## 3 Technical Principles, Methodology, Sampling, and Analysis
### Sample Collection and Analytical Testing  
In accordance with the \"from known to unknown\" principle, a feasibility test of the method was conducted on a known section of Line L00, which is located approximately 3 km north of the Guangzhou deposit. This section--where the ore body is exposed through drilling engineering and geological conditions that are similar to those of the study area--features 53 measurement points established at 25 m intervals. In the unknown area, covering approximately 2.75 square kilometers outside the Guangzhou deposit (Figure 3), a total of 21 survey lines and 462 measurement points were systematically arranged based on a mineral exploration grid of 100 m \(\times\) 25 m for predictive research. Figure 3: Geological map (**a**) and tectonic location map (**b**) of the study area. Revised based on a specific work report from the Nuclear Geological Brigade of Guangxi Zhuang Autonomous Region, 310. 1—Quaternary; 2—Yintang Formation, Lower Carboniferous; 3—Yaoyunling Formation, Lower Carboniferous; 4—Rongxian Formation, Upper Devonian; 5—Dongcun Formation, Upper Devonian (Members 2—3); 6—Dongcun Formation, Upper Devonian (Member 1); 7—Guilin Formation, Upper Devonian (Member 2); 8—Guilin Formation, Upper Devonian (Member 1); 9—Tangjiawan Formation, Middle Devonian; 10—Xindu Formation, Middle Devonian (Member 5); 11—Xindu Formation, Middle Devonian (Member 4); 12—Xindu Formation, Middle Devonian (Member 3); 13—Xindu Formation, Middle Devonian (Member 2); 14—Xindu Formation, Middle Devonian (Member 1); 15—Caledonian granite; 16—stratigraphic unconformity boundary; 17—fault; 18—inferred fault; 19—exploration line number. This electrochemical extraction measurement utilizes an independently powered, low-voltage dipole electric extraction device developed by the Hidden Ore Deposit Prediction Research Institute of the Guilin University of Technology. This device comprises two main components: a power supply system and an ion absorber. The power supply employs low-voltage direct currents, while the ion absorber consists of specially treated adsorption materials with specific specifications, in addition to cylindrical graphite carbon rods wrapped in filter paper. A wire is extended from one end of the carbon rod and connected to the power-supply system, thereby forming the ground electricity-extraction device (Figure 4). The key features of this device include its compact size, low operating voltage, self-contained power supply, and ease of operation [35]. The field sampling work was carried out in strict compliance with the technical specifications for geo-electrochemical extraction and measurement. Two sampling pits, each approximately 30 cm in depth, were established at 1 m intervals perpendicular to the measurement line's direction between sampling points (based on the visible residual layer soil). Initially, the soil samples required for measuring soil ionic conductivity and thermally released mercury were collected. Subsequently, ground electro-extraction electrodes, in conjunction with the extraction solution, were parallelly placed within the sampling pits and backfilled sequentially according to the soil-extraction sequence. Following a 48 h electro-extraction period, the ground electro-extraction device was retrieved [36]. Following air-drying at room temperature, the adsorption materials wrapped around the anode and cathode of the ion extraction apparatus were sent to the Testing Center of Guilin Institute of Mineral Geology under the China Nonferrous Metals Industry. The samples were decomposed using nitric-acid-hydrogen peroxide-aqua regia extraction. Subsequently, elements such as U, Th, W, Mo, and As were analyzed and tested via inductively coupled plasma mass spectrometry (ICP-MS). The detection limits of the current determination method are shown in Table 1[20; 37]. The soil samples were dried and sieved through a 100-mesh aperture sieve.