The Kasuga High Sulfidation gold deposit is hosted in the silicified Late Miocene andesite of Nansatsu Volcanic Rocks in the southern part of the Satsuma Peninsula, Southwest Japan. Optical microscopic observations and X -ray fluorescence spectrometry (Horiba XGT -5000) analysis of two silicified andesite samples from the Kasuga ore body revealed that the rocks underwent different degrees of hydrothermal alteration and no tectonic deformation afterward. Crystallographic orientations of quartz composing the silicified andesite samples studied using Electron Backscatter Diffraction, EBSD (EDAX GE -1, TSL -OIM) displayed different trends in the c -axis orientations between the samples. The c -axes of quartz grains are mainly oriented sub -horizontal or plunging at low angles in the less -silicified andesite. The highly silicified sample has larger quartz grains with c -axes plunging at high angles. The difference in c -axis orientations is provably related to the silicification processes in the earlier and later stages of hydrothermal alteration. The results of this study suggest that quartz c -axis orientations of rocks deformed under low strain regimes are potentially inherited from initial undeformed state, for example crystallization from hydrothermal solutions.
Oxygen isotope data (δ 18 O) of quartz are reported for the San-yo and Ryoke belt granites, metamorphic rocks, and late-stage siliceous veins. The analyzed quartz showed δ 18 O values of 9.7-12.9‰ (relative to VSMOW) in granites, 15.1-17.3‰ in biotite schist, 16.4-17.8‰ in siliceous schist. The δ 18 O values of quartz in foliation-parallel and -normal veins are 16.6‰ and 17.3‰, respectively. The δ 18 O values of quartz in the granite samples are relatively higher than those crystallized from I-type granite magma (ca. 5-8‰) and similar with values of S-type granite magma (ca. 9-12‰). These features suggest partial melting of the chemically modified crust with sedimentary precursors to form the parental magma of granites. Hafnium isotope data of zircons from those granites, reported in an earlier publication, exhibited by ε Hf (t) values between +1.1 and -4.8, provide additional evidence for the formation of the granites from a continental crust with some incorporation of hydrothermally altered reworked crust before partial melting. The relatively higher δ 18 O values (> 15‰) of quartz in siliceous veins indicate their precipitation from silica-and 18 O-rich fluids that were extracted from the slab-dehydration process during late-stages of their evolution. 1 8 O values ca. +5.7±0.3‰ but exhibit a wider range if basalts/gabbros are altered ca. 0 to +12‰ (Kolodny
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