Hydrothermal processes and contrasting styles of mineralization in the western Woodlark and eastern Manus basins of the western Pacific

Abstract: The western Woodlark Basin (initial rifting of continental crust) and eastern Manus Basin (rifted arc crust) offshore astern Papua New Guinea display contrasting styles of hydrothermal activity and mineralization. I the eastern Marius basin, en echelon felsic and mafic volcanic ridges have formed in a pull-apart basin of the rifted New Britain arc terrane. Here, the PACMANUS Cu-Zn-Pb-Ag-Au sulphide deposit is forming within an area of about 800 • 350 m on the flank of a dacite lava dome atop a prominent 20 km long and 250-350 m high volcanic ridge. The ridge is andesitic in its lower reaches, dacitic to rhyolitic on top and is adjacent to an extensive field of basalt. At Woodlark, submarine rhyolite domes are devoid of hydrothermal products, but extensive Fe-Si-Mn oxyhydrox-ide deposits are forming from low temperature fluids on Franklin Seamount, an axial basaltic andesite volcano near the tip of the oceanic propagator. Protruding through and perhaps underlying these oxyhydroxides are inactive, higher temperature, precious metal-rich (Ag to 545 ppm, Au to 21 ppm), barite-silica spires. The Franklin Seamount deposits are thought o cap a disseminated sulphide deposit within the volcano and represent a failed massive sulphide system. Both Franklin Seamount and PACMANU