Airborne electromagnetic (AEM) data are being acquired by Geoscience Australia (GA) under the Australian Government's Onshore Energy Security Program (OESP) in areas considered to have potential for uranium or thorium mineralisation. In contrast to deposit-scale investigations carried out by industry these surveys are designed to reveal new geological information at a regional scale. The Frome AEM survey shown in Figure 1 was flown by Fugro Airborne Surveys for GA, using the TEMPESTTM time-domain system. The survey was conducted with the aims of reducing exploration risk, stimulating exploration investment and enhancing prospectivity within the region primarily for uranium, but also for other commodities including copper, gold, silver, lead, zinc, iron ore and potable groundwater. The Frome AEM survey was primarily designed to be a regional mapping program for mapping surface and subsurface geological features that may be associated with sandstone-hosted uranium systems. The data are also capable of being interpreted for landscape evolution studies within the flanks of the tectonically active Curnamona Province and Flinders Ranges of South Australia. In this article we present an enhanced set of conductivity estimates which are now available from the GA website free of charge. These conductivity estimates reveal new geological information

This publication is an outcome of a meeting entitled "Transient and Induced Variations in Aeromagnetics" that was held in Canberra on 18 September 1996 to discuss the effects of rapid fluctuations of the geomagnetic field on high-resolution aeromagnetic surveys and airborne detection systems. The meeting brought together people from the exploration and mining industry, Defence, Government Science, and Universities with common interests in the nature and applications of external magnetic fields and of the electromagnetic properties of the Earth's crust and oceans. Inevitably, much of the focus was on the use of base stations and tie lines for correcting for the influence of geomagnetic fluctuations in survey data. However, the discussion ranged widely from magnetospheric physics to the magnetic effects of ocean swells at aeromagnetic elevations.

Displays the coverage of publicly available digital airborne electomagnetic survey data. The map legend is coloured according to the line spacing of the survey.

Extended abstract regarding the Frome AEM data set and Murray Basin geology and landscape evolution

The holistic inversion approach for frequency domain AEM data (Brodie and Sambridge, 2006) has previously been employed to simultaneously calibrate, process and invert raw frequency-domain data where prior information was available. An alternative formulation has been developed, which is suitable in the case where explicit prior information is not available. It incorporates: a multi-layer vertically-smooth conductivity model; a simplified bias parameterization; horizontal smoothing with respect to elevation; and cluster computer parallelisation. Without using any prior data, an inversion of 8.0 million data for 3.4 million parameters yields results that are consistent with independently derived calibration parameters, downhole logs and groundwater elevation data. We conclude that the success of the holistic inversion method is not dependent on a sophisticated conceptual model or the direct inclusion of surrey-area specific prior information. In addition, acquisition costs could potentially be reduced by employing the holistic approach which may eliminate the need for high altitude zero-level measurements.

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

Data from a VTEM airborne electromagnetic survey over resistive terrain is examined. Forward modelling and analysis of high-altitude lines shows that the amplitudes of random noise, bucking error, processing corrections and geological signals can be large compared to the geological signal in the resistive terrain. The negative impacts of the low geological signal to noise ratio on conductivity estimates generated by layered-earth inversion and conductivity transformations are demonstrated. The reader is alerted to the degree of uncertainty and non-uniqueness that is inherent in conductivity estimates generated from similar datasets.

The Frome airborne electromagnetic (AEM) survey is the last and largest (in line kilometres and area) of the three AEM surveys flown under the Onshore Energy Security Program at Geoscience Australia. The survey covered about 95 000 km2 (about six 1:250 000 map sheets) and covered the Frome Embayment, northern Murray Basin and the flanks of the Eromanga Basin in South Australia. Survey data are providing new insights into the stratigraphy of the Frome Embayment and Murray Basin, and will add to our knowledge of the sources and sinks of sandstone related uranium mineral systems, as well as base metals, gold and copper, in this highly prospective area, as well as ground water resources. This seminar will present highlights of the survey and demonstrate AEM data integrated with other data sets to develop 3D models to explorable depths, lowering exploration risk.

Airborne Electromagnetic data are being acquired by Geoscience Australia (GA) under the Australian Government's Onshore Energy Security Program (OESP) in areas considered to have potential for uranium or thorium mineralisation. The surveys have been managed and interpreted by GA's Airborne Electromagnetic Acquisition and Interpretation project. In contrast to deposit scale investigations, conducted by industry, these surveys are designed to reveal new geological information at a regional scale. The Pine Creek airborne electromagnetic survey show in Figure 1 is comprised of three survey areas; Woolner Granite, Rum Jungle and Kombolgie. TEMPESTTM data were acquired for the Woolner Granite and Rum Jungle surveys and VTEMTM data were acquired for the Kombolgie survey. The Kombolgie survey, in the Pine Creek Orogen of the Northern Territory, covered sections of the Alligator River, Cobourg Peninsula, Junction Bay, Katherine, Milingimbi and Mount Evelyn, 1:250 000 map sheets (Costelloe et al., 2009). A total of 8 800 line km of VTEMTM data were acquired in 2008, covering an area of 32 000 km2. In 2009 the processed response data and EM FlowTM commercial version 3.30 (Macnae et al., 1998, Stolz and Macnae 1998) conductivity estimates to 600 m depth, produced by the survey contractor Geotech Airborne, were made available to the public in the GA Phase-1 data release. In this article we discuss an enhanced set of conductivity estimates, which are now available from the GA website free of charge. These new conductivity estimates, reveal new geological information to depths approaching 2 km in the more resistive portion of the survey area. They were generated by GA using the most recent version (5.23-13) of EM FlowTM.

In many floodplain landscapes in Australia, surface-groundwater interactions are poorly understood. There is limited mapping of recharge and discharge zones along the major river systems, and only generalised quantification of hydrological fluxes based on widely spaced surface gauging stations. This is compounded by a lack of temporal data, with poor understanding of how surface-groundwater interactions change under different rainfall, river flow and flood regimes. In this study, high resolution LiDAR, in-river sonar, and airborne electromagnetic (AEM) datasets (validated by drilling) have been integrated to produce a detailed 3-Dimensional map of surface geomorphology and hydrogeology. These maps enable potential recharge zones in the river and adjacent landscape to be identified and assessed under different flow regimes. These potential recharge zones and groundwater flow pathways were then compared against the spatial continuity of (and presence of) 'holes' in near-surface and deeper aquitard layers derived from the AEM. These 3D mapping constructs provide a framework for considering groundwater processes. Hydrochemistry data, allied with hydraulic data from a bore monitoring network, demonstrate the importance of recharge during significant flood events. In many places, the AEM data also affirm the spatial association between fresher groundwater resources and sites of river/floodplain leakage. At a more localised scale, hydrogeochemical data allows discrimination of lateral and vertical fluxes. Overall, this integrated approach provides an important conceptual framework to constrain hydrogeological modelling, and assessments of sustainable yield. The constructs are also invaluable in an assessment of managed recharge options and locations.