ABSTRACT
The mine operator has several main objectives to meet when he/she uses a mining method. Most important of these are to increase productivity and safety, as well as reduce costs. This paper presents current mining practices in Canada in view of these objectives. The modern selective and bulk mining methods as well as their costs are discussed. The paper includes a discussion of the principal variation in mining practices in terms of mining methods and equipment, dilution, ore losses and cost. It presents a methodology intended to evaluate cut-off grades and cut-off NSR (Net Smelter Return), based on operating costs and on total costs (including amortization). Particular attention has been paid to a comparison of total costs concerning modern selective and bulk mining methods. This methodology is particularly useful to make a distinction between mining resources and mining reserves. It has been proven that in the case of selective mining methods one can mine economically only higher grade orebodies, whose mean NSR value should be in excess of 80 à 145 $/t. These methods however, help us assure an adequate control of dilution and that of additional losses of mining reserves. Therefore, they reduce a risk of lower profitability compared to the one estimated in the feasibility study for a given mining project. In these circumstances the only uncontrollable factors that remain are metal prices and fluctuations of exchange rate. Bulk mining methods, on the other hand, make it feasible to mine lower grade orebodies, having a mean NSR value in excess of 50 – 85$/t. However, in their case it is more difficult to control effectively dilution and additional losses of mine reserves. This in turn increases a risk to achieve lower profitability as compared to that estimated in a feasibility study. Indeed, in many mines using these methods several cases of collapsing rock walls and backfill have been observed. They are among principal reasons of severe additional ore dilution that can reach 50% and more. It is concluded that concerning future developments in underground mining methods in Canada in the near future one may expect increasing application of open stoping as well as the implementation of drilling and loading remotely controlled from the surface.
