Authors: Antonio Sotil, Victor Soto, Ken Brouwer
Conference: Tailings and Mine Waste 2020
Date: November 15-18, 2020

ABSTRACT
The Candelaria Mine is an active open pit copper mine operated by Compañía Contractual Minera Candelaria located in the Atacama region of Chile, 20 km south of Copiapó. The Candelaria Tailings Storage Facility (TSF) was deactivated in 2018 and a surface cap is planned for closure of the impoundment. Mining activities will generate approximately 800 Mt of waste rock during ongoing open pit mining operations, and the decommissioned TSF provides an opportunity for TSF closure capping activities to be integrated with long term waste rock disposal.

Capping the Candelaria TSF will provide significant storage capacity for waste rock within a reasonable hauling distance from the open pit, reduce additional site disturbance during ongoing mine operations, and minimize post-closure water management by providing a naturally appearing convex, free-draining, stable post-closure landform. As an added benefit, the waste rock load will 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.

The closure cap will be developed on the Candelaria TSF by progressive placement of a thick (20 m to 60 m) waste rock cap with flat 20H:1V overall slopes. Engineering work to support permitting applications includes detailed field studies to characterize the current and future tailings behaviour, and design studies to optimize the final geometry, supported by geotechnical analyses. The field component incorporates two site investigation programs to evaluate tailings properties before and after construction of two 30 m high surcharge loads simulating the future loading during the staged development of the closure cap. The closure cap will provide economic benefits for secure waste rock storage, while enhancing impoundment stability as the tailings mass is stabilized through stress densification. These improvements will lead to a reduction in the risks associated with the project, both during ongoing mine operations and after closure of the facilities.

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