Episyenite formation in the Toki granite, central Japan

Nishimoto, Shoji; Yoshida, Hidekazu; Asahara, Yoshihiro; Tsuruta, Takao; Ishibashi, Masayuki; Katsuta, Nagayoshi

doi:10.1007/s00410-013-0960-8

Cited by 15 publications

(12 citation statements)

References 48 publications

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“…In addition, Al immobility is a common assumption or conclusion in studies of alkali metasomatism (e.g. Cuney et al 2012;Hecht et al 1999;Nishimoto et al 2014;Rubie 1982; see also Dolejš and Wagner 2008). Thus, we believe that the immobile Al isocon can be used adequately to model mass transfer in this system.…”

Section: Mass Transfer Modeling Of Episyenite and Dehydrated Granitementioning

confidence: 85%

“…3), yet lack the vuggy texture that is common in episyenites (e.g. Nishimoto et al 2014). Moreover, hastingsite dehydration (Thomas 1982), granoblastic recrystallization of plagioclase ( Fig.…”

Section: Discussionmentioning

confidence: 99%

“…Rubie (1982) calculated a volume decrease of 0-20% for the fenites of the Kisingiri alkaline complex in western Kenya, the decrease depending on whether quartz was removed (into adjacent ijolitic magma) or reacted with the metasomatizing fluid to produce aegirine-augite in situ. Estimation of volume change requires assuming one or more elements to be immobile (Grant 1986) and/or assessment of physical constraints such as open pores (Appleyard and Woolley 1979;Nishimoto et al 2014). Any component that participates in fluid-rock reactions (e.g., Al during albitization of plagioclase; Hövelmann et al 2010) may be immobile in practice, if it is consumed in situ in crystallization of metasomatic phases.…”

Section: Mass Transfer Modeling Of Episyenite and Dehydrated Granitementioning

confidence: 99%

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Clinopyroxene episyenites in a Proterozoic rapakivi granite, SE Finland — recrystallization textures, mass transfer and implications for the petrology of A-type granite complexes

et al. 2019

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Na-metasomatic augite and aegirine-augite episyenites are hosted by subalkaline amphibole granites in the 1.644 Ga Suomenniemi rapakivi granite complex, southeastern Finland. In an examined drill core, episyenites are bordered by up to 50cm-wide zones of Na-enriched augite-bearing granite in which alkali feldspar forms rims on plagioclase, and aggregates of augite and magnetite have formed by fluid-induced dehydration of hastingsite and biotite. In the episyenites, quartz has been partially removed, alkali feldspar (An <1 Ab 50 Or 50 ) and plagioclase have been partially recrystallized to granoblastic polygonal aggregates, and clinopyroxene (augite or aegirine-augite) has coarsened and been enriched in the aegirine component. Mass balance modeling implies addition of mainly Na, depletion of Si, F, Rb, Ba, Sr and 10-20% volume loss (by quartz dissolution) in the episyenitized zones in the drill core. Quartz-depletion and recrystallization may have been caused by several superimposed stages of alteration, probably related to voluminous dike-and A-type granite magmatism in the Suomenniemi area 10-15 m.y. after the emplacement of the Suomenniemi complex. Because of the coarse recrystallization textures and near-solidus recrystallization temperatures, distinguishing these fenite-like metasomatic rocks from igneous syenites is not trivial. In epizonal A-type granite complexes, high-temperature episyenites may be more common than currently thought.

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Section: Mass Transfer Modeling Of Episyenite and Dehydrated Granitementioning

confidence: 85%

Section: Discussionmentioning

confidence: 99%

Section: Mass Transfer Modeling Of Episyenite and Dehydrated Granitementioning

confidence: 99%

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Clinopyroxene episyenites in a Proterozoic rapakivi granite, SE Finland — recrystallization textures, mass transfer and implications for the petrology of A-type granite complexes

et al. 2019

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“…In addition, many albitite/microclinite occurrences in the Jurassic-Cretaceous Nigerian ring complexes can probably be classified as episyenites [36]. Recently, episyenite has also been described from central Japan, hosted by the Cretaceous Toki granite [25], being the first episyenite discovered in an island arc setting.…”

Section: Episyenite Occurrences On a Global Scalementioning

confidence: 99%

Episyenites—Characteristics, Genetic Constraints, and Mineral Potential

Suikkanen

Rämö

2019

Mining, Metallurgy & Exploration

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Episyenites are sub-solidus, quartz-depleted alkali-feldspar-rich rocks. They form veins and lenticular bodies in granitoid rocks and migmatites in a late-to post-orogenic or anorogenic setting. Leaching of quartz is usually a response to a flux of weakly saline hydrothermal solution in circulation cells above cooling intrusions, where sufficient fluid-rock ratios and thermal gradients are achieved. Fluid Si-undersaturation is achieved by rapid cooling within the field of retrograde Si solubility or by temperature and pressure increase outside retrograde conditions. Some quartz may also be consumed in metasomatic reactions and in response to pressure fluctuation in sealed episyenite bodies. The small size and overall rarity of episyenites imply that conditions for episyenite formation are not commonly encountered in the crust. In addition to quartz depletion, episyenites record complex histories of metasomatic alteration and hydrothermal mineral growth. Nearly all episyenites have undergone Na-metasomatism, which may have led to the formation of nearly monomineralic albitite, and which is occasionally followed by late K-metasomatism, phyllic alteration, and argillization. Depending on the effectiveness of later compaction, recrystallization and vug-filling episyenites may preserve the macroscopic porosity formed by quartz dissolution and brittle deformation. Vuggy episyenites can act as significant sinks for metals carried by crustal fluids and host many significant U, Sn, and Au deposits worldwide. Rare earth-critical syenitic fenites around alkaline intrusions share mineralogical and genetic traits with episyenites.

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“…Ademais, epissienitos também hospedam depósitos de Au (Jébrak, 1991), W-Sn (Cheilletz e Giuliani, 1982;Charoy e Pollard, 1989), Sn (Costi et al, 2002;Borges et al, 2009) e Cu-Zn-Sn-W (Cabellero, 1993;Tornos et al, 2000). Por outro lado, há também ocorrências conhecidas de epissienitos não mineralizados (Petersson e Eliasson, 1997;Recio et al, 1997;Petersson et al, 2012;Nishimoto et al, 2014).…”

Section: Introductionunclassified

Interação entre magmas graníticos e a origem de epissienitos potássicos estaníferos do granito Madeira, mina Pitinga, Amazonas

Borges¹,

Gaia²,

Costi³

et al. 2018

Geol. USP. Sér. cient.

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Disponível on-line no endereço www.igc.usp.br/geologiausp -21 -Resumo O estudo petrográfico de amostras da zona de contato entre as fácies albita-granito de borda e feldspato alcalino-granito hipersolvus porfirítico, na borda oeste do plúton Madeira, identificou rochas com características texturais e composicionais herdadas das duas fácies. Tal feição é interpretada como um processo de interação entre os dois magmas graníticos, colocados e cristalizados contemporaneamente. Em condições subsolidus, fluidos hidrotermais causaram alteração potássica pervasiva, ou epissienitização, caracterizada pela dissolução de quartzo das fácies graníticas, gerando cavidades e aumentando a permeabilidade das rochas alteradas. Paralelamente, a albita da fácies de borda do albita-granito foi desestabilizada e substituída por microclínio hidrotermal e, nos estágios mais tardios, as cavidades foram preenchidas por quartzo, microclínio, fluorita, hematita, cassiterita, fengita, clorita, pirita, esfalerita, galena e calcopirita. Os epissienitos potássicos são rochas de coloração vermelha escura a marrom, granulação fina a média, ricas em microclínio hidrotermal, apresentando-se ora porosas, ora com cavidades preenchidas por quartzo e sulfetos. A cassiterita das rochas epissienitizadas é mais pura e relativamente mais pobre em Nb do que aquela presente no albita-granito magmático. Os fluidos que desencadearam a epissienitização devem ter sido oxidados, ricos em K, alcalinos e subsaturados em sílica. Propõem-se duas hipóteses para a sua origem: 1) por separação de uma fase fluida a partir do líquido magmático formador do granito hipersolvus; 2) pela ação do mesmo fluido que desencadeou o processo de autometassomatismo do albita-granito de núcleo, gerando sua fácies de borda.Palavras-chave: Mina Pitinga; Interação entre magmas graníticos; Processos hidrotermais; Epissienitos potássicos; Cassiterita. AbstractThe petrographic study in samples from the contact zone between the border albite-rich granite and the porphyritic hypersolvus alkali feldspar granite, in the western border of the Madeira pluton, allowed for the recognition of rocks with inherited textural and mineralogical features of both facies. This is interpreted as resulting from the interaction between two coeval granite magmas, which were simultaneously emplaced in the crust. Later, in subsolidus stage, the action of hydrothermal fluids caused a pervasive potassic metassomatism, identified as episyenitization, that initially caused the quartz dissolution of the granitic rocks, generating vugs and increasing the altered rocks' permeability. At the same time, the albite of the border albite-rich granite had been dissolved and replaced for microcline, and, in low-temperature hydrothermal stages, cavities were filled by quartz, microcline, fluorite, hematite, cassiterite, phengite, chlorite, pyrite, sphalerite, galena and chalcopyrite. The potassic episyenites are dark red to brown colored, medium to fine grained, microcline-rich, locally porous rocks and commonly with vugs filled...

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Episyenite formation in the Toki granite, central Japan

Cited by 15 publications

References 48 publications

Clinopyroxene episyenites in a Proterozoic rapakivi granite, SE Finland — recrystallization textures, mass transfer and implications for the petrology of A-type granite complexes

Clinopyroxene episyenites in a Proterozoic rapakivi granite, SE Finland — recrystallization textures, mass transfer and implications for the petrology of A-type granite complexes

Episyenites—Characteristics, Genetic Constraints, and Mineral Potential

Interação entre magmas graníticos e a origem de epissienitos potássicos estaníferos do granito Madeira, mina Pitinga, Amazonas

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