Want to find out more about the Gawler Craton Airborne Survey? Read our frequently asked questions.
The Gawler Craton is the name of the oldest and largest geological province in South Australia, occupying over 40% of the state’s total area. It is characterised by ancient geology dating back approximately 3,000 Million years and hosts the world class Olympic Dam copper deposit. Refer to our map for an indication of the Gawler Craton Airborne Survey boundaries.
An airborne survey captures high resolution geophysical and topographic mapping data. The survey is performed by low-flying aircraft, using sensors that will acquire magnetic intensity, radiometric and elevation data that will help us to better understand the geology, and inform stakeholders in how best to manage our natural resources in South Australia. This mapping data will be freely available online via the Department’s South Australian Resource Information Gateway (SARIG) application.
The Gawler Craton Airborne Survey aircraft will have instruments capturing Magnetic intensity, Radiometrics and Ground Elevation. You can learn more about these and other geoscientific data by reading our geophysical data page.
Data captured by the survey reveals the composition of rocks at and beneath the earth’s surface. After being made freely available to the public via SARIG, the information will provide a greater understanding of the geoscience framework, enabling land management, resource potential and water research activities. Together, these will support a balanced approach to future economic, environmental and community programs in South Australia.
No, the aircraft will not be capturing any information or data, other than geophysical and elevation data.
The results of the survey will not directly detect the presence of copper, but will greatly improve our understanding of the physical properties of the geology in the region (e.g. how magnetic different rock units are at depth, below the surface).
To determine the location of areas with enriched copper, mineral exploration companies will need to independently assess all available data, be granted an Exploration Licence by the Government and perform chemical analyses on samples obtained from an area of interest. Exploration companies work within legislative requirements, which include liaison with landowners and community stakeholders.
Further information on landowner rights when working with mineral exploration companies can be found via our land access community information webpages.
If the map does not look right on your computer, try refreshing the page while holding down the Ctrl key on your computer keyboard. This will reload the page, ignoring anything “cached” on your computer and has been found to solve most of the map display issues we have encountered so far.
Following completion of a survey block, the survey contractor needs time to process the data they have acquired into a final set of products. For survey blocks of this size, the time required is around ten weeks per block. Subsequent to the contractor's data processing, federal and state government agencies will perform a final quality check and prepare the data for release. This will add four to six weeks to the final release date. Data can then be downloaded from both the Geoscience Australia and SARIG data portals. Subscribing to the email updates will ensure you are notified of data releases and other milestone events.
Data acquired during the Gawler Craton Airborne Survey (GCAS) have been made available to the public through data packages and reports made available through the GCAS community information website, SARIG and Geoscience Australia. Located data, grids and processing reports make up the primary deliverables. Data types acquired are total magnetic intensity, radiometrics and digital elevation models. Magnetic data measures the strength of the magnetic field; radiometrics measures the concentration of radioelements at the surface and elevation measures the height of the earth’s surface. A suite of enhanced images and magnetic source depth models are also being made available as additional download packages and reports.
Airborne survey data are acquired along “flight lines”, the pre-determined lines the aircraft flies during the survey. For the Gawler Craton Airborne Survey flight lines were 200m apart and the ground clearance was 60m. Flight direction is most often dictated by the strike, or prevailing direction of the underlying geology”, with a preference to fly orthogonal to strike. The aircraft ground speed is approximately 70m/sec. All data are acquired as “located data”. Located data are points along the flight lines. Each instrument measuring data has its own frequency of measurement or sampling rate (samples per second). The speed of the aircraft, coupled with the sampling rate dictates the spread of data along each flight line. Magnetic data was acquired at 10 or 20Hz (10 – 20 measurements per second), which equates to a sample every 3.5 to 7 metres. Radiometric data is acquired at 1 Hz, or approximately every 70 metres, elevation data is acquired at 1 - 2 Hz, or approximately every 35 to 70 metres. The acquisition system information for each survey block is detailed in the geophysical contractor’s acquisition and processing report, available for each GCAS block upon release of the data.
Located magnetic data are used primarily by geophysicists for quantitative modelling to determine the source depth of the magnetic signal, as an input in the creation of 2.5D and 3D models or to generate magnetic “profiles” along flight lines. Profile information can also be interpreted geologically. Located elevation data are used to generate elevation profiles that complement the magnetic profile data or are used to map changes in ground elevation along the acquisition lines. Radiometric located data as profiles are seldom used for interpretation but may be used to pinpoint the location of radioelement anomalies or for quality control. Located data along flight lines provides the highest resolution of the acquired data because it includes each and every acquired point of data.
Located data are processed to produce “grids” - 2D interpolations of the located data. Before gridding takes place the data must be “levelled”. Levelling is a process that makes the data internally consistent and is a highly specialised technical process performed by skilled practitioners. Levelling uses “tie lines” – lines flown orthogonal to the acquisition lines, specifically for the purpose of levelling the survey. Once the located data are levelled, “micro-levelling” is usually required. As the name implies, micro-levelling makes the located data internally consistent at a finer scale. This fine scale micro-levelling prepares the located data for “gridding”.
Gridding is a process of interpolating the located data into a 2D surface that covers the survey region. Data is represented as a matrix of grid cells. Magnetic grids are used by geophysicists and geologists to interpret geology and geological structure; perform 3D “inversions” of the magnetic data and compute depth estimates to the source of the magnetic response. Gridded data is used for mineral exploration targeting, geological interpretation and presentation of the data.
Radiometric grids are used to directly detect element concentrations of Potassium (K), Thorium (Th) and Uranium (U). This is of benefit to mineral explorers targeting certain commodities. Radiometric grids also provide scientists with insight into landscape evolution, including transport of cover materials, helping geologist unravel the evolutionary history of the landscape. Elevation grids are used for a number of scientific and community purposes, however the resolution and quality of elevation data acquired by aircraft flying 200m flight lines is lower than some freely available satellite derived elevation models (i.e. 1 second shuttle radar topography mission). Nevertheless, the elevation grids are made available as part of a package of deliverables.
Enhancements performed by the survey contractors and available on initial release of the data include a reduction to pole (RTP) and first vertical derivative (1VD). Further enhancements have been performed by the GSSA and its collaborator s on GCAS magnetic data, including second vertical derivative; total gradient of TMI; tilt of TMI; trend of TMI, trend consistency of TMI and Bzz of TMI (vertical gradient of the vertical component). Magnetic source depth estimation has been performed across the entire GCAS survey area and is being made available as part of value-added packages which also contains the image enhancements listed above.
The data enhancements provided during this project are enhancements often performed by exploration companies on data they themselves acquire. By performing these enhancements at the outset, the Government of South Australia is providing the exploration industry with a higher resolution and more consistent mapping of the magnetic field than is available from the previous multi-survey coverage. Advantages of the new survey data are evident on inspection of the primary total magnetic intensity (TMI) data (i.e.: improved resolution and detail), but it is on enhancement of that TMI data to assist recovery of geological information that the advantages are most clearly expressed. Many of the enhancements performed are of limited application to the previous TMI data across the area because of insufficiencies and imperfections in that data together with abrupt contrasts on passing between surveys of different line spacing, flying height or flight-line orientation. The advantage of consistency and close line spacing also supports higher resolution and more confident source depth mapping from the magnetic field data. The output of this effort is a collection of images and digital data products generated to facilitate geological interpretation. The products are not themselves interpretive, but provide more direct access to interpretation than does the directly measured data itself. These products, and in particular the magnetic source depth estimates, are designed to provide the genesis of a ‘live’ resource which can be progressively upgraded rather than simply replaced as further studies are undertaken in the area, the depth solution database is added to, or new drillholes are reported.