Geophysics of the Porgera gold mine, Papua New Guinea

Abstract

The giant gold deposit of Porgera, located in the Enga Province in highland Papua New Guinea, had a 1997 reserve of 82.6 Mt at 4.4 g/t, or 11.6 Moz. The high-grade mineralisation, most of which has been mined out, is associated with quartz-roscoellite veining along the Romane Fault Zone (Zone VII). Early prospecting in the late 1930s discovered alluvial gold in the Porgera valley. From 1964 to 1983 the Waruwari deposit was defined by drilling east-oriented holes. In 1983 the Romane Fault mineralisation was discovered using drill holes oriented to the south. While geochemistry and drilling have been credited with the discovery of zone VII, geophysics has played an integral part in defining the extent of the Porgera Intrusive Complex. If used earlier in the exploration process, geophysics may have led to the discovery of zone VII before more than 200 holes were drilled into the deposit. Geophysics has been used extensively in the exploration program at Porgera to target buried intrusives. Airborne magnetics has successfully mapped the intrusives, along the contacts with which mineralisation is associated. IP and radiometrics have defined the extent of hydrothermal alteration and a combination of 3D magnetic modelling and Audio MagnetotelluricsAMT has defined the system at depth in the latest round of work.