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.

The International Geo-Sample Number (IGSN) provides a globally unique identifier for physical samples used to generate analytical data. This unique identifier provides the ability to link each physical sample to any analytical data undertaken on that sample, as well as to any publications derived from any data derived on the sample. IGSN is particularly important for geochemical and geochronological data, where numerous analytical techniques can be undertaken at multiple analytical facilities not only on the parent rock sample itself, but also on derived sample splits and mineral separates. Australia now has three agencies implementing IGSN: Geoscience Australia, CSIRO and Curtin University. All three have now combined into a single project, funded by the Australian Research Data Services program, to better coordinate the implementation of IGSN in Australia, in particular how these agencies allocate IGSN identifiers. The project will register samples from pilot applications in each agency including the CSIRO National Collection of Mineral Spectra database, the Geoscience Australia sample collection, and the Digital Mineral Library of the John De Laeter Centre for Isotope Research at Curtin University. These local agency catalogues will then be aggregated into an Australian portal, which will ultimately be expanded for all geoscience specimens. The development of this portal will also involve developing a common core metadata schema for the description of Australian geoscience specimens, as well as formulating agreed governance models for registering Australian samples. These developments aim to enable a common approach across Australian academic, research organisations and government agencies for the unique identification of geoscience specimens and any analytical data and/or publications derived from them. The emerging pattern of governance and technical collaboration established in Australia may also serve as a blueprint for similar collaborations internationally.

The Walloon Coal Measures (WCM) in the Clarence-Moreton and the Surat basins in Qld and northern NSW contain up to approximately 600 m of mudstone, siltstone, sandstone and coal. Wide-spread exploration for coal seam gas (CSG) within both basins has led to concerns that the depressurisation associated with the resource development may impact on water resources in adjacent aquifers. In order to predict potential impacts, a detailed understanding of sedimentary basins hydrodynamics that integrates geology, hydrochemistry and environmental tracers is important. In this study, we show how different hydrochemical parameters and isotopic tracers (i.e. major ion chemistry, dissolved gas concentrations, 13C-DIC, 18O, 87Sr/86Sr, 3H, 14C, 2H and 13C of CH4) can help to improve the knowledge on groundwater recharge and flow patterns within the coal-bearing strata and their connectivity with over- or underlying formations. Dissolved methane concentrations in groundwaters of the WCM in the Clarence-Moreton Basin range from below the reporting limit (10 µg/L) to approximately 50 mg/L, and samples collected from nested bore sites show that there is also a high degree of vertical variability. Other parameters such as groundwater age measurements collected along distinct flow paths are also highly variable. In contrast, 87Sr/86Sr isotope ratios of WCM groundwaters are very uniform and distinct from groundwaters contained in other sedimentary bedrock units, suggesting that 87Sr/86Sr ratios may be a suitable tracer to study hydraulic connectivity of the Walloon Coal Measures with over- or underlying aquifers, although more studies on the systematic are required. Overall, the complexity of recharge processes, aquifer connectivity and within-formation variability confirms that a single tracer that cannot provide all information necessary to understand aquifer connectivity in these sedimentary basins, but that a multi-tracer approach is required.

Several belts of poorly-exposed igneous rocks occur in the Grampians-Stavely Zone of western Victoria, close to the interpreted Cambrian east Gondwana continental margin. Previous geochemical studies on the outcropping igneous rocks around Mount Stavely, Mount Dryden and in the Black Range have recognised characteristics similar to those found in modern magmatic arcs. These rocks are collectively considered to form part of a single Middle to Late Cambrian arc system, referred to as the Stavely Arc. While outcropping examples of the Stavely Arc magmas are well studied, the character of other (likely) arc-related rocks imaged by magnetic data beneath recent, thin cover has remained enigmatic. New geochemical data from a recent stratigraphic drilling program, together with analysis of rocks from government and industry drill holes has allowed for a more complete understanding of the Stavely Arc package. A range of rock associations have been recognised, including low-Ti boninite-like rocks, back-arc-related tholeiitic rocks, adakitic porphyry intrusives, serpentinites, and highly-depleted mafic to intermediate volcanics and intrusives. The majority of arc-related rocks comprise low- to high-K calc-alkaline basalt, andesite, dacite, and geochemically-related quartz diorite, which display similar N-MORB-normalised trace element patterns, LREE-enriched REE patterns and moderately evolved to weakly juvenile Nd isotopic compositions (Nd 500 Ma = -3.95 to +0.46). High-Al basalts intersected during stratigraphic drilling also show weakly-developed calc-alkaline compositions. However, these are distinguished from the other calc-alkaline rocks by higher Al2O3, N-MORB-like trace element patterns, relatively flat REE patterns and much more juvenile Nd isotopic compositions (Nd 500 Ma = +4.73 to +6.33). High-Al basalts are spatially associated with boninites intersected by mineral exploration drilling. The earliest geochronological evidence for Stavely Arc magmatism is provided by an isotopically juvenile felsic intrusive with an interpreted arc-related origin dated at ~510 Ma. This age is synchronous with tholeiitic dolerite from the western Grampians-Stavely Zone interpreted to have been emplaced in a back-arc extensional setting. Available ages for volcanic rocks of the Stavely Arc are only known from the Mount Stavely Belt, and show that arc magmatism reached maturity around ~505-500 Ma. Overall geochemical systematics suggest that the majority of calc-alkaline rocks of the Stavely Arc have affinities with modern island arcs with (limited) continental crust involvement. It is unlikely that the thickness of any pre-existing Precambrian crust was great, given the Nd isotopic compositions and lack of inherited Mesoproterozoic or older zircons. In comparison, the more juvenile isotopic characteristics, weakly-developed subduction-related features, and spatial association with boninites of the high-Al basalts are more consistent with a more primitive arc setting, and may represent an (early?) phase of Stavely Arc magmatism in which there was insignificant crustal involvement. Similar geochemical characteristics, ages, and inferred tectonic setting are consistent with the Stavely Arc forming part of a larger Middle to Late Cambrian arc system that also includes the Mount Wright Arc in New South Wales and the Jamison Volcanic Group (Selwyn Block) in central Victoria.

Geochemical tracers have been used for many years to improve the understanding of reservoir dynamics in geothermal systems. Tracers can be classified as either conservative or reactive, and can be used in liquid-phase, vapour-phase or two-phase reservoirs at temperatures of 300C or more. They are commonly used to map flow pathways between injection and production wells in a geothermal field, to monitor the effects of reinjection and identify wells that might experience premature thermal breakthrough if left unmanaged. Tracer tests also provide information about reservoir fluid residence time, fluid recharge location or direction, swept pore volumes, inter-well connectivity, temperatures, fracture surface area, flow-storage capacity relationships and volumetric fluid sweep efficiencies. In addition, tracer data can be used with numerical transport codes to help validate 2D or 3D reservoir models. Thus, tracer tests can provide powerful insight into geothermal reservoir characteristics, and they can be performed at many stages of project development, from small-scale demonstration projects (e.g. an injection-production well doublet) through to large-scale commercial fields (e.g. Wairakei, New Zealand). New 'smart' tracers have the potential to be used with a single well to evaluate changes in fracture surface area following reservoir stimulation, and thus have applications to both conventional and unconventional (engineered) geothermal projects.

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.

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.

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.

The Tongo 1 borehole was drilled approximately 83 km NE of White Cliffs, 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.

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 Total sediment metabolism, %carbonate, organic isotope (C and N) and organic and inorganic element data from 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