<div>This report contains information about the operation of Geoscience Australia’s ten permanent geomagnetic observatories, repeat stations and other relevant information covering the period from 2017 to 2021.</div><div>Information regarding the activities and services of Geoscience Australia’s Geomagnetism program, distribution of geomagnetic data, geomagnetic instrumentation and data processing procedures is also provided.</div><div><br></div>

<div>Geoscience Australia (GA), in collaboration with the New South Wales (NSW) Government’s Geological Survey of NSW, undertook a horizontal magnetic gradient and radiometric survey in the Yathong area of NSW. This survey was fully funded by the NSW Government as part of a project to find deep groundwater for use in times of drought.</div><div><br></div><div>Survey Name: Yathong</div><div>Datasets Acquired: Horizontal Magnetic Gradient, Radiometrics, and Elevation</div><div>Geoscience Australia Project Number: P5023</div><div>Acquisition Start Date: 21/05/2023</div><div>Acquisition End Date: 14/09/2023</div><div>Flight line spacing: 200 m</div><div>Flight line direction: East-West (090-270 degrees)</div><div>Total distance flown: 65,503.75 line-km's</div><div>Nominal terrain clearance: 80 m</div><div>Data Acquisition: Magspec Airborne Surveys Pty Ltd</div><div>Project Management: Geoscience Australia</div><div>Quality Control: Geoscience Australia</div><div>Dataset Ownership: Geological Survey of New South Wales</div><div>Datum: Geocentric Datum of Australia 2020 (GDA2020)</div><div>Projection: Map Grid of Australia Zone 55 (MGA55)</div><div><br></div><div>Included in this release:</div><div><br></div><div>1. Point-located Data - ASCII-column (.dat) and NetCDF (.nc) format.</div><div>• Magnetic diurnal;</div><div>• Magnetic gradient raw-edited;</div><div>• Magnetic gradient reduced;</div><div>• Radiometrics raw-edited;</div><div>• Radiometrics reduced.</div><div><br></div><div>2. Gridded data - ERMapper (.ers) format.</div><div>• Gradient enhanced Total Magnetic Intensity (TMI);</div><div>• Gradient enhanced TMI Reduced to Pole (RTP);</div><div>• Gradient enhanced TMI RTP with First Vertical Derivative (1VD);</div><div>• Dose rate (with NASVD and standard processing);</div><div>• Potassium concentration (with NASVD, standard processing);</div><div>• Thorium concentration (with NASVD, standard processing);</div><div>• Uranium concentration (with NASVD, standard processing);</div><div>• Radar-derived digital elevation model (geoidal).</div><div><br></div><div>3. Reports.</div><div>• Calibration report;</div><div>• Operations and processing summary report.</div>

Over 8,200 line kilometres of gravity and magnetic data, acquired during the 2020 Otway Basin Seismic Program (OBSP), were combined with public domain survey and satellite data to produce seamless maps of the NW-SE trending deep-water Otway Basin. These data provide valuable information on the geometry and spatial extent of igneous rocks in the deep-water basin. While the top of basement can effectively be imaged from seismic reflection datasets onshore in the Otway Basin, it remains problematic in parts of the deep-water offshore region due to variable seismic data quality. Modelling of the magnetic line data provides an estimate of the depth to the top of basement, an important interface for understanding hydrocarbon prospectivity because it plays a key role in characterising the tectonic evolution of the basin, and thus the thermal maturation history of hydrocarbons. Magnetic modelling was performed using a profile-based curve matching technique producing a depth estimate to the top of the magnetic body that is assumed to be the top of the basement. However, this assumption is flawed where there are volcanic or igneous intra-sedimentary rocks in the basin, as is the case for the Otway Basin where the interpretation of seismic reflection data shows highly reflective events corresponding to igneous features. In most parts of the basin, the modelling results show two layers: a shallow layer (depths < 1000m) corresponding to near surface volcanics, and a deeper layer (depths > 1000m) attributed to the top of the magnetic basement. Magnetic basement shows some similarities with basement picked on seismic reflection data, though in some areas the magnetic basement is shallower. The results also show that the depth to basement is not well resolved in areas with abundant intra-sedimentary igneous rocks. Further investigation is needed in such areas. Presented at the 2024 Australian Society of Exploration Geophysicists (ASEG) Discover Symposium

The Geological Survey of South Australia (GSSA) designed the Gawler Craton Airborne Survey (GCAS) to provide high resolution magnetic, gamma-ray and elevation data covering the northern portion of the Gawler Craton. In total, 1.66 million line km were planned over an area of 295,000 km2 , covering approximately 30% of the state of South Australia. The survey design of 200 m spaced lines at a ground clearance of 60 m can be compared with the design of existing regional surveys which generally employed 400 m line spacing and a ground clearance of 80 m. The new survey design results in ~2 x the data coverage and ~25% closer to the ground when compared to previous standards for regional surveys in South Australia. Due to the enormous scale of the survey, the data were acquired using four contractors who employed ten systems to fly the sixteen blocks. To standardise the data from the multitude of systems, Geoscience Australia (GA) employed a comprehensive set of technical specifications. As part of these specifications the contractors were required to fly each of the ten systems over a series of test lines termed the “Whyalla Test Lines” (Whyalla). The final GCAS data provide truly impressive high resolution regional scale products. These will allow more detailed geological interpretation of the prospective Gawler Craton. Survey blocks available for download include: Tallaringa North, block 1A Tallaringa South, block 1B Coober Pedy West, block 8A Billa Kalina, block 8B Childara, block 9A Lake Eyre, block 10 The following grids are available in this download: • Laser-derived digital elevation model grids (m). Height relative to the Australian Height Datum. • Radar-derived digital elevation model grids (m). Height relative to the Australian Height Datum. • Total magnetic intensity grid (nT). • Total magnetic intensity grid with variable reduction to the pole applied (nT). • Total magnetic intensity grid with variable reduction to the pole and first vertical derivative applied (nT/m). • Dose rate concentration grid (nGy/hr). • Potassium concentration grid (%). • Thorium concentration grid (ppm). • Uranium concentration grid (ppm). • NASVD processed dose rate concentration grid (nGy/hr). • NASVD processed potassium concentration grid (%). • NASVD processed thorium concentration grid (ppm). • NASVD processed uranium concentration grid (ppm). The following point located data are available in this download: • Elevation. Height relative to the Australian Height Datum. Datum: GDA94 • Total Magnetic Intensity. Datum: GDA94 • Radiometrics. Datum: GDA94

Survey Name: East Tasmania Datasets Acquired: Magnetics, Radiometrics and Elevation Geoscience Australia Project Number: P5020 Acquisition Start Date: 20/03/2022 Acquisition End Date: 23/06/2022 Flight line spacing: 200 m Flight line direction: East-West (090-270) Total distance flown: 57,709 line-km's Nominal terrain clearance: 80 m Data Acquisition: Magspec Airborne Surveys Pty Ltd Project Management: Geoscience Australia Quality Control: Geoscience Australia Dataset Ownership: Geoscience Australia and Mineral Resources Tasmania Datum: Geocentric Datum of Australia 2020 (GDA2020) Projection: Map Grid of Australia 55 (MGA55) Included in this release: 1. Point-located Data - ASCII-column (.dat) or NetCDF (.nc) format. • Magnetic diurnal; • Magnetics raw-edited; • Magnetics reduced; • Radiometrics raw-edited; • Radiometrics reduced. 2. Gridded data - ERMapper (.ers) format. • Total magnetic intensity (TMI); • TMI reduced to pole (RTP); • TMI RTP with first vertical derivative (1VD) applied; • Dose rate (with NASVD and standard processing); • Potassium concentration (with NASVD, standard processing); • Thorium concentration (with NASVD, standard processing); • Uranium concentration (with NASVD, standard processing); • Radar-derived digital elevation model (geoidal). 3. Reports. • Calibration report; • Operations and processing summary report. © Commonwealth of Australia (Geoscience Australia) and Mineral Resources Tasmania, Government of Tasmania 2022. With the exception of the Commonwealth Coat of Arms and where otherwise noted, this product is provided under a Creative Commons Attribution 4.0 International Licence (http://creativecommons.org/licenses/by/4.0/legalcode).

<p>The Exploring for the Future (EFTF) initiative aims to reduce the technical risk of mineral exploration by providing pre-competitive data and information to support investment and mineral exploration in northern Australia – a key part of ensuring Australia's future economic prosperity. <p>To support the EFTF initiative, the presence of hydrothermal alteration systems associated with iron oxide copper-gold (IOCG) deposits were estimated throughout the Tennant Creek -– Mt Isa Project area of northern Australia. These zones are of economic interest due to their potential to host copper, gold, uranium and rare earth element mineralisation. <p>To predict the presence of IOCG-related alteration, gravity and magnetic intensity data were used to produce 3D models of density and magnetic susceptibility, respectively. The inversion models provide an indication of the volume and distribution of these physical properties within the subsurface and were used to define volumes with relatively high densities and high magnetic susceptibilities as proxies for magnetite-rich alteration and volumes with high density, but low magnetic susceptibility, as proxies for hematite-rich alteration. <p>Contact zones between these two sets of volumes are considered to be the most favourable areas for potential IOCG mineralisation. However, the inversion modelling inevitably will have mapped a number of ‘false positives’, which will require more detailed inversion modelling and/or other data sets to discriminate these from true IOCG-related alteration.

Survey Name: Cobar magnetic and radiometric survey, 2021 Datasets Acquired: Magnetics, Radiometrics and Elevation Geoscience Australia Project Number: P5009 Acquisition Start Date: 8/06/2021 Acquisition End Date: 10/08/2021 Flight line spacing: 200 m Flight line direction: East-West (090-270) Total distance flown: 53,617 line-km Nominal terrain clearance: 60 m Blocks: 7 Data Acquisition: Magspec Airborne Surveys Project Management: Geoscience Australia Quality Control: Baigent Geosciences P.L. on behalf of Geoscience Australia Dataset Ownership: Geological Survey of NSW and Geoscience Australia Included in this release: 1. Point-located Data ASCII-column data with accompanying description and definition files. • Magnetics corrected i. Magnetic data with corrections for diurnal, IGRF, tie-levelling, micro-levelling. ii. Elevation data converted to geoidal values and a digital elevation model. • Radiometrics corrected i. Equivalent ground concentrations of radioelements with and without NASVD spectral filtering and standard IAEA processing, pressure, temperature and survey altitude. 2. Grids Gridded data in ERMapper (.ers) format (GDA94, MGA55). • Total magnetic intensity (TMI). • TMI reduced to pole (RTP). • TMI RTP with first vertical derivative applied. • Dose rate (with NASVD and standard processing). • Potassium concentration (%, with NASVD, standard processing). • Thorium concentration (ppm, with NASVD, standard processing). • Uranium concentration (ppm, with NASVD, standard processing). • Radar-derived digital elevation model (geoidal). 3. Images Data in tagged image format (TIF), (GDA94, MGA55). • Total magnetic intensity (TMI). • TMI reduced to pole (RTP). • TMI RTP with first vertical derivative applied. • Dose rate (with NASVD and standard processing). • Potassium concentration (% with NASVD, standard processing). • Thorium concentration (ppm, with NASVD, standard processing). • Uranium concentration (ppm, with NASVD, standard processing). • Radar-derived digital elevation model (geoidal). 4. Reports • P5009_2585_V3_GA_Cobar_Logistics_Report • P5009_BGS_GA_CobarQCReport © Geological Survey of New South Wales and Commonwealth of Australia (Geoscience Australia) 2021. With the exception of the Commonwealth Coat of Arms and where otherwise noted, this product is provided under a Creative Commons Attribution 4.0 International License. (http://creativecommons.org/licenses/by/4.0/legalcode).

<div>As part of the Australia's Resources Framework Project, in the Exploring for the Future Program, Geoscience Australia and CSIRO have undertaken a magnetic source depth study across four areas. These are: 1) the western part of Tasmania that is the southernmost extension of the Darling-Curnamona-Delamerian (DCD) project area; 2) northeastern Queensland; 3) the Officer Basin area of western South Australia and southeastern West Australia; and 4) the 'Eastern Resources Corridor' (ERC) covering eastern South Australia, southwest Queensland, western New South Wales and western Victoria. This study has produced 2005 magnetic estimates of depth to the top of magnetization. The solutions are derived by a consistent methodology (targeted magnetic inversion modelling, or TMIM; also known as ‘sweet-spot’ modelling). </div><div><br></div><div>The magnetic depth estimates produced as part of this study provide depth constraints in data-poor areas. They help to construct a better understanding of the 3D geometry of the Australian continent, and aid cover thickness modelling activities. </div><div><br></div><div>A supplementary interpretation data release is also available through Geoscience Australia's enterprise catalogue (ecat) at https://pid.geoscience.gov.au/dataset/ga/149499.</div><div><br></div><div>Geoscience Australia’s Exploring for the Future program provides precompetitive information to inform decision-making by government, community and industry on the sustainable development of Australia's mineral, energy and groundwater resources. By gathering, analysing and interpreting new and existing precompetitive geoscience data and knowledge, we are building a national picture of Australia’s geology and resource potential. This leads to a strong economy, resilient society and sustainable environment for the benefit of all Australians. This includes supporting Australia’s transition to net zero emissions, strong, sustainable resources and agriculture sectors, and economic opportunities and social benefits for Australia’s regional and remote communities. The Exploring for the Future program, which commenced in 2016, is an eight year, $225m investment by the Australian Government. This work contributes to building a better understanding of the Australian continent, whilst giving the Australian public the tools they need to help them make informed decisions in their areas of interest.</div>

<div>This document defines the technical standards set by Geoscience Australia for the acquisition, processing and supply of airborne magnetic, horizontal magnetic gradient and radiometric (gamma-ray spectrometric) data. The technical standards cover the requirements for equipment, calibrations, quality control checks, reporting and data formats for airborne surveys.</div><div><br></div><div><br></div><div><strong>Table of Contents</strong></div><div><br></div><div>Attachment 1A – Data Acquisition and Processing</div><div><br></div><div>1 Aircraft</div><div>2 Flight and Tie Lines</div><div>3 Global Navigation Satellite System (GNSS)</div><div>4 Parallax Correction</div><div>5 Altimeter</div><div>6 Barometer</div><div>7 Digital Elevation Model</div><div>8 Magnetic System Equipment</div><div>9 Magnetic Gradient System Equipment</div><div>10 Magnetic / Gradient Calibration and Quality Tolerances</div><div>11 Magnetic Base Station (Diurnal Monitoring)</div><div>12 Magnetic Data Reduction</div><div>13 Magnetic Gradient Data Reduction</div><div>14 Radiometric System Equipment</div><div>15 Radiometric Calibration and Quality Tolerances</div><div>16 Radiometric Data Reduction</div><div><br></div><div>Attachment 1B – Reporting and Data Supply</div><div><br></div><div>1 General</div><div>2 Calibration Report</div><div>3 Daily Acquisition Report</div><div>4 Weekly Acquisition Report</div><div>5 Operations and Processing Summary Report</div><div>6 Supply Schedule</div><div><br></div><div>Attachment 1C – Data Formats</div><div><br></div><div>1 General</div><div>2 Point-Located Data Files</div><div>3 Definition Files</div><div>4 Description Files</div><div>5 Raw-Edited Magnetic Data File</div><div>6 Reduced Magnetic Data File</div><div>7 Diurnal Magnetic Data File</div><div>8 Raw-Edited Magnetic Gradient Data File</div><div>9 Reduced Magnetic Gradiometry Data File</div><div>10 Raw-Edited Radiometric Data File</div><div>11 Reduced Radiometric Data File</div><div>12 Gridded Data Files</div><div>13 Image Enhanced GeoTIFF Files

<div>Near-surface magnetizations are ubiquitous across many areas of Australia and complicate reliable estimation of depth to deeper magnetizations. We have selected four test areas in which we use equivalent source dipoles to represent and quantify the near-surface magnetizations. We present a synthetic modelling study that demonstrates that field variations from the near-surface magnetizations substantially degrade estimation of depth to a magnetization 500 metres below the modelled sensor elevation and that these problems persist even for anomalies with significantly higher amplitudes. However, preferential attenuation of the fields from near surface magnetizations by upward continuation proved quite effective in improving estimation of depth to those magnetizations.</div> This Abstract was submitted/presented at the 2023 Australasian Exploration Geoscience Conference (AEGC) 13-18 March (https://2023.aegc.com.au/)