Mineral Prospectivity of the Middle Devonian Dulladerry Volcanics, Central-West New South Wales

The middle-Devonian Dulladerry Volcanics is a complex of A-type, predominantly rhyolitic ignimbrites, lavas and breccias. They form a NNW trending belt some 90 km long and 10-20 km wide, east of Parkes, NSW. The volcanics are dominated by widespread ignimbrite units with minor basalts, sediments and rarer andesites. The volcanics were deposited in a sub-aerial, possibly continental rift setting and are similar in chemistry and age to the Eden - Comerong - Yalwal Volcanic Zone (EVZ) on the NSW south coast. The volcanics exhibit an unusual Atype chemistry (high Zr, Y, Nb, REE, Ga). This distinctive composition illustrates that the volcanics are not comagmatic with the adjacent Yeoval Granite Complex or Eugowra Granite, which show typical I-type fractionation trends. Epithermal gold veins occur in basalt and andesite in the Dulladerry Volcanics at Mt Aubrey (Hopf, 1992), near Baldry. Alteration also occurs in the Glen Isla and Red Hill areas, with epithermal sinter recognised at Glen Isla. Copper and minor gold mineralisation occurs at the contact of rhyolite and andesite at Reedy Creek, but is not of epithermal origin. The analogous EVZ also contains several epithermal gold fields and it is this style of mineralisation which provides the most prospective targets in the Dulladerry Volcanics. Although the Dulladerry Volcanics also contain high background levels of REE and metals such as Zn and Pb, the general lack of fractionation and water-undersaturated character of A-type magmas does not lend itself to the development of significant concentrations of these elements into a fluid phase and mineralisation. The prospectivity of A-type volcanics in general could not be regarded as high. However, an indicator of some fractionation in the Dulladerry Volcanics is provided by the fairly low abundance (average 230 ppm) and wide range (