The mine is located in western Mali. Exploitation of gold-bearing oxide and sulfide ores commenced in 1997, meaning acid mine drainage (AMD) is of potential concern.
The current life of mine (LOM) projection is for cessation of active operations in 2020, after which the mine will transition to "care and maintenance" status. For this project, a series of milestones were identified to reach the final objective of sustainable closure of the existing tailings storage facility (TSF) and return water dam (RWD). Project milestones include: (1) risk-based selection of the preferred closure strategy, (2) design and implementation of a final deposition plan for the remaining LOM, (3) monitoring during final deposition to maintain conformance with closure design objectives; and (4) development of a final closure design that is achievable, practical, emphasizes use of on-site and locally available materials and labor skills, and requires minimal post-closure care and monitoring.
Geosyntec's Scope of Services
Working with the client, Geosyntec identified the preferred closure strategy for the TSF and RWD using a risk-based procedure that included four main steps: (1) identify closure and post-closure risks as drivers for closure and post-closure technical requirements to mitigate such risks, (2) technical description of acceptable closure options, (3) ranking closure options using an Analytical Hierarchy Process (AHP) with criteria based on constructability, sustainability, performance risks, costs, and other factors, and (4) defined post-closure care obligations and compatible post-closure land uses. Thereafter, Geosyntec developed a LOM deposition plan to achieve the final landform specified for the preferred closure strategy. Part of this plan included monitoring procedures for SEMOS's field staff to maintain the required underflow/overflow tailings splits during cycloning. Geosyntec developed the final closure design while final deposition and monitoring was completed. The design assumes the RWD will be removed as a risk source. The closure design for the TSF utilizes an evapotranspirative (ET) cover constructed using a layer of oxides tailings vegetated with vetiver and native grass and shrub species as the most technically appropriate and cost-effective solution. To increase the reliability of the ET cover design and obtain a more-accurate understanding of its long-term performance for seepage control and minimization of AMD, Geosyntec arranged for detailed hydro-mechanical characterization of the tailings at specialized geotechnical laboratories in the U.S.
An optimal set of options was generated using AHP to rank design elements according to risk mitigation, facilitating selection of the preferred closure strategy by combining highly-ranked options into an integrated package of closure construction activities and post-closure landforms. The preferred closure strategy focused on minimizing residual risks, maintenance and monitoring obligations, and restrictions on post-closure land uses. Geosyntec's final closure design helps AGA meet its goals for sustainable closure and reclamation of the Sadiola Mine in compliance with international regulations and guidance.
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- Location: Republic of Mali
- Client: AngloGold Ashanti
- Project Practice Areas: Environmental Management, Geotechnical
- Type of Facility: Gold mine
- Services Provided: Risk-based assessment of closure options to meet sustainable closure objectives, Technical/financial feasibility analysis to identify preferred closure strategy and compatible post-closure land uses, Final deposition and monitoring program, Final closure design, Post-closure monitoring protocols and completion criteria
- Type of Work: Closure strategy and design
- Governing Regulation: International regulations