Ratio Of He Research Articles

3He and Fe Spectral Properties in 3He-rich Solar Energetic Particle Events

We have surveyed 3He-rich events on the Solar Orbiter mission from 2020 April to 2024 April, selecting isolated injections whose rollover 3He spectral shape is presumed to represent the initial acceleration state, unprocessed by subsequent activity such as coronal mass ejections or jets. A main goal has been to find relationships between the spectra of 3He and heavy ions C–Fe, in order to explore a common acceleration mechanism in spite of the fact that these events show 3He enrichments of up to ∼104, while the heavy-ion enrichment is rarely larger than ∼10. Selecting 34 3He injections, we find that heavy ions are always present, and arrive at the same time as the 3He signaling a common origin. Concentrating on Fe since it is a minor ion but with higher abundance than many others, we find its spectral shape and intensity is similar to 3He. In ∼two-thirds of the cases, if the 3He spectrum is shifted to lower energy by a factor 3.0 ± 1.3, it nearly coincides with the Fe spectrum, illustrating their close connection. Several plasma wave turbulence models have calculated spectra that also show the ion rollovers around 1 MeV nucleon−1. The unique mass-to-charge ratio of 3He allows it to interact more efficiently with the turbulence, thereby gaining several times more energy per nucleon than the other heavy ions. In the spectral rollover region this can lead to the observed enormous enhancements of 3He. The acceleration appears to be associated with magnetic reconnection in emerging flux regions on the Sun.

Pristine helium from the Karoo mantle plume within the shallow asthenosphere beneath Patagonia

Mantle xenoliths usually represent fragments derived from the depleted and degassed lithospheric mantle with 3He/4He isotope ratios (6 ± 1 RA) lower than those of mid-ocean ridge basalts (8 ± 1 RA). Otherwise, basalts from oceanic islands related to hotspots often have high 3He/4He ratios (>10 RA), suggesting a deep and pristine undegassed mantle source. Here we present a striking high-3He/4He component (up to 27.68 RA) recorded by spinel-facies mantle xenoliths from Patagonia. Remarkably, the highest ratios were found in a long-lived trans-lithospheric suture zone related to the Carboniferous-Permian collision of two continental blocks: the Deseado and the North Patagonian massifs. The mantle xenoliths with notably high-3He/4He ratios are inferred to be fragments of the shallow asthenosphere rising through the eroded and rejuvenated thin lithosphere. The pristine helium component is derived from the western margin of the Karoo mantle plume, related to the initial stages of the Gondwana fragmentation.

Steady-State simulation of cryogenic distillation used for helium isotope separation

Helium-3 (3He) is an invaluable and scarce resource with applications in various scientific and industrial fields. It is typically found mixed with helium- 4(4He) in natural gas and nuclear off-gas, which is industrial source of helium. Therefore, separation of the helium isotope is necessary. Cryogenic distillation is a preferred method of separation due to its higher separation coefficient and processing capacity. In this study, a numerical steady-state simulation of cryogenic distillation column for helium isotope has been conducted using programming. The mathematical model for the equilibrium-state cryogenic distillation process was established and solutions of the thermodynamic formulation was proposed. The simulation provided the distribution of 3He and 4He along each distillation column as well as the profiles of temperature and flow rates along the column, based on the designed specifications including the composition of the feeding mixture, feed flow rate and pressure. The required heat duty of the condenser and reboiler was also calculated, and the column dimensions were estimated. Besides, we have studied the effects of the reflux ratio and feed concentration of 3He on the final isotopic contents of the top and bottom products. The results demonstrated that the distillation simulation could provide crucial theoretical support for the smooth execution of future laboratory experiments.

Genesis of the Abunabu antimony deposits in the Tethys Himalayan metallogenic belt: Evidence from He–Ar and S isotopes of stibnite

Introduction: The Abunabu antimony mining area is located between the Indus–Yarlung Tsangpo suture and the southern Tibetan detachment system. Ore deposits in the mining area provide an excellent opportunity to understand the nature and genesis of antimony mineralisation in the Tethys Himalayan metallogenic belt.Methods: In this study, we analysed the He–Ar and S isotopic compositions of stibnite-hosted fluid inclusions as a basis for investigating the sources of ore-forming fluids in the Abunabu mining area and the Tethys Himalayan metallogenic belt.Results: The analysed stibnites have 4He contents of 0.016 × 10−7–1.584 × 10–7 cm3 STP/g, 40Ar contents of 1.37 × 10−7–2.94 × 10–7 cm3 STP/g, 40Ar/36Ar ratios of 303.8–320.7, and 3He/4He (Ra) ratios of 0.021–0.351. These isotopic features indicate that the ore-forming fluids were primarily metamorphic fluids of crustal origin, with small amounts of magmatic-derived materials and modified air-saturated water with low 40Ar*/4He ratios. The δ34S values of stibnite vary within a narrow range of −4.9‰ to −3.5‰, with a mean value of −4.31‰, indicating a deep magmatic origin.Discussion: On the basis of these results and a compilation of data for sulphide deposits in the metallogenic belt, we infer that compositional variations in the He and Ar isotopes of the ore-forming fluids of each antimony deposit in the Tethys Himalayan metallogenic belt are independent of each other. This suggests that antimony deposits in the belt had similar ore-forming fluid sources and mixing processes and that differences in the metallogenic tectonic setting within the belt emerged only in the later stages of deposit evolution. Our new results and compiled data also show that antimony–gold deposits and lead–zinc–antimony polymetallic deposits in the Tethys Himalayan metallogenic belt differ in their sulphur isotopic compositions and that multiple sulphur sources were involved in each of these types of deposit.

Heat, noble gases and CO2 sources in geothermal fields of Mexico

The Trans-Mexican Volcanic Belt (TMVB) and the Gulf Extensional Province (Baja California) are the regions in Mexico with the highest heat flow and where the main geothermal energy resources are currently exploited. Here, previously published and newly collected heat and volatile species (He, Ar and CO2) data from 132 fluid samples of four geothermal areas belonging to TMVB (Los Azufres, Los Humeros, Acoculco and Cerritos Colorados) and two in Baja California (Cerro Prieto and Las Tres Vírgenes) were analyzed. The goal was to identify heat sources, understand how heat is transported into the geothermal reservoirs and how the multiple fluid sources (meteoric, magmatic and crustal) in the reservoir might impact the heat in each field. Distinct R/Ra ratios (where R is the measured 3He/4He ratio and Ra is the atmospheric ratio) are observed in the TMVB and Baja California geothermal fields, with those in the TMVB displaying significantly higher R/Ra values (7.14–7.27) than those in Baja California (1.21–6.62), indicating a higher contribution of mantle helium from possibly younger, active magmatic heat sources. Lower R/Ra values in Baja California might reflect local tectonic features, where reservoirs are primarily affected by crustal contributions from an old, subducted fossil slab related to the Farallon Plate. The analysis of heat to 3He ratios (or Q/3He) together with information provided by 4He/36Ar ratios suggest that heat and volatiles are transferred into the hydrothermal system by advection. The magma bodies beneath the geothermal areas of interest are sufficiently voluminous to provide aqueous fluids by exsolution to sustain this advective flow. The release of He and Ar from magma, during its degassing, appears to be controlled by their diffusivities, fractionating the pristine mantle 4He/36Ar ratio toward higher values, while advection transfers volatiles more rapidly than heat, fractionating the pristine mantle Q/3He ratios toward lower values. The Q/3He vs. 4He/3He relationship shows that boiling and dilution by meteoric water led to further fractionation of heat and volatiles, particularly in Los Azufres and Los Humeros fields, while Cerro Prieto has Q/3He ratios close to those at mid-ocean ridges or fractionated by circulation of low-heat, 4He-rich fossil waters. Distinct sources of heat and volatiles are also reflected in the CO2 content, the major dry gas component in these geothermal fields. Main sources of CO2 are mantle carbon (1%-51%) and limestone (34%–100%) from local sources and the subducting slab, although expected fractionation of the C isotopic composition and CO2/3He during magma ascent and degassing introduce uncertainties on the precise estimation of each source contributing C to the studied geothermal reservoirs. Yet, contribution of carbon from sediments might be minor (0%–35%), and mainly found in Cerro Prieto and Las Tres Virgenes fields located in Baja California, which are affected by the release of volatiles from the subducted Farallon plate and presence of connate waters in the reservoir of Cerro Prieto.

Improved understanding of the origin and accumulation of hydrocarbons from multiple source rocks in the Lishui Sag: Insights from statistical methods, gold tube pyrolysis and basin modeling

Hydrocarbon source correlations and the determination of hydrocarbon accumulation models in petroliferous basins with multiple potential source rocks are significant for hydrocarbon exploration. In this study, on the basis of gas chromatography and gas chromatography-mass spectrometry experiments, the oil origin was determined by a multiparameter oil-source correlation based on statistical methods. Through gold tube pyrolysis, fluid inclusion analysis, laser Raman analysis of inclusions and basin modeling, this study deeply explores the origin and accumulation of oil and gas in the Lishui Sag, East China Sea Basin. The oil in the west sub-sag is a mixture from source rocks of the Yueguifeng and Lingfeng formations (Danian-Selandian), while the oil in the east sub-sag is derived from source rocks of the Yueguifeng Formation (Danian). The hydrocarbon gas reservoir of the LA well block in the middle of the sag contains mainly oil-associated gas derives from the Yueguifeng Formation (Danian). The 3D basin modeling shows that the oil and gas generated by source rocks of the Yueguifeng and Lingfeng formations (Danian-Selandian) migrated upward into the reservoirs in the Mingyuefeng Formation (Thanetian). Due to the poor preservation conditions in the northern part of the study area, a large amount of oil and gas escaped and failed to accumulate. Controlled by fluid potential and faults, hydrocarbons in the Lishui Sag mainly migrated from the source kitchen to the slope zone. The stable carbon isotope data combined with the 3He∕4He ratios show that the CO2 in the Lishui Sag are mantle-derived inorganic gas related to volcanic activity. The filling of CO2, caused the loss and reaccumulation of early filled oil and gas, which impacted the distribution of oil and gas reservoirs in the Lishui Sag. Therefore, the migration and accumulation mechanism of CO2 should be fully considered in oil and gas exploration in the Lishui Sag.

Insights from Fumarole Gas Geochemistry on the Recent Volcanic Unrest of Pico do Fogo, Cape Verde

We report the results of the geochemical monitoring of the fumarolic discharges at the Pico do Fogo volcano in Cape Verde from 2007 to 2016. During this period Pico do Fogo experienced a volcanic eruption (November 23, 2014) that lasted 77 days, from a new vent ∼2.5 km from the fumaroles. Two fumaroles were sampled, a low (F1∼100°C) and a medium (F2∼300°C) temperature. The variations observed in the δ18O and δ2H in F1 and F2 suggest different fluid source contributions and/or fractionation processes. Although no significant changes were observed in the outlet fumarole temperatures, two clear increases were observed in the vapor fraction of fumarolic discharges during the periods November 2008–2010 and 2013–2014. Also, two sharp peaks were observed in CO2/CH4ratios at both fumaroles, in November 2008 and November 2013. This confirms that gases with a strong magmatic component rose towards the surface within the Pico do Fogo system during 2008 and 2013. Further, F2 showed two CO2/Stotalpeaks, the first in late 2010 and the second after eruption onset, suggesting the occurrence of magmatic pulses into the volcanic system. Time series of He/CO2, H2/CO2and CO/CO2ratios are low in 2008–2009, and high in 2013–2014 period, supporting the hypothesis of fluid input from a deeper magmatic source. Regarding to the isotopic composition, increases in air-corrected3He/4He ratios are observed in both fumaroles; F1 showed a peak in 2010 from a minimum in 2009 during the first magmatic reactivation onset and another in late 2013, while F2 displayed a slower rise to its maximum in late 2013. The suite of geochemical species analyzed have considerably different reactivities, hence these integrated geochemical time-series can be used to detect the timing of magmatic arrivals to the base of the system, and importantly, indicate the typical time lags between gas release periods at depth and their arrival at the surface. The high3He/4He ratios in both fumaroles in the range observed for mid-ocean ridge basalts, indicating that He is predominantly of upper mantle origin. This work supports that monitoring of the chemical and isotopic composition of the fumaroles of the Pico do Fogo volcano is a very important tool to understand the processes that take place in the magmatic-hydrothermal system and to be able to predict future episodes of volcanic unrest and to mitigate volcanic risk.

Sources and transport of fluid and heat at the newly-developed Theistareykir Geothermal Field, Iceland

Successful management of geothermal energy requires detailed understanding of physical and chemical conditions within the field prior to exploitation. It is thus crucial to identify fluids involved and their residence times, as well as the heat source, so as to assess the potential of the resource in terms of energy production. To this end, a geochemical study of relatively undisturbed fluids from the newly-developed Theistareykir geothermal field, Northern Volcanic Zone, Iceland was carried out on production wells, fumaroles, and mud pots. Noble gas (He, Ne, Ar, Kr, and Xe) elemental and isotopic abundances and stable isotopes (δ18O and δ2H) were measured to determine the system fluid sources and dynamics as exploitation proceeds. Results of this study, together with previously published data, show that four fluid sources are present: modern and local meteoric water (48.9%); sub-modern meteoric water from regional highlands precipitation (10.6%); pre-Holocene glaciated meteoric water (40.4%) with strongly depleted δ2H values of −127‰, calculated 40K-40Ar* fluid residence times from 57 ± 20 ka to 92 ± 30 ka and a (U/Th)-4He fluid residence times from 96 ± 50 ka to 160 ± 80 ka; and, finally, 3He-rich magmatic fluids. Concomitant enrichment in 18O and radiogenic 4He suggests that some fluids reside a long time in the reservoir, exchanging O and He with reservoir rocks. Maximum estimated helium isotopic ratios, 3He/4He (R), of 11.45 Ra (Ra = atmospheric ratio) show that the magma beneath Theistareykir is a depleted mid-ocean ridge basalt (MORB) mantle (DMM), with less influence (8.7 to 12.7%) of the Icelandic mantle plume source. Calculated heat (Q)/3He ratios plotted vs. R/Ra and 4He/36Ar ratios suggest that convective heat transport dominates the eastern part of the field where the magmatic heat source is located, while in other parts of the field, heat conduction seems to be dominant. Boiling and phase separation exists in the field, as indicated by δ18O values which fall to the left of the Global Meteoric Water Line in a δ18O vs. δ2H plot, but Q/3He ratios indicate that boiling affects only 1–10% of the fluid reservoir. With this obtained knowledge, any subsequent changes in the field conditions during the exploitation phase of Theistareykir can be better understood, helping to sustainably manage the resource.

Geochemical survey of the Colpitas-Taapaca volcanic-hydrothermal system, northern Chile

This work presents chemical and isotopic (δ13C-CO2, δ13C-CH4, 3He, 4He, 20Ne, 40Ar, 36Ar, δ18O and δD) data of fluid discharges from Colpitas-Taapaca volcanic-hydrothermal system, located close to the Taapaca Volcanic Complex, with the aim to investigate the physical-chemical conditions of the fluid source and to provide a preliminary evaluation of the geothermic potential of the study area. Colpitas thermal springs (to 56 °C) and part of the cold springs (≤18°C) from this area have a Na+-Cl- composition and Total Dissolved Solids (TDS) values (from 6,059 to 19,118 mg/L). Putre springs also show a Na +-Cl -composition, TDS values up to 7,887 mg/L, and outlet temperatures from 21 to 31 °C. Colpitas cold springs, with a Ca2+-SO42- composition and relatively low TDS values (≤1,350 mg/L), are likely produced by interaction of shallow water with uprising H2S- rich hydrothermal gases. This process is likely also controlling the chemistry of Jurase thermal springs, which have the highest outlet temperatures of the study area (up to 68 °C), a Ca2+-SO42- composition and TDS values ≤2,355 mg/L. Eventually, Las Cuevas springs have temperatures up to 36 °C, a Na+-HCO3- composition and low TDS values (≤1,067 mg/L), typical features of springs related to a shallow aquifer. The δ18O-H2O and δD-H2O values indicate that all waters have a dominant meteoric origin. Enrichments in 18O and D shown by Colpitas and Putre thermal waters are likely due to steam loss and water- rock interaction, masking a possible direct steam contribution from magmatic degassing. Gas emissions from Colpitas bubbling pools are dominated by CO2, with significant concentrations of CH4, H2S and H2. The Rc/Ra values (up to 2.04) of Colpitas gases indicate a significant contribution of magmatic to mantle He, whereas the high CO2/ 3He ratios, combined with d 13C-CO2 values ranging from -7.66 to -5.63 ‰ vs. PDB, imply a dominant crustal CO2 source, mostly involving limestone. Estimated temperatures based on the composition of waters and gases from Colpitas are up to 215 °C. Higher temperatures (240 °C) are estimated for Putre thermal waters, although these waters, as well as those from Jurase and Las Cuevas, are too immature for a reliable application of geothermometric techniques. Based on the theoretical reservoir temperature and the measured Cl total output, the thermal energy released from Colpitas thermal area is estimated at up to 13.9 Mw. Such results suggest the occurrence of a promising heat source, possibly related to Taapaca volcanic complex, and encourage the development of future research based on combined geophysical and geochemical approaches, in order to provide a reliable evaluation of the geothermal potential of the whole area.

Reversible scavenging traps hydrothermal iron in the deep ocean

Recent studies suggest that seafloor hydrothermal vents could be an important source of iron (Fe) to the surface ocean, stimulating plankton growth and biological carbon export. However, quantifying the supply of hydrothermal Fe to the surface ocean requires accurately modeling its stabilization and removal processes, which are poorly known. Here, we determine the physical speciation of dissolved Fe along an oceanographic transect following a coherent hydrothermal plume that emanates from the East Pacific Rise (EPR) and persists westward over 4,000 km in the Tropical South Pacific. Our observations show that the plume persists horizontally, but descends vertically, and consists primarily of very large Fe colloids. Guided by these observations, we develop a new size-resolved mechanistic model of hydrothermal Fe dispersion in this region, in which the stabilization of hydrothermal Fe is explained by a reversible particulate exchange process. This model accurately captures the lateral dispersion, downward settling and physical speciation of hydrothermal Fe along this transect. An alternate model that uses a hydrothermal source of Fe-binding ligands to facilitate Fe transport within the deep ocean can reproduce the long-range transport of hydrothermal Fe, but does not reproduce the vertical descent of the plume. Our model shows that hydrothermal Fe vented from the EPR is trapped in the deep ocean, and only 1% of this iron ever makes it to the surface where it can stimulate biological productivity. At the global scale, 3-5% of hydrothermal Fe makes it to the surface ocean, the vast majority of which originates from Southern Ocean vents and upwells in the Southern Ocean. Our best estimate of the global supply of hydrothermal Fe to the surface ocean, based on data-constrained estimates of ocean circulation, mantle 3He venting, and the hydrothermal Fe:3He ratio from the EPR, is 0.12±0.07 Gmolyr−1. This is about 60-70 times lower than the supply of Fe from aerosol dust deposition, but could be regionally important in the Antarctic zone of the Southern Ocean.

An intermediate-depth source of hydrothermal 3He and dissolved iron in the North Pacific

We observed large water column anomalies in helium isotopes and trace metal concentrations above the Loihi Seamount. The 3He/4He of the added helium was 27.3 times the atmospheric ratio, clearly marking its origin to a primitive mantle plume. The dissolved iron to 3He ratio (dFe:3He) exported to surrounding waters was 9.3±0.3×106. We observed the Loihi 3He and dFe “signal” at a depth of 1100 m at several stations within ∼100 – 1000 km of Loihi, which exhibited a distal dFe:3He ratio of ∼4×106, about half the proximal ratio. These ratios were remarkably similar to those observed over and near the Southern East Pacific Rise (SEPR) despite greatly contrasting geochemical and volcanic-tectonic origins. In contrast, the proximal and distal dMn:3He ratios were both ∼1×106, less than half of that observed at the SEPR. Dissolved methane was minimally enriched in waters above Loihi Seamount and was distally absent. Using an idealized regional-scale model we replicated the historically observed regional 3He distribution, requiring a hydrothermal 3He source from Loihi of 10.4 ± 4.2 mola−1, ∼2% of the global abyssal hydrothermal 3He flux. From this we compute a corresponding dFe flux of ∼40 Mmola−1. Global circulation model simulations suggest that the Loihi-influenced waters eventually upwell along the west coast of North America, also extending into the shallow northwest Pacific, making it a possibly important determinant of marine primary production in the subpolar North Pacific.

Accurate Determination of the Absolute 3He/4He Ratio of a Synthesized Helium Standard Gas (Helium Standard of Japan, HESJ): Toward Revision of the Atmospheric 3He/4He Ratio

AbstractThe helium standard of Japan, referred to as HESJ, is an interlaboratory standard for the 3He/4He ratio. While the ratio of 3He and 4He of the HESJ was previously determined by a relative comparison to atmospheric helium, the absolute value of the 3He/4He ratio of the HESJ has not been directly determined yet. Therefore, it relies on the early measurements of that of atmospheric helium. The accuracy of the absolute 3He/4He ratios of the atmosphere and other working standards including HESJ is crucial in some applications of helium isotopes, such as tritium‐3He dating, surface‐exposure age determination based on cosmogenic 3He, and the accurate measurement of the neutron lifetime. In this work, new control samples of helium gases with 3He/4He ratios of 14, 28, and 42 ppm were fabricated with accuracy of 0.25–0.38% using a gas‐handling system for a neutron lifetime experiment at Japan Proton Accelerator Research Complex. The relative 3He/4He ratios of these samples and the HESJ were measured using a magnetic‐sector type, single‐focusing, noble gas mass spectrometer with a double collector system. As a result, the absolute 3He/4He ratio of the HESJ was determined as 27.36 ± 0.11 ppm. The atmospheric 3He/4He ratio was determined as 1.340 ± 0.006 ppm, based on this work.

New determination of the 3He mixing ratio in the Earth's lower atmosphere from an international tritium intercomparison exercise

The light isotope of helium, 3He, is essentially a primordial substance entrapped within the Earth's interior during the formation of the planet. It is released into the atmosphere by volcanic/magmatic activity, and eventually escapes to outer space. 3He is also produced by the radioactive beta-decay of tritium. Hence, measurements of 3He can be used to derive the concentration of tritium. The so-called “3He ingrowth” method uses a mass spectrometer to detect the amount of 3He that accumulates in a sample during a given period of storage. The 3He measurements are classically calibrated against an air standard. The method thus relies on the accurate knowledge of the atmospheric mixing ratio of 3He. This value is based on mass spectrometric measurements with gravimetrically or volumetrically prepared 3He standard mixtures. Here, we apply the 3He ingrowth method in reverse, using a solution of tritiated water prepared for an international comparison of tritium activity measurements to precisely determine the 3He mixing ratio of our air standard. The measured atmospheric mixing ratio of 3He, based on a series of ten measurements, is [3He] = 7.12 ± 0.06 ppt. This value is between 1% and 2% lower than previous determinations reported in the literature. However, all results remain statistically consistent.

Plate tectonic cycling modulates Earth's 3He/22Ne ratio

The ratio of 3He and 22Ne varies throughout the mantle. This observation is surprising because 3He and 22Ne are not produced in the mantle, are highly incompatible during mantle melting, and are not recycled back into the mantle by subduction of oceanic sediment or basaltic crust. Our new compilation yields average 3He/22Ne ratios of 7.5 ± 1.2 and 3.5 ± 2.4 for mid-ocean ridge basalt (MORB) mantle and ocean island basalt (OIB) mantle sources respectively. The low 3He/22Ne of OIB mantle approaches planetary precursor 3He/22Ne values; ∼1 for chondrites and ∼1.5 for the solar nebula. The high 3He/22Ne of the MORB mantle is not similar to any planetary precursor, requiring a mechanism for fractionating He from Ne in the mantle and suggesting isolation of distinct mantle reservoirs throughout geologic time. New experimental results reported here demonstrate that He and Ne diffuse at rates differing by one or more orders of magnitude at relevant temperatures in mantle materials. We model the formation of a MORB mantle with an elevated 3He/22Ne ratio through kinetically modulated chemical exchange between dunite channel-hosted basaltic liquids and harzburgite wallrock beneath mid-ocean ridges. Over timescales relevant to mantle upwelling beneath spreading centers, He may diffuse tens to hundreds of meters into wallrock while Ne is effectively immobile, producing a mantle lithosphere regassed with respect to He and depleted with respect to Ne, with a net elevated 3He/22Ne. Subduction of high 3He/22Ne mantle lithosphere throughout geologic time would generate a MORB source with high 3He/22Ne. Mixing models suggest that to preserve a high 3He/22Ne reservoir, MORB mantle mixing timescales must be on the order of hundreds of millions of years or longer, that mantle convection has not been layered about the transition zone for most of geologic time, and that Earth's convecting mantle has lost at least 96% of its primordial volatile elements. The most depleted, highest 3He/22Ne mantle may be best preserved in the lower mantle where relatively high viscosities impede mechanical mixing.

Age and metal source of orogenic gold deposits in Southeast Guizhou Province, China: Constraints from Re–Os and He–Ar isotopic evidence

The orogenic gold deposits in Southeast Guizhou are an important component of the Xuefeng polymetallic ore belt and have significant exploration potential, but geochronology research on these gold deposits is scarce. Therefore, the ore genetic models are poorly constrained and remain unclear. In the present study, two important deposits (Pingqiu and Jinjing) are investigated, including combined Re–Os dating and the He–Ar isotope study of auriferous arsenopyrites. It is found that the arsenopyrites from the Pingqiu gold deposit yielded an isochron age of 400 ± 24 Ma, with an initial 187Os/188Os ratio of 1.24 ± 0.57 (MSWD = 0.96). An identical isochron age of 400 ± 11 Ma with an initial 187Os/188Os ratio of 1.55 ± 0.14 (MSWD = 0.34) was obtained from the Jinjing deposit. These ages correspond to the regional Caledonian orogeny and are interpreted to represent the age of the main stage ore. Both initial 187Os ratios suggest that the Os was derived from crustal rocks. Combined with previous rare earth element (REE), trace elements, Nd–Sr–S–Pb isotope studies on scheelite, inclusion fluids with other residues of gangue quartz, and sulfides from other gold deposits in the region, it is suggested that the ore metals from Pingqiu and Jinjing were sourced from the Xiajiang Group. The He and Ar isotopes of arsenopyrites are characterized by 3He/4He ratios ranging from 5.3 × 10−4 Ra to 2.5 × 10−2 Ra (Ra = 1.4 × 10−6, the 3He/4He ratio of air), 40Ar*/4He ratios from 0.64 × 10−2 to 15.39 × 10−2, and 40Ar/36Ar ratios from 633.2 to 6582.0. Those noble gas isotopic compositions of fluid inclusions also support a crustal source origin, evidenced by the Os isotope. Meanwhile, recent noble gas studies suggest that the amount of in situ radiogenic 4He generated should not be ignored, even when Th and U are present at levels of only a few ppm in host minerals.

Submarine Basaltic Glasses from the Galapagos Archipelago: Determining the Volatile Budget of the Mantle Plume

We report new major, trace and volatile element contents (H_2O, CO_2, F, S, Cl), and new Sr, Nd, Pb and He isotopes on submarine glasses from the Galapagos Archipelago from several dredging expeditions. Four groups are distinguishable on the basis of composition and geographical distribution: the Fernandina group (^3He/^4He > 22 R_A), which is similar to the less degassed primitive mantle; the Sierra Negra group (enriched Pb and Sr isotopes, ^3He/^4He = 8–20 R_A), produced by mixing the Floreana (HIMU-type) and Fernandina end-members; the Pinta group (high Δ7/4, Δ8/4 and Th/La ratios, ^3He/^4He = 6–9 R_A), an enriched mantle (EM)-type mantle indicative of recycled material in the source; and the depleted mantle (DM) group, characterized by an isotopic composition similar to mid-ocean ridge basalts (MORB). Only a single submarine glass with the isotopic composition of the Floreana end-member has been identified in the sample suite. Degassing has significantly lowered the glass CO_2 content with little effect on the H_2O concentration. Volatile data for oceanic basalts reveal that CO_2–H_2O gas–melt equilibration at eruption depth is common in ocean island basalts (OIB) and rare in MORB, suggesting different ratios of melt transport to bubble formation and gas–melt equilibration. The Galapagos glasses range from sulfide saturated to undersaturated, and a subset of samples indicate that S degasses at pressures ≤ 400 bars. Assimilation of hydrothermally altered material affected the volatile contents of a number of samples in the groups. Once shallow-level processes have been accounted for, we evaluate the volatile contents in the different Galapagos mantle sources. Ratios between volatile and refractory elements with similar incompatibilities are used to estimate the volatile budget of the Galapagos mantle plume. Most of the glasses from the Fernandina, Sierra Negra and Pinta groups have high volatile/refractory element ratios, whereas a few pristine DM group lavas have ratios similar to those measured in MORB. The volatile/refractory element ratios are consistent with previous reports for the high ^3He/^4He, HIMU and MORB components. The values measured for the Pinta group, however, are higher than those found in other OIB associated with the presence of recycled material (EM-type). Our data suggest that mixing between the different mantle components is pervasive throughout the archipelago, which acts to normalize the volatile data between the groups. The Fernandina component can be modeled by a 6–20% mixture of the high ^3He/^4He primitive mantle component with the MORB source, assuming a two-layered mantle and using existing estimates of helium concentrations. The resulting estimated volatile content and H/C mass ratio for the high ^3He/^4He primitive mantle are consistent with previous estimates, but calculated C/3He ratios are lower than the canonical ratio. This indicates the following: (1) the estimates require ∼20–50 times higher C or lower ^3He contents, which is difficult to reconcile with the measured volatile/refractory ratios in oceanic basalts; (2) the C/^3He ratio is not constant throughout the mantle; (3) an impact erosion model, rather than a two-layered mantle model, is more consistent with the relatively constant C/3He ratios observed in oceanic basalts, although it is unclear how representative oceanic basalts are of the lower mantle. The high volatile content of the high ^3He/^4He component will affect mantle dynamics and melt migration during plume–ridge interaction as this component would be predicted to be less viscous than the ambient mantle. The lower viscosity material would have an enhanced vertical upwelling, which could explain the buoyancy flux of the Galapagos plume without the need for a temperature anomaly. A lower viscosity, high ^3He/^4He component could also provide an explanation for the lack of high ^3He/^4He in Galapagos Spreading Center lavas erupting in the vicinity of the Galapagos plume.

High-sensitivity measurement ofHe3−He4isotopic ratios for ultracold neutron experiments

Research efforts ranging from studies of solid helium to searches for a neutron electric dipole moment require isotopically purified helium with a ratio of 3He to 4He at levels below that which can be measured using traditional mass spectroscopy techniques. We demonstrate an approach to such a measurement using accelerator mass spectroscopy, reaching the 10e-14 level of sensitivity, several orders of magnitude more sensitive than other techniques. Measurements of 3He/4He in samples relevant to the measurement of the neutron lifetime indicate the need for substantial corrections. We also argue that there is a clear path forward to sensitivity increases of at least another order of magnitude.

Stars with discrepant v sin i as derived from the Ca II λ3933 Å and Mg II λ4481 Å lines. V. HD 182255 and HD 214923—SPB stars in binary systems

The axial rotation of a star plays an important role in its evolution, the physical conditions in its atmosphere and the appearance of its spectrum.We analyzed the CCD spectra of two stars for which their projected rotational velocity differs remarkably when derived from Ca II λ3933 A and Mg II λ4481 A lines. We estimated the projected rotational velocity of HD182255 to be 15.5 kms−1, although in various spectra of this star the line widths correspond to values as high as 28.5 km s−1. We found the HeI λ4471.498 A line to be shifted to longer wavelengths by 0.046 A, thus indicating a presence of the 3He I isotope in the atmosphere of this star with the 3He : 4He ratio from 0.2 to 0.6.We also found an absorption feature at the position of the forbidden line He I λ4470.02A. We found the lines ofMg II and CII originating from higher excited levels to be missing in the spectra of HD 182255. For HD 214923 we determined the projected rotational velocity v sin i = 165km s−1 from the profiles of the metallic lines and Ca II λ3933A, whereas for helium lines v sin i ≈ 130km s−1 is more appropriate. Radial velocity analysis results in three long periods of ≈ 105, 34, and 15 days, and a short period of ≈ 22 hours, close to the pulsational one mentioned earlier in the literature.

Coastal upwelling off Peru and Mauritania inferred from helium isotope disequilibrium

Abstract. Upwelling is an important process, bringing gases and nutrients into the ocean mixed layer. The upwelling velocities, however, are too small to be measured directly. Here we use the surface disequilibrium of the 3He / 4He ratio measured in two coastal upwelling regions off Peru in the Pacific ocean and off Mauritania in the Atlantic ocean to calculate the regional distribution of vertical velocities. To also account for the fluxes by diapycnal mixing, microstructure-based observations of the vertical diffusivity have been performed on all four cruises analysed in this study. The upwelling velocities in the coastal regions vary between 1.1 ± 0.3 × 10−5 and 2.8 ± 1.5 × 10−5 m s−1 for all cruises. Vertical velocities are also inferred from the divergence of the wind-driven Ekman transport. In the coastal regimes, both methods agree within the error range. Further offshore, the helium-derived vertical velocity still reaches 1 × 10−5 m s−1, whereas the wind-driven upwelling from Ekman suction is smaller by up to 1 order of magnitude. One reason for this difference is ascribed to eddy-induced upwelling. Both advective and diffusive nutrient fluxes into the mixed layer are calculated based on the helium-derived vertical velocities and the vertical diffusivities. The advective part of these fluxes makes up at about 50 % of the total. The nutrient flux into the mixed layer in the coastal upwelling regimes is equivalent to a net community production (NCP) of 1.3 ± 0.3 g C m2 d−1 off Peru and 1.6–2.1 ± 0.5 g C m2 d−1 off Mauritania.

Tracing injected CO2 in the Cranfield enhanced oil recovery field (MS, USA) using He, Ne and Ar isotopes

The He, Ne and Ar isotopic composition of gases collected in 2009 and 2012 from 13 production wells, injection wells and the CO2 supply pipeline at the Cranfield CO2-enhanced oil recovery field (MS, USA) have been measured in order to determine the extent to which they trace the fate of injected CO2 in the reservoir. In the absence of samples of CO2 pre-injection reservoir gas we use the Ne isotope composition of the production and injection well gases to determine the isotopic composition of the natural gas. The noble gas isotopes display binary mixing trends between the injected CO2 and a CH4-rich natural gas that is characterised by radiogenic He, Ne and Ar isotope ratios. 3He/4He and 40Ar*/4He ratios (where 40Ar* represents the non-atmospheric 40Ar) display coherent relationships with CO2 concentrations that can be used to trace and quantify the injected CO2 in an engineered site over a sustained period of injection. The presence of a small amount of air-derived Ar, from a non-atmospheric source, in many gas samples rules out using 40Ar/36Ar to track the injected CO2. The noble gases identify the loss of a significant proportion of the CO2 from the gas phase sampled by five production wells in 2009. Using 3He/4He and 40Ar*/4He ratios to reconstruct the major gas composition, it appears that between 22% and 96% of the CO2 has been lost in individual wells. This study demonstrates that the naturally occurring noble gases have the potential to trace the fate and quantify the sequestration of CO2 at injection sites.