The distribution of metal (loid)s in the Guanajuato River Basin reflects a complex interplay of geological inheritance, sedimentary processes, and ∼500 years of historical mining. We analyzed 71 samples spanning bedrock, mine tailings, soils, stream/overbank sediments, surface water, and groundwater to characterize geochemical variability, evaluate mining-related geochemical signatures, and assess environmental and health risks. Multivariate statistics were applied to evaluate geochemical relationships among environmental matrices, complemented by Random Forest model to assess their relative affinity to geogenic and mining related reference classes. Bicarbonate-type waters dominate the basin; groundwater is enriched in Na, Si, F, As, and Zn, whereas surface waters exhibit higher overall mineralization and Ca–Mg–SO 4 signatures. Two principal geochemical associations were identified in the solid matrix samples: Al–Fe–Cr–V–Ni (geogenic) and S–As–Cd–Pb–Cu–Zn (mineralized/mining-related). The exploratory Random Forest model (OOB error of 0.12) identified S, Cd, and As the leading predictors of affinity to the predefined reference classes. However, these findings should be considered exploratory because the model was trained on a limited dataset (12 lithological and 13 mine tailings samples). Ecological risk is highest in mine tailings, driven primarily by elevated As, Cd, and Cu. Water quality and human health risks are restricted to localized groundwater and downstream surface water sites, where quantified As concentrations are the principal contributor to potentially unacceptable carcinogenic risk. Overall, historical mining has amplified and redistributed preexisting hydrothermal geochemical signatures rather than introducing entirely new elemental assemblages. The integrated evaluation of multiple environmental matrices provides a framework for interpreting mining-related impacts in naturally mineralized basins.
Advance indicator mineral research integrating field concentration and mineral identification techniques improves the exploration of critical minerals in the areas of transported cover. This article presents the development and evaluation of improved research methods for identification of heavy and indicator minerals, which are commonly applied in the exploration of precious, base, and critical metals. The results demonstrate that indicator mineral separation can be significantly optimized through tailored sample handling and enrichment techniques, enabling the selection of suitable processing methods for samples of varying sizes, grain-size fractions, and specific gravity classes. The use of on-site analytical methods, particularly portable XRD and XRF analyzers, markedly accelerates exploration workflows while reducing the reliance on costly laboratory analyses, resulting in substantial cost savings. In addition, advanced laboratory techniques, such as automated mineral identification using FE-SEM-EDS, enhance the efficiency and accuracy of mineral identification and provide reliable validation for field-based analyses. Several case studies in northern Finland confirm the robustness, usability, and data processing performance of both field and laboratory methods. This new concept has proven effective for discovering new sources of critical minerals, accelerating exploration, and reducing costs. Practical piloting further demonstrates the applicability of the developed methodological concept, with documented outcomes supporting industrial use and future exploration projects.
Ultramafic rocks rich in iron-bearing minerals are promising sources of geochemical hydrogen generation through water-rock reactions. This study investigates how mineral composition, temperature, pressure, and initial pH influence hydrogen generation during hydrothermal water-rock reactions, using laboratory experiments and reactive-transport/thermodynamic simulations. Three novel contributions are made: a controlled experimental dataset isolating the effect of fayalite-to-forsterite ratio on hydrogen yield; a geochemical model combining thermodynamic equilibrium with Arrhenius kinetics, validated against experiments and used to explore conditions beyond the tested range; and an extension to core-scale flow-through experiments demonstrating that transport processes in fractured rock fundamentally alter hydrogen generation behavior relative to powdered-sample systems. Mineral composition is the dominant control on hydrogen yield, followed by temperature. pH effects are pressure-dependent, and pressure alone has a modest positive effect. These results highlight critical parameter interactions and transport-reaction coupling that must be resolved before laboratory findings can be reliably translated to field-scale geological hydrogen systems.
Jie Sun, Zhiguo Zhang, Zengxia Zhao, Guoqiang Tang, Xuelian Xing
The North Qilian Orogenic Belt is a key region for understanding the evolution of the Paleo-Asian Ocean and continental accretion. The Dachadaban area preserves a complete ophiolite suite and coeval granitoid intrusions. Zircon and apatite U–Pb geochronology, whole-rock geochemistry, and Sr–Nd isotopic analyses were conducted on intermediate–felsic intrusions from this area. Zircon and apatite ages of 512–504 Ma (Late Cambrian) record a regional magmatic pulse. The rocks are metaluminous to weakly peraluminous, high-K calc-alkaline, enriched in LILEs (Rb, Th) and depleted in HFSEs (Nb, Ta, Ti), with right-inclined REE patterns and moderate negative Eu anomalies, typical of island-arc granitoids. Initial 87 Sr/ 86 Sr ratios (0.7205–0.7286), ε Nd (t) values (−9.7 to −6.4), and T DM2 ages (2019–1751 Ma) indicate magmas derived mainly from partial melting of Paleoproterozoic crust with ca. 20%–30% mantle input. Zircon Ti-thermometry indicates crystallization temperatures ranging from approximately 692 °C–826 °C, accompanied by a shift in oxygen fugacity from relatively oxidized to reduced conditions and a concomitant decrease in water content. Apatite and whole-rock geochemical characteristics collectively indicate an evolution from I-type to A-type granitoids. Tectonic discrimination suggests that this magmatism occurred in a back-arc extensional setting driven by slab rollback during waning subduction, rather than in a post-collisional environment. Earlier-formed I-type granites underwent dehydration melting under thermal perturbation and decompression, producing late-stage A 2 -type granites, marking a transition of the North Qilian Orogen from convergence to extension at ca. 512–503 Ma.
Rute Salgueiro, Teresa Pena Silva, Iván Martín-Méndez, Daniel de Oliveira, Maria João Batista, Carlos Inverno
Actual and future demands for critical raw materials and strategic raw materials (CRM/SRM) justify the global search for their potential sources and the exploration approaches to reach them. This study discloses the characterization of rare earth elements (REE) and other CRM-bearing alluvial heavy minerals samples sourced from the late- to post-tectonic Variscan Castelo Branco Massif (Portugal). It also contributes to an understanding of REE, Th, and U anomalies from local and correspondent stream sediments identified in past geochemical surveys. The alluvial samples were subjected to semiquantitative analysis of their minerals under a binocular microscope and to chemical analysis through portable X-ray fluorescence. A varied mineralogical association and a geochemical fingerprint compatible with their main granitic source was identified, revealing several minerals that carry CRM, in which REE and titanium minerals stood out. The titanium minerals have the higher average abundance (54%), being ilmenite-dominant (50%), as supported by the relatively higher Ti content of these samples (up to 28.88%). The REE minerals occur as accessories and have a summing average of 12%, in which monazite is the most abundant (4.97%). Geochemical data support alluvial monazite as the mineral with the highest REE and Th concentrations, as described in the literature on its granitic source. In addition, the magnetic fraction of samples (∼85%) that includes monazite and xenotime presents LREE anomalous contents (up to 4,557 mg/kg) in relation to their granitic source, NASC, and even to ΣREE anomalous values revealed by local stream sediments. The Th (up to 1,969 mg/kg) and U (up to 244 mg/kg) contents follow the same trend. Nevertheless, the nonmagnetic mineral fraction that includes apatite and zircon reaches higher U contents (up to 448 mg/kg). This study indicates that the SRM Ti (ilmenite) and LREE (monazite) have the potential to form placer deposits sourced from Castelo Branco granitic rocks in a wider area, which is supported by the regional Ti placers exploited in the past. The occurrence of other accessory elements/minerals with industrial applicability associated with those placers may also represent future added value.
