The setting, style, and role of magmatism in the formation of volcanogenic massive sulfide deposits

Abstract

Throughout Earth’s history, all volcanogenic massive sulfide (VMS)-hosting environments are associated with specific assemblages of mafic and felsic rocks with distinct petrochemistry (petrochemical assemblages) indicative of formation at anomalously high temperatures within extensional geodynamic environments. In mafic-dominated (juvenile/ophiolitic) VMS environments, there is a preferential association with mafic rocks with boninite and low-Ti tholeiite, mid-ocean ridge basalt (MORB), and/or back-arc basin basalt affinities representing forearc rifting or back-arc initiation, mid-ocean ridges or back-arc basin spreading, or back-arc basins, respectively. Felsic rocks in juvenile oceanic arc environments in Archean terrains are high field strength element (HFSE) and rare earth element (REE) enriched. In post-Archean juvenile oceanic arc terrains, felsic rocks are commonly HFSE and REE depleted and have boninite like to tholeiitic signatures. In VMS environments that are associated with continental crust (i.e., continental arc and back-arc) and dominated by felsic volcanic and/or sedimentary rocks (evolved environments), felsic rocks are the dominant hosts to mineralization and are generally HFSE and REE enriched with calc-alkalic, A-type, and/or peralkalic affinities, representing continental arc rifts, continental back-arcs, and continental back-arcs to continental rifts, respectively. Coeval mafic rocks in evolved environments have alkalic (within-plate/ocean island basalt like) and MORB signatures that represent arc to back-arc rift versus back-arc spreading, respectively. The high-temperature magmatic activity in VMS environments is directly related to the upwelling of mafic magma beneath rifts in extensional geodynamic environments (e.g., mid-ocean ridges, back-arc basins, and intra-arc rifts). Underplated basaltic magma provides the heat required to drive hydrothermal circulation. Extensional geodynamic activity also provides accommodation space at the base of the lithosphere that allows for the underplated basalt to drive hydrothermal circulation and induce crustal melting, the latter leading to the formation of VMS-associated rhyolites in felsic-dominated and bimodal VMS environments. Rifts also provide extensional faults and the permeability and porosity required for recharge and discharge of VMS-related hydrothermal fluids. Rifts are also critical in creating environments conducive to preservation of VMS mineralization, either through shielding massive sulfides from seafloor weathering and mass wasting or by creating environments conducive to the precipitation of subseafloor replacement-style mineralization in sedimented rifts. Subvolcanic intrusions are also products of the elevated heat flow regime common to VMS-forming environments. Shallow-level intrusive complexes (i.e., within 1–3 km of the seafloor) may not be the main drivers of VMS-related hydrothermal circulation, but are likely the manifestation of deeper-seated mantle-derived heat (i.e., ~3–10 km depth) that drives hydrothermal circulation. These shallower intrusive complexes are commonly long-lived (i.e., millions of years), and reflect a sustained thermally anomalous geodynamic environment. Such a thermally anomalous environment has the potential to drive significant hydrothermal circulation, and, therefore multi-phase, long-lived subvolcanic intrusive complexes are excellent indicators of a potentially fertile VMS environment. The absence of intrusive complexes, however, does not indicate an area of low potential, as they may have been moved or removed due to post-VMS tectonic activity. In some cases, shallow-level intrusive systems contribute metals to the VMS-hydrothermal system.

Appendix: sources of lithogeochemical data

Mafic rocks

Mafic-dominated VMS settings

Snow Lake and Flin Flon, Stern et al. (1995); Kamiskotia, Hocker et al. (2005); Kidd Creek, Kerrich et al. (1998) and Wyman et al. (1999); Kutcho, Barrett et al. (1996); Rambler/Ming, Piercey et al. (1997) and Bailey (2002); Blake River Group (Noranda), Lafleche et al. (1992a, b); West Shasta, Brouxel et al. (1988), Bence and Taylor (1985), and Lapierre et al. (1985); Betts Cove: Bedard (1999); Troodos, Cameron (1985) and Rogers et al. (1989); Ice Deposit, Piercey (unpublished data); Josephine (Turner Albright), Harper (2003); Fyre Lake, Piercey et al. (2001a, 2004); and Windy Craggy, Peter and Scott (1999).

Modern VMS environments

Bransfield Strait, Keller et al. (2002); Okinawa Trough, Shinjo et al. (1999); Manus Basin, Sinton et al. (2003); Juan de Fuca (Axial Seamount), Rhodes et al. (1990); East Pacific Rise, Allan et al. (1987); Middle Valley, Stakes and Franklin (1994); Lau Basin, Ewart et al. (1994); TAG hydrothermal field (mid-Atlantic), Smith and Humphris (1998); Escanaba Trough: Saunders et al. (1982); Guaymas, Davis and Clague (1987).

Continental crust-associated VMS settings

Avoca, Leat et al. (1986) and McConnell et al. (1991); Eskay Creek, Barrett and Sherlock (1996); Kudz Ze Kayah (Finlayson Lake), Piercey et al. (2002a); Parys Mountain, Barrett et al. (2001); Tulsequah: Sebert and Barrett (1996); Bathurst, Rogers and van Staal (2003); Delta-Bonnifield, Dusel-Bacon et al. (2004); Iberian Pyrite Belt, Almodóvar et al. (1997) and Mitjavila et al. (1997).

Felsic rocks

Archean felsic rocks

Pilbara, Vearncombe and Kerrich (1999); Kidd Creek, Prior et al. (1999); Sturgeon Lake, Lesher et al. (1986); Noranda, Lesher et al. (1986) and Péloquin (1999)(regional); South Bay, Lesher et al. (1986); Kamiskotia, Hart (1984), Barrie and Pattison (1999); and High Lake, Petch (2004).

Post-Archean felsic rocks from mafic-dominated settings

Flin Flon, Syme (1998); Rambler (Ming), Bailey (2002) and Piercey et al. (1997); West Shasta, Bence and Taylor (1985) and Lapierre et al. (1985); Kutcho, Barrett et al. (1996); and Snow Lake, Bailes and Galley (1999, 2001).

Post-Archean felsic rocks from continental crust-dominated settings

Eskay Creek, Barrett and Sherlock (1996); Delta-Bonnifield, Dusel-Bacon et al. (2004); Finlayson Lake, Piercey et al. (2001b); Iberian Pyrite Belt, Almodóvar et al. (1997); Bransfield Strait, Petersen et al. (2004); Okinawa Trough, Shinjo and Kato (2000); Mount Read, Crawford et al. (1992); Parys Mountain, Barrett et al. (2001); Avoca, Leat et al. (1986) and McConnell et al. (1991) and Bathurst, Rogers et al. (2003).