Hydrogeochemical process, evaluation of pollution source apportionment and baseline characteristics of surface water in the Quadrilátero Ferrífero, Minas Gerais, Brazil

High-resolution hydrogeochemical mapping of the Quadrilátero Ferrífero (QF), which is one of the world's most important metallogenetic provinces, faces challenges related to the quality of its surface waters. The QF is strongly influenced by mining but also impacted by agriculture and the discharge of domestic/industrial effluents. Located in the state of Minas Gerais, southeastern Brazil, this study was performed between 2022 and 2023 and spanned two important river basins, São Francisco and Doce. A total of 880 and 864 surface water samples were collected during the rainy and dry seasons, respectively, and 99 physicochemical, inorganic and organic parameters were analyzed. The freshwaters of the QF were enriched in Fe, Mn and Ni, and their composition was strongly controlled by the weathering of the local lithologies and influenced by anthropogenic activities, such as agriculture, changes in land use practices, mining and metallurgy. Generally, the waters were neutral to slightly alkaline and were predominantly classified as mixed bicarbonate waters. Spearman's correlation indicated the significant influence of the carbonate and silicate rocks (HCO 3 -Ca-Mg-Sr), metamafic and metavolcano-sedimentary sequences (Fe-Ni), weathering of feldspathic rocks (Na-K), and impacts caused by effluents from domestic sewage and/or other anthropogenic activities (Na-Cl-SO 4 ). Baseline geochemical values for the study area were determined using robust statistical methods, showing elevated concentrations of Fe, Mn, Al, and Ni compared to environmental guideline standards. In the rainy season, Fe reached 7.28 mg/L (mMAD) and 13.18 mg/L (TIF), while Mn reached 0.78 mg/L (mMAD) and 1.6 mg/L (TIF). These values reflect enhanced leaching and runoff in a naturally enriched region. These findings enhance the understanding of surface water geochemistry and support the development of quality guidelines for sustainable watershed management in the QF river basins.