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MILPILLAS UNDERGROUND - STORAGE ZONE

The nature of the Milpillas mine’s underground drives and storage areas was intrinsically linked to its “cut-and-fill” mining method and the unique geological characteristics of the deposit. The mine’s infrastructure consisted of a network of drives (tunnels) excavated to access and extract the ore. These drives were carefully designed to follow the complex ore bodies, which included lenticular, flat-lying oxide zones at varying elevations, as well as deeper supergene sulphide zones. The underground layout facilitated the movement of equipment, personnel, and ore, as well as providing ventilation and drainage. To maintain ground stability in the created voids, waste material or cemented fill was introduced, creating a new working platform for the next mining cycle. This systematic approach allowed for selective extraction, maximizing recovery of the valuable Copper while ensuring operational safety and efficiency.

Storage areas underground are typically integrated into the mining cycle. After extraction, ore was crushed within the mine and then transported to surface leaching yards. Given the “cut-and-fill” method, excavated areas were often backfilled with waste material after ore removal, contributing to ground stability. While specific storage capacities for raw ore underground are not widely detailed, the efficient flow of material from extraction to surface processing implied a well-managed system for temporary holding and transport within the mine’s extensive network of tunnels. A significant challenge for underground operations at Milpillas was water management, as the mine historically faced issues with flooding due to groundwater infiltration. Efficient pumping systems were crucial to dewater the mine and ensure safe and continuous operations. Once the ore was extracted, it is brought to the surface for further processing.

Original photos courtesy of Max LomelĂ­n (Author: silvia)