Thursday, 3 May 2012

Geology in the air

A few months ago the New South Wales Geological Survey released their preliminary data package for the Grafton-Tenterfield Airborne Geophysical Survey (link to info here). The survey was conducted as part of a program that has been going on for several years known as New Frontiers New South Wales. Nearly all of the state has now had high quality data obtained for it instead of the old, poor quality data for the whole state. But why has this been done?

Area of latest survey from NSW DPI
The regional survey has been conducted to better understand the geology of the region and as a result this information may guide mineral exploration as well as provide additional data that can help land management especially in relation to soil transport, erosion potential and soil chemistry. This is done through three primary measurements: radiometrics (measurement of natural radiation), magnetics (measurement of how magnetic the earth is), and DEM (measurement of the elevation of the earth). How these can be used to understand the earth through the aerial survey is outlined below:

Radiometric measurements show the relative abundance of three naturally occurring elements in the rock and soil these are Potassium, Thorium and Uranium. The different ratios of these elements can distinguish broadly between different rock types without the need to visit the site and the intensity can be used to do the same. If an area shows up as being rich in radioactive elements it may be underlain by a granite or similar rock as the radioactivity is directly related to the mineralogy of the parent rocks. If an area is eroded the visibility (or comparative lack of) of radioactive minerals may be seen in downstream. The different types of radiation also provides an indication of the chemistry of the soil and rock. This process can only show the radiation on the surface (e.g. in soils, sediment and exposed rock)

Magnetic measurements do a similar thing as far as identifying elements. But instead of radioactive elements it shows the abundance of iron especially in the form mineral magnetite. Again, the geophysical response will be based on the rock mineralogy. Rocks such as basalt will have a strong response (more iron) and so will wet areas. However, unlike radiometrics, magnetics can show deeper structures in the earth such as buried plutons, faults, dykes and others. This means that drilling is not necessarily required to have a good idea of what lies beneath the surface. It is interesting stuff and the maps produced are often very pretty colours! All of the measurements require “calibration” with a digital elevation model (DEM) which shows the shape of the earth.

Recently (2005?) obtained information in the New England and Tamworth areas have shown up major hidden fault systems, areas prospective for gold, deformation of sedimentary basins that may increase prospectivity for oil and gas, new granite plutons, hidden granites, a better understanding of volcanism including confirmation of new volcanic centres and its associated rock (such as the Maybole Volcano). One aspect that appears promising that the survey will aid in determining the viability for is geothermal energy. Geothermal energy may be obtained from related to deep buried granites and magnetics can be used to find likely locations.

It is interesting to note that I have seen reports in the media (and formal submissions to Coal Seam Gas parliamentary inquiries) that some people have been upset by being “buzzed” by aeroplanes from companies undertaking coal-seam gas exploration. Looking at the timing, this may be related to concern about Coal Seam Gas exploration by several companies in the area and I tend to think that it is likely that the aeroplane may have been part of the regional geophysical survey.

It is important to know just how useful this information is to understanding our planet, even if the information can be used in a way that some do not appreciate. Geology usually has two aspects, one is scientific (understanding the world we live) and the other is applied (using such knowledge for other purposes such as mining). The geophysical information obtained by New Frontiers New South Wales is purely scientific but this knowledge can be applied to Mining but it can also be applied for Environmental purposes. Unlike many others, I am cautious about stopping research because of what it may be potentially be able to be applied to.

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