Predictions of mine waste geochemistry in arctic conditions

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SRK News | Issue 55: Mine Water Management

Jessica Charles, Consultant (Geochemistry)
 

The management and use of water is a critical concern for mine project viability and profitability. This is especially true of mining in arctic environments where water issues are compounded by too little water (lack of seasonal water availability) and periods of too much water (snow melt). These extreme issues have implications for water management, treatment and discharge to pristine environments.

Acid rock drainage and metal leaching can be a major environmental liability that greatly complicates and adds to the expense of site water management. Predicting source term water quality from mine waste facilities is becoming a pre-requisite for the ESIA and permitting process. It facilitates the implementation of efficient waste rock management plans, and can help determine if mitigation measures are required during life of mine (LOM) and post-closure, to prevent environmental impacts. Winter conditions in the Fennoscandian region 11 Predictions of mine waste geochemistry in arctic conditions.

To make meaningful predictions of long-term leachate quality, a detailed knowledge of site-specific hydrologic, climatic and geological conditions is required. Quantitative parameters are needed from systematic laboratory studies on waste materials and representative field measurements. SRK typically modifies testwork and predictive methods to account for lower temperatures, spring snow melt and slower weathering kinetics in Arctic conditions, in addition to other input parameters including, oxygen supply and grain size.

SRK completed predictive numerical calculations to assess long-term leachate chemistry from a proposed waste rock dump (WRD) at an iron ore deposit in Northern Sweden. Annual temperatures at the site range from -30°C in winter months to 25°C during summer, with a period of spring snowmelt (April-June). The calculations were undertaken to support the environmental permitting process.

SRK worked with the client to develop an effective waste management strategy to minimise potential environmental impacts.

Source terms for LOM and post-closure were developed from static and kinetic testwork carried out on lithologically representative drillcore samples. The WRD material consists of:

(i) Potentially acid forming skarn (sulfur content >1%), ~30% waste; and

(ii) Non-acid forming material types (sulfur content <1%), ~70% waste.

Modelling results demonstrated that predicted metal loading from the WRD is greatest during spring snowmelt for LOM, when seepage through the WRD is greatest and the material is uncovered. Segregating high sulfur waste material and applying a qualified cover proved to be the most effective strategy for minimising water quality impacts on the adjacent water course post-closure.

As global resource demand increases and mining techniques advance, mining in arctic regions becomes ever more feasible. Robust mine water management plans from site-specific seepage quality predictions are vital for permitting such projects in these pristine environments. By incorporating arctic environmental conditions (low temperatures and spring snow melt) in modelling, SRK can outline potential environmental impacts and define mitigation measures in the early phases of project development.

SRK United Kingdom