From earliest Archean time, felsic volcanic sequences and their associated intrusive rocks have been especially favorable hosts for a variety of valuable hydrothermal ore deposits, including massive polymetallic sulfide and porphyry-style copper-gold bodies. Ancient volcanic arcs or backarcs related to subduction at convergent plate margins are commonly the established or inferred geological setting for such mineral occurrences. Investigating hydrothermal activity in analogous modern settings has obvious merit as an approach to understanding ore genesis, a critical requirement for mineral exploration in older sequences.
Rare opportunities for analog research in economic geology arose following discoveries in the late 1970s of hot springs and polymetallic sulfides on the floor of the Galapagos spreading center (Corliss et al., 1979; Malahoff et al., 1983) and shortly thereafter of actively forming "black smoker chimneys" at 21°N on the East Pacific Rise (Francheteau et al., 1979; Spiess et al., 1980). An immediate and, at the time, novel outcome was recognition of hot and buoyant hydrothermal fluids that precipitate metallic sulfides directly where they vent onto the seafloor and mix with cold seawater. The discoveries also stimulated great interest in the associated chemosynthetic microbial communities and macrofauna, as well as the influence of hydrothermal venting on ocean chemistry. With such a diverse range of scientific interest and applications, the Ocean Drilling Program (ODP) developed an early priority for projects that would examine subseafloor phenomena and processes below active vent fields. The first ODP expeditions to hydrothermal sites focused on divergent plate boundaries at mid-ocean spreading ridges, where mafic volcanism predominates. During Leg 139 (Mottl, Davis, Fisher, and Slack, 1994) Middle Valley was drilled on the thickly sedimented Juan de Fuca Ridge, northeastern Pacific Ocean. During Leg 158 (Herzig, Humphris, Miller, and Zierenberg, 1998) the Trans-Atlantic Geotraverse (TAG) site on the sediment-starved Mid-Atlantic Ridge was investigated. During Leg 169 (Zierenberg, Fouquet, Miller, and Normark, 2000) Middle Valley was revisited and Escanaba Trough on nearby Gorda Ridge was investigated.
Mineral deposits formed at oceanic spreading centers are usually fated to become lost to the geological record though ultimate subduction. Although major advances of fundamental importance to ore genesis arose from drilling mid-ocean basaltic settings, it was desirable to extend ODP's program to a conceptually more appropriate active hydrothermal site associated with felsic volcanism in a convergent margin tectonic setting. Accordingly, Leg 193 was planned and undertaken at the PACMANUS hydrothermal site, discovered in 1991 (Binns and Scott, 1993) on Pual Ridge, a dacite-dominated neovolcanic edifice in the eastern Manus backarc basin of the Bismarck Sea, Papua New Guinea.
Leg 193 departed from Guam on 14 November 2000, occupied station from 18 November to 29 December, and ended at Townsville (Australia) on 3 January 2001. This synthesis chapter summarizes the plethora of frontier research subsequently conducted at laboratories in Australia, Canada, Germany, Japan, Korea, Norway, Papua New Guinea, United Kingdom, United States, and Portugal by shipboard scientific participants. In addition to work now published, results of unpublished and uncompleted projects are included where known to the authors.