SRK was commissioned by Agnico Eagle in 2019 to undertake hydrogeological and geochemical modelling of the Kittilä gold mine in Finnish Lapland. The purpose of the study was to predict future inflows to the underground mine as well as the quality and chemical loading of discharges produced by the operation to assess whether there is adequate treatment capacity to ensure environmental permit compliance.
The study consisted of an initial appraisal of existing data, both to learn about the Kittilä operation in its physical and geochemical setting and to establish information gaps. This was followed by the development of geological and structural models for the deposit through the very successful collaboration of Agnico Eagles's site geology team and the SRK structural geologists. The resulting Leapfrog model coupled with the latest mine design and development schedule formed the basis for the numerical groundwater model, the main purpose of which was to generate a schedule of mine inflows for use in the subsequent geochemical model. The latter model also drew on the geochemical characteristics of the ore and groundwaters in the surrounding rock mass to predict concentrations and loadings of specific chemicals that were listed in the Environmental Permit for the mine. The primary object of the modelling was to establish whether, by how much and when chemicals listed in the permit might exceed the stated discharge limit.
Over the years, the Client has acquired a significant body of information covering local lithologies, geological structures, hydrogeology and rock mass chemistry and this enabled SRK to develop a detailed conceptual understanding of the local surface and groundwater regime. The resulting transient, groundwater model, which was built using Modflow USG predicted that inflow to the underground mine would peak around 11 years after the onset of mining and thereafter it would undergo a steady decline for the remaining period of operation. The pattern of behaviour produced by the model was benchmarked against other operations globally and, consequently SRK was able to show that the model outcome was reasonable. This was because future development will be concentrated at greater depth under existing workings, where the store of groundwater will already be depleted, rather than developing ore reserves at shallow depths along strike, in new areas that are untapped for groundwater.
The predictive geochemical modelling was undertaken by SRK using a combination of mass balance techniques in Microsoft Excel and thermodynamic calculations using the United States Geological Survey (USGS) thermodynamic code PHREEQC. It was developed using the flow rate schedule generated by the groundwater model coupled with background groundwater chemistry and elemental release rates from the progressive development and exposure of underground wall rock and rock fill to mine water.
SRK’s combined hydrogeological and geochemical approach was successful in predicting the temporal and spatial distribution of major ion and metal concentrations and their loadings, as listed in the Environmental Permit, and to also highlight areas of remaining uncertainty. The latter have been important in steering subsequent field- and laboratory-based activities intended to further improve confidence in discharge predictions for the Kittilä mine.
