Por: Walter Ticona Ayala y Cristhian Guillen Cáceres, Blasting Engineer en Exsa; Gino Mayta Córdova, jefe Perforación y Voladura, Nexa Resources Perú, y Ned Vásquez Sánchez, Lead Technical Services en Exsa.

Abstract

Raise boring is the most important phase for an efficient opening in the exploitation of the Sub Level Stoping (SLS) method, on which depends the success and the result of the blasting; being the efficiency of this type of blasting the unit operation of vital importance to meet the challenges for the proposed mining plans.

90% of ore production at Cerro Lindo has been from ore body (OB) mining, and most of the production has been from negative benching, where free faces have been generated by using the drop raise boring method; however, during the 2021 - 2022 period, SLS mining with raise boring increased by approximately 45%, which is due to the increase in secondary and tertiary pit mining.

In this transition, the Raise Boring construction method presents difficulties for access due to limitations in the preparation and rehabilitation of workings; therefore, it has been decided to open the free face (slot), by raise boring with lengths up to 25m.

Therefore, the following has been considered for the implementation: i.- for drilling, the ITH equipment with down-the-hole hammer has been used; ii.- for stoping, the hexagonal cut design is used iii.- for the loading scheme, 1.0 lb. booster is used as primer and ampho as loading column; and iv.- electronic detonators are used for the initiation system, where the timing considers four phases that are synchronized in packets independently. 

Also, this implementation was supported by the use of tools and activities for perforation control, simulation and evaluation such as: measurement, processing and interpretation of in-situ drill deviation, logging and analysis of the vibration level generated, and the simulation of perforation designs and electronic detonation sequences in order to reconcile the results obtained in the field and optimize the proposed design.

The results obtained during the implementation of the electronic initiation system for the generation of long hole stopings were satisfactory, achieving an advance efficiency of over 97% and the planned opening (section), guaranteeing the performance of the blasts executed.

The savings generated from the execution of longhole stopes, compared to the RB (Raise Boring) method, is 8.3kUSD/hole mined, which represents a 30% reduction in the budget for each raise executed, and in addition, preparation and development savings have been estimated at 10.0kUSD/pit mined.