecological value derived from socio-economic analyses for the implementation of artificial recharge using greywater, treated waste water or storm water to replenish the groundwater deficit and to retain uplift of the saline groundwater water.

We explore the effects of a changing climate on groundwater dynamics based on thermo-hydraulic simulations to reconstruct the temperature and pressure below the State of Brandenburg between 1950 and 2010. In this time period, observations point to ~1°C surface temperature warming, large annual fluctuations in groundwater recharge, and periods of high groundwater abstraction volume — all leading to water stress conditions. Our input structural model integrates Permian to Cenozoic sedimentary units with essential geological features controlling the regional groundwater flow, including salt structures, permeable glacial valleys, and aquitard discontinuities. We use a grid-based hydrologic model to derive inflow and outflow rates across the top boundary of the subsurface model. Simulation outputs are verified against data from available observation wells.

The simulation results demonstrate that the regional flow pattern in the deep aquifers (>1 km deep) is mainly controlled by the basin geometry, while shallow groundwater dynamics is heavily influenced by high-frequency climate forcing. Seasonal fluctuations in groundwater level are observed in areas of shallow (<10 m) water table, with the highest levels corresponding to months of greater recharge rates. Where the water table is deeper, it responds to precipitation pulses with a delay of several months. Seasonal groundwater heating and cooling is limited to the first 10–30 meters, except within glacial valleys where high hydraulic gradients and permeabilities lead to a deepening of the advective heat transport. In addition, we identified periods and regions of significant groundwater abstraction and sustained groundwater warming over the entire simulation period within urban areas.

Water stress is increasing in Northeast Germany due to climate change. New approaches for water management are needed to mitigate the impacts on the water system and water users. Therefore, our study deals with the development of a web-based toolbox for subsurface water storage with focus on the lower catchment of the river Spree in the federal state of Brandenburg.

Our approach is based on a systematic combination of site selection criteria and spatial data on land use, soil, groundwater and potential water sources. This will provide relevant information for the preliminary planning of managed groundwater recharge measures by authorities and water suppliers. Considering surpluses from runoff and surface waters, also caused by extreme weather events, suitable locations for surface-induced recharge will be identified.

Supported by additional modelling-based indications for implementation, efficiency and costs, as well as simplified site selection through a query system, the toolbox will offer an initial knowledge for such planning considerations.

TCEs stands for technology-critical elements, a group of chemical elements for which imbalances between supply and demand exist or are considered likely to exist. The concept is economic and geopolitical and is not based on any scientific consideration. The term TCE is linked to competition for natural resources, now dramatically intensified by geopolitical instability and the green-energy transition.

Since it is a geopolitical concept, the elements that are considered as TCEs depend on the country and change over time; basically, they depend on the "eye of the beholder". For example, in the EU list of 2023, compared to the 30 Critical Raw Materials (CRMs) of 2020, there are six new CRMs (arsenic, feldspar, helium and manganese, plus copper and nickel as Strategic Raw Materials) and two have disappeared (indium and natural rubber).

Currently, the European Union considers a large number of materials to be technologically critical (mostly, but not all, chemical elements): 51. Given that the total number of elements in the periodic table is 118, of which 94 occur naturally on Earth and the remaining 24 are synthetic, this means that we are talking about ≈50% of all naturally occurring chemical elements!

In this context, what are the reasons for studying the environmental and (eco)toxicological effects of TCEs? Obviously, they will be different in the European Union than in the producer countries. In this communication, the reasons and research needs on both sides of the so-called supply chain (producers and end-users) will be analysed.

Technology-critical elements (TCEs) show a dramatic increase in industrial applications in recent years and decades. Technological applications in our everyday life have come a long way in the number of used elements, with almost every element of the periodic table today. Based on the fact that many TCEs are recycled only to a very small extent or not at all, TCEs may become contaminants of high concern in the future.

Yet, important knowledge gaps remain about the environmental behavior of TCEs and their uptake into the food chain. Therefore, tools are needed that enable a sound and reliable determination of TCEs in order to further understand their impact on the environment. We present the advantages of N₂O as a reaction gas for inductively coupled plasma tandem mass spectrometry (ICP-MS/MS) for the multi elemental analysis of the majority of TCEs (e.g.: Ga, Ge, In and Ta). Thus, allowing the determination with LODs between 0.00023 µg L^-1 (Eu) and 0.13 µg L^-1 (Te). In addition, we used a microwave assisted closed vessel digestion to determine non-certified TCE mass fractions within four commonly used reference materials in the field of environmental marine chemistry: NIST 2976 (mussel tissue), NIST 1566a (oyster tissue), BCR 668 (mussel tissue) and NCS ZC73034 (prawn). Presenting mass fractions for Ga (11 µg kg^-1 ± 9 µg kg^-1 - 63 µg kg^-1 ± 8 µg kg^-1) and In (0.39 µg kg^-1 ± 0.29 µg kg^-1 – 0.7 µg kg^-1 ± 0.7 µg kg^-1) as non-certified elements within all of these CRMs.

TCEs have a wide-spread range of applications and are released into the aquatic environment in various ways. For their sound determination in natural waters not only new analytical methods are needed but also reference materials for method validation. Even though a wide variety of certified reference materials (CRMs) of different water matrices are available, certified values of many elements, especially TCEs, do not exist. In this study, an online preconcentration method coupled with ICP-MS/MS was used for the quantification of 34 elements among which are 21 TCEs. The method was applied to 17 water CRMs and measured data is combined with a comprehensive literature review on non-certified values in the CRMs resulting in the suggestion of consensus values for various TCEs.

The method is applied to a set field samples from German rivers and from the North Sea in order to trace different inputs of TCEs into the aquatic environment: In and Ga ware analyzed as tracers for offshore wind farms where they are applied in corrosion protection systems. The Gd anomaly was used as a proxy of coastal and riverine inputs into the North Sea in an attempt to differentiate anthropogenic from geogenic signal. The concentrations in seawater ranged between 0.011 ng L^-1 ± 0.001 ng L^-1 and 0.27 ng L^-1 ± 0.15 ng L^-1 for In and between 1.37 ng L^-1 ± 0.05 ng L^-1 and 4.9 ng L^-1 ± 0.5 ng L^-1 for Ga and Gd anomalies of up to 4 were found in the North Sea.

The picturesque fjords along Norway’s coastline play an important role for the country’s tourism and aquaculture industry. Despite their economic importance for the country, surprisingly little is known about the occurrence and behaviour of rare earths and yttrium (REY) in Norwegian fjords. We will present dissolved (0.2 µm-filtered) REY data for different sites and depths from several Norwegian fjords with focus on the Seaward Basin in the Trondheimfjord. Our sample set is complemented by data for rivers feeding into the fjord (Orkla, Gaula, Nidelva, Stjørdalselva) and for two waste water treatment plants (WWTPs) releasing their effluents into the Seaward Basin.

All fjordwaters show REY concentrations in a similar range with decreasing concentrations with increasing water depth. Their shale-normalised (_SN) REY patterns share common features with typical seawater patterns, however, light and middle REY are less fractionated compared to open-ocean water. Samples taken close to river mouths have notably higher REY concentrations in surface layers with very flat REY_SN patterns, similar to the rivers investigated and characteristic of boreal rivers with a high nanoparticle and colloid load. In contrast, the truly dissolved (< 1 kDa) REY in river water of the Nidelva show patterns similar to those of seawater.

The effluents of the WWTPs carry a strong anthropogenic Gd signal into the Trondheimfjord, which results from the application of Gd-based contrast agents in magnetic resonance imaging. However, no anomalous enrichment of Gd is detected in the Seaward Basin itself because the large water volume immediately dilutes and obliterates the anthropogenic signal.

Contrasting sediments behave radically differently in aquatic systems, releasing elements of concern. Their behavior is a function of mineralogy, geochemical composition, and the conditions of the medium (e.g., ionic composition, pH). One way of understanding the reactivity of contrasting sediments, but also the operationally defined fraction of the associated elements is to use selective extraction protocols. Nevertheless, these are generally used without verifying the adequacy of the extraction times, in accordance with the sediment characteristics, nor the potential impact of element-specific behavior to the extracting reagents, biasing the final interpretation. This study aims at providing such understanding for the rare earth elements (including lanthanides, yttrium, and scandium). The sediments used originate from modern aquatic sedimentary environments of both terrestrial and marine-transitional origin, associated to either natural (beach and riverbank sediments) or anthropogenic (mine tailings) sources. A qualitative mineralogical determination of the sediments was performed via XRD. Element mobility was studied via selective extraction protocols applied in parallel, with a kinetic approach, and sequentially. Quantitative analysis of the total concentrations of major and trace elements was determined via XRF-EDX, ICP-OES and ICP-MS, to obtain elemental correlations and total REY+Sc sediment content for mass balance purposes. For each extraction solution, the elemental concentrations were quantified via ICP-MS. The information gained in this study provides further experimental results on the unknown aquatic behavior of REY+Sc elements, for which there is currently an increasing demand for major technological applications.

Acknowledgements:

Funded as part of the Excellence Strategy of the German Federal and State Governments.

Germany has a long history in metal ore mining stretching over a period of more than 1000 years. Both small and large heaps or dumps remain in the mining districts typically without any safety measures (coverage, monitoring etc.). Often these sites are still a considerable point source for pollutants like metals, metalloids or processing chemicals. However, extraction technologies have been much less effective in the past and for certain elements (e.g. Ge) no technical application has been known. As such, mine waste including historic waste or ore dumps and tailings may represent a considerable and easily extractable future resource especially for technology critical elements.

We investigate the mineralogy, geochemistry and leaching behaviour of different types of mine residues in former mining districts of the Black Forest, Wiesloch and the Donnersberg area. With respect to the critical raw materials Ge, Sb, barite and fluorite, several of the investigated mine waste seem to be of potential economic interest. But elements like Pb, Zn (both in the wt% range) or Ag (>100 mg/kg) are also promising with regard to reprocessing in some of the investigated districts. From an environmental point of view, Pb, Zn, As, Cd, Sb und Tl are of concern regarding their concentration and leachability. Both, the content and potential mobility largely depend on the ore type, the period of extraction and the processing technique applied. We think that extracting raw materials from mine residues has the advantage of gaining metals locally and giving back space to nature and society at the same time.

Due to the Green Deal proposed by the European Union, several industry sectors in Europe are forced to change the production techniques towards a zero-carbon dioxide emission until 2050. For the steel industry the substitution of fossil fuel, used in the blast furnace (BF), by hydrogen as reduction agent relates to the introduction of new technologies and aggregates. Nowadays, only a small amount of shaft furnaces using natural gas for reduction of iron ores to produce direct reduced iron (DRI). However, this combination is one of the favoured future hydrogen operated routes of alternative steel making in the European Union. The crude steel is, thereby, produced from solid DRI together with scrap molten within the electric arc furnace (EAF). Thus, the minor and trace element composition of the produced EAF slags is directly inherited from the input materials because no density driven phases separation takes place in the DRI which is one major difference to the traditional BF route.

Here we present the results of mineralogical, chemical as well as construction technological investigations carried out on one exemplary slag from the EAF route were app. 2/3 of the input material was sponge iron. The main emphasis of the presented study lies on the ongoing applicability of the EAF slags produced in the future as secondary product in the context of steel industry feature the planned reduction of carbon dioxide emissions.

Basic oxygen furnace slag (BOFS) is a by-product of steelmaking of which about 10.4 Mt are produced annually in the EU. BOFS is mostly used in road construction, earthwork and hydraulic engineering. However, in this use, the iron bound in BOFS is lost and the opportunity to produce higher value products from BOFS is forgone.

In recent decades, many researchers have investigated the production of both Portland cement clinker and crude iron from BOFS via a thermochemical reductive treatment. The reductive treatment of liquid BOFS causes a reduction of iron oxides to metallic iron, which separates from the mineral phase due to its higher density and can be recovered. An advantage of this process is that simultaneously the chemical composition of the reduced BOFS is adapted to that of Portland cement clinker and the hydraulic reactive mineral alite (Ca₃SiO₅) is formed.

In this study, German BOFS was reduced in a small-scale electric arc furnace and a low-iron mineral product rich in alite was produced. Despite a chemical and mineralogical composition similar to that of Portland cement clinker, the reduced BOFS produced less heat of hydration, and its reaction was delayed compared to Portland cement. However, adding gypsum accelerated the hydration rate of the reduced BOFS.

Further research to improve the hydraulic properties of the reduced BOFS is essential. If successful, the production of a hydraulic material and crude iron from BOFS could have economic and ecological benefits for both the cement and steel industry.

In the processing of construction and demolition waste (CDW), the sorting of the delivered mixtures is one of the decisive process steps in order to produce pure recyclates, which can be used, for example, as a cement substitute or as a raw material component for the brick production. A previously unused method for the separation of fine brick particles as sand utilises rare-earth magnets. This method is based on differences in magnetic susceptibility, which have been confirmed by measurements on bricks and concretes. Sorting tests carried out using a roll magnetic separator with a field strength of 1,4 Tesla at a belt thickness of 0,7 mm confirmed the separability of brick-concrete-mixtures and provided insights into the most important influencing variables. In addition to manual sorting the quantification of the contents of concrete or brick in the magnetic and non-magnetic fractions was determined with laser-induced breakdown spectroscopy (LIBS) and artificial intelligence-based optical quality assurance. Thus, in addition to the proof of seperability, a first step to faster ways for quality control has been accomplished.

Marine sediment archives provide invaluable records of continental erosion and dynamics, important for understanding both crustal deformation and climatic processes. Yet these archives are influenced by autogenic and allogenic processes. Rigorous interpretation of these records therefore requires unravelling of these various intertwined factors, and a good understanding of source-to-sink.

The Bengal Fan is the largest marine sedimentary fan in the world. It, and its smaller “sister” the Indus Fan, as well as the Nicobar Fan, archive the erosional history of the Himalayas, the largest mountain belt in the world. Various IODP, and previously DSDP expeditions have cored the fans, and the material extensively studied to elucidate the history of the fans’ hinterland tectonics, source to sink dispersal patterns, and climatic variations through time, with an emphasis on the response to the Asian monsoons. Yet unravelling the competing influences on the sediment archives in this tectonically active region is challenging.

In this talk I will provide an overview on the use of isotopic provenance studies to discuss aspects of the progress made in using the archives to determine Himalayan tectonics, as well as in deconvolving autogenic versus allogenic influences and in our understanding of source-to-sink.

Ocean sediments are considered to contain microbial biomass that equals the stock of organic matter on all the continents combined. Knowledge on the spatiotemporal distribution and abundance of microbial life in marine subsurface sediments, however, is still sparse. A region particularly understudied in this respect is the Antarctic continental margin, in which the deep biosphere is largely terra incognita. A 794 m-long sediment sequence (Site U1532), recovered during IODP Expedition 379: “Amundsen Sea West Antarctic Ice Sheet History” provides the unique opportunity to study the composition and abundance of the deep biosphere in polar regions of the Southern Hemisphere. Porewater profiles of sulfate and methane concentrations indicate that the sulfate-methane transition zone (SMTZ) is located at a depth of ~660 mbsf, making it one of the deepest SMTZ ever encountered. Stable carbon isotope measurements attest to the biological origin of the methane and provide direct evidence for an active deep-dwelling microbial community. Cell abundances decline with depth by three orders of magnitudes but increase again within the SMTZ. Complementary biomarker analysis indicates that this change in cell abundances is associated with a shift in the microbial community to predominantly methanogens throughout the SMTZ. Our data thus provides first insights into the microbial diversity and abundance of the deep biosphere in the yet largely unstudied marine subsurface sediments surrounding Antarctica. Combining our results with previous data of cell abundances in marine sediments suggests that current projections of microbial biomass appears to be overestimated and need to be downsized.

Permanent carbonate mineralisation in basalt is a promising solution for Carbon Capture and Storage of anthropogenic greenhouse gases without the risk of leakage. While this process is known to occur at relatively low temperatures below 100°C, new research on Large Igneous Provinces (LIPs) and young rift basins suggests that much of the thermogenic gases mobilised during contact metamorphism can remain trapped and mineralised in the sills that mobilised them. This discovery is the result of two distinct drilling investigations on land (KARIN) and at sea (IODP Exp 385). It shows that basalts may not only trigger the sudden release of thermogenic gas, but also represent an important carbon sink. The two examples of carbonate trapping in sills presented here are from the Karoo and Guaymas basins. Results indicate that a large fraction of epimagmatic fluids charged with thermogenic gas systematically penetrated inside the sills during cooling. Our numerical solutions suggest that in both cases the higher permeability of the sill acquired during cooling and crystallisation compared to that of its host, ultimately dictates the fate of the thermogenic gas that accumulates in the igneous body. On this basis, we conclude on the role of basalts in the Earth’s carbon cycle from a geological and anthropogenic perspective.

Continuous limnic archives may record millions of years of climatic and environmental change at their locality. Typically, such archives reflect environmental conditions in the lakes’ catchments, but also the imprint of large-scale atmospheric systems e.g. related to insolation and/or global ice-sheet dynamics. These parameters may vary considerably in space and time, and our understanding on patterns across continents that relate to this forcing is still incomplete. Comparing sedimentation rates from limnic archives covering fundamental changes in the Earth’s system like the Mid-Pleistocene transition (change from 41kyr to 100kyr cycle world) has potential to shed light into spatial differences in Earth’s climate response, if applied carefully.

To better understand the sedimentation history of lakes, and especially their reaction to climate transitions, we compare sedimentation rates from lakes. In a second step, we systematically align several records to facilitate best comparability. We focus on limnic records that have been investigated during ICDP projects, and specifically assess the influence of the Mid-Pleistocene transition and the Mid-Brunhes transition on sedimentation rates.

The ICDP-Project BASE investigated Archean Surface Environments by coring the ca. 3220 Ma Moodies Group of the Barberton Greenstone Belt, South Africa, Oct. 2021 – August 2022. This unit represents some of the oldest shallow-water and terrestrial siliciclastic strata worldwide; it contains fossil microbial life. Because the BGB had repeatedly seen intensive gold exploration and features several active gold mines along its northern margin, the eight BASE drill sites, largely located within the 2018 declared Barberton-Makhonjwa Mountains WHS, had to counter initial suspicion that they masked a gold exploration project, largely controlled by foreign interests. We obtained goodwill, interest, and permits from the local population and from local, regional, and national government, respectively, and ensured safe and incident-free drilling operations by designing and executing a multi-faceted approach: Prior to project start, we contributed regularly to local and regional newspapers, had the planning workshop extensively covered by media, and cultivated contacts with stakeholders and local property owners. The Education/Outreach/Publication program employed a Barbertonian geologist full time to work with traditional government, radio stations, TV, schools, and institutions of higher learning. We set aside half of our core processing space in downtown Barberton as an exhibition area, trained all staff as tour guides, maintained an open-door policy, and encouraged visitors to observe us as we processed core. Delegations, school classes, and associations could inform themselves first-hand on the core retrieval process on field trips to drill sites. After operations, BASE added a room to the local museum dedicated to WHS geoscience research.

Subducted oceanic crust plays an important role in controlling the chemical budget of the crust and mantle and in the composition of arc lavas. Oceanic eclogites represent fragments of oceanic crust that have been through a subduction zone and were subsequently exhumed and exposed. A range of geochemical signatures in oceanic eclogites have been studied to unravel the fluid-rock interaction processes. A key tracer is the trace-element boron and its isotope ratio (¹¹B/¹⁰B) in oceanic eclogites with its great potential for quantifying mass transfer processes at convergent margins. Current models predict a strong decrease of δ¹¹B values in the subducting crust with progressive dehydration to values much below that of the depleted mantle (appr. -7 ‰).

We have analyzed elemental abundances and boron isotopic compositions of oceanic metamorphic rocks, from Zambezi Belt, Cabo Ortegal complex, Raspas Complex, Syros Island, and Tian Shan. Whole-rock B/Pr ratios were used to quantify the progress of dehydration. The boron isotopic composition of almost all samples (approximately -10 to +5 ‰) ranges from δ¹¹B values close to that of fresh MORB to that of typical altered oceanic crust. Also, the sample set shows no correlation between δ¹¹B values and B/Pr, as would be expected from current theoretical models. Our results, thus, demonstrate that B isotopic fractionation in subducted oceanic crust is much smaller than predicted. We suggest that this discrepancy can be resolved by accepting high pH values in high-pressure hydrous fluids, which show a much smaller boron isotope fractionation in equilibrium with B-bearing silicates.

Dehydration of oceanic lithosphere during subduction is a key process in the Earth's deep volatile cycle. Field observations and studies of obducted meta-serpentinites that underwent dehydration at depth often show an interconnected, channelized vein network that formed during dehydration and served as pathway for fluid release from the dehydrating rock. Previous studies show that chemical heterogeneities in the bulk-rock composition lead to channelization of fluid flow from the onset of the dehydration process and how subsequent reactive fluid flow in the porous network causes further dehydration and channelization. On larger scales, fluid release from the rock is governed by mechanical processes such as porosity waves. While the micro- and meso-scale have been studied so far, this large-scale fluid release mechanism has not yet been explored for dehydrating serpentinite.

Here, we present a model for reactive porosity waves that investigates the large-scale fluid release from a dehydrating serpentinite. The model combines viscous rheology with the transport of dissolved silica in the fluid which has been shown to be a key metasomatic agent in the dehydration process. As input for our model, we use a multi-scale dataset of fully hydrated serpentinite from an ophiolite taken as representative for serpentinized oceanic lithosphere entering a subduction zone. We use the data to explore the formation of the vein network during dehydration and the behavior during large-scale fluid escape by reactive porosity waves.

Rutile is potentially very important for the transport of water during subduction metamorphism after the breakdown of hydrous phases, as it is one of the most hydrous nominally anhydrous minerals (up to several 1000 μg/g H₂O) and commonly occurs in a variety of lithologies and P-T conditions across subduction zones.

We present results from quantitative in-situ Fourier Transform Infrared (FTIR) spectroscopy of rutile from different subduction settings (P-T, lithology, geothermal gradients) and high-resolution FTIR mapping to evaluate the variability of H₂O contents in rutile and retention of H⁺.

Observed H₂O contents are highly variable. Granulite facies rutile have low H₂O contents (<150 μg/g) with high-P granulites showing up to ~400 μg/g H₂O. The highest average H₂O contents were observed in low-T eclogite facies rutile (500–1700 μg/g). Amphibolite- and high-T – high-P eclogite facies rutile has intermediate H₂O contents (~200–400 μg/g). Rutile from UHP shows greatly varying H₂O contents (<10–700 μg/g).

FTIR maps of high-P granulite-, high-T – high-P eclogite facies and UHP rutile show evidence for diffusive H⁺ loss, while low-T eclogite- and amphibolite facies rutile are homogeneous or show growth zoning and thus retain their original H₂O contents. Therefore, the typically variable and lower H₂O contents at higher P-T conditions result from H⁺ loss at temperatures above ~650–700 °C.

Generally, H₂O contents are distinctive for specific subduction zone conditions, especially when coupled with Zr-in-rutile thermometry and trace-element geochemistry, e.g. high H₂O contents above 500 μg/g coupled with Zr contents below 200 μg/g indicate cold subduction geotherms.

The recycling of volatiles like H₂O from the surface into the interior is critical as it influences the physical and chemical properties of the mantle. One of the essential effects H₂O has on the mantle is the reduction of the solidus temperature, as this can trigger partial melting. On the one hand, the process of partial melting is vital for arc and ore deposit formation. On the other hand, it is thought to be a requirement for the generation of the continental crust.

Even though intensive work has been done on investigating the stability fields of hydrous phases experimentally and thermodynamically depending on pressure, temperature, and composition, it is still debated to which depths and in which quantities H₂O can be recycled. However, the parameters influencing the mineral stability and break-down (e.g., pressure, temperature, composition, oxygen fugacity) change constantly during the recycling process. To include these changes, global convection models are required which take the varying conditions over time into account. While numerous studies exist, that model the subduction process itself, the recycling of H₂O is not considered to date in most of the simulations, or strongly simplified models are applied.

We model the quantity of H₂O that can be recycled as well as the depth to which the recycling is possible. For this purpose, we test individual parameters affecting the H₂O recycling and dehydration from the subducting slab. To benchmark our simulations, we compare our results with seismological observations of the Pacific plate subducting beneath northeast Japan.

The site selection process for the deep geological repository for Swiss radioactive waste is in its final phase. Using 3D-seismics and deep boreholes, Nagra has collected the data for selecting the most suitable site. In autumn 2022, Nagra announced that a general license application would be prepared for a combined repository for high- and low-/intermediate-level waste in the Nördlich Lägern region.

The 13 technical criteria used for site comparison comprise safety-related aspects including barrier properties and their long-term stability, as well as the constructability of the repository and access facilities. Phases 1 and 2 of the process resulted in the selection of three potential sites in the external Alpine Foreland of Northern Switzerland, all with the ~100 m thick Jurassic Opalinus Clay as host rock. The sites fulfill the requirements for repositories for low- and intermediate-level waste as well as for high-level waste and spent fuel.

In the final Phase 3 of site selection, the remaining sites were investigated by means of 3D-seismics and 9 deep boreholes. The boreholes aimed at assessing the barrier properties of the clay-mineral rich rock sequence, including the bounding aquifers. To address the long-term stability of the geological barrier, the Quaternary erosion history was investigated with 11 cored boreholes.

In our contribution, we provide an overview of key results from the seismic surveying and the boreholes in the three siting regions. Based on these investigations, we present and discuss the geological differences between the regions that have led to the proposed site.

The main criterion concerning the planned deep geological repository comprises its long-term safety, which must be ensured for a period of hundreds of thousands of years. Therefore, particular attention is being devoted to the selection of a suitable site for the facility. As far as the Czech Republic is concerned, it is planned that the DGR will be constructed in a suitable crystalline rock mass. Nine potential sites were originally selected for consideration, all of which were subjected to detailed geological survey assessment. The DGR site selection process was preceded by the extensive collection and evaluation of the relevant data covering the detailed site description and assessment of local conditions. Recently, SÚRAO has conducted a huge amount of research at the sites via e.g. field research, terrain reconnaissance, geological mapping, hydrogeological mapping and sampling, geophysical surveys, the measurement of seismic phenomena, etc. As a result of the research, 3D geoscientific models of the rock conditions were created, which allowed for the assessment of the sites. The nine sites were compared based on safety, feasibility and environmental impact studies following which, on 21 December 2020, the government approved the selection of the four sites recommended by SÚRAO – Březový potok, Horka, Hrádek and Janoch. Further research and exploration work aimed at the eventual selection of the final and backup sites will be conducted up to 2028. The result of this complex characterization will be compiled into a set of site descriptive models describing both – geological setting and long-term evolution of the sites.

The site selection process for deep geological repository is a long-term project based on numerous disciplines. In the Czech Republic the geological characterisation was performed on nine selected sites in crystalline rocks, from which four were taken into account for ongoing geological survey and detailed site description.

This contribution will present the approach to the geological characterisation, which was, is and will be used for selection of final deep geological repository site on an example of Hrádek locality. The Hrádek locality is based in Moldanubian granitoid and metamorphic rocks of Bohemian massif in the central part of Czech Republic. In the previous phase, mostly archive data were used in combination with local field studies, in order to present a 3D geological model as an input for other models (e.g. hydraulic, transport, discrete fracture network model). The ongoing phase of geological characterisation includes mainly field studies, geological and hydrogeological mapping in combination with geophysical research and future borehole research, geophysical profiling and hydrogeological monitoring. All the data collected will be included in 3D geological model with uncertainty assessment with the aim to compare and evaluate the best site for future deep geological repository.

The upper crust of the Earth is used more and more to transport and extract raw materials and energy. It is also used for the final disposal of radioactive waste in deep geological repositories. An accurate knowledge of the hosting rock and surrounding formation coupled to comprehensive modelling are fundamental to demonstrate the geological site has the required properties for safe and long-term underground storage. Besides other criteria, geomechanics plays an important role. Especially, the estimation of the contemporary stress state in the upper crust is a challenge. In-situ data of maximum and minimum horizontal stress magnitudes (S_Hmax and S_hmin) are required to calibrate 3-D geomechanical models.

During the recent exploration phase for a deep geological repository for radioactive waste in Switzerland, a unique dataset of stress magnitude data has been acquired from eight cored boreholes. Rock mechanical properties were constrained from geophysical logging and laboratory testing. The empirically correlated rock properties were not simply averaged, but a probability distribution was provided. The stress field was explored by conducting more than 120 tests in different stratigraphic units, to estimate the magnitudes of S_Hmax and S_hmin.

We present the results of a 3‑D geomechanical-numerical model that shows the best-fit with respect to the measured stress magnitudes. Considering the uncertainties of the tests and the ones resulting from rock property variability, the model can reproduce most of the measurements. However, we do show not only the best-fit result, but a bandwidth of individual stress components within a P₀₅-P₉₅ probability range.

The safe disposal of radioactive waste is a critical and frequently discussed topic in society. The Bundesgesellschaft für Endlagerung (BGE) was assigned with the selection of a suitable site for the disposal of high-level radioactive waste in Germany and, in the first phase of the selection procedure, has defined various selection criteria and sub-areas, seven of which cover the crystalline basement in Germany. For most of these sub-areas, little or no information is available on the crystalline host rocks and their properties, which would allow a narrowing of the site selection and identification of a suitable repository. Therefore, the AMPEDEK project establishes a reference database for the characterization of crystalline rocks in Germany. For this purpose, the database will contain information on the mineralogical, geochemical, petrophysical, and rock mechanical properties of predominantly igneous and metamorphic rocks of the Variscan basement. In the first phase, existing data from the literature or state geological offices were compiled and the structure of the database was established. In the second phase, ~500 drill cores and rock samples from quarries were analyzed in the laboratory to close existing data gaps. The goal was to sample as many different lithologies as possible to create a database that covers the majority of the relevant areas. The database currently contains ~8600 data points from 8 states and will be used to select smaller areas for Phase 2 of the site selection process and thus for detailed surface geological exploration campaigns.

Granites represent suitable crystalline host rocks for nuclear waste repositories because of their mechanical strength and apparent isotropy. However, all granites have a primary structural and petrophysical anisotropy that developed during the emplacement and crystallization of the melt. The primary anisotropy likely controls the orientation of post-magmatic structural features such as extensional fractures. This secondary anisotropy controls potential fluid pathways. Thus, a causal relationship between primary and secondary anisotropies could be an important constraint in terms of the site selection process. We present the first results of a systematic study of German felsic plutonites. We focus on samples of syn-variscan peraluminous granite plutons from two localities, namely the Fichtelgebirge and the Erzgebirge. These areas represent different tectonic settings during intrusion, i.e., compression and transtension, respectively. To estimate their primary anisotropy, we analyzed the crystallographic preferred orientation (CPO) of the rock-forming minerals. CPOs were measured using the neutron time-of-flight (ToF) texture diffractometer “SKAT” and electron backscatter diffraction (EBSD). Based on this data intrinsic bulk rock elastic properties are modeled. All granites show weak but distinct preferred orientations of the rock-forming minerals, which are coherent on a local scale. The quartz textures, for example, show similar CPOs, with point maxima of the positive rhombs combined with small-circle to crossed-girdle c-axis distributions. However, the orientation with respect to the geographic reference system strongly varies on a regional scale. We will discuss the CPOs regarding their tectonic setting and correlate the primary anisotropy with the post-magmatic fracture patterns of the particular granites.

Most high-grade metamorphic gneiss units in Germany exhibit a strong late-Variscan thermal imprint recorded by the presence of migmatites and granitic intrusions.

A nuclear waste repository in this setting is challenging because the amalgamation of various gneisses and magmatic rocks must be predicted and assessed to a search depth of 1500 m. Understanding the 3D-architecture of such basement units relies on better exposed regions than found in Germany. In this contribution, we use selected field areas to show the difficulty to predict the variability of high-grade metamorphic rock types at depth.

The Argentera Massif in the western Alps represents an ideal field analogue as it displays a variety of para- and orthogneisses and their equivalent migmatites along continuous surface outcrops. Detailed field observations from this area help to constrain the structural and lithological anisotropy of a typical Moldanubian crustal segment.

Except for the occurrence of large amphibolite lenses, gneisses and migmatites exhibit textural gradients at various scales rather than distinct lithological boundaries. Sharp boundaries on the other hand result from cross-cutting shear-zones that developed under retrograde greenshist facies conditions and discordant intrusions.

Whereas the overall 3D-geometry and anisotropy of the gneiss terrane may be described with the help of 3D models it is generally not possible to predict the spatial distribution of lithotypes and dominant textures for a given rock volume.

This contribution indicates why foliated gneisses and migmatites are less suitable as host rocks for a high-level radioactive waste repository compared with late granitoid intrusions that are more homogeneous.

The recent exploration for nuclear waste repositories includes the evaluation of safety mechanisms in case of a leakage of radiotoxic material. Possible retention mechanisms like the uptake of these elements from the conducting aquifer into ubiquitous fracture minerals like calcite have drawn much attention. In laboratory experiments, it has been shown that especially actinides are efficiently scavenged by (re)crystallization of calcite¹. To assess the long-term immobilization potential of calcite and the effect of low temperature alteration, element mobility in natural analogues needs to be studied.

A suitable study site is the Wenzel ore mine in the Black Forest (S-Germany), which was actively mined until 1823. Here, hydrothermal calcite veins are exposed at the tunnel wall. After it´s shut down the mine was naturally flooded and calcite remained in contact to groundwater for approx. 175 years until the mine was drained and reopened to the public in 1999.

Elemental distributions of La and Sr, which are considered as analogue elements for actinides and Ra are revealed by µXRF and LA-ICP-MS maps at high spatial resolution of 2 µm. First results show a complex pattern of Sr-enriched and depleted layers at the calcite-groundwater interface, which alternate at the 10 – 200 µm scale. In addition, localized enrichments of La appear, exceeding the pristine calcite concentrations by a factor of 4. Both features are interpreted as a result of secondary element mobility and discussed with respect of the retention potential of calcite during low temperature alteration.

¹Curti E. (1999) Applied Geochemistry 14: 433-445