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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]

Interbedded sandstones, shales, and coal seams were formed in marine-continental transitional environments of coal measures, and the gas source of its tight sand gas has been uncertain, which hinders the progress of natural gas exploration. This article uses the Longtan tight sand gas in west Guizhou as an example to investigate the reservoir features, gas charging history, and main source rock of tight sand gas by examining thin sections, scanning electron microscopy images, X-ray diffraction results, and the fluid inclusions with burial and thermal histories and noble gas analysis. The Longtan sandstones in this study are classified as litharenites which are characterized by low compositional and textural maturities, and high clay contents, and are distinguished petrographically from conventional sandstones by the extensive existence of micropores and microfractures. The results of the homogenization temperatures of the fluid inclusions show that the Longtan tight sand gas is a single-stage accumulation which occurred during the Late Triassic. Furthermore, through the analysis of the helium and argon isotopes of noble gases, a calculation model was established for determining the shale and coal contributions to the tight sand gas. The research results show that the Longtan tight sand gas mainly belongs to the crust-derived gas, mostly from the Longtan shale-derived contribution and to a lesser extent from the Longtan coal-derived contribution. The measured 40Ar/36Ar values of the Longtan shales and coals are consistent with the forecasted 40Ar/36Ar values from the calculation model, demonstrating that the model is viable to calculate the source rock contribution to the tight sand gas. Therefore, the Longtan shales as main source rocks can generate hydrocarbons to charge neighboring tight sandstones to form tight gas accumulation in the Longtan Formation, which provides an opportunity for tight gas development in west Guizhou. [ABSTRACT FROM AUTHOR]

Helium gas is a scarce but important strategic resource, which is usually associated with natural gas. Presently, only one extra-large helium-rich gas field has been found in China: the Hetianhe Gas Field in the Tarim Basin. This paper reports a new example, the Dongsheng Gas Field (DGF) in the Ordos Basin. In this study, 92 natural gas samples from the DGF were analyzed for helium content and isotope composition using isotope mass spectrometry. The natural gas samples were found to have an average helium content of 0.133%, with 65 (70.7%) of the samples having a helium content of 0.1% or more. Based on the proven natural gas reserves of the DGF, the proven geological helium reserves were calculated to be 1.96×108 m3, suggesting that it represents the first extra-large helium-rich natural gas reservoir to be hosted in tight sandstone in China. The 3He/4He ratios of 5 natural gas samples from the DGF are within the range of 3.03×10−8−3.44×10−8. Therefore, the helium in the gas field is thought to be of typical crustal origin and to have formed in the granitic basement that is rich in uranium and thorium. The accumulation of helium-rich natural gas was controlled by regional tectonic activities. Activity along the fault connecting the reservoir with the basement caused release of the helium gas, which entered the overlying strata along the fault and accumulated with conventional hydrocarbon gas. Based on the structural background and the distribution of helium source rocks in the Ordos Basin, the main helium source rocks with high exploration potential are located in deep strata within the north and middle parts of the basin. [ABSTRACT FROM AUTHOR]

The permeability characteristics of natural fracture systems are crucial to the production potential of shale gas wells. To investigate the permeability behavior of a regional fault that is located within the Wufeng Formation, China, the gas permeability of shale samples with natural micro-fractures was measured at different confining pressures and complemented with helium pycnometry for porosity, computed micro-tomographic (µCT) imaging, and a comparison with well testing data. The cores originated from a shale gas well (HD-1) drilled at the Huayingshan anticline in the eastern Sichuan Basin. The measured Klinkenberg permeabilities are in the range between 0.059 and 5.9 mD, which roughly agrees with the permeability of the regional fault (0.96 mD) as estimated from well HD-1 productivity data. An extrapolation of the measured permeability to reservoir pressures in combination with the µCT images shows that the stress sensitivity of the permeability is closely correlated to the micro-fracture distribution and orientation. Here, the permeability of the samples in which the micro-fractures are predominantly oriented along the flow direction is the least stress sensitive. This implies that tectonic zones with a large fluid potential gradient can define favorable areas for shale gas exploitation, potentially even without requirements for hydraulic fracture treatments. [ABSTRACT FROM AUTHOR]

[Display omitted] • Isotopes of natural gas are controlled by the distribution and type of source rocks. • Helium and Argon isotopes can discern the gas generated from carbonate source rocks. • Biomarkers are effective for tracing the oil sources in high-over mature stage. Natural gas-source correlation is a challenging aspect of natural gas exploration in deep strata. The Middle-Permian carbonate succession in the Sichuan Basin, southwest China, particularly in the Maokou Formation, is a hotspot for natural gas exploration. However, determining the natural gas source in the Maokou Formation is challenging because of the high maturity and complexity of potential source rocks. In this study, we analyzed the genesis and sources of natural gas in the central - northern Sichuan Basin while considering the geological conditions and systematically utilizing the gas components, stable and rare-gas isotopes, and solid bitumen biomarkers. The results indicate that (1) the natural gas in the northern Sichuan Basin comprises a mixture originating from the source rocks of the Maokou and Wujiaping formations; (2) the Qiongzhusi Formation is the major source of natural gas in the north slope (and the Maokou Formation source rock could be used as an important supplement); (3) the natural gas in the Moxi - Longnvsi structure comprises a mixture originating from the source rocks of the Qiongzhusi and Maokou formations. From south to north and west to east, the major source rocks of the gas reservoirs changed from belonging to the Qiongzhusi Formation to the Maokou and Wujiaping formations. This study is the first to combine multiple geochemical methods and consider different geological settings to identify the gas source of a deep carbonate gas reservoir. Our study provides a reliable method for determining the natural gas-source correlation of gas reservoirs that contain highly mature and complex gas sources. [ABSTRACT FROM AUTHOR]

Multiple metamorphic buried-hill hydrocarbon reservoirs have been recently discovered in the Bozhong Depression, Bohai Bay Basin. Among them, the buried-hill reservoirs in the BZ13, BZ19 and BZ26 regions have the largest condensate gas reserve in eastern China. The hydrocarbon-bearing reservoir has a large thickness with a maximum of ∼1 km, making the oil-equivalent reserve exceed 5 × 108 tons. This study used petrography, isotopes, gas composition, zircon U–Pb geochronology, X-ray diffraction, electronic probe and hydrothermal dissolution experiments to discuss the formation mechanisms of the metamorphic buried-hill reservoirs. The results indicate that the reservoirs 500 m below the surface of the buried hill have been significantly altered by the mantle-derived CO 2. This is supported by the carbon isotope of CO 2 , He isotope of the helium gas, strong negative excursions in δ18O PDB , positive excursions in δ13C PDB , Co/Ni ratio greater than 1 in pyrite and secondary characteristic minerals such as dawsonite. Hydrothermal dissolution experiments using CO 2 result in the precipitation of kaolinite, ankerite and quartz cements, which is consistent with petrographic observation. The mantle-derived CO 2 reacts with feldspars, hornblende, biotite and carbonates, creates secondary dissolution pores and significantly improves reservoir quality. Moreover, partial carbonate cements exhibit negative excursions in δ13C PDB and the depletion of light rare earth elements, indicating the influence of organic acids-bearing low-temperature hydrothermal fluids. Therefore, three development models illustrating the formation of metamorphic buried-hill reservoirs were proposed. This study may serve as a reference for the hydrocarbon exploration in metamorphic buried-hill reservoirs. • Lithology and geochronology of an Archaean metamorphic buried-hill in the Bozhong Depression were clarified. • There are three distinct zones within metamorphic buried-hill reservoirs. • Deep hydrothermal fluids have a significant impact on metamorphic buried-hill reservoirs. • Three reservoir development models were proposed based on the variability of geological features. [ABSTRACT FROM AUTHOR]

The origin and formation mechanism of N 2 -rich Lower Cambrian shale gas remain ambiguous, posing serious exploration risks in the Lower Cambrian shale gas in South China. In this study, high-vacuum-pulsed electromagnetic and helium-filled ball-mill rock-crushing methods were developed to measure the released gas contents, compositions and nitrogen isotopes of N 2 in shale-crushed gas from Lower Cambrian organic-rich shales in South China. Key factors in N 2 enrichment in shale gas and its origins were investigated. Results showed that mineral compositions and thermal maturity affected the contents and compositions of shale-crushed gas. Carbonate cementation, and feldspar dissolution and reprecipitation, formed isolated pores filled with migrated bitumen and thus generated high gas contents with larger CH 4 /N 2 ratios of shale-crushed gas. The thermal maturation of Lower Cambrian organic-rich shale can be further divided into the early and late stages of overmaturation with a boundary of 3.4–3.5%EqVR o. The contents and CH 4 /N 2 ratios of shale-crushed gas continued to increase at the early stage of overmaturation, and then a rapid decrease at the late stage of overmaturation (>3.4–3.5%EqVR o), reflecting the release of large amounts of N 2 by intensified aromatization of organic matter. An empirical equation of TON b = 0.0138 × TOC with R 2 >0.98 was used to estimate the relative contribution of inorganic nitrogen (TIN b) and organic nitrogen (TON b) to the bulk of nitrogen content in the overmature Cambrian shale. The EqVR o -δ15N N2 plot allows identification of N 2 derived from thermal decomposition of ammonium-bearing clay minerals or residual kerogen. The N 2 generated at the early stage of overmaturation (including at wells LX03, EYY1, SNY1 and W001-4) in Lower Cambrian shale gas is characterized by δ15N N2 values ranging from −2 to +2‰, mainly reflecting thermal deammoniation and decomposition of ammonium-bearing clay minerals. In contrast, the N 2 generated at the late stage of overmaturation (DQ outcrop) in Lower Cambrian shale gas is characterized by δ15N N2 values greater than +4‰, indicating thermal cracking of pyridinic nitrogen and pyrrolic nitrogen. The N 2 generated from thermal transformation of ammonium-bearing clay minerals and pyridinic nitrogen and pyrrolic nitrogen is the main source of N 2 -rich shale gas in the Lower Cambrian shale of South China. • Helium-filled ball-mill rock-crushing and degassing method is developed to measure the δ15N N2 of shale-crushed gas. • Establish an empirical equation to estimate the relative content of inorganic nitrogen and organic nitrogen in the overmature shales. • Establish the EqVR o -δ15N N2 plot to identify N 2 origins in overmature shale gas. • Thermal maturity and nitrogen contents are the key controls in N 2 enrichment in high-over mature shale gas. [ABSTRACT FROM AUTHOR]

The Qulong porphyry Cu–Mo deposit, generated in the Miocene post-collisional extension environment of the Gangdese Copper (Molybdenum) Metallogenic Belt, is one of the largest porphyry Cu deposits in China. This study reports the noble gas isotopic compositions of volatiles released from fluid inclusion reserved in pyrite from the Qulong deposit. 3He/4He and 40Ar/36Ar ratios range from 0.54 to 1.015 Ra and 300–359, respectively. Concentrations of 4He and 40Ar range from 1.77 to 2.62 × 10−8 cm3 STP and 1.7–34 × 10−8 cm3 STP, respectively. The isotopic composition of noble gases indicates that the ore-forming fluids of the Qulong Cu–Mo deposit were a mixture of fluid containing mantle component, which is exsolved from the porphyry magma, and crustal fluid characterized by atmospheric Ar and crustal radiogenic He. The δ34S values of pyrite and molybdenite range from − 0.52‰ to 0.31‰, with an average of − 0.12‰, indicating a magmatic origin. More mantle components were involved in the Cu–Mo deposit than in the Mo–Cu deposit in the Qulong-Jiama ore-district. [ABSTRACT FROM AUTHOR]

The mechanisms of the occurrence of nonequilibrium oxygen isotope fractionation between olivine and plagioclase phenocrysts and the groundmass of rocks (from alkaline basalts to alkaline rhyolites) of Changbaishan volcano are considered. The basaltic trachyandesite–trachyte–comendite–pantellerite rock series shows a systematic increase of the δ18O values of feldspar (from 5.4 to 7.8‰) and the rock groundmass (from 5.6 to 7.1‰). In contrast, the δ18О values of olivine decrease from 5.35‰ typical of mantle peridotites to significantly lower values (3.88–4.14‰). This is accompanied by changes in olivine composition from the Mg-rich (Fo = 74–79) to almost pure fayalite (Fo = 1), thus indicating a positive correlation between the Mg–number and δ18О of olivine. It is shown that feldspar and the rock groundmass are close to the oxygen isotopic equilibrium, whereas olivine–rock groundmass and olivine–feldspar pairs did not approach the oxygen isotopic equilibrium. The main mechanisms leading to the oxygen isotopic disequilibrium in the mineral–melt system are considered. An approach to the estimation of oxygen isotope equilibrium between the phenocrysts and melts is proposed. It takes into account the degree of melt polymerization (NBO/T ratio). This approach makes it possible to explain the positive correlation between δ18О values and olivine Mg-numbers in the Changbaishan lavas, as well as the occurrence of low δ18O values (down to +3‰) in ferrous olivine from alkaline–salic rocks. The δ18О values observed in the olivine and the rock groundmass reflect changes in the degree of melt polymerization during crystal fractionation. The proposed model does not require an additional geological process, in particular, the contribution of a low–δ18О material in the formation of the Changbaishan differentiated rock series. [ABSTRACT FROM AUTHOR]

The genesis of andesitic and dioritic rocks in continental arcs is hotly debated, and proposed models include slab melting, juvenile mafic lower-crustal melting, mafic and felsic magma mixing, and mantle-derived melts that underwent a MASH (melting, assimilation, storage, and homogenization) process. The controversy comes from the possibility of their polygenesis and the ambiguity of bulk-rock isotope tracers, not to mention the processes of magma evolution. Here, we report on our investigations in the southern Yidun Terrane (a Triassic continental arc in SW China) into the petrogenesis of two stages of the dioritic Xiuwacu intrusions (phases 1 and 2), the mafic microgranular enclaves (MMEs) hosted by the phase 1 intrusion, as well as the andesitic Hongshan intrusions. We used U-Pb zircon dating, in situ zircon Hf-O isotope analyses, bulk-rock Sr-Nd isotope analyses, and trace element analyses of the zircons from different stages of the intrusions and the MMEs to shed light on their sources and mantle–crust interactions involved in their petrogenesis. Our results suggest that the Xiuwacu MMEs from the phase 1 intrusion crystallized from a melt. Their variable zircon Hf-O isotopic compositions (εHf(t) = +0.4 to +5.3 and δ18O = 4.80‰ to 7.79‰) indicate they were formed by the mixing of mantle-derived basaltic melts and felsic melts. The phase 1 intrusion have an origin similar to that of the MMEs, as indicated by their homogeneous zircon Hf-O isotopic compositions (εHf(t) = +1.3 to +3.9 and δ18O = 6.58‰ to 7.31‰), which fall within the range of the isotopic compositions of the MMEs. The discovery of several inherited zircons and a small recrystallized felsic microgranular enclave hosted by an MME reveals that the MMEs contain relatively more felsic components. Even so, the MMEs still have lower silica contents (62.1–63.4 wt%) than those of the phase 1 intrusion (63.4–70.5 wt%), and this indicates that direct magma mixing of basaltic and felsic melts generated the andesitic MMEs, whereas a crystal fractionation process is required for the dioritic phase 1 intrusion. The porphyritic phase 2 and Hongshan intrusions formed at ~216 Ma, after the phase 1 intrusion, and they had higher oxygen fugacities and crystallization temperatures than the phase 1 intrusion. Given the conclusions of previous researchers that slab breakoff probably occurred at ~216 Ma, we propose that the Xiuwacu phase 2 and Hongshan intrusions formed during the slab breakoff process, the former by partial melting of the newly underplated basaltic lower crust in the MASH zone, and the latter by differentiation of mantle-derived basaltic melts at relatively high pressures. Unlabelled Image • Direct basaltic and felsic melts mixing generate the andesitic MMEs. • Crystal fractionation of basaltic magmas is critical to form dioritic magmas. • Partial melting of newly underplated lower crust is significant during slab break-off. [ABSTRACT FROM AUTHOR]

Helium isotopic compositions are considered to be ideal tracers to identify whether mantle materials have been added to crustal rocks or fluids. In this paper, we present the helium isotopic compositions of the Songduo eclogites in the Lhasa terrane, Tibet. We found that garnet and omphacite in the eclogites have different helium retention characteristics. The 4He content of most omphacite grains are about 10–20 times of that of garnet, suggesting that omphacite has a higher ability to capture 4He than garnet. Similarly, there is about 10–20 times difference in 4He content between omphacite and garnet in the same eclogite samples. The 3He/4He ratios of garnet and omphacite in these rocks range from 0.27 to 0.60 Ra (relative to the modern air 3He/4He ratio, 1.4×10−6). These ratios are within the range of both mantle- and crust-derived helium, suggesting mixed sources. The Songduo eclogites have much higher 3He/4He ratios than those observed in the Dabie eclogites of eastern China. Such high ratios are typically thought to be associated with deep mantle sources. We cautiously conclude that deep mantle materials might have been involved during the formation of the Songduo eclogites. [ABSTRACT FROM AUTHOR]

• Mineral successions and Fe-Li mica compositions are used to decipher magmatic-hydrothermal evolution process. • For precipitation of tin, changes of the redox condition play an important role. • Ore elements originate from the mixing of crustal and mantle components. • The tin-tungsten and copper-zinc-lead-silver mineralization in the Weilasituo area represent a single metallogenic system. China's W–Sn resources are dominant on a global scale. A series of Sn–polymetallic deposits has been found in recent years at depth on the flanks of known volcanic–subvolcanic Cu–Pb–Zn–Ag deposits in the Southern Great Xing'an Range, NE China. The large-scale Weilasituo tin–polymetallic deposit, formed at the depth of the Weilasituo Cu–Zn deposit, is most typical of these types of deposit. Tin–polymetallic orebodies are hosted in the early Paleozoic Xilingol Complex, and their mineralization is closely related to Early Cretaceous quartz porphyry. In this contribution, bulk-rock and mica chemical compositions, Re–Os geochronology, and He–Ar isotopic analyses are described in addressing the ore-formation mechanism of the deposit. Geochemical characteristics indicate that the ore-bearing quartz porphyry corresponds to the I-type granite serie. Five types of mica have been identified in the study area based on detailed petrography and EPMA and LA–ICP–MS analyses: (i) early magmatic Fe–Li mica in albitized quartz porphyry; (ii) late magmatic Fe–Li mica in mineralized quartz porphyry; (iii) hydrothermal Fe–Li mica in a cryptoexplosive breccia pipe (distributed around breccia fragments); (iv) Fe–Li mica in quartz veins; and (v) Fe–Li mica in plagioclase gneiss (wall rock). Magmatic zinnwaldite from the upper mineralized part of the quartz porphyry is enriched in Nb (100–160 ppm) and Ta (100–150 ppm). Hydrothermal zinnwaldite from the explosive breccia, quartz veins, and surrounding gneiss is unusually rich in Mg (up to 3.4 wt% MgO) and Sn (up to 200 ppm). 3He/4He ratios of the Weilasituo tin–polymetallic and Cu–Zn deposits are in the ranges 3.38–4.91 Ra and 4.8–4.9 Ra, respectively, indicating ore-forming fluids sourced from mixed crustal and mantle materials. Molybdenite Re–Os dating of W mineralization yielded an isochron age of 129.0 ± 4.6 Ma, similar to the porphyry crystallization and mineralization ages of the Weilasituo tin–polymetallic deposit, and also consistent with the mineralization age of the Cu–Zn deposit. We propose a new metallogenic model, with all subtypes of W–Sn–Cu–Pb–Zn–Ag mineralization in the Weilasituo area belonging to a single complex metallogenic system. Compared with other ore districts, ore-related granitoids in the Southern Great Xing'an Range display relatively uniform emplacement ages and were derived from partial melting of juvenile lower crust rather than old basement. Their ore-forming fluid source was greater influenced by mantle fluids than which found in South China. [ABSTRACT FROM AUTHOR]

Abstract The severe shortage of helium resources is an impending global problem. However, the helium accumulation processes and conditions favorable for helium enrichment in reservoirs remain poorly understood, which makes helium exploration challenging. Noble gases are good tracers of subsurface fluids provenance, migration and storage, as well as indicators of the nature and quantity of associated phases. In this study the variation of major gases and noble gases data in Weihe Basin provide us with an excellent opportunity to understand the groundwater evolution and helium accumulation processes. Twelve gas samples collected from wellheads of geothermal wells can be classified into three groups, in which Group A has high concentrations of N 2 (58.57–91.66%) and He (0.32–2.94%); Group B has high contents of CH 4 (52.94% and 69.50%) and low concentrations of He (0.057% and 0.062%); Group C has a high content of CH 4 (71.70%) and He (2.11%). Helium isotopic ratios are predominantly radiogenic in origin and therefore crustally derived. Measured elemental ratios of noble gases are compared with multiple fractionation models for Group A and B samples, implying that open system heavy oil-water fractionation with excess heavy noble gases has occurred in the basin with V oil /V water ratios of 0.06–0.18. The amount of helium in Group A and B samples requires the release of all 4He produced in the crust since 0.30–1.98 Ma into the groundwater. The Group C sample requires an additional He flux from adjacent granitic bodies. The accumulation of helium and hydrocarbon in the Weihe Basin can be explained by a 4-stage process. Accumulation of commercially viable helium requires high He flux from source rocks, the existence of a free gas phase of major gas components (CH 4 in most cases, N 2 or CO 2) and minimal major gas addition after formation of the free gas phase. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • The Lesser Xing'an–Zhangguangcai Range is the most important Mo ore belt in the CAMD. • The giant Mo deposits developed multiple Mo-bearing hydrothermal fluid activities. • The ore-forming fluids of the giant porphyry Mo deposits were mainly crustal fluids. Abstract The Lesser Xing'an Range–Zhangguangcai Range metallogenic belt, located at the eastern segment of the Central Asian metallogenic domain, hosts two giant Mo porphyry deposits, the Early Jurassic Luming deposit and the Middle Jurassic Daheishan deposit. In this study, the He–Ar and S isotopic compositions of sulfides from different hydrothermal stages of the Daheishan and Luming deposits were determined. Fluid inclusions hosted in pyrites shown that 3He/4He ratios of the Luming and Daheishan deposit range from 0.02 to 0.32 Ra, and 0.7 to 2.5 Ra, respectively. 40Ar/36Ar ratios of the Luming and Daheishan deposit range from 313.3 to 535.1, and 309.9 to 360.6, respectively. He and Ar isotopic compositions suggest that the ore-forming fluids of the Luming deposit are mainly crustal-derived fluids, with near atmospheric Ar and crustal He values. Mantle-derived fluids are a minor component. In contrast, the ore-forming fluids of the Daheishan deposit are a mixture between a crust-derived fluid and a mantle-derived fluid. The δ34S values of the sulfide samples from the Luming deposit (4.98–7.14‰) and the Daheishan deposit (1.83–2.88‰) indicate that the sulfur in the ore-forming fluids was primarily derived from granitic magma. The isotopic compositions across the stages within one deposit have no variability. The similar He–Ar and S isotopic compositions of the sulfides from the different Mo-bearing hydrothermal stages of these two giant Mo deposits indicate that the overprinting of the multiple stages of Mo-bearing hydrothermal fluids may be a key factor in the formation of giant porphyry Mo deposits. Meanwhile, the westward subduction of the Paleo-Pacific plate might have played an important role for the formation of the giant Mo deposits in the Lesser Xing'an Range–Zhangguangcai Range metallogenic belt. [ABSTRACT FROM AUTHOR]

By 2013, more than 20 gas fields related to Late Paleozoic coal measures have been discovered in China, primarily distributed in the Bohai Bay, Ordos, Sichuan, and Junggar Basins. The total proven reserve in these gas fields is more than 3200 × 10 9  m 3 , accounting for 30.1% of the proven gas reserves in China. After analyzing the molecular compositions, stable carbon isotopes, and helium isotopes of 375 gas samples, genetic types and origins of the natural gas, as well as the secondary alterations it experienced, are discussed in this study. Most of the natural gas related to the Late Paleozoic coal measures are coal-type gas, with some of the gases from the Sichuan Basin and the Jingbian gas field in the Ordos Basin being oil-type gases generated from marine mudstones in the Permian Longtan Formation and marine carbonates in the Ordovician Majiagou Formation, respectively. The equivalent vitrinite reflectance values based on stable carbon isotopes of natural gases vary from 0.8% to 2.5%, indicating the mature to over mature stage. Positive carbon isotope series (δ 13 C-CH 4  < δ 13 C-C 2 H 6  < δ 13 C-C 3 H 8 ) are observed in most gas samples, and carbon isotope reversals occur in the forms of δ 13 C-CH 4  > δ 13 C-C 2 H 6 and δ 13 C-CH 4  < δ 13 C-C 2 H 6  > δ 13 C-C 3 H 8 . The form of δ 13 C-CH 4  > δ 13 C-C 2 H 6 is primarily resulted from the mixing of oil-type gases of different maturities, while the form of δ 13 C-CH 4  < δ 13 C-C 2 H 6  > δ 13 C-C 3 H 8 is primarily resulted from the mixing of coal-type gases of different maturities. High concentrations of hydrogen sulfide in natural gas from the Sichuan Basin and the Chenghai gas field in the Bohai Bay Basin are resulted from thermochemical sulfate reduction (TSR), which causes, to some extent, the fractionation of carbon isotopes. By contrast, the fractionation of methane carbon isotopes resulting from the TSR effect is not clear. Carbon dioxide from the Bohai Bay and Junggar Basins is primarily biogenic, generated via the thermal decomposition of organic matter, while that from the Ordos Basin, Sichuan Basin, and Chenghai gas field is generated via the thermal decomposition of carbonates. Carbon dioxide related to the TSR effect has also contributed to the Sichuan Basin and Chenghai gas field. [ABSTRACT FROM AUTHOR]

[Display omitted] • The work systematically compiles noble gas data in natural gas from sedimentary basins in China. • The application of noble gases is constrained to trace fluid origins and reflect regional tectonic settings. • Using noble gases to understand hydrocarbon accumulation and guide resource exploration needs more attention. • Noble gases in CO 2 fields from eastern China show great potential in exploring geological CO 2 sequestration. Natural gas has a critical place in global fuel energy mix, not least as a transition to low carbon emissions. It plays an important role in national energy production and consumption in China. The complex transport and interaction processes of fluids at reservoirs are key to the formation of a gas reserve. The abundance and isotopic composition of noble gases have proved to be a powerful tracer of physical processes and interaction history of reservoir fluids. Noble gas studies of natural gas systems in China started in the 1970s and recent studies are leading examples of the application of the technique. Here we present the first systematic compilation of published noble gas data of natural gases from sedimentary basins in China and review their application and implications to date. Helium isotopes are most commonly used to trace fluid origins, providing a constraint on regional tectonic settings. Argon isotopes are used to indicate the source rock age, the reliability of which, however, is assessed in the work. Noble gases are increasingly used to determine gas accumulation history, estimate oil/gas reserves and evaluate sweet spots for oil/gas exploration. This review points out the limited application of noble gases in sedimentary basins and the slow development of analytical techniques for noble gas isotopes in China. The potential for noble gas studies in exploring the characteristics of local crust and mantle is discussed, as is the identification of the potential for future study of geothermal systems, enhanced oil/coalbed methane recovery and geological CO 2 sequestration. [ABSTRACT FROM AUTHOR]

Changbaishan Volcano is located in northeastern China, approximately 1400 km west of the west Pacific subduction zone. Although the west Pacific plate and Changbaishan Volcano are spatially associated with each other, no previous evidence has demonstrated the existence of a direct material connection between the two. In this study, we utilize helium ( 3 He/ 4 He, CO 2 / 3 He) and carbon isotopes (δ 13 C) from the hot springs of Changbaishan Volcano to exclude the possibility of a direct material connection between the volcano and the west Pacific plate at source. A total of 22 gas samples were collected from three hot springs at Changbaishan Volcano in 2002, 2006, 2014 and 2015; isotopic and geochemical analyses were performed on these samples to trace the possible sources of these gases. Our analysis reveals that values for air-corrected 3 He/ 4 He ratios range from 3.98 R A to 6.03 R A (where R A represents the atmospheric 3 He/ 4 He ratio), CO 2 / 3 He ratios vary from 2.20 × 10 8 to 1.92 × 10 11 , and δ 13 C values vary from − 7.9‰ to − 1.6‰. By comparing these measured values to those of typical mantle and crustal sources, we can infer that hot spring gases from Changbaishan Volcano are mostly characterized by inputs from two isotopically distinct sources: deep mantle fluids and shallower, slab-derived fluids. Fluids liberated from the shallower magma chamber are likely to include ancient Izanagi subduction zone fluids, whereas fluids originating from deeper magma chamber likely consist of MORB-like asthenospheric mantle fluids. Based on these results, we suggest that helium and carbon isotopes in hot springs demonstrate the absence of a direct material connection between Changbaishan Volcano and the west Pacific plate. [ABSTRACT FROM AUTHOR]

Volcanic basins in North China have great potential for the discovery of volcanic-related uranium deposits. However, most of the traditional geochemical exploration that have the inadequacies of the unexpected errors, weak anti-interference ability and exception information have become untenable in exploring uranium deposits overlain by volcanic rocks and sediments. To identify and track the abnormal geochemical source, feldspar infrared stimulated luminescence (IRSL) and quartz optically stimulated luminescence (OSL) were utilized for the first time to explore deeply concealed volcanic-related uranium deposits in North China. Our results confirm that feldspar IRSL-based drill-core samples are oversaturated and therefore fail to trace the deep uranium orebodies. In contrast, quartz OSL in sedimentary covers over the drill holes hosting economic and subeconomic uranium mineralization yields older apparent ages than their actual depositional ages. The high apparent ages of quartz OSL in the sediments and low helium isotope ratios (3He/4He) of the drill core indicated that the soil radon gas (Rn) anomaly was caused by Rn migration from deeply buried uranium ore decay. • Feldspar IRSL signals of drill-cores fail to indicate the deep uranium deposits. • The OSL apparent age is in proportion to the ore-bearing potential of the drill holes. • The abnormal OSL age is caused by the deeply buried uranium orebody. • The OSL age and the 3He/4He indicate that the soil Rn gas is an ore-causing anomaly. [ABSTRACT FROM AUTHOR]

Natural gases from the Sichuan Basin, China were analyzed to investigate helium abundances and isotopic composition in order to assess crustal vs. mantle inputs into the Sinian to Jurassic gas reservoirs that occur at depths up to 4900 m. In general, gases from the Sinian and pre-Sinian strata in south Sichuan have relatively high abundances of helium compared to those from the east, central and west Sichuan, implying an increase of crustal helium with time. All gas samples demonstrate very low helium isotopic ratios (³He/4He designated R) with an average of 0.016 Ra (n = 78, where Ra is the isotope ratio found in the atmosphere), indicative of a crustal origin. This is further supported by the relatively stable upper mantle found in west China. In contrast, the thin and active lithosphere in the east part of China is favorable for the injection of mantle-derived volatiles into gas reservoirs. This explains why gases from the east part of China generally have R/Ra > 1 while those in the west have R/Ra ­ 0.1. [ABSTRACT FROM AUTHOR]

Abstract: Continental basalts commonly exhibit similar geochemical compositions to oceanic island basalts, but their origin is still enigmatic in chemical geodynamics. This involves a resolution to the nature of crustal components in their mantle sources. For this purpose, we have studied the He and Ar isotopic compositions of mineral phenocrysts from Cenozoic continental basalts in eastern China. The results are combined with existing data for whole-rock geochemistry, yielding two trends between noble gas isotopic and other geochemical indicators. First is high 3He/4He ratios of 6.6 to 7.5RA and low 4He/40Ar* ratios of 0.07 to 1.39 in association with varying (La/Yb)N values from 10.4 to 31.8. Second is low 3He/4He ratios of 0.6 to 2.4RA and variable 4He/40Ar* ratios from 0.68 to 15.47 in association with low (La/Yb)N values of 11.3 to 12.0. Phenocryst 40Ar/36Ar ratios vary from 331.0 to 1677.4, in which the low ratios are associated with the low (La/Yb)N values. In combination with whole-rock Ba/Th and Sr/Y ratios as well as initial Sr and Nd isotopic ratios, we suggest three-component mixing between enriched MORB mantle, altered oceanic basalt and seafloor sediment to generate the mantle sources. The two kinds of crustal components would be incorporated into the mantle sources in the form of felsic melts. One is adakitic melt deriving from the altered oceanic basalt and thus low in Ba/Th ratios but high in Sr/Y, (La/Yb)N and εNd(t) values. The other is sialic melt originating from the seafloor sediment and thus high in Ba/Th ratios but low in Sr/Y, (La/Yb)N and εNd(t) values. The atmospheric Ar and crustal He noble gas components would be carried by the both seawater–hydrothermally altered basalt and seafloor sediment on the oceanic crust. These oceanic crust-derived melts would serve as a metasomatic agent to transfer the supracrustal He and Ar isotopic signatures to the mantle sources. The felsic melts would react with the mantle wedge peridotite during slab–mantle interaction in oceanic subduction channel. Therefore, the noble gas isotopic compositions of mantle sources for intraplate basalts are primarily determined by the budget between the mantle and crustal components during the melt–peridotite in oceanic subduction factory. [Copyright &y& Elsevier]

Highlights: [•] Helium–argon isotopic data on pyrites from skarn iron and gold deposits. [•] Ore-forming fluids record varying degree of crust–mantle interaction. [•] Mesozoic ore deposits provide insights into the craton destruction. [Copyright &y& Elsevier]

Sedimentary basins in China are globally special for retaining large volumes of carbon dioxide. To date, over 40 CO 2 gas fields (>60 vol% CO 2) and many more CO 2 -rich hydrocarbon fields (15–60 vol% CO 2) have been discovered across China. Valuable knowledge of CO 2 migration, accumulation, and long-term sequestration processes in sedimentary basins can be acquired by analysing various CO 2 fields in China. This paper reviews three key aspects of CO 2 reservoirs in Chinese sedimentary basins: (1) CO 2 origin, (2) factors controlling the distribution of CO 2 gas, and (3) the long-term effect of CO 2 emplacement on reservoir rocks. Both the eastern and western parts of China have several giant sedimentary basins. CO 2 -rich gases are predominantly discovered in eastern China among rift basins, with sandstone, carbonate, and volcanic rocks being the principal reservoirs. Analyses of carbon and helium isotopes suggest that the high abundance of CO 2 in eastern China is primarily of mantle origin, with subordinate crustal CO 2. Igneous intrusives and faults control the migration and accumulation of CO 2 -rich gases within the basins. The offshore Yinggehai Basin, however, is an exception in eastern China, where the majority of CO 2 appears to be of crustal origin, resulting from thermolysis of carbonate minerals. For this type of CO 2 , mud diapirs in the deep basin, which serve as upward passages for geothermal fluids, control the distribution of CO 2 -rich gases. In comparison, sedimentary basins in western China generally contain minor amounts of CO 2 (< 5 vol%) in the produced gases. The low-concentration CO 2 is mostly of crustal origin, from the decomposition of organic matter and carbonate minerals or, in a few places, from the thermochemical sulphate reduction process. Pore fluids in CO 2 reservoirs of China are characterised by high salinity, owing to elevated concentrations of Na+ and HCO- 3 induced by CO 2 emplacement. Pervasive dissolutions of feldspars are widely observed in sandstone and volcanic reservoirs in China, and dawsonite is the most common authigenic mineral. Dawsonite growth did not cause significant variations in the reservoir porosity in most cases. Mantle-derived CO 2 has been suggested to promote kerogen maturation and oil migration in sedimentary basins, thereby helping to form some oilfields in China. [ABSTRACT FROM AUTHOR]

• Geothermal fluid from Fengshun Tangkeng area for power generation is recharged by precipitation from surrounding mountains. • Silicate minerals dissolution, cation exchange in the reservoir and volatile migration from mantle are dominant geochemical processes for geothermal fluid evolution. • About 5.6–12.2% He and Ne are from mantle through regional scale faults systems with orientations of NE and NW. • Mixing with shallow groundwater occurs during geothermal fluid ascending process. This paper aims to determine the recharge sources, geochemical evolution and secondary reactions during ascending process of geothermal fluid with wellhead temperature of 92 °C in the Dengwu power plant of Fengshun area through analysis of hydrogeochemical and isotopic compositions of both geothermal water and gases. Results show that geothermal water for power generation is slightly alkaline HCO 3 -Na type with TDS of 291–369 mg/L and it is N 2 dominated. It is originally recharged by precipitation from surrounding mountainous areas with altitude of 475–683 m and circulates in the granite reservoir for about 7 ka to 9 ka years as evidenced by 14C and tritium dating after infiltration through faults systems of NE, NW and EW orientations. Under reservoir conditions, dissolution of silicate minerals like albite, microcline, muscovite and plagioclase leading to alkaline metal elements of K, Na, Ca and Mg and trace elements of Li, Sr and Rb releasing into the fluid. In addition, previous dissolved Ca2+and Mg2+ by eluviations exchange with Na+ and K+ absorbed on silicate reservoir and this process greatly improved concentrations of Na+ and K+, resulting in the dominant proportions of Na+ (91.3–95.8 meq%) in the geothermal water. And dissolution of CO 2 coming from air-saturated precipitation and organic matter or biogenesis promotes the water-rock interactions in granite reservoir. Helium and neon isotope analysis indicate that up to 12.2% of volatile of mantle migrate into the deep geothermal fluid through the regional scale faults system, e.g., Locus Mountain fault. During the ascending process, mixing with shallow groundwater and RongJiang River water make the geothermal water with lower temperature and TDS outflow along the NW orientated fault in forms of springs and artificial boreholes. It is speculated that the 5760 m3/day of geothermal fluid for power generation from fractured media of granite reservoir are mixture of original geothermal fluid in deep, shallow groundwater and Rongjiang River water. [ABSTRACT FROM AUTHOR]

The Yinjiagou poly-metallic deposit is located at the southern margin of the North China Craton (SMNCC). Pyrite, the most economically important mineral, is associated with Cu, Mo, Au, Pb, Zn and Ag mineralization. Two main mineralization stages have been identified and studied: a porphyry stage, including the quartz–molybdenite and quartz–sericite–pyrite (QSP) veins, and a vein stage, including the early and the late (economically most important) pyrite stages. Three types of fluid inclusions are distinguished in quartz and pyrite, including liquid-rich, vapor-rich biphase (LV) and halite-bearing inclusions. The transmitted and infrared microthermometry produced several results. (1) Each of the three types of fluid inclusions is trapped in the quartz of the porphyry stage, with homogenization temperatures of 335–419°C and salinities of 4.7–49.6wt.% NaCl equiv. The coexistence of halite-bearing inclusions and low density, vapor-rich biphase (LV) inclusions indicates that the fluid was boiling. The boiling elevated the Fe and S levels in the hyper-saline fluid, as reflected by the development of pyrite, chalcopyrite and S daughter minerals in the halite-bearing inclusions. (2) The fluid in the early pyrite also displays features characteristic of boiling, with homogenization temperatures of 352–>400°C and salinities of 3.7–42.4wt.% NaCl equiv, whereas the late pyrite only contains liquid-rich biphase (LV) inclusions, with homogenization temperatures of 263–354°C and salinities of 6.0–21.3wt.% NaCl equiv. The relationship between the decreasing salinity and the corresponding decreasing homogenization temperature clearly indicates extensive mixing and dilution. (3) Finally, the infrared calibration indicates that the impact of infrared light intensity on the microthermometric results for the Yinjiagou pyrite-hosted fluid inclusions is limited. The He Ar isotopic analysis of the fluid inclusions in the pyrite indicates two different fluid sources that involve abundant mantle input. The 3He/4He ratios in the porphyry stage are relatively uniform, ranging from 1.39 to 1.78 Ra (Ra=1.39×10−6 for air), corresponding to 16–22% mantle 4He contribution. This relatively constant range represents the actual helium isotopic composition of the fluids emanating from the cooling intrusions at depth. The range of 3He/4He ratios in the vein stage is wide, varying from 0.80 to 5.26Ra, corresponding to 9–65% mantle 4He. The significant variation in the 3He/4He ratios in the vein stage reflects mixing between two fluids. These data indicate that there are two different fluid sources and separate evolutionary processes for the porphyry and vein stages and support a multi-stage mineralization model. The veinlet molybdenite mineralization was induced by the boiling and associated cooling of a magma-sourced fluid that emanated from intrusions at depth. The QSP veins are likely to be pressure release zones and late fluid flow channels. The early pyrite mineralization may be attributed to the influx of a dominantly mantle-derived fluid with high 3He/4He ratio (5.26Ra), which is most likely related to a later, more mafic magmatic event. The precipitation of the most economically important pyrite resulted from the mixing and diluting of this mantle-derived fluid with a surface-derived fluid. Additionally, the high 3He/4He ratios indicate a strongly extensional setting, which is most likely related to the Late Jurassic to Early Cretaceous lithospheric modification and thinning of the SMNCC. [ABSTRACT FROM AUTHOR]

Abstract: Tight sandstone gas belongs to unconventional natural gas. There is no unanimous agreement about the source of tight sandstone gas source. Both the Yuanba and Tongnanba gas fields in the Sichuan Basin produce tight sandstone gas from Xujiahe Formation gas reservoirs. The geochemical data such as the carbon and helium isotopes of the 14 gas samples from the Xujiahe Formation of 9 wells in the Yuanba gas field show that the gas mainly consists of coal-derived gas from the self-source type, oil-type gas from other source, and a small amount of abiogenic gas, suggesting combination gas sources. The similar geochemical data of 5 gas samples from the Xujiahe Formation of 5 wells in the Tongnanba gas field indicate that the gas consists of oil-type gas from other source, accompanied by a small amount of abiogenic gas, also being of mixed origins. Therefore the Xujiahe Formation tight sandstone gases of the Yuanba and Tongnanba gas fields do not come from coal measure alone. They have a variety of sources, mainly the coal-derived gas or oil-type gas of organic origin or the mixture of them. [Copyright &y& Elsevier]

Abstract: The large scale Mesozoic magmatism and related metallogeny in the Taihang Mountains (TM) provide important clues for the lithospheric thinning of the North China Craton (NCC). Among the ore deposits, the vein gold mineralization of Shihu in the Fuping region and the skarn ore deposit of Xishimen in the Wu''an region represent typical Mesozoic metallogeny in the TM. In the Shihu gold mine, the Mapeng batholith is dominantly composed of monzogranite and granodiorite, whereas, the Wu''an pluton in the Xishimen iron mine mainly comprises monzonite and diorite. Here we present zircon LA–ICP-MS U–Pb data from 8 samples which reveal the timing of magmatism in the TM as ca. 130Ma, which is contemporaneous with the large-scale metallogeny in the margins of the NCC. The δ34S values recorded in the sulfide minerals from the Shihu gold deposit and the Xishimen skarn iron deposit show a range of 2.2‰–5.0‰, and 11.6‰–18.7‰, respectively. Helium isotopic compositions of fluid inclusions in pyrite from the Shihu gold deposit vary from 0.12 to 1.98Ra (where Ra is the 3He/4He ratio of air=1.39×10−6), with calculated mantle helium values of 1.4%–25%, whereas, those of the Xishimen skarn iron deposit range from 0.06 to 0.19Ra, with calculated mantle helium of 0.7%–2.2%. The S–He–Ar isotopic data suggest a lower crustal origin for the ore-forming components, with variable inputs of mantle source. The large population of inherited zircons in our samples, with 207Pb/206Pb ages ranging between 2500Ma and 1800Ma, also supports crustal participation. Our data reveal that the Shihu gold deposit witnessed greater mantle input than the Xishimen skarn iron deposit, suggesting that the continental lithosphere is markedly thinner under the Fuping region than that under the Wu''an region. Our interpretation is also supported by published data from two ultra-broadband high-precision magnetotelluric sounding profiles across the TM region showing a variation in the lithosphere thickness from 155km to 70km while moving from the south (Wu''an region) to the north (Fuping region). Our study suggests that inhomogeneous lithospheric thinning in the central NCC occurred at least as early as ca. 130Ma ago. [Copyright &y& Elsevier]

Chemical and isotopic compositions have been measured for N2-He-rich bubbling gases discharging from hot springs in the Hainan Island, Southern China. Observed 3He/4He ratios (0.1-1.3 RA) indicate the occurrence of a mantle component throughout the island, which has been highly diluted by a crustal radiogenic 4He component. The occurrence of mantle-derived helium is high in the northern island (12%-16% of total He) and gradually decreases towards southern coast (l%-3% of total He). Such a distribution pattern is most likely controlled by the Pleocene-Quaternary volcanic activities in the northern island and groundwater circulation along the deep major faults. The 40Ar/36Ar and N2/Ar ratios suggest that N2 and Ar of the hot spring gases are mostly meteoric. Although δ13C values of CO2 (-20‰ to −27‰) with low concentrations are consistent with the biogenic origin, the combination of 3He/4He and δ13CCO2 suggests a two end-member mixing of mantle and crustal components with CO2/3He ratios of 2×109 and 8×1011, respectively. However, the low CO2/3He ratios (1-22×106) can not be ascribed in terms of the simple mixing but has to be explained by the addition of radiogenic 4He and loss of CO2 by calcite precipitation in the hydrothermal system, which is most likely controlled by the degree of gas-water-rock interaction. [ABSTRACT FROM AUTHOR]

Abstract: This paper describes and discusses the hydrochemical and isotopic characteristics of samples collected from some geothermal springs or wells in the Xining basin of the northeastern Tibetan Plateau, China. The results show that the groundwater runoff, circulation depth, recharge period, and residence times vary greatly, while dominating both the geothermal reservoir temperature and heat preservation in different tectonic units of the Xining Basin. Particularly, recharge by young cold surface water quickly and greatly reduces the temperature of geothermal systems. As for heat source, the general low temperature, immature waters as well as, helium isotope (3He/4He and 4He/20 Ne ratio) show that there seems to be no hot, mantle sourced fluids to increase the geothermal temperature. Crustal magmatic fluids, the radiogenic heat of radioactive elements, and the fault friction produced heat can all be possible contributing factors to the Xining basin heat sources. One can conclude that future investigation for geothermal resources should be closer to northern margin of Laji Moutain deep large fault zone where the high heat-flow can provide heat source while the mixing of surface water with groundwater is relatively slow. [Copyright &y& Elsevier]

The age-accumulation effect of Ar in hydrocarbon source rocks was discussed in accordance with the decay law of radioactive elements. In terms of the mean values of Ar/Ar, the old Sinian gas reservoirs (mean values of Ar/Ar: 7009) were definitely distinguished from the Permian gas reservoirs (mean values of Ar/Ar: 1017) in Weiyuan, Sichuan Province, and the gas source of the Permian gas reservoir (mean values of Ar/Ar: 5222) in well Wei-7 with the Weiyuan structure is defined as the Sinian system. Based on the values of Ar/Ar, the coal-type gases (The source rocks are of the C-P system; mean values of Ar/Ar: 1125) are definitely distinguished from the oil-type gases (The source rocks are of the Tertiary system; mean values of Ar/Ar: 590) in the Tertiary reservoirs of the Zhongyuan Oilfield. Besides, Ar/Ar values also have a positive effect on the oil-source correlation of oil reservoirs in ancient hidden mountains. According to the crust-mantle interchange information reflected by He/He values, petroliferous provinces in China can be divided into three major tectonic regions. (1) The eastern active region: The crust-mantle volatile matter exchanges actively, and the He/He values are mainly around 10, partly around 10. (2) The central stable region: The He/He values are all around 10. (3) The western sub-stable region: The He/He values are mainly around 10, and around 10 on the edges of the basins. Helium contents of some gas wells in China's eastern petroliferous region reach the industrial abundance (He≈0.05%-0.1%), the He/He values reach 10, and the equivalent values for the mantle-source components in helium gas can reach 30%-50%. As viewed from this, a new type of crust-mantle composite helium resources has been proposed. Geneses of some CO gas reservoirs in the east of China and some issues concerning mantle-source methane were discussed in the light of the helium and carbon isotopes of CO and CH in natural gases. In the discussion on helium isotopic characteristics of inclusions in the reservoirs, it was discovered that the He/He values are close to those in natural gases. That is to say, this phenomenon is related to regional tectonism. The He/He, CO/He and CH/He data were used to discuss the tectonic activities of fault zones in a certain number of regions in China. [ABSTRACT FROM AUTHOR]

Based on conservation of energy principle and heat flow data in China continent, the upper limit of 1.3 μW/m3 heat production is obtained for continental crust in China. Furthermore, using the data of heat flow and helium isotope ratio of underground fluid, the heat productions of different tectonic units in China continent are estimated in range of 0.58-1.12 μW/m3 with a median of 0.85 μW/m3. Accordingly, the contents of U, Th and K2O in China crust are in ranges of 0.83-1.76 μg/g, 3.16-6.69 μg/g, and 1.0%-2.12%, respectively. These results indicate that the abundance of radioactive elements in the crust of China continent is much higher than that of Archean crust; and this fact implies China's continental crust is much evolved in chemical composition. Meanwhile, significant lateral variation of crustal composition is also exhibited among different tectonic units in China continent. The crust of eastern China is much enriched in incompatible elements such as U, Th and K than that of western China; and the crust of orogenic belts is more enriched than that of platform regions. It can also be inferred that the crusts of eastern China and orogenic belts are much felsic than those of western China and platform regions, respectively, derived from the positive correlation between the heat production and SiO2 content of bulk crust. This deduction is consistent with the results derived from the crustal seismic velocity data in China. According to the facts of the lower seismic velocity of China than the average value of global crust, and the higher heat production of China continent compared with global crust composition models published by previous studies, it is deduced that the average composition models of global continent crust by Rudnick and Fountain (1995), Rudnick and Gao (2003), Weaver and Tarney (1984), Shaw et al. (1986), and Wedepohl (1995) overestimate the abundance of incompatible elements such as U, Th and K of continental crust. [ABSTRACT FROM AUTHOR]

Abstract: Measurements of cross sections of the 95Mo(n, α)92Zr reaction at E n=4.0, 5.0 and 6.0MeV were carried out at the 4.5MV Van de Graaff of Peking University, China. A twin gridded ionization chamber and two large-area 95Mo samples were adopted. Fast neutrons were produced through the D(d, n)3He reaction by using a deuterium gas target. A small 238U fission chamber was employed for absolute neutron flux determination. Present data are compared with existing evaluations and measurement. [Copyright &y& Elsevier]

Abstract: The Xiangshan U deposit, the largest hydrothermal U deposit in China, is hosted in late Jurassic felsic volcanic rocks although the U mineralization post dates the volcanics by at least 20 Ma. The mineralization coincides with intrusion of local mantle-derived mafic dykes formed during Cretaceous crustal extension in South China. Ore-forming fluids are rich in CO2, and U in the fluid is thought to have been dissolved in the form of UO2 (CO3)2 2− and UO2 (CO3) 3 4− complexes. This paper provides He and Ar isotope data of fluid inclusions in pyrites and C isotope data of calcites associated with U mineralization (pitchblende) in the Xiangshan U deposit. He isotopic compositions range between 0.1 and 2.0Ra (where Ra is the 3He/4He ratio of air=1.39×10−6) and correlates with 40Ar/36Ar; although there is potential for significant 3He production via 6Li(n,α)3H(β)3He reactions in a U deposit (due to abundant neutrons), nucleogenic production cannot account for either the 3He concentration in these fluids, nor the correlations between He and Ar isotopic compositions. It is more likely that the high 3He/4He ratios represent trapped mantle-derived gases. A mantle origin for the volatiles of Xiangshan is consistent with the δ 13C values of calcites, which vary from −3.5‰ to −7.7‰, overlapping the range of mantle CO2. The He, Ar and CO2 characteristics of the ore-forming fluids responsible for the deposit are consistent with mixing between 3He- and CO2-rich mantle-derived fluids and CO2-poor meteoric fluids. These fluids were likely produced during Cretaceous extension and dyke intrusion which permitted mantle-derived CO2 to migrate upward and remobilize U from the acid volcanic source rocks, resulting in the formation of the U deposit. Subsequent decay of U within the fluid inclusions has reduced the 3He/4He ratio, and variations in U/3He result in the range in 3He/4He observed with U/3He ratios in the range 5–17×103 likely corresponding to U concentrations in the fluids <0.2 ppm. [Copyright &y& Elsevier]

We report methane (CH 4) with variable carbon isotopes (between −60.9‰ and − 26.8‰) from Changbaishan, the most dangerous volcano in NE China. Furthermore, recent chemical and isotopic data of He, CO 2 , and CH 4 in hot spring gases at Changbaishan volcano are also presented. Bubbling gas samples were collected periodically from 2014 to 2019 in three hot spring areas in the Changbaishan volcanic field: one on the shoreline of the Tianchi caldera lake and two on the north and southwest flanks. The helium isotopes of the bubbling gases from the three hot spring areas suggested a major magmatic source, up to 5.8 Ra (where Ra represents the atmospheric 3He/4He ratios). However, the CH 4 exhibited a biotic signature in carbon isotopes (δ13C) as low as −60.9‰, and the concentrations of CH 4 among the three hot spring areas exhibited remarkable variations from 0.02% to 17.04%. After evaluating the influence of air contamination, crustal and organic contributions, and thermodynamic processes, we suggest that CH 4 from the three hot spring areas primarily originated from two sources: (1) a previously formed gas reservoir in the crust with significant contributions from the ancient subductions and (2) the MORB-like materials from the present upwelling asthenosphere. Based on these observations, we propose a model to explain the processes that formed these two sources, which demonstrates the existence of ancient subduction fluids in the subcontinental lithospheric mantle. In addition, our study of volcanic gases does not support the conspicuous material connections between the subducting west Pacific slab and Changbaishan volcano. Finally, based on our results, suggestions for volcanic gas monitoring at the Changbaishan volcano are provided. • Magmatic CH 4 from Changbaishan volcano display variable carbon isotopes. • Helium and CH 4 contents are positively correlated in Changbaishan volcanic gases. • A two-source model is proposed for the volcanic gases of Changbaishan volcano. • Material contribution of Pacific slab is not found in the volcanic gases. [ABSTRACT FROM AUTHOR]

Extraterrestrial particles have higher 3He/4He ratios than those of terrestrial sediments (> 100 Ra versus <0.03 Ra, where Ra is the 3He/4He ratio normalized to the atmospheric value of 1 .4×10-6). The inter-planetary dust particles (IDPs), which are very rich in 3He, continuously bombard the Earth and can accumulate in deposits. IDPs sedimentation rate changes can significantly influence 3He concentration in the Earth surface sediments. Since IDPs are not easy to detect in terrestrial deposits, measuring helium isotopes is a helpful approach to examine changes in IDPs. Helium concentration and helium isotopic composition magnetic substances and the quartz particles were examined for helium concentration and helium isotopic ratio. Results show that the 3He/4He ratio and the 3He concentrations of the magnetic substances are clearly higher than those of the bulk samples and the quartz particles, and, the 3He/4He ratio of the extracted magnetic substances is also higher than that of the average level of the Earth's crust. The higher helium content in the magnetic fractions can be explained by an influx of IDPs. [ABSTRACT FROM AUTHOR]

Abstract: Volcanic activity in Northeast China and adjacent regions is widespread, with eruption ages ranging from Late Cretaceous (80 Ma) to about 300 years ago. Volcanic rock types are principally basanite, alkali olivine basalt, and tholeiite, with minor evolved trachyte and rhyolite. Ultramafic xenoliths, mainly spinel lherzolite and harzburgite, are common in alkali olivine basalt and basanite. We present new major and trace element data from 11 volcanic fields, and helium isotope data from ultramafic xenoliths of three of those fields. 3He/4He ratio ranges from 5 to 7 times the atmospheric ratio, indicating that previously reported high 3He/4He ratios are likely due to the contamination by cosmogenic 3He. There is currently no evidence for a high-3He/4He mantle plume component beneath NE China. Sr–Nd–Pb isotopic data from the literature are reinterpreted to result from mixing between a FOZO end-member and a LoMu end-member. The LoMu end-member appears to reside within continental lithosphere. Major and trace elements do not indicate significant contributions from a subducted slab. Differences in depth and the extent of partial melting in the asthenosphere, both locally within individual fields and regionally between the different volcanic fields, explain most of the correlations between major and trace elements observed in this study, with deeper melting usually associated with a smaller degree of melting. Highly potassic basalts are associated with the LoMu end-member and are interpreted to be the products of lithosphere melting. [Copyright &y& Elsevier]

Abstract: The origins of gases from hot springs and earthquake activity in the western part of Sichuan Province, Southwestern China, are discussed in terms of helium and carbon isotopes and energy released by earthquakes. δ 13C values of CO2 in free and dissolved gases range from −3.34 to −17.09‰, and 3He/4He ratios vary from 1.5×10−8 to 3.63×10−6. The isotopic compositions indicate that carbon dioxide from the hot springs is a mixture of crustal and mantle CO2, and helium is derived from the crust, mantle and atmosphere. The thermal springs in different earthquake and/or fault zones, as well as in different parts of the same zone, have different values of δ 13C and 3He/4He. The more tectonically active the district is, the larger the δ 13C and 3He/4He values and the greater the frequency of earthquakes. This means that more heat energy is derived from the deep earth with upward migration of anatectic fluids in the active-tectonic district, such as in the Kangding district. Therefore, hot spring gases (He, CO2 etc.) may be important geochemical markers for determination of seismological and tectonic activity. [Copyright &y& Elsevier]

Discusses the isotopic composition of helium in garnet and omphacite of eclogite in the Dabie Mountains in central China. Look at the geological significance of the isotopic composition of helium; Concentrations of Helium in garnet and omphacite; Geological characteristic of helium isotope in eclogite.

Discusses the investigation of isotopic compositions of helium in hot spring gases sampled from the Liaodong Peninsula, China. 3HE/4HE ratios; Similarity of distribution pattern to regional heat flow valves; Internal relationship between mantle degassing and seismic activity.

Widespread Mesozoic granitoids in the Cathaysia Block of South China are associated with intensive reworking of the lower crust as a result of magma underplating. This inference is based mainly on studies of mafic igneous rocks, whereas there is little evidence from lower-crustal rocks. Lower-crustal xenoliths in Mesozoic basalts in the Daoxian region within the Cathaysia Block might record information on the relationship between magma underplating and remelting of the pre-existing crust beneath the block. The xenoliths are mainly mafic granulites, with minor felsic granulites. The mafic granulites have low SiO 2 contents (47.22–49.46 wt%) and high Mg# values (77.8–82.4), suggesting that their protoliths were derived from a mantle source. The felsic granulite xenoliths have high SiO 2 (69.56–70.27 wt%) and low MgO (1.63–2.50 wt%) contents, and zircons in these xenoliths yield negative ε Hf (t) values (−6.1 to −12.6) and high δ18O values (6.8–7.6‰), consistent with a crustal source. Both mafic and felsic granulite xenoliths record magmatic (226–218 Ma) and metamorphic (218–193 Ma) events, suggesting a genetic link between mafic and felsic rocks in the lower crust. We propose that the magma underplating was responsible for the origin of the mafic granulites and partial melting of pre-existing lower crust, as recorded by the felsic xenoliths. The granulite xenoliths also contain abundant inherited zircons that formed during the Archean–Neoproterozoic (2584–659 Ma), early Paleozoic (peaking at ca. 425 Ma), and late Paleozoic (peaking at ca. 261 Ma). Zircons from the Daoxian granulite xenoliths have distinct Hf O isotopic compositions that record the multistage evolution of the lower crust beneath the Cathaysia Block. This evolution involved the accretion of juvenile crust during the late Archean (ε Hf (t) = +4.2 to +4.6) and late Paleozoic (ε Hf (t) = +1.3 to +5.3; δ18O = 5.8–6.2‰), crustal reworking during the Neoproterozoic (ε Hf (t) = −7.5 to −11.8; δ18O = 5.1–9.5‰) and early Paleozoic (ε Hf (t) = −0.5 to −2.2; δ18O = 7.3–7.5‰), and crustal accretion with significant reworking during the early Mesozoic (ε Hf (t) = −19.2 to +5.9; δ18O = 6.8–7.6‰). The U Pb ages and Hf O isotopic data of zircons from the Daoxian granulite xenoliths are consistent with the distribution of Phanerozoic igneous rocks in the Cathaysia Block. These data support the inference that Mesozoic magma underplating triggered the remelting of pre-existing crustal materials and produced extensive granitoid magmatism. • Daoxian granulite xenoliths record multistage accretion/reworking of lower crust. • Mafic xenoliths are related to early Mesozoic magma underplating. • Felsic xenoliths originated mainly from remelting of pre-existing lower crust. • Underplating triggered Mesozoic remelting of lower crust in the Cathaysia Block. [ABSTRACT FROM AUTHOR]

• Mesozoic orogenic gold mineralization occurred in the northern margin of North China Craton. • Gold mineralization largely post-dated regional metamorphism. • Gold deposit formed as a result of reactivation of metasomatized mantle. The genesis of orogenic gold deposits in the northern margin of the North China Craton (NCC) is still ambiguous, and this is addressed in this case study on the Zhangquanzhuang gold deposit. This deposit shows features typical of orogenic gold deposits, including quartz vein-type mineralization controlled by shear zones, sericite-quartz-pyrite-carbonate alteration along shear zones, absence of connection to any magmatic intrusion, and occurrence of native gold and electrum. The Zhangquanzhuang gold deposit, which is hosted in Archean high-grade metamorphic rocks, was formed in Mesozoic and largely later than the regional metamorphism. In this deposit, the Pb isotope compositions of sulfides in ores have low 206Pb/204Pb ratios of 16.874–17.007, 207Pb/204Pb ratios of 15.368–15.410, and 208Pb/204Pb ratios of 37.023–37.215, and these are much less radiogenic than those of regional metamorphic and magmatic rocks. This finding precludes the possible derivation of ore fluid from regional magmatism and metamorphism. In pyrite-hosted fluid inclusions in the ores, the 3He/4He and 40Ar/36Ar ratios are 1.26–1.75 Ra and 1622–2816, respectively, showing prominent signature of mantle sources. These geochemical features, together with the large temporal discrepancy between regional metamorphism and mineralization, suggest that ore fluid and metal had a subcrustal source similar to the gold deposits in the Jiaodong gold province in the southeastern margin of the NCC. The calculated δ 34S H2S values for the ore fluid are 2.31–4.48‰, which are heavier than the δ 34S of depleted mantle. The δ 18O of ore-related quartz mostly cluster around 11‰, implying high δ 18O of subcrust-derived ore fluid. The stable O and S isotope data indicate that the subcrustal source has been metasomatized by subducted crustal sediments. [ABSTRACT FROM AUTHOR]

Subduction zones are important in materials' cycling between Earth's surface and mantle. As Li isotopic compositions of sedimentary carbonates (δ7Li = 5.2‰–31‰) differing markedly from those of the mantle (2.0‰–5.7‰), it is important to know if Li isotopic compositions of carbonates could be used to tracing deep carbon cycling. Here we report that meta -sedimentary carbonates could preserve their original heavy Li isotopic signatures (with δ7Li values up to 21.5‰) when subducted from surface to the mantle depths (the yellow arrow) and that the related carbonatitic or carbonate-rich silicate melts may retain various degrees of heavy Li isotopic signatures locally in the mantle (the yellow arrow). We infer that some mantle-derived magmas may have recorded the elevated δ7Li signatures induced by recycled carbonates (the yellow arrow) and thus Li isotopic geochemistry could be useful in tracing deep carbon cycling. • We firstly investigated the Li isotopic compositions of UHP marbles. • The δ7Li of UHP marbles is heavier than that of the upper mantle. • UHP marbles could form heavy Li isotopic heterogeneity in local mantle. • Li isotopes of UHP marbles are potential tools for tracing subduction and material-cycling. Subduction zones are important in materials' cycling between Earth's surface and mantle. We report lithium (Li) contents and isotopic compositions (δ7Li) of ultrahigh-pressure (UHP) marbles of the Dabie-Sulu orogen, with the aim of elucidating the geochemical behavior of Li isotopes during deep subduction of surficial carbonates and exploring the application of Li isotopes in tracing subduction and material-cycling. Pure UHP marbles (with δ7Li values up to 21.5‰) show significantly heavier isotopic compositions than those of the mantle (2.0‰–5.7‰; average 3.7‰), while impure marbles containing some silicates have δ7Li values as low as 1.3‰. Weathering, fluid infiltration, and isotopic fractionation have negligible effects on the Li isotopic compositions of UHP marbles. Exhumed UHP marbles might be good samples to study those residual carbonates entering into the deep mantle. When subducted carbonates transport heavy Li isotopic signatures to mantle depths, they may result in local Li isotopic heterogeneity. As Li is a trace element and UHP marbles have significantly different δ7Li signatures to the mantle, Li isotopic geochemistry might be useful in tracing deep carbon cycling. [ABSTRACT FROM AUTHOR]

Helium is an exhaustible natural resource and the main commercial helium was separated from helium-rich natural gas. The helium in the sedimentary basin is mainly the radiogenic origin of crustal rocks with high level of uranium and thorium. Data from 242 natural gas samples were used to investigate the distribution and formation mechanism of helium-rich gases in the Sichuan Basin of China. All gas samples show remarkably low 3He/4He ratios with ranging from 0.002 to 0.05 Ra, which represent typical crustal helium. The Weiyuan gas pool in the southern Sichuan Basin possesses high levels of helium (1500–18770 ppm, average 2785.7 ppm) in Precambrian and Cambrian strata. A positive relationship were observed in the helium and nitrogen contents increased with reservoir layer age for all Weiyuan gas samples. Presinian granite was considered as the main helium source for the Weiyuan gas pool. Gaoshiti–Moxi and Weiyuan gas pools belonged to the same ancient gas pool before the Late Cretaceous, but the helium abundance of Gaoshiti–Moxi gas pool is relatively low (200–891 ppm). The change of pressure and fracture system caused by the uplift of Weiyuan structure in the Himalayan orogenesis led to the helium accumulation and enrichment of Weiyuan gas pool. The shale of the Silurian Longmaxi Formation has high contents of uranium and thorium and generated a large amount of helium while forming large quantities of hydrocarbon gases. Generally, the helium abundance of shale gases and conventional gases generated from the Longmaxi Formation ranges from 63 to 1500 ppm and some of the gas pool are sufficient for commercial helium resource exploitation. Therefore, the relative quantities of helium and hydrocarbon gases are act as a key factor influencing the formation of helium-rich natural gas reservoirs. • Helium in the sedimentary basin is mainly the radiogenic origin. • Helium-rich gas is generally the crust-derived heterogenous type. • Presinian granite was the main source of helium in the Weiyuan gas field. [ABSTRACT FROM AUTHOR]

The Wulandele molybdenum deposit is a porphyry-type Mo deposit in the Dalaimiao area of northern Inner Mongolia, China. Molybdenite Re-Os dating yields a model age of 134.8 ± 1.9 Ma, with the fine-grained monzogranite most closely related to the mineralization. The lithogeochemical data show that the monzogranite is weakly peraluminous, high-K calc-alkaline series, with reduced to slightly oxidized, highly fractionated I-type granite characteristics. The relatively low initial 87Sr/86Sr (range from 0.705347 to 0.705771), weakly negative εNd(t) (range from −2.0 to −1.3), and crust-mantle mixing of Pb isotopes suggest that the monzogranite originated from the partial melting of mafic juvenile lower continental crust derived from the depleted mantle, with a minor component of ancient continental crust. Combined with the regional tectonic evolution, we argue that the partial melting, then injection, of the monzogranite melt was probably triggered by collapse or delamination of the thickened lithosphere, which was mainly in response to the post-orogenic extensional setting of the Mongol–Okhotsk belt; this is possibly coupled with a back-arc extension related to Paleo-Pacific plate subduction. The extensively fractional crystallization of the monzogranite melt is the crucial enrichment process, resulting in magmatic hydrothermal Mo mineralization in the Wulandele deposit, and the Cretaceous granitoids are generally favorable to form Mo mineralization in the Dalaimiao area. [ABSTRACT FROM AUTHOR]

• Mid-Permian strata in South China are characterized by high positive δ13C carb values. • Decarbonation during tectono-thermal events is the mechanism for 13C enrichment. • Emplacement causing regression and doming was responsible for δ13C carb fluctuations. During the Permian, Emeishan mantle plume activity created a large igneous province and deeply impacted carbon isotope records in marine carbonate strata in South China. To evaluate the isotopic variations caused by this catastrophic event, 140 carbonate samples from four sections were collected and analyzed. The δ13C carb values in the upper section of the Qixia Formation gradually increased, stabilized at ~4.0‰ in the lower-middle sections of the Maokou Formation, and then abruptly decreased in the upper section of the Maokou Formation. This isotopic evolution trend is likely related to mantle plume geochemical processes occurring during these respective stages. Large amounts of upwelling heat from the emplacement of the mantle plume triggered large-scale decarbonation reactions in the continental crust resulting in CO 2 production enriched in 13C. Substantial amounts of 13C-enriched CO 2 directly affected the isotope compositions of marine carbonates during this time. Temporal and spatial fluctuations in carbon isotopes were also controlled by terrestrial materials as a result of regression and doming caused by plume emplacement. The abrupt decrease in δ13C carb in the upper section of the Maokou Formation reflects the onset of volcanism, resulting in the breakdown of organic materials. These findings emphasize the contribution of a carbon reservoir (with a thermal decarbonation origin) in the upper crust, particularly against the Permian tectono-thermal background. This mechanism, which is similar to biological isotope fractionation in the carbon cycle, should not be overlooked. [ABSTRACT FROM AUTHOR]

There are dispute on the calculation principle and parameters selection of helium resource prediction in Weihe Basin.Here gas compositions and helium isotopes data of 101 oil & gas wells and geothermal wells in Weihe Basin were collected；helium accumulation conditions analyzed；the helium resources calculated on the basis of comprehensive selection and evaluation of various parameters.The results showed that the volume fraction of helium is 1.50% in average and 9.23% to maximum.Helium source rocks，groundwater systems，carrier gases and fractures are the control conditions of helium production，migration and accumulation，in which the granite body in southern margin of the basin and concealed magnetic body interior basin are most likely the helium source rocks.Evaluation of helium resources in Weihe Basin are as follows:(1)the helium resource is calculated to be 21.30×108 m3 on the basis of the geothermal fluid reserves，the gas-water ratio，the volume fraction of helium gas；(2)according to the effective area of the helium source rocks，water cycle depth，rock density，uranium and thorium concentrations，the helium quantities produced since the formation of granite rocks，depression of the basin and formation of reservoir are 185.21×108 m3，37.58×108 m3 and 4.16×108 m3 respectively，showing the good helium resource prospect in Weihe Basin. [ABSTRACT FROM AUTHOR]

Niutuozhen geothermal field is located in the Jizhong graben, belonging to the northern part of Bohai Bay Basin in North China. Chemical and isotopic analyses were carried out on 14 samples of the geothermal fluids discharged from Neogene Minghuazhen (Nm), Guantao (Ng), and Jixianian Wumishan (Jxw) formations. The δ2H and δ18O in water, δ13C in CH4, δ13C in CO2, and 3He/4He ratio in the gases were analyzed in combination with chemical analyses on the fluids in the Niutuozhen geothermal field. The chemical and isotopic compositions indicate a meteoric origin of the thermal waters. The reservoir temperatures estimated by chemical geothermometry are in the range between 60 and 108 °C. The results show that the gases are made up mainly by N2 (18.20–97.42 vol%), CH4 (0.02–60.95 vol%), and CO2 (0.17–25.14 vol%), with relatively high He composition (up to 0.52 vol%). The chemical and isotopic compositions of the gas samples suggest the meteoric origin of N2, predominant crustal origins of CH4, CO2, and He. The mantle-derived He contributions are calculated to be from 5 to 8% based on a crust–mantle binary mixing model. The deep temperatures in the Jxw reservoir were evaluated based on gas isotope geothermometry to be in the range from 141 to 165 °C. The mantle-derived heat fraction in the surface heat flow is estimated to be in the range of 48–51% based on 3He/4He ratios. [ABSTRACT FROM AUTHOR]

The article focuses on a study that investigates helium and argon isotope geochemistry of ore-forming fluids in Zhemulang gold deposit in Southern Tibet, China. The study shows that the ore-forming fluid of the gold deposit is a mixture of crustal fluid and mantle-derived fluid. Also the study reveals that crust-mantle interaction and the injection of mantle-derived fluids during collision might have played an important role in the mineralization of the deposit.

The article offers information on the research "He and Ar Isotopes of Fluid Inclusions in the Taoxikeng Tungsten Deposit, South China" by Song Shengqiong and colleagues. It concludes that the ore-forming fluids of the region are fluid contains atmospheric argon and crustal helium, and mantle components and formed by crustal melting.