magnetics
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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. These line dataset from the Murrindal, Vic, 1996 VIMP Survey (GSV3060) survey were acquired in 1995 by the VIC Government, and consisted of 15589 line-kilometres of data at 200m line spacing and 80m terrain clearance. To constrain long wavelengths in the data, an independent data set, the Australia-wide Airborne Geophysical Survey (AWAGS) airborne magnetic data, was used to control the base levels of the survey data. This survey data is essentially levelled to AWAGS.
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Legacy product - no abstract available
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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.
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Legacy product - no abstract available
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Three seismic lines (10GA-CP1, 10GA-CP2 and 10GA-CP3), which cross north to south across the Capricorn Orogen of Western Australia, have recently been collected by Geoscience Australia, ANSIR and the Geological Survey of Western Australia. The interpretation of these seismic lines is aimed at providing insight into the geologic structure of the Capricorn Orogen and to explore the relationship between the Pilbara and Yilgarn cratons. To aid in further interpretation and to add value to the seismic data an analysis of the available potential field data (gravity and magnetics) has also been undertaken. A range of geophysical data analysis techniques have been applied and include: multi-scale edge detection (worms), forward modelling and 3D inversion. By applying all three analysis techniques to the potential-field data major trends, contrasting properties and regional blocks relating to the subsurface geology have been determined, in turn, allowing for a detailed comparison with the seismic interpretation. Note that all results referred to in this abstract are preliminary and subject to change.