Niobium (Nb) is classified as a 'critical mineral' due to its irreplaceable applications in superalloys and superconductors but limited supply chain. This study employs high-energy resolution fluorescence-detected X-ray absorption spectroscopy (HERFD-XAS) at the Nb K-edge to investigate Nb(V) mobility in fluids containing various ligands, namely fluoride [F-], chloride [Cl-], carbonate [CO3-], and hydroxide [NaOH], under hydro-thermal conditions (25-413 C; 800 bar). Ab initio simulations of X-ray absorption near-edge structure (XANES) spectra were combined with shell-by-shell modelling of extended X-ray absorption fine structure (EXAFS) data to elucidate the nature and geometry of the aqueous Nb(V) complexes. Key findings are that Nb(V) predominantly forms eight-coordinated hydroxyfluoride complexes (e.g., [NbF6O2] moiety) in acidic F-rich solutions, whereas high-chloride acidic conditions favour six-coordinated chlorohydroxy complexes (e.g., [NbCl4O2] moiety). Competitive ligand interactions between F-and Cl-are modulated by temperature and pH, with higher temperature or low pH promoting Cl-dominated coordination. Carbonate solutions exhibit retrograde Nb solubility and promote lower solubility than acidic F/Cl solutions above 282 C, with spectral features suggesting the presence of [NbO6]-like moieties in polynuclear clusters and/or nanoparticles. Comparative analysis with tantalum (Ta) highlights distinct geochemical behaviours: Ta dissolution depends strictly on F concentration, whereas Nb demonstrates greater coordination flexibility in Cl-bearing solution systems. These findings challenge conventional views that dismiss the role of chloride in Nb transport. Differences in Nb and Ta complexation provide a geochemical discriminator, leading to Nb/Ta ratios that are low near intrusions, increase outwards in intrusion-related hydrothermal systems, and are highest in metamorphic fluids.

Hydrometallurgical treatment via heap or in-situ leaching are cost-effective alternatives to conventional pyrometallurgy for Cu-recovery from low-grade ores, but are hampered by slow kinetics and low recovery. This study examined the impact of pH pre-treatment (0 followed by 2, or vice-versa) and NaCl addition on ferric-activated (5 g/L Fe3+) sulfuric acid leaching of low-grade chalcopyrite ores from the Cadia porphyry copper deposit. The overall reactivity during 20 days of leaching was calcite > clinochlore > muscovite > K-feldspar > quartz, depending on lixiviant pH and the cm-scale abundance, texture, grain size, reactivity, and spatial location of gangue minerals in the ore fragments. Addition of NaCl at seawater concentrations had neglectable effect on the pH-driven early dissolution of gangue minerals. Early particle-scale porosity was induced by calcite dissolution, but quickly led to gypsum precipitation and pore clogging. Dissolution of calcite veins penetrating deep into the samples allowed the growth of reaction rims along dissolving veins and pores. Calcite dissolution was followed by clinochlore dissolution, forming lamellar siliceous residues. These siliceous residues locked and shielded chalcopyrite grains from lixiviant early in the leaching process; ion sorption on these residues can also retain Cu or other ions used as additives or catalysts. This study highlights that many processes that limit the efficiency and rate of Cu recovery are controlled by the nature, composition, abundance, as well as the texture of gangue minerals, in addition to ore-mineral colocation. Detailed multi-scale characterisation, from cm- down to mu m, is required to optimize Cu-recovery in complex low-grade ores.

Over 300 years since its naming, chalcopyrite remains a mineral of mystery despite its economic necessity, as Joël Brugger and Barbara Etschmann explain.

Copper concentrates account for approximately 80% of the global copper production. The predominant method for processing these concentrates is pyrometallurgy, primarily through high-temperature smelting. An alternative approach is hydrometallurgical processing, which involves leaching under moderate to high temperatures and/or high-pressure conditions; however, these requirements often lead to increased capital and processing costs. This work explores a third alternative: mechanochemical processing of copper concentrates. In this method, the combined application of intensive grinding and oxidative reagents enhances leaching kinetics, significantly reducing the overall leaching time. A series of mechanochemical tests were conducted using chalcopyrite samples sourced from both a single hand specimen and an industrial copper concentrate. The tests employed a ring mill under low-moisture conditions, combined with different oxidising agents to evaluate their effectiveness in copper extraction. Three types of oxidants were tested: ferric chloride (FeCl3), ferric sulfate (Fe2(SO4)3), and ferric sulfate combined with silver as a catalytic agent. These oxidants were applied at varying stoichiometric ratios. Among the tested conditions, the highest copper recovery (68%) was achieved using ferric chloride after 25 min of reactive grinding. Ferric sulfate with silver as a catalyst also demonstrated promising results, achieving a 58% copper recovery under the same grinding time. These results demonstrate the potential of mechanochemical processing as an alternative to other conventional leaching technologies for treating copper concentrates.

Rare earth elements are crucial for developing alternative energy sources, such as batteries, for current and future applications. Mineral exploration and processing rely on thermodynamic models, which require accurate properties for all of the involved minerals and solutes. Modeling REE deportment in geological and engineered systems is challenging due to their tendency to occur in trace amounts in ore minerals, hindering direct experimental determination of key thermodynamic properties. This study uses quantum-mechanical calculations and literature values of standard thermodynamic entities to determine incorporation mechanisms and energies for different reference and host phases using solid and aqueous environments. This approach can be transferred to a wide range of applications. This study investigates the coupled substitution of light rare-earth elements (lanthanum to gadolinium) and Na+ for two Ca2+ sites in fluorapatite. With fluoride source phases, incorporation enthalpies become more negative with increasing temperature, while Gibbs free energies become more positive. When using enthalpies and Gibbs free energies of formation for chloride reference phases, which are more soluble than the fluorides, in combination with the quantum-mechanical data of the fluorides, the incorporation energies are more positive. To eliminate dependence on the anion in the reference phases and to understand the thermodynamics between host/incorporated solid and aqueous cations (REEaq 3+, Na/Cuaq +, and Ca2+), dissolution energies of the reference phases are added. This procedure enables the calculation of bulk REE/Ca equilibrium ratios in fluorapatite as a function of aqueous REE3+, Na+, and Ca2+ activities via equilibrium constants.

Waste from metal mining is a global and escalating issue. Risks are particularly severe for reactive minerals, which, upon exposure to oxygen, water and/or microbial activity, can cause widespread contamination (e.g., acid drainage from sulfide oxidation). This study investigates the nature of colloids within historic U-REE-Cu-rich mine wastes from Mount Painter in the Northern Flinders Ranges, South Australia. The primary mineralogical hosts of uranium (torbernite) and rare earth elements (monazite-(Ce)) are phosphate minerals, which are insoluble phases typically considered to limit U and REE mobility in groundwater. However, single particle ICP-MS analysis revealed substantial concentrations of polymetallic nanoparticles enriched in U-REE-(Fe) and concentrated within the surface layers (0-10 cm) of the waste. Microbial diversity is highest near the surface, which is interpreted to promote the dissolution of phosphate minerals and the transformation of liberated metals into nanoparticles. This correlation suggests the potential for microbial consortia to extract metals from stable minerals and transform them into environmentally mobile colloidal forms, with significant implications for the biogeochemical cycling and environmental management of metals such as U and REE released by mining of both base metals and critical minerals.

Understanding the incorporation of rare earth elements (REE) into their principal host minerals is fundamental to tracing geological processes, improving ore deposit formation models, assessing the resource potential of a deposit, and designingeffective and environmentally sustainable extraction processes. This study investigates the speciation and fractionation of europium (Eu) and cerium (Ce) in hydrothermally synthesized sulfate (anhydrite) and sulfide (sphalerite) minerals. Electron probe microanalysis reveals that Ce and Eu preferentially partition into anhydrite rather than sphalerite, consistent with the Goldschmidt Rules. Furthermore, we show that Eu concentration and oxidation state are decoupled within single anhydrite crystals: synchrotron X-ray absorption near-edge structure (XANES) and microprobe cathodoluminescence (CL) data both show that Eu3+ predominates in the core and Eu2+ increases from the core to the rim, whereas Ce3+ is the only oxidation state of Ce in anhydrite under the same conditions. In contrast, Eu and/or Ce concentrations oscillate from the core to the rim of anhydrite crystals, with the lowest concentration around the rim. Correlations among elemental concentrations in anhydrite show that Eu3+ and Ce3+ replace Ca2+ via a coupled substitution with Na+, and Eu2+ replaces Ca2+ via an isomorphous substitution. Complementary ab initio molecular simulations indicate that the incorporation of Eu and Ce caused only small local distortions of the anhydrite crystal structure, with more substantial distortion commonly observed around vacancies and Na sites; the extent of distortion is proportional to the differences between the effective ionic radii of Ca2+ and substituted Eu, Ce, and Na ions. This study demonstrates that hydrothermal anhydrite can incorporate up to several weight percent of REE, with a complex incorporation process controlled by the evolution of fluid composition and local fluid-mineral interactions. Spatially resolved oxidation state and concentration analyses provide deeper insights into fluid evolution than bulk REE measurements.

Understanding elements uptake and release from minerals in source rocks is crucial for comprehending critical metals accumulation, yet the mechanisms and kinetics of element mobilization at the atomic scale remain mostly unknown. Here, we analyzed the distribution of cobalt (Co) in natural pyrite from a Cu-Co ore deposit and found that metals distribution is best described by steady-state diffusion with constant flux and concentration-dependent diffusivities, rather than transient-state diffusion with time-evolving concentrations. First-principles calculations and diffusion modelling further demonstrate that this diffusion is accelerated by vacancy pathways and is far more efficient than traditional vacancy-mediated lattice diffusion, with element transfer rates higher by almost two orders of magnitude. We conclude that steady-state lattice diffusion induced by vacancies in the presence of fluid can be an efficient mechanism promoting the preferential release of metals into ore fluids and the accumulation of metals during ore formation.

Understanding the speciation and thermodynamic properties of aqueous tungsten (W) complexes under various conditions is essential for predicting W transport in hydrothermal fluids relevant to ore formation and geothermal systems. Although previous experimental and geochemical modelling studies have provided insights into W solubility in hydrothermal systems, a comprehensive molecular-level understanding of W in hydrothermal fluids remains elusive. In this study, we employed ab initio molecular dynamics (MD) simulations to determine the speciation and coordination geometries of W(VI) complexes in NaCl, NaHS, and NaF-bearing brines at temperatures up to 600 degrees C and pressures up to 2 kbar. These theoretical calculations were complemented by synchrotron in-situ X-ray Absorption Spectroscopy measurements of W(VI) in chloride-, sulfide-, and fluoride-rich solutions under pressures of 600 bar and temperatures ranging from 25 to 429 degrees C. The speciation and geometrical properties obtained from ab initio MD simulations are in reasonably good agreement with the in-situ X-ray Absorption Spectroscopy data. Our study reveals that W-Cl complexes are not stable, and W is transported as tungstates (H2WO4(aq), HWO4- and WO42-)in NaCl-rich fluids. In sulfur-rich fluids under near-neutral pH and reduced conditions (sulfide predominant), S2- ions gradually replace O2- in tungstates to form thiotungstate complexes (WO4-xSx2-, where x = 1, 2, 3, 4). The MD results suggest that fluoride (F-) plays a significant role in W transport by forming WO3F- and WO3F22- complexes, or their hydrated ions. We employed thermodynamic integration to determine the formation constants of the WO3F- and WO3F22- complexes at temperatures up to 600 degrees C and 2 kbar, and extrapolated these properties across a broader range of temperatures and pressures. This study underscores the significance of W-F complexes in W transportation in fluoride-bearing, acidic to neutral (pH < 8) hydrothermal fluids. In contrast, W is most likely transported as thiotungstate complexes in sulfur-bearing hydrothermal fluids within a neutral to alkaline pH range (e.g., pH 5-8.5 at 300 degrees C) under reduced (sulfide-stable) conditions in the Earth's crust. Existing models for W transport in hydrothermal ore fluids need to consider the influence of W-F and thiotungstate species.

The high field strength elements (HFSE) Ti, Nb, and rare earth elements (REE) are commonly regarded as immobile during hydrothermal activity and metamorphism, making them important tracers of geological processes. Here, we report a Ti-REE-Nb-As mineralization recently discovered in quartz, feldspar, muscovite +/- biotite, fluorapatite, hematite, epidote, and dravite-schorl veins hosted in quartz +/- feldspar +/- muscovite +/- biotite gneisses from the Monte Leone nappe (Switzerland/Italy). The veins formed during prograde metamorphism and were boudinaged and/or folded during peak metamorphism under lower amphibolite facies. The mineralization consists of megacrysts (>> 2 cm) of allanite-(Ce) and Nb-REE-rich titanite-(I). Titanite-(I) displays prominent primary oscillatory- and sector-zonings in Y+REE and Nb. Allanite-(Ce) and titanite are also present as metamorphic minerals disseminated in the host-rock. The vein-hosted megacrysts and their host rocks have identical Nd isotope systematics, indicating that the HFSE mineralization results from small-scale remobilization of host-rock components.Localized, fluid-assisted dissolution of vein-hosted allanite-(Ce), epidote, and dravite-schorl during retrograde alpine deuteric alteration resulted in cavities lined with chlorite, muscovite, hematite, and diverse REE minerals. The same fluids caused titanite-(I) to break down into a porous assemblage of acicular niobian rutile with lamellae of crichtonite-group minerals and/or hematite and a suite of REE-Nb-Ti micro-minerals. A few titanite (titanite-II) crystals preserve an intermediate stage of the dissolution-reprecipitation process. Unlike titanite-(I), they display a patchwork-like micro-texture (100 mu m sized subgrains with inhomogeneous Nb concentrations); they host lamellae of crichtonite-group minerals within cleavage planes of the parent titanite, as well as secondary Y+Nb+REE oxides and calcite along subgrain boundaries. The occurrence of calcite indicates that CO2-enriched fluids promoted the destabilization of titanite-(I). Highly localized fluid flow accounts for the common occurrence of fresh and altered allanite-(Ce) and titanite in close proximity.The HFSE-enriched veins reveal a complex history of mobility of minor elements (Ti, Nb, REE, As +/- B, Be) together with major components (Si, Al, K, Na, Fe) from the host rock, resulting in their early (prograde) concentration within the veins, and their remobilization upon the action of oxidized CO2-bearing fluids during retrograde metamorphism. In general, crystallization of enriched phases during prograde metamorphism may be an important step in determining the fertility of a source rock for hydrothermal HFSE deposits.

Ethnographic accounts of Melanesian exchange systems, such as the Kula and Hiri, have significantly influenced the development of anthropology. These accounts primarily focus on male agency framed by heroic seafaring ventures, while the agency of women and their cultural practices—key to the interconnectedness of Melanesian societies—has often been overlooked. On Papua New Guinea’s south coast details of women’s cultural practices are available in ethnography, and the remains of the pottery they made survive well in archaeological contexts. This paper reports the results of Scanning Electron Microscopy based Automated Mineralogy (SEM-AM) analyses of selected pottery sherds from two regions on the Papua New Guinea’s south coast located 80 km apart. The sherds are very similar in form and decoration, so we employed precise mineral characterisations to assign the pottery sherds to mineralogical groups and test whether they originated in the same manufacturing location and were traded along the coast. The mineralogical analyses uncovered nuances of past social entanglements, revealing that seafaring alliances and networks were maintained through kinship. We argue that in this instance, pottery-making traditions spread along the coast through the movement of women and intermarriage.

Uranium is found in various types of rocks. HERFD-XRF imaging at the U M4 edge is a novel non-destructive technique that visualizes the distribution of U(IV), (V), and (VI) oxidation states at concentration levels ranging from ppm to wt%, offering unprecedented insights into uranium habitat and valence.

Windows are essential for advancing energy efficiency, yet fabricating window materials that simultaneously achieve high visible light transmission, exceptional and ultrabroadband near-infrared (NIR) shielding, neutral color appearance, excellent stability, and cost-effective, sustainable production remains a significant challenge. This study introduces ferrous ion-doped phosphosilicate glass (Fe2+-PSG), a material that meets all these criteria, establishing itself as a promising candidate for energy-efficient windows. Comprehensive characterization using Raman spectroscopy, synchrotron X-ray absorption near edge spectroscopy (XANES), UV-Vis-NIR transmission spectroscopy, and structural analysis reveals that the glass achieves superior visible light transmission performance (Tlum = 84.1 +/- 0.3 %) and a neutral color temperature of 6753 +/- 45 K. These remarkable properties are primarily attributed to the formation of colorless ferrous [FeO6] units, whose unique coordination environment is precisely controlled through phosphorus incorporation. Superior ultrabroadband NIR-shielding (750-2500 nm), with a high NIR-shielding figure of merit of 1.8 +/- 0.1, is enabled by the incorporation of larger alkali ions such as K+ and Cs+. Additionally, Fe2+-PSG demonstrates exceptional stability, maintaining its performance after 12 months under ambient conditions and 24 h in hot water at 80 degrees C and in air at 120 degrees C. These high-performance characteristics are attributed to structural modifications that alter the splitting energy of ferrous ions, enabling precise control over optical properties across the visible and NIR spectrum. Manufactured using the scalable and cost-effective melt-quench method, Fe2+-PSG offers a practical solution for sustainable window production, addressing limitations of current technologies and paving the way for real-world applications.

To meet growing demand for renewable technologies that will mitigate climate change, the world requires a sustainable supply of rare earth elements (REEs). Uranium (U) is a common impurity in REE ores that causes socio-environmental challenges during mining and processing. Sustainable REE extraction thus relies on targeting ores with little U, which necessitates an understanding of the conditions under which U accumulates in REE minerals. Here we show that rhabdophane and monazite - two common hydrothermal REE ore minerals - can incorporate U in its oxidised U(V) and U(VI) forms. Contrary to current understanding, this demonstrates that reducing conditions are not required for U to accumulate in hydrothermal REE minerals. Rather, the higher availabilities of U in oxidising and/or Ce-poor fluids can also drive significant accumulation. Four redox scenarios are consequently theorized for predicting the capacity of aqueous-fluid-affected REE ores for accumulating U. This framework may assist in evaluating the environmental sustainability of various REE deposits, thereby guiding decisions on exploration and extraction. Results also confirm the capacity of both minerals to immobilise fluid-soluble U(VI) during formation, with implications for their application as mineral barriers in U-contaminated systems.

Copper extraction from chalcopyrite is challenging, because acid dissolution is slow, occurring incongruently via a complex three-step reaction mechanism. Silver has been known to catalyse copper extraction from chalcopyrite since the 1970's; yet the mechanism remains controversial. Microcharacterisation of experimental products obtained under optimal leaching conditions (50-150 lm chalcopyrite grains in ferric/ferrous-sulfate solution with a redox potential around 500 mV vs. Ag/AgCl, approximately 1ppm Ag; [Ag] 6.4 x 10-6 mol/L; 70 degrees C; 4 days) highlights the heterogeneity of the reaction: lm-thick layers of a porous copper-sulfide with variable composition formed both in cracks within, and on the surface of the chalcopyrite grains. There is no evidence for formation of Ag-rich phases (Ag2S(s), Ag0 (s)). The fundamental three-step reaction mechanism remains the same with or without added silver; silver merely accelerates the initial dissolution step. An integrated model for the catalytic effect of silver is proposed that incorporates recent advances in the reactivity of sulfide minerals. The initial reaction follows a 'Fluid-Induced Solid State Diffusion Mechanism', where diffusion of Fe in the chalcopyrite lattice is driven towards the surface by its rapid removal into solution, resulting in a Fe-deficient surface layer. The large Ag+ ion, relative to Cu+ /Fe3+, diffuses into this Fe-deficient surface layer and accelerates chalcopyrite dissolution in the subsequent step, whereby chalcopyrite is replaced by copper sulfides via an interface coupled dissolution reprecipitation reaction as a consequence of the sulfide-rich micro-environment at the mineral surface. Effective Ag+ recycling is key to the catalytic effect of silver, and occurs as a result of the strong affinity of Ag+ for bisulfide ligands accumulating at the surface of dissolving chalcopyrite. (c) 2025 China University of Geosciences (Beijing) and Peking University. Published by Elsevier B.V. on behalf of China University of Geosciences (Beijing). This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).