Satsuma-Iwojima Volcano Research Articles

Mercury concentrations in fumarolic gas condensates and mercury chemical forms in fumarolic gases: Case study on Satsuma-Iwojima Volcano

The mercury concentrations in fumarolic gas condensates collected from volcanic areas in Hokkaido, Miyazaki, and Kagoshima Prefectures, Japan, were investigated. Mercury concentrations ranged from 0.12 to 135 μgl 1 in 44 collected samples. It was found that there was a positive correlation between mercury and chloride concentrations in fumarolic gas condensates collected from Satsuma-Iwojima Volcano, Kagoshima Prefecture. It was considered that the mercury in fumarolic gas was discharged in the form of mercury (I or II) chloride. However, the results from mercury chemical equilibrium calculations for the vapor in fumarolic gases indicated that mercury was discharged mainly in the form of metallic mercury vapor.

B1-32 熱・電磁気学的調査に基づく薩摩硫黄島火山のマグマ : 熱水系(ラハール・水蒸気爆発・熱水系,口頭発表)

B1-32 熱・電磁気学的調査に基づく薩摩硫黄島火山のマグマ : 熱水系(ラハール・水蒸気爆発・熱水系,口頭発表)

Conduit magma convection of a rhyolitic magma: Constraints from cosmic-ray muon radiography of Iwodake, Satsuma-Iwojima volcano, Japan

Quantitative re-evaluation of the muon radiography data obtained by Tanaka et al. (2009) was conducted to constrain conduit magma convection at the Iwodake rhyolitic cone of Satsuma-Iwojima volcano, Japan. Re-evaluation of the measurement error considering topography and fake muon counts confirms the existence of a low-density body of 300m in diameter and with 0.9–1.0gcm−3 at depths of 135–190m from the summit crater floor. The low-density material is interpreted as rhyolitic magma with 60% vesicularity on average, and existence of this unstable highly vesiculated magma at shallow depth without any recent eruptive or intrusive activity is considered as evidence of conduit magma convection. The structure of the convecting magma column top was modeled based on density calculations of vesiculated ascending and outgassed descending magmas, compared with the observed density anomaly. The existence of the low-density anomaly was confirmed by comparison with published gravity measurements, and the predicted degassing at the shallow magma conduit top agrees with observed heat discharge anomaly distribution localized at the summit area. This study confirms that high viscosity of silicic magmas can be compensated by a large size conduit to cause the conduit magma convection phenomena. The rare occurrence of conduit magma convection in a rhyolitic magma system at Iwodake is suggested to be due to its specific magma features of low H2O content and high temperature.

Development of a muon radiographic imaging electronic board system for a stable solar power operation

Cosmic-ray muon radiography is a method that is used to study the internal structure of volcanoes. We have developed a muon radiographic imaging board with a power consumption low enough to be powered by a small solar power system. The imaging board generates an angular distribution of the muons. Used for realtime reading, the method may facilitate the prediction of eruptions. For real-time observations, the Ethernet is employed, and the board works as a web server for a remote operation. The angular distribution can be obtained from a remote PC via a network using a standard web browser. We have collected and analyzed data obtained from a 3-day field study of cosmic-ray muons at a Satsuma-Iwojima volcano. The data provided a clear image of the mountain ridge as a cosmic-ray muon shadow. The measured performance of the system is sufficient for a stand-alone cosmic-ray muon radiography experiment.

Imaging Density Distribution of a Big Object by Muography and its Application to the Analysis of Gas-liquid Two-phase Flow in a Conduit during Volcanic Eruption

This paper reviews the principle of cosmic-ray muon radiography (muography) and its application to the analysis of gas-liquid two-phase flow in a conduit during volcanic eruption. Muography is a useful technique for imaging internal density distribution of a big object (e.g., a volcano, a blast furnace, etc.). By measuring muon path lengths and absorption along different paths through the object, one can deduce average density along the path inside the object. According to numerical modeling of gas-liquid two-phase flow in the volcanic conduit during a dome-forming eruption, magma porosity (i.e., density) inside the conduit largely changes depending on magma flux even if the porosity at the surface is kept low. The increase in the porosity inside the conduit may induce the transition to explosive eruption. This implies that high-resolution measurement of the porosity distribution inside the conduit is essential for predicting the transition of eruption styles. Recent progress in a muon detector system enables us to perform this measurement, such as in Mt. Iwodake of Satsuma-Iwojima Volcano, Japan. Spatial resolution of muography is adequate for detecting the variation of the porosity inside the conduit. Applications to industrial plant monitoring are also discussed.

Characteristics and source modeling of broadband seismic signals associated with the hydrothermal system at Satsuma–Iwojima volcano, Japan

The broadband seismic data observed at Satsuma–Iwojima volcanic island in southwestern Japan show a wide variety of interesting features. One of them is the periodic and frequency-dependent amplitude modulation of volcanic tremors. Another interesting feature is the occurrence of very long period (VLP) seismic pulses synchronized with the tremor amplitude modulation. Both the tremor amplitude modulation and the VLP pulses have fairly regular intervals of 46–50 min, suggesting a spatially fixed, non-destructive repetitive source. We performed waveform inversions to reveal the source mechanism of the VLP pulses, assuming a point source embedded in a medium that realistically represented the topography of the island. Numerical tests showed that the Green's functions used in the inversion were significantly affected by the topography. The observed VLP pulses were well explained by the rapid expansion of an inclined crack 100 m beneath the floor of the summit crater, which had a seismic moment of 3 × 10 10 Nm. Both the characteristic amplitude modulation and the VLP pulses are explained systematically by a model consisting of a water-filled crack and a network of gas paths. The water-filled crack was heated above the boiling temperature of the water in it. A sudden break of the unstable superheated state caused sudden vaporization and a pressure increase, which was observed as the VLP pulse. The network of gas paths consisted of swollen portions and constricted portions, which worked as tremor generators when vapor from the water-filled crack passed through.

High SiF4/HF ratio detected in Satsuma-Iwojima volcano’s plume by remote FT-IR observation

Remote FT-IR measurements of volcanic plume of Mt. Iwodake, Satsuma-Iwojima volcano, Japan, were carried out in October 1996 to understand plume chemistry of the volcano, especially characteristics of fluorine-bearing species in the plume. The SO2/HCl molar ratio in the plume was about 4, that is larger than the ratio in high-temperature gases. The high content of SO2 is suggested to be caused by sulfur combustion in the crater. An average SiF4/HF molar ratio of 0.57 was observed for the plume, which is about one order of magnitude higher than the previously reported ratio. The result shows that SiF4 is an important species and has similar to even larger contribution for fluorine output from Satsuma-Iwojima volcano than HF. The SiF4 flux of Satsuma-Iwojima volcano is about 13 t/d, that is the largest SiF4 flux from volcanoes in the world. The observed SiF4/HF ratio cannot be explained only by the high-temperature fumarolic composition of the volcano according to the thermodynamic calculations. The ratio can be explained if contribution of F-rich low-temperature fumaroles to the total gas flux of the volcano is as high as 40%.

Mafic-felsic magma interaction at Satsuma-Iwojima volcano, Japan: Evidence from mafic inclusions in rhyolites

Geochemical and petrographic studies of the rhyolites and mafic inclusions from Satsuma-Iwojima volcano were carried out in order to investigate evolution of a silicic, bimodal magma system during the post-caldera stage. Abundant mafic inclusions, which are fine-grained with vesicles in their cores, are present in the Showa-Iwojima rhyolitic lava. Inclusions with similar textures are found in Iwodake volcanic bombs but are less common than in the Showa-Iwojima lava. The major and trace element compositions of the inclusions plot along mixing lines connecting the host rhyolites with spatially and temporally associated basaltic to basaltic andesite magmas. Plagioclase phenocrysts in the inclusions have a large variation in core compositions (An42 to An96), and exhibit various zoning profiles and reaction textures, indicating they coexisted with melts ranging from basaltic to rhyolitic composition. Pyroxenes also exhibit a wide range in composition and a variety of zoning patterns consistent with multiple sources. These results suggest that a stratified magma chamber exists beneath the volcano, consisting of a lower basaltic layer, an upper rhyolitic layer and an episodically-present, thin middle layer of andesite. Variations in the chemistry of the Iwodake and Showa-Iwojima mafic inclusions suggest that multiple injections of very similar basaltic magma have occurred since the growth of the Iwodake dome. More extensive textural disequilibrium shows that the Showa-Iwojima rhyolites formed through more extensive interaction with mafic magma. The mafic-felsic interaction is consistent with degassing model of a magma chamber estimated by other researchers, which consists of degassing of upper rhyolitic magma by convection in a conduit and supply of a CO2-rich volatile phase from underlying basaltic magma to the rhyolitic magma.

Radionuclide behavior in high-temperature gases from Satsuma Iwojima volcano, Japan

Radionuclide and sulfur measurements were performed on samples from plume and hot fumarolic gas discharged from Satsuma Iwojima volcano, Japan. Such measurements in volcanic plumes contribute to a better understanding of degassing mechanisms (emanation coefficient of metals, degassing magma volume, residence time of the magma). At Satsuma Iwojima, inferred emanation coefficients of 210Pb and 210Po were estimated to be 0.07 and 2.5%, respectively, the lowest values obtained to date in volcanic gases. These values may be “apparent” emanation coefficients, due to the high viscosity of the degassing magma, which prevents efficient degassing of such low concentration components. The volume of the degassing reservoir (rhyolite layer) is estimated to be 0.24 km3, assuming no radionuclide recharge from the underlying basaltic reservoir to the degassing rhyolite.

Soil gas emission of volcanic CO2 at Satsuma-Iwojima volcano, Japan

Soil gas surveys were carried out in November 1999 and October 2000 at Satsuma-Iwojma volcano, southwest Japan. The chemical composition of the soil gas was a mixture of CO2 and air components, with CO2 concentrations ranging from 0.03 to 59 vol%. The origin of the soil CO2 was evaluated on the basis of the variation of δ13CCO2 and CO2 concentration. Although most of the CO2 is of biogenic origin, large volcanic contributions of greater than 50% were found close to the caldera rim, where soil temperature anomalies were observed. Emission rate of volcanic CO2 was estimated by assuming simple mixing among volcanic, atmospheric, and biogenic CO2. High rates of diffuse emission of volcanic CO2 were also observed at the caldera rim and close to some hot springs, indicating that part of the volcanic-gas discharge ascends through fissures along the caldera rim. The flux of the volcanic CO2 through the soil is estimated to be 20 t day−1; this is 25% of the total CO2 flux through soil and 20% of the CO2 flux from volcanic fumaroles in the main crater of Iwodake.

Deposition of trace elements from high temperature gases of Satsuma-Iwojima volcano

The Satsuma-Iwojima volcano has been emitting continuously high temperature (600° to 900°C) gases for at least 800 years. We identified the minerals that form in response to closed-system cooling of these gases and from air-mixing reactions. Major differences compared with the sublimates observed at other volcanoes are the occurrence of wulfenite (PbMoO4) and several mixed chlorides. This is the first report of wulfenite in fumarolic deposits. Thermochemical modeling shows that wulfenite precipitates between 540° and 490°C from a gas with lower sulfur content and/or higher fO2, and a higher Mo content (log fSO2 = −2.1, log fH2S = −5, log ffO2 = −18.6, log fH2MoO4 = −4.5, T = 500°C) than the previously reported gas composition. The occurrence of abundant K, Pb, Fe, Zn, Rb and Cs mixed chlorides may be promoted by the low S/Cl of the Satsuma-Iwojima high temperature gases. Natural sublimates of metallic elements (molybdenite, wulfenite, anglesite, Tl-Pb and Tl-Bi sulfides, Mo oxydes and Pb oxides) are deposited along the fumarolic conduit and on the ground under conditions of variable temperatures and fO2. The increase in fO2 due to the mixing of the gases with the atmosphere reduces the volatility of several elements (As, Sn, Na, K and Pb) by promoting their condensation at higher temperatures. As air mixes with volcanic gas in the fumarolic plume, we can expect to find these metals as aerosols.

Degassing process of Satsuma-Iwojima volcano, Japan: Supply of volatile components from a deep magma chamber

Satsuma-Iwojima volcano continuously releases magmatic volatiles from the summit of Iwodake, a rhyolitic lava dome. The temperature of fumaroles is high, between 800° and 900°C, and the water-rich composition of volcanic gases has not changed essentially over the past 10 years. Sulfur dioxide flux measured by COSPEC is almost constant with an average of 550 t/d since 1975. The present volcanic gas is likely degassed from a rhyolitic magma whose composition is similar to that erupted in 1934, 2 km east of Satsuma-Iwojima. Comparison of silicate melt inclusions and volcanic gas compositions indicates that the magma degassing pressure is very low, implying magma-gas separation at a very shallow level. The mass rate of magma degassing is estimated at 10 m3/s using the volatile content of the magma and the fluxes of magmatic volatiles. The rhyolitic parental magma is volatile-undersaturated in the deep magma chamber, as suggested by melt inclusion studies. Magma convection in a conduit, driven by the density difference between higher density degassed and lower density non-degassed magmas, explains the high emission rate of magmatic volatiles released at shallow depth from such a magma chamber, that is gas-undersaturated at depth. Model calculations require the conduit diameter to be greater than 50 m as a necessary condition for convection of the rhyolitic magma. Long-term convective degassing has resulted in the rhyolitic magma in the deep chamber to become depleted in volatile components. The melt-inclusion studies indicate that the rhyolitic magma responsible for discharging the present volcanic gas has been degassed during the long degassing history of the volcano and is now supplied with CO2-rich volatile components from an underlying basaltic magma. The total volcanic gas flux over 800 years requires degassing of 80–120 km3 of basaltic magma.

Self-potential anomaly of Satsuma-Iwojima volcano

We conducted self-potential (SP) surveys twice at Satsuma-Iwojima volcano where an intense fumarolic activity continued for more than 1000 years from a summit crater of Iwodake, a lava dome of rhyolite. A positive anomaly of 200 ∼ 250 mV was detected on the Iwodake edifice, although the survey area was limited because of the steep topography and existence of high temperature fumaroles. The anomaly seems to be centered at the summit crater of Iwodake and can roughly be explained by a pair of conduction current source and sink located around the sea level beneath the summit crater. Depth of the current source might indicate the upper end of a liquid-phase water upflow zone, where the liquid-phase water vaporizes due to heat and depressurization. The above model does not explain the additional positive SP anomaly around the summit crater and on the western flank. The anomaly around the su mmit might be caused by suppression of meteoric water downflow by high temperature volcanic gases. The positive anomaly on the western flank might be caused by local fluid upflows associated with fumaroles on the flank.

Evaluation of recent activity at Satsuma-Iwojima —Felt earthquake on June 8, 1996—

Emission of large amount of volcanic gas occurs at the summit crater of Satsuma-Iwojima volcano located south of Kyushu, Japan. Sakurajima Volcanological Observatory (SVO), DPRI, Kyoto University has conducted seismic observation at a permanent station 1.5 km WNW of the summit crater since June 1995. Volcanic earthquakes at the volcano are classified into A-type (high frequency), B-type (low frequency), C-type (monochromatic) and tremor. A-type earthquake generated by shear fracture and B-type earthquake with volumetric source are dominant at the volcano. Volcanic activity of Satsuma-Iwojima was evaluated from seismicity of the volcanic earthquakes. During the period of 1995–1998, the seismicity has remained at a constant level with seismic energy release rate of 7×1014 erg/year. The seismicity was as high as that during 1975–1977. The energy release rate of volcanic earthquakes at the volcano has been stable at least for recent 20 years. Within the stable activity, a minor increase in activity occurred in mid-1990’s, as shown by a felt earthquake (M2.9) on June 8, 1996. The earthquake on June 8, 1996 may be related to topographic changes and ground deformation around the summit crater, because a crack with length of 100 m was found at southeast rim of the summit crater in October 1996 and the benchmark near the crack moved eastward by 6 cm during the period from June 1995 to April 1997. The stable activity for 20 years and minor inflation of activity estimated from seismic observation coincides with those from SO2 flux, highest fumarolic temperatures and gas equilibrium temperatures. Although daily number of B-type earthquakes with smaller amplitude increased almost 10 times in September 1998, this increase in the seismicity did not accompany any change of eruptive activity. Unstable seismicity of B-type earthquake may reflect fluctuations of condition in the gas conduit.

Degassing activity from Iwodake rhyolitic cone, Satsuma-Iwojima volcano, Japan: Formation of a new degassing vent, 1990–1999

Large changes in the surface manifestation of degassing activity were observed from 1990 to 1999 at the summit crater of Iwodake cone of Satsuma-Iwojima volcano. During this period, a new high-temperature fumarolic area formed in the center of the crater floor and became a degassing vent with a diameter of 40 m. Altered volcanic rocks were ejected during the course of vent formation. Although glass fragments were observed in the ejected ash, the glass comes from altered Iwodake rhyolite that covers the crater floor. The highest fumarolic temperature and equilibrium temperatures of volcanic gases had a maximum of about 900°C at the beginning of the vent formation. The flux of SO2, measured by COSPEC, varied from 300 to 700 ton/day and correlated directly with maximum fumarole temperature. During this period, open fractures formed along the southern rim of the crater almost contemporaneously with the vent formation and changes in the nature of fumarolic discharges. The continuous and intense degassing at Satsuma-Iwojima is likely caused by volatile transport from a deep magma chamber through a convecting magma column. An increase in the magma convection rate might have caused these large changes in surface manifestations, including increase in the SO2 flux and fumarolic temperatures, ground deformation, and the vent formation.

Iodine isotope ratios and halide concentrations in fluids of the Satsuma-Iwojima volcano, Japan

Fumarolic condensates and acid spring waters from Satsuma-Iwojima were sampled between 1993 and 1998 and analyzed for 129I/I and 36Cl/Cl ratios and chloride, bromine, and iodine concentrations. Halogen concentrations suggest that the fumarolic condensates represent mostly magmatic fluids, but that the hot springs are a mixture between magmatic fluids and meteoric water with some presence of seawater. The magmatic component is best preserved in the high-temperature fumaroles collected in 1998 and has a 129I/I ratio of 756 ± 47 × 10−15. This 129I/I ratio yields an iodine age of 15.5 ± 1.5 Ma, which is compatible with derivation of iodine from subducted marine sediments in this region. Ratios of I/Cl, and Br/Cl in the fumaroles also indicate that halides in the magmatic component were mainly derived from marine sediments subducted in the Nankai Trough. These observations suggest that recycling of subducted sediments is an active source of halides in the Satsuma-Iwojima volcanic system. The comparison of 129I/I ratios obtained from fumaroles over the sampling period shows that a recent meteoric component was present in 1993, but not in 1998. This observation might reflect reorganization of the fumarolic system during this period, which expelled the more recent meteoric water from the fumarolic system after 1993. The acid hot springs on the flanks of the volcano maintain a 129I isotopic signature indicative of substantial dilution of magmatic waters by mixing with old meteoric water and seawater. Fumarolic gases and hot spring waters were also analyzed for 36Cl/Cl, but the measured ratios were at, or below, the detection limit of AMS, also indicating that recent contributions of Cl from meteoric water are small in the fumaroles and coastal hot springs.

Variation of volatile concentration in a magma system of Satsuma-Iwojima volcano deduced from melt inclusion analyses

Chemical analyses of 30 melt inclusions from Satsuma-Iwojima volcano, Japan, were carried out to investigate volatile evolution in a magma chamber beneath the volcano from about 6300yr BP to the present. Large variations in volatile concentrations of melts were observed. (1) Water concentration of rhyolitic melts decreases with time; 3–4.6wt.% at the time of latest caldera-forming eruption of Takeshima pyroclastic flow deposit (ca. 6300yr BP), 3wt.% for small pyroclastic flow (ca. 1300yr BP) of Iwodake, post-caldera rhyolitic dome, and 0.7–1.4wt.% for submarine lava eruption (Showa-Iwojima) in 1934. (2) Rhyolitic melts of the Takeshima and Iwodake eruptions contained CO2 of less than 40ppm, while the Showa-Iwojima melt has higher CO2 concentration of up to 140ppm. (3) Water and CO2 concentrations of basaltic to andesitic melt of Inamuradake, a post-caldera basaltic scoria cone, are 1.2–2.8wt.% and ≤290ppm, respectively.Volatile evolution in the magma chamber is interpreted as follows: (1) the rhyolitic magma at the time of the latest caldera-forming eruption (ca. 6300yr BP) was gas-saturated due to pressure variation in the magma chamber because the large variation in water concentration of the melt was attributed to exsolution of volatile in the magma prior to the eruption. Iwodake eruption (ca. 1300yr BP) was caused by a remnant of the caldera-forming rhyolitic magma, suggested from the similarity of major element composition between these magmas. (2) Volatile composition of the Showa-Iwojima rhyolitic melt agrees with that of magmatic gases presently discharging from a summit of Iwodake, indicating the low pressure degassing condition. (3) The degassing of the magma chamber by magma convection in a conduit of Iwodake during non-eruptive but active degassing period for longer than 800 years decreased water concentration of the rhyolitic magma. (4) Geological and petrological observations indicate that a stratified magma chamber, which consists of a lower basaltic layer and an upper rhyolitic layer, might have existed during the post-caldera stage. Addition of CO2 from the underlying basaltic magma to the upper gas-undersaturated (degassed) rhyolitic magma increased CO2 concentration of the rhyolitic magma.

B70 薩摩硫黄島火山のマグマ-ガスシステム : 後カルデラ期の高温流紋岩質マグマの脱ガス

B70 薩摩硫黄島火山のマグマ-ガスシステム : 後カルデラ期の高温流紋岩質マグマの脱ガス

PV30 薩摩硫黄島における温泉・地下水流動系について

PV30 薩摩硫黄島における温泉・地下水流動系について

Flux of volatiles and ore-forming metals from the magmatic-hydrothermal system of Satsuma Iwojima volcano

Research Article| July 01, 1994 Flux of volatiles and ore-forming metals from the magmatic-hydrothermal system of Satsuma Iwojima volcano Jeffrey W. Hedenquist; Jeffrey W. Hedenquist 1Geological Survey of Japan, 1-1-3 Higashi, Tsukuba 305, Japan Search for other works by this author on: GSW Google Scholar Masahiro Aoki; Masahiro Aoki 1Geological Survey of Japan, 1-1-3 Higashi, Tsukuba 305, Japan Search for other works by this author on: GSW Google Scholar Hiroshi Shinohara Hiroshi Shinohara 1Geological Survey of Japan, 1-1-3 Higashi, Tsukuba 305, Japan Search for other works by this author on: GSW Google Scholar Author and Article Information Jeffrey W. Hedenquist 1Geological Survey of Japan, 1-1-3 Higashi, Tsukuba 305, Japan Masahiro Aoki 1Geological Survey of Japan, 1-1-3 Higashi, Tsukuba 305, Japan Hiroshi Shinohara 1Geological Survey of Japan, 1-1-3 Higashi, Tsukuba 305, Japan Publisher: Geological Society of America First Online: 02 Jun 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 Geological Society of America Geology (1994) 22 (7): 585–588. https://doi.org/10.1130/0091-7613(1994)022<0585:FOVAOF>2.3.CO;2 Article history First Online: 02 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Jeffrey W. Hedenquist, Masahiro Aoki, Hiroshi Shinohara; Flux of volatiles and ore-forming metals from the magmatic-hydrothermal system of Satsuma Iwojima volcano. Geology 1994;; 22 (7): 585–588. doi: https://doi.org/10.1130/0091-7613(1994)022<0585:FOVAOF>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The Satsuma Iwojima volcano, southwest Japan, degasses 5 x 106 t/yr H2O, 9 x 10 4 t/yr S, and 6 x 104 t/yr Cl from high-temperature (≤880 °C) fumaroles atop a now-altered rhyolite dome that erupted 1200 yr ago. Acidic hot springs (pH 1.1-1.8) discharge ∼20 x 106 t/yr H2O to the sea; this water is composed of ∼1 part magmatic vapor absorbed by 6 parts meteoric ground water. The Cl and SO4 in solution originate from the vapor, whereas cation components are derived largely by dissolution of the rhyolite. The flux of Pb, Zn, Cu, and Mo in the vapor and acidic springs ranges from 0.1 to 10 t/yr each, whereas the Au flux is 10-5 and 10-3 t/yr, respectively. The low concentrations of NaCl and metals in the vapor are due to the condensation of a hypersaline liquid from the vapor during ascent and depressurization, meaning that the atmospheric-pressure vapor does not reflect the composition of the fluid exsolving from the magma. Neither this low-pressure vapor nor the acidic waters can account for high-sulfidation Cu-Au ore deposits deduced to have formed in this environment; such mineralization requires the subsequent ascent of a metal-rich fluid. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.