The Minto Mine is an open pit and underground copper-gold-silver mine located 240 km northwest of Whitehorse in the Yukon Territory. Ensero has provided a wide range of environmental management, passive water treatment, and assessment/permitting support services to the operation since 2005 for several project development milestones, including:

  • Mine Construction and Commissioning (2005-2007) – conducted collection, management and reporting for all site environmental data and much of the regulatory support for the project, including licence and permit compliance reporting for both federal and territorial authorizations and obligations.
  • Major Water Management Optimizations (2009-2010) – led the development of site-specific water quality objectives and water management plan improvements through the YESAB and YWB Water Use Licence Amendment processes.
  • Numerous Mine Phase Expansions (2010–current) – led the development of YESAB Project Proposals and WUL applications, and the successful procurement of Water Licence and Quartz Mining Licence amendments.
  • Operational Monitoring Support (2005-current) – contributed specialist expertise and program development for key water quality, hydrometeorological, and federal Environmental Effects Monitoring programs.
  • Passive Water Treatment Design and Testing (2013-current) – contributed specialist expertise for the feasibility evaluation, design, and testing of a constructed wetland treatment system for closure (case study below).

These initiatives have required Ensero to coordinate multidisciplinary technical teams with varied supporting scopes towards technically and economically defensible proposals that minimize the potential for significant adverse effects. Ensero has provided strategic impact assessment and regulatory process advice throughout the evaluations of these project developments. Ensero has been the lead technical representative for Minto at Public Hearings for Water Use Licence Amendments in 2010, 2012 and 2014. Ensero has also acted as the Lead Consultant or contributor to numerous Reclamation and Closure Plan updates since 2007, and has provided support to parent companies Sherwood Copper Corp. and Capstone Mining Corp for 3rd party due diligence exercises, including financial and environmental audits, lending institution investigations and economic analyses. Lead or support work on each of these milestone initiatives has involved very close technical liaison with Selkirk First Nation and their advisors. This close working relationship resulted in broad technical consensus with SFN at the 2010 Yukon Water Board Public Hearing on Water Management Amendments.

Constructed Wetland Photo taken by R. Martz, Copyright Ensero Solutions 2021

Passive Treatment Case Study

The Minto Mine is evaluating a constructed wetland treatment system (CWTS) for water treatment at closure as part of the Reclamation and Closure Plan. CWTS are desirable for closure water treatment because once established, they can become self-sustaining ecosystems with the plants providing yearly renewal of carbon to fuel microbial activity. Ensero was engaged to provide specialist expertise for the design, piloting, and implementation of the CWTS at the Minto Mine. The CWTS is currently in the demonstration‐scale and optimization stage preceding full-scale implementation.

CWTS evaluation for the Minto Mine was initiated with a site assessment in 2013. During the assessment, local plants suitable for a CWTS and naturally-occurring biogeochemical treatment processes were identified. The geochemical and microbiology data validated the concept that a CWTS could be designed to function in the long-term closure conditions at the Mine. Following the site assessment, pilot-scale testing was undertaken off-site at Ensero to evaluate several CWTS designs with local plants and substrate types. Synthetic water was designed to mimic predicted worst-case water chemistry during early and long-term closure (high and low nitrogen, respectively). Through pilot-scale testing the recommended CWTS design for long-term passive treatment was identified and used to guide the design and implementation of a demonstration-scale system at the Mine.

The demonstration-scale CWTS was constructed at the Minto Mine in August 2014. The CWTS was commissioned, and subsequently tested through a variety of scenarios that have continued to optimize the full-scale CWTS design. The CWTS has successfully treated constituents of potential concern in the mine site’s sub‐arctic continental climate. Carex aquatilis (aquatic sedge) and aquatic mosses (bryophytes) from natural wetlands onsite were used for planting, with the CWTS designed to target specific environmental conditions that enable denitrifying, selenium-, and sulfate‐reducing bacteria to treat nutrients, metals and metalloids in the water.