Closure and Post-Closure Case Study: San Manuel Heap Leach Facility, Arizona, USA
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Authors
Braun, Terry
Ludwick, David
Balasko, Clara
Issue Date
2025-10-20/2025-11-21
Type
Conference Paper
Language
en_US
Keywords
Gold , Copper , Nickel , Uranium and Other Metal Leaching
Alternative Title
Abstract
This paper presents a case study of the active closure and post-closure monitoring period for the San Manuel Heap Leach Facility (HLF) at the BHP San Manuel copper mine in Pinal County, Arizona, USA. Prior to closure, this HLF contained approximately 90 million tons of oxide ore and covered a 237-acre HDPE-lined footprint adjacent to the northeastern extent of the open pit and in-situ recovery wellfield. Operations at the HLF started in 1985 and ended in 2002. With formal suspension of mining operations at the San Manuel Mine Site in June 1999, BHP started the formal process of closure of the mine site and HLF. Site-specific challenges to closure of this copper HLF included short-term management of the acidic solution inventory circulating through the HLF, design of a regrade surface that achieves physical mass and erosional stability, installation of a surface water control system to contain contact water, and long-term management of residual draindown from the HLF. In 2004, the project received owner funding to commence detailed engineering and construction for permanent closure. Final closure of the HLF included expansion of the HDPE-lined footprint to accommodate the proposed regrade design, management of residual solution drain down, incorporation of landform elements and selection of a final cover system. During the active closure period, the original cover system design failed to perform as designed and the project team re-designed the system prior to completion of construction activities in 2008. BHP completed construction activities in 2008. Post-closure monitoring and inspection results include cover stability, recording long-term draindown rates, stormwater runoff volumes and maintenance activity. The long-term erosional performance of the final regrade and rock armor cover system informs future engineering trade-off studies for alternative cover systems at other sites.
Description
This paper was presented at the Heap Leach Solutions Conference, October 19-21, 2025, Sparks, Nevada.