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

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.

Provides an overview of the Project in the context of the Onshore Energy Security Program in advance of the presentations dealing with the acquisition, data, procedures and interpretation results of the survey.

Geoscience Australia (GA) has recently released regional AEM data in two survey areas of the Pine Creek region. The Woolner Granite-Rum Jungle survey in the western part of the region was flown using TEMPESTTM and the Kombolgie survey in the eastern part was flown using VTEMTM. These data assist mapping shallow subsurface geological features for mineral explorations including uranium. Conductivity estimates derived for the Woolner-Rum Jungle surveys using GA's Layered Earth Inversion (GA-LEI) algorithm reveal several unconformities and conductors in sedimentary sequences interpreted mostly within the top 300-400 m of the crust, including: 1. The Depot Creek unconformity over the Paleoproteroic Pine Creek Orogen and Archean. A 3D model derived from these data shows the geometry and lateral extent of part of the Depot Creek unconformity with a clarity previously not available; 2. Strong conductors of carbonaceous and pyritic materials in the South Alligator River Group and Mt Partridge Group, 3. Moderate to week conductors revealed in the sedimentary sequences of the Birrindudu, Daly and Bonaparte Basins, and 4. Faults and folds. EM FlowTM (Version 5.23-13) sections from the Kombolgie survey not only map the Kombolgie unconformity over the Pine Creek Orogen and Archean and other conductors in the Katherine River Group, but also map conductors in pre-Kombolgie basement to a depth up to 2 km. Penetration to this depth represents a major breakthrough in AEM survey capability, achieved in part due to the extremely resistive rocks in the area. Geological cross-section interpretations based on conductivity images also incorporate available drill hole data to help improve section reliability. The implications of these AEM data for uranium and gold mineral systems in the Pine Creek region are discussed in the companion paper by Jaireth et al. (this volume).

The continuing world demand for potash (potassium salts) is driving a new exploration boom in the Australian minerals industry for this valuable resource, listed by Geoscience Australia (GA) as a strategic commodity (Mernagh 2013). The Food and Agriculture Organization of the United Nations (FAO) predicts a rising demand for fertilizers, with potash demand increasing at 3.7% per annum (FAO 2012), and Rabobank predicts that demand will exceed supply by up to 100% by 2020 (Rabobank 2012). This demand is driving the application of airborne electromagnetics (AEM) to map salinity as a proxy for potential potash resources in salt lakes. This short paper describes a few of the applications and is written in response to an industry request to GA for information on how AEM might be used to explore for potash.

The first airborne scintillometer surveys to be carried out by the Geophysical Section of the Bureau have now been completed. In this work the Shoran radar positioning system was also used for the first time. Detailed surveys were made over an area of about one thousand square miles surrounding the Rum Jungle granite and one of about twenty square miles in the Edith River district. In addition, flights were made over several other known granite masses in the northern part of the Northern Territory and along both sides of the railway line from Batchelor to Katherine. In addition to the Dakota aircraft, an Auster aircraft was chartered for some experimental low-level flights over areas of special interest selected on the basis of indications discovered during the survey by the Dakota. Instruments and methods used in the course of the surveys, results, and conclusions are discussed.

Geoscience Australia (GA) has recently released regional airborne electromagnetic data (AEM) in two survey areas of the Pine Creek region. The Woolner Granite-Rum Jungle survey in the western part of the region was flown using TEMPESTTM and the Kombolgie survey in the eastern part was flown using VTEMTM. These data assist in mapping geological features deemed to be critical for fertile unconformity-related uranium and sandstone-hosted uranium systems. These mapped features in combination with other datasets are used to assess the prospectivity of uranium systems.

During 2008 and 2009, and under the Australian Government's Onshore Energy Security Initiative, Geoscience Australia acquired airborne electromagnetic (AEM) data over the Pine Creek Orogen of the Northern Territory. The survey area was split into three areas for acquisition. VTEM data was acquired in the Kombolgie area east of Kakadu National Park between August and November 2008. TEMPEST data was acquired west of Kakadu National Park with the area split in two to facilitate the use of two aircraft: the Woolner Granite area in the north was acquired between October and December 2008; and the Rum Jungle area (this data set) adjoining to the south, which was acquired between October 2008 and May 2009. The main purpose of the surveys was to provide additional geophysical/geological context for unconformity style uranium mineral systems and thereby promote related exploration. The survey data will also provide information on depth to Proterozoic/Archean basement, which is of general interest to explorers, and will be used as an input into ground water studues in the region.