Enhancement of Permeability Activated by Supercritical Fluid Flow through Granite

Table 1

Types of hydrothermal fluid fracture of the Toki granite. The characteristics of the fracture are shown based on data from three boreholes obtained in this study. The clay type was related to crustal deformation and erosion. Permeability was divided into three categories based on the existing in situ permeability test data [18].

No.	Type name; (short name)	Veins; (main filling minerals)	Mesofracture; (microfracture)	Fracture density; (microfracture)	Permeability	Metamorphic facies
I	Microfracture type	Glassy vein (hornblende, plagioclase, quartz, K-feldspar)	Parallel fracture (microfracture network)	Small (large)	High	Amphibolite
II	Self-sealing type (sealing type)	Quartz vein, filling texture (biotite, quartz, K-feldspar)	Minor (grain boundary microfracture, parallel microfracture)	Small (large)	Low	Epidote-amphibolite, partly greenschist
III	Initial fracture type (initial type)	Quartz vein, filling texture, sericite filling (chlorite, quartz, K-feldspar, epidote, sericite, calcite)	Low- to middle-angle fractures (parallel microfracture)	Small	Medium	Epidote-amphibolite, partly greenschist
IV	Chlorite filling type; (chlorite type)	Chlorite filling, filling texture (chlorite, quartz, K-feldspar, epidote)	High-angle fracture with displacement, open fracture (parallel microfracture)	Small	High	Epidote-amphibolite, partly greenschist
V	Sericite filling type; (sericite type)	Sericite filling, brecciated glassy vein (sericite, calcite, albite)	Fracture network with low- to middle-angle open fractures	Large	High	Greenschist
VI	Smectite sealing type; (clay type)	Brecciated glassy vein (smectite, sericite, calcite)	Smectite filling fracture	Large	Low	—