Hydrochemical Characteristics of Groundwater and Formation Mechanism of Sr–Rich Mineral Water in the Northern Carbonate Region, Yiyuan

The Cambrian carbonate rocks exhibit widespread distribution in the Yiyuan area, constituting a prominent strontium–enriched mineral water zone in central Shandong Province (strontium concentrations up to 35.22 mg/L). Through integrated hydrogeological surveys, geochemical analyses, and dynamic monitoring datasets, this study delineates distinct hydrogeological units including Sancha and Tumen formations. The investigation elucidates groundwater chemical characteristics, mineral water enrichment controlling factors, and geochemical formation mechanisms. Results demonstrate that groundwater in the study area is predominantly fresh (mean total dissolved solids (TDS) 531.05 mg/L) with neutral to slightly alkaline pH (mean 7.67 ± 2.45% C.V.). Dominant ionic species include Na⁺ (12.58 mg/L) and HCO₃⁻ (236.50 mg/L), reflecting an HCO₃–SO₄–Ca water type derived from carbonate and sulfate mineral dissolution. Three sequential kinetic processes govern groundwater chemical evolution: (1) Primary phase ion establishment via silicate (feldspar–dominated), carbonate, and evaporite weathering; (2) Secondary phase modifications through calcite/gypsum dissolution, cation exchange (clay–bound Ca²⁺/Mg²⁺ displacement releasing Na⁺), and localized evaporation concentration; (3) Disturbance phase alterations caused by agricultural fertilization/domestic sewage (NO₃⁻ up to 99.70 mg/L) and industrial wastewater (abnormal SO₄²⁻ levels). Strontium concentrations exhibit depth–dependent enrichment (0.41–6.91 mg/L at 20–296 m depth), positively correlating with thermal gradients (17–24°C) and hydrodynamic circulation depth. This investigation provides a robust scientific foundation for sustainable resource management and geochemical heritage conservation.