Flow of Hydrothermal Solution in the Crust and Mechanism of Rock Alteration

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The simulator of water-rock interaction among multi-cracks in hot-dry rock has been developed. The possibility to predict the lifetime of heat extraction from hot-dry rock due to deformation of cracks was proposed by using flow type autoclave with temperature gradient. Besides, lithification of rock powders was investigated under static and flow conditions. Lithification easily occurred under static conditions with mechanical compression of the powders. It was confirmed by observation of the natural fractures in Hishikari-gold mine and the chronological calculation of deposited minerals that the distribution of the fractures agreed with fractal theory and the natural veins were formed by intermittent repeat of mineral deposition. Cracks artificially produced in hot-dry rock for heat extraction are predicted to be tubular in shape by water-rock interaction. A new method to produce fresh cracks for controlling heat extraction was developed by blocking the tubular cracks. Passing slurry consisting of lithium magnesium silicate through the cracks under hydrothermal conditions, resulted in solidification of smectite group clay minerals in the cracks. A sensor was developed to measure pH of solutions passing through cracks under hydrothermal conditions. The accuracy of pH measured by the sensor was confirmed by comparison with theoretical thermodynamic calculation. Discussion on dissolution-deposition process from electrochemical aspect confirmed that complex formation by reaction of metal oxides and hydroxides caused deposition and the deposit had a large effect on mechanical properties of the rock matrix.The results obtained by this research gave the method to control the multi-cracks in hot-dry rocks for practical heat extraction of generate. The facilities designed in this research are useful for many area of researches such as geochemistry, environmental science, and materials science.