Geochemical Fingerprinting Research Articles

Atmospheric particulates over the northwestern Pacific during the late Holocene: Volcanism, dust, and human perturbation.

Mineral aerosols form a key component of Earth's dynamic biogeochemical systems, yet their composition and mass are variable in time. We reconstruct patterns in mineral aerosol flux from East Asia, the second largest global dust source, in a peat mire in northern Japan. Using geochemical fingerprinting, we show for the past ~3600 years that high but variable tephra flux dominated regional aerosol loads. A human signal was discernible as elevated pollutant metals, along with East Asian mainland dust, identifiable by its geochemical signature. After ~700 years before the present, dust flux increased as the westerly jet intensified and moved south, the summer monsoon strength reduced, and agriculture expanded. From the 20th century, dust flux increased by two times. Attributable largely to human activity, this demarks a major change in aerosol export to the northwestern Pacific with accompanying increases in fluxes for key micronutrients and increased pollution flux by 16 times.

Petrogenesis and tectonic setting of mafic magmatism within the Laguna Amarga Metamorphic Complex, Andes of Catamarca, Argentina: Insights into the opening of the Cuyania/Precordillera terrane from the Ouachita rift

Neoproterozoic crystalline basement rocks are exposed as fault-bounded blocks over the high Andes of Catamarca. The crystalline basement is stratigraphically grouped into the unique Laguna Amarga Metamorphic Complex and represents the northern extension of the Cuyania/Precordillera terrane. Tabular bodies of meta-mafic rocks are widespread in the basement interspersed within a thick sequence of meta-sedimentary rocks derived from siliciclastic, calc-silicate, and limestone protoliths. Overall, the geochemical characteristics of meta-mafic rocks are in the compositional range of Normal-Mid Ocean Ridge Basalt (Normal-MORB), reflecting a common depleted-mantle source with varying degrees of partial melting. While preserving the typical bulk chemistry of MORB magmatism, some mafic magma underwent differentiation at emplacement, leading to the development of high-Ti mafic rocks. New U-Pb zircon geochronology reveals three distinct age peaks, with two coinciding with ages identified in the metasedimentary host rocks. The dominant Mesoproterozoic age cluster is linked to inherited zircon crystals assimilated within a single meta-mafic rock. In contrast, zircon ages from the late Ordovician to early Devonian are attributed to metamorphic overgrowths. Notably, the third age cluster, delineates a Late Neoproterozoic magmatic event, indicating the temporal span of mafic magmatism. The finding agrees with the best available age (576 ± 17 Ma) for mafic magmatism on the Precordillera Mafic-Ultramafic Belt. Stratigraphic relationships and geochemical fingerprints enable correlation among the meta-mafic rocks from Laguna Amarga, tracing a belt of mafic magmatism with an oceanic affinity that extends southward. Building upon previous works, this study reaffirms that the rift-drift transition of the Cuyania/Precordillera terrane, linked to the Ouachita rift opening from southeastern Grenville, evolved during the latest Neoproterozoic.

The Silent VOICE—Searching for Geochemical Markers to Track the Impact of Late Jurassic Rift Tectonics

AbstractA causal mechanism for the Volgian Isotopic Carbon Excursion (VOICE) remains enigmatic. Elemental geochemical profiles of the Deer Bay Formation, Sverdrup Basin, Arctic Canada that record the VOICE and contemporaneous strata are herein examined to provide insight into depositional environments during Late Jurassic‐Early Cretaceous time. Silver (Ag) and Cadmium (Cd) are enriched across the VOICE at localities on Axel Heiberg Island, and in Tithonian (∼Volgian) strata of Ellef Ringnes Island. Other redox‐sensitive trace elements do not exhibit spatially or temporally consistent patterns and indicate oxic conditions. A lack of relationship across the VOICE between Ag and the quality, quantity, and isotopic composition of organic matter suggests that the negative isotope excursion and interval of Ag enrichment are not merely functions of changes in organic matter source or amount, while a lack of spatially consistent change in geochemical indices of weathering similarly excludes climate change and/or sediment provenance as a driver. Therefore, in a ventilated setting and without marked changes in organic matter content, Ag enrichment may be due to hydrothermal activity. Contemporaneous Ag enrichment in strata from Svalbard suggests that a source of hot fluid sufficient to produce Ag‐rich seawater may have been related to rifting in the adjacent proto‐Amerasia Basin. Hydrothermal activity may also have been a widespread source of isotopically depleted carbon. This work develops new geochemical fingerprints that may be used to trace the spatial extent of hydrothermal events that do not leave an extinction pattern but may nonetheless have a far‐reaching influence on biogeochemical systems.

Geochemical fingerprinting of Norway spruce from the Eastern Carpathians: Sr isotopic and multi-elemental signatures

Ensuring efficient wood traceability within procurement chains is essential for establishing sustainable forest management and minimizing environmental damage in countries that produce and export timber. While some progress has been made with key legislative reforms to tackle this issue, the effectiveness of law enforcement still relies on the availability of appropriate analytical tools to determine the provenance of wood. This study documents the Sr isotopic and multi-elemental signatures of Norway spruce trees in the Eastern Carpathians, Romania – an area known for intensive forest logging. The research focused on trees from Rodna, Rarău, and Călimani, analyzing tree rings from 1970 to 2020 to assess temporal variability and develop site-specific geochemical fingerprints. In conjunction with tree samples, corresponding soil, groundwater, and river samples were analyzed, providing a comprehensive view of the bioavailable 87Sr/86Sr ratios in these ecosystems. The study found a strong correlation between the Sr isotope ratios in the wood and those in corresponding water and soil samples, confirming that the wood accurately mirrors local geochemical signatures. The Sr isotope ratios were consistent across most of the cores from trees within the same site but varied among sites within the same region. Principal Component Analysis of the Sr isotopic and multi-elemental data highlighted closer clustering of samples from the Călimani area, though distinguishing the samples from the Rodna and Rarău regions proved more difficult due to overlapping data points. This study broadens our understanding of geochemical variability and its implications. The insights gained provide a valuable foundation for future research aimed at enhancing wood traceability methods.

Deciphering geochemical fingerprints and health implications of groundwater fluoride contamination in mica mining regions using machine learning tactics.

The contribution of mica mining activities to fluoride (F-) contamination in groundwater has been chased in this study. For the purpose, groundwater samples (n = 40, replicated thrice) were collected during the post-monsoons (September-October) from a mica mining area in the Tisri block of Giridih district, Jharkhand. The study has employed a synergy of classical aquifer chemistry, statistical approaches, different indices, Self-Organising Maps (SOM), and Sobol sensitivity index (SSI) to unveil the underlying aquifer chemistry, identify the impacts of mining activities on groundwater quality and its associated health hazard. Fluoride levels varied from 0.34 to 2.8ppm, with 40% of samples exceeding the World Health Organization's permissible limit (1.5ppm). Physicochemical analysis revealed significant differences in electrical conductivity (EC), total dissolved solids (TDS), total hardness (TH) and major ion concentrations (Na+, HCO3-, Ca2+) between fluoride-contaminated (FC) and fluoride-uncontaminated (FU) groups. Higher Na+ and HCO3- associated with F- contaminated samples, were indicative of silicate weathering and carbonate dissolution as primary geogenic sources for this ion. Health risk assessment (HRA) revealed hazard quotient (HQ) values exceeding unity, indicating non-carcinogenic risks, particularly for children in most samples from group FC. The mean Water Quality Index (WQI) of FC group (156.76 ± 7.30) was significantly higher (p < 0.05) than group FU indicating of its unsuitability. SOM could accurately (80%) predict presence of fluoride in water samples based on other major ions. Sobol sensitivity analysis successfully identified fluoride concentration and body weight as most impactful parameters affecting human health. The integration of advanced modelling techniques and geospatial analysis as Inverse Distance Weightage (IDW) maps has provided a robust framework for ongoing groundwater quality monitoring in mining-affected regions and can help proactive intervention in risk-prone areas. Overall, this comprehensive study takes us a step ahead towards ensuring safe drinking water access for the global community.

Whole rock lithogeochemical analysis of the Mount Read Volcanics: a new tool for geochemical exploration

The Mount Read Volcanics (MRV) of western Tasmania is a belt of Middle to Late Cambrian submarine volcanics and volcaniclastics and one of the major base and precious metal provinces within Australia. Exploration success in the MRV has been in decline in recent years due to a variety of challenges including intensely altered rocks with complex stratigraphy and lithofacies variation, and a lack of accessible outcrop. As a result, local and regional mapping of the MRV is often restricted to Group-level stratigraphy, rendering geological mapping ineffective for identifying decametre-scale mine stratigraphy. Surface rock chip and drill hole samples were collected and analysed using commercially available geochemical assays to create a regional geochemical dataset of the MRV, covering the entire province and all major stratigraphic units. From these data, a lithogeochemical methodology was developed, utilizing Ti/Nb and V/Sc systematics that effectively characterizes the samples according to composition and magmatic processes. This method is shown to be robust to biases due to alteration and lithofacies, eliminating the need for highly selective sampling or extensive data filtering. To demonstrate the utility of this method in an exploration context, data from the K-lens of the Rosebery polymetallic volcanic-hosted massive sulfide (VHMS) deposit was used as a case study. Using Ti/Nb–V/Sc systematics, a rock composition classification was developed that allowed for discrimination of the footwall, hanging wall and host stratigraphy of the Rosebery mine sequence. A geochemical fingerprint for the footwall stratigraphy to mineralization was developed, and by correlating this signature to the regional unclassified samples, geochemical analogues for the Rosebery footwall were readily identified. This approach rapidly reduces the exploration search space and provides valuable information for future mineral exploration. The methodology is applicable in other terrains; however, appropriate orientation studies are required to investigate potential biases due to lithofacies, alteration and mineralogical variability.

From onset of Cadomian subduction to forearc-arc-continent collision: Insights from the Neoproterozoic Calzadilla Metaophiolite (SW Iberia)

ABSTRACT The Cadomian basement of SW Iberian Massif appears in the so-called Ossa-Morena Complex, which contains several allochthonous terranes that are key for deciphering the evolution of the Gondwana margin during the Neoproterozoic. In this context, the Calzadilla Ophiolite represents the remnants of an oceanic Ediacaran lithosphere formed by a boninitic mafic crust that overlies a serpentinized ultramafic section, the latter being the biggest outcrop of Cadomian serpentinites in Europe. In this work, the petrological and geochemical nature of the mantle section is analysed, as well as the tectonothermal evolution of both, the mafic crust and the ultramafic section. The algebraic analysis of whole rock geochemistry of the serpentinites indicates that the protolith corresponds to harzburgite. The geochemical fingerprint of the serpentinites, as well as the primary spinel crystals composition, shows that peridotites underwent high degrees of partial melting (up to 16%) in a forearc setting. Thermodynamic modelling and average PT methods were applied to serpentinites and mafic dykes from the ultramafic section as well as to amphibolites from the mafic section, both of which experienced progradation up to 4–5 kbar and 525–575°C. According to the data, the protoliths of the Calzadilla Ophiolite were formed in a peri-Gondwanan arc system developed during the subduction of oceanic crust below Gondwana. The roll-back of the subducting slab would induce the opening of the forearc basin at c. 602 Ma, protolith age of amphibolites from crustal section, with an extensive partial melting of the mantle wedge and the formation of boninitic-affinity magmas that constitute the mafic section of the Calzadilla Ophiolite. Metasomatism and serpentinization of the mantle wedge would occur via melt- and fluid–rock interactions. A compression-dominated stage at c. 540 led to the emplacement of the Calzadilla Ophiolite onto the Cadomian magmatic arc, with the development of the amphibolite-facies metamorphic imprint.

Geochemical fingerprints of early diagenesis in shallow-water marine carbonates: Insights from paired δ44/40Ca and δ26Mg values

We present a suite of major element stable isotope (δ13C, δ18O, δ44/40Ca, δ26Mg), and selected trace element (Sr/Ca and Mg/Ca) data from Pleistocene sediments from the Great Barrier Reef (IODP Expedition 325), as well as Holocene surface sediments from the Bahamas (Triple Goose Creek, Andros Island) to identify geochemical fingerprints associated with early marine and meteoric diagenesis. Sediments from both sites exhibit co-variation in δ13C and δ18O values, depletion in trace elements, and distinct geochemical trends in δ26Mg and δ44/40Ca values that reflect differences between diagenetic alteration in marine and meteoric fluids. While marine diagenesis results in lower Sr/Ca ratios, higher δ44/40Ca values, and little effect on bulk sediment δ26Mg values, meteoric diagenesis leads to lower Sr/Ca ratios, lower δ44/40Ca values, and lower δ26Mg values. Using a numerical model of diagenesis, we show how diagenetic alteration by meteoric fluids must occur after an initial period of diagenetic alteration by marine fluids, a two-stepped diagenetic history that complicates the interpretation of geochemical data in meteorically altered marine carbonate sediments. Finally, we discuss how paired metal isotopes may serve as a robust indicator of meteoric alteration in ancient shallow-water marine carbonate sediments.

Geochemical fingerprints of Dongpu Depression crude oils in Bohai Bay Basin, northern China: Insights from biomarkers and isotopic compositions of selected alkylnaphthalenes and alkylphenanthrenes

The Dongpu Depression is a rift lake in the Bohai Bay Basin of eastern China, where abundant oil and gas resources were discovered. Previous geochemical investigations of Dongpu Depression oils have revealed a notable lack of data regarding the isotopic compositions of individual polycyclic aromatic hydrocarbons (PAHs) from the discovered Cenozoic crude oils. Using gas chromatography-mass spectrometry (GC–MS) and gas chromatography-isotope ratio mass spectrometry (GC-IRMS), a novel approach combining molecular parameters and stable carbon isotope compositions of individual PAH was applied to study the depositional environment conditions, the different source inputs, the maturation stage and to identify the potential family of five crude oils selected from Dongpu Depression.A decrease of Ga/C30H together with low Pr/Ph ratios and changes in isotopic compositions indicate that the five Dongpu Depression oils were derived from OM deposited in an anoxic saline environment with a stratified water column where mixing of saline water and freshwater occurred. The low isoprenoid, tricyclic and tetracyclic terpane ratios in combination with the δ13C values of 1,6-DMN, 1,2,5-TMN, 1,3,6,7-TeMN, 9-MP and 1-MP attest that their sources have a mixed origin with high aquatic organism (planktonic) input and a lower land plant (C3 plant) contribution. The δ13C values of phenanthrene between −30.0 ‰ and −20.0 ‰ indicate that the studied Dongpu Depression oils belong to a single family generated from the peak to the late oil generation stage (Rc-TNR-2 between 0.85 and 1.15 %). A correlation with various basins indicates that oil samples featured by δ13C values of Phen between −30.0 ‰ and −20.0 ‰ correspond to crude oils derived from mixing of aquatic and high plant contributions with different degrees of mixtures, which have not yet reached their cracking stage (Rc < 2.0 %). Crude oils from the Carboniferous and Mesozoic-Cenozoic Tarim rocks, Australian petroleum systems, Termit Basin, Bongor Basin, Fushan Depression and the studied Dongpu Depression oils belong to that group of oils. Crude oils characterized by lighter phenanthrene isotopic compositions (δ13C values of Phen < −30.0 ‰) are mainly derived from marine/aquatic input and have already entered the cracking window (Rc > 2.0 %). This group of oils is represented in this study by the Cambrian-Ordovician Tarim Basin oil samples. The research shows the importance of the aromatic isotopic compositions in petroleum system characterization and could be used as a reference for a practical exploration campaign of petroleum.

Sediment subduction in Hadean revealed by machine learning

Due to the scarcity of rock samples, the Hadean Era predating 4 billion years ago (Ga) poses challenges in understanding geological processes like subaerial weathering and plate tectonics that are critical for the evolution of life. The Jack Hills zircon from Western Australia, the primary Hadean samples available, offer valuable insights into magma sources and tectonic genesis through trace element signatures. However, a consensus on these signatures has not been reached. To address this, we developed a machine learning classifier capable of deciphering the geochemical fingerprints of zircon. This allowed us to identify the oldest detrital zircon originating from sedimentary-derived "S-type" granites. Our results indicate the presence of S-type granites as early as 4.24 Ga, persisting throughout the Hadean into the Archean. Examining global detrital zircon across Earth's history reveals consistent supercontinent-like cycles from the present back to the Hadean. These findings suggest that a significant amount of Hadean continental crust was exposed, weathered into sediments, and incorporated into the magma sources of Jack Hills zircon. Only the early operation of both subaerial weathering and plate subduction can account for the prevalence of S-type granites we observe. Additionally, the periodic evolution of S-type granite proportions implies that subduction-driven tectonic cycles were active during the Hadean, at least around 4.2 Ga. The evidence thus points toward an early Earth resembling the modern Earth in terms of active tectonics and habitable surface conditions. This suggests the potential for life to originate in environments like warm ponds rather than extreme hydrothermal settings.

Integrating soil geochemistry and machine learning for enhanced mineral exploration at the dayu gold deposit, south China block

Combining traditional geochemical methods with advanced analytical techniques is a hallmark of contemporary exploration efforts. This study explores the intricate geological dynamics of the Dayu gold deposit, located in the Dayao Uplift of the South China Block. Using a multidisciplinary approach that includes soil geochemistry, conventional geochemical methods and advanced computational techniques such as machine learning and Discriminant Projection Analysis (DPA), we aim to uncover the deposit formation information. Our results reveal a complex pattern of element anomalies, which serve as a geochemical fingerprint of the Au mineralization processes that shaped the deposit over geological time. Principal Component Analysis (PCA) and cluster analysis on soil samples highlight significant correlation among Au and its pathfinder elements. By leveraging the predictive capabilities of machine learning algorithms, particularly Convolutional Neural Networks (CNN), we improve exploration strategies, enhance the precision of target delineation and guide sampling efforts. DPA further identifies distinct discriminant functions, aiding in group differentiation and providing insights into prospective mineralization zones. This study exemplifies the integration of traditional and innovative methodologies, offering a pathway to a deeper understanding of mineralization processes and improving the effectiveness of exploration in complex geological terrains. The findings advance our knowledge of the Dayu gold deposit and demonstrate the potential of these integrated approaches in similar geological settings.

Slab melting boosts the mantle wedge contribution to Li-rich magmas

The lithium cycling in the supra-subduction mantle wedge is crucial for understanding the generation of Li-rich magmas that may potentially source ore deposition in continental arcs. Here, we look from the mantle source perspective at the geological processes controlling the Li mobility in convergent margins, by characterizing a set of sub-arc mantle xenoliths from the southern Andes (Coyhaique, western Patagonia). The mineral trace element signatures and oxygen fugacity estimates (FMQ > + 3) in some of these peridotite xenoliths record the interaction with arc magmas enriched in fluid-mobile elements originally scavenged by slab dehydration. This subduction-related metasomatism was poorly effective on enhancing the Li inventory of the sub-arc lithospheric mantle, underpinning the inefficiency of slab-derived fluids on mobilizing Li through the mantle wedge. However, major and trace element compositions of mantle minerals in other xenoliths also record transient thermal and chemical anomalies associated with the percolation of slab window-related magmas, which exhibit an “adakite”-type geochemical fingerprint inherited by slab-derived melts produced during ridge subduction and slab window opening event. As these melts percolated through the shallow (7.2–16.8 kbar) and hot (952–1054 °C) lithospheric mantle wedge, they promoted the crystallization of metasomatic clinopyroxene having exceptionally high Li abundances (6–15 ppm). Numerical modeling shows that low degrees (< 10%) of partial melting of this Li-rich and fertile sub-arc lithospheric mantle generates primitive melts having two-fold Li enrichment (~13 ppm) compared with average subduction-zone basalts. Prolonged fractional crystallization of these melts produces extremely Li-enriched silicic rocks, which may stoke the Li inventory of mineralizing fluids in the shallow crust.

Geochemical Evidence of Water-Fluxed Crustal Melting in the Northern Colombian Andes

Abstract The compositions of crustal magmas are powerful tools for understanding the formation and differentiation of continents. However, the geochemical fingerprints that distinguish the two dominant mechanisms of crustal melting, namely dehydration and water-fluxed melting, are still controversial. To provide new insights into this problem, we discuss the petrogenesis of the Paipa Volcanic Complex (PVC), an isolated Quaternary volcanic field in the Colombian Eastern Cordillera. The PVC is characterized by peraluminous trondhjemite-like rhyolites with exceptionally high Na2O contents (~6 wt %), super-chondritic Nb/Ta (~27), elevated Sr/Y ratios (~120), spoon-shaped REE patterns, and enriched isotopic compositions that overlap with those of the local basement. They also exhibit high pre-eruptive H2O contents (~up to 9.5 wt %) and abundant Paleozoic zircon inheritances. We demonstrate that these characteristics are inconsistent with a process of intra-crustal differentiation from a mafic or intermediate mantle-derived precursor. Instead, we propose that the origin of the PVC is best explained by melting the local (meta)sedimentary basement under H2O-saturated conditions, at middle-crustal pressures (~1.3 GPa) and relatively low temperatures (~690–740°C), following the complete breakdown of plagioclase and biotite, and the formation of reactive peritectic amphibole. This scenario differs from the high-temperature dehydration melting conditions that have been widely proposed for the Andes and globally, which result in the production of water undersaturated magmas in equilibrium with anhydrous lithologies rich in plagioclase and/or garnet. Accordingly, we speculate that an external H2O flux was ultimately sourced from a buoyant, cold, and hydrated mantle wedge that was extensively metasomatized by fluids derived from the Nazca and Caribbean flat-slab fronts. These conditions depressed the asthenospheric mantle potential temperature, likely inhibiting mantle melting. In turn, they facilitated the infiltration and ascent of mantle-derived H2O through pre-existing crustal faults and shear zones. Our results indicate that water-fluxed melting could be a plausible mechanism for generating crustal magmas in orogenic regions where the availability of free H2O has been difficult to confirm.

Origin and multi-episodic melt/fluid interactions revealed by the subducted serpentinites in the North Qilian Belt, NW China: Implications for the compositional heterogeneity of the fossil oceanic mantle

In nature, serpentinites act as reservoirs of water and fluid-mobile elements and play an essential role in arc magmatism, fluid metasomatism, and elemental circulation in subduction zones. This paper presents new mineral and whole-rock geochemical analyses of the Qingshuigou serpentinite massif and discusses its petrogenesis, tectonic setting, and mantle metasomatism. The chemical composition (e.g., REE, Y, Mg, and Al) and petrological observations (e.g., pseudomorph and hourglass textures) of serpentines demonstrate that the serpentinites’ protoliths belong to the peridotites. Their degrees of partial melting were estimated to be 15–20 % using Yb, Cr, Ti, and HREEs, indicating that these peridotite protoliths were residual in origin after high degrees of mantle melting. They were relics of the subducted lithospheric mantle in the subduction zone, based on their geochemical similarities with subducted serpentinites. Notably, the Qingshuigou serpentinites show several geochemical fingerprints of melt-rock interactions, such as the U-shaped REE patterns, elevated Zr/Ti, Zr/Hf, and Nb/Ta ratios; this led us to propose that the peridotite protoliths of the serpentinites were not merely melting remnants but were significantly modified by melt metasomatism. Also, they experienced two stages of fluid/rock interactions in the subduction zone: early-stage serpentinization at shallow depths and lizardite/chrysotile to antigorite transition at an elevated depth. Combined with the published data of ophiolitic peridotites from the North Qilian Belt, the compositional heterogeneity of these peridotites and associated serpentinites might be associated with the nature of melt/fluid metasomatism under different geodynamic backgrounds.

Assessment of particulate Zn and Pb sources in the Orne watershed (Northeast France) using geochemical tools.

The Orne River, a tributary of the Moselle River, was highly impacted by industrial activities for more than one century. Land use along the Orne River is highly contrasted, with local specificity from its source to its junction with the Moselle River. The intense industrial activity left behind tons of steelmaking wastes (SMW) on the land surface and within the Orne riverbed. To assess the sources of particulate Zn and Pb transported as suspended sediment in the Orne River, different sets of samples from likely Zn- and Pb-bearing particle sources within the Orne watershed were collected. Three sets of samples were taken from potential sources representing detrital, urban, and inherited industrial particles. Mineralogy, element contents, and Zn and Pb isotope compositions were obtained to characterize and reveal the fingerprint of each set of samples. Soil samples were collected on distinct geomorphological areas characterized by different soil types and land uses. They all display detrital minerals assigned to the geological background. Urban dusts and steelmaking residues display specific mineral phases (sulfates and iron oxides, respectively). Element compositions present strong discrepancies between the distinct sets of samples. SMWs are particularly enriched in Fe, Zn, and Pb. Concerning isotopic composition, SMWs exhibit δ66Zn values ranging from - 0.67 to 1.66‰. Urban samples display δ66Zn values between - 0.11 and 0.13‰, and soils present δ66Zn values between - 0.24 and 0.47‰. The 206Pb/204Pb ratio was estimated to range from 17.550 to 18.807 for soils, from 17.973 to 18.219 for urban samples, and from 18.313 to 18.826 for SMWs. For each of the three sets of samples (soils, urban, industrial), variations of geochemical fingerprint were observed. For soils, the relatively large variations of Zn and Pb isotopic compositions were attributed to distinct land use and the contribution of atmospheric deposition. For industrial samples, the variations were more intense and may be attributed either to distinct industrial processes in the production of pig iron or to distinct furnace-flume treatment modes. The three sets of samples (urban, industrial, and detrital) could be distinguished based on Zn and Pb contents and isotopes. Finally, this study not only highlighted the sources that released particulate Zn and Pb into the Orne River system, it also demonstrated that urban particles are well defined in terms of Zn and Pb isotopic signatures, and those isotopic signatures could be extrapolated to other case studies.

Forensic Geochemistry Reveals International Ship Dumping as a Source of New Oil Spill in Brazil's Coastline (Bahia) in Late 2023.

In the present study, we applied forensic geochemistry to investigate the origin and fate of spilled oils like tarballs stranded at the beaches of Bahia, in northeastern Brazil, in September 2023, based on their fingerprints. Saturated and aromatic compounds were assessed by gas chromatography, and the oceanic surface circulation patterns were deciphered to determine the geographic origin of the spill. Contamination by petroleum represents an enormous threat to the unique, species-rich ecosystems of the study area. The geochemical fingerprint of the oil spilled in 2023 did not correlate with those of previous events, including the one in 2019, the one in early 2022 in Ceará, and an extensive spill across the Brazilian Northeast in late 2022. However, the fingerprint did correlate with crude oils produced by Middle Eastern countries, most likely Kuwait. The oil of the 2023 spill had a carbonate marine origin from early mature source rocks. These findings, together with the moderate weathering of the 2023 tarballs and the ocean circulation patterns at the time of the event, indicate that the oil was discharged close to the shore of Brazil, to the east or southeast of Salvador, by a tanker on an international route in the South Atlantic.

Ranking the oil contribution of individual layers in a lacustrine shale oil system based on non-hydrocarbon analysis by FT-ICR MS

Identifying the dominating oil-producing layer(s) within a shaly system, typically characterized by multiple layers with similar properties, is always a critical yet formidable task, as the oil component disparities among these closely adjacent layers are too minor to be resolved by the traditional geochemical fingerprints. This challenge is now likely addressed by high-resolution Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS), which can resolve thousands of non-hydrocarbons that could serve as new fingerprints. Taking a typical shaly system in the Ordos Basin in China as an example, the specific proportions of non-hydrocarbon compounds from the retained petroleum of different source rock layers (rock extracts) and the produced oil at the wellhead were identified by FT-ICR MS. Their compositional similarity was calculated using a multidimensional scaling (MDS) method, and the layers hosting the retained petroleum with higher compositional similarity to the produced oils are considered to be the main contributors to oil production. The results show that the main producing layers identified by FT-ICR MS differ from those proposed based on traditional fingerprints like the Rock-Eval parameters. A typical example is that the thick low-TOC shales, conventionally proposed to be unessential to oil production, seem to have a similar contribution, if not higher, to their thick silty counterparts. This divergence may be attributed to the fact that the conventional fingerprints primarily rely on the rock extracts from a vertical well section, which may only represent a limited lateral area, while the non-hydrocarbon similarity approach involving the produced oil appears to be more realistic, as it can consider the engineering processes, like the horizontal well track and the hydraulic fracturing effects. The current approach provides a novel route for identifying the dominating producing layer(s) in a shale oil system, which may have extensive potential for optimizing the production strategy of shale oil wells.

Cretaceous magmatic arc in Hainan and the peri-South China Sea as evidenced by geochemical fingerprinting of granitoids in the region

Mesozoic magmatic rocks occur widely in the South China Block and are generally interpreted as the manifestations of the subduction of the Paleo-Pacific oceanic lithosphere beneath Asia. Subduction-driven magmatism in southeast (SE) China continued from the Late Permian through the Late Cretaceous with an inferred lull between 125 Ma and 115 Ma that is known in the literature as the Cretaceous “magmatic quiescence”. We report in-situ zircon U–Pb ages, Hf–O and whole-rock Sr–Nd isotopes, and whole-rock geochemistry of Cretaceous granitoids on Hainan Island and discuss their magmatic evolution within the framework of the Late Mesozoic geodynamics of SE China. We recognize two main stages of the emplacement of Cretaceous granitoids on Hainan, first around 120 Ma and then around 100–95 Ma, displaying high-K calc-alkaline, I-type geochemical affinities. Granites in both age groups are enriched in LILE and LREE, but depleted in Nb, Ta, Ba, Sr, and Eu. The 120 Ma granites have zircon εHf(t) values of –2.6 to 2.3 corresponding to Hf crustal model ages, ranging from 0.79 Ga to 1.03 Ga, and δ18O values ranging from 6.9‰ to 7.7‰. Zircons from 100–95 Ma granites have εHf(t) values of –4.2 to 1.1 corresponding to Hf crustal model ages of 1.08 Ga to 1.42 Ga, and δ18O values ranging from 6.7‰ to 8.4‰. Increasing εHf(t) values of the Cretaceous Hainan granites with younger crystallization ages indicate addition of more juvenile components and reworking of crustal material into their melt evolution. The εNd(t) values of the 120 Ma and 100–95 Ma granitoids range between –4.1 to –0.4 and –7.7 to –4.0, respectively. The calculated two–stage model age of the 100–95 Ma granitoids clusters between 1.25 Ga and 1.53 Ga. These isotopic data suggest that magmas of the Cretaceous granitoids were produced by partial melting of Mesoproterozoic metabasaltic rocks, which make up much of the crystalline basement of the southern Cathaysia block. The geochemical and isotopic characteristics of the Cretaceous granitoids on Hainan resemble those of magmatic arcs in the Circum–Pacific orogenic belts and identical to those of nearly coeval granitoid intrusions in the continental fragments within the South China Sea basin. We interpret these Cretaceous granitoids in the Peri–South China Sea region as the remnants of a once contiguous Late Mesozoic magmatic arc system that bounded the southern margin of the entire continental Southeast Asia. Our findings do not support the existence of an episode of magmatic quiescence in the geological record of SE China during the Aptian.

Impact of long-term mining activity on groundwater dynamics in a mining district in Xinjiang coal Mine Base, Northwest China: insight from geochemical fingerprint and machine learning.

Long-term coal mining could lead to a serious of geo-environmental problems. However, less comprehensive identification of factors controlling the groundwater dynamics were involved in previous studies. This study focused on 68 groundwater samples collected before and after mining activities, Self-Organizing Maps (SOM) combining with Principal Component Analysis (PCA) derived that the groundwater samples were classified into five clusters. Clusters 1-5 (C1-C5) represented the groundwater quality affected by different hydrochemical processes, mainly including mineral (carbonate and evaporite) dissolution and cation exchange, which were controlled by the hydrochemical environment at different stages of mining activities. Combining with the time-series data, the Extreme Gradient Boosting Decision Trees (XGBoost) derived that the mine water inflow (feature relative importance of 40.0%) and unit goaf area (feature relative importance of 29.2%) were dominant factors affecting the confined groundwater level, but had less or lagged impact on phreatic groundwater level. This was closely related to the height of the water flow fractured zone and hydraulic connection between aquifers. The results of this study on the coupled evolution of groundwater dynamics could enhance our understanding of the effects of mining on aquifer systems and contribute to the prevention of water hazards in the coalfields.

Pyrite geochemical fingerprinting on skarn ore-forming processes: A case study from the Huangshaping W–Sn–Cu–Pb–Zn deposit in the Nanling Range, South China

Pyrite geochemistry has been extensively used to reveal ore-forming processes in diverse ore deposits, but its application in skarn systems is not well understood. The Huangshaping deposit in the Nanling Range (South China) uniquely develops W–Sn–Pb–Zn and Cu–Pb–Zn skarn mineralization systems, and both two systems have formed multi-types of pyrite, which provides a good window to reveal the mineralization histories of different skarn systems using pyrite trace element geochemistry. In the Cu–Pb–Zn system, texturally homogeneous Py1 mainly occurs in calcite veins within the host rock, whereas texturally homogeneous Py2 in the calcite-sulfide stage mainly occurs in skarn orebodies. Py3 in the siderite-sulfide stage replaces Py2 and commonly develops abundant pores or fractures, resembling the “bird's eye” texture. In the W–Sn–Pb–Zn system, Py4 in calcite veins can be divided into the oscillatory-zoned Py4a and irregular Py4b under BSE, and Py4b commonly replaces Py4a as veins or overgrowth. Texturally homogeneous Py5 in the calcite-sulfide stage occurs in skarn orebodies and is replaced by Py6 with a “bird's eye” texture in the siderite-sulfide stage.In the Cu–Pb–Zn system, Py1 may have formed by fluid cooling during its ascent along the hydraulic fractures indicated by its enrichment of Co, Ni, As, Sb, and Tl, whereas Py2 is likely formed under higher temperature and pH conditions caused by intense fluid-rock interactions evidenced by its depletion of Co, Ni, As, Sb, and Tl as well as its enrichment of Zn and Ag. In the W–Sn–Pb–Zn system, Py4b has higher contents of Co, Ni, As, Sb, and Tl than Py4a and similar contents of Ag, Zn, and Mo with Py4a, suggesting that decreasing temperature may have controlled the formation of Py4b. Py5 is featured by the depletion of As, Sb, Tl, and Mo as well as the enrichment of Zn and Ag, indicating that Py5 is likely formed under higher temperature and pH conditions resulting from the intense fluid-rock interactions. Marcasite replaces pyrrhotite and then is replaced by pyrite may be an important precipitation mechanism for pyrite with a “bird's eye” texture (Py3 and Py6) in both two skarn systems at Huangshaping. This study demonstrates that fluid-rock interaction is an important mechanism for sulfide precipitation at Huangshaping, which shows that pyrite geochemistry has good potential to reveal mineralization histories in skarn systems.