Author: Antonio Sotil, Amy Adams, Craig Hall
Conference: 2nd International Congress on Planning for Closure of Mining Operations
Date: November 7-9, 2018

ABSTRACT
Many tailings impoundments provide long-term storage for saturated, semi-fluid fine grained materials. Closure of these tailings impoundments represents an ongoing priority and a potential challenge for owners and professionals due to the potentially fluid nature of the impounded tailings in the event of a hypothetical dam breach.

One solution is to cap and shape the impoundment surface using waste rock or other materials to promote surface runoff, minimize dusting, and densify the underlying tailings through consolidation. Poor surface trafficability can hinder capping operations, and the cap itself may not fully mitigate the potential for deeper saturated tailings to fluidize and flow in the event of a dam breach.

This paper provides an overview of a case study for the decommissioning of the Nye Tailings Impoundment at the Stillwater Mine. Additional details on the site investigations and tailings characterization work that has been completed to support decommission of the impoundment are included in Adams et al (2018) that was presented at the 2018 Canadian Dam Association (CDA) conference. The closure plan includes capping the loose saturated tailings with waste rock along with a cover of surface soils to reclaim the impoundment and create a stable landform. Initial staged construction of the closure cap will be accomplished using a geotextile to improve trafficability during placement of the initial rockfill capping layer.

A potential opportunity to enhance the closure of the impoundment can be achieved through the progressive development of a large waste rock storage area over the capped tailings surface. This closure enhancement would provide significant storage capacity for waste rock and reduce additional site disturbance during ongoing mine operations. As an added benefit, the waste rock load would promote consolidation, densification, and dewatering of the underlying tailings, further reducing the potential for the impounded tailings to fluidize and flow in the event of a hypothetical dam breach. This integrated waste management strategy for the Stillwater Mine will provide operational benefits for ongoing waste rock management while concurrently developing a stable reclaimed post closure landform to enhance the reclamation objectives for the mine site.

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