The Southern Thomson Orogen VTEM-plus® Airborne Electromagnetic Survey was conducted by Geoscience Australia as part of a collaborative project with its partners the Geological Survey of New South Wales and the Geological Survey of Queensland. The Survey contributes to the Australian Academy of Science's UNCOVER Initiative and Geoscience Australia's response to this as part of the National Mineral Exploration Strategy. Geoscience Australia contracted Geotech Airborne Ltd to acquire VTEM-plus® airborne electromagnetic (AEM) data over part of the Southern Thomson Orogen in Queensland and New South Wales in April and May 2014. The data were also processed by Geotech Airborne Ltd using its FullWaveForm® processing techniques. The survey is designed to assess the under-cover geology and prospectivity of the Southern Thomson Orogen around Hungerford and Eulo and straddles the New South Wales-Queensland border. The survey comprises two parts: 1. A regular regional survey on 5000 m spaced East-West lines totalling 3352 line km and covering an area of 16 261 km2. 2. Two regional traverses adjacent various roads totalling 915 line km. The Southern Thomson Orogen is a priority area for mineral systems research. Much of the area lies underneath cover of sedimentary basins and is a poorly-understood element of Australia's geology. The Orogen contains Cambro-Ordovician rocks that have potential for Iron Oxide Copper-Gold (IOCG) resources, porphyry copper-gold and Volcanic-Hosted Massive Sulphide (VHMS) deposits. Survey data will add to knowledge of cover thickness and character and will inform future geological mapping in the region. The Southern Thomson Orogen VTEM-plus® AEM Survey data release includes the final contractor supplied (Phase 1) datasets AEM survey. The data will be available from Geoscience Australia's web site free of charge: http://www.ga.gov.au/about/what-we-do/projects/minerals/current/continental-geophysics/airborne-electromagnetics The data release package includes: 1. Point-located electromagnetic dB/dt and derived B-field data with associated position, altimeter, orientation, magnetic gradiometer, and derived ground elevation data. These data are in ASCII column format with associated README and ASEG-GDF2 header files. The dataset consists of a separate download file for the: a. Main survey block Part 1 (flight lines 1000-1171) b. Main survey block Part 2 (flight lines 1180-1360) c. Traverse lines (flight lines 3000-3006 and 4000-4007) d. Repeat lines e. High altitude lines. 2. Waveform files for every flight containing the 192 kHz sampling of the transmitter current and receiver waveforms. 3. Point-located conductivity estimates derived using the EM Flow® conductivity depth imaging (CDI) algorithm with associated position, altimeter, orientation, magnetic gradiometer, and derived ground elevation data. Data include the conductivity estimate for each 5 m interval and selected depth slices. These data are in ASCII column format with associated README and ASEG-GDF2 header files. All regular survey, traverses and repeat lines are included in a single download file. 4. Gridded data, at 1 km cell size in, for the conductivity depth slices derived from the EM Flow® CDI data, magnetics and elevation data in ER Mapper® binary raster grid format with associated header files. 5. Graphical multiplots, in PDF format, for each flight line showing EM Flow® CDI sections and profiles of Z-component dB/dt data, magnetics, powerline monitor, height and orientation data. 6. Operations Report. 7. ESRI shapefiles and KML files of flight lines. 8. Metadata and License files.

Unconformity-type uranium deposits are high-grade and constitute over a third of the world's uranium resources. The Cariewerloo Basin, South Australia, is a region of high prospectivity for unconformity-related uranium as it contains many similarities to an Athabasca-style unconformity deposit. These include features such as Mesoproterozoic red-bed sediments, Paleoproterozoic reduced crystalline basement enriched in uranium (~15-20 ppm) and reactivated basement faults. An airborne electromagnetic (AEM) survey was flown in 2010 using the Fugro TEMPEST system to delineate the unconformity surface at the base of the Pandurra Formation. However highly-conductive regolith attenuated the signal in the northern and eastern regions, requiring application of deeper geophysical methods. In 2012 a magnetotelluric (MT) survey was conducted along a 110 km transect of the north-south trending AEM line. MT data were collected at 29 stations and successfully imaged the depth to basement, and additionally providing evidence for deeper fluid pathways. The AEM data were integrated into the regularisation mesh as a-priori information generating an AEM constrained resistivity model and also correcting for static shift. The AEM constrained resistivity model best resolved resistive structures, allowing strong contrast with conductive zones.

For the first time, the 3 D model reveals upper-mantle enhanced conductivity anomalies beneath Archaean cratonic regions and Phanerozoic terranes imaged by the AWAGS dataset. These anomalies are consistent with the results of two recent magnetotelluric surveys, one along a profile in the Yilgarn-Officer Basin-Musgrave Block, another in the Gawler Craton region. Across much of central Australia a resistivity gradient in the middle lithosphere is observed. This region corresponds well with a recognised seismic velocity gradient across the middle-lithosphere boundary. Resistivity differences are also observed for the first time beneath Archaean cratons in Western Australia. The Pilbara Craton is represented as an enhanced conductivity anomaly at middle lithosphere depth, corresponding well with the lower-velocity anomaly evident in surface wave tomography models. The Yilgarn Craton is imaged as a resistive body, exceeding 104 ohm m, continuing to greater depths.

The 2016 Southern Thomson Orogen VTEM™Plus AEM Survey was conducted by Geoscience Australia as part of a collaborative investigation between the Commonwealth of Australia (Geoscience Australia) and its partners the State of New South Wales (Department of Trade and Investment, Geological Survey of New South Wales) and the State of Queensland (Department of Natural Resources and Mines, Geological Survey of Queensland). The Project aims to better understand the geological character and mineral potential of the southern Thomson Orogen region, focusing on the border between New South Wales and Queensland, by acquiring and interpreting multi-disciplinary geophysical, geochemical and geological data. The primary intended impact of this work is to provide the mineral exploration industry with pre-competitive data and knowledge that reduces risk and encourages mineral exploration in the region. Geoscience Australia contracted Geotech Airborne Pty Ltd to acquire VTEM™Plus AEM data over part of the Southern Thomson Orogen in Queensland and New South Wales in May and June 2016.The data were also processed by Geotech Airborne Ltd using its FullWaveForm® processing techniques. The survey area consists of 2415 line km of time-domain AEM geophysical data acquired in five survey blocks. The majority of traverse lines were spaced at 5000 m in an east-west direction, further details about each blocks flight line specifications can be found in Table 1. The original data supplied by Geotech Airborne Pty Ltd has been modified to contain the final data fields of principal interest, enabling a manageable data file size. This data is available from Geoscience Australia's website free of charge. The comprehensive dataset is available from Geoscience Australia by emailing mineralgeophysics@ga.gov.au. The data release package includes: - Point-located electromagnetic dB/dt and derived B-field data with associated position, altimeter, orientation, magnetic gradiometer, and derived ground elevation data. These data are in ASCII column format with associated README and ASEG-GDF2 header files. The dataset consists of a separate download file for the: - Survey Lines - Repeat lines - Waveform files for every flight containing the 192 kHz sampling of the transmitter current and receiver waveforms. - Point-located conductivity estimates derived using the EM Flow® conductivity depth imaging (CDI) algorithm with associated position, altimeter, orientation, magnetic gradiometer, and derived ground elevation data. Data include the conductivity estimate for each 5 m interval and selected depth slices. - Gridded data, at 1 km cell size in, for the conductivity depth slices derived from the EM Flow® CDI data, magnetics and elevation data in ER Mapper® binary raster grid format with associated header files. - Graphical multiplots, in PDF format, for each flight line showing EM Flow® CDI sections and profiles of Z-component dB/dt data, magnetics, powerline monitor, height and orientation data. - Contractor supplied Operations Report. - ESRI shapefiles and KML files of flight lines. - Metadata and License files.

Ross C Brodie James Reid Monte Carlo Inversion of SkyTEM AEM data from Lake Thetis, Western Australia A SkyTEM airborne electromagnetic dataset was inverted using a 1D reversible jump Markov chain Monte Carlo algorithm. The inversion of each dual-moment sounding generates an ensemble of 300,000 models that fit the data. The algorithm automatically varies the number of layers in the large range of models that are tested. Analysis of the statistical properties of the ensemble yields a wealth of information on the probable conductivity distribution plus the mean, mode, median and most likely summary models. Robust information on the non-uniqueness and uncertainty of the results is also afforded by the ensemble. These are conveyed on conductivity map and section products. Estimates of the probable depths to interfaces are a further outcome. These depth estimates show great potential as an aid for mapping geological surfaces. The resulting conductivity maps and sections are coherent and appear to be geologically realistic on face value. However it is demonstrated with 3D modelling that a plausible hydrogeological interpretation on the sections is likely to be an artefact of 1D inversion of a 3D geological scenario. Key words: Electromagnetic, airborne, inversion, Monte Carlo, uncertainty, 3D.

Nuclear Magnetic Resonance data may be used to estimate physical properties such as water content, NMR relaxation time, and porosity of formations penetrated by boreholes. These data were acquired as part of the Exploring for the Future (EFTF) program at field sites within the East Kimberley and Southern Stuart Corridor field areas.

Alan Yusen Ley-Cooper Ross C. Brodie Inversion of SPECTREM AEM data for conductivity and system geometry We evaluate the use of airborne electromagnetic data from the SPECTREM2000 system flown for ore body detection, regolith mapping and assessment of aquifers. Since the position and orientation of the receiver bird are not measured, the primary field at the bird cannot be known and removed precisely. In order to successfully invert the AEM data, and produce conductivity-depth models, we first reinstate the removed primary field estimate and convert the data from ppm units to Teslas. We then simultaneously inverted the X and Z component data, to solve for a 1D layered conductivity model and receiver position. The SPECTREM system has flown many line kilometres in other parts of the world but substantially less in Australia. Through further processing and inversions we have resolved conductivity-depth structures very similar to those previously obtained from other well-established AEM systems flown under Australian conditions. We also present a section of AEM data with logged drilling core data as a means of assessment of our inversion models against an independent data set. Key words: Airborne EM, inversion, geometry, SPECTREM, electrical conductivity.

Orogenic gold deposits provide a significant source of the world’s gold, but their depth of formation is contentious. One hypothesis is that orogenic gold deposits formed along crustal faults over a wide range of depths spanning sub-greenschist to granulite facies. Other authors suggest that the source is restricted to a smaller range of crustal depths (~20-30 km) and temperatures (~550⁰C) that correspond to the transition from greenschist to amphibolite metamorphic facies. Rapid burial of C and S-rich oceanic sediments and amphibolite-grade metamorphism leads to the production of large amounts of fluid in a short amount of time. In order to help discriminate between these competing hypotheses, we compiled thirty years of magnetotelluric (MT) and geomagnetic depth sounding (GDS) data across western Victoria and south-eastern South Australia. This region contains one of the world’s foremost and largest orogenic gold regions that has produced 2% of historic worldwide gold production. Three-dimensional inversion of the MT and GDS data shows a remarkable correlation between orogenic gold deposits with >1 t production and a <20 ohm.m low-resistivity region at crustal depths >20 km. Such depths are at the pressures and temperatures of greenschist to amphibolite-grade metamorphism that releases HS- ligands for Au from C and pyrite (FeS2) rich sediment interbedded with mafic oceanic rocks. Carbon is then precipitated through retrograde hydration reactions with CO2 precipitating as conductive flake graphite. Thus, our model indicates that orogenic gold in western Victoria is most likely sourced from C and FeS2 rich oceanic sediments at amphibolite-grade facies. Citation: Heinson, G., Duan, J., Kirkby, A. et al. Lower crustal resistivity signature of an orogenic gold system. Sci Rep 11, 15807 (2021). https://doi.org/10.1038/s41598-021-94531-8

This package contains Airborne Electromagnetic (AEM) data from the regional survey flown over the Great Artesian Basin intake beds in Queensland, Australia in May-June 2021. A total of 4,612.3 line km of transient EM and magnetic data were acquired. The projected grid coordinates have been supplied in GD2020 / MGA Zone 55. The aim of the survey is to provide geophysical information to support investigations of the regional groundwater system and to better understand the architecture of the aquifers within the upper few hundred metres of the GAB intake beds. It will provide data to allow for the study of the following at a reconnaissance scale: a) trends in regolith thickness and variability b) variations in bedrock conductivity c) conductivity of key bedrock (lithology related) conductive units under cover d) the groundwater resource potential of the region Geoscience Australia (GA) flew the survey as part of the Great Artesian Basin (GAB) Project. The Australian Government, through the National Water Infrastructure Fund – Expansion, commissioned GA to undertake the GAB project. The project is led by GA, in collaboration with the Department of Agriculture, Water and the Environment; Department of Infrastructure, Transport, Regional Development and Communications; the Bureau of Meteorology; and state and territory government water agencies across Queensland, South Australia, New South Wales and the Northern Territory.

A SkyTEM airborne electromagnetic (AEM) survey was flown over Surat and Galilee regions of Queensland, Australia during July 2017. The Surat-Galilee area was surveyed, with multiple survey sites in Orana, Injune and Galilee. The area is comprised of 1293 line kilometres in Orana, 552 line kilometres in Injune and 2922 line kilometres in Galilee. A total of 4767 line kilometres were flown for this survey. The projected grid coordinates have been supplied in GDA94 MGA Zone 55 for Galilee and Injune and in MGA zone 56 for Orana. The aim of the survey is to provide at a reconnaissance scale: a) trends in regolith thickness and variability b) variations in bedrock conductivity c) conductivity of key bedrock (lithology related) conductive units under cover d) the groundwater resource potential of the region e) palaeovalley systems known to exist in the region.