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.

Despite the increasing interest in geologic co-sequestration of CO2 and H2S, the long-term consequences of the chemical interactions involved in this process remain largely unknown on a reservoir scale. A Mississippian aged CO2-H2S reservoir in LaBarge Field, Wyoming, USA is an ideal study site to investigate mineral and fluid reactions related to gaseous H2S and CO2. We conducted two reaction path models based on mineralogical, fluid, gas, and stable isotope compositional data to discern the role of CO2 influx upon the generation of H2S through thermochemical sulphate reduction (TSR). We discriminate between two models-one in which TSR is triggered by temperature at a given burial depth and one where TSR is triggered by ingress of CO2. The reaction path model based upon burial-controlled TSR and later CO2 influx is consistent with mineralogical observations and stable isotope measurements from drill cores. The models show that CO2 influx leads to calcite precipitation which is only limited by the calcium concentration in the fluid. This modelling approach is useful in constraining the timing of fluid flux in the reservoir and gives further insight into the mineralogical consequences of the gas, water, and rock interactions occurring in the reservoir. In terms of geologic co-sequestration this implies that the addition of CO2 into a reducing carbonate system can result in calcite precipitation, instead of anhydrite as previously thought. Furthermore, it is only limited by the availability of Ca2+ and will therefore not diminish the amount of H2S in the system.