Magnetic estimates open new horizons

Source: Geoscience Australia 

Scientists, researchers and minerals and energy resource explorers will be able to obtain a greater understanding in future of the thickness of sediments over basement rocks which have potential to contain mineral deposits and geothermal resources.

This follows development of software which estimates the depth of barren cover over basement rocks by analysing the airborne magnetic data acquired over the Australian mainland and Tasmania by the Federal, State and Territory governments during the past 60 years.

The new software uses a new depth to magnetic source estimation method, which, when combined with drill hole, seismic and other data, establishes reliable estimates of the depth to crystalline rock beneath sedimentary cover.

Geoscience Australia geophysicist, Tony Meixner, said that about 80 per cent of the Australian landmass remains unexplored or under-explored and the lack of knowledge about the depth of surface cover acts as a major impediment to mineral discovery.

“The cover material ranges from shallow soil horizons to recent sedimentary basins that may extend for hundreds of kilometres and be up to 10 kilometres deep. Knowledge of the depth of this cover will influence whether or not mining companies decide to explore for mineral and energy resources in a particular region,” Mr Meixner said.

“Because the older basement rocks beneath the more recent sedimentary basins are generally strongly magnetised while the overlying sediments are mostly non-magnetic, or weakly magnetised, it is possible to estimate the depth of cover material by analysing the airborne magnetic data using advanced computer modelling” he said.

The computer software applies a spectral filter, or frequency analysis, to a selected window of a magnetic grid and estimates the average depth to magnetic source rocks for the selected datasets. The window is moved progressively across the dataset to build a grid of source depths. The new software incorporates updates which take into account the fractal nature of rock magnetism.

Mr Meixner said that these improvements have increased the accuracy of depth estimation over the original spectral method.

“The enhanced understanding of the thickness of barren cover over vast areas of Australia provided by the new software will help explorers to make informed decisions about the cost and the difficulty associated with identifying mineral resources in the basement,” Mr Meixner said.

Researchers have applied the new software to a region in central Australia to create the Depth to magnetic basement of the Arunta-Georgina-Amadeus-Musgrave region map.


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