Mina Justa is an open pit mine located in San Juan de Marcona, 530 km from Lima, Peru at an elevation of approximately 700 masl. The Mina Justa tailings storage facility (TSF) began operations in March 2021 (Stage 1) and will have a total capacity of more than 100 Mt at the end of its life (Stage 4). The dams containing tailings have been raised following the downstream construction method and they will reach a maximum height of 35 m.
Knight Piésold has contributed to implementing industry best practices and global initiatives based on international guidelines by the International Council on Mining and Metals (ICMM) and the Mining Association of Canada (MAC) to successfully promote a long-term sustainable project from the early stages.
Services provided by Knight Piésold have included geotechnical investigation and characterization, water balance, hydraulic design, detailed dam engineering, dam breach analysis, and consequence analysis. In addition, during construction, Knight Piésold provided technical support and quality assurance. Furthermore, Knight Piésold provided ongoing support at the beginning of the tailings discharge with the intention of being able to convey the operating philosophy.
The Mina Justa TSF is located in a highly seismic area wherein associated MCE acceleration is in the order of 0.89 g; likewise, collapsible soils were found at the foundation of the dam. These details have been key elements to developing geotechnical analyses for the dam. The dam has been built with non-PAG mine waste material, compacted in layers using high-tonnage mining haul trucks (260 t) and has a geosynthetic liner on the upstream slope face of the dam. As part of the design, the thickened tailings disposal strategy was chosen, and tailings were discharged using spigots.
Since 2019, Knight Piésold has supported Marcobre as Engineer of Record (EOR) of the Mina Justa TSF to achieve its performance indicators and policies in each phase of the facility. One of the main challenges of this service has been properly integrating the strategic aspects of tailings management and the operational activities of the mine.
During surveillance of the TSF in the first year of operation, a quantitative risk assessment and an update of the analysis of consequences of the tailings deposit have been carried out, for current failure modes considered credible during operation.