The middle to lower Jurassic sequence in Australia's Surat Basin has been identified as a potential reservoir system for geological CO2 storage. The sequence comprises three major formations with distinctly different mineral compositions, and generally low salinity formation water (TDS<3000 mg/L). Differing geochemical responses between the formations are expected during geological CO2 storage. However, given the prevailing use of saline reservoirs in CCS projects elsewhere, limited data are available on CO2-water-rock dynamics during CO2 storage in such low-salinity formations. Here, a combined batch experiment and numerical modelling approach is used to characterise reaction pathways and to identify geochemical tracers of CO2 migration in the low-salinity Jurassic sandstone units. Reservoir system mineralogy was characterized for 66 core samples from stratigraphic well GSQ Chinchilla 4, and six representative samples were reacted with synthetic formation water and high-purity CO2 for up to 27 days at a range of pressures. Low formation water salinity, temperature, and mineralization yield high solubility trapping capacity (1.18 mol/L at 45°C, 100 bar), while the paucity of divalent cations in groundwater and the silicate reservoir matrix results in very low mineral trapping capacity under storage conditions. Formation water alkalinity buffers pH at elevated CO2 pressures and exerts control on mineral dissolution rates. Non-radiogenic, regional groundwater-like 87Sr/86Sr values (0.7048-0.7066) indicate carbonate and authigenic clay dissolution as the primary reaction pathways regulating solution composition, with limited dissolution of the clastic matrix during the incubations. Several geochemical tracers are mobilised in concentrations greater than found in regional groundwater, most notably cobalt, concentrations of which are significantly elevated regardless of CO2 pressure or sample mineralogy.

Regolith carbonate or secondary carbonate is a key component of the regolith, particularly in many Mediterranean, arid and semi-arid regions of Australia. National maps of regolith carbonate distribution have been compiled from regional soil, regolith and geological mapping with varying degrees of confidence and consistency. Here we apply a decision tree approach based on a piecewise linear regression model to estimate and map the near-surface regolith carbonate concentration at the continental scale. The model is based on relationships established from the 1311 field sites of the National Geochemical Survey of Australia (NGSA) and 49 national environmental covariate datasets. Regolith carbonate concentration (weight %) was averaged from the <2 mm grain size-fractions of samples taken from two depth ranges (0-10 cm and ~60-80 cm) at each NGSA site. The final model is based on the average of 20 runs generated by randomly selecting 90% training and 10% validation splits of the input data. Results present an average coefficient of determination (R2) of 0.56 on the validation dataset. The covariates used in the prediction are consistent with our understanding of the controls on the sources (inputs), preservation and distribution of regolith carbonate within the Australian landscape. The model produces a continuous, quantitative prediction of regolith carbonate abundance in surficial regolith at a resolution of 90 m with associated estimates of model uncertainty. The model-derived map is broadly consistent with our current knowledge of the distribution of carbonate-rich soil and regolith in Australia. This methodology allows the rapid generation of an internally consistent and continuous layer of geoinformation that may be applicable to other carbonate-rich landscapes globally. The methodology used in this study has the potential to be used in predicting other geochemical constituents of the regolith.

Lithium (Li) concentrations in catchment outlet sediment samples were measured as part of the National Geochemical Survey of Australia (NGSA; www.ga.gov.au/ngsa). Samples were collected at or near the outlet of 1186 catchments covering ~81% of Australia during 2007-2009. At each site a top outlet sediment (TOS) sample (0-10 cm depth) and a bottom outlet sediment (BOS) sample (~60-80 cm depth) were collected; each split into a 'coarse' (<2 mm) and a 'fine' (<75 mm) grain-size fraction. Li data is available for the Mobile Metal Ion (MMI®; TOS 'coarse' only) and Aqua Regia (AR) digestion techniques. Censored data (reported to be below the Lower Limit of Detection, LLD) account for 32% of the MMI® data (LLD = 0.005 mg/kg) and are absent from the AR dataset (LLD = 0.1 mg/kg); replacement values were imputed using a nearest neighbour method. The median MMI® value is three orders of magnitude lower than the median AR concentration. Further, there is an increase in median Li for the AR digestion following the order TOS 'coarse < BOS 'coarse' < TOS 'fine' < BOS 'fine'; in other words the deep or 'fine' samples have higher Li concentrations than their surface or 'coarse' counterparts. In order to assess the 'availability' of Li, the ratio of MMI® to AR Li (Li_Mi/Ai) was calculated and plotted. Li availability ranges from almost non-existent up to 14%. The map of Li_Mi/Ai shows that the regions of high Li availability correspond to the Yilgarn Craton, much of eastern South Australia, the southernmost, westernmost and central Northern Territory, south and western Queensland, western New South Wales and Victoria and a few coastal areas. These commonly are regions where salt lakes occur. However, assessment of Li content of source rocks and groundwaters and absence of active hydrogeological setting highlight limitations for the potential for Li-rich brines in Australian salt lakes.

In the 50 years since the first commercial discovery in 1965 at Barracouta-1, and 46 years since production commenced from the Barracouta field, a total of 16.5 TCF of gas, 4026 MMbbl of oil, 385 MMbbl of condensate and 752 MMbbl of LPG have been found in the Gippsland Basin (Estimated Ultimate Recovery, as at the end of 2012). Despite these extensive resources, all from CretaceousPaleogene Latrobe Group reservoirs, there are questions regarding the effective petroleum systems, contributing source rock units, and the migration pathways between source and reservoir. Resolution of these uncertainties is essential to improve our understanding of the remaining prospectivity and for creating new exploration opportunities, particularly in the eastern, less explored part of the basin, but also for mitigating risk for the potential sequestration of carbon dioxide along the southern and western flanks. Geochemical fingerprinting of reservoir fluids has identified that the oil and gas originate from multiple sources. The most pervasive hydrocarbon charge into the largely produced fields overlying the Central Deep has a terrestrial source affinity, originating from lower coastal plain facies (Kingfish, Halibut, Mackerel), yet the oils cannot be correlated using source-related biomarker parameters to source rocks either within the Halibut Subgroup (F. longus biozone) at Volador-1, one of the deepest penetrations of the Upper Cretaceous section, or to older sections, penetrated on the flanks of the basin. However, within the underlying SantonianCampanian Golden Beach Subgroup an oil-source correlation has been established between the Anemone-1A oil and the marginal marine Anemone Formation (N. senectus biozone) at Anemone-1/1A and Archer-1. A similar correlation is indicated for the Angler-1 condensate to the Chimaera Formation (T. lilliei biozone) in the deepest section at Volador-1 and Hermes-1. In the Longtom field, gas reservoired within the Turonian Emperor Subgroup, potentially has a source from either the lacustrine Kipper Shale or the Albian portion of the Strzelecki Group. The molecular and carbon isotopic signatures of oil and gas from the onshore Wombat field are most similar to hydrocarbons sourced from the AptianAlbian Eumeralla Formation in the Otway Basin, also implicating a Strzelecki source in the Gippsland Basin. These results imply that sediments older than the Paleocene are significant sources of petroleum within the basin.

The Janina 1 borehole was drilled approximately 110 km W of Bourke, New South Wales. The borehole was designed to test aeromagnetic anomalies in the basement rocks and to test the electrical conductivity properties of cover and basement rocks to validate airborne electromagnetic (AEM) data.

The Milcarpa 1 borehole was drilled approximately 9 km SSE of Hungerford, Queensland, adjacent to the road between Hungerford and Wanaaring, NSW. The borehole was designed to test aeromagnetic anomalies in the basement rocks, test the electrical conductivity properties of cover and basement rocks to validate airborne electromagnetic (AEM) data, and to test pre-drilling geophysical cover thickness estimates.

Geoscience Australia defines a sample as a feature observed, measured or collected in the field. A specimen is a physical individual sample collected during the field work. This data set represents a subset of all Sampling data held by Geoscience Australia that have been collected as part of drilling activities (ie relate to Australian Boreholes). The data will be utilised by other data domains by providing Sampling context to various Observation & Measurement data.

One gram of sample No. 1 and 2 grams of No. 2 were dissolved in about 100mL of hot water. After dissolving the soluble portions the solutions were filtered and the undissolved portions dissolved and weighed. This weight subtracted from the original weight of the sample gave the amount of soluble salts. The filtrate was diluted to 250 mls with distilled water, 100 mls being used for Ca and Mg determination. The results of this experiment are given in the report.

The National Geochemical Survey of Australia (NGSA) was carried out to bridge a vast knowledge gap about the concentration and distribution of chemical elements at the Earth's surface and consequent poor understanding of processes controlling their distribution. The aim of the project was to contribute to derisking exploration for energy and mineral resources through the pre-competitive (government-funded) delivery of a new spatial layer of compositional data and information. Surface (0-10 cm depth) and shallow (~60-80 cm) samples of catchment outlet sediments were collected from 1315 sites located near the outlet of 1186 catchments (~10 % of which were sampled in duplicate) from across Australia. The total area covered by the survey was 6.174 million km2, or ~81% of Australia, at an average sampling density of 1 site per ~5200 km2. A number of field parameters (e.g., soil colour, pH), bulk parameters (e.g., electrical conductivity, particle size distribution) and geochemical parameters (i.e., multi-element composition of dry sieved <2 mm and <75 -m grain-size fractions) were determined. The grain-size fractions were analysed to determine (1) Total, (2) Aqua Regia soluble, and (3) Mobile Metal Ion (MMI®) extractable element contents. This data was collated into a spreadsheet and graphically represented as a series of 529 geochemical maps (www.ga.gov.au/ngsa). These constitute the first continental-scale series of geochemical maps based on internally consistent, state-of-the-art data pertaining to the same sampling medium collected, prepared and analysed in a uniform and thoroughly documented manner and over a short time period for Australia. They are being used to better understand the accumulation, mobility and significance of chemical elements in the near-surface environment. They provide a new, additional pre-competitive dataset for the energy and mineral resource exploration industry, which can help prioritise areas for further exploration investment and thus reduce risk. Further, some of this new information is already finding use in natural resource management and environmental monitoring. Applications to date and ongoing and future directions are discussed.

A benthic sediment sampling survey (GA0356) to the nearshore areas of outer Darwin Harbour was undertaken in the period from 03 July to 14 September 2016. Partners involved in the survey included Geoscience Australia (GA), the Australian Institute of Marine Science (AIMS) and the Department of Environment and Natural Resources within the Northern Territory Government (NT DENR) (formerly the Department of Land and Resource Management (DLRM)). This survey forms part of a four year (2014-2018) science program aimed at improving knowledge about the marine environments in the regions around Darwin and Bynoe Harbour’s through the collection and collation of baseline data that will enable the creation of thematic habitat maps to underpin marine resource management decisions. This project is being led by the Northern Territory Government and is supported by the INPEX-led Ichthys LNG Project, in collaboration with - and co-investment from GA and AIMS. The program builds upon an NT Government project (2011-2011) which saw the collection of baseline data (multibeam echosounder data, sediment samples and video transects) from inner Darwin Harbour (Siwabessy et al. 2015). This dataset comprises sediment oxygen demand measurements on seabed sediments. Radke, L., Smit, N., Li, J., Nicholas, T., Picard, K. 2017. Outer Darwin Harbour Shallow Water Sediment Survey 2016: GA0356 – Post-survey report. Record 2017/06. Geoscience Australia, Canberra. http://dx.doi.org/10.11636/Record.2017.006 This research was funded by the INPEX-led Ichthys LNG Project via the Northern Territory (NT) Government Department of Land Resource Management (DLRM) (now the Department of Environment and Natural Resources (DENR)), and co-investment from Geoscience Australia (GA) and Australian Institute of Marine Science (AIMS). We are grateful to the following agencies for providing boats and staff, and to the following personal for help with sample acquisition: NT DENR (Danny Low Choy and Rachel Groome), NT Fisheries (Wayne Baldwin, Quentin Allsop, Shane Penny, Chris Errily, Sean Fitzpatrick and Mark Grubert), NT Parks and Wildlife (Ray Chatto, Stewart Weorle, and Luke McLaren) and the Larrakia Rangers (Nelson Tinoco, Kyle Lewfat, Alan Mummery and Steven Dawson). Special thanks to the skippers Danny Low Choy, Wayne Baldwin, Stewart Weorle and Luke McLaren whose seamanship strongly guided the execution of this survey. AIMS generously allowed use of the aquarium and laboratory at the Arafura Timor Sea Research Facility, and Simon Harries and Kirsty McAllister helped with the setup. We would also like to acknowledge and thank GA colleagues including: Matt Carey, Ian Atkinson and Craig Wintle (Engineering and Applied Scientific Services) for the organisation of field supplies and the design of the new core incubation set-up. This dataset is published with the permission of the CEO, Geoscience Australia