On the southern flank of Lihir Island, a group of three volcanic cones were discovered at water depths from 1000-1500
m. The volcanoes are located in a narrow zone of recent seismic activity and elevated heat flow (up to 100 mW/m2).
The recovered rocks consist of fresh alkali-olivine basalts, clinopyroxene-rich basalts, and porphyritic phlogopite
basalts. One of the volcanoes has a recently erupted ejecta blanket (recovery of warm ash!), containing a suite of
abundant mafic to ultramafic xenoliths. These xenoliths appear to represent a unique cross-section of subduction- modified mantle material sampled by volatile-rich primary fore-arc magma during its ascent to the seafloor. The most
spectacular finding was the discovery of an active hydrothermal system with associated vent fauna and mineralization at
Edison Seamount, and the recovery of unusually gold-rich (up to 43 ppm Au) hydrothermal precipitates in 1050 m water
depth at the top of Conical Seamount, only 25 km south of the world-class epithermal Ladolam gold deposit on Lihir.
The discovery of submarine hydrothermal vents associated with highly alkaline, quartz-undersaturated fore-arc volcanics
represents a significant departure from similar hydrothermal systems on the mid-ocean ridges and in back-arc basins.
The high gold grades in hydrothermal precipitates at Conical Seamount may indicate the first documented example of a
shallow-marine epithermal system analogous to those known on land, and has important implications for the gold
potential of submarine arc environments.