Predicting Inflow Rates for Open Pit & Underground Mining at Aurora Mine

Project Background

The Aurora Mine project required evaluation of groundwater conditions associated with proposed open pit and underground mining operations. The study focused on predicting potential inflow rates to multiple open pits and underground workings, as well as generating pore pressure distributions for use in geomechanical modeling. Available datasets from site investigations were reviewed to develop the hydrogeologic framework required to define potential dewatering requirements and inform geotechnical design of the mine.

Objectives

• Simulate groundwater conditions at the proposed mine site and perform steady-state and transient model calibrations.
• Simulate progressive excavation of the open pit and several underground designs, including sub-level retreat (SLR) and sub-level caving (SLC).
• Predict inflow rates during pit excavation, ramp development, and underground mining operations.
• Predict pore pressure distributions to be used in geomechanical analysis of country rock behavior.
• Predict reduction of baseflow in the Cuyini River over the Life of Mine (LOM) as well as potential drawdown of the groundwater table by the end of mining.

ITASCA’s Role

ITASCA conducted a comprehensive hydrogeologic assessment beginning with a review of available data and gap analysis. First, a conceptual hydrogeologic model of the site was developed, and then a three-dimensional, finite-element groundwater flow model was constructed in MINEDW incorporating five open pits and one underground mine. The model included six shear zones expected to intersect either the open pits or the underground mine. The zone of relaxation (ZOR) related to the mining, provided from the geomechanical model, was also simulated in the groundwater model with approximately one order of magnitude higher hydraulic conductivity than the in‐situ bedrock.

The MINEDW model was calibrated to the available hydrogeologic data under both steady-state and transient conditions, and the calibrated model was used to assess future dewatering and post-mining groundwater conditions. The model was created using the internal mesh-generation software and other core features of MINEDW, including boundary conditions, implementation of open pit and pit lakes, as well as gridding features such as pinchouts.

Featured ITASCA Software

Results & Impact

The modeling results provided quantitative predictions of groundwater inflow rates to open pits, ramps, and underground workings for several mine design plans. These predictions supported evaluation of dewatering requirements and operational planning.

Simulated pore pressure distributions were exported for direct use in geomechanical analyses, enabling an integrated assessment of open pit wall stability and surface subsidence.

The model outputs were accepted by both the mining operator and funding agencies as part of pre-feasibility and feasibility evaluations, supporting advancement of the project. The study contributed to defining groundwater management strategies and informed geotechnical design considerations critical to mine development.

Key Outcomes

• Informed Decision-Making: Groundwater inflow predictions supported mine planning and feasibility assessments.
• Design Support: Results informed dewatering strategies and geotechnical design considerations.
• Project Advancement: Model acceptance by stakeholders supported continued development of Aurora Mine.

References

• Liu, H. (2013). Hydrogeology Groundwater Flow Model. Aurora Gold Project Key Findings Technical Presentation.
• Severin, J., Telford, M., Liu, H., Noone, D., & Robinson, C. (2013). Hydro‐mechanical analysis of a foliated rockmass for a proposed sublevel retreat mine. Continuum and Distinct Element Numerical Modeling in Geomechanics (Proceedings, 3rd International FLAC/DEM Symposium, Hangzhou, China, October 2013).