Magino Gold Project

Argonaut Gold Inc. (Argonaut) proposes to develop the Magino Gold Project located at the former Magino underground mine site in Northern-Central Ontario, Canada, 10 km southeast from the town of Dubreuilville. The historic underground mine located at the Project site operated from 1988 to 1992, producing 105,543 troy ounces of gold. A tailings impoundment and waste rock piles remain on site from historic mining operations along with a polishing pond and some infrastructure. The new project would use open pit mining methods within the footprint of the old underground workings, in proximity of Goudreau Lake. The mine waste from open pit mining would be stored in a nearby Tailings Management Facility (TMF) and Mine Rock Management Facility (MRMF).

In 2013, Argonaut retained RGC to assist with the completion of a pre-feasibility (PFS) groundwater study in support of an EIS for the Magino Gold Project.  The hydrogeological site characterization completed by RGC for this study included:

• Design, supervision & interpretation of packer testing in fractured bedrock.
• Design & interpretation of a full-scale bedrock aquifer test by pumping from the historic underground workings.

The groundwater modelling completed by RGC for project design (PFS) and project permitting (EIS) included:

• Two-dimensional seepage modelling to design a cutoff wall between Goudreau Lake and the proposed open pit.
• Development and calibration of a 3D site-wide groundwater flow model for the Magino site for current conditions using steady-state baseline data and results of the underground mine dewatering test.
• Prediction of the effects of project development (open pit excavation and operation of a Tailings Management Facility (TMF) and Mine Rock Management Facility (MRMF)) on local groundwater and surface water.

Transient pit dewatering was simulated using three consecutive fully transient groundwater flow models for a period of thirteen years, with transient boundary conditions reflecting the progressive excavation of the open pit and gradual expansion of the TMF. The transient pit dewatering model predicts a gradual increase in groundwater inflow to the pit. The pit inflow approaches a steady state from Year 5 onwards.  The 3D flow models were also used to predict the transient drawdown in the surrounding bedrock aquifer during pit development. The transient mine development model predicts that the seepage rate from the TMF and its seepage collection system will gradually increase due to the increase in the height of the tailings deposit, and hence hydraulic head allowing seepage into the underlying foundation soils and shallow bedrock. About 60% of this seepage is predicted to migrate towards and into the open pit. The results of the groundwater modelling informed an environmental assessment of the Magino Gold Project (completed by others). The EIS for the Magino Gold project was submitted in 2017 and project approval was obtained in early 2019.

• Hydrogeological site characterization including design, supervision and interpretation of hydraulic testing
• Numerical modelling of groundwater flow for the design of a cutoff wall, and characterization under current conditions and with project development

Argonaut Gold Inc.

Contaminant Control

Groundwater Impact Assessment