Case study: Media Luna paste system

In 2019, Torex Gold Resources (Torex) sought to expands its operations at the El-Limon Guajes (ELG) site in Guerrero State, Mexico, by developing a new underground resource known as the Media Luna (ML) deposit. This deposit, which contains significant gold, copper and silver mineralisation, presented several interesting challenges due to its separation from the existing site infrastructure by the Rio Balsas: a large river in the mountainous region of Guerrero. To access the new orebodies, Torex elected to construct a 6.5 km tunnel under the Rio Balsas to connect the existing ELG infrastructure to the ML deposit. At the outset of the ML project, Paterson & Cooke (P&C) and Torex agreed to take a collaborative approach, which extended from the early stages of feasibility assessments through to detailed design. The team initially focused on trade-offs and test work to determine an effective strategy to provide paste backfill to the underground mine. The inclusion of new copper and iron sulphide flotation circuits in the existing ELG process plant, which will generate two tailings streams with differing material properties, influenced the design of the paste plant. Material characterisation test work revealed a high pyrrhotite content ranging from 60 to 75%, in one of the tailings streams, prompting additional test work including self-heating and geochemical kinetic tests. Given the challenging terrain and early mineralogical findings, careful consideration was required to determine a suitable paste plant location that would ensure efficient tailings and binder delivery, and, ultimately, delivery of high-quality paste backfill to the underground stopes. This paper reflects on the unique challenges encountered throughout the project and the team’s tenacity in handling adversity while making difficult yet necessary decisions to ensure that Torex will have a world-class paste plant when backfill operations start-up in 2025.