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EIS funded seismic survey begins near Esperance

Friday, 4 May 2012

Seismic surveys have commenced near Esperance to provide data in the search for better geological understanding and further resources in the region.

Funded by the State Government’s Exploration Incentive Scheme (EIS), the Albany-Fraser Orogen deep crustal seismic reflection survey will provide imaging that will help define prospective areas.

The surveys are being coordinated by the Department of Mines and Petroleum’s (DMP) Geological Survey of WA (GSWA).

A subsequent line will follow the Trans Australia Railway Access Road as far east as Haig, with a shorter fourth line being surveyed near AngloGold Ashanti’s Tropicana gold deposit.

“Understanding the structure of the old pieces of crust that have been stuck together as the Australian continental plate assembled, can provide clues to finding sites that form major mineral deposits,” GSWA Chief Geoscientist Roger Hocking said.

“We’re trying to see how the Earth’s crust is joined together down in the area between Esperance and the northwestern edge of the Nullarbor, up near the Tropicana gold discovery."

“There are a couple of major fractures in the Earth’s crust along there, joining quite different types of crust. These fractures commonly focus and carry fluids from the Earth’s mantle up through the crust, to form major mineral deposits,” he said.

Mr Hocking said understanding the basic structure of the Earth allows for more intelligent exploration for resources.

The Yilgarn Craton margin contains significant gold resources such as Tropicana, and understanding its geometry will help define prospective areas.

Seismic reflection data is generated by vibrating the ground using three large specialised trucks in-line. Seismic waves travel down through the Earth and are reflected from surfaces and fault structures that mark changes in rock type.

“Geophones spread out along the survey line record the return of the reflected seismic waves; the seismic waves take longer to return from deeper reflectors,” Mr Hocking said.

“As the survey progresses an image is built up that is a vertical slice through the crust. Listening for up to 20 seconds at each recording point allows us to ‘see’ through the base of the crust and into the mantle.”

He said while the surveys were being conducted there will be some speed restrictions in place to 60kmh for safety reasons.

“There will be a 25km length of road where the restrictions will apply, but these will change on a daily basis as the survey progresses.”

The survey commenced near Condingup, about 70kms east of Esperance, before moving to Kambalda and then east along the Trans Line to Haig over a three week period.

“We’ve tried to keep disruption to a minimum, and we thank affected residents for their patience during this important project,” Mr Hocking said.

The acquisition and interpretation of the seismic reflection data is being managed by Geoscience Australia (GA) and by ANSIR, the Canberra-based National Research Facility for Earth Sounding, under the National Geoscience Agreement.

It represents one of a series of deep crustal seismic reflection surveys that are being collected across Australia as part of the National GeoTransect Program to build up a three dimensional image of the Australian continent, and its evolution through time.

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