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. This paper presents a practical methodology implemented at the María Teresa mine for the three-level sequential recovery of ore pillars in SLS. The main technical challenge is to minimize instability and failure of the CHF walls exposed during secondary stope extraction, while ensuring optimal fragmentation from the large-scale blasts and achieving effective dilution control. The approach integrates geomechanical stability assessments, optimized ring drill-and-blast designs, drilling quality control measures, blast vibration studies, and 3D post-blast stope surveys. 2. METHODOLOGY The three-level sequential recovery of ore pillars was developed based on a comprehensive understanding of the deposit's natural conditions (geology, geometry, and hydrogeology), the surrounding rock mass response, the performance of drilling and blasting designs, drilling execution quality, blast-induced damage control, and field-measured outcomes in terms of fragmentation and overbreak. To ensure process reliability and validate performance, the implementation followed a structured, five-stage methodology: (1) Geological and Geomechanical characterization (2) Blast Vibration Monitoring (3) Drilling Quality Control, (4) Blast pattern design and simulation and (5) Volumetric surveys of mined stopes. 2.1 Geological and Geomechanical characterization 2.1.1 Local Geology The host rocks consist predominantly of volcanic and subvolcanic sequences of Late Cretaceous age, ranging in composition from basaltic andesite to rhyodacite (calc-alkaline series). 2.1.2 Deposit characteristics The María Teresa deposit consists primarily of lenticular massive sulfide bodies whose longitudinal axes are preferentially oriented N150°E (Figure 1). These orebodies have irregular geometries that grade laterally and with depth into lower-grade veinlet mineralization. One of the largest orebodies contributing to current production is the Sofía D body. It is with approximate dimensions of 700 m along its major axis (N150°E), up to 200 m in width, and vertical thickness decreasing from 70 m in the southwest to only a few meters in the northeast. Along the same N150°E structural lineament, a new mineralized zone exceeding 300 m in length - currently under exploration - has been identified and designated Sofía E.
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