Porphyry Copper Potential in Japan Based on Magmatic Oxidation State

Hattori, Kéiko

doi:10.1111/rge.12160

Cited by 24 publications

(7 citation statements)

References 104 publications

(146 reference statements)

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“…Despite a paucity of apparently suitable tectonic and magmatic conditions for the transport of metals that may lead to the formation of porphyry copper deposits (Hattori, ; Sillitoe, ), there are significant magmatic–hydrothermal systems in Japan associated with andesitic stratovolcano complexes. Some of these systems are active but many others have existed in the past, as evidenced by the abundance of volcanic‐hosted base‐ and precious‐metal deposits of epithermal and similar affinity.…”

Section: Discussionmentioning

confidence: 99%

“…We find that many magmatic–hydrothermal systems in Japan, both active and extinct, share features with the porphyry system, including fluid characteristics deduced from related hydrothermal alteration mineralogy at the level of the epithermal environment. Whether or not the magmas that are driving these systems in Japan have (or had) the potential to transport and release significant copper and other metals to hydrothermal systems to potentially form an ore deposit is not considered here; this aspect is addressed by Sillitoe () and Hattori (). Arribas and Mizuta () and Izawa and Hayashi () note evidence in a number of mineralized districts in northern Honshu and southern Kyushu, respectively, for features that are characteristic of the more distal expressions of the porphyry system, i.e.…”

Section: Introductionmentioning

confidence: 99%

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Features of Large Magmatic–Hydrothermal Systems in Japan: Characteristics Similar to the Tops of Porphyry Copper Deposits

2018

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Volcanic complexes in Japan such as Kusatsu Shirane, Honshu, and Kuju‐Hatchobaru and Kirishima, Kyushu, host active magmatic–hydrothermal systems that are several kilometers in diameter and typically asymmetric to the intrusive center. Their heat flow is driven by multiple intrusions at <5–10 km depth over a period on the order of ~105 years. These hydrothermal systems consist of advecting fluids of magmatic origin (either vapor with acidic components condensed into meteoric water, or a subsequent liquid of varying reactivity) that interact with convecting meteoric water. The amount of the magmatic component depends on location relative to the intrusive center, local controls on permeability, and the temporal evolution of the intrusions. The proportion of meteoric water diluent typically increases from proximal to distal locations (over several kilometer distance), and with time after intrusion (> several thousands of years). Some of the neutral pH solutions in these large hydrothermal systems, up to ~5 km from volcanic vents, support geothermal energy developments, with strong structural control on fluid flow. Near active volcanic vents, the magmatic vapor component of hydrothermal systems can form acidic condensates (pH ~ 1.5) that are responsible for strong alteration of the host rock. The resulting residual quartz and advanced argillic minerals are typical of shallow‐formed lithocap alteration that is associated with deeper porphyry copper deposits in similar arc‐hosted volcanic settings. Around the world, this near‐surface lithocap alteration, influenced by structures as well as lithology, may be barren in metals, even where associated with mineralized porphyry intrusions at depth. Such intrusion‐proximal alteration is widespread in both active and extinct settings in Japan. In addition, distal geothermal hot springs typically have a magmatic water component, albeit minor, with a pH that varies from ~3 to near‐neutral; deep alteration intersected in drill holes is characterized by alunite–dickite–pyrophyllite or chlorite–wairakite, respectively. These alteration assemblages are typical of their extinct equivalents, intermediate sulfidation epithermal veins, with mineralogical complexities caused by temporal evolution as well as spatial variation (e.g. along different structures). Such active and extinct magmatic–hydrothermal systems signify the presence of shallow degassing or degassed intrusions, respectively. Where similar intrusions in volcanic arcs around the world are eroded to ~1 to 2 km depth, the tops of porphyry copper deposits are commonly exposed, marked by a transition of white mica upward to pyrophyllite‐dominant alteration. Active magmatic–hydrothermal systems on the flanks of arc volcanoes in Japan are dynamic – both cycling as well as evolving – and share characteristics with extinct systems that host epithermal and porphyry ore deposits.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Features of Large Magmatic–Hydrothermal Systems in Japan: Characteristics Similar to the Tops of Porphyry Copper Deposits

2018

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“…Oxygen fugacity is estimated to be similar to typical oxidised arc magma conditions in zone R2 (~ΔNNO + 1), producing favourable conditions for sulphur transport and deposition (e.g. Hattori, 2018). The higher oxygen fugacity estimated in some xenolith cores by the presence of anhydrite and CaTs clinopyroxene cores (≤ ΔNNO + 4) is potentially too high for Cu transfer, as an upper limit to mineralisation at the hematite-magnetite (~ΔNNO + 4) buffer may exist for porphyry copper deposition (Sun et al, 2013).…”

Section: Volatiles and Metal Transportmentioning

confidence: 98%

Magmatic and Metasomatic Effects of Magma–Carbonate Interaction Recorded in Calc-silicate Xenoliths from Merapi Volcano (Indonesia)

Whitley

Halama

Gertisser

et al. 2020

Journal of Petrology

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Magma-carbonate interaction is an increasingly recognised process occurring at active volcanoes worldwide, with implications for the magmatic evolution of the host volcanic systems, their eruptive behaviour, volcanic CO2 budgets, and economic mineralisation. Abundant calc-silicate skarn xenoliths are found at Merapi volcano, Indonesia. We identify two distinct xenolith types: magmatic skarn xenoliths, which contain evidence of formation within the magma, and exoskarn xenoliths, which more likely represent fragments of crystalline metamorphosed wall-rocks. The magmatic skarn xenoliths comprise distinct compositional and mineralogical zones with abundant Ca-enriched glass (up to 10 wt% relative to lava groundmass), mineralogically dominated by clinopyroxene (En15-43Fs14-36Wo41-51) + plagioclase (An37-100) ± magnetite in the outer zones towards the lava contact and by wollastonite ± clinopyroxene (En17-38Fs8-34Wo49-59) ± plagioclase (An46-100) ± garnet (Grs0-65Adr24-75Sch0-76) ± quartz in the xenolith cores. These zones are controlled by Ca transfer from the limestone protolith to the magma and by transfer of magma-derived elements in the opposite direction. In contrast, the exoskarn xenoliths are unzoned and essentially glass-free, representing equilibration at sub-solidus conditions. The major mineral assemblage in the exoskarn xenoliths is wollastonite + garnet (Grs73-97Adr3-24) + Ca-Al-rich clinopyroxene (CaTs0-38) + anorthite ± quartz, with variable amounts of either quartz or melilite (Geh42-91) + spinel. Thermobarometric calculations, fluid inclusion microthermometry and newly calibrated oxybarometry based on Fe3+/ΣFe in clinopyroxene indicate magmatic skarn xenolith formation conditions of ∼850 ± 45 °C, < 100 MPa and at an oxygen fugacity between the NNO and HM buffer. The exoskarn xenoliths, in turn, formed at 510-910 °C under oxygen fugacity conditions between NNO and air. These high oxygen fugacities are likely imposed by the large volumes of CO2 liberated from the carbonate. Halogen and sulphur-rich mineral phases in the xenoliths testify to the infiltration by a magmatic brine. In some xenoliths this is associated with the precipitation of copper-bearing mineral phases by sulphur dissociation into sulphide and sulphate, indicating potential mineralisation in the skarn system below Merapi. Compositions of many xenolith clinopyroxene and plagioclase crystals overlap with that of magmatic minerals, suggesting that the crystal cargo in Merapi magmas may contain a larger proportion of skarn-derived xenocrysts than previously recognised. Assessment of xenolith formation timescales demonstrates that magma-carbonate interaction and associated CO2 release could affect eruption intensity, as recently suggested for Merapi and similar carbonate-hosted volcanoes elsewhere.

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“…Some of these factors are discussed in this volume (e.g. Hattori, 2018;Sillitoe, 2018;Watanabe et al, 2018;Williamson et al, 2018).…”

Section: Previous Studiesmentioning

confidence: 99%

Potential for Porphyry Copper Deposits in Northern Tōhoku (or the Exploration Potential for Base and Precious Metal Deposits in Japan 2020)

Arribas

Mizuta

2018

Resource Geology

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There are no known porphyry copper deposits in Japan. Attempts were made in the past to explain this paradox as the Japanese islands sit above a subduction zone of the type widely accepted to give rise to porphyry-type deposits within subvolcanic magmatic-hydrothermal systems. Is it possible that porphyry copper systems are incompatible with the volcanoplutonic setting of the Japanese islands? In other words, is the established model for the genesis of porphyry copper systems not completely correct, or is it that the elusive Japanese porphyry deposit has not yet been found? We argue that, until proven otherwise, the answer lies in the latter option. In this article, we focus on Akita Prefecture and the surrounding areas and consider the potential for the existence of porphyry copper deposits mainly from an empirical and practical point of view, in contrast with the obviously important petrogenetic and/or tectonic perspectives. We argue that this region is representative of the T ohoku province of northern Honshu and that it serves as a proxy for Japan in general. Akita is rich in mineralization styles and deposits, including two main magmatic-hydrothermal deposit types of Neogene age: (i) middle Miocene submarine stratiform volcanogenic massive sulfide (VMS) deposits (Kuroko) and (ii) late Miocene to Pleistocene Ag-Au-bearing polymetallic epithermal/subepithermal veins. In particular the Au-Ag-bearing polymetallic veins, which are comparable to intermediate-sulfidation epithermal deposits commonly associated with porphyry copper systems, were discovered and mined for several centuries before the first Kuroko deposits were found in the late 1800s. Osarizawa, the last active vein mine, closed in 1978. Kuroko deposits, the main source of metal production in Akita in the 20th century, had peak of production in the 1970s, followed by a rapid decline during the 1980s and complete cessation of all mining by 1995. Not surprisingly, the end of mining in Akita, combined with a series of strategic decisions made by the Government and the Japanese metal mining industry, coincided with a cessation of mineral exploration, both in Akita and throughout Japan, with the exception of VMS deposits offshore and limited exploration for bonanza-grade, low-sulfidation epithermal gold deposits in Hokkaido. Our analysis of post-1945 regional exploration in northern T ohoku indicates that Kuroko deposits were by far the dominant target and that the number of drill holes in the 1990s accounted for less than 4% of the total completed from the early 1960s to 1995. These data indicate that essentially no mineral exploration has been conducted in T ohoku for Au-Agbearing polymetallic vein deposits during the past 30+ years. We conclude that exploration stopped too early and certainly before it could have benefited from the significant applicable metallogenic and technological breakthroughs of the last few decades.

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Porphyry Copper Potential in Japan Based on Magmatic Oxidation State

Cited by 24 publications

References 104 publications

Features of Large Magmatic–Hydrothermal Systems in Japan: Characteristics Similar to the Tops of Porphyry Copper Deposits

Features of Large Magmatic–Hydrothermal Systems in Japan: Characteristics Similar to the Tops of Porphyry Copper Deposits

Magmatic and Metasomatic Effects of Magma–Carbonate Interaction Recorded in Calc-silicate Xenoliths from Merapi Volcano (Indonesia)

Potential for Porphyry Copper Deposits in Northern Tōhoku (or the Exploration Potential for Base and Precious Metal Deposits in Japan 2020)

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