‘Geology and Gold Deposits of Woodlark Island, ’

Woodlark Island, is located ~ 650 km east of Port Moresby and lies on the eastern extremity of the Woodlark Rise. It was a historic mining centre, being the first continuous underground gold mine in PNG and by 1910 had produced 43% of all PNG’s gold. It is a remote island, heavily forested in tropical jungle and receives over 5 metres of rain annually. From base to top, the main stratigraphy of the island consists of Eocene Loluai Volcanics (MOR sequence), Late Oligocene to Early Miocene Suloga and Nasai Limestones and Wonai Hill Beds, Mid-Miocene Okiduse Volcanics and Pleistocene Formation.

The known gold mineralization occurs within an uplifted central horst block and is hosted by the mid-Miocene Okiduse Volcanics, typical calc-alkaline island arc andesites (predominantly volcaniclastics and epiclastics). Within the central horst block, numerous faults occur, some of which are post-50 ka in age. LIDAR imagery has been crucial in determining the location and nature of these faults. The main gold prospects include Busai, Kulumadau and Woodlark King, though numerous smaller prospects also exist. For the Kulumadau deposit, there is a dominant structural control on the gold mineralization while for the Busai deposit there are both lithological and structural controls. Unusually, gold occurs as ‘free gold’ with a low Ag content and most of the gold postdates the main base metal mineralizing episode. Preliminary geochronology suggests that gold mineralisation postdates volcanism by ~ 1 Ma. An unusual type of gold mineralisation was also found in the form of palaeoplacer heavy mineral beach sands within the Kiriwina Formation. This type of mineralization should occur elsewhere within the SW Pacific region. Current resources are at 2 million ounces of gold and there is a current mining application with the PNG government.