Geochemical Composition Research Articles

Are enhanced rock weathering rates overestimated? A few geochemical and mineralogical pitfalls

There is considerable uncertainty when quantifying carbon dioxide removal (CDR) from enhanced rock weathering (ERW). Faster CDR rates mean ERW may significantly impact climate change mitigation, and more carbon credits will financially benefit private companies. However, overestimating CDR risks undermining ERW if meaningless carbon credits are counted. Here, we aim to contribute to the discussion of CDR quantification by describing three potential pitfalls relating to the geochemical and mineralogical compositions of rock powders. First, rock powders used for ERW are often mineralogically complex and may initially exhibit fast dissolution rates due to reactive surfaces and phases, leading to overestimating long-term CDR rates. Second, the dissolution of accessory carbonates within ERW rock powders will tend to dominate cation and dissolved inorganic carbon fluxes, which, if not identified, can be misconstrued as silicate weathering and overestimate CDR. Third, methods that rely on measuring cations may be prone to misinterpretation as cations will often not be balanced with dissolved inorganic carbon, e.g., during strong acid weathering. As another example, mineral dissolution during solid-phase testing (e.g., cation exchange) is also unrelated to carbonic acid weathering and, thus, may overestimate CDR rates. To avoid these pitfalls, we recommend (1) incorporating high-dosage test plots into ERW trials that avoid reapplication of rock powders that replenish initially fast reactivity, (2) screening rock powders for carbonate minerals using sensitive techniques and distinguishing carbonate and silicate weathering, and (3) measuring carbon to verify carbon dioxide removal. High-quality carbon credits must be durable, additional, and not overestimated.

Formation mechanism of boehmite and diaspore in karstic bauxites: trace element geochemistry in source materials using large sample geochemical dataset and random forest model

Abstract Boehmite and diaspore are the two economic ore minerals of karstic bauxites. Although their genesis has been studied from different perspectives, their formation mechanism is controversial. Random forest (RF) model of machine learning was employed to extract the combining characteristics of trace elements in boehmite-type bauxite (BTB) and diaspore-type bauxite (DTB). The BTB predominantly exhibits higher median concentrations of Co, Ni, V, and Cr, while the DTB exhibits a more significant enrichment in elements of U, Hf, Th, and Zr. Combining the characteristics of La/Yb and Ga/Al ratios, it is found that disparities between BTB and DTB are mirroring to those between basic rocks and intermediate-felsic rocks. Furthermore, the Zr-Cr-Ga diagram and Ni/Zr versus Cr/Zr plot were utilized to examine the correlation between karstic bauxite (BTB or DTB), lateritic bauxite, and their respective weathered parent rocks. It is found that BTB exhibits consistent characteristics with lateritic bauxite weathered from basic rock and its parent rocks. Similarly, DTB displays consistent characteristics with lateritic bauxite weathered from intermediate-felsic rock and its parent rocks. Through studying the relationship between Ni content and Fe3+/Fe2+ ratios, it has been discovered that the presence of trace elements like Ni in source materials can affect or regulate ore-forming process, ultimately driving the transformation of gibbsite into either boehmite or diaspore. Consequently, the formation of BTB and DTB is significantly influenced, or even governed, by the composition of their source materials. Our study initially highlights a novel insight into the significant impact of source material’s geochemical composition on the formation of boehmite and diaspore, which is associated with weathered igneous rocks categories.

Analysis of impact of anthropogenic factors on the landscape-geochemical state of the Nura river basin

The study examines the formation of anthropogenic landscapes under the influence of multiple factors, including pollutants, radioactive substances, radiation, noise, and the extraction of natural resources. Society's transformation of natural landscapes into anthropogenic ones has become a global phenomenon, acquiring new characteristics due to scientific and technological advancements in mining, industrial chemistry, and agriculture. The Nura River basin, dominated by the metallurgical complex of Qarmet, serves as a key area for this investigation. This enterprise is the largest mining and metallurgical facility in Kazakhstan, producing a range of materials, including coated metals and raw industrial products. Geochemical analyses were conducted within the Nura River basin to assess the environmental impact of industrial activities. Water and soil samples were collected systematically, and pollutant concentrations were determined using accredited laboratory methods. Data were processed through statistical analysis to identify patterns and causal relationships. The research revealed significant pollution in the Nura River basin, predominantly caused by industrial discharges containing heavy metals and other contaminants. Elevated concentrations of pollutants were linked to the metallurgical activities of Qarmet and other industrial enterprises. The transformation of natural landscapes into anthropogenic ones was found to be closely associated with the intensity of these activities. The study highlights the critical influence of industrial processes on the geochemical composition of landscapes within the Nura River basin. The findings underline the need for improved environmental management, including the modernization of industrial processes and waste treatment systems, to mitigate anthropogenic impacts and ensure sustainable development in the region.

Geochemistry and formation conditions of the natural water composition in the nothern outskirts of Kazan

Kazan is located on the left bank of the Kuibyshev water reservoir in the east of the Russian Plain. The Blue Lakes, which are unique salt-water karst lakes in the Middle Volga region, appear to be a real natural treasure in the northern outskirts of the city. On the basis of field and analytical data obtained in 2023, the geochemical composition of the natural water is studied in the Blue Lakes, the Solonka and Kazanka rivers, uprising springs, and snow cover. Significant variations in the hydrochemical field are controlled by the effect of discharging relatively deep sulfate calcium groundwater from the lower Permian carbonate-sulfate deposits with a mineralization of about 2.5 g/l. The shares of these artesian waters in the river discharge have been determined. They are about 80% for the mouth of the Solonka River in the initial period of summer low water and about 50–60% for the lower reaches of the Kazanka River in the initial period of winter low water. Maximum values of deep water inflows are observed in river valleys along fracture zones of submeridional and northeastern orientation. The stability of hydrochemical parameters in the studied water bodies over time is shown, which is due to a high rate of water exchange and a low anthropogenic impact on the environment. Complexes of microcomponents concentrated in artesian and near-surface waters have been identified. In artesian waters such components are: Ca, Sr, Mg, Li, U, Re, Se; and in the near-surface – K, Fe, Mn, Ba, As, Co. It is noted that in order to determine the degree of surface water pollution, it is important to take into account the conditions of their composition formation and to distinguish between excess concentrations caused by natural and anthropogenic factors.

Material source, sedimentary environment, and mineralization process of Shengzhou diatomite deposit in Eastern Zhejiang Province, China

ABSTRACT The Shengzhou diatomite deposit, located in the Shengzhou-Xinchang basin, is recognized as one of the largest diatomite deposits in China. The scanning electron microscopy (SEM-EDS), mineral compositions and elemental geochemistry of the samples were analysed to identify the nutrient sources, depositional environments, and mineralization process. Through scanning electron microscopy, the predominant diatom species observed are Aulacoseira granulata (Ehrenberg) Simonsen and Cyclotella shengxianensis Huang and Cai. The results of X-ray diffraction (XRD) analysis results indicate that the mineral composition of diatomite mainly consists of opal-A, quartz, clay minerals, feldspar, carbonate minerals, and pyrite. The results of XRF and ICP-MS analysis show that the content of SiO2 ranges from 59.11% to 69.44%, and the trace nutrient elements such as Mo, U, V, Co, Ni, Cu, and Zn are enriched. The correlation of geochemical composition between diatomite and Cretaceous volcanic rocks in the study area indicates that the weathering of volcanic rocks provides nutrients for diatom growth. Multiple geochemical indicators (Sr/Ba, V/Cr, Ni/Co, U/Th, V/(V+Ni), C-value, CIA, and Sr/Cu) and palaeontological evidence indicate that the diatomite was formed in a freshwater, oxic, and hot-humid environment. As the diatomite is susceptible to denudation, the overlying basalt may protect the deposit.

Microbial diversity and biogeochemical interactions in the seismically active and CO2- rich Eger Rift ecosystem.

The Eger Rift subsurface is characterized by frequent seismic activity and consistently high CO2 concentrations, making it a unique deep biosphere ecosystem and a suitable site to study the interactions between volcanism, tectonics, and microbiological activity. Pulses of geogenic H2 during earthquakes may provide substrates for methanogenic and chemolithoautotrophic processes, but very little is currently known about the role of subsurface microorganisms and their cellular processes in this type of environment. To assess the impact of geologic activity on microbial life, we analyzed the geological, geochemical, and microbiological composition of rock and sediment samples from a 238m deep drill core, running across six lithostratigraphic zones. We evaluated the diversity and distribution of bacterial and archaeal communities. Our investigation revealed a distinct low-biomass community, with a surprisingly diverse archaeal population, providing strong support that methanogenic archaea reside in the Eger subsurface. Geochemical analysis demonstrated that ion concentrations (mostly sodium and sulfate) were highest in sediments from 50 to 100m depth and in weathered rock below 200m, indicating an elevated potential for ion solution in these areas. Microbial communities were dominated by common soil and water bacteria. Together with the occurrence of freshwater cyanobacteria at specific depths, these observations emphasize the heterogenous character of the sediments and are indicators for vertical groundwater movement across the Eger Rift subsurface. Our investigations also found evidence for anaerobic, autotrophic, and acidophilic communities in Eger Rift sediments, as sulfur-cycling taxa like Thiohalophilus and Desulfosporosinus were specifically enriched at depths below 100m. The detection of methanogenic, halophilic, and ammonia-oxidizing archaeal populations demonstrate that the unique features of the Eger Rift subsurface environment provide the foundation for diverse types of microbial life, including the microbial utilization of geologically derived CO2 and, when available, H2, as a primary energy source.

Carbonate mineralogy and geochemistry of bryozoans along the South African coast

The main aim of this study was to investigate whether environmental or biological factors predominantly influence bryozoan biomineralization along the South African coast (spanning from 29.263°S; 16.87°E to 27.540°S; 32.677°E), a region known for its diverse oceanographic conditions. New data into the mineralogical (calcite vs. aragonite) and geochemical (Mg content in calcite) composition of bryozoans are provided, enhancing the global database and understanding of biomineralization patterns. To date, there has been a notable scarcity of data on bryozoan skeletal composition in tropical and subtropical regions, representing a significant gap in our knowledge and understanding of the impacts of climate change on marine, calcifying organisms. Our research reveals a diverse array of carbonate skeletons across nearly half of the known bryozoan species in the region, with calcitic forms dominating, followed by bimineralic and aragonite-based forms. The prevalence of aragonite-containing skeletons, particularly within the Cheilostomatida, mirrors global patterns, indicating a correlation with sea temperature gradients. Significant mineralogy and magnesium calcite variability exists within the Flustrina and Membraniporina suborders (Cheilostomatida). Despite exploring various environmental parameters such as temperature, salinity, or impact of currents (Agulhas, Benguela, or mixed), no clear correlation with mineralogical patterns emerged. Instead, the study underscores the substantial influence of biological control on bryozoan skeletal carbonate mineralogy and geochemistry. These findings highlight the importance of comprehensive, multi-parametric analyses to unravel environmental signals in bryozoan biomineralization, contributing to a deeper understanding of the impacts of climate and local conditions on marine calcifiers.

Electrical properties as a tool for oil and gas exploration: A case study of Wadi Saal, east Central Sinai, Egypt

Abstract Some rock samples (39) have been obtained from Wadi Saal, East Central Sinai, Egypt, for studying electrical, petrographical, and petrophysical parameters. The petrographal analysis shows two major facies. Carbonate (limestone) facies with low porosity (11%) and permeability (69 mD), and sandstone facies with high porosity (28%) and permeability (5901 mD) indicate good reservoir characteristics. Porosity values are related to the bulk density, whereas permeability is controlled by rock porosity and irreducible water saturation. Alternating current (AC) electrical properties were measured with frequency (42 Hz–5 MHz) for samples. Electrical characteristic differences are affected with texture changes, mineralogy, porosity, tortuosity, pore-water salinity, mineral concentrations, permeability, and fluid content. Conductivity and impedance decrease whenever an insulator is existed. The dielectric constant increases with conductor composition (below the percolation) and falls with frequency beyond it. The conductivity expands with the number of conductor pathways connecting the electrodes. The primary objective of this work is to use laboratory AC electrical measurements to shed some light on the relationship between the texture, petrography, petrophysics, and geochemical composition of materials (sandstone and limestone). The goal is to study electrical properties of these mixtures at varying clay concentrations and saturation levels. These analyses could enhance oil and gas recovery by shedding light on reservoir rock electrical characteristics.

Adhesion of Silicate Impact Melts on Impact Glasses of Chang'e‐5 Regolith

AbstractMicroscopic silicate melts are ubiquitous on surfaces of lunar regolith particles, and they record physicochemical processes of regolith reworking on the Moon. Similar microstructures are visible on surfaces of the Chang'e‐5 lunar impact glass particles, which are predominantly sourced from local mare deposits. Therefore, the microscopic silicate melts provide an invaluable opportunity to study the movements, provenances, and chemical alterations of substances involved in regolith reworking. However, the small lateral sizes and thicknesses of the surface silicate melts are a challenge for quantifying their internal structures and geochemical compositions, hampering interpretations of their origin. Here we report structural and geochemical characteristics for microscopic silicate pancakes, domes and foams on surfaces of Chang'e‐5 impact glass particles. Based on the contact and compositional differences between the surface microscopic silicate melts and their host glass, we reveal that these microstructures are consistent with being formed during impact bombardment in regolith via adhesion of impact melts to earlier‐existing glasses. Most of the microscopic silicate melts have minor compositional differences with the host glass. Our mixing calculations for compositions of impact melt formed from various proportions of local regolith minerals at the landing site reveal a dominant precursor from the local mare deposits. Few portions of the microscopic silicate melts have exotic compositions that are different from the local regolith materials, confirming that ejecta from the other geochemical terrains is minor at the landing site. Our results show that regolith formation and reworking at the Chang'e‐5 sampling site mainly involved local mare deposits.

Aqueous oxidation of coal-associated pyrite and standard pyrite mineral towards understanding the depyritization kinetics and acid formations

In coal mining areas, the ambient atmospheric and aqueous oxidation of pyrite minerals (FeS2) associated with coal as well as the other accompanying strata is significant in understanding the extent of acid mine drainage (AMD), the cause of severe environmental pollution. Therefore, in this paper, the oxidation kinetics of the coal-associated pyrite (CAPy) present in a coal sample (TpHM1) has been studied via aqueous leaching depyritization experiments at variety of temperatures and time intervals without the incorporation of any oxidizer. The outcomes obtained are juxtaposed with the standard pyrite mineral (SPM) oxidation at the same experimental conditions. Also, the coal and SPM slurry residues and filtrates obtained after aqueous leaching at 25 °C and 90 °C for 0 h and 24 h, respectively, were extensively analyzed through high-resolution transmission electron microscopy (HR-TEM), Powder X-ray diffraction (P-XRD), and X-ray-photoelectron spectroscopy (XPS) for evaluation of the mineralogical composition and proportions of iron and sulfur components during progression of the oxidation reaction. Both the reactions obey pseudo first-order kinetics during pyrite (FeS2) oxidation but a significant difference in the experimentally found activation energies (Ea) and rate constants (k) values of oxidation kinetics of both CAPy and SPM may be attributed to the varied geochemical compositions of the coal associated pyrite (CAPy). The rate constant for CAPy is much greater than that of SPM implying a higher Ea around 10.838 kJ/mol for SPM as compared to 1.941 kJ/mol for CAPy. The CAPy in coal (TpHM1) is more susceptible to atmospheric oxidation than that of SPM, leading to the formation of acid mine drainage with lower pH. In this paper, the pH values on the basis of stoichiometric pyrite oxidation reaction were calculated and compared with the pH values obtained after aqueous leaching of CAPy to interpret the extent of acid formation and pyrite dissolution. Hence, with the assistance of the current study, further studies on the effects of mineral impurities, whereabouts of pyrite minerals in coal seams, the significance of compositional differences in the CAPy, the effect of metal oxides, and the role of alkalinity producing neutralizing agents of coal in the oxidative dissolution process of pyrite can be investigated.

Geochemical composition of suspended sediments generated after erosive rainfall events in nested agroforestry catchments with Mediterranean climate

Geochemical composition of suspended sediments generated after erosive rainfall events in nested agroforestry catchments with Mediterranean climate

Validating ex210Pb sediment dating methods applied to a large anthropogenically-impacted river basin

Sediment dynamics in five sites within the Mobile River Basin, Alabama, impacted by (i) dam-and-lock use, (ii) urbanization, (iii) industrial/mining practices, (iv) flooding, and (v) storm surge events were evaluated to understand better anthropogenic impacts on regional sediment budgets. Three widely used sediment dating models based on excess 210Pb (ex210Pb) (i.e., Constant Rate of Supply, CRS, Constant Initial Concentration, CIC, and Advective Dispersion Equation, ADE) and two recently developed ones (i.e., Porosity Variation, PV and Porosity Variation Without Diffusion, PVWD) were tested to determine their applicability to these anthropogenically altered lacustrine and coastal areas. To verify results from ex210Pb models, we used conventional time markers, including regional hydrograph records and historical aerial images. We found that the traditional time-marker 137Cs is no longer helpful due to its current low inventories in the sediments. Drainage-to-lake area ratios were used to determine relative runoff and atmospheric radionuclide contributions. Statistical analysis of physical properties such as porosity, bulk and dry density, water content, and sediment geochemical compositions were utilized to support sediment transport and site development hypotheses. When constructing the sediment history at each site using these proxies, we found that the conventional CIC and ADE models produced unreliable ages because of violation of requirements for exponentially decreasing porosity and ex210Pb activity with depth. We found that two new models, PV and PVWD, that account for heterogeneous porosity, produced more reliable sediment ages. These two models produced ages with lower uncertainties than the CRS model, outperforming the other conventional models tested. We conclude that the PV and PVWD models are more appropriate for environments experiencing erosional and abrupt depositional events, which in our study resulted from dam construction and storm-surge events. Model sensitivity analysis showed that decreasing average particle density produces younger sediment ages by the PV and PVWD models. Higher ex210Pb activity analytical uncertainty resulted in lower sedimentation rates and higher estimated ages by all five models.

Monitoring of hydrogeochemistry and hydrological isotopes in karst springs of Tezbent Plateau, Tebessa region, north-east of Algeria

The karst springs of Tezbent Plateau were studied to gain insight into the hydrogeological and hydrodynamic behaviour of this karstic system. Four springs and six domestic wells were analysed for hydrogeochemical constituents, δ18O, and δ2H from September 2021 to June 2022. The Tezbent mountain range, located in northeastern Algeria, drains carbonate aquifers through several significant karst springs. The physical and chemical characteristics of water samples were analysed in order to assess the groundwater origins and identify the factors influencing its geochemical composition. Ionic speciation and mineral dissolution/precipitation were calculated. It was found that geology, specifically the presence of carbonate formations, elevation, and the rate of karst development, are the primary factors influencing groundwater composition and seasonal variations. The carbonate chemistry serves as a diagnostic indicator of karst development effects. The interaction between groundwater and surrounding host rocks is believed to be the primary process influencing the observed chemical characteristics of groundwater in the study area. The δ18O and δ2H values of groundwater samples indicate the meteoric origin of the groundwater recharge and suggest a minimal evaporation impact on the isotopic composition.

Environmental degradation and recovery after termination of whaling in sub-Antarctic fjord, South Georgia

Polar ecosystems are considered very fragile, however, due to the short observation record it is hard to assess the recovery processes of the coastal and fjord environments after a major disturbance. Here, we provide a unique case study from South Georgia (sub-Antarctic), an area seriously affected by the whaling industry. The study focuses on King Edward Cove, serving as a sheltered harbor for the former whaling station at Grytviken, as well as other parts of Cumberland Bay considered to represent generally pristine areas. We studied 210Pb dated sediment cores, which were subjected to analysis of sediment geochemical composition, concentrations of anthropogenic organic markers and biomarkers, foraminiferal assemblage changes, as well as sedimentary ancient DNA. Three distinct phases have been identified. The oldest one, predating ca. 1970, recorded the whaling period, and was characterized by anoxic conditions, high organic carbon content, contamination with heavy metals, organic markers, distinct DNA signature and lack of foraminiferal microfossils. It took only a few years to establish a new ecosystem with a fully developed foraminiferal assemblage and decreased contamination characteristic for the middle phase (ca. 1970–2000). Ancient DNA suggests macro-zoobenthic recovery being delayed by a several years in comparison to benthic foraminifera. In the youngest period, around Cumberland Bay, the increase of iceberg rafted debris from rapidly retreating tidewater glaciers was noted, while the improved oxygen availability in bottom waters in King Edward Cove can be likely ascribed to frequent water mixing due to increasing traffic of large cruise vessels. The recorded pace of ecosystem recovery from major anthropogenic disturbance appears similar to that observed in the temperate fjords from the Northern Hemisphere, however, the effects of new anthropogenic threat and the ongoing climate change are already resulting in the new ecosystem disturbance.

Morphology, epidermal features and δ13C signature of Lopingian (late Permian) conifers

Conifers, the most successful group of Permian gymnosperms, dominate the famous Bletterbach (Dolomites, NE-Italy) plant fossil assemblage, a highly diverse and well-documented late Permian (Lopingian) flora. An integrated analysis of morphology, cuticles and isotope geochemistry was carried out on approximately 50 conifer shoots across five genera (Ortiseia, Majonica, Dolomitia, Pseudovoltzia and Quadrocladus) and eight species, including three (Pseudovoltzia sjerpii, Quadrocladus solmsii, Quadrocladus cf. orobiformis) described for the first time from Bletterbach. Taxon-specific carbon isotope analyses reveal intra-specific and/or intra-generic variability, identifying a unique geochemical composition for Majonica alpina, which may reflect a possible species-specific geochemical signature or adaptation to particular environmental conditions. The isotopic differences observed between leaves and axes indicate the preservation of distinct isotopic ratios in photosynthetic versus heterotrophic tissues, underscoring the importance of sampling multiple plant parts to accurately capture individual and taxonomic isotopic variability. The study of stable isotopes of organic carbon on well-preserved plant remains is enhanced the paleoenvironmental reconstruction of the Bletterbach flora.

Lateritization and enrichment of ferruginous protore during the peneplanation between uplifts – the case of Mekaneselam iron deposit, NW Ethiopian plateau

ABSTRACT Mekaneselam iron deposit is located in the NW Ethiopian Plateau. The area is constituted by limestone at the bottom followed by mudstone, sandstone and basalt at the top. Geological mapping, geochemical, mineralogical and stratigraphic investigations were conducted to explain the genesis of the deposit. The orebody is hosted by the quartz arenitic Upper Sandstone. At places where the sandstone is removed by erosion the orebody is unconformably overlain by basalt. It occurs as stratified bed and massive (the primary ore orebodies), and lateritic residual to reworked clastic varieties (the secondary/residual ore bodies). The dominant ore minerals are hematite and goethite with gangue minerals quartz and kaolinite. Geochemical composition is dominated by Fe2O3 and SiO2 with subordinate amount of Al2O3. The alkalis and alkaline earth elements were not detected in almost all samples. The stratigraphy, orebody morphology, mineralogy and geochemistry suggest that mineralization was a two-stage process. A primary ore deposition took place during sedimentation of the host sandstone and formed a ferruginous protore. This was later upgraded through deep tropical weathering and lateritization. The supergene process is believed to be facilitated by the relatively long-term peneplanation happened in Ethiopia after the Cretaceous and before the plume-induced Oligocene uplifts of East/Northeast Africa.

Time-Dependent Evolution And Source Heterogeneities of Ocean Island Basalts From a Weak Plume, São Jorge, Azores

Abstract The geochemical composition of ocean island basalts (OIBs) from the Azores (AZ) reflects the spatial distribution, shape and temporal evolution of small-scale geochemical heterogeneities within their mantle plume source. Here, we investigate the time-related evolution of volcanism at São Jorge Island, Central AZ. New field observations, a magnetic survey, 40Ar/39Ar and 14C ages and geochemical data indicate that the fissural volcanic activity at São Jorge produced at least four main mafic volcanic complexes (V. C.). The oldest V. C., São João, produced the thickest lava piles at ca. 1.3 Ma in the eastern part of the island. After a period of quiescence, the Serra do Topo V. C. was produced at ca. 0.8–0.5 Ma in the central part of the island. The Rosais V. C. was emplaced between ca. 0.4 and 0.1 Ma on the entire island. Finally, the Holocene Manadas V.C. volcanism became active in the western part of the island and includes three historic eruptions (1580, 1808 and 1964 CE). Magmas were formed at low melting degrees from a peridotitic mantle with possible minor contributions of recycled components. Olivine compositions and whole-rock trace element ratios discard a significant contribution from pyroxenitic source rocks. Melting temperatures (ca. 1420–1480 °C) were slightly higher than those of the ambient upper mantle. The four V.C. are characterized by distinct geochemical compositions in terms of incompatible trace elements and Sr-Nd-Pb isotopic ratios. The oldest V.C., São João, is characterized by Pb isotopic compositions (e.g. markedly negative Δ7/4 and 8/4 values) plotting well below the Northern Hemisphere Reference Line (NHRL). The Upper Pleistocene (Rosais V.C.) lavas from the north-western cliffs have compositions similar to enriched mantle (EM) end-member basalts (e.g. high 207Pb/204Pb at moderate 206Pb/204Pb; high Ba/Nb), which are rare among northern hemisphere OIBs. Finally, high 206Pb/204Pb (up to 20), reflecting contribution from a HIMU-type component characterizes the Holocene Manadas lavas and is occasionally found in lavas from other VCs from 1.3 to 0.1 Ma. These findings indicate that magmas from São Jorge and the nearby Central AZ islands were sourced from a strongly heterogeneous mantle plume, which displayed localized filaments of heterogeneous material that were rapidly exhausted (in ca. 0.2 Ma). The dominant component at São Jorge and in the Central AZ in general appears to be the HIMU-type end-member, which instead is not significant in the Eastern AZ. Possibly, the Central and Eastern AZ were produced by distinct branches of the AZ mantle plume, as would also be consistent with previous tomographic studies.

Recycling of subducted continent slab in an accretionary orogen: Insight from the Liangwan potassic granitoids in the Tongbai orogen, Central China

Granitoids provide a vital window to probe the lithological configuration and chemical evolution of orogenic belts. In this contribution, we present an integrated study of mineral compositions, zircon UPb ages and HfO isotopes, titanite UPb ages and SmNd isotopes, as well as whole-rock element and Sr–Nd–Hf isotope compositions of the Liangwan granitic pluton in the northern Paleozoic accretionary orogenic unit of the Tongbai orogen, central China. The Liangwan pluton is composed mainly of monzogranites and contains abundant mafic microgranular enclaves (MMEs). The monzogranites have relatively high silica contents (SiO2 = 67.40–69.91 wt%) and mainly exhibit shoshonite to high-K calc-alkaline and metaluminous features. The MMEs have similar mineral and geochemical compositions and zircon and titanite UPb ages of ca. 129 Ma to the monzogranites, suggesting that they are likely early-crystalized cumulates of the host monzogranites. The MMEs and monzogranites are both characterized by enrichment of large ion lithophile elements but depletion of high field-strength elements. The monzogranites have whole-rock initial Sr (Isr) of 0.7069–0.7074, εNd(t) of −14.2 to −13.7, and εHf(t) of −17.5 to −17.2, zircon εHf(t) of −17.8 to −17.0 and δ18O values of 5.27–5.98 ‰, and titanite εNd(t) of −14.50 to −13.78. These features are distinct from the rocks in the northern Tongbai accretionary orogenic unit but similar to those of the post-collisional granitoids in the southern Tongbai collisional orogenic unit. The Liangwan pluton was likely stemmed from the subducted South China Block (SCB) underneath the northern segment of the Tongbai orogen. Our results show that the subducted continental mass can act as an alternative source for the magmatic rocks occurred in the accretionary unit.

Variation in the Composition of Municipal Solid Waste Incineration Ash

Unlike municipal solid waste bottom ash (MSWBA), fly ash (MSWFA) is landfilled due to its toxicity. However, MSWFA may also be a source of elements. Ash samples collected from a Portuguese MSW incinerator from different locations and over six months were analyzed. Their geochemical composition was normalized to the upper continental crust (UCC) and compared since metal enrichment may be used as an indicator for potential recovery. The potential recovery economic viability was also assessed for metals K, Sb, Cu, Pb, and Zn, considering the ore cut-off grade and minimum industrial grade (MIG) from Chinese geological and mineral industry standards. Compared to the global samples, only the Baghouse 1 FA size fraction’s coarse fraction showed a slight enrichment (1- to 5-fold) in Bi, Nb, and Zr. After wet sieving, most trace elements were enriched in all fractions, but Sb, Bi, Pb, Zn, Ag, As, Cd, Sn, Se, and Hg were depleted in the coarse fractions and enriched in the fine ones. For Baghouse 1 samples collected over 6 months, the normalization to the UCC showed enrichment of Zn and Pb between 10× and 50×, Zr, Cu, In, and Se between 50× and 100×, and Ag, Mn, Cd, Sb, and Bi at more than 100×. Over six months, the Baghouse 1 FA soluble fraction ranged between 21 wt.% and 30 wt.%, and its precipitates comprised 27% CaO, 6% Na2O, and 9% K2O. The K concentration in the MSWFA was above the cut-off and the MIG, and K could be concentrated in precipitates via simple washing.

Land-Use Impacts on Soil Erosion: Geochemical Insights from an Urban Drinking Catchment, South-Central Chile

We investigate the influence of land use and land cover (LU/LC) changes on soil erosion and chemical weathering processes within the Nonguén watershed in the Coastal Cordillera of south-central Chile. The watershed is divided into three sub-basins, each characterized by distinct LU/LC patterns: native forest and exotic plantations. A comprehensive geochemical analysis, including trace elements and lithium (Li) isotopes, was conducted on river water and suspended sediment samples collected from streams within these sub-basins to assess how land management practices, particularly plantation activities, influence the geochemical composition of river systems. Our results show that sub-basins dominated by exotic plantations exhibit significantly higher concentrations of major and trace elements in suspended sediments compared to sub-basins dominated by native forests. The elevated trace element concentrations are primarily attributed to increased physical erosion due to forestry activities such as clear-cutting and soil disturbance, which enhance sediment mobilization. Notably, concentrations of elements such as Fe, Al, and As in plantation-dominated sub-basins are raised to ten times higher than in native-dominated sub-basins. In contrast, sub-basins with native forest cover exhibit lower levels of sediment transport and trace element mobilization, suggesting that native vegetation exerts a stabilizing effect that mitigates soil erosion. Despite the substantial differences in sediment transport and element concentrations, Li isotopic data (δ7Li) show minimal fractionation across the different LU/LC types. This indicates that land use changes impact the chemical weathering processes less compared to physical erosion. The isotopic signatures suggest that physical erosion, rather than chemical weathering, is the dominant process influencing trace element distribution in plantation-dominated areas. The study provides critical insights into how forestry practices, specifically the expansion of exotic plantations, accelerate soil degradation and affect the geochemical composition of river systems. The increased sediment loads, and trace element concentrations observed in plantation-dominated sub-basins, raise concerns about the long-term sustainability of forest management practices, particularly regarding their impacts on water quality in urban catchment areas. These results are of significant relevance for environmental management and policy, as they underscore the need for more investigation and sustainable land use strategies to minimize soil erosion and preserve water resources in regions undergoing rapid LU/LC changes.