This talk is based on work carried out in the Geological Survey of NSW by Cam Quinn, Ian Percival and Dick Glen, originally as a contribution to pmd*CRC.
It asks the question whether Ordovician basaltic to andesitic volcanic (and related sedimentary) rocks, and importantly mineralised porphyries, of the Lachlan Orogen in the central west of New South Wales really did form in an intraoceanic island arc, above a west-dipping subduction zone between the Gondwana plate in the west and the paleo-Pacific plate in the east, as has been widely accepted.
The talk will draw on new field and conodont data that question the arc interpretation, and instead support a setting for the formation of these rocks (and critically, the emplacement of porphyries) well behind the Ordovician plate boundary.
If this new model is correct, then the porphyry copper-gold deposits at Cadia Valley, Northparkes and elsewhere are not arc-related, thereby opening up new avenues for mineral exploration in backarc settings.
Rugby Club, 5:30 for 6:00, Thursday 30th May, 2013