Guangzhou Institute of Geochemistry
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A new calcite reference material for <i>in situ</i> oxygen isotope analysis using secondary ion mass spectrometry: development and application constraints
No full textThe oxygen isotopic microanalysis of calcite is essential for obtaining high spatial resolution data linked to microstructures, a challenge for conventional techniques. This analysis, however, relies heavily on matrix-matched reference materials, of which only a few calcite standards are available. In this study, an inorganically precipitated calcite vein sample (WS-1) was evaluated through 225 SIMS oxygen isotope analyses and was found to have a homogeneous isotopic composition, with an external reproducibility <= 0.21 parts per thousand (1 sigma), suggesting its potential as a SIMS reference material. The precise delta 18OVPDB value, determined via traditional gas-source IRMS, was -16.52 +/- 0.13 parts per thousand (1SD). Matrix effects were assessed using various carbonates, including abiotic aragonite (VS001/1-A), three abiotic calcites (NBS18, Cal-1, WS-1), and a high-Mg calcite (gorgonian coral). The results revealed negligible matrix effects between abiotic aragonite and calcites but significant differences between calcites and high-Mg calcite, likely due to Mg content or differences in biogenic crystal morphology and trace organic composition. This study demonstrates the utility of in situ oxygen isotopic microanalysis for calcite but emphasizes the need for caution when analyzing high-Mg calcitic skeletons
Deciphering the key drivers of oxidative potential during ammonium nitrate-mediated aqueous-phase photoreaction of methoxyphenols
No full textMethoxyphenols are released in abundance from lignin pyrolysis during biomass burning. Apart from being atmospheric brown carbon components that absorb solar radiation and warm the climate, methoxyphenols also undergo photoreaction in the atmospheric aqueous phase and form secondary organic aerosols (aqSOA). While efforts have been devoted to understanding chemical evolutions and climate-related optical properties of aqSOA, their potential health impacts also require timely investigations. Herein, we used the dithiothreitol (DTT) assay to investigate oxidative potential of the aqSOA formed during the 8-h aqueous-phase photoreaction of two typical methoxyphenols, vanillin and vanillic acid, under pH 2 or 8, and with or without ammonia nitrate. The highest DTT consumption rates (RDTT) were observed for vanillin aqSOA formed in the presence of ammonia nitrate and at pH 8. At pH 2, although RDTT increased rapidly during early photoreaction, it reduced after prolonged illumination. High-resolution mass spectrometry and linear regression analyses were performed to correlate the photoreaction products with the observed RDTT. Results showed that three products that present quinone, lactone and dimer structures, respectively, should be the key drivers of elevated RDTT for aqSOA formed during photoreaction of vanillin and vanillic acid alone, whereas it shifted to the nitrogen-containing aromatic compounds during their photoreaction with ammonia nitrate. Our results have revealed the role of nitrogencontaining aromatic compounds in the oxidative potential and health effects of aqSOA from biomass burning, which was rarely recognized before and warrants immediate assessments
Substitution mechanism controls on compositional variations and spectral responses of white micas in major hydrothermal systems
No full textWhether the shorter or longer wavelengths of diagnostic absorption features of white mica serve as a better vector to mineralization remains controversial. This uncertainty stems from a limited understanding of the compositional substitution mechanisms that control spectral variations. This study compiled published datasets of white mica with both available composition and spectroscopy data from five major hydrothermal systems, including porphyry, epithermal, skarn, orogenic, and volcanogenic massive sulfides (VMS) deposits. Three types of white micas, each dominated by distinct substitution mechanisms-interlayer-dominated (Na+ K+, and Ca2+, Ba2+ 2 K+), Tschermak-dominated (Al-VI(3+) + Al-IV(3+) Fe-VI(2+), Mg-VI(2+) + Si-IV(4+)), and illitic-dominated (K+ + Al-IV(3+) Si-IV(4+) + [](interlayer))-have been identified, accounting for the observed inconsistencies in spectral responses. The interlayer substitution is associated with shorter absorption feature ( 2215 nm) with delta vibration. Tschermak-dominated white mica is the most widespread among diverse systems. Illitic substitution, however, leads to compositional changes that are not detectable in shortwave infrared (SWIR, 1300-2500 nm) regions, thus rarely providing vectoring indicators. This study suggests that data from white mica characterized by different dominant substitution mechanisms should be distinctly evaluated, thereby enhancing the efficacy of SWIR spectroscopy for mineral exploration
Substitution mechanism controls on compositional variations and spectral responses of white micas in major hydrothermal systems
No full textWhether the shorter or longer wavelengths of diagnostic absorption features of white mica serve as a better vector to mineralization remains controversial. This uncertainty stems from a limited understanding of the compositional substitution mechanisms that control spectral variations. This study compiled published datasets of white mica with both available composition and spectroscopy data from five major hydrothermal systems, including porphyry, epithermal, skarn, orogenic, and volcanogenic massive sulfides (VMS) deposits. Three types of white micas, each dominated by distinct substitution mechanisms-interlayer-dominated (Na+ K+, and Ca2+, Ba2+ 2 K+), Tschermak-dominated (Al-VI(3+) + Al-IV(3+) Fe-VI(2+), Mg-VI(2+) + Si-IV(4+)), and illitic-dominated (K+ + Al-IV(3+) Si-IV(4+) + [](interlayer))-have been identified, accounting for the observed inconsistencies in spectral responses. The interlayer substitution is associated with shorter absorption feature ( 2215 nm) with delta vibration. Tschermak-dominated white mica is the most widespread among diverse systems. Illitic substitution, however, leads to compositional changes that are not detectable in shortwave infrared (SWIR, 1300-2500 nm) regions, thus rarely providing vectoring indicators. This study suggests that data from white mica characterized by different dominant substitution mechanisms should be distinctly evaluated, thereby enhancing the efficacy of SWIR spectroscopy for mineral exploration
Coexisting hematite induces and accelerates the transformation of ferrihydrite: Pathway and underlying mechanisms
No full textCrystallization induced by heterogeneous surfaces is an important process in geochemistry, biomineralization, and material synthesis, but the effects of heterogeneous surfaces on the transformation of metastable phases into new crystals remain poorly understood. In this work, we studied the transformation behaviors of ferrihydrite (Fhy) in the presence of hematite (Hem) nanoplates with specific exposed facets ({001} and {113}) at different pH (4, 7, and 12). Our results reveal that the Hem nano-plates can induce the transformation of Fhy to Hem/Gth (goethite) and accelerate the transformation rate. This effect is primarily achieved by modulating the dissolution-recrystallization process, i.e., accelerating the dissolution of Fhy and promoting the heterogeneous crystallization (to form new Hem/Gth) at the surface of added Hem nanoplates, and solution pH plays a crucial role in these processes. Specifically, a relatively low supply of dissolved Fe3+ from Fhy at pH 4 favors island growth of new Hem at the {001} facets of Hem nanoplates and layer-by-layer growth at the {113} facets, which eventually results in the formation of thermodynamically stable pseudo-cubic morphology (exposing {012} facets). Because of the very low solubility of Fhy at pH 7, the induced transformation of Fhy by Hem nanoplates is relatively weak. While at pH 12, a high supply of dissolved Fe3+ from Fhy benefits the layer-by-layer growth at {001} facets of Hem and the significant heteroepitaxial growth of Gth at the {113} facets. Besides the induced transformation, the direct solid-state transformation of Fhy into Hem and the homogeneous crystallization of dissolved Fe3+ also contribute to the transformation of Fhy. This study reveals the mechanisms of induced transformation of Fhy in the presence of Hem nanoparticles, which will advance our understanding of the significant effects of heterogeneous surfaces in modulating metastable phases and supplement the transformation mechanisms of Fhy
Iron isotope fractionation during transcrustal magmatic differentiation: Implications for continental crustal formation in subduction zones
No full textEarth's continental crust is hypothesized to originate from mantle melting in subduction zones. However, mantle melts are typically Fe-rich, with light Fe isotopes (delta Fe-56 = 0.05 parts per thousand), unlike the Fe-depleted and heavy Fe isotope (delta Fe-56 can be up to 0.2 parts per thousand) compositions of continental crust. The mechanisms responsible for this paradox remain elusive. Here, we report Fe isotope data from a suite of co-magmatic Middle Triassic continental arc rocks in the Ailaoshan tectonic zone (Yunnan, SW China). Gabbroic diorites have light Fe isotopes (delta Fe-56 = 0.04 parts per thousand-0.09 parts per thousand), while granodiorites and normal-arc granites have slightly heavier values (delta Fe-56 = 0.07 parts per thousand-0.14 parts per thousand). Adakitic granites, with high Sr/Y (61-183) and La/Yb (47-90) ratios, exhibit the heaviest delta Fe-56 (0.16 parts per thousand-0.19 parts per thousand). Rayleigh fractionation modeling results suggest that fractionation of isotopically light Fe minerals (e.g., olivine, pyroxene, and amphibole) can reproduce the Fe isotopic variations in most samples, but fails to explain the high Sr/Y, La/Yb, and delta Fe-56 values of adakitic granites, which would require Fe-rich garnet fractionation. Notably, the different Fe isotopes of the adakitic granites and non-adakitic rocks reveal two distinct transcrustal magmatic differentiation pathways: lower crustal, high-pressure, garnet-dominated fractionation; and middle-upper crustal, amphibole-dominated fractionation. The heavy Fe isotopic and Fe-depleted characteristics of the Ailaoshan magmatic arc suites are more comparable to the calc-alkaline arc magmas from normal to thick crust arcs (e.g., the Andean arc), but remarkably different from the tholeiitic arc magmas from thin crust arcs (e.g., the Mariana arc). This study highlights the role of amphibole and garnet fractionation in magmatic calc-alkaline differentiation. We propose that a thickened crust would permit a longer magmatic differentiation column, thus facilitating felsic and Fe-depleted continental crustal formation. The fractionated Fe-rich, garnet-bearing arc cumulates with light Fe isotopes are density-unstable and may be recycled into the mantle by lower crustal foundering
Hydrothermal origin of platinum-group minerals during serpentinization of the podiform chromitites from the Kizildag ophiolite in southern Turkiye
No full textPlatinum-group minerals (PGMs) in podiform chromitites usually occur in the interior and/or edge of chromite. However, the origin of PGMs in podiform chromitites has long been a matter of debate. Here we examined sub-micro to nanoscale textural features, morphologies, and compositions of PGMs from the disseminated, banded, massive and nodular chromitites in the Kizildag ophiolite in southern Turkiye, and found both primary and secondary PGMs. The aim of this study is to reveal the transformation processes from primary to secondary PGMs, thereby taking a thorough examination of the origin of these PGMs. Primary PGMs include laurite and Os-Ir alloy, which are prevalent in all samples. They are typically enclosed within or located at the edge of chromite, and formed either prior to or contemporaneously with the crystallization of chromite at temperature of 1100-1200 degrees C and logfS(2) values of -2 to -1. In contrast, PGE-bearing pentlandite are commonly present at the edge of chromite, corresponding to an increase of fS(2) with the progressive crystallization of chromite. These primary PGMs and PGE-bearing pentlandite in the intergranular space of chromite are susceptible to alter and transform into secondary PGMs and base metal mineral assemblages, which include Os-Ru nanophases (Os-Ru nanoparticle and OsRu3 nanoalloy) + awaruite (FeNi3) + trevorite (Fe2NiO4) in nodular chromitite, Os-rich laurite + Os-Ir(Ru) alloy/oxide + pentlandite + millerite (NiS) in banded and massive chromitite, and Ru(Ir) oxide + heazlewoodite (Ni3S2) in disseminated chromitite. The development of these diverse assemblages can be attributed to the degrees of serpentinization of chromitites. The nodular chromitite underwent weak serpentinization and had low water/rock ratios (<similar to 1), fS(2) and fO(2), leading to the conversion of IPGE (Os, Ir and Ru)bearing pentlandite into Os-Ru nanoparticle- and OsRu3 nanoalloy-bearing awaruite. The massive and disseminated chromitites had high water/rock ratios and high fS(2) and fO(2) relative to those of the nodular chromitite during serpentinization, and consequently the corresponding pentlandite was transformed into heazlewoodite and/or millerite associated with S loss. Meanwhile, Ir, Os and possibly Ru were released from laurite to form Os-Ir(Ru) alloy/oxide at the edge of laurite. Our observation highlights that primary PGMs and pentlandite in the chromitites of the Kizildag ophiolite have been modified under different physical-chemical conditions during serpentinization, resulting in the formation of complex secondary PGMs and base metal mineral assemblages
Species-specific accumulation of microplastics in different bird species from South China: A comprehensive analysis
No full textMicroplastics are widespread in many bird species, but the inter-specific variations of microplastic contamination are still unclear. The present study measured microplastics in 24 bird species from South China and investigated the impacts of bird physiological and ecological traits on microplastic contamination. The median abundances of microplastics ranged between 5-167 particles per individual or 0.023-3.58 particles per g body weight. Approximately 60 % of microplastics were within the size range 20-50 mu m, with the primary polymer types of polypropylene (PP) and polyethylene terephthalate (PET). There was no significant correlation between microplastic abundances and bird body weights and trophic levels (delta N-15) in different bird species. Insectivorous birds had significantly higher abundances of microplastics smaller than 0.1 mm than granivorous, piscivorous, and carnivorous birds (p 1 mm) than other bird species. Microplastic contamination in different bird species was more influenced by diet source rather than trophic level and body weight. Potential ecotoxicological risks were observed for most insectivorous species in the preliminary risk assessment. Particular concern should be paid on insectivorous birds, which have been scarcely studied for microplastics but were at high exposure risks of microplastics among bird species
Onboard measurements of organic vapor emissions from river vessels under various operational conditions
No full textThe emission factors and characteristics of pollutants from river vessels are critical for understanding the environmental impact of ship emissions, particularly in inland waterways. However, research gaps remain regarding emissions of volatile organic compounds (VOCs) and intermediate-volatility organic compounds (IVOCs) from river vessels. In this study, we collected and analyzed organic vapor emissions, including nonmethane hydrocarbon (NMHCs), oxygenated volatile organic compounds (OVOCs) and IVOCs, from three river vessels under different operating conditions. The results show that the average emission factors of NMHCs, and IVOCs from river vessels are significantly higher than those from ocean-going vessels. Inland waterways' proximity to residential areas increases the risk of pollutant transport to urban environments, heightening the importance of managing river vessel emissions. Notably, older auxiliary engines displayed higher organic vapor emissions compared to main engines, underscoring the need for better control measures for aging engines. By analyzing the emission characteristics of organic vapors from river vessels, it was found that, unlike other pollution sources where C12 n-alkanes are the major contributors of IVOCs, the contributions of C12-C15 nalkanes in river vessel exhaust are similar, with C14 n-alkane having the highest contribution. OVOCs constituted more than 50% to ozone formation potentials of organic vapors, while IVOCs were responsible for over 90% of the secondary organic aerosol (SOA) formation. Given these findings, targeted efforts to reduce OVOCs and IVOCs emissions from river vessels should prioritized to mitigate their environmental impact
Bimetal-organic framework derived single-atom-like Co/Fe catalysts for peroxydisulfate activation: The dual amplification of radical and nonradical pathways
No full textA novel single-atom-like Co/Fe catalyst (i.e., Co/Fe-N-C) was synthesized by pyrolysis of a Zn/Co/Fe zeolitic imidazolate framework, and applied in peroxydisulfate (PDS) activation for removal of organic contaminants from wastewater. The isolated diatomic metal-nitrogen sites were detected by X-ray adsorption fine-structure. The degradation of four contaminants (i.e., phenol, bisphenol A, 2,4-dichlorophenol, and N-methyl-2-pyrrolidone) with a concentration of 100 mg/L could be degraded separately within 20 min by the Co/Fe-N-C system with 10 mmol/L of PDS, 0.5 g/L of catalyst dosage, and initial pH of 3. Besides, 79.2 % of phenol could be mineralized in 120 min, and the turn-over frequency value of the catalyst was calculated to be 27.17 min(-1), which was higher than the commonly reported homogeneous PS-AOPs. Moreover, the Co/Fe-N-C exhibited high stability (mineralization rate over 70 % after 5 cycles), a wide initial pH range (3-9), and high catalytic performance at 5-20 mmol/L of PDS concentrations. Based on the analysis of radical scavenging experiments and electron spin resonance spectra, the radical and non-radical pathways for PDS activation were proved in the system, and the contribution of phenol degradation by each pathway was clarified