September 2001 MONTHLY MEETING


David Robson

Chief Geophysicist – Geological Survey of NSW

The Search for Opal at Lightning Ridge –

Outline of Exploration NSW geophysical activities

DATE: Wednesday 19 September 2001

VENUE: Rugby Club, Level 3, Rugby Place (near Pitt & Alfred St) Sydney

TIME: 5.30pm for 6pm


Electrical, electromagnetic, magnetic, induced polarisation and seismic reflection surveys have all been trialed by the New South Wales Department of Mineral Resources at Lightning Ridge. The electrical and electromagnetic methods appear to provide a means to define the conductive Finch clay facies (or “opal level”), the overlying and moderately resistive Wallangulla Sandstone and the highly resistive surface gravel and silcrete (or “shincracker”) layers. Localised linear features appear to be well-defined in both TEM and high-definition ground magnetic data as electrically resistive and high frequency magnetic anomalies. Results indicate that an ultra-detailed airborne electromagnetic survey may assist in the future search for opal at Lightning Ridge.

Following this presentation Dave will give a brief outline the Department of Mineral Resources’ Exploration NSW geophysical activities for 2001 / 2002.


17 October

14 November – students night

Visit the ASEG NSW Branch Homepage

President: Steve Webster

Secretary: Michael Moore
Treasurer: Phillip Schmidt