oa Potential field modelling of VHMS and sequences in the Captains Flat area, NSW

The Geological Survey of New South Wales has commenced 2nd edition geological mapping of the Captains Flat area, southeast of Canberra. This project is a southern extension to the recently completed mapping over the Braidwood 1:100 000 and Goulburn 1:250 000 scale map sheets. Silurian-Devonian extensional basin sequences, within the Braidwood and Goulburn sheets, extend into the Captains Flat area. The basin sequences are known to host economic Zn, Cu and Pb VHMS mineralisation (e.g. Woodlawn, Currawang, Captains Flat).

TMI data from north of Captains Flat was modelled using inversion to test the existence and determine the geometry of a syncline identified by the mapping. Evidence of a syncline was not resolved by the inversion modelling, but modelling of the magnetic anomalies has provided further geological information. TMI modelling of this area is currently the only way to determine the extents of the magnetic formations as access to the site has been denied by the landholder. Units within the syncline are host to VHMS, in particular the Kohinoor Volcanics. Inversion modelling indicates sources that are near vertical tabular bodies, with a depth to top of 10- 110 m, they extending on average approximately 500 m down dip and having a strike extent up to 220 m. Results also indicate that other volcaniclastic formations have not been geologically mapped.