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14 November 2001

Electromagnetic Survey identifies sandstone and claystone

Department geologists Dave Robson, John Watkins and Lindsay Gilligan Opal miners responded to the opportunity to attend Monday's Airborne Electromagnetic Survey Seminar.

Departmental geologists Lindsay Gilligan, Dave Robson and John Watkins made presentations on behalf of the Department of Mineral Resources.

$90,000 released under the Auspice of Exploration NSW, funded the pilot survey which sought to establish how this technique identifies with the terrain.

The study was conducted to a depth of ten metres, aiming to detect the claystone areas. Through electromagnetism the geologists sought to define a conductor in the faults and claystone. "With limited training miners will be able to undertake their own electromagnetic surveys,' said John Watkins.

The areas targeted were determined by the budget available. The usefulness of data supplied by prospects as acknowledge and encouraged. The survey will be followed up with ground surveys.

The relevance of the opal corridor and its significance in the occurrence of opal was detailed. New maps will be prepared for the Walgett to Angledool area.

Presentation of the volume of information will be available via CD Roms. "Opal fields appear in discreet areas, why is that?"

Fossils tell us we are in a coastal plain fresh water setting. The effects of channels, structural control and influence of faults were described in specific areas.

That microbes exist where silica is formed; there is bacteria build up on non-precious opal and the quest for miners is to locate "uninfected" precious opal (no bacteria) were challenging thought to take on board.

The study has confirmed the theory that sandstone and claystone may be detected through electromagnetics and magnetics.

It has further confirmed the existence of the given system, channels, billabongs and faults. The findings have been described as "a bit of a tease, which will require follow-up drilling to gain a further understanding.

If you would like further information on this electromagnetic survey contact the Lightning Ridge Miners Association, the Glengarry Grawin Sheepyard Miners Association or the Department of Mineral Resources.

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