Geoscience Australia is releasing into the public domain software for the inversion of airborne electromagnetic (AEM) data to a 1D conductivity depth structure. The software includes two different algorithms for 1D inversion of AEM data. The first is a gradient based deterministic inversion code for multi-layer (smooth model) and few-layered (blocky-model) inversions. The second is a reversible-jump Markov chain Monte Carlo stochastic inversion algorithm suitable for assessing model uncertainty. A forward modelling program and some other ancillary programs are also included. The code is capable of inverting data from all of the commercial time-domain systems available in Australia today, including dual moment systems. The software is accessible in three forms. As C++ source code, as binary executables for 64 bit Windows® PCs, and as a service on the Virtual Geophysics Laboratory (VGL). The code is fully parallelized for execution on a high performance cluster computer system or on a multi-core shared memory workstation via either the MPI or the OpenMP programming models.

The 2016 Lawn Hill VTEM™Plus airborne electromagnetic (AEM) survey was funded under the Queensland Government’s Future Resources (Mount Isa Geophysics) Initiative and managed by Geoscience Australia on behalf of the Geological Survey of Queensland. The survey covers an area of 3215 km2 which aims to attract explorers into ‘greenfield’ terranes and contribute to the discovery of the next generation of major mineral and energy deposits under shallow sedimentary cover. The survey is an extension to the 2016 East Isa VTEM™Plus Survey (eCAT:104700)

Airborne electromagnetic (AEM) data are an immensely useful tool for mapping cover thickness and under cover geology in Australia. The regional AEM surveys conducted by Geoscience Australia (GA) are an ideal starting point for integrating legacy AEM datasets across a range of scales with other information, e.g. borehole stratigraphy and shallow seismic data, to add to a national cover thickness map. Geoscience Australia is working towards this end as part of the UNCOVER Initiative.

Geoscience Australia flew three regional airborne electromagnetic (AEM) surveys as part of the Australian Government's 5-year Onshore Energy Security Program in 2007-08 (Paterson, WA), 2009 (Pine Creek, NT) and 2010 (Frome, SA). The aims of the surveys were to reduce risk and stimulate exploration investment for uranium by providing reliable pre-competitive data. When the data and interpretations of the surveys were released, there was a measurable upswing in industry investment in and around the survey areas and a number of new discoveries were made using the new data. Geoscience Australia is committed to the Australian Academy of Science's Searching the Deep Earth (UNCOVER) initiative, which has been adopted by Geoscience Australia as part of its long-term strategic planning. To assist this initiative, we are assessing the potential of AEM to characterise areas that are prospective for a range of commodities including gold, copper, lead, zinc, nickel, platinum group elements and rare earth elements, as well as uranium. The assessment will also extend to the potential for mapping geology under cover to explorable depths (< 400 m), mapping cover thickness around the flanks of major outcrop areas and providing new information on groundwater resources. Potential new areas for regional AEM surveying could include (in no particular order of priority): the Westmoreland region; the Georgetown Inlier; the Mt Isa region; the Broken Hill region, the Peake and Denison Ranges; the Eyre Peninsula (Gawler Craton); the Ngalia-Amadeus region; the Musgrave Province; the Windimurra Igneous Complex; the Capricorn-Ashburton area; the Lachlan-Thomson orogens; the Stawell and Ballarat areas; the southeast Yilgarn region (Yilgarn Craton flanks); and, the Tanami area.

The magnetotelluric (MT) method is increasingly being applied to mineral exploration under cover with several case studies showing that mineral systems can be imaged from the lower crust to the near surface. Driven by this success, the Australian Lithospheric Architecture Magnetotelluric Project (AusLAMP) is delivering long-period data on a 0.5° grid across Australia, and derived continental scale resistivity models that are helping to drive investment in mineral exploration in frontier areas. Part of this investment includes higher-resolution broadband MT surveys to enhance resolution of features of interest and improve targeting. To help gain best value for this investment it is important to have an understanding of the ability and limitations of MT to resolve features on different scales. Here we present synthetic modelling of conductive, narrow, near-vertical faults 500 m to 1500 m wide, and show that a station spacing of around 14 km across strike is sufficient to resolve these into the upper crust. However, the vertical extent of these features is not well constrained, with near-vertical planar features commonly resolved as two separate features. This highlights the need for careful interpretation of anomalies in MT inversion. In particular, in an exploration scenario, it is important to consider that a lack of interconnectivity between a lower crustal/upper mantle conductor and conductors higher up in the crust and the surface might be apparent only, and may not reflect reduced mineral prospectivity. Appeared in Exploration Geophysics Journal 05 Dec 2022

Water content and NMR relaxation times are the most important properties estimated from surface nuclear magnetic resonance (SNMR) data. These properties are estimated during the geophysical inversion of SNMR data. 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.

Precompetitive AEM data and associated scientific analysis assists exploration under cover by reducing risk, stimulating investment and promoting exploration for commodities. In recent years, Geoscience Australia has flown three regional Airborne Electromagnetic (AEM) surveys covering three percent of Australia. Data and associated interpretations from regional surveys in the Paterson, Pine Creek and Lake Frome regions have led to tenement take up, stimulated exploration for a number of commodities and have given rise to many Eureka moments. This presentation will outline significant results from the use of Geoscience Australia AEM data and interpretations, results that have been announced by industry via the Australian Stock Exchange and other publications.

For the AusAEM Year 1 survey an inertial measurement unit (IMU) was installed for the first time on the TEMPEST receiver bird to measure its orientation and to augment GPS derived positioning of the receiver. This has given us the opportunity to develop better quality control and calibration procedures, which would otherwise not be possible. Theoretical modelling of the primary field on high altitude zero-lines, using the full position/orientation information, revealed discrepancies between observed and modelled data. It alerted us to time-lag parallaxes between EM and bird position/orientation data, some spurious IMU data on many pre-flight zero-lines, and a coordinate system sign convention inconsistency. The modelling also revealed systematic differences that we could attribute to the calibration of the receiver pitch and EM data scaling. We developed an inversion algorithm to solve for a receiver pitch offset and an EM scaling calibration parameter, for each zero-line, which minimised the systematic discrepancies. It eventuated that the calibration parameters fell into five distinct populations explicable by significant equipment changes. This gave us the confidence to use the medians of these populations as parameters to calibrate the data. The work shows the value of the new receiver bird orientation data and the importance of accurate IMU calibration after any modification. It shows the practical utility of quantitative modelling in the quality control workflow. It also demonstrates how modelling and inversion procedure can be used to successfully diagnose calibration issues in fixed-wing AEM data. Presented at the 2019 Australasian Exploration Geoscience Conference

The magnetotelluric (MT) data were acquired along a total of 690 km of the Youanmi deep seismic reflection traverses 10GA-YU1, 10GA-YU2 and 10GA-YU3-in Western Australia. This was a collaborative project between Geoscience Australia (GA) and the Geological Survey of Western Australia (GSWA), which provided the funding. The aim of the MT survey was to produce information of the electrical conductivity structure of the crust and upper mantle. This information is complementary to that obtained from deep seismic reflection, gravity, magnetic and geological data, which together provide new knowledge of the crustal architecture, rock properties and geodynamics of the region, important for helping to determine the potential for both mineral and energy resources. Data are supplied as EDI files with support information.

<p>The Southern Thomson Orogen VTEMplus® 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 VTEMplus® 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. <p>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: <p>1. A regular regional survey on 5000 m spaced east-west flight lines totalling 3352 line km and covering an area of 16 261 km2. <p>2. Two regional traverses adjacent to roads totalling 915 line km. <p>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. <p>Previously Released Data (Phase 1) <p>In August 2014 the processed data from the Southern Thomson Orogen VTEMplus® AEM Survey were released in the Phase 1 data release package that is available free of charge from Geoscience Australia's web site (see https://pid.geoscience.gov.au/dataset/ga/81852). The Phase 1 package includes the final processed electromagnetic data, waveform files, multiplots, conductivity estimates from the EM Flow® conductivity depth imaging algorithm, and an operations and processing report, all produced by the contractor Geotech Airborne Ltd. <p>Current Release (Phase 2) <p>This Phase 2 data release package contains results from the electromagnetic inversion of the data in the Phase 1 release. The inversion results were generated using two different types of algorithm, a deterministic regularized gradient based algorithm, which we call GALEISBS (Roach, 2010), and a reversible-jump Markov chain Monte Carlo algorithm, which we call GArjMcMC (Brodie and Sambridge, 2012; Brodie and Reid, 2013). Both algorithms assume a layered earth or 1D conductivity structure. Each airborne electromagnetic sounding is inverted independently and the results are then stitched into combined sections. <p>The deterministic GALEISBS inversion products are available for download in four logical parts based on the type of derived product. These are zipped into the following four files: <p>1. galeisbs_point_located_data.zip <p>2. galeisbs_sections.zip <p>3. galeisbs_georeferenced_sections.zip <p>4. galeisbs_gocad_sgrids.zip <p>The stochastic GArjMcMC inversion products are available for download in five logical parts based on the type of derived product. These are zipped into the following five files; <p>1. rjmcmc_point_located_data.zip <p>2. rjmcmc_sections.zip <p>3. rjmcmc_georeferenced_sections.zip <p>4. rjmcmc_gocad_sgrids.zip <p>5. rjmcmc_probability_map_plots.zip