The influence of oxygen isotope exchange between CO2 and H2O in natural CO2-rich spring waters: Implications for geothermometry

Karolytė, Rūta; Serno, Sascha; Johnson, Gareth; Gilfillan, Stuart

doi:10.1016/j.apgeochem.2017.06.012

Cited by 54 publications

(31 citation statements)

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“…The δ 18 O-CO 2(g) data (≈ 15‰) are subject to caution due to the inherent difficulty in obtaining representative samples especially because of the fast exchange between H 2 O and CO 2(g) (Panichi et al 1977;Gemery et al 1996). Nevertheless, these values are in the same order of magnitude of deep originated volcanic δ 18 O-CO 2(g) values calculated in Karolyte et al (2017). As a whole, the CO 2(g) isotopic signature of δ 13 C and δ 18 O seems to be compatible with a deep magmatic origin and scarcely affected by isotopic exchanges with subsurface waters, testified by quantitatively high and rapidly uprising CO 2(g) at the Shiwaga gas field.…”

Section: Co 2 Gas Isotopic Signaturementioning

confidence: 90%

“…Other mechanism such as precipitation-dissolution reactions, bubble formation, exchange with atmosphere, Fig. 3 δ 2 H vs. δ 18 O diagram of waters sampled at the Shiwaga gas field: with black circle: springs (S), gray circle: puddles (P) white circle: rivers samples (R), black line: regional meteoric water line (RMWL), gray line: global meteoric water line (GMWL) and dotted line: Shiwaga water line (SHI-WL) salinity effect, kinetic fractionation, which may affect the δ 18 O-H 2 O (Broecker and Siems 1984;Jähne et al 1987;Chiodini et al 2000), cannot likely be considered responsible for such large 18 O-shift (Karolyte et al 2017 (Bottinga 1968), whereas a mean value of 30.5‰ was measured (Table 1). This suggests that either time interaction between groundwater and gas is too short to reach isotopic equilibration or spring waters (δ 18 O ≈ − 15‰) result from a mixing, in 45 and 55% proportions, between (1) CO 2(g) equilibrated water (δ 18 O ≈ − 27‰) and (2) rainfall water unaffected by CO 2(g) (δ 18 O ≈ − 4‰), respectively.…”

Section: Discussionmentioning

confidence: 99%

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Evidence of a water δ18O negative shift driven by intensive deep CO2 upflow at Shiwaga gas field (Rungwe, Tanzania)

et al. 2018

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Located on the flank of Ngozi volcanoes (Tanzania), the Shiwaga gas field is a spot of intense CO 2(g) emanations. Physicochemical measurements on different types of waters (rivers, puddles, and springs) as water and gas sampling were discontinuously performed over 10 years for equilibrated partial CO 2 pressure calculations and stable isotopic analyses. The most striking result shows that meteoric H 2 O and deep originated CO 2(g) exchanges are responsible for a negative 18 O-shift of the studied waters in relation with waters electrical conductivity, pH, and pCO 2 eq changes. In spring waters, a maximum shift of − 11.2‰ in δ 18 O was observed and pCO 2 eq values up to 1196 mbar were computed. Although this trend has already been reported around the world, such extended shift is rarely measured and requires an important amount of CO 2(g) , with a CO 2(g) / H 2 O ratio up more than 0.5 mol/mol. This approach is useful to better understand the hydro-geochemical processes involved in such environments. Moreover, this study evidences that an inventory as a monitoring of these gas fields are needed for the management of natural hazards and local resources.

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Section: Co 2 Gas Isotopic Signaturementioning

confidence: 90%

Section: Discussionmentioning

confidence: 99%

Evidence of a water δ18O negative shift driven by intensive deep CO2 upflow at Shiwaga gas field (Rungwe, Tanzania)

et al. 2018

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“…Recharge Source of the Hot Springs. As components of water molecules, stable hydrogen and oxygen isotopes are useful indicators of groundwater studies, which provide information on water origin, recharge and migration pathways, fault and fracture permeability to fluids, and so on [20]. The stable isotopes are commonly used to distinguish among meteoric, marine, and magmatic origins of spring water.…”

Section: Discussionmentioning

confidence: 99%

Hydrogeochemistry, Geothermometry, and Genesis of the Hot Springs in the Simao Basin in Southwestern China

et al. 2019

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In the Simao Basin in southwest China widely occur red beds of poor permeability. Nevertheless, more than 100 springs exist in the basin, some of which are hot springs with varying temperature. Hot springs contain abundant information on hydrogeochemical processes and groundwater circulation. In this study, hydrochemical and isotopic analyses and mixed models are used to examine the sources of recharge, heat, and solutes of the hot springs to better understand the subsurface processes and formation mechanisms of different hot springs in the basin. Three types of springs are found in the Simao Basin: springs of HCO3-Na type occur in the metamorphic rocks, springs of HCO3-Ca(Mg) and Cl-HCO3-Na-Ca types in the carbonate rocks, and springs of Cl(SO4)-SO4(Cl)-HCO3-Na(Ca) type in the red beds. Data of δ2H and δ18O indicate that the hot springs in the Simao Basin are meteoric in origin. Incongruent dissolution is the dominant process affecting the chemical compositions of the spring waters. The hydrochemical constituents of the hot springs in the metamorphic rocks, carbonate rocks, and red beds are influenced by the weathering of albite and the dissolution of carbonate, gypsum, anhydrite, and halite. The geothermal waters are mixed with shallow cold waters in their ascending processes, and the mixing ratios of cold water range from 58% to 94%. Due to the effect of mixing, the reservoir temperatures (51°C-127°C) calculated with the quartz geothermometer are regarded as the minimum reservoir temperatures. More reliable reservoir temperatures (91°C-132°C) are estimated with the fixed-Al method. The following mechanisms contribute to the formation of hot springs in the Simao Basin: the groundwater receives recharge from infiltration of precipitation and undergoes deep circulation, during which groundwater is heated by heat flow and incongruently dissolves the subsurface minerals and emerges in the form of hot springs along the permeable fracture or fault zones.

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“…Previous geochemical modelling work showed that CO2 does not cause significant amounts of bedrock mineral dissolution in the Ordovician aquifer (Karolytė et al, 2017) and there is no geological evidence for addition of large amounts of crustal CO2 from other sources (e.g. carbonate metamorphism).…”

Section: Radiogenic 4 He Stripping From Enriched Pore-watermentioning

confidence: 97%

Tracing the migration of mantle CO2 in gas fields and mineral water springs in south-east Australia using noble gas and stable isotopes

Karolytė

Johnson

Gyӧre

et al. 2019

Geochimica et Cosmochimica Acta

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Geochemical monitoring of CO2 storage requires understanding of both innate and introduced fluids in the crust as well as the subsurface processes that can change the geochemical fingerprint of CO2 during injection, storage and any subsequent migration. Here, we analyse a natural analogue of CO2 storage, migration and leakage to the atmosphere, using noble gas and stable isotopes to constrain the effect of these processes on the geochemical fingerprint of the CO2. We present the most comprehensive evidence to date for mantle-sourced CO2 in southeast Australia, including well gas and CO2-rich mineral spring samples from the Otway Basin and Central Victorian Highlands (CVH). 3 He/ 4 He ratios in well gases and CO2 springs range from 1.21 to 3.07 RA and 1.23-3.65 RC/RA, respectively. We present chemical fractionation models to explain the observed range of 3 He/ 4 He ratios, He, Ne, Ar, Kr, Xe concentrations and δ 13 C(CO2) values in the springs and the well gases. The variability of 3 He/ 4 He in the well gases is controlled by the gas residence time in the reservoir and 2 associated radiogenic 4 He accumulation. 3 He/ 4 He in CO2 springs decrease away from the main mantle fluid supply conduit. We identify one main pathway for CO2 supply to the surface in the CVH, located near a major fault zone. Solubility fractionation during phase separation is proposed to explain the range in noble gas concentrations and δ 13 C(CO2) values measured in the mineral spring samples. This process is also responsible for low 3 He concentrations and associated high CO2/ 3 He, which are commonly interpreted as evidence for mixing with crustal CO2. The elevated CO2/ 3 He can be explained solely by solubility fractionation without the need to invoke other CO2 sources. The noble gases in the springs and well gases can be traced back to a single end-member which has suffered varying degrees of radiogenic helium accumulation and late stage degassing. This work shows that combined stable and noble gas isotopes in natural gases provide a robust tool for identifying the migration of injected CO2 to the shallow subsurface.

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The influence of oxygen isotope exchange between CO2 and H2O in natural CO2-rich spring waters: Implications for geothermometry

Cited by 54 publications

References 64 publications

Evidence of a water δ18O negative shift driven by intensive deep CO2 upflow at Shiwaga gas field (Rungwe, Tanzania)

Evidence of a water δ18O negative shift driven by intensive deep CO2 upflow at Shiwaga gas field (Rungwe, Tanzania)

Hydrogeochemistry, Geothermometry, and Genesis of the Hot Springs in the Simao Basin in Southwestern China

Tracing the migration of mantle CO2 in gas fields and mineral water springs in south-east Australia using noble gas and stable isotopes

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