Lithium Isotopes Research Articles

A novel ion-pair strategy for efficient separation of lithium isotopes using crown ethers

• A novel and facile ion-pair strategy for 6 Li/ 7 Li separation is presented. • An exceptionally high distribution of Li + is achieved for CEs using this strategy. • The strategy shows good separation performance of 6 Li/ 7 Li. • Weakening the interactions related to Li + can facilitate the separation of 6 Li/ 7 Li. Effective separation of lithium isotopes ( 6 Li and 7 Li) is of great importance for the development of nuclear energy. Crown ethers (CEs) are widely used and reported separation systems, but the distribution coefficient of Li ( D Li ) is relatively low by CEs ( D Li , 10 − 2 –10 −5 ) and mainly depends on the anion type of Li salt. Herein, a novel and facile ion-pair strategy by introducing tetrachloridoferrate ([FeCl 4 ] − ) as counter anion is presented, which helps to overcome the Hofmeister bias and facilitates the efficient transfer of Li + from extremely hydrophilic chlorides. An exceptionally high D Li of 54 is achieved for benzo-15-crown-5 (B15C5), surpassing those of solvent extraction from solely Li salt aqueous solution. This strategy also demonstrates good separation performance of 6 Li/ 7 Li. The maximum 6 Li/ 7 Li separation factors ( α 6 L i / 7 L i ) of 1.038 and 1.049 are obtained for B15C5 and benzo-12-crown-4 (B12C4) in dichloroethane at 273 K. The highly efficient phase transfer of Li + can be attributed to the formation of stable [Li(B15C5)(H 2 O)][FeCl 4 ] or [Li(B12C4) 2 ][FeCl 4 ] ion pairs. Theoretical studies based on density functional theory (DFT) calculations suggest that the coordination and electrostatic environment of Li + plays an essential role in the separation of 6 Li/ 7 Li. Weakening the coordination and electrostatic interactions associated with Li + can facilitate the separation of 6 Li/ 7 Li. Additionally, B15C5 can be easily recycled by using ultra-pure water as the stripping solution. This work provides an industrially promising system for 6 Li/ 7 Li separation.

The evolution of lithium isotope signatures in fluids draining actively weathering hillslopes

The stable isotopes of lithium (Li) serve as a robust proxy of silicate weathering. The fate and transport of these isotopes in the dissolved load of major rivers have been characterized to infer changes in both contemporary weathering regimes and paleo-conditions. In this contribution, we deconvolve this integrated signal into the individual processes that fractionate Li at the inception of silicate weathering by directly measuring Li isotope ratios of waters (δ7Li) transiting through a rapidly eroding first-order hillslope. We use these data to develop a multicomponent reactive transport framework, which shows that net dissolution of weathered material generates light δ7Li signatures (as low as −9.2‰) in the shallow portion of the vadose zone. An increase in δ7Li deeper into the vadose zone (as much as +18‰) reflects an increasing contribution of secondary mineral formation. Below the water table, congruent weathering occurs and imparts elevated cation concentrations and bedrock δ7Li. Silicate weathering continues within the saturated zone as groundwater travels downslope (δ7Li = +13 to + 24‰) to the stream. The stream signatures (δ7Li = +28 to +29‰) reflect the terminus of this network of silicate weathering reactions and the relative magnitude of each contributing process (e.g., transitions in secondary mineral formation, dissolution of weathered material). We show that fluid progressing through the weathering profile of this first-order hillslope is distinguished by a sequence of characteristic Li isotope signatures, which can be reproduced in a forward, process-based model framework. This model development offers an improved quantitative basis for the use of metal(loid) stable isotopes in disentangling catchment-scale chemical weathering fluxes.

Bioaccumulation of Lithium Isotopes in Mussel Soft Tissues and Implications for Coastal Environments

Bioaccumulation of Lithium Isotopes in Mussel Soft Tissues and Implications for Coastal Environments

Multi-stage cross-flow separation of lithium isotopes by organic liquid film method

In this paper, a novel method, multi-stage cross-flow separation of lithium isotopes by organic liquid film method was investigated. A green organic extraction phase was formed with ionic liquid-B15C5-anisole, and the bis(trifluoromethanesulfonyl)imide solution was used as a multi-stage cross-flow balance liquid. The abundance of 6Li in the 20-stage cross-flow extraction increased from 7.51% to 8.17%. The effect of the concentration of bis(trifluoromethanesulfonyl)imide on the stripping of lithium ions in the organic extraction phase and the loss of lithium ions during the multi-stage cross-flow process was studied. Also, the number of theoretical cross-flow stages of the abundance of 6Li (30%) that can be used as nuclear fuel was predicted.

Temperature effect on lithium isotope separation by electrodialysis using La0.57Li0.29TiO3 electrolyte

The effect of temperature on lithium isotope separation by electrodialysis using La0.57Li0.29TiO3 (LLTO) electrolyte was investigated in the temperature range 298.15–323.15 K. The rates of mass 6 and 7 lithium isotopes (6Li and 7Li) moving through LLTO into pure water by electrodialysis were determined by inductively coupled mass spectrometry. An Arrhenius-type temperature dependence was observed for the rate of transfer of 6Li and 7Li into pure water by electrodialysis. The apparent activation energy of this lithium isotope transfer is the energy required for dissolution/elution of Li+ into/from LLTO or Li+ diffusion in LLTO crystals. The results of these experiments provided indication that the apparent activation energy of 6Li is approximately 5% lower than that of 7Li owing to the quantum effect. It was also shown that in electrodialysis using LLTO as the electrolyte, the isotope enrichment coefficient of 6Li may increase at lower temperature.

Deep neural network potentials for diffusional lithium isotope fractionation in silicate melts

Diffusional isotope fractionation has been widely used to explain lithium (Li) isotope variations in minerals and rocks. Isotopic mass dependence of Li diffusion can be empirically expressed as D7LiD6Li=67β, where D is the diffusivity of a Li isotope. The knowledge about temperature and compositional dependence of the β factor which is essential for understanding diffusion profiles and mechanisms remains unclear. Based on the potential energy and interatomic forces generated by deep neural networks trained with ab initio data, we performed deep potential molecular dynamics (DPMD) simulations of several Li pseudo-isotopes (with mass = 2, 7, 21, 42 g/mol) in albite, hydrous albite, and model basalt melts to evaluate the β factor. Our calculated diffusivities for 7Li in albite and model basalt melts at 1800 K compare well with experimental results. We found that β in albite melt decreases from 0.267±0.006 at 4000 K to 0.225±0.004 at 1800 K. The presence of water appears to slightly weaken the temperature dependence of β, with β decreasing from 0.250±0.012 to 0.228±0.031 in hydrous albite melt. The calculated β in model basalt melt takes much smaller values, decreasing from 0.215±0.006 at 4000 K to 0.132±0.015 at 1800 K. Our prediction of β in albite and hydrous albite melts is in good agreement with experimental data. More importantly, our results suggest that Li isotope diffusion in silicate melts is strongly dependent on melt composition. The temperature and compositional effects on β can be qualitatively explained in terms of ionic porosity and the coupled relationship between Li diffusion and the mobility of the silicate melt network. Two types of diffusion experiments are suggested to test our predicted temperature and compositional dependence of β. This study shows that DPMD is a promising tool to simulate the diffusion of elements and isotopes in silicate melts.

Lithium isotopic features of Quaternary basaltic saprolite, Zhanjiang, China: Atmospheric input and clay-mineral adsorption

Silicate weathering, in particular basalt, accounting only for one-sixth of the continental crust volume, accounts for one-third of atmospheric CO2 drawn down during weathering, as such, playing an important role in long-term carbon cycling. Li contents and isotopic compositions of a tropical regolith developed on young basalt (ca. 1 Ma) were investigated to elucidate Li isotopic fractionation during basalt weathering so as to trace basalt weathering. Li isotopic composition of sand from Asian dust-source regions and local dust near the basaltic saprolite weathering profile were studied as possible atmospheric contributors of Li to the saprolite. Saprolite has δ7Li values of −6.8‰ to −2.2‰, which is much lighter than that of fresh basalt (+3.5‰). Approximately 30% of the Li was lost from the upper saprolite profile, without significant isotopic fractionation. Lithium is enriched at the bottom of the profile, showing the lightest Li isotopic composition (δ7Li = −6.6‰ to −2.6‰). Calculations indicates that marine aerosols are the main source of atmospheric Li input to the profile. Adsorption of Li by secondary minerals results Li isotopic fractionation, accompanying desorption and resorption of Li by secondary minerals, resulting enriched Li and light Li isotopic composition in the regolith. A model established that Li isotopes showed sensitivity to continental weathering, supporting that Li isotopes can serve as an indicator of continental weathering. Continental weathering in the study area recorded the reasons of heavier Li isotopic composition of river water and seawater suggesting that Li isotopes can be used to study the circulation of materials on the Earth's surface. This has a guiding role in studying the Li isotopic composition of shale and rivers. The influence of temperature and precipitation on the fractionation behavior of lithium isotopes during silicate weathering warrants further investigation.

Lithium isotope behavior during magmatic differentiation and fluid exsolution in the Jiajika granite–pegmatite deposit, Sichuan, China

The Jiajika lithium (Li) deposit in Sichuan Province is the largest pegmatite-type Li deposit in China. The petrogenesis and metallogenesis of the Jiajika granitic pegmatites remain debatable. This study presents the Li isotopic compositions of two-mica granites, Li-rich and Li-poor pegmatites, and muscovites in Li-poor and Li-rich pegmatites to unravel the Li enrichment mechanism in the Jiajika deposit. The two-mica granites have a lower average δ7Li values than those of the Li-rich and Li-poor pegmatites. The Li contents of the two-mica granites are almost the same as those of the Li-poor pegmatites but are much lower than those of the Li-rich pegmatites. Muscovites in the Li-rich pegmatites have higher average Li contents and δ7Li values than those of the Li-poor pegmatites. All these results indicate the Jiajika granitic pegmatites were the final products of the extreme fractional crystallization of two-mica granitic magmas rather than direct anatectic melts, and that the Li-poor pegmatites derived from early differentiation of the two-mica granitic magmas before they evolved into Li-rich pegmatites during the late stage of magmatic differentiation. The lower average δ7Li values of the more evolved Li-rich pegmatites compared with the Li-poor pegmatites may have been caused by fluid exsolution and kinetic diffusive fractionation during melt-fluid separation. We discovered that fluid exsolution during melt-fluid separation can cause significant Li isotopic fractionation, with 7Li enriched in a H2O-poor silicate-rich melt system. Considering the crystallization ages of the two-mica granites and granitic pegmatites and other geochemical evidence (e.g., major- and trace-element compositions), the magmatic differentiation and fluid exsolution in the late stage of the granitic magma evolution together with the Li-rich surrounding strata led to the multistage enrichments in lithium, thus contributing to the formation of the Jiajika large Li deposit.

Горячий лазерный термояд или низкотемпературные ядерные реакции? Анализ и перспективы первых экспериментов по лазерному синтезу

The paper considers the features and quantitative characteristics of the first successful laser experiments on the formation of a thermonuclear plasma and registration of neutrons in nuclear fusion reactions under pulsed irradiation of a LiD crystal. Quantitative analysis shows that the production of neutrons recorded in these experiments is not associated with thermonuclear reactions in hot laser plasma. The most probable mechanism of neutron generation is associated with nuclear reactions at low energies and is due to the formation of coherent correlated states (CCS) of deuterons. In this experiment, such states can be formed in two different processes: due to the effect of a shock wave in the undisturbed part of the target lattice on the vibrational state of deuterium nuclei or when deuterium nuclei with energy of about 500 eV move in the lattice. This part of the deuterium nuclei corresponds to the high-energy "tail" of the Maxwellian distribution of the total flux of particles entering from the laser plasma into the interplanar channel. In this second case, the process of the formation of the CCS is associated with the longitudinal periodicity of the interplanar crystal channel, which is equivalent to a nonstationary oscillator in the own coordinate system of moving particle. The expediency of repeating these experiments is shown, in which, in addition to neutrons, one should expect a more efficient generation of other nuclear fusion products due to low-energy reactions involving lithium isotopes from the target composition.

Structure and Functionality of an Alkylated LixSiyOz Interphase for High-Energy Cathodes from DNP-ssNMR Spectroscopy.

Degradation processes at the cathode–electrolyte interface are a major limitation in the development of high-energy lithium-ion rechargeable batteries. Deposition of protective thin coating layers on the surface of high-energy cathodes is a promising approach to control interfacial reactions. However, rational design of effective protection layers is limited by the scarcity of analytical tools that can probe thin, disordered, and heterogeneous phases. Here we propose a new structural approach based on solid-state nuclear magnetic resonance spectroscopy coupled with dynamic nuclear polarization (DNP) for characterizing thin coating layers. We demonstrate the approach on an efficient alkylated LixSiyOz coating layer. By utilizing different sources for DNP, exogenous from nitroxide biradicals and endogenous from paramagnetic metal ion dopants, we reveal the outer and inner surface layers of the deposited artificial interphase and construct a structural model for the coating. In addition, lithium isotope exchange experiments provide direct evidence for the function of the surface layer, shedding light on its role in the enhanced rate performance of coated cathodes. The presented methodology and results advance us in identifying the key properties of effective coatings and may enable rational design of protective and ion-conducting surface layers.

Engineering study on lithium isotope separation by ion exchange chromatography

We have been studying the lithium isotope separation by ion exchange chromatography for the engineering development. We performed the lithium isotope separation experiments by chromatography. From the results, we estimated the migration lengths required to obtain the 20 %, 50 %, and 90 % enriched lithium-6, the required lengths are 340, 1600, and 5800 m, respectively. We studied the detection methods of lithium adsorption band boundary in order to design the circular type chromatographic equipment, which type equipment is required for the industrial plant. Based on these investigations, we designed the automatic circular type chromatographic equipment with the boundary interface detector and manufactured the prototype equipment.

Lithium isotopes and partition coefficients in inorganic carbonates: Proxy calibration for weathering reconstruction

We report Li measurements from cave-analogue carbonate-precipitation experiments in order to: i) assess the expected isotope fractionation factors applicable to speleothem growth, and ii) contribute to the wider understanding of lithium incorporation in carbonates. The experimental setup closely mimics natural processes (e.g. precipitation driven by CO2 degassing, low ionic strength solution, thin solution film) but within a laboratory setting that allows for controlled growth conditions (temperature, pCO2, drip rate, carbonate saturation index and the composition of the initial solution). For the main batch of calcite growth experiments our average 1000lnαcalcite-solution is -8.5±2(2σ). This low sensitivity of 1000lnα to in-cave growth conditions is encouraging for weathering intensity reconstruction using speleothem samples. At each temperature, growth rate was varied independently with calcite saturation indices ranging between 0.1 and 0.6, with no significant impact on either D(Li) or 1000lnα. For the full range of growth conditions (considering all temperatures and calcite saturation indices) we observe a small but significant decrease in 1000lnα, which we do not attribute to temperature. Based on an inter-study comparison we define LogDLi = 0.09(±0.04)×GR-3.2(±0.2), where GR is growth rate in units of 10-8mmolcm-2s-1. This is similar to the previously defined relationship over a reduced range of growth rates. Over this study’s full range of growth rates, 1000lnα = -0.13(±0.04)×GR-7.1(±0.3) is significant at the ρ=0.018 level, consistent with a surface entrapment control. Future experiments should test factors such as growth rate and pH, independently of other variables, to further assess their role in defining 1000lnα. A subset of 20 °C experiments, with increasing [Mg]solution, provides 1000lnα for calcite, high-magnesian calcite (HMC) and aragonite. Our values of 1000lnα for these three mineralogies range between -7.3 and -10.7. For HMC and aragonite in particular there is close agreement with other published values of 1000lnα for CaCO3 grown in laboratory and in natural settings. In agreement with measurements in bulk carbonates, benthic foraminifera and brachiopods, this suggests that differences in 1000lnα between carbonate mineralogies may not always be as large as suggested by some earlier studies.

Lithium and potassium isotope fractionation during silicate rock dissolution: An experimental approach

This study experimentally investigates the isotopic behaviors of Li and K during the dissolution of silicate rocks (i.e., basalt and granite). Proton-driven dissolution (in 0.8 M HNO3) and ligand-driven dissolution (in 5 mM critic acid or oxalic acid) experiments were performed in batch-closed systems over 15 days. We provide a time-series interpretation of Li and K isotope fractionation during silicate dissolution in ultra-acidic (unidirectional) and near-natural (biologically affected) environments. As the reaction progressed, we measured large isotope fractionation between the liquid (l) phase and the pristine silicate (s) phase, ranging from −10.3 to 0.1‰ (Δ7Lil-s) and from −1.01 to −0.11‰ (Δ41Kl-s) through the early stage of dissolution (<24 h). The enrichment of lighter Li and K isotopes in the solutions rapidly diminished as rock dissolution continued and gradually approached equilibrium to the end of experiments. In contrast, resorption of pre-leached isotopically lighter Li on silicate residuals during ligand-driven dissolution produced lighter isotope enrichment in the solutions compared to the initial rock by up to 2.8‰. Despite the preferential dissolution of specific minerals, the isotope fractionation patterns of Li and K do not vary with lithology, indicating limited inter-mineral isotopic differences. During the experiments, the Li and K isotopic pattern could be divided into two-to-three stages. The initial enrichment of light isotopes in the liquids can be ascribed to the kinetic isotope effect, confounded by diffusion and ion solvation. A later transition towards no isotope fractionation of Li and K may be explained by (i) the masking effect from dissolution, and (ii) an imprint from the destruction of 7Li/41K-enriched surface layers. Lateral resorption of solute Li after ~100 h reaction could be facilitated by the electrostatic attraction from increasing surface negative charges and active hydroxyls with increasing pH during ligand-driven dissolution (pH ~ 4) relative to proton-driven dissolution (pH ~ 0.2). Therefore, the presence of organic ligands impacts dissolution stoichiometry, and potentially modifies Li isotope fractionation in natural weathering environments. In comparison, K isotope fractionation driven by rock dissolution stops immediately (within days) after starting the experiments. This research helps to understand the mechanisms of Li and K isotope fractionation during chemical weathering and trace long-term climate change using geological records.

Pedogenic processes in loess-paleosol sediments: Clues from Li isotopes of leachate in Luochuan loess

Tracing pedogenic processes is fundamental for reconstructing climatic and environmental changes using loess deposits. Lithium isotopes can serve as a sensitive tracer to unravel these processes, owing to its active behaviors without effect by redox and biological reactions. This study investigated the Li contents and δ7Li values of leachate and residue ([Li]leachate, [Li]residue, δ7Lileachate and δ7Liresidue) of the upper 12.5 m Luochuan loess-paleosol sediment (since the last interglacial) on the Chinese Loess Plateau, in order to better understand pedogenic processes in loess. The [Li]leachate, varying from 0.39 to 1.97 μg/g, is mainly derived from the adsorption phase, with a significant variation in δ7Lileachate, from −6.55‰ to +12.88‰. Both [Li]leachate and δ7Lileachate variations reflect weathering and adsorption processes during different periods. The [Li]residue vary from 34.4 to 46.3 μg/g (averaging 38.4 μg/g) and their δ7Liresidue vary from −3.66‰ to +2.44‰ (averaging −0.22 ± 1.68‰), both in agreement with the upper continental crust values. At initial stage after loess deposited (stage I), high [Li]leachate but low δ7Lileachate are results of preferential adsorption of 6Li by clays and migration of 7Li with soil solution during weathering and eluviation processes. When overlying loess was deposited and experienced pedogenesis as the stage I, 7Li migrated downward and was adsorbed by clays (stage II), resulting in high [Li]leachate and δ7Lileachate in underlying loess. When loess has superimposed pedogenic and adsorption processes as the stages I and II, loess became as paleosol with highest δ7Lileachate in underlying carbonate accumulation layer. A persistent increase in δ7Lileachate indicates dominant control of post-depositional adsorptions on Li fractionation along solution migrations during weathering and eluviation of overlying deposits, and vice versa. These results highlight that variations in [Li]leachate and δ7Lileachate can be used to trace soil water migration processes and the magnitude of pedogenic processes in loess-paleosol sediment at different periods.

Lithium isotope separation effect of N-phenylaza-15-crown-5

Azacrown ethers contain multiple coordination sites, which show specific complexation to alkali metal ions. In this research, a neoteric liquid-liquid extraction system was investigated for the selective separation of lithium isotope using N-phenylaza-15-crown-5 (Ph-N15C5) as chelating agent and [BMIm][NTf2] and anisole as extraction solvent. The effects of the counter anions of lithium salt, concentrations of crown ether, temperature, extraction equilibrium time and concentrations of lithium salt solution on the separation of lithium isotope with Ph-N15C5 were studied. The maximum extraction efficiency of lithium ions was 41.54% and the maximum single-stage separation factor (α) of 6Li/7Li obtained in the present study was 1.025, indicating that the lighter isotope 6Li was enriched in organic phase while the heavier isotope 7Li was concentrated in the aqueous phase. The complexation ratio of the lithium crown ether complex was determined as 1:1 by the slope analysis method. The lithium ions in the aqueous phase were extracted into the organic phase to form [Li(Ph-N15C5)]+ complex. The thermodynamic data obtained at different temperatures demonstrated that lithium isotope exchange was a spontaneous exothermic process, and lowering the temperature was beneficial to increase the separation factor. In addition, the system reached the extraction equilibrium after 60 min. This high efficiency and green liquid-liquid extraction system has potential application in lithium isotope separation.

The influence of water\u2013rock interactions on household well water in an area of high prevalence chronic kidney disease of unknown aetiology (CKDu)

Poor drinking water quality in household wells is hypothesised as being a potential contributor to the high prevalence of chronic kidney disease of uncertain aetiology (CKDu) among the farming communities of the Medawachchiya area, Anuradhapura, Sri Lanka. One of the natural processes that can affect water quality is the dissolution of minerals contained within an aquifer by water–rock interactions (WRIs). Here we present a comprehensive assessment of WRIs and their influence on the water chemistry in household wells and spring waters in the Medawachchiya area by combining measurements of environmental isotopes, such as strontium, lithium and stable carbon isotopes and inorganic chemistry parameters, and modelling geochemical mass balance reactions between rainfall and groundwater samples. Our results reveal the presence of strontium, dissolved from both silicate and carbonate minerals, with high isotopic (87Sr/86Sr) ratios of up to 0.7316. Geochemical mass balance modelling and prior 87Sr/86Sr studies on the Wanni Complex bedrock suggest these strontium values may be the result of biotite dissolution. We also identify lithium and uranium contributed from the dissolution of silicates, albeit at concentrations too low to constitute a known health risk. In contrast, the levels of magnesium and calcium in our samples are high and demonstrate that, despite the felsic bedrock, well water chemistry in the Medawachchiya area is dominated by carbonate dissolution.

Lithium and potassium isotope fractionation during silicate rock dissolution: An experimental approach

Lithium and potassium isotope fractionation during silicate rock dissolution: An experimental approach

Chemical and lithium isotope characteristics of murakamiite and Li–rich pectolite from Iwagi Islet, Southwest Japan

Chemical and lithium isotope characteristics of murakamiite and Li–rich pectolite from Iwagi Islet, Southwest Japan

Lithium isotopes and Cu-Au concentrations in hydrothermal alterations from Solfatara Volcano, Campi Flegrei caldera complex, and La Fossa volcano, Vulcano Island, Italy: Insights into epithermal ore forming environments

Hydrothermally-altered rocks collected at Solfatara volcano, Campi Flegrei caldera complex, Italy, are comparable to zones of steam-heated alterations found at low sulfidation epithermal deposits, and volcanic gases collected at Solfatara have temperatures and C-O-H isotopic compositions akin to those forming low sulfidation epithermal deposits. By contrast, hydrothermal alterations collected at La Fossa volcano, Vulcano island, Italy, are comparable to zones of residual vuggy silica formed in high sulfidation epithermal deposits, and volcanic gases collected at La Fossa have temperatures and C-O-H isotopic compositions comparable to those forming high sulfidation epithermal deposits. At Solfatara, amorphous and hydrous opal-A is responsible for shifts in δ7Li values, from +2.2‰ in fresher rocks, to −3.6‰ in most altered rocks, with increases in Au and Cu concentrations (up to 3 ppb and 96 ppm). The increase in Au and Cu concentrations in progressively-altered rocks resulted from the transport of Cu-Au in magmatic-hydrothermal fluids and their partitioning into pyrite, Fe oxides, phyllosilicates, sulfates, and/or opal-A. It is proposed that the combination of opal-A, decreases in δ7Li values, and increases in Cu and Au concentrations represent an exploration vector for low sulfidation epithermal veins. At La Fossa, α-cristobalite is responsible for shifts in δ7Li values, ranging from −0.9‰ in least-altered rocks, to +4.7‰ in most altered rocks, with decreases in Au-Cu concentrations. The decrease in Au and Cu concentrations in progressively-altered rocks may have resulted from the metasomatism of pyrite and Fe oxides, the dissolution of clinopyroxene and opal, and the invasion of the samples by α-cristobalite. The combination of α-cristobalite, increases in δ7Li values, and decreases in Cu and Au concentrations are proposed as proxies for potential high sulfidation epithermal disseminations. Alternating phases of high eruptive activity and quiescent degassing at volcanoes generally, and at Solfatara and La Fossa specifically, suggest that the physicochemical conditions of individual subvolcanic hydrothermal systems should also be alternating, between conditions that are characteristic of low- and high sulfidation epithermal ore-forming environments, and that the related zones of silicification should be alternating between low δ7Li and high Cu-Au values dominated by opal-A, and higher δ7Li and lower Cu-Au values dominated by α-cristobalite.

Reconstructing Neoproterozoic seawater chemistry from early diagenetic dolomite

Abstract The pairing of calcium and magnesium isotopes (δ44/40Ca, δ26Mg) has recently emerged as a useful tracer to understand the environmental information preserved in shallow-marine carbonates. Here, we applied a Ca and Mg isotopic framework, along with analyses of carbon and lithium isotopes, to late Tonian dolostones, to infer seawater chemistry across this critical interval of Earth history. We investigated the ca. 735 Ma Coppercap Formation in northwestern Canada, a unit that preserves large shifts in carbonate δ13C values that have been utilized in global correlations and have canonically been explained through large shifts in organic carbon burial. Under the backdrop of these δ13C shifts, we observed positive excursions in δ44/40Ca and δ7Li values that are mirrored by a negative excursion in δ26Mg values. We argue that this covariation is due to early diagenetic dolomitization of aragonite through interaction with contemporaneous seawater under a continuum of fluid- to sediment-buffered conditions. We then used this framework to show that Tonian seawater was likely characterized by a low δ7Li value of ∼13‰ (∼18‰ lower than modern seawater), as a consequence of a different Li cycle than today. In contrast, δ13C values across our identified fluid-buffered interval are similar to modern seawater. These observations suggest that factors other than shifts in global seawater chemistry are likely responsible for such isotopic variation.