The 1.66 million line kilometre Gawler Craton Airborne Survey (GCAS) is now moving into its final stage, with 99% of its magnetic, radiometric and elevation data acquisition now complete (Figure 1)...

The Geological Survey of South Australia and Geoscience Australia are pleased to announce the completion of the acquisition phase of the 1.67 million line kilometre Gawler Craton Airborne Survey (G...

Magnetic field anomalies measured by the Gawler Craton Aeromagnetic Survey (GCAS) have revealed anomalies of amplitude > 18,000 nT over Paragon Bore. The flying height is 60 metres above ground and depth to basement is 150 metres below ground, so the causative basement sources clearly have magnetizations of extreme intensity. We apply an iterative processing of the GCAS TMI data to a vector-consistent TMI. This also supplies vector component grids which we downward continue to the ground surface and then transform to declination and inclination maps. We invert the measured TMI using a model of multiple ellipsoids to enable inclusion of substantial self-demagnetization effects. Vector components forward computed from the inversion model at ground level are also transformed to declination and inclination maps which closely match those derived from the filter transform. Deviations of declination and inclination about the regional values are -15° to +21° and -14° to +5° respectively. High magnetic susceptibility values reported from borehole intersections (up to 1.6 SI in 2 boreholes) are mostly associated with banded iron formation (BIF) and metasomatic magnetite-rich rocks. These values are about 1/3rd of the equivalent inversion model intersection susceptibilities. We suggest that this apparent discrepancy is due to self-demagnetization effects in the susceptibility measurements and the presence of substantial (possibly viscous) remanent magnetization.

In 2017 the Government of South Australia, in partnership with Geoscience Australia began the world’s largest airborne geophysical and terrain imaging program, the Gawler Craton Airborne Survey (GC...

This contribution presents a method for efficiently classifying geophysical anomalies and identifying regions and features that share characteristics of many known iron-oxide-copper-gold (IOCG) deposits of the Gawler Craton, and can therefore be used in drill target prioritization. Residual Bouguer gravity and reduced-to-pole total magnetic intensity grids over the Gawler Craton were transformed, generating polygon datasets representing populations of locally anomalous gravity and magnetic intensity. Taken as simple anomaly polygons, there are a very large number of features across the Gawler Craton (>39,000 TMI and >10,000 gravity). Superimposing mineral deposits over these features shows a clear spatial correlation between IOCG deposits and occurrences, and anomalies (>90% of deposits within 1,000 m of an anomaly), but leaves thousands of anomalies of varying magnitudes that cannot all be related to IOCG mineralization. Eliminating TMI and gravity anomalies with a separation of more than 1,000 m reduced the search space to ~20,000 TMI features and ~8,500 gravity features. Limiting the search to a statistically derived gravity threshold ≥0.4 mGal gravity anomalies, the exploration space is reduced to 798 gravity features with coincident TMI features within the Olympic Copper-Gold Province. The Anselin Local Morans I method was used to delineate geographic regions based upon spatial clustering of high magnitude anomalies. The spatial distribution and clustering characteristics of the gravity anomalies provide additional information and can be related to differing basement geology and deposit style. Terranes where lithologies and Cu-Au occurrences are commonly magnetite-rich show clustered high-magnitude gravity anomalies, and correlated spatially with the Mount Woods and Moonta domains within the eastern Gawler Craton. Importantly, it was found that the central, and currently most endowed, the Olympic Domain, was distinct in that it was dominated by spatial outliers (discrete high-magnitude density features). These results could be used as a starting point in developing IOCG exploration strategies, due to the high number of additional untested, spatially coincident gravity and magnetic anomalies that warrant further investigation.

Thousands of geophysical surveys have been acquired over South Australia. Many hundreds of these are airborne surveys, notably magnetic, radiometric, and electromagnetic surveys. In the past the go...