1858 THREE LEVEL SEQUENTIAL RECOVERY OF ORE PILLARS IN SUBLEVEL STOPPING: A GEOMECHANICAL APPROACH TO BLAST DESIGN FOR SUSTAINABLE UNDERGROUND MINING *O. Barrios1, E. Asencios2, H. Soria2, N. Vásquez1 1Orica Blasting Engineering, Orica Mining Services, Peru, (*Presenting author: omar.barrios@orica.com) 2Colquisiri Mining Company, Mine Planning Department, Peru ABSTRACT Sublevel Stoping (SLS) is a widely used underground mining method for extracting massive ore bodies, high thickness stratiform orebodies, and narrow vein-type orebodies. Its key advantages include high mineral recovery rates—often exceeding 90%—and efficient mechanization of the mining cycle, resulting in improved productivity and reduced operational costs. At the María Teresa mine, operated by Minera Colquisiri, SLS is applied to primary stopes, leaving intermediate pillars (secondary stopes) for later recovery through a descending, retreating sequence. This process involves preparing crosscuts at four access levels and executing radial positive drilling over three secondary blocks. The main technical challenge is achieving recovery above 90% while controlling overbreak and dilution in lateral walls composed of cemented hydraulic fill. These walls are exposed to final openings approximately 60 m in height, 12 m wide, and 15 m long, requiring rigorous geomechanical stability, optimized blast design, and differentiated planning. KEYWORDS Sublevel Stoping (SLS), sequential stope recovery, underground mine design, geomechanics and stability, cemented hydraulic fill, overbreak control, blast optimization, drill deviation measurement, blast vibration monitoring, stope recovery efficiency, sustainable mining infrastructure, retreat mining strategy, World Mining Congress 1. INTRODUCTION Colquisiri Mining Company operates the María Teresa underground mine, located in Huaral Province, Department of Lima, Peru, at an average elevation of 150 m above sea level (approximate coordinates: 11° 21' 45" S, 77° 8' 25" W; UTM Zone 18S WGS84: approximately 8,735,000 m N, 311,000 m E). The operation exploits a volcanogenic massive sulfide (VMS) polymetallic deposit characterized by lenticular ore bodies. The principal mineralized structure currently under extraction is the Sofía D ore body, which supports a daily production rate of approximately 1,600 metric tons of ore delivered to an on-site concentrator plant producing zinc, lead, silver, and copper concentrates. The site operates in close proximity to agricultural land and incorporates full recirculation of process water together with contained tailings management to limit environmental footprint. Sublevel open Stoping (SLS) with cemented hydraulic backfill is the selected mining method at María Teresa mine. The mining sequence employs a primary-to-secondary stope extraction pattern in a descending and retreating configuration. Secondary stopes act as temporary rib pillars between primary stopes during the initial extraction phase and are subsequently recovered using a multi-level sequential approach that involves access development and drilling from three separate levels. Final secondary stope dimensions reach heights of up to approximately 60 m (spanning multiple sublevels), widths of 12 m, and lengths of 15 m. Consequently, the exposed cemented hydraulic fill (CHF) walls constitute one of the primary bounding surfaces during secondary stope production.
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