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Sodium nitrate ores from the Atacama Desert in South America were economically important as they represented huge natural resources for the fertilizer and explosives industries during the early nineteenth to early twentieth centuries. Nitrogen and oxygen isotope ratios (δ15N and δ18O) of these desert nitrates generally show unique compositions (from close to 0 and up to ca. +50 ‰, respectively). The nitrates indicate the provenance as atmospheric in origin due to the mass-independent photochemical reaction of nitric oxide (NO) with ozone (O3) in the atmosphere to produce nitrate (NO3-). This paper examines the previously existing isotope data for specimens acquired from the Atacama Desert. It then reports new data from dual isotope analysis of historic nitrate specimens archived in museums in the UK. In the stable isotope signatures for nitrates from two areas of the Atacama Desert, Tarapaca in the north and Antofagasta in the south, were examined, and this analysis enabled a more detailed definition of their isotopic compositional ranges. This improved database is useful for tracing the provenance of the historic nitrates used in gunpowder and saltpetre, and also the cause of nitrate pollution in natural environments for which routine chemistry alone cannot provide the definite evidence for the origin.

The Imnyakh Formation (1500–1800 m thick), which is developed east of the Mama–Bodaibo Synclinorium (inner zone of the Patom Upland), comprises crystalline limestones (marbles) and carbonate shales (metamorphic marls). The carbon and strontium isotope compositions (δ13Cav = –9.0 ± 0.4‰, 87Sr /86Sr = 0.70810–0.70845) in these rocks are completely identical to those in unmetamorphosed limestones of the Zhuya Group (outer zone) and the Torgo Formation (adjacent part of the Siberian Platform), which are comparable with the global Ediacaran C isotope anomaly (Shuram–Wonoka event). Metamorphism was not accompanied by the removal of Sr whose content in marbles of the Imnyakh Formation are as high (up to 6290 μg/g) as in limestones of the Zhuya Group in the deepest parts of the Patom paleobasin. Thus, metamorphism was only manifested in the depletion of rocks with the heavy oxygen isotope by 3–4‰ (δ18Oav = 17.2 ± 1‰), relative to unmetamorphosed limestones. Carbonates of the pre-Imnyakh black carbonate-bearing shales and deep black crystalline limestones in the Khomolkha and Ugakhan formations are characterized by wide variations of δ13C (–4.0 to 7‰) and δ18O (15.2 to 23.4‰), indicating strong postsedimentary alterations. Nevertheless, their Early Vendian (Early Ediacaran) age is confirmed by such features as position in the section, abnormally high δ13C values, and the minimum value 87Sr /86Sr = 0.70753 recorded in a sample with the Sr content of 11700 μg/g. Although the isotope systems of carbonates in the Sogdiondon and Vitim formations (δ13C –14.2 to –3.7‰, δ18O 12.2 to 13.4‰, and 887Sr/86Sr 0.71120 to 0.71337) occurring at the Neoproterozoic sequence base in the Zhuya River underwent even stronger modification, it is possible that δ13C values in these formations were initially negative. In terms of the C and O isotope compositions (δ13Cav = –9.5 ± 0.7‰, δ18Oav = 17.3 ± 1.8‰), crystalline limestones and carbonate shales in the metamorphosed analogs of the Zhuya Group from the Mama River mouth (west of the synclinorium) are similar to the Imnyakh Formation. Current problems of the correlation, age, duration, and origin of the largest in geological history negative C isotope anomaly are discussed.

To constrain the mechanisms governing the extremely large variations of Mg and Fe isotopes in magmatic Fe–Ti oxides in layered mafic intrusions, we investigate Mg isotopic compositions of magnetite, coupled with its chemical data and whole-rock major element and Sr-Nd isotope compositions from the Baima layered mafic intrusion in the Emeishan large igneous province, SW China. The Baima intrusion is mainly composed of magnetite-wehrlite and magnetite-troctolite (i.e., oxide-rich rocks) in the Lower Zone, and troctolite and gabbro (i.e., oxide-barren rocks) in the Middle and Upper Zones. Magnetite separates display large Mg isotopic variation, with δ26Mg ranging from −0.17 ± 0.06 to +0.58 ± 0.04‰ in the oxide-rich rocks and from −0.18 ± 0.06 to +0.98 ± 0.04‰ in the oxide-barren ones. The lack of correlation of δ26Mg with trace elements in magnetite and whole-rock Sr-Nd isotopic compositions indicates that the large Mg isotopic variation in magnetite was not produced by fractional crystallization, magma mixing, crustal contamination, and/or trapped liquid shift. Instead, equilibrium isotope fractionation induced by Mg–Fe re-equilibration between magnetite and ilmenite at different subsolidus temperatures controlled the Mg isotopic variation in the oxide-rich rocks; and kinetic isotope fractionation driven by Mg–Fe inter-diffusion between magnetite and olivine and/or clinopyroxene dominated the oxide-barren rocks. Both processes were primarily controlled by the assemblage and modal abundance of coexisting minerals to which magnetite adjoins. Overall, fractional crystallization and subsequent subsolidus diffusion played crucial roles in the genesis of the Fe–Ti oxides in the Baima intrusion. Our results also reveal widespread isotope disequilibrium between coexisting minerals in mafic magma chambers and suggest that Mg isotope geochemistry has a great potential to characterize the formation of Fe–Ti oxides in layered mafic intrusions.

Epithermal metal deposits along convergent plate margins are of large economic value, however, the origin of the typical metal spectrum (Au, Ag, Sb, As, Hg) in these deposits remains debated. Here, we study the Hg isotope geochemistry of the vein-style Erdaokan Ag-Pb-Zn deposit of epithermal type in the eastern part of the Central Asian Orogenic Belt in NE China, to provide direct constraints on its metal source. Bulk ore samples and early-stage hydrothermal minerals (magnetite, pyrite, and quartz) show negative δ202Hg (−1.52 to −0.18‰) and positive Δ199Hg (−0.03 to 0.17‰) values similar to those of previously reported epithermal Au deposits in NE China, and also of marine systems in general. However, late-stage calcite shows weak negative to positive δ202Hg (-0.61 to 0.90‰) and significant negative Δ199Hg (−0.18 to −0.02‰), similar to the Late Paleozoic sandstone country rocks (δ202Hg, −1.09 to 0.76‰; Δ199Hg, −0.09 to 0.04‰). Hydrothermally altered gabbro and diorite show large variations in δ202Hg (−1.83 to 0.50‰) and Δ199Hg (−0.14 to 0.15‰) which overlap with those of the ore and country rocks, indicating a mixed source. The Δ199Hg signature in the bulk ore and early-stage hydrothermal minerals likely derives from dehydration of the subducted oceanic slab, whereas Hg in late-stage calcite is likely derived from the sedimentary country rocks. Hydrothermal deposits in different tectonic settings have distinct Δ199Hg signals, and our study suggests that Hg isotopes are a robust tool to distinguish metal sources of hydrothermal ore deposits.

Significant bromine (Br) isotope composition variations are found in natural salts and brines, which are often even larger than those of co-existing chlorine isotope compositions. The cause of such large Br isotope variations remains elusive. In this study, equilibrium Br isotope fractionations among Br-bearing gaseous molecules, aqueous species and crystalline minerals are provided via the density functional theory (DFT) based first-principles calculations. These fractionation factors form the base for future Br isotope geochemistry studies. Specifically, the first-principles molecular dynamics (FPMD) method is used to evaluate the tricky solvation effects, i.e., dozens of snapshots of FPMD trajectories are selected and re-optimized to their lowest energy atomic coordinates, then the reduced partition function ratios (i.e., β factors) of aqueous Br-bearing species are obtained by computing the average values of those snapshots. In this way, the configurational effects of aqueous Br-bearing species are included. For crystalline compounds, the static first-principles periodic DFT methods are used. We find that the β factors generally increase as the oxidation states of Br increase, indicating that heavy Br isotopes tend to be enriched in substances with higher Br oxidation states. The aqueous Br-bearing species in brines have detectable but small Br isotope fractionations with each other. However, the fractionations between gaseous molecules and NaBr(aq) are significantly larger, e.g., Δ81BrCH3Br(gas)-NaBr(aq) is 0.95 ± 0.041‰ at 20 °C. As for minerals, the fractionation between Br-halite(p) (pure NaBr crystal) and NaBr(aq) is close to zero, but for Br-halite(1/124) (Na125Cl124Br1) and NaBr(aq), the fractionation is 0.206 ± 0.041‰. Similar results are found for the fractionations between Br-sylvite, Br-bischofite and Br-bearing solutions, indicating that Br isotope compositions are closely related to Br/Cl ratios in minerals. By using the calculated isotope fractionation factors, we have modeled the Br isotope composition variations during salt precipitation processes. At 20 °C, the total variations of Br isotopes of salts and brines are found to be −0.45‰ to +0.21‰ and −0.39‰ to 0‰, respectively. They are much smaller than the observed Br isotope variations in natural samples. There must be other ways to fractionate Br isotopes to the extent that observed in nature. Based on the predicted equilibrium Br isotope fractionations among substances with different Br oxidation states, the large Br isotope variations in nature can be explained by the change of Br oxidation state. The sudden change of Br isotope compositions hence can be used as a new indicator for the change of redox conditions.

Mineralized quartz veins within Phanerozoic orogenic belts provide important insights into fluid source and transport, source(s) of S, and genetic implications for ore deposit formation. Here, investigations on mineralized veins hosted by the Hog Mountain tonalite, southernmost Appalachians, were performed using scanned electron microscopy, microprobe analysis, and secondary ion mass spectrometry.The small, reduced Hog Mountain tonalite hosts three different mineralized vein types dominated by Au-bearing quartz veins with a simple base metal sulfide assemblage and spatially associated Au phases (electrum > native gold > maldonite) with Bi phases (native bismuth > unnamed Bi3Te ≈ hedleyite > bismuthinite). In contrast, barren to low-grade arsenopyrite and sphalerite-pyrite-arsenopyrite-galena-chalcopyrite (Zn-Fe-As-Pb-Cu) veinlets are rare. Base metal sulfides are stoichiometrically homogeneous with the exception of sphalerite and galena that have noticeable enrichments in Fe and Cd, and Bi and Ag, respectively. Trace element concentrations (Au, Ag, Bi, Te, Se, and transition metals) in major and minor base metal sulfides are generally low. In situ sulfur isotope analyses on base metal sulfides from different vein types show two distinct populations: (1) δ34Ssulfide = 12.9 ± 1.4‰ in low-grade arsenopyrite and Zn-Fe-As-Pb-Cu veinlets and (2) δ34Ssulfide = 7.7 ± 0.9‰ in mineralized quartz veins.Based on mineral chemistry, two fluid phases were responsible for metal deposition at Hog Mountain. Fluid phase I with low-soluble Au formed rare, barren to low-grade arsenopyrite and Zn-Fe-As-Pb-Cu veinlets from highly acidic, relatively high temperature fluid with moderate ƒS2 and variable ƒO2. In contrast, a reduced, near-neutral, low ƒS2 fluid phase II had higher soluble Au concentrations and created the dominant Au-bearing quartz veins in which Au was deposited via scavenging by Bi melts syngenetic at lower temperatures. Isotopic modeling shows that both fluid phases sourced their S from the metasedimentary rocks hosting the tonalite and adjacent, coeval gold deposits, with the tonalite contributing some S to fluid phase II, resulting in lower δ34S values. Our results are consistent with mineral assemblage, mineral chemistry, and sulfur source(s) from other intrusion-hosted Phanerozoic orogenic gold deposits and support the syngenetic Au scavenging model by Bi melts as a viable Au deposition process in orogenic gold deposits.

Partial melts derived from crustal anatexis exhibit large variations in field characteristics, composition, and isotope geochemistry. The relative influence of melting process and magmatic differentiation on such heterogeneity is a subject of ongoing debate. Boron and molybdeum isotopes have the potential to shed light on the genesis of crustal melts, but the behaviors of B and Mo isotopes during crustal anatexis and differentiation are unclear. Here, we present geochemical and isotopic data, including whole-rock Sr–Nd–B–Mo and mineral B–Mo data, for the Conadong leucogranites in the Himalayan Block, to provide new insights into these issues. The studied samples include two-mica granites (biotite + muscovite), muscovite leucogranites (muscovite ± garnet), and biotite-rich granites. The two-mica granites were derived from muscovite dehydration melting of metasedimentary rocks. Their initial Sr and Nd isotopic compositions show positive correlation, implying non-modal partial melting associated with dissolution of accessory phases. The B contents (3.44–21.2 ppm) of the two-mica granites decrease but their δ11B (−15.80‰ to −13.25‰) and δ98Mo (−0.15‰ to 0.34‰) values increase with increasing Sr and Ba contents. This may have been controlled by different phases involved in non-modal melting (i.e., muscovite and feldspar). The muscovite leucogranites display features of residual liquids. Their δ11B (−15.38‰ to −11.90‰) and δ98Mo (−0.15‰ to 0.17‰) values negatively correlate with Sr and Ba contents, which can be ascribed to shallow-crustal crystal–liquid separation and melt–fluid interaction. The biotite-rich granites are least evolved, with large variations in their initial Sr–Nd isotopic compositions. They show relatively heavy whole-rock B isotopic compositions of −11.97‰ to −9.00‰. These may indicate that biotite-rich granites may be contaminated by entrained restitic minerals (e.g., biotite, feldspar and accessory minerals). Overall, this study demonstrates that compositional diversity of anatectic melts is controlled primarily by melting processes in the source and secondarily by emplacement-level crystal–liquid separation. Both non-modal partial melting and crystal–liquid separation could result in B–Mo isotopic fractionation in anatectic melts.

Magnesium (Mg) isotopes fractionate during rock/mineral weathering and leaching, secondary mineral neoformation, adsorption/desorption, and plant-related Mg recycling, but the mechanisms and extent of fractionation are not well understood. Here, we report the fate of Mg and its isotopes during basalt weathering and soil development in the Hawaiian Islands by sampling soils of varying age (0.3, 20, 150, 1400, and 4100 ka) in undisturbed humid rainforests. Magnesium concentrations in bulk soils are variable with depth and age, ranging from 0.07 to 8.79 wt.%, and significant Mg depletions (up to 99%) relative to parent basalts are visible after 20 ka. Bulk soils display a large age-dependent range of δ26Mg values ranging from −0.60 to +0.26‰. A sequential leaching scheme showed that labile Mg is depleted whereas residual Mg is enriched in isotopically heavy Mg. The two youngest soils (0.3 ka) display δ26Mg value similar to basalt for both labile or residual Mg, indicating either that basalt weathering causes little Mg isotope fractionation or that δ26Mg value is overwhelmed by the primary minerals during 0.3 ka. However, in the older soils (≥20 ka), the δ26Mg values of both labile and residual Mg vary non-linearly as a function of time, with an increase in the difference between them. These variations are explained by both plant-related Mg recycling and progressive mineral transformations, evolving from short-range-order (SRO) minerals (allophane and ferrihydrite) to more crystalline products (goethite, gibbsite and kaolin minerals). Indeed, plant-related Mg recycling causes the enrichment of light Mg isotopes in the labile Mg, while secondary phases incorporate more and more heavy Mg isotopes with time. These results reconcile experimental and field studies and highlight a weathering control of Mg isotopes delivered to the oceans.

New approaches in isotope geochemistry require the development of novel methods for the isotopic analysis of crude oil, a typically complex and very hard to digest organic geological matrix. In this work, methods were developed for the determination of isotope ratios of Mg, Sr and Pb in crude oil by multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS). Two sample preparation methods, (i) microwave-assisted wet digestion within an ultra-high pressure digestion cavity (MAWD-PDC) and (ii) solubilization of inorganic solids as obtained after the ASTM D4807 test method, were evaluated. Using MAWD-PDC, up to 0.5 g of crude oil was efficiently digested using only 6 mL of 14.4 mol L−1 HNO3 (75 min, temperature up to 250 °C). MAWD-PDC was shown to be a suitable sample preparation method for subsequent determination of Mg, Sr and Pb isotope ratios. On the other hand, the ASTM method does not require sophisticated equipment. With this approach up to 10 g of oil can be dissolved in toluene and filtered through a nylon membrane and elements present as inorganic solids, such as Mg and Sr, are retained on the membrane and can be easily recovered in water. However, Pb was not recovered. Column chromatographic protocols for target element isolation were fine-tuned for each analyte to ensure quantitative yields. No statistical difference was observed between the results for Mg and Sr isotope ratios obtained using both sample preparation methods. A proof-of-concept study showed that the Mg–Sr–Pb isotopic composition of the Brazilian crude oils was within the range observed for seawater and the deposit bedrock, suggesting that the methods developed can be considered as promising tools to decipher the formation history of oil reservoirs.

The dark mudstone lithofacies of Mamu Formation was deposited during the Campano-Maastrichtian flooding episode. It is laterally heterogeneous, and has been subdivided into marsh, bay and central basin subenvironments in order of proximality. Arising from recommendation from a previous study, we evaluated its hydrocarbon generating potential using multidisciplinary tools involving visual kerogen analysis, as well as bulk and isotope geochemistry. Seventy-seven sample materials were taken from 3-outcrop sites at Uzebba, Okpekpe and Imiegba locations, Benin flank, SW Anambra Basin, Nigeria. The results show that bulk of the samples have good organic richness. Kerogen quality is dominantly of gas prone Type III kerogen. However, visual kerogen analysis indicates the presence of an oil prone Type II/III kerogen in the central basin subenvironments. An immature thermal maturity is inferred based on spore colour index (SCI) of less than 6 on the SCI chart (thermal alteration index of 10m of combined (continuous) outcropping and subcropping thickness Keywords: Kerogen, palynofacies, stable isotope geochemistry, shale gas

The Upper Neoproterozoic–Lower Cambrian section in the Olekma River basin is divided (from bottom to top) into the Dikimdia, Seralakh, Porokhtakh, and Pestrotsvetnaya formations, which are mainly composed of dolostones with a subordinate amount of sandstone, silty shales, gypsum, anhydrite, and native sulfur. The isotope data available allow one to substantially correct the stratigraphic units of the Olekma section, which is probably the most completed section on the Siberian Platform, including the transitional strata from the Vendian (Ediacaran) to the Cambrian. The Dikimdia Formation dolostones have typical Late Ediacaran values of 87Sr/86Sr = 0.70837–0.70843 and abnormally high δ13С values (up to 5.1‰), which gives reason to correlate this formation with the Ust’-Yudoma Formation (the stratotype area), the Dengying Formation in South China (548–550 Ma), the Uluntuy Formation of the Baikal Group, and the terminal Ediacaran sections in some other areas. The 87Sr/86Sr ratio decreases upward and reaches a minimum (0.70803–0.70818) near the Porokhtakh–Pestrotsvetnaya boundary. The lowermost part of the Porokhtakh Formation contains a negative carbon isotope excursion (δ13С = –4.4‰) marking the base of the Nemakit-Daldynian Stage, whereas ~8 m below the base of the Pestrotsvetnaya Formation the positive “pre-Tommotian” excursion (δ13С = 4.1‰) is located. There is a sharp decrease in Fe and Mn contents from ~3800 and ~300 ppm to ~2000 and ~130 ppm, respectively, in dolostones at the Ediacaran–Cambrian transition boundary which corresponds to the Seralakh–Porokhtakh boundary. High δ18О values (26.0 ± 1.2‰) do not provide reasons to associate the carbon isotope excursions, the 87Sr/86Sr trend, and variations of Fe and Mn contents with diagenetic alterations.

Research subject. The article presents the results of dating two dolerite dikes differing in geochemical features from a section along the Iset river in the area of Smolinskoe settlement (the Eastern zone of the Middle Urals). Materials and methods. The dating was performed by an U-Pb ID-TIMS technique for single zircon grains using an artificial 205Pb/235U tracer in the laboratory of geochronology and isotope geochemistry of the Geological Institute of the Kola Science Centre of the Russian Academy of Sciences. The lead isotopic composition and uranium and lead concentrations were measured using a Finnigan-MAT (RPQ) seven-channel mass spectrometer in dynamic mode using a secondary electron multiplier and RPQ quadrupole in ion counting mode. Results. The dikes were dated 330 ± 3 Ma and 240 ± 2 Ma. Conclusions. The research results indicate different ages of dolerite dikes developed within the Eastern zone of the Middle Urals. The oldest of the two established age levels corresponds to the Early Carboniferous era. This fact, along with the proximity of the dolerites to the petrochemical features of the basaltoids of the Early Carboniferous Beklenischevsky volcanic complex, allows these bodies to be considered as hypabyssal comagmates of these volcanics. The youngest obtained age level – Triassic – indicates that the introduction of some dolerite dikes was associated with the final phases of the trapp formation developed rarely within the eastern outskirts of the Urals and widely further east in the foundation (pre-Jurassic basement) of the West-Siberian Plate.

The kinetic isotope effect (KIE) produced by the phosphoric acid digestion reaction of carbonates has been well studied since the beginning of stable isotope geochemistry, but its molecular-level m...

Faults are commonly the largest fractures in a fracture network, forming the backbone of the permeability system in low-permeability rocks. Faults in outcrops of the Austin Chalk — an important oil and gas reservoir in south Texas, Louisiana, and westernmost Mississippi — exemplify deformation and fluid histories of subseismic-scale faults in mechanically layered chalk-dominated strata. Exposures of near-horizontal Austin Chalk in southwest Texas contain northwest- and southeast-dipping normal faults with exposed heights of meters to tens of meters and displacements of centimeters to decimeters. Local fault dips are steep to vertical through chalk and limestone beds and moderate through marl, mud rock, and clay-rich ash beds, producing refracted fault profiles. Failure surface characteristics indicate various failure modes, including tensile, hybrid, shear, and (locally) compactive shear behavior depending on the host lithology. Dilational zones associated with steep fault segments host calcite veins. Crack–seal textures in fault zone veins record repeated reactivation of refracted fault profiles. Fluid inclusion and stable isotope geochemistry analyses of fault veins indicate formation at depths of 1.4 to 2.9 km (4593 to 9514 ft) and possibly of 4.2 km (13,780 ft). Fluids include locally sourced saline waters and externally sourced waters and oil in rocks that did not reach oil maturation conditions. Inclusions of 30° API to greater than 50° API oil are found in veins 30 km (19 mi) updip from the Eagle Ford Formation oil zone. These results illustrate the migration of oil and other fluids within subseismic-scale Austin Chalk faults and fundamental control of lithology on fault zone architecture.

Ice core records of atmospheric methane ( CH 4 ) and its isotopic composition provide important information about biogeochemical cycles in the past. Interpreting these data requires that they faithfully record the composition of the atmosphere. In this study, we describe anomalies of up to 30–40 ppb CH 4 that are only observed in dust-rich ( > ∼ 60 ng Ca/g ice), glacial-period ice measured with standard melt-refreeze methods. The stable isotopic composition of CH 4 is also significantly affected. Results from the GISP2 and NEEM ice cores from Greenland show that excess CH 4 is either released or produced in the presence of liquid water in amounts which are highly correlated with the abundance of Ca 2 + and mineral dust in the sample. Additional experiments show that excess CH 4 is unaffected by the addition of HgCl 2 (a microbial inhibitor) and is not related to ice core storage time. Dust concentrations in Antarctic ice cores are an order of magnitude lower than in Greenlandic ice cores and no excess CH 4 was observed in samples from the Antarctic WAIS Divide (WD) and South Pole (SPICE) ice cores. While the overall structure of the ice core atmospheric methane history is minimally impacted by excess CH 4 , the impacts on the isotopic record and on inverse models used to reconstruct CH 4 sources are greater. We propose three potential mechanisms to explain the presence of excess CH 4 : (1) that CH 4 is adsorbed on dust particles prior to deposition on the ice sheet and is slowly desorbed during the melt-extraction step of sample analysis; (2) that dust acts as a micro-environment within the ice sheet for methanogenic extremophiles; or (3) that excess CH 4 is a product of abiotic degradation of organic compounds during the melt-extraction step of sample analysis.

Jarosite is a common mineral in acidic, sulfate-rich environments where it is critical in regulating the acidity of aquatic systems and the mobility of trace elements and potential contaminants. This research aims to understand jarosite formation and recrystallization in these environments by examining the stable iron isotope geochemistry of jarosite at two coastal sites in Victoria, Australia: Fossil Beach and Southside Beach. Jarosite occurs at high abundance as beds, veins, surface coatings and nodules within oxidized zones of sulfidic sediment outcrops and as pebbles, cobbles, and boulders at the base of the outcrops within the intertidal zone, making these two beaches ideal natural laboratories. Synchrotron powder X-ray diffraction (XRD) and ICP-MS results indicate that samples are comprised predominantly of natrojarosite, often with substantial K substitution. Rietveld refinement of XRD patterns shows that most jarosite samples are a solid-solution of Na-K jarosite, differing from previous observations that (near-)end-member mixing predominantly occurs in nature. The iron isotope composition of the jarosite samples have δ56Fe values between −1.91 and +1.24‰ (relative to IRMM-014), an exceptionally large range that partially overlaps with the δ56Fe values of the sulfidic sediment precursor (−0.54 to +1.30‰). There is a negative relationship between the alkali ratio [Na/(Na + K)] and iron isotope composition, with the heavier iron isotopes preferentially partitioned into K-rich jarosite. The large range in δ56Fe values of jarosite likely results from a combination of the variable δ56Fe values of the precursor sulfides, thermodynamic differences between Na- versus K-bearing jarosite, and an open-system Rayleigh distillation during jarosite formation.

Bottled water in the UK has a ~20 % share of the soft drinks market with a sales value of >£1.5 billion. Bottled water is susceptible to fraud and it is important to characterise the chemical signature of aquifers used by the bottled water industry. Measuring 18O/16O and 2H/1H ratios in bottled water is one important step in fraud prevention and aquifer characterisation as these ratios in groundwater tend to be stable or change very slowly through time. Here we characterise the isotopic signature of 30 brands of bottled water sold in the UK. The average δ18O of bottled waters is –7.4 and –48.4 for δ2H. This isotopic composition is closely related to that of the annual rainfall and follows latitudinal and longitudinal gradients which combine to explain 77 % of the δ18O variance.

Rare earth elements (REE) and Nd isotope compositions of surface and groundwaters from the Indian River Lagoon in Florida were measured to investigate the influence of submarine groundwater discharge (SGD) on these parameters in coastal waters. The Nd flux of the terrestrial component of SGD is around 0.7±0.03 μmol Nd/day per m of shoreline across the nearshore seepage face of the subterranean estuary. This translates to a terrestrial SGD Nd flux of 4±0.2 mmol/day for the entire 5,880 m long shoreline of the studied portion of the lagoon. The Nd flux from bioirrigation across the nearshore seepage face is 1±0.05 μmol Nd/day per m of shoreline, or 6±0.3 mmol/day for the entire shoreline. The combination of these two SGD fluxes is the same as the local, effective river water flux of Nd to the lagoon of 12.7±5.3 mmol/day. Using a similar approach, the marine-sourced SGD flux of Nd is 31.4±1.6 μmol Nd/day per m of shoreline, or 184±9.2 mmol/day for the investigated portion of the lagoon, which is 45 times higher than the terrestrial SGD Nd flux. Terrestrial-sourced SGD has an εNd(0) value of −5±0.42, which is similar to carbonate rocks (i.e., Ocala Limestone) from the Upper Floridan Aquifer (−5.6), but more radiogenic than the recirculated marine SGD, for which εNd(0) is −7±0.24. Marine SGD has a Nd isotope composition that is identical to the εNd(0) of Fe(III) oxide/oxyhydroxide coated sands of the surficial aquifer (−7.15±0.24 and −6.98±0.36). These secondary Fe(III) oxides/oxyhydroxides formed during subaerial weathering when sea level was substantially lower during the last glacial maximum. Subsequent flooding of these surficial sands by rising sea level followed by reductive dissolution of the Fe(III) oxide/oxyhydroxide coatings can explain the Nd isotope composition of the marine SGD component. Surficial waters of the Indian River Lagoon have an εNd(0) of −6.47±0.32, and are a mixture of terrestrial and marine SGD components, as well as the local rivers (−8.63 and −8.14). Nonetheless, the chief Nd source is marine SGD that has reacted with Fe(III) oxide/oxyhydroxide coatings on the surficial aquifer sands of the subterranean estuary.

The newly discovered Juyuan tungsten deposit is hosted in Triassic granite in the Beishan Orogen, NW China. The tungsten mineralization occurred as quartz veins, and the main ore minerals included wolframite and scheelite. The age, origin, and tectonic setting of the Juyuan tungsten deposit, however, remain poorly understood. According to the mineralogical assemblages and crosscutting relationships, three hydrothermal stages can be identified, i.e., the early stage of quartz veins with scheelite and wolframite, the intermediate stage of quartz veinlets with sulfides, and the late stage of carbonate-quartz veinlets with tungsten being mainly introduced in the early stage. Quartz formed in the two earlier stages contained four compositional types of fluid inclusions, i.e., pure CO2, CO2-H2O, daughter mineral-bearing, and NaCl-H2O, but the late-stage quartz only contained the NaCl-H2O inclusions. The inclusions in quartz formed in the early, intermediate, and late stages had total homogenization temperatures of 230–344 °C, 241−295 °C, and 184−234 °C, respectively, with salinities no higher than 7.2 wt.% NaCl equiv (equivalent). Trapping pressures estimated from the CO2-H2O inclusions were 33−256 MPa and 36−214 MPa in the early and intermediate stages, corresponding to mineralization depths of 3–8 km. Fluid boiling and mixing caused rapid precipitation of wolframite, scheelite, and sulfides. Through boiling and inflow of meteoric water, the ore-forming fluid system evolved from CO2-rich to CO2-poor in composition and from magmatic to meteoric, as indicated by decreasing δ18Owater values from early to late stages. The sulfur and lead isotope compositions in the intermediate-stage suggest that the Triassic granite was a significant source of ore metals. The biotite 40Ar/39Ar age from the W-bearing quartz shows that the Juyuan tungsten system was formed at 240.0 ± 1.0 Ma, coeval with the emplacement of granitic rocks at the deposit. Integrating the data obtained from the studies including regional geology, ore geology, biotite Ar-Ar geochronology, fluid inclusion, and C-H-O-S-Pb isotope geochemistry, we conclude that the Juyuan tungsten deposit was a quartz-vein type system that originated from the emplacement of the granites, which was induced by collision between the Tarim and Kazakhstan–Ili plates. A comparison of the characteristics of tungsten mineralization in East Tianshan and Beishan suggests that the Triassic tungsten metallogenic belt in East Tianshan extends to the Beishan orogenic belt and that the west of the orogenic belt also has potential for the discovery of further quartz-vein-type tungsten deposits.

Gas samples were collected from 25 m long horizontal boreholes drilled into the excavation field at 10° inclination to the longwall face in two mining areas, Pesje and Preloge, in the Velenje Coal Mine, Slovenia, from 2013 to 2018. The degassing mechanism of coalbed gas and its stable isotopic composition (δ13CCO2, δ13CCH4, and δ2HCH4) were investigated in boreholes in advance of eight working faces. The major coalbed gas constituents were CO2 and methane. Gas concentrations and isotope values revealed that the methane is biogenic in origin with δ13CCH4 values of -69.4 to -29.5 ‰, δ2HCH4 values of -301 to -222 ‰, and a fractionation factor (αCO2-CH4) of 0.998-1.073, suggesting that methane derives from microbial acetate fermentation and CO2 reduction. The carbon dioxide methane index values ranged from 50.0-98.3 vol.% and δ13CCO2 values from -11.8 to -0.5 ‰, indicating that CO2 is biogenic and endogenic in origin. The degassing mechanism results in isotope fractionation of methane and CO2 for carbon isotopes up to 39.9 ‰ and up to 8.5 ‰, respectively, depending on the position of the excavation fields in space, e.g. under pre-mined coal area, fresh overburden.

The separation of Ce from other rare earth elements has not been well established because of their similar geochemical properties. In this study, we report a single-stage extraction technique to purify Ce from natural samples with Eichrom DGA resin. This method separates Ce effectively from matrices and interfering elements, such as Ba, La, and Nd. The Ce elution curve would not drift with different Ce loading masses and rock types. The Ce isotope compositions were measured using a Thermo Scientific Neptune Plus multicollector (MC)-inductively coupled plasma (ICP)-mass spectrometry (MS) instrument. The instrumental mass bias of Ce isotopes was corrected with a sample-standard bracketing combined with a Sm-doping method. The δ142Ce values of standard solutions (CDUT-Ce and JMC304) relative to National Institute of Standards and Technology SRM 3110 measured were +0.128 ± 0.028‰ (2SD, N = 30) and 0.005 ± 0.038‰ (2SD, N = 30), respectively. The reproducibility for δ142Ce was better than 0.040‰. The Ce isotopic compositions of nine United States Geological Survey standard rocks, including carbonatite, basalt, andesite, quartz latite, dolerite, rhyolite, and granodiorite, were measured in this study. Our result showed that δ142Ce values of these rocks varied slightly, indicating that insignificant fractionation occurred during igneous processes. The technique proposed in this study is simple and time-efficient, which is beneficial for further studies on Ce isotope geochemistry.

Saltpetre (KNO3; potassium nitrate) is one of the major ingredients of gunpowder. Simplex saltpetre (total 126 samples) together with gunpowder (total 93 samples) commodities which are curr...

Isotopic reference materials (IRMs) are crucial for securing accurate and precise isotope ratio measurements of non-traditional stable isotopic systems and for enabling comparison of isotope ratio data obtained at different labs. Fe and Mg isotopic analysis have gained considerable interest as it expands our understanding of critical geological and biological processes. However, the isotopic reference materials used for Fe (IRMM-014) and Mg (DSM3) isotopic analysis are either out of stock or not readily available. In this work, we report on the use of multi-collector inductively coupled plasma-mass spectrometry (MC-ICP-MS) for determination of the isotopic composition of the two new isotopic reference materials IRMM-524A and ERM-AE143, which can be used for high-precision isotopic analysis of Fe and Mg, respectively, instead of IRMM-014 and DSM3. The Fe isotopic composition of IRMM-524A, determined as the intercept of the best-fitting straight line (linear regression) through the data points for multiple reference materials of geological and biological origin, measured relative to both the conventional and new isotopic reference materials is δ56FeIRMM-014 = −0.004 ± 0.014‰ (2SD) and δ57FeIRMM-014 = +0.005 ± 0.024‰ (2SD), and thus, within the experimental uncertainty it is the same as the value for IRMM-014. Using the same regression method, ERM-AE143 is shown to be isotopically lighter than DSM3, with δ26MgDSM3 = −3.295 ± 0.040‰ (2SD), and δ25MgDSM3 = −1.666 ± 0.043‰ (2SD). These new reference materials can be recommended as secondary isotopic standards or as a replacement for the conventional or primary reference materials when these become exhausted. Additionally, we provide a comprehensive set of Fe and Mg isotopic compositions for 21 geological and 10 biological reference materials, as a contribution to the field of isotope geochemistry, as well as to the blooming field of isotope ratio applications in biomedicine.

The high precision measurement of doubly substituted (“clumped”) isotopologues in CO2 is a topic of significant interest in isotope geochemistry. Here we describe the performance of a new isotope r...

The Wufeng and Longmaxi organic-rich shales host the largest shale gas plays in China. This study examined the petrography, rare earth element (REE) and other trace-element geochemistry, Sm-Nd geochronology, and isotope geochemistry (87Sr/86Sr, δ18O, δ13C) of fracture-cementing minerals within core samples of the Wufeng and Longmaxi Formations from the Jiaoshiba shale gas field in order to (1) characterize the mineral phases occurring in the veins (mineralized fractures); (2) determine the ages of the calcite by the Sm-Nd isochron dating method; (3) understand the sources of calcite-precipitating fluids; and (4) explore the possible mechanisms responsible for calcite vein formation in shale gas systems. The fractures hosted in the Longmaxi Formation are mineralized with quartz as the predominant fracture cement, and calcite as an intracementation phase postdating the earlier quartz cement. In contrast, the fractures hosted in the Wufeng Formation are dominantly mineralized by calcite, which occurs either as the only cement present or as a cement phase predating later quartz cement. Calcite veins within the Longmaxi Formation have a Sm-Nd isochron age of 160 ± 13 Ma and δ13C values of –4.71‰ to –3.11‰, δ18O values of 17.1‰–17.4‰, and 87Sr/86Sr values of 0.72437–0.72869. Calcite veins within the Wufeng Formation yielded a Sm-Nd isochron age of 133 ± 15 Ma and are characterized by δ13C values of –2.29‰ to –1.03‰, δ18O values of 17.3‰–17.7‰, and 87Sr/86Sr values of 0.72202–0.72648. The similarity between 87Sr/86Sr values of the calcite and those of their respective surrounding host rocks (0.72670–0.72875 of the Longmaxi shales; 0.72030–0.72648 of the Wufeng shales), combined with relatively depleted δ13C and uniform fluid δ18O isotopic features, indicates that the calcite-precipitating fluids within the Wufeng and Longmaxi Formations were derived largely from their respective surrounding host-rock sources. REE data equally indicate that the distinguishable Eu anomalies (6.20–19.35; 4.45–11.91), Y anomalies (1.03–1.50; 1.44–1.70), and Y/Ho ratios (28.80–39.16; 38.86–45.18) of calcite veins within the Longmaxi and Wufeng Formations were controlled by their respective surrounding host rocks. The Sm-Nd isochron ages and fluid inclusion data of fracture cements suggest that fracture opening and calcite precipitation in composite veins within the Wufeng and Longmaxi Formations were triggered by gas generation overpressurization.

Recent work has demonstrated that titanium (Ti) isotopes undergo mass-dependent isotope fractionation during magmatic differentiation, leaving evolved silicic melts preferentially enriched in heavy Ti isotopes. Preferential incorporation of light Ti isotopes in crystallizing Fe-Ti oxides is thought to be the mechanism responsible for this fractionation in magmatic rocks. To test this hypothesis, we present Ti isotope measurements of Fe-Ti oxide mineral separates of Kilauea Iki lava lake samples. We find that the Ti in Fe-Ti oxides is isotopically light while Ti in the residual melt and minerals is isotopically heavy. This result is consistent with the results of density functional theory (DFT) calculations in other studies, which show progressive heavy isotope enrichment for Ti from 6-fold, 5-fold, through 4-fold coordinated minerals. We therefore conclude that Ti isotopes in silicate melts undergo isotope fractionation during the crystallization of Fe-Ti oxides because Ti in oxides is primarily in 6-fold coordination whereas Ti in silicate melts is in 5- or 4-fold coordination (Ti in more evolved magmas tends to be in lower coordination). Based on our mineral separate results, we estimate the fractionation factor at 1000 °C between silicate and oxide Δ49Tisilicate-oxide to be 0.39 ± 0.06‰. This result is consistent with the fractionation factors inferred in previous studies based on Ti isotopic analyses and modeling of bulk rock measurements. We use this fractionation factor and the fractionation factors proposed by previous workers in Rhyolite MELTS to model the δ49Ti evolution of plume lavas. We find the model to generally predict the fractionations observed in Kilauea Iki, as well as the fractionations previously observed in volcanics from Hekla, Iceland and Afar, East Africa.

Active fumarolic solfataric zones represent important structures of dormant volcanoes, but unlike emitted fluids, their mineralizations are omitted in the usual monitoring activity. This is the case of the Campi Flegrei caldera in Italy, among the most hazardous and best-monitored explosive volcanoes in the world, where the landscape of Puteoli is characterized by an acid sulfate alteration that has been active at least since Roman time. This paper provides temperature, mineralogical, textural, compositional and stable isotope data for those solfataric terrains sampled at the crater and Pisciarelli slope of the Solfatara volcano between 2013 and 2019. Temperatures vary between 40 and 95 ∘C. Minerals include alunite with grain sizes generally larger than 20 µm, alunogen, native sulfur, well-ordered kaolinite, and, common at Pisciarelli, pyrite, illite and NH4 sulfates. Sulfate terrains have higher contents of Ti, Ba, Au, As, Hg and Tl relative to their parent substrate. The Pisciarelli slope is anomalous in terms of the presence of NH4. δ34S values for sulfides and native S range between −3.00 ‰ and 0.49 ‰ and from −4.42 ‰ to 0.80 ‰, respectively. Sulfates show δ34S and δ18O values in the range of −2.78 ‰ to 2.09 ‰ and between 4.60 ‰ and 31.33 ‰, respectively. The style of mineralization and the stable isotope geochemistry do produce complex and not completely consistent classifications and genetic constraints. We merge our data with volcanological information, data from exploration drillings and geophysical results. With the conceptual model, we suggest a series of shallow and deep aquifers interconnected like “communicating vessels” through a main fault system that downthrows Solfatara with respect to Pisciarelli. Fluid outflow from the different discrete aquifers hosted in sediments – and possibly bearing organic imprints – is the main dataset that allows determination of the steam-heated environment with a supergene setting superimposed. Supergene conditions and high-sulfidation relicts, together with the narrow sulfate alteration zone buried under the youngest volcanic deposits, point to the existence of an evolving paleo-conduit. The data will contribute to monitoring and evaluating the volcanic hazards.

With developments in multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS), applications of metal stable isotopes received increasing attentions in the studies of source and fate of heavy metals in the environment. In light of the rapid progresses in this emerging field, we attempted to review the recent findings comprehensively in a way that environmental scientists can easily read. This review started with an introduction of basic terminologies in isotope geochemistry, followed with detailed descriptions of instrumentation and analytical procedures, and finally focused on the cases of three typical metal stable isotopes (Ag, Hg and Zn) to illustrate how they were applied to address environmental issues. Additionally, future perspectives on the applicability, opportunities, and limitations of metal stable isotope techniques as novel approaches in advancing environmental chemistry were discussed.

The sulfur isotope composition was measured in the main morphological types and generations of sulfides composing the ores of the Dzhusa deposit and the contents of trace elements were measured using highly sensitive laser ablation-inductively coupled plasma-mass spectrometry (LA–ICP–MS) for the first time. According to the sulfur isotope geochemistry, we assume that a deep magmatic source made a predominant contribution to the ore-forming fluid. Using the STATISTICA software modules, correlation analysis was performed and the trace element distribution patterns in sulfides were revealed.

Redox-sensitive trace elements and sulfur isotope compositions obtained via in situ analyses of sedimentary pyrites from marine black shales are used to track atmosphere-ocean redox conditions between ∼1730 and ∼1360 Ma in the McArthur Basin, northern Australia. Three black shale formations within the basin (Wollogorang Formation 1730 ± 3 Ma, Barney Creek Formation 1640 ± 3 Ma, and Upper Velkerri Formation 1361 ± 21 Ma) display systematic stratigraphic variations in pyrite trace-element compositions obtained using LA-ICP-MS. The concentrations of several trace elements and their ratios, such as Se, Zn, Se/Co, Ni/Co, Zn/Co, Mo/Co, Se/Bi, Zn/Bi, Ni/Bi, increase from the stratigraphically lower Wollogorang Formation to the Upper Velkerri Formation. Cobalt, Bi, Mo, Cu, and Tl show a consistent decrease in abundance while Ni, As, and Pb show no obvious trends. We interpret these trace element trends as a response to the gradual increase of oxygen in the atmosphere-ocean system from ∼1730 to 1360 Ma. Elements more mobile during erosion under rising atmospheric oxygen show an increase up stratigraphy (e.g., Zn, Se), whereas elements that are less mobile show a decrease (e.g., Co, Bi). We also propose the increase of elemental ratios (Se/Co, Ni/Co, Zn/Co, Mo/Co, Ni/Bi, and Zn/Bi) up stratigraphy are strong indicators of atmospheric oxygenation. Sulfur isotopic compositions of marine pyrite (δ34Spyrite) from these formations, obtained using SHRIMP-SI, are highly variable, with the Wollogorang Formation exhibiting less variation (δ34S = –29.4 to +9.5‰; mean –5.03‰) in comparison to the Barney Creek (δ34S = –13.8 to +41.8‰; mean +19.88‰) and Velkerri Formations (δ34S = –14.2 to +52.8‰; mean +26.9‰). We propose that the shift in mean δ34S to heavier values up-section corresponds to increasing deep water oxygenation from ∼1730 to 1360 Ma. Incursion of oxygenated waters possibly caused a decrease in the areal extent of anoxic areas, at the same time, creating a possibly efficient reducing system. A stronger reducing system caused the δ34S of the sedimentary pyrites to become progressively heavier. Interestingly, heavy δ34S in pyrites overlaps with the increase in the concentration of certain trace elements (and their ratios) in sedimentary pyrites (Se, Zn, Se/Co, Ni/Co, Zn/Co, Mo/Co, Ni/Bi, and Zn/Bi). This study concludes that there was a gradual increase of atmospheric oxygen accompanied by ocean oxygenation through the first ∼400 million years of the Boring Billion (1800–1400 Ma) in the McArthur Basin.

Aquatic plants are major input sources of autochthonous organic matter in lake sediments, but investigations on fatty acid (FA) and n-alkane distributions in aquatic plants are currently limited, greatly hindering the applications of their isotope geochemistry in lacustrine environments. Here, the reported n-alkyl lipid distributions of aquatic plants in globally studied lakes, together with newly obtained aquatic plant n-alkyl lipid data in Chinese lakes (Yunnan and Inner Mongolia), are used to understand their distribution characteristics. The results show that aquatic plants have predominantly mid-chain lipids (C23–C25n-alkanes and C22–C24 FAs), differing from that of terrestrial plants (dominant by long-chain lipids), but the long-chain n-alkanes (e.g., C27 and C29) and long-chain FAs (e.g., C26 and C28) also show high abundances in most samples. Submerged plants have high concentrations of long-chain n-alkanes (avg. 47 µg g−1) and long-chain FAs (avg. 170 µg g−1), close to those in terrestrial plants, indicating that submerged plants may make large contributions of long-chain n-alkyl lipids to lake sediments, while the contributions of long-chain n-alkyl lipids derived from algae to lake sediments may be small because of their low concentrations (avg. 2 µg g−1 for n-alkanes and 9 µg g−1 for FAs). We find that lipid molecular proxies (including ACL14–32 and ATR14–18) can be reliably used to distinguish the FAs sourced from algae and other plants, and Paq’ values can be utilized to distinguish the n-alkane sources between submerged plants and terrestrial plants. Aquatic plants do not have significant δD differences among different chain-length n-alkanes and FAs for each sample, suggesting that the offset between δD values of different chain-length n-alkyl lipids in lake sediments can help determine sedimentary lipid input sources and infer paleohydrological changes.

A travertine fissure ridge and travertine mound are situated ~800 m from each other at the western margin of the active tectono-volcanic Sanandaj-Sirjan zone (western Iran). Despite their close proximity, the two geobodies show a difference in morphology, lithofacies, lithotypes, diagenesis and geochemistry. Petrographic analysis of the fissure ridge carbonates revealed homogeneous sparitic fabrics with dendritic structures reflecting precipitation under fast-flowing conditions from calcite supersaturated spring water. The mound carbonates are much more heterogeneous and display dominantly micritic fabrics with (mainly volcanic) clasts reflecting a lower energy flow regime and lower calcite saturation. In contrast to the limited diagenetic overprint of the fissure ridge carbonates, the more porous mound carbonates are affected by dissolution, cementation, and formation of Mn/Fe-oxide/hydroxides, attesting of a strong control on porosity by early diagenetic processes. The widespread bright luminescent calcite phases especially in sparitic fabrics within both geobodies display high Mn concentrations in calcite indicating suboxic precipitation conditions. The overlapping 87Sr/86Sr signatures and δ13C signatures point to a mixture of CO2 that dominantly originated from dissolution of the marine carbonate Qom Formation (Oligo-Miocene). The different δ18O signatures, indicate different upwelling systems caused by different substrate settings. The fissure ridge formed on a hard and brittle limestone substrate with precipitation from dominantly subsurface-sourced fluids. The mound travertine formed on top of fairly unconsolidated and fractured volcanic strata. The depleted δ18O signatures and impure micrite-dominated fabrics of the mound travertine reflect precipitation from thermal water that mixed with surrounding groundwater. This difference is also reflected in a different calculated precipitation temperature that varies between 4 and 21 °C for the mound versus 25–50 °C for the fissure ridge. Our findings show that subsurface geology exerts a major control on precipitation processes resulting in differences in travertine morphology, sedimentology, diagenesis, and geochemistry, despite that the travertine bodies occur adjacent to each other.

A combined bulk and position-specific isotope study was conducted on natural gases collected from an unconventional gas field in the Late-Devonian to Early Mississippian Woodford Shale in the southwestern Arkoma Basin in Oklahoma. The set of natural gases records a hitherto underreported case, where gases become wetter with decreasing isotope compositions in an early stage of maturation. A first dataset of position-specific isotope compositions of propane with demonstrated accuracy and precision show that while the bulk δ2H values of propane increased by 30‰ with maturity, position-specific hydrogen isotope deviations of propane (Δ2-1) increased by 80‰. Position-specific δ2H values showed that δ2H values of the central H in propane increased by 70‰ with maturity, but those of terminal H in propane remained constant. This contrasting behavior could have resulted from the hydrogen isotope exchange between shale water and propane with a half-time of the center H, varying strongly from ∼310 to ∼6 m.y. at ∼140–185 °C. On the other hand, bulk and position-specific δ13C values of propane remain nearly constant during the maturation. Position-specific isotope compositions of propane at the highest maturity yield an equilibrium temperature that is consistent with its maturity, thus possibly serving as single-compound isotope geothermometry.

The Paleoproterozoic Kalahari Manganese Field is the largest known land-based manganese (Mn) deposit on Earth and comprises five erosional relics of the iron- and manganese-rich Hotazel Formation. A total of 19 manganese ore samples from the lower manganese ore horizon of the Hotazel Formation were selected for analysis based on their relative metasomatic alteration states. These samples range from primary diagenetic, classic supergene enriched, hydrothermally enriched (Wessels-type ore) and thrusted manganese ore. When normalised to Post-Archaean Australian shale composites, rare earth elemental analyses on the selected samples indicate significant relative enrichments within the thrusted manganese ore, an ore type that hasn’t been studied from a geochemical point of view, so far. A comparison between these respective enrichments and 87Sr/86Sr ratios indicates a distinct link between REE enrichments and associated alteration events, and a progressive increase in 87Sr/86Sr isotope values. An isotopic relationship between fluid infiltration events and REE redistribution within the Hotazel Formation has been established, highlighting unique isotope signatures necessary in better defining and characterising metasomatism within the Paleoproterozoic Kalahari Manganese Field.

The Binh Do Pb-Zn deposit in the Phu Luong region (Thai Nguyen Province, northern Vietnam) is located on the southern margin of the South China Block. The fault-controlled Pb-Zn orebodies are mainly hosted in Upper Paleozoic carbonate formations. In order to reveal the mineralization type and metallogenesis of this deposit, multi-isotopic (S, Pb, H and O) analyses on typical ore and gangue minerals were conducted. The average ore sulfide δ34SΣS value is 4.3‰, suggestive of magmatic sulfur. The ore sulfide Pb isotope compositions are homogeneous, with the 206Pb/204Pb, 207Pb/204Pb and 208Pb/204Pb values of 18 501 to 18 673 15.707 to 15 798, and 38 911 to 39.428, respectively. Lead isotope model ages of the ore sulfides (240-220 Ma) are consistent with the timing of regional Triassic S-type granite emplacement (250-220 Ma), suggesting that the metals may have been granite-derived. The quartz δDV-SMOW (-82.4‰ to -70.5‰) and δ18OH2O (-0.4‰ to +6.4‰) values suggest that the ore-forming fluids were composed of mixed magmatic and meteoric waters. Combined with the geological features of the Pb-Zn deposit in the region, we propose that the Pb-Zn deposits belong to magmatic-hydrothermal type, rather than MVT-type as previously suggested. The Triassic granites may have contributed the ore-forming material and heat that drove the hydro-thermal system. The ore-forming fluids may have migrated into interlayer faults and fractures of the carbonate strata, diluted by subsurface meteoric water and deposited successively the vein-type and stratiform-type Pb-Zn ores.

There is a renewed interest in K isotope geochemistry driven by the advances in analytical precision and it is emerging as a useful tracer in a variety of disciplines ranging from Earth sciences to biology. However, high-quality K isotopic data for reference materials are still limited but highly needed. Here, we report high-precision stable K isotopic compositions (δ41K) for 23 commercially available international reference materials, including igneous, sedimentary, and metamorphic rocks, as well as an in-house seawater standard. Potassium in digested samples was separated by cation-exchange chromatography with Bio-Rad AG50W-X8 (200–400 mesh) resin in 0.5 N HNO3 media. Potassium isotopes were measured on a Nu Plasma II high-resolution MC-ICPMS. The reproducibility of K isotopic analysis, based on over one year of measurements of pure K solutions and rock standards, was ≤0.06‰ (95% confidence interval). Synthetic solutions made by mixing single element standards to represent various rock matrices confirmed the accuracy of our methods. The 23 reference materials have δ41K values ranging from −0.562‰ to −0.253‰ and the seawater standard has a much higher δ41K value of 0.143‰. The comprehensive dataset presented here provides a reference for quality control and inter-laboratory comparison of high-precision K isotopic analyses for future studies.

The Proterozoic Eon spans Earth's middle age during which many important transitions occurred. These transitions include the oxygenation of the atmosphere, emergence of eukaryotic organisms and growth of continents. Since the sulfur and oxygen cycles are intricately linked to most surface biogeochemical processes, these transitions should be recorded in changes to the isotopic composition of marine and terrestrial sulfate minerals. Here we present oxygen (∆17O, δ18O) and sulfur (∆33S, δ34S) isotope records of Proterozoic sulfate from currently available data together with new measurements of 313 samples from 33 different formations bearing Earth's earliest unambiguous evaporites at 2.4 Ga through to Ediacaran aged deposits. This record depicts distinct intervals with respect to the expression of sulfate isotopes that are not completely captured by established intervals in the geologic timescale. The most salient pattern is the muted ∆17O signatures across the GOE, late Proterozoic and Ediacaran with values that are only slightly more negative than modern marine sulfate, contrasting with highly negative values across the mid-Proterozoic and Cryogenian. We combine these results with estimates of atmospheric composition to produce a gross primary production (GPP) curve for the Proterozoic. Through these results we argue that changes in GPP across Earth history likely help account for many of the changes in the Proterozoic Earth surface environment such as rising atmospheric oxygen, large fluctuations in the size of the marine sulfate reservoir and variations in the isotopic composition of sedimentary sulfate.

Oxygen and carbon isotope (δ18O and δ13C) data from bulk carbonates are widely applied proxies for temperature, the precipitation/evaporation ratio and productivity in lacustrine palaeohydrology and palaeoclimatology. In case of the terminal and alkaline Lake Van, however, previous studies have shown that bulk oxygen isotope compositions are in disagreement with other proxies when interpreted in a conventional manner. Similarly, the reports on the nature and the timing and site of carbonate precipitation in Lake Van are inconsistent. This study provides evidence on the mineralogy (X-ray powder diffraction analysis, scanning electron microscope imaging, confocal Raman microscopy, electron microprobe analysis) and isotope composition (δ18O and δ13C) of non-skeletal carbonate minerals in a Lake Van sedimentary profile spanning the last ca. 150 kyr. Carbonate phases present in the sediment include aragonite, low-Mg calcite, and calcian dolomite. Dolomite forms as an early diagenetic phase and occurs episodically in high concentrations driving the bulk isotope record towards the higher dolomite δ18O and varying δ13C values. Aragonite and low-Mg calcite precipitate in the surface water and are present in the sediments in varying amounts (relative aragonite to calcite content for dolomite-poor samples Ar/(Ar + Cc) of 93 to 41 wt%). In an attempt to explain this variation, we revised a precipitation model based on annually laminated sediments containing both aragonite and calcite spatially separated in light and dark coloured laminae, respectively. According to our model, spring calcite precipitation, under close-to-freshwater conditions, is followed by evapoconcentration-driven aragonite precipitation in late summer. The precipitation of these carbonate polymorphs from chemically differing surface waters (i.e. freshwater-influenced and evapoconcentrated) leads to distinctly different oxygen and carbon isotope signatures between sedimentary penecontemporaneous aragonite and calcite. The δ18O and δ13C values of aragonite relative to calcite are significantly higher by several per mille than inferred from aragonite-calcite fractionation factors alone, suggesting that the generalised assumption of sedimentary coeval calcite and aragonite precipitating from water with the same isotopic composition is flawed. The here proposed revised hydrologically-separated carbonate precipitation model is not only taking (i) differences in the isotopic fractionation between carbonate minerals into account, but also (ii) considering the hydrological conditions and the processes favouring the precipitation of a given mineral and ultimately controlling its isotopic composition. If mixed mineralogies are present, this mineralogy-specific approach has the potential of refining environmental reconstructions and reconciling apparently equivocal interpretations of different proxy records.

Biogenic carbonate minerals are widely used as archives in paleoenvironmental research, providing substantial information for past depositional and diagenetic regimes. However, nearly all biogenic carbonates undergo post-mortem diagenetic alteration to variable degrees. Diagenetic features are essentially caused by complex fluid-solid interaction including recrystallization and neomorphosis of shell architecture and related geochemical resetting. A common conception is that a given primary shell texture is replaced by a secondary fabric via micro-scale dissolution-reprecipitation reactions that may reach geochemical and/or isotopic equilibrium with the diagenetic fluid. Here we document that the process of petrographic and geochemical alteration of a biogenic carbonate archive progresses stepwise, and the re-equilibration processes can be separated in space and time. More specifically, attached and bound aqueous fluids within the shell organic matter and fluid inclusions likely play a crucial role in the early stages of alteration within a relatively rock-buffered system. Degradation of organics was observed via decreased sulfur concentration and decreased fluorescence. In this early stage of alteration, the conversion of micro-scale aragonite biominerals to metastable diagenetic calcite (meso)crystals is documented by RAMAN spectroscopy, electron backscatter diffraction (EBSD), and a decrease in strontium concentrations. Further stabilization to larger, neomorphosed calcite crystals resulted from re-equilibration with external fluids and was evidenced by EBSD, oxygen isotope data, and further reduction of strontium. Spatial chemical and isotope data were used to decipher the impact of fluid availability and transfer behavior, i.e. carbonate-buffered versus diagenetic-fluid buffered, and isotope and element exchange behavior, and analyzed in context to textural alteration features. These data suggest that during diagenesis, the evolution to more sustainable (diagenetically induced) fabrics is accompanied by individual reaction steps traced by elemental and isotopic signatures. Kinetics, and thus degree of diagenetic alteration of biominerals at a given exposure to physicochemical alteration conditions is initially strongly controlled by the micro- to nano-scale internal architecture governing the availability and transfer of aqueous fluids. Results shown here have significance for those concerned with biogenic carbonate archives and have wider implications for a mechanistic understanding of carbonate diagenesis.

The boron (B) isotope-pH proxy for marine carbonates has been widely used to reconstruct past ocean pH values. Unlike seawater, the apparent dissociation constant of boric acid (KB) and the δ11B values of brines from the terrestrial salt lakes in western China vary. However, relevant studies concerning the B isotope geochemistry of brine-carbonate systems in terrestrial salt lakes are limited. In this study, thirty-nine clastic samples from a sediment core (ISL1A) from the Qarhan Salt Lake in the Qaidam Basin were collected. These carbonates were analyzed for δ11B, B, Mg, Sr and Ca. Using our new data as well as published pH values, total dissolved solids (TDS), element concentrations, and δ11B values of brines in western China, we reached the following conclusions. (1) During evaporation process, salinity increases, the δ11B values of brines in salt lakes increase, and the pKB (−logKB) and pH values simultaneously decrease. (2) The large heterogeneity in the δ11B values of the carbonates (−2.74‰ to +7.64‰) from core ISL1A is mainly due to the δ11B values of the brines, rather than pKB and pH. (3) B isotopic fractionation with a small αcarbonate-brine of 0.997 in a brine-carbonate system conforms to the Rayleigh fractionation model. (4) Our comparison of the δ11B values of these carbonates with other records from core ISL1A suggests that the δ11B values of the carbonates in the arid Qaidam Basin can be used as a new proxy for the salinity of paleo-lake water.

Groundwater in the Cambrian-Vendian aquifer system in Estonia is characterised by the most depleted isotopic composition known in Europe (δ18O down to −23‰). The water most likely originates from glacial meltwater recharge from the Fennoscandian Ice Sheet in the Pleistocene. The aquifer system is characterised by relative high methane concentrations (up to 50% of dissolved gases, estimated absolute concentration up to 1600 μmol L−1), the origin of which has so far remained unclear. In this paper, we focus on the origin of methane, the factors controlling its spatial distribution and its isotope geochemistry in the aquifer system. The data reveal a large spatial variability in methane concentration, δ13CCH4 and δ2HCH4 values (from −6 to −105‰ and from −220 to −420‰, respectively). We show that local oxidation processes rather than different pathways of methane formation, have affected the initial isotopic composition of methane. Using the least modified δ13CCH4 values (from −85 to −105‰), we conclude that methane most likely originates from the organic material overridden by the Fennoscandian Ice Shield during the Late Weichselian glaciation, that was carried into the aquifer system with infiltrating glacial meltwater. The estimated δ18O values of the water, where the methane was formed, are −17 ± 1.5‰ supporting the inference that the methane was formed during the Middle Weichselian interstadial. The study shows that groundwater of glacial origin in the Cambrian-Vendian aquifer system can serve as an alternative palaeoenvironmental archive to be used for studying the variations in climatic and environmental conditions in Northern Europe during glacial–interglacial cycles of the Pleistocene.

It has been estimated that up to 25% of Indigenous human remains held in Australian institutions are unprovenanced. Geochemical tracers like strontium isotope ratios ( Sr/ Sr) have been used globally for over 40 years to discern human provenance and provide independent data to aid in repatriation efforts. To reliably apply this technology, landscape Sr/ Sr isotope ratio variability must be quantified. In Australia, only a few studies have used this technique and they are lacking in detail. Here, we present Australia's first regional strontium isotope ratio variability study. We measured strontium isotope ratios in soil, plant, water, and faunal material throughout Cape York, Queensland, the most northerly point of mainland Australia. Results show a close correlation between surface soil leachates, vegetation, surface water, and faunal Sr/ Sr results with extremely high values (0.78664) associated with ancient Precambrian geology. Our study suggests that measuring Sr/ Sr in soil and plant samples offer a reliable approach for assessing regional Sr isotope distribution, although the inclusion of mammal and freshwater samples is also important to assess exogenous inputs. This study provides an important tool for modern and prehistoric provenance studies and may aid in answering some of Australia's most enduring archaeological questions.

Elemental and isotopic pattern of n(87Sr)/n(86Sr) and δ88Sr/86SrSRM987 were used to characterise groundwater and recharge of saline ponds in a clastic aquifer in East Austria. Therefore, shallow, a...

The genetic identification of different types of natural gas is notably important for assessment of its sources and exploration potential. The chemical and isotopic (C and H, in particular) compositions of natural gas vary significantly due to the complexity of its generation, migration, and accumulation processes. The “coal-type” gas generated from humic matter is generally enriched in 13C as compared to "oil-type" gas generated from sapropelic organic matter. However, gas originating from fresh-brackish water environments is depleted in 13C whereas gas from saline environments is enriched in 13C. Notwithstanding organic precusors and sedimentary environments, both isotope compositions of alkanes tend to become enriched both in 13C and 2H with prograde thermal evolution. Therefore, in addition to thermal maturity, source material is the major controlling factor of carbon isotope compositions, whereas sedimentary environment is predominant in governing hydrogen isotopes. Secondary processes, including thermochemical sulfate reduction (TSR) and diffusion, result in an enrichment of the gases in 13C and 2H due to mass-dependent kinetic isotope effect. Microbial degradation causes a decrease in propane content and an enrichment in 12C and 2H of the residual propane. The abiogenic gases may include methane from deep mantle and high molecular weight hydrocarbons through Fischer-Tropsch type (FTT) synthesis. Methane of mantle origin possesses a narrow range of isotope compositions, although it is still a tall task to determine the exact values. In contrast, isotopes of alkane gases synthesized from FTT processes are in a wide range. In sedimentary basins, the mixing of gases from multiple sources and/or through different secondary processes may pose a challenage to identification of their origins. The detailed assessment is provided here with case studies from major oil and gas basins in China. This review provides identification of misconceptions in genetic types of natural gas using carbon and hydrogen isotopes of alkanes, and sheds insights into using isotope geochemistry as an important diagnostic tool for energy exploration as well.

A simple and quick method for simultaneous purification of Cu, Zn and Mo and accurate and precise measurement of their isotopic composition in geological samples using multi-collector inductively coupled plasma mass spectrometry (MC-ICP-MS) has been developed. The method involves the use of a single chromatographic column filled with the anion exchange resin AG-MP-1 for complex matrix removal and further purification of these three elements. The external standard-sample-standard bracketing (SSB) procedure combined to internal standard addition was used for accurate mass bias correction and precise Cu, Zn and Mo isotopic ratio measurements. The method was applied to different geological materials, as granodiorite (GSP 2-USGS), limestone (JLS-1, Japan), Buffalo River Sediments (NIST SRM - 8704) and sediments from Amazon River Basin. The mean precision for these samples was: 0.08 ‰ for δ65/63Cu; 0.05 ‰ for δ66/67Zn and 0.04 ‰ for δ98/95Mo. The main advantage is that the proposed method is simple and rapid, and carries out the quantitative recovery of elements of different atomic masses and at very low concentration ranges, mainly for Mo. In addition, optimizations made the calibration and correction of instrumental mass bias easier, leading to consistent results with other methods that are currently published. The comparison of isotopic compositions of Cu and Mo obtained for granodiorite with respect to data reported in the literature demonstrate that the simpler and multi-element method developed in this study can be properly used within the required limits of accuracy as a multi-proxy tool in isotope geochemistry.

Platinum-group element (PGE) geochemistry may be used to constrain the timing of sulfide saturation in magmas, which influences the Cu and Au fertility of evolving magmatic systems. We report new geochronological and geochemical data, with emphasis on PGE geochemistry, for a suite of regional porphyritic hornblende–diorite intrusions and ore-bearing porphyries from the super-giant Escondida and smaller Zaldivar Cu deposits of Northern Chile. The regional dioritic intrusions have zircon U–Pb ages between 39·6 to 37·1 Ma, which overlap with the ages of the ore-bearing Escondida and Zaldivar porphyries (38·1 to 35·0 Ma). Whole-rock major and trace element, and Sr–Nd–Pb and zircon O–Hf isotope geochemistry indicate that the regional diorites and ore-bearing porphyries are co-magmatic and originated from the same mantle-derived magma by fractional crystallization, with minor contamination by Paleozoic crust (∼10%). The low concentrations of PGE in the regional diorites show that they reached sulfide saturation before the MgO content of the melt fell to 4·7 wt %, the MgO content of the most primitive sample analysed. The fraction of sulfide melt which separated from the melts that formed the regional diorites is estimated to be ∼0·12 wt %; this resulted in the partitioning of highly chalcophile elements (Au and PGE) into a sulfide phase that was retained in cumulus rocks at depth. However, the fraction of sulfide melt was too low to have a significant effect on the Cu content of the fractionating melt. As a consequence, when the evolving melt eventually reached volatile saturation, it contained enough Cu (40 ± 10 ppm) to form a super-giant Cu deposit. In contrast, Au was largely stripped from the melt by sulfide precipitation, with the result that the mineralization at Escondida is Cu dominant, with only minor Au. The Zaldivar deposit, on the other hand, contains even less Au, which is attributed to a longer fractionation interval between sulfide and volatile saturation. This study provides evidence to support previously proposed models which suggest that the timing of sulfide saturation, the amount of sulfide melt produced, the water content and oxidation state of the melt, and the magma volume are critical factors in determining the potential to form a porphyry Cu deposit. Plots of Pd/MgO against Y can be used as empirical indicators of magma fertility for porphyry mineralization, and to discriminate between Cu–Au and Cu-dominated systems, but cannot predict the size of the deposit. The super-giant status of the Escondida deposit is attributed to it being underlain by a large batholith with a calculated minimum mass of 10 12 tonnes (∼400 km 3 ).

Combined whole-rock lead isotope and high-precision trace element data are reported for shales from the Wolverine deposit and surrounding prospects (e.g., Puck, Fisher, Sable) to elucidate the source of Pb in the shales and their potential utility as an exploration vector. Shales exhibit distinct variations in time-integrated U/Th/Pb evolution with proximity to mineralization. Distal samples resemble the local crustal Pb isotope composition of the northern Cordilleran continental crust (i.e., shale curve). More proximal samples exhibit evidence for hydrothermal activity, but were not significantly mineralized. They have very high U/Th and U/Pb and anomalous present-day 206 Pb/204Pb (>20) coincident with elevated Y/Ho, Zr/Hf, and carbonate alteration. These signatures were derived from oxygenated seawater and imprinted on the shales by oxygenated, CO2-rich hydrothermal fluids that contained uranyl carbonate ions (e.g., UO2(CO3) 3 4– ). It is envisioned that this was due to shallow-level (within 50 m of the seafloor), near-vent ingress of oxygenated seawater associated with hydrothermal venting. A third population of samples is most proximal to mineralization. These, too, have trace element signatures (i.e., high Y/Ho, Zr/Hf, CO2-U enrichment) inherited from seawater, but they do not exhibit anomalous present-day 206Pb/ 204 Pb, being more juvenile in 206 Pb/ 204 Pb, 207 Pb/ 204 Pb, and 208Pb/204Pb. This isotope composition coincides with enrichments in Pb, Zn, Cu, Tl, Sb, W, and Sn (±Cu, Mo). The Pb enrichment associated with mineralization effectively buffered these samples from appreciable Pb isotope evolution, despite overprinting by uranyl carbonate. The juvenile Pb associated with the shales proximal to mineralization argues for deep-penetrative circulation of hydrothermal fluids and leaching of Pb from mafic igneous rocks at depth and/or influence from juvenile magmas at depth (i.e., magmatic fluids). Both of these processes were likely critical for the genesis of mineralization at Wolverine. This study illustrates the utility of quadrupole inductively coupled plasma-mass spectrometry (ICP-MS) for providing sufficiently precise and accurate Pb isotope determinations for district-scale metallogenic evaluations. Furthermore, the coupling of solution ICP-MS Pb isotopes with high-precision trace element geochemistry from the same digest provides a powerful tool for regional exploration studies for hydrothermal mineralization in shale basins.