Characteristics of soil contamination by potentially toxic elements in mine areas of Mongolia

Soil contamination by potentially toxic elements (PTEs), such as metal(loid)s, in mining areas was characterized on a nationwide scale in Mongolia to understand the contamination status throughout the country, according to mine types. Positive matrix factorization (PMF) analysis exhibited better classification and explanation of soil contamination according to ore types compared to conventional statistical analysis methods such as principal component analysis (PCA) and hierarchical cluster analysis (HCA). The results of PMF analysis for metal(loid) contents in 1425 topsoil samples collected from 272 mines illuminated four Factors, which primarily contributed to As (Factor 1), Pb, Zn, and Cd (Factor 2), Ni (Factor 3), and Cu and Cd (Factor 4) contaminations, respectively. In hard-rock gold mines, As was enriched and the contribution of Factor 1 was high (31.2%) due to the affinity between As and Au. In placer gold mines, the contribution of Factor 3 (41.8%) was high due to the affinity between Ni and weathering-resistant heavy minerals. For base metal, fluorite, and coal mines, contributions of Factors 2 (32.1-50.9%) and 4 (17.7-33.6%) were high owing to sulfides containing Pb-Zn-d and Cu. These impacts of mine types were altered by local geology (e.g., skarn). Meanwhile, Hg amalgamation contributed to Hg contamination in a few hard-rock gold mines. These results suggest that soil contaminants in mining areas are mainly affected by the type of deposits with geochemical affinities, region-specific ore characteristics, and artificial processing. Understanding these effects will help establish national strategies for countermeasures, such as soil rehabilitation in mining areas.