<p>The hydraulic connections between aquifers can be identified by examining relationships in groundwater hydrochemical characteristics. Traditional hydrochemical analysis often relies on a limited set of major ions, which may not always be available in areas with small datasets. A broader consideration of ions, including trace ions, can provide richer hydrochemical information, which is conducive to the accurate identification of hydraulic connections between aquifers. In this study, groundwater chemistry for the two major aquifers in the Niaoshan Mine, China, hosted within the Shitoumiaozi and Shitouhezi Formations, was analyzed. The results indicate that the groundwater chemistry types are Na–HCO₃, Na·Ca–HCO₃, and Ca·Mg·Na–HCO₃. The combination of water-isotope and hydrochemical analysis of water–rock interactions allowed the main ions to be selected using the importance-through-intercriteria-correlation (CRITIC) weighting method, which accounted for the variability and conflicts among ions and redistributed the indicator weights. These optimized weights were then integrated into a grey situation decision-making model to identify hydraulic connections between aquifers within the Shitoumiaozi and Shitouhezi Formations, indicating a high degree of hydraulic connectivity facilitated by fault distribution.</p>