Mineralogical study on volcanic ash of the eruption on September 27, 2014 at Ontake volcano, central Japan: correlation with porphyry copper systems

Minami, Yusuke; Imura, Takumi; Hayashi, Shigenari; Ohba, Takayoshi

doi:10.1186/s40623-016-0440-2

Cited by 46 publications

(65 citation statements)

References 20 publications

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“…The assemblage of hydrothermal minerals identified in all samples comprised quartz, plagioclase, cristobalite, alunite, gypsum, kaolinite, smectite, and pyrite. This mineral assemblage is similar to that of the ash-fall deposits from the 2014 eruption (Minami et al 2016). …”

Section: Matrix Components In Syneruptive-spouted Type Lahar Depositssupporting

confidence: 51%

“…The mineral assemblage identified from samples of the syneruptive-spouted type lahar deposits is similar to that of the ash-fall deposits from the same eruption (Minami et al 2016). Minami et al (2016) estimated that ash falls were derived mainly from shallow depths, within 2 km of Water quality (turbidity and pH) and rainfall changes following the 2014 eruption.…”

Section: Discussionmentioning

confidence: 69%

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Characteristics of the syneruptive-spouted type lahar generated by the September 2014 eruption of Mount Ontake, Japan

Sasaki¹,

Chiba²,

Kishimoto³

et al. 2016

Earth Planet Sp

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Mount Ontake erupted at 11:52 am on September 27, 2014, which generated pyroclastic density currents, ballistic projectiles, ash falls, and a small-scale lahar that spouted directly from craters formed by the eruption. Because this lahar may have been generated by water released from within these craters, we refer to this lahar as a "syneruptivespouted type lahar" in this study. The lahar of the 2014 eruption was small relative to the other syneruptive type lahars reported in the past that were snowmelt type or crater lake breakout type lahars. Nevertheless, in the 2014 event, the syneruptive-spouted type lahar extended approximately 5 km downstream from the Jigokudani crater via the Akagawa River, with an estimated total volume of ~1.2 × 10 5 m 3. We have reviewed other representative syneruptivespouted type lahars that have been reported in Japan. The syneruptive-spouted type lahar attributed to the September 2014 eruption had the longest runout distance and largest volume of all cases studied. The mineral assemblage identified from samples of the lahar deposits is similar to that of ash-fall deposits from the same eruption. Previous workers deduced that the ash was derived mainly from shallow depths (within 2 km of the surface). The syneruptivespouted type lahar deposits are therefore also considered to have originated from shallow depths. A syneruptivespouted type lahar is a small-scale phenomenon that causes little direct damage to infrastructure, but has long-term influence on water quality. Increases in turbidity and decreases in pH are expected to occur in the Mount Ontake area downstream of Nigorisawa after heavy rainfall events in the future. Therefore, the potential indirect (but long term) damage of syneruptive-spouted type lahars should be considered for hazard mapping and planning volcanic disaster prevention measures.

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Section: Matrix Components In Syneruptive-spouted Type Lahar Depositssupporting

confidence: 51%

Section: Discussionmentioning

confidence: 69%

Characteristics of the syneruptive-spouted type lahar generated by the September 2014 eruption of Mount Ontake, Japan

Sasaki¹,

Chiba²,

Kishimoto³

et al. 2016

Earth Planet Sp

View full text Add to dashboard Cite

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“…Similar silica pseudomorphs were recently reported from hydrothermal eruptions at Mt. Ontake (Japan) in 2014 (Minami et al, 2016), phreatomagmatic events at Cotopaxi, Ecuador (Gaunt et al, 2016), and altered rocks from the Poás Crater in Costa Rica (Rodríguez and van Bergen, 2017). At Kawah Ijen, a variety of opaline ejecta were described from the 1817 phreatomagmatic eruption by van Hinsberg et al (2010a).…”

Section: Introductionmentioning

confidence: 52%

“…Dry and wet explosions resulted in widespread generation of ballistic debris, pyroclastic density currents and a lahar whose mudrich waters were disgorged from within the volcano. Silica is ubiquitous in the eruptive products, and nearly all erupted materials were hydrothermally altered (Minami et al, 2016). The authors did not attempt to differentiate the specific form of amorphous or crystalline silica, but figures clearly show the presence of pseudomorphic replacement of volcanic textures with silica.…”

Section: Speculations On the Connection Between Phreatomagmatic Activmentioning

confidence: 99%

Opal-A in Glassy Pumice, Acid Alteration, and the 1817 Phreatomagmatic Eruption at Kawah Ijen (Java), Indonesia

et al. 2018

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At Kawah Ijen (Indonesia), vigorous SO 2 and HCl degassing sustains a hyperacid lake (pH ∼0) and intensely alters the subsurface, producing widespread residual silica and advanced argillic alteration products. In 1817, a VEI 2 phreatomagmatic eruption evacuated the lake, depositing a widespread layer of muddy ash fall, and sending lahars down river drainages. We discovered multiple types of opaline silica in juvenile low-silica dacite pumice and in particles within co-erupted laharic sediments. Most spectacular are opal-replaced phenocrysts of plagioclase and pyroxene adjacent to pristine matrix glass and melt inclusions. Opal-bearing pumice has been found at numerous sites, including where post-eruption infiltration of acid water is unlikely. Through detailed analyses of an initial sampling of 1817 eruption products, we find evidence for multiple origins of opaline materials in pumice and laharic sediments. Evidently, magma encountered acid-altered materials in the subsurface and triggered phreatomagmatic eruptions. Syn-eruptive incorporation of opal-alunite clasts, layered opal, and fragment-filled vesicles of opal and glass, all suggest magma-rock interactions in concert with vesiculation, followed by cooling within minutes. Our experiments at magmatic temperature confirm that the opaline materials would show noticeable degradation in time periods longer than a few tens of minutes. Some glassy laharic sedimentary grains are more andesitic than the main pumice type and may represent older volcanic materials that were altered beneath the lake bottom and were forcefully ejected during the 1817 eruption. A post-eruptive origin remains likely for most of the opal-replaced phenocrysts in pumice. Experiments at 25 • C and 100 • C reveal that when fresh pumice is bathed in Kawah Ijen hyperacid fluid for 6 weeks, plagioclase is replaced without altering either matrix glass or melt inclusions. Moreover, lack of evidence for high-temperature annealing of the opal suggests that post-eruption alteration of pumice is more likely than pre-eruption envelopment of Lowenstern et al. Opal in Glassy Pumice euhedral opal-replaced phenocrysts in dacitic melt. At Ijen and elsewhere, the ascent of magma into hydrous acid-altered mineral assemblages (e.g., opal, kaolinite, alunite) could induce rapid dehydration of hydrous minerals and amorphous materials, generating considerable steam and contributing to magmatic-hydrothermal and phreatomagmatic explosions.

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“…Such episodic events are very short (years) relative to the lifetimes of porphyry systems associated with individual intrusions, on the order of <10 5 years (~10 4 years for the initial potassic stage), as determined by dating results (Arribas et al, 1995a;Garwin, 2002;Buret et al, 2016) and consistent with the constraints from modeling (Cathles, 1977;Shinohara & Hedenquist, 1997;Weis, 2015). If the episodic fracture events reach the surface, they may be represented by phreatomagmatic activity, such as the eruption of altered material from active volcanic-hydrothermal systems at White Island, New Zealand, and Ontake, Japan (Hedenquist et al, 1993;Minami et al, 2016).…”

Section: Discussionmentioning

confidence: 99%

Zonation of Sulfate and Sulfide Minerals and Isotopic Composition in the Far Southeast Porphyry and Lepanto Epithermal Cu–Au Deposits, Philippines

2017

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The world-class Far Southeast (FSE) porphyry system, Philippines, includes the FSE Cu-Au porphyry deposit, the Lepanto Cu-Au high-sulfidation deposit and the Victoria-Teresa Au-Ag intermediate-sulfidation veins, centered on the intrusive complex of dioritic composition. The Lepanto and FSE deposits are genetically related and both share an evolution characterized by early stage 1 alteration (deep FSE potassic, shallow Lepanto advanced argillic-silicic, both at~1.4 Ma), followed by stage 2 phyllic alteration (at~1.3 Ma); the dominant ore mineral deposition within the FSE porphyry and the Lepanto epithermal deposits occurred during stage 2. We determined the chemical and S isotopic composition of sulfate and sulfide minerals from Lepanto, including stage 1 alunite (12 to 28 permil), aluminum-phosphate-sulfate (APS) minerals (14 to 21 permil) and pyrite (À4 to 2 permil), stage 2 sulfides (mainly enargite-luzonite and some pyrite, À10 to À1 permil), and late stage 2 sulfates (barite and anhydrite, 21 to 27 permil). The minerals from FSE include stage 2 chalcopyrite (1.6 to 2.6 permil), pyrite (1.1 to 3.4 permil) and anhydrite (13 to 25 permil). The whole-rock S isotopic composition of weakly altered syn-mineral intrusions is 2.0 permil. Stage 1 quartz-alunite-pyrite of the Lepanto lithocap, above about 650 m elevation, formed from acidic condensates of magmatic vapor at the same time as hypersaline liquid formed potassic alteration (biotite) near sea level. The S isotopic composition of stage 1 alunite-pyrite record temperatures of approximately 300-400°C for the vapor condensate directly over the porphyry deposit; this cooled to <250°C as the acidic condensate flowed to the NW along the Lepanto fault where it cut the unconformity at the top of the basement. Stage 1 alunite at the base of the advanced argillic lithocap over FSE contains cores of APS minerals with Sr, Ba and Ca; based on back-scattered electron images and ion microprobe data, these APS minerals show a large degree of chemical and S-isotopic heterogeneity within and between samples. The variation in S isotopic values in these finely banded stage 1 alunite and APS minerals (16 permil range), as well as that of pyrite (6 permil range) was due largely to changes in temperature, and perhaps variation in redox conditions (average~2:1 H 2 S:SO 4 ). Such fluctuations could have been related to fluid pulses caused by injection of mafic melt into the diorite magma chamber, supported by mafic xenoliths hosted in diorite of an earlier intrusion. Resource Geology Vol. 67, bs_bs_banner fluids were relatively oxidized in the Lepanto lithocap, with an H 2 S:SO 4 ratio of about 4. The oxidation resulted from cooling, which was caused by boiling during ascent and then dilution with steam-heated meteoric water in the lithocap. This cooling also resulted in the sulfidation state of minerals increasing from chalcopyrite stability in the porphyry deposit to that of enargite in the lithocap-hosted high-sulfidation deposit. The temperature at the base of the lithoca...

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Mineralogical study on volcanic ash of the eruption on September 27, 2014 at Ontake volcano, central Japan: correlation with porphyry copper systems

Cited by 46 publications

References 20 publications

Characteristics of the syneruptive-spouted type lahar generated by the September 2014 eruption of Mount Ontake, Japan

Characteristics of the syneruptive-spouted type lahar generated by the September 2014 eruption of Mount Ontake, Japan

Opal-A in Glassy Pumice, Acid Alteration, and the 1817 Phreatomagmatic Eruption at Kawah Ijen (Java), Indonesia

Zonation of Sulfate and Sulfide Minerals and Isotopic Composition in the Far Southeast Porphyry and Lepanto Epithermal Cu–Au Deposits, Philippines

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