Hydrochemical analysis of surface water flow from an abandoned iron ore mine

Abstract Purpose. The purpose of this research is to investigate the potential formation of contaminants in abandoned mining areas due to the interaction between rocks, water, and air, as well as their impact on surface water quality around the mine area. Methods. Mineralogical analysis using an optical microscope and X-ray diffraction (XRD) on iron ore samples obtained from the stockpiles and chemical analysis of water obtained from the mining site and downstream river. Findings. Iron ore at the study site is dominated by iron oxide minerals such as magnetite, hematite, and goethite. Additionally, quartz, birnessite, pyrite, and chalcopyrite minerals were also found. The mineral content indicates the presence of two sulfide minerals that have the potential to form acid mine drainage, namely; pyrite (FeS2) and chalcopyrite (CuFeS2). The pH measurement results of the water flowing from the iron ore stockpile have a pH of 2.9, while the void and surrounding river vary from 6.4 to 8.2. Originality. Identifying iron ore minerals by combining polarized light microscopy and XRD can enhance the reliability of the observation results. Both methods showed the same results in identifying sulfide minerals, with chalcopyrite in the excavated iron ore stockpile and pyrite in the crushed iron ore stockpile. The formation of acid mine drainage at abandoned mine sites is only a local phenomenon, and after being diluted by other water flows, the water's pH returns to neutral. Practical implications. This research activity was conducted during the rainy season when overflow occurred, with water spilling from the mine pit lake to the surrounding areas. The results show that the formation of acid mine drainage and the high concentration of total Fe that occurred in one of the stockpiles did not affect the change in water quality around the mine, and there is potential for water in the mine void to be used as a water source for the surrounding community. Keywords: abandoned mine, iron ore, XRD, acid mine drainage, pit lake