Journal de la métallurgie des poudres et des mines

Abstrait

Granite Fracture Initiation and Growth: Petrographic Evidence of Hydrothermal Alteration

Takeshi Yugusuchi

Granite contains biotites that have undergone varied degrees of modification. In order to determine the origin and progression of granite fractures, this study examines the correlations among alteration markers, areal microvoid fractions in chloritized biotite, and macroscopic fracture frequencies in the Toki granite, central Japan. Understanding potential hydrogeological applications can help with proper characterizations of the frequency distribution of macroscopic fractures in granite, which supports safety assessments for geological disposal and storage. To collect samples for the analysis, 191 m of borehole 06MI03 were bored. A total of 24 samples that showed variations in the frequency of macroscopic fractures were chosen. The amount of hydrothermal alteration and the frequency of fractures inside granites are to be assessed utilising novel approaches such as biotite chloritization and petrographic alteration indicators [1]. The ratio of the alteration product area to the original mineral area is known as the alteration indicators. Additionally, through image analysis, the area fraction of microvoids in minerals was used to quantitatively define the volume of microscopic fractures and micropores in the mineral. Samples with high areal microvoid fractions and large alteration markers also have significant macroscopic fracture frequencies. Macroscopic fractures are caused by microvoids, which form at temperatures between 350 and 780°C. Alteration markers and other intrinsic characteristics can be used to assess microvoids. Later faulting and unloading (extrinsic processes) transformed microscopic fractures into macroscopic ones. The characterization of the existing and future distributions of macroscopic fracture frequencies depends on intrinsic parameters, which are utilised to determine the origin of macroscopic fractures