The arcuate New Ireland Basin is 150 km wide and trends northwest for 600 km between Feni and Mussau islands in northern Papua New Guinea. Multichannel seismic reflection data combined with refraction data show that much of the basin is a simple structural downwarp filled with up to 7 km of strata. Island outcrops and offshore reflection data indicate that New Ireland Basin contains thick sequences of Eocene to earliest Miocene volcanic rocks, Miocene shallow marine volcaniclastic rocks, Miocene shelf limestones, and latest Miocene to Holocene pelagic carbonates and volcaniclastic turbidites.

Exploration for hydrocarbons in New Ireland Basin has been limited to geophysical surveys and to a few dredge and core stations. Offshore surveys show depocenters that contain more than 1000 m of Miocene clastics, overlain by about 2000 m of Miocene shelf carbonates and 2000 m of younger volcaniclastic rocks and bathyal carbonates. Counterparts of these units are exposed on New Ireland, where outcrop geology suggests, if these units are deeply buried offshore, that they may have some potential as both source and reservoir rocks for oil and gas.

Possible hydrocarbon traps offshore include reeflike buildups and fore-reef deposits in the Miocene limestones as well as

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anticlines, normal faults, and stratigraphic pinch-outs along the basin margins. One multichannel seismic reflection line revealed a flat high-amplitude reflection, or "bright spot," within the core of an anticline some 20 km east of New Ireland. The bright spot is about 2 km wide and occurs 1.2 s (1700 to 1800 m) beneath the sea floor in water depths of 2500 to 2600 m.

Quaternary calderas developed during late-stage volcanism in each of the four island groups along the Tabar-to-Feni islands. Recent exploration within one caldera on Lihir Island, Luise, has revealed a sizable gold discovery. The gold occurs within pyrite in volcanic rocks adjacent to a 350,000-year-old monzonite intrusion. Exploration by drilling in the caldera indicates about 18.4 million ounces of gold in 167 million tons of host rock, which averages 3.4 g/t and excludes any host rock with less than 1.5 g/t.