Cl Isotope Research Articles

Multiple hydrothermal events at martian surface revealed by H and Cl isotope systematics of melt inclusions and hydrous minerals from chassignite NWA 2737

The chassignites and nakhlites could have co-magmatic origin but display distinct hydrogen and chlorine isotopic compositions, indicating that they may have experienced distinct hydrothermal activities on Mars. However, the details are not yet fully understood. Here, we performed H and Cl isotopic investigations on hydrous minerals (kaersutite and apatite) and glass-bearing melt inclusions from chassignite NWA 2737 to unravel the details of the hydrothermal events experienced by chassignites on Mars. Our results demonstrate that at least two hydrothermal events on Mars have been recorded in NWA 2737. A D- and 37Cl-rich martian crustal/underground fluid was added to the parent magma of NWA 2737 prior to the entrapment of melt inclusions and later interaction of the parent rock with a D-poor fluid, probably deriving from magma degassing. The notable high-δD values (up to 6239‰) of kaersutite in NWA 2737 are comparable with those recorded in younger shergottites, suggesting that the martian exchangeable water reservoir has retained a nearly constant δD value over the past 1.3 Ga.

Elucidating the Fate of the Organochlorine Pesticide Chlordecone under Abiotic Reductive and Oxidative Processes: Kinetics, Transformation Products, and C vs Cl Isotope Fractionation.

Pollution of French West Indies (FWI) soils by the organochlorine pesticide chlordecone poses environmental and societal concerns due to its long-term persistence. Assessing chlordecone degradation remains challenging due to analytical constraints to identify transformation products. Here, multielement compound-specific isotope analysis (ME-CSIA) was used to identify changes in stable isotope signatures of chlordecone produced during abiotic transformation reactions under reducing and oxidative conditions. Effective chlordecone transformation was shown in reactions with zerovalent iron (ZVI), vitamin B12 and sodium sulfide (VSS), alkaline ascorbic acid (AA), and sodium persulfate activated by microwave irradiation (MWPS). Significant enrichment of 13C and 37Cl was observed in all abiotic reactions, with εC,bulk and εCl,bulk values ranging from -4.3 ± 0.4‰ to -2.3 ± 0.2‰ and from -2.6 ± 0.4‰ to -1.3 ± 0.3‰, respectively. Distinct mechanisms were evidenced in dual isotope plots, resulting in Λ values of 1.17 ± 0.28 for ZVI, 1.26 ± 0.50 for VSS, 2.06 ± 0.30 for AA, and 2.90 ± 0.50 for MWPS. Two major products were formed, 10-monohydrochlordecone and 8-monohydrochlordecone. Cl-CSIA data suggested that the first Cl substitution at the C10-position likely produced secondary Cl isotope effects (via nucleophilic substitution). Overall, results suggest that ME-CSIA can help quantify in situ chlordecone degradation, distinguishing between different ongoing degradation mechanisms and fingerprinting pollutant sources from chlordecone formulations (Curlone).

Coordinated microanalysis of volatiles in apatite and silicate minerals in ancient lunar basalts

Despite being essentially water-free, nominally anhydrous minerals such as plagioclase and pyroxene represent the biggest reservoir of water in most lunar rocks due to their sheer abundance. Apatite, which incorporates F, Cl, and OH into its mineral structure as essential crystal components, on the other hand, is the only other volatile-bearing phase common in lunar samples. Here, we present the first coordinated study of volatiles (e.g., H2O, Cl, F, and S) in nominally anhydrous minerals combined with isotopic measurements in apatite from the ancient lunar basalt fragments from meteorite Miller Range (MIL) 13317. Apatite in MIL 13317 basalt contains ∼ 2000 ppm H2O and has an elevated δD values (+ 523–737 ‰), similar to Apollo mare basalts, but has high δ37Cl values (+ 29–36 ‰), similar to apatite found in several KREEP-rich samples. MIL 13317 is unique compared with other lunar basalts; it has both elevated δD and δ37Cl values currently only observed in highlands sample 79215 (a granulitic impactite). Based on measurements of H2O in nominally anhydrous minerals and in apatite, the source magma of MIL 13317 basalt is estimated to contain ∼ 130–330 ppm H2O. Assuming reasonable levels of partial melting of the lunar mantle and magmatic degassing during eruption of the basalt, the Moon contained at least one reservoir with < 100 ppm H2O, a δD value of < 0 ‰ similar to carbonaceous chondrites, and extensively fractionated Cl isotopes prior to 4.332 Gyr, the crystallization age of the MIL 13317 basalt.

Cycling of fluid-mobile elements through the forearc: Insights from the Cl, B, and Li isotope composition of Costa Rican spring fluids

Loss of slab-derived volatile and fluid-mobile elements (FME) through the forearc may represent a large, unaccounted for flux out of convergent margins. To address volatile recycling through the forearc and potential changes in fluid source from the progressively dehydrating subducting slab, we collected water samples from 44 different cold and thermal (>40 °C) springs on a transect across the outer forearc (∼20–40 km to the subducting slab), forearc (∼40–80 km to the slab), and arc (∼80–120 km to the slab) in Costa Rica. We focused on the heavy halogens (Cl, Br, I), as well as B and Li, given their high fluid mobility and thus limited potential for modification by subsequent fluid-rock interaction. Chlorine, boron, and lithium stable isotope ratios show dramatic ranges from −1.7 to +1.0 ‰ (n = 43), −12.0 to +30.9 ‰ (n = 35), and −2.4 to + 27.5 ‰ (n = 38), respectively, with distinct changes across the transect consistent with a sedimentary pore fluid component in the outer forearc, fluids sourced from dehydration of the slab (sediment and altered oceanic crust) in the forearc, and minimal slab input near the arc. Variations in elemental ratios (Br/Cl, I/Cl, B/Cl, Li/B) across the transect are also largely consistent with evolving FME sources during subduction. Boron isotope ratios in some higher-temperature fluids are modified due to phase separation, whereas, lithium and chlorine isotope ratios are minimally modified. Springs located in the outer forearc along a major fault (Falla Morote) deviate from the consistent across-arc trend and record almost the full range of observed isotopic values. This extreme range in values along the fault likely represents a combination of adsorption/desorption effects, weathering, and mixing with crustal fluids. Mass balance calculations show that up to ∼ 70 % of Cl, ∼50 % of Br, ∼30 % of B, ∼15 % of I, and minimal Li may be recycled through the outer forearc and forearc springs of the Costa Rican margin, therefore fluid emission via springs in global forearc regions are a potentially significant output for FME at convergent margins.

Dual C–Cl isotope fractionation offers potential to assess biodegradation of 1,2-dichloropropane and 1,2,3-trichloropropane by Dehalogenimonas cultures

1,2-dichloropropane (1,2-DCP) and 1,2,3-trichloropropane (1,2,3-TCP) are hazardous chemicals frequently detected in groundwater near agricultural zones due to their historical use in chlorinated fumigant formulations. In this study, we show that the organohalide-respiring bacterium Dehalogenimonas alkenigignens strain BRE15 M can grow during the dihaloelimination of 1,2-DCP and 1,2,3-TCP to propene and allyl chloride, respectively. Our work also provides the first application of dual isotope approach to investigate the anaerobic reductive dechlorination of 1,2-DCP and 1,2,3-TCP. Stable carbon and chlorine isotope fractionation values for 1,2-DCP (ƐC = −13.6 ± 1.4 ‰ and ƐCl = −27.4 ± 5.2 ‰) and 1,2,3-TCP (ƐC = −3.8 ± 0.6 ‰ and ƐCl = −0.8 ± 0.5 ‰) were obtained resulting in distinct dual isotope slopes (Λ12DCP = 0.5 ± 0.1, Λ123TCP = 4 ± 2). However direct comparison of ΛC-Cl among different substrates is not possible and investigation of the C and Cl apparent kinetic isotope effects lead to the hypothesis that concerted dichloroelimination mechanism is more likely for both compounds. In fact, whole cell activity assays using cells suspensions of the Dehalogenimonas-containing culture grown with 1,2-DCP and methyl viologen as electron donor suggest that the same set of reductive dehalogenases was involved in the transformation of 1,2-DCP and 1,2,3-TCP. This study opens the door to the application of isotope techniques for evaluating biodegradation of 1,2-DCP and 1,2,3-TCP, which often co-occur in groundwaters near agricultural fields.

Anaerobic biotransformation of hexachlorocyclohexane isomers in aqueous condition: Dual C[sbnd]Cl isotope fractionation and impact on microbial community compositions

Hexachlorocyclohexane (HCH) isomers are persistent organic pollutants (POPs) with high toxicity, lipid solubility, chemical stability. Despite the current ban on usage of Lindane, residual contamination cannot be ignored, and HCH are frequently detected in groundwater and threaten human health. Cultures capable of degrading α-HCH, β-HCH, γ-HCH, and δ-HCH individually have been enriched in anoxic aqueous conditions. Compound-Specific Isotope Analysis (CSIA) was applied to examine the transformation mechanisms of different HCH isomers by the four enrichment cultures. 16S rRNA sequencing techniques were employed to examine the community composition of the enrichment cultures and detect changes in these communities resulting from adding individual HCH isomers. The results indicated that the ability of the enrichment cultures for dichloroelimination of HCH isomers was inconsistent. During dichloroelimination, different bond cleavage mode of β- and δ-HCH led to distinct isotopic effects. HCH isomers had significant impact on the microbial community, while different microbial communities showed comparable isotopic effects during the transformation of a specific HCH isomer. In addition, bacteria in the phyla Proteobacteria and Firmicutes were proposed as the dominant dechlorinators. This study provides a novel perspective on the mode of bond cleavage during HCH dichloroelimination and the effect of HCH on microbial communities, which could potentially support the evaluation of HCH transformation by CSIA and their effects on the microecosystems of groundwater.

Earth's “Missing” Chlorine May Be in the Core

AbstractThe budget of volatile halogens in the bulk silicate Earth, fluorine and chlorine, differs distinctly from that of chondritic meteorites. Arguably, the bulk silicate Earth shows a low abundance of Cl, while the F budget is in line with the expected volatility trend. One hypothesis for the missing Cl is its sequestration into Earth's core during planetary segregation, but experimental data on partitioning between silicate and metallic melts are limited in pressure and remain inconclusive. Here we use computational quantum mechanical methods to study F and Cl geochemistry during core–mantle differentiation over a wide pressure and temperature range. Our calculations reveal that with increasing pressure and temperature, chlorine shows an enhanced affinity for iron metal. The Cl metal–silicate partition coefficient increase from −1.89 ± 0.84 at 10 GPa and 3000 K to 1.62 ± 0.80 at 130 GPa and 5000 K, while corresponding calculations for F show minimal variations in metal–silicate partitioning across the pressure–temperature conditions investigated, yielding values between −3.61 ± 0.81 and −3.37 ± 0.80. The shift in shows a transition from lithophile to siderophile behavior. Further calculations on isotopic partitioning show negligible fractionation of Cl isotopes (37Cl/35Cl) between the mantle and core. Our results suggest that metallic iron within Earth's mantle and core may serve as an important Cl reservoir, potentially accounting for up to 40% of Earth's overall Cl inventory.

Estimates of chlorine isotope fractionation factors using density functional theory: Applications to ore-forming systems

Chloride is the most important anion in ore-forming hydrothermal fluids, and chlorine isotopes are therefore potentially sensitive tracers of the origin and evolution of ore-forming fluids. However, they remain a relatively under-utilized tool in ore deposit geochemistry due to the lack of knowledge of chlorine isotope fractionation during ore-forming processes. Using first-principles density functional theory, this study estimates chlorine isotope fractionation factors for various ore-forming processes. All metal-Cl complexes in hydrothermal fluids are enriched in 37Cl compared to chloride ions, but the change in δ37Cl of the fluid trapped in ore minerals is small after the destabilization of metal-chloride complexes during ore mineral deposition. In the precipitation of evaporite minerals from brine, the sequence of enrichment of the heavy Cl isotope (37Cl) is halite > carnallite > aqueous chloride > kainite > sylvite > bischofite. The results of this study agree with the experimental observations that progressive precipitation of halite from brine lowers the δ37Cl value of the residual fluid until the formation of K-Mg chlorides. In low-temperature deposits, δ37Cl values for fluid inclusions and minerals reflect those of the hydrothermal fluid provenance and the mixing of this fluids with saltwater or basinal brines. In high-temperature magmatic-hydrothermal ore deposits that undergo liquid–vapour phase separation, chlorine isotopes fractionate among phases of silicate melt, vapour and chloride-rich liquid. The considerable range in δ37Cl in fluid inclusions may also reflect fluid mixing and hydrothermal alteration. At ambient temperature, the δ37Cl values may reflect evaporative processes and, in the case of chemical weathering of metallic mineral deposits, may record the supergene enrichment of the metals. This study highlights the use of chlorine isotopes as a new tool for interpreting ore-forming processes.

Chlorine isotope evidence for Farallon-derived metasomatism of the North American lithospheric mantle

Metasomatism of the sub-continental lithospheric mantle (SCLM) can result in enrichment in volatile elements introduced via subduction of seawater-altered oceanic lithosphere. Subduction-related metasomatism can introduce chlorine isotope heterogeneity to the SCLM inherited from the subducted source, which can be used to characterize the source of metasomatism. This study presents Cl isotope compositions (δ37Cl) of variably metasomatized continental lithospheric mantle xenoliths from the Colorado Plateau and southern Rio Grande Rift (southwestern United States). Fertile mantle xenoliths that represent asthenosphere that has recently been emplaced at the base of the North American lithosphere have δ37Cl values of 0.0 ‰ to +0.1 ‰, suggesting that the convecting mantle has an average δ37Cl value similar to seawater and chondrites. In contrast, metasomatized xenoliths span a range of δ37Cl values from +0.1 ‰ to +1.9 ‰, extending above the average convecting mantle value. The range in δ37Cl values can be explained by mixing between a subduction-related fluid with δ37Cl values between +1.0 ‰ and +1.9 ‰ and a shallow crustal fluid with a δ37Cl value less than +0.3 ‰. The most likely source of the high δ37Cl subduction-related signature is the lower crust in the subducted Farallon plate. Lower crustal Cl likely entered the SCLM either through direct dehydration of lawsonite ± phengite in the deeply subducted Farallon plate or from a mixed serpentinite-oceanic crust source in the subducted Farallon. Regardless of the mechanism, this study provides evidence for subduction of crustal Cl into the mantle, which can introduce isotopic heterogeneity into the SCLM and has implications for the volatile cycling in the HIMU mantle and SCLM.

Is Cl isotope fractionation in the seawater-evaporite system dependent on seawater chemistry?

Published values, near 1.0003, of the fractionation factor for stable Cl isotopes between halite and brine (αhal-br) fail to account for several sets of δ37Cl data for marine evaporitic halite. Clustered negative values of δ37Cl data, including some that appear to correspond to basal halite, would require measurable secular change in δ37Cl of marine chloride during the Phanerozoic if αhal-br is invariant. Such change is inconsistent with understanding of the geochemical cycle of Cl. Alternatively, marine δ37Cl has remained constant, but αhal-br has undergone secular change between values of about 1.0003 and 0.9996 in Phanerozoic marine evaporite settings. Such an interpretation is favored by the occurrence of clustered negative δ37Cl values at times when potash-facies evaporite contained sylvite rather than MgSO4 minerals, reflecting long-term secular change in seawater chemistry. Values of αhal-br may therefore depend on brine composition.

Deciphering the origin(s) of H and Cl in Apollo 15 quartz monzodiorites: Evidence for multiple processes and reservoirs

Apollo 15 quartz monzodiorites (QMDs) are reported to contain some of the most deuterium-depleted apatite found in lunar samples. In this study, apatite from six Apollo 15 QMDs, including three samples from 15405 not previously investigated, were analyzed for their H and Cl isotopes. Apatite in 15405 are extremely 2H (or D)-poor, with δD values ranging from −658 ± 53 to −378 ± 113‰, comparable to apatite data from related samples 15403 and 15404. In addition to new H isotope data, the first Cl-isotope data for lunar QMDs are presented. Apatite in 15405 and related samples are enriched in 37Cl with respect to Earth, with measured δ37Cl values ranging from +13 to +37‰. These values are within the reported δ37Cl range for KREEP-rich samples. The fact that the Cl isotopic composition of apatite in QMDs are similar to those in other lunar lithologies, but the H isotopic data are distinct and unique, provides possible further evidence for the existence of a D-poor reservoir in the lunar interior. Raman spectroscopy of the silica polymorph in sample 15405 reveals it to be a mixture of quartz and cristobalite. Based on available experimental data on the stability of various silica phases over a range of pressure and temperature regime, a deep-seated origin in the crust for QMDs may be possible which would support an endogenous origin of the H-Cl isotope systematics of the QMDs. The role of impact-induced transformation of silica phases and its contributing towards low D/H ratio in apatite, however, cannot be ruled out.

Isotope Detection in Microwave-Assisted Laser-Induced Plasma

Isotope detection and identification is paramount in many fields of science and industry, such as in the fusion and fission energy sector, in medicine and material science, and in archeology. Isotopic information provides fundamental insight into the research questions related to these fields, as well as insight into product quality and operational safety. However, isotope identification with established mass-spectrometric methods is laborious and requires laboratory conditions. In this work, microwave-assisted laser-induced breakdown spectroscopy (MW-LIBS) is introduced for isotope detection and identification utilizing radical and molecular emission. The approach is demonstrated with stable B and Cl isotopes in solids and H isotopes in liquid using emissions from BO and BO2, CaCl, and OH molecules, respectively. MW-LIBS utilizes the extended emissive plasma lifetime and molecular-emission signal-integration times up to 900 μs to enable the use of low (~4 mJ) ablation energy without compromising signal intensity and, consequently, sensitivity. On the other hand, long plasma lifetime gives time for molecular formation. Increase in signal intensity towards the late microwave-assisted plasma was prominent in BO2 and OH emission intensities. As MW-LIBS is online-capable and requires minimal sample preparation, it is an interesting option for isotope detection in various applications.

Isotopic fractionation of chlorine and potassium during chloride sublimation under lunar conditions

The Moon is depleted in volatile elements and compounds, and lunar samples exhibit a wide range of Cl isotopic compositions, which is believed to result from the volatilization of metal chlorides (e.g., NaCl, KCl, and FeCl2). However, the Cl isotopic fractionation behavior during volatilization is not well constrained, particularly for metal chlorides. Furthermore, the effect of metal chloride evaporation on metal isotopes is poorly known. In the present study, we performed NaCl and KCl sublimation experiments to study Cl and K isotopic fractionations at temperatures ranging from 923 K to 1061 K and at pressures of 7×10–5 bar to 1 bar in an N2 atmosphere. The isotope fractionation factors of 37/35Cl(αgas–solid) from NaCl sublimation experiments are 0.9985±0.0002, 0.9958±0.0004, and 0.99807±0.00004 at 1, 10–2, and 7×10–5 bar, respectively. Those of 41/39K(αgas–solid) and 37/35Cl(αgas–solid) from KCl sublimation experiments are 0.99884±0.00004 and 0.9988±0.0003 at 1 bar, 0.9977±0.0002 and 0.9972±0.0003 at 10–2 bar, and 0.9989±0.0002 and 0.9989±0.0001 at 7×10–5 bar, respectively. Chlorine and K isotopes fractionate more at 10–2 bar than at 7×10–5 bar and 1 bar. The saturation index in all the sublimation experiments was >95%, which resulted in near-equilibrium isotopic fractionation at the sublimation interface. Therefore, the isotopic fractionation was controlled by mass transfer processes in the gas and solid phases. The isotopic fractionation at 10–2 bar was controlled by the chemical diffusion of sublimated gas in an N2 atmosphere with almost no convection effect, (i.e., Pe number close to zero), whereas the isotopic fractionation at 1 bar was suppressed by atmospheric convection with a turbulence factor of 0.4±0.1 (i.e., Pe number >1). The extremely high sublimation rate and the very slow diffusion in the sublimating solid at 7×10–5 bar suppressed isotopic fractionations. Based on our experimental results, calculations using Cl/K and Na/K in lunar materials reveal that degassing of KCl contributed very little (<0.2‰) to the K isotopic fractionation (>0.58‰) during lunar magma ocean degassing. The Cl isotopic fractionation factor from lunar samples is similar to our results at 10–2 bar. This similarity of Cl isotope fractionation indicates that there may have been a transient atmosphere above the lunar magma ocean.

Oxygen and chlorine isotope fractionation during microbial perchlorate reduction in static and flow through systems

Perchlorate (ClO4−) is an oxyanion with both anthropogenic and natural sources that is widespread on earth and throughout the solar system. Stable isotope ratio measurements are a powerful tool to assess the origin and predict the fate of perchlorate in the environment. The aim of this study was to perform an experimental survey of parameters that influence microbial O and Cl isotope fractionation during microbial perchlorate reduction, covering microbiological (genetic background and community context) and environmental (temperature, salinity, electron donor type and limitation) factors. A new method for the purification of perchlorate for isotope ratio mass spectrometry (IRMS) was developed to allow for more efficient sample preparation and suitable for samples containing small amounts of perchlorate (0.4–2 mg). Although most experiments, regardless of treatment, yielded a consistent isotope enrichment factor ratio (Λ = ε18O/ε37Cl ∼ 2.5), a greater variability was observed of individual isotope enrichment factors (ε18O and ε37Cl). Although most experiments yielded isotope enrichment factors (epsilon) in the larger negative range of previously published values, smaller negative values of ε18O and ε37Cl were observed for a halophilic isolate, Haloarcula marismortui, (ε18O = −15 to −22‰ and ε37Cl = −5 to −7‰), and in sediment column experiments (ε18O = −4 to −15‰ and ε37Cl = −1 to −6‰). Given the complexity of isolating individual parameters from our proposed model, we view our dataset as a survey that points to future opportunities where a particular parameter could be isolated to better understand controls on O and Cl isotope fractionation during microbial perchlorate reduction.

Origin of boron and lithium-rich salt lakes in center of Tibetan- plateau: Evidence from B and Cl isotopes

Tuotuohe Basin, one of sedimentary basins in Qinghai-Tibet Plateau, has a large number of salt lakes, and these salt lakes are typically rich in boron, lithium and other rare elements. The origin and extent of these resources is still unknown. In this study, we present a detailed analysis of several chemical compositions (Na/Cl, B/Cl, B/Li and Br/Cl molar ratios) δ11B and δ37Cl characteristics of salt lakes in the Tuotuohe Basin. The evidences of δ11B and δ37Cl have proved that the salt lakes in the Tuotuohe Basin are a type of leached brine. The amount of B isotopes in the water of these lakes is in the range of +0.17‰ to +12.52‰, suggesting that the salt lakes have a terrestrial origin. δ37Cl and Cl/Br relations suggest that brines in Tuotuohe Basin belong to halite dissolving and also influenced by rainwater and the leaching of volcanic rocks during the evolution process. The characteristics of the δ11B–B relationship are similar to those observed in the Tibetan geothermal area, indicating that these 2 places have the same B sources. Moreover, they have a crustal origin (Marine carbonate rocks and volcanic rocks) instead of a deep mantle source.

Origin of Halite in the Lanping–Simao Basin, Southeastern Tibetan Plateau, China: Evidence from Sr and Cl Isotopes

AbstractThe Lanping–Simao Basin is located on the southeastern Tibetan Plateau, China, and contains massive evaporites. The origin of evaporites in the basin has been hotly debated because of the strong transformation by tectonic movement. Forty halite samples from borehole MK‐3 in the Mengyejing area of the basin were collected and analyzed using XRD, Cl‐Sr isotopes and chemical compositions to trace the origin of the evaporites in the basin. The Br × 103/Cl ratios of the halite samples are between 0 and 0.55, most of which are synchronized with the law of seawater evaporation and at the stage of halite precipitation from seawater, indicating that the evaporites are mainly of marine origin. The 87Sr/86Sr ratios range from 0.707489 to 0.711279; after correction, the 87Sr/86Sr 145 Ma ratios range from 0.704721 to 0.707611, equivalent with the 87Sr/86Sr ratios of seawater at 145 Ma, indicating a marine origin. The decay of 87Rb in the evaporite during deposition, change of the depositional environment and the unsealed environment at a later period resulted in the present 87Sr/86Sr ratios of some samples being high. The δ37Cl value compositions range from –0.38‰ to 0.83‰, which is consistent with the δ37Cl value composition of the world marine halite (–0.6‰ to 0.4‰), further confirming that seawater is the main origin. In addition, the high δ37Cl value of some samples at the boundary of the upper and lower evaporite layers might be related to the influence of δ37Cl‐rich brine and the incomplete dissolution of the halite.

The role of fluid mixing in the formation of vein-type Zn-Pb deposits in eastern Guizhou Province, SW China: Insights from elemental compositions and chlorine isotopes of fluid inclusions

• Multiple fluid sources are identified by variation range of Cl isotopes and Cl/Br ratios from. • Vein-type Zn-Pb mineralization is triggered by mixing of evaporated seawater and magmatic hydrothermal fluids . • Quantitative model shows that the mixing volume ratios of both sources are between 1:9 and 4:6. Numerous hydrothermal vein-type Zn–Pb deposits worldwide are characterized by low-temperature metallogeny, no spatial relationship with plutons, and strong water-rock interaction, which result in the difficulty of constraining the fluid origin and the process of ore formation by traditional geochemistry. In this study, we employ chemical and chlorine isotopic composition of bulk fluid inclusions from ore-bearing and ore-barren quartz veins to constrain the possible sources of ore-forming fluids and the process of metal precipitation in the hydrothermal systems of the economic vein-type mineralization in eastern Guizhou Province, SW China. Our new geochemical data are indicative of two end-members in the systems, one identified in the ore-bearing veins with high K/Na, Li/Na, Cl/Br ratios, and δ 37 Cl values representing magmatic hydrothermal fluids, another distinguished in the ore-barren veins with low Cl/Br ratios and δ 37 Cl values representing evaporated seawater. We conclude there is a systematic variation of these geochemical data as the results of the mixing between the former and the latter end-member. In the meantime, the mixing is quantitively assessed to study the mixing volume ratios of both end-members. Based on our data and our own previous study, a genetic fluid mixing model involving the magmatic hydrothermal fluids related to deep magma activity and the evaporated seawater is established for the formation of the vein-type Zn–Pb deposits. This study provides a novel geochemical approach for recognizing hydrothermal mineralizing systems.

Chemical and isotopic evolution of flowback fluids from the Utica Gas Shale Play, Eastern Ohio USA

Hydraulic fracturing flowback fluids were collected from two Utica/Point Pleasant well pads in eastern Ohio. One site was in the wet gas zone (UPPW), while the site ∼50 km south consisted of four wells on the same pad in the dry gas zone (UPPS). Samples of input fluids also were collected before and during hydraulic fracturing. Flowback fluids are Na-Ca-Cl brines with total dissolved salt (TDS) concentrations that increase over several months from ∼100 to 200 g/L. The slightly higher TDS of the dry gas fluids are in part due to recycled flowback used as input fluids, and in part due to lower volume of water used in hydraulic fracturing. Concentrations of most major ions (Ca2+, Mg2+, Na+, Sr2+, Fe, Mn, Cl−, Br−) are similar for the five wells sampled, although small but systematic changes occur in the major element ratios over time.Most notably, an increase in the Sr/Cl ratio corresponds to an increase in the 87Sr/86Sr ratio in the fluids, suggesting interactions with a more radiogenic Sr source in the subsurface. Dissolved Ba concentrations and Ra activities were different between the two sites, reflecting a high SO42− fluid used at the UPPW site, and water-rock reactions occurring during hydraulic fracturing at the UPPS site.Water oxygen (δ18O) and hydrogen (δD) isotopes for input fluids used in the UPPW4 well and fresh water used for the UPPS wells fall on the Global Meteoric waterline (GMWL). Flowback fluids from both sites are relatively enriched in δ18O and δD compared to the input, but do not appear to follow a simple mixing trend, suggesting reaction and isotopic exchange with carbonates and fractionation due to imbibition in the rock. Cl isotopes, δ37Cl in the FP fluids varied from ∼ −0.43 to +0.13‰, the largest variation was observed in the earlier stages of flowback, while in the later stages δ37Cl exhibited a small but systematic increase over time, suggesting diffusion control of isotopic composition.Some of the trace species measured (dissolved Fe, Mn, thiosulfate and organic acids) do not follow the same trends as the major ions, suggesting contributions from input fluids, or microbially mediated reactions are exerting control on their concentrations. Input water chemistry exerts an important control on the Sr and Ba concentrations in flowback water. High SO42− in the input fluids used for hydraulically fracturing the wet gas well leads to precipitation of barite-celestite in flowback fluids.

(Student Award, 1st Place, Invited) Thermal Etching of Metal Oxides: Mechanisms Revealed By Quadrupole Mass Spectrometry

Thermal etching of metal oxides can occur spontaneously or by sequential surface reactions during atomic layer etching (ALE). This thermal etching does not require the use of plasmas or energetic species to remove material. Thermal etching can be studied by measuring the decrease of film thickness. However, the mechanisms of thermal etching still require the identification of volatile etch products. To address this issue, we have used quadrupole mass spectrometry (QMS) to detect volatile etch products during thermal etching. A custom reactor was built to measure the etch products with high sensitivity. This reactor uses molecular beam techniques to direct the etch products with line-of-sight to the QMS ionizer. Figure 1 shows a schematic of the QMS reactor. Nested inlet lines allow two reactants to be transported to the sample holder.This talk will explore the thermal etching of metal oxides using three different approaches: (1) chlorination followed by ligand addition; (2) exposure to acetylacetone; and (3) fluorination followed by ligand exchange or conversion. For the first approach, chlorination followed by ligand addition will be utilized for CoO thermal ALE with SO2Cl2 as the chlorination reactant and tetramethylethylenediamine (TMEDA) as the ligand-addition reactant at 250°C. The proposed mechanism for CoO thermal ALE is shown in Figure 2. SO2Cl2 converts the CoO surface to a CoCl2 layer and yields SO3. Then the TMEDA adds to CoCl2 and forms volatile CoCl2(TMEDA) etch products. QMS studies were able to confirm the formation of CoCl2(TMEDA) etch products. Figure 3 displays the CoCl2(TMEDA) etch products observed for the 5th CoO ALE cycle during the TMEDA exposure at 250°C. The natural abundance of the Cl isotopes affirmed that CoCl2(TMEDA) was the volatile etch product.Additional time-resolved experiments were able to monitor the reactants and volatile etch products. Figure 4 displays the ion intensities of C3N8N+ (largest crack of TMEDA) and CoCl(TMEDA)+ (largest crack of CoCl2TMEDA) during the TMEDA exposure at 250°C. The self-limiting nature of the ligand-addition reaction is revealed by the decrease of the CoCl(TMEDA)+ ion intensity with time while the TMEDA ion intensity remains constant. Chlorination followed by ligand addition was also utilized for the thermal ALE of other first row transition metal oxides (Fe2O3, NiO, and ZnO). M(TMEDA)Cl2 was observed as the volatile etch product for M= Fe and Ni. Zn(TMEDA)Cl was observed for ZnO.For the second approach, acetylacetone (Hacac) and hexafluoroacetylacetone (Hhfac) have been known to spontaneously etch a variety of metal oxides including ZnO, CuOx and Fe2O3. In addition, some thermal ALE procedures have been developed using Hacac together with an oxidation reactant to clean the metal oxide surface after the Hacac exposure. This talk will highlight results for ZnO etching using sequential Hacac and O3 exposures and also consecutive Hacac exposures. Zn(acac)2 was observed by the QMS studies during the alternating Hacac and O3 exposures on ZnO throughout the Hacac exposures at 250°C. Additional experiments using Hacac exposures with no O3 exposures also observed the continuous yield of Zn(acac)2. These experiments provide evidence for the spontaneous etching of ZnO by Hacac according to the reaction: ZnO + 2Hacac -> Zn(acac)2 +H2O. This reaction is believed to proceed spontaneously through a ligand substitution/hydrogen transfer mechanism. Other metal oxides were also etched using sequential Hacac and O3 exposures including V2O5, Fe2O3, CoO and CuO at 250°C. M(acac)2 species were observed for M=Co, Fe and Cu. VO(acac)2 was observed for V2O5.Lastly, for the third approach, Al2O3 thermal ALE was explored using sequential BCl3 and HF exposures at 300°C. This thermal ALE process could occur by (A) conversion of Al2O3 to B2O3 by BCl3 followed by the spontaneous etching of B2O3 by HF or (B) fluorination of Al2O3 to AlF3 followed by the ligand exchange of AlCl3 with BCl3 to produce volatile AlCl3. QMS analysis revealed that initial exposures of BCl3 on Al2O3 led to a conversion reaction forming B2O3 and volatile AlCl3. Subsequently, the HF exposure on B2O3 released BF3 and H2O. After removing the B2O3 conversion layer, the HF proceeded to fluorinate Al2O3 to form a AlF3 layer and volatile H2O. Additional BCl3 exposures then underwent ligand exchange with the AlF3 layer to form BFCl2 and AlCl3. The BCl3 continued to convert the underlying Al2O3 to B2O3. Moreover, the BCl3 exposures were also observed to spontaneously etch the B2O3 conversion layer. QMS studies revealed that the reaction of BCl3 with the B2O3 conversion layer or initial B2O3 substrates produced B3O3Cl3, a boroxine ring species. BCl3 has the unusual ability to convert Al2O3 to B2O3 and then spontaneously etch the B2O3. Figure 1

Global rovibrational fits for AlCl, BiCl, and BiF: Benchmarks for novel physics

Global fits combining existing rotational spectroscopy data for both chlorine isotopologues of AlCl and BiCl provide 2x/8x improved precision in hyperfine parameters like the nuclear electric quadrupole moment coupling terms (eQq) for use in novel physics applications, and include Born–Oppenheimer Breakdown (BOB) terms. The BiF fit combines existing data for a range of rotational transitions, providing an almost 3x more precise eQq benchmark for theoretical work on related molecules used in searches for the electric dipole moment of the electron (eEDM). Our AlCl nuclear electric quadrupole moment ratio Q(35Cl):Q(37Cl) of 1.26858(37) confirms many previous values, while enabling a more precise BiCl eQq value and informing reference work choices for nuclear physics Q-values for both Cl isotopes.