ALBERT

Description: Scheelite (CaWO4) is an economically important W mineral in skarns that form when magmatic fluids exsolved from a granitic intrusion react with carbonate wall rocks. In the Fujiashan W skarn deposit, scheelite formed during four stages of the hydrothermal skarn development. We present cathodoluminescence (CL) images and in situ trace element and Sr-O isotope data of scheelite from these four stages, i.e., scheelite in prograde and retrograde skarn, quartz-sulfide veins, and late calcite replacements. Scheelite from prograde skarn and quartz sulfide veins are homogeneous and show oscillatory zoning textures in CL images, whereas scheelite from retrograde skarn and late carbonate stages display dissolution-reprecipitation and patchy textures. The brightness of CL textures decreases with a higher substitution of Mo. Molybdenum-rich scheelite (up to 2.1 wt%) is characterized by relatively high contents of Nb and Ta (up to 156 and 0.9 ppm, respectively), positive Eu anomalies, high-δ18O values (5.2 to 5.9‰), and relatively low-87Sr/86Sr values (0.70661 to 0.70727), and has grown in a system with a continuous supply of magmatic fluid. Molybdenum-poor scheelite (0.2 wt%) has low contents of Nb and Ta, negative Eu anomalies, low-δ18O values (4.2 to 4.3‰), and relatively high-87Sr/86Sr ratios (0.70748 to 0.70804). This type of scheelite formed in a system with a restricted flow of magmatic fluid during scheelite precipitation became increasingly depleted in elements that substitute into scheelite. The continued reaction of the magmatic fluid with the wall rocks and the precipitation of minerals from the fluid resulted in a systematic change of the δ18O and 87Sr/86Sr ratios. Chemical and isotopic variations in scheelite may reflect the pulsed flow of a magmatic fluid and do not require the involvement of different fluids or contrasting redox conditions.

Description: To enhance the EU's economic autonomy, feasible options for local sourcing of critical raw materials that would allow for shorter supply routes along with ethical and responsible value chains are under contemplation. Social acceptance of mining in Europe is, however, low, and the establishment of new mining sites faces strong public opposition. Therefore, innovative solutions for the production of primary raw materials need to be developed. A new idea for raw material extraction is the extraction of essential elements from geothermal fluids. Deep geothermal fluids, increasingly used for energy production, often contain high concen-trations of dissolved ions and gases in commercially interesting concentrations. The EU-funded project CRM-geothermal aims to develop new technologies to extract these highly relevant elements, including helium, during geothermal production cycles. In this way, an environmentally friendly and socially acceptable exploration and exploitation method could be deployed. One aim of the CRM-geothermal project is to gain an overview of the actual quantities of critical raw materials in various geothermal fluids in Europe by taking and analyzing fluid samples. In Turkey for instance, classical high enthalpy (volcanic) systems exist, which are representative for many geothermal areas worldwide. The sites are located at the edges of tectonic plates and close to areas undergoing volcanic activity. The brines are mixed with seawater and circulate in the deeper crust. The data publication contains analyses results of three gas samples from Tuzla, two samples from Seferihisar geothermal power plant and one sample from the Dikili geothermal field in Turkey, taken in 2023 as part of the CRM-geothermal project.

Description: Age-progressive seamount tracks generated by lithospheric motion over a stationary mantle plume have long been used to reconstruct absolute plate motion (APM) models. However, the basis of these models requires the plumes to move significantly slower than the overriding lithosphere. When a plume interacts with a convergent or divergent plate boundary, it is often deflected within the strong local mantle flow fields associated with such regimes. Here, we examined the age progression and geometry of the Samoa hotspot track, focusing on lava flow samples dredged from the deep flanks of seamounts in order to best reconstruct when a given seamount was overlying the mantle plume (i.e., during the shield-building stage). The Samoan seamounts display an apparent local plate velocity of 7.8 cm/yr from 0 to 9 Ma, 11.1 cm/yr from 9 to 14 Ma, and 5.6 cm/yr from 14 to 24 Ma. Current fixed and mobile hotspot Pacific APM models cannot reproduce the geometry of the Samoa seamount track if a long-term fixed hotspot location, currently beneath the active Vailulu’u Seamount, is assumed. Rather, reconstruction of the eruptive locations of the Samoan seamounts using APM models indicates that the surface expression of the plume migrated ~2° northward in the Pliocene. Large-scale mantle flow beneath the Pacific Ocean Basin cannot explain this plume migration. Instead, the best explanation is that toroidal flow fields—generated by westward migration of the Tonga Trench and associated slab rollback—have deflected the conduit northward over the past 2–3 m.y. These observations provide novel constraints on the ways in which plume-trench interactions can alter hotspot track geometries.

Description: The Martian surface and shallow subsurface lacks stable liquid water, yet hygroscopic salts in the regolith may enable the transient formation of liquid brines. This study investigated the combined impact of water scarcity, UV exposure, and regolith depth on microbial survival under Marslike environmental conditions. Both vegetative cells of Debaryomyces hansenii and Planococcus halocryophilus, alongside with spores of Aspergillus niger, were exposed to an experimental chamber simulating Martian environmental conditions (constant temperatures of about − 11 °C, low pressure of approximately 6 mbar, a CO2 atmosphere, and 2 h of daily UV irradiation). We evaluated colonyforming units (CFU) and water content at three different regolith depths before and after exposure periods of 3 and 7 days, respectively. Each organism was tested under three conditions: one without the addition of salts to the regolith, one containing sodium chlorate, and one with sodium perchlorate. Our results reveal that the residual water content after the exposure experiments increased with regolith depth, along with the organism survival rates in chlorate-containing and salt-free samples. The survival rates of the three organisms in perchlorate-containing regolith were consistently lower for all organisms and depths compared to chlorate, with the most significant difference being observed at a depth of 10–12 cm, which corresponds to the depth with the highest residual water content. The postulated reason for this is an increase in the salt concentration at this depth due to the freezing of water, showing that for these organisms, perchlorate brines are more toxic than chlorate brines under the experimental conditions. This underscores the significance of chlorate salts when considering the habitability of Martian environments.

Description: More than 20 yr of measurement data of the gravity missions GRACE (Gravity Recovery And Climate Experiment) and GRACE-FO (GRACE-Follow-On) allow detailed investigations of long-term trends in continental terrestrial water storage (TWS). However, the spatial resolution of conventional GRACE/GRACE-FO data products is limited to a few hundred kilometres which restrains from investigating hydrological trends at smaller spatial scales. In this study GRACE and GRACE-FO data have been used to calculate TWS trends with maximized spatial resolution. Conventionally, GRACE/GRACE-FO is presented as a series of either unconstrained gravity fields post-processed with spatial low pass filters or constrained inversions commonly known as Mascon products. This paper demonstrates that both approaches to suppress spatially correlated noise are mathematically equivalent. Moreover, we demonstrate that readily inverting all available sensor data from GRACE/GRACE-FO for a single TWS trend map, together with annual variations and a mean gravity field, provides additional spatial detail not accessible from the standard products. The variable trade-off between spatial and temporal resolution as a unique feature of satellite gravimetry allows for gravity products that are tailored towards specific geophysical applications. We show additional signal content in terms of long-term water storage trends for four dedicated examples (Lake Victoria, Northwest India, Bugachany Reservoir and High Plains Aquifer) for which external information from other remote sensing instruments corroborates the enhanced spatial resolution of the new mean-field trend product.

Description: The deepest geoid low globally with respect to hydrostatic equilibrium is in the Ross Sea area. Nearby in West Antarctica is a residual topography high. Both are in a region with thin lithosphere, where a mantle plume has been suggested. Hence upper mantle viscosity could be regionally reduced, allowing for faster rebound than elsewhere upon melting of the West Antarctic Ice Sheet, one of the global climate system’s tipping elements. To study possible causes of the geoid low / topography high combination, we compute the effects of disk-shaped density anomalies. With -1% density anomaly and a global average radial viscosity structure, geoid low and topography high can be explained with disk radius about 10° and depth range ~150-650 km. Alternatively, there may be two separate disks somewhat laterally displaced, one just below the lithosphere and mainly causing a dynamic topography high and one below the transition zone causing the geoid low. If viscosity in the uppermost mantle is reduced by a factor 10 (from 50 to 350 km depth) to 100 (from 100 to 220 km), one shallow disk in the depth range 50-350 km would also be sufficient. In order to test the feasibility of such density models, we perform computations of a thermal plume that enters at the base of a cartesian box corresponding to a region in the upper mantle, as well as some whole-mantle thermal plume models, with ASPECT. These plume models have typically a narrow conduit and the plume tends to only become wider as it spreads beneath the lithosphere, typically shallower than ~300 km. These results are most consistent with the shallow disk model with reduced uppermost mantle viscosity, hence providing further support for such low viscosities beneath West Antarctica.

Description: The large Weilasituo Sn-polymetallic deposit is a recent exploration discovery in the southern Great Xing’an Range, northeast China. The ore cluster area shows horizontal mineralization zoning, from the inner granite body outward, consisting of high-T Sn–W–Li mineralization, middle-T Cu–Zn mineralization and peripheral low-T Pb–Zn–Ag mineralization. However, the intrinsic genetic relationship between Sn-W-Li mineralization and peripheral vein-type Pb–Zn–Ag–Cu mineralization, the formation mechanism and the deep geological background are still insufficiently understood. Here, we use fluid inclusions, trace elements concentrations in quartz and sphalerite, and H–O isotope studies to determine the genetic mechanism and establish a metallogenic model. Fluid inclusion microthermometry and Laser Raman spectroscopic analysis results demonstrates that the aqueous ore-forming fluids evolved from low-medium salinity, medium–high temperature to low salinity, low-medium temperature fluids. Laser Raman spectroscopic analysis shows that CH4 is ubiquitous in fluid inclusions of all ore stages. Early ore fluids have δ18OH2O (v–SMOW) values from + 5.5 to + 6.2‰ and δD values of approximately − 67‰, concordant with a magmatic origin. However, the late ore fluids shifted toward lower δ18OH2O (v–SMOW) (as low as 0.3‰) and δD values (~ − 136‰), suggesting mixing between external fluids derived from the wall rocks and a contribution from meteoric water. Ti-in-quartz thermometry indicates a magmatic crystallization temperature of around 700 °C at a pressure of 1.5 kbar for the magmatic ore stage. Cathodoluminescence (CL) imaging and trace element analysis of quartz from a hydrothermal vug highlight at least three growth episodes that relate to different fluid pulses; each episode begins with CL-bright, Al-Li-rich quartz, and ends with CL-dark quartz with low Al and Li contents. Quartz from Episode 1 formed from early Sn-(Zn)-rich fluids which were likely derived from the quartz porphyry. Quartz from episodes 2 and 3 formed from Zn-(Sn)-Cu-rich fluid. The early magmatic fluid is characterized by low fS2. The SO2 produced by magma degassing reacted with heated water to form SO42−, causing the shift from low fS2 to high fS2. The SO42− generated was converted to S2– by mixing with CH4-rich, Fe and Zn-bearing external fluid which led to late-stage alteration and dissolution of micas in vein walls, thus promoting crystallization of pyrrhotite, Fe-rich sphalerite and chalcopyrite and inhibiting the precipitation of anhydrite. This study shows that ore formation encompassed multiple episodes involving steadily evolved fluids, and that the addition of external fluids plays an important role in the formation of the later Cu–Zn and Ag–Pb–Zn mineralization in the Weilasituo ore district.

Description: The Mufushan area, which has abundant rare-metal pegmatites within and around the Mufushan Granite Complex, has become a major target for Ta-Nb-(Li-Be) exploration in South China. The age and origin of the pegmatites and associated rare-metal mineralization are still under debate. Here, we report the in situ U-Pb ages and geochemical characteristics of granites and pegmatites in the Guanyuan and Duanfengshan districts, which are located in the central and northern parts of the Mufushan Complex. Combined zircon, apatite and monazite U-(Th)-Pb dating revealed that biotite, two-mica, and muscovite granites from the Guanyuan and Duanfengshan districts were emplaced at 143–139 Ma, which overlaps with the U-Pb ages of columbite-group minerals (CGM) from different internal zones of the Duanfengshan pegmatites (142–140 Ma). Whole-rock major and trace element compositions and Sr-Nd-Hf isotope data reveal that the granites and pegmatites experienced continuous evolution from biotite, two-mica, and muscovite granites to pegmatite and that the magma originated from the partial melting of mica schists that are abundant in the Mufushan area. Temporal, chemical and mineralogical evidence indicates a genetic link between muscovite granite and Ta-Nb pegmatites. The textures and chemical compositions of CGM from different pegmatites exhibit features typical of magmatic CGM, indicating that fractional crystallization was the driving force that promoted Ta-Nb enrichment. The increasing alumina satu- ration index [ASI: molar Al/(Ca–1.67P + Na + K)] of pegmatitic melt due to albite crystallization may have been the main factor controlling CGM deposition, explaining why major Ta-Nb mineralization is bound to albite pegmatites. The Duanfengshan and other rare-metal pegmatites in the Mufushan area are derivatives of the most evolved granitic facies (i.e., muscovite granite) of the Mufushan Complex. The Duanfengshan and Renli pegmatite fields indicate that the Early Cretaceous (~140 Ma) may have been an important, underappreciated epoch for the formation of pegmatite-related rare-metal resources in the Mufushan area and beyond in South China.

Description: Geomechanics play an important role in any underground activity, such as carbon dioxide (CO2) and hydrogen (H2) geo-storage, owing to the considerable hazards linked to the injection and withdrawal of fluids into and from the subsurface. In order to quantify these risks, knowledge of full stress tensor is required. Yet, most of our stress information in the Australian target basins for geo-storage is limited to the stress orientations, while stress magnitude data is sparse. 3D geomechanical modelling has proved to be an invaluable tool for prediction of full stress tensor. Nevertheless, a model requires some stress magnitude data in order to tune the model to be representative of real stress state. In situations where stress magnitude data is lacking, this means that the model is susceptible to significant uncertainties. Herein, we present a novel strategy for stress modelling, which involves the utilisation of indirect data such as borehole breakouts, drilling-induced fractures, seismic activity records, and formation integrity tests to calibrate a 3D geomechanical model. We employ the northern Bowen Basin, an onshore basin in Queensland, Australia, as a case study for a comprehensive 3D geomechanical modelling approach. We assess all the indirect information in the model’s volume to narrow down the model predictions and find the most reliable stress state. This innovative approach is an important step forward in stress modelling of Australian basins, where lack of stress magnitudes is a great challenge for geomechanical assessment of geo-storage.