Understanding groundwater chemistry and quality in karst aquifers is essential for sustainable water-resource management because of geological and hydrogeochemical heterogeneity. This study aimed to investigate the hydrogeochemistry of karst aquifers in Lorestan Province and identify the processes controlling groundwater chemistry. For this purpose, water samples were collected from ten springs and three wells during three sampling periods from 2021 to 2023 and analyzed for physicochemical parameters, major ions, trace elements, and metals. The data were interpreted using hydrochemical diagrams, ionic ratios, saturation indices, and multivariate statistical analyses, including hierarchical cluster analysis, fuzzy clustering, principal component analysis, and principal component analysis based on centered log-ratio transformation. The results showed that groundwater samples can be divided into four hydrochemical groups, A, B, C, and D. Groups B and C showed a calcium–magnesium pattern with bicarbonate dominance, indicating carbonate control and water–rock interaction. Group A had a more mixed composition with relative enrichment in sulfate and chloride and was influenced by mineral dissolution, limited mixing, and local geochemical conditions. In contrast, Group D was distinguished from the other groups by Na–Cl facies, high EC, different ionic composition, and low Br/Cl, Li/Cl, Sr/Cl, and Ba/Cl ratios, indicating the influence of evaporitic units, particularly the Gachsaran Formation. Samples S2 and S3, with increased SO₄, Cl, and Na, highlighted the role of gypsum, halite, and evaporitic components, whereas S1, S6, S7, and P3 showed intermediate or mixed behavior. The statistical analyses showed that hydrochemical boundaries between some groups are gradual and that not all samples are completely separated. Trace-element ratios were also useful for interpreting local geochemical differences and identifying distinct samples. Overall, the integration of major ions, trace-element ratios, saturation indices, and statistical analyses provided a process-based framework for differentiating hydrochemical patterns and interpreting groundwater chemistry variations in the karst–structural aquifer of Lorestan Province.