Stope design and dilution control for sublevel stoping method
The geology can be described as a volcanogenic massive sulphide deposit that strikes NW and dips 65° SW on average, 1,350 m long, 83 m wide and 245 m deep, featuring a jointing system that predominantly strikes NE-SW and a secondary orthogonal system striking NW-SE at the mineralised zone. The rock mass quality was mainly rated as fair (rock mass rating = 40 to 50) and in some specific sectors as poor. Our scope was to design the openings and dilution control for stopes without personnel entry.
The Potvin Modified Stability Graph method was used to correlate with Clark and Pakalnis’s Equivalent Lineal Over-Excavation (ELOS).
Stope dimensions were recommended for both fair and poor quality rock, taking into account the results of the rock mass geomechanical model and the current status of the mining activity. Based on the back analysis results of mined stopes and the kinematic wedge analysis, a standard support design was prepared.
A comparative analysis of the over-excavation height at the dome of the stope versus the stope width without support, concluded that the height of the unsupported dome was almost half the width of the stope, indicating the fault depth was mostly controlled by the rock mass quality.
Regarding the stopes with cable bolting support at the roof, we observed that the over-excavation in the stopes had been eliminated.
Our study concluded that:
1. The stability graphic method and ELOS were complemented with a back-analysis of the mined stopes.
2. Understanding the over-excavation type and its magnitude, measured at the existing stopes, helped to determine efficiently the dimensions of the cable bolting support needed at the stope domes.
3. The over-excavation control at the front walls and hanging wall of the stopes favors the continuity of the mining cycle and the mining of secondary or adjacent stopes.
