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Near-surface leakage detection is often a crucial part of verifying the success of CO 2 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 CO 2 anomalies outside natural variation in the subsurface that may be related to leakage. CO 2 concentrations and δ 13 C-CO 2 values (of DIC, dissolved gas, and soil gas) were investigated to establish a baseline modelling of natural chemical processes leading to CO 2 occurrence and δ 13 C-CO 2 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 (<20 m depth). The Glenhaven site and its five monitoring station are located in an area which is a candidate for a future small scale carbon storage pilot project. We combine major ion, stable isotope data of groundwater and soil gas as well as physical hydrogeology data with extensive isotope models to explain the pathways and origins of groundwater and CO 2 . The results indicate shallow aquitard claystone units at the site restrict vertical groundwater leakage and inter-aquifer mixing. Groundwater chemistry is controlled by transpiration of plants, cation exchange, weathering and meteoric recharge to produce Na-Cl and Na-HCO 3 -Cl type waters. δ 18 O and δ 2 H values suggest a shallow meteoric recharge source largely unaffected by evaporation. CO 2 concentrations in soil and dissolved in groundwater range between 631 and 47,516 ppm and δ 13 C values average −17 and −21‰. The mixing of three potential CO 2 sources is discussed: 1) the aerobic decay of C 3 plant matter, 2) the aerobic decay of C 4 plant matter and, 3) shallow coal related CO 2 . Despite this, the variability of CO 2 concentrations and equivocal sources is not likely to hinder leakage detection in the future of site monitoring. [ABSTRACT FROM AUTHOR]

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°C) than similar stratigraphic horizons in the north. The irregular downhole variation of illite crystallinity values provides further information on 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 at 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 ∼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 east of the Termite 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 (δ18O = 3.5-9.7‰ V-SMOW; δD = -94 to -36‰ V-SMOW). The extent of the 18O 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 an extensive ferroan carbonate alteration halo. Modeling suggests that the ore siderite formed at temperatures of 120° to 150°C, whereas siderite and ankerite in the alteration halo formed at temperatures of 150° to 180°C. The calculated isotopic compositions of the fluids are consistent with 18O-rich basinal brines and mixed inorganic and organic carbon sources (δ18O = 3-10‰ V-SMOW; δ18C = -7 to -3‰ 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 18O and 13C depleted relative to the sedimentary carbonates. The good agreement between temperature estimates from illite crystallinity and organic reflectance (160°-270°C) and inverse correlation with carbonate δ18O values indicates that organic maturation and carbonate precipitation in the northeast Lawn Hill platform resulted from interaction with the 1250 to 1150 Ma fluids.… [ABSTRACT FROM AUTHOR]

Abstract: 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±0.2ka and 23.2±0.4ka, 21.7±0.4ka and 19.2±0.2ka, 17.3±0.1ka and 16.2±0.3ka, and at 11.8±0.2ka. 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 O 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. [Copyright &y& Elsevier]