This is a dynamic pit wall, still progressing towards its final position which is the final pit wall. Its envelope is defined during the mining planning. The temporary position of the excavation boundaries is based on economic criteria and aims at optimizing the project NPV. Although the operator can configure it freely, he must nevertheless respect the security and restoration criteria.
Safety criteria: any pit or quarry must ensure, at all times, the safety of people and equipment. The geometry of the walls for a pit being exploited is governed, in Quebec, by section 41 of the Regulation respecting occupational health and safety in mines. This Article covers, among other things, rock competence, drilling and blasting techniques, etc.
Restoration criteria: All operators must adhere to the restoration configuration. The final geometry of the walls of the excavation is governed, in Quebec, by Article 39 of the Regulation on Quarries and Sand Pits. This article deals, among other things, with the height of the benches, the width and frequency of the berms, etc.
Mining planning role
Mining planning is used to establish the exploitation sequences over time, in terms of bank height, width and frequency of berms, push-backs, etc. of a deposit. The operator, with a view to maximizing the NPV (waste rock movement, sales objectives, grade control, etc.), has the flexibility to configure its operations, provided that it complies with the conditions of Articles 41 (in any time) and 39 (when reaching the final pit design).
Mining planning will allow this transition, from the temporary pit wall to the final pit wall, safely and at no additional cost
Figure 2 shows an ultimate pit designed with the Vulcan modelling software.
The block model shows that the mineralization consists of subhorizontal mineralized zones, 5 to 8 m thick. These zones are separated by waste zones that sometimes exceed 10 m at the centre of the ore body and to the east.
On the one hand, the mine planning will attempt to mine the deposit using 5 m benches in mineralized zones less than 10 m thick, in order to improve selectivity. On the other hand, it will try to mine the thickest zones with 10 m benches, in order to improve the productivity.
At the same time mine planning will have to ensure that the walls of the excavation comply, at all times, with health and safety rules. It must also ensure that restoration conditions are met once arrived at the ultimate pit design.
The long-term mining sequences are presented by the following five phases.
Figure 3 shows the position of the pit walls at the end of phase 1.
Figure 4 shows the position of the pit walls at the end of phase 2.
Figure 5 shows the position of the pit walls at the end of phase 3.
Figure 6 shows the position of the pit walls at the end of phase 4.
Figure 7 shows the position of the pit walls at the end of phase 5.
As long as an open pit or quarry grows inside the ultimate pit shell, the operator can configure the geometry of the excavation to maximize the net present value of the operation, provided that it respects the following two constraints: