Hydrochemical characteristics of groundwater movement and evolution in the Xinli deposit of the Sanshandao gold mine using FCM and PCA methods

The objective of this study is to characterize the physicochemical properties of groundwater in the Sanshandao gold deposit, analyze the laws of motion and evolution of the groundwater system, and provide evidence for the design of undersea mining and safety warnings, using combined fuzzy c-means (FCM) and principal component analysis (PCA) methods. Thirteen physicochemical indicators and two isotopic indicators were surveyed from 100 fissure water samples and 13 typical water samples from Xinli, a deposit of the Sanshandao gold mine in China. First, PCA was used to extract four PCs (with explained variances 48, 25, 10 and 7 %) and the characteristics of the hydrochemistry indicators of each PC were examined. The four PCs are identified as the processes of concentration and dilution, sericite rock orientation and carbonatization, potash feldspathization, and dissolution of carbon dioxide. Next, using the four PCs developed from PCA, 100 fissure water samples were grouped into four spatially continuous clusters using the FCM cluster method. With the aid of graphic technology, the four fuzzy clusters were determined as deep saline water, shallow saline water, bedrock brine and mixed wastewater, following careful analysis of the hydrochemical characteristics of each cluster combined with a related hydrogeological report. Finally, further analysis of the PCA and FCM results determined factors constituting the groundwater system, including sources of water, flow path, mixing zone, local fissure zone, and impact of mining on the groundwater system. This study shows that the combination of PCA and FCM is important for understanding hydrochemical characteristics of a groundwater system.