Abstract Pore fluid pressure and differential stress are among the most important controls on the mechanical behavior of mineralizing systems. Their separate influences can be readily identified on failure mode diagrams, which show failure envelopes for pore fluid factor or pore fluid pressure at failure against differential stress. The effect of the intermediate principal stress can be shown on such diagrams by using a failure criterion that includes all three principal stresses, such as the Murrell extension to the Griffith criterion. The effect is apparent from the significant variation of the position of the failure envelope as a function of the ratio between the three principal stresses, which is therefore another important control on failure. Characteristic regimes for different gold deposit types occur as distinctive fields on failure mode diagrams. Carlin, epithermal, and volcanogenic massive sulfide (VMS) deposit types have low absolute pore fluid pressures. Iron oxide copper-gold (IOCG), intrusion-related gold, and porphyry deposits encompass low to intermediate values of pore fluid pressure, while the field of lode gold deposits may extend to the highest pore fluid pressures. Lode gold, IOCG, and epithermal deposit types may have the largest values of differential stress. Carlin and VMS deposits are associated with normal stress regimes; the other deposit types may have structures that that formed in either normal or reverse stress regimes. Exploring the effects of the stress ratio and refining these currently broadly defined regimes for the mechanics of mineralization are important future directions for research.

Abstract The Miocene Kışladağ deposit (~17 Moz), located in western Anatolia, Turkey, is one of the few global examples of Au-only porphyry deposits. It occurs within the West Tethyan magmatic belt that can be divided into Cretaceous, Cu-dominant, subduction-related magmatic arc systems and the more widespread Au-rich Cenozoic magmatic belts. In western Anatolia, Miocene magmatism was postcollisional and was focused in extension-related volcanosedimentary basins that formed in response to slab roll back and a major north-south slab tear. Kışladağ formed within multiple monzonite porphyry stocks and dikes at the contact between Menderes massif metamorphic basement and volcanic rocks of the Beydağı stratovolcano in the Uşak-Güre basin. The mineralized magmatic-hydrothermal system formed rapidly (<400 kyr) between ~14.75 and 14.36 Ma in a shallow (<1 km) volcanic environment. Volcanism continued to at least 14.26 ± 0.09 Ma based on new age data from a latite lava flow at nearby Emiril Tepe. Intrusions 1 and 2 were the earliest (14.73 ± 0.05 and 14.76 ± 0.01 Ma, respectively) and best mineralized phases (average median grades of 0.64 and 0.51 g/t Au, respectively), whereas younger intrusions host progressively less Au (Intrusion 2A: 14.60 ± 0.06 Ma and 0.41 g/t Au; Intrusion 2 NW: 14.45 ± 0.08 Ma and 0.41 g/t Au; Intrusion 3: 14.39 ± 0.06 and 14.36 ± 0.13 Ma and 0.19 g/t Au). A new molybdenite age of 14.60 ± 0.07 Ma is within uncertainty of the previously published molybdenite age (14.49 ± 0.06 Ma), and supports field observations that the bulk of the mineralization formed prior to the emplacement of Intrusion 3. Intrusions 1 and 2 are altered to potassic (biotite-K-feldspar-quartz ± magnetite) and younger but deeper sodic-calcic (feldspar-amphibole-magnetite ± quartz ± carbonate) assemblages, both typically pervasive with disseminated to veinlet-hosted pyrite ± chalcopyrite ± molybdenite and localized quartz-feldspar stockwork veinlets and sodic-calcic breccias. Tourmaline-white mica-quartz-pyrite alteration surrounds the potassic core both within the intrusions and outboard in the volcanic rocks. Tourmaline was most strongly developed on the inner margins of the tourmaline-white mica zone, particularly along the Intrusion 1 volcanic contact where it formed breccias and veins, including Maricunga-style veinlets. Field relationships show that the early magmatic-hydrothermal events were cut by Intrusion 2A, which was then overprinted by Au-bearing argillic (kaolinite-pyrite ± quartz) alteration, followed by Intrusion 3 and late-stage, low-grade to barren argillic and advanced argillic alteration (quartz-pyrite ± alunite ± dickite ± pyrophyllite). Gold deportment changes with each successive hydrothermal event. The early potassic and sodic-calcic alteration controls much of the original Au distribution, with the Au dominantly deposited with feldspar and lesser quartz and pyrite. Tourmaline-white mica and argillic alteration events overprinted and altered the early Au-bearing feldspathic alteration and introduced additional Au that was dominantly associated with pyrite. Analogous Au-only deposits such as Maricunga, Chile, La Colosa, Colombia, and Biely Vrch, Slovakia, are characterized by similar alteration styles and Au deportment. The deportment of Au in these Au-only porphyry deposits differs markedly from that in Au-rich porphyry Cu deposits where Au is typically associated with Cu sulfides.

Abstract The Kişladağ porphyry gold deposit (16.8 Moz) is located in western Anatolia, Turkey, and is hosted in a nested complex of monzonite porphyries that intruded coeval volcanic rocks of the Beydagi stratovolcano and the Menderes metamorphic basement. The intrusions and volcanic rocks have a high K calc-alkaline to shoshonitic affinity similar to the regional volcanic rocks of western Anatolia. Three main intrusive phases are recognized with average gold grades highest in the early intrusions, Intrusion 1 (~0.8 g/t Au) and Intrusion 2 (~0.7 g/t Au), followed by the weakly mineralized Intrusion 3 (typically <0.2 g/t Au). The highest gold (~0.84 g/t) is also associated with the higher temperature potassic (biotite-K feldspar ± actinolite) core of the deposit in Intrusion 1. Molybdenum is most closely associated with Au, whereas the Cu concentration on average is unusually low (~200 ppm) but increases with depth (500-1,000 ppm). Surrounding and partly overlapping the potassic zone is a distinct tourmaline-white mica (± pyrite ± albite ± quartz) alteration with tourmaline abundant up to 500 m from the center of the deposit. White mica is more widely distributed with compositions varying from proximal muscovite-paragonite to distal phengite. Stockwork veinlets are common within the potassic and tourmaline-white mica zones and evolve from volumetrically minor quartz-rich, to quartz-pyrite, to quartz-pyrite with tourmaline envelopes, to the most abundant pyrite-tourmaline veins and breccias, and finally pyrite-only veins. A poorly mineralized advanced argillic alteration assemblage (quartz-alunite ± dickite ± pyrophyllite ± pyrite) postdates the tourmaline-white mica alteration and is particularly abundant in the eastern flank of the deposit and as a lithocap. The most widespread alteration is argillic comprising kaolinite ± smectite ± pyrite ± quartz, and overprinting all alteration phases, and is particularly widespread in the surrounding volcanic package. New geochronological results from the Kisladag deposit constrain the timing and duration of the main gold mineralization stage to <0.4 m.y. (14.76 ± 0.01-14.36 ± 0.02 Ma). The system evolved in the following sequence: (1) Intrusion 1 (>14.76 ± 0.01 Ma), (2) Intrusion 2 (14.76 ± 0.01 Ma), (3) potassic alteration coeval with mineralization (14.4 ± 0.1 Ma), and (4) Intrusion 3 (14.36 ± 0.02 Ma). The deposition of gold is constrained by the emplacement of the sulfide mineralization dated at 14.49 ± 0.06 Ma by Re-Os on molybdenite. The Kişladağ deposit is classified as a gold-only porphyry deposit due to its exceptionally low Cu/Au ratio («0.03). There are few economically significant global analogues—examples include the Maricunga porphyry deposits (9.8 Moz Au) in Chile and La Colosa (33.2 Moz Au) in Columbia. The low Cu/Au ratio may in part be related to the shallow level of emplacement (<1 km?) but also reflects the postcollisional setting. The deposit formed at least 50 m.y. after closure of the northern Neotethys ocean that was related to Cretaceous collision and compression, and 15 m.y. after the commencement slab roll-back of the southern Neotethys ocean and the onset of upper plate extension in the late Eocene to early Oligocene. The Miocene volcanic rocks that host Kisladag are in part related to a slab tear that resulted in upwelling of asthenospheric mantle, which melted previously metasomatized subcontinental lithospheric mantle. Postcollision extension, fertile upper mantle, shallow subduction, and slab tear-induced magmatism, and shallow level of emplacement may have been important factors in the gold-rich nature of Kisladag.

Abstract Volcanic arcs that have a submarine component ( n = 21) include both intra-oceanic and island arcs. Combined, they have a total length of almost 22,000 km with ~93 percent in the Pacific region. We estimate that 696 volcanoes occur along these arcs, with at least 209 (30%) being submarine. The 13 best studied arcs total 14,260 km and include 526 volcanoes with a spacing of 22 to 32 km (mean = 27 km). Less than 3 percent of arc length has been systematically surveyed for sea-floor hydrothermal emissions. Submarine hydrothermal venting along these arcs therefore remains overwhelmingly undetected. The southern Kermadec arc northeast of New Zealand represents ~260 km of intra-oceanic arc that has been systematically surveyed for hydrothermal plumes. Here, seven of the 13 (55%) volcanoes surveyed are hydrothermally active. Depths to the vents range between 250 and 1,660 m below sea level. Venting is characterized by hydrothermal plumes that are chemically heterogeneous when compared to midocean ridge sites, i.e., they range from being highly enriched in dissolved ionic species (e.g., Fe) and 3 He, CO 2 , and sulfur gases, to 3 He rich but with very low concentrations of ionic species. By contrast, surveys of the Tabar-Lihir-Tanga-Feni island arc offshore Papua New Guinea and the Ghizo Ridge fore-arc offshore the Solomon Islands show no detectable submarine hydrothermal activity. Instead, hydrothermal and volcanic activity is confined to the summits of subaerial islands, as illustrated by the Luise volcano on Lihir Island, which is host to the giant Ladolam gold deposit. The Izu-Bonin intra-oceanic arc extends for 1,200 km south from Japan and is host to 26 submarine volcanoes. Myojin Knoll is a caldera volcano that has a number of hydrothermal vents (180°–330°C) in association with the large (~9 × 10 6 t) gold-rich Sunrise massive sulfide deposit. Suiyo seamount is also host to numerous hydrothermal vents (up to 317°C) associated with sulfide chimneys and mounds. These are the only two submarine arc-related hydrothermal systems for which a complete suite of vent fluid analyses has been obtained. Thirty-one active vent sites (for the period 1984–2002) have been documented worldwide on submarine arc volcanoes; circumstantial evidence suggests hydrothermal activity at an additional 11 sites. Twothirds of these sites occur in water depths of <1,000 m. The injection of hydrothermal emissions into the mid and upper levels of the oceans has implications for tracer studies of mid-depth geostrophic flow. The shallowest vent sites can deliver Fe to the euphotic zone (100- to 200-m water depth) thus giving arc-related vent sites an environmental influence generally lacking at midocean ridges. Magma bodies underlying vent sites in arc settings may play a significant role in the supply of magmatic volatiles and metals to their overlying hydrothermal systems. The shallower hydrothermal circulation cells expected on arc volcanoes, relative to midocean ridges, implies that any magmatic fluid component will be more evident in the expelled vent fluids. The venting of hydrothermal systems at relatively shallow depths and with high gas contents will assist phase separation and should promote the formation of economic massive sulfide (Cu-Zn ± Pb ± Au) deposits, making them attractive for exploration and possible exploitation.

Abstract The New Zealand American PLUme Mapping Expedition (NZAPLUME) provided the first systematic survey of chemical emissions along a submarine volcanic frontal arc. Chemical plumes emanated from seven of 13 volcanoes that line a 260 km-long section of the southern Kermadec arc northeast of New Zealand. Hydrothermal plumes ranged in depth from <200 to 1500 m and are generally more shallow than plumes over mid-ocean ridges (MORs). The chemical signatures of plumes along the southern Kermadec arc are unusually diverse and have concentration anomalies for CO 2 , H 2 S and Fe that can exceed those for MOR settings by 5–10 times, or more. Projected end-member fluid concentrations of carbon and sulphur gases at some volcanoes require a magmatic vapour source, while unusually high Fe concentrations and Fe/Mn values are consistent with venting an iron-rich magmatic brine. Thus, vent-fluid emissions on the Kermadec arc volcanoes often appear as hybrid mixtures of hydrothermally evolved sea water influenced by water-rock reaction with compositionally diverse arc lavas, and exsolved magmatic fluid present as gaseous (CO 2 and SO 2 +H 2 S) and liquid (Fe-rich brines) components. While rock-buffered fluids in arc settings are expected to vary compositionally from one another and from MOR fluids, it is the magmatic components that clearly differentiate arc emissions as being super-enriched in sulphur gases and ionic metals. These first systematic observations of spatially frequent and chemically robust fluid emissions from southern Kermadec arc forecast arcs as being a potentially important source of chemicals to the oceans.

Abstract Hydrothermal activity on submarine volcanic arcs in the western Pacific Ocean is known but mostly unexplored. In March 1999, the New Zealand American PLUme Mapping Expedition (NZAPLUME) cruise conducted the first systematic exploration of hydrothermal venting along a sizeable section of an intra-oceanic arc, visiting 13 volcanoes along 260 km of the southern Kermadec arc, just northeast of New Zealand. Conclusive evidence of hydrothermal plumes exists for seven of the 13 volcanoes; at two other volcanoes plume indications were weak and uncertain. The hydrothermal origin of the particle plumes was confirmed by positive anomalies in the ratios of sulphur, iron and copper to titanium relative to non-plume particles, in mass concentrations similar to particles collected from hydrothermal plumes over mid-ocean ridges. The spatial density of active sites along the southern Kermadec arc is at least 2.7 per 100 km (2.7/100 km), probably not significantly different from the weakly constrained value of c. 1/100 km on slow- and intermediate-rate mid-ocean ridges. An analysis of the number of hydrothermal fields produced for the magma delivery rate in each of these environments suggests that the southern Kermadec arc presently has relatively abundant hydrothermal activity. While this result cannot yet be generalized to other Pacific arcs, submarine volcanoes may contribute significantly to the global hydrothermal budget.