Lalor is a recently discovered auriferous Zn-Cu volcanogenic massive-sulphide deposit. It is located in the Paleoproterozoic Snow Lake arc assemblage, host to numerous past producing Cu-Zn and Zn-Cu volcanogenic massive-sulphide deposits. With an estimated tonnage of 25 Mt of ore (reserves+resources) including 73 t Au, Lalor is the largest volcanogenic massive-sulphide deposit in the Snow Lake area and its Au-rich nature provides a unique opportunity to document processes responsible for precious-metal enrichment in volcanogenic massive-sulphide systems. The Lalor deposit host rocks are predominantly volcanic (± intrusive) rocks that have been variably altered, deformed, and metamorphosed to amphibolite grade. A combination of immobile element geochemistry and petrographic observations is necessary to properly characterize the volcanic rocks due to major postemplacement modifications. Seven distinct chemostratigraphic units and two postvolcanogenic massive-sulphide intrusive (dyke) units are present in the Lalor host succession. Mafic to felsic volcanic units have calc-alkaline to transitional magmatic affinities. Some of these units are compositionally similar to the Moore basalt (units M1a and M1b) and Powderhouse dacite (unit F2) which represent the footwall of the Chisel, Chisel North, Ghost, and Lost volcanogenic massive-sulphide deposits; this suggests that the Lalor deposit is located within the volcanogenic massive-sulphide-fertile uppermost portion of the lower Chisel subsequence. The presence of massive-sulphide ore lenses in calc-alkaline mafic rocks lying above the Powderhouse dacite-like unit indicates the continuation of volcanogenic massive-sulphide-forming hydrothermal activity after the cessation of felsic volcanism in the lower Chisel subsequence. The presence of dykes with a trace-element signature similar to that of the Threehouse basalt, which is present immediately above the other volcanogenic massive-sulphide deposits of the lower Chisel subsequence, suggests the presence of this unit at a higher stratigraphic position in the now structurally truncated sequence.

Massive sulfide deposits from the modern seafloor are often seen as a potential metal resource for humankind. With the existing geochemical database and lacking information on the third dimension for most deposits it seems premature to comment on the economic significance of seafloor massive sulfides. Published geochemical analyses of sulfide samples indicate that some deposits may contain important metal concentrations, however, the data on surface grab samples from these deposits may not relate to the true metal content of these deposits. Results from recent shallow drilling of various hydrothermal systems presented here highlight the importance of seafloor drilling to validate grades and tonnages of seafloor massive sulfides.

With issue no. 4 of volume 103 we introduce a new Editor for Economic Geology . I am pleased to announce that the Publications Board has selected Dr. Lawrence D. Meinert as the incoming Editor of the journal. Larry will join me as co-editor for the remainder of Volume 103. As in 2001, when I first served …

The Kuroko deposits of NE Honshu are a key type deposit for the study of volcanogenic massive sulfide deposits. However, these deposits have not been studied in detail since the early 1980's and knowledge of their mode of formation is now dated. In this study, we present the analysis of 12 samples of the Kuroko deposits, 12 samples of submarine hydrothermal minerals from the Sunrise deposit and 6 samples from Suiyo Seamount, both of which are located on the Izu-Ogasawara (Bonin) Arc, for 27 elements. For the Kuroko deposit, Cd>Sb>Ag>Pb>Hg>As>Zn>Cu are highly enriched, Au>Te>Bi>Ba>Mo are moderately enriched, In>Tl are somewhat enriched and Fe is not significantly enriched relative to the average continental crust. Within each of these deposits, a similar pattern of element associations is apparent: Zn-Pb with As, Sb, Cd, Ag, Hg, Tl and Au; Fe-Cu-Ba with As, Sb, Ag, Tl, Mo, Te and Au; Si-Ba with Ag and Au; CaSO4. The enrichment of the chalcophilic elements in these deposits is consistent with hydrothermal leaching of these elements from the host rocks which are dominantly rhyolite-dacite in the case of the Kuroko deposits, rhyolite in the case of the Sunrise deposit and dacite-rhyolite in the case of the Suiyo Seamount deposit. However, this pattern of element enrichment is also similar to that observed in fumarolic gas condensates from andesitic volcanoes. This suggests that there may be a significant magmatic contribution to the composition of the hydrothermal fluids responsible for the formation of the Kuroko deposits, although it is not yet possible to quantify the relative contributions of these two sources of elements.The compositional data show that Sunrise and Suiyo Seamount deposits are much closer compositionally to the Kuroko deposits from NE Honshu than are the submarine hydrothermal deposits from the JADE site in the Okinawa Trough which contain, on average, significantly higher concentrations of Pb, Zn, Sb, As and Ag than each of these deposits. In spite of the greater similarity in tectonic setting of the Hokuroku Basin in which the Kuroko, deposits formed to the Okinawa Trough (intracontinental rifted back-arc basin) compared to Myojin Knoll and Suiyo Seamount (active arc volcanoes), it appears that submarine hydrothermal deposits from Myojin Knoll and Suiyo Seamount are closer analogues of the Kuroko deposit than are those from the Okinawa Trough. The present data are consistent with the magmatic hydrothermal model for the formation of Kuroko-type deposits as formulated by Urabe and Marumo [Urabe, T., Marumo, K., 1991. A new model for Kuroko-type deposits of Japan. Episodes 14, 246-251]. (C) 2008 Elsevier B.V. All rights reserved.

Gold-rich volcanogenic massive sulfide (VMS) deposits consist of synvolcanic banded and concordant massive sulfide lenses and adjacent stockwork feeder zones in which gold concentration in g/t Au exceeds the combined Cu, Pb, Zn grades in wt percent and thus constitutes the main commodity. The Agnico-Eagle LaRonde Penna deposit is a world-class Au-rich VMS (production, reserves and resources of 58.8 Mt at 4.31 g/t Au) located in the eastern part of the Blake River Group of the Abitibi greenstone belt. The deposit comprises four stacked massive sulfide lenses within the upper member of the Bousquet Formation (2698–2697 Ma). The two main ore zones, 20 North and 20 South, are sheetlike, massive to semimassive polymetallic sulfide lenses and stringer zones. Both lenses and sulfide stringers are deformed and transposed by the main foliation. The 20 North lens (Zn-Au-Ag-Cu-Pb) is the main orebody. It is subdivided into two zones: the 20N Au and 20N Zn zones. The 20N Au zone is a transposed and ribbon-textured gold- and copper-rich pyrite-chalcopyrite stringer zone overlain to the south by a 10- to 30-m-thick massive pyrite-sphalerite-galena lens (20N Zn zone). The 20 South lens is an 8- to 10-m-thick gold- and zinc-rich massive sulfide and stringer zone located about 10 to 15 m below the Cadillac Group sedimentary rocks (<2687 Ma). At depth (≥1,900 m below surface), the 20 North and 20 South lenses grade into aluminous zones composed mainly of quartz-pyrite-kyanite-andalusite-muscovite-Zn–rich staurolite assemblages that host transposed sulfide stringers and local semimassive to massive Au-rich pyrite and chalcopyrite layers. The synvolcanic hydrothermal alteration now corresponds to mappable upper greenschist-lower amphibo-lite–grade metamorphic assemblages. The footwall of the 20 North lens is characterized by a large discordant to semiconformable distal quartz-biotite ± garnet assemblage, which transitions laterally into a proximal quartz-garnet-biotite-muscovite zone. The abundance of pink Mn-rich garnet porphyroblasts increases toward the 20N Au zone. The hanging wall of the 20 North lens is characterized by a meter-thick zone of fracture-controlled pink alteration composed of quartz, biotite, rutile and/or anatase, and titanite associated with barren sulfide stringers. The garnet-rich assemblage in the footwall records gains in MnO, Fe2O3(total), and MgO and losses of Na2O. In the hanging wall, Fe2O3(total), S, and CO2 were added to the rocks with a slight increase in K2O, and CaO. At depth (≥ 1,900 m), the Au-rich aluminous replacement zone is a (up to 30 m) thick, highly strained zone composed of a quartz-pyrite-kyanite-andalusite-chalcopyrite-gold assemblage. All oxides except Al2O3, SiO2, and Fe2O3(total) were strongly leached. The metamorphosed hydrothermal alteration associated with the 20 South lens is characterized by a pink quartz-biotite-rutile-titanite assemblage very similar to that in the hanging wall of the 20 North lens. Toward the ore zone, the pink assemblage is gradually replaced by a proximal quartz-muscovite-green mica-pyrite assemblage, which hosts the sulfide mineralization. The aluminous alteration at LaRonde Penna is interpreted to be the metamorphic equivalent of an advanced argillic alteration and has many similarities to that of metamorphosed high-sulfidation systems and particularly a class of Au-rich VMS characterized by aluminous alteration. The LaRonde Penna and Bousquet 2-Dumagami deposits are interpreted to represent one large hydrothermal system in which variable contributions of hydrothermally modified seawater and magmatic volatiles contributed to the different styles of alteration and mineralization. The study illustrates that diverse styles of Au-rich VMS can coexist within the same deposit. In terms of exploration, almost all sulfide lenses or hydrothermal alterations minerals are located at or near volcanic hiatuses within the Bousquet Formation. These hiatuses represent major exploration targets especially when located in the upper part of the Bousquet Formation. The aluminous alteration zones have accommodated most of the postore strain due to their ductility and are transformed into schists. Consequently, the alteration product coincides spatially with the deformation zones despite the lack of a genetic relationship. Quartz-and Mn-rich garnet-biotite assemblages and/or aluminous schists with anomalous gold and/or zinc in intermediate to felsic transitional to calc-alkaline volcanic or volcaniclastic rocks located underneath a sedimentary cover represent excellent targets for Au-rich VMS in metamorphosed terranes.

Southern Kermadec arc stratovolcanoes (of predominantly basaltic and andesitic composition) provide a depth transect of the transition between effusive and explosive submarine volcanism. Observations along ∼4.6 km of towed-camera track from the crests and upper flanks of the Clark and Rumble III volcanoes reveal a consistent pattern of substrate types that are interpreted to record effusive and explosive eruption processes. Below 700 m water depth, substrates are dominated by massive/blocky flows, pillow lavas, pillow and angular block talus, localized sheet flows, and minor granule-sand volcaniclastic detritus. The latter typically forms a substrate mode of 5–20%. Above 450 m, sand lapilli (that is in part winnowed and rippled), have a substrate mode of 50–100%, with minor components of massive flows, pillow lavas, and coarse talus. This difference in abundance of sand lapilli between 450 and 700 m is interpreted to record the transition between effusive and explosive (both phreatic and phreatomagmatic) eruptions. Between 600 and 700 m, a varied distribution of sand-lapilli abundance is interpreted as recording a mix of effusive and explosive eruptions, consistent with possible differences in the physical interaction of magma–water and known compositional magma heterogeneity.

How well do we know the composition of oceanic crust? Countless studies have described the occurrence of mid‐ocean ridge basalt (MORB) at spreading centers, and few would argue that the bulk composition of oceanic crust is other than basaltic. Nevertheless, silicic volcanism (>55 wt.% SiO2) does occur along part of the northern East Pacific Rise (10.5°N; Thompson et al. [1989]),on the 095° propagator of the Galápagos Spreading Center [Clague et al., 1981],and was recently discovered on the Pacific‐Antarctic Ridge (PAR) near its intersection with the Foundation seamount chain [Hekinian et al., 1997, 1999]. Silicic lavas were recovered from a 290‐km‐long section of the northern PAR adjacent to the active Foundation plume (Figure 1) during cruise 157 of the F/S Sonne, which took place in June and July 2001. Furthermore, widespread hydrothermal activity indicates that the volcanogenic massive sulfidesilicic lava association is not only restricted to subduction and back arc settings.

High-temperature (250°C) hydrothermal vents and massive anhydrite deposits have been found in a shallow water, sediment-filled graben near 66°36′N in the Tjornes Fracture Zone north of Iceland. The site is located about 30km offshore, near the small island of Grimsey. The main vent field occurs at a depth of 400m and consists of about 20 large-diameter (up to 10m) mounds and 1–3m chimneys and spires of anhydrite and talc. A north–south alignment of the mounds over a 1-km strike length of the valley floor suggests that their distribution is controlled by a buried fault. Widespread shimmering water and extensive white patches of anhydrite in the sediment between the mounds indicates that the entire 1-km2 area occupied by the vents is thermally active. A 2-man research submersible JAGO was used to map the area and to sample vent waters, gases, and chimneys. Actively boiling hydrothermal vents occur on most of the mounds, and extensive two-phase venting indicates that the field is underlain by a large boiling zone (200×300m). The presence of boiling fluids in shallow aquifers beneath the deposits was confirmed by sediment coring. The highest-temperature pore fluids were encountered in talc- and anhydrite-rich sedimentary layers that occur up to 7m below the mounds. Baked muds underlie the talc and anhydrite layers, and pyrite is common in stockwork-like fractures and veins in the hydrothermally altered sediments. However, massive sulfides (pyrite–marcasite crusts) were found in only one relict mound. Subseafloor boiling has likely affected the metal-carrying capacity of the hydrothermal fluids, and deposition of sulfides may be occurring at greater depth. Although the mounds and chimneys at Grimsey resemble other deposits at sedimented ridges (e.g. Middle Valley, Escanaba Trough, Guaymas Basin), the shallow water setting and extensive boiling of the hydrothermal fluids represent a distinctive new type of seafloor hydrothermal system.

A research cruise has documented changes in rift tectonics, volcanism, and hydrothermalism along the least studied and most enigmatic sector of a crustal complex in the southwest Pacific Ocean. Results from the longitudinal transect are expected to provide insight into processes involving the Kermadec arc‐Havre backarc (KAHB) system, a continuum from oceanic spreading to continental rifting at a convergent plate boundary KAHB forms the central sector of an active, 2000‐km arc‐backarc complex between Tonga and New Zealand (Figure 1).The expedition also engaged in the first comprehensive survey of submarine vents in the Taupo Volcanic Zone (TVZ) at the south end of the KAHB system. Identified in the off‐shore segment of TVZ were three major hydrothermal vent areas associated with late Quaternary fault structures. Data from the expedition and from other recent research in the same area addressed questions concerning the type of hydrothermal venting, magmatic heterogeneity along and across KAHB, the style of backarc rifting, and tectonic and magmatic consequences of anomalous terranes colliding with the subduction margin.

Hot springs in active geothermal areas such as Yellowstone National Park, the Geysers geothermal field in California, and the Taupo volcanic zone in New Zealand are notably enriched in the trace metals Au, Ag, As, Sb, and Hg. Such near-surface hot springs have formed many of the world's important deposits of gold and silver and some of the largest deposits of mercury. The majority of these are associated with continental geothermal systems in subaerial environments. Here we report the discovery of active mercury-depositing hot springs in a submarine setting, at nearly 200 m water depth, within the offshore extension of the Taupo volcanic zone of New Zealand. These vents contain the first documented occurrence of elemental mercury on the sea floor and provide an important link between offshore hydrothermal activity and mercury-depositing geothermal systems on land. The discovery has implications for mercury transport in sea-floor hydrothermal systems and underscores the importance of submarine volcanic and geothermal activity as a source of mercury in the oceans.