## 2 Methods and Materials  
In this study, 29 representative samples of typical altered rocks within the study area were taken from the surface, borehole cores, exploration caves, and the interior of the water tunnels, some of which are shown in Figure 2. The samples were subjected to geophysical and chemical tests, such as thin section identification, X-ray diffraction, whole-rock major element tests, and electron probe micro-analyzer (EPMA (Houston, TX, USA)) and oxygen isotope testing. In Rock and Mineral Testing Center, Zhengzhou, China, an A1 polarized light microscope and a D/max-2500 PC Japanese Rigaku X-ray diffractometer were used for thin section identification and X-ray diffraction, respectively, to observe and analyze the internal structure of the altered rocks, and to investigate the composition and content changes of the major minerals. The quantitative analysis of in-situ major elements of minerals was performed by using an electron probe microanalyzer in Wuhan SampleSolution Analytical Technology Co., Ltd., Wuhan, China. The analysis was completed using JXA-8230 of JEOL; the voltage and current analyzed are 15 KV and 20 nA, the peak analysis time of the Ca, Ti, Al, Si, Mn, Fe, Na, Mg, K, P, etc., element is 10 s, and the background analysis time is 5 s. The calibration standard samples for the content of major elements use 53 kinds of mineral standard samples, 44 kinds of elemental standard samples, and 15 kinds of rare earth element standard samples provided by SPI company (Chicago, IL, USA). The data correction method adopts the ZAF correction method of JEOL. Figure 1: Simplified lithology of the study area (modified from [36]). The Zsx Primus II wavelength dispersive X-ray fluorescence spectrometer (XRF) produced by RIGAKU (Wilmington, MA, USA), Japan was used for the analysis of major elements in the whole rock. The X-ray tube is a 4.0 Kw end window Rh target, and the test conditions are voltage: 50 kV; current: 60 mA. All major element analysis lines are k\(\alpha\), the standard curve uses the national standard material, and the rock standard sample is reference materials [37]. The data were corrected by a theoretical \(\alpha\) coefficient method, and the relative standard deviation (RSD) is less than 2%. The sample pretreatment of the whole rock major element analysis was performed by the melting method. The flux is a mixture of lithium tetraborate, lithium tetraborate, and lithium fluoride (45:10:5). Ammonium nitrate and lithium bromide were used as oxidant and release agent, respectively. The melting temperature was 1050 \({}^{\circ}\)C and the melting time was 15 min. Loss on Ignition (LOI) was determined by the weight loss method LOI = 100 \(\times\) (m\({}_{0}\) + m\({}_{1}\) \(-\) m\({}_{2}\))/m\({}_{1}\). (m\({}_{0}\): crucible mass; m\({}_{1}\): sample mass; m\({}_{2}\): sample residue after 1000 \({}^{\circ}\)C loss on ignition + empty crucible mass). Oxygen isotope testing was conducted at the Beijing Institute of Geology of the Nuclear Industry, using a Delta V Advantage gas isotope mass spectrometer, adopting the \"Determination of Oxygen Isotope Composition of Silicate and Oxide Minerals by the Bromine Pentafluoride Method\" [38]. The altered granite samples were ground to 200 mesh (0.075 mm) with an agate mortar and pestle, and the specimens containing about 5 mg of oxygen were weighed and placed in a vacuum drying oven, and then baked and degassed at 105 \({}^{\circ}\)C for 2 h before being transferred to a desiccator. The nickel reactor was filled with 0.4 MPa argon, and the specimens in the desiccator were loaded into the reactor for vacuum treatment, while the specimens and reactor were heated and degassed externally at 200 \({}^{\circ}\)C for 30 min after transferring to a high vacuum, followed by evacuation, freezing, evacuation and thawing again.