Isotope Geochemistry Research Articles

A Chromatographic Approach for High-Precision Eu Isotope Analysis.

Eu isotopes are promising tracers across various scientific domains such as planetary, earth, and marine science, yet their high-precision analysis has been challenging due to the similar geochemical properties of rare earth elements (REEs). In this study, a novel two-column chromatographic approach was developed utilizing AG50W-X12 and TODGA resins to separate Eu effectively from matrix and interfering elements like Ba, Nd, Sm, and Gd, while ensuring high Eu yields (99.4 ± 0.4%, n = 19) and low blanks (<20 pg). The robustness of this method is evidenced by various rock types and different Eu loading masses. The efficient purification of Eu facilitated the establishment of a high-precision calibration technique with standard-sample bracketing (SSB) and internal normalization (Nd). When a Nu Plasma 1700 multicollector-inductively coupled plasma-mass spectrometry (MC-ICP-MS) instrument was employed, repeated purification and analysis of various Geological Reference Materials (GRMs) confirmed that the long-term external precision of δ153/151Eu is better than 0.04‰ (2 standard deviation (2SD)), which represents a 2-5-fold increase in precision compared to previously reported methods. Additionally, the high-precision Eu isotopic compositions of five GRMs, including basalts, andesite, syenite, and marine sediment, were measured. The high-precision Eu isotope techniques presented herein open up new avenues for Eu isotope geochemistry.

Effect of CO2 and H2SO4 on the dissolution of a carbonate basement and alteration of silicates in a volcano-sedimentary system in central Mexico

This study explores the hydrogeochemical and isotopic characteristics of groundwater in the Irapuato Valley and Celaya Valley Aquifers in central Mexico, specifically focusing on the role of CO2 in mineral alteration during water-rock interaction. The study is grounded in the principles of hydrogeochemistry and stable isotope geochemistry, analyzing the impact of CO2 and H2SO4 on the weathering of carbonates and silicates. Hydrogeochemical analysis, including Piper diagrams, and isotopic measurements (δ13C, δ18O, δ2H), were conducted on water samples from wells in four municipalities (Irapuato, Salamanca, Villagrán, and Juventino Rosas). The data was statistically evaluated using Shapiro-Wilk tests to assess normality, skewness, and kurtosis, ensuring the reliability of the findings. The results indicate that HCO3− dominates the groundwater composition, with CO2 and H2SO4 significantly influencing mineral alteration processes. The isotopic data suggest that CO2 is primarily released from carbonate rock degassing, with slight isotopic enrichment in δ13C due to water-carbonate interaction. Hydrothermal fluids contribute to the geochemical evolution of the aquifer, leading to the formation of minerals such as tridymite, alunite, and kaolinite. Additionally, some groundwater samples exhibit evidence of thermalism and water-rock interactions, influencing their isotopic signatures and temperatures. These findings underscore the importance of CO2 in groundwater chemistry and highlight the need for further studies to understand regional flow dynamics and the potential impact of geothermal systems on water quality.

Metallogenic model of the Lykling ophiolite-hosted lode Au deposit, Scandinavian Caledonides: Insight from fluid inclusions, mineral chemistry and stable isotope geochemistry

The Lykling lode Au deposit represents a unique example of gold mineralization in the Upper Allochthone of the Scandinavian Caledonides. The mineralization is hosted by the Early Ordovician Lykling Ophiolite Complex and the intruding trondhjemite unit and spatially associated with two generations of mafic dykes that crosscut both the ophiolitic complex and trondhjemite. Field observations indicate that the mafic dykes did not play an active role in the emplacement of Au at Lykling, however their contacts with the immediate host rocks (i.e., gabbro and trondhjemite) may have focused ore-forming fluids.Three main stages in the evolution of the hydrothermal system in the Lykling area are documented by two generations of auriferous quartz veins: 1) older quartz-carbonate veins hosted by moderately angled brittle-ductile shear zones and 2) younger quartz-sulfide veins that fill steeply dipping brittle faults. Stage 1 resulted in deposition of barren quartz and gold-free pyrite from moderately saline NaCl-CaCl2-H2O ± CO2 fluids at temperatures between ∼310–330 °C and pressures in the range from 2.7 to 3.5 kbars. Under the given physicochemical conditions Au was mobile in the form of its chloride complexes. Stage 2 is associated with multiple episodes of ductile deformation punctuated by concomitant brecciation reflecting brittle-ductile transition processes. Fluid inclusion data reveals a decrease in temperature and pressure that may result in the formation of stable Au-bisulfide complexes and making the hydrothermal mobility of Au sensitive to changes in pressure. Consequently, the fluctuation in pressure controlled by the development of brittle-ductile structures likely resulted in the precipitation of native gold in quartz veins. Stage 3 represents a pure brittle event which is accompanied by a significant decrease in the fCO2/fS2 ratio. Mixing of higher-temperature and moderate-salinity fluids with cooler fluids has been recognized as the principal trigger for deposition of sulfides and a paragenetically late phase of native gold in the Lykling hydrothermal system.The Lykling ophiolite-hosted lode Au deposit shows numerous similarities with orogenic gold deposits elsewhere, including structural controls during mineralizing events, deposition from moderately to low salinity CO2-bearing aqueous solutions, deposition from a focused fluid flow along trans-crustal fault zones with a mixed brittle-ductile character and the spatial association with regionally metamorphosed terranes. In contrast to the great majority of the known orogenic gold deposits, the Lykling ophiolite-hosted lode Au deposit records a magmatic origin of volatiles. Therefore, taking into consideration field relationships and the regional setting of the Lykling deposit, we argue that its formation is concomitant with emplacement of the Sunnhordland Batholith during post-collisional thinning of the crust and associated localized uplift within the Lykling Ophiolite Complex.

Diagenetic evolution and cementation mechanism in deep Carbonate reservoirs: A case study of Dengying Fm. 2 in Penglai, Sichuan Basin, China

The Dengying Formation in the Penglai region of the Sichuan Basin is renowned for hosting high-quality dolomite reservoirs. However, the understanding of their formation mechanisms and spatial distribution patterns remains enigmatic. This study undertakes a comprehensive petrographic analysis of the second member of the Dengying Formation, primarily focusing on its burial history, reservoir characteristics, and an examination of the types, stages, and developmental patterns of cementation within the dolomite reservoir. This is achieved through the application of isotopic geochemistry, inclusion temperature analysis, and laser U-Pb dating. The findings reveal that cements within the second member of the Dengying Formation predominantly occur in pores and fractures, often exhibiting euhedral and subhedral morphologies. These cements also exhibit evidence of replacing original non-skeletal grains and micrites in semi-euhedral and other forms. Broadly, the cements can be classified into four types: calcium cement (the most abundant), dolomite cement, quartz, and pyrite. The formation of calcareous and siliceous cements closely aligns with the sedimentation and burial processes of the Dengying Formation as a whole. The early to late stages of early-middle diagenesis play a crucial role in the formation of dolomite within the second member. Notably, the degree of euhedral dolomite formation directly correlates with the specific diagenetic stage. Our research indicates that the development of high-quality reservoirs in deep-to-ultra-deep microbial dolomites is a result of complex multi-factor interactions and multi-stage discontinuous modifications, leading to strong heterogeneity within the reservoirs. Microbial dolomite carbonates inherently exhibit high initial porosity, with the favorable sedimentary facies serving as the fundamental basis for reservoir development. Dissolution processes during the syngenetic and quasi-syngenetic periods, in conjunction with epigenetic karstification, further augment porosity and expand the reservoir's capacity. During burial and deep burial stages, various acidic fluids play a pivotal role in preserving and modifying the early-formed pores. In the deep environment characterized by high temperature and pressure, microbial dolomite reservoirs undergo intricate diagenetic evolution and possess complex pore preservation mechanisms. Remarkably, even under exceptional ultra-deep conditions, high-quality microbial dolomite carbonate reservoirs can still develop and be preserved, presenting significant potential for oil and gas exploration.

Heavy metal migration and lithium isotope fractionation under extreme weathering of basalt on tropical Hainan Island, China

Basalt weathering can cause heavy metal enrichment in soils, and lithium isotopes serve as an effective tracer for this weathering process. However, the relations among weathering intensity, heavy metal migration, and Li isotope fractionation remain unclear. We conducted systematic examinations of a basalt weathering profile on tropical Hainan Island in China. The characteristics of mineralogy, elemental and Li isotopic geochemistry indicate that the profile has undergone changes from initial to advanced and ultimately extreme weathering stages. The corresponding dominant minerals are primary minerals, clay minerals such as kaolin-group, and the Al–Fe–Ti (hydro)oxides. The variations of Fe-group heavy metals within the profile are very similarly to that of Fe, exhibiting a pattern of loss-gain-loss. Newly formed secondary minerals preferentially incorporate lighter 6Li, leading to a gradual increase in Li content and a decrease in δ7Li. Due to the high δ7Li value of rainwater input, the ongoing impact of secondary mineral adsorption is partially counteracted. This results in the δ7Li of laterite and topsoil being maintained within a narrow range (−3.2‰ ∼ −1.9‰), despite the broader variation observed across the entire profile (−3.2‰ ∼ +2.8‰). Comparing basalt weathering profiles in different climatic zones reveals a very complex Li isotope behavior and its controlling factors. Therefore, it is essential to carefully evaluate the influence of atmospheric input, secondary mineral adsorption, dissolution, and redeposition processes on Li isotopes. Throughout the entire profile, Cr, Ni, and Cu exhibit enrichment relative to soil background values, indicating that the weathering of tropical basalt may pose potential environmental risks for these elements.

Preface to the Special Issue on "The Hydrochemistry and Isotope Geochemistry of Alkaline Lakes and Brine Systems": A Tribute to Paolo Censi

Preface to the Special Issue on "The Hydrochemistry and Isotope Geochemistry of Alkaline Lakes and Brine Systems": A Tribute to Paolo Censi

Geology and S-Pb isotope geochemistry of the Hatu gold deposit in West Junggar, NW China: Insights into ore genesis and metal source

Geology and S-Pb isotope geochemistry of the Hatu gold deposit in West Junggar, NW China: Insights into ore genesis and metal source

Zircon U-Pb geochronology, major, trace elemental, and Sr-Nd-Pb isotopic geochemistry: constraints on the age and magmatic origin of Mesozoic mafic dykes in the Guangxi Zhuang Autonomous Region, South China

ABSTRACT As a direct product of lithospheric extension, the mafic dyke group have become an ideal object for studying the formation, evolution and dynamics of both the crust and continental orogenic belts. Given the scientific significance of mafic dykes and their utility in addressing outstanding questions concerning the origin and development mafic dyke swarms Mesozoic age with-in the South China Plate, in this study, 54 representative mafic dykes within the Guangxi Zhuang Autonomous Region, South China, were examined. Research methods include laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb age-dating, whole rock geochemistry, and the Sr-Nd-Pb isotope geochemistry of the studied mafic dykes. The results indicate that these rocks formed between 139 Ma and 113 Ma and have typical doleritic and lamellar textures. They fall into the alkaline and shoshonitic series, are characterized by enrichment of light rare earth elements, some large ion lithophile elements (Rb, Ba, and Sr), Th, U, and Pb, and have depleted Nb, Ta, Hf, and Ti. Moreover, the mafic dykes studied have high initial87Sr/86Sr ratios (0.7055–0.7057), negative εNd(t) values (from −15.2 to −11.4), and relatively constant initial Pb isotopic ratios (that are Enriched Mantle-1 (EM I)-like; 206Pb/204Pb = 16.765–16.816, 207Pb/204Pb = 15.429–15.476, and208Pb/204Pb = 36.882–37.144). The above results indicate that the group of dolerites and lamprophyres studied herein were likely derived from magma generated via low-degree partial melting (1.0%–10%) of an EM1-like garnet-lherzolite mantle source. The parental magmas to these fractionated olivine-, clinopyroxene-, plagioclase, and Ti-bearing phases, with negligible crustal contamination during ascent and dyke emplacement. On the basis of existing research and evidence from this study, we propose a reasonable model for the origin of the mafic dykes: the ancient Pacific Plate subducting below the South China plate led to extension of the lithosphere, an upsurge of the asthenosphere, which triggered partial melting of the lower mantle lithosphere in the Early Cretaceous, and the formation of the parent magma to the Mesozoic mafic dykes in the Guangxi Zhuang Autonomous Region study area. The involvement of slab-derived fluids from the subduction of the ancient Pacific Plate was responsible for metasomatism of the mantle source to these mafic magmas.

Mineral, bulk rock, and isotope geochemistry of the Late Cretaceous Sabzevar ophiolite in NE Iran and the magmatic and tectonic evolution of a continental back-arc basin oceanic crust in the Mesozoic Tethyan orogenic belt

Mineral, bulk rock, and isotope geochemistry of the Late Cretaceous Sabzevar ophiolite in NE Iran and the magmatic and tectonic evolution of a continental back-arc basin oceanic crust in the Mesozoic Tethyan orogenic belt

New Data on the Regional Stratigraphic Scale of the Paleoproterozoic of the Fennoscandian Shield (Isotope Geochemistry and Age of Supracrustal Rock Complexes of the Inari Terrane, Kola Peninsula)

New Data on the Regional Stratigraphic Scale of the Paleoproterozoic of the Fennoscandian Shield (Isotope Geochemistry and Age of Supracrustal Rock Complexes of the Inari Terrane, Kola Peninsula)

Cathodoluminescence Petrography and Stable Isotope Geochemistry of Carbonate Rocks to Evaluate Diagenetic Evolution of the Middle Jurassic Samana Suk Formation (SSF), Kahi Section, Nizampur Basin, NW Himalayas, Pakistan

Cathodoluminescence Petrography and Stable Isotope Geochemistry of Carbonate Rocks to Evaluate Diagenetic Evolution of the Middle Jurassic Samana Suk Formation (SSF), Kahi Section, Nizampur Basin, NW Himalayas, Pakistan

Geochemical and Isotopic evidence for volcanism on the Alleppey Terrace, southwest Indian continental margin

The Arabian Sea consists of prominent undersea bathymetric highs whose genesis is often attributed to volcanism either related to the 90-85 Ma Marion or the 70-65 Ma Reunion hot spot activity on the Indian Plate. The enigmatic Alleppey Terrace (AT) is one such significant bathymetric high in the southwestern continental margin of India. We studied the siliciclastic sediments deposited on the AT and the adjacent shelf region using major/trace element, and Sr-Nd isotope geochemistry to decipher their provenances and implications of the findings for the origin of the Terrace. Geochemical data suggest that the AT sediments are chemically distinct from the adjacent shelf sediments, with the former having been sourced from juvenile mafic rocks and the latter from significantly older, felsic continental crustal rocks. Although currently located at a water depth of ∼300 m, AT was likely exposed above the sea level in the past and had undergone subaerial weathering and lateritization. The εNd of AT sediments (−17.1 to −10.9), which is much radiogenic than that of the shelf sediments (−26.4 to −22.2), indicates significant presence of a juvenile basaltic component - likely derived from in situ weathering of the local seafloor/basement. The common component in both the terrace and shelf sediments appears to be terrigenous, deposited by the local rivers draining the Western Ghats. Conspicuous similarities of trace element ratios and isotopic compositions of the terrace sediments with those of the volcanic rocks temporally and spatially related to the Deccan volcanism suggest that the AT may contain traces of the end Cretaceous Reunion-Deccan plume/hotspot activity on the India subcontinent.

Multi-stage evolution of the monzonitic Larvik Plutonic Complex (Oslo Rift, Norway) and its implications for the formation of the Kodal Fe-Ti-P(−REE) deposit

The Larvik Plutonic Complex is a monzonitic complex that was emplaced early during the formation of the Permian Oslo Rift (southern Norway). It extends across its entire width (around 50 km), and is made up of a majority of larvikite (augite monzonite) and lardalite (nepheline monzogabbro to nepheline syenite) distributed in ten successive intrusive units that partially intersect each other. The Larvik Plutonic Complex also hosts occurrences of singular Fe-Ti-P-rich rocks of magmatic origin, including the Kodal deposit. These are mainly composed of titanomagnetite, ilmenite, titanaugite and apatite, the latter also featuring rare earth elements (REE) enrichment. Here, we aim to unravel the conditions that allowed the Kodal deposit to form, and determine why other mineralized bodies are not seen elsewhere in the Larvik Plutonic Complex. We compared the petrography and elemental and isotope (Sr, Nd and Hf) geochemistry of both the Kodal mineralization and the neighboring larvikite, in order to provide evidence of their petrogenetic relationship. Both lithologies share the same isotopic ratios (87Sr/86Sr(i): 0.7035–0.7043; εNd(i): +2.37 − +3.48; εHf(i): +3.39 − +9.16), which would suggest a single homogeneous source. The very low dispersion of our isotopic data also suggests that crustal contamination levels in the area were low to negligible. Normalized trace diagrams of larvikite in several localities of the Larvik Plutonic Complex also show enrichments in most incompatible elements, which becomes more prevalent towards the Kodal deposit. Elements like Sr and Eu(2+) follow an opposite trend, because of their compatibility in plagioclase. We therefore infer that the region around the Kodal deposit hosts more fractionated larvikite due to the previous crystallization of successive plagioclase cumulates. We deduce that the Kodal lobe corresponds to a more evolved intrusion, which is no part of Pluton V per se, as considered in the literature until now, but instead derives at least from a monzonitic magma at the origin of the plutons V to VIII). This also implies that the formation of Fe-Ti-P mineralization at Kodal was most likely a consequence of enrichment of the residual melt in alkaline elements and incompatible elements. These conditions support an early hypothesis of formation by silicate-liquid immiscibility, along with petrographic evidence of disequilibrium at the mineralogical scale. However, further analyses would be required to test the hypotheses of silicate-liquid immiscibility against an accumulation of the Fe-Ti-P mineralization from an evolved intermediate magma.

On accurate calculations of equilibrium H/D fractionations at super-cold conditions (≤200 K) I: Full Partition Function Ratio (FPFR) vs. Path Integral Monte Carlo (PIMC)

Accurate estimations of Hydrogen/Deuterium (H/D) isotope effects have been a long-standing problem since the beginning of stable isotope geochemistry, primarily due to their strong nuclear quantum effects (NQEs). Currently, the D/H ratio plays a key role in deciphering the origin and evolution of water ice and organics in the solar system. Additionally, the Big-bang origin of Deuterium necessitates that the observed D/H variations be linked to isotope exchange reactions, such as HD + H2O ↔ H2 + HDO. Therefore, an accurate benchmark dataset describing the equilibrium H/D isotope fractionations at low temperatures (≤ 200 K) is essential for interpreting rapidly accumulating astrochemical observation data. In this study, we implemented and compared two methods developed for evaluating the NQEs of H/D isotopes: 1) the Full Partition Function Ratio (FPFR) method and 2) the Path Integral Monte Carlo (PIMC) method. Both were assessed for their accuracy and efficiency in estimating equilibrium isotope effects (EIEs) using 10 common interstellar small molecules (H2, HF, HCl, HCN, HNC, H2O, H2S, NH3, HCHO, and CH4) as examples. Most of them are calculated at high precision for the first time. For the FPFR method, several higher-order corrections to the Urey-Bigeleisen-Mayer model were considered, including anharmonicity, quantum mechanical rotation with nuclear-spin statistics, and corrections to the Born-Oppenheimer approximation. For the PIMC method, four different actions related to the thermal density matrix are used. These include the primitive and three fourth-order actions (Takahashi and Imada, Suzuki-Chin and Chin approximations), based on the direct scaled-coordinates transformation. Three main conclusions are obtained: 1) Under the framework of Born-Oppenheimer approximation, the PIMC method holds the same and even slightly better accuracy (more comprehensive descriptions of quantum anharmonicities) in estimating EIEs for H/D isotopes as the FPFR method. However, both methods suffer from the neglection of the DBOC when using the Born-Oppenheimer potential energy surfaces. For the PIMC method, additional corrections for particle distinguishability must be considered when nuclear spin statistics exhibit its effects at low temperatures (e.g., < 160 K for H2). 2) Among the four actions, three fourth-order actions show better convergence and efficiency (2.2 to 26.5 times speedups at 50 K) than the primitive action, making them superior candidates for PIMC simulations at super-cold (≤ 200 K) conditions. 3) A combination of accurate potential energy surface with the PIMC method serves as an alternative way for theoretical estimations of H/D isotope effects.

Alkaline Devonian magmatism of the Menorca Island: Tracking the mantle isotopic sources in the realm of the western Paleo-Tethys Ocean

Several locations with alkaline magmatism are recognised in Silurian-Devonian basins along the southern variscan autochthon units (e.g. Central Iberian Zone) of the northern Gondwana margin. The origin of the Devonian basins and their magmatism has not been studied in the context of the passive margin of Gondwana. The basement of Menorca, Balearic Islands, consists of a deep Devonian-Carboniferous basin with mafic igneous rocks, the Tramuntana Gabbros. In this study, we trace the geodynamic setting and isotopic sources of the Tramuntana Gabbros through elemental geochemistry, isotopic geochemistry (SrNd) and UPb geochronology in zircons. These gabbros are the product of an intraplate alkaline magmatism with immobile trace element and REE contents similar to those of Ocean Island Basalts. Average 87Sr/86Sr(370) of 0.708456 and εNd(370) of +4.0 indicate a source similar to a Type-2 enriched mantle with average TDM of 665 Ma, suggesting a relatively old metasomatized mantle. Concordant UPb ages of c. 597 Ma (Ediacaran, radiometric age) from a single population of 31 zircons separated from the Tramuntana Gabbros (Devonian, biostratigraphic age) reinforce the presence of older units in the corresponding lithospheric mantle. The Tramuntana Gabbros and the Devonian-Carboniferous sequences of Menorca limit the westward extension of the Paleo-Tethys Ocean, whose development never reached these westernmost regions. Assuming a common sublithospheric mantle source for the peri-Gondwanic Devonian alkaline rocks and considering the previous Cadomian (Neoproterozoic) subduction to be the most favourable origin of the separated zircons, the bulk rock TDM and zircon UPb data obtained from the Tramuntana Gabbros track the mixing, recycling, and mantle accretion in this peri-Gondwanic section from Precambrian to Devonian times.

Principle of Hydrogen Isotope Geochemistry Paleo‐altimeter and its Potential in Reconstructing Paleo‐elevation of the Southeastern Tibetan Plateau

AbstractThe reconstruction of paleo‐elevation serves a dual purpose to enhance our comprehension of geodynamic processes affecting terrestrial landforms and to contribute significantly to the interpretation of atmospheric circulation and biodiversity. The oxygen (δ18Ow) and deuterium (δDw) isotopes in atmospheric precipitation are systematically depleted with the increase of altitude, which are typical and widely applicated paleo‐altimeters. The utilization of hydrogen isotope of hydrous silicate minerals within the shear zone system, volcanic glass, and plant leaf wax alkanes offers valuable insights for addressing evaporation and diagenesis. In this paper, we review the principle, application conditions, and influencing factors of the hydrogen isotope paleo‐altimeter. In addition, we discuss the feasibility of utilizing this technique for quantitatively estimating the paleo‐elevation of the southeastern Tibetan Plateau, where multiple shear zones extend over hundred kilometers parallel to the topographic gradient.

Gas isotope geochemistry of Tangquan hot spring system in Nanjing (China)

Tangquan hot springs is one of the three well-known geothermal systems in Nanjing, Jiangsu Province, eastern China. Previous studies have shown its high flow rate and ideal water chemistry favorable for utilization. Here we further examine the potential of the hot springs using gas geochemistry in this paper. 35 water samples and 16 gas samples were collected for chemical isotopic analyses. The geothermal gases are found to be primarily atmospheric in origin, containing high nitrogen, oxygen and carbon dioxide gases. Carbon isotope shows that the origin of CO2 and CH4 are thermal metamorphic in the upper crust. The isotope ratio of helium is 3.47–4.73 Ra, indicating that mantle He accounts for 44–60% in total of geothermal gases. These findings furnish the grounds to infer geothermal potential at the deeper part of the geothermal system. The immediate geothermal reservoir has a temperature of 90 °C, but the temperature of deeper part of the system could reach 150–205 °C, using the carbon gas isotope geothermometer. These findings show a promising future of deep geothermal resources in the region.

Atmosphere and biological impact during sulfide formation in the Archean Central-Vozhma sulfide deposit (Karelia)

Relevance. The need of new knowledge about the early stages of the Earth. Sulfur isotope analysis of sulfide minerals is a powerful tool to understand the processes during the Archaean and Paleoproterozoic. Combined with other data, isotope geochemistry provides an insight into sulfur sources of sulfides from ancient sulfide volcanosedimentary deposits; geochemical factors affecting Archaean sulfide volcanosedimentary ore formation; adjust genetic models and determine the degree of influence of bacteria on the mineral formation. Aim. To identify the sources of sulfur during the formation of sulfide deposits via isotope analysis, and to evaluate bacteria affect mineral formation. Objects. They were obtained from the core of boreholes of Mesoarchaean volcanosedimentary sulfide Central-Vozhma deposit, being a part of the Sumozersko-Kenozersky greenstone belt of the Karelian craton. Methods. Mineralogical studies of rock and ore samples were carried out using optical microscopy; scanning electron microscopy and energy dispersive X-ray spectroscopy. The ratios of four stable sulfur isotopes were analyzed in sulfide minerals of the deposit (33S/32S, 34S/32S, 36S/32S). Results. The results obtained demonstrated the polygenic source of sulfur in sulfides. The sulfides have both positive and negative Δ33S values, indicating the presence of atmospheric sulfur formed under UV photolysis during mineral formation. Sulfide minerals include the following components: Seawater sulfate sulfur of photolytic genesis showed a negative anomaly Δ33S (∼ –0.4‰). It was the source of authigenic pyrite. Sulfides crystallized as a result of biological sulfate reduction demonstrated a narrow range of δ34S values (–2.64‰˂0˂+4.27‰). Elemental sulfur of photolytic genesis mobilized from the host sedimentary rocks by hydrothermal fluids. This sulfur, with a positive Δ33S anomaly (up to +1.6‰) took part in the massive sulfide ores formation.

SIMS Data Correction Procedure for Quasi‐Simultaneous Arrival (QSA) Under‐counting and Ramifications of Misapplication

Isotope geochemistry requires isotope ratios measured using secondary ion mass spectrometry (SIMS) to be made with optimal precision and accuracy. Under some analytical conditions when using electron multiplier detectors, secondary ions may be under‐counted because of quasi‐simultaneous arrival (QSA) at the first dynode. The relative magnitude of the associated QSA correction to raw measured isotopic ratios can be up to seventy permil or more. Therefore, not applying the correction, or misapplication of it could lead to significant inaccuracies in published isotope ratio data. Examples and ramifications of the latter are described in addition to a straightforward procedure for QSA under‐counting correction.

Holocene Paleoclimate Changes around Qinghai Lake in the Northeastern Qinghai-Tibet Plateau: Insights from Isotope Geochemistry of Aeolian Sediment

The stable carbon isotope composition of total organic matter (δ13Corg) has been utilized in aeolian sediments, serving as an indicator for reconstructing terrestrial paleoenvironments. The Qinghai Lake (QHL) Basin is a climate-sensitive region of significant importance in paleoclimatic reconstruction. However, the reconstructed climatic variations based on δ13Corg in aeolian sediments in the QHL Basin in the northeastern Qinghai-Tibet Plateau (QTP) are lacking, and their paleoclimatic significance remains poorly understood. By conducting δ13Corg measurements on the Niaodao (ND) aeolian profile near QHL, we reconstructed the paleoclimate changes of 11 ka–present. The variation range of the δ13Corg values in the ND profile indicated the terrestrial ecosystems were not the sole contributor to lacustrine organic matter. The δ13Corg values are an indicator of historical temperature changes in the study area, exhibiting similar trends with the reconstruction of Chinese summer temperatures, East Asian air temperature, global temperature, and Northern Hemisphere summer insolation at 37° N. The temperature increased with high frequency and amplitude oscillations, with strong aeolian activity and low total organic carbon accumulation during the Early Holocene. The temperature was maintained at a high and stable level, with the weakest aeolian activity and intensified pedogenesis during the Middle Holocene. The temperature decreased at a high rate, with renewed aeolian activity and weak pedogenesis during the Late Holocene.