Tailings and Waste Rock
The waste rock (including overburden) and tailings that we produce represent our largest volume of waste. Managing the volume of waste rock and tailings produced in our mining operations presents significant environmental, safety and engineering challenges. In 2015, we produced approximately 349 million and 215 million metric tons of waste rock and tailings, respectively. The primary risks associated with managing waste rock stockpiles and tailings relate to structural stability, geochemistry, water quality and dust generation. Management of this waste is regulated in the jurisdictions where we operate, and our programs are designed to be in compliance with applicable national, state and local laws, permits and approved Environmental Impact Studies.
The tailings storage facility (TSF) failure at the Imperial Metals owned Mount Polley Mine in British Columbia on August 4, 2014, and the Samarco Mineração S.A.-owned TSF failure in Minas Gerais, Brazil, on November 5, 2015, were among the largest unplanned discharges of tailings in history, with significant loss of life, environmental impacts and social license impacts. The failures led to multiple investigation reports, regulatory updates, and professional organizations’ guideline updates. Our internal tailings experts reviewed available documents, confirming that our processes and systems are aligned with relevant publicly available recommendations. The independent investigation report for the Samarco failure, the ICMM Tailings Storage Facility Review report (which considers the ICMM Health and Safety Critical Control Management guide) and other documents are pending.
Freeport-McMoRan’s objective is to have zero structural failures of TSFs. We have an active tailings management program designed to advance continual improvement and assessment, currently operating 19 TSFs and managing 52 TSFs that are inactive or have been fully reclaimed. At our Cerro Verde operation in Peru, we completed construction and commissioning of the Linga TSF starter dam, with a targeted capacity of approximately 2 billion metric tons of tailings material. We also commissioned the Morenci, Arizona starter dam, increasing tailings capacity by approximately 568 million metric tons.
At the operational level, TSF stability is managed by qualified internal engineers, with design, analyses and review by qualified external Engineer(s) of Record (EoRs). We follow established operations, maintenance and communication protocols. We also regularly inspect and monitor phreatic level trends, deposition plans and adherence to good operational construction practices, water management controls, seepage management, decant systems and other stability components. In addition, we periodically review as-built in situ conditions through field and laboratory geotechnical testing programs.
At the corporate level, TSF stability is managed through our Tailings Stewardship Program, which includes a multi-disciplinary group of internal and external experts, and the Tailings Stewardship Team (TST), which evaluates the design, operation and maintenance of TSFs to ensure that we follow good stewardship practices. In 2015, our TST conducted annual field inspections at 16 active and 37 inactive TSFs. We also seek the advice of Technical Review Boards, which are comprised of internationally recognized experts retained by us, regarding our EoRs’ design and analysis, as well as our management of dam stability to ensure alignment with industry good practices. As of December 2015, we have Technical Review Boards established to review TSFs at five operations, with four more planned for 2016 and 2017.
Freeport-McMoRan has a critical controls management system in place. Focus areas progressing in 2016 include:
Operations and surveillance systems
Operational critical control examples
At TSFs located in arid regions, our tailings management program includes measures to reduce fugitive dust emissions from the surface of tailings impoundments, and increase reclaimed water capture to reduce freshwater consumption. Our efforts to limit dust generation include the application of magnesium chloride, polymers, watering and wind fencing.
PTFI’s controlled riverine tailings management system, which has been approved by the Indonesian government, uses the unnavigable river system in the mountainous highlands near our mine to transport tailings to an engineered area in the lowlands where the tailings and other sediments are managed in a deposition area referred to as the ModADA. Levees have been constructed to laterally contain the footprint of the tailings and to limit their area of impact in the lowlands. The ModADA Management Board (MMB) is a multi-disciplinary expert panel that meets on site approximately twice each year to assess performance and risks associated with the ModADA and coastal zone area. The MMB focuses on the structural integrity of the levees and the geochemical stability of the deposition area, as well as associated stakeholder engagement. PTFI also hosts a Tailings Management Communication Forum, comprised of government stakeholders, academia and NGOs, which convenes periodically to discuss various aspects of PTFI’s controlled riverine tailings management system and associated opportunities, including tailings utilization programs.
Waste rock and overburden are managed in stockpiles for possible future mineral recovery, reclamation or other projects. These stockpiles are regularly monitored and evaluated for structural stability in accordance with local seismic design criteria. At PTFI, overburden stockpiles are subject to erosion caused by the large amounts of rainfall in the region (average annual rainfall is 200 inches). The eroded stockpile material is eventually deposited in the tailings management area in the lowlands. This additional material, while predicted in our environmental studies, influences both the amounts and timing of deposition of finer tailings material in the estuary.