Por: Alain Mestanza Oblitas, Minera Chinalco Perú.

Trabajo con Mención Honrosa en el Foro TIS de PERUMIN 37. 

Abstract

Underground mining in central Peru, particularly in the area now operated by Minera Chinalco, dates back to the late 19th and early 20th centuries, when companies such as the Cerro de Pasco Copper Corporation began extracting polymetallic veins (lead, zinc, silver, and copper). However, prior to the arrival of foreign companies, smaller-scale mining was already present during the colonial and even pre-Hispanic periods.

This technical study was carried out at Chinalco Peru’s Toromocho open-pit operation, located at more than 4,500 masl in the Junín region. The deposit had previously been mined underground (approximately 100-120 years ago) and is now exploited using open-pit methods.

As a result of the transition from underground to open-pit extraction, there is a significant presence of old workings (drifts, shafts, raises, and others). One of the most important historical underground components is the “Pique Central” (Central Shaft), which is 375 meters deep with a rectangular section of 6.8 m x 12.6 m. The shaft collar is located at elevation 4,545 masl in Phase 5, and its current function is to collect contact water discharges from operations. These waters are pumped from Pond C and then discharged by gravity from Pond A, before being conveyed through the Kingsmill Tunnel (elevation 4,170 masl), ultimately reaching the Kingsmill Water Treatment Plant (Yauli). Due to its critical role, preserving the structural stability and operability of the Central Shaft is essential to ensure sustainability and compliance with water management commitments established in the operation’s Environmental Management Instruments (IGA).