The San Rafael Mine, which is operated by Minsur S.A. (Minsur), is an underground mine located 120 km from the city of Puno in southeast Peru, in the eastern cordillera of the Andes at 4,500 masl. It is the third largest tin producer in the world.
The B2 tailings storage facility (TSF) was out of operation from 2003 to 2018. Starting in 2018, the process for mining previously stored tailings began due to its high tin content. The B2 TSF has 6.5 Mt of stored tailings, covering an area of approximately 20 ha, and 45 kt of tin extraction is expected. Dike 2.5, which is founded on "jet grouting" columns, is a structure located in the southern part of B2 TSF that separates B2 TSF from the water pond of B3 TSF, which is an operating TSF located directly to the south of B2 TSF.
To safely and effectively carry out mining of stored tailings in B2 TSF, tailings characterization studies were conducted. Geotechnical studies showed that the stored tailings had a "high" liquefaction potential for both static and seismic loading conditions. Deformation analyses were, therefore, required for both loading conditions.
Deformation analyses for static conditions were performed to define bench heights of mining excavation works, while deformation analyses induced by seismic loads were carried out to verify the overall slope performance of the deposit during and after an earthquake. Based on the results, geotechnical and operational risks associated with mining activities were evaluated, and procedures and control measures that allowed for an adequate tailings mining process were defined.
Monitoring activities are currently being conducted to create conditions for safe operation and to ensure that the personnel involved in the tailings mining process have a proper understanding of the associated risks.
Knight Piésold was appointed by Minsur as the geotechnical designer for this project in 2018. Since then, Knight Piésold has provided geotechnical and geochemical tailings characterization, stability analysis, deformation analysis, and other services.
Presently, B2 TSF is being mined, and engineering designs are underway for the construction and operation of the New B2 TSF, which consists of the disposal of tailings in the empty B2 TSF once mining activities are over.