Soil Contamination Around an Iron Ore Mining and Beneficiation Complex in the Semiarid Zone of Northern Kazakhstan

Soil contamination around iron ore complexes in semiarid zones is usually described by total metal concentrations, which underestimate the labile mobile pool. At the Sokolovka-Sarbai mining and beneficiation complex (SSGPO, Northern Kazakhstan), total (EPA 3051A) and mobile (neutral NH4OAc, pH 7) forms of ten heavy metals were analyzed in 87 site-horizon composites (29 sites × 3 pits × 3 horizons; 261 field samples). Descriptive indices flag Co as the only moderately contaminated element (I_geo 1.16) and Mn as the only one in persistent deficit (Kc_total 0.62); Co and Mn show the largest mobility-factor increments above background (Δ_MF +17.8 and +22.3 p.p.). The priority toxic elements As, Cd and Pb remain at or near depth-matched background in the total fraction (median Kc_total 0.98–1.09; I_geo < 0 for all three), although Pb shows a moderate mobile-fraction enrichment (median Kc_mobile 2.6); mercury was not among the ten metals analyzed. Factor analysis of mobile forms resolves two independent sources (F1-siderophile Cr-Ni-Fe-Mn-Co; F2-Zn-dominant, non-sphalerite) and a humus-driven sorption pool (F3), coherently localized in the dump2A-pit2 sector; mobile-fraction attribution greatly outperforms the total fraction (21 vs. 0 FDR-significant trends). The raw Mn-deficit-Co-mobility correlation (ρ = −0.54) is fully mediated by humus (partial ρ = +0.05). Total Mn deficit and enhanced Co lability are therefore interpreted as coupled consequences of a single humus-Ca-pH Kastanozem geochemistry rather than a causal “Mn-buffer depletion → Co mobilization” chain. Because the dataset is cross-sectional, this distinction remains correlational; sequential fractionation and mineralogical verification are priorities for future work.