Abstract: Fault identification is crucial to the safe construction of tunnels and the prevention and control of geological disasters.Themineral anomaly characteristics of rocks were used as identification signs of faults.In this study,we proposed a fault identification method based on the characterization analysisis of mineralogical anomalies of rocks,taking a water diversion tunnel in Xinjiang as an example.A portable X-ray diffractometer measured the mineral composition and content of the rocks with a mileage of 49+485-50+050 along the tunnel.The calc-alkaline,alkaline,and relatively Mg-rich Variscan granites were subjected to chloritization and vermiculitization by fault stress and Fe and Mg-rich hydrothermal fluids.Mg-rich clay minerals such as smectite+talc+serpentine+sepiolite assemblage indicated that the mineral transformation pattern was Mg-flux transformation in the F₁₇ fault zone.We identified the internal structure of the F₁₇ reverse fault based on the quantitative differences in the anomalous enrichment of vermiculite and chlorite and the anomalous decrease of plagioclase and biotite at different mileages along the tunnel.Mileage 49+650-49+760 is located in the damage zone of the footwall,mileage 49+760-49+850 is located in the fault core,and mileage 49+850-50+000 is located in the damage zone of the hanging wall.The fault identification method and case study analysis developed in this study can provide references and lessons for the identification of reverse faults when TBM excavates in granite.