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Radon (Rn) and helium (He) gases from uranium decay form distinct anomalies related to buried uranium deposits. In order to trace the geochemical anomalous sources from the volcanic-related uranium deposits in deeply buried areas, systematical Rn contents and He isotope ratios were analyzed from the Daguanchang uranium deposit. The soil gas Rn concentrations above the deep uranium are ten times higher than those in barren areas, indicating that instantaneous Rn content measurements can be used to detect deeply buried uranium. The helium isotope ratios (3He/4He) of the unmineralized samples from the mineralized drill hole (ZK1) are relatively lower and uniform compared to those of the samples from no-mineral drill hole (ZK2). However, the Th and U contents of the drill core samples from ZK1 are slightly lower than those of the samples from ZK2, indicating that the lower 3He/4He ratios in ZK1 are most likely due to the addition of 4He from underlying uranium intervals. The differences in the instantaneous Rn contents are consistent with the variations in the He isotope ratios of the drill core samples. These results demonstrate that soil gas Rn and 3He/4He ratios are useful tracers and can indicate the existence of deeply buried volcanic-related hydrothermal uranium ores. [ABSTRACT FROM AUTHOR]

A series of marginal-sea basins and fault-depression basins were formed in eastern China under the background of subduction of the West Pacific plate. Different types of helium-rich natural gas reservoirs (He>1000 ppm, 1 ppm=1 µmol mol−1) have been found in these basins: helium-rich CO2 gas reservoirs, helium-rich N2 gas reservoirs, and helium-rich hydrocarbon gas reservoirs. Based on the analysis of gas geochemical data, the source and accumulation mechanism of helium in these helium-rich natural gas reservoirs were discussed. Helium-rich natural gas has relatively high 3He/4He ratios (0.88–4.91 Ra, average 2.82 Ra). The 3He/4He ratio characteristics of mantle xenoliths and mantle-derived CO2 gas reservoirs indicate that the helium in these helium-rich natural gas reservoirs is mainly mantle-derived (>70%). The original mantle volatile is mainly CO2 with a low helium concentration (He<200 ppm), and the enrichment of mantle-derived helium in the gas reservoir is mainly related to the dissolution and mineralization of CO2. During this process, the CO2/3He ratio decreases from 2×109 to approximately 2×106. As CO2 dissolves and mineralizes, the concentration of conservative gases (He and N2) increases in the remaining CO2 gas proportionally to the loss of CO2. Large amounts of carbonate minerals, such as dawsonite, which are relatively enriched in 13C, are found in CO2 reservoirs in eastern China. The relative enrichment of 12C in residual CO2 gas is important evidence of the dissolution and mineralization of CO2. The relative abundance of mantle-derived helium and N2 gas increases thousands of times during the dissolution and mineralization of CO2, which is the main accumulation mechanism of mantle-derived helium-rich CO2 gas reservoirs and helium-rich N2 gas reservoirs. Helium-rich gas from the mantle is mixed with alkane gas generated by organic matter in the sedimentary basin to form helium-rich hydrocarbon gas reservoirs. [ABSTRACT FROM AUTHOR]

Investigations of the hot spring water and gas in the volcanic region are involved in assessing geothermal resources and understanding groundwater circulation, volcano, and earthquake activities. The origins of water and gas of the hot springs, lakes, rivers, and rain in the Arxan volcanic region (AVR), northeastern (NE) China, were investigated by conducting a field survey and geochemical analysis. The low electrical conductivity (40–835 μS/cm) and low total dissolved solids (TDS, 23.83–540.00 mg/L) of the water samples indicate that they are fresh water. δ18O and δD values of the water samples range from −4.1% to −16.0% and from −61.3% to −119.9%, respectively. Enrichment of heavy isotopes in the rainwater and the crater lake waters was caused by evaporation. The component H2O of the water samples predominantly originated from the meteoric water, with less than 1 vol% contributed by deep-earth fluids. Ions in the rain sample were predominantly derived from sea salt and continental aerosol. Ions in the surface water samples had multiple origins (mineral dissolution, atmospheric, and anthropogenic sources). While the ions in the hot spring water were predominantly derived from both the dissolution of rocks and deep-earth fluids, the latter contributed 73%–87% of Cl− and 86%–99% of Na+ to the hot spring waters. Gases from the hot springs were composed of more than 95% N2 and less than 5% O2 and Ar, with 3He/4He ratios of 0.14–1.17 RA (RA=1.4×10−6). Excess N2, Ar, He, and CO2 of the hot springs were mainly derived from both the crust and upper mantle. About 3%–23% of the total He in the bubbling gases from the crater lake waters and hot springs is derived from the mantle, implying a supplement of heat energy from the mantle to the geothermal systems. Significantly, about 12% of the He dissolved in the Budonghe water is derived from the mantle, indicating that plenty of mantle-derived heat transported by deep-earth fluids keeps the river water from freezing. Our results indicate that Cl and Na ions and 3He/4He ratio are the feasible geochemical indicators for source partitioning of geothermal fluids.

Knowing the age distribution of water abstracted from public water supply wells helps to ensure customer trust in drinking water sources and underpin predictions of water quality evolution. We sampled the mixed water of 39 large public supply well fields for major ion chemistry, 3H, 3He, 18O, 2H, 14CDIC, 13CDIC and noble gases and determined the Noble Gas Temperature (NGT). We used a discrete travel time distribution model to quantify the age distributions using 3H, 4He, 14C apparent age and NGT as the 4 distinctive tracers. Helium‐4 and NGT provided information on the older part of the age distributions and showed that the 14C apparent ages are often the result of mixing of waters ranging between 2,000 and 35,000 years old, instead of being discrete ages with a limited variance as previously assumed. The results reveal a large range of age distributions, comprising vulnerable well fields with >60% young water (<100 years) and well fields with >30% paleo groundwater (>25,000 years) and all forms of intermediate distributions. The age distributions match the hydrogeological setting; well fields with age distributions skewed towards older ages appear in the Roer Valley Graben structure, where fluvial and marine aquitards and sealed faults provide protection from recent recharge. Waters from this graben exhibit paleoclimate signals, with a clear relation between NGT (range 3.2–9.3 °C), 4He (up to 3.3 × 10−6 ccSTP/g) and δ18O (range −8.5‰ to −5.9‰VSMOW). Moreover, 3He/4He ratios of these graben waters suggest a certain influx of He from mantle origin. Key Points: Thirty nine well fields show diverging patterns of isotopes and noble gases revealing different vulnerability and resilience under contaminant stressMultiple age tracers can constrain the age distribution of mixed water from public supply well fields using a discrete groundwater age modelThe combined age distribution of the total of 0.2 km3 annually abstracted water for public drinking water estimates: 9% is of recent origin, 56% is of Holocene age and 35% of Pleistocene age, with the percentage of the last paleo‐fraction increasing in time [ABSTRACT FROM AUTHOR]

Studies of helium isotope ratios in groundwaters discharging as springs within the Tunka-Oka-Sayan rift in the East Sayan area reveal an anomaly extending for 350 km along the East Sayan fault on the extension of the Tunka anomaly in the southwestern flank of the Baikal rift system. The calculated heat flow values (qR) agree with the measured ones (qT), and the heat flow anomalies correlate with those in the 3He/4He ratios throughout the Oka-Sayan and Bilin-Busiyn-Gol rifts. The correlation of the geophysical and geochemical parameters confirms that both are controlled by heat and mass transfer. Both mantle helium and heat apparently originate from a mantle plume beneath the South Baikal volcanic province (SBVP). The concordant 3He/4He and heat flow patterns in the Oka-Sayan fault record ongoing rifting and magmatism along the East Sayan Fault zone. The helium isotope and heat flow anomalies are consistent with the presence of low-velocity zones in the upper 200 km beneath the southwestern Baikal rift zone as far as the southern edge of the Siberian craton, which are detectable in seismic tomography images. Magmatism in the extreme southwest of the Baikal rift zone was maintained by active tectonic movements in the Pliocene and by the activity of the SBVP mantle plume. The obtained helium isotope data and high heat flow values indicate that rifting and magmatism propagate northwestward along the East Sayan Fault zone. This pattern fits the geothermal model for continental rifts implying that magmatic activity in the western end of BRS has been controlled by lithospheric deformation. The geothermal model for the Baikal-Mongolia region covers the area northwest of the system of three rift basins along the East Sayan faults. [ABSTRACT FROM AUTHOR]

Helium is an important, scarce, and strategic resource that is critical to national security and advanced technology development. Although helium originates from mantle degassing and the radioactive decay of uranium (U) and thorium (Th) in minerals, commercial helium resources are primarily derived from natural gas reservoirs with He concentrations higher than 1000 ppm. The gas geochemistry characteristics of 920 natural gas samples from nine petroliferous basins in China were used to classify and discuss the enrichment mechanisms of helium. Helium-bearing natural gas reservoirs can be divided into the following three types: basement source-migration-rich accumulation, self-generating and self-preserving, and crust–mantle complex types. The basement source-migration-rich accumulation, which is the most common type of proven helium-rich natural gas reservoir, occurs primarily in inherited anticlines and dome traps located on basement uplifts. Ancient shale systems demonstrate the potential to form helium-rich shale gas that belongs to the self-generating and self-preserving type. Crust–mantle complex helium-rich natural gas reservoirs develop in petroliferous basins in active magmatic–tectonic areas. The origins of helium and hydrocarbon gas are different, but the entrainment of helium during hydrocarbon gas accumulation is a key factor influencing the formation of helium-rich natural gas reservoirs. The nitrogen concentration in helium-rich gas samples is often extremely high, indicating that the nitrogen and the helium are derived from the same source rock or both are extracted from water by migrating gas. • Helium-rich gas includes basement source-migration-rich accumulation, self-generating and self-preserving, and crust–mantle complex types. • Exsoluion gathering of underground dissolved helium is the key mechanism of helium enrichment. • High-quality matching between helium and natural gas is crucial for the helium-rich gas accumulation. [ABSTRACT FROM AUTHOR]

Abstract: We report on the variation of the elemental (He, Ne, and Ar) and isotopic (He and Ar) compositions of olivine- and clinopyroxene-hosted fluid inclusions hosted in lavas, pyroclastics, and cumulate xenoliths from the last 60ka of the eruptive history of Stromboli volcano, Italy. Samples belong to (i) the present-day activity as represented by shoshonitic (SHO) basalts, i.e., pumices with low porphyritic (LP) content and high porphyritic (HP) scoriae; (ii) the subalkaline versus alkaline products erupted at Stromboli during its subaerial history among the extreme magmatic series, i.e., calc-alkaline (CA) and potassic (KS); and (iii) the only known ultramafic cumulates (San Bartolo wehrlite xenoliths, SBX) outcropping in the island, carried to the surface by recent (ca. 2ka) basaltic lava. To interpret the results better, we also investigated trace elements in the clinopyroxenes of wehrlite xenoliths and the Sr and Nd isotopes of all of the products in which the 3He/4He ratio was measured. Wehrlite xenoliths are igneous cumulates crystallized at mantle depth that mostly consist of clinopyroxene and olivine crystals with limited compositional variation. The texture, mineral chemistry, pattern of trace elements and Sr–Nd-isotope ratios (in clinopyroxene) suggest that these cumulates were produced by the early crystallization of a primitive basaltic magma with CA or HKCA–SHO affinity. The gas contents measured in the mafic crystals decrease from the wehrlite xenoliths through LP pumice, CA and KS lavas and, finally, to the HP scoria. This observation is consistent with crystallization and fluid entrapment from mantle depths to progressively shallower crustal levels. The low gas content extracted from the HP crystals did not allow measurement of their 3He/4He ratios. Most of the investigated crystals exhibit a 3He/4He ratio in the range of 4.0–4.9 Ra, with only the KS mafic minerals exhibiting lower 3He/4He values (≤3.5 Ra). The low values of He-isotope ratios relative to those of the most-uncontaminated mantle source of the Aeolian lavas (i.e., 3He/4He ~7 Ra at Alicudi) and in common volcanic arcs suggest that the Stromboli mantle wedge is more contaminated by sediments and aqueous fluids derived by the active subduction of the Ionian slab. We also hypothesize that a process of mantle He loss that occurred during the mantle metasomatism contributed to the decrease of 3He/4He. The low 3He/4He values of the KS minerals with respect to the other Stromboli magmatic series are consistent with the higher Sr- and lower Nd-isotope ratios measured in the same samples and are attributed to source heterogeneity. Finally, data for the 3He/4He ratios from mafic minerals were compared with those of currently emitted hydrothermal fluids, which are regularly sampled for volcano surveillance. The maximum 3He/4He ratio found in the hydrothermal fluids matched the maximum ratio measured in the LP fluid inclusions (i.e., 4.6 Ra) and thus corresponds to the upper limit that should be expected for surface gases during or before high-intensity eruptive events in which a deep gas component is released from the magma. These data also represent a reference for Stromboli volcanic surveillance. [Copyright &y& Elsevier]

New stable isotope and noble gas data obtained from fumarolic and bubbling gases and hot spring waters sampled from Deception Island, Antarctica, were analysed to constrain the geochemical features of the island's active hydrothermal system and magmatism in the Bransfield back-arc basin. The ³He/4He ratios of the gases (, 9.8 × 10-6), which are slightly lower than typical MORB values, suggest that the Deception Island magma was generated in the mantle wedge of a MORB-type source but the signature was influenced by the addition of radiogenic 4He derived from subducted components in the former Phoenix Plate. The N2/He ratios of fumarolic gas are higher than those of typical mantle-derived gases suggesting that N2 was added during decomposition of sediments in the subducting slab. The δ13C values of -5 to -6‰ for CO2 also indicate degassing from a MORB-type mantle source. The H2/Ar- and SiO2 geothermometers indicate that the temperatures in the hydrothermal system below Deception Island range from ∼150°C to ∼300°C. The δD and δ18O values measured from fumarolic gas and hot spring waters do not indicate any contribution of magmatic water to the samples. The major ionic components and δD-δ18O-δ34S values indicate that hot spring waters are a mixture of local meteoric water and seawater. Mn and SiO2 in spring waters were enriched relative to seawater reflecting water-rock interaction at depth. [ABSTRACT FROM AUTHOR]

Abstract: An automatic station for soil gas monitoring was set up on an active fault zone of SW Taiwan. After more than one year of continuous measurements, some spike-like anomalous high radon and thoron concentrations could be observed. A similar soil radon spectrum was also obtained from an independent monitoring station, which was only 100m away. These anomalous peaks usually occurred a few days or weeks before the earthquakes . This indicates that variations of both soil radon and thoron can serve as useful tools for earthquake surveillance, esp. at fault zones. [Copyright &y& Elsevier]

The magma activity of the North Luzon Arc is considered to have ceased, due to collision with the Asian continental margin, since late Miocene. New fission track dates of zircons taken from dike swarms in the central Coastal Range of East Taiwan show very young ages of ∼0.5Ma. Furthermore, the high 3He/4He ratios (∼2.5RA; RA is the air ratio) of hot spring gases near the same area indicate that more than 30% of a mantle-derived source component is necessary to account for the helium composition. These results suggest the existence of later remnant magmatic activity (more than 4Ma) in the central Coastal Range. Therefore, arc magmatism may survive longer than the previously expected after collision. [Copyright &y& Elsevier]

Gas compositions of mud volcanoes reveal multiple sources for gas exhalation in SW Taiwan. For comparison, two sites, Yan-chao (YC) and Chung-lun (CL), were chosen for measurements of soil Rn concentrations using a portable radon detector. The 222Rn concentrations at the YC site were ca. 5200Bq/m3. However, the average 222Rn concentrations at the CL site exhibited higher value of ca. 16,800Bq/m3. With the reference of the gas flux and compositions from the nearby mud pool, the soil 222Rn concentrations are largely controlled by the flux of carrier gases exhaled from deep reservoirs. [Copyright &y& Elsevier]

The Magumsan thermal waters of the southeastern Korean Peninsula are pumped out of six deep wells (average depth, 300 m) at temperatures of 30.8–49 °C. The thermal waters are chemically classified into two groups: NaHCO3 type (<31 °C) and NaCl (HCO3, SO4) type (>40 °C), both of which have chemical compositions that are distinct from local groundwater (Ca–HCO3 type). δ18O and δD values suggest that the thermal waters originate from meteoric water and they are isotopically fractionated by silicate hydration or H2S exchange. δ34S values (+7.0 to +15%) of dissolved sulfate in the thermal waters reflect enrichment in 34S through kinetically controlled oxidation of magmatic pyrite in the thermal aquifer and mixing with paleo-seawater. On the 3He/4He vs. 4He/20Ne diagram, the thermal waters plot along a single air mixing line of dominant crustal He, which indicates that the heat source for the thermal waters is non-volcanogenic thermal energy that is generated from the decay of radioactive elements in crustal rocks. Chalcedony geothermometry and thermodynamic equilibrium calculations using the PHREEQC program indicate a reservoir temperature for the immature thermal waters of 54–86 °C and 55–83 °C, respectively. [ABSTRACT FROM AUTHOR]