Airborne Electromagnetics
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The Ord is one of the largest rivers in northern Australia and is located in the Kimberley region of Western Australia. In this study we show that the lower Ord landscape near Kununurra in Western Australia consists of a large scale ancient landscape, possibly pre-Cambrian, being exhumed from beneath flat-lying Cambrian to Carboniferous cover rocks. Additional post-Permian landscapes are being formed by this process. The Ord Valley alluvium is of late Pleistocene to Holocene in age and consts off upward fining gravels, sands and clays infilling an inset valley profile. The Ord River initially flowed to the sea via the keep River estuary, however a major avulsion, possibly due to sedimentatain topping a low point in the surrounding valley walls, occurred possibly as recently as 1,800 years ago. As a result to mouth of the Ord shifted some 100 km to the east, to Cambridge Gulf, its course through the former alluvial plain and along the new course across the coastal plain was incised, and a scabland formed across the low point of Tararar Bar. This association of very ancient (pre-Paleozoic) landscape elements and by thin, very young weathering profiles and young sedimentary accumulations in alluvial valleys is paradoxical in the broader Australian pattern where very ancient landscape elements are associated with ancient sedimentary infill and weathering profiles.
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The Pine Creek AEM survey was flown over the Pine Creek Orogen in the Northern Territory during 2008 and 2009 as part of the Australian Government's Onshore Energy Security Program at Geoscience Australia (GA). The survey covers an area of 74,000 km2 from Darwin to Katherine in the Northern Territory which hosts several world class deposits, including the Ranger Uranium Mine, Nabarlek, Mt Todd, Moline and Cosmo Howley. Aimed at regional mapping, uranium exploration, reducing exploration risk and promoting exploration activity, the program worked closely with industry partners to infill wide regional line spacing (5km) with deposit scale line spacing (less than 1km). The survey results are relevant in exploration for a variety of commodities and resources, including uranium, copper, lead, zinc, gold, nickel and groundwater. Geoscience Australia's interpretation products include sample-by-sample layered earth inversion products comprising located data, geo-located conductivity depth sections, depth slice grids, elevation slice grids, inversion report and an interpretation report. All data and products are available from GA as well as the Northern Territory Geological Survey Geophysical Image Web Server.
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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.
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Short article describing a new method of defining depth of investigation for airborne electromagnetic surveys
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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 (this data set) 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 adjoining to the south, 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 studies in the region. This dataset includes the subscriber company data K1 K2 and K3.
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At present calcrete-hosted uranium deposits constitute only 1% of Australia's uranium resources. Most known deposits (nine out of eleven) are associated with Cenozoic drainage systems in the Yilgarn Craton, and similar drainage systems in the Gascoyne Province and Ngalia Basin. In the Paterson region calcrete-hosted uranium mineralisation has been reported only in the Lake Waukarlycarly area but no major deposit of this type has yet been found.
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Geoscience Australia (GA) has recently completed two regional-scale Airborne Electromagnetic (AEM) surveys: one in the Paterson Region, WA; and the other in the Pine Creek region, NT. These surveys provide AEM data at line spacings of 200 m to 6 km covering an area greater than 110 000 km2. The surveys were designed to promote more detailed investigations by the mineral exploration industry. An inherent risk in using AEM surveys is that the depth of penetration of the primary electromagnetic field is highly variable. Although forward modelling is undertaken before the AEM campaign, the depth to which we can reliably invert the AEM signal to generate conductivity models is not known until after the survey is flown. In order to estimate the penetration depth of the AEM surveys, we calculate the depth of investigation (DOI) based on the GA layered-earth inversion algorithm, which is influenced by both conductivity measurements and reference model assumptions. We define the DOI as the maximum depth at which the inversion is influenced more by the conductivity data than the reference model. We present the DOI as a 2D grid across both the Paterson and Pine Creek AEM surveys. Labelled the 'AEM go-map', the DOI grid helps to promote AEM exploration by decreasing risk when industry undertakes follow-up surveys within these regions.
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The Broken Hill Managed Aquifer Recharge (BHMAR) project is part of a larger strategic effort aimed at securing Broken Hill's water supply and identifying significant water-saving measures for the Darling River system. Hydrogeological investigations to rapidly identify and assess potential MAR targets and groundwater resources over a large area (>7,500 km2), included acquisition of an airborne electromagnetics (AEM) survey, a 7.5 km drilling program (100 sonic and rotary mud holes), and complementary field and laboratory hydrogeochemical investigations. The study identified an excellent aquifer (the Calivil Formation), with high storage capacity, very high transmissivities (up to 50 l/s), and significant volumes of fresh groundwater. The aquifer is sandwiched between variably thick clay aquitards, and can be characterised as varying from a confined to a 'leaky confined' system. The hydraulic properties make the Calivil Formation aquifer potentially suitable for groundwater extraction and/or MAR injection, with excellent recovery efficiencies predicted. Mapping identified a number of potential suitable locations for MAR options, for which entry-level risk assessments were carried out. Targets were prioritised, and a pre-commissioning semi-quantitative residual risk assessment carried out for a priority site. Assessment of 12 hazard types included hydrogeological modelling, laboratory column clogging studies and geochemical assessment to assess source water treatment requirements. The study found that all of the scientific/technical risks for MAR at the priority target are low. The integrated analysis has identified a range of possible MAR options including injection, passive or enhanced recharge, and/or conjuctive use involving a combination of surface, groundwater extraction and/or MAR options.
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The National Geochemical Survey of Australia project represents an essential component of the Australian Government's Onshore Energy Security Initiative. The national geochemical survey involves the use of field-tested methods for collection and analysis of transported regolith samples representative of catchments covering most of Australia. The project is a collaboration between Geoscience Australia and State and Northern Territory geoscience agencies, which will provide an internally consistent geochemical dataset useful for calibration and ground-truthing of airborne radiometrics surveys. The survey also will help to fill gaps in current airborne radiometrics and geochemical coverages of Australia, provide multi-element characterisation and ranking of radiometric anomalies and aid in first-order investigation of the nature of geothermal hot-spots. As a result it will support and add value to numerous other Onshore Energy Security Initiative projects and have wider applications in mineral exploration and in environmental assessment and management. This report details the methodology underpinning the determination of the theoretical sampling points using terrain and hydrological analysis; and the protocols for sample collection. It will be used for knowledge transfer during training sessions for the State and Northern Territory field parties who also will receive field equipment and consumables which will ensure there is consistent sampling throughout the project. A digital data entry template has been designed to enable efficient and consistent in-field data capture, which also will streamline data entry into Geoscience Australia's corporate databases.
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The record is a presentation given by Adrian Fisher to staff of the Aditya-Birla Nifty copper mine and to staff at the Geological Survey of Western Australia, August 2007. It describes the planning behind the Paterson AEM survey, to be acquired in 2007-2008.