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 (< 5 to 600 ppm) of Ba in the felsic volcanics. A further comparison is drawn with the Permian A-type Featherbed
Volcanics of north Queensland. These volcanics are sparsely mineralised
(minor U, Au), but lie adjacent to a well mineralised complex of
fractionated I- and some A-type granites containing deposits of Sri, W,
Mo, Bi, Au, Cu, Pb and Zn. Fractionated I-type granites of the Yeoval
Granite Complex most probably underlie a thin skin of Dulladerry
Volcanics, providing a secondary target for gold and base metal
exploration beneath the volcanics based on geophysical interpretation of
acromagnetic data.