Cargo Porphyry Cu-Au Deposit – Where is the High Grade Core?

Abstract

The Cargo Copper-Gold Porphyry deposit lies within the world class porphyry belt of the Ordovician Macquarie volcanic arc. It is one of several porphyry complexes in the Lachlan Orogen including Cadia Valley (42.8 MOz Au), Northparkes, Cowal and Copper Hill. The Cargo Porphyry Intrusive Complex is a calc-alkaline suite of late Ordovician age (467 Ma) intrusives comprising quartz monzodiorite and diorite intruded by coeval andesitic and trachy-andesitic volcanics. The most prominent NW trending structural zone is characterised by areas of strong silicification, pyritisation and tectonic brecciation together with stockwork and sheeted quartz veining. It is up to 300 m wide bounded on the southern side by a major 60o SW dipping normal fault and on the Northern side by 75o SW dipping shear zones. Mineralization and alteration is zoned from a western core of fracture controlled, potassic altered porphyry (Cu-Mo-Au) to a peripheral zone of phyllic altered gold rich quartz-sulphide veining up to 200 m wide, surrounded by an outer propylitic zinc rich halo. The peripheral zone of Cargo contains gold rich sheeted quartz veins which hosted 14 small gold workings in the late 1800’s. Two lode systems, Dalcoath and Spur, have JORC inferred resource of 4 Mt @ 1.19g/t gold for 154,000 Oz Au. A classically zoned porphyry Cargo’s geochemical footprint is comparable in size to the famous Bingham Canyon and the Bougainville Panguna deposits despite the fact that Cargo’s porphyry deposits’ western half has been faulted away.