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22 November 1998 |
Ref 98/270 |
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If it wasn't for Mickey Mouse, CSIRO might have missed its
calling as the world leader in 3D Magnetic Modelling, an exciting
new technique for use in the search for new mineral deposits.
Dr Peter Hornby, CSIRO Exploration and Mining, says he and his
colleagues were becoming so frustrated in their hunt for a significant
improvement to traditional modelling procedures that they looked
to Disneyland for some light relief. The breakthrough came soon
after.
"We were able to trick our computers into believing that
the image from a standard two-dimensional magnetic survey of
a real-life exploration tenement (area) came from an underground
ore body cast in Mickey's image," says Dr Hornby.
"It showed us that from a purely mathematical point of view,
any geological configuration, even the most bizarre, can fit
a field dataset exactly. The absurdity was the spur we needed
to push on in search of an improvement," he says.
The result is a 3D Magnetic Modelling process which leads the
world. It's taken 18 months to develop and is about to be commercialised
through the project's collaborative partner Fractal Graphics,
a 3D geological modelling specialist. The Australian Geodynamics
Co-operative Research Centre is also a participant in the project.
"Others in France and the US are doing similar things but
we have not seen the theory developed as thoroughly and as deeply,"
Dr Hornby says.
It is Dr Hornby's mathematical artistry which has made the CSIRO's
3D Magnetic Modelling process unique. From commonplace magnetic
and gravitational survey datasets, his calculations have extrapolated
2D images to 3D images faster, with greater accuracy and much
greater objectivity, than a geologist could ever hope to achieve
by hand tracing, the traditional process.
The 3D modelling allows the geologist to see not just the gravitational
and magnetic signals from the ground surface, but also gives
natural and plausible predictions of the magnetic and gravitational
status of the terrain below ground.
Understanding how the underground terrain was formed provides
the clues miners need for deciding where to drill and mine. Gravitational
pull indicates the size and density of rock formations, while
their composition can be revealed by their magnetic signal intensity.
The 3D Magnetic Modelling process works like this: Conventional
gravitational and magnetic maps of tenements (from data collected
during aerial surveys) show broad lumps and wrinkles at the surface,
sometimes many tens of kilometres wide. Boundaries or edges of
the different geological structures in the earth's crust are
often the cause of these broad humps.
Traditionally, geologists have traced lines along these humps
and wrinkles to produce new maps of geological boundaries. But
drawing a line on a hump 10 kilometres across is still largely
a hit and miss affair.
Dr Hornby's process has sharpened the image of these edges, achieved
by breaking them down to their major features, stripping away
the 'noise' they contain, and then rebuilding them. The sharper
images allow very detailed analysis of small local features.
The finished computer images show deep halo-like bands known
as "worms" hovering above the surface features. They
are a feature of the gravitational and magnetic fields of the
earth. Specifically, they are where the fields are varying fastest.
Technically, they are edges in a "wavelet transform"
of the underground terrain.
The worms are coloured across a spectrum which ranges from red
to blue - the rate of change of colour and the pattern of colour
distribution reflects how fast the field is changing at that
point, which in turn indicates the depth and type of underground
object.
By following the contour lines created by the worms back down
into the earth's crust, what lies underground is revealed in
vivid three-dimensional colour.
More information :
Dr Peter Hornby CSIRO 08 9284 8444 (W).08 9307 5592 (H)
Images are available from WWW at http://www.agcrc.csiro.au/projects/3054CO/index.html
Also available in hard copy.
(Australia's largest scientific research organisation)
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