Geoscience Australia (GA) has implemented an Onshore Energy Security Program (OESP) to identify Australia's onshore energy resources. The objectives of the OESP are to provide essential pre-competitive geoscientific data to lower exploration risk and stimulate investment in exploration for Australia's uranium, thorium, geothermal and onshore petroleum resources. The program is funded under a new Energy Security Initiative announced by the Australian Government in August 2006. As a key component of the OESP GA will be conducting geophysical surveys across Australia for the next four years collecting the following data: deep seismic reflection, magnetotelluric, airborne magnetic, radiometric, electromagnetic and ground based gravity. The demand for resources, and increased funding by the Commonwealth, States and NT, have been the driving factors in the recent improvement in the regional geophysical coverage of Australia.

This report summarises the result of a study into seawater intrusion into coastal aquifers in the Northern territory coastal plain using AEM data, down hole geophysics, and bore hole geology carried out by Geoscience Australia on behalf of the National Water Commission and in partnership with NRETAS. The study showed that ground-validated AEM is able to map areas of saline aquifers in the area and differentiate them from bedrock conductors.

The Gilmore Project is a pilot study designed to test holistic systems approaches to mapping mineral systems and dryland salinity in areas of complex regolith cover. The project is coordinated by the Australian Geological Survey Organisation, and involves over 50 scientists from 14 research organisations. Research partners include: Cooperative Research Centres for Advanced Mineral Exploration Technologies (CRC AMET), Landscape Evolution and Mineral Exploration (CRC LEME), the CRC for Sensor Signal and Information Processing, and the Australian Geodynamics Cooperative Research Centre (AGCRC) Land & Water Sciences Division of Bureau of Rural Sciences (BRS) NSW Department of Land & Water Conservation and the NSW Department of Mineral Resources. Various universities including the Australian National University, University of Canberra, Macquarie University, Monash University, University of Melbourne, and Curtin University of Technology, and Australian National Seismic Imaging Resource (ANSIR). The project area lies on the eastern margin of the Murray-Darling Basin in central-west NSW. The project area was chosen for its overlapping mineral exploration (Au-Cu) and salinity management issues, and the availability of high-resolution geophysical datasets and drillhole materials and datasets made available by the minerals exploration industry. The project has research agreements with the minerals exploration industry, and is collaborating with rural land-management groups, and the Grains Research and Development Corporation. The study area (100 x 150 km), straddles the Gilmore Fault Zone, a major NNW-trending crustal structure that separates the Wagga-Omeo and the Junee-Narromine Volcanic Belts in the Lachlan Fold Belt. The project area includes tributaries of the Lachlan and the Murrumbidgee Rivers, considered to be two of the systems most at risk from rising salinities. This project area was chosen to compare and contrast salt stores and delivery systems in floodplain (in the Lachlan catchment) and incised undulating hill landscapes (Murrumbidgee catchment). The study area is characteristic of other undulating hill landscapes on the basin margins, areas within the main and tributary river valleys, and the footslopes and floodplains of the Murray-Darling Basin itself. Studies of the bedrock geology in the study area reveal a complex architecture. The Gilmore Fault Zone consist of a series of subparallel, west-dipping thrust faults, that juxtapose, from west to east, Cambro-Ordovician meta-sediments and granites of the Wagga Metamorphics, and further to the east, a series of fault-bounded packages comprising volcanics and intrusions, and siliciclastic meta-sediments. Two airborne electromagnetic (AEM) surveys were flown in smaller areas within the two catchments. Large-scale hydrothermal alteration and structural overprinting, particularly in the volcanics, has added to the complexity within the bedrock architecture.

In 2008-2009 Geoscience Australia, contracted Fugro Airborne Surveys and Geotech Airborne, to respectively acquire TEMPEST and VTEM airborne electromagnetic (AEM) data with broad line spacings covering more than 71 000 km² in the Pine Creek region, Northern Territory. The Pine Creek survey (Figure 1) is the second regional AEM survey funded by the Onshore Energy Security Program (OESP) at Geoscience Australia. Geoscience Australia funded the flying of 19 500 line km, subscriber companies funded 10 400 line km. The 5 000 m line spacing provide regional information with 1 666 m, 555 m and closer line spacing providing detail for mineral systems analysis and deposit scale mapping. One of the main survey objectives was to reduce exploration risk and encourage exploration in the region by mapping, under cover, in areas where gravity and magnetics are quiet. Geological targets included detecting: conductive unites within the Pine Creek Orogen (PCO) sequence; Kombolgie Sandstone / PCO unconformity; Tolmer Group/ Finniss River Group unconformity. Geoscience Australia undertook conductivity logging (Figure 2) in the Pine Creek region. Conductivity logs were processed and as input into forward models, ground truth AEM results and for geological interpretations. To facilitate interpretation, subsurface electrical conductivity predictions using a layered earth inversion (sample by sample) algorithm developed by Geoscience Australia (GA-LEI) were derived from the AEM survey data. Conductivity characterisation of large regional units using the AEM data show: the Rum Jungle Complex is a consistently resistive area with an average conductivity value of less than 2 m/S; the Mt Partridge Group has a conductivity value up to 100 m/S; the Kombolgie Sandstone has a conductivity range of less than 2 m/S in more areas. Detecting conductivity contrasts in areas with known uranium prospectivity aids in a mineral systems analysis and geological interpretation of uranium deposits.

Presentation to minerals industry representatives at the Geological Survey of Western Australia, 4 May 2010.

A wide-angle reflection seismic survey coincident with a regional transect through Northeastern Yilgarn Craton focused on the Leonora-Laverton Tectonic Zone, Western Australia, was carried out to supplement deep seismic reflection studies. The major objectives were: to collect high-density refraction information for offsets of up to 60 km; to carry out a comparative study of near-vertical and wide-angle seismic images of the crust in the study area; to obtain velocity information for the upper crust. The survey deployed 120 short period recorders with a 500 m spacing. Acquisition parameters used for the wide-angle reflection experiment were selected so that it would to fit into the schedule and technology of the conventional reflection survey. The same vibrations were recorded in both surveys simultaneously. The major challenge in processing the wide-angle data was to manage the huge volume of information. The processing sequence included sorting into receiver and source gathers, cross-correlation with reference sweeps and stacking original seismic traces to form single source point traces, producing seismograms from individual traces and finally creating seismic record sections from separate seismograms. High amplitude seismic signal from vibroseis sources was recorded at least up to 50 km offsets in the first arrivals, and later arrivals were observed down to 12 s next to sources. A preliminary upper crustal model developed from the wide-angle data shows that the thickness of a high velocity layer, corresponding to the greenstone rocks, is 4.0-4.5 km. The boundary separating this layer from a low velocity layer below it is possibly a compositional boundary between greenstones and underlying felsic gneisses. There is no evidence for high velocity material below this boundary. Assuming the Moho belongs to deepest reflections modelled, total crustal thickness in the region can be speculatively estimated in the range 32-37 km.

Airborne Geophysical Data Acquired as part of the Gawler Mineral Promotion Project. Includes point located, gridded and image data. TEMPEST electromagnetics, magnetics and elevation data.

Alan Yusen Ley-Cooper Ross C. Brodie Inversion of SPECTREM AEM data for conductivity and system geometry We evaluate the use of airborne electromagnetic data from the SPECTREM2000 system flown for ore body detection, regolith mapping and assessment of aquifers. Since the position and orientation of the receiver bird are not measured, the primary field at the bird cannot be known and removed precisely. In order to successfully invert the AEM data, and produce conductivity-depth models, we first reinstate the removed primary field estimate and convert the data from ppm units to Teslas. We then simultaneously inverted the X and Z component data, to solve for a 1D layered conductivity model and receiver position. The SPECTREM system has flown many line kilometres in other parts of the world but substantially less in Australia. Through further processing and inversions we have resolved conductivity-depth structures very similar to those previously obtained from other well-established AEM systems flown under Australian conditions. We also present a section of AEM data with logged drilling core data as a means of assessment of our inversion models against an independent data set. Key words: Airborne EM, inversion, geometry, SPECTREM, electrical conductivity.

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

The product consists of 5,291 line kilometres of time-domain airborne electromagnetic (AEM) geophysical data acquired in the Fitzroy River Catchment of the West Kimberley region, the electrical conductivity models derived from the dataset, and the survey operations and processing report. The data were acquired using the heliborne SkyTEM-312 AEM system. A locality diagram for the survey is shown below. The survey was funded by the Government of Western Australia, as part of its Water for Food Initiative, through the Department of Water (WA DoW). The survey was managed by Geoscience Australia as part of a national collaborative framework project agreement with WA DoW. The aim of the survey was to map the electrical properties of the top 200-300 metres of the sub-surface geology and hydrogeology within the study area. Geoscience Australia contracted SkyTEM Australia Pty Ltd to acquire the AEM data using the SkyTEM-312 system in September and October 2015. The data were also processed by SkyTEM Australia Pty Ltd using its in-house processing and inversion techniques. The Kimberley Region in north-west Australia is a priority area for the development of irrigated agriculture. The hydrogeology of the area is poorly understood, hence the primary aim of the AEM survey was to provide geophysical data in support of groundwater investigations. Specific objectives of the AEM survey included mapping the extent of regional Canning Basin aquifers to aid assessment of groundwater resources and sustainable yield estimates for agricultural development; provide AEM data in transects to underpin studies of surface-groundwater interactions (groundwater discharge and recharge potential) associated with the major rivers, and permanent river pools in particular; detect and assess potential groundwater salinity hazards within proposed irrigation areas; and map the seawater intrusion (SWI) interface. Very specific mapping objectives were developed for each sub-area, and the survey was designed with these detailed local objectives in mind. The survey design reflects two scales of investigation: 1. Two areas (Knowsley-Mowanjum and GoGo-Fitzroy Crossing) with higher density flight line spacing (400 m) in areas with advanced plans for development of irrigated agriculture; 2. Irregular grid of regional transects and lines acquired along river tracts reflecting the reconnaissance nature of regional investigations in a frontier hydrogeological area. Much of the area lies underneath cover of sedimentary basins and is a poorly-understood element of Australia¿s geology. The Fitzroy Trough is also host to a number of mineral systems including diamonds and base metal mineralisation, as well as shale gas resources. The survey data should assist with understanding of the basin geology and neotectonics, while lamproite pipes have also been intersected in a number of flight lines. The survey data will also add to the knowledge of the thickness and character of alluvium and regolith cover and will inform future geological mapping in the region. The data will be available from Geoscience Australia¿s web site free of charge. The data release package includes: 1. Point-located electromagnetic line data with associated position, height, orientation, transmitter current, and derived ground elevation data. These data are in ASCII column format with associated ASEG-GDF2 header files. All regular survey, repeat lines and high altitude lines are included in the dataset. The dataset is split into Parts 1 and 2 based on the differences in the receiver gate times for each part. 2. Point-located magnetic line data with associated position, height, orientation, and derived ground elevation data. These data are in ASCII column format with associated ASEG-GDF2 header files. All regular survey, repeat lines and high altitude lines are included in the dataset. 3. Point-located line data for conductivity estimates derived by SkyTEM Australia Pty Ltd using its Automated Laterally Constrained Inversion (aLCI) algorithm with associated position, height, orientation, and derived ground elevation data. Data include the conductivity estimate for each of the 30 inversion model layers, the layer elevation, estimated depth of investigation, and data fit residuals. These data are in ASCII column format with associated ASEG-GDF2 header files. All regular survey and repeat lines are included in the dataset. 4. Gridded data for the derived ground elevations, total magnetic intensity, and the conductivity of the 30 aLCI inversion model layers. The grids are in ER Mapper® binary raster grid format with associated header files. The grids have a cell size of 100 m. For the aLCI inversion layer conductivity grids, there are versions that are masked (set to undefined) below the estimated depth of investigation and unmasked. 5. Graphical multiplots and spatial images derived from the aLCI inversion. The multiplots show the derived aLCI conductivity depth sections and selected data panels for each individual flight line in Portable Network Graphics (PNG) and Portable Document Format (PDF) formats. The spatial images show colour images of the conductivity for each aLCI model layer and are in PNG, PDF and geo-located Tagged Image Format (TIF) files suitable for use in MAPINFO. 6. The survey Operations and Processing Report, which provides the details of the AEM system, logistics, data acquisition, data processing and the aLCI inversion parameters. 7. ESRI shapefiles and KML files of flight lines. Summary Survey Name West Kimberley Airborne EM Survey, WA, 2015 (Water for Food) State Western Australia Sub Region West Kimberley Area 20,314 km2 Line km 5,291 km Survey Completed 17 October 2015 AEM system SkyTEM-312 Processing SkyTEM Australia Pty Ltd