Predictive maps of the subsurface can be generated when geophysical datasets are modelled in 2D and 3D using available geological knowledge. Inversion is a process that identifies candidate models which explain an observed dataset. Gravity, magnetic, and electromagnetic datasets can now be inverted routinely to derive plausible density, magnetic susceptibility, or conductivity models of the subsurface. The biggest challenge for such modelling is that any geophysical dataset may result from an infinite number of mathematically-plausible models, however, only a very small number of those models are also geologically plausible. It is critical to include all available geological knowledge in the inversion process to ensure only geologically plausible physical property models are recovered. Once a set of reasonable physical property models are obtained, knowledge of the physical properties of the expected rocks and minerals can be used to classify the recovered physical models into predictive lithological and mineralogical models. These predicted 2D and 3D maps can be generated at any scale, for Government-funded precompetitive mapping or drilling targets delineation for explorers.

The Paterson AEM survey was flown over the Paterson Orogen, the eastern Pilbara Craton and the on-lapping Officer and Canning Basins in NW Western Australia between September 2007 and October 2008 as part of the Commonwealth Government's Onshore Energy Security Program. The survey was designed to provide pre-competitive data for enhancing uranium and other mineral exploration. Flight lines were at a variety of spacings from 6, 2 and 1 km to 200 m targeting known deposits and other covered highly prospective rocks for a total area of 45,330 km2. The survey data has afforded new insights into the Paleozoic paleotopography of the region which is blanketed by regolith including Phanerozoic sediments including Permian glaciogene, Mesozoic and Cenozoic sediments. These insights have major implications for mineral prospectivity.

The Ord Valley Airborne Electromagnetics (AEM) Interpretation Project was undertaken to provide information in relation to salinity and groundwater management in the Ord River Irrigation Area (ORIA), and to guide its future expansion. The project included the acquisition of 5,936 line km of AEM data acquired using the SKYTEM time domain system, the acquisition of a Light Ranging and Detection (LiDAR) survey, and complementary drilling, borehole geophysics, laboratory analysis and interpretation services. Within the limits of available bore data and the scales of airborne data acquisition, this study provided greater spatial detail on critical elements of the hydrostratigraphy in the sedimentary alluvial aquifer systems. This included the indicative 3D extent and thickness of gravel, sand, silt, clay units as well as salt stores and groundwater quality. It also produced first generation of salinity hazard maps. The AEM mapping identified discrete palaeochannels, interpreted as elements of the palaeo-Ord drainage system. Overall, the amount and extent of gravel and sand aquifers present in the study area was significantly less than previously thought, with gravel aquifers present in laterally confined palaeochannel systems. There was also several buried bedrock ridges and shallow pediments that were interpreted to reduce aquifer storage and throughflow. In the Mantinea Plain-Carlton Hill-Parry's Lagoon area, the presence of a marine sand aquifer containing very saline groundwater was confirmed. The 3D mapping provided an important framework for hydrodynamic analysis and hydrogeochemical process studies. In summary, the project demonstrated the potential for 'calibrated' AEM systems and iTEM Fast Approximate Inversion software to shorten project timelines for studies that involve the analysis and interpretation of AEM data.

Short article describing detection of interpreted unconformity between Coolbro Sandstone and Rudall Complex rocks near the Kintyre uranium deposit, Western Australia

The use of airborne electromagnetics (AEM) for hydrogeological investigations often requires high resolution data. Optimisation of AEM data therefore requires careful consideration of AEM system suitability, calibration, validation and inversion methods. In the Broken Hill managed Aquifer Recharge (BHMAR) project, the helicopter-borne SkyTEM transient EM system was selected after forward modeling of system responses and assessment of test line data over potential targets. The survey involved acquisition of 31,834 line km of data over an area of 7,500 km2 of the River Darling Floodplain, and was acquired by two systems over a 9-week period.. Initial Fast Approximate Inversions (FAI) provided within 48 hours of acquisition were used to target 100 sonic and rotary mud holes for calibration and validation. A number of different (Laterally and Spatially Constrained) inversions of the AEM data were carried out, with refinements made as additional information on vertical and lateral constraints became available. Finally, a Wave Number Domain Approximate Inversion procedure with a 1D multi-layer model and constraints in 3D, was used to produce a 3D conductivity model. This inversion procedure only takes days to run, enabling the rapid trialing to select the most appropriate vertical and horizontal constraints. Comparison of borehole induction logs with adjacent AEM fiduciary points confirms high confidence levels in the final inversion. Using this approach has produced quantitative estimates of the 3D conductivity structure that provide a reliable platform for identifying new groundwater resources and a range of MAR options, and developing new geological and hydrogeological conceptual models. Integration of the AEM data with borehole lithology, textural, mineralogical, groundwater and pore fluid hydrochemical and borehole NMR data has enabled maps of hydrostratigraphy, hydraulic conductivity, groundwater salinity, salt store and neotectonics to be produced.

The Frome airborne electromagnetic (AEM) survey is the largest of three regional AEM surveys flown under the 5-year Onshore Energy Security Program (OESP) by Geoscience Australia (GA). The aim of the survey is to reduce risk and stimulate exploration investment for uranium by providing reliable pre-competitive data. The Frome AEM survey was flown between 22 May and 2 November 2010, is approximately 95 450 km2 in area and collected 32 317 line km of new data at an average flying height of 100 m. The Frome AEM survey covers the Marree (pt), Callabonna (pt), Copley (pt), Frome (pt), Parachilna (pt), Curnamona, Olary and Chowilla (pt) 1:250 000 standard map sheets in South Australia and was flown largely at 2.5 km line spacing, with the northern portion flown at 5 km line spacing. GA partnered with, the Department of Primary Industries and Resources South Australia and an industry consortium. The survey results indicate a depth of investigation (DOI - depth of reliable signal penetration) of up to 400 m in areas of thin cover and resistive basement (e.g., Adelaidean rocks in the Olary Ranges). In Cenozoic - Mesozoic sediments in the Frome Embayment and the Murray Basin the DOI is up to 100-150 m. A range of under-cover features are revealed, including (but not limited to): extensions to known palaeovalley networks in the Frome Embayment; the under-cover extent of the Benagerie Ridge; regional faults in the Frome Embayment and Murray Basin; folded and faulted Neoproterozoic rocks in the Adelaide Fold Belt; Cenozoic - Mesozoic stratigraphy in the Frome Embayment; neotectonic offsets in the Lake Eyre Basin; conductive Neoproterozoic rocks associated with copper-gold mineralisation; and, coal-bearing structures in the Leigh Creek area, as well as groundwater features.

Under the Community Stream Sampling and Salinity Mapping Project, the Australian Government through the Department of Agriculture, Fisheries and Forestry and the Department of Environment and Heritage, acting through Bureau of Rural Sciences, funded an airborne electromagnetic (AEM) survey to provide information in relation to land use questions in selected areas along the River Murray Corridor (RMC). The proposed study areas and major land use issues were identified by the RMC Reference Group at its inception meeting on 26th July, 2006. This report has been prepared to facilitate recommendations on the Barr Creek - Gunbower study area. The work was developed in consultation with the RMC Technical Working Group (TWG) to provide a basis for the RMC Reference Group and other stake holders to understand the value and application of AEM data to the study area. This understanding, combined with the Reference Groups assessment of the final results and taking in account policy and land management issues, will enable the Reference Group to make recommendations to the Australian Government.

The floodplain of the lower Balonne River is in the upper reaches of the Murray Darling Basin. The region has been extensively developed for agriculture, in particular irrigated cotton, and is highly productive. Multidisciplinary investigations to inform land management generated extensive sets of remotely sensed data including Landsat TM, airborne gamma-ray radiometrics, aerial photography, ASTER imagery, and digital elevation models. These datasets provided the basis for regolith and geomorphic mapping. The wealth of data has allowed characterisation of the lower Balonne River system which is typical of many of the dryland rivers of southern Queensland. The geomorphic map of the lower Balonne floodplain has 8 major units based on landform and geomorphic processes. Bedrock consists of the slightly deformed and extensively weathered marine Cretaceous Griman Creek Formation. Coincident with erosion and weathering, Paleogene quartz gravels were deposited and are now extensively cemented and preserved as remnants forming zones of inverted relief. Much of the present landscape consists of a series of juxtaposed depositional units that have infilled an incised valley system. The different depositional units show the palaeo-Balonne River migrating to the west. This is interpreted to be a result of tectonic depression and tilting to the west, causing avulsion and anastomosing of the palaeo-channels. The modern Balonne River system consists of a number of easily recognised segments. In the north, the modern channel is incised as a single channel. To the south the channel opens out onto an anastomosing plain with branching and reconnecting small-scale channels. Source bordering dunes, currently inactive, have also formed along the western and eastern sides of the modern river and are prominent in large dunes in the south along the present Moonie River. Their absence in older landscape elements points to increasing aridity over time in the river system.

Geoscience Australia is a proscribed agency of the Australian Government, and has been acquiring precompetitive geophysics over the Australian continent and making it available to industry and researchers for over fifty years. Geophysical methods are especially important for effective exploration in Australia because the ancient landscape has been deeply weathered and fresh rocks are concealed beneath a thick layer of weathered material, referred to as regolith. The Onshore Energy Security Program is Geoscience Australia's latest precompetitive program and is designed to reduce risk in exploration for Australia's onshore hydrocarbon, uranium, thorium, and geothermal energy resources. The program will acquire and deliver pre-competitive geophysical and geochemical data as well as geological interpretations and other value-added products for the exploration industry.

More recently the O'Farrell government has called for expressions of interest to explore for uranium across NSW. Fugro Airborne Services Pty Ltd also called for expressions of interest in flying a large TEMPEST AEM survey in NSW covering the NSW Curnamona Province and portions of the Murray-Darling Basin and Lake Eyre Basin, abutting the SA border, to complement the Frome AEM Survey. The following is a brief summary of some of the main points discussed and presented during 3 presentations at the NSWGS on 19 September 2012, and in follow-up discussions on 20 September 2012. Approximately 40 people attended the three presentations. A discussion after the talks centred around using AEM in NSW for regional mapping including for uranium, porphyry copper-gold systems and massive sulphide systems. PowerPoint presentations were left with NSWGS. Three abstracts describing these presentations are included at the end of this document.