Mineralogical and Geochemical Study of Acid Mine Drainage from 100 Years of Coal Mining in Svalbard (78° N)

Abstract: Waste rock piles from coal mining of tertiary bituminous coal in Longyearbyen, Svalbard, show sulfide oxidation and subsequent acid mine drainage (AMD) production. The aim was to establish deeper understanding of AMD prediction based on Mineralogy and Geochemistry of coal and AMD samples. Mineralogical investigation of both coal and rock samples was performed with Automated SEM (ZEISS-Sigma VP300-Mineralogic System) as well as RAMAN. ICP-MS analysis was performed on solid and water samples. The pH from in situ measurements of AMD between 2,5-7,0. Eh varied from 222-569 mV (corresponding pe value of 3,7-9,6). This study showed that time of AMD in an oxidative environment was a key factor in iron concentration and iron speciation the AMD. This could not however be concluded in terms of age of mine site but rather the site-specific setting. The main minerals found in coal samples were pyrite (FeS2), siderite (FeCO3), calcite (CaCO3) and apatite (Ca5(PO4)3). Pyrites were identified with framboidal and euhedral textures and were found inside the maceral matter and in over- and underlying rocks respectively. SEM analysis of coal samples indicated that the modes of mineral formation was changing over the course of the Longyear seam. This study found that framboidal or euhedral textures of pyrite had different impacts in the AMD production. Framboidal pyrite was found to generate a greater amount of acidity than euhedral pyrites due to larger specific surface area and could therefore pose larger problems in AMD management.