Geochemical and mineralogical aspects of acid mine drainage associated with 100 years of coal mining in the arctic, Svalbard (78°N)

Abstract

Acid mine drainage (AMD) is a pressing issue due to increasing mining activities in arctic climate zones. Over 100 years of coal mining in Svalbard presents an ideal study case for the development of AMD in arctic regions.The mined coal (low liptinite type oil prone coal) has less than 1.1 wt% sulphur with micro inclusions of pyrite but the contacting silt and sandstones contain pyrite nodules of centimeter size. These forms of pyrite are left to oxidize on multiple large waste rock piles. Simple accounting of the acid producing and neutralizing potential reveals that all studied lithologies are prone to produce acid waters despite a relatively low pyrite content but with an almost absent neutralization potential.During spring and summer, there are small streams draining the waste rock piles with a pH of 2.5 to 3.7, buffered by an iron hydroxide assemblage. The sulphate concentration of the water samples correlates well with the sum of the cations, indicating that pyrite oxidation is the dominant weathering process. There is no correlation between the age of the waste rock piles and the acidity of the effluents and the system might be controlled by the geometry of the waste rock piles combined with the local hydrology.Mass balance calculations for one of the mine sites estimates that AMD will continue for another 150 years. The sole operating mine site to date is likely to face a similar prospect once lime buffering measures seize.