Tennant Creek and Mt Isa are the preeminent mineral resource hubs for the Northern Territory and Queensland. The region between these two hubs is a vast prospective exploration frontier, covered by a thin veneer of sediments, which has been overlooked for exploration in the past. Regional soil sampling surveys are an excellent means of identifying the mineral potential of such regions as they can reveal what lies beneath the cover. Geoscience Australia, as part of the Federal Government’s Exploring for the Future program, undertook an extensive soil sampling survey in collaboration with the Northern Territory Geological Survey and the Geological Survey of Queensland. Catchment outlet sediment samples were collected at 776 sites (including duplicates) and analysed for their elemental composition. The data reveal areas with future potential for base metals including copper. The data are also valuable for agricultural management, allowing farmers to measure soil fertility to maintain sustainable crop production and inform cattle grazing management over the Barkly Tablelands region of the Northern Territory. This information can be used to guide safe and responsible agricultural development in the future. Further, the survey establishes robust geochemical baseline data sets relevant to many environmental issues which can be utilised in development decision making. The survey was undertaken over a period of two months utilising two helicopters from Northern Australia Helicopters based in Katherine. Samples were prepared for analysis over five months by an indigenous company supervised by Geoscience Australia staff at the Centre of Appropriate Technology in Alice Springs. Analysis of the samples was performed by Geoscience Australia in Canberra and SGS Australia mineral services in Perth. This data release includes (1) information on the sampling sites, (2) bulk sample properties (Munsell colours, pH, electrical conductivity), (3) results of the total chemical analyses of the fine (<75 m) fraction of the samples (XRF, ICP-MS) and (4) results of the partial leach analyses of the Mobile Metal Ion™ (MMI™) extractions (0–2 mm fraction, ICP-MS). Included is also a set of digital images of geochemical maps based on this dataset. This dataset is the first of a series of staged data releases from the Northern Australia Geochemical Survey. Relevant data, information and images are available through the GA website (http://www.ga.gov.au/eftf/fis/nags).

Geochemical surveys deliver fundamental data, information and knowledge about the concentration and spatial distribution of chemical elements, isotopes and compounds in the natural environment. Typically near-surface sampling media, such as soil, sediment, outcropping rocks and stream or groundwater, are used. The application of such datasets to fields such as mineral exploration, environmental management, and geomedicine has been widely documented. In this presentation I reflect on a sabbatical experience with the Australian Federal Police (AFP) in 2017-2018 that allowed me to extend the interpretation of geochemical survey data beyond these established applications. In particular, with my collaborators we explore ways in which geochemical survey data and maps can be used to indicate the provenance of an evidentiary sample collected at a crime scene or obtained for instance from items belonging to a suspect intercepted at border entry. Because soils are extremely diverse mineralogically, geochemically and biologically, it should theoretically be possible to exclude very large swathes of territory (>90%) from further provenancing investigation using soil data. In a collaboration between Geoscience Australia (GA), the AFP and the University of Canberra (UC), a recent geochemical survey of the urban/suburban Canberra region in southeastern Australia is being used as a testbed for developing different approaches to forensic applications of geochemical surveys. A predictive soil provenancing method at the national scale was also developed and tested for application where no actual detailed, fit-for-purpose geochemical survey data exist. Over the next few years, GA, AFP and UC are collaborating with Flinders University to add biome data from soil and soil-derived dust to further improve the provenancing technique. This Abstract was presented at the 2021 Goldschmidt Conference (https://conf.goldschmidt.info/goldschmidt/2021/meetingapp.cgi)

<p>This data release is part of the Federal Government’s Exploring for the Future program undertake by Geoscience Australia in collaboration with the Northern Territory Geological Survey and the Geological Survey of Queensland. It is the second staged release of data from the North Australian Geochemical Survey which sampled catchment outlet sediments at 780 sites (including duplicates) for geochemical analysis. </p> <p>The survey area was chosen to encompass the preeminent mineral provinces of Tennant Creek and Mt Isa, with the region between these two provinces providing a vast prospective exploration frontier, covered by a thin veneer of sediments and basalts, which has been overlooked for mineral exploration in the past. The data are not only useful for mineral exploration but also for agriculture and environmental management. For agriculture, this dataset can be used to assess soil fertility to maintain sustainable crop production and inform cattle grazing management over such areas as the Barkly Tablelands. The survey establishes a robust geochemical baseline dataset relevant to many environmental issues which can be utilised in development decision making into the future.</p> <p>This data release includes (1) results of the total chemical analyses of the coarse (<2 mm) fraction of sampled sediments (XRF, ICP-MS), (2) results of the aqua regia analyses of the coarse and fine fractions (<2 mm and <75 µm, respectively), and (3) results of the fire assay analysis of the coarse and fine fractions. Included is a set of georeferenced digital images of geochemical maps based on this dataset.</p>

<div>A novel method of estimating the silica (SiO2) and loss-on-ignition (LOI) concentrations for the North American Soil Geochemical Landscapes (NASGL) project datasets is proposed. Combining the precision of the geochemical determinations with the completeness of the mineralogical NASGL data, we suggest a ‘reverse normative’ or inversion approach to calculate first the minimum SiO2, water (H2O) and carbon dioxide (CO2) concentrations in weight percent (wt%) in these samples. These can be used in a first step to compute minimum and maximum estimates for SiO2. In a recursive step, a ‘consensus’ SiO2 is then established as the average between the two aforementioned estimates, trimmed as necessary to yield a total composition (major oxides converted from reported Al, Ca, Fe, K, Mg, Mn, Na, P, S, and Ti elemental concentrations + ‘consensus’ SiO2 + reported trace element concentrations converted to wt% + ‘normative’ H2O + ‘normative’ CO2) of no more than 100 wt%. Any remaining compositional gap between 100 wt% and this sum is considered ‘other’ LOI and likely includes H2O and CO2 from the reported ‘amorphous’ phase (of unknown geochemical or mineralogical composition) as well as other volatile components present in soil. We validate the technique against a separate dataset from Australia where geochemical (including all major oxides) and mineralogical data exist on the same samples. The correlation between predicted and observed SiO2 is linear, strong (R2 = 0.91) and homoscedastic. We also compare the estimated NASGL SiO2 concentrations with another publicly available continental-scale survey over the conterminous USA, the ‘Shacklette and Boerngen’ dataset. This comparison shows the new data to be a reasonable representation of SiO2 values measured on the ground over the same study area. We recommend the approach of combining geochemical and mineralogical information to estimate missing SiO2 and LOI by the recursive inversion approach in datasets elsewhere, with the caveat to validate results.</div><div><br></div><div>The major oxide concentrations, including those for the estimated SiO2 and LOI, for the NASGL A and C horizons are available for download, as CSV files. A worked example for five selected NASGL C horizon samples is also available for download, as an XLSX file.</div> <b>Citation:</b> P. de Caritat, E. Grunsky, D.B. Smith; Estimating the silica content and loss-on-ignition in the North American Soil Geochemical Landscapes datasets: a recursive inversion approach. <i>Geochemistry: Exploration, Environment, Analysis</i> 2023; 23 (3): 2023-039 doi: https://doi.org/10.1144/geochem2023-039 This article appears in multiple journals (Lyell Collection & GeoScienceWorld)

The National Geochemical Survey of Australia (NGSA) is Australia’s first national-scale geochemical survey. It was delivered to the public on 30 June 2011, after almost five years of stakeholder engagement, strategic planning, sample collection, preparation and analysis, quality assurance/quality control, and preliminary data analytics. The project was comprehensively documented in seven initial open-file reports and six data and map sets, followed over the next decade by more than 70 well-cited scientific publications. This review compiles the body of work and knowledge that emanated from the project to-date as an indication of the impact the NGSA had over the decade 2011-2021. The geochemical fabric of Australia as never seen before has been revealed by the NGSA. This has spurred further research and stimulated the mineral exploration industry. This paper also critically looks at operational decisions taken at project time (2007-2011) that were good and perhaps – with the benefit of hindsight – not so good, with the intention of providing experiential advice for any future large-scale geochemical survey of Australia or elsewhere. Strengths of the NGSA included stakeholder engagement, holistic approach to a national survey, involvement of other geoscience agencies, collaboration on quality assurance with international partners, and targeted promotion of results. Weaknesses included gaining successful access to all parts of the nation, and management of sample processing in laboratories. <b>Citation:</b> Patrice de Caritat; The National Geochemical Survey of Australia: review and impact. <i>Geochemistry: Exploration, Environment, Analysis </i>2022;; 22 (4): geochem2022–032. doi: https://doi.org/10.1144/geochem2022-032 This article appears in multiple journals (Lyell Collection & GeoScienceWorld)