『Abstract
　Metals such as Cu, Mo, Au, Sn, and W in porphyry and related epithermal mineral deposits are derived predominantly from the associated magmas, via magmatic-hydrothermal fluids exsolved upon emplacement into the mid- to upper crust. Four main sources exist for magmas, and therefore metals, in convergent and collided plate margins: the subducting oceanic plate basaltic crust, subducted seafloor sediments, the asthenospheric mantle wedge between the subducting and overriding plates, and the upper plate lithosphere. This paper firstly examines the source of normal arc magmas, and concludes that they are predominantly derived from partial melting of the metasomatized mantle wedge, with possible minor contributions from subducted sediments. Although some metals may be transferred from the subducting slab via dehydration fluids, the bulk of the metals in the resultant magmas are probably derived from the asthenospheric mantle. The most important contributions from the slab from a metallogenic perspective are H2O, S, and Cl, as well as oxidants. Partial melting of the subducted oceanic crust and/or sediments may occur under some restricted conditions, but is unlikely to be a widespread process (in Phanerozoic arcs), and does not significantly differ metallogenically from slab-dehydration processes.
　Primary, mantle-derived arc magmas are basaltic, but differ from mid-ocean ridge basalt in having higher water contents (〜10×higher), oxidation states (〜2 log fO2 units higher), and concentrations of incompatible elements and other volatiles (e.g., S and Cl). Concentrations of chalcophile and siderophile metals in these partial melts depend critically on the presence and abundance of residual sulfide phases in the mantle source. At relatively high abundances of sulfides thought to be typical of active arcs where fS2 and fO2 are high (magma/sulfide ratio = 10²-10⁵), sparse, highly siderophile elements such as Au and PGE will be retained in the source, but magmas may be relatively undepleted in abundant, moderately chalcophile elements such as Cu (and perhaps Mo). Such magmas have the potential to form porphyry Cu±Mo deposits upon emplacement in the upper crust. Gold-rich porphyry deposits would only form where residual sulfide abundance was very low (magma/sulfide ratio ＞10⁵), perhaps due to unusually high mantle wedge oxidation states.
　In contrast, some porphyry Mo and all porphyry Sn-W deposits are associated with felsic granitoids, derived primarily from melting of continental crust during intra-plate rifting events. Nevertheless, mantle-derived magmas may have a role to play as a heat source for anatexis and possibly as a source of volatiles and metals. In post-subduction tectonic settings Tulloch and Kimbrough, 2003, such as subduction reversal or migration, arc collision, continent-continent collision, and post-collisional rifting, a subducting slab source no longer exists, and magmas are predominantly derived from partial melting of the upper plate lithosphere. This lithosphere will have undergone significant modification during the previous subduction cycle, most importantly with the introduction of large volumes of hydrous, mafic (amphibolitic) cumulates residual from lower crustal differentiation of arc basalts. Small amounts of chalcophile and siderophile element-rich sulfides may also be left in these cumulates. Partial melting of these subduction-modified sources due to post-subduction thermal readjustments or asthenospheric melt invasion will generate small volumes of calc-alkaline to mildly alkaline magmas, which may redissolve residual sulfides. Such magmas have the potential to form Au-rich as well as normal Cu±Mo porphyry and epithermal Au systems, depending on the amounts of sulfide present in the lower crustal source. Alkalic-type epithermal Au deposits are an extreme end-member of this range of post-subduction deposits, formed from subduction-modified mantle sources in extensional or transtensional environments.
　Ore formation in porphyry and related epithermal environments is critically dependent on the partitioning of metals from the magma into an exsolving magmatic-hydrothermal fluid phase. This process occurs most efficiently at depths greater than 〜6 km, within large mid- to upper crustal batholithic complexes fed by arc or post-subduction magmas. Under such conditions, metals will partition efficiently into a single-phase, supercritical aqueous fluid (〜2-13 wt.％ NaCl equivalent), which may exist as a separate volatile plume or as bubbles entrained in buoyant magma. Focusing of upward flow of bubbly magma and/or fluid into the apical regions of the batholotic complex forms cupolas, which represent high mass- and heat-flux channelways towards the surface. Cupolas may be self-organizing to the extent that once formed, further magma and fluid flow will be enhanced along the weakened and heated axes. Cupolas may form initially as breccia pipes by volatile phase (rather than magma) reaming-out of extensional structures in the brittle cover rocks, to be followed immediately by magma injection to form cylindrical plugs or dikes.
　Cupola zones may extend to surface, where magmas and fluids vent as volcanic products and fumaroles. Between the surface and the underlying magma chamber, a very steep thermal gradient exists (700゜-800℃ over ＜5 km), which is the primary cause of vertical focusing of ore mineral deposition. The bulk of metals (Cu±Mo±Au) that forms porphyry ore bodies are precipitated over a narrow temperature interval between 〜425゜ and 320℃, where isotherms in the cupola zone rise to within 〜2 km of the surface. Over this temperature range, four important physical and physicochemical factors act to maximize ore mineral deposition: (1) silicate rocks transition from ductile to brittle behavior, thereby greatly enhancing fracture permeability and enabling a threefold pressure drop; (2) silica shows retrograde solubility, thereby further enhancing permeability and porosity for ore deposition; (3) Cu solubility dramatically decreases; and (4) SO2 dissolved in the magmatic-hydrothermal fluid phase disproportionates to H2S and H2SO4, leading to sulfide and sulfate mineral deposition and the onset of increasingly acidic alteration.
　The bulk of the metal flux into the porphyry environment may be carried by moderately saline supercritical fluids or vapors, with a volumetrically lesser amount by saline liquid condensates. However, these vapors rapidly become dilute at lower temperatures and pressures, such that they lose their capacity to transport metals as chloride complexes. They retain significant concentrations of sulfur species, however, and bisulfide complexing of Cu and Au may enable their continued transport into the epithermal regime. In the high-sulfidation epithermal environment, intense acidic (advanced-argillic) alteration is caused by the flux of highly acidic magmatic volatiles (H2SO4, HCl) in this vapor phase. Ore formation, however, is paragenetically late, and may be located in these extremely altered and leached cap rocks largely because of their high permeability and porosity, rather than there being any direct genetic connection. Ore-forming fluids, where observed, are low- to moderate-salinity liquids, and are thought to represent later-stage magmatic-hydrothermal fluids that have ascended along shallow (cooler) geothermal gradients that either do not, or barely, intersect the liquid-vapor solvus. Such fluids “contract” from the original supercritical fluid or vapor to the liquid phase. Brief intersection of the liquid-vapor solvus may be important in shedding excess chloride and chloride-complexed metals (such as Fe), so that bisulfide-complexed metals remain in solution. Such a restrictive pressure-temperature path is likely to occur only transiently during the evolution of a magmatic-hydrothermal system, which may explain the rarity of high-sulfidation Cu-Au ore deposits, despite the ubiquitous occurrence of advanced-argillic alteration in the lithocaps above porphyry-type systems.

Keywords: Porphyry deposit; Epithermal deposit; Subduction; Post-subduction; Magmatic-hydrothermal fluid; Ore formation
Contents
1. Introduction
2. Magma generation in convergent and collided margins: geochemical characteristics and partitioning of metals
　2.1. Slab dehydration and asthenospheric melting in subduction zones
　　2.1.1. Behavior of metals
　2.2. Sediment dehydration and/or melting in subduction zones
　　2.2.1. Behavior of metals
　2.3. Oceanic slab melting in subduction zones
　　2.3.1. Behavior of metals
　2.4. Supra-subduction zone lithospheric melting: the MASH process
　　2.4.1. Behavior of metals
　　2.4.2. Sources of Mo
　2.5. Lithospheric melting during post-subduction events
　　2.5.1. Behavior of metals in subduction-modified sources
　2.6. Crustal melting during post-collisional stress relaxation
　　2.6.1. Sources of metals
3. Behavior of metals during magma fractionation and fluid exsolution in the upper crust
　3.1. Partitioning of metals from magma into exsolving hydrothermal fluid
4. Magmatic-hydrothermal ore formation
　4.1. Porphyry Cu ore formation
　4.2. Epithermal Cu-Au ore formation
　　4.2.1. high-sulfidation epithermal Cu-Au deposits
　　4.2.2. Low-sulfidation epithermal Au deposits (including alkalic-type deposits)
5. Summary and conclusions
　5.1. Sources of magmas and metals
　5.2. Porphyry and epithermal ore formation
Acknowledgments
References

Fig. 1. Structure and processes beneath an oceanic island arc (sources: Tatsumi and Eggins, 1995; Schmidt and Poli, 1998; Winter, 2001; Poli and Schmidt, 2002; Fumagalli and Poli, 2005). Primary hydrous basaltic arc magmas are derived from partial melting of the metasomatized asthenospheric mantle wedge. Mineral zones shown in the subducting plate indicate lower limits of stability of hydrous phases in the basaltic oceanic crust and peridotitic mantle lithosphere. Abbreviation: Ctd=chloritoid. Fig. 3. Schematic section through a continental arc, showing the development of a MASH or “hot zone” at the base of the crust where basaltic arc magmas pool at their level of neutral buoyancy, differentiate, and interact with crustal rocks and melts. Evolved, less dense, andesitic magmas rise into the mid-to-upper crust where they pool at their new level of neutral buoyancy to form batholithic complexes. Along with volcanic structures, porphyry and epithermal deposits may form at shallower levels above these batholithic complexes where exsolved magmatic fluids ascend, cool, and interact with near-surface upper crustal rocks.Modified fromRichards (2003, 2005); sources: Hildreth andMoorbath (1988),Winter (2001), Annen et al. (2006), and Sillitoe (2010). Fig. 4. Post-subduction tectonic environments conducive to the formation of porphyry and epithermal deposits by remobilization of previously subduction-modified lithosphere (modified from Richards, 2009). (a) Porphyry Cu±Mo deposits formed in normal arc settings; a continental arc is shown, but similar processes can occur in mature island arcs. (b-d) During post-subduction tectonic processes, previously subduction-modified sub-continental lithospheric mantle (SCLM) or lower crustal hydrous cumulate zones residual from previous arc magmatism (black layer) may undergo small-volume partial melting. Such magmas may remobilize Au as well as Cu±Mo left behind in residual sulfide phases by arc magmatism, leading to the potential formation of porphyry Cu±Au±Mo and alkalic-type epithermal Au deposits. Magmas may be characterized by high Sr/Y and La/Yb ratios due to the presence of hornblende (±garnet, titanite) in the amphibolitic lower crustal source rocks. See text for discussion. Fig. 7. Schematic cross-section through a typical coupled arc batholith.cupola.volcanic system, with associated porphyry Cu±Au and linked high sulfidation Cu.Au epithermal deposits. Also shown are the thermal structure, fluid flow pathways and characteristics during the main stage of hydrothermal activity, and overlapping hydrothermal alteration zones. Propylitic alteration by circulating heated groundwaters can be assumed to affect all the supracrustal rocks in the field of view, with greatest intensity (epidote, actinolite) close to the intrusions, fading to background distally. Modified from Richards (2005); sources: Sillitoe (1973, 2010), Dilles (1987), Shinohara and Hedenquist (1997), Hedenquist et al. (1998), and Fournier (1999). Richards(2011)による『Magmatic to hydrothermal metal fluxes in convergent and collided margins』から