The PACMANUS hydrothermal field in the eastern Manus Basin is a site hosted by felsic lavas (Binns and Scott, 1993; Yang and Scott, 1996), with extensive subsurface alteration (Binns, Barriga, Miller, et al., 2002). The hydrothermal vent field lies near the bathymetric peak of a high-standing, 20-km-long Y-shaped ridge, called the Pual Ridge (Binns and Scott, 1993). The Pual Ridge and the PACMANUS site are composed of felsic volcanic lavas, ranging from andesite to rhyodacite (Binns et al., 1995). Discontinuous hydrothermal deposits were viewed from camera tows throughout a 3-km x 800-m zone along the Pual Ridge, displaying chimney deposits up to 20 m high (Binns, Barriga, Miller, et al., 2002). In addition to chimney deposits, thin blue-gray crusts associated with white patches (interpreted as bacterial mats) indicate potential hydrothermal deposits produced by low-temperature discharge. The polymetallic sulfide deposits, which are rich in copper, zinc, lead, silver, and gold, are derived from seawater–rock interactions, with possible mixing of magmatic fluids (Yang and Scott, 1996).
Permeability measurements were made on samples from three locations: Snowcap (Holes 1188A and 1188F), Roman Ruins (Holes 1189A and 1189B), and Satanic Mills (Hole 1191A). Snowcap is an area of extensive diffusive venting with low-temperature hydrothermal fluids. The mineralization and hydrothermal alteration patterns extend to the bottom of the cored interval at ~387 meters below seafloor (mbsf). However, there are no significant developments of massive base metal sulfides or precious metal enrichments in the recovered sections. Roman Ruins is the most developed area of active sulfide–sulfate chimneys in the PACMANUS hydrothermal field, with chimneys as tall as 20 m, though averaging 3 m (Binns, Barriga, Miller et al., 2002). Hole 1189A was drilled to a depth of ~126 mbsf, and Hole 1189B was drilled to 206 mbsf. Although Holes 1189A and 1189B were in close proximity (~35 m), variations between Holes 1189A and 1189B in the recovered intervals are quite large, with a possible stockwork zone intersected in Hole 1189B. Satanic Mills is a chimney field with high-temperature fluid discharge covered by a hard, vesicular dacite/rhyodacite crust, as found at the other sites. Early collapse of the hole limited the depth of drilling to ~20 mbsf; however, drilling did provide samples of the hard crust layer. The samples taken from this region provided permeability information about the less altered volcanics found near the surface.