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Evaporites and carbonates intercalated with volcanic beds are distributed in the Jialingjiang and Leikoupo Formations straddling the boundary of the Lower and Middle Triassic in the Sichuan Basin. ...

Strontium isotopes, water chemistry and whole rock chemistry have been used to investigate the evolution of water from its surface meteoric composition into methane-rich groundwater. Previous studies established that co-produced Surat Basin coal seam gas waters from the Walloon Subgroup (Queensland, Australia) are meteoric in origin and are distinct across the main production regions but the dominant hydrochemical processes have yet to be determined. In this study, strontium isotope ratios (87Sr/86Sr) were measured on production waters from 36 coal seam gas wells, 14 sequentially leached host rock samples and 6 whole rock samples to improve understanding of the water-rock reactions that control spatial variability in solute and isotope chemistry. Strontium isotope ratios of Walloon Subgroup production waters across all production areas are uniformly low in value, ranging from 0.70338 to 0.70456. The majority of values are significantly lower than shallow Walloon formation waters in the recharge zone and extend the lower range of 87Sr/86Sr ratios recorded for Surat Basin groundwaters. These very low 87Sr/86Sr ratios (0.70338) are reached early along the flow paths, within 10 km of the shallow recharge area waters, before then undergoing a gradual increase with flow distance. Mineralogical and geochemical analyses of whole rock samples representing each of the main lithologies across the Walloon Subgroup has identified that the low 87Sr/86Sr ratios are not derived from any one interval but rather the combination of the same few minerals that are present in every unit. The rapid accumulation of relatively non-radiogenic strontium early in the flow path across all three gas producing regions has been attributed to a combination of fluid-rock interactions occurring within the Walloon Subgroup itself. Initial surface 87Sr/86Sr ratio values are quickly dominated through a combination of processes whereby recharge waters with low Sr concentrations are absorbed onto montmorillonite clays via cation exchange and this combined with weathering of plagioclase causes a re-equilibration of the groundwater to lower 87Sr/86Sr ratios. Strontium ratios then start to slowly increase again with flow distance through silicate weathering of K-feldspars and muscovites, which are present at low levels across the basin. Local geological features such as the Hutton-Wallumbilla fault and the Kogan and Undulla anticlines appear to influence flow paths and consequently water and gas composition.

Near-surface leakage detection is often a crucial part of verifying the success of CO2 sequestration projects, and it cannot be achieved without a detailed description of the natural state of an operational site prior to injection. Without baseline studies, it is difficult to define CO2 anomalies outside natural variation in the subsurface that may be related to leakage. CO2 concentrations and δ13C-CO2 values (of DIC, dissolved gas, and soil gas) were investigated to establish a baseline modelling of natural chemical processes leading to CO2 occurrence and δ13C-CO2 fractionation in the soil-groundwater interface on an example at the Glenhaven site in Queensland, Australia. This was analysed within the context of the hydrogeology and hydrogeochemistry of a shallow aquifer system (

This study was carried out to document the source and stable isotopic characteristics of coal bed gas and associated coal bed water samples of the Raniganj Basin, West Bengal, India. The Raniganj Basin is one of the largest coal bed gas-producing sites in India. However, the gas isotopic composition of this basin was not well investigated until now. The exploration has been focused on mature coals with a high content of assumed thermogenic methane. Interestingly, the present study has revealed that although the gas is thermogenic, there is a significant effect of microbial activities in gas generation. The gas explored from this Basin contains almost 98–99% methane (CH4) in general with very little portions of other hydrocarbons and thus, this gas can be considered as “dry gas”. It is consistent also with late-stage microbial alteration of thermogenic gases. The δ13C and δD values of CH4 range from −47.4 to −49.7‰ and −207 to −211‰ respectively across the three wells as well as from −48.8 to −50.1‰ and −209 to −211‰ respectively in the gas samples collected from gas gathering station. The Whiticar style cross plot of these two parameters reveals that the gas samples have mixed thermogenic and biogenic sources and the microbial gas was generated through the CO2 reduction pathway rather than the acetate fermentation pathway. The difference in δD values of water and methane samples [δD (H2O-CH4)], that varies from 173 to 175‰, may also exhibit that the biogenic methane was produced through reduction of CO2. The stable hydrogen and oxygen isotopic signatures of formation water samples (δD and δ18O-H2O) stand with the mixed origin of the gas. The cross-plot of these two parameters reveals that the water samples lie almost along the Global Meteoric Water Line (GMWL), which may suggest the combined effect of methanogenesis due to mixing of coal seam formation water with modern meteoric water. In summary, the produced coal bed gas from the Raniganj Basin, although being largely thermogenic in origin, has been influenced by secondary microbial alteration.

Hydrochemical data responds at a much slower rate to changes in groundwater conditions than does the propagation of hydraulic pressure, and therefore may provide more insight to groundwater flow paths. In low rank coal measures, where gas is biogenic, it is important to understand the fluid-rock and microbial interactions that affect the spatial and temporal distribution of groundwater composition. Pressure data may not reflect true groundwater conditions pre-anthropogenic influence, nor does it provide information on the main drivers of groundwater composition, actual aquifer behaviour or even prove groundwater flow. This study uses a process-based approach to interpret a combination of tracer (Cl, C, Sr/Sr, O/O) and hydrochemical data obtained from coal seam gas production wells to identify the main geochemical processes and thus controls on the groundwater composition in different coal seam producing areas of the Walloon Subgroup, Surat Basin, Australia. This is arguably one of the largest coal seam gas producing regions in the world. Tracer data measured in this study show that the Walloon Subgroup behaves as a stagnant aquitard, as indicated by the almost total loss of cosmogenic tracers over relatively short groundwater flow distances (~15 km), suggestive of very low ground water flow velocities. The range of Cl is 9.0 to 23.8 (x 10) while the Cl values across the Undulla anticline in the eastern edge of the basin, are essentially the same (12.2–14.7) within analytical error. It is argued that these isotopic values represent secular equilibrium for the Walloon Subgroup. Radiometric carbon (C) levels across all three production areas (Roma, Undulla Nose, Kogan Nose) are also too low (range = 0.12–1.95 pMC) for viable field interpretation largely owing to the long residence time of the groundwater and the local activity of methanogens. Groundwater flow velocity was estimated to be

Carbon and hydrogen isotope compositions of CH 4 generated via methanogenesis in cultures of South Sumatra Basin (SSB) coalbed methane (CBM) formation waters grown on coal, acetate and H 2 + CO 2 were investigated. CH 4 production and molecular analysis confirmed the presence of active microbial communities that are able to convert coal into CH 4 using both acetoclastic and hydrogenotrophic pathways. The representative bacterial sequences were dominated by Bacteroidetes , Firmicutes and Deltaproteobacteria , while Methanosaeta and Methanosarcina were the most prevalent archaeal methanogens present in the cultures. CH 4 produced in this study's culturing experiments has δ 13 C values in the range of − 50 ‰ to − 20 ‰, with most values falling outside the current understanding of the carbon isotopic boundaries for biogenic CH 4 (− 110 ‰ to − 30 ‰). However, the corresponding apparent carbon isotopic α factor ( α c = 1.02 ± 0.006), and isotopic effect ( e c = − 20.1 ‰ ± 15.3) showed that CH 4 in SSB cultures was predominantly produced by acetoclastic methanogenesis, which is consistent with the results of molecular DNA analysis. In addition, the calculated contribution of CO 2 reduction from the δ 13 C values of coal-treated cultures was overall 4 production in the SSB cultures. The outcome of this experimental study also suggests that δ 2 H-CH 4 values may not provide a reliable basis for distinguishing methanogenic pathways, while apparent carbon isotopic fractionation factor ( α c ) and isotope effect ( e c ) are considered more useful indicators of the methanogenic pathway. The high δ 13 C-CH 4 values (≥ 30 ‰) and the dominance of Methanosaeta over Methanosarcina indicate that methanogens within the SSB cultures were operating at low substrate concentrations. An unusually positive δ 13 C-CH 4 suggests a substrate depletion effect, which is thought to be related to a decrease in the relative abundance of key bacterial coal degraders with formation water inoculum storage time. Closer observation of δ 13 C-CH 4 values during the growth of cultures within a single experiment also showed a 13 C-enrichment trend over time. At log phase of growth, the CH 4 produced was 13 C-depleted when compared to the stationary phase that also indicates substrate depletion effects. Finally, the δ 13 C-CH 4 values encountered in this study (as high as − 20 ‰) highlight the possible positive extension of δ 13 C-CH 4 values of acetoclastic methanogenesis from those currently reported in the literature for natural and experimental samples (as high as − 30 ‰).

The Surat Basin hosts various industries that extract groundwater including coal seam gas (CSG), feedlots, and agriculture. With water drawdown, gas has been observed in some bores drawing groundwater from different aquifers across the Basin. While methane can occur naturally in aquifers, biogenic CSG has been extracted from the Walloon Coal Measures raising questions on the sources of gas in overlying aquifers. Current standard monitoring uses a direct fill approach to measure dissolved methane concentrations in vials; however, this approach may lose gas present above solubility levels. Water and gas sampling was performed on bores in the Springbok, Gubberamunda, Mooga, Hutton, and Precipice Sandstones, the Orallo Formation, and the Condamine Alluvium. Water bores and CSG production wells from the Walloon Coal Measures were also sampled. We compared direct fill with a closed sampling method for dissolved gas, plus a method for sampling the total free and dissolved gas in the field. Higher dissolved and total methane concentrations were measured using closed sampling methods, especially in gassy bores. The majority of our sampled aquifer gases and waters have stable isotopic signatures distinct from CSG, where methane had likely been formed insitu in shallow aquifers by primary microbial CO2 reduction or fermentation processes. In several gassy bores, the source of the methane could not be clearly identified. This study indicates that (1) current monitoring methods may be underestimating methane concentrations above identified thresholds especially in gassy bores and (2) a combination of isotopic techniques may distinguish methane sources and interaquifer disconnectivity in the majority of cases.

The Walloon Subgroup coal seam gas (CSG) play in the Surat Basin, Queensland, is Australia's pre-eminent onshore gas field. Concerted multi-disciplinary research is underway investigating the distribution, origin and composition of waters and gases in this dominantly microbial CSG reservoir, to guide both continued production and potential microbially enhanced coal bed methane (MECoM) applications. However, prior to the present research, a detailed study of co-produced waters and gases from across the Surat Basin was not available in the public domain. This study tested whether co-produced water compositional and stable isotopic data show relationships with production gas stable isotope compositions, to elucidate further evidence for microbial CO2 reduction and explore the down-dip geochemical evolution of Walloon coal bed waters and gases. A total of 41 wells were sampled with 50 water and 25 gas samples spanning the 3 major production areas of the Surat Basin. Detailed isotopic and hydrochemical analysis of these samples revealed distinct spatial trends between the different production locales. Water compositions were distinct for each of the production regions reflecting the different lithologies of adjacent recharge zones, differing fluid–rock interactions, likely different microbial consortia, and the extent of methanogenesis. On the western side of the basin near Roma, waters were the ‘freshest’ with the lowest median values for alkalinity (861 mg/L), and Cl− (588 mg/L) and a δ13CDIC of 14.2‰. On the eastern side of the basin, the Kogan Nose waters were the most saline with the highest median values for Na+ (1955 mg/L), Cl− (2280 mg/L) and δ13CDIC (20.0‰). Also in the east, in the present gas fairway, the Undulla Nose waters had the highest median alkalinity (1841 mg/L) and were found to have a Na+ excess (median = 1050 mg/L) and a lower than expected median δ13CDIC (14.0‰). Co-mingled, produced methane carbon isotope values (δ13C − 57.0‰ to − 44.5‰) from both the upper (Juandah) and lower (Taroom) coal measures plot within the mixed ‘thermogenic/microbial’ genetic field. By contrast, deuterium isotopic difference [Δ2H(H2O–CH4)] values and cross-plots of δ2H–H2O and δ18O–H2O suggest that microbially mediated CO2 reduction is the dominant methane generation process in situ. At a given depth, the Undulla Nose waters in the east are more depleted in 2H and 18O than elsewhere in the Surat Basin, which may suggest these samples have been more heavily impacted by water–rock–microbial reactions. 14C values from the 3 production regions (0.115 to 1.769 pmC; age: 32,400 to > 50,000 years before present (B.P.)) suggest that Walloon coals likely recharged in the last ~ 50,000 years (limit of radiocarbon dating). Consistent with these dates, δ2H–H2O and δ18O–H2O values for the Surat Basin (δ2H − 32‰ to − 56‰, δ18O − 5.9‰ to − 9.0‰) echo the stable isotopic composition of meteoric waters during the initial part of the last glacial period in southeast Queensland. Based on a strong correlation between δ2H–CH4 and δ2H–H2O, we suggest that methane was generated since the Late Pleistocene. PCA analysis showed a degree of positive correlation between total alkalinity and both the δ13CDIC (median 14.2‰) and δ13C–CH4 (median − 52.1‰) vectors that is consistent with finite reservoir effects. The results inform ongoing studies of gas distribution and origins and MECoM potential in the Surat Basin, and underpin a broader study examining aquifer interactions.

The sustainable in situ regeneration of microbial (biogenic) methane or microbially enhanced coal bed methane (‘MECoM’) is an emerging concept being investigated globally. Promising results and recommendations of a preliminary culture study of Walloon Subgroup co-produced coal seam gas (CSG) waters from the Surat Basin, Queensland established the presence of viable methanogens and suggested that in situ methanogenesis could be stimulated using physical and chemical reservoir treatments. This paper represents the culmination of a stepwise basin analysis project ultimately aimed at siting potential in situ bioreactor locations in the eastern Surat Basin. The integration of stratigraphically located data on the molecular and isotopic composition of desorbed gases, host coal properties and spatially associated waters through the core production zone has allowed the spatial variability and relative influence of hydro-geological factors on methanogenesis to be evaluated in detail for the first time. Higher gas contents and systematically enriched CH 4 and CO 2 carbon isotopic compositions in the stratigraphically central coal seams (oldest-youngest: in the upper Taroom Coal Measures, Tangalooma Sandstone lower Juandah Coal Measures) are best explained by increased rates of microbial CO 2 reduction and substrate depletion. There is a building case to trial MECoM in the central coal seams in a depleted/underperforming well in an area of high permeability. Integrated microbiological, chemical engineering, hydro-chemical and geological studies are ongoing to further enhance understanding of Walloon Subgroup CSG and the bioreactor potential of the Surat Basin.

Coupling carbon and nitrogen isotopes and petrography of coals and related intra-seam carbonaceous mudstone partings from basins in northern China provides insight into regional palaeoenvironments and palaeoclimate during the late Carboniferous–early Permian. The carbon isotopic composition (δ13Ccoal, VPDB) of coal samples from the Taiyuan and Shanxi formations of Qinshui and North China-Bohaiwan basins ranges from −25.3‰ to −22.7‰, with an average of −23.7‰. The average δ13Ccoal value is −23.6‰ in the late Carboniferous, −23.4‰ in the early Permian and −23.5‰ in the mid–early Permian. By contrast, equivalent early Permian coals in the southern North China-Bohaiwan Basin to the east were found to be significantly more negative at −25.2‰, likely as a function of regional aridity changes. Related δ15N in coal seams ranges from +2.3‰ to +4.7‰, with an average of +3.7‰. Within the thick, economically important #15coal seam of the Qinshui Basin, δ15Ncoal is significantly more negative than δ15N in mudstone partings (avg. +7.1‰), implying that the coals underwent a stronger degree of microbial degradation during peat formation. δ15N of mudstone partings varies stratigraphically, with significantly more positive δ15N (+8.1‰, +8.3‰) for the lower partings and lower δ15N (+4.8‰) for the upper parting. This may reflect varying degrees of microbial activity, but could reflect higher thermal maturity in the upper part of the seam as indicated in the coal rank profile. δ13Ccoal in this region was used to calculate the carbon isotopic composition of atmospheric CO2(δ13Ca). Calculated δ13Ca ranges from −6.0‰ to −3.4‰, with an average of −4.5‰, which is more positive than the δ13Ca of modern atmospheric CO2(−8.5‰, Graven et al., 2017). Two δ13Ca excursions are noted: a positive one (magnitude 3.7‰) in the late Carboniferous and a tentative negative excursion (magnitude 6.0‰) in the mid–early Permian. The positive shift coincided with a sea-level transgression in the Qinshui Basin. The rise in sea level may have led to the burial of more terrestrial plant debris that decreased photosynthesis and enriched atmospheric CO2in 13C. More data are needed to understand mid-early Permian variation in δ13C, as this could reflect a regional aridity or humidity effect rather than a global signal.

This study used compositional and stable isotopic analysis to test hypotheses on the distribution and origins of Walloon Subgroup coal seam gas (CSG) in the eastern Surat Basin, Queensland, Australia. The Middle Jurassic Walloon Subgroup play differs from many other low-rank CSG plays-particularly in methane carbon isotopic signature, i.e., the CSG is not as 'microbial' as could be expected. The carbon isotope compositions of desorbed methane from three cored appraisal wells fall within the generally accepted range for thermogenic or mixed gas (δ13C -58.5‰ to -45.3‰). The δ13C-CH4 values from stratigraphically placed coal core samples increased (became more 'thermogenic') from the top of the upper (Juandah) coal measures to the base of the Tangalooma Sandstone. Below the Tangalooma Sandstone, in the lower (Taroom) coal measures, the δ13C-CH4 values decreased with increasing depth. These positively parabolic δ13C profiles tracked total measured gas content in two out of the three wells studied. The third well displayed lower variance of δ13C-CH4 and gas content increased uniformly with depth.A genetic classification based on methane stable carbon isotopes alone might interpret this pattern as a transition from microbially- to thermogenically-sourced methane in the central coal seams. However, a δ13C-CO2 profile for one well tracks total gas content and δ13C-CH4, and exhibits an inverse relationship with δD-CH4. These results, together with the mostly dry nature of the gas samples [(C1/(C2+C3)) ratios up to ~10,000] and relatively uniform δD-CH4 values (δD -238‰ to -202‰), suggest that microbial CO2 reduction is the primary source of Walloon Subgroup methane. As such, stratigraphic variations in gas content mainly reflect the extent of microbial methanogenesis. We suggest that peak microbial utilisation of H2-CO2 occurred at the Tangalooma Sandstone level, enriching the residual CO2 pool and derived methane in 13C. Carbon [δ13C(CO2-CH4)] and deuterium isotopic differences [δD(H2O-CH4)], and cross-plots of δD-H2O and δ18O-H2O are also consistent with kinetic isotope fractionation during microbial-mediated carbonate reduction. The results are relevant for applying microbially enhanced coal bed methane (MECoM) in the Surat Basin.

The Late Permian coal measures of the Bowen Basin, Australia express both environmental and climatic changes that occurred prior to the Permian Triassic (P–T) boundary. In order to decouple the influence of environmental factors (salinity, pH, base level and temperature) from depositional and climatic factors (atmospheric CO2) in organic δ13C, a high resolution study was performed on 24 coal seams (total 24.6 m) in the Late Permian stratigraphy in the northern Bowen Basin. The Late Permian stratigraphy of the Bowen Basin records a transition from deltaic and lacustrine conditions within the Tinowan Formation and Black Alley Shale Formation, to fluvial deposition in the Kaloola and Bandanna Formations. Intermittent volcanism is recorded by tuff layers during periods of peat accumulation. Variations of coal lithotypes were recorded and formed the basis of sampling for petrography and isotope analysis. Coal samples were etched to expose cellular anatomy, and systematically identified to recognise palaeoflora assemblages. When observed within seam, δ13C of the coal varied cyclically (13C enriched-depleted-enriched) as a response to environmental changes expressed in palaeoflora communities. The total range of δ13C was − 26.6‰ to − 21.9‰. The overall trend of δ13C progresses to increasing 13C enrichment, corresponding with dull lithotypes (rich in inertinite) which indicate fluctuations in base level. The 13C enrichment peaks at − 22.5‰ within the Kaloola Member and shifting rapidly toward a depletion (maximum − 26.6‰) of 13C in the upper Bandanna Formation, prior to the P–T boundary. These changes are expressed in palaeoflora communities where ecosystems shifted from dominant Glossopteris flora, to climax community flora including Palaeosmunda, Cycadales and Ginkgo, suited to temperate, early Mesozoic climates. The results of this study represent an insight into the effects of environmental variables on 13C uptake of plants. The identification of flora within coal gives an insight into palaeowetland evolution, and can be partnered with classic petrographical techniques for integrated analysis in coals. Both the geochemistry and the anatomical aspects of coal represent an important tool for future palaeowetland research.

High-CO2-containing coal seams in the Oaky Creek area of the Bowen Basin, eastern Australia provide natural analogues of the processes likely to occur as a result of CO2 injection and storage in coal systems. We conducted mineralogical, stable and radiogenic isotope and major element analyses of mudstones and sandstones adjacent to the coal seams and stable isotope and compositional studies of coal seam gas desorbed from the coals to establish the impact of the high CO2 levels and the mechanisms that keep the CO2 naturally sequestered. Siderite is the earliest carbonate phase present and occurs with kaolinite in mudstones and sandstones. It is interpreted to have formed under low-temperature, reducing conditions where methanogenesis has produced residual 13C-enriched CO2. Enhanced kaolinite concentrations adjacent to a low-CO2-containing coal seam reflect interaction with acidic fluids produced during the coalification of organic matter. Stable isotope data for carbonates and Rb–Sr isochron ages for illit...

Intensive carbonate and clay mineral authigenesis took place throughout the Late Permian Bowen-Gunnedah-Sydney basin system in eastern Australia. We conducted isotopic and trace element analyses of carbonate and clay minerals from clastic sedimentary rocks of the Gunnedah Basin and the Denison Trough in the Bowen Basin. Rb-Sr isochron age data of the illitic clays are consistent with episodic hydrothermal fluid flow events that occurred in association with Gondwana rifting accompanied by alkaline magmatism at similar to 85 Ma and similar to 95 Ma. Stable isotope data of carbonate and clay minerals from the Gunnedah Basin are indicative of meteoric waters from a high-latitude environment as the main fluid source, whereas trace element, Sr and Nd isotope data highlight mixing of meteoric fluids with magmatic and/or crustal components, with a possible input from marine carbonates for some samples. Trace metals, oxygen and strontium isotopes of dawsonites from the Denison Trough are interpreted to have been mobilised by fluids that interacted with evolved clastic sedimentary and marine carbonate end members. According to the carbon isotope data, CO2 for calcite and ankerite precipitation was sourced mainly from thermal degradation of organic matter and magmatism, whereas the CO2 used for dawsonite formation is inferred to have been derived from magmatic and marine sources. In the low permeability environments (particularly in coal seams), the increasing accumulation and oversaturation of CO2 particularly promote the precipitation of dawsonite. (C) 2011 Elsevier Ltd. All rights reserved.

Southwest Turkey is seismically active as a result of the Hellenic subduction process in the Eastern Mediterranean. We conducted high-resolution micro-sampling, high-precision U-series dating and microchemical analysis on an extensional vein system in a tectonically active but non-hydrothermal area. U/Th age data and microscopic observations provide evidence of repeated fracturing of a previously sealed crack system followed by a new increment of veining. Repeated injection of veinlets suggests that the vein system was formed by the crack-seal mechanism. Four major U/Th age groups for the emplacement of the vein system fall between 23.9 +/- 0.2 ka and 23.2 +/- 0.4 ka, 21.7 +/- 0.4 ka and 19.2 +/- 0.2 ka, 17.3 +/- 0.1 ka and 16.2 +/- 0.3 ka, and at 11.8 +/- 0.2 ka. Stable and Sr isotope geochemistry of the calcite vein samples indicates that surface water interacting with the soil cover was the major component of the groundwater system from which the extensional veins precipitated. Trace element and 0 isotope data of the vein system are interpreted to reflect carbonate precipitation associated with seismic cycles involving fluids with different trace element compositions and CO2 contents. Initial carbonate precipitation during a single seismic cycle occurred from CO2-dominated fluids that were degassed from the original CO2 water mixture. This was followed consecutively by carbonate precipitation from the remaining water, which was relatively impure with higher trace element contents. Millimetre to submillimetre-scale U-series dating in conjunction with geochemistry of carbonate veins related to active tectonism offers an innovative means of constraining the absolute timing of late Quaternary seismic and inter-seismic events. (C) 2010 Elsevier B.V. All rights reserved.

High-CO2 coal seams occur in many sedimentary basins world-wide and provide natural analogues of the processes likely to occur as a result of CO2 injection and storage in coal systems. CO2 is stored in coal predominantly as adsorbed molecules on micropore surfaces (adsorption trapping) that allow higher densities and greater volumes of CO2 at shallower depths than in sandstone and carbonate reservoirs. In the longer term CO2 will dissolve in formation water and react with minerals in the host formation (solubility/ionic trapping) and may be precipitated as carbonate minerals (mineral trapping). A recent study suggests that solubility trapping is the predominant CO2 sink in natural gas fields (Gilfillan et al., 2009), whereas our natural analogue studies in the Bowen and Gunnedah Basins, eastern Australia, indicate that CO2 has been stored in coal and sandstone formations since the Mesozoic through a combination of adsorption and mineral carbonation reactions. These differences reflect the different mineralogies and hydrogeology of the CO2-rich natural gas fields studied by Gilfillan et al. (2009) and coal systems. Our work shows that natural analogue studies of sites that have stored CO2 over geological time scales are essential to determine the mechanisms of CO2 storage and the level of characterisation required for storage site equivalents. (C) 2011 Published by Elsevier Ltd.

Coal bed methane (CBM) is a significant growing industry in Queensland's energy sector. It is, however, a relatively new industry with little local water quality data and stable isotope compositions of production waters and gases available in the public domain. This study aims to determine whether water quality and stable isotope data can be correlated with gas and groundwater production and flow pathways, and identify zones of recharge and water mixing. Stable isotope analysis and accessory water quality tests were conducted on CBM production gas and water samples collected from two CBM producing bituminous coal seams within a single field in the Bowen Basin. In the production field, the reservoir seams are gently folded with eastwardly dipping fold axes, and compartmentalised by an ENE normal fault on the flank of a broad central anticline that contains minor faults. For one seam, splitting and a change in coal quality parallels the fault and fold axes. Although virgin reservoir conditions were similar, differing production performance north and south of the main fault suggests it acts as a barrier to water and gas flow along strike. The stable isotope analysis on the production water showed that waters with more positive δD and δ18O compositions were associated with areas of higher water production and shallower depths, whereas more negative δD and δ18O compositions were associated with lower water production and high gas production. The gas isotope analysis showed that production gases had both biogenic and thermogenic origins and that secondary biogenic gas generated through CO2 reduction comprises a significant portion of the CBM produced from this field. More negative CH4 δ13C values characterize the zones of meteoric recharge in shallow, up-dip areas. Gas production data and CO2 δ13C values suggest that this may result from 13CH4 stripping by the recharge waters and/or increased biogenic activity in this area. Smaller CO2–CH4 carbon isotopic fractionation values characterized zones of meteoric recharge, whereas higher isotopic fractionation values characterized the high gas production domain.

Water reuse is becoming an integral component of the water management strategy on mine sites. This practise is being driven by corporate sustainability goals, community and societal pressures to demonstrate improved water stewardship, as well as climate and regulatory pressures. However, water reuse often results in water quality compromise which can then result in decreased recovery through problems in processing circuits, product quality, and an increased likelihood of discharge of water that cannot meet environmental regulatory requirements. On most mine sites, there is usually a disjuncture between water quantity management and water quality management with the latter being managed solely as an environmental problem. It is becoming increasingly clear that water quality and quantity must be managed as an integrated system. In order to integrate water quality and quantity management to achieve multiple objectives the dynamics of water and constituents must be understood. Using examples from a st...

The sulfur isotope record in late Archean and early Paleoproterozoic rocks is of considerable importance because it provides evidence for changes in early Earth atmospheric oxygen levels and potentially constrains the origin and relative impact of various microbial metabolisms during the transition from an anoxic to oxic atmosphere. Mass independently fractionated (MIF) sulfur isotopes reveal late Archean and early Paleoproterozoic sulfur sources in different pyrite morphologies in Western Australia's Hamersley Basin. Multiple sulfur isotope values in late Archean pyrite vary according to morphology. Fine grained pyrite has positive sulfur MIF, indicating a reduced elemental sulfur source, whereas pyrite nodules have negative sulfur MIF, potentially derived from soluble sulfate via microbial sulfate reduction. The Hamersley Basin δ 34 S–Δ 33 S record suggests that the extent of oxygenation of the surface ocean fluctuated through the Late Archean from at least 2.6 Ga, more than 150 million yr before the Great Oxidation Event. In the early Paleoproterozoic, there is less distinction between pyrite morphologies with respect to sulfur isotope fractionation, and pyrite from the Brockman Iron Formation trends toward modern sulfur isotope values. An important exception to this is the strong negative MIF recorded in layer parallel pyrite in Paleoproterozoic carbonate facies iron formation. This may suggest that deeper water hydrothermal environments remained anoxic while shallower water environments became more oxidised by the early Paleoproterozoic. The results of the current study indicate that sulfide paragenesis is highly significant when investigating Archean and early Paleoproterozoic multiple sulfur isotope compositions and sulfur sources.

Isa Superbasin strata in the Lawn Hill Platform host major base metal sulfide mineralization including the giant Century Zn-Pb deposit. Mineral paragenesis, organic maturation, K-Ar dating and stable isotope studies demonstrate that long-lived structures such as the Termite Range Fault acted as hot fluid conduits several times during the Paleoproterozoic and Mesoproterozoic. K-Ar dating of illites, in combination with other datasets, may identify three thermal events in the Lawn Hill Platform at 1500, 1440-1400 and 1250-1150 Ma. 1500 Ma is a Late Isan Orogeny age recorded only in the south that may reflect exhumation of a provenance region. The 1440-1300 Ma ages are related to fault reactivation and a thermal/?fluid pulse at ~1440-1400 Ma, with subsequent enhanced cooling. The youngest thermal/fluid flow event at 1250-1150 Ma is recorded mainly in the northeast and is probably related to the assembly of Rodinia. An extensive carbonate alteration halo in the footwall of the circa 1575 Ma Century Zn-Pb deposit extends some 15 km along strike. Calculations of fluid oxygen and carbon isotope composition based on model temperatures of 120°C for the ore zone siderites and 180°C for siderites and ankerites in the regional carbonate alteration halo indicate similar ore and alteration fluid compositions (d18O = 3 to 10 per mil; d13C = -7 to -3 per mil). This fluid isotope composition is consistent with highly evolved basinal brines and mixed inorganic and organic carbon sources. The good agreement between maximum temperature estimates from illite crystallinity and organic reflectance and inverse correlation with carbonate oxygen isotopes in northeast Lawn Hill platform boreholes indicate thermal maturation and carbonate formation resulted from interaction with the 1250-1150 Ma fluids. The calculated fluid isotope compositions are consistent with an evolved basinal brine (d18O = 5.1 to 9.4 per mil V- SMOW; d13C = -13.2 to -3.7 per mil V-PDB) that contained a significant organic carbon component. Differences in carbon and oxygen isotope systematics of alteration carbonate are significant to their use with lithogeochemical vectors in mineral exploration in the northern Australian basins.

Mudrocks and carbonates of the Isa superbasin in the Lawn Hill platform in northern Australia host major base metal sulfide mineralization, including the giant strata-bound Century Zn-Pb deposit. Mineral paragenesis, stable isotope, and K-Ar dating studies demonstrate that long-lived structures such as the Termite Range fault acted as hot fluid conduits several times during the Paleoproterozoic and Mesoproterozoic in response to major tectonic events. Illite and chlorite crystallinity studies suggest the southern part of the platform has experienced higher temperatures (up to 300 degrees C) than similar stratigraphic horizons in the north. The irregular downhole variation of illite crystallinity values provides further information oil the thermal regime in the basin and shows that clay formation was controlled not only by temperature increase with depth but also by high water/rock ratios along relatively permeable zones. K-Ar dating of illite, in combination with other data, may indicate three major thermal events in the central and northern Lawn Hill platform Lit 1500, 1440 to 1400, and 1250 to 1150 Ma. This study did not detect the earlier Century base metal mineralizing event at 1575 Ma. 1500 Ma ages are recorded only in the south and correspond to the age of the Late Isan orogeny and deposition of the Lower Roper superbasin. They may reflect exhumation of a provenance region. The 1440 to 1300 Ma ages are related to fault reactivation and a thermal pulse at similar to 1440 to 1400 Ma possibly accompanied by fluid flow, with subsequent enhanced cooling possibly due to thermal relaxation or further crustal exhumation. The youngest thermal and/or fluid-flow event at 1250 to 1150 Ma is recorded mainly to the cast of the Tern-lite Range fault and may be related to the assembly of the Rodinian supercontinent. Fluids in equilibrium with illite that formed over a range of temperatures, at different times in different parts of the platform. have relatively uniform oxygen isotope compositions and more variable hydrogen isotope compositions (delta O-18 = 3.5-9.7 parts per thousand V-SMOW; delta D = -94 to -36 parts per thousand V-SMOW). The extent of the 180 enrichment and the variably depleted hydrogen isotope compositions suggest the illite interacted with deep-basin hypersaline brines that were composed of evaporated seawater and/or highly evolved meteoric water. Siderite is the most abundant iron-rich gangue phase in the Century Zn-Pb deposit, which is surrounded by all extensive ferroan carbonate alteration halo. Modeling suggests that the ore siderite formed at temperatures of 120 degrees to 150 degrees C, whereas siderite and ankerite in the alteration halo formed at temperatures of 150 degrees to 180 degrees C. The calculated isotopic compositions of the fluids are consistent with O-18-rich basinal brines and mixed inorganic and organic carbon Sources (6180 = 3-10 parts per thousand V-SMOW, delta C-13 = -7 to -3 parts per thousand V-PDB). in the northeast Lawn Hill platform carbonate-rich rocks preserve marine to early diagenetic carbon and oxygen isotope compositions, whereas ferroan carbonate cements in siltstones and shales in the Desert Creek borehole are O-18 and C-13 depleted relative to the sedimentary carbonates. The good agreement between temperature estimates from illite crystallinity and organic reflectance (160 degrees-270 degrees C) and inverse correlation with carbonate delta O-18 values indicates that organic maturation and carbonate precipitation in the northeast Lawn Hill platform resulted from interaction with the 1250 to 1150 Ma fluids. The calculated isotopic compositions of the fluid are consistent with evolved basinal brine (delta O-18 = 5.1-9.4 parts per thousand V-SMOW; delta C-13 = -13.2 to -3.7 parts per thousand V-PDB) that contained a variable organic carbon component from the oxidation and/or hydrolysis of organic matter in the host sequence. The occurrence of extensive O-18- and C-13-depleted ankerite and siderite alteration in Desert Creek is related to the high temperature of the 1250 to 1150 Ma fluid-flow event in the northeast Lawn Hill platform, in contrast to the lower temperature fluids associated with the earlier Century Zn-Pb deposit in the central Lawn Hill platform.

Mineralogical, hydrochemical and S isotope data were used to constrain hydrogeochemical processes that produce acid mine drainage from sulfidic waste at the historic Mount Morgan Au–Cu mine, and the factors controlling the concentration of SO4 and environmentally hazardous metals in the nearby Dee River in Queensland, Australia. Some highly contaminated acid waters, with metal contents up to hundreds of orders of magnitude greater than the Australia–New Zealand environmental standards, by-pass the water management system at the site and drain into the adjacent Dee River. Mine drainage precipitates at Mt. Morgan were classified into 4 major groups and were identified as hydrous sulfates and hydroxides of Fe and Al with various contents of other metals. These minerals contain adsorbed or mineralogically bound metals that are released into the water system after rainfall events. Sulfate in open pit water and collection sumps generally has a narrow range of S isotope compositions (δ34S = 1.8–3.7‰) that is comparable to the orebody sulfides and makes S isotopes useful for tracing SO4 back to its source. The higher δ34S values for No. 2 Mill Diesel sump may be attributed to a difference in the source. Dissolved SO4 in the river above the mine influence and 20 km downstream show distinctive heavier isotope compositions (δ34S = 5.4–6.8‰). The Dee River downstream of the mine is enriched in 34S (δ34S = 2.8–5.4‰) compared with mine drainage possibly as a result of bacterial SO4 reduction in the weir pools, and in the water bodies within the river channel. The SO4 and metals attenuate downstream by a combination of dilution with the receiving waters, SO4 reduction, and the precipitation of Fe and Al sulfates and hydroxides. It is suggested here that in subtropical Queensland, with distinct wet and dry seasons, temporary reducing environments in the river play an important role in S isotope systematics

A new, fast, continuous flow technique is described for the simultaneous determination of 633 S and delta(34)S using SO masses 48, 49 and 50. Analysis time is similar to5min/sample with measurement precision and accuracy better than +/-0.3parts per thousand. This technique, which has been set up using IAEA Ag2S standards S-1, S-2 and S-3, allows for the fast determination of mass-dependent or mass-independent fractionation (MIF) effects in sulfide, organic sulfur samples and possibly sulfate. Small sample sizes can be analysed directly, without chemical pre-treatment. Robustness of the technique for natural versus artificial standards was demonstrated by analysis of a Canon Diablo troilite, which gave a delta(33)S of 0.04parts per thousand and a delta(34)S of -0.06parts per thousand compared to the values obtained for S-1 of 0.07parts per thousand and -0.20parts per thousand, respectively. Two pyrite samples from a banded-iron formation from the 3710 Ma Isua Greenstone Belt were analysed using this technique and yielded MIF (Delta(33)S of 2.45 and 3.31parts per thousand) comparable to pyrite previously analysed by secondary ion probe. Copyright (C) 2004 John Wiley Sons, Ltd.

Oxygen and hydrogen isotope analyses were carried out on authigenic clay minerals from Late Permian coal measures of the Bowen Basin (Australia). In the northern Bowen Basin, the oxygen isotope compositions of the mixed-layer illite/smectite show significant irregular variations with respect to depth, which parallel the changes in the extent of the illitisation reaction and are interpreted as reflecting changes in water/rock ratio in turn related to permeability. The δ18O and δD values of illite–smectite and kaolinite in the northern Bowen Basin and the calculated fluid isotopic composition (δ18O=−3‰ to +1‰; δD=−70‰ to −90‰) in equilibrium with these clays are considerably lower than those typically reported for deeply buried sedimentary basins. These stable isotope data, together with relatively high inferred palaeotemperatures (up to 235°C) and abnormally high geothermal gradients are consistent with a hydrothermal origin for clay mineral formation in the northern Bowen Basin. The hydrothermal system is interpreted to be a result of the Late Triassic extensional tectonic regime, which developed in large parts of eastern Australia and affected the northern part of the Bowen Basin. In the southern Bowen Basin, by contrast, clays are more enriched in 18O and deuterium, which is explained by lower temperatures (in the shallow coal measures) and a significant enrichment in the fluid isotopic composition (δ18O=−3.6‰ to +5.6‰, δD=−66‰ to −35‰) under low water/rock ratio conditions, especially in deeper pelitic rocks.

Raine Island is a small vegetated coral cay that is capped by recent insular phosphate rock. On the northeastern shore, phosphate rock also extends into the intertidal zone, where it is juxtaposed against calcareous beachrock. A petrological and isotopic study was carried out on the phosphate rock in order to clarify some of the uncertainties concerning the genesis of insular phosphate rocks in general and on Raine Island in particular. The main phosphate mineral is dahllite (carbonate hydroxyapatite), which occurs as microlaminated grain coatings and as a bioclast replacement. Minor pore-filling whitlockite ( tricalcium phosphate) was recorded in one sample. Organic carbon is intimately associated with phosphate cement and accounts for color variations between microlaminae. Phosphate 18Op (SMOW) values range from 14.4 to 16.6o/oo, indicating that phosphatic porewaters were entirely fresh and had not undergone evaporative 18O enrichment. Phosphate cement records the passage of both downward-percolating near-surface porewater and seaward-moving groundwater at or close to the freshwater-saltwater interface. Intertidal phosphatic rock on the northeastern shore is a rare example of a lithified, intertidal tropical beach sand deposit with a definite fresh-water origin.

Recent developments in multiple sulfur isotope analysis of sulfide and sulfate minerals provide a new tool for investigation of ore-forming processes and sources of sulfur in Archean hydrothermal systems, with important implications for the Archean sulfur cycle, the origin and impact of various microbial metabolisms and the chemistry of surface waters. In the current study we show that most of the sulfides and sulfates in the 3.49 Ga Dresser Formation and 3.24 Ga Panorama Zn–Cu field of Western Australia have non zero Δ33S values that indicate variable proportions of seawater sulfate and elemental sulfur of UV-photolysis origin were incorporated into the deposits. Our results show that the multiple sulfur isotope systematics of the Dresser Formation sulfides and sulfates mainly reflect mixing between mass independently fractionated sulfur reservoirs with positive and negative Δ33S. Pyrite occurring with barite is depleted in 34S relative to the host barite that has been interpreted as evidence for microbial sulfate reduction. We note, however, that the reported quadruple sulfur isotope systematics of pyrite-barite pairs are equally permissive of a thermochemical origin for this pyrite, which is consistent with inferred formation temperatures for the chert-barite units in excess of 100°C. The variably positive Δ33S anomalies of the Panorama VHMS deposits, disequilibrium relations among sulfides and sulfates and general trend of increasing sulfide Δ33S with stratigraphic height in individual ore systems most likely reflects temperature evolution and fluid mixing through the life of the hydrothermal system. The absence of sulfides with significant negative Δ33S anomalies suggests that volcanic sulfur, not seawater sulfate, was the dominant sulfur source for the Panorama mineral system. The data presented here require Paleoarchean seawater to be at least locally sulfate bearing.

The Permo-Trias sic Bowen Basin is the northernmost structural element of the ca. 2000 km long Bowen—Gunnedah—Sydney Basin System in eastern Australia (Figure 1). The Bowen Basin formed through back-arc extension and foreland subsidence prior to the break-up of Gondwana, resulting in a series of distinct domains reflecting basement morphology and the effects of tectonism (Fielding et al., 1990; Murray, 1990; de Caritat and Braun, 1992). It contains up to 10 000 m of terrestrial and shallow marine siliciclastic sediments (Totterdell et al., 1995), and is economically significant, containing abundant coal and widespread accumulations of coal seam and natural gas.

Coal seam gases collected from Bowen Basin cores have moderately negative methane carbon isotope compositions (−51 ± 9 per mil) which overlap the published range for Australian coal seam methane of −60 ± 11 per mil. No systematic relationship between coal rank and methane δ13C value is apparent. A thermogenic origin for methane has been assigned when its carbon isotope composition is heavier than −60 per mil, although biogenic methane generated in closed systems may have similar δ13C values from −60 to −40 per mil depending on the methanogenic pathway and the carbon isotope composition of the source. Subordinate inputs from biogenic methane could account for some of the isotopic variability of the desorbed methane; however, a good correlation between desorbed methane volumes and bitumen/pyrobitumen content suggests that much of the methane sorbed in the coal was produced by secondary cracking of bitumen.