The spatial assessment of acid mine drainage potential within a low-grade ore dump: the role of preferential flow paths

The potential release of pollutants from a low-grade ore dump in the Miduk mine was evaluated based on geochemical and mineralogical characteristics. The main environmental risks associated with the dump were the potential for acid mine drainage (AMD) generation and the transport of acidic leachate with high contents of toxic elements (As, Pb, Cu and Zn) into the depths of Earth. Geochemical characteristics of rocks such as the content of sulphur species (Stotal, Spyrite and Ssulphate) were assessed. In addition, the elemental composition of the rock and leaching solution samples were determined. Based on both static and NAG tests, materials with a paste pH < 4 had the high potential of AMD generation. Principal component analysis (PCA) was employed to integrate the results of AMD prediction tests with mineralogical and geochemical compositions of the rocks. Based on PCA, eight principal components (PC1–PC8) were accounted for 93% of the total variance of data. Two components of PC2 and PC3 were determined as primary factors of AMD generation. The extracted principal components were interpolated within the dump by ordinary kriging method. Based on the environmental risk map of the PC3, the main source of AMD generation is the north-eastern part of the dump, which spatially varied from the dump surface up to a depth of 3 m. Heterogeneous distribution of preferential paths by providing different oxygen and moisture contents is responsible for non-uniform pyrite oxidation at different parts of the dump. The results of the present study will provide useful information for further rock dump management approaches.