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    Total magnetic intensity (TMI) data measures variations in the intensity of the Earth's magnetic field caused by the contrasting content of rock-forming minerals in the Earth crust. Magnetic anomalies can be either positive (field stronger than normal) or negative (field weaker) depending on the susceptibility of the rock. The data are processed via standard methods to ensure the response recorded is that due only to the rocks in the ground. The results produce datasets that can be interpreted to reveal the geological structure of the sub-surface. The processed data is checked for quality by GA geophysicists to ensure that the final data released by GA are fit-for-purpose. This Magnetic Anomaly Map of Australia, Seventh Edition, 2019 TMI Greyscale image is a greyscale image of the TMI grid of the Magnetic Anomaly Map of Australia, Seventh Edition, 2019. The 2019 Total magnetic Intensity (TMI) grid of Australia has a grid cell size of ~3 seconds of arc (approximately 80 m). This grid only includes airborne-derived TMI data for onshore and near-offshore continental areas. Since the sixth edition was released in 2015, data from 234 new surveys have been added to the database, acquired mainly by the State and Territory Geological Surveys. The new grid was derived from a re-levelling of the national magnetic grid database. The survey grids were levelled to each other, and to the Australia Wide Airborne Geophysical Survey (AWAGS), which serves as a baseline to constrain long wavelengths in the final grid. It is estimated that 33 500 000 line-kilometres of survey data were acquired to produce the 2019 grid data, about 2 000 000 line-kilometres more than for the previous edition. The grid used to produce this greyscale image has a cell size of 0.00083 degrees (approximately 80m). This greyscale image shows the magnetic response of subsurface features with contrasting magnetic susceptibilities. The image can also be used to locate structural features such as dykes.

  • Standard curves for interpretation of the magnetic anomalies due to spheres have been derived. The anomalies in the vertical component, and the horizontal component in the direction of the traverse, are each found to be represented by a single family of curves. The horizontal component is found to be not represented by a single family, and separate curves for each field inclination and traverse azimuth are presented. Curves for the anomaly in the total intensity were not computed.

  • A depth to magnetic basement map has been produced for the Gawler-Curnamona region of South Australia. The map combines depth to magnetic source estimates with outcrop, drill hole and seismic data. The spectral domain method of analysing the slope of straight line segments in the power spectrum was used to produce the majority of the magnetic source depth estimates. The spectral domain method was incorporated into a semi-automated in-house software package to rapidly produce the regional scale map. The reliability of the depth to magnetic basement map is heavily dependent on the reliability of the depth to magnetic source estimation methods. There are a number of factors that can lead to errors, such as data quality and wrongly assigning magnetic sources to the cover or basement. The spectral domain method tends to slightly over estimate depths, however the average absolute errors are less than %30 when compared to known depths which is considered reasonable for the production of this type of regional scale map. The map delineates large areas of prospective Gawler Craton and Curnamona Province basement beneath less than 300 m of cover material, providing a useful tool for the mineral explorer. The map also delineates large areas under thick sequences of sediments, greater than 1000 m, which may prove of interest for the hydrocarbon explorer or act as a thermal blanket for the geothermal explorer.

  • Legacy product - no abstract available

  • The Australian Geological Survey Organistaion (AGSO) has produced a set of digital bathymetry, gravity and magnetic grids for the southwest quadrant of Australia (24 - 46S, 106-140E), using all available land, marine and satellite data. The work was done in cooperation with Desmond Fitzgerald & Associates (DFA), and with significant bathymetric data input from the Australian Hydrographic Office (AHO). The results were obtained by performing a network adjustment on marine ship-track data, and combining these with onshore and satellite-derived data.

  • The map addresses the distribution of Archaean rocks of the central Eastern Goldfields of Western Australia. Interpretation was undertaken at 1:250 000 scale for both Geoscience Australia aeromagnetic data (400m linespacing) and Fugro Airborne Surveys Pty. Ltd. data (200m linespacing). The Archaean rocks are subdivided into undivided gneiss-migmatite-granite (Agmg), banded gneiss (Agn), greenstone (Aa), and granite plutons (Ag). Where important relative differences in magnetisation are mapped, the geophysical map units include the suffixes _h (high), _m (medium), _l (low) and _r (remanent) for the level of magnetisation. Dykes, faults, and unassigned small intrusives are also mapped. The map is derived from a subset of a more extensive interpretation covering the exposed extent of the Yilgarn Craton.