## 3 Technical Principles, Methodology, Sampling, and Analysis  
### Technical Principles  
(1) Geo-electrochemical extraction measurements, also known as the geo-electrochemical extraction method, are carried out under natural conditions. Due to the potential difference between various minerals within deep ore bodies, electrochemical dissolution occurs, generating metal ions, colloids, or complexes. These ions migrate toward the surface through groundwater flow, diffusion, and electrodynamic effects, forming ion halos. Upon the application of an artificial electric field, the pre-existing electrochemical equilibrium is perturbed, initiating the directional migration of cations and anions towards respective electrodes. This process establishes a continuous ionic replenishment chain through successive displacement, facilitating the upward transportation of deep-seated mineralization signals to shallow horizons. A renewed dynamic equilibrium is subsequently achieved following sustained current application. This technique directly detects the surface ion anomalies  
Figure 2: Schematic geological cross-section of the Daxijiang faulted basin, Northern Guangxi [24]. 1—Bianxi Formation: Sandstone interbedded with shale; 2—Baidong Formation: limestone; 3—Huang’ai Formation: sandstone interbedded with shale; 4—Xindu Formation: sandstone with basal conglomerate; 5—Tangiawan Formation: dolomite and biocules limestone; 6—Guilin Formation: limestone and dolomite; 7—Dongcun Formation: argallocous dolomite and sandstone; 8—Yaoyunling Formation: limestone; 9—Tingtang Formation: sandstone and shale interbedded with limestone; 10—Huangjin Formation: limestone; 11—Simen Formation: sandstone and shale with lenticular limestone, coal-bearing; 12—Caledonian granite; 13—Yanshanian granite; 14—mineralized fault zone and numbers; 15—coal sea. corresponding to the composition of deep ore bodies, and the method is characterized by its simplicity and high efficiency. Moreover, practical applications demonstrate that the distribution of these anomalies often aligns with the vertical projection of deep ore bodies, making it especially suitable for the exploration of concealed mineral deposits [11; 25; 26];  
(2) The soil ionic conductivity measurement technique operates on analogous electrochemical dissolution principles driven by oxidation-reduction potential gradients within concealed ore bodies. When ore masses become intersected by fissure water systems or groundwater tables, a natural electrolytic environment is established. Contrasting oxidative conditions between upper and lower ore body sections generate electrochemical potential disparities, thereby inducing electron transfer processes that disrupt electrical neutrality. This disequilibrium triggers the directional migration of cations and anions through electrochemical mobilization, ultimately culminating in the enrichment of ionic species within near-surface soil horizons to form characteristic ionic dispersion halos [25; 27]. Electrical conductivity, though a geophysical parameter, serves as an effective geo-chemical indicator by measuring the total conductive ion concentration in soils to reflect the coincident halos of U\({}^{6+}\), WO\({}_{4}\)\({}^{2-}\), SO\({}_{4}\)\({}^{2-}\), Ca\({}^{2+}\), and Fe\({}^{3+}\) ions. This integrated approach demonstrates superior capability in revealing deep-seated mineralization signals compared to individual element analysis. In particular, in geologically complex terrains where conventional geophysical and geochemical exploration methods fail to achieve breakthroughs, soil ionic conductivity measurements have proven to be an exceptional technique for mineral exploration [28; 29; 30];  
(3) Thermally released soil mercury measurement represents a mineral exploration technique grounded in mercury's distinctive geochemical properties (liquid state at ambient temperatures, high volatility, and strong thiophilicity and migration capacity).