Role of micropores, mass transfer, and reaction rate in the hydrothermal alteration process of plagioclase in a granitic pluton

Yuguchi, Takashi; Shoubuzawa, Kaho; Ogita, Yasuhiro; Yagi, Koshi; Ishibashi, Masayuki; Sasao, Eiji; Nishiyama, Tadao

doi:10.2138/am-2019-6786

Cited by 22 publications

(19 citation statements)

References 37 publications

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“…In unaltered areas, the dye occurs as low-frequency, long and linear shapes ( Figure 3 A-2 and B-2). The POM, PFM, and BSE images of altered plagioclase (sample 9-4) in Figure 4 show that the altered area irregularly branches out in multiple directions, indicating the infiltration channels of hydrothermal fluids ( Yuguchi et al., 2019 ). The plagioclase also includes altered areas with large amounts of fluorescent dye observed in the PFM images and unaltered areas with small amounts of dye ( Figure 4 A-2 and B-2).…”

Section: Resultsmentioning

confidence: 99%

“…The laboratory consists of two vertical shafts (a main and a ventilation shaft) that are 500 m deep and range from 201 m above sea level (a.s.l., ground level) to an altitude of -299 m a.s.l.. (shaft bottom). Biotite chloritization ( Yuguchi et al., 2015 ) and plagioclase alteration ( Yuguchi et al., 2019 ) have been reported from the ventilation shaft at a depth of ~500 m (-299 m a.s.l.). The samples used in this study were collected from the deepest part of the ventilation shaft (-274 to -314 m a.s.l.).…”

Section: Methodsmentioning

confidence: 99%

“…The petrography of the Toki granite at the sample site has been described in detail by Yuguchi et al. (2015 , 2019) . Many BSE images of the plagioclase and biotite minerals was collected to compare the distribution of microfractures and micropores in the PFM and BSE images.…”

Section: Methodsmentioning

confidence: 99%

“…The distribution of microfractures and micropores, and petrographic information were obtained by overlaying the FLM and POM images using digital image processing. Yuguchi et al. (2019) described the distribution and shapes of micropores within altered plagioclase based on backscattered electron (BSE) images obtained using SEM.…”

Section: Introductionmentioning

confidence: 99%

“…(2016a) is favourable for low magnification observations, real-time observations of both microfractures and petrographic information cannot be made because the FLM and POM images have to be captured separately and then overlain. Although SEM analysis, such as that reported by Yuguchi et al. (2019) , can be used to observe the chemical variation of plagioclase and micropores with higher resolution, the distribution of micropores over a wide area cannot be evaluated.…”

Section: Introductionmentioning

confidence: 99%

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Analysis of the distribution of microfractures and micropores within granitic rock using simultaneous polarization–fluorescence microscopy

Yuguchi

Usami

Ishibashi

2020

Heliyon

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The analysis of the distribution of microfractures and micropores is important to accurately characterise mass transfer within a rock body. In this paper, a new ‘simultaneous polarization–fluorescence microscopy’ method is presented, which can be used to analyse the distribution of microscopic voids, including microfractures and micropores, in granitic rock. In this method, thin sections prepared with fluorescent dye are analysed under a polarizing microscope equipped with a fluorescent reflected light source. Using both the transmitted and the fluorescent light sources, both the distribution of microfractures and micropores, and petrographic characteristics (mineral occurrences) can be determined efficiently and simultaneously. The distribution of microfractures and micropores observed in images of granites obtained using simultaneous polarization–fluorescence microscopy is consistent with the distribution observed in backscattered electron images. The low magnification characterisation of the distribution of microscopic voids also provides targeting for subsequent studies including scanning electron microscopy under high magnification, chemical analysis, and image processing.

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Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

Analysis of the distribution of microfractures and micropores within granitic rock using simultaneous polarization–fluorescence microscopy

Yuguchi

Usami

Ishibashi

2020

Heliyon

Self Cite

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Sulphide geochemistry of the superlarge Tiegelongnan Cu (Au) deposit in Tibet, China: Implication for the mineralization process

Lin

Wang

et al. 2021

Geological Journal

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The Tiegelongnan deposit in central Tibet presents a typical high‐sulfidation porphyry Cu (Au) mineralization system. Optical microscopy, scanning electron microscopy–energy dispersive spectrometry (SEM–EDS), and laser ablation inductively coupled plasma mass spectrometry (LA–ICPMS) were used to understand the mineralization processes. The advanced argillic alteration zone directly contacts the phyllic alteration zone, which is linked to the Early Cretaceous porphyritic intrusions. In this study, the spatial distributions of chief copper sulphides with variable gangue minerals are illustrated. The deep inner phyllic zone typically produced an end‐member assemblage of chalcopyrite–sericite (±dolomite), which trended upwards to produce more bornite–sericite (±siderite ± magnesite), and subsequently, the advanced argillic alteration yielded the representative end‐member assemblage of tennantite–alunite ± (aluminium‐phosphate‐sulphate, namely, APS, ±kaolinite). In the phyllic–advanced argillic transition zone, intensive covellite precipitation with the widespread occurrence of sericite–kaolinite (±APS) assemblage is proposed as an important feature in this study, which is mainly produced on the southwest side of the ore‐body centre. The typical co‐occurrence of chalcopyrite with dolomite at great depths indicates that it was related to a gently acidic fluid containing CO2; however, the pervasive tennantite–alunite association present at shallower levels suggests that fluids with SO2 were mainly involved and produced stronger acidic conditions. Acidic fluids are demonstrated to highly accelerate water‐rock alteration. Trace element analyses of the copper sulphides reflect that Au concentrations of bornite and tennantite are higher than chalcopyrite and covellite and present small signal variations. Moreover, comparing the presence of micron‐sized Au‐telluride in tennantite under advanced argillic alteration with the nano‐sized native gold in bornite resulting from phyllic alteration suggests that to a certain extent, Au enrichment is affected by the shift of more Te contents in fluid towards shallower levels, which could promote Au precipitation. Additionally, the Se contents of the selected samples were typically concentrated in chalcopyrite, bornite, and covellite, which yielded contents an order of magnitude greater than those in tennantite, indicating the intimate hydrothermal origin of the first three sulphides. Overall, the sulphide–gangue mineral associations and their copper sulphide geochemistry indicate that the hypogene–chalcopyrite of low Au contents from the phyllic zone closely corresponds to the action of gentle acidic fluids with CO2, while more acidic fluids with SO2 are involved in the formation of supergene tennantite with relatively high values of Au and Te in the advanced argillic alteration.

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Porosity generation via spatially uncoupled dissolution precipitation during plagioclase replacement in quartz undersaturated fluids

Nurdiana,

Okamoto,

Uno

et al. 2024

Contrib Mineral Petrol

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The replacement of feldspars is commonly characterized by pseudomorphism and reaction-induced pore generation. However, the effects of compositions of feldspars and fluids on porosity generation during alteration are still poorly understood. In this study, we conducted a series of hydrothermal experiments on plagioclase replacement by 2 M KCl or NaCl aqueous solutions at 600 °C and 150 MPa for 1–8 days, using plagioclase with different compositions (anorthite, An96Ab4; labradorite, An66Ab33Or1; albite, An1Ab99) with or without quartz. Albite replacement by K-feldspar was not affected by the presence of quartz, whereas anorthite was unaltered in the quartz-absent fluid. The replacement of labradorite by KCl(aq) showed different results: in the presence of quartz, labradorite was altered by K-feldspar, whereas in the absence of quartz, alteration proceeded significantly with the generation of large pores hosted by secondary anorthite coupled with euhedral K-feldspar overgrowth. Such textural relationship and oxygen isotope-labeled experiments reveal that silica-deficient fluid enhances the uncoupled dissolution reprecipitation process. The Si and Al ions in the reacted aqueous solution diffused outside the labradorite grains and encountered K+-rich solutions to grow K-feldspar. The experiments with polycrystalline rocks composed of amphibole + labradorite using 2 M KCl aqueous solution indicated the replacement of labradorite grains by anorthite and K-feldspar overgrowth, as found in single-crystal experiments. Our results indicate that the silica concentration in the fluids has different influences on the saturation indices of albite, anorthite, and K-feldspars in saline fluids, which significantly affect the replacement textures and porosity generation in crustal rocks.

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Role of micropores, mass transfer, and reaction rate in the hydrothermal alteration process of plagioclase in a granitic pluton

Cited by 22 publications

References 37 publications

Analysis of the distribution of microfractures and micropores within granitic rock using simultaneous polarization–fluorescence microscopy

Analysis of the distribution of microfractures and micropores within granitic rock using simultaneous polarization–fluorescence microscopy

Sulphide geochemistry of the superlarge Tiegelongnan Cu (Au) deposit in Tibet, China: Implication for the mineralization process

Porosity generation via spatially uncoupled dissolution precipitation during plagioclase replacement in quartz undersaturated fluids

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